Reactive nitrogen oxygen species metabolize N-acetylbenzidine

A close association has been reported for certain types of cancers influenced by aromatic amines and infection/inflammation. Reactive nitric oxygen species (RNOS), components of the inflammatory response, are bactericidal and tumoricidal, and contribute to the deleterious effects attributed to inflammation on normal tissues. This study assessed the possible transformation of the aromatic amine N-acetylbenzidine (ABZ) by RBOS. RNOS were generated by various conditions to react with ABZ, and samples were evaluated by HPLC. Conditions which generate nitrogen dioxide radical (NO₂^- + myeloperoxidase + H₂O₂, ONOO^-, and NO₂^- + HOCI) produced primarily a single new product termed 3′-nitro-ABZ. The myeloperoxidase-catalyzed reaction with 0.3 mM NO₂^- was completely inhibited by 1 mM cyanide, and not effected by 100 mM chloride with or without 1 mM taurine. In contrast, conditions which generate N₂O₃, such as spermine NONOate, did not produce 3′-nitro-ABZ, but rather two compounds termed 4′-OH-AABP and AABP. ¹H NMR and mass spectrometry identified 3′-nitro-ABZ as 3′-nitro-N-acetylbenzidine, 4′-OH-AABP as 4′-OH-4-acetylaminobiphenyl, and AABP as 4-acetylaminobiphenyl. Human polymorphonuclear neutrophils incubated with [³H]-ABZ and stimulated with β-phorbol 12-myristate 13-acetate produced 3′-nitro-ABZ in the presence of NO₂^- (0.1-1 mM). Neutrophil 3′-nitro-ABZ formation was verified by mass spectrometry and was consistent with myeloperoxidase oxidation of NO₂^-. The results demonstrate that ABZ forms unique products in the presence of nitrosating and nitrating RNOS, which could influence the carcinogenic process and serve as biomarkers for these reactive species.