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Posts Tagged ‘lymphokines’


Nitric Oxide has a Ubiquitous Role in the Regulation of Glycolysis – with a Concomitant Influence on Mitochondrial Function

 

Reporter, Editor, and Topic Co-Leader: Larry H. Bernstein, MD, FACP, Clinical Pathologist and Biochemist

 

 

Apoptosis signaling pathways

Apoptosis signaling pathways (Photo credit: AJC1)

This discussion is a followup on a series of articles elucidating the importance of NO, eNOS, iNOS, cardiovascular and vascular endothelium effects, and therapeutic targets.

This mechanism of action and signaling actions have been introduced so that we identify endocrine, paracrine, and such effects in the normal, stressed, and dysfunctional state. The size and breadth of this vital adaptive process is now further explored.

The title is short, befitting a subtitle.  The full topic may be considered “Nitric Oxide has a ubiquitous role in the regulation of glycolysis -with a concomitant influence on mitochondrial function that is active in endothelium, platelets, vascular smooth muscle and neural cells and the balance has a role in chronic inflammation, asthma, hypertension, sepsis and cancer”.

Vascular endothelium

Vascular endothelium (Photo credit: Wikipedia)

Related articles

 

 

Nitric Oxide Synthase

Nitric Oxide Synthase (Photo credit: Wikipedia)

 

 

Nitric Oxide has a ubiquitous role in the regulation of glycolysis with a concomitant influence on mitochondrial function that is active in endothelium, platelets, vascular smooth muscle and neural cells and the balance has a role in chronic inflammation, asthma, hypertension, sepsis and cancer.

Uncoupling of aerobic glycolysis
Potential cytotoxic mediators of endothelial cell (EC) apoptosis include increased formation of reactive oxygen and nitrogen species (ROSRNS) during the atherosclerotic process. Nitric oxide (NO) has a biphasic action on oxidative cell killing with low concentrations protecting against cell death, whereas higher concentrations are cytotoxic. High levels of NO can be produced by inducible nitric-oxide synthase in response to cytokine stimulation, primarily from macrophages, and elevated levels of NO is injurious to endothelium.Ccytochrome c release and caspase activation are involved in NO induced apoptosis. ROS also induces mitochondrial DNA damage in ECs, and this damage is accompanied by a decrease in mitochondrial RNA (mtRNA) transcripts, mitochondrial protein synthesis, and cellular ATP levels. Mitochondria have been recognized to play a pivotal role in the signaling cascade of apoptosis leading to atherosclerosis-induced damage in endothelial cells.
The processes involved in the signaling pathways leading to apoptosis are complex but have some degree of convergence between cell types including those in the vasculature. Release of cytochrome c from mitochondria is a proapoptotic signal, which activates several downstream signaling events including formation of the apoptosome and activation of caspases. Ubiquinol cytochrome c reductase (complex III) is a site for ROS formation, and cytochrome c oxidase (complex IV) is a target for the interaction of NO in mitochondria.
The impact of the inhibition of mitochondrial protein synthesis is particularly important in NO-dependent cytotoxicity, and depends also on other factors such as glycolysis. These authors examined whether the inhibition of mitochondrial protein synthesis by chloramphenicol increases the susceptibility of endothelial cells to undergo NO-dependent apoptosis in glucose-free media. Bovine aortic endothelial cells were treated with chloramphenicol, which resulted in a decreased ratio of mitochondrial complex IV to cytochrome c and increased oxidant production in the cell. Inhibition of mitochondrial protein synthesis was associated with a greater susceptibility of the cells to apoptosis induced by NO in glucose-free medium.
Inhibition of mitochondrial protein synthesis results in increased endothelial cell susceptibility to nitric oxide-induced apoptosis. A Ramachandran, DR Moellering, E Ceaser, S Shiva, J Xu, and V Darley-Usmar. PNAS May 14, 2002: 99(10): 6643–6648 http://www.pnas.orgcgidoi10.1073pnas.102019899

Nitric oxide (NO) is a ubiquitous signaling molecule whose physiological roles mediated through the activation of the soluble guanylate cyclase are now clearly recognized. At physiological concentrations, NO also inhibits the mitochondrial enzyme cytochrome c oxidase (complex IV) in competition with oxygen, and recently we have suggested that the interplay between the two gases allows this enzyme to act as an oxygen sensor in cells. In addition, NO plays a variety of patho-physiological roles, some of which also may be the consequence of its action at a mitochondrial level. We have characterized the sequence of events that follow inhibition of complex IV by continuous exposure to NO.
The mitochondrion is a key organelle in the control of cell death. Nitric oxide (NO) inhibits complex IV in the respiratory chain and is reported to possess both proapoptotic and antiapoptotic actions. We investigated the effects of continuous inhibition of respiration by NO on mitochondrial energy status and cell viability. Serum-deprived human T cell leukemia (Jurkat) cells were exposed to NO at a concentration that caused continuous and complete (;85%) inhibition of respiration. Serum deprivation caused progressive loss of mitochondrial membrane potential (Dcm) and apoptotic cell death. In the presence of NO, Dcm was maintained compared to controls, and cells were protected from apoptosis. Similar results were obtained by using staurosporin as the apoptotic stimulus. As exposure of serum-deprived cells to NO progressed (>5 h), however, Dcm fell, correlating with the appearance of early apoptotic features and a decrease in cell viability. Glucose deprivation or iodoacetate treatment of cells in the presence of NO resulted in a collapse of Dcm, demonstrating involvement of glycolytic ATP in its maintenance. Under these conditions cell viability also was decreased. Treatment with oligomycin and or bongkrekic acid indicated that the maintenance of Dcm during exposure to NO is caused by reversal of the ATP synthase and other electrogenic pumps. Thus, blockade of complex IV by NO initiates a protective action in the mitochondrion to maintain Dcm; this results in prevention of apoptosis. It is likely that during cellular stress involving increased generation of NO this compound will trigger a similar sequence of events, depending on its concentration and duration of release. (mitochondrial membrane potential ; apoptosis ; necrosis)

The effect of nitric oxide on cell respiration: A key to understanding its role in cell survival or death. B Beltra, A Mathur, MR Duchen, JD. Erusalimsky, and S Moncada. PNAS Dec 19, 2000; 97(26):4602–14607.

Another study by this group shows that inhibition of respiration by exogenous nitric oxide (NO) in Jurkat cells leads to mitochondrial membrane hyperpolarization dependent on the utilization of glycolytic ATP by the F1Fo-ATPase and other transporters acting in reverse mode. This process also occurs in astrocytes, which are highly glycolytic cells, but not in neurons , which do not invoke glycolysis to maintain ATP concentrations. In addition, this hyperpolarization correlates with protection against apoptotic cell death. Others found an early phase of mitochondrial hyperpolarization after treatment of a variety of cells with different pro-apoptotic stimuli, which precedes the generation of free. At present, no satisfactory explanation has been proposed to explain the mechanism of hyperpolarization, the reasons why free radicals are released from the mitochondrion, or the connection of these phenomena with apoptosis.
The authors surmise that a pro-apoptotic stimulus, anti-Fas Ab, leads to release of endogenous NO from Jurkat cells in sufficient amounts to inhibit cell respiration and cause a hyperpolarization dependent on the reversal of the F1Fo-ATPase. Moreover, the reduction of the mitochondrial electron transport chain, after inhibition of cytochrome oxidase by NO, leads to generation of superoxide anion (O2). They suggest the process is a cellular defense response that may be overcome by pro-apoptotic mechanisms that occur in parallel.

Inhibition of mitochondrial respiration by endogenous nitric oxide: A critical step in Fas signaling. B Beltran, M Quintero, E Garcıa-Zaragoza, E O’Connor, JV. Esplugues, and Salvador Moncada. PNAS June 25, 2002 99(13): 8892–8897. http://www.pnas.orgcgidoi10.1073pnas.092259799

Nitric oxide has been shown to render cells resistant to oxidative stress. Mechanisms proposed for the ability of nitric oxide to protect cells against oxidative stress include reactions of nitric oxide and the induction of adaptive responses that require protein synthesis. Nitric oxide forms iron complexes preventing the formation of strong oxidants. In addition, reactions of nitric oxide with lipid and or organic radicals protect against membrane peroxidation and peroxidative chemistry-induced cell injury. Exposure to low, nonlethal doses of nitric oxide induces adaptive responses that render cells resistant to lethal concentrations of nitric oxide and or peroxides, such as, the induction of hemoxygenase-1 (HO-1) and Mn superoxide dismutase. The up-regulation of HO-1 was accompanied by an increase in ferritin to account for the release of iron from HO-1, indicating a role of both iron heme and nonheme iron for peroxide-mediated cellular injury. Further, nitric oxide, by regulating critical mitochondrial functions such as respiration, membrane potential, and release of cytochrome c, is able to trigger defense mechanisms against cell death induced by pro-apoptotic stimuli.
This study investigates the potential contribution of nitric oxide’s ability to protect cells from oxidative stress, low steady state levels of nitric oxide generated by endothelial nitric oxide synthase (eNOS) and the mechanisms of protection against H2O2. Spontaneously transformed human ECV304 cells, which normally do not express eNOS, were stably transfected with a green fluorescent-tagged eNOS cDNA. The eNOS-transfected cells were found to be resistant to injury and delayed death following a 2-h exposure to H2O2 (50–150 mM). Inhibition of nitric oxide synthesis abolished the protective effect against H2O2 exposure. The ability of nitric oxide to protect cells depended on the presence of respiring mitochondria. ECV3041 eNOS cells with diminished mitochondria respiration are injured to the same extent as non-transfected ECV304 cells, and recovery of mitochondrial respiration restores the ability of nitric oxide to protect against H2O2-induced death. Nitric oxide had a profound effect in cell metabolism, because ECV3041eNOS cells had lower steady state levels of ATP and higher utilization of glucose via the glycolytic pathway than ECV304 cells. However, the protective effect of nitric oxide against H2O2 exposure is not reproduced in ECV304 cells after treatment with azide and oligomycin suggesting that the dynamic regulation of respiration by nitric oxide represent a critical and unrecognized primary line of defense against oxidative stress.

Dynamic regulation of metabolism and respiration by endogenously produced nitric oxide protects against oxidative stress. E Paxinou, M Weisse, Q Chen, JM Souza, et al. PNAS Sept 25, 2001; 98( 20): 11575–11580. http://www.pnas.orgycgiydoiy10.1073ypnas.201293198.

Nitric oxide (NO) mediates a variety of biological effects including relaxation of blood vessels, cytotoxicity of activated macrophages, and formation of cGMP by activation of glutamate receptors of neurons. NO has also been implicated for such pathophysiological conditions as destruction of tumor cells by macrophages, rheumatoid arthritis, and focal brain ischemia. Some of these effects of NO are associated with hypoxic conditions. O2 radicals and ions that result from reactivity of NO are presumed to be involved in NO cytotoxicity. These investigators report that adaptive cellular response controlled by the transcription factor hypoxia-inducible factor 1 (HIF-1) in hypoxia is suppressed by NO. Induction of erythropoietin and glycolytic aldolase A mRNAs in hypoxically cultured Hep3B cells, a human hepatoma cell line, was completely and partially inhibited, respectively, by the addition of sodium nitroprusside (SNP), which spontaneously releases NO. A reporter plasmid carrying four hypoxia-response element sequences connected to the luciferase structural gene was constructed and transfected into Hep3B cells. Inducibly expressed luciferase activity in hypoxia was inhibited by the addition of SNP and two other structurally different NO donors, S-nitroso-Lglutathione and 3-morpholinosydnonimine, giving IC50 values of 7.8, 211, and 490 mM, respectively. Inhibition by SNP was also observed in Neuro 2A and HeLa cells, indicating that the inhibition was not cell-type-specific. The vascular endothelial growth factor promoter activity that is controlled by HIF-1 was also inhibited by SNP (IC50 5 6.6 mM). Induction generated by the addition of cobalt ion (this treatment mimics hypoxia) was also inhibited by SNP (IC50 5 2.5 mM). Increased luciferase activity expressed by cotransfection of effector plasmids for HIF-1a or HIF-1a-like factor in hypoxia was also inhibited by the NO donor. We also showed that the inhibition was performed by blocking an activation step of HIF-1a to a DNA-binding form.
Inhibition of hypoxia-inducible factor 1 activity by nitric oxide donors in hypoxia. K Sogawa, K Numayama-Tsuruta, M Ema, M Abe, et al. Proc. Natl. Acad. Sci. USA (Biochemistry) June 1998; 95:7368–7373. 1998. The National Academy of Sciences 0027-8424.98.957368-6. http:yywww.pnas.org.

The role of nitrogen metabolism in the survival of prolonged periods of waterlogging was investigated in highly flood-tolerant, nodulated Lotus japonicus plants. Alanine production revealed to be a critical hypoxic pathway. Alanine is the only amino acid whose biosynthesis is not inhibited by nitrogen deficiency resulting from RNA interference silencing of nodular leghemoglobin. The metabolic changes that were induced following waterlogging can be best explained by the activation of alanine metabolism in combination with the modular operation of a split tricarboxylic acid pathway. The sum result of this metabolic scenario is the accumulation of alanine and succinate and the production of extra ATP under hypoxia. The importance of alanine metabolism is discussed with respect to its ability to regulate the level of pyruvate, and this and all other changes are discussed in the context of current models concerning the regulation of plant metabolism.
Glycolysis and the Tricarboxylic Acid Cycle Are Linked by Alanine Aminotransferase during Hypoxia Induced by Waterlogging of Lotus japonicus[W][OA]. M Rocha, F Licausi, WL Arau´ jo, A Nunes-Nesi, et al. Plant Physiology Mar 2010; 152: 1501–1513. http://www.plantphysiol.org 2010 Amer Soc Plant Biologists

DNA damage occurs in ischemia, excitotoxicity, inflammation, and other disorders that affect the central nervous system (CNS). Extensive DNA damage triggers cell death and in the mature CNS, this occurs primarily through activation of the poly(ADP-ribose) polymerase-1 (PARP-1) cell death pathway. PARP-1 is an abundant nuclear enzyme that, when activated by DNA damage, consumes nicotinamide adenine dinucleotide (NAD)+ to form poly(ADP-ribose) on acceptor proteins. The PARP-1 activation leads to cell death. We used mouse astrocyte cultures to explore the bioenergetic effects of NAD+ depletion by PARP-1 and the role of NAD+ depletion in this cell death program. PARP-1 activation led to a rapid but incomplete depletion of astrocyte NAD+, a near-complete block in glycolysis, and eventual cell death. Repletion of intracellular NAD restored glycolytic function and prevented cell death. The addition of non-glucose substrates to the medium, pyruvate, glutamate, or glutamine, also prevented astrocyte death after PARP-1 activation.
These findings suggest a sequence of events in which NAD+ depletion is a key event linking DNA damage to metabolic impairment and cell deathm. A similar scenario has been proposed by Zong et al. (2004), based on the finding that cell types that depend on aerobic glycolysis for ATP production exhibit a particularly high sensitivity to DNA damage and PARP-1 activation. In mature brain, glucose is normally the dominant metabolic substrate due to relatively slow transport of other metabolites across the blood– brain barrier. Oncein brain, glucose may be metabolized directly by neurons and glia or may be metabolized to lactate in glia and thelactate subsequently shuttled to neurons for oxidative metabolism (Dringen et al., 1993; Pellerin and Magistretti,1994; Wender et al., 2000; Dienel and Cruz, 2004). In either case, a block in glycolytic flux produced by NAD depletion will block energy metabolism in both neurons and glia in brain. Interestingly, the lactate shuttle hypothesis raises the possibility that activation of PARP-1 selectively in astroglia might also block energy metabolism in neurons.

These studies suggest PARP-1 activation leads to rapid depletion of the cytosolic but not the mitochondrial NAD+ pool. Depletion of the cytosolic NAD+ pool renders the cells unable to utilize glucose as a metabolic substrate. Under conditions where glucose is the only available metabolic substrate, this leads to cell death. This cell death pathway is particularly germane to brain because glucose is normally the only metabolic substrate that is transported rapidly across the blood–brain barrier. © 2004 Wiley-Liss, Inc.
Key words: mitochondria; permeability transition; poly(ADP-ribose) polymerase; ischemia; peroxynitrite
NAD+as a metabolic link between DNA damage and cell death. DNA damage induced by alkylating agents, oxidative stress, or other agents causes PARP-1 activation. PARP-1 activation leads to depletion in cytosolic NAD with, initially, a relative preservation of mitochondrial NAD and mitochondrial function. The depletion in cytosolic NAD+ blocks glycolysis, and in cells in which glucose is the primary energy substrate, this in turn leads to a block in substrate flux to mitochondria. The resulting mitochondrial dysfunction leads to mitochondrial permeability transition (MPT) and subsequent downstream events culminating in cell death.
NAD+ as a Metabolic Link Between DNA Damage and Cell Death. W Ying, CC Alano, P Garnier, and RA Swanson. Journal of Neuroscience Research 2005;79:216–223
Key words: glycolysis, mitochondrial energy production, nitric oxide
Abbreviations: NO, nitric oxide; SNAP, S-nitroso-N-acetylpenicyllamine; SNP, sodium nitroprusside.
The results indicate that: 1) in porcine platelets NO is able to diminish mitochondrial energy production through the inhibition of cytochrome oxidase, 2) the inhibitory effect of NO on platelet secretion (but not aggregation) can be attributed to the reduction of mitochondrial energy production.
Nitric oxide (NO) has been increasingly recognized as an important intra- and intercellular messenger molecule with a physiological role in vascular relaxation, platelet physiology, neurotransmission and immune responses (Moncada et al., 1991; Radomski et al., 1996; Szabó, 1996; Riedel et al., 1999; Titheradge 1999). In vitro NO is a strong inhibitor of platelet adhesion and aggregation (Radomski et al., 1996; Riedel et al., 1999;nSogo et al., 2000). In the blood stream, platelets remain in contact with NO that is permanently released from the endothelial cells and from activated macrophages (Moncada et al., 1991; Riedel et al., 1999; Titheradge 1999). It has been suggested that the activated platelet itself is able to produce NO (Lantoine et al., 1995; Zhou et al., 1995; Radomski et al., 1996). The mechanism responsible for the inhibitory effect of NO on platelet responses is not entirely clear. It is believed that the main intracellular target for NO in platelets is soluble cytosolic guanylate cyclase (Waldman & Walter 1989; Schmidt et al., 1993; Wang et al., 1998). NO activates the enzyme (Schmidt et al., 1993). Thus, elevated intracellular cGMP level inhibits platelet activation. There are suggestions, however, that elevated cGMP may not be the only intracellular factor directly involved in the inhibition of platelet activation (Gordge et al., 1998; Sogo et al., 2000; Beghetti et al., 2003).
Platelets are fairly active metabolically and have a total ATP turnover rate of about 3–8 times that of resting mammalian muscle (Akkerman, 1978; Akkerman et al., 1978; Holmsen, 1981; Niu et al., 1996). Platelets contain mitochondria which enable these cells to produce energy both in the oxidative and anaerobic way (Holmsen, 1981). Under aerobic conditions, ATP is produced by aerobic glycolysis using glucose or glycogen which can account for 30–50% of total ATP production, and by oxidative metabolism using glucose and glycogen (6–11%), amino-acids (7%) or free fatty acids (20–40%) (Holmsen 1981; Guppy et al., 1990; Niu et al., 1996).
The inhibition of mitochondrial respiration by removing oxygen or by respiratory chain blockers (antimycin A, cyanide, rotenone) results in the stimulation of glycolytic flux (Guppy et al., 1990). This phenomenon is known as Pasteur effect and indicates that in platelets glycolysis and mitochondrial respiration are tightly functionally connected (Akkerman, 1978; Holmsen, 1981; Guppy et al., 1995; Niu et al., 1996). It has been reported that the activation of human platelets by high concentration of thrombin is accompanied by an acceleration of lactate production and an increase in oxygen consumption (Akkerman & Holmsen, 1981; Niu et al., 1996).
The results presented here suggest that also porcine blood platelets stimulated by collagen produce more lactate. This indicates that both glycolytic and oxidativeATP production supports platelet responses. This also indicates that blocking of energy production in platelets may decrease their responses. It is well established that platelet responses have different metabolic energy (ATP) requirements increasing in the order: aggregation< dense and alfa granule secretion < acid hydrolase secretion (Holmsen et al., 1982; Verhoeven et al., 1984; Morimoto & Ogihara, 1996).
The present results indicate that exogenously added NO (in the form of NO donors)stimulates glycolysis in intact porcine platelets. Since in platelets glycolysis and mitochondrial respiration are tightly functionally connected, this can be interpreted to mean that the stimulatory effectof NO on glycolysis in intact platelets may be produced by non-functional mitochondria.This can be really the case since NO donors are able to inhibit both mitochondrial respiration and platelet cytochrome oxidase. Interestingly, the concentrations of NO donors inhibiting mitochondrial respiration and cytochrome oxidase were similar to those stimulating glycolysis in intact platelets.
Studies performed on intact J774 cells have shown that mitochondrial complex I is inhibited only after a prolonged (6–18 h) exposure to NO and that this inhibition appears to result from S-nitrosylation of critical thiols in the enzyme complex (Clementi et al., 1998). Further studies are needed to establish whether long term exposure of platelets to NO affects Mitochondrial complexes I and II.
Comparison of the concentrations of SNP and SNAP affecting cytochrome oxidase activityand mitochondrial respiration with those reducing the platelet responses indicates that NO cannot significantly reduce platelet aggregation through the inhibition of oxidative energy production. By contrast, the concentrations of the NO donors inhibiting platelet secretion, mitochondrial respiration and cytochrome oxidase were similar. This and the fact that the platelet release reaction strongly depends on the oxidative energy production may suggest that in porcine platelets NO can affect platelet secretion through the inhibition of mitochondrial energy production at the step of cytochrome oxidase.

Taking into account that platelets may contain NO synthase and are able to produce significant amounts of NO (Berkels et al., 1997)it seems possible that nitric oxide can function in these cells as a physiological regulator of mitochondrial energy production.
Nitric oxide and platelet energy metabolism. M Tomasiak, H Stelmach, T Rusak and J Wysocka. Acta Biochimica Polonica 2004; 51(3):789–803

These authors previously investigated the bioenergetic consequences of activating J774.A1 macrophages (MФ) with interferon (IFN)γ and lipopolysaccharide (LPS) and found that there is a nitric oxide (NO)-dependent mitochondrial impairment and stabilization of hypoxia inducible factor (HIF)-1α, which synergize to activate glycolysis and generate large
quantities of ATP. We now demonstrate, using TMRM fluorescence and time-lapse confocal microscopy, that these cells maintain a high mitochondrial membrane potential (ΔΨm) despite the complete inhibition of respiration. The maintenance of high ΔΨm is due to the utilization of a significant proportion of glycolytically generated ATP as a defence mechanism against cell death. This is achieved by the reverse functioning of FoF1-ATP synthase and adenine nucleotide translocase (ANT). Treatment of activated MФ with inhibitors of either of these enzymes, but not with inhibitors of the respiratory chain complexes I to IV, led to a collapse in ΔΨm and to an immediate increase in intracellular [ATP], due to the prevention of ATP hydrolysis by the FoF1-ATP synthase. This collapse in ΔΨm was followed by translocation of Bax from cytosol to the mitochondria, release of cytochrome c into the cytosol, activation of caspase 3 and 9 and subsequent apoptotic cell death. Our results indicate that during inflammatory activation “glycolytically competent cells” such as MФ utilize significant amounts of the glycolytically-generated ATP to maintain ΔΨm and thereby prevent apoptosis.

Activated macrophages utilize glycolytic ATP to maintain mitochondrial membranepotential and prevent apoptotic cell death. A Garedew, SO Henderson, S Moncada. Cell Death and Differentiation. 2010. DOI : 10.1038/cdd.2010.27
The effects of the sodium nitroprusside (SNP), a nitric oxide (NO) donor clinically used in the treatment of hypertensive emergencies on the energy production of rat reticulocytes were investigated. Rat reticulocyte-rich red blood cell suspensions were aerobically incubated without (control) or in the presence of different concentrations of SNP (0.1, 0.25, 0.5, 1.0 mM). SNP decreased total and coupled, but increased uncoupled oxygen consumption. This was accompanied by the stimulation of glycolysis, as measured by increased glucose consumption and lactate accumulation. Levels of all glycolytic intermediates indicate stimulation of hexokinase-phosphofructo kinase (HK-PFK), glyceraldehyde 3-phosphate dehydrogenase (GAPD) and pyruvate kinase (PK) activities in the presence of SNP. Due to the decrease of coupled oxygen consumption in the presence of SNP, ATP production via oxidative phosphorylation was significantly diminished. Simultaneous increase of glycolytic ATP production was not enough to provide constant ATP production. In addition, SNP significantly decreased ATP level, which was accompanied with increased ADP and AMP levels. However, the level of total adenine nucleotides was significantly lower, which was the consequence of increased catabolism of adenine nucleotides (increased hypoxanthine level). ATP/ADP ratio and adenylate energy charge level were significantly decreased. In conclusion, SNP induced inhibition of oxidative phosphorylation, stimulation of glycolysis, but depletion of total energy production in rat reticulocytes. These alterations were accompanied with instability of energy status.

Effects of Exogenous Donor of Nitric Oxide – Sodium Nitroprusside on Energy Production of Rat Reticulocytes. SD MALETIĆ, L M DRAGIĆEVIĆ-DJOKOVIĆ, BI OGNJANOVIĆ, RV ŽIKIĆ, AŠ ŠTAJN, MB SPASIĆ.
Physiol. Res. 2004;53: 439-447.

Key points to take from this:
1. The role of NO in regulating cellular death is in many organs and central to this function is the stabilization of mitochondria through sufficient levels of NO. High levels of eNO leads to mitochondrial dysfunction that increases the dependence of ATP generated from glycolysis.
2. This is accompanied by inhibition of oxidative phosphorylation and stimulation of glycolysis, which brings the discussion to a different domain – cancer growth and Warburgh Effect.
3. This is accompanied by PPAR activation, cytoplasmic NAD+ depletion, and inhibition of glycolysis (critical in cells dependent on aerobic glycolysis), depletion of total energy production, and apoptosis.
4. Maintenance of high glycolytic generation of ATP is essential for cellular defense, but the oxygen consumption is uncoupled.
5. NO donors inhibiting mitochondrial respiration and cytochrome oxidase are similar to those stimulating glycolysis

More    (pharmaceuticalintelligence.com)

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Ulcerative colitis

Ulcerative colitis (Photo credit: Wikipedia)

Tofacitinib, an Oral Janus Kinase Inhibitor, in Active Ulcerative Colitis

Reporter: Larry Bernstein, MD

This is an overview of a recently published article about a new treatment for ulcerative colitis. It also reviews the use of a class of drug in inflammatory conditions, and introduces the problem of sepsis.

Tofacitinib, an Oral Janus Kinase Inhibitor, in Active Ulcerative Colitis.
WJ Sandborn, S Ghosh, J Panes, I Vranic, C Su, for the Study A3921063 Investigators
N Engl J Med 2012; 367:616-624 August 16, 2012
http://www.nejm.org/doi/full/10.1056/NEJMoa1112168?query=TOC

 

Ulcerative colitis  is a chronic inflammatory disease of the colon that belongs to a group of diseases lumped together as Inflammatory Bowel Disease (IBD). There is a distinction to be made between Crohn’s disease, which may be limited to the small intestine (regional enteritis), the terminal ileum, or a portion of the transverse colon, and ulcerative colitis.

In ulcerative colitis the inflammation is limited to the mucosa and submucosa, but in Crohn’s disease there is a deep penetration of the intestinal wall (fistula) that may extend to the peritoneum causing abscess, scarring, peritonitis and possibly volvulus, obstruction and gangrenous bowel, which necessitate surgical resection. IBD tends to occur in children and young adults, repeats in families, and requires dietary management (fluid intake, Metamucil, restriction of fiber) . It is characterized by abdominal pain, diarrhea, bleeding, weight loss, and episodic fever, but also may be associated with joint pain.
Conservative medical treatment focuses on suppressing the immune response using 5-ASA, azathioprine, 6-mercaptopurine. If severe, biologic therapy is used to treat patients with severe Crohn’s disease that does not respond to any other types of medication, such as a TNF (tumor necrosis factor) inhibitor which can have secondary effects, and they are not universally effective. The importance of immunity can’t be understated, it involves a large portion of immune system and primitive Toll-like receptors (TLRs) that trigger signaling pathways. TLRs represent an important mechanism by which the host detects a variety of microorganisms that colonize in the gut. Endothelial and epithelial cells, and resident macrophages are potent producers of inflammatory cytokines, interleukins, IL-1, IL-6, and TNF-α, which are distinguished from another set that is treated in this study. In addition, there is a balance that has to be achieved between suppression and upregulation in treatment, which is referred to as immunomodulation.
The opposite of immunosuppression is upregulation It is cental to recent advances in chemotherapy of melanolma, small cell carcinoma and NSCCL of lung, and treatment resistant prostate cancer. An example is ipilimumab, whic upregulates cytotoxic T-cells to destroy cancer cells, but it has runaway destructive effects on the GI tract.

This study investigates the use of tofacitinib (CP-690,550), an oral inhibitor of Janus kinases 1, 2, and 3 with in vitro functional specificity for kinases 1 and 3 over kinase 2, which is expected to block signaling involving gamma chain–containing cytokines including interleukins 2, 4, 7, 9, 15, and 21. These cytokines are integral to lymphocyte activation, function, and proliferation.

The mechanism of drug action

Jak 1 and 3 inhibitor, which is targeted at blocking signaling involving gamma chain–containing cytokines including interleukins 2, 4, 7, 9, 15, and 21. The result would be to block signaling involving (gamma chains)–suppressing “lymphokines” 2, 4, 7, 9, 15, and 21. The lymphocyte pool is regional, being the antibody mediated immune system of the Bursa of Fabricius (B-lymphocytes, as opposed to the thymic derived T-cells) that form the largest immune organ extending the length of the intestines and the stomach.  The family transmission suggests an epigenetic event.

  • Gastrointestinal Tract
  • Oropharynx – Tonsils
  • Distal small intestine (ilieum) – Peyer’s Patches
  • Appendix, cecum

However, this classification of the lymphocytes has much greater complexity than I indicate.  The so called B-cells have receptors that recognize foreign antigen, but the T-cells have similar receptors and are tied to both the innate and the adaptive immune response.  Lymphocytes are the predominant cells of the immune system, but macrophages and plasma cells are present also.  Lymphocytes circulate, alternating between the circulatory blood stream and the lymphatic channels.  The end result of the immune reaction is the production of specific antibodies and antigen-reactive cells. These cells are called lymphocytes and are found in the blood and in the lymphoid system.

See Appendix

Trial features: double-blind, placebo-controlled, phase 2 trial; Patients were randomly assigned to receive tofacitinib at a dose of 0.5 mg, 3 mg, 10 mg, or 15 mg or placebo twice daily for 8 weeks.
Study goal: evaluated the efficacy of tofacitinib in 194 adults with moderately to severely active ulcerative colitis.

Primary outcome: a clinical response at 8 weeks, defined as an absolute decrease from baseline in the score on the Mayo scoring system for assessment of ulcerative colitis activity (possible score, 0 to 12, with higher scores indicating more severe disease) of 3 or more and a relative decrease from baseline of 30% or more with an accompanying decrease in the rectal bleeding subscore of 1 point or more or an absolute rectal bleeding subscore of 0 or 1.
Results and conclusion: The primary outcome, clinical response at 8 weeks, occurred in 32%, 48%, 61%, and 78% of patients receiving tofacitinib at a dose of 0.5 mg (P=0.39), 3 mg (P=0.55), 10 mg (P=0.10), and 15 mg (P<0.001), respectively, as compared with 42% of patients receiving placebo.
Clinical remission (defined as a Mayo score ≤2, with no subscore >1) at 8 weeks occurred in 13%, 33%, 48%, and 41% of patients receiving tofacitinib at a dose of 0.5 mg (P=0.76), 3 mg (P=0.01), 10 mg (P<0.001), and 15 mg (P<0.001), respectively, as compared with 10% of patients receiving placebo. Three patients treated with tofacitinib had an absolute neutrophil count of less than 1500.
Patients with moderately to severely active ulcerative colitis treated with tofacitinib were more likely to have clinical response and remission than those receiving placebo. (Funded by Pfizer; ClinicalTrials.gov number, NCT00787202.)
Commentary: The study is only phase 2, and it is also limited to disease of the descending colon. The next phase will be necessary to determine the effect on a larger population at the selected dose, and will be necessary to determine both the size of the effect and identify unexpected adverse effects. We also have to keep in mind that the success of the study would limit the treatment to a subset of patients with IBD.

Efficacy of Proposed Treatment:

  • it is effective at about 40% remission for 8 weeks compared to 10% for placebo, or an adjusted actual 30% for 8 weeks.
  • A much larger study needs to be done to see how well the dose holds up, as well as the dosing interval. There are two factors that will affect the t1/2 of the drug so that 1/2 dose could be replaced at the end of t1/2.
  • The dose of 15 mg was no better for clinical response.
  • I would think that the next trial might give a loading dose of 15 mg, and then 7 mg (better that 3 mg) would be replaced every t1/2.  But this is more complicated than usual.

I identified two steps, not one direct effect.

  • The inhibitor has to balance the production rate versus the removal rate of the T-cell population. The drug itself is not measured, only the effect. I know that albumin, the liver produced protein, has a half-life of removal of 21 days. Platelets are short shelf-life as well as rapid turnaround in plasma.
  •  I don’t know what is the local production and removal rate of lymphocytes in the gut. That would be the key determinant for dosing.

The following may shed some light on what has been discussed:

Common characteristics of the lymphoid system.

  • The lymphoid system involves organs and tissues where lymphocytic cells originate as lymphocyte precursors that mature and differentiate, and either lodge in the lymphoid organs or move throughout the body.
  • Precursor cells originate in the yolk sac, liver, spleen, or bursa of Fabricius (or its mammalian equivalent, the bone marrow) in an embryo or fetus.
  • Stem cells from bone marrow or embryonic tissues are deposited and mature into lymphocytes in the central or primary lymphoid organs, which include the thymus and the bursa or bone marrow. Upon maturation, the lymphocytes undergo further maturation toward immunocompetence and production of immunoglobulins or sensitized lymphocytes.

Adaptive immunity has 2 main classes:

  • Antibody-mediated – B Lymphocyte
  • Cell-mediated – T Lymphocyte

Lymph follicles are our point of reference:

  • Organized concentrations of Lymphocytes
  • No capsule, covered by epithelia
  • Nodules are unit structure seen in a node
  • Oval concentrations in meshwork of reticular cells

If pathogens initially evade constitutive defenses, they may yet be attacked by more specific inducible defenses. The inducible defenses are so-called because they are induced upon primary exposure to a pathogen or one of its products. The inducible defenses must be triggered in a host, take time to develop, and are a function of the immune response. The type of resistance thus developed in the host is called acquired immunity.

Three important features of the immunological system relevant to host defense and/or “immunity are:

1. Specificity. An antibody or reactive T cell will react specifically with the antigen that induced its formation; it will not react with other antigens. Generally, this specificity is of the same order as that of enzyme-substrate specificity or receptor-ligand specificity.

  • The specificity of the immune response is explained on the basis of the clonal selection hypothesis: during the primary immune response, a specific antigen selects a pre-existing clone of specific lymphocytes and stimulates exclusively its activation, proliferation and differentiation.

2.  Memory. The immunological system has a “memory”.

  • Once the immunological response has reacted to produce a specific type of antibody or reactive T cell, it is capable of producing more of the antibody or activated T cell more rapidly and in larger amounts.

3. Tolerance. An animal generally does not undergo an immunological response to its own (potentially-antigenic) components.

  • The animal is said to be tolerant, or unable to react to its own potentially-antigenic components.

Gene expression – CD28 signal transduction , λδ T repertoire and antigen reactivity

Efficient lymphokine gene expression appears to require both T-cell antigen receptor (TCR) signal transduction and an uncharacterized second or costimulatory signal. CD28 is a T-cell differentiation antigen that can generate intracellular signals that synergize with those of the TCR to increase T-cell activation and interleukin-2 (IL-2) gene expression.

  • These investigators examined the effect of CD28 signal transduction on granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin 3 (IL-3), and gamma interferon (IFN-gamma) promoter activity.
  • Stimulation of CD28 in the presence of TCR-like signals increases the activity of the GM-CSF, IL-3, and IFN-gamma promoters by three- to sixfold.
  • As previously demonstrated for the IL-2 promoter, the IL-3 and GM-CSF promoters contain distinct elements of similar sequence which specifically bind a CD28-induced nuclear complex.
  • Mutation of the CD28 response elements in the IL-3 and GM-CSF promoters abrogates the CD28-induced activity without affecting phorbol ester- and calcium ionophore-induced activity.
  • These studies indicate that the TCR and CD28-regulated signal transduction pathways, coordinately regulate the transcription of several lymphokines, and the influence of CD28 signals on transcription is mediated by a common complex.

Fraser JD, Weiss A.  Regulation of T-cell lymphokine gene transcription by the accessory molecule CD28. Mol Cell Biol. 1992 Oct;12(10):4357-63.

These investigators looked at the relevance λδ T repertoire and the antigen reactivity of clones isolated from CSF in multiple sclerosis (MS).

  • they found an increased percentage of V delta 1+ cells as compared to peripheral blood of the same donors.
  • Phenotypic analysis of cells from MS CSF with V gamma- and V delta-specific monoclonal antibodies (mAb) showed that the V delta 1 chain is most frequently associated with gamma chains belonging to the V gamma 1 family.
  • Sequence analysis of TCR genes revealed heterogeneity of junctional regions in both delta and gamma genes indicating polyclonal expansion. gamma delta clones were established and some recognized glioblastoma, astrocytoma or monocytic cell lines.
  • Stimulation with these targets induced serine esterase release and lymphokine expression characteristic of the TH0-like phenotype.
  • Remarkably, these tumor-reactive gamma delta cells were not detected in the peripheral blood using PCR oligotyping, but were found in other CSF lines independently established from the same MS patient.
  • in the CSF there is a skewed TCR gamma delta repertoire and suggest that gamma delta cells reacting against brain-derived antigens might have been locally expanded.

Nick S, Pileri P, Tongiani S, Uematsu Y, Kappos L, De Libero G. T cell receptor gamma delta repertoire is skewed in cerebrospinal fluid of multiple sclerosis patients: molecular and functional analyses of antigen-reactive gamma delta clones. Eur J Immunol. 1995 Feb;25(2):355-63. PMID: 1328852 [PubMed – indexed for MEDLINE] PMCID: PMC360359 Free PMC Article

B Cells and T Cells:  Addendum

users.rcn.com/jkimball.ma.ultranet/…/B/B_and_Tcells.htmlShareAIDS; Building the T-cell Repertoire; Gamma/Delta T Cells … T cells specific for this structure (i.e., with complementary TCRs) bind the B cell and; secrete lymphokines that: … Each chain has a variable (V) region and a constant (C) region.

Although mature lymphocytes all look pretty much alike, they are extraordinarily diverse in their functions. The most abundant lymphocytes are:

  • B lymphocytes (often simply called B cells) and
  • T lymphocytes (likewise called T cells).
  • B cells are produced in the bone marrow.
  •  The precursors of T cells are also produced in the bone marrow but leave the bone marrow and mature in the thymus (which accounts for their designation).
  • Each B cell and T cell is specific for a particular antigen. What this means is that each is able to bind to a particular molecular structure.

The specificity of binding resides in a receptor for antigen:

  • the B cell receptor (BCR) for antigen and
  • the T cell receptor (TCR) respectively.

Both BCRs and TCRs share these properties:

  • They are integral membrane proteins.
  • They are present in thousands of identical copies exposed at the cell surface.
  • They are made before the cell ever encounters an antigen.
  • They are encoded by genes assembled by the recombination of segments of DNA.

How antigen receptor diversity is generated.

  • They have a unique binding site.
  • This site binds to a portion of the antigen called an antigenic determinant or epitope.
    The binding, like that between an enzyme and its substrate depends on complementarity of the surface of the receptor and the surface of the epitope.
  • The binding occurs by non-covalent forces (again, like an enzyme binding to its substrate).

Successful binding of the antigen receptor to the epitope, if accompanied by additional signals, results in:

  • stimulation of the cell to leave G0 and enter the cell cycle.
  • Repeated mitosis leads to the development of a clone of cells bearing the same antigen receptor; that is, a clone of cells of the identical specificity.

BCRs and TCRs differ in:

  • their structure;
  • the genes that encode them;
  • the type of epitope to which they bind.

heavy (H) plus kappa (κ) or lambda (λ) chains for BCRs;

alpha (α) and beta (β) or gamma (γ) and delta (δ) chains for TCRs)

……is encoded by several different gene segments.

The genome contains a pool of gene segments for each type of chain. Random assortment of these segments makes the largest contribution to receptor diversity.

There are two types of T cells that differ in their TCR:

alpha/beta (αβ) T cells. Their TCR is a heterodimer of an alpha chain with a beta chain. Each chain has a variable (V) region and a constant (C) region. The V regions each contain 3 hypervariable regions that make up the antigen-binding site. [Link]

gamma/delta (γδ) T cells. Their TCR is also a heterodimer of a gamma chain paired with a delta chain.

The discussion that follows now concerns alpha/beta T cells. Gamma/delta T cells, which are less well understood, are discussed at the end [Link].

The TCR (of alpha/beta T cells) binds a bimolecular complex displayed at the surface of some other cell called an antigen-presenting cell (APC).

Most of the T cells in the body belong to one of two subsets. These are distinguished by the presence on their surface of one or the other of two glycoproteins designated:

  • CD8+ T cells bind epitopes that are part of class I histocompatibility molecules. Almost all the cells of the body express class I molecules.
  • CD4+ T cells bind epitopes that are part of class II histocompatibility molecules. Only specialized antigen-presenting cells express class II molecules.

These include:

  • dendritic cells
  • phagocytic cells like macrophages and
  • B cells!

Building the T-cell Repertoire

T cells have receptors (TCRs) that bind to antigen fragments nestled in MHC molecules. But,

  • all cells express class I MHC molecules containing fragments derived from self proteins;
  • many cells express class II MHC molecules that also contain self peptides.

This presents a risk of the T cells recognizing these self-peptide/self-MHC complexes and mounting an autoimmune attack against them. Fortunately, this is usually avoided by a process of selection that goes on in the thymus (where all T cells develop).

Appendix

FDA approves Abbott Humira as Ulcerative Colitis therapy
PBR Staff Writer Published 01 October 2012
The USFDA has approved Abbott’s Humira (adalimumab) for the treatment of adult patients with moderate to severe Ulcerative Colitis (UC) when certain other medicines have not worked well enough.
Humira, which works by inhibiting tumour necrosis factor-alpha (TNF-alpha), was previously approved for the treatment of moderate to severe Crohn’s disease.

Abbott Global Pharmaceutical Research and Development senior vice president John Leonard said, “Since the first FDA approval of HUMIRA in late 2002, Abbott has continued to investigate the medication in multiple conditions with the goal of bringing this treatment option to more patients who may benefit from it.”

The approval was based on the data from two phase 3 studies, ULTRA 1 and ULTRA 2, both of which enrolled adult patients who had moderately to severely active UC despite concurrent or prior treatment with immunosuppressants.  This should have special significance in view of the past history, which may be explainable, but also keep in mind the serious risks of complications.

It is worthy of comment that anti-TNF treatment was previously rejected in trials for use in sepsis leading to Multiple Organ Dysfunction Syndrome and cardiovascular collapse (shock).  More recently an anti-Factor Xa drug, Xygris,  to prevent hypercoagulability only in severe sepsis was withdrawn.

Anti TNF for sepsis

1.   In a group of patients with elevated interleukin-6 levels, the mortality rate was 243 of 510 (47.6%) in the placebo group and 213 of 488 (43.6%) in the afelimomab group. Using a logistic regression analysis, treatment with afelimomab was associated with an adjusted reduction in the risk of death of 5.8% (p = .041) and a corresponding reduction of relative risk of death of 11.9%. Mortality rates for the placebo and afelimomab groups in the interleukin-6 test negative population were 234 of 819 (28.6%) and 208 of 817 (25.5%), respectively. In the overall population of interleukin-6 test positive and negative patients, the placebo and afelimomab mortality rates were 477 of 1,329 (35.9%)and 421 of 1,305 (32.2%), respectively.

Panacek EAMarshall JCAlbertson TEJohnson DH, at al.  Efficacy and safety of the monoclonal anti-tumor necrosis factor antibody F(ab’)2 fragment afelimomab in patients with severe sepsis and elevated interleukin-6 levelsCrit Care Med. 2004 Nov;32(11):2173-82.

2. No survival benefit was found for the total study population, but patients with increased circulating TNF concentrations at study entry appeared to benefit by the high dose anti-TNF antibody treatment. Increased interleukin (IL)-6 levels predicted a fatal outcome (p =.003), but TNF levels were not found to be a prognostic indicator. TNFlevels were higher (206.7 +/- 60.7 vs. 85.9 +/- 26.1 pg/mL; p <.001) and outcome was poor (41% vs. 71% survival; p =.007) in patients who were in shock at study entry when compared with septic patients not in shock.

Fisher CJ JrOpal SMDhainaut JFStephens S, et al. Influence of an anti-tumor necrosis factor monoclonal antibody on cytokine levels in patients with sepsis. The CB0006 Sepsis Syndrome Study Group.  Critical Care Medicine [1993, 21(3):318-327] (PMID:8440099)

3.  Large clinical trials involving anti-TNF-alpha MAb have proven to be less conclusive and less successful than clinicians had hoped. The International Sepsis Trial (INTERSEPT), reported by Cohen and Carlet,[14] was designed to assess the safety and efficacy of Bay x 1351, a murine MAb to recombinant human TNF-alpha in patients with sepsis. The INTERSEPT trial was an international, multicenter trial involving 564 patients, 420 of whom were in septic shock. The main study end point — 28-day survival — showed no significant benefit for the treatment group vs controls. Prospectively, the researchers identified 2 secondary variables: shock reversal and frequency of organ failure. Post-28-day survival, treatment groups showed a more rapid reversal of shock compared with placebo, as well as a significant delay in time to first organ failure. The researchers concluded that the anti-TNF-alpha antibody may have a role as adjunctive therapy, but that such a putative role requires more in the way of clinical trial confirmation.

In the TNF-alpha MAb Sepsis Study Group trial, also called the North American Sepsis Trial I (NORASEPT I), Abraham and associates[15] evaluated the efficacy and safety of an anti-TNF-alpha MAb in the treatment of patients with sepsis syndrome. A total of 994 patients in 31 hospitals were enrolled in a randomized, prospective, multicenter, double-blind, placebo-controlled clinical trial. Patients were stratified into shock/nonshock subgroups, then randomized to receive a single infusion of 15 mg/kg of anti-TNF-alpha MAb, 7.5 mg/kg of anti-TNF-alpha MAb, or placebo. The researchers found that among all infused patients, there was no difference in mortality among those receiving therapy and those on placebo. In septic shock patients (n = 478), however, there was a trend toward a reduction in all-cause mortality, which was most evident 3 days after infusion. At day 3, 25 of 162 patients treated with the 15 mg/kg dose died; 22 of 156 treated with 7.5 mg/kg died, but 44 of 160 placebo-treated patients died (15 mg/kg: 44% mortality reduction vs placebo, P = .01; 7.5 mg/kg: 48% reduction vs placebo, P = .004). However, at day 28, the reduction in mortality of shock patients was not significant for either dose of the anti-TNF-alpha MAb relative to placebo.

All studies of MAb against TNF in septic patients and found an absolute risk reduction of 3.5%. The most recently published clinical trial found an absolute reduction in mortality of 3.7%.

Of note, therapy with MAb against TNF has been proven efficacious for treatment of rheumatoid arthritis and is approved by the US Food and Drug Administration for this purpose.

New directions in research on severe sepsis. Human trials with TNF alpha.  Medscape.

4. Why the poor results with sepsis?

This would be sufficient for another discussion.  That can be left for another day.

Sepsis

Sepsis syndrome, or sepsis, is an adverse systemic response to infection that includes fever, rapid heartbeat and respiration, low blood pressure and organ dysfunction associated with compromised circulation.

LPS is a major constituent of Gram-negative bacterial cell walls (see section 3-0) and is essential for membrane integrity. The portion of LPS that causes shock is the innermost and most highly conserved phosphoglycolipid, lipid A. Lipid A is a phosphoglycolipid consisting of a core hexosamine disaccharide with ester- and amide-linked acylated fatty acid tails arranged in either asymmetric or symmetric arrays that anchor the structure in the membrane. It acts by potently inducing inflammatory responses that are life-threatening when systemic, and is known as bacterial endotoxin.  Mice deficient in any of the LPS receptor components are more
susceptible to Gram-negative bacterial infection but, at the same time, are less susceptible to the sepsis syndrome.

TLRs have a lethal function in the septic shock syndrome. The physiological function of signaling through phagocyte TLRs is to induce the release of the cytokines TNF, IL-1, IL-6, IL-8 and IL-12 and trigger the inflammatory response, which is critical to containing bacterial infection in the tissues. However, if infection disseminates in the blood, the widespread activation of phagocytes in the bloodstream is catastrophic. Increase in the numbers of circulating neutrophils, or neutrophilia, is driven by effects of colony stimulating factors, such as G-CSF.

Time course of sepsis. The clinical manifestations of sepsis are manifested by successive waves of the serum cytokine cascade. In humans injected with purified LPS, TNF rises almost immediately and peaks at 1.5 h; the sharp decline of TNF may be due to modulation by its soluble receptor sTNFR. A second wave of cytokines that peaks at 3 h activates the acute-phase response
in the liver, the systemic pituitary response (via IL-6 and IL-1), and the activation and chemotaxis of neutrophils (via IL-6, IL-8 and  G-CSF). Neutrophil activation results in the release of lactoferrin from neutrophil secondary granules; the activation of endothelial procoagulants with the rise of tissue plasminogen activator (t-PA). Pituitary-derived adrenocorticotropic hormone (ACTH)  and migration inhibition factor (MIF) peak at 5 h and coincide with peak levels of the regulatory cytokines IL-Ra and IL-10 that counteract the release or activity of inflammatory cytokines. Diffuse endothelial activation is shown by the appearance of soluble E-selectin that peaks at about 8 h and remains elevated for several days.

Susceptibility to LPS Toxicity in Gene Knockout Mice

Defect:
High LPS; Low LPS/D-Gal

Proteins

 

LPS recognition
CD14
LBP
TLR4
MD-2
MyD88
SR-A

phagocyte function
Hck/Fgr
CAM-1
L-selectin
GM-CSF
TNFR1

inflammation
TNFR2
IL-1Ra
IL-1β
IFN-γR
caspase 1
The proteins encoded by the deleted genes are listed. SR-A is scavenger receptor A; Hck and Fgr are Src-family kinases with an essential role in integrin-mediated migration of neutrophils out of the bloodstream.

The Immune Response to Bacterial InfectionSepsis Syndrome: Bacterial Endotoxin
Chapter 9-3.  2007. p 232-233. New Science Press Ltd

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