Stem cells: new tools in gastroenterology and hepatology

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.

Intestinal stem cells and celiac disease

Stem cells (SCs) are the key to tissue genesis and regeneration. Given their central role in homeostasis, dysfunctions of the SC compartment play a pivotal role in the development of cancers, degenerative disorders, chronic inflammatory pathologies and organ failure. The gastrointestinal tract is constantly exposed to harsh mechanical and chemical conditions and most of the epithelial cells are replaced every 3 to 5 d. According to the so-called Unitarian hypothesis, this renewal is driven by a common intestinal stem cell (ISC) residing within the crypt base at the origin of the crypt-to-villus hierarchical migratory pattern. Celiac disease (CD) can be defined as a chronic immune-mediated disease that is triggered and maintained by dietary proteins (gluten) in genetically predisposed individuals. Many advances have been achieved over the last years in understanding of the pathogenic interactions among genetic, immunological and environmental factors in CD, with a particular emphasis on intestinal barrier and gut microbiota. Conversely, little is known about ISC modulation and deregulation in active celiac disease and upon a gluten-free diet. Nonetheless, bone marrow-derived SC transplantation has become an option for celiac patients with complicated or refractory disease. This manuscript summarizes the “state of the art” regarding CD and ISCs, their niche and potential role in the development and treatment of the disease.

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.

Stem and progenitor cells in liver regeneration and repair

Mammalian liver has a unique capacity to regenerate following resection or injury, and recovery of liver mass is mainly through proliferation of remaining adult hepatocytes. However, in pathologic conditions, especially during acute liver failure (ALF) and advanced stages of chronic liver disease (CLD), regeneration eventually fails and orthothopic liver transplantation (OLT) represents the only curative approach. The clinical scenario of a world-wide increasing incidence of end-stage CLD and an associated lack of organ availability has led several laboratories to explore the feasibility and efficiency of experimental alternatives to OLT involving cellular therapy. This review presents experimental and clinical studies performed in the last 10-15 years where adult and embryonic hepatocytes, hepatic stem/progenitor cells and extrahepatic stem cells have been used as transplantable cell sources.

CD133+ stem cell mobilization after partial hepatectomy depends on resection extent and underlying disease

BACKGROUND

Bone marrow stem cells (BMSC) can participate to liver regeneration. However, conflicting results have been reported on this topic in patients undergoing liver resection.

AIMS

To assess the impact of liver resection extent and presence of underlying liver disease in modulating BMSC mobilization.

METHODS

We enrolled 29 patients undergoing liver resection of different extents, 5 surgical controls and 10 blood donors. Circulating CD133+ BMSC were measured by flow cytometry at different time-points after surgery. The hepatic commitment of mobilized BMSC was investigated by polymerase chain reaction. Liver specimens were collected during surgery for histopathological analysis. Hepatocyte growth factor and granulocyte-colony stimulating factor serum levels were measured by enzyme-linked immunosorbent assay.

RESULTS

BMSC mobilization was found in patients undergoing major liver resection, especially in the presence of underlying disease. Ductular reactions were noted in patients with chronic hepatopathy and the hepatic progenitor-like cells expressed CD133, NCAM, cytokeratin-19, and alpha-fetoprotein. Hepatocyte growth factor and granulocyte-colony stimulating factor levels increased following liver resection and the contemporaneous presence of liver disease was associated with their highest raise.

CONCLUSIONS

Liver repair is mainly an endogenous process. BMSC become important in case of extensive resection, especially in the presence of underlying hepatopathy and hepatic progenitor-like cells activation. Hepatocyte growth factor and granulocyte-colony stimulating factor seem to be involved in the dynamics underlying hepatic regeneration and BMSC recruitment.

Establishment of cancer cell lines from rat hepatocholangiocarcinoma and assessment of the role of granulocyte-colony stimulating factor and hepatocyte growth factor in their growth, motility and survival

BACKGROUND/AIMS

Oval cells (OCs), putative hepatic stem cells, may give rise to liver cancers. We developed a carcinogenesis regimen, based upon induction of OC proliferation prior to carcinogen exposure. In our model, rats subjected to 2-acetylaminofluorene/ partial-hepatectomy followed by aflatoxin injection (APA regimen) developed well-differentiated hepatocholangiocarcinomas. The aim of this study was to establish and characterize cancer cell lines from this animal model.

METHODS

Cancer cells were cultured from animals sacrificed eight months after treatment, and single clones were selected. The established cell lines, named LCSCs, were characterized, and their tumorigenicity was assessed in vivo. The roles of granulocyte-colony stimulating factor (G-CSF) and hepatocyte growth factor (HGF) in LCSC growth, survival and motility were also investigated.

RESULTS

From primary tumors, six cell lines were developed. LCSCs shared with the primary tumors the expression of various OC-associated markers, including cMet and G-CSF receptor. In vitro, HGF conferred protection from death by serum withdrawal. Stimulation with G-CSF increased LCSC growth and motility, while the blockage of its receptor inhibited LCSC proliferation and migration.

CONCLUSIONS

Six cancer cell lines were established from our model of hepatocholangiocarcinoma. HGF modulated LCSC resistance to apoptosis, while G-CSF acted on LCSCs as a proliferative and chemotactic agent.

Isolation and characterization of hepatic stem cells, or "oval cells," from rat livers

The pace of research on the potential therapeutic uses of liver stem cells or "oval cells" has accelerated significantly in recent years. Concurrent advancements in techniques for the isolation and characterization of these cells have helped fuel this research. Several models now exist for the induction of oval cell proliferation in rodents. Protocols for the isolation and culture of these cells have evolved to the point that they may be set up in any laboratory equipped for cell culture. The advent of magnetic cell sorting has eliminated reliance on expensive flow cytometric sorting equipment to generate highly enriched populations of oval cells. Our laboratory has had much success in using the oval cell surface marker Thy-1 in combination with magnetic sorting to produce material suitable for testing the influence of a myriad of chemical signaling molecules on the oval cell phenotype. This chapter will describe our basic strategy for oval cell induction and isolation. Additionally, two in vitro procedures are described which the reader may find useful in the early stages of developing an oval cell research project.

Stem cells, a two-edged sword: Risks and potentials of regenerative medicine

The recent advancements in stem cell (SC) biology have led to the concept of regenerative medicine, which is based on the potential of SC for therapies aimed to facilitate the repair of degenerating or injured tissues. Nonetheless, prior to large scale clinical applications, critical aspects need to be further addressed, including the long-term safety, tolerability, and efficacy of SC-based treatments. Most problematic among the risks of SC-based therapies, in addition to the possible rejection or loss of function of the infused cells, is their potential neoplastic transformation. Indeed, SCs may be used to cure devastating diseases, but their specific properties of self-renewal and clonogenicity may render them prone to generate cancers. In this respect, ‘Stemness’ might be seen as a two-edged sword, its bright side being represented by normal SCs, its dark side by cancer SCs. A better understanding of SC biology will help fulfill the promise of regenerative medicine aimed at curing human pathologies and fighting cancer from its roots.

Stem cell-based therapy in gastroenterology and hepatology

Protagonists of a new scientific era, stem cells are promising tools on which regenerative medicine relies for the treatment of human pathologies. Stem cells can be obtained from various sources, including embryos, fetal tissues, umbilical cord blood, and also terminally differentiated organs. Once forced to expand and differentiate into functional progenies, stem cells may become suitable for cell replacement and tissue engineering. The manipulation and/or stimulation of adult stem cells seems to be particularly promising, as it could improve the endogenous regenerative potential without risks of rejection and overcome the ethical and political issues related to embryonic stem cell research. Stem cells are already leaving the bench and reaching the bedside, despite an incomplete knowledge of the genetic control program driving their fate and plasticity. In gastroenterology and hepatology, the first attempts to translate stem cell basic research into novel therapeutic strategies have been made for the treatment of several disorders, such as inflammatory bowel diseases, diabetes mellitus, celiachy and acute or chronic hepatopaties. Nonetheless, critical aspects need to be further addressed, including the long-term safety, tolerability and efficacy of cell-based treatments, as well as their carcinogenic potential. Aim of this review is to summarize the state-of-the-arts on gastrointestinal and hepatic stem cells and on stem cell-based therapies in gastroenterology and hepatology, highlighting both the benefits and the potential risks of these new tools for the treatment and prevention of human diseases.

Improvement of mortality rate and decrease in histologic hepatic injury after human cord blood stem cell infusion in a murine model of hepatotoxicity

BACKGROUND AND AIMS

Because of their plasticity potential local and systemic application of cord blood stem cells may represent excellent candidates for cell-based therapeutic strategies in toxic liver injuries. It is already known that intraperitoneal administration of hematopoietic stem cells provides rapid liver homing in animal models of hepatic injury. We sought to assess the efficacy of a hematopoietic stem cell infusion to decrease the histologic damage and the mortality rate of animals previously damaged by allyl alcohol.

MATERIAL AND METHODS

NOD/SCID mice were divided into two groups. (1) animals treated by intraperitoneal administration of allyl alcohol and (2) animals treated with allyl alcohol and 24 hours later with an intraperitoneal infusion of human cord blood cells. Flow cytometry, histology, immunohistochemistry, and RT-PCR were performed to monitor human cell engraftment by evidences of human hepatic markers.

RESULTS

Human stem cells were able to transdifferentiate into hepatocytes, improve liver regeneration after damage, and reduce the mortality rate even when requiring qualitative and quantitative differences in the transdifferentiation processes. The mortality rate decreased from 70% to 20%, with a significant improvement in the histologic findings.

CONCLUSION

We demonstrated that the infusion of hematopoietic stem cells into the liver in the early stage of damage might initiate endogenous hepatic tissue regeneration that oppose the injury inflicted by toxicants.

How does human stem cell therapy influence gene expression after liver injury? Microarray evaluation on a rat model

BACKGROUND

Tissue homeostasis is guaranteed by stem proliferating reserve, depending on dynamic changes in gene expression. A high plasticity is shown by the haematopoietic stem cells, potential source for liver regeneration.

AIM

We aimed to evaluate the gene expression modifications induced by human haematopoietic stem cell therapy after liver injury in rats.

SUBJECTS

Rats were sorted as follows: (A) human-haematopoietic stem cell injection after allyl alcohol liver damage; (B) only haematopoietic stem cell injection; (C) only allyl alcohol injection; and (D) sacrifice without any treatment.

METHODS

Livers, spleens and bone marrows were analysed with flow-cytometry. Livers were also studied by reverse-transcription PCR, histology, immunohistochemistry and microarray analysis; selected genes were confirmed by real-time PCR.

RESULTS

In subset A, haematopoietic stem cells were selectively recruited by liver, with respect to the group B, and they improved the liver regeneration process compared to group C. As regards microarrays, haematopoietic stem cell infusion upregulates 265 genes and downregulates 149 genes. Differentially regulated genes belong to a broad range of functional pathways, including proliferation, differentiation, adhesion/migration and transcripts related to oval-cell activation. Real-time PCR validated array results.

CONCLUSIONS

Our study confirmed the capacity of haematopoietic stem cells to contribute to liver regeneration. Moreover, microarray analysis led to the identification of genes whose regulation strongly correlates with a more efficient process of liver repair after haematopoietic stem cell injection.

No Evidence of Hematopoietic Stem Cell Mobilization in Patients Submitted to Hepatectomy or in Patients With Acute on Chronic Liver Failure

BACKGROUND

Liver regeneration is a heterogeneous phenomenon involving the proliferation of different cell lineages in response to injury. Under a strong positive selection pressure bone marrow derived stem cells may be involved in this process, by making a contribution to both parenchymal restoration and endothelial cell replacement. We investigate bone marrow stem cell migration to the liver in patients undergoing hepatectomy or with acute on chronic liver failure.

METHODS

We enrolled 6 patients submitted to hepatectomy, 6 patients to cholecystectomy and 8 patients with acute decompensation of liver cirrhosis. Mobilization of CD34+ cells was evaluated by cytofluorimetry on peripheral blood samples at different time points; baseline, 1, 3, 7, 15 and 30 days after surgery and at admission, 1, 7 and discharge among patients with acute on chronic liver failure. 10 healthy subjects undergoing blood donation were also enrolled to evaluated the basal value of CD34+ cells.

RESULTS

White blood cell counts remained in the normal range (4.1-9.8 x 10(9)/L) in all groups throughout the follow-up. In all patients of Groups 1, 2 and 3, circulating CD34+ failed to show statistically significant differences both as the absolute number and as the percentage at any time point compared to healthy controls.

CONCLUSIONS

Bone marrow derived cell mobilization can not be detected after hepatectomy or during an acute decompensation on a cirrhotic liver. Under these circumstances liver regeneration can probably call upon mature hepatocytes and endogenous progenitor cells. The involvement of extrahepatic progenitors if any, is a rare and limited phenomenon.

Human Cordonal Stem Cell Intraperitoneal Injection Can Represent a Rescue Therapy After an Acute Hepatic Damage in Immunocompetent Rats

BACKGROUND AND AIM

Tissue homeostasis and turnover require reserve stem proliferating cells. Several studies performed on immunodeficient animals have suggested a degree of plasticity by the hematopoietic stem cell compartment that may represent source for liver regeneration. We sought to explore the hepatic differentiation potential of hematopoietic stem cells from human cord blood, after toxic liver damage induced by allyl-alcohol in immunocompetent rats.

MATERIALS AND METHODS

Wistar rats were divided into groups (A) allyl-alcohol intraperitoneal injection with hematopoietic stem cell intraperitoneal infusion at 1 day and sacrifice 3 days later; (B) stem cell injection and sacrifice 3 days later; (C) allyl-alcohol infusion and sacrifice 4 days later; and (D) sacrifice without any treatment. Livers, spleens, and bone marrows were analysed for human stem cells using flow-cytometry; livers were also tested by histology and immunohistochemistry to study the pattern of hepatic regeneration after damage and human stem cell conversion into hepatocyte-like cells, respectively.

RESULTS

Flow-cytometry revealed selective recruitment of human hematopoietic stem cells by damaged livers (group A) compared with control group B. In addition, liver damage was reduced in animals treated with stem cells. Immunohistochemistry demonstrated that human stem cells could convert hepatic cells.

CONCLUSIONS

Our study demonstrated that hematopoietic stem cells selectively recruited by injured livers can contribute to hepatic regeneration after acute toxic damage in immunocompetent recipients.

A human umbilical cord stem cell rescue therapy in a murine model of toxic liver injury

BACKGROUND

Several studies have demonstrated that bone marrow contains a subpopulation of stem cells capable of participating in the hepatic regenerative process, even if some reports indicate quite a low level of liver repopulation by human stem cells in the normal and transiently injured liver.

AIMS

In order to overcome the low engraftment levels seen in previous models, we tried the direct intraperitoneal administration of human cord blood stem cells, using a model of hepatic damage induced by allyl alcohol in NOD/SCID mice.

METHODS

We designed a protocol based on stem cell infusion following liver damage in the absence of irradiation. Flow cytometry, histology, immunohistochemistry and RT-PCR for human hepatic markers were performed to monitor human cell engraftment.

RESULTS

Human stem cells were able to transdifferentiate into hepatocytes, to improve liver regeneration after damage and to reduce the mortality rate both in both protocols, even if with qualitative and quantitative differences in the transdifferentiation process.

CONCLUSIONS

We demonstrated for the first time that the intraperitoneal administration of stem cells can guarantee a rapid liver engraftment. Moreover, the new protocol based on stem cell infusion following liver damage in the absence of irradiation may represent a step forward for the clinical application of stem cell transplantation.

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Review article: a medicine based on cell transplantation -- is there a future for treating liver diseases?

Cell-based therapies, comprising isolated hepatocyte transplantation, ex vivo gene therapy and bioartificial liver devices, may actually design a new scenario in the treatment of patients with liver failure. Recent advances in the liver repopulation field and the considerable excitement surrounding the use of haematopoietic stem cells for a 'regenerative medicine', allow us to see under a new light the alternative cell sources actually under investigation. In particular, the major drawbacks and the most important advantages of xenogenic primary cells, tumour-derived cell lines, immortalised hepatocytes and stem cells in the wide range of experimental and clinical applications are presented. Even if up to now none of them represent a 'gold standard' in the clinical practice, the intersecting advances in the development of mechanical components of artificial devices and in the liver biology and bioengineering will open tantalising possibilities to treat patients with liver failure, by tailoring the therapeutic choice on the basis of the aetiology and the stage of liver disease.