Exenatide regulates pancreatic islet integrity and insulin sensitivity in the nonhuman primate baboon Papio hamadryas.

The glucagon-like peptide-1 receptor agonist exenatide improves glycemic control by several and not completely understood mechanisms. Herein, we examined the effects of chronic intravenous exenatide infusion on insulin sensitivity, β cell and α cell function and relative volumes, and islet cell apoptosis and replication in nondiabetic nonhuman primates (baboons). At baseline, baboons received a 2-step hyperglycemic clamp followed by an l-arginine bolus (HC/A). After HC/A, baboons underwent a partial pancreatectomy (tail removal) and received a continuous exenatide (n = 12) or saline (n = 12) infusion for 13 weeks. At the end of treatment, HC/A was repeated, and the remnant pancreas (head-body) was harvested. Insulin sensitivity increased dramatically after exenatide treatment and was accompanied by a decrease in insulin and C-peptide secretion, while the insulin secretion/insulin resistance (disposition) index increased by about 2-fold. β, α, and δ cell relative volumes in exenatide-treated baboons were significantly increased compared with saline-treated controls, primarily as the result of increased islet cell replication. Features of cellular stress and secretory dysfunction were present in islets of saline-treated baboons and absent in islets of exenatide-treated baboons. In conclusion, chronic administration of exenatide exerts proliferative and cytoprotective effects on β, α, and δ cells and produces a robust increase in insulin sensitivity in nonhuman primates

Physiological and molecular determinants of insulin action in the baboon

OBJECTIVE-To quantitate insulin sensitivity in lean and obese nondiabetic baboons and examine the underlying cellular/ molecular mechanisms responsible for impaired insulin action to characterize a baboon model of insulin resistance. RESEARCH DESIGN AND METHODS-Twenty baboons received a hyperinsulinemic-euglycemic clamp with skeletal muscle and visceral adipose tissue biopsies at baseline and at 30 and 120 min after insulin. Genes and protein expression of key molecules involved in the insulin signaling cascade (insulin receptor, insulin receptor substrate-1, p85, phosphatidylinositol 3-kinase, Akt, and AS160) were sequenced, and insulin-mediated changes were analyzed. RESULTS-Overall, baboons show a wide range of insulin sensitivity (6.2 \ub1 4.8 mg \ub7 kg -1 \ub7 min -1), and there is a strong inverse correlation between indexes of adiposity and insulin sensitivity (r =-0.946, P < 0.001 for % body fat; r =-0.72, P < 0.001 for waist circumference). The genes and protein sequences analyzed were found to have 3c 98% identity to those of man. Insulin-mediated changes in key signaling molecules were impaired both in muscle and adipose tissue in obese insulin-resistant compared with lean insulin-sensitive baboons. CONCLUSIONS-The obese baboon is a pertinent nonhuman primate model to examine the underlying cellular/molecular mechanisms responsible for insulin resistance and eventual development of type 2 diabetes