Effects of selenium deficiency on the response of cardiac tissue to ischemia and reperfusion.

Over a 10-week period, female Wistar rats received a diet containing a low level of selenium, cofactor of the antioxidant enzyme glutathione peroxidase (GPx) in order to examine the influence of deficiency of this trace element (i) on tissue antioxidant enzyme defence systems, and (ii) on the susceptibility of the myocardium to ischemia-reperfusion injury. At the end of the dietary treatment, hearts were perfused at constant flow (11 ml/min) before being subjected to 15 min of global normothermic ischemia, followed by 30 min of reperfusion. The effects of selenium deficiency were estimated by studying functional recovery of various cardiac parameters (left ventricular developed pressure LVDevP, heart rate HR, and the product HR x LVDevP), as well as ultrastructural tissue characteristics. Furthermore, superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities were measured at the end of the reperfusion period. Results suggest that: (a) the activity of GPx is decreased by selenium deficiency while SOD activity remains unchanged, (b) the recovery of cardiac function and myocardial ventricular ultrastructure during reperfusion are altered in the selenium-deficient group compared to controls. These results illustrate the crucial role that selenium, the co-factor of one of the major antioxidant enzymes of the myocardium, plays in determining the vulnerability of the heart to ischemia and reperfusion.

Age-dependent changes in myocardial susceptibility to zero flow ischemia and reperfusion in isolated perfused rat hearts: relation to antioxidant status.

Ageing is associated with an increase in myocardial susceptibility to ischemia and a decrease in post-ischemic recovery of function. In the present study, we have examined the effects of ageing on (i) myocardial ischemic contracture, (ii) the reperfusion syndrome and lipid peroxidation upon reperfusion, and (iii) the activity of enzymes involved in reactive oxygen species elimination. Hearts from male Wistar rats aged 4 (adults), 16 (old) or 24 months (senescent) were subjected to 20-min zero flow ischemia and 30-min reperfusion ex vivo. Cardiac activity of superoxide dismutase, catalase, and glutathione peroxidase, as well as cardiac content of thiobarbituric acid reactants were assessed in frozen heart samples. The effects of ageing on ischemic contracture of the sarcomeres were assessed on electromicrographs of tissues taken at the end of ischemia. In our experimental conditions, ischemic contracture of the sarcomeres increased progressively during ageing. In contrast, the severity of the reperfusion syndrome increased between 4 and 16 months of age, and then decreased up to 24 months of age. We propose that the peak of susceptibility of the myocardium to reperfusion observed during moderate ageing might be related to a decrease in the ability of cardiomyocytes to dismutate hydrogen peroxide as suggested by the observed decrease in catalase activity. Finally, the better resistance to the reperfusion syndrome exhibited by senescent rats compared to old rats might be due to a natural selection of a subpopulation of rats which is particularly resistant to oxidative stress.

EUK-8 a synthetic catalytic scavenger of reactive oxygen species protects isolated iron-overloaded rat heart from functional and structural damage induced by ischemia/reperfusion.

The effects of EUK-8, a synthetic, catalytic scavenger of reactive oxygen species, on isolated iron-overloaded rat hearts submitted to ischemia-reperfusion were studied. In the absence of EUK-8, functional parameters (systolic and diastolic pressures, oxygen consumption as estimated by the product heart rate times left ventricular diastolic pressure) were severely impaired 1 minute and 15 minutes after reperfusion following a 15 minute ischemic episode. Dimethylthiourea (10 mM), a hydroxyl radical scavenger, had a minimally protective effect. In contrast, EUK-8 at a concentration of 50 microM in the perfusion medium maintained these parameters at close to their preischemia values. Electron microscopic analysis of heart tissues after 15 minutes ischemia followed by 15 minutes reperfusion showed extensive damage to mitochondria and sarcomeres in untreated hearts, while the extent of damage was significantly lower in EUK-8-treated hearts. The functional and structural protection afforded by EUK-8 were significantly better than those induced by dimethylthiourea. These data suggest that EUK-8 may be therapeutically useful in preventing heart damage induced by ischemia-reperfusion, for example, during thrombolytic treatment of myocardial infarction.

Effect of dietary antioxidant trace element supply on cardiac tolerance to ischemia-reperfusion in the rat.

Over a 10-week period, female Wistar rats received a diet containing various levels of four trace elements (Zn, Cu, Mn, Se), co-factors of antioxidant enzymes (superoxide dismutase SOD, glutathione peroxidase GPx), in order to examine the influence of supplementation or deficiency of these elements (i) on tissue antioxidant enzyme defence systems, and (ii) on the susceptibility of the myocardium to ischemia-reperfusion injury. At the end of the dietary treatment, hearts were perfused at constant flow (11 ml/min) before being subjected to 15 min of total global normothermic ischemia, followed by reperfusion. The effects of the various diets (deficient, standard or supplemented) were estimated by studying functional recovery of various cardiac parameters (left ventricular developed pressure LVDP, dP/dtmax, heart rate x LVDP) as well as ultrastructural tissue characteristics. Furthermore, SOD and GPx activities were measured before ischemia and at the end of the reperfusion period. Results suggest that: (a) the activity of antioxidant enzymes increased or decreased significantly when diet was respectively supplemented with, or deficient in, trace elements, but was not further modified by an ischemia-reperfusion episode: (b) the recovery of cardiac function during reperfusion, and ventricular myocardial ultrastructure were significantly improved under the influence of trace element supplementation when compared to both standard and deficient groups. These results illustrate the protective effect of trace elements which are co-factors of antioxidant enzymes in limiting ischemia-reperfusion induced injury, and suggest a possible use in the field of anti-ischemic therapy.

Oral selenium supplementation in rats reduces cardiac toxicity of adriamycin during ischemia and reperfusion.

The aim of the present study was to assess whether an 8-wk oral selenium supplementation (standard food enriched with 2500 micrograms Se/kg) in rats might prevent the cardiotoxicity of adriamycin (ADR) treatment. ADR was administered at a dose of 2.5 mg/kg body wt intraperitoneally twice weekly for 3 wk. One week after the end of ADR treatment, rats (n = 10 per group) were killed and their hearts were perfused on a Langendorff mode and subjected to a 30-min period of low-flow ischemia (residual flow = 0.1 ml/min) followed by reperfusion (15 min). The results were as follows: 1) selenium supplementation significantly increased the activity of cardiac mitochondrial glutathione peroxidase (GPx) in ADR-treated rats (control: 206 +/- 17.4 IU/g protein; Se: 277 +/- 24.5 IU/g protein, p < 0.05); 2) selenium supplementation reduced myocardial malondialdehyde content in ADR-treated rats (control: 1220 +/- 49.1 nmol/g protein; Se: 1010 +/- 75.9 nmol/g protein; p < 0.05); and 3) ADR treatment significantly increased the degree of reperfusion-induced structural alterations to sarcomeres compared to untreated hearts. Again, this phenomenon was abolished by selenium supplementation. In conclusion, this study demonstrates that selenium supplementation is able to limit ADR cardiotoxicity in isolated rat hearts submitted to a sequence of ischemia/reperfusion.

Effect of iron overload in the isolated ischemic and reperfused rat heart.

It has been suggested that iron might play a pivotal role in the development of reperfusion-induced cellular injury through the activation of oxygen free radical producing reactions. The present study examined the effects of myocardial iron overload on cardiac vulnerability to ischemia and reperfusion. Moreover, the effect of the iron chelator deferoxamine in reversing ischemia-reperfusion injury was studied. Animals were treated with iron dextran solution (i.m. injection, 25 mg every third day during a 5 week period). The control group received the same treatment without iron. Isolated rat hearts were perfused at constant flow (11 ml/min) and subjected to a 15 minute period of global normothermic ischemia followed by reperfusion for 15 minutes. The effects of iron overload were investigated using functional and biochemical parameters, as well as ultrastructural characteristics of the ischemic-reperfused myocardium compared with placebo values. The results suggest that (a) a significant iron overload was obtained in plasma and hepatic and cardiac tissues (x2.5, x16, and x8, respectively) after chronic intramuscular administration of iron dextran (25 mg); (b) during normoxia, iron overload was associated with a slight reduction in cardiac function and an increase in lactate dehydrogenase (LDH) release (x1.5); (c) upon reperfusion, functional recovery was similar whether the heart had been subjected to iron overload or not. However, in the control group left ventricular end-diastolic pressure remained higher than in preischemic conditions, an effect that was not observed in the iron-overloaded group. Moreover, LDH release was markedly increased in the iron-loaded group (x4.2); (d) iron overload was associated with a significant worsening of the structural alterations observed during reperfusion, particularly at the mitochondrial and sarcomere level; (e) after 15 minutes of reperfusion, the activity of the anti-free-radical enzyme, glutathione peroxidase (GPX), was significantly reduced in iron-overloaded hearts, whereas catalase activity was increased; (e) the overall modifications observed in the presence of iron overload were prevented by deferoxamine. In conclusion, this study underlines the possible role of cardiac iron in the development of injury associated with ischemia and reperfusion, and the possible importance of the use of an iron-chelating agent in anti-ischemic therapy.

Ultrastructural basis of the free-radical scavenging effect of indapamide in experimental myocardial ischemia and reperfusion.

Reperfusion of acutely ischemic cardiac tissue is associated with several characteristic pathophysiological changes that are generally referred to as "reperfusion injury." It has been hypothesized that some of these changes are mediated by oxygen-derived free radicals. Indapamide, a nonthiazide diuretic, has been shown to exert free-radical scavenging properties comparable to that of alpha-tocopherol. The purpose of the present work was to investigate whether indapamide (IDP) may limit ultrastructural signs of reperfusion injury in an experimental model of myocardial ischemia and reperfusion in isolated rat hearts. Rats received a chronic oral administration of IDP (7 days at 3 mg/kg body weight/day) before excision of the heart. IDP was also added to the perfusion fluid at a final concentration of 10(-4) M. Isolated hearts were perfused under control conditions for 20 min and then submitted to 15 min of global no-flow ischemia, before being reperfused for 15 min. Hearts were fixed by glutaraldehyde perfusion fixation and left ventricular ultrastructure was studied on ultra-thin sections by electron microscopy. Micrographs were taken following a random procedure to obtain a representative overview of the whole section. In the untreated group, marked ultrastructural alterations were observed including contraction bands, disrupted membranes, and swollen mitochondria. In the indapamide-treated group, the degree of morphological injury was significantly lessened. It is concluded that indapamide protects the ultrastructure of ventricular myocytes against reperfusion injury. This effect might be related to the oxygen free-radical scavenging property of the drug.