Bioartificial liver support devices: historical perspectives

Early-Phase Clinical Trials of Bio-Artificial Organ Technology: A Systematic Review of Ethical Issues

Regenerative medicine has emerged as a novel alternative solution to organ failure which circumvents the issue of organ shortage. In preclinical research settings bio-artificial organs are being developed. It is anticipated that eventually it will be possible to launch first-in-human transplantation trials to test safety and efficacy in human recipients. In early-phase transplantation trials, however, research participants could be exposed to serious risks, such as toxicity, infections and tumorigenesis. So far, there is no ethical guidance for the safe and responsible design and conduct of early-phase clinical trials of bio-artificial organs. Therefore, research ethics review committees will need to look to related adjacent fields of research, including for example cell-based therapy, for guidance. In this systematic review, we examined the literature on early-phase clinical trials in these adjacent fields and undertook a thematic analysis of relevant ethical points to consider for early-phase clinical trials of transplantable bio-artificial organs. Six themes were identified: cell source, risk-benefit assessment, patient selection, trial design, informed consent, and oversight and accountability. Further empirical research is needed to provide insight in patient perspectives, as this may serve as valuable input in determining the conditions for ethically responsible and acceptable early clinical development of bio-artificial organs.

Inventing Engineered Organoids for end-stage liver failure patients

End-stage liver disease (ESLD) is a term used clinically in reference to a group of liver diseases with liver transplantation as the choice of treatment. Due to the limitations of liver transplantation, alternative treatments are needed. The use of primary human hepatocytes represents a valid alternative treatment, but the limitations related to hepatocyte quality, viability, function, conservation, and storage need to be overcome. Transplanted hepatocytes have only been followed for 6–9 months. Therefore, long-term causes of failures are not yet established, including rejection, apoptosis, or other causes. Other alternative therapies to replace liver transplantation include plasmapheresis, hemodiafiltration, and artificial livers. Unfortunately, these methods are highly limited due to availability, high cost, anaphylaxis reaction, development-deposition of immune-complexes, and restricted functionality. Liver organoids, which utilize stem cells instead of ‘impractical’ adult hepatocytes, may be a solution for the development of a complex bioartificial liver. Recent studies have explored the benefits of differentiating mature hepatocytes from stem cells inside a bioreactor. When the use of human-induced Hepatocytes (hiHeps) was investigated in mouse and pig models of liver failure, liver failure markers were decreased, hepatocyte function indicated by albumin synthesis improved, and survival time increased. Bioartificial liver treatment may decrease the infiltration of inflammatory cells into liver tissue by down-regulating pro-inflammatory cytokines.

Advances in cell sources of hepatocytes for bioartificial liver

BACKGROUND

Orthotopic liver transplantation (OLT) is the most effective therapy for liver failure. However, OLT is severely limited by the shortage of liver donors. Bioartificial liver (BAL) shows great potential as an alternative therapy for liver failure. In recent years, progress has been made in BAL regarding genetically engineered cell lines, immortalized human hepatocytes, methods for preserving the phenotype of primary human hepatocytes, and other functional hepatocytes derived from stem cells.

DATA SOURCES

A systematic search of PubMed and ISI Web of Science was performed to identify relevant studies in English language literature using the key words such as liver failure, bioartificial liver, hepatocyte, stem cells, differentiation, and immortalization. More than 200 articles related to the cell sources of hepatocyte in BAL were systematically reviewed.

RESULTS

Methods for preserving the phenotype of primary human hepatocytes have been successfully developed. Many genetically engineered cell lines and immortalized human hepatocytes have also been established. Among these cell lines, the incorporation of BAL with GS-HepG2 cells or alginate-encapsulated HepG2 cells could prolong the survival time and improve pathophysiological parameters in an animal model of liver failure. The cBAL111 cells were evaluated using the AMC-BAL bioreactor, which could eliminate ammonia and lidocaine, and produce albumin. Importantly, BAL loading with HepLi-4 cells could significantly improve the blood biochemical parameters, and prolong the survival time in pigs with liver failure. Other functional hepatocytes differentiated from stem cells, such as human liver progenitor cells, have been successfully achieved.

CONCLUSIONS

Aside from genetically modified liver cell lines and immortalized human hepatocytes, other functional hepatocytes derived from stem cells show great potential as cell sources for BAL. BAL with safe and effective liver cells may be achieved for clinical liver failure in the near future.

Extracorporeal liver perfusion system for artificial liver support across a membrane

BACKGROUND

An extracorporeal porcine liver perfusion (ECPLP) system circumvents the limitations of hepatocyte based bio-artificial liver, but its clinical application has been limited so far due to the potential risk of transmission of porcine endogenous retroviruses. The aim of this study was to develop an ECPLP model that can provide artificial hepatic support across a semi-permeable membrane, which has the potential to block porcine viruses due to its pore size.

MATERIALS AND METHODS

Livers from white landrace pigs were perfused with normothermic oxygenated blood using Medtronic BP560 centrifugal pump (Medtronic, Inc., Minneapolis. MN). This ECPLP system was used to support a "surrogate" patient across the filter Evaclio-EC4A. Function of liver was measured by indocyanine green retention at 15 min (ICGR15). Clearance of galactose, ammonia, and para-aminobenzoic acid infused into the "surrogate" patient circulation was calculated to assess liver support across the membrane. The study was designed as test (n = 15) versus control (n = 5), with control experiments having no liver in the circuit.

RESULTS

For the test experiments, we perfused 15 livers with mean hepatic artery pressure of 87 mm Hg and flows of 1.2 L/min. ICGR15 in test experiments was 11%. Ammonia clearance was 945 mg/min/kg, galactose metabolic rate was 111.7 mg/min/Kg, and the hippurate ratio was 91% in the test. In contrast, the control experiments did not show any significant change in the concentration of any of these compounds.

CONCLUSION

Our ECPLP model was able to provide hepatic support in an experimental setting across a hollow fiber filter. Further work on an anhepatic animal is needed prior to application in human trials.

Three-dimensional culture of human embryonic stem cell derived hepatic endoderm and its role in bioartificial liver construction

The liver carries out a range of functions essential for bodily homeostasis. The impairment of liver functions has serious implications and is responsible for high rates of patient morbidity and mortality. Presently, liver transplantation remains the only effective treatment, but donor availability is a major limitation. Therefore, artificial and bioartificial liver devices have been developed to bridge patients to liver transplantation. Existing support devices improve hepatic encephalopathy to a certain extent; however their usage is associated with side effects. The major hindrance in the development of bioartificial liver devices and cellular therapies is the limited availability of human hepatocytes. Moreover, primary hepatocytes are difficult to maintain and lose hepatic identity and function over time even with sophisticated tissue culture media. To overcome this limitation, renewable cell sources are being explored. Human embryonic stem cells are one such cellular resource and have been shown to generate a reliable and reproducible supply of human hepatic endoderm. Therefore, the use of human embryonic stem cell-derived hepatic endoderm in combination with tissue engineering has the potential to pave the way for the development of novel bioartificial liver devices and predictive drug toxicity assays.

Isolation and culture of adult human liver progenitor cells: in vitro differentiation to hepatocyte-like cells

Highly differentiated normal human hepatocytes represent the gold standard cellular model for basic and applied research in liver physiopathology, pharmacology, toxicology, virology, and liver biotherapy. Nowadays, although livers from organ donors or medically required resections represent the current sources of hepatocytes, the possibility to generate hepatocytes from the differentiation of adult and embryonic stem cells represents a promising opportunity. The aim of this chapter is to describe our experience with the isolation from adult human liver and culture of non-parenchymal epithelial cells. Under appropriate conditions, these cells differentiate in vitro in hepatocyte-like cells and therefore appear to behave as liver progenitor cells.

A method for the effective formation of hepatocyte spheroids using a biodegradable polymer nanosphere

Cultures of hepatocytes in spheroid form are known to maintain higher cell viability and exhibit better hepatocyte functions than those in monolayer cultures. In this study, a method for the formation of hepatocyte spheroids was developed using biodegradable polymer nanospheres. The addition of poly(lactic-co-glycolic acid) nanospheres to hepatocyte cultures in spinner flasks increased the efficiency of hepatocyte spheroid formation (the number of cells in spheroids divided by the total cell number) as compared with hepatocyte cultures without nanospheres (control). The viability and mitochondrial activity of the hepatocyte spheroids in the nanosphere-added cultures were significantly higher than those in the control. In addition, the mRNA expression levels of albumin and phenylalanine hydroxylase, both of which are hepatocyte-specific proteins, were significantly higher in the nanosphere-added cultures than in the control. This new culture method improves upon the conventional method of forming hepatocyte spheroids in terms of spheroid formation efficiency, cell viability, and hepatocyte function.

Hepatic Stem Cells: In Search of

The field of stem cell biology has exploded with the study of a wide range of cellular populations involving endodermal, mesenchymal, and ectodermal organs. One area of extensive study has included the identification of hepatic stem and progenitor cell subpopulations. Liver stem cells provide insights into the potential pathways involving liver regeneration that are independent of mature hepatocytes. Hepatic progenitor cells are either bipotent or multipotent and capable of multiple rounds of replication. They have been identified in fetal as well as adult liver. Various injury models have been used to expand this cellular compartment. The nomenclature, origin, and function of the hepatic progenitor cell populations are areas of ongoing debate. In this review, we will discuss the different definitions and functions of hepatic progenitor cells as well as the current research efforts examining their therapeutic potential.

Similarities in the immunoglobulin response and VH gene usage in rhesus monkeys and humans exposed to porcine hepatocytes

Background

The use of porcine cells and organs as a source of xenografts for human patients would vastly increase the donor pool; however, both humans and Old World primates vigorously reject pig tissues due to xenoantibodies that react with the polysaccharide galactose α (1,3) galactose (αGal) present on the surface of many porcine cells. We previously examined the xenoantibody response in patients exposed to porcine hepatocytes via treatment(s) with bioartficial liver devices (BALs), composed of porcine cells in a support matrix. We determined that xenoantibodies in BAL-treated patients are predominantly directed at porcine αGal carbohydrate epitopes, and are encoded by a small number of germline heavy chain variable region (V_H) immunoglobulin genes. The studies described in this manuscript were designed to identify whether the xenoantibody responses and the IgV_H genes encoding antibodies to porcine hepatocytes in non-human primates used as preclinical models are similar to those in humans. Adult non-immunosuppressed rhesus monkeys (Macaca mulatta) were injected intra-portally with porcine hepatocytes or heterotopically transplanted with a porcine liver lobe. Peripheral blood leukocytes and serum were obtained prior to and at multiple time points after exposure, and the immune response was characterized, using ELISA to evaluate the levels and specificities of circulating xenoantibodies, and the production of cDNA libraries to determine the genes used by B cells to encode those antibodies.

Results

Xenoantibodies produced following exposure to isolated hepatocytes and solid organ liver grafts were predominantly encoded by genes in the V_H3 family, with a minor contribution from the V_H4 family. Immunoglobulin heavy-chain gene (V_H) cDNA library screening and gene sequencing of IgM libraries identified the genes as most closely-related to the IGHV3-11 and IGHV4-59 germline progenitors. One of the genes most similar to IGHV3-11, V_H3-11^cyno, has not been previously identified, and encodes xenoantibodies at later time points post-transplant. Sequencing of IgG clones revealed increased usage of the monkey germline progenitor most similar to human IGHV3-11 and the onset of mutations.

Conclusion

The small number of IGV_H genes encoding xenoantibodies to porcine hepatocytes in non-human primates and humans is highly conserved. Rhesus monkeys are an appropriate preclinical model for testing novel reagents such as those developed using structure-based drug design to target and deplete antibodies to porcine xenografts.

History of xenotransplantation

The present historical review reports the clinical experiences of transplantations from animal to human. The first transplantation attempts were made without any knowledge of the species barrier. The pioneers of xenotransplantation realized xenotransfusions as early as the 16th century, then cell and tissue xenotransplantations in the 19th century. At the beginning of the 20th century, xenotransplantation of testicles became the latest craze. At the same time, and later in the 1960s, organ xenotransplantations were attempted, with disappointing results. Mathieu Jaboulay, Serge Voronoff, Keith Reemtsma, James Hardy, Denton Cooley, Thomas Starzl, Christiaan Barnard and Leonard Bailey were among the pionneers of xenotransplantation. Recent trials concerned above all tissue and cell xenotransplantations. Nowadays, with encapsulation, transgenesis, and cloning, great advances have been made for controlling xenograft rejection, but ethical questions linked to the risk of infections have become a major pre-occupation within the scientific community and the general population.

Oncostatin M stimulates proliferation and functions of mouse fetal liver cells in three-dimensional cultures

In order to develop a tissue engineered bioartificial liver (BAL), long-term three-dimensional (3-D) culture of fetal liver cells (FLCs) utilizing porous polymer as a scaffold was performed for up to 1 month. The effects of the basal medium and supplementation with oncostatin M (OSM) on the proliferation and differentiation of mouse FLCs were examined in both 3-D culture and conventional monolayer dish culture. Compared with monolayer culture, cell numbers and hepatic function of FLCs were better maintained by 3-D culture. When two kinds of basal media were tested in this study, Williams' medium E (WE) was superior to minimum essential medium alpha (alphaMEM) in expressing hepatic function of FLCs in both 3-D and monolayer cultures, although higher cell densities were obtained with alphaMEM. OSM potently stimulated both cell growth and metabolic activity, especially in 3-D culture. When WE supplemented with OSM was used for 3-D culture, albumin secretion by FLCs increased dramatically after day 5, and a high level of secretion was maintained until the end of culture. During a period of over 1 month, no decrease of albumin secretion was observed. In conclusion, this 3-D culture method was expected to be one of the realistic attempts to develop a tissue engineered BAL.

Hybrid artificial liver support system for treatment of severe liver failure

AIM: To construct a novel hybrid artificial liver support system (HALSS) and to evaluate its efficacy in patients with severe liver failure.

METHODS: Hepatocytes were isolated from suckling pig by the modified Seglen’s method. Isolated hepatocytes were cultured in a spinner flask for 24 h to form spheroids before use and the functions of spheroids were detected. HALSS consisted of a plasma separator, a hemo-adsorba and a bioreactor with hepatocytes spheroids in its extra-fiber space. HALSS was applied to 10 patients with severe liver failure. The general condition and the biochemical indexes of the patients were studied just before and after the treatment.

RESULTS: The number of cells per liver was about 2-4×10¹⁰ (mean, 3.1±1.5×10¹⁰). The cell viabilities were more than 95%. After 24 h of spheroid culture, most hepatocytes formed spheroids. The levels of albumin and urea in the medium of spheroid culture were higher than those in supernatant of petri dish culture (P = 0.0015 and 0.0001, respectively). The capacity of albumin production and urea synthesis remained stable for more than one wk and declined rapidly after two weeks in vitro. In HALSS group, the duration of HALSS treatment was 6-10 h each time. All patients tolerated the treatment well without any fatal adverse reaction. After HALSS treatment, the general condition, psychic state, encephalopathy and hepatic function of the patients were improved. The survival rate of the HALSS group, Plasmapheresis group and control group was 30% (3/10), 20% (2/10) and 0% (0/10), respectively (P = 0.024). Two weeks after treatment, Tbil and ALT decreased and the PTA level elevated in HALSS group and pasmapheresis group (P value: 0.015 vs 0.020, 0.009 vs 0.012 and 0.032 vs 0.041, respectively). But there was no significant change of blood albumin concentration before and after treatment in HALSS group and Plasmapheresis group.

CONCLUSION: The HALSS established by us is effective in supporting liver function of patients with severe liver failure.

Toward the survival and function of xenogeneic hepatocyte grafts

Xenogeneic hepatocyte transplantation might offer an unobtrusive alternative to whole liver allotransplantation. Having previously found that the immune response to such grafts can be controlled by immunosuppression, we sought approaches to collection and delivery that would optimize survival and function after transplantation. Porcine hepatocytes were isolated by a 2-step collagenase technique and then: 1) used immediately; 2) stored in University of Wisconsin (UW) solution at 4 degrees C; 3) cultured in supplemented Williams E medium; or 4) cryopreserved in UW solution with 10% dimethyl sulfoxide (DMSO). The fate and function of the hepatocytes was determined after they were injected into the spleens of immunodeficient mice. Freshly isolated hepatocytes had better viability (92.2 +/- 1.9%) than hepatocytes cultured for 24 hours (78.4 +/- 6.3%), hypothermically preserved in UW solution for 24 hours (85.8 +/- 3.1%), or cryopreserved (65.0 +/- 2.6%). Freshly isolated hepatocytes secreted more albumin after transplantation than hepatocytes that were cultured, hypothermically stored, or cryopreserved. In conclusion, culture and storage profoundly compromises the function of isolated hepatocytes after transplantation. Freshly isolated hepatocytes are the preferred source for transplantation.