Research progress of stem cell therapy for liver cirrhosis

Chun-Liu Guo,Xiao-Xi Huang

Department of Gastroenterology,Affliated Haikou hospital of Xiangya Medical College of Central South University,Haikou 570208,China

Keywords:Stem cells Liver cirrhosis Treatment

ABSTRACT Liver cirrhosis is the terminal stage caused by various chronic liver injury.There are many complications and death in the late stage.There is no effective treatment method at present.In recent years,with the rapid development of regenerative medicine,the treatment of liver cirrhosis based on stem cell transplantation technology has become a new research hotspot.Scholars at home and abroad have carried out a series of basic and clinical research,and achieved certain results,which brings new hope for the majority of patients with liver cirrhosis.This article reviews the research progress of various types of stem cells in the treatment of liver cirrhosis.

Liver cirrhosis is the terminal stage caused by various chronic liver injuries,and is characterized by the formation of pseudolobules,diffuse fibrosis of liver tissue,and proliferation of blood vessels inside and outside the liver.Approximately 1 million people die from complications of liver cirrhosis each year in the world,which is the 11th most common cause of death in the world,and seriously threatens human health [1].For decompensated liver cirrhosis,medical treatment is not effective.Orthotopic liver transplantation (OLT) is considered the only effective treatment,but due to high medical costs,shortage of donor liver sources,and many postoperative complications Factors such as lifelong immune rejection have greatly restricted the wide application of OLT in clinical practice.Therefore,there is an urgent need to find a safe and effective alternative that can be widely used.Stem cells are cells with the potential for self-renewal and multi-directional differentiation.As the "seed" cells of regenerative medicine,stem cells are currently used in nerve [2],blood [3],cardiovascular [4],bone and joint [5],etc.A beneficial attempt was made in this systemic disease.Stem cells can be induced to differentiate into hepatocytes under certain conditions,providing a new option for the treatment of liver cirrhosis.According to different sources,they can be divided into liver-derived hepatic stem cells and non-hepatic-derived hepatic stem cells.

1.Hepatic stem cell

Liver-derived hepatic stem cells,also known as endogenous hepatic stem cells,mainly include small hepatocyte-like progenitor cells (SHPC),hepatic oval cells (HOC),and hepatocyte cells (HC).Among them,HOC is the most researched.

1.1 Hepatic oval cells(HOC)

HOC,also known as hepatic progenitor cells (HPCs),is a kind of stem cell with bidirectional differentiation potential,which can be induced to differentiate into hepatocytes and bile duct epithelial cells under certain conditions.Therefore,it may become a source of regeneration of liver cells .

Studies have shown that HPCs have a positive contribution to liver cell regeneration.Lu et al.[6] induced hepatocyte apoptosis by targeted deletion of Mdm2,and then transplanted HPCs into the liver of mice,and found that the transplanted HPCs can differentiate into hepatocytes and bile duct cells,thereby significantly improving the structure and function of the damaged liver .A recent study showed that the absence of Lgr5+hepatic progenitor cells can increase CCl4-induced liver fibrosis,and when hepatocyte damage or HGF and Rspo1 combine to induce more Lgr5+hepatic progenitor cells,it can promote liver function Recovery of obstacles and alleviation of liver fibrosis [7].

The content of HPCs in the liver is very low and it is difficult to separate.In recent years,the differentiation of HPCs in vitro has attracted people's interest.Katsuda et al.[8] used a small molecule mixture of Y-27632,a-83-01 and CHIR99021 to transform mature rat hepatocytes into proliferative bipotent cells in vitro,called chemically induced hepatic progenitor cells (CLiPs).In order to further confirm the feasibility of this technology in human liver cells,Kim et al.[9] isolated human liver cells from healthy and diseased donor livers and used A83-01 and CHIR99021 (AC) under the action of EGF and HGF.The combined treatment of two small molecules successfully reprogrammed human hepatocytes into hepatic progenitor cells,called human chemical hepatic progenitor cells(hCdHs).Both studies have shown that HPCs from chemical sources can differentiate into mature hepatocytes and bile duct epithelial cells in vivo and in vitro,effectively replacing chronically damaged liver tissue,and can be cultured stably.

The effectiveness of HPCs transplantation to treat liver cirrhosis has been initially confirmed in animal experiments.Awan et al.[10]differentiated bone marrow mesenchymal stem cells into HPCs by pretreatment and implanted them into mice with liver fibrosis.They observed that HPCs can improve liver function by reducing apoptosis and the release of lactate dehydrogenase..Zhao Li et al.[11] found that HPCs transplantation can reduce ALT and AST activity and liver index in a mouse model induced by 2.0% CCL4,and improve survival.However,it is still unclear whether there will be side effects and tumor formation after transplantation,and further research is needed.

2.Non-hepatic hepatic stem cells

Non-hepatic hepatic stem cells,also known as exogenous hepatic stem cells,mainly include embryonic stem cells (ESCs),endothelial progenier cells (EPCs),mesenchymal stem cells (MSCs),Hematopoietic stem cells (HSCs) and induced pluripotent stem cells(iPSCs),etc.

2.1 Embryonic stem cells(ESCs)

ESCs are a type of cells isolated from early embryos or primitive gonads.They have the potential to proliferate and differentiate to form various tissue cells,and have broad application prospects in cell replacement therapy.

There are also related studies on the use of ESCs to treat liver diseases.Tolosa et al.[12] transplanted a European human embryonic stem cell line (VAL9) into mice with acute liver failure induced by acetaminophen and found that it can effectively fill liver tissue and restore liver function.A recent study [13] established a sustained release system of growth factors using nanomaterials,which can continuously promote the differentiation of mouse embryonic stem cells (mESCs) into hepatocyte-like cells (HLCs) and culture them in vitro Produce more functional hepatocytes.When the mESCs processed by this system are transplanted into mice with liver injury,they can differentiate into HLCs in vivo and have obvious repair effects on liver injury.

Although ESCs have the molecular basis for the treatment of liver cirrhosis,they have not yet been approved for clinical treatment due to the limitations of immune rejection,medical ethics,tumorigenicity and other factors.

2.2 Endothelial progenier cells(EPCs)

EPCs are immature endothelial cells,which are pluripotent stem cells,mainly found in bone marrow,cord blood and peripheral blood.It can promote the formation of new blood vessels and tissue repair through differentiation into mature endothelial cells,release of a large number of nutritional factors and cytoprotective factors,and paracrine effects [15,16].Therefore,it may be beneficial to the treatment of liver cirrhosis.

Based on the extensive study of EPCs transplantation in the treatment of liver cirrhosis in animal experiments,Sakamoto et al.[17] injected bone marrow-derived EPCs into the rat liver cirrhosis model via the tail vein once a week for 4 consecutive weeks.They found that EPCs transplantation can be Increase liver blood flow,reduce liver fibrosis and portal pressure.Other studies have shown that combined transplantation of bone marrow-derived hepatic stem cells (BDHSCs) and bone marrow-derived endothelial progenitor cells (BM-EPCs) can significantly improve liver function and liver fibrosis,and the therapeutic effect is significantly better than that of single cell transplantation.Promising treatment method [18,19].However,a recent study came to the opposite conclusion.This experiment transplanted cirrhotic EPCs into cirrhotic rats prepared by bile duct ligation.The results showed that transplantation of cirrhotic EPCs can promote the differentiation of liver sinusoidal endothelial cells (LSEC) and liver Stellate cells (HSC) are activated,thereby increasing liver angiogenesis and liver fibrosis,further aggravating portal hypertension.This difference in results may be related to the different preparation methods of liver cirrhosis models and the different sources of EPCs.

In order to further evaluate the feasibility of EPCs in clinical application,D'avola et al.[20] injected EPCs into 11 patients with decompensated liver cirrhosis through the hepatic artery and followed up for 12 months.The results showed that the end-stage liver disease score model was significant Improved (P=0.042)and 5 out of 9 patients who survived 90 days showed a decrease in hepatic venous pressure gradient (HVPG),and no serious adverse events occurred during the follow-up period.A phase 3 randomized controlled trial (clinicaltrials.gov identifier:NCT03109236) is currently underway,which may provide definitive data on the potential clinical benefits of EPCs-based treatment of patients with end-stage cirrhosis.

2.3 Mesenchymal stem cells(MSCs)

MSCs are a type of non-hematopoietic stem cells that are derived from the early mesoderm of development and have self-replication and multi-differentiation potential.They are most often extracted from bone marrow,and can also be obtained from adipose tissue,umbilical cord tissue,liver,dental pulp and other tissues .Studies have found that MSCs can differentiate into HLCs,and exert immunomodulatory,anti-inflammatory,anti-fibrosis,anti-oxidative stress and anti-apoptosis effects on liver cells [21].It is the most valuable cell replacement method in the treatment of liver cirrhosis.Adult stem cells.

MSCs can be transplanted in many different ways,and there are still controversies about the best way to treat liver fibrosis with MSCs transplantation.Wang Min et al.[25] transplanted MSCs into mice with liver cirrhosis via portal vein,peripheral vein and abdominal cavity,and found that the therapeutic effects of the three transplantation routes were not significantly different.Idriss et al.[27]believe that compared with intrasplenic transplantation,intravenous transplantation of BMSCs can reduce the expression of IL-1β,IL-6,and INF-ɣ genes,thereby more effectively inhibiting inflammation.The results of Zheng et al.[28] showed that the therapeutic effects of hUCMSCs transplantation through tail vein and intrahepatic injection were equivalent.According to the current research,there is no unified conclusion,and further research is needed.

There are many sources of MSCs.BMSC is currently the most widely studied mesenchymal stem cells,but there are problems such as potential damage to the donor and a small number of available.Therefore,finding new sources of MSCs has become a research hotspot in recent years

2.3.1 Placenta

Jiong et al.[28] transplanted hPMSCs into hepatic fibrosis rats through the tail vein,and found that hPMSC transplantation can reduce the expression of TGF-β1 and α-SMA and inhibit the activation of hepatic stellate cells,thereby repairing liver fibrosis.Improve liver function

2.3.2 Deciduous teeth

Yamaza et al.[30] transplanted human deciduous tooth stem cells(SHED) into CCL4-induced hepatic fibrosis mice through the spleen,and found that the transplanted SHED can differentiate into hepatocytes and significantly reduce fibrotic substances and inflammatory factors Enhance the expression of anti-inflammatory factors,thus exhibiting anti-fibrosis and anti-inflammatory effects.

2.3.3 Menstrual blood

Human menstrual blood is also a potential source of liver cells,called menstrual blood-derived stem cells (MenSCs).Compared with BMSCs,MenSCs has the advantages of non-invasive collection process,high proliferation rate,pluripotency and low immunogenicity [31].Chen et al.[32] first reported the effect of MenSCs transplantation on liver fibrosis in mice.It shows that MenSCs can significantly improve liver function,reduce collagen deposition,and inhibit LX-2 cells (liver by secreting paracrine cytokines such as monocyte chemoattractant protein-1,interleukin-6,hepatocyte growth factor and osteoprotegerin).Stellate cells)proliferation.

The safety of MSCs transplantation therapy has always been an issue of close concern.Studies have shown that MSCs transplantation may differentiate into unwanted tissues,including bone and cartilage[33].In addition,it may also inhibit anti-tumor immune responses and Promote angiogenesis and promote tumor growth and metastasis[34].Therefore,continuous monitoring and long-term follow-up of animal models treated with MSCs are still needed to determine their carcinogenic effects and other adverse effects.

2.4 Hematopoietic stem cells(HSCs)

HSCs are located in the bone marrow and are adult stem cells in the blood system.They have the ability to differentiate into all cells of the blood and immune system [35].HSCs in bone marrow can be mobilized after tissue damage or artificial activation,leaving the bone marrow and entering the blood.Granulocyte colony stimulating factor (G-CSF) is the most widely studied and used mobilizer.Compared with other types of stem cells,HSCs have the advantages of being easy to obtain,low cost,and can be derived from the body without the use of immunosuppressive agents.

In recent years,the research based on HSCs transplantation to treat liver cirrhosis has achieved remarkable results.King et al.[36] repeatedly infused purified HSCs into mice with liver fibrosis injury and found that compared with the control group,liver scar formation in mice treated with HSCs transplantation was reduced by 49.7%,and suggested that HSCs promote macrophages.And neutrophils are recruited to mediate its anti-fibrosis effect.Combined application of sphingosine 1-phosphate receptor agonist (FTY720)can enhance this effect.Guo et al.[37] retrospectively analyzed the long-term clinical efficacy of 282 patients with liver cirrhosis who received autologous HSCs transplantation and found that the survival time of the experimental group was significantly higher than that of the control group,1 year,2 years,3 years,and 5 years after transplantation.Liver function was significantly improved.And there was no significant difference in the total incidence of liver cancer between the two groups (21.1% vs 20.4%).In addition,a number of clinical studies have also shown that HSCs transplantation can effectively improve the liver function,liver tissue morphology and the quality of life of patients with advanced cirrhosis [38-41].However,the results of a recent multicenter,randomized controlled trial in the United Kingdom have shown that G-CSF or G-CSF plus HSCs infusion cannot improve liver dysfunction or fibrosis,and may also increase the risk of adverse events in patients[42] .

On the whole,stem cells are safe to treat liver cirrhosis,and the inconsistent treatment effect may be due to differences in the research population and stem cell types.Therefore,the effect and long-term safety of HSCs transplantation in patients with liver cirrhosis still need to be further explored and verified.

2.5 Induced pluripotent stem cells(iPSCs)

iPSCs were first discovered by researchers in 2006 [43].They are pluripotent stem cells that induce and reprogram adult cells into an undifferentiated state through a specific medium.They have the same proliferation and differentiation potential as ESCs,while avoiding Ethical issues [44] are the most promising stem cells.

iPSCs can be induced to differentiate into HLCs in vitro,which is a potential source of hepatocytes.Takayama et al.transplanted 1106 human iPS-HLCs into acute and chronic liver failure model mice through the spleen.Survival rate and serum albumin levels have increased significantly,and it is suggested that the therapeutic effect of human iPS-HLCs is mainly achieved by the secretion of hepatocyte growth factor (HGF).The results of another study showed that human iPS-HLC thin slice transplantation can activate HGF/c-Met signal to prevent hepatocytes from cell death,thereby improving liver damage,and the comparison found that the transplantation efficiency of human iPS-HLC thin slice transplantation is significantly higher than Intrasplenic transplantation .

Although iPSCs avoided ethical issues and immune rejection,and achieved certain results in animal experiments,they still face the risk of teratoma formation,which limits their clinical application.

3.Problems and prospects

With the progress of regenerative medicine in recent years,stem cell transplantation based on the treatment of liver cirrhosis has shown a good application prospect,and certain results have been achieved in basic and clinical research.However,there are still many problems to be solved before large-scale clinical application.For example,the specific mechanism of stem cell transplantation in the treatment of liver cirrhosis has not yet been fully clarified;the types of stem cells that can be used for clinical treatment are still small;cell preparation,dosage,and route in clinical trials,Followup,curative effect,etc.are still not uniform;lack of multi-center,large sample randomized controlled study data,the level of evidence needs to be improved.With the gradual maturity of technology and theory,stem cell transplantation for the treatment of liver cirrhosis will be more safe,effective and convenient.