Metabolism of styrene by mouse and rat isolated lung cells

Styrene is pneumotoxic in mice. It is metabolized by pulmonary microsomes of both mouse and rat to styrene oxide (SO), presumed to be the toxic metabolite of styrene, and known to be genotoxic. To determine which pulmonary cell types are responsible for styrene metabolism, and which cytochromes P450 are associated with the bioactivation of styrene, we isolated enriched fractions of mouse and rat Clara and type II cells in order to determine the rate of styrene metabolism, with and without chemical inhibitors. Mouse Clara cells readily metabolized styrene to SO. Diethyldithiocarbamate, a CYP2E1 inhibitor, caused less inhibition of SO formation in Clara cells isolated from mice than previously found with pulmonary microsomes. As in microsomes, 5-phenyl-1-pentyne, a CYP2F2 inhibitor, inhibited the formation of both enantiomers. alpha-Naphthoflavone, a CYP1A inhibitor, did not inhibit SO formation in Clara cells. alpha-Methylbenzylaminobenzotriazole, a CYP2B inhibitor, exhibited minimal inhibition of SO production at 10 microM and less at 1 microM. The microsomal and isolated cell studies indicate that CYP2E1 and CYP2F2 are the primary cytochromes P450 involved in pulmonary styrene metabolism. Styrene metabolizing activity was much greater in Clara cells than in type II pneumocytes, which demonstrated essentially no activity. Styrene-metabolizing activity was several-fold higher in the mouse than in rat Clara cells. The more pneumotoxic and genotoxic form, R-SO, was preferentially formed in mice, and S-SO was preferentially formed in rats. These findings indicate the importance of Clara cells in styrene metabolism and suggest that differences in metabolism may be responsible for the greater susceptibility of the mouse to styrene-induced toxicity.