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

Effects of Cryopreservation on Cell Metabolic Activity and Function of Biofabricated Structures Laden with Osteoblasts

Biofabrication and maturation of bone constructs is a long-term task that requires a high degree of specialization. This specialization falls onto the hierarchy complexity of the bone tissue that limits the transfer of this technology to the clinic. This work studied the effects of the short-term cryopreservation on biofabricated osteoblast-containing structures, with the final aim to make them steadily available in biobanks. The biological responses studied include the osteoblast post-thawing metabolic activity and the recovery of the osteoblastic function of 3D-bioprinted osteoblastic structures and beta tricalcium phosphate (β-TCP) scaffolds infiltrated with osteoblasts encapsulated in a hydrogel. The obtained structures were cryopreserved at −80 °C for 7 days using dimethyl sulfoxide (DMSO) as cryoprotectant additive. After thawing the structures were cultured up to 14 days. The results revealed fundamental biological aspects for the successful cryopreservation of osteoblast constructs. In summary, immature osteoblasts take longer to recover than mature osteoblasts. The pre-cryopreservation culture period had an important effect on the metabolic activity and function maintain, faster recovering normal values when cryopreserved after longer-term culture (7 days). The use of β-TCP scaffolds further improved the osteoblast survival after cryopreservation, resulting in similar levels of alkaline phosphatase activity in comparison with the non-preserved structures. These results contribute to the understanding of the biology of cryopreserved osteoblast constructs, approaching biofabrication to the clinical practice.

Biopolymer gels as a basis of cryoprotective medium for testicular tissue of rats

Cryopreservation of testis tissue is a promising approach to save fertility in prepubertal boys under going gonadotoxic cancer therapies. The using biopolymers as a basis of cryoprotective medium can be effective for the optimization of cryopreservation protocols of immature testicular tissue. The research purpose was to determine morphological parameters and metabolic activity of seminiferous tubules of immature rat testes under exposure to cryoprotective solution (DMSO) based on collagen or fibrin gels (CG or FG) as one of the first stages of developing the cryopreservation protocol. It was found that 30-min exposure of tissue samples to CG and FG with 0.6 M DMSO did not impair the spermatogenic epithelium and metabolic activity of the cells (MTT test and total lactate dehydrogenase activity). The use of FG at the time of exposure of 45 min did not lead to significant changes in the metabolic activity in contrast to other groups. The findings could be used to substantiate and develop the effective techniques for cryopreservation of immature seminiferous tubules.

Cryopreservation of human umbilical vein and porcine corneal endothelial cell monolayers

Cryopreservation of endothelium is one of the major challenges in the cryopreservation of complex tissues. Human umbilical vein endothelial cells (HUVECs) in suspension are available commercially and recently their post-thaw cell membrane integrity was significantly improved by cryopreservation in 5% dimethyl sulfoxide (Me₂SO) and 6% hydroxyethyl starch (HES). However, cryopreservation of cells in monolayers has been elusive. The exact mechanisms of damage during cell monolayer cryopreservation are still under investigation. Here, we show that a combination of different factors contribute to significant progress in cryopreservation of endothelial monolayers. The addition of 2% chondroitin sulfate to 5% Me₂SO and 6% HES and cooling at 0.2 or 1 °C/min led to high membrane integrity (97.3 ± 3.2%) immediately after thaw when HUVECs were cultured on a substrate with a coefficient of thermal expansion similar to that of ice. The optimized cryopreservation protocol was applied to monolayers of primary porcine corneal endothelial cells, and resulted in high post-thaw viability (95.9 ± 3.7% membrane integrity) with metabolic activity 12 h post-thaw comparable to unfrozen control.

Advances in the slow freezing cryopreservation of microencapsulated cells

Over the past few decades, the use of cell microencapsulation technology has been promoted for a wide range of applications as sustained drug delivery systems or as cells containing biosystems for regenerative medicine. However, difficulty in their preservation and storage has limited their availability to healthcare centers. Because the preservation in cryogenic temperatures poses many biological and biophysical challenges and that the technology has not been well understood, the slow cooling cryopreservation, which is the most used technique worldwide, has not given full measure of its full potential application yet. This review will discuss the different steps that should be understood and taken into account to preserve microencapsulated cells by slow freezing in a successful and simple manner. Moreover, it will review the slow freezing preservation of alginate-based microencapsulated cells and discuss some recommendations that the research community may pursue to optimize the preservation of microencapsulated cells, enabling the therapy translate from bench to the clinic.

Collagen Gel Immobilisation Provides a Suitable Cell Matrix for Long Term Human Hepatocyte Cultures in Hybrid Reactors

An easy to apply culture technique is presented that protects a monolayer configuration of liver cells within an extracellular matrix. The Immobilising Gel (IG)-Technique not only preserves hepatocyte morphology and supports a variety of differentiated cell functions over long term periods, but also offers higher resistance of IG-culture systems against shear forces of fluids in a hybrid reactor device, as compared to other culture techniques. Human hepatocyte cultures in IG-Technique: DNA-normalised levels for the total production of cholinesterase, albumin, urea and lactate remained high throughout the investigational period (50 days). Glutamic-Pyruvic-Transaminase (GPT) release decreased after peak values during early culture adaptation. Electron Microscopic (EM) findings after the shear forces experiment revealed undisturbed subcellular structures and a preserved intercellular morphology, including bile canaliculi and desmosomes. We conclude that the IG-technique is of considerable advantage as compared to other culture systems, especially in the field of dynamic applications, e.g. hybrid reactors for artificial organ development.

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

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

Freezing Characteristics of Isolated Pig and Human Hepatocytes

The cellular response of isolated hepatocytes from pigs, humans, and human hepatoblastoma cells to freezing was characterized using cryomicroscopy and analyzed using a thermodynamic model for water transport and Intracellular Ice Formation (IIF). The value for the reference permeability, Lpg, was found to be 5.8(10)-13, 1.62(10)13, and 2.7(10)-14 m/Ns for pig, human, and Hep G2/C3A cells, respectively. The activation energy, Elp, was found to be 480 kJ/mol for pig hepatocytes, 216 kJ/mol for human, and 121 kJ/mol for Hep G2/C3A cells. The average temperature at which IIF (TavgIIF) occurs was calculated to be -7.24 + 2.3°C for pig hepatocytes, -8.5 + 2.6°C for human hepatocytes, and -9.6 + 4.5°C for Hep G2/C3A cells. These results indicate that the freezing characteristics of pig and human cells are distinct and that the specific freezing characteristics need to be understood for the development of appropriate freezing protocols.

Using reconfigurable microfluidics to study the role of HGF in autocrine and paracrine signaling of hepatocytes

Cancer, developmental biology and tissue injury present multiple examples where groups of cells residing in close proximity communicate via paracrine factors. It is nearly impossible to dissect such cellular interactions in vivo and is quite challenging in vitro. The goal of this study is to utilize a reconfigurable microfluidic device in order to study paracrine signal exchange between groups of primary hepatocytes in vitro. Previously, we demonstrated that hepatocytes residing on protein spots containing collagen and hepatocyte growth factor (HGF) spots expressed epithelial (hepatic) phenotypes and also rescued them in neighboring hepatocytes on collagen spots that did not receive direct HGF stimulus. Herein, we designed a microfluidic device with parallel fluidic channels separated by retractable (reconfigurable) walls and employed this device to investigate interactions between groups of HGF-stimulated and unstimulated hepatocytes. Using a novel reconfigurable microfluidic device, we demonstrate that cultivation of HGF-containing protein spots upregulates the production of endogenous HGF in hepatocytes and that these HGF molecules diffuse over, causing phenotype enhancement in the recipient cells. We also show that selective treatment of the recipient hepatocytes with a c-met inhibitor (SU11274) diminishes the rescue effect, as gauged by the down-regulation of albumin and HGF expression. Our study is one of the first to demonstrate paracrine signaling via HGF in primary hepatocytes. More broadly, tools and methods described here may be used to study paracrine signaling in other types of cells and will have relevance for various fields of biomedical research from cancer to immunology.

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

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

Cryopreservation effects on recombinant myoblasts encapsulated in adhesive alginate hydrogels

Cell encapsulation in hydrogels is widely used in tissue engineering applications, including encapsulation of islets or other insulin-secreting cells in pancreatic substitutes. Use of adhesive, biofunctionalized hydrogels is receiving increasing attention as cell-matrix interactions in three-dimensional (3-D) environments can be important for various cell processes. With pancreatic substitutes, studies have indicated benefits of 3-D adhesion on the viability and/or function of insulin-secreting cells. As long-term storage of microencapsulated cells is critical for their clinical translation, cryopreservation of cells in hydrogels is being actively investigated. Previous studies have examined the cryopreservation response of cells encapsulated in non-adhesive hydrogels using conventional freezing and/or vitrification (ice-free cryopreservation); however, none have systematically compared the two cryopreservation methods with cells encapsulated within an adhesive 3-D environment. The latter would be significant, as evidence suggests adhesion influences the cellular response to cryopreservation. Thus, the objective of this study was to determine the response to conventional freezing and vitrification of insulin-secreting cells encapsulated in an adhesive biomimetic hydrogel. Recombinant insulin-secreting C2C12 myoblasts were encapsulated in oxidized RGD-alginate and cultured for 1 or 4days post-encapsulation, cryopreserved, and assessed up to 3days post-warming for metabolic activity and insulin secretion, and 1day post-warming for cell morphology. Besides certain transient differences in the vitrified group relative to the fresh control, both conventional freezing and vitrification maintained the metabolism, secretory activity, and morphology of the recombinant C2C12 cells. Thus, due to a simpler procedure and slightly superior results, conventional freezing is recommended over vitrification for the cryopreservation of C2C12 cells encapsulated in oxidized, RGD-modified alginate.

Sandwich-cultured hepatocytes: utility for in vitro exploration of hepatobiliary drug disposition and drug-induced hepatotoxicity

INTRODUCTION

The sandwich-cultured hepatocyte (SCH) model has become an invaluable in vitro tool for studying hepatic drug transport, metabolism, biliary excretion and toxicity. The relevant expression of many hepatocyte-specific functions together with the in vivo-like morphology favor SCHs over other preclinical models for evaluating hepatobiliary drug disposition and drug-induced hepatotoxicity.

AREAS COVERED

In this review, the authors highlight recommended procedures required for reproducibly culturing hepatocytes in sandwich configuration. It also provides an overview of the SCH model characteristics as a function of culture time. Lastly, the article presents a summary of the most prominent applications of the SCH model, including hepatic drug clearance prediction, drug-drug interaction potential and drug-induced hepatotoxicity.

EXPERT OPINION

When human (cryopreserved) hepatocytes are used to establish sandwich cultures, the model appears particularly valuable to quantitatively investigate clinically relevant mechanisms related to in vivo hepatobiliary drug disposition and hepatotoxicity. Nonetheless, the SCH model would largely benefit from better insight into the fundamental cell signaling mechanisms that are critical for long-term in vitro maintenance of the hepatocytic phenotype. Studies systematically exploring improved cell culture conditions (e.g., co-cultures or extracellular matrix modifications), as well as in vitro work identifying key transcription factors involved in hepatocyte differentiation are currently emerging.

Preservation of microplate-attached human hepatoma cells and their use in cytotoxicity tests

We investigated the feasibility of hypothermic- orcryogenically-preserved human hepatoma Hep G2 cell preculturedin 96-well plates in cytotoxicity testings. First, we observedthat microplates precoated with both collagen (CN) and pronectin (PN) showed significantly improved living cell adhesion (71.0 +/- 5.5%) after 48 hr of cryopreservation with 10%-DMSO containing culture medium, whereas non-coated surfaces gave very low living cell adhesion (33.5 +/- 2.1%). Hypothermic preservation was most suitable for short-term storage, and cryogenic preservation at -20 degrees C allowed cells to be used within a week of the storage period. Only cryopreservation in a deep freezer (-85 degrees C) gave satisfactory results in much longer period of storage. Second, we evaluated the cytotoxicity of ten chemicals during 48 hr of exposure using hypothermically - (4 degrees C for 2 days) or cryogenically - (-85 degrees C for 7 days) preserved cells cultured inCN/PN-precoated microplates in comparison with results fromfreshly inoculated cells. Although almost the same LD(50)values were obtained, LD(10) values of relatively hydrophilic chemicals obtained with cryopreserved cell were significantly lowered. These results shown that CN/PN-precoating is effective in keeping cells attached even in recultivation of preserved cells and that the toxicities of relatively hydrophilic chemicals tend to be overestimated when we use preserved cells in that manner.

Incorporation of DMSO and dextran-40 into a gelatin/alginate hydrogel for controlled assembled cell cryopreservation

A new cell cryopreservation strategy for cell-assembling constructs was proposed. With this strategy, different concentrations of dimethysulfoxide (DMSO) and dextran-40 were directly incorporated into the cell/gelatin/alginate systems, prototyped according to a predesigned structure, cryopreserved at -80 °C for 10 days and followed a thawing process at 17 °C. The rheological properties, bonding water contents and melting points of the gelatin/alginate hydrogel systems were changed with the addition of different amounts of DMSO. The microscopy analysis, (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrasodium bromide (MTT) and hematoxylin and eosin (HE) staining indicated that the cell numbers were progressively in a selected DMSO concentration range. With DMSO 5% (v/v) alone, the metabolic rate in the construct attained (81.3±5.7)%. A synergistic effect was achieved with the combination of the DMSO/gelatin/alginate and dextran-40/gelatin/alginate hydrogel systems. These results indicated that the inclusion of DMSO and dextran-40 in the hydrogel could effectively enhance the cell preservation effects. This cryopreservation strategy holds the ability to be widely used in organ manufacturing techniques.

Cryopreservation of primary porcine liver cells in an organotypical sandwich model in a clinically relevant flat membrane bioreactor

To overcome the logistical difficulties of continuously supplying freshly-isolated, primary porcine liver cells to bioartificial liver support bioreactors, we developed a cryopreservation method using an organotypical sandwich model in a flat membrane bioreactor (FMB). We measured albumin secretion rate, urea synthesis rate and 7-ethoxy coumarin (ECOD) in long-term cultures of cryopreserved cells (up to 14 days). The albumin secretion rate was 62% that of non-cryopreserved cells at days 11 and 14. The ECOD activity was 54% that of fresh, control cells initially and increased up to 79% by the 14th day. The urea synthesis rate was stable at 60% that of the control. This study showed that cryopreserved cells can recover liver-specific functions. This result has the potential to dramatically expand the clinical application of bioartificial liver supports.

Cryopreservation in situ of cell monolayers on collagen vitrigel membrane culture substrata: ready-to-use preparation of primary hepatocytes and ES cells

Cryopreservation is generally performed on cells in suspension. In the case of adherent cells such as hepatocytes, a loss of their ability to attach is a more serious problem than a decreased viability after cryopreservation. We herein report a novel technology of direct in situ cryopreservation of cells cultured on collagen vitrigel membranes, which have excellent mechanical strength and can be easily handled by tweezers even when coated with cultured cells. Rat primary hepatocytes, mitomycin C-treated mouse fibroblasts (feeder cells for ES cells), and mouse ES cells on the feeder cells were cultured on collagen vitrigel membranes for 1 day. The membranes with cells attached were then plucked up from the dish, soaked in cryopreservation medium containing 10% dimethyl sulfoxide, frozen using a controlled-rate freezer, and transferred to liquid nitrogen. The cells cultured on plastic cell culture dishes were also frozen as controls. After storage in liquid nitrogen for periods from 1 week to 3 months, the cryopreserved membranes with the cells still attached were thawed by adding warmed culture medium. Cell viability estimated by morphology and functional staining with calcein showed significant improvement in comparison to cells cryopreserved without the collagen vitrigel membrane. The recoveries of living cells after cryopreservation were 26.7%, 76.2%, and 58.6% for rat hepatocytes, mitomycin C-treated mouse fibroblasts, and mouse ES cells on collagen vitrigel membranes, respectively. In contrast, essentially no cells at all remained on the plastic cell culture dishes after thawing. Because adherent cell storage under these conditions is very convenient, the use of this technique employing collagen vitrigel membranes should be generally applicable to the cryopreservation of adherent cells that are otherwise problematic to store as frozen stocks.

An improved purification approach with high cell viability and low cell loss for cryopreserved hepatocytes

A modified purification procedure is described for effectively eliminating dead cells after hepatocyte cryopreservation. Isolated hepatocytes from six pig tissue samples were cryopreserved in liquid nitrogen for 2 weeks. After thawing, we developed a pre-incubation step prior to gradient centrifugation. The hepatocytes were subsequent cultured in suspension overnight (12-16 h), and then dead cells were eliminated by Ficoll 400 purification. The results showed that a high viability (mean of 96%) of cells was obtained, with a low viable cell loss in number (2-5%), by using this modified method.

Cryopreservation of adherent cells: strategies to improve cell viability and function after thawing

The commonly applied cryopreservation protocols routinely used in laboratories worldwide were developed for simple cell suspensions, and their application to complex systems, such as cell monolayers, tissues, or biosynthetic constructs, is not straightforward. In particular for monolayer cultures, cell detachment and membrane damage are often observed after cryopreservation. In this work, combined strategies for the cryopreservation of cells attached to Matrigel-coated well plate's surfaces were investigated based on cell entrapment in clinicalgrade, ultra-high viscosity alginate using two cell lines, neuroblastoma N2a and colon adenocarcinoma Caco-2, with distinct structural and functional characteristics. As the cryopreservation medium, serum-free CryoStor solution was compared with serum-supplemented culture medium, both containing 10% DMSO. Using culture medium, entrapment beneath an alginate layer was needed to improve cell recovery by minimizing membrane damage and cell detachment after thawing; nevertheless, up to 50% cell death still occurred within 24 h after thawing. The use of CryoStor solution represented a considerable improvement of the cryopreservation process for both cell lines, allowing the maintenance of high postthaw membrane integrity as well as full recovery of metabolic activity and differentiation capacity within 24 h postthawing; in this case, entrapment beneath an alginate layer did not confer further protection to cryopreserved Caco-2 cells, but was crucial for maintenance of attachment and integrity of N2a neuronal networks.

In vitro cultivation and cryopreservation of duck embryonic hepatocytes

Hepatitis B-virucidal testing of biocides in quantitative suspension tests using duck hepatitis B virus (DHBV) requires primary duck embryonic hepatocytes for viral propagation. To improve the test system and availability of these cells, commercial culture plates with different growth surfaces were tested for cell cultivation and different approaches for cryopreservation of hepatocyte suspension were examined. After 12 days of culture, the largest amounts of hepatocytes were grown in CellBIND and TTP plates and CellBIND surface showed the lowest tendency of monolayer detachment nearly comparable with collagen 1-coated CELLCOAT plates. For cryopreservation of hepatocyte suspension, the use of growth medium supplemented with fetal calf serum (FCS) and dimethyl sulfoxide (ME(2)SO), FCS supplemented with ME(2)SO or cryosafe-1 as cryoprotective agents provided the highest rates of surviving cells after thawing. The freezing-thawing process did not significantly reduce the susceptibility of hepatocytes to infection with DHBV. In conclusion, plates without collagen 1 such as CellBIND are recommended for cultivation of primary duck embryonic hepatocytes in infectivity experiments of DHBV for virucidal testing of biocides. The use of cryopreserved hepatocytes is possible when freshly isolated cells from the liver of duck embryos are not available.

Permissive and suppressive effects of dexamethasone on enzyme induction in hepatocyte co-cultures

1. Steroids are known to act as permissive factors in hepatocytes. This study shows that dexamethasone (DEX) is a permissive factor for induction of CYP2B1/2, CYP3A1, CYP2A1 and probably also CYP2C11 in cultures with primary rat hepatocytes. 2. The induction factor of phenobarbital (PB)-induced formation of 16beta-hydroxytestosterone (OHT), a testosterone biotransformation product predominantly formed by CYP2B1, is increased 18-fold by the addition of 32 nM DEX to the culture medium. Interestingly, higher concentrations of DEX up to 1000 nM led to a concentration-dependent maximally 5-fold decrease (p = 0.002) of phenobarbital-induced 16beta-OHT formation compared with the effect observed with 32 nM DEX. Thus, DEX shows permissive and suppressive effects on enzyme induction depending on the concentration of the glucocorticoid. 3. Qualitatively similar but smaller permissive and suppressive effects of DEX were observed for PB-induced CYP3A1 activity as evidenced by formation of 2beta-, 6beta- and 15beta-OHT. 4. DEX is a permissive factor for induction of CYP2A1 activity by 3-methylcholanthrene (3MC), as evidenced by the formation of 7alpha-OHT. Without addition of DEX, 3MC did not induce formation of 7alpha-OHT, whereas an almost 3-fold induction occurred in the presence of DEX. In contrast to CYP2B and CYP3A, concentrations up to 1000 nM DEX were not suppressive for the induction of CYP2A1. 5. We described recently a technique that allows preparation of cultures from cryopreserved hepatocytes. An almost identical influence of dexamethasone on enzyme induction was observed here in cultures from cryopreserved compared with freshly isolated hepatocytes. 6. Cultures with primary hepatocyte cultures represent a well-established technique for the study of drug-drug interactions. However, a large interlaboratory variation is known. Our study provides evidence that differences in glucocorticoid concentration in the culture medium contribute to this variation.

Microencapsule technique protects hepatocytes from cryoinjury

AIM

Hepatocyte transplantation is a potential alternative to whole organ liver transplantation. To realize this procedure, a hepatocyte bank system capable of supplying large numbers of hepatocytes must be established. We previously reported an easy method for cryopreserving hepatocytes using a microencapsulation technique. Here, we investigated how cryoinjury to microencapsulated hepatocytes could be avoided during cryopreservation.

METHODS

Hepatocytes from Sprague-Dawley rats were harvested in situ using a two-step ethylenediaminetetraacetic acid (EDTA)/collagenase digestion protocol. The cells were microencapsulated using alginate-poly L-lysine. The microencapsulated hepatocytes were put into vials and immediately immersed in liquid nitrogen. The growth of ice crystals in the vials containing the microencapsulated hepatocytes was observed using cryomicroscopy. The microencapsulated hepatocytes were sectioned for ultrastructural examination to investigate their intracellular conditions. Finally, total RNA was isolated from the cryopreserved microencapsulated hepatocytes and analyzed for hepatocyte nuclear factor (HNF) using reverse transcriptase polymerase chain reaction (RT-PCR) analysis.

RESULTS

Cryomicroscopy showed that the alginate microencapsulation technique protected the hepatocytes from physical damage caused by the growth of extracellular ice crystals. Ultrastructural examination revealed that the intracellular environment of the microencapsulated hepatocytes was maintained. The RT-PCR analysis additionally suggested that the alginate gel also maintained the HNF level.

CONCLUSION

Our microencapsulation technique protects hepatocytes from cryoinjury. This novel technique could be utilized by hepatocyte banks.

Long-term maintenance of the drug transport activity in cryopreservation of microencapsulated rat hepatocytes

Transplantation of isolated hepatocytes has been proposed to compensate for essential functions lacking in liver failure or for genetic defects that alter a specific liver metabolic pathway. Hepatocyte utilization for these purposes would be facilitated with a reliable, reproducible, and effective method of long-term hepatocyte storage. We have recently developed a simple new system for cryopreservation of hepatocytes that encapsulates alginate microspheres and maintains liver-specific function. The aim of this study was to elucidate the transport and drug-metabolizing enzyme activities of cryopreserved microencapsulated hepatocytes stored for a long time. Morphological examinations showed there is no apparent injury of the hepatocytes during cryopreservation processes. A drug-metabolizing enzyme (testosterone 6beta-hydroxylase, a specific probe for CYP3A2) and drug transport activities [salicylate, allopurinol, and prostaglandin E2 (PGE2), typical substrates of rOat2] in cryopreserved microencapsulated hepatocytes were maintained up to 120 days. Our results thus demonstrate for the first time that cryopreservation of primary rat hepatocytes by the encapsulation technique allows long-term retention of drug metabolism and drug transport activities.

Cryopreservation of adherent neuronal networks

Neuronal networks have been widely used for neurophysiology, drug discovery and toxicity testing. An essential prerequisite for future widespread application of neuronal networks is the development of efficient cryopreservation protocols to facilitate their storage and transportation. Here is the first report on cryopreservation of mammalian adherent neuronal networks. Dissociated spinal cord cells were attached to a poly-d-lysine/laminin surface and allowed to form neuronal networks. Adherent neuronal networks were embedded in a thin film of collagen gel and loaded with trehalose prior to transfer to a freezing medium containing DMSO, FBS and culture medium. This was followed by a slow rate of cooling to -80 degrees C for 24 h and then storage for up to 2 months in liquid nitrogen at -196 degrees C. The three components: DMSO, collagen gel entrapment and trehalose loading combined provided the highest post-thaw viability, relative to individual or two component protocols. The post-thaw cells with this protocol demonstrated similar neuronal and astrocytic markers and morphological structure as those detected in unfrozen cells. Fluorescent dye FM1-43 staining revealed active recycling of synaptic vesicles upon depolarizing stimulation in the post-thaw neuronal networks. These results suggest that a combination of DMSO, collagen gel entrapment and trehalose loading can significantly improve conventional slow-cooling methods in cryopreservation of adherent neuronal networks.

A novel method of cryopreservation of rat and human hepatocytes by using encapsulation technique and possible use for cell transplantation

Encapsulated hepatocyte transplantation is a promising approach to cell transplantation without immunosuppression as an alternative to whole organ liver transplantation. However, the shortage of donor cells for hepatocyte transplantation has not been resolved, and at this critical point, it seems necessary to establish a method of hepatocyte cryopreservation to allow clinical application of hepatocyte transplantation and the development of a bioartificial liver system in the near future. In this study we demonstrated that cryopreserved microencapsulated rat and human hepatocytes can retain their hepatic function and that cryopreserved microencapsulated human hepatocytes transplanted into rat spleen remain viable without immunosuppression. Rat and human hepatocytes were isolated by a collagenase digestion method, and they were microencapsulated with poly-L-lysine. The microencapsulated rat hepatocytes were transferred to culture medium (DMEM containing 10% FBS and 10% DMSO) and immediately frozen in liquid nitrogen. A warm water bath (37 degrees C) was used to thaw the microencapsulated hepatocytes. Hepatic function, drug metabolism, and cell morphology were assessed after 90 days of cryopreservation. After 1 week of cryopreservation, microencapsulated hepatocytes were cultured for up to 2 weeks to assess their hepatic function and morphology. The morphology of human hepatocytes was assessed after 30 days of cryopreservation. Cryopreserved human hepatocytes were transplanted into rat spleen to assess their morphology. Cryopreserved microencapsulated hepatocytes retained their viability and were strongly positive for expression of albumin, OAT2, CYP3A2, and CYP3A9. Two weeks after cultivation, the cryopreserved microencapsulated rat hepatocytes had retained their hepatic function (urea synthesis). Cryopreserved microencapsulated human hepatocytes also mainly survived and retained their hepatic function for at least 30 days after cryopreservation. Moreover, entrapped cryopreserved human hepatocytes also survived and expressed albumin in rat spleen after transplantation. We demonstrated a novel method of long-term cryopreservation of rat and human hepatocytes by using an encapsulation technique, with retention of biological activity and excellent survival of the cryopreserved microencapsulated human hepatocytes transplanted into rat spleen. We believe that this novel approach to hepatocytes cryopreservation provides a new direction in encapsulated cell therapy with the goal of clinical application in the near future.

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

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

Cryopreservation of adherent human embryonic stem cells

Standard human embryonic stem (HES) cell cryopreservation methodologies, including slow freezing and vitrification of colonies in suspension, are plagued by poor viability and high differentiation rates upon recovery. To facilitate research studies and clinical applications of HES cells, we have developed a cryopreservation technique based on stabilizing HES colonies adherent to or embedded in a Matrigel matrix. This method increases cell viability by over an order of magnitude compared with cryopreservation in suspension and reduces differentiation. Loading adherent HES cells with the disaccharide trehalose prior to cryopreserving in a dimethylsulfoxide-containing cryoprotectant solution further improves cell viability under certain conditions. Our proposed approach has the potential to reduce the time required to amplify frozen stocks of HES cells, minimize risk of clonal selection during freeze-thaw cycles, and facilitate storage of HES cell clone libraries.

The viability and function of cryopreserved hepatocyte spheroids with different cryopreservation solutions

We sought to evaluate the viability and function of cryopreserved hepatocyte spheroids using different cryopreservation solutions in order to elucidate the efficiency of cryopreservation. Hepatocytes isolated from a Sprague-Dawley rat were formed into spheroids by 24 hours of rotational culture. The spheroids were cryopreserved using a programmed linear freezer in a liquid nitrogen tank for 24 hours in four different cryopreservation solutions: UW solution (UW), William E media (WE), fetal bovine serum (FBS), and a mixture (MIX). After thawing, they were cultured for 4 days. With each hepatocyte spheroid, the viability using the MTT assay and hepatocyte-specific functions, such as ammonia clearance, urea nitrogen synthesis, and albumin secretion, were analyzed. The viabilities of cryopreserved hepatocyte spheroids were 64.8% +/- 10.2% (UW), 33.2% +/- 9.7% (WE), 69.3% +/- 8.7% (FBS), and 48.4% +/- 15.5% (MIX). Ammonia clearance of spheroids cyropreserved in UW solution was 0.93 +/- 0.13 mmol/L per well per day, which was not significantly different from freshly cultured spheroids. From the aspect of urea nitrogen synthesis, spheroids cryopreserved with UW, FBS, and MIX solution were not significantly different from freshly cultured spheroids. The amount of albumin secretion by the UW cryopreserved spheroids was significantly greater than that of other cryopreserved spheroids. Cryopreserved hepatocyte spheroids in UW solution were not significantly different from freshly cultured spheroids with respect to viability and function. UW solution was superior to other cryopreservation solutions for viability and functions.

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

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

A Survey of Consumer Attitudes to the Supply and Use of Human Hepatocytes in the United Kingdom

Human hepatocytes are the model of choice for pharmacotoxicological studies, but their acquisition is often problematic due to ethical and logistical difficulties. The UK Human Tissue Bank is a not-for-profit organisation that acquires and processes human tissue, with a specialist interest in the isolation of human hepatocytes. A recent in-house survey of the processing of liver tissue over 1 year revealed that freshly isolated hepatocytes were underutilised due to mismatched consumer demand, despite the published need for them. We present the results of a telephone survey to investigate the reasons behind this paradox. This survey highlighted some problem areas, including “out of hours” availability of cells and personnel difficulties, but overall, demonstrated the value of such a service, with numerous researchers taking advantage of available good quality human hepatocytes. Although further work is required in optimising long-term storage protocols through cryopreservation, we have demonstrated that tissue handling of this type can be successful and beneficial to the pharmaceutical and biotechnology industries.

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.

Cryopreservation of rat hepatocyte monolayers: cell viability and cytochrome P450 content in post-thaw cultures

Cryopreservation of primary hepatocyte monolayers may provide a means of long-term storage of the cells for in vitro studies of xenobiotic metabolism and toxicity. Rat hepatocytes can be stored at -70 degrees C as simple monolayers attached to collagen-coated dishes, and post-thaw cultures can be continued for up to 72 h. Throughout this post-thaw period viability of the cells was demonstrated by retention of intracellular fluorescence after exposure to carboxyfluorescein diacetate (CFDA) and examination by confocal laser scanning microscopy (CLSM). CLSM images revealed an uneven distribution of CFDA-derived fluorescence within hepatocytes post-thaw, particularly in Williams' E medium, indicating generation and retention of carboxyfluorescein within the intracellular organelles. The membranes of the intracellular organelles appear to be less sensitive to freeze/thaw damage than the cell membrane. Viability was not compromised with storage for up to 28 days at -70 degrees C. Cytochrome P450 content was retained in post-thaw culture to a similar extent as in non-frozen cultures. Cryopreserved rat hepatocyte monolayers may provide a useful in vitro model for studying xenobiotic metabolism and toxicity.

Hepatic progenitors and strategies for liver cell therapies

Liver cell therapies, including liver cell transplantation and bioartificial livers, are being developed as alternatives to whole liver transplantation for some patients with severe liver dysfunction. Hepatic progenitors are proposed as ideal cells for use in these liver cell therapies given their ability to expand extensively, differentiate into all mature liver cells, have minimal immunogenicity, be cryopreservable, and reconstitute liver tissue when transplanted. We summarize our ongoing efforts to develop clinical programs of hepatic progenitor cell therapies with a focus on hepatic stem cell biology and strategies that have emerged in analyzing that biology.

Cultures with cryopreserved hepatocytes: applicability for studies of enzyme induction

The use of hepatocyte cultures is well established for the study of drug-drug interactions. However, the major hindrance for the use of human hepatocyte cultures is that human hepatocytes are only occasionally available. This problem could be overcome by cryopreservation. Although cryopreserved hepatocytes have been recommended for short term applications in suspension, studies on induction of enzyme activity, requiring a more prolonged maintenance of cryopreserved hepatocytes in culture, represent a new field of research. In the present study, we established a technique that allows preparation of rat hepatocyte co-cultures, using cryopreserved hepatocytes. After incubation with phenobarbital (0.75 mM; 72 h) induction factors for the isoenzyme-dependent regio and stereoselective testosterone hydroxylations were 1.6, 2.2, 1.0, 2.1, 5.6, 2.4, 3.6, 4.5 and 0.9 for 2alpha-, 2beta-, 6alpha-, 6beta-, 7alpha-, 15beta-, 16alpha- and 16beta-hydroxytestosterone and 4-androsten-3,17 dione. Regarding induction factors of less than 2-fold, as questionable these induction factors were similar to those of cultures with freshly isolated hepatocytes and the induction pattern of the individual hydroxylation products was similar to the in vivo situation. In addition 3-methylcholanthrene (5 microM; 72 h) induced exclusively the formation of 7alpha-hydroxytestosterone (6.6-fold) in cultures with cryopreserved hepatocytes. This specificity also correlates to that obtained in rats. Although these induction factors were clearly satisfactory in cryopreserved cultures, the absolute activities of the main testosterone hydroxylation products were reduced when compared to fresh cultures. For instance, 6beta-hydroxytestosterone, the main metabolite in solvent controls was reduced to 79%, 7alpha-hydroxytestosterone, the main metabolite after induction with 3-MC, was reduced to 66% and 16beta-hydroxytestosterone, the main metabolite after induction with PB, was reduced to 52%. Similarly, EROD activity after induction with 3-methylcholanthrene in cryopreserved cultures was reduced to 62%, compared with that in fresh cultures. Although further optimization and validation is required, the data show that cytochrome P450 activities can clearly be induced in co-cultures of cryopreserved hepatocytes, in a fashion which for the investigated inducers, is similar to that in cultures from freshly isolated hepatocytes and similar to the in vivo situation.

Extracorporeal support and hepatocyte transplantation in acute liver failure and cirrhosis

The relative shortage of donor organs and lack of immediate availability mean that many patients with acute liver failure die before orthotopic liver transplantation can be performed. An effective temporary liver support system could improve the chance of survival with or without a transplant being ultimately carried out. Recent technological advances resulting in improved maintenance of hepatocyte viability and function in culture and bioreactor designs which facilitate adequate perfusion of the cellular component and removal of products of cellular metabolism have led to the development of a number of bioartificial devices for liver support. Three such devices have undergone preliminary clinical evaluation in the setting of acute liver failure, with a statistically significant reduction in raised intracerebral pressure along with improvements in consciousness level and some biochemical parameters associated with treatment with one of these. Several other devices with different characteristics have shown promise in vitro and/or in animal models but await clinical evaluation. Several new totally artificial systems have also been described, along with the emergence of isolated hepatocyte transplantation, with reports of successful 'bridging' to liver transplantation. Controlled trials on a multicentre basis in well-defined patient groups and with standardized outcome measures will be required to properly evaluate the clinical value of each of these approaches to providing liver support in acute liver failure and cirrhosis. A better understanding of mechanisms underlying multiorgan failure and of factors inhibiting liver regeneration, thereby allowing a more targeted approach, will be essential to the further development of effective liver support strategies in these settings.

Cryopreserved porcine hepatocyte cultures

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

Survival and function of isolated hepatocytes after cryopreservation

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

Hepatocytes entrapped in collagen gel following 14 days of storage at 4 degrees C: preservation of hybrid artificial liver

Preservation of hepatocytes is a key technical factor toward the successful clinical application of hybrid artificial livers. It was possible to culture hepatocytes that had been preserved with collagen gel for 8 and 14 days in 4 degrees C University of Wisconsin solution. Phase-difference and scanning electron microscopy showed that most of the stored hepatocytes maintained a round-shaped morphology. In the 14 day preservation group, on Days 2 and 8, respectively, ureogenesis was 98.3% and 69.6%, gluconeogenesis was 65.2% and 80.7%, lidocaine clearance was 81.7% and 72.5%, urea synthesis after ammonia load was 47.6% and 57.5% of those in the comparable control group. This implies that preserved hepatocytes maintained adequate functional capability even after 14 days of preservation. We suggest that our preservation method will be valuable for the future application and development of a practical hybrid artificial liver.

Porcine hepatocytes for biohybrid artificial liver devices: a comparison of hypothermic storage techniques

Two hypothermic preservation techniques were investigated to assess their possible role in on-demand cell supply for bioartificial liver support devices. Porcine hepatocytes from slaughterhouse organs were isolated and either cold stored in a modified University of Wisconsin solution for up to 72 h or directly cultured in a sandwich configuration, frozen at Day 3 of culture, and stored for up to 30 days with subsequent long-term culture (14 days) in both groups. Cold storage for 72 h resulted in a decreased viability of cells (58.7 +/- 7.9%) with well preserved ultrastructures in the remainder of cells. In subsequent culture, albumin secretion was slightly increased, and cytochrome P450 IA1 dependent 7-ethoxy-coumarine deethylation activity was reduced to about 40% of control values. After cryopreservation, hepatocyte cultures revealed no severe damage to ultrastructures of cells, and functional parameters (albumin, 7-ethoxycoumarine deethylation) were comparable with controls after an initial drop in activity directly after thawing. Length of storage time did not influence results. Both hypothermic preservation protocols might eventually play an important role for bioartificial liver processing and on-demand cell supply, dependent on the individual reactor design.

Cryopreservation of rat hepatocyte monolayer cultures

1. Most previous attempts to cryopreserve hepatocytes have used suspensions stored at either -70 degrees C or in liquid nitrogen, and the major problem is that these do not, on subsequent thawing, attach well in culture. This limits their use in studies of drug metabolism and xenobiotic-induced toxicity. In this manuscript we demonstrate successful cryopreservation of rat hepatocytes as monolayers attached to a collagen film. 2. Monolayers can be frozen and thawed without significant loss of cells, and although damage to the internal and plasma membranes is evident immediately post-thaw, a remarkable repair process takes place over 24-48 h post-thaw. Immediately post-thaw only 10% of the cells exclude Trypan Blue, but by 48 h 80-90% of the thawed cells are viable, indicating that repair of the plasma membranes has taken place. 3. The cells post-thaw retain aspects of liver-specific function including cytochrome P450 content and albumin synthesis. However, cytosolic proteins are lost through the damaged membranes and, probably because of this, urea synthesis from ammonia is retained at only 25% of pre-freeze values. 4. A cryopreservation method based on adherent hepatocytes on a collagen substrate overcomes the problems encountered with culture of cryopreserved hepatocyte suspensions, and may provide a practical means of establishing a 'bank' of hepatocytes from several donors and species.

Assessment of artificial liver support technology

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

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

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

Effects of dimethyl sulfoxide on cultured rat hepatocytes in sandwich configuration

A recently developed sandwich culture system, in which hepatocytes are sandwiched between two layers of collagen, has been shown to be capable of maintaining long-term expression of hepatocellular function (J. C. Y. Dunn et al., Biotechnol. Prog. 7, 237-245, 1991). The development of an adequate technique for the cryopreservation of hepatocytes in such a stable culture configuration would ensure a ready supply of hepatocytes for use in bioreactors or bioartificial liver support devices. This report describes the effects of exposing hepatocytes in sandwich culture to different concentrations of the cryoprotectant dimethyl sulfoxide (Me2SO) at 22 degrees C on Day 7 of culture. Cell function, morphology, and cytoskeletal organization were followed for 14 days after exposure. Hepatocellular morphology and albumin secretion remained normal when cultures were exposed for up to 120 min to predicted final Me2SO concentrations up to 1.33 M. Exposure for less than 60 min to equilibrium concentrations of up to 3.33 M Me2SO did not adversely affect cell morphology or albumin secretion rate, but at the highest concentration (3.33 M), increase of the exposure time to 60 or 120 min resulted in dramatic, irreversible cell damage and loss of function. Actin filament organization was shown to be undisturbed when the cells were exposed to 1.33 M Me2SO for 60 min, but was irreversibly disrupted by exposure to 3.33 M for 120 min. Based on these results, a simple and safe procedure is suggested for the addition of Me2SO to hepatocytes in a sandwich culture configuration and its subsequent removal, which will be valuable for studies on hepatocyte cryopreservation.

Hepatocytes in collagen sandwich: evidence for transcriptional and translational regulation

The influence of extracellular matrix configuration on the tissue-specific function of cultured hepatocytes was investigated. Adult rat hepatocytes sandwiched between two layers of collagen gel were compared to cells cultured on a single layer of collagen gel for differences in the total RNA content, the level of albumin-specific mRNA, the rate of albumin gene transcription, and the rate of albumin mRNA translation. Adult hepatocytes in the sandwich system maintained the level of albumin mRNA similar to that found in the normal liver for at least six weeks, whereas the level of albumin mRNA declined rapidly in the single gel system. After one week of culture, hepatocytes in the single gel system could be induced to recover the high level of albumin mRNA and albumin production when a second layer of collagen gel was overlaid at that time. Furthermore, sandwiched hepatocytes maintained significantly higher transcriptional activity compared to cells in the single gel system. In addition to transcriptional control, the ultimate rate of albumin production was shown to depend on the rate of translation, which increased with culture time and reached a plateau in one to two weeks. This increase in translational activity over time in culture was observed in both the sandwich and the single gel systems and, thus, appeared to be independent of the configuration of extracellular matrix.

Cryopreservation of isolated hepatocytes: intracellular ice formation under various chemical and physical conditions

Kinetics of intracellular ice formation (IIF) for isolated rat hepatocytes was studied using a cryomicroscopy system. The effect of the cooling rate on IIF was investigated between 20 and 400 degrees C/min in isotonic solution. At 50 degrees C/min and below, none of the hepatocytes underwent IIF; whereas at 150 degrees C/min and above, IIF was observed throughout the entire hepatocyte population. The temperature at which 50% of hepatocytes showed IIF (50TIIF) was almost constant with an average value of -7.7 degrees C. Different behavior was seen in isothermal subzero holding temperatures in the presence of extracellular ice. 50TIIF from isothermal temperature experiments was approximately -5 degrees C as opposed to -7.7 degrees C for constant cooling rate experiments. These experiments clearly demonstrated both the time and temperature dependence of IIF. On the other hand, in cooling experiments in the absence of extracellular ice, IIF was not observed until approximately -20 degrees C (at which temperature the whole suspension was frozen spontaneously) suggesting the involvement of the external ice in the initiation of IIF. The effect of dimethyl sulfoxide (Me2SO) on IIF was also quantified. 50TIIF decreased from -7.7 degrees C in the absence of Me2SO to -16.8 degrees C in 2.0 M Me2SO for a cooling rate of 400 degrees C/min. However, the cooling rate (between 75 and 400 degrees C/min) did not significantly affect 50TIIF (-8.7 degrees C) in 0.5 M Me2SO. These results suggest that multistep protocols will be required for the cryopreservation of hepatocytes.