INVOLVEMENT OF OXIDATIVE STRESS IN THE GENOTOXICITY AND CYTOTOXICITY OF NITRO-AROMATIC DERIVATIVES: AN ESR SPIN TRAPPING STUDY COUPLED TO GENOTOXICITY ASSAYS IN HUMAN LYMPHOCYTES.

Nitro-aromatic compounds (NACs), which are atmospheric contaminants formed via environmental nitration processes, were shown more genotoxic than their unnitrated precursors (1). There is abundant knowledge on (i) the occurrence of NACs-induced DNA damage through metabolites formed by ring oxidation, nitroreduction or conjugation reactions, and (ii) oxidative stress implication on apoptosis and inflammation. However, the mechanisms underlying the promotion of genotoxicity in relation with the setting of oxidative stress remain to be elucidated. Here, we aimed to establish whether NACs-induced genotoxicity is parallel to the activation of free radical sources in human lymphocytes exposed to environmentally relevant doses of nitro-phenolic or pyrenic derivatives (1-10 microg/ml) for 24-48 h. Oxidative stress was assessed (i) by electron spin resonance techniques using DEPMPO (2), Me4CyDEPMPO (3) or mitochondrial-targeted spin traps, and (ii) by measuring biochemical indices, i.e., protein carbonyls, lipid peroxides and antioxidant depletion. From superoxide and hydroxyl radical spin adducts spectroscopic detection, two free radical cellular sources were found triggered along to NACs exposure, i.e., NADPH oxidase and mitochondria, this latter being likely predominant. The cytokinesis-blocked micronucleus assay (4) provided the first evidence for a superoxide-related aneugenic mechanism at low NACs doses and a dominant clastogenic mechanism as the doses increased.