Expression of cytochromes P450 3A in mouse lung: effects of dexamethasone and pregnenolone 16alpha-carbonitrile

Expression of cytochromes P450 3A (CYP3A) has been reported in the lung, but its regulation has received little attention. In the present study, we assessed lung levels of Cyp3a mRNA, protein and activity in control mice and in mice treated with either dexamethasone (DEX), pregnenolone 16alpha-carbonitrile (PCN) or a mixture of DEX+PCN. Lung expression of the pregnane X receptor (PXR) was also investigated. Constitutive levels of Cyp3a mRNA were found in the lung from control mice by polymerase chain reaction after reverse transcription of total RNA (RT-PCR). These levels were significantly increased (2.0-fold, P<0.05) in mice treated with DEX and further enhanced (2.7-fold increase, P<0.01) in mice treated with DEX+PCN. In control mice, basal levels of Cyp3a protein and activity were also found, as assessed by western blot and measure of testosterone 6beta-hydroxylation, respectively. In mice treated with DEX or DEX+PCN, changes in Cyp3a protein and activity exhibited the same pattern as those in Cyp3a mRNA. In contrast, PCN alone failed to trigger consistent increases in lung Cyp3a mRNA, protein and activity. PXR mRNA was not detected in the lung from control or PCN-treated mice by RT-PCR, but was found at significant levels in the lungs from mice treated with DEX or DEX+PCN. Our results show that expression of Cyp3a is upregulated by glucocorticoids in mouse lung, and that this effect is potentiated by antiglucocorticoids. This potentiation may involve PXR, expression of which is induced in the lung of glucocorticoid-treated mice.

Inhibition of cytochrome P450 2E1 by propofol in human and porcine liver microsomes

While almost anesthetics are metabolized by the cytochrome P450 (CYP) 3A4, some major volatile ones such as halothane and sevoflurane are metabolized by CYP2E1 in humans. To determine whether 2,6-diisopropylphenol (propofol), a widely used intravenous anesthetic agent, known to inhibit CYP3A4 and CYP1A2, also inhibits CYP2E1, 6-OH hydroxylation of chlorzoxazone, a prototypical CYP2E1 substrate, was estimated using two pools of human microsomes and one pool of porcine microsomes from seven livers. Basal human enzyme activities were characterized by a V(max) of 1426+/-230 and 288+/-29 pmol min(-1)mg(-1) protein and a K(m) of 122+/-47 and 149+/-42 microM, while the corresponding porcine activities were associated with a V(max) of 352+/-42 pmol min(-1)mg(-1) protein and a K(m) of 167+/-38 microM. A competitive inhibition of CYP2E1 by propofol was observed with low inhibition constants in the therapeutic range in both porcine (19 microM) and human (48 microM) liver microsomes. These in vitro results suggest that propofol could have a protective effect on toxic metabolite activation of compounds catalyzed by CYP2E1.

Investigations on the effects of oltipraz on the nucleotide excision repair in the liver

Recent studies support the view that in addition to its effect on both phase I and phase II xenobiotic metabolizing enzymes, the synthetic chemopreventive agent oltipraz also increases the nucleotide excision repair (NER) which represents the major pathway of elimination of chemical carcinogen DNA adducts. Since most carcinogens are activated in the liver, we investigated the influence of oltipraz on NER activity of this target tissue by using two different approaches. First, we employed an assay based on the measurement of DNA repair in cisplatin-damaged plasmid DNA incubated in the presence of cell-free extracts prepared from either rat liver or human hepatoma HepG2 cells treated by oltipraz. Secondly, we analyzed the removal of aflatoxin B(1)-derived DNA adducts formed in primary human hepatocytes exposed to oltipraz after treatment with this mycotoxin. Whatever the strategy used, NER activity was not altered in liver cells. These data demonstrated that liver cells actively repair bulky DNA adducts by NER and that oltipraz does not influence their NER activity neither in vivo nor in vitro, consequently strongly suggesting that the chemopreventive agent oltipraz is acting before the initiation step of cancer development.

Phenobarbital induction of aldehyde dehydrogenase type 2 mRNA in mouse liver: a candidate region on chromosome 7 for a putative regulatory gene

Phenobarbital (PB) strongly induces in the liver the expression of many genes encoding detoxication enzymes, such as the aldehyde dehydrogenase type 2 in the mouse (Aldh2). With the aim of identifying genes involved in this response, we have undertaken an approach based on a genetic analysis in mice. In a previous report, the genetic analysis of both the C57BL/6J (B6) x DBA/2J (D2) F1 and the (F1 x F1) F2 led us to the hypothesis that Aldh2 responsiveness to PB was under the control of one major locus independent of the structural gene. In the present study, the genetic analysis of the inducibility by PB of Aldh2 in the backcross population B6D2F1 x D2 has allowed us to confirm the involvement of a major regulatory gene in this mechanism. By searching for genetic linkage between this locus and a series of microsatellites DNA markers, we obtained indicative evidence for a region on chromosome 7, which may carry this gene.

Regulation of phenobarbital induction of the cytochrome P450 2b9/10 genes in primary mouse hepatocyte culture. Involvement of calcium- and cAMP-dependent pathways

Phenobarbital (PB) has long been known as an inducer of drug-metabolizing enzymes in liver, but the molecular mechanism underlying this induction is still poorly understood. Using primary mouse hepatocyte culture, we have investigated the possible involvement of different regulatory pathways in PB action, by exposing PB-treated cells to various protein kinase/phosphatase modulators. Our results showed a negative role of the cAMP-dependent pathway, as treatment with cAMP-dependent protein kinase (PKA) activators (10 microM dibutyryl-cAMP and 50 microM forskolin) dramatically inhibited PB-induced Cyp2b9/10 mRNA accumulation, whereas PKA inhibitor potentiated the PB responsiveness of this gene. The cGMP-dependent protein kinase (PKG) seems to play a positive role as PKG inhibitor reduced the PB-induced level of Cyp2b9/10 mRNA. We also obtained two lines of evidence for the involvement of Ca2+ in modulating PB action. Firstly, measurements of intracellular Fura-2 fluorescence ratio in murine hepatocytes showed that long-term PB incubation (24 and 48 h) led to a significant increase of [Ca2+]i. Secondly, treatment with an intracellular Ca2+ chelator (BAPTA-AM) nearly completely abolished PB-induced Cyp2b9/10 expression. Ca2+ thus appeared to mediate PB action likely via Ca2+/calmodulin-dependent protein kinase II, as KN62, a specific inhibitor of this enzyme, also dramatically inhibited PB induction of the Cyp2b9/10 genes.

Involvement of cyclic nucleotide- and calcium-regulated pathways in phenobarbital-induced cytochrome P-450 3A expression in mouse primary hepatocytes

Several of the hepatic microsomal cytochromes P-450 (CYP) including CYP3A are inducible by phenobarbital (PB). However, the intracellular pathways involved in the action of PB on CYP3A remain poorly known. With the aim to unravel some of the main aspects of PB signaling, we first devised a simple model of mouse cultured primary hepatocytes in which CYP3A mRNA and protein were strongly induced by PB in the absence of dexamethasone and were at maximum levels after a 48-h treatment with a 2-mM dose of PB. Under these culture conditions, we studied the effects of inhibitors and activators of different protein kinases or phosphatases on CYP3A mRNA and protein induction by PB. CYP3A-induced expression was inhibited by activators of cyclic AMP-dependent protein kinase (PKA) (dibutyryl-cyclic AMP and forskolin) whereas inhibition of PKA by PKA inhibitor enhanced induction. 8-br-cGMP produced effects similar to the activators of PKA, and so did the specific inhibitor of cGMP-dependent protein kinase, beta-phenyl-1, N(2)-etheno-8-bromoguanosine-3,5'-cyclic monophosphorothioate, Rp-isomer (Rp-8-Br-PET-cGMPS). Inhibition of Ca(2+)/calmodulin-dependent protein kinase by KN-62 or the intracellular Ca(2+) chelator BAPTA-AM produced an inhibition of CYP3A induction by PB. Specific inhibitors of protein kinase C, mitogen-activated protein kinase kinase, phosphatidylinositol-3-kinase, or serine/threonine phosphatase did not produce any effect. Taken together, our results suggest that CYP3A induction by PB is regulated positively by calmodulin-dependent protein kinase and cGMP-dependent protein kinase, and negatively by PKA in mouse hepatocytes in primary culture.

Survival and function of isolated hepatocytes after cryopreservation

Cryopreservation in liquid nitrogen is presently the only way for long-term storage of isolated hepatocytes. Freeze-thaw conditions are not well defined yet; the most critical parameters appear to be the choice of the cryoprotectant, composition of the freezing medium, and cooling and thawing rates. Comparable results have been obtained with hepatocytes from various species, including man. Cryopreservation usually results in low cell recovery and early alterations of functional activities. However, both phase I and phase II xenobiotic metabolism is still active after thawing, at least during a short period. Moreover, survival and function of cryopreserved hepatocytes can be improved when these cells have a high energy status, are cryopreserved after immobilization in a gel, separated from dead cells on a Percoll gradient or placed in more favorable culture conditions (e.g. in coculture with liver non parenchymal cells). Additional studies are needed to improve freeze-thaw protocols and to better characterize liver parenchymal cells after storage, including evaluation of their responsiveness to specific inducers.

A multi-laboratory evaluation of cryopreserved monkey hepatocyte functions for use in pharmaco-toxicology

Ethical, economic and technical reasons hinder regular supply of freshly isolated hepatocytes from higher mammals such as monkey for preclinical evaluation of drugs. Hence, we aimed at developing optimal and reproducible protocols to cryopreserve and thaw parenchymal liver cells from this major toxicological species. Before the routine use of these protocols, we validated them through a multi-laboratory study. Dissociation of the whole animal liver resulted in obtaining 1-5 billion parenchymal cells with a viability of about 86%. An appropriate fraction (around 20%) of the freshly isolated cells was immediately set in primary culture and various hepato-specific tests were performed to examine their metabolic, biochemical and toxicological functions as well as their ultrastructural characteristics. The major part of the hepatocytes was frozen and their functionality checked using the same parameters after thawing. The characterization of fresh and thawed monkey hepatocytes demonstrated the maintenance of various hepato-specific functions. Indeed, cryopreserved hepatocytes were able to survive and to function in culture as well as their fresh counterparts. The ability for synthesis (proteins, ATP, GSH) and conjugation and secretion of biliary acids was preserved after deep freeze storage. A better stability of drug metabolizing activities than in rodent hepatocytes was observed in monkey. After thawing, Phase I and Phase II activities (cytochrome P450, ethoxycoumarin-O-deethylase, aldrin epoxidase, epoxide hydrolase, glutathione transferase, glutathione reductase and glutathione peroxidase) were well preserved. The metabolic patterns of several drugs were qualitatively and quantitatively similar before and after cryopreservation. Lastly, cytotoxicity tests suggested that the freezing/thawing steps did not change cell sensitivity to toxic compounds.

Isolation of a cyp2b10-like cDNA and of a clone derived from a cyp2b10-like pseudogene

By screening Balb/c male mouse liver cDNA library with a rat CYP2B1 cDNA probe, we have isolated a 1795 bp cyp2b10-like clone, referred to as P16. Its sequence exhibited 34 base differences (98% similarity) with the cyp2b10 published sequence, together with a 97% identity at the amino acid sequence level. By RT-PCR and PCR analyses with Balb/c female and male liver RNA and genomic DNA, using a region showing 8 base differences between the P16 and the cyp2b10 sequences, we have confirmed the identity of our cloned cDNA, and failed in finding a PCR product exhibiting a sequence 100% identical with that of cyp2b10. Our results therefore suggest that the P16 sequence is the authentic cyp2b10 sequence. We have also isolated a partial clone, P21, which 1609 bp sequence overlapped with that of P16, except for a T-->G transversion, giving rise to a premature TGA stop codon, indicating that it was derived from a pseudogene.

Phenobarbital induces cytochrome P4501A2 hnRNA, mRNA and protein in the liver of C57BL/6J wild type and aryl hydrocarbon receptor knock-out mice

The aryl hydrocarbon receptor mediates the transcriptional response to a variety of hydrocarbons of members of the aryl hydrocarbon gene battery. Phenobarbital does not bind the aryl hydrocarbon receptor with high affinity but induces, in liver cells, expression of cytochrome P4501A. Using both wild type and aryl hydrocarbon receptor knock out C57BL/6J mice, we demonstrate that phenobarbital induced hnRNA, mRNA and protein for the cytochrome P-4501A2 gene in the presence or absence of the aryl hydrocarbon receptor. Using the DNA binding site for the aryl hydrocarbon receptor as a probe, gel retardation analyses showed that phenobarbital treatment induced protein binding, regardless of the presence of the aryl hydrocarbon receptor.

Long-term maintenance of drug-metabolizing enzyme activities in rat hepatocytes after cryopreservation

Recent studies have demonstrated that freshly isolated adult hepatocytes from various species can be hypothermically preserved for a short period or cryopreserved for a prolonged period before seeding in primary culture. This study was designed to determine whether rat hepatocytes could be maintained functional for a prolonged period after either hypothermic preservation or cryopreservation. Cold storage was carried out in University of Wisconsin solution (UW) and freezing in Leibovitz medium added with 10% fetal calf serum and 16% dimethyl sulfoxide. Rat hepatocytes were then set up either in pure conventional culture or in coculture with rat liver epithelial cells. Various functions were measured over 4- and 15-day periods, i.e., albumin secretion rate, deethylation of ethoxyresorufin and phenacetin, dealkylation of pentoxyresorufin, glucuronidation and sulfoconjugation of paracetamol, and N-acetylation of procainamide. No major differences were observed between unfrozen, frozen, and UW-preserved cells. While in pure culture all the functions tested were markedly decreased after 3 or 4 days, they remained high over the 15-day period in coculture, being either maintained or increased after 7-12 days compared to initial values. These results clearly demonstrate that when maintained under suitable culture conditions, rat hepatocytes can fully recover after hypothermic preservation or cryopreservation and therefore represent a suitable in vitro model system for pharmacotoxicological studies.

Regulation of the major detoxication functions by phenobarbital and 3-methylcholanthrene in co-cultures of rat hepatocytes and liver epithelial cells

In the present study, we analysed the expression of monooxygenase activities and mRNAs associated with cytochrome P-450 (CYP), including CYP1A1/2, CYP2B1/2, CYP2C6, CYP2E1, CYP3A1/2, glutathione transferase alpha (GST alpha), aldehyde dehydrogenase and epoxide hydrolase in co-cultures of primary rat hepatocytes and rat liver epithelial cells. We observed that pentoxyresorufin O-deethylation activity was well maintained and ethoxyresorufin O-deethylation activity gradually decreased during co-culture time. In addition, we showed that phenobarbital and 3-methylcholanthrene treatments resulted in a significant increase of these activities. Two general patterns of accumulation of liver-specific mRNAs were observed. CYP1A1/2, CYP2B1/2, CYP3A1/2, GST alpha, aldehyde dehydrogenase and epoxide hydrolase mRNAs were maintained at a stable level, whereas CYP2C6 and CYP2E1 mRNAs showed a continuous decline. In addition, we observed a strong increase of CYP1A1/2 (13.6-fold) and GST alpha (3.9-fold) mRNA expression in 3-methylcholanthrene-treated co-cultures and induction of CYP2B1/2 (19-fold), CYP2C6 (10-fold), CYP3A1/2 (11.2-fold), GST alpha (9-fold), aldehyde dehydrogenase (6-fold) and epoxide hydrolase (5-fold) mRNA expression in phenobarbital-treated co-cultures. Furthermore, we demonstrated that liver-specific gene expression was restricted to hepatocytes, with the notable exception of epoxide hydrolase and CYP2E1 which were expressed in both cell types during the co-culture, as shown by the selective recovery of both hepatocytes and rat liver epithelial cells. Finally, to investigate whether co-cultures could be used to study the molecular mechanisms regulating CYP transcription, we performed transfection of hepatocytes, before the establishment of the co-culture, with large CYP2B1 (3.9 kb) or CYP2B2 (4.5 kb) promoter chloramphenicol acetyltransferase constructs or with a construct containing a 163-bp DNA sequence element reported to confer phenobarbital responsiveness. A 2-3-fold increase over the basal level of chloramphenicol acetyltransferase activity was observed in phenobarbital-treated co-cultures transfected with the phenobarbital-responsive element construct, although phenobarbital had no effect on large CYP2B1 or CYP2B2 promoter fragments. Our results demonstrate that the co-culture system provides a good tool for studying drug metabolism, and shows promise as a new tool for analysing transcriptional regulation under the influence of xenobiotics within primary hepatocytes.

Isolation of a new mouse cDNA clone: hybrid form of cytochrome P450 2b10 and NADPH-cytochrome P450 oxidoreductase

We have isolated a novel cDNA sequence from a male mouse liver library. It consists of an open reading frame containing no stop codon of 1348 bp which share 98% similarity with the cytochrome P450 2b10 followed by 95 nucleotides sharing 88% identity with the mouse NADPH cytochrome P450 oxidoreductase. Proteins are encoded by the opposite DNA strands. Genomic amplification excludes a library artefact or a de novo recombination event. RT-PCR analyses revealed expression of this clone in the liver of male and female mice as well as in kidney, lung and intestine. This cDNA was not, however, induced by phenobarbital. Preliminary results indicate that this cDNA could span more than 2.5 kb. This study is the first description of a cytochrome P450 cDNA sequence encoding part of both a cytochrome P450 and the NADPH cytochrome P450 oxidoreductase in mammalian liver.

Genetic analysis of the phenobarbital regulation of the cytochrome P-450 2b-9 and aldehyde dehydrogenase type 2 mRNAs in mouse liver

The aim of this study was to investigate the effect of the genetic background on the phenobarbital inducibility of cytochrome P-450 2b-9, cytochrome P-450 2b-10 and aldehyde dehydrogenase type 2 mRNAs in mice. We analysed the basal expression and the phenobarbital inducibility of both cytochrome P-450 mRNAs by semi-quantitative specific reverse transcription-PCR analyses in five inbred mouse strains (A/J,BALB/cByJ,C57BL/6J, DBA/2J and SWR/J). Male mice constitutively expressed cytochrome P-450 2b-9 and cytochrome P-450 2b-10 mRNAs, but a number of differences in their response to phenobarbital were observed. In all these mouse strains, phenobarbital induced cytochrome P-450 2b-10 mRNA whereas it could have either a positive or a negative effect on cytochrome P-450 2b-9 expression, depending on the strain and the sex of the mice. Specifically, phenobarbital increased cytochrome P-450 2b-9 expression in C57BL/6J males while it decreased it in DBA/2J mice. Interestingly, dexamethasone was able to mimic the phenobarbital effect on both cytochromes P-450 in these two strains. Aldehyde dehydrogenase type 2 mRNA was always induced by phenobarbital, except in the C57BL/6J strain. Genetic analysis revealed that the phenobarbital-inducible phenotype was either a semi-dominant or a recessive trait in F1 animals from a C57BL/6J x DBA/2J cross for the cytochrome P-450 2b-9 and the aldehyde dehydrogenase type 2 genes, respectively. This study suggests that the genetic basis for phenobarbital induction in mice depends on the target gene, and that more than one regulatory step would by involved in this response pathway.

trans-Acting factors, detoxication enzymes and hepatitis B virus replication in a novel set of human hepatoma cell lines

A panel of four novel human hepatoma cell lines was isolated from a single tumor from a male individual. BC1, B16 and B16A2 lines were well differentiated, while cells of the B9 line were only poorly differentiated, being essentially negative for the functions analyzed. These cell lines have been surveyed for expression of a large set of plasma proteins, accumulation of liver-specific mRNAs and DNA-binding activity of ubiquitous and liver-enriched transcription factors. BC1 cells expressed the highest levels of albumin mRNA, whereas B16 and B16A2 cells accumulated the largest amounts of haptoglobin mRNA. In addition, B16 and B16A2 cells were unique in that they expressed CYP2E1 mRNA, a species absent from the available human liver cells, including HepG2 hepatoma cells, and 3-methylcholanthrene-inducible CYP1A2 mRNA. The activities of genes encoding transcription factors were evidenced in all four cell lines which expressed mRNAs for nuclear factor interleukin 6 and hepatocyte nuclear factor 1 (HNF) together with the DNA-binding activity of NFY and AP1 nuclear proteins. Strikingly, HNF-1 and HNF-4-like DNA-binding activities were restricted to BC1, B16 and B16A2 cells, supporting the idea of the potential role of these (or closely related) factors in the maintenance and/or in the establishment of the differentiated phenotype. B9 cells contained variant HNF1-like DNA-binding activity, similar to dedifferentiated rat hepatoma cells of the H5 line. CCAAT/enhancer-binding protein and HNF-3-like activities were found in all cell lines, although at a lower level and/or activity in B9 cells. Finally, transfection experiments of plasmids containing the whole hepatitis-B virus genome demonstrated that B16 cells, but not B9 cells, were able to support hepatitis-B virus replication and virion production, in agreement with the notion that HNF-1 activity is necessary for viral replication. We believe that the specific complement of transcription factors expressed in the differentiated BC1, B16 and B16A2 cells, and in the poorly differentiated B9 cells, will allow studies on the regulation of hepatic gene expression in these human lines, and will also aid the analysis of xenobiotic metabolism and the biology of hepatitis-B virus replication.

Rat liver epithelial cells express functional cytochrome P450 2E1

Rat liver epithelial cells (RLECs) isolated by trypsinization of the livers of normal 10 day old rats are largely used in co-culture with primary hepatocytes. The aim of the present study was to investigate the expression of biotransformation enzyme-encoding genes in three preparations of RLEC lines. Although no expression of cytochrome P450 1A1/2 (CYP1A1/2), CYP2B1/2, CYP2C6 or CYP3A mRNAs could be detected, we found that all of the different preparations of RLECs expressed a high level of CYP2E1 mRNA. We demonstrated the presence of the CYP2E1 apoprotein in microsomes of RLECs by immunoblot analyses, together with chlorzoxazone 6-hydroxylation, an activity known to be mainly catalyzed by CYP2E1. In addition, acetone treatment of these cells resulted in an increase in both CYP2E1 apoprotein and chlorzoxazone 6-hydroxylation activity levels. Finally, we showed the susceptibility of RLECs to N-methyl formamide- and diethylnitrosamine-induced toxicity, suggesting metabolic activation by CYP2E1. Thus, RLECs may cooperate with hepatocytes to CYP2E1-mediated metabolism in the co-culture model. In addition, transfection experiments with a CYP2E1 promoter construct, in which the proximal 539 bp containing the binding site for HNF1alpha were inserted upstream of the chloramphenicol acetyl transferase gene, demonstrated a strong induction upon co-transfection with an HNF1alpha expression plasmid. Thus, RLECs provide a useful tool for studying metabolism and cytotoxicity of CYP2E1 substrates in the absence of other expressed CYPs, and for analyzing CYP2E1 promoter function.

Interleukin-1 beta antagonizes phenobarbital induction of several major cytochromes P450 in adult rat hepatocytes in primary culture

We have investigated the effects of interleukin (IL)-1 beta and IL6 on expression and phenobarbital (PB) induction of ethoxyresorufin O-deethylase (EROD) and pentoxyresorufin O-deethylase (PROD) activities, as well as on mRNA levels of cytochromes P450 (CYP) 1A, 2B, 2C, 2E and 3A, in rat hepatocytes in primary culture. IL6 slightly antagonized PB-induced PROD activity. Strikingly, IL1 beta strongly inhibited basal EROD and PROD activities, and fully blocked their induction by PB in a dose-dependent fashion. Furthermore IL1 beta completely suppressed PB induction of all CYP mRNAs analyzed. Our results demonstrate that IL1 beta can suppress basal CYP activities, as well as PB-inducible expression of five CYP mRNAs in rat hepatocytes in primary culture.

Transforming growth factor-beta 1 down-regulates basal and polycyclic aromatic hydrocarbon-induced cytochromes P-450 1A1 and 1A2 in adult human hepatocytes in primary culture

The effects of interleukin (IL)-1 beta, IL-4, IL-6, tumor necrosis factor (TNF)-alpha, interferon (IFN)-alpha, IFN-gamma, and transforming growth factor (TGF)-beta 1 on cytochrome P-450 (CYP) 1A expression and polycyclic aromatic hydrocarbon (PAH)-mediated induction in primary human hepatocyte cultures were determined. Most cytokines that were previously found to decrease basal CYP expression could counteract PAH induction of CYP1A mRNA and its associated ethoxyresorufin-O-deethylation (EROD) activity. IL-1 beta and TNF-alpha blocked 3-methylcholanthrene (3-MC)-induced EROD activity by up to 25 and 44%, respectively. IFN-alpha and IFN-gamma antagonized EROD induction by up to 61 and 70%, respectively. TGF-beta 1 proved to be the most effective cytokine, because 72 hr of treatment with 2 ng/ml TGF-beta 1 produced nearly 100% inhibition of 3-MC- and benzo(a)pyrene-induced CYP1A1 and CYP1A2 mRNAs and EROD activity. Treatment with cycloheximide in combination with 3-MC led to superinduction of CYP1A mRNA, under which conditions TGF-beta 1 did not block induction, suggesting the requirement for protein synthesis for the suppressive effect of the cytokine. In addition, TGF-beta 1 augmented AP-1-binding activity, suggesting that fos and/or jun protooncogene products could be implicated in the response. Our results demonstrate that IL-1 beta, TNF-alpha, and IFNs antagonized PAH-mediated induction of CYP1A gene expression in human hepatocytes. In addition, we report the finding of a novel effect of TGF-beta 1, which was able to prevent CYP1A1 and -1A2 induction by two different PAHs.

Halothane-induced cytotoxicity to rat centrilobular hepatocytes in primary culture is not increased under low oxygen concentration

BACKGROUND

Halothane can be metabolized by both oxidative and reductive pathways in the liver. This anesthetic can induce direct liver injury preferentially localized in centrilobular areas, probably in relation with lower oxygen tension. The reductive pathway has been related to liver damage; however, a correlation between lower oxygen concentration in centrilobular areas, the extent of reductive metabolism of halothane, and the degree of liver injury has not yet been demonstrated. This study was designed to better evaluate the toxicity of the reduced metabolites by using centrilobular and periportal rat hepatocyte subpopulations.

METHODS

Adult rat hepatocytes, either as whole cell preparations or after separation in centrilobular and periportal cell subpopulations, were placed in primary culture and exposed to either 2% or 4% halothane under various oxygen concentrations. The enriched centrilobular hepatocyte subpopulations isolated by the digitonin-collagenase method were characterized by immunolocalization of glutamine synthetase. Three oxygen concentrations were tested: 5%, 20%, and 95%, and the main parameters measured were cell viability and fluoride ion formation.

RESULTS

Viability of centrilobular hepatocytes was similar under 5% and 20% O2, but the unpurified hepatocyte population was more susceptible to 5% O2 (P < 0.01). Significantly higher cytochrome P-450 content was found in whole hepatocyte populations under 5% versus 20% oxygen, indicating that centrilobular hepatocytes that contained higher cytochrome P-450 monooxygenase activities were less sensitive to low oxygen concentrations. Halothane toxicity to centrilobular hepatocytes was enhanced under 95% versus 20% O2 (P < 0.05). By contrast, no significant difference was observed when the cells were maintained under 5% O2, although fluoride ions, indicative of reductive metabolism of halothane, were found in much higher amounts in the culture medium. Moreover, under 20% O2, halothane toxicity was significantly greater in centrilobular versus unpurified hepatocytes (P < 0.05).

CONCLUSIONS

Isolated centrilobular hepatocytes appear to be more sensitive to halothane than their periportal counterparts in vitro. However, the authors' results support the conclusion that increased reductive metabolism of halothane induced by decreasing oxygen concentration is not a critical parameter for the occurrence of liver damage in these cells.

Cytokines down-regulate expression of major cytochrome P-450 enzymes in adult human hepatocytes in primary culture

Cytokines are thought to cause the depression of cytochrome P-450 (CYP)-associated drug metabolism in humans during inflammation and infection. We have examined the role of five cytokines, i.e., interleukin-1 beta, interleukin-4, interleukin-6, tumor necrosis factor-alpha, and interferon-gamma, on the expression of CYP1A2, CYP2C, CYP2E1, CYP3A, and epoxide hydrolase in primary human hepatocyte cultures. Steady state P-450 and epoxide hydrolase mRNA levels, as well as ethoxyresorufin-O-deethylase and nifedipine oxidation activities, which are mainly supported by CYP1A1/1A2 and CYP3A, respectively, were measured. Interleukin-1 beta, interleukin-6, and tumor necrosis factor-alpha were found to be the most potent depressors of P-450 enzymes. After 3 days of treatment, both mRNA levels and enzyme activities were depressed, typically by at least 40%, whatever the cytokine and the enzyme considered. Interferon-gamma also suppressed CYP1A2 and CYP2E1 mRNA levels and ethoxyresorufin-O-deethylase activity but had no effect on CYP3A and epoxide hydrolase mRNAs. In addition, interleukin-4 had the opposite effect, compared with other cytokines, on CYP2E1 mRNA, which was increased up to 5-fold; ethoxyresorufin-O-deethylase and nifedipine oxidation activities were not significantly affected. These results provide the first demonstration that various cytokines act directly on human hepatocytes to affect expression of major P-450 genes and that a wide range of responses can be observed among the enzymes for a given cytokine, suggesting that different regulatory mechanisms may be involved.

Viability and function in primary culture of adult hepatocytes from various animal species and human beings after cryopreservation

Cryopreserved hepatocytes from various animal species and human beings were tested for their ability to survive and function in primary culture. The freeze/thaw protocol primarily designed for rat hepatocytes was used with slight modifications for the cells of all other species; it consisted of suspending parenchymal cells in the Leibovitz L15 medium containing 10% fetal calf serum and 10% to 16% dimethyl sulfoxide. After transient storage at 4 degrees C cell suspensions were transferred to -20 degrees C and then to -70 degrees C before being plunged in liquid nitrogen. Hepatocytes were stored for a few weeks to 4 yr. Prolonged storage did not augment loss of cell viability and function. Cell viability after thawing was estimated by the trypan blue exclusion test, and attachment efficiency to plastic was estimated by measuring intracellular lactate dehydrogenase content. Similar values were obtained for most species tested; after cryopreservation cell viability and attachment were decreased by 10% to 25% and by 40% to 50%, respectively. A lower attachment rate was found with dog hepatocytes. Total cytochrome P-450 and protein synthesis were compared in fresh and cryopreserved cells from four species after 4, 24, 48 or 72 hr of culture. Similar values were found in both cells after 24 or 48 hr of culture. In addition, drug-metabolizing activities were measured in human hepatocytes from five donors. In most cases phenacetin deethylation activity was decreased whereas procainamide N-acetylation and paracetamol sulfoconjugation and glucuronidation were increased in cryopreserved cells.(ABSTRACT TRUNCATED AT 250 WORDS)

A Multicentre Study of Acute In Vitro Cytotoxicity in Rat Hepatocytes: Tentative Correlation Between In Vitro Toxicities and In Vivo Data

A multicentre validation study of the acute in vitro cytotoxicities of 31 liquid or solid chemicals was carried out by six laboratories, using primary rat hepatocyte cultures as a model system. We report here a comparison of neutral red uptake IC50 and LD50 values. Oral, i.p. and i.v. LD50 values were available for 27, 24 and 18 chemicals, respectively, and an IC50 value was obtained for 15, 14 and 11 of these compounds, respectively. A significant correlation was found only between IC50 and i.v. LD50 values.

Viability and primary culture of rat hepatocytes after hypothermic preservation: the superiority of the Leibovitz medium over the University of Wisconsin solution for cold storage

Hepatocytes isolated from adult rat livers were hypothermically preserved for 24 or 48 hr before being plated under conventional culture conditions. They were stored either in the Leibovitz medium, a cell culture medium with and without polyethylene glycol (PEG), a compound known to suppress ischemia-induced cell swelling, or in the University of Wisconsin solution, the most effective solution for cold organ preservation. After 24 or 48 hr of storage at 4.5 degrees C in Leibovitz medium, cell viability and adherence efficiency to plastic dish, were only slightly reduced, whereas University of Wisconsin hepatocytes had a decreased viability and (especially after 48-hr storage) lost their adhesion ability; they did not survive in vitro. The metabolic competence of hepatocytes maintained in Leibovitz medium was retained over the 3 days of culture, as shown by low extracellular levels of the membrane-bound and cytosolic hepatic enzymes, as well as by intracellular glutathione content, albumin secretion rate and several phase I and phase II drug metabolic reactions very close to those found with fresh hepatocytes maintained under similar culture conditions. Addition of polyethylene glycol to the Leibovitz medium resulted in slightly higher viability and function of hepatocytes after cold storage. These results clearly demonstrate that viability of a transplanted liver does not correlate with long-term in vitro viability of isolated hepatocytes after hypothermic preservation in University of Wisconsin solution. They also suggest that nutritional and energy substrates as found in the Leibovitz medium are probably required to define a suitable solution for cold preservation of isolated parenchymal cells. The findings with Leibovitz medium favor the conclusion that hypothermically preserved hepatocytes could be used for various metabolic studies and for the treatment of liver insufficiency.

Primary culture of adult rat hepatocytes after 48-hour preservation of the liver with cold UW solution

Rat livers were perfused and stored for 48 hr in cold University of Wisconsin solution before dissociation by the two-step collagenase method. At that time, glycogen content was significantly reduced, but no obvious changes in albumin, beta-actin and aldolase B mRNAs and in glutathione levels were observed. Enzymatic perfusion yielded 280 +/- 30 x 10(6) viable hepatocytes vs. 520 +/- 40 x 10(6) viable hepatocytes from unstored organs. Cell viability determined by trypan blue exclusion was 74% and 90%, respectively. Hepatocytes from University of Wisconsin-preserved livers had a 29% reduced adenosine triphosphate content, but glutathione levels did not significantly differ from those found in unstored cells. When put into culture, hepatocytes formed typical monolayers of granular epithelial cells and did not exhibit alteration of their fine structure when compared with cells from unstored organs. After 24 and 48 hr, they showed variations in cytochrome P-450 content and ethoxyresorufin O-deethylase activity similar to those observed with unstored cells. By contrast, overall protein synthesis and albumin secretion rate were 40% and 30% lower, respectively. Hepatocytes from University of Wisconsin-preserved organs could be cryopreserved and further cultured as unstored cells. The University of Wisconsin solution was also used to preserve isolated hepatocytes. Viability of freshly isolated hepatocytes was decreased by only 10% after 48 hr of hypothermic liver storage when assayed by intracellular lactate dehydrogenase content. However, after 4 hr of storage, in contrast with hepatocytes preserved in L15 Leibovitz medium, the cells attached poorly to plastic and exhibited morphological alterations.(ABSTRACT TRUNCATED AT 250 WORDS)