A multi-laboratory evaluation of cryopreserved monkey hepatocyte functions for use in pharmaco-toxicology

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.

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.

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.

Comparison of University of Wisconsin and ET-Kyoto preservation solutions for the cryopreservation of primary human hepatocytes

Primary human hepatocytes are clinically used for transplantation or in bioartificial liver devices for the treatment of patients with liver failure. We aimed to assess whether an organ preservation solution containing trehalose, namely ET-Kyoto solution (ETK), could improve human liver cell viability when used for cryopreservation in comparison to the University of Wisconsin solution (UW). Our study showed beneficial effects of ETK when used in combination with other cryoprotectants on the viability of thawed hepatocytes. Indeed, no significant difference was seen between the viability of freshly isolated cells and cryopreserved cells when cryopreserved with ETK combined with other cryoprotectants. In contrast, a significant decrease of viability was observed in cells cryopreserved with UW or ETK combined with dimethysulfoxide (DMSO) only, or with UW combined with other cryoprotectants, compared to freshly isolated cells. No significant difference was observed between the four different groups of cryopreserved hepatocytes with regards to cell recovery rate or cell attachment after thawing. However, a significant decrease in cell metabolic activity was found in cells cryopreserved with UW 10% DMSO compared to the other groups. In conclusion, our study confirms the beneficial effect of ETK for the cryopreservation of human hepatocytes in combination with other cryoprotective agents.

Suppression of cell death in primary rat hepatocytes by alpha1-acid glycoprotein

In screening for effective additives for the long-term culture of hepatocytes, the hepatoprotective effect of alpha1-acid glycoprotein (AGP) was observed. AGP prevented primary hepatocytes from undergoing cell death induced by the chemical toxin, bromobenzene. Moreover, AGP added to medium was found to maintain the number of viable hepatocytes for as long as 6 d. The hepatoprotective effect of AGP was lost by removing sialic acid groups at the N-glycan chain terminal of AGP. It is shown that the complete form of N-glycan chain is needed for the hepatoprotectivity of AGP.

The effect of antioxidants and a caspase inhibitor on cryopreserved rat hepatocytes

Hepatocyte transplantation and use of bioartificial liver support systems have been suggested as potential therapies for fulminant hepatic failure. Cryopreservation in liquid nitrogen is presently the major method of long-term storage of isolated hepatocytes. However, cryopreservation can result in low cell recovery and reduction in differentiated function. Several possible mechanisms of cell death during cryopreservation have been proposed. The most important mechanisms appear to be oxidative stress and apoptosis. In this study, we isolated fresh rat hepatocytes and cryopreserved them in three media: University of Wisconsin (UW) solution, an antioxidant-containing medium, and medium containing a caspase inhibitor. Viability and function of hepatocytes cryopreserved in these media were examined. Cryopreservation conditions had no effect on hepatocyte viability after thawing. However, after culture we found significant improvements in viability and function in both antioxidant- and caspase inhibitor-treated hepatocytes at 6 and 24 h.

Novel function of rare catechin, epigallocatechin-3-(3″-O-methyl)gallate, against cold injury in primary rat hepatocytes

Epigallocatechin-3-(3''-O-methyl)gallate (EGCg-3''-OMe) is a rare component in green tea leaf and its bioactivity is hardly known. In this paper, we report that EGCg-3''-OMe has the function for cold preservation of primary rat hepatocytes. Confluent primary cultured hepatocytes were suspended in a storage solution, culture medium or cell banker (CB). EGCg-3''-OMe was tested as a supplement in the storage solution together with a general cryoprotectant, dimethylsulfoxide (DMSO). After 24 h cold preservation of cells at 4 degrees C followed by 1 h rewarming, cell viability and urea-synthesizing activity, one of the most important liver functions, were measured. EGCg-3''-OMe dose-dependently maintained cell viability and this effect was equal to that of a commercial CB at the highest concentration. Cell viability was also maintained after a further 24 h incubation at 37 degrees C of the cold-preserved hepatocytes. Conversely, urea-synthesizing activity was dose-dependently reduced by EGCg-3''-OMe. Cell protection by EGCg-3''-OMe due to the decrease in metabolic activity in cold-preserved cells was suggested. The decreased hepatic function of cells caused by EGCg-3''-OMe was rescued after a further 24 h incubation of cells at 37 degrees C.

Survival of spumavirus, a primate retrovirus, in laboratory media and water

The persistence of a previously characterized spumavirus strain (strain SV-522) was investigated utilizing various laboratory media and waters, including Eagle's minimal essential medium (EMEM) plus 0% fetal bovine serum (EMEM-0%), EMEM-2%, EMEM-10%, Chlamydia transport medium (CTM), phosphate-buffered saline, distilled, estuarine, and marine water, human serum, and the germicides, ethyl alcohol (70%) and sodium hypochlorite (10%). Experiments were performed at 4 degrees C and/or 23 degrees C. Infectivity endpoints were determined in stock aliquots upon initiation of testing and then after 3, 5, 7, and 10 days. The virus was reisolated from all diluents after 5 days at 23 degrees C and in EMEM-10% after 7 days. The virus was detected in CTM, EMEM-2%, EMEM-10%, and estuarine and marine waters after 7 days at 4 degrees C. Differences in the persistence of the virus may be ascribed to temperature and organic load. Water ionic strengths (e.g., estuarine vs. marine water) had no effect on modifying persistence of viral particles. Infectivity of spumavirus was undetectable after 30 s in 70% ethanol or 10% sodium hypochlorite. After 30 min at 23 degrees C, spumavirus infectivity in normal but not heat-inactivated human serum increased by almost 100-fold. Persistence of infectivity of primate spumavirus after 7 days in media and waters, and the agent's infectious potential in the human host, emphasize a need for cautious recognition during the manipulation of primate cells/organs and in the handling of primates themselves.

In vitro models to study hepatotoxicity

Drug discovery and development consists of a series of processes starting with the demonstration of pharmacological effects in experimental cell and animal models and ending with drug safety and efficacy studies in patients. A main limitation is often the unacceptable level of toxicity with the liver as the primary target organ. Therefore, approaches to study hepatic toxicity in the early phase of drug discovery represent an important step towards rational drug development. A variety of in vitro liver models have been developed in the past years. Next to their use in drug development, they can also be applied to study environmental toxins and their hepatotoxicity. The 3 main approaches are ex vivo isolated and perfused organ models, precision-cut liver slices and cell culture models. Although the advantage of whole organ perfusions is based on the assessment of physiologic parameters such as bile production and morphologic parameters such as tissue histology, cell culture models can be efficiently used to assess cellular metabolism, cytotoxicity and genotoxicity. The advantage of precision-cut liver slices is based on the juxtaposition of cellular assays and tissue morphology. None of these models can be compared as they all focus on different fields of hepatoxicology. For the future, the ideal setup for testing the hepatic toxicity of a new compound could of primary studies in cell or slice cultures to assess cellular effects and secondary studies using ex vivo perfused organs to examine gross organ function parameters and histology.