Biomedical subjects

Y Funae

Publications and source records attributed to Y Funae.

At least 91 records · Page 5Linked to original sources

PubMed1996

(+)-cis-3,5-dimethyl-2-(3-pyridyl) thiazolidin-4-one hydrochloride (SM-12502) as a novel substrate for cytochrome P450 2A6 in human liver microsomes.

(+)-cis-3,5-dimethyl-2-(3-pyridyl)thiazolidin-4-one hydrochloride (SM-12502) was oxidized by human liver microsomes to produce the S-oxide as a sole metabolite. Indirect evidence suggested that the S-oxidation was catalyzed by cytochrome P450 (CYP). Eadie-Hofstee plots showed biphasic pattern, suggesting that at least two enzymes were involved in the S-oxidation in human liver microsomes. Kinetic parameters of the S-oxidase with high-affinity showed Km and Vmax values of 20.9 +/- 4.4 microM and 0.111 +/- 0.051 nmol/min/mg microsomal protein, respectively. The S-oxidase activity was inhibited by coumarin and anti-CYP2A antibody. Among the contents of forms of CYP 20 samples of human liver microsomes, the content of CYP2A6 correlated with S-oxidase activity measured with 50 microM SM-12502 (r = .808, P < .0005). A close correlation (r = .908, P < .0001) was observed between activities of SM-12502 S-oxidase and coumarin 7-hydroxylase. Microsomes from genetically engineered human B-lymphoblastoid cells expressing CYP2A6 metabolized SM-12502 to the S-oxide efficiently. The results indicate that CYP2A6 isozyme is a major form of CYP responsible for the S-oxidation of SM-12502 in human liver microsomes. Thus, SM-12502 will be a useful tool in further research to analyze a human genetic polymorphism of CYP2A6.

Animals↗

PubMed1996

Expression and zonal distribution of CYP2D16 in the guinea pig adrenal cortex: relationship to xenobiotic metabolism.

We recently cloned a CYP2D subfamily member (CYP2D16) from a guinea pig adrenal cDNA library and investigated the expression of CYP2D16 in the guinea pig adrenal cortex and its relationship to adrenal xenobiotic metabolism. A modified sodium dodecyl sulfate-polyacrylamide gel electrophoresis technique revealed three major bands in the molecular mass range of cytochromes P450 in guinea pig adrenal microsomes. Two of the bands were immunoreactive with anti-CYP17 (54 kDa) or anti-CYP21 (52 kDa) antibody. The third band (50 kDa) was immunoreactive with antibody raised against CYP2D1 and with anti-CYP1A1/1A2 antibody. Microsequencing of the 50-kDa band yielded an amino-terminal sequence of 38 amino acids identical to that deducted from the CYP2D16 cDNA. In addition, Northern blot analyses indicated the CYP1A1 was not expressed in the adrenal gland, suggesting that only CYP2D16 composed the microsomal 50-kDa band. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot analyses demonstrated greater expression of CYP2D16 in microsomes from the inner zone (zona reticularis) of the adrenal cortex than from the outer zones, coinciding with the major site of adrenal xenobiotic metabolism. Bufuralol-1'-hydroxylase activity, a marker for CYP2D isozymes, was also greater in inner- than in outer-zone microsomal preparations and was highly correlated with CYP2D16concentrations. Northern blot analysis with a full-length CYP2D16 cDNA as the probe gave strong bands with adrenal inner zone RNA preparations and relatively weak bands with outer zone RNA. CYP2D16 mRNA was also detectable in liver and kidney RNA preparations, but at lower levels than in the adrenal inner zone, and it was not detectable in testes, lung, intestines, or heart. Overall, the results demonstrate that CYP2D16 is expressed at highest levels in the inner zone of the guinea pig adrenal cortex and suggest a major role for this isozyme in adrenal xenobiotic metabolism.

Amino Acid Sequence↗

PubMed1996

Suppressed expression of phenobarbital-inducible hepatic cytochrome P-450s in Eisai-hyperbilirubinuria rats (EHBR/Eis).

The differential induction of hepatic cytochrome P-450 (P450) was studied in Eisai-hyperbilirubinuria rats (EHBR/Eis). This rat is a mutant that has as high a concentration of bilirubin in the urine as in the plasma. A single administration of trans-stilbene oxide (TSO, 2 mmol/kg), a phenobarbital (PB)-type P450 inducer, did not increase total P450, the CYP2B1/2 or the CYP2C6 in EHBR/Eis liver. TSO was able to induce delta-aminolevulinic acid synthetase and heme oxygenase, rate-limiting enzymes in heme biosynthesis and degradation, respectively, in both EHBR/Eis and Sprague-Dawley rat (SDR), the strain from which EHBR/Eis is derived. TSO also produced similar effects on glutathione depletion and on the activities of other drug-metabolizing enzymes in both strains. A 23-fold increase in CYP2B1/2 mRNA in the SDR liver was observed 24 hr after TSO treatment. In the EHBR/Eis strain, however, TSO increased CYP2B1/2 mRNA only 2-fold. In addition, repeated injection of TSO failed to induce P450 isozymes, CYP2B1/2, CYP2C6 or CYP3A2 in EHBR/Eis. On the other hand, there was essentially no difference in the induced levels of CYP1A1/2 apoprotein and mRNA between twins of SDR and EHBR/Eis livers treated with 3-methylcholanthrene or 1-benzylimidazole. The increased levels of both CYP2B1/2 apoprotein and mRNA from EHBR/Eis liver treated with TSO and 1-benzylimidazole were much smaller (2.5- and 5-fold increases, respectively) than from the SDR liver (17.5- and 15-fold increases, respectively). Although PB expressed CYP2B1/2 apoprotein and mRNA to a similar extent in both homozygous and heterozygous EHBR/Eis livers, CYP3A2 and CYP2C6 were less responsive to PB in homozygous EHBR/Eis. Repeated treatment with TSO induced these isozymes in heterozygote but not in homozygote. These findings suggest that the suppressed expression of PB-inducible P450 isozyme genes in the EHBR/Eis liver may be a general phenomenon associated with PB-type inducers. Therefore, EHBR/Eis may be experimentally useful for studying the mechanism of P450 induction by PB and PB-type inducers.

Animals↗

PubMed1996

Cytochrome P450s of isolated rat hepatocytes in spheroid and monolayer cultures.

The maintenance of cytochrome P450s (P450s) and NADPH-cytochrome P450 reductase (P450 reductase) in the monolayer and spheroid cultures of hepatocytes from male rats was examined. The content of total P450 in monolayer culture decreased to almost none after 144 hr, whereas the level in spheroid culture remained within 6-13% of initial values during an incubation period of 144-192 hr. P450 2C11, a major P450 in male rat, in monolayer cells rapidly decreased in 144 hr, while the level in spheroid cells after 144 hr and 192 hr maintained 25% and 15%, respectively, of initial level. On the other hand, P450 2A1 and P450 2E1 in both monolayer and spheroid cells rapidly decreased. P450 reductase in both cells showed a gradual decline reaching a level of 43-44% of the initial level at 96 hr, and remained within 16-17% of the initial value during an incubation period of 192 hr. These results indicate that P450 2C11 in spheroid cells maintained more stable than in the monolayer cells, and that P450 reductase in both cultures declined only moderately, compared with P450s.

Animals↗

PubMed1996

Reductive metabolism of halothane by cytochrome P450 isoforms in rats and humans.

Cytochrome P450 (P450)-halothane complex formation, an index of reductive metabolism of halothane, was investigated by using rat hepatic microsomes and purified rat P450s under anaerobic conditions. P450-halothane complex formation was produced by the hepatic microsomes from phenobarbital and dexamethasone treated rats. Anti-P450 3A2 and 2B1/2 antibodies extensively inhibited complex formation in hepatic microsomes from dexamethasone and phenobarbital treated rats, respectively. In reconstituted systems using purified rat P450s, P450 3A2 and 2B1 complexed halothane efficiently. Complex formation was also recognized in human hepatic microsomes under anaerobic conditions.

Anaerobiosis↗

PubMed1996

Role of human cytochrome P4502A6 in C-oxidation of nicotine.

Nicotine is primarily metabolized to cotinine in humans. In this study, human cytochrome P450 (CYP) isoform involved in cotinine formation was identified. The formation of cotinine in 16 human liver microsomes was determined with a 50 microM nicotine concentration and with a cytosol preparation as a source of aldehyde oxidase. Cotinine formation in human liver microsomes significantly correlated with immunochemically determined CYP2A6 levels (r = 0.663, p < 0.05), coumarin 7-hydroxylase activities (r = 0.831, p < 0.01), and cotinine 3'-hydroxylase activities (r = 0.735, p < 0.01) that are responsible for CYP2A6. In inhibition studies, cotinine formation in human liver microsomes was inhibited by coumarin and rabbit anti-rat CYP2A1 antibody specifically. When the capability of microsomes of B-lymphoblastoid cells expressing human CYPs to perform biotransformation of nicotine to cotinine was determined, cDNA-expressed CYP2A6 exhibited the highest cotinine formation. The KMapp values from microsome expressing CYP2A6 cDNA were similar to the value obtained from human liver microsomes. The large interindividual variabilities in cotinine formation and immunochemically determined CYP2A6 levels were observed in human liver microsomes, suggesting genetic polymorphism of CYP2A6. Nicotine is a new in vivo probe for phenotyping of CYP2A6 in humans.

Aryl Hydrocarbon Hydroxylases↗

PubMed1995

Induction of CYP isoenzymes in various organs of rats by 3-methylcholanthrene or beta-naphthoflavone.

Induction of cytochrome P450 (CYP) isoenzymes in various organs of rats treated with 3-methylcholanthrene (3-MC) and beta-naphthoflavone (BNF) was immunohistochemically and biochemically investigated. Fifteen male F344 rats were divided into three equal groups. Group 1 was untreated as a control. On days 3, 4, 13 and 14, group 2 animals received 3-MC (20 mg/kg body wt i.p.) dissolved in corn oil while group 3 animals were given BNF (50 mg/kg body wt i.p.) dissolved in corn oil, at days 1, 2, 3, 4, 11, 12, 13 and 14. On days 4 and 14, two or three animals in each group were sacrificed, 15 h after administration of the last test compound. Induction of CYP 1A1, 2C11, 2D1, 2E1, 3A2 and 4A1 in various organs was immunohistochemically examined and the levels of CYP 1A1 protein were measured by Western blotting. 3-MC and BNF induced CYP isoenzymes not only in the liver, but also in the small intestine, large intestine, prostate and seminal vesicles. The results indicate that xenobiotic metabolism can occur in various organs.

Animals↗

PubMed1995

Mutagenic activation of 3-methoxy-4-aminoazobenzene by mouse renal cytochrome P450 CYP4B1: cloning and characterization of mouse CYP4B1.

A new P450 responsible for mutagenic activation of 3-methoxy-4-aminoazobenzene (3-MeO-AAB) which is a potent procarcinogen was purified from renal microsomes of male mice using an index of umu gene expression. The purified P450 had high bioactivation toward 3-MeO-AAB and also 2-aminofluorene and 2-aminoanthracene. The antibody against this P450 completely inhibited mutagenic activation of 3-MeO-AAB of mouse renal microsomes. With immunoblotting, this form was present abundantly in renal microsomes of male mice but not in those of female mice. This P450 was also present in pulmonary microsomes of male and female mice but not in hepatic microsomes. The NH2-terminal amino acid sequence analysis indicated that this form belonged to the CYP4B subfamily. Thus, mouse kidney cDNA library was screened with rat CYP4B1 probe. The cDNA-deduced amino acid sequence of isolated cDNA consisted of 511 amino acids and bore 90, 86, and 84% similarities to rat, rabbit, and human CYP4B1, respectively. The NH2-terminal amino acid sequence of the purified renal P450 and amino acid sequence of BrCN-digested peptides from the purified P450 agreed with the cDNA-deduced amino acid sequence. These results suggest that CYP4B1 is a major form in renal microsomes of male mice and plays a major role in mutagenic activation of 3-MeO-AAB. In extrahepatic tissue, CYP4B1 may contribute to chemical carcinogenesis.

Amino Acid Sequence↗

PubMed1995

Metabolism of highly persistent PCB congener, 2,4,5,2',4',5'-hexachlorobiphenyl, by human CYP2B6.

Metabolism of 2,4,5,2',4',5'-hexachlorobiphenyl was studied with cDNA-expressed human P450 2B isoform, CYP2B6. 3-Hydroxy-2,4,5,2',4',5'-hexachlorobiphenyl was identified as a major metabolite, and the formation activity was compared with that of dog CYP2B11 and guinea pig P450GP-1. The activity of 3-hydroxylation was comparable with that of P450GP-1, but one-tenth of CYP2B11. These results indicate that P450 2B in humans as well as other animal species can metabolize 2,4,5,2',4',5'-hexachlorobiphenyl, and the reason why this PCB congener remained most abundantly in human bodies is discussed.

Animals↗

PubMed1995

Purification and characterization of a form of cytochrome P450 from bear liver microsomes.

A form of P450 [termed P450(b-1)] was purified from male bear liver microsomes. The specific content of the final P450(b-1) preparation was 11.26 nmol/mg protein, and recovery was 0.20% of the microsomal P450. The apparent molecular weight of P450(b-1) was 54,000. The absorption spectrum of P450(b-1) indicated that this protein was a low- and high-spin mixed type P450 in the oxidized form. The carbon monoxide complex of reduced P450(b-1) showed an absorption peak at 450.5 nm. The reconstituted system containing P450(b-1) catalyzed the metabolism of aminopyrine, benzo[a]pyrene, 7-ethoxycoumarin, imipramine and propranolol, of which P450(b-1) most strongly catalyzed aminopyrine N-demethylation and imipramine N-demethylation. The N-terminal amino acid sequence of P450(b-1) was highly homologous to that of P450-D1 from liver microsomes of male beagle dogs. P450(b-1) showed similarities in spectral properties, N-terminal amino acid sequence, and catalytic activities to rat P450 2C11. P450(b-1) was immunochemically cross-reactive with anti-P450 2C11 antibody and very weakly cross-reactive with anti-P450 2E1 antibody, but did not react with anti P450 1A1 or 2B1 antibodies. On the basis of these results, we suggest that P450(b-1) belongs to the P450 2C subfamily.

Amino Acid Sequence↗

PubMed1995

Maintenance of phenobarbital-inducible Cyp2b gene expression in C57BL/6 mouse hepatocytes in primary culture as spheroids.

Expression of the Cyp2b-9 and Cyp2b-10 genes was investigated in primary cultured adult C57BL/6NCrj mouse hepatocytes in monolayers or during the formation of spheroids (multicellular aggregates). Both the constitutive and phenobarbital-inducible expression of Cyp2b-9 and Cyp2b-10 mRNA decreased rapidly after transferring the hepatocytes to monolayer culture. The decrease was dependent on cell-density, and became more rapid in more densely seeded cells. However, in spheroid culture, the Cyp2b-9 and Cyp2b-10 mRNAs were induced by phenobarbital at high levels for at least 4 days either with continuous exposure from the start of cultivation or for 24 h before harvesting. The expression of both Cyp2b-9 and Cyp2b-10 species was confirmed by either reverse transcriptase-polymerase chain reaction or Western blotting. Although more Cyp2b-9 than Cyp2b-10 was expressed in the liver of control mice, the amounts of the latter became relatively overwhelming in untreated hepatocytes because of a faster decline of Cyp2b-9 species in culture. The level of mRNA induced by phenobarbital was concentration-dependent, the highest being at 2 or 4 mM, which was equivalent to in vivo treatment levels. There was more Cyp2b-10 species than those of Cyp2b-9 after exposure to phenobarbital both in vivo and in vitro. Phenobarbital also induced CYP1A2 mRNA, which was again peculiar to spheroid culture. Although the expression levels of both Cyp2b-9 and Cyp2b-10 species was very low in hepatocytes cultured without dexamethasone even in the presence of phenobarbital, the addition of 10(-7) or 10(-6) M dexamethasone caused an increase in the mRNA. When given concomitantly with phenobarbital, the expression was greatly enhanced. Nicotinamide or isonicotinamide similarly enhanced the expression of the two mRNA species, but the levels in monolayer cultures were still far lower than those in vivo. In contrast to the findings for mRNA expression, the protein levels in the presence of nicotinamide were similar to those in vivo under both monolayer and spheroid conditions. Since previous efforts to maintain expression of the CYP2B1 and CYP2B2 genes in primary cultured rat hepatocytes, orthologous to mouse Cyp2b-9 and Cyp2b-10 genes, required special cell attachment factors, our spheroid culture system, in which mouse hepatocytes are simply seeded onto noncoated dishes, has advantages for mechanistic studies.

Animals↗

PubMed1995

Metabolism of a new local anesthetic, ropivacaine, by human hepatic cytochrome P450.

BACKGROUND: Ropivacaine is a local anesthetic with a long duration of action. Although it is less toxic than bupivacaine, local anesthetic toxicity is possible when the plasma concentration is increased. Because ropivacaine is an amide-type local anesthetic, it is metabolized by cytochrome P450 (P450) in the liver, and its elimination and plasma concentration can be dependent on the level of P450. The purpose of this investigation was to elucidate the metabolism of ropivacaine by human hepatic P450. METHODS: The metabolism of ropivacaine was compared using recombinant human and purified rat hepatic P450 isozymes. An inhibition study using antibodies against rat P450 was performed using hepatic microsomes from human and rat to identify which P450s are involved in ropivacaine metabolism. RESULTS: Ropivacaine was metabolized to 2',6'-pipecoloxylidide (PPX), 3'-hydroxyropivacaine (3'-OH Rop), and 4'-hydroxyropivacaine (4'-OH Rop) by hepatic microsomes from human and rat. PPX was a major metabolite of both human and rat hepatic microsomes. In a reconstituted system with rat P450. PPX was produced by CYP2C11 and 3A2, 4'-OH Rop by CYP1A2, and 3'-OH Rop by CYP1A2 and 2D1. Formation of PPX in rat hepatic microsomes was inhibited by anti CYP3A2, but not by CYP2C11 antibody, and formation of 3'-OH Rop was inhibited by CYP1A2 and 2D1 antibodies. Anti CYP3A2 and 1A2 antibodies inhibited the formation of PPX and 3'-OH Rop in human hepatic microsomes, respectively. Recombinant human P450s expressed in lymphoblast cells were used for further study. CYP3A4 and 1A2 formed the most PPX and 3'-OH Rop, respectively. Ropivacaine N-dealkylation and 3'-hydroxylation activities correlated well with the level of CYP3A4 and 1A2 in human hepatic microsomes, respectively. CONCLUSIONS: Ropivacaine was metabolized to PPX, 3'-OH Rop, and 4'-OH Rop by hepatic P450. PPX was a major metabolite in human hepatic microsomes. CYP3A4 was involved in producing PPX. CYP1A2 was involved in the formation of 3'-OH Rop in human hepatic microsomes.

Amides↗

PubMed1995

Cytochrome P450 isozymes involved in aromatic hydroxylation and side-chain N-desisopropylation of alprenolol in rat liver microsomes.

Alprenolol 4-hydroxylation and N-desisopropylation in liver microsomes from male Wistar rats were kinetically analyzed to be biphasic. In the 4-hydroxylation at a low substrate concentration (5 microM), significant strain [Wistar > Dark Agouti (DA)] and sex (male > female) differences were observed, and the differences decreased at a high substrate concentration (1 mM). In the N-desisopropylation, only a strain difference (Wistar > DA) was observed at the low substrate concentration. Cytochrome P450BTL (P450BTL, corresponding to CYP2D2) in a reconstituted system with 5 microM alprenolol had high 4-hydroxylase activity, which was about 10 times that of P450ml corresponding to CYP2C11, and N-desisopropylase activity at a similar extent to P450ml. The two microsomal activities at 5 microM alprenolol were efficiently decreased by antibodies against P450BTL and by sparteine, a typical substrate of the CYP2D subfamily. Polyclonal antibodies against P450ml and P450PB-1 (corresponding to CYP3A2) partially suppressed only N-desalkylation at 5 microM, whereas they reduced the two activities at 1 mM. P450ml showed a high N-desisopropylase activity at a substrate concentration of 1 mM, where the sex difference was not observed. Furthermore, P450PB-2 corresponding to CYP2C6, which is one of the major P450 isozymes in female rats, also had 4-hydroxylase and N-desalkylase activities. These results suggest that a CYP2D isozyme(s) is the primary enzyme in alprenolol 4-hydroxylation and N-desisopropylation in a lower substrate concentration range, and that the involvement of some male-specific P450 isozyme(s) other than CYP2C11 or CYP3A2 may cause the sex difference in the 4-hydroxylation. In a higher substrate concentration range, CYP2C11 is thought to play a major role particularly in N-desisopropylation in male rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Alprenolol↗

PubMed1995

Involvement of CYP2C in the metabolism of cannabinoids by human hepatic microsomes from an old woman.

The hepatic microsomal metabolism of cannabinoids was studied using the liver from an old woman. delta 8-Tetrahydrocannabinol, delta 9-tetrahydrocannabinol and cannabinol were biotransformed to their respective 11-hydroxy metabolites by a microsomal fraction with specific activities (pmol/min/mg protein) of 29.1, 47.1 and 27.9, respectively. In addition, both 11-oxo-delta 8-tetrahydrocannabinol and 11-oxo-delta 9-tetrahydrocannabinol were metabolized to the corresponding carboxylic acids with the microsomes. An antibody against mouse CYP2C29 almost completely inhibited 11-hydroxylation of the cannabinoids and microsomal aldehyde oxygenase (MALDO) activity for 11-oxo-delta 8-tetrahydrocannabinol and 11-oxo-delta 9-tetrahydrocannabinol, used as substrates, whereas an antibody against rat CYP3A2 conversely stimulated the 11-hydroxylation of delta 8-tetrahydrocannabinol and MALDO activity for 11-oxo-delta 8-tetrahydrocannabinol. The results indicate that a member of CYP2C is primarily responsible for the metabolism of the above cannabinoids in the human hepatic microsomes.

Aged↗

PubMed1995

Induction of hepatic P450s in rat by essential wood and leaf oils.

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.

Animals↗

PubMed1995

Induction of hepatic microsomal P450 by 4-phenylalkylpyridines in rat: chain length-dependent and sex-related differential induction of P450s.

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. P450 induction gradually declined with increasing chain length of the 4-phenylalkylpyridines. 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. In the female rat, however, we could not observe such a chain length-dependent differential induction of the P4501A subfamily. 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. These results provide new information on the differential effects of pyridine-containing compounds on P450 induction in the rat.

Aminopyrine N-Demethylase↗

PubMed1995

Cytochrome P4502D isozymes catalyze the 4-hydroxylation of methamphetamine enantiomers.

The 4-hydroxylation of S(+)- and R(-)-methamphetamine by rat liver microsomes was examined in Sprague-Dawley and Dark Agouti strains to determine the role of cytochrome P4502D (CYP2D) subfamily isozymes in catalyzing the reaction. In the study, anti-P450-BTL IgG, bufuralol, and quinine, a substrate and inhibitors of CYP2D isozymes, respectively, were found to block approximately 90% of the reaction as catalyzed by microsomes from Sprague-Dawley rats. Reconstituted systems of CYP2D isozymes purified from rat liver microsomes also mediated the reaction. These observations and the minimal activity found in microsomes from Dark Agouti rats support the notion that methamphetamine, like other phenylisopropylamine compounds, is oxidized on the 4-position of the aromatic ring by CYP2D isozymes.

Animals↗

PubMed1995

Mepyramine, a histamine H1 receptor antagonist, inhibits the metabolic activity of rat and human P450 2D forms.

The interaction of antihistaminics, including mepyramine, with rat hepatic cytochrome P450s (P450s) was investigated. We first investigated mepyramine binding to eight forms of rat hepatic P450s. Mepyramine bound specifically to P450 2D1, which suggests that it inhibits P450 2D activity. Histamine H1 receptor antagonists (mepyramine, diphenhydramine, chlorpheniramine and triprolidine) inhibited the lidocaine 3-hydroxylation activity catalyzed by P450 2D1 but did not inhibit the testosterone hydroxylation activities catalyzed by P450s other than P450 2D forms. The Ki values of these antagonists for the catalytic activity of P450 2D1 were low and were similar to those of quinine and quinidine, which are specific inhibitors of P450 2D forms. The Ki value of mepyramine was especially low, at 34 nM. Furthermore, the effects of mepyramine on human P450 2D6 were investigated. Among the ten forms of human P450 expressed in yeast, mepyramine bound specifically to P450 2D6 in a binding assay. In human hepatic microsomes, mepyramine inhibited the debrisoquine 4-hydroxylation activity catalyzed by P450 2D6. These results indicate that histamine H1 receptor antagonists such as mepyramine are potent inhibitors of P450 2D forms because of their high affinity for these enzymes.

Animals↗