Norcocaine and N-hydroxynorcocaine formation in human liver microsomes: role of cytochrome P-450 3A4.
Cocaine was metabolized to norcocaine by microsomes prepared from lymphoblastoid cells expressing transfected human P-450 3A4. The specific activities of norcocaine formation by microsomes prepared from three human liver samples correlated with the amount of P-450 3A immunoreactive protein detected by immunoblot. Triacetyloleandomycin, a specific inhibitor of P-450 3A isoforms, inhibited formation of norcocaine from cocaine, but not formation of N-hydroxynorcocaine from norcocaine. The chemical identity of the norcocaine and N-hydroxynorcocaine produced by human liver microsomes was established by combination of gas chromatography and mass spectrometry. Thus, human P-450 3A4 is a cocaine demethylase, and P-450 isoforms of the 3A family are responsible for the majority of norcocaine production by human hepatic microsomes.
LeDuc
B W
BW
Department of Biochemistry, Tufts University School of Medicine, Boston, MA 02111.
Sinclair
P R
PR
Shuster
L
L
Sinclair
J F
JF
Evans
J E
JE
Greenblatt
D J
DJ
D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid; D003042:Cocaine / Q000031:analogs & derivatives / Q000378:metabolism*; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000502:physiology*; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D015151:Immunoblotting; D066298:In Vitro Techniques; D008862:Microsomes, Liver / Q000378:metabolism*; D006899:Mixed Function Oxygenases / Q000502:physiology*
C008671:norcocaine; C036718:8-hydroxynorcocaine; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; C104464:CYP3A protein, human; D051544:Cytochrome P-450 CYP3A; D003042:Cocaine