AT1 blockade prevents glucose-induced cardiac dysfunction in ventricular myocytes -: Role of the AT1 receptor and NADPH oxidase

Enhanced tissue angiotensin (Ang) II levels have been reported in diabetes and might lead to cardiac dysfunction through oxidative stress. This study examined the effect of blocking the Ang II type 1 (AT(1)) receptor on high glucose - induced cardiac contractile dysfunction. Rat ventricular myocytes were maintained in normal- (NG, 5.5 mmol/L) or high- (HG, 25.5 mmol/L) glucose medium for 24 hours. Mechanical and intracellular Ca2+ properties were assessed as peak shortening (PS), time to PS (TPS), time to 90% relengthening (TR90), maximal velocity of shortening/relengthening (+/-dL/dt), and intracellular Ca2+ decay (tau). HG myocytes exhibited normal PS; decreased +/-dL/dt; and prolonged TPS, TR90, and tau. Interestingly, the HG-induced abnormalities were prevented with the AT(1) blocker L-158,809 (10 to 1000 nmol/L) but not the Janus kinase-2 (JAK2) inhibitor AG-490 (10 to 100 mumol/L). The only effect of AT(1) blockade on NG myocytes was enhanced PS at 1000 nmol/L. AT(1) antagonist-elicited cardiac protection against HG was nullified by the NADPH oxidase activator sodium dodecyl sulfate (80 mumol/L) and mimicked by the NADPH oxidase inhibitors diphenyleneiodonium (10 mumol/L) or apocynin (100 mumol/ L). Western blot analysis confirmed that the protein abundance of NADPH oxidase subunit p47(phox) and the AT(1) but not the AT(2) receptor was enhanced in HG myocytes. In addition, the HG-induced increase of p47(phox) was prevented by L-158,809. Enhanced reactive oxygen species production observed in HG myocytes was prevented by AT(1) blockade or NADPH oxidase inhibition. Collectively, our data suggest that local Ang II, acting via AT(1) receptor-mediated NADPH oxidase activation, is involved in hyperglycemia-induced cardiomyocyte dysfunction, which might play a role in diabetic cardiomyopathy.