Protective effects of glycyrrhizic acid by rectal treatment on a TNBS-induced rat colitis model

Objectives The research compared rectal and oral treatments with glycyrrhizic acid for trinitrobenzene sulfonic acid (TNBS)-induced colitis in rats. Methods Wistar rats were randomly divided into seven groups: one normal and six with colitis, including TNBS, glycyrrhizic acid (2, 10 and 50 mg/kg, rectally treated and 10 mg/kg, orally treated) and sulfasalazine (positive control, 225 mg/kg rectally treated) groups. Colitis was induced by colonic administration of TNBS in 30% ethanol. Key findings There were significant pathological changes in colon in TNBS-treated groups, and rectal glycyrrhizic acid significantly attenuated colitis. Myeloperoxidase, tumour necrosis factor-alpha and interleukin-1 beta of colon tissue or serum in the rectal glycyrrhizic acid groups were markedly reduced when compared with the TNBS group, and lower than in the orally treated glycyrrhizic acid group. It was further noted that, in vitro, glycyrrhizic acid (up to 100 mu g/ml) inhibited interleukin-6 and elevated interleukin-10 production in lipopolysaccharide-activated macrophages, and significantly inhibited proliferation of spleen lymphocytes, suggesting the immunoregulatory function of glycyrrhizic acid. Conclusions Rectally administered glycyrrhizic acid has significant protective effects against TNBS-induced colitis in rats, and the rectal route may be a complementary treatment for inflammatory bowel disease.