b3 adrenergic stimulation restores nitric oxide/redox balance and enhances endothelial function in hyperglycemia

Abstract

Background--Perturbed balance between NO and O2.-. (ie, NO/redox imbalance) is central in the pathobiology of diabetesinduced vascular dysfunction. We examined whether stimulation of β3 adrenergic receptors (β3 ARs), coupled to endothelial nitric oxide synthase (eNOS) activation, would re-establish NO/redox balance, relieve oxidative inhibition of the membrane proteins eNOS and Na+-K+ (NK) pump, and improve vascular function in a new animal model of hyperglycemia. Methods and Results--We established hyperglycemia in male White New Zealand rabbits by infusion of S961, a competitive highaffinity peptide inhibitor of the insulin receptor. Hyperglycemia impaired endothelium-dependent vasorelaxation by "uncoupling" of eNOS via glutathionylation (eNOS-GSS) that was dependent on NADPH oxidase activity. Accordingly, NO levels were lower while O2.- levels were higher in hyperglycemic rabbits. Infusion of the β3 AR agonist CL316243 (CL) decreased eNOS-GSS, reduced O2.-, restored NO levels, and improved endothelium-dependent relaxation. CL decreased hyperglycemia-induced NADPH oxidase activation as suggested by co-immunoprecipitation experiments, and it increased eNOS co-immunoprecipitation with glutaredoxin-1, which may reflect promotion of eNOS de-glutathionylation by CL. Moreover, CL reversed hyperglycemia-induced glutathionylation of the β1 NK pump subunit that causes NK pump inhibition, and improved K+-induced vasorelaxation that reflects enhancement in NK pump activity. Lastly, eNOS-GSS was higher in vessels of diabetic patients and was reduced by CL, suggesting potential significance of the experimental findings in human diabetes. Conclusions-β3 AR activation restored NO/redox balance and improved endothelial function in hyperglycemia. β3 AR agonists may confer protection against diabetes-induced vascular dysfunction.