Supplementary Material for: Systemic co-administration of low dose oxytocin and glucagon like peptide-1 additively decreases food intake and body weight

Introduction: GLP-1 receptor agonists are the number one drug prescribed for the treatment of obesity and type 2 diabetes. These drugs are not, however, without side-effects and in an effort to maximize therapeutic effect while minimizing adverse effects, gut hormone co-agonists received considerable attention as new drug targets in the fight against obesity. Numerous previous reports identified the neuropeptide oxytocin (OXT) as a promising anti-obesity drug. The aim of this study is to evaluate OXT as a possible co-agonist for GLP-1 and examine the effects of its co-administration on food intake (FI) and body weight (BW) in mice. Methods: FI and c-Fos levels were measured in the feeding-centers of the brain in response to an intraperitoneal injection of saline, OXT, GLP-1 or OXT/GLP-1. The action potential frequency and cytosolic Ca2+ ([Ca2+]i) in response to OXT, GLP-1 or OXT/GLP-1were measured in ex-vivo PVN neuronal cultures. Finally, FI and BW changes were compared in diet induced obese mice treated with saline, OXT, GLP-1 or OXT/GLP-1 for 13 days. Results: Single injection of OXT/GLP-1 additively decreased FI, and increased c-Fos expression specifically in the paraventricular (PVN) and supraoptic nucleus (SON). 70% of GLP-1 receptor positive neurons in the PVN also expressed OXT receptors, and OXT/GLP-1 co-administration dramatically increased firing and [Ca2+]i in the PVN OXT neurons. The chronic OXT/GLP-1 co-administration decreased BW without changing FI. Conclusion: Chronic OXT/GLP-1 co-administration decreases BW, possibly via the activation of PVN OXT neurons. OXT might be a promising candidate as an incretin co-agonist in obesity treatment.

引言：胰高血糖素样肽-1（GLP-1）受体激动剂是当前治疗肥胖与2型糖尿病的一线处方药物。然而，此类药物并非毫无不良反应，为实现治疗效果最大化同时尽可能降低副作用，肠道激素共激动剂作为对抗肥胖的新型药物靶点受到广泛关注。既往多项研究已证实神经肽催产素（OXT）是极具潜力的抗肥胖药物。本研究旨在评估催产素作为GLP-1共激动剂的可行性，并考察二者联合给药对小鼠摄食量（FI）与体质量（BW）的影响。

方法：分别向小鼠腹腔注射生理盐水、催产素、GLP-1或催产素/GLP-1联合制剂，随后检测其脑部摄食中枢的摄食量与c-Fos蛋白表达水平。此外，通过离体室旁核（PVN）神经元培养体系，检测催产素、GLP-1或二者联合给药对神经元动作电位频率与胞质钙离子浓度（[Ca²+]i）的影响。最后，将饮食诱导肥胖小鼠连续13天分别给予生理盐水、催产素、GLP-1或联合制剂，对比各组小鼠的摄食量与体质量变化。

结果：单次联合注射催产素与GLP-1可产生相加性效应，降低小鼠摄食量，并特异性上调室旁核（PVN）与视上核（SON）的c-Fos蛋白表达水平。室旁核中70%的GLP-1受体阳性神经元同时表达催产素受体；联合给药可显著提升室旁核催产素神经元的放电频率与胞质钙离子浓度。长期联合给药可降低小鼠体质量，且不改变其摄食量。

结论：长期联合给予催产素与GLP-1可通过激活室旁核催产素神经元降低小鼠体质量。催产素有望成为肥胖治疗中肠促胰岛素共激动剂的潜在候选药物。