To assess the mechanistic effects of the glucagon-like peptide 1 (GLP-1) receptor agonist liraglutide and the dipeptidyl peptidase 4 (DPP-4) inhibitor sitagliptin on (exocrine) pancreatic physiology and morphology.
For this randomized, double-blind, parallel-group trial, 55 patients with type 2 diabetes treated with metformin and/or sulfonylurea agents were included. Participants received liraglutide 1.8 mg (n = 19), sitagliptin 100 mg (n = 19), or matching placebos (n = 17) once daily for 12 weeks. The primary end point was change in exocrine function (intraduodenal pancreatic fluid secretion, lipase activity, fecal elastase-1, and chymotrypsin). Secondary end points included changes in plasma enzyme concentrations and pancreatic morphology (per MRI).
No patient developed pancreatitis. Sitagliptin increased intraduodenal pancreatic fluid secretion by 16.3 mL (95% CI –0.3 to 32.9; P = 0.05), whereas liraglutide did not change exocrine pancreatic function. Neither therapy increased lipase/amylase levels after 12 weeks. However, liraglutide increased lipase levels after 6 weeks (23.5 U/L [95% CI 2.1–44.8]; P = 0.03) and sitagliptin increased amylase levels after 2 and 6 weeks (13.7 U/L [95% CI 3.4–23.9]; P = 0.03). Both drugs increased plasma trypsinogen after 12 weeks (liraglutide: 34.6 µg/mL [95% CI 15.1–54.2], P = 0.001; sitagliptin: 23.9 µg/mL [95% CI 4.9–42.9], P = 0.01). Neither changed pancreatic morphology, although liraglutide tended to increase pancreatic volume (7.7 cm3 [95% CI –1.2 to 16.6]; P = 0.09). Treatment-induced volume expansion was associated with increased amylase levels.
A 12-week treatment with liraglutide or sitagliptin only resulted in a brief and modest increase of plasma pancreatic enzyme concentrations in patients with type 2 diabetes. Apart from a minimal sitagliptin-induced increase in intraduodenal fluid secretion, pancreatic exocrine function was unaffected. The long-term clinical consequences of these discrete changes require further study.