Alpha particles initiate biological production of superoxide anions and hydrogen peroxide in human cells.
The mechanism(s) by which high-linear energy transfer a particles, like those emitted by inhaled radon and radon daughters, cause lung cancer has not been elucidated. Conceivably, DNA damage that is induced by a particles may be mediated by the metabolic generation of reactive oxygen species (ROS), in addition to direct a particle-DNA interactions and hydroxyl radical-DNA interactions. Using normal human lung fibroblasts, we investigated the hypothesis that densely ionizing alpha particles may induce the intracellular generation of superoxide (O2.-) and hydrogen peroxide (H2O2). Ethidium bromide and 2',7'-dichlorofluorescein, fluorescent products of the membrane-permeable dyes hydroethidine and 2',7'-dichlorofluorescin diacetate, respectively, were used to monitor the intracellular production of O2.- and H2O2, respectively, by flow cytometry. Compared to sham-irradiated cells, fibroblasts that were exposed to alpha particles (0.4-19 cGy) had significant increases in intracellular O2.- production, along with concomitant 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 does not require direct nuclear or cellular "hits" by the a particles. In this latter regard, we additionally report that unirradiated cells also show the ROS response when they are incubated with serum-containing culture medium that has been exposed to a particles or when they are incubated with supernatants from a-irradiated cells. Our overall results support the possibility that a particles, at least in part, may mediate their DNA-damaging effects indirectly via a ROS-related mechanism.
Narayanan
P K
PK
Cell and Molecular Biology Group, Life Sciences Division, Los Alamos National Laboratory, New Mexico 87545, USA.
Goodwin
E H
EH
Lehnert
B E
BE
D000512:Alpha Particles; D002478:Cells, Cultured; D003470:Culture Media; D004307:Dose-Response Relationship, Radiation; D005347:Fibroblasts / Q000528:radiation effects; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism*; D008168:Lung / Q000166:cytology; D010084:Oxidation-Reduction; D017382:Reactive Oxygen Species / Q000378:metabolism*; D013481:Superoxides / Q000378:metabolism*; D013997:Time Factors
D003470:Culture Media; D017382:Reactive Oxygen Species; D013481:Superoxides; D006861:Hydrogen Peroxide