Detection of oxygen-derived free radical generation in the canine postischemic heart during late phase of reperfusion

Measurement of free radicals using electron paramagnetic resonance spectroscopy during open aorto-iliac arterial reconstruction

BACKGROUND

Aortic cross-clamping during abdominal aortic aneurysm (AAA) open repair leads to development of ischemia-reperfusion injury. Electron paramagnetic resonance spectroscopy (EPR) spin-trapping is a valuable method of direct measurement of free radicals. The objective of the study was to evaluate the results of EPR as a direct method of free radical measurement and degree of inflammatory response in open operative treatment of patients with AAA and aorto-iliac occlusive disease (AIOD).

MATERIAL/METHODS

The study was performed on a group of 32 patients with AAA and 25 patients with AIOD scheduled for open repair. Peripheral venous blood for EPR spectroscopy and for SOD, GPx, ox-LDL, Il-6, TNF-alfa, CRP, and HO-1 were harvested. Selected parameters were established accordingly to specified EPR and immunohistochemical methods and analyzed between groups by Mann-Whitney U test and Wilcoxon matched-pairs signed-ranks test with Bonferroni correction.

RESULTS

Free radicals level was correlated with the time of the aortic cross-clamping after the reperfusion of he first and second leg in AAA (r=0.7; r=0.47). ox-LDL in AAA decreased 5 min after reperfusion of the first leg (32.99 U/L, range: 14.09-77.12) and 5 min after reperfusion of the second leg (26.75 U/L, range: 11.56-82.12) and 24 h after the operation (25.85 U/L, range: 14.29-49.70). HO-1 concentration increased to above the level before intervention 24 h after surgery. The activities of GPx and SOD decreased 5 min after the first-leg reperfusion in AAA. Twenty-four hours after surgery, inflammatory markers increased in AAA to CRP was 14.76 ml/l (0.23-38.55), IL-6 was 141.22 pg/ml (84.3-591.03), TNF-alfa was 6.82 pg/ml (1.76-80.01) and AIOD: CRP was 18.44 mg/l (2.56-33.14), IL-6: 184.1 pg/ml (128.46-448.03), TNF-alfa was 7.74 pg/ml (1.74-74.74).

CONCLUSIONS

EPR spin-trapping demonstrates temporarily elevated level of free radicals in early phase of reperfusion, leading to decrease antioxidants in AAA. Elevated free radical levels decreased 24 h after surgery due to various endogenous antioxidants and therapies.

Cardiac myosin binding protein-C as a central target of cardiac sarcomere signaling: a special mini review series

Cardiac myosin binding protein-C (cMyBP-C) is a cardiac-specific thick filament assembly, accessory, and regulatory protein. Physiologically, it is a key regulator of cardiac contractility. With more than 200 mutations in the cMyBP-C gene directly linked to the development of cardiomyopathy and heart failure, cMyBP-C clearly plays a critical role in heart function. At baseline, cMyBP-C is highly phosphorylated, a condition required for normal cardiac function. However, the level of cMyBP-C phosphorylation is significantly decreased during heart failure, indicating that the level of cMyBP-C phosphorylation is directly linked to signaling and cardiac function. Early studies indicated that cMyBP-C interacts with myosin and titin, whereas studies now show that it also interacts with thin filament proteins. However, the exact role(s) of cMyBP-C in the heart remain(s) to be elucidated. As such, we invited experts in the field of cardiac muscle to identify and address key issues related to cMyBP-C by contributing a mini review on such topics as structure, function, regulation, cardiomyopathy, proteolysis, and gene therapy. Starting from this issue, Pflügers Archiv European Journal of Physiology will publish two invited mini review articles each month to discuss the most recent advances in the study of cMyBP-C.

Free radical reaction products and antioxidant capacity in beating heart coronary artery surgery compared to conventional bypass

Oxygen-derived free radicals are important agents of tissue injury during ischemia and reperfusion. The aim of this study was to investigate changes in protein and lipid oxidation and antioxidant status in beating heart coronary artery surgery and conventional bypass and to compare oxidative stress parameters between the two bypass methods. Serum lipid hydroperoxide, nitric oxide, protein carbonyl, nitrotyrosine, vitamin E, and β-carotene levels and total antioxidant capacity were measured in blood of 30 patients undergoing beating heart coronary artery surgery (OPCAB, off-pump coronary artery bypass grafting) and 12 patients undergoing conventional bypass (CABG, on-pump coronary artery bypass grafting). In the OPCAB group, nitric oxide and nitrotyrosine levels decreased after reperfusion. Similarly, β-carotene level and total antioxidant capacity also decreased after anesthesia and reperfusion. In the CABG group, nitric oxide and nitrotyrosine levels decreased after ischemia and reperfusion. However, protein carbonyl levels elevated after ischemia and reperfusion. Vitamin E, β-carotene, and total antioxidant capacity decreased after ischemia and reperfusion. Significantly decreased nitration and impaired antioxidant status were seen after reperfusion in both groups. Moreover, elevated protein carbonyls were found in the CABG group. The off-pump procedure is associated with lower degree of oxidative stress than on-pump coronary surgery.

Cysteine 723 in the C-linker segment confers oxidative inhibition of hERG1 potassium channels

Excess reactive oxygen species (ROS) play a crucial role under pathophysiological conditions, such as ischaemia/reperfusion and diabetes, potentially contributing to cardiac arrhythmia. hERG1 (KCNH2) potassium channels terminate the cardiac action potential and malfunction can lead to long-QT syndrome and fatal arrhythmia. To investigate the molecular mechanisms of hERG1 channel alteration by ROS, hERG1 and mutants thereof were expressed in HEK293 cells and studied with the whole-cell patch-clamp method. Even mild ROS stress induced by hyperglycaemia markedly decreased channel current. Intracellular H2O2 or cysteine-specific modifiers also strongly inhibited channel activity and accelerated deactivation kinetics. Mutagenesis revealed that cysteine 723 (C723), a conserved residue in a structural element linking the C-terminal domain to the channel's gate, is critical for oxidative functional modification. Moreover, kinetics of channel closure strongly influences ROS-induced modification, where rapid channel deactivation diminishes ROS sensitivity. Because of its fast deactivation kinetics, the N-terminally truncated splice variant hERG1b possesses greater resistance to oxidative modification.

Ischemic, genetic and pharmacological origins of cardiac arrhythmias: the contribution of the Quebec Heart Institute

Research in the field of basic electrophysiology at the Quebec Heart Institute (Laval Hospital, Quebec City, Quebec) has evolved since its beginning in the 1990s. Interests were focused on cardiac arrhythmias induced by drugs, allelic variants and metabolic factors produced during ischemia. The results have contributed to the creation of new standards in drug development, more specifically, testing all new drugs for their potential effects on cardiac potassium currents, which could produce life-threatening proarrhythmic effects. In a French-Canadian population, three heterozygous single nucleotide polymorphisms in hK(v)1.5, a gene encoding for a major atrial repolarizing current, were found. These variants affect the expression level of the hK(v)1.5 channel and change the inactivation process in the presence of its accessory beta subunit. Because these effects could shorten atrial action potential, their presence was tested in postcoronary bypass patients and a higher prevalence was found in patients with postoperative atrial fibrillation. Finally, three potentially proarrhythmic factors characteristic of ischemia were identified: pH decrease; oxygen free radicals, which both increase the flow of K(+) ions through human ether-a-go-go-related gene and hK(v)1.5, producing a reduction in action potential duration, frequently leading to cardiac arrhythmias; and lysophosphatidylcholine, a metabolite involved in the production of cardiac arrhythmias early during ischemia that was shown to be a major cause of electrical uncoupling. Over the past decade, the Quebec Heart Institute has provided a significant amount of original data in the field of basic cardiac electrophysiology, specifically concerning arrhythmias originating from pharmacological agents, genetic background and cardiac ischemia.

Ischemia-Induced Norepinephrine Release, but not Norepinephrine-Derived Free Radicals, Contributes to Myocardial Ischemia - Reperfusion Injury

BACKGROUND

Norepinephrine (NE)-derived free radicals may contribute to myocyte injury after ischemia -reperfusion, so the influence of sympathetic denervation on myocardial ischemia - reperfusion injury was investigated in the present study.

METHODS AND RESULTS

Cardiac sympathetic denervation was produced in Wistar rats by a solution of 10% phenol 1 week before ischemia. Atenolol (0.5 mg/kg) was intravenously administered 10 min before the coronary occlusion. The left coronary artery was occluded for 30 min and thereafter reperfused. Cardiac interstitial fluid was collected by a microdialysis probe and free radicals in dialysate were determined by electron paramagnetic resonance (EPR) spin trapping, using 5,5-dimethyl-1-pyrroline-N-oxide as a spin trap. The ratio of infarct size to the ischemic area at risk (I/R) was decreased in both the phenol and atenolol groups compared with control (28.5+/-11.3, 31.8+/-10.7 vs 50.6+/-14.7%, p<0.05). During the coronary occlusion, concentrations of interstitial NE increased markedly in the control and atenolol groups, but was unchanged in the phenol group. EPR signal intensity (relative value to internal standard) was maximal at 1 h after reperfusion and was similar in the phenol and control groups (0.32+/-0.15 vs 0.45+/-0.19).

CONCLUSIONS

Cardiac denervation protected myocyte against ischemia-reperfusion injury through decreasing direct NE toxicity, but not through decreasing NE-derived free radicals.

Hydrogen peroxide modulates the Kv1.5 channel expressed in a mammalian cell line

Reactive oxygen species have been implicated in different types of cardiac arrhythmias including human atrial fibrillation. Kv1.5, the presumed molecular correlate of I(Kur), is an important determinant of human atrial repolarization. The aim of this study was to assess the effects of H(2)O(2), at pathophysiologically relevant concentrations (20-1,000 microM), on Kv1.5 expressed in Chinese hamster ovary cell line. Kv1.5 cDNA in pcDNA3 expression vector and CD8, a surface marker protein, were cotransfected in cells by calcium phosphate precipitation. Kv1.5 activation kinetics were significantly accelerated while the activation curve was negatively shifted by 10 mV (V(1/2) changed from -9.3 to -19.0 mV) in the presence of 100 microM H(2)O(2). The shift in Kv1.5 peak current I-V curve was voltage-dependent, the current amplitude being increased for voltages <+20 mV but decreased for high depolarizing voltages. The rapid activation time constant obtained from a bi-exponential fitting was decreased from 16.1+/-3.4 ms to 8.8+/-1.5 ms for a -20 mV depolarization ( n=9; P=0.01) and from 4.3+/-2.1 ms to 2.3+/-0.4 ms when cells were depolarized to +20 mV ( P<0.05). Kv1.5 steady-state inactivation was not modified by H(2)O(2). Intracellular application of SOD or catalase reduced the H(2)O(2) induced shift of activation I-V curve and SOD significantly decreased Kv1.5 amplitude at +40 mV ( n=9; P<0.05). In conclusion, H(2)O(2) increased Kv1.5 current amplitude at voltages corresponding to the action potential repolarization phase and accelerated Kv1.5 channel opening. These changes can reduce the action potential duration, leading to a shortening of the atrial effective refractory period. H(2)O(2)-induced changes in Kv1.5 properties could thus be involved in initiation or perpetuation of AF.

Lysophosphatidylcholine-induced myocardial damage is inhibited by pretreatment with poloxamer 188 in isolated rat heart

Lysophosphatidylcholine (LPC) accumulates in myocardial tissues and coronary sinus during ischemia, and plays important role in the development of ischemia-reperfusion injury and ischemic ventricular arrhythmia. The aim of this study was to examine whether pretreatment of poloxamer 188 (P-188), a nonionic and non-toxic surfactant, can prevent the cardiac dysfunction induced by exogenous LPC perfusion in Langendorff perfused rat heart model. LPC (6 microM) significantly (p < 0.05) decreased heart rate (HR) and left ventricular developed pressure (LVDP) from 274.3 +/- 23.2 to 175.0 +/- 42.9/min and from 115.9 +/- 11.3 to 26.7 +/- 7.1 mmHg, respectively. The LPC-induced reduction of HR and LVDP did not recover by washout of LPC. Pretreatment with P-188 (1 mM for 30 min) inhibited completely the LPC-induced decreases of HR and LVDP. The pretreatment with P-188 also prevented the LPC-induced increases of left ventricular end-diastolic pressure (LVEDP) and GOT release, significantly (p < 0.05). The coronary perfusion pressure (CPP) rose (p < 0.01) by the LPC perfusion from 71.9 +/- 5.3 to 121.9 +/- 13.0 mmHg, significantly, but pretreatment of P-188 did not affect the LPC-induced vasoconstriction. Our results suggest that exogenous LPC causes irreversible cardiac injury by the sarcolemmal membrane disruption followed by Ca overload, and this LPC-induced cardiac injury, probably, can be prevented by the pretreatment with poloxamer 188.

A new hydroxyl radical scavenger "EPC" on cadaver heart transplantation in a canine model

This study was performed to determine if an "arrested" heart, resuscitated with cardiopulmonary bypass (CPB) after the cessation of beating, can be successfully transplanted, and whether a hydroxyl radical scavenger EPC can reduce ischemic and reperfusion injury during resuscitation of the arrested heart and following orthotopic heart transplantation. A total of 16 pairs of canines were divided into a control group of eight pairs and an EPC-treated group of eight pairs. Cardiac arrest of the donor heart was induced by the discontinuation of respiratory support after the induction of brain death. The cadaver heart was then resuscitated and core-cooled to myocardial temperature of 15 degrees C using CPB. The donor heart was harvested using cold cardioplegia and orthotopically transplanted. All of the transplanted hearts in the EPC group were weaned from CPB without any inotropic support after 60 min of bypass support, whereas all the animals in the control group required 5 micrograms/kg/min dopamine (P = 0.001). Moreover, cardiac function (Emax) 1 h after orthotopic heart transplantation was better preserved in the EPC group than in the control group, at 110 +/- 36% vs. 70 +/- 21% of the post brain death values (P = 0.02) These findings demonstrate that EPC reduces posttransplant reperfusion injury, and thus it may prove to be a valuable adjunct in this challenging model.

T-0162, a novel free radical scavenger, reduces myocardial infarct size in rabbits

1. We investigated the effects of 1-(3-tert-butyl-2-hydroxy-5-methoxyphenyl)-3-(3-pyridylmethyl)urea hydrochloride (T-0162), a novel low-molecular weight free radical scavenger, on the generation of superoxide anions and hydroxyl radicals in vitro and in vivo and on myocardial infarct (MI) size in an in vivo model of MI in rabbits. 2. It was found that T-0162 scavenged both superoxide anions and hydroxyl radicals in a concentration-dependent manner in vitro. 3. In an in vivo rabbit model with 30 min coronary occlusion and 30min reperfusion, T-0162 scavenged hydroxyl radicals generated in the myocardium during reperfusion. 4. Anaesthetized open-chest Japanese white male rabbits were subjected to 30 min coronary occlusion and 48 h reperfusion. The control group (n = 10) was infused with 10% lecithin solution for 220 min from 10 min before occlusion to 180 min after reperfusion. The pretreatment group (n = 10) was infused with T-0162 dissolved in 10% lecithin solution for 220 min from 10 min before occlusion to 180 min after reperfusion at a rate of 400 microg/kg per min. The post-treatment group (n = 10) was injected with an i.v. bolus of 10 mg/kg T-0162 and was then infused with 400 microg/kg per min T-0162 for 190 min from 10 min before reperfusion to 180 min after reperfusion. After 48 h reperfusion, infarct size was measured histologically and expressed as a percentage of area at risk (AAR). 5. There was no significant difference in haemodynamic parameters among the three groups throughout the experimental period. The per cent infarct size of the AAR in the T-0162 groups (24.8+/-4.3 and 30.5+/-3.9% for pre- and posttreatment groups, respectively) was significantly reduced compared with control (44.7+/-4.1%; P<0.05). There was no significant difference in the AAR among the three groups. 6. In conclusion, T-0162 reduces MI size through the inhibition of reperfusion injury.

Effects of EPC-K1 on lipid peroxidation in experimental spinal cord injury

STUDY DESIGN

A study in which levels of lipid peroxidation were measured, the thiobarbituric acid-reactive substances were estimated in an experimental rat model, and the recovery was assessed.

OBJECTIVE

To ascertain the occurrence of thiobarbituric acid-reactive substances in the damaged spinal cord, and to investigate the effectiveness of a hydroxyl radical scavenger EPC-K1, a phosphate diester linkage of vitamins E and C, in attenuating the severity of spinal cord injury.

SUMMARY OF BACKGROUND DATA

Lipid peroxidation has been reported to play an important role in spinal cord injury. There is no report on the use of EPC-K1 to attenuate the severity of spinal cord injury in either animal or human studies.

METHODS

Spinal cord injury was induced by placing a 25-g weight on T12, and the animals were divided into six groups. Group 1 (sham) received only laminectomy. Group 2 (control) received spinal cord injury. Group 3 received EPC-K1 5 minutes before injury. Group 4 received it 5 minutes after injury. Group 5 received it 3 hours after injury. Group 6 received it five times, respectively: at 5 minutes, then 1, 2, 3, and 4 hours after injury. The levels of thiobarbituric acid-reactive substances were measured in the spinal cord, and the recovery was assessed.

RESULTS

The thiobarbituric acid-reactive substances content increased after injury, with two peaks, at 1 and 4 hours. Concentration at the 4-hour peak was lower in nitrogen mustard-induced leukocytopenia rats than in the control rats. The EPC-K1 injection reduced thiobarbituric acid-reactive substances content at 1 and 4 hours after injury in Group 3 (respectively, 34.3% and 42.7% vs. control) and only that at 4 hours in Group 6 (24.9% vs. control). Motor function recovery and histologic findings were better in these two groups than in Group 2.

CONCLUSION

Repeated injection of EPC-K1 attenuated the severity of spinal cord injury.

Cardiac reperfusion injury: aging, lipid peroxidation, and mitochondrial dysfunction

Cardiac reperfusion and aging are associated with increased rates of mitochondrial free radical production. Mitochondria are therefore a likely site of reperfusion-induced oxidative damage, the severity of which may increase with age. 4-Hydroxy-2-nonenal (HNE), a major product of lipid peroxidation, increases in concentration upon reperfusion of ischemic cardiac tissue, can react with and inactivate enzymes, and inhibits mitochondrial respiration in vitro. HNE modification of mitochondrial protein(s) might, therefore, be expected to occur during reperfusion and result in loss in mitochondrial function. In addition, this process may be more prevalent in aged animals. To begin to test this hypothesis, hearts from 8- and 24-month-old rats were perfused in Langendorff fashion and subjected to periods of ischemia and/or reperfusion. The rate of state 3 respiration of mitochondria isolated from hearts exposed to ischemia (25 min) was approximately 25% less than that of controls, independent of age. Reperfusion (40 min) caused a further decline in the rate of state 3 respiration in hearts isolated from 24- but not 8-month-old rats. Furthermore, HNE modification of mitochondrial protein (approximately 30 and 44 kDa) occurred only during reperfusion of hearts from 24-month-old rats. Thus, HNE-modified protein was present in only those mitochondria exhibiting reperfusion-induced declines in function. These studies therefore identify mitochondria as a subcellular target of reperfusion damage and a site of age-related increases in susceptibility to injury.

Inducible nitric oxide synthase augments injury elicited by oxidative stress in rat cardiac myocytes

The effects of nitric oxide (NO) produced by cardiac inducible NO synthase (iNOS) on myocardial injury after oxidative stress were examined: Interleukin-1 beta induced cultured rat neonatal cardiac myocytes to express iNOS. After induction of iNOS, L-arginine enhanced NO production in a concentration-dependent manner. Glutathione peroxidase (GPX) activity in myocytes was attenuated by elevated iNOS activity and by an NO donor, S-nitroso-N-acetyl-penicillamine (SNAP). Although NO production by iNOS did not induce myocardial injury, NO augmented release of lactate dehydrogenase from myocyte cultures after addition of H2O2 (0.1 mM, 1 h). Inhibition of iNOS with N omega-nitro-L-arginine methyl ester ameliorated the effects of NO-enhancing treatments on myocardial injury and GPX activity. SNAP augmented the myocardial injury induced by H2O2. Inhibition of GPX activity with antisense oligodeoxyribonucleotide for GPX mRNA increased myocardial injury by H2O2. Results suggest that the induction of cardiac iNOS promotes myocardial injury due to oxidative stress via inactivation of the intrinsic antioxidant enzyme, GPX.

Salutary effect of adjunctive intracoronary nicorandil administration on restoration of myocardial blood flow and functional improvement in patients with acute myocardial infarction

Salutary effect of nicorandil, a K+ adenosine triphosphate channel opener, on restoration of myocardial blood flow and functional improvement after coronary revascularization was investigated in 20 patients with first anterior acute myocardial infarction. Ten patients received intracoronary administration of nicorandil (2 mg) after coronary revascularization; the other 10 patients received coronary revascularization only and served as control subjects. Myocardial contrast echocardiography and two-dimensional echocardiography were performed to assess microvascular integrity and regional function in the infarcted area. Nicorandil improved peak contrast intensity ratio (p < 0.001), calculated as the ratio of peak contrast intensity in the infarcted and noninfarcted areas, indicating the restoration of myocardial blood flow to the infarcted myocardium. Regional wall motion improved more significantly in 1 month in patients who received nicorandil (p < 0.01). Thus our results suggested the usefulness of intracoronary nicorandil administration after coronary revascularization for restoring blood flow and functional improvement in patients with acute myocardial infarction.

Decreased sulfhydryl groups in the reperfused myocardial tissue of a rat model of myocardial infarction

The aim of this study was to determine whether myocardial injury resulting from temporary ischemia followed by reperfusion can be measured by assaying sulfhydryl groups in the affected tissue of a rat model of myocardial infarction. We studied 3 groups: a control group (n = 6), which underwent surgery without left coronary artery (LCA) ligation; group NoR (n = 9), in which the LCA was ligated for 3 h; and group I + R (n = 7), in which 30 min LCA ligation was followed by 3 h reperfusion. The sulfhydryl group content of myocardial tissue was assayed by measuring the fluorescence produced by incubating heart sections with N-(7-dimethylamino-4-methyl-3-coumarinyl) maleimide (DACM), which binds sulfhydryl groups. The fluorescence intensity (FI) of normal and infarcted myocardium was quantified by our computerized system of microscopic fluorophotometry. Indices such as sulfhydryl group content, the size of the low-FI area [% AREA(lower FI)] and the relative decrease in FI [%FI(decrease)]) in the infarct zone were calculated. Both %AREA(lower FI) and %FI(decrease) were significantly higher in the infarcted zone of animals in NoR and I + R groups than in control animals. Both indices were higher in infarct tissue from animals in the I + R group than in the NoR group. These changes suggest that sulfhydryl group content is significantly reduced in tissue that has been subjected to ischemia-reperfusion. Microscopic fluorophotometry, as defined by DACM staining of myocardial tissue, may help to delineate areas of myocardial reperfusion injury.

The relationship between the adenine nucleotide metabolism and the conversion of the xanthine oxidase enzyme system in ischemia-reperfusion of the rat small intestine

The time course of the energy metabolism after reperfusion, the relationship between the conversion of xanthine dehydrogenase to xanthine oxidase (D-to-O conversion) during ischemia, and the changes of the energy metabolism after reperfusion were studied using an ischemia-reperfusion model in the small intestine of the rat. The rat jejunum underwent an occlusion of the superior mesenteric artery and vein for either 30 minutes (group 1, n = 6) or 90 minutes (group 2, n = 6) with collateral interruption, and then it was reperfused. The contents of the adenine nucleotides in the small intestine of the rat were measured by high-performance liquid chromatography (HPLC) before ischemia, and 30, 60, and 90 minutes of ischemia, as well as 30, 60, 120, and 180 minutes after reperfusion. The recovery level of adenosine triphosphate (ATP) in group 1 (6.05 +/- 0.80 mumol/g dry weight) 30 minutes after reperfusion was significantly higher than that in group 2 (2.28 +/- 1.12 mumol/g dry weight) (P < .001). In addition, the ATP content after reperfusion in group 2 did not change from 30 to 180 minutes after reperfusion. The D-to-O conversion during ischemia in group 1 was not significantly greater than that before ischemia; however, that of group 2 did increase significantly during ischemia (P < .005). These results suggest that the tissue damage from ischemia-reperfusion injury after reperfusion under 90 minutes' ischemia is accomplished within the first 30 minutes after reperfusion. Therefore, the ATP level at 30 minutes after reperfusion may be useful for the evaluation of intestinal viability. Thus, the conversion of the xanthine oxidase enzyme system might play an important role in the expression of ischemia-reperfusion injury.

Induction of manganese superoxide dismutase in rat cardiac myocytes increases tolerance to hypoxia 24 hours after preconditioning

Manganese superoxide dismutase (Mn-SOD) is induced in ischemic hearts 24 h after ischemic preconditioning, when tolerance to ischemia is acquired. We examined the relationship between Mn-SOD induction and the protective effect of preconditioning using cultured rat cardiac myocytes. Exposure of cardiac myocytes to brief hypoxia (1 h) decreased creatine kinase release induced by sustained hypoxia (3 h) that follows when the sustained hypoxia was applied 24 h after hypoxic preconditioning (57% of that in cells without preconditioning). The activity and content of Mn-SOD in cardiac myocytes were increased 24 h after hypoxic preconditioning (activity, 170%; content, 139% compared with cells without preconditioning) coincidentally with the acquisition of tolerance to hypoxia. Mn-SOD mRNA was also increased 20-40 min after preconditioning. Antisense oligodeoxyribonucleotides corresponding to the initiation site of Mn-SOD translation inhibited the increases in the Mn-SOD content and activity and abolished the expected decrease in creatine kinase release induced by sustained hypoxia after 24 h of hypoxic preconditioning. Sense oligodeoxyribonucleotides did not abolish either Mn-SOD induction or tolerance to hypoxia. These results suggest that the induction of Mn-SOD in myocytes by preconditioning plays a pivotal role in the acquisition of tolerance to ischemia at a later phase (24 h) of ischemic preconditioning.

Polymorphonuclear leukocytes-induced injury in hypoxic cardiac myocytes

Growing evidence suggests that free radicals derived from polymorphonuclear leukocytes (PMNs) play an important role in myocardial ischemia-reperfusion injury. To elucidate the cellular mechanism by which activated PMNs exacerbate ischemic myocardial damage, we investigated the extent of cell injury, assessed by the morphological deterioration, free radical generation, and lipid peroxidation in mouse embryo myocardial cells coincubated with activated PMNs. The generation of PMN-derived free radicals was related to the extent of myocardial cell injury. When myocardial cell sheets were subjected to hypoxia and glucose-free media, myocardial cells were injured (cristalysis in the mitochondria and disruption of the sarcolemma) after adding various PMN activators, and the injury extended to the adjacent cells. Chemiluminescent emission and production of thiobarbituric acid-reactive substances in the coincubated cells increased markedly compared with myocardial cells or PMNs alone. The augmented lipid peroxidation coincided with the progression of myocardial cell injury. Catalase inhibited the myocardial cell injury by 52%, the chemiluminescence by 46%, and lipid peroxidation by 50%, whereas superoxide dismutase exhibited less pronounced inhibition. These results indicate that a chain reaction of lipid peroxidation in myocardial cells induced by PMN-derived free radicals closely correlates with membrane damage and contributes to the propagation of irreversible myocardial cell damage.

gamma-Glutamylcysteine ethyl ester for myocardial protection in dogs during ischemia and reperfusion

OBJECTIVES

The aim of this study was to examine the infarct-limiting effects of gamma-glutamylcysteine ethyl ester, a newly discovered synthetic precursor of glutathione biosynthesis, in a canine model of myocardial infarction.

BACKGROUND

Reduced glutathione plays an important role in protecting cells against damage induced by reactive oxygen species during myocardial ischemia and reperfusion. Gamma-glutamylcysteine ethyl ester is capable of penetrating into cells in its intact form and increasing intracellular glutathione levels.

METHODS

Dogs were subjected to a 90-min coronary occlusion followed by 5 h of reperfusion. An intravenous bolus injection of gamma-glutamylcysteine ethyl ester (3 or 10 mg/kg body weight) was administered immediately before reperfusion. Regional myocardial blood flow was measured with the use of colored microspheres.

RESULTS

Gamma-glutamylcysteine ethyl ester effectively reduced infarct size in a dose-dependent manner (mean +/- SEM 26.4 +/- 3.5% in the low dose group [3 mg/kg, n = 10] and 19.0 +/- 3.4% in the high dose group [10 mg/kg, n = 10]; each p < 0.05 vs. the value in the control group [40.6 +/- 4.8%, n = 10]). There were no differences between the control and treated groups in hemodynamic variables or regional myocardial blood flow either during the ischemic period or after reperfusion. The reduced glutathione content of ischemic myocardium in the control group (0.62 +/- 0.11 mumol/g, p < 0.01) was significantly lower than that in nonischemic myocardium (1.46 +/- 0.07 mumol/g), and it was preserved by treatment in a dose-dependent manner (3 mg/kg, 0.83 +/- 0.06 mumol/g; 10 mg/kg, 0.92 +/- 0.14 mumol/g; each p < 0.05 vs. control level). There were no differences in oxidized glutathione content between nonischemic and ischemic myocardium or among the three groups.

CONCLUSIONS

Gamma-glutamylcysteine ethyl ester, a precursor of glutathione, significantly attenuates myocardial ischemia and reperfusion injury when administered immediately before reperfusion.

Effects of membrane lipid peroxidation by tert butyl hydroperoxide on the sodium current in isolated feline ventricular myocytes

Membrane lipid peroxidation is known to play a pivotal role in the genesis of coronary reperfusion arrhythmias in both experimental and clinical settings. To elucidate the electrophysiological mechanisms underlying these arrhythmias, the effects of tert butyl hydroperoxide (TBH) on the Na+ current (INa) in isolated feline ventricular myocytes were studied using whole-cell patch clamp techniques under 100% O2 bubbling. This agent at 20 mM inhibited INa from 2.2 +/- 1.3 to 1.7 +/- 1.0 nA (P < 0.01, n = 7) without changing time courses of INa inactivation. Twenty millimoles TBH shifted the steady-state inactivation curve for INa from -77.4 +/- 1.7 to -81.3 +/- 1.8 mV when measured at INa half inhibition voltage (P < 0.01, n = 7), but did not affect the slope factor. The kinetics of INa recovery from inactivation remained unchanged. These findings suggest that lipid peroxidation in the membrane by TBH reduces INa conductance and voltage-dependent INa availability, most likely as a result of structural damage to the Na+ channels.

Microdialysis study of ischemia-induced hydroxyl radicals in the canine heart

A new experimental approach for spin-trapping of oxygen radicals in a selected region of the heart in situ is described. This approach is based on microdialysis, and it permits the detection of oxygen radicals in conditions of local ischemia and restoration of normal blood flow. Increased hydroxyl radical generation in an ischemic area of canine myocardium, as a result of 40 min local occlusion, has been studied.

Protective role in vivo of coenzyme Q10 during reperfusion of ischemic limbs

The authors prepared an experimental animal model of ischemia and reperfusion of the limbs to evaluate in vivo the reactive oxygen species involvement and protective role of coenzyme Q10 in reperfusion injury. A group of male rabbits (untreated group) underwent clamping of abdominal aorta for 3 hr and then declamping; at intervals blood sampling was drawn for coenzyme Q10, vitamin E, lactic acid and creatine kinase assays. Another group of male rabbits (treated group) underwent the same ischemia period but before declamping coenzyme Q10 was administered intra aorta. In untreated group, coenzyme Q10 and vitamin E plasma levels decreased while lactic acid and creatine kinase plasma levels increased during reperfusion. These data demonstrate that, after only 3 hr of ischemia, the extremities show a biochemical reperfusion injury, and this involves an increased consumption of antioxidants such as coenzyme Q10 and vitamin E. In the treated group, the increase of creatine kinase plasma levels during reperfusion was not significant, while the decrease in vitamin E was more marked.

Brief myocardial ischemia affects free radical generating and scavenging systems in dogs

This study examined whether brief repeated myocardial ischemia altered free radical generating and scavenging activity in a dog model. In dogs preconditioned with four 5-min left anterior descending coronary artery (LAD) occlusions and reperfusions, we examined transcardiac changes in both the function of neutrophils, cells which are major free radical generators, and in myocardial antioxidant enzyme activity, as an indication of free radical scavenging. Neutrophil function was assessed by determining luminol-enhanced whole blood chemiluminescence (CL) induced by zymosan. Blood was taken simultaneously from the carotid artery and the cardiac vein running along the occluded LAD. Preconditioning with sublethal ischemia significantly reduced whole blood CL in the cardiac vein compared with the carotid artery after the first and fourth 5-min reperfusions, while there was no difference in neutrophil count between these sampling sites. Immediately after brief repeated ischemia and reperfusion, manganese-superoxide dismutase (SOD) activity was significantly enhanced, and glutathione reductase activity was markedly reduced in the ischemic, compared with the non-ischemic, myocardium. There were no differences in the myocardial activities of copper, zinc-SOD, glutathione peroxidase, and glutathione S-transferase between the ischemic and non-ischemic regions. Also, no difference was observed between the reduced myocardial glutathione levels in these regions, although the oxidized glutathione level was significantly higher in the ischemic regions of the subepicardial and subendocardial areas. We demonstrated that brief repeated ischemia affects free radical generating and scavenging systems in the ischemic myocardium.

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

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

Trolox C, a lipid-soluble membrane protective agent, attenuates myocardial injury from ischemia and reperfusion

The lipophilic antioxidant Trolox C, a vitamin E analog, was administered to isolated, buffer-perfused rabbit hearts subjected to 25 min of global stop-flow ischemia and 30 min of reperfusion. In six hearts, Trolox C (200 microM) was infused for 15 min immediately prior to ischemia and for the first 15 min of reperfusion. Six control hearts received only vehicle. Gas chromatography analysis confirmed that effective myocardial levels of Trolox were attained. At 30 min reperfusion, the recovery of left ventricular developed pressure was 56 +/- 3% of baseline in control hearts versus 70 +/- 4% in Trolox-treated hearts (p < .01). There was also significant improvement in recovery of Trolox-treated hearts in diastolic pressure and both maximum and minimum values of the first derivative of left ventricular pressure (dP/dt). Creatine phosphokinase release into the coronary effluent at 30 min of reperfusion was 16.5 +/- 8.4 IU/min in untreated and 6.3 +/- 1.0 IU/min (p < .05) in Trolox-treated hearts. Thus Trolox C, a lipophilic antioxidant, attenuated myocardial injury during stop-flow ischemia and reperfusion.

Study of a Fenton type reaction: effect of captopril and chelating reagents

The purpose of this study was to determine if captopril, an angiotensin-converting enzyme inhibitor, could interact with iron ions and so modify a Fenton type reaction. Results indicate that different degrees of thiobarbituric acid-reactive substance from deoxyribose are obtained in an ascorbate-driven Fenton system depending on the order of addition of captopril and iron to the incubation medium. Similar results were obtained with the chelating reagents ethylenediaminetetraacetic acid and diethylenetriaminepentaacetic acid, indicating that the buffer solution plays a relevant role when a particular iron complex is formed with a chelating agent. These metal complexes produce oxidizing species in a Fenton type system whose nature is discussed.

Free radical formation during splanchnic artery occlusion shock

Free radical (FR) formation in the rat intestinal lumen was measured using the spin-trapping technique and electron paramagnetic resonance spectroscopy. Intestinal ischemia was produced by occluding the celiac and the superior mesenteric arteries for 30 min followed by reperfusion. The lumen was filled with a solution of PBN (N-tert-butyl-alpha-phenyl-nitrone) and the intestine was squeezed to enhance the interaction between the PBN solution and the intestinal mucosal cells. Free radicals were produced upon reperfusion, with peaks at 5 and 90 min. Post-ischemic treatment with superoxide dismutase (20 mg.kg(-1)) inhibited the increase of FR production during the second peak by 36%. In a single study in a group of leucocytopenic rats (WBC < 1500/mm(3)), the increase of FR production during the second peak was decreased by 80%. However, these treatments did not inhibit the FR production during the first peak in either group. In contrast, pretreatment with allopurinol (40 and 100 mg.kg(-1) injection at 24 and 3 hours before ischemia, respectively) inhibited the FR production during the first peak by 76%, but did not inhibit during the second peak. The changes in lipid peroxidation in the intestinal mucosa, specific gravity of the intestine and in the hematocrit were correlated to the FR production in the second peak. These results suggest that a major cause of tissue injury after reperfusion in the ischemic intestine may largely be produced by neutrophils.

Efficacy of a hydroxyl radical scavenger (VF 233) in preventing reperfusion injury in the isolated rabbit heart

We tested the hypothesis that 3,4,5,-trihydroxybenzamidoxime (VF 233), a demonstrated hydroxyl radical scavenger and an effective Fe3+ chelator, attenuates reperfusion injury and improves isovolumic left ventricular function. Eighteen isolated, perfused rabbit hearts with intracavitary balloons were subjected to normothermic, global ischemia until the initiation of ischemic contracture. Effects on the adenine nucleotide pool metabolites were determined by high-pressure liquid chromatography from right ventricular biopsy specimens before ischemia and at 15-minute intervals throughout reperfusion. In the experimental group (n = 9), a 5-mL bolus of 1 mol/L VF 233 was given immediately before reperfusion and followed by a continuous infusion (0.125 mumol/min). The control group (n = 9) received the vehicle solution at identical times. Rabbits treated with VF 233 had significant improvement in left ventricular function (expressed as percent return of left ventricular peak developed pressure) within 15 minutes of reperfusion (55.0 +/- 3.0 versus 66.2 +/- 4.1; p less than 0.05 by analysis of variance) after global ischemia and remained significantly improved throughout the reperfusion period. Myocardial adenine nucleotide pool intermediates were not significantly different between groups. These results demonstrate that administration of VF 233 significantly improves ventricular function but does not affect adenine nucleotide metabolism after ischemia and reperfusion.

Reduction of infarct size by cell-permeable oxygen metabolite scavengers

The timely restoration of blood flow to severely ischemic myocardium limits myocardial infarct size. However, experimental studies demonstrate that the myocardial salvage achieved is suboptimal because of additional injury that occurs during reperfusion, due in part to the generation of reactive oxygen metabolites. Initially, superoxide (O2-) was considered to be the central mediator of reperfusion injury. While there are several potential pathways of O2- generation in reperfused myocardium, O2- is poorly reactive toward tissue biomolecules. However, O2-, in the presence of redox-active metals such as iron, generates .OH or hydroxyl-like species that are highly reactive with cell constituents. Thus, while O2- may initiate reaction sequences leading to myocardial injury, it may not be the actual injurious agent. In vitro studies suggest that oxygen metabolite injury occurs at intracellular sites and involves iron-catalyzed processes. Consistent with this mechanism, extracellular oxygen metabolite scavengers have not convincingly reduced infarct size. However, treatment around the time of reperfusion, after ischemia is well established, with cell-permeable scavengers of .OH reduce infarct size. Results with these cell-permeable agents suggest that in the intact animal during regional ischemia and reperfusion, oxygen metabolite injury also occurs at intracellular sites. Cell-permeable scavenger agents are a promising class of drugs for potential clinical use, though further experimental and toxicologic studies are required.

The protective effect of desferal on rat myocardial mitochondria is not prolonged after withdrawal of desferal

Reperfusion of ischaemic myocardium is necessary to sustain tissue viability (without it the tissue becomes necrotic), but reperfusion, on the other hand, can damage cells which have survived ischaemia. There is now considerable evidence that oxygen radicals, especially hydroxyl radicals produced via the Haber-Weiss and Fenton reactions, are responsible for reperfusion damage. Various investigators have reported that desferal, an iron chelator, has a beneficial effect on the myocardium during ischaemia and reperfusion. The aim of this study was two-fold: i) whether superoxide anions in the absence of LMWI can impair mitochondrial function, and ii) whether the protective effect of desferal on the mitochondrial function persists after withdrawal of desferal. Experiments were done on isolated rat hearts subjected to normothermic ischaemic cardiac arrest (NICA), with or without desferal, followed by 15-min reperfusion with desferal, followed by 15-min perfusion without desferal, or a hypoxanthine/xanthine oxidase medium that generates superoxide anions (with or without desferrioxamine (desferal) in the perfusate). Mitochondrial function (QO2 (state 3), ADP/O and OPR) as well as LMWI were measured. Our results indicated that i) superoxide anions and/or hydrogen peroxide can, independently of LMWI, damage the mitochondria, and ii) withdrawal of desferal after the respiratory burst resulted in the same or more severe mitochondrial damage than without any desferal.

Captopril does not scavenge superoxide: captopril prevents O2-. production by chelating copper

The purpose of this study was to use a direct method, that of electron spin resonance spectroscopy, to evaluate the ability of captopril, an angiotensin-converting enzyme inhibitor, to prevent the superoxide-mediated formation of phenyl radicals. Results indicate that, under certain conditions, captopril is a potent inhibitor of the generation of phenyl radicals, produced by the autoxidation of phenylhydrazine. The inhibitory effect of captopril, however, was better understood as a direct interaction of the drug with the metals that catalyze the autoxidation process rather than as a reaction of captopril with the free radicals generated. This last conclusion was supported by the finding that captopril was not able to inhibit the superoxide anion-mediated reduction of nitroblue tetrazolium.

Stunning: a radical re-view

The recovery from trauma, whether ischemia or some other form of tissue injury, is never instantaneous; time is always required for repair and the return of normal metabolism and function. To what extent the delay in recovery of contractile activity (stunning) after a brief period of ischemia represents convalescence from ischemia-induced injury, as opposed to the expression of reperfusion-induced injury, is perhaps not as clear as the proponents of stunning would hope. Definitive evidence for a distinct reperfusion-induced pathology, which compromises the recovery of contractile function from the depressed state induced by ischemia, is elusive. If reperfusion-induced injury accounts for a significant proportion of stunning, then the molecular mechanisms responsible for initiating the event and those responsible for orchestrating the event at the level of the contractile protein are far from clear. Perturbations of calcium homeostasis are frequently cited as responsible for the depressed contractile state, however, some metabolic derangement must precede any pathologically induced ionic disturbance. In this connection, evidence indicates that free-radical-induced oxidant stress, during the early moments of reperfusion, may modify the activity of a number of thiol-regulated proteins that are directly, or indirectly, responsible for controlling the movement of calcium. Sarcolemmal sodium-calcium exchange and the calcium release channel of the sarcoplasmic reticulum may be activated, whereas the sarcolemmal calcium pump and sodium-potassium ATPase, together with the calcium pump of the sarcoplasmic reticulum, may be inhibited. Under the conditions prevailing during ischemia and reperfusion, this would be expected to promote an early intracellular calcium overload. It is difficult to reconcile such a change with the decreased inotropic state that characterizes stunning; however, it seems likely that the calcium overload is transient and that the stunned myocardium rapidly reestablishes normal levels of intracellular calcium. It is still difficult to explain adequately the reduced inotropic state; clearly, the mechanism of stunning is not quite as simple as its definition.

U74006F, a novel 21-aminosteroid, inhibits in vivo lipid peroxidation but fails to limit infarct size in a canine model of myocardial ischemia reperfusion

Peroxidation of membrane lipids has been suggested to play a role in the pathogenesis of myocardial ischemia/reperfusion injury. We therefore assessed the efficacy of U74006F, a potent in vitro vitamin E-like inhibitor of lipid peroxidation, in limiting infarct size in a canine model of transient coronary artery occlusion. Twenty dogs underwent 2 hours of occlusion of the left anterior descending coronary artery and 6 hours of reperfusion. U74006F or saline solution was administered continuously from 1 hour of occlusion to the end of the experiment. U74006F blunted any increase in production of conjugated dienes (an index of lipid peroxidation) at both 30 minutes (1.73 +/- 0.16 mol/L x 10(-4) vs 2.62 +/- 0.22 in control dogs, p less than 0.05) and 6 hours (1.39 +/- 0.22 vs 2.06 +/- 0.18 in control dogs, p less than 0.05) after reperfusion. Furthermore, 6 hours after reflow vitamin E levels tended to be lower than baseline values in control dogs and higher than baseline values in dogs treated with U74006F. However, analysis of infarct size indicated no statistically significant difference between the two groups when expressed either as a percentage of the left ventricle (10.4 +/- 1.8% in U74006F vs 15.2 +/- 2.4% in control dogs) or as a percentage of the area at risk (33.0 +/- 5.5% in U74006F vs 37.8 +/- 4.5% in control dogs). Although U74006F appeared to be a potent in vivo inhibitor of lipid peroxidation, it failed to limit infarct size after 2 hours of occlusion and 6 hours of reperfusion in this canine model.

Superoxide dismutase triggers activation of "primed" platelets

Superoxide dismutase (SOD) triggers activation of human platelets exposed to subthreshold concentrations of arachidonic acid and collagen. The subthreshold concentrations used are not able to activate platelets but "prime" platelets to be activated by SOD. The addition of SOD to arachidonic acid-or collagen-primed platelets induced aggregation, thromboxane A2 production, and release of [3H]serotonin. Superoxide dismutase does not have any effect on resting platelets and ADP-, thrombin-, calcium ionophore A23187-, PAF-, or U46619-stimulated platelets. Furthermore, superoxide dismutase-dependent platelet activation is fully prevented by catalase and/or aspirin, suggesting a role for H2O2 and the involvement of the cyclooxygenase pathway of arachidonic acid in such activation.

Coronary venous retroinfusion of deferoxamine reduces infarct size in pigs

The efficacy of coronary venous retroinfusion of the iron chelator deferoxamine was studied in 24 pentobarbital-anesthetized open chest pigs with a 60 min occlusion of the left anterior descending coronary artery followed by 3 h of reperfusion. Eight retrogradely treated pigs were given 10 mg/kg body weight of deferoxamine by way of the anterior interventricular vein and eight systemically treated pigs received the same doses of deferoxamine intravenously. Drug infusions lasted for 5 min, beginning 15 min before reperfusion. Eight control pigs received systemic intravenous saline solution. Myocardial area at risk and necrotic area were assessed by the monastral blue dye and the triphenyltetrazolium chloride staining method, respectively. There were no significant differences in hemodynamics or regional myocardial function (sonomicrometry) among the groups. Infarct size expressed as percent of risk area was 73.9 +/- 13.5% in the control group, 70.6 +/- 16.4% in the systemically treated group and 48.5 +/- 21.4% (p less than 0.05) in the retrogradely treated group. In conclusion, deferoxamine significantly reduced infarct size after coronary occlusion only when given regionally by way of the coronary vein. Because there was no significant hemodynamic effect caused by deferoxamine infusion, it is suggested that this drug prevents postischemic reperfusion injury by a direct cardioprotective effect.

Therapeutic potential of vitamin E against myocardial ischemic-reperfusion injury

Myocardial ischemia is a disease process characterized by reduced coronary flow such that the supply of nutritive blood to heart muscle (myocardium) is insufficient for normal myocardial aerobic metabolism. Prompt reestablishment of coronary flow by invasive and noninvasive clinical procedures is the most direct and effective means of limiting myocardial damage in ischemic heart disease patients, although reperfusion carries with it an injury component which may reflect, at least to some degree, the toxic effects of partially reduced oxygen species and their participation in degenerative cellular processes such as membrane lipid peroxidation. Vitamin E, a lipophilic, chain-breaking antioxidant, is a prominent membrane constituent in heart muscle, where it modulates/regulates various aspects of heart muscle-cell metabolism and function. Vitamin E's beneficial effects against experimentally induced oxidative damage to the heart, along with inverse epidemiological correlations between plasma vitamin E level and either anginal pain or mortality due to ischemic heart disease, suggest that vitamin E might have protective and therapeutic roles against myocardial ischemic-reperfusion injury. Laboratory investigations aimed at addressing this possibility have demonstrated that vitamin E supplementation protects isolated hearts against ischemic-reperfusion injury, and relatively more inconsistent and limited data document cardioprotective effects of vitamin E in some animal models of myocardial ischemia-reperfusion, especially when administered prior to the ischemic period. Clinical attempts to establish whether vitamin E has therapeutic benefit in ischemic heart disease patients remain inconclusive, having relied upon a variety of nonuniformly controlled protocols and a single, rather subjective endpoint (anginal pain). Consequently, although laboratory data constitute a conceptual context for and indirect support of the idea that vitamin E could be a cardioprotectant against ischemic-reperfusion injury, compelling clinical evidence regarding vitamin E's therapeutic potential in the ischemic heart-disease patient is lacking. Elective coronary revascularization would appear to provide an attractive clinical setting for evaluating the therapeutic efficacy of vitamin E in the context of cardiac ischemia-reperfusion. Further biochemical work would still be required to define how vitamin E exerts any cardioprotective effect observed in these patients.

Transcardiac alteration of neutrophil function before and after coronary thrombolysis in human myocardial infarction

We examined function of isolated neutrophils taken from aorta and coronary sinus before and after thrombolytic reperfusion in 17 patients whose infarct-related coronary arteries were totally occluded. Before reperfusion in left coronary artery disease, free radical generation by activated neutrophils in coronary sinus, assessed by ferricytochrome c reduction (phorbol myristate acetate, 10 ng/ml) and luminol-enhanced chemiluminescence (A23187, 2 microM), was reduced by 20% (P less than 0.05) and 30% (P less than 0.05), respectively, compared with those in aorta. Neutrophil aggregation (A23187, 10 microM) and chemotactic activity (formyl-methionyl-leucyl-phenylalanine, 5 microM) were also reduced in coronary sinus by 21% and 20%. After reperfusion the extent of such neutrophil function in coronary sinus recovered and was similar to that in aorta. There were no significant differences between neutrophil counts in aorta and coronary sinus before and after reperfusion. In right coronary artery disease, no significant changes were seen in these functions of neutrophils of aorta and coronary sinus before and after reperfusion. These results indicate that function of neutrophils passing through coronary circulation fluctuated significantly in association with reperfusion, suggesting (1) factor(s) that depress neutrophil function are produced in coronary circulation during myocardial ischemia and their effects are overcome after reperfusion or (2) activated neutrophils, trapped in the ischemic coronary bed, are washed out to coronary sinus after reperfusion.

Cardioprotective effects of amlodipine on ischemia and reperfusion in two experimental models

The cardioprotective effect of amlodipine, a long-acting dihydropyridine derivative, was studied in 2 experimental models of ischemia and reperfusion. Isolated and blood-perfused feline hearts were made globally ischemic for 60 minutes and then reperfused for 60 minutes. Alterations of left ventricular developed pressure and compliance were monitored in both amlodipine-treated hearts and saline-treated control animals. Changes in perfusion pressure indicated that amlodipine significantly reduced myocardial oxygen consumption and coronary vascular resistance. Furthermore, a progressive increase in resting left ventricular diastolic pressure indicated that amlodipine, administered before the onset of global ischemia, attenuated the development of ischemic contracture. Return of contractile function 60 minutes after reperfusion and maintenance of tissue concentrations of electrolytes were significantly better in the amlodipine-treated group than in the control animals. In intact canine hearts, regional myocardial ischemia was induced for 90 minutes, followed by 6 hours of reperfusion. Although the hemodynamic variables and the size of the region of risk did not differ significantly between treated animals and control animals, the infarct size was significantly smaller in the amlodipine-treated group than in the control animals, and a gradual reduction in coronary blood flow was observed in the control group that was prevented in the amlodipine group. A comparison of these findings with those observed with oxygen radical scavengers also is discussed. A detailed report of these studies was published in The American Journal of Cardiology (1989;64:101I-116I). This review is included here to maintain continuity of the symposium for the convenience of the reader.

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

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