ALPHA-PARTICLES INITIATE BIOLOGICAL PRODUCTION OF SUPEROXIDE ANIONS AND HYDROGEN-PEROXIDE IN HUMAN-CELLS

The mechanism(s) by which high-linear energy transfer alpha particles, like those emitted by inhaled radon and radon daughters, cause lung c ancer has not been elucidated. Conceivably, DNA damage that is induced by (alpha particles may be mediated by the metabolic generation of re active oxygen species (ROS), in addition to direct alpha particle-DNA interactions and hydroxyl radical-DNA interactions, Using normal human lung fibroblasts, we investigated the hypothesis that densely ionizin g alpha particles may induce the intracellular generation of superoxid e (O-2(._)) and hydrogen peroxide (H2O2). Ethidium bromide and 2',7'-d ichlorofluorescein, fluorescent products of the membrane-permeable dye s hydroethidine and 2',7'-dichlorofluorescin diacetate, respectively, were used to monitor the intracellular production of O-2(._) and H2O2, respectively, by flow cytometry. Compared to sham-irradiated cells, f ibroblasts that were exposed to alpha particles (0.4-19 cGy) had signi ficant increases in intracellular O-2(._) production, along with conco mitant increases in H2O2 production, Further analyses suggest that the plasma membrane-bound NADPH-oxidase is primarily responsible for this increased intracellular generation of ROS and that the ROS response d oes not require direct nuclear or cellular ''hits'' by the alpha parti cles, In this latter regard, we additionally report that unirradiated cells also show the ROS response when they are incubated with serum-co ntaining culture medium that has been exposed to alpha particles or wh en they are incubated with supernatants from alpha-irradiated cells, O ur overall results support the possibility that alpha particles, at le ast in part, may mediate their DNA-damaging effects indirectly via a R OS-related mechanism.