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Objective: To investigate the ability of the novel proton pump inhibitor rabeprazole to induce cytochrome P450 (CYP) isoenzymes and inhibit CYP3A-mediated cyclosporin metabolism in vitro. Methods: Microsomes were isolated from cultured human hepatocytes that were incubated with rabeprazole, omeprazole and reference CYP1A2 and CYP3A4 inducers. CYP1A2, CYP2D6, CYP2E1 and CYP3A4 were determined by Western blot analysis, and CYP1A and CYP3A monoxygenase activity were determined by enzyme assays. The metabolism of cyclosporin by human liver microsomes in the presence and absence of rabeprazole and omeprazole were also compared. Results: Rabeprazole (50 µmol/L) did not induce accumulation of CYP1A2 or increase CYP1A monoxygenase activity in cultured human hepatocytes, whereas omeprazole (50 µmol/L) induced both CYP1A2 accumulation and its associated monoxygenase activity. Rabeprazole modestly induced CYP3A4 and the associated monoxygenase activity in one of three hepatocyte cultures, whereas omeprazole induced CYP3A4 in all three cultures and monoxygenase activity in one culture. At high drug concentrations, both rabeprazole and omeprazole inhibited cyclosporin metabolism by human liver microsomes in a concentration-dependent manner; the concentration of drug that inhibited cyclosporin metabolism by 50% (IC) values were 62 and 101 µmol/L, respectively. Conclusions: Rabeprazole may have lower potential than omeprazole for causing CYP-mediated drug interactions, inasmuch as it does not induce CYP1A2 and only modestly induces CYP3A4 at high concentrations. At concentrations above what would be expected in humans with a 20mg dose, rabeprazole, like omeprazole, inhibits CYP3A-mediated cyclosporin metabolism. [ABSTRACT FROM AUTHOR]

Type I interferons (IFN) are cytokines that are rapidly secreted upon microbial infections and regulate all aspects of the immune response. In humans 15 type I IFN subtypes exist, of which IFN α2 and IFN β are used in the clinic for treatment of different pathologies. IFN α2 and IFN β are non redundant in their expression and in their potency to exert specific bioactivities. The more recently identified type III IFNs (3 IFN λ or IL-28/IL-29) bind an unrelated cell-type restricted receptor. Downstream of these two receptor complexes is a shared Jak/Stat pathway. Several mechanisms that contribute to the shut down of the IFN-induced signaling have been described at the molecular level. In particular, it has long been known that type I IFN induces the establishment of a desensitized state. In this work we asked how the IFN-induced desensitization integrates into the network built by the multiple type I IFN subtypes and type III IFNs. We show that priming of cells with either type I IFN or type III IFN interferes with the cell's ability to further respond to all IFN α subtypes. Importantly, primed cells are differentially desensitized in that they retain sensitivity to IFN β. We show that USP18 is necessary and sufficient to induce differential desensitization, by impairing the formation of functional binding sites for IFN α2. Our data highlight a new type of differential between IFNs α and IFN β and underline a cross-talk between type I and type III IFN. This cross-talk could shed light on the reported genetic variation in the IFN λ loci, which has been associated with persistence of hepatitis C virus and patient's response to IFN α2 therapy.

Coagulation is the complex process by which activation of plasmatic haemostasis proteins ends up with the generation of fibrin. Most of the plasma coagulation proteins are synthesized in hepatocytes. The aim of this chapter is to describe experimental procedures allowing to measure the secretion by primary human hepatocytes and functional activity (including production of fibrillar material from extracellular medium) of haemostasis proteins including factors II, V, VII, VIII, PIVKA-II (protein induced by vitK 1 absence or antagonist II), antithrombin and protein S. In addition, we show how treatments of hepatocyte cultures with vitamin K and/or warfarin affect the secretion of haemostasis proteins. The results demonstrate that primary cultures of human hepatocytes constitute an invaluable model for investigating haemostasis protein expression and activity and therapeutic strategies targeting these proteins.

Investigations on the biology of hepatitis C virus (HCV) have been hampered by the lack of small animal models. Efforts have therefore been directed to designing practical and robust cellular models of human origin able to support HCV replication and production in a reproducible and physiologically pertinent manner. Different systems have been constructed based on hepatoma or other cell lines, sub-genomic and genomic replicons, productive replicons, and immortalized hepatocytes. Although these models are practical for high-throughput screenings, they present several drawbacks related to the nature of the virions and the fact that the cells are not differentiated. Adult primary human hepatocytes infected with natural serum-derived HCV virions represent the model that most closely mimics the physiological situation. This chapter describes our experience with this culture model.

Investigations on the biology of hepatitis C virus (HCV) have been hampered by the lack of small animal models. Efforts have therefore been directed to designing practical and robust cellular models of human origin able to support HCV replication and production in a reproducible, reliable and consistent manner. Many different models based on different forms of virions and hepatoma or other cell types have been described including virus-like particles, pseudotyped particles, subgenomic and full length replicons, virion productive replicons, immortalised hepatocytes, fetal and adult primary human hepatocytes. This review focuses on these different cellular models, their advantages and disadvantages at the biological and experimental levels, and their respective use for evaluating the effect of antiviral molecules on different steps of HCV biology including virus entry, replication, particles generation and excretion, as well as on the modulation by the virus of the host cell response to infection.

Hepatitis C virus-positive serum (HCVser, genotypes 1a to 3a) or HCV cell culture (JFH1/HCVcc) infection of primary normal human hepatocytes was assessed by measuring intracellular HCV RNA strands. Anti-CD81 antibodies and siRNA-CD81 silencing markedly inhibited (>90%) HCVser infection irrespective of HCV genotype, viral load, or liver donor, while hCD81-large intracellular loop (LEL) had no effect. However, JFH1/HCVcc infection of hepatocytes was modestly inhibited (40 to 60%) by both hCD81-LEL and anti-CD81 antibodies. In conclusion, CD81 is involved in HCVser infection of human hepatocytes, and comparative studies of HCVser versus JFH1/HCVcc infection of human hepatocytes and Huh-7.5 cells revealed that the cell-virion combination is determinant of the entry process.

Background/aims: The direct implication of low-density lipoprotein receptor (LDLR) in hepatitis C virus (HCV) infection of human hepatocyte has not been demonstrated. Normal primary human hepatocytes infected by serum HCV were used to document this point., Methods: Expression and activity of LDLR were assessed by RT-PCR and LDL entry, in the absence or presence of squalestatin or 25-hydroxycholesterol that up- or down-regulates LDLR expression, respectively. Infection was performed in the absence or presence of LDL, HDL, recombinant soluble LDLR peptides encompassing full-length (r-shLDLR4-292) or truncated (r-shLDLR4-166) LDL-binding domain, monoclonal antibodies against r-shLDLR4-292, squalestatin or 25-hydroxycholesterol. Intracellular amounts of replicative and genomic HCV RNA strands used as end point of infection were assessed by RT-PCR., Results: r-shLDLR4-292, antibodies against r-shLDLR4-292 and LDL inhibited viral RNA accumulation, irrespective of genotype, viral load or liver donor. Inhibition was greatest when r-shLDLR4-292 was present at the time of inoculation and gradually decreased as the delay between inoculation and r-shLDLR4-292 treatment increased. In hepatocytes pre-treated with squalestatin or 25-hydroxycholesterol before infection, viral RNA accumulation increased or decreased in parallel with LDLR mRNA expression and LDL entry., Conclusions: LDLR is involved at an early stage in infection of normal human hepatocytes by serum-derived HCV virions.

The constitutive androstane receptor (CAR) and the pregnane X receptor (PXR) play a major part in the control of drug metabolism and transport. We have previously shown that PXR and CAR expression is controlled by the glucocorticoid receptor (GR) and proposed the existence of a signal transmission cascade GR-(PXR/CAR)-drug metabolizing and transporter systems. In the current study, we investigated the effect of ketoconazole and other azole-derived drugs, miconazole and fluconazole, on the transcriptional activity of the human GR (hGR) in HeLa and HepG2 cells, and in primary human hepatocytes. The data show that ketoconazole inhibits GR transcriptional activity and competes with dexamethasone for hGR binding. In primary human hepatocytes, ketoconazole inhibits the expression of 1) GR-responsive genes tyrosine aminotransferase and both PXR and CAR; 2) CAR and PXR target genes, including cytochromes P450 (P450) CYP2B6, CYP2C9, and CYP3A4; UDP-glucuronosyltransferase 1A1, glutathione S-transferases A1 and A2; and transporter proteins (phase III) solute carrier family 21 form A6 and multidrug resistance protein 2. In parallel experiments, ketoconazole affected neither the expression of GR, the expression of glyceraldehyde-3-phosphate dehydrogenase, nor the inducible expression of CYP1A1 and 1A2. Miconazole behaved like ketoconazole, whereas fluconazole had no effect. We conclude that, in addition to their well known inhibitory effect on P450 enzyme activities, ketoconazole and miconazole are antagonists of hGR. These results provide a novel molecular mechanism by which these compounds may exert adverse and toxic effects on drug metabolism and other functions in human.

Cross-talk between nuclear receptors involved in the control of drug metabolism is being increasingly recognised as a source of drug side effects. Omeprazole is a well known activator of the aryl hydrocarbon receptor (AhR). We investigated the regulation of AhR by omeprazole-sulphide, a degradation metabolite of omeprazole, using CYP1A mRNA induction, reporter gene assay, receptor DNA binding, ligand binding, nuclear translocation, trypsin digests, and drug metabolism analysis in mouse Hepa-1c1c7, human HepG2 cells and primary human hepatocytes. Omeprazole-sulphide is a pure antagonist of AhR in Hepa-1c1c7 and HepG2 hepatoma cell lines. In Hepa-1c1c7 cells, omeprazole-sulphide is a ligand of AhR, inhibits AhR activation to a DNA-binding form, induces a specific pattern of AhR trypsin digestion and inhibits AhR nuclear translocation and subsequent degradation in response to 2,3,7,8-tetrachlorodibenzo-p-dioxin. However, in highly differentiated primary human hepatocytes treated with rifampicin an agonist of the pregnane X receptor (PXR), omeprazole-sulphide behaves as an agonist of AhR. Inhibition of drug metabolizing enzymes by ketoconazole restores the antagonist effect of omeprazole-sulphide. Metabolic LC/MS analysis reveals that omeprazole-sulphide (AhR antagonist) is efficiently converted to omeprazole (AhR activator) by cytochrome P450 CYP3A4, a target gene of PXR, in primary human hepatocytes but not in hepatoma cells in which PXR is not expressed. This report provides the first evidence for a cross-talk between PXR/CYP3A4 and AhR. In addition, it clearly shows that conclusions drawn from experiments carried out in cell lines may lead to erroneous in vivo predictions in man.

This study was designed to investigate the ability of long-term primary cultures of adult human hepatocytes to secrete the main haemostasis proteins. Factors II, V, VII, VIII, PIVKA-II (protein induced by vitamin K 1 absence or antagonist II), fibrinogen and antithrombin were quantified in culture medium by immunological methods and by measuring the coagulant activity of factors II, V and VII. All the haemostasis protein antigens except the factor VIII antigen (FVIII:Ag) were found in the culture medium throughout the culture period. The clotting activity of each factor correlated well with antigen level. In addition, fibrinogen and fibrin were detected in the fibrillar material following incubation of the culture medium with thromboplastin. Moreover, adding vitamin K 1 to the culture medium resulted in a significant increase of factors II and VII and a reciprocal decrease of the PIVKA-II, and adding von Willebrand factor resulted in a drastic increase of the level of FVIII:Ag. We conclude that, in our culture system, normal adult human hepatocytes retain their capacity to secrete haemostasis proteins for at least 30 days.

Identification of cytochrome P-450 isoenzymes (CYPs) involved in perazine 5-sulphoxidation and N-demethylation was carried out using human liver microsomes and cDNA-expressed human CYPs (Supersomes). In human liver microsomes, the formation of perazine metabolites correlated significantly with the level of CYP1A2 and ethoxyrezorufin O-deethylase activity, as well as with the level of CYP3A4 and cyclosporin A oxidase activity. Moreover, the formation of N-desmethylperazine also correlated well with S-mephenytoin 4'-hydroxylase activity (CYP2C19). alpha-Naphthoflavone (a CYP1A2 inhibitor) and ketoconazole (a CYP3A4 inhibitor) significantly decreased the rate of perazine 5-sulphoxidation, while ticlopidine (a CYP2C19 inhibitor) strongly reduced the rate of perazine N-demethylation in human liver microsomes. The cDNA-expressed human CYPs generated different amounts of perazine metabolites, but the preference of CYP isoforms to catalyze perazine metabolism was as follows (pmol of product/pmol of CYP isoform/min): 1A1>2D6>2C19>1A2>2B6>2E1>2A6 approximately 3A4>2C9 for 5-sulphoxidation and 2C19>2D6>1A1>1A2>2B6>3A4>2C9>2A6 for N-demethylation. In the light of the obtained results and regarding the contribution of each isoform to the total amount of CYP in human liver, it is concluded that CYP1A2 and CYP3A4 are the main isoenzymes catalyzing 5-sulphoxidation (32% and 30%, respectively), while CYP2C19 is the main isoform catalyzing perazine N-demethylation (68%). CYP2C9, CYP2E1 CYP2C19 and CYP2D6 are engaged to a lesser degree in 5-sulphoxidation, while CYP1A2, CYP3A4 and CYP2D6 in perazine N-demethylation (6-10%, depending on the isoform).

The olivacine derivative 9-hydroxy-5,6-dimethyl-N-[2-(dimethylamino)ethyl)-6H-pyrido(4,3-b)-carbazole-1-carboxamide (S 16020) exhibits a potent antitumor activity. However, when administered in cancer patients, its blood clearance increases after repeated administrations, whereas the volume of distribution remains constant, suggesting that the drug is able to induce its own metabolism. The aim of this work was to identify the enzymes involved in S 16020 metabolism and determine whether this molecule is an enzyme inducer in human hepatocytes in primary cultures. Among a battery of cDNA-expressed cytochromes P450 (P450s) and flavin monooxygenase (FMO), only CYP1A1, CYP1A2, and FMO3 were able to generate detectable amounts of metabolites of S 16020. In primary hepatocytes, S 16020 behaved as a CYP1A inducer, producing an increase in CYP1A2 protein, acetanilide 4-hydroxylation, ethoxyresorufin O-deethylation, and chlorzoxazone 6-hydroxylation to an extent similar to that of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a prototypical CYP1A inducer. The levels of other P450 proteins, including CYP2A6, CYP2B6, CYP2C9, CYP2C19, CYP2E1, and CYP3A4, and related activities were not affected by S 16020. In primary hepatocytes, pretreatment of cells with S 16020 or TCDD produced a significant and similar increase of S 16020 metabolism, consistent with the previous indications on the role of CYP1As. We conclude that CYP1As and FMO3 are the major phase I enzymes involved in the metabolism of S 16020 and that this molecule is a potent hydrocarbon-like inducer able to stimulate its own metabolism in primary human hepatocytes and liver.

The metabolism of perazine in a primary culture of human hepatocytes after treatment of cells with TCDD (a CYP1A1/2 inducer) or rifampicin (mainly a CYP3A4 inducer) were studied in vitro. The concentrations of perazine and its main metabolites (perazine 5-sulfoxide, N-desmethylperazine) formed in hepatocytes were assayed in the extracellular medium using the HPLC method. TCDD and rifampicin induced the formation of perazine 5-sulfoxide, however, such an effect was not observed in the case of N-desmethylperazine. The accumulation of perazine 5-sulfoxide in the extracellular medium was enhanced until up to 4 h by rifampicin, and until up to 8 h byTCDD. After 24 h, perazine and perazine 5-sulfoxide were not detected in the extracellular medium of the inducer-treated cultures, except for perazine 5-sulfoxide in the TCDD-treated cultures The obtained results indicate that CYP1A2 and CYP3A4 are involved in the perazine metabolism via 5-sulfoxidation pathway.

The xenobiotic-mediated induction of three major human liver cytochrome P450 genes, CYP2B6, CYP2C9, and CYP3A4, is known to be regulated by the constitutive androstane receptor (CAR) and the pregnane X receptor (PXR). CAR and PXR are regulated, at least in part, by the glucocorticoid receptor (GR) and the hypothesis of a signal transduction cascade GR-[CAR/PXR]-P450 has been proposed. This study was aimed at testing this hypothesis in primary human hepatocytes by using the tubulin network disrupting agent colchicine. Colchicine (COL) decreased both basal and rifampicin- and phenobarbital-inducible expression of CYP2B6, CYP2C8/9, and CYP3A4. A parallel down-regulation of mRNA expression of CAR, PXR, and tyrosine aminotransferase, a prototypic gene directly regulated by GR, was observed. COL affected neither the level of GR mRNA nor ligand binding to GR. To evaluate the effect of colchicine on GR-mediated gene transactivation, HeLa cells stably or transiently transfected with a GR-responsive element-dependent luciferase reporter gene were used. COL decreased the dexamethasone-induced luciferase expression in stably transfected cell line by 50%, whereas GR transactivation in transiently transfected cells was not affected by COL. In contrast, ligand-dependent GR translocation in the human embryonic kidney 293 cell line transiently transfected with GFP-GR was inhibited by COL. We conclude that alteration of the signal transduction mediated through the GR-[CAR/PXR]-P450 cascade by colchicine is responsible for the down-regulation of CYP2C9 and CYP3A4, implicating cytoskeleton as necessary for correct functioning of this cascade under physiological conditions.

The metabolism of the nonsteroidal antiinflammatory drug flobufen, 4-(2',4'-difluorobiphenyl-4-yl)-2-methyl-4-oxobutanoic acid, was studied in primary cultures of human hepatocytes prepared by two-step collagenase perfusion of livers from four donors. Racemic flobufen or its individual enantiomers, R-(+)- and S-(-)-flobufen were used as substrates. Aliquots of culture medium were collected during 24-h incubation. The time-dependent disappearance of flobufen enantiomers and the formation of metabolites (stereoisomers of dihydroflobufen (DHF)) in hepatocytes were measured by chiral HPLC. The reduction of flobufen in human hepatocytes was stereoselective ((+)-R-flobufen was preferentially metabolized) and stereospecific ((2R;4S)-DHF and (2S;4S)-DHF stereoisomers were mostly formed). Although the structure of flobufen is different from the profens (2-arylpropionates), flobufen undergoes chiral inversion in human hepatocytes. The inversion of R-(+)-flobufen to S-(-)-flobufen predominates. The individual DHF stereoisomers were incubated in hepatocyte cultures and their biotransformation studied. The unidirectional chiral inversion of (2S;4S)-DHF to (2R;4S)-DHF and (2R;4R)-DHF to (2S;4R)-DHF was observed. Stereoselective oxidation of the DHFs to flobufen was also detected. Thus, flobufen metabolism in primary cultures of human hepatocytes is much more complicated (via chiral inversion and DHF re-oxidation) than was presumed from a preliminary achiral point of view., (Copyright 2003 Wiley-Liss, Inc.)

1. The aim of the present study was to identify human cytochrome p-450 isoforms (CYPs) involved in 5-sulphoxidation and N-demethylation of the simplest phenothiazine neuroleptic promazine in human liver. 2. The experiments were performed in the following in vitro models: (A). a study of promazine metabolism in liver microsomes-(a). correlations between the rate of promazine metabolism and the level and activity of CYPs; (b). the effect of specific inhibitors on the rate of promazine metabolism (inhibitors: CYP1A2-furafylline, CYP2D6-quinidine, CYP2A6+CYP2E1-diethyldithiocarbamic acid, CYP2C9-sulfaphenazole, CYP2C19-ticlopidine, CYP3A4-ketoconazole); (B). promazine biotransformation by cDNA-expressed human CYPs (Supersomes 1A1, 1A2, 2A6, 2B6, 2C9, 2C19, 2E1, 3A4); (C). promazine metabolism in a primary culture of human hepatocytes treated with specific inducers (rifampicin-CYP3A4, CYP2B6 and CYP2C inducer, 2,3,7,8-tetrachlordibenzeno-p-dioxin (TCDD)-CYP1A1/1A2 inducer). 3. In human liver microsomes, the formation of promazine 5-sulphoxide and N-desmethylpromazine was significantly correlated with the level of CYP1A2 and ethoxyresorufin O-deethylase and acetanilide 4-hydroxylase activities, as well as with the level of CYP3A4 and cyclosporin A oxidase activity. Moreover, the formation of N-desmethylpromazine was correlated well with S-mephenytoin 4'-hydroxylation. 4. Furafylline (a CYP1A2 inhibitor) and ketoconazole (a CYP3A4 inhibitor) significantly decreased the rate of promazine 5-sulphoxidation, while furafylline and ticlopidine (a CYP2C19 inhibitor) significantly decreased the rate of promazine N-demethylation in human liver microsomes. 5. The cDNA-expressed human CYPs generated different amounts of promazine metabolites, but the rates of CYP isoforms to catalyse promazine metabolism at therapeutic concentration (10 microM) was as follows: 1A1>2B6>1A2>2C9>3A4>2E1>2A6>2D6>2C19 for 5-sulphoxidation and 2C19>2B6>1A1>1A2>2D6>3A4>2C9>2E1>2A6 for N-demethylation. The highest intrinsic clearance (V(max)/K(m)) was found for CYP1A subfamily, CYP3A4 and CYP2B6 in the case of 5- sulphoxidation, and for CYP2C19, CYP1A subfamily and CYP2B6 in the case of N-demethylation. 6. In a primary culture of human hepatocytes, TCDD (a CYP1A subfamily inducer), as well as rifampicin (mainly a CYP3A4 inducer) induced the formation of promazine 5-sulphoxide and N-desmethylpromazine. 7. Regarding the relative expression of various CYPs in human liver, the obtained results indicate that CYP1A2 and CYP3A4 are the main isoforms responsible for 5-sulphoxidation, while CYP1A2 and CYP2C19 are the basic isoforms that catalyse N-demethylation of promazine in human liver. Of the other isoforms studied, CYP2C9 and CYP3A4 contribute to a lesser degree to promazine 5-sulphoxidation and N-demethylation, respectively. The role of CYP2A6, CYP2B6, CYP2D6 and CYP2E1 in the investigated metabolic pathways of promazine seems negligible.

Benfluron (B, [5-(2-N-oxo-2-N',N"-dimethylaminoethoxy)-7-oxo-7H-benzo[c]fluorene]) is a potential benzo[c]fluorene antineoplastic agent with high activity against a broad spectrum of experimental tumors in vitro and in vivo. The structure of B has been modified to repress its rapid deactivation through carbonyl reduction on C7. 3,9-Dimethoxybenfluron (D, [3,9-dimethoxy-5-(2-N-oxo-2-N',N"-dimethylaminoethoxy)-7-oxo-7H-benzo[c]fluorene]) is one of the B derivatives developed. The present paper was designed to compare the C7 carbonyl reduction of B and D in microsomes, cytosol and hepatocytes from human liver. Two purified human enzymes, microsomal 11beta-hydroxysteroid dehydrogenase 1 (11beta-HSD 1) and cytosolic carbonyl reductase, were tested if they are responsible for B and D carbonyl reduction in the respective fractions. Indeed, carbonyl reduction of D in comparison to that of B was 4 and 6-10 times less extensive in human liver microsomes and cytosol, respectively. Moreover, about 10-20 times higher amounts of dihydro B than dihydro D were detected in primary culture of human hepatocytes. 11beta-HSD 1 was shown to be able to reduce B and D. For this enzyme, about 10 times higher rates of carbonyl reduction were observed for B than for D. Likewise, CR participates in B and D carbonyl reduction, although smaller amounts of both reduced metabolites were detected. In summary, carbonyl reduction of D was significantly less extensive than that of B in all in vitro experiments. This lower rate of D inactivation was especially pronounced in hepatocytes which represent a close to in vivo situation. Our results clearly demonstrate that dimethoxy substitution protects the carbonyl group of the benzo[c]fluorene moiety against the deactivation by microsomal and cytosolic reductases. Detailed knowledge on the participating enzymes may serve as a basis for the co-application of specific inhibitors in chemotherapy to further improve the pharmacokinetics of benzo[c]fluorene derivatives.

The effects of perazine on the activities of CYP1A2 and CYP3A4 in a primary culture of human hepatocytes of one patient were studied in vitro. The CYPs activities were assessed by measuring the rate of acetanilide 4-hydroxylation (CYP1A2) and cyclosporine A oxidation (CYP3A4) after treatment with TCDD (a CYP1A subfamily inducer) or rifampicin (mainly a CYP3A4 inducer). The amounts of the metabolites formed in hepatocytes were assayed in the extracellular medium using the HPLC method. TCDD and rifampicin induced the formation of 4-hydroxyacetanilide and cyclosporine A metabolites (monohydroxycyclosporine A, dihydroxycyclosporine A, N-desmethylcyclosporine A), respectively. The formation of 4-hydroxyacetanilide was strongly inhibited by three different concentrations of perazine (10, 25 and 50 microM) reaching 8, 3 and 2% of the control value, respectively. In the case of CYP3A4 activity, no such an effect of perazine was observed. Perazine showed only a week inhibition of the activity of cyclosporine A oxidase (to 96-86% of the control value). The obtained results suggest a strong inhibitory effect of perazine on human CYP1A2 activity with predicted Ki value similar to those of the known for CYP1A2 inhibitors, such as furafylline and fluvoxamine.

Although cytochrome P450 2C9 (CYP2C9) is a major CYP expressed in the adult human liver, its mechanism of regulation is poorly known. In previous work, we have shown that CYP2C9 is inducible in primary human hepatocytes by xenobiotics including dexamethasone, rifampicin, and phenobarbital. The aim of this work was to investigate the molecular mechanism(s) controlling the inducible expression of CYP2C9. Deletional analysis of CYP2C9 regulatory region (+21 to -2088) in the presence of various hormone nuclear receptors suggested the presence of two functional response elements, a glucocorticoid receptor-responsive element (-1648/-1684) and a constitutive androstane receptor-responsive element (CAR, -1783/-1856). Each of these were characterized by co-transfection experiments, directed mutagenesis, gel shift assays, and response to specific antagonists RU486 and androstanol. By these experiments we located a glucocorticoid-responsive element imperfect palindrome at -1662/-1676, and a DR4 motif at -1803/-1818 recognized and transactivated by human glucocorticoid receptor and by hCAR and pregnane X receptor, respectively. Identification of these functional elements provides rational mechanistic basis for CYP2C9 induction by dexamethasone (submicromolar concentrations), and by phenobarbital and rifampicin, respectively. CYP2C9 appears therefore to be a primary glucocorticoid-responsive gene, which in addition, may be induced by xenobiotics through CAR/pregnane X receptor activation.

The expression and inducibility of four CYP2C genes, including CYP2C8, -2C9, -2C18, and -2C19, was investigated in primary cultures of human hepatocytes. By the use of RNase protection assay and specific antibodies, each CYP2C mRNA and protein were quantified unequivocally. The four CYP2C mRNAs were expressed in human livers and cultured primary hepatocytes, but only the CYP2C18 protein was not detected. Compounds known to activate the pregnane X receptor (PXR) such as rifampicin, or the constitutively activated receptor (CAR) such as phenobarbital, induced CYP2C8, CYP2C9, and to a lesser extent CYP2C19 mRNAs and proteins. CYP2C18 mRNA was expressed but not inducible. The concentration dependence of CYP2C8 and CYP2C9 mRNAs in response to rifampicin and phenobarbital paralleled that of CYP3A4 and CYP2B6, the maximum accumulation being reached with 10 microM rifampicin and 100 microM phenobarbital. In contrast, dexamethasone produced maximum induction of CYP2C8 and CYP2C9 mRNAs at 0.1 microM while in these conditions neither CYP3A4 nor CYP2B6 was significantly induced. Moreover, the concentration dependence of CYP2C8 and CYP2C9 mRNAs in response to dexamethasone paralleled that of tyrosine aminotransferase. Furthermore, dexamethasone, which has been recently shown to up-regulate PXR and CAR expression through the glucocorticoid receptor, potentiated CYP2C8 and CYP2C9 mRNA induction in response to rifampicin and phenobarbital. Collectively, these results suggest the possible implication of at least three receptors in the regulation of CYP2C8 and CYP2C9 expression, i.e., glucocorticoid receptor, PXR, and/or CAR.

The marked impairment of hepatic drug metabolism during inflammation and infections has been known for many years and shown to result from down-regulation of cytochrome P450s (CYP) by cytokines. However, the mechanism of this repression is unknown. Using primary cultures of human hepatocytes, we show here that interleukin-6 (IL-6) rapidly and markedly decreases the expression of PXR (pregnane X receptor) and CAR (constitutively activated receptor) mRNAs, but does not affect the levels of dioxin receptor and glucocorticoid receptor mRNA. In parallel, IL-6 decreases both rifampicin- and phenobarbital-mediated induction of CYP2B6, CYP2C8, CYP2C9, and CYP3A4. As the transcriptional activity of PXR and CAR is not affected by IL-6 in cell-based reporter assays, our data suggest that the loss of CYP2 and CYP3 inducibility results from the negative regulation of PXR and CAR gene expression by this cytokine., (Copyright 2000 Academic Press.)

Eletriptan (Relpax) is a novel 5-hydroxytryptamine (serotonin)(1D/1B) agonist currently in development for the acute treatment of migraine. The aim of this work was to evaluate the relative induction potency of eletriptan in vitro compared with well characterized cytochrome P-450 (CYP) inducers with primary cultures of human hepatocytes and to relate this to the situation in vivo. Eletriptan was a weak inducer of CYP3A4 protein and cyclosporin A oxidation in four of the six cultures used, whereas rifampicin was a potent inducer in all cultures. Induction was concentration dependent and not detectable at eletriptan concentrations of 5 microM and lower. The amplitude of the increase in CYP3A4 protein and activity by 25 microM eletriptan was significantly lower, with a mean of 19 (P =.0015) and 26% (P =.0002), respectively, of that observed in response to 25 microM rifampicin. CYP2A6, a protein with minor pharmacological implication, also was induced by eletriptan and rifampicin in two cultures but was not detected in the others. The levels of other CYP proteins, including CYP1A2, CYP2C9, CYP2C19, CYP2D6, and CYP2E1, were not affected by eletriptan. Because the maximum blood concentration of eletriptan in humans after a therapeutic dose (maximum 80 mg) is 0.5 microM, the in vitro model would predict no clinically significant induction of CYP3A4 protein in vivo. This has been confirmed subsequently in a clinical study, with 6beta-hydroxycortisol/cortisol ratios as marker of CYP3A4 activity. Eletriptan is therefore not an inducer of CYP3A4 at clinical doses.