Experimental Study Of 5-Aminosalicylic Acid By Enema On Inflammatory Bowel Disease Rat Model

Aim: To investigate the effects and the mechnisms of national 5-aminosalicylic acid (5-ASA) enema treating the rat model of colitis induced by acetic acids or 2,4,6-trinitrobenzene sulfonic acids (TNBS).Methods: After setting up the inflammatory bowel disease (IBD) model of rats induced by acetic acids or TNBS, the rats were treated by enema containing national 5-ASA in different doses. Then the assay of myeloperoxidase (MPO), malondiadehyde (MDA), superoxide dismutase(SOD), glutathione perosidase (GSHpx), catalase (CAT), nitric oxide (NO), lactic dehydrogenase (LDH) and mucus by ultra violent spectrophotometry; the detection of protaglandin E₂ (PGE₂), thromboxane B2 (1X82) and interleukin-8 (IL-8) by radioimmunoassay; the determinationof IL-1, IL-2, turner necrosis factor (TNF)-α and transforming growth factor (TGF)-βbybiotechlogy; the expression of inducible nitric oxide synthase (iNOS)and Cyclooxygenase-2 (COX-2) by immunohistochemical staining, were carried out to observe the the effects and the mechnisms of 5-ASA in vivo and in vitro.Results: 1. The macroscopic and histologic alterations of the IBD rats induced by acetic acids or TNBS were very similar to that in human. The treatment of 5-ASA by enema showed the dose- and course-dependent manner. With the increasement of dosage of 5-ASA, the value of colonic mucosal damage index ,occult blood test and the level of MPO decreased significantly. Only treatment with 5-ASA of dosage of 100mg·kg^-1by enema for 7 days, it showed the improvement on the histology of acetic acid-inducedcolitis, 5-ASA of 25, 50, 100 mg'kg"1 for 21 days had the improvement on the histology of TNBS-induced colitis model in rat. 2. In the course of setting up IBD rats model, it exhibited the elevation of the production of oxygen free radicals, nitric oxide and arachidonic acid metabolism. After treatment of 5-ASA, the elevation as above was reversed and at the same time ,the expression of COX-2 and iNOS was decreased partly. The level of IL-1, IL-2, IL-8 and TNF- a in colon tissue of TNBS induced colitis model in rats was increased,but the content of TGF- P was decreased, the level of IL-1 , IL-2 and TNF- a in circulation were increased. The activity of peritoneal macrophages and the content of IL-2 produced by spleen lymphocyte were enhanced, whearas 5-ASA could correct this immunity disturbance in some degree, but had little influence on IL-2 from circulation and spleen lymphocyte. 3. The free radicals, caused by the reaction of FeS(>4 and H2O2,could injury the colonic mucosal epithial cells directly. Our study ensured that 5-ASA could prevent this injury with decreasing the contents of LDH, NO, MD A; stimulate the synthesis of mucus and enhance the action of anti-oxidantase. In vitro, 5-ASA could directly prevent inflammatory cells in TNBS-induced colitis from producing NO, IL-1, IL-2, MD A and decreasing the tissue MPO activity.Conclusion: Our study proved that the national 5-ASA enema on rat IBD model has the effective treatment on IBD in rat which depend on the dosage and duration. Mechanism is probably related to its antioxidation, anti-inflammatory, immunodepression and direct cell-protection.