Heterogeneity and plasticity of hepatocyte lineage cells

Are hematopoietic stem cells involved in hepatocarcinogenesis?

THE LIVER HAS THREE CELL LINEAGES ABLE TO PROLIFERATE AFTER A HEPATIC INJURY: the mature hepatocyte, the ductular "bipolar" progenitor cell termed "oval cell" and the putative periductular stem cell. Hepatocytes can only produce other hepatocytes whereas ductular progenitor cells are considerate bipolar since they can give rise to biliary cells or hepatocytes. Periductular stem cells are rare in the liver, have a very long proliferation potential and may be multipotent, being this aspect still under investigation. They originate in the bone marrow since their progeny express genetic markers of donor hematopoietic cells after bone marrow transplantation. Since the liver is the hematopoietic organ of the fetus, it is possible that hematopoietic stem cells may reside in the liver of the adult. This assumption is proved by the finding that oval cells express hematopoietic markers like CD34, CD45, CD 109, Thy-1, c-kit, and others, which are also expressed by bone marrow-derived hematopoietic stem cells (BMSCs). Few and discordant studies have evaluated the role of BMSC in hepatocarcinogenesis so far and further studies in vitro and in vivo are warranted in order to definitively clarify such an issue.

Expression of nestin in remodelling of α-naphthylisothiocyanate-induced acute bile duct injury in rats

The function of the intermediate filament protein nestin is poorly understood. The significance of nestin expression was assessed in α-naphthylisothiocyanate (ANIT)-induced cholangiocyte injury lesions in F344 rats. Liver samples obtained from rats injected intraperitoneally with ANIT (75 mg/kg) on post-injection days 0 (control) and 1-12 were labelled immunohistochemically for expression of nestin and markers specific for mesenchymal cells (vimentin), hepatic stellate cells (HSCs) (desmin and glial fibrillary acidic protein [GFAP]), endothelial cells (rat endothelial cell antigen [RECA]-1), cholangiocytes (cytokeratin [CK] 19) and cellular proliferation (Ki67). Cholangiocyte injury led to infiltration of neutrophils and macrophages followed by aggregation of mesenchymal cells and regeneration of bile ducts. Nestin expression was detected in mesenchymal cells (vimentin positive) on days 1-7 with a peak on days 3-5 and in newly-formed RECA-1-positive endothelial cells on day 3. Nestin expression was also observed in regenerating CK19-positive cholangiocytes on days 2-5, with a peak on day 3. Labelling for Ki67 showed proliferation of cholangiocytes, mesenchymal cells and HSCs. Real-time reverse transcriptase polymerase chain reaction with microdissected samples showed significantly elevated nestin mRNA on day 3. The findings suggest an association between nestin expression and cellular proliferation. Based on these findings, it was considered that nestin-expressing mesenchymal cells, HSCs and endothelial cells may be possible progenitors of repopulating cholangiocytes. Nestin expression may serve as an indicator for cellular remodelling and behaviour of injured and repopulating bile ducts.

Ameliorative effect of bone marrow-derived stem cells on injured liver of mice infected with Schistosoma mansoni

The technique of stem cells or hepatocytes transplantation has recently improved in order to bridge the time before whole-organ liver transplantation. In the present study, unfractionated bone marrow stem cells (BMSCs) were harvested from the tibial and femoral marrow compartments of male mice, which were cultured in Dulbecco's modified Eagle's medium (DMEM) with and without hepatocyte growth factor (HGF), and then transplanted into Schistosoma mansoni-infected female mice on their 8th week post-infection. Mice were sacrificed monthly until the third month of bone marrow transplantation, serum was collected, and albumin concentration, ALT, AST, and alkaline phosphatase (ALP) activities were assayed. On the other hand, immunohistopathological and immunohistochemical changes of granuloma size and number, collagen content, and cells expressing OV-6 were detected for identification of liver fibrosis. BMSCs were shown to differentiate into hepatocyte-like cells. Serum ALT, AST, and ALP were markedly reduced in the group of mice treated with BMSCs than in the untreated control group. Also, granuloma showed a marked decrease in size and number as compared to the BMSCs untreated group. Collagen content showed marked decrease after the third month of treatment with BMSCs. On the other hand, the expression of OV-6 increased detecting the presence of newly formed hepatocytes after BMSCs treatment. BMSCs with or without HGF infusion significantly enhanced hepatic regeneration in S. mansoni-induced fibrotic liver model and have pathologic and immunohistopathologic therapeutic effects. Also, this new therapeutic trend could generate new hepatocytes to improve the overall liver functions.

Bone marrow-derived stem cells and hepatocarcinogenesis in hepatitis B virus transgenic mice

BACKGROUND

Several studies have demonstrated that cancer can develop with the contribution of bone marrow-derived cancer stem cells. We evaluated the possible involvement of bone marrow-derived stem cells in hepatocarcinogenesis in a hepatitis B virus (HBV) transgenic mouse model.

METHODS

Bone marrow cells from wild type male mice were transplanted into sublethally irradiated, female, HBV transgenic mice with hepatocarcinoma nodules. Four months later, liver tissue was examined to localize neoplastic nodules/foci and characterize cells by evaluating the Y-chromosome and the hepatocyte lineage marker hepatocyte nuclear factor-1 (HNF1), as well as the HBsAg encoding gene (HBs-Eg) and HBsAg protein (HBs-Pr) (present only in cells of female origin).

RESULTS

Hepatocytes were HBs-Eg/HBs-Pr-positive in "normal" tissue, while resulted only HBs-Eg-positive in regenerative areas. Neoplastic foci/nodules were both HBs-Eg/HBs-Pr-negative. In the liver, 19 ± 5% of cells were Y-chromosome-positive and about one fifth were HNF1-positive. Y-chromosome and HBs-Eg colocalized in HNF1-positive cells. Y-chromosome-positive cells never localized in neoplastic foci/nodules (HBs-Pr/HBs-Eg-negative).

CONCLUSIONS

Bone marrow-derived stem cells participate in the hepatic regenerative process but not in neoplastic growth. Simultaneous detection of both Y-chromosome and HBs-Eg in the nucleus of an HNF1-positive cell (hepatocyte) demonstrates a phenomenon of cell fusion.

Comparative evaluation of differentiation potential of menstrual blood- versus bone marrow-derived stem cells into hepatocyte-like cells

Menstrual blood has been introduced as an easily accessible and refreshing stem cell source with no ethical consideration. Although recent works have shown that menstrual blood stem cells (MenSCs) possess multi lineage differentiation capacity, their efficiency of hepatic differentiation in comparison to other stem cell resources has not been addressed so far. The aim of this study was to investigate hepatic differentiation capacity of MenSCs compared to bone marrow-derived stem cells (BMSCs) under protocols developed by different concentrations of hepatocyte growth factor (HGF) and oncostatin M (OSM) in combination with other components in serum supplemented or serum-free culture media. Such comparison was made after assessment of immunophenotye, trans-differentiation potential, immunogenicity and tumorigeicity of these cell types. The differential expression of mature hepatocyte markers such as albumin (ALB), cytokeratin 18 (CK-18), tyrosine aminotransferase and cholesterol 7 alpha-hydroxylase activities (CYP7A1) at both mRNA and protein levels in differentiating MenSCs was significantly higher in upper concentration of HGF and OSM (P1) compared to lower concentration of these factors (P2). Moreover, omission of serum during differentiation process (P3) caused typical improvement in functions assigned to hepatocytes in differentiated MenSCs. While up-regulation level of ALB and CYP7A1 was higher in differentiated MenSCs compared to driven BMSCs, expression level of CK-18, detected level of produced ALB and glycogen accumulation were lower or not significantly different. Therefore, based on the overall comparable hepatic differentiation ability of MenSCs with BMSCs, and also accessibility, refreshing nature and lack of ethical issues of MenSCs, these cells could be suggested as an apt and safe alternative to BMSCs for future stem cell therapy of chronic liver diseases.

Potential of regenerative medicine techniques in canine hepatology

Liver cell turnover is very slow, especially compared to intestines and stomach epithelium and hair cells. Since the liver is the main detoxifying organ in the body, it does not come as a surprise that the liver has an unmatched regenerative capacity. After 70% partial hepatectomy, the liver size returns to normal in about two weeks due to replication of differentiated hepatocytes and cholangiocytes. Despite this, liver diseases are regularly encountered in the veterinary clinic. Dogs primarily present with parenchymal pathologies such as hepatitis. The estimated frequency of canine hepatitis depends on the investigated population and accounts for 1%-2% of our university clinic referral population, and up to 12% in a general population. In chronic and severe acute liver disease, the regenerative and replicative capacity of the hepatocytes and/or cholangiocytes falls short and the liver is not restored. In this situation, proliferation of hepatic stem cells or hepatic progenitor cells (HPCs), on histology called the ductular reaction, comes into play to replace the damaged hepatocytes or cholangiocytes. For unknown reasons the ductular reaction is often too little and too late, or differentiation into fully differentiated hepatocytes or cholangiocytes is hampered. In this way, HPCs fail to fully regenerate the liver. The presence and potential of HPCs does, however, provide great prospectives for their use in regenerative strategies. This review highlights the regulation of, and the interaction between, HPCs and other liver cell types and discusses potential regenerative medicine-oriented strategies in canine hepatitis, making use of (liver) stem cells.

Unbalanced distribution of materials: the art of giving rise to hepatocytes from liver stem/progenitor cells

Liver stem/progenitor cells (LSPCs) are able to duplicate themselves and differentiate into each type of cells in the liver, including mature hepatocytes and cholangiocytes. Understanding how to accurately control the hepatic differentiation of LSPCs is a challenge in many fields from preclinical to clinical treatments. This review summarizes the recent advances made to control the hepatic differentiation of LSPCs over the last few decades. The hepatic differentiation of LSPCs is a gradual process consisting of three main steps: initiation, progression and accomplishment. The unbalanced distribution of the affecting materials in each step results in the hepatic maturation of LSPCs. As the innovative and creative works for generating hepatocytes with full functions from LSPCs are gradually accumulated, LSPC therapies will soon be a new choice for treating liver diseases.

Role of stem cells in repair of liver injury: Experimental and clinical benefit of transferred stem cells on liver failure

Although the liver has a high regenerative capacity, as a result of massive hepatocyte death, liver failure occurs. In addition to liver failure, for acute, chronic and hereditary diseases of the liver, cell transplantation therapies can stimulate regeneration or at least ensure sufficient function until liver transplantation can be performed. The lack of donor organs and the risks of rejection have prompted extensive experimental and clinical research in the field of cellular transplantation. Transplantation of cell lineages involved in liver regeneration, including mature hepatocytes, fetal hepatocytes, fetal liver progenitor cells, fetal stem cells, hepatic progenitor cells, hepatic stem cells, mesenchymal stem cells, hematopoietic stem cells, and peripheral blood and umbilical cord blood stem cells, have been found to be beneficial in the treatment of liver failure. In this article, the results of experimental and clinical cell transplantation trials for liver failure are reviewed, with an emphasis on regeneration.

Failure of fibrotic liver regeneration in mice is linked to a severe fibrogenic response driven by hepatic progenitor cell activation

Failure of fibrotic liver to regenerate after resection limits therapeutic options and increases demand for liver transplantation, representing a significant clinical problem. The mechanism underlying regenerative failure in fibrosis is poorly understood. Seventy percent partial hepatectomy (PHx) was performed in C57Bl/6 mice with or without carbon tetrachloride (CCl4)-induced liver fibrosis. Liver function and regeneration was monitored at 1 to 14 days thereafter by assessing liver mass, alanine aminotransferase (ALT), mRNA expression, and histology. Progenitor (oval) cell mitogen tumor necrosis factor-like weak inducer of apoptosis (TWEAK) and TWEAK-neutralizing antibody were used to manipulate progenitor cell proliferation in vivo. In fibrotic liver, hepatocytes failed to replicate efficiently after PHx. Fibrotic livers showed late (day 5) peak of serum ALT (3542 ± 355 IU/L compared to 93 ± 65 IU/L in nonfibrotic livers), which coincided with progenitor cell expansion, increase in profibrogenic gene expression and de novo collagen deposition. In fibrotic mice, inhibition of progenitor activation using TWEAK-neutralizing antibody after PHx resulted in strongly down-regulated profibrogenic mRNA, reduced serum ALT levels and improved regeneration. Failure of hepatocyte-mediated regeneration in fibrotic liver triggers activation of the progenitor (oval) cell compartment and a severe fibrogenic response. Inhibition of progenitor cell proliferation using anti-TWEAK antibody prevents fibrogenic response and augments fibrotic liver regeneration. Targeting the fibrogenic progenitor response represents a promising strategy to improve hepatectomy outcomes in patients with liver fibrosis.

Hepatic stem cell niches

Stem cell niches are special microenvironments that maintain stem cells and control their behavior to ensure tissue homeostasis and regeneration throughout life. The liver has a high regenerative capacity that involves stem/progenitor cells when the proliferation of hepatocytes is impaired. In recent years progress has been made in the identification of potential hepatic stem cell niches. There is evidence that hepatic progenitor cells can originate from niches in the canals of Hering; in addition, the space of Disse may also serve as a stem cell niche during fetal hematopoiesis and constitute a niche for stellate cells in adults.

Contribution of mature hepatocytes to small hepatocyte-like progenitor cells in retrorsine-exposed rats with chimeric livers

The potential lineage relationship between hepatic oval cells, small hepatocyte-like progenitor cells (SHPCs), and hepatocytes in liver regeneration is debated. To test whether mature hepatocytes can give rise to SHPCs, rats with dipeptidyl peptidase IV (DPPIV) chimeric livers, which harbored endogenous DPPIV-deficient hepatocytes and transplanted DPPIV-positive hepatocytes, were subjected to retrorsine treatment followed by partial hepatectomy (PH). DPPIV-positive hepatocytes comprised about half of the DPPIV chimeric liver mass. Tissues from DPPIV chimeric livers after retrorsine/PH treatment showed large numbers of SHPC clusters. None of the SHPC clusters were stained positive for DPPIV in any analyzed samples. Furthermore, serial sections stained for gamma-glutamyl-transpeptidase (GGT, a marker of fetal hepatoblasts) and glucose-6-phosphatase (G6Pase, a marker of mature hepatocytes) showed inverse expression of the two enzymes and a staining pattern consistent with a lineage that begins with GGT(+)/G6Pase(-) to GGT(-)/G6Pase(+) within a single SHPC cluster. Using double immunofluorescence staining for markers specific for hepatic oval cells and hepatocytes in serial sections, oval cell proliferations with CK-19(+)/laminin(+) and OV-6(+)/C/EBP-α(-) were shown to extend from periportal areas into the SPHC clusters, differentiating into hepatic lineage by progressive loss of CK-19/laminin expression and appearance of C/EBP-α expression towards the cluster side. Cells in the epithelial cell adhesion molecule (EpCAM(+)) SHPC clusters showed membranous EpCAM(+)/HNF-4α(+) (hepatocyte nuclear factor-4α) staining and were contiguous to the surrounding cytoplasmic EpCAM(+)/HNF-4α(-) ductular oval cells. Extensive elimination of oval cell response by repeated administration of 4,4'-methylenedianiline (DAPM) to retrorsine-exposed rats impaired the emergence of SHPC clusters.

CONCLUSION

These findings highly suggest the hepatic oval cells but not mature hepatocytes as the origin of SHPC clusters in retrorsine-exposed rats.

Differentiation capacity of hepatic stem/progenitor cells isolated from D-galactosamine-treated rat livers

Oval cells and small hepatocytes (SHs) are known to be hepatic stem and progenitor cells. Although oval cells are believed to differentiate into mature hepatocytes (MHs) through SHs, the details of their differentiation process are not well understood. Furthermore, it is not certain whether the induced cells possess fully mature functions as MHs. In the present experiment, we used Thy1 and CD44 to isolate oval and progenitor cells, respectively, from D-galactosamine-treated rat livers. Epidermal growth factor, basic fibroblast growth factor, or hepatocyte growth factor could trigger the hepatocytic differentiation of sorted Thy1(+) cells to form epithelial cell colonies, and the combination of the factors stimulated the emergence and expansion of the colonies. Cells in the Thy1(+) -derived colonies grew more slowly than those in the CD44(+) -derived ones in vitro and in vivo and the degree of their hepatocytic differentiation increased with CD44 expression. Although the induced hepatocytes derived from Thy1(+) and CD44(+) cells showed similar morphology to MHs and formed organoids from the colonies similar to those from SHs, many hepatic differentiated functions of the induced hepatocytes were less well performed than those of mature SHs derived from the healthy liver. The gene expression of cytochrome P450 1A2, tryptophan 2,3-dioxygenase, and carbamoylphosphate synthetase I was lower in the induced hepatocytes than in mature SHs. In addition, the protein expression of CCAAT/enhancer-binding protein alpha and bile canalicular formation could not reach the levels of production of mature SHs.

CONCLUSION

The results suggest that, although Thy1(+) and CD44(+) cells are able to differentiate into hepatocytes, the degree of maturation of the induced hepatocytes may not be equal to that of healthy resident hepatocytes. (HEPATOLOGY 2013).

Transplantation of umbilical cord blood-derived mesenchymal stem cells for treatment of liver cirrhosis: Research progress

Cirrhosis is a serious threat to human health. Currently, there have been no available radical measures that can effectively block the process of this disease. The research progress in the field of stem cells brings an opportunity for the treatment of cirrhosis. Having a wide variety of sources, weak immunogenicity, and strong proliferation and differentiation ability, human umbilical cord blood-derived mesenchymal stem cells have been demonstrated to be promising in the treatment of liver cirrhosis. This article reviews the biological characteristics of human umbilical cord blood mesenchymal stem cells and their application in the treatment of cirrhosis.

Probing the hepatic progenitor cell in human hepatocellular carcinoma

Objective. The intrahepatic stem cells, also known as hepatic progenitor cells (HPCs), are able to differentiate into hepatocytes and bile duct epithelia. By exposure of different injuries and different hepatocarcinogenic regimens, the mature hepatocytes can no longer effectively regenerate; stem cells are involved in the pathogenesis of hepatocellular carcinoma. Methods. Immunohistochemistry was performed on 107 paraffin-embedded hepatocellular carcinoma specimens with the marker of hepatocyte and hepatocellular carcinoma (HepPar1), biliary differentiation (CK7,CK19), haemopoietic stem cell (HSC) (c-kit/CD117, CD34, and Thy-1/CD90), HPC specific markers (OV-6), and Ki-67, p53 protein. Results. HPCs can be identified in the tumor nodules, around the edge of tumor nodules, and in the portal tracts of the paracirrhosis nodules being positive in HepPar1, CK7, CK19, and OV-6, but they failed to immunostain with CD117, CD34, and CD90. The HPCs positive in Ki-67 are observed in the tumor and paracirrhosis tissues. In 107 specimens, 40.2% (43/107) HCC tissues expressed p53 protein, lower than that of the HPCs around the tumor nodules (46.7%, 50/107) and much higher than that of the HPCs around the paracirrhosis nodules (8.41%, 9/107). Conclusion. Human hepatocellular carcinogenesis may be based on transformation of HPCs, not HSCs, through the formation of the transitional cells (hepatocyte-like cells and bile ductal cells).

Therapeutic effect of transplanting magnetically labeled bone marrow stromal stem cells in a liver injury rat model with 70%-hepatectomy

Background

There are only few reports about the use of bone marrow stromal stem cells (BMSCs) for the treatment of traumatic liver injury. This study aimed to study the therapeutic effect of fluorescence-labeled BMSCs administered to rats subject to traumatic liver injury.

Material/Methods

Male SD rats with a 70% resection of the liver were injected with feridex-labeled BMSCs which could be induced to functional hepatocytes in vitro. Liver function was assayed and the liver scanned by 1.5-T MRI at 12 hrs and on days 1, 3, 5, 7, and 14 post-operation. The pathological changes of liver sections were monitored.

Results

The serum levels of alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, direct bilirubin, and total bilirubin in the transplantation group were significantly lower than the control group. The MRI showed rats of the transplantation group had an oval low signal area at 12 hr after operation; the low signal range gradually expanded and the signal intensity gradually decreased over 14 days after operation. The low signal range in the control group disappeared 12 hr after the operation. After Prussian blue staining, rats of the transplantation group contained blue granules with no significant hypertrophy or edema in hepatocytes, while the control group showed no blue granules with significant hypertrophy and edema.

Conclusions

The BMSCs transplanted into the injured rat liver gradually migrate to the surrounding liver tissue and partially repair the liver surgical injury in rats. BMSCs may represent an effective therapeutic approach for acute liver injury.

CD34+ hematopoietic stem cells mobilization, paralleled with multiple cytokines elevated in patients with HBV-related acute-on-chronic liver failure

BACKGROUND

Recent studies indicate that bone marrow (BM)-derived stem cells contribute to liver regeneration. But limited information is available on the dynamic and mechanisms of mobilization of BM-derived hematopoietic stem cells (HSCs) after acute-on-chronic liver failure (ACLF).

AIMS

The purpose of this study was to assess the mobilization of BM-derived CD34+ HSCs in ACLF patients, and elucidate the association of stress-induced cytokines in HSCs mobilization and/or liver repair in ACLF patients.

METHODS

Thirty patients with HBV-related ACLF, 30 patients undergoing chronic hepatitis B, and 20 healthy controls were enrolled. The percentages of peripheral blood CD34+ cells were determined by two-color flow cytometry. The hepatic commitment of mobilized CD34+ cells was investigated by RT-PCR. The serum levels of stress-induced cytokines were determined by enzyme-linked immunosorbent assays.

RESULTS

A significant increase of circulating CD34+ cells was observed in ACLF patients. RT-PCR analyses showed that the mobilized CD34+ cells expressed both CD34 mRNA and liver-specific markers including cytokeratin 19 and α-fetoprotein. In parallel with mobilization of BM-derived CD34+ cells, elevated serum levels of hepatocyte growth factor, interleukin-6, stem cell factor, granulocyte colony-stimulating factor and matrix metalloproteinase 9 were observed in ACLF patients.

CONCLUSION

We demonstrated that ACLF led to mobilization of CD34+ cells, which had a hepatic differentiation potential.

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.

Classical and alternative activation of rat hepatic sinusoidal endothelial cells by inflammatory stimuli

The ability of rat hepatic sinusoidal endothelial cells (HSEC) to become activated in response to diverse inflammatory stimuli was analyzed. Whereas the classical macrophage activators, IFNγ and/or LPS upregulated expression of iNOS in HSEC, the alternative macrophage activators, IL-10 or IL-4+IL-13 upregulated arginase-1 and mannose receptor. Similar upregulation of iNOS and arginase-1 was observed in classically and alternatively activated Kupffer cells, respectively. Removal of inducing stimuli from the cells had no effect on expression of these markers, demonstrating that activation is persistent. Washing and incubation of IFNγ treated cells with IL-4+IL-13 resulted in decreased iNOS and increased arginase-1 expression, while washing and incubation of IL-4+IL-13 treated cells with IFNγ resulted in decreased arginase-1 and increased iNOS, indicating that classical and alternative activation of the cells is reversible. HSEC were more sensitive to phenotypic switching than Kupffer cells, suggesting greater functional plasticity. Hepatocyte viability and expression of PCNA, β-catenin and MMP-9 increased in the presence of alternatively activated HSEC. In contrast, the viability of hepatocytes pretreated for 2 h with 5 mM acetaminophen decreased in the presence of classically activated HSEC. These data demonstrate that activated HSEC can modulate hepatocyte responses following injury. The ability of hepatocytes to activate HSEC was also investigated. Co-culture of HSEC with acetaminophen-injured hepatocytes, but not control hepatocytes, increased the sensitivity of HSEC to classical and alternative activating stimuli. The capacity of HSEC to respond to phenotypic activators may represent an important mechanism by which they participate in inflammatory responses associated with hepatotoxicity.

Bmi1 is required for hepatic progenitor cell expansion and liver tumor development

Bmi1 is a polycomb group transcriptional repressor and it has been implicated in regulating self-renewal and proliferation of many types of stem or progenitor cells. In addition, Bmi1 has been shown to function as an oncogene in multiple tumor types. In this study, we investigated the functional significance of Bmi1 in regulating hepatic oval cells, the major type of bipotential progenitor cells in adult liver, as well as the role of Bmi1 during hepatocarcinogenesis using Bmi1 knockout mice. We found that loss of Bmi1 significantly restricted chemically induced oval cell expansion in the mouse liver. Concomitant deletion of Ink4a/Arf in Bmi1 deficient mice completely rescued the oval cell expansion phenotype. Furthermore, ablation of Bmi1 delayed hepatocarcinogenesis induced by AKT and Ras co-expression. This antineoplastic effect was accompanied by the loss of hepatic oval cell marker expression in the liver tumor samples. In summary, our data demonstrated that Bmi1 is required for hepatic oval cell expansion via deregulating the Ink4a/Arf locus in mice. Our study also provides the evidence, for the first time, that Bmi1 expression is required for liver cancer development in vivo, thus representing a promising target for innovative treatments against human liver cancer.

Mesenchymal stem cell-derived hepatocytes for functional liver replacement

Mesenchymal stem cells represent an alternate cell source to substitute for primary hepatocytes in hepatocyte transplantation because of their multiple differentiation potential and nearly unlimited availability. They may differentiate into hepatocyte-like cells in vitro and maintain specific hepatocyte functions also after transplantation into the regenerating livers of mice or rats both under injury and non-injury conditions. Depending on the underlying liver disease their mode of action is either to replace the diseased liver tissue or to support liver regeneration through their anti-inflammatory and anti-apoptotic as well as their pro-proliferative action.

Liver regeneration after liver transplantation

BACKGROUND/PURPOSE

The liver has a remarkable capacity to regenerate after injury or resection. The aim of this review is to outline the mechanisms and factors affecting liver regeneration after liver transplantation.

METHODS

Relevant studies were reviewed using Medline, PubMed and Springer databases.

RESULTS

A variety of cytokines (such as interleukin-6 and tumor necrosis factor-α), growth factors (like hepatocyte growth factor and transforming growth factor-α) and cells are involved in liver regeneration. Several factors affect liver regeneration after transplantation such as ischemic injury, graft size, immunosuppression, steatosis, donor age and viral hepatitis.

CONCLUSION

Liver regeneration has been studied for many years. However, further research is essential to reveal the complex processes affecting liver regeneration, which may provide novel strategies in the management of liver transplantation recipients and donors.

Inhibition of kupffer cell activity improves transplantation of human adipose-derived stem cells and liver functions

Numerous approaches to cell transplantation of the hepatic or the extrahepatic origin into liver tissue have been developed; however, the efficiency of cell transplantation remains low and liver functions are not well corrected. The liver is a highly immunoreactive organ that contains many resident macrophages known as Kupffer cells. Here, we show that the inhibition of Kupffer cell activity improves stem cell transplantation into liver tissue and corrects some of the liver functions under conditions of liver injury. We found that, when Kupffer cells were inhibited by glycine, numerous adipose-derived stem cells (ASCs) were successfully transplanted into livers, and these transplanted cells showed hepatoprotective effects, including decrease of liver injury factors, increase of liver regeneration, and albumin production. On the contrary, injected ASCs without glycine recruited numerous Kupffer cells, not lymphocytes, and showed low transplantation efficiency. Intriguingly, successfully transplanted ASCs in liver tissue modulated Kupffer cell activity to inhibit tumor necrosis factor-α secretion. Thus, our data show that Kupffer cell inactivation is an important step in order to improve ASC transplantation efficiency and therapeutic potential in liver injuries. In addition, the hepatoprotective function of glycine has synergic effects on liver protection and the engraftment of ASCs.

Rodent animal models for surrogate analysis of cell therapy in acute liver failure

Without therapeutic intervention acute liver failure (ALF) is the consequence of a progredient destruction of the liver parenchyma due to metabolic exhaustion of the hepatocytes. Perivenous hepatocytes are responsible for the detoxification of noxious compounds via the cytochrome P450 enzyme system. Liver transplantation is the only remaining therapeutic option in the end-stage of the disease. Assuming that metabolic capacity could be provided by healthy hepatocytes and thus substitute for the genuine parenchymal cells hepatocyte transplantation since quite some time is considered to be an alternative to whole liver transplantation. While this hypothesis achieved proof-of-concept in animal trials clinical breakthrough is still awaiting success, the reasons of which are ongoing matter of debate. In recent times mesenchymal stem cells (MSC) came into focus as a transplantable cell source to treat ALF. Interestingly, as demonstrated in various rodent animal models their mode of action is rather based on trophic support of hepatocytes remaining in the damaged host parenchyma rather than substitution of tissue loss. Mechanistically, either direct or indirect paracrine effects from the transplanted cells acting pro-proliferative, anti-apoptotic, and anti-inflammatory seem to trigger the regenerative response of the residual healthy hepatocytes in the otherwise lethally injured liver parenchyma. Thus, allogeneic MSC may be the best choice for the treatment of ALF taking advantage of their short-term benefit to sustain the critical phase of the acute insult avoiding long-term immunosuppression.

Granulocyte colony-stimulating factor mobilizes CD34(+) cells and improves survival of patients with acute-on-chronic liver failure

BACKGROUND & AIMS

Acute-on-chronic liver failure (ACLF) develops in patients with chronic liver disease and has high mortality. Mobilization of bone marrow-derived stem cells with granulocyte colony-stimulating factor (G-CSF) could promote hepatic regeneration.

METHODS

Consecutive patients with ACLF were randomly assigned to groups given 5 μg/kg G-CSF subcutaneously (12 doses; group A, n = 23) or placebo (group B, n = 24) plus standard medical therapy. We assessed survival until day 60; Child-Turcotte-Pugh (CTP), Model for End-Stage Liver Disease (MELD), and Sequential Organ Failure Assessment (SOFA) scores; and the development of other related complications.

RESULTS

After 1 week of treatment, group A had higher median leukocyte and neutrophil counts than group B (P < .001). Sixteen patients in group A (69.6%) and 7 in group B (29%) survived; the actuarial probability of survival at day 60 was 66% versus 26%, respectively (P = .001). Treatment with G-CSF also reduced CTP scores in group A by a median of 33.3% compared with an increase of 7.1% in group B (P = .001), along with MELD (median reduction of 15.3% compared with an increase of 11.7% in group B; P = .008) and SOFA scores (median reduction of 50% compared with an increase of 50% in group B; P = .001). The percentages of patients who developed hepatorenal syndrome, hepatic encephalopathy, or sepsis were lower in group A than in group B (19% vs 71% [P = .0002], 19% vs 66% [P = .001], and 14% vs 41% [P = .04], respectively). After 1 month of treatment, G-CSF increased the number of CD34(+) cells in the liver (by 45% compared with 27.5% in group B; P = .01).

CONCLUSIONS

G-CSF therapy more than doubles the percentage of patients with ACLF who survive for 2 months; it also significantly reduces CTP, MELD, and SOFA scores and prevents the development of sepsis, hepatorenal syndrome, and hepatic encephalopathy.

Genetic abolishment of hepatocyte proliferation activates hepatic stem cells

Quiescent hepatic stem cells (HSCs) can be activated when hepatocyte proliferation is compromised. Chemical injury rodent models have been widely used to study the localization, biomarkers, and signaling pathways in HSCs, but these models usually exhibit severe promiscuous toxicity and fail to distinguish damaged and non-damaged cells. Our goal is to establish new animal models to overcome these limitations, thereby providing new insights into HSC biology and application. We generated mutant mice with constitutive or inducible deletion of Damaged DNA Binding protein 1 (DDB1), an E3 ubiquitin ligase, in hepatocytes. We characterized the molecular mechanism underlying the compensatory activation and the properties of oval cells (OCs) by methods of mouse genetics, immuno-staining, cell transplantation and gene expression profiling. We show that deletion of DDB1 abolishes self-renewal capacity of mouse hepatocytes in vivo, leading to compensatory activation and proliferation of DDB1-expressing OCs. Partially restoring proliferation of DDB1-deficient hepatocytes by ablation of p21, a substrate of DDB1 E3 ligase, alleviates OC proliferation. Purified OCs express both hepatocyte and cholangiocyte markers, form colonies in vitro, and differentiate to hepatocytes after transplantation. Importantly, the DDB1 mutant mice exhibit very minor liver damage, compared to a chemical injury model. Microarray analysis reveals several previously unrecognized markers, including Reelin, enriched in oval cells. Here we report a genetic model in which irreversible inhibition of hepatocyte duplication results in HSC-driven liver regeneration. The DDB1 mutant mice can be broadly applied to studies of HSC differentiation, HSC niche and HSCs as origin of liver cancer.

Transdifferentiation of mature hepatocytes into bile duct/ductule cells within a collagen gel matrix

The phenotype of hepatocytes has been thought to be fixed once they are terminally differentiated. However, we and other investigators have demonstrated that mature hepatocytes can transform into bile duct/ductule cells in various experimental conditions in vitro. Since the normal bile duct system is almost invariably surrounded by dense periportal collagenous matrices, we placed isolated hepatocytes in a collagen-rich environment to address whether mature hepatocytes can transform into ductular cells. Here, we describe in detail our three-dimensional collagen culture method for the induction of transdifferentiation of mature rat hepatocytes into bile ductular cells. Our in vitro system might be useful for the elucidation of the mechanisms of the aberrant differentiation of hepatocytes in the diseased liver.

Ethanol metabolism activates cell cycle checkpoint kinase, Chk2

Chronic ethanol abuse results in hepatocyte injury and impairs hepatocyte replication. We have previously shown that ethanol metabolism results in cell cycle arrest at the G2/M transition, which is partially mediated by inhibitory phosphorylation of the cyclin-dependent kinase, Cdc2. To further delineate the mechanisms by which ethanol metabolism mediates this G2/M arrest, we investigated the involvement of upstream regulators of Cdc2 activity. Cdc2 is activated by the phosphatase Cdc25C. The activity of Cdc25C can, in turn, be regulated by the checkpoint kinase, Chk2, which is regulated by the kinase ataxia telangiectasia mutated (ATM). To investigate the involvement of the regulators of Cdc2 activity, VA-13 cells, which are Hep G2 cells modified to efficiently express alcohol dehydrogenase, were cultured in the presence or absence of 25 mM ethanol. Immunoblots were performed to determine the effects of ethanol metabolism on the activation of Cdc25C, Chk2, and ATM. Ethanol metabolism increased the active forms of ATM and Chk2, as well as the phosphorylated form of Cdc25C. Additionally, inhibition of ATM resulted in approximately 50% of the cells being rescued from the G2/M cell cycle arrest and ameliorated the inhibitory phosphorylation of Cdc2. Our findings demonstrated that ethanol metabolism activates ATM. ATM can activate the checkpoint kinase Chk2, resulting in phosphorylation of Cdc25C and ultimately in the accumulation of inactive Cdc2. This may, in part, explain the ethanol metabolism-mediated impairment in hepatocyte replication, which may be important in the initiation and progression of alcoholic liver injury.

Triple labeling with three thymidine analogs reveals a well-orchestrated regulation of hepatocyte proliferation during liver regeneration

AIM

  After a two-thirds partial hepatectomy (PHx) in rodents, the remaining cells will proliferate and restore the lost liver mass within 7 days. Previous studies have proved that the residual hepatocytes proliferate in a synchronous manner. However, the existing data can not reflect the chronicle of individual hepatocytes proliferation during liver regeneration.

METHODS

  In this study, a combination of pulse and continuous labeling using three thymidine analogs, Bromodeoxyuridine (BrdU), Chlorodeoxyuridine (CldU) and Iododeoxyuridine (IdU), were used to analyze the cell proliferation of rat liver after PHx. This strategy allows us to follow an individual cell for more than one cell cycle and to define how many cells and which cells undergo multiple divisions.

RESULTS

  The residual hepatocytes clustered into three subpopulations to initiate the proliferation sequentially, and the corresponding percentage of each was 32%, 17%, and 36%. Meanwhile, the remaining 15% of hepatocytes never proliferated. In addition, the periportal hepatocytes were the first to respond to PHx stimulation and re-proliferated synchronously at 54 h. Furthermore, at least 11% of residual hepatocytes were identified to divide thrice or more.

CONCLUSION

  Based on the present analysis, we concluded a sequential model of the initial proliferation in residual hepatocytes, and for the first time, quantitatively elucidated the proliferation manner of three subpopulations during liver regeneration.

Clinicopathological analysis of 14 patients with combined hepatocellular carcinoma and cholangiocarcinoma

BACKGROUND

Combined hepatocellular carcinoma and cholangiocarcinoma (cHCC-CC) is an uncommon subtype of primary hepatic carcinoma, and its prognosis is poor. This study was undertaken to investigate the prognosis and the clinicopathological characteristics of cHCC-CC, including their possible cellular origin.

METHODS

Among 852 patients with a primary hepatic carcinoma who underwent hepatectomy from January 1998 to April 2008 at our hospital, cHCC-CC was identified in 14 patients. The clinicopathological characteristics of the 14 patients were analyzed retrospectively. The expression of the liver stem cell markers (c-kit, CD90, CD133 and CK19) in the tumor tissue was detected by immunohistochemistry, and the Kaplan-Meier method was used to evaluate survival.

RESULTS

Among the 14 patients, 9 presented with abdominal pain, 3 with anorexia and debilitation, and the remaining two patients were asymptomatic. The mean age was 53.6+/-3.0 (range 38-74) years. Among the included patients, 11 had an elevated serum alpha-fetoprotein level, 13 were infected with hepatitis B virus, 9 had vascular invasion and 1 had lymph node metastasis. The average diameter of the tumors was 9.9+/-1.1 (range 5.0-16.0) cm. The median overall survival time was 7.9+/-1.0 months. In addition, the presence of the liver stem cell markers, c-kit, CD90, CD133 and CK19 was 71.4%, 85.7%, 92.9% and 78.6%, respectively. All four markers were simultaneously expressed in eight cases.

CONCLUSIONS

cHCC-CC has aggressive characteristics and the prognosis is extremely dismal. The high expression of liver stem cell markers in the tumor tissue suggests that these tumors may derive from liver stem cells.

Fate tracing of mature hepatocytes in mouse liver homeostasis and regeneration

Recent evidence has contradicted the prevailing view that homeostasis and regeneration of the adult liver are mediated by self duplication of lineage-restricted hepatocytes and biliary epithelial cells. These new data suggest that liver progenitor cells do not function solely as a backup system in chronic liver injury; rather, they also produce hepatocytes after acute injury and are in fact the main source of new hepatocytes during normal hepatocyte turnover. In addition, other evidence suggests that hepatocytes are capable of lineage conversion, acting as precursors of biliary epithelial cells during biliary injury. To test these concepts, we generated a hepatocyte fate-tracing model based on timed and specific Cre recombinase expression and marker gene activation in all hepatocytes of adult Rosa26 reporter mice with an adenoassociated viral vector. We found that newly formed hepatocytes derived from preexisting hepatocytes in the normal liver and that liver progenitor cells contributed minimally to acute hepatocyte regeneration. Further, we found no evidence that biliary injury induced conversion of hepatocytes into biliary epithelial cells. These results therefore restore the previously prevailing paradigms of liver homeostasis and regeneration. In addition, our new vector system will be a valuable tool for timed, efficient, and specific loop out of floxed sequences in hepatocytes.

Hierarchies of transcriptional regulation during liver regeneration

The remarkable capacity of the liver to regenerate after severe injury or disease has excited interest for centuries. The goal of harnessing this process in treatment of liver disease, and the appreciation of the parallels between regeneration and tumor development in the liver, remain a major driver for research in this area. Studies of liver regeneration as a model system offer a view of intricate and precisely timed regulatory pathways that drive the process toward completion. Successful regeneration of the liver mass demands a hierarchal and well-controlled balance between proliferative and metabolic functions, which is orchestrated by signaling and regulation of transcription factors. Control and regulation of these cascades of transcriptional activities, necessary for induction, renewal, and cessation of liver growth, are the focus of this chapter.

Identification of circulating CD90 CD73 cells in cirrhosis of liver

AIM

To identify circulating CD90(+) CD73(+) CD45(-) cells and evaluate their in vitro proliferating abilities.

METHODS

Patients with cirrhosis (n = 43), and healthy volunteers (n = 40) were recruited to the study. Mononuclear cells were isolated and cultured from the peripheral blood of controls and cirrhosis patients. Fibroblast-like cells that appeared in cultures were analyzed for morphological features, enumerated by flow cytometry and confirmed by immunocytochemistry (ICC). Colony forming efficiency (CFE) of these cells was assessed and expressed as a percentage.

RESULTS

In comparison to healthy volunteers, cells obtained from cirrhotic patients showed a significant increase (P < 0.001) in the percentage of CD90(+) CD73(+) CD45(-) cells in culture. Cultured cells also showed 10 fold increases in CFE. Flow cytometry and ICC confirmed that the proliferating cells expressed CD90(+) CD73(+) in the cultures from cirrhosis patients.

CONCLUSION

These results indicate the presence of circulating CD90(+) CD73(+) CD45(-) cells in patients with liver cirrhosis that have the potential to proliferate at a higher rate.

Liver stem cells

The capacity of hepatocytes and cholangiocytes to contribute to their own maintenance has long been recognized. More recently, studies have indicated the presence of both intra-hepatic and extra-hepatic stem/progenitor cell populations. The intraorgan compartment probably derives primarily from the biliary tree, most particularly the most proximal branches, i.e. the canals of Hering and smallest ductules. The extra-organ compartment is at least in part derived from diverse populations of cells from the bone marrow. These three tiers of liver cell regeneration serve to maintain the normal organ and to regenerate damaged parenchyma in response to a variety of insults. The nature and extent of the insult determines the balance between these stem/progenitor compartments.

Use of hepatocyte and stem cells for treatment of post-resectional liver failure: are we there yet?

Post-operative liver failure following extensive resections for liver tumours is a rare but significant complication. The only effective treatment is liver transplantation (LT); however, there is a debate about its use given the high mortality compared with the outcomes of LT for chronic liver diseases. Cell therapy has emerged as a possible alternative to LT especially as endogenous hepatocyte proliferation is likely inhibited in the setting of prior chemo/radiotherapy. Both hepatocyte and stem cell transplantations have shown promising results in the experimental setting; however, there are few reports on their clinical application. This review identifies the potential stem cell sources in the body, and highlights the triggering factors that lead to their mobilization and integration in liver regeneration following major liver resections.

Advances in understanding the relationship between liver cancer stem cells and metastasis and relapse of liver cancer

Many factors may affect the prognosis of liver cancer, including late diagnosis, cirrhosis, and insensitivity of tumor cells to chemotherapy, and postoperative metastasis and relapse. Previous studies on the metastasis and relapse of liver cancer focused mainly on the migration and shedding of liver cancer cells, adhesion of liver cancer cells to surrounding tissue, and generation of peripheral vessels. The advances in research on liver cancer stem cells (LCSCs) have led to a better understanding of the metastasis and relapse of liver cancer. This paper gives a comprehensive review of LCSCs at the genetic level in terms of their origin and surface markers, signaling pathways involved, and treatment implications.

Management of Liver Failure: From Transplantation to Cell-Based Therapy

The severe shortage of deceased donor organs has driven a search for alternative methods of treating liver failure. In this context, cell-based regenerative medicine is emerging as a promising interdisciplinary field of tissue repair and restoration, able to contribute to improving health in a minimally invasive fashion. Several cell types have allowed long-term survival in experimental models of liver injury, but their therapeutic potential in humans should be regarded with deep caution, because few clinical trials are currently available and the number of patients enrolled so far is too small to assess benefits versus risks. This review summarizes the current literature on the physiological role of endogenous stem cells in liver regeneration and on the therapeutic benefits of exogenous stem cell administration with specific emphasis on the potential clinical uses of mesenchymal stem cells. Moreover, critical points that still need clarification, such as the exact identity of the stem-like cell population exerting the beneficial effects, as well as the limitations of stem cell-based therapies, are discussed.

Neurofibromatosis type 2/Merlin: sharpening the myth of prometheus

The molecular signals that control the maintenance and activation of liver stem/progenitor cells are poorly understood, and the role of liver progenitor cells in hepatic tumorigenesis is unclear. We report here that liver-specific deletion of the neurofibromatosis type 2 (NF2) tumor suppressor gene in the developing or adult mouse specifically yields a dramatic, progressive expansion of progenitor cells throughout the liver without affecting differentiated hepatocytes. All surviving mice eventually developed both cholangiocellular and hepatocellular carcinoma,suggesting that Nf2-/-progenitors can be a cell of origin for these tumors. Despite the suggested link between NF2 and the Hpo/Wts/Yki signaling pathway in Drosophila, and recent studies linking the corresponding Mst/Lats/Yap pathway to mammalian liver tumorigenesis, our molecular studies suggest that Merlin is not a major regulator of YAP in liver progenitors,and that the overproliferation of Nf2-/-liver progenitors is instead driven by aberrant epidermal growth factor receptor (EGFR) activity. Indeed, pharmacologic inhibition of EGFR blocks the proliferation of Nf2-/-liver progenitors in vitro and in vivo, consistent with recent studies indicating that the NF2-encoded protein Merlin can control the abundance and signaling of membrane receptors such as EGFR. Together,our findings uncover a critical role for NF2/Merlin in controlling homeostasis of the liver stem cell niche.

Infection, stem cells and cancer signals

The association of cancer with preceding parasitic infections has been observed for over 200 years. Some such cancers arise from infection of tissue stem cells by viruses with insertion of viral oncogenes into the host DNA (mouse polyoma virus, mouse mammary tumor virus). In other cases the virus does not insert its DNA into the host cells, but rather commandeers the metabolism of the infected cells, so that the cells continue to proliferate and do not differentiate (human papilloma virus and cervical cancer). Cytoplasmic Epstein Barr virus infection is associated with a specific gene translocation (Ig/c-myc) that activates proliferation of affected cells (Burkitt lymphoma). In chronic osteomyelitis an inflammatory reaction to the infection appears to act through production of inflammatory cytokines and oxygen radical formation to induce epithelial cancers. Infection with Helicobacter pylori leads to epigenetic changes in methylation and infection by a parasite. Clonorchis sinensis also acts as a promoter of cancer of the bile ducts of the liver (cholaniocarcinoma). The common thread among these diverse pathways is that the infections act to alter tissue stem cell signaling with continued proliferation of tumor transit amplifying cells.

Liver stem/progenitor cells in the canals of Hering: cellular origin of hepatocellular carcinoma with bile duct tumor thrombi?

It is generally believed that the invasion of hepatocellular carcinoma (HCC) into the biliary tree ultimately leads to the formation of bile duct tumor thrombi (BDTT). However, recent studies revealed that primary tumor might be small, even undetectable, and there was no histopathologic evidence of direct tumor invasion into bile duct wall in some patients. During the last decade, efforts on stem cell biology may shed light on the pathogenesis of BDTT. Presently, accumulating evidence supports the following notions: (1) the canals of Hering (CoH) are the most likely origin of liver stem/progenitor cells (LSPCs) in adult livers; (2) similar signalling pathways may regulate self-renewal in LSPCs and liver cancer cells, and a substantial proportion of liver tumors may often originate from the transformation of LSPCs; and (3) liver cancer contains rare cells with stem cell-like properties, which could derive from malignant transformation of LSPCs. Herein, we propose that HCC with BDTT, especially with small or undetectable primary lesion and/or no histopathologic evidence for bile duct invasion, might arise from LSPCs residing in the CoH and, possibly, some primary lesions are formed firstly within the intrahepatic biliary tree. When "tumor thrombi" extends mainly along bile duct, there might be "BDTT" alone; when it invades into surrounding parenchyma, there might often be small "primary tumor" with "BDTT". If this holds true, the putative type may be a particular subset of HCC, and most importantly it would facilitate our understanding of stem-cell origin of HCC.

Stem cells in acute liver failure

Patients with acute liver failure are a particularly challenging group, with unique difficulties faced in treatment decisions. Life-saving therapy is available, but organ shortage, delays in transplantation, and complications in management result in a high mortality in this group of patients even after transplant. Any pharmacologic intervention that improved outcomes in this population of critically ill patients would be of great benefit. Based on available evidence, different scenarios of participation of HSCs in liver recovery are conceivable. Encouraging HSCs to differentiate into hepatocytes or supply paracrine and cellular level support to accelerate ongoing local repair mechanisms and assist a failing liver with inadequate mass and functional capacity might be directed to occur effectively in humans. Evidence within small animal models of liver injury and observations within the human population suggest that this might also be encouraged. The use of pharmacologic agents to mobilize hematopoietic stem cells is well established and effectively used in a different population of patients. As such, extending the use of these drugs, such as plerixafor, to the human population has a sound basis. However, there is a need for clarification of the mechanisms by which these cells exert their effect as well as which specific population of cells is involved in the regenerative process. To be clinically relevant in scenarios of acute liver failure, stem cell mobilizing strategies would have to impact survival when administered well after injury. Applications in other settings may also prove useful. Limits to liver resection exist where the size of the future liver remnant governs the extent of resection possible. Preexisting functional impairment may be restrictive, and strategies involving stem cells may assist the future liver remnant in both normal and functionally impaired livers. Benefit has already been reported from treatment with G-CSF in other injured tissues, including the injured myocardium and acutely injured kidney. However, as yet no clinical trial exists to assess the effects of stem cell mobilization in humans with acute liver failure. The familiarity in the use of and success demonstrated in the clinical and experimental use of plerixafor and G-CSF make exploration of hematopoietic stem cells as therapy in patients with acute liver failure appealing.

Clinicopathological characteristics of 20 cases of hepatocellular carcinoma with bile duct tumor thrombi

BACKGROUND

Hepatocellular carcinoma (HCC) with bile duct tumor thrombi (BDTT) is a rare type of primary liver cancer, and its clinical and pathological characteristics remain to be defined.

AIMS

To investigate the clinical and pathological characteristics of HCC with BDTT.

METHODS

Among 676 HCC patients who underwent surgical treatment from Dec. 2002 to Dec. 2008 at the author's hospital, HCC with BDTT was identified in 20 patients. The clinical and pathological characteristics of the 20 patients were measured or analyzed retrospectively. The integrity of the involved bile duct was examined macroscopically and microscopically, the expression of liver stem cell markers was investigated by immunohistochemistry, and the Kaplan-Meier method was adopted for evaluating survival.

RESULTS

Among the 20 patients, the diameter of the primary tumor was less than 5 cm in 13 patients (range: 0.5-10 cm, mean 4.47±0.68 cm). Most of the primary tumors lacked an intact tumor capsule (15/20, 75%), had simultaneous blood vessel invasion (12/20, 60%), and were poorly differentiated (13/20, 65%). There was no evidence of bile duct wall infiltration by the tumor cells macroscopically or microscopically. The positive rate of the liver stem cell markers c-kit, CD90, CD133, and EpCAM was 90, 90, 85 and 85%, respectively. Postoperative overall survival rates at 1, 2, and 3 years were 73.1, 41.1, and 20.6%, respectively. The log-rank test showed that the overall survival rates were significantly worse for HCC patients with BDTT than for HCC patients without BDTT (P=0.016).

CONCLUSIONS

HCC with BDTT has aggressive characteristics and the long-term prognosis is extremely dismal.

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.

Stem cell-based therapies for liver diseases: state of the art and new perspectives

Millions of patients worldwide suffer from end-stage liver pathologies, whose only curative therapy is liver transplantation (OLT). Given the donor organ shortage, alternatives to OLT have been evaluated, including cell therapies. Hepatocyte transplantation has been attempted to cure metabolic liver disorders and end-stage liver diseases. The evaluation of its efficacy is complicated by the shortage of human hepatocytes and their difficult expansion and cryopreservation. Recent advances in cell biology have led to the concept of "regenerative medicine", based on the therapeutic potential of stem cells (SCs). Different types of SCs are theoretically eligible for liver cell replacement. These include embryonic and fetal SCs, induced pluripotent cells, annex SCs, endogenous liver SCs, and extrahepatic adult SCs. Aim of this paper is to critically analyze the possible sources of SCs suitable for liver repopulation and the results of the clinical trials that have been published until now.