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1. In humans, ambroxol is metabolized to dibromoanthranilic acid (DBAA) and 6,8-dibromo-3-(trans-4-hydroxycyclohexyl)-1,2,3,4-tetrahydroquinazoli ne (DHTQ). The formation of DHTQ proceeds non-enzymatically, whereas that of DBAA requires NADPH. Studies have been performed to identify the CYP isozyme(s) involved in the formation of DBAA using human liver microsomes and microsomes expressing recombinant human CYP isozymes (1A1, 1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1, 3A4 and 4A11). 2. The apparent Vmax and Km for the formation of DBAA were 472+/-192 pmol/ min/mg protein and 248+/-40.6 microM respectively (mean +/- S.D., n = 3). 3. Of the recombinant CYP examined, only CYP3A4 metabolized ambroxol to DBAA. The apparent Vmax and Km were 1.42 pmol/min/pmol P450 and 287 microM respectively. 4. Among the CYP inhibitors examined (furafylline, sulphaphenazole, quinidine, diethyldithiocarbamic acid, ketoconazole), only ketoconazole inhibited the production of DBAA (> 80%) at 1 microM and anti-CYP3A antiserum almost completely inhibited the formation of DBAA. 5. These results suggest that CYP3A4 is predominantly involved in the metabolism of ambroxol to DBAA in humans.

1. Cytochrome P450 (P450) isoforms responsible for the N-deethylation and cyclohexane-hydroxylation of (+/-)-4-diethylamino-1,1-dimethylbut-2-yn-1-yl 2-cyclohexyl-2-hydroxy-2-phenylacetate monohydrochloride monohydrate (NS-21) have been identified in rat and man. 2. Anti-CYP2C11 antibody inhibited the N-deethylation of S- and R-NS-21 in rat hepatic microsomes by 84 and 66% respectively, indicating that CYP2C11 is mainly responsible for these activities in male rats. 3. Of several human recombinant P450 isoforms, CYP3A4 had the activities for the N-deethylation of S- and R-NS-21. In addition, triacetyloleandomycin (TAO), an inhibitor of the CYP3A subfamily, significantly inhibited the N-deethylation of S- and R-NS-21 in human hepatic microsomes by 67 and 69%, respectively. CYP3A4 therefore contributes to it in man. 4. Quinine, an inhibitor of the rat CYP2D subfamily, significantly inhibited the cyclohexane-4-cis-hydroxylation of S-NS-21 by 48% in rat hepatic microsomes. In contrast, this inhibitor had little effect on the cyclohexane-4-trans-hydroxylation of S-NS-21, and the cyclohexane-4-cis- and trans-hydroxylation of R-NS-21. 5. Human recombinant CYP3A4 catalysed the cyclohexane-4-trans-hydroxylation of S-NS-21, and CYP2D6 supported the cyclohexane-4-cis- and trans-hydroxylation of S-NS-21. Quinidine, an inhibitor of human CYP2D6, had little effect on these latter activities in human hepatic microsomes. TAO significantly inhibited the cyclohexane-4-trans-hydroxylation of S-NS-21 by 75%, indicating that CYP3A4 catalyses this reaction.

1. During liver regeneration in the male rat, the metabolic activities of imipramine were differentially affected depending on the specific metabolic pathways. Imipramine N-demethylation was markedly reduced whereas 2-hydroxylation showed only a moderate reduction following partial hepatectomy. 2. A slight decline was observed in the hepatic microsomal content of CYP2D apoprotein, whereas a substantial decrease occurred in CYP2C11 content during liver regeneration. Since imipramine 2-hydroxylation and N-demethylation are mediated by CYP2D and 2C11 respectively, metabolic pathway-specific alterations in the activities of imipramine metabolism are explained by the isozyme selective alteration in the levels of CYPs in regenerating liver. 3. No significant effect of regeneration was observed on expression of CYP2B1 and 2E1 apoproteins. CYP3A2 apoprotein, one of the male-specific CYP isoforms, was significantly suppressed in regenerating liver showing a similar pattern of alteration to the levels of CYP2C11. The alteration pattern of the CYP1A1 level was different to the above with a moderate decline at the first day post-operation and a marked rebound thereafter. 4. In the partially hepatectomized male rate, no significant increase in androstenedione 5-alpha reductase activity, an activity predominant in the female rat, was detected. It is concluded that the pattern of alterations of hepatic oxidative metabolism during liver regeneration was not related to the functional feminization of the liver.

1. The effects of essential oils extracted from the wood and leaves of Chamaecyparis obtusa, Cryptomeria japonica and Thujopsis dolabrata on P450s in the hepatic microsomes of the male rat have been investigated. 2. Essential oils did not affect the content of total P450s measured photometrically. However, some metabolic activities and the levels of some forms of P450, including 2B1, were significantly increased, indicating their induction by essential oils. 3. The effects of components derived from essential oils (alpha-pinene, 1,8-cineole, cadinene and borneol) on P450s in rat hepatic microsomes were investigated. The activities of testosterone 2 beta-, 6 beta-, 16 alpha- and 16 beta-hydroxylation and the levels of P4502B1 and 3A2 were increased by 1,8-cineole and cadinene. The induction of P450s by essential oils is thought to be caused by cadinene, a major component. The P450 isoform induced by cadinene is similar to that induced by phenobarbital. However, the magnitude of induction by cadinene was less than that by phenobarbital at the dose levels studied. 4. P4502B1 and 3A2 were induced by essential oils in the perivenous area in the hepatic lobe.

1. The effects of 4-phenylalkylpyridines (chain length of 0-5, 7, 9 and 11 carbon atoms) on the induction of hepatic microsomal P450 and its multiple forms (1A1/2 (1A1, 1A2), 3A2, 2B1/2, 2C6 and 2E1) in the male and female rat have been investigated.2. P450 induction gradually declined with increasing chain length of the 4-phenylalkylpyridines.3. Immunoblot analysis revealed that three pyridine compounds having methylene units of 0, 1 and 2 only induced P4501A2, whereas those having 4, 5 or 7 methylene units only induced 1A1 in the male rat.4. In the female rat, however, we could not observe such a chain length-dependent differential induction of the P4501A subfamily.5. Induced levels of P4503A2 and 2E1 were dependent on total P450 specific content, but 2C6 was increased in a chain length-dependent manner in both sexes.6. These results provide new information on the differential effects of pyridine-containing compounds on P450 induction in the rat.

1. The changes in the activity of drug-metabolizing enzymes and in the content of P450 isozymes in renal and hepatic microsomes after treatment of the male Sprague-Dawley rat with cis-diamminedichloroplatinum (Cisplatin, CDDP) were examined. 2. NADPH-P450 reductase activity in renal microsomes was significantly increased by treatment with CDDP, but lauric acid omega- and (omega-1)-hydroxylation activities of renal microsomes were not increased. 3. The level of P4502C23 was increased significantly and levels of P4504A2 and 4A8 tended to increase in renal microsomes. 4. In hepatic microsomes, lauric acid omega-hydroxylation activity was increased, but (omega-1)-hydroxylation activity was not. Levels of P4502C11 and 3A2, which are male-specific forms, were decreased, whereas levels of P4502A1, 2C7 and 2E1 were increased in hepatic microsomes. The levels of P4504A2 and 4A3 were increased by CDDP and the level of P4504A1 was not changed. Changes in the protein levels of P450 by CDDP were consistent with those in the mRNA levels reported previously (LeBlanc et al. 1992). 5. Male-specific forms in rat liver such as P4502C11 were decreased by CDDP, but those in the kidney such as P4504A2 was not. Therefore, CDDP has different influences on the regulation of hepatic and renal P450s.

1. The effect of cyclosporin A, an immunosuppressive drug, on the levels of individual cytochromes P450 of rat liver was studied by immunoblotting with specific antibodies. Changes in the metabolic activities of the microsomal enzymes were similarly studied. 2. Total P450 was decreased by treatment with cyclosporin A for 17 days. NADPH-P450 reductase activity was also decreased by treatment with cyclosporin A for 10 days and decreased further after 17 days. 3. Cytochromes 2B2 and 2C6 concentrations were decreased by treatment with cyclosporin A for 17 and 10 days, respectively. Administration of cyclosporin A for 17 days also decreased the levels of the male specific cytochromes 2C11 and 3A2, and consequently decreased testosterone 2 alpha-, 16 alpha-, 2 beta- and 6 beta-hydroxylation activities. Shorter periods (7 and 10 days) of cyclosporin A treatment decreased the level of cytochrome 3A2, which metabolizes cyclosporin A. In contrast, the level of cytochrome 2C13 was unchanged.