Patterns of 8-hydroxydeoxyguanosine formation in DNA and indications of oxidative stress in rat and human pleural mesothelial cells after exposure to crocidolite asbestos

Oxidative damage is a proposed mechanism of asbestos-inducedcarcinogenesis, but the detection of oxidative DNA lesions in target cellsof asbestos-induced mesothelioma has not been examined. In studies here,DNA was isolated from both rat pleural mesothelial (RPM) cells and a humanmesothelial cell line (MET5A) after exposure in vitro to crocidoliteasbestos at various concentrations. DNA was then examined for formation of8-hydroxydeoxyguanosine (8-OHdG) at 24, 48 and 72 h using HPLC withelectrochemical detection. In addition, steady- state mRNA levels ofmanganese-containing superoxide dismutase (MnSOD) were assessed as anindication of oxidative stress. Whereas RPM cells showed dose-dependent andsignificant increases in 8-OHdG formation in response to crocidoliteasbestos or iron-chelated crocidolite fibers (but not after exposure toglass beads), MET5A cells showed decreases in 8-OHdG. Both cell typesexhibited elevations in message levels of MnSOD. In comparison with humanMET5A cells, RPM cells exhibited increased cytotoxicity and apoptosis inresponse to asbestos, as documented by cell viability assays and flowcytometry analysis using propidium iodide. Results in RPM cells indicatethat asbestos causes oxidative damage that may result in potentiallymutagenic lesions in DNA and/or apoptosis, despite compensatory increasesin expression of an antioxidant enzyme.