Myeloperoxidase (MPO) released by activated neutrophils can initiate and promote carcinogenesis. MPO produces hypochlorous acid (HOCl) that oxidizes the genomic DNA in inflammatory cells as well as in surrounding epithelial cells. DNA-centered radicals are early intermediates formed during DNA oxidation. Once formed, DNA-centered radicals decay by mechanisms that are not completely understood, producing a number of oxidation products that are studied as markers of DNA oxidation. In this study we employed the 5,5-dimethyl-1-pyrroline N-oxide-based immuno-spin trapping technique to investigate the MPO-triggered formation of DNA-centered radicals in inflammatory and epithelial cells and to test whether resveratrol blocks HOCl-induced DNA-centered radical formation in these cells. We found that HOCl added exogenously or generated intracellularly by MPO that has been taken up by the cell or by MPO newly synthesized produces DNA-centered radicals inside cells. We also found that resveratrol passed across cell membranes and scavenged HOCl before it reacted with the genomic DNA, thus blocking DNA-centered radical formation. Taken together our results indicate that the formation of DNA-centered radicals by intracellular MPO may be a useful point of therapeutic intervention in inflammation-induced carcinogenesis.Activation of neutrophils can initiate chemical mutagenesis and carcinogenesis by producing oxidative damage to the genome in the inflammatory environment (1-3). Myeloperoxidase (MPO, 4 donor hydrogen peroxide, oxidoreductase, EC 1.11.1.7), is a hemeprotein found in the azurophilic granules of neutrophils (4 -6). MPO uses H 2 O 2 to oxidize chloride ions, converting them into the powerful oxidant hypochlorous acid (HOCl/OCl Ϫ , pK a ϭ 7.46) (5). Although other mammalian peroxidases can oxidize a number of halides and pseudohalides to hypohalous and pseudohypohalous acids, MPO is the only mammalian enzyme that produces HOCl under physiological conditions (5). In sites of inflammation, H 2 O 2 used in the MPOcatalyzed oxidation of chloride is produced by dismutation of superoxide radical anion (O 2 . ). It is noteworthy that DNA is negatively charged and MPO is a cationic protein (5), which suggests that they can bind each other by electrostatic interactions. MPO is known to be taken up by cells surrounding an inflammatory site (7). It might be anticipated that this would make them highly vulnerable to DNA damage induced by H 2 O 2 . DNA-chloramines, which are less reactive than HOCl, are produced when HOCl reacts with DNA at its heterocyclic (ring) amino groups of guanosine and thymine groups and with exocyclic amino groups of guanosine, adenosine, and cytidine (8). Once formed, DNA-chloramines appear to undergo both one-and two-electron decay to produce DNA nitrogen-centered radicals, a process that is catalyzed by reduced metals and is promoted by UV irradiation and high temperatures (8 -9). Importantly, nitrogen-and carboncentered radicals can be trapped by 5,5-dimethyl-1-pyrroline N-oxide (DMPO) to form radic...