Liver repopulation and long-term function of rat small hepatocyte transplantation as an alternative cell source for hepatocyte transplantation

Allogeneic Liver Transplantation and Subsequent Syngeneic Hepatocyte Transplantation in a Rat Model: Proof of Concept for in vivo Tissue Engineering

Objectives: Stable long-term functioning of liver cells after transplantation in humans is still not achieved successfully. A new approach for successful engraftment of liver cells may be the transplantation of syngeneic cells into an allogeneic liver graft. We therefore developed a new rat model for combined liver and liver cell transplantation (cLCTx) under stable immunosuppression. Materials and Methods: After inducing a mitotic block, liver grafts from female donor rats (Dark Agouti) were transplanted into female recipients (Lewis). In male Lewis rats, liver cell proliferation was induced with subsequent cell isolation and transplantation into female recipients after organ transplantation. Y-chromosome detection of the transplanted male cells was performed by quantitative polymerase chain reaction (qPCR) and fluorescence in situ hybridization (FisH) with localization of transplanted cells by immunohistochemistry. Results: Immunohistochemistry demonstrated the engraftment of transplanted cells, as confirmed by FisH, showing repopulation of the liver graft with 15.6% male cells (± 1.8 SEM) at day 90. qPCR revealed 14.15% (± 5.09 SEM) male DNA at day 90. Conclusion: Engraftment of transplanted syngeneic cells after cLCTx was achieved for up to 90 days under immunosuppression. Immunohistochemistry indicated cell proliferation, and the FisH results were partly confirmed by qPCR. This new protocol in rats appears feasible for addressing long-term functioning and eventually the induction of operational tolerance in the future.

Preoperative hepatocyte transplantation improves the survival of rats with nonalcoholic steatohepatitis-related cirrhosis after partial hepatectomy

Liver failure after liver resection for cirrhosis is a critical problem, and no effective therapy except liver transplantation is currently available. The objective of this study was to examine whether hepatocyte transplantation (HT) reduces the poststandard liver resection mortality rate of rats with nonalcoholic steatohepatitis (NASH)-related cirrhosis. Liver resection for hepatocellular carcinoma (HCC) combined with NASH-related cirrhosis has become increasingly common. We developed a rat model of acute liver failure after two-thirds partial hepatectomy (PH) for NASH-related cirrhosis. The mechanism by which HT improved the survival of the model rats was examined in short- and long-term investigations. Female DPPIV(-) recipient F344 rats were fed the choline-deficient l-amino acid (CDAA)-defined diet for 12 weeks. Some of the rats were transplanted with male F344 DPPIV(+) rat hepatocytes 24 h before undergoing PH. The overall post-PH survival of each group was evaluated, and short- and long-term pathological and molecular biological evaluations were also performed. Overall survival was significantly longer in the HT group than the non-HT group (7-day survival rates: 46.7% and 7.7%, respectively). Compared with the recipient livers of the non-HT group, numerous Ki-67(+) hepatocytes and few TUNEL(+) hepatocytes were observed in the livers of the HT group. At 6 months after the HT, the DPPIV(+) hepatocytes had partially replaced the recipient liver and formed hepatocyte clusters in the spleen. Preoperative HT might improve the survival of rats with NASH-related cirrhosis after PH by preventing the host hepatocytes from accelerating their growth and falling into apoptosis.

Construction of liver tissue in vivo with preparative partial hepatic irradiation and growth stimulus: investigations of less invasive techniques and progenitor cells

BACKGROUND

The selective proliferation of transplanted hepatocytes with a growth stimulus, such as partial hepatectomy or hepatocyte growth factor, concomitant with hepatic irradiation (HIR), which can suppress proliferation of host hepatocytes, has been reported. We have conducted experiments that focused on less invasive and clinically applicable techniques and progenitor cells.

MATERIALS AND METHODS

First, dipeptidyl-peptidase IV-F344 or jaundiced Gunn rats underwent partial HIR (only 30% of whole liver) and portal vein branch ligation (PVBL) of one lobe, followed by intrasplenic hepatocyte transplantation at 1 × 10(7). Second, after partial HIR and PVBL, two types of progenitor cells were transplanted (i.e., small hepatocytes (SHs) or adipose-derived mesenchymal stem cells.

RESULTS

Sixteen weeks after transplantation, the donor cells constituted > 70% of the hepatocytes of the irradiated lobe, showing connexin 32, phosphoenolpyruvate carboxykinase-1, and glycogen storage. Moreover, the serum bilirubin level had decreased significantly in the jaundiced Gunn rats and remained at this level throughout the 24 wk experimental period. The SHs grew more quickly than the hepatocytes. After 8 wk, around 40% of the host hepatocytes had been replaced by transplanted SHs. Although the donor adipose-derived mesenchymal cells were engrafted after 8 wk, their proliferation was not observed.

CONCLUSIONS

HIR, combined with PVBL, can be given to a selective liver lobe and is a less-invasive but effective method for proliferation of transplanted hepatocytes. Even a smaller number of SHs can construct liver tissue with their prevailing proliferative ability.

Therapeutic liver repopulation for metabolic liver diseases: Advances from bench to bedside

Metabolic liver diseases are characterized by inherited defects in hepatic enzymes or other proteins with metabolic functions. Therapeutic liver repopulation (TLR), an approach of massive liver replacement by transplanted normal hepatocytes, could be used to provide the missing metabolic function elegantly. However, partial and transient correction of the underlying metabolic defects due to very few integrated donor cell mass remains the major obstacle for the effective and widespread use of this approach. Little engraftment and proliferation insufficiency lead to the poor outcome. This article reviews the advances in the mechanisms of initial engraftment and selective proliferation and suggests some effective treatment strategies, from pharmacological preconditioning to stem cell transplantation, to optimize liver repopulation with liver cell transplantation. Enhancing cell viability and plating efficiency, increasing sinusoidal spaces, regulation of sinusoidal endothelial cell barrier and controlling inflammatory reaction may promote initial cell engraftment. Liver-directed irradiation, reversible portal vein embolization and fetal liver stem/progenitor cell transplantation induce preferential proliferation of donor cells substantially without severe side-effects. Furthermore, it seems better to use combined approaches to achieve a high level of liver repopulation for the management of metabolic liver diseases.

Freshly isolated hepatocyte transplantation in acetaminophen-induced hepatotoxicity model in rats

CONTEXT: Hepatocyte transplantation is an attractive therapeutic modality for liver disease as an alternative for orthotopic liver transplantation. OBJECTIVE: The aim of the current study was to investigate the feasibility of freshly isolated rat hepatocyte transplantation in acetaminophen-induced hepatotoxicity model. METHODS: Hepatocytes were isolated from male Wistar rats and transplanted 24 hours after acetaminophen administration in female recipients. Female rats received either 1x10(7) hepatocytes or phosphate buffered saline through the portal vein or into the spleen and were sacrificed after 48 hours. RESULTS: Alanine aminotransferase levels measured within the experiment did not differ between groups at any time point. Molecular analysis and histology showed presence of hepatocytes in liver of transplanted animals injected either through portal vein or spleen. CONCLUSION: These data demonstrate the feasibility and efficacy of hepatocyte transplantation in the liver or spleen in a mild acetaminophen-induced hepatotoxicity model.

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

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

COMMD1-deficient dogs accumulate copper in hepatocytes and provide a good model for chronic hepatitis and fibrosis

New therapeutic concepts developed in rodent models should ideally be evaluated in large animal models prior to human clinical application. COMMD1-deficiency in dogs leads to hepatic copper accumulation and chronic hepatitis representing a Wilson’s disease like phenotype. Detailed understanding of the pathogenesis and time course of this animal model is required to test its feasibility as a large animal model for chronic hepatitis. In addition to mouse models, true longitudinal studies are possible due to the size of these dogs permitting detailed analysis of the sequence of events from initial insult to final cirrhosis. Therefore, liver biopsies were taken each half year from five new born COMMD1-deficient dogs over a period of 42 months. Biopsies were used for H&E, reticulin, and rubeanic acid (copper) staining. Immunohistochemistry was performed on hepatic stellate cell (HSC) activation marker (alpha-smooth muscle actin, α-SMA), proliferation (Ki67), apoptosis (caspase-3), and bile duct and liver progenitor cell (LPC) markers keratin (K) 19 and 7. Quantitative RT-PCR and Western Blots were performed on gene products involved in the regenerative and fibrotic pathways. Maximum copper accumulation was reached at 12 months of age, which coincided with the first signs of hepatitis. HSCs were activated (α-SMA) from 18 months onwards, with increasing reticulin deposition and hepatocytic proliferation in later stages. Hepatitis and caspase-3 activity (first noticed at 18 months) increased over time. Both HGF and TGF-β1 gene expression peaked at 24 months, and thereafter decreased gradually. Both STAT3 and c-MET showed an increased time-dependent activation. Smad2/3 phosphorylation, indicative for fibrogenesis, was present at all time-points. COMMD1-deficient dogs develop chronic liver disease and cirrhosis comparable to human chronic hepatitis, although at much higher pace. Therefore they represent a genetically-defined large animal model to test clinical applicability of new therapeutics developed in rodent models.

Copper-induced hepatitis: the COMMD1 deficient dog as a translational animal model for human chronic hepatitis

Chronic inflammatory liver disease regardless of aetiology leads to failing regeneration and fibrosis, ending in cirrhosis. Both in man and in animals this worldwide health problem has no definitive cure. Chronic liver injury causes hepatic stellate cells to proliferate and differentiate into matrix-producing cells. New therapeutic options will be developed upon detailed understanding of the molecular mechanisms driving liver fibrosis. This may lead to new anti-fibrotic therapies which need to be tested in suitable models before application in the veterinary and human clinic. On the other side, to restore the failing regenerative capacity of the diseased liver cells, adult progenitor cells are of interest, as an alternative to whole organ transplantation. In order to find the most suitable large animal model it is important to recognise that the typical histopathological reaction pattern of the liver can differ between mammalian species. It is therefore imperative that specialists in veterinary internal medicine and pathology, being familiar with the diseases and pathologies of the liver in different animal species, are teaming-up in finding the best models for veterinary and human liver diseases. Several large animal models have been mentioned, like pigs, sheep, and dogs. Based on the observations that man and dog share the same hepatopathies and have identical clinical, pathological and pathogenetic reaction patterns during the development of liver disease, the dog seems to be a properly suited species to test new therapeutic strategies for pets and their best friends.

Liver reconstruction on the chorioallantoic membrane of the chick embryo

The liver from a 6-day-old chick embryo was transplanted on the chorioallantoic membrane of a 9-day-old chick embryo to observe the process of liver regeneration histologically. When a piece of the liver was implanted on the chorioallantoic membrane, only cells in the superficial zone of the graft adhering to the chorioallantoic membrane survived. Eventually, these surviving cells in the superficial zone proliferated with hematopoiesis, resulting in the formation of clusters of blood cells surrounded by the hepatocytes (or hepatic parenchymal cells). Semi-thin serial sections showed that these clusters of blood cells were confined to the space formed by hepatocytes. Furthermore, structures similar to the hepatic cord, sinusoid, central vein, and bile duct appeared in the reconstructed liver eleven days after transplantation. Meanwhile, when a pellet of the dissociated liver cells was transplanted onto the chorioallantoic membrane, two types of liver like structures were reconstructed: one was clusters of hepatocytes accompanied by sinusoids after hematopoiesis, and the other was a simple accumulation of hepatocytes without any sinusoids or hematopoiesis. The sinusoids found in the former type became clear following the connection between the space in the transplant and vessels of the chorioallantoic membrane. These findings indicated that the reconstructed liver was primarily produced by the accumulation of hepatocytes accompanied by hematopoietic cells, followed by the formation of sinusoidal spaces. We therefore consider that hematopoiesis is important for liver regeneration with a normal structure. Transplantation of the liver in the chorioallantoic membrane could be also useful for research into liver regeneration.

Growth ability and repopulation efficiency of transplanted hepatic stem cells, progenitor cells, and mature hepatocytes in retrorsine-treated rat livers

Cell-based therapies as an alternative to liver transplantation have been anticipated for the treatment of potentially fatal liver diseases. Not only mature hepatocytes (MHs) but also hepatic stem/progenitor cells are considered as candidate cell sources. However, whether the stem/progenitor cells have an advantage to engraft and repopulate the recipient liver compared with MHs has not been comprehensively assessed. Therefore, we used Thy1(+) (oval) and CD44(+) (small hepatocytes) cells isolated from GalN-treated rat livers as hepatic stem and progenitor cells, respectively. Cells from dipeptidylpeptidase IV (DPPIV)(+) rat livers were transplanted into DPPIV(-) livers treated with retrorsine following partial hepatectomy. Both stem and progenitor cells could differentiate into hepatocytes in host livers. In addition, the growth of the progenitor cells was faster than that of MHs until days 14. However, their repopulation efficiency in the long term was very low, since the survival period of the progenitor cells was much shorter than that of MHs. Most foci derived from Thy1(+) cells disappeared within 2 months. Many cells expressed senescence-associated β-galactosidase in 33% of CD44-derived foci at day 60, whereas the expression was observed in 13% of MH-derived ones. The short life of the cells may be due to their cellular senescence. On the other hand, the incorporation of sinusoidal endothelial cells into foci and sinusoid formation, which might be correlated to hepatic maturation, was completed faster in MH-derived foci than in CD44-derived ones. The survival of donor cells may have a close relation to not only early integration into hepatic plates but also the differentiated state of the cells at the time of transplantation.

Liver tissue engineering: promises and prospects of new technology

Today, many patients suffer from acute liver failure and hepatoma. This is an area of high unmet clinical need as these conditions are associated with very high mortality. There is an urgent need to develop techniques that will enable liver tissue engineering or generate a bioartificial liver, which will maintain or improve liver function or offer the possibility of liver replacement. Liver tissue engineering is an innovative way of constructing an implantable liver and has the potential to alleviate the shortage of organ donors for orthotopic liver transplantation. In this review we describe, from an engineering perspective, progress in the field of liver tissue engineering, including three main aspects involving cell sources, scaffolds and vascularization.

Hepatic stem cells and liver development

The liver consists of many cell types with specialized functions. Hepatocytes are one of the main players in the organ and therefore are the most vulnerable cells to damage. Since they are not everlasting cells, they need to be replenished throughout life. Although the capacity of hepatocytes to contribute to their own maintenance has long been recognized, recent studies have indicated the presence of both intrahepatic and extrahepatic stem/progenitor cell populations that serve to maintain the normal organ and to regenerate damaged parenchyma in response to a variety of insults.The intrahepatic compartment most likely derives primarily from the biliary tree, particularly the most proximal branches, i.e. the canals of Hering and smallest ductules. The extrahepatic compartment is at least in part derived from diverse populations of cells from the bone marrow. Embryonic stem cells (ES's) are considered as a part of the extrahepatic compartment. Due to their pluripotent capabilities, ES cell-derived cells form a potential future source of hepatocytes, to replace or restore hepatic tissues that have been damaged by disease or injury. Progressing knowledge about stem cells in the liver would allow a better understanding of the mechanisms of hepatic homeostasis and regeneration. Although a human stem cell-derived cell type equivalent to primary hepatocytes does not yet exist, the promising results obtained with extrahepatic stem cells would open the way to cell-based therapy for liver diseases.

Thy1-positive cells have bipotential ability to differentiate into hepatocytes and biliary epithelial cells in galactosamine-induced rat liver regeneration

In galactosamine (GalN)-induced rat liver injury, hepatic stem/progenitor cells, small hepatocytes (SHs) and oval cells, transiently appear in the initial period of liver regeneration. To clarify the relationship between SHs and oval cells, CD44(+) and Thy1(+) cells were sorted from GalN-treated livers and used as candidates for SHs and oval cells, respectively. Some Thy1(+) cells isolated 3 days after GalN-treatment (GalN-D3) formed CD44(+) cell colonies, but those from GalN-D2 could form few. GeneChip (Affymetrix, Inc, Santa Clara, CA) analysis of the sorted cells and cultured Thy1(+) cells suggested that hepatocytic differentiation progressed in the order Thy1(+) (GalN-D3), Thy1(+) cell colony (Thy1-C), and CD44(+) (GalN-D4) cells. When Thy1(+), Thy1-C, and CD44(+) cells were transplanted into retrorsine/PH rat livers, they could proliferate to form hepatocytic foci. At 30 days after transplantation most cells forming the foci derived from CD44(+) cells possessed C/EBPalpha(+) nuclei, whereas only a few cells derived from Thy1-C showed this positivity. When Thy1(+) (GalN-D3) cells were cultured between collagen gels in medium with hepatocyte growth factor(+)/dexamethasone(-)/dimethyl sulfoxide(-), ducts/cysts consisting of biliary epithelial cells appeared, whereas with CD44(+) and Thy1(+) (GalN-D2) cells they did not. Taken together, these results indicate that the commitment of Thy1(+) cells to differentiate into hepatocytes or biliary epithelial cells may occur between Day 2 and Day 3. Furthermore, some Thy1(+) cells may differentiate into hepatocytes via CD44(+) SHs.

Cell source of liver functional reconstruction

Recent years, various new techniques, such as bioartificial liver system, hepatocyte transplantation and tissue engineering, were being employed to fight against the liver diseases. However, the shortage of liver cells has become a prominent problem. This review focuses on the current research progress of the liver cell differentiation source, and it also discusses the advantages and disadvantages of various hepatic stem cells and nonhepatic stem cells, expecting to provide a reference for liver cell source selection during tissue engineering, an adequate and suitable source for bioartificial liver and hepatocyte transplantation and to help to treat liver diseases.

Small human hepatocytes in rotary culture for treatment of alcohol addicts? A pilot study

BACKGROUND

Current approaches to support alcohol addict and/or benzodiazepine-treated patients with liver failure include culturing human cells to take over basic metabolic functions for a certain time.

METHODS

Small human hepatocytes (SH) were grown in a rotary cell culture system, and their potential to metabolize alcohol and the benzodiazepines oxazepam and diazepam was evaluated. Control experiments were performed with SV40-immortalized HEP cells and cell respective drug-free media.

RESULTS

Our results show that SH in rotary culture are able to metabolize ethanol in reasonable amounts compared with evaporation controls (p<0.01). Moreover, SH are also able to metabolize oxazepam and diazepam which proves their ability to perform conjugation and the presence of functional cytochrome P450 enzymes. Basic metabolic activities such as glucose consumption, albumin and urea production are not significantly influenced by the drugs used, which is a precondition for clinical use of these cells. Significantly increased lactate dehydrogenase release indicates enhanced cell death in cultures of SH incubated with either ethanol (p<0.05) or diazepam (p<0.005), but stable viability at or above 90% suggests that cell proliferation is able to keep up with drug-induced cell death.

CONCLUSION

Our preliminary study provides evidence that SH are basically suited to support alcohol-abusing and/or benzodiazepine-treated patients undergoing liver failure.