Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.14.13.97 (CYP3A4)
 6,365 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In vitro studies with human liver microsomes and P450 probe substrates were performed to characterize selectivity and mechanism of cytochrome P450 inhibition by nelfinavir mesylate. At therapeutic concentrations (steady-state plasma concentrations approximately 4 microM), nelfinavir was found to be a competitive inhibitor of only testosterone 6beta-hydroxylase (CYP3A4) with a Ki concentration of 4. 8 microM. At supratherapeutic concentrations, nelfinavir competitively inhibited dextromethorphan O-demethylase (CYP2D6), S-mephenytoin 4-hydroxylase (CYP2C19), and phenacetin O-deethylase (CYP1A2) with Ki concentrations of 68, 126, and 190 microM, respectively. Nelfinavir did not appreciably inhibit tolbutamide 4-hydroxylase (CYP2C9), paclitaxel 6alpha-hydroxylase (CYP2C8), or chlorzoxaxone 6beta-hydroxylase (CYP2E1) activities. The inhibitory potency of nelfinavir toward CYP3A4 suggested the possibility of in vivo inhibition of this isoform, whereas in vivo inhibition of other P450s was considered unlikely. In a one-sequence crossover study in 12 healthy volunteers, nelfinavir inhibited the elimination of the CYP3A substrate terfenadine and the carboxylate metabolite of terfenadine. The 24-hr urinary recoveries of 6beta-hydroxycortisol were reduced by an average of 27% during nelfinavir treatment, consistent with CYP3A inhibition by nelfinavir. Inhibition of CYP3A4 by nelfinavir in vitro was NADPH-dependent requiring the catalytic formation of a metabolite or a metabolic intermediate. The catechol metabolite of nelfinavir (M3) was considered unlikely to be responsible for inhibition as the addition of catechol O-methyl transferase, S-adenosyl methionine, and ascorbic acid to the preincubation mixture did not protect against the loss of testosterone 6beta-hydroxylase activity. Also, the addition of M3 to human liver microsomes did not inhibit CYP3A4. Although incubations with nelfinavir showed a time- and concentration-dependent loss of CYP3A4 activity, the partial or complete recovery of enzyme activity upon dialysis indicated that inhibition was reversible. Microsomal incubations with nelfinavir and NADPH did not result in a loss of spectral P450 content compared with the NADPH control. Glutathione, N-acetylcysteine, and catalase did not attenuate CYP3A4 inhibition by nelfinavir. Collectively, these results suggest that the probable mechanism for CYP3A4 inhibition by nelfinavir is a transient metabolic intermediate or stable metabolite that coordinates tightly but reversibly to the heme moiety of the P450.
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PMID:Characterization of the selectivity and mechanism of human cytochrome P450 inhibition by the human immunodeficiency virus-protease inhibitor nelfinavir mesylate. 966 Aug 42

Mono-specific antibodies against the human cytochrome P450 (P450) enzymes CYP1A1, CYP1A2, CYP1B1, CYP2A6, CYP2B6, CYP2D6, CYP2E1, CYP3A4, CYP3A5 and CYP4A11 and an antibody that binds to CYP2C8, CYP2C9 and CYP2C19 have been produced by immunising rabbits with synthetic peptides representing small regions of each of these P450 enzymes. The specificity of the antibodies was confirmed by immunoblotting using recombinant P450 enzymes and samples of human hepatic microsomal fraction. Each of the antibodies bound only to their respective target P450 enzyme(s). The relative intensity of immunoreactive bands was compared with a variety of P450 activities and correlations were found between CYP1A2 and phenacetin O-deethylase activity, CYP2A6 and coumarin 7-hydroxylase activity, CYP2C9 and tolbutamide 4-hydroxylase activity, CYP2C19 and S-mephenytoin 4-hydroxylase activity, CYP2D6 and debrisoquine 4-hydroxylase activity, CYP2E1 and chlorzoxazone 6-hydroxylase activity, CYP3A4 and midazolam 1'-hydroxylase activity, and CYP4A11 and lauric acid 12-hydroxylase activity. A proportion of the 30 liver samples examined lacked CYP2A6 (7%), CYP2C19 (10%) or CYP2D6 (13%), consistent with the polymorphic expression of these P450 enzymes in human liver. Although CYP3A5 was detected in most individuals (97%), expression was polymorphic with 20% containing substantially higher levels. CYP2B6 was expressed in 20% of the human liver samples, with one sample containing a particularly high level. No immunodetectable CYP1A1 or CYP1B1 was found, consistent with the low level of expression of these P450 enzymes in human liver. The results demonstrate the utility of the antipeptide approach for producing specific antibodies against human P450 enzymes, enabling a comprehensive panel of antibodies against human P450 enzymes to be produced.
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PMID:Development of a comprehensive panel of antibodies against the major xenobiotic metabolising forms of cytochrome P450 in humans. 974 76

The effects of methanol, ethanol, dimethyl sulfoxide (DMSO), and acetonitrile were studied in vitro on nine individual, cDNAexpressed cytochrome P-450 activities (phenacetin O-deethylase for CYP1A1 and CYP1A2, coumarin 7-hydroxylase for CYP2A6, testosterone 6beta-hydroxylase for CYP3A4, 7-ethoxy-4-trifluoromethylcoumarin deethylase for CYP2B6, paclitaxel 6alpha-hydroxylase for CYP2C8, diclofenac 4'-hydroxylase for CYP2C9, S-mephenytoin 4-hydroxylase for CYP2C19, and (+/-)-bufuralol 1'-hydroxylase for CYP2D6) in commercially available human lymphoblastoid microsomes. These data show that specific solvents have enzyme-selective effects on P-450 activities. Methanol did not substantially inhibit (</=10%) any of the activities at 0.3%, but did inhibit CYP1A1, CYP2B6, CYP2C9, and CYP2D6 by 12 to 26% at 1%. In contrast, 0.1% ethanol inhibited CYP1A1, CYP2B6, and CYP2C19 by 20 to 30%. Ethanol at 1% did not inhibit CYP1A2, CYP3A4, CYP2C8, and CYP2C9. DMSO inhibited CYP3A4, CYP2C19, and CYP2D6 by 15 to 25% at 0.1%. However, DMSO had little effect on CYP1A2, CYP2A6, and CYP2C8. Acetonitrile, like methanol, did not inhibit any P-450 activity at 0.3% solvent except for CYP1A1 (26%) and CYP2B6 (13%). At 1%, acetonitrile decreased activities of CYP1A1 and CYP2B6 by 40 to 60%, and inhibited CYP2A6, CYP3A4, CYP2C19, and CYP2D6 activity by 10 to 20%. Acetonitrile also increased CYP2C9 activity by 10 to 15% above control values at 1 to 3% solvent. Excluding solubility considerations, methanol and acetonitrile appear to be the most suitable solvents for the introduction of substances to cytochrome P-450 incubations for in vitro metabolism studies.
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PMID:Effect of methanol, ethanol, dimethyl sulfoxide, and acetonitrile on in vitro activities of cDNA-expressed human cytochromes P-450. 992 10