Blockade of Electron Transport during Ischemia Protects Cardiac Mitochondria

Nitrite augments tolerance to ischemia/reperfusion injury via the modulation of mitochondrial electron transfer

Nitrite (NO(2)(-)) is an intrinsic signaling molecule that is reduced to NO during ischemia and limits apoptosis and cytotoxicity at reperfusion in the mammalian heart, liver, and brain. Although the mechanism of nitrite-mediated cytoprotection is unknown, NO is a mediator of the ischemic preconditioning cell-survival program. Analogous to the temporally distinct acute and delayed ischemic preconditioning cytoprotective phenotypes, we report that both acute and delayed (24 h before ischemia) exposure to physiological concentrations of nitrite, given both systemically or orally, potently limits cardiac and hepatic reperfusion injury. This cytoprotection is associated with increases in mitochondrial oxidative phosphorylation. Remarkably, isolated mitochondria subjected to 30 min of anoxia followed by reoxygenation were directly protected by nitrite administered both in vitro during anoxia or in vivo 24 h before mitochondrial isolation. Mechanistically, nitrite dose-dependently modifies and inhibits complex I by posttranslational S-nitrosation; this dampens electron transfer and effectively reduces reperfusion reactive oxygen species generation and ameliorates oxidative inactivation of complexes II-IV and aconitase, thus preventing mitochondrial permeability transition pore opening and cytochrome c release. These data suggest that nitrite dynamically modulates mitochondrial resilience to reperfusion injury and may represent an effector of the cell-survival program of ischemic preconditioning and the Mediterranean diet.

Local delivery of PKCepsilon-activating peptide mimics ischemic preconditioning in aged hearts through GSK-3beta but not F1-ATPase inactivation

In adult heart, selective PKCepsilon activation limits ischemia (I)-reperfusion (R) damage and mimics the protection associated with ischemic preconditioning. We sought to determine whether local delivery of PKCepsilon activator peptide psiepsilon-receptor for activated C-kinase (psiepsilon-RACK) is sufficient to produce a similarly protected phenotype in aged hearts. Langendorff-perfused hearts isolated from adult (5 mo; n = 9) and aged (24 mo; n = 9) male Fisher 344 rats were perfused with psiepsilon-RACK conjugated to Tat (500 nM) or Tat only (500 nM) for 10 min before global 31-min ischemia. Western blotting was used to measure mitochondrial targeting of PKCepsilon, PKCdelta, phospho (p)-GSK-3beta (Ser(9)) and GSK-3beta in hearts snap-frozen during I. Recovery of left ventricular developed pressure was significantly improved by psiepsilon-RACK (P < 0.01) and infarct size reduced in 24-mo rats vs. age-matched controls (60% vs. 34%; P < 0.01). Mitochondrial PKCepsilon levels were 30% greater during I with psiepsilon-RACK in aged vs. control rats (P < 0.01). Interestingly, mitochondrial GSK-3beta levels were threefold greater in aged vs. adult rats during I, and psiepsilon-RACK prevented this increase (P < 0.01). Mitochondrial p-GSK-3beta levels were also greater in aged rats after psiepsilon-RACK (P < 0.01), and subsequent inhibition of GSK-3beta with SB-216763 (3 muM) before I/R elicited protection similar to that of psiepsilon-RACK (n = 3/group). Mitochondrial proteomic analysis further identified group differences in the F(1)-ATPase beta-subunit, and coimmunoprecipitation studies revealed a novel interaction with PKCepsilon. F(1)-ATPase-PKCepsilon association was affected by psiepsilon-RACK in adult but not aged rats. Our results provide evidence, for the first time, for PKCepsilon-mediated protection in aged rat heart after I/R and suggest a central role for mitochondrial GSK-3beta but not F(1)-ATPase as a potential target of PKCepsilon to limit I/R damage with aging.

Ischemic preconditioning does not protect via blockade of electron transport

Ischemic preconditioning (IPC) before sustained ischemia decreases myocardial infarct size mediated in part via protection of cardiac mitochondria. Reversible blockade of electron transport at complex I immediately before sustained ischemia also preserves mitochondrial respiration and decreases infarct size. We proposed that IPC would attenuate electron transport from complex I as a potential effector mechanism of cardioprotection. Isolated, Langendorff-perfused rat hearts underwent IPC (3 cycles of 5-min 37°C global ischemia and 5-min reperfusion) or were perfused for 40 min without ischemia as controls. Subsarcolemmal (SSM) and interfibrillar (IFM) populations of mitochondria were isolated. IPC did not decrease ADP-stimulated respiration measured in intact mitochondria using substrates that donate reducing equivalents to complex I. Maximally expressed complex I activity measured as rotenone-sensitive NADH:ubiquinone oxidoreductase in detergent-solubilized mitochondria was also unaffected by IPC. Thus the protection of IPC does not occur as a consequence of a partial decrease in complex I activity leading to a decrease in integrated respiration through complex I. IPC and blockade of electron transport both converge on mitochondria as effectors of cardioprotection; however, each modulates mitochondrial metabolism during ischemia by different mechanisms to achieve cardioprotection.

Protein kinase C-epsilon coimmunoprecipitates with cytochrome oxidase subunit IV and is associated with improved cytochrome-c oxidase activity and cardioprotection

We have utilized an in situ rat coronary ligation model to establish a PKC-epsilon cytochrome oxidase subunit IV (COIV) coimmunoprecipitation in myocardium exposed to ischemic preconditioning (PC). Ischemia-reperfusion (I/R) damage and PC protection were confirmed using tetrazolium-based staining methods and serum levels of cardiac troponin I. Homogenates prepared from the regions at risk (RAR) and not at risk (RNAR) for I/R injury were fractionated into cell-soluble (S), 600 g low-speed centrifugation (L), Percoll/Optiprep density gradient-purified mitochondrial (M), and 100,000 g particulate (P) fractions. COIV immunoreactivity and cytochrome-c oxidase activity measurements estimated the percentages of cellular mitochondria in S, L, M, and P fractions to be 0, 55, 29, and 16%, respectively. We observed 18, 3, and 3% of PKC-delta, -epsilon, and -zeta isozymes in the M fraction under basal conditions. Following PC, we observed a 61% increase in PKC-epsilon levels in the RAR M fraction compared with the RNAR M fraction. In RAR mitochondria, we also observed a 2.8-fold increase in PKC-epsilon serine 729 phosphoimmunoreactivity (autophosphorylation), indicating the presence of activated PKC-epsilon in mitochondria following PC. PC administered before prolonged I/R induced a 1.9-fold increase in the coimmunoprecipitation of COIV, with anti-PKC-epsilon antisera and a twofold enhancement of cytochrome-c oxidase activity. Our results suggest that PKC-epsilon may interact with COIV as a component of the cardioprotection in PC. Induction of this interaction may provide a novel therapeutic target for protecting the heart from I/R damage.

The responses of HT22 cells to the blockade of mitochondrial complexes and potential protective effect of selenium supplementation

Mitochondria are the major reactive oxygen species (ROS) – generating sites in mammalian cells. Blockade of complexes in the electron transport chain (ETC) increases the leakage of single electrons to O₂ and therefore increases ROS levels. Complexes I and III have been reported to be the major ROS-generating sites in mitochondria. In this study, using mouse hippocampal HT22 cells as in vitro model, we monitored the change of intracellular ROS level in response to the blockade of ETC at different complex, and measured changes of gene expression of antioxidant enzymes and phase II enzymes, also evaluated potential protective effect of selenium (Se) supplementation to the cells under this oxidative stress. In summary, our results showed that complex I was the major ROS-generating site in HT22 cells. Complex I blockade upregulated the mRNA levels of glutamylcysteine synthetase heavy and light chains, glutathione-S-transferases omega1 and alpha 2, hemoxygenase 1, thioredoxin reductase 1, and selenoprotein H. Unexpectedly, the expression of the enzymes that directly scavenge ROS decreased, including superoxide dismutases 1 and 2, glutathione peroxidase 1, and catalase. Se supplementation increased glutathione levels and glutathione peroxidase activity, indicating a potential protective role in oxidative stress caused by ETC blockade.

Acute vincristine pretreatment protects adult mouse cardiac myocytes from oxidative stress

Vincristine is a chemotherapeutic agent that disrupts microtubules. We noted that paclitaxel (Taxol), which stabilizes microtubules, protected cultured adult mouse cardiac myocytes from oxidative stress induced by H(2)O(2). We hypothesized that vincristine, which disrupts microtubules, should have the opposite effect. To our surprise, we found that pretreatment with concentrations of vincristine ranging from 30 to 120 micromol/L for 60 min preserved myocyte viability and morphology after incubation with 30 micromol/L of H(2)O(2) for 35 min as measured by trypan blue exclusion. The cardioprotective effects of vincristine were also observed during prolonged hypoxia. With continuous exposure to vincristine, survival lasted for as long as 24 h, but longer periods of exposure up to 42 h resulted in extensive cell death. Despite microtubule disruption evidenced on deconvolution microscopy, vincristine activated a prosurvival pathway resulting in increased phosphorylation of Akt, ERK and GSK-3beta and in reduced cytochrome C release into the cytosol. Pharmacological inhibitors of Akt and Erk attenuated the cardioprotective effect of vincristine. We conclude that short-term pretreatment with vincristine exerts dramatic protective effects in cultured adult mouse myocytes subjected to acute oxidative stress. Despite causing microtubule disruption, vincristine initiates a prosurvival signaling pathway. As vincristine and doxorubicin are often used in conjunction to treat patients, it is possible that vincristine could be used to modify the cardiotoxicity of doxorubicin.

The role of mitochondria in protection of the heart by preconditioning

A prolonged period of ischaemia followed by reperfusion irreversibly damages the heart. Such reperfusion injury (RI) involves opening of the mitochondrial permeability transition pore (MPTP) under the conditions of calcium overload and oxidative stress that accompany reperfusion. Protection from MPTP opening and hence RI can be mediated by ischaemic preconditioning (IP) where the prolonged ischaemic period is preceded by one or more brief (2–5 min) cycles of ischaemia and reperfusion. Following a brief overview of the molecular characterisation and regulation of the MPTP, the proposed mechanisms by which IP reduces pore opening are reviewed including the potential roles for reactive oxygen species (ROS), protein kinase cascades, and mitochondrial potassium channels. It is proposed that IP-mediated inhibition of MPTP opening at reperfusion does not involve direct phosphorylation of mitochondrial proteins, but rather reflects diminished oxidative stress during prolonged ischaemia and reperfusion. This causes less oxidation of critical thiol groups on the MPTP that are known to sensitise pore opening to calcium. The mechanisms by which ROS levels are decreased in the IP hearts during prolonged ischaemia and reperfusion are not known, but appear to require activation of protein kinase Cε, either by receptor-mediated events or through transient increases in ROS during the IP protocol. Other signalling pathways may show cross-talk with this primary mechanism, but we suggest that a role for mitochondrial potassium channels is unlikely. The evidence for their activity in isolated mitochondria and cardiac myocytes is reviewed and the lack of specificity of the pharmacological agents used to implicate them in IP is noted. Some K⁺ channel openers uncouple mitochondria and others inhibit respiratory chain complexes, and their ability to produce ROS and precondition hearts is mimicked by bona fide uncouplers and respiratory chain inhibitors. IP may also provide continuing protection during reperfusion by preventing a cascade of MPTP-induced ROS production followed by further MPTP opening. This phase of protection may involve survival kinase pathways such as Akt and glycogen synthase kinase 3 (GSK3) either increasing ROS removal or reducing mitochondrial ROS production.

Role of the anion nitrite in ischemia-reperfusion cytoprotection and therapeutics

The anion nitrite (NO(2)(-)) constitutes a biochemical reservoir for nitric oxide (NO). Nitrite reduction to NO may be catalyzed by hemoglobin, myoglobin or other metal-containing enzymes and occurs at increasing rates under conditions of physiologic hypoxia or ischemia. A number of laboratories have now demonstrated in animal models the ability of nitrite to provide potent cytoprotection following focal ischemia-reperfusion (IR) injury of the heart, liver, brain, and kidney. While the mechanism of nitrite-mediated cytoprotection remains to be fully characterized, the release of nitrite-derived NO following IR appears to be central to this mechanism. The evidence of nitrite-mediated cytoprotection against IR injury in multiple animal models opens the door to potential therapeutic opportunities in human disease. Here we review the mechanisms for nitrite formation in blood and tissue, its metabolic equilibrium with NO, nitrate, and NO-modified proteins, the evidence supporting nitrite-mediated cytoprotection, and the potential mechanisms driving cytoprotection, and we explore the opportunities for the therapeutic application of nitrite for human disease.

Effects of Salviae Mitiorrhizae and Cortex Moutan extract on the rat heart after myocardial infarction: a proteomic study

In this study, we characterized the therapeutical effects of Salviae Mitiorrhizae (Danshen) and Cortex Moutan (Danpi) extract (SDD) on Sprague-Dawley rats subjected to coronary artery ligation, and applied proteomic approach to investigate its potential mechanism of action. The chemical composition of SDD was investigated by HPLC/MS(n) analysis. Measurement for serum levels of creatine kinase (CK), creatine kinase-MB (CK-MB), nitrite and histological study for infarct area of heart were performed. Moreover, protein abundance profiles of myocardium were compared by two-dimensional gel electrophoresis and altered proteins were identified by MALDI-TOF-MS. The results showed SDD significantly decreased CK, CK-MB concentration in serum and infarct area of heart, while increased the release of nitrite in rats with coronary occlusion. Increased concentration of ATP and total adenine nucleotide indicated the energy metabolism has been improved in ischemic heart induced by SDD. Proteomic data revealed that 23 proteins associated with energy metabolism, oxidative stress and cytoskeleton were modulated in SDD treated rats.

Missense mutations in the BCS1L gene as a cause of the Björnstad syndrome

BACKGROUND

The Björnstad syndrome, an autosomal recessive disorder associated with sensorineural hearing loss and pili torti, is caused by mutation of a previously unidentified gene on chromosome 2q34-36.

METHODS

Refined genetic mapping and DNA sequencing of 44 genes between D2S2210 and D2S2244 revealed BCS1L mutations. Functional analyses elucidated how BCS1L mutations cause the Björnstad syndrome.

RESULTS

BCS1L encodes a member of the AAA family of ATPases that is necessary for the assembly of complex III in the mitochondria. In addition to the Björnstad syndrome, BCS1L mutations cause complex III deficiency and the GRACILE syndrome, which in neonates are lethal conditions that have multisystem and neurologic manifestations typifying severe mitochondrial disorders. Patients with the Björnstad syndrome have mutations that alter residues involved in protein-protein interactions, whereas mutations in patients with complex III deficiency alter ATP-binding residues, as deduced from the crystal structure of a related AAA-family ATPase. Biochemical studies provided evidence to support this model: complex III deficiency mutations prevented ATP-dependent assembly of BCS1L-associated complexes. All mutant BCS1L proteins disrupted the assembly of complex III, reduced the activity of the mitochondrial electron-transport chain, and increased the production of reactive oxygen species. However, only mutations associated with complex III deficiency increased mitochondrial content, which further increased the production of reactive oxygen species.

CONCLUSIONS

BCS1L mutations cause disease phenotypes ranging from highly restricted pili torti and sensorineural hearing loss (the Björnstad syndrome) to profound multisystem organ failure (complex III deficiency and the GRACILE syndrome). All BCS1L mutations disrupted the assembly of mitochondrial respirasomes (the basic unit for respiration in human mitochondria), but the clinical expression of the mutations was correlated with the production of reactive oxygen species. Mutations that cause the Björnstad syndrome illustrate the exquisite sensitivity of ear and hair tissues to mitochondrial function, particularly to the production of reactive oxygen species.

Fluorescent determination of cardiolipin using 10-N-nonyl acridine orange

Cardiolipin (CL) plays an essential role as a marker for cell apoptosis. Quantitative detection of phospholipids (PLs) by UV absorbance is problematic due to the presence of few double bonds in the structure. Although 10-N-nonyl acridine orange (NAO) has been utilized for fluorescent visualization of liposomes and mitochondria through its interaction with CL, in this work, we have developed a specific fluorescent method for CL in solution using NAO. The interaction of sodium n-dodecyl sulfate (SDS), used to treat cells prior to lipid extraction, and other PLs found in cell membranes such as phosphatidic acid (PA), phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), phosphatidiylserine (PS), and sphingomyelin (SM) with NAO is investigated. The fluorescence intensity of the 0.5 microM NAO signal is strongly quenched by SDS below 25% methanol in water but with a methanol content above 50%, no quenching of NAO by SDS is observed. No fluorescence quenching of NAO with a 50% methanol/50% water solvent by the previously mentioned PLs or 4-20 microM cholesterol with the exception of PG at above 8 microM is noted. Using this 50% methanol/50% water solvent, the fluorescence signal due to the NAO-CL interaction is quite stable from 3 to at least 15 min. With excitation and emission wavelengths set at 518 and 530 nm, respectively, 20 microM NAO provides an inverse linear fluorescence response at 0.2-10 microM CL with a correlation coefficient of 0.9929. The detection limit is 0.2 microM and the limit of quantification is 0.6 microM. Structurally analogous acridine orange and phenosafranin dyes are less effective as fluorescent probes for CL. The CL in the whole cell and membrane samples is quantitatively determined by standard addition to range from 0.2 to 1.5 microM. The level of CL in cell membrane samples, previously subjected to staurosporine which initiates cell apoptosis, is increased but not significantly through use of the t-test.

Sarcoplasmic ATP-sensitive potassium channel blocker HMR1098 protects the ischemic heart: implication of calcium, complex I, reactive oxygen species and mitochondrial ATP-sensitive potassium channel

The aim of this study was to investigate the effects of HMR1098, a selective blocker of sarcolemmal ATP-sensitive potassium channel (sarcK(ATP)), in Langendorff-perfused rat hearts submitted to ischemia and reperfusion. The recovery of heart hemodynamic and mitochondrial function, studied on skinned fibers, was analyzed after 30-min global ischemia followed by 20-min reperfusion. Infarct size was quantified on a regional ischemia model after 2-h reperfusion. We report that the perfusion of 10 microM HMR1098 before ischemia, delays the onset of ischemic contracture, improves recovery of cardiac function upon reperfusion, preserves the mitochondrial architecture, and finally decreases infarct size. This HMR1098-induced cardioprotection is prevented by 1 mM 2-mercaptopropionylglycine, an antioxidant, and by 100 nM nifedipine, an L-type calcium channel blocker. Concomitantly, it is shown that HMR1098 perfusion induces (i) a transient and specific inhibition of the respiratory chain complex I and, (ii) an increase in the averaged intracellular calcium concentration probed by the in situ measurement of indo-1 fluorescence. Finally, all the beneficial effects of HMR1098 were strongly inhibited by 5-hydroxydecanoate and abolished by glibenclamide, two mitoK(ATP) blockers. This study demonstrates that the HMR1098-induced cardioprotection occurs indirectly through extracellular calcium influx, respiratory chain complex inhibition, reactive oxygen species production and mitoK(ATP) opening. Taken together, these data suggest that a functional interaction between sarcK(ATP) and mitoK(ATP) exists in isolated rat heart ischemia model, which is mediated by extracellular calcium influx.

Reversible blockade of electron transport during ischemia protects mitochondria and decreases myocardial injury following reperfusion

Cardiac mitochondria sustain damage during ischemia and reperfusion, contributing to cell death. The reversible blockade of electron transport during ischemia with amobarbital, an inhibitor at the rotenone site of complex I, protects mitochondria against ischemic damage. Amobarbital treatment immediately before ischemia was used to test the hypothesis that damage to mitochondrial respiration occurs mainly during ischemia and that protection of mitochondria during ischemia leads to decreased cardiac injury with reperfusion. Langendorff-perfused Fischer-344 rat hearts were treated with amobarbital (2.5 mM) or vehicle for 1 min immediately before 25 min of global ischemia. Both groups were reperfused for 30 min without additional treatment. Subsarcolemmal (SSM) and interfibrillar (IFM) populations of mitochondria were isolated after reperfusion. Ischemia and reperfusion decreased state 3 and increased state 4 respiration rate in both SSM and IFM. Amobarbital treatment protected oxidative phosphorylation measured following reperfusion and improved the coupling of respiration. Cytochrome c content measured in SSM and IFM following reperfusion decreased in untreated, but not in amobarbital-treated, hearts. H(2)O(2) release from SSM and IFM isolated from amobarbital-treated hearts during reperfusion was markedly decreased. Amobarbital treatment before ischemia improved recovery of contractile function (percentage of preischemic developed pressure: untreated 51 +/- 4%, n = 12; amobarbital 70 +/- 4%, n = 11, p < 0.01) and substantially reduced infarct size (untreated 32 +/- 2%, n = 7; amobarbital 13 +/- 2%, n = 7, p < 0.01). Thus, mitochondrial damage occurs mainly during ischemia rather than during reperfusion. Reperfusion in the setting of preserved mitochondrial respiratory function attenuates the mitochondrial release of reactive oxygen species, enhances contractile recovery, and decreases myocardial infarct size.

Tyk2 tyrosine kinase expression is required for the maintenance of mitochondrial respiration in primary pro-B lymphocytes

Tyk2, a member of the Jak family of protein tyrosine kinases, is critical for the biological actions of alpha/beta interferon (IFN-alpha/beta). Although Tyk2(-/-) mice are phenotypically normal, they exhibit abnormal responses to inflammatory challenges in a variety of cells isolated from Tyk2(-/-) mice. The reported phenotypic alterations in both Tyk2-null cells and mice are consistent with the possibility that the expression of this tyrosine kinase may regulate mitochondrial function. We report here that Tyk2-null pro-B cells are markedly deficient in basal oxygen consumption and exhibit a significant decrease in steady-state cellular ATP levels compared to wild-type cells. Tyk2-null cells also exhibit impaired complex I, III, and IV function of the mitochondrial electron transport chain. Reconstitution of Tyk2-null pro-B cells with either the wild type or a kinase-inactive mutant of Tyk2 restores basal mitochondrial respiration. By contrast, the kinase activity of Tyk2 is required for maintenance of both complex I-dependent mitochondrial respiration as well as induction of apoptosis in cells incubated with IFN-beta. Consistent with the role of Tyk2 in the regulation of tyrosine phosphorylation of Stat3, expression of a constitutively active Stat3 can restore the mitochondrial respiration in Tyk2-null cells treated with IFN-beta. Finally, Tyk2(-/-) mice show decreased exercise tolerance compared to wild-type littermates. Our results implicate a novel role for Tyk2 kinase and Stat3 phosphorylation in mitochondrial respiration.

Modulation of electron transport protects cardiac mitochondria and decreases myocardial injury during ischemia and reperfusion

Mitochondria are increasingly recognized as lynchpins in the evolution of cardiac injury during ischemia and reperfusion. This review addresses the emerging concept that modulation of mitochondrial respiration during and immediately following an episode of ischemia can attenuate the extent of myocardial injury. The blockade of electron transport and the partial uncoupling of respiration are two mechanisms whereby manipulation of mitochondrial metabolism during ischemia decreases cardiac injury. Although protection by inhibition of electron transport or uncoupling of respiration initially appears to be counterintuitive, the continuation of mitochondrial oxidative phosphorylation in the pathological milieu of ischemia generates reactive oxygen species, mitochondrial calcium overload, and the release of cytochrome c. The initial target of these deleterious mitochondrial-driven processes is the mitochondria themselves. Consequences to the cardiomyocyte, in turn, include oxidative damage, the onset of mitochondrial permeability transition, and activation of apoptotic cascades, all favoring cardiomyocyte death. Ischemia-induced mitochondrial damage carried forward into reperfusion further amplifies these mechanisms of mitochondrial-driven myocyte injury. Interruption of mitochondrial respiration during early reperfusion by pharmacologic blockade of electron transport or even recurrent hypoxia or brief ischemia paradoxically decreases cardiac injury. It increasingly appears that the cardioprotective paradigms of ischemic preconditioning and postconditioning utilize modulation of mitochondrial oxidative metabolism as a key effector mechanism. The initially counterintuitive approach to inhibit mitochondrial respiration provides a new cardioprotective paradigm to decrease cellular injury during both ischemia and reperfusion.

Cardioprotective mechanisms ofPrunus cerasus(sour cherry) seed extract against ischemia-reperfusion-induced damage in isolated rat hearts

The effects of kernel extract obtained from sour cherry ( Prunus cerasus) seed on the postischemic cardiac recovery were studied in isolated working rat hearts. Rats were treated with various daily doses of the extract for 14 days, and hearts were then isolated and subjected to 30 min of global ischemia followed by 120 min of reperfusion. The incidence of ventricular fibrillation (VF) and tachycardia (VT) fell from their control values of 92% and 100% to 50% (not significant) and 58% (not significant), 17% ( P < 0.05), and 25% ( P < 0.05) with the doses of 10 mg/kg and 30 mg/kg of the extract, respectively. Lower concentrations of the extract (1 and 5 mg/kg) failed to significantly reduce the incidence of VF and VT during reperfusion. Sour cherry seed kernel extract (10 and 30 mg/kg) significantly improved the postischemic recovery of cardiac function (coronary flow, aortic flow, and left ventricular developed pressure) during reperfusion. We have also demonstrated that the extract-induced protection in cardiac function significantly reflected in a reduction of infarct size. Immunohistochemistry indicates that a reduction in caspase-3 activity and apoptotic cells by the extract, beside other potential action mechanisms of proanthocyanidin, trans-resveratrol, and flavonoid components of the extract, could be responsible for the cardioprotection in ischemic-reperfused myocardium.

Role of cardiolipin alterations in mitochondrial dysfunction and disease

Cardiolipin (CL) is a structurally unique dimeric phospholipid localized in the inner mitochondrial membrane where it is required for optimal mitochondrial function. In addition to its role in maintaining membrane potential and architecture, CL is known to provide essential structural and functional support to several proteins involved in mitochondrial bioenergetics. A loss of CL content, alterations in its acyl chain composition, and/or CL peroxidation have been associated with mitochondrial dysfunction in multiple tissues in a variety of pathological conditions, including ischemia, hypothyroidism, aging, and heart failure. Recently, aberrations in CL metabolism have been implicated as a primary causative factor in the cardioskeletal myopathy known as Barth syndrome, underscoring an important role of CL in human health and disease. The purpose of this review is to provide an overview of evidence that has linked changes in the CL profile to mitochondrial dysfunction in various pathological conditions. In addition, a brief overview of CL function and biosynthesis, and a discussion of methods used to examine CL in biological tissues are provided.

Dehydroepiandrosterone inhibits complex I of the mitochondrial respiratory chain and is neurotoxic in vitro and in vivo at high concentrations

Dehydroepiandrosterone (DHEA) is widely used as a food supplement and considered to be relatively safe. In animal studies, however, additions of high concentrations of DHEA to the diet have led to hepatotoxicity as well as liver mitochondrial dysfunction. This study was therefore designed to find out whether DHEA is able to inhibit the respiratory activity also in neuronal mitochondria and to reveal whether this leads to functional disturbance in the brain. Using different mitochondrial substrates, we show here that DHEA suppresses the mitochondrial respiration in permeabilized neurons (half maximal inhibitory concentration 13 microM) by inhibiting complex I of the mitochondrial electron transport chain. Treatment with DHEA was associated with increased glucose expenditure in intact cultures and led to neuronal death. The latter was most prominent in hypoglycemic conditions. Mice fed with pellet containing 0.6% DHEA for 3 months showed a significant neuronal loss in the cerebral cortex and hippocampus, a slightly decreased dopamine/dihydroxyphenylacetic acid ratio, as well as motor impairment. The main conclusion of the present study is that high concentrations of DHEA inhibit complex I of the mitochondrial respiratory chain and are neurotoxic in vitro and in vivo.

Adverse effects of free fatty acid associated with increased oxidative stress in postischemic isolated rat hearts

The mechanisms of the adverse effects of free fatty acids on the ischemic-reperfused myocardium are not fully understood. Long-chain fatty acids, including palmitate, uncouple oxidative phosphorylation and should therefore promote the formation of oxygen-derived free radicals, with consequent adverse effects. Conversely, the antianginal agent trimetazidine (TMZ), known to inhibit cardiac fatty acid oxidation, could hypothetically lessen the formation of reactive oxygen species (ROS) and thus improve reperfusion mechanical function. Isolated perfused rat hearts underwent 30 min of total global ischemia followed by 30 min of reperfusion. Hearts were perfused with glucose 5.5 mmol/l or palmitate 1.5 mmol/l with or without TMZ (100 micromol/l). Ascorbyl free radical (AFR) release during perfusion periods was measured by electron spin resonance as a marker of oxidative stress. Post-ischemic recovery in the palmitate group of heart was lower than in the glucose group with a marked rise in diastolic tension and reduction in left ventricular developed pressure (Glucose: 85 +/- 11 mmHg; Palmitate: 10 +/- 6 mmHg; p < 0.001). TMZ decreased diastolic tension in both glucose- and in palmitate-perfused hearts. Release of AFR within the first minute of reperfusion was greater in palmitate-perfused hearts and in hearts perfused with either substrate, this marker of oxidative stress was decreased by TMZ (expressed in arbitrary units/ml; respectively: 8.49 +/- 1.24 vs. 1.06 +/- 0.70 p < 0.05; 12.47 +/- 2.49 vs. 3.37 +/- 1.29 p < 0.05). Palmitate increased the formation of ROS and reperfusion contracture. TMZ, a potential inhibitor of palmitate-induced mitochondrial uncoupling, decreased the formation of free radicals and improved postischemic mechanical dysfunction. The novel conclusion is that adverse effects of fatty acids on ischemic-reperfusion injury may be mediated, at least in part, by oxygen-derived free radicals.

Volatile anesthetics evoke prolonged changes in the proteome of the left ventricule myocardium: defining a molecular basis of cardioprotection?

BACKGROUND

Volatile anesthetics can alter cardiac gene and protein expression. Of those underlying molecular changes in gene and protein expression in the myocardium after exposure to volatile anesthetics that have been identified, some of them have been related to cardioprotection.

METHODS

We used two-dimensional gel electrophoresis and mass spectrometry to identify changes in the protein expression of the left ventricle myocardium of anesthesized rats. We maintained anesthesia for 3 h using isoflurane, sevoflurane or desflurane, respectively, at 1.0 minimum alveolar concentration (MAC) and dissected the left ventricular myocardium either immediately or 72 h after the end of anesthesia.

RESULTS

We found changes of at least twofold in 106 proteins of the more than 1.600 protein spots discriminated in each gel. These differentially expressed proteins are associated with functions in glycolysis, mitochondrial respiration and stress response. No obvious difference could be observed between the patterns of differential expression of the three volatile anesthetics.

CONCLUSION

We provide the first study of post-anesthetic protein expression profiles associated with three common volatile anesthetics. These volatile anesthetics promote a distinct change in the myocardial protein expression profile, whereby changes in the expression pattern still exist 72 h after anesthesia. These proteome changes are closely related to cardioprotection and ischemic preconditioning, indicating a common functional signaling of volatile anesthestics.

Protein kinase Cepsilon interacts with cytochrome c oxidase subunit IV and enhances cytochrome c oxidase activity in neonatal cardiac myocyte preconditioning

We have previously identified a phorbol ester-induced PKCepsilon (protein kinase Cepsilon) interaction with the ( approximately 18 kDa) COIV [CO (cytochrome c oxidase) subunit IV] in NCMs (neonatal cardiac myocytes). Since PKCepsilon has been implicated as a key mediator of cardiac PC (preconditioning), we examined whether hypoxic PC could induce PKCepsilon-COIV interactions. Similar to our recent study with phorbol esters [Ogbi, Chew, Pohl, Stuchlik, Ogbi and Johnson (2004) Biochem. J. 382, 923-932], we observed a time-dependent increase in the in vitro phosphorylation of an approx. 18 kDa protein in particulate cell fractions isolated from NCMs subjected to 1-60 min of hypoxia. Introduction of a PKCepsilon-selective translocation inhibitor into cells attenuated this in vitro phosphorylation. Furthermore, when mitochondria isolated from NCMs exposed to 30 min of hypoxia were subjected to immunoprecipitation analyses using PKCepsilon-selective antisera, we observed an 11.1-fold increase in PKCepsilon-COIV co-precipitation. In addition, we observed up to 4-fold increases in CO activity after brief NCM hypoxia exposures that were also attenuated by introducing a PKCepsilon-selective translocation inhibitor into the cells. Finally, in Western-blot analyses, we observed a >2-fold PC-induced protection of COIV levels after 9 h index hypoxia. Our studies suggest that a PKCepsilon-COIV interaction and an enhancement of CO activity occur in NCM hypoxic PC. We therefore propose novel mechanisms of PKCepsilon-mediated PC involving enhanced energetics, decreased mitochondrial reactive oxygen species production and the preservation of COIV levels.

Depletion of cardiolipin and cytochrome c during ischemia increases hydrogen peroxide production from the electron transport chain

Mitochondrial electron transport is a major source of reactive oxygen species (ROS) during cardiac ischemia and reperfusion. In the isolated rabbit heart, 30 and 45 min of ischemia decrease the contents of cardiolipin and cytochrome c in subsarcolemmal mitochondria (SSM) located beneath the plasma membrane. In contrast, interfibrillar mitochondria (IFM) in the interior of the myocyte do not sustain a decrease in cardiolipin. We proposed that the depletion of cardiolipin and the accompanying cytochrome c loss during ischemia were critical events that amplified ROS production by mitochondria. The total production of H2O2 was measured in submitochondrial particles (SMP) prepared from rabbit heart SSM and IFM after 0, 15, 30, and 45 min of ischemia. With NADH as substrate, total H2O2 production was increased only in SMP from SSM after 30 and 45 min ischemia, when ischemia decreased the content of cardiolipin and cytochrome c. In contrast, ischemia did not augment H2O2 generation in SMP from IFM with preserved cardiolipin and cytochrome c content. Thus, during the evolution of ischemic injury, H2O2 production from the electron transport chain increased after depletion of cardiolipin and the loss of cytochrome c.

Protective effect of melatonin against mitochondrial dysfunction associated with cardiac ischemiareperfusion: role of cardiolipin

Reactive oxygen species (ROS) are considered an important factor in ischemia/reperfusion injury to cardiac myocytes. Mitochondrial respiration, mainly at the level of complex I and III, is an important source of ROS generation and hence a potential contributor of cardiac reperfusion injury. Appropriate antioxidant strategies could be particularly useful to limit this ROS generation and associated mitochondrial dysfunction. Melatonin has been shown to effectively protect against ischemic-reperfusion myocardial damage. The mechanism by which melatonin exerts this cardioprotective effect is not well established. In the present study we examined the effects of melatonin on various parameters of mitochondrial bioenergetics in a Langerdoff isolated perfused rat heart model. After isolation of mitochondria from control, ischemic-reperfused and melatonin-treated ischemic-reperfused rat heart, various bioenergetic parameters were evaluated such as rates of mitochondrial oxygen consumption, complex I and complex III activity, H2O2 production as well as the degree of lipid peroxidation, cardiolipin content, and cardiolipin oxidation. We found that reperfusion significantly altered all these mitochondrial parameters, while melatonin treatment had strong protective effect attenuating these alterations. This effect appears to be due, at least in part, to the preservation, by ROS attack, of the content and integrity of cardiolipin molecules which play a pivotal role in mitochondrial bioenergetics. Protection of mitochondrial dysfunction was associated with an improvement of post-ischemic hemodynamic function of the heart. Melatonin had also strong protective effect against oxidative alterations to complex I and III as well as to cardiolipin in isolated mitochondria.

Estrogen prevents cardiomyocyte apoptosis through inhibition of reactive oxygen species and differential regulation of p38 kinase isoforms

From human and animal studies, estrogen is known to protect the myocardium from an ischemic insult. However, there is limited knowledge regarding mechanisms by which estrogen directly protects cardiomyocytes. In this report, we employed an in vitro model, in which cultured rat cardiomyocytes underwent prolonged hypoxia followed by reoxygenation (H/R), to study the cardioprotective mechanism of estrogen. 17-beta-estradiol (E2) acting via estrogen receptors inhibited H/R-induced apoptosis of cardiomyocytes. Mitochondrial reactive oxygen species (ROS) generated from H/R activated p38alpha MAPK, and inhibition of p38alpha with SB203580 significantly prevented H/R-induced cell death. E2 suppressed ROS formation and p38alpha activation by H/R and concomitantly augmented the activity of p38beta. Unlike p38alpha, p38beta was little affected by H/R. Dominant negative p38beta protein expression decreased E2-mediated cardiomyocyte survival and ROS suppression during H/R stress. The prosurvival signaling molecule, phosphoinositol-3 kinase (PI3K), has previously been linked to cell survival following ischemia-reperfusion injury. Here, E2-activated PI3K was found to inhibit ROS generated from H/R injury, leading to inhibition of downstream p38alpha. We further linked these signaling pathways in that p38beta was activated by E2 stimulation of PI3K. Thus, E2 differentially modulated two major isoforms of p38, leading to cardiomyocyte survival. This was achieved by signaling through PI3K, integrating cell survival mediators.

Mitochondrial dysfunction associated with cardiac ischemia/reperfusion can be attenuated by oxygen tension control. Role of oxygen-free radicals and cardiolipin

Reactive oxygen species (ROS) are considered an important factor in ischemia/reperfusion injury to cardiac myocites. Mitochondrial respiration is an important source of ROS generation and hence a potential contributor to cardiac reperfusion injury. Appropriate treatment strategy could be particularly useful to limit this ROS generation and associated mitochondrial dysfunction. In the present study, we examined the effect of lowering the oxygen tension, at the onset of the reperfusion, on various parameters of mitochondrial bioenergetics in rat heart tissue. After isolation of mitochondria from control, ischemic, normoxic and hypoxic reperfused rat heart, various bioenergetic parameters were evaluated such as rates of mitochondrial oxygen consumption, complex I and complex III activity, H2O2 production and in addition, the degree of lipid peroxidation, cardiolipin content and cardiolipin oxidation. We found that normoxic reperfusion significantly altered all these mitochondrial parameters, while hypoxic reperfusion had a protective effect attenuating these alterations. This effect appears to be due, at least in part, to a reduction of mitochondrial ROS generation with subsequent preservation of cardiolipin integrity, protection of mitochondrial function and improvement of post-ischemic hemodynamic function of the heart.

Protein kinase A-mediated phosphorylation modulates cytochrome c oxidase function and augments hypoxia and myocardial ischemia-related injury

We have investigated the effects of hypoxia and myocardial ischemia/reperfusion on the structure and function of cytochrome c oxidase (CcO). Hypoxia (0.1% O(2) for 10 h) and cAMP-mediated inhibition of CcO activity were accompanied by hyperphosphorylation of subunits I, IVi1, and Vb and markedly increased reactive O(2) species production by the enzyme complex in an in vitro system that uses reduced cytochrome c as an electron donor. Both subunit phosphorylation and enzyme activity were effectively reversed by 50 nm H89 or 50 nm myristoylated peptide inhibitor (MPI), specific inhibitors of protein kinase A, but not by inhibitors of protein kinase C. In rabbit hearts subjected to global and focal ischemia, CcO activity was inhibited in a time-dependent manner and was accompanied by hyperphosphorylation as in hypoxia. Additionally, CcO activity and subunit phosphorylation in the ischemic heart were nearly completely reversed by H89 or MPI added to the perfusion medium. Hyperphosphorylation of subunits I, IVi1, and Vb was accompanied by reduced subunit contents of the immunoprecipitated CcO complex. Most interestingly, both H89 and MPI added to the perfusion medium dramatically reduced the ischemia/reperfusion injury to the myocardial tissue. Our results pointed to an exciting possibility of using CcO activity modulators for controlling myocardial injury associated with ischemia and oxidative stress conditions.

The protection of bioenergetic functions in mitochondria by new synthetic chromanols

alpha-Tocopherol is the most important lipophilic antioxidant of the chromanol type protecting biomembranes from lipid peroxidation (LPO). Therefore, alpha-tocopherol and its derivatives are frequently used in the therapy or prevention of oxygen radical-derived diseases. In the present study, novel chromanol-type antioxidants (twin-chromanol, cis- and trans-oxachromanol) as well as the well-known short-chain analogue of alpha-tocopherol, pentamethyl-chromanol, were tested for their antioxidative potency in rat heart mitochondria (RHM). Our experiments revealed that the bioenergetic parameters of mitochondria were not deteriorated in the presence of chromanols (up to 50 nmol/mg protein). Exposure of RHM to cumene hydroperoxide and Fe2+ (final concentrations 50 microM each), inducing LPO, significantly affected their bioenergetic parameters which were determined in the presence of glutamate and malate (substrates of mitochondrial complex I). Alterations of the bioenergetic parameters were partially prevented in a concentration-dependent manner by preincubating RHM with antioxidants before adding the radical-generating system. In the lower concentration range, twin-chromanol turned out to be more efficient than pentamethyl-chromanol, both being far more protective than cis- and trans-oxachromanol. Measurement of protein-bound SH groups and thiobarbituric acid-reactive substances revealed that this protective effect was due to their antioxidative action. Furthermore, HPLC measurements of alpha-tocopherol and alpha-tocopheryl quinone in rat liver mitochondria demonstrated an alpha-tocopherol-sparing effect of twin-chromanol. In conclusion, new chromanol-type antioxidants, especially twin-chromanol, were able to improve bioenergetic and biochemical parameters of mitochondria exposed to oxidative stress.

Blockade of electron transport before cardiac ischemia with the reversible inhibitor amobarbital protects rat heart mitochondria

Cardiac ischemia damages the mitochondrial electron transport chain. Irreversible blockade of electron transport at complex I by rotenone decreases ischemic damage to cardiac mitochondria by decreasing the loss of cytochrome c and preserving respiration through cytochrome oxidase. Therapeutic intervention to protect myocardium during ischemia and reperfusion requires the use of a reversible inhibitor that allows resumption of oxidative metabolism during reperfusion. Amobarbital is a reversible inhibitor at the rotenone site of complex I. We asked whether amobarbital administered immediately before ischemia protected respiratory function. Isolated rat hearts were perfused for 15 min followed by 25-min global ischemia at 37 degrees C. Amobarbital-treated hearts received drug for 1 min before ischemia. Subsarcolemmal (SSM) and interfibrillar (IFM) populations of mitochondria were isolated after ischemia, and oxidative phosphorylation was measured. Amobarbital protected oxidative phosphorylation, including through cytochrome oxidase, in both SSM and IFM in a dose-dependent manner, with an optimal dose of 2 to 2.5 mM. Amobarbital also preserved cytochrome c content in both SSM and IFM. Thus, reversible blockade of the electron transport chain during ischemia protects mitochondrial respiration.

Inhibition of the mitochondrial calcium uniporter by the oxo-bridged dinuclear ruthenium amine complex (Ru360) prevents from irreversible injury in postischemic rat heart

Mitochondrial calcium overload has been implicated in the irreversible damage of reperfused heart. Accordingly, we studied the effect of an oxygen-bridged dinuclear ruthenium amine complex (Ru360), which is a selective and potent mitochondrial calcium uniporter blocker, on mitochondrial dysfunction and on the matrix free-calcium concentration in mitochondria isolated from reperfused rat hearts. The perfusion of Ru360 maintained oxidative phosphorylation and prevented opening of the mitochondrial permeability transition pore in mitochondria isolated from reperfused hearts. We found that Ru360 perfusion only partially inhibited the mitochondrial calcium uniporter, maintaining the mitochondrial matrix free-calcium concentration at basal levels, despite high concentrations of cytosolic calcium. Additionally, we observed that perfused Ru360 neither inhibited Ca2+ cycling in the sarcoplasmic reticulum nor blocked ryanodine receptors, implying that the inhibition of ryanodine receptors cannot explain the protective effect of Ru360 in isolated hearts. We conclude that the maintenance of postischemic myocardial function correlates with an incomplete inhibition of the mitochondrial calcium uniporter. Thus, the chemical inhibition by this molecule could be an approach used to prevent heart injury during reperfusion.