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Rabbit liver microsomal system: study of interaction with two model N-nitrosamines and their metabolism
M Sulc1, B Kubícková, V Máslová
1Department of Biochemistry, Faculty of Science, Charles University, Hlavova 2030, 128 43 Prague 2, Czech Republic. mis@natur.cuni.cz
General Physiology and Biophysics
|April 9, 2005
Summary
Ethanol (EtOH) induction, particularly via CYP2E1, enhances rabbit liver microsome metabolism of N-nitrosodimethylamine (NDMA) and N-nitrosomethylaniline (NMA). Phenobarbital (PB) induction alters NDMA metabolism kinetics.
Area of Science:
- Biochemistry
- Pharmacology
- Toxicology
Background:
- Cytochrome P-450 (CYP) isoforms are crucial for metabolizing xenobiotics, including N-nitrosamines.
- Ethanol (EtOH) and phenobarbital (PB) are known inducers of specific CYP isoforms.
- N-nitrosodimethylamine (NDMA) and N-nitrosomethylaniline (NMA) are potentially carcinogenic N-nitrosamines requiring metabolic activation.
Purpose of the Study:
- To investigate the role of EtOH- and PB-induced rabbit liver microsomes in the metabolism of NDMA and NMA.
- To characterize the binding interactions and kinetic parameters of NDMA and NMA metabolism by different CYP isoforms.
Main Methods:
- Incubation of rabbit liver microsomes (control, EtOH-induced, PB-induced) with NDMA or NMA.
- Difference spectroscopy to analyze substrate binding to CYP isoforms.
- Measurement of formaldehyde formation to quantify oxidative bio-activation.
- Kinetic analysis using Michaelis-Menten constants (K(m)).
Main Results:
- NMA bound to CYP isoforms as a heme ligand in control and EtOH microsomes, but showed substrate-type spectra in PB microsomes.
- NDMA did not exhibit binding spectra with the studied microsomal systems.
- EtOH induction decreased K(m) values for both NDMA and NMA, indicating enhanced metabolism.
- PB treatment increased the K(m) value for NDMA, suggesting altered metabolism.
Conclusions:
- EtOH-inducible CYP isoforms, primarily CYP2E1, are key for the binding and N-demethylation of NDMA and NMA in rabbit liver microsomes.
- The findings highlight the differential impact of EtOH and PB induction on N-nitrosamine metabolism by specific CYP isoforms.
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