Oral delivery of GLP-1 analogues by recombinant Lactococcus lactis restores pancreatic islet structure through intestinal mucosal absorption in diabetic mice

Summary Background The oral delivery of native glucagon like peptide-1 (GLP-1) using recombinant probiotics has shown hypoglycaemic effects and glucose tolerance improvement in diabetic mice. However, the pharmacological mechanisms remain incompletely understood. This study aimed to clarify whether GLP-1 analogues cross the intestinal mucosal barrier and exert systemic hypoglycaemic effects. Methods The recombinant Lactococcus lactis (L. lactis) was constructed for oral delivery of long-duration GLP-1 (LGLP) or exendin-4 (EX4). The hypoglycemic effects in vivo were investigated in db/db mice. The pancreatic islet structure and DNA replication were studied with BrdU-labelled double immunofluorescence. The peptide absorptions in vitro and in vivo were traced with tetramethylrhodamine (TMR) labelled LGLP or EX4. The Ussing Chamber test with rat intestinal mucosa and the absorption test in the ligated loops of intestinal tube were used to verify the absorption of GLP-1 analogues. Findings The supernatant of recombinant L. lactis expressing LGLP or EX4 stimulated proliferation and insulin secretion in rat insulinoma cell INS-1 in vitro. The LGLP-recombinant L. lactis significantly reduced fasting blood glucose, improved oral glucose tolerance, especially increased the number and size of pancreatic islets after oral administration for 4 weeks in diabetic mice. TMR-labelled LGLP or EX4 peptides were internalized by intestinal epithelial cells in vitro. LGLP and EX4 peptides crossed the rat intestinal mucosa and entered the opposite chamber in a receptor-mediated endocytosis manner in the Ussing Chamber test. Following injection into the ligated intestinal loops, a small amount of TMR-labelled LGLP or EX4 was observed in the lamina propria of intestinal villi, pancreas and other tissues through mucosal absorption. Interpretation Oral delivery of GLP-1 analogues by recombinant L. lactis restored the structure of pancreatic islets and exerted systemic hypoglycaemic effects through receptor-mediated intestinal mucosa absorption. Funding The study was supported by the 10.13039/501100001809National Natural Science Foundation of China, the Science and Technology Program Key Projects of Guangdong Province (China), the Science and Technology Planning Project of Guangdong Province (China), and the Biomedical Innovation Foundation of China Pharmaceutical Association & Yiling Pharmaceutical Company.