Investigation of functional and morphological integrity of freshly isolated and cryopreserved human hepatocytes

Cryopreservation of assay-ready hepatocyte monolayers by chemically-induced ice nucleation: preservation of hepatic function and hepatotoxicity screening capabilities

Cell culture plays a critical role in biomedical discovery and drug development. Primary hepatocytes and hepatocyte-derived cell lines are especially important cellular models for drug discovery and development. To enable high-throughput screening and ensure consistent cell phenotypes, there is a need for practical and efficient cryopreservation methods for hepatocyte-derived cell lines and primary hepatocytes in an assay-ready format. Cryopreservation of cells as adherent monolayers in 96-well plates presents unique challenges due to low volumes being susceptible to supercooling, leading to low recovery and well-to-well variation. Primary cell cryopreservation is also particularly challenging due to the loss of cell viability and function. In this study, we demonstrate the use of soluble ice nucleator materials (IN) to cryopreserve a hepatic-derived cell line (HepG2) and primary mouse hepatocytes, as adherent monolayers. HepG2 cell recovery was near 100% and ∼75% of primary hepatocytes were recovered 24 hours post-thaw compared to just 10% and 50% with standard 10% DMSO, respectively. Post-thaw assessment showed that cryopreserved HepG2 cells retain membrane integrity, metabolic activity, proliferative capacity and differentiated hepatic functions including urea secretion, cytochrome P450 levels and lipid droplet accumulation. Cryopreserved primary hepatocytes exhibited reduced hepatic functions compared to fresh hepatocytes, but functional levels were similar to commercial suspension-cryopreserved hepatocytes, with the added benefit of being stored in an assay-ready format. In addition, normal cuboidal morphology and minimal membrane damage were observed 24 hours post-thaw. Cryopreserved HepG2 and mouse hepatocytes treated with a panel of pharmaceutically active compounds produced near-identical dose-response curves and EC50 values compared to fresh hepatocytes, confirming the utility of cryopreserved bankable cells in drug metabolism and hepatotoxicity studies. Cryopreserved adherent HepG2 cells and primary hepatocytes in 96 well plates can significantly reduce the time and resource burden associated with routine cell culture and increases the efficiency and productivity of high-throughput drug screening assays.

Technologies for Vitrification Based Cryopreservation

Cryopreservation is a unique and practical method to facilitate extended access to biological materials. Because of this, cryopreservation of cells, tissues, and organs is essential to modern medical science, including cancer cell therapy, tissue engineering, transplantation, reproductive technologies, and bio-banking. Among diverse cryopreservation methods, significant focus has been placed on vitrification due to low cost and reduced protocol time. However, several factors, including the intracellular ice formation that is suppressed in the conventional cryopreservation method, restrict the achievement of this method. To enhance the viability and functionality of biological samples after storage, a large number of cryoprotocols and cryodevices have been developed and studied. Recently, new technologies have been investigated by considering the physical and thermodynamic aspects of cryopreservation in heat and mass transfer. In this review, we first present an overview of the physiochemical aspects of freezing in cryopreservation. Secondly, we present and catalog classical and novel approaches that seek to capitalize on these physicochemical effects. We conclude with the perspective that interdisciplinary studies provide pieces of the cryopreservation puzzle to achieve sustainability in the biospecimen supply chain.

Human Hepatocytes Isolated from Explanted Livers: A Powerful Tool to Understand End-stage Liver Disease and Drug Screening

The use of primary human hepatocytes has been hampered by limited availability of adequate numbers of fresh and viable cells due to the ongoing shortage of liver donors. Thus, there is no surplus of healthy organs from which freshly isolated cells can be prepared when needed. However, primary hepatocytes can be successfully isolated from explanted liver specimens obtained from patients receiving orthotopic liver transplantation for decompensated liver cirrhosis or for metabolic liver disease without end-stage liver disease and are a valuable resource for the pharmaceutical industry research. This review focuses on the isolation, characterization and cryopreservation of hepatocytes derived from therapeutically resected livers with various hepatic diseases.

Cryopreservation: An Overview of Principles and Cell-Specific Considerations

The origins of low-temperature tissue storage research date back to the late 1800s. Over half a century later, osmotic stress was revealed to be a main contributor to cell death during cryopreservation. Consequently, the addition of cryoprotective agents (CPAs) such as dimethyl sulfoxide (DMSO), glycerol (GLY), ethylene glycol (EG), or propylene glycol (PG), although toxic to cells at high concentrations, was identified as a necessary step to protect against rampant cell death during cryopreservation. In addition to osmotic stress, cooling and thawing rates were also shown to have significant influence on cell survival during low temperature storage. In general, successful low-temperature cell preservation consists of the addition of a CPA (commonly 10% DMSO), alone or in combination with additional permeating or non-permeating agents, cooling rates of approximately 1ºC/min, and storage in either liquid or vapor phase nitrogen. In addition to general considerations, cell-specific recommendations for hepatocytes, pancreatic islets, sperm, oocytes, and stem cells should be observed to maximize yields. For example, rapid cooling is associated with better cryopreservation outcomes for oocytes, pancreatic islets, and embryonic stem cells while slow cooling is recommended for cryopreservation of hepatocytes, hematopoietic stem cells, and mesenchymal stem cells. Yields can be further maximized by implementing additional pre-cryo steps such as: pre-incubation with glucose and anti-oxidants, alginate encapsulation, and selecting cells within an optimal age range and functional ability. Finally, viability and functional assays are critical steps in determining the quality of the cells post-thaw and improving the efficiency of the current cryopreservation methods.

Alternative Cell Sources for Liver Parenchyma Repopulation: Where Do We Stand?

Acute and chronic liver failure is a highly prevalent medical condition with high morbidity and mortality. Currently, the therapy is orthotopic liver transplantation. However, in some instances, chiefly in the setting of metabolic diseases, transplantation of individual cells, specifically functional hepatocytes, can be an acceptable alternative. The gold standard for this therapy is the use of primary human hepatocytes, isolated from livers that are not suitable for whole organ transplantations. Unfortunately, primary human hepatocytes are scarcely available, which has led to the evaluation of alternative sources of functional hepatocytes. In this review, we will compare the ability of most of these candidate alternative cell sources to engraft and repopulate the liver of preclinical animal models with the repopulation ability found with primary human hepatocytes. We will discuss the current shortcomings of the different cell types, and some of the next steps that we believe need to be taken to create alternative hepatocyte progeny capable of regenerating the failing liver.

Successful energy shift from glycolysis to mitochondrial oxidative phosphorylation in freshly isolated hepatocytes from humanized mice liver

Mitochondrial toxicity is a factor of drug-induced liver injury. Previously, we reported an in vitro rat hepatocyte assay where mitochondrial toxicity was more sensitively evaluated, using sugar resource substitution and increased oxygen supply. Although this method could be applicable to human cell-based assay, cryopreserved human hepatocyte (CHH) has some disadvantages/uncertainty, including unstable same donor supply and potential organelle damage due to cryopreservation. Herein, we compared the mitochondrial functions of freshly-isolated hepatocytes from humanized chimeric mice liver (PXB-cells) and three CHH lots to determine the better cell source for mitochondrial toxicity assay. Two CHH lots declined after replacing glucose with galactose. To confirm the shift in energy production from glycolysis to oxidative phosphorylation, lactate and oxygen consumption rate (indicators of glycolytic activity and mitochondrial oxidative phosphorylation, respectively) were measured. In PXB-cells, lactate amount decreased, while oxygen consumption in 100 min increased. These effects were less evident in CHH. The cytotoxicity of the select respiratory chain inhibitors was enhanced in PXB-cells upon sugar replacement, but no change occurred with negative control drugs (bicalutamide and metformin). Altogether, PXB-cells was less vulnerable to sugar resource substitution than CHH. The substitution activated mitochondrial function and enhanced cytotoxicity of respiratory chain inhibitors in PXB-cells.

Impact of Percoll purification on isolation of primary human hepatocytes

Research and therapeutic applications create a high demand for primary human hepatocytes. The limiting factor for their utilization is the availability of metabolically active hepatocytes in large quantities. Centrifugation through Percoll, which is commonly performed during hepatocyte isolation, has so far not been systematically evaluated in the scientific literature. 27 hepatocyte isolations were performed using a two-step perfusion technique on tissue obtained from partial liver resections. Cells were seeded with or without having undergone the centrifugation step through 25% Percoll. Cell yield, function, purity, viability and rate of bacterial contamination were assessed over a period of 6 days. Viable yield without Percoll purification was 42.4 × 10⁶ (SEM ± 4.6 × 10⁶) cells/g tissue. An average of 59% of cells were recovered after Percoll treatment. There were neither significant differences in the functional performance of cells, nor regarding presence of non-parenchymal liver cells. In five cases with initial viability of <80%, viability was significantly increased by Percoll purification (71.6 to 87.7%, p = 0.03). Considering our data and the massive cell loss due to Percoll purification, we suggest that this step can be omitted if the initial viability is high, whereas low viabilities can be improved by Percoll centrifugation.

Analysis of the Effects of Cryopreservation on Rat Hepatocytes Using SELDI-TOF Mass Spectrometry

Successful cryopreservation of hepatocytes is essential to the future of hepatocyte transplantation as a treatment for liver disease, and also for the improved in vitro use of hepatocytes for research. However, hepatocyte function is adversely affected by even the best cryopreservation protocols. To investigate possible mechanisms for these changes, total cell lysates were prepared from fresh and cryopreserved rat hepatocytes and the proteome profiles compared using SELDI-TOF-MS ProteinChip? technology. In addition, in vitro functional assays (viability, attachment efficiency, and lactate dehydrogenase leakage) were performed on the corresponding fresh and cryopreserved hepatocytes. Sixty-one peptides were identified as being significantly changed after cryopreservation. Thirty-seven peaks were significantly increased and 24 were significantly decreased after cryopreservation. The peak intensity of a number of these peptides was found to correlate with the in vitro function of the hepatocytes. Seven peptides correlated with in vitro function after cryopreservation and 10 peptides correlated with both fresh and cryopreserved function. The peptides significantly decreased after cryopreservation could include cytosolic enzymes or cofactors, which leaked out of the cells due to cryopreservation-induced membrane damage. The peptides significantly increased after cryopreservation could be retained products of cleavage of larger intracellular polypeptides and proteins or the result of aggregation of peptides caused by physical changes in the cell due to the cryopreservation process. Proteome profiling using SELDI-TOF-MS could be a useful tool to assess the effects of isolation and cryopreservation of hepatocytes, particularly if the findings are extended to human hepatocytes.

Hepatocyte transplantation program: Lessons learned and future strategies

This review aims to share the lessons we learned over time during the setting of the hepatocyte transplantation (HT) program at the Hepatic Cell Therapy Unit at Hospital La Fe in Valencia. New sources of liver tissue for hepatocyte isolation have been explored. The hepatocyte isolation and cryopreservation procedures have been optimized and quality criteria for assessment of functionality of hepatocyte preparations and suitability for HT have been established. The results indicate that: (1) Only highly viable and functional hepatocytes allow to recover those functions lacking in the native liver; (2) Organs with steatosis (≥ 40%) and from elderly donors are declined since low hepatocyte yields, viability and cell survival after cryopreservation, are obtained; (3) Neonatal hepatocytes are cryopreserved without significant loss of viability or function representing high-quality cells to improve human HT; (4) Cryopreservation has the advantage of providing hepatocytes constantly available and of allowing the quality evaluation and suitability for transplantation; and (5) Our results from 5 adults with acute liver failure and 4 from children with inborn metabolic diseases, indicate that HT could be a very useful and safe cell therapy, as long as viable and metabolically functional human hepatocytes are used.

Human neonatal hepatocyte transplantation induces long-term rescue of unconjugated hyperbilirubinemia in the Gunn rat

Crigler-Najjar type 1 disease is a rare inherited metabolic disease characterized by high levels of unconjugated bilirubin due to the complete absence of hepatic uridine diphosphoglucuronate-glucuronosyltransferase activity. Hepatocyte transplantation (HT) has been proposed as an alternative treatment for Crigler-Najjar syndrome, but it is still limited by the quality and the low engraftment and repopulation ability of the cells used. Because of their attachment capability and expression of adhesion molecules as well as the higher proportion of hepatic progenitor cells, neonatal hepatocytes may have an advantage over adult cells. Adult or neonatal hepatocytes were transplanted into Gunn rats, a model for Crigler-Najjar disease. Engraftment and repopulation were studied and compared by immunofluorescence (IF). Additionally, the serum bilirubin levels, the presence of bilirubin conjugates in rat serum, and the expression of uridine diphosphate glucuronosyltransferase 1 family polypeptide A1 (UGT1A1) in rat liver samples were also analyzed. Here we show that neonatal HT results in long-term correction in Gunn rats. In comparison with adult cells, neonatal cells showed better engraftment and repopulation capability 3 days and 6 months after transplantation, respectively. Bilirubinemia decreased in the transplanted animals during the whole experimental follow-up (6 months). Bilirubin conjugates were also present in the serum of the transplanted animals. Western blots and IF confirmed the presence and expression of UGT1A1 in the liver. This work is the first to demonstrate the advantage of using neonatal hepatocytes for the treatment of Crigler-Najjar in vivo.

Hypothermic storage of human hepatocytes for transplantation

Transplantation of human hepatocytes is gaining recognition as a bridge or an alternative to orthotopic liver transplantation for patients with acute liver failure and genetic defects. Since most patients require multiple cell infusions over an extended period of time, we investigated hepatic functions in cells maintained in University of Wisconsin solution at 4°C up to 72 h. Eleven different assessments of hepatic viability and function were investigated both pre- and posthypothermic storage, including plating efficiency, caspase-3/7 activity, ammonia metabolism, and drug-metabolizing capacity of isolated hepatocytes. Long-term function, basal, and induced cytochrome P450 activities were measured after exposure to prototypical inducing agents. Cells from 47 different human liver specimens were analyzed. Viability significantly decreased in cells cold stored in UW solution, while apoptosis level and plating efficiency were not significantly different from fresh cells. Luminescent and fluorescent methods assessed phases I and II activities both pre- and post-24-72 h of cold preservation. A robust induction (up to 200-fold) of phase I enzymes was observed in cultured cells. Phase II and ammonia metabolism remained stable during hypothermic storage, although the inductive effect of culture on each metabolic activity was eventually lost. Using techniques that characterize 11 measurements of hepatic viability and function from plating efficiency, to ammonia metabolism, to phases I and II drug metabolism, it was determined that while viability decreased, the remaining viable cells in cold-stored suspensions retained critical hepatic functions for up to 48 h at levels not significantly different from those observed in freshly isolated cells.

Incubation with dimethyl sulfoxide prior to cryopreservation improves functionality of thawed human primary hepatocytes

BACKGROUND

Efficient cryopreservation of human hepatocytes is essential for their use in cell therapy. This study investigated the effects of adding melatonin and/or dimethyl sulfoxide (DMSO) to pre-incubation and/or freezing solutions on the viability and function of thawed human hepatocytes.

METHODS

Isolated human hepatocytes were pre-incubated for 90 min at 4°C in Williams' Medium E (WEM), WEM containing 5 mM melatonin dissolved in DMSO, or WEM containing the equivalent amount of DMSO (1%). The hepatocytes were frozen in University of Wisconsin solution (UW) and 10% DMSO, with or without 5 mM melatonin. After thawing, viability, plating efficiency, mitochondrial dehydrogenase activity (MTT), and albumin and urea production were analyzed.

RESULTS

Viability and plating efficiency were not affected by melatonin or DMSO in pre-incubation media. Unexpectedly, hepatocytes pre-incubated with DMSO had significantly higher MTT (29.7% vs. control, p<0.01), albumin (82.8% vs. control, p<0.05), and urea amounts (26.2% vs. control, p=0.06) than those incubated only with WEM. Hepatocytes pre-incubated in media containing melatonin had amounts between those of cells incubated with DMSO or only with WEM (p<0.05 for MTT and p>0.05 for albumin and urea values). Also, the addition of melatonin to the freezing media did not significantly improve any of the studied parameters (p>0.05).

DISCUSSION

Adding 1% DMSO to pre-incubation media prior to the cryopreservation of human hepatocytes preserves hepatocyte function after thawing. These findings could be considered in current hepatocyte cryopreservation protocols.

Hepatocytes maintain greater fluorescent bile acid accumulation and greater sensitivity to drug-induced cell death in three-dimensional matrix culture

Primary hepatocytes undergo phenotypic dedifferentiation upon isolation from liver that typically includes down regulation of uptake transporters and up regulation of efflux transporters. Culturing cells between layers of collagen in a three‐dimensional (3D) “sandwich” is reported to restore hepatic phenotype. This report examines how 3D culturing affects accumulation of fluorophores, the cytotoxic response to bile acids and drugs, and whether cell to cell differences in fluorescent anion accumulation correlate with differences in cytotoxicity. Hepatocytes were found to accumulate fluorescent bile acid (FBA) at significantly higher levels than the related fluorophores, carboxyfluorescein diacetate, (4.4‐fold), carboxyfluorescein succinimidyl ester (4.8‐fold), and fluorescein (30‐fold). In 2D culture, FBA accumulation decreased to background levels by 32 h, Hoechst nuclear accumulation strongly decreased, and nuclear diameter increased, indicative of an efflux phenotype. In 3D culture, FBA accumulation was maintained through 168 h but at 1/3 the original intensity. Cell to cell differences in accumulated FBA did not correlate with levels of liver zonal markers L‐FBAP (zone 1) or glutamine synthetase (zone 3). Cytotoxic response to hydrophobic bile acids, acetaminophen, and phalloidin was maintained in 3D culture, and cells with higher FBA accumulation showed 12–18% higher toxicity than the total population toward hydrophobic bile acids (P < 0.05). Long‐term imaging showed oscillations in the accumulation of FBA over periods of hours. Overall, the studies suggest that high accumulation of FBA can indicate the sensitivity of cultured hepatocytes to hydrophobic bile acids and other toxins.

These studies use automated image analysis and fluorescent dye accumulation to demonstrate that 3D culturing enhances organic anion accumulation and cytotoxic response in long‐term hepatocyte cultures. The level of anion accumulation was found to vary through days in culture and also between single cells, and higher fluorescent bile acid accumulation correlated with higher toxic response to hydrophobic bile acids.

Neonatal livers: a source for the isolation of good-performing hepatocytes for cell transplantation

Hepatocyte transplantation is an alternative therapy to orthotopic liver transplantation for the treatment of liver diseases. However, the supply of hepatocytes is limited given the shortage of organs available to isolate good-functioning quality cells. Neonatal livers may be a potential source alternative to adult livers to obtain good-performing hepatic cells for hepatocyte transplantation, which has not yet been explored profoundly. High-yield preparations of viable hepatocytes were isolated from 1- to 23-day-old liver donors, cryopreserved, and banked. Cell integrity and functional quality assessment were performed after thawing. Neonatal hepatocytes showed better postthawing recovery compared with adult hepatocytes, as shown by the viability values that did not differ significantly from freshly isolated cells, a higher expression of adhesion molecules (β1-integrin, β-catenin, and E-cadherin), better attachment efficiency, cell survival, and a lower number of apoptotic cells. The metabolic performance of thawed hepatocytes has been assessed by ureogenesis and drug-metabolizing capability (cytochrome P450 and UDP-glucuronosyltransferase enzymes). CYP2A6, CYP2C9, CYP2E1, and CYP3A4 activities were found in all cell preparations, while CYP1A2, CYP2B6, CYP2C19, and CYP2D6 activities were detected only in hepatocytes from a few neonatal donors. The expression of UGT1A1 and UGT1A9 (transcripts and protein) was detected in all hepatocyte preparations, while activity was measured only in some preparations, probably due to lack of maturity of the enzymes. However, isoforms UGT1A6 and UGT2B7 showed considerable activity in all preparations. Compared to adult liver, the hepatocyte isolation procedure in neonatal livers also provides thawed cell suspensions with a higher proportion of hepatic progenitor cells (EpCAM(+) staining), which could also participate in regeneration of liver parenchyma after transplantation. These results could imply important advantages of neonatal hepatocytes as a source of high-quality cells to improve human hepatocyte transplantation applicability.

Evaluating the Effects of Dithiothreitol and Fructose on Cell Viability and Function of Cryopreserved Primary Rat Hepatocytes and HepG2 Cell Line

BACKGROUND

Hepatocytes are used as an in vitro model to evaluate drug metabolism. Human hepatocyte transplant has been considered as the temporary treatment of acute liver failure. Optimization freezing methods is very important to preserve both cell viability and function which are achieved by cryopreservation mostly always.

OBJECTIVES

The present study aimed to investigate the cryoprotective effect of DTT and fructose on primary rat hepatocytes and HepG2 cells.

MATERIALS AND METHODS

Both fresh rat hepatocytes and HepG2 cell line were incubated with fructose (100 and 200 mM) and dithiothreitol (DTT) (25, 50, 100, 250, and 500 μM) at 37°C for 1 and 3 hours, respectively. The preincubated hepatocytes were cryopreserved for two weeks. Hepatocytes viability and function were determined post thawing and the results were compared with the control group.

RESULTS

The viability of both rat hepatocytes and HepG2 cells were significantly increased after one hour preincubation with fructose 200 mM. Preincubation with DTT (50 μM, 100 μM. 250 μM and 500 μM) improved the viability and function upon thawing in both cell types (P < 0.001). In rat hepatocytes, no significant change was observed in albumin, urea production, and LDH leakage after preincubation with fructose or DTT. In HepG2 cells, albumin and urea production were significantly increased after preincubation with DTT (500 μM, 1 hour). The GSH content was significantly increased in DTT (250 and 500 μM, 1 hour) groups in both rat hepatocyte and HepG2 cells.

CONCLUSIONS

Incubation of hepatocytes with fructose and DTT prior to the cryopreservation can increase the cell viability and function after thawing.

Human hepatocyte propagation system in the mouse livers: functional maintenance of the production of coagulation and anticoagulation factors

We previously reported that cell-based therapies using isolated hepatocytes including hepatocyte transplantation and liver tissue engineering approaches provide therapeutic benefits to hemophilia. For clinical application of these approaches, it is important to establish an active hepatocyte proliferation system that enables providing a sufficient number of hepatocytes. We also reported that human hepatocytes, which were transplanted into the liver of urokinase-type plasminogen activator transgenic severe combined immunodeficiency (uPA/SCID) mice, were able to proliferate while retaining their ability to produce coagulation factor IX. The objective of this study was to explore the functionalities of other coagulation and anticoagulation factors of the propagated human hepatocytes in uPA/SCID mice. Human hepatocytes were transplanted into the liver of uPA/SCID mice, and the propagation status of human hepatocytes in the mice was monitored by the increase in serum human albumin levels and immunohistochemical evaluation on the liver sections. Using uPA/SCID livers with various stages of human hepatocyte propagation, we analyzed the gene expression levels of coagulation factors (prothrombin, factor VII, factor X, and factor VIII) and anticoagulation factors (protein C and protein S) by real-time polymerase chain reaction (PCR) using human-specific primers. As a result, the total amount of raw messenger RNA expression levels increased in all genes analyzed according to the progress of hepatocyte propagation and proliferation. Except for factor VIII, the gene expression levels of the highly repopulated uPA/SCID mouse livers with human hepatocyte showed higher levels than those of normal human livers, indicating that propagated human hepatocytes in the uPA/SCID system possess full functions to produce most of the coagulation-related factors. The current work demonstrated that human hepatocytes can be propagated in experimental animals while maintaining normal gene expression levels of coagulation-related factors. It could be speculated that the propagated cells serve as a cell source for the treatment of various types of coagulation factor deficiencies.

Hepatocyte Is a Sole Cell Type Responsible for the Production of Coagulation Factor IX In Vivo

Coagulation factor IX (FIX) is synthesized by hepatocytes, and the lack of this protein causes hemophilia B. Liver nonparenchymal cells, including liver sinusoidal endothelial cells (LSECs) and extrahepatic cells in the body, are scarcely shown to have an ability to synthesize and secrete FIX. The present study investigated the existence of cells responsible for synthesizing FIX other than hepatocytes in mice using gene expression analyses and FIX-specific clotting assays. Among the several organs investigated, including liver, lung, spleen, kidney, brain, intestine, and tongue, FIX mRNA expressions were observed only in the liver. From the liver, hepatocytes and LSECs were isolated. FIX mRNA expression and FIX protein secretion were observed exclusively in the hepatocytes. Furthermore, the clotting activity of FIX secreted from the cultured hepatocytes was found to be dependent on the concentration of vitamin K₂. These findings indicated that the hepatocyte is the only cell type that biochemically produces functional FIX in vivo. This highlights the importance of hepatocytes or cells that are fully differentiated toward the hepatic lineage for possible application for regenerative medicine and for targeting gene delivery to establish new cell-based treatments for hemophilia B.

Influence of platelet lysate on the recovery and metabolic performance of cryopreserved human hepatocytes upon thawing

BACKGROUND

Storage of human hepatocytes is essential for their use in research and liver cell transplantation. However, cryopreservation and thawing (C/T) procedures have detrimental effects on the viability and functionality compared with fresh cells. The aim of this study was to upgrade the standard C/T methodology to obtain better quality hepatocytes for cell transplantation to improve the overall clinical outcome.

METHODS

Human hepatocytes isolated from donor livers were cryopreserved in University of Wisconsin solution with 10% dimethyl sulfoxide (standard medium), which was supplemented with 10% or 20% of platelet lysate. Thawing media supplemented with up to 30 mM glucose was also investigated. The effects on cell viability, adhesion proteins (e-cadherin, β-catenin, and β1-integrin) expression, attachment efficiency, apoptotic indicators, Akt signaling, ATP levels, and cytochrome P450 activities have been evaluated.

RESULTS

The results indicate that the hepatocytes cryopreserved in a medium supplemented with platelet lysate show better recovery than those preserved in the standard medium: higher expression of adhesion molecules, higher attachment efficiency and cell survival; decreased number of apoptotic nuclei and caspase-3 activation; maintenance of ATP levels; and drug biotransformation capability close to those in fresh hepatocytes. Supplementation of thawing media with glucose led to a significant decrease in caspase-3 activation and to increased adhesion molecules preservation and Akt signal transduction after C/T. Minor nonsignificant changes in cell viability and attachment efficiency were observed.

CONCLUSIONS

These promising results could lead to a new cryopreservation procedure to improve human hepatocyte cryopreservation outcome.

Derivation of high-purity definitive endoderm from human parthenogenetic stem cells using an in vitro analog of the primitive streak

Human parthenogenetic stem cells (hpSCs) are pluripotent stem cells with enormous potential as cell sources for cell-based therapies: hpSCs may have histocompatibilty advantages over human embryonic stem cells (hESCs) and derivation of hpSCs does not require viable blastocyst destruction. For translation of all pluripotent stem cell-based therapies, derivation of differentiated cell products that are not contaminated with undifferentiated cells is a major technical roadblock. We report here a novel method to derive high-purity definitive endoderm (DE) from hpSCs, based on reproducing features of the normal human embryonic microenvironment. The method mimics the developmental process of transition through a primitive streak, using a differentiation device that incorporates a three-dimensional extracellular matrix (ECM) combined with a porous membrane. Treatment of undifferentiated hpSCs above the membrane results an epithelial-to-mesenchymal transition (EMT); thus, responsive cells acquire the ability to migrate through the membrane into the ECM, where they differentiate into DE. Importantly, the resultant DE is highly purified, and is not contaminated by undifferentiated cells, as assessed by OCT4 expression using immunocytochemistry and flow cytometry. The functional properties of the DE are also preserved by the process: DE differentiated in the device can generate a highly enriched population of hepatocyte-like cells (HLCs) characterized by expression of hepatic lineage markers, indocyanine green clearance, glycogen storage, cytochrome P450 activity, and engraftment in the liver after transplantation into immunodeficient mice. The method is broadly applicable and we obtained purified DE using hESCs, as well as several hpSC lines. The novel method described here represents a significant step toward the efficient generation of high-purity cells derived from DE, including hepatocytes and pancreatic endocrine cells, for use in regenerative medicine and drug discovery, as well as a platform for studying cell fate specification and behavior during development.

Primary human hepatocytes on biodegradable poly(l-lactic acid) matrices: a promising model for improving transplantation efficiency with tissue engineering

Liver transplantation is an established treatment for acute and chronic liver disease. However, because of the shortage of donor organs, it does not fulfill the needs of all patients. Hepatocyte transplantation is promising as an alternative method for the treatment of end-stage liver disease and as bridging therapy until liver transplantation. Our group has been working on the optimization of matrix-based hepatocyte transplantation. In order to increase cell survival after transplantation, freshly isolated human hepatocytes were seeded onto biodegradable poly(l-lactic acid) (PLLA) polymer scaffolds and were cultured in a flow bioreactor. PLLA discs were seeded with human hepatocytes and exposed to a recirculated medium flow for 6 days. Human hepatocytes formed spheroidal aggregates with a liver-like morphology and active metabolic function. Phase contrast microscopy showed increasing numbers of spheroids of increasing diameter during the culture period. Hematoxylin and eosin histology showed viable and intact hepatocytes inside the spheroids. Immunohistochemistry confirmed sustained hepatocyte function and a preserved hepatocyte-specific cytoskeleton. Albumin, alpha-1-antitrypsin, and urea assays showed continued production during the culture period. Northern blot analysis demonstrated increasing albumin signals. Scanning electron micrographs showed hepatocyte spheroids with relatively smooth undulating surfaces and numerous microvilli. Transmission electron micrographs revealed intact hepatocytes and junctional complexes with coated pits and vesicles inside the spheroids. Therefore, we conclude that primary human hepatocytes, precultured in a flow bioreactor on a PLLA scaffold, reorganize to form morphologically intact liver neotissue, and this might offer an optimized method for hepatocyte transplantation because of the expected reduction of the initial cell loss, the high regenerative potential in vivo, and the preformed functional integrity.

Functional characterization of hepatocytes for cell transplantation: customized cell preparation for each receptor

The first indication of hepatocyte transplantation is inborn liver-based metabolic disorders. Among these, urea cycle disorders leading to the impairment to detoxify ammonia and Crigler-Najjar Syndrome type I, a deficiency in the hepatic UDP-glucuronosyltransferase 1A1 present the highest incidence. Metabolically qualified human hepatocytes are required for clinical infusion. We proposed fast and sensitive procedures to determine their suitability for transplantation. For this purpose, viability, attachment efficiency, and metabolic functionality (ureogenic capability, cytochrome P450, and phase II activities) are assayed prior to clinical cell infusion to determine the quality of hepatocytes. Moreover, the evaluation of urea synthesis from ammonia and UDP-glucuronosyltransferase 1A1 activity, a newly developed assay using beta-estradiol as substrate, allows the possibility of customizing cell preparation for receptors with urea cycle disorders or Crigler-Najjar Syndrome type I. Sources of human liver and factors derived from the procurement of the liver sample (warm and cold ischemia) have also been investigated. The results show that grafts with a cold ischemia time exceeding 15 h and steatosis should not be accepted for hepatocyte transplantation. Finally, livers from non-heart-beating donors are apparently a potential suitable source of hepatocytes, which could enlarge the liver donor pool.

Optimization of the cryopreservation and thawing protocol for human hepatocytes for use in cell transplantation

Cryopreservation of human hepatocytes is important for their use in hepatocyte transplantation. On thawing, cryopreserved hepatocytes often have reduced viability and metabolic function in comparison with fresh cells. The aim of this study was to modify the different steps in the standard cryopreservation procedure in an attempt to improve the overall outcome. Human hepatocytes with a viability of 69% +/- SD 16% were isolated from donor livers with a collagenase perfusion technique. Different cell densities, concentrations, rates, and methods of addition of dimethyl sulfoxide were tested for the freezing solution. Modified controlled-rate freezer programs were tested to obtain a linear decrease in the temperature. Once they were frozen, the storage time and thawing method for hepatocytes were investigated. The effects on thawed cell viability and attachment, lactate dehydrogenase release, cytochrome P450 1A1/2 activity, and albumin synthesis were determined. The results were used to produce an improved cryopreservation protocol suitable for good manufacturing practice conditions. With a cell density of 10(7) cells/mL in University of Wisconsin solution containing 300 mM glucose, 10% (vol/vol) dimethyl sulfoxide was added dropwise over 5 minutes, and was immediately frozen. Thawing was done rapidly at 37 degrees C, and dilution was performed with Eagle's minimum essential medium containing 300 mM glucose and 4% human serum albumin. Hepatocytes could be stored at -140 degrees C without significant further loss of function for up to 3 years. With this protocol, hepatocytes had a viability of 52% +/- 9%, an attachment efficiency of 48% +/- 8%, and lactate dehydrogenase leakage of 17% +/- 4%. This protocol is currently in use to cryopreserve hepatocytes for use in cell transplantation at our center.

Hepatocyte cryopreservation: Is it time to change the strategy?

Liver cell transplantation presents clinical benefit in patients with inborn errors of metabolism as an alternative, or at least as a bridge, to orthotopic liver transplantation. The success of such a therapeutic approach remains limited by the quality of the transplanted cells. Cryopreservation remains the best option for long-term storage of hepatocytes, providing a permanent and sufficient cell supply. However, isolated adult hepatocytes are poorly resistant to such a process, with a significant alteration both at the morphological and functional levels. Hence, the aim of the current review is to discuss the state of the art regarding widely-used hepatocyte cryopreservation protocols, as well as the assays performed to analyse the post-thawing cell quality both in vitro and in vivo. The majority of studies agree upon the poor quality and efficiency of cryopreserved/thawed hepatocytes as compared to freshly isolated hepatocytes. Intracellular ice formation or exposure to hyperosmotic solutions remains the main phenomenon of cryopreservation process, and its effects on cell quality and cell death induction will be discussed. The increased knowledge and understanding of the cryopreservation process will lead to research strategies to improve the viability and the quality of the cell suspensions after thawing. Such strategies, such as vitrification, will be discussed with respect to their potential to significantly improve the quality of cell suspensions dedicated to liver cell-based therapies.

Benzylpenicillin, acetylcysteine and silibinin as antidotes in human hepatocytes intoxicated with alpha-amanitin

Fatalities due to mushroom poisonings are increasing worldwide, with high mortality rate resulting from ingestion of amanitin-producing species. Intoxications caused by amanitin-containing mushrooms represent an unresolved problem in clinical toxicology since no specific and fully efficient antidote is available. The objective of this study was a comparative evaluation of benzylpenicillin (BPCN), acetylcysteine (ACC) and silibinin (SIL) as an antidotes in human hepatocytes intoxicated with alpha-amanitin (alpha-AMA). All experiments were performed on cultured human hepatocytes. Cytotoxicity evaluation of cultured cells using MTT assay and measurement of lactate dehydrogenase (LDH) activity was performed at 12, 24 and 48h of exposure to alpha-AMA and/or antidotes. The significant decline of cell viability and significant increase of LDH activity were observed in all experimental hepatocyte cultures after 12, 24 and 36h exposure to alpha-AMA at concentration 2microM. Exposure of the cells to alpha-AMA resulted also in significant reduction of cell spreading and attachment. However, addition of tested antidotes to experimental cultures significantly stimulated cell proliferation and attachment. In cell cultures exposed simultaneously to alpha-AMA and tested antidotes cytotoxic parameters (MTT and LDH) were not significantly different from control incidences. The cytoprotective effect of all antidotes was not dose-related, which reflects a high efficacy of all these substances. Administration of studied antidotes was not associated with any adverse effects in hepatocytes. The administration of ACC, BPCN or SIL to human hepatocyte cultures showed a similar strong protective effect against cell damage in alpha-AMA toxicity.

An optimised method for cryopreservation of human hepatocytes

Successful cryopreservation of hepatocytes is essential for their use in hepatocyte transplantation. Cryopreservation allows hepatocytes to be available for emergency treatment of acute liver failure and also for planned treatment of liver-based metabolic disorders. In addition, cryopreservation of human hepatocytes can facilitate their use in metabolism and toxicity studies. Cryopreservation can adversely affect the viability and function, especially reduce the attachment efficiency, of hepatocytes on thawing.The cryopreservation process can be divided into steps so that improvements can be made on the 'standard' protocols that are followed in some laboratories. These steps are as follows: pre-incubation of cells; freezing solution, cryoprotectants and cytoprotectants; freezing process; storage; thawing; post-thawing culture. This chapter presents an optimised protocol for cryopreservation of human hepatocytes as developed at King's College Hospital.

Hypothermic storage of isolated human hepatocytes: a comparison between University of Wisconsin solution and a hypothermosol platform

Until now little is known about the functional integrity of human hepatocytes after hypothermic storage. In order to address this limitation, we evaluated several commercially available hypothermic preservation media for their abilities to protect freshly isolated hepatocytes during prolonged cold storage. Human hepatocytes were isolated from non-transplantable/rejected donor livers and resuspended in ice-cold University of Wisconsin solution (UW), HypoThermosol-Base (HTS-Base), or HypoThermosol-FRS (HTS-FRS) with or without the addition of fetal bovine serum. Cells were stored at 4 degrees C for 24-72 h, and evaluated for hepatocyte viability (trypan blue exclusion, or labeling with fluorochromes), cell attachment, and function. The energy status of hepatocytes was evaluated by measurement of intracellular adenosine 5'-triphosphate. To determine whether the test cells expressed metabolic functions of freshly isolated cells, the activities of major phase I (cytochromes P450, FMO) and phase II (UGT, ST) drug-metabolizing enzymes were examined. Although hepatocytes are shown to be satisfactory after 24 h storage in all of the tested solutions, the cell viability, energy status, and xenobiotic metabolism following cold preservation in HTS-FRS was consistently and, in some cases, markedly higher when compared with other systems. The same metabolites for each of the tested substrates were detected in all groups of cells. Moreover, the use of HTS-FRS eliminates the need for serum in preservation solutions. HTS-FRS represents an improved solution compared to HTS-Base and UW for extending the shipping/storage time of human hepatocytes.

Functional assessment of the quality of human hepatocyte preparations for cell transplantation

Hepatocyte transplantation is an alternative therapy to orthotopic liver transplantation for the treatment of liver diseases. Good quality freshly isolated or cryopreserved human hepatocytes are needed for clinical transplantation. However, isolation, cryopreservation, and thawing processes can seriously impair hepatocyte viability and functionality. The aim of the present study was to develop a fast and sensitive procedure to estimate the quality of hepatocyte preparations prior to clinical cell infusion. To this end, cell viability, attachment efficiency, and metabolic competence (urea synthesis and drug-metabolizing P450 activities) were selected as objective criteria. Viability of hepatocyte suspension was estimated by trypan blue staining. DNA content of attached cells 50 min after hepatocyte platting to fibronectin/collagen-coated dishes was quantified to estimate adherence capacity. Urea production was determined after incubating hepatocyte suspensions with 2 mM C1NH4 for 30 min. The cytochrome P450 function was assayed by a 30-min incubation of hepatocyte suspension with a cocktail mixture containing selective substrates for seven individual P450 activities (CYP1A2, 2A6, 2C9, 2C19, 2D6, 2E1, and 3A4). The assay can be applied to both freshly isolated and cryopreserved hepatocyte suspensions, and the results are available within 1 h, which could help to make short-term decisions: 1) to assess the suitability for cell transplantation of a preparation of freshly isolated hepatocytes or a particular batch of thawed cells, or 2) to estimate the convenience of banking a particular cell preparation.

Cryopreservation-induced nonattachment of human hepatocytes: role of adhesion molecules

Good quality cryopreserved human hepatocytes are becoming an important source for clinical hepatocyte transplantation. However, the process of cryopreservation leads to both structural and functional impairment of hepatocytes. The aim of this study was to investigate the mechanisms of cryopreservation-induced nonattachment in human hepatocytes. Hepatocytes were cryopreserved after isolation from unused donor liver tissue. Cell attachment to collagen-coated plates was measured. A cDNA gene array system for 96 cell adhesion-related molecules was used to determine mRNA expression in fresh and cryopreserved hepatocytes. Two cell adhesion molecule proteins were investigated further: beta1-integrin, a cell-matrix adhesion molecule, and E-cadherin, a cell-cell adhesion molecule. Attachment efficiency was significantly decreased after cryopreservation of human hepatocytes. Twenty-two genes were downregulated after cryopreservation including integrins, cadherins, catenins, and matrix metalloproteinases (MMPs). Beta1-Integrin gene and protein expression were significantly decreased in cultured cryopreserved hepatocytes compared to fresh hepatocytes. There was a significant correlation between loss of beta1-integrin and attachment in cryopreserved cells. Degradation of E-cadherin was increased in cryopreserved hepatocytes. The process of cryopreservation leads to downregulation of cell adhesion molecules at the gene and the cellular level. New cryopreservation protocols are needed to prevent these effects on cell attachment.

Radiation-induced hepatitis B virus reactivation in liver mediated by the bystander effect from irradiated endothelial cells

PURPOSE

Hepatitis B virus (HBV) reactivation is one unique pathogenesis in Asian carriers with liver toxicity after radiotherapy for hepatobiliary malignancies. This study attempts to delineate the biological mechanism of radiation-induced HBV reactivation.

EXPERIMENTAL DESIGN

Primary cultures of hepatocytes (PCC) were prepared from the noncancerous liver tissue removed perioperatively from 12 HBV carriers with hepatocellular carcinoma (HCC). The conditioned medium of irradiated PCCs, HCC, and endothelial cells from patients was transferred to PCCs or HepG2.2.15 cells (a human hepatoblastoma cell line transfected with HBV DNA) before subsequent irradiation. Forty-eight hours after irradiation, HBV DNA was measured by real-time quantitative PCR. Specific cytokines were determined by cytokine array and ELISA analysis. Preradiotherapy and postradiotherapy sera from 10 HBV carriers and 16 non-HBV carriers were analyzed for viral loads and cytokine activities.

RESULTS

Radiation induced HBV DNA replication in (a) irradiated PCCs cultured with the conditioned medium from irradiated PCCs (2.74-fold; P=0.004) and endothelial cells (9.50-fold; P=3.1x10(-10)), but not from HCCs (1.07-fold), and in (b) irradiated HepG2.2.15 cells (17.7-fold) cocultured with human umbilical vascular endothelial cells. Cytokine assay revealed increased expression of interleukin-6 (IL-6) in conditioned medium from irradiated human umbilical vascular endothelial cells. All 16 patients with liver irradiated had the increased serum IL-6 compared with 3 of 10 patients with irradiation excluding liver (P<0.001). All nine HBV carriers with liver irradiated had postradiotherapy increases in both HBV DNA and IL-6.

CONCLUSIONS

Radiation-induced liver toxicity with HBV reactivation is from a bystander effect on irradiated endothelial cells releasing cytokines, including IL-6.

Effect of cryopreservation on viability, activation and growth of in situ and isolated ovine early-stage follicles

Isolated or cortical tissue-enclosed (in situ) sheep early-stage follicles were exposed to 1.5 M dimethyl sulfoxide (DMSO), ethylene glycol (EG) or unexposed, or frozen/thawed in the presence of these cryoprotectants and then cultured for 5 days in enriched minimal essential medium (MEM) or not cultured. Cultured and uncultured follicles were classified as non-viable/viable when they were stained/not stained with trypan blue, respectively. Follicular diameter was measured and the percentages of primordial and developing follicles calculated. Exposure of isolated or in situ follicles to DMSO or EG led to a marked decrease in the percentage of viable follicles. The percentage of viable isolated and in situ follicles further decreased when they were in vitro-cultured for 5 days, EG-exposed follicles generally showing a more damaging effect than DMSO-exposed follicles. Cultured follicles, both isolated and in situ, which were exposed to EG and DMSO, as well as in situ follicles, which had been frozen/thawed in the presence of one of these cryoprotectants, showed similar growth rates as cultured, untreated follicles, while in these groups significantly lower percentages of primordial follicles and higher percentages of more advanced follicular stages were observed. Among the treated groups, the highest percentage (71-75%) of developing follicles was observed after culturing cryoprotectant-exposed isolated follicles. In contrast, when cryopreserved, isolated follicles were cultured, they did not increase in diameter and did not develop into more advanced stages. In conclusion, exposure to or cryopreservation in the presence of EG and DMSO, as well as their further in vitro culture, negatively affected the viability of ovine isolated and in situ early-stage follicles. In vitro growth of early-stage follicles and activation of primordial follicles were better maintained when follicles had been frozen/thawed and cultured in situ.

Cryopreservation of primary human hepatocytes: the benefit of trehalose as an additional cryoprotective agent

Problems with the limited availability of human hepatocytes for cell transplantation may be overcome by efficient cryopreservation techniques and formation of appropriate cell banking. In this study we investigated the effect of the disaccharide trehalose on the cryopreservation of human hepatocytes. For analysis, liver cells were frozen in culture medium containing 10% dimethyl sulfoxide (DMSO) that was supplemented with varying concentrations of trehalose. During the postthawing culture period, viability, plating efficiency, total protein, cell proliferation, enzyme leakage, albumin and urea formation, as well as phase I and II metabolism were analyzed. In the pilot study, among the concentrations investigated, 0.2 M trehalose showed the best overall outcome. Compared to the use of DMSO alone, we found significant improvement in postthaw cell viability (62.9 +/- 13 vs. 46.9 +/- 11%, P < 0.01) and plating efficiency (41.5 +/- 18 vs. 17.6 +/- 13%, P < 0.01) in the trehalose group. The use of trehalose as an additive for cryopreserving human hepatocytes resulted in a significantly increased total protein level in the attached cells, higher secretion of albumin and a lower aspartate aminotransferase (AST) level after thawing. In conclusion, the use of trehalose as cryoprotective agent significantly improves the outcome of human hepatocyte cryopreservation.

Cryopreservation of isolated human hepatocytes for transplantation: State of the art

Hepatocytes isolated from unused donor livers are being used for transplantation in patients with acute liver failure and liver-based metabolic defects. As large numbers of hepatocytes can be prepared from a single liver and hepatocytes need to be available for emergency and repeated treatment of patients it is essential to be able to cryopreserve and store cells with good thawed cell function. This review considers the current status of cryopreservation of human hepatocytes discussing the different stages involved in the process. These include pre-treatment of cells, freezing solution, cryoprotectants and freezing and thawing protocols. There are detrimental effects of cryopreservation on hepatocyte structure and metabolic function, including cell attachment, which is important to the engraftment of transplanted cells in the liver. Cryopreserved human hepatocytes have been successfully used in clinical transplantation, with evidence of replacement of missing function. Further optimisation of hepatocyte cryopreservation protocols is important for their use in hepatocyte transplantation.

Fuentes alternativas de hepatocitos para la terapia celular

There is an urgent need to search for alternatives to whole organ transplantation. Several methods have been proposed. Among these strategies, cell transplantation is currently one of the most promising. To achieve this aim, in addition to highly differentiated adult hepatocytes, the use of stem cells is considered a highly attractive therapeutic method for the treatment of liver disease and for temporary support of hepatic function until a liver becomes available for organ transplantation. This strategy is based on the ability of stem cells to differentiate into different cellular types according to their environment. Therefore, stem cells could be an unlimited source of hepatic cells for transplantation and gene therapy. Bone marrow is considered the most promising source of adult stem cells, partly due to the versatility of the cells obtained in repairing damaged tissues of several lineages. Several different types of stem cells have been described in bone marrow: hematopoietic, mesenchymal, side population and multipotent adult stem cells. Bone marrow cells have been hypothesized as a third recruitment source in liver regeneration in addition to hepatocytes and endogenous liver stem cells. Consequently, attempts have been made to differentiate them into hepatic lineage for their subsequent use in hepatic cell therapy. The present article reviews the progress made in this field or research.

Large-scale isolation of human hepatocytes for therapeutic application

During the last decade, hepatocyte transplantation has been suggested as a safe and potentially effective clinical option for the treatment of acute or decompensating chronic liver failure as well as for hereditary liver disease. Currently, one of the major limiting factors for clinical application is the insufficient access to suitable liver cell preparations. In cooperation with the German and Catalane organ procurement organizations, a routine procedure for the isolation of hepatocytes from donor organs rejected for transplantation (n = 117) has been established. The process is performed according to the current EC Guidelines for Good Manufacturing Practice (cGMP) and all corresponding national laws and regulations concerning donor organ and tissue procurement. In about 50% of the cases (n = 58) the three-step perfusion procedure has been completed with an average total cell yield of 5.9 x 10(9) cells per organ, the cell preparations displaying a mean viability of 64%. The mean specific yield was 3.6 x 10(6) total and 2.6 x 10(6) viable cells per gram liver tissue, respectively. Specific cell yields from three infantile donor livers were considerably higher. No correlation between isolation efficiency and cold ischemia time or donor age was found within the adult organ donors. In contrast, organs with a severe steatosis generally did not result in successful cell isolation. Results of sterility and endotoxin determination are also presented. In summary, a standardized and cGMP conform method of hepatocyte isolation from nontransplantable liver organs was established, which reproducibly yields large amounts of hepatocytes suitable for therapeutic application.

In vitro methods in human drug biotransformation research: implications for cancer chemotherapy

Anticancer drugs have a complex pharmacological and toxicological profile with a narrow therapeutic index. It is therefore critical to understand the factors that contribute to the marked intersubject variability in the pharmacokinetics and pharmacodynamics often observed with anticancer compounds. Since hepatic and extra-hepatic drug metabolism represents a major drug disposition pathway, extensive efforts are made to thoroughly investigate metabolism of anticancer compounds during the pre-clinical and clinical development phases as well as to address issues encountered during the clinical use of an approved drug. In recent years there has been a significant paradigm shift in pre-clinical/non-clinical drug metabolism studies. Most importantly, this has included a reduced reliance on animal models and increased use of human tissues (i.e. human liver microsomes and other cellular fractions, primary culture of human hepatocytes, cDNA expressed human-specific enzymes and cell-based reporter assays). Typically, experiments are performed using these tools to identify the phase I and/or phase II enzymes involved in metabolism of the drug/investigational agent and for metabolic fingerprinting. Additionally, issues pertaining to the rate, extent and mechanism(s) of the inhibition or induction of the metabolic pathways are also investigated. These studies provide important clues about various aspects of the disposition of a therapeutic agent including first-pass metabolism, elimination half-life, overall bioavailability and the potential for drug-drug interactions. The methodologies used for in vitro assessment of drug metabolism and their applications to drug development and clinical therapeutics with special emphasis on anticancer drugs are reviewed in this manuscript.

The effects of cryopreservation on human hepatocytes obtained from different sources of liver tissue

Successful cryopreservation of human hepatocytes is important to establish hepatocyte banks for clinical use or in vitro research. The availability of donor tissue from unused liver segments/lobes and non-heart-beating donors (NHBD) has provided newer sources of hepatocytes. The quality of hepatocytes at the time of cryopreservation is important as cells isolated from liver tissue of borderline quality may not withstand the stresses associated with cryopreservation and subsequent thawing. Human hepatocytes were cryopreserved after isolation from mainly donor tissues (n = 40). In vitro assessment of the viability and function of the fresh and thawed cryopreserved hepatocytes was performed. Viability, attachment efficiency, enzyme activity, and albumin production of hepatocytes were all significantly decreased, and LDH leakage significantly increased, on thawing after cryopreservation. The viability of cryopreserved hepatocytes isolated from tissue rejected for orthotopic liver transplantation (36 +/- 15%) was significantly lower than those isolated from tissue where part was used for liver transplantation (47 +/- 14%, p = 0.002), but there were no significant differences in functional parameters. The viability of cryopreserved hepatocytes isolated from NHBD tissue (29 +/- 9%, p = 0.001) and from steatotic donor tissue (35 +/- 11%, p = 0.019) was significantly lower than those isolated from normal donor tissue (49 +/- 14%). There was no difference in functional parameters, except for albumin production of hepatocytes from NHBD tissue (2.9 +/- 1.0 microg/h/mg protein) being significantly lower than those from normal donor tissue (4.8 +/- 2.8 microg/h/mg protein, p = 0.03). The viability and attachment efficiency of cryopreserved hepatocytes isolated from liver tissue from resections for tumors was significantly higher, and the LDH leakage significantly lower, than those isolated from all donor tissue. Hepatocytes isolated from NHBD and steatotic tissue were more vulnerable to the effects of cryopreservation. Further research is required to improve hepatocyte isolation and cryopreservation protocols for different types of liver tissue.

Preincubation of rat and human hepatocytes with cytoprotectants prior to cryopreservation can improve viability and function upon thawing

Cryopreservation of human hepatocytes is important for the treatment of liver disease by hepatocyte transplantation and also for the use of hepatocytes as an in vitro model of the liver. One factor in the success of cryopreservation is the quality of cells before freezing. Preincubation of hepatocytes with cytoprotective compounds to allow recovery from the isolation process prior to cryopreservation, such as those that will boost cellular adenosine triphosphate (ATP) content or antioxidants, may improve the viability and function of cells upon thawing. Rat hepatocytes were used to investigate the effects of preincubation with 10 compounds: precursors (glucose, fructose, glutathione, and S-adenosyl-L-methionine), antioxidants (ascorbic acid and alpha-lipoic acid), and compounds with multiple effects (N-acetylcysteine, pentoxifylline, prostaglandin E1, and tauroursodeoxycholic acid). Human hepatocytes were then used to investigate 5 of the original 10 compounds (glucose, fructose, alpha-lipoic acid, S-adenosyl-L-methionine, and pentoxifylline). Glucose preincubation (100 - 300 mM) improved the viability and attachment efficiency of rat hepatocytes and improved the viability and reduced lactate dehydrogenase (LDH) leakage of human hepatocytes. Fructose preincubation (100 - 300 mM) improved the viability and attachment efficiency of rat hepatocytes and improved the attachment efficiency of human hepatocytes. alpha-lipoic acid preincubation (0.5 - 5 mM) improved the viability and attachment efficiency of both rat and human hepatocytes. At a concentration of 2.5 mM alpha-lipoic acid also improved the albumin production of human hepatocytes. In conclusion, preincubation of hepatocytes prior to cryopreservation can improve the viability and function of thawed cells and may provide a method of obtaining better-quality cryopreserved hepatocytes for transplantation.

Preincubation of rat and human hepatocytes with cytoprotectants prior to cryopreservation can improve viability and function upon thawing

Cryopreservation of human hepatocytes is important for the treatment of liver disease by hepatocyte transplantation and also for the use of hepatocytes as an in vitro model of the liver. One factor in the success of cryopreservation is the quality of cells before freezing. Preincubation of hepatocytes with cytoprotective compounds to allow recovery from the isolation process prior to cryopreservation, such as those that will boost cellular adenosine triphosphate (ATP) content or antioxidants, may improve the viability and function of cells upon thawing. Rat hepatocytes were used to investigate the effects of preincubation with 10 compounds: precursors (glucose, fructose, glutathione, and S-adenosyl-L-methionine), antioxidants (ascorbic acid and alpha-lipoic acid), and compounds with multiple effects (N-acetylcysteine, pentoxifylline, prostaglandin E(1), and tauroursodeoxycholic acid). Human hepatocytes were then used to investigate 5 of the original 10 compounds (glucose, fructose, alpha-lipoic acid, S-adenosyl-L-methionine, and pentoxifylline). Glucose preincubation (100-300 mM) improved the viability and attachment efficiency of rat hepatocytes and improved the viability and reduced lactate dehydrogenase (LDH) leakage of human hepatocytes. Fructose preincubation (100-300 mM) improved the viability and attachment efficiency of rat hepatocytes and improved the attachment efficiency of human hepatocytes. alpha-lipoic acid preincubation (0.5-5 mM) improved the viability and attachment efficiency of both rat and human hepatocytes. At a concentration of 2.5 mM alpha-lipoic acid also improved the albumin production of human hepatocytes. In conclusion, preincubation of hepatocytes prior to cryopreservation can improve the viability and function of thawed cells and may provide a method of obtaining better-quality cryopreserved hepatocytes for transplantation.

Optimization of conditions for clinical human hepatocyte infusion

Cytotoxicity and apoptosis are common problems in the isolation and storage of human hepatocytes. In vitro environments of hepatocytes during cell infusion may be critical to reducing cellular damage and enhancing cell viability. We examined the effects of donor liver histology (40-50% steatosis vs. normal), incubation time, temperature, and three solutions for infusion on banked primary human hepatocytes, by studying: trypan blue exclusion, AST release, LDH release, MTT assay, detection of DNA ladder, and a hepatocyte proliferation assay. In addition, the microstructure functions of the endoplasmic reticulum and mitochondria of the intact hepatocytes were determined by measuring correlates of UGT 1A1 and cytochrome P-450 3A (CYP3A4) activity. In general, hepatocyte viability decreased significantly within 60 min after thawing. Cells suspended in 5% dextrose lactated Ringers solution (D5LR) maintained greater cell viability. Hepatocytes from normal liver donors showed less AST and LDH enzyme leak in comparison with cells from fatty liver donors. Mild hypothermic temperature (32 degrees C) inhibited cellular damage that otherwise significantly increased at 60 min. Hepatocytes did not proliferate until 12 h from thaw, regardless of supernatant or conditions of suspension. CYP3A4 activity and a marker for UGT 1A1 activity in hepatocytes from normal donor livers were higher than those from steatotic donor livers. These findings suggest that hepatocytes suspended for infusion after isolation from normal liver donors have normal biological functions and less cellular damage/necrosis in contrast with those isolated from fatty liver donors. These damages are inhibited significantly by maintaining hepatocytes at a mild hypothermic temperature (32 degrees C). D5LR alone maintained the best cell viability for up to 60 min. Media of D5LR + adenosine and HMM were able to partially inhibit hepatocyte apoptosis in hepatocytes from steatotic livers.

Allogeneic Cell Therapy for the Treatment of Liver Disease

The scarcity of human organs available for transplantation is clearly evident. Efforts to maximize the use of available organs and to increase the number of donors have increased the number of transplantations performed, but at a rate that remains far behind the rate of growth of the waiting list. Thus, the likelihood of a patient with severe liver disease receiving a liver replacement is decreasing. In order to offer treatment to most patients with liver disease, alternatives to whole-organ replacement must be found. Cell-based treatments, in which suspensions of liver cells are injected into patients with liver failure and reconstitute the patient's liver functions, may be that alternative. Here, we report on a regulatory-compliant process for the production of a cryopreserved cell therapy product that yields viable, metabolically active hepatocytes that can be infused directly into patients with the goal of reconstituting liver function.

Analysis of the functional integrity of cryopreserved human liver cells including xenografting in immunodeficient mice to address suitability for clinical applications

BACKGROUND

The availability of well-characterized human liver cell populations that can be frozen and thawed will be critical for cell therapy. We addressed whether human hepatocytes can recover after cryopreservation and engraft in immunodeficient mice.

METHODS

We isolated cells from discarded human livers and studied the properties of cryopreserved cells. The viability of thawed cells was established with multiple in vitro assays, including analysis of liver gene expression, ureagenesis, cytochrome P450 activity, and growth factor-induced cell proliferation. The fate of transplanted cells was analysed in immunodeficient NOD-SCID mice.

RESULTS

After thawing, the viability of human hepatocytes exceeded 60%. Cells attached to culture dishes, proliferated following growth factor stimulation and exhibited liver-specific functions. After transplantation in NOD-SCID mice, cells engrafted in the peritoneal cavity, a heterologous site, as well as the liver itself, retained hepatic function and proliferated in response to liver injury. Transplanted hepatocytes were integrated in the liver parenchyma. Occasionally, transplanted cells were integrated in bile ducts.

CONCLUSIONS

Cryopreserved human liver cell showed the ability to retain functional integrity and to reconstitute both hepatic and biliary lineages in mice. These studies offer suitable paradigms aimed at characterizing liver cells prior to transplantation in people.

Preparation of equine isolated hepatocytes

In this study a detailed description of the equine hepatocyte isolation procedure is presented. Livers were obtained from horses slaughtered at the local slaughterhouse. For blood removal and liver preservation the following steps are suggested: perfusion with the oxygenated HBSS (0-2 degrees C, with continuous flow of 500-800 ml/min for 3-6 min), protection from ischemia injury by flushing with ice-cold University of Wisconsin Solution (UW, flow rate of 500-800 ml/min), and finally immersion of the liver lobe in UW solution (2 degrees C) during its transport to the laboratory. For equine isolated hepatocyte preparation a "three-step" perfusion procedure was elaborated: rewarming, chelating and collagenase perfusion. We found optimal cell yield and viability under the following conditions: rewarming with UW (38 degrees C) for 8-14 min, chelating with calcium free Hanks' Balanced Salt Solution (HBSS, 38 degrees C) supplemented with 1 mM ethylene glycol-bis[beta-aminoethyl esther]-N,N,N'N'-tetracetic acid at the flow rate of 450 ml/min for 6 min and enzymatic digestion with HBSS supplemented with 0.1% collagenase at 38 degrees C and 450 ml/min flow rate for 8-27 min. These conditions consistently generated cell harvests of 21 x 10(6)+/-4.86 cells/g of perfused liver tissue with viability of 82.7%+/-10.2.