Stereoselective metabolism of endosulfan by human liver microsomes and human cytochrome P450 isoforms.
Endosulfan (6,7,8,9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydro-6,9-methano-2,3,4-benzo(e)dioxathiepin-3-oxide) is a broad-spectrum chlorinated cyclodiene insecticide. This study was performed to elucidate the stereoselective metabolism of endosulfan in human liver microsomes and to characterize the cytochrome P450 (P450) enzymes that are involved in the metabolism of endosulfan. Human liver microsomal incubation of endosulfan in the presence of NADPH resulted in the formation of the toxic metabolite, endosulfan sulfate. The intrinsic clearances (CL(int)) of endosulfan sulfate from beta-endosulfan were 3.5-fold higher than those from alpha-endosulfan, suggesting that beta-endosulfan would be cleared more rapidly than alpha-endosulfan. Correlation analysis between the known P450 enzyme activities and the rate of the formation of endosulfan sulfate in the 14 human liver microsomes showed that alpha-endosulfan metabolism is significantly correlated with CYP2B6-mediated bupropion hydroxylation and CYP3A-mediated midazolam hydroxylation, and that beta-endosulfan metabolism is correlated with CYP3A activity. The P450 isoform-selective inhibition study in human liver microsomes and the incubation study of cDNA-expressed enzymes also demonstrated that the stereoselective sulfonation of alpha-endosulfan is mediated by CYP2B6, CYP3A4, and CYP3A5, and that that of beta-endosulfan is transformed by CYP3A4 and CYP3A5. The total CL(int) values of endosulfan sulfate formation catalyzed by CYP3A4 and CYP3A5 were consistently higher for beta-endosulfan than for the alpha-form (CL(int) of 0.67 versus 10.46 microl/min/pmol P450, respectively). CYP2B6 enantioselectively metabolizes alpha-endosulfan, but not beta-endosulfan. These findings suggest that the CYP2B6 and CYP3A enzymes are major enzymes contributing to the stereoselective disposition of endosulfan.
School of Agricultural Biotechnology, Seoul National University, Seoul 151-742, South Korea.
Hwa-Kyung
HK
Lee
Joon-Kwan
JK
Moon
Chul-Hee
CH
Chang
Hoon
H
Choi
Hee-Won
HW
Park
Byeoung-Soo
BS
Park
Hye-Suk
HS
Lee
Eul-Chul
EC
Hwang
Young-Deuk
YD
Lee
Kwang-Hyeon
KH
Liu
Jeong-Han
JH
Kim
D001189:Aryl Hydrocarbon Hydroxylases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D065702:Cytochrome P-450 CYP2B6; D051544:Cytochrome P-450 CYP3A; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004726:Endosulfan / Q000737:chemistry / Q000378:metabolism* / Q000633:toxicity; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D007306:Insecticides / Q000737:chemistry / Q000378:metabolism* / Q000633:toxicity; D007654:Ketoconazole / Q000494:pharmacology; D007700:Kinetics; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology*; D010089:Oxidoreductases, N-Demethylating / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D013237:Stereoisomerism; D013852:Thiotepa / Q000494:pharmacology
D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors; D007306:Insecticides; D011994:Recombinant Proteins; D003577:Cytochrome P-450 Enzyme System; D013852:Thiotepa; D001189:Aryl Hydrocarbon Hydroxylases; C585599:CYP2B6 protein, human; C510164:CYP3A5 protein, human; D065702:Cytochrome P-450 CYP2B6; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; D010089:Oxidoreductases, N-Demethylating; D004726:Endosulfan; D007654:Ketoconazole