High Sensitivity to Cholic Acid-induced Colonic Tumorigenesis Makes Female PIRC Rats (F344/NTac-Apc am1137 ) a Suitable Model for Studying CRC-promoting Agents.

Background/Aim: Rats of the adenomatous polyposis coli (Apc)-mutated female polyposis in rat (PIRC) (F344/NTac-Apc(am1137)) model exhibit a low level of intestinal tumorigenesis and are thus potentially exploitable as a model for identifying substances increasing colorectal cancer (CRC). Materials and Methods: To test this possibility, we treated such rats with the bile acid (BA) cholic acid (CA) (0.3% w/w in the diet), known to promote CRC, and assessed tumorigenesis. Results: Precancerous colonic lesions (mucin-depleted foci) and intestinal tumors were dramatically increased in CA-treated rats compared to controls (p<0.01). Colon mucosa proliferation was higher and apoptosis lower than those in controls. Expression of nuclear receptor 1h4 (Nr1h4) gene [encoding for BA receptor farnesoid X receptor (FXR)], organic solute transporter beta (Ostb) and fatty acid-binding protein 6 (Fabp6), FXR-dependent BA transporters, were dramatically down-regulated in CA-treated rats. Conclusion: CA-increased tumorigenesis in female PIRC rats, with mechanisms involving increased proliferation, reduced apoptosis and marked down-regulation of genes controlling BA homeostasis. Since BAs have been implicated in CRC, we suggest that female PIRC rats can be used to identify CRC-promoting agents.