Hydroxyl radical adduct of 5-aminosalicylic acid: A potential marker of ozone-induced oxidative stress

The use of 5-aminosalicylic acid in assessment of reactive oxygen species f ormation was investigated by in vitro Fenton and ozonation reactions, and b y in vivo ozone-exposure experiments. Enzymatic hydroxylation was evaluated by a microsomal assay. Fischer 344 male rats (250 g) injected with 5-amino salicylic acid (100 mg.kg(-1) i.p.; 30 min) were exposed to ozone (0, 1, 2 ppm; nose only, 2 h); bronchoalveolar lavage, lung homogenates, and plasma were recovered. Oxidation products of 5-aminosalicylic acid were as follows : salicylic acid, by deamination; 2,3-dihydroxybenzoic acid and 2,5-dihydro xybenzoic acid, from radical or enzymatic hydroxylation; 5-amino-2-hydroxy- N,N'-bis(3-carboxy-4-hydroxyphenyl)-1,4-benzoquinonediimine, a condensation product of oxidized 5-aminosalicylic acid; and 5-amino-2,3,4,6-tetrahydrox ybenzoic acid, attributed to hydroxyl radical attack without deamination, i dentified by HPLC electrochemical (HPLC-EC) detector system analysis and by GC-MS analysis of trimethylsilyl derivatives. 5-Aminotetrahydroxybenzoic a cid was not formed enzymatically. 5-Aminotetrahydroxybenzoic acid, but not 5-aminosalicylic acid, was significantly elevated in bronchoalveolar lavage (+86%) and lung homogenates (+56%) in response to 2 ppm ozone (p < 0.05); no significant changes were detected in plasma. The data indicate that hydr oxylation of 5-aminosalicylic acid is a potential specific probe for in viv o oxidative stress.