NORCOCAINE AND N-HYDROXYNORCOCAINE FORMATION IN HUMAN LIVER-MICROSOMES - ROLE OF CYTOCHROME-P-450-3A4

Cocaine was metabolized to norcocaine by microsomes prepared from lymp hoblastoid cells expressing transfected human P-450 3A4. The specific activities of norcocaine formation by microsomes prepared from three h uman liver samples correlated with the amount of P-450 3A immunoreacti ve protein detected by immunoblot. Triacetyloleandomycin, a specific i nhibitor 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 chroma tography and mass spectrometry. Thus, human P-450 3A4 is a cocaine dem ethylase, and P-450 isoforms of the 3A family are responsible for the majority of norcocaine production by human hepatic microsomes.