Protective effect of methylene blue on TNBS-induced colitis in rats mediated through the modulation of inflammatory and apoptotic signalling pathways

Ulcerative colitis (UC) is a common type of chronic, idiopathic inflammatory bowel disease (IBD) that affects the mucosal lining of the colon. Long-term UC remission has shed light on the necessity of modified therapeutic strategies. In this study, UC was induced in rats by intrarectal administration of 2,4,6-trinitrobenzene sulfonic acid (TNBS). The anticolitis effect of methylene blue (MB), a well-known dye and antioxidant and a potent mitochondrial enhancer was tested. MB was injected intraperitoneally (i.p.) at a dose of 1 mg/kg, 2 mg/kg or 4 mg/kg, and colosalazine was administered orally (p.o.) at a dose of 500 mg/kg 11 days after the administration of TNBS, which was injected on the 8th day. All treatment group results were compared to the TNBS group results. Macroscopically, limited body weight loss and decrease in the colon weight per unit length ratio were observed in the MB groups. MB improved histological damage and decreased the expression of myeloperoxidase (MPO) and accumulation of CD4(+) lymphocytes observed by immunohistochemistry. Downregulation of Bax/Bcl(2) protein expression was detected using Western blotting, and increased mRNA expression of nuclear factor erythroid 2-related factor 2 (Nrf2) was measured by qPCR. MB produced biochemical alterations, such as significant decrease in interleukin-6 (IL-6), interleukin-17 (IL-17) and intercellular adhesion molecule-1 (ICAM-1) levels measured by enzyme-linked immunosorbent assay (ELISA). Significant decrease in malondialdehyde (MDA) and inducible nitric oxide synthase (iNOS) levels as well as significant increase in superoxide dismutase (SOD) and mitochondrial cytochrome c oxidase levels were observed with MB, and these effects were similar to those produced by colosalazine. Thus, MB altered disease pathogenesis and could be a promising and challenging therapeutic target for UC treatment.