Metabolism of styrene in the human liver in vitro: interindividual variation and enantioselectivity.
1. The interindividual variation and enantioselectivity of the in vitro styrene oxidation by cytochrome P450 have been investigated in 20 human microsomal liver samples. Liver samples were genotyped for the CYP2E1*6 and CYP2E1*5B alleles. 2. Kinetic analysis indicated the presence of at least two forms of styrene-metabolizing cytochrome P450. The enzyme constants for the high-affinity component were subject to appreciable interindividual variation, i.e. Vmax1 ranged from 0.39 to 3.20 nmol mg protein(-1) min(-1) (0.96+/-0.63) and Km1 ranged from 0.005 to 0.03 mM (0.011+/-0.006). Inhibition studies with chemical inhibitors of CYP2E1, CYP1A2, CYP2C8/9 and CYP3A4 demonstrated that CYP2E1 was the primary enzyme involved in the high-affinity component of styrene oxidation. No relationship between the interindividual variation in Vmax1 and Km1 and the genetic polymorphisms of the CYP2E1 gene was found. 3. Cytochrome P450-mediated oxidation of styrene demonstrated a moderate enantioselectivity, with an enantiomeric excess (ee) of (S)-styrene oxide of 15% (range 4-27%) at low styrene concentration and an ee of (R)-styrene oxide of 7% (range -11 to +22%) at high styrene concentration. This points towards the involvement of at least two cytochrome P450, with different enantioselectivities. 4. The data indicate that cytochrome P450-mediated styrene oxidation is subject to considerable interindividual variation, but only to a moderate product enantioselectivity.
Wenker
M A
MA
Coronel Institute, Academic Medical Center, Amsterdam, The Netherlands. M.Wenker@amc.uva.nl
Kezić
S
S
Monster
A C
AC
De Wolff
F A
FA
D000328:Adult; D001189:Aryl Hydrocarbon Hydroxylases; D019388:Cytochrome P-450 CYP1A2; D065727:Cytochrome P-450 CYP2C8; D019392:Cytochrome P-450 CYP2E1 / Q000235:genetics* / Q000378:metabolism*; D065691:Cytochrome P-450 CYP2E1 Inhibitors; D051544:Cytochrome P-450 CYP3A; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D000077604:Fomepizole; D014644:Genetic Variation; D006801:Humans; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D006899:Mixed Function Oxygenases / Q000378:metabolism; D010084:Oxidation-Reduction; D011110:Polymorphism, Genetic; D011720:Pyrazoles / Q000494:pharmacology; D039181:Steroid 16-alpha-Hydroxylase; D013250:Steroid Hydroxylases / Q000037:antagonists & inhibitors / Q000378:metabolism; D020058:Styrene / Q000378:metabolism*
D065691:Cytochrome P-450 CYP2E1 Inhibitors; D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors; D011720:Pyrazoles; D020058:Styrene; D000077604:Fomepizole; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; D013250:Steroid Hydroxylases; D019392:Cytochrome P-450 CYP2E1; D001189:Aryl Hydrocarbon Hydroxylases; C504573:CYP1A2 protein, human; C450259:CYP2C8 protein, human; C104464:CYP3A protein, human; D019388:Cytochrome P-450 CYP1A2; D065727:Cytochrome P-450 CYP2C8; D051544:Cytochrome P-450 CYP3A; D039181:Steroid 16-alpha-Hydroxylase; C510163:CYP3A4 protein, human