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Changes in cytochrome P450 enzymes by 1,1-dichloroethylene in rat liver and kidney
N Hanioka1, H Jinno, T Nishimura
1Division of Environmental Chemistry, National Institute of Health Sciences, Kamiyoga, Tokyo, Japan.
Abstract:
We examined the effect of 1,1-dichloroethylene (1,1-DCE) on microsomal cytochrome P450 (P450) enzymes in rat liver and kidney. Rats were treated intraperitoneally with 1,1-DCE daily for 4 days, at doses of 200, 400, and 800 mg/kg. Among the P450-dependent monooxygenase activities in liver microsomes, testosterone 2alpha-hydroxylase (T2AH), which is associated with CYP2C11 activity, was remarkably decreased by 800 mg/kg 1,1-DCE. The level relative to control activity was < 10%. Furthermore, immunoblotting showed that 1,1-DCE (> or = 400 mg/kg) significantly decreased CYP2C11/6 protein levels in liver microsomes. In addition, 7-methoxyresorufin O-demethylase (MROD), 7-ethoxycoumarin O-deethylase (ECOD), benzphetamine N-demethylase (BZND), chlorzoxazone 6-hydroxylase (CZ6H), and testosterone 6beta-hydroxylase (T6BH) activities were significantly decreased by the highest dose of 1,1-DCE (by 40-70%). However, the activities of other P450-dependent monooxygenases, namely 7-ethoxyresorufin O-deethylase (EROD), 7-benzyloxyresorufin O-debenzylase (BROD), aminopyrine N-demethylase (APND), erythromycin N-demethylase (EMND), lauric acid omega-hydroxylase (LAOH), and testosterone 7alpha-hydroxylase (T7AH) were not affected by 1,1-DCE at any dose. Immunoblotting showed CYP1A1/2, CYP2B1/2, CYP2E1, and CYP3A2/1 protein levels were significantly decreased by 60-66% by 1,1-DCE (800 mg/kg), whereas that of CYP4A1/2 was not affected by any dose of 1,1-DCE. By contrast, among the P450-dependent monooxygenase activities in kidney microsomes, only CZ6H activity was increased by 1,1-DCE (1.6-fold at 800 mg/kg). Also, it was observed that 1,1-DCE (800 mg/kg) significantly increased CYP2E1 protein levels by immunoblotting (approximately 1.5-fold). These results suggest that 1,1-DCE changes the constitutive P450 isoforms in the rat liver and kidney, and that these changes closely relate to the toxicity of 1,1-DCE.
Insights
1,1-dichloroethylene (1,1-DCE) significantly alters rat liver and kidney cytochrome P450 (P450) enzymes. These changes in P450 isoforms are linked to 1,1-DCE toxicity.
Area of Science:
- Biochemistry
- Toxicology
- Pharmacology
Background:
- Cytochrome P450 (P450) enzymes are crucial for metabolizing xenobiotics and endogenous compounds.
- Understanding how environmental toxins like 1,1-dichloroethylene (1,1-DCE) affect P450 enzymes is vital for assessing toxicity.
- Previous research indicates potential interactions between halogenated hydrocarbons and P450 systems.
Purpose of the Study:
- To investigate the impact of 1,1-dichloroethylene (1,1-DCE) on hepatic and renal microsomal P450 enzymes in rats.
- To determine which specific P450 isoforms and their associated activities are modulated by 1,1-DCE exposure.
- To correlate observed P450 alterations with the potential toxicity mechanisms of 1,1-DCE.
Main Methods:
- Rats were administered 1,1-DCE intraperitoneally daily for four days at doses of 200, 400, and 800 mg/kg.
- Liver and kidney microsomes were isolated to assess P450-dependent monooxygenase activities.
- Immunoblotting was employed to quantify specific P450 protein levels (e.g., CYP2C11, CYP1A1/2, CYP2E1).
Main Results:
- 1,1-DCE significantly decreased testosterone 2alpha-hydroxylase (T2AH) activity (<10% of control) and CYP2C11/6 protein levels in liver microsomes.
- Activities of MROD, ECOD, BZND, CZ6H, and T6BH were reduced by 40-70% at the highest 1,1-DCE dose, alongside decreased CYP1A1/2, CYP2B1/2, CYP2E1, and CYP3A2/1 protein levels.
- In kidney microsomes, 1,1-DCE increased chlorzoxazone 6-hydroxylase (CZ6H) activity (1.6-fold) and CYP2E1 protein levels (1.5-fold).
Conclusions:
- 1,1-DCE exposure significantly alters constitutive P450 isoforms in rat liver and kidney.
- The observed modulation of specific P450 enzymes, particularly CYP2C11 and CYP2E1, is likely involved in the toxic effects of 1,1-DCE.
- These findings highlight the potential for 1,1-DCE to disrupt xenobiotic metabolism and contribute to its overall toxicity profile.