Department of Immunology, Key Laboratory of Immune Microenvironment and Disease of the Educational Ministry of China, NHC Key Laboratory of Hormones and Development, Tianjin Key Laboratory of Metabolic Diseases, Chu Hsien-I Memorial Hospital & Tianjin Institute of Endocrinology, Tianjin Medical University, Tianjin, China.
Center for Cardiovascular Diseases, The Province and Ministry Co-Sponsored Collaborative Innovation Center for Medical Epigenetics, Tianjin Medical University, Tianjin, China.
Diabetologia. 2023 Nov;66(11):2139-2153. doi: 10.1007/s00125-023-05985-6. Epub 2023 Aug 15.
AIMS/HYPOTHESIS: An increasing body of evidence has shown that the catabolism of branched-chain amino acids (BCAAs; leucine, isoleucine and valine) is impaired in obese animals and humans, contributing to the development of insulin resistance and type 2 diabetes. Promoting BCAA catabolism benefits glycaemic control. It remains unclear whether BCAA catabolism plays a role in the therapeutic efficacy of currently used glucose-lowering drugs such as metformin.
Mice were treated with vehicle or metformin (250 mg/kg per day) for more than 4 weeks to investigate the effects of metformin in vivo. In vitro, primary mouse hepatocytes and HepG2 cells were treated with 2 mmol/l metformin. The therapeutic efficacy of metformin in the treatment of type 2 diabetes was assessed in genetically obese (ob/ob) mice and high-fat-diet-induced obese (DIO) mice. Enhancing BCAA catabolism was achieved with a pharmacological agent, 3,6-dichlorobenzo[b]thiophene-2-carboxylic acid (BT2). The ob/ob mice were treated with a low-BCAA diet or intermittent protein restriction (IPR) to reduce BCAA nutritional intake.
Metformin unexpectedly inhibited the catabolism of BCAAs in obese mice, resulting in an elevation of BCAA abundance. AMP-activated protein kinase (AMPK) mediated the impact of metformin on BCAA catabolism in hepatocytes. Importantly, enhancing BCAA catabolism via a pharmacological agent BT2 significantly potentiated the glucose-lowering effect of metformin while decreasing circulating BCAA levels in ob/ob and DIO mice. Similar outcomes were achieved by a nutritional approach of reducing BCAA intake. IPR also effectively reduced the circulating BCAA abundance and enhanced metformin's glucose-lowering effect in ob/ob mice. BT2 and IPR treatments reduced the expression of fructose-1,6-bisphosphatase 1, a rate-limiting enzyme in gluconeogenesis, in the kidney but not liver, indicating the involvement of renal gluconeogenesis.
CONCLUSIONS/INTERPRETATION: Metformin self-limits its therapeutic efficacy in the treatment of type 2 diabetes by triggering the suppression of BCAA catabolism. Enhancing BCAA catabolism pharmacologically or reducing BCAA intake nutritionally potentiates the glucose-lowering effect of metformin. These data highlight the nutritional impact of protein on metformin's therapeutic efficacy and provide new strategies targeting BCAA metabolism to improve metformin's effects on the clinical outcome in diabetes.
目的/假设：越来越多的证据表明，支链氨基酸（BCAA；亮氨酸、异亮氨酸和缬氨酸）的分解代谢在肥胖动物和人类中受损，导致胰岛素抵抗和 2 型糖尿病的发展。促进 BCAA 分解代谢有益于血糖控制。目前尚不清楚 BCAA 分解代谢是否在二甲双胍等常用降糖药物的治疗效果中发挥作用。
用载体或二甲双胍（250mg/kg/天）处理小鼠超过 4 周，以研究二甲双胍在体内的作用。在体外，用 2mmol/l 二甲双胍处理原代小鼠肝细胞和 HepG2 细胞。在遗传性肥胖（ob/ob）小鼠和高脂肪饮食诱导肥胖（DIO）小鼠中评估二甲双胍治疗 2 型糖尿病的疗效。用一种药理学药物 3,6-二氯苯并[b]噻吩-2-羧酸（BT2）增强 BCAA 分解代谢。用低 BCAA 饮食或间歇性蛋白质限制（IPR）处理 ob/ob 小鼠，以减少 BCAA 营养摄入。
二甲双胍出人意料地抑制了肥胖小鼠的 BCAA 分解代谢，导致 BCAA 丰度升高。AMP 激活的蛋白激酶（AMPK）介导了二甲双胍对肝细胞中 BCAA 分解代谢的影响。重要的是，通过药理学药物 BT2 增强 BCAA 分解代谢显著增强了二甲双胍的降糖作用，同时降低了 ob/ob 和 DIO 小鼠循环 BCAA 水平。通过减少 BCAA 摄入的营养方法也取得了类似的结果。IPR 还能有效降低 ob/ob 小鼠循环 BCAA 丰度，并增强二甲双胍的降糖作用。BT2 和 IPR 处理降低了肾脏中果糖-1,6-二磷酸酶 1（糖异生的限速酶）的表达，但在肝脏中没有，表明肾糖异生的参与。
结论/解释：二甲双胍通过触发 BCAA 分解代谢的抑制，自我限制其在 2 型糖尿病治疗中的疗效。用药理学方法增强 BCAA 分解代谢或用营养方法减少 BCAA 摄入可增强二甲双胍的降糖作用。这些数据强调了蛋白质对二甲双胍治疗效果的营养影响，并提供了针对 BCAA 代谢的新策略，以改善二甲双胍对糖尿病临床结局的影响。
