Hyperglycemia is a hallmark characteristic of diabetes, resulting in elevated blood glucose levels, due in part to a chronic elevation in endogenous hepatic glucose production (GP). Recent work has highlighted the gut microbiota as a salient contributor to energy and glucose homeostasis. One potential mechanism may be through increased short-chain fatty acid (SCFA) signaling mechanisms. SCFAs are bacterial breakdown products of nondigestible dietary fibers, occurring mainly in the colon, and have been shown to improve glucose homeostasis. Interestingly, recent work has highlighted that ingested nutrients can activate small intestinal nutrient-sensing mechanisms to lower hepatic glucose production via a neuronal gut-brain-liver axis mediated via gut peptide signaling. However, no one has directly tested whether colonic SCFAs can regulate GP via a similar colonic neuronal mechanism. To test this, we directly infused SCFAs (acetate, propionate, butyrate; 10mM or 100mM) into the colon during a pancreatic euglycemic clamp, the gold standard for measuring endogenous glucose production and uptake, in high-fat diet (HFD) fed rats that we previously found to have diminished levels of SCFAs in the large intestine. Administration of either acetate, propionate or butyrate (10mM or 100mM) directly into the colon of HFD-fed rats resulted in an increased glucose infusion rate needed to maintain euglycemia, which was due to a significant decrease in endogenous GP compared to saline infusion. Furthermore, we found that this was mediated via GLP-1 receptor signaling, as co-administration of exendin-9 with either SCFA (10mM) abolished the GP-lowering effect. Additionally, portal levels of GLP-1 were significantly increased at the end of the pancreatic clamp in rats receiving infusion of acetate, butyrate, or propionate compared to saline. Taken together, this work demonstrates that colonic SCFAs can activate a GLP-1 receptor mediated pathway in the colon to lower endogenous GP.
A.I.L. Lane: None. S.N. Weninger: None. F. Duca: None.
National Institutes of Health (R01DK121804)