Activities of several phase I and phase II xenobiotic biotransformation enzymes in cultured hepatocytes from male and female rats

Evaluation of Pharmaceuticals for DNA Damage in the Chicken Egg Genotoxicity Assay (CEGA)

DNA damage is an established initiating event in the mutagenicity and carcinogenicity of genotoxic chemicals. Accordingly, assessment of this endpoint is critical for chemicals which are being developed for use in humans. To assess the ability of the Chicken Egg Genotoxicity Assay (CEGA) to detect genotoxic pharmaceuticals, a set of 23 compounds with different pharmacological and reported genotoxic effects was tested for the potential to produce nuclear DNA adducts and strand breaks in the embryo-fetal livers using the ³²P-nucleotide postlabeling (NPL) and comet assays, respectively. Due to high toxicity, two aneugens, colchicine and vinblastine, and an autophagy inhibitor, hydroxychloroquine, could not be evaluated. Out of the 20 remaining pharmaceuticals, 10 including estrogen modulators, diethylstilbestrol and tamoxifen, antineoplastics cyclophosphamide, etoposide, and mitomycin C, antifungal griseofulvin, local anesthetics lidocaine and prilocaine, and antihistamines diphenhydramine and doxylamine, yielded clear positive outcomes in at least one of the assays. The antihypertensive vasodilator hydralazine and antineoplastics streptozotocin and teniposide, produced only DNA strand breaks, which were not dose-dependent, and thus, the results with these 3 pharmaceuticals were considered equivocal. No DNA damage was detected for 7 compounds, including the purine antagonist 6-thioguanine, antipyretic analgesics acetaminophen and phenacetin, antibiotic ciprofloxacin, antilipidemic clofibrate, anti-inflammatory ibuprofen, and sedative phenobarbital. However, low solubility of these compounds limited dosages tested in CEGA. Overall, results in CEGA were largely in concordance with the outcomes in other systems in vitro and in vivo, indicating that CEGA provides reliable detection of DNA damaging activity of genotoxic compounds. Further evaluations with a broader set of compounds would support this conclusion.

Cytotoxicity of 28 MEIC Chemicals to Rat Hepatocytes using Two Viability Endpoints: Correlation with Acute Toxicity Data in Rat and Man

28 of the chemicals on the MEIC list were tested on rat hepatocytes in culture. Firstly, the metabolic capacities of the cell model were characterised, i.e. cytochrome P450 content and conjugation activities. Two independent endpoints, MTT (tetrazolium salt) reduction (for mitochondrial integrity) and neutral red uptake (NRU, for lysosomal integrity), were then used to measure the cytotoxicities of the test compounds after incubation with the cells for 24 hours. The relative toxicities of the test chemicals were measured by the determination of IC50 values for each parameter. Statistical analysis revealed a correlation between the results obtained in the two assays. The NRU assay, however, proved to be more sensitive than the MTT reduction assay. When the in vitro results were compared with those obtained from an in vivo data bank, good agreement was found with the acute toxicities of the test products in rats, with the exception of thioridazine, malathion, copper sulphate (all overestimated) and potassium cyanide (underestimated). In addition, a good correlation between basal cytotoxicity values for rat hepatocytes and LD50 for rats or lethal doses for humans was observed. These results suggest that the MTT reduction and/or NRU assays could be useful indicators of the cytotoxic potential of chemicals in rat hepatocyte cultures and thus provide information on the intrinsic lethal toxicity of compounds and their metabolites to rats and humans.

Evaluation of the Function of Primary Human Hepatocytes Co-Cultured with the Human Hepatic Stellate Cell (HSC) Line LI90

Most bioartificial liver devices utilise primary hepatocytes alone although some have considered the use of non parenchymal cells in addition. However the effects of co-culture of human hepatocytes with different sinusoidal cell types has not been fully investigated. In this study we have examined the influence of co-culturing primary human hepatocytes with the human hepatic stellate cell (HSC) line, LI90. Cultures were monitored by light microscopy and on days 4, 8 and 14 urea synthesis and cytochrome P450 activity were measured. Morphologically LI90 cells proliferated to fill spaces between and into adjacent islands of hepatocytes. On day 14 cytochrome P450 activity in co-culture was significantly improved compared to hepatocytes cultured alone. By contrast, urea synthesis in hepatocytes was unaffected by single or co-culture. Therefore it can be concluded that a combination of primary human hepatocytes with LI90 cells is beneficial for growth and some stability of hepatocytes and may therefore be appropriate for seeding bioartificial liver devices.

Morphological and Functional Evaluation of Isolated Rat Hepatocytes in three Dimensional Culture Systems

Various three-dimensional configurations, such as polyester tissue and woven-nonwoven, hydrophilic polyester fabric, either collagen-coated or uncoated, were investigated as potential scaffold for hepatocyte culture, in view of their use in bioreactors for hybrid liver support systems. Attachment, morphology and ultrastructure of primary adult rat hepatocytes were evaluated, as well as urea production and ammonium detoxification during a 24h incubation period in serum-free tissue culture medium. As control, hepatocytes were also plated onto collagen-coated dextran microcarriers and on plastic petri dishes, either collagen-coated or uncoated. In all the three-dimensional cultures, hepatocytes appeared morphologically intact without any statistically significant difference in metabolic activity. Collagen-coating did not influence cell attachment to polyester substrates, whereas woven-nonwoven hydrophilic polyester fabric may offer some potential advantages as three-dimensional system for hepatocyte culture in hybrid liver support systems.

ECM proteins in a microporous scaffold influence hepatocyte morphology, function, and gene expression

It is well known that a three-dimensional (3D) culture environment and the presence of extracellular matrix (ECM) proteins facilitate hepatocyte viability and maintenance of the liver-specific phenotype in vitro. However, it is not clear whether specific ECM components such as collagen or fibronectin differentially regulate such processes, especially in 3D scaffolds. In this study, a series of ECM-functionalized inverted colloidal crystal (ICC) microporous scaffolds were fabricated and their influence on Huh-7.5 cell proliferation, morphology, hepatic-specific functions, and patterns of gene expression were compared. Both collagen and fibronectin promoted albumin production and liver-specific gene expression of Huh-7.5 cells, compared with the bare ICC scaffold. Interestingly, cells in the fibronectin-functionalized scaffold exhibited different aggregation patterns to those in the collagen-functionalized scaffold, a variation that could be related to the distinct mRNA expression levels of cell adhesion-related genes. Based on these results, we can conclude that different ECM proteins, such as fibronectin and collagen, indeed play distinct roles in the phenotypic regulation of cells cultured in a 3D environment.

Phenotypic regulation of liver cells in a biofunctionalized three-dimensional hydrogel platform

Loss of function is a major challenge for hepatocytes that are cultured on two-dimensional (2D) cell culture platforms. Biofunctionalized three-dimensional (3D) scaffolds produced by microfabrication strategies can overcome these limitations by presenting vital environmental cues, strong mechanical properties, and three-dimensional geometry to enable high-fidelity liver tissue engineering. Herein, we report the detailed investigation of hepatocarcinoma (Huh 7.5) cellular behavior in a collagen-functionalized microsphere-templated poly(ethylene glycol) (PEG) hydrogel scaffold which promotes 3D hepatic sheet morphology. Collagen conjugation led to improved liver-specific functions, including albumin production and cytochrome P450 (CYP450) activity. Importantly, the gene expression of numerous cell-adhesion markers was enhanced along with stimulated innate hepatocyte fibronectin production. Taken together, the findings reveal a close connection between hepatic cell morphology and gene expression, offering evidence that surface-coated collagen in the 3D hydrogel platform triggers the upregulation of hepatocyte-specific transcription factors and the secretion of liver metabolic markers.

Reactive oxygen species and cytotoxicity in rainbow trout hepatocytes: effects of medium and incubation time

This study evaluated the effects of exposure medium and culture age on intracellular reactive oxygen species (ROS) development and cytotoxicity in fish hepatocytes following exposure to copper (Cu). ROS was quantified using the fluorescent probes DHR 123 and CM-H2DCFDA following exposure to Cu in Leibovitz' medium (L-15) or Tris-buffered saline (TBS). Similarly, culture age effects were investigated using 1-, 2- and 4-day-old cultured hepatocytes by exposing them to Cu in TBS. The exposure in L-15 resulted in significantly higher ROS compared to TBS using CM-H2DCFDA, but not DHR 123. The age of the primary cultures significantly affected the development of ROS for both probes. None of the exposures caused cytotoxicity in the hepatocytes. The results showed that both factors may affect responses to stressors, and suggested that the use of a simple medium such as TBS may be preferable for some applications. It is also preferable to use 1-day-old primary hepatocyte cultures.

The immortalisation of rat hepatocytes by transfection with SV40 sequences

Abbreviations EGTA - ethylene bis(oxyethylenenitrilo)-tetraacetic acid; F12 - Ham's F12; FBS - foetal bovine serum; HBSS - Hank's balanced salt solution; HDM - hormonally defined medium; HEPES - 4-(2-hydroxyethyl)-1-piperazine ethanesulphonic acid; NBS - new born calf serum; WME - Williams' medium E.

Toxic responses in primary rat hepatocytes exposed with occupational dust collected from work environment of bone-based industrial unit

In this in vitro study we investigated the toxic responses in hepatocytes treated with occupational dust to which workers are exposed in bone-based industrial units. The present study investigated the toxicity mechanism of bone-based occupational dust, from a particular industrial unit, on isolated rat hepatocytes. The hepatocytes were isolated by collagenase perfusion method and cell viability was determined by trypan blue exclusion and MTT [3-(4,5-dimethyl thiazol-2-yl)-2,5-diphenyl tetrazolium bromide] assay treated with occupational dust at 0.1-1.0 mgmL(-1), for 120 min. The cell viability decreased significantly in a concentration-dependent manner. Dust induced significant membrane damage measured by lactate dehydrogenase (LDH) and glutathione (GSH) release in culture media for 30-, 60- and 120 min treatment duration. The toxicity was found to be correlated with the induction of lipid peroxidation (LPO). In addition, nitric oxide (NO), and hydrogen peroxide (H(2)O(2)) generation by occupational dusts were also found to be time- and concentration-dependent. Over all the present study provides initial evidences for the toxic potential of occupational dust generated in bone-based industries and, therefore, the dust exposure to workers in unorganized industrial units should be controlled.

Prediction of metabolic clearance of bisphenol A (4,4 '-dihydroxy-2,2-diphenylpropane) using cryopreserved human hepatocytes

This study investigated the kinetics of glucuronidation of bisphenol A (BPA; 4,4'-dihydroxy-2,2-diphenylpropane) in cryopreserved human hepatocytes (HCs). Incubation conditions were developed using Sprague-Dawley rat HCs. For determination of the kinetic constants of BPA glucuronidation rates with human HCs, viable HCs (0.125 x 10(6)) were incubated with [(14)C]BPA (1.3-52 microM) for 10 min. The glucuronidation reaction demonstrated Michaelis-Menten kinetics and yielded a mean K(m) for males and females of 9 +/- 3 and 8 +/- 2 microM, respectively. The V(max) values of these reactions were 438 +/- 129 pmol/min/10(6) for male HCs and 480 +/- 208 pmol/min/10(6) for female HCs. The scaled intrinsic clearance (CL(int)) for male human HCs was 149 +/- 67 ml/min/kg (range 53-246) and for female HCs was 165 +/- 89 ml/min/kg (range 73-336). Overall, there are no apparent gender differences in the glucuronidation of BPA. These CL(int) values were then extrapolated to estimate total hepatic metabolic clearance (CL(met)) using a nonrestrictive well stirred model. The estimated CL(met) value for both male and female HCs was 6 ml/min/kg, which represents 30% of hepatic blood flow. Thus, in vivo clearance seems to depend highly on plasma protein binding. These in vitro results correlate well with in vivo studies in humans, which report extensive glucuronidation of BPA.

Kinetics of arsenic methylation by freshly isolated B6C3F1 mouse hepatocytes

The toxic and carcinogenic effects of arsenic may be mediated by both inorganic and methylated arsenic species. The methylation of arsenic(III) is thought to take place via sequential oxidative methylation and reduction steps to form monomethylarsenic (MMA) and dimethylarsenic (DMA) species, but recent evidence indicates that glutathione complexes of arsenic(III) can be methylated without oxidation. The kinetics of arsenic methylation were determined in freshly isolated hepatocytes from male B6C3F1 mice. Hepatocytes (>90% viability) were isolated by collagenase perfusion and suspended in Williams' Medium E with various concentrations of arsenic(III) (sodium m-arsenite). Aliquots of the lysed cell suspension were analyzed for arsenic species by hydride generation-atomic absorption spectrometry. The formation of MMA(III) from sodium arsenite (1 microM) was linear with respect to time for >90 min. DMA(III) formation did not become significant until 60 min. MMA(V) and DMA(V) were not consistently observed in the incubations. These results suggest that the glutathione complex mechanism of methylation plays an important role in arsenic biotransformation in mouse hepatocytes. Metabolism of arsenic(V) was not observed in mouse hepatocytes, consistent with inhibition of arsenic(V) active cellular uptake by phosphate in the medium. The formation of MMA(III) increased with increasing arsenic(III) concentrations up to approximately 2 microM and declined thereafter. The concentration dependence is consistent with a saturable methylation reaction accompanied by uncompetitive substrate inhibition of the reaction by arsenic(III). Kinetic analysis of the data suggested an apparent K(M) of approximately 3.6 microM arsenic(III), an apparent V(max) of approximately 38.9 microg MMA(III) formed/L/h/million cells, and an apparent K(I) of approximately 1.3 microM arsenic(III). The results of this study can be used in the physiologically based pharmacokinetic model for arsenic disposition in mice to predict the concentration of MMA(III) in liver and other tissues.

Cytotoxic effect and role of exogenous antioxidants in carpet dust mediated toxicity in rat hepatocytes in vitro

Carpet industries bear a great deal of economic and commercial significance in India. In order to safe guard the workers against the health hazards caused by dust in their occupational environment; it necessitates studying the biological importance of these dusts. The present study was designed to investigate the toxicity of carpet dust (knotted and tuffted) on isolated rat hepatocytes. The hepatocytes were isolated by collagenase perfusion method and cells were incubated with different concentration of carpet dust (100-5000 microg/10(6) cells) with various time (30-180 min) intervals. An exogenous antioxidant vitamin-E also used to find out the role of antioxidants and free radical production in carpet dust mediated toxicity. Cell viability by trypan blue exclusion and leakage of enzyme lactate dehydrogenase (LDH) were determined. Reduced glutathione (GSH), formation of thiobarbituric acid reactive substance (TBARS) were also measured. A significant decrease in the cell viability was observed after 60, 180 min upon incubation with tuffted carpet dust, while knotted carpet dust caused a significant decrease in the viability after 180 min. LDH leakage was parallel to the cell viability. Thiobarbituric acid reactive substance was significantly increased at 30 and 60 min with carpet dust treated hepatocytes. Dust at 1000 and 5000 microg dose level showed significantly increased formation of TBARS at 30 min incubation. However, when hepatocytes were co-incubated with carpet dust and Vit-E (10, 15 microM), a significant decrease in LDH release and TBARS production was observed while 15 microM Vit-E showed an enhanced protection than 10 microM Vit-E treated hepatocytes. The effect of carpet dust on cell viability, LDH leakage, TBARS production, GSH depletion was time and dose-dependent. Moreover, we observed that tuffted carpet dust causes greater effect than knotted one on the above mentioned parameters. Our studies also revealed that Vit-E in culture media diminishes the carpet dust mediated toxicity.

Para-nitrophenol glucuronidation and sulfation in rat and human liver slices

Para-nitrophenol (PNP) is a well-known substrate for both phase I (hydroxylation at cytochrome P450) and phase II reactions (glucuronidation and sulfation). HPLC separation of PNP conjugates has already been described, but not for respective studies with liver slices, which nowadays have proven to be a suitable model for metabolic studies. Therefore we adapted an HPLC method for the simultaneous measurement of PNP glucuronidation (PNP-G) and sulfation (PNP-S) in this in vitro system. Both activities are substantially maintained over an incubation period of 24 h. PNP-G activity, however, seems to be better preserved, as indicated by stable values for PNP-G but reduced PNP-S values after 48 h liver slice preincubation. 24 h exposure of the slices to beta-naphthoflavone or phenobarbital does not change PNP-G or PNP-S activities.

Comparison of the stability of some major cytochrome P450 and conjugation reactions in rat, dog and human hepatocyte monolayers

The stability of four major cytochrome P450 isoenzymes (CYPIA, CYP2B, CYP2E1 and CYP3A) and of two phase II conjugation enzymes (glucuronyl- and sulfotransferases) was investigated in primary cultures of rat, dog and human hepatocytes in the same conditions. 7-ethoxyresorufin deethylation (EROD), 7-methoxycoumarin demethylation (MCOD), chlorzoxazone (CLOX) 6-hydroxylation, 1'- and 4-hydroxylation of midazolam (MDZ), and p-nitrophenol glucuronidation and sulfation, were used respectively. The EROD activity was stable over 72 hours in rat and dog and only 48 hours in human hepatocytes. The MCOD activity was also stable in rat but decreased in dog by 30% within 72 hours The CLOX hydroxylase activity was most stable in human whereas in rat and dog it fell down to 30% within 72 and 24 hours, respectively. The MDZ hydroxylase activity showed the same unstability profile in the three species investigated. Both conjugation reactions were either stable or showed an increase by up to 60-70% in all three species over 72 hours. The enzymes tested showed different stabilities in rat, dog and human hepatocytes over 72 hours, thus demonstrating the limitations of hepatocyte monolayers as models for metabolic investigations and emphasising the need for validation/characterization studies before routine use.

Alterations of antioxidant enzyme expression in response to hydrogen peroxide

The effect of hydrogen peroxide (H2O2) on the expression of different antioxidant enzymes was investigated in primary rat hepatocytes and the rat hepatoma H4IIE cell line. Catalase mRNA expression and enzyme activity decreased during rat hepatocyte culture. Exposure of hepatocytes to H2O2 prevented this decrease in catalase mRNA expression, catalase expression was induced 2-fold. MnSOD message levels showed a peak after 12 h of culture and MnSOD enzyme activity increased similarly. MnSOD mRNA expression was also induced after exposure to H2O2. Cu/ZnSOD mRNA expression remained constant during culturing and was not affected by H2O2 treatment. In confluent hepatoma H4IIE cells catalase mRNA expression was lower than in early hepatocyte cultures and could be induced 2-fold upon treatment with H2O2. Actinomycin D alone caused the same amount of induction of catalase mRNA in rat hepatocytes as in combination with H2O2. Exposure of hepatocytes to cycloheximide did not influence the induction of catalase mRNA by H2O2. In rat hepatoma H4IIE cells the induction of catalase mRNA by H2O2 was prevented by the addition of actinomycin D or cycloheximide. Although induction of catalase mRNA by H2O2 was found in rat hepatocytes and H4IIE cells, gene expression of catalase does not appear to be regulated in both cell types in the same manner.

Perifusion of co-cultured hepatocytes: optimization of studies on drug metabolism and cytotoxicity in vitro

The combination of co-cultivation of hepatocytes and epithelial cell lines with a newly developed perifusion system was used for in vitro studies on drug metabolism and cytotoxicity. This approach improved the viability and enhanced the induction of the biotransforming capacity of the hepatocytes. As demonstrated for the induction of 7-ethoxyresorufin O-deethylase activity by 3-methylcholanthrene or benzanthracene, co-cultured hepatocytes in the perifusion system responded more sensitively to these inducers than without perifusion, most likely owing to stable (steady-state) concentrations of the inducers under the former conditions and rapidly declining concentrations under the latter conditions. The perifusion approach rendered it possible to determine the kinetics of drug metabolism during single or sequential incubations. After induction with 3-methylcholanthrene and phenobarbital, phase I metabolism of lonazolac to the monohydroxylated product in perifused co-cultures closely (87%) approached the values reported for the in vivo production, whereas in stationary co-cultures only 52% could be reached. Likewise, cytotoxic effects could be detected more precisely in the perifused co-cultures. If cells were pretreated with 0.2 mmol/L galactosamine for 3 h, perifusion with increasing concentrations of menadione differentially killed epithelial RL-ET-14 cells and hepatocytes at low and high concentrations, respectively, while in stationary co-cultures no differential effect was observed and only the higher concentrations were cytotoxic for both cells. Prevention by incubation with S-adenosylmethionine of menadione cytotoxicity up to a menadione concentration of 250 micromol/L was seen only in the perifused co-cultures, whereas in stationary cultures only a slight shift of the cytotoxic concentration exerting 50% cell damage to higher values was noted. These results demonstrate the versatile application of perifused co-cultures for studies on drug metabolism including induction of cytochrome P450-dependent enzymes and steady-state kinetics of biotransformation, as well as cytotoxic and protective effects of different drugs.

Induction of CYP3A and associated terfenadine N-dealkylation in rat hepatocytes cocultured with 3T3 cells

Long-term culture of hepatocytes has been challenged by the loss of differentiated functions. In particular, there is a rapid decline in cytochrome P450 (CYP). In this study, we cocultured rat hepatocytes with 3T3 fibroblasts for 10 days, and examined hepatocyte viability, morphology, and expression of CYP3A. Terfenadine was incubated with the cultures, and its biotransformation was quantitatively analyzed by HPLC. Terfenadine is metabolized by two major pathways: C-hydroxylation to an alcohol metabolite which is further oxidized to a carboxylic acid, and N-dealkylation to azacyclonol. In rat liver, only the N-dealkylation pathway appears to be mediated by CYP3A since anti-rat CYP3A antibody inhibited azacyclonol but not alcohol metabolite formation in incubations of terfenadine with liver microsomes. Freshly isolated rat hepatocytes were seeded on top of confluent 3T3 cells. Cultures were maintained in Williams' E medium supplemented with 10% fetal bovine serum and either 0.1 mumol/L or 5 mumol/L dexamethasone. In pure hepatocyte cultures, viability, as determined by lactate dehydrogenase (LDH) activity, decreased steadily to less than 30% of initial levels by day 10. In cocultures, LDH activity remained high and was 70% of initial levels on day 10. The half-life of terfenadine disappearance was optimally maintained in cocultures treated with 5 mumol/L dexamethasone, and was associated with the increased formation of azacyclonol. On day 5, nearly 50% of added 5 mumol/L terfenadine was converted to azacyclonol within 6 h, whereas the conversion was only 4% on day 1. Western and RNA-slot blot analyses confirmed that treatment with 5 mumol/L dexamethasone induced CYP3A mRNA expression and CYP3A protein expression. This coculture system could offer a useful approach in the study of drugs and xenobiotics metabolized by CYP3A.

P-glycoprotein expression and function in rat hepatocytes in culture

Expression of P-glycoprotein, which confers multidrug resistance to a broad range of anticancer drugs, was studied in rat hepatocytes in culture. P-glycoprotein was localized in the plasma membrane by immunohistochemical staining and was evaluated by western blotting with C219 as primary antibody and quantification of the coloured spots. The conditions of culture (time in culture, cell density at seeding) had a strong effect on the expression of P-glycoprotein. Expression increases with time in culture. At 10 x 10(6) cells/75 cm2 flasks, which is the normal density seeding for hepatocytes in culture, the increase of P-glycoprotein was 17% between 4 and 24 hr in culture, 52% between 24 and 48 hr and 37% between 48 and 96 hr. At low density cell seeding (2 x 10(6) cells/75 cm2), the expression of P-glycoprotein was higher than at normal density from the first day in culture (+20%). This difference of expression was maintained until 96 hr of culture and was maximum at 48 hr (+44%). This P-glycoprotein was functional and this overexpression was correlated with a decrease of doxorubicin retention in hepatocytes.

Expression of liver functions in immortalised rat hepatocyte cell lines

The differentiated hepatic function of two rat liver cell lines, P9 and SV40RH1, immortalised by transfection with SV40 DNA has been investigated in terms of the glutathione synthesis, and the activities of gamma-glutamyltransferase, glutathione-S-transferase and UDP-glucuronosyltransferase. SV40RH1 is a highly differentiated cell line at early passage, but the expression of some aspects of its differentiated phenotype is unstable and some functions are lost by passage 12-13. P9 is a less-well differentiated cell line, with relatively stable expression of functions between passages 4 and 13. In terms of differentiated function both cell lines represent a marked improvement over primary cultures of rat hepatocytes which de-differentiate rapidly within 24-48 h in culture. This retention of liver function in proliferating cell lines offers the opportunity to use such cells in in vitro toxicological studies.

Applicability of cultured hepatocytes derived from goat, sheep and cattle in comparative drug metabolism studies

1. Using trimethoprim (TMP), scoparone (SCOP), ethylmorphine (EtM), 1-naphthol (1-N) and phenol red (PhR) as test substrates, biotransformation activities were investigated in cultured hepatocytes from male and female rat, male and female goat, and female sheep and cattle. 2. As compared with rat hepatocytes, the total culture cytochrome P450 content was relatively well maintained in ruminant hepatocytes. In 72 h, it decreased to approximately half the initial content, whereas in rat hepatocytes only 30% was maintained. In ruminant hepatocytes, sulphation of 1-N remained fairly stable, glucuronidation of PhR decreased gradually, and glucuronidation of 1-N increased during the 72-h culture period. 3. Oxidative metabolism of TMP was rapid in goat and sheep hepatocytes, as compared with rat hepatocytes, reflecting species differences in TMP pharmacokinetics in vivo. In contrast with rat hepatocytes, 6-O-demethylation was by far the major pathway of scoparone metabolism in ruminant hepatocytes. The glucuronidation and sulphation activities were similar among the species. 4. In goat liver cells, sex differences in some oxidative biotransformations were observed, females being more active than males. In rat hepatocytes, a reverse sex difference was observed. 5. In conclusion, cultured hepatocytes from agricultural target species appear a useful in vitro model to study comparative metabolism of veterinary drugs and other xenobiotics. Comparing rat and ruminant, sex and species differences and similarities in drug metabolism can be observed that reflect the in vivo situation.

Rat hepatocyte cultures and co-cultures in biotransformation studies of xenobiotics

Long-term cultures of hepatocytes could represent a suitable in vitro model for biotransformation studies of xenobiotics. At present however, no ideal culture system can be proposed since, in all existing models, phenotypic changes occur, affecting selectively some components of phase I and/or phase II xenobiotic metabolism. From the authors' own results and recent studies of several other investigators, carried out on rat hepatocytes, it becomes clear that four groups of factors may affect biotransformation capacity: soluble medium factors, extracellular matrix components, cell-cell interactions and factors affecting replication. For the maintenance of liver-specific functions, it seems of utmost importance that the tridimensional shape of the hepatocytes is kept. Usually, phase II enzymatic activity is better kept than that of phase I. The cytochrome P450 dependent monoxygenases, in particular, are easily lost. Interesting is the observation that co-cultures of rat hepatocytes with rat liver epithelial cells exhibit higher and much better preserved phase I and phase II biotransformation than monocultures. Clearly, further research is needed to improve this promising in vitro model.

Sulphadimidine metabolism in vitro: I. Sex differences in acetylation and hydroxylation in cultured rat hepatocytes

The hydroxylation and acetylation of 0.5 mM sulphadimidine (SDD) was studied in primary cultures of hepatocytes from male and female rats, and from castrated male and sham operated male rats. In addition, SDD metabolism was investigated in hepatocytes from castrated male rats treated with testosterone, prior to liver cell isolation. In male rat hepatocytes a significantly higher hydroxylation activity was observed than in hepatocytes from female and castrated male rats. Acetylation activity was higher in females. Testosterone induced hydroxylation but did not affect acetylation. These results correlate well with data from previous in vivo studies, showing the relevance of this in vitro model.

Effects of selected secondary metabolites of Fusarium moniliforme on unscheduled synthesis of DNA by rat primary hepatocytes

The Fusarium moniliforme mycotoxins--fusarin C, fumonisin B1, moniliformin and bikaverin--were evaluated for genotoxicity by their ability to induce unscheduled DNA synthesis (UDS) in primary rat hepatocytes. Isolated hepatocytes were exposed to several concentrations of moniliformin (5.0-500 microM), bikaverin (1.0-500 microM), fumonisin B1 (0.5-250 microM), or fusarin C (1.0-100 microM). Aflatoxin B1, a known inducer of UDS, was included as a positive control. UDS was determined by autoradiography of cells after their exposure to [3H]thymidine. The highest doses of fusarin C and bikaverin caused cell death, but no cytotoxicity was observed in cells exposed to moniliformin or fumonisin B1. Fumonisin B1, moniliformin and bikaverin were not genotoxic in the UDS assay. The results of the UDS assay with fusarin C were inconclusive since a marginal effect on UDS was obtained.

Actin filament alteration as a potential marker for cholestasis: a study in isolated rat hepatocyte couplets

It has been suggested that modification of the pericanalicular microfilament network (F-actin) plays a role in cholestasis. The purposes of this study were to assess (i) the process of F-actin network reorganization in isolated rat hepatocyte couplets (IRHC) in order to define the optimal study conditions in this model, (ii) the effect of cholestatic and hepatotoxic but non-cholestatic compounds on F-actin distribution in IRHC. F-actin was stained with fluorescein isothiocyanate phalloidin and fluorimetric measurements were performed in single couplets using a scanning laser cytometer, ACAS 570. F-actin distribution was assessed by the ratio of canalicular area fluorescence/total couplet fluorescence (CF/TF). The organization of the F-actin filaments was restored in IRHC 3-6 h after plating. At non-cytotoxic concentrations, most cholestatic compounds induced a significant accumulation of F-actin around the bile canaliculus as indicated by increased fluorescence in the pericanalicular area and by the increased CF/TF ratio as compared to the controls. This accumulation could be a consequence of an inhibition of F-actin depolymerization or a higher organization of actin (redistribution, bundling or reorientation). Hepatotoxic but non-cholestatic compounds did not induce any change in pericanalicular F-actin. Abnormalities of pericanalicular F-actin therefore appear to be a specific marker of hepatocellular cholestasis.

Microcarrier-attached rat hepatocytes as a xenobiotic-metabolizing system in cocultures

A method for the primary culture of rat liver cells on collagen-coated dextran microcarriers is described. Ethoxycoumarin deethylase (EOD) activity 24 hr after inoculation was comparable for liver cells cultured on microcarriers and on collagen-coated dishes. Cells were cultured on microcarriers for up to 48 hr and retained 25% of the initial EOD-activity that was seen in freshly isolated liver cells. Microcarrier-attached hepatocytes were cocultured with BALB/c 3T3 cells to study the metabolism-mediated cytotoxicity of cyclophosphamide (CPA). In the absence of hepatocytes, growth of 3T3 cells was not affected by CPA at concentrations up to 3600 microM. In coculture with hepatocytes, cytotoxicity of CPA was expressed in a time- and concentration-dependent manner. At high concentrations, CPA slightly depressed the EOD-activity of hepatocytes. Our results indicate that cocultivation of microcarrier-attached rat liver cells with target cells represents a valuable approach to the study of the metabolism-mediated toxicity of xenobiotics in vitro.

Expression and regulation of drug metabolizing enzymes in an immortalized rat hepatocyte cell line

A hepatic cell line has been immortalized after simian vacuolating virus 40 infection of adult rat hepatocytes maintained in defined culture conditions. This cell line, designated SVHep B4, expressed nuclear large T antigen, exhibited an extended lifespan (50 subcultures) and had a hepatocyte-like morphology. Expression and regulation of drug metabolizing enzymes were studied in long-term cultures of SVHep B4 cells. Significant activities of phase I and phase II enzymes were detected. gamma-Glutamyltransferase, a marker often increased in neoplastic and dedifferentiated hepatocytes, showed a low activity whereas the hepatospecific enzyme tyrosine aminotransferase was expressed at levels similar to those in liver. Responsiveness of drug metabolizing enzymes to inducers was investigated with phenobarbital, dexamethasone and methylcholanthrene. IIB and IA subfamilies of cytochrome P450 were increased, respectively, by phenobarbital (170%) and methylcholanthrene (500%). Glucuronidation of 1-naphthol was increased by phenobarbital (140%) and 3-methylcholanthrene (160%). Phenobarbital, methylcholanthrene and dexamethasone were found to increase significantly gamma-glutamyltransferase while tyrosine aminotransferase activity was enhanced by dexamethasone. Stable expression and inducibility of drug metabolizing enzymes in long-term cultures of the SVHep B4 cell line demonstrate that immortalization of adult hepatocytes represents a promising tool for drug biotransformation studies in vitro.

The concentration and temporal relationships of acetaminophen-induced changes in intracellular and extracellular total glutathione in freshly isolated hepatocytes from untreated and 3-methylcholanthrene pretreated Sprague-Dawley and Fischer rats

Fischer rats are more sensitive to acetaminophen-induced hepatotoxicity than Sprague-Dawley rats, however, the mechanisms for this enhanced sensitivity remain unclear. The susceptibility to hepatotoxicity is determined largely by the balance between acetaminophen toxification and detoxification. Since glutathione plays a critical role in the detoxification process, it would be of interest to compare the effects of acetaminophen on hepatic glutathione homeostasis in the Sprague-Dawley and Fischer rat, and relate these effects to cytotoxicity. To this end, we measured the sequential changes of intracellular and extracellular total glutathione in freshly isolated hepatocytes from untreated and 3-methylcholanthrene pretreated Fischer and Sprague-Dawley rats, both in the absence (basal) and presence of acetaminophen. In the basal state, the intracellular total glutathione content was significantly (P less than 0.01) increased in hepatocytes from untreated Fischer rats. Nevertheless, the sequential release of total glutathione into the medium and the sequential depletion of intracellular total glutathione were quantitatively similar in hepatocytes from untreated Fischer and Sprague-Dawley rats. Following exposure to acetaminophen, there was a striking dose and time associated depletion of intracellular total glutathione in untreated hepatocytes from both rat strains, and quantitatively the depletion was similar in untreated hepatocytes from both rat strains. This degree of depletion of intracellular total glutathione was not associated with acetaminophen-induced cytotoxicity in Sprague-Dawley hepatocytes, whereas significant (P less than 0.05) cytotoxicity was demonstrated in Fischer hepatocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Rat adult hepatocytes in primary pure and mixed monolayer culture. Comparison of the maintenance of mixed function oxidase and conjugation pathways of drug metabolism

The stabilities of several drug oxidation and conjugation pathways in adult rat hepatocytes were investigated in two systems: a primary pure culture lasting 3 days and a primary mixed culture (hepatocytes co-cultured with epithelial cells) lasting 10 days. The cytochrome P450 content in hepatocytes drastically declined within 48 hr in both culture systems. Cytochrome P450-dependent mixed function oxidase was measured by the O-dealkylation of ethoxyresorufin (EROD) and of pentoxyresorufin (PROD). UPD-glucuronosyl transferase (UDP-GT) activity was measured using 1-naphthol and morphine as substrates. In both culture systems, the activities of enzymes belonging to the 3-methylcholanthrene-inducible family, namely EROD and 1-naphthol UDP-GT, were much better maintained than those of PROD and morphine UDP-GT, which belong to the phenobarbitone-inducible family: in pure cultures, EROD and 1-naphthol UDP-GT activities declined to 60% of initial values within 3 days; in mixed cultures, EROD activity was stable throughout the 10 day culture period, whereas that of 1-naphthol UDP-GT was stable until day 4 but had declined to 70% of the initial value by day 8. In contrast, PROD and morphine UDP-GT activities declined to approx. 30% of the initial values within 2 days in both culture systems, and had dropped to approx. 10% of the initial value within 8 days in mixed culture. Reduced glutathione (GSH) levels fluctuated, but remained high throughout culture. GSH conjugation declined to 40% of initial values within 3 days in pure culture, whereas it remained relatively constant in mixed culture. Comparison of these two culture systems therefore showed that although the inclusion of epithelial cells did prolong hepatocyte viability, there was a change in relative enzyme activities in both systems, suggesting a shift towards a more de-differentiated drug metabolism pattern.

Differential stability of drug-metabolizing enzyme activities in primary rat hepatocytes, cultured in the absence or presence of dexamethasone

The effects of primary hepatocyte culture on the rat cytochrome P450-dependent monooxygenase system and several conjugating enzyme activities were examined using a culture system similar to those used for evaluation of chemicals as potential genotoxins. Cytochrome P450 and cytochrome b5 contents progressively decreased throughout the 72-h culture period to less than 25% of initial values, whereas cytochrome P450 reductase rapidly decreased by 50% during attachment, but then remained stable. Cytochrome P450-dependent testosterone hydroxylase activities decreased more rapidly in culture than did cytochrome P450 content reaching less than 50% of attachment levels by 24 h. Cytochrome P450IIIA immunoreactive protein decreased at a similar rate to testosterone-6 beta-hydroxylase. Activated UDP-glucuronyltransferase activities towards 1-naphthol and testosterone declined more slowly over the 72 h than cytochrome P450 and remained at 50-60% of initial values at 72 h. UDP-glucuronyltransferase activity towards digitoxigenin monodigitoxoside (DIG) did not decrease during culture. Glutathione-S-transferase and sulfotransferase activities also declined during the 72 h at rates which appeared to be isozyme-dependent. Addition of 1 microM dexamethasone (DEX) to the culture medium increased UDP-glucuronyltransferase activity towards DIG, cytochrome P450 reductase and testosterone-6 beta-hydroxylase activities up to 2.5-, 2.0- and 7-fold, respectively and induced cytochrome P450IIIA immunoreactive protein(s) in the hepatocytes after 24 and 48 h of culture; DEX was less effective at the 72 h time-point. DEX treatment also significantly accelerated the decreases in glutathione-S-transferase activities and in sulfotransferase activities towards 1-naphthol and estrone. Thus, it appears that primary rat hepatocytes cultured under standard conditions, not only rapidly lose their monooxygenase capabilities, but also some of their capacity for conjugation. Furthermore, the use of DEX in cell culture medium to enhance cell survival does not maintain total drug-metabolizing enzyme capability, but appears to transiently and selectively increase expression of certain isozymes at the expense of others.

Selective release of glutathione transferase subunits from primary cultured rat hepatocytes by carbon tetrachloride and deoxycholic acid

The change in the activity of glutathione (GSH) transferases by carbon tetrachloride or deoxycholic acid, which induced hepatotoxicity, was studied using primary cultured rat hepatocytes. The activity of GSH transferases in the hepatocytes was decreased after the treatment with carbon tetrachloride or deoxycholic acid in their concentration- and incubation time-dependent manners. On the other hand, these compounds elicited the release of the activity of GSH transferases into the medium. Glycyrrhizin, an antihepatotoxic agent, inhibited the release of both aspartate transaminase (AST) and GSH transferases induced by carbon tetrachloride or deoxycholic acid. All subunits comprised of GSH transferases could not be released by these compounds. The main subunits of GSH transferases released by hepatotoxicity were identified as 3 and 4. These results indicate that hepatotoxicity is accompanied by the selective release of GSH transferase isozymes (class mu) following the loss of the enzymes activity in the cells.

Influence of the isolation method on the stability of differentiated phenotype in cultured rat hepatocytes

Primary cultures of adult rat hepatocytes were established using two different isolation procedures: a two-step collagenase perfusion and a method using ethylenediaminetetraacetate (EDTA) as the dissociating agent. Both techniques provided good yields of hepatocytes with comparable viability. The evolution of hepato-specific protein levels and several drug-metabolizing enzyme activities were followed for 8 days in cultured hepatocytes obtained by both methods. EDTA-isolated hepatocytes maintained a low gamma glutamyltransferase (GGT) activity, whereas collagenase-treated cells acquired a high GGT level. Transferrin secretion and tyrosine aminotransferase (TAT), alanine aminotransferase (ALT), and microsomal epoxide hydrolase (mEH) activities were stable in both EDTA- and collagenase-isolated hepatocytes, whereas albumin secretion, aspartate amino transferase (AST) activity, total cytochromes P-450 content, IA1 and IIB1 P-450 isoenzymes, NADPH-cytochrome P-450 reductase (EC 1.6.2.4) levels, and bilirubin glucuronidation decreased faster in collagenase-treated cells. The most important difference observed was the maintainance of the mixed-function oxidase system in EDTA-isolated hepatocytes. These results emphasize the critical role of isolation technique in stabilization of differentiated hepatocytes in primary culture.

Phase I and phase II xenobiotic biotransformation in cultures and co-cultures of adult rat hepatocytes

The aim of this study was to measure the activity of phase I and II key enzymes in the biotransformation of xenobiotics and their inducibility by phenobarbital (2 mM) in two currently used in vitro models, namely adult rat hepatocytes, conventionally cultured or co-cultured with rat epithelial cells derived from primitive biliary duct cells. For phase I, the cytochrome P450 content and the enzymic activities of 7-ethoxycoumarin O-deethylase and aldrin epoxidase have been determined, for phase II glutathione S-transferase activity was measured. In conventional cultures, all phase I parameters investigated declined continuously as a function of culture time. Two mM phenobarbital had inducing effects on 7-ethoxycoumarin O-deethylase and glutathione S-transferases but not on aldrin epoxidase. In co-cultures, after an initial decrease, a steady state situation developed for all the parameters measured, lasting for at least 10 days. The cytochrome P450 content, the 7-ethoxycoumarin O-deethylase, aldrin epoxidase and glutathione S-transferase activities were maintained from 3 to 4 days on at 25, 100, 15 and 50%, respectively, of their corresponding value obtained for freshly isolated hepatocytes. After phenobarbital treatment, the parameters mentioned were significantly increased with the exception of the aldrin epoxidase activity of which the inducibility was nearly completely lost.

Influence of hormones and drugs on glutathione-S-transferase levels in primary culture of adult rat hepatocytes

GST activities against 1-Chloro-2,4-dinitrobenzene (CDNB) and 1,2-dichloro-4-nitrobenzene (DCNB) were measured in isolated and cultured adult rat hepatocytes. Within 24 h in culture, both GST activities decreased to about 70% and either stabilized at this level (CDNB) or recovered (DCNB) to the initial level. Use of hyaluronidase in addition to collagenase during the isolation of the cells strongly reduced both activities and its stimulation by various drugs for up to 168 h. The hormones insulin, glucagon, triiodothyronine, estradiol, testosterone, and progesterone did not affect GST activity, while dexamethasone showed some interference. In the presence of dexamethasone the activity against CDNB was mainly stimulated by the combination of methylcholanthrene (MC) and phenobarbital (PB) to about 260% within 168 h. The activity against DCNB was stimulated predominantly by MC alone reaching 170% after 168 h. Quantification of the GST subunits Ya, Yb1 and Yp by an ELISA technique revealed a strong decrease of Ya, a transient increase of Yb1 after 24 h followed by a moderate decrease, and a stable low level of the transformation marker Yp during cultivation. The level of Ya was markedly induced by PB, particularly in combination with MC. The level of Yb1 was equally induced by MC or PB with no synergistic effect. Yp was not affected by these drugs. None of the hormones affected the level of these GST subunits. These results indicate that the physiological type of regulation of the GSTs is maintained during primary culture and no signs of dedifferentiation or transformation are observed. Furthermore, they demonstrate that the interaction of drugs and hormones and their inducing potential can be efficiently studied in the cultured hepatocytes.

Effects of culture duration on hydrogen peroxide-induced hepatocyte toxicity

The effects of culture duration on primary cultured mouse hepatocyte antioxidant levels (superoxide dismutase, catalase, glutathione peroxidase, vitamin E, and glutathione) and susceptibility to glucose oxidase (GO)- and hydrogen peroxide (H2O2)-induced cell killing and lipid peroxidation were examined. Membrane fatty acid composition was also evaluated. Adult male B6C3F1/CrlBR mouse hepatocytes were isolated by collagenase perfusion of the liver and cultured on 60-mm plastic dishes in Leibovitz's L-15 medium supplemented with glucose (1 mg/ml), dexamethasone (1 microM), fetal bovine serum (10%, v/v), and gentamicin sulfate (50 micrograms/ml) for 0 hr (freshly isolated cells) to 96 hr. Hepatocyte toxicity (determined by lactate dehydrogenase release and lipid peroxidation) after a 2-hr exposure to GO (0.8-80 micrograms/ml) or H2O2 (1-5 mM) decreased with increased time in culture. This decreased hepatocyte sensitivity to GO and H2O2 toxicity was not related to antioxidant enzyme activity since superoxide dismutase, catalase, and glutathione peroxidase declined during the 96-hr culture period. In contrast, glutathione and vitamin E levels in the cultured hepatocytes rose to 274.9 +/- 8.3% and 220.6 +/- 18.6% of the levels in freshly isolated cells (129.6 +/- 11.5 nmol and 0.10 +/- 0.01 nmol per 10(6) hepatocytes, respectively). The percentage of polyunsaturated fatty acids in hepatocyte phospholipids and triglycerides decreased with culture duration while the percentage of oleic acid increased in esterified and free fatty acid pools after 2 hr in culture. Total fatty acids were not affected by time in culture. These results suggest that the decreased hepatocyte susceptibility to the toxic effects of hydrogen peroxide may have been due to elevations in cellular GSH and vitamin E levels and decreases in membrane polyunsaturated fatty acids. The data also indicate that hepatocytes in primary culture undergo changes in antioxidant levels and fatty acid composition that may affect free radical toxicity at different times in culture.

In vitro screens from CNS, liver and kidney for systemic toxicity

The development and evaluation of in vitro systems from target organs for preliminary assessments of the potential for systemic toxic effects has been receiving increased attention. This review presents a synopsis of progress made in developing toxicity screens for three common target organs and identifies further work needed for more complete validation.

The role of CCl4 biotransformation in the activation of hepatocyte phospholipase C in vivo and in vitro

Rats treated with a single 0.5 ml/kg dose (ip) of CCl4 exhibited a threefold increase in liver microsomal phospholipase C (PLC) activity that was enhanced by phenobarbital and diminished by metyrapone pretreatment, respectively. Hepatocytes and hepatocellular fractions exposed to 0.5 mM CCl4 in vitro also exhibited a rapid rise in PLC activity that was reduced by metyrapone. Metyrapone also reduced the CCl4-related increase in the PLC-mediated reductions in cellular phosphatidylcholine content. The influence of CCl4 biotransformation on the activation of liver cell PLC was assessed in vitro. Covalent binding of 14CCl4 metabolites to isolated hepatocyte proteins and lipids was linear through 20 min of incubation and then quickly plateaued. The association of CCl4 metabolites with cellular phospholipids was inhibited by metyrapone and preceded the CCl4-dependent rise in PLC activity. CCl4-mediated increases in PLC activity were rapid and preceded reductions in cell viability. The translocation of cytosolic PLC to membranes such as the endoplasmic reticulum may explain the rapid, metabolite-dependent activation of PLC.PLC activation by haloalkanes was proportional to dose and incubation time in the order of CBrCl3 greater than CCl4 greater than CHCl3 greater than CFCl3 which corresponds to the observed hepatotoxic potential of these agents in vivo and in vitro. Haloalkane-dependent increases in PLC activity were inhibited by metyrapone. These results suggest that chemical metabolites activate PLC in vitro and in vivo. Therefore, the activation of a PLC that degrades membrane phospholipids may represent an important step in the pathogenic scheme of chemical-mediated liver cell necrosis.

Application of a cellular test battery in the decision point approach to carcinogen identification

The assessment of the potential carcinogenicity of a chemical requires a systematic approach taking into account various types of data. Important information on the DNA reactivity and other genetic effects of chemicals can be obtained from a battery of cellular tests. A battery is described which includes DNA repair in hepatocytes, mutagenesis in Salmonella typhimurium, mutagenesis, chromosome alterations, and transformation in mammalian cells. The interpretation of findings in this battery for the identification of potential carcinogenicity of chemicals is discussed.

Influence of medium composition and culture conditions on glutathione S-transferase activity in adult rat hepatocytes during culture

Glutathione S-transferase (GST) activity was measured in adult rat hepatocytes during either pure culture or coculture with another rat liver cell type in various media. Addition of nicotinamide, selenium, or dimethylsulfoxide, deprivation of cyst(e)ine and the use of two complex media were tested. Whatever the conditions used, after a constant decrease during the first 24 h, GST remained active over the whole culture period (1-2 wk). However, various patterns were observed: GST activity either remained relatively stable to approximately 50% of the initial value or showed a moderate or strong increase. The highest values were found in pure hepatocyte cultures maintained in the presence of nicotinamide or dimethylsulfoxide. Similar changes were observed using 1-chloro-2,4-dinitrobenzene or 1,2-dichloro-4-nitrobenzene as substrates for GST. Addition of 10(-4) M indomethacin resulted in 37 to 60% inhibition of enzyme activity. Thus, these results demonstrate that GST remained expressed during culture but its levels markedly varied depending on the medium composition and type and age of culture.

The content and activity of cytochrome P-450 in long-term culture of hepatocytes from male and female rats

The content of cytochrome P-450 and the capacity for O-demethylation have been measured in cultures of hepatocytes from male and female rats for a period of 21 days. The effect of dexamethasone, insulin, glucagon, phenobarbital and hemin was investigated. In hepatocytes from female rats the content of cytochrome P-450 was unchanged after one day of culture. From day 1 to day 3 the content of cytochrome P-450 decreased by 65% and only the combined addition of dexamethasone, phenobarbital and hemin diminished the fall. After the initial fall, addition of 0.1 microM dexamethasone resulted in a stable value. Addition of 1 microM dexamethasone or 1 mM phenobarbital gave rise to an induction of cytochrome P-450 (285%). The high level of cytochrome P-450 was maintained for 3 weeks. In hepatocytes from male rats the content of cytochrome P-450 decreased by 40% after one day of culture. From day 1 to day 3 the content decreased by 45% and the decrease continued irrespective of the presence of hormones and/or phenobarbital. The O-demethylase activity in cultures of hepatocytes from female rats correlated to the cytochrome P-450 content independent of medium composition and age of the cultures, whereas no correlation was found in cultures from male rats. The present study demonstrates that hepatocytes from female rats in cultures retain O-demethylase activity for at least 3 weeks and that, with the experimental conditions used, the response to the hormones and inducers is different for hepatocytes from male and female rats.

Intracellular lactate dehydrogenase concentration as an index of cytotoxicity in rat hepatocyte primary culture

In searching for a reliable index for cytotoxicity testing in rat hepatocyte primary culture, lactate dehydrogenase (LDH) concentrations in lysates of attached hepatocytes and LDH released into the culture medium were compared under conditions of exposure to various dosages of sodium chloride, sodium salicylate, R-warfarin, acetaminophen, phenylbutazone, and furosemide (frusemide). The amount of intracellular LDH was assessed by inducing the cells to release the enzyme with 0.1% Triton X-100. The induced LDH leakage was completed in 1 hr and the LDH activity was stable in storage at 10 degrees for 2 weeks. We found that intracellular LDH is a direct indicator of the number of viable hepatocytes in contrast to the LDH released, because released LDH does not account for the significant number of cells detached from monolayer but which are not leaky, during the 6-hr test period. Based on IC50 values (50% inhibitory concentration), the relative cytotoxicities are R-warfarin greater than phenylbutazone greater than furosemide greater than acetaminophen greater than sodium salicylate greater than sodium chloride.

Gas chromatography-mass spectrometry analysis of tert.-butyldimethylsilyl derivatives of 2-acetylaminofluorene and metabolites in isolated rat hepatocytes

A new technique for the conversion of 2-acetylaminofluorene and several ring-hydroxylated metabolites to mono- and di-tert.-butyldimethylsilyl derivatives was developed to permit their analysis by gas chromatography-mass spectrometry in order to quantify the metabolism of 2-acetylaminofluorene incubated in freshly isolated rat hepatocytes. This new gas chromatography-mass spectrometry method allowed the separation, identification and quantitation of seven known metabolites comprising five arylhydroxylated compounds, 2-aminofluorene and N-hydroxy-2-acetylaminofluorene.

Effect of sodium butyrate on primary cultures of adult rat hepatocytes

Sodium butyrate, at millimolar concentrations, seems to mediate or initiate multiple effects on many mammalian cells in culture. Although many transformed cell lines respond to butyrate treatment with acquisition of normal cellular characteristics, the effect of butyrate on a normal cell type, the parenchymal hepatocyte, has not been studied. Serum-free primary cultures of adult rat hepatocytes maintain many adult characteristics, yet after several days in culture a loss of adult characteristics occurs while fetal characteristics are often reexpressed. Therefore, we investigated whether butyrate treatment would improve the morphologic and biochemical characteristics of cultured hepatocytes. Exposure to 5 mM butyrate for 3 d did not affect hepatocyte viability or morphology but retarded the progressive decline in cytochrome P-450 levels and 5'-nucleotidase activity. The spontaneous increase in alkaline phosphatase activity was reduced and the induction of tyrosine aminotransferase was inhibited after 3 d in culture. The fetal liver characteristic, gamma glutamyltranspeptidase, was not affected by butyrate treatment. Results of this study suggest that butyrate represents a nontoxic compound capable of improving the maintenance of cell culture characteristics of adult rat hepatocytes.

Comparison of metabolic activation of carcinogens in human, rat, and hamster hepatocytes

The activities to activate and detoxify procarcinogens were compared in intact hepatocytes from humans, Sprague-Dawley rats and Syrian golden hamsters. Mutagenic metabolites that were released from the isolated hepatocytes were detected by mutation induction in co-cultivated Salmonella typhimurium TA98. Hepatocytes from the 3 animal species all activated aflatoxin B1 (AFB1), acetylaminofluorene (AAF) and aminofluorene (AF) and released active metabolites to induce mutation in the indicator S. typhimurium T98. Hamster hepatocytes were more effective than were human and rat hepatocytes to mediate mutation of Salmonella TA98 by AFB1, AAF and AF. Hepatocytes of human and rat failed to mediate mutation by 1-aminopyrene (1-AP). Indeed, at low concentration of 1-AP and 1-nitropyrene (1-NP), the presence of the hepatocytes decreased the number of TA98 revertants. Only at higher concentrations of 1-aminopyrene and 1-nitropyrene did hamster hepatocytes increase mutation frequencies of indicator cells over the control groups. It seems that hepatocytes, particularly human hepatocytes, are better able to absorb and detoxify 1-AP and 1-NP than to activate them.