Activated leukocytes oxidatively damage DNA, RNA, and the nucleotide pool through halide-dependent formation of hydroxyl radical

A variety of chronic inflammatory conditions are associated with an increas ed risk for the development of cancer, Because of the numerous links betwee n DNA oxidative damage and carcinogenesis, a potential role for leukocyte-g enerated oxidants in these processes has been suggested. In the present stu dy, we demonstrate a novel free transition metal ion-independent mechanism for hydroxyl radical ((OH)-O-.)mediated damage of cellular DNA, RNA, and cy tosolic nucleotides by activated neutrophils and eosinophils. The mechanism involves reaction of peroxidase-generated hypohalous acid (HOCl or HOBr) w ith intracellular superoxide (O-2(.-)) forming (OH)-O-., a reactive oxidant species implicated in carcinogenesis. Incubation of DNA with either isolat ed myeloperoxidase (MPO) or eosinophil peroxidase (EPO), plasma levels of h alides (Cl- and Br-), and a cell-free O-2(.-) -generating system resulted i n DNA oxidative damage. Formation of 8-hydroxyguanine (8-OHG), a mutagenic base which is a marker for (OH)-O-.-mediated DNA damage, required peroxidas e and halides and occurred in the presence of transition metal chelators (D TPA +/- desferrioxamine), and was inhibited by catalase, superoxide dismuta se (SOD), and scavengers of hypohalous acids. Similarly, exposure of DNA to either neutrophils or eosinophils activated in media containing metal ion chelators resulted in 8-OHG formation through a pathway that was blocked by peroxidase inhibitors, hypohalous acid scavengers, and catalytically activ e (but not heat-inactivated) catalase and SOD. Formation of 8-OHG in target cells (HA1 fibroblasts) occurred in all guanyl nucleotide-containing pools examined following exposure to both a low continuous flux of HOCl (at subl ethal doses, as assessed by [C-14]adenine release and clonogenic survival), and hyperoxia (to enhance intracellular O-2(.-) levels). Mitochondrial DNA , poly A RNA, and the cytosolic nucleotide pool were the primary targets fo r oxidation. Moreover, modest but statistically significant increases in th e 8-OKG content of nuclear DNA were also noted. These results suggest that the peroxidase-H2O2-halide system of leukocytes is a potential mechanism co ntributing to the well-established link between chronic inflammation, DNA d amage, and cancer development.