Abstract

Objective- Impaired cardiovascular function in diabetes is partially attributed to pathological overexpression of inducible nitric oxide synthase (iNOS) in cardiovascular tissues. We examined whether the hyperglycemia-induced increased expression of iNOS is PKCβ₂ dependent and whether selective inhibition of PKCβ reduces iNOS expression and corrects abnormal hemodynamic function in streptozotocin (STZ)-diabetic rats.

Research design and methods- Cardiomyocytes and aortic vascular smooth muscle cells (VSMC) from non-diabetic rats were cultured in low (5.5 mM) or high (25 mM) glucose or mannitol (19.5 mM mannitol + 5.5mM glucose) conditions in the presence of a selective PKCβ inhibitor, LY333531 (20nM). Further, the in vivo effects of PKCβ inhibition on iNOS mediated cardiovascular abnormalities were tested in STZ diabetic rats.

Results- Exposure of cardiomyocytes to high glucose activated PKCβ₂ and increased iNOS expression that was prevented by LY333531. Similarly, treatment of VSMC with LY333531 prevented high glucose-induced activation of nuclear factor kappa B (NF-κB), extracellular signal-regulated kinase (ERK1/2) and iNOS overexpression. Suppression of PKCβ₂ expression by small interference RNA (siRNA) decreased high-glucose—induced NF-κB and ERK1/2 activation and iNOS expression in VSMC. Administration of LY333531 (1 mg/kg/day) decreased iNOS expression and formation of peroxynitrite in the heart and superior mesenteric arteries and corrected the cardiovascular abnormalities in STZ diabetic rats, an action that was also observed with a selective iNOS inhibitor, LNIL.

Conclusions- Collectively, these results suggest that inhibition of PKCβ₂ may be a useful approach for correcting abnormal hemodynamics in diabetes by preventing iNOS mediated nitrosative stress.