Background: Enhanced expression of adhesion molecules by the endothelium may account for vascular damage in diabetics and nondiabetic patients who develop stress hyperglycemia during acute myocardial infarction. We analyzed the phosphorylation of protein kinase Cbeta2 (PKCbeta2) at serine/threonine residues, which may contribute to the endothelial dysfunction during acute hyperglycemia. Furthermore, this study was designed to investigate whether selective blockade of this regulatory mechanism may prevent the development of endothelial hyperadhesiveness.

Methods and results: Incubation of the human aortic endothelial cells with high glucose (22.2 mmol/L) resulted in significant increase of vascular cell adhesion molecule (VCAM)-1 protein expression (172+/-15% versus control; P<0.01). Phorbol 12-myristate 13-acetate, a potent activator of PKC, mimicked the effect of high glucose on VCAM-1 expression. High glucose led to a rapid increase (181+/-22% versus control; P<0.01) of membrane-bound PKCbeta, reflecting activation of this enzyme. The nonselective inhibitor of PKCbeta1 and PKCbeta2 isoforms LY379196, as well as CGP53353, a highly selective inhibitor of PKCbeta2, prevented in a dose-dependent manner upregulation of VCAM-1. Incubation with high glucose was associated with increased PKCbeta2 phosphorylation at the Ser-660 residue, and both LY379196 and CGP53353 prevented this event. Exposure of the cells to high glucose also reduced the protein level of the inhibitory subunit of nuclear factor-kappaB, IkappaBalpha, leading to its enhanced binding activity. Selective inhibition of PKCbeta abolished IkappaBalpha degradation.

Conclusions: Our findings demonstrate for the first time that phosphorylation of Ser-660 represents a selective regulatory mechanism for glucose-induced upregulation of VCAM-1. Therefore, PKCbeta2-selective inhibitors may be promising drugs for treatment of endothelial dysfunction during acute hyperglycemia and possibly in diabetes.