Abstract
BackgroundGlucagon-like peptide-1 (GLP-1) is recognized as an important regulator of glucose homeostasis. Efforts to utilize GLP-1 mimetics in the treatment of diabetes have yielded clinical benefits. A major hurdle for an effective oral therapy has been the difficulty of finding a non-peptidic GLP-1 receptor (GLP-1R) agonist. While its oral bioavailability still poses significant challenges, Boc5, one of the first such compounds, has demonstrated the attainment of GLP-1R agonism in diabetic mice. The present work was to investigate whether subchronic Boc5 treatment can restore glycemic control and induce sustainable weight loss in diet-induced obese (DIO) mice, an animal model of human obesity and insulin resistance.Methodology/Principal FindingsDIO mice were treated three times a week with Boc5 (0.3, 1 and 3 mg) for 12 weeks. Body weight, body mass index (BMI), food intake, fasting glucose, intraperitoneal glucose tolerance and insulin induced glucose clearance were monitored regularly throughout the treatment. Glucose-stimulated insulin secretion, β-cell mass, islet size, body composition, serum metabolic profiles, lipogenesis, lipolysis, adipose hypertrophy and lipid deposition in the liver and muscle were also measured after 12 weeks of dosing. Boc5 dose-dependently reduced body weight, BMI and food intake in DIO mice. These changes were associated with significant decreases in fat mass, adipocyte hypertrophy and peripheral tissue lipid accumulation. Boc5 treatment also restored glycemic control through marked improvement of insulin sensitivity and normalization of β-cell mass. Administration of Boc5 (3 mg) reduced basal but enhanced insulin-mediated glucose incorporation and noradrenaline-stimulated lipolysis in isolated adipocytes from obese mice. Furthermore, circulating leptin, adiponectin, triglyceride, total cholesterol, nonesterified fatty acid and high-density lipoprotein/low-density lipoprotein ratio were normalized to various extents by Boc5 treatment.Conclusions/SignificanceBoc5 may produce metabolic benefits via multiple synergistic mechanisms and may represent an attractive tool for therapeutic intervention of obesity and diabetes, by means of non-peptidic GLP-1R agonism.
Highlights
In the past decades, obesity has become a worldwide epidemic due to excessive energy intake and lack of physical exercises [1,2]
For pair-fed mice constrained to a food intake equivalent to that of the 3 mg Boc5 treatment group, a similar weight and body mass index (BMI) changes were observed, the effect was less pronounced than the Boc5-treated counterparts (P,0.01; Figures 1A and 1B)
Glucagon-like peptide-1 (GLP-1) is recognized as an important endogenous regulator of glucose and lipid homeostasis
Summary
Obesity has become a worldwide epidemic due to excessive energy intake and lack of physical exercises [1,2]. Gastrointestinal hormones secreted in response to nutrient ingestion play essential roles at multiple levels in the regulation of energy homeostasis [11], and have been regarded as potential therapeutic targets for safe and sustainable weight loss [12]. Peptidic GLP-1 receptor (GLP-1R) agonists, exemplified by the first incretin mimetic, Exendin-4 (Exenatide), exert many of the glucose regulatory actions observed with GLP-1 [17], thereby possessing favorable effects in the treatment of T2DM [18]. In addition to the benefits in glycemic control, chronic treatment of GLP-1 analogues was capable of inducing significant weight loss in rodents or patients with T2DM [18,19]. The present work was to investigate whether subchronic Boc treatment can restore glycemic control and induce sustainable weight loss in diet-induced obese (DIO) mice, an animal model of human obesity and insulin resistance
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