The independent effects of oxygen radical scavengers on canine infarct size. Reduction by superoxide dismutase but not catalase

Neutrophil depletion limited to reperfusion reduces myocardial infarct size after 90 minutes of ischemia. Evidence for neutrophil-mediated reperfusion injury

Reperfusion of ischemic myocardium may accelerate necrosis of injured myocytes. To determine the role of neutrophil leukocytes in this process, we examined whether neutrophil depletion during reperfusion could modify infarct size in anesthetized dogs. The proximal circumflex coronary artery was occluded for 90 minutes and then reperfused for 2 hours via an extracorporeal circuit with either whole blood (n = 11) or with blood depleted of neutrophils by leukocyte filters (n = 11). The leukocyte filters caused near-total neutropenia in blood reperfusing the ischemic myocardium (7 +/- 7 neutrophils/microliters compared with 2,551 +/- 317/microliters in controls, mean +/- SEM; p less than 0.001. Infarct size was measured by planimetry of myocardial slices stained with triphenyltetrazolium chloride (TTC), and the accuracy of TTC for identifying necrotic myocardium was verified by electron microscopy. The size of the ischemic risk region was the same in the control (41.6 +/- 1.0%) and neutropenic (41.8 +/- 2.1%) groups. Collateral blood flow to the risk region was the same in control (0.15 +/- 0.03 ml/min/g) and neutropenic (0.13 +/- 0.03 ml/min/g) groups. Among dogs with collateral flow less than 0.2 ml/min/g, infarct size was reduced in the neutropenic group (27.7 +/- 6.7% of risk region, n = 8), compared with control dogs (52.5 +/- 5.7%; n = 7; p = 0.02). Multiple linear regression described the relation between infarct size, risk region size, and collateral flow in the control group, and the same regression relation was used to predict infarct size for the neutropenic group. Mean predicted infarct size in the neutropenic group (n = 11) was 16.8 +/- 3.4% of left ventricle, whereas mean observed infarct size was 9.6 +/- 3.1% (p less than 0.01). The extent of the no-reflow zone (absence of thioflavin-S-fluorescence) was also less in the neutropenic than the control group (2.2 +/- 0.8% vs. 8.1 +/- 2.7% of the risk region, p less than 0.05). Neutropenia limited to the reperfusion period is associated with significant reductions in the extent of the infarct and no-reflow zones after 90 minutes of ischemia. These findings support the hypothesis that reperfusion necrosis occurs after prolonged myocardial ischemia and indicate that neutrophil leukocytes are important mediators of such reperfusion injury.

Superoxide dismutase: possible therapeutic use in cardiovascular disease

Superoxide dismutase (SOD) for parenteral administration is in clinical use in several European countries, where it is prescribed principally for treatment of musculoskeletal inflammation, especially osteoarthritis. However, new possibilities for its usefulness are arising from recent progresses of the pathophysiology of several diseases. From the beginning of this decade there has been a virtual explosion of the available informations about the mechanisms and control of free radical-mediated tissue injury. This progress has led us to the threshold of what will probably be broad clinical applications in the next future. Taking into account the mortality and morbidity caused by cardiovascular injury, the most promising application of SOD in human therapy seems to relay in the protection against ischaemia and post-ischaemic reperfusion damage of various organs and tissues but, particularly, of the myocardium. A large body of evidence suggests that myocardial damage following both global or regional ischaemia can be ameliorated by the blockade of free radical mediated injury. SOD has been proposed as a protective agent in various experimental models. The premises of this action, and the available results will be reviewed.

The metabolic consequences of hydroperoxide perfusion on the isolated rat heart

Perfusion of rat hearts with Krebs-Henseleit bicarbonate buffer containing low concentrations of hydrogen peroxide or t-butylhydroperoxide (50-500 microM) caused an imbalance in the relative synthesis versus utilization rates of ATP, leading to a net hydrolysis of ATP and phosphocreatine. Hydrogen peroxide also caused an 80% inactivation of glyceraldehyde-3-phosphate dehydrogenase, resulting in an inhibition of glycolysis and a rapid accumulation of sugar phosphates as detected with 31P-NMR spectroscopy. This inhibition was partially reversible with peroxide-free perfusion, resulting in a cessation of high-energy-phosphate hydrolysis and a decrease in the accumulated inorganic phosphate and sugar phosphate. t-Butylhydroperoxide toxicity was irreversible. Providing an alternative, non-glycolytic substrate (butyrate) did not protect against the toxicity of hydrogen peroxide, but altered the relative importance of sugar phosphate formation versus ATP hydrolysis. Experiments with heart homogenates in vitro suggest that the inhibition of glyceraldehyde-3-phosphate dehydrogenase is a consequence of a direct reaction of the enzyme with hydrogen peroxide or one of its metabolites. Hearts subjected to total global ischemia (10-20 min), followed by reperfusion with oxygenated buffer, showed no detectable inactivation of glyceraldehyde-3-phosphate dehydrogenase, indicating that ischemia and reperfusion do not result in the production of high global concentrations of hydrogen peroxide.

Reperfusion injury and its pharmacologic modification

Reperfusion injury includes a spectrum of events, such as reperfusion arrhythmias, vascular damage and no-reflow, and myocardial functional stunning. The concept of reperfusion injury remains controversial with many proposed mechanisms when applied to humans, whereas in animal models, there are two main proposed mechanisms: calcium over-load and formation of oxygen free radicals. To prove that reperfusion injury is specifically caused by reperfusion would require evidence that an intervention given at the time of reperfusion can diminish or abolish the injury as in the case of arrhythmias, which are thought to be mediated by excess recycling of cytosolic calcium with delayed afterdepolarizations and ventricular automaticity. In the case of myocardial stunning, the phenomenon may be mediated, at least in part, by a burst of free radicals formed within the first minute of reperfusion and improved by free radical scavengers given at the time of reperfusion. The alternate hypothesis is that cytosolic calcium overload damages mechanisms for normal intracellular calcium regulation so that the stunned myocardium responds to agents that are thought to increase intracellular cytosolic calcium, such as beta-receptor agonists. A further component of reperfusion injury, under active investigation, is microvascular damage with alterations at the level of platelets, leukocytes, and endothelial integrity. From the therapeutic point of view, the divergent results of experimental interventions and the possibility that the abrupt onset of reperfusion in animals differs from the situation in humans with thrombolysis means that the best way currently available to limit reperfusion injury is by minimizing the ischemic period by early reperfusion and by optimizing the metabolic status of the ischemic myocardium at the end of the ischemic period.

Reduction of lipid peroxidation in reperfused isolated rabbit hearts by diltiazem

The calcium-channel inhibiting agent, diltiazem, has been shown to enhance salvage of reperfused myocardium independent of effects on coronary blood flow or myocardial work. Because lipid peroxidation may be a mediator of reperfusion injury and modifiable by calcium-sensitive pathways, we evaluated the effects of diltiazem on the formation of malondialdehyde (MDA), a product of lipid peroxidation, in isolated rabbit hearts perfused with buffer under control conditions or after 60 minutes of ischemia with or without 3 minutes of reperfusion. Diltiazem (5 x 10(-7)M) reduced tissue MDA content in seven reperfused hearts compared with levels measured in 14 hearts reperfused without drug (1.54 +/- 1.09 [SD] compared with 3.57 +/- 1.88 nmol/g, p less than 0.05). Superoxide dismutase and catalase were ineffective in reducing tissue MDA content in reperfused hearts (n = 8; MDA concentration, 3.88 +/- 2.82 nmol/g) although they were effective in preventing lipid peroxidation in separate studies in which oxygen-centered free radicals were generated directly by an infusion of xanthine oxidase and hypoxanthine. These results suggest that the salutary effects of diltiazem in the setting of reperfusion may be mediated by reduction of lipid peroxidation at a locus not accessible to scavengers of oxygen-centered free radicals or by a mechanism not mediated by free radical pathways.

Free radicals and myocardial protection: a surgical viewpoint

Oxygen-derived free radicals are now considered important contributors to tissue injury associated with ischemia and reperfusion. Transition metals, primarily iron, greatly enhance the generation of these active species, which can destroy a large variety of biomolecules, in particular the lipid components of cell membranes. This review tries to demonstrate why cardiopulmonary bypass and aortic cross-clamping are situations that predispose to oxygen free radical production, and how "anti-free radical" agents such as enzymatic scavengers, antioxidants, and iron chelators may prove to be useful therapeutic adjuncts in the clinical setting of open heart surgery.

Effect of oxygen free radicals on cardiovascular function at organ and cellular levels

Oxygen free radicals (OFR) have been implicated as a causative factor of cell damage in several pathologic conditions. It is possible that OFR could have effects on cardiac function and contractility. The present investigation deals with the effects of OFR in the absence and in the presence of scavangers of OFR (superoxide dismutase and catalase) on cardiac function, index of cardiac contractility, serum creatine kinase (CK), and blood lactate, PO2 and pH in the anesthetized dogs. The hemodynamic measurements and collection of blood samples for measurement of CK, lactate, PO2 and pH were made before and at various intervals after administration of OFR for 1 hour. Xanthine and xanthine oxidase were used to generate OFR. OFR produced a decrease in cardiac function and indices of myocardial contractility and an increase in the serum CK. OFR produced an increase in the systemic and pulmonary vascular resistance. Although there was a tendency for an increase in the blood lactate, the increase was not significant. The blood PO2 and pH were not affected. Superoxide dismutase (SOD), alone or in combination with catalase, tended to protect cardiac function against the deleterious effects of OFR. Scavangers of OFR prevented the OFR-induced rise in serum CK. Although the protective effect of SOD plus catalase was slightly better than SOD alone, the results were not significantly different from each other. These results suggest that OFR are cardiac depressant and increase the peripheral vascular resistance besides causing cellular damage. Scavangers of OFR may be beneficial in counteracting the deleterious effects of OFR on hemodynamic parameters and cellular integrity.

Treatment of reperfusion injury with intracoronary calcium channel antagonists and reduced coronary free calcium concentration in regionally ischemic, reperfused porcine hearts

The effect of intracoronary diltiazem, EGTA (ethylene-bis-(beta-aminomethylether)-N,N'-tetraacetic acid), nifedipine, verapamil and isotonic saline solution as placebo on reperfusion injury was investigated in regionally ischemic, reperfused porcine hearts. The left anterior descending coronary artery was distally occluded for 45 min and was reperfused for 3 days. Intracoronary infusion was started immediately before reperfusion and continued during 45 min of reperfusion. Infarct size was determined as the ratio of infarcted (tetrazolium stain) to ischemic myocardium (dye technique). Regional systolic shortening was assessed by sonomicrometry. Apart from left ventricular end-diastolic pressure before ischemia and during 45 min of reperfusion, global hemodynamic values in the five treatment groups did not differ; in particular, calculated left ventricular oxygen consumption before and during ischemia was equally low. Intracoronary EGTA decreased coronary venous free calcium concentration to about 70% of baseline value. Infarct size was reduced from 76 +/- 10% (control group, n = 8) to 60 +/- 10% (p less than 0.01) by intracoronary diltiazem (n = 8) and to 55 +/- 15% (p less than 0.01) by intracoronary EGTA (n = 8). Insignificant reductions in infarct size were found after treatment with intracoronary verapamil (63 +/- 18%, n = 8) and intracoronary nifedipine (68 +/- 9%, n = 7). Regional systolic shortening of the risk region, which did not differ among the groups before occlusion and during ischemia, recovered to the greatest extent in the EGTA-treated pigs (p less than 0.01 compared with values in the control group). Treatment with intracoronary calcium antagonists resulted in only marginal improvement of systolic shortening.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of superoxide dismutase on myocardial infarct size in the canine heart after 6 hours of regional ischemia and reperfusion: a demonstration of myocardial salvage

Available data demonstrate that oxygen free radicals and derived reactive species of oxygen are produced during myocardial ischemia as well as upon reperfusion of the ischemic tissue. The present study was designed to determine if polyethylene glycol-conjugated superoxide dismutase (PEG-SOD), with its extended plasma half-life in excess of 30 hours in contrast to the native form of the enzyme (Native-SOD), could provide protection to the ischemic myocardium subjected to a 6-hour regional ischemia followed by reperfusion for 24 hours. We hypothesized that myocardial injury due to an ischemic interval is a dynamic process involving the sustained production of cytotoxic oxygen radicals that may continue beyond the ischemic interval. The ability to demonstrate a protective effect of the free radical scavenger enzyme superoxide dismutase would require the continued presence of the antioxidant during the ischemic interval and especially during reperfusion. To test this hypothesis, 22 anesthetized, open-chest dogs underwent 6 hours of circumflex coronary artery occlusion followed by reperfusion for 24 hours. Rapid administration of either Native-SOD (1,000 U/kg), PEG-SOD (1,000 U/kg), PEG-albumin (PEG-ALB), or 0.9% sodium chloride solution for injection (saline) was administered via the left atrium 15 minutes before occlusion of the vessel. A continuous infusion of an additional 1,000 U/kg of the respective enzyme interventions or an equivalent volume of PEG-ALB or saline was given during the 6-hour coronary artery occlusion and terminated 15 minutes after reperfusion. The animals were euthanized 24 hours after reperfusion, and the myocardial region at risk and the infarct region were quantitated by the tetrazolium method. The area of myocardium at risk of infarction, expressed as a percent of the left ventricle, did not differ among the groups: Native-SOD (n = 8), 46.2 +/- 1.8%; PEG-SOD (n = 6), 45.7 +/- 2.1%; PEG-ALB, 38.4 +/- 2.3% (n = 4); and saline 46.0 +/- 2.1% (n = 4). Hemodynamic parameters, the calculated rate-pressure-product, as well as regional myocardial blood flow (radiolabeled microsphere method) in the endocardial, midmyocardial, and epicardial segments of the risk and the nonrisk regions were comparable for all groups. Mean infarct size, determined 24 hours after reperfusion, in the group treated with PEG-SOD was 47.1 +/- 2.9% of the area at risk (n = 6), significantly smaller than that observed in each of the other treatment groups: Native-SOD, 63.5 +/- 2.2% (n = 8); PEG-ALB, 64.6 +/- 2.4% (n = 4); saline, 70.8 +/- 2.2% (n = 4).(ABSTRACT TRUNCATED AT 400 WORDS)

Superoxide dismutase decreases early reperfusion release of conjugated dienes following regional canine ischemia

Oxygen radical-induced myocardial lipid peroxidation may cause injury during regional ischemia and reperfusion. However, in vivo detection of lipid peroxidation is difficult. Since conjugated dienes are lipid peroxidation products of unsaturated fatty acids, we evaluated the potential value of detection of these double-bonded fatty acids as a marker of oxygen radical injury. In seven untreated and five superoxide dismutase-treated anesthetized dogs exposed to 90 min of coronary occlusion and subsequent reperfusion, coronary sinus plasma draining the ischemic and reperfused region was assayed for dienes. Lipids were extracted and diene optical density measured at 233 nm wavelength. Superoxide dismutase (5 mg/kg, total dose) was infused into the left atrium during ischemia and the first 30 min of reperfusion. Coronary sinus diene optical density increased in untreated animals at 5 and 10 min of reperfusion (reperfusion optical density (x +/- SEM): 5 min = 1.49 +/- 0.20 absorbance units, 10 min = 1.36 +/- 0.06; both p less than 0.05 vs preocclusion optical density = 1.10 +/- 0.05 and 25 min reperfusion = 1.20 +/- 0.07). No increase in diene optical density occurred in superoxide dismutase-treated dogs. Myocardial lipid peroxidation products, as conjugated dienes, increased in coronary sinus plasma during early reperfusion and this increase was prevented by superoxide dismutase infusion.

Endothelial and myocardial injury during ischemia and reperfusion: pathogenesis and therapeutic implications

Early reperfusion remains the most effective way of limiting myocardial necrosis and improving ventricular function in experimental models and human patients. However, the introduction of oxygen and cellular elements, especially the neutrophil, into the ischemic zone may initiate a deleterious cascade of events that limits myocardial salvage after reperfusion. Although the pathogenesis of reperfusion injury remains controversial, recent studies have suggested that the endothelium may play a critical role. Endothelial cells maintain flow in the microcirculation by secreting a number of vasodilatory compounds and substances that prevent plugging of capillaries by inhibiting neutrophil adherence and platelet aggregation. Reperfusion of ischemic myocardium accelerates structural and functional changes in endothelial cells, resulting in a progressive decrease in microcirculatory flow ("no reflow" phenomenon). Numerous studies suggest that activated neutrophils mediate vascular damage by releasing reactive oxygen species and potent proteolytic enzymes. The administration of therapeutic agents that limit endothelial disruption and neutrophil plugging has shown promising results in limiting myocardial reperfusion injury in experimental models.

Dimethylthiourea, but not dimethylsulfoxide, reduces canine myocardial infarct size

We studied the effect of treatment with two diffusible, low molecular weight scavengers of toxic oxygen metabolites, dimethylthiourea (DMTU) and dimethylsulfoxide (DMSO), on canine infarcts caused by 90 min of ischemia and 3 h of reperfusion. Infarct size was determined by incubating ventricular slices with triphenyl tetrazolium chloride. Areas at risk were determined by autoradiography of 99Tc microspheres injected in vivo during ischemia and were similar (p greater than 0.05) in DMTU, DMSO, and saline treated dogs. However, the ratio of infarct size to area at risk was reduced (p less than 0.05) in dogs treated 30 min before reperfusion with 500 mg/kg DMTU (31.1 +/- 4.6%, n = 9) compared with saline treated dogs (53.4 +/- 4.6% n = 9). In contrast, the ratio of infarct size to area at risk was not significantly different (p greater than 0.05) in dogs treated with 2000 mg/kg DMSO 30 min before reperfusion (43.7 +/- 4.3%) compared to saline treated dogs. The serum concentration of DMTU (4.5 mM) was one-tenth that of DMSO (48 mM) in early reperfusion. Therefore, DMTU but not DMSO protected against post-ischemic cardiac reperfusion injury.

Superoxide dismutase reduces reperfusion arrhythmias but fails to salvage regional function or myocardium at risk in conscious dogs

To determine if oxygen free radical scavengers administered before coronary artery reperfusion can limit reperfusion arrhythmias, increase the return of regional function in ischemic myocardium, and reduce tissue necrosis at 1 week after 90-minute coronary artery occlusion and reperfusion, conscious dogs were treated with superoxide dismutase (SOD) and catalase before and for 1 hour after coronary artery reperfusion. Another group was treated with recombinant SOD (rSOD) because the commercially available SOD and catalase contained endotoxin. The conscious dogs were studied 3-4 weeks after implanting left ventricular pressure gauges, ultrasonic wall thickness gauges in the posterior left ventricular wall, left atrial catheters, and arterial catheters, Doppler flow transducers, and hydraulic occluders on the left circumflex coronary artery. The only beneficial effect observed was that the number of arrhythmic beats per minute in the rSOD-treated group was significantly lower (p less than 0.05) when compared with a control group after coronary artery reperfusion. Treatment neither increased the amount of recovery of wall thickening in the ischemic zone nor reduced infarct size when expressed either as a percentage of the area at risk or as a function of collateral blood flow in the ischemic zone. For example, infarct size as a percentage of the area at risk was 32.6 +/- 5.8%, 37.4 +/- 6.4%, 28.3 +/- 5.1% in the control, SOD and catalase-, and rSOD-treated groups, respectively. Thus, although treatment with oxygen free radical scavengers invoked a transient reduction in the number of reperfusion arrhythmias, this treatment in conscious dogs failed to improve regional myocardial dysfunction or reduce the amount of necrosis when compared with a control group. The lack of a sustained salutary effect may indicate that longer periods of treatment with free radical scavengers are required in chronic preparations.

Myocardial ischemia and reperfusion: the role of oxygen radicals in tissue injury

Thrombolytic therapy has gained widespread acceptance as a means of treating coronary artery thrombosis in patients with acute myocardial infarction. Although experimental data have demonstrated that timely reperfusion limits the extent of infarction caused by regional ischemia, there is growing evidence that reperfusion is associated with an inflammatory response to ischemia that exacerbates the tissue injury. Ischemic myocardium releases archidonate and complement-derived chemotactic factors, e.g., leukotriene B4 and C5a, which attract and activate neutrophils. Reperfusion of ischemic myocardium accelerates the influx of neutrophils, which release reactive oxygen products, such as superoxide anion and hydrogen peroxide, resulting in the formation of a hydroxyl radical and hypochlorous acid. The latter two species may damage viable endothelial cells and myocytes via the peroxidation of lipids and oxidation of protein sulfhydryl groups, leading to perturbations of membrane permeability and enzyme function. Neutrophil depletion by antiserum and inhibition of neutrophil function by drugs, e.g., ibuprofen, prostaglandins (prostacyclin and PGE1), or a monoclonal antibody, to the adherence-promoting glycoprotein Mo-1 receptor, have been shown to limit the extent of canine myocardial injury due to coronary artery occlusion/reperfusion. Recent studies have challenged the hypothesis that xanthine-oxidase-derived oxygen radicals are a cause of reperfusion injury. Treatment with allopurinol or oxypurinol may exert beneficial effects on ischemic myocardium that are unrelated to the inhibition of xanthine oxidase. Furthermore, the human heart may lack xanthine oxidase activity. Further basic research is needed, therefore, to clarify the importance of xanthine oxidase in the pathophysiology of reperfusion injury.(ABSTRACT TRUNCATED AT 250 WORDS)

Superoxide dismutase: improving its pharmacological properties by conjugation with human serum albumin

Superoxide Dismutase has been reported to offer important pharmacological advantages in modifying oxygen toxicity as a result of its ability to scavenge oxygen free radicals. This has proven most exciting in reducing damage associated with post-reperfusion damage following myocardial ischemia. Unfortunately Superoxide Dismutase has a circulation life time of only a few minutes making the exact time of its administration crucial and somewhat impractical. We report here on the production of SOD-Albumin conjugates which have important advantages over free SOD in terms of stability, extended circulation time and reduced immunogenicity.

Early treatment with deferoxamine limits myocardial ischemic/reperfusion injury

Oxygen-derived free radicals (the superoxide anion O2- and hydroxyl radical.OH) have been implicated in myocardial injury associated with coronary artery occlusion followed by reperfusion. Transition metals (such as iron or copper) are needed to catalyze the formation of the .OH radical and subsequent .OH-mediated lipid peroxidation, yet the role of these transition metals in the pathogenesis of myocyte necrosis remains undefined. To address this issue, 21 dogs underwent 2 h of coronary artery occlusion and 4 h of reperfusion. Each animal was randomly assigned into 1 of 3 treatment groups: 7 received the iron chelator deferoxamine beginning 30 min preocclusion, 7 received deferoxamine beginning 5 min prior to reperfusion, while 7 dogs served as saline controls. Deferoxamine effectively chelated free iron in both treatment groups (total urine iron content averaged 42 +/- 16, 662 +/- 177 and 803 +/- 2.5 micrograms in control, pretreated, and deferoxamine at reperfusion groups respectively; p less than 0.05), but had no significant effect on in vivo area at risk (AR), hemodynamic parameters, collateral blood flow during occlusion, or myocardial blood flow following reperfusion. Area of necrosis (AN) in dogs pretreated with deferoxamine (34.6 +/- 3.7% of the AR; p less than 0.05) was significantly smaller than that observed in the saline control group (55.4 +/- 4.7% of the AR). Deferoxamine administered at the time of reperfusion, however, had no significant effect on infarct size (AN/AR = 54.3 +/- 8.7%, p = NS vs. controls). Thus, early treatment with the iron chelator deferoxamine acutely reduced the extent of myocyte necrosis produced by 2 h of transient coronary artery occlusion in the canine model.(ABSTRACT TRUNCATED AT 250 WORDS)

"Reperfusion injury" by oxygen-derived free radicals? Effect of superoxide dismutase plus catalase, given at the time of reperfusion, on myocardial infarct size, contractile function, coronary microvasculature, and regional myocardial blood flow

Do oxygen-derived free radicals, generated at the time of reperfusion, lethally injure viable, previously ischemic myocardium, damage vascular endothelium, and impair recovery of postischemic contractile function? To address these issues, 23 anesthetized open-chest dogs underwent 2 hours of left anterior descending coronary artery occlusion followed by 4 hours of reperfusion. Immediately prior to reflow, each dog was randomized to receive either the free radical scavenging agents superoxide dismutase (SOD) + catalase, or saline alone. SOD + catalase had no significant beneficial effect on infarct size measured by triphenyltetrazolium staining: area of necrosis averaged 38.5 +/- 6.1% vs. 46.3 +/- 6.2% of the area at risk in treated compared with control animals respectively (p = NS). Furthermore, infusion of SOD + catalase did not alter contractile function of the viable subepicardium: mean segment shortening (measured using sonomicrometry) at 4 hours postreperfusion was -23 +/- 5% of baseline, preocclusion values in controls dogs and -24 +/- 9% of preocclusion values in animals that received the scavenging agents. However, SOD + catalase treatment preserved the endocardial microvasculature (assessed by semiquantitative electron microscopic analysis) and enhanced regional myocardial blood flow after reperfusion. Specifically, mean score for microvascular injury was 0.41 +/- 0.14 vs. 0.10 +/- 0.08 (p less than 0.05) in control compared with SOD + catalase treated groups, and blood flow averaged 0.56 +/- 0.11 vs. 1.27 +/- 0.33 ml/min/g tissue (p less than 0.05), respectively, in the previously ischemic endocardium at 2 hours postreflow. Thus, SOD + catalase given at the time of reperfusion had no acute beneficial effect on either the extent of myocyte necrosis or postischemic contractile function in this canine model. SOD + catalase did, however, attenuate both endocardial vascular injury and the "low reflow" phenomenon. These data suggest that microvascular injury and low reflow following prolonged (2 hour) but transient coronary occlusion may be mediated by oxygen-derived free radicals generated at the time of reperfusion.

Superoxide dismutase conjugated to polyethylene glycol provides sustained protection against myocardial ischemia/reperfusion injury in canine heart

Disagreement regarding the cardioprotective role of superoxide dismutase may relate to the use of different durations for induction of ischemic injury and reperfusion. The present study employed superoxide dismutase conjugated to polyethylene glycol (PEG-SOD), which has a half-life greater than 30 hours. Two protocols differing in the mode of administration and the duration of the reperfusion interval were used. Dogs were subjected to occlusion of the circumflex coronary artery for 90 minutes, then reperfused for 6 hours (Protocol A) or 4 days (Protocol B). The dogs received either polyethylene glycol conjugated to albumin (PEG-ALB) or PEG-SOD (1,000 U/kg). In Protocol A, treatment was administered starting 15 minutes before coronary occlusion and continued for 2 hours, terminating 15 minutes after reperfusion. Infarct size was determined 6 hours later. In Protocol B, the conjugated proteins were given 15 minutes before reperfusion and ended simultaneously with reperfusion. Infarct size was measured after 4 days. Infarct size (percentage of area at risk) in control (n = 9) and treated (n = 9) dogs in Protocol A differed between groups: 46.7 +/- 3.5% versus 28.3 +/- 2.9%, respectively (p less than or equal to 0.005); risk regions did not differ: 42.8 +/- 1.5% versus 43.8 +/- 2.1%, respectively. Myocardial salvage also was observed in Protocol B. Infarct size in control (n = 13) and treated (n = 13) groups was 44.2 +/- 2.6% versus 29.2 +/- 1.6%, respectively (p less than or equal to 0.005), with risk regions being 44.4 +/- 1.4% versus 46.0 +/- 1.6% (p = NS). Hemodynamic variables did not differ during the period of coronary artery occlusion. The respective collateral blood flows to the inner two thirds of the ischemic myocardium determined 60 minutes after occlusion were 0.05 +/- 0.01 ml/min/g and 0.06 +/- 0.04 ml/min/g (p = 0.806) for the PEG-ALB and PEG-SOD treated groups, respectively. Infarct size was related inversely to collateral blood flow in the PEG-ALB treated group. This relation shifted downward (analysis of covariance, p = 0.017). Plasma SOD activity in Protocols A sustained for 6 hours. Significant enzymatic activity was present after 4 days in Protocol B. Previous negative studies with native SOD may be related to the short half-life of its free-radical scavenging capacity, which compromises the chances of observing a protective effect after 4 days of reperfusion. The present results support our previous observations, as well as those of other investigators, demonstrating that superoxide dismutase can reduce that component of myocardial injury associated with reperfusion.

Cardioprotective actions of human superoxide dismutase in two reperfusion models of myocardial ischaemia in the rat

1. In rats under ether anaesthesia, the left coronary artery was ligated and reperfused after 10 min of ischaemia. Forty-eight hours later the myocardium was analyzed for creatine kinase (CK) activity. 2. Human superoxide dismutase (h-SOD) given 1 min after occlusion and again 6 h later significantly improved survival and retarded the loss of myocardial CK. 3. In rat isolated hearts perfused at 15% of normal flow for 30 min followed by re-establishment of normal flow for 20 min, perfusion pressure increased by 72% and myocardial CK decreased by 44%. No significant changes occurred in wet-to-dry heart weight ratio. 4. Administration of h-SOD at 2.5 or 5.0 mg, significantly attenuated the elevated post-ischaemic perfusion pressure and the loss of myocardial CK activity in rat perfused hearts. 5. h-SOD appears to be an effective anti-ischaemic agent in the intact animal as well as the isolated perfused heart of the rat subjected to low flow followed by reperfusion at normal flow. The mechanism of this cardioprotective effect is not totally dependent upon the formed elements of the blood, but may be partially due to a direct cytoprotective effect.

Experimental study on myocardial salvage by coronary thrombolysis and mechanical recanalization

Salvage of the ischemic myocardium by coronary thrombolysis and mechanical recanalization (simulated angioplasty) was studied in a canine experimental model of acute myocardial infarction induced by coronary occlusive thrombus at the left anterior descending coronary artery. Forty-four open-chest dogs divided into three groups were studied. Group I (n = 15, control group) was observed for 6 hours following the onset of infarct. In group II (n = 14, thrombolysis group), thrombolysis was obtained by intravenous administration of urokinase 2 hours after the onset of infarct. In group III (n = 15, mechanical recanalization group), simulated angioplasty was performed 2 hours after infarct. Coronary reperfusion was continued for 4 hours in groups II and III. The areas of left ventricular risk and infarct were measured by double staining methods with Evans blue dye and triphenyl tetrazolium hydrochloride. There were no significant differences in control blood flow and risk area in the three groups. Myocardial infarct area/risk area was 65 +/- 3% in group I, 45 +/- 1% in group II, and 35 +/- 2% in group III (group I vs II, p less than 0.001; group II vs III, p less than 0.001). Restored coronary blood flow in the left anterior descending artery was 8 +/- 1 ml/min in group II and 14 +/- 1 ml/min in group III (p less than 0.001). The data suggest that coronary mechanical recanalization is more effective than thrombolysis in salvaging the ischemic myocardium in the early phase of myocardial infarction, most probably because coronary blood flow is better restored by mechanical recanalization.

Therapy to reduce free radicals during early reperfusion does not limit the size of myocardial infarcts caused by 90 minutes of ischemia in dogs

It has been postulated that oxygen-centered free radicals are produced in significant quantities upon reperfusion of ischemic myocardium and could cause the death of myocytes that are still reversibly injured at the end of ischemia ("reperfusion injury"). However, we have shown previously that anti-free radical therapies including superoxide dismutase (SOD) and inhibitors of xanthine oxidase did not limit infarct size after 40 minutes of ischemia and 4 days of reperfusion in dogs. To test whether 40 minutes of ischemia is too brief a period to produce the prerequisite conditions for free radical-mediated necrosis upon reperfusion, we studied infarcts produced by 90 minutes of ischemia followed by reperfusion. Dogs in an SOD-catalase group received a 60-minute infusion of SOD (15,000 units/kg) and catalase (55,000 units/kg) beginning 25 minutes before and ending 35 minutes after reperfusion. A second group of dogs received a single injection of the xanthine oxidase inhibitor oxypurinol (20 mg/kg) 25 minutes before reperfusion. Infarct size was assessed histologically relative to the size of the area at risk and to collateral blood flow to the ischemic region. Infarct size as a percentage of the area at risk was similar in the control group (40.7 +/- 5.5%, n = 11), the SOD-catalase group (38.0 +/- 6.4%; n = 8), and the oxypurinol-treated group (41.4 +/- 6.1%; n = 7) [p = not significant (NS) by analysis of variance]. In controls, there was an inverse relation between infarct size and collateral blood flow; neither of the treatments altered this relation (p = NS by analysis of covariance).(ABSTRACT TRUNCATED AT 250 WORDS)

The xanthine oxidase inhibitor oxypurinol does not limit infarct size in a canine model of 40 minutes of ischemia with reperfusion

Free radicals such as superoxide (.O2-) produced by xanthine oxidase might cause cell death during reperfusion after myocardial ischemia. The effect of the xanthine oxidase inhibitor allopurinol on infarct size in ischemia-reperfusion models has been variable, possibly because of differences in treatment duration. Adequate inhibition of xanthine oxidase may require a sufficient pretreatment period to permit conversion of allopurinol to oxypurinol, the actual inhibitor of superoxide production. To test more definitively whether xanthine oxidase-derived free radicals cause cell death during reperfusion, the effect of oxypurinol on infarct size was evaluated in an ischemia-reperfusion model. Open chest dogs underwent 40 min of circumflex coronary artery occlusion followed by reperfusion for 4 days. Twelve dogs were treated with oxypurinol (10 mg/kg body weight intravenously 10 min before occlusion and 10 mg/kg intravenously 10 min before reperfusion) and 11 control dogs received drug vehicle alone (pH 10 normal saline solution). Nine control dogs from a concurrent study also were included. Infarct size was measured histologically and analyzed with respect to its major baseline predictors, including anatomic area at risk and collateral blood flow (measured with radioactive microspheres). Infarct size as a percent of the area at risk averaged 23.8 +/- 2.7% (mean +/- SEM) in the oxypurinol group (n = 10) and 23.1 +/- 4.2% in the control group (n = 17) (p = NS). Collateral blood flow to the inner two thirds of the ischemic wall averaged 0.08 +/- 0.01 ml/min per g in the oxypurinol group and 0.09 +/- 0.02 ml/min per g in the control group.(ABSTRACT TRUNCATED AT 250 WORDS)

An enzyme immunoassay for cuprozinc superoxide dismutase using monoclonal antibodies. Application for pharmacokinetic study

We developed an enzyme immunoassay for determining human cuprozinc superoxide dismutase (h-SOD) using two kinds of monoclonal antibodies prepared by immunizing h-SOD to BALB/c mice. This method was sensitive and specific enough to determine exogenous h-SOD injected into rats. When intravenously injected into rats, much of the immunoreactive h-SOD accumulated in the kidney and was rapidly excreted in the urine. We observed both a modified and an unmodified form of exogenous h-SOD in rat urine.

Free radicals in medicine. II. Involvement in human disease

This review explores evidence that free radicals might be involved in various human disease processes. Such involvement is difficult to prove because direct evidence is often lacking and is based on animal models of the disease process. Evidence for free radical involvement includes demonstrating abnormal free radical production in the disease, finding that deliberately applying free radical-producing systems into the cellular locus responsible for the disease reproduces its manifestations, and showing that free radical scavengers control facets of the disease process. Confirmation of free radical involvement in a particular disease may have clinical relevance, inasmuch as clinically applicable techniques are currently being developed to remove free radicals from cellular sites where they are injurious and, in other situations such as chemotherapy, techniques or drugs that produce free radicals are available to destroy harmful cells.

Intracoronary superoxide dismutase for the treatment of "reperfusion injury", A blind randomized placebo-controlled trial in ischemic, reperfused porcine hearts

The effect of recombinant human superoxide dismutase (rh-SOD) on infarct size was investigated in porcine hearts. The left anterior descending coronary artery was occluded in each of 24 anesthetized pigs for 45 min and reperfused for 24 h. The animals were randomly assigned to either rh-SOD (n = 12) or placebo treatment (n = 12). 2 min before reperfusion, an intracoronary (i.c.) infusion of rh-SOD (total dose: 2000 U/kg) or placebo was started which lasted for up to 45 min reperfusion. At the end of the experiment, the infarcted myocardium was assessed using a tetrazolium stain (NBT) and related to the risk region which was determined with a fluorescent dye. Two pigs of the SOD group and one of the control group died before the end of the experiments. Except for a lower calculated myocardial oxygen consumption and a lower dp/dtmax in the SOD group during ischemia, hemodynamic parameters of the two groups did not differ significantly. rh-SOD i.c. treatment during reperfusion did not reduce infarct size significantly. Infarct size amounted to 74 +/- 13% in the control group and to 66 +/- 19% in the treated group. The incidence of reperfusion arrhythmias was not affected by rh-SOD treatment. It is concluded that i.c. rh-SOD treatment at the beginning of reperfusion neither significantly reduces infarct size nor diminishes the incidence of reperfusion arrhythmias in this preparation.

Differential effects of superoxide dismutase on high energy phosphates, creatine kinase release, and arrhythmias during post-ischaemic reperfusion in isolated rat hearts

In isolated rat hearts, 25 min of global ischaemia led to significant decreases in the ATP, creatine phosphate (CP), and glycogen contents and increased glucose-6-phosphate (G-6-P) and lactate in the myocardium. During a subsequent reperfusion for 15 min only the CP level, but not ATP and glycogen were restored. G-6-P and lactate were reduced, but remained still elevated in comparison with non-ischaemic hearts. The post-ischaemic coronary flow volume and creatine kinase (CK) release increased significantly compared with preischaemic values. Arrhythmias such as extrasystoles, ventricular tachycardia, flutter and fibrillation, occurred, especially during the first few minutes of reperfusion. Application of the oxygen radical scavenger, superoxide dismutase (SOD), enhanced the myocardial creatine phosphate content during reperfusion. In fibrillating hearts, SOD also increased the ATP content in comparison with non-treated hearts. Superoxide dismutase was effective only during reperfusion and not during the preceding ischaemia. Neither the CK release nor reperfusion arrhythmias were decreased by the radical scavenger. The results suggest that the superoxide radical is involved in the reduction of high energy phosphates during post-ischaemic reperfusion and that this effect can be antagonised by the superoxide anion scavenger superoxide dismutase.

Reperfusion injury

Several lines of evidence point to a major role of oxygen free radicals in the pathogenesis of cell death or dysfunction in a variety of disease processes. Recent studies from this as well as other laboratories have demonstrated that oxygen free radicals play a major role in the pathogenesis of post-ischemic reperfusion injury in the heart. We have recently developed methods for direct measurement of radical species and/or specific byproducts of radical injury. Timely administration of oxygen radical scavengers reduced the quantity of free radicals generated following reperfusion and in addition improved recovery of post-ischemic ventricular function and metabolism. In a regionally ischemic model the free radical scavenger recombinant human superoxide dismutase also administered at the time of reflow was shown to limit infarct size. In this article we review the biophysical and molecular mechanisms of oxygen free radical generation that are viewed as contributing to post-ischemic reperfusion injury. We also discuss the mechanisms by which the body defends against free radical attack and the interrelationships of free radical injury to other mechanisms of tissue injury.

Evidence of direct toxic effects of free radicals on the myocardium

The hypothesis that oxygen-derived free radicals do indeed play a role in myocardial ischemic and reperfusion injury has received a lot of support. Experimental results have shown that free radical scavengers can protect against certain aspects of myocardial ischemic injury and that on reperfusion the heart approaches a level that is more normal than those hearts not receiving additional scavenging agents. Superoxide dismutase, catalase, glutathione peroxidase, hydroxyl radical scavengers and iron chelators such as desferrioxamine have proven successful in providing an increased level of recovery. These results indicate, as would be expected, that superoxide, hydrogen peroxide and hydroxyl radicals may all, at some point, either contribute to the injury or be important in generating a subsequent radical which causes damage. In addition, solutions capable of generating free radicals have been shown to cause damage to myocardial cells and the vascular endothelium that is similar to the damage observed during myocardial ischemic and reperfusion injury. Alterations in function, structure, flow, and membrane biochemistry have been documented and compared to ischemic injury. The continued investigation of the role of free radicals in ischemic injury is warranted in the hope of further elucidating the mechanisms involved in free radical injury, the sources of their generation, and in defining a treatment that will provide significant protection against this particular aspect of ischemic damage.

Oxygen free radicals and myocardial reperfusion injury

Diseases involving tissue reperfusion following ischemia are gaining significance in emergency medicine. The significance of reperfusion injury and the probable role of oxygen-derived free radicals has been described in many tissues, particularly the heart. During myocardial reperfusion a burst of oxygen-derived free radicals overwhelms normal cellular defenses. These radicals may have several detrimental effects. They can oxidize lipids, leading to membrane dysfunction. They can also alter nucleic and other proteins. Cellular dysfunction and death may ensue. Prevention of oxygen-derived free radical injury appears possible and may be feasible for several disease processes, including myocardial reperfusion after infarction.

The effect of six prostaglandins, prostacyclin and iloprost on generation of superoxide anions by human polymorphonuclear leukocytes stimulated by zymosan or formyl-methionyl-leucyl-phenylalanine

Prostaglandins (PG) E2,E1,6-keto-E1 and D2 at concentrations of 0.15-0.80 microM inhibited by 25% the generation of superoxide anions (O2-) in human polymorphonuclear leukocytes (PMNs) stimulated with formyl-methionyl-leucyl-phenylalanine (FMLP). The potency of that inhibition by either PGD2 or PGE1 was the same when zymosan was used as a stimulator whereas PGE2 and 6-keto-PGE1 were by 13 and 21 times less potent inhibitors of O2-) in zymosan-stimulated as compared to FMLP-activated PMNs. PGF2 alpha inhibited the generation of O2- by activated PMNs only when used at the highest concentration studied (30 microM). Prostacyclin, 6-keto-PGF1 alpha and Iloprost (a carbacyclin analogue of prostacyclin) at concentrations up to 30 microM showed no significant inhibition of O2- in human PMNs stimulated either with FMLP or with zymosan. It is concluded that PGD2 and PGEs use a common basic mechanism for inhibition of the generation of O2- by PMNs activated with FMLP or zymosan. PGD2 is most generously furnished with these properties. In addition to this basic mechanism PGE2 and 6-keto-PGE1 abrogate the FMLP-induced response by occupation of formyl peptide receptor of PMNs. It is hypothesised that inhibition of the generation of O2- in PMNs and, possibly, in other cells by PGD2, PGE2 and by products of prostacyclin biotransformation might be responsible for their cytoprotective action in myocardial infarction, stroke, liver damage and peripheral vascular disease.

Recombinant superoxide dismutase reduces oxygen free radical concentrations in reperfused myocardium

It has been proposed that oxygen free radicals mediate damage that occurs during postischemic reperfusion. Recombinant human superoxide dismutase (r-h-SOD) has been shown to be effective at reducing reperfusion injury, but it is not known if this infused enzyme actually reduces oxygen free radical concentrations in the myocardial tissue. Electron paramagnetic resonance spectroscopy was used to directly measure the effect of r-h-SOD on free radical concentrations in the postischemic heart. Hearts were freeze clamped at 77 degrees K after 10 min of normothermic global ischemia followed by 10 s of reflow with control perfusate (n = 7) or perfusate containing 60,000 U r-h-SOD (n = 7). The spectra of these hearts exhibited three different signals: signal A isotropic, g = 2.004, identical to the carbon-centered ubiquinone free radical; signal B anisotropic with axial symmetry, g parallel = 2.033, g perpendicular = 2.005, identical to the oxygen-centered alkyl peroxyl free radical; and the signal C an isotropic triplet, g parallel = 2.000, an = 24 G, similar to a nitrogen-centered free radical such as a peroxyl amine. With r-h-SOD administration the concentration of the oxygen free radical, signal B, was reduced 49% from 6.8 +/- 0.3 microM to 3.5 +/- 0.3 microM (P less than 0.01) and the concentration of the nitrogen free radical, signal C, was reduced 38% from 3.4 +/- 0.3 to 2.1 +/- 0.3 microM (P less than 0.01). The concentration of the carbon-centered free radical, signal A, however, was increased 51% from 3.3 +/- 0.2 to 5.0 +/- 0.2 microM (P less than 0.01). Identical reperfusion with peroxide-inactivated r-h-SOD did not alter the concentrations of free radicals indicating that the specific enzymatic activity of r-h-SOD is required to decrease the concentrations of reactive oxygen free radicals. Additional measurements performed varying the duration of reflow demonstrate a burst of oxygen free radical generation peaking at 10 s of reperfusion. r-h-SOD entirely abolished this burst. These studies demonstrate that superoxide-derived free radicals are generated during postischemic reperfusion and suggest that the beneficial effect of r-h-SOD is due to its specific enzymatic scavenging of superoxide free radicals.

Improvement of postischemic myocardial function and metabolism induced by administration of deferoxamine at the time of reflow: the role of iron in the pathogenesis of reperfusion injury

Reperfusion of ischemic myocardium has been postulated to result in a specific oxygen radical-mediated component of tissue injury. In a previous study we demonstrated improved recovery of ventricular function and metabolism when the superoxide radical scavenger superoxide dismutase was administered at the time of postischemic reflow. Studies in vitro, have suggested that superoxide toxicity might be mediated via the generation of more reactive hydroxyl radicals in an iron-catalyzed reaction. The present study was designed to test the hypothesis that myocardial reperfusion injury might be reduced by administration of the iron chelator deferoxamine at the time of reflow, most likely by preventing hydroxyl radical formation. Sixteen isolated Langendorff rabbit hearts, perfused within the bore of a superconducting magnet, were subjected to 30 min of normothermic (37 degrees C) total global ischemia followed by 45 min of reperfusion. At reflow eight treated hearts received a 10 ml bolus containing 50 mumol of deferoxamine followed by an infusion of 11 mumol/min for the first 15 min of reflow. The hearts were then perfused with standard perfusate for an additional 30 min. Eight untreated control hearts received a similar bolus of perfusate followed by 45 min of standard reperfusion. Serial 5 min 31P nuclear magnetic resonance spectra were recorded. Myocardial phosphocreatine (PCr) content fell to 5% to 7% of control during ischemia in both groups of hearts. Deferoxamine-treated hearts recovered 99 +/- 10% of control PCr content, while untreated hearts recovered 60 +/- 16% (p less than .05). Intracellular pH fell to 5.9 during ischemia in both groups, before showing more rapid and complete recovery in treated hearts (p less than .01). Recovery of developed pressure reached 70 +/- 6% of control in treated hearts compared with 35 +/- 10% in untreated hearts (p less than .05). Iron content of the perfusate was 7 microM, and by electron paramagnetic resonance spectroscopy was in the form of Fe3+-EDTA complexes. In the effluent of treated hearts iron was in the form of Fe3+-deferoxamine chelates. In summary, administration of the iron chelator deferoxamine at the time of postischemic reflow results in greater recovery of myocardial function and energy metabolism, which supports the hypothesis that iron plays an important role in the pathogenesis of reperfusion injury.

Superoxide dismutase and the reduction of reperfusion-induced arrhythmias: in vivo dose-response studies in the rat

Using anesthetized rats we have investigated the dose-response characteristics for the ability of superoxide dismutase (SOD) to reduce the vulnerability of the rat heart to reperfusion-induced arrhythmias in vivo. Hearts (n = 15 in each group) were subjected to 7 min of regional ischemia followed by 10 min of reperfusion. In the control group (saline), 73% (11/15) of the hearts fibrillated during reperfusion, 20% (3/15) had atrioventricular block and 47% (7/15) died as a result of ventricular arrhythmias. Superoxide dismutase, administered as an intravenous bolus 2 min prior to reperfusion exerted a marked protective effect. At its most effective dose (10 mg/kg body wt i.e. 27,000 IU/kg body wt) reperfusion-induced ventricular fibrillation was reduced to 33% (5/15). Reperfusion-induced atrioventricular block was eliminated (0/15) and mortality was reduced to 7% (1/15, p less than 0.05). The protective effects were however very dose-dependent and at higher doses SOD exhibited no antiarrhythmic actions during reperfusion. These results, together with our previous findings in vitro, lend further support to our proposition that oxygen-derived free radicals may play a role in the induction of potentially lethal cardiac arrhythmias and that antifree radical interventions, even when given after the onset of ischemia, can be highly protective.

Effects of allopurinol on myocardial ischemic injury induced by coronary artery ligation and reperfusion

The effects of allopurinol pretreatment (1 mg/ml in the drinking water for 7 days at an estimated daily dose of 75 mg/kg) on biochemical and chemical changes occurring following left circumflex coronary artery ligation (40 min) and reperfusion (60 min) were examined in pentobarbital-anesthetized rabbits. During the ischemic phase, allopurinol pretreatment provided significant preservation of cellular ATP levels and of mitochondrial ATP generation as compared with untreated animals (P less than 0.05). During the reperfusion phase, allopurinol pretreatment significantly prevented the decrease in left ventricular pressure, sodium and calcium accumulation and decreases in sarcolemmal Na+,K+-stimulated and sarcoplasmic reticulum K+,Ca2+-stimulated ATPase activities as compared with untreated animals (P less than 0.05). In contrast, the decrease in mitochondrial (azide-sensitive) ATPase during ischemia and the partial recovery during reperfusion were unaffected by allopurinol pretreatment. Our results indicate that the myocardial protective effects of allopurinol may differ mechanistically in the ischemic and reperfusion phases of injury. The fact that rabbit hearts do not contain detectable xanthine oxidase activity would seem to preclude an obligatory role of this enzyme both in the generation of myocardial ischemic/reperfusion injury and in the protective actions of allopurinol.

Failure of superoxide dismutase to limit size of myocardial infarction after 40 minutes of ischemia and 4 days of reperfusion in dogs

Reactive oxygen species such as the superoxide anion (.O2-) have recently been implicated as important agents involved in causing cell death in the setting of myocardial ischemia and reperfusion. When superoxide anion is involved in ischemic injury the administration of superoxide dismutase (SOD) may limit infarct size by reducing the level of superoxide anions in the myocardium. The study described herein was done to determine whether SOD could limit myocardial infarct size when infarcts were produced in dogs by a 40 min occlusion of the circumflex coronary artery followed by 4 days of reperfusion. The animals in the SOD treatment group received a 1 hr intra-atrial infusion of SOD, at a rate of 250 U/kg/min starting 15 min after occlusion and ending 35 min after reperfusion; control dogs received a saline infusion over the same time frame. Infarct size was determined histologically and expressed as a percentage of the anatomic area at risk (AAR). Infarct size was similar in the two groups, averaging 26.2 +/- 2.5% in the control group (n = 10) and 21.1 +/- 4.8% in the SOD group (n = 11) (p = .40). Hemodynamic variables were not statistically different in the two groups during the occlusion. The transmural mean collateral blood flow at 10 min into the 40 min occlusion was 0.13 +/- 0.02 ml/min/g in the controls and 0.17 +/- 0.03 ml/min/g in the SOD group (p = NS); moreover, SOD did not alter collateral blood flow. In control dogs, infarct size was inversely related to collateral blood flow; analysis of covariance showed that SOD did not shift this relationship. Thus, SOD did not limit infarct size in this study. The results of the current study are consistent with our previous study in which allopurinol, a xanthine oxidase inhibitor, did not limit infarct size in this same experimental preparation. The results suggest that superoxide anions that are accessible to the infused SOD are not a major cause of myocyte death caused by 40 min of severe ischemia followed by reperfusion.