Influence of pancreatic islets on growth and differentiation of hepatocytes in co-culture

Improvement of hepatocyte engraftment by co-transplantation with pancreatic islets in hepatocyte transplantation

Because of the fragility of isolated hepatocytes, extremely poor engraftment of transplanted hepatocytes remains a severe issue in hepatocyte transplantation. Therefore, improving hepatocyte engraftment is necessary to establish hepatocyte transplantation as a standard therapy. Since the pancreatic islets are known to have favorable autocrine effects, we hypothesized that the transplanted islets might influence not only the islets but also the nearby hepatocytes, subsequently promoting engraftment. We evaluated the effects of islet co-transplantation using an analbuminemic rat model (in vivo model). Furthermore, we established a mimicking in vitro model to investigate the underlying mechanisms. In an in vivo model, the hepatocyte engraftment was significantly improved only when the islets were co-transplanted to the nearby hepatocytes (p < 0.001). Moreover, the transplanted hepatocytes appeared to penetrate the renal parenchyma together with the co-transplanted islets. In an in vitro model, the viability of cultured hepatocytes was also improved by coculture with pancreatic islets. Of particular interest, the coculture supernatant alone could also exert beneficial effects comparable to islet coculture. Although insulin, VEGF, and GLP-1 were selected as candidate crucial factors using the Bio-Plex system, beneficial effects were partially counteracted by anti-insulin receptor antibodies. In conclusion, this study demonstrated that islet co-transplantation improves hepatocyte engraftment, most likely due to continuously secreted crucial factors, such as insulin, in combination with providing favorable circumstances for hepatocyte engraftment. Further refinements of this approach, especially regarding substitutes for islets, could be a promising strategy for improving the outcomes of hepatocyte transplantation.

Recent advances in the design of implantable insulin secreting heterocellular islet organoids

Islet transplantation has proved one of the most remarkable transmissions from an experimental curiosity into a routine clinical application for the treatment of type I diabetes (T1D). Current efforts for taking this technology one-step further are now focusing on overcoming islet donor shortage, engraftment, prolonged islet availability, post-transplant vascularization, and coming up with new strategies to eliminate lifelong immunosuppression. To this end, insulin secreting 3D cell clusters composed of different types of cells, also referred as heterocellular islet organoids, spheroids, or pseudoislets, have been engineered to overcome the challenges encountered by the current islet transplantation protocols. β-cells or native islets are accompanied by helper cells, also referred to as accessory cells, to generate a cell cluster that is not only able to accurately secrete insulin in response to glucose, but also superior in terms of other key features (e.g. maintaining a vasculature, longer durability in vivo and not necessitating immunosuppression after transplantation). Over the past decade, numerous 3D cell culture techniques have been integrated to create an engineered heterocellular islet organoid that addresses current obstacles. Here, we first discuss the different cell types used to prepare heterocellular organoids for islet transplantation and their contribution to the organoids design. We then introduce various cell culture techniques that are incorporated to prepare a fully functional and insulin secreting organoids with select features. Finally, we discuss the challenges and present a future outlook for improving clinical outcomes of islet transplantation.

Coculture With Ischemia/Reperfusion-Preconditioned Hepatocytes Improves Islet Function and Survival

In clinical islet transplantation, hepatic ischemia and insufficient neovascularization of transplanted islets are barriers to islet survival and function. However, hepatocytes have a potency to protect themselves against ischemia. We hypothesized that ischemia/reperfusion preconditioning (IRP) of hepatocytes might beneficially affect islet cells in a coculture system. Primary islets were cocultured with primary hepatocytes, and hepatocyte IRP was conducted by subjecting cells to hypoxic conditions for single 15-minute/30-minute hypoxia, or 2 tandem 15-minute/30-minute hypoxic treatments (hypoxic-normoxic-hypoxic). We show that gene expression levels of insulin-like growth factor 1 (IGF-1), hepatocyte growth factor (HGF), transforming growth factor-α (TGF-α), and TGF-β1 in hepatocytes were increased by IRP. IRP hepatocytes secreted hepatocyte growth factor and insulin-like growth factor-1. Coculture of islets with IRP hepatocytes enhanced islet insulin secretion in glucose challenge test and expression of the survival-related gene Bcl-2 and the regenerating gene-1α (Reg-1α). Islets cocultured with the 30-minute double-IRP hepatocytes displayed significantly higher viability in the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and terminal deoxynucleotidyl transferase dUTP nick end labeling stain compared with that of islets subjected to 30 minutes of hypoxia. These results suggest that islet coculture with IRP hepatocytes can improve islet survival and insulin secretion.

A TLR9 agonist promotes IL-22-dependent pancreatic islet allograft survival in type 1 diabetic mice

Pancreatic islet transplantation is a promising potential cure for type 1 diabetes (T1D). Islet allografts can survive long term in the liver parenchyma. Here we show that liver NK1.1+ cells induce allograft tolerance in a T1D mouse model. The tolerogenic effects of NK1.1+ cells are mediated through IL-22 production, which enhances allograft survival and increases insulin secretion. Increased expression of NKG2A by liver NK1.1+ cells in islet allograft-transplanted mice is involved in the production of IL-22 and in the reduced inflammatory response to allografts. Vaccination of T1D mice with a CpG oligonucleotide TLR9 agonist (ODN 1585) enhances expansion of IL-22-producing CD3-NK1.1+ cells in the liver and prolongs allograft survival. Our study identifies a role for liver NK1.1+ cells, IL-22 and CpG oligonucleotides in the induction of tolerance to islet allografts in the liver parenchyma.

Coculture of hepatocytes with islets

Bioartificial liver support (BAL) systems are potential new therapeutic approaches for use as liver support to prevent nutrient deficiencies, hypoxia, or ischemia before the acquisition of donated organs. To investigate whether islets are beneficial for hepatocyte function and survival, we cocultured BALB/c mouse islets with C57BL/6J hepatocytes to assess hepatocyte viability, function, and apoptosis. We observe cell viability to decrease progressively by 50% from day 0 to day 3 among isolated hepatocytes (group A) and hepatocytes cocultured with islets (group B). However, group A was prone to necrosis and reduced albumin secretion during culture. In contrast, at day 7 group B maintained albumin secretion (0.3351 ± 0.0581 vs 0.1451 ± 0.0329 μg/h/mL; P < .05). Early apoptosis was observed at day 3 among group A but at day 7 in group B. In addition, quantitative analysis of the apoptotic cells revealed group B to show a delayed phenotype of both early and late apoptosis compared with group A. Our results indicated that islets could retain hepatocyte function and delay apoptosis, suggesting that the coculture system is potentially applicable to develop a high-performance BAL.

3D co-culturing model of primary pancreatic islets and hepatocytes in hybrid spheroid to overcome pancreatic cell shortage

Here, a spheroidal 3D co-culture model of primary (rat) pancreatic islets and hepatocytes with uniform size and shape was developed using hemispheric concave microwell arrays. We conducted morphological and functional analyses of hybrid spheroids versus mono-cultures of islets or hepatocytes (controls). For the establishment of a 3D hybrid model, a broad range of cell ratios - 1:1, 1:3, 1:5, 1:7, 3:1, 5:1 and 7:1 mixture - of hepatocytes and pancreatic islets were used. As control, each hepatocyte and pancreatic islet were mono-cultured forming 3D spheroids. The transient morphology of spheroid formation in 9 culture models was observed using optical microscopy. Cell viability under these culture environments was assessed, and the morphologies of the outer and inner porous cell-spheroid structures were investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and imaging of stained spheroid sections. The pancreatic islet-specific function of hybrid spheroids was evaluated by measuring insulin secretion and in vivo test by xenotransplantation of encapsulated spheroids in microfibers with a consistent maintenance of normal blood glucose levels over 4 weeks, while liver-specific functions were measured in terms of albumin secretion, urea secretion and cytochrome P450 activity. These diverse observations and evaluations validated the positive and bidirectional effects of co-cultured 3D spheroids. The proposed 3D co-culture model demonstrated that both cells appeared to support each other's functions strongly in spheroids, even though smaller proportions of each cell type was evaluated compared to mono-culture models, suggesting that the proposed model could help overcome the problem of cell shortages in clinical applications.

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.

Generating hepatic cell lineages from pluripotent stem cells for drug toxicity screening

Hepatotoxicity is an enormous and increasing problem for the pharmaceutical industry. Early detection of problems during the drug discovery pathway is advantageous to minimize costs and improve patient safety. However, current cellular models are sub-optimal. This review addresses the potential use of pluripotent stem cells in the generation of hepatic cell lineages. It begins by highlighting the scale of the problem faced by the pharmaceutical industry, the precise nature of drug-induced liver injury and where in the drug discovery pathway the need for additional cell models arises. Current research is discussed, mainly for generating hepatocyte-like cells rather than other liver cell-types. In addition, an effort is made to identify where some of the major barriers remain in translating what is currently hypothesis-driven laboratory research into meaningful platform technologies for the pharmaceutical industry.

Morphological and functional analysis of rat hepatocyte spheroids generated on poly(L-lactic acid) polymer in a pulsatile flow bioreactor

Liver neo-tissue suitable for transplantation has not been established. Primary rat hepatocytes were cultured on three-dimensional biodegradable polymer matrices in a pulsatile flow bioreactor with the intention of inducing tissue formation and improving cell survival. Functional and structural analysis of the hepatocytes forming liver neo-tissue was performed. Biodegradable poly(L-lactic acid) (PLLA) polymer discs were seeded with 4 x 10(6) primary rat hepatocytes each, were exposed to a pulsatile medium flow of 24 mL/min for 1, 2, 4, or 6 days and were investigated for monoethylglycinexylidine (MEGX) formation, ammonia detoxification, Cytokeratin 18 (CK18) expression, and preserved glycogen storage. Fine structural details were obtained using scanning and transmission electron microscopy. Spheroids of viable hepatocytes were formed. MEGX-specific production was maintained and ammonia removal capacity remained high during the entire flow-culture period of 6 days. CK18 distribution was normal. Periodic-acid- Schiff reaction demonstrated homogenous glycogen storage. The hepatocytes reassembled to form intercellular junctions and bile canaliculi. Functional and morphological analysis of rat hepatocytes forming spheroids in a pulsatile flow bioreactor indicated preserved and intact hepatocyte morphology and specific function. Pulsatile flow culture on PLLA scaffolds is a promising new method of hepatic tissue engineering leading to liver neo-tissue formation.

Injectable Liver: A Novel Approach Using Fibrin Gel as a Matrix for Culture and Intrahepatic Transplantation of Hepatocytes

Cell transplantation and tissue engineering with liver cells are currently under investigation as experimental therapies for certain liver diseases. In this study we evaluated a fibrin-based gel matrix as carrier for hepatocytes in culture. Furthermore, a novel technique for direct intrahepatic injection of fibrin gel-immobilized hepatocytes was developed and evaluated in a rat model. Hepatocytes were harvested from rats. Fibrin matrix was generated with modified fibrin sealant. Cells, in medium containing epidermal growth factor and insulin, were seeded in a drop of fibrin matrix onto plastic culture dishes. Cell numbers were assessed by DNA content. Hepatocyte differentiation was evaluated by reverse transcription-polymerase chain reaction (RT-PCR) and immunohistology (IH) for cytokeratin (CK)-18 and albumin. PKH26-labeled fibrin gel-immobilized hepatocytes were transplanted into liver by direct injection underneath the capsule. Fluorescence microscopy of explanted liver was performed to identify PKH26+ donor cells. Neotissue was characterized by IH for the markers CK-18, ED1, and desmin. Culture in a fibrin matrix allowed stable cell numbers and three-dimensional neotissue formation. RT-PCR and IH showed preservation of liver-specific markers CK-18 and albumin in vitro. Transplanted cells were identified by fluorescence microscopy after 2 and 7 days. CK-18 and desmin staining showed integration of hepatocytes and hepatic stellate cells into the host liver. Fibrin matrix is an appropriate environment for hepatocytes in culture. Direct intrahepatic injection of fibrin gel-immobilized hepatocytes is technically feasible. We conclude that fibrin gel immobilization is an attractive tool for the development of tissue engineering-based liver support systems.

Methods of human islet culture for transplantation

The ability to maintain isolated human islet preparations in tissue culture has recently been adopted by most islet transplant centers, and improves the safety as well as the practicality of islet transplantation. Maintaining islet viability and recovery, however, remains challenging in a clinical setting, due to stringent conditions required for culture. Islet culture is further complicated by the fact that islets do not form a monolayer. This review aims to clarify media, supplementation, and conditions that have been shown to be relevant to human islets, as well as to offer avenues of future research. Factors examined that may influence islet survival include base medium, glucose concentration, vitamin, inorganic ion, lipid, hormone, growth factor, amino acid, and binding protein composition and concentration, as well as culture temperature and seeding density. In addition, this article reviews novel techniques, such as coculture and matrices, that have been employed in an attempt to improve islet survival and functional viability.

Three-dimensional co-culture of rat hepatocyte spheroids and NIH/3T3 fibroblasts enhances hepatocyte functional maintenance

Functional maintenance of primary hepatocytes in culture can be improved by several distinct approaches involving optimization of the extracellular matrix microenvironment, media composition and cell-cell interactions, both homotypic and heterotypic. Using a galactose-decorated surface, we have developed a method to combine these two approaches by co-culturing rat primary hepatocyte spheroids with NIH/3T3 mouse fibroblast cells. Spheroids were performed by culturing hepatocytes for 3 days on galactosylated poly(vinylidene difluoride) membrane; NIH/3T3 cells were subsequently seeded and co-cultured with the spheroids. Results showed that although NIH/3T3 cells alone responded poorly to the galactosylated PVDF surface and displayed limited attachment, NIH/3T3 fibroblasts attached to the periphery of the hepatocyte spheroids and proliferated around them. Co-cultured hepatocyte spheroids exhibited significantly higher liver-specific functions as compared to spheroids cultured alone. Albumin secretion level in this co-culture system peaked on day 11, which was 1.8- and 2.9-times higher than the peak expression level in spheroid homo-culture control in serum-free (day 3) and serum-containing media (day 4), respectively. The albumin secretion function was maintained for at least two weeks; it was 5.1 (in serum-free medium) and 17.8 (in serum-containing medium) times higher than spheroid homo-culture on day 13. Similarly, the co-culture system also expressed approximately 5.5- and 3.1-times higher 3-methylcholanthrene-induced cytochrome P450 enzymatic activity on day 14 as compared to the homo-culture control in serum-free and serum-containing medium, respectively. In conclusion, this unique co-culture system demonstrated the synergistic roles of homotypic cell-cell interaction, heterotypic cell-cell interaction, cell-substrate interaction and soluble stimuli in hepatocyte functional maintenance.

Factors influencing stem cell differentiation into the hepatic lineage in vitro

A major area of research in transplantation medicine is the potential application of stem cells in liver regeneration. This would require well-defined and efficient protocols for directing the differentiation of stem cells into the hepatic lineage, followed by their selective purification and proliferation in vitro. The development of such protocols would reduce the likelihood of spontaneous differentiation of stem cells into divergent lineages upon transplantation, as well as reduce the risk of teratoma formation in the case of embryonic stem cells. Additionally, such protocols could provide useful in vitro models for studying hepatogenesis and liver metabolism. The development of pharmokinetic and cytotoxicity/genotoxicity screening tests for newly developed biomaterials and drugs, could also utilize protocols developed for the hepatic differentiation of stem cells. Hence, this review critically examines the various strategies that could be employed to direct the differentiation of stem cells into the hepatic lineage in vitro.

Influence of pancreatic islets on spheroid formation and functions of hepatocytes in hepatocyte-pancreatic islet spheroid culture

Hepatotrophic stimulation of hepatocytes is necessary to preserve long-term function of hepatocytes in hepatocyte transplantation and bioartificial liver system. The main source of hepatotrophic factors in portal venous blood seems to be the pancreatic islets. It was also reported that hepatocyte spheroids, tightly packed multicellular aggregates, showed enhanced liver-specific activities and a prolonged differentiated state compared with cells that were maintained as a monolayer. On the basis of these two facts, the authors tried to form hepatocyte-pancreatic islet spheroids and to evaluate the influence of pancreatic islets on spheroid formation and functions of hepatocytes in spheroid culture. Hepatocytes and pancreatic islet cells were harvested from adult male Sprague-Dawley rats weighing 200-250 g. Hepatocytes were cultured in spinner flasks with either basic nonstimulated medium (hepatocytes only [group BH] and cocultures with islet cells [group BI]) or hormone-stimulated medium (hepatocytes only [group HH] and cocultures with islet cells [group HI]). The size and morphology of spheroids, as determined by phase-contrast microscopy, and liver-specific functions, such as albumin secretion, urea synthesis, and ammonia removal, were compared among groups. The results were as follows: the size of spheroids, 66 +/- 53.4 microm, in group BH on day 2 was smaller than in group BI (179 +/- 66.2 microm on day 2, p < 0.05). In group BI, group HH, and group HI, smooth spheroids were observed on culture day 2. However, in group BH rugged incomplete aggregates were observed on the same day. In groups with basal medium, group BI showed better results in terms of hepatocyte-specific function such as albumin secretion, urea synthesis, and ammonia removal compared with group BH on days 2 and 3 (p < 0.05). In groups with hormone-defined medium, cocultures had no impact on albumin secretion rate, urea synthetic rate, and ammonia removal rate. In conclusion, we made a new type of hepatocyte-pancreatic islet spheroid, using a rotational culture method. Pancreatic islets in a spheroid culture system stimulated hepatocyte spheroid formation and some hepatocyte-specific functions in vitro.

Hepatic tissue engineering

Fulminant hepatic failure (FHF) attributes to rising medical cost and accounts for many deaths each year in the United States. Currently, the only solution is organ transplantation. Due to increasing donor organ shortage, many in need of transplantation continue to remain on the waiting list. Liver Assist Devices (LADs) are being used to temporarily sustain liver function and bridge the period between FHF and transplantation. Hepatic Tissue Engineering is a step toward alleviating the need for donor organs; yet many challenges must be overcome including scaffold choice, cell source and immunological barriers. Bioreactors have aided in hepatocyte survival and have proven to sustain viable cells for several weeks. Achieving the necessary functions required for hepatic replacement is aided by the incorporation of growth factors and mitogens many that now can be bound to the polymer scaffold and released in a timely manner. Utilizing concepts such as MicroElectroMechanical systems (MEMs) technology, our laboratory is able to mimic the natural vasculature of the liver and sustain functional and viable hepatocytes. Expanding and improving upon this platform technology, advancements made will continue toward the development of a fully functioning and implantable liver.

N/A

N/A

Microencapsulated hepatocytes and islets as in vivo bioartificial liver support system

AIM: To confirm the xenotransplantation of microencapsulated hepatocytes and islets as a temporary bioartificial liver support system for mice with acute liver failure (ALF).

METHODS: Mice were rendered ALF by a single intra-peritoneal injection of D-galactosamine (D-gal) and their tail blood was sampled to examine differences in blood ALT, albumin (ALB), total bilirubin (TB) and glucose (GLU) between 4 experimental groups. Rat hepatocytes and islets were collected and microencapsulated referring to both Sun’s and Fritschy’s methods. Mice were grouped into control group (CG), free hepatocyte group (FHG), microencapsulated hepatocyte group (MHG) and microencapsulated hepatocyte plus islet group (HIG). Tissue samples were subjected to microscopic and electron microscopic (EM) examinations.

RESULTS: The highest survival was observed in HIG, surprisingly at 100% (16/16), while the lowest was in CG at 12.5% (2/16), with inter-group statistical difference P < 0.05. ALT levels revealed no statistical difference between groups but the ALB level of HIG descended by the slightest margin {q = (0.54, 0.24, 1.33), P < 0.05} at the time when it reached the lowest point in all groups. TB of HIG returned to normal reference range (NRR) statistically sooner than that of others after a fierce elevation. No statistical inter-group difference was observed in GLU levels. Fusion between hepatocytes and beta cells was demonstrated giving rise to theoretical assumptions.

CONCLUSION: Hepatocytes to be microencapsulated together with islets should be a preferred in vivo hepatic functional supporting system, which can dramatically prolong survival and improve living status.

Tissue Factory: Conceptual Design of a Modular System for the in Vitro Generation of Functional Tissues

Tissue factory is a modular system designed to generate artificial tissues under optimal perfusion culture conditions. The microenvironment within the culture containers can be fine-tuned to meet the physiological needs of individual tissues, so that the generation of differentiated three-dimensional tissue constructs becomes possible. An optimal physiological environment is created by modulating a liquid phase as well as an artificial interstitium surrounding the growing construct. An innovative construction principle allows production of tissue culture containers, gas exchangers, and gas expanders at minimal material expenditure. Therefore it will be possible for the first time to produce sterile one-way perfusion culture modules for the generation of artificial tissues. The modules can be used separately as well as in a combined module. The system is designed to provide a possible platform for the standardized production of artificial tissues for future applications in biomedicine.

Influence of flow conditions and matrix coatings on growth and differentiation of three-dimensionally cultured rat hepatocytes

Maintenance of liver-specific function of hepatocytes in culture is still difficult. Improved culture conditions may enhance the cell growth and function of cultured cells. We investigated the effect of three-dimensional culture under flow conditions, and the influence of surface modifications in hepatocyte cultures. Hepatocytes were harvested from Lewis rats. Cells were cultured on three-dimensional polymeric poly-lactic-co-glycolic acid (PLGA) matrices in static culture, or in a pulsatile flow-bioreactor system. Different surface modifications of matrices were investigated: coating with collagen I, collagen IV, laminin, or fibronectin; or uncoated matrix. Hepatocyte numbers, DNA content, and albumin secretion rate were assessed over the observation period. Culture under flow condition significantly enhanced cell numbers. An additional improvement of this effect was observed, when matrix coating was used. Cellular function also showed a significant increase (4- to 5-fold) under flow conditions when compared with static culture. Our data showed that culture under flow conditions improves cell number, and strongly enhances cellular function. Matrix modification by coating with extracellular matrix showed overall an additive stimulatory effect. Our conclusion is that combining three-dimensional culture under flow conditions and using matrix modification significantly improves culture conditions and is therefore attractive for the development of successful culture systems for hepatocytes.

Liver tissue engineering: a role for co-culture systems in modifying hepatocyte function and viability

A major limitation in the construction of a functional engineered liver is the short-term survival and rapid de-differentiation of hepatocytes in culture. Heterotypic cell-cell interactions may have a role to play in modulating long-term hepatocyte behavior in engineered tissues. We describe the potential of 3T3 fibroblast cells in a co-culture system to modulate function and viability of primary isolated rat hepatocytes. Over an 18-day period after isolation, hepatocytes in pure culture rapidly declined in viability, displayed sparse bile canaliculi, and lost two function markers, the secretion of albumin and ethoxyresorufin O-dealkylase (EROD) activity. In comparison, the hepatocytes within the co-cultures maintained viability, possessed well-formed canalicular systems, and displayed both functional markers. Fixed 3T3 cells or 3T3 cell conditioned medium did not substitute for the viable 3T3 cell co-culture system in preserving hepatocyte viability and functionality.

Priming of hepatocytes for cell culture by partial hepatectomy prior to cell isolation

The combination of ex vivo gene transfer and a sufficient transplant model for hepatocytes may permit treatment of single enzyme-based metabolic liver diseases. Induction of replicative potential (priming) in hepatocyte cultures may enhance the efficiency of gene transfer under stable in vitro conditions. It is known that hepatocyte replication is increased in vivo after partial hepatectomy. We investigated the effect of partial hepatectomy prior to cell isolation on hepatocytes in vitro. Male Lewis rats served as donors. Hepatocytes were isolated by collagenase digestion from either intact livers or from livers 48 h after 70% hepatectomy (PH). Cells were seeded on collagen-coated culture dishes with hormone-supplemented culture media. Hepatocyte morphology, number, albumin secretion rate, and mono-ethyl-glycin-xylidid (MEGX)-biotransformation capacity were assessed on days 1, 3, and 5 in culture. PH significantly increased hepatocyte number and albumin secretion of cultured hepatocytes over the whole observation period. In contrast, MEGX-biotransformation capacity was significantly decreased. Morphology of cultured hepatocytes was not affected by PH prior to hepatocyte isolation. These results suggest a prolonged and complex response of hepatocytes to PH in vitro. Hepatocyte priming by PH is a promising approach toward stable cultures of proliferating hepatocytes and may provide a model for in vitro studies of hepatic regeneration mechanisms. Further research on hepatocyte priming toward an application in ex vivo gene transfer and hepatic tissue engineering seems justified.