The effects of sulfasalazine metabolites on hemoglobin-catalyzed lipid peroxidation

Ulcerative colitis (UC) is a recurrent inflammation of the colon and rectum that is characterized by subepithelial hemorrhage, epithelial cell necrosis, infiltration of large numbers of phagocytic leukocytes (neutrophils, eosinophils, macrophages), and mucosal ulcerations. Recent evidence suggests that mucosal lipid peroxidation may play an important role in that pathogenesis of the inflammation-induced intestinal injury. Using hemoglobin (Hb)-catalyzed, H2O2-dependent peroxidation of phospholipid as a model of oxidative injury to membrane lipids, we assessed the ability of the anti-inflammatory drugs sulfasalazine (SAZ), olsalazine, and their metabolites, 5-aminosalicylic acid (5-ASA), N-acetyl-5-ASA, and sulfapyridine (SP) to inhibit this reaction. We found that Hb interacted with H2O2 to yield the radical and nonradical forms of ferryl Hb (Hb(V)) which were capable of initiating the peroxidation of a phospholipid. This interaction did not result in the peroxide-dependent release of iron from the hemoprotein. In addition, we demonstrated that the pharmacologically active moiety of SAZ (or olsalazine), 5-ASA, was significantly better at inhibiting the Hb-catalyzed peroxidative reaction. The concentration of 5-ASA required to inhibit lipid peroxidation by 50% (IC50) was determined to be 50 microM. Neither parent compound (SAZ, olsalazine) nor the pharmacologically inactive metabolite (SP) were effective in attenuating the lipid peroxidation at concentrations up to 100 microM. The N-acetylated derivative of 5-ASA was less effective as an inhibitor in this system possessing an IC50 of 100 microM. The mechanism by which 5-ASA inhibited lipid peroxidation appeared to be due to its ability to donate electrons to and thus scavenge the radical and nonradical forms of HB(IV).(ABSTRACT TRUNCATED AT 250 WORDS)