Mo1788 Vasoactive Intestinal Polypeptide and Neuronal Nitric Oxide Synthase Act via Parallel Pathways As Mediators of GLP-2 Anti-Inflammatory Activity

Glucagon-like peptide-2 (GLP-2) has potent anti-inflammatory effects in the intestinal mucosa. Vasoactive intestinal polypeptide (VIP) neurons in the enteric neuronal plexus have been shown to be important in these actions using pharmacologic blockers; but little is known about other specific subsets of neurotransmitters, such as nNOS. Aim: To investigate the role of VIP and nNOS signaling, individually and together, in mediating the antiinflammatory effects of GLP-2. Methods: With animal committee use approval, mice with selective knockouts of VIP-/-, nNOS-/-, and combined VIP-/-/ nNOS-/were used, with wild type (WT) controls; all animals were treated with trinitrobenzene sulfonic acid (TNBS) to induce colitis. Animals received (1-33) GLP-2 (50 μg/kg s.c. bid) or saline for 5 days. Mice were sacrificed and colonic tissue was taken for inflammation indices (myeloperoxidase [MPO] and histological damage scores), immunohistochemistry (BrdU:proliferation marker; Caspase-3: apoptosis marker), and mucosal cytokine levels (TNFα, IL1β, IFNγ, IL10). Results: GLP-2 treatment resulted in significant anti-inflammatory effects in VIP-/-and nNOS-/animals, but had no effects in the VIP-//nNOS-/treated animals. The response included improved weight and mucosal inflammation indices with reduced levels of proinflammatory cytokines (TNFα, IL1β, IFNγ), and reduced proliferation and apoptosis rates. In VIP-/nNOS-/animals treated with GLP-2 these cytokines and cell kinetic rates remained unchanged. (See table, n=8 per group, data: Mean±SEM, *p<0.05 by ANOVA) Conclusions: These findings suggest that the anti-inflammatory effects of GLP-2 can be mediated by either VIP or nNOS pathways, however when both pathways are abolished concomitantly, the anti-inflammatory effects of GLP-2 are lost. Further study is required to identify the enteric neuronal circuitry which mediates these potent anti-inflammatory effects