Observation of hepatotoxic effects of 2-n-pentylaminoacetamide (Milacemide) in rat liver by a combined in vivo/in vitro approach

Milacemide or 2-n-pentylaminoacetamide hydrochloride, a new glycine derivative, was found to cause elevations of plasma transaminases in patients suffering from severe depression and Alzheimer's disease. However, no signs of liver toxicity were observed during the course of earlier conducted subchronic and chronic in vivo studies in rodents and cynomolgus monkeys. In this study an in vivo/in vitro approach has been proposed to detect early alterations in key metabolic and functional liver capacities. Milacemide was administered by continuous i.v. infusion for 7 days to male Sprague-Dawley rats using subcutaneously implanted osmotic pumps. Doses were given of 0, 250 and 500 mg/kg per day. Body weight and food intake were recorded and at day 7 of exposure, Milacemide concentration, glucose, urea, triglycerides and cholesterol levels and alanine (ALT) and aspartate aminotransferase (AST) activities were measured in plasma. Non-esterified fatty acids were determined in serum. On day 8, after overnight fasting, hepatocytes were isolated. A portion of the cells derived from untreated animals (no osmotic pumps) were cultured in a primary monolayer and exposed in vitro to different Milacemide concentrations. The xenobiotic biotransformation capacity of the isolated hepatocytes was studied by measuring the cytochrome P450 content, ethoxycoumarin-O-deethylase (ECOD), pentoxyresorufin-O-deethylase (PROD), ethoxyresorufin-O-deethylase (EROD), aldrin epoxidase (AE), epoxide hydrolase (EH) and glutathione S-transferase (GST) enzyme activities. Triglycerides, cholesterol and phospholipid contents were measured on the isolated cells. At plasma concentrations of 43 and 130 microM Milacemide, the ALT activity was unchanged or significantly decreased, whereas the AST activity was increased in both cases. Other clinical chemistry parameters remained unchanged. Weight gain was significantly lower in rats treated with the high Milacemide dose. In addition, decreased food consumption was observed in all treated animals leading to significantly lower food efficiency factors for the rats treated with the high dose. Milacemide had a specific inhibitory effect on xenobiotic biotransformation: ECOD activity decreased to 60% of the control value for both Milacemide doses, PROD activity remained unaffected whereas EROD activity decreased to 65% of the control value. A decrease was also observed at the highest drug concentration for AE (to 41%), EH (to 65%), cytochrome P450 content (to 80%) and GST (to 85%). At 500 mg Milacemide kg/day, hepatocyte triglycerides levels increased 3.1-fold while cholesterol and phospholipid levels remained unaffected. Electron and light microscopy on total liver and isolated hepatocytes indicated a concentration-dependent accumulation of lipid droplets, the occurrence of numerous vacuoles in the cytoplasm and other structural abnormalities. When the cultured hepatocytes of control animals (without osmotic pumps) were exposed to Milacemide, the appearance of vacuoles and myeloid bodies could be confirmed in vitro. The results of this study using an in vivo/in vitro approach clearly show potential hepatotoxic properties of Milacemide, an effect not observed in conventional toxicity studies.

Effect of folate supplementation on clinical chemistry and hematologic changes related to bidisomide administration in the rat

In a chronic toxicity study in the rat, bidisomide administered as a dietary admixture produced a dose-related lowering of reticulocytes and leucocytes. Plasma alanine aminotransferase activity was increased at 300 mg/kg and decreased at 900 mg/kg. The potential mechanisms of these effects were investigated by comparing the responses in groups of male Sprague-Dawley rats receiving a control diet, or 300 or 1200 mg/kg/day bidisomide. Subsets of these groups were co-treated subcutaneously with folinic acid or with a vitamin B1, B6, B12 complex. Subsets of control and 300 mg/kg groups were maintained on a 20-25% feed restriction regimen for 3 months, to mimic the depression in body weight gain observed in animals receiving 1200 mg/kg. Body weight gains were significantly reduced at 1200 mg/kg and in all feed-restricted animals. Plasma and liver alanine aminotransferase (ALT) and plasma aspartate aminotransferase (AST) levels were also reduced at this dose level. At 300 mg/kg, plasma transaminases, glutamate dehydrogenase (GLDH) and sorbitol dehydrogenase (SDH) activities were increased. These changes were prevented in animals receiving folinic acid supplementation. Plasma glucose, triglycerides, and unsaturated and total iron binding capacities were decreased, while plasma iron levels tended to increase, mainly at the high dose. Vitamin supplementation prevented a decrease in reticulocyte counts at 300 mg/kg. Bidisomide increased urinary formimino-glutamic acid (FIGLU) excretion but did not affect methylmalonic acid (MMA) or taurine excretion. The effect on FIGLU at 1200 mg/kg was prevented by folinic acid co-treatment. Absolute liver weight was lowered at both dose levels and in feed-restricted animals. However, the relative liver weights were unaffected. Thymidine kinase and thymidylate synthase activity of the bone marrow cells were not altered by the bidisomide treatment. Except for the increase in plasma transaminase, GLDH and SDH levels at 300 mg/kg, changes in clinical chemistry parameters are considered to result mainly from nutritional restrictions. Changes in hematologic parameters appear to be related to the combination of decreased feed consumption (leukocytes) and decreased availability or utilization of folates (reticulocytes). This alteration, however, did not affect DNA synthesis in bone marrow. The prevention by folinic acid, but not by feed restriction, of the elevation of liver enzymes at 300 mg/kg is an intriguing, yet unexplained finding. There was no evidence that bidisomide affected B6 and B12 availability.

Deoxyuridine suppression test on isolated rat bone marrow cells and the in vitro effect of bidisomide

The deoxyuridine suppression test was performed on isolated rat bone marrow cells in order to study the effect of bidisomide, a new Class I antiarrhythmic agent, on folate-dependent DNA synthesis. Methotrexate and 5-fluorouracil, two known inhibitors of DNA synthesis, were included in the study to validate the test system. Methotrexate and 5-fluorouracil, at a concentration of 5.5 mum, decreased thymidine incorporation into DNA by way of the de novo pathway (thymidylate synthase activity). The salvage pathway of DNA synthesis (thymidine kinase activity), however, was not affected by these anticancer drugs. Bidisomide up to 1 mm did not affect the folate-dependent thymidylate synthase activity, nor the thymidine kinase activity of isolated rat bone marrow cells.

Comparative metabolism of SC-42867 and SC-51089, two PGE2 antagonists, in rat and human hepatocyte cultures

1. The metabolism of SC-42867 and SC-51089, two PGE2 antagonists, was studied in cultured rat and human hepatocytes. Both compounds possess an 8-chlorodibenzoxazepine moiety, but differ from each other by the nature of the side chain connected to the nitrogen atom. SC-42867 and SC-51089 and their in vitro metabolites were separated by reversed-phase hplc. The major metabolites of both compounds were identified by mass spectrometry (ms) analysis. 2. SC-42867 was metabolized on the tricyclic moiety only. Oxidative N-dealkylation with opening of the oxazepine ring was the major metabolic pathway obtained in rat hepatocytes. The metabolic profile obtained in cultured human hepatocytes was comparable with that of cultured rat hepatocytes. However, the compound was metabolized to a much lower extent by the human cells. 3. SC-51089 was extensively metabolized by both cultured rat and human hepatocytes. Human cells metabolized this compound quite differently than cultured rat hepatocytes. Aromatic hydroxylation with consequent glucuronidation and sulphation were the main metabolic pathways observed in cultured human hepatocytes. Oxidative N-dealkylation with opening of the oxazepine ring and consequent glucuronidation was the major metabolic pathway observed in rat hepatocytes. Further metabolism occurred, in contrast with the human hepatocytes, mainly on the side chain. 4. The present in vitro results are compared with data of previous in vivo studies performed in rat.

Maintenance and induction in co-cultured rat hepatocytes of components of the cytochrome P450-mediated mono-oxygenase

Hepatocytes grown in culture rapidly lose many of the cytochromes P450 (CYP) responsible for metabolizing foreign compounds. Among the proteins most readily lost are members of the CYP2B subfamily. We have investigated, by RNase protection assays, the ability of rat hepatocytes, cultured conventionally or co-cultured with rat liver epithelial cells, to maintain the expression of genes encoding members of the CYP2B subfamily, and the inducibility of this expression by phenobarbital. After 4 days of conventional hepatocyte culture CYP2B mRNAs were undetectable, but remained inducible by phenobarbital. In co-cultured hepatocytes the abundance of the mRNAs remained relatively constant from 4-14 days. After 7 days of co-culture the concentration of the mRNAs was increased 12-15-fold by phenobarbital. RNase protection assays with probes capable of distinguishing between CYP2B1 and 2B2 mRNAs demonstrated that the ratios of the abundance and inducibility of the two mRNAs were the same in co-culture as in vivo. Co-cultured hepatocytes also maintained the expression of genes coding for two other components of the cytochrome P450-mediated mono-oxygenase, namely cytochrome P450 reductase and cytochrome b5.

Transcriptional- and post-transcriptional-dependent regulation of glutathione S-transferase expression in rat hepatocytes as a function of culture conditions

Transcriptional activity of the glutathione S-transferase (GST) alpha (subunits 1 and 2), mu (subunits 3 and 4) and pi (subunit 7) gene families has been analyzed using the nuclear 'run-on' technique on adult rat hepatocytes maintained for 4 days in conventional culture and for 4 and 12 days in co-culture with rat liver epithelial cells. Several medium conditions are included in this study, namely with or without fetal calf serum and with nicotinamide or dimethylsulphoxide. Hepatocytes co-cultured for 4 days maintain approximately 30-70% of the alpha gene family transcriptional activity, whatever the medium conditions, when compared to freshly isolated hepatocytes. A marked decrease is observed after 12 days of co-culture or when hepatocytes are maintained in conventional culture. The transcriptional activity of the mu gene family is maintained at 40-160% when hepatocytes are cultured with or without fetal calf serum, and is inducible by nicotinamide (approximately 4-fold) and dimethylsulphoxide (approximately 2-fold) in conventional culture and/or in co-culture. In contrast to freshly isolated hepatocytes, GST pi gene transcriptional activity is observed in conventional and co-cultured hepatocytes, irrespective of the medium conditions. Dimethylsulphoxide treatment however, represses the expression of GST 7 in vitro. These results demonstrate that the expression of GST alpha, mu and pi genes in conventional and co-cultured rat hepatocytes is controlled primarily at the level of transcription. It cannot be excluded, however, that dimethylsulphoxide stabilizes the GST mRNA levels in vitro.

Expression of glutathione S-transferase during rat liver development

The ontogeny of rat liver glutathione S-transferase (EC 2.5.1.18) (GSTs) during foetal and postnatal development was investigated. The GSTs are dimers, the subunits of which belong to three multigene families, Alpha (subunits 1, 2, 8 and 10), Mu (subunits 3, 4, 6, 9 and 11) and Pi (subunit 7) [Mannervik, Alin, Guthenberg, Jennsson, Tahir, Warholm & Jörnvall (1985) Proc. Natl. Acad. Sci. U.S.A. 82, 7202-7206; Kispert, Meyer, Lalor, Coles & Ketterer (1989) Biochem. J. 260, 789-793]. There is considerable structural homology within each gene family, with the result that whereas reverse-phase h.p.l.c. successfully differentiates individual subunits, immunocytochemical and Northern-blotting analyses may only differentiate families. Enzymic activity, h.p.l.c. and Northern blotting indicated that expression of GST increased from very low levels at 12 days of foetal growth to substantial amounts at day 21. At birth, GST concentrations underwent a dramatic decline and remained low until 5-10 days post partum, after which they increased to adult levels. During the period under study, GST subunits underwent differential expression. The Mu family had a lower level of expression than the Alpha family, and, within the Alpha family, subunit 1 was more dominant in the adult than the foetus. Subunit 2 is the major form in the foetus. Most noteworthy were subunits 7 and 10, which were prominent in the foetus, but present at low levels post partum. Immunocytochemical analysis of the 17-day foetal and newborn rat livers showed marked differences in the distribution of GSTs in hepatocytes. In the 17-day foetal liver Pi greater than Alpha greater than Mu whereas in the newborns Alpha greater than Mu much greater than Pi. Erythropoietic cells were not stained for any of the three GST families. Steady-state mRNA concentrations in the foetus correlated with the relative transcription of the Alpha, Mu and Pi class genes. However, in those genes expressed post partum, namely the Alpha and Mu class, low transcriptional activity was associated with high concentrations of mRNA. This suggests that there is a switch from transcriptional control to post-transcriptional control at birth. GST 7-7 appears to be regulated predominantly by transcription throughout the period of liver development under observation.

Effect of the aging process on the gender and phenobarbital dependent expression of glutathione S-transferase subunits in brown Norway rat liver

The effect of age, gender and phenobarbital treatment on the hepatic cytosolic glutathione S-transferase subunit composition was studied in Brown Norway rats. Affinity chromatography followed by reversed phase HPLC was used in order to separate the various glutathione S-transferase subunits. Corresponding steady-state mRNA levels were measured by Northern Blot analysis using cDNA clones hybridizing to mRNA encoding glutathione S-transferase subunits 1/2, 3/4 and 7, respectively. In all the age groups studied (15, 25, 53, 99, 112 and 136 weeks) the total amount of glutathione S-transferase protein was in untreated rats significantly higher in males (132 micrograms/mg cytosolic protein) than in females (91 micrograms/mg cytosolic protein) and significant gender dependent differences in the subunit composition were demonstrated. Aging seemed to be of minor importance in untreated as well as in phenobarbital treated rats. Under control conditions, the subunit composition of male rats between 15 and 136 weeks old consisted of 28, 12, 11 and 49% of subunits 1, 2, 3 and 4 respectively and of female animals of the same age groups of 38, 26, 7 and 30%, respectively. In all the age groups studied phenobarbital administration (45 mg/kg body weight, i.p., once a day for 7 days) doubled total glutathione S-transferase protein in both genders and affected the subunit composition in a significant way, emphasizing the already existing differences between genders. Subunits 1, 2 and 3, especially, were increased in male rats in comparison to females resulting in the observation that levels of glutathione S-transferase subunits studied became higher in males than in their female counterparts. The HPLC results were confirmed by steady-state mRNA analysis. In untreated rats, higher levels of mRNA encoding glutathione S-transferase subunits 1/2 and 3/4 were present in male than in female livers. Phenobarbital treatment increased mRNA levels in both genders. Subunit 7 was never detected. These effects were demonstrated in both young and old rats.

Regulation of glutathione S-transferase gene expression by phenobarbital in cultured adult rat hepatocytes

Previous studies, by using Northern blotting analyses, showed that phenobarbital (PB) affects the steady-state mRNA levels of glutathione S-transferase (GST) subunits 1/2, 3/4 and 7 in both conventional cultures of adult rat hepatocytes and co-cultures, with rat liver epithelial cells [Vandenberghe et al., 1989, FEBS Lett. 251, 59-64; Morel et al., 1989, FEBS Lett. 258, 99-102]. To determine whether PB acts at the transcriptional level, nuclear 'run on' experiments using cDNA probes hybridizing to GST subunits 1/2, 3/4 and 7 mRNA were performed on purified nuclei isolated from control and PB treated hepatocytes seeded under conventional and co-culture conditions. Data from this study demonstrate that the increase in steady-state mRNA levels observed in both conventional culture and co-culture after 4 days PB exposure results from an increased transcriptional activity of the GST genes. However, a substantial increase in steady-state mRNA levels in the absence of a commensurate increase in transcriptional activity at 12 days of co-culture, indicates that the barbiturate has also a stabilizing effect in vitro on the GST mRNAs.

Differential inhibition of rat hepatic glutathione S-transferase isoenzymes in the course of fascioliasis

The effects of a subclinical fascioliasis at various stages of its development (at week 3, 6 and 9 after infection by oral administration of 20 metacercariae of Fasciola hepatica) in rats were determined on the activity of enzymes involved in liver metabolism of glutathione and on the subunit pattern of cytosolic glutathione S-transferase. The parasitic pathology was ascertained by clinical observation of the rats and at autopsy. Hepatic microsomal cytochrome P-450 content was significantly decreased in infected rats by week 3 and 6 post-infection. Not correlatively, the catalytic activities of glutathione S-transferase towards 1-chloro-2,4-dinitrobenzene and 1,2-dichloro-4-nitrobenzene were significantly lowered in last stages of the experimental fascioliasis (by week 6 and 9 post-infection). These decreases were correlated to that of subunit 1 as determined by means of high-performance liquid chromatography of cytosolic proteins whereas subunit 6 could also be decreased. Fascioliasis did not alter cytosolic glutathione, glutathione reductase and glutathione peroxidase activities or plasma glutathione S-transferase activity accepting 1-chloro-2,4-dinitrobenzene as the substrate.

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.

Hepatic cytosolic glutathione S-transferase activities in ageing brown Norway rats--importance of sex differences and phenobarbital treatment for studies of ageing

Age-associated alterations of hepatic cytosolic glutathione S-transferase activities towards 1-chloro-2,4-dinitrobenzene and 1,2-dichloro-4-nitrobenzene were investigated in Brown Norway rats of both sexes (11-144 weeks old), under control conditions and after administration of phenobarbital. With both substrates, small changes in glutathione S-transferase activities are observed for the control rats (15-53 weeks old). For these specific age groups, male glutathione S-transferase activities are significantly higher than those of their female counterparts, with sex-related differences being most pronounced after 1,2-dichloro-4-nitrobenzene conjugation. Using 1-chloro-2,4-dinitrobenzene as a 'general' substrate, the sex-differences tend to decrease from the age of 53 weeks onwards to become non-significant at the age of 112 weeks. Phenobarbital administration significantly increases the total and the isoenzymes 3-3 and 3-4 activities in both sexes, with the highest and the lowest increase being observed in the youngest and oldest animals, respectively. It therefore can be concluded that some age-related variations exist as far as the glutathione S-transferase activity of both control and phenobarbital-treated rats are concerned, but that the changes observed are rather small. On the contrary, the parameters 'Sex' and 'Phenobarbital treatment' are found to be responsible for the major activity changes observed.

Allogeneic cultured epidermal grafts heal chronic ulcers although they do not remain as proved by DNA analysis

To investigate whether allogeneic cultured keratinocytes are rejected or not, and to find out how beneficial their effect on wound healing could be, patients with chronic ulcers were grafted with allogeneic cultured human keratinocytes. In order to examine the epidermal origin of the healed wound, DNA analysis was performed and compared to donor and recipient blood-cell DNA. Healing was observed in 84% of the grafted ulcers by granulation tissue stimulation and would edge effect. In little time 60% of the grafted chronic ulcers healed completely. Although no rejection was observed, DNA analysis revealed that the grafted allogeneic keratinocytes were finally replaced by the patient's own epidermis. This study confirmed that cultured allogeneic keratinocytes that have been grafted on ulcers, play an important role in the wound healing process.

Changes in expression of mRNA coding for glutathione S-transferase subunits 1-2 and 7 in cultured rat hepatocytes

mRNA hybridizing to probes for glutathione S-transferase (GST) subunits 1 and 2 (probe pGSTr 155) and subunit 7 (probe pGSTr 7) has been measured by Northern blot analysis in adult rat hepatocytes both in conventional monoculture and in co-culture with epithelial cells. In addition, several media conditions were used, namely with and without fetal calf serum (FCS) and with and without nicotinamide or dimethyl sulfoxide (DMSO). In monoculture, mRNA coding for subunits 1 and 2 was extensively reduced in the presence of FCS. In the absence of FCS, after an initial decrease, an increase of subunits 1 and 2 mRNA was noticed on day 6. When nicotinamide or DMSO was added to the medium, the GST subunits 1 and 2 mRNA level increased during the culture period. In co-culture, an initial reduction in levels of mRNA encoding subunits 1 and 2 was less marked and the values measured increased with co-culture time. Nicotinamide tended to reduce these mRNA levels, whereas DMSO increased them. In contrast, in conventional culture, mRNA encoding subunit 7 was expressed de novo and this induction was prevented by DMSO but not by nicotinamide. Similar results were obtained with co-culture.

Changes in expression and "de novo" synthesis of glutathione S-transferase subunits in cultured adult rat hepatocytes

Glutathione S-transferase (GST) isoenzymes of conventionally and co-cultured adult rat hepatocytes were purified and the GST subunits were separated by reversed phase HPLC in order to study the development of the GST subunit composition as a function of culture time and culture conditions. Several media conditions were tested, namely medium with and without fetal calf serum and with nicotinamide or dimethyl sulphoxide. Compared to the GST subunit composition of freshly isolated hepatocytes, changes in culture and media conditions result in a modification of the subunit profile. General observations are a decrease of subunits 1 and 2, an increase of subunit 3, a stabilization of subunit 4 and "de novo" expression of subunit 7. When [35S] methionine was added to the various culture media, and the thus labelled subunits were purified and separated, it was shown that cultured adult rat hepatocytes are able to synthesize the different GST proteins. Furthermore, the GST subunit composition, measured during various culture conditions, is probably a reflection of the "de novo" synthesis in vitro.

Regulation of glutathione S-transferase subunits 3 and 4 in cultured rat hepatocytes

mRNA levels of glutathione S-transferase (GST) subunits 3 and 4 were measured with a specific cDNA probe in adult rat hepatocytes maintained either in conventional culture or in coculture with rat liver epithelial cells. Four media conditions were used, i.e. with or without fetal calf serum (FCS) and with nicotinamide or dimethylsulfoxide (DMSO). When FCS was present in the culture medium, GST subunit 3 and 4 mRNAs were expressed at a level close to that found in freshly isolated hepatocytes during the whole culture period both in conventional culture and in coculture. All other culture conditions resulted in an increase of GST 3 and 4 mRNA levels. After exposure to phenobarbital an increase in GST 3 and 4 mRNA levels was demonstrated in both culture systems. Comparison with previous findings on the expression of GST subunits 1, 2 and 7 in the same culture conditions indicates that the different classes of GST are regulated independently.

Effect of phenobarbital on the expression of glutathione S-transferase isoenzymes in cultured rat hepatocytes

Cultured adult rat hepatocytes were treated daily with 3.2 mM phenobarbital (PB) in order to study its effect on the expression of cytosolic glutathione S-transferase isoenzymes. Glutathione S-transferase (GST) activities, using 1-chloro-2,4-dinitrobenzene and 1,2-dichloro-4-nitrobenzene as substrates, were increased when PB was present in the culture medium. After purification and separation of GST on glutathione Sepharose 6 B and reversed-phase HPLC, respectively, it was observed in vitro that PB caused an increase in the relative amounts of subunits 1, 3 and 7 compared to subunits 2 and 4. Using Northern blot technique, elevated levels of GST subunit 1/2 and 7 mRNA were measured, after addition of PB to the cultures.

The inducing and inhibiting effects of sodium valproate in vivo on the biotransformation systems of xenobiotics in isolated rat hepatocytes

1. The induction and inhibition of some biotransformation enzymes by valproate have been studied in hepatocytes isolated from rats treated with sodium valproate either i.p. or by subcutaneous implantation of osmotic pumps. 2. When valproate was given i.p., the cytochromes P-450 and b5, and aldrin epoxidase and glutathione S-transferase activities were significantly induced. 3. In contrast, valproate administered by osmotic pumps induced 7-ethoxycoumarin-O-deethylase activity, whereas aldrin expoxidase and glutathione S-transferase activities were significantly inhibited. At a valproate serum concentration of about 100 micrograms/ml for 2 weeks a significant induction of the cytochromes P-450 and b5 was observed. 4. Since there is a large difference between the half-lives of valproate in man and rodent, constant-rate delivery of valproate represents a better model for induction studies than i.p. injection.

Hepatotoxicity and molecular aspects of hepatocyte function in primary culture

1. The application of primary cultures of hepatocytes in testing for hepatotoxicity of drugs is reviewed. 2. Hepatotoxicity results principally from the biotransformation of toxic agents. This process is very complex and specific and involves a powerful system of multigenic isozyme families for both phase I and phase II drug metabolizing reactions. Many of the isozymes are specifically expressed in the liver in relation to the maturation or differentiation state, and are specifically induced, possibly through a complex temporally programmed gene regulation. 3. This highly specific, coordinated, molecular regulation is difficult to maintain in vitro. Isolation of hepatocytes induces a prompt differential decline of liver-specific gene transcription, which leads to preferential loss of the most specific functions, including those of the drug metabolizing isozymes, whereas repair of cell damage remains active. 4. The use of serum-free, hormonally defined media stabilizes specific hepatic functions, but not transcriptional activity, for 4-5 days. Defined media retain active DNA replication but do not permit clonal growth of hepatocytes. Co-culturing hepatocytes with primitive biliary cells prolongs cell survival and their functional capacities for several weeks, including some of the transcriptional activity.

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.

Critical evaluation of 7-ethoxycoumarin O-deethylase activity measurement in intact isolated rat hepatocytes

In the determination of 7-ethoxycoumarin O-deethylase activity in intact isolated rat hepatocytes various factors influence the assay, including: the decay of 7-ethoxycoumarin fluorescence which is temperature and pH dependent; the measured fluorescence which has to be adjusted for the inner filter effect; glucose addition to the medium which influences the activity; all organic solvents which inhibit the enzymic activity, with dimethylformamide provoking the smallest effect (partial competitive inhibition); the enzymic reaction which is inhibited by the product of reaction; and the presence of bovine serum albumin in the medium which affects the enzymic activity. Biphasic kinetics are observed for the O-deethylation of ethoxycoumarin in intact isolated rat hepatocytes. For the high-affinity component, Km and Vmax values are 5 microM and 43 pmol/min X 10(6) cells and for the low-affinity component are 414 microM and 915 pmol/min X 10(6) cells. Addition of the substrate in dimethylformamide or omitting bovine serum albumin from the medium cause important changes in these kinetic parameters.

Inhibition of gluconeogenesis by sodium valproate and its metabolites in isolated rat hepatocytes

The effects of sodium valproate (VP) and the sodium salts of its metabolites (2-en-VP, 4-en-VP, 4-OH-VP, 5-OH-VP and 2-propylglutaric acid) on gluconeogenesis have been examined using isolated rat hepatocytes. VP and its metabolites have a concentration-dependent inhibitory effect on gluconeogenesis from lactate: with increasing drug concentration, the lag in the onset of gluconeogenesis increases and the rate of glucose synthesis decreases. The toxic effect on glucose synthesis from lactate is very dependent on the metabolite used: the inhibitory effect is highest for VP and 4-en-VP, followed by 5-OH-VP, 4-OH-VP, 2-en-VP and finally by 2-propylglutaric acid. Thus, delta-dehydrogenation and omega-oxidation products in particular have a toxic effect on gluconeogenesis in isolated rat hepatocytes. Induction of the omega-oxidation pathway by enzymes inducers such as phenobarbitone may play a role in the eventual hepatotoxicity of VP. With glycerol the gluconeogenic substrate, the inhibitory effect of VP is also present, although to a smaller extent than with lactate. Glucagon abolishes the inhibitory action of VP.