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-induced carcinogenesis, but the detection of oxidative DNA lesions in target cells of asbestos-induced mesothelioma has not been examined. In studies here, DNA was isolated from both rat pleural mesothelial (RPM) cells and a human mesothelial cell line (MET5A) after exposure in vitro to crocidolite asbestos at various concentrations. DNA was then examined for formation of 8-hydroxydeoxyguanosine (8-OHdG) at 24, 48 and 72 h using HPLC with electrochemical detection. In addition, steady-state mRNA levels of manganese-containing superoxide dismutase (MnSOD) were assessed as an indication of oxidative stress. Whereas RPM cells showed dose-dependent and significant increases in 8-OHdG formation in response to crocidolite asbestos or iron-chelated crocidolite fibers (but not after exposure to glass beads), MET5A cells showed decreases in 8-OHdG. Both cell types exhibited elevations in message levels of MnSOD. In comparison with human MET5A cells, RPM cells exhibited increased cytotoxicity and apoptosis in response to asbestos, as documented by cell viability assays and flow cytometry analysis using propidium iodide. Results in RPM cells indicate that asbestos causes oxidative damage that may result in potentially mutagenic lesions in DNA and/or apoptosis, despite compensatory increases in expression of an antioxidant enzyme.