Nitric oxide prevents apoptosis of human endothelial cells from high glucose exposure during early stage

Abstract

Hyperglycemia is a major cause of diabetic vascular disease. High glucose can induce reactive oxygen species (ROS) and nitric oxide (NO) generation, which can subsequently induce endothelial dysfunction. High glucose is also capable of triggering endothelial cell apoptosis. Little is known about the molecular mechanisms and the role of ROS and NO in high glucose-induced endothelial cell apoptosis. This study was designed to determine the involvement of ROS and NO in high glucose-induced endothelial cell apoptosis. Expression of endothelial nitric oxide synthase (eNOS) protein and apoptosis were studied in cultured human umbilical vein endothelial cells (HUVECs) exposed to control-level (5.5 mM) and high-level (33 mM) glucose at various periods (e.g., 2, 12, 24, 48 h). We also examined the effect of high glucose on H2O2 production using flow cytometry. The results showed that eNOS protein expression was up-regulated by high glucose exposure for 2–6 h and gradually reduced after longer exposure in HUVECs. H2O2 production and apoptosis, which can be reversed by vitamin C and NO donor (sodium nitroprusside), but enhanced by NOS inhibitor (NG-nitro-L-arginine methyl ether), were collated to a different time course (24–48 h) to HUVECs. These results provide the molecular basis for understanding that NO plays a protective role from apoptosis of HUVECs during the early stage (<24 h) of high glucose exposure, but in the late stage (>24 h), high glucose exposure leads to the imbalance of NO and ROS, resulting to the observed apoptosis. This may explain, at least in part, the impaired endothelial function and vascular complication of diabetic mellitus that would occur at late stages. J. Cell. Biochem. 75:258–263, 1999. © 1999 Wiley-Liss, Inc.