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T Cresteil

Publications and source records attributed to T Cresteil.

At least 19 recordsLinked to original sources
PubMed2003

Oxidative metabolism of amprenavir in the human liver. Effect of the CYP3A maturation.

Amprenavir is a human immunodeficiency virus-1 (HIV-1) protease inhibitor intended to be used to treat HIV-infected children. Although a pediatric dosage is proposed by the manufacturer, no data are currently available on the pharmacokinetics of amprenavir in neonates and infants. Amprenavir being primarily eliminated after oxidative biotransformation, we explored its in vitro metabolism by cytochrome P450 (P450)-dependent monooxygenases. In our conditions, five metabolites were formed in vitro and subsequently analyzed by liquid chromatography-mass spectrometry; P450-dependent oxidations occurred either on the tetrahydrofuran ring (M3 and M4), the aniline ring (M5), and the aliphatic chain (M2) or resulted from the N-dealkylation and loss of the tetrahydrofuran ring (M1). The two major metabolites, respectively M3 and M2 were formed by human liver microsomes with K(m) between 10 and 70 microM. CYP3A4 and to a lesser extent CYP3A5 were major contributors for the formation of M2, M3, and M5 metabolites, whereas CYP3A7 had no or little activity. This assumption was confirmed by inhibition with ketoconazole and ritonavir (two potent inhibitors of CYP3A) whereas sulfaphenazole (2C9 inhibitor) and quinidine (2D6 inhibitor) were inefficient. The metabolism of amprenavir was negligible in microsomes from either fetuses or neonates and steadily increased after the first weeks of life in relation with the maturation of CYP3A4/5. In conclusion, results demonstrated that the capacity of the human liver to oxidize amprenavir is low during the first weeks after birth and that dosage could be substantially reduced during the early neonatal period.

Adult↗
PubMed2001

Evidence of impaired cisapride metabolism in neonates.

AIMS: Cisapride has been shown to cause QTc prolongation in neonates in the absence of any of the known risk factors ascribed to children or adults (excessive dosage, drug-drug interactions). Our hypothesis was that the early neonatal liver may show defective elimination of cisapride resulting in its accumulation in the immature child. Owing to the difficulties associated with in vivo pharmacokinetic studies in a paediatric population, we explored the in vitro metabolism of cisapride by human cytochrome P450. METHODS: Experiments were conducted with recombinant CYPs stably expressed in mammalian cells and with liver microsomes obtained from human foetuses, neonates, infants and adults. Cisapride metabolites were measured by high performance liquid chromatography. RESULTS: The rate of biotransformation of cisapride was greater by recombinant CYP3A4 than by CYP3A7 (0.77 +/- 0.5 and 0.01 +/- 0.01 nmol metabolites formed in 24 h, respectively), whereas CYP1A1, 1A2, 2C8, 2C9 and 3A5 showed no activity. Norcisapride formation was significantly correlated with testosterone 6beta-hydroxylation, a CYP3A4 catalysed reaction (r = 0.71, P = 0.03) but not with the 16-hydroxylation of dehydroepiandrosterone, catalysed by CYP3A7 (r = 0.30, P = 0.29) by microsomes from a panel of livers from foetuses, neonates and infants. No or negligible cisapride metabolic activity was observed in microsomes from either foetuses or neonates aged less than 7 days, which contained mostly CYP3A7 and no CYP3A4. The metabolism of cisapride steadily increased after the first week of life in parallel with CYP3A4 activity to reach levels exceeding adult values. CONCLUSIONS: The low content of CYP3A4 in the human neonatal liver appears to be responsible for its inability to oxidize cisapride and could explain its accumulation in plasma leading to the cases of QTc prolongation reported in this paediatric population.

Adult↗
PubMed2001

Molecular regulation of genes encoding xenobiotic-metabolizing enzymes: mechanisms involving endogenous factors.

It is widely recognized that xenobiotic-metabolizing enzymes play a fundamental role in the basic processes of carcinogenesis and toxicity on one hand, and chemoprevention and drug efficacy on the other. Realization that different factors can profoundly affect the expression of these enzymes at the genome level has resulted in an enhanced appreciation of the importance these genes play in our modern industrialized age. There continues to be rapid proliferation of studies addressing the molecular regulation of these genes. The discovery of common signal transduction pathways and transcription factors that dictate tissue and developmental-specific expression, as well as variation in expression within a given tissue, suggest that there may be significant interaction among these various regulatory systems. This report is a summary of a symposium that was part of the Structure, Function and Regulation of Cytochromes P450 and Xenobiotic Metabolizing Enzymes satellite meeting of the 2000 joint meeting of the American Society for Biochemistry and Molecular Biology, the American Society for Pharmacology and Experimental Therapeutics, the French Pharmacological Society, and the Pharmacological Society of Canada held in Boston, Massachusetts. This symposium brought together several speakers who addressed specific receptor-mediated signal transduction pathways involved in the regulation of xenobiotic-metabolizing enzymes, as well as other molecular mechanisms whereby endogenous factors are involved in controlling tissue- and developmental-specific expression.

Enzymes↗
PubMed2000

Identification of human cytochrome P450s involved in the formation of all-trans-retinoic acid principal metabolites.

Cytochrome P450 (P450)-dependent metabolism of all-trans-retinoic acid (atRA) is important for the expression of its biological activity. Because the human P450s involved in the formation of the principal atRA metabolites have been only partially identified, the purpose of this study was to identify the human P450s involved in atRA metabolism. The use of phenotyped human liver microsomes (n = 16) allowed the identification of the following P450s: 2B6, 2C8, 3A4/5, and 2A6 were involved in the formation of 4-OH-RA and 4-oxo-RA; 2B6, 2C8, and 2A6 correlated with the formation of 18-OH-RA; and 2A6, 2B6, and 3A4/5 activities correlated with 5, 6-epoxy-RA formation (30-min incubation, 10 microM atRA, HPLC separation, UV detection 340 nm). The use of 15 cDNA-expressed human P450s from lymphoblast microsomes, showed the formation of 4-OH-RA by CYP3A7 > CYP3A5 > CYP2C18 > CYP2C8 > CYP3A4 > CYP2C9, whereas the 18-OH-RA formation involved CYPs 4A11 > 3A7 > 1A1 > 2C9 > 2C8 > 3A5 > 3A4 >2C18. Kinetic studies identified 3A7 as the most active P450 in the formation of three of the metabolites: for 4-OH-retinoic acid, 3A7 showed a V(max)/K(m) of 127.7, followed by 3A5 (V(max)/K(m) = 25.6), 2C8 (V(max)/K(m) = 24.5), 2C18 (V(max)/K(m) = 15.8), 3A4 (V(max)/K(m) = 5.7), 1A1 (V(max)/K(m) = 5.0), and 4A11 (V(max)/K(m) = 1.9); for 4-oxo-RA, 3A7 showed a V(max)/K(m) of 13.4, followed by a 10-fold lower activity for both 2C18 and 4A11 (V(max)/K(m) = 1.2); and for 18-OH-RA, 3A7 showed a V(max)/K(m) of 10.5 compared with a V(max)/K(m) of 2.1 for 4A11 and 2.0 for 2C8. 5,6-Epoxy-RA was only detected at high substrate concentrations in this system (>10 microM), and P450s 2C8, 2C9, and 1A1 were the most active in its formation. The use of embryonic kidney cells (293) stably transfected with human P450 cDNA confirmed the major involvement of P450s 3A7, 1A1, and 2C8 in the oxidation of atRA, and to a lesser extent, 1A2, 2C9, and 3A4. In conclusion, several human P450s involved in atRA metabolism have been identified, the expression of which was shown to direct atRA metabolism toward the formation of specific metabolites. The role of these human P450s in the biological and anticancer effects of atRA remains to be elucidated.

Antineoplastic Agents↗
PubMed2000

Ontogenesis of CYP2C-dependent arachidonic acid metabolism in the human liver: relationship with sudden infant death syndrome.

A modification of the human monooxygenase system have been previously associated with the sudden infant death syndrome (SIDS): the hepatic CYP2C content was markedly enhanced and resulted from an activation of CYP2C gene transcription. To determine the possible consequence of the up-regulation of CYP2C in SIDS, we examined the metabolism of arachidonic acid (AA) an endogenous substrate of CYP2C involved in the physiologic regulation of vascular tone. The overall AA metabolism was extremely low during the fetal period and rose after birth to generate 14,15 epoxyeicosatrienoic acid (EET), 11,12 EET and the sum of 5,6 dihydroxyeicosatrienoic acid (diHETE)+omega/omega-1 hydroxy AA. In SIDS, the accumulation of CYP2C proteins was associated with a significant increase in the formation of 14,15 and 11,12 diHETE, which were shown to be supported by individually expressed CYP2C8 and 2C9 and HETE1 (presumably 15 HETE). This increase was markedly inhibited by addition of sulfaphenazole, a selective inhibitor of CYP2C9. So, we propose that the higher CYP2C content in SIDS stimulates the production of EETs and diHETEs and might have severe pathologic consequences in children.

8,11,14-Eicosatrienoic Acid↗
PubMed2000

Metabolism of irinotecan (CPT-11) by CYP3A4 and CYP3A5 in humans.

7-Ethyl-10[4-(1-piperidino)-1-piperidino] carbonyloxy-camptothecin (CPT-11), a DNA topoisomerase I inhibitor, undergoes several metabolic pathways to generate conjugated and unconjugated derivatives that could be excreted from the body. The objective of this study was to determine the oxidative metabolites of CPT-11 recovered in human urine samples and to identify cytochrome P450 (CYP) involved in their formation. In addition to the already known metabolites of CPT-11 [SN-38, SN-38-G, 7-ethyl-10-[4-N-(5-aminopentanoic acid)-1-piperidino]carbonyloxycamptothecin (APC), and 7-ethyl-10-(4-amino-1-piperidino) carbonyloxycamptothecin (NPC)], we isolated three oxidized metabolites from the urine of two children and two adults given CPT-11. M1 and M2 (molecular weight, 602) were hydroxylated, respectively, on the CPT moiety and on the terminal piperidine ring of CPT-11. M3 had a molecular mass of 602, but its urine concentration in patients was too low to establish its chemical structure by liquid chromatography/mass spectrometry. In vitro incubations with cells expressing CYP2C8, CYP2C9, CYP1A1, CYP1A2, or CYP3A7 did not produce any detectable metabolites. Only CYP3A4 produced both APC and NPC, resulting from the oxidation of the piperidinylpiperidine side chain of CPT-11 along with metabolite M2. The metabolism of CPT-11 by CYP3A5 was markedly different because neither APC or NPC nor M2 was produced, whereas only one new metabolite, M4 (molecular weight, 558), was generated by de-ethylation of the CPT moiety. No previous study has reported the presence of the M4 metabolite. Production of APC, NPC, M2, and M4 was prevented by ketoconazole, a specific CYP3A inhibitor. The parameters of CPT-11 biotransformation into M2 and M4 were examined using cell lines expressing, respectively, with CYP3A4 and CYP3A5, indicating that CPT-11 is preferentially metabolized by CYP3A4. In conclusion, CYP3A plays a major role in the metabolism of CPT-11, with some differences of the metabolic profile exhibited by 3A4 and 3A5.

Adolescent↗
PubMed1999

Transcriptional activation of CYP2C, MxA and Fas in sudden infant death syndrome.

The expression of cytochrome P4502C has been shown to be upregulated in sudden infant death syndrome (SIDS) and could be linked to viral infection through the release of interferon alpha and interleukins. MxA is a reliable marker of IFNalpha release and its level was significantly enhanced in SIDS reflecting the release of IFNalpha in response to viral infection. Similarly, the concentration of Fas protein was increased in SIDS (2.6x control) and indicated a stimulation of the Fas gene expression. Accumulation of MxA and Fas proteins were visible in liver and to a lesser extent in lung and kidney. The amount of RNA encoding CYP2C9 (4.4x control), 2C8 (2.5x) and 2C18 (2.3x) was markedly higher in SIDS than in age-matched children and would suggest a transcriptional activation of CYP2C gene expression. Finally, CYP2C genes were shown to be adjacent to two IFN-inducible genes (IFI54 and IFI56) on chromosome 10. We conclude that in SIDS a viral infection leads to the release of IFNalpha which could activate a battery of IFN-inducible genes. This might modify the chromatin structure and facilitate the accessibility to promoter/regulatory sequences of CYP2C and Fas genes close to IFN-inducible gene on chromosome 10.

Adaptor Proteins, Signal Transducing↗
PubMed1998

Delayed ontogenesis of CYP1A2 in the human liver.

The ontogenesis of CYP1A proteins was investigated in a human liver bank composed of fetal, neonatal and adult samples. In immunoblots, a polyclonal antibody raised against rat CYP1A1, cross-reacted with cDNA-expressed human CYP1A1 and CYP1A2. In adult liver microsomes, this antibody reacted with a single band identified as the CYP1A2 protein, while no CYP1A1 could be detected. CYP1A2 protein was absent in microsomes prepared from fetal and neonatal livers and its levels increased in infants aged 1-3 months to attain 50% of the adult value at one year. Enzymatic activities supported by CYP1A proteins were assayed on these samples. Methoxyresorufin demethylase supported by the CYP1A2 recombinant protein followed the same ontogenic profile as the CYP1A2 protein. In liver microsomes, the demethylation of imipramine was essentially due to CYP1A2 and to a smaller extent to CYP3A. In fetuses and early neonates, CYP3A proteins were responsible for the low demethylation of imipramine (3-4% of the adult activity) before the onset of CYP1A2 and the subsequent rise of activity. Immunodetection and enzymatic activities were consistent with the absence of CYP1A1 and the late expression of CYP1A2 in the human liver, compared to the early rise of CYP3A4, CYP2C, CYP2D6, and CYP2E1 proteins.

Adult↗
PubMed1998

Onset of xenobiotic metabolism in children: toxicological implications.

The level of expression of cytochromes P450 shows a wide interindividual variability, depending on the age and tissue investigated. Several lines of evidence indicate that the human foetal liver is an active site for the biotransformation of drugs, chemicals and hydrophobic endogenous molecules. Besides this high degree of maturity, many studies have shown a discrepancy in the onset of activities and suggested that cytochrome P450 isoforms developed independently. Thus, many cytochromes P450 are absent or barely detectable in the foetal liver and develop postnatally. The postnatal evolution of P450 was explored in a liver bank constituted with samples collected from neonates aged less than 24 h to 10 years. Three major groups of cytochrome P450 could be described: a first group of cytochromes P450 expressed in the foetal liver includes the CYP3A7 and 4A1, mostly active on endogenous substrates; a second group (termed early neonatal P450) includes CYP2D6 and 2E1. They surged within hours after birth although proteins could not be detected in foetal samples. A third group of P450s (neonatal P450) develops later. CYP3A4 and CYP2Cs rose during the first weeks after parturition and CYP1A2 was the last isoform to be expressed in the human liver. Among phase II enzymes, epoxide hydrolase and glutathione S-transferase pi are very active in the foetal liver, whereas glutathione S-transferases mu and alpha and UDP-glucuronosyltransferases develop within 3 months after birth. These data clearly emphasize the delayed maturation of certain biotransformation pathways in the human liver during the perinatal period and constitute a scientific basis for improving safety during chemical exposure in children.

Adult↗
PubMed1998

Expression of CYP2E1 in human lung and kidney during development and in full-term placenta: a differential methylation of the gene is involved in the regulation process.

Methylation of dinucleotide CG residues located in the 5' end of the CYP2E1 gene has been demonstrated to play a role in the control of gene expression in the human developing liver. This study was undertaken to examine the CYP2E1 RNA content of human lung, kidney and full-term placenta and to determine whether the expression of CYP2E1 was controlled by its methylation status in these tissues. CYP2E1 was expressed at a very low level in the lung and kidney at whatever age, and at a variable level in full-term placentas. The restriction profile of genomic DNA was identical in lung and kidney and corresponded to a heavy methylation of HpaII/MspI sites located within the promoter, the first exon and first intron of the CYP2E1 gene. A different pattern of methylation was obtained in full-term placentas, indicating that CpG residues located in the 5' end of the gene were predominantly but not fully demethylated. However, the variable level of CYP2E1 RNA in full-term placentas suggests the involvement of other elements in the regulation process of CYP2E1 in this tissue.

Adult↗
PubMed1997

Expression of CYP3A in the human liver--evidence that the shift between CYP3A7 and CYP3A4 occurs immediately after birth.

CYP3A isoforms are responsible for the biotransformation of a wide variety of exogenous chemicals and endogenous steroids in human tissues. Two members of the CYP3A subfamily display developmentally regulated expression in the liver; CYP3A7 is expressed in the fetal liver, whereas CYP3A4 is the major cyrochrome P-450 isoform present in the adult liver. To gain insight into the descriptive ontogenesis of CYP3A isoforms during the neonatal period, we have developed several approaches to explore a neonatal liver bank. Although CYP3A4 and CYP3A7 are structurally closely related, they differ in their capacity to carry out monooxygenase reactions. We have cloned CYP3A4 and CYP3A7 and established stable transfectants in Ad293 cells to investigate their substrate specificities. The 16alpha hydroxylation of dehydroepiandrosterone is catalyzed by both proteins, but CYP3A7 has a higher affinity and maximal velocity than CYP3A4. Conversely, the conversion of testosterone into its 6beta derivative is essentially supported by CYP3A4. We used these two probes to determine the ontogenic evolution at the protein level; CYP3A7 was very active in the fetal liver and its activity was maximal during the first week following birth before to progressively decline and reached a very low level in adult livers. Conversely, the activity of CYP3A4 was extremely weak in the fetus and began to raise after birth to reach 30-40% of the adult activity after one month. CYP3A4 RNA accumulation displays a similar pattern of evolution; when probed with an oligonucleotide, its concentration increased rapidly after birth to reach a plateau as soon as the first week of age. These data supports the assumption that CYP3A4 expression is transcriptionally activated during the first week after birth and is accompanied by a simultaneous decrease of CYP3A7 expression, in such a way that the overall CYP3A protein content and the level of pentoxyresorufin dealkylase catalyzed by the two proteins remain nearly constant.

Adult↗
PubMed1997

Developmental expression of CYP2C and CYP2C-dependent activities in the human liver: in-vivo/in-vitro correlation and inducibility.

Experiments were performed in vivo and in vitro to date the onset of hepatic CYP2C isoforms and CYP2C-dependent activities during the perinatal period in humans. Proteins were not detected by immunoblotting in fetal livers and developed in the first few weeks after birth, irrespective of the gestational age at birth. Similarly, the hydroxylation of tolbutamide, a marker for CYP2C9 was undetected in fetal liver microsomes and rose in the first month after birth. In adult liver preparations, the hydroxylation of diazepam correlated well with the CYP3 A content of microsomes (r = 0.858, p < 0.01) and with the 6 beta hydroxylation of testosterone (r = 0.830, p < 0.005), whereas demethylation was related to the bulk of CYP2C proteins (r = 0.865, p < 0.005). In fetal liver microsomes, hydroxylation and demethylation activities accounted for less than 5% of the adult activities and both increased immediately after birth to reach adult activities at 1 year of age. When diazepam was given for sedative purpose in neonates and infants, the in-vivo urinary excretion of desmethyl diazepam, temazepam and oxazepam was extremely low in 1-2 day newborns (less than 5 nmol metabolites excreted in 24 h per kg body weight) and developed in the first week after birth. In newborns, barbiturates and to a lesser extent steroids, acted as inducers of CYP2C isoforms and increased tolbutamide hydroxylation, diazepam demethylation and diazepam hydroxylation by 2 to 10-fold. The surge of CYP2C proteins was caused by an accumulation of RNAs occurring in the first week after birth. The hepatic content in CYP2C8, 2C9 and 2C18 RNA displayed the same profile of evolution, which suggested a coregulation of their synthesis during the neonatal period. Taken together, these biochemical and clinical data enable dating of the onset of CYP2C proteins to the first weeks after birth, which is of considerable clinical importance in pediatric pharmacology.

Adult↗
PubMed1997

Biotransformation of taxoids by human cytochromes P450: structure-activity relationship.

The metabolism of paclitaxel and docetaxel by human liver microsomes was investigated in vitro. The main metabolite of paclitaxel formed in vitro was the 6 alpha-hydroxypaclitaxel: its formation largely exceeded the formation of other metabolites hydroxylated on the lateral chain by rat liver microsomes and initially characterized in rat bile. In contrast, in vitro studied showed that the initial metabolite of docetaxel resulted from the hydroxylation of the tert-butyl of the lateral chain at C13 and that the same metabolites were formed in human and animal models. Comparison of individual CYP protein content of human microsomes and catalytic activities with taxoid biotransformation, showed that 2 distinct isoforms were assigned to the 6 alpha-hydroxylation (CYP2C) and to the hydroxylation of the lateral chain (CYP3A4). Chemical and immunological inhibitions confirmed these assumptions. The effect of antineoplastic drugs potentially associated with taxoids during chemotherapy has been tested in vitro on paclitaxel and docetaxel biotransformations. In the therapeutic range, vincristine, vinblastine, doxorubicine and cisplatin elicited a moderate or no inhibition of paclitaxel and docetaxel metabolism, as well as cimetidine, ranitidine and diphenylhydramine used to prevent major side effects associated with taxoid therapy. In patients given barbiturates, the hydroxylation on the lateral chain of paclitaxel and docetaxel was markedly stimulated and resulted from the induction of CYP3A isoforms. These results clearly demonstrated that the biotransformation of paclitaxel and docetaxel by human liver microsomes was supported by 2 distinct CYP proteins and that drug interactions could modify the therapeutic efficiency of taxoids during chemotherapy.

Animals↗
PubMed1996

Cytochrome P-450 expression in sudden infant death syndrome.

In the human liver, the major rise of the cytochrome P-450 isoform content occurs during the first months following birth (e.g., the high vulnerability period to sudden infant death syndrome (SIDS), a syndrome frequently associated with viral infection and drug hypersensitivity. We examined the expression of individual P-450 isoforms in liver samples collected postmortem from SIDS infants and compared values with those of control adults and children of the same age suffering from various pathologies. Hepatic microsomes were prepared and examined for their content in total P-450, the level of individual isoforms (CYP1A2, CYP2E1, CYP4A, CYP3A, and CYP2C) determined with specific antibodies and for their enzymatic activities. Total RNA was extracted and probed with several CYP cDNAs and oligomers. The overall hepatic P-450 content was not modified in SIDS infants. Among cytochrome P-450 isoforms, only CYP2C was markedly increased. This rise resulted from an accumulation of RNA encoding CYP2C and was associated with a stimulation of diazepam demethylation. The precocious expression of CYP2C in SIDS could result in a higher production of epoxyeicosatrienoic acids in the neonate, believed to act as relaxant of pulmonary smooth muscles. Its consequence might be the induction of fatal apnea in SIDS.

Base Sequence↗
PubMed1996

Detection of cytochrome P450 gene expression in human placenta in first trimester of pregnancy.

Human first-trimester placentas were screened for the expression of xenobiotic-metabolizing cytochrome P450 (CYP) genes. mRNAs of CYP1A1, CYP1A2, CYP2C, CYP2D6, CYP2E1, CYP2F1, CYP3A4, CYP3A5, CYP3A7, and CYP4B1 were identified by reverse transcriptase-polymearse chain reaction (RT-PCR) in at least some of the six placental samples studied. CYP2A and CYP2B message were absent in all samples. The level of all of these CYP mRNAs was lower compared to the corresponding levels in liver or lung. the catalytic activity marker (7-ethoxyresorufin O-deethylase) was inducible in the placentas by maternal cigarette smoking. Thus, the regulatory system of placental CYP1A1, mediated by the Ah-receptor, appears to be developed as early as the first trimester of pregnancy. Three immunoreactive bands from placental microsomes were detected by an antihuman CYP3A4 antibody, but no functional activity of CYP3A enzymes could be detected. These results show that placental tissue during the first trimester of pregnancy has the potential of expressing several CYP genes, and forms a basis for subsequent analysis of these forms at the protein and functional level.

Base Sequence↗
PubMed1996

Developmental expression of CYP2E1 in the human liver. Hypermethylation control of gene expression during the neonatal period.

Cytochromes P-450 are responsible for the biotransformation of drugs and other hydrophobic molecules by the liver. Several isoforms coexist which display an asynchronous onset during the perinatal period suggesting the involvement of multiple mechanisms of regulation. In this paper, we have shown that the CYP2E1 protein and its associated activity could not be detected in the fetal liver and rise during the first few hours following birth independently of the gestational age (between 25-40 weeks). During this period, the CYP2E1 RNA content remains fairly low: the stabilization of the low amount of existing CYP2E1 protein by endogenous ketone bodies could explain the early neonatal rise of the protein level. From 1 month to 1 year, the protein content gradually increases and is accompanied by the accumulation of CYP2E1 RNA, suggesting a transcriptional activation of the gene during the late neonatal period. We examined the methylation status of CpG residues in the 5' flanking region, first exon and first intron of CYP2E1 gene cleaved with HpaII/MspI. Genomic DNA from fetal liver shows several hypermethylated spots in the first-exon-first-intron region, which progressively disappear in neonatal samples. We conclude that during the neonatal period, the accumulation of hepatic CYP2E1 RNA is correlated with the degree of methylation at the 5' end of the CYP2E1 gene.

Adult↗
PubMed1996

Metabolism of docetaxel by human cytochromes P450: interactions with paclitaxel and other antineoplastic drugs.

The metabolism of docetaxel by human liver microsomes was investigated in vitro and compared with that of paclitaxel. A main docetaxel metabolite was generated by human liver microsomes in the presence of NADPH: retention time in high pressure liquid chromatography and its ion fragmentation in mass spectrometry were identical to those of the authentic derivative hydroxylated at the butyl group of the C13 side chain. Kinetic measurements and chemical and immunological inhibitions demonstrated that CYP3A was implicated in the hydroxylation of docetaxel: Km (2 microM) and Vm values of docetaxel for human liver microsomes were comparable to those calculated for the formation of metabolite p-hydroxy-phenyl C3' paclitaxel (M4). Docetaxel hydroxylation correlated only with the CYP3A content of microsomes and with CYP3A-dependent 6 beta-hydroxylation of testosterone and 16-hydroxylation of dehydroepiandrosterone. The formation of hydroxydocetaxel was strongly reduced by CYP3A inhibitors such as ketoconazole, midazolam, erythromycin, testosterone, orphenadrine, and troleandomycin, whereas quinidine (CYP2D6), hexobarbital, tolbutamide, and mephenytoin (CYP2C) had no or little effect. The hydroxylation of docetaxel exhibited a highly positive correlation with the formation of metabolite M4 of paclitaxel (r = 0.929, P < 0.0001, n = 12), but not with its 6-hydroxylation (r = 0.48, P > 0.15). Docetaxel abolished the hydroxylation of paclitaxel metabolite M4, but was totally inactive on its 6 alpha-hydroxylation. Conversely, paclitaxel reduced significantly the hydroxylation of docetaxel. We examined in vitro the possible interaction among docetaxel, paclitaxel, and drugs which could be associated during chemotherapy. Cisplatin, verapamil, doxorubicin, vinblastine, and vincristine at concentrations usually recommended did not markedly modify taxoid metabolism. Ranitidine and diphenylhydramine had no effect, but 100 microM cimetidine partially inhibited the formation of 6 alpha-hydroxypaclitaxel. Pretreatment of patients with barbiturates strikingly stimulated docetaxel hydroxylation, whereas no acceleration of docetaxel hydroxylation was noticed in a patient receiving steroids.

Antineoplastic Agents, Phytogenic↗