Reduction of infarct size by cell-permeable oxygen metabolite scavengers

On-line regeneration of electrochemical biosensor for in vivo repetitive measurements of striatum Cu2+ under global cerebral ischemia/reperfusion events

The detection of Cu²⁺ ion, one of the metal ions substantial in cerebral physiology, is critical in studying brain activities and understanding brain functions. However, repetitive measurements of Cu²⁺ in the progress of physiological and pathological events is still challenging, because lack of the platform for repetitive on-line detection-regeneration cycle. Herein we report the design of a regenerated electrochemical biosensor combined with the in vivo microdialysis system. In this biosensor, hyperbranched polyethyleneimine (hPEI) acts as a regenerated recognition unit for Cu²⁺. Just by a simple rinse of ethylenediaminetetraacetic acid (EDTA) disodium salt, the Cu²⁺ and Cu⁺ ions on the biosensor interface were chelated with EDTA disodium salt, thus achieving the regeneration of the biosensor. In addition, 6-(ferrocenyl)hexanethiol (FcHT) serves as the inner reference moiety to elevate the sensing accuracy over regeneration cycles. As a result, this ratiometric electrochemical biosensor not only revealed high sensitivity and selectivity, but also exhibited excellent stability during multiple regeneration processing. This biosensor was capable of determining Cu²⁺ with a linear range between 0.05 and 12 μM and low detection limit (LOD) of 13 nM. Then, the platform has been successfully applied in repetitive Cu²⁺ analysis in rat brain under global cerebral ischemia/reperfusion events. The combination of results from 7 rats indicates global cerebral ischemia caused an obvious increase of the Cu²⁺ level, while reperfusion brought this level back to normal.

Dexrazoxane prevents myocardial ischemia/reperfusion-induced oxidative stress in the rat heart

INTRODUCTION

Dexrazoxane (Dex), used clinically to protect against anthracycline-induced cardiotoxicity, possesses iron-chelating properties. The present study was designed to examine whether Dex could inhibit the ischemia/reperfusion (I/R) induced damage to the rat heart.

MATERIALS AND METHODS

Isolated perfused rat hearts were exposed to global ischemia (37 degrees C) and 60 min reperfusion. Dex was perfused for 10 min prior to the ischemia, or administered intraperitoneally (150 mg) 30 min prior to anesthesia of the rats. I/R caused a significant hemodynamic function decline in control hearts during the reperfusion (e.g., the work index LVDP X HR declined to 42.7+/-10%). Dex (200 microM) applied during the preischemia significantly increased the hemodynamic recovery following reperfusion (LVDP X HR recovered to 55.7+/-8.8%, p<0.05 vs. control). Intraperitoneal Dex, too, significantly increased the hemodynamic recovery of the reperfused hearts. I/R caused an increase in oxidation of cytosolic proteins, while Dex decreased this oxidation.

DISCUSSION

The decrease in proteins carbonylation and correlative hemodynamic improvement suggests that Dex decreases I/R free radical formation and reperfusion injury.

Pretreatment with alcoholic extract of shape Crataegus oxycantha (AEC) activates mitochondrial protection during isoproterenol – induced myocardial infarction in rats

Crataegus oxycantha (hawthorn) is used in herbal and homeopathic medicine as a cardiotonic. The present study was done to investigate the effect of the alcoholic extract of Crataegus oxycantha (AEC) on mitochondrial function during experimentally induced myocardial infarction in rat. AEC was administered orally to male albino rats (150-200 g), at a dosage of 0.5 ml/100 g body weight/day, for 30 days. At the end of the experimental period, the animals were administered isoproterenol (85 mg/kg body weight, s.c) for 2 days at an interval of 24 h. After 48 h, the rats were anaesthetized and sacrificed. The hearts were homogenized for biochemical and electron microscopic analysis. AEC pretreatment maintained mitochondrial antioxidant status, prevented mitochondrial lipid peroxidative damage and decrease in Kreb's cycle enzymes induced by isoproterenol in rat heart.

Cardioprotective effects of Ilex paraguariensis extract: evidence for a nitric oxide-dependent mechanism

AIM

To examine the effects of an Ilex paraguariensis (Ip) extract on postischemic alterations derived from 20 min of global ischemia and 30 min of reperfusion.

METHODS

Isolated rat hearts were treated 10 min before ischemia and the first 10 min of reperfusion with Ip 30 microg/ml. In other hearts, chelerythrine (1 microM), a protein kinase C blocker, or l(G)-nitro l-arginine methyl ester (l-NAME), a nitric oxide synthase inhibitor, were administered prior to Ip infusion. Left ventricular developed pressure (LVDP), +dP/dt(max), -dP/dt(max), and left ventricular end diastolic pressure (LVEDP) were used to assess myocardial function. Thiobarbituric acid reactive substances (TBARS) were measured.

RESULTS

Ip treatment produced an improvement of postichemic recovery (LVDP=96+/-8%; +dP/dt(max)=95+/-10%; -dP/dt(max)=90+/-12% vs. 57+/-6%, 53+/-6% and 57+/-8%, respectively, in untreated hearts) and an attenuation of the increase of LVEDP and TBARS content. Chelerythrine did not modify and l-NAME abolished the protection induced by Ip.

CONCLUSIONS

These data are the first demonstration that Ip extract attenuates the myocardial dysfunction provoked by ischemia and reperfusion and that this cardioprotection involves a diminution of oxidative damage through a nitric oxide-dependent mechanism.

Oxidative damage during chagasic cardiomyopathy development: role of mitochondrial oxidant release and inefficient antioxidant defense

In this study, we evaluated the oxidant status and antioxidant defense capabilities of the heart during the course of Trypanosoma cruzi infection and disease development in a murine model system. Our data show that the extent of protein carbonylation and lipid peroxidation is increased in the heart, but not the skeletal muscle, of infected mice. The level of oxidative injury biomarkers in the myocardium consistently increased with chronic disease severity. The antioxidant defense constituted by catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GSR), and reduced glutathione was increased in murine heart and skeletal tissue in response to the stress of T. cruzi infection. After the initial burst, CAT, GPx, and GSR remained unresponsive to the severity of chronic tissue damage in chagasic hearts. The cardiac level of Mn(2+) superoxide dismutase (MnSOD) was diminished in chagasic mice. Our data suggest that the host responds to acute injuries by activating antioxidant defenses that are of sufficient magnitude to scavenge the reactive oxidants in skeletal tissue. The myocardia of infected mice, however, sustain increased oxidative injuries with disease progression. We surmise that MnSOD deficiencies, resulting in the increased release of mitochondrial free radicals, lead to sustained oxidative stress that exceeds the cardiac antioxidant defense capacity and contribute to persistent oxidative damage in chagasic myocardium.

Cardioprotective and antioxidant effects of apomorphine

Apomorphine is a potent antioxidant that infiltrates through biological membranes. We studied the effect of apomorphine (2 microM) on myocardial ischemic-reperfusion injury in the isolated rat heart. Since iron and copper ions (mediators in formation of oxygen-derived free radicals) are released during myocardial reperfusion, apomorphine interaction with iron and copper and its ability to prevent copper-induced ascorbate oxidation were studied. Apomorphine perfused before ischemia or at the commencement of reperfusion demonstrated enhanced restoration of hemodynamic function (i.e. recovery of the work index (LVDP x HR) was 69.2 +/- 4.0% with apomorphine pre-ischemic regimen vs. 43.4 +/- 9.01% in control hearts, p < 0.01, and 76.3 +/- 8.0% with apomorphine reperfusion regimen vs. 30.4 +/- 11.1% in controls, p < 0.001). This was accompanied by decreased release of proteins in the effluent and improved coronary flow recovery in hearts treated with apomorphine after the ischemia. Apomorphine forms stable complexes with copper and with iron, and inhibits the copper-induced ascorbate oxidation. It is suggested that these iron and copper chelating properties and the redox-inactive chelates formed by transition metals and apomorphine play an essential role in post-ischemic cardioprotection.

Effects of iNOS-related NO on hearts exposed to liposoluble iron

Inducible nitric oxide synthase (iNOS) protects heart against ischemia/reperfusion injury. However, it is unknown whether the beneficial effects of iNOS are mediated by the interaction of NO with radical oxygen species (ROS). To address this issue, we examined the effects of liposoluble iron-induced ROS generation in isolated perfused hearts from rats treated with lipopolysaccharide (LPS). LPS administration (10 mg/kg, i.p., 6 h before heart removal) induced iNOS expression and increased NO production as indicated by a 3-fold elevation of nitrite level in coronary effluents relative to control hearts. An enhanced expression of hemeoxygenase 1 protein was also observed in septic hearts compared to control. Iron-induced perfusion and contractile deficits were ameliorated by LPS with more important coronary than myocardial benefits. In iron-loaded hearts, oxidative stress as measured by the 2,3 dihydroxybenzoic acid/salicylic acid concentration ratio in cardiac tissue was 23% lower in septic than in control heart although the difference did not reach significance. In addition, the presence of the NO synthase inhibitor N-nitro-L-arginine in the perfusion medium totally blocked NO production but did not reverse the protective effects of LPS. The results indicate that LPS protects from iron-induced cardiac dysfunction by mechanisms independent on ex vivo NO production and suggest that NO acts as a trigger rather than a direct mediator of the cardioprotective effects of LPS in heart exposed to iron.

Time window of nitroxide effect on myocardial ischemic-reperfusion injury potentiated by iron

Transition metals such as iron and copper potentiate the postischemic reperfusion (I/R) injury induced by oxygen-derived radical and nonradical toxic species (ROS). Various natural and synthetic antioxidants have been previously tested to ameliorate such injury, yet the limitations of the common antioxidants are well known. An alternative strategy for combating oxidative damage is presented wherein cell-permeable, nitroxide stable radicals, which act as SOD-mimics and oxidize reduced metals thus prompting the Fenton-like chemistry, are investigated for utility in ameliorating I/R injury. Our study concentrates on the early effect of nitroxide on the myocardial I/R injury. Isolated rat hearts in the Langendorff configuration were equilibrated with Krebs-Henseleit buffer and then subjected to 18 min of normothermic global ischemia followed by 20 min reperfusion. Iron administered as Fe(III)-citrate (10 microM) did not affect the cardiac function under normoxia but did potentiate I/R injury and decreased the recovery during reperfusion. The iron-induced damage was manifested by further deterioration of the cardiac hemodynamic function and the energy status as reflected by decreased tissue level of phosphorylated nucleotides. Nitroxide at 200 microM protected against the iron-potentiated I/R injury by improving the recovery of the hemodynamic function and the cardiac energy status. Exogenously added iron requires bioreduction to form deleterious Fe(II) bound to critical cellular sites. The nitroxide, which enters the cell and oxidizes the reduced metal instantaneously, provided protection even when administered 2 or 3.5, but not 5 min, after the onset of reperfusion. Thus, its narrow therapeutic time window provides insight into the schedule of the I/R injurious process.

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.

Improving the preservation of isolated rat skeletal muscles stored for 16 hours at 4 degrees C

BACKGROUND

Limiting factors for long-term cold preservation of isolated skeletal muscles are increased intracellular calcium levels, the occurrence of hypercontraction, and the overproduction of oxygen free radicals. In the present study, we investigated whether muscle preservation during cold storage could be improved by additives that can protect against such processes or by oxygen supply.

METHODS

The soleus (SOL) and a strip of the cutaneus trunci muscle (CT) from the rat were isolated and stored for 16 hr at 4 degrees C in Bretschneider's Histidine Tryptophane Ketoglutarate (HTK) and subsequently acclimatized in Krebs-Henseleit solution for 90 min at room temperature. The protective effects of 2,3-butanedione monoxime (BDM; reduces intracellular calcium release and inhibits fiber contraction) and of the following antioxidants were investigated: N-tert-butyl-alpha-phenylnitrone (PBN), trolox, desferal, and deferione. The antioxidants and BDM were added to both HTK and Krebs-Henseleit solution. Dose-response curves were made for each of the additives (n> or =4 for each dose). To evaluate the effect of oxygen supply, HTK was aerated with 95% O2/5% CO2. Muscle function (P0), energy metabolism (ATP), and cytoarchitecture were analyzed. The measured values were compared with those of fresh unstored muscles (% of control) and with those of muscles stored in HTK without any additive (multivariate analysis of variance, P<0.05).

RESULTS

We found a significant protection of the contractile function (P0) of both muscles after the addition of 1 mM of trolox (SOL: 46% of control; CT: 53%) and after the addition of 3 mM or 0.3 mM of deferione to the SOL and CT, respectively (P0 for both muscles: 55%), whereas no protection was found with PBN (0.03-1 mM) and Desferal (0.001-1 mM). The addition of BDM (10 or 30 mM) resulted in the highest increase of P0 (84% and 60% for the SOL and CT, respectively). The combinations BDM-trolox and BDM-deferione did not further improve the preservation of the SOL function, but P0 values (88% and 91% of control, respectively) were not different from those found for control muscles. Oxygenation of HTK was only beneficial for the SOL (P0: 83%). The improved preservation of muscle function was accompanied by a reduction of the twitch threshold current, increased by storage, suggesting a protective effect of the intervention on the preservation of the muscle cell membrane integrity. Biochemical and histological data corresponded well with the functional data.

CONCLUSIONS

The results showed that the addition of BDM and antioxidants (trolox and deferione) to the bathing solutions improved the preservation of the function, metabolism, and cytoarchitecture of isolated skeletal muscles after cold storage for 16 hr.

Effects of a novel, low-molecular weight inhibitor of lipid peroxidation on ischemia-reperfusion injury in isolated rat hearts and in cultured cardiomyocytes

We investigated the effect of H290/51, a novel, low-molecular-weight inhibitor of lipid peroxidation, on cardiac ischemia-reperfusion injury. Lactate dehydrogenase (LD) release from cultured cardiomyocytes exposed to 1 h hypoxia and 4 h reoxygenation was measured after pretreatment with different concentrations of H290/51. In another series, Langendorff-perfused rat hearts were exposed to 30 min global ischemia and 60 min reperfusion (n=minimum 10 in each group): 1. Control ischemia-reperfusion. 2. Vehicle throughout the experiment. 3. Vehicle during stabilization, and H290/51 (10(-6) mol/l) during reperfusion. 4. H290/51 throughout the experiments. During reoxygenation of isolated cardiomyocytes, H290/51 dose dependently inhibited LD release with an pIC50 value of 7.2+/-0.4 (mean+/-SEM), with 10(-6) mol/l as the lowest efficient concentration. In isolated hearts ischemia-reperfusion induced severe reperfusion arrhythmias, reduced left ventricular developed pressure (LVDP) and coronary flow (CF), and increased LV end-diastolic pressure (LVEDP). LD activity in the effluent increased. H290/51 throughout perfusion (group 4) reduced the occurrence of severe reperfusion arrhythmias (p < .0001), attenuated the decrease of LVDP (p < .008), and CF (p < .006), the increase of LVEDP (p < .008), and the release of LD (p < .002). Tissue contents of thiobarbituric acid-reactive substances did not increase during reperfusion in controls, but was reduced in group 4 (p < .004). H290/51 given only during reperfusion (group 3) tended to improve cardiac function, but significantly so only for increase of CF (p < .01). The lipid peroxidation inhibitor H290/51 attenuated cardiac injury induced by ischemia-reperfusion.

Perfusing isolated rat hearts with hydrogen peroxide: an experimental model of cardiac dysfunction caused by reactive oxygen species

A model of cardiac dysfunction induced by reactive oxygen species (ROS) was established by adding hydrogen peroxide (H2O2) to the perfusate of isolated, Langendorff-perfused rat hearts, and the mechanism of functional injury was investigated. The following groups were included: 1 (n = 7), control perfusion; 2 (n = 11), perfusion with H2O2 (180 mumol 1(-1) for 10 min followed by recovery for 50 min; 3 (n = 4), control perfusion with N-acetylcysteine (NAC, 100 mumol 1(-1); 4 (n = 7), perfusion with H2O2 and NAC; 5 (n = 4), control perfusion with thiourea (15 mmol 1(-1), 6 (n = 7), H2O2 and thiourea together; 7 (n = 4), control perfusion with catalase (150 U ml-1); 8 (n = 7), catalase and H2O2, 9 (n = 4), control perfusion with deferoxamine (5 mmol 1(-1); and 10 (n = 7), deferoxamine and H2O2. coronary flow (CF), left ventricular developed pressure (LVDP), left ventricular end-diastolic pressure (LVEDP), and heart rate (HR) were measured. All values are mean +/- SEM. When given alone, catalase, thiourea, NAC and deferoxamine did not influence left ventricular pressures, but NAC, catalase and thiourea increased CF. H2O2 increased CF (maximum 146 +/- 6% of baseline value after 5 min, p < 0.001 compared to group 1), decreased LVDP (minimum 14 +/- 5% of baseline value after 10 min, p < 0.0004), and increased LVEDP (from 0 mmHg to a maximum of 54 +/- 7 mmHg after 5 min recovery, p < 0.0003). All these changes gradually reversed during recovery. Catalase and thiourea both inhibited the H2O2-induced effects, but catalase inhibition was more complete. Neither NAC nor deferoxamine had any effect on H2O2-induced cardiac dysfunction. In conclusion, H2O2 perfusion is a convenient and reversible model of ROS-induced functional injury to isolated rat hearts. H2O2, rather than the hydroxyl radical, seems to be the main injurious ROS in this model.

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.

Effects of N-acetylcysteine in the rat heart reperfused after low-flow ischemia: evidence for a direct scavenging of hydroxyl radicals and a nitric oxide-dependent increase in coronary flow

The capacity of N-acetylcysteine to directly scavenge hydroxyl radical produced by rat hearts reperfused after 90 min of low-flow ischemia was assessed by the hydroxylation of 4-hydroxybenzoate into 3,4-dihydroxybenzoate using a gas chromatography-mass spectrometric assay. Reperfused hearts showed a massive release of 3,4-dihydroxybenzoate, lactate dehydrogenase, and total glutathione, contained less reduced and oxidized glutathione, but maintained spontaneous beating and coronary flow rates close to preischemic values. Compared to untreated hearts: reperfused hearts treated with N-acetylcysteine from the start of ischemia (i) released four times less 3,4-dihydroxybenzoate, but similar amounts of lactate dehydrogenase or glutathione, (ii) showed a nitric oxide-dependent increase in coronary flow rate, and (iii) contained less oxidized glutathione, but similar amounts of reduced glutathione. Reperfused hearts receiving N-acetylcysteine since the last 5 min of ischemia had also a four-times lower 3,4-dihydroxybenzoate release, but their coronary flow rate response was similar to that of untreated hearts. These results indicate that N-acetylcysteine can directly scavenge hydroxyl radicals produced by reperfused ischemic hearts, although this effect is not associated with any protective effects as indicated by the lactate dehydrogenase and glutathione release and cannot explain the nitric oxide-dependent reperfusion hyperemia.

Action of reactive oxygen species and their antagonists on twitch tension of the rat phrenic nerve-diaphragm

Reactive oxygen species have been implicated in normal and pathological processes of many tissues, including skeletal muscle. I extended previous studies by examining the effect of these intermediates and eight of their antagonists (superoxide dismutase, catalase, deferoxamine, [Cu(II)]2(3,5-diisopropylsalicylate)4, 1,2-dimethyl-3-hydroxy-pyridone, 1,3-dimethyl-2-thiourea, N-(2-mercaptopropionyl)-glycine, vitamin E) on indirectly stimulated twitch tension of an in vitro neuroskeletomuscular preparation, the phrenic nerve-diaphragm of the rat. In the absence of exogenous reactive oxygen species, none of the antagonists potentiated twitch tension, and all but one (N-[2-mercaptopropionyl]-glycine) of the membrane-permeant antagonists attenuated twitch tension. The reactive oxygen intermediate-generating system of purine plus xanthine oxidase reduced indirectly stimulated twitch tension by 36% while having no effect on directly stimulated twitch tension. Catalase (but not superoxide dismutase or deferoxamine) eliminated the reduction in twitch tension, indicating that hydrogen peroxide played a role in the reduction. The membrane-permeant antagonists [Cu(II)]2(3,5-diisopropylsalicylate)4 and 1,2-dimethyl-3-hydroxy-pyridone also eliminated the reduction in twitch tension caused by reactive oxygen species, suggesting that hydrogen peroxide could have acted intracellularly through an iron-catalyzed Haber-Weiss reaction to produce hydroxyl radical, which in turn reacted with intracellular components, thereby reducing twitch tension.

Transient reduction of autoantibodies against oxidized LDL in patients with acute myocardial infarction

Fifteen consecutive patients (mean age 66 +/- 14, range 31-82) with an acute myocardial infarction (MI) suitable for thrombolytic therapy were included in this study. Autoantibodies against oxidized low-density lipoprotein (LDL) were determined by enzyme-linked immunosorbent assay (ELISA). Patients (n = 10) with marked elevation of the MB isoenzyme of creatinine kinase (CK-MB)-mass had significant decreases of oLDL-Ab during the acute phase, with a minimum after 8 h following the onset of thrombolytic therapy (within-group significance: p < .001; between groups: p = .01). Patients (n = 5) with CK-MB-mass values less than 70 ng/ml did not show this phenomenon. Furthermore, significant correlations existed between CK-MB-mass and oLDL-Ab after 6 and 8 h (n = 15; r = .72; p = .003) and the time of the highest CK-MB-mass values (after 12 h) and the time of the maximal decrease of oLDL-Ab (after 8 h) (r = .74; p = .003). Our observations provide further evidence for the release of free radicals and for increased lipid peroxidation during reperfusion after prolonged ischemia. The decrease of oLDL-Ab appears to be a marker for the severity of MI.

Ischemic heart disease and antioxidants: mechanistic aspects of oxidative injury and its prevention

The disease state of myocardial ischemia results from a hypoperfusion-induced insufficiency of heart-muscle oxidative metabolism due to inadequate coronary circulation. Myocardial ischemia is an important, lifespan-limiting medical problem and a major economic health-care concern. Reperfusion, although avidly pursued in the clinic as essential to the ultimate survival of acutely ischemic heart muscle, may itself carry an injury component. Cardiac reperfusion injury appears to reflect, at least in part, an oxidant burden established upon reoxygenation of ischemic myocardium. Laboratory evidence demonstrates that oxidative stress to the heart-muscle cell (cardiomyocyte) can elicit the three known types of ischemia-reperfusion injury that directly affect the myocardium: arrhythmia, stunning, and infarction. The limited clinical occurrence of serious reperfusion arrhythmias has restricted the importance of antioxidants as antiarrhythmic agents against this form of myocardial ischemia-reperfusion damage. Despite the utmost clinical significance of lethal cardiomyocyte injury as a negative prognostic indicator for the ischemic heart-disease patient, inconsistent results of antioxidant interventions in reducing infarct size have somewhat tempered interest in antioxidant infarct trials. By contrast, the negative clinical consequences of stunning may indeed be preventable by utilizing antioxidants to help restore postischemic cardiac pump function. Several as yet unanswered questions remain regarding oxidative stress in the reperfused heart, its significance to cardiomyocyte damage, and its ability to elicit specific postischemic myocardial derangements. Targeted mechanistic studies are required to address these questions and to define the pathogenic role of oxidative stress (and, hence, the therapeutic potential of antioxidant intervention) in myocardial ischemia-reperfusion injury. The overall aim of current research in this area is to enable the cardiac surgeon/cardiologist to advance beyond the largely palliative drugs now available for management of the coronary heart-disease patient and attack directly the pathogenic determinants of heart-muscle ischemia-reperfusion injury. Optimal use of antioxidants may help address this important medical need.

Tissue iron overload and mechanisms of iron-catalyzed oxidative injury

Tissue iron overload causes clinical syndromes that involve the heart, liver, and pancreas. While tissue iron uptake occurs by both transferrin-dependent and independent processes, tissue uptake in the iron overload syndromes occurs predominantly via transferrin-independent mechanisms. Increased redox-active iron present in hemeproteins and the cytosolic iron pool can catalyze oxidative damage to lipids, proteins, and nucleic acids, either by oxyradical dependent or independent mechanisms. Iron-catalyzed injury results in damage to cell constituents, including mitochondria, lysosomes, and the sarcolemmal membrane. These mechanisms of iron-mediated damage are involved in the pathogenesis of organ dysfunction in primary hemochromatosis, transfusion-related iron overload, ischemia-reperfusion injury, and cardiac anthracycline toxicity.

Reactive oxygen intermediates and ischemia-reperfusion injury release tissue plasminogen activator from isolated rat hearts

Tissue plasminogen activator (t-PA) is a marker of endothelial cell injury or activation. The release of t-PA from isolated rat hearts (Langendorff model) subjected to ischemia-reperfusion or reactive oxygen intermediates (ROI) generated by H2O2 was investigated. H2O2 (200 microM) increased t-PA activity in the coronary effluent to 305 +/- 84% of initial value (mean +/- SEM, p < 0.04 vs controls) at the end of a 10 min intervention. The hydroxyl radical scavenger thiourea (10 mM) only partially inhibited the increase (175 +/- 27%, p < 0.01 compared to controls). 20 min normothermic ischemia increased t-PA activity to 416 +/- 108% (p < 0.005 compared to controls) at the start of reperfusion. In conclusion, cardiac injury by ischemia-reperfusion or ROI increases release of t-PA.

Inhibition of lipoxygenase and cyclooxygenase augments cardiac injury by H2O2

The role of arachidonic acid metabolites in the cardiac effects of toxic oxygen metabolites (TOM) was investigated in buffer-perfused rat hearts (Langendorff model). Hydrogen peroxide (H2O2, 200 microM) was given for 10 min to generate TOM, followed by 30 min recovery. H2O2 reduced left ventricular developed pressure (LVDP), increased left ventricular end-diastolic pressure (LVEDP), and increased coronary flow (CF). The hydroxyl radical scavenger thiourea inhibited the H2O2-induced effects. Perfusion with three lipoxygenase inhibitors, AA861, BWA4C, and diethylcarbamazine, in addition to H2O2, augmented the decrease of LVDP and the increase of LVEDP induced by H2O2. The cyclooxygenase inhibitor indomethacin had the same effects. The H2O2-induced increase in CF was not influenced by diethylcarbamazine, but inhibited by all other drugs. Control perfusion with drugs alone did not influence cardiac function. In conclusion, inhibition of lipoxygenase and cyclooxygenase augmented the depression of cardiac function induced by TOM. Leukotrienes and prostanoids appear to be protective against H2O2-induced cardiac injury.

Copper and iron are mobilized following myocardial ischemia: possible predictive criteria for tissue injury

Direct evidence for substantial mobilization of copper in the coronary flow immediately following prolonged, but not short, cardiac ischemia is presented. In the first coronary flow fraction (CFF) of reperfusion (0.15 ml), after 35 min of ischemia, the level of copper (as well as of iron) was 8- to 9-fold higher than the preischemic value. The levels in subsequent CFFs decreased and reached the preischemic value, indicating that both metals appear in a burst at the resumption of coronary flow. When the first CFF was used in a reaction mixture containing ascorbate and salicylate, the latter underwent chemical hydroxylation and was converted to its dihydroxybenzoate derivatives. Likewise, this CFF promoted the ascorbate-driven DNA degradation. Subsequent 150 CFFs were serially collected and demonstrated low activities. Following 18 min of ischemia, the copper level in the first CFF of reperfusion was only 15% over the preischemic value. In contrast, the mobilization of iron into coronary flow was significant but markedly lower than after 35 min. The levels of copper and the redox activity of the first CFF correlated well with the degree of loss of cardiac function, after 18 and 35 min of ischemia, respectively. After 18 min of ischemia, cardiac function was about 50% and the damage is considered reversible, whereas after 35 min the functional loss exceeded 80% and is considered irreversible. These results are in accord with the causative role that copper and iron can play in heart injury following ischemia, by virtue of their capacity to catalyze the production of hydroxyl radicals, and could lead to the development of new modalities for intervention in tissue injury.

Toxic oxygen metabolites and leukocytes in reperfusion injury. A review

Toxic oxygen metabolites (TOM) are generated by activated leukocytes and ischemic tissue upon reperfusion, and are cardiotoxic in vitro. Generation of TOM during reperfusion in vivo has been measured directly and indirectly. TOM contribute to myocardial stunning, causing systolic and diastolic dysfunction. TOM may also play a role in the pathogenesis of reperfusion arrhythmias. It is uncertain if TOM cause cell death during reperfusion. Inhibition of TOM with antioxidants may be important for myocardial protection during cardiac surgery.