18-LB: Increased Acidosis and Free-Radical Production Causes Recurrent Hypoglycemia–Induced Increase in Post-ischemic ER Stress in Treated Diabetic Rats

Cerebral ischemia is a serious complication of diabetes. Treatment of diabetes causes recurrent hypoglycemia (RH). Prior RH exposure increases ischemic brain damage in insulin-treated diabetic (ITD) rats. However, the mechanism of this injury is not well understood. We showed that ischemic acidosis increases reactive oxygen species (ROS) production in RH-exposed ITD (ITD + RH) rats. As enhanced acidosis and ROS production in normal subjectsactivate PERK, we hypothesized that increased ischemic acidosis and ROS production in RH-exposed ITD rats activate PERK. Therefore, we determined if the administration of tris-(hydroxymethyl)-aminomethane (THAM; an alkalizing agent) and N-acetylcysteine (NAC; an antioxidant) decrease RH-induced post-ischemic PERK activation in ITD + RH rats. Wistar rats were treated with insulin 2-3 weeks after streptozotocin induced diabetes. After 2 weeks, hyperinsulinemic hypoglycemia was induced for 3 hours for 5 days. Following groups were employed: (I) ITD + vehicle (Veh) (n = 6); (II) ITD + RH + Veh (n = 7); (III) ITD + RH + THAM (0.3 M, 3 ml/kg/hr, i.v.) (n = 6); and (IV) ITD + RH + NAC (150 mg/kg, i.v.) (n = 6). Transient global cerebral ischemia was induced by bilateral carotid artery occlusion with hypotension a day after RH. THAM/Veh was infused from 15 min before to 88 minutes after ischemia. NAC/Veh was administered 5 min before and 12 h after ischemia. Based on Western blot analysis, pPERK to total PERK ratio in the ITD + RH + THAM and ITD + RH + NAC groups were significantly lower by 32% and 26%, respectively, when compared with ITD + RH + Veh group. CHOP levels in the ITD + RH + THAM and ITD + RH + NAC group were lower by 38% and 63%, respectively, when compared with ITD + RH + Veh group. Therefore, ischemic acidosis and ROS production may mediate RH-induced ischemic activation of PERK. Understanding the ischemic damage in RH-exposed ITD rats may help identify new treatments for diabetes induced increase in ischemic injury.