Intramuscular transplantation of engineered hepatic tissue constructs corrects acute and chronic liver failure in mice

Innovative pharmacotherapy for hepatic metabolic and chronic inflammatory diseases in China

Liver disease constitutes a significant global health concern, particularly in China where it has distinctive characteristics. China grapples with a staggering 300 million cases, predominantly due to hepatitis B and metabolic non-alcoholic fatty liver disease. Additionally, hepatocellular carcinoma has become a prevalent which is a lethal type of cancer. Despite the scarcity of innovative treatment options, Chinese hepatologists and researchers have achieved notable breakthroughs in the prevention, diagnosis, management and treatment of liver diseases. Traditional Chinese medicines have found widespread application in the treatment of various liver ailments owing to their commendable pharmacological efficacy and minimal side effects. Furthermore, there is a growing body of research in extracellular vesicles, cell therapy and gene therapy, offering new hope in the fight against liver diseases. This paper provides a comprehensive overview of the epidemiological characteristics of liver diseases and the diverse array of treatments that Chinese scholars and scientists have pursued in critical field.

Impact of L-ornithine L-aspartate on non-alcoholic steatohepatitis-associated hyperammonemia and muscle alterations

BACKGROUND

Metabolic dysfunction-associated fatty liver disease (MAFLD) is the most common chronic liver disease in the world. Progression toward non-alcoholic steatohepatitis (NASH) is associated with alterations of skeletal muscle. One plausible mechanism for altered muscle compartment in liver disease is changes in ammonia metabolism. In the present study, we explored the hypothesis that NASH-associated hyperammonemia drives muscle changes as well as liver disease progression.

MATERIALS AND METHODS

In Alms1-mutant mice (foz/foz) fed a 60% fat diet (HFD) for 12 weeks; we investigated hepatic and muscular ammonia detoxification efficiency. We then tested the effect of an 8 week-long supplementation with L-ornithine L-aspartate (LOLA), a known ammonia-lowering treatment, given after either 4 or 12 weeks of HFD for a preventive or a curative intervention, respectively. We monitored body composition, liver and muscle state by micro computed tomography (micro-CT) as well as muscle strength by four-limb grip test.

RESULTS

According to previous studies, 12 weeks of HFD induced NASH in all foz/foz mice. Increase of hepatic ammonia production and alterations of urea cycle efficiency were observed, leading to hyperammonemia. Concomitantly mice developed marked myosteatosis. First signs of myopenia occurred after 20 weeks of diet. Early LOLA treatment given during NASH development, but not its administration in a curative regimen, efficiently prevented myosteatosis and muscle quality, but barely impacted liver disease or, surprisingly, ammonia detoxification.

CONCLUSION

Our study confirms the perturbation of hepatic ammonia detoxification pathways in NASH. Results from the interventional experiments suggest a direct beneficial impact of LOLA on skeletal muscle during NASH development, though it does not improve ammonia metabolism or liver disease.

Cell Therapy and Bioengineering in Experimental Liver Regenerative Medicine: In Vivo Injury Models and Grafting Strategies

Purpose of Review

To describe experimental liver injury models used in regenerative medicine, cell therapy strategies to repopulate damaged livers and the efficacy of liver bioengineering.

Recent Findings

Several animal models have been developed to study different liver conditions. Multiple strategies and modified protocols of cell delivery have been also reported. Furthermore, using bioengineered liver scaffolds has shown promising results that could help in generating a highly functional cell delivery system and/or a whole transplantable liver.

Summary

To optimize the most effective strategies for liver cell therapy, further studies are required to compare among the performed strategies in the literature and/or innovate a novel modifying technique to overcome the potential limitations. Coating of cells with polymers, decellularized scaffolds, or microbeads could be the most appropriate solution to improve cellular efficacy. Besides, overcoming the problems of liver bioengineering may offer a radical treatment for end-stage liver diseases.

Paradoxical Association of Postoperative Plasma Sphingosine-1-Phosphate with Breast Cancer Aggressiveness and Chemotherapy

Sphingosine-1-phosphate (S1P) is a bioactive lipid mediator that has been shown to serve an important regulatory function in breast cancer progression. This study analyzes plasma S1P levels in breast cancer patients undergoing adjuvant therapy as compared to healthy control volunteers. 452 plasma S1P samples among 158 breast cancer patients, along with 20 healthy control volunteers, were analyzed. Mean S1P levels did not significantly differ between cancer patients and controls. Smoking was associated with higher S1P levels in cancer patients. Baseline S1P levels had weak inverse correlation with levels of the inflammatory mediator interleukin- (IL-) 17 and CCL-2 and positive correlation with tumor necrosis factor alpha (TNF-α). Midpoint S1P levels during adjuvant therapy were lower than baseline, with near return to baseline after completion, indicating a relationship between chemotherapy and circulating S1P. While stage of disease did not correlate with plasma S1P levels, they were lower among patients with Her2-enriched and triple-negative breast cancer as compared to luminal-type breast cancer. Plasma S1P levels are paradoxically suppressed in aggressive breast cancer and during adjuvant chemotherapy, which raises the possibility that postoperative plasma S1P levels do not reflect S1P secretion from resected breast cancer.

Current strategies to generate mature human induced pluripotent stem cells derived cholangiocytes and future applications

Stem cell research has significantly evolved over the last few years, allowing the differentiation of pluripotent cells into almost any kind of lineage possible. Studies that focus on the liver have considerably taken a leap into this novel technology, and hepatocyte-like cells are being generated that are close to resembling actual hepatocytes both genotypically and phenotypically. The potential of this extends from disease models to bioengineering, and even also innovative therapies for end-stage liver disease. Nonetheless, too few attention has been given to the non-parenchymal cells which are also fundamental for normal liver function. This includes cholangiocytes, the cells of the biliary epithelium, without whose role in bile modification and metabolism would impair hepatocyte survival. Such can be observed in diseases that target them, so called cholangiopathies, for which there is much yet to study so as to improve therapeutical options. Protocols that describe the induction of human induced pluripotent stem cells into cholangiocytes are scarce, although progress is being achieved in this area as well. In order to give the current view on this emerging research field, and in hopes to motivate further advances, we present here a review on the known differentiation strategies with sight into future applications.

Alteration of FXR phosphorylation and sumoylation in liver in the development of adult catch-up growth

Catch-up growth in adult, is increasingly recognized as an important causative factor for the extremely prevalent insulin resistance-related diseases especially in developing countries/territories. We aimed to investigate the alteration of bile acids level, phosphorylation and sumoylation of its interacting protein, bile acid receptor/farnesoid X receptor and their downstream signaling pathway, as well as insulin sensitivity and lipid profile in catch-up growth in adult rats. Male Sprague-Dawley rats were randomly allocated into four groups for two sampling points: caloric restriction group, catch-up growth in adult refed with normal chow and their normal chow controls for four or eight weeks (N4, N8 individually).We found that total serum bile acids and farnesoid X receptor phosphorylation increased without significant changes in farnesoid X receptor sumoylation and its downstream small heterodimer partner expression at the end of caloric restriction stage, while the visceral fat decreased and insulin resistance never occurred in these animals; After refeeding, total serum bile acids, farnesoid X receptor phosphorylation and sumoylation, as well as Cyp7a1, SREBP-1c mRNA levels were higher with significant decrease in small heterodimer partner expression, which is associated fat accumulation, and drastic insulin resistance in whole body and skeletal muscle. Our findings demonstrated that the fat accumulation and insulin resistance are associated with increases of bile acids, alteration of farnesoid X receptor phosphorylation, and sumoylation and its downstream signaling pathway. These changes of bile acids, farnesoid X receptor phosphorylation and sumoylation, as well as their downstream signaling might be of importance in the etiology of fat accumulation and insulin resistance in catch-up growth in adult.

Liver-Regenerative Transplantation: Regrow and Reset

Liver transplantation, either a partial liver from a living or deceased donor or a whole liver from a deceased donor, is the only curative therapy for severe end-stage liver disease. Only one-third of those on the liver transplant waiting list will be transplanted, and the demand for livers is projected to increase 23% in the next 20 years. Consequently, organ availability is an absolute constraint on the number of liver transplants that can be performed. Regenerative therapies aim to enhance liver tissue repair and regeneration by any means available (cell repopulation, tissue engineering, biomaterials, proteins, small molecules, and genes). Recent experimental work suggests that liver repopulation and engineered liver tissue are best suited to the task if an unlimited availability of functional induced pluripotent stem (iPS)-derived liver cells can be achieved. The derivation of iPS cells by reprogramming cell fate has opened up new lines of investigation, for instance, the generation of iPS-derived xenogeneic organs or the possibility of simply inducing the liver to reprogram its own hepatocyte function after injury. We reviewed current knowledge about liver repopulation, generation of engineered livers and reprogramming of liver function. We also discussed the numerous barriers that have to be overcome for clinical implementation.

Transplantation of human adipose stem cell-derived hepatocyte-like cells with restricted localization to liver using acellular amniotic membrane

Introduction

Adult stem cell-derived hepatocytes transplantation holds considerable promise for future clinical individualized therapy of liver failure or dysfunction. However, the low engraftment of the available hepatocytes in the liver disease microenvironment has been a major obstacle.

Methods

Acellular human amniotic membrane was developed as a three-dimensional scaffold and combined with hepatocyte-like cells derived from human adipose stem cells to engineer a hepatic tissue graft that would allow hepatocyte engraftment in the liver effectively.

Results

The hepatic tissue grafts maintained hepatocyte-specific gene expression and functionality in vitro. When transplanted into the surgical incision in livers for engraftment, the engineered hepatic grafts significantly decreased the degree of liver injury caused by a carbon tetrachloride treatment and generated cords that were similar to the ductal plates in the liver between the acellular human amniotic membrane and the liver of receipts at day 3 post-transplantation. The hepatic tissue grafts maintained the expression of human hepatocyte-specific markers albumin, hepatocyte nuclear factor 4α, and cytochrome P450 2B6 in the liver of receipts, and acquired human-specific drug metabolism ability at eight weeks post-transplantation.

Conclusions

The acellular human amniotic membrane has the ability to maintain the functional phenotype of the hepatocyte-like cells derived from human adipose stem cells. Functional acellular human amniotic membrane-hepatocytes grafts integrated with the liver decreases the acute liver injury of mice. These engineered tissue constructs may support stem cell-based individualized therapy for liver disease and for bioartificial liver establishment.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-015-0208-9) contains supplementary material, which is available to authorized users.

Brief Report: Immune Microenvironment Determines the Immunogenicity of Induced Pluripotent Stem Cell Derivatives

The breakthrough of induced pluripotent stem cells (iPSCs) has raised the possibility that patient-specific iPSCs can provide autologous cells for cell therapy without the concern for immune rejection. However, the immunogenicity of iPSC-derived cells remains controversial. Using syngeneic C57BL/6 (B6) mouse transplantation model, several studies indicate that B6 iPSC-derived cells exhibit some levels of immunogenicity when transplanted into B6 mice subcutaneously. In contrast, one recent study has concluded that various lineages of B6 iPSC-derived cells exhibit no immunogenicity when transplanted under the kidney capsule of B6 mice. To resolve the controversy concerning this critical issue of iPSC biology, we used the same B6 transplantation model to demonstrate that the immune response toward antigens is dependent on the immune environment of the transplantation site. Immunogenic antigen-expressing B6 embryonic stem cells (ESCs) as well as B6 iPSCs and their terminally differentiated cells survived under the kidney capsule but are immune rejected when transplanted subcutaneously or intramuscularly. The cotransplantation of mature B6 dendritic cells under the kidney capsule leads to immune rejection of B6 iPSC-derived grafts but not B6 ESC-derived grafts, indicating that the lack of detectable immune response to iPSC-derived grafts under the kidney capsule is due to the lack of functional antigen presenting cells.

Pluripotent Stem Cells to Rebuild a Kidney: The Lymph Node as a Possible Developmental Niche

Kidney disease poses a global challenge. Stem cell therapy may offer an alternative therapeutic approach to kidney transplantation, which is often hampered by the limited supply of donor organs. While specific surface antigen markers have yet to be identified for the analysis and purification of kidney stem/progenitor cells for research or clinical use, the reprogramming of somatic cells to pluripotent cells and their differentiation into the various kidney lineages might represent a valuable strategy to create a renewable cell source for regenerative purposes. In this review, we first provide an overview of kidney development and explore current knowledge about the role of extra- and intrarenal cells in kidney repair and organogenesis. We then discuss recent advances in the 1) differentiation of rodent and human embryonic stem cells (ESCs) into renal lineages; 2) generation of induced pluripotent stem cells (iPSCs) from renal or nonrenal (kidney patient-derived) adult cells; 3) differentiation of iPSCs into renal lineages; and 4) direct transcriptional reprogramming of adult renal cells into kidney progenitor cells. Finally, we describe the lymph node as a potential three-dimensional (3D) in vivo environment for kidney organogenesis from pluripotent stem cells.

New Tools in Experimental Cellular Therapy for the Treatment of Liver Diseases

The current standard of care for end stage liver disease is orthotopic liver transplantation (OLT). Through improvement in surgical techniques, immunosuppression, and general medical care, liver transplantation has become an effective treatment over the course of the last half-century. Unfortunately, due to the limited availability of donor organs, there is a finite limit to the number of patients who will benefit from this therapy. This review will discuss current research in experimental cellular therapies for acute, chronic, and metabolic liver failure that may be appropriate when liver transplantation is not an immediate option.

The lymph node as a new site for kidney organogenesis

The shortage of organs for kidney transplantation has created the need to develop new strategies to restore renal structure and function. Given our recent finding that the lymph node (LN) can serve as an in vivo factory to generate or sustain complex structures like liver, pancreas, and thymus, we investigated whether it could also support kidney organogenesis from mouse renal embryonic tissue (metanephroi). Here we provide the first evidence that metanephroi acquired a mature phenotype upon injection into LN, and host cells likely contributed to this process. Urine-like fluid-containing cysts were observed in several grafts 12 weeks post-transplantation, indicating metanephroi transplants' ability to excrete products filtered from the blood. Importantly, the kidney graft adapted to a loss of host renal mass, speeding its development. Thus, the LN might provide a unique tool for studying the mechanisms of renal maturation, cell proliferation, and fluid secretion during cyst development. Moreover, we provide evidence that inside the LN, short-term cultured embryonic kidney cells stimulated with the Wnt agonist R-Spondin 2 gave rise to a monomorphic neuron-like cell population expressing the neuronal 200-kDa neurofilament heavy marker. This finding indicates that the LN might be used to validate the differentiation potential of candidate stem cells in regenerative nephrology.

Three-dimensional culture in a microgravity bioreactor improves the engraftment efficiency of hepatic tissue constructs in mice

Tissue-engineered liver using primary hepatocytes has been considered a valuable new therapeutic modality as an alternative to whole organ liver transplantation for different liver diseases. The development of clinically feasible liver tissue engineering approaches, however, has been hampered by the poor engraftment efficiency of hepatocytes. We developed a three-dimensional (3D) culture system using a microgravity bioreactor (MB), biodegradable scaffolds and growth-factor-reduced Matrigel to construct a tissue-engineered liver for transplantation into the peritoneal cavity of non-obese diabetic severe combined immunodeficient mice. The number of viable cells in the hepatic tissue constructs was stably maintained in the 3D MB culture system. Hematoxylin-eosin staining and zonula occludens-1 expression revealed that neonatal mouse liver cells were reorganized to form tissue-like structures during MB culture. Significantly upregulated hepatic functions (albumin secretion, urea production and cytochrome P450 activity) were observed in the MB culture group. Post-transplantation analysis indicated that the engraftment efficiency of the hepatic tissue constructs prepared in MB cultures was higher than that of those prepared in the static cultures. Higher level of hepatic function in the implants was confirmed by the expression of albumin. These findings suggest that 3D MB culture systems may offer an improved method for creating tissue-engineered liver because of the higher engraftment efficiency and the reduction of the initial cell function loss.

Exploiting the unique regenerative capacity of the liver to underpin cell and gene therapy strategies for genetic and acquired liver disease

The number of genetic or acquired diseases of the liver treatable by organ transplantation is ever-increasing as transplantation techniques improve placing additional demands on an already limited organ supply. While cell and gene therapies are distinctly different modalities, they offer a synergistic alternative to organ transplant due to distinct architectural and physiological properties of the liver. The hepatic blood supply and fenestrated endothelial system affords relatively facile accessibility for cell and/or gene delivery. More importantly, however, the remarkable capacity of hepatocytes to proliferate and repopulate the liver creates opportunities for new treatments based on emerging technologies. This review will summarise current understanding of liver regeneration, describe clinical and experimental cell and gene therapeutic modalities and discuss critical challenges to translate these new technologies to wider clinical utility. This article is part of a Directed Issue entitled: "Regenerative Medicine: the challenge of translation".

Ectopic transplantation sites for cell-based therapy

PURPOSE OF REVIEW

This review outlines the concept of cell-based therapy to restore tissue function, and addresses four key points to consider in cell transplantation: source, surveillance, safety, and site. Whereas each point is essential, additional attention should be given to transplantation sites if cell therapy is going to be successful in the clinic. Various ectopic locations are discussed, and the strengths and weaknesses of each are compared as suitable candidates for cell therapy.

RECENT FINDINGS

Studies in rodents often demonstrate cell transplantation and engraftment in ectopic sites, with little evidence to suggest why it may also work in humans. For example, transplantation to the subcapsular space of the kidney is often performed in rodents, but has not been a good predictor of clinical success. Recent work has shown that the lymph node may be a good site for transplantation of multiple tissue types, and several reasons are highlighted as to why it should be considered for future studies.

SUMMARY

The use of cell-based therapy in the clinic has been hampered by the lack of appropriate sites for transplantation. The lymph node is a promising alternative for cell transplantation, and offers hope for clinical application.

Assembly of human organs from stem cells to study liver disease

Recently, significant developments in the field of liver tissue engineering have raised new possibilities for the study of complex physiological and pathophysiological processes in vitro, as well as the potential to assemble entire organs for transplantation. Human-induced pluripotent stem cells have been differentiated into relatively functional populations of hepatic cells, and novel techniques to generate whole organ acellular three-dimensional scaffolds have been developed. In this review, we highlight the most recent advances in organ assembly regarding the development of liver tissue in vitro. We emphasize applications that involve multiple types of cells with a biomimetic spatial organization for which three-dimensional configurations could be used for drug development or to explain mechanisms of disease. We also discuss applications of liver organotypic surrogates and the challenges of translating the highly promising new field of tissue engineering into a proven platform for predicting drug metabolism and toxicity.

Bone marrow-derived stem cells ameliorate hepatic fibrosis by down-regulating interleukin-17

BACKGROUND

Accumulating evidences have identified the immunoregulatory features of stem cells. In this study, the immunoregulation of bone marrow-derived stem cells (BMSCs) transplanted into patients with HBV-related decompensated cirrhosis and mouse model of liver injury induced by carbon tetrachloride (CCl4) administration was observed.

RESULTS

Compared with healthy controls, patients with HBV-related decompensated cirrhosis showed significantly higher levels of TNF-alpha, IL-12, TGF-beta1, IL-17, and IL-8. However, only IL-17 was markedly decreased after autologous BMSCs transplantation during their follow-up. The same results were found in the CCl4-treated mice. Furthermore, we found that exogenous IL-17 partly abolished the therapeutic effect of BMSCs whereas IL-17-specific antibody promoted improvement of liver injury in CCl4-treated mice, resembling the therapeutic effect of BMSCs transplantation.

CONCLUSIONS

These data suggested that BMSCs transplantation induces a decrease of IL-17 level, which at least in part delineates the mechanisms of stem cells-mediated therapeutic benefit on liver disease.

Engineered liver for transplantation

Orthotopic liver transplantation is the only definitive treatment for end stage liver failure and the shortage of donor organs severely limits the number of patients receiving transplants. Liver tissue engineering aims to address the donor liver shortage by creating functional tissue constructs to replace a damaged or failing liver. Despite decades of work, various bottoms-up, synthetic biomaterials approaches have failed to produce a functional construct suitable for transplantation. Recently, a new strategy has emerged using whole organ scaffolds as a vehicle for tissue engineering. This technique involves preparation of these organ scaffolds via perfusion decellularization with the resulting scaffold retaining the circulatory network of the native organ. This important phenomenon allows for the construct to be repopulated with cells and to be connected to the blood torrent upon transplantation. This opinion paper presents the current advances and discusses the challenges of creating fully functional transplantable liver grafts with this whole liver engineering approach.

The protective effect of intrasplenic transplantation of Ad-IL-18BP/IL-4 gene-modified fetal hepatocytes on ConA-induced hepatitis in mice

Background

Concanavalin A (ConA)-induced hepatitis is an experimental murine model mirroring the pathology of human autoimmune hepatitis.

Aim

To investigate the effects of intrasplenically transplanted fetal hepatocytes (BNL.CL2) transfected with recombinant adenovirus vector expressing the IL-18 binding protein (IL-18BP) and IL-4 fusion protein on ConA-induced hepatitis in mice.

Methods

Ad-IL-18BP/IL-4 was used to infect BNL.CL2 cells. IL-4 and IL-18BP fusion protein expression were detected by ELISA and Western blotting. BNL.CL2 cells infected with Ad-IL-18BP/IL-4 were intrasplenically transplanted into mice. After 10 days, mice were injected with ConA (15 mg/kg), and sacrificed 18 hours later. Liver injury was assessed by serum transaminase and liver histology. TNF-α, IL-18, IL-4, IL-10, IL-12p70 and monocyte-chemoattracting protein (MCP)-1 levels in serum and liver homogenates were detected by ELISA. Signaling molecules in liver homogenates were analyzed by Western blotting.

Results

Ad-IL-18BP/IL-4 effectively expressed the IL-18BP/IL-4 fusion protein for more than 14 days in BNL.CL12 cells. Treatment of mice with Ad-IL-18BP/IL-4-BNL.CL2 before ConA injection significantly reduced the elevated plasma levels of transaminases compared with ConA control groups. TNF-α, IL-18, IL-12p70 and MCP-1 levels in serum and liver homogenates from mice transplanted with Ad-IL-18BP/IL-4-BNL.CL2 were lower and IL-4 and IL-10 levels were higher than control groups. Phosphorylation levels of NF-κB p65, AKT, p38 and JNK1/2 in liver homogenates were markedly suppressed by Ad-IL-18BP/IL-4.

Conclusions

Ad-IL-18BP/IL-4 was effectively transfected into mouse BNL.CL2 cells. Intrasplenic transplantation of Ad-IL-18BP/IL-4-BNL.CL12 cells alleviated the severity of inflammation in ConA-induced experimental hepatitis and provides a useful basis for the targeted gene therapy of liver disease.

Application of whole-organ tissue engineering in hepatology

Initially hailed as the ultimate solution to organ failure, engineering of vascularized tissues such as the liver has stalled because of the need for a well-structured circulatory system that can maintain the cells seeded inside the construct. A new approach has evolved to overcome this obstacle. Whole-organ decellularization is a method that retains most of the native vascular structures of the organ, providing microcirculatory support and structure, which can be anastomosed with the recipient circulation. The technique was first applied to the heart and then adapted for the liver. Several studies have shown that cells can be eliminated, the extracellular matrix and vasculature are reasonably preserved and, after repopulation with hepatocytes, these grafts can perform hepatic functions in vitro and in vivo. Progress is rapidly being made as researchers are addressing several key challenges to whole-organ tissue engineering, such as ensuring correct cell distribution, nonparenchymal cell seeding, blood compatibility, immunological concerns, and the source of cells and matrices.

Cells and materials for liver tissue engineering

Liver transplantation is currently the most efficacious treatment for end-stage liver diseases. However, one main problem with liver transplantation is the limited number of donor organs that are available. Therefore, liver tissue engineering based on cell transplantation that combines materials to mimic the liver is under investigation with the goal of restoring normal liver functions. Tissue engineering aims to mimic the interactions among cells with a scaffold. Particular materials or a matrix serve as a scaffold and provide a three-dimensional environment for cell proliferation and interaction. Moreover, the scaffold plays a role in regulating cell maturation and function via these interactions. In cultures of hepatic lineage cells, regulation of cell proliferation and specific function using biocompatible synthetic, biodegradable bioderived matrices, protein-coated materials, surface-modified nanofibers, and decellularized biomatrix has been demonstrated. Furthermore, beneficial effects of addition of growth factor cocktails to a flow bioreactor or coculture system on cell viability and function have been observed. In addition, a system for growing stem cells, liver progenitor cells, and primary hepatocytes for transplantation into animal models was developed, which produces hepatic lineage cells that are functional and that show long-term proliferation following transplantation. The major limitation of cells proliferated with matrix-based transplantation systems is the high initial cell loss and dysfunction, which may be due to the absence of blood flow and the changes in nutrients. Thus, the development of vascular-like scaffold structures, the formation of functional bile ducts, and the maintenance of complex metabolic functions remain as major problems in hepatic tissue engineering and will need to be addressed to enable further advances toward clinical applications.

Human-scale whole-organ bioengineering for liver transplantation: a regenerative medicine approach

At this time, the only definitive treatment of hepatic failure is liver transplantation. However, transplantation has been limited by the severely limited supply of human donor livers. Alternatively, a regenerative medicine approach has been recently proposed in rodents that describe the production of three-dimensional whole-organ scaffolds for assembly of engineered complete organs. In the present study, we describe the decellularization of porcine livers to generate liver constructs at a scale that can be clinically relevant. Adult ischemic porcine livers were successfully decellularized using a customized perfusion protocol, the decellularization process preserved the ultrastructural extracellular matrix components, functional characteristics of the native microvascular and the bile drainage network of the liver, and growth factors necessary for angiogenesis and liver regeneration. Furthermore, isolated hepatocytes engrafted and reorganized in the porcine decellularized livers using a human-sized organ culture system. These results provide proof-of-principle for the generation of a human-sized, three-dimensional organ scaffold as a potential structure for human liver grafts reconstruction for transplantation to treat liver disease.

In vivo tissue engineering of musculoskeletal tissues

Tissue engineering of musculoskeletal tissues often involves the in vitro manipulation and culture of progenitor cells, growth factors and biomaterial scaffolds. Though in vitro tissue engineering has greatly increased our understanding of cellular behavior and cell-material interactions, this methodology is often unable to recreate tissue with the hierarchical organization and vascularization found within native tissues. Accordingly, investigators have focused on alternative in vivo tissue engineering strategies, whereby the traditional triad (cells, growth factors, scaffolds) or a combination thereof are directly implanted at the damaged tissue site or within ectopic sites capable of supporting neo-tissue formation. In vivo tissue engineering may offer a preferential route for regeneration of musculoskeletal and other tissues with distinct advantages over in vitro methods based on the specific location of endogenous cultivation, recruitment of autologous cells, and patient-specific regenerated tissues.

Prospects for Induced Phiripotent Stem Cell-Derived Hepatocytes in Cell Therapy

Induced pluripotent stem (iPS) cells, first established in 2006, have the same characteristics of self-renew-ability and pluripotency as embryonic stem (ES) cells. iPS cells are inducible from patient-specific somatic cells; therefore, they hold significant advantages for overcoming immunological rejection as well as the ethical issues associated with the derivation of ES cells from embryos. Generation of patient-derived hepatocytes by iPS technology and their use in cell transplantation therapy for patients with liver disease is quite attractive. Here, we discuss recent advances and challenges in hepatocyte differentiation from iPS cells and their utility in cell therapy.

A whole-organ regenerative medicine approach for liver replacement

BACKGROUND & AIMS

The therapy of choice for end-stage liver disease is whole-organ liver transplantation, but this option is limited by a shortage of donor organs. Cell-based therapies and hepatic tissue engineering have been considered as alternatives to liver transplantation, but neither has proven effective to date. A regenerative medicine approach for liver replacement has recently been described that includes the use of a three-dimensional organ scaffold prepared by decellularization of xenogeneic liver. The present study investigates a new, minimally disruptive method for whole-organ liver decellularization and three different cell reseeding strategies to engineer functional liver tissue.

METHODS

A combination of enzymatic, detergent, and mechanical methods are used to remove all cells from isolated rat livers. Whole-organ perfusion is used in a customized organ chamber and the decellularized livers are examined by morphologic, biochemical, and immunolabeling techniques for preservation of the native matrix architecture and composition. Three different methods for hepatocyte seeding of the resultant three-dimensional liver scaffolds are evaluated to maximize cell survival and function: (1) direct parenchymal injection, (2) multistep infusion, or (3) continuous perfusion.

RESULTS

The decellularization process preserves the three-dimensional macrostructure, the ultrastructure, the composition of the extracellular matrix components, the native microvascular network of the liver, and the bile drainage system, and up to 50% of growth factor content. The three-dimensional liver matrix reseeded with the multistep infusion of hepatocytes generated ∼90% of cell engraftment and supported liver-specific functional capacities of the engrafted cells, including albumin production, urea metabolism, and cytochrome P450 induction.

CONCLUSIONS

Whole-organ liver decellularization is possible with maintenance of structure and composition suitable to support functional hepatocytes.