Role of nitric oxide, tetrahydrobiopterin and peroxynitrite in glucose toxicity-associated contractile dysfunction in ventricular myocytes

Aims/hypothesis. Local overproduction of nitric oxide is seen in early stages of diabetes, which can react with superoxide (O-2(-)) to form peroxynitrite (ONOO-). The aim of this study was to examine the effect of scavengers for nitric oxide, O-2(-), ONOO- and NOS cofactor tetrahydrobiopterin (BH4) on high glucose-induced cardiac contractile dysfunction. Methods. Ventricular myocytes were cultured for 24 h with either normal (N, 5.5 mmol/l) or high (25.5 mmol/l) glucose, with or without the nitric oxide scavengers haemoglobin (100 nmol/l), PTIO (100 mumol/l), the NOS inhibitor L-NMMA (100 mumol/l), superoxide dismutase (SOD, 500 U/ml), the ONOO- scavengers urate (100 mumol/l), MnTABP (100 mumol/l), BH4 (10 mumol/l) and its inactive analogue NH4 (10 mumol/l), and the GTP cyclohydrolase I inhibitor DAHP (1 mmol/l). Myocyte mechanics, NOS protein expression and activity were evaluated. Results. High glucose myocytes showed reduced peak shortening, decreased maximal velocity of shortening/relengthening (+/- dL/dt), prolonged relengthening (TR90) and normal shortening duration (TPS) associated with reduced cytosolic Ca2+ rise compared to normal myocytes. The high glucose-induced abnormalities were abrogated or attenuated by urate, MnTBAP, L-NMMA, BH4, and SOD, whereas unaffected by haemoglobin, PTIO and NH4. L-NMMA reduced peak shortening while PTIO and DAHP depressed +/- dL/dt and prolonged TPS or TR90 in normal myocytes. High glucose increased NOS activity, protein expression of eNOS but not iNOS, which were attenuated by L-NMMA and BH4, respectively. Conclusion/interpretation. These results suggested that NOS cofactor, NO and ONOO- play a role in glucose-induced cardiomyocyte contractile dysfunction and in the pathogenesis of diabetic cardiomyopathy.