Mechanisms underlying endothelial dysfunction in diabetes mellitus

Incubation of endothelial cells in vitro with high concentrations of glucos e activates protein kinase C (PKC) and increases nitric oxide synthase (NOS III) gene expression as well as superoxide production. The underlying mech anisms remain unknown. To address this issue in an in vivo model, diabetes was induced with streptozotocin in rats. Streptozotocin treatment led to en dothelial dysfunction and increased vascular superoxide production, as asse ssed by lucigenin- and coelenterazine-derived chemiluminescence. The bioava ilability of vascular nitric oxide (as measured by electron spin resonance) was reduced in diabetic aortas, although expression of endothelial NOS III (mRNA and protein) was markedly increased. NOS inhibition with N-G-nitro-L -arginine increased superoxide levels in control vessels but reduced them i n diabetic vessels, identifying NOS as a superoxide source. Similarly, we f ound an activation of the NADPH oxidase and a 7-fold increase in gp91(phox) mRNA in diabetic vessels. In vitro PKC inhibition with chelerythrine reduc ed vascular superoxide in diabetic vessels, whereas it had no effect on sup eroxide levels in normal vessels. In vivo PKC inhibition with N-benzoyl-sta urosporine did not affect glucose levels in diabetic rats but prevented NOS III gene upregulation and NOS-mediated superoxide production, thereby rest oring vascular nitric oxide bioavailability and endothelial function. The r eduction of superoxide in vitro by chelerythrine and the normalization of N OS III gene expression and reduction of superoxide in vivo by N-benzoyl-sta urosporine point to a decisive role of PKC in mediating these phenomena and suggest a therapeutic potential of PKC inhibitors in the prevention or tre atment of vascular complications of diabetes mellitus. The full text of thi s article is available at http://www.circresaha.org.