P-270 Vasoactive Intestinal Peptide Protects Mitochondria in Colon Epithelia Against Proinflammatory Cytokines in Citrobacter Rodentium Infection: Implications in Inflammatory Bowel Disease

Background

Altered cytokine environment acts as an important determinant of mitochondrial dysfunction in affected colon epithelial cells in addition to the direct actions of the pathogen.¹ As mitochondrial dysfunction is a known contributor for cell death, in IBD diseases where excessive apoptosis with insufficient proliferation has been proposed as a mechanism for mucosal ulceration, excessive cell death in the intestinal epithelium mediated by mitochondrial dysfunction has to be regulated as irregularities might cause IBD.^2–5 As noticed in our earlier study, C. rodentium infection induced increased IFNγ and TNFα generation that lead to reduction in the quantity and activity of mitochondrial respiratory complexes I and IV, as well as phosphorylation capacity, mitochondrial transmembrane potential and ATP generation at day 10, 14 and 19 post infection.¹ Considering the anti-inflammatory and anti-apoptotic properties of vasoactive intestinal peptide (VIP) as observed in non-IBD conditions, the current study focussed on directly assessing the therapeutic effect of VIP in ameliorating the IFNγ and TNFα induced mitochondrial dysfunction in colitis affected colon epithelial cells in the middle phase of infection (14 days post-infection) utilizing Citrobacter rodentium induced murine model.

Methods

Every C57BL/6 mice receiving 100 μL of C. rodentium strain ICC169 (5 × 109 CFU) by single oral-gavage were sacrificed on day 14 post-infection. Infected mice were divided into 3 groups for VIP treatment (0.5 nmol/mouse/day by i.p.)—Group I: day 5 to 10, Group II: day 5 to 14, Group III: day 10 to 14. Colon samples collected from individual mice were utilized for the study of mitochondrial functional parameters and histopathological features of colitis.

Results

Therapeutic impact of VIP on mitochondrial dysfunction was better observed in Group I mice compared to other groups. The VIP treatment partially alleviated decreased activities of complex I and IV, restored mitochondrial phosphorylation capacity, mitochondrial transmembrane potential and ATP loss. However, VIP proved less effective in ameliorating histopathological features of colitis or lowering bacterial count or modifying bacterial localization.

Conclusions

Exogenous VIP administered in low concentration to infected mice proved partially beneficial in alleviating mitochondrial dysfunction in the murine colon epithelial cells with less impact in ameliorating the histopathological severity of colitis in the middle phase of infection. The therapeutic efficacy of VIP as observed in our initial study encourages us to carry out further experiments to optimize the dose of VIP treatment as VIP in higher doses may cause downregulation of VIP receptors as noticed in a previous study.⁶