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Respective Roles of Human Cytochrome P‐4502E1, 1A2, and 3A4 in the Hepatic Microsomal Ethanol Oxidizing System
Author(s) -
Salmela Katja S.,
Kessova Irina G.,
Tsyrlov Ilya B.,
Lieber Charles S.
Publication year - 1998
Publication title -
alcoholism: clinical and experimental research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.267
H-Index - 153
eISSN - 1530-0277
pISSN - 0145-6008
DOI - 10.1111/j.1530-0277.1998.tb05926.x
Subject(s) - cyp1a2 , cyp2e1 , microsome , cyp3a4 , chemistry , ethanol , cytochrome , biochemistry , cytochrome p450 , isozyme , monooxygenase , metabolism , enzyme
The microsomal ethanol oxidizing system comprises an ethanolinducible cytochrome P‐4502E1, but the involvement of other P‐450s has also been suggested. In our study, human CYP2E1, CYP1A2, and CYP3A4 were heterologously expressed in HepG2 cells, and their ethanol oxidation was assessed using a corresponding selective inhibitor: all three P‐450 isoenzymes metabolized ethanol. Selective inhibitors‐4‐methylpyrazole (CYP2E1), furafylline (CYP1A2), and troleandomycin (CYP3A4)?also decreased microsomal ethanol oxidation in the livers of 18 organ donors. The P‐450‐dependent ethanol oxidizing activities correlated significantly with those of the specific monooxygenases and the immunochemically determined microsomal content of the respective P‐450. The mean CYP2E1‐dependent ethanol oxidation in human liver microsomes [1.41 ± 0.11 nmol min ‐1 (mg protein) ‐1 ] was twice that of CYP1A2 (0.61 ± 0.07) or CYP3A4 (0.73 ± 0.11) (p < 0.05). Furthermore, CYP2E1 had the highest (p < 0.05) specific activity [28 ± 2 nmol min ‐1 (nmol CYP2E1) ‐1 versus 17 ± 3 nmol min ‐1 (nmol CYP1A2) ‐1 , and 12 ± 2 nmol min ‐1 (CYP3A4) ‐1 , respectively]. Thus, in human liver microsomes, CYP2E1 plays the major role. However, CYP1A2 and CYP3A4 contribute significantly to microsomal ethanol oxidation and may, therefore, also be involved in the pathogenesis of alcoholic liver disease.