钠—葡萄糖协同转运蛋白2抑制剂增加α细胞胰高血糖素和GLP-1分泌保护β细胞功能及其机制

SGLT2抑制剂除降糖外还可以保护β细胞功能。胰高血糖素和GLP-1对维持β细胞功能很重要。高血糖通过SGLT依赖的Na+细胞内转运调节KATP影响胰高血糖素分泌，SGLT2抑制剂升高胰高血糖素和GLP-1水平。在前期研究野生型和KATP通道SUR1敲除小鼠胰岛素、胰高血糖素分泌特点及机制的基础上，本项目拟以肥胖糖尿病小鼠和KATP通道SUR1敲除小鼠为模型，给予SGLT2抑制剂，观察其对胰岛胰高血糖素、胰岛素和GLP-1分泌的影响。用膜片钳技术测量细胞膜电位变化，同时测定细胞内pH值以及Ca2+和Na+浓度，再通过SUR1敲除小鼠活体试验验证KATP参与该过程的调节。由此论证SGLT2抑制剂增加胰岛α细胞胰高血糖素和GLP-1分泌，机制是抑制Na+离子进入α细胞，影响了细胞内外的离子平衡和膜电位，激活KATP，促进了α细胞去极化，从而为SGLT2抑制剂保护胰岛β细胞功能提供新的机制解释。

Besides exerting therapeutic activity by facilitating glucose excretion through the kidney, sodium glucose co-transporter 2 (SGLT2) inhibitors are also important new glucose-lowering agents that could preserve and improve β cell function in T2DM. Although as an antihypoglycemic hormone, glucagon actually plays an important role with glucagon-like peptide-1 (GLP-1) in the maintenance and regulation of insulin secretion from β cell. Hyperglycemia impairs glucagon secretion by SGLT dependent elevation of intracellular Na+, thus leading to dysregulated KATP channel activity in α cell. Previous studies from rodents and human indicated that SGLT2 inhibitors elevate the levels of glucagon and GLP-1, which may result in the protective effects on β cell function. We investigated the profiles and mechanisms involved of insulin and glucagon in wide-type and KATP channel absent (SUR1 knockout) mouse. This study will explore the effects of two SGLT2 inhibitor dapagliflozin and canagliflozin with different SGLT2 selectivity on glucagon, GLP-1 and insulin secretion in islets from obese diabetic wild-type and SUR1 knockout mouse, respectively. Patch clamp recording technique is used to determine the changes of cell membrane potential in α cell. Intracellular pH, cytoplasmic Na+ and Ca2+ will also be measured. In vivo experiments during fasting and re-fed status will also be conducted to test the role of KATP in the regulation of glucagon in α cell. We suppose SGLT2 inhibitors prevents Na+ uptake and intracellular acidification, promoting α cell depolarization, thus stimulate glucagon secretion. Our results will provide a new explanation of mechanisms for β cell preservation by SGLT2 inhibitors.