Cytochrome P-450 3A4 (nifedipine oxidase) is responsible for the C-oxidative metabolism of 1-nitropyrene in human liver microsomal samples

The nitrated polycyclic aromatic hydrocarbon 1-nitropyrene is a ubiquitous environmental pollutant. The role of cytochromes P-450 in the human metabolism of [3H]-1-nitropyrene was investigated using human liver microsomes. The range of microsomal metabolism from 16 individual liver specimens was 0.13 to 0.99 nmol/min/mg protein. Using 3 microsomal samples exhibiting different maximal velocities, the Km of 1-nitropyrene metabolism was 3.3 +/- 0.5 microM, indicating that perhaps a single or similar cytochromes P-450 was involved in the metabolism of 1-nitropyrene in these samples. The P-450 3A inhibitor triacetyloleandomycin inhibited 86 +/- 8% of the microsomal metabolism of 1-nitropyrene. Further evidence for the role of P-450 3A in human microsomal metabolism of 1-nitropyrene was gained using inhibitory anti-P-450 3A antibodies. Using 3 separate microsomal samples, antibody conditions that inhibited approximately 90% of the metabolism of the P-450 3A4-specific substrate nifedipine inhibited approximately 60-70% of the metabolism of 1-nitropyrene. Human liver microsomes demonstrated a preference for 1-nitropyren-3-ol formation over 1-nitropyren-6-ol or 1-nitropyren-8-ol, which is in contrast to that noted in rodents where the 6-ol and 8-ol are preferentially formed over the 3-ol, yet in agreement with earlier studies on the metabolism of 1-nitropyrene using Vaccinia-expressed human cytochromes P-450. These results indicate that the human hepatic metabolism of 1-nitropyrene is carried out by at least two or more P-450s including those in the P-450 3A subfamily. These studies also suggest that the metabolism of this compound by humans may differ from that in rodents in both the cytochromes that are involved and the specific metabolites that are formed.

Characterization of the 4 S polycyclic aromatic hydrocarbon-binding protein in human liver and cells

The 4 S polycyclic aromatic hydrocarbon (PAH)-binding protein (PBP) is a soluble protein that binds PAHs with high affinity in mouse, rat, and rabbit. Until now, this protein had not been detected in human placenta or human cells in culture by cytosol labeling and gradient centrifugation assay. Thanks to a preliminary fractionation of cytosol by sedimentation on sucrose gradient or/and gel permeation chromatography, we found that PBP was present in liver, MCF-7 cell line, and hepatocytes of human. To accurately quantitate PBP binding and determine specific binding parameters, a reduction in the amount of charcoal used to adsorb nonspecifically bound benzo[a]pyrene was required. By saturation analysis, the concentration of specific binding sites for [3H]BP in PBP fraction from human liver was 4.6 pmol/mg of protein compared with 14.7 +/- 1.4 pmol/mg in the same fraction from DBA/2J mouse liver. Kinetic studies analyzed by Scatchard and Woolf plots indicate that human liver and MCF-7 cells contain a low-affinity PBP form: the Kd derived from Woolf plot analysis were 14.2 +/- 1.4 and 26.2 +/- 1.8 nM, respectively. DBA/2J mouse possesses a higher-affinity PBP form, the same analysis indicating a Kd of 6.1 +/- 0.3 nM. These data demonstrate that, by comparison to the mouse liver, a lower-affinity form of PBP is present in reduced concentration in human liver, explaining the impossibility of detecting this protein by sedimentation of human cytosol in sucrose gradient.

Omeprazole, an inducer of human CYP1A1 and 1A2, is not a ligand for the Ah receptor

Omeprazole is a benzimidazole derivative which induces both P450 1A1 and 1A2 in human liver in vitro and in vivo. Northern blot analysis of polyA RNA prepared from primary cultures of human hepatocytes indicates that both 1A1 and 1A2 messages are induced by beta-naphthoflavone and omeprazole. Co-treatment of cells with these inducers and with actinomycin D or cycloheximide results in no accumulation of both mRNA or superinduction of 1A1 mRNA, respectively. 9S enriched fraction of cytosol was prepared either from human hepatocytes in culture or from human liver tissue and analyzed by sucrose density gradient sedimentation for its capacity to bind 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), omeprazole or omeprazole sulfone (a metabolite of omeprazole in man). Whereas 2 microM TCDD displaced almost totally [3H]TCDD from the Ah receptor, both omeprazole and omeprazole sulfone did not, even at 5000-fold molar excess. In addition, when [14C] omeprazole was incubated with 9S enriched fraction of human liver or hepatocyte cytosol, no interaction could be detected in sucrose density gradient. These experiments suggest that omeprazole is not a ligand for the human liver Ah receptor.

Cloning of a major heparan sulfate proteoglycan from brain and identification as the rat form of glypican

We have obtained the complete coding sequence of a highly conserved heparan sulfate proteoglycan which we previously characterized biochemically after isolation from rat brain. An open reading frame of 558 amino acids encodes a protein with a molecular mass of 62 kDa containing three peptide sequences present in the isolated proteoglycan. The total sequence obtained is 3.5 kb long, including 1.6 kb of 3'-untranslated sequence and 0.2 kb of 5'-untranslated sequence. The deduced amino acid sequence and the 3'- and 5'-untranslated sequences have 89% and 66-80% identity, respectively, with those of a phosphatidylinositol-anchored human lung fibroblast heparan sulfate proteoglycan (glypican) for which mRNA is detectable in a large number of human cell lines. Our data therefore demonstrate that this major heparan sulfate proteoglycan of brain is the rat form of glypican.

Cloning and primary structure of neurocan, a developmentally regulated, aggregating chondroitin sulfate proteoglycan of brain

We have obtained the complete coding sequence of neurocan, a chondroitin sulfate proteoglycan of rat brain which is developmentally regulated with respect to its molecular size, concentration, carbohydrate composition, sulfation, and immunocytochemical localization. Two degenerate oligonucleotides, based on amino acid sequence data from the proteoglycan isolated from adult brain by immunoaffinity chromatography with the 1D1 monoclonal antibody, were used as sense and antisense primers in the polymerase chain reaction with a brain cDNA library as template to generate an unambiguous cDNA probe. A second probe for the N-terminal portion of the early postnatal form of the proteoglycan was obtained by reverse transcription/polymerase chain reaction. The composite sequence of overlapping cDNA clones is 5.2-kilobases (kb) long, including 1.3 kb of 3'-untranslated sequence and 76 base pairs of 5'-untranslated sequence. An open reading frame of 1257 amino acids encodes a protein with a molecular mass of 136 kDa containing 10 peptide sequences present in the adult and/or early postnatal brain proteoglycans. The deduced amino acid sequence revealed a 22-amino acid signal peptide followed by an immunoglobulin domain, tandem repeats characteristic of the hyaluronic acid-binding region of aggregating proteoglycans, and an RGDS sequence. The C-terminal portion (amino acids 951-1215) has approximately 60% identity to regions in the C termini of the fibroblast and cartilage proteoglycans, versican and aggrecan, including two epidermal growth factor-like domains, a lectin-like domain, and a complement regulatory protein-like sequence. The central 595-amino acid portion of neurocan has no homology with other reported protein sequences. The proteoglycan contains six potential N-glycosylation sites and 25 potential threonine O-glycosylation sites. In the adult form of the proteoglycan (which represents the C-terminal half of neurocan) a single 32-kDa chondroitin 4-sulfate chain is linked at serin-944, whereas three additional potential chondroitin sulfate attachment sites (only two of which are utilized) are present in the larger proteoglycan species. A probe corresponding to a region of neurocan having no homology with versican or aggrecan hybridized with a single band at approximately 7.5 kb on Northern blots of mRNA from both 4-day and adult rat brain (but not with muscle, kidney, liver, or lung mRNA), indicating that the 1D1 proteoglycan of adult brain, containing a 68-kDa core protein, is generated by a developmentally regulated in vivo proteolytic processing of the 136-kDa species which is predominant in early postnatal brain.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of corticosteroids on the expression of cytochromes P450 and on cyclosporin A oxidase activity in primary cultures of human hepatocytes

Prednisone, prednisolone, and methylprednisolone are currently administered in association with cyclosporin A in the postoperative treatment of transplant patients. The aim of this work was to evaluate the effects of these corticosteroids on the expression of several forms of cytochromes P450 (P450), including P450 1A2, 2D6, 2E1, and 3A, and on cyclosporin A oxidase activity in human liver. For this purpose, human hepatocytes prepared from lobectomies were maintained in culture in a serum-free medium, in collagen-coated dishes, for 96-144 hr, in the absence or presence of 50-100 microM corticosteroids, rifampicin, or dexamethasone. To mimic more closely the current clinical protocol, hepatocyte cultures were also co-treated with corticosteroids and cyclosporin A or ketoconazole (a selective inhibitor of P450 3A). Cyclosporin A oxidase activity, intracellular retention of cyclosporin A oxidized metabolites within hepatocytes, accumulation of P450 proteins and corresponding messages, and de novo synthesis and half-lives of these P450 were measured in parallel in these cultures. Our results, obtained from seven different hepatocyte cultures, showed that 1) dexamethasone and prednisone, but not prednisolone or methylprednisolone, were inducers of P450 3A, at the level of protein and mRNA accumulation, as well as of cyclosporin A oxidase activity, known to be predominantly catalyzed by these P450; 2) although corticosteroids are known to be metabolized in human liver, notably by P450 3A, partial or total inhibition of this P450 by cyclosporin or ketoconazole, respectively, did not affect the inducing efficiency of these molecules; 3) corticosteroids did not affect the half-life of P450 3A or the accumulation of other forms of P450, including 1A2, 2D6, and 2E1; 4) chronic treatment of cells with cyclosporin did not affect P450 3A accumulation; 5) corticosteroids were all competitive inhibitors of cyclosporin A oxidase in human liver microsomes, with Ki values of 61 +/- 12, 125 +/- 25, 190 +/- 38, and 210 +/- 42 microM for dexamethasone, prednisolone, prednisone, and methylprednisolone, respectively; and 6) chronic treatment of cells with corticosteroids did not influence the excretion of oxidized metabolites of cyclosporin from the cells. These results support most of clinical reports dealing with mutual interactions between cyclosporin A and corticosteroids.

Mitotic responsiveness of cultured adult human hepatocytes to epidermal growth factor, transforming growth factor alpha, and human serum

The present study was undertaken to evaluate the ability of human hepatocytes to respond in culture to various mitotic agents including epidermal growth factor (EGF), transforming growth factor alpha (TGF-alpha), or serum from patients with fulminant hepatitis. Human hepatocytes were maintained in culture on collagen-coated plates in a chemically and hormonally defined serum-free medium at low cell density. Twelve hours after plating, cultures were treated with increasing amounts of EGF (1-100 ng/mL), TGF-alpha (1-100 ng/mL), or human serum (1%-10%) for 0-96 hours. Proliferative response was assessed by determining against time the rate of DNA synthesis by [3H]thymidine incorporation in DNA, the labeling index, the expression of cyclin A, the amount of DNA, and the number of cells. The rate of DNA synthesis reached a maximum after 48 hours of treatment with 20 ng/mL EGF, 40 ng/mL TGF-alpha, or 5%-10% of human serum (fulminant hepatitis); the average increase with respect to untreated cells was 4.35 times with EGF, 5.4 times with TGF-alpha, and 4-6 times with serum from patients with fulminant hepatitis. The maximum expression of cyclin A coincided with the maximum of DNA synthesis. After 72 hours of treatment with EGF or human serum (fulminant hepatitis), the amount of DNA increased by 75%-100% (P less than 0.001) and the number of cells by 50% (P less than 0.001). These results show that adult human hepatocytes respond to mitogens, as expected from previous studies on animal hepatocytes, and provide experimental basis for future investigations in the field of human liver regeneration.

Purification of two cytochrome P450 isozymes related to CYP2A and CYP3A gene families from monkey (baboon, Papio papio) liver microsomes. Cross reactivity with human forms

Two cytochrome P450 isozymes, FA and FI, were isolated and characterized from liver microsomes of phenobarbital-induced baboons (Papio papio). The cytochrome FA possesses the same N-terminal amino acid sequence as P450 MK2 from crab-eating monkeys (Macaca irus) and closely resembles the human P450 3A isozymes. This cytochrome was able to oxidize nifedipine and hydroxylate testosterone at the 6 beta position. The second baboon cytochrome (FI) is closely related to the P450 2A subfamily and has the same N-terminal sequence as human P450 2A7. Like human P450 2A forms, it is highly active as a coumarin 7-hydroxylase. Antibodies against P450 FA and FI cross-react with two human liver proteins of 51 kDa and 49 kDa, respectively. The concentration of the first protein in the human samples, was five-times greater than the second. However, the latter showed marked interindividual variation. In primary cultures of human hepatocytes, rifampicin is a strong inducer of the 51-kDa protein and a moderate inducer of the 49-kDa protein, while phenobarbital has the opposite effect on the two proteins.

Effects of imidazole derivatives on cytochromes P450 from human hepatocytes in primary culture

The expression of several forms of cytochrome P450 including P450 1A2, 2D6, 2E1, and 3A was investigated in human hepatocytes maintained in primary culture for 96 h in the absence or presence of 50 microM of various imidazole derivatives. These included ketoconazole, clotrimazole, miconazole, fluconazole, secnidazole and metronidazole. In addition, the typical inducers rifampicin and beta-naphthoflavone were used for comparison. Western and Northern blot analysis of microsomes and RNA prepared from these cultures as well as de novo synthesis experiments revealed that, among the imidazole derivatives tested, only clotrimazole was a strong rifampicin-like inducer of P450 3A. The expression of the other forms of P450 tested was not affected by the treatments. Analysis of the inhibition of 13 monoxygenase activities, including ethoxyresorufin and phenacetin O-deethylases, coumarin 7 alpha-, lauric acid 11- and 12-, mephenytoin 4-, debrisoquin 4-, and aniline hydroxylases, benzphetamine, aminopyrine, mephenytoin and erythromycin demethylases, and cyclosporin oxidase (representative of 10 different forms of P450 in human liver microsomes) revealed that ketoconazole was a strong and selective in vitro inhibitor of P450 3A (cyclosporin oxidase) with a Ki less than 1 microM. Clotrimazole and miconazole were also strong inhibitors of P450 3A-mediated activities in contrast to the other imidazole derivatives.

[Cyclosporin A metabolism and induction of cytochrome P-450 in orthoptic hepatic transplantation in rats]

The aim of our study were 1) to establish that cyclosporin (CsA) metabolism was correlated with the rate of cytochrome P4503A (cyt.) in Wistar rats induced with dexamethasone (Dex.), 2) to demonstrate that the induction of cyt. with Dex. in liver "rat donor" was transmissible to "recipient rat" after liver transplantation. Sixty rats were divided in 5 groups. In group T, a single dose of CsA (10 mg/kg) was administered intravenously in 10 rats; in group D, 10 rats were treated with Dex (300 mg/kg daily for 4 days) and then received CsA as above; in group BN 5 rats were treated with beta-naphthoflavone. Thirty five rats underwent a liver transplantation either from "non induced donors" (group G, n = 11) or from "induced donors with Dex." (group GD, n = 24) followed by CsA injection the next day. For each rat, CsA plasma levels were determined by radioimmunoassay in 6 samples. Liver microsomes cyt. from samples of the liver of donor rats (group G and GD) or after sacrifice (group T, D, BN) were quantitated by immunoblot analysis and estimated from densitometric analysis of the blot. Mean maximal plasma concentration (Cmax) were 2,822 +/- 997 ng/ml in group T, 1,447 +/- -458 ng/ml in group D, 2,685 +/- 1,383 ng/ml in group G, 1,337 +/- 713 ng/ml in group GD and 3,094 +/- 685 ng/ml in group BN. Considering the Cmax and the ASC (area under curve), there was a significant difference between all groups and separately between groups T and D, G and GD.(ABSTRACT TRUNCATED AT 250 WORDS)

Induction, regulation and messenger half-life of cytochromes P450 IA1, IA2 and IIIA6 in primary cultures of rabbit hepatocytes. CYP 1A1, 1A2 and 3A6 chromosome location in the rabbit and evidence that post-transcriptional control of gene IA2 does not involve mRNA stabilization

A study on the regulation and induction of expression of cytochromes P450-IA1, IA2 and IIIA6 genes has been undertaken using primary cultures of adult rabbit hepatocytes grown in a serum-free chemically and hormonally defined medium. In 72-h-old cultures, 50 microM beta-naphthoflavone induced both IA1 and IA2 mRNA, the maximal level being reached after 4 h and 12 h, respectively. This was shown to result from an increase in the rate of transcription of gene IA1. In contrast, gene IA2 was constitutively transcribed in untreated cells, but mRNA only accumulated in the presence of beta-naphthoflavone which, however, did not affect the rate of transcription. Actinomycin D fully blocked induction of both IA1 and IA2 mRNA in response to their inducer. In untreated cells the presence of cycloheximide allowed a 'constitutive' expression of gene IA1, while in beta-naphthoflavone-treated cells, it produced a super-induction of IA1 but no modification of IA2 gene expression. Rifampicin (50 microM) strongly increased the IA1 mRNA level and rate of transcription only in cycloheximide-treated cells. Rifampicin and dexamethasone, two prototypical inducers of P450-IIIAs, induced both large and small IIIA6 mRNAs in a time-dependent fashion, the maximum level being reached after 24 h. This was related to a large increase in the rate of transcription of the gene. Cycloheximide significantly decreased the accumulation of both IIIA6 mRNAs in response to rifampicin, while actinomycin D fully blocked induction. The half-lives of IA1, IA2 and IIIA6 mRNAs were determined by two different methods, namely actinomycin D and [3H]uridine-chase experiments. In untreated cells, the half-lives for IA1, IA2 and IIIA6 mRNAs were 14 h, 16 h and 19 h, respectively when determined by the uridine chase and 18 h, 25 h and 22 h when determined by the actinomycin-D chase. These values were not modified significantly in cells treated with beta-naphthoflavone or rifampicin, indicating that neither of these inducers affected the stability of IA1 and IA2 or IIIA6 messages, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)

Developmental expression of rabbit cytochrome P450 CYP1A1, CYP1A2 and CYP3A6 genes. Effect of weaning and rifampicin

Developmental expression of CYP1A1, CYP1A2 and CYP3A6 in the rabbit have been studied. Cytochromes P450IA1, P450IA2 and P450IIIA6 exhibited comparable patterns of developmental expression. Present at low level (less than 0.05 nmol/mg) in the new born animal up to week 3, these proteins sharply accumulated between weeks 3 and 4 to reach a maximum by week 4 (P450IA1, 0.2 nmol/mg; P450IA2, 0.8 nmol/mg; P450IIIA6, 0.12 nmol/mg) and decreased in the adult (P450IA1, 0.2 nmol/mg; P450IA2, 0.4 nmol/mg; P450IIIA6, 0.09 nmol/mg). Cytochromes P450IA1 and P450IA2 were not expressed in the untreated fetus. Onset of CYP3A6 gene expression occurred at day 30 of gestation and both transcription and mRNA accumulation were transplacentally inducible by rifampicin only shortly before birth, i.e. after treatment of the females between days 28 and 30 of gestation. Both long (1.85 kb) and short (1.7 kb) mRNA transcripts were expressed in untreated or rifampicin-treated fetuses. CYP3A6 gene expression was also induced by rifampicin in 1-week-old and 2-week-old animals. Developmental expression of CYP1A1 and CYP1A2 genes was shown to be closely related to the diet change accompanying weaning which occurs at weeks 3-4. In animals subjected to either delayed (week 6) or early (week 2) weaning, sharp accumulation of messages, proteins and related activities were delayed or anticipated accordingly with respect to normal weaning. Artificially scheduled weaning gave similar results when repeated with biological-grade lucern (grown in the absence of chemical fertilizers, pesticides, etc.), the main constituent of commercial rabbit chow. While CYP3A6 gene expression could be brought forward by early weaning at week 2, both message and protein did not exhibit increased accumulation after delayed weaning at week 6, and remained at the low level of the new born animal. Treatment of 1-week-old and 2-week-old animals with triiodothyronine or of 3-week-old animals with propylthiouracil, an antithyroid factor, did not modify the normal pattern of developmental expression of genes CYP1A1, CYP1A2 and CYP3A6. It is concluded that (a) the onset of CYP3A6 gene expression in the fetus occurs at day 30 of gestation, (b) expression of this gene may be induced transplacentally by rifampicin, (c) CYP1A1, CYP1A2 and CYP3A6 gene expression is sharply activated at weaning, and (d) thyroid hormones appear not to be responsible for the pattern of developmental expression of these genes in the rabbit.

Removal of N-linked oligosaccharides of presumptive ectoderm impairs neural induction in Pleurodeles waltl

Studies were carried out on the embryo of the amphibian Pleurodeles waltl to investigate the potential role of the N-linked oligosaccharides of the ectodermal cell membrane in the neural induction process. Glycopeptidase F (GPase F) was used to cleave N-linked oligosaccharides on presumptive ectoderm. Removal of oligosaccharide moieties from ectoderm membrane glycoconjugates completely inhibited natural neural induction in vitro. On the other hand, Swainsonine (Sw) and 1-deoxynojirimycin (dNM), specific inhibitors of enzymes involved in glycosylation, provoked strong and persistent changes in the structure of the N-linked oligosaccharides of presumptive ectoderm but did not prevent neuralisation of treated ectoderm. We conclude that N-linked carbohydrates are implicated in the phenomenon of neural induction. However, the structural integrity of N-linked carbohydrates of target tissue is not itself critical in this process. The existence of specific carbohydrates on presumptive ectoderm was still questioned as receptors of neural signal.

Cyclosporin A drug interactions. Screening for inducers and inhibitors of cytochrome P-450 (cyclosporin A oxidase) in primary cultures of human hepatocytes and in liver microsomes

In previous papers we demonstrated that cyclosporin A (CsA) was specifically oxidized in rabbit and human liver by cytochrome P-450IIIA. We therefore anticipated that any drug that is an inducer or an inhibitor of this cytochrome should lead to interaction with CsA when given in association with it. In order to confirm this hypothesis, primary cultures of human hepatocytes and human liver microsomes were used to "reproduce" in vitro clinically significant interactions observed between CsA and drugs known either as specific inducers (i.e., rifampicin) or as specific inhibitors (i.e., erythromycin) of P-450IIIA. Our results were in close agreement with the clinical reports. Human hepatocytes maintained in primary cultures for 72 hr in the presence of 50 microM rifampicin exhibited increased levels of P-450IIIA, determined by Western blot using specific antibodies, and concomitant increase in CsA oxidase activity, determined by HPLC analysis of extra and intracellular media. Conversely, these cultures exhibited erythromycin concentration-dependent decreases in CsA oxidase activity when incubated in the presence of 5, 20, and 100 microM erythromycin. In addition, a Lineweaver-Burk analysis of the erythromycin-mediated inhibition of CsA oxidase activity in human liver microsomes revealed competitive inhibition (with Ki of 75 microM) as expected, this macrolide being a specific substrate of P-450IIIA. Using this experimental approach, 59 molecules representative of 17 different therapeutic classes were screened for inducers and inhibitors of CsA oxidase activity. Our results allowed us to elucidate the molecular mechanism of previously observed, but unexplained, drug interactions involving CsA, and to detect drugs that should interfere with CsA metabolism as inducers or inhibitors. Drugs detected as potential inducers of CsA oxidase included: rifampicin, sulfadimidine, phenobarbital, phenytoin, phenylbutazone, dexamethasone, sulfinpyrazone, and carbamazepine. Drugs detected as potential competitive inhibitors included: triacetyloleandomycin, erythromycin, josamycin, midecamycin, ketoconazole, miconazole, midazolam, nifedipin, diltiazem, verapamil, nicardipine, ergotamine, dihydroergotamine, glibenclamide, bromocriptine, ethynylestradiol, progesterone, cortisol, prednisone, prednisolone, and methylprednisolone. Finally, cefoperazone, cefotaxime, ceftazidime, isoniazide, doxycycline, spiramycin, sulfamethoxazole, norfloxacin, pefloxacin, vancocin, trimethoprim, amphotericin B, valproic acid, quinidine, cimetidine, ranitidine, omeprazole, diclofenac, aspirin, paracetamol, debrisoquine, guanoxan, captopril, furosemide, acetazolamide, sparteine, gliclazide, and imipramine were found not to interfere with the hepatic metabolism of CsA.

Omeprazole is an aryl hydrocarbon-like inducer of human hepatic cytochrome P450

Omeprazole is a new drug used for its high efficiency as an inhibitor of gastric acid secretion. This substituted benzimidazole molecule had been shown to decrease several liver cytochrome P450-mediated monooxygenase activities both in vitro and in vivo. The present work was undertaken to determine whether this drug was an inducer of cytochrome P450 in humans. Primary cultures of human hepatocytes were maintained in a serum-free, chemically defined medium for 0-96 hours in the absence or in the presence of omeprazole (1-100 mumol/L) or of other cytochrome P450 inducers such as 3-methylcholanthrene, beta-naphthoflavone, or rifampicin for comparison. Omeprazole produced a time- and concentration-dependent increase in (a) cytochrome P450IA2 accumulation determined by western blot in microsomes from omeprazole-treated cells, while the level of other cytochrome P450 forms including P450IID6, IIE1, and IIIA was not increased in the same culture; (b) several monoxygenase activities, including phenacetin deethylase and acetanilide hydroxylase (cytochrome P450IA2) and ethoxyresorufin deethylase and benzpyrene hydroxylase (cytochrome P450IA1); (c) cytochrome P450IA2 de novo synthesis, determined by immunoprecipitation of cell lysate from [3H]Leu-labeled cells; (d) cytochromes P450IA1 and IA2 mRNAs, determined by northern blot analysis. An in vivo study was carried out on liver microsomes from five patients for whom hepatic biopsy specimens were available before and after repeated administration of omeprazole (20 mg/day for 4 days). In all cases, several-fold increases in cytochrome P450IA2 and specific cytochrome P450IA subfamily-dependent monooxygenase activities were observed in agreement with the results from cell culture. It was concluded that omeprazole is an aryl hydrocarbon-like inducer of cytochrome P450 secretion in human liver both in vitro and in vivo. This drug is therefore likely to increase the metabolism of any xenobiotic specifically oxidized by a cytochrome P450IA subfamily. This could potentiate the hepatotoxicity of phenacetin or paracetamol and activation of procarcinogens.

Identification of the rabbit and human cytochromes P-450IIIA as the major enzymes involved in the N-demethylation of diltiazem

Oxidative metabolism of diltiazem (DTZ), a calcium channel blocker, was investigated in rabbit and human liver microsomes as well as in primary cultures of human hepatocytes. DTZ N-demethylation, the major metabolic pathway in man, was strongly increased by treatment of animals, patients, and hepatocyte cultures with rifampicin and other inducers of the P-450IIIA subfamily. In a reconstituted system with purified forms of P-450 and NADPH cytochrome P-450 reductase, P-450IIIA7 exhibited the highest DTZ N-demethylase activity. In both rabbit and human liver microsomes, this activity was highly correlated with erythromycin demethylase, a characteristic substrate of P-450IIIA, or with an immunoquantitated level of P-450IIIA, and was specifically inhibited by anti-P-450IIIA7 polyclonal and monoclonal antibodies. Cyclosporin A, another specific substrate of P-450IIIA in rabbit and human, competitively inhibited DTZ N-demethylase in both species. In primary cultures of human hepatocytes treated with various inducers, including rifampicin, dexamethasone, phenobarbital, phenylbutazone or beta-naphthoflavone, the rate of release of N-demethyl-DTZ in the extracellular medium was highly correlated with the intracellular level of P-450IIIA, which appeared to be strongly induced by rifampicin and phenobarbital and to a lesser extent by dexamethasone and phenylbutazone. In aggregate, these results are consistent with the view that in both rabbit and human, cytochromes P-450 from the P-450IIIA subfamily are the major enzymes involved in the N-demethylation of DTZ. Accordingly, drugs which may be specific substrates or inducers of this P-450 are likely to influence both the side effects and the efficacy of this molecule.

Metabolic activation of the new tricyclic antidepressant tianeptine by human liver cytochrome P450

Incubation of [14C]tianeptine (0.5 mM) with human liver microsomes and a NADPH-generating system resulted in the in vitro covalent binding of a tianeptine metabolite to microsomal proteins. This covalent binding required oxygen and NADPH. It was decreased by piperonyl butoxide (4 mM) by 81%, and SKF 525-A (4 mM) by 87%, two relatively non-specific inhibitors of cytochrome P450, and by glutathione (4 mM) by 70%, a nucleophile. Covalent binding was decreased by 54% in the presence of troleandomycin (0.1 mM), a specific inhibitor of the glucocorticoid-inducible cytochrome P450 IIIA3, but remained unchanged in the presence of quinidine (0.1 mM) or dextromethorphan (0.1 mM), two inhibitors of cytochrome P450 IID6. Preincubation with IgG antibodies directed against cytochrome P450 IIIA3 decreased covalent binding by 65% whereas either preimmune IgG or IgG antibodies directed against P450 IA1, an isoenzyme inducible by polycyclic aromatic compounds, exhibited no significant inhibitory effect. We conclude that tianeptine is activated by human liver cytochrome P450 into a reactive metabolite. This activation is mediated in part by glucocorticoid-inducible isoenzymes but not by P450 IID6 (the isoenzyme which oxidizes debrisoquine) nor by P450 IA1 (an isoenzyme inducible by polycyclic aromatic compounds). The predictive value of this study regarding possible idiosyncratic and immunoallergic reactions in humans remains unknown.

Purification of a sheep liver cytochrome P-450 from the P450IIIA gene subfamily. Its contribution to the N-dealkylation of veterinary drugs

Oral administration of troleandomycin at a dose of 100 mg/kg/day for 6 days to three adult male Lacaune sheep produced a 1.6-fold increase in specific content of liver microsomal cytochrome P-450. In sodium dodecyl sulfate-polyacrylamide gel electrophoresis, microsomal preparations from treated animals exhibited a strong band in the zone of electrophoretic mobility of cytochromes P-450. This band corresponded to a cytochrome P-450 which cross-reacted with rabbit P450IIIA6 antibodies, as demonstrated by immunoblotting. The ovine isozyme was purified to electrophoretic homogeneity by means of successive DEAE cellulose, CM cellulose and hydroxylapatite chromatographic separations. This hemoprotein had an apparent molecular weight of 52 kD as determined by calibrated sodium dodecyl sulfate-polyacrylamide gel electrophoresis and was characterized in terms of spectral data, NH2-terminal amino acid sequence, immunologic and catalytic properties. This study revealed some interspecies differences with the orthologous rabbit isozyme. The contribution of this form to the N-demethylation of erythromycin and of three veterinary drugs: chlorpromazine, chlorpheniramine and bromhexine was demonstrated from inhibition by TAO, from immunoinhibition studies, using polyclonal antibodies raised in rabbit and from the existence of significant correlations between its microsomal level and these N-demethylase activities. In contrast, the results suggest that ovine P450IIIA could not be predominantly involved in the N-dealkylation of benzphetamine, ephedrine, ivermectine or spiramycin.

Ontogenesis of rabbit liver cytochrome P450. Evidence for a cytochrome P450-IIE (3a)-related form prevailing during the post-natal period

The liver hydroxylating system, mainly composed of cytochromes P450, is not highly active during foetal life. If develops after birth and reaches the adult level several weeks post-partum. We have studied the ontogenesis of rabbit cytochrome P450 during the post-natal period. Total P450 as well as isozymes 2, 3b, 3c, 4 and 6 were measured. The evolution of these proteins with ageing, together with qualitative modification of an electrophoretic profile, produced evidence of an early developing P450 prevailing from one week to three weeks after birth. We isolated and characterized a cytochrome, called P450 2y, from two-week liver microsomes. It is closely related to P450 3a, an adult form of rabbit P450 induced by ethanol. They have similar molecular masses, the same lambda max of CO-reduced spectrum and exhibit immunological cross-reactivity. However, we cannot conclude that the two proteins are identical from N-terminal amino acid analysis or the two-dimensional gel electrophoresis pattern. These results, as well as the recent evidence of two different genes coding for the P450 3a family, strengthen the idea that P450 2y and 3a are distinct proteins. P450 2y seems to be an early developing form abundant soon after birth, while P450 3a is a delayed form appearing like most P450 isozymes during the fourth post-natal week. Besides the quantitative development during perinatal life, there is an important qualitative modification of liver cytochrome P450 content.