Little evidence of bone marrow-derived hepatocytes in the replacement of injured liver

Co-Culture of Human Mesenchymal Stromal Cells and Primary Mouse Hepatocytes

Human mesenchymal stromal cells (MSC) are adult stem cells, which feature hepatotropism by supporting liver regeneration through amelioration of hepatic inflammation and lipid accumulation in a mouse model of non-alcoholic steatohepatitis (NASH), a more advanced stage of fatty liver. It remains open, how MSC impact on hepatocytic lipid metabolism. To study MSC actions on fatty liver mechanistically, we established an in vitro model of co-culture comprising MSC and isolated mouse hepatocytes at a ratio of 1:1. Lipid storage in hepatocytes was induced by the treatment with medium deficiency of methionine and choline (MCD). The protocol can be adapted for the use of other lipid storage-inducing agents such as palmitic acid and linoleic acid. This co-culture model allows to study, e.g., whether MSC act indirectly via MSC-born paracrine mechanisms or through direct physical interactions between cells beside others. The protocol allows us to detect the formation of extensions (filopodia) from MSC to contact the fatty hepatocytes or other MSC within 24 h of co-culture. These structures may represent tunneling nanotubes (TNT), allowing for long-range intercellular communication.

Mitochondrial Transfer by Human Mesenchymal Stromal Cells Ameliorates Hepatocyte Lipid Load in a Mouse Model of NASH

Mesenchymal stromal cell (MSC) transplantation ameliorated hepatic lipid load; tissue inflammation; and fibrosis in rodent animal models of non-alcoholic steatohepatitis (NASH) by as yet largely unknown mechanism(s). In a mouse model of NASH; we transplanted bone marrow-derived MSCs into the livers; which were analyzed one week thereafter. Combined metabolomic and proteomic data were applied to weighted gene correlation network analysis (WGCNA) and subsequent identification of key drivers. Livers were analyzed histologically and biochemically. The mechanisms of MSC action on hepatocyte lipid accumulation were studied in co-cultures of hepatocytes and MSCs by quantitative image analysis and immunocytochemistry. WGCNA and key driver analysis revealed that NASH caused the impairment of central carbon; amino acid; and lipid metabolism associated with mitochondrial and peroxisomal dysfunction; which was reversed by MSC treatment. MSC improved hepatic lipid metabolism and tissue homeostasis. In co-cultures of hepatocytes and MSCs; the decrease of lipid load was associated with the transfer of mitochondria from the MSCs to the hepatocytes via tunneling nanotubes (TNTs). Hence; MSCs may ameliorate lipid load and tissue perturbance by the donation of mitochondria to the hepatocytes. Thereby; they may provide oxidative capacity for lipid breakdown and thus promote recovery from NASH-induced metabolic impairment and tissue injury.

Therapeutic potential effect of bone marrow-derived mesenchymal stem cells on chronic liver disease in murine Schistosomiasis Mansoni

Some reports have shown that mesenchymal stem cells (MSCs) therapy could ameliorate chemically-induced hepatic fibrosis. This research assesses the therapeutic action of bone marrow mesenchymal stem cells (BM-MSCs) on chronic diseased liver in Schistosoma mansoni infected mice. All infected female mice divided into three groups, one group (15 mice) treated with oral praziquantel (PZQ), second group (15 mice) received intravenous injection of BM-MSCs and third group (15 mice) treated with both MSCs + PZQ. Two control groups (15 mice each) subdivided into one infected and second healthy one. BM-MSCs were obtained from bones of both femur and tibia of male mice (30 mice), then cultured and characterized morphologically by detection of CD105 by flow cytometer. Liver tissues for all groups were examined histopathologically. Measuring of the collagen 1 gene expression was done by real-time PCR and immunohistochemical study to detect stem cells differentiation for detection of MSCs engraftments in liver tissue. MSCs treatment caused marked improvement and regression of fibrosis, and prevents deposition of collagen and reduced the expression of collagen 1 gene in infected mice on their liver tissues, especially when used with PZQ in mice treatment. It can be concluded that, MSCs is a good therapeutic method for liver fibrosis caused by S. mansoni infection.

Cell fusion in the liver, revisited

There is wide agreement that cell fusion is a physiological process in cells in mammalian bone, muscle and placenta. In other organs, such as the cerebellum, cell fusion is controversial. The liver contains a considerable number of polyploid cells: They are commonly believed to originate by genome endoreplication, although the contribution of cell fusion to polyploidization has not been excluded. Here, we address the topic of cell fusion in the liver from a historical point of view. We discuss experimental evidence clearly supporting the hypothesis that cell fusion occurs in the liver, specifically when bone marrow cells were injected into mice and shown to rescue genetic hepatic degenerative defects. Those experiments-carried out in the latter half of the last century-were initially interpreted to show “transdifferentiation”, but are now believed to demonstrate fusion between donor macrophages and host hepatocytes, raising the possibility that physiologically polyploid cells, such as hepatocytes, could originate, at least partially, through homotypic cell fusion. In support of the homotypic cell fusion hypothesis, we present new data generated using a chimera-based model, a much simpler model than those previously used. Cell fusion as a road to polyploidization in the liver has not been extensively investigated, and its contribution to a variety of conditions, such as viral infections, carcinogenesis and aging, remains unclear.

Circulating CD34+ hematopoietic stem/progenitor cells paralleled with level of viremia in patients chronically infected with hepatitis B virus

Introduction: Liver regeneration is a heterogeneous process involving proliferation of different cell types in response to injury. Bone marrow derived stem cells may be involved in this process, by making contribution to parenchymal restoration and cellular replacement. We aimed to investigate the correlation between level of circulating mobilized CD34+ hematopoietic stem progenitor cells (HSPCs) and viremia level in patients chronically infected with hepatitis B virus (HBV).

Methods: Blood samples were prospectively collected for assessing percentage and absolute counts of circulating CD34+ HSPCs and viral load level using flow cytometry and RT-PCR respectively. Patients with chronic hepatitis B (CHB) (n = 30), Entecavir (ETV) treated subjects (n = 30) and 20 age and gender matched healthy controls were enrolled in this study. Results were expressed as mean ± SD.

Results and discussion: A significant increase in circulating CD34+ HSPCs level was observed in CHB patients (5 ± 3.1, 324 ± 195 × 10³/ml) as compared to ETV treated subjects (0.57 ± 0.27,1022 ± 325) and healthy controls (0.53 ± 0.37, 694 ± 254, P < 0.001) in regards to percentage and absolute counts respectively. Levels of CD34+ HSPCs strongly and positively correlated with HBV DNA viral load levels in CHB patients (r² = 0.8417, 0.649, P < 0.001).Thus, in chronic liver disorders (CHB), when reduced regenerative capacity of hepatocytes is reached, BMSCs mobilization occurs and their level increases in peripheral blood. The level of circulating CD34+ cells in peripheral blood of CHB patients paralleled with the hepatitis B viral load.

Portal Vein Embolization with Contralateral Application of Stem Cells Facilitates Increase of Future Liver Remnant Volume in Patients with Liver Metastases

OBJECTIVES

This study aimed to evaluate the progress of future liver remnant volume (FLRV) in patients with liver metastases after portal vein embolization (PVE) with the application of hematopoietic stem cells (HSCs) and compare it with a patients control group after PVE only.

METHODS

Twenty patients (group 1) underwent PVE with contralateral HSC application. Subsequently, CT volumetry with the determination of FLRV was performed at weekly intervals, in total three weeks. A sample of twenty patients (group 2) who underwent PVE without HSC application was used as a control group.

RESULTS

The mean of FLRV increased by 173.2 mL during three weeks after the PVE/HSC procedure, whereas by 98.9 mL after PVE only (p = 0.015). Furthermore, the mean daily growth of FLRV by 7.6 mL in group 1 was significantly higher in comparison with 4.1 mL in group 2 (p = 0.007).

CONCLUSIONS

PVE with the application of HSC significantly facilitates growth of FLRV in comparison with PVE only. This method could be one of the new suitable approaches to increase the resectability of liver tumours.

Recellularization of rat liver scaffolds by human liver stem cells

In the present study, rat liver acellular scaffolds were used as biological support to guide the differentiation of human liver stem-like cells (HLSC) to hepatocytes. Once recellularized, the scaffolds were maintained for 21 days in different culture conditions to evaluate hepatocyte differentiation. HLSC lost the embryonic markers (alpha-fetoprotein, nestin, nanog, sox2, Musashi1, Oct 3/4, and pax2), increased the expression of albumin, and acquired the expression of lactate dehydrogenase and three subtypes of cytochrome P450. The presence of urea nitrogen in the culture medium confirmed their metabolic activity. In addition, cells attached to tubular remnant matrix structures expressed cytokeratin 19, CD31, and vimentin. The rat extracellular matrix (ECM) provides not only a favorable environment for differentiation of HLSC in functional hepatocytes (hepatocyte like) but also promoted the generation of some epithelial-like and endothelial-like cells. When fibroblast growth factor-epidermal growth factor or HLSC-derived conditioned medium was added to the perfusate, an improvement of survival rate was observed. The conditioned medium from HLSC potentiated also the metabolic activity of hepatocyte-like cells repopulating the acellular liver. In conclusion, HLSC have the potential, in association with the natural ECM, to generate in vitro a functional "humanized liver-like tissue."

The therapeutic effects of bone marrow-derived mesenchymal stem cells and simvastatin in a rat model of liver fibrosis

Liver fibrosis is the excessive accumulation of extracellular matrix (ECM) proteins including collagen that occurs in most types of chronic liver diseases. Studies concerning the capacity of mesenchymal stem cells (MSCs) and simvasatain (SIMV) to repair fibrotic tissues through reducing inflammation, collagen deposition, are still controversial. This study aimed to investigate the therapeutic efficacy of bone marrow (BM)-derived MSCs and SIMV on carbon tetrachloride (CCl4)-induced liver fibrosis in rats. Rats were divided into: normal, CCl4, CCl4/MSCs, CCl4/SIMV, CCl4/MSCs/SIMV, and SIMV groups. BM-derived MSCs were detected by RT-PCR of CD29 and were then infused into the tail vein of female rats that received CCl4 injection to induce liver fibrosis. Sex-determining region Y (SRY) gene on Y-chromosome gene was assessed by PCR to confirm homing of the male stem cells in liver tissue of the female recipients. Serum liver function tests, liver procollagens I and III, tissue inhibitors of metalloproteinase-1 (TIMP-1), endoglin, matrix metalloproteinase-1 (MMP-1) gene expressions, transforming growth factor-beta (TGF-β1) immunostaining, and histopathologicl examination were performed. MSCs and SIMV decreased liver procollagens I and III, TIMP-1 and endoglin gene expressions, TGF-β1 immunostaining, and serum liver function tests compared with the CCl4 group. MMP-1 expression was increased in the CCl4/MSCs group. Histopathological examination as well as fibrosis score supports the biochemical and molecular findings. It can be concluded that MSCs and SIMV were effective in the treatment of hepatic CCl4-induced fibrosis-rat model. Treatment with MSCs was superior to SIMV. This antifibrotic effect can be attributed to their effect on the MMPs/TIMPs balance which is central in fibrogenesis.

Concise review: bone marrow autotransplants for liver disease?

There are increasing reports of using bone marrow-derived stem cells to treat advanced liver disease. We consider several critical issues that underlie this approach. For example, are there multipotent stem cell populations in human adult bone marrow? Can they develop into liver cells or supporting cell types? What are stromal stem/progenitor cells, and can they promote tissue repair without replacing hepatocytes? Does reversal of end-stage liver disease require new hepatocytes, a new liver microenvironment, both, neither or something else? Although many of these questions are unanswered, we consider the conceptual and experimental bases underlying these issues and critically analyze results of clinical trials of stem cell therapy of end-stage liver disease.

Bone marrow stem cell therapy for liver disease

Liver disease is a rising cause of mortality and morbidity, and treatment options remain limited. Liver transplantation is curative but limited by donor organ availability, operative risk and long-term complications. The contribution of bone marrow (BM)-derived stem cells to tissue regeneration has been recognised and there is considerable interest in the potential benefits of BM stem cells in patients with liver disease. In chronic liver disease, deposition of fibrous scar tissue inhibits hepatocyte proliferation and leads to portal hypertension. Although initial reports had suggested transdifferentiation of stem cells into hepatocytes, the beneficial effects of BM stem cells are more likely derived from the ability to breakdown scar tissue and stimulate hepatocyte proliferation. Studies in animal models have yielded promising results, although the exact mechanisms and cell type responsible have yet to be determined. Small-scale clinical studies have quickly followed and, although primarily designed to examine safety and feasibility of this approach, have reported improvements in liver function in treated patients. Well-designed, controlled studies are required to fully determine the benefits of BM stem cell therapy.

Effect of transplantation route on stem cell migration to fibrotic liver of rats via cellular magnetic resonance imaging

BACKGROUND AIMS

Assessing mesenchymal stromal cells (MSCs) after grafting is essential for understanding their migration and differentiation processes. The present study sought to evaluate via cellular magnetic resonance imaging (MRI) if transplantation route may have an effect on MSCs engrafting to fibrotic liver of rats.

METHODS

Rat MSCs were prepared, labeled with superparamagnetic iron oxide and scanned with MRI. Labeled MSCs were transplanted via the portal vein or vena caudalis to rats with hepatic fibrosis. MRI was performed in vitro before and after transplantation. Histologic examination was performed. MRI scan and imaging parameter optimization in vitro and migration under in vivo conditions were demonstrated.

RESULTS

Strong MRI susceptibility effects could be found on gradient echo-weighted, or T2∗-weighted, imaging sequences from 24 h after labeling to passage 4 of labeled MSCs in vitro. In vivo, MRI findings of the portal vein group indicated lower signal in liver on single shot fast spin echo-weighted, or T2-weighted, imaging and T2∗-weighted imaging sequences. The low liver MRI signal increased gradually from 0-3 h and decreased gradually from 3 h to 14 days post-transplantation. The distribution pattern of labeled MSCs in liver histologic sections was identical to that of MRI signal. It was difficult to find MSCs in tissues near the portal area on day 14 after transplantation; labeled MSCs appeared in fibrous tuberculum at the edge of the liver. No MRI signal change and a positive histologic examination were observed in the vena caudalis group.

CONCLUSIONS

The portal vein route seemed to be more beneficial than the vena caudalis on MSC migration to fibrotic liver of rats via MRI.

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.

Perspective on liver regeneration by bone marrow-derived stem cells-a scientific realization or a paradox

Bone marrow (BM)-derived stem cells are reported to have cellular plasticity, which provoked many investigators to use of these cells in the regeneration of nonhematopoietic tissues. However, adult stem cell plasticity contradicts our classic understanding on progressive restriction of the developmental potential of a cell type. Many alternate mechanisms have been proposed to explain this phenomenon; the working hypotheses for elucidating the cellular plasticity of BM-derived stem cells are on the basis of direct differentiation and/or fusion between donor and recipient cells. This review dissects the different outcomes of the investigations on liver regeneration, which were performed with the use of BM-derived stem cells in experimental animals, and reveals some critical factors to explain cellular plasticity. It has been hypothesized that the competent BM-derived stem/progenitor cells, under the influence of liver-regenerating cues, can directly differentiate into hepatic cells. This differentiation takes place as a result of genetic reprogramming, which may be possible in the chemically induced acute liver injury model or at the stage of fetal liver development. Cellular plasticity emerges as an important phenomenon in cell-based therapies for the treatment of many liver diseases in which tissue regeneration is necessary.

Hepatogenic differentiation of mesenchymal stem cells in a rat model of thioacetamide-induced liver cirrhosis

Implantation of bone-marrow-derived MSCs (mesenchymal stem cells) has emerged as a potential treatment modality for liver failure, but in vivo differentiation of MSCs into functioning hepatocytes and its therapeutic effects have not yet been determined. We investigated MSC differentiation process in a rat model of TAA (thioacetamide)-induced liver cirrhosis. Male Sprague-Dawley rats were administered 0.04% TAA-containing water for 8 weeks, MSCs were injected into the spleen for transsplenic migration into the liver, and liver tissues were examined over 3 weeks. Ingestion of TAA for 8 weeks induced micronodular liver cirrhosis in 93% of rats. Injected MSCs were diffusely engrafted in the liver parenchyma, differentiated into CK19 (cytokeratin 19)- and thy1-positive oval cells and later into albumin-producing hepatocyte-like cells. MSC engraftment rate per slice was measured as 1.0-1.6%. MSC injection resulted in apoptosis of hepatic stellate cells and resultant resolution of fibrosis, but did not cause apoptosis of hepatocytes. Injection of MSCs treated with HGF (hepatocyte growth factor) in vitro for 2 weeks, which became CD90-negative and CK18-positive, resulted in chronological advancement of hepatogenic cellular differentiation by 2 weeks and decrease in anti-fibrotic activity. Early differentiation of MSCs to progenitor oval cells and hepatocytes results in various therapeutic effects, including repair of damaged hepatocytes, intracellular glycogen restoration and resolution of fibrosis. Thus, these results support that the in vivo hepatogenic differentiation of MSCs is related to the beneficial effects of MSCs rather than the differentiated hepatocytes themselves.

Inhibition of collagen deposit in obstructed rat bladder outlet by transplantation of superparamagnetic iron oxide-labeled human mesenchymal stem cells as monitored by molecular magnetic resonance imaging (MRI)

Bladder outlet obstruction (BOO) caused by collagen deposit is one of the most common problems in elderly males. The present study is to investigate if human mesenchymal stem cells (MSCs) are capable of inhibiting collagen deposition and improve cystometric parameters in bladder outlet obstruction in rats. Human MSCs were labeled with nanoparticles containing superparamagnetic iron oxide (SPION), and transplanted in rat BOO lesion site. Forty 6-week-old female Sprague-Dawley rats were divided into four groups (group 1: control, group 2: sham operation, group 3: BOO, and group 4: BOO rats receiving SPION-hMSCs). Two weeks after the onset of BOO, 1 × 10(6) SPION-hMSCs were injected into the bladder wall. Serial T2-weighted MR images were taken immediately after transplantation of SPION-labeled human MSCs and at 4 weeks posttransplantation. T2-weighted MR images showed a clear hypointense signal induced by the SPION-labeled MSCs. While the expression of collagen and TGF-β protein increased after BOO, the expression of both returned to the original levels after MSC transplantation. Expression of HGF and c-met protein also increased in the group with MSC transplantation. Maximal voiding pressure and residual urine volume increased after BOO but they recovered after MSC transplantation. Human MSCs transplanted in rat BOO models inhibited the bladder fibrosis and mediated recovery of bladder dysfunction. Transplantation of MSC-based cell therapy could be a novel therapeutic strategy against bladder fibrosis in patients with bladder outlet obstruction.

Therapeutic application of stem cells in gastroenterology: An up-date

Adult stem cells represent the self-renewing progenitors of numerous body tissues, and they are currently classified according to their origin and differentiation ability. In recent years, the research on stem cells has expanded enormously and holds therapeutic promises for many patients suffering from currently disabling diseases. This paper focuses on the possible use of stem cells in the two main clinical settings in gastroenterology, i.e., hepatic and intestinal diseases, which have a strong impact on public health worldwide. Despite encouraging results obtained in both regenerative medicine and immune-mediated conditions, further studies are needed to fully understand the biology of stem cells and carefully assess their putative oncogenic properties. Moreover, the research on stem cells arouses fervent ethical, social and political debate. The Italian Society of Gastroenterology sponsored a workshop on stem cells held in Verona during the XVI Congress of the Federation of Italian Societies of Digestive Diseases (March 6-9, 2010). Here, we report on the issues discussed, including liver and intestinal diseases that may benefit from stem cell therapy, the biology of hepatic and intestinal tissue repair, and stem cell usage in clinical trials.

In vivo differentiation of magnetically labeled mesenchymal stem cells into hepatocytes for cell therapy to repair damaged liver

OBJECTIVES

It was unclear whether systemically administered mesenchymal stem cells (MSCs) labeled with magnetic nanoparticles can transdifferentiate into hepatocytes. In the present study, we built a new in vivo murine model for monitoring the transdifferentiation of magnetically labeled green fluorescent protein (GFP) positive MSCs into albumin-positive hepatocytes, under the carbon tetrachloride (CCl4) induced persistent liver damage. We also tracked magnetically labeled MSCs by using magnetic resonance imaging (MRI) in vivo.

MATERIALS AND METHODS

Among the liver damage groups, magnetically labeled GFP-positive MSCs (group A), GFP-positive MSCs (group B), and saline alone (group C) were intravenously injected. In control groups without CCl4 administration magnetically labeled GFP-positive MSCs (group D) were infused, whereas nothing was given in group E. MRI examinations were performed 24 hours and 4 weeks after cell injection in group A, B, and C. Liver-to-muscle contrast-to-noise ratios on T2*-weighted MR images were measured. At 4 weeks, 3 serum biologic liver function markers were analyzed, and mice in all groups were killed for histologic examination.

RESULTS

The results showed that migration of transplanted magnetic labeled cells to the liver was successfully documented with in vivo MRI. Serum liver function markers were changed for all liver damage groups than nondamage control groups (P < 0.05), but still insignificant compared with group C (P > 0.05). Hematoxylin and eosin and Masson staining confirmed the presence of liver damage and hepatic fibrosis in group A, B, and C. Positive Prussian blue stained cells were highly correlated with GFP-positive cells in group A with an average matching rate of 95%. In group D, no iron-GFP-positive cells can be found in the liver. Albumin was expressed in (34% ± 6%) and (35% ± 7%) of GFP-positive cells in group A and B, respectively, and there was no significant difference between the 2 groups.

CONCLUSIONS

Our data demonstrate that magnetic labeling technique synchronized well in GFP expressing MSCs and did not interfere with the transdifferentiation process and amending function of MSCs in vivo. Both magnetically labeled and unlabeled MSCs appeared to have the potential to differentiate into hepatocytes.

Hepatocyte growth factor incorporated chitosan nanoparticles augment the differentiation of stem cell into hepatocytes for the recovery of liver cirrhosis in mice

Background

Short half-life and low levels of growth factors in the niche of injured microenvironment necessitates the exogenous and sustainable delivery of growth factors along with stem cells to augment the regeneration of injured tissues.

Methods

Here, recombinant human hepatocyte growth factor (HGF) was incorporated into chitosan nanoparticles (CNP) by ionic gelation method and studied for its morphological and physiological characteristics. Cirrhotic mice received either hematopoietic stem cells (HSC) or mesenchymal stemcells (MSC) with or without HGF incorporated chitosan nanoparticles (HGF-CNP) and saline as control. Biochemical, histological, immunostaining and gene expression assays were carried out using serum and liver tissue samples. One way analysis of variance was used for statics application

Results

Serum levels of selected liver protein and enzymes were significantly increased in the combination of MSC and HGF-CNP (MSC+HGF-CNP) treated group. Immunopositive staining for albumin (Alb) and cytokeratin 18 (CK18), and reverse transcription-polymerase chain reaction (RT-PCR) for Alb, alpha fetoprotein (AFP), CK18, cytokeratin 19 (CK19) ascertained that MSC-HGF-CNP treatment could be an effective combination to repopulate liver parenchymal cells in the liver cirrhosis. Zymogram and western blotting for matrix metalloproteinases 2 and 9 (MMP2 and MMP9) revealed that MMP2 actively involved in the fibrolysis of cirrhotic tissue. Immunostaining for alpha smooth muscle actin (αSMA) and type I collagen showed decreased expression in the MSC+HGF-CNP treatment. These results indicated that HGF-CNP enhanced the differentiation of stem cells into hepatocytes and supported the reversal of fibrolysis of extracellular matrix (ECM).

Conclusion

Bone marrow stem cells were isolated, characterized and transplanted in mice model. Biodegradable biopolymeric nanoparticles were prepared with the pleotrophic protein molecule and it worked well for the differentiation of stem cells, especially mesenchymal phenotypic cells. Transplantation of bone marrow MSC in combination with HGF-CNP could be an ideal approach for the treatment of liver cirrhosis.

Granulocyte colony-stimulating factor treatment ameliorates liver injury and improves survival in rats with D-galactosamine-induced acute liver failure

Only liver transplantation is currently available therapy for the patients with acute liver failure (ALF). This study was designed to determine whether administration of granulocyte colony-stimulating factor (G-CSF) has therapeutic efficacy in animals with ALF. Female Sprague-Dawley (SD) rats were intraperitoneally injected with a single dose of d-galactosamine (d-GalN, 1.4g/kg) to induce ALF. After 2h, the rats were randomized to receive G-CSF (50μg/kg/day), or saline vehicle injection for 5 days. Rats were observed for survival and assessed for liver injury by serum alanine transaminase (ALT) measurement and histological analysis. CD34+ cells in bone marrow were assessed by flow cytometry. CD34+ cells and Ki-67+ hepatocytes in liver tissue were evaluated by immunohistochemistry. In the ALF model, 5-day survival after d-GalN injection was 33.3% (10/30), while G-CSF administration following d-GalN resulted in 53.3% (16/30) survival (p=0.027). G-CSF treated rats had lower ALT level and less hepatic injury compared with saline vehicle rats. The increases of CD34+ cells in bone marrow and liver tissue and Ki-67+ cells in liver tissue in G-CSF treated rats were higher than those in saline rats. No correlation was observed between CD34+ cells and Ki-67+ hepatocytes in liver tissue in both G-CSF and vehicle rats. It is suggested that G-CSF increases survival rate, decreases liver injury and enhances hepatocyte proliferation in rats with d-GalN-induced ALF possibly through actions including but not limiting to CD34+ cell mobilization, and that G-CSF may be of potential value in treating ALF.

Possibility of differentiation of hematopoietic stem cells into liver cells

Bone marrow-derived hematopoietic stem cells have the potential to undergo multilineage differentiation. Recent studies have shown that, in a given microenvironment, hematopoietic stem cells can differentiate into liver cells. However, some researchers hold a dissenting view. This review discusses the possibility of differentiation of hematopoietic stem cells into liver cells.

Culture of omentum-induced regenerating liver yielded hepatocyte-committed stem cells

Earlier we showed that when omentum, activated by inert particles, is allowed to fuse to a wedge cut in the liver, it induces stem cell proliferation in the liver resulting in massive liver regeneration. Here, we attempt to culture stem cells from the omentum-induced regenerating liver tissue. Cells from regenerating liver tissue were harvested and cultured. Cultured cells were characterized by immune staining, fluorescence activated cell sorting analysis, growth factor assay, in vitro differentiation, and their ability to engraft to injured sites in vivo. Culture yielded cells with a mesenchymal stem cell phenotype that could be maintained in culture indefinitely. These cells, called regenerating liver stem cells, expressed both adult and embryonic stem cell markers, secreted high levels of vascular endothelial growth factor, and expressed albumin. When grown on matrigel in the presence of hepatocyte growth factor, these cells differentiated into hepatocyte-like cells in culture, but they did not differentiate to adipogenic and osteogenic lineages when grown in specific differentiation medium. The differentiated cells expressed α-fetoprotein and secreted high levels of albumin and urea. After systemic injection, the undifferentiated cells engrafted only to the injured sites in the liver and not to the normal areas of the liver. In conclusion, omentum-induced regenerating liver yields hepatocyte-committed stem cells in culture. Such cells could prove to be useful in cell transplantation therapies.

Autologous bone marrow infusion activates the progenitor cell compartment in patients with advanced liver cirrhosis

Several clinical trials of bone marrow cell infusion in patients with liver cirrhosis (LC) have shown clinical improvement, despite conflicting results from animal models. We investigated serial pathological features and the clinical impact after autologous bone marrow infusion (ABMI) in patients with advanced LC. Ten patients with advanced LC due to chronic hepatitis B virus infection underwent ABMI. Serological tests, MRI, and liver biopsies were performed, and quality of life was assessed by a questionnaire. Median serum albumin and hemoglobin levels increased significantly after ABMI. All patients showed an improvement in quality of life, with no serious adverse events. Liver volume, measured by MRI, increased in 80% of the patients, and ascites decreased after ABMI. Child-Pugh scores were also significantly improved at 6 months after ABMI. In the serially biopsied livers, a gradually increasing activation of the hepatic progenitor cell (HPC) compartment, including HPC activation (ductular reaction) and HPC differentiation (intermediate hepatocyte), reached a peak after 3 months, with continued proliferation of hepatocytes, and returned to baseline levels after 6 months. There was no significant change in grade or stage of liver fibrosis or stellate cell activation after ABMI. ABMI is suggested to improve liver function and to activate the progenitor cell compartment. Although clinical improvement was sustained for more than 6 months, histological changes in the liver returned to baseline 6 months after ABMI. Further comparative studies are warranted.

Potentials of regenerative medicine for liver disease

Liver transplantation is still the only effective treatment for end-stage liver disease. However, because of the serious worldwide shortage of donated organs, an alternative cellular therapy would be desirable. Animal studies and preclinical trials have indicated that hepatocyte transplantation can serve as an alternative to liver transplantation. Unfortunately, however, the harvesting of hepatocytes is associated with the same problem as organ transplantation, i.e., a lack of a suitable cell source. Therefore, current stem cell technology, which is attempting to establish an unlimited supply of hepatocytes, would facilitate the clinical application of hepatocyte transplantation. This review summarizes current knowledge of embryonic and adult stem cell differentiation into hepatocytes and discusses how liver stem cells could be applied clinically in the future.

Reversibility of liver fibrosis

Liver cirrhosis is a major cause of morbidity and mortality worldwide and has very limited therapeutic options. Regardless of the aetiology, hepatic fibrosis is a characteristic feature of chronic liver disease. Our knowledge regarding the pathogenesis of this scarring has grown exponentially in the past 25 years. It has now clear that this is a highly dynamic process and the long-held dogma that it is irreversible and relentlessly progressive is now being challenged. In this review, we will summarise the key pathogenic mechanisms at play and will focus on the evidence demonstrating that liver fibrosis is reversible in humans and animal models. In particular, we will examine the role of hepatic stellate cells, MMPs, TIMPs and macrophages in this process. Finally, we will discuss some of the studies aimed to therapeutically target the resolution of fibrosis and their potential for translation into a badly-needed treatment modality in the clinical setting.

Repopulation efficiencies of adult hepatocytes, fetal liver progenitor cells, and embryonic stem cell-derived hepatic cells in albumin-promoter-enhancer urokinase-type plasminogen activator mice

Fetal liver progenitor cell suspensions (FLPC) and hepatic precursor cells derived from embryonic stem cells (ES-HPC) represent a potential source for liver cell therapy. However, the relative capacity of these cell types to engraft and repopulate a recipient liver compared with adult hepatocytes (HC) has not been comprehensively assessed. We transplanted mouse and human HC, FLPC, and ES-HPC into a new immunodeficient mouse strain (Alb-uPA(tg(+/-))Rag2(-/-)gamma(c)(-/-) mice) and estimated the percentages of HC after 3 months. Adult mouse HC repopulated approximately half of the liver mass (46.6 +/- 8.0%, 1 x 10(6) transplanted cells), whereas mouse FLPC derived from day 13.5 and 11.5 post conception embryos generated only 12.1 +/- 3.0% and 5.1 +/- 1.1%, respectively, of the recipient liver and smaller cell clusters. Adult human HC and FLPC generated overall less liver tissue than mouse cells and repopulated 10.0 +/- 3.9% and 2.7 +/- 1.1% of the recipient livers, respectively. Mouse and human ES-HPC did not generate HC clusters in our animal model. We conclude that, in contrast to expectations, adult HC of human and mouse origin generate liver tissue more efficiently than cells derived from fetal tissue or embryonic stem cells in a highly immunodeficient Alb-uPA transgenic mouse model system. These results have important implications in the context of selecting the optimal strategy for human liver cell therapies.

Transplantation of interleukin 10-modified bone marrow-derived liver stem cells reduces accumulation of extracellular matrix in fibrotic liver in rats

AIM: To investigate the effects of transplanting interleukin 10 (IL-10)-modified bone marrow-derived liver stem cells (BDLSCs) on accumulation of extracellular matrix in fibrotic liver in rats.

METHODS: Rat beta-2 microglobulin (β₂m)^-/Thy-1⁺ BDLSCs were isolated by magnetic bead cell sorting (MACS), and transduced with adenovirus-mediated IL-10 gene. The level of IL-10 protein secretion by BDLSCs was assessed by ELISA. The rats were divided randomly into four groups: normal group, model group, BDLSCs group and BDLSCs plus IL-10 group. IL-10 gene-modified BDLSCs from male rats were transplanted into female liver fibrosis rats via a branch of the portal vein. Sry gene was amplified by PCR to evaluate the implantation of BDLSCs in liver. Collagen area in liver tissues was detected by Van Gieson's (VG) staining. Expression of α-smooth muscle actin (α-SMA) protein in liver tissue was determined by Western blot. Hydroxyproline (Hyp) in liver tissues was quantified by the alkaline hydrolysis method. Extracellular matrix (ECM) proteins in serum were quantified by ELISA.

RESULTS: BDLSCs were successfully isolated by MACS. IL-10 secreted by IL-10 gene-modified BDLSCs presented persistently at a high level. Transduced BDLSCs were implanted successfully into impaired liver. Transplantation of IL-10 gene-modified BDLSCs lessened deposition of collagen, decreased α-SMA expression and thereby suppressed activation of hepatic stellate cells. Compared with the BDLSCs group, the level of Hyp in liver tissue decreased markedly in the BDLSCs plus IL-10 group (255.0 ± 50.5 μg/g vs 373.0 ± 26.7 μg/g, P < 0.01), and the levels of ECM proteins in serum also decreased (40.5 ± 7.7 μg/L vs 79.4 ± 10.3 μg/L, 61.5 ± 16.4 μg/L vs 77.7 ± 12.6 μg/L, 14.3 ± 0.8 μg/L vs 14.9 ± 1.5 μg/L, P < 0.01 or 0.05).

CONCLUSION: Transplantation of IL-10 gene-modified BDLSCs can effectively decrease accumulation of ECM in fibrotic liver in rats, suggesting the potential utility of this novel combined strategy of cell transplantation with gene therapy for the treatment of liver fibrosis.

Translational research to identify clinical applications of hepatocyte growth factor

Hepatocyte growth factor (HGF), originally purified from the plasma of patients with fulminant hepatic failure, has been shown to carry out various physiological functions. HGF not only stimulates liver regeneration, but also acts as an antiapoptotic factor in in vivo experimental models. Therefore, HGF is a promising therapeutic agent for the treatment of fatal liver diseases, including fulminant hepatic failure. After performing a number of preclinical tests, our group began an investigator-initiated registered phase I/II clinical trial of patients with fulminant hepatic failure to examine the safety and clinical efficacy of recombinant human HGF. In this article, we will discuss the basic research results as well as the translational research that underpins current attempts to use HGF in various clinical settings.

Liver cancer stem cells: implications for a new therapeutic target

Hepatocellular carcinoma (HCC) is an aggressive tumour with a poor prognosis. Current therapeutic strategies against this disease target mostly rapidly growing differentiated tumour cells. However, the result is often dismal due to the chemoresistant nature of this tumour type. Recent research efforts on stem cells and cancer biology have shed light on new directions for the eradication of cancer stem cells (CSCs) in HCC. The liver is a distinctive organ with the ability of tissue renewal in response to injury. Based on the hypothesis that cancer development is derived from the hierarchy of the stem cell system, we will briefly discuss the origin of liver stem cells and its relation to HCC development. We will also summarize the current CSC markers in HCC and discuss their relevance to the treatment of this deadly disease.

Stem/progenitor cells in liver injury repair and regeneration

Morbidity and mortality from cirrhosis is increasing rapidly in the world. Currently, orthotopic liver transplantation is the only definitive therapeutic option. However, its clinical use is limited, because of poor long-term graft survival, donor organ shortage and high costs associated with the procedure. Stem cell replacement strategies are therefore being investigated as an attractive alternative approach to liver repair and regeneration. In this review we discuss recent preclinical and clinical investigations that explore the therapeutic potential of stem cells in repair of liver injuries. Several types of stem cells. including embryonic stem cells, haematopoietic stem cells and mesenchymal stem cells, can be induced to differentiate into hepatocyte-like cells by defined culture conditions in vitro. Stem cell transplantation has been shown to significantly improve liver function and increase animal survival in experimentally-induced liver-injury models. Moreover, several pilot clinical studies have reported encouraging therapeutic effects in patients treated with stem cells. Although there remain many unresolved issues, the available data support the notion that stem cell technology may lead to the development of effective clinical modalities for human liver diseases.

Canine bone marrow cells differentiate into hepatocyte-like cells and placental hydrolysate is a potential inducer

Hepatocyte growth factor (HGF) can stimulate human and rat bone marrow (BM) cells to differentiate into hepatocytes. A human placental hydrolysate (hPH) stimulates proliferation of hepatocytes, but its role as a potential inducer of BM cells to form hepatocytes is unclear. To determine if canine BM cells stimulated with HGF or hPH differentiate into hepatocyte-like cells, BM cells were cultured with HGF or hPH. The cultured cells underwent morphological examination, expression of albumin and cytokeratin 18 (CK18), hepatic function tests including uptake of low-density lipoprotein (LDL) and cytochrome P (CYP) 450 activity. Albumin mRNA and protein expression of albumin and CK18 proteins were detected in cultures with HGF and hPH. Furthermore, these cells demonstrated LDL uptake and CYP450 activity. These results indicate that canine BM cells can differentiate into hepatocyte-like cells when stimulated by both HGF and that hPH may be an effective inducer of hepatic differentiation.

[Clinical application of stem cells in liver diseases]

Most liver diseases lead to hepatic dysfunction with organ failure. Liver transplantation is the best curative therapy, but it has some limitations such as donor shortage, possibility of rejection, and maintenance of immunosuppressant. New therapies have been actively searched for over several decades, primarily in the form of artificial liver support devices and hepatocyte transplantation, but both of these modalities remain experimental. Stem cells have recently shown promise in cell therapy because they have the capacity for self-renewal and multilineage differentiation, and are applicable to human diseases. Very recent reports of unexpected plasticity in adult bone marrow have raised hopes of stem cell therapy offering exciting therapeutic possibilities for patients with chronic liver disease. Both rodent and human embryonic stem cells, bone marrow hematopoietic stem cells, mesenchymal stem cells, umbilical cord blood cells, fetal liver progenitor cells, adult liver progenitor cells, and mature hepatocytes have been reported to be capable of self-renewal, giving rise to daughter hepatocytes both in vivo and in vitro. These cells can repopulate livers in animal models of liver injury and appear to be able to improve liver function. However, significant challenges still exist before these cells can be used in humans, such as the lack of consensus about the immunophenotype of liver progenitor cells, uncertainty of the physiological role of reported candidate stem/progenitor cells, practicality of obtaining sufficient quantity of cells for clinical use, and concerns over ethics, long-term efficacy, and safety. There have been reports of phase 1 trials using stem cell transplantation in humans for liver diseases, but more effective trials are needed. We review the use of stem cells (focusing on adult ones) and the reported human clinical trials, and highlight the challenges facing clinicians in their quest to use liver stem cells to save lives.

Therapeutic potential of adult bone marrow stem cells in liver disease and delivery approaches

Hematopoietic stem cells (HSCs) and mesenchymal stem cell (MSCs) are two main subtypes of bone marrow stem cells. Extensive studies have been carried out to investigate the therapeutic potential of BMSCs in liver disease. A number of animal and human studies demonstrated that either HSCs or MSCs could be applied to therapeutic purposes in certain liver diseases. The diseased liver may recruit migratory stem cells, particularly from the bone marrow, to generate hepatocyte-like cells either by transdifferentiation or cell fusion. Transplantation of BMSCs has therapeutic effects of restoration of liver mass and function, alleviation of fibrosis and correction of inherited liver diseases. There are still controversial results over the potential effects of BMSCs on liver diseases, and some of the discrepancies are thought to be lied in the differences of experimental protocols, differences in individual research laboratory, and the uncertainties of the techniques employed. Several potential approaches for BMSCs delivery in liver diseases have been proposed in animal studies and human trials. BMSCs can be delivered via intraportal vein, systemic infusion, intraperitoneal, intrahepatic, intrasplenic. The optimal stem cells delivery should be easy to perform, less invasive and traumatic, minimum side effects, and with high cells survival rate. In this review, we focus on the up-to-date evidence of therapeutic effects of BMSCs on liver disease, the characteristics of various delivery approaches, and the considerations for future studies.

Cell fusion is a physiological process in mouse liver

A large portion of hepatocytes are polyploid cells, thought to arise through endoduplication followed by aborted cytokinesis. However, several recent reports describing liver cell fusion with exogenously derived bone marrow cells have been published. The exact significance of this finding is unclear, because the adopted protocols involve ablation regimens, damaged livers and artificial injections of adult cells. By creating chimeric mice bearing distinct reporter genes (LacZ and GFP), we show that in an unperturbed setting, hepatocytes carrying both markers can be detected via immunohistochemistry and polymerase chain reaction analysis. To further corroborate these findings with a direct visualization of the chromosome content at the single-cell level, we performed genotype analysis via fluorescence in situ hybridization on XY/XX chimeric mice with a Y chromosome-specific paint and an X chromosome-specific bacterial artificial chromosome clone probes.

CONCLUSION

This technique confirmed the occurrence of cell fusion in adult mouse liver.

Exogenous bone marrow cells do not rescue non-irradiated mice from acute renal tubular damage caused by HgCl2, despite establishment of chimaerism and cell proliferation in bone marrow and spleen

OBJECTIVE

Various studies have shown that bone marrow stem cells can rescue mice from acute renal tubular damage under a conditioning advantage (irradiation or cisplatin treatment) favouring donor cell engraftment and regeneration; however, it is not known whether bone marrow cells (BMCs) can contribute to repair of acute tubular damage in the absence of a selection pressure for the donor cells. The aim of this study was to examine this possibility.

MATERIALS AND METHODS

Ten-week-old female mice were assigned into control non-irradiated animals having only vehicle treatment, HgCl(2)-treated non-irradiated mice, HgCl(2)-treated non-irradiated mice infused with male BMCs 1 day after HgCl(2), and vehicle-treated mice with male BMCs. Tritiated thymidine was given 1 h before animal killing.

RESULTS

Donor BMCs could not alleviate non-irradiated mice from acute tubular damage caused by HgCl(2), deduced by no reduction in serum urea nitrogen combined with negligible cell engraftment. However, donor BMCs could home to the bone marrow and spleen and display proliferative activity. This is the first report to show that despite no preparative myeloablation of recipients, engrafted donor BMCs can synthesize DNA in the bone marrow and spleen.

CONCLUSIONS

Exogenous BMCs do not rescue non-irradiated mice from acute renal tubular damage caused by HgCl(2), despite establishment of chimerism and cell proliferation in bone marrow and spleen.

Allogeneic bone marrow transplantation restores liver function in Fah-knockout mice

OBJECTIVE

In murine models, transplantation of wild-type bone marrow cells (BMC) can counterbalance genetic liver defects by fusion between transplanted marrow cells and resident hepatocytes. This phenomenon, however, is of no immediate clinical use because all syngeneic BMC harbor the same underlying genetic defect.

MATERIALS AND METHODS

Describing the fusion between transplanted allogeneic BMC and resident hepatocytes in a murine model of hereditary tyrosinemia type I (fumarylacetoacetate hydrolase [Fah] knockout mouse), we transplanted BMC from fully allogeneic BALB/c donors into Fah(-/-) recipients after lethal total body irradiation.

RESULTS

Following hematopoietic reconstitution, recipients remained healthy without pharmacological support (withdrawal of 2-2-nitro-4-fluoromethylbenzoyl-1,3-cyclohexanedione [NTBC]). Metabolic serum parameters improved nearly to wild-type levels. Livers of recipient animals contained up to 10% functional hepatocytes that stained positive for wild-type Fah, as well as both donor and recipient major histocompatibility complex. Flow cytometry confirmed this coexpression on a single cell level. Application of T-cell-depleted bone marrow reduced onset of early graft-vs-host disease.

CONCLUSIONS

We introduce the observation that allogeneic bone marrow transplantation can lead to stable cell fusion of BMC with recipient hepatocytes and restored liver function in a model of otherwise lethal genetic liver disease. Thus, in principle, allogeneic cell fusion can be a possible management of hereditary liver diseases. Long-term immunological properties of fusion cells have to be further investigated.

Murine embryonic stem cell-derived hepatic progenitor cells engraft in recipient livers with limited capacity of liver tissue formation

Directed endodermal differentiation of murine embryonic stem (ES) cells gives rise to a subset of cells with a hepatic phenotype. Such ES cell-derived hepatic progenitor cells (ES-HPC) can acquire features of hepatocytes in vitro, but fail to form substantial hepatocyte clusters in vivo. In this study, we investigated whether this is due to inefficient engraftment or an immature phenotype of ES-HPC. ES cells engrafted into recipient livers of NOD/SCID mice with a similar efficacy as adult hepatocytes after 28 days. Because transplanted unpurified ES-HPC formed teratomas in the spleen and liver, we applied an albumin promoter/enhancer-driven reporter system to purify ES-HPC by cell sorting. RT-PCR analyses for hepatocyte-specific genes showed that the cells exhibited a hepatic phenotype, lacking the expression of the pluripotency marker Oct4, comparable to cells of day 11.5 embryos. Sorted ES-HPC derived from beta-galactosidase transgenic ES cells were injected into fumaryl-acetoacetate-deficient (FAH(-/-)) SCID mice and analyzed after 8 to 12 weeks. Staining with X-gal solution revealed the presence of engrafted cells throughout the liver. However, immunostaining for the FAH protein indicated hepatocyte formation at a very low frequency, without evidence for large hepatocyte cluster formation. In conclusion, the limited repopulation capacity of ES-HPC is not caused by a failure of primary engraftment, but may be due to an immature hepatic phenotype of the transplanted ES-HPC.

Transplanted bone marrow stromal cells are not cellular origin of hepatocellular carcinomas in a mouse model of carcinogenesis

AIM: To investigate the malignant potential of hepatic stem cells derived from the bone marrow stromal cells (BMSCs) in a mouse model of chemical hepatocarcino-genesis.

METHODS: BMSCs from male BALB/c mice were harvested and cultured, then transplanted into female syngenic BALB/c mice via portal vein. Hepato-carcinogenesis was induced by 6 mo of treatment with diethylnitrosamine (DEN). Six months later, the liver was removed from each treated mouse and evaluated by immunohistochemistry and fluorescence in situ hybridization (FISH).

RESULTS: Twenty-six percent of recipient mice survived and developed multiple hepatocellular carcinomas (HCCs). Immunohistochemically, HCC expressed placental form of glutathione-S-transferase (GST-P) and α-fetoprotein, but did not express cytokeratin 19. Y chromosome positive hepatocytes were detected by fluorescent in situ hybridization (FISH) in the liver of mice treated with DEN after BMSCs transplantation while no such hepatocytes were identified in the liver of mice not treated with DEN. No HCC was positive for the Y chromosome by FISH.

CONCLUSION: Hepatic stem cells derived from the bone marrow stromal cells have a low malignant potential in our mouse model of chemical hepatocarcinogenesis.

Role of bone marrow stem cells in hepatic fibrosis

Differentiation of bone marrow stem cells into hepatocytes and their curative roles in liver fibrosis have gained increasing popularity recently. However, further investigation has shown a opposite idea that the bone marrow stem cells don't have this ability. Some researchers have proposed that bone marrow stem cells can differentiate into stellate cells or fibroblasts, hence serving as a participator of hepatic fibrosis. This article aims to review the role of bone marrow cells in hepatic fibrosis.

Bone marrow multipotent mesenchymal stromal cells do not reduce fibrosis or improve function in a rat model of severe chronic liver injury

The objective of our study was to evaluate the therapeutic potential of bone marrow mesenchymal stromal cells (MSC) in a rat model of severe chronic liver injury. Fourteen female Wistar rats were fed exclusively an alcoholic liquid diet and received intraperitoneal injections of carbon tetrachloride every other day during 15 weeks. After this period, eight animals (MSC group) had 1 x 10(7) cells injected into the portal vein while six animals (placebo group) received vehicle. Blood analysis was performed to evaluate alanine aminotransferase (ALT), aspartate aminotransferase (AST), and albumin before cell therapy and 1 and 2 months after cell or placebo infusion. Fibrosis was evaluated before and 1 month after cell or placebo injection by liver biopsies. Two months after cell delivery, animals were sacrificed and histological analysis of the livers was performed. Fibrosis was quantified by histomorphometry. Biopsies obtained before cell infusion showed intense collagen deposition and septa interconnecting regenerative nodules. One month after cell injection, this result was unaltered and differences in fibrosis quantification were not found between MSC and placebo groups. ALT and AST returned to normal values 2 weeks after cell or placebo infusion, without significant differences between experimental groups. Two months after cell or placebo injection, albumin had also returned to normal values and histological results were maintained, again without differences between MSC and placebo groups. Therefore, under our experimental conditions, MSC were unable to reduce fibrosis or improve liver function in a rat model of severe chronic liver injury.

Research progress in directional differentiation from bone marrow stem cells into hepatocyte-like cells

Recent researches indicate that bone marrow stem cells not only can differentiate into bone, cartilage, fat, muscle cells and various blood cells, but also can differentiate into cells of trans-germinal layer, such as ectoderm original neuronal cells, endoderm original hepatocytes, insular cells, under suitable microenvironment. It is called "plasticity" or "trans-differentiation". This paper reviews the research advances that bone marrow stem cell differentiation into hepatocyte-like cells and their clinical application in liver disease treatment.

Stem cells for liver tissue repair: Current knowledge and perspectives

Stem cells from extra- or intrahepatic sources have been recently characterized and their usefulness for the generation of hepatocyte-like lineages has been demonstrated. Therefore, they are being increasingly considered for future applications in liver cell therapy. In that field, liver cell transplantation is currently regarded as a possible alternative to whole organ transplantation, while stem cells possess theoretical advantages on hepatocytes as they display higher in vitro culture performances and could be used in autologous transplant procedures. However, the current research on the hepatic fate of stem cells is still facing difficulties to demonstrate the acquisition of a full mature hepatocyte phenotype, both in vitro and in vivo. Furthermore, the lack of obvious demonstration of in vivo hepatocyte-like cell functionality remains associated to low repopulation rates obtained after current transplantation procedures. The present review focuses on the current knowledge of the stem cell potential for liver therapy. We discuss the characteristics of the principal cell candidates and the methods to demonstrate their hepatic potential in vitro and in vivo. We finally address the question of the future clinical applications of stem cells for liver tissue repair and the technical aspects that remain to be investigated.