GCG and diabetes mellitus: However, the direct effect mechanism of GLP-1 on vascular injury in diabetes and its relationship with ROS and downstream signaling pathway is largely unknown.17 To determine the role of GLP-1 in oxidative stress and apoptosis induced by high glucose, we paired cultures of human umbilical vein endothelial cells (HUVECs) isolates that were exposed to high concentration of glucose and GLP-1 in order to investigate the effects of GLP-1 on oxidative stress and cell apoptosis induced by high concentration of glucose.