Related Experiment Videos
Metabolism of styrene by mouse and rat isolated lung cells
D E Hynes1, D B DeNicola, G P Carlson
1Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University, West Lafayette, Indiana 47907, USA.
Abstract:
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.
Insights
Clara cells in the lungs are key to metabolizing styrene into toxic styrene oxide (SO). Mouse Clara cells are more active than rat cells, potentially explaining why mice are more susceptible to styrene toxicity.
Area of Science:
- Toxicology
- Pulmonary Medicine
- Biochemistry
Background:
- Styrene is a pneumotoxic chemical metabolized in the lungs to styrene oxide (SO), a genotoxic compound.
- Pulmonary cell types and specific cytochrome P450 enzymes responsible for styrene bioactivation remain unclear.
Purpose of the Study:
- To identify pulmonary cell types involved in styrene metabolism.
- To determine the specific cytochrome P450 enzymes responsible for styrene bioactivation in the lungs.
Main Methods:
- Isolated enriched fractions of mouse and rat Clara and type II cells.
- Measured styrene metabolism to styrene oxide (SO) in the presence and absence of chemical inhibitors targeting specific cytochrome P450 enzymes (CYP2E1, CYP2F2, CYP1A, CYP2B).
Main Results:
- Mouse Clara cells exhibited significant styrene metabolism to SO, while type II pneumocytes showed negligible activity.
- CYP2E1 and CYP2F2 were identified as the primary cytochrome P450 enzymes involved in pulmonary styrene metabolism.
- Styrene metabolism was several-fold higher in mouse Clara cells than in rat Clara cells, with preferential formation of the more toxic R-SO enantiomer in mice.
Conclusions:
- Clara cells are the primary site of pulmonary styrene metabolism.
- CYP2E1 and CYP2F2 play crucial roles in styrene bioactivation.
- Differences in Clara cell metabolism and enantiomer formation may underlie the greater susceptibility of mice to styrene-induced toxicity.