GLP-1 and GIP Reduce Insulin Clearance in Individuals with Pancreatic-Insufficient Cystic Fibrosis (PI-CF)

PI-CF is characterized by impaired insulin secretion with disruption of the enteroinsular axis and alterations in incretin secretion and action. We have reported augmented glucose-dependent insulin secretion to glucose-potentiated arginine (GPA) testing with GLP-1 infusion but not GIP, with these effects independent of glucose tolerance in PI-CF. We aimed to assess the effect of incretin infusion on insulin clearance during GPA testing and explore its relationship to second-phase insulin response in individuals with PI-CF in a retrospective analysis. Thirty-two individuals with PI-CF and abnormal glucose tolerance underwent GPA testing of islet function following intravenous infusion of incretin or placebo in a randomized cross-over study design. Sixteen individuals were randomized to incretin infusion with GLP-1 and sixteen with GIP. Insulin clearance was assessed by the molar ratio of acute C-peptide to insulin response over the 5-minutes following glucose-potentiation of arginine-induced insulin and C-peptide secretion (target glucose ~230 mg/dL). Insulin clearance was related to second-phase insulin secretion by hyperbolic function (y=P1/(P2 + x) with a reduction in insulin clearance for increasing second-phase insulin secretion (R2=0.20; p<0.001). A reduction in insulin clearance was observed with both GLP-1 vs. placebo (mean±SD 2.7±2.1 vs. 15.5±5.7; p<0.001) and GIP vs. placebo (2.4±0.8 vs. 18.0±10.8; p<0.001). GLP-1 and GIP appear to reduce insulin clearance in individuals with PI-CF presumably through effects at the liver. Reduced insulin clearance is most apparent following GIP infusion where there is no augmentation of second-phase insulin secretion, supporting that the effect of GIP occurs independently of an increase in pre-hepatic insulin secretion. Further work should explore underlying mechanisms of incretin-induced reduction in insulin clearance in PI-CF that could support therapeutic approaches to improve glucose homeostasis. Disclosure A.Flatt: None. A.Doliba: None. A.J.Peleckis: None. R.C.Rubenstein: None. A.Kelly: None. M.R.Rickels: Consultant; Sernova, Corp., Vertex Pharmaceuticals Incorporated, Zealand Pharma A/S, Research Support; Dompé. Funding National Institutes of Health (R01DK97830, UL1TR001878, P30DK19525, T32DK007314); Cystic Fibrosis Foundation (to M.R.R.)