SUPEROXIDE INHIBITION FOLLOWING DIFFERENT STIMULI OF RESPIRATORY BURST AND METABOLISM OF AMINOSALICYLATES IN NEUTROPHILS

Reactive oxygen species such as superoxide radicals have been proposed to play an important role in the pathogenesis of inflammatory bowel d isease. Some of the antiinflammatory actions of aminosalicylates have been ascribed to their capability to scavenge superoxide radicals dire ctly or to inhibit its production in stimulated neutrophils. However, as a controversy still exists with regard to the precise mechanisms of inhibition and the metabolism within inflammatory cells, we compared scavenger properties of 5-aminosalicylic acid, 4-aminosalicylic acid, N-acetyl aminosalicylic acid, olsalazine, and benzalazine in systems w ith defined superoxide radical generation such as the dimethyl sulfoxi de-NaOH and the potassium superoxide system. We also studied possible inhibition of the superoxide production following different stimuli of the respiratory burst in neutrophils and investigated the uptake and potential metabolism (N-acetylation) of 5-aminosalicylic acid in lipop olysaccharide-primed and resting neutrophils. We found that 5-aminosal icylic acid and 4-aminosalicylic acid had defined scavenger properties in the dimethyl sulfoxide-NaOH or potassium superoxide systems, respe ctively, whereas compounds with a modified aminophenolic structure had no effects. At the cellular level, 5-aminosalicylic acid inhibited ph orbol myristate acetate (100 ng/ml)-activated superoxide generation to 82.3 +/- 9.3%, the formylmethionyl leucyl peptide (10(-5) M) to 61.0 +/- 6.8%, and the NaF; (20 mM)-stimutated production to 32.3 +/- 3.2% (X +/- SD, P < 0.01). The actions of the other drugs were less pronoun ced. Almost identical retention times (R(t) = 11.2 min) of H-3-labeled phorbol myristate acetate in the presence and absence of 5-aminosalic ylic acid revealed no in vitro interactions. 5-Aminosalicylic acid per meates cells in a dose- and time-dependent manner; there was, however, no acetylation of 5-aminosalicylic acid regardless whether the cells had been stimulated or not with lipopolysaccharide. From our results w e suggest that (1) the extra- (scavenger) and intracellular inhibition of superoxide radicals by 5-aminosalicylic acid may be an important m echanism of action, (2) an intact aminophenolic structure may be neces sary for such actions, and (3) the inability of inflammatory neutrophi ls to acetylate and, therefore, inactivate 5-aminosalicylic acid could be an important determinant for its local actions.