Evidence for a Role of Superoxide Generation in Glucose-Induced β-Cell Dysfunction In Vivo

Abstract

OBJECTIVE— Prolonged elevation of glucose can adversely affect β-cell function. In vitro studies have linked glucose-induced β-cell dysfunction to oxidative stress; however, whether oxidative stress plays a role in vivo is unclear. Therefore, our objective was to investigate the role of oxidative stress in an in vivo model of glucose-induced β-cell dysfunction. RESEARCH DESIGN AND METHODS— Wistar rats were infused intravenously with glucose for 48 h to achieve 20 mmol/l hyperglycemia with/without co-infusion of one of the following antioxidants: taurine (2-amino ethanesulfonic acid) (TAU), an aldehyde scavenger; N-acetylcysteine (NAC), a precursor of glutathione; or tempol (4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl) (TPO), a superoxide dismutase mimetic. This was followed by islet isolation or hyperglycemic clamp. RESULTS— A 48-h glucose infusion decreased glucose-stimulated insulin secretion (GSIS) and elevated reactive oxygen species (ROS), total superoxide, and mitochondrial superoxide in freshly isolated islets. TPO prevented the increase in total and mitochondrial superoxide and the β-cell dysfunction induced by high glucose. However, TAU and NAC, despite completely normalizing H2DCF-DA (dihydro-dichlorofluorescein diacetate)-measured ROS, did not prevent the increase in superoxide and the decrease in β-cell function induced by high glucose. TPO but not TAU also prevented β-cell dysfunction induced by less extreme hyperglycemia (15 mmol/l) for a longer period of time (96 h). To further investigate whether TPO is effective in vivo, a hyperglycemic clamp was performed. Similar to the findings in isolated islets, prolonged glucose elevation (20 mmol/l for 48 h) decreased β-cell function as assessed by the disposition index (insulin secretion adjusted for insulin sensitivity), and co-infusion of TPO with glucose completely restored β-cell function. CONCLUSIONS— These findings implicate superoxide generation in β-cell dysfunction induced by prolonged hyperglycemia.