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Pulmonary CYP2E1 bioactivates 1,1-dichloroethylene in male and female mice
1Department of Anatomy and Cell Biology, Queen's University, Kingston, Ontario, Canada.
Abstract:
Pulmonary cytotoxicity induced by 1,1-dichloroethylene (DCE) has been linked to the generation of reactive intermediates through a cytochrome P450-dependent pathway. In the present studies, our objectives were to investigate and compare cytochrome P450 isozyme-selective bioactivation of DCE in vitro in the lungs of male and female mice. Our results showed that CYP2E1-dependent p-nitrophenol hydroxylation was significantly higher in microsomes from female (0.45 +/- 0.01 nmol/mg protein/min) than from male (0.38 +/- 0.02 nmol/mg protein/min) mice. Lung microsomes from male mice incubated in the presence of an NADPH-generating system and increasing amounts of DCE (5-20 mM) exhibited corresponding decreases in p-nitrophenol hydroxylase activity (19%-50%); however, greater decreases (26%-70%) were observed in lung microsomes from female mice incubated under the same conditions. In contrast, alterations in CYP2B1-dependent 7-pentoxyresorufin O-dealkylation and CYP1A1-dependent 7-ethoxyresorufin O-dealkylation were not detected in any microsomal preparation incubated with DCE. Reaction with an anti-CYP2E1 antibody abolished the inhibition of p-nitrophenol hydroxylation by DCE. Protein immunoblotting revealed significant decreases in the intensity of the bands of microsomal samples incubated previously with DCE; in contrast, alterations in heme content were not evoked by reaction with DCE. Our results have demonstrated that CYP2E1, and not CYP2B1 or CYP1A1, mediated the bioactivation of DCE. Furthermore, this bioactivation occurred to a greater extent in lung microsomes from female than from male mice, which suggests that females may be at slightly greater risk for DCE-induced pneumotoxicity.
Insights
1,1-dichloroethylene (DCE) lung toxicity is linked to reactive intermediates. This study found that cytochrome P450 2E1 (CYP2E1) mediates DCE bioactivation, with higher activity in female mice, suggesting increased risk.
Area of Science:
- Toxicology
- Biochemistry
- Pharmacology
Background:
- Pulmonary cytotoxicity from 1,1-dichloroethylene (DCE) involves reactive intermediates generated via cytochrome P450 pathways.
- Understanding sex-based differences in this bioactivation is crucial for risk assessment.
Purpose of the Study:
- To investigate and compare the cytochrome P450 isozyme-selective bioactivation of DCE in vitro.
- To determine the specific isozymes involved and assess sex-based differences in lung microsomes of male and female mice.
Main Methods:
- Incubation of lung microsomes from male and female mice with DCE (5-20 mM) and an NADPH-generating system.
- Assay of specific cytochrome P450 activities (CYP2E1, CYP2B1, CYP1A1) and inhibition studies using anti-CYP2E1 antibody.
- Protein immunoblotting to assess changes in enzyme levels and heme content.
Main Results:
- Cytochrome P450 2E1 (CYP2E1)-dependent p-nitrophenol hydroxylation was higher in female than male mice.
- DCE significantly inhibited p-nitrophenol hydroxylase activity, with greater inhibition observed in female mice.
- CYP2B1 and CYP1A1 activities were not affected by DCE; inhibition of CYP2E1 was abolished by anti-CYP2E1 antibody, confirming CYP2E1 mediation.
- Protein immunoblotting showed decreased CYP2E1 levels after DCE incubation, without affecting heme content.
Conclusions:
- Cytochrome P450 2E1 (CYP2E1) is the primary isozyme responsible for 1,1-dichloroethylene (DCE) bioactivation in mouse lungs.
- DCE bioactivation by CYP2E1 occurs to a greater extent in female mice compared to male mice.
- These findings suggest that female mice may face a slightly elevated risk of DCE-induced pneumotoxicity due to higher CYP2E1-mediated bioactivation.