Biochemical functionality and recovery of hepatocytes after deep freezing storage

Cryopreservation of Rat and Monkey Liver Slices

A method for the long-term storage of liver slices by cryopreservation was developed. The viability of liver slices was determined by analysing the leakage of alanine aminotransferase, urea production, and the metabolism of testosterone. Rat liver slices were found to be optimally cryopreserved by exposure for 30 minutes to 12% dimethyl sulphoxide (v/v) at 2°C before freezing. Subsequent direct immersion in liquid nitrogen was more effective than a cooling rate of ±1°C/mmute, which reduced viability. Storage at a temperature of -80°C lowered viability compared to storage at -196°C.

These conditions for optimal cryopreservation were used to cryopreserve rat, rhesus monkey and cynomolgus monkey liver slices. The viability of these liver slices was maintained at: 74%, 86% and 85%, respectively, when alanine aminotransferase content was measured; 80%, 109% and 82%, respectively, when urea production was measured; and 109%, 60% and 85%, respectively, when the metabolism of testosterone was measured. Viability was maintained for at least one month. The results show that, by using the method presented here, liver slices from these species can be stored while maintaining viabilities similar to initial values. This method will facilitate the optimal use of liver slices and reduce the number of experimental animals used.

The Coumarin 7-Hydroxylation Microassay in Living Hepatic Cells in Culture

Coumarin 7-hydroxylation was evaluated in hepatic cells from various species, cultured in 96-well plates. This microassay involved incubating living cultured cells with the substrate, followed by fluorimetric quantification of the product released into the culture supernatant, after hydrolysis of the conjugates of 7-hydroxycoumarin that were formed. Fluorescence was measured directly in the wells by using a microplate fluorescence reader. The major advantages of this technique are its simplicity and automation, the small number of cells required, the reduction in sample handling and assay time, and the possibility of performing repeated assays with the same cell monolayer, since no injury to cells is detectable during the assay. By using this microassay, it was shown that human hepatocytes hydroxylated coumarin at higher rates than did rabbit, dog or rat hepatocytes, and that no appreciable metabolic activity was observed in hepatoma cells (Hep G2 and FaO). In addition, methoxsalen was found to be a potent inhibitor of cytochrome P4502A6 activity in living human hepatocytes.

Cryopreservation protocol for human biliary tree stem/progenitors, hepatic and pancreatic precursors

Human biliary tree stem/progenitor cells (hBTSCs) are being used for cell therapies of patients with liver cirrhosis. A cryopreservation method was established to optimize sourcing of hBTSCs for these clinical programs and that comprises serum-free Kubota’s Medium (KM) supplemented with 10% dimethyl sulfoxide (DMSO), 15% human serum albumin (HSA) and 0.1% hyaluronans. Cryopreserved versus freshly isolated hBTSCs were similar in vitro with respect to self-replication, stemness traits, and multipotency. They were able to differentiate to functional hepatocytes,cholangiocytes or pancreatic islets, yielding similar levels of secretion of albumin or of glucose-inducible levels of insulin. Cryopreserved versus freshly isolated hBTSCs were equally able to engraft into immunocompromised mice yielding cells with human-specific gene expression and human albumin levels in murine serum that were higher for cryopreserved than for freshly isolated hBTSCs. The successful cryopreservation of hBTSCs facilitates establishment of hBTSCs cell banking offering logistical advantages for clinical programs for treatment of liver diseases.

Long-Term Functional Recovery of Hepatocytes after Cryopreservation in a Three-Dimensional Culture Configuration

Hepatocyte cryopreservation is essential to ensure a ready supply of cells for use in transplantation or as part of an extracorporeal liver assist device to provide on-demand liver support. To date, most of the work on hepatocyte cryopreservation has been performed on isolated hepatocytes, and has generally yielded cells which display low viability and greatly reduced short-term function. This report presents the development of a freezing procedure for hepatocytes cultured in a sandwich configuration. A specially designed freezing unit was used to provide controlled temperatures throughout the freeze-thaw cycle. Cooling rate, warming rate, and final freezing temperature were evaluated as to their effect on hepatocyte function as judged by albumin secretion. Under optimized conditions (cooling at 5°C/min and warming at ≥400°C/min), freezing to −40°C resulted in full recovery of albumin secretion within 2-3 days post-freezing, whereafter albumin secretion levels remained normal for the duration of the experiments (2 wks). Freezing to −80°C lead to an approximate 70% recovery of long-term protein secretion when compared to control cultures. In addition, the overall hepatocyte morphology as judged by light microscopy, closely followed the functional results. The sandwich culture configuration, thus, enables hepatocytes to maintain a satisfactory level of long-term protein secretion after a freeze-thaw cycle under optimized conditions, and offers an attractive tool for further studies into the mechanisms of freezing injury and subsequent hepatocellular recovery. These results are a promising step in the development of satisfactory storage procedures for hepatocytes.

Cryopreservation of Hepatocytes

The use of cryopreserved hepatocytes has increased in the last decade due to the improvement of the freezing and thawing methods, and has even achieved acceptance by the US Food and Drug Administration for use in drug metabolizing enzyme induction studies. This chapter provides an overview of the theories behind the process of cryopreservation as well as practical advice on methods to cryopreserve hepatocytes, which retain functions similar to fresh cells after thawing. Parameters, such as cell density, cryoprotectants, freezing media, storage conditions, and thawing techniques, should be critically considered. Special emphasis is put on human hepatocytes, but information for the cryopreservation of animal hepatocytes is also described.

Recent advances in 2D and 3D in vitro systems using primary hepatocytes, alternative hepatocyte sources and non-parenchymal liver cells and their use in investigating mechanisms of hepatotoxicity, cell signaling and ADME

This review encompasses the most important advances in liver functions and hepatotoxicity and analyzes which mechanisms can be studied in vitro. In a complex architecture of nested, zonated lobules, the liver consists of approximately 80 % hepatocytes and 20 % non-parenchymal cells, the latter being involved in a secondary phase that may dramatically aggravate the initial damage. Hepatotoxicity, as well as hepatic metabolism, is controlled by a set of nuclear receptors (including PXR, CAR, HNF-4α, FXR, LXR, SHP, VDR and PPAR) and signaling pathways. When isolating liver cells, some pathways are activated, e.g., the RAS/MEK/ERK pathway, whereas others are silenced (e.g. HNF-4α), resulting in up- and downregulation of hundreds of genes. An understanding of these changes is crucial for a correct interpretation of in vitro data. The possibilities and limitations of the most useful liver in vitro systems are summarized, including three-dimensional culture techniques, co-cultures with non-parenchymal cells, hepatospheres, precision cut liver slices and the isolated perfused liver. Also discussed is how closely hepatoma, stem cell and iPS cell-derived hepatocyte-like-cells resemble real hepatocytes. Finally, a summary is given of the state of the art of liver in vitro and mathematical modeling systems that are currently used in the pharmaceutical industry with an emphasis on drug metabolism, prediction of clearance, drug interaction, transporter studies and hepatotoxicity. One key message is that despite our enthusiasm for in vitro systems, we must never lose sight of the in vivo situation. Although hepatocytes have been isolated for decades, the hunt for relevant alternative systems has only just begun.

Molecular mechanism of diclofenac hepatotoxicity: Association of cell injury with oxidative metabolism and decrease in ATP levels

A certain number of case reports of adverse hepatic reactions to diclofenac are known, suggesting that diclofenac-associated hepatitis may be more common than previously recognized. In order to discriminate among possible molecular mechanisms of toxicity, the following were investigated: (a) cytotoxicity of diclofenac on metabolizing (rat hepatocytes) and non-metabolizing hepatic cells (HepG2, FaO); (b) changes in calcium homoeostasis, glutathione (GSH), lipid peroxidation and ATP levels, and (c) diclofenac metabolism in relation to cytotoxicity. The results indicate that toxicity is associated with the oxidative metabolism of the drug, and correlated with the formation of a minor oxidation metabolite. Inhibitors of diclofenac metabolism concomitantly reduced the toxicity of the drug. Hepatocyte injury was preceded by a decrease in ATP levels. No oxidative stress (no changes in GSH, no lipid peroxidation) could be demonstrated at this early stage. Cytotoxicity was prevented when cells were incubated with fructose, suggesting that the inability of mitochondria to produce ATP is the probable cause of diclofenac hepatotoxicity.

Evaluation of the cytotoxicity of 10 chemicals in human and rat hepatocytes and in cell lines: Correlation between in vitro data and human lethal concentration

The cytotoxicity of 10 chemicals from the Multicentre Evaluation of In vitro Cytotoxicity (MEIC) list (nos 21-30) was evaluated in human and rat cultured hepatocytes and in two established cell lines (HepG2 and 3T3) according to the MEIC programme organized by the Scandinavian Society of Cell Toxicology. The MTT test was used as the endpoint of cytotoxicity after 24hr of exposure to the chemicals. Theophylline, phenobarbital and paraquat were the least cytotoxic compounds in the cellular systems (IC(50) = 450-17,000 mum) except for the 3T3 cells. The seven remaining chemicals (dextropropoxyphene, propranolol, arsenic trioxide, cupric sulfate, mercuric chloride, thioridazine and thallium sulfate) showed a similar relative cytotoxic ranking in the four in vitro systems in the lower range of concentrations (IC(50) = 2-350 mum). The data suggest that these 10 chemicals have a basal cytotoxic effect common to the four in vitro systems, and probably none of these compounds could be considered either hepatotoxic or species specific. The correlation between in vitro data and human lethal blood concentrations showed that the predictability of the in vitro systems was similar to that of in vivo rodent tests (LD(50)) only when low cytotoxic concentrations (IC(10)) were used for correlation.

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.

Hyaluronan-supplemented buffers preserve adhesion mechanisms facilitating cryopreservation of human hepatic stem/progenitor cells

The supply of human hepatic stem cells (hHpSCs) and other hepatic progenitors has been constrained by the limited availability of liver tissues from surgical resections, the rejected organs from organ donation programs, and the need to use cells immediately. To facilitate accessibility to these precious tissue resources, we have established an effective method for serum-free cryopreservation of the cells, allowing them to be stockpiled and stored for use as an off-the-shelf product for experimental or clinical programs. The method involves use of buffers, some serum-free, designed for cryopreservation and further supplemented with hyaluronans (HA) that preserve adhesion mechanisms facilitating postthaw culturing of the cells and preservation of functions. Multiple cryopreservation buffers were found to yield high viabilities (80-90%) of cells on thawing of the progenitor cells. Serum-free CS10 supplemented with 0.05% hyaluronan proved the most effective, both in terms of viabilities of cells on thawing and in yielding cell attachment and formation of expanding colonies of cells that stably maintain the stem/progenitor cell phenotype. Buffers to which 0.05 or 0.1% HAs were added showed cells postthaw to be phenotypically stable as stem/progenitors, as well as having a high efficiency of attachment and expansion in culture. Success correlated with improved expression of adhesion molecules, particularly CD44, the hyaluronan receptor, E-cadherin, β4 integrin in hHpSCs, and β1 integrins in hepatoblasts. The improved methods in cryopreservation offer more efficient strategies for stem cell banking in both research and potential therapy applications.

Optimisation of the cryopreservation of primary hepatocytes

The use of cryopreserved hepatocytes has increased in the last decade due to the improvement of the freezing and thawing methods and has even achieved acceptance by the U.S. Food and Drug Administration for use in drug-metabolising enzyme induction studies. This chapter provides an overview of the theories behind the process of cryopreservation and some of the most important advances which have led to the ability to cryopreserve hepatocytes, which when thawed retain functions similar to fresh cells. Parameters such as cell density, cryoprotectants and freezing media should be considered as well as storage conditions and thawing techniques. Special emphasis is placed on human hepatocytes but information for the cryopreservation of animal hepatocytes is also described. Finally, a suggested method for optimising cryopreservation method is outlined.

Application of cryopreserved cells to HERG screening using a non-radioactive Rb+ efflux assay

The aim of the present study was to test the use of cryopreserved cells for human ether-ago- go (hERG) channel screening. A stable Chinese hamster ovary-K1 cell line expressing hERG channels was used in a non-radioactive Rb+ efflux assay for screening hERG channel activity. Cells prepared from normal cultures and following cryopreservation were compared with regard to time course of Rb+ efflux response at different concentrations of KCl, overall cell morphology, signal-to noise assay window, assay robustness, and 50% inhibitory concentration (IC50) of the hERG blocker dofetilide. Our results showed that cryopreserved hERG-expressing cells at 1, 2, and 3 days following plating at different cell densities had no obvious morphological changes in comparison to the growing cells. The assay window, Z' factor, and IC50 of dofetilide were also very similar in all series of cells tested. It was concluded that the cryopreserved hERG cells prepared using the protocol described are as effective as growing hERG cells in the non-radioactive Rb+ efflux assay.

Phase I and II metabolism and carbohydrate metabolism in cultured cryopreserved porcine hepatocytes

Primary porcine hepatocytes were cryopreserved using freezing boxes or a programmable freezer (PF). Upon thawing and culturing in 12-well plates cryopreserved hepatocytes were compared with their fresh controls on days 1 and 2 after plating. Cryopreserved hepatocytes attached approximately as well as fresh hepatocytes and useful cultures were obtained. In cryopreserved hepatocytes, coumarin 7-hydroxylation, 6beta-testosterone hydroxylation and p-nitrophenol glucuronidation were reduced to about 10-40, 35 and 40%, respectively, compared to their fresh counterparts. Glycogen synthesis in cryopreserved hepatocytes was reduced to about 30% on day 1 of culture and about 47% on day 2 of culture compared to the synthesis in fresh hepatocytes. Both fresh and cryopreserved hepatocytes increased the synthesis by twofold in response to stimulation with insulin. Reduced basal levels of glycogen and of glycogen synthesis could be explained by an increased energy demand in cryopreserved hepatocytes needing to repair damages caused by cryopreservation. Glycogenolysis was reduced to about 50% in cryopreserved hepatocytes and gluconeogenesis to about 40% of the glucose production in fresh hepatocytes. In both fresh and cryopreserved hepatocytes the glucose production from glycogenolysis and gluconeogenesis, respectively, was increased fourfold in response to stimulation with glucagon. Overall, the hepatocytes cryopreserved in boxes had a tendency to perform better than hepatocytes cryopreserved in a programmable freezer. In conclusion, the cryopreserved hepatocytes were metabolic active; however, to a lower extent than the fresh hepatocytes, although, the cryopreserved hepatocytes responded as well as the fresh hepatocytes to insulin and glucagon.

Cryopreservation of viable hepatocyte monolayers in cryoprotectant media with high serum content: metabolism of testosterone and kaempherol post-cryopreservation

Little work in the literature focuses on the cryopreservation of primary hepatocytes as monolayer cultures, yet this technique offers many distinct advantages over other cryopreservation systems, including high recovery, high post-thaw nutrient penetration, and low numbers of trapped dead cells. This article investigates the cryopreservation of primary rat hepatocytes at -78 degrees C attached as monolayers to collagen coated culture dishes, and describes efforts to increase post-thaw viability and function through manipulation of the freeze/thaw protocol. Different concentrations of foetal calf serum (FCS) with 10% (v/v) dimethyl sulphoxide (ME2SO) were tested as cryopreservation media, and high cryoprotectant serum levels were found to be important in maintaining membrane integrity and function in the cryopreserved rat hepatocyte monolayer cultures. Cultures cryopreserved with 90% (v/v) FCS plus 10% (v/v) ME2SO maintain 79.7+/-6.5% of the monolayer area as viable cells with normal morphology (by image analysis), 112.7+/-14.2% protein concentration, 55.4+/-4.2% carboxyfluorescein diacetate de-acetylation, 27.2+/-7.5% kaempherol glucuronidation (a measure of UDP-glucuronosyl transferase activity), and 39.3+/-7.3% testosterone hydroxylation (a measure of cytochrome P-450 activity) compared with non-cryopreserved controls. This method of cryopreservation may provide a simple, convenient means of long-term storage of hepatocytes for in vitro metabolism studies.

RXR activators molecular signalling: involvement of a PPAR alpha-dependent pathway in the liver and kidney, evidence for an alternative pathway in the heart

(1) In this study we compared the molecular signalling elicited by rexinoids, selective retinoid X receptor (RXR)-activators, in several organs (i.e. liver, kidney, heart) and in hepatocytes of various species. (2) RXR plays the pivotal role of a hetero-dimerization partner for the members of the class II subset of nuclear receptors which regulate the transcription of numerous target genes, following chemical activation. Several of these selective activators are currently used to treat hyperlipidaemia (fibrates), type II diabetes (glitazones), or skin disorders (retinoic acid). Although these therapeutic pathways are not fully elucidated, receptor activation is considered a pre-requisite for efficacy. Therefore RXR, which accepts numerous dimeric partners, is considered a worthwhile pharmacological target. (3) We analysed a number of biochemical and molecular responses to rexinoids which were given orally to mice. Our results showed a prominent involvement of the peroxisome proliferator-activated receptor (PPARalpha) as a majority of the observed hepatic and renal regulations were abolished in PPARalpha-knockout animals. Therefore we documented the species-specificity of these rexinoid actions which were reproduced in rat primary hepatocyte cultures but not in cultures of rabbit or human origin. Conversely, we established that the regulation of the pyruvate dehydrogenase kinase (PDK4) gene in the heart, by rexinoids, is independent of PPARalpha expression. (4) Our results support the obligatory expression of the active, although quiescent, PPARalpha to sustain a subset of relevant regulations attributable to rexinoids in the liver and kidney. Their cardiac molecular signalling unveiled an alternate transduction pathway and therefore opens new prospects in the therapeutic potential of rexinoids.

Proliferation of rat small hepatocytes after long-term cryopreservation

BACKGROUND/AIMS

The demand for clinical use of hepatocytes is escalating because cell transplantation will be an alternative to orthotopic liver transplantation and the shortage of liver donors is a serious problem throughout the world. However, the supply of fresh differentiated hepatocytes is limited and methods for cryopreservation of hepatocytes that can proliferate with hepatic functions are not satisfactorily established.

METHODS

Colonies of small hepatocytes were collected and then maintained at -80 degrees C for more than 6 months. Albumin secretion and mRNA expression of thawed cells were measured by enzyme linked immunosorbent assay and Northern blotting, respectively, and the expression of hepatic functions was examined by immunoblotting. The ultrastructure of cryopreserved cells was also examined.

RESULTS

About 60% of the cryopreserved colonies attached on dishes and then proliferated. The average area of small hepatocyte colonies was about 7.5 times larger at day 15 than at day 1. Albumin production increased with time in culture. In addition, the cells produced other serum proteins such as transferrin and fibrinogen, and expressed carbamoyl phosphate synthetase I and tryptophan 2,3-dioxygenase.

CONCLUSIONS

Small hepatocytes maintain growth ability and hepatic differentiated functions even after long-term cryopreservation.

Antifungal activities and cytotoxicity studies of six new azasordarins

GW 471552, GW 471558, GW 479821, GW 515716, GW 570009, and GW 587270 are members of a new family of sordarin derivatives called azasordarins. The in vitro activities of these compounds were evaluated against clinical isolates of yeasts, including Candida albicans, Candida non-albicans, and Cryptococcus neoformans strains. Activities against Pneumocystis carinii, Aspergillus spp., less common molds, and dermatophytes were also investigated. Azasordarin derivatives displayed significant activities against the most clinically important Candida species, with the exception of C. krusei. Against C. albicans, including fluconazole-resistant strains, MICs at which 90% of the isolates tested are inhibited (MIC(90)s) were 0.002 microg/ml with GW 479821, 0.015 microg/ml with GW 515716 and GW 587270, and 0.06 microg/ml with GW 471552, GW 471558, and GW 570009. The MIC(90)s of GW 471552, GW 471558, GW 479821, GW 515716, GW 570009, and GW 587270 were 0.12, 0.12, 0.03, 0.06, 0.12, and 0.06 microg/ml, respectively, against C. tropicalis and 4, 0.25, 0.06, 0.25, 0.5, and 0.5 microg/ml, respectively, against C. glabrata. In addition, some azasordarin derivatives (GW 479821, GW 515716, GW 570009, and GW 58720) were active against C. parapsilosis, with MIC(90)s of 2, 4, 4, and 1 microg/ml, respectively. The compounds were extremely potent against P. carinii, showing 50% inhibitory concentrations of <or=0.001 microg/ml. However Cryptococcus neoformans was resistant to all compounds tested (MIC > 16 microg/ml). These azasordarin derivatives also showed significant activity against emerging fungal pathogens, which affect immunocompromised patients, such as Rhizopus arrhizus, Blastoschizomyces capitatus, and Geotrichum clavatum. Against these organisms, the MICs of GW 587270 ranged from 0.12 to 1 microg/ml, those of GW 479821 and GW 515716 ranged from 0.12 to 2 microg/ml, and those of GW 570009 ranged from 0.12 to 4 microg/ml. Against Fusarium oxysporum, Scedosporium apiospermum, Absidia corymbifera, Cunninghamella bertholletiae, and dermatophytes, GW 587270 was the most active compound, with MICs ranging from 4 to 16 microg/ml. Against Aspergillus spp., the MICs of the compounds tested were higher than 16 microg/ml. The in vitro selectivity of azasordarins was investigated by cytotoxicity studies performed with five cell lines and primary hepatocytes. Concentrations of compound required to achieve 50% inhibition of the parameter considered (Tox(50)s) of GW 570009, GW 587270, GW 479281, and GW 515716 in the cell lines ranged from 60 to 96, 49 to 62, 24 to 36, and 16 to 38 microg/ml, respectively. The cytotoxicity values of GW 471552 and GW 471558 were >100 microg/ml for all cell lines tested. Tox(50)s on hepatocytes were in the following order: GW 471558 > GW 471552 > GW 570009 > GW 587270 > GW 515716 > GW 479821, with values ranging from higher than 100 microg/ml to 23 microg/ml. The cytotoxicity results obtained with fully metabolizing rat hepatocytes were in total agreement with those obtained with cell lines. In summary, the in vitro activities against important pathogenic fungi and the selectivity demonstrated in mammalian cell lines justify additional studies to determine the clinical usefulness of azasordarins.

Influence of verapamil on the efflux and metabolism of 14C moxidectin in cultured rat hepatocytes

Moxidectin (MOX) is an antiparasitic drug widely used in cattle, sheep and companion animals. As a result of the implication of cytochrome P450 3 A in the metabolism of MOX and the role of competitor substrates of P-glycoprotein (Pgp) in modification of the bioavailability of endectocides, we studied the influence of verapamil (a multidrug-resistance reversing agent) on the metabolism of 14C moxidectin in cultured rat hepatocytes over 72 h. The metabolism of MOX remained low: 10.79 +/- 1.99% of the total 14C moxidectin for the main detected metabolite in verapamil-treated cells and 7.17 +/- 0.74% for the control cells after 24 h. The main detected metabolite in rat hepatocytes was the same as that detected in rat hepatic microsomes (the C29 monohydroxymethyl metabolite). Verapamil increased the quantity of MOX in the cells after 24, 48 and 72 h. Examination of the Area Under the concentration time Curve (AUC) of the main detected metabolite revealed a significant increase in the exposure of cells to MOX after verapamil treatment throughout the experiment. It is hypothesized that verapamil interfered with MOX as a substrate for Pgp during the initial incubation period. After this initial interaction, verapamil metabolites were able to interfere with Pgp. This experiment demonstrated the implication of Pgp in the transport of MOX and allowed prediction of the drug-drug interactions which might modify the bioavailability of endectocides.

Characterization of drug metabolizing activities in pig hepatocytes for use in bioartificial liver devices: comparison with other hepatic cellular models

BACKGROUND/AIMS

The pig is considered the best donor of hepatocytes for bioartificial liver devices, but little is known about the metabolic capability of pig hepatocytes. Therefore, we have evaluated drug metabolizing activities in pig hepatocytes and liver microsomes and compared the results with those of man and other animal hepatic cellular models that are potential sources of cells for bioreactors, such as rat, rabbit and dog hepatocytes and hepatoma cell lines.

METHODS

Total cytochrome P450 levels, six phase 1 activities representative of the most relevant cytochrome P450 enzymes (7-ethoxycoumarin O-deethylase, 7-ethoxy-, 7-methoxy- and 7-benzoxyresorufin O-dealkylases, coumarin 7-hydroxylase and p-nitrophenol hydroxylase), two phase 2 activities (glutathione S-transferase and UDP-glucuronyltransferase) and CYP-dependent regioselective testosterone metabolism were evaluated in in vitro models of different species.

RESULTS

The pattern of specific cytochrome P450 activities and the metabolic profile of testosterone in intact hepatocytes were essentially the same as those measured in liver microsomes. Relatively low ethoxy-, methoxy-, and benzoxyresorufin O-dealkylation rates were found in pig liver microsomes and hepatocytes as compared to hepatic in vitro human models. However, in contrast with the other species studied, stereoselective testosterone oxidation profiles were practically identical in human and pig models. Finally, the metabolic capability of hepatoma cell lines was very limited in comparison with that of hepatocytes.

CONCLUSIONS

Pig hepatocytes are able to maintain in culture the phase 1 and phase 2 activities found in liver microsomes. The high metabolic similarities found between pig and human hepatocytes lend support to the use of pig hepatocytes in bioartificial liver devices.

Cryopreserved porcine hepatocyte cultures

Cryopreservation of freshly isolated hepatocytes is regarded the standard technique for long term storage of liver cells. Frankly, we were not successful in reproducing viability rates of about 70% of that which have been reported by most authors as results of various freezing protocols for hepatocyte suspensions. In fact, we saw mostly devastating results. We assume that intracellular ice crystal formation as well as osmotic changes during freezing and thawing of liver cells cause hazardous effects, especially on membranes of cells after enzymatic isolation, and, thus, generally result in a severe loss in number and impaired specific hepatocyte functions in subsequent culture. We tried to improve results by freezing cell cultures instead. We allowed hepatocytes to regain a more stable condition prior to storage and placed them in tissue flasks in a uniform configuration, rather than to pack cell suspensions in vials or bags under rather indefinable conditions. Porcine hepatocytes (viability 92+/-2%) were isolated from slaughterhouse organs and cultured in a double gel (sandwich) configuration. At day 3, cultures were rate controlled frozen (RCF) and stored in a cell bank for three hours (Group A) or 14 days at -80 degrees C (Group B), respectively. Non-frozen cells (NF) and cultures subjected to a linear freezing rate of -10 degrees C/min (LFR, Group C) with 3 h of storage served as controls from identical cell batches. Upon thawing, at day 2 of subsequent culture, fluorescence microscopy studies revealed a survival rate of 75+/-10% (mean+/-S.D.) in the RCF groups. Time of storage (3 h, 14 d) did not influence results. Survival in Group C was 10+/-5%. Cell integrity was measured by LDH-release, which indicated a larger damage of cells in the LFR group, and thereby resembled the morphological findings. Functional parameters, such as albumin synthesis and CYT P 450-activity were comparable to non-frozen liver cells at 48 h after thawing in the RCF groups (A + B), and showed significantly higher levels in these groups as compared to the LFR Group (C). We recommend to freeze hepatocytes in culture in a rate controlled fashion rather than cell suspensions. This way a cell bank of cryopreserved hepatocyte cultures for batch controlled investigations can be easily obtained. This could ameliorate the availability of rare (human) cell material and might also improve the quality of data generated from in vitro experiments in hepatology or pharmacology/toxicology with liver cells from identical sources. It remains to be seen whether this technique might also be of value in hybrid bioartificial liver devices to make these systems become readily available upon clinical demand.

Survival and function of isolated hepatocytes after cryopreservation

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

Endogenous nitric oxide is responsible for the early loss of P450 in cultured rat hepatocytes

Loss of P450 during the early hours of monolayer formation is known to be the more serious limitation of primary cultured hepatocytes as an adequate model for the study of drug metabolism, toxicity and P450 induction. This study reports that endogenous nitric oxide (NO) formation is activated shortly after isolation by the classical collagenase-based liver perfusion methods. Both rapid P450 loss and aerobic mitochondrial energy metabolism impairment -- with subsequent changes on glucose metabolism -- are directly related to the high local generation of the radical at this stage. These effects can be reverted by the sole addition of NO biosynthesis inhibitors during liver perfusion and early culture hours, which allows catalytically active P450 to be preserved at levels close to those of the intact liver.

Evaluation of the Cytotoxic Effects of MEIC Chemicals 31–50 on Primary Culture of Rat Hepatocytes and Hepatic and Non-hepatic Cell Lines

The cytotoxicities of 20 chemicals (numbers 31–50) from the Multicenter Evaluation of In Vitro Cytotoxicity (MEIC) programme were assessed with a primary culture of rat hepatocytes and with two hepatic cell lines (Hep G2 and FaO) and one non-hepatic cell line (3T3). The cytotoxicities of the chemicals were evaluated by using the MTT test after the cells had been exposed to the chemicals for 24 hours. For a better evaluation of results, dose–response curves were mathematically linearised and cytotoxicity was expressed as IC50 values and IC10 values (the concentration causing 50% and 10% loss of cell viability, respectively). We found that all the compounds showed similar acute basal cytotoxicity in all four cellular systems (regardless of whether the cells were, or were not, metabolically competent or were or were not of human origin). When these results were used to predicit human toxicity in terms of a mathematical parameter (prediction error [PE]), we found that all four systems gave similar predictions of human toxicity. The best cytotoxicity parameter included in the PE calculation was the IC50/10, because of an underestimation of human toxicity by in vitro systems. However, when PEs were calculated for rodent toxicity, better results were obtained. Data from the literature obtained by using other experimental models for predicting human toxicity were analysed according to the same criteria. We conclude that cellular systems are better predictive tools for human toxicity than are prokaryotic cells or whole-organism models.

Immunochemical detection of protein adducts in cultured human hepatocytes exposed to diclofenac

The non-steroidal anti-inflammatory drug diclofenac is reported to cause, in rare cases, fulminant hepatic necrosis associated with chronic use of the drug. In order to investigate the possibility that covalent protein adducts of reactive metabolites of diclofenac might be responsible for the hepatotoxicity produced by this drug, we developed an antibody against a diclofenac-keyhole limpet hemocyanin adduct. The anti-diclofenac antibody did recognize diclofenac-protein adducts on Western blots of homogenates of cultured human hepatocytes exposed to diclofenac. The major detected adduct was a 60 kDa protein, which was present in both human and rat hepatocytes. These results suggest that binding of diclofenac to human hepatocytes is, like in rats, selective and that a 60 kDa protein appears to be the major target for alkylation. Immunoblots of homogenates of liver sinusoidal lining cells (LSLC) from rats treated with diclofenac also exhibited adducts with a 60 kDa protein. This fact suggest a role for LSLC in processing of chemically altered proteins in the liver.

A specific microassay for evaluating hepatic LDH activity in co-cultures of hepatocytes with other cells

This study describes the development of a simple, rapid and reproducible microassay for determining the intracellular LDH activity of rat hepatocytes present in a co-culture system with other cells. The procedure involves treatment of cellular homogenates with an anti-LDH antiserum that specifically inhibits the LDH activity of rat hepatocytes. The assay is performed in 96-well plates and LDH activity can be measured directly in the same wells using a colorimetric method. The difference in LDH activity values measured before and after antiserum incubation reflects the LDH content of the hepatocytes in the sample. The advantages of this method are the small number of cells required, a reduction in sample handling and the possibility of differentiating LDH activity in hepatic and non-hepatic cells. The possible applications of this technique as a parameter for biochemical data and as a test for cytotoxicity studies in co-cultures are also discussed.

Cytochrome P450 activities in pure and co-cultured rat hepatocytes. Effects of model inducers

The stability and inducibility of several P450 activities (namely, P450 1A1; 2A1, 2B1/2, 2C11, and 3A1) were studied in rat hepatocytes co-cultured with the MS epithelial cell line derived from monkey kidney. The results revealed that these monooxygenase activities were systematically higher in co-cultures than in conventional hepatocyte cultures. Pure cultures showed a rapid loss of monooxygenase activities, which were undetectable after 5 days. In contrast, all isozymes assayed were measurable in co-cultured hepatocytes on Day 7 (about 15 to 40% of the initial activities of Day 0 of culture). The beneficial effects of the co-culture system seemed to be more selective for certain cytochrome P450 isoforms, with P450 1A1 and 3A1 being the best stabilized isozymes after 1 wk. A clear response to inducers was observed in co-cultures, each isozyme showing a different induction pattern. 3-Methylcholanthrene produced a strong increase in P450 1A1 (7-ethoxyresorufin O-deethylase) activity and a low increase in P450 2A1 (testosterone 7 alpha-hydroxylation), whereas no changes were observed in the other activities. Phenobarbital treatment resulted in increases in P450 2B1/2 (7-pentoxyresorufin O-depentylase and 16 alpha- and 16 beta-hydroxylation of testosterone) activities, while minor effects were observed on P450 3A1 (testosterone 6 beta-hydroxylation) activity. Dexamethasone markedly increased P450 3A1 (testosterone 6 beta- and 15 beta-hydroxylation) activity and, to a lesser extent, P450 2B1/2 (16 beta-hydroxylation).

Assessment of artificial liver support technology

Despite more than 30 yr of research and development, an artificial liver has still not yet become clinical reality. Although previous attempts using a multiplicity of techniques including hemodialysis, hemoperfusion, plasma exchange, extracorporeal perfusion, and crosshemodialysis have shown minor improvement in patients with acute hepatic failure, limited clinical trials have failed to demonstrate any survival benefit. Encouraged by the progress on techniques that maintain long-term cultures of hepatocytes, more recent efforts have been directed at the use of hepatocytes as the basis of liver support. This review takes a critical look at past and present concepts in the development of artificial liver supports and both qualitatively and quantitatively evaluates the advantages and disadvantages of the available methodology.

Cocaine hepatotoxicity: two different toxicity mechanisms for phenobarbital-induced and non-induced rat hepatocytes

Hepatocytes isolated from both phenobarbital-induced and control rats were short-term cultured and exposed to cocaine (8-2000 microM) for varying times. Intracellular lactate dehydrogenase activity, free calcium levels ([Ca2+]i), reduced glutathione (GSH) and lipid peroxidation were investigated to evaluate the toxic effect of cocaine on hepatocytes. Cytochrome P450 induction by phenobarbital potentiated the in vitro cytotoxicity of cocaine by a factor of 13 (IC50 = 84 microM in induced cells vs 1100 microM in non-induced cells). This difference in the susceptibility of the two types of hepatocytes to cocaine correlated well with the activity of cytochrome P450 2B1/2. Rapid depletion of GSH, reaching 30% of the control levels, and massive lipid peroxidation thereafter were the two most remarkable phenomena preceding cell death in phenobarbital-induced hepatocytes. On the other hand, a sustained rise in [Ca2+]i starting 2 hr after incubation with cocaine was the most noteworthy finding in non-induced liver cells. We suggest two different pathways for cocaine hepatotoxicity: in phenobarbital-induced hepatocytes oxidative metabolism of the drug causes GSH depletion, subsequent extensive lipid peroxidation and cell death, at low concentrations of cocaine. In non-induced hepatocytes these changes are less relevant, and the major alteration caused by cocaine is a non-transient rise in [Ca2+]i that is evident at higher concentrations of the drug.

Nucleation and growth of ice crystals inside cultured hepatocytes during freezing in the presence of dimethyl sulfoxide

A three-part, coupled model of cell dehydration, nucleation, and crystal growth was used to study intracellular ice formation (IIF) in cultured hepatocytes frozen in the presence of dimethyl sulfoxide (DMSO). Heterogeneous nucleation temperatures were predicted as a function of DMSO concentration and were in good agreement with experimental data. Simulated freezing protocols correctly predicted and explained experimentally observed effects of cooling rate, warming rate, and storage temperature on hepatocyte function. For cells cooled to -40 degrees C, no IIF occurred for cooling rates less than 10 degrees C/min. IIF did occur at faster cooling rates, and the predicted volume of intracellular ice increased with increasing cooling rate. Cells cooled at 5 degrees C/min to -80 degrees C were shown to undergo nucleation at -46.8 degrees C, with the consequence that storage temperatures above this value resulted in high viability independent of warming rate, whereas colder storage temperatures resulted in cell injury for slow warming rates. Cell damage correlated positively with predicted intracellular ice volume, and an upper limit for the critical ice content was estimated to be 3.7% of the isotonic water content. The power of the model was limited by difficulties in estimating the cytosol viscosity and membrane permeability as functions of DMSO concentration at low temperatures.

Cryopreservation and long-term storage of primary rat hepatocytes: effects on substrate-specific cytochrome P450-dependent activities and unscheduled DNA synthesis

The effects of cryopreservation and long-term storage on substrate-specific cytochrome P450-dependent activities and unscheduled DNA synthesis were studied in freshly isolated and cryopreserved hepatocytes derived from adult male Fischer 344 and Sprague-Dawley rats. Primary rat hepatocytes were isolated via an in situ collagenase perfusion technique, cryopreserved at -196 degrees C, and thawed at 5 weeks and 104 and 156 weeks post-freezing. In Fischer 344 and Sprague-Dawley rats, cryopreserved hepatocytes were equivalent or similar to freshly isolated hepatocytes in substrate-specific activities for 7-ethoxyresorufin-O-deethylase and dimethylnitrosamine-N-demethylase and unscheduled DNA synthesis responses. No significant differences in activities toward 7-ethoxyresorufin-O-deethylase and dimethylnitrosamine-N-demethylase, the substrate-specific activities for cytochromes P4501A1 and P4501A2 and cytochrome P4502E1, respectively, were observed between freshly isolated and cryopreserved hepatocytes. Similar unscheduled DNA synthesis responses, a measure of DNA damage and repair, were observed after exposure to the genotoxic carcinogens 2-acetylamino-fluorene, 7,12-dimethylbenz[a]anthracene, and dimethylnitrosamine; although some decreases were also observed in Fischer 344 hepatocytes after 104 weeks and Sprague-Dawley hepatocytes after 156 weeks in the highest concentrations tested. These results suggest that cryopreserved hepatocytes, stored for extended periods of time in liquid nitrogen, are metabolically equivalent to freshly isolated hepatocytes in their ability to activate precarcinogens.

Preservation of the rate and profile of xenobiotic metabolism in rat hepatocytes stored in liquid nitrogen

A simple procedure for cryopreservation of rat hepatocytes that allows recovery of viable cells retaining activities of phase I and phase II drug metabolism equivalent to freshly isolated cells is described. The cooling process was initiated 30 min after incubation of freshly isolated hepatocytes at 37 degrees in Krebs-Ringer bicarbonate buffer containing 15 mM glucose to allow for metabolic equilibration. At the end of this period, hepatocyte suspensions were supplemented with 1.7% albumin, 13.3% dimethyl sulfoxide, and the synthetic buffers, 3-[N-morpholino]propanesulfonic acid (MOPS) and N-[2-hydroxyethyl]piperazine-N'-[2-ethanesulfonic acid] (HEPES). Hepatocytes were cooled in a stepwise manner to -196 degrees by holding the cells for 1 hr at -20 degrees and then for 1 hr at -70 degrees before transfer into liquid nitrogen. After thawing and removal of damaged cells by centrifugation in Percoll, the total recovery of viable hepatocytes subjected to freezing was about 42%. The contents of ATP, ADP, and AMP were not altered significantly in cells stored in liquid nitrogen. The metabolic competence of cryopreserved hepatocytes was further confirmed by their ability to synthesize urea from NH4Cl and ornithine at the same high rate that was observed in freshly isolated cells (693 +/- 68 and 740 +/- 68 nmol.mg dry wt-1 x hr-1, respectively). Similarly, cryopreservation did not affect drug-metabolizing systems as indicated by the metabolism of benzo[a]pyrene and 7-ethoxycoumarin, two model substrates. In both freshly isolated and cryopreserved hepatocytes, 7-ethoxycoumarin was O-deethylated to 7-hydroxycoumarin at essentially the same rates (8.66 +/- 0.75 and 8.25 +/- 0.53 nmol.mg dry wt-1.hr-1, respectively) and 7-hydroxycoumarin accumulated in hepatocyte suspensions almost exclusively in the conjugated form. The storage of hepatocytes in liquid nitrogen also did not affect the complex metabolism of benzo[a]pyrene to total oxygenated metabolites and, more importantly, to metabolites conjugated with glutathione, glucuronic acid, and sulfuric acid. Thus, cryopreserved hepatocytes represent a valid and convenient model to study drug biotransformation in intact cells.

Thawed human hepatocytes in primary culture

In drug metabolism studies, isolated and cultured human hepatocytes provide a useful model for overcoming the difficulty of extrapolating from animal data. In vitro studies with human hepatocytes are scarce because of the lack of livers and suitable methods of storage. After developing a new method for cryopreservation of human hepatocytes, we evaluated the effects of deep freezing storage on their viability, morphology, and functional and toxicological capabilities in classical culture conditions. Freshly isolated human hepatocytes were cryopreserved in medium containing 10% Me2SO and 20% fetal calf serum, using a Nicool ST20 programmable freezer (-1.9 degrees C/min for 18 min and -30 degrees C/min for 4 min). Cells were stored in liquid nitrogen. Viability of thawed human hepatocytes was 50-65% as assessed by erythrosin exclusion test prior to purification on a Percoll density gradient. Morphological criteria showed that thawed human hepatocytes require an adaptation period to the medium after seeding. Functional assessments showed that human hepatocytes which survive freezing and thawing preserve their protein synthesis capabilities and are able to secrete a specific protein, anionic peptidic fraction, which is involved in the hepatic uptake of bile-destined cholesterol. We then studied Midazolam biotransformation to test metabolic functions, and erythromycin toxicity by Neutral Red test (cell viability) and 3-(4,5-dimethylthiazol-2-yl)-diphenyl tetrazolium bromide test (cell metabolism). All of these experiments indicated that thawed human hepatocytes should be used 38 h after seeding for optimum recovery of their functions: membrane integrity, protein synthesis, and stabilization of drug metabolism enzymes.

Characterization of cryopreserved rat liver parenchymal cells by metabolism of diagnostic substrates and activities of related enzymes

The metabolism of testosterone and benzo(a)pyrene (BaP) which is mediated by diverse enzymes was determined in cryopreserved rat liver parenchymal cells and compared with that found in freshly isolated cells. In addition, the activities of single xenobiotic-metabolizing enzymes were measured by using specific substrates. The cytochrome P450 (P450)-mediated total metabolic conversion of testosterone was reduced to 55% in cryopreserved cells. The metabolite profile, i.e. the formation of single metabolites compared with total metabolic conversion, was however unchanged when compared with freshly isolated cells. A concomitant reduction in the activities of the involved P450 isoenzymes can therefore be postulated. The amount of detected phase I-metabolites of BaP was unaffected by the cryopreservation method. The formation of phase II-metabolites and total metabolic conversion of BaP in cryopreserved cells was however reduced to about 50-60%. The reduced glutathione S-transferase and more obviously phenol sulfotransferase activities measured in cryopreserved cells, may explain the impaired conjugation of BaP. The ratio between phase I- and phase II-metabolites was thus changed by cryopreservation. Density separation on Percoll yielded cryopreserved cells with a viability and metabolic capacity not measurably different from freshly isolated cells. To this extent, cryopreserved, Percoll-purified liver parenchymal cells are a useful in vitro system for drug metabolism studies. However due to the extensive loss in cell number during this procedure (recovery = 22% of freshly isolated cells) the application of this system is limited.

S-adenosyl-L-methionine reverses the cholestatic effect of ethinylestradiol in rat hepatocytes by increasing its catabolism

In this study, ethinylestradiol inhibited the uptake of taurocholate by cultured rat hepatocytes, increasing the Km while leaving the Vmax unchanged. S-Adenosyl-L-methionine (SAMe) had no effect on taurocholate uptake or release, but was able to reverse the competitive inhibition induced by ethinylestradiol. S-Adenosyl-L-homocysteine did not reverse this inhibition, which suggests that the methyl group of SAMe affects its activity. Several possible mechanisms for the action of SAMe were investigated. The methylation of cell membrane phospholipids was eliminated as a possible mechanism. The presence of SAMe greatly increased the catabolism of ethinylestradiol by hepatocytes and reduced its covalent binding to hepatocyte macromolecules. In culture supernatants, both highly polar (conjugated) and non-conjugated metabolites could be detected. Moreover, most of the metabolites were methylated. This suggests that SAMe may revert the effects of ethinylestradiol of taurocholate uptake by increasing its catabolic rate by hepatocytes.

Artificial liver. State of the art

If an effective hepatic assist system existed, it could serve as a bridge to transplantation. Most of the patients waiting for liver transplantation have chronic liver insufficiency but are not in hepatic coma. Various hepatic assist systems have been used to salvage patients with acute liver insufficiency. Most attempts have been disappointing. The methods used have included plasma exchange, plasma adsorption, double filtration, cryofiltration, thermofiltration, the combination of plasma exchange and amino acid hemodialysis, and others. For patients with chronic liver disease with moderate liver function impairment and limited to one or only a few areas of metabolic abnormality, a hepatic assist might allow the life of the patient to be maintained temporarily. The application of hepatic assist methods for chronic liver disease patients treated at the Cleveland Clinic has been encouraging. One of the patients who suffered from sclerosing cholangitis has maintained a near-normal life for almost five years by 170 plasma treatments. This is in spite of the fact that, at the onset of treatment, the patient was nearly comatose. Unfortunately, this patient did not wish to receive a liver transplantation. Based upon this experience, the concept of a bridge to transplantation approach to hepatic assist devices appears feasible. In addition, it is speculated that hepatic assistance during the early recovery stage of liver transplantation and during mild episodes of rejection may be useful.

Co-cultures of hepatocytes with epithelial-like cell lines: expression of drug-biotransformation activities by hepatocytes

To improve long-term expression of drug biotransformation activities in hepatocytes, we have examined the suitability of several epithelial-like cell lines (MDCK, MS and L-132) for supporting functional co-cultures with rat hepatocytes. Cells were selected on the basis of their compatibility with hepatocytes, formation of stable monolayers in the absence of serum and lack of drug biotransformation activities. The expression of individual elements of the biotransformation system was evaluated in these co-cultures. Co-cultured hepatocytes remained viable and showed a characteristic polygonal shape for more than a week. Depending on the cell line used, levels of aryl hydrocarbon hydroxylase and 7-ethoxycoumarin O-deethylase activities of co-cultured hepatocytes oscillated between 24-47% of their initial value after 4 days in culture. The highest levels of monooxygenase activity were found in hepatocytes co-cultured with MS cells (41-47%). In contrast, these activities decreased to 6% when hepatocytes were maintained in pure culture for the same period. The activities of the conjugating enzymes UDP-glucuronyltransferase and glutathione S-transferase were maintained at nearly the initial levels during the complete period of study, both in pure and mixed-cultures, regardless of the cell line used. MS cells adapted themselves much better to serum-free culture conditions, and the co-culture with rat hepatocyte was technically easier. After one week, total cytochrome P450 and reduced glutathione in rat hepatocytes/MS co-cultures were 31% and 127% respectively of the day O values, whereas they were undetectable in pure culture. A clear induction of monooxygenase activities by methylcholanthrene, phenobarbital and ethanol could be observed by the 5th day in MS cells/hepatocyte co-cultures. The fact that the results of our work show the suitability of MS cells, an epithelial-derived cell line, for improving the expression of biotransformation enzymes of cultured hepatocytes opens new possibilities of simplifying co-cultures for their use in drug-metabolism studies.

Drug metabolizing enzymes in rat hepatocytes co-cultured with cell lines

We have developed new co-cultures of continuous cell lines 3T3 (clone A31) and C3H/10T1/2 (clone 8) with hepatocytes as an alternative to co-cultures with noncontinuous epithelial cells. In this biological system we studied in detail the expression of the hepatic biotransformation system. After 7 d in culture, total cytochrome P-450 content and the monooxygenase activities aryl hydrocarbon hydroxylase and 7-ethoxycoumarin o-deethylase still maintained about 30% of their initial value, whereas in pure cultured hepatocytes these activities were undetectable. A significant response to induction by methylcholanthrene and phenobarbital of monooxygenase activities was observed in co-cultures for 7 d. NADPH-cytochrome c reductase activity remained unchanged for at least 7 d in co-cultured hepatocytes, whereas in pure cultures this activity was reduced to about 75% of the initial value after only 24 h. Finally, the activity of the conjugating enzymes UDP-Gt and GSH-t was maintained at nearly the initial levels during the complete period of study. The easy handling of continuous cell lines and the maintenance of the biotransformation system of hepatocytes in co-culture make this approach simpler and easier to standardize.

A new approach to the cryopreservation of hepatocytes in a sandwich culture configuration

Current methods of cryopreservation of hepatocytes in single cell suspensions result in low overall yields of hepatocytes, demonstrating long-term preservation of hepatocellular functions. A novel culture method has recently been developed to culture liver cells in a sandwich configuration of collagen layers in order to stabilize the phenotypic expression of these cells in vitro (J. C. Y. Dunn, M. L. Yarmush, H. G. Koebe, and R. G. Tompkins, FASEB J. 3, 174, 1989). Using this culture system, rat hepatocytes were frozen with 15% (v/v) Me2SO to -70 degrees C, and stored at approximately -100 degrees C. Following rapid thawing, long-term function was assessed by measuring albumin secretion in culture for 7-14 days postfreezing. Comparison was made with cryopreservation of liver cells in single cell suspensions. Cryopreservation of liver cells in suspension resulted in only a 2% yield of cells which could be successfully cultured; albumin secretion rates in these cultured cells over 48 hr were 26-30% of secretion rates for nonfrozen hepatocytes. Freezing cultured liver cells in the sandwich configuration after 3, 7, and 11 days in culture maintained 0, 26, and 19% of the secretion rates of nonfrozen hepatocytes, respectively. Morphology of the cryopreserved cells appeared grossly similar to cells without freezing; however, this morphological result was patchy and represented approximately 30% of the cells in culture. These results represent the first demonstration of any quantitative long-term preservation of hepatocellular function by cryopreservation, suggesting that cultured hepatocytes can survive freezing and maintain function.

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.