βHB inhibits glucose-induced GLP-1 secretion in GLUTag and human jejunal enteroids

Ingestion of nutrients stimulates incretin secretion from the enteroendocrine cells (EECs) of the epithelial layer of the gut. Glucagon-like peptide-1 (GLP-1) is one of these incretins that stimulates postprandial insulin release and signals satiety to the brain. Understanding the regulation of incretin secretion might open up for new therapeutic options for obesity and type-2 diabetes mellitus. To investigate the inhibitory effect of the ketone body β-hydroxybutyrate (βHB) on glucose-induced GLP-1 secretion from EECs. In vitro cultures of murine GLUTag cells and differentiated human jejunal enteroid monolayers were stimulated with glucose to induce GLP-1 secretion. The effect of βHB on this glucose-induced GLP-1 secretion was studied. ELISA and ECLIA methods were used to quantify GLP-1. GLUTag cells stimulated with glucose and βHB were analyzed using global proteomics focusing on cellular signaling pathways and results were verified by western blot. Results demonstrated βHB had a significant inhibitory effect on glucose-induced GLP-1 secretion at a dose of 100 mM in GLUTag cells. In the differentiated human jejunal enteroid monolayers glucose-induced secretion of GLP-1 was inhibited at a much lower dose of 10 mM βHB. Addition of βHB to GLUTag cells resulted in decreased phosphorylation of AKT and STAT3 and also influenced the expressions of IRS-2, DGKε and FFAR3. In conclusion, βHB displays an inhibitory effect on glucose-induced GLP-1 secretion in vitro in murine GLUTag cells and in differentiated human jejunal enteroid monolayers. This effect may be mediated through multiple downstream mediators of G-protein coupled receptor activation, such as AKT, STAT3 and PI3K signaling.