Protective effects of tranilast on experimental colitis in rats

The present study aimed to verify the efficacy of tranilast (TL) for treating inflammatory bowel disease (IBD) with the use of an experimental colitis model. The experimental colitis model was prepared by intrarectal instillation of 2,4,6-trinitrobenzenesulfonic acid (TNBS; 40 mg/kg) dissolved in water containing 25% ethanol. The pharmacological effects of TL after repeated oral administration were evaluated by biomarker and histological analyses, and the pharmacokinetic behavior of TL was also examined after single oral administration. The intrarectal instillation of TNBS solution caused colitis, as evidenced by ca. 2.2-, 5-, and 3-fold increases in myeloperoxidase (MPO) activity, infiltrated cell numbers, and the thickness of the submucosa in the colon, respectively. However, orally-taken TL (10 mg/kg, twice a day for 9 days) led to a 92% reduction in the increase of the MPO level by TNBS enema, and cellular infiltration and thickened submucosa in the experimental colitis model tended to also be suppressed by repeated oral administration of TL. The oral bioavailability of TL in TNBS-treated rats was calculated to be as low as ca. 6.5%, and the poor oral absorption of TL may be a limitation of the treatment for IBD. TL could attenuate TNBS-induced colitis on the basis of the obtained results, and the anti-inflammatory effects would have clinical relevance to the therapeutic outcomes of TL in IBD patients. Although further improvement in the oral bioavailability of TL might be required for better pharmacological outcomes, TL would be an efficacious agent for treating IBD.