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Posts Tagged ‘Renal function’


Risks for Patients’ and Physician’s Health in the Cath Lab

Reporter and Curator: Aviva Lev-Ari, PhD, RN

On Thursday, June 27th, 2013, Bayer HealthCare, Nuance® Healthcare, and The Mount Sinai Hospital held a live webinar outlining how one of America’s leading Radiology Departments is pioneering the next generation of imaging informatics. If you were unable to watch it live, or would like to view it again, it is now available online here.
The Mount Sinai Hospital in New York has taken Contrast Dose Management and IT interoperability to a new level with two industry-leading forces – Bayer’s Certegra® Informatics Platform and Nuance’s PowerScribe® 360 | Reporting.
The FREE 60-minute webinar includes:
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Emerging Contrast Dose Management Best Practices as a Standard of Care at The Mount Sinai Hospital
Experiences with Informatics including Point of Care Documentation, Injection Protocol Management for Patient-Based Dosing, Interfacing with IT Systems, and Analytics
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Risks for Physician’s Health in the Cath Lab

EuroIntervention. 2012 Jan;7(9):1081-6. doi: 10.4244/EIJV7I9A172.

Brain tumours among interventional cardiologists: a cause for alarm? Report of four new cases from two cities and a review of the literature.

Source

Interventional Cardiology, Rambam Medical Center, Bruce Rappaport Faculty of Medicine, the Technion, Israel Institute of Technology, Haifa, Israel. aroguin@technion.ac.il

Abstract

AIMS:

Interventional cardiologists who work in cardiac catheterisation laboratories are exposed to low doses of ionising radiation that could pose a health hazard. DNA damage is considered to be the main initiating event by which radiation damage to cells results in development of cancer.

METHODS AND RESULTS:

We report on four interventional cardiologists, all with brain malignancies in the left hemisphere. In a literature search, we found five additional cases and thus present data on six interventional cardiologist and three interventional radiologists who were diagnosed with brain tumours. All worked for prolonged periods with exposure to ionising radiation in the catheterisation laboratory.

CONCLUSIONS:

In interventional cardiologists and radiologists, the left side of the head is known to be more exposed to radiation than the right. A connection to occupational radiation exposure is biologically plausible, but risk assessment is difficult due to the small population of interventional cardiologists and the low incidence of these tumours. This may be a chance occurrence, but the cause may also be radiation exposure. Scientific study further delineating occupational risks is essential. Since interventional cardiologists have the highest radiation exposure among health professionals, major awareness of radiation safety and training in radiological protection are essential and imperative, and should be used in every procedure.

Risks for Patients’ Health in the Cath Lab

Contrast-Induced Nephropathy

  • Author: Renu Bansal, MD; Chief Editor: Vecihi Batuman, MD, FACP, FASN

SOURCE

http://emedicine.medscape.com/article/246751-medication#showall

Contrast-induced nephropathy (CIN) is defined as the impairment of renal function and is measured as either a 25% increase in serum creatinine (SCr) from baseline or 0.5 mg/dL (44 µmol/L) increase in absolute value, within 48-72 hours of intravenous contrast administration. (See Etiology.)

For renal insufficiency (RI) to be attributable to contrast administration, it should be acute, usually within 2-3 days, although it has been suggested that RI up to 7 days post–contrast administration be considered CIN; it should also not be attributable to any other identifiable cause of renal failure. A temporal link is thus implied.[1] Following contrast exposure, SCr levels peak between 2 and 5 days and usually return to normal in 14 days. (See Clinical and Workup.)

Complications

CIN is one of the leading causes of hospital-acquired acute renal failure. It is associated with a significantly higher risk of in-hospital and 1-year mortality, even in patients who do not need dialysis.

Nonrenal complications include procedural cardiac complications (eg, Q-wave MI, coronary artery bypass graft [CABG], hypotension, shock), vascular complications (eg, femoral bleeding, hematoma, pseudoaneurysm, stroke), and systemic complications (eg, acute respiratory distress syndrome [ARDS], pulmonary embolism).

There is a complicated relationship between CIN, comorbidity, and mortality. Most patients who develop CIN do not die from renal failure. Death, if it does occur, is more commonly from either a preexisting nonrenal complication or a procedural complication.

Concerns

Many physicians who refer patients for contrast procedures and some who perform the procedure themselves are not fully informed about the risk of CIN. A survey found that less than half of referring physicians were aware of potential risk factors, including diabetes mellitus. (See Differentials.)

CIN suffers from a lack of consensus regarding its definition and treatment. Studies differ in regard to the marker used for renal function (SCr vs eGFR), the day of initial measurement and remeasurement of the marker, and the percentage increase used to define CIN. This makes it difficult to compare studies, especially in terms of the efficacy of various treatment modalities. (See Treatment and Medication.)[2]

The reported incidence of CIN might be an underestimation. SCr levels normally rise by day 3 of contrast administration. Most patients do not remain hospitalized for so long and there is no specific protocol to order outpatient SCr levels 3-5 days after the procedure.

Other renal function markers

The use of SCr as a marker of renal function has its limitations. Indicators such as the estimated glomerular filtration rate (eGFR) and cystatin C are increasingly considered to be more reliable and accurate reflectors of existing renal function.[3, 4]

The eGFR can be calculated using the Modification of Diet in Renal Disease (MDRD) formula or the Cockroft-Gault formula. The Cockroft-Gault formula calculates eGFR using age, sex, and body weight, which are factors that, independent of GFR, influence SCr. The MDRD equation also includes blood urea nitrogen (BUN) and serum albumin.

The eGFR works best at low creatinine values. SCr and GFR share a curvilinear relationship. At lower SCr values, doubling SCr is associated with a corresponding 50% decrease in GFR. However, in elderly patients with chronic kidney disease(CKD) who have high SCr values at baseline, a 25% rise in SCr is actually indicative of a relatively modest reduction in GFR. Nonetheless, even a 25% increase in SCr in this situation has been shown to have great impact, especially in terms of inhospital and 1-year mortality.[5]

Serum cystatin C is a serum protein that is secreted by nucleated cells. It is freely filtered by the glomerulus and has been found to be an accurate marker of GFR. Compared with SCr, cystatin C changes much earlier after contrast administration and is not subject to confounding factors, such age, sex, and muscle mass, that influence SCr values independent of the underlying GFR. Cystatin C is increasingly being used as a marker of renal function in cardiac surgical patients.

Patient education

Patients with risk factors for CIN should be educated about the necessity of follow-up care with their physicians with a postprocedure SCr estimation, especially if the initial procedure was done on an outpatient basis.

Etiology

Contrast media (CM) act on distinct anatomic sites within the kidney and exert adverse effects via multiple mechanisms. They cause a direct cytotoxic effect on the renal proximal tubular cells, enhance cellular damage by reactive oxygen species, and increase resistance to renal blood flow. They also exacerbate renal vasoconstriction, particularly in the deeper portions of the outer medulla. This is especially important in patients with CKD, because their preexisting abnormal vascular pathobiology is made worse by the effects of CM.[6, 7]

Renal (particularly medullary) microcirculation depends on a complex interplay of neural, hormonal, paracrine and autocrine influences. Of note are the vasodilator nitric oxide (NO) and the vasoconstrictors vasopressin, adenosine (when it acts via the high affinity A1 receptors), angiotensin II, and endothelins. Prostaglandins cause a redistribution of blood flow to the juxtamedullary cortex and, therefore, are protective.

NO, in particular, seems to be very important, with antiplatelet, vasodilatory, insulin sensitizing, anti-inflammatory, and antioxidant properties. It has been suggested that plasma levels of asymmetrical dimethylarginine (ADMA), which is an endogenous inhibitor of all NO synthase isoforms, can be used as a marker of CIN, especially in patients with unfavorable outcomes.

CM-mediated vasoconstriction is the result of a direct action of CM on vascular smooth muscle and from metabolites such as adenosine and endothelin. Additionally, the osmotic property of CM, especially in the tubular lumen, decreases water reabsorption, leading to a buildup of interstitial pressure. This, along with the increased salt and water load to the distal tubules, reduces GFR and causes local compression of the vasa recta. All of this contributes to worsening medullary hypoxemia and renal vasoconstriction in patients who are already volume depleted.

Finally, CM also increase resistance to blood flow by increasing blood viscosity and by decreasing red cell deformability. This intravascular sludging generates local ischemia and causes activation of reactive oxygen species that result in tubular damage at a cellular level.

Comparison of contrast-agent nephropathy potential

The ability of different classes of CM to cause CIN is influenced by their osmolality, ionicity (the ability of the contrast media to dissociate in water), and molecular structure. Each of these characteristics, in turn, influences their behavior in body fluid and their potential to cause adverse effects. (See Table 1, below.)[8]

Agents are classified as high, low, or iso-osmolar, depending on their osmolality in relation to blood. Low-osmolarity contrast media (LOCM) is actually a misnomer, since these agents have osmolalities of 600-900 mOsm/kg and so are 2-3 times more hyperosmolar than blood. High-osmolarity contrast media (HOCM) are 5-7 times more hyperosmolar than blood, with osmolalities greater than 1500 mOsm/kg.

Molecular structure of CM refers to the number of benzene rings. Most CM that were developed in the 1990s are dimers with 2 benzene rings. Dimeric CM, while nonionic and with low osmolarity, have high viscosity, which may influence renal tubular blood flow.

The ratio of iodine to dissolved particles describes an important relationship between opacification and osmotoxicity of the contrast agent. The higher ratios are more desirable. High-osmolar agents have a ratio of 1.5, low-osmolar agents have a ratio of 3, and iso-osmolar agents have the highest ratio, 6.

While the safety of LOCM over HOCM in terms of CIN seems intuitive, clinical evidence of it came from a meta-analysis by Barrett and Carlisle.[9] They showed the benefit of using LOCM over HOCM mostly in high-risk patients. The Iohexol Cooperative Study was a large, prospective, randomized, double-blinded, multicenter trial that compared the risk of developing CIN in patients receiving the low-osmolarity agent iohexol versus the high-osmolarity agent diatrizoate. While the HOCM group was 3.3 times more likely to develop CIN compared with the LOCM group, this was seen only in patients with preexisting CKD (baseline SCr greater than or equal to 1.5 mg/dL). In addition to CKD; diabetes mellitus, male sex, and contrast volume were found to be independent risk factors.

Even within the LOCM category, the risk is not the same for all agents. High-risk patients receiving iohexol have a higher likelihood of developing CIN than do patients receiving another agent (ie, iopamidol) in the same class.

When LOCM were compared with iso-osmolar contrast media (IOCM), the Nephrotoxicity in High-Risk Patients Study of Iso-Osmolar and Low-Osmolar Non-Ionic Contrast Media (NEPHRIC study), arguably the most definitive study in this category to date, found that the odds of developing CIN in high-risk patients were almost 9 times greater for the study’s iohexol group than for the investigation’s iodixanol group (iso-osmolar contrast agent). The incidence of CIN was 3% in the iodixanol group versus 26% in the iohexol group.[10] These results, though promising, were not duplicated in some subsequent studies.

When iodixanol was used, the Rapid Protocol for the Prevention of Contrast-Induced Renal Dysfunction (RAPPID) trial found a 21% incidence of CIN,[11] and the Contrast Media and Nephrotoxicity Following Coronary Revascularization by Angioplasty (CONTRAST) trial found a 33% incidence of CIN.[12] Finally, the Renal Toxicity Evaluation and Comparison Between Visipaque (Iodixanol) and Hexabrix (Ioxaglate) in Patients With Renal Insufficiency Undergoing Coronary Angiography (RECOVER) trial compared the iso-osmolar contrast medium iodixanol to the low-osmolarity agent ioxaglate and found a significantly lower incidence of CIN with iodixanol than with ioxaglate (7.9% vs 17%, respectively).[13]

Thus, although the data are by no means uniform, they seem to suggest that the iso-osmolar contrast agent iodixanol may be associated with smaller increases in SCr and lower rates of CIN when compared with low-osmolar agents, especially in patients with CKD and in those with CKD and diabetes mellitus.[14]

Risk factors

Risk factors for CIN can be divided into patient-related, procedure-related, and contrast-related factors (although the risk factors for CIN are still being identified and remain poorly understood). Patient-related risk factors are as follows:

  • Age
  • CKD
  • Diabetes mellitus
  • Hypertension
  • Metabolic syndrome
  • Anemia
  • Multiple myeloma
  • Hypoalbuminemia
  • Renal transplant
  • Hypovolemia and decreased effective circulating volumes – As evidenced by congestive heart failure (CHF), an ejection fraction (EF) of less than 40%, hypotension, and intra-aortic balloon counterpulsation (IABP) use

Procedure-related risk factors are as follows:

  • Urgent versus elective
  • Arterial versus venous
  • Diagnostic versus therapeutic

Contrast-related risk factors are as follows:

  • Volume of contrast
  • Contrast characteristics, including osmolarity, ionicity, molecular structure, and viscosity

The single most important patient-related risk factor is preexisting CKD, even more so than diabetes mellitus.[15] Patients with CKD in the setting of diabetes mellitus have a 4-fold increase in the risk of CIN compared with patients without diabetes mellitus or preexisting CKD.

Table: Physiochemical Properties of Contrast Media

Although the data is by no means uniform, they seem to suggest that the iso-osmolar contrast agent iodixanol may be associated with smaller increases in SCr and lower rates of CIN when compared with low-osmolar agents, especially in patients with CKD and in those with CKD and diabetes mellitus.[14] Guidelines from the American Heart Association (AHA)/American College of Cardiology (ACC) for the management of acute coronary syndromes patients with CKD recommend the use of IOCM (Class I, level of Evidence).

Table 1. Physiochemical Properties of Contrast Media[16] (Open Table in a new window)

Class of Contrast Agent Type of Contrast Agent Iodine Dose(mg/mL) Iodine/Particle Ratio Viscosity(cPs at 37°C) Osmolality(mOsm/kg H2 O) Molecular Weight (Da)
High-osmolar monomers(ionic) Diatrizoate (Renografin)Ioxithalamate (Telebrix) 370350 1.51.5 2.32.5 18702130 636643
Low-osmolar dimers(ionic) Ioxaglate (Hexabrix) 320 3 7.5 600 1270
Low-osmolar monomers(nonionic) Iohexol (Omnipaque)Iopamidol (Isovue)Iomeprol (Iomeron)

Ioversol (Optiray)

Iopromide (Ultravist)

Iopentol (Imagopaque)

350370400

350

370

350

333

3

3

3

10.49.412.6

9

10

12

780790620

790

770

810

821777778

807

791

835

Iso-osmolar dimers(nonionic) Iodixanol (Visipaque)Iotrolan (Isovist) 320320 66 11.88.5 290290 15501620

Epidemiology

Occurrence in the United States

CIN is the third leading cause of hospital-acquired renal failure. Decreased renal perfusion and surgery (or in some studies, nephrotoxic medications) are the number one and number two causes, respectively.

An analysis of 15 prospective and retrospective studies from 1976-1996 report an incidence of CIN of 3.1-31%. The number varies depending on the definition used for CIN; the contrast agent characteristics, including the type, amount, duration, and route of administration; preexisting risk factors; and length of follow-up (including the day of measurement of postcontrast serum creatinine).

In patients without risk factors, the incidence may be as low as 2%. With the introduction of risk factors, like diabetes, the number rises to 9%, with incidences being as high as 90% in diabetics with CKD. Therefore, the number and the type of preexisting risk factors directly influence the incidence of renal insufficiency. It is also procedure dependant, with 14.5% overall in patients undergoing coronary interventions compared to 1.6-2.3% for diagnostic intervention, as reported in literature.[17]

Race- and age-related demographics

While African Americans with diabetic nephropathy have a faster acceleration of end-stage renal disease (ESRD), independent of other variables, race has not been found to be a risk factor for CIN.

The incidence of CIN in patients older than age 60 years has been variously reported as 8-16%. It has also been shown that in patients with acute MI who have undergone coronary intervention, an age of 75 years or older is an independent risk factor for CIN.

Prognosis

CIN is normally a transient process, with renal functions reverting to normal within 7-14 days of contrast administration. Less than one-third patients develop some degree of residual renal impairment.

Dialysis is required in less than 1% of patients, with a slightly higher incidence in patients with underlying renal impairment (3.1%) and in those undergoing primary PCI for myocardial infarction (MI) (3%). However, in patients with diabetes and severe renal failure, the rate of dialysis can be as high as 12%.

Of the patients who need dialysis, 18% end up on permanent dialysis therapy. However, many of these patients will have had advanced renal insufficiency and concomitant diabetic nephropathy and will have been destined for dialysis regardless of the episode of CIN.

A growing body of knowledge indicates that acute kidney injury after contrast medium can be a harbinger of CKD or ESRD. In one observational study, the population studied appeared representative of the general population undergoing angiography and the rate of acute kidney ingury was consonant with other studies. The finding that persistent kidney damage can occur after contrast-induced acute kidney injury highlights the potential for acceleration of the progression of kidney injury in individuals with pre-existing CKD.[18]

Mortality

Patients who require dialysis have a considerably worse mortality rate, with reported rates of 35.7% inhospital mortality (compared with 7.1% in the nondialysis group) and a 2-year survival rate of only 19%.

CIN by itself may be an independent mortality risk factor. Following invasive cardiology procedures, patients with normal baseline renal function who develop CIN have reduced survival compared with patients with baseline chronic CKD who do not develop CIN.

Gadolinium-based agents

Gadolinium-based CM (used for magnetic resonance imaging [MRI]), when compared with iodine-based CM, have a similar, if not worse, adverse effect profile in patients with moderate CKD and eGFR of less than 30 mL/min. Their use has been implicated in the development of nephrogenic systemic fibrosis, a chronic debilitating condition with no cure.

A review of 3 series and 4 case reports suggested that the risk of renal insufficiency with gadolinium is similar to that of iodinated radiocontrast dye. The reported incidence varies from 4% in stage 3 CKD to 20% in stage 4 CKD. It may even be worse, as suggested by some investigators. A prospective study of 57 patients found that acute renal failure was seen in 28% of patients in the gadolinium group, compared with 6.5% of patients in the iodine group, despite prophylactic saline and N-acetylcysteine (NAC).

The risk factor profile is similar to that for iodinated CM; increased incidence of acute renal failure is seen in older patients and in those with lower baseline creatinine clearance, diabetic nephropathy, anemia, and hypoalbuminemia.

Risk stratification scoring systems

CIN is the result of a complex interplay of many of the above risk factors. The presence of 2 or more risk factors is additive, and the likelihood of CIN rises sharply as the number of risk factors increases. Researchers have tried to objectively quantify and predict the contribution of each risk factor to the ultimate outcome of CIN.

Risk stratification scoring systems have been devised to calculate an individual patient’s risk of developing CIN. This has mostly been done in patients undergoing percutaneous coronary intervention (PCI), especially those with preexisting risk factors. Mehran et al developed the following scoring system based on points awarded to each of 7 multivariate predictors[19] :

  • Hypotension = 5 points
  • IABP use = 5 points
  • CHF = 5 points
  • SCr of greater than 1.5 mg/dL = 4 points
  • Age greater than 75 years = 4 points
  • Anemia = 3 points
  • Diabetes mellitus = 3 points
  • Contrast volume = 1 point for each 100 cc used

Based on the total calculated score, patients were divided into low-risk (score of less than or equal to 5), moderate-risk (score of 6-10), high-risk (score of 11-15), and very–high-risk (score of greater than or equal to 16) categories. The rate of CIN and the requirement for dialysis were 7.5 and 0.04%, 14 and 0.12%, 26.1 and 1.09%, and 57.3 and 12.6%, respectively, for each of the 4 groups.

Bartholomew et al worked to create another scoring system and took into consideration 8 variables, including creatinine clearance of less than 60 mL/min, IABP use, urgent coronary procedure, diabetes mellitus, CHF, hypertension, peripheral vascular disease (PVD), and volume of contrast used.[20]

History and Physical Examination

History

Patients usually present with a history of contrast administration 24-48 hours prior to presentation, having undergone a diagnostic or therapeutic procedure (eg, PCI). The renal failure is usually nonoliguric.

Physical examination

A physical examination is useful for ruling out other causes of acute nephropathy, such as cholesterol emboli (eg, blue toe, livedo reticularis) or drug-induced interstitial nephritis (eg, rash). Patients may have evidence of volume depletion or may be in decompensated CHF.

Diagnostic Considerations

Conditions to consider in the differential diagnosis of CIN include the following:

  • Atheroembolic renal failure – More than 1 week after contrast, blue toes, livedo reticularis, transient eosinophilia, prolonged course, and lower recovery
  • Acute renal failure (includes prerenal and postrenal azotemia) – There may also be associated dehydration from aggressive diuresis, exacerbated by preexisting fluid depletion; the acute renal failure is usually oliguric, and recovery is anticipated in 2-3 weeks
  • Acute interstitial nephritis (triad of fever, skin rash, and eosinophilia) – Also eosinophiluria; the nephritis is usually from drugs such as penicillin, cephalosporins, and nonsteroidal anti-inflammatory drugs (NSAIDs)
  • Acute tubular necrosis – Ischemia from prerenal causes; endogenous toxins, such as hemoglobin, myoglobin, and light chains; exogenous toxins, such as antibiotics, chemotherapeutic agents, organic solvents, and heavy metals

Approach Considerations

SCr concentration usually begins to increase within 24 hours after contrast agent administration, peaks between days 3 and 5, and returns to baseline in 7-10 days. Serum cystatin C (which has been suggested as a surrogate marker of renal function in lieu of SCr) is increased in patients with CIN.

Nonspecific formed elements can appear in the urine, including renal tubular epithelial cells, pigmented granular casts, urate crystals, and debris. However, these urine findings do not correlate with severity.

Urine osmolality tends to be less than 350 mOsm/kg. The fractional excretion of sodium (FENa) may vary widely. In the minority of patients with oliguric CIN, the FENa is low in the early stages, despite no clinical evidence of volume depletion.

Histology

CM cause direct toxic effects on renal tubular epithelial cells, characterized by cell vacuolization, interstitial inflammation, and cellular necrosis. In a study, these characteristic changes, called osmotic nephrosis, were observed in 22.3% of patients undergoing renal biopsy, within 10 days of contrast exposure.[21]

Approach Considerations

Hydration therapy is the cornerstone of CIN prevention. Renal perfusion is decreased for up to 20 hours following contrast administration. Intravascular volume expansion maintains renal blood flow, preserves nitric oxide production, prevents medullary hypoxemia, and enhances contrast elimination.

However, a number of other CIN therapies have been investigated, including the use of statins, bicarbonate, N-acetylcysteine (NAC), ascorbic acid, the adenosine antagonists theophylline and aminophylline, vasodilators, forced diuresis, and renal replacement therapy. Patients with CIN should be managed in consultation with a nephrologist.

Hydration Therapy

The first study revealing the benefit of hydration in CIN prevention came from Solomon et al.[22] They also found forced diuresis to be inferior to hydration with 0.45% saline. Fluids with different compositions and tonicity have since been studied, including bicarbonate and mannitol.

Normal saline has been found to be superior to half-normal saline in terms of its enhanced ability in intravascular volume expansion. It also causes increased delivery of sodium to the distal nephron, prevents rennin-angiotensin activation, and thus maintains increased renal blood flow. In terms of route of administration, oral fluids, while beneficial, are not as effective as intravenous hydration.[23, 24]

The CIN Consensus Working Panel found that adequate intravenous volume expansion with isotonic crystalloids (1-1.5 mL/kg/h), 3-12 hours before the procedure and continued for 6-24 hours afterward, decreases the incidence of CIN in patients at risk. The panel studied 6 clinical trials with different protocols for volume expansion. The studies differed in the type of fluid used for hydration (isotonic vs half-normal saline), route, duration, timing, and amount of fluid used.[25]

For hospitalized patients, volume expansion should begin 6 hours prior to the procedure and be continued for 6-24 hours postprocedure. For outpatients, administration of fluids can be initiated 3 hours before and continued for 12 hours after the procedure. Postprocedure volume expansion is more important than preprocedure hydration. It has been suggested that a urine output of 150 mL/h should guide the rate of intravenous fluid replacement, although the CIN Consensus Working Panel did not find it useful to recommend a target urine output.

CHF poses a particular challenge. Patients with compensated CHF should still be given volume, albeit at lower rates. Uncompensated CHF patients should undergo hemodynamic monitoring, if possible, and diuretics should be continued. In emergency situations, one’s clinical judgment should be used, and, in the absence of any baseline renal function, adequate postprocedure hydration should be carried out.

What is interesting, however, is that, while hydration remains the cornerstone for CIN prevention, a randomized, controlled trial comparing a strategy of volume expansion with no volume expansion has not been performed to date.

Statins

Statins are widely used in coronary artery disease (CAD) for their pleiotropic effects (favorable effects on endothelin and thrombus formation, plaque stabilization, and anti-inflammatory properties), and it was believed that, given the vascular nature of CIN, they might have similar renoprotective effects. The data for statin use, however, are retrospective and anecdotal; they are taken mostly from patients already on statins who underwent PCI.[26]

A significantly lower incidence of CIN was found in patients treated with statins preoperatively (CIN incidence of 4.37% in the statin group vs 5.93% in the nonstatin group). However, prospective trials looking at statin use in patients undergoing noncardiac procedures are needed to better qualify this initial promise.

Bicarbonate Therapy

Bicarbonate therapy alkalinizes the renal tubular fluid and, thus, prevents free radical injury. Hydrogen peroxide and an oxygen ion (from superoxide) react to form a hydroxide ion, all agents of free radical injury. This reaction, called the Harber-Weiss reaction, is activated in an acidic environment. Bicarbonate, by alkalinizing the environment, slows down the reaction. It also scavenges reactive oxygen species (ROS) from NO, such as peroxynitrite.

Bicarbonate protocols most often include infusion of sodium bicarbonate at the rate of 3 mL/kg/hour an hour before the procedure, continued at 1 mL/kg/hour for 6 hours after. Some investigators have used 1 mL/kg/hour for 24 hours, starting 12 hours before the procedure. The exact duration, however, remains a matter of debate. Hydration with sodium bicarbonate has been found by some researchers to be more protective than normal saline alone.

Treatment controversy

A 2008 retrospective cohort study at the Mayo Clinic assessed the risk of CIN associated with the use of sodium bicarbonate, NAC, and the combination of sodium bicarbonate with NAC and found that, compared with no treatment, sodium bicarbonate used alone was associated with an increased risk of CIN. NAC alone or in combination with sodium bicarbonate did not significantly affect the incidence of CIN. The results were obtained after adjusting for confounding factors, including total volume of hydration, medications, baseline creatinine, and contrast iodine load.[27] Given the above new information, it is recommended that the use of sodium bicarbonate to prevent CIN should be further evaluated.

N-acetylcysteine

NAC is acetylated L-cysteine, an amino acid. Its sulfhydryl groups make it an excellent antioxidant and scavenger of free oxygen radicals. It also enhances the vasodilatory properties of nitric oxide. Twelve meta-analyses covering 29 randomized, controlled trials have been published on the effect of NAC therapy in CIN. They all suffer from significant heterogeneity. The standard oral NAC regimen consists of 600 mg twice daily for 24 hours before and on the day of the procedure. Higher doses of 1 g, 1200 mg, and 1500 mg twice daily have also been studied, with no significant dose-related or route-related (oral vs intravenous) difference. NAC has very low oral bioavailability; substantial interpatient variability and inconsistency between the available oral products obscure the picture further.[3, 24, 28]

Treatment controversy

The latest controversy relating to NAC therapy questioned the parameter on which its effectiveness was based. It was suggested that the beneficial effect of NAC in CIN is related to its SCr-lowering ability rather than to improved GFR. It was believed that NAC directly reduces SCr by increasing SCr’s excretion (tubular secretion), decreasing its production (augments activity of creatine kinase), or interfering with its laboratory measurement, enzymatic or nonenzymatic (Jaffe method).

This was supported by a study that demonstrated a significant decrease in SCr after 4 doses of 600 mg of oral NAC in healthy volunteers with normal kidney function and no exposure to radiocontrast media.[29] This would bring doubt into the results of at least 13 randomized, controlled trials that showed NAC to be protective in CIN, with SCr used as the endpoint. However, Haase et al compared the effect of NAC on SCr by simultaneously studying its effect on cystatin C and found that NAC did not artifactually lower SCr when measured by the Jaffe method.[30]

The CIN Working Panel concluded that the existing data on NAC therapy in CIN is sufficiently varied to preclude a definite recommendation.[25] In the practice of medicine, though, it remains part of the standard of care and is routinely administered because of its low cost, lack of adverse effects, and potential beneficial effect, as demonstrated by the relative risk reduction of CIN, ranging from 0.37-0.73, as reported in several meta-analyses.

Renal Replacement Therapy

Less than 1% of patients with CIN ultimately go on to require dialysis, the number being slightly higher in patients with underlying renal impairment (3.1%) and in those undergoing primary PCI for MI (3%). However, in patients with diabetes and severe renal failure, the rate of dialysis can be as high as 12%. Patients who get dialyzed do considerably worse, with inhospital mortality rates of 35.7% (compared with 7.1% in the nondialysis group) and a 2-year survival rate of only 19%.

CM have molecular weights that range between 650 and 1600 mOsm/kg. They have low lipophilicity, low plasma protein binding, and minimal biotransformation. They quickly equilibrate across capillary membranes and have volumes of distribution equivalent to that of the extracellular fluid volume. In patients with normal renal function, CM are excreted with the first glomerular passage and the decrease in their plasma concentration follows a 2-part exponential function, a distribution phase and an elimination phase. However, in patients with renal impairment, the renal clearance values are reduced. For example, 50% of the low-osmolarity contrast agent iomeprol is eliminated within 2 hours in healthy subjects, compared with 16-84 hours in patients with severe renal impairment.

In patients already on dialysis, the commonly sited issues with contrast administration include volume load and direct toxicity of contrast to the remaining nonfunctional nephrons and nonrenal tissues. Thus, the perceived need for emergent dialysis and contrast removal.

Rodby attempted to address these concerns, calculating that the administration of 100 mL of hyperosmolar contrast would move 265 mL of water from the intracellular to the extracellular compartment, resulting in an increase in extracellular volume by 365 mL. The increase in intravascular space would therefore be only a third, or 120 mL. Fluid shifts with LOCM are even less. He also found that extrarenal toxicity of CM was cited in mostly single case reports, and no objective evidence could be identified in 3 prospective studies.[31]

The risk of acute damage from contrast is therefore greatest in patients with CKD. This can be explained by the increase in single nephron GFR and, thus, the filtered load of contrast per nephron. This is akin to a double hit to the remaining nephrons; increased contrast load and prolonged tubular exposure. While this may not seem to be a concern in patients with ESRD who are already on dialysis, residual renal function, in fact, plays a big role in their outcome, more so in patients on peritoneal dialysis. Its preservation is therefore important.[31]

CM can be effectively and efficiently removed by hemodialysis (HD). Factors that influence CM removal include blood flow, membrane surface area, molecular size, transmembrane pressure, and dialysis time. High-flux dialysis membranes with blood flows of between 120-200 mL/min can remove almost 50% of iodinated CM within an hour and 80% in 4 hours. Even in patients with CKD, in whom contrast excretion is delayed, it was found that 70-80% of contrast can be removed by a 4-hour HD treatment. In view of the limited benefit of therapies such as hydration, bicarbonate and NAC, dialysis may seem like the definitive answer.

However, an excellent meta-analysis by Cruz et al—8 trials (6 randomized and 2 nonrandomized, controlled studies) were included in the analysis, with a pooled sample size of 412 patients—indicated that periprocedural extracorporeal blood purification (ECBP) does not significantly reduce the incidence of CIN in comparison with standard medical therapy. ECBP in the study consisted of HD (6 trials), continuous venovenous hemofiltration (1 trial), and continuous venovenous hemodiafiltration (1 trial).[32]

Cruz et al found that the incidence of CIN in the standard medical therapy group was 35.2%, compared with 27.8% in the ECBP group. Renal death (combined endpoint of death or dialysis dependence) was 12.5% in the standard medical therapy group, compared with 7.9% in the ECBP group.

An important consideration is the role of ECBP therapy in patients with severe renal impairment (ie, stage 5 CKD) not yet on maintenance dialysis. A study by Lee et al indicated that in patients with chronic renal failure who are undergoing coronary angiography, prophylactic HD can improve renal outcome. The study included 82 patients with stage 5 CKD who were not on dialysis and who were referred for coronary angiography.[33] The patients were randomly assigned to either undergo prophylactic HD (initiated within 81 ± 32 min) or to receive intravenous normal saline (control group).

The baseline creatinine of the dialysis group was 13.2 mL/min/1.73 m2, comparable to that of the control group (12.6 mL/min/1.73 m2). The investigators’ primary endpoint was change in creatinine clearance in the 2 groups on day 4, which was found to be statistically significant (0.4 ± 0.9 mL/min/1.73 m2 in the dialysis group vs 2.2 ± 2.8 mL/min/1.73 m2 in the control group).

Lee et al found that 35% of the control group required temporary renal replacement therapy, compared with 2% of the dialysis group. In addition, long-term, postdischarge dialysis was required in 13% of the control patients but in none of the dialysis patients. Among those patients who did not require chronic dialysis, an increase in SCr at discharge of over 1 mg/dL from baseline was found in 13 patients in the control group and in 2 patients in the dialysis group.

The study, though hopeful, does raise some concerns. While the change in creatinine clearance on day 4 from baseline was statistically significant, the day 4 creatinine clearance itself was not significantly different between the 2 groups. Also, the results were not expressed as CIN incidence. This patient population is very fragile and is already on the verge of dialysis. How much time off dialysis a single HD session was able to buy these patients was not discussed. The duration of follow-up was also not clear.

Marenzi et al found better outcomes in patients who received venovenous hemofiltration both pre- and post-CM administration than in patients who received post-CM hemofiltration or no hemofiltration at all. These outcomes included a lower likelihood of CIN, no need for HD, and no 1-year mortality, in the pre-/post-CM group.[34]

The biggest confounder in studies of continuous renal replacement therapy (CRRT) is that the outcome measure (SCr) is affected by the treatment itself. While the advantage of CRRT is the lack of delay in its institution, contrast clearance rates would be 1 L/h (16.6 mL/min provided a maximal sieving coefficient for contrast across the hemofiltration membrane of 1), substantially less than standard HD.

Furthermore, continuous venovenous hemofiltration is expensive, highly invasive, and requires trained personnel; the procedure itself needs to be performed in the intensive care unit (ICU). In the face of equivocal benefit of a highly invasive and expensive procedure, the role of continuous venovenous hemofiltration has yet to be accepted as a prophylactic treatment for avoiding CIN.

Dialysis immediately after contrast administration has been suggested for patients already on long-term HD and for those at very high risk of CIN. Three studies looked at its necessity and found that LOCM can be given safely to patients with ESRD who are being maintained on HD without the added expense or inconvenience of emergent postprocedural HD.

The only condition in which HD might be argued to have a beneficial role is in patients on peritoneal dialysis who rely on their residual renal function. In this setting, HD performed soon after CM administration may provide enhanced removal and therefore protect residual renal function. It should be noted, however, that these patients on peritoneal dialysis would therefore need an additional HD procedure with concomitant vascular access, as the clearance with peritoneal dialysis would be far too slow to offer any protection.

In a study to determine if renal replacement therapy in concert with contrast administration helps, Frank et al found that although the overall clearance of contrast was significantly increased by dialysis, the peak plasma concentration of iomeprol 15 minutes after contrast administration was not significantly changed by simultaneous dialysis. In their report, the investigators prospectively studied 17 patients with chronic renal insufficiency (SCr >3 mg/dL), dialysis independent, who were then randomized to receive high-flux HD over 6 hours simultaneously with contrast administration, and[35]

In the study, Frank et al also found that to be clinically effective, simultaneous dialysis should reduce the risk of developing ESRD by 50%. If type 1 and type 2 errors are set at 0.01, the result could be accepted only if none of the 48 sequential patients with simultaneous dialysis required dialysis during the 8 weeks after contrast exposure. To reject the hypothesis, 239 sequential patients with simultaneous dialysis would have to be included. Therefore, most CIN studies, are seriously underpowered.

Studies of HD for CIN vary with respect to the definition of CIN used, the patient population, the type and volume of CM, how long after CM administration HD is started, and, finally, the dialysis treatment modality itself. While existing studies do not show HD to be superior to hydration alone for CIN prevention, if HD is used in conjunction with hydration and CIN protective therapy, such as NAC and bicarbonate, it might prove to be efficacious in some high-risk patients. However, most studies have had only an 8-week follow-up period. While the initiation of long-term dialysis was 5-15%, the progression to uremia over a long-term follow-up period is still unanswered.[16]

Other Therapies

Ascorbic acid, which has antioxidant properties, was studied for its ability to counter the effect of free radicals and reactive oxygen species. One study found that oral ascorbic acid administered in a 3-g dose preprocedure and two 2-g doses postprocedure was associated with a 62% risk reduction in CIN incidence.[36]

Theophylline and aminophylline are adenosine antagonists that counteract the intrarenal vasoconstrictor and tubuloglomerular feedback effects of adenosine. They have been found to have a statistically significant effect in preventing CIN in high-risk patients. However, their use is limited by their narrow therapeutic window and adverse effects profile.

Vasodilators, such as calcium channel blockers, dopamine/fenoldopam, atrial natriuretic peptide, and L-arginine, all with different mechanisms of action, have a favorable effect on renal hemodynamics. However, their use for CIN prevention has not been borne out by most controlled trials, and they are not routinely recommended at this point.

Forced diuresis with furosemide and mannitol was studied in the hope that this procedure would dilute CM within the tubular lumen and enhance their excretion. Furosemide and mannitol in fact worsen CIN by causing dehydration in patients who may already have intravascular volume depletion. Their use at this time is discouraged.

Deterrence and Prevention

The best therapy for CIN is prevention. Physicians need to be increasingly aware that CIN is a common and potentially serious complication. Patients at risk should be identified early, especially those with CKD (ie, eGFR < 60 mL/min/1.73 m2). A detailed history inquiring for risk factors, especially diabetes mellitus, should be ascertained.

In patients with risk factors for CIN, the possibility of alternative imaging studies that do not need contrast should be explored. MRI with gadolinium is no longer considered a safe alternative to contrast because of the risk of nephrogenic systemic fibrosis, an irreversible, debilitating condition seen mostly in patients with an eGFR of less than 30 mL/min/1.73 m2.

In patients with a moderate to severe risk of CIN, creatinine clearance rates or eGFR should be estimated by either the MDRD formula or the Cockroft-Gault formula and then measured again 24-48 hours after contrast administration.

In the emergency setting, where the benefit of very early imaging studies outweighs that of waiting, the imaging procedure can be carried out without an initial estimation of SCr or eGFR.

Intra-arterial administration of iodinated CM poses a greater risk for CIN than does the intravenous approach. For patients at an increased risk for CIN receiving intra-arterial contrast, nonionic iso-osmolar agents (iodixanol) are associated with the lowest risk of CIN.

The amount of contrast used during the procedure should be limited to as little as possible and kept under 100 mL. Most investigators have found this to be the cut-off value below which no patient needed dialysis. The risk of CIN increases by 12% for each 100 mL of contrast used beyond the first 100 mL. Most angiographic diagnostic studies usually require 100 mL of contrast, compared with 200-250 mL for angioplasty. The maximum amount of contrast that can be used safely should be individualized, taking into account the preexisting renal function.

Various formulas for calculating the maximal safe CM dose have been suggested. Two most often cited are those suggested by Cigarroa et al and the European Society of Urogenital Radiology (ESUR).[37, 38] Cigarroa et al, in a retrospective study of 115 patients undergoing cardiac catheterization and angiography, using the HOCM diatrizoate, suggested that the dose of CM should not exceed 5 mL/kg of body weight (maximum 300 mL divided by SCr [mg/dL]). The ESUR, in turn, has published maximal LOCM volumes for various SCr cut-off values.

While the formulas from Cigarroa and the ESUR take into account the SCr, it has been suggested that the eGFR (a more accurate predictor of renal function) and the iodine dose of CM should be reflected in any estimates or predictions of safe CM dosages. There exists, however, no unimpeachably safe CM dose algorithm for CIN prevention.

The length of time between 2 contrast procedures should be at least 48-72 hours. Rapid repetition of contrast administration has been found to be a univariate risk factor for CIN.

Potentially nephrotoxic drugs (eg, NSAIDs, aminoglycosides, amphotericin B, cyclosporin, tacrolimus) should be withdrawn at least 24 hours prior, in patients at risk (eGFR < 60 mL/min).

Metformin, though not nephrotoxic, should be used prudently, because if renal failure does occur, there is risk of concomitant lactic acidosis. Therefore, metformin should be stopped at the time of the procedure and resumed 48 hours later if renal function remains normal.

Angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs) cause a 10-15% rise in SCr by reducing intraglomerular pressure. While they should not be started at this time, whether they should be discontinued remains a matter of debate. Much of the literature in this area is unclear and controversial.

Minimizing contrast administration

The amount of contrast used during the procedure should be limited to as little as possible and kept under 100 mL. Most investigators have found this to be the cut-off value below which no patient needed dialysis. The risk of CIN increases by 12% for each 100 mL of contrast used beyond the first 100 mL. Most angiographic diagnostic studies usually require 100 mL of contrast, compared with 200-250 mL for angioplasty. The maximum amount of contrast that can be used safely should be individualized, taking into account the preexisting renal function.

Various formulas for calculating the maximal safe CM dose have been suggested. Two most often cited are those suggested by Cigarroa et al and the European Society of Urogenital Radiology (ESUR).[37, 38] Cigarroa et al, in a retrospective study of 115 patients undergoing cardiac catheterization and angiography, using the HOCM diatrizoate, suggested that the dose of CM should not exceed 5 mL/kg of body weight (maximum 300 mL divided by SCr [mg/dL]). The ESUR, in turn, has published maximal LOCM volumes for various SCr cut-off values.

While the formulas from Cigarroa and the ESUR take into account the SCr, it has been suggested that the eGFR (a more accurate predictor of renal function) and the iodine dose of CM should be reflected in any estimates or predictions of safe CM dosages. There exists, however, no unimpeachably safe CM dose algorithm for CIN prevention.

RAAS blockade

A prospective, 50-month Mayo study found renin-angiotensin-aldosterone system (RAAS) blockade, particularly in older patients with CHD, exacerbates CIN (43% incidence of dialysis and 29% progression to ESRD).[39] The marker used for renal function was eGFR, as calculated by the MDRD formula. The study recommended that RAAS blockade be withheld 48 hours prior to contrast exposure.

RAAS blockage, however, can improve renal perfusion and decrease proximal tubular reabsorption, including CM absorption by the tubular cells. This effect can be documented with the increase in the fractional excretion of urea seen with low-dose RAAS therapy in patients with CHF and moderate CKD (the majority of the CIN-susceptible population).[40] In this group, reduction in intraglomerular pressure and filtration fraction from RAAS therapy might decrease tubular CM concentration and therefore lessen its adverse effects.

Medication Summary

NAC is acetylated L-cysteine, an amino acid. As previously mentioned, its sulfhydryl groups make it an excellent antioxidant and scavenger of free oxygen radicals. It also enhances the vasodilatory properties of nitric oxide. Twelve meta-analyses covering 29 randomized, controlled trials have been published on the effect of NAC therapy in CIN. They all suffer from significant heterogeneity. The standard oral NAC regimen consists of 600 mg twice daily for 24 hours before and on the day of the procedure. Higher doses of 1 g, 1200 mg, and 1500 mg twice daily have also been studied, with no significant dose-related or route-related (oral vs intravenous) difference. NAC has very low oral bioavailability; substantial interpatient variability and inconsistency between the available oral products obscure the picture further.[24, 28]

Antidote, Acetaminophen

Class Summary

Used for prevention of contrast toxicity.

N-acetylcysteine (Acetadote)

Used for prevention of contrast toxicity in susceptible individuals such as those with diabetes mellitus. May provide substrate for conjugation with toxic metabolites.

Antilipemic Agents

Class Summary

These agents are used for their favorable effects on endothelin and thrombus formation, plaque stabilization and anti-inflammatory properties by improving lipid profile.

Simvastatin (Zocor)

Indicated for hyperlipoproteinemia (Type III). Inhibit 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA reductase), which in turn inhibit cholesterol synthesis, and increases cholesterol metabolism. Increase HDL cholesterol and decrease LDL-C, total-C, apolipoprotein B, VLDL cholesterol, and plasma triglycerides.

Atorvastatin (Lipitor)

The most efficacious of the statins at high doses. Inhibits 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA reductase), which in turn inhibits cholesterol synthesis and increases cholesterol metabolism. Reports have shown as much as a 60% reduction in LDL-C. The Atorvastatin versus Revascularization Treatment study (AVERT) compared 80 mg atorvastatin daily to standard therapy and angioplasty in patients with CHD. While events at 18 mo were the same between both groups, the length of time until the first CHD event occurred was longer with aggressive LDL-C lowering. The half-life of atorvastatin and its active metabolites is longer than that of all the other statins (ie, approximately 48 h compared to 3-4 h).

May modestly elevate HDL-C levels. Clinically, reduced levels of circulating total cholesterol, LDL-C, and serum TGs are observed.

Before initiating therapy, patients should be placed on a cholesterol-lowering diet for 3-6 mo; the diet should be continued indefinitely.

Lovastatin (Mevacor, Altoprev)

Adjunct to dietary therapy in reducing serum cholesterol. Immediate-release (Mevacor) and extended-release (Altocor) are available.

Fluvastatin (Lescol, Lescol XL)

Synthetically prepared HMG-CoA reductase inhibitor with some similarities to lovastatin, simvastatin, and pravastatin. However, structurally distinct and has different biopharmaceutical profile (eg, no active metabolites, extensive protein binding, minimal CSF penetration).

Used as an adjunct to dietary therapy in decreasing cholesterol levels.

Pravastatin (Pravachol)

Effective in reducing circulating lipid levels and improving the clinical and anatomic course of atherosclerosis.

Rosuvastatin (Crestor)

HMG-CoA reductase inhibitor that in turn decreases cholesterol synthesis and increases cholesterol metabolism. Reduces total-C, LDL-C, and TG levels and increases HDL-C level. Used adjunctively with diet and exercise to treat hypercholesterolemia.

SOURCE

Managing Your Risks: Patient and Physician Health in the Cath Lab

flouro image

In this post we’ll explore the issue of radiation exposure, occupational risks in the catheterization lab, and how that can impact your care.

I. Patient Risks in the Cath Lab

Fluoroscopy is a type of medical imaging used during percutaneous coronary interventions that displays a continuous x-ray image. Blood flow and artery blockages are not able to be seen using x-ray only imaging. Physicians inject a contrast solution into the arteries so that when an x-ray beam is passed through the tissue, the physician can get a real-time image of the coronary arteries. On average, angioplasty procedures will last about an hour, this means the patient is exposed to ionizing radiation from the fluoroscopy for a significant amount of time. Lengthy procedures lead to greater exposure to the radiation of fluoroscopy.

Radiation has a cumulative effect and leads to increased risk for many conditions, most notably, cancer.  In healthcare where radiation is required for treatment, there is a prevailing philosophy called ALARA, which stands for as low as (is) reasonably achievable.   Wherever possible, physicians should be looking for ways to limit exposure to radiation to limit the cumulative effects of radiation on patients. Along with the risks posed by radiation, patients in the cath lab also face potentially high doses of the contrast medium which can cause a condition known as contrast induced nephropathy. The contrast solution that is so valuable to imaging can be toxic to the kidneys, and when the body is unable to process the contrast, it leads to CIN in which the kidneys shut down.  While most patients who develop CIN typically recover within 1- 2 weeks, it can cause serious renal (kidney) complications in patients with certain risk factors including diabetes, prior kidney transplant, chronic kidney disease, and hypertensive disorders. Therefore, physicians need to keep a constant watch on the contrast volume used during procedures to minimize the risk of CIN.

II. Occupational Hazards in the Cath Lab

It is well documented that Interventional Cardiologists face serious dangers of long-term radiation exposure in the cath lab. Risks to clinicians include: skin damage to hands and exposed tissue, injury to the lens of the eye/ cataracts, and in some cases the development of brain tumors and other cancers. In a 2012 study, researchers found an increased incidence of left hemisphere brain tumors in a study group of interventional cardiologists that may be attributed to the prolonged exposure to ionizing radiation to the left side of the head during interventional procedures.

Via LifeScience PLUS

Physicians in the Cardiac Cath Lab (Via LifeScience PLUS)

Lead aprons are the standard convention used in Cath labs across the US to reduce radiation exposure to physicians and staff; however these protective barriers can weigh between 15-20 pounds and place up to 300 pounds per square inch of pressure on vertebral disks. In one study more than 400 interventionalists were surveyed and 71% of the study population reported some type of orthopedic disease. According to Dr. Tom Ports, Director of Interventional Cardiology at University of San Francisco, the leading cause of early retirement for interventional cardiologists is spinal injury!

Attention to the danger of radiation exposure and other risks in the cath lab for both patients and staff is on the rise. As more focus is being brought upon safety practices in the cath lab, improved procedural measures are being put in place to protect physicians and staff, and improve the quality of care for patients.

http://blog.corindus.com/?p=124

REFERENCES

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The Cardiorenal Syndrome in Heart Failure: Cardiac? Renal? syndrome?

Writer and Curator: Larry H. Bernstein, MD, FCAP

and

Curator: Aviva Lev-Ari, PhD, RN 

Triposkiadis F, Starling RC, Boudoulas H, Giamouzis G, Butler J.
Heart Fail Rev. 2012 May;17(3):355-66. http://dx.doi.org/10.1007/s10741-011-9291-x Review

There has been increasing interest on the so-called cardiorenal syndrome (CRS), defined as

  • a complex pathophysiological disorder of the heart and kidneys where by acute or chronic dysfunction in one organ may induce acute or chronic dysfunction in the other.

In this review, we contend that there is lack of evidence warranting the adoption of a specific clinical construct such as the CRS within the heart failure (HF) syndrome by demonstrating that:

(a) the approaches and tools regarding the definition of kidney involvement in HF are suboptimal;
(b) development of renal failure in HF is often confounded by age, hypertension, and diabetes;
(c) worsening of renal function (WRF) in HF may be largely independent of alterations in cardiac function;
(d) the bidirectional association between HF and renal failure is not unique and represents one of the several such associations encountered in HF; and
(e) inflammation is a common denominator for HF and associated noncardiac morbidities.

Based on these arguments, we believe that

  • dissecting one of the multiple bidirectional associations in HF and
  • constructing the so-called cardiorenal syndrome is not justified pathophysiologically.

Fully understanding of all morbid associations and not only the cardiorenal, that is of great significance for the clinician who is caring for the patient with HF.

Ultrafiltration in Heart Failure with Cardiorenal Syndrome

N Engl J Med 2013; 368:1157-1160 http://dx.doi.org/10.1056/NEJMc1300456

Bart et al. (Dec. 13 issue)1 report the results of the Cardiorenal Rescue Study in Acute Decompensated Heart Failure (CARRESS-HF). They state that ultrafiltration was inferior to a strategy of stepped pharmacologic therapy with respect to the

It is unclear at first sight why renal function should be different at 96 hours only when serum creatinine concentrations are used as a marker of renal function,

  • but not when the level of cystatin C or the glomerular filtration rate are used.

How can this discrepancy be explained?

According to the study Ultrafiltration in Decompensated Heart Failure with Cardiorenal Syndrome

Bart BA., Goldsmith SR., Lee KL, Givertz MM, et al.
N Engl J Med 2012; 367:2296-2304 http://dx.doi.org/10.1056/NEJMoa1210357

Ultrafiltration is an alternative strategy to diuretic therapy for the treatment of patients with acute decompensated heart failure.

Little is known about the efficacy and safety of ultrafiltration in patients with acute decompensated heart failure

  • complicated by persistent congestion and worsened renal function.

Ultrafiltration was inferior to pharmacologic therapy with respect to the bivariate end point of

  1. the change in the serum creatinine level and body weight 96 hours after enrollment (P=0.003),
  2. owing primarily to an increase in the creatinine level in the ultrafiltration group.
  • At 96 hours, the mean change in the creatinine level was −0.04±0.53 mg per deciliter (−3.5±46.9 μmol per liter) in the pharmacologic-therapy group,
  • as compared with +0.23±0.70 mg per deciliter (20.3±61.9 μmol per liter) in the ultrafiltration group (P=0.003).

A higher percentage of patients in the ultrafiltration group than in the pharmacologic-therapy group had a serious adverse event (72% vs. 57%, P=0.03).
In a randomized trial involving patients hospitalized for acute decompensated heart failure,

  1. worsened renal function, and
  2. persistent congestion,

the use of a stepped pharmacologic-therapy algorithm was superior to a strategy of ultrafiltration for

  • the preservation of renal function at 96 hours,
  • with a similar amount of weight loss with the two approaches. 

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Nitric Oxide and it’s Impact on Cardiothoracic Surgery (tildabarliya)
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CABG or PCI: Patients with Diabetes – CABG Rein Supreme (Aviva Lev-Ari)
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Endothelin Receptors in Cardiovascular Diseases: The Role of eNOS Stimulation (Aviva Lev-Ari)
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Long-Term Mortality in Treated Hypertensive Patients: Serum Uric Acid Level, Longitudinal Blood Pressure and Renal Function

Aviva Lev-Ari, PhD, RN

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Renal Sympathetic Denervation: Updates on the State of Medicine

Aviva Lev-Ari, PhD,RN

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Chapter 8: Nitric Oxide and Kidney Dysfunction

https://pharmaceuticalintelligence.com/biomed-e-books/perspectives-on-nitric-oxide-in-disease-mechanisms-v2/

8.1 Part I: The Amazing Structure and Adaptive Functioning of the Kidneys: Nitric Oxide

Larry H. Bernstein, MD, FCAP

8.2 Part II: Nitric Oxide and iNOS have Key Roles in Kidney Diseases

Larry H. Bernstein, MD, FCAP

8.3 Part III: The Molecular Biology of Renal Disorders: Nitric Oxide

Larry H. Bernstein, MD, FCAP

8.4 Part IV: New Insights on Nitric Oxide Donors

Larry H. Bernstein, MD, FCAP

8.5 The Essential Role of Nitric Oxide and Therapeutic Nitric Oxide Donor Targets in Renal Pharmacotherapy

What is Acute Heart Failure?

What is Acute Heart Failure? (Photo credit: Novartis AG)

English: Physiology of Nephron

English: Physiology of Nephron (Photo credit: Wikipedia)

Forrester-classification for classification of...

Forrester-classification for classification of Congestive heart failure ; Forrester-Klassifikation zur Einteilung einer akuten Herzinsuffizienz (Photo credit: Wikipedia)

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Reporter: Aviva Lev-Ari, PhD, RN

 

 

  • Original Article

HYPERTENSIONAHA.113.00859 Published online before print May 20, 2013,doi: 10.1161/​HYPERTENSIONAHA.113.00859

Serum Uric Acid Level, Longitudinal Blood Pressure, Renal Function, and Long-Term Mortality in Treated Hypertensive Patients
  1. Jesse Dawson,
  2. Panniyammakal Jeemon,
  3. Lucy Hetherington,
  4. Caitlin Judd,
  5. Claire Hastie,
  6. Christin Schulz,
  7. William Sloan,
  8. Scott Muir,
  9. Alan Jardine,
  10. Gordon McInnes,
  11. David Morrison,
  12. Anna Dominiczak,
  13. Sandosh Padmanabhan,
  14. Matthew Walters

+Author Affiliations


  1. From the Institute of Cardiovascular and Medical Sciences (J.D., P.J., L.H., C.J., C.H., C.S., S.M., A.J., G.M., A.D., S.P., M.W.), West of Scotland Cancer Surveillance Unit (W.S., D.M.), College of Medical, Veterinary & Life Sciences, University of Glasgow, Glasgow, United Kingdom.
  1. Correspondence to Matthew Walters, Institute of Cardiovascular and Medical Sciences, College of Medical, Veterinary & Life Sciences, Western Infirmary, University of Glasgow, Glasgow G11 6NT, United Kingdom. E-mail matthew.walters@glasgow.ac.uk; or Sandosh Padmanabhan, BHF Glasgow Cardiovascular Research Centre, Institute of Cardiovascular and Medical Sciences, 126 University Pl, University of Glasgow, Glasgow G12 8TA, United Kingdom. E-mail Sandosh.padmanabhan@glasgow.ac.uk

Abstract

Uric acid may have a role in the development of hypertension and renal dysfunction. We explored the relationship among longitudinal blood pressure, renal function, and cardiovascular outcomes in a large cohort of patients with treated hypertension. We used data from the Glasgow Blood Pressure Clinic database. Patients with a baseline measure of serum uric acid and longitudinal measures of blood pressure and renal function were included. Mortality data were obtained from the General Register Office for Scotland. Generalized estimating equations were used to explore the relationship among quartiles of serum uric acid, blood pressure, and estimated glomerular filtration rate. Cox proportional hazard models were developed to assess mortality relationships. In total, 6984 patients were included. Serum uric acid level did not influence the longitudinal changes in systolic or diastolic blood pressure but was related to change in glomerular filtration rate. In comparison with patients in the first quartile of serum uric acid, the relative decrease in glomerular filtration rate in the fourth was 10.7 (95% confidence interval, 7.9–13.6 mL/min per 1.73 m2) in men and 12.2 (95% confidence interval, 9.2–15.2 mL/min per 1.73 m2) in women. All-cause and cardiovascular mortality differed across quartiles of serum uric acid in women only (P<0.001; hazard ratios for all-cause mortality 1.38 [95% confidence interval, 1.14–1.67] for the fourth quartile of serum uric acid compared with the first). Serum uric acid level was not associated with longitudinal blood pressure control in adults with treated hypertension but was related to decline in renal function and mortality in women.

Key Words:

  • Received February 19, 2013.
  • Revision received April 23, 2013.
  • Accepted April 23, 2013.

http://hyper.ahajournals.org/content/early/2013/05/20/HYPERTENSIONAHA.113.00859.abstract.html?papetoc

 

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Subtitle: The Balance of Nitric Oxide, Peroxinitrite, and NO donors in Maintenance of Renal Function

Curator and Author: Larry H. Bernstein, MD, FCAP

The Nitric Oxide and Renal is presented in FOUR parts:

Part I: The Amazing Structure and Adaptive Functioning of the Kidneys: Nitric Oxide

Part II: Nitric Oxide and iNOS have Key Roles in Kidney Diseases

Part III: The Molecular Biology of Renal Disorders: Nitric Oxide

Part IV: New Insights on Nitric Oxide donors 

Conclusion to this series is presented in

The Essential Role of Nitric Oxide and Therapeutic NO Donor Targets in Renal Pharmacotherapy

Evolution of kidney function

The Emergence of  a Mammalian Kidney as Subterranian Life Crawls from Sea to Land
In fish the nerves that activate breathing take a short journey from an ancient part of the brain, the brain stem, to the throat and gills. For the ancient tadpole, the nerve controlling a reflex related to hiccup in man served a useful purpose, allowing the entrance to the lung to remain open when breathing air but closing it off when gulping water – which would then be directed only to the gills. For humans and other mammals it provides a bit of evidence of our common ancestry. DNA evidence has pinned iguanas and chameleons as the closest relatives to snakes.

In utero, we develop three separate kidneys in succession, absorbing the first two before we wind up with the embryonic kidney that will become our adult kidney. The first two of these reprise embryonic kidneys of ancestral forms, and in the proper evolutionary order. The pronephric kidney does not function in human and other mammalian embryos. It disappears and gives rise to the Mesonephric kidney. This kidney filters wastes from the blood and excretes them to the outside of the body via a pair of tubes called the mesonephric ducts (also “Wolffian ducts”). The mesonephric kidney goes on to develop into the adult kidney of fish and amphibians. This kidney does function for a few weeks in the human embryo, but then disappears as our final kidney forms, which is the Metanephric kidney.

The Metanephric kidney begins developing about five weeks into gestation, and consists of an organ that filters wastes from the blood and excretes them to the outside through a pair ureters. In the embryo, the wastes are excreted directly into the amniotic fluid. The metanephric kidney is the final adult kidney of reptiles, birds, and mammals. The first two kidneys resemble, in order, those of primitive aquatic vertebrates (lampreys and hagfish) and aquatic or semiaquatic vertebrates (fish and amphibians): an evolutionary order. The explanation, then, is that we go through developmental stages that show organs resembling those of our ancestors.

Take a step back and we see that fresh water fish have glomerular filtration. Cardiac contraction provides the pressure to force the water, small molecules, and ions into the glomerulus as nephric filtrate. The essential ingredients are then reclaimed by the tubules, returning to the blood in the capillaries surrounding the tubules. The amphibian kidney also functions chiefly as a device for excreting excess water. But the problem is to conserve water, not eliminate it. The frog adjusts to the varying water content of its surroundings by adjusting the rate of filtration at the glomerulus. When blood flow through the glomerulus is restricted, a renal portal system is present to carry away materials reabsorbed through the tubules. Bird kidneys function like those of reptiles (from which they are descended). Uric acid is also their chief nitrogenous waste.

All mammals share our use of urea as their chief nitrogenous waste. Urea requires much more water to be excreted than does uric acid. Thus, mammals produce large amounts of nephric filtrate but are able to reabsorb most of this in the tubules. Even so, humans lose several hundred ml each day in flushing urea out of the body. In his hypothesis of the evolution of renal function Homer Smith proposed that the formation of glomerular nephron and body armor had been adequate for the appearance of primitive vertebrates in fresh water and that the adaptation of homoisotherms to terrestrial life was accompanied by the appearance of the loop of Henle.

In the current paper, the increase in the arterial blood supply and glomerular filtration rate and the sharp elevation of the proximal reabsorption are viewed as important mechanisms in the evolution of the kidney. The presence of glomeruli in myxines and of nephron loops in lampreys suggests that fresh water animals used the preformed glomerular apparatus of early vertebrates, while mechanisms of urinary concentration was associated with the subdivision of the kidney into the renal cortex and medulla. The principles of evolution of renal functions can be observed at several levels of organizations in the kidney.
Natochin YV. Evolutionary aspects of renal function. Kidney International 1996; 49: 1539–1542; doi:10.1038/ki.1996.220.
Smith HW: From Fish to Philosopher. Boston, Little, Brown, 1953.

The Kidney: Anatomy and Physiology

The kidney lies in the lower abdomen capped by the adrenal glands. It has an outer cortex and an inner medulla. The basic unit is the nephron, which filters blood at the glomerulus, and not only filters urine eliminating mainly urea, also uric acid, and other nitrogenous waste, but also reabsorbs Na+ in exchange for H+/(reciprocal K+) through the carbonic anhydrase of the epithelium. In addition, it serves as a endocrine organ and receptor through the renin-angiotensin/aldosterone system, sensitivity to water loss controlled by distal acting antidiuretic hormone, and is sensitive to the natriuretic peptides of the heart. The kidney is an elegant structure with a high concentration of glomeruli in the cortex, and in the medulla one finds a U-shaped tube that is critical in functioning of a countercurrent multiplier system with a descending limb, Loop of Henley, and ascending limb.

The glomerulus is a dense ball of capillaries (glomerular capillaries) that branches from the afferent arteriole that enters the nephron. Because blood in the glomerular capillaries is under high pressure, substances in the blood that are small enough to pass through the pores (fenestrae, or endothelial fenestrations) in the capillary walls are forced out and into the encircling glomerular capsule. The glomerular capsule is a cup-shaped body that encircles the glomerular capillaries and collects the material (filtrate) that is forced out of the glomerular capillaries. The filtrate collects in the interior of the glomerular capsule, the capsular space, which is an area bounded by an inner visceral layer (that faces the glomerular capillaries) and an outer parietal layer.

The glomerular filtrate passes into the proximal convoluted tubule (PCT),  a winding tube in the renal cortex.  The PCT is mitochondria roch and has a high-energy yield.  The large surface area of these cells support their functions of reabsorption and secretion. The filtrate passes down the descending tubule and reaches the Loop of Henle. The  loop is shaped like a hairpin and consists of a descending limb that drops into the renal medulla and an ascending limb that rises back into the renal cortex.  The distal convoluted tubule (DCT) coils within the renal cortex and empties into the collecting duct.   In the final portions of the DCT and the collecting duct, there are cells that respond to the hormones aldosterone and antidiuretic hormone (ADH), and there are cells that secrete H+ in an effort to maintain proper pH.

The juxtaglomerular apparatus (JGA) is an area of the nephron where the afferent arteriole and the initial portion of the distal convoluted tubule are in close contact. Here, specialized smooth muscle cells of the afferent arteriole, called granular juxtaglomerular (JG) cells, act as mechanoreceptors that monitor blood pressure in the afferent arteriole. In the adjacent distal convoluted tubule, specialized cells, called macula densa, act as chemoreceptors that monitor the concentration of Na+ and Cl in the urine inside the tubule. Together, these cells help regulate blood pressure and the production of urine in the nephron.

The operation of the human nephron consists of three processes:

  • Glomerular filtration
  • Tubular reabsorption
  • Tubular secretion

The net filtration pressure (NFP) determines the quantity of filtrate that is forced into the glomerular capsule. The NFP, estimated at about 10 mm Hg, is the sum of pressures that promote filtration less the sum of those that oppose filtration. The following contribute to the NFP:

  • The glomerular hydrostatic pressure (blood pressure in the glomerulus) promotes filtration.
  • The glomerular osmotic pressure  is created as a result of the movement of water and solutes out of the glomerular capillaries. The increase in the concentration of solutes in the glomerular capillaries draws into the glomerular capillaries.
  • The capsular hydrostatic pressure inhibits filtration. This pressure develops as water collects in the glomerular capsule.

As the filtrate flows through the glomerulus into the descending limb, glucose is reabsorbed  to a threshhold maximum, and H+ is converted by the carbonic anhydrase  to water and CO2, except with serious acidemia, in which K+ is reabsorbed with H+ loss to the filtrate, resulting in a hyperkalemia. In the descending limb Na+ is absorbed into the interstitium, and the hypertonic interstitium draws water back for circulation, regulated by the action of ADH on the epithelium of the ascending limb. The result in terms of basic urinary clearance, the volume of urine loss is moderated by the amount needed for circulation (10 units of whole blood) without dehydration, and an amount sufficient for metabolite loss (including drug metabolites). The urine flows into the kidney pelvis and flow down the ureters.

The reabsorption of most substances from the tubule to the interstitial fluids requires a membrane-bound transport protein that carries these substances across the tubule cell membrane by active transport. When all of the available transport proteins are being used, the rate of reabsorption reaches a transport maximum (Tm), and substances that cannot be transported are lost in the urine.

The blood reaches the glomerulus by way of the afferent arteriole and leaves by way of the efferent arteriole. In a book by the Harvard Pathologist Shields Warren on diabetes he made a distinction between hypertension and diabetes in that efferent arteriolar sclerosis is present in both, but diabetes is uniquely identified by afferent arteriolar sclerosis. In diabetes you also have a typical glomerulosclerosis, which might be related to the same hyalinization found in the pancreatic islets – a secondary amyloidosis.

The renal artery for each kidney enters the renal hilus and successively branches into segmental arteries and then into interlobar arteries, which pass between the renal pyramids toward the renal cortex. The interlobar arteries then branch into the arcuate arteries, which curve as they pass along the junction of the renal medulla and cortex. Branches of the arcuate arteries, called interlobular arteries, penetrate the renal cortex, where they again branch into afferent arterioles, which enter the filtering mechanisms, or glomeruli, of the nephrons.

Summary

The criticality of renal function is traced to the emergence of animal forms from the sea to land, and its evolutionary change is recapitulated in the embryo.  We have already described the key role that nitric oxide and the NO synthases play in reduction of oxidative stress, and we have seen that a balance has to be struck between pro- and anti-oxidative as well as inflammatory elements for avoidance of diseases, specifically involving the circulation, but effectively not limited to any organ system. In addition, we have noted the importance of oxidative stress and modifications in mitochondrial function in oncogenesis related to a reliance on aerobic glycolysis to support both energy and synthetic activities in growth and proliferation of the “cancer” cell, that becomes more like a cancer “prototype” than its forebears.  In this discussion we pay attention to kidney function, and what follows is the adaptive role of NO and NO donors. This is an extension of a series of posts on NO and NO related disorders.

Frontal section through the kidney

Frontal section through the kidney (Photo credit: Wikipedia)

Structures of the kidney: Renal pyramid Interl...

Structures of the kidney: Renal pyramid Interlobar artery Renal artery Renal vein Renal hylum Renal pelvis Ureter Minor calyx Renal capsule Inferior extremity Superior extremity Interlobar vein Nephron Renal sinus Major calyx Renal papilla Renal column (no distinction for red/blue (oxygenated or not) blood, arteriole is between capilaries and larger vessels) (Photo credit: Wikipedia)

Distribution of blood vessels in cortex of kid...

Distribution of blood vessels in cortex of kidney. (Although the figure labels the efferent vessel as a vein, it is actually an arteriole.) (Photo credit: Wikipedia)

English: Nephron, Diagram of the urine formati...

English: Nephron, Diagram of the urine formation. The number inside tubular urine concentration in mOsm/l – when ADH acts  (Photo credit: Wikipedia)

Anatomy of the Kidneys. CliffsNotes. www.cliffsnotes.com/…/Anatomy-of-the-Kidneys

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Subtitle: Nitric Oxide, Peroxinitrite, and NO donors in Renal Function Loss

Curator and Author: Larry H. Bernstein, MD, FCAP

The Nitric Oxide and Renal is presented in FOUR parts:

Part I: The Amazing Structure and Adaptive Functioning of the Kidneys: Nitric Oxide

Part II: Nitric Oxide and iNOS have Key Roles in Kidney Diseases

Part III: The Molecular Biology of Renal Disorders: Nitric Oxide

Part IV: New Insights on Nitric Oxide donors 

Conclusion to this series is presented in

The Essential Role of Nitric Oxide and Therapeutic NO Donor Targets in Renal Pharmacotherapy

Part II.  Oxidative Stress and  Regulating a Balance of Redox Potential is Central to Disordered Kidney Function

We have already described the key role that nitric oxide and the NO synthases play in reduction of oxidative stress. The balance that has to be regulated between pro- and anti-oxidative as well as inflammatory elements necessary for renal function, critically involves the circulation of the kidney. It poses an inherent risk in the kidney, where the existence of a rich circulatory and high energy cortical outer region surrounds a medullary inner portion that is engaged in the  retention of water, the active transport of glucose, urea and uric acid nitrogenous waste, mineral balance and pH.  In this discussion we shall look at kidney function, NO, and the large energy fluxes in the medullary tubules and interstitium.   This is a continuation of of a series of posts on NO and NO related disorders, and the kidney in particular.

Part IIa. Nitric Oxide role in renal tubular epithelial cell function

Tubulointerstitial Nephritides
As part of the exponential growth in our understanding of nitric oxide (NO) in health and disease over the past 2 decades, the kidney has become appreciated as a major site where NO may play a number of important roles. Although earlier work on the kidney focused more on effects of NO at the level of larger blood vessels and glomeruli, there has been a rapidly growing body of work showing critical roles for NO in tubulointerstitial disease. In this review we discuss some of the recent contributions to this important field.
Mattana J, Adamidis A, Singhal PC. Nitric oxide and tubulointerstitial nephritides. Seminars in Nephrology 2004; 24(4):345-353.
Nitric oxide donors and renal tubular (subepithelial) matrix
Nitric oxide (NO) and its metabolite, peroxynitrite (ONOO-), are involved in renal tubular cell injury. If NO/ONOO- has an effect to reduce cell adhesion to the basement membrane, does this effect contribute to tubular obstruction and would it be partially responsible for the harmful effect of NO on the tubular epithelium during acute renal failure (ARF)?
Wangsiripaisan A, et al. examined the effect of the NO donors

  1. (z)-1-[2-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1- ium-1, 2-diolate (DETA/NO),
  2. spermine NONOate (SpNO), and
  3. the ONOO- donor 3-morpholinosydnonimine (SIN-1)

on cell-matrix adhesion to collagen types I and IV, and also fibronectin
using three renal tubular epithelial cell lines:

  1. LLC-PK1,
  2. BSC-1,
  3. OK.

It was only the exposure to SIN-1 that caused a dose-dependent impairment in cell-matrix adhesion. Similar results were obtained in the different cell types and matrix proteins. The effect of SIN-1 (500 microM) on LLC-PK1 cell adhesion was not associated with either cell death or alteration of matrix protein and was attenuated by either

  1. the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide,
  2. the superoxide scavenger superoxide dismutase, or
  3. the ONOO- scavenger uric acid in a dose-dependent manner.

These investigators concluded in this seminal paper that ONOO- generated in the tubular epithelium during ischemia/reperfusion has the potential to impair the adhesion properties of tubular cells, which then may contribute to the tubular obstruction in ARF.

Wangsiripaisan A, Gengaro PE, Nemenoff RA, Ling H, et al. Effect of nitric oxide donors on renal tubular epithelial cell-matrix adhesion. Kidney Int 1999; 55(6):2281-8.

The reaction mechanism of Nitric oxide synthase

The reaction mechanism of Nitric oxide synthase (Photo credit: Wikipedia)

Nitric Oxide Synthase

Nitric Oxide Synthase (Photo credit: Wikipedia)

English: Reactions leading to generation of Ni...

English: Reactions leading to generation of Nitric Oxide and Reactive Nitrogen Species. Novo and Parola Fibrogenesis & Tissue Repair 2008 1:5 doi:10.1186/1755-1536-1-5 (Photo credit: Wikipedia)

Coexpressed Nitric Oxide Synthase and Apical β1 Integrins 

In sepsis-induced acute renal failure, actin cytoskeletal alterations result in shedding of proximal tubule epithelial cells (PTEC) and tubular obstruction. This study examined the hypothesis that inflammatory cytokines, released early in sepsis, cause PTEC cytoskeletal damage and alter integrin-dependent cell-matrix adhesion. The question of whether the intermediate nitric oxide (NO) modulates these cytokine effects was also examined.

After exposure of human PTEC to

  1. tumor necrosis factor-α,
  2. interleukin-1α, and
  3. interferon-γ,

the actin cytoskeleton was disrupted and cells became elongated, with extension of long filopodial processes.

Cytokines induced shedding of

  • viable,
  • apoptotic, and
  • necrotic PTEC,

which was dependent on NO synthesized by inducible NO synthase (iNOS) produced as a result of cytokine actions on PTEC.

Basolateral exposure of polarized PTEC monolayers to cytokines induced maximal NO-dependent cell shedding, mediated in part through NO effects on cGMP. Cell shedding was accompanied by dispersal of

  • basolateral β1 integrins and
  • E-cadherin,

with corresponding upregulation of integrin expression in clusters of cells elevated above the epithelial monolayer.

These cells demonstrated coexpression of iNOS and apically redistributed β1 integrins. These authors point out that the major ligand involved in cell anchorage was laminin, probably through interactions with the integrin α3β1. This interaction was downregulated by cytokines but was not dependent on NO. They posulate a mechanism by which inflammatory cytokines induce PTEC damage in sepsis, in the absence of hypotension and ischemia.

Glynne PA, Picot J and Evans TJ. Coexpressed Nitric Oxide Synthase and Apical β1 Integrins Influence Tubule Cell Adhesion after Cytokine-Induced Injury. JASN 2001; 12(11): 2370-2383.
Potentiation by Nitric Oxide of Apoptosis in Renal Proximal Tubule Cells

Proximal tubular epithelial cells (PTEC) exhibit a high sensitivity to undergo apoptosis in response to proinflammatory stimuli and immunosuppressors and participate in the onset of several renal diseases. This study examined the expression of inducible nitric oxide (NO) synthase after challenge of PTEC with bacterial cell wall molecules and inflammatory cytokines and analyzed the pathways that lead to apoptosis in these cells by measuring changes in the mitochondrial transmembrane potential and caspase activation.

The data show that the apoptotic effects of proinflammatory stimuli mainly were due to the expression of inducible NO synthase. Cyclosporin A and FK506 inhibited partially NO synthesis. However, both NO and immunosuppressors induced apoptosis, probably through a common mechanism that involved the irreversible opening of the mitochondrial permeability transition pore. Activation of caspases 3 and 7 was observed in cells treated with high doses of NO and with moderate concentrations of immunosuppressors. The conclusion is that the cooperation between NO and immunosuppressors that induce apoptosis in PTEC might contribute to the renal toxicity observed in the course of immunosuppressive therapy.

HORTELANO S, CASTILLA M, TORRES AM, TEJEDOR A, and BOSCÁ L. Potentiation by Nitric Oxide of Cyclosporin A and FK506- Induced Apoptosis in Renal Proximal Tubule Cells. J Am Soc Nephrol 2000; 11: 2315–2323.

Part IIb. Related studies with ROS and/or RNS on nonrenal epithelial cells

Reactive nitrogen species block cell cycle re-entry
Endogenous sources of reactive nitrogen species (RNS) act as second messengers in a variety of cell signaling events, whereas environmental sources of RNS like nitrogen dioxide (NO2) inhibit cell survival and growth through covalent modification of cellular macromolecules.

Murine type II alveolar cells arrested in G0 by serum deprivation were exposed to either NO2 or SIN-1, a generator of RNS, during cell cycle re-entry. In serum-stimulated cells, RNS blocked cyclin D1 gene expression, resulting in cell cycle arrest at the boundary between G0 and G1. Dichlorofluorescin diacetate (DCF) fluorescence indicated that RNS induced sustained production of intracellular hydrogen peroxide (H2O2), which normally is produced only transiently in response to serum growth factors.

Loading cells with catalase prevented enhanced DCF fluorescence and rescued cyclin D1 expression and S phase entry.

These studies indicate environmental RNS interfere with cell cycle re-entry through an H2O2-dependent mechanism that influences expression of cyclin D1 and progression from G0 to the G1 phase of the cell cycle.
Yuan Z, Schellekens H, Warner L, Janssen-Heininger Y, Burch P, Heintz NH. Reactive nitrogen species block cell cycle re-entry through sustained production of hydrogen peroxide. Am J Respir Cell Mol Biol. 2003;28(6):705-12. Epub 2003 Jan 10.
Peroxynitrite modulates MnSOD gene expression

Peroxynitrite (ONOO-) is a strong oxidant derived from nitric oxide (‘NO) and superoxide (O2.-), reactive nitrogen (RNS) and oxygen species (ROS) present in inflamed tissue. Other oxidant stresses, e.g., TNF-alpha and hyperoxia, induce mitochondrial, manganese-containing superoxide dismutase (MnSOD) gene expression.

3-morpholinosydnonimine HCI (SIN-1) (10 or 1000 microM)  increased MnSOD mRNA, but did not change hypoxanthine guanine phosphoribosyl transferase (HPRT) mRNA.
Authentic peroxynitrite (ONOO ) (100-500 microM) also increased MnSOD mRNA but did not change constitutive HPRT mRNA expression.  ONOO stimulated luciferase gene expression driven by a 2.5 kb fragment of the rat MnSOD gene 5′ promoter region.

MnSOD gene induction due to ONOO- was inhibited effectively by L-cysteine (10 mM) and partially inhibited by N-acetyl cysteine (50 mM) or pyrrole dithiocarbamate (10 mM).
.NO from 1-propanamine, 3-(2-hydroxy-2-nitroso-1-propylhydrazine) (PAPA NONOate) (100 or 1000 microM) did not change MnSOD or HPRT mRNA, nor did either H202 or NO2-, breakdown products of SIN-1 and ONOO, have any effect on MnSOD mRNA expression; ONOO- and SIN-1 also did not increase detectable MnSOD protein content or increase MnSOD enzymatic activity.
Nevertheless, increased steady state [O2.-] in the presence of .NO yields ONOO , and ONOO has direct, stimulatory effects on MnSOD transcript expression driven at the MnSOD gene 5′ promoter region inhibited completely by L-cysteine and partly by N-acetyl cysteine in lung epithelial cells. This raises a question of whether the same effect is seen in renal tubular epithelium.

Jackson RM, Parish G, Helton ES. Peroxynitrite modulates MnSOD gene expression in lung epithelial cells. Free Radic Biol Med. 1998; 25(4-5):463-72.

Comparative impacts of glutathione peroxidase-1 gene knockout on oxidative stress

Selenium-dependent glutathione peroxidase-1 (GPX1) protects against reactive-oxygen-species (ROS)-induced oxidative stress in vivo, but its role in coping with reactive nitrogen species (RNS) is unclear. Primary hepatocytes were isolated from GPX1-knockout (KO) and wild-type (WT) mice to test protection of GPX1 against cytotoxicity of

  • superoxide generator diquat (DQ),
  • NO donor S-nitroso-N-acetyl-penicillamine (SNAP) and
  • peroxynitrite generator 3-morpholinosydnonimine (SIN-1).

Treating cells with SNAP (0.1 or 0.25 mM) in addition to DQ produced synergistic cytotoxicity that minimized differences in apoptotic cell death and oxidative injuries between the KO and WT cells. Less protein nitrotyrosine was induced by 0.05-0.5 mM DQ+0.25 mM SNAP in the KO than in the WT cells.

Total GPX activity in the WT cells was reduced by 65 and 25% by 0.5 mM DQ+0.1 mM SNAP and 0.5 mM DQ, respectively.

Decreases in Cu,Zn-superoxide dismutase (SOD) activity and increases in Mn-SOD activity in response to DQ or DQ+SNAP were greater in the KO cells than in the WT cells.

The study indicates GPX1 was more effective in protecting hepatocytes against oxidative injuries mediated by ROS alone than by ROS and RNS together, and knockout of GPX1 did not enhance cell susceptibility to RNS-associated cytotoxicity. Instead, it attenuated protein nitration induced by DQ+SNAP.
To better understand the mechanism(s) underlying nitric oxide (. NO)-mediated toxicity, in the presence and absence of concomitant oxidant exposure, postmitotic terminally differentiated NT2N cells, which are incapable of producing . NO, were exposed to PAPA-NONOate (PAPA/NO) and 3-morpholinosydnonimine (SIN-1).
Exposure to SIN-1, which generated peroxynitrite (ONOO) in the range of 25-750 nM/min, produced a concentration- and time-dependent delayed cell death.

In contrast, a critical threshold concentration (>440 nM/min) was required for . NO to produce significant cell injury.
There is a largely necrotic lesion after ONOO exposure and an apoptotic-like morphology after . NO exposure. Cellular levels of reduced thiols correlated with cell death, and pretreatment with N-acetylcysteine (NAC) fully protected from cell death in either PAPA/NO or SIN-1 exposure.

NAC given within the first 3 h posttreatment further delayed cell death and increased the intracellular thiol level in SIN-1 but not . NO-exposed cells.
Cell injury from . NO was independent of cGMP, caspases, and superoxide or peroxynitrite formation.
Overall, exposure of non-. NO-producing cells to . NO or peroxynitrite results in delayed cell death, which, although occurring by different mechanisms,
appears to be mediated by the loss of intracellular redox balance.

Gow AJ, Chen Q, Gole M, Themistocleous M, Lee VM, Ischiropoulos H. Two distinct mechanisms of nitric oxide-mediated neuronal cell death show thiol dependency. Am J Physiol Cell Physiol. 2000; 278(6):C1099-107.

Oxidative stress

Oxidative stress (Photo credit: Wikipedia)

English: Binding of CAPON results in a reducti...

English: Binding of CAPON results in a reduction of NMDA receptor/nitric oxide synthase (NOS) complexes, leading to decreased NMDA receptor–gated calcium influx and a catalytically inactive nitric oxide synthase. Overexpression of either the full-length or the novel shortened CAPON isoform as reported by Brzustowicz and colleagues is, therefore, predicted to lead to impaired NMDA receptor–mediated glutamate neurotransmission. (Photo credit: Wikipedia)

NO2 effect on phosphatidyl choline

Nitrogen dioxide (NO2) inhalation affects the extracellular surfactant as well as the structure and function of type II pneumocytes. The studies had differences in oxidant concentration, duration of exposure, and mode of NO2 application.

This study evaluated the influence of the NO2 application mode on the phospholipid metabolism of type II pneumocytes . Rats were exposed to identical NO2 body doses (720 ppm x h), which were applied continuously (10 ppm for 3 d), intermittently (10 ppm for 8 h per day, for 9 d), and repeatedly (10 ppm for 3 d, 28 d rest, and then 10 ppm for 3 d). Immediately after exposure, type II cells were isolated and evaluated for

  • cell yield,
  • vitality,
  • phosphatidylcholine (PC) synthesis, and
  • secretion.

Type II pneumocyte cell yield was only increased from animals that had been continuously exposed to NO2, but vitality of the isolated type II pneumocytes was not affected by the NO2 exposure modes. Continuous application of 720 ppm x h NO2 resulted in increased activity of the cytidine-5-diphosphate (CDP)-choline pathway.

  • After continuous NO2 application,
  • specific activity of choline kinase,
  • cytidine triphosphate (CTP):cholinephosphate cytidylyltransferase,
  • uptake of choline, and
  • pool sizes of CDP-choline and PC

were significantly increased over those of controls.

Intermittent application of this NO2 body dose provoked less increase in PC synthesis and the synthesis parameters were comparable to those for cells from control animals after repeated exposure. Whereas PC synthesis in type II cells was stimulated by NO2, their secretory activity was reduced. Continuous exposure reduced the secretory activity most, whereas intermittent exposure nonsignificantly reduced this activity as compared with that of controls. The repeated application of NO2 produced no differences.

The authors conclude that type II pneumocytes adapt to NO2 atmospheres depending on the mode of its application, at least for the metabolism of PC and its secretion from isolated type II pneumocytes.   Further studies are necessary to determine whether additional metabolic activities will also adapt to NO2 atmospheres, and if these observations are specific for NO2 or represent effects generally due to oxidants.  The reader, however, asks whether this effect could also be found in renal epithelial cells, for which PC is not considered vital as for type II pneumocytes and possibly related to surfactant activity in the lung.

Müller B, Seifart C, von Wichert P, Barth PJ. Adaptation of rat type II pneumocytes to NO2: effects of NO2 application mode on phosphatidylcholine metabolism. Am J Respir Cell Mol Biol. 1998; 18(5): 712-20.

iNOS involved in immediate response to anaphylaxis

The generation of large quantities of nitric oxide (NO) is implicated in the pathogenesis of anaphylactic shock. The source of NO, however, has not been established and conflicting results have been obtained when investigators have tried to inhibit its production in anaphylaxis.

This study analyzed the expression of inducible nitric oxide synthase (iNOS) and endothelial nitric oxide synthase (eNOS) in a mouse model of anaphylaxis.

BALB/c mice were sensitized and challenged with ovalbumin to induce anaphylaxis. Tissues were removed from the heart and lungs, and blood was drawn at different time points during the first 48 hours after induction of anaphylaxis. The Griess assay was used to measure nitric oxide generation. Nitric oxide synthase expression was examined by reverse transcriptase polymerase chain reaction and immunohistochemistry.

A significant increase in iNOS mRNA expression and nitric oxide production was evident as early as 10 to 30 minutes after allergen challenge in both heart and lungs. In contrast, expression of eNOS mRNA was not altered during the course of the experiment.

The results support involvement of iNOS in the immediate physiological response of anaphylaxis.

Sade K, Schwartz IF, Etkin S, Schwartzenberg S, et al. Expression of Inducible Nitric Oxide
Synthase in a Mouse Model of Anaphylaxis. J Investig Allergol Clin Immunol 2007; 17(6):379-385.

Part IIc. Additional Nonrenal Related NO References

Nitrogen dioxide induces death in lung epithelial cells in a density-dependent manner.
Persinger RL, Blay WM, Heintz NH, Hemenway DR, Janssen-Heininger YM.
Am J Respir Cell Mol Biol. 2001 May;24(5):583-90.
PMID: 11350828 [PubMed – indexed for MEDLINE] Free Article
2.
Molecular mechanisms of nitrogen dioxide induced epithelial injury in the lung.
Persinger RL, Poynter ME, Ckless K, Janssen-Heininger YM.
Mol Cell Biochem. 2002 May-Jun;234-235(1-2):71-80. Review.
PMID: 12162462 [PubMed – indexed for MEDLINE]
3.
Nitric oxide and peroxynitrite-mediated pulmonary cell death.
Gow AJ, Thom SR, Ischiropoulos H.
Am J Physiol. 1998 Jan;274(1 Pt 1):L112-8.
PMID: 9458808 [PubMed – indexed for MEDLINE] Free Article
4.
Mitogen-activated protein kinases mediate peroxynitrite-induced cell death in human bronchial epithelial cells.
Nabeyrat E, Jones GE, Fenwick PS, Barnes PJ, Donnelly LE.
Am J Physiol Lung Cell Mol Physiol. 2003 Jun;284(6):L1112-20. Epub 2003 Feb 21.
PMID: 12598225 [PubMed – indexed for MEDLINE] Free Article
5.
Peroxynitrite inhibits inducible (type 2) nitric oxide synthase in murine lung epithelial cells in vitro.
Robinson VK, Sato E, Nelson DK, Camhi SL, Robbins RA, Hoyt JC.
Free Radic Biol Med. 2001 May 1;30(9):986-91.
PMID: 11316578 [PubMed – indexed for MEDLINE]
6.
Nitric oxide-mediated chondrocyte cell death requires the generation of additional reactive oxygen species.
Del Carlo M Jr, Loeser RF.
Arthritis Rheum. 2002 Feb;46(2):394-403.
PMID: 11840442 [PubMed – indexed for MEDLINE]
7.
Colon epithelial cell death in 2,4,6-trinitrobenzenesulfonic acid-induced colitis is associated with increased inducible nitric-oxide synthase expression and peroxynitrite production.
Yue G, Lai PS, Yin K, Sun FF, Nagele RG, Liu X, Linask KK, Wang C, Lin KT, Wong PY.
J Pharmacol Exp Ther. 2001 Jun;297(3):915-25.
PMID: 11356911 [PubMed – indexed for MEDLINE] Free Article

Summary

In this piece I have covered the conflicting roles of endogenous end inducible nitric oxide (eNOS and iNOS) in the reaction to reactive oxygen and nitrogen stress (ROS, RNS), and many experiments directed at sorting out these effects using continuous and intermittent  delivery of NO2, production of ONOO- from .NO, and  several agents that are used to upregulate and downregulate the underlying mechanism of response.  These investigations are not only carried out in experiments on renal function and apoptosis, but also there are similar examples taken from studies of lung and liver.  This forms a backdrop for the assessment of renal diseases:

  • immune related
  • acute traumatic injury
  • chronic

The continuation of the discussion will be in essays that follow.

A scheme of the shear stress-induced EDRF-NO m...

A scheme of the shear stress-induced EDRF-NO mechanism (Photo credit: Wikipedia)

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The Molecular Biology of Renal Disorders: Nitric Oxide – Part III

Subtitle: Nitric Oxide, Peroxinitrite, and NO donors in Renal Function Loss 

Curator and Author: Larry H. Bernstein, MD, FCAP

Four Parts present this topic:

Part I: The Amazing Structure and Adaptive Functioning of the Kidneys: Nitric Oxide

Part II: Nitric Oxide and iNOS have Key Roles in Kidney Diseases

Part III: The Molecular Biology of Renal Disorders: Nitric Oxide

Part IV: New Insights on Nitric Oxide donors 

Conclusion to this series is presented in

The Essential Role of Nitric Oxide and Therapeutic NO Donor Targets in Renal Pharmacotherapy

Part III.  The Molecular Biology of Renal Disorders

Renal function affecting urine formation, electrolyte balance, nitrogen excretion, and vascular tone becomes acutely and/or chronically dysfunctional in metabolic, systemic inflammatory and immunological diseases of man. We have already described the key role that nitric oxide and the NO synthases play in reduction of oxidative stress, and we have seen that a balance has to be struck between pro- and anti-oxidative as well as inflammatory elements for avoidance of diseases, specifically involving the circulation. Similar stresses are important in the circulation, in liver disease, in pulmonary function, and in neurodegenerative disease.  In this discussion we continue to look at kidney function, NO and NO donors. This is an extension of a series of posts on NO and NO related disorders.

Part IIIa. Acute renal failure

Acute renal failure (ARF), characterized by sudden loss of the ability of the kidneys to

  1. excrete wastes,
  2. concentrate urine,
  3. conserve electrolytes, and
  4. maintain fluid balance,

is a frequent clinical problem, particularly in the intensive care unit, where it is associated with a mortality of between 50% and 80%.

This clinical entity was described as an acute loss of kidney function that occurred in severely injured crush victims because of histological evidence for patchy necrosis of renal tubules at autopsy. In the clinical setting, the terms ATN and acute renal failure (ARF) are frequently used interchangeably. However, ARF does not include increases in blood urea due to reversible renal vasoconstriction (prerenal azotemia) or urinary tract obstruction (postrenal azotemia). Acute hemodialysis was first used clinically during the Korean War in 1950 to treat military casualties, and this led to a decrease in mortality of the ARF clinical syndrome from about 90% to about 50%.

In the half century that has since passed, much has been learned about the pathogenesis of ischemic and nephrotoxic ARF in experimental models, but there has been very little improvement in mortality. This may be explained by changing demographics: the age of patients with ARF continues to rise, and comorbid diseases are increasingly common in this population. Both factors may obscure any increased survival related to improved critical care.

Examining the incidence of ARF in several military conflicts does, however, provide some optimism. The incidence of ARF in seriously injured casualties decreased between World War II and the Korean War, and again between that war and the Vietnam War, despite the lack of any obvious difference in the severity of the injuries. What was different was the rapidity of the fluid resuscitation of the patients. Fluid resuscitation on the battlefield with the rapid evacuation of the casualties to hospitals by helicopter began during the Korean War and was optimized further during the Vietnam War. For seriously injured casualties the incidence of ischemic ARF was one in 200 in the Korean War and one in 600 in the Vietnam War. This historical sequence of events suggests that early intervention could prevent the occurrence of ARF, at least in military casualties.

In experimental studies it has been shown that progression from an azotemic state associated with

  • renal vasoconstriction and
  • intact tubular function (prerenal azotemia)

to established ARF with tubular dysfunction occurs if the renal ischemia is prolonged. Moreover, early intervention with fluid resuscitation was shown to prevent the progression from prerenal azotemia to established ARF.

Diagnostic evaluation of ARF

One important question, therefore, is how to assure that an early diagnosis of acute renal vasoconstriction can be made prior to the occurrence of tubular dysfunction, thus providing the potential to prevent progression to established ARF. In this regard, past diagnostics relied on observation of the patient response to a fluid challenge:

  • decreasing levels of blood urea nitrogen (BUN) indicated the presence of reversible vasoconstriction, while
  • uncontrolled accumulation of nitrogenous waste products, i.e., BUN and serum creatinine, indicated established ARF.

This approach, however, frequently led to massive fluid overload in the ARF patient with resultant pulmonary congestion, hypoxia, and premature need for mechanical ventilatory support and/or hemodialysis. On this background the focus turned to an evaluation of urine sediment and urine chemistries to differentiate between renal vasoconstriction with intact tubular function and established ARF. It was well established that if tubular function was intact, renal vaso-constriction was associated with enhanced tubular sodium reabsorption. Specifically, the fraction of filtered sodium that is rapidly reabsorbed by normal tubules of the vasoconstricted kidney is greater than 99%. Thus, when nitrogenous wastes, such as creatinine and urea, accumulate in the blood due to a fall in glomerular filtration rate (GFR) secondary to renal vasoconstriction with intact tubular function,

the fractional excretion of filtered sodium (FENa = [(urine sodium × plasma creatinine) / (plasma sodium × urine creatinine)]) is less than 1%.

An exception to this physiological response of the normal kidney to vasoconstriction is when the patient is receiving a diuretic, including mannitol, or has glucosuria, which decreases tubular sodium reabsorption and increases FENa. It has recently been shown in the presence of diuretics that a rate of fractional excretion of urea (FEurea) of less than 35 indicates intact tubular function, thus favoring renal vasoconstriction rather than established ARF as a cause of the azotemia.

Mechanisms of ARF

 

Based on the foregoing comments, this discussion of mechanisms of ARF will not include nitrogenous-waste accumulation due to renal vasoconstriction with intact tubular function (prerenal azotemia) or urinary tract obstruction (postrenal azotemia). The mechanisms of ARF involve both vascular and tubular factors.

An ischemic insult to the kidney will in general be the cause of the ARF. While a decrease in renal blood flow with diminished oxygen and substrate delivery to the tubule cells is an important ischemic factor, it must be remembered that a relative increase in oxygen demand by the tubule is also a factor in renal ischemia.

Approximately 30–70% of these shed epithelial tubule cells in the urine are viable and can be grown in culture. Recent studies using cellular and molecular techniques have provided information relating to the structural abnormalities of injured renal tubules that occur both in vitro and in vivo.

In vitro studies using chemical anoxia have revealed abnormalities in the proximal tubule cytoskeleton that are associated with translocation of Na+/K+-ATPase from the basolateral to the apical membrane. A comparison of cadaveric transplanted kidneys with delayed versus prompt graft function has also provided important results regarding the role of Na+/K+-ATPase in ischemic renal injury.  This study demonstrated that, compared with kidneys with prompt graft function, those with delayed graft function had a significantly greater cytoplasmic concentration of Na+/K+-ATPase and actin-binding proteins — spectrin (also known as fodrin) and ankyrin — that had translocated from the basolateral membrane to the cytoplasm. Such a translocation of Na+/K+-ATPase from the basolateral membrane to the cytoplasm could explain the decrease in tubular sodium reabsorption that occurs with ARF.

The mechanisms whereby the critical residence of Na+/K+-ATPase in the basolateral membrane, which facilitates vectorial sodium transport, is uncoupled by hypoxia or ischemia have been an important focus of research. The actin-binding proteins, spectrin and ankyrin, serve as substrates for the calcium-activated cysteine protease calpain. In this regard, in vitro studies in proximal tubules have shown a rapid rise in cytosolic calcium concentration during acute hypoxia, which antedates the evidence of tubular injury as assessed by lactic dehydrogenase (LDH) release.  There is further evidence to support the importance of the translocation of Na+/K+-ATPase from the basolateral membrane to the cytoplasm during renal ischemia/reperfusion.

Specifically, calpain-mediated breakdown products of the actin-binding protein spectrin have been shown to occur with renal ischemia. Calpain activity was also demonstrated to be increased during hypoxia in isolated proximal tubules. Measurement of LDH release following calpain inhibition has demonstrated attenuation of hypoxic damage to proximal tubules. There was no evidence in proximal tubules during hypoxia of an increase in cathepsin, another cysteine protease. Further studies demonstrated a calcium-independent pathway for calpain activation during hypoxia. Calpastatin, an endogenous cellular inhibitor of calpain activation, was shown to be diminished during hypoxia in association with the rise in another cysteine protease, caspase. This effect of diminished calpastatin activity could be reversed by caspase inhibition. Proteolytic pathways that may be involved in calpain-mediated proximal tubule cell injury during hypoxia are illustrated. Calcium activation of phospholipase A has also been shown to contribute to renal tubular injury during ischemia.

Location of renal medulla

Location of renal medulla (Photo credit: Wikipedia)

Diagram of renal corpuscle structure

Diagram of renal corpuscle structure (Photo credit: Wikipedia)

English: Reactions leading to generation of Ni...

English: Reactions leading to generation of Nitric Oxide and Reactive Nitrogen Species. Novo and Parola Fibrogenesis & Tissue Repair 2008 1:5 doi:10.1186/1755-1536-1-5 (Photo credit: Wikipedia)

The reaction mechanism of Nitric oxide synthase

The reaction mechanism of Nitric oxide synthase (Photo credit: Wikipedia)

Tubular obstruction in ischemic ARF.

 

The existence of proteolytic pathways involving cysteine proteases, namely calpain and caspases, may therefore explain the decrease in proximal tubule sodium reabsorption and increased FENa secondary to proteolytic uncoupling of Na+/K+-ATPase from its basolateral membrane anchoring proteins. This tubular perturbation alone, however, does not explain the fall in GFR that leads to nitrogenous-waste retention and thus the rise in BUN and serum creatinine.

Decreased proximal tubule sodium reabsorption may lead to a decreased GFR during ARF. First of all, brush border membranes and cellular debris could provide the substrate for intraluminal obstruction in the highly resistant portion of distal nephrons. In fact, microdissection of individual nephrons of kidneys from patients with ARF demonstrated obstructing casts in distal tubules and collecting ducts. This observation could explain the dilated proximal tubules that are observed upon renal biopsy of ARF kidneys. The intraluminal casts in ARF kidneys stain prominently for Tamm-Horsfall protein (THP), which is produced in the thick ascending limb.

Importantly, THP is secreted into tubular fluid as a monomer but subsequently may become a polymer that forms a gel-like material in the presence of increased luminal Na+ concentration, as occurs in the distal nephron during clinical ARF with the decrease in tubular sodium reabsorption. Thus, the THP polymeric gel in the distal nephron provides an intraluminal environment for distal cast formation involving

  • viable,
  • apoptotic, and
  • necrotic cells.

The loss of the tubular epithelial cell barrier and/or the tight junctions between viable cells during acute renal ischemia could lead to a leak of glomerular filtrate back into the circulation. If this occurs and normally non-reabsorbable substances, such as inulin, leak back into the circulation, then a falsely low GFR will be measured as inulin clearance. It should be noted, however, that the degree of extensive tubular damage observed in experimental studies demonstrating tubular fluid backleak is rarely observed with clinical ARF in humans. Moreover, dextran sieving studies in patients with ARF demonstrated that, at best, only a 10% decrease in GFR could be explained by backleak of filtrate. Cadaveric transplanted kidneys with delayed graft function, however, may have severe tubular necrosis, and thus backleak of glomerular filtration may be more important in this setting.

Inflammation and NO

There is now substantial evidence for the involvement of inflammation in the pathogenesis of the decreased GFR associated with acute renal ischemic injury. In this regard, there is experimental evidence that iNOS may contribute to tubular injury during ARF. Hypoxia in isolated proximal tubules has been shown to increase NO release, and Western blot analysis in ischemic kidney homogenates has demonstrated increased iNOS protein expression. An antisense oligonucleotide was shown to block the upregulation of iNOS and afford functional protection against acute renal ischemia. Moreover, when isolated proximal tubules from iNOS, eNOS, and neuronal NO synthase (nNOS) knockout mice were exposed to hypoxia, only the tubules from the iNOS knockout mice were protected against hypoxia, as assessed by LDH release. The iNOS knockout mice were also shown to have lower mortality during ischemia/reperfusion than wild-type mice. There is also evidence that the scavenging of NO by oxygen radicals produces peroxynitrite that causes tubule damage during ischemia.

  • While iNOS may contribute to ischemic injury of renal tubules, there is evidence that the vascular effect of eNOS in the glomerular afferent arteriole is protective against ischemic injury.
  • In this regard, eNOS knockout mice have been shown to be more sensitive to endotoxin-related injury than normal mice.
  • Moreover, the protective role of vascular eNOS may be more important than the deleterious effect of iNOS at the tubule level during renal ischemia.

The basis for this tentative conclusion is the observation that treatment of mice with the nonspecific NO synthase (NOS) inhibitor L-NAME, which blocks both iNOS and eNOS, worsens renal ischemic injury.

It has also been demonstrated that NO may downregulate eNOS and is a potent inducer of heme oxygenase-1, which has been shown to be cytoprotective against renal injury. The MAPK pathway also appears to be involved in renal oxidant injury. Activation of extracellular signal–regulated kinase (ERK) or inhibition of JNK has been shown to ameliorate oxidant injury–induced necrosis in mouse renal proximal tubule cells in vitro. Upregulation of ERK may also be important in the effect of preconditioning whereby early ischemia affords protection against a subsequent ischemia/reperfusion insult. Alterations in cell cycling have also been shown to be involved in renal ischemic injury. Upregulation of p21, which inhibits cell cycling, appears to allow cellular repair and regeneration, whereas homozygous p21 knockout mice demonstrate enhanced cell necrosis in response to an ischemic insult.

Downregulated Upregulated
eNOS heme-oxygenase-1
ERK JNK
  p21

Prolonged duration of the ARF clinical course and the need for dialysis are major factors projecting a poor prognosis. Patients with ARF who require dialysis have a 50–70% mortality rate. Infection and cardiopulmonary complications are the major causes of death in patients with ARF. Excessive fluid administration in patients with established ARF may lead to

  • pulmonary congestion,
  • hypoxia,
  • the need for ventilatory support,
  • pneumonia, and
  • multiorgan dysfunction syndrome (80–90% mortality).

Until means to reverse the diminished host defense mechanisms in azotemic patients with clinical ARF are available, every effort should be made to avoid invasive procedures such as the placement of bladder catheters, intravenous lines, and mechanical ventilation. Over and above such supportive care, it may be that combination therapy will be necessary to prevent or attenuate the course of ARF. Such combination therapy must involve agents with potential beneficial effects on vascular tone, tubular obstruction, and inflammation.

Schrier RW, Wang W, Poole B, and Mitra A. Acute renal failure: definitions, diagnosis, pathogenesis, and therapy. The Journal of Clinical Investigation 2004; 114(1):5-14.

http://www.jci.org

Part IIIb.  Additional Related References on NO, oxidative stress and Kidney

Shelgikar PJ, Deshpande KH, Sardeshmukh AS, Katkam RV, Suryakarl AN. Role of oxidants and antioxidants in ARF patients undergoing hemodialysis. Indian J Nephrol 2005;15: 73-76.

Lee JW. Renal Dysfunction in Patients with Chronic Liver Disease. Electrolytes Blood Press 7:42-50, 2009ㆍdoi: 10.5049/EBP.2009.7.2.42.

Saadat H, et al.  Endothelial Nitric Oxide Function and Tubular Injury in Premature Infants. Int J App Sci and Technol 2012; 7(6): 77-81. www.ijastnet.com.

 

Amaresan MS. Cardiovascular disease in chronic kidney disease. Indian J Nephrol 2005;15: 1-7.

Traditional risk factors for CVD in CKD

  • Hypertension
  • Older Age
  • Diabetes Mellitus
  • Male gender
  •  White Race
  • Physical inactivity
  • High LDL
  • Low HDL
  • Smoking
  • Menopause
  • LVH

CKD Related CV Risk Factors

 

Blood Pressure ADMA (Asymmetric Dimethyl Arginine
Na+ Retention Hypervolemia
Insulin Resistance Anemia
Adiponectin Proteinuria & Hypoalbuminemia
Inflammation 5 Lipoxygenase
Homocysteinemia Genetic factors
ROS Lp (a)   
NO synthesis Iron over load
Ca++ x P++ Vit. C or E

 

 

S Vikrant, SC Tiwari. Essential Hypertension – Pathogenesis and Pathophysiology. J Indian Acad Clinical Medicine 2001; 2(3):141-161.

Pathogenesis of salt dependent hypertension. The hypothesis proposes that early hypertension is episodic and is mediated by a hyperactive sympathetic nervous system or activated renin-angiotensin system.

Cell membrane alterations

Hypotheses linking abnormal ionic fluxes to increased peripheral resistance through increase in cell sodium, calcium, or pH.

The hypertension that is more common in obese people may arise in large part from the insulin resistance and resultant hyperinsulinaemia that results from the increased mass of fat.

However, rather unexpectedly, insulin resistance may also be involved in hypertension in non-obese people.

The explanation for insulin resistance found in as many as half of nonobese hypertensive is not obvious and may involve one or more aspects of insulin’s action

Proposed mechanisms by which insulin resistance and/or hyperinsulinemia may lead to increased blood pressure.

  • Enhanced renal sodium and water reabsorption.
  • Increased blood pressure sensitivity to dietary salt intake
  • Augmentation of the pressure and aldosterone responses to AII
  • Changes in transmembrane electrolyte transport
  1. Increased intracellular sodium
  2. Decreased Na+/K+ – ATPase activity
  3. Increased intracellular Ca2+ pump activity
  4. Increased intracellular Ca2+ accumulation
  5. Stimulation of growth factors

Summary:  This portion of the discussion concerns mainly acute renal failure, but also expands upon the development of longer term renal tubular disease.  The last consideration is the link between essential hypertension, obesity and insulin resistance, and impaired renal water retention, sodium retention, decreased Na+/K+ – ATPase activity.  The issue of early intervention with fluid resuscitation is tempered by the risk of pulmonary edema as a significant complication.  A review of the literature indicates that both eNOS and iNOS have counter-effects in the genesis of ARF and CRF.  The protective role of vascular eNOS may be more important than the deleterious effect of iNOS at the tubule level during renal ischemia.

 

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Subtitle: Nitric Oxide, Peroxinitrite, and NO donors in Renal Function Loss

Curator and Author: Larry H. Bernstein, MD, FCAP

The Nitric Oxide and Renal is presented in FOUR parts:

Part I: The Amazing Structure and Adaptive Functioning of the Kidneys: Nitric Oxide

Part II: Nitric Oxide and iNOS have Key Roles in Kidney Diseases

Part III: The Molecular Biology of Renal Disorders: Nitric Oxide

Part IV: New Insights on Nitric Oxide donors 

Conclusion to this series is presented in

The Essential Role of Nitric Oxide and Therapeutic NO Donor Targets in Renal Pharmacotherapy

The criticality of renal function is easily overlooked until significant loss of nephron mass is overtly seen.  The kidneys become acutely and/or chronically dysfunctional in metabolic,  systemic inflammatory and immunological diseases of man.  We have described how the key role that nitric oxide and the NO synthases (eNOS and iNOS) play competing roles in reduction or in the genesis of reactive oxygen  species.  There is  a balance to be struck between pro- and anti-oxidative as well as inflammatory elements for avoidance of diseases, specifically involving the circulation, but effectively not limited to any organ system.  In this discussion we shall look at kidney function, NO and NO donors.  This is an extension of a series of posts on NO and NO related disorders.

Part IV. New Insights on NO donors

 

This study investigated the involvement of nitric oxide (NO) into the irradiation-induced increase of cell attachment. These experiments explored the cellular mechanisms of low-power laser therapy.

HeLa cells were irradiated with a monochromatic visible-tonear infrared radiation (600–860 nm, 52 J/m2) or with a diode laser (820 nm, 8–120 J/m2) and the number of cells attached to a glass matrix was counted after 30 minute incubation at 37oC. The NO donors

  • sodium nitroprusside (SNP),
  • glyceryl trinitrate (GTN), or
  • sodium nitrite (NaNO2)

were added to the cellular suspension before or after irradiation. The action spectra and the concentration and fluence dependencies obtained were compared and analyzed. The well-structured action spectrum for the increase of the adhesion of the cells, with maxima at 619, 657, 675, 740, 760, and 820 nm, points to the existence of a photoacceptor responsible for the enhancement of this property (supposedly cytochrome c oxidase, the terminal respiratory chain enzyme), as well as signaling pathways between the cell mitochondria, plasma membrane, and nucleus. Treating the cellular suspension with SNP before irradiation significantly modifies the action spectrum for the enhancement of the cell attachment property (band maxima at 642, 685, 700, 742, 842, and 856 nm).

The action of SNP, GTN, andNaNO2 added before or after irradiation depends on their concentration and radiation fluence.

The NO donors added to the cellular suspension before irradiation eliminate the radiation induced increase in the number of cells attached to the glass matrix, supposedly by way of binding NO to cytochrome c oxidase. NO added to the suspension after irradiation can also inhibit the light-induced signal downstream. Both effects of NO depend on the concentration of the NO donors added. The results indicate that NO can control the irradiation-activated reactions that increase the attachment of cells.

Karu TI, Pyatibrat LV, and Afanasyeva NI. Cellular Effects of Low Power Laser Therapy Can be Mediated by Nitric Oxide. Lasers Surg. Med 2005; 36:307–314.

Interferon a-2b (IFN-a) effect on barrier function of renal tubular epithelium

 

IFNa treatment can be accompanied by impaired renal function and capillary leak.  This study shows IFNa produced dose-dependent and time-dependent decrease in transepithelial resistance (TER) ameliorated by tyrphostin, an inhibitor of phosphotyrosine kinase with increased expression of occludin and E-cadherin In conclusion, IFNa can directly affect barrier function in renal epithelial cells via overexpression or missorting of the junctional proteins occludin and E-cadherin.

Lechner J, Krall M, Netzer A, Radmayr C, et al.  Effects of interferon a-2b on barrier function and junctional complexes of renal proximal tubular LLC-pK1 cells. Kidney Int 1999; 55:2178-2191.

Ischemia-reperfusion injury

 

The pathophysiology of acute renal failure (ARF) is complex and not well understood. Numerous models of ARF suggest that oxygen-derived reactive species are important in renal ischemia-reperfusion (I-R) injury, but the nature of the mediators is still controversial. Treatment with

  • oxygen radical scavengers,
  • antioxidants, and
  • iron chelators such as
  1.                   superoxide dismutase,
  2.                   dimethylthiourea,
  3.                   allopurinol, and
  4.                    deferoxamine

are protective in some models, and suggest a role for the hydroxyl radical formation. However, these compounds are not protective in all models of I-R injury, and direct evidence for the generation of hydroxyl radical is absent. Furthermore, these inhibitors have another property in common. They all directly scavenge or inhibit the formation of peroxynitrite (ONOO−), a highly toxic species derived from nitric oxide (NO) and superoxide. Thus, the protective effects seen with these inhibitors may be due in part to their ability to inhibit ONOO− formation.

Even though reactive oxygen species are thought to participate in ischemia-reperfusion (I-R) injury,  induction of inducible nitric oxide synthase (iNOS) and production of high levels of nitric oxide (NO) also contribute to this injury. NO can combine with superoxide to form the potent oxidant peroxynitrite (ONOO−). NO and ONOO− were investigated in a rat model of renal I-R injury using the selective iNOS inhibitor L-N6-(1-iminoethyl)lysine (L-NIL).

I-R surgery significantly increased plasma creatinine levels to 1.9 ± 0.3 mg/dl (P < .05) and caused renal cortical necrosis. L-NIL administration (3 mg/kg) in animals subjected to I-R significantly decreased plasma creatinine levels to 1.2 ± 0.10 mg/dl (P < .05 compared with I-R) and reduced tubular damage.

ONOO− formation was evaluated by detecting 3-nitrotyrosine-protein adducts, a stable biomarker of ONOO− formation.

  1. The kidneys from I-R animals had increased levels of 3-nitrotyrosine-protein adducts compared with control animals
  2. L-NIL-treated rats (3 mg/kg) subjected to I-R showed decreased levels of 3-nitrotyrosine-protein adducts.

These results support the hypothesis that iNOS-generated NO mediates damage in I-R injury possibly through ONOO− formation.

In summary, 3-nitrotyrosine-protein adducts were detected in renal tubules after I-R injury. Selective inhibition of iNOS by L-NIL

  • decreased injury,
  • improved renal function, and
  • decreased apparent ONOO− formation.

Reactive nitrogen species should be considered potential therapeutic targets in the prevention and treatment of renal I-R injury.

Walker LM, Walker PD, Imam SZ, et al. Evidence for Peroxynitrite Formation in Renal Ischemia-Reperfusion Injury: Studies with the Inducible Nitric Oxide Synthase InhibitorL-N6-(1-Iminoethyl)-lysine1.  2000.

Role of TNFa independent of iNOS

Renal failure is a frequent complication of sepsis, mediated by renal vasoconstrictors and vasodilators. Endotoxin induces several proinflammatory cytokines, among which tumor necrosis factor (TNF) is thought to be of major importance. Tumor necrosis factor (TNF) has been suggested to be a factor in the acute renal failure in sepsis or endotoxemia. Passive immunization by anti-TNFa prevented development of septic shock in animal experiments. The development of ARF involves excessive intrarenal vasoconstriction.

Recent studies also suggest involvement of nitric oxide (NO), generated by inducible NO synthase (iNOS), in the pathogenesis of endotoxin-induced renal failure. TNF-a leads to a decrease in glomerular filtration rate (GFR). The present study tested the hypothesis that the role of TNF-a in endotoxic shock related ARF is mediated by iNOS-derived NO.

 

An injection of lipopolysaccharide (LPS) constituent of gram-negative bacteria to wild-type mice resulted in a 70% decrease in glomerular filtration rate (GFR) and in a 40% reduction in renal plasma flow (RPF) 16 hours after the  injection.

The results occurred independent of

  • hypotension,
  • morphological changes,
  • apoptosis, and
  • leukocyte accumulation.

In mice pretreated with TNFsRp55, only a 30% decrease in GFR was observed without a significant change in RPF as compared with controls.

 

Effect of TNFsRp55 (10 mg/kg IP) on renal function in wild-type mice.

Mice were pretreated with TNFsRp55 for one hour before the administration of 5 mg/kg intraperitoneal endotoxin. GFR (A) and RPF (B) were determined 16 hours thereafter. Data are expressed as mean 6, SEM, N 5 6. *P , 0.05 vs. Control; §P , 0.05 vs. LPS, by ANOVA.

 

The serum NO concentration was significantly lower in endotoxemic wild-type mice pretreated with TNFsRp55, as compared with untreated endotoxemic wild-type mice. In LPS-injected iNOS knockout mice and wild-type mice treated with a selective iNOS inhibitor, 1400W, the development of renal failure was similar to that in wild-type mice. As in wild-type mice,TNFsRp55 significantly attenuated the decrease in GFR (a 33% decline, as compared with 75% without TNFsRp55) without a significant change in RPF in iNOS knockout mice given LPS.

 

These results demonstrate a role of TNF in the early renal dysfunction (16 h) in a septic mouse model independent of

  • iNOS,
  • hypotension,
  • apoptosis,
  • leukocyte accumulation,and
  • morphological alterations,

thus suggesting renal hypoperfusion secondary to an imbalance between, as yet to be defined renal vasoconstrictors and vasodilators.

Knotek M, Rogachev B, Wang W,….., Edelstein CL, Dinarello CA, and Schrier RW.  Endotoxemic renal failure in mice: Role of tumor necrosis factor independent of inducible nitric oxide synthase. Kidney International 2001; 59:2243–2249

Ischemic acute renal failure

Inflammation plays a major role in the pathophysiology of acute renal failure resulting from ischemia. In this review, we discuss the contribution of endothelial and epithelial cells and leukocytes to this inflammatory response. The roles of cytokines/chemokines in the injury and recovery phase are reviewed. The ability of the mouse kidney to be protected by prior exposure to ischemia or urinary tract obstruction is discussed as a potential model to emulate as we search for pharmacologic agents that will serve to protect the kidney against injury.

the inflammatory mediators produced by tubular epithelial cells and activated leukocytes in renal ischemia/reperfusion (I/R) injury.

Tubular epithelia produce TNF-a, IL-1, IL-6, IL-8, TGF-b, MCP-1, ENA-78, RANTES, and fractalkines, whereas leukocytes produce TNF-a, IL-1, IL-8, MCP-1, ROS, and eicosanoids. The release of these chemokines and cytokines serve as effectors for a positive feedback pathway enhancing inflammation and cell injury

the cycle of tubular epithelial cell injury and repair following renal ischemia/reperfusion.

Tubular epithelia are typically cuboidal in shape and apically-basally polarized; the Na+/K+-ATPase localizes to basolateral plasma membranes, whereas cell adhesion molecules, such as integrins localize basally. In response to ischemia reperfusion, the Na+/K+-ATPase appears apically, and integrins are detected on lateral and basal plasma membranes.

Some of the injured epithelial cells undergo necrosis and/or apoptosis detaching from the underlying basement membrane into the tubular space where they contribute to tubular occlusion. Viable cells that remain attached,

  • dedifferentiate,
  • spread, and
  • migrate to
  • repopulate the denuded basement membrane.

With cell proliferation, cell-cell and cell-matrix contacts are restored, and the epithelium redifferentiates and repolarizes, forming a functional, normal epithelium

Inflammation is a significant component of renal I/R injury, playing a considerable role in its pathophysiology. Although significant progress has been made in defining the major components of this process, the complex cross-talk between endothelial cells, inflammatory cells, and the injured epithelium with each generating and often responding to cytokines and chemokines is not well understood. In addition, we have not yet taken full advantage of the large body of data on inflammation in other organ systems.

Furthermore, preconditioning the kidney to afford protection to subsequent bouts of ischemia may serve as a useful model challenging us to therapeutically mimic endogenous mechanisms of protection. Understanding the inflammatory response prevalent in ischemic kidney injury will facilitate identification of molecular targets for therapeutic intervention.

Bonventre JV and Zuk A. Ischemic acute renal failure: An inflammatory disease? Forefronts in Nephrology  2002;.. :480-485

Gene expression profiles in renal proximal tubules

In kidney disease renal proximal tubular epithelial cells (RPTEC) actively contribute to the progression of tubulointerstitial fibrosis by mediating both an inflammatory response and via epithelial-to-mesenchymal transition. Using laser capture microdissection we specifically isolated RPTEC from cryosections of the healthy parts of kidneys removed owing to renal cell carcinoma and from kidney biopsies from patients with proteinuric nephropathies. RNA was extracted and hybridized to complementary DNA microarrays after linear RNA amplification. Statistical analysis identified 168 unique genes with known gene ontology association, which separated patients from controls.

Besides distinct alterations in signal-transduction pathways (e.g. Wnt signalling), functional annotation revealed a significant upregulation of genes involved in

  • cell proliferation and cell cycle control (like insulin-like growth factor 1 or cell division cycle 34),
  • cell differentiation (e.g. bone morphogenetic protein 7),
  • immune response,
  • intracellular transport and
  • metabolism

in RPTEC from patients.

On the contrary we found differential expression of a number of genes responsible for cell adhesion (like BH-protocadherin) with a marked downregulation of most of these transcripts. In summary, our results obtained from RPTEC revealed a differential regulation of genes, which are likely to be involved in

  • either pro-fibrotic or
  • tubulo-protective mechanisms

in proteinuric patients at an early stage of kidney disease.

Rudnicki M, Eder S, Perco P, Enrich J, et al. Gene expression profiles of human proximal tubular epithelial cells in proteinuric nephropathies. Kidney International 2006; xx:1-11.

Kidney International advance online publication, 20 December 2006; doi:10.1038/sj.ki.5002043. http://www.kidney-international.org

 

Oxidative stress involved in diabetic nephropathy

Diabetic Nephropathy (DN) poses a major health problem. There is strong evidence for a potential role of the eNOS gene. The aim of this case control study was to investigate the possible role of genetic variants of the endothelial Nitric Oxide Synthase (eNOS) gene and oxidative stress in the pathogenesis of nephropathy in patients with diabetes mellitus.

The study included 124 diabetic patients;

  • 68 of these patients had no diabetic nephropathy (group 1) while
  • 56 patients exhibited symptoms of diabetic nephropathy (group 2).
  • Sixty two healthy non-diabetic individuals were also included as a control group.

Blood samples from subjects and controls were analyzed to investigate the eNOS genotypes and to estimate the lipid profile and markers of oxidative stress such as malondialdehyde (MDA) and nitric oxide (NO). No significant differences were found in the frequency of eNOS genotypes between diabetic patients (either in group 1 or group 2) and controls (p >0.05).

Also, no significant differences were found in the frequency of eNOS genotypes between group 1 and group 2 (p >0.05).

Both group 1 and group 2 had significantly higher levels of nitrite and MDA when compared with controls (all p = 0.0001). Also group 2 patients had significantly higher levels of nitrite and MDA when compared with group 1 (p = 0.02, p = 0.001 respectively).

The higher serum level of the markers of oxidative stress in diabetic patients particularly those with diabetic nephropathy suggest that oxidative stress and not the eNOS gene polymorphism is involved in the pathogenesis of the diabetic nephropathy in this subset of patients

Badawy A, Elbaz R, Abbas AM, Ahmed Elgendy A, et al. Oxidative stress and not endothelial Nitric Oxide Synthase gene polymorphism involved in diabetic nephropathy. Journal of Diabetes and Endocrinology 2011; 2(3): 29-35.

Metformin in renal ischemia reperfusion

 

Renal ischemia plays an important role in renal impairment and transplantation.

Metformin is a biguanide used in type 2 diabetes, it inhibits hepatic glucose production and increases peripheral insulin sensitivity.  While the mode of action of metformin is incompletely understood, it appears to have anti-inflammatory and antioxidant effects involved in its beneficial effects on insulin resistance.

Control, Sham, ischemia/reperfusion (I/R) and Metformin treated I /R groups

A renal I/R injury was done by a left renal pedicle occlusion to induce ischemia for 45 min followed by 60 min of reperfusion with contralateral nephrectomy. Metformin pretreated I/R rats in a dose of 200 mg/kg/day for three weeks before ischemia induction.

Nitric oxide (NO), tumor necrosis factor alpha (TNF α) , catalase (CAT) and reduced glutathione (GSH) activities were determined in renal tissue, while creatinine clearance (CrCl) , blood urea nitrogen (BUN) were measured and 5 hour urinary volume and electrolytes were estimated .

BUN and CrCl levels in the I/R group were significantly higher than in control rats (p<0.05) table (1).

Table 1: Creatinine clearance (Cr Cl) and blood urea nitrogen( BUN) levels in control and test groups. Mean ± SD.

Groups CrCl (ml/min) BUN mg/dl
Control group 1.30 ±0.11 14.30±0.25
Sham group+metformin 1.27±0.09 15.70±0.19
I/R group P1 1.85±0.25<0.001*** 28.00±0.62<0.001***
I/R+metformin group P2 P3 1.55±0.220.001**0.028* 18.10±1.00<0.001***<0.001***

P1: Statistical significance between control group and saline treated I/R group.

P2 Statistical significance between control group and Metformin treated I/R group.

P3 Statistical significance between saline treated I/R group and Metformin treated I/R group.

When metformin was administered before I/R, BUN and CrCl levels were still significantly higher than control group but their elevation were significantly lower in comparison to I/R group alone (P<0.05).

TNF α and NO levels were significantly higher in the I/R group than those of the control group (Table 2).

Pre-treatment with metformin significantly lowered their levels in comparison to I/R group (P<0.05).

 

Table 2: Tumour necrosis factior α (TNF α)and inducible nitric oxide (iNO)levels in control and test groups. (Mean ± SD).

Groups TNF α (pmol/mg tissue) iNO nmol/ mg tissue
Control group 17.60 ±5.98 2.54 ± 0.82
Sham group+ metformin 16.70 ±5.50 2.35 ±0.80
I/R group P1 54. 00±6.02<0.001*** 4.50±0.89<0.001**
I/R+ metformin group P2 P3 39 ± 14.01<0.001***0.006** 3.53±0.950.02*0.03*

P1: Statistical significance between control group and saline treated I/R group.

P2 Statistical significance between control group and Metformin treated I/R group.

P3 Statistical significance between saline treated I/R group and Metformin treated I/R group

These results showed significant increase in

  • NO,
  • TNF α,
  • BUN ,
  • CrCl and

significant decrease in

  • urinary volume ,
  • electrolytes,
  • CAT and
  • GSH activities

in the I/R group than those in the control group.

Metformin

  1. decreased significantly NO, TNF α, BUN and CrCl while
  2. increased urinary volume, electrolytes, CAT and GSH activities.

Lipid peroxidation is related to I/R induced tissue injury. Production of inducible NO synthase (NOS) under lipid peroxidation and inflammatory conditions results in the induction of NO

which react with

  • O2
  • liberating peroxynitrite (OONO).

NO itself inactivates the antioxidant enzyme system CAT and GSH.

Alteration in NO synthesis have been observed in other kidney injuries as nephrotoxicity and acute renal failure induced by endotoxins. Treatment with iNOS inhibitors improved renal function and decreased peroxynitrite radical which is believed to be responsible for the shedding of proximal convoluted tubules in I/R.

Metformin produced anti-inflammatory renoprotective effect on CrCl and diuresis in renal I/R injury.

 

Malek HA. The possible mechanism of action of metformin in renal ischemia reperfusion in rats.  The Pharma Research Journal 2011; 6(1):42-49.

Possible role of NO donors in ARF

 

The L-arginine-nitric oxide (NO) pathway has been implicated in many physiological functions in the kidney, including

  • regulation of glomerular hemodynamics,
  • mediation of pressure-natriuresis,
  • maintenance of medullary perfusion,
  • blunting of tubuloglomerular feedback (TGF),
  • inhibition of tubular sodium reabsorption and
  • modulation of renal sympathetic nerve activity.

Its net effect in the kidney is to promote natriuresis and diuresis, contributing to adaptation to variations of dietary salt intake and maintenance of normal blood pressure.

RAS Renal hemodynamics Sodium balance
  Medullary perfusion                                           
  Pressure-natriuresis  
     
Salt intake Tubulo-glomerular feedback Blood pressure
  Tubular sodium reabsorption  
     
Blood pressure Renal sympathetic activity Regulation
Extrarenal factors Intrarenal functions Physiological roles

 

Role of nitric oxide in renal physiology. RAS, renin-angiotensin system

Nitric oxide has been implicated in many physiologic processes that influence both acute and long-term control of kidney function. Its net effect in the kidney is to promote natriuresis and diuresis, contributing to adaptation to variations of dietary salt intake and maintenance of normal blood pressure. A pretreatment with nitric oxide donors or L-arginine may prevent the ischemic acute renal injury. In chronic kidney diseases, the systolic blood pressure is correlated with the plasma level of asymmetric dimethylarginine, an endogenous inhibitor of nitric oxide synthase.

A reduced production and biological action of nitric oxide is associated with an elevation of arterial pressure, and conversely, an exaggerated activity may represent a compensatory mechanism to mitigate the hypertension.

JongUn Lee. Nitric Oxide in the Kidney : Its Physiological Role and Pathophysiological Implications. Electrolyte & Blood Pressure 2008; 6:27-34.

Renal Hypoxia and Dysoxia following Reperfusion

 

Acute renal failure (ARF) is a common condition which develops in 5% of hospitalized patients. Of the patients who develop ARF, ~10% eventually require renal replacement therapy. Among critical care patients who have acute renal failure and survive, 2%-10% develop terminal renal failure and require long-term dialysis.

The kidneys are particularly susceptible to ischemic injury in many clinical conditions such as renal transplantation, treatment of suprarenal aneurysms, renal artery reconstructions, contrast-agent induced nephropathy, cardiac arrest, and shock. One reason for renal sensitivity to ischemia is that the kidney microvasculature is highly complex and must meet a high energy demand. Under normal, steady state conditions, the oxygen (O2) supply to the renal tissues is well in excess of oxygen demand.

Under pathological conditions, the delicate balance of oxygen supply versus demand is easily disturbed due to the unique arrangement of the renal microvasculature and its increasing numbers of diffusive shunting pathways.

The renal microvasculature is serially organized, with almost all descending vasa recta emerging from the efferent arterioles of the juxtamedullary glomeruli. Adequate tissue oxygenation is thus partially dependent on the maintenance of medullary perfusion by adequate cortical perfusion. This, combined with the low amount of medullary blood flow (~10% of total renal blood flow) in the U-shaped microvasculature of the medulla allows O2 shunting between the descending and ascending vasa recta and contributes to the high sensitivity of the medulla and cortico-medullary junction to decreased O2 supply.

Whereas past investigations have focused mainly on tubular injury as the main cause of ischemia-related acute renal failure, increasing evidence implicates alterations in the intra-renal microcirculation pathway and in the O2 handling. Indeed, although acute tubular necrosis (ATN) has classically been believed to be the leading cause of ARF, data from biopsies in patients with ATN have shown few or no changes consistent with tubular necrosis. The role played by microvascular dysfunction, however, has generated increasing interest. The complex pathophysiology of ischemic ARF includes the inevitable reperfusion phase associated with oxidative stress, cellular dysfunction and altered signal transduction.

During this process, alterations in oxygen transport pathways can result in cellular hypoxia and/or dysoxia. In this context, the distinction between hypoxia and dysoxia is that cellular hypoxia refers to the condition of decreased availability of oxygen due to inadequate convective delivery from the microcirculation. Cellular dysoxia, in contrast, refers to a pathological condition where the ability of mitochondria to perform oxidative phosphorylation is limited, regardless of the amount of available oxygen. The latter condition is associated with mitochondrial failure and/or activation of alternative pathways for oxygen consumption. Thus, we would expect that an optimal balance between oxygen supply and demand is essential to reducing damage from renal ischemia-reperfusion (I/R) injury (Figure 1).

Complex interactions exist between tubular injury, microvascular injury, and inflammation after renal I/R. On the one hand, insults to the tubule cells promotes the liberation of a number of inflammatory mediators, such as TNF-á, IL-6, TGF-â, and chemotactic cytokines (RANTES, monocyte chemotactic protein-1, ENA-78, Gro-á, and IL-8). On the other hand, chemokine production can promote leukocyte-endothelium interactions and leukocyte activation, resulting in renal blood flow impairment and the expansion of tubular damage.

renal hemodynamics and electrolyte reabsorption

Adequate medullary tissue oxygenation, in terms of balanced oxygen supply and demand, is dependent on the maintenance of medullary perfusion by adequate cortical perfusion and also on the high rate of O2 consumption required for active electrolyte transport. Furthermore, renal blood flow is closely associated with renal sodium transport.

In addition to having a limited O2 supply due to the anatomy of the microcirculation anatomy, the sensitivity of the medulla to hypoxic conditions results from this high O2 consumption. Renal sodium transport is the main O2-consuming function of the kidney and is closely linked to renal blood flow for sodium transport, particularly in the thick ascending limbs of the loop of Henle and the S3 segments of the proximal tubules.

Medullary renal blood flow is also highly dependent on cortical perfusion, with almost all descending vasa recta emerging from the efferent arteriole of juxta medullary glomeruli. A profound reduction in cortical perfusion can disrupt medullary blood flow and lead to an imbalance between O2 supply and O2 consumption. On theother hand, inhibition of tubular reabsorption by diuretics increases medullary pO2 by decreasing the activity of Na+/K+-ATPases and local O2 consumption.

 

Mitochondrial activity and NO-mediated O2 consumption

The medulla has been found to be the main site of production of NO in the kidney. In addition to the actions described above, NO appears to be a key regulator of renal tubule cell metabolism by inhibiting the activity of the Na+-K+-2Cl cotransporter and reducing Na+/H+ exchange. Since superoxide (O2) is required to inhibit solute transport activity, it was assumed that these effects were mediated by peroxynitrite (OONO). Indeed, mitochondrial nNOS upregulation, together with an increase in NO production, has been shown to increase mitochondrial peroxynitrite generation, which in turn, can induce cytochrome c release and promote apoptosis. NO has also been shown to directly compete with O2 at the mitochondrial level. These findings support the idea that NO acts as an endogenous regulator to match O2 supply to O2 consumption, especially in the renal medulla.

NO reversibly binds to the O2 binding site of cytochrome oxidase, and acts as a potent, rapid, and reversible inhibitor of cytochrome oxidase in competition with molecular O2. This inhibition could be dependent on the O2 level, since the IC50 (the concentration of NO that reduces the specified response by half) decreases with reduction in O2 concentration. The inhibition of electron flux at the cytochrome oxidase level switches the electron transport chain to a reduced state, and consequently leads to depolarization of the mitochondrial membrane potential and electron leakage.

 

To summarize, while the NO/O2 ratio can act as a regulator of cellular O2 consumption by matching decreases in O2 delivery to decreases in cellular O2 cellular, the inhibitory effect of NO on mitochondrial respiration under hypoxic conditions further impairs cellular aerobic metabolism This leads to a state of “cytopathic hypoxia,” as described in the sepsis literature.

Only cell-secreted NO competes with O2 and to regulate mitochondrial respiration. In addition to the 3 isoforms (eNOS, iNOS, cnNOS), an α-isoform of neuronal NOS, the mitochondrial isoform (mNOS) located in the inner mitochondrial membrane, has also been shown to regulate mitochondrial respiration.

These data support a role for NO in the balanced regulation of renal O2 supply and O2 consumption after renal I/R However, the relationships between the determinants of O2 supply, O2 consumption, and renal function, and their relation to renal damage remain largely unknown.

Sustained endothelial activation

Ischemic renal failure leads to persistent endothelial activation, mainly in the form of endothelium-leukocyte interactions and the activation of adhesion molecules.

This persistent activation can

  • compromise renal blood flow,
  • prevent the recovery of adequate tissue oxygenation, and
  • jeopardize tubular cell survival despite the initial recovery of renal tubular function.

A 30-50% reduction in microvascular density was seen 40 weeks after renal ischemic injury in a rat model. Vascular rarefaction has been proposed to induce chronic hypoxia resulting in tubulointerstitial fibrosis via the molecular activation of fibrogenic factors such as

  • transforming growth factor (TGF)-β,
  • collagen, and
  • fibronectin,

all of which may play an important role in the progression of chronic renal disease.

Adaptation to hypoxia

 

Over the last decade, the role of hypoxia-inducible factors (HIFs) in O2 supply and adaptation to hypoxic conditions has found increasing support. HIFs are O2-sensitive transcription factors involved in O2-dependent gene regulation that mediate cellular adaptation to O2 deprivation and tissue protection under hypoxic conditions in the kidney.

NO generation can promote HIF-1α accumulation in a cGMP-independent manner. However, Hagen et al. (2003) showed that NO may reduce the activation of HIF in hypoxia via the inhibitory effect of NO on cytochrome oxidase. Therefore, it seems that NO has pleiotropic effects on HIF expression, with various responses related to different pathways.

HIF-1α upregulates a number of factors implicated in cytoprotection, including angiogenic growth factors, such as

  • vascular endothelial growth factors (VEGF),
  • endothelial progenitor cell recruitment via the endothelial expression of SDF-1,
  • heme-oxygenase-1 (HO-1), and
  • erythropoietin (EPO), and
  • vasomotor regulation.

HO-1 produces carbon monoxide (a potent vasodilator) while degrading heme, which may preserve tissue blood flow during reperfusion. Thus, it has been suggested that

  • the induction of HO-1 can protect the kidney from ischemic damage by decreasing oxidative damage and NO generation.
  • in addition to its anti-apoptotic properties, EPO may protect the kidney from ischemic damage by restoring the renal microcirculation

(by stimulating the mobilization and differentiation of progenitor cells toward an endothelial phenotype and by inducing NO release from eNOS).

 

Pharmacological interventions

Use of pharmacological interventions which act at the microcirculatory level may be a successful strategy to overcome ischemia-induced vascular damage and prevent ARF.

Activated protein C (APC), an endogenous vitamin K-dependent serine protease with multiple biological activities, may meet these criteria. Along with antithrombotic and profibrinolytic properties, APC can reduce the chemotaxis and interactions of leukocytes with activated endothelium. However, renal dysfunction was not improved in the largest study published so far. In addition, APC has been discontinued by Lilly for the use intended in severe sepsis.

  •  neither drugs with renal vasodilatory effects (i.e., dopamine, fenoldopam, endothelin receptors blockers, adenosine antagonists) or
  • agents that decrease renal oxygen consumption (i.e., loop diuretics) have been shown to protect the kidney from ischemic damage.

We have to bear in mind that a magic bullet to treat the highly complex condition of which is renal I/R is not in sight.  We can expect that understanding the balance between O2 delivery and O2 consumption, as well as the function of O2-consuming pathways (i.e., mitochondrial function, reactive oxygen species generation) will be central to this treatment strategy.

Take home point

 

The deleterious effects of NO are thought to be associated with the NO generated by the induction of iNOS and its contribution to oxidative stress both resulting in vascular dysfunction and tissue damage. Ischemic injury also leads to structural damage to the endothelium and leukocyte infiltration. Consequently, renal tissue hypoxia is proposed to promote the initial tubular damage, leading to acute organ dysfunction.

Comment: I express great appreciation for refeering to this work, which does provide enormous new insights into hypoxia-induced acute renal failure, and ties together the anatomy, physiology, and gene regulation through signaling pathways.

Ince C, Legrand M, Mik E , Johannes T, Payen D. Renal Hypoxia and Dysoxia following Reperfusion of the Ischemic Kidney. Molecular Medicine (Proof) 2008; pp36. www.molmed.org

English: Major cellular sources of ROS in livi...

English: Major cellular sources of ROS in living cells. Novo and Parola Fibrogenesis & Tissue Repair 2008 1:5 doi:10.1186/1755-1536-1-5 (Photo credit: Wikipedia)

Figure 1

Figure 1 (Photo credit: Libertas Academica)

The reaction mechanism of Nitric oxide synthase

The reaction mechanism of Nitric oxide synthase (Photo credit: Wikipedia)

Nitric oxide and non-hemodynamic functions of the kidney

 

One of the major scientific advances in the past decade in understanding of the renal function and disease is the prolific growth of literature incriminating nitric oxide (NO) in renal physiology and pathophysiology. NO was first shown to be identical with endothelial derived relaxing factor (EDRF) in 1987 and this was followed by a rapid flurry of information defining the significance of NO in not only vascular physiology and hemodynamics but also in neurotransmission, inflammation and immune defense systems.

Although most actions of NO are mediated by cyclic guanosine monophosphate (cGMP) signaling, S-nitrosylation of cysteine residues in target  proteins constitutes another well defined non-cGMP dependent mechanism of NO effects.

Recent years have witnessed a phenomenal scientific interest in the vascular biology, particularly the relevance of nitric oxide (NO) in cardiovascular and renal physiology and pathophysiology. Although hemodynamic actions of NO received initial attention, a variety of non-hemodynamic actions are now known to be mediated by NO in the normal kidney,which include

  • tubular transport of electrolyte and water,
  • maintenance of acid-base homeostasis,
  • modulation of glomerular and interstitial functions,
  • renin-angiotensin activation and
  • regulation of immune defense mechanism in the kidney.

Table 1 : Functions of NO in the kidney

1. Renal macrovascular and microvascular dilatation (afferent > efferent)

2. Regulation of mitochondrial respiration.

3. Modulation renal medullary blood flow

4. Stimulation of fluid, sodium and HCO3 – reabsorption in the proximal tubule

5. Stimulation of renal acidification in proximal tubule by stimulation of NHE activity

6. Inhibition of Na+, Cl- and HCO3 – reabsorption in the mTALH

7. Inhibition of Na+ conductance in the CCD

8. Inhibition of H+-ATPase in CCD

One of the renal regulatory mechanisms related to maintenance of arterial blood pressure involves the phenomenon of pressure-natriuresis in response to elevation of arterial pressure. This effect implies inhibition of tubular sodium reabsorption resulting in natriuresis, in an effort to lower arterial pressure. Experimental evidence indicates that intra-renal NO modulates pressure natriuresis.

Furthermore many studies have confirmed the role of intra renal NO in mediating tubulo-glomerular feedback (TGF).  In vivo micropuncture studies have shown that NO derived from nNOS in macula densa specifically inhibits the TGF responses leading to renal afferent arteriolar vasoconstriction in response to sodium reabsorption in the distal tubule. Other recent studies support the inhibitory role of NO from eNOS and iNOS in mTALH segment on TGF effects.

Recent observations in vascular biology have yielded new information that endothelial dysfunction early in the course might contribute to the pathophysiology of acute renal failure. Structural and functional changes in the vascular endothelium are demonstrable in early ischemic renal failure. Altered NO production and /or decreased bioavailability of NO comprise the endothelial dysfunction in acute renal failure.

Several studies have indicated imbalance of NOS activity with enhanced expression and activity of iNOS and decreased eNOS in ischemic kidneys. The imbalance results from enhanced iNOS activity and attenuated eNOS activity in the kidney.

Many experimental studies support a contributory role for NO in glomerulonephritis (GN). Evidence from recent studies pointed out that NO may be involved in peroxynitrite formation, pro-inflammatory chemokines and signaling pathways in addition to direct glomerular effects that promote albumin permeability in GN.

Although originally macrophages and other leukocytes were first considered as the source renal NO production in GN, it is now clear iNOS derived NO from glomerular mesangial cells are the primary source of NO in GN.

In most pathological states, the role of NO is

  • dependent on the stage of the disease,
  • the nitric oxide synthase (NOS) isoform involved and
  • the presence or absence of other modifying intrarenal factors.

Additionally NO may have a dual role in several disease states of the kidney such as

  • acute renal failure,
  • inflammatory nephritides,
  • diabetic nephropathy and
  • transplant rejection.

A rapidly growing body of evidence supports a critical role for NO in tubulointerstitial nephritis (TIN). In the rat model of autoimmune TIN, Gabbai et al. demonstrated increased iNOS expression in the kidney and NO metabolites in urine and plasma. However the effects of iNOS on renal damage in TIN seem to have a biphasic effect- since iNOS specific inhibitors (eg. L-Nil) are renoprotective in the acute phase while they actually accelerated the renal damage in the chronic phase. Thus chronic NOS inhibition is used to induce chronic tubulointerstitial injury and fibrosis along with mild glomerulosclerosis and hypertension.

Major pathways of L-arginine metabolism.

  • L-arginine may be metabolized by the urea cycle enzyme arginase to L-ornithine and urea
  • by arginine decarboxylase to agmatine and CO2 or
  • by NOS to nitric oxide (NO) and L-citrulline.

Adapted from Klahr S: Can L-arginine manipulation reduce renal disease?  Semin Nephrol 1999; 61:304-309.

It is obvious that kidney is not only a major source of arginine and nitric oxide but NO plays an important role in the water and electrolyte balance and acid-base physiology and many other homeostatic functions in the kidney. Unfortunately we are far from a precise understanding of the significance of NO alterations in various disease states primarily due to conflicting data from the existing literature.

Therapeutic potential for manipulation of L-arginine- nitric oxide axis in renal disease states has been discussed. More studies are required to elucidate the abnormalities in NO

metabolism in renal diseases and to confirm the therapeutic potential of L-arginine.

Sharma SP. Nitric oxide and the kidney. Indian J Nephrol 2004;14: 77-84

Inhibition of Constitutive Nitric Oxide Synthase

 

Excess NO generation plays a major role in the hypotension and systemic vasodilatation characteristic of sepsis. Yet the kidney response to sepsis is characterized by vasoconstriction resulting in renal dysfunction.

We have examined the roles of inducible nitric oxide synthase (iNOS) and endothelial NOS (eNOS) on the renal effects of lipopolysaccharide administration by comparing the effects of specific iNOS inhibition, L-N6-(1-iminoethyl)lysine (L-NIL), and 2,4-diamino-6-hydroxy-pyrimidine vs. nonspecific NOS inhibitors (nitro-L-arginine-methylester). cGMP responses to carbamylcholine (CCh) (stimulated, basal) and sodium nitroprusside in isolated glomeruli were used as indices of eNOS and guanylate cyclase (GC) activity, respectively.

LPS significantly decreased blood pressure and GFR (P =0.05) and inhibited the cGMP response to CCh. GC activity was reciprocally increased. L-NIL and 2,4-diamino-6-hydroxy-pyrimidine administration prevented the decrease in GFR, restored the normal response to CCh, and GC activity was normalized. In vitro application of L-NIL also restored CCh responses in LPS glomeruli.

Neuronal NOS inhibitors verified that CCh responses reflected eNOS activity. L-NAME, a nonspecific inhibitor, worsened GFR, a reduction that was functional and not related to glomerular thrombosis, and eliminated the CCh response. No differences were observed in eNOS mRNA expression among the experimental groups.

Selective iNOS inhibition prevents reductions in GFR, whereas nonselective inhibition of NOS further decreases GFR. These findings suggest that the decrease in GFR after LPS is due to local inhibition of eNOS by iNOS, possibly via NO autoinhibition.

Schwartz D, Mendonca M, Schwartz I, Xia Y, et al. Inhibition of Constitutive Nitric Oxide Synthase (NOS) by Nitric Oxide Generated by Inducible NOS after Lipopolysaccharide Administration Provokes Renal Dysfunction in Rats. J. Clin. Invest. 1997; 100:439–448.

Salt-Sensitivity and Hypertension

Renin-angiotensin system (RAS) plays a key role in

  • the regulation of renal function,
  • volume of extracellular fluid and
  • blood pressure.

The activation of RAS also induces oxidative stress, particularly superoxide anion (O2-) formation. Although the involvement of O2 – production in the pathology of many diseases has been long known, recent studies also strongly suggest its physiological regulatory function of many organs including the kidney.

However, a marked accumulation of O2- in the kidney alters normal regulation of renal function and may contribute to the development of salt-sensitivity and hypertension. In the kidney, O2- acts as vasoconstrictor and enhances tubular sodium reabsoption.

Nitric oxide (NO), another important radical that exhibits opposite effects than O2 -, is also involved in the regulation of kidney function. O2- rapidly interacts with NO and thus, when O2- production increases, it diminishes the bioavailability of NO leading to the impairment of organ function.

As the activation of RAS, particularly the enhanced production of angiotensin II, can induce both O2- and NO generation, it has been suggested that physiological interactions of RAS, NO and O2- provide a coordinated regulation of kidney function.

The imbalance of these interactions is critically linked to the pathophysiology of salt-sensitivity and hypertension.

Kopkan L, Červenka L. Renal Interactions of Renin-Angiotensin System, Nitric Oxide and Superoxide Anion: Implications in the Pathophysiology of Salt-Sensitivity and Hypertension. Physiol. Res. 2009; 58 (Suppl. 2): S55-S67.

 

Epicrisis

 

In this review I attempted to evaulate complex and still incomplete and conflicting conclusions from many studies.  I thus broke the report into three major portions:

1 The kidney and its anatomy, physiology, and ontogeny.

2 The pathological disease variation affecting the kidney

a  a tie in to eNOS and iNos, nitric oxide, cGMP and glutaminase – in acute renal failure, hypertension, chronic renal failure, dialysis

the pathology of acute tubular necrosis, glomerular function, efferent arteriolar and kidney medullary circulatory impairment, and cast formation related to Tamm Horsfall protein

b   The role of NO, eNOS and iNOS in disorders of the lund alveolar cell and subendothelial matrix, and of liver disease also affecting the kidney, and the heart.

c   Additional references

3.  a          Acute renal failure, oxidate stress, ischemia-reperfusion injury, tubulointerstitial chronic inflammation

b          Additional references

4.    Nitric oxide donors – opportunities for therapeutic targeting?

As we see this in as full a context as possible, it is hard to distinguish the cart from the horse.  We know that there is an unquestionable role of NO, and a competing balance to be achieved between eNOS, iNOS, an effect on tubular water and ion-cation reabsorptrion, a role of TNFa, and consequently an impofrtant role in essential/malignant hypertension, with the size of the effect related to the stage of disorder, the amount of interstitial fibrosis, the remaining nephron population, the hypertonicity of the medulla, the vasodilation of the medularry circullation, and the renin-angiotensin-aldosterone system.  Substantial data and multiple patientys with many factors per patient would be need to extract the best model using a supercomputer.

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