Modulation of glucagon-like peptide-1 release by berberine: In vivo and in vitro studies

Glucagon-like peptide (GLP)-1 is a potent glucose-dependent insulinotropic gut hormone released from intestinal L cells. Our previous studies showed that berberine increased GLP-1 secretion in streptozotocin-induced diabetic rats. The aim of this study was to investigate whether berberine affected GLP-1 release in normal rats and inNCI-H716 cells. Proglucagon and prohormone convertase 3 genes regulating GLP-1 biosynthesis were analyzed by RT-PCR. Effects of pharmacological inhibitors on berberine-mediated GLP-1 releasewere studied. In vivo, 5-week treatment of berberine enhancedGLP- 1 secretion induced by glucose load and promoted proglucagon mRNA expression as well as L cell proliferation in intestine. In vitro, berberine concentration-dependently stimulated GLP-1 release in NCI-H716 cells. Berberine also promoted both prohormone convertase 3 and proglucagon mRNA expression. Chelerythrine (inhibitor of PKC) concentration-dependently suppressed berberinemediated GLP-1 secretion. Compound C (inhibitor of AMPK) also inhibited berberine-mediated GLP-1 secretion. But only low concentrations of H89 (inhibitor of PKA) showed inhibitory effects on berberine-mediated GLP-1 release. The present results demonstrated that berberine showed its modulation on GLP-1 via promoting GLP-1 secretion and GLP-1 biosynthesis. Some signal pathways including PKC-dependent pathway were involved in this process. Elucidation of mechanisms controlling berberine-mediated GLP-1 secretion may facilitate the understanding of berberine's antidiabetic effects.