Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:Q8NEX9 (reductase)
 26,410 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

S-Methyl N,N-diethyldithiocarbamate (MeDDC), a metabolite of the alcohol deterrent disulfiram, is converted to MeDDC sulfine and then S-methyl N,N-diethylthiocarbamate sulfoxide, the proposed active metabolite in vivo. Several isoforms of CYP450 and to a lesser extent flavin monooxygenase (FMO) metabolize MeDDC in the liver. The human kidney contains FMO1 and several isoforms of CYP450, including members of the CYP3A, CYP4A, CYP2B, and CYP4F subfamilies. In this study the metabolism of MeDDC by the human kidney was examined, and the enzymes responsible for this metabolism were determined. MeDDC was incubated with human renal microsomes from five donors or with insect microsomes containing human FMO1, CYP4A11, CYP3A4, CYP3A5, or CYP2B6. MeDDC sulfine was formed at 5 microM MeDDC by renal microsomes at a rate of 210 +/- 50 pmol/min/mg of microsomal protein (mean +/- S.D., n = 5) and by FMO1 at 7.6 +/- 0.2 nmol/min/nmol (n = 3). Oxidation of 5 microM MeDDC was negligible by all CYP450 tested (< or =0.03 nmol/min/nmol). Inhibition of FMO by methimazole or heat diminished MeDDC sulfine formation 75 to 89% in renal microsomes. Inhibition of CYP450 in renal microsomes by N-benzylimidazole or antibody to the CYP450 NADPH reductase had no effect on MeDDC sulfine production. Benzydamine N-oxidation, a probe for FMO activity, correlated with MeDDC sulfine formation in renal microsomes (r = 0.951, p = 0.013). The K(M) values for MeDDC sulfine formation by renal microsomes and recombinant human FMO1 were 11 and 15 microM, respectively. These results demonstrate a role for the kidney and FMO1 in the metabolism of MeDDC in humans.
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PMID:Metabolism of a disulfiram metabolite, S-methyl N,N-diethyldithiocarbamate, by flavin monooxygenase in human renal microsomes. 1115 1

1,8-Cineole, the monoterpene cyclic ether known as eucalyptol, is one of the components in essential oils from Eucalyptus polybractea. We investigated the metabolism of 1,8-cineole by liver microsomes of rats and humans and by recombinant cytochrome P450 (P450 or CYP) enzymes in insect cells in which human P450 and NADPH-P450 reductase cDNAs had been introduced. 1,8-Cineole was found to be oxidized at high rates to 2-exo-hydroxy-1,8-cineole by rat and human liver microsomal P450 enzymes. In rats, pregenolone-16alpha-carbonitrile (PCN) and phenobarbital induced the 1,8-cineole 2-hydroxylation activities by liver microsomes. Several lines of evidence suggested that CYP3A4 is a major enzyme involved in the oxidation of 1,8-cineole by human liver microsomes: (1), 1,8-cineole 2-hydroxylation activities by liver microsomes were inhibited very significantly by ketoconazole, a CYP3A inhibitor, and anti-CYP3A4 immunoglobulin G; (2), there was a good correlation between CYP3A4 contents and 1,8-cineole 2-hydroxylation activities in liver microsomes of eighteen human samples; and (3), of various recombinant human P450 enzymes examined, CYP3A4 had the highest activities for 1,8-cineole 2-hydroxylation; the rate catalyzed by CYP3A5 was about one-fourth of that catalyzed by CYP3A4. Kinetic analysis showed that K(m) and V(max) values for the oxidation of 1,8-cineole by liver microsomes of human sample HL-104 and rats treated with PCN were 50 microM and 91 nmol/min/nmol P450 and 20 microM and 12 nmol/min/nmol P450, respectively. The rates observed using human liver microsomes and recombinant CYP3A4 were very high among other CYP3A4 substrates reported so far. These results suggest that 1,8-cineole, a monoterpenoid present in nature, is one of the effective substrates for CYP3A enzymes in rat and human liver microsomes.
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PMID:Oxidation of 1,8-cineole, the monoterpene cyclic ether originated from eucalyptus polybractea, by cytochrome P450 3A enzymes in rat and human liver microsomes. 1115 12

Multiple forms of cytochrome P450 (P450 or CYP) enzymes play important roles in the oxidation of structurally diverse xenobiotics and endobiotics. Interindividual variations in the level and activity of P450 enzymes were investigated in the human liver microsomes. Although the total P450 content was higher in Caucasian samples than in Japanese ones, the relative levels (percentage of total P450) of individual forms of P450 determined immunochemically were not very different. CYP3A (about 30% of total P450) and CYP2C (about 20%) enzymes were major forms. Different P450 enzymes in the human liver play major roles in a variety of drug oxidations and the hepatic contents of these P450 forms could be affective to determine which P450 enzymes play major roles in drug metabolism in individual humans. Recently recombinant P450 enzymes from different sources, e.g., microsomes of human lymphoblastoid cells, of yeast, and insect cells infected with baculovirus systems, and Escherichia coli membranes containing coexpressed P450 and reductase, have been widely used for drug metabolism research. However, the marker activities or kinetic parameters of human P450 enzymes reported are not always similar. Cytochrome b5 can enhance the activities of recombinant P450 systems in some cases using different mechanisms. These differences in activities may be a critical factor for understanding the roles of human P450 enzymes involved in drug metabolism. This review provides useful information for the study of drug biotransformation in humans and for the basis of drug toxicities and carcinogenesis.
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PMID:[Roles of human cytochrome P450 enzymes involved in drug metabolism and toxicological studies]. 1119 84

This report describes the effect of alpha-naphthoflavone (alpha-NF), a known substrate, inhibitor and activator of several cytochromes P450 (CYP), on rabbit CYP3A6. Hepatic microsomes of rabbit pretreated with rifampicine (RIF), enriched with CYP3A6, as well as purified CYP3A6 reconstituted with isolated NADPH:CYP reductase were used as enzymatic systems in this study. The data from difference spectroscopy experiments showed that alpha-NF does yield a type I binding spectrum. This compound is oxidized by microsomal CYP3A6 into two metabolites (5,6-epoxide and trans-7,8-dihydrodiol). While alpha-NF is a substrate of CYP3A6, it also acts as an enzyme modulator. Under the conditions used, stimulation of 17beta-estradiol 2-hydroxylation by alpha-NF was observed. In contrast, this compound reversibly inhibited N-demethylation of erythromycin and tamoxifen, competitively with respect to these substrates, having the K(i) values of 51.5 and 18.0 microM, respectively. Moreover, alpha-NF was found to be an effective inactivator of progesterone and testosterone 6beta-hydroxylation catalyzed by CYP3A6 in RIF-microsomes. In addition, time- and concentration-dependent inactivation of human CYP3A4-mediated 6beta-hydroxylation of testosterone by alpha-NF, was determined. The inactivation of CYP3A6 followed pseudo-first-order kinetics and was dependent on both NADPH and alpha-NF. The concentrations required for half-maximal inactivation (K(i)) were 80.1 and 108.5 microM and the times required for half of the enzyme to be inactivated were 10.0 and 11.9 min for 6beta-hydroxylation of progesterone and testosterone, respectively. The loss of the enzyme activity was not recovered following dialysis, while 90% of the ability to form a reduced CO complex remained. This indicates the binding of alpha-NF to a CYP apoprotein molecule rather than to a heme moiety. Protection from inactivation was seen in the presence of all tested CYP3A substrates. Progesterone and testosterone protected CYP3A6 against inactivation competitively with respect to inactivator, erythromycin non-competitively and 17beta-estradiol showed a mixed type of protection. Here, we described for the first time that alpha-NF is capable of irreversible inhibition of microsomal rabbit CYP3A6 and human CYP3A4. The obtained results strongly suggest that the CYP3A active center contains at least two and probably three distinct binding sites for substrates.
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PMID:alpha-Naphthoflavone acts as activator and reversible or irreversible inhibitor of rabbit microsomal CYP3A6. 1164 Sep 17

1. Oxidation of 1,4-cineole, a monoterpene cyclic ether, was studied in rat and human liver microsomes and recombinant cytochrome P450 (P450 or CYP) enzymes expressed in insect cells in which human P450 and NADPH-P450 reductase cDNAs have been introduced. On analysis with gas chromatography/mass spectrometry, 2-exo-hydroxy-1,4-cineole was identified as a principal oxidation product of 1,4-cineole catalysed by rat and human P450 enzymes. 2. CYP3A4 was a major enzyme involved in the 2-hydroxylation of 1,4-cineole by human liver microsomes, based on the following lines of evidence. First, 1,4-cineole 2-hydroxylation activities catalysed by human liver microsomes were inhibited by ketoconazole, a potent inhibitor of CYP3A activities, and an anti-CYP3A4 antibody. Second, there was a good correlation beteeen CYP3A4 contents and 1,4-cineole 2-hydroxylation activities in liver microsomes of eighteen human samples examined. Finally, of 10 recombinant human P450 enzymes examined, CYP3A4 had the highest activity for 1,4-cineole 2-hydroxylation. 3. Liver microsomal 1,4-cineole 2-hydroxylation activities were induced in rat by pregnenolone 16alpha-carbonitrile and dexamethasone and extensively inhibited by ketoconazole, indicative of the possible roles of CYP3A enzymes in this reaction. 4. Kinetic analysis showed that Vmax/Km for 1,4-cineole 2-hydroxylation catalysed by liver microsomes was higher in a human sample HL-104 (4.6 microM(-1) min(-1)) than those of rat treated with pregnenolone 16alpha-carbonitrile (0.49 microM(-1) min(-1)) and dexamethasone (0.36 microM(-1) min(-1)). 5. 1,8-Cineole, a structurally related monoterpene previously shown to be catalysed by CYP3A enzymes, inhibited 1,4-cineole 2-hydroxylation catalysed by human liver microsomes, whereas 1,4-cineole did not inhibit 1,8-cineole 2-hydroxylation activities. Both compounds caused inhibition of testosterone 6beta-hydroxylation by human liver microsomes, the former compound being more inhibitory than the latter. 6. These results suggest that 1,4-cineole and 1,8-cineole, two plant essential oils present in Citrus medica L. var. acida and Eucalyptus polybractea, respectively, are converted to 2-hydroxylated products by CYP3A enzymes in rat and human liver microsomes. It is unknown at present whether the 2-hydroxylation products of these compounds are more active biologically than the parent compound.
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PMID:Roles of cytochrome P450 3A enzymes in the 2-hydroxylation of 1,4-cineole, a monoterpene cyclic ether, by rat and human liver microsomes. 1169 50

N-nitrosodiethylamine (NDEA) is able to induce tumours in the rat oesophagus. It has been suggested that this could be due to tissue specific expression of NDEA activating cytochrome P450 enzymes. We investigated this by characterizing the oesophageal monooxygenase complex of male Wistar rats and comparing it with that of the liver. Total amount of cytochrome P450, NADPH P450 reductase, cytochrome b5 and cytochrome b5 reductase of the oesophageal mucosa was approximately 7% of what was found in the liver. In addition, major differences were found in the cytochrome P450 isoenzyme composition between these organs: CYP 2B1/2B2 and CYP3A were found only in the liver, whereas CYP1A1 was constitutively expressed only in the oesophagus. Of the two well-known nitrosamine metabolizing enzymes, CYP2A3 was found only in the oesophagus whereas CYP2E1 was exclusively expressed in the liver. Catalytic studies, western blotting and RT-PCR analyses confirmed the expression of CYP2A3 in the oesophagus. CYP2A enzymes are known to be good catalysts of NDEA metabolism. Oesophageal microsomes had a K(m) for NDEA metabolism, which was about one-third of that of hepatic microsomes, but they showed similar activities when compared per nmol of total P450. NDEA activity in the oesophagus was significantly increased by coumarin (CO), which also induced oesophageal CYP2A3. Immunoinhibition of the microsomal NDEA activity showed that up to 70% of this reaction is catalysed by CYP2A3 in the oesophagus, whereas no inhibition of the hepatic NDEA activity could be achieved by the anti-CYP2A5 antibody. NDEA, but not N-nitrosodimethylamine (NDMA) inhibited the oesophageal metabolism of CO. The results of the present investigation show major differences in the enzyme composition of the oesophageal and hepatic monooxygenase complexes, and are in accordance with the hypothesis that the NDEA organotropism could, to a large extent, be due to the tissue specific expression of the activating enzymes.
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PMID:Rat oesophageal cytochrome P450 (CYP) monooxygenase system: comparison to the liver and relevance in N-nitrosodiethylamine carcinogenesis. 1169 52

Recent studies indicate that the Tg2576 transgenic mouse model of Alzheimer's disease [tg(hAPP)] demonstrates disturbances in plasma glucose and neuroendocrine function reminiscent of Alzheimer's disease (AD). Alterations in any one of these systems can have a profound effect on hepatic cytochrome P450 (CYP) expression. Additionally, the recent discovery that amyloid beta 1-42 can induce the expression of CYP reductase in neuronal cultures further suggests that hepatic CYP-related metabolism may be affected by the expression of mutant human amyloid precursor protein in these tg(hAPP) mice. Therefore, the current study was conducted to investigate the activity and protein content of several CYP isoforms in the livers and kidneys of aged (20-month-old) tg(hAPP) mice. tg(hAPP) mice exhibit significant elevations in hepatic CYP2B, CYP2E1-, CYP3A- and CYP4A-associated activities and CYP4A immunoreactive protein compared with wild-type. In contrast to the liver, a significant depression in renal CYP2E1- and CYP4A-associated activities were demonstrated in tg(hAPP) mice. The presence of the mutant hAPP protein was detected in the brain, kidney and livers of tg(hAPP) mice.
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PMID:Elevated hepatic and depressed renal cytochrome P450 activity in the Tg2576 transgenic mouse model of Alzheimer's disease. 1184 64

Multiple forms of cytochrome P450 play important roles in metabolic activation of a variety of environmental procarcinogens. Large species differences in substrate specificities between experimental animals and humans are critical factors in evaluation of chemical safety. To study the role of human P450s in genotoxic activation of environmental chemicals, transgenic bacteria expressing both human P450s and P450 reductase have been developed for the mutagenicity test. Mice lacking CYP1A2, and CYP1B1, and CYP2E1 were prepared to investigate the mechanism of procarcinogen activation in vivo. The first human transgenic animals were mice carrying human fetus-specific CYP3A7. Using these transgenic mice, mutagenic activation of a natural mycotoxin, aflatoxin B1, catalyzed by CYP3A7 in vivo was demonstrated. This observation was clear in extrahepatic tissues that did not express mouse CYP3A enzymes. In conclusion, P450s are key factors involved in metabolic activation of environmental procarcinogens for their biological actions.
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PMID:[P450 and carcinogenesis]. 1197 25

The human cytochromes P450 (P450) CYP3A contribute to the biotransformation of 50% of oxidatively metabolized drugs. The predominant hepatic form is CYP3A4, but recent evidence indicates that CYP3A5 contributes more significantly to the total liver CYP3A than was originally thought. CYP3A7 is the major fetal form and is rarely expressed in adults. To compare the metabolic capabilities of CYP3A forms for 10 substrates, incubations were performed using a consistent molar ratio (1:7:9) of recombinant CYP3A, P450 reductase, and cytochrome b5. A wide range of substrate concentrations was examined to determine the best fit to kinetic models for metabolite formation. In general, K(m) or S(50) values for the substrates were 3 to 4 times lower for CYP3A4 than for CYP3A5 or CYP3A7. For a more direct comparison of these P450 forms, clearance to the metabolites was determined as a linear relationship of rate of metabolite formation for the lowest substrate concentrations examined. The clearance for 1'-hydroxy midazolam formation at low substrate concentrations was similar for CYP3A4 and CYP3A5. For CYP3A5 versus CYP3A4, clearance values at low substrate concentrations were 2 to 20 times lower for the other biotransformations. The clearance values for CYP3A7-catalyzed metabolite formation at low substrate concentrations were substantially lower than for CYP3A4 or CYP3A5, except for clarithromycin, 4-OH triazolam, and N-desmethyl diltiazem (CYP3A5 - CYP3A7). The CYP3A forms demonstrated regioselective differences in some of the biotransformations. These results demonstrate an equal or reduced metabolic capability for CYP3A5 compared with CYP3A4 and a significantly lower capability for CYP3A7.
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PMID:Comparative metabolic capabilities of CYP3A4, CYP3A5, and CYP3A7. 1212 5

To identify an appropriate animal model for the study of drug interaction via CYP3A4 inhibition, the inhibition of in vitro mexazolam metabolism by various 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors [simvastatin (lactone), simvastatin acid, fluvastatin, atorvastatin, cerivastatin, pravastatin lactone, and pravastatin (acid)] in male and female rat liver microsomes was investigated and compared with that by HMG-CoA reductase inhibitors in human liver microsomes reported previously. The metabolism of mexazolam in male and female rat liver microsomes was inhibited by all the HMG-CoA reductase inhibitors examined except pravastatin (acid). The K(i) values in female rats were lower than those in male rats, demonstrating the presence of a sex difference in the inhibition potency of HMG-CoA reductase inhibitors toward mexazolam. Using anti-cytochrome P450 (P450) antisera, the main P450 isozyme responsible for the metabolism of mexazolam was identified as CYP3A in female rats and CYP2C11 in male rats. Based on these results, we speculate that the sex difference in the inhibition potency of HMG-CoA reductase inhibitors for mexazolam observed in rats is caused by their different inhibition potencies against CYP2C11 and CYP3A isoforms. For mexazolam metabolism, the results obtained in female rats, rather than those in male rats, seem to be a much better reflection of the results in humans. Since species and sex differences were observed in P450 isozymes in the present study, our results show that establishing appropriate experimental conditions, in particular with respect to the P450 isozymes responsible for the drug metabolism in question, is indispensable for the investigation of drug interactions using rats as a model animal for humans.
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PMID:Sex difference in inhibition of in vitro mexazolam metabolism by various 3-hydroxy-3-methylglutaryl-coenzyme a reductase inhibitors in rat liver microsomes. 1212 8


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