URSODEOXYCHOLATE INHIBITS INDUCTION OF NOS IN HUMAN INTESTINAL EPITHELIAL-CELLS AND IN-VIVO

Ursodeoxycholate (UDCA) has anti-inflammatory and chemoprotective effe cts in animal models of inflammatory bowel disease and colon cancer. B ecause overproduction of nitric oxide (NO) by the inducible isoform of NO synthase (iNOS) is implicated in the pathogenesis of these conditi ons, we investigated the ability of UDCA to inhibit NO production in t ransformed human intestinal epithelial (DLD-1) cells. Nitrite/nitrate production was measured by the Griess reaction, enzymatic activity of iNOS was assessed by conversion of L-arginine to L-citrulline, and pro tein and mRNA were measured by Western and Northern blotting. Dose-dep endent inhibition of interleukin-1 beta- and interferon-gamma-stimulat ed nitrite/nitrate production was observed when cells were preincubate d for 6 h with UDCA (0-800 mu M), and a substantial inhibition (81 +/- 3.2%) was seen at 500 mu M. In cytokine-stimulated cells, UDCA reduce d iNOS mRNA, protein, and enzyme activity without exerting cytotoxicit y. UDCA had a minimal direct inhibitory effect on iNOS enzyme activity . UDCA pretreatment also reduced the expression of iNOS in the colonic epithelium of rats treated with bacterial lipopolysaccharide. Thus UD CA inhibits the induction of epithelial iNOS in vitro and in vivo, and this effect may contribute to the anti-inflammatory and chemoprotecti ve actions of UDCA.