DNA Strand Break Formation Following Exposure of Bovine Pulmonary Artery and Aortic Endothelial Cells to Reactive Oxygen Products

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Abstract
Experiments were performed to investigate the hypothesis that exposure of vascular endothelial cells to low levels of reduced oxygen products results in DNA strand breakage as an early event and to determine if endothelial cells derived from bovine pulmonary artery demonstrate a susceptibility to oxidant injury that is different from that of cells derived from bovine aorta. Endothelial cells grown in culture were exposed to H2O2 (either added directly or generated from glucose oxidase) or superoxide radical (generated from xanthine oxidase), and DNA strand breakage was determined using fluorescent analysis of DNA unwinding. Cell injury was also assessed by measuring the release of lactate dehydrogenase (LDH) or the release of 51Cr from prelabeled cells. Whereas LDH or 51Cr release detected injury resulting from exposure of endothelial cells to greater than or equal to 100 microM H2O2 and was apparent only 2 or more h after exposure, DNA strand breakage was detectable after 15 min of exposure of endothelial cells to 50 microM H2O2. Approximately equivalent DNA strand breakage resulted from exposure to 50 microM H2O2, to 25 mU glucose oxidase, or to 10 mU xanthine oxidase; this injury is similar to that seen following exposure to 10 gray X-radiation. DNA strand breakage following exposure of cells to xanthine oxidase was preventable by catalase but not by superoxide dismutase or hydroxyl radical scavengers, suggesting that H2O2 is the active extracellular oxidant mediating DNA strand breaks. No differences were seen in the susceptibility of pulmonary artery or aortic endothelial cells to oxidant injury.