Abstract
Glucagon, an essential regulator of glucose and lipid metabolism, also promotes weight loss in obese mice. We have shown that hepatic Farnesoid X Receptor (FXR, a bile acid receptor) and bile acids (BA) play an important role in the anti-obesity effect of glucagon in mice. Specifically, glucagon-receptor (GCGR) agonism is a potent regulator of BA metabolism, increasing total plasma BA levels and preferentially raising cholic and chenodeoxycholic acid levels. These findings led us to hypothesize that BA, signaling via hepatic FXR, contributes to GCGR-stimulated weight loss. Furthermore, we reasoned that BA sequestration may impair GCGR-mediated weight loss by reducing the availability of BA to stimulate FXR-action. Thus, to elucidate the role of BA in GCGR-mediated weight loss, we utilized anion-exchange BA-binding resins (BARS; Cholestyramine and Colesevelam) to prevent intestinal (ileal) re-uptake and reduce plasma total cholesterol, LDL, and BAs via fecal excretion. Diet-induced obese (DIO) C57Bl/6J mice were randomized to groups matched for body-weight and administered daily GCGR agonism (IUB288, 10 nmol/kg, s.c.) or vehicle, in the presence or absence of BARS. Consistent with our prior findings, IUB288-treatment reduced body weight in DIO mice. Counter to our original hypothesis, IUB288+Cholestyramine (3% in high fat diet, HFD [58% kcal%]) enhanced IUB288-stimulated weight loss. Similar body-weight loss effects following combined IUB288 and BARS treatment were replicated both at a lower dose of Cholestyramine (1.5% in HFD), as well as in combination with both low- (2% in HFD) and high- (4% in HFD) dose Colesevelam. IUB288-stimulated weight loss is accompanied by suppression of food intake (FI), while Colesevelam alone did not significantly lower FI at either dose (2 or 4% in HFD). However, 4% Colesevelam with IUB288 completely suppressed FI, while 2% Colesevelam stimulated a reduced, though not complete suppression. GCGR agonism is a potent stimulus of weight loss; however, its impairment of glucose tolerance reduces its value as a monotherapy. Excitingly, Cholestyramine (3% in HFD) rescued IUB288-induced glucose intolerance, restoring glucose excursion to levels observed in control (vehicle-treated) mice. Together these studies suggest BARS may enhance the anti-obesity effect of GCGR agonism, beneficially regulate feeding behaviors, and prevent GCGR-stimulated glucose dysregulation in DIO mice. Furthermore, these studies argue that GCGR agonsim combined with BARS treatment may represent a novel therapeutic approach for obesity and obesity-associated glucose intolerance.
OR28-5 Bile Acid Sequestration Accelerates Glucagon Receptor-Mediated Body Weight Loss in Obese Mice
