Isolation of human progenitor liver epithelial cells with extensive replication capacity and differentiation into mature hepatocytes

A Novel Sprague-Dawley Rat Model Presents Improved NASH/NAFLD Symptoms with PEG Coated Vitexin Liposomes

Chronic liver disease (CLD) is a global threat to the human population, with manifestations resulting from alcohol-related liver disease (ALD) and non-alcohol fatty liver disease (NAFLD). NAFLD, if not treated, may progress to non-alcoholic steatohepatitis (NASH). Furthermore, inflammation leads to liver fibrosis, cirrhosis, and hepatocellular carcinoma. Vitexin, a natural flavonoid, has been recently reported for inhibiting NAFLD. It is a lipogenesis inhibitor and activates lipolysis and fatty acid oxidation. In addition, owing to its antioxidant properties, it appeared as a hepatoprotective candidate. However, it exhibits low bioavailability and low efficacy due to its hydrophobic nature. A novel rat model for liver cirrhosis was developed by CCL4/Urethane co-administration. Vitexin encapsulated liposomes were synthesized by the ‘thin-film hydration’ method. Polyethylene glycol (PEG) was coated on liposomes to enhance stability and stealth effect. The diseased rats were then treated with vitexin and PEGylated vitexin liposomes, administered intravenously and orally. Results ascertained the liposomal encapsulation of vitexin and subsequent PEG coating to be a substantial strategy for treating liver cirrhosis through oral drug delivery.

Caffeine disrupts ataxia telangiectasia mutated gene-related pathways and exacerbates acetaminophen toxicity in human fetal immortalized hepatocytes

Preterm infants are at greater risk for adverse drug effects due to hepatic immaturity. Multiple interventions during intensive care increases potential for drug interactions. In this setting, high-dose caffeine used for apnea in premature infants may increase acetaminophen toxicity by inhibiting ataxia telangiectasia mutated (ATM) gene activity during DNA damage response. To define caffeine and acetaminophen interaction, we modeled infantile prematurity in late-gestation fetal stage through human immortalized hepatocytes and liver organoids. The acute toxicity studies included assays for cell viability, mitochondrial dysfunction and ATM pathway-related DNA damage. Fetal cells expressed hepatobiliary properties, albeit with lower metabolic, synthetic and antioxidant functions than more mature hepatocytes. Acetaminophen in IC50 amount of 7.5 millimolar caused significant oxidative stress, mitochondrial membrane potential impairments, and DNA breaks requiring ATM-dependent repair. Caffeine markedly exacerbated acetaminophen toxicity by suppressing ATM activity in otherwise nontoxic 2.5 millimolar amount. Similarly, the specific ATM kinase antagonist, KU-60019, reproduced this deleterious interaction in 5 micromolar amount. Replicative stress from combined acetaminophen and caffeine toxicity depleted cells undergoing DNA synthesis in S phase and activated checkpoints for G0/G1 or G2/M restrictions. Synergistic caffeine and acetaminophen toxicity in liver organoids indicated these consequences should apply in vivo. The antioxidant, N-acetylcysteine, decreased oxidative damage, mitochondrial dysfunction and ATM pathway disruption to mitigate caffeine and acetaminophen toxicity. We concluded that hepatic DNA damage, mitochondrial impairment and growth-arrest after combined caffeine and acetaminophen toxicity will be harmful for premature infants. Whether caffeine and acetaminophen toxicity may alter outcomes in subsequently encountered hepatic disease needs consideration.

Hepatic progenitors of the fetal liver: Interactions with hematopoietic stem cells

The aim of this review is to summarize and give an overview on the findings of signaling between hepatic and hematopoietic progenitors of the liver. To date, there are not many findings published in the field, and the aim of this review is to cover all current publications in this area. The liver is the main site of hematopoiesis during fetal development. However, little is known about how hepatic and other non-hematopoietic progenitors potentially influence hematopoiesis and vice versa. The concurrent peaks of hepatic and hematopoietic progenitor proliferation during development indicate interactions that could possibly be mediated through cell-cell contact, extracellular matrices, cytokines and growth factors, or other signaling molecules. For example, hepatic progenitors, such as hepatic stem cells and hepatoblasts, possess characteristic surface markers that can be cleaved, giving rise to fragments of various lengths. A surface molecule of hepatoblasts has been demonstrated to play an essential role in hematopoiesis. Particularly, these effects on hematopoiesis were distinct, depending on whether it was membrane-bound or cleaved. In this review, the various hepatic and hematopoietic progenitor cell types are concisely described, and the current findings of their potential interactions are summarized.

Hepatic differentiation of human pluripotent stem cells by developmental stage-related metabolomics products

Endogenous cell signals regulate tissue homeostasis and are significant for directing the fate of stem cells. During liver development, cytokines released from various cell types are critical for stem/progenitor cell differentiation and lineage expansions. To determine mechanisms in these stage-specific lineage interactions, we modeled potential effects of soluble signals derived from immortalized human fetal liver parenchymal cells on stem cells, including embryonic and induced pluripotent stem cells. For identifying lineage conversion and maturation, we utilized conventional assays of cell morphology, gene expression analysis and lineage markers. Molecular pathway analysis used functional genomics approaches. Metabolic properties were analyzed to determine the extent of hepatic differentiation. Cell transplantation studies were performed in mice with drug-induced acute liver failure to elicit benefits in hepatic support and tissue regeneration. These studies showed signals emanating from fetal liver cells induced hepatic differentiation in stem cells. Gene expression profiling and comparison of regulatory networks in immature and mature hepatocytes revealed stem cell-derived hepatocytes represented early fetal-like stage. Unexpectedly, differentiation-inducing soluble signals constituted metabolomics products and not proteins. In stem cells exposed to signals from fetal cells, mechanistic gene networks of upstream regulators decreased pluripotency, while simultaneously inducing mesenchymal and epithelial properties. The extent of metabolic and synthetic functions in stem cell-derived hepatocytes was sufficient for providing hepatic support along with promotion of tissue repair to rescue mice in acute liver failure. During this rescue, paracrine factors from transplanted cells contributed in stimulating liver regeneration. We concluded that hepatic differentiation of pluripotent stem cells with metabolomics products will be significant for developing therapies. The differentiation mechanisms involving metabolomics products could have an impact on advancing recruitment of stem/progenitor cells during tissue homeostasis.

Differentiation in stem/progenitor cells along fetal or adult hepatic stages requires transcriptional regulators independently of oscillations in microRNA expression

Understanding mechanisms in lineage differentiation is critical for organ development, pathophysiology and oncogenesis. To determine whether microRNAs (miRNA) may serve as drivers or adjuncts in hepatic differentiation, we studied human embryonic stem cell-derived hepatocytes and primary hepatocytes representing fetal or adult stages. Model systems were used for hepatic lineage advancement or regression under culture conditions with molecular assays. Profiles of miRNA in primary fetal and adult hepatocytes shared similarities and distinctions from pluripotent stem cells or stem cell-derived early fetal-like hepatocytes. During phenotypic regression in fetal or adult hepatocytes, miRNA profiles oscillated to regain stemness-associated features that had not been extinguished in stem cell-derived fetal-like hepatocytes. These oscillations in stemness-associated features were not altered in fetal-like hepatocytes by inhibitory mimics for dominantly-expressed miRNA, such as hsa-miR-99b, -100, -214 and -221/222. The stem cell-derived fetal-like hepatocytes were permissive for miRNA characterizing mature hepatocytes, including mimics for hsa-miR-122, -126, -192, -194 and -26b, although transfections of the latter did not advance hepatic differentiation. Examination of genome-wide mRNA expression profiles in stem cell-derived or primary fetal hepatocytes indicated targets of highly abundant miRNA regulated general processes, e.g., cell survival, growth and proliferation, functional maintenance, etc., without directing cell differentiation. Among upstream regulators of gene networks in stem cell-derived hepatocytes included HNF4A, SNAI1, and others, which affect transcriptional circuits directing lineage development or maintenance. Therefore, miRNA expression oscillated in response to microenvironmental conditions, whereas lineage-specific transcriptional regulators, such as HNF4A, were necessary for directing hepatic differentiation. This knowledge will be helpful for understanding the contribution of stem cells in pathophysiological states and oncogenesis, as well as for applications of stem cell-derived hepatocytes.

Immortalized common marmoset (Callithrix jacchus) hepatic progenitor cells possess bipotentiality in vitro and in vivo

Common marmoset (Callithrix jacchus) is emerging as a clinically relevant nonhuman primate model for various diseases, but is hindered by the availability of marmoset cell lines, which are critical for understanding the disease pathogenesis and drug/toxicological screening prior to animal testing. Here we describe the generation of immortalized marmoset hepatic progenitor cells (MHPCs) by lentivirus-mediated transfer of the simian virus 40 large T antigen gene in fetal liver polygonal cells. MHPCs proliferate indefinitely in vitro without chromosomal alteration and telomere shortening. These cells possess hepatic progenitor cell-specific gene expression profiles with potential to differentiate into both hepatocytic and cholangiocytic lineages in vitro and in vivo and also can be genetically modified. Importantly, injected MHPCs repopulated the injured liver of fumarylacetoacetate hydrolase (Fah)-deficient mice with hepatocyte-like cells. MHPCs also engraft as cholangiocytes into bile ducts of 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC)-induced bile ductular injured mice. MHPCs provide a tool to enable efficient derivation and genetic modification of both hepatocytes and cholangiocytes for use in disease modeling, tissue engineering, and drug screening.

In Vitro Functionality of Human Fetal Liver Cells and Clonal Derivatives under Proliferative Conditions

Mature human hepatocytes are not suitable for large-scale in vitro applications that rely on hepatocyte function, due to their limited availability and insufficient proliferation capacity in vitro. In contrast, human fetal liver cells (HFLC) can be easily expanded in vitro. In this study we evaluated the hepatic function of HFLCs under proliferative conditions, to determine whether HFLCs can replace mature hepatocytes for in vitro applications. HFLCs were isolated from fetal livers of 16 weeks gestation. Hepatic functions of HFLCs were determined in primary culture and after expansion in vitro. Clonal derivatives were selected and tested for hepatic functionality. Results were compared to primary mature human hepatocytes in vitro. No differences were observed between primary HFLCs and mature human hepatocytes in albumin production and mRNA levels of various liver-specific genes. Ureagenesis was 4.4-fold lower and ammonia elimination was absent in HFLCs. Expanding HFLCs decreased hepatic functions and increased cell stretching. In contrast, clonal derivatives had stable functionality and morphology and responded to differentiation stimuli. Although their hepatic functions were higher than in passaged HFLCs, functionality was at least 20 times lower compared to mature human hepatocytes. HFLCs cannot replace mature human hepatocytes in in vitro applications requiring extensive in vitro expansion, because this is associated with decreased hepatic functionality. Selecting functional subpopulations can, at least partly, prevent this. In addition, defining conditions that support hepatic differentiation is necessary to obtain HFLC cultures suitable for in vitro hepatic applications.

Cryopreserved Fetal Liver Cell Transplants Support the Chronic Failing Liver in Rats with CCl4-Induced Cirrhosis

Hepatocyte transplantation is a promising method for supporting hepatic function in a broad spectrum of liver diseases. The aim of this work was to test the efficacy of human fetal liver cells to support the chronic failing liver in an experimental model of carbon tetrachloride (CCl4)-induced cirrhosis in rats. Liver cirrhosis was induced by intraperitoneal administration of CCl4 at a dose of 0.2 ml (50% v/v solution)/100 g body weight, twice a week for 3 months in rats. Ten days after stopping CCl4 administration (experimental day 0), rats received intrasplenic injection of cryopreserved fetal liver cells (FLC, 1 × 107 cells in 0.3 ml medium). As a cirrhotic control group, CCl4-induced cirrhotic rats were used with intrasplenic injection of an equal volume of medium alone. Animals were sacrificed on experimental day 15. Human fetal liver cell transplantation almost completely prevented the death of cirrhotic animals during the 2 weeks after treatment, while high ongoing mortality was seen in the cirrhotic control group. Cell transplantation into the spleen normalized total bilirubin and TBARSs levels and increased albumin levels in blood serum, as well as restoring mitochondrial function and liver detoxification function (assessed by cytochrome P450 contents and activity) compared with the activities seen in the cirrhosis control group. In parallel with this restoration of biochemical and functional liver indices, morphological patterns of liver recovery or regeneration after liver cell transplantation were demonstrated in day 15 samples by light microscopy. These were absent in the group that had received only medium alone.

A 3-D cell culture system to study epithelia functions using microcarriers

In vitro cell culture models used to study epithelia and epithelial diseases would benefit from the recognition that organs and tissues function in a three-dimensional (3D) environment. This context is necessary for the development of cultures that more realistically resemble in vivo tissues/organs. Our aim was to establish and characterize biologically meaningful 3D models of epithelium. We engineered 3D epithelia cultures using a kidney epithelia cell line (MDCK) and spherical polymer scaffolds. These kidney epithelia were characterized by live microscopy, immunohistochemistry and transmission electron microscopy. Strikingly, the epithelial cells displayed increased physiological relevance; they were extensively polarized and developed a more differentiated phenotype. Using such a growth system allows for direct transmission and fluorescence imaging with few restrictions using wide-field, confocal and Light Sheet Fluorescence Microscopy. We also assessed the wider relevance of this 3D culturing technique with several epithelial cell lines. Finally, we established that these 3D micro-tissues can be used for infection as well as biochemical assays and to study important cellular processes such as epithelial mesenchymal transmission. This new biomimetic model could provide a broadly applicable 3D culture system to study epithelia and epithelia related disorders.

Total Parenteral Nutrition-Induced Cholestasis: Prevention and Management

When cholestasis occurs in patients receiving total parenteral nutrition, it is the result of many pathogenic pathways converging on the hepatic acinus. The result may be a temporary rise in liver function tests. The resulting fibrosis, portal hypertension, and jaundice are hallmarks of type 3 intestinal-associated liver disease to which children are more susceptible than adults. The key to prevention is in identifying high-risk scenarios, meticulous monitoring, and personalized prescription of parenteral nutrition solutions combined with an active approach in reducing the impact of inflammatory events when they occur by prompt use of antibiotics and line locks.

Transplantation of hESC-derived hepatocytes protects mice from liver injury

Background

Hepatic cell therapy has become a viable alternative to liver transplantation for life-threatening liver diseases. However, the supply of human hepatocytes is limited due to the shortage of suitable donor organs required to isolate high-quality cells. Human pluripotent stem cells reflect a potential renewable source for generating functional hepatocytes. However, most differentiation protocols use undefined matrices or factors of animal origin; as such, the resulting hepatocytes are not Good Manufacturing Practice compliant. Moreover, the preclinical studies employed to assess safety and function of human embryonic stem cell (hESC)-derived hepatocytes are generally limited to immunodeficient mice. In the present study, we evaluate the generation of hepatocytes under defined conditions using a European hESC line (VAL9) which was derived under animal-free conditions. The function capacity of VAL9-derived hepatocytes was assessed by transplantation into mice with acetaminophen-induced acute liver failure, a clinically relevant model.

Methods

We developed a protocol that successfully differentiates hESCs into bipotent hepatic progenitors under defined conditions, without the use of chromatin modifiers such as dimethyl sulphoxide. These progenitors can be cryopreserved and are able to generate both committed precursors of cholangiocytes and neonate-like hepatocytes.

Results

Thirty days post-differentiation, hESCs expressed hepatocyte-specific markers such as asialoglycoprotein receptor and hepatic nuclear factors including HNF4α. The cells exhibited properties of mature hepatocytes such as urea secretion and UGT1A1 and cytochrome P450 activities. When transplanted into mice with acetaminophen-induced acute liver failure, a model of liver damage, the VAL9-derived hepatocytes efficiently engrafted and proliferated, repopulating up to 10 % of the liver. In these transplanted livers, we observed a significant decrease of liver transaminases and found no evidence of tumourigenicity. Thus, VAL9-derived hepatocytes were able to rescue hepatic function in acetaminophen-treated animals.

Conclusions

Our study reveals an efficient protocol for differentiating VAL9 hESCs to neonatal hepatocytes which are then able to repopulate livers in vivo without tumour induction. The human hepatocytes are able to rescue liver function in mice with acetaminophen-induced acute toxicity. These results provide proof-of-concept that replacement therapies using hESC-derived hepatocytes are effective for treating liver diseases.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-015-0227-6) contains supplementary material, which is available to authorized users.

Characterization of lipid metabolism in a novel immortalized human hepatocyte cell line

The development of hepatocyte cell models that represent fatty acid partitioning within the human liver would be beneficial for the study of the development and progression of nonalcoholic fatty liver disease (NAFLD). We sought to develop and characterize a novel human liver cell line (LIV0APOLY) to establish a model of lipid accumulation using a physiological mixture of fatty acids under low- and high-glucose conditions. LIV0APOLY cells were compared with a well-established cell line (HepG2) and, where possible, primary human hepatocytes. LIV0APOLY cells were found to proliferate and express some mature liver markers and were wild type for the PNPLA3 (rs738409) gene, whereas HepG2 cells carried the Ile(148)Met variant that is positively associated with liver fat content. Intracellular triglyceride content was higher in HepG2 than in LIV0APOLY cells; exposure to high glucose and/or exogenous fatty acids increased intracellular triglyceride in both cell lines. Triglyceride concentrations in media were higher from LIV0APOLY compared with HepG2 cells. Culturing LIV0APOLY cells in high glucose increased a marker of endoplasmic reticulum stress and attenuated insulin-stimulated Akt phosphorylation whereas low glucose and exogenous fatty acids increased AMPK phosphorylation. Although LIV0APOLY cells and primary hepatocytes stored similar amounts of exogenous fatty acids as triglyceride, more exogenous fatty acids were partitioned toward oxidation in the LIV0APOLY cells than in primary hepatocytes. LIV0APOLY cells offer the potential to be a renewable cellular model for studying the effects of exogenous metabolic substrates on fatty acid partitioning; however, their usefulness as a model of lipoprotein metabolism needs to be further explored.

A Convenient and Efficient Method to Enrich and Maintain Highly Proliferative Human Fetal Liver Stem Cells

Pluripotent human hepatic stem cells have broad research and clinical applications, which are, however, restricted by both limited resources and technical difficulties with respect to isolation of stem cells from the adult or fetal liver. In this study, we developed a convenient and efficient method involving a two-step in situ collagenase perfusion, gravity sedimentation, and Percoll density gradient centrifugation to enrich and maintain highly proliferative human fetal liver stem cells (hFLSCs). Using this method, the isolated hFLSCs entered into the exponential growth phase within 10 days and maintained sufficient proliferative activity to permit subculture for at least 20 passages without differentiation. Immunocytochemistry, immunofluorescence, and flow cytometry results showed that these cells expressed stem cell markers, such as c-kit, CD44, epithelial cell adhesion molecule (EpCAM), oval cell marker-6 (OV-6), epithelial marker cytokeratin 18 (CK18), biliary ductal marker CK19, and alpha-fetoprotein (AFP). Gene expression analysis showed that these cells had stable mRNA expression of c-Kit, EpCAM, neural cell adhesion molecule (NCAM), CK19, CK18, AFP, and claudin 3 (CLDN-3) throughout each passage while maintaining low levels of ALB, but with complete absence of cytochrome P450 3A4 (C3A4), phosphoenolpyruvate carboxykinase (PEPCK), telomeric repeat binding factor (TRF), and connexin 26 (CX26) expression. When grown in appropriate medium, these isolated liver stem cells could differentiate into hepatocytes, cholangiocytes, osteoblasts, adipocytes, or endothelial cells. Thus, we have demonstrated a more economical and efficient method to isolate hFLSCs than magnetic-activated cell sorting (MACS). This novel approach may provide an excellent tool to isolate highly proliferative hFLSCs for tissue engineering and regenerative therapies.

BMP-4 induced proliferation and oriented differentiation of rat hepatic oval cells into hepatocytes

OBJECTIVE

To explore the role of bone morphogenetic protein 4 (BMP-4) in hepatic progenitor cells (HPCs).

METHODS

The effect of BMP-4 on rat hepatic oval cells was examined by using the WB-F344 rat hepatocytic epithelial stem-cell-like cell line. This hepatocytic cell line could exert various hepatocyte functions including the secretion of albumin and urea. Immunohistochemistry was used to examine the effects of BMP-4 and its antagonist, Noggin, on the proliferation and differentiation of these cells, cellular uptake and excretion of indocyanine green, the periodic acid-schiff (PAS) assay for glycogen storage and the expression of hepatic markers.

RESULTS

Our results showed for the first time that BMP-4 may acted as a potential inducer of hepatic differentiation in rat hepatic oval cells.

CONCLUSIONS

This cell source offers a much-needed attractive and expandable source for future investigations of drug screening, stem cell technologies and cellular transplantation, in a society with increasing levels of liver disease and damage.

Mesenchymal stem cells from the human umbilical cord ameliorate fulminant hepatic failure and increase survival in mice

BACKGROUND

Cell therapy has been promising for various diseases. We investigated whether transplantation of human umbilical cord mesenchymal stem cells (hUCMSCs) has any therapeutic effects on D-galactosamine/lipopolysaccharide (GalN/LPS)-induced fulminant hepatic failure in mice.

METHODS

hUCMSCs isolated from human umbilical cord were cultured and transplanted via the tail vein into severe combined immune deficiency mice with GalN/LPS-induced fulminant hepatic failure. After transplantation, the localization and differentiation of hUCMSCs in the injured livers were investigated by immunohistochemical and genetic analyses. The recovery of the injured livers was evaluated histologically. The survival rate of experimental animals was analyzed by the Kaplan-Meier method and log-rank test.

RESULTS

hUCMSCs expressed high levels of CD29, CD73, CD13, CD105 and CD90, but did not express CD31, CD79b, CD133, CD34, and CD45. Cultured hUCMSCs displayed adipogenic and osteogenic differentiation potential. Hematoxylin and eosin staining revealed that transplantation of hUCMSCs reduced hepatic necrosis and promoted liver regeneration. Transplantation of hUCMSCs prolonged the survival rate of mice with fulminant hepatic failure. Polymerase chain reaction for human alu sequences showed the presence of human cells in mouse livers. Positive staining for human albumin, human alpha-fetoprotein and human cytokeratin 18 suggested the formation of hUCMSCs-derived hepatocyte-like cells in vivo.

CONCLUSIONS

hUCMSC was a potential candidate for stem cell based therapies. After transplantation, hUCMSCs partially repaired hepatic damage induced by GalN/LPS in mice. hUCMSCs engrafted into the injured liver and differentiated into hepatocyte-like cells.

Adipose tissue-derived mesenchymal stem cells differentiated into hepatocyte-like cells in vivo and in vitro

Cell-based therapy is a potential alternative to liver transplantation. The goal of the present study was to examine the in vivo and in vitro hepatic differentiation potential of adipose tissue-derived mesenchymal stem cells (AT-MSCs) and to explore its therapeutic use. AT-MSCs were isolated and cultured with hepatic differentiation medium. Bioactivity assays were used to study the properties of AT-MSCs. The morphology of differentiated AT-MSCs in serum-free hepatic differentiation medium changed into polygonal epithelial cells, while the morphology of AT-MSCs in a similar medium containing 2% fetal bovine serum remained unchanged. The differentiated cells cultured without serum showed hepatocyte-like cell morphology and hepatocyte-specific markers, including albumin (ALB) and α-fetoprotein. The bioactivity assays revealed that hepatocyte-like cells could take up low-density lipoprotein (LDL) and store glycogen. Furthermore, trichostatin A (TSA) enhanced ALB production and LDL uptake by the hepatocyte-like cells, analogous to the functions of human liver cells. ALB was detected in the livers of the CCl₄-injured mice one month post-transplantation. This suggested that transplantation of the human AT-MSCs could relieve the impairment of acute CCl₄-injured livers in nude mice. This therefore implied that adipose tissue was a source of multipotent stem cells which had the potential to differentiate into mature, transplantable hepatocyte-like cells in vivo and in vitro. In addition, the present study determined that TSA was essential to promoting differentiation of human MSC towards functional hepatocyte-like cells. The relief of liver injury following treatment with AT-MSCs suggested their potential as a novel therapeutic method for liver disorders or injury.

Immortalization of Human Fetal Hepatocyte by Ectopic Expression of Human Telomerase Reverse Transcriptase, Human Papilloma Virus (E7) and Simian Virus 40 Large T (SV40 T) Antigen Towards Bioartificial Liver Support

BACKGROUND

Generation of genetically stable and non-tumoric immortalization cell line from primary cells would be enormously useful for research and therapeutic purposes, but progress towards this goal has so far been limited. It is now universal acceptance that immortalization of human fetal hepatocytes based on recent advances of telomerase biology and oncogene, lead to unlimited population doubling could be the possible source for bioartificial liver device.

METHODS

Immortalization of human fetal hepatocytes cell line by ectopic expression of human telomerase reverse transcriptase (hTERT), human papilloma virus gene (E7) and simian virus 40 large T (SV40 T) antigens is main goal of present study. We used an inducible system containing human telomerase and E7, both of which are cloned into responder constructs controlled by doxycycline transactivator. We characterized the immortalized human fetal hepatocyte cells by analysis of green fluorescent cells (GFP) positive cells using flow cytometry (FACs) cell sorting and morphology, proliferative rate and antigen expression by immunohistochemical analysis. In addition to we analysized lactate formation, glucose consumption, albumin secretion and urea production of immortalized human fetal hepatocyte cells.

RESULTS

After 25 attempts for transfection of adult primary hepatocytes by human telomerase and E7 to immortalize them, none of the transfection systems resulted in the production of a stable, proliferating cell line. Although the transfection efficiency was more than 70% on the first day, the vast majority of the transfected hepatocytes lost their signal within the first 5-7 days. The remaining transfected hepatocytes persisted for 2-4 weeks and divided one or two times without forming a clone. After 10 attempts of transfection human fetal hepatocytes using the same transfection system, we obtained one stable human fetal hepatocytes cell line which was able albumin secretion urea production and glucose consumption.

CONCLUSION

We established a conditional human fetal hepatocytes cell line with mesenchymal characteristics. Thus immortalization of human fetal hepatocytes cell line by telomerase biology offers a great challenge to examine basic biological mechanisms which are directly related to human and best cell source having unlimited population doubling for bioartificial support without any risk of replicative senescence and pathogenic risks.

Revival, characterization, and hepatitis B virus infection of cryopreserved human fetal hepatocytes

Primary human hepatocytes are considered the ideal cellular model for in-vitro studies of liver-specific pathology, such as hepatitis B virus (HBV) infection. However, poor accessibility, limited cell numbers, and lot-to-lot variation of primary human hepatocytes limit their broad application. Human fetal hepatocytes were isolated from postmortem embryonic liver tissues by two-step collagenase perfusion and cryopreserved. A monolayer of cryopreserved human fetal hepatocytes was established by optimizing such conditions as cell density and viability and purification of viable cells by Percoll. Finally, revived human fetal hepatocytes were characterized and infected with HBV. A large number of viable human fetal hepatocytes could be isolated and cryopreserved, with seeding density and viability being critical for the establishment of a compact monolayer culture. Using low-viability cryopreserved human fetal hepatocytes, a typical monolayer was established by purification with Percoll. The revived cells were actively proliferative, showed identical morphologic characteristics to non-cryopreserved cells, and had a typical hepatic gene expression profile. Moreover, this optimized model was susceptible to HBV infection and could be used to screen entry inhibitors against HBV infection. In conclusion, these methods can be used on human fetal hepatocytes to provide a cell bank for studies of the early stages of HBV infection.

Human fetal hepatic progenitor cells are distinct from, but closely related to, hematopoietic stem/progenitor cells

Much controversy surrounds the identity and origin of human hepatic stem and progenitor cells in part because of a lack of small animal models in which the developmental potential of isolated candidate cell populations can be functionally evaluated. We show here that adoptive transfer of CD34(+) cells from human fetal liver into sublethally irradiated NOD-SCID Il2rg(-/-) (NSG) mice leads to an efficient development of not only human hematopoietic cells but also human hepatocyte-like cells in the liver of the recipient mice. Using this simple in vivo assay in combination with cell fractionation, we show that CD34(+) fetal liver cells can be separated into three distinct subpopulations: CD34(hi) CD133(hi), CD34(lo) CD133(lo), and CD34(hi) CD133(neg). The CD34(hi) CD133(hi) population contains hematopoietic stem/progenitor cells (HSPCs) as they give rise to T cells, B cells, NK cells, dendritic cells, and monocytes/macrophages in NSG mice and colony-forming unit (CFU)-GEMM cells in vitro. The CD34(lo) CD133(lo) population does not give rise to hematopoietic cells, but reproducibly generates hepatocyte-like cells in NSG mice and in vitro. The CD34(hi) CD133(neg) population only gives rise to CFU-GM and burst-forming unit-erythroid in vitro. Furthermore, we show that the CD34(lo) CD133(lo) cells express hematopoietic, hepatic, and mesenchymal markers, including CD34, CD133, CD117, epithelial cell adhesion molecule, CD73, albumin, α-fetal protein, and vimentin and transcriptionally are more closely related to HSPCs than to mature hepatocytes. These results show that CD34(lo) CD133(lo) fetal liver cells possess the hepatic progenitor cell properties and that human hepatic and hematopoietic progenitor cells are distinct, although they may originate from the same precursors in the fetal liver.

Long-term maintenance of human fetal hepatocytes and prolonged susceptibility to HBV infection by co-culture with non-parenchymal cells

Within a few days of being isolated, primary human hepatocytes undergo a rapid dedifferentiation process and lose susceptibility to hepatitis B virus (HBV) infection in vitro. This fact has limited their further application. In this study, a convenient and feasible method of preventing this dedifferentiation was established, by co-culturing human fetal hepatocytes with hepatic non-parenchymal cells to maintain the differentiation features of human fetal hepatocytes. Isolated hepatic cells were seeded at a low density, and cultured in dimethyl sulfoxide-free medium for a month to allow rapid proliferation of non-parenchymal cells. Subsequently, 2% dimethyl sulfoxide was added to induce formation of typical hepatic islands, in which hepatocytic features could be further maintained for up to an additional 3 months. These hepatic islands, formed of piled-up hepatocytes, were surrounded and invaded by non-parenchymal cells. Protein expression profiles showed that the human fetal hepatocytes underwent a rapid maturation process, and the hepatocytic features were well preserved. Most importantly, these human fetal hepatocytes still exhibited susceptibility to HBV infection after long-term maintenance, for as long as 10 weeks. This co-culture method has overcome the pre-existing disadvantages of primary human hepatocytes for virological studies, and provides a valuable approach to long-term maintenance of primary human hepatocytes for studies of HBV infection for prolonged periods.

Fn14•TRAIL effectively inhibits hepatocellular carcinoma growth

Background

New strategies for the treatment of hepatocellular carcinoma (HCC) are needed, given that currently available chemotherapeutics are inefficient. Since tumor growth reflects the net balance between pro-proliferative and death signaling, agents shifting the equilibrium toward the latter are of considerable interest. The TWEAK:Fn14 signaling axis promotes tumor cell proliferation and tumor angiogenesis, while TRAIL:TRAIL-receptor (TRAIL-R) interactions selectively induce apoptosis in malignant cells. Fn14•TRAIL, a fusion protein bridging these two pathways, has the potential to inhibit tumor growth, by interfering with TWEAK:Fn14 signaling, while at the same time enforcing TRAIL:TRAIL-R-mediated apoptosis. Consequently, Fn14•TRAIL's capacity to inhibit HCC growth was tested.

Results

Fn14•TRAIL induced robust apoptosis of multiple HCC cell lines, while sparing non-malignant hepatocyte cell lines. Differential susceptibility to this agent did not correlate with expression levels of TRAIL, TRAIL-R, TWEAK and Fn14 by these lines. Fn14•TRAIL was more potent than soluble TRAIL, soluble Fn14, or a combination of the two. The requirement of both of Fn14•TRAIL's molecular domains for function was established using blocking antibodies directed against each of them. Subcutaneous injection of Fn14•TRAIL abrogated HCC growth in a xenograft model, and was well tolerated by the mice.

Conclusions

In this study, Fn14•TRAIL, a multifunctional fusion protein originally designed to treat autoimmunity, was shown to inhibit the growth of HCC, both invitro and invivo. The demonstration of this fusion protein’s potent anti-tumor activity suggests that simultaneous targeting of two signaling axes by a single fusion can serve as a basis for highly effective anti-cancer therapies.

Human Liver Progenitor Cells for Liver Repair

Because of their high proliferative capacity, resistance to cryopreservation, and ability to differentiate into hepatocyte-like cells, stem and progenitor cells have recently emerged as attractive cell sources for liver cell therapy, a technique used as an alternative to orthotopic liver transplantation in the treatment of various hepatic ailments ranging from metabolic disorders to end-stage liver disease. Although stem and progenitor cells have been isolated from various tissues, obtaining them from the liver could be an advantage for the treatment of hepatic disorders. However, the techniques available to isolate these stem/progenitor cells are numerous and give rise to cell populations with different morphological and functional characteristics. In addition, there is currently no established consensus on the tests that need to be performed to ensure the quality and safety of these cells when used clinically. The purpose of this review is to describe the different types of liver stem/progenitor cells currently reported in the literature, discuss their suitability and limitations in terms of clinical applications, and examine how the culture and transplantation techniques can potentially be improved to achieve a better clinical outcome.

Liver tissue engineering and cell sources: issues and challenges

Liver diseases are of major concern as they now account for millions of deaths annually. As a result of the increased incidence of liver disease, many patients die on the transplant waiting list, before a donor organ becomes available. To meet the huge demand for donor liver, alternative approaches using liver tissue engineering principles are being actively pursued. Even though adult hepatocytes, the primary cells of the liver are most preferred for tissue engineering of liver, their limited availability, isolation from diseased organs, lack of in vitro propagation and deterioration of function acts as a major drawback to their use. Various approaches have been taken to prevent the functional deterioration of hepatocytes including the provision of an adequate extracellular matrix and co-culture with non-parenchymal cells of liver. Great progress has also been made to differentiate human stem cells to hepatocytes and to use them for liver tissue engineering applications. This review provides an overview of recent challenges, issues and cell sources with regard to liver tissue engineering.

Advances in cell sources of hepatocytes for bioartificial liver

BACKGROUND

Orthotopic liver transplantation (OLT) is the most effective therapy for liver failure. However, OLT is severely limited by the shortage of liver donors. Bioartificial liver (BAL) shows great potential as an alternative therapy for liver failure. In recent years, progress has been made in BAL regarding genetically engineered cell lines, immortalized human hepatocytes, methods for preserving the phenotype of primary human hepatocytes, and other functional hepatocytes derived from stem cells.

DATA SOURCES

A systematic search of PubMed and ISI Web of Science was performed to identify relevant studies in English language literature using the key words such as liver failure, bioartificial liver, hepatocyte, stem cells, differentiation, and immortalization. More than 200 articles related to the cell sources of hepatocyte in BAL were systematically reviewed.

RESULTS

Methods for preserving the phenotype of primary human hepatocytes have been successfully developed. Many genetically engineered cell lines and immortalized human hepatocytes have also been established. Among these cell lines, the incorporation of BAL with GS-HepG2 cells or alginate-encapsulated HepG2 cells could prolong the survival time and improve pathophysiological parameters in an animal model of liver failure. The cBAL111 cells were evaluated using the AMC-BAL bioreactor, which could eliminate ammonia and lidocaine, and produce albumin. Importantly, BAL loading with HepLi-4 cells could significantly improve the blood biochemical parameters, and prolong the survival time in pigs with liver failure. Other functional hepatocytes differentiated from stem cells, such as human liver progenitor cells, have been successfully achieved.

CONCLUSIONS

Aside from genetically modified liver cell lines and immortalized human hepatocytes, other functional hepatocytes derived from stem cells show great potential as cell sources for BAL. BAL with safe and effective liver cells may be achieved for clinical liver failure in the near future.

Implication of hepatic stem cells in functional liver repopulation

The liver has an enormous potential to restore the parenchymal tissue loss due to injury. This is accomplished by the proliferation of either the hepatocytes or liver progenitor cells in cases where massive damage prohibits hepatocytes from entering the proliferative response. Under debate is still whether hepatic stem cells are involved in liver tissue maintenance and regeneration or even whether they exist at all. The definition of an adult tissue-resident stem cell comprises basic functional stem cell criteria like the potential of self-renewal, multipotent, i.e. at least bipotent differentiation capacity and serial transplantability featuring the ability of functional tissue repopulation. The relationship between a progenitor and its progeny should exemplify the lineage commitment from the putative stem cell to the differentiated cell. This is mainly assessed by lineage tracing and immunohistochemical identification of markers specific to progenitors and their descendants. Flow cytometry approaches revealed that the liver stem cell population in animals is likely to be heterogeneous giving rise to progeny with different molecular signatures, depending on the stimulus to activate the putative stem cell compartment. The stem cell criteria are met by a variety of cells identified in the fetal and adult liver both under normal and injury conditions. It is the purpose of this review to verify hepatic stem cell candidates in the light of the stem cell definition criteria mentioned. Also from this point of view adult stem cells from non-hepatic tissues such as bone marrow, umbilical cord blood or adipose tissue, have the potential to differentiate into cells featuring functional hepatocyte characteristics. This has great impact because it opens the possibility of generating hepatocyte-like cells from adult stem cells in a sufficient amount and quality for their therapeutical application to treat end-stage liver diseases by stem cell-based hepatocytes in place of whole organ transplantation.

Attenuation of Acetaminophen-Induced Hepatotoxicity In Vivo and In Vitro by a 43-kD Protein Isolated from the Herb Cajanus indicus L

ABSTRACT The aim of this study was to evaluate the hepatoprotective role of a 43-kD protein (Hp-P) isolated from the leaves of Cajanus indicus L. against acetaminophen (APAP)-induced toxicity in mouse liver and in isolated hepatocytes. The hepatotoxicity of APAP and the hepatoprotective activity of Hp-P in vivo were determined by measuring the liver-specific serum marker enzymes alanine amino transferase (ALT) and alkaline phosphatase (ALP) in murine sera and observing the histological changes in the mice liver treated with the protein before and after (2 mg/kg body weight for 5 days) APAP (at a dose of 300 mg/kg body weight for 2 days) administration. The cell viability, LDH leakage, GSH level, and lipid peroxidation were measured in isolated hepatocytes to evaluate the cytotoxic effect of APAP and the protective role of Hp-P in vitro. Experimental results showed that APAP induced hepatotoxicity in vivo as revealed from the changes in serum-specific marker enzyme levels and histology of liver. It also induced cytotoxicity in hepatocytes as observed from the changes in cell viability and LDH leakage. Pretreatment with Hp-P prevented the APAP-induced elevation of ALT and ALP in murine sera. In addition, posttreatment with Hp-P significantly altered most of the changes induced by APAP. Although some natural recovery has been observed in toxin controls, the Hp-P-induced recovering process is more rapid than the natural ones. In histological studies, less centrilobular necrosis was found in the liver treated with Hp-P before and after APAP intoxication compared to the liver treated with APAP alone. Radical scavenging experiment showed that Hp-P scavenges DPPH radicals directly. Studies also showed that APAP-induced reduced cell viability and cellular LDH leakage could be prevented by the combinatorial effect of Hp-P. Besides, treatment of hepatocytes with Hp-P and APAP together maintained the normal GSH level. APAP-induced enhanced lipid peroxidation was also decreased when cells were treated with APAP and Hp-P together. Hp-P alone, on the other hand, did not induce any alterations of the studied parameters. Results of this study have been compared with a known antioxidant, alpha-tocopherol. Data from both the in vivo (before and after APAP administration) and in vitro studies suggest that Hp-P has potent hepato- and cytoprotective properties against APAP-induced toxicity.

Protein Isolate from the Herb Phyllanthus niruri Modulates Carbon Tetrachloride-Induced Cytotoxicity in Hepatocytes

ABSTRACT Phyllanthus niruri is a well-known hepatoprotective herbal plant. In the present study, hepatoprotective potential of the protein isolate of P. niruri was investigated against carbon tetrachloride (CCl(4))-induced hepatoxicity in vitro. Isolated hepatocytes were treated with CCl(4) and also separately with various concentrations of the protein isolate of P. niruri along with CCl(4). Levels of different marker enzymes related to hepatic integrity and different antioxidant enzymes as well as lipid peroxidation products in hepatocytes were measured in normal, control (toxicity induced), and protein isolate-treated cells. Administration of CCl(4) increased the leakage of glutamate pyruvate transaminase (GPT) by four fold and lactate dehydrogenase (LDH) by 84% in cell suspension, along with increased lipid peroxidation (114%), and reduced the levels of antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT) to almost 30% and 37% of the normal values, respectively. Treatment with the protein isolate of P. niruri significantly altered these changes. GPT value almost came down to normal levels and LDH value was reduced to 32% of normal values. Depletion of SOD and CAT activities were restored significantly to 75% and 87% of normal values, respectively. Lipid peroxidation was also reduced significantly. In the DPPH free radical scavenging activity, the protein isolate was also able to quench the free radical. Results suggest that the protein isolate of P. niruri protects hepatocytes against CCl(4)-induced oxidative damage and may be used as an effective cytoprotector against CCl(4)-induced hepatotoxicity.

Side Population Cells From an Immortalized Human Liver Epithelial Cell Line Exhibit Hepatic Stem-Like Cell Properties

The existence of hepatic stem cells in human livers is controversial. We investigated whether the side population (SP) cells derived from an immortalized human liver epithelial cell line THLE-5b possess the properties of hepatic stem-like cells. SP cells derived from THLE-5b were isolated using flow cytometry and were assayed for the expression of phenotypic markers by reverse transcription polymerase chain reaction and immunostaining. THLE-5b SP cells retained the capacity to generate both SP and non-SP cells, showed a capacity for self-renewal, and were more efficient in colony formation than non-SP cells. Neither the SP nor the non-SP cells formed tumors when transplanted into athymic nude mice or severe combined immunodeficient mice. The expression level of stem cell-associated markers such as an ATP-binding cassette membrane transporter, epithelial cell adhesion molecule, c-kit, Thy-1, and octomer binding transcription factor 4 was higher in SP cells than in non-SP cells. When cultivated as rotation-mediated aggregates, the expression of liver-specific genes including tryptophan oxygenase and CYP3A4 was up-regulated in SP cells, suggesting that THLE-5b SP cells have the ability to differentiate into a hepatocyte phenotype. One of the clonal cell lines derived from the SP cells expressed stem cell-associated markers. These results indicate that SP cells derived from THLE-5b possess hepatic stem-like cell properties and suggest that THLE-5b can be used as a model of normal human liver progenitor or stem cell line.

Therapeutic potential of transplanted placental mesenchymal stem cells in treating Chinese miniature pigs with acute liver failure

BACKGROUND

Stem cell-based therapy to treat liver diseases is a focus of current research worldwide. So far, most such studies depend on rodent hepatic failure models. The purpose of this study was to isolate mesenchymal stem cells from human placenta (hPMSCs) and determine their therapeutic potential for treating Chinese experimental miniature pigs with acute liver failure (ALF).

METHODS

hPMSCs were isolated and analyzed for their purity and differentiation potential before being employed as the donor cells for transplantation. ALF models of Chinese experimental miniature pigs were established and divided into four groups: no cell transplantation; hPMSCs transplantation via the jugular vein; X-ray-treated hPMSCs transplantation via the portal vein; and hPMSCs transplantation via the portal vein. The restoration of biological functions of the livers receiving transplantation was assessed via a variety of approaches such as mortality rate determination, serum biochemical analysis, and histological, immunohistochemical, and genetic analysis.

RESULTS

hPMSCs expressed high levels of CD29, CD73, CD13, and CD90, had adipogenic, osteogenic, and hepatic differentiation potential. They improved liver functions in vivo after transplantation into the D-galactosamine-injured pig livers as evidenced by the fact that ALT, AST, ALP, CHE, TBIL, and TBA concentrations returned to normal levels in recipient ALF pigs. Meanwhile, histological data revealed that transplantation of hPMSCs via the portal vein reduced liver inflammation, decreased hepatic denaturation and necrosis, and promoted liver regeneration. These ameliorations were not found in the other three groups. The result of 7-day survival rates suggested that hPMSCs transplantation via the portal vein was able to significantly prolong the survival of ALF pigs compared with the other three groups. Histochemistry and RT-PCR results confirmed the presence of transplanted human cells in recipient pig livers (Groups III, IV).

CONCLUSIONS

Our data revealed that hPMSCs could not only differentiate into hepatocyte-like cells in vitro and in vivo, but could also prolong the survival time of ALF pigs. Regarding the transplantation pathways, the left branch of the portal vein inside the liver was superior to the jugular vein pathway. Thus, hPMSCs transplantation through the portal vein by B-ultrasonography may represent a superior approach for treating liver diseases.

In vivo hepatic differentiation of mesenchymal stem cells from human umbilical cord blood after transplantation into mice with liver injury

AIM

The aim of this study was to analyze the hepatic differentiation potential of human umbilical cord blood-derived mesenchymal stem cells (hUCBMSCs) after transplantation into severe combined immune deficiency (SCID) mice with liver injury induced by D-galactosamine/lipopolysaccharide (GalN/LPS) and to explore the possibility that cells can partially repair GalN/LPS-induced hepatic damage.

METHODS

Mononuclear cells (MNCs) were isolated from fresh human umbilical cord blood, characterized by flow cytometry, and then transplanted into GalN/LPS-injured mice. Specimens were collected at 7, 14, 21, and 28 days after hUCBMSC transplantation. Histopathological changes were analyzed by hematoxylin and eosin staining. Polymerase chain reaction (PCR) for a specific marker of human cells, the human Alu sequence, was performed to locate exogenous hUCBMSCs in mouse livers. Expression of human hepatocyte-specific markers such as human albumin (hALB), human alpha-fetoprotein (hAFP), human cytokeratin 18 (hCK18), and human cytokeratin 19 (hCK19) were analyzed by reverse transcriptase (RT)-PCR and immunohistochemical staining.

RESULTS

The hUCBMSCs were positive for the human MSC-specific markers CD271, CD29, CD90, CD105, and CD73, but negative for CD31, CD79b, CD133, CD34, and CD45. Histological findings showed that the hepatic damage in mice was attenuated after hMSC administration, and liver architecture was much better preserved. Human cells in the injured liver of recipient mice were detected by PCR for the human Alu sequence. In addition, expression of markers of hepatic lineage, including hALB, hAFP, hCK18, and hCK19, was detected by immunohistochemistry and RT-PCR in mouse livers after hUCBMSC transplantation, suggesting the formation of hepatocyte-like cells in vivo.

CONCLUSION

MSCs from hUCB exhibit the potential to differentiate into hepatocyte-like cells in the livers of hUCB-transplanted mice as well as partially repair the liver damage induced by GalN/LPS.

Molecular perturbations restrict potential for liver repopulation of hepatocytes isolated from non-heart-beating donor rats

Organs from non-heart-beating donors are attractive for use in cell therapy. Understanding the nature of molecular perturbations following reperfusion/reoxygenation will be highly significant for non-heart-beating donor cells. We studied non-heart-beating donor rats for global gene expression with Affymetrix microarrays, hepatic tissue integrity, viability of isolated hepatocytes, and engraftment and proliferation of transplanted cells in dipeptidyl peptidase IV-deficient rats. In non-heart-beating donors, liver tissue was morphologically intact for >24 hours with differential expression of 1, 95, or 372 genes, 4, 16, or 34 hours after death, respectively, compared with heart-beating donors. These differentially expressed genes constituted prominent groupings in ontological pathways of oxidative phosphorylation, adherence junctions, glycolysis/gluconeogenesis, and other discrete pathways. We successfully isolated viable hepatocytes from non-heart-beating donors, especially up to 4 hours after death, although the hepatocyte yield and viability were inferior to those of hepatocytes from heart-beating donors (P < 0.05). Similarly, although hepatocytes from non-heart-beating donors engrafted and proliferated after transplantation in recipient animals, this was inferior to hepatocytes from heart-beating donors (P < 0.05). Gene expression profiling in hepatocytes isolated from non-heart-beating donors showed far greater perturbations compared with corresponding liver tissue, including representation of pathways in focal adhesion, actin cytoskeleton, extracellular matrix-receptor interactions, multiple ligand-receptor interactions, and signaling in insulin, calcium, wnt, Jak-Stat, or other cascades.

CONCLUSION

Liver tissue remained intact over prolonged periods after death in non-heart-beating donors, but extensive molecular perturbations following reperfusion/reoxygenation impaired the viability of isolated hepatocytes from these donors. Insights into molecular changes in hepatocytes from non-heart-beating donors offer opportunities for improving donor cell viability, which will advance the utility of non-heart-beating donor organs for cell therapy or other applications.

Regenerative Cells for Transplantation in Hepatic Failure

Human embryonic stem (ES) cells and induced pluripotent stem (iPS) cells have an enormous potential; however, their potential clinical application is being arrested due to various limitations such as teratoma formation followed by tumorigenesis, emergent usage, and the quality control of cells, as well as safety issues regarding long-term culture are also delaying their clinical application. In addition, human ES cells have two crucial issues: immunogenicity and ethical issues associated with their clinical application. The efficient generation of human iPS cells requires gene transfer, yet the mechanism underlying pluripotent stem cell induction has not yet been fully elucidated. Otherwise, although human adult regenerative cells including mesenchymal stem cells have a limited capacity for differentiation, they are nevertheless promising candidates for tissue regeneration in a clinical setting. This review highlights the use of regenerative cells for transplantation in hepatic failure.

Fetal liver cell transplantation as a potential alternative to whole liver transplantation?

Because organ shortage is the fundamental limitation of whole liver transplantation, novel therapeutic options, especially the possibility of restoring liver function through cell transplantation, are urgently needed to treat end-stage liver diseases. Groundbreaking in vivo studies have shown that transplanted hepatocytes are capable of repopulating the rodent liver. The two best studied models are the urokinase plasminogen activator (uPA) transgenic mouse and the fumarylacetoacetate hydrolase (FAH)-deficient mouse, in which genetic modifications of the recipient liver provide a tissue environment in which there is extensive liver injury and selection pressure favoring the proliferation and survival of transplanted hepatocytes. Because transplanted hepatocytes do not significantly repopulate the (near-)normal liver, attention has been focused on finding alternative cell types, such as stem or progenitor cells, that have a higher proliferative potential than hepatocytes. Several sources of stem cells or stem-like cells have been identified and their potential to repopulate the recipient liver has been evaluated in certain liver injury models. However, rat fetal liver stem/progenitor cells (FLSPCs) are the only cells identified to date that can effectively repopulate the (near-)normal liver, are morphologically and functionally fully integrated into the recipient liver, and remain viable long-term. Even though primary human fetal liver cells are not likely to be routinely used for clinical liver cell repopulation in the future, using or engineering candidate cells exhibiting the characteristics of FLSPCs suggests a new direction in developing cell transplantation strategies for therapeutic liver replacement. This review will give a brief overview concerning the existing animal models and cell sources that have been used to restore normal liver structure and function, and will focus specifically on the potential of FLSPCs to repopulate the liver.

Bottom-up signaling from HGF-containing surfaces promotes hepatic differentiation of mesenchymal stem cells

The capacity of stem cells to differentiate into specific cell types makes them very promising in tissue regeneration and repair. However, realizing this promise requires novel methods for guiding lineage-specific differentiation of stem cells. In this study, hepatocyte growth factor (HGF), an important morphogen in liver development, was co-printed with collagen I (Col) to create arrays of protein spots on glass. Human adipose stem cells (ASCs) were cultured on top of the HGF/Col spots for 2weeks. The effects of surface-immobilized HGF on hepatic differentiation of ASCs were analyzed using RT-PCR, ELISA and immunocytochemistry. Stimulation of stem cells with HGF from the bottom-up caused an upregulation in synthesis of α-fetoprotein and albumin, as determined by immunocytochemistry and ELISA. RT-PCR results showed that the mRNA levels for albumin, α-fetoprotein and α1-antitrypsin were 10- to 20-fold higher in stem cells cultured on the HGF/Col arrays compared to stem cells on Col only spots. Our results show that surfaces containing HGF co-printed with ECM proteins may be used to differentiate mesenchymal stem cells such as ASCs into hepatocyte-like cells. These results underscore the utility of growth factor-containing culture surfaces for stem cell differentiation.

Hepatocyte differentiation of human fibroblasts from cirrhotic liver in vitro and in vivo

BACKGROUND

Mesenchymal stem cells (MSCs) and fibroblasts have intimate relationships, and the phenotypic homology between fibroblasts and MSCs has been recently described. The aim of this study was to investigate the hepatic differentiating potential of human fibroblasts in cirrhotic liver.

METHODS

The phenotypes of fibroblasts in cirrhotic liver were labeled by biological methods. After that, the differentiation potential of these fibroblasts in vitro was characterized in terms of liver-specific gene and protein expression. Finally, an animal model of hepatocyte regeneration in severe combined immunodeficient (SCID) mice was created by retrorsine injection and partial hepatectomy, and the expression of human hepatocyte proteins in SCID mouse livers was checked by immunohistochemical analysis after fibroblast administration.

RESULTS

Surface immunophenotyping revealed that a minority of fibroblasts expressed markers of MSCs and hepatic epithelial cytokeratins as well as alpha-smooth muscle actin, but homogeneously expressed vimentin, desmin, prolyl 4-hydroxylase and fibronectin. These fibroblasts presented the characteristics of hepatocytes in vitro and differentiated directly into functional hepatocytes in the liver of hepatectomized SCID mice.

CONCLUSIONS

This study demonstrated that fibroblasts in cirrhotic liver have the potential to differentiate into hepatocyte-like cells in vitro and in vivo. Our findings infer that hepatic differentiation of fibroblasts may serve as a new target for reversion of liver fibrosis and a cell source for tissue engineering.

New concepts in liver regeneration

The unique ability of the liver to regenerate itself has fascinated biologists for years and has made it the prototype for mammalian organ regeneration. Harnessing this process has great potential benefit in the treatment of liver failure and has been the focus of intense research over the past 50 years. Not only will detailed understanding of cell proliferation in response to injury be applicable to other dysfunction of organs, it may also shed light on how cancer develops in a cirrhotic liver, in which there is intense pressure on cells to regenerate. Advances in molecular techniques over the past few decades have led to the identification of many regulatory intermediates, and pushed us onto the verge of an explosive era in regenerative medicine. To date, more than 10 clinical trials have been reported in which augmented regeneration using progenitor cell therapy has been attempted in human patients. This review traces the path that has been taken over the last few decades in the study of liver regeneration, highlights new concepts in the field, and discusses the challenges that still stand between us and clinical therapy.

The existence of multipotent stem cells with epithelial-mesenchymal transition features in the human liver bud

During early stage of embryonic development, the liver bud, arising from the foregut endoderm, is the beginning for the formation of future liver three-dimensional structure. While the gene expression profiles associated with this developmental stage have been well explored, the detailed cellular events are not as clear. Epithelial-mesenchymal transition (EMT) was thought to be essential for cell migration in the early vertebrate embryo but seldom demonstrated in human liver development. In this study, we tried to identify the cell populations with both stem cell and EMT features in the human liver bud. Our in situ studies show that the phenotype of EMT occurs at initiation of human liver development, accompanied by up-regulation of EMT associated genes. A human liver bud derived stem cell line (hLBSC) was established, which expressed not only genes specific to both mesenchymal cells and hepatic cells, but also octamer-binding protein 4 (OCT4) and nanog. Placed in appropriate media, hLBSC differentiated into hepatocytes, adipocytes, osteoblast-like cells and neuron-like cells in vitro. When transplanted into severe combined immunodeficiency mice pre-treated by carbon tetrachloride, hLBSC engrafted into the liver parenchyma and proliferated. These data suggests that there are cell populations with stem cell and EMT-like properties in the human liver bud, which may play an important role in the beginning of the spatial structure construction of the liver.

Effect of transplantation of mesenchymal stem cells induced into early hepatic cells in streptozotocin-induced diabetic mice

Cellular replacement therapy for diabetes mellitus has received much attention. In this study we investigated the effect of transplantation of bone marrow-derived mesenchymal stem cells (BM-MSCs) induced into endoderm and early hepatic cells in streptozotocin (STZ)-induced diabetic mice. Mouse BM-MSCs were cultured in the presence of hepatocyte growth factor (HGF) and fibroblast growth factor (FGF-4) for 2 weeks and transplanted into diabetic mice. Blood glucose levels, intraperitoneal glucose tolerance test, serum insulin, body weight and islets histology were analyzed. The results demonstrated that transplantation of syngeneic induced MSCs could reverse STZ-induced diabetes in mice. The treatment of mice with hyperglycemia and islet destruction resulted in the repair of pancreatic islets. Blood glucose levels, intraperitoneal glucose tolerance test, and serum insulin were significantly recovered in induced BM-MSCs (iBM-MSCs) group. In addition, in the iBM-MSCs group the body weight and the number of islets were significantly increased compared to other groups. The results demonstrate that BM-MSCs induced into endoderm and early hepatic cells are suitable candidates for cell-based therapy of diabetes mellitus.

Transplantation of immortalized human fetal hepatocytes prevents acute liver failure in 90% hepatectomized mice

AIM

The aim of this study was to investigate whether human fetal hepatocytes are amenable to simian virus 40 large T-antigen (SV40Tag) mediated immortalization and whether the immortalized cells rescue mice with acute liver failure induced by 90% hepatectomy.

METHODS

We constructed a retroviral vector expressing a thermolabile mutant SV40Tag for transfer into primary human fetal hepatocytes. We quantitatively detected the synthetic ability for albumin and urea by the immortalized cells, which were subcutaneously inoculated into mice with severe combined immunodeficiency (SCID) to evaluate tumorigenzcity. The immortalized cells were also transplanted into the spleens of mice with acute liver failure.

RESULTS

One clone resulting after selection, referred to as HepCL, was highly differentiated, growing steadily in a chemically defined serum-free medium. HepCL cells were positive for albumin, cytokeratin 18, and cytokeratin 19 immunocytochemical staining. The average synthetic efficacies of HepCL cells for albumin and urea were comparable to that of unmodified primary human fetal hepatocytes. The population doubling time of HepCL cells in the logarithmic growth phase was approximately 17 hours. HepCL cells showed no oncogenicity in immunodeficient mice at 16 months. Mice receiving HepCL cells (G1) and primary human fetal hepatocytes (G2) showed significantly lower blood ammonia levels after 90% hepatectomy. Pairwise comparisons between the 4 groups showed that xenotransplantation of HepCL (G1) or primary fetal hepatocytes (G2) significantly improved survivals of recipient mice.

CONCLUSIONS

HepCL may be useful as a source of hepatic function for cell-based therapeutics in acute liver failure.

Culture of newborn monkey liver epithelial progenitor cells in chemical defined serum-free medium

Studies with hepatic progenitor cells from non-human primates would allow better understanding of their human counterparts. In this study, rhesus monkey liver epithelial progenitor cells (mLEPCs) were derived from a small piece of newborn livers in chemical defined serum-free medium. Digested hepatic cells were treated in Ca(2+)-containing medium to form cell aggregates. Two types of cell aggregates were generated: elongated spindle cells and polygonal epithelial cells. Elongated spindle cells were expressed as vimentin and brachyury, and they were disappeared within 5 d in our cultures. The remaining type consisted of small polygonal epithelial cells that expressed cytokeratin 7 (CK7), CK8, CK18, nestin, CD49f, and E-cad, the markers of hepatic stem cells, but were negative for alpha-fetoprotein, albumin, and CK19. They can proliferate and be passaged, if on laminin or rat tail collagen gel, to initiate colonies. When cultured with dexamethasone and oncostatin M, the expression of mature hepatocyte markers, such as alpha-1-antitrypsin, intracytoplasmic glycogen storage, indocyanine green uptake, and lipid droplet generation, were induced in differentiated cells. If transferred onto mouse embryonic fibroblasts feeders, they gave rise to CK19-positive cholangiocytes with formation of doughnut-like structure. Thus, mLEPCs with bipotency were derived from newborn monkey liver and may serve as a preclinical model for assessment of cell therapy in humans.

Differentiation and characterization of metabolically functioning hepatocytes from human embryonic stem cells

Human embryonic stem cells (hESCs) may provide a cell source for functional hepatocytes for clinical applications and drug development. Initially, the hESC population was enriched to be more than 85% definitive endoderm (DE) as assessed by the expression of CXCR4, SOX17, and FOXA2. We then successfully converted DE into hepatic progenitors with 93% of the cells being positive for alpha-feto protein within 9 days. The percentage of albumin positive cells gradually increased to 90% at days 20-22 after differentiation. Moreover, our hESC-derived hepatocytes (hEH) developed a complete biotransformation system including phase I and II metabolizing enyzmes and phase III transporters. Nuclear receptors, which are critical in regulating the expression of metabolizing enzymes, were also expressed by our hEH. Using ultraperformance liquid chromatography-tandem mass spectrometry technology, we identified seven metabolic pathways of the drug bufuralol including four newly-reported ones in our hEH, which are the same as those in freshly isolated human primary hepatocytes (hPH). In addition, the results of the metabolism of four drugs indicate that our hEH have the capacity to metabolize these drugs at levels that are comparable to hPH. In conclusion, we have generated a relatively homogenous population of hepatocytes from hESCs, which appear to have complete metabolic function that is comparable to primary liver cells. These results represent a significant step towards the efficient differentiation of mature hepatocytes for cell-based therapeutics as well as for pharmacology and toxicology studies.

Emerging use of stem cells in regenerative medicine

Stem cells represent a unique opportunity for regenerative medicine to cure a broad number of diseases for which current treatment only alleviates symptoms or retards further disease progression. However, the number of stem cells available has speedily increased these past 10 years and their diversity presents new challenges to clinicians and basic scientists who intend to use them in clinics or to study their unique properties. In addition, the recent possibility to derive pluripotent stem cells from somatic cells using epigenetic reprogramming has further increased the clinical interest of stem cells since induced pluripotent stem cells could render personalized cell-based therapy possible. The present review will attempt to summarize the advantages and challenges of each type of stem cell for current and future clinical applications using specific examples.

An implantable vascularized protein gel construct that supports human fetal hepatoblast survival and infection by hepatitis C virus in mice

Background

Widely accessible small animal models suitable for the study of hepatitis C virus (HCV) in vivo are lacking, primarily because rodent hepatocytes cannot be productively infected and because human hepatocytes are not easily engrafted in immunodeficient mice.

Methodology/Principal Findings

We report here on a novel approach for human hepatocyte engraftment that involves subcutaneous implantation of primary human fetal hepatoblasts (HFH) within a vascularized rat collagen type I/human fibronectin (rCI/hFN) gel containing Bcl-2-transduced human umbilical vein endothelial cells (Bcl-2-HUVEC) in severe combined immunodeficient X beige (SCID/bg) mice. Maturing hepatic epithelial cells in HFH/Bcl-2-HUVEC co-implants displayed endocytotic activity at the basolateral surface, canalicular microvilli and apical tight junctions between adjacent cells assessed by transmission electron microscopy. Some primary HFH, but not Huh-7.5 hepatoma cells, appeared to differentiate towards a cholangiocyte lineage within the gels, based on histological appearance and cytokeratin 7 (CK7) mRNA and protein expression. Levels of human albumin and hepatic nuclear factor 4α (HNF4α) mRNA expression in gel implants and plasma human albumin levels in mice engrafted with HFH and Bcl-2-HUVEC were somewhat enhanced by including murine liver-like basement membrane (mLBM) components and/or hepatocyte growth factor (HGF)-HUVEC within the gel matrix. Following ex vivo viral adsorption, both HFH/Bcl-2-HUVEC and Huh-7.5/Bcl-2-HUVEC co-implants sustained HCV Jc1 infection for at least 2 weeks in vivo, based on qRT-PCR and immunoelectron microscopic (IEM) analyses of gel tissue.

Conclusion/Significance

The system described here thus provides the basis for a simple and robust small animal model of HFH engraftment that is applicable to the study of HCV infections in vivo.

Human Fetal Liver-Derived Stem Cell Transplantation as Supportive Modality in the Management of End-Stage Decompensated Liver Cirrhosis

Liver transplantation is the only existing modality for treating decompensated liver cirrhosis. Several factors, such as nonavailability of donors, combined with operative risks, complications associated with rejection, usage of immunosuppressive agents, and cost intensiveness, make this strategy available to only a few people. With a tremendous upsurge in the mortality rate of patients with liver disorders worldwide, there is a need to search for an alternative therapeutic tool that can combat the above limitations and serve as a supportive therapy in the management of liver diseases. Cell therapy using human fetal liver-derived stem cells can provide great potential to conservatively manage end-stage liver diseases. Therefore, the present investigation aimed to study and prove the safety and efficacy of human fetal liver-derived stem cell transplantation in patients with end-stage liver cirrhosis. Twenty-five patients with liver cirrhosis of different etiologies were infused with human fetal liver-derived stem cells (EpCAM+ve) labeled with Tc-HMPAO through hepatic artery. Our high throughput analysis using flow cytometry, RT-PCR, and cellular characterization exemplifies fetal liver cells with their high proliferation rate could be the best source for rejuvenating the diseased liver. Further, no episodes related to hepatic encephalopathy recurred in any of the subjects following hepatic stem cell transplantation. There was marked clinical improvement observed in terms of all clinical and biochemical parameters. Further, there was decrease in mean MELD score ( p < 0.01) observed in 6 months follow-up in all patients. Therapy using human fetal liver stem/progenitor cells offers a potentially supportive modality to organ transplantation in the management of liver diseases.

In vivo tracking of dual-labeled mesenchymal stem cells homing into the injured common carotid artery

The aim of this study is to conduct in vivo, noninvasive magnetic resonance imaging of labeled rat bone mesenchymal stem cells (BMSCs) as they home into the site of injured common carotid artery following allograft transplantation. Our study was approved by the Institutional Committee on Animal Research. Purified rat BMSCs were dual labeled with superparamagnetic iron oxide (SPIO) particle and fluorescent DiI dye, and subsequently transplanted into recipient rats injured in the left common carotid arteries. Immediately before and 3 hr, 3, 7 and 12 days after transplantation, the labeled cells were monitored in vivo using a 7T micromagnetic resonance imaging (7T micro-MRI) scanner. The signal-to-noise ratios (SNRs) at the injured sites were corroborated with histological examination using Prussian blue staining and fluorescent imaging. Rat BMSCs were labeled with SPIO and DiI at 100% efficiency. When compared with the baseline level before transplantation, the SNR decreased significantly on Days 3 and 7 after injection in the experimental group (Dunnet t test, P < 0.05), whereas insignificant differences were observed after 3 hr and 12 days (Dunnet t test, P > 0.05). In the control group, no significant differences in SNR were found among different time points (ANOVA, P > 0.05). Histological analyses illustrated that red fluorescence and Prussian blue-positive cells were mainly distributed around the lesion areas of injured common carotid arteries. Rat BMSCs can be efficiently labeled with SPIO and DiI, and the directional homing of labeled cells to the site of injured common carotid arteries after intravascular transplantation could be tracked in vivo with 7T micro-MRI.