Free radical-induced alterations of myocardial membrane proteins

Mitochondrial Dysfunction and Myocardial Ischemia-Reperfusion: Implications for Novel Therapies

Mitochondria have emerged as key participants in and regulators of myocardial injury during ischemia and reperfusion. This review examines the sites of damage to cardiac mitochondria during ischemia and focuses on the impact of these defects. The concept that mitochondrial damage during ischemia leads to cardiac injury during reperfusion is addressed. The mechanisms that translate ischemic mitochondrial injury into cellular damage, during both ischemia and early reperfusion, are examined. Next, we discuss strategies that modulate and counteract these mechanisms of mitochondrial-driven injury. The new concept that mitochondria are not merely stochastic sites of oxidative and calcium-mediated injury but that they activate cellular responses of mitochondrial remodeling and cellular reactions that modulate the balance between cell death and recovery is reviewed, and the therapeutic implications of this concept are discussed.

Phospholipase A2 activation regulates cytotoxicity of methylmercury in vascular endothelial cells

Mercury has been identified as a risk factor for cardiovascular disease among humans. Through diet, mainly fish consumption, humans are exposed to methylmercury, the biomethylated organic form of environmental mercury. As the endothelium is an important player in homeostasis of the cardiovascular system, here, the authors tested their hypothesis that methylmercury activates the lipid signaling enzyme phospholipase A(2) (PLA(2)) in vascular endothelial cells (ECs), causing upstream regulation of cytotoxicity. To test this hypothesis, the authors used bovine pulmonary artery ECs (BPAECs) cultured in monolayers, following labeling of their membrane phospholipids with [(3)H]arachidonic acid (AA). The cells were exposed to methylmercury chloride (MMC) and then the release of free AA (index of PLA(2) activity) and lactate dehydrogenase (LDH; index of cytotoxicity) were determined by liquid scintillation counting and spectrophotometry, respectively. MMC significantly activated PLA(2) in a dose-dependent (5 to 15 microM) and time-dependent (0 to 60 min) fashion. Sulfhydryl (thiol-protective) agents, calcium chelators, antioxidants, and PLA(2)-specific inhibitors attenuated the MMC-induced PLA(2) activation, suggesting the role of thiols, reactive oxygen species (ROS), and calcium in the activation of PLA(2) in BPAECs. MMC also induced the loss of thiols and increase of lipid peroxidation in BPAECs. MMC induced cytotoxicity in BPAECs as observed by the altered cell morphology and LDH leak, which was significantly attenuated by PLA(2) inhibitors. This study established that PLA(2) activation through thiols, calcium, and oxidative stress was associated with the cytotoxicity of MMC in BPAECs, drawing attention to the involvement of PLA(2) signaling in the methylmercury-induced vascular endothelial dysfunctions.

Quinol type compound in cytochrome c preparations leads to non-enzymatic reduction of cytochrome c during the measurement of complex III activity

Measurement of complex III activity is critical to the diagnosis of human mitochondrial disease and the study of mitochondrial pathobiology. Activity is measured as the maximal rate of antimycin A-sensitive reduction of exogenous cytochrome c by detergent-solubilized mitochondria. Complex III activity exhibited an unexpected variation based upon the commercial source of cytochrome c owing to an increase in the antimycin A-insensitive background reduction of cytochrome c and variable increases in total activity. Analysis of cytochrome c (producing a high-background) by fast protein liquid chromatography yielded a contaminant peak containing a lipid extractable component with redox spectra and mass spectroscopy fragmentation suggestive of a quinol. Measurement of inhibitor-sensitive rates are critical for the accurate and reproducible measurement of complex III activity and serve as a key quality control to screen for non-enzymatic reactions that obscure complex III activity.

Lipid peroxidation, oxidative stress genes and dietary factors in breast cancer protection: a hypothesis

We have recently proposed that lipid peroxidation may be a common mechanistic pathway by which obesity and hypertension lead to increased renal cell cancer risk. During this exercise, we noted a risk factor swap between breast and kidney cancer (oophorectomy and increased parity, detrimental for kidney, beneficial for breast; high blood pressure, detrimental for kidney, beneficial for breast when it occurs during pregnancy; alcohol, beneficial for kidney, detrimental for breast, and so on). We have subsequently proposed the hypothesis that lipid peroxidation represents a protective mechanism in breast cancer, and reviewed the evidence of the role of lipid peroxidation on established hormonal and non-hormonal factors for breast cancer. Here, we review the evidence in support of lipid peroxidation playing a role in the relationships between dietary factors and breast cancer. Available evidence implicates increased lipid peroxidation products in the anti-carcinogenic effect of suspected protective factors for breast cancer, including soy, marine n-3 fatty acids, green tea, isothiocyanates, and vitamin D and calcium. We also review the epidemiological evidence supporting a modifying effect of oxidative stress genes in dietary factor-breast cancer relationships.

Blockade of Electron Transport during Ischemia Protects Cardiac Mitochondria

Subsarcolemmal mitochondria sustain progressive damage during myocardial ischemia. Ischemia decreases the content of the mitochondrial phospholipid cardiolipin accompanied by a decrease in cytochrome c content and a diminished rate of oxidation through cytochrome oxidase. We propose that during ischemia mitochondria produce reactive oxygen species at sites in the electron transport chain proximal to cytochrome oxidase that contribute to the ischemic damage. Isolated, perfused rabbit hearts were treated with rotenone, an irreversible inhibitor of complex I in the proximal electron transport chain, immediately before ischemia. Rotenone pretreatment preserved the contents of cardiolipin and cytochrome c measured after 45 min of ischemia. The rate of oxidation through cytochrome oxidase also was improved in rotenone-treated hearts. Inhibition of the electron transport chain during ischemia lessens damage to mitochondria. Rotenone treatment of isolated subsarcolemmal mitochondria decreased the production of reactive oxygen species during the oxidation of complex I substrates. Thus, the limitation of electron flow during ischemia preserves cardiolipin content, cytochrome c content, and the rate of oxidation through cytochrome oxidase. The mitochondrial electron transport chain contributes to ischemic mitochondrial damage that in turn augments myocyte injury during subsequent reperfusion.

Biological significance of phospholipid hydroperoxide glutathione peroxidase (PHGPx, GPx4) in mammalian cells

Reactive oxygen species (ROS) are known mediators of intracellular signal cascades. Excessive production of ROS may lead to oxidative stress, loss of cell function, and cell death by apoptosis or necrosis. Lipid hydroperoxides are one type of ROS whose biological function has not yet been clarified. Phospholipid hydroperoxide glutathione peroxidase (PHGPx, GPx4) is a unique antioxidant enzyme that can directly reduce phospholipid hydroperoxide in mammalian cells. This contrasts with most antioxidant enzymes, which cannot reduce intracellular phospholipid hydroperoxides directly. In this review, we focus on the structure and biological functions of PHGPx in mammalian cells. Recently, molecular techniques have allowed overexpression of PHGPx in mammalian cell lines, from which it has become clear that lipid hydroperoxides also have an important function as activators of lipoxygenase and cyclooxygenase, participate in inflammation, and act as signal molecules for apoptotic cell death and receptor-mediated signal transduction at the cellular level.

Withania somnifera (ASHWAGANDHA) ATTENUATES ANTIOXIDANT DEFENSE IN AGED SPINAL CORD AND INHIBITS COPPER INDUCED LIPID PEROXIDATION AND PROTEIN OXIDATIVE MODIFICATIONS

Withania somnifera is classified in Ayurveda, the ancient Indian system of medicine, as a rasayana, a group of plant-derived drugs which promote physical and mental health, augment resistance of the body against disease and diverse adverse environmental factors, revitalize the body in debilitated conditions and increase longevity. We investigated the effects of Withania somnifera on copper-induced lipid peroxidation and antioxidant enzymes in aging spinal cord of Wistar rats. The activity of glutathione peroxidase (GPx) decreased significantly in the spinal cord from adult to aged mice. Treatment with Withania somnifera successfully attenuated GPx activity and inhibited lipid peroxidation in a dose dependent manner. Withania somnifera inhibited both the lipid peroxidation and protein oxidative modification induced by copper. These effects were similar to those of superoxide dismutase and mannitol. The results indicate the therapeutic potential of Withania somnifera in aging and copper-induced pathophysiological conditions.

Training-induced apoptosis in skeletal muscle

Apoptosis or programmed cell death is a genetically controlled response of cells to commit suicide and is associated with DNA fragmentation or laddering. The common inducers of apoptosis include Ca2+i and oxygen free radicals/oxidative stress, which are also implicated in the pathogenesis of exercise-induced myopathies. To examine training-induced apoptosis, Thoroughbred horses were subjected to 3 months training programme on a treadmill. At the end of the training programme venous blood samples were taken for a creatine kinase (CK) assay. In addition, muscle biopsy samples were obtained for a membrane lipid peroxidation measurement by malondialdehyde (MDA) assay and for apoptosis detection. Apoptosis was studied by visualising the apoptotic myocytes on the paraffin sections by the modified TUNEL method. DNA laddering was evaluated by subjecting the DNA obtained from the biopsies to 1.5% agarose gel electrophoresis. There was a significant increase (P<0.05) of protein-bound MDA, and a nonsignificant trend (P = 0.14) for the control group to have higher levels of CK compared to the trained group. Under light microscopy, percentage of the TUNEL positive cells was higher (P<0.001) in the training group. This result was corroborated with the findings of DNA fragmentation by gel electrophoresis, which showed higher ladders of DNA band at the same group. In conclusion, these results clearly demonstrate that there is training-induced apoptosis in skeletal muscle. It is probable that apoptosis allows the work/recovery/rebound/supercompensation cycle, when unaccustomed muscle cells activate programmed cell death and are replaced by new and stronger cells, which is the mechanism for training-induced increases in fitness.

Effects of chemical ischemia on purine nucleotides, free radical generation, lipids peroxidation and intracellular calcium levels in C2C12 myotube derived from mouse myocytes

To elucidate the mechanisms of ischemia-mediated myopathy using in vitro model, changes of purine nucleotides, membrane lipid peroxidation(TBARS), intracellular calcium ([Ca2+]i)levels, generation of free radicals, and deoxyribonucleic acid (DNA) fragmentation were examined in mouse-derived C2C12 myotubes under the condition with an inhibition of glycolytic and oxidative metabolism as the ischemic condition. In purine nucleotides, intracellular adenosine triphosphate (ATP) and guanosine triphosphate (GTP) concentrations rapidly and significantly decreased after the treatment with ischemia. No remarkable differences were observed in other purine nucleotides, with the exception of inosine monophosphate (IMP) and extracellular hypoxanthine levels, both of which increased significantly during the ischemia. The lactate dehydrogenase activity in culture supernatant of C2C12 myotubes increased significantly from 2 to 4 hr after the ischemia. On the generation of free radicals, no spectrum was detected in supernatants throughout the observation period, whereas supernatant TBARS concentration increased rapidly and significantly after the ischemia. The relative intensity of [Ca2+]i significantly increased after the ischemia. On the fragmented deoxyribonucleic acid(DNA), no TUNEL positive cells was detected in C2C12 myotubes after 1 hr of the ischemia, however the positive cell percentage subsequently increased. From these results, it was suggested that the ischemic condition induced changes of membrane permeability and increase of [Ca2+]i, both of which lead to cell membrane damage, although a free radical generation was not detected. The ischemic condition also induced the release of substrate hypoxanthine for free radical generation and might initiate the apoptotic pathway in C2C12 myotubes.

Myocardial ischemia selectively depletes cardiolipin in rabbit heart subsarcolemmal mitochondria

Mitochondria contribute to myocyte injury during ischemia. After 30 and 45 min of ischemia in the isolated perfused rabbit heart, subsarcolemmal mitochondria (SSM), located beneath the plasma membrane, sustain a decrease in oxidative phosphorylation through cytochrome oxidase. In contrast, oxidation through cytochrome oxidase in interfibrillar mitochondria (IFM), located between the myofibrils, remains unaffected. Cytochrome oxidase activity in the intact membrane requires an inner mitochondrial membrane lipid environment enriched in cardiolipin. During ischemia, the content of cardiolipin decreased only in SSM, whereas the content of other phospholipids was preserved. Ischemia did not alter the composition of the cardiolipin that remained in SSM. Cardiolipin content was preserved in IFM during ischemia. Thus cardiolipin is a relatively early target of ischemic mitochondrial damage, leading to loss of oxidative phosphorylation through cytochrome oxidase in SSM.

Mitochondrial dysfunction in cardiac disease: ischemia--reperfusion, aging, and heart failure

Mitochondria contribute to cardiac dysfunction and myocyte injury via a loss of metabolic capacity and by the production and release of toxic products. This article discusses aspects of mitochondrial structure and metabolism that are pertinent to the role of mitochondria in cardiac disease. Generalized mechanisms of mitochondrial-derived myocyte injury are also discussed, as are the strengths and weaknesses of experimental models used to study the contribution of mitochondria to cardiac injury. Finally, the involvement of mitochondria in the pathogenesis of specific cardiac disease states (ischemia, reperfusion, aging, ischemic preconditioning, and cardiomyopathy) is addressed.

Inhibitory effects of astragali radix, crude drug in Oriental medicines on lipid peroxidation and protein oxidative modification of mouse brain homogenate by copper

Astragali Radix, the root of Astragalus membranaceus Bunge, is a crude drug used widely in Oriental medicines. It is a major component of Ougi-Keishi-gomotsu-to, a traditional herbal medicine, used for neurop patients with abnormal sensations and neuropathic pain of the legs. It was shown to have inhibitory effects on lipid peroxidation and protein oxidative modification by copper. The effects were similar to and stronger than those of mannitol and superoxide dismutase as free radical scavengers. These results demonstrated that Astragali Radix has inhibitory effects on oxidative stress induced by metal.

Inhibitory effects of Astragali Radix, a crude drug in Oriental medicines, on lipid peroxidation and protein oxidative modification by copper

Effects of Astragali Radix, the root of Astragalus membrauaceus Bunge, were investigated on oxidative stress such as lipid peroxidation and protein oxidative modification by copper. The results showed that these effects are similar to those of mannitol and superoxide dismutase as a free radical scavenger. It was demonstrated that Astragali Radix have inhibitory effects on oxidative stress induced by copper.

Hydroxyl radical generation and lipid peroxidation in C2C12 myotube treated with iodoacetate and cyanide

To mimic exercise-induced events such as energetic impairment, free radical generation, and lipid peroxidation in vitro, mouse-derived C2C12 myotubes were submitted to the inhibition of glycolytic and/or oxidative metabolism with 1 mM iodoacetate (IAA) and/or 2 mM sodium cyanide (CN), respectively, under 5% CO2/95% air up to 180 min. Electron spin resonance (ESR) analysis with a spin-trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) revealed time-course increases in spin adducts from hydroxyl radical (DMPO-OH) and carbon-centered radical (DMPO-R) in the supernatant of C2C12 myotubes treated with the combination of IAA + CN. In this condition, malondialdehyde (MDA) and lactate dehydrogenase (LDH) were released into the supernatant. By the addition of iron-chelating 1 mM deferoxamine to the C2C12 preparation with IAA + CN, both ESR signals of DMPO-OH and DMPO-R were completely abolished, and the release of MDA and LDH were significantly reduced, while cyanide-resistant manganese superoxide dismutase had negligible effects on these parameters. Hence, a part of the injury of C2C12 myotube under IAA + CN was considered to result from the lipid peroxidation, which was induced by hydroxyl radical generated from iron-catalyzed systems such as the Fenton-type reaction. This in vitro model would be a helpful tool for investigating the free radical-related muscle injury.

Inhibitory effects of Ougi-keishi-gomotsu-to, a traditional herbal medicine, on lipid peroxidation and protein oxidative modification of mouse brain homogenate induced by copper

Ougi-Keishi-gomotsu-to a traditional herbal medicine, is used clinically for patients with abnormal sensations and pain in the legs in neuropathy. It was shown to have inhibitory effects on lipid peroxidation and protein oxidative modification of brain homogenate induced by copper. Its effect was stronger than those of mannitol and alpha-tocopherol as free radical scavenger and antioxidant. These results demonstrated that Ougi-kelshi-gomotsu-to has antioxidative effects on neuron injury derived from oxidative stress induced by metal.

Biochemistry and pathology of radical-mediated protein oxidation

Radical-mediated damage to proteins may be initiated by electron leakage, metal-ion-dependent reactions and autoxidation of lipids and sugars. The consequent protein oxidation is O2-dependent, and involves several propagating radicals, notably alkoxyl radicals. Its products include several categories of reactive species, and a range of stable products whose chemistry is currently being elucidated. Among the reactive products, protein hydroperoxides can generate further radical fluxes on reaction with transition-metal ions; protein-bound reductants (notably dopa) can reduce transition-metal ions and thereby facilitate their reaction with hydroperoxides; and aldehydes may participate in Schiff-base formation and other reactions. Cells can detoxify some of the reactive species, e.g. by reducing protein hydroperoxides to unreactive hydroxides. Oxidized proteins are often functionally inactive and their unfolding is associated with enhanced susceptibility to proteinases. Thus cells can generally remove oxidized proteins by proteolysis. However, certain oxidized proteins are poorly handled by cells, and together with possible alterations in the rate of production of oxidized proteins, this may contribute to the observed accumulation and damaging actions of oxidized proteins during aging and in pathologies such as diabetes, atherosclerosis and neurodegenerative diseases. Protein oxidation may also sometimes play controlling roles in cellular remodelling and cell growth. Proteins are also key targets in defensive cytolysis and in inflammatory self-damage. The possibility of selective protection against protein oxidation (antioxidation) is raised.

Effects of a novel low-molecular weight antioxidant on cardiac injury induced by hydrogen peroxide

H290/51, an indenoindole derivative, is a novel low-molecular weight (287.8) inhibitor of lipid peroxidation. Its effect on cardiac injury induced by exogenous reactive oxygen intermediates (ROI) was investigated. ROI were generated by adding H2O2 (180 mu M) to the perfusate of isolated rat hearts (Langendorff model, n = 9) for 10 min. H2O2 reduced left ventricular developed pressure (LVDP = left ventricular systolic pressure -- left ventricular end-diastolic pressure) from 90 +/- 6 to a minimum of 25 +/- 2 mmHg (mean +/- SEM) after 10 min (p < 0.001), elevated left ventricular end-diastolic pressure (LVEDP) from 0 to 32 +/- 7 mmHg after 20 min (p < 0.0001), and increased coronary flow (CF). Lactate dehydrogenase (LDH) release in the coronary effluent and thiobarbituric acid-reactive substances (TBARS) in cardiac tissue increased (TBARS from 0.6 +/- 0.04 to 3.1 +/- 0.4 nmol/g tissue after 10 min of H2O2 administration, p < 0.001). Addition of H290/51 (1 mu M, n = 12) from the start of H2O2 exposure, attenuated the H2O2-induced increase of LVEDP (9 +/- 3 mmHg at 20 min, p < 0.006) and reduced the release of LDH (p < 0.02 at 30 min). LVDP was not significantly influenced. The increase of TBARS was abolished by H290/51 (p < 0.001). In conclusion, H290/51 inhibited lipid peroxidation, and attenuated functional and biochemical injury induced by H2O2 exposure.

Endogenous ubiquinol prevents protein modification accompanying lipid peroxidation in beef heart submitochondrial particles

This article is a study of the relationship between lipid peroxidation and protein modification in beef heart submitochondrial particles, and the protective effect of endogenous ubiquinol (reduced coenzyme Q) against these effects. ADP-Fe3+ and ascorbate were used to initiate lipid peroxidation and protein modification, which were monitored by measuring TBARS and protein carbonylation, respectively. Endogenous ubiquinone was reduced by the addition of succinate and antimycin. The parameters investigated included extraction and reincorporation of ubiquinone, and comparison of the effect of ubiquinol with those of various antioxidant compounds and enzymes, as well as the iron chelator EDTA. Under all conditions employed there was a close correlation between lipid peroxidation and protein carbonylation, and the inhibition of these effects by endogenous ubiquinol. SDS-PAGE analysis revealed a differential effect on individual protein components and its prevention by ubiquinol. Conceivable mechanisms behind the observed oxidative modifications of membrane phospholipids and proteins and of the role of ubiquinol in preventing these effects are considered.

Anoxia induces changes in translatable mRNA populations in turtle organs: a possible adaptive strategy for anaerobiosis

The effects of anoxic submergence (16 h at 15 degrees C) on cellular mRNA contents were assessed in five organs of anoxia tolerant turtles Trachemys scripta elegans. Poly(A)+ RNA was extracted from liver, red and white skeletal muscle, kidney and heart of control and anoxic turtles, as well as from heart and kidney of turtles allowed 24 h aerobic recovery (at 15 degrees C) after anoxia exposure. Poly(A)+ RNA content increased by 30% in white muscle from anoxic turtles relative to control animals but was unchanged by metabolic state in other organs. Extracted mRNA was translated in vitro in a wheat germ lysate system and the 35S-labelled polypeptides that were produced were separated by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. Overall translational activity of the mRNA pool [cpm 35S-methionine incorporated per microgram poly(A)+ RNA] was altered by anoxia exposure in three organs, increasing by 38 and 18% in liver and kidney and decreasing by 42% in red muscle. Anoxia exposure also led to qualitative changes in the protein products that resulted from in vitro translation. Sodium dodecyl sulphate polyacrylamide gel electrophoresis revealed the presence of a novel 19.5-kDa polypeptide in liver of anoxia-exposed animals as well as increased amounts of two other proteins at 28.6 and 79.9 kDa. In heart a new translation product of 26.8 kDa appeared in anoxia, and in kidney a 32.8-kDa polypeptide was produced during the aerobic recovery period after anoxia exposure. Anoxia stimulated the appearance of a 37.5-kDa protein in red skeletal muscle but anoxic red muscle also lost proteins of 40, 32, and 28.2 kDa that were present in aerobic controls. Anoxia exposure did not change the proteins produced by in vitro translation in white muscle. The results suggest that anoxia exposure triggers rapid cellular responses in T. s. elegans that modify translatable mRNA populations in organs, leading to new protein transcripts.(ABSTRACT TRUNCATED AT 400 WORDS)

In vitro oxidative inactivation of glutathione S-transferase from a freeze tolerant reptile

We have previously reported that when garter snakes. Thamnophis sirtalis parietalis, a freeze tolerant species, were exposed to 5 h freezing at -2.5 degrees C organs showed increases in the activities of anti-oxidant enzymes, especially catalase in skeletal muscle. This was interpreted to be an adaptation to deal with the potentially injurious postischemic situation of thawing. The present work analyzes in vitro oxidative inactivation of a possible target of postischemic-induced free radical damage, the secondary anti-oxidant defense glutathione-S transferase, and the protective role of endogenous catalase. Approximately 50% of GST activity from snake muscle homogenates was lost within 2 min after addition of H2O2 plus Fe(II) (0.4-2 mM) in media containing azide whereas addition of iron alone resulted in no damaging effects. The opposing effects of dimethyl sulfoxide and EDTA in modifying this process strongly suggested the involvement of .OH radicals in the GST inactivation. A partial recovery of the activity was promoted by mercaptoethanol, indicating that sulphydryl groups oxidation participate in the mechanism of GST inactivation. Pre-incubation of the reaction media containing H2O2 caused protection of the GST activity only in the absence of azide, indicating that endogenous catalase modulates the extent of oxyradical damage. The protective pre-incubation effect was more efficacious when employing homogenates from lung and liver, organs that have higher catalase activities, as well as homogenates from freezing-exposed muscle (that show an 80% increase in catalase activity, compared with control). The protection against GST inactivation observed in muscle from frozen snakes demonstrates that increased anti-oxidant defenses during freezing exposure can be a key factor in controlling in vitro oxyradical damage. The implications for natural freeze tolerance are discussed.

Peroxidative damage to cardiac mitochondria: identification and purification of modified adenine nucleotide translocase

Rat myocardial membranes exposed to free radical-generating systems exhibit both lipid peroxidation and protein alterations. The most sensitive protein, a 28-kDa polypeptide, was previously shown to increase slightly in apparent molecular weight before disappearing completely from the protein profile [N. L. Parinandi, C. W. Zwizinski, and H. H. O. Schmid (1991) Arch. Biochem. Biophys. 289, 118-123]. We now report that isolated cardiac mitochondria contain a 28-kDa protein which responds in the same manner to treatment with Cu2+/t-butylhydroperoxide. The protein exhibits several characteristic properties of the mitochondrial adenine nucleotide translocase. This assignment is supported by the finding that carboxyatractyloside, a specific inhibitor of the adenine nucleotide translocase, can prevent the oxidant-induced changes in the 28-kDa protein. Efficient purification schemes for the isolation of milligram quantities of unmodified and oxidatively altered adenine nucleotide translocase from rat heart mitochondria are described.