PKCβ inhibition with ruboxistaurin reduces oxidative stress and attenuates left ventricular hypertrophy and dysfuntion in rats with streptozotocin-induced diabetes

Oxidative stress plays critical roles in the development of diabetic cardiovascular complications, including myocardial hypertrophy. The beta isoform of PKC (protein kinase C) is preferentially overexpressed in the myocardium of diabetic subjects accompanied with increased activation of the pro-oxidant enzyme NADPH oxidase, which may exacerbate oxidative stress. We hypothesized that myocardial PKC beta is a major upstream mediator of oxidative stress in diabetes and that PKC beta inhibition can attenuate myocardial hypertrophy and dysfunction. Control or streptozotocin-induced diabetic rats were treated with the selective PKC beta inhibitor RBX (ruboxistaurin; 1 mg/kg of body weight per day) or the antioxidant NAC (N-acetylcysteine) for 4 weeks. LV (left ventricular) dimensions and functions were detected by echocardiography. 15-F-2t-isoprostane (a specific index of oxidative stress) and myocardial activities of superoxide dismutase as well as protein levels of NADPH oxidase were assessed by immunoassay or Western blotting. Echocardiography revealed that the LV mass/body weight ratio was significantly increased in diabetic rats (P < 0.01 compared with the control group) in parallel with the impaired LV relaxation. A significant increase in cardiomyocyte cross-sectional area was observed in diabetic rats accompanied by an increased production of O-2(-) (superoxide anion) and 15-F-2t-isoprostane (all P < 0.05 compared with the control group). RBX normalized these changes with concomitant inhibition of PKC beta(2) activation and prevention of NADPH oxidase subunit p67(phax) membrane translocation and p22(phax) overexpression. The effects of RBX were comparable with that of NAC, except that NAC was inferior to RBX in attenuating cardiac dysfunction. It is concluded that RBX can ameliorate myocardial hypertrophy and dysfunction in diabetes, which may represent a novel therapy in the prevention of diabetic cardiovascular complications.