Involvement of the cytochrome P-450IID subfamily in minaprine 4-hydroxylation by human hepatic microsomes.
4-Hydroxylation of minaprine was measured on microsomal fractions prepared from 25 different human liver samples. In vitro formation of 4-hydroxyminaprine exhibited a large interindividual variability. Indeed, minaprine 4-hydroxylase activity ranged between 0.033 and 0.421 nmol/min/mg microsomal protein. Two samples presented a particularly low enzyme activity. Minaprine 4-hydroxylation followed Michaelis-Menten kinetics with KM and Vmax values of 5.26 microM and 0.478 nmol/min/mg microsomal protein, respectively, for one particular representative sample. The effects of various compounds (substrates or inhibitors of cytochrome P-450 isoforms) on 4-hydroxyminaprine formation were investigated. Selective substrates for P-450IA [benzo(a)pyrene, theophylline, and phenacetin], IIC (hexobarbital), IIE (aniline), and IIIA (erythromycin, nifedipine, and troleandomycin) cytochrome subfamilies did not inhibit 4-hydroxyminaprine formation. The nonspecific cytochrome P-450 inhibitor, cimetidine, slightly inhibited minaprine 4-hydroxylation. The classical substrates of the P-450IID cytochrome subfamily (debrisoquine, propranolol, and sparteine) inhibited minaprine 4-hydroxylation, as did the known P-450IID specific inhibitor, quinidine. These compounds inhibited minaprine 4-hydroxylase with Ki values of 16.5 (debrisoquine), 14.4 (propranolol), 61.9 (sparteine), and 0.146 microM (quinidine). 4-Hydroxyminaprine formation rate was shown not to be correlated with the activity of both erythromycin N-demethylase (r = 0.29, non-significant) and aniline hydroxylase (r = -0.15, NS). In contrast, minaprine 4-hydroxylase was well correlated with both debrisoquine 4-hydroxylase activity (r = 0.501, p less than 0.05) and immunoquantified cytochrome P-450IID6 (r = 0.579, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
Marre
F
F
Institut National de la Sante et de la Recherche Medicale U278, Faculte de Pharmacie, Marseille, France.
Fabre
G
G
Lacarelle
B
B
Bourrie
M
M
Catalin
J
J
Berger
Y
Y
Rahmani
R
R
Cano
J P
JP
D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D003647:Debrisoquin / Q000378:metabolism*; D006801:Humans; D006900:Hydroxylation; D066298:In Vitro Techniques; D008862:Microsomes, Liver / Q000378:metabolism*; D006899:Mixed Function Oxygenases / Q000378:metabolism; D011724:Pyridazines / Q000378:metabolism*; D013379:Substrate Specificity
D065607:Cytochrome P-450 Enzyme Inhibitors; D011724:Pyridazines; C006149:minaprine; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; D003647:Debrisoquin