1,25-hydroxyvitamin D relieves colitis in rats via down-regulation of toll-like receptor 9 expression

AIM: To investigate the therapeutic and immunoregulatory effects of 1,25-dihydroxyvitamin D (1,25(OH)D(3)) on 2,4,6-trinitrobenzenesulfonic acid (TNBS) -induced colitis in rats. METHODS: Experimental colitis induced by enema administration of TNBS plus ethanol was treated with 5-aminosalicylic acid (5-ASA) and/or 1,25(OH)D(3). Disease activity was measured using the disease activation index (DAI), colon macroscopic damage index (CMDI), histological colonic damage score, and myeloperoxidase (MPO) activity. The expression of toll-like receptor 9 (TLR9) in the colon was determined by reverse transcription-polymerase chain reaction and immunohistochemistry. RESULTS: Rats with TNBS-induced colitis had significantly elevated DAI, CMDI, histological colonic damage score, and MPO activity (all P < 0.001) compared to rats without colitis. Treatment with 5-ASA or 1,25(OH)D(3) ameliorated colitis by lowering CMDI (P = 0.049, P = 0.040, respectively), histological colonic damage score (P = 0.010, P = 0.005, respectively), and MPO activity (P = 0.0003, P = 0.0013, respectively) compared with the TNBS group. Combined treatment with 5-ASA and 1,25(OH)D(3) significantly decreased MPO activity (P = 0.003). 1,25(OH)D(3) attenuated colitis without causing hypercalcemia or renal insufficiency. TNBS significantly increased the number of TLR9 positive cells compared to control (P < 0.010), while 5-ASA, 1,25(OH)D3, and combined treatment with 5-ASA and 1,25(OH)D3 significantly decreased it compared to TNBS group (all P < 0.010). In TNBS group a moderate correlation was observed between MPO activity and the number of TLR9-positive cells (r = 0.654, P < 0.001). CONCLUSION: TLR9 expression correlates with the extent of inflammation in TNBS-induced colitis. 1,25(OH)D(3) relieves this inflammation possibly by decreasing TLR9 expression.