Dissecting mechanisms by which GI surgery delays diabetes onset in UCD-T2DM rats

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DESCRIPTION (provided by applicant): With the increased prevalence of type-2 diabetes mellitus (T2DM), new strategies for diabetes prevention are urgently needed. We have developed and characterized a novel rat model of T2DM, the UCD-T2DM rat, which more accurately models the pathophysiology of T2DM in humans than other available rodent models. Using this rat model we have demonstrated that ileal interposition (IT) and vertical sleeve gastrectomy (VSG) delay the onset of diabetes by 4-6 months (equivalent to 10-15 years in a human lifespan). Similar to human clinical studies, this delay in onset is associated with increases of postprandial GLP-1 secretion and circulating bile acids. Furthermore, VSG-operated UCD-T2DM rats exhibit significant decreases of circulating ghrelin. All 3 of these post-operative changes (GLP-1, bile acids and ghrelin) have been suggested to play a role in the improvement of glucose homeostasis after bariatric surgery, however whether any or all of these changes are causally involved has not been previously demonstrated. Evaluation of the contribution of each one of these mechanisms (GLP-1, bile acids and ghrelin) to the observed improvements of glucose and lipid metabolism after IT and VSG surgery is a necessary step in understanding the mechanisms responsible for the metabolic improvements observed after bariatric surgery. Thus, we are proposing the following specific aims: 1: To investigate the relative contribution of increased GLP-1, increased bile acids and decreased ghrelin to the effect of VSG to improve glucose homeostasis and delay diabetes onset in UCD-T2DM rats. To this end, 3 studies involving addition and ablation of the change will be performed. Study 1a will include: sham, sham + sitagliptin, VSG, VSG + exendin 9-39. Study 1b will include: sham, sham + cholic acid, VSG, VSG + apical bile salt transporter inhibitor. Study 1c will include: sham, sham + ghrelin antagonist, VSG, VSG + ghrelin replacement. In all studies in vivo glucose homeostasis, �-cell mass, endoplasmic reticulum stress and plasma, liver and intestinal content bile acid profiles will be assessed. 2: To investigate the relative contribution of GLP-1 and bile acids in the effect of IT surgery to improve glucose homeostasis and delay diabetes onset in UCD-T2DM rats. To this end, 2 studies will be performed as outlined for Study 1a and Study 1b in SA1. 3: To test the hypothesis that VSG and IT surgery in combination will prevent the onset of diabetes in UCD-T2DM rats. To this end, 6 weight-matched groups will be studied: sham-IT, sham-VSG, sham-IT/VSG, IT, VSG, IT/VSG. The animals will be followed until diabetes onset or up to 2 years of age. In vivo glucose homeostasis will be assessed and tissues taken from a subset of animals at 1.5 months after surgery for assessment of �-cell mass, ER stress and bile acid profiles of plasma, liver and intestinal contents. New therapeutic targets will be pursued by performing microarray analysis of enteroendocrine cells isolated via laser capture dissection from selected gut segments and analyzing gut microbial populations by pyrosequencing.