Improved survival of fulminant liver failure by transplantation of microencapsulated cryopreserved porcine hepatocytes in mice

A comprehensive review of advances in hepatocyte microencapsulation: selecting materials and preserving cell viability

Liver failure represents a critical medical condition with a traditionally grim prognosis, where treatment options have been notably limited. Historically, liver transplantation has stood as the sole definitive cure, yet the stark disparity between the limited availability of liver donations and the high demand for such organs has significantly hampered its feasibility. This discrepancy has necessitated the exploration of hepatocyte transplantation as a temporary, supportive intervention. In light of this, our review delves into the burgeoning field of hepatocyte transplantation, with a focus on the latest advancements in maintaining hepatocyte function, co-microencapsulation techniques, xenogeneic hepatocyte transplantation, and the selection of materials for microencapsulation. Our examination of hepatocyte microencapsulation research highlights that, to date, most studies have been conducted in vitro or using liver failure mouse models, with a notable paucity of experiments on larger mammals. The functionality of microencapsulated hepatocytes is primarily inferred through indirect measures such as urea and albumin production and the rate of ammonia clearance. Furthermore, research on the mechanisms underlying hepatocyte co-microencapsulation remains limited, and the practicality of xenogeneic hepatocyte transplantation requires further validation. The potential of hepatocyte microencapsulation extends beyond the current scope of application, suggesting a promising horizon for liver failure treatment modalities. Innovations in encapsulation materials and techniques aim to enhance cell viability and function, indicating a need for comprehensive studies that bridge the gap between small-scale laboratory success and clinical applicability. Moreover, the integration of bioengineering and regenerative medicine offers novel pathways to refine hepatocyte transplantation, potentially overcoming the challenges of immune rejection and ensuring the long-term functionality of transplanted cells. In conclusion, while hepatocyte microencapsulation and transplantation herald a new era in liver failure therapy, significant strides must be made to translate these experimental approaches into viable clinical solutions. Future research should aim to expand the experimental models to include larger mammals, thereby providing a clearer understanding of the clinical potential of these therapies. Additionally, a deeper exploration into the mechanisms of cell survival and function within microcapsules, alongside the development of innovative encapsulation materials, will be critical in advancing the field and offering new hope to patients with liver failure.

Three Dimensional Bioprinting for Hepatic Tissue Engineering: From In Vitro Models to Clinical Applications

Fabrication of functional organs is the holy grail of tissue engineering and the possibilities of repairing a partial or complete liver to treat chronic liver disorders are discussed in this review. Liver is the largest gland in the human body and plays a responsible role in majority of metabolic function and processes. Chronic liver disease is one of the leading causes of death globally and the current treatment strategy of organ transplantation holds its own demerits. Hence there is a need to develop an in vitro liver model that mimics the native microenvironment. The developed model should be a reliable to understand the pathogenesis, screen drugs and assist to repair and replace the damaged liver. The three-dimensional bioprinting is a promising technology that recreates in vivo alike in vitro model for transplantation, which is the goal of tissue engineers. The technology has great potential due to its precise control and its ability to homogeneously distribute cells on all layers in a complex structure. This review gives an overview of liver tissue engineering with a special focus on 3D bioprinting and bioinks for liver disease modelling and drug screening.

Cellular therapies in liver and pancreatic diseases

Over the past two decades, developments in regenerative medicine in gastroenterology have been greatly enhanced by the application of stem cells, which can self-replicate and differentiate into any somatic cell. The discovery of induced pluripotent stem cells has opened remarkable perspectives on tissue regeneration, including their use as a bridge to transplantation or as supportive therapy in patients with organ failure. The improvements in DNA manipulation and gene editing strategies have also allowed to clarify the physiopathology and to correct the phenotype of several monogenic diseases, both in vivo and in vitro. Further progress has been made with the development of three-dimensional cultures, known as organoids, which have demonstrated morphological and functional complexity comparable to that of a miniature organ. Hence, owing to its protean applications and potential benefits, cell and organoid transplantation has become a hot topic for the management of gastrointestinal diseases. In this review, we describe current knowledge on cell therapies in hepatology and pancreatology, providing insight into their future applications in regenerative medicine.

Functional Assessment of Cardiac Arrest Hepatocytes and Effect of Mechanical Perfusion on Function in a Rat Model

BACKGROUND

Hepatocyte transplantation has been reported to be useful for metabolic diseases and acute liver failure. However, the shortage of donors limits its widespread use. The use of livers from donors after circulatory death, which are currently unavailable for liver transplantation, may alleviate donor shortage. In this study, we investigated the effects of mechanical perfusion on cardiac arrest hepatocytes in a rat model using cardiac arrest donor livers, and we evaluated the function of cardiac arrest hepatocytes.

METHODS

F344 rat hepatocytes isolated from livers removed during cardiac pulsation were compared with those isolated from livers removed after 30 minutes of warm ischemia after cardiac arrest. We then compared hepatocytes isolated from livers removed after 30 minutes of warm ischemia with those isolated after 30 minutes of mechanical perfusion before isolation. The yield per liver weight, ammonia removal capacity, and adenosine diphosphate/adenosine triphosphate ratio were evaluated.

RESULTS

Thirty minutes of warm inhibition reduced hepatocyte yield but did not alter ammonia removal capacity and energy status. Mechanical perfusion increased hepatocyte yield and improved the adenosine diphosphate/adenosine triphosphate ratio after 30 minutes of warm inhibition.

CONCLUSION

Thirty minutes of warm ischemic time may decrease isolated hepatocyte yield without degrading their function. If increased yields are obtained, livers from donors dying of cardiac arrest could be used for hepatocyte transplantation. The results also suggest that mechanical perfusion may positively affect the energy status of hepatocytes.

Freezing biological organisms for biomedical applications

Biological organisms play important roles in human health, either in a commensal or pathogenic manner. Harnessing inactivated organisms or living organisms is a promising way to treat diseases. As two types of freezing, cryoablation makes it simple to inactivate organisms that must be in a non-pathogenic state when needed, while cryopreservation is a facile way to address the problem of long-term storage challenged by living organism-based therapy. In this review, we present the latest studies of freezing biological organisms for biomedical applications. To begin with, the freezing strategies of cryoablation and cryopreservation, as well as their corresponding technical essentials, are illustrated. Besides, biomedical applications of freezing biological organisms are presented, including transplantation, tissue regeneration, anti-infection therapy, and anti-tumor therapy. The challenges and prospects of freezing living organisms for biomedical applications are well discussed. We believe that the freezing method will provide a potential direction for the standardization and commercialization of inactivated or living organism-based therapeutic systems, and promote the clinical application of organism-based therapy.

The Influence of Interdisciplinary Work towards Advancing Knowledge on Human Liver Physiology

The knowledge accumulated throughout the years about liver regeneration has allowed a better understanding of normal liver physiology, by reconstructing the sequence of steps that this organ follows when it must rebuild itself after being injured. The scientific community has used several interdisciplinary approaches searching to improve liver regeneration and, therefore, human health. Here, we provide a brief history of the milestones that have advanced liver surgery, and review some of the new insights offered by the interdisciplinary work using animals, in vitro models, tissue engineering, or mathematical models to help advance the knowledge on liver regeneration. We also present several of the main approaches currently available aiming at providing liver support and overcoming organ shortage and we conclude with some of the challenges found in clinical practice and the ethical issues that have concomitantly emerged with the use of those approaches.

Sulfated Alginate Reduces Pericapsular Fibrotic Overgrowth on Encapsulated cGMP-Compliant hPSC-Hepatocytes in Mice

Intra-peritoneal placement of alginate encapsulated human induced pluripotent stem cell-derived hepatocytes (hPSC-Heps) represents a potential new bridging therapy for acute liver failure. One of the rate-limiting steps that needs to be overcome to make such a procedure more efficacious and safer is to reduce the accumulation of fibrotic tissue around the encapsulated cells to allow the free passage of relevant molecules in and out for metabolism. Novel chemical compositions of alginate afford the possibility of achieving this aim. We accordingly used sulfated alginate and demonstrated that this material reduced fibrotic overgrowth whilst not impeding the process of encapsulation nor cell function. Cumulatively, this suggests sulfated alginate could be a more suitable material to encapsulate hPSC-hepatocyte prior to human use.

Biomaterials for Cell-Surface Engineering and Their Efficacy

Literature in the field of stem cell therapy indicates that, when stem cells in a state of single-cell suspension are injected systemically, they show poor in vivo survival, while such cells show robust cell survival and regeneration activity when transplanted in the state of being attached on a biomaterial surface. Although an attachment-deprived state induces anoikis, when cell-surface engineering technology was adopted for stem cells in a single-cell suspension state, cell survival and regenerative activity dramatically improved. The biochemical signal coming from ECM (extracellular matrix) molecules activates the cell survival signal transduction pathway and prevents anoikis. According to the target disease, various therapeutic cells can be engineered to improve their survival and regenerative activity, and there are several types of biomaterials available for cell-surface engineering. In this review, biomaterial types and application strategies for cell-surface engineering are presented along with their expected efficacy.

Alginate microencapsulated human hepatocytes for the treatment of acute liver failure in children

BACKGROUND & AIMS

Liver transplantation (LT) is the most effective treatment for patients with acute liver failure (ALF), but is limited by surgical risks and the need for life-long immunosuppression. Transplantation of microencapsulated human hepatocytes in alginate is an attractive option over whole liver replacement. The safety and efficacy of hepatocyte microbead transplantation have been shown in animal models. We report our experience of this therapy in children with ALF treated on a named-patient basis.

METHODS

Clinical grade human hepatocyte microbeads (HMBs) and empty microbeads were tested in immunocompetent healthy rats. Subsequently, 8 children with ALF, who were awaiting a suitable allograft for LT, received intraperitoneal transplantation of HMBs. We monitored complications of the procedure, assessing the host immune response and residual function of the retrieved HMBs, either after spontaneous native liver regeneration or at the time of LT.

RESULTS

Intraperitoneal transplantation of HMBs in healthy rats was safe and preserved synthetic and detoxification functions, without the need for immunosuppression. Subsequently, 8 children with ALF received HMBs (4 neonatal haemochromatosis, 2 viral infections and 2 children with unknown cause at time of infusion) at a median age of 14.5 days, range 1 day to 6 years. The procedure was well tolerated without complications. Of the 8 children, 4 avoided LT while 3 were successfully bridged to LT following the intervention. HMBs retrieved after infusions (at the time of LT) were structurally intact, free of host cell adherence and contained viable hepatocytes with preserved functions.

CONCLUSION

The results demonstrate the feasibility and safety of an HMB infusion in children with ALF.

LAY SUMMARY

Acute liver failure in children is a rare but devastating condition. Liver transplantation is the most effective treatment, but it has several important limitations. Liver cell (hepatocyte) transplantation is an attractive option, as many patients only require short-term liver support while their own liver recovers. Human hepatocytes encapsulated in alginate beads can perform the functions of the liver while alginate coating protects the cells from immune attack. Herein, we demonstrated that transplantation of these beads was safe and feasible in children with acute liver failure.

Liver Tissue Engineering as an Emerging Alternative for Liver Disease Treatment

Chronic liver diseases affect thousands of lives throughout the world every year. The shortage of liver donors for transplantation has been the main driving force to employ alternative methods such as liver tissue engineering (LTE) in fabricating a three-dimensional transplantable liver tissue or enhancing cell delivery techniques alleviating the need for liver donors. LTE consists of three components, cells, ECM (extracellular matrix), and signaling molecules, which we discuss the first and second. The three most common cell sources used in LTE are human and animal primary hepatocytes, and stem cells for different applications. Two major categories of ECM are used to mimic the microenvironment of these cells, named scaffolds and microbeads. Scaffolds have been made by numerous methods with a wide range of synthetic and natural biomaterials. Cell encapsulation has also been utilized by many polymeric biomaterials. To investigate their functions, many properties have been discussed in the literature, such as biochemical, geometrical, and mechanical properties, in both of these categories. Overall, LTE shows excellent potential in assisting hepatic disorders. However, some challenges exist that prevent the practical use of it clinically, making LTE an ongoing research subject in the scientific society.

Establishment of gene-edited pigs expressing human blood-coagulation factor VII and albumin for bioartificial liver use

BACKGROUND AND AIM

Bioartificial livers (BALs) are considered as a solution to bridge patients with acute liver failure to liver transplantation or to assist in spontaneous recovery for patients with end-stage liver disease. Pig is the best donor of hepatocytes for BALs in clinical trials, because metabolic and detoxification function of its liver are close to human. However, using pig hepatocytes for BALs remains controversial for safety concern owing to nonhuman proteins secretion. Herein, we attempt to establish modified pigs expressing humanized liver proteins, blood-coagulation factor VII (F7), and albumin (ALB). These pigs should also be porcine endogenous retrovirus subtype C (PERV-C) free so that their ability of transmitting PERV to human could be diminished seriously.

METHODS

We devised both homology-dependent and independent knock-in approaches to insert a fusion of hF7 and hALB gene downstream the site of pig endogenous F7 promoter in pig fetal fibroblasts negative for PERV-C. The modified pigs were then generated through somatic cell nuclear transfer.

RESULTS

We obtained 14 and 10 cloned pigs by homology-dependent and independent approaches, respectively. Among them, 19 cloned pigs were with expected gene modification and 13 are alive to date. These modified pigs can successfully express hF7 and hALB in the liver and serum, and the expressed hF7 exhibits normal coagulation activity.

CONCLUSIONS

The gene-edited pigs expressing hF7 and hALB in the liver were generated successfully. We anticipate that our pigs could provide an alternative cell source for BALs as a promising treatment for patients with acute liver failure.

A Simple and Useful Predictive Assay for Evaluating the Quality of Isolated Hepatocytes for Hepatocyte Transplantation

No optimal assay for assessing isolated hepatocytes before hepatocyte transplantation (HTx) has been established, therefore reliable and rapid assays are warranted. Isolated rat hepatocytes were dipped in a water bath (necrosis model), and were also cultured with Okadaic acid (apoptosis model) or vehicle, followed by cellular assessment including trypan blue exclusion (TBE) viability, ADP /ATP ratio, plating efficiency (PE), DNA quantity and ammonia elimination. Hepatocytes were transplanted into the liver of analbuminemic rats, subsequently engraftment was assessed by serum albumin and the histology of transplanted grafts. In the necrosis model, the ADP/ATP ratio was strongly and negatively correlated with the TBE (R² = 0.559, P < 0.001). In the apoptosis model, the ADP/ATP ratio assay, PE, DNA quantification and an ammonia elimination test clearly distinguished the groups (P < 0.001, respectively). The ADP/ATP ratio, PE and DNA quantity were well-correlated and the ammonia elimination was slightly correlated with the transplant outcome. TBE could not distinguish the groups and was not correlated with the outcome. The ADP/ATP ratio assay predicted the transplant outcome. PE and DNA quantification may improve the accuracy of the retrospective (evaluations require several days) quality assessment of hepatocytes. The ADP/ATP ratio assay, alone or with a short-term metabolic assay could improve the efficiency of HTx.

Advances in the slow freezing cryopreservation of microencapsulated cells

Over the past few decades, the use of cell microencapsulation technology has been promoted for a wide range of applications as sustained drug delivery systems or as cells containing biosystems for regenerative medicine. However, difficulty in their preservation and storage has limited their availability to healthcare centers. Because the preservation in cryogenic temperatures poses many biological and biophysical challenges and that the technology has not been well understood, the slow cooling cryopreservation, which is the most used technique worldwide, has not given full measure of its full potential application yet. This review will discuss the different steps that should be understood and taken into account to preserve microencapsulated cells by slow freezing in a successful and simple manner. Moreover, it will review the slow freezing preservation of alginate-based microencapsulated cells and discuss some recommendations that the research community may pursue to optimize the preservation of microencapsulated cells, enabling the therapy translate from bench to the clinic.

Beneficial Effects of Human Mesenchymal Stromal Cells on Porcine Hepatocyte Viability and Albumin Secretion

Porcine hepatocytes transplanted during acute liver failure might support metabolic functions until the diseased liver recovers its function. Here, we isolated high numbers of viable pig hepatocytes and evaluated hepatocyte functionality after encapsulation. We further investigated whether coculture and coencapsulation of hepatocytes with human multipotent mesenchymal stromal cells (MSC) are beneficial on hepatocyte function. Livers from 10 kg pigs (n = 9) were harvested, and hepatocytes were isolated from liver suspensions for microencapsulation using alginate and poly(ethylene-glycol)- (PEG-) grafted alginate hydrogels, either alone or in combination with MSC. Viability, albumin secretion, and diazepam catabolism of hepatocytes were measured for one week. 9.2 ± 3.6 × 109 hepatocytes with 95.2 ± 3.1% viability were obtained after isolation. At day 3, free hepatocytes displayed 99% viability, whereas microencapsulation in alginate and PEG-grafted alginate decreased viability to 62% and 48%, respectively. Albumin secretion and diazepam catabolism occurred in free and microencapsulated hepatocytes. Coencapsulation of hepatocytes with MSC significantly improved viability and albumin secretion at days 4 and 8 (p < 0.05). Coculture with MSC significantly increased and prolonged albumin secretion. In conclusion, we established a protocol for isolation and microencapsulation of high numbers of viable pig hepatocytes and demonstrated that the presence of MSC is beneficial for the viability and function of porcine hepatocytes.

Testing of microencapsulated porcine hepatocytes in a new model of fulminant liver failure in baboons

BACKGROUND

There is no standard therapy for acute liver failure. Hepatocyte transplantation has been proposed for temporary liver function support, while the injured liver regenerates or while waiting for transplantation. We have previously shown such efficacy for microencapsulated porcine hepatocytes in mice with fulminant liver failure. We aimed to establish a large animal model for fulminant liver failure to assess the efficacy of microencapsulated porcine hepatocytes in temporary liver function support.

METHODS

The model was developed in baboons; for testing microencapsulated hepatocytes, the best condition was 75% hepatectomy and 60 min warm ischemia time. Fulminant liver failure was characterized by steep increases in liver biochemical parameters, severe steatosis, and massive hepatocyte necrosis during the first 10 days. Hepatocytes from miniature swine were microencapsulated in alginate-poly-l-lysine microspheres, and transplanted intraperitoneally immediately after hepatectomy and warm ischemia (80-120 mL packed hepatocytes in 200-350 mL microspheres, about 30%-50% of the baboon's native liver volume).

RESULTS

In the control group, three of five animals were sacrificed after 6-10 days because of fulminant liver failure, and two of five animals recovered normal liver function and survived until elective euthanasia (28 days). In the treatment group of four animals, one animal developed liver failure but survived to 21 days, and three animals recovered completely with normal liver function.

CONCLUSIONS

The results indicate that microencapsulated porcine hepatocytes provide temporary liver function support in baboons with fulminant liver failure. These data support development of this cell therapy product toward clinical trials in patients with acute liver failure.

Microencapsulation of Hepatocytes and Mesenchymal Stem Cells for Therapeutic Applications

Encapsulated hepatocyte transplantation and encapsulated mesenchymal stem cell transplantation are newly developed potential treatments for acute and chronic liver diseases, respectively. Cells are microencapsulated in biocompatible semipermeable alginate-based hydrogels. Microspheres protect cells against antibodies and immune cells, while allowing nutrients, small/medium size proteins and drugs to diffuse inside and outside the polymer matrix. Microencapsulated cells are assessed in vitro and designed for experimental transplantation and for future clinical applications.Here, we describe the protocol for microencapsulation of hepatocytes and mesenchymal stem cells within hybrid poly(ethylene glycol)-alginate hydrogels.

Hepatocyte Transplantation in Special Populations: Clinical Use in Children

Orthotopic liver transplantation remains the only proven cure for end-stage liver failure. Despite significant advances in the field, the clinical demand for donor organs far outweighs the supply. Hepatocyte transplantation has been proposed as an alternative approach to whole liver transplant in select diseases. Several international centers have reported experimental trials of human hepatocyte transplantation in acute liver failure and liver-based metabolic disorders. This chapter provides an introduction to hepatocyte transplantation from both a technical and clinical perspective. We will also focus on the special needs of pediatric patients, since historically the majority of clinical hepatocyte transplants have involved infants and children.

Encapsulated platelets modulate kupffer cell activation and reduce oxidative stress in a model of acute liver failure

Acute liver failure (ALF) is characterized by massive hepatocyte cell death. Kupffer cells (KC) are the first cells to be activated after liver injury. They secrete cytokines and produce reactive oxygen species, leading to apoptosis of hepatocytes. In a previous study, we showed that encapsulated platelets (PLTs) increase survival in a model of ALF. Here, we investigate how PLTs exert their beneficial effect. Wistar rats submitted to 90% hepatectomy were treated with PLTs encapsulated in sodium alginate or empty capsules. Animals were euthanized at 6, 12, 24, 48, and 72 hours after hepatectomy, and livers were collected to assess oxidative stress, caspase activity, and gene expression related to oxidative stress or liver function. The number of KCs in the remnant liver was evaluated. Interaction of encapsulated PLTs and KCs was investigated using a coculture system. PLTs increase superoxide dismutase and catalase activity and reduce lipid peroxidation. In addition, caspase 3 activity was reduced in animals receiving encapsulated PLTs at 48 and 72 hours. Gene expression of endothelial nitric oxide synthase and nuclear factor kappa B were elevated in the PLT group at each time point analyzed. Gene expression of albumin and factor V also increased in the PLT group. The number of KCs in the PLT group returned to normal levels at 12 hours but remained elevated in the control group until 72 hours. Finally, PLTs modulate interleukin (IL) 6 and IL10 expression in KCs after 24 hours of coculture. In conclusion, these results indicate that PLTs interact with KCs in this model and exert their beneficial effect through reduction of oxidative stress that results in healthier hepatocytes and decreased apoptosis. Liver Transplantation 22 1562-1572 2016 AASLD.

Microencapsulation of porcine thyroid cell organoids within a polymer microcapsule construct

Hypothyroidism is a common condition of hormone deficiency, and oral administration of thyroid hormones is currently the only available treatment option. However, there are some disadvantages with this treatment modality including compliance challenges to patients. Therefore, a physiologically based alternative therapy for hypothyroidism with little or no side-effects is needed. In this study, we have developed a method for microencapsulating porcine thyroid cells as a thyroid hormone replacement approach. The hybrid wall of the polymer microcapsules permits thyroid hormone release while preventing immunoglobulin antibodies from entry. This strategy could potentially enable implantation of the microcapsule organoids containing allogeneic or xenogeneic thyroid cells to secret hormones over time without the need for immunosuppression of recipients. Porcine thyroid cells were isolated and encapsulated in alginate-poly-L-ornithine-alginate microcapsules using a microfluidic device. The porcine thyroid cells formed three-dimensional follicular spheres in the microcapsules with decent cell viability and proliferation. Thyroxine release from the encapsulated cells was higher than from unencapsulated cells ( P < 0.05) and was maintained during the entire duration of experiment (>28 days). These results suggest that the microencapsulated thyroid cell organoids may have the potential to be used for therapy and/or drug screening.

Hepatocyte cell therapy in liver disease

Liver disease is a leading cause of morbidity and mortality. Liver transplantation remains the only proven treatment for end-stage liver failure but is limited by the availability of donor organs. Hepatocyte cell therapy, either with bioartificial liver devices or hepatocyte transplantation, may help address this by delaying or preventing liver transplantation. Early clinical studies have shown promising results, however in most cases, the benefit has been short lived and so further research into these therapies is required. Alternative sources of hepatocytes, including stem cell-derived hepatocytes, are being investigated as the isolation of primary human hepatocytes is limited by the same shortage of donor organs. This review summarises the current clinical experience of hepatocyte cell therapy together with an overview of possible alternative sources of hepatocytes. Current and future areas for research that might lead towards the realisation of the full potential of hepatocyte cell therapy are discussed.

Current status of hepatocyte xenotransplantation

The treatment of acute liver failure, a condition with high mortality, comprises optimal clinical care, and in severe cases liver transplantation. However, there are limitations in availability of organ donors. Hepatocyte transplantation is a promising alternative that could fill the medical need, in particular as the bridge to liver transplantation. Encapsulated porcine hepatocytes represent an unlimited source that could function as a bioreactor requiring minimal immunosuppression. Besides patients with acute liver failure, patients with alcoholic hepatitis who are unresponsive to a short course of corticosteroids are a target for hepatocyte transplantation. In this review we present an overview of the innate immune barriers in hepatocyte xenotransplantation, including the role of complement and natural antibodies; the role of phagocytic cells and ligands like CD47 in the regulation of phagocytic cells; and the role of Natural Killer cells. We present also some illustrations of physiological species incompatibilities in hepatocyte xenotransplantation, such as incompatibilities in the coagulation system. An overview of the methodology for cell microencapsulation is presented, followed by proof-of-concept studies in rodent and nonhuman primate models of fulminant liver failure: these studies document the efficacy of microencapsulated porcine hepatocytes which warrants progress towards clinical application. Lastly, we present an outline of a provisional clinical trial, that upon completion of preclinical work could start within the upcoming 2-3 years.

3D liver models on a microplatform: well-defined culture, engineering of liver tissue and liver-on-a-chip

The liver, the largest organ in the human body, is a multi-functional organ with diverse metabolic activities that plays a critical role in maintaining the body and sustaining life. Although the liver has excellent regenerative and recuperative properties, damages caused by chronic liver diseases or viral infection may lead to permanent loss of liver functions. Studies of liver disease mechanism have focused on drug screening and liver tissue engineering techniques, including strategies based on in vitro models. However, conventional liver models are plagued by a number of limitations, which have motivated the development of 'liver-on-a-chip' and microplatform-based bioreactors that can provide well-defined microenvironments. Microtechnology is a promising tool for liver tissue engineering and liver system development, as it can mimic the complex in vivo microenvironment and microlevel ultrastructure, by using a small number of human cells under two-dimensional (2D) and three-dimensional (3D) culture conditions. These systems provided by microtechnology allow improved liver-specific functions and can be expanded to encompass diverse 3D culture methods, which are critical for the maintenance of liver functions and recapitulation of the features of the native liver. In this review, we provide an overview of microtechnologies that have been used for liver studies, describe biomimetic technologies for constructing microscale 2D and 3D liver models as well as liver-on-a-chip systems and microscale bioreactors, and introduce applications of liver microtechnology and future trends in the field.

Experimental hepatocyte xenotransplantation--a comprehensive review of the literature

Hepatocyte transplantation (Tx) is a potential therapy for certain diseases of the liver, including hepatic failure. However, there is a limited supply of human livers as a source of cells and, after isolation, human hepatocytes can be difficult to expand in culture, limiting the number available for Tx. Hepatocytes from other species, for example, the pig, have therefore emerged as a potential alternative source. We searched the literature through the end of 2014 to assess the current status of experimental research into hepatocyte xenoTx. The literature search identified 51 reports of in vivo cross-species Tx of hepatocytes in a variety of experimental models. Most studies investigated the Tx of human (n = 23) or pig (n = 19) hepatocytes. No studies explored hepatocytes from genetically engineered pigs. The spleen was the most common site of Tx (n = 23), followed by the liver (through the portal vein [n = 6]) and peritoneal cavity (n = 19). In 47 studies (92%), there was evidence of hepatocyte engraftment and function across a species barrier. The data provided by this literature search strengthen the hypothesis that xenoTx of hepatocytes is feasible and potentially successful as a clinical therapy for certain liver diseases, including hepatic failure. By excluding vascular structures, hepatocytes isolated from genetically engineered pig livers may address some of the immunological problems of xenoTx.

Cell therapy for liver disease: From liver transplantation to cell factory

Work over several decades has laid solid foundations for the advancement of liver cell therapy. To date liver cell therapy in people has taken the form of hepatocyte transplantation for metabolic disorders with a hepatic basis, and for acute or chronic liver failure. Although clinical trials using various types of autologous cells have been implemented to promote liver regeneration or reduce liver fibrosis, clear evidence of therapeutic benefits have so far been lacking. Cell types that have shown efficacy in preclinical models include hepatocytes, liver sinusoidal endothelial cells, mesenchymal stem cells, endothelial progenitor cells, and macrophages. However, positive results in animal models have not always translated through to successful clinical therapies and more realistic preclinical models need to be developed. Studies defining the optimal repopulation by transplanted cells, including routes of cell transplantation, superior engraftment and proliferation of transplanted cells, as well as optimal immunosuppression regimens are required. Tissue engineering approaches to transplant cells in extrahepatic locations have also been proposed. The derivation of hepatocytes from pluripotent or reprogrammed cells raises hope that donor organ and cell shortages could be overcome in the future. Critical hurdles to be overcome include the production of hepatocytes from pluripotent cells with equal functional capacity to primary hepatocytes and long-term phenotypic stability in vivo.

Advances in cell encapsulation technology and its application in drug delivery

INTRODUCTION

Cell encapsulation technology has improved enormously since it was proposed 50 years ago. The advantages offered over other alternative systems, such as the prevention of repetitive drug administration, have triggered the use of this technology in multiple therapeutic applications.

AREAS COVERED

In this article, improvements in cell encapsulation technology and strategies to overcome the drawbacks that prevent its use in the clinic have been summarized and discussed. Different studies and clinical trials that have been performed in several therapeutic applications have also been described.

EXPERT OPINION

The authors believe that the future translation of this technology from bench to bedside requires the optimization of diverse aspects: i) biosafety, controlling and monitoring cell viability; ii) biocompatibility, reducing pericapsular fibrotic growth and hypoxia suffered by the graft; iii) control over drug delivery; iv) and the final scale up. On the other hand, an area that deserves more attention is the cryopreservation of encapsulated cells as this will facilitate the arrival of these biosystems to the clinic.

Alginate microencapsulated hepatocytes optimised for transplantation in acute liver failure

Background and Aim

Intraperitoneal transplantation of alginate-microencapsulated human hepatocytes is an attractive option for the management of acute liver failure (ALF) providing short-term support to allow native liver regeneration. The main aim of this study was to establish an optimised protocol for production of alginate-encapsulated human hepatocytes and evaluate their suitability for clinical use.

Methods

Human hepatocyte microbeads (HMBs) were prepared using sterile GMP grade materials. We determined physical stability, cell viability, and hepatocyte metabolic function of HMBs using different polymerisation times and cell densities. The immune activation of peripheral blood mononuclear cells (PBMCs) after co-culture with HMBs was studied. Rats with ALF induced by galactosamine were transplanted intraperitoneally with rat hepatocyte microbeads (RMBs) produced using a similar optimised protocol. Survival rate and biochemical profiles were determined. Retrieved microbeads were evaluated for morphology and functionality.

Results

The optimised HMBs were of uniform size (583.5±3.3 µm) and mechanically stable using 15 min polymerisation time compared to 10 min and 20 min (p<0.001). 3D confocal microscopy images demonstrated that hepatocytes with similar cell viability were evenly distributed within HMBs. Cell density of 3.5×10⁶ cells/ml provided the highest viability. HMBs incubated in human ascitic fluid showed better cell viability and function than controls. There was no significant activation of PBMCs co-cultured with empty or hepatocyte microbeads, compared to PBMCs alone. Intraperitoneal transplantation of RMBs was safe and significantly improved the severity of liver damage compared to control groups (empty microbeads and medium alone; p<0.01). Retrieved RMBs were intact and free of immune cell adherence and contained viable hepatocytes with preserved function.

Conclusion

An optimised protocol to produce GMP grade alginate-encapsulated human hepatocytes has been established. Transplantation of microbeads provided effective metabolic function in ALF. These high quality HMBs should be suitable for use in clinical transplantation.

Alginate hydrogel protects encapsulated hepatic HuH-7 cells against hepatitis C virus and other viral infections

Cell microencapsulation in alginate hydrogel has shown interesting applications in regenerative medicine and the biomedical field through implantation of encapsulated tissue or for bioartificial organ development. Although alginate solution is known to have low antiviral activity, the same property regarding alginate gel has not yet been studied. The aim of this work is to investigate the potential protective effect of alginate encapsulation against hepatitis C virus (HCV) infection for a hepatic cell line (HuH-7) normally permissive to the virus. Our results showed that alginate hydrogel protects HuH-7 cells against HCV when the supernatant was loaded with HCV. In addition, alginate hydrogel blocked HCV particle release out of the beads when the HuH-7 cells were previously infected and encapsulated. There was evidence of interaction between the molecules of alginate hydrogel and HCV, which was dose- and incubation time-dependent. The protective efficiency of alginate hydrogel towards HCV infection was confirmed against a variety of viruses, whether or not they were enveloped. This promising interaction between an alginate matrix and viruses, whose chemical mechanisms are discussed, is of great interest for further medical therapeutic applications based on tissue engineering.

Species-specific regulation of fibrinogen synthesis with implications for porcine hepatocyte xenotransplantation

BACKGROUND

Patients with liver failure could potentially be bridged with porcine xenogeneic liver cell transplantation. We examined species-specific differences between primary human and porcine hepatocytes in the regulation of coagulation protein expression and function.

METHODS

Isolated primary human and porcine hepatocytes were stimulated with either porcine or human interleukin (IL)-6 (10 ng/ml), IL-1β (10 ng/ml), and tumor necrosis factor-alpha (TNF-α, 30 ng/ml). mRNA expression of coagulation factors were measured by RT-PCR and real-time PCR. Cell culture supernatants were used for the measurement of fibrinogen by ELISA and determination of fibrin clot generation.

RESULTS

Fibrinogen expression in human hepatocytes increased after IL-6 treatment (P = 0.010) and decreased after TNF-α treatment (P = 0.005). Porcine hepatocytes displayed a lower increase in fibrinogen expression after IL-6 treatment as compared to hepatocytes of human origin (P = 0.021). Porcine hepatocytes responded contrarily following TNF-α treatment with an increased expression of fibrinogen resulting in a significant species-specific difference between human and porcine hepatocytes (P = 0.029). Fibrin polymer generation by human hepatocytes was stable and widely branched after IL-6 treatment, while stimulation with TNF-α displayed no fibrin generation at all. In contrast, treatment of porcine hepatocytes with TNF-α resulted in generation of a stable and widely branched fibrin polymer, and stimulation with IL-6 only leads to generation of partial fibrin aggregates.

CONCLUSION

We identified species-specific differences in the regulation of fibrinogen mRNA expression and fibrin generation under inflammatory stimuli. In hepatic xenotransplantation of porcine origin, these interspecies differences might lead to a loss of physiological coagulation function and a loss of transplanted cells.

Platelet increases survival in a model of 90% hepatectomy in rats

BACKGROUND & AIMS

Ninety per cent hepatectomy in rodents is a model for acute liver failure. It has been reported that platelets have a strong effect enhancing liver regeneration, because of the production of several growth factors such as serotonin. The aim of this study was to investigate the role of microencapsulated platelets on 90% hepatectomy in rats.

METHODS

Platelets (PLT) were microencapsulated in sodium alginate and implanted in the peritoneum of rats after 90% partial hepatectomy (PH). Control group received empty capsules (EC). Animals were euthanized at 6, 12, 24, 48 and 72 h post PH (n=9-12/group/time) to evaluate liver regeneration rate, mitotic index, liver content, serum and tissue levels of Interleukin 6 (IL-6) and serotonin and its receptor 5-hydroxytryptamine type 2B (5Ht2b). Survival rate in 10 days was evaluated in a different set of animals (n=20/group).

RESULTS

Platelets group showed the highest survival rate despite the lowest liver regeneration rate at any time point. Mitotic and BrdU index showed no difference between groups. However, the number of hepatocytes was higher and the internuclear distance was shorter for PLT group. Liver dry weight was similar in both groups indicating that water was the main responsible factor for the weight difference. Gene expression of IL-6 in the liver was significantly higher in EC group 6 h after PH, whereas 5Ht2b was up-regulated at 72 h in PLT group.

CONCLUSIONS

Platelets enhance survival of animals with 90% PH, probably by an early protective effect on hepatocytes and the increase in growth factor receptors.

Liver support strategies: cutting-edge technologies

The treatment of end-stage liver disease and acute liver failure remains a clinically relevant issue. Although orthotopic liver transplantation is a well-established procedure, whole-organ transplantation is invasive and increasingly limited by the unavailability of suitable donor organs. Artificial and bioartificial liver support systems have been developed to provide an alternative to whole organ transplantation, but despite three decades of scientific efforts, the results are still not convincing with respect to clinical outcome. In this Review, conceptual limitations of clinically available liver support therapy systems are discussed. Furthermore, alternative concepts, such as hepatocyte transplantation, and cutting-edge developments in the field of liver support strategies, including the repopulation of decellularized organs and the biofabrication of entirely new organs by printing techniques or induced organogenesis are analysed with respect to clinical relevance. Whereas hepatocyte transplantation shows promising clinical results, at least for the temporary treatment of inborn metabolic diseases, so far data regarding implantation of engineered hepatic tissue have only emerged from preclinical experiments. However, the evolving techniques presented here raise hope for bioengineered liver support therapies in the future.

Direct reprogramming of human fibroblasts to functional and expandable hepatocytes

The generation of large numbers of functional human hepatocytes for cell-based approaches to liver disease is an important and unmet goal. Direct reprogramming of fibroblasts to hepatic lineages could offer a solution to this problem but so far has only been achieved with mouse cells. Here, we generated human induced hepatocytes (hiHeps) from fibroblasts by lentiviral expression of FOXA3, HNF1A, and HNF4A. hiHeps express hepatic gene programs, can be expanded in vitro, and display functions characteristic of mature hepatocytes, including cytochrome P450 enzyme activity and biliary drug clearance. Upon transplantation into mice with concanavalin-A-induced acute liver failure and fatal metabolic liver disease due to fumarylacetoacetate dehydrolase (Fah) deficiency, hiHeps restore the liver function and prolong survival. Collectively, our results demonstrate successful lineage conversion of nonhepatic human cells into mature hepatocytes with potential for biomedical and pharmaceutical applications.

Effects of coencapsulation of hepatocytes with adipose-derived stem cells in the treatment of rats with acute-on-chronic liver failure

Introduction

Cell transplantation is an alternative to liver transplantation, which is hampered by short survival time and immunorejection. The goal of this study was to evaluate the therapeutic potential of hepatocytes coencapsulated with adipose-derived stem cells (ADSCs) in treating acute-on-chronic liver failure (ACLF).

Methods

Rat hepatocytes and ADSCs were isolated, and coencapsulated by alginate-poly-L-lysinealginate microencapsulation. The morphological and functional changes of heterotypic interactions were characterized. ACLF in rats was induced by D-galactosamine administration following CCl4-induced cirrhosis. These rats were subjected to intraperitoneal transplantation of 5 × 10⁷ coencapsulated hepatocytes with ADSCs, 5 × 10⁷ encapsulated hepatocytes alone, or empty vehicles after 24 h, respectively. The survival rate and liver functions were assessed.

Results

Hepatocyte performance levels such as albumin secretion and urea synthesis induction were all significantly enhanced in the coencapsulation group compared with the homo-encapsulated hepatocytes group (p<0.05). The results of cell cycle analysis showed that larger populations of hepatocytes with ADSC treatment were accumulated in the G2-S phase, and there were fewer in the G0-G1 phase compared to encapsulation of hepatocytes alone. Intraperitoneal transplantation of coencapsulated hepatocytes with ADSCs not only increased the survival rate, but also improved liver functions in a rat model of ACLF.

Conclusions

Transplantation of coencapsulated hepatocytes and ADSCs might be a promising strategy for cell-based therapy of acute liver diseases.

Process engineering of high voltage alginate encapsulation of mesenchymal stem cells

Encapsulation of stem cells in alginate beads is promising as a sophisticated drug delivery system in treatment of a wide range of acute and chronic diseases. However, common use of air flow encapsulation of cells in alginate beads fails to produce beads with narrow size distribution, intact spherical structure and controllable sizes that can be scaled up. Here we show that high voltage encapsulation (≥ 15 kV) can be used to reproducibly generate spherical alginate beads (200-400 μm) with narrow size distribution (± 5-7%) in a controlled manner under optimized process parameters. Flow rate of alginate solution ranged from 0.5 to 10 ml/h allowed producing alginate beads with a size of 320 and 350 μm respectively, suggesting that this approach can be scaled up. Moreover, we found that applied voltages (15-25 kV) did not alter the viability and proliferation of encapsulated mesenchymal stem cells post-encapsulation and cryopreservation as compared to air flow. We are the first who employed a comparative analysis of electro-spraying and air flow encapsulation to study the effect of high voltage on alginate encapsulated cells. This report provides background in application of high voltage to encapsulate living cells for further medical purposes. Long-term comparison and work on alginate-cell interaction within these structures will be forthcoming.

Microfluidic production of single micrometer-sized hydrogel beads utilizing droplet dissolution in a polar solvent

In this study, a microfluidic process is proposed for preparing monodisperse micrometer-sized hydrogel beads. This process utilizes non-equilibrium aqueous droplets formed in a polar organic solvent. The water-in-oil droplets of the hydrogel precursor rapidly shrunk owing to the dissolution of water molecules into the continuous phase. The shrunken and condensed droplets were then gelled, resulting in the formation of hydrogel microbeads with sizes significantly smaller than the initial droplet size. This study employed methyl acetate as the polar organic solvent, which can dissolve water at 8%. Two types of monodisperse hydrogel beads-Ca-alginate and chitosan-with sizes of 6-10 μm (coefficient of variation < 6%) were successfully produced. In addition, we obtained hydrogel beads with non-spherical morphologies by controlling the degree of droplet shrinkage at the time of gelation and by adjusting the concentration of the gelation agent. Furthermore, the encapsulation and concentration of DNA molecules within the hydrogel beads were demonstrated. The process presented in this study has great potential to produce small and highly concentrated hydrogel beads that are difficult to obtain by using conventional microfluidic processes.

Control of Liver Tissue Reconstitution in Mesenteric Leaves: The Effect of Preculture on Mouse Hepatic Progenitor Cells Prior to Transplantation

Our objective is to control the reconstitution of liverlike tissues at extrahepatic sites using hepatic progenitor cells (HPCs) andin vitropreculture prior to transplantation. We prepared cell-based hybrid grafts by culturing HPCs isolated from fetal E14.5 mouse livers on biodegradable, highly porous 3-dimensional poly-L-lactic acid (PLLA) scaffolds for 1 week in basal medium (the basal condition) or 10 mM nicotinamide (NA) and 1% dimethyl sulfoxide (DMSO) supplemented conditions (the ND-positive condition) prior to implantation. Sections of hybrid grafts cultured for 1 week showed that HPCs grew and spread on the surface of scaffolds under both basal and ND (+) conditions. Most of these cells were albumin (+) and CK18 (+). CK19 (+) cells were also present under the basal condition but not the ND (+) condition. Cultured hybrid grafts were implanted into the mesenteric leaves of mice and removed after 1 month. Transplanted tissues cultured under the basal condition consisted of albumin (+) hepatocyte-like and CK19 (+) biliary epithelial cell (BEC)-like cells organized in duct-like structures. In contrast, integrated tissues cultured under the ND (+) condition alone had differentiated albumin (+) hepatocyte-like cells and were relatively larger than those under the basal condition. Hepatocyte-like cells of transplanted hybrid grafts cultured under both conditions were periodic acid-Schiff (PAS) staining-positive and expressed transcription factors, hepatocyte nuclear factor (HNF) 4 and CCAAT/enhancer-binding protein (C/EBP) α. These findings suggest that combining progenitor cells andin vitropreculture may potentially regulate liverlike tissues at extrahepatic sites.

Liver tissue engineering and cell sources: issues and challenges

Liver diseases are of major concern as they now account for millions of deaths annually. As a result of the increased incidence of liver disease, many patients die on the transplant waiting list, before a donor organ becomes available. To meet the huge demand for donor liver, alternative approaches using liver tissue engineering principles are being actively pursued. Even though adult hepatocytes, the primary cells of the liver are most preferred for tissue engineering of liver, their limited availability, isolation from diseased organs, lack of in vitro propagation and deterioration of function acts as a major drawback to their use. Various approaches have been taken to prevent the functional deterioration of hepatocytes including the provision of an adequate extracellular matrix and co-culture with non-parenchymal cells of liver. Great progress has also been made to differentiate human stem cells to hepatocytes and to use them for liver tissue engineering applications. This review provides an overview of recent challenges, issues and cell sources with regard to liver tissue engineering.

Impact of alginate composition: from bead mechanical properties to encapsulated HepG2/C3A cell activities for in vivo implantation

Recently, interest has focused on hepatocytes' implantation to provide end stage liver failure patients with a temporary support until spontaneous recovery or a suitable donor becomes available. To avoid cell damage and use of an immunosuppressive treatment, hepatic cells could be implanted after encapsulation in a porous biomaterial of bead or capsule shape. The aim of this study was to compare the production and the physical properties of the beads, together with some hepatic cell functions, resulting from the use of different material combinations for cell microencapsulation: alginate alone or combined with type I collagen with or without poly-L-lysine and alginate coatings. Collagen and poly-L-lysine increased the bead mechanical resistance but lowered the mass transfer kinetics of vitamin B12. Proliferation of encapsulated HepG2/C3A cells was shown to be improved in alginate-collagen beads. Finally, when the beads were subcutaneously implanted in mice, the inflammatory response was reduced in the case of alginate mixed with collagen. This in vitro and in vivo study clearly outlines, based on a systematic comparison, the necessity of compromising between material physical properties (mechanical stability and porosity) and cell behavior (viability, proliferation, functionalities) to define optima hepatic cell microencapsulation conditions before implantation.

Therapeutic applications of encapsulated cells

The synergy of some promising advances in the fields of cell therapy and biomaterials together with improvements in the fabrication of more refined and tailored microcapsules for drug delivery have triggered the progress of cell encapsulation technology. Cell microencapsulation involves immobilizing the transplanted cells within a biocompatible scaffold surrounded by a membrane in attempt to isolate the cells from the host immune attack and enhance or prolong their function in vivo. This technology represents one strategy which aims to overcome the present difficulties related to local and systemic controlled release of drugs and growth factors as well as to organ graft rejection and thus the requirements for use of immunomodulatory protocols or immunosuppressive drugs. This chapter gives an overview of the current situation of cell encapsulation technology as a controlled drug delivery system, and the essential requirements of the technology, some of the therapeutic applications, the challenges, and the future directions under investigation are highlighted.

Microencapsulation for the Therapeutic Delivery of Drugs, Live Mammalian and Bacterial Cells, and Other Biopharmaceutics: Current Status and Future Directions

Microencapsulation is a technology that has shown significant promise in biotherapeutics, and other applications. It has been proven useful in the immobilization of drugs, live mammalian and bacterial cells and other cells, and other biopharmaceutics molecules, as it can provide material structuration, protection of the enclosed product, and controlled release of the encapsulated contents, all of which can ensure efficient and safe therapeutic effects. This paper is a comprehensive review of microencapsulation and its latest developments in the field. It provides a comprehensive overview of the technology and primary goals of microencapsulation and discusses various processes and techniques involved in microencapsulation including physical, chemical, physicochemical, and other methods involved. It also summarizes the state-of-the-art successes of microencapsulation, specifically with regard to the encapsulation of microorganisms, mammalian cells, drugs, and other biopharmaceutics in various diseases. The limitations and future directions of microencapsulation technologies are also discussed.

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.