Abstract
Glucagon-like peptide 1 (GLP-1) receptor (GLP-1R) agonists and dipeptidyl peptidase-4 (DPP-4) inhibitors attenuate postprandial lipaemia through mechanisms that remain unclear. As dyslipidaemia is a contributing risk factor for cardiovascular disease in type 2 diabetes, we examined the mechanisms linking pharmacological and physiological regulation of GLP-1 action to control of postprandial lipid metabolism. Postprandial lipid synthesis and secretion were assessed in normal and fructose-fed hamsters and in wild-type mice that were treated with or without sitagliptin. Apolipoprotein B-48 (ApoB-48) synthesis and secretion were also examined in primary enterocyte cultures. The importance of exogenous vs endogenous GLP-1R signalling for regulation of intestinal lipoprotein synthesis and secretion was assessed in mice and hamsters treated with the GLP-1R agonist exendin-4, the GLP-1R antagonist exendin(9-39) and in Glp1r (+/+) vs Glp1r (-/-) mice. Sitagliptin decreased fasting plasma triacylglycerol, predominantly in the VLDL fraction, as well as postprandial triacylglycerol-rich lipoprotein (TRL)-triacylglycerol, TRL-cholesterol and TRL-ApoB-48 in hamsters and mice. GLP-1R activation with exendin-4 alone also decreased plasma and TRL-ApoB-48 in hamsters and mice, and reduced secretion of ApoB-48 in hamster enterocyte cultures. Conversely, blockade of endogenous GLP-1R signalling by the antagonist exendin(9-39) or genetic elimination of GLP-1R signalling in Glp1r (-/-) mice enhanced TRL-ApoB-48 secretion in vivo. Co-administration of exendin(9-39) also abolished the hypolipidaemic effect of sitagliptin. Potentiation of endogenous incretin action via DPP-4 inhibition or pharmacological augmentation of GLP-1R signalling reduces intestinal secretion of triacylglycerol, cholesterol and ApoB-48. Moreover, endogenous GLP-1R signalling is essential for the control of intestinal lipoprotein biosynthesis and secretion.
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