PI-CF patients with 1-hour OGTT glucose ≥155 mg/dL already manifest impaired β-cell secretory capacity with associated early-phase insulin secretion defects. Avoiding hyperglycemia in patients with EGI may be important for preventing excessive insulin demand indicated by disproportionately increased proinsulin secretion.

Purpose Impaired incretin secretion may contribute to the defective insulin secretion and abnormal glucose tolerance (AGT) that associate with worse clinical outcomes in pancreatic insufficient cystic fibrosis (PI-CF). The study objective was to test the hypothesis that dipeptidyl peptidase-4 (DPP-4) inhibitor-induced increases in intact incretin hormone (glucagon-like peptide-1 [GLP-1] and glucose-dependent insulinotropic polypeptide [GIP]) concentrations augment insulin secretion and glucagon suppression and lower post-prandial glycemia in PI-CF with AGT. Methods Twenty-six adults from Children’s Hospital of Philadelphia and University of Pennsylvania CF Center with PI-CF and AGT (defined by oral glucose tolerance test glucose [mg/dL]: early glucose intolerance [1-hour ≥155 & 2-hour <140], impaired glucose tolerance [2-hour ≥140 and <200 mg/dl], or diabetes [2-hour ≥200]) were randomized to a 6-month double-blind trial of DPP-4 inhibitor sitagliptin 100 mg daily or matched-placebo; 24 completed the trial (n=12 sitagliptin; n=12 placebo). Main outcome measures were mixed-meal tolerance test (MMTT) responses for intact GLP-1 and GIP, insulin secretory rates (ISR), glucagon suppression, and glycemia and glucose-potentiated arginine (GPA) test-derived measures of β- and α-cell function. Results Following 6-months of sitagliptin vs. placebo, MMTT intact GLP-1 and GIP responses increased (P <0.001), ISR dynamics improved (P <0.05), and glucagon suppression was modestly enhanced (P <0.05) while GPA test responses for glucagon were lower. No improvements in glucose tolerance or β-cell sensitivity to glucose, including for second-phase insulin response were found. Conclusions In glucose intolerant PI-CF, sitagliptin intervention augmented meal-related incretin responses with improved early insulin secretion and glucagon suppression without affecting post-prandial glycemia.

Impaired insulin and incretin secretion underlie abnormal glucose tolerance (AGT) in pancreatic insufficient cystic fibrosis (PI-CF). Whether the incretin hormones glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) can enhance pancreatic islet function in CF is not known. We studied 32 adults with PI-CF and AGT randomized to receive either GLP-1 (n=16) or GIP (n=16) during glucose-potentiated arginine (GPA) testing of islet function on two occasions with either incretin or placebo infused by randomized, double-blind, cross-over fashion. Another 4 adults with PI-CF and normal glucose tolerance (NGT) and 4 matched non-CF controls underwent similar assessment with GIP. In PI-CF with AGT, GLP-1 substantially augmented second-phase insulin secretion, but without effect on the acute insulin response to GPA or the proinsulin secretory ratio (PISR), while GIP infusion did not enhance second phase or GPA-induced insulin secretion but increased the PISR. GIP also did not enhance second-phase insulin in PI-CF with NGT but did so markedly in non-CF controls. These data indicate that GLP-1, but not GIP, augments glucose-dependent insulin secretion in PI-CF, supporting the likelihood that GLP-1 agonists could have therapeutic benefit in this population. Understanding loss of GIP's insulinotropic action in PI-CF may lead to novel insights into diabetes pathogenesis.

<p>  </p> <p>Impaired insulin and incretin secretion underlie abnormal glucose tolerance (AGT) in pancreatic insufficient cystic fibrosis (PI-CF). Whether the incretin hormones glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) can enhance pancreatic islet function in CF is not known. We studied 32 adults with PI-CF and AGT randomized to receive either GLP-1 (<em>n</em>=16) or GIP (<em>n</em>=16) during glucose-potentiated arginine (GPA) testing of islet function on two occasions with either incretin or placebo infused by randomized, double-blind, cross-over fashion. Another 4 adults with PI-CF and normal glucose tolerance (NGT) and 4 matched non-CF controls underwent similar assessment with GIP. In PI-CF with AGT, GLP-1 substantially augmented second-phase insulin secretion, but without effect on the acute insulin response to GPA or the proinsulin secretory ratio (PISR), while GIP infusion did not enhance second phase or GPA-induced insulin secretion but increased the PISR.  GIP also did not enhance second-phase insulin in PI-CF with NGT but did so markedly in non-CF controls. These data indicate that GLP-1, but not GIP, augments glucose-dependent insulin secretion in PI-CF, supporting the likelihood that GLP-1 agonists could have therapeutic benefit in this population.  Understanding loss of GIP’s insulinotropic action in PI-CF may lead to novel insights into diabetes pathogenesis. </p>

Individuals with pancreatic insufficient cystic fibrosis (PI-CF) and glucose intolerance demonstrate impaired incretin and insulin secretion. The goal of this study was to assess β-cell responsiveness to the incretin hormones glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) during glucose potentiated arginine (GPA) testing in adults with PI-CF and abnormal glucose tolerance. Participants were randomized to receive either GLP-1 (n=15) or GIP (n=15) and then underwent GPA testing during either incretin or placebo infusion in a randomized, cross-over fashion. OGTT was similar between groups (1hr: 214±8 vs. 208±7 mg/dL; 2hr: 141±18 vs. 150±18 mg/dL). During GPL-1 infusion, fasting glucose was lower after 30 min vs. placebo (p&lt;0.001), and during the 230 mg/dL glucose clamp the glucose infusion rate (GIR) was higher (p&lt;0.001). Second phase insulin levels were substantially increased prior to arginine administration under 230 mg/dL clamp conditions vs. placebo (p&lt;0.001), but no difference in the acute insulin response (AIR) to GPA was present. At 230 mg/dL, proinsulin and C-peptide were increased under GLP-1 vs. placebo (both p&lt;0.001), but the proinsulin secretory ratio (PISR) was unchanged. During GIP infusion, fasting glucose was slightly lower after 30 min vs. placebo (p&lt;0.05), but no difference in the GIR required to achieve 230 mg/dL was found. Second phase insulin levels were not different during the 230 mg/dL glucose clamp. The AIR to GPA was lower during GIP vs. placebo (p&lt;0.01). Second phase proinsulin and C-peptide levels were higher with GIP vs. placebo (both p&lt;0.01) with an increased PISR (p&lt;0.05). These results indicate that GLP-1 augments glucose-dependent insulin secretion while GIP may lead to disproportionate proinsulin secretion in glucose intolerant PI-CF. Further studies should determine whether GLP-1 may provide a therapeutic benefit in this population. Disclosure J.N. Eiel: None. S. Nyirjesy: None. A.J. Peleckis: None. D. De Leon: Employee; Spouse/Partner; Merck & Co., Inc.. Research Support; Self; Zealand Pharma A/S. Consultant; Self; XOMA Corporation, ProSciento. Research Support; Self; Biomarin Corporation. D. Hadjiliadis: None. C. Kubrak: None. A. Tami: None. S. Sheikh: None. R.C. Rubenstein: None. A. Kelly: None. M.R. Rickels: Consultant; Self; Hua Medicine, Xeris Pharmaceuticals, Inc..