Exendin-4 Protects Against Sulfonylurea-Induced β-Cell Apoptosis

Sulfonylurea is one of the commonly used anti-diabetic drugs that stimulate insulin secretion from β-cells. Despite their glucose lowering effects in type 2 diabetes mellitus, long-term treatment brought on secondary failure characterized by β-cell exhaustion and apoptosis. ER stress induced by Ca²⁺ depletion in endoplasmic reticulum (ER) is speculated be one of the causes of secondary failure, but it remains unclear. Glucagon like peptide-1 (GLP-1) has anti-apoptotic effects in β-cells after the induction of oxidative and ER stress. In this study, we examined the antiapoptotic action of a GLP-1 analogue in β-cell lines and islets against ER stress induced by chronic treatment of sulfonylurea. HIT-T15 and dispersed islet cells were exposed to glibenclamide for 48 h, and apoptosis was evaluated using Annexin/PI flow cytometry. Expression of the ER stress-related molecules and sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA) 2/3 was determined by real-time PCR and western blot analysis. Chronic exposure to glibenclamide increased apoptosis by depletion of ER Ca²⁺ concentration through reduced expression of SERCA 2/3. Pretreatment with Exendin-4 had an anti-apoptotic role through ER stress modulation and ER Ca²⁺ replenishing by SERCA restoration. These findings will further the understanding of one cause of glibenclamide-induced β-cell loss and therapeutic availability of GLP-1-based drugs in secondary failure by sulfonylurea during treatment of diabetes.