Impairment of Endothelial-Myocardial Interaction Increases the Susceptibility of Cardiomyocytes to Ischemia/Reperfusion Injury (original) (raw)
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Proceedings of the National Academy of Sciences, 2007
Coronary vasodilation is impaired in the postischemic heart with a loss of endothelial nitric oxide synthase (eNOS) activity, but the mechanisms underlying ischemia-induced eNOS dysfunction are not understood. For nitric oxide (NO) synthesis, eNOS requires the redox-sensitive cofactor tetrahydrobiopterin (BH 4); however, the role of BH 4 in ischemia-induced endothelial dysfunction remains unknown. Therefore, isolated rat hearts were subjected to varying durations of ischemia, and the alterations in NOS-dependent vasodilation were measured and correlated with assays of eNOS activity and cardiac BH 4 concentrations. Ischemia timedependently decreased cardiac BH 4 content with 85, 95, or 97% irreversible degradation after 30, 45, or 60 min of ischemia, respectively. Paralleling the decreases in BH 4, reductions of eNOS activity were seen of 58, 86, or 92%, and NOS-derived superoxide production was greatly increased. Addition of 10 M BH4 enhanced eNOS activity in nonischemic hearts and partially restored activity after ischemia. It also suppressed NOS-derived superoxide production. Impaired coronary flow during postischemic reperfusion was improved by BH 4 infusion. Thus, BH4 depletion contributes to postischemic eNOS dysfunction, and BH 4 treatment is effective in partial restoration of endothelium-dependent coronary flow. Supplementation of BH 4 may therefore be an important therapeutic approach to reverse endothelial dysfunction in postischemic tissues.
Advances in Pharmacological Sciences, 2010
Reduced nitric oxide (NO) bioavailability and increased oxidative stress are major factors mediating ischemia/reperfusion (I/R) injury. Tetrahydrobiopterin (BH 4 ) is an essential cofactor of endothelial NO synthase (eNOS) to produce NO, whereas dihydrobiopterin (BH 2 ) can shift the eNOS product profile from NO to superoxide, which is further converted to hydrogen peroxide (H 2 O 2 ) and cause I/R injury. The effects of BH 4 and BH 2 on oxidative stress and postreperfused cardiac functions were examined in ex vivo myocardial and in vivo femoral I (20 min)/R (45 min) models. In femoral I/R, BH 4 increased NO and decreased H 2 O 2 releases relative to saline control, and these effects correlated with improved postreperfused cardiac function. By contrast, BH 2 decreased NO release relative to the saline control, but increased H 2 O 2 release similar to the saline control, and these effects correlated with compromised postreperfused cardiac function. In conclusion, these results suggest that promoting eNOS coupling to produce NO and decrease H 2 O 2 may be a key mechanism to restore postreperfused organ function during early reperfusion.
Biochimica et Biophysica Acta (BBA) - General Subjects, 2000
Induction of endothelial nitric oxide synthase (eNOS) contributes to the mechanism of heart protection against ischemia^reperfusion damage. We analyzed the effects of hypoxia and hyperoxia on eNOS expression in isolated working rat hearts after ischemia^reperfusion damage. Adult male Wistar rats were submitted to chronic hypoxia (2 weeks) and hyperoxia (72 h). The hearts were submitted to 15 min of ischemia and reperfused for 60 min, then we evaluated hemodynamic parameters and creatine phosphokinase (CPK) release. eNOS expression was estimated by RT^PCR ; enzyme localization was evaluated by immunohistochemistry and the eNOS protein levels were detected by Western blot. All hemodynamic parameters in hypoxic conditions were better with respect to other groups. The CPK release was lower in hypoxic (P 6 0.01) than in normoxic and hyperoxic conditions. The eNOS deposition was significantly higher in the hypoxic group versus the normoxic or hyperoxic groups. The eNOS protein and mRNA levels were increased by hypoxia versus both other groups. Chronic hypoxic exposure may decrease injury and increase eNOS protein and mRNA levels in heart subjected to ischemiar eperfusion. ß
Cardiovascular Research, 2003
The role of nitric oxide (NO) in myocardial ischemia/reperfusion injury remains controversial as both NO donors and NO synthase (NOS) inhibitors have shown to be protective. We generated transgenic (TG) mice that overexpress endothelial NOS (eNOS) exclusively in cardiac myocytes to determine the effects of high cardiac NO levels on ischemia/reperfusion injury and cellular Ca(2+) homeostasis. Wild-type (WT) mice served as controls. Hearts were perfused in vitro and subjected to 20 min of total no-flow ischemia and 30 min of reperfusion (n=5 per group). Left ventricular function, cGMP levels and intracellular Ca(2+) transients (Ca(2+)(i)) were determined. Left ventricular pressure was reduced (maximum, -33%) and basal cardiac cGMP was increased (twofold) in TG hearts, and the changes were reversed by NOS blockade with N(G)-nitro-L-arginine methyl ester (L-NAME). Relative to baseline, recovery of reperfusion contractile function was significantly better in hearts from TG (98%) than WT (51%) mice, and L-NAME abolished this effect. Heart rate and coronary perfusion pressure were not different between groups. Systolic and diastolic Ca(2+)(i) concentrations were similar in WT and TG hearts, but Ca(2+)(i) overload during early reperfusion tended to be less in TG hearts. Kinetic analysis of pressure curves and Ca(2+)(i) transients revealed a faster left ventricular diastolic relaxation and abbreviated aequorin light signals in TG hearts at baseline and during reperfusion. High levels of NO/cGMP strongly protect against ischemia/reperfusion injury, the protection is largely independent of changes in Ca(2+)(i) modulation, but relates to reduced preischemic performance. Myocyte-specific NO augmentation may aid in studies of the (patho)physiological roles of cardiac-derived NO.
European Journal of Cardio-Thoracic Surgery, 2010
Objective: In contrast to the clinical evidence, experimental studies showed that chronic hypoxia (CH) confers a certain degree of protection against ischaemia-reperfusion damage. We studied the effects of daily reoxygenation during CH (CHReox) on hearts exposed to ischaemiareperfusion. We also separated the intrinsic effects on the myocardium of CH and CHReox from those related to circulatory and nervous factors. Methods: Fifty-one Sprague-Dawley rats were maintained for 15 days under CH (10% O 2 ) or CHReox (10% O 2 + 1 h day À1 exposure to air). Normoxic (N, 21% O 2 ) rats were the control. The animals were randomly assigned to one of the three following protocols: (1) protocol A: hearts (n = 7 per group) were subjected to 30-min occlusion of the left anterior descending (LAD) coronary artery followed by 3-h reperfusion, with measurement of the injury by tetrazolium staining; (2) protocol B: the end-diastolic pressure (EDP) and left ventricular developed pressure  heart rate (LVDP  HR) were measured in Langendorff-perfused isolated hearts (n = 5 per group) during 30-min global ischaemia and 45-min reperfusion; and (3) protocol C: hearts (n = 5 per group) were frozen for the determination of levels of endothelial nitric oxide synthase (eNOS) by Western blotting. Results: CHReox hearts displayed greater phosphorylation of the eNOS and enhanced plasma level of nitrates and nitrites in comparison to CH hearts (P < 0.0001, Bonferroni's post-test). The infarct size was greater in CH than in N hearts (P < 0.0001, Bonferroni's post-test) while it was reduced in CHReox in comparison to CH and N hearts (P < 0.0001). At the end of reperfusion, EDP was higher in CH than CHReox and N hearts (P = 0.01, Bonferroni's post-test) while LVDP  HR was higher in CHReox and N than in CH hearts (P = 0.03, Bonferroni's post-test). Conclusions: Exposure to CH results in impairment of myocardial tolerance to ischaemia-reperfusion, greater injury and reduced recovery of performance, in agreement with clinical evidence. Infarct size, diastolic contracture and myocardial performance have been reduced, respectively, by 63%, 64% and 151% with daily reoxygenation compared with chronic hypoxia by accelerating intrinsic adaptive changes. #
Endothelial nitric oxide synthase overexpression attenuates conqestive heart failure in mice
Proceedings of the National Academy of Sciences of the United States of America, 2003
Previous studies indicate that deficiency of endothelial nitric oxide synthase (eNOS)derived NO exacerbates myocardial reperfusion injury. We hypothesized that overexpression of eNOS would reduce the extent of myocardial ischemia-reperfusion (MI-R) injury. We investigated two distinct strains of transgenic mice overexpressing the eNOS gene (eNOS Tg). Bovine eNOS was overexpressed in one strain (eNOS Tg-Kobe) while the human eNOS gene was overexpressed in the other strain (eNOS Tg-RT). Nontransgenic and eNOS Tg mice were subjected to 30 minutes of coronary artery occlusion followed by 24 hours of reperfusion and the extent of myocardial infarction was determined. Myocardial infarct size was reduced by 33% in the eNOS Tg-Kobe strain (p < 0.05 vs. NTg) and by 32% in the eNOS Tg-RT strain (p < 0.05 vs.
Acta Pharmacologica Sinica, 2005
Aim: To investigate the role of inducible nitric oxide synthase (iNOS)-derived nitric oxide (NO) in the cardioprotection of intermittent hypoxia (IH) against ischemia/reperfusion (I/R) injury. Methods: Langendorff-perfused isolated rat hearts were used to measure variables of left ventricular function during baseline perfusion, ischemia, and reperfusion period. Nitrate plus nitrite (NOx) content in myocardium was measured using a biochemical method. iNOS mRNA and protein expression in rat left ventricles were detected using reverse transcription polymerase chain reaction (RT-PCR) and Western blot, respectively. Results: Myocardial function recovered better in IH rat hearts than in normoxic control hearts. The iNOS-selective inhibitor aminoguanidine (AG) (100 µmol/L) significantly inhibited the protective effects of IH, but had no influence on normoxic rat hearts. The baseline content of NOx in IH hearts was higher than that in normoxic hearts. After 30 min ischemia, the NOx level in normoxic hearts increased compared to the corresponding baseline level, whereas there was no significant change in IH hearts. However, the NOx level in IH hearts was still higher than that of normoxic hearts during ischemia and reperfusion period. AG 100 µmol/L significantly diminished the NOx content in IH and normoxic hearts during ischemia and reperfusion period. The baseline levels of iNOS mRNA and protein in IH hearts were higher than those of normoxic hearts. Compared to the corresponding baseline level, iNOS mRNA and protein levels in normoxic rat hearts increased and those in IH rat hearts decreased after reperfusion. The addition of AG 100 µmol/L significantly decreased iNOS mRNA and protein expression in IH rat hearts after I/R. Conclusion: IH upregulated the baseline level of iNOS mRNA and protein expression leading to an increase in NO production, which may play an important role in the cardiac protection of IH against I/R injury.
Journal of Surgical Research, 2000
Background. While endothelial nitric oxide synthase (eNOS) is an important regulator of vascular tone, it is also constitutively expressed in cardiac myocytes and contributes to the regulation of myocardial function. The role of eNOS in ischemia-reperfusion is uncertain, however, with some studies showing beneficial effects while other studies demonstrate increased cardiac injury. We hypothesized that the beneficial effects of eNOS would predominate, and thus that targeted deletion of eNOS would exacerbate myocardial dysfunction following ischemia-reperfusion.