Metabolic effects of sustained activation of the GLP-1 receptor alone and in combination with background GIP receptor antagonism in high fat-fed mice.

AIM: Enzyme-resistant glucagon-like peptide-1 (GLP-1) receptor agonists and GIP receptor antagonists have been proposed to have therapeutic potential for the treatment of type 2 diabetes. Such benefits are based on actions mediated primarily through stimulation of insulin secretion or alleviation of insulin resistance respectively. This study examined the long-term actions of the stable GLP-1 receptor agonist (D-Ala(8))GLP-1 and the GIP receptor antagonist (Pro(3))GIP alone and in combination in high fat-fed mice. METHODS: Mice on high-fat diet for 155 days were injected once daily with (D-Ala(8))GLP-1 or (Pro(3))GIP (25 nmol/kg body weight) for 24 days. In the following 24-day period, half of the (Pro(3))GIP-treated mice were administered an additional dose of (D-Ala(8))GLP-1 (25 nmol/kg body weight), while the remaining mice continued their original treatment regimes. RESULTS: Daily intraperitoneal injections of (D-Ala(8))GLP-1 or (Pro(3))GIP restored glycaemic control to normal levels and significantly (p < 0.05) improved glucose tolerance compared with high-fat controls by day 24. Food intake and body weights were not affected. On day 48, all treatment groups displayed significantly improved glucose tolerance (p < 0.05) and insulin sensitivity (p < 0.001) compared with high-fat controls on day 48. HDL cholesterol levels were significantly increased in mice treated with (D-Ala(8))GLP-1 alone (p < 0.05) or in combination with (Pro(3))GIP (p < 0.01) compared with normal chow-fed controls. CONCLUSIONS: These results illustrate efficacy of (Pro(3))GIP and (D-Ala(8))GLP-1 for treatment of glucose intolerance and insulin resistance caused by high-fat feeding. Combination therapy appeared to have little benefit over either treatment alone.

(Pro(3))GIP[mPEG]: novel, long-acting, mPEGylated antagonist of gastric inhibitory polypeptide for obesity-diabetes (diabesity) therapy.

BACKGROUND AND PURPOSE: Antagonism of the gastric inhibitory polypeptide (GIP) receptor with daily injection of proline-3 gastric inhibitory polypeptide ((Pro(3))GIP) can reverse or prevent many of the metabolic abnormalities associated with diet-induced obesity-diabetes (diabesity). This study has examined the ability of a novel and longer-acting form of (Pro(3))GIP, (Pro(3))GIP mini-polyethylene glycol ((Pro(3))GIP[mPEG]), to counter diet-induced diabesity in mice, using a daily and intermittent dosing regime. EXPERIMENTAL APPROACH: We studied the actions of (Pro(3))GIP[mPEG] at the GIP receptor in vitro and in vivo in both dietary and genetic diabesity. KEY RESULTS: (Pro(3))GIP[mPEG] was completely resistant to degradation by dipeptidyl peptidase IV. (Pro(3))GIP[mPEG] inhibited GIP-induced cAMP and insulin production in vitro. A greater and prolonged antagonism of GIP-induced glucose-lowering action was followed (Pro(3))GIP[mPEG] administration, compared with (Pro(3))GIP. In contrast with (Pro(3))GIP, mice injected once every 3 days for 48 days with (Pro(3))GIP[mPEG] displayed reduced body weight gain and hyperinsulinemia with improved glucose tolerance and insulin secretory responses, compared with high-fat-fed controls. Daily i.p. injection of (Pro(3))GIP, (Pro(3))GIP[mPEG] or (Pro(3))GIP b.i.d. for 21 days also decreased body weight, circulating plasma insulin levels and improved glucose tolerance, compared with high-fat controls. Plasma triglycerides were decreased by (Pro(3))GIP[mPEG] and (Pro(3))GIP b.i.d. treatment groups. The observed changes were accompanied by enhancement of insulin sensitivity in all treatment regimes. (Pro(3))GIP[mPEG] was also effective over 16 days treatment of genetically obese-diabetic ob/ob mice. CONCLUSIONS AND IMPLICATIONS: These data demonstrate the utility of GIP receptor antagonism for the treatment of diabesity and the potential offered by (Pro(3))GIP[mPEG] as a long-acting stable GIP receptor antagonist.

Daily administration of the GIP-R antagonist (Pro3)GIP in streptozotocin-induced diabetes suggests that insulin-dependent mechanisms are critical to anti-obesity-diabetes actions of (Pro3)GIP.

AIM: Glucose-dependent insulinotropic polypeptide-receptor (GIP-R) antagonism using (Pro3)GIP improves glucose tolerance and ameliorates insulin resistance and abnormalities of islet structure and function in a commonly used model of obesity-diabetes, namely ob/ob mice. The effect of GIP-R antagonism in a streptozotocin (STZ)-induced model of insulin deficiency has not been evaluated. The present study has investigated the effects of daily administration of (Pro(3))GIP to STZ-treated mice. METHODS: Swiss TO mice received once-daily injection of (Pro3)GIP (25 nmol/kg body weight) or saline 4 days prior to and 16 days after injection of STZ, and effects on metabolic parameters and islet architecture were assessed. RESULTS: (Pro3)GIP treatment had no significant effect on hyperphagia or body weight loss. However, hyperglycaemia and glycated haemoglobin were worsened, glucose tolerance further decreased and insulin sensitivity was impaired by (Pro3)GIP. These effects were observed on an STZ-induced background characterized by severe reductions of circulating insulin, beta-cell mass and pancreatic insulin stores. CONCLUSIONS: These data indicate that the beneficial actions of the GIP-R antagonist, (Pro3)GIP, in obesity-diabetes appear to be largely mediated through insulin-dependent mechanisms that merit further investigation.

Chemical gastric inhibitory polypeptide receptor antagonism protects against obesity, insulin resistance, glucose intolerance and associated disturbances in mice fed high-fat and cafeteria diets.

AIMS/HYPOTHESIS: Gastric inhibitory polypeptide (GIP) receptor antagonism with (Pro(3))GIP improves glucose tolerance and ameliorates insulin resistance and abnormalities of islet structure/function in ob/ob mice. This study examined the ability of (Pro(3))GIP to counter the development of obesity, insulin resistance and diabetes in mice fed high-fat and cafeteria diets. MATERIALS AND METHODS: Young Swiss TO mice on standard chow or high-fat, cafeteria or high-carbohydrate diets received daily injections of either saline or (Pro(3))GIP (25 nmol kg(-1)day(-1)) over 16 weeks. Food intake, body weight, and circulating glucose and insulin were measured frequently. At 16 weeks, glucose tolerance, insulin sensitivity, HbA(1c), circulating hormones and plasma lipids were assessed. Adipose tissue, liver and muscle were excised and weighed, and their histology and triacylglycerol content were further examined. RESULTS: (Pro(3))GIP significantly reduced body weight, enhanced locomotor activity, and improved HbA(1c), glucose tolerance, beta cell responsiveness and insulin sensitivity in mice fed high-fat and cafeteria diets (p < 0.05 to p < 0.01). Similarly, (Pro(3))GIP significantly reduced plasma corticosterone and triacylglycerols (p < 0.05 to p < 0.001), while glucagon, resistin and adiponectin were unchanged. (Pro(3))GIP decreased adipose tissue mass (p < 0.01) and the triacylglycerol content of liver, muscle and adipose tissue (p < 0.01 to p < 0.001). Adipocyte size and liver morphology were partially normalised. (Pro(3))GIP did not significantly affect any of these parameters in mice fed a high-carbohydrate diet. CONCLUSIONS/INTERPRETATION: (Pro(3))GIP protects against obesity, insulin resistance, glucose intolerance and associated disturbances in mice fed high-fat and cafeteria diets. This highlights chemical GIP receptor antagonism as a new possibility for the treatment of obesity and associated metabolic disturbances.

Early administration of the glucose-dependent insulinotropic polypeptide receptor antagonist (Pro3)GIP prevents the development of diabetes and related metabolic abnormalities associated with genetically inherited obesity in ob/ob mice.

AIMS/HYPOTHESIS: Ablation of gastric inhibitory polypeptide (GIP) receptor action is reported to protect against obesity and associated metabolic abnormalities. The aim of this study was to use prediabetic ob/ob mice to examine whether 60 days of chemical GIP receptor ablation with (Pro(3))GIP is able to counter the development of genetic obesity-related diabetes. MATERIALS AND METHODS: Young (5-7 weeks) ob/ob mice received once daily i.p. injections of either saline vehicle or (Pro(3))GIP (25 nmol kg(-1) day(-1)) over a 60 day period. Food intake, body weight and circulating glucose and insulin were measured at frequent intervals. At 60 days, glucose tolerance, response to native GIP, postprandial responses, insulin sensitivity, HbA(1c), circulating hormones and plasma lipids were assessed. RESULTS: Body weight and food intake in (Pro(3))GIP-treated mice did not differ from ob/ob controls. GIP receptor blockade significantly improved non-fasting glucose (p < 0.001), HbA(1c) (p < 0.05), glucose tolerance (p < 0.001), meal tolerance (p < 0.001) and insulin sensitivity (p < 0.05). Remarkably, (Pro(3))GIP treatment prevented the age-related development of diabetes, as none of these parameters differed significantly between treated ob/ob mice and normal age-matched lean controls. Circulating levels of glucagon, corticosterone, adiponectin and total cholesterol were unchanged by (Pro(3))GIP, while levels of triacylglycerol, LDL-cholesterol and resistin were decreased (p < 0.05) compared with those in control ob/ob mice. Plasma and pancreatic insulin concentrations were generally lower after (Pro(3))GIP treatment than in control ob/ob mice (p < 0.01), but plasma insulin levels remained substantially raised (p < 0.001) compared with those observed in lean controls. CONCLUSIONS/INTERPRETATION: These data indicate that sustained GIP receptor antagonism provides an effective means of preventing the development of many of the metabolic abnormalities of obesity-driven diabetes.