Interleukin-13 inhibits nitric oxide production in human colonic mucosa

Background/Aims: Nitric oxide synthesis is increased in rectal biopsies fro m patients with ulcerative colitis and colonic epithelial cells are conside red to be a major source of nitric oxide in intestinal inflammation. Methodology: Human colonic biopsies from normal bowel mucosa and colonic ep ithelial cell line HT-29 were cultured in the presence of the inflammatory cytokines IL-1 alpha+TNF-alpha+IFN-alpha added after 1 hour pretreatment wi th vehicle or Interleukin-13. Nitrite levels were determined at 30 hours in culture supernatants by a fluorometric assay. Results: Unstimulated human colonic biopsies and HT-29 cells produced a bas al amount of nitrite. Stimulation with IL-1 alpha+TNF-alpha+IFN-alpha induc ed significant (P<0.001) increase of nitrite generation by both human colon ic biopsies and HT-29 cells. The presence of Interleukin-13 produced signif icant (P<0.001) suppression of the cytokine-induced nitrite generation from both colonic biopsies and HT-29 cells. Conclusions: Nitric oxide generation in human colonic mucosa is susceptible to manipulation by proinflammatory cytokines. Interleukin-13 has an inhibi tory effect on cytokine induced nitrite production in colonic mucosa and co uld play an anti-inflammatory role in intestinal inflammation.