The cumulative nature of pyruvate's dual mechanism for myocardial protection

Pyruvate Upregulates Hepatic FGF21 Expression by Activating PDE and Inhibiting cAMP–Epac–CREB Signaling Pathway

Fibroblast growth factor 21 (FGF21) functions as a polypeptide hormone to regulate glucose and lipid metabolism, and its expression is regulated by cellular metabolic stress. Pyruvate is an important intermediate metabolite that acts as a key hub for cellular fuel metabolism. However, the effect of pyruvate on hepatic FGF21 expression and secretion remains unknown. Herein, we examined the gene expression and protein levels of FGF21 in human hepatoma HepG2 cells and mouse AML12 hepatocytes in vitro, as well as in mice in vivo. In HepG2 and AML12 cells, pyruvate at concentrations above 0.1 mM significantly increased FGF21 expression and secretion. The increase in cellular cAMP levels by adenylyl cyclase activation, phosphodiesterase (PDE) inhibition and 8-Bromo-cAMP administration significantly restrained pyruvate-stimulated FGF21 expression. Pyruvate significantly increased PDE activities, reduced cAMP levels and decreased CREB phosphorylation. The inhibition of exchange protein directed activated by cAMP (Epac) and cAMP response element binding protein (CREB) upregulated FGF21 expression, upon which pyruvate no longer increased FGF21 expression. The increase in plasma pyruvate levels in mice induced by the intraperitoneal injection of pyruvate significantly increased FGF21 gene expression and PDE activity with a reduction in cAMP levels and CREB phosphorylation in the mouse liver compared with the control. In conclusion, pyruvate activates PDEs to reduce cAMP and then inhibits the cAMP–Epac–CREB signaling pathway to upregulate FGF21 expression in hepatocytes.

Small-Molecule Inhibitors of Reactive Oxygen Species Production

Reactive oxygen species (ROS) are involved in physiological cellular processes including differentiation, proliferation, and apoptosis by acting as signaling molecules or regulators of transcription factors. The maintenance of appropriate cellular ROS levels is termed redox homeostasis, a balance between their production and neutralization. High concentrations of ROS may contribute to severe pathological events including cancer, neurodegenerative, and cardiovascular diseases. In recent years, approaches to target the sources of ROS production directly in order to develop tool compounds or potential therapeutics have been explored. Herein, we briefly outline the major sources of cellular ROS production and comprehensively review the targeting of these by small-molecule inhibitors. We critically assess the value of ROS inhibitors with different mechanisms-of-action, including their potency, mode-of-action, known off-target effects, and clinical or preclinical status, while suggesting future avenues of research in the field.

Protection from systemic pyruvate at resuscitation in newborn lambs with asphyxial cardiac arrest

BACKGROUND

Infants with hypoxic-ischemic injury often require cardiopulmonary resuscitation. Mitochondrial failure to generate adenosine triphosphate (ATP) during hypoxic-ischemic reperfusion injury contributes to cellular damage. Current postnatal strategies to improve outcome in hypoxic-ischemic injury need sophisticated equipment to perform servo-controlled cooling. Administration of intravenous pyruvate, an antioxidant with favorable effects on mitochondrial bioenergetics, is a simple intervention that can have a global impact. We hypothesize that the administration of pyruvate following the return of spontaneous circulation (ROSC) would improve cardiac function, systemic hemodynamics, and oxygen utilization in the brain in newborn lambs with cardiac arrest (CA).

METHODS

Term lambs were instrumented, delivered by C-section and asphyxia induced by umbilical cord occlusion along with clamping of the endotracheal tube until asystole; Lambs resuscitated following 5 min of CA; upon ROSC, lambs were randomized to receive pyruvate or saline infusion over 90 min and ventilated for 150 min postinfusion. Pulmonary and systemic hemodynamics and arterial gases monitored. We measured plasma pyruvate, tissue lactate, and ATP levels (heart and brain) in both groups.

RESULTS

Time to ROSC was not different between the two groups. Systolic and diastolic blood pressures, stroke volume, arterial oxygen content, and cerebral oxygen delivery were similar between the two groups. The cerebral metabolic rate of oxygen was higher following pyruvate infusion; higher oxygen consumption in the brain was associated with lower plasma levels but higher brain ATP levels compared to the saline group.

CONCLUSIONS

Pyruvate promotes energy generation accompanied by efficient oxygen utilization in the brain and may facilitate additional neuroprotection in the presence of hypoxic-ischemic injury.

Escherichia coli mediated resistance of Entamoeba histolytica to oxidative stress is triggered by oxaloacetate

Amebiasis, a global intestinal parasitic disease, is due to Entamoeba histolytica. This parasite, which feeds on bacteria in the large intestine of its human host, can trigger a strong inflammatory response upon invasion of the colonic mucosa. Whereas information about the mechanisms which are used by the parasite to cope with oxidative and nitrosative stresses during infection is available, knowledge about the contribution of bacteria to these mechanisms is lacking. In a recent study, we demonstrated that enteropathogenic Escherichia coli O55 protects E. histolytica against oxidative stress. Resin-assisted capture (RAC) of oxidized (OX) proteins coupled to mass spectrometry (OX-RAC) was used to investigate the oxidation status of cysteine residues in proteins present in E. histolytica trophozoites incubated with live or heat-killed E. coli O55 and then exposed to H2O2-mediated oxidative stress. We found that the redox proteome of E. histolytica exposed to heat-killed E. coli O55 is enriched with proteins involved in redox homeostasis, lipid metabolism, small molecule metabolism, carbohydrate derivative metabolism, and organonitrogen compound biosynthesis. In contrast, we found that proteins associated with redox homeostasis were the only OX-proteins that were enriched in E. histolytica trophozoites which were incubated with live E. coli O55. These data indicate that E. coli has a profound impact on the redox proteome of E. histolytica. Unexpectedly, some E. coli proteins were also co-identified with E. histolytica proteins by OX-RAC. We demonstrated that one of these proteins, E. coli malate dehydrogenase (EcMDH) and its product, oxaloacetate, are key elements of E. coli-mediated resistance of E. histolytica to oxidative stress and that oxaloacetate helps the parasite survive in the large intestine. We also provide evidence that the protective effect of oxaloacetate against oxidative stress extends to Caenorhabditis elegans.

Pyruvate Protects Giardia Trophozoites from Cysteine-Ascorbate Deprived Medium Induced Cytotoxicity

Giardia lamblia, an anaerobic, amitochondriate protozoan parasite causes parasitic infection giardiasis in children and young adults. It produces pyruvate, a major metabolic product for its fermentative metabolism. The current study was undertaken to explore the effects of pyruvate as a physiological antioxidant during oxidative stress in Giardia by cysteine-ascorbate deprivation and further investigation upon the hypothesis that oxidative stress due to metabolism was the reason behind the cytotoxicity. We have estimated intracellular reactive oxygen species generation due to cysteine-ascorbate deprivation in Giardia. In the present study, we have examined the effects of extracellular addition of pyruvate, during oxidative stress generated from cysteine-ascorbate deprivation in culture media on DNA damage in Giardia. The intracellular pyruvate concentrations at several time points were measured in the trophozoites during stress. Trophozoites viability under cysteine-ascorbate deprived (CAD) medium in presence and absence of extracellular pyruvate has also been measured. The exogenous addition of a physiologically relevant concentration of pyruvate to trophozoites suspension was shown to attenuate the rate of ROS generation. We have demonstrated that Giardia protects itself from destructive consequences of ROS by maintaining the intracellular pyruvate concentration. Pyruvate recovers Giardia trophozoites from oxidative stress by decreasing the number of DNA breaks that might favor DNA repair.

Neuroprotective profile of pyruvate against ethanol-induced neurodegeneration in developing mice brain

Exposure to ethanol during developmental stages leads to several types of neurological disorders. Apoptotic neurodegeneration due to ethanol exposure is a main feature in alcoholism. Exposure of developing animals to alcohol induces apoptotic neuronal death and causes fetal alcohol syndrome. In the present study, we observed the possible protective effect of pyruvate against ethanol-induced neurodegeneration. Exposure of developing mice to ethanol (2.5 g/kg) induces apoptotic neurodegeneration and widespread neuronal cell death in the cortex and thalamus. Co-treatment of pyruvate (500 mg/kg) protects neuronal cell against ethanol by the reduced expression of caspase-3 in these brain regions. Immunohistochemical analysis and TUNNEL at 24 h showed that apoptotic cell death induced by ethanol in the cortex and thalamus is reduced by pyruvate. Histomorphological analysis at 24 h with cresyl violet staining also proved that pyruvate reduced the number of neuronal cell loss in the cortex and thalamus. The results showed that ethanol increased the expression of caspase-3 and thus induced apoptotic neurodegeneration in the developing mice cortex and thalamus, while co-treatment of pyruvate inhibits the induction of caspase-3 and reduced the cell death in these brain regions. These findings, therefore, showed that treatment of pyruvate inhibits ethanol-induced neuronal cell loss in the postnatal seven (P7) developing mice brain and may appear as a safe neuroprotectant for treating neurodegenerative disorders in newborns and infants.

Absence of glucose transporter 4 diminishes electrical activity of mouse hearts during hypoxia

Insulin resistance, which characterizes type 2 diabetes, is associated with reduced translocation of glucose transporter 4 (GLUT4) to the plasma membrane following insulin stimulation, and diabetic patients with insulin resistance show a higher incidence of ischaemia, arrhythmias and sudden cardiac death. The aim of this study was to examine whether GLUT4 deficiency leads to more severe alterations in cardiac electrical activity during cardiac stress due to hypoxia. To fulfil this aim, we compared cardiac electrical activity from cardiac-selective GLUT4-ablated (G4H-/-) mouse hearts and corresponding control (CTL) littermates. A custom-made cylindrical 'cage' electrode array measured potentials (Ves) from the epicardium of isolated, perfused mouse hearts. The normalized average of the maximal downstroke of Ves ( (|d Ves/dt(min)|na), which we previously introduced as an index of electrical activity in normal, ischaemic and hypoxic hearts, was used to assess the effects of GLUT4 deficiency on electrical activity. The |d Ves/dt(min)|na of G4H −/− and CTL hearts decreased by 75 and 47%, respectively (P < 0.05), 30 min after the onset of hypoxia. Administration of insulin attenuated decreases in values of |d Ves/dt(min)|na in G4H −/− hearts as well as in CTL hearts, during hypoxia. In general, however, G4H −/− hearts showed a severe alteration of the propagation sequence and a prolonged total activation time. Results of this study demonstrate that reduced glucose availability associated with insulin resistance and a reduction in GLUT4-mediated glucose transport impairs electrical activity during hypoxia, and may contribute to cardiac vulnerability to arrhythmias in diabetic patients.

Different effects of monocarboxylates on neuronal survival and beta-amyloid toxicity

Glucose is a principal metabolic fuel in the central nervous system, but, when glucose is unavailable, the brain can utilize alternative metabolic substrates such as monocarboxylates to sustain brain functions. This study examined whether the replacement of glucose with monocarboxylates (particularly pyruvate and lactate) had an equivalent effect of glucose on neuronal survival in rat hippocampal organotypic slice cultures, or ameliorate the neurotoxicity induced by amyloid beta-peptide (Abeta). The possible mechanism was also explored. We found that pyruvate and lactate alone increased cell death in the hippocampal slice cultures at 24 and 48 h. Supplementation of glucose-containing culture media and Abeta-treated culture media with pyruvate, but not lactate, attenuated cell death as strong as with trolox, known as a reactive oxygen species scavenger, and niacinamide, an NAD(+) precursor, and this protective effect was reversed by alpha-cyano-4-hydroxycinnamic acid. Pyruvate significantly increased the aconitase activity and the NAD(+) levels in the hippocampal slices in the presence of Abeta, but did not maintain the ATP levels. Our results indicate that pyruvate and lactate alone cannot replace glucose as an alternative energy source to preserve the neuronal viability in the hippocampal slice cultures. Pyruvate, in the presence of glucose, improves neuronal survival in the hippocampal slice cultures and also protects neurons against Abeta-induced cell death in which mitochondrial NAD(P) redox status may play a central role.

Oxidant Stress and Damage in Post-Ischemic Mouse Hearts: Effects of Adenosine

Despite the general understanding that ischemia-reperfusion (I/R) promotes oxidant stress, specific contributions of oxidant stress or damage to myocardial I/R injury remain poorly defined. Moreover, whether endogenous 'cardioprotectants' such as adenosine act via limiting this oxidant injury is unclear. Herein we characterized effects of 20 min ischemia and 45 min reperfusion on cardiovascular function, oxidative stress and damage in isolated perfused mouse hearts (with glucose or pyruvate as substrate), and examined whether 10 microM adenosine modified these processes. In glucose-perfused hearts post-ischemic contractile function was markedly impaired (< 50% of pre-ischemia), cell damage assessed by lactate dehydrogenase (LDH) release was increased (12 +/- 2 IU/g vs. 0.2 +/- 0.1 IU/g in normoxic hearts), endothelial-dependent dilation in response to ADP was impaired while endothelial-independent dilation in response to nitroprusside was unaltered. Myocardial oxidative stress increased significantly, based on decreased glutathione redox status ([GSSG]/[GSG + GSSH] = 7.8 +/- 0.3% vs. 1.3 +/- 0.1% in normoxic hearts). Tissue cholesterol, native cholesteryl esters (CE) and the lipid-soluble antioxidant alpha-tocopherol (alpha-TOH, the most biologically active form of vitamin E) were unaffected by I/R, whereas markers of primary lipid peroxidation (CE-derived lipid hydroperoxides and hydroxides; CE-O(O)H) increased significantly (14 +/- 2 vs. 2 +/- 1 pmol/mg in normoxic hearts). Myocardial alpha -tocopherylquinone (alpha-TQ; an oxidation product of alpha -TOH) also increased (10.3 +/- 1.0 vs. 1.7 +/- 0.2 pmol/mg in normoxic hearts). Adenosine treatment improved functional recovery and vascular function, and limited LDH efflux. These effects were associated with an anti-oxidant effect of adenosine, as judged by inhibition of I/R-mediated changes in glutathione redox status (by 60%), alpha-TQ (80%) and CE-O(O)H (100%). Provision of 10 mM pyruvate as sole substrate (to by-pass glycolysis) modestly reduced I/R injury and changes in glutathione redox status and alpha-TQ, but not CE-O(O)H. Adenosine exerted further protection and anti-oxidant actions in these hearts. Functional recoveries and LDH efflux correlated inversely with oxidative stress and alpha -TQ (but not CE-O(O)H) levels. Collectively, our data reveal selective oxidative events in post-ischemic murine hearts, which are effectively limited by adenosine (independent of substrate). Correlation of post-ischemic cardiovascular outcomes with specific oxidative events (glutathione redox state, alpha-TQ) supports an important anti-oxidant component to adenosinergic protection.

Pyruvate provides cardioprotection in the experimental model of myocardial ischemic reperfusion injury

The present study was designed to evaluate the cardioprotective potential of pyruvate and to characterize the mechanism underlying the protection. Wistar albino rats were randomly divided into three groups. Two groups were administered saline orally (sham, ischemia-reperfusion (I-R) control group) and animals of third group received pyruvate (500 mg/kg) for 4 weeks. On the 29th day, animals of the I-R control and pyruvate treated groups underwent 45 min of occlusion of the left anterior descending (LAD) coronary artery and were thereafter reperfused for 60 min. In the I-R control group, a significant cardiac necrosis, depressed mean arterial pressure (MAP) and heart rate (HR), decline in myocardial antioxidant status and elevation in lipid peroxidation were observed as compared to sham control. Pyruvate treatment restored the myocardial antioxidant status and favorably modulated the altered MAP as compared to I-R control. Furthermore, I/R-induced lipid peroxidation was significantly inhibited by pyruvate treatment. These beneficial cardioprotective effects translated into significant improvement in MAP. Histopathological examination and restored specific myocardial injury marker CK-MB isoenzyme activity further confirmed protective effects of pyruvate. In conclusion, our study has demonstrated that the beneficial effect of pyruvate likely results from improved MAP and suppression of oxidative stress.

Metabolic cardioprotection by pyruvate: recent progress

Pyruvate, a natural metabolic fuel and antioxidant in myocardium and other tissues, exerts a variety of cardioprotective actions when provided at supraphysiological concentrations. Pyruvate increases cardiac contractile performance and myocardial energy state, bolsters endogenous antioxidant systems, and protects myocardium from ischemia-reperfusion injury and oxidant stress. This article reviews and discusses basic and clinically oriented research conducted over the last several years that has yielded fundamental information on pyruvate's inotropic and cardioprotective mechanisms. Particular attention is placed on pyruvate's enhancement of sarcoplasmic reticular Ca2+ transport, its antioxidant properties, and its ability to mitigate reversible and irreversible myocardial injury. These research efforts are establishing the essential foundation for clinical application of pyruvate therapy in numerous settings including cardiopulmonary bypass surgery, cardiopulmonary resuscitation, myocardial stunning, and cardiac failure.

The intermediary metabolite pyruvate attenuates stunning and reduces infarct size in in vivo porcine myocardium

The intermediary metabolite pyruvate has been shown to exert significant beneficial effects in in vitro models of myocardial oxidative stress and ischemia-reperfusion injury. However, there have been few reports of the ability of pyruvate to attenuate myocardial stunning or reduce infarct size in vivo. This study tested whether supraphysiological levels of pyruvate protect against reversible and irreversible in vivo myocardial ischemia-reperfusion injury. Anesthetized, open-chest pigs ( n = 7/group) underwent 15 min of left anterior descending coronary artery (LAD) occlusion and 3 h of reperfusion to induce stunning. Load-insensitive contractility measurements of regional preload recruitable stroke work (PRSW) and PRSW area (PRSWA) were generated. Vehicle or pyruvate (100 mg/kg iv bolus + 10 mg·kg–1·min–1 intra-atrial infusion) was administered during ischemia and for the first hour of reperfusion. In infarct studies, pigs ( n = 6/group) underwent 1 h of LAD ischemia and 3 h of reperfusion. Group I pigs received vehicle or pyruvate for 30 min before and throughout ischemia. In group II, the infusion was extended through 1 h of reperfusion. In the stunning protocol, pyruvate significantly improved the recovery of PRSWA at 1 h (50 ± 4% vs. 23 ± 3% in controls) and 3 h (69 ± 5% vs. 39 ± 3% in controls) reperfusion. Control pigs exhibited infarct sizes of 66 ± 1% of the area at risk. The pyruvate I protocol was associated with an infarct size of 49 ± 3% ( P < 0.05), whereas the pyruvate II protocol was associated with an infarct size of 30 ± 2% ( P < 0.05 vs. control and pyruvate I). These findings suggest that pyruvate attenuates stunning and decreases myocardial infarction in vivo in part by reduction of reperfusion injury. Metabolic interventions such as pyruvate should be considered when designing the optimal therapeutic strategies for limiting myocardial ischemia-reperfusion injury.

Hypoxia-induced lipid peroxidation in rat brain and protective effect of carnitine and phosphocreatine

The exposure to hypobaric hypoxia increased lipid peroxidation as indicated by thiobarbituric acid-reactive substances [TBARS] in rat brain. Plasma lactate/pyruvate ratio was used as a marker of hypoxia. We compared the protective effect of alpha-tocopherol with the effect of L-carnitine or phosphocreatine. Rats pretreated with alpha-tocopherol, L-carnitine, or phosphocreatine had lower TBARS levels after the exposure to hypobaric hypoxia. However, lactate/ pyruvate ratio was improved only in rats pretreated with L-carnitine or phosphocreatine. We conclude from our data that, contrary to alpha-tocopherol, protective effects of L-carnitine and phosphocreatine administrations are due to their regulation of metabolic reactions during hypobaric hypoxia rather than to their scavenger activity.

Pyruvate restores contractile function and antioxidant defenses of hydrogen peroxide-challenged myocardium

PURPOSE

Pyruvate, a natural energy-yielding fuel in myocardium, neutralizes peroxides by a direct decarboxylation reaction, and indirectly augments the glutathione (GSH) antioxidant system by generating NADPH reducing power via citrate formation. The possibility that pyruvate's antioxidant actions could mediate its enhancement of contractile performance in prooxidant-challenged myocardium was investigated in isolated working guinea-pig hearts reversibly injured by hydrogen peroxide.

METHODS

Hearts were challenged by 10 min perfusion with 100 microM H(2)O(2), followed by 90 min H(2)O(2)-free perfusion. Metabolic and antioxidant treatments (each 5m M) were administered at 30-90 min post-H(2)O(2). Phosphocreatine phosphorylation state, GSH/glutathione disulfide redox potential (GSH/GSSG) and key enzyme activities were measured in snap-frozen myocardium.

RESULTS

H(2)O(2) exposure depleted myocardial energy and antioxidant reserves and produced marked contractile impairment that persisted throughout the H(2)O(2) washout period. Relative to untreated post-H(2)O(2) myocardium, pyruvate restored contractile performance, increased GSH/GSSG 52% and maintained phosphocreatine phosphorylation state; in contrast, lactate lowered cardiac performance and phosphorylation state. Neither the pharmacological antioxidant N -acetylcysteine (NAC) nor the pyruvate analog alpha-ketobutyrate increased cardiac function; both treatments increased GSH/GSSG but lowered phosphocreatine potential. H(2)O(2) partially inactivated aconitase, creatine kinase and glyceraldehyde 3-phosphate dehydrogenase (GAPDH), but all three enzymes spontaneously recovered during H(2)O(2) washout. Pyruvate did not further activate these enzymes and unexpectedly inhibited GAPDH by 60-70%.

CONCLUSION

Pyruvate promoted robust contractile recovery of H(2)O(2)-challenged myocardium by the combination of citrate-mediated antioxidant mechanisms and maintenance of myocardial energy reserves.

NAD-dependent malate dehydrogenase protects against oxidative damage in Escherichia coli K-12 through the action of oxaloacetate

Reactive oxygen species including hydrogen peroxide (H(2)O(2)) and hydroxyl radical (OH) can be generated by ionizing radiation and has the potential to induce diseases. We provide the evidence that NAD-dependent malate dehydrogenase (MDH) is involved in the antioxidant role in preventing H(2)O(2) or γ-radiation-induced damage in Escherichia coli through the action of oxaloacetate. The E. colimdh mutant strain defective in MDH activity was more sensitive to H(2)O(2) or γ-radiation than was the wild type strain, when challenged in the exponential growth phase. The mdh mutant cells pretreated with oxaloacetate (2.5 mM), a product of NAD-dependent MDH activity, prior to H(2)O(2) treatment or γ-irradiation are resistant to H(2)O(2) or γ-radiation-induced damage, so cell survivability is restored to similar levels with the wild type. The SOS induction of umu'-'lacZ fusion gene by H(2)O(2) is significantly repressed by pretreatment of oxaloacetate in a dose-dependent way. These results indicate that oxaloacetate effectively protects E. coli cells against damage caused by oxidative stress. Oxaloacetate strongly prevented the DNA strand breaks by OH in a metal-catalyzed oxidation (MCO) system that generated H(2)O(2) as a mediator. By contrast, the prevention of DNA damage by oxaloacetate in an γ-irradiation system that directly generates OH from H(2)O in vitro was far less than that in an MCO system. Our results demonstrated that oxaloacetate, metabolite of NAD-dependent MDH action, plays a role as an antioxidant, possibly by scavenging H(2)O(2).

Sodium pyruvate is better than sodium chloride as a resuscitation solution in a rodent model of profound hemorrhagic shock

Pyruvate is an energy substrate that has both inotropic and antioxidant properties. In this study, we tested the hypothesis that survivorship would be better after resuscitation with 1.7% sodium pyruvate than 0.9% sodium chloride in a profound hemorrhagic shock model. The study was performed in a blinded manner. Rats were randomly assigned into two groups (ten in each group), a sodium chloride resuscitation group and a sodium pyruvate resuscitation group. After a 60-min shock period, we infused 80 ml/kg of a resuscitation solution. We continuously monitored mean arterial pressure and heart rate for 50 min after resuscitation. We recognized death by the disappearance of blood pressure pulsation and precordial movement. We performed a comparison of survivorship at 50 min post resuscitation using a Z-test of proportions. Nine (90%) of the animals that received sodium pyruvate were living 50 min after resuscitation, whereas only three (30%) of the animals that received sodium chloride survived to the same time point. We conclude that sodium pyruvate is better than sodium chloride as a resuscitation solution in a model of profound hemorrhagic shock.

Pyruvate: metabolic protector of cardiac performance

Pyruvate, a metabolic product of glycolysis and an oxidizable fuel in myocardium, increases cardiac mechanical performance and energy reserves, especially when supplied at supraphysiological concentrations. The inotropic effects of pyruvate are most impressive in hearts that have been reversibly injured (stunned) by ischemia/reperfusion stress. Glucose appears to be an essential co-substrate for pyruvate's salutary effects in stunned hearts, but other fuels including lactate, acetate, fatty acids, and ketone bodies produce little or no improvement in postischemic function over glucose alone. In contrast to pharmacological inotropism by catecholamines, metabolic inotropism by pyruvate increases cardiac energy reserves and bolsters the endogenous glutathione antioxidant system. Pyruvate enhancement of cardiac function may result from one or more of the following mechanisms: increased cytosolic ATP phosphorylation potential and Gibbs free energy of ATP hydrolysis, enhanced sarcoplasmic reticular calcium ion uptake and release, decreased cytosolic inorganic phosphate concentration, oxyradical scavenging via direct neutralization of peroxides and/or enhancement of the intracellular glutathione/NADPH antioxidant system, and/or closure of mitochondrial permeability transition pores. This review aims to summarize evidence for each of these mechanisms and to consider the potential utility of pyruvate as a therapeutic intervention for clinical management of cardiac insufficiency.

Antioxidative properties of pyruvate and protection of the ischemic rat heart during cardioplegia

Formation of oxygen free radicals during heart transplantation seems to be related to the alterations occurring during ischemia and reperfusion and could explain the short preservation time of donor hearts. The aim of our study was (a) to analyze the protective effects of pyruvate during cold cardioplegia and ischemia/reperfusion sequence, and (b) to investigate in vitro the radical scavenging properties of this compound. After 30 min of perfusion, isolated working rat hearts were arrested by cardioplegic solution, stored 4 h in B21 solutions at 4 degrees C, and reperfused with Krebs-Henseleit buffer for 45 min. Pyruvate (2 mM) was added to Krebs-Henseleit, cardioplegic, and storage solutions, and functional parameters were recorded throughout the experiments. In a second part, control hearts and hearts treated with pyruvate were cannulated via the aorta and perfused for 30 min by the Langendorff method, arrested by cardioplegic solution, stored 4 h in B21 solutions at 4 degrees C, and reperfused for 45 min by the Langendorff method. Malonedialdehyde and alpha-tocopherol levels were determined on heart homogenate. In situ detection of apoptotic cells also was performed on tissue samples (left ventricle) at the end of the ischemia/reperfusion sequence. To demonstrate in vitro the antioxidant effects of pyruvate, we monitored (a) its hydroxyl radical scavenging properties by using electron paramagnetic resonance (EPR) spectroscopy, and (b) the decrease of fluorescence of allophycocyanin, in the presence of a Fenton system (H2O2/Cu2+). Ischemia for 4 h, followed by myocardial reperfusion, resulted in substantially reduced mechanical function. Hearts subjected to this ischemia and pretreated with pyruvate showed a significant improvement in the function recovery. After the ischemia/reperfusion protocol, no significant decrease of malonedialdehyde levels was shown on hearts treated with pyruvate. However, alpha-tocopherol levels were higher in the pyruvate group compared with the control group. At the end of the reperfusion period, levels of apoptotic cells were significantly lower in hearts treated with pyruvate compared with control hearts. EPR studies showed that pyruvate was an efficient hydroxyl scavenger, with a median inhibitory concentration (IC50) of 8 mM. The allophycocyanin assay also showed a dose-dependent effect of pyruvate against hydroxyl radicals. In conclusion, these findings showed that pyruvate could prevent reperfusion injuries in the isolated heart, probably by its antioxidative properties. The application of pyruvate may contribute to the preservation of hearts for organ transplantation.

Antioxidant properties of pyruvate mediate its potentiation of beta-adrenergic inotropism in stunned myocardium

This study tested the hypothesis that pyruvate's antioxidant actions, particularly its enhancement of the endogenous glutathione system, mediate its potentiation of beta-adrenergic inotropism in stunned myocardium. Isolated working guinea pig hearts, metabolizing 10 m M glucose and stunned by 45 min of low flow ischemia, were treated with 5 m M pyruvate, 5 m M N-acetylcysteine (NAC) and/or 2 n M isoproterenol beginning 15 min after reperfusion. The antioxidant NAC alone did not increase cardiac power (mJ/min/g wet: 11 +/- 1 in untreated and 15 +/- 2 in NAC treated stunned hearts), but NAC potentiated the increase in power produced by 2 n M isoproterenol (isoproterenol alone: 50+/-10; NAC plus isoproterenol: 133 +/- 24). Addition of NAC doubled cyclic AMP content but lowered cytosolic phosphorylation potential by 32% in isoproterenol-stimulated hearts. Stunning decreased the glutathione antioxidant ratio (GSH/GSSG) by 68%. The antioxidant ratio was completely restored by pyruvate alone or in combination with isoproterenol, but only partially restored by isoproterenol alone. Combining isoproterenol and NAC increased the GSH/GSSG ratio by an additional 36%. The combined treatment of pyruvate and isoproterenol increased the NADPH/NADP(+) ratio almost three-fold, and produced the greatest accumulation of glucose-6-phosphate of any treatment.

CONCLUSIONS

like pyruvate, the antioxidant NAC potentiated beta-adrenergic inotropism of stunned myocardium. Unlike pyruvate, NAC did not increase cellular energy reserves, thus effectively limiting its potentiation of beta-adrenergic stimulation. Thus, pyruvate's potentiation of beta-adrenergic stimulation in stunned myocardium is most likely the result of the combined effects of its antioxidant and energetic properties.

Bioenergetic effect of liposomal coenzyme Q10 on myocardial ischemia reperfusion injury

The antioxidant and bioenergetic effects of CoQ10 are well known but its clinical utility is limited by the requirement for enteral administration. A newly developed liposomal CoQ10 (CoQ) is water soluble and capable of intravenous administration. The purpose of this study is to determine the mechanism by which acute administration CoQ protects myocardium from reperfusion (Rp) injury. Rats were pretreated with CoQ 10 mg/kg i.v. 30 min prior to the experiment. Control rats were pretreated with liposome only. Hearts were excised and subjected to equilibration, 25 min of normothermic ischemia and 40 min of Rp on a Langendorff apparatus. At end Rp, CoQ hearts recovered 74 +/- 5% of their DP vs. 50 +/- 9% in control (p < 0.05). Aerobic efficiency was maintained (0.66 +/- 0.02 vs. control, 0.5 +/- 0.04, p < 0.003) and CoQ hearts lost less CK activity vs. control (p < 0.02). PCr and ATP were higher than control (p < 0.05, 0.02, respectively). Results show that i.v. CoQ improves recovery of function, aerobic efficiency, CK activity, and recovery of PCr and ATP after Rp. This suggests that acute administration of liposomal CoQ improves myocardial tolerance to I/R via its role as an antioxidant as well as improving oxygen utilization and high energy phosphate production.

Pyruvate protects neurons against hydrogen peroxide-induced toxicity

Hydrogen peroxide (H2O2) is suspected to be involved in numerous brain pathologies such as neurodegenerative diseases or in acute injury such as ischemia or trauma. In this study, we examined the ability of pyruvate to improve the survival of cultured striatal neurons exposed for 30 min to H2O2, as estimated 24 hr later by the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazoliumbromide assay. Pyruvate strongly protected neurons against both H2O2 added to the external medium and H2O2 endogenously produced through the redox cycling of the experimental quinone menadione. The neuroprotective effect of pyruvate appeared to result rather from the ability of alpha-ketoacids to undergo nonenzymatic decarboxylation in the presence of H2O2 than from an improvement of energy metabolism. Indeed, several other alpha-ketoacids, including alpha-ketobutyrate, which is not an energy substrate, reproduced the neuroprotective effect of pyruvate. In contrast, lactate, a neuronal energy substrate, did not protect neurons from H2O2. Optimal neuroprotection was achieved with relatively low concentrations of pyruvate (</=1 mM), whereas at high concentration (10 mM) pyruvate was ineffective. This paradox could result from the cytosolic acidification induced by the cotransport of pyruvate and protons into neurons. Indeed, cytosolic acidification both enhanced the H2O2-induced neurotoxicity and decreased the rate of pyruvate decarboxylation by H2O2. Together, these results indicate that pyruvate efficiently protects neurons against both exogenous and endogenous H2O2. Its low toxicity and its capacity to cross the blood-brain barrier open a new therapeutic perspective in brain pathologies in which H2O2 is involved.

The mechanisms of coenzyme Q10 as therapy for myocardial ischemia reperfusion injury

It has been hypothesized that CoQ10 (CoQ) pretreatment protects myocardium from ischemia reperfusion (I/R) injury by its ability to increase aerobic energy production as well as its activity as an antioxidant. Isolated hearts from rats pretreated with either CoQ 20 mg/kg i.m. and 10 mg/kg i.p. or vehicle 24 and 2 h prior to the experiment, were subjected to 15 min of equilibration (EQ), 25 min of ischemia, and 40 min of reperfusion (RP). Developed pressure, +/-dp/dt, myocardial oxygen consumption, and myocardial aerobic efficiency (DP/MVO2) were measured. 31P NMR spectroscopy was used to determine ATP and PCr concentrations. Lucigenin-enhanced chemiluminescence of the coronary sinus effluent was utilized to determine oxidative stress through the protocol. CoQ pretreatment improved myocardial function after ischemia reperfusion. CoQ pretreatment improved tolerance to myocardial ischemia reperfusion injury by its ability to increase aerobic energy production, and by preserving myocardial aerobic efficiency during reperfusion. Furthermore, the oxidative burst during RP was diminished with CoQ. Similarly it was hypothesized that CoQ protected coronary vascular reactivity after I/R via an antioxidant mechanism. Utilizing a newly developed lyposomal CoQ preparation given i.v. 15 min prior to ischemia, ischemia reperfusion was carried out on Langendorff apparatus as previously described. Just prior to ischemia and after RP, hearts were challenged with bradykinin (BK) and sodium nitroprusside (SNP) and change in coronary flow was measured. CoQ pretreatment protected endothelial-dependent and endothelial-independent vasodilation after I/R. We conclude that CoQ pretreatment protects coronary vascular reactivity after I/R via OH radical scavenger action.

Elucidation of a tripartite mechanism underlying the improvement in cardiac tolerance to ischemia by coenzyme Q10 pretreatment

Coenzyme Q10, which is involved in mitochondrial adenosine triphosphate production, is also a powerful antioxidant. We hypothesize that coenzyme Q10 pretreatment protects myocardium from ischemia reperfusion injury both by its ability to increase aerobic energy production and by protecting creatine kinase from oxidative inactivation during reperfusion. Isolated hearts (six per group) from rats pretreated with either coenzyme Q10, 20 mg/kg intramuscularly and 10 mg/kg intraperitoneally (treatment) or vehicle only (control) 24 and 2 hours before the experiment were subjected to 15 minutes of equilibration, 25 minutes of ischemia, and 40 minutes of reperfusion. Developed pressure, contractility, compliance, myocardial oxygen consumption, and myocardial aerobic efficiency were measured. Phosphorus 31 nuclear magnetic resonance (31P-NMR) spectroscopy was used to determine adenosine triphosphate and phosphocreatine concentrations as a percentage of a methylene diphosphonic acid standard. Hearts were assayed for myocardial coenzyme Q10 and myocardial creatine kinase activity at end equilibration and at reperfusion. Treated hearts showed higher myocardial coenzyme Q10 levels (133 +/- 5 micrograms/gm ventricle versus 117 +/- 4 micrograms/gm ventricle, p < 0.05). Developed pressure at end reperfusion was 62% +/- 2% of equilibration in treatment group versus 37% +/- 2% in control group, p < 0.005. Preischemic myocardial aerobic efficiency was preserved during reperfusion in treatment group (0.84 +/- 0.08 mm Hg/(microliter O2/min/gm ventricle) vs 1.00 +/- 0.08 mm Hg/(microliter O2/min/gm ventricle) at equilibration, p = not significant), whereas in the control group it fell to 0.62 +/- 0.07 mm Hg/(microliter O2/min/gm ventricle, p < 0.05 vs equilibration and vs the treatment group at reperfusion. Treated hearts showed higher adenosine triphosphate and phosphocreatine levels during both equilibration (adenosine triphosphate 49% +/- 2% for the treatment group vs 33% +/- 3% in the control group, p < 0.005; phosphocreatine 49% +/- 3% in the treatment group vs 35% +/- 3% in the control group, p < 0.005) and reperfusion (adenosine triphosphate 18% +/- 3% in the treatment group vs 11% +/- 2% in the control group, CTRL p < 0.05; phosphocreatine 45% +/- 2% in the treatment group vs 23% +/- 3% in the control group, p < 0.005). Creatine kinase activity in treated hearts at end reperfusion was 74% +/- 3% of equilibration activity vs 65% +/- 2% in the control group, p < 0.05). Coenzyme Q10 pretreatment improves myocardial function after ischemia and reperfusion. This results from a tripartite effect: (1) higher concentration of adenosine triphosphate and phosphocreatine, initially and during reperfusion, (2) improved myocardial aerobic efficiency during reperfusion, and (3) protection of creatine kinase from oxidative inactivation during reperfusion.