Styrene exposure is highest among workers in the reinforced plastics industry with exposure seen for 5 consecutive days during the work week. Styrene is both hepatotoxic and pneumotoxic in mice, in addition to causing lung tumors. Human epidemiological studies are inconclusive as to the carcinogenicity of styrene so it is important to understand the mechanism responsible for styrene tumors in mice. Previous studies showed significant decreases in CC10 protein for 5 days following a single dose of the active metabolite R-styrene oxide (R-SO), yet little change in the bax/bcl-2 protein ratio was seen until 10 days following styrene or R-SO administration. Styrene or R-SO was given to CD-1 mice for 5 consecutive days. Mice were euthanized 24 h, 10 days or 30 days following the last dose, and CC10, bax and bcl-2 mRNA and protein levels were determined in isolated Clara cells. CC10 mRNA levels were decreased at 24 h for both styrene and R-SO. R-SO decreased CC10 protein levels up to 10 days following the last dose. Increases in the bax/bcl-2 mRNA and protein ratio were seen 24 h following R-SO administration. Styrene did not significantly increase the bax/bcl-2 mRNA ratio until 10 days after treatment, with the bax/bcl-2 protein ratio increased at both 10 days and 30 days. It is likely that oxidative stress is involved in the toxicity caused by styrene and that minimal apoptosis may be involved. Chronically decreased CC10 levels may lead to increases in oxidative stress in Clara cells, the main target for styrene toxicity in the lung, and may be an early indicator for lung carcinogenesis in mice. © 2009 Elsevier Ireland Ltd. All rights reserved.
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