Abstract
BackgroundPatients with diabetes are prone to develop cardiac hypertrophy and more susceptible to myocardial ischemia–reperfusion (I/R) injury, which are concomitant with hyperglycemia-induced oxidative stress and impaired endothelial nitric oxide (NO) synthase (eNOS)/NO signaling. Caveolae are critical in the transduction of eNOS/NO signaling in cardiovascular system. Caveolin (Cav)-3, the cardiomyocytes-specific caveolae structural protein, is decreased in the diabetic heart in which production of reactive oxygen species are increased. We hypothesized that treatment with antioxidant N-acetylcysteine (NAC) could enhance cardiac Cav-3 expression and attenuate caveolae dysfunction and the accompanying eNOS/NO signaling abnormalities in diabetes.MethodsControl or streptozotocin-induced diabetic rats were either untreated or treated with NAC (1.5 g/kg/day, NAC) by oral gavage for 4 weeks. Rats in subgroup were randomly assigned to receive 30 min of left anterior descending artery ligation followed by 2 h of reperfusion. Isolated rat cardiomyocytes or H9C2 cells were exposed to low glucose (LG, 5.5 mmol/L) or high glucose (HG, 25 mmol/L) for 36 h before being subjected to 4 h of hypoxia followed by 4 h of reoxygenation (H/R).ResultsNAC treatment ameliorated myocardial dysfunction and cardiac hypertrophy, and attenuated myocardial I/R injury and post-ischemic cardiac dysfunction in diabetic rats. NAC attenuated the reductions of NO, Cav-3 and phosphorylated eNOS and mitigated the augmentation of O2 −, nitrotyrosine and 15-F2t-isoprostane in diabetic myocardium. Immunofluorescence analysis demonstrated the colocalization of Cav-3 and eNOS in isolated cardiomyocytes. Immunoprecipitation analysis revealed that diabetic conditions decreased the association of Cav-3 and eNOS in isolated cardiomyocytes, which was enhanced by treatment with NAC. Disruption of caveolae by methyl-β-cyclodextrin or Cav-3 siRNA transfection reduced eNOS phosphorylation. NAC treatment attenuated the reductions of Cav-3 expression and eNOS phosphorylation in HG-treated cardiomyocytes or H9C2 cells. NAC treatment attenuated HG and H/R induced cell injury, which was abolished during concomitant treatment with Cav-3 siRNA or eNOS siRNA.ConclusionsHyperglycemia-induced inhibition of eNOS activity might be consequences of caveolae dysfunction and reduced Cav-3 expression. Antioxidant NAC attenuated myocardial dysfunction and myocardial I/R injury by improving Cav-3/eNOS signaling.
Highlights
Patients with diabetes are prone to develop cardiac hypertrophy and more susceptible to myocardial ischemia–reperfusion (I/R) injury, which are concomitant with hyperglycemia-induced oxidative stress and impaired endothelial nitric oxide (NO) synthase/NO signaling
This notion is supported by our previous findings that decreased Cav-3 expression and cardiac NO bioavailability are detected in hearts from rats with chronic streptozotocin (STZ)induced diabetes [19, 20], which are associated with more serious myocardial I/R injury [19, 21]
Our data suggested that inhibition of excessive oxidative stress by N-acetylcysteine (NAC), an antioxidant which has been proven by us [22,23,24,25,26] and others [27, 28] to be effective in attenuating oxidative stress in diabetic hearts, could restore Cav-3 expression and improve endothelial nitric oxide (NO) synthase (eNOS)/NO signaling, which attenuate diabetic cardiomyopathy and myocardial I/R injury in diabetic rats
Summary
Patients with diabetes are prone to develop cardiac hypertrophy and more susceptible to myocardial ischemia–reperfusion (I/R) injury, which are concomitant with hyperglycemia-induced oxidative stress and impaired endothelial nitric oxide (NO) synthase (eNOS)/NO signaling. This notion is supported by our previous findings that decreased Cav-3 expression and cardiac NO bioavailability are detected in hearts from rats with chronic streptozotocin (STZ)induced diabetes [19, 20], which are associated with more serious myocardial I/R injury [19, 21] It remains unclear whether or not excessive production of ROS mediated diabetic abnormalities is an independent manifestation of hyperglycemic injury or is linked to impaired Cav-3 expression and eNOS/NO signaling in diabetes. Our data suggested that inhibition of excessive oxidative stress by N-acetylcysteine (NAC), an antioxidant which has been proven by us [22,23,24,25,26] and others [27, 28] to be effective in attenuating oxidative stress in diabetic hearts, could restore Cav-3 expression and improve eNOS/NO signaling, which attenuate diabetic cardiomyopathy and myocardial I/R injury in diabetic rats
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