Ischemia-induced changes in myocardial paramagnetic metabolites: implications for intracellular oxy-radical generation

Evaluation of mitochondrial redox status and energy metabolism of X-irradiated HeLa cells by LC/UV, LC/MS/MS and ESR

To evaluate the metabolic responses in tumour cells exposed to ionizing radiation, oxygen consumption rate (OCR), cellular lipid peroxidation, cellular energy status (intracellular nucleotide pool and ATP production), and mitochondrial reactive oxygen species (ROS), semiquinone (SQ), and iron-sulphur (Fe-S) cluster levels were evaluated in human cervical carcinoma HeLa cells at 12 and 24 h after X-irradiation. LC/MS/MS analysis showed that levels of 8-iso PGF_2α and 5-iPF_2α-VI, lipid peroxidation products of membrane arachidonic acids, were not altered significantly in X-irradiated cells, although mitochondrial ROS levels and OCR significantly increased in the cells at 24 h after irradiation. LC/UV analysis revealed that intracellular AMP, ADP, and ATP levels increased significantly after X-irradiation, but adenylate energy charge (adenylate energy charge (AEC) = [ATP + 0.5 × ADP]/[ATP + ADP + AMP]) remained unchanged after X-irradiation. In low-temperature electron spin resonance (ESR) spectra of HeLa cells, the presence of mitochondrial SQ at g = 2.004 and Fe-S cluster at g = 1.941 was observed and X-irradiation enhanced the signal intensity of SQ but not of the Fe-S cluster. Furthermore, this radiation-induced increase in SQ signal intensity disappeared on treatment with rotenone, which inhibits electron transfer from Fe-S cluster to SQ in complex I. From these results, it was suggested that an increase in OCR and imbalance in SQ and Fe-S cluster levels, which play a critical role in the mitochondrial electron transport chain (ETC), occur after X-irradiation, resulting in an increase in ATP production and ROS leakage from the activated mitochondrial ETC.

Mitochondria-Targeted Antioxidants: Future Perspectives in Kidney Ischemia Reperfusion Injury

Kidney ischemia/reperfusion injury emerges in various clinical settings as a great problem complicating the course and outcome. Ischemia/reperfusion injury is still an unsolved puzzle with a great diversity of investigational approaches, putting the focus on oxidative stress and mitochondria. Mitochondria are both sources and targets of ROS. They participate in initiation and progression of kidney ischemia/reperfusion injury linking oxidative stress, inflammation, and cell death. The dependence of kidney proximal tubule cells on oxidative mitochondrial metabolism makes them particularly prone to harmful effects of mitochondrial damage. The administration of antioxidants has been used as a way to prevent and treat kidney ischemia/reperfusion injury for a long time. Recently a new method based on mitochondria-targeted antioxidants has become the focus of interest. Here we review the current status of results achieved in numerous studies investigating these novel compounds in ischemia/reperfusion injury which specifically target mitochondria such as MitoQ, Szeto-Schiller (SS) peptides (Bendavia), SkQ1 and SkQR1, and superoxide dismutase mimics. Based on the favorable results obtained in the studies that have examined myocardial ischemia/reperfusion injury, ongoing clinical trials investigate the efficacy of some novel therapeutics in preventing myocardial infarct. This also implies future strategies in preventing kidney ischemia/reperfusion injury.

Detection of mitochondrial dysfunction by EPR technique in mouse model of dilated cardiomyopathy

Tgalphaq44 mice with targeted overexpression of activated Galphaq protein in cardiomyocytes mimic many of the phenotypic characteristics of dilated cardiomyopathy in humans. However, it is not known whether the phenotype of Tgalphaq44 mice would also involve dysfunction of cardiac mitochondria. The aim of the present work was to examine changes in EPR signals of semiquinones and iron in Fe-S clusters, as compared to classical biochemical indices of mitochondrial function in hearts from Tgalphaq44 mice in relation to the progression of heart failure. Tgalphaq44 mice at the age of 14 months displayed pulmonary congestion, increased heart/body ratio and impairment of cardiac function as measured in vivo by MRI. However, in hearts from Tgalphaq44 mice already at the age of 10 months EPR signals of semiquinones, as well as cyt c oxidase activity were decreased, suggesting alterations in mitochondrial electron flow. Furthermore, in 14-months old Tgalphaq44 mice loss of iron in Fe-S clusters, impaired citrate synthase activity, and altered mitochondrial ultrastructure were observed, supporting mitochondrial dysfunction in Tgalphaq44 mice. In conclusion, the assessment of semiquinones content and Fe(III) analysis by EPR represents a rational approach to detect dysfunction of cardiac mitochondria. Decreased contents of semiquinones detected by EPR and a parallel decrease in cyt c oxidase activity occurs before hemodynamic decompensation of heart failure in Tgalphaq44 mice suggesting that alterations in function of cardiac mitochondria contribute to the development of the overt heart failure in this model.

Biomarkers of oxidative damage to predict ischaemia-reperfusion injury in an isolated organ perfusion model of the transplanted kidney

Ischaemia-reperfusion (IR) injury is known to be a risk factor influencing both short and long-term graft function following transplantation. The pathophysiology of IR injury is suggested to involve elevated reactive oxygen species production resulting in oxidative damaged cellular macromolecules. The objective of this study was to evaluate oxidative damage following IR using an isolated organ perfusion model of the transplanted kidney, in order to determine a simple, preferably non-invasive biomarker for IR injury. Porcine kidneys were retrieved with 10 or 40 min warm ischaemic (WI) time and haemoperfused for 6 h on an isolated organ perfusion machine. ELISA was used to detect carbonyls, 8-isporostane and 8-hydroxy-2'-deoxyguanosine, representing protein, lipid and DNA damage respectively in pre and post reperfusion samples of plasma, urine and biopsy material. Plasma carbonyl and 8-isporostane and were significantly increased in the 40 min group compared to pre-perfusion (0.96 +/- 0.10 vs. 0.62 +/- 0.06, P < 0.001 and 1.57(1.28-4.9) vs. 0.36(0.09-0.59), P < 0.05). The levels also correlated with creatinine clearance used to determine renal function (r = - 0.6150, P < 0.01 and r = - 0.7727, P < 0.01). The results of this study suggest both plasma carbonyl and 8-isporostane to be reliable biomarkers to predict the level IR injury.

Oxygen free radicals and redox biology of organelles

The presence and supposed roles of reactive oxygen species (ROS) were reported in literature in a myriad of instances. However, the breadth and depth of their involvement in cellular physiology and pathology, as well as their relationship to the redox environment can only be guessed from specialized reports. Whatever their circumstances of formation or consequences, ROS seem to be conspicuous components of intracellular milieu. We sought to verify this assertion, by collecting the available evidence derived from the most recent publications in the biomedical field. Unlike other reviews with similar objectives, we centered our analysis on the subcellular compartments, namely on organelles, grouped according to their major functions. Thus, plasma membrane is a major source of ROS through NAD(P)H oxidases located on either side. Enzymes of the same class displaying low activity, as well as their components, are also present free in cytoplasm, regulating the actin cytoskeleton and cell motility. Mitochondria can be a major source of ROS, mainly in processes leading to apoptosis. The protein synthetic pathway (endoplasmic reticulum and Golgi apparatus), including the nucleus, as well as protein turnover, are all exquisitely sensitive to ROS-related redox conditions. The same applies to the degradation pathways represented by lysosomes and peroxisomes. Therefore, ROS cannot be perceived anymore as a mere harmful consequence of external factors, or byproducts of altered cellular metabolism. This may explain why the indiscriminate use of anti-oxidants did not produce the expected "beneficial" results in many medical applications attempted so far, underlying the need for a deeper apprehension of the biological roles of ROS, particularly in the context of the higher cellular order of organelles.

The role of mitochondria in ischemia/reperfusion injury in organ transplantation

In organ transplantation, ischemia/reperfusion (I/R) results in damage that may affect cell viability and lead to organ failure. I/R injury involves a complex cascade of events, including loss of energy, derangement of the ionic hemostasis, production of reactive oxygen species, and cell death. In this context, mitochondria may be critical organelles, since they undergo major changes that may contribute to the injury occurring during I/R.

The role of mitochondria in ischemia/reperfusion injury

In organ transplantation, ischemia/reperfusion injury is a multifactorial process that leads to organ damage and primary graft dysfunction. Injury to the organ is mediated by a complex chain of events that involves depletion of energy substrates, alteration of ionic homeostasis, production of reactive oxygen species, and cell death by apoptosis and necrosis. There is increasing evidence that mitochondria play a role in this process because of the profound changes experienced during ischemia and reperfusion. Understanding the mechanisms that lead to mitochondrial damage may be important for developing strategies aimed at improving graft outcome. In this review, we examine the role of mitochondria in ischemia/reperfusion injury and the possible mechanisms that may contribute to organ dysfunction.

Antiarrhythmic effect of magnolol and honokiol during acute phase of coronary occlusion in anesthetized rats: influence of L-NAME and aspirin

This study was designed to evaluate the in vivo effect of magnolol and honokiol on the acute phase of coronary ligation in the presence of nitric oxide inhibitor (L-NAME) or cyclooxygenase inhibitor (aspirin). After Sprague-Dawley rats were anesthetized with urethane, the changes of ventricular arrhythmia induced by coronary ligation for 30 min were determined with or without pretreatment with study medications. The incidence and duration of ventricular arrhythmia were significantly reduced after intravenous pretreatment (15 min before coronary ligation) with 10(-7) g/kg magnolol or 10(-7) g/kg honokiol. However, the antiarrhythmic effect of magnolol or honokiol could be abolished with the pretreatment of 1 mg/kg L-NAME, but not with pretreatment of 100 mg/kg aspirin. The abolishment of the myocardial beneficial effect of magnolol and honokiol by L-NAME, instead of aspirin, suggests an involvement of an increased nitric oxide synthesis in the protection offered by magnolol and honokiol against arrhythmia during myocardial ischemia.

Changes of superoxide dismutase in cultured rat aortic smooth muscle cells (A7r5) by an incubation of vitamin E

Supplementation of antioxidants such as vitamin E and vitamin C as health promotion food is popular recently. Epidemiological studies supported the beneficial effect of these antioxidants because oxygen free radicals have been linked to the process of diseases and aging. The present study evaluated the effect of alpha-tocopherol (vitamin E) on the changes of superoxide dismutase (SOD) in cultured rat aortic smooth muscle cells (A7r5) after a short-term (2 days) or long-term (7 days) incubation. Incubation of A7r5 cells with vitamin E at a concentration of 50 micromol/l for 2 days caused an increase of both the activity and mRNA level of SOD. At higher concentrations, such as 100 or 200 micromol/l, vitamin E failed to enhance SOD more effectively. However, after incubation for 7 days, vitamin E caused a decrease in both the activity and mRNA level of SOD in a concentration-dependent manner. Otherwise, the protein amount of SOD remained the same in these samples regardless of the concentration of vitamin E or the duration of incubation. The obtained results suggest that vitamin E can increase the effect of SOD to result in the beneficial influence of this antioxidant only at low concentration under a short-term supplementation because a down-regulation of SOD was observed in cells receiving a long-term incubation.

Electron spin resonance analysis of heme-nitrosyl and reduced iron-sulfur centered complexes in allogeneic, heterotopic cardiac transplants: effects of treatment with pyrrolidine dithiocarbamate

Inhibition of inducible nitric oxide synthase (iNOS) prolongs allograft survival suggesting a role for nitric oxide (.NO) in allograft rejection. Induction of iNOS is regulated by the oxidant-sensitive, nuclear factor kappa B (NF-kappaB) in many cell types. In the present study using electron spin resonance (ESR) spectroscopy, we evaluated whether pyrrolidine dithiocarbamate (PDTC), a metal chelator and antioxidant, might limit .NO production during the development of rejection in cardiac allografts. We performed either isogeneic (Lewis to Lewis) or allogeneic (Wistar-Furth to Lewis) heterotopic abdominal cardiac transplantation. Allograft recipients received daily injections of PDTC or aminoguanidine (a known inhibitor of iNOS). At postoperative days 4 or 6, grafted and native hearts of transplant recipients were flushed with cardioplegic solution to remove blood contamination. ESR data of allografts revealed a triplet nitrogen signal (aN=17.5 G) and centered at g=2.012 and an additional broad signal at g=2.08. This signal was not seen in either isografts or native hearts of either isograft or allograft recipients. Based upon these parameters, these signals are attributed to nitrosomyoglobin. This signal was inhibited by treatment with aminoguanidine or PDTC. Under these conditions, PDTC also prolonged graft survival from 6.6+/-0.2 to 11.7+/-0.3 days. Thus, it is conceivable that nitrosylmyoglobin formation precedes rejection in cardiac allografts and inhibition of nitrosomyoglobin with agents such as PDTC contribute to improved graft survival.

Neuroprotective effects of hypothermia and U-78517F in cerebral ischemia are due to reducing oxygen-based free radicals: an electron paramagnetic resonance study with gerbils

Free radicals are implicated as causative agents in various forms of tissue destruction. Considerable circumstantial evidence suggests that oxygen-based free radicals generated as blood flow returns to formerly ischemic brain areas are mainly responsible for the neurodegeneration that follows periods of cerebral ischemia. In general, oxygen-based free radicals are highly reactive and exist for only a brief period of time. This makes the direct measurement of many of these free radicals rather difficult. Much of the current knowledge of free radicals in cerebral ischemia is based on observations of chemical changes brought about by the free radicals rather than on direct observations of the free radicals themselves. Low temperature electron paramagnetic resonance spectroscopy is one method that allows the direct study of free radicals. Compared to samples from sham-operated controls, samples of hippocampus taken from gerbils exposed to 15 min of forebrain ischemia followed by 15 min of reperfusion, frozen in liquid nitrogen less than 20 sec after sacrifice, and scanned by low temperature (100 K) electron paramagnetic resonance, show a significant increase in oxygen-based free radicals and a decrease in carbon-based ubiquinone-like free radicals. The ischemia-induced increase in oxygen-based free radicals is prevented by the intraperitoneal injection of the antioxidant drug U-78517F at the start of reperfusion and by hypothermia. However, neither intervention alters the ischemia-induced reduction in the ubiquinone-like free radicals. This suggests that the neuroprotective actions of hypothermia and U-78517F include a direct reduction in the oxygen-based free radical burden of the post-ischemic tissue.

Uncoupling of mitochondrial oxidative phosphorylation alters lipid peroxidation-derived free radical production but not recovery of postischemic rat hearts and post-hypoxic endothelial cells

The contribution of mitochondrial free radical production towards the initiation of lipid peroxidation (LPO) and functional injury in the post-ischemic heart is unclear. Using the isolated rat heart model, the effects of the uncoupler of mitochondrial oxidative phosphorylation dinitrophenol (DNP, 50 microM final) on post-ischemic lipid peroxidation-derived free radical production and functional recovery were assessed. Hearts were subjected to 30 min total global ischemia followed by 15 min of reperfusion in the presence of DNP. As expected, DNP enhanced oxygen consumption before (11.3 +/- 0.9 mumol/min, p < 0.001) and during reperfusion (at 10 min: 7.9 +/- 0.7 mu umol/min), compared to the heart with control treatment (8.2 +/- 0.5 and 6.7 +/- 0.3, respectively). This effect was only associated with a higher incidence of ventricular tachycardia during reperfusion (80 vs. 50% for control treatment, p < 0.05). Electron spin resonance spectroscopy (ESR) and spin trapping with alpha-phenyl-tert-butylnitrone PBN-radical adducts (untreated: 6.4 +/- 1.0 nM, at 10 min) decreased in the presence of DNP (1.7 +/- 0.4 nM, p < 0.01). The radical concentration inversely correlated with myocardial oxygen consumption. Total liberation of free radical adducts during the initial 10 min of reperfusion was reduced by DNP (0.59 +/- 0.09 nmol, p < 0.01) compared to the respective control treatment (1.26 +/- 0.16 nmol). Similar effects, prevention of PBN adduct formation and unchanged viability in the presence of DNP, were obtained with endothelial cells during post-hypoxic reoxygenation. Since inhibition of mitochondrial phosphorylation can inhibit the formation of LPO-derived free radicals after an ischemic/hypoxic interval, mitochondria may represent an important source of free radicals capable of initiating lipid peroxidative injury during reperfusion/reoxygenation.

S-nitrosoglutathione induces formation of nitrosylmyoglobin in isolated hearts during cardioplegic ischemia--an electron spin resonance study

Previously, it has been shown that *NO donor S-nitrosoglutathione (GSNO) improves the postischemic functional recovery in crystalloid buffer-perfused isolated rat hearts subjected to cardioplegic ischemia. Supplementation of cardioplegic solution with nitronyl nitroxide, a scavenger of *NO, antagonized this protective effect. Using low temperature ESR, we have detected nitrosylmyoglobin (MbNO) in rat hearts subjected to cardioplegic ischemia in the presence of GSNO (20-200 mumol/l). During aerobic reperfusion MbNO signal intensity gradually decreased, but persisted for up to 30 min of aerobic reperfusion. We conclude that MbNO is an endogenous marker of *NO release in myocardial tissues. Implications of MbNO formation are discussed with respect to cardioprotection during ischemia- and reperfusion-induced myocardial injury.

A hydroxylated analog of the beta-adrenoceptor antagonist, carvedilol, affords exceptional antioxidant protection to postischemic rat hearts

The antioxidant and cardioprotective effects of the beta-adrenoceptor antagonist, carvedilol, and its hydroxylated analog. BM-910228, were compared using the postischemic rat heart model. Hearts were infused with either agent (0.01, 0.10, or 10 nM final, or drug-free infusate) for 10 min prior to 30 min global ischemia, and also during the initial 15 min of reperfusion. Recovery of postischemic hemodynamic parameters (left ventricular systolic and developed pressures, mean diastolic pressure, cardiac output, coronary flow rate, and cardiac pressure-volume work), and the extent of postischemic tissue lactate dehydrogenase (LDH) loss, lipid hydroperoxide (LOOH) formation, and lipid peroxidation (LPO)-derived free radical production were assessed and compared among the treatment groups. The depressive pharmacological properties (beta- and alpha-blockade) of both agents masked the extent of postischemic hemodynamic recovery, except at the lowest dose (10 pM) of the analog, which provided significant improvements in systolic and developed pressures, and cardiac work. Treatment with both agents provided significant dose-dependent reductions in postischemic LOOH formation and lipid alkoxyl radical production, as determined by electron spin resonance spectroscopy and alpha-phenyl-tert-butylnitrone. (PBN) spin trapping (PBN/alkoxyl adduct hyperfine splitting alpha N = 13.63 G and alpha H = 1.93 G). Although both agents reduced oxidative injury, the hydroxylated analog was clearly the superior antioxidant (equipotent at doses two to three orders of magnitude lower) compared to the parent compound. This was also reflected with respect to three orders of magnitude lower) compared to the parent compound. This was also reflected with respect to drug-mediated improvement in myocardial preservation (reduced LDH release), which paralleled the antioxidant protective effects. Because neither agent displayed significant primary radical scavenging ability at doses (< or = 10 nM), which did provide substantial inhibition of postischemic LOOH and alkoxyl formation, our data suggest that the antioxidant properties of carvedilol and its analog are mediated primarily through a LPO chair-breaking mechanism. Moreover, the significant antioxidant protection afforded by the analog BM-910228 at subnanomolar levels places this agent into an exclusive category reserved for exceptionally potent antioxidants.

Cellular reducing equivalents and oxidative stress

Energy has been proposed to play a role in the ability of cells and tissues to defend against oxidative stress, even though the ultimate antioxidant capacity of a tissue is determined by the supply of reducing equivalents. The pathways involved in supplying reducing equivalents in response to an oxidative stress remain unclear, particularly if competing reactions such as ATP synthesis are active. Glutathione (GSH), a major component of cellular antioxidant systems, is maintained in the reduced form by glutathione reductase. Although this enzyme is specific for NADPH, the ability of intact cells, isolated mitochondria (which are a major source of free radicals and contain antioxidant systems independent of the rest of the cell), and whole tissues to supply reducing equivalents and maintain normal levels of GSH appears to involve NADH. This article reviews available data regarding the source and pathways by which reducing equivalents are made available to reduce exogenous oxidants, and suggests energy is not a factor. An improved understanding of the mechanism by which reducing equivalents are supplied by tissues to respond to an oxidative stress may direct future research toward designing strategies for augmenting the ability of tissues to defend themselves against oxidative stress induced by reperfusion or xenobiotics.

Effects of oxidant exposure on substrate utilization and high-energy phosphates in isolated rat hearts

The effects of a xanthine oxidase-mediated free radical-generating system containing purine and iron-loaded transferrin or solutions containing hydrogen peroxide and iron-loaded transferrin on substrate utilization and high-energy phosphates were evaluated by nuclear magnetic resonance (NMR) spectroscopy in isolated perfused rat hearts. Hearts were supplied with lactate, acetate, and glucose, and the contribution of each substrate to acetyl coenzyme A was measured in control hearts and in the presence of a free radical-generating system. Perfused hearts were monitored by 31P NMR, and tissue extracts were analyzed by 13C NMR. Free radicals decreased the phosphocreatine and beta-ATP peak areas and reduced contractile function. Under control conditions, lactate, acetate, and endogenous sources were the major contributors of acetyl coenzyme A units, with only 5% originating from glucose. In the presence of a xanthine oxidase-mediated free radical-generating system, the glucose contribution increased to 54%, while contributions from acetate and endogenous sources were significantly reduced. Both 13C and 31P NMR analyses showed no significant accumulation of glycolytic sugar phosphates, suggesting little inhibition of glyceraldehyde-3-phosphate dehydrogenase. The increased contribution of glucose to the tricarboxylic acid cycle relative to acetate and endogenous sources is consistent with activation of pyruvate dehydrogenase. In contrast, hearts exposed to a hydrogen peroxide-based free radical-generating system showed an increase in lactate utilization, a decrease in acetate utilization, and no change in glucose utilization compared with control hearts. Glycolytic sugar phosphates were found to accumulate, suggesting possible inhibition of glyceraldehyde-3-phosphate. Thus, different radicals or their metabolites may have varying effects on myocardial metabolism.

Detection of alkoxyl and carbon-centered free radicals in coronary sinus blood from patients undergoing elective cardioplegia

Confirmation of the involvement of free radicals in postischemic injury in human heart has been elusive. The present study was performed to determine the presence of free radicals in coronary sinus blood from patients undergoing elective open heart surgery and cardioplegia. Six patients who were scheduled for nonurgent elective open heart surgery were used in this study. Coronary sinus blood samples were withdrawn at 1, 3, 5, 10, 15, 20, and 25 min in post-cross-clamp and immediately mixed with isosmotic alpha-phenyl-tert-butylnitrone (PBN) and then centrifuged to obtain plasma. Plasma samples were extracted with toluene and analyzed using electron spin resonance (ESR) spectroscopy. We observed ESR spectra consistent with the formation of alkoxyl and carbon-centered radical adducts of PBN (aN = 13.6 G, a beta H = 1.9 G, and aN = 14.1 G, a beta H = 4.2 G) in six of six patients. We obtained complete free radical production time courses during reperfusion from five patients, and all demonstrated a biphasic profile with an initial burst from 5 to 10 min followed by a second maxima at 25 min. Total PBN-adduct production during reperfusion increased in patients subjected to longer aortic cross-clamp times (global ischemia). These data demonstrate that postcardioplegia free radical production is detectable in coronary sinus blood using an ex vivo spin-trapping technique and that the extent of formation may be related to the severity of ischemia.

Comparisons of ESR and HPLC methods for the detection of OH. radicals in ischemic/reperfused hearts. A relationship between the genesis of free radicals and reperfusion arrhythmias

In this study we compared two methods, electron spin resonance (ESR) spectroscopy and high performance liquid chromatography (HPLC), which are currently used to detect directly hydroxyl radical (OH.) formation in the ischemic and reperfused heart. Isolated buffer-perfused rat hearts were subjected to 30 min of normothermic global ischemia followed by 30 min of reperfusion. 5,5-Dimethyl-pyrroline-N-oxide (DMPO) was used as a spin-trap agent to detect OH. radicals by ESR and HPLC. In additional HPLC studies, salicylic acid was infused into the heart for the detection of OH. radicals. In all studies, the effects of superoxide dismutase (SOD) and catalase (CAT) on the OH. generation were examined. The results of our studies indicate that, irrespective of the method, OH. was always detected when an ischemic heart was reperfused and showed ventricular fibrillation. The OH. concentration increased dramatically between 60 and 90 sec of reperfusion, peaked between 180 and 210 sec, and then progressively decreased. In all cases, both SOD and CAT were able to reduce the formation of OH. radicals, with SOD being relatively more effective. Our results indicate that OH. was produced only in the fibrillating hearts that peaked between 180 and 210 sec (1.64 +/- 0.09 nmol/mL measured by ESR), but not in the non-fibrillating hearts. Although SOD or CAT reduced the OH. formation, they had no effects on the incidence of reperfusion-induced ventricular fibrillation (VF) and ventricular tachycardia (VT). However, when SOD (5 x 10(4) IU/L) was coadministered with CAT (5 x 10(4) IU +/- L), the incidence of reperfusion-induced VF (total) and VT was reduced from their control value of 92 and 100 to 33 (P < 0.05) and 50% (P < 0.05), respectively. The results of this study indicate that the HPLC method, as well as ESR, can be used to detect OH. formation in ischemic/reperfused hearts. Because of the convenience, reproducibility and greater sensitivity, the HPLC technique may be more suitable for OH. detection. Our results further suggest the potential therapeutic value of the combination therapy of SOD and CAT for the reduction of reperfusion-induced VF and VT.

Recent advances in the role of reactive oxygen intermediates in ischemic injury. I. Evidence demonstrating presence of reactive oxygen intermediates; II. Role of metals in site-specific formation of radicals

This article has attempted to bring the reader up to date on advances in selected facets of the area of reactive oxygen intermediate-induced ischemic injury. Specifically, we have discussed the more recent reports that provide evidence for the presence of these species in reperfused ischemic tissue. In addition, we have attempted to introduce the reader to the relatively new concept of "site-specific" formation of radicals and how the use of "push-pull" techniques, such as chelation by high-affinity chelators or displacement by non-redox-active metals such as zinc, may decrease postischemic reperfusion injury. Finally, we have identified a class of compounds that affect the oxidation state of redox-active metals, and have demonstrated how these compounds may also represent a new therapeutic modality. In conclusion, both academic and nonacademic surgeons should have profited from reading this article. For the academic surgeon, who may do research, several new cytoprotectants requiring further study in both in vitro and in vivo models have been identified. For the nonacademic surgeon in clinical practice the realization that there are several promising areas of research that may yield new therapies to mitigate postischemic reperfusion injury should have been gained.

Effects of oxygen free radicals on isolated cardiac myocytes from guinea-pig ventricle: electrophysiological studies

Free oxygen radicals are formed during early reperfusion and are thought to contribute to some types of reperfusion abnormalities, including arrhythmias and myocardial stunning. The purpose of this study was to investigate electrophysiological effects of oxygen free radicals using voltage clamped single ventricular myocytes from guinea-pig hearts. Oxygen free radicals were produced enzymatically by the direct addition of xanthine oxidase (XOD, 0.04 U/ml) in the experimental chamber to a solution containing hypoxanthine (0.96 mM). The generation of oxygen radicals was confirmed by the formation of adrenochrome from adrenaline. Oxygen radicals caused automaticity of isolated myocytes within 20-30 min, followed by later hypercontracture. The percentage of rod-shaped cells declined sigmoidally as a function of time, with a half maximal value at 40.9 +/- 1.6 min, and a Hill slope of -0.10 +/- 0.01 (n = 26). These effects were prevented by a combination of superoxide dismutase (10(5) U/L) plus catalase (10(6) U/L). The rate at which cells underwent morphological shape changes was unchanged by ryanodine (0.5 microM) which is thought to act on the sarcoplasmic reticulum or by the Ca2+ channel blockers nisoldipine (1 microM) or Cd2+ (30 microM). Cellular automaticity and hypercontracture were delayed by variable degrees, and sometimes completely prevented, by zero (1 mM EGTA) extracellular Ca2+, MnCl2 (2 mM) and LaCl3 (50 microM), and amiloride (1 mM). On the other hand, in the presence of a low extracellular Na+ (30 mM) or caffeine (10 mM), hypercontracture occurred at a faster time scale. Whole cell voltage clamping revealed a decrease of the inward rectifying K+ current (IK1), and a decrease of the peak of the L-type Ca2+ current (ICa,L). The total ICa,L during the clamp step was increased, mainly because of an increased time constant of inactivation (47.6 +/- 4.7 ms to 72.7 +/- 15.5 ms after 30 min, n = 4, P less than 0.05). We conclude that oxygen radicals cause automaticity and hypercontracture of isolated myocytes, that these effects may be due to an increased intracellular Ca2+ concentration ([Ca2+]i), and despite an increased ICa,L, that the enhanced Ca2+ influx may occur predominantly via the Na/Ca exchange.

The use of fluorescent probes to assess oxidative processes in isolated-perfused rat heart tissue

The formation of reactive oxygen species (ROS) in intact heart tissue has been assessed by direct ESR measurements, and indirectly by the formation of characteristic tissue products and the protective effects of various antioxidants. The development of lipid soluble esters of compounds which can be trapped intracellularly after hydrolysis, and which fluoresce after oxidation, has provided a new tool to investigate ROS in vitro. The utility of 2',7'-dichlorofluorescin diacetate (DCFDA) in isolated-perfused rat heart tissue was investigated in the present study. DCFDA and its deacetylated form were incubated with various levels of hydrogen peroxide or t-butylhydroperoxide (tBOOH). Conversion of the diacetate form to a fluorescent product required 4-5 h with hydrogen peroxide and up to 24 h with tBOOH. In contrast, the deacetylated form fluoresced at 80% of maximum levels 1 h after the addition of 100 mM tBOOH. DCFDA was loaded into heart tissue by infusing for 10 min at a final concentration of 10 microM in Krebs-Henseleit bicarbonate buffer. After a 10 min washout period, analysis of freeze-clamped heart tissue revealed that the trapped material was readily converted to a fluorescent product by tBOOH, indicating hydrolysis had occurred. Fluorescence of material trapped in heart tissue was approximately 24% of the maximum achieved after oxidation with 100 mM tBOOH. This value decreased to 18 and 13% when the loading and washout periods were from 0 to 20 or 10 to 30 min of hypoxia, respectively. Similar results were obtained with the less readily oxidized dicarboxy derivative of DCFDA. Infusion of 500 microM tBOOH increased the oxidation of DCFDA in heart tissue from 24 to 31%.(ABSTRACT TRUNCATED AT 250 WORDS)

Postanoxic oxidative injury in rat hepatocytes: lactate-dependent protection against tert-butylhydroperoxide

Previous studies in this laboratory showed that hypoxia and anoxia enhance the susceptibility of hepatocytes to tert-butylhydroperoxide (TBH)-induced oxidative injury. To determine whether preceding exposure to anoxia affects postanoxic sensitivity to oxidative injury, viability was studied in hepatocytes incubated under anoxic conditions followed by reoxygenation without or with tert-butylhydroperoxide addition. Results showed that a preceding exposure to 60 min of anoxia substantially increased the vulnerability of cells to injury by the oxidant. Because substantial tissue lactate can accumulate during anoxia, the effect of increased lactate on postanoxic injury due to TBH was determined. Results showed that added lactate protected in a concentration-dependent manner. The TBH elimination rate was stimulated by lactate, and the pyruvate production rate approached the rate of TBH elimination. Thus, lactate protects against postanoxic oxidative injury by supplying reducing equivalents for peroxide reduction. This suggests that lactate accumulation during ischemia may be beneficial and that supplementation with lactate could be considered as a means to protect against postischemic injury.

The inactivation of mitochondrial F1 ATPase by H2O2 is mediated by iron ions not tightly bound in the protein

Exposure to purified mitochondrial F1 ATPase to continuous flux of H2O2 resulted in significant loss (up to 60%) of the ATP hydrolytic activity. The presence of chelating agents including desferrioxamine or previous selective removal of the iron ions not tightly bound in the protein completely prevented the inactivation, whereas re-loading of the enzyme with F3+ restored the sensitivity to H2O2. A marked protective effect was provided as well by mannitol or by Cu,Zn superoxide dismutase. The results indicated the decomposition of H2O2 by redox-active iron-protein adducts as responsible for the enzyme inactivation, probably through site-directed generation of more highly reactive oxygen species. A possible role for iron associated to F1 component in the oxidation, aging and turnover of ATP synthase complex in vivo may be suggested on the basis on these results.

Postischemic free radical production in the venous blood of the regionally ischemic swine heart. Effect of deferoxamine

BACKGROUND

We tested the hypothesis that secondarily produced free radicals can be detected in venous coronary effluent without the need for direct exposure of postischemic tissue to the spin trapping agent alpha-phenyl-tert-butylnitrone (PBN).

METHODS AND RESULTS

The left anterior descending coronary artery (LAD) of pigs was ligated for 15, 30, 40, or 60 minutes, and the tissue was subsequently reperfused for 60 minutes. Venous effluent (6.5 ml) from the risk area was withdrawn sequentially at 1.5-minute intervals during reperfusion. The effluent blood was immediately infused (4.5 ml/min) with an isotonic saline solution containing 120 mM PBN: Preischemic control effluent samples were collected in an identical fashion. Plasma from each sample was extracted in organic solvent and subsequently analyzed by electron spin resonance (ESR) spectroscopy. Another group of pigs received an infusion of the metal chelator deferoxamine mesylate (25 mg/kg/hr) into the right atrium starting 1 hour before the 40-minute ligation and continuing throughout ligation and reperfusion. We were able to demonstrate the postischemic production of ESR signals for PBN adduct(s) from untreated hearts having spectral characteristics similar to an alkoxyl adduct (PBN-RO.; hyperfine splitting constants for beta-hydrogen [alpha H] = 2.0-2.25 G; nitrogen [alpha N] = 13.5-13.75 G). The reperfusion time course of PBN adduct production had a unique pattern: 1) multiple low-level bursts during the initial 15 minutes of reperfusion, and 2) a prominent PBN adduct signal during a relatively late time (20-25 minutes) of reperfusion. Total postischemic PBN adduct production rose with increasing duration (15-60 minutes) of ischemia and was associated with a progressive elevation of total lactate dehydrogenase in the effluent. Infusion of deferoxamine markedly diminished PBN adduct production as well as total release of lactate dehydrogenase.

CONCLUSIONS

These data suggest the potential feasibility of using an ex vivo ESR spin trapping technique in blood-perfused models of cardiovascular injury and that chelatable free iron contributes to the production of alkoxyl radicals.

Oxidative stress during hypoxia in isolated-perfused rat heart

These data suggest that oxidative stress occurs at the low oxygen tensions which exist during perfusion of rat heart tissue with hypoxic medium. Importantly, no evidence was found for additional oxidative injury after 4 min reoxygenation when enzyme release is maximal in this system suggesting the oxygen paradox is unrelated to oxidative stress. However, the oxidative changes evident after 10-15 min of hypoxia do support the occurrence of free radical mediated injury at low oxygen tensions, and it is possible this injury is involved in the changes which lead to cell lysis at reoxygenation. The source of this oxidative stress is not known, but appears to be greater in mitochondria and may arise from an increased production of reactive oxygen species by this organelle. Whether the observed oxidative changes are directly injurious to a cell is not yet clear.

Propranolol preserves ultrastructure in adult cardiocytes exposed to anoxia/reoxygenation: a morphometric analysis

The protective effect of d,l-propranolol was studied using freshly isolated canine ventricular cardiocytes (1.5 x 10(6)/mL) exposed to 30 min anoxia (95% N2/5% CO2) and 0, 3, 20, and 45 min of reoxygenation (95% O2/5% CO2). In addition to preventing lipid peroxide formation, propranolol maintained cellular viability, and minimized ultrastructural alterations. In the absence of propranolol, the outer mitochondria become swollen and rounded up within the first few minutes of reoxygenation. The perinuclear mitochondrial area increased only slightly. We observed that the cellular injury process proceeded differentially from the exterior to the interior, with a mitochondrial area increase and outer membrane rupture. Sarcolemmal damage was also observed with prevalent blebbing and membrane loss. The Z-lines became wider and more diffuse with reoxygenation. Injury to the nuclear double membrane was observed. Incubation with propranolol showed significant protection during postanoxia reoxygenation. In contrast, the more water soluble beta-blocker atenolol only exhibited slight protection. In addition, d-propranolol (the non beta-blocking isomer) and the antioxidant enzymes, SOD and catalase, showed significant protection. These data support previous findings concerning the antioxidant properties of propranolol which appear to be independent of beta-receptor blockade.

Ascorbyl free radical as a reliable indicator of free-radical-mediated myocardial ischemic and post-ischemic injury. A real-time continuous-flow ESR study

The real-time kinetics of the release of ascorbyl free radicals in the coronary perfusate from isolated rat hearts submitted to an ischemia/reperfusion sequence has been achieved by continuous-flow ESR using high-speed acquisition techniques. Enhanced ESR detection of ascorbyl free radicals was obtained by addition of dimethyl sulfoxide (Me2SO), a strong cation chelator and oxidizing agent. A continuous-flow device allowed a direct monitoring of the ascorbyl free radical and/or ascorbate leakage in coronary perfusate by observation of the ascorbyl radical doublet (aH = 0.188 mT and g = 2.0054). 1. The results showed that ascorbyl free radical release occurred mainly during sequences of low-flow ischemia (90 min) coupled or not with 30 min of zero-flow ischemia followed by reperfusion (60 min). The kinetic profiles of ascorbyl-free-radical detection confirm in quantitative terms the expected correlation between the duration of the ischemic insult and the magnitude of ascorbate extracellular release upon reperfusion. There is indication that ascorbyl free radical depletion could be secondary to oxygen-derived-free-radical-induced cellular damage. 2. The amount of residual ascorbic acid was quantitated on myocardial tissue at the end of reperfusion using Me2SO as extracting solvent. Intense oxidation of ascorbate and chemical stabilization of the resulting free radical species provided by Me2SO allowed ESR measurement of a marked tissue ascorbate depletion related to the duration of ischemia. 3. Perfusion of superoxide dismutase during low-flow ischemia and the first 10 min of reperfusion greatly inhibited both extracellular release and endogenous ascorbate depletion. These results suggest that the ascorbate redox system constitutes a major protective mechanism against free-radical-induced myocardial injury. 4. The proposed direct ESR detection of ascorbyl free radicals in the coronary perfusates or in tissue extracts does not require extensive chemical preparation and conditioning of effluent or tissue samples. It provides an interesting straightforward alternative to the evaluation of detrimental free radical processes affecting the myocardium during ischemia and reperfusion.

Luminol enhanced chemiluminescence of the perfused rat heart during ischemia and reperfusion

We show that the production of Luminol reactive oxygen radicals in the perfused rat heart under ischemia and reperfusion can be monitored continuously by measuring the chemiluminescence of Luminol-perfused hearts. Luminol did not affect the monitored physiological parameters of the hearts. Chemiluminescence increased during ischemia and reperfusion. Superoxide dismutase treatment of the heart before ischemia, but not catalase, abolished these increases.

DMPO and reperfusion injury: arrhythmia, heart function, electron spin resonance, and nuclear magnetic resonance studies in isolated working guinea pig hearts

With the use of isolated working guinea pig hearts with normothermic global ischemia, it was shown that 5,5-dimethyl-pirroline-N-oxide (DMPO), an organic spin trap agent designed specifically to form stable adducts with oxygen free radicals in electron spin resonance studies, can dramatically reduce the vulnerability of the heart to reperfusion-induced arrhythmias. Studied in concentrations ranging from 10 to 500 mumol/L, DMPO exerted a dose-dependent protective effect. Thus, after 30 minutes of global ischemia, the incidence of ventricular fibrillation (total) and tachycardia was reduced from control values of 100% and 100% to 100% and 100%, 91% and 100%, 25% (p less than 0.001) and 50% (p less than 0.05), and 25% (p less than 0.001) and 41% (p less than 0.05), respectively, with DMPO concentrations of 10, 30, 100, and 500 mumol/L. Maximum signals of DMPO-OH adduct, with the use of electron spin resonance studies, were observed after 3 minutes of reperfusion in fibrillated hearts but were not detected in nonfibrillated hearts. Results of nuclear magnetic resonance studies of myocardial adenosine triphosphate, creatine phosphate, pH, and inorganic phosphate showed that these parameters were not significantly changed by treatment with DMPO, and consequently myocardial heart function was not improved, although there was a dissociation between myocardial adenosine triphosphate content and left ventricular developed pressure during reperfusion. The data presented here indicate that oxygen free radicals play an important role in the development of reperfusion-induced arrhythmias but trapping these cytotoxic free radicals does not improve the recovery of postischemic heart function and high-energy phosphate contents in isolated working guinea pig hearts.

Superoxide radical as electron donor for oxidative phosphorylation of ADP

When isolated rat heart mitochondria are subject to xanthine/xanthine oxidase generated free radicals, nmol quantities of ADP are phosphorylated to ATP. This effect is proportional to xanthine oxidase concentration, and is relatively independent of ADP concentration. Exogenous superoxide dismutase partially suppresses the phosphorylation. Micromolar concentrations of iron salts completely eliminate the phosphorylation. Catalase has no effect. The likely electron source, then, is superoxide radicals. The reduced minus oxidised spectra of superoxide-bombarded mitochondria show that superoxide enters the electron transport chain by reducing cytochrome c and complex IV. Mitochondria retain their ability to phosphorylate ADP in more traditional ways under the experimental conditions described. Superoxide under physiological conditions in vivo may be a source of electrons for the oxidative phosphorylation of ADP.

Hydrogen peroxide generation by mitochondria isolated from regionally ischemic and nonischemic dog myocardium

We occluded the left anterior descending coronary artery of anesthetized, open-chest dogs, for 1 or 2 h. Some hearts were reperfused for 1 h after 1 h of ischemia. We isolated mitochondria from the central ischemic zone (CIZ) and a surrounding nonischemic zone (NIZ) of the left ventricle, and assayed H2O2 production using a horseradish peroxidase-dual wavelength spectrophotometric technique. Mitochondria, studied in the absence of exogenous respiratory chain inhibitors, generated H2O2 during State 4 respiration with succinate as the substrate. NIZ mitochondria in all groups produced ca. 1.5 nmols H2O2/min/mg protein (no significant differences between groups). The State 4 O2 consumption rates of NIZ mitochondria from hearts subjected to 1 h ischemia plus reperfusion, or 2 h of ischemia (ca. 30 nmols/min/mg) were significantly higher than that of NIZ mitochondria of hearts subjected to only 1 h of ischemia (23 nmols/min/mg). Thus, the ratio between H2O2 produced and State 4 O2 consumption fell from 6.5% to 5%. Mitochondria from all CIZ samples had State 4 O2 consumption rates that were not different from corresponding NIZ values. However CIZ mitochondria of hearts subjected to 1 h ischemia without reperfusion produced less H2O2 (1.1 +/- 0.1 nmols/min/mg), and had a slightly reduced H2O2/O2 ratio (4.4 +/- 0.7%), compared with their NIZ samples (1.5 +/- 0.1 nmols/min/mg; 5.3%). Reperfusion after 1 h of ischemia abolished these regional differences. The CIZ mitochondria from hearts subjected to 2 h ischemia produced only 0.75 +/- 0.22 nmols H2O2/min/mg (2.5% of State 4 O2 consumption). These values were 50% of corresponding NIZ values, and were significantly less than for any other group or tissue region. If similar phenomena occur in conscious animals subjected to incomplete regional ischemia, especially of relatively brief duration or if accompanied by reduced intracellular defenses against oxidants such as H2O2, they suggest that mitochondria persist as H2O2 sources and so may contribute to the oxidant load and myocardial dysfunction.

A new approach to the direct detection of free radicals in the intact myocardium

A new method for the direct ESR detection of free radicals in rat myocardial tissue is described. Isolated rat atria are continuously monitored for heart rate and contractile force; at the end of the experimental period the beating organs are inserted into quartz ESR tubes and immediately frozen in liquid nitrogen. Spectra obtained from these preparations show the presence of very weak radical signals. When ESR spectra are recorded on samples obtained from pools of rat atria pulverized under liquid nitrogen, the radical lines are markedly stronger than those observed for intact organs; contaminating metals are also frequently detected. These findings indicate that crushing or grinding procedures carried out under liquid nitrogen produce artifactual ESR active species. The new method described in the present paper does not involve mechanical interventions and therefore should yield reliable artifact-free results.

Reappraisal of the e.p.r. signals in (post)-ischaemic cardiac tissue

The present study was designed to measure directly, using e.p.r. spectroscopy, oxygen-derived free radicals in (post)-ischaemic or (post)-anoxic rat hearts. Rat hearts were rapidly freeze-clamped at 77 K under normoxic, anoxic, ischaemic or reperfusion conditions. The samples were measured at three different temperatures (13, 77 and 115 K) and at several microwave power levels, and were compared with isolated rat heart mitochondria. Samples were prepared both by grinding and as tissue cuts. The two preparation techniques gave identical e.p.r. results, which excludes the occurrence of grinding artifacts. No free radical signals linked to reperfusion injury were detected. Several electron transfer centres known in the mitochondrial respiratory chain were measured. The signals previously assigned to post-ischaemic reperfusion injury were found to originate from electron transfer centres of the respiratory chain, predominantly the iron-sulphur cluster S-1 in succinate dehydrogenase. The differences in signal intensity between normoxic, ischaemic and reperfused hearts were found to result from the different redox stages of these centres under the various conditions tested. These findings do not necessarily imply that oxygen-derived free radicals are not formed in cardiac tissue during (post)-ischaemic reperfusion. The constitutive background of paramagnetism from the respiratory chain, however, seriously hampers the direct detection of comparatively low concentrations of free radicals in cardiac tissue. It is therefore expedient to focus future experiments in this field on the use of spin-trapping agents.

Metabolic changes and mitochondrial dysfunction early following transthoracic countershock in dogs

The mechanisms of myocardial injury and necrosis following transthoracic shocks from a direct current cardiac defibrillator were investigated in adult greyhounds. Myocardial lactate extraction became negative maximally at 1 minute, following two (mean -22% +/- SEM23) or five (-193% +/- 135) shocks and returned to baseline in 6-15 minutes. Myocardial necrosis assessed at 4 hours following the shock period was 0.05 g (+/- 0.03) after two shocks, 6.69 g (+/- 1.76) after five shocks and zero in controls. In further experiments, dogs received five or zero (dummy) shocks and mitochondria were isolated from their hearts following excision within 1 minute of receiving the final shock. Maximal oxygen consumption in right ventricular mitochondria was lower than the unshocked controls with both glutamate (66.9 +/- 9.4 nanoatoms of oxygen/mg per minute, n = 9 vs 86.6 +/- 13.6 nanoatoms/mg per minute, n = 7) and succinate (96.2 +/- 8.7 nanoatoms/mg per minute, n = 9 vs 119.5 +/- 14.4 nanoatoms/mg per minute, n = 7) as substrates. Using electron spin resonance spectroscopy, an increase in a peroxyl-free radical with g = 2.031 was detected in myocardial tissue after two internal shocks (50 joules stored energy, 0.5-minute intervals). We conclude that mitochondrial dysfunction and free-radical generation are likely contributors to cellular injury following multiple countershocks.