title: Identification of human cytochrome P450 isoforms involved in the 7-hydroxylation of chlorpromazine by human liver microsomes.
abstract: Studies to identify the cytochrome P450 (CYP) isoform(s) involved in chlorpromazine 7-hydroxylation were performed using human liver microsomes and cDNA-expressed human CYPs. The kinetics of chlorpromazine 7-hydroxylation in human liver microsomes showed a simple Michaelis-Menten behavior. The apparent Km and Vmax values were 3.4+/-1.0 microM and 200.5+/-83.7 pmol/min/mg, respectively. The chlorpromazine 7-hydroxylase activity in human liver microsomes showed good correlations with desipramine 2-hydroxylase activity (r = 0.763, p < 0.05), a marker activity for CYP2D6, and phenacetin O-deethylase activity (r = 0.638, p < 0.05), a marker activity for CYP1A2. Quinidine (an inhibitor of CYP2D6) completely inhibited while alpha-naphthoflavone (an inhibitor of CYP1A2) marginally inhibited the chlorpromazine 7-hydroxylase activity in a human liver microsomal sample showing high CYP2D6 activity. On the other hand, alpha-naphthoflavone inhibited the chlorpromazine 7-hydroxylase activity to 55-65% of control in a human liver microsomal sample showing low CYP2D6 activity. Among eleven cDNA-expressed CYPs studied, CYP2D6 and CYP1A2 exhibited significant activity for the chlorpromazine 7-hydroxylation. The Km values for the chlorpromazine 7-hydroxylation of both cDNA-expressed CYP2D6 and CYP1A2 were in agreement with the Km values of human liver microsomes. These results suggest that chlorpromazine 7-hydroxylation is catalyzed mainly by CYP2D6 and partially by CYP1A2.
authors.affiliation: Laboratory of Biochemical Pharmacology and Toxicology, Faculty of Pharmaceutical Sciences, Chiba University, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Yoshii
authors.forename: K
authors.initials: K
authors.lastname: Kobayashi
authors.forename: M
authors.initials: M
authors.lastname: Tsumuji
authors.forename: M
authors.initials: M
authors.lastname: Tani
authors.forename: N
authors.initials: N
authors.lastname: Shimada
authors.forename: K
authors.initials: K
authors.lastname: Chiba
mesh_terms: D014150:Antipsychotic Agents / Q000378:metabolism*; D002746:Chlorpromazine / Q000378:metabolism*; D019388:Cytochrome P-450 CYP1A2 / Q000032:analysis* / Q000235:genetics / Q000378:metabolism; D065609:Cytochrome P-450 CYP1A2 Inhibitors; D019389:Cytochrome P-450 CYP2D6 / Q000032:analysis* / Q000235:genetics / Q000378:metabolism; D065690:Cytochrome P-450 CYP2D6 Inhibitors; D018076:DNA, Complementary / Q000235:genetics; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D006900:Hydroxylation; D066298:In Vitro Techniques; D007527:Isoenzymes / Q000032:analysis* / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D008862:Microsomes, Liver / Q000201:enzymology* / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism
chemical_list: D014150:Antipsychotic Agents; D065609:Cytochrome P-450 CYP1A2 Inhibitors; D065690:Cytochrome P-450 CYP2D6 Inhibitors; D018076:DNA, Complementary; D004791:Enzyme Inhibitors; D007527:Isoenzymes; D011994:Recombinant Proteins; D019388:Cytochrome P-450 CYP1A2; D019389:Cytochrome P-450 CYP2D6; D002746:Chlorpromazine