Human liver quality is a dominant factor in the outcome of in vitro studies

Predicting the in vivo developmental toxicity of fenarimol from in vitro toxicity data using PBTK modelling-facilitated reverse dosimetry approach

In vitro methods are widely used in modern toxicological testing; however, the data cannot be directly employed for risk assessment. In vivo toxicity of chemicals can be predicted from in vitro data using physiologically based toxicokinetic (PBTK) modelling-facilitated reverse dosimetry (PBTK-RD). In this study, a minimal-PBTK model was constructed to predict the in-vivo kinetic profile of fenarimol (FNL) in rats and humans. The model was verified by comparing the observed and predicted pharmacokinetics of FNL for rats (calibrator) and further applied to humans. Using the PBTK-RD approach, the reported in vitro developmental toxicity data for FNL was translated to in vivo dose-response data to predict the assay equivalent oral dose in rats and humans. The predicted assay equivalent rat oral dose (36.46 mg/kg) was comparable to the literature reported in vivo BMD10 value (22.8 mg/kg). The model was also employed to derive the chemical-specific adjustment factor (CSAF) for interspecies toxicokinetics variability of FNL. Further, Monte Carlo simulations were performed to predict the population variability in the plasma concentration of FNL and to derive CSAF for intersubject human kinetic differences. The comparison of CSAF values for interspecies and intersubject toxicokinetic variability with their respective default values revealed that the applied uncertainty factors were adequately protective.

Best Practices and Progress in Precision-Cut Liver Slice Cultures

Thirty-five years ago, precision-cut liver slices (PCLS) were described as a promising tool and were expected to become the standard in vitro model to study liver disease as they tick off all characteristics of a good in vitro model. In contrast to most in vitro models, PCLS retain the complex 3D liver structures found in vivo, including cell–cell and cell–matrix interactions, and therefore should constitute the most reliable tool to model and to investigate pathways underlying chronic liver disease in vitro. Nevertheless, the biggest disadvantage of the model is the initiation of a procedure-induced fibrotic response. In this review, we describe the parameters and potential of PCLS cultures and discuss whether the initially described limitations and pitfalls have been overcome. We summarize the latest advances in PCLS research and critically evaluate PCLS use and progress since its invention in 1985.

In Vitro-In Vivo Inaccuracy: The CYP3A4 Anomaly

When predicting hepatic clearance using in vitro to in vivo extrapolation (IVIVE), microsomes or hepatocytes are commonly used. Here, we examine intrinsic clearance values and IVIVE results in human hepatocytes and microsomes for compounds metabolized by a variety of enzymes. The great majority of CYP3A4 substrates examined had higher intrinsic clearance values in microsomes compared with hepatocytes, whereas the values were more similar between the two incubations for substrates of other enzymes. We hypothesize that this may be due to interplay between CYP3A4 and the efflux transporter P-glycoprotein, as they have been shown to exhibit coordinated regulation. When examining the prediction accuracy for substrates of other enzymes between microsomes and hepatocytes, average fold errors as well as overall error were similar, demonstrating once again that IVIVE methods are not adequately defined and understood. SIGNIFICANCE STATEMENT: For CYP3A4 substrates, microsomes give markedly higher predictive in vitro to in vivo extrapolation than for other metabolic enzymes, which is not found for hepatocytes. We hypothesize that this could be a result of CYP3A4-P-glycoprotein interplay or coordinated regulation in hepatocytes that would not be observed in microsomes.

In Vitro-In Vivo Extrapolation and Hepatic Clearance-Dependent Underprediction

Accurately predicting the hepatic clearance of compounds using in vitro to in vivo extrapolation (IVIVE) is crucial within the pharmaceutical industry. However, several groups have recently highlighted the serious error in the process. Although empirical or regression-based scaling factors may be used to mitigate the common underprediction, they provide unsatisfying solutions because the reasoning behind the underlying error has yet to be determined. One previously noted trend was intrinsic clearance-dependent underprediction, highlighting the limitations of current in vitro systems. When applying these generated in vitro intrinsic clearance values during drug development and making first-in-human dose predictions for new chemical entities though, hepatic clearance is the parameter that must be estimated using a model of hepatic disposition, such as the well-stirred model. Here, we examine error across hepatic clearance ranges and find a similar hepatic clearance-dependent trend, with high clearance compounds not predicted to be so, demonstrating another gap in the field.

Hepatocyte isolation from resected benign tissues: Results of a 5-year experience

AIM

To analyze retrospectively a 5-year experience of human hepatocyte isolation from resected liver tissues with benign disease.

METHODS

We established a method of modified four-step retrograde perfusion to isolate primary human hepatocytes. Samples were collected from the resected livers of patients with intrahepatic duct calculi (n = 7) and liver hemangioma (n = 17). Only the samples weighing ≥ 15 g were considered suitable for hepatocyte isolation. By using the standard trypan blue exclusion technique, hepatocyte viability and yield were immediately determined after isolation.

RESULTS

Twenty-four liver specimens, weighing 15-42 g, were immediately taken from the margin of the removed samples and transferred to the laboratory for hepatocyte isolation. Warm ischemia time was 5-35 min and cold ischemia time was 15-45 min. For the 7 samples of intrahepatic duct calculi, the method resulted in a hepatocyte yield of 3.49 ± 2.31 × 10⁶ hepatocytes/g liver, with 76.4% ± 10.7% viability. The 17 samples of liver hemangioma had significantly higher yield of cells (5.4 ± 1.71 × 10⁶ cells/g vs 3.49 ± 2.31 × 10⁶ cells/g, P < 0.05) than the samples of intrahepatic duct calculi. However, there seems to be no clear difference in cell viability (80.3% ± 9.67% vs 76.4% ± 10.7%, P > 0.05). We obtained a cell yield of 5.31 ± 1.87 × 10⁶ hepatocytes/g liver when the samples weighed > 20 g. However, for the tissues weighing ≤ 20 g, a reduction in yield was found (3.08 ± 1.86 × 10⁶ cells/g vs 5.31 ± 1.87 × 10⁶ cells/g, P < 0.05).

CONCLUSION

Benign diseased livers are valuable sources for large-number hepatocyte isolation. Our study represents the largest number of primary human hepatocytes isolated from resected specimens from patients with benign liver disease. We evaluated the effect of donor liver characteristics on cell isolation, and we found that samples of liver hemangioma can provide better results than intrahepatic duct calculi, in terms of cell yield. Furthermore, the size of the tissues can affect the outcome of hepatocyte isolation.

Maximising the use of freshly isolated human hepatocytes

INTRODUCTION

Freshly isolated human hepatocytes are the best model for predicting adverse drug reactions. However, their preparation and use present the investigator with many variables that are beyond their control. These include operation continuity and timing, size and number of cut surfaces on liver tissue and the prior history of the patient. To exploit the potential of freshly isolated human hepatocytes a method is required to preserve the cells in their initial in vivo like state. This experimental pausing allows experiments to be prioritised at convenient times of the day.

METHODS

A novel approach for selecting viable human hepatocytes by functional attachment to a gelatin gel is described rather than relying on their physical characteristics. The cells are preserved as a monolayer on the semi-solid support at 10°C as single spherical entities.

RESULTS

The hepatocytes can be released into suspension, when required, by a temperature transition to 37°C for 20min. The cells can be used in suspension or as a monolayer. The length of preservation depends upon the source tissue. Hepatocytes from normal liver can be maintained for at least 4days and demonstrated to have the same level of CYP3A4 and the enzymes involved in glucuronidation and sulphation as freshly isolated cells. Cells from fatty liver, attached to gelatin, vary in their preservation time but it is at least 24h and so confluent monolayers, that survive at 37°C can be generated the following day.

DISCUSSION

The technique enables freshly isolated human hepatocytes to be used more effectively. They can be preserved in times of plenty so more experimentation is possible. Alternatively, with poorer fatty cells the initial attachment on gelatin enables confluent monolayers of lipid rich cells to be studied.

Preparation and culture of precision-cut organ slices from human and animal

1.Human and animal precision-cut organ slices are being widely used to obtain drug metabolism and toxicity profiles in vitro. These data are then used to predict what might be seen in human patients. The accuracy of this prediction and extrapolation of the findings based on human or animal in vitro systems to the findings that occur in vivo is dependent on both the quality of the tissue itself and the quality of the in vitro system. 2.The quality of human organs used in research is dependent on procurement methods, warm ischaemia time, preservation solutions, cold ischaemia time, and donor-specific factors. It is important to confirm that the organs being used are highly viable and fully functional before using them in scientific studies. 3.The optimal preparation and incubation of organ slices is also essential in maintaining slice viability and function. It is important to prepare the slices in a cold preservation solution, to prepare the slices at a correct thickness, and to incubate the slices in a system where the slice rotates in out of the oxygen atmosphere and medium. 4.Meeting the criteria outlined here will lead to successful organ slice cultures for investigating drug-induced mechanisms and organ-specific toxicity.

Preparation and incubation of precision-cut liver and intestinal slices for application in drug metabolism and toxicity studies

Precision-cut tissue slices (PCTS) are viable ex vivo explants of tissue with a reproducible, well defined thickness. They represent a mini-model of the organ under study and contain all cells of the tissue in their natural environment, leaving intercellular and cell-matrix interactions intact, and are therefore highly appropriate for studying multicellular processes. PCTS are mainly used to study the metabolism and toxicity of xenobiotics, but they are suitable for many other purposes. Here we describe the protocols to prepare and incubate rat and human liver and intestinal slices. Slices are prepared from fresh liver by making a cylindrical core using a drill with a hollow bit, from which slices are cut with a specially designed tissue slicer. Intestinal tissue is embedded in cylinders of agarose before slicing. Slices remain viable for 24 h (intestine) and up to 96 h (liver) when incubated in 6- or 12-well plates under 95% O(2)/5% CO(2) atmosphere.

Transcranial near infrared laser treatment (NILT) increases cortical adenosine-5'-triphosphate (ATP) content following embolic strokes in rabbits

Transcranial near infrared laser therapy (NILT) improves behavioral outcome following embolic strokes in embolized rabbits and clinical rating scores in acute ischemic stroke (AIS) patients; however, the cellular mechanism(s) involved in NILT neuroprotection have not been elucidated. It has been proposed that mitochondrial energy production may underlie a response to NILT, but this has not been demonstrated using an in vivo embolic stroke model. Thus, we evaluated the effect of NILT on cortical ATP content using the rabbit small clot embolic stroke model (RSCEM), the model originally used to demonstrate NILT efficacy and initiate the NEST-1 clinical trial. Five minutes following embolization, rabbits were exposed to 2 min of NILT using an 808 nm laser source, which was driven to output either continuous wave (CW), or pulsed wave modes (PW). Three hours after embolization, the cerebral cortex was excised and processed for the measurement of ATP content using a standard luciferin-luciferase assay. NILT-treated rabbits were directly compared to sham-treated embolized rabbits and naïve control rabbits. Embolization decreased cortical ATP content in ischemic cortex by 45% compared to naive rabbits, a decrease that was attenuated by CW NILT which resulted in a 41% increase in cortical ATP content compared to the sham embolized group (p>0.05). The absolute increase in ATP content was 22.5% compared to naive rabbits. Following PW NILT, which delivered 5 (PW1) and 35 (PW2) times more energy than CW, we measured a 157% (PW1 p=0.0032) and 221% (PW2 p=0.0001) increase in cortical ATP content, respectively, compared to the sham embolized group. That represented a 41% and 77% increase in ATP content compared to naive control rabbits. This is the first demonstration that embolization can decrease ATP content in rabbit cortex and that NILT significantly increases cortical ATP content in embolized rabbits, an effect that is correlated with cortical fluence and the mode of NILT delivery. The data provide new insight into the molecular mechanisms associated with clinical improvement following NILT.

Studying cytochrome P450 kinetics in drug metabolism

BACKGROUND

Determination of cytochrome P450 enzyme-mediated kinetics in vitro can be useful for predicting drug dosing and clearance in humans. Expressed P450s, human liver microsomes, human hepatocytes (both fresh and cryopreserved), and human liver slices are used to estimate K(m) and V(max) values for determination of intrinsic clearance of the drug for scale-up to predict in vivo clearance.

OBJECTIVE

To describe the advantages and disadvantages of the various in vitro systems used to estimate kinetic parameters for disposition of drugs and the various kinetic profiles that can be observed.

METHODS

A review of the literature was conducted to evaluate the utility of the various in vitro preparations, the methods for determining kinetic parameters and the types of kinetic profiles that may be observed.

RESULTS/CONCLUSIONS

The choice of in vitro system for determining kinetic parameters will depend on the objective of the studies, as each system has advantages and disadvantages. Kinetic parameter determinations must be carefully assessed to assure that the correct kinetic model is applied and the most accurate kinetic parameters are determined.

Precision-cut liver slices from rats of different ages: basal cytochrome P450-dependent monooxygenase activities and inducibility

The biotransformation capacity - of the cytochrome P450 (CYP) system for example - is lower but inducibility is more pronounced in neonates than in adults. On the other hand, both enzyme activities and inducibility decline with senescence. Precision-cut rat liver slices are widely used as an in vitro tool for the examination of drug toxicity, xenobiotic metabolism or enzyme induction. The aim of the present study was to assess whether age-related changes in CYP activities and induction observed in vivo are also mirrored in vitro in liver slices. For this purpose, different CYP model reactions were measured in precision-cut liver slices from one-day-old, 40-day-old and one-year-old rats after in vitro exposure to various inducers. Similar to the in vivo situation, basal CYP activities were distinctly lower and inducibility was much more pronounced in liver slices from neonatal than in those from adult animals. Also, enzyme activities were mostly somewhat lower in liver slices from aged rats compared to those from 40-day-old rats. However, CYP inducibility was less pronounced than with younger animals too. Thus, precision-cut rat liver slices are a suitable in vitro tool for investigating age-related changes in CYP activities and induction as well as developmental differences in drug metabolism and toxicity.

Expression profiling of interindividual variability following xenobiotic exposures in primary human hepatocyte cultures

To examine the magnitude of human variability across the entire transcriptome after chemical challenge, we profiled gene expression responses to three different prototypic chemical inducers in primary human hepatocyte cultures from ten independent donors. Correlation between basal expression in any two hepatocyte donors ranged from r(2) values of 0.967 to 0.857, and chemical treatment tended to negatively impact correlation between donors. Including anticipated target genes, 10,812, 8373, and 7847 genes were changed in at least one donor by Aroclor 1254 (A1254), di(2-ethylhexyl) phthalate (DEHP), and phenobarbital (PB), respectively. A subset of these gene targets (n=41) were altered with a high level of reproducibility in at least 9 donors, gene responses that correlated well with literature-reported mechanism of action. Filtering responses to the level of gene subsets clarified the biological impact associated with the respective chemical effectors, in lieu of substantial interindividual variation among donor responses. In these respects, the use of hierarchical clustering methods successfully grouped seven of the ten donors into chemical-specific rather than donor-specific clusters. However, at the whole-genome level, the magnitude of conserved gene expression changes among donors was surprisingly small, with fewer than 50% of the gene responses altered by a single chemical conserved in more than one donor. The use of higher level descriptors, such as those defined by the PANTHER classification system, may enable more consistent categorization of gene expression changes across individuals, as increased reproducibility was identified using this method.

In vitro metabolism of beclomethasone dipropionate, budesonide, ciclesonide, and fluticasone propionate in human lung precision-cut tissue slices

Background

The therapeutic effect of inhaled corticosteroids (ICS) may be affected by the metabolism of the drug in the target organ. We investigated the in vitro metabolism of beclomethasone dipropionate (BDP), budesonide (BUD), ciclesonide (CIC), and fluticasone propionate (FP) in human lung precision-cut tissue slices. CIC, a new generation ICS, is hydrolyzed by esterases in the upper and lower airways to its pharmacologically active metabolite desisobutyryl-ciclesonide (des-CIC).

Methods

Lung tissue slices were incubated with BDP, BUD, CIC, and FP (initial target concentration of 25 μM) for 2, 6, and 24 h. Cellular viability was assessed using adenosine 5'-triphosphate content and protein synthesis in lung slices. Metabolites and remaining parent compounds in the tissue samples were analyzed by HPLC with UV detection.

Results

BDP was hydrolyzed to the pharmacologically active metabolite beclomethasone-17-monopropionate (BMP) and, predominantly, to inactive beclomethasone (BOH). CIC was hydrolyzed initially to des-CIC with a slower rate compared to BDP. A distinctly smaller amount (approximately 10-fold less) of fatty acid esters were formed by BMP (and/or BOH) than by BUD or des-CIC. The highest relative amounts of fatty acid esters were detected for BUD. For FP, no metabolites were detected at any time point. The amount of drug-related material in lung tissue (based on initial concentrations) at 24 h was highest for CIC, followed by BUD and FP; the smallest amount was detected for BDP.

Conclusion

The in vitro metabolic pathways of the tested ICS in human lung tissue were differing. While FP was metabolically stable, the majority of BDP was converted to inactive polar metabolites. The formation of fatty acid conjugates was confirmed for BMP (and/or BOH), BUD, and des-CIC.

In Vitro metabolism of ciclesonide in human lung and liver precision-cut tissue slices

Ciclesonide is a new-generation inhaled corticosteroid developed to treat the inflammation associated with persistent asthma. In order to identify the properties of ciclesonide responsible for anti-inflammatory activity, ciclesonide metabolism was investigated in human lung and liver precision-cut tissue slices. Three human lung and three human liver tissue slices were incubated with 25 microM [14C]-ciclesonide for 2, 6 and 24 h. Cellular viability was assessed using adenosine 5'-triphosphate content and protein synthesis in lung slices and adenosine 5'-triphosphate content and potassium retention in liver slices. Ciclesonide and ciclesonide metabolites were analysed in tissue samples using high-performance liquid chromatography with ultraviolet and radiochemical detection. Metabolite identity was confirmed using mass spectrometry. In lung slices, the inactive parent compound, ciclesonide, was initially converted to the active metabolite, desisobutyryl-ciclesonide, and subsequently converted to fatty acid conjugates. The reversible formation of fatty acid conjugates was a major pathway of ciclesonide metabolism in human lung slices. The primary conjugate was identified as desisobutyryl-ciclesonide oleate. Ciclesonide was metabolized to at least five polar metabolites in the liver. Dihydroxylated desisobutyryl-ciclesonide was the major polar metabolite in liver slices. Activation and fatty acid esterification in the lung followed by rapid inactivation in the liver may explain the improved safety profile and prolonged anti-inflammatory activity of ciclesonide.

A novel simplified ultra-rapid freezing technique for cryopreservation of tissue slices

Cryopreservation offers the potential to maximize the use and availability of biological materials that have a limited supply. This study demonstrates an enhanced technique for the parallel cryopreservation of a series of liver tissue slices using a tray modeled from aluminium foil and low concentrations of a cryoprotectant. Cooling and warming rates of approximately 2000 and 3900 degrees C min(-1), respectively, were achieved as the thermal capacity of the foil-tray was significantly reduced compared to the aluminium sandwich device introduced by Day et al. [S.H. Day, D.A. Nicoll-Griffith, J.M. Silva, Cryopreservation of rat and human liver slices by rapid freezing, Cryobiology 38 (1999) 154-159]. Additionally, the two critical steps involved in the sandwich approach, i.e., clamping the plates and complete filling of the entire space between the plates with liquid, can be omitted using the foil tray. The viability of the slices was verified by measuring tetrazolium salt reduction capacity, cytosolic enzyme lactate dehydrogenase leakage, and ethoxycoumarin metabolism.

Cryopreservation of rat hippocampal slices by vitrification

Although much interest has attended the cryopreservation of immature neurons for subsequent therapeutic intracerebral transplantation, there are no reports on the cryopreservation of organized adult cerebral tissue slices of potential interest for pharmaceutical drug development. We report here the first experiments on cryopreservation of mature rat transverse hippocampal slices. Freezing at 1.2 degrees C/min to -20 degrees C or below using 10 or 30% v/v glycerol or 20% v/v dimethyl sulfoxide yielded extremely poor results. Hippocampal slices were also rapidly inactivated by simple exposure to a temperature of 0 degree C in artificial cerebrospinal fluid (aCSF). This effect was mitigated somewhat by 0.8 mM vitamin C, the use of a more "intracellular" version of aCSF having reduced sodium and calcium levels and higher potassium levels, and the presence of a 25% w/v mixture of dimethyl sulfoxide, formamide, and ethylene glycol ("V(EG) solutes"; Cryobiology 48, pp. 22-35, 2004). It was not mitigated by glycerol, aspirin, indomethacin, or mannitol addition to aCSF. When RPS-2 (Cryobiology 21, pp. 260-273, 1984) was used as a carrier solution for up to 50% w/v V(EG) solutes, 0 degree C was more protective than 10 degrees C. Raising V(EG) concentration to 53% w/v allowed slice vitrification without injury from vitrification and rewarming per se, but was much more damaging than exposure to 50% w/v V(EG). This problem was overcome by using the analogous 61% w/v VM3 vitrification solution (Cryobiology 48, pp. 157-178, 2004) containing polyvinylpyrrolidone and two extracellular "ice blockers." With VM3, it was possible to attain a tissue K(+)/Na(+) ratio after vitrification ranging from 91 to 108% of that obtained with untreated control slices. Microscopic examination showed severe damage in frozen-thawed slices, but generally good to excellent ultrastructural and histological preservation after vitrification. Our results provide the first demonstration that both the viability and the structure of mature organized, complex neural networks can be well preserved by vitrification. These results may assist neuropsychiatric drug evaluation and development and the transplantation of integrated brain regions to correct brain disease or injury.

Precision-cut organ slices to investigate target organ injury

Drug-induced organ injury is a multifaceted process, involving numerous cell types and mediators, and remains a significant safety issue in pharmaceutical development and clinical therapy. Organ slices, an in vitro model representing the multicellular, structural and functional features of in vivo tissue, is a promising model for elucidating mechanisms of drug-induced organ injury and for characterising species susceptibilities. Time- and concentration-dependent drug-induced effects on organ slice gene expression, function and morphology are providing insight into the molecular and biochemical pathways leading to organ dysfunction, an altered morphology and the induction of repair pathways. Human organ slice studies are valuable for bridging the extrapolation of animal-derived data and for identifying mechanisms relevant for humans. The liver is the major organ used in organ slice studies; however, the utility of extrahepatic-derived slices, as well as cocultures for investigating multiple organ involvement in tissue injury is increasing. Organ slice investigations can further our understanding of the cell types and cell interactions involved in drug-induced injury and the consequences of drug-induced off-target effects for identifying compound liabilities that will impact safety.

Organ slices for the evaluation of human drug toxicity

Human organ slices, an in vitro model representing the multicellular and functional features of in vivo tissue, is a promising model for characterizing mechanisms of drug-induced organ injury and for identifying biomarkers of organ injury. Target organ injury is a significant clinical issue. In vitro models, which compare human and animal tissue to improve the extrapolation of animal in vivo studies for predicting human outcome, will contribute to improving drug candidate selection and to defining species susceptibilities in drug discovery and development programs. A critical aspect to the performance and outcome of human organ slice studies is the use of high quality tissue, and the use of culture conditions that support optimum organ slice survivability, in order to accurately reproduce mechanisms of organ injury in vitro. The attribute of organ slices possessing various cell types and interactions contributes to the overall biotransformation, inflammatory response and assessment of injury. Regional differences and changes in morphology can be readily evaluated by histology and special stains, similar to tissue obtained from in vivo studies. The liver is the major organ of which slice studies have been performed, however the utility of extra-hepatic derived slices, as well as co-cultures is increasing. Recent application of integrating gene expression, with human organ slice function and morphology demonstrate the increased potential of this model for defining the molecular and biochemical pathways leading to drug-induced tissue changes. By gaining a more detailed understanding of the mechanisms of drug-induced organ injury, and by correlating clinical measurements with drug-induced effects in the in vitro models, the vision of human in vitro models to identify more sensitive and discriminating markers of organ damage is attainable.

LPS-induced downregulation of MRP2 and BSEP in human liver is due to a posttranscriptional process

Endotoxin-induced cholestasis in rodents is caused by hepatic downregulation of transporters, including the basolateral Na+-dependent taurocholate transporter (ntcp) and the canalicular bile salt export pump (bsep) and multidrug resistance-associated protein 2 (mrp2). Details about the regulation of the human transporter proteins during this process are lacking. We used precision-cut human and rat liver slices to study the regulation of transporter expression during LPS-induced cholestasis. We investigated the effect of LPS on nitrate/nitrite and cytokine production in relation to the expression of inducible nitric oxide synthase, NTCP, BSEP, and MRP2 both at the level of mRNA with RT-PCR and protein using immunofluorescence microscopy. In liver slices from both species, LPS-induced expression of inducible nitric oxide synthase was detected within 1-3 h and remained increased over 24 h. In rat liver slices, this was accompanied by a significant decrease of rat ntcp and mrp2 mRNA levels, whereas bsep levels were not affected. These results are in line with previous in vivo studies and validate our liver slice technique. In LPS-treated human liver slices, NTCP mRNA was downregulated and showed an inverse correlation with the amounts of TNF-alpha and Il-1beta produced. In contrast, MRP2 and BSEP mRNA levels were not affected under these conditions. However, after 24-h LPS challenge, both proteins were virtually absent in human liver slices, whereas marker proteins remained detectable. In conclusion, we show that posttranscriptional mechanisms play a more prominent role in LPS-induced regulation of human MRP2 and BSEP compared with the rat transporter proteins.

Tissue collection, transport and isolation procedures required to optimize human hepatocyte isolation from waste liver surgical resections. A multilaboratory study

BACKGROUND

The European Center for Validation of Alternative Methods (ECVAM) has funded a prevalidation study in three laboratories (France, USA and UK) on the use of human hepatocyte cultures to predict cytochrome P-450 induction.

AIMS AND METHODS

As first stage of this prevalidation study, the purpose of the present work was to set criteria for optimization and harmonization of hepatocyte isolation from human tissue among laboratories to establish a routine procedure. This was achieved by combining and/or comparing the data generated by the two independent European laboratories (France and UK).

RESULTS

The results confirmed that surgical waste material is a valuable source for obtaining high quality hepatocytes under certain pre-, intra- and post-operative conditions: cell yield of viable hepatocytes was not significantly affected by age and sex of patients, nor indications for resection, steatosis or cholestasis. Cold ischeamia up to 5 hours did not influence viable cell yield allowing transport of material.

CONCLUSION

The use of biopsy sizes between 50-100 g, cannulation with 2-4 cannulae, digestion with collagenase-containing digestion medium at a flow rate of 25 ml/cannula for 20 minutes, with cut surface being glued in order to reform Glisson's capsule, should optimize the total yield of viable human hepatocytes obtained per preparation of waste liver surgical resections.

An update on in vitro test methods in human hepatic drug biotransformation research: pros and cons

The liver is the predominant organ in which biotransformation of foreign compounds takes place, although other organs may also be involved in drug biotransformation. Ideally, an in vitro model for drug biotransformation should accurately resemble biotransformation in vivo in the liver. Several in vitro human liver models have been developed in the past few decades, including supersomes, microsomes, cytosol, S9 fraction, cell lines, transgenic cell lines, primary hepatocytes, liver slices, and perfused liver. A general advantage of these models is a reduced complexity of the study system. On the other hand, there are several more or less serious specific drawbacks for each model, which prevents their widespread use and acceptance by the regulatory authorities as an alternative for in vivo screening. This review describes the practical aspects of selected in vitro human liver models with comparisons between the methods.

New hepatocyte in vitro systems for drug metabolism: metabolic capacity and recommendations for application in basic research and drug development, standard operation procedures

Primary hepatocytes represent a well-accepted in vitro cell culture system for studies of drug metabolism, enzyme induction, transplantation, viral hepatitis, and hepatocyte regeneration. Recently, a multicentric research program has been initiated to optimize and standardize new in vitro systems with hepatocytes. In this article, we discuss five of these in vitro systems: hepatocytes in suspension, perifusion culture systems, liver slices, co-culture systems of hepatocytes with intestinal bacteria, and 96-well plate bioreactors. From a technical point of view, freshly isolated or cryopreserved hepatocytes in suspension represent a readily available and easy-to-handle in vitro system that can be used to characterize the metabolism of test substances. Hepatocytes in suspension correctly predict interspecies differences in drug metabolism, which is demonstrated with pantoprazole and propafenone. A limitation of the hepatocyte suspensions is the length of the incubation period, which should not exceed 4hr. This incubation period is sufficiently long to determine the metabolic stability and to allow identification of the main metabolites of a test substance, but may be too short to allow generation of some minor, particularly phase II metabolites, that contribute less than 3% to total metabolism. To achieve longer incubation periods, hepatocyte culture systems or bioreactors are used. In this research program, two bioreactor systems have been optimized: the perifusion culture system and 96-well plate bioreactors. The perifusion culture system consists of collagen-coated slides allowing the continuous superfusion of a hepatocyte monolayer with culture medium as well as establishment of a constant atmosphere of 13% oxygen, 82% nitrogen, and 5% CO2. This system is stable for at least 2 weeks and guarantees a remarkable sensitivity to enzyme induction, even if weak inducers are tested. A particular advantage of this systemis that the same bioreactor can be perfused with different concentrations of a test substance in a sequential manner. The 96-well plate bioreactor runs 96 modules in parallel for pharmacokinetic testing under aerobic culture conditions. This system combines the advantages of a three-dimensional culture system in collagen gel, controlled oxygen supply, and constant culture medium conditions, with the possibility of high throughput and automatization. A newly developed co-culture system of hepatocytes with intestinal bacteria offers the possibility to study the metabolic interaction between liver and intestinal microflora. It consists of two chambers separated by a permeable polycarbonate membrane, where hepatocytes are cultured under aerobic and intestinal bacteria in anaerobic conditions. Test substances are added to the aerobic side to allow their initial metabolism by the hepatocytes, followed by the metabolism by intestinal bacteria at the anaerobic side. Precision-cut slices represent an alternative to isolated hepatocytes and have been used fo the investigation of hepatic metabolism, hepatotoxicity, and enzyme induction. A specific advantage of liver slices is the possibility to study toxic effects on hepatocytes that are mediated or modified by nonparenchymal cells (e.g., by cytokine release from Kupffer cells) because the physiological liver microarchitecture is maintained in cultured slices. For all these in vitro systems, a prevalidation has been performed using standard assays for phase I and II enzymes. Representative results with test substances and recommendations for application of these in vitro systems, as well as standard operation procedures are given.

Cryopreservation of precision-cut tissue slices for application in drug metabolism research

Cryopreservation of tissue slices greatly facilitates their use in drug metabolism research, leading to efficient use of human organ material and a decrease of laboratory animal use. In the present review, various mechanisms of cryopreservation such as equilibrium slow freezing, rapid freezing and vitrification, and their application to cryopreservation of tissue slices are discussed as well as the viability parameters often used to evaluate the success of cryopreservation. Equilibrium freezing prevents intracellular ice formation by inducing cellular dehydration, but (large) ice crystals are still formed in the interstitial space of the slices. Upon rapid freezing, (small) intra- and extracellular ice crystals are formed which slices from some tissues can resist. Vitrification prevents the formation of both intra- and extracellular ice crystals while an amorphous glass is formed of the slice liquid constituents. To vitrify, however, high molarity solutions of cryoprotectants are required that may be toxic to the slices. The use of mixtures of high molarity of cryoprotectants overcomes this problem. We conclude that vitrification is the approach that most likely will lead to the development of universal cryopreservation methods for tissue slices of various organs from various animal species. In the future this may lead to the formation of a tissue slice bank from which slices can be derived at any desirable time point for in vitro experimentation.

Incubation at 37 degrees C prior to cryopreservation decreases viability of liver slices after cryopreservation by rapid freezing

Precision-cut liver slices are to some extent resistant to ice formation induced by rapid freezing. Susceptibility to rapid freezing damage has been shown to be (partly) dependent on intrinsic properties of cells. In the present study an attempt was made to decrease the susceptibility of rat liver slices for rapid freezing damage: the slices were pre-incubated at 37 degrees C under oxygen, prior to cryopreservation to recover from low ATP levels, impaired ion regulation and cell swelling induced by their preparation. It was shown that, unexpectedly, recovery of cellular homeostasis prior to the cryopreservation procedure by the 37 degrees C pre-incubation markedly decreased viability of rapidly frozen slices (in which ice was formed), but not of vitrified slices (in which no ice was formed), in a time- and temperature-dependent manner. UW was found to protect slices from this 'warm pre-incubation phenomenon.' Apparently, pre-incubation prior to freezing causes certain cellular alterations that render slices more susceptible to rapid freezing damage.