Hybrid artificial liver using hepatocyte organoid culture

Emerging role and promise of nanomaterials in organoid research

Organoids are 3D stem cell-derived self-organization of cells. Organoid bioengineering helps recreate and tailor their architecture in vitro to generate mini organ-like properties, providing the opportunity to study fundamental cell behavior in heterogeneous populations and as a tool to model various diseases. Nanomaterials (NMs) are becoming indispensable in regenerative medicine and in developing treatment modalities for various diseases. Therefore, organoid-NM interactions are set to gain traction for the development of advanced diagnostics and therapeutics. Here, we discuss the interactions of NMs with distinctive organoid types, organoid matrices, trafficking and cargo delivery, organs-on-a-chip, bioprinting, downstream therapeutic implications, and future approaches.

Organoids: a promising new in vitro platform in livestock and veterinary research

Organoids are self-organizing, self-renewing three-dimensional cellular structures that resemble organs in structure and function. They can be derived from adult stem cells, embryonic stem cells, or induced pluripotent stem cells. They contain most of the relevant cell types with a topology and cell-to-cell interactions resembling that of the in vivo tissue. The widespread and increasing adoption of organoid-based technologies in human biomedical research is testament to their enormous potential in basic, translational- and applied-research. In a similar fashion there appear to be ample possibilities for research applications of organoids from livestock and companion animals. Furthermore, organoids as in vitro models offer a great possibility to reduce the use of experimental animals. Here, we provide an overview of studies on organoids in livestock and companion animal species, with focus on the methods developed for organoids from a variety of tissues/organs from various animal species and on the applications in veterinary research. Current limitations, and ongoing research to address these limitations, are discussed. Further, we elaborate on a number of fields of research in animal nutrition, host-microbe interactions, animal breeding and genomics, and animal biotechnology, in which organoids may have great potential as an in vitro research tool.

Development of three-dimensional (3D) spheroid cultures of the continuous rainbow trout liver cell line RTL-W1

In vitro experimental systems based on continuous piscine cell lines can be used as an alternative to animal tests for obtaining qualitative and quantitative information on the possible fate and effect of chemicals in fish. However, their capability to reproduce complex metabolic processes and toxic responses as they occur in vivo is limited due to the lack of organ-specific tissue architecture and functions. Here we introduce a three-dimensional (3D) in vitro experimental system based on spheroidal aggregate cultures (spheroids) of the continuous rainbow trout liver cell line RTL-W1 and provide a first description of their structural and functional properties including growth, viability/longevity, metabolic activity, ultrastructure and cytochrome P450 1A (CYP1A) expression determined by bright-field, multi-photon fluorescence and transmission electron microscopy as well as RT-qPCR analysis. Our results show that RTL-W1 cells in 3D spheroids (ø ~ 150 µm) (including those in the interior) were viable, metabolically active and had higher basal and β-naphthoflavone-induced CYP1A expression levels than conventional 2D cell cultures. Furthermore, they displayed ultrastructural characteristics similar to differentiated hepatocytes. The available evidence suggests that 3D RTL-W1 spheroids may have enhanced hepatotypic functions and be a superior in vitro model to assess hepatic biotransformation, bioaccumulation and chronic toxicity compared to conventional cell monolayer cultures.

Characterisation of a functional rat hepatocyte spheroid model

Many in vitro liver cell models, such as 2D systems, that are used to assess the hepatotoxic potential of xenobiotics suffer major limitations arising from a lack of preservation of physiological phenotype and metabolic competence. To circumvent some of these limitations there has been increased focus on producing more representative 3D models. Here we have used a novel approach to construct a size-controllable 3D hepatic spheroid model using freshly isolated primary rat hepatocytes (PRH) utilising the liquid-overlay technique whereby PRH spontaneously self-assemble in to 3D microtissues. This system produces viable spheroids with a compact in vivo-like structure for up to 21 days with sustained albumin production for the duration of the culture period. F-actin was seen throughout the spheroid body and P-glycoprotein (P-gp) and multidrug resistance-associated protein 2 (MRP2) transporters had polarised expression on the canalicular membrane of hepatocytes within the spheroids upon formation (day 3). The MRP2 transporter was able to functionally transport 5 μM 5-chloromethylfluorescein diacetate (CMFDA) substrates into these canalicular structures. These PRH spheroids display in vivo characteristics including direct cell-cell contacts, cellular polarisation, 3D cellular morphology, and formation of functional secondary structures throughout the spheroid. Such a well-characterised system could be readily exploited for pre-clinical and non-clinical repeat-dose investigations and could make a significant contribution to replace, reduce and refine the use of animals for applied research.

Rapid creation system of morphologically and functionally communicative three-dimensional cell-dense tissue by centrifugation

This study reports a rapid fabrication system of a morphologically and functionally communicative three-dimensional (3D) cell-dense tissue without scaffolds by centrifugation. The tight adhesion between C2C12 myoblasts and culture surface was accelerated without significant cell damage by centrifugation (80 x g, 37 °C, 30 min). A thicker tissue created on a temperature-responsive culture surface was harvested by decreasing temperature. The 3D myoblast tissues having approximately 200 μm-thickness were created at 1.5 h [centrifugation (80 x g, 37 °C) for 30 min and tissue harvest for 1 h]. However, in the case of without centrifugation, the myoblast tissues had fragile parts even at 7.5 h after the incubation. Additionally, electrically/functionally communicative and thicker human induced pluripotent stem (iPS) cell-derived cardiac tissues were created rapidly by the centrifugation and cultivation at 37 °C. We report a centrifugation system that significantly shortens the creation time of 3D tissues. We envision that this procedure will contribute to the field of tissue engineering and regenerative medicine. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 34:1447-1453, 2018.

Impact of cell types and culture methods on the functionality of in vitro liver systems - A review of cell systems for hepatotoxicity assessment

Xenobiotic safety assessment is an area that impacts a multitude of different industry sectors such as medicinal drugs, agrochemicals, industrial chemicals, cosmetics and environmental contaminants. As such there are a number of well-developed in vitro, in vivo and in silico approaches to evaluate their properties and potential impact on the environment and to humans. Additionally, there is the continual investment in multidisciplinary scientists to explore non-animal surrogate technologies to predict specific toxicological outcomes and to improve our understanding of the biological processes regarding the toxic potential of xenobiotics. Here we provide a concise, critical evaluation of a number of in vitro systems utilised to assess the hepatotoxic potential of xenobiotics.

Formation of a Sheet-Shaped Organoid Using Rat Primary Hepatocytes for Long-Term Maintenance of Liver-Specific Functions

In recent years, use of hepatocyte aggregates has led to development of a hybrid artificial liver support system (HALSS) that has high performance. However, in general, their thickness is 100 μm or more, and generation of a dead cell layer due to oxygen exhaustion inside the aggregates has been a universal problem. The present study proposes a novel organoid culture method with better performance than previous organoid culture methods by forming a sheet-shaped organoid (organoid-sheet) with a thickness of approximately 100 μm. The cell number of the organoid-sheet was maintained at approximately 75% of the initial number at 4 days of culture. On the other hand, that of a cylindrical organoid (cylindroid), which formed inside of a plasma separation hollow fiber with 285 μm inner diameter in our previous study, decreased to approximately 50% within 2 days. The ammonia removal rate of the cells in the organoid-sheet was higher than that of the cells in the cylindroid on the first day, but it decreased during the culture time. At day 15, the rate was reduced by almost 50% with respect to the value on the first day. The cells in the cylindroid displayed a lower ammonia removal rate. A significant difference was not observed between the albumin synthesis rates of the two cultures on the first day. However, over a period of time the cells in the organoid-sheet showed a higher albumin synthesis rate than cells in the cylindroid. As this novel organoid maintains these functions for at least 1 month, it is expected to be applied for the development of a HALSS with higher performance.

Monitoring cytochrome P450 activity in living hepatocytes by chromogenic substrates in response to drug treatment or during cell maturation

The metabolic activity of hepatocytes is a central prerequisite for drug activity and a key element in drug-drug interaction. This central role in metabolism largely depends on the activity of the cytochrome P450 (CYP450) enzyme family, which is not only dependent on liver cell maturation but is also controlled in response to drug and chemical exposure. Here, we report the use of VividDye fluorogenic CYP450 substrates to directly measure and continuously monitor metabolic activity in living hepatocytes. We observed time- and dose-dependent correlation in response to established and putative CYP450 inducers acting through the aryl hydrocarbon receptor and drug combinations. Using repetitive addition of VividDye fluorogenic substrate on a daily basis, we demonstrated the new application of VividDye for monitoring the maturation and dedifferentiation of hepatic cells. Despite a lack of high specificity for individual CYP450 isoenzymes, our approach enables continuous monitoring of metabolic activity in living cells with no need to disrupt cultivation. Our assay can be integrated in in vitro liver-mimetic models for on-line monitoring and thus should enhance the reliability of these tissue model systems.

Isolated Hepatocytes versus Hepatocyte Spheroids: In Vitro Culture of Rat Hepatocytes

The use of hepatocytes that express liver-specific functions to develop an artificial liver is promising. Unfortunately, the loss of specialized liver functions (dedifferentiation) is still a major problem. Different techniques, such as collagen entrapment, spherical multicellular aggregates (spheroids), and coculture of hepatocytes with extracellular matrix, have been used to improve the performance of hepatocytes in culture. The aim of this study was to compare two different models of hepatocyte isolation in culture: isolated hepatocytes (G1) and hepatocyte spheroids (60% hepatocytes, 40% nonparenchymal cells, and extracellular matrix) (G2). To test functional activity of hepatocytes, both synthetic and metabolic, production of albumin and benzodiazepine transformation into metabolites was tested. G2 showed a high albumin secretion, while a decrease after 15 days of culture in G1 was noted. Diazepam metabolites were higher in G2 than in G1 in all samples, but had statistical significance at days 14 and 21 (p < 0.01). The glycogen content, after 30 days of culture, was very low in G1 (14.2 ± 4.4%), while in G2 it was 72.1 ± 2.6% (p < 0.01). Our study confirms the effectiveness of a culture technique with extracellular matrix and nonparenchymal cells. Maintenance of a prolonged functional activity has been related to restoration of cell polarity and close cell-to-cell contact. We showed that isolated hepatocytes maintain their functional activity for a period significantly reduced, when compared to the hepatocyte spheroids. We confirmed the role of extracellular matrix as a crucial component to promote hepatocyte homeostasis, and the close link between cellular architecture and tissue-specific functions.

cDNA Microarray Analysis in Hepatocyte Differentiation in Huh 7 Cells

The risk of xenozoonosis infections poses the greatest obstacle against the clinical application of a hybrid artificial liver support system (HALSS). Primary human hepatocytes are an ideal source for HALSS, but the shortage of human livers available for hepatocyte isolation limits this modality. To resolve this issue, we previously demonstrated the upregulation of hepatocyte-specific function by spheroid formation in polyurethane foam and by culturing with the histone deacetylase inhibitor, trichostatin A (TSA), in a human hepatoma cell line (Huh 7). In this article we analyze the gene expression profile using cDNA microarray (1281 genes) in spheroid formation or culturing with TSA in Huh 7 to determine the target genes in hepatocyte differentiation. In both the spheroid formation and in the culture with TSA, the Oct-3/4 transcription factor was upregulated more than twofold, while the early growth response-1 (EGR-1) transactivator was downregulated less than 0.5-fold. These results indicate that expressions of Oct-3/4 and EGR-1 may be key factors in the induction of hepatocyte differentiation in Huh 7.

Integration of single-layer skin hollow fibers and scaffolds develops a three-dimensional hybrid bioreactor for bioartificial livers

Bioartificial liver support systems are expected to be an effective therapy as a "bridge" for liver transplantation or reversible acute liver disease. A major roadblock in the application of bioartificial livers is the need for a bioreactor that fully meets the requirements of hepatocyte culture, mass transfer and immunobarriers. In this study, we developed a three-dimensional hybrid bioreactor (3DHB) on a base of single-layer skin polyethersulfone hollow fibers by integrating with polyurethane scaffolds. The mass transfer of bilirubin and albumin from the intracapillary space to the extracapillary space of the hollow fibers was not significantly different between 3DHBs and hollow fiber bioreactors (HFBs). Cell viability staining showed that high-density hepatocytes were uniformly found in different regions of the 3DHB after 7 days of culture. Liver-specific functions of human mature hepatocytes cultured in the 3DHB, such as albumin secretion, urea production, ammonia removal rate and cytochrome P450 activity, were maintained stably and were significantly higher compared with the HFB. These results indicated that the 3DHB has good mass transfer and improves cell distribution and liver-specific functions. Meanwhile, the ammonia and unconjugated bilirubin concentrations in plasma from patients with liver failure were significantly decreased during 6 h of circulation by hepatocytes cultured in the 3DHB. Most hepatocytes in the 3DHB were viable after 6 h exposure to the patient plasma. We further demonstrated that bioartificial liver systems with 3DHB can remove toxins from and endure the deleterious effects of the patient plasma. Therefore, the 3DHB has the potential to accomplish different actions for the clinical application of bioartificial livers.

Recent advances in 2D and 3D in vitro systems using primary hepatocytes, alternative hepatocyte sources and non-parenchymal liver cells and their use in investigating mechanisms of hepatotoxicity, cell signaling and ADME

This review encompasses the most important advances in liver functions and hepatotoxicity and analyzes which mechanisms can be studied in vitro. In a complex architecture of nested, zonated lobules, the liver consists of approximately 80 % hepatocytes and 20 % non-parenchymal cells, the latter being involved in a secondary phase that may dramatically aggravate the initial damage. Hepatotoxicity, as well as hepatic metabolism, is controlled by a set of nuclear receptors (including PXR, CAR, HNF-4α, FXR, LXR, SHP, VDR and PPAR) and signaling pathways. When isolating liver cells, some pathways are activated, e.g., the RAS/MEK/ERK pathway, whereas others are silenced (e.g. HNF-4α), resulting in up- and downregulation of hundreds of genes. An understanding of these changes is crucial for a correct interpretation of in vitro data. The possibilities and limitations of the most useful liver in vitro systems are summarized, including three-dimensional culture techniques, co-cultures with non-parenchymal cells, hepatospheres, precision cut liver slices and the isolated perfused liver. Also discussed is how closely hepatoma, stem cell and iPS cell-derived hepatocyte-like-cells resemble real hepatocytes. Finally, a summary is given of the state of the art of liver in vitro and mathematical modeling systems that are currently used in the pharmaceutical industry with an emphasis on drug metabolism, prediction of clearance, drug interaction, transporter studies and hepatotoxicity. One key message is that despite our enthusiasm for in vitro systems, we must never lose sight of the in vivo situation. Although hepatocytes have been isolated for decades, the hunt for relevant alternative systems has only just begun.

An ex vivo perfusion system emulating in vivo conditions in noncirrhotic and cirrhotic human liver

Various models are used for investigating human liver diseases and testing new drugs. However, data generated in such models have only limited relevance for in vivo conditions in humans. We present here an ex vivo perfusion system using human liver samples that enables the characterization of parameters in a functionally intact tissue context. Resected samples of noncirrhotic liver (NC; n = 10) and cirrhotic liver (CL; n = 12) were perfused for 6-h periods. General and liver-specific parameters (glucose, lactate, oxygen, albumin, urea, and bile acids), liver enzymes (aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, glutamate dehydrogenase, and γ-glutamyl transferase), overall (M65) and apoptotic (M30) cell-death markers, and indicators of phase-I/phase-II biotransformations were analyzed. The measurement readings closely resembled (patho)physiological characteristics in patients with NC and CL. Mean courses of glucose levels reflected the CLs' reduced glycogen storage capability. Furthermore, CL samples exhibited significantly stronger increases in lactate, bile acids, and the M30/M65 ratio than NC specimens. Likewise, NC samples exhibited more rapid phase-I transformations of phenacetin, midazolam, and diclofenac and phase-I to phase-II turnover rates of the respective intermediates than CL tissue. Collectively, these findings reveal the better hepatic functionality in NC. Perfusion of human liver tissue with this system emulates in vivo conditions and clearly discriminates between noncirrhotic and cirrhotic tissue. This highly reliable device for investigating basic hepatic functionality and testing safety/toxicity, pharmacokinetics/pharmacodynamics and efficacies of novel therapeutic modalities promises to generate superior data compared with those obtained via existing economic perfusion systems.

Controlled formation of heterotypic hepatic micro-organoids in anisotropic hydrogel microfibers for long-term preservation of liver-specific functions

We have developed a hydrogel-based cell cultivation platform for forming 3D restiform hepatic micro-organoids consisting of primary rat hepatocytes and feeder cells (Swiss 3T3 cells). Sodium alginate solutions containing hepatocytes/3T3 cells were continuously introduced into a microfluidic channel to produce cell-incorporating anisotropic Ba-alginate hydrogel microfibers, where hepatocytes at the center were closely sandwiched by 3T3 cells. Hydrogel fiber-based cultivation under high oxygen tension enabled the formation of heterotypic micro-organoids with a length of up to 1 mm and a diameter of ∼50 μm, mimicking the hepatic cord structures found in the liver, while maintaining a high hepatocyte viability (∼80%) over 30 days. Long-term observation of up to 90 days revealed a significant enhancement of hepatic functions because of heterotypic and homotypic cell-cell interactions, including albumin secretion and urea synthesis as well as expression of hepatocyte-specific genes, compared with conventional monolayer culture and single cultivation in the hydrogel fibers. The encapsulated hepatic constructs were recovered as scaffold-free micro-organoids by enzymatically digesting the hydrogel matrices using alginate lyase. This technique for creating heterotypic micro-organoids with precisely ordered multiple cell types will be useful for the development of a new liver tissue engineering approach and may be applicable to the fabrication of extracorporeal bioartificial liver (BAL) devices and assessment tools for drug development and testing.

Cytocentrifugation: a convenient and efficient method for seeding tendon-derived cells into monolayer cultures or 3-D tissue engineering scaffolds

Tendon and ligament injuries are very common, requiring some 200,000 reconstructions per year in the USA. Autografting can be used to repair these but donor tissue is limited and harvesting leads to morbidity at the graft sites. Tissue engineering has been used to grow simple tissues such as skin, cartilage and bone and due to their low vascularity and simple structure, tendons should be ideal candidates for such an approach. Scaffolds are essential for tissue engineering as they provide structure and signals that regulate growth. However, they present a physical barrier to cell seeding with the majority of the cells congregating at the scaffold surface. To address this we used centrifugation to enhance penetration of tendon-derived cells to the centres of 3-D scaffolds. The process had no apparent deleterious effects on the cells and both plating efficiency and cell distribution improved. After attachment the cells continued to proliferate and deposit a collagenous matrix. Scaffold penetration was investigated using layers of Azowipes allowing the separation and examination of individual leaves. At relatively low g-forces, cells penetrated a stack of 6 Azowipes leaving cells attached to each leaf. These data suggest that cytocentrifugation improves the penetration and homogeneity of tendon derived cells in 3-D and monolayer cultures.

Hemoglobin regulates the metabolic, synthetic, detoxification, and biotransformation functions of hepatoma cells cultured in a hollow fiber bioreactor

Hepatic hollow fiber (HF) bioreactors constitute one type of extracorporeal bioartificial liver assist device (BLAD). Ideally, cultured hepatocytes in a BLAD should closely mimic the in vivo oxygenation environment of the liver sinusoid to yield a device with optimal performance. However, most BLADs, including hepatic HF bioreactors, suffer from O2 limited transport toward cultured hepatocytes, which reduces their performance. We hypothesize that supplementation of hemoglobin-based O2 carriers into the circulating cell culture medium of hepatic HF bioreactors is a feasible and effective strategy to improve bioreactor oxygenation and performance. We examined the effect of bovine hemoglobin (BvHb) supplementation (15g/L) in the circulating cell culture medium of hepatic HF bioreactors on hepatocyte proliferation, metabolism, and varied liver functions, including biosynthesis, detoxification, and biotransformation. It was observed that BvHb supplementation supported the maintenance of a higher cell mass in the extracapillary space, improved hepatocyte metabolic efficiency (i.e., hepatocytes consumed much less glucose), improved hepatocyte capacity for drug metabolism, and conserved both albumin synthesis and ammonia detoxification functions compared to controls (no BvHb supplementation) under the same experimental conditions.

Effect of a hepatocyte growth factor/heparin-immobilized collagen system on albumin synthesis and spheroid formation by hepatocytes

A hepatocyte growth factor (HGF)/heparin-immobilized collagen system was used as a synthetic extracellular matrix for hepatocyte culture. The albumin synthesis, nucleus numbers and morphology of the hepatocytes were determined separately to evaluate the hepatocyte number and hepatocyte-specific function under this system. The benefits of the HGF/heparin-immobilized collagen system for hepatocyte culture were confirmed by three types of culture methods in vitro, namely 2D film cultures, 2D gel cultures and 3D gel cultures. In 2D collagen film cultures, hepatocytes exhibited the highest albumin synthesis (1.42 microg/well/day) in HGF/heparin-immobilized collagen films at 7 days of culture. Heparin inhibited hepatocyte adhesion while HGF promoted hepatocyte migration, and spheroid formation was easily detected in HGF/heparin-immobilized collagen films. In 2D collagen gel cultures, albumin synthesis of around 15 microg/well/day was detected and maintained for more than 18 days on HGF/heparin-immobilized collagen gels. Similar findings were obtained in 3D HGF/heparin-immobilized collagen gel cultures, which exhibited albumin synthesis of up to 30 microg/well/day. The albumin synthesis by hepatocytes was two-fold higher in 3D gel cultures compared with 2D gel cultures, and was maintained for over 2 weeks compared with 2D film cultures using the HGF/heparin-immobilized collagen system. Taken together, the HGF/heparin-immobilized collagen system was effective for albumin synthesis by hepatocytes in both 2D film cultures and 3D gel cultures, and therefore shows good potential for tissue engineering use.

Strain-dependent viral dynamics and virus-cell interactions in a novel in vitro system supporting the life cycle of blood-borne hepatitis C virus

We developed an in vitro system that can be used for the study of the life cycle of a wide variety of blood-borne hepatitis C viruses (HCV) from various patients using a three-dimensional hollow fiber culture system and an immortalized primary human hepatocyte (HuS-E/2) cell line. Unlike the conventional two-dimensional culture, this system not only enhanced the infectivity of blood-borne HCV but also supported its long-term proliferation and the production of infectious virus particles. Both sucrose gradient fractionation and electron microscopy examination showed that the produced virus-like particles are within a similar fraction and size range to those previously reported. Infection with different HCV strains showed strain-dependent different patterns of HCV proliferation and particle production. Fluctuation of virus proliferation and particle production was found during prolonged culture and was found to be associated with change in the major replicating virus strain. Induction of cellular apoptosis was only found when strains of HCV-2a genotype were used for infection. Interferon-alpha stimulation also varied among different strains of HCV-1b genotypes tested in this study.

CONCLUSION

These results suggest that this in vitro infection system can reproduce strain-dependent events reflecting viral dynamics and virus-cell interactions at the early phase of blood-borne HCV infection, and that this system can allow the development of new anti-HCV strategies specific to various HCV strains.

Evaluation of a bioreactor with stacked sheet shaped organoids of primary hepatocytes

Hepatocyte organoids have an in vivo-like cell morphology and maintain cell viability and function in vitro. On the other hand, the oxygen supply to hepatocytes is sometimes limited in the core of organoids that are more than 100 mum in thickness. In this study, we designed and examined a new bioreactor using sheet-shaped organoids (organoid-sheets) in which the thickness was controlled to prevent hepatocyte death in the core of organoid due to limitation of oxygen supply. The cell culture space consisted of stacked organoid formation spaces and medium flow channels. Each space was separated by flat porous polycarbonate membranes, and the organoid thickness was controlled at 100 microm with a stainless steel spacer. Freshly isolated hepatocytes (7.0 x 10(7)) were immobilized in the bioreactor, yielding a cell density of 4.5 x 10(7) cells/cm(3)-bioreactor. Of the five flow rates tested (1.0, 5.0, 10, 20, and 50 mL/min), the bioreactor with the 10 mL/min had the highest ammonia removal and albumin secretion activities for at least 14 days. In conclusion, a new bioreactor controlling organoid thickness is useful for achieving high cell density culture and the maintenance of hepatocyte function to avoid cell death in the core of the organoids due to limitation of oxygen supply. The bioreactor may be useful for the development of various applications using cultured hepatocytes.

A new culture technique for hepatocyte organoid formation and long-term maintenance of liver-specific functions

To develop a useful hybrid artificial liver, it is important to use cultured hepatocytes that maintain liver-specific functions for a long time. These requirements were achieved recently by the use of a hepatocyte multicellular aggregate (organoid) with a tissue-like structure. In this study, we developed a three-dimensional culture of hepatocytes that formed an organoid. Primary rat hepatocytes were immobilized inside hollow fibers (for plasma separation) by centrifugation. Hepatocytes formed a cylindrical organoid (cylindroid) of 200 mum in diameter by day 2 of culture. We used two types of culture media, medium A (Williams' medium E containing insulin and epidermal growth factor) and medium B (Dulbecco's modified Eagle's medium containing insulin, epidermal growth factor, and hydrocortisone). In medium A, the hepatocyte cylindroid diminished after 14 days of culture and liver-specific functions of the hepatocyte cylindroid nearly disappeared after 1 month of culture. In contrast, hepatocyte cylindroid cultured in medium B maintained its morphology and liver-specific functions for 2-5 months. These results indicate that a combination of the new culture technique and suitable culture medium is effective for expression and maintenance of liver-specific functions of hepatocytes. This culture technique will be helpful in the development of a hybrid artificial liver.

Convection and hemoglobin-based oxygen carrier enhanced oxygen transport in a hepatic hollow fiber bioreactor

Hepatic hollow fiber bioreactors are a promising class of bioartificial liver assist device (BLAD). The development of this type of device is currently hindered by limited oxygen transport to cultured hepatocytes, due to low solubility of oxygen in aqueous media. In order to increase the oxygen spectrum to cultured hepatocytes housed within a hollow fiber bioreactor, several different engineering strategies were explored in this study. These included: supplementing the circulating media stream of the hollow fiber bioreactor with a hemoglobin-based oxygen carrier (bovine red blood cells) with defined oxygen binding and release kinetics and operating the bioreactor with media flow through the hollow fiber membrane into the extracapillary space (ECS). We hypothesize that these two strategies can be used to improve hepatocyte oxygenation and possibly attain an in vivo-like pO(2) spectrum, similar to that observed in vivo in the liver sinusoid. This work is significant, since provision of an in vivo-like pO(2) spectrum should create a fully functional BLAD that could potentially bridge thousands of liver failure patients towards native liver regeneration of damaged tissue or, if necessary, orthotopic liver transplantation.

Bioartificial liver systems: why, what, whither?

Acute liver disease is a life-threatening condition for which liver transplantation is the only recognized effective therapy. While etiology varies considerably, the clinical course of acute liver failure is common among the etiologies: encephalopathy progressing toward coma and multiple organ failure. Detoxification processes, such as molecular adsorbent recirculating system (MARS®) and Prometheus, have had limited success in altering blood chemistries positively in clinical evaluations, but have not been shown to be clinically effective with regard to patient survival or other clinical outcomes in any Phase III prospective, randomized trial. Bioartificial liver systems, which use liver cells (hepatocytes) to provide metabolic support as well as detoxification, have shown promising results in early clinical evaluations, but again have not demonstrated clinical significance in any Phase III prospective, randomized trial. Cell transplantation therapy has had limited success but is not practicable for wide use owing to a lack of cells (whole-organ transplantation has priority). New approaches in regenerative medicine for treatment of liver disease need to be directed toward providing a functional cell source, expandable in large quantities, for use in various applications. To this end, a novel bioreactor design is described that closely mimics the native liver cell environment and is easily scaled from microscopic (<1 ml cells) to clinical (∼600 ml cells) size, while maintaining the same local cell environment throughout the bioreactor. The bioreactor is used for study of primary liver cell isolates, liver-derived cell lines and stem/progenitor cells.

Hepatic differentiation of embryonic stem cells in HF/organoid culture

OBJECTIVE

The use of embryonic stem cells (ES cells) has recently received much attention as a novel cell source for various hybrid artificial organs. To use ES cells, it is necessary to be able to produce functional mature cells from ES cells in large quantities. We applied HF/organoid culture, where cultured cells formed cylindrical multicellular aggregates (organoids) in the lumen of hollow fibers, to mouse and cynomolgus monkey ES cells for hepatic differentiation.

MATERIALS AND METHODS

ES cells were injected into hollow fibers. The hollow fibers were centrifuged to induce organoid formation and cultured in medium including factors for hepatic differentiation. To determine the characteristics of cells in the bundle, we evaluated gene expression and liver-specific functions.

RESULTS

ES cells immobilized inside hollow fibers proliferated and formed cylindrical organoids. In mouse ES cell cultures, the expression of mRNAs of hepatocyte-specific genes increased with culture time. Ammonia removal activity detected at 15 days increased with culture time. Albumin secretion activity detected at 12 days increased by 21 days. In cynomolgus monkey ES cell cultures, ES cells showed spontaneous ammonia removal functions. The maximum levels of these functions per unit volume of the hollow fibers were roughly comparable to those of primary hepatocyte-organoids.

CONCLUSIONS

ES cells differentiated into hepatocyte-like cells using the organoid culture technique. The results indicated that the combination of ES cells and an organoid culture technique was useful to obtain mature hepatocytes.

Evaluation of a hybrid artificial liver module with liver lobule-like structure in rats with liver failure

We studied the recovery of rats with fulminant hepatic failure (FHF) by treating them with our original hybrid artificial liver support system (HALSS). We developed an original artificial liver module having a liver lobule-like structure (LLS). This module consists of many hollow fibers regularly arranged in close proximity and hepatocyte aggregates (organoids) induced into the extra capillary space of the module by centrifugal force. The LLS module can express some liver specific functions at high levels and maintain them for several months in vitro. In this study, we evaluated the efficacy of our LLS-HALSS by using rats with FHF induced by a method that combined partial hepatectomy with hepatic ischemia. In the animal experiments, blood ammonia levels rapidly increased in the control group (sham-HALSS group). These rats died during or immediately after application of the sham-HALLS. On the other hand, in the LLS module application group (LLS-control group), the increase in blood ammonia was completely suppressed and all rats recovered. Blood constituents at 4 weeks after application were at normal levels, and the weight of the liver was the same as that of a normal rat. These results indicate that HALSS may be useful for treating liver failure patients until liver transplantation can be performed or until regeneration of the native liver occurs.

Mass transfer and metabolic reactions in hepatocyte spheroids cultured in rotating wall gas-permeable membrane system

Isolated hepatocytes in spheroid configuration exhibit a high degree of cell-cell contacts, which are important in the maintenance of viability and liver specific functions. In the absence of a vascular network, the cells in a large spheroid size experience mass transfer limitations of metabolites and oxygen in the core of aggregates. In this paper transport phenomena related to the diffusion and reaction of oxygen, glucose and lactate are mathematically described and experimentally verified for hepatocyte spheroids cultured in a rotating-wall polystyrene system (RWPS) not permeable for gases and in a rotating-wall membrane system (RWMS) with oxygen-permeable membrane. The concentration profiles of glucose, oxygen and lactate in the hepatocyte spheroids were estimated for different diameters of aggregates by solving the mass transfer equations for simultaneous diffusion and reaction, by finite element method. Simulation results evidenced that, for aggregates with size lower than 300 microm cultured in both RWPS and RWMS systems, the concentration profiles of glucose and lactate towards the core of spheroids (effective diffusion coefficients in the order of 10(-11)m(2)/s) are not significantly affected by the metabolic rate (c.a 10(-6)microg/mm(3)/s for glucose and about one order of magnitude less for lactate). On the contrary, the transport of oxygen (diffusion coefficient: 3.4 x 10(-10)m(2)/s, reaction rate: 1.5 x 10(-5)microg/mm(3)/s) is critically affected by the size of the multicellular spheroids and significant gradients in oxygen concentration may develop in spheroids. Aggregates with a size greater than 200 microm suffer severe oxygen limitation in the most part of its size attaining the lowest partial pressure in the centre. The improved viability predicted by the model culturing hepatocyte spheroids in the RWMS, characterized by a higher O(2) permeability with respect to RWPS, was experimentally confirmed. The results demonstrated that the mathematical model used in this study represents a useful support to experimental procedures in order to obtain hepatocyte spheroids with optimal size.

Three-dimensional numerical modeling and computational fluid dynamics simulations to analyze and improve oxygen availability in the AMC bioartificial liver

A numerical model to investigate fluid flow and oxygen (O(2)) transport and consumption in the AMC-Bioartificial Liver (AMC-BAL) was developed and applied to two representative micro models of the AMC-BAL with two different gas capillary patterns, each combined with two proposed hepatocyte distributions. Parameter studies were performed on each configuration to gain insight in fluid flow, shear stress distribution and oxygen availability in the AMC-BAL. We assessed the function of the internal oxygenator, the effect of changes in hepatocyte oxygen consumption parameters in time and the effect of the change from an experimental to a clinical setting. In addition, different methodologies were studied to improve cellular oxygen availability, i.e. external oxygenation of culture medium, culture medium flow rate, culture gas oxygen content (pO(2)) and the number of oxygenation capillaries. Standard operating conditions did not adequately provide all hepatocytes in the AMC-BAL with sufficient oxygen to maintain O(2) consumption at minimally 90% of maximal uptake rate. Cellular oxygen availability was optimized by increasing the number of gas capillaries and pO(2) of the oxygenation gas by a factor two. Pressure drop over the AMC-BAL and maximal shear stresses were low and not considered to be harmful. This information can be used to increase cellular efficiency and may ultimately lead to a more productive AMC-BAL.

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.

3D tissue culture substrates produced by microthermoforming of pre-processed polymer films

We describe a new technology based on thermoforming as a microfabrication process. It significantly enhances the tailoring of polymers for three dimensional tissue engineering purposes since for the first time highly resolved surface and bulk modifications prior to a microstructuring process can be realised. In contrast to typical micro moulding techniques, the melting phase is avoided and thus allows the forming of pre-processed polymer films. The polymer is formed in a thermoelastic state without loss of material coherence. Therefore, previously generated modifications can be preserved. To prove the feasibility of our newly developed technique, so called SMART = Substrate Modification And Replication by Thermoforming, polymer films treated by various polymer modification methods, like UV-based patterned films, and films modified by the bombardment with energetic heavy ions, were post-processed by microthermoforming. The preservation of locally applied specific surface and bulk features was demonstrated e.g. by the selective adhesion of cells to patterned microcavity walls.

Galactose-carrying polymers as extracellular matrices for liver tissue engineering

Extracellular matrix (ECM) plays important roles in tissue engineering because cellular growth and differentiation, in the two-dimensional cell culture as well as in the three-dimensional space of the developing organism, require ECM with which the cells can interact. Especially, the bioartificial liver-assist device or regeneration of the liver-tissue substitutes for liver tissue engineering requires a suitable ECM for hepatocyte culture because hepatocytes are anchorage-dependent cells and are highly sensitive to the ECM milieu for the maintenance of their viability and differentiated functions. Galactose-carrying synthetic ECMs derived from synthetic polymers and natural polymers bind hepatocytes through a receptor-mediated mechanism, resulting in enhanced hepatocyte functions. Attachment and functions of hepatocytes were affected by physico-chemical properties including ECM geometry as well as the type, density and orientation of galactose. Also, cellular environment, medium composition and dynamic culture system influenced liver-specific functions of hepatocytes beside ECM.

Novel hepatocyte culture system developed using microfabrication and collagen/polyethylene glycol microcontact printing

The better understanding of cell biology and cell communication requires novel culture systems that better represent the natural cell environment in tissues and organs. We developed a spherical organoid (spheroid) microarray culture system using a combination of microfabrication and microcontact printing. The system consisted of a chip that had cylindrical cavities of 300 microm diameter at a density of 700 cavities/cm2. The bottom faces of these cavities were defined as two different regions that either supported or inhibited cell adhesion. In the cell adhesion region, the center of the bottom face of a 100 microm diameter in a cavity was modified with collagen (Col), and in the non-adhesion region, the entire region around the cavity, except the Col spots, was modified with polyethylene glycol. Primary hepatocytes spontaneously formed spheroids with a uniform diameter at the center of each cavity on the chip. Hepatocytes forming spheroids had a cuboidal cell shape, similar to hepatocytes in vivo, and stably maintained liver-specific phenotypes, such as liver-enriched transcriptional factors, albumin secretion, urea cycle enzymes, and intercellular adhesion molecules. This novel culture system may be applicable as a cellular platform for fundamental studies in cell biology and tissue engineering applications.

Hepatocyte organoid culture in elliptic hollow fibers to develop a hybrid artificial liver

A novel organoid culture was developed in which hepatocytes maintain high liver functions for more than several weeks in vitro. The main disadvantage of tissue-engineered organoids is the lack of a blood vessel structure between the aggregated cells. Because of depletion of oxygen, the thickness from the surface of an organoid at which hepatocytes can survive is limited. This study showed that a rat hepatocyte organoid that forms by using centrifugal force in a hollow fiber (HF) had a survival limit thickness of about 80 - 100 microm from the surface of the organoid. Based on the value, we designed an elliptic HF having less than 150 microm minor diameter by using a simple annealing method. All hepatocytes were supplied with oxygen and formed an organoid without a dead cell layer in this HF A hepatocyte organoid in an elliptic HF maintained ammonia removal activity twice as high as in the original HF for at least one month during culture. Albumin secretion activity of an organoid in an elliptic HF was also maintained for at least one month and was the same level as that of liver in a living body. In conclusion, organoid culture by using an elliptic HF seems to be a promising technique to develop a hybrid artificial liver.

Influence of pancreatic islets on spheroid formation and functions of hepatocytes in hepatocyte-pancreatic islet spheroid culture

Hepatotrophic stimulation of hepatocytes is necessary to preserve long-term function of hepatocytes in hepatocyte transplantation and bioartificial liver system. The main source of hepatotrophic factors in portal venous blood seems to be the pancreatic islets. It was also reported that hepatocyte spheroids, tightly packed multicellular aggregates, showed enhanced liver-specific activities and a prolonged differentiated state compared with cells that were maintained as a monolayer. On the basis of these two facts, the authors tried to form hepatocyte-pancreatic islet spheroids and to evaluate the influence of pancreatic islets on spheroid formation and functions of hepatocytes in spheroid culture. Hepatocytes and pancreatic islet cells were harvested from adult male Sprague-Dawley rats weighing 200-250 g. Hepatocytes were cultured in spinner flasks with either basic nonstimulated medium (hepatocytes only [group BH] and cocultures with islet cells [group BI]) or hormone-stimulated medium (hepatocytes only [group HH] and cocultures with islet cells [group HI]). The size and morphology of spheroids, as determined by phase-contrast microscopy, and liver-specific functions, such as albumin secretion, urea synthesis, and ammonia removal, were compared among groups. The results were as follows: the size of spheroids, 66 +/- 53.4 microm, in group BH on day 2 was smaller than in group BI (179 +/- 66.2 microm on day 2, p < 0.05). In group BI, group HH, and group HI, smooth spheroids were observed on culture day 2. However, in group BH rugged incomplete aggregates were observed on the same day. In groups with basal medium, group BI showed better results in terms of hepatocyte-specific function such as albumin secretion, urea synthesis, and ammonia removal compared with group BH on days 2 and 3 (p < 0.05). In groups with hormone-defined medium, cocultures had no impact on albumin secretion rate, urea synthetic rate, and ammonia removal rate. In conclusion, we made a new type of hepatocyte-pancreatic islet spheroid, using a rotational culture method. Pancreatic islets in a spheroid culture system stimulated hepatocyte spheroid formation and some hepatocyte-specific functions in vitro.