Leaders in Pharmaceutical Business Intelligence (LPBI) Group

Heart-Lung-Kidney: Essential Ties

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

 

Introduction

The basic functioning of the heart, and the kidney have been covered in depth elsewhere, and pulmonary function less, except in this series.  The relationship between them on the basis of endocrine, signaling, and metabolic balance is the focus in this piece.

Other elated articles can be found in http://pharmaceuticalintelligence.com:

The Amazing Structure and Adaptive Functioning of the Kidneys: Nitric Oxide – Part I
http://pharmaceuticalintelligence.com/2012/11/26/the-amazing-structure-and-adaptive-functioning-of-the-kidneys/

Nitric Oxide and iNOS have Key Roles in Kidney Diseases – Part II
http://pharmaceuticalintelligence.com/2012/11/26/nitric-oxide-and-inos-have-key-roles-in-kidney-diseases/

Stroke and Bleeding in Atrial Fibrillation with Chronic Kidney Disease
http://pharmaceuticalintelligence.com/2012/08/16/stroke-and-bleeding-in-atrial-fibrillation-with-chronic-kidney-disease/

Risks of Hypoglycemia in Diabetics with Chronic Kidney Disease (CKD)
http://pharmaceuticalintelligence.com/2012/08/01/risks-of-hypoglycemia-in-diabetics-with-ckd/

Acute Lung Injury
http://pharmaceuticalintelligence.com/2015/02/26/acute-lung-injury/

Neonatal Pathophysiology
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Altitude Adaptation
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Action of Hormones on the Circulation
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Innervation of Heart and Heart Rate
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Neural Activity Regulating Endocrine Response
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Thyroid Function and Disorders
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Highlights in the History of Physiology
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The Evolution of Clinical Chemistry in the 20th Century
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More…

Sodium homeostasis

Icariin attenuates angiotensin II‑induced hypertrophy and apoptosis in H9c2 cardiomyocytes by inhibiting reactive oxygen species‑dependent JNK and p38 pathways

H Zhou, Y Yuan, Y Liu, Wei Deng, Jing Zong, Zhou‑Yan Bian, Jia Dai and Qi‑Zhu Tang
Exper and Therapeutic Med 7: 1116-1122, 2014
http://dx.doi.org:/10.3892/etm.2014.1598

Icariin, the major active component isolated from plants of the Epimedium family, has been reported to have potential protective effects on the cardiovascular system. However, it is not known whether icariin has a direct effect on angiotensin II (Ang II)‑induced cardiomyocyte enlargement and apoptosis. In the present study, embryonic rat heart‑derived H9c2 cells were stimulated by Ang II, with or without icariin administration. Icariin treatment was found to attenuate the Ang II‑induced increase in mRNA expression levels of hypertrophic markers, including atrial natriuretic peptide and B‑type natriuretic peptide, in a concentration‑dependent manner. The cell surface area of Ang II‑treated H9c2 cells also decreased with icariin administration. Furthermore, icariin repressed Ang II‑induced cell apoptosis and protein expression levels of Bax and cleaved‑caspase 3, while the expression of Bcl‑2 was increased by icariin. In addition, 2′,7’‑dichlorofluorescein diacetate incubation revealed that icariin inhibited the production of intracellular reactive oxygen species (ROS), which were stimulated by Ang II. Phosphorylation of c‑Jun N‑terminal kinase (JNK) and p38 in Ang II‑treated H9c2 cells was blocked by icariin. Therefore, the results of the present study indicated that icariin protected H9c2 cardiomyocytes from Ang II‑induced hypertrophy and apoptosis by inhibiting the ROS‑dependent JNK and p38 pathways.

Short-term add-on therapy with angiotensin receptor blocker for end-stage inotrope-dependent heart failure patients: B-type natriuretic peptide reduction in a randomized clinical trial

Marcelo E. Ochiai, ECO Brancalhao, RSN Puig, KRN Vieira, et al.
Clinics. 2014; 69(5):308-313
http://dx.doi.org:/10.6061/clinics/2014(05)02

OBJECTIVE: We aimed to evaluate angiotensin receptor blocker add-on therapy in patients with low cardiac output during decompensated heart failure. METHODS: We selected patients with decompensated heart failure, low cardiac output, dobutamine dependence, and an ejection fraction ,0.45 who were receiving an angiotensin-converting enzyme inhibitor. The patients were randomized to losartan or placebo and underwent invasive hemodynamic and B-type natriuretic peptide measurements at baseline and on the seventh day after intervention. ClinicalTrials.gov: NCT01857999. RESULTS: We studied 10 patients in the losartan group and 11 patients in the placebo group. The patient characteristics were as follows: age 52.7 years, ejection fraction 21.3%, dobutamine infusion 8.5 mcg/kg.min, indexed systemic vascular resistance 1918.0 dynes.sec/cm5.m2, cardiac index 2.8 L/min.m2, and B-type natriuretic peptide 1,403 pg/mL. After 7 days of intervention, there was a 37.4% reduction in the B-type natriuretic peptide levels in the losartan group compared with an 11.9% increase in the placebo group (mean difference, – 49.1%; 95% confidence interval: -88.1 to -9.8%, p = 0.018). No significant difference was observed in the hemodynamic measurements. CONCLUSION: Short-term add-on therapy with losartan reduced B-type natriuretic peptide levels in patients hospitalized for decompensated severe heart failure and low cardiac output with inotrope dependence.

Development of a Novel Heart Failure Risk Tool: The Barcelona Bio-Heart Failure Risk Calculator (BCN Bio-HF Calculator)

Josep Lupon, Marta de Antonio, Joan Vila, Judith Penafiel, et al.
PLoS ONE 9(1): e85466. http://dx.doi.org:/10.1371/journal.pone.0085466

Background: A combination of clinical and routine laboratory data with biomarkers reflecting different pathophysiological pathways may help to refine risk stratification in heart failure (HF). A novel calculator (BCN Bio-HF calculator) incorporating N-terminal pro B-type natriuretic peptide (NT-proBNP, a marker of myocardial stretch), high-sensitivity cardiac troponin T (hs-cTnT, a marker of myocyte injury), and high-sensitivity soluble ST2 (ST2), (reflective of myocardial fibrosis and remodeling) was developed. Methods: Model performance was evaluated using discrimination, calibration, and reclassi-fication tools for 1-, 2-, and 3-year mortality. Ten-fold cross-validation with 1000 bootstrapping was used. Results: The BCN Bio-HF calculator was derived from 864 consecutive outpatients (72% men) with mean age 68.2612 years (73%/27% New York Heart Association (NYHA) class I-II/III-IV, LVEF 36%, ischemic etiology 52.2%) and followed for a median of 3.4 years (305 deaths). After an initial evaluation of 23 variables, eight independent models were developed. The variables included in these models were age, sex, NYHA functional class, left ventricular ejection fraction, serum sodium, estimated glomerular filtration rate, hemoglobin, loop diuretic dose, β-blocker, Angiotensin converting enzyme inhibitor/Angiotensin-2 receptor blocker and statin treatments, and hs-cTnT, ST2, and NT-proBNP levels. The calculator may run with the availability of none, one, two, or the three biomarkers. The calculated risk of death was significantly changed by additive biomarker data. The average C-statistic in cross-validation analysis was 0.79. Conclusions: A new HF risk-calculator that incorporates available biomarkers reflecting different pathophysiological pathways better allowed individual prediction of death at 1, 2, and 3 years.

TNF and angiotensin type 1 receptors interact in the brain control of blood pressure in heart failure

Tymoteusz Zera, Marcin Ufnal, Ewa Szczepanska-Sadowska
Cytokine 71 (2015) 272–277
http://dx.doi.org/10.1016/j.cyto.2014.10.019

Accumulating evidence suggests that the brain renin-angiotensin system and proinflammatory cytokines, such as TNF-α, play a key role in the neuro-hormonal activation in chronic heart failure (HF). In this study we tested the involvement of TNF-α and angiotensin type 1 receptors (AT1Rs) in the central control of the cardiovascular system in HF rats. Methods: we carried out the study on male Sprague–Dawley rats subjected to the left coronary artery ligation (HF rats) or to sham surgery (sham-operated rats). The rats were pretreated for four weeks with intracerebroventricular (ICV) infusion of either saline (0.25 µl/h) or TNF-α inhibitor etanercept (0.25 µg/0.25 µl/h). At the end of the pretreatment period, we measured mean arterial blood pressure (MABP) and heart rate (HR) at baseline and during 60 min of ICV administration of either saline (5 µl/h) or AT1Rs antagonist losartan (10 µg/5 µl/h). After the experiments, we measured the left ventricle end-diastolic pressure (LVEDP) and the size of myocardial scar. Results: MABP and HR of sham-operated and HF rats were not affected by pretreatments with etanercept or saline alone. In sham-operated rats the ICV infusion of losartan did not affect MABP either in saline or in etanercept pretreated rats. In contrast, in HF rats the ICV infusion of losartan significantly decreased MABP in rats pretreated with saline, but not in those pretreated with etanercept. LVEDP was significantly elevated in HF rats but not in sham-operated ones. Surface of the infarct scar exceeded 30% of the left ventricle in HF groups, whereas sham-operated rats did not manifest evidence of cardiac scarring. Conclusions: our study provides evidence that in rats with post-infarction heart failure the regulation of blood pressure by AT1Rs depends on centrally acting endogenous TNF-α.

Statins in heart failure—With preserved and reduced ejection fraction. An update

Dimitris Tousoulis , E Oikonomou, G Siasos, C Stefanadis
Pharmacology & Therapeutics 141 (2014) 79–91
http://dx.doi.org/10.1016/j.pharmthera.2013.09.001

HMG-CoA reductase inhibitors or statins beyond their lipid lowering properties and mevalonate inhibition exert also their actions through a multiplicity of mechanisms. In heart failure (HF) the inhibition of isoprenoid intermediates and small GTPases, which control cellular function such as cell shape, secretion and proliferation, is of clinical significance. Statins share also the peroxisome proliferator-activated receptor pathway and inactivate extracellular-signal-regulated kinase phosphorylation suppressing inflammatory cascade. By down-regulating Rho/Rho kinase signaling pathways, statins increase the stability of eNOS mRNA and induce activation of eNOS through phosphatidylinositol 3-kinase/Akt/eNOS pathway restoring endothelial function. Statins change also myocardial action potential plateau by modulation of Kv1.5 and Kv4.3 channel activity and inhibit sympathetic nerve activity suppressing arrhythmogenesis. Less documented evidence proposes also that statins have antihypertrophic effects – through p21ras/mitogen activated protein kinase pathway – which modulate synthesis of matrix metalloproteinases and procollagen 1 expression affecting interstitial fibrosis and diastolic dysfunction. Clinical studies have partly confirmed the experimental findings and despite current guidelines new evidence supports the notion that statins can be beneficial in some cases of HF. In subjects with diastolic HF, moderately impaired systolic function, low B-type natriuretic peptide levels, exacerbated inflammatory response and mild interstitial fibrosis evidence supports that statins can favorably affect the outcome. Under the lights of this evidence in this review article we discuss the current knowledge on the mechanisms of statins’ actions and we link current experimental and clinical data to further understand the possible impact of statins’ treatment on HF syndrome.

Since 1980 when the first 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor or statin was introduced in clinical practice, statins have been extensively used in the treatment of patients with dyslipidemia as well as of those with coronary artery disease (CAD). Importantly, large scale trials and metanalysis have documented their significant benefits in terms of primary and secondary CAD prevention which out-weigh any potential side effects. Statins’ benefits extend, according to recent studies, even in patients with normal or low cholesterol levels and beyond their lipid lowering effects, indicating their multiple protective mechanisms.

Heart failure (HF) is a complex syndrome with different definitions and its diagnosis is based on a combination of symptoms, clinical signs and imaging or laboratory data. different categorization schemes have been used dividing HF in acute or chronic, in systolic or diastolic, and in ischemic or dilated simply reflecting the complexity of the syndrome and the multiplicity of the pathophysiologic mechanisms implicated in the disease development and progression. In addition to the diverse pathophysiology of HF the syndrome is also characterized by high morbidity and mortality. Recent treatment advantages such as angiotensin converting enzyme inhibitors and beta blockers have not yet proven their clinical benefit in subjects with diastolic HF.

As the most common cause of HF is CAD and statins have proven their benefits in a wide spectrum of diseases directly or indirectly associated with atherosclerotic cardiovascular disease, HMG-CoA reductase inhibitors have been tested in subjects with HF. Interestingly, non-randomized, observational and retrospective early studies in subjects with HF of ischemic and non-ischemic etiology have suggested that statins are associated with improved outcomes. Thereafter, two large scale randomized control trials failed to demonstrate any benefits in mortality of HF patients treated with rosuvastatin and subsequently current HF guidelines do not include recommendations for statin use except from when they are indicated for comorbidities, such as established CAD.

Statins inhibit HMG-CoA reductase. This enzyme catalyzes the conversion of 3-hydroxy-3-methylglutaryl-coenzyme A to L-mevalonic acid, which is the rate-limiting step in the cholesterol synthesis pathway. Inhibition of the mevalonate pathway and of cholesterol synthesis triggers an increase in LDL receptor activity by stimulating production of mRNA for LDL receptor in liver. The induction of LDL receptors is responsible for the observed increase in plasma clearance of LDL cholesterol. CAD is the cause of approximately two-thirds of cases of systolic HF. The beneficial effects of statins-induced LDL reduction are well established in patients with atherosclerosis and CAD. Nevertheless, the results from statin treatment, even in ischemic HF cases, are not straightforward and several mechanisms have been proposed for this paradox.

The figure demonstrates the multiplicity of HMG CoA reductase inhibitors mechanisms and their effects. ↓: decrease; ↑ increase; FPP: farnesyl pyrophosphate: GGPP: geranylgeranyl pyrophosphate; Ras, Rac, Rho; small GTPases; eNOS: endothelial nitric oxide synthase; ATP: adenosine triphosphate; PI-3 kinase: phosphatidylinositol 3-kinase; AMPK: AMP activated protein kinase; GTP: Guanosine triphosphate; NADPH: Nicotinamide adenine dinucleotide phosphate; ERK: extracellular-signal-regulated kinase; Shadow box represents adverse mechanism and actions of HGM CoA reductase inhibitors.

The anti-inflammatory effects of HMG CoA reductase inhibitors in atherosclerosis have been early recognized. Statins also have a potent anti-inflammatory effect in HF models. Importantly, there is a link between inflammation and HF pathogenesis and is now widely accepted that pro-inflammatory cytokines cause systolic dysfunction, myocardial hypertrophy, activate a fetal gene program in cardiac myocytes, disturb extracellular matrix structure, cause cardiac cachexia etc. In addition, data from the Vesnarinone trial (VEST) in 384 patients with HF demonstrate a decline in survival with increasing TNFα levels confirming the notion that circulating cytokines are associated with adverse prognosis of HF patients.

The proposed, by the aforementioned mechanisms, anti-inflammatory effects of statins have been confirmed experimentally. Indeed, in a rat HF model with preserved ejection fraction (EF), treatment with rosuvastatin resulted in a significant additional improvement in HF and cardiac remodeling, partly due to decreased myocardial inflammation. In rats after acute myocardial infarction simvastatin treatment for 4 weeks beneficially modified the levels of TNFα, interleukin (IL)-1, 6 and 10 in the infarct regions. Importantly, in 446 patients with systolic HF, followed up for a period of 24 months, statins’ treatment was associated with a decrease in serum levels of C-reactive protein (CRP), IL-6 and tumor necrosis factor-alpha receptor II. Recently, in a randomized study of 22 subjects with ischemic HF short term atorvastatin treatment achieved a significant decrease in serum levels of intracellular adhesion molecule-1.

Taken together we can conclude that HMG CoA reductase inhibitors can modify inflammatory status by modulation of PRAP and ERK pathways by down regulating Toll like receptor 4 mRNA expressions and LDL oxidation and by reducing soluble lipoprotein-associated phospholipase A2 mass and activity. Importantly, the theoretical anti-inflammatory properties were confirmed in experimental and clinical HF models.

Endothelial dysfunction contributes to the pathogenesis of HF and can enhance adverse left ventricle (LV) remodeling and increase afterload in subjects with HF. Interestingly, statins have been constantly associated with improved endothelial function in subjects with a variety of cardiovascular diseases. Endothelium derived nitric oxide (NO) is an important determinant of endothelial function and HMG-CoA reductase inhibitors can up regulate endothelial NO synthase (eNOS) by different mechanisms.

Statins induce down regulation of Rho/Rho kinase signaling pathways, increasing the stability of eNOS mRNA and its expression . In addition, in human endothelial cells the Rho-kinase inhibitor, hydroxyfasudil leads to the activation of the phosphatidylinositol 3-kinase/Akt/eNOS pathway. Statins also induce activation of eNOS through the rapid activation of the serine–threonine protein kinase Akt. The beneficial effects of Akt activation are not limited to eNOS phoshorylation but extend to the promotion of new blood vessels growth. HMG CoA reductase inhibitors can further affect endothelial function through their effect on caveolin-1. Caveolin-1 binds to eNOS inhibiting NO production. Incubation of endothelial cells with atorvastatin promotes NO production by decreasing caveolin-1 expression, regardless of the level of extracellular LDL-cholesterol. These effects were reversed with mevalonate highlighting the therapeutic potential of inhibiting cholesterol synthesis in peripheral cells to correct NO-dependent endothelial dysfunction associated with hypercholesterolemia and possibly other diseases.

Although the experimentally confirmed benefits of HMG CoA reductase inhibitors in diastolic dysfunction and left ventricle stiffness, few data exist concerning the underlying mechanisms. As diastolic dysfunction precedes myocardial hypertrophy the anti-hypertrophic pathways mentioned in the previous section (inhibition of RhoA/Ras/ERK, PRAPγ pathways, inhibition of a large G(h) protein-coupled pathway etc.), may also contribute to the restoration of diastolic function. Moreover, in angiotensin II induced diastolic dysfunction in hypertensive mice, pravastatin not only improved diastolic function but also down-regulated collagen I, transforming growth factor-beta, matrix metalloproteinases (MMPs)-2 and -3, atrial natriuretic factor, IL-6 TNFα, Rho kinase 1 gene expression, and upregulated eNOS gene expression. These findings suggest the potential involvement of Rho kinase 1 in the beneficial effects of pravastatin in diastolic HF. Taken together data suggest that HMG CoA reductase inhibitors might be beneficial in patients with diastolic HF, a hypothesis that remains to be confirmed by clinical studies. Nevertheless, mechanistic studies have not fully explored the pathways affecting diastolic function and most data until now are indirect. Therefore efforts should be focus on the underline mechanisms affecting collagen synthesis, MMPs activity extracellular matrix synthesis and overall diastolic function in HF subjects under statin treatment.

Statins through inhibition of small GTPases can modulate MMPs activity in several cell types such as endothelial cells and human macrophages. In rat and human cardiac fibroblasts, stimulated with either transforming growth factor β1 or angiotensin II, atorvastatin reduced collagen synthesis and α1-procollagen mRNA as well as gene expression of the profibrotic peptide connective tissue growth factor 4. This antifibrotic action may contribute to the anti-remodelling effect of statins. In mouse cardiac fibroblasts treated with angiotensin II, the combination of pravastatin and pioglitazone blocked angiotensin II p38 MAPK and p44/42 MAPK activation and procollagen expression-1.

Several studies have documented the impact of statin treatment on arrhythmia potential. The arrhythmic protective effects of statins can be attributed not only to anti-inflammatory properties but also to changes in myocardial action potential plateau by modulation of Kv1.5 and Kv4.3 channel activity. Atorvastatin and simvastatin block Kv1.5 and Kv4.3 channels shifting the inactivation curve to more negative potentials following a complex mechanism that does not imply the binding of the drug to the channel pore. Moreover, in hypertrophied neonatal rat ventricular myocytes simvastatin alleviated the reduction of Kv4.3 expression, I(to) currents in subepicardial myocardium from the hypertrophied left ventricle. Furthermore, pravastatin in an animal model attenuated reperfusion induced lethal ventricular arrhythmias by inhibition of calcium overload.

Taking together experimental and cellular evidence supporting an effect of statin treatment in myocardial contractility is spare and for the time being we cannot definitively conclude on the clinical impact of HMG CoA reductase inhibitors in myocardial systolic performance.

Half of the cases of HF are attributed to diastolic dysfunction and the prognosis of HF with preserved EF is as ominous as the prognosis of HF with systolic dysfunction. Unfortunately, no treatment has yet been shown, convincingly, to reduce morbidity and mortality in patients with HF and preserved EF, while this group of patients is usually excluded from large prospective randomized trials and accordingly few data exist for the role of statins in this heterogeneous population.

As there is substantially lack of evidence concerning the effects of HMG CoA reductase inhibitors in subjects with HF and preserved EF the first indirect hypothesis was extrapolated from observational prospective studies in subjects with ischemic heart disease and no evidence of congestive HF. Indeed, in a cohort of 430 consecutive patients with ischemic heart disease and a mean EF of 57% Okura et al. observed that subjects under HMG CoA reductase inhibitors treatment had decreased E/E′ ratio—corresponding to a better diastolic function—and a significantly higher survival rate (Okura et al., 2007). According to the authors those beneficially effects can be attributed to improved endothelial function and vasodilatory response to reactive hyperemia, attenuation of myocardial hypertrophy, and interstitial fibrosis.

Despite the positive results from mechanistic and experimental studies clinical studies have failed to confirm a definitive role of HMG CoA reductase inhibitors in HF. Nevertheless, by extrapolating experimental and mechanistic data in clinical settings we further understand how HMG-CoA reductase inhibitors can beneficially affect subgroups of HF subjects such as those with preserved EF, low B-type natriuretic peptide levels, exacerbated inflammatory response and limited interstitial fibrosis. Nevertheless, as a definitive mechanism is lacking, there is uncertainty about the decisive mode of action and further mechanistic studies are needed to reveal how HMG-CoA reductase inhibitors act in HF substrate.

Pro- A-Type Natriuretic Peptide, Proadrenomedullin, and N-Terminal Pro-B-Type Natriuretic Peptide Used in a Multimarker Strategy in Primary Health Care in Risk Assessment of Patients with Symptoms of Heart Failure

Urban Alehagen, Ulf Dahlstr€Om,  Jens F. Rehfeld, And Jens P. Goetze
J Cardiac Fail 2013; 19(1):31-39. http://dx.doi.org/10.1016/j.cardfail.2012.11.002

Use of new biomarkers in the handling of heart failure patients has been advocated in the literature, but most often in hospital-based populations. Therefore, we wanted to evaluate whether plasma measurement of N-terminal pro-B-type natriuretic peptide (NT-proBNP), midregional pro-A-type  atriuretic peptide (MR-proANP), and midregional proadrenomedullin (MR-proADM), individually or combined, gives prognostic information regarding cardiovascular and all-cause mortality that could motivate use in elderly patients presenting with symptoms suggestive of heart failure in primary health care. Methods and Results: The study included 470 elderly patients (mean age 73 years) with symptoms of heart failure in primary health care. All participants underwent clinical examination, 2-dimenstional echocardiography, and plasma measurement of the 3 propeptides and were followed for 13 years. All mortality was registered during the follow-up period. The 4th quartiles of the biomarkers were applied as cutoff values. NT-proBNP exhibited the strongest prognostic information with 4-fold increased risk for cardiovascular mortality within 5 years. For all-cause mortality MR-proADM exhibited almost 2-fold and NTproBNP 3-fold increased risk within 5 years. In the 5e13-year perspective, NT-proBNP and MR-proANP showed significant and independent cardiovascular prognostic information. NT-proBNP and MR-proADM showed significant prognostic information regarding all-cause mortality during the same time. In those with ejection fraction (EF) !40%, MR-proADM exhibited almost 5-fold increased risk of cardiovascular mortality with 5 years, whereas in those with EF O50% NT-proBNP exhibited 3-fold increased risk if analyzed as the only biomarker in the model. If instead the biomarkers were all below the cutoff value, the patients had a highly reduced mortality risk, which also could influence the handling of patients. Conclusions: The 3 biomarkers could be integrated in a multimarker strategy for use in primary health care.

Novel Biomarkers in Heart Failure with Preserved Ejection Fraction

Kevin S. Shah, Alan S. Maisel
Heart Failure Clin 10 (2014) 471–479
http://dx.doi.org/10.1016/j.hfc.2014.04.005

KEY POINTS

• Heart failure with preserved ejection fraction (HFPEF) is a common subtype of congestive heart failure for which therapies to improve morbidity and mortality have been limited thus far.
• Numerous biomarkers have emerged over the past decade demonstrating prognostic significance in HFPEF, including natriuretic peptides, galectin-3, soluble ST2, and high-sensitivity troponins.
• These markers reflect the multiple mechanisms implicated in the pathogenesis of HFPEF, and future research will likely use these markers to not only help determine heart failure phenotypes but also target specific therapies.

Heart failure (HF) is a global epidemic, defined as an abnormality of cardiac function leading to the inability to deliver oxygen at a rate adequate to meet the requirements of tissues. It is truly a clinical syndrome of symptoms and signs resulting from this cardiac abnormality. Over the past decade, further characterization into 2 entities has occurred: HF with preserved ejection fraction (HFPEF) and HF with reduced ejection fraction (HFREF). HFPEF, previously termed diastolic HF, encompasses the syndrome of HF with a preserved ejection fraction. Cutoffs for this ejection fraction typically are from 45% to 50%. The prevalence of HF is upward of 1% to 2% of the adult population, with an increased prevalence found in elderly and female patients. Multiple studies have shown that the prevalence of HFPEF is actually comparable with the number of patients with HFREF. As expected, most deaths from HFPEF are cardiovascular, comprising 51% to 70% of mortality.

The pathophysiology of HFPEF is controversial and remains poorly understood. Originally, HFPEF was thought to be a primary manifestation of diastolic dysfunction of the left ventricle. However, patients with HFREF are known to also commonly have impaired ventricular relaxation. The primary mechanism of left ventricular (LV) dysfunction is based on structural remodeling and endothelial dysfunction, lending itself to LV stiffness, and increased left atrial pressure. This pressure change is what drives pulmonary venous congestion and subsequent symptomatology. The ventricular stiffness commonly seen in HFPEF is attributed to multiple mechanisms, including fibrosis, excessive collagen deposition, cardiomyocyte stiffness, and slow LV relaxation.

The natriuretic peptides (NPs) are the cornerstone biomarker in congestive HF (CHF). Many of the details of the role of NPs are covered in an article – Florea VG, Anand IS. Biomarkers. Heart Fail Clin 2012;8(2):207–24. The Breathing Not Properly trial originally helped establish the role of B-type natriuretic peptide (BNP) in the diagnosis of CHF. BNP and the N-terminal prohormone BNP (NT-proBNP) have been shown in numerous trials to be an excellent tool for ruling out CHF as a cause of acute dyspnea. Aside from a strong negative predictive value, NPs correlate with HF severity, prognostication, outpatient CHF management, and screening. When attempting to use NPs specifically to distinguish between HFPEF and HFREF, results have shown that NPs do not have a particular cutoff, but are typically elevated in HFPEF in comparison with patients without HF. These levels of NPs in HFPEF are typically lower than levels in patients with HFREF.

Although the role of novel renal biomarkers has not been fully explored specifically in HFPEF, they likely have an impactful role in the assessment and management of acute kidney injury (AKI) and the cardiorenal syndrome. Two biomarkers are briefly discussed here: neutrophil gelatinase-associated lipocalin (NGAL) and cystatin C. NGAL is a 25-kDa protein in the lipocalin family of proteins with a role in inflammation and immune modulation.

The future of biomarkers and their utility in HF is very promising, starting with the potential for using biomarkers as end points in trials. Biomarkers serve as surrogates for various pathophysiologic mechanisms, and there are potential benefits in using them as trial end points. Advantages include the ability to obtain quick and early data, as well as possibly better understand the nature of the disease. However, the counterargument against using biomarkers as trial end points includes whether treatment effects on a biomarker reliably predict effects on a clinically meaningful end point.
Reduced cGMP signaling activates NF-κB in hypertrophied hearts of mice lacking natriuretic peptide receptor-A

Elangovan Vellaichamy, Naveen K. Sommana, Kailash N. Pandey
Biochemical and Biophysical Research Communications 327 (2005) 106–111
http://dx.doi.org:/10.1016/j.bbrc.2004.11.153

Mice lacking natriuretic peptide receptor-A (NPRA) develop progressive cardiac hypertrophy and congestive heart failure. However, the mechanisms responsible for cardiac hypertrophic growth in the absence of NPRA signaling are not yet known. We sought to determine the activation of nuclear factor-κB (NF-κB) in Npr1 (coding for NPRA) gene-knockout (Npr1-/-) mice exhibiting cardiac hypertrophy and fibrosis. NF-κB binding activity was 4-fold greater in the nuclear extract of Npr1-/-mutant mice hearts as compared with wild-type (Npr1+/+) mice hearts. In parallel, inhibitory κB kinase-b activity and IκB-α protein phosphorylation were also increased 3- and 4-fold, respectively, in hypertrophied hearts of mutant mice. cGMP levels were significantly reduced 5-fold in plasma and 10-fold in ventricular tissues of mutant mice hearts  relative to wild-type controls. The present findings provide direct evidence that ablation of NPRA/cGMP signaling activates NF-κB binding activity associated with hypertrophic growth of mutant mice hearts.

Regulation of guanylyl cyclase/natriuretic peptide receptor-A gene expression

Renu Garg, Kailash N. Pandey
Peptides 26 (2005) 1009–1023
http://dx.doi.org:/10.1016/j.peptides.2004.09.022

Natriuretic peptide receptor-A (NPRA) is the biological receptor of the peptide hormones atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP). The level and activity of this receptor determines the biological effects of ANP and BNP in different tissues mainly directed towards the maintenance of salt and water homeostasis. The core transcriptional machinery of the TATA-less Npr1 gene, which encodes NPRA, consists of three SP1 binding sites and the inverted CCAAT box. This promoter region of Npr1 gene has been shown to contain several putative binding sites for the known transcription factors, but the functional significance of most of these regulatory sequences is yet to be elucidated. The present review discusses the current knowledge of the functional significance of the promoter region of Npr1 gene and its transcriptional regulation by a number of factors including different hormones, growth factors, changes in extracellular osmolarity, and certain physiological and patho-physiological conditions.

Atrial natriuretic peptide (ANP), a member of natriuretic peptide family is a polypeptide consisting of 28 amino acids and was discovered as a potent vasodilator and diuretic hormone produced in granules of the atrium. The natriuretic peptide family consists of the peptide hormones ANP, brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP), each of which is derived from a separate gene. ANP and BNP are cardiac derived peptides, which are secreted and up-regulated in myocardium in response to different patho-physiological stimuli, while CNP is an endothelium-derived mediator that plays an important paracrine role in the vasculature. All of these natriuretic peptides elicit a number of vascular, renal, and endocrine effects mainly directed towards the maintenance of blood pressure and extracellular fluid volume by binding to their specific cell surface receptors. ANP exerts its effects at a number of sites including the kidney, where it produces natriuretic and diuretic responses; the adrenal gland, where it inhibits aldosterone synthesis and secretion; vascular smooth muscle cells, where it produces vasorelaxation; the endothelial cells, where it may regulate vascular permeability; gonadal cells, where it affects synthesis of androgen and estradiol. Each of these target sites of ANP activity has been shown to possess specific high affinity receptors for ANP. To date, three different subtypes of natriuretic peptide receptors have been characterized, purified, and cloned, i.e. natriuretic peptide receptors A, B, and C also designated as NPRA, NPRB, and NPRC, respectively. ANP and BNP specifically bind to NPRA, which contains guanylyl cyclase catalytic activity and produces intracellular secondary messenger cGMP in response to hormone binding.

NPRA is considered the biological receptor of ANP and BNP because most of the physiological effects of these hormones are triggered by generation of cGMP or its cell permeable analogs. Recent studies with mice lacking the Npr1 gene, demonstrated that genetic disruption of NPRA increases the blood pressure and causes hypertension in these animals. On the other hand, the effect of ANP was found to be increased linearly in Npr1 gene-duplicated mice
in a manner consistent with gene copy number. All this clearly indicates that the level of NPRA expression determines the extent of the biological effects of ANP and BNP. But the intervention strategies aimed at controlling NPRA expression are limited by the paucity of studies in this area. The cDNA and gene encoding NPRA designated as Npr1 has been cloned and characterized in mouse, rat, bull frog, euryhaline eel, and medaka fish. The primary structure of this gene is essentially same in all the different species and contains 22 exons interrupted by 21 introns.  The Npr1 gene sequence has been found to be interspersed with a number of repetitive elements including (SINES), (MER2), and tandem repeat elements in all the different species.

Although the Npr1 gene transcriptional regulation is only poorly understood, the activity and expression of NPRA assessed primarily through ANP stimulated cGMP accumulation are found to be regulated by a number of factors including auto-regulation by natriuretic peptides themselves, other hormones such as endothelin, glucocorticoids, and angiotensin II (ANG II), growth factors, changes in extracellular ion composition, and certain physiological and patho-physiological conditions.

The core molecular machinery of the TATA-less Npr1 gene consisting of SP1 binding sites and the inverted CCAAT box has been authenticated to be indeed functional in rat promoter element. It has been shown that the molecular machinery that regulates the basal expression of Npr1 gene consists of three SP1 binding sites in conjunction with an inverted CCAAT box present in the proximal promoter region. Mutation in any of these SP1 binding sites which
are located within 350 bp upstream of transcription start site in rat Npr1 promoter inhibited SP1 and SP3 binding and decreased the promoter activity by 50–75%, while simultaneous mutation of all the three led to a >90% reduction in promoter activity. The proximal SP1 binding site was much more effective than the distal sites in inducing the expression implying that the proximity to the core transcriptional machinery contributes to the magnitude of the observed effect. The over-expression of either SP1 or SP3 resulted in the induction of the wild type Npr1 promoter, confirming that these transcription factors serve as positive regulators of the Npr1 gene expression.

A number of natriuretic peptides such as ANP, BNP, CNP, and urodilatin (i.e. ANP95–126) can down-regulate ligand dependent NPRA activity after as little as 2 h prior exposure to the ligand, which remains suppressed until 48 h of exposure in cultured cells. The early reduction of NPRA activity is independent of changes in Npr1 gene expression as the pretreatment of cultured cells with actinomycin D (an inhibitor of transcription) for 1 h failed to block the response to ANP implying that ligand acts, at least early on, through a post transcriptional mechanism in reducing NPRA activity. The sustained reduction of NPRA activity, on the other hand, has been shown in fact due to reduction in NPRA mRNA levels (∼50%) by treatment with 100nM ANP for 48 h. This reduction could also be affected by treatment of cultured cells with 8-Br-cGMP with similar kinetic response and was amplified by phosphodiesterase inhibitors, but was not shared by NPRC-selective ligand cANF, suggesting that the down regulation of Npr1 gene expression is mediated by elevations of intracellular cGMP involving either NPRA or NPRB. .. The cGMP regulatory region was pinpointed to position−1372 to−1354 bp from the transcription start site of Npr1 by gel shift assays and footprinting analysis, which indicated its interaction with transcriptional factor(s). Further cross-competition experiments with mutated oligonucleotides led to the definition of a consensus sequence (−1372 bp AaAtRKaNTTCaAcAKTY −1354 bp) for the novel cGMP-RE, which is conserved in the human (75% identity) and mouse (95% identity) Npr1 promoters. The combination of these transcriptional and post-transcriptional ligand-dependent regulatory mechanisms provides the cells with greater flexibility in both initiating and maintaining the suppression of NPRA activity.

The peptide hormone Ang II is an important component of renin-angiotensin system (RAS) and exerts its biological effects such as blood pressure regulation, vasoconstriction, and cell proliferation in many tissues including the kidney, adrenal glands, brain, and vasculature. The two vasoactive peptide hormones, Ang II (vasoconstrictive) and ANP (vasodilatory), interact and mutually antagonize the biological effects of each other at various levels. ANP has been shown to inhibit Ang II-induced contraction of isolated glomeruli and cultured mesangial cells, as well as Ang II-stimulated activation of protein kinase C and mitogen activated protein kinase in vascular smooth muscle cells in a cGMP-dependent manner. Inversely, Ang II has been shown to down-regulate guanylyl cyclase activity of the biological receptor of ANP, NPRA, by activating protein kinase C and/or by stimulating protein tyrosine phosphatase activity, thereby inhibiting the ANP stimulated cGMP accumulation. Ang II also reduces the ANP dependent cGMP levels by stimulating cGMP hydrolysis, apparently
via a calcium dependent cGMP phosphodiesterase.

Endothelin is a vasoconstrictor peptide that was originally isolated from porcine endothelial cells. It is produced as three isoforms (ET1-3) that bind to two receptor subtypes (ETA and ETB). ET is produced in the kidney and subject to regulation by a number of local and systemic factors including immune cytokines and extracellular tonicity. Since, endothelin is avidly expressed in the nephron segment, where NPRA is up-regulated by osmotic stimulus, it was investigated whether endothelin plays a role in the control of basal or osmotically regulated Npr1 gene expression in these cells. The endogenous endothelin and not the exogeneously administered endothelin inhibit the basal but not osmotically stimulated expression of Npr1. The type A (BQ610) and type B (IRL 1038) endothelin receptor antagonists increased the level of NPRA mRNA by two to three-fold, whereas co-administration of exogenous endothelin resulted in partial reversal of this stimulatory effect of receptor antagonists. The increase in extracellular tonicity reduces the endothelin mRNA accumulation (∼15% of control levels) in inner medullary collecting duct cells but this reduction is not found to be linked to the stimulation of NPRA activity/expression in response to osmotic stress.

Glucocorticoids influence the cardiovascular system and induce a rapid increase in blood pressure. Glucocorticoids are known to regulate
transcription in many systems, possibly by interacting with glucocorticoid responsive elements and associated chromatin proteins. These have been shown to affect the atrial endocrine system by regulating both the synthesis and secretion of ANP in vitro and in vivo. Thus, it seems plausible that glucocorticoid may also interact with the atrial endocrine system by modulating ANP receptor levels. The stimulation of vascular smooth muscle cells from rat mesenteric artery with dexa-methasone (a highly specific synthetic glucocorticoid agonist) caused an increase in NPRA mRNA levels in a time dependent manner which reached a plateau after 48 h of glucocorticoid administration. This mRNA increase was mimicked by cortisol and inhibited by glucocorticoid receptor antagonists RU38486. Also cGMP generated by NPRA in dexamethasone treated cells was higher than in control cells and this production was mimicked by cortisol and blocked by RU 38486. These results suggest that glucocorticoids exert a positive effect on NPRA transcription in rat mesenteric arteries.

Previous studies have shown that guanylyl cyclase activity of NPRA is either activated, or inhibited by an increase in extracellular tonicity. Though none of these studies were definitive in terms of elucidating the mechanisms involved, they suggested that the activation predominates with longer exposure (∼24 h), while the inhibition with short-term exposure (minutes) to the osmotic stimulus. More recently, the mechanism(s) underlying the activation of NPRA expression by osmotic stimulus has been investigated. The NaCl (75 mM) or sucrose (150 mM), but not osmotically inert solute, urea (150 mM) increased NPRA activity, gene expression, and promoter activity after as early as 4 h reaching a maximum at 24 h in inner medullary collecting duct cells. The osmotic stimulus also activated extracellular signal regulated kinase (ERK), c-Jun-NH2-terminal kinase (JNK), and p38 mitogen activated protein kinase- (p38 MAPK-β). The inhibition of p38 MAPK-βwith SB20580 completely  blocked the osmotic stimulation of receptor activity and expression, and caused a dose-dependent reduction in promoter activity, whereas inhibition of ERK with PD98059 had no effect.

The expression of NPRB, the biological receptor of CNP, has been shown to be regulated by a number of factors including natriuretic peptide ligands, intracellular cAMP levels, water deprivation, TGF-1, dexamethasone treatment, as well as renal sodium status, as its mRNA levels were upregulated in the renal cortex of sodium depleted animals. NPRB expression has also been found to be regulated by alternative splicing. Three isoforms of NPRB have been identified of which NPRB1 is the full length form and responds maximally to CNP, NPRB2 isoform contains a 25 amino acid deletion in protein kinase homology domain and NPRB3 contains a partial extracellular ligand binding domain and fails to bind the ligand. The relative expression levels of the three isoforms vary across different tissues. Since, the smaller splice variants of NPRB act as dominant negative isoforms by blocking formation of active NPRB1 homodimers, these isoforms might play important role in the tissue specific regulation of receptor, NPRB.

The NPRC expression has also been found to be down-regulated by its ligands and their secondary messenger, cGMP, hormones, growth factors, dietary salt supplementation, β-adrenergic blocker, and physiological as well as patho-physiological conditions. On the other hand, NPRC expression gets augmented by TGF-β1, 1,25-dihydroxy VitaminD3 and during conditions like chronic heart failure.

Hypertension is the leading cause of human deaths in today’s world. The natriuretic peptide system plays a well defined role in the regulation of blood pressure and fluid volume. The cellular and physiological effects of natriuretic peptides (ANP, BNP, and CNP) are mediated by their specific receptors NPRA, NPRB, and NPRC. The transcriptional regulation of these receptors has been studied since their identification, but still remains poorly understood. Better understanding and the elucidation of different molecular mechanisms responsible for the regulation of NPRA expression would provide us the framework to develop the therapeutic strategies to manipulate the expression levels of this receptor and to control the biological actions of ANP and BNP during different patho-physiological conditions.

Inhibition of Heat Shock Protein 90 (Hsp90) in Proliferating Endothelial Cells Uncouples Endothelial Nitric Oxide Synthase Activity

Jingsong Ou, Zhijun Ou, AW Ackerman, KT Oldham, & KA Pritchard, Jr.
Free Radical Biol Med 2003; 34(2):269–276
PII S0891-5849(02)01299-6

Dual increases in nitric oxide (•NO) and superoxide anion (O2^•-) production are one of the hallmarks of endothelial cell proliferation. Increased expression of endothelial nitric oxide synthase (eNOS) has been shown to play an important role in maintaining high levels of •NO generation to offset the increase in O2^•- that occurs during proliferation. Although recent reports indicate that heat shock protein 90 (hsp90) associates with eNOS to increase •NO generation, the role of hsp90 association with eNOS during endothelial cell proliferation remains unknown. In this report, we examine the effects of endothelial cell proliferation on eNOS expression, hsp90 association with eNOS, and the mechanisms governing eNOS generation of •NO and O2^•-. Western analysis revealed that endothelial cells not only increased eNOS expression during proliferation but also hsp90 interactions with the enzyme. Pretreatment of cultures with radicicol (RAD, 20 µM), a specific inhibitor that does not redox cycle, decreased A23187-stimulated •NO production and increased L^ω-nitroargininemethylester (L-NAME)-inhibitable O2^•-generation. In contrast, A23187 stimulation of controls in the presence of L-NAME increased O2^•- generation, confirming that during proliferation eNOS generates •NO. Our findings demonstrate that hsp90 plays an important role in maintaining •NO generation during proliferation. Inhibition of hsp90 in vascular endothelium provides a convenient mechanism for uncoupling eNOS activity to inhibit •NO production. This study provides new understanding of the mechanisms by which ansamycin antibiotics inhibit endothelial cell proliferation. Such information may be useful in the development and design of new antineoplastic agents in the future.

Natriuretic Peptides, Ejection Fraction, and Prognosis – Parsing the Phenotypes of Heart Failure

James L. Januzzi, JR
J Amer Coll Cardiol 2013; 61(14): 1507-9
http://dx.doi.org/10.1016/j.jacc.2013.01.039

Since the first pivotal studies introduced the natriuretic peptides as biomarkers for the diagnosis of heart failure (HF), use of both B-type natriuretic peptide (BNP) and its N-terminal equivalent (NT-proBNP) has grown not only for this indication, but also for establishing HF prognosis as well. Indeed, a vast array of studies has established the natriuretic peptides as the biomarker gold standard to prognosticate risk for a wide array of relevant complications in HF (ranging from ventricular arrhythmias to pump failure). In these studies, the prognostic information provided by BNP and NT-proBNP in HF was independent of a number of relevant covariates, including left ventricular ejection fraction (LVEF).

It has been known for quite a while that patients with heart failure and preserved ejection fraction (HFpEF) typically have lower natriuretic peptide values than do those with heart failure and reduced ejection fraction (HFrEF). A conundrum is thus present: whereas both BNP and NTproBNP tend to be lower in HFpEF, when these peptides are elevated in this setting, they remain prognostic; this intriguing circumstance has been relatively poorly studied. It is in this setting that van Veldhuisen et al. examined the impact of LVEF on the prognostic merits of BNP in the COACH (Coordinating Study Evaluating Outcomes of Advising and Counseling in Heart Failure) study in the present issue of the Journal. The investigators found—as expected—that BNP levels were lower in HFpEF, but for a given BNP concentration, prognosis of those with HFpEF in COACH was just as poor as those with HFrEF at matched BNP values. Stated differently, a high BNP in a patient with HFpEF imparted similar prognostic information as it would in someone with HFrEF. Actually, whereas LVEF was not obviously prognostically impactful, when considered across the range of ventricular function, an elevated BNP concentration in the most normal range of LVEF seemed to be associated with a higher risk than at the lower ranges of pump function. Although it is previously established that BNP or NT-proBNP are prognostic independently of LVEF, the well-executed analysis by van Veldhuisen et al. (van Veldhuisen DJ, Linssen GCM, Jaarsma T, et al. B-type natriuretic peptide and prognosis in heart failure patients with preserved and reduced ejection fraction. J Am Coll Cardiol 2013;61:1498–506.) allows for a more in-depth examination of this phenomenon and raises some important questions.

Phenotypic Definition of the Patient With Heart Failure

Natriuretic Peptides in Heart Failure with Preserved Ejection Fraction

Mark Richards, James L. Januzzi Jr, Richard W. Troughton
Heart Failure Clin 10 (2014) 453–470
http://dx.doi.org/10.1016/j.hfc.2014.04.006

KEY POINTS

• Threshold values of B-type natriuretic peptide (BNP) and N-terminal prohormone B-type natriuretic peptide (NT-proBNP) validated for diagnosis of undifferentiated acutely decompensated heart failure (ADHF) remain useful in patients with heart failure with preserved ejection fraction (HFPEF), with minor loss of diagnostic performance.
• BNP and NT-proBNP measured on admission with ADHF are powerfully predictive of in-hospital mortality in both HFPEF and heart failure with reduced EF (HFREF), with similar or greater risk in HFPEF as in HFREF associated with any given level of either peptide.
• In stable treated heart failure, plasma natriuretic peptide concentrations often fall below cut-point values used for the diagnosis of ADHF in the emergency department; in HFPEF, levels average approximately half those in HFREF.
• BNP and NT-proBNP are powerful independent prognostic markers in both chronic HFREF and chronic HFPEF, and the risk of important clinical adverse outcomes for a given peptide level is similar regardless of left ventricular ejection fraction.
• Serial measurement of BNP or NT-proBNP to monitor status and guide treatment in chronic heart failure may be more applicable in HFREF than in HFPEF.

 

The bioactivity of atrial NP (ANP) and B-type NP (BNP) encompasses short-term and longterm hemodynamic, renal, neurohormonal, and trophic effects. The relationship between cardiac hemodynamic load, plasma concentrations of ANP and BNP, and the cardioprotective profile of NP bioactivity have led to investigation of both biomarker and therapeutic potential of

NPs in HF.

PlasmaBNPandNT-proBNP thresholds (100pg/mL and 300 pg/mL, respectively) used in the diagnosis of undifferentiated ADHF retain good diagnosticperformance for acute HFPEF

 

Plasma NPs are related to multiple echo indicators of cardiac structure and function in both HFREF and HFPEF.

Box 1Causes of increased plasma cardiac natriuretic peptides Cardiac Heart failure, acute and chronic Acute coronary syndromes Atrial fibrillation Valvular heart disease Cardiomyopathies Myocarditis Cardioversion Left ventricular hypertrophy Noncardiac Age Female sex Renal impairment Pulmonary embolism Pneumonia (severe) Obstructive sleep apnea Critical illness Bacterial sepsis Severe burns Cancer chemotherapy Toxic and metabolic insults

 

BNP and NT-proBNP fall below ADHF thresholds in stable HFREF in approximately 50% and 20% of cases, respectively. Levels in stable HFPEF are even lower, approximately half those in HFREF.

Whereas BNPs have 90% sensitivity for asymptomatic LVEF of less than 40% in the community (a precursor state for HFREF), they offer no clear guide to the presence of early community based HFPEF.

Guidelines recommend BNP and NT-proBNP as adjuncts to the diagnosis of acute and chronic HF and for risk stratification. Refinements for application to HFPEF are needed.

The prognostic power of NPs is similar in HFREF and HFPEF. Defined levels of BNP and NT-proBNP correlate with similar short-term and long-term risks of important clinical adverse outcomes in both HFREF and HFPEF.

Diagnostic algorithm for suspected heart failure presenting either acutely or nonacutely. a In the acute setting, mid-regional pro–atrial natriuretic peptide may also be used (cutoff point 120 pmol/L; ie, <120 pmol/L 5 heart failure unlikely). b Other causes of elevated natriuretic peptide levels in the acute setting are an acute coronary syndrome, atrial or ventricular arrhythmias, pulmonary embolism, and severe chronic obstructive pulmonary disease with elevated right heart pressures, renal failure, and sepsis. Other causes of an elevated natriuretic level in the nonacute setting are old age (>75 years), atrial arrhythmias, left ventricular hypertrophy, chronic obstructive pulmonary disease, and chronic kidney disease. c Exclusion cutoff points for natriuretic peptides are chosen to minimize the false-negative rate while reducing unnecessary referrals for echocardiography. d Treatment may reduce natriuretic peptide concentration, and natriuretic peptide concentrations may not be markedly elevated in patients with heart failure with preserved ejection fraction. BNP, B-type natriuretic peptide; ECG, electrocardiogram; NT-proBNP, N-terminal prohormone of B-type natriuretic peptide. (From McMurray JJ, Adamopoulos S, Anker SD, et al. The task force for the diagnosis and treatment of acute and chronic heart failure 2012 of the European Society of Cardiology. ESC guidelines for the diagnosis and treatment of acute and chronic heart failure 2012. Eur Heart J 2012;33:1787–847; with permission.)

Natriuretic Peptide Receptor-A Negatively Regulates Mitogen-Activated Protein Kinase and Proliferation of Mesangial Cells: Role of cGMP-Dependent Protein Kinase

Kailash N. Pandey, Houng T. Nguyen, Ming Li, and John W. Boyle
Biochem Biophys Res Commun 271, 374–379 (2000)
http://dx.doi.org:/10.1006/bbrc.2000.2627

peptide (ANP) and its guanylyl cyclase/natriuretic peptide receptor-A (NPRA) on mitogen-activated protein kinase/extracellular signal-regulated kinase 2 (MAPK/ERK2) activity in rat mesangial cells overexpressing NPRA. Agonist hormones such as platelet-derived growth factor (PDGF), fibroblast growth factor (FGF), angiotensin II (ANG II), and endothelin-1 (ET-1) stimulated 2.5- to 3.5-fold immunoreactive MAPK/ERK2 activity in these cells. ANP inhibited agonist-stimulated activity of MAPK/ERK2 by 65–75% in cells overexpressing NPRA, whereas in vector transfected cells, its inhibitory effect was only 18–20%. NPRA antagonist A71915 and KT5823, a specific inhibitor of cGMP-dependent protein kinase (PKG) completely reversed the inhibitory effect of ANP on MAPK/ERK2 activity. ANP also inhibited the PDGF stimulated [³H]thymidine uptake by almost 70% in cells overexpressing NPRA, as compared with only 20–25% inhibition in vector-transfected cells. These
results demonstrate that ANP/NPRA system negatively regulates MAPK/ERK2 activity and proliferation of mesangial cells in a PKG-dependent manner.

 

Regulation of lipoprotein lipase by Angptl4

Wieneke Dijk and Sander Kersten
Trends in Endocrin and Metab, Mar2014; 25(3):146-155
http://dx.doi.org/10.1016/j.tem.2013.12.005

Triglyceride (TG)-rich chylomicrons and very low density lipoproteins (VLDL) distribute fatty acids (FA) to various tissues by interacting with the enzyme lipoprotein lipase (LPL). The protein angiopoietin-like 4 (Angptl4) is under sensitive transcriptional control by FA and the FA-activated peroxisome proliferator activated receptors (PPARs), and its tissue expression largely overlaps with that of LPL. Growing evidence indicates that Angptl4 mediates the physiological fluctuations in LPL activity, including the decrease in
adipose tissue LPL activity during fasting. This review focuses on the major ambiguities concerning the mechanism of LPL inhibition by Angptl4, as well as on the physiological role of Angptl4 in lipid metabolism, highlighting its function in a variety of tissues, and uses this information to make suggestions for further research.

Box 1. LPL and TG metabolism

LPL belongs to a family of lipases that also includes hepatic lipase, pancreatic lipase, and endothelial lipase. Because LPL is essential in the lipolytic processing of chylomicrons and VLDL, LPL is primarily expressed in tissues that either require large amounts of FA as fuel or are responsible for TG storage, which include heart, skeletal muscle, and adipose tissue. Upon production by the underlying parenchymal cells, LPL is released into the subendothelial space and is transported to the luminal side of the capillary endothelium by the GPI-anchored protein GPIHBP1, which after transport continues to anchor LPL to the capillary endothelium. The essential role for LPL in the clearance of plasma TG is well-demonstrated by the severe hypertriglyceridemia of patients carrying homozygous mutations in the LPL gene. Generalized deletion of LPL in mice results in severe hypertriglycer-idemia, resulting in the premature death of pups within 24 h after birth. Analogous to the deletion of LPL, the mislocalization of LPL to the subendothelial spaces due the absence or misfolding of GPIHBP1 also results in severe chylomicronemia and hypertriglyceridemia. The LPL enzyme is catalytically active as a non-covalent head-to-tail dimer with a catalytic N-terminal domain and a non-catalytic C terminal domain. Folding of LPL into its dimer conformation occurs in the endoplasmic reticulum, chaperoned by lipase maturation factor 1, calreticulin, and calnexin. In its active 3D conformation, the catalytic site of LPL is postulated to be covered by a lid, which can be opened by the binding of chylomicrons and VLDL to the C terminus. The active LPL dimers rapidly exchange subunits, indicating that a dynamic equilibrium exists between LPL dimers and dimerization-competent monomers. Dimerization-competent monomers have, however, not yet been isolated, and it is unclear whether this monomer is catalytically active. The enzymatic activity of LPL is lost when the LPL dimer is converted into inactive, folded monomers. This conversion to inactive monomers is mainly regulated via post-translational mechanisms and is dependent on nutritional state. Enzymatic activity of inactive monomers can be regained in vitro by the addition of calcium, indicating that inactivation of LPL is a reversible process.

One of the key questions is whether (patho)physiological variations in LPL activity are mediated via regulation of Angptl4 cleavage and/or oligomerization, and which factors are involved in modulating Angptl4 in vivo. Recent biochemical evidence suggests that FA may be able to promote dissociation of oligomers, which, by destabilizing the protein, would impair its ability to inhibit LPL. Destabilization of Angptl4 by FA is, however, seemingly at odds with the marked stimulatory effect of FA on Angptl4 production observed in vitro and in vivo.

The currently accepted molecular model for the inhibition of LPL by Angptl4 is that Angptl4 stimulates the conversion of catalytically active LPL dimers into inactive monomers – following in vitro studies showing that coincubation of LPL and Angptl4 increases the abundance of LPL monomers. Subsequent studies revealed that the proportion of LPL dimers is reduced in post-heparin plasma of mice that overexpress Angptl4 in favor of LPL monomers, providing in vivo support for the dimer-to monomer conversion. The elucidation of the purported biochemical mechanism has strengthened the status of Angptl4 as a LPL inhibitor, but several questions related to the in vivo mechanism remain unanswered. Whereas the original in vitro experiments favored the hypothesis that Angptl4 enzymatically and irreversibly catalyzes the LPL dimer-to-monomer conversion, an in vivo study of Angptl4 transgenic mice suggested that Angptl4 is physically bound to LPL monomers, thereby driving the LPL dimer–monomer equilibrium towards inactive monomers. The latter study also revealed that the relative decrease in post-heparin plasma LPL activity upon Angptl4 overexpression is much more pronounced than the relative decrease in heparin-releasable LPL dimers, pointing to an additional or alternative mechanism. In support, a recently published study suggests that Angptl4, instead of acting as a catalyst, functions as a conventional, non-competitive inhibitor that binds to LPL to prevent the hydrolysis of substrate LPL and Angptl4 are regulated by changes in nutritional state in a tissue-specific manner, reflecting the different functions of these tissues and the corresponding variations in physiological requirements for lipids. Below, we discuss current knowledge on the regulation of Angptl4 and LPL in response to various physiological stimuli and address the importance of Angptl4 in lipid uptake. An overview of the role of Angptl4 in physiological regulation of lipid metabolism is presented in Figure 2.

Figure 1. Hypothetical model for mechanisms of lipoprotein lipase (LPL) inhibition by Angptl4. Angiopoietin-like 4 (Angptl4) and LPL are expressed in the parenchymal cells of muscle, heart, and adipose tissue. Following secretion of LPL and Angptl4 into the subendothelial space, transport of LPL to the capillary lumen is mediated by two mechanisms. The principal transport mechanism (1) relies on GPIHBP1 [glycosylphosphatidylinositol (GPI)-anchored high density lipoprotein-binding protein] picking up LPL from the subendothelial space and transporting it to the capillary lumen. This action by GPIHBP1 is opposed by Angptl4, which is bound to extracellular matrix (ECM) proteins and which retains and inhibits LPL. In the presence of GPIHBP1, high expression levels of Angptl4 are needed to overcome the competition with GPIHBP1. Angptl4 secreted into the capillary lumen, primarily as N-terminal truncation fragment generated by cleavage by proprotein convertases (PCs), inhibits LPL activity on the endothelium by promoting the irreversible conversion of LPL dimers into inactive monomers and/or via a reversible mechanism that requires binding of Angptl4 to LPL. The second transport mechanism involves a so far unidentified carrier and can be disrupted by Angptl4. In the absence of GPIHBP1, Angptl4 fully retains LPL in the subendothelial space (a). The additional loss of Angptl4 liberates LPL and allows it to be transported to the endothelial surface via the unidentified carrier (b). This model suggests that Angptl4 and LPL start interacting before arrival in the capillary lumen, either in the parenchymal cells or in the subendothelial space. Abbreviation: HSPG, heparan sulfate proteoglycan.

Figure 2. Regulation and role of angiopoietin-like 4 (Angptl4) in lipid metabolism. Angptl4 is expressed in parenchymal cells of white adipose tissue (WAT), liver, intestine, heart and muscle, as well as in macrophages, where it is subject to cell- and tissue-specific regulation. Angptl4 is a sensitive target of peroxisome proliferator-activated receptor (PPAR) transcription factors in several tissues. In WAT the expression of Angptl4 is induced during fasting and by the transcription factors PPARg, glucocorticoid receptor (GR), and hypoxia inducible factor 1a (HIF1a). In WAT Angptl4 stimulates lipolysis of stored triglycerides (TG) and inhibits lipoprotein lipase (LPL) activity. Expression of Angptl4 in liver is stimulated by PPARa, PPARd, and GR. Because the liver does not express LPL, Angptl4 is mainly released into the blood, affecting LPL activity in peripheral tissues. Angptl4 may also impact upon hepatic lipase activity in liver. Expression of Angptl4 in heart and skeletal muscle is potently induced by fatty acids (FA) via PPARd activation. Angptl4 inhibits LPL activities in cardiac and likely skeletal muscle. FA also stimulate Angptl4 expression in macrophages via PPARd, leading to local inhibition of LPL activity. We hypothesize that macrophage LPL enables uptake of remnant particles containing lipid antigens, which are subsequently presented to natural killer T cells. In the intestine, FA stimulate Angptl4 expression via one of the PPARs. Angptl4 produced by enterocytes may be released towards the lumen and inhibit pancreatic lipase activity. Angptl4 produced by enteroendocrine cells is released towards the blood and may inhibit LPL in distant tissues.

Box 2. Outstanding questions

1. What is the importance of Angptl4 cleavage and oligomerization to Angptl4 function in vivo?
2. What is the precise biochemical mechanism behind the inhibition of LPL activity by Angptl4?
3. At which cellular location(s) does the inhibition of LPL by Angptl4 occur and, if at multiple locations, what is the relative contribution of both tissue-produced Angptl4 compared to circulating Angptl4 with respect to inhibition of tissue LPL activity.
4. What is the interplay between GPIHBP1 and Angptl4 in the regulation of LPL activity?
5. What is the protein structure of Angptl4 and LPL?
6. Does Angptl4 also regulate LPL activity in brown adipose tissue and skeletal muscle and, if so, how is the expression of Angptl4 regulated in these tissues?
7. What is the potential of Angptl4 as a biomarker in the context of disorders of lipid metabolism?

In the past decade, angiopoietin-like proteins have been demonstrated to regulate plasma TG levels powerfully in mice and humans. The elucidation of these proteins as inhibitors of LPL activity has led to a paradigm shift in how clearance of circulating TG and thereby tissue uptake of FA are regulated. Most of our understanding of angiopoietin-like proteins has resulted from detailed study of Angptl4.

A major portion of the physiological variation in LPL activity in various tissues can be attributed to regulation of Angptl4 production. We predict that Angptl4 will turn out to be equally important for governing LPL activity in muscle during exercise, in brown adipose tissue during cold, and in several tissues during fasting.

Besides the increasing recognition of the pivotal role of Angptl4 in lipid metabolism as an inhibitor of LPL, major insight has been gained into the molecular mechanism of action of Angptl4. Key questions remain, however, especially related to the interaction between LPL, GPIHBP1, and Angptl4 on the endothelium and in the subendothelial space. Several points of interest have been highlighted throughout the text; these include the elucidation of the molecular structure for LPL and Angptl4 by X-ray crystallography and the clarification of in vivo Angptl4 cleavage and oligomerization.

Native Low-Density Lipoprotein Induces Endothelial Nitric Oxide Synthase Dysfunction: Role of Heat Shock Protein 90 And Caveolin-1

Kirkwood A. Pritchard, Jr., Allan W. Ackerman, Jingsong Ou, et al.
Free Radical Biol & Med 2002; 33(1):52–62 PII S0891-5849(02)00851-1

Although native LDL (n-LDL) is well recognized for inducing endothelial cell (EC) dysfunction, the mechanisms remain unclear. One hypothesis is n-LDL increases caveolin-1 (Cav-1), which decreases nitric oxide (•NO) production by binding endothelial nitric oxide synthase (eNOS) in an inactive state. Another is n-LDL increases superoxide anion (O2^•-), which inactivates •NO. To test these hypotheses, EC were incubated with n-LDL and then analyzed for •NO, O2•-, phospho-eNOS (S1179), eNOS, Cav-1, calmodulin (CaM), and heat shock protein 90 (hsp90). n-LDL increased NOx by more than 4-fold while having little effect on A23187-stimulated nitrite production. In contrast, n-LDL decreased cGMP under basal and A23187-stimulated conditions and increased O2^•-by a mechanism that could be inhibited by L-nitroargininemethylester (L-NAME) and BAPTA/AM. n-LDL increased phospho-eNOS by 149%, eNOS by [1]34%, and Cav-1 by 28%, and decreased the association of hsp90 with eNOS by 49%. n-LDL did not appear to alter eNOS distribution between membrane fractions (-85%) and cytosol (-15%). Only 3–6% of eNOS in membrane fractions was associated with Cav-1. These data support the hypothesis that n-LDL increases O2^•-, which scavenges •NO, and suggest that n-LDL uncouples eNOS activity by decreasing the association of hsp90 as an initial step in signaling eNOS to generate O2^•-.

In conclusion, n-LDL decreases the association of hsp90 with eNOS, increases phospho-eNOS levels, and increases eNOS-dependent O2^•-generation. These findings suggest that activation of eNOS without adequate levels of hsp90 may signal eNOS to switch from •NO to O2^•-generation. Such changes in eNOS radical product generation may play an important role in impairing endothelial and vascular function.

New insights into IGF-1 signaling in the heart

Rodrigo Troncoso, C Ibarra, JM Vicencio, E Jaimovich, and S Lavandero
Trends in Endocrin and Metab, Mar 2014; 25(3):128-131
http://dx.doi.org/10.1016/j.tem.2013.12.002

Insulin-like growth factor 1 (IGF-1) signaling regulates contractility, metabolism, hypertrophy, autophagy, senescence, and apoptosis in the heart. IGF-1 deficiency is associated with an increased risk of cardiovascular disease, whereas cardiac activation of IGF-1 receptor (IGF-1R) protects from the detrimental effects of a high-fat diet and myocardial infarction. IGF-1R activates multiple pathways through its intrinsic tyrosine kinase activity and through coupling to heterotrimeric G protein. These pathways involve classic second messengers, phosphorylation cascades, lipid signaling, Ca2+ transients, and gene expression. In addition, IGF-1R triggers signaling in different subcellular locations including the plasma membrane, perinuclear T tubules, and also in internalized vesicles. In this review, we provide a fresh and updated view of the complex IGF-1 scenario in the heart, including a critical focus on therapeutic strategies.

The hormone insulin-like growth factor 1 (IGF-1) is a small peptide of 7.6 kDa, which is composed of 70 amino acids and shares 50% homology with insulin. IGF-1 plays key roles in regulating proliferation, differentiation, metabolism, and cell survival. It is mainly synthesized and secreted by the liver in response to hypothalamic growth hormone (GH); its plasma concentration is finely regulated (Box 1). However, other tissues also produce IGF-1, which acts locally as an autocrine and paracrine hormone. IGF-1 exhibits pleiotropic effects in many organs and is also involved in the development of several pathologies.

Box 1. IGF-1 synthesis and biodisponibilityInsulin-like growth factor 1 (IGF-1) is a 70 amino acid peptide hormone with endocrine, paracrine, and autocrine effects. It shares >60% structure homology with IGF-2 and 50% with pro-insulin. IGF- 1 is mainly synthesized in the liver in response to hypothalamic growth hormone (GH). In the peripheral circulation it exerts negative feedback on the somatotrophic axis suppressing pituitary GH release. IGF-1 can also be generated in almost all tissues, but liver synthesis accounts for nearly 75% of circulating IGF-1 levels. As a hormone with a wide range of physiological roles, IGF-1 circulating levels must be strictly controlled. Around 98% of circulating IGF-1 is bound to insulin-like growth factor binding protein (IGFBP). Six forms of high affinity IGFBP have been described, with IGFBP3 binding approximately 90% of circulating IGF-1. Also, IGFBP1–6 and their fragments have significant intrinsic biological activity independent of IGF-1 interaction.

Canonical and noncanonical IGF-1 signaling pathways Activation of IGF-1R requires the sequential phosphorylation of three conserved tyrosine residues within the activation loop of the catalytic domain. From these phosphorylated motifs, tyrosine 950 contained in an NPXY motif provides a docking site for the recruitment of adaptor proteins, such as insulin receptor substrate-1 (IRS-1) and Shc, as an obligatory step to initiate signaling cascades. Two canonical pathways are activated by IGF-1R in cardiomyocytes – the phosphatidylinositol-3 kinase (PI3K)/Akt pathway and the extracellular signal-regulated kinase (ERK) pathway. Both pathways have been extensively studied, and their involvement in the pro-hypertrophic and pro-survival actions in cardiomyocytes is well established. Interestingly, a noncanonical signaling mechanism for IGF-1R in cardiomyocytes has been described in several recent studies. These studies show that some of the effects of IGF-1 are inhibited by the heterotrimeric Gi protein blocker Pertussis toxin (PTX) in several cell lines, suggesting that IGF-1R is a dual-activity receptor that triggers tyrosine-kinase-dependent responses as well as Gi-protein-dependent pathways. This duality has been reported in cultured neonatal cardiomyocytes; IGF-1R can activate ERK and Akt but also phospholipase C (PLC), which increases inositol 1,4,5 triphosphate (InsP3; IP3) leading to nuclear Ca2+ signals.

The cardiac effects of IGF-1 are mediated by activation of the plasma membrane IGF-1R, which belongs to the receptor tyrosine kinase (RTK) family. IGF-1R comprises a α2β2 heterotetrameric complex of approximately 400 kDa. Structurally, IGF-1R has two extracellular a-subunits that contain the ligand-binding sites. Each α-subunit couples to one of two membrane-spanning β-subunits, which contain an intracellular domain with intrinsic tyrosine kinase activity. Both subunits of IGF-1R are the product of one single gene, which is synthesized as a 180 kDa precursor. The immature IGF-1R full peptide is further glycosylated, dimerized, and proteolytically processed for assembly of the mature receptor isoforms a and b. In neonatal and adult rat cardiomyocytes, the IGF-1R precursor peptide and the processed α and β receptor subunits have been detected. Binding of IGF-1 to its receptor initiates a complex signaling cascade in cardiomyocytes.

Figure 1. not shown. Canonical and noncanonical signaling pathways activated by insulin-like growth factor 1 (IGF-1) in cardiomyocytes. Binding of IGF-1 to plasma membrane IGF-1 receptor (IGF-1R) leads to receptor autophosphorylation in the intracellular β-subunits. Docking of Grβ2 to the phosphorylated IGF-1Rβ subunits leads to extracellular signal-regulated kinase (ERK) phosphorylation through the Ras/Raf/Mitogen-activated protein kinase (MEK) axis. Phosphorylated ERK can translocate to the nucleus to control gene expression. Phosphorylated β-subunits also provide docking sites for insulin receptor substrate-1 (IRS-1), which mediates phosphatidylinositol-3 kinase (PI3K) activation and Akt phosphorylation. Downstream targets of activated Akt are mechanistic target of rapamycin (mTOR), which suppresses autophagy and promotes protein synthesis by activating S6K and eukaryotic translation initiation factor 4E binding protein 1 (4EBP1). Akt also phosphorylates and inactivates Bad, thus inhibiting apoptosis. IGF-1R activation also promotes its interaction with a Pertussis-toxin-sensitive heterotrimeric Gi protein, which mediates the activation of phospholipase C (PLC) and hydrolysis of plasma membrane phosphatidylinositol 4,5 biphosphate (PIP2) to form inositol 1,4,5 triphosphate (InsP3; IP3) which activates InsP3 receptors located at the endoplasmin reticulum (ER)/nuclear envelope Ca2+ store, producing nucleoplasmic and cytoplasmic Ca2+ increases. The former is involved in the regulation of specific target genes and the latter promotes mitochondrial Ca2+ uptake, which increases mitochondrial respiration and metabolism, further preventing apoptosis and regulating autophagy. Canonical signaling pathways include the ERK and Akt axes, and are shown in red, whereas the noncanonical G protein pathway is shown in blue. Both pathways interact as Ca2+ contributes to ERK activation and additionally both Akt and ERK can compensate each other’s activation. Abbreviations: MEK, Mitogen-activated protein kinase; mTOR, mechanistic target of rapamycin; 4EBP1, eukaryotic translation initiation factor 4E binding protein 1; PIP2, phosphatidylinositol 4,5 biphosphate.

Figure 2. not shown. Classical versus proposed models of nuclear Ca2+ signaling in cardiomyocytes. The insulin-like growth factor 1 receptor (IGF-1R) can specifically regulate nuclear Ca2+ signaling independently of the role of Ca2+ on excitation–contraction coupling. On the classic model, inositol 1,4,5 triphosphate (InsP3; IP3) produced after IGF-1R activation travels from the peripheral plasma membrane to the nucleus, where it activates InsP3 receptors. In this model InsP3 bypasses its receptors present on the sarcoplasmic reticulum, which would lead to cytosolic Ca2+ signals. The novel model that we propose is based on recent findings, where the IGF-1R signaling complex is present in T-tubule invaginations toward the nucleus. In these compartments, IGF-1R activation leads to locally restricted InsP3 production that allows nuclear Ca2+ signals to regulate gene expression of genes associated with the development of cardiomyocyte hypertrophy. Abbreviations: RyR, ryanodine receptor; ECC, excitation–contraction coupling; PLC, phospholipase C; DHPR, dihydropyridine receptor.

The beneficial roles of IGF-1 in the cardiovascular system largely explain the interest in the development of new IGF-1-based treatments for cardiovascular disease. So far the FDA has approved two drugs for the treatment of IGF-1 deficiency: mecasermin (Increlex1), a human recombinant IGF-1 analog; and mecasermin rinfabate (IPLEX1), a binary protein complex of human recombinant IGF-1 and human recombinant IGBP-3. The safety of a chronic systemic IGF-1 therapy is open to question because it could promote severe adverse effects, such as an increased risk of cancer. To avoid these problems, several researchers have selectively overexpressed IGF-1 and IGF-1R in the heart.

Box 2. Outstanding questionsInsulin-like growth factor 1 (IGF-1) is an old friend of the heart. Despite the well-known protective effects of IGF-1 on cardiac function and the antiapoptotic effects of this peptide, novel evidence opens new questions to this longstanding relationship. ·       How do the multiple signaling pathways triggered by IGF-1 receptor (IGF-1R) interact with each other? ·       What lies further than extracellular signal-regulated kinase (ERK)/Akt/Ca2+ activation toward heart function? ·       Do these signaling pathways regulate cardiac fibroblast or endothelial cell function? ·       Which are the specific downstream signaling pathways of the different pools of IGF-1R and their role in regulating cardiomyocyte survival, hypertrophy, metabolism, proliferation? ·       What drives IGF-1R to such specific subcellular compartments? ·       What is the relevance of the hybrid IGF-1R/insulin receptors on cardiovascular disease? ·       Does a crosstalk exist between insulin receptor and IGF-1R in the heart under physiological and pathological conditions? ·       Is one pathway more beneficial than the other? ·       Will stem cell therapy of cardiac progenitors be able to provide concrete treatment opportunities? ·       Is IGF-1 a key regulator of this outcome?

Abundant evidence supports the key physiological roles of IGF-1 in the heart. In cardiomyocytes, IGF-1 activates multiple downstream signaling pathways for controlling cell death, metabolism, autophagy, differentiation, transcription, and protein synthesis (Figure 1). Of great interest are the findings that the entire IGF-1R complex is strategically located in perinuclear sarcolemmal invaginations that locally control nuclear Ca2+ signaling and transcriptional upregulation (Figure 2). This novel evidence changesmthe classical paradigm of IGF-1 signaling and adds a new level of complexity that may be relevant for other signaling receptors in the heart: interorganelle communication between plasma membrane invaginations and the nucleus.
The strategic localization of IGF-1R in these structures and the association with heterotrimeric G proteins may explain the differences in the phenotypic response induced by IGF-1 and others agonists, like endothelin-1 and angiotensin II, that also signal through intracellular Ca2+. By activating a noncanonical, selective mechanism of nuclear Ca2+ release, IGF-1 can regulate the expression of a specific set of cardiac genes via the generation of a particular signal-encoding pattern, leading to adaptive cardiac hypertrophy, antiapoptotic effects, and metabolic adaptation.

Pulmonary Hypertension in Heart Failure with Preserved Ejection Fraction – any Pathophysiological Role of Mitral Regurgitation

Marco Guazzi
http://dx.doi.org:/10.1016/j.jacc.2009.04.088

read with interest the study by Lam et al. (1) as an important contribution to the pathophysiological and clinical impact of pulmonary hypertension (PH) in hypertensive patients with heart failure and preserved left ventricular ejection fraction (HFpEF). Recent guidelines on arterial PH recognize HFpEF as a growing cause of left-sided PH, but a definitive appreciation of its true prevalence and prognostic relevance is lacking. The present study provides some new important information on this subject.

It is noteworthy that HFpEF was associated, in a high rate of cases (83%), with a typical hemodynamic pattern of precapillary PH, and a strong correlation was found between pulmonary artery systolic pressure and pulmonary capillary wedge pressure. Most important, pulmonary artery systolic pressure, rather than other echocardiography-derived measures of diastolic dysfunction, was the only significant multivariate predictor of mortality, a finding that was confirmed even when combined comorbid diseases potentially contributing to PH development, such as chronic obstructive pulmonary disease, were taken into account.

In patients with systolic heart failure, a major determinant of PH development is mitral regurgitation. Whether mitral regurgitation could be a putative factor in the pathogenesis of PH in HFpEF patients remains an open and intriguing question.

Accordingly, it would be of interest if the authors could provide some details on how many HFpEF patients exhibited mitral regurgitation, especially in comparison with control hypertensive patients without HFpEF.

Lam CSP, Roger VL, Rodeheffer RJ, Borlaug BA, Enders FT, Redfield MM. Pulmonary hypertension in heart failure with preserved ejection fraction: a community-based study. J Am Coll Cardiol 2009; 53:1119–23.

Midregion Prohormone Adrenomedullin and Prognosis in Patients Presenting with Acute Dyspnea Results from the BACH (Biomarkers in Acute Heart Failure) Trial

Alan Maisel, MD, Christian Mueller, Richard M. Nowak,W. Frank Peacock, et al.
J Am Coll Cardiol 2011; 58(10):1057–67
http://dx.doi.org:/10.1016/j.jacc.2011.06.006

Objectives The aim of this study was to determine the prognostic utility of midregion proadrenomedullin (MR-proADM) in all patients, cardiac and noncardiac, presenting with acute shortness of breath.
Background The recently published BACH (Biomarkers in Acute Heart Failure) study demonstrated that MR-proADM had superior accuracy for predicting 90-day mortality compared with B-type natriuretic peptide (area under the curve: 0.674 vs. 0.606, respectively, p < 0.001) in acute heart failure.
Methods The BACH trial was a prospective, 15-center, international study of 1,641 patients presenting to the emergency department with dyspnea. Using this dataset, the prognostic accuracy of MR-proADM was evaluated in all patients enrolled for predicting 90-day mortality with respect to other biomarkers, the added value in addition to clinical variables, as well as the added value of additional measurements during hospital admission.
Results Compared with B-type natriuretic peptide or troponin, MR-proADM was superior for predicting 90-day all-cause mortality in patients presenting with acute dyspnea (c index = 0.755, p < 0.0001). Furthermore, MR-proADM added significantly to all clinical variables (all adjusted hazard ratios: HR=3.28), and it was also superior to all other biomarkers. MRproADM added significantly to the best clinical model (bootstrap-corrected c index increase: 0.775 to 0.807; adjusted standardized hazard ratio: 2.59; 95% confidence interval: 1.91 to 3.50; p < 0.0001). Within the model, MR-proADM was the biggest contributor to the predictive performance, with a net reclassification improvement of 8.9%. Serial evaluation of MR-proADM performed in patients admitted provided a significant added value compared with a model with admission values only (p< 0.0005). More than one-third of patients originally at high risk could be identified by the biomarker evaluation at discharge as low-risk patients. Conclusions MR-proADM identifies patients with high 90-day mortality and adds prognostic value to natriuretic peptides in patients presenting with acute shortness of breath. Serial measurement of this biomarker may also prove useful for monitoring, although further studies will be required. (Biomarkers in Acute Heart Failure [BACH]; NCT00537628)

Invasive Hemodynamic Characterization of Heart Failure with Preserved Ejection Fraction

Mads J. Andersen, Barry A. Borlaug
Heart Failure Clin 10 (2014) 435–444
http://dx.doi.org/10.1016/j.hfc.2014.03.001

KEY POINTS

• Invasive hemodynamic assessment in heart failure with preserved ejection fraction (HFpEF) was originally a primary research tool to advance the understanding of the pathophysiology of HFpEF.
• The role of invasive hemodynamic assessment in HFpEF is expanding to the diagnostic arena where invasive assessment offers a robust, sensitive, and specific way to diagnose or exclude HFpEF in patients with unexplained dyspnea and normal ejection fraction.
• In future years, invasive hemodynamic profiling may more rigorously phenotype patients to individualized therapy and, potentially, deliver novel device-based structural interventions.

The circulatory system serves to deliver substrates to the body via the bloodstream while removing the byproducts of cellular metabolism. Hemodynamics broadly refers to the study of the forces involved in the circulation of blood, which are governed by to the physical properties of the heart and vasculature and their dynamic regulation by the autonomic nervous system.

Afterload represents the forces opposing ventricular ejection and can be quantified by systolic left ventricular (LV) wall stress and aortic input impedance or its individual components (resistance, compliance, characteristic impedance). Wall stress is inconvenient because it depends on heart size and geometry, whereas impedance is cumbersome because it is a frequency-domain parameter that cannot be easily coupled with time-domain measures of ventricular function. Effective arterial elastance (Ea), defined by the ratio of LV end-systolic pressure (ESP) to stroke volume, provides a robust measure of total arterial load. Ea is not a directly measured parameter but, instead, a net or lumped stiffness of the vasculature that incorporates both mean and oscillatory components of afterload (Fig. 1). Preload reflects the degree of myofiber stretch before the onset of contraction, which, in turn, dictates the force and velocity of contraction according to the Frank-Starling principle. In everyday practice, preload is often conceptualized as equivalent to LV filling pressures. However, in fact, preload is most accurately reflected by the LV volume at end-diastole volume (EDV). Filling pressures are related to EDV by the LV diastolic chamber stiffness, which differs in healthy volunteers and subjects with HFpEF.

Fig. 1. Not shown. Ventricular-arterial coupling in the pressure-volume plane. Pressure volume loop at steady state is shown in dark black. The area subtended by the loop (shaded) represents the stroke work. Stroke volume is the difference between end-diastolic volume (EDV) and end-systolic volume (ESV). Ea is defined by the negative slope connecting the ESP and ESV coordinates with EDV and pressure = 0. With acute preload reduction (dotted line loops) there is progressive reduction in EDV, ESV, and ESP. The linear slope of the endsystolic pressure volume relationship (ESPVR) is LV end-systolic elastance (Ees). The curvilinear slope of the end diastolic pressure–volume relationship (EDVPR) is derived by fitting pressure volume coordinates measured during diastasis to the equation shown. The exponential power or stiffness constant (b) obtained is a measure of LV diastolic stiffness. (Adapted from Borlaug BA, Kass DA. Invasive hemodynamic assessment in heart failure. Heart Fail Clin 2009;5(2):217–28; with permission.)

Fig. 3. Not shown. Left ventricular diastolic reserve in HFpEF. In the normal healthy adult, the rate of LV pressure decay during isovolumic contraction (t) is rapid and increases markedly during exercise in association with a reduction in LVmin, allowing for suction of blood into the LV, with no increase in left atrial pressure or LV end-diastolic pressure (LVEDP) despite an increase in LV end-diastolic volume and marked shortening of the cycle length. In HFpEF, relaxation is prolonged at baseline (increased t) with inadequate hastening (shortening of t) during exercise, contributing to an inability to reduce LVmin and, consequently, a complete lack of suction effects. LV filling then completely depends on left atrial hypertension, which develops in tandem with marked elevation in LVEDP. (Data from Borlaug BA, Jaber WA, Ommen SR, et al. Diastolic relaxation and compliance reserve during dynamic exercise in heart failure with preserved ejection fraction. Heart 2011;97(12):964–9.)

Fig. 4. Preload and filling pressures in HFpEF. (A) Cumulative distribution plot shows that acute changes in stroke volume with nitroprusside infusion are lower in HFpEF (black) compared with HFrEF (red). Because afterload (Ea) is lowered, any acute reduction in SV must be related to reduction in preload volume (EDV) and nearly 40% of HFpEF patients experienced stroke volume reduction with nitroprusside, despite high filling pressures (PCWP 20–25 mm Hg), indicating increased reliance on high pressures to achieve adequate EDV. *p<0.0001 compared with HFrEF. (B) LVEDP in a healthy adult (blue) and in a HFpEF patient with increased LV diastolic stiffness (green). At the same preload (EDV), pressure is more than twofold higher in HFpEF. In contrast, at the same LV diastolic pressure (15 mm Hg), LV volume is much lower in HFpEF, indicating decreased LV diastolic capacitance. V15, volume at end-diastolic pressure = 15 mm Hg; LVEDP. (Adapted from Schwartzenberg S, Redfield MM, From AM, et al. Effects of vasodilation in heart failure with preserved or reduced ejection fraction implications of distinct pathophysiologies on response to therapy. J Am Coll Cardiol 2012;59(5):442–51; with permission.)

Updated Clinical Classification of Pulmonary Hypertension

Gérald Simonneau, Ivan M. Robbins, Maurice Beghetti, et al.
J Am Coll of Cardiol   2009; 54(1), Suppl S
http://dx.doi.org:/10.1016/j.jacc.2009.04.012

The aim of a clinical classification of pulmonary hypertension (PH) is to group together different manifestations of disease sharing similarities in pathophysiologic mechanisms, clinical presentation, and therapeutic approaches. In 2003, during the 3rd World Symposium on Pulmonary Hypertension, the clinical classification of PH initially adopted in 1998 during the 2nd World Symposium was slightly modified. During the 4th World Symposium held in 2008, it was decided to maintain the general architecture and philosophy of the previous clinical classifications. The modifications adopted during this meeting principally concern Group 1, pulmonary arterial hypertension (PAH). This subgroup includes patients with PAH with a family history or patients with idiopathic PAH with germline mutations (e.g., bone morphogenetic protein receptor-2, activin receptor-like kinase type 1, and endoglin). In the new classification, schistosomiasis and chronic hemolytic anemia appear as separate entities in the subgroup of PAH associated with identified diseases. Finally, it was decided to place pulmonary venoocclusive disease and pulmonary capillary hemangiomatosis in a separate group, distinct from but very close to Group 1 (now called Group 1=). Thus, Group 1 of PAH is now more homogeneous. (J Am Coll Cardiol 2009; 54: S43–54)
Updated Evidence-Based Treatment Algorithm in Pulmonary Arterial Hypertension

Robyn J. Barst,  J. Simon R. Gibbs, Hossein A. Ghofrani, et al.
J Am Coll Cardiol 2009; 54(1), Suppl S,

Uncontrolled and controlled clinical trials with different compounds and procedures are reviewed to define the risk benefit profiles for therapeutic options in pulmonary arterial hypertension (PAH). A grading system for the level of evidence of treatments based on the controlled clinical trials performed with each compound is used to propose an evidence-based treatment algorithm. The algorithm includes drugs approved by regulatory agencies for the treatment of PAH and/or drugs available for other indications. The different treatments have been evaluated mainly in idiopathic PAH, heritable PAH, and in PAH associated with the scleroderma spectrum of diseases or with anorexigen use. Extrapolation of these recommendations to other PAH subgroups should be done with caution. Oral anticoagulation is proposed for most patients; diuretic treatment and supplemental oxygen are indicated in cases of fluid retention and hypoxemia, respectively. High doses of calcium-channel blockers are indicated only in the minority of patients who respond to acute vasoreactivity testing. Nonresponders to acute vasoreactivity testing or responders who remain in World Health Organization (WHO) functional class III, should be considered candidates for treatment with either an oral phosphodiesterase-5 inhibitor or an oral endothelin-receptor antagonist. Continuous intravenous administration of epoprostenol remains the treatment of choice in WHO functional class IV patients. Combination therapy is recommended for patients treated with PAH monotherapy who remain in WHO functional class III. Atrial septostomy and lung transplantation are indicated for refractory patients or where medical treatment is unavailable. (J Am Coll Cardiol 2009;54:S78–84)

Inhibition and down-regulation of gene transcription and guanylyl cyclase activity of NPRA by angiotensin II involving protein kinase C

Kiran K. Arise, Kailash N. Pandey
Biochem and Biophys Res Commun 349 (2006) 131–135
http://dx.doi.org:/10.1016/j.bbrc.2006.08.003

The objective of this study was to investigate the role of protein kinase C (PKC) in the angiotensin II (Ang II)-dependent repression of Npr1 (coding for natriuretic peptide receptor-A, NPRA) gene transcription. Mouse mesangial cells (MMCs) were transfected with Npr1 gene promoter-luciferase construct and treated with Ang II and PKC agonist or antagonist. The results showed that the treatment of MMCs with 10 nM Ang II produced a 60% reduction in the promoter activity of Npr1 gene. MMCs treated with 10 nM Ang II exhibited 55% reduction in NPRA mRNA levels, and subsequent stimulation with 100 nM ANP resulted in 50% reduction in guanylyl cyclase (GC) activity. Furthermore, the treatment of MMCs with Ang II in the presence of PKC agonist phorbol ester (100 nM) produced an almost 75% reduction in NPRA mRNA and 70% reduction in the intracellular accumulation of cGMP levels. PKC antagonist staurosporine completely reversed the effect of Ang II and phorbol ester. This is the first report to demonstrate that ANG II-dependent transcriptional repression of Npr1 gene promoter activity and down-regulation of GC activity of translated protein, NPRA is regulated by PKC pathways.

Transcriptional regulation of guanylyl cyclase/natriuretic peptide receptor-A gene

Prerna Kumar, Kiran K. Arise, Kailash N. Pandey
peptides 27 (2006) 1762–1769
http://dx.doi.org:/10.1016/j.peptides.2006.01.004

Activation of natriuretic peptide receptor-A (NPRA) produces the second messenger cGMP, which plays a pivotal role in maintaining blood pressure and cardiovascular homeostasis. In the present study, we have examined the role of trans-acting factor Ets-1 in transcriptional regulation of Npr1 gene (coding for NPRA).Using deletional analysis of the Npr1 promoter, we have defined a 400 base pair (bp) region as the core promoter, which contains consensus binding sites for transcription factors including: Ets-1, Lyf-1, and GATA-1/2. Over-expression of Ets-1 in mouse mesangial cells (MMCs) enhanced Npr1 gene transcription by 12-fold. However, overexpression of GATA-1 or Lyf-1 repressed Npr1 basal promoter activity by 50% and 80%, respectively. The constructs having a mutant Ets-1 binding site or lacking this site failed to respond to Ets-1 activation of Npr1 gene transcription. Collectively, the present results demonstrate that Ets-1 greatly stimulates Npr1 gene promoter activity, implicating its critical role in the regulation and function of NPRA at the molecular level.

Several agents that are known to upregulate Ets-1 transcription, include RA, TNF-alpha, VEGF, and TPA. Ets-1 is upregulated at exposure to agonists such as serum in vitro and is expressed in injured vasculature. MAPK-mediated phosphorylation positively regulates the transcriptional activation functions of Ets-1 by recruiting CBP/p300. Not much is known about Ets-1 expression or regulation in mesangial cells. A temporal increase of mesangial cell Ets-1 expression has been reported which correlates with mesangial cell activation
in mesangioproliferative glomerulonephritis suggesting involvement of PDGF-B. There might be a possibility that during glomerulonephritis increased Ets-1 expression upregulates Npr1 gene as a protective mechanism. Npr1 gene has been shown to negatively regulate mitogen-activated protein kinase and proliferation of mesangial cells.

In conclusion, our results demonstrate that the precise control of Npr1 gene transcriptional activity is achieved through a synergy of activators and repressors in which Ets-1 plays an integral role as a transcriptional activator. Comparatively, Lyf-1 and GATA-1 act as repressors, inhibiting and regulating the transcriptional activity of Npr1 gene promoter. The present findings suggest that Ets-1 plays a critical role in enhancing Npr1 gene transcription and may have an important influence in hypertension and cardiovascular homeostasis at the molecular level.

Krüppel-like transcription factor 11 (KLF11) overexpression inhibits cardiac hypertrophy and fibrosis in mice

Yue Zheng, Ye Kong, Feng Li
Biochem and Biophys Res Commun 443 (2014) 683–688
http://dx.doi.org/10.1016/j.bbrc.2013.12.024

The Krüppel-like factors (KLFs) belong to a subclass of Cys2/His2 zinc-finger DNA-binding proteins. The KLF family member KLF11 is originally identified as a transforming growth factor b (TGF-b)-inducible gene and is one of the most studied in this family. KLF11 is expressed ubiquitously and participates  in diabetes and regulates hepatic lipid metabolism. However, the role of KLF11 in cardiovascular system is largely unknown. Here in this study, we reported that KLF11 expression is down-regulated in failing human hearts and hypertrophic murine hearts. To evaluate the roles of KLF11 in cardiac hypertrophy, we generated cardiac-specific KLF11 transgenic mice. KLF11 transgenic mice do not show any difference from their littermates at baseline. However, cardiac-specific KLF11 overexpression protects mice from TAC-induced cardiac hypertrophy, with reduced radios of heart weight (HW)/body weight (BW), lung weight/BW and HW/tibia length, decreased left ventricular wall thickness and increased fractional shortening. We also observe lower expression of hypertrophic fetal genes in TAC-challenged KLF11 transgenic mice compared with WT mice. In addition, KLF11 reduces cardiac fibrosis in mice underwent hypertrophy. The expression of fibrosis markers are also down-regulated when KLF11 is overexpressed in TAC-challenged mice. Taken together, our findings identify a novel anti-hypertrophic and anti-fibrotic role of KLF11, and KLF11 activator may serve as candidate drug for heart failure patients.

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