Fumarylacetoacetate hydrolase deficient pigs are a novel large animal model of metabolic liver disease

Liver fibrosis pathologies and potentials of RNA based therapeutics modalities

Liver fibrosis (LF) occurs when the liver tissue responds to injury or inflammation by producing excessive amounts of scar tissue, known as the extracellular matrix. This buildup stiffens the liver tissue, hinders blood flow, and ultimately impairs liver function. Various factors can trigger this process, including bloodborne pathogens, genetic predisposition, alcohol abuse, non-steroidal anti-inflammatory drugs, non-alcoholic steatohepatitis, and non-alcoholic fatty liver disease. While some existing small-molecule therapies offer limited benefits, there is a pressing need for more effective treatments that can truly cure LF. RNA therapeutics have emerged as a promising approach, as they can potentially downregulate cytokine levels in cells responsible for liver fibrosis. Researchers are actively exploring various RNA-based therapeutics, such as mRNA, siRNA, miRNA, lncRNA, and oligonucleotides, to assess their efficacy in animal models. Furthermore, targeted drug delivery systems hold immense potential in this field. By utilizing lipid nanoparticles, exosomes, nanocomplexes, micelles, and polymeric nanoparticles, researchers aim to deliver therapeutic agents directly to specific biomarkers or cytokines within the fibrotic liver, increasing their effectiveness and reducing side effects. In conclusion, this review highlights the complex nature of liver fibrosis, its underlying causes, and the promising potential of RNA-based therapeutics and targeted delivery systems. Continued research in these areas could lead to the development of more effective and personalized treatment options for LF patients.

Producing Human Livers From Human Stem Cells Via Blastocyst Complementation

The need for organ transplants exceeds donor organ availability. In the quest to solve this shortage, the most remarkable area of advancement is organ production through the use of chimeric embryos, commonly known as blastocyst complementation. This technique involves the combination of different species to generate chimeras, where the extent of donor cell contribution to the desired tissue or organ can be regulated. However, ethical concerns arise with the use of brain tissue in such chimeras. Furthermore, the ratio of contributed cells to host animal cells in the chimeric system is low in the production of chimeras associated with cell apoptosis. This review discusses the latest innovations in blastocyst complementation and highlights the progress made in creating organs for transplant.

Transcriptomic Analysis of Liver in Silver sillago, Sillago sihama Fed with High-Level Low-Gossypol Cottonseed Meal in Replacement of Fishmeal Diet

Understanding the molecular mechanisms involved in adaptation to alternate diets has become a significant concern, as increasing amounts of fishmeal (FM) protein in aquafeeds are being substituted with plant protein. Thus, the goal of this study was to assess growth performance, quality, and liver function of juvenile Sillago sihama (S. sihama) through growth indices, whole-body composition, histology of the liver, and RNA-sequencing (RNA-seq), after they were fed a formulated diet with 64% low-gossypol cottonseed meal (LCSM) for 56 days, compared to those fed a traditional FM-based diet. Indicators of growth, including final body weight (FBW), weight gain rate (WGR), specific growth rate (SGR), protein efficiency ratio (PER), and condition factor (CF), were considerably lower in the 64% LCSM (R64) group than in the FM diet group. In the R64 diet, the whole crude lipid was significantly lower than in the FM diet. The hematoxylin–eosin section showed that dietary high levels of LCSM resulted in diffuse lipid vacuolation in the liver of S. sihama. According to a liver transcriptome analysis, high LCSM intake in the diet significantly impacted lipid synthesis and catabolism, elevated pathways for cholesterol synthesis, blocked several amino acid metabolic pathways, and adversely affected hepatic gluconeogenesis and glycolysis. The findings of this study indicate that feeding high levels of LCSM in S. sihama is harmful to the growth of the organism and can harm the liver’s structural integrity, as well as obstruct the normal metabolism of amino acids, lipids, and carbohydrates. Therefore, it is not recommended to substitute LCSM for high levels of FM in the diet of S. sihama.

Patch grafting of organoids of stem/progenitors into solid organs can correct genetic-based disease states

Patch grafting, a novel strategy for transplantation of stem/progenitor organoids into porcine livers, has been found successful also for organoid transplantation into other normal or diseased solid organs in pigs and mice. Each organoid contained ∼100 cells comprised of biliary tree stem cells (BTSCs), co-hepato/pancreatic stem/progenitors, and partnered with early lineage stage mesenchymal cells (ELSMCs), angioblasts and precursors to endothelia and stellate cells. Patch grafting enabled transplantation into livers or pancreases of ≥108th (pigs) or ≥106th-7th (mice) organoids/patch. Graft conditions fostered expression of multiple matrix-metalloproteinases (MMPs), especially secretory isoforms, resulting in transient loss of the organ's matrix-dictated histological features, including organ capsules, and correlated with rapid integration within a week of organoids throughout the organs and without emboli or ectopic cell distribution. Secondarily, within another week, there was clearance of graft biomaterials, followed by muted expression of MMPs, restoration of matrix-dictated histology, and maturation of donor cells to functional adult fates. The ability of patch grafts of organoids to rescue hosts from genetic-based disease states was demonstrated with grafts of BTSC/ELSMC organoids on livers, able to rescue NRG/FAH-KO mice from type I tyrosinemia, a disease caused by absence of fumaryl acetoacetate hydrolase. With the same grafts, if on pancreas, they were able to rescue NRG/Akita mice from type I diabetes, caused by a mutation in the insulin 2 gene. The potential of patch grafting for cell therapies for solid organs now requires translational studies to enable its adaptation and uses for clinical programs.

In vivo lentiviral vector gene therapy to cure hereditary tyrosinemia type 1 and prevent development of precancerous and cancerous lesions

Conventional therapy for hereditary tyrosinemia type-1 (HT1) with 2-(2-nitro-4-trifluoromethylbenzoyl)−1,3-cyclohexanedione (NTBC) delays and in some cases fails to prevent disease progression to liver fibrosis, liver failure, and activation of tumorigenic pathways. Here we demonstrate cure of HT1 by direct, in vivo administration of a therapeutic lentiviral vector targeting the expression of a human fumarylacetoacetate hydrolase (FAH) transgene in the porcine model of HT1. This therapy is well tolerated and provides stable long-term expression of FAH in pigs with HT1. Genomic integration displays a benign profile, with subsequent fibrosis and tumorigenicity gene expression patterns similar to wild-type animals as compared to NTBC-treated or diseased untreated animals. Indeed, the phenotypic and genomic data following in vivo lentiviral vector administration demonstrate comparative superiority over other therapies including ex vivo cell therapy and therefore support clinical application of this approach.

Hereditary tyrosinemia type 1 (HT1) is an inborn error of metabolism caused by a deficiency in fumarylacetoacetate hydrolase (FAH). Here, the authors show in an animal model that HT1 can be treated via in vivo portal vein administration of a lentiviral vector carrying the human FAH transgene.

Development of RAG2-/-IL2Rγ-/Y immune deficient FAH-knockout miniature pig

Human hepatocyte transplantation for liver disease treatment have been hampered by the lack of quality human hepatocytes. Pigs with their large body size, longevity and physiological similarities with human are appropriate animal models for the in vivo expansion of human hepatocytes. Here we report on the generation of RAG2^-/-IL2Rγ^-/YFAH^-/- (RGFKO) pigs via CRISPR/Cas9 system and somatic cell nuclear transfer. We showed that thymic and splenic development in RGFKO pigs was impaired. V(D)J recombination processes were also inactivated. Consequently, RGFKO pigs had significantly reduced numbers of porcine T, B and NK cells. Moreover, due to the loss of FAH, porcine hepatocytes continuously undergo apoptosis and consequently suffer hepatic damage. Thus, RGFKO pigs are both immune deficient and constantly suffer liver injury in the absence of NTBC supplementation. These results suggest that RGFKO pigs have the potential to be engrafted with human hepatocytes without immune rejection, thereby allowing for large scale expansion of human hepatocytes.

Advances in pig models of human diseases

Animal models of human diseases play a critical role in medical research. Pigs are anatomically and physiologically more like humans than are small rodents such as mice, making pigs an attractive option for modeling human diseases. Advances in recent years in genetic engineering have facilitated the rapid rise of pig models for use in studies of human disease. In the present review, we summarize the current status of pig models for human cardiovascular, metabolic, neurodegenerative, and various genetic diseases. We also discuss areas that need to be improved. Animal models of human diseases play a critical role in medical research. Advances in recent years in genetic engineering have facilitated the rapid rise of pig models for use in studies of human disease. In the present review, we summarize the current status of pig models for human cardiovascular, metabolic, neurodegenerative, various genetic diseases and xenotransplantation.

Generation of immunodeficient pig with hereditary tyrosinemia type 1 and their preliminary application for humanized liver

Background

Mice with humanized livers are important models to study drug toxicology testing, development of hepatitis virus treatments, and hepatocyte transplantation therapy. However, the huge difference between mouse and human in size and anatomy limited the application of humanized mice in investigating human diseases. Therefore, it is urgent to construct humanized livers in pigs to precisely investigate hepatocyte regeneration and human hepatocyte therapy. CRISPR/Cas9 system and somatic cell cloning technology were used to generate two pig models with FAH deficiency and exhibiting severe immunodeficiency (FAH/RAG1 and FAH/RAG1/IL2RG deficiency). Human primary hepatocytes were then successfully transplanted into the FG pig model and constructed two pigs with human liver.

Results

The constructed FAH/RAG1/IL2RG triple-knockout pig models were characterized by chronic liver injury and severe immunodeficiency. Importantly, the FG pigs transplanted with primary human hepatocytes produced human albumin in a time dependent manner as early as 1 week after transplantation. Furthermore, the colonization of human hepatocytes was confirmed by immunochemistry staining.

Conclusions

We successfully generated pig models with severe immunodeficiency that could construct human liver tissues.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-022-00760-3.

Decreased SLC27A5 Suppresses Lipid Synthesis and Tyrosine Metabolism to Activate the Cell Cycle in Hepatocellular Carcinoma

Tyrosine is an essential ketogenic and glycogenic amino acid for the human body, which means that tyrosine is not only involved in protein metabolism, but also participates in the metabolism of lipids and carbohydrates. The liver is an important place for metabolism of lipids, carbohydrates, and proteins. The metabolic process of biological macro-molecules is a basis for maintaining the physiological activities of organisms, but the cross-linking mechanism of these processes is still unclear. Here, we found that the tyrosine-metabolizing enzymes, which were specifically and highly expressed in the liver, were significantly down-regulated in hepatocellular carcinoma (HCC), and had a correlation with a poor prognosis of HCC patients. Further analysis found that the reduction of tyrosine metabolism would activate the cell cycle and promote cell proliferation. In addition, we also found that the solute carrier family 27 member 5 (SLC27A5) regulates the expression of tyrosine-metabolizing enzymes through nuclear factor erythroid 2-related factor 2 (NRF2). Therefore, the SLC27A5 and tyrosine-metabolizing enzymes that we have identified coordinate lipid and tyrosine metabolism, regulate the cell cycle, and are potential targets for cancer treatment.

Fumarylacetoacetate hydrolase gene as a knockout target for hepatic chimerism and donor liver production

A reliable source of human hepatocytes and transplantable livers is needed. Interspecies embryo complementation, which involves implanting donor human stem cells into early morula/blastocyst stage animal embryos, is an emerging solution to the shortage of transplantable livers. We review proposed mutations in the recipient embryo to disable hepatogenesis, and discuss the advantages of using fumarylacetoacetate hydrolase knockouts and other genetic modifications to disable hepatogenesis. Interspecies blastocyst complementation using porcine recipients for primate donors has been achieved, although percentages of chimerism remain persistently low. Recent investigation into the dynamic transcriptomes of pigs and primates have created new opportunities to intimately match the stage of developing animal embryos with one of the many varieties of human induced pluripotent stem cell. We discuss techniques for decreasing donor cell apoptosis, targeting donor tissue to endodermal structures to avoid neural or germline chimerism, and decreasing the immunogenicity of chimeric organs by generating donor endothelium.

Survival-Assured Liver Injury Preconditioning (SALIC) Enables Robust Expansion of Human Hepatocytes in Fah-/- Rag2-/- IL2rg-/- Rats

Although liver-humanized animals are desirable tools for drug development and expansion of human hepatocytes in large quantities, their development is restricted to mice. In animals larger than mice, a precondition for efficient liver humanization remains preliminary because of different xeno-repopulation kinetics in livers of larger sizes. Since rats are ten times larger than mice and widely used in pharmacological studies, liver-humanized rats are more preferable. Here, Fah-/- Rag2-/- IL2rg-/- (FRG) rats are generated by CRISPR/Cas9, showing accelerated liver failure and lagged liver xeno-repopulation compared to FRG mice. A survival-assured liver injury preconditioning (SALIC) protocol, which consists of retrorsine pretreatment and cycling 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione (NTBC) administration by defined concentrations and time intervals, is developed to reduce the mortality of FRG rats and induce a regenerative microenvironment for xeno-repopulation. Human hepatocyte repopulation is boosted to 31 ± 4% in rat livers at 7 months after transplantation, equivalent to approximately a 1200-fold expansion. Human liver features of transcriptome and zonation are reproduced in humanized rats. Remarkably, they provide sufficient samples for the pharmacokinetic profiling of human-specific metabolites. This model is thus preferred for pharmacological studies and human hepatocyte production. SALIC may also be informative to hepatocyte transplantation in other large-sized species.

Limited Expansion of Human Hepatocytes in FAH/RAG2-Deficient Swine

BACKGROUND

The mammalian liver's regenerative ability has led researchers to engineer animals as incubators for expansion of human hepatocytes. The expansion properties of human hepatocytes in immunodeficient mice are well known. However, little has been reported about larger animals that are more scalable and practical for clinical purposes. Therefore, we engineered immunodeficient swine to support expansion of human hepatocytes and identify barriers to their clinical application.

METHODS

Immunodeficient swine were engineered by knockout of recombinase activating gene 2 (RAG2) and fumarylacetoacetate hydrolase (FAH). Immature human hepatocytes (ihHCs) were injected into fetal swine by intrauterine cell transplantation (IUCT) at day 40 of gestation. Human albumin was measured as a marker of engraftment. Cytotoxicity against ihHCs was measured in transplanted piglets and control swine.

RESULTS

Higher levels of human albumin were detected in cord blood of newborn FAH/RAG2-deficient (FR) pigs compared to immunocompetent controls (196.26 ng/dL vs 39.29 ng/dL, p = 0.008), indicating successful engraftment of ihHC after IUCT and adaptive immunity in the fetus. Although rare hepatocytes staining positively for human albumin were observed, levels of human albumin did not rise after birth but declined suggesting rejection of xenografted ihHCs. Cytotoxicity against ihHCs increased after birth 3.8% (95% CI: [2.1%, 5.4%], p < 0.001) and correlated inversely to declining levels of human albumin (p = 2.1 x 10-5, R2 = 0.17). Circulating numbers of T-cells and B-cells were negligible in FR pigs. However, circulating natural killer (NK) cells exerted cytotoxicity against ihHCs. NK cell activity was lower in immunodeficient piglets after IUCT than naive controls (30.4% vs 40.1% (p = 0.011, 95% CI for difference [2.7%, 16.7%]).

CONCLUSION

Immature human hepatocytes successfully engrafted in FR swine after IUCT. NK cells were a significant barrier to expansion of hepatocytes. New approaches are needed to overcome this hurdle and allow large scale expansion of human hepatocytes in immunodeficient swine.

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.

Fumarylacetoacetate hydrolase is required for fertility in rice

The rice OsFAH gene functions identically to that of Arabidopsis SSCD1 encoding FAH. Loss of OsFAH causes rice sterility. Fumarylacetoacetate hydrolase (FAH) is the last enzyme in the tyrosine (Tyr) degradation pathway that is crucial for animals. By genetic analysis of the mutant of Short-day Sensitive Cell Death 1 gene encoding Arabidopsis FAH, we first found the pathway also plays a critical role in plants (Han et al., Plant Physiol 162:1956-1964, 2013). To further understand the role of the Tyr degradation pathway in plants, we investigated a biological function of the rice FAH. Firstly, the cDNA of rice FAH gene (OsFAH) was cloned and confirmed to be able to rescue the Arabidopsis Short-day Sensitive Cell Death 1 mutant defective in the FAH. Then, we identified the OsFAH T-DNA insertion mutant and generated the OsFAH RNA interference lines, and found that loss of OsFAH results in rice sterility. Furthermore, we analyzed expression of the OsFAH gene in roots, stems, leaves and young panicles at booting stage of rice and found that its transcript level was highest in young panicles and lowest in roots. In addition, the expression analysis of β-glucuronidase driven by OsFAH promoter in transgenic Arabidopsis showed that the OsFAH promoter was highly active in aerial tissues in vegetative stage, and sepals, filaments and stigma in reproductive stage. These results suggested that FAH plays an important role in rice fertility.

Genetically blocking HPD via CRISPR-Cas9 protects against lethal liver injury in a pig model of tyrosinemia type I

Hereditary tyrosinemia type I (HT1) results from the loss of fumarylacetoacetate hydrolase (FAH) activity and can lead to lethal liver injury (LLI). Therapeutic options for HT1 remain limited. The FAH^−/− pig, a well-characterized animal model of HT1, represents a promising candidate for testing novel therapeutic approaches to treat this condition. Here, we report an improved single-step method to establish a biallelic (FAH^−/−) mutant porcine model using CRISPR-Cas9 and cytoplasmic microinjection. We also tested the feasibility of rescuing HT1 pigs through inactivating the 4-hydroxyphenylpyruvic acid dioxygenase (HPD) gene, which functions upstream of the pathogenic pathway, rather than by directly correcting the disease-causing gene as occurs with traditional gene therapy. Direct intracytoplasmic delivery of CRISPR-Cas9 targeting HPD before intrauterine death reprogrammed the tyrosine metabolism pathway and protected pigs against FAH deficiency-induced LLI. Characterization of the F1 generation revealed consistent liver-protective features that were germline transmissible. Furthermore, HPD ablation ameliorated oxidative stress and inflammatory responses and restored the gene profile relating to liver metabolism homeostasis. Collectively, this study not only provided a novel large animal model for exploring the pathogenesis of HT1, but also demonstrated that CRISPR-Cas9-mediated HPD ablation alleviated LLI in HT1 pigs and represents a potential therapeutic option for the treatment of HT1.

Development of Ectopic Livers by Hepatocyte Transplantation Into Swine Lymph Nodes

Orthotopic liver transplantation continues to be the only effective therapy for patients with end-stage liver disease. Unfortunately, many of these patients are not considered transplant candidates, lacking effective therapeutic options that would address both the irreversible progression of their hepatic failure and the control of their portal hypertension. In this prospective study, a swine model was exploited to induce subacute liver failure. Autologous hepatocytes, isolated from the left hepatic lobe, were transplanted into the mesenteric lymph nodes (LNs) by direct cell injection. At 30-60 days after transplantation, hepatocyte engraftment in LNs was successfully identified in all transplanted animals with the degree of ectopic liver mass detected being proportional to the induced native liver injury. These ectopic livers developed within the LNs showed remarkable histologic features of swine hepatic lobules, including the formation of sinusoids and bile ducts. On the basis of our previous tyrosinemic mouse model and the present pig models of induced subacute liver failure, the generation of auxiliary liver tissue using the LNs as hepatocyte engraftment sites represents a potential therapeutic approach to supplement declining hepatic function in the treatment of liver disease.

CRISPR/Cas9-Mediated Gene Correction in Newborn Rabbits with Hereditary Tyrosinemia Type I

Patients with hereditary tyrosinemia type I (HT1) present acute and irreversible liver and kidney damage during infancy. CRISPR-Cas9-mediated gene correction during infancy may provide a promising approach to treat patients with HT1. However, all previous studies were performed on adult HT1 rodent models, which cannot authentically recapitulate some symptoms of human patients. The efficacy and safety should be verified in large animals to translate precise gene therapy to clinical practice. Here, we delivered CRISPR-Cas9 and donor templates via adeno-associated virus to newborn HT1 rabbits. The lethal phenotypes could be rescued, and notably, these HT1 rabbits reached adulthood normally without 2-(2-nitro-4-trifluoromethylbenzyol)-1,3 cyclohexanedione administration and even gave birth to offspring. Adeno-associated virus (AAV)-treated HT1 rabbits displayed normal liver and kidney structures and functions. Homology-directed repair-mediated precise gene corrections and non-homologous end joining-mediated out-of-frame to in-frame corrections in the livers were observed with efficiencies of 0.90%-3.71% and 2.39%-6.35%, respectively, which appeared to be sufficient to recover liver function and decrease liver and kidney damage. This study provides useful large-animal preclinical data for rescuing hepatocyte-related monogenetic metabolic disorders with precise gene therapy.

Ex Vivo Cell Therapy by Ectopic Hepatocyte Transplantation Treats the Porcine Tyrosinemia Model of Acute Liver Failure

The effectiveness of cell-based therapies to treat liver failure is often limited by the diseased liver environment. Here, we provide preclinical proof of concept for hepatocyte transplantation into lymph nodes as a cure for liver failure in a large-animal model with hereditary tyrosinemia type 1 (HT1), a metabolic liver disease caused by deficiency of fumarylacetoacetate hydrolase (FAH) enzyme. Autologous porcine hepatocytes were transduced ex vivo with a lentiviral vector carrying the pig Fah gene and transplanted into mesenteric lymph nodes. Hepatocytes showed early (6 h) and durable (8 months) engraftment in lymph nodes, with reproduction of vascular and hepatic microarchitecture. Subsequently, hepatocytes migrated to and repopulated the native diseased liver. The corrected cells generated sufficient liver mass to clinically ameliorate the acute liver failure and HT1 disease as early as 97 days post-transplantation. Integration site analysis defined the corrected hepatocytes in the liver as a subpopulation of hepatocytes from lymph nodes, indicating that the lymph nodes served as a source for healthy hepatocytes to repopulate a diseased liver. Therefore, ectopic transplantation of healthy hepatocytes cures this pig model of liver failure and presents a promising approach for the development of cures for liver disease in patients.

Heterotopic vascularization and functionalization of implantable bio engineered hepatic tissue alleviates liver injury in rats

BACKGROUND

The challenge of using bioengineered liver lies in sustaining the quantity of high-quality hepatocytes and the vasculature for blood perfusion. We characterized the heparinization of a porcine decellularized liver scaffold (DLS) as a carrier to support hepatocyte angiogenesis, thereby developing functional and vascularized hepatic tissue useful to treat liver injury.

METHOD

The porcine DLS was obtained by the removal of cellular components and then subjected to heparinization by the end-point attachment technique. The heparinized DLSs were recellularized with rat hepatocyte spheroids to construct engineered hepatic tissue. The hepatic tissue was heterotopically implanted in the omentum majus of a rat model with liver injury induced by carbon tetrachloride (CCl₄ ).

RESULTS

Hepatocyte spheroids in the heparinized DLS remained viable for at least 10 weeks in vivo. The entire scaffold was populated with hepatocytes and arranged well. The volume of the heparinized DLS group was expanded over 400-fold. Liver-specific functions such as albumin synthesis, glycogen storage and cytochrome P 3A4 activity were highly expressed in the hepatic tissue. In addition, endothelial cells were recruited, as shown by CD31 staining, and new blood vessels formed, as visualized by fluorescein isothiocyanate-labelled dextran intravital confocal microscopy. The heparinized bioengineered hepatic tissue alleviated CCl₄ -induced liver injury by regulating the deposition and degradation of the extracellular matrix.

CONCLUSION

Primary hepatocyte spheroids survived for an extended time on the heparinized DLS and expanded to generate vascularized and functional bioengineered hepatic tissue that can alleviate liver injury in rats.

Long-Term Outcomes and Practical Considerations in the Pharmacological Management of Tyrosinemia Type 1

Tyrosinemia type 1 (TT1) is a rare metabolic disease caused by a defect in tyrosine catabolism. TT1 is clinically characterized by acute liver failure, development of hepatocellular carcinoma, renal and neurological problems, and consequently an extremely poor outcome. This review showed that the introduction of 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione (NTBC) in 1992 has revolutionized the outcome of TT1 patients, especially when started pre-clinically. If started early, NTBC can prevent liver failure, renal problems, and neurological attacks and decrease the risk for hepatocellular carcinoma. NTBC has been shown to be safe and well tolerated, although the long-term effectiveness of treatment with NTBC needs to be awaited. The high tyrosine concentrations caused by treatment with NTBC could result in ophthalmological and skin problems and requires life-long dietary restriction of tyrosine and its precursor phenylalanine, which could be strenuous to adhere to. In addition, neurocognitive problems have been reported since the introduction of NTBC, with hypothesized but as yet unproven pathophysiological mechanisms. Further research should be done to investigate the possible relationship between important clinical outcomes and blood concentrations of biochemical parameters such as phenylalanine, tyrosine, succinylacetone, and NTBC, and to develop clear guidelines for treatment and follow-up with reliable measurements. This all in order to ultimately improve the combined NTBC and dietary treatment and limit possible complications such as hepatocellular carcinoma development, neurocognitive problems, and impaired quality of life.

Hepatotoxicity and Toxicology of In Vivo Lentiviral Vector Administration in Healthy and Liver-Injury Mouse Models

General safety and toxicology assessments supporting in vivo lentiviral vector-based therapeutic development are sparse. We have previously demonstrated the efficacy of a lentiviral vector expressing fumarylacetoacetate hydrolase (LV-FAH) to cure animal models of hereditary tyrosinemia type 1. Therefore, we performed a complete preclinical toxicological evaluation of LV-FAH, in a large cohort (n = 20/group) of wildtype mice and included matched groups of N-nitrosodiethylamine/carbon tetrachloride (DEN/CCl4)-induced liver injury mice to assess specific toxicity in fibrotic liver tissue. Mice receiving LV-FAH alone (109 TU/mouse) or in combination with DEN/CCl4 presented clinically similar to control animals, with only slight reductions in total body weight gains over the study period (3.2- to 3.7-fold vs. 4.2-fold). There were no indications of toxicity attributed to administration of LV-FAH alone over the duration of this study. The known hepatotoxic combination of DEN/CCl4 induced fibrotic liver injury, and co-administration with LV-FAH was associated with exaggeration of some findings such as an increased liver:body weight ratio and progression to focal hepatocyte necrosis in some animals. Hepatocellular degeneration/regeneration was present in DEN/CCl4-dosed animals regardless of LV-FAH as evaluated by Ki-67 immunohistochemistry and circulating alpha fetoprotein levels, but there were no tumors identified in any tissue in any dose group. These data demonstrate the inherent safety of LV-FAH and support broader clinical development of lentiviral vectors for in vivo administration.

Biofabrication of Autologous Human Hepatocytes for Transplantation: How Do We Get There?

Directed differentiation of hepatocytes from induced pluripotent stem cells (iPSCs) holds promise as source material for treating some liver disorders. The unlimited availability of perfectly differentiated iPSC-derived hepatocytes will dramatically facilitate cell therapies. While systems to manufacture large quantities of iPSC-derived cells have been developed, we have been unable to generate and maintain stable and mature adult liver cells ex vivo. This short review highlights important challenges and possible solutions to the current state of hepatocyte biofabrication for cellular therapies to treat liver diseases. Successful cell transplantation will require optimizing the best cell function, overcoming limitations to cell numbers and safety, as well as a number of other challenges. Collaboration among scientists, clinicians, and industry is critical for generating new autologous stem cell-based therapies to treat liver diseases.

Cold storage of porcine hepatocyte spheroids for spheroid bioartificial liver

BACKGROUND AND AIMS

Cell-based therapies for liver disease such as bioartificial liver rely on a large quantity and high quality of hepatocytes. Cold storage was previously shown to be a better way to preserve the viability and functionality of hepatocytes during transportation rather than freezing, but this was only proved at a lower density of rat hepatocytes spheroids. The purpose of this study was to optimize conditions for cold storage of high density of primary porcine hepatocyte spheroids.

METHODS

Porcine hepatocytes were isolated by a three-step perfusion method; hepatocyte spheroids were formed by a 24 hours rocked culture technique. Hepatocyte cell density was 5 × 10⁶ /mL in 1000 mL spheroid forming medium. Spheroids were then maintained in rocked culture at 37°C (control condition) or cold stored at 4°C for 24, 48 or 72 hours in four different cold storage solutions: histidine-tryptophan-ketoglutarate (HTK) alone; HTK + 1 mM deferoxamine (DEF); HTK + 5 mM N-acetyl-L-cysteine (NAC); and HTK + 1 mM DEF + 5 mM NAC. The viability, ammonia clearance, albumin production, gene expression, and functional activity of cytochrome P450 enzymes were measured after recovery from the cold storage.

RESULTS

In this study, we observed that cold-induced injury was reduced by the addition of the iron chelator. Viability of HTK + DEF group hepatocyte spheroids was increased compared with other cold storage groups (P < 0.05). Performance metrics of porcine hepatocyte spheroids cold stored for 24 hours were similar to those in control conditions. The hepatocyte spheroids in control conditions started to lose their ability to clear ammonia while production of albumin was still active at 48 and 72 hours (P < 0.05). In contrast, the viability and functionality of hepatocyte spheroids including ammonia clearance and albumin secretion were preserved in HTK + DEF group at both 48- and 72-hour time points (P < 0.05).

CONCLUSIONS

The beneficial effects of HTK supplemented with DEF were more obvious after cold storage of high density of porcine hepatocyte spheroids for 72 hours. The porcine hepatocyte spheroids were above the cutoff criteria for use in a spheroid-based bioartificial liver.

Understanding the marvels behind liver regeneration

Tissue regeneration is a process by which the remaining cells of an injured organ regrow to offset the missed cells. This field is relatively a new discipline that has been a focus of intense research by clinicians, surgeons, and scientists for decades. It constitutes the cornerstone of tissue engineering, creation of artificial organs, and generation and utilization of therapeutic stem cells to undergo transformation to different types of mature cells. Many medical experts, scientists, biologists, and bioengineers have dedicated their efforts to deeply comprehend the process of liver regeneration, striving for harnessing it to invent new therapies for liver failure. Liver regeneration after partial hepatectomy in rodents has been extensively studied by researchers for many years. It is divided into three important distinctive phases including (a) Initiation or priming phase which includes an overexpression of specific genes to prepare the liver cells for replication, (b) Proliferation phase in which the liver cells undergo a series of cycles of cell division and expansion and finally, (c) termination phase which acts as brake to stop the regenerative process and prevent the liver tissue overgrowth. These events are well controlled by cytokines, growth factors, and signaling pathways. In this review, we describe the function, embryology, and anatomy of human liver, discuss the molecular basis of liver regeneration, elucidate the hepatocyte and cholangiocyte lineages mediating this process, explain the role of hepatic progenitor cells and elaborate the developmental signaling pathways and regulatory molecules required to procure a complete restoration of hepatic lobule. This article is categorized under: Adult Stem Cells, Tissue Renewal, and Regeneration > Regeneration Signaling Pathways > Global Signaling Mechanisms Gene Expression and Transcriptional Hierarchies > Cellular Differentiation.

Autologous Gene and Cell Therapy Provides Safe and Long-Term Curative Therapy in A Large Pig Model of Hereditary Tyrosinemia Type 1

Orthotopic liver transplantation remains the only curative therapy for inborn errors of metabolism. Given the tremendous success for primary immunodeficiencies using ex-vivo gene therapy with lentiviral vectors, there is great interest in developing similar curative therapies for metabolic liver diseases. We have previously generated a pig model of hereditary tyrosinemia type 1 (HT1), an autosomal recessive disorder caused by deficiency of fumarylacetoacetate hydrolase (FAH). Using this model, we have demonstrated curative ex-vivo gene and cell therapy using a lentiviral vector to express FAH in autologous hepatocytes. To further evaluate the long-term clinical outcomes of this therapeutic approach, we continued to monitor one of these pigs over the course of three years. The animal continued to thrive off the protective drug NTBC, gaining weight appropriately, and maintaining sexual fecundity for the course of his life. The animal was euthanized 31 months after transplantation to perform a thorough biochemical and histological analysis. Biochemically, liver enzymes and alpha-fetoprotein levels remained normal and abhorrent metabolites specific to HT1 remained corrected. Liver histology showed no evidence of tumorigenicity and Masson's trichrome staining revealed minimal fibrosis and no evidence of cirrhosis. FAH-immunohistochemistry revealed complete repopulation of the liver by transplanted FAH-positive cells. A complete histopathological report on other organs, including kidney, revealed no abnormalities. This study is the first to demonstrate long-term safety and efficacy of hepatocyte-directed gene therapy in a large animal model. We conclude that hepatocyte-directed ex-vivo gene therapy is a rational choice for further exploration as an alternative therapeutic approach to whole organ transplantation for metabolic liver disease, including HT1.

Lentiviral Vector-mediated Gene Therapy of Hepatocytes Ex Vivo for Autologous Transplantation in Swine

Gene therapy is an ideal choice to cure many inborn errors of metabolism of the liver. Ex-vivo, lentiviral vectors have been used successfully in the treatment of many hematopoietic diseases in humans, as their use offers stable transgene expression due to the vector's ability to integrate into the host genome. This method demonstrates the application of ex vivo gene therapy of hepatocytes to a large animal model of hereditary tyrosinemia type I. This process consists of 1) isolation of primary hepatocytes from the autologous donor/recipient animal, 2) ex vivo gene delivery via hepatocyte transduction with a lentiviral vector, and 3) autologous transplant of corrected hepatocytes via portal vein injection. Success of the method generally relies upon efficient and sterile removal of the liver resection, careful handling of the excised specimen for isolation of viable hepatocytes sufficient for re-engrafting, high-percentage transduction of the isolated cells, and aseptic surgical procedures throughout to prevent infection. Technical failure at any of these steps will result in low yield of viable transduced hepatocytes for autologous transplant or infection of the donor/recipient animal. The pig model of human type 1 hereditary tyrosinemia (HT-1) chosen for this approach is uniquely amenable to such a method, as even a small percentage of engraftment of corrected cells will lead to repopulation of the liver with healthy cells based on a powerful selective advantage over native-diseased hepatocytes. Although this growth selection will not be true for all indications, this approach is a foundation for expansion into other indications and allows for manipulation of this environment to address additional diseases, both within the liver and beyond, while controlling for exposure to viral vector and opportunity for off-target toxicity and tumorigenicity.

A Pre-Clinical Large Animal Model of Sustained Liver Injury and Regeneration Stimulus

A feasible large animal model to evaluate regenerative medicine techniques is vital for developing clinical applications. One such appropriate model could be to use retrorsine (RS) together with partial hepatectomy (PH). Here, we have developed the first porcine model using RS and PH. RS or saline control was administered intraperitoneally to Göttingen miniature pigs twice, two weeks apart. Four weeks after the second dose, animals underwent PH. Initially, we tested different doses of RS and resection of different amounts of liver, and selected 50 mg/kg RS with 60% hepatectomy as our model for further testing. Treated animals were sacrificed 3, 10, 17 or 28 days after PH. Blood samples and resected liver were collected. Serum and liver RS content was determined by Liquid Chromatograph-tandem Mass Spectrometer. Blood analyses demonstrated liver dysfunction after PH. Liver regeneration was significantly inhibited 10 and 17 days after PH in RS-treated animals, to the extent of 20%. Histological examination indicated hepatic injury and regenerative responses after PH. Immunohistochemical staining demonstrated accumulation of Cyclin D1 and suppression of Ki-67 and PCNA in RS-treated animals. We report the development of the first large animal model of sustained liver injury with suppression of hepatic regeneration.

Hepatocyte spheroids as an alternative to single cells for transplantation after ex vivo gene therapy in mice and pig models

BACKGROUND

Autologous hepatocyte transplantation after ex vivo gene therapy is an alternative to liver transplantation for metabolic liver disease. Here we evaluate ex vivo gene therapy followed by transplantation of single-cell or spheroid hepatocytes.

METHODS

Pig and mouse hepatocytes were isolated, labeled with zirconium-89 and returned to the liver as single cells or spheroids. Biodistribution was evaluated through positron emission tomography-computed tomography. Fumarylacetoacetate hydrolase-deficient pig hepatocytes were isolated and transduced with a lentiviral vector containing the Fah gene. Animals received portal vein infusion of single-cell or spheroid autologous hepatocytes after ex vivo gene delivery. Portal pressures were measured and ultrasound was used to evaluate for thrombus. Differences in engraftment and expansion of ex vivo corrected single-cell or spheroid hepatocytes were followed through histologic analysis and animals' ability to thrive off 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione.

RESULTS

Positron emission tomography-computed tomography imaging showed spheroid hepatocytes with increased heterogeneity in biodistribution as compared with single cells, which spread more uniformly throughout the liver. Animals receiving spheroids experienced higher mean changes in portal pressure than animals receiving single cells (P < .01). Additionally, two animals from the spheroid group developed portal vein thrombi that required systemic anticoagulation. Immunohistochemical analysis of spheroid- and single-cell-transplanted animals showed similar engraftment and expansion rates of fumarylacetoacetate hydrolase-positive hepatocytes in the liver, correlating with similar weight stabilization curves.

CONCLUSION

Ex vivo gene correction of autologous hepatocytes in fumarylacetoacetate hydrolase-deficient pigs can be performed using hepatocyte spheroids or single-cell hepatocytes, with spheroids showing a more heterogeneous distribution within the liver and higher risks for portal vein thrombosis and increased portal pressures.

Curative ex vivo liver-directed gene therapy in a pig model of hereditary tyrosinemia type 1

We tested the hypothesis that ex vivo hepatocyte gene therapy can correct the metabolic disorder in fumarylacetoacetate hydrolase-deficient (Fah(-/-)) pigs, a large animal model of hereditary tyrosinemia type 1 (HT1). Recipient Fah(-/-) pigs underwent partial liver resection and hepatocyte isolation by collagenase digestion. Hepatocytes were transduced with one or both of the lentiviral vectors expressing the therapeutic Fah and the reporter sodium-iodide symporter (Nis) genes under control of the thyroxine-binding globulin promoter. Pigs received autologous transplants of hepatocytes by portal vein infusion. After transplantation, the protective drug 2-(2-nitro-4-trifluoromethylbenzyol)-1,3 cyclohexanedione (NTBC) was withheld from recipient pigs to provide a selective advantage for expansion of corrected FAH(+) cells. Proliferation of transplanted cells, assessed by both immunohistochemistry and noninvasive positron emission tomography imaging of NIS-labeled cells, demonstrated near-complete liver repopulation by gene-corrected cells. Tyrosine and succinylacetone levels improved to within normal range, demonstrating complete correction of tyrosine metabolism. In addition, repopulation of the Fah(-/-) liver with transplanted cells inhibited the onset of severe fibrosis, a characteristic of nontransplanted Fah(-/-) pigs. This study demonstrates correction of disease in a pig model of metabolic liver disease by ex vivo gene therapy. To date, ex vivo gene therapy has only been successful in small animal models. We conclude that further exploration of ex vivo hepatocyte genetic correction is warranted for clinical use.

In Vitro Generated Hepatocyte-Like Cells: A Novel Tool in Regenerative Medicine and Drug Discovery

Hepatocyte-like cells (HLCs) are generated from either various human pluripotent stem cells (hPSCs) including induced pluripotent stem cells (iPSCs) and embryonic stem cells (ESCs), or direct cell conversion, mesenchymal stem cells as well as other stem cells like gestational tissues. They provide potential cell sources for biomedical applications. Liver transplantation is the gold standard treatment for the patients with end stage liver disease, but there are many obstacles limiting this process, like insufficient number of donated healthy livers. Meanwhile, the number of patients receiving a liver organ transplant for a better life is increasing. In this regard, HLCs may provide an adequate cell source to overcome these shortages. New molecular engineering approaches such as CRISPR/ Cas system applying in iPSCs technology provide the basic principles of gene correction for monogenic inherited metabolic liver diseases, as another application of HLCs. It has been shown that HLCs could replace primary human hepatocytes in drug discovery and hepatotoxicity tests. However, generation of fully functional HLCs is still a big challenge; several research groups have been trying to improve current differentiation protocols to achieve better HLCs according to morphology and function of cells. Large-scale generation of functional HLCs in bioreactors could make a new opportunity in producing enough hepatocytes for treating end-stage liver patients as well as other biomedical applications such as drug studies. In this review, regarding the biomedical value of HLCs, we focus on the current and efficient approaches for generating hepatocyte-like cells in vitro and discuss about their applications in regenerative medicine and drug discovery.

Fumarylacetoacetate Hydrolase Knock-out Rabbit Model for Hereditary Tyrosinemia Type 1

Hereditary tyrosinemia type 1 (HT1) is a severe human autosomal recessive disorder caused by the deficiency of fumarylacetoacetate hydroxylase (FAH), an enzyme catalyzing the last step in the tyrosine degradation pathway. Lack of FAH causes accumulation of toxic metabolites (fumarylacetoacetate and succinylacetone) in blood and tissues, ultimately resulting in severe liver and kidney damage with onset that ranges from infancy to adolescence. This tissue damage is lethal but can be controlled by administration of 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione (NTBC), which inhibits tyrosine catabolism upstream of the generation of fumarylacetoacetate and succinylacetone. Notably, in animals lacking FAH, transient withdrawal of NTBC can be used to induce liver damage and a concomitant regenerative response that stimulates the growth of healthy hepatocytes. Among other things, this model has raised tremendous interest for the in vivo expansion of human primary hepatocytes inside these animals and for exploring experimental gene therapy and cell-based therapies. Here, we report the generation of FAH knock-out rabbits via pronuclear stage embryo microinjection of transcription activator-like effector nucleases. FAH^-/- rabbits exhibit phenotypic features of HT1 including liver and kidney abnormalities but additionally develop frequent ocular manifestations likely caused by local accumulation of tyrosine upon NTBC administration. We also show that allogeneic transplantation of wild-type rabbit primary hepatocytes into FAH^-/- rabbits enables highly efficient liver repopulation and prevents liver insufficiency and death. Because of significant advantages over rodents and their ease of breeding, maintenance, and manipulation compared with larger animals including pigs, FAH^-/- rabbits are an attractive alternative for modeling the consequences of HT1.

Dynamic microRNAome profiles in the developing porcine liver

Increasing evidence suggests that micro (mi)RNAs play important roles in various biological process. To evaluate the roles of miRNA in the porcine liver, we investigated the dynamic profiles of microRNAomes using liver tissue from pigs during the embryonic period (embryonic day 90), weaning stage (postnatal day 30), and adult stage (7 years old). A total of 186 unique miRNAs were differentially expressed during liver development. We also identified that 17, 13, and 6 miRNAs were specifically abundant at embryonic day 90, postnatal day 30, and at 7 years, respectively. Besides regulating basic cellular roles in development, miRNAs expressed at the three developmental stages also participated in regulating “embryonic liver development,” “early hepatic growth and generating a functioning liver,” and “energy metabolic processes,” respectively. Our study indicates that miRNAs are extensively involved in liver development, and provides a valuable resource for the further elucidation of miRNA regulatory roles during liver development.

Fah Knockout Animals as Models for Therapeutic Liver Repopulation

Several animal models of Fah deficiency have been developed, including mice, pigs and most recently rats. Initially, the murine models were developed with the intent to mirror the human disease for pathophysiologic and therapeutic studies. However, it soon became apparent that Fah-positive hepatocytes have a potent selective growth advantage in mutant liver and can extensively repopulate the diseased organ. For this reason, Fah mutant mice have become a workhorse for liver biology and are widely used in liver stem cell and hepatic gene therapy research. Immune deficient Fah-knockout mice can be repopulated with human hepatocytes, creating "mice with human livers". These chimeric animals have become an important preclinical model for infectious diseases, metabolism and gene therapy. The potent expansion of human hepatocytes in Fah knockout mice has given rise to the concept of using Fah mutants as living bioreactors to produce large quantities of fully mature hepatocytes. As a consequence, larger animal models of Fah deficiency have recently been developed.

Concise Review: Liver Regenerative Medicine: From Hepatocyte Transplantation to Bioartificial Livers and Bioengineered Grafts

Donor organ shortage is the main limitation to liver transplantation as a treatment for end-stage liver disease and acute liver failure. Liver regenerative medicine may in the future offer an alternative form of therapy for these diseases, be it through cell transplantation, bioartificial liver (BAL) devices, or bioengineered whole organ liver transplantation. All three strategies have shown promising results in the past decade. However, before they are incorporated into widespread clinical practice, the ideal cell type for each treatment modality must be found, and an adequate amount of metabolically active, functional cells must be able to be produced. Research is ongoing in hepatocyte expansion techniques, use of xenogeneic cells, and differentiation of stem cell-derived hepatocyte-like cells (HLCs). HLCs are a few steps away from clinical application, but may be very useful in individualized drug development and toxicity testing, as well as disease modeling. Finally, safety concerns including tumorigenicity and xenozoonosis must also be addressed before cell transplantation, BAL devices, and bioengineered livers occupy their clinical niche. This review aims to highlight the most recent advances and provide an updated view of the current state of affairs in the field of liver regenerative medicine. Stem Cells 2017;35:42-50.

The Liver in Tyrosinemia Type I: Clinical Management and Course in Quebec

HT1 is a severe autosomal recessive disorder due to the deficiency of fumarylacetoacetate hydrolase (FAH), the final enzyme in the degradation of tyrosine. Before the era of treatment with 2-(2-N-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione (NTBC), even with newborn screening and optimal diet therapy, HT1 patients often developed liver failure. Death was common in patients who did not undergo liver transplantation. For the last two decades, NTBC has revolutionized the management of HT1 patients. In screened newborns treated within the first month of life, we have not observed hepatocarcinoma. If patients are not detected at birth by neonatal screening, the diagnosis and treatment must be performed on an emergency basis, and patients are at risk for complications. Long term adhesion to treatment and reliable early detection of hepatocellular carcinoma (HCC) are two important challenges. In this chapter, we describe the clinical, biological, histo-pathological and imaging findings of HT1 in Québec before the era of NTBC. We also describe the hepatic status of nontransplanted tyrosinemic patients in Quebec and current management practices in the Quebec NTBC Study.

Chronic Phenotype Characterization of a Large-Animal Model of Hereditary Tyrosinemia Type 1

Hereditary tyrosinemia type 1 (HT1) is an autosomal recessive disease caused by deficiency in fumarylacetoacetate hydrolase, the last enzyme in the tyrosine catabolic pathway. In this study, we investigated whether fumarylacetoacetate hydrolase deficient (FAH^-/-) pigs, a novel large-animal model of HT1, develop fibrosis and cirrhosis characteristic of the human disease. FAH^-/- pigs were treated with the protective drug 2-(2-nitro-4-trifluoromethylbenzoyl)-1, 3 cyclohexandione (NTBC) at a dose of 1 mg/kg per day initially after birth. After 30 days, they were assigned to one of three groups based on dosing of NTBC. Group 1 received ≥0.2 mg/kg per day, group 2 cycled on/off NTBC (0.05 mg/kg per day × 1 week/0 mg/kg per day × 3 weeks), and group 3 received no NTBC thereafter. Pigs were monitored for features of liver disease. Animals in group 1 continued to have weight gain and biochemical analyses comparable to wild-type pigs. Animals in group 2 had significant cessation of weight gain, abnormal biochemical test results, and various grades of fibrosis and cirrhosis. No evidence of hepatocellular carcinoma was detected. Group 3 animals declined rapidly, with acute liver failure. In conclusion, the FAH^-/- pig is a large-animal model of HT1 with clinical characteristics that resemble the human phenotype. Under conditions of low-dose NTBC, FAH^-/- pigs developed liver fibrosis and portal hypertension, and thus may serve as a large-animal model of chronic liver disease.

Efficient liver repopulation of transplanted hepatocyte prevents cirrhosis in a rat model of hereditary tyrosinemia type I

Hereditary tyrosinemia type I (HT1) is caused by a deficiency in the enzyme fumarylacetoacetate hydrolase (Fah). Fah-deficient mice and pigs are phenotypically analogous to human HT1, but do not recapitulate all the chronic features of the human disorder, especially liver fibrosis and cirrhosis. Rats as an important model organism for biomedical research have many advantages over other animal models. Genome engineering in rats is limited till the availability of new gene editing technologies. Using the recently developed CRISPR/Cas9 technique, we generated Fah(-/-) rats. The Fah(-/-) rats faithfully represented major phenotypic and biochemical manifestations of human HT1, including hypertyrosinemia, liver failure, and renal tubular damage. More importantly, the Fah(-/-) rats developed remarkable liver fibrosis and cirrhosis, which have not been observed in Fah mutant mice or pigs. Transplantation of wild-type hepatocytes rescued the Fah(-/-) rats from impending death. Moreover, the highly efficient repopulation of hepatocytes in Fah(-/-) livers prevented the progression of liver fibrosis to cirrhosis and in turn restored liver architecture. These results indicate that Fah(-/-) rats may be used as an animal model of HT1 with liver cirrhosis. Furthermore, Fah(-/-) rats may be used as a tool in studying hepatocyte transplantation and a bioreactor for the expansion of hepatocytes.

Genetically engineered livestock for biomedical models

To commemorate Transgenic Animal Research Conference X, this review summarizes the recent progress in developing genetically engineered livestock species as biomedical models. The first of these conferences was held in 1997, which turned out to be a watershed year for the field, with two significant events occurring. One was the publication of the first transgenic livestock animal disease model, a pig with retinitis pigmentosa. Before that, the use of livestock species in biomedical research had been limited to wild-type animals or disease models that had been induced or were naturally occurring. The second event was the report of Dolly, a cloned sheep produced by somatic cell nuclear transfer. Cloning subsequently became an essential part of the process for most of the models developed in the last 18 years and is stilled used prominently today. This review is intended to highlight the biomedical modeling achievements that followed those key events, many of which were first reported at one of the previous nine Transgenic Animal Research Conferences. Also discussed are the practical challenges of utilizing livestock disease models now that the technical hurdles of model development have been largely overcome.

Stem Cell Therapies for Treatment of Liver Disease

Cell therapy is an emerging form of treatment for several liver diseases, but is limited by the availability of donor livers. Stem cells hold promise as an alternative to the use of primary hepatocytes. We performed an exhaustive review of the literature, with a focus on the latest studies involving the use of stem cells for the treatment of liver disease. Stem cells can be harvested from a number of sources, or can be generated from somatic cells to create induced pluripotent stem cells (iPSCs). Different cell lines have been used experimentally to support liver function and treat inherited metabolic disorders, acute liver failure, cirrhosis, liver cancer, and small-for-size liver transplantations. Cell-based therapeutics may involve gene therapy, cell transplantation, bioartificial liver devices, or bioengineered organs. Research in this field is still very active. Stem cell therapy may, in the future, be used as a bridge to either liver transplantation or endogenous liver regeneration, but efficient differentiation and production protocols must be developed and safety must be demonstrated before it can be applied to clinical practice.

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.

Noninvasive 3-dimensional imaging of liver regeneration in a mouse model of hereditary tyrosinemia type 1 using the sodium iodide symporter gene

Cell transplantation is a potential treatment for the many liver disorders that are currently only curable by organ transplantation. However, one of the major limitations of hepatocyte (HC) transplantation is an inability to monitor cells longitudinally after injection. We hypothesized that the thyroidal sodium iodide symporter (NIS) gene could be used to visualize transplanted HCs in a rodent model of inherited liver disease: hereditary tyrosinemia type 1. Wild-type C57Bl/6J mouse HCs were transduced ex vivo with a lentiviral vector containing the mouse Slc5a5 (NIS) gene controlled by the thyroxine-binding globulin promoter. NIS-transduced cells could robustly concentrate radiolabeled iodine in vitro, with lentiviral transduction efficiencies greater than 80% achieved in the presence of dexamethasone. Next, NIS-transduced HCs were transplanted into congenic fumarylacetoacetate hydrolase knockout mice, and this resulted in the prevention of liver failure. NIS-transduced HCs were readily imaged in vivo by single-photon emission computed tomography, and this demonstrated for the first time noninvasive 3-dimensional imaging of regenerating tissue in individual animals over time. We also tested the efficacy of primary HC spheroids engrafted in the liver. With the NIS reporter, robust spheroid engraftment and survival could be detected longitudinally after direct parenchymal injection, and this thereby demonstrated a novel strategy for HC transplantation. This work is the first to demonstrate the efficacy of NIS imaging in the field of HC transplantation. We anticipate that NIS labeling will allow noninvasive and longitudinal identification of HCs and stem cells in future studies related to liver regeneration in small and large preclinical animal models.

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.

Potential and Challenges of Induced Pluripotent Stem Cells in Liver Diseases Treatment

Tens of millions of patients are affected by liver disease worldwide. Many of these patients can benefit from cell therapy involving living metabolically active cells, either by treatment of their liver disease, or by prevention of their disease phenotype. Cell therapies, including hepatocyte transplantation and bioartificial liver (BAL) devices, have been proposed as therapeutic alternatives to the shortage of transplantable livers. Both BAL and hepatocyte transplantation are cellular therapies that avoid use of a whole liver. Hepatocytes are also widely used in drug screening and liver disease modelling. However, the demand for human hepatocytes, heavily outweighs their availability by conventional means. Induced pluripotent stem cells (iPSCs) technology brings together the potential benefits of embryonic stem cells (ESCs) (i.e., self-renewal, pluripotency) and addresses the major ethical and scientific concerns of ESCs: embryo destruction and immune-incompatibility. It has been shown that hepatocyte-like cells (HLCs) can be generated from iPSCs. Furthermore, human iPSCs (hiPSCs) can provide an unlimited source of human hepatocytes and hold great promise for applications in regenerative medicine, drug screening and liver diseases modelling. Despite steady progress, there are still several major obstacles that need to be overcome before iPSCs will reach the bedside. This review will focus on the current state of efforts to derive hiPSCs for potential use in modelling and treatment of liver disease.