The potential use of cultured hepatocytes in predicting the hepatotoxicity of xenobiotics

The Predictive Potential of a Battery of Ecotoxicological Tests for Human Acute Toxicity, as Evaluated with the First 50 MEIC Chemicals

The acute toxicities of the first 50 chemicals (dextropropoxyphene hydrochloride excluded) of the multicentre evaluation of in vitro cytotoxicity (MEIC) programme were determined on four aquatic invertebrates and a bacterial strain (Photobacterium phosphoreum for the Microtox™ test) commonly used in ecotoxicology testing. Three of the aquatic invertebrate tests consisted of cyst-based toxicity tests (Artoxkit M with Artemia salina, Streptoxkit F with Streptocephalus proboscideus, and Rotoxkit F with Brachionus calyciflorus), and the Daphnia magna test. Results of simple linear regression analyses indicated that the rodent tests (rat and/or mouse) were better than the ecotoxicological tests for predicting acute oral lethal doses in man. However, it appears that the batteries of ecotoxicological tests resulting from the partial least squares method appear to be better than the rodent tests for predicting human oral lethal doses.

Evaluation of the cytotoxicity of ten chemicals on human cultured hepatocytes: Predictability of human toxicity and comparison with rodent cell culture systems

The cytotoxic effect of the first 10 chemicals on the MEIC list (evaluated in the Multicentre Evaluation of In Vitro Cytotoxicity organized by the Scandinavian Society of Cell Toxicology) was evaluated on human and rat cultured hepatocytes and in the non-hepatic murine 3T3 cell line. The MTT test was used as an endpoint to evaluate cytotoxicity after 24 hr of exposure to the chemicals. The predictability of human toxicity using human hepatocytes was analysed and compared with the results using rodent cell culture systems and rat and mouse LD(50) tests. Ferrous sulphate, diazepam and isopropyl alcohol produced about the same toxicity in all three cell culture models; paracetamol and acetylsalicylic acid were more toxic to human and rat hepatocytes than to mouse 3T3 cells; amitriptyline, ethylene glycol, methanol and ethanol were more toxic to human hepatocytes than to rodent cells. Digoxin was the most cytotoxic chemical to human hepatocytes (IC(50), 4.9 nm), the alcoholic compounds (isopropanol, ethylene glycol, ethanol and methanol) were the least toxic (IC(50), 125-819 mm) and paracetamol, acetylsalicylic acid, ferrous sulphate, diazepam and amitriptyline showed intermediate cytotoxicities (IC(50), 0.05-6 mm). The data suggest that for these 10 chemicals, acute toxicity in humans was more accurately predicted using human hepatocytes than using rat hepatocytes or mouse non-hepatic 3T3 cells.

The use of hepatocytes to investigate drug toxicity

The liver is very active in metabolizing foreign compounds and the major target for toxicity caused by drugs. Hepatotoxicity may be the result of the drug itself or, more frequently, a result of the bioactivation process and the production of reactive metabolites. Prioritization of compounds based on human hepatotoxicity potential is currently a key unmet need in drug discovery, as it can become a major problem for several lead compounds in later stages of the drug discovery pipeline. Therefore, evaluation of potential hepatotoxicity represents a critical step in the development of new drugs. Cultured hepatocytes are increasingly used by the pharmaceutical industry for the screening of hepatotoxic potential of new molecules. Hepatocytes in culture retain hepatic key functions and constitute a valuable tool to identify chemically induced cellular damage. Their use has notably contributed to the understanding of mechanisms responsible for hepatotoxicity (disruption of cellular energy status, alteration of Ca(2+) homeostasis, inhibition of transport systems, metabolic activation, oxidative stress, covalent binding, etc.). Assessment of current cytotoxicity and hepatic-specific biochemical effects is limited by the inability to measure a wide spectrum of potential mechanistic changes involved in the drug-induced toxic injury. A convenient selection of endpoints allows a multiparametric evaluation of drug toxicity. In this regard, cytomic, proteomic, toxicogenomic and metabonomic approaches help to define patterns of hepatotoxicity for early identification of potential adverse effects of the drug to the liver.

Prooxidant activity and toxicity of nordihydroguaiaretic acid in clone-9 rat hepatocyte cultures

Nordihydroguaiaretic acid (NDGA) is a polyphenol. It is present at high concentrations in the leaves of the evergreen desert shrub, Larrea tridentate (Creosote bush), which has a long history of medicinal use traditionally by the native Americans and Mexicans. It is generally believed that the antioxidant properties of NDGA are responsible for the medicinal value of this desert shrub. The clone-9 rat hepatocyte cultures were used as an in vitro model to assess the hepatotoxic potential of NDGA and to determine whether it exhibits any prooxidant activity. The hepatocyte cultures were treated with NDGA for 2 h at 37 degrees C at concentrations of 0-100 microM. After the treatment period the cells, the culture supernatants and cell lysates were assayed for evaluation of prooxidant activity and toxicity of NDGA. Oxidative stress level and oxidative cell injury as measured by the peroxidation of membrane lipids and DNA double-strand breaks were used to index prooxidant activity. Cytotoxicity as measured by the leakage of the liver enzyme lactate dehydrogenase (LDH) into the culture medium, mitochondrial function and extent of cell proliferation were used as the endpoints of toxicity. Significant concentration-dependent differences were observed in these biomarkers over the concentration range examined demonstrating the prooxidant activity and toxicity of NDGA in clone-9 rat hepatocyte cultures.

Gene expression analysis of the hepatotoxicant methapyrilene in primary rat hepatocytes: an interlaboratory study

Genomics technologies are used in several disciplines, including toxicology. However, these technologies are relatively new, and their applications require further investigations. When investigators apply these technologies to in vitro experiments, two major issues need to be clarified: a) can in vitro toxicity studies, in combination with genomics analyses, be used to predict the toxicity of a compound; and b) are the generated toxicogenomics data reproducible between laboratories? These questions were addressed by an interlaboratory study with laboratories of four pharmaceutical companies. We evaluated gene expression patterns from cultured rat primary hepatocytes after a 24-hr incubation with methapyrilene (MP). Extensive data analysis showed that comparison of genomics data from different sources is complex because both experimental and statistical variability are important confounding factors. However, appropriate statistical tools allowed us to use gene expression profiles to distinguish high-dose-treated cells from vehicle-treated cells. Moreover, we correctly identified MP in an independently generated in vitro database, underlining that in vitro toxicogenomics could be a predictive tool for toxicity. From a mechanistic point of view, despite the observed site-to-site variability, there was good concordance regarding the affected biologic processes. Several subsets of regulated genes were obtained by analyzing the data sets with one method or using different statistical analysis methods. The identified genes are involved in cellular processes that are associated to the exposure of primary hepatocytes to MP. Whether they are specific for MP and are cause or consequence of the toxicity requires further investigations.

Spontaneous apoptosis, necrosis, energy status, glutathione levels and biotransformation capacities of isolated rat hepatocytes in suspension: effect of the incubation medium

Isolated hepatocytes in suspension express most of the functional activities of the intact liver and offer an easy-to-handle in vitro system for investigating both the biotransformation and damaging effects induced after a single exposure to xenobiotics upto 3-4h. There is, however, a general lack of consensus with respect to the choice of a suitable suspension medium. This motivated us to perform a comparative study of the effects of five frequently used bicarbonate-based media (Ca(2+)-containing Krebs-Henseleit buffer (KHB) with or without 25mM HEPES, 10mM glucose and 2% (g/v) BSA supplements, and Williams' E culture medium) on the viability (LDH leakage, caspase-3 processing and activity, Bid/Bax expression) and functionality (energy status, glutathione content, phases I and II biotransformation) of freshly isolated rat hepatocytes in suspension upto 3h. Also included was the bicarbonate-free HEPES buffer that does not require carbogen gassing, and is therefore handled more easily. The results clearly demonstrated that the type of incubation medium profoundly affected the functionality of the suspended hepatocytes, changing their sensitivity and response to exogenous damaging effects. While HEPES buffer and Williams' E medium offered the lowest background of spontaneous cell death, bicarbonate-based buffers and media seemed more suitable for obtaining both phases I and II biotransformation. Williams' E medium ensured a constant glutathione content of the cells and a lower level of oxidative stress.

Microstructured scaffolds for liver tissue cultures of high cell density: Morphological and biochemical characterization of tissue aggregates

Very high cell densities and optimal vascularization characterize among others organs and tissues in vivo. In order to study organ-specific functions in vitro or to make use of them in medical devices/treatments in the future, this natural architecture should be rebuilt. An important aspect in this context is the appropriate ratio of medium to cell volume being so far not optimally reestablished in most of the currently available in vitro systems. To improve such culture conditions, we constructed a microstructure to culture hepatocytes and (without any addition of extracellular matrix material) characterized liver tissue in the form of evenly sized aggregates. The liver-specific differentiation status of such aggregates was monitored by their ability to perform CYP450 dependent xenobiotic metabolism along with the measurement of albumin secretion. Freshly isolated adult rat hepatocytes show an initial loss of total CYP450 content and of associated activities (mixed function oxidases). However, in the aggregate system, this level did not decrease further but remained stable or even increased throughout the culture period of 10-13 days. The CYP450 dependent metabolism of the hepatocytes is able to respond to classic inducing agents. The described culture efficiently supports liver-specific functions of adult rat hepatocytes and seems to be suited not only for use in an extracorporeal liver device but also for the formation of evenly sized small aggregates to be of use in transplantation of differentiated liver tissue. Moreover, after design variations, the microstructure can be applied for functional analysis of metabolically active hepatocytes as well as for toxicological and pharmacological validation.

Molecular basis of drug phototoxicity: photosensitized cell damage by the major photoproduct of tiaprofenic acid

Tiaprofenic acid is a photosensitizing nonsteroidal anti-inflammatory drug, whose major photoproduct (decarboxytiaprofenic acid) is also a potent photosensitizer. Because of the lack of the carboxylate moiety, this photoproduct is more lipophilic and might bind more efficiently to cell membranes, thereby causing phototoxic damage. To verify the feasibility of this hypothesis, we have prepared the 3H-labeled analogs of tiaprofenic acid and its photoproduct and examined the binding, persistence and phototoxicity of the photoproduct using poorly metabolizing (fibroblasts) and actively metabolizing cells (hepatocytes). The photoproduct of tiaprofenic acid accumulates in both cell types as it is formed. Upon removal of the photoproduct from the culture medium, it rapidly disappears from hepatocytes but not from fibroblasts. Consequently, irradiation of fibroblasts previously incubated with the photoproduct and kept in culture in the dark for 20 h results in generalized cell damage while this effect is not observed in hepatocytes. Because of its long persistence in poorly metabolizing skin cells and its reluctance to photobleaching, the formation of this photoproduct in skin may be of relevance to explain the in vivo phototoxicity of tiaprofenic acid.

Collagen gel immobilization: a useful cell culture technique for long-term metabolic studies on human hepatocytes

1. Primary cultures of human hepatocytes have already been employed in various applications for the study of xenobiotic metabolism. Most of these approaches were performed either on freshly isolated cells or on short-term primary cultures. Standard culture techniques do not maintain functional stability of P450 enzymes for > 1 week in vitro. 2. The aim of this study was to demonstrate the beneficial effect of an easy to apply, extracellular matrix configuration on the long-term performance of cultured human liver cells. Light microscopical examination of the cultures indicated that the cells remained viable over 1 month. As revealed by electron microscopy, hepatocytes exhibited bile canaliculi and desmosomes and were rich in mitochondria and endoplasmatic reticulum, indicating metabolic activity. 3. An early culture phase (3 days after isolation) could be described with decreasing DNA content of the cultures, peak values of alanine-amino-transferase (ALAT), and increasing albumin synthesis. After this adaptive period stable levels for DNA content and albumin synthesis were noted; ALAT returned to low values. 4. Functional activity was monitored by measurements of P450 1A1-dependent O-demethylation of p-nitroanisole to p-nitrophenol, which appeared to be constant over 3 weeks and weakly inducible by 1 mM phenobarbital. Another set-up examined conjugation of acetaminophen at subtoxic concentrations: acetaminophen was metabolized to its glucuronide and sulphate; 3-(glutathione-S-yl)-acetaminophen was not detected. Almost identical metabolism was found, comparing day 3 with 16 of culture. 5. We concluded that collagen gel immobilization not only provides mechanical support to cultured hepatocytes, but also supports long-term differentiated function of the cells for metabolic studies.

Human acute toxicity prediction of the first 50 MEIC chemicals by a battery of ecotoxicological tests and physicochemical properties

Five acute bioassays consisting of three cyst-based tests (with Artemia salina, Streptocephalus proboscideus and Brachionus calyciflorus), the Daphnia magna test and the bacterial luminescence inhibition test (Photobacterium phosphoreum) are used to determine the acute toxicity of the 50 priority chemicals of the Multicentre Evaluation of In Vitro Cytotoxicity (MEIC) programme. These tests and five physiocochemical properties (n-octanol-water partition coefficient, molecular weight, melting point, boiling point and density) are evaluated either singly or in combination to predict human acute toxicity. Acute toxicity in human is expressed both as oral lethal doses (HLD) and as lethal concentrations (HLC) derived from clinical cases. A comparison has also been made between the individual tests and the conventional rodent tests, as well as between rodent tests and the batteries resulting from partial least squares (PLS), with regard to their predictive power for acute toxicity in humans. Results from univariate regression show that the predictive potential of bioassays (both ecotoxicological and rodent tests) is generally superior to that of individual physicochemical properties for HLD. For HLC prediction, however, no consistent trend could be discerned that indicated whether bioassays are better estimators than physicochemical parameters. Generally, the batteries resulting from PLS regression seem to be more predictive than rodent tests or any of the individual tests. Prediction of HLD appears to be dependent on the phylogeny of the test species: cructaceans, for example, appear to be more important components in the test battery than rotifers and bacteria. For HLC prediction, one anostracan and one cladoceran crustacean are considered to be important. When considering both ecotoxicological tests and physicochemical properties, the battery based on the molecular weight and the cladoceran crustacean predicts HLC substantially better than any other combination.

Photodynamic lipid peroxidation by the photosensitizing nonsteroidal antiinflammatory drugs suprofen and tiaprofenic acid

The photochemistry of the photosensitizing nonsteroidal antiinflammatory drugs tiaprofenic acid and suprofen involves the intermediacy of short-lived species (i.e. radicals). The data obtained in the present work strongly suggest that such intermediates may be responsible for the phototoxicity of 2-arylpropionic acids by inducing photodynamic lipid peroxidation at drug concentrations likely to be reached in the skin. This has been investigated using linoleic acid as a model lipid and determining the amount of hydroperoxides by measuring the spectrophotometric absorption at 233 nm, associated with the formation of dienic hydroperoxides. The major photoproducts of tiaprofenic acid and suprofen are derivatives bearing an ethyl side chain. Photoproducts of this type, due to the lack of polar moieties, are highly lipophilic and likely to accumulate in the lipid bilayer of cell membranes. Taking into account their ability to induce photodynamic lipid peroxidation and their marked photostability, it is conceivable that such photoproducts can participate in many catalytic cycles, playing a significant role in the mechanism of photosensitization by tiaprofenic acid and suprofen.

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.

Involvement of drug-derived peroxides in the phototoxicity of naproxen and tiaprofenic acid

Photodegradation of naproxen and tiaprofenic acid in aqueous buffered solutions leads to decarboxylated products with ethyl, 1-hydroxyethyl and/or acetyl side chains. The photomixtures obtained in the presence of oxygen were clearly more toxic to cultured hepatocytes than those obtained under anaerobic conditions. This effect was more noticeable in the case of naproxen. Based on the composition of the oxygenated photomixtures and the relative toxicity of the different photoproducts, it is possible to account for most of the observed toxicity in the case of tiaprofenic acid but not in the case of naproxen. This is explained as a result of the presence of drug-derived peroxidic species in the photomixtures and their contribution to the observed toxicity. Peroxides were determined by the peroxidase-catalyzed oxidation of dichlorodihydrofluorescein to its fluorescent analog. The amount of peroxides present in naproxen photomixtures was much higher than in the case of tiaprofenic acid. A dose-dependent depletion of intracellular glutathione was observed when hepatocytes were incubated with peroxide-containing naproxen photomixtures. This effect was prevented by the addition of catalase or N-acetylcysteine to the culture medium.

Studies on the age-dependent effects of galactosamine in primary rat hepatocyte cultures

Galactosamine (GalN) has been known to induce liver injury by depletion of uracil nucleotides. The objective of the present work was to examine age-dependent toxicity of GalN in primary hepatocyte cultures. Hepatocytes from fetal (Day 20 of gestation), neonatal (2.5-day), adult (5-month), and aged (30-month) rats were established as monolayered cultures. LDH leakage, cell viability, UTP, UDP, and UMP were measured as end points of toxicity in cultures exposed to 5 mM GalN. LDH leakage was increased and cell viability was decreased in adult rat hepatocytes at 48 and 60 hr after treatment. Although similar effects were observed in hepatocytes from aged rats, these cells appeared resilient to GalN toxicity as indicated by significantly less LDH leakage and cell death. Fetal and neonatal rat hepatocytes also exhibited greater resiliency to GalN based on the same end points. The UTP, UDP, and UMP levels of aged hepatocytes (30-month) were higher than control adult levels to begin with and dropped after GalN treatment. The level of UMP at 60 hr was similar to that of normal adult cells, but the UTP and UDP levels were significantly higher in aged hepatocytes in comparison to those of adult hepatocytes. The levels of uracil nucleotides in the fetal and neonatal cells were the same as those in adult cells, but did not decrease significantly after exposure to GalN. These findings show that aged rat hepatocytes have a higher set point for uracil nucleotides, which is consistent with the relative resiliency of these cells to GalN injury. Neonatal and fetal cells have the same set point for these nucleotides as adult rats, but are relatively resistant to GalN-induced depletion. In conclusion, the differences in toxicity of GalN may reside in age-related differences in the regulation of uracil nucleotide biochemistry.

Potentiation of cocaine hepatotoxicity by ethanol in human hepatocytes

The hepatotoxic effects of cocaine on the human liver and the effect of ethanol on cocaine-induced hepatotoxicity have been examined in adult human hepatocytes cultured in chemically defined conditions. Cultures were exposed to concentrations of cocaine ranging from 10(-2) to 10(-5) M. Cytotoxicity was evaluated after 24 hr of continuous exposure to cocaine by measuring the leakage of intracellular LDH and the ability of cells to reduce MTT. According to these end-point parameters, half-maximal cytotoxic concentrations of cocaine for human hepatocytes (IC50) were 6.8 and 7.8 mM, respectively. Lower concentrations of cocaine, however, impaired basic metabolic functions of human hepatocytes. Exposure of cells to 2 mM cocaine for 24 hr resulted in a 50% decrease in hepatic glycogen, a 40% decrease in cellular glutathione content, and a 40% decrease in urea synthesis with respect to control values. For most of the metabolic parameters assayed, significant alterations were observed at 0.5 mM cocaine. Glycogen reloading of hepatocytes began to be inhibited in the presence of 0.60 mM cocaine (IC10). Ethanol greatly potentiated cocaine-induced hepatotoxicity. After a 48 hr pretreatment of human hepatocytes with 50 mM ethanol, low concentration of cocaine (0.25 mM) that had no effects on hepatocyte metabolism in the absence of ethanol caused a 20% inhibition of the urea synthesis rate, a 40% degradation of glycogen stores, and a 30% reduction in glutathione content. The results of our work show that ethanol increases the effects of cocaine on human hepatocytes by a factor of 10.

Interaction between aflatoxin B1 and oxytetracycline in isolated rat hepatocytes

Isolated rat hepatocytes were used as an in vitro model to investigate a possible interaction between oxytetracycline (OXT) and aflatoxin B1 (AFB1). LDH leakage, RNA and protein synthesis and glycogen accumulation were measured in the presence of both drugs, either separately or in combination. The evolution of LDH leakage during the incubation was identical in untreated and treated cells. AFB1 inhibited RNA and protein synthesis at a concentration of 10(-7) M and 10(-6) M, respectively, and higher, whereas OXT did not influence RNA synthesis but inhibited protein synthesis at the highest tested concentration, 10(-3) M. As far as glycogen is concerned, rats were injected with glucagon before sacrifice in order to obtain a constant synthesis rate in isolated hepatocytes. AFB1 inhibited the accumulation of glycogen from 10(-6) M upward. This effect was never observed before 90 min of incubation. OXT had no effect on glycogen synthesis. In the presence of both drugs, no interaction was demonstrated as far as RNA and protein synthesis were concerned, but OXT opposed the inhibition induced by AFB1 on glycogen accumulation. If the "in vivo" protection, provided by OXT against AFB1-induced toxicity, is due to a direct interference in the toxic mechanisms of the mycotoxin, these results show that OXT does not influence the AFB1-inhibition of RNA and protein synthesis. The latter are early and sensitive parameters inhibited by AFB1. On the contrary, taking into consideration the results on glycogen accumulation, it seems more interesting to investigate further this metabolism.

Neutral red (NR) assay for cell viability and xenobiotic-induced cytotoxicity in primary cultures of human and rat hepatocytes

Neutral red (NR) in medium was absorbed and concentrated in lysosomes of cultured rat and human hepatocytes. NR uptake increased with the time of incubation and reached a plateau in 2 hr. Uptake was proportional to the concentration of the NR solution and the numbers of viable liver cells. Prolonged culture of hepatocytes increased the numbers of lysosomes, and thus, the dye accumulation. The NR can be extracted from lysosomes for quantitative measurement of hepatocyte viability and cytotoxicity of xenobiotics. With this assay, several serum-free media (e.g., Waymouth's, MEM, LHC-8, etc.) were compared for the maintenance of viable hepatocytes in vitro. Interestingly, LHC-8 medium, which is used to grow human bronchial epithelial cells, best preserved viable rat hepatocytes. The cytotoxic effects of dimethylnitrosamine (DMN) and aflatoxin B1 (AFB1) were examined by NR assay on rat and human hepatocyte cultures and were found to be dependent on dose and time of the exposures. NR50 was 20 mM for DMN and 0.072 microM for AFB1 in rat hepatocytes with 24 hr of exposures and reduced to 12.5 mM for DMN and 0.053 mu microM for AFB1 with 48 hr exposures. Human hepatocytes were more resistant to the toxicity of both chemicals; NR50 values were 100 mM DMN and 1.8 microM AFB1 respectively, for 24 hr treatments. Compared with lactate dehydrogenase (LDH) leakage test, the NR assay was simpler and more sensitive in determining the viability and cytotoxicity of xenobiotics in primary cultures of hepatocytes.

In Vitro Toxicity to Two Cellular Systems of the First Ten Chemicals on the MEIC List

The cytotoxic effects of the first 10 chemicals on the MEIC list were evaluated with two experimental cellular systems, monolayer cultures of rat hepatocytes and cell lines (Hep G2 and 3T3). Three endpoints were measured to evaluate cytotoxicity, intracellular LDH activity, cellular protein content and the MTT test. The results show that:

1. digoxin, amitriptyline and diazepam were the most cytotoxic chemicals (IC50:0.01-0.5mM);

2. alcoholic compounds (sopropanol, ethylene glycol, ethanol and methanol) produced the lowest toxic effects (IC50: 100–1500mM);

3. paracetamol, acetylsalicylic acid and ferrous sulphate showed an intermediate cytotoxic action (C50: 0.05–15mM);

4. regarding the sensitivity of the cellular systems, paracetamol, acetylsalicylic acid, diazepam and ferrous sulphate were more toxic to rat hepatocytes, while digoxin produced a different toxic effect on hepatic and non-hepatic cells; and

5. the other chemicals did not show significant differences in their toxicity in the different cellular systems studied.

Hepatotoxicity of Opiates and Cocaine on Different Hepatic Cellular Systems

We have studied the hepatotoxic effects of cocaine and opioids (morphine, heroin, meperidine, methadone and buprenorphine) on two experimental cellular systems: primary monolayer cultures of rat hepatocytes and hepatoma cell lines (FaO and Hep G2). Three methods were used to evaluate cytotoxicity: intracellular measurement of LDH activity, measurement of total attached cellular protein content, and the MTT test. The results show that:

1) Morphine, heroin and cocaine were more toxic to 1-24-hour primary cultures (IC50: 0.16-0.56mM) than to the other liver-derived cells (IC50: 0.62-8.00mM).

2) Meperidine and methadone produced more evident toxic effects on the hepatoma cell lines (IC50: 0.6–2.0 and 0.08–0.25mM, respectively) than on the primary hepatocyte cultures (IC50: 1.7–4.5 and 0.25–0.50mM, respectively).

3) The toxicity of buprenorphine was similar in all cellular systems (IC50: 0.03–0.13mM).

4) With regard to their toxic potential, we found that buprenorphine and methadone were the most toxic compounds in the majority of the tests. On the other hand, meperidine was least toxic to primary hepatocyte cultures, but showed higher toxicity than morphine, heroin and cocaine to the hepatoma cell lines.