Introduction: Oxyntomodulin (OXM) is a gut hormone released from intestinal L cell. Synthetic OXM and its analog reduce food intake and body weight in both rodents and human beings by being administered intravenously. However, people find intravenous administration difficult because of its side effects and inconvenience. The aim of this study is to develop a novel oral delivery system for OXM and its analog using genetically engineered Bifidobacterium as the carrier.
Methods: An OXM gene expression vector pBBADs-OXM for the Bifidobacterium genus was constructed. Human OXM sequence was fused with extracellular exo-xylanase (XynF) signal peptide (Xs) from Bifidobacterium longum under the control of the pBAD promoter. B. longum NCC2705 was transformed with the recombinant plasmid pBBADs-OXM by electroporation, and the transformed B. longum was selected using MRS plates containing 60 microg ml(-1) ampicillin. The OXM expression in vitro was identified by western blot and enzyme-linked immunosorbent assay (ELISA) assay after L-arabinose induction. Overweight BALB/c mice were treated with B. longum transformed with OXM after 0.2% L-arabinose induction every day for 4 weeks to investigate the effects of OXM-transformed B. longum on food intake and body weight by oral administration. The B. longum transformed with the green fluorescent protein (GFP) gene was used as negative control; orlistat, a gastrointestinal lipase inhibitor, was used as positive control; Normal saline (NS, 0.9% saline) was used as blank control. The food intakes of each group were measured every day, and body weights were measured once a week. Normal BALB/c (2 months old) mice were treated with OXM-transformed B. longum after induction by intragastric administration every day for 6 days to reveal the mechanism of transformed B. longum, with OXM exerting its biological function by oral administration. Plasma OXM, plasma ghrelin and the OXM of intestinal contents were detected by the ELISA method. Plasma glucose and triglyceride levels were analyzed using the Automatic Biochemistry Analyzer.
Results: Transformed B. longum with OXM was selected and identified without biological and morphological alteration. An approximately 4-5 kDa OXM peptide was detected in both the supernatant and the cell pellet of transformed B. longum after L-arabinose induction in vitro. The food intake, body weight and blood triglyceride level of overweight mice treated with OXM-transformed B. longum were all significantly reduced compared with that of the GFP negative control group and NS control group (P<0.01). Interestingly, the plasma triglyceride level of the GFP group was significantly decreased compared with that of the NS control group (P<0.01). The OXM level in the intestinal contents of the OXM group was significantly increased compared with that of the GFP negative control group and the NS group (P<0.05). The plasma ghrelin level of the OXM group was significantly decreased compared with that of the GFP and NS groups (P<0.01). Unexpectedly, the ghrelin level of the GFP group was significantly increased compared with that of the NS control group (P<0.01).
Conclusion: A novel oral delivery system of Bifidobacterium for human OXM has been successfully established. The expression of recombinant OXM can be detected in the supernatant and cell pellet of transformed B. longum. OXM-transformed B. longum reduces food intake, body weight and plasma lipid level in overweight mice by oral administration.