Formation of porcine hepatocyte spherical multicellular aggregates (spheroids) and analysis of drug metabolic functions

In vivo-like 3-D model for sodium nitrite- and acrylamide-induced hepatotoxicity tests utilizing HepG2 cells entrapped in micro-hollow fibers

To address the need for a high throughput toxicity test in the modern food industry, an in vivo-like 3-D cell model was constructed in this study to provide an alternative to controversial long-term animal models and to improve the sensitivity and accuracy of the traditional monolayer model. The model formed cell cylindroids within polyvinylidene fluoride (PVDF) hollow fibers and therefore mimicked the microenvironment of liver tissue. Microscopy methods were used, and liver-specific functions were measured to demonstrate the superiority of the model compared to the monolayer model, as well as to optimize the model for best cell performances. Later, toxicity tests of sodium nitrite and acrylamide were conducted in both the 3-D model and the monolayer model to study the sensitivity of the 3-D model in toxicity responses. As expected, HepG2 cells within the 3-D model responded at lower concentrations and shorter exposure times compared to cells within the monolayer model. Furthermore, western blot analysis of apoptosis pathways also supported the argument.

High Metabolic Function of Primary Human and Porcine Hepatocytes in a Polyurethane Foam/Spheroid Culture System in Plasma from Patients with Fulminant Hepatic Failure

It has been demonstrated that plasma from patients with fulminant hepatic failure (FHF) interferes extensively with cellular function. We placed primary human and primary porcine hepatocytes in a polyurethane foam (PUF)/spheroid culture system and compared the metabolic functions in the plasma of patients with FHF in a 24-h stationary culture to those in a monolayer culture. The PUF/spheroid culture system using primary human and primary porcine hepatocytes significantly decreased ammonia content during 28-day culture. Fisher's ratio significantly increased at culture days 3 and 7. Tauroursodeoxycholic acid significantly increased and glycochenodeoxycholic acid and taurochenodeoxycholic acid decreased in the FHF patients' plasma at culture day 3. During at least a 24-h culture in the FHF patients' plasma, metabolic functions of primary human and primary porcine hepatocytes were almost identical. The present results indicate that the PUF/spheroid culture system using primary human or primary porcine hepatocytes demonstrated more advantageous metabolic functions in the plasma from patients with FHF than the monolayer culture.

Morphological and Functional Analysis of Hepatocyte Spheroids Generated on Poly-HEMA-Treated Surfaces under the Influence of Fetal Calf Serum and Nonparenchymal Cells

Poly (2-hydroxyethyl methacrylate) (HEMA) has been used as a clinical material, in the form of a soft hydrogel, for various surgical procedures, including endovascular surgery of liver. It is a clear liquid compound and, as a soft, flexible, water-absorbing material, has been used to make soft contact lenses from small, concave, spinning molds. Primary rat hepatocyte spheroids were created on a poly-HEMA-coated surface with the intention of inducing hepatic tissue formation and improving liver functions. We investigated spheroid formation of primary adult rat hepatocyte cells and characterized hepatic-specific functions under the special influence of fetal calf serum (FCS) and nonparencymal cells (NPC) up to six days in different culture systems (e.g., hepatocytes + FCS, hepatocytes – FCS, NPC + FCS, NPC – FCS, co-culture + FCS, co-culture – FCS) in both the spheroid model and sandwich model. Immunohistologically, we detected gap junctions, Ito cell/Kupffer cells, sinusoidal endothelial cells and an extracellular matrix in the spheroid model. FCS has no positive effect in the sandwich model, but has a negative effect in the spheroid model on albumin production, and no influence in urea production in either model. We found more cell viability in smaller diameter spheroids than larger ones by using the apoptosis test. Furthermore, there is no positive influence of the serum or NPC on spheroid formation, suggesting that it may only depend on the physical condition of the culture system. Since the sandwich culture has been considered a “gold standard” in vitro culture model, the hepatocyte spheroids generated on the poly-HEMA-coated surface were compared with those in the sandwich model. Major liver-specific functions, such as albumin secretion and urea synthesis, were evaluated in both the spheroid and sandwich model. The synthesis performance in the spheroid compared to the sandwich culture increases approximately by a factor of 1.5. Disintegration of plasma membranes in both models was measured by lactate dehydrogenase (LDH) release in both models. Additionally, diazepam was used as a substrate in drug metabolism studies to characterize the differences in the biotransformation potential with metabolite profiles in both models. It showed that the diazepam metabolism activities in the spheroid model is about 10-fold lower than the sandwich model. The poly-HEMA-based hepatocyte spheroid is a promising new platform towards hepatic tissue engineering leading to in vitro hepatic tissue formation.

Tethered spheroids as an in vitro hepatocyte model for drug safety screening

Hepatocyte spheroids mimic many in vivo liver-tissue phenotypes but increase in size during extended culture which limits their application in drug testing applications. We have developed an improved hepatocyte 3D spheroid model, namely tethered spheroids, on RGD and galactose-conjugated membranes using an optimized hybrid ratio of the two bioactive ligands. Cells in the spheroid configuration maintained 3D morphology and uncompromised differentiated hepatocyte functions (urea and albumin production), while the spheroid bottom was firmly tethered to the substratum maintaining the spheroid size in multi-well plates. The oblate shape of the tethered spheroids, with an average height of 32 μm, ensured efficient nutrient, oxygen and drug access to all the cells within the spheroid structure. Cytochrome P450 induction by prototypical inducers was demonstrated in the tethered spheroids and was comparable or better than that observed with hepatocyte sandwich cultures. These data suggested that tethered 3D hepatocyte spheroids may be an excellent alternative to 2D hepatocyte culture models for drug safety applications.

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.

Formation and characterization of three dimensional human hepatocyte cell line spheroids on chitosan matrix for in vitro tissue engineering applications

Chitosan was used as a matrix to induce three-dimensional spheroids of HepG2 cells. Chitosan films were prepared and used for culturing Hep G2 cells. Attachment kinetics of the cells was studied on the chitosan films. The optimum seeding density of the Hep G2 cells, required for three-dimensional spheroid formation was determined and was found to be 5 x 10(4)/ml. The growth kinetics of Hep G2 cells was studied using (3-(4, 5-Dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide) (MTT) assay, and morphology of the cells was studied through optical photographs taken at various days of culture. The liver cell functions of the spheroids were determined by measuring albumin and urea secretions. The results obtained from these studies have shown that the culture of Hep G2 cells on chitosan matrix taking appropriate seeding density resulted in the formation of three-dimensional spheroids and exhibited higher amount of albumin and urea synthesis compared to monolayer culture. These miniature "liver tissue like" models can be used for in vitro tissue engineering applications like preliminary evaluation of the toxicity of drugs and chemicals.

Efficacy of a larger version of the hybrid artificial liver support system using a polyurethane foam/spheroid packed-bed module in a warm ischemic liver failure pig model for preclinical experiments

We have reported the usefulness of a polyurethane foam packed-bed culture system of hepatocyte spheroids as a hybrid artificial liver support system (PUF-HALSS). The aim of this study was to evaluate in detail the efficacy in serum parameters regarding the liver function of a larger version of the PUF-HALSS containing 2 x 10(10) porcine hepatocytes for clinical use in warm ischemic liver failure pigs. Warm ischemic liver failure pigs weighing 25 kg were divided into two groups: (1) a control group (n = 3), in which each pig was attached to a PUF-HALSS without hepatocytes, and (2) a HALSS group (n = 3), in which each pig was attached to a PUF-HALSS. In the HALSS group, the increase of blood ammonia was completely suppressed and blood lactate levels were significantly suppressed. The Fisher's ratio was better maintained, and the increase of total bile acid, glycochenodeoxycholic acid, and taurochenodeoxycholic acid was significantly suppressed in the HALSS group. Serum creatinine levels were significantly lower, and blood glucose levels were significantly higher in the HALSS group. Serum levels of tumor necrosis factor- a were not elevated in either group. In conclusion, the larger version of the PUF-HALSS demonstrated many advantages as a liver support system in warm ischemic liver failure pigs.

Liver Regeneration Using a Hybrid Artificial Liver Support System

We have developed two types of hybrid artificial liver support system (HALSS) that use hepatocyte organoid culture: (1) a PUF-HALSS comprising an artificial liver module using polyurethane foam (PUF), in which hepatocytes form spheroids in its pores, and maintained liver-specific functions for at least ten days in vitro; (2) an LLS-HALSS that uses a liver lobule-like structure (LLS) module containing hollow fibers with a microregular arrangement in which hepatocytes in the extra-fiber space of the module form the organoids by centrifugation that maintain liver-specific functions for at least two months in vitro. In preclinical experiments, a PUF-HALSS was applied to a pig having liver failure. To evaluate the effect of liver regeneration, a PUF- and an LLS-HALSS were applied to a rat having reversible hepatic failure. Each HALSS was effective in supporting liver function, stabilization of general conditions and recovery from liver failure state. These results indicate that these HALSS may be useful to treat liver failure patients until liver transplantation or until regeneration of the native liver.

Efficacy of a polyurethane foam/spheroid artificial liver by using human hepatoblastoma cell line (Hep G2)

We invesigated the availability of human hepatoblastoma cell line (Hep G2), compared with human primary hepatocytes (HH) and porcine primary hepatocytes (PH), as a cell source for the hybrid artificial liver support system (HALSS) by using polyurethane foam (PUF). All three kinds of hepatocytes spontaneously formed spherical multicellular aggregates (spheroids) of 100-200 microm diameter in the pores of PUF within 3 days of culture. In a PUF stationary culture, Hep G2 spheroids recovered the ammonia removal activity that was lost in monolayer culture, although the removal for each unit cell number was about one tenth that of HH spheroids and about one eighth of PH spheroids. The synthesis activities of albumin and fibrinogen of each unit cell number of Hep G2 were also upregulated by PUF spheroid culture, and were about twice as high as in monolayer culture. The albumin secretion activity of Hep G2 spheroids was almost the same as that of PH spheroids. HH scarcely secreted these proteins in this experiment, probably because they were cultured in a serum-free medium. In the PUF module in a circulation culture, HH had high ammonia removal and low synthesis activities similar to stationary culture. Hep G2 proliferated to a high cell density, such as about 4.8 x 10(7) cells/cm3-module at 10 days of culture. Although Hep G2 spheroids had low ammonia removal activity in each cell, the removal rate in the PUF module was almost the same as for PH at 7 days of culture because of the high cell density culture by cell proliferation. The albumin secretion rate by Hep G2 in the PUF module also increased with cell proliferation and was about 10 times higher than the initial for the rate for PH at 7 days of culture. These results suggest that Hep G2 is a potential cell source PUF-HALSS.

Characterisation of some cytotoxic endpoints using rat liver and HepG2 spheroids as in vitro models and their application in hepatotoxicity studies. I. Glucose metabolism and enzyme release as cytotoxic markers

Cytotoxicity endpoints, spontaneous glucose secretion/consumption and LDH and gamma-GT release, were characterised in rat liver and HepG2 spheroids as in vitro models for toxicology studies. Preprepared rat liver spheroids and HepG2 spheroids cultured in a six-well plate format were exposed to varying concentrations of galactosamine, propranolol, diclofenac, and paracetamol. All four model toxins significantly affected glucose secretion, which agreed well with LDH and/or gamma-GT release in rat liver spheroids. These toxins also significantly increased LDH and/or gamma-GT release in HepG2 spheroids. Whereas glucose consumption in HepG2 spheroids did not show conclusive results, LDH activities in both types of spheroids were similar and their levels were relatively high. Accordingly, the level of LDH leakage in both types of spheroids was much higher than gamma-GT after exposure to the toxins. In contrast, gamma-GT activity in HepG2 spheroids was sixfold higher than that in rat liver spheroids. This study revealed that galactosamine interfered with the gamma-GT assay and paracetamol interfered with the LDH assay. It demonstrated, for the first time, that glucose secretion by liver spheroids can be used as a functional indicator of cytotoxicity. Test compounds may interfere with enzymatic assays as indicated by LDH and gamma-GT release in this study. Combining functional parameters together with two or more indicators of enzyme releases can provide a reliable cytotoxicity evaluation. Liver and HepG2 spheroids as in vitro models showed good predictions in chemical-induced hepatic cytotoxicity.

Hybrid-artificial liver support system

We originally developed a multi-capillary polyurethane foam packed-bed module as a hybrid-artificial liver support system (HALSS) and have applied for the permission of the clinical application to our institutional ethical committee. We summarized here the history, recent obstacles in clinical applications, and future prospects of HALSS, including our own.

Development of a hybrid artificial liver using polyurethane foam/hepatocyte spheroid culture in a preclinical pig experiment

We describe a preclinical study of our original hybrid artificial liver support system (HALSS) for a clinical trial. We designed a HALSS comprising a multi-capillary polyurethane foam packed-bed module (MC-PUF module) containing a total 200 g (2 x 10(10) cells) porcine hepatocytes, and an extracorporeal circulation device. Almost all porcine hepatocytes in the MC-PUF module formed many spherical multicellular aggregates (spheroids). This extracorporeal circulation device was improved to promote solute exchange between a living body and a MC-PUF module by including a plasma bypass line in the circulation loop. The efficacy of the HALSS was evaluated using a 25-kg pig with warm ischemic liver failure by portocaval shunt and ligation of hepatic artery (HALSS group, n=3). As a control experiment, the same system without hepatocytes in the module was used with the same kind of liver failure pig (Control group, n=3). The blood ammonia in the control group was 143 N-microg/dl at the start of circulation, and rapidly increased to 351 N-microg/dl at 2 hours and to 704 N-microg/dl at 6 hours. But the blood ammonia in the HALSS group was completely suppressed, and remained less than the hepatic coma level (over 200 N-microg/dl) during the circulation time. The blood glucose in the control group gradually decreased, and became less than 40 mg/dl within 6 hours of circulation. But the blood glucose in the HALSS group was maintained well, and remained the normal glucose level (50 - 105 mg/dl) for more than 20 hours of circulation. Improvement in blood creatinine and lactate, and the stabilization of vital signs and urinary excretion, were observed in the HALSS group. The survival time of the pigs in the HALSS group was 19.3 hours compared with 8.9 hours in the control group. In conclusion, our HALSS was effective to stabilize the general conditions of the body in addition to supporting various liver functions. These results suggest that our HALSS has a strong possibility to be used in treating liver failure patients. We have applied for approval of the clinical trial of our HALSS to our institutional ethics committee.

Hybrid artificial liver using hepatocyte organoid culture

We developed 2 types of hybrid artificial liver modules using hepatocyte organoid culture. One was a polyurethane foam (PUF)/hepatocyte spheroid packed-bed module. Hepatocytes spontaneously formed spheroids in the PUF pores, and they maintained liver-specific functions well for at least 2 weeks in vitro. As a preclinical experiment, a hybrid artificial liver with 200 g porcine hepatocytes was applied to a pig (25 kg) with liver failure and showed that the hybrid artificial liver was effective in support of liver functions and stabilization of general conditions. We established a new technique of hepatocyte organoid formation using centrifugal force. A hepatocyte organoid formed by centrifugation in hollow fibers maintained functions for more than 4 months in vitro. We developed a new sinusoid-like structure module having hollow fibers arranged by spacers in a micro-regular arrangement. Inoculated hepatocytes in the extra-fiber space of the module formed the organoid by centrifugation, and they maintained the functions for at least 1 month in vitro. The results indicated that this module seems to be promising as a hybrid artificial liver.

Evaluation of the effect of culture matrices on induction of CYP3A isoforms in cultured porcine hepatocytes

Several bioartificial liver devices have been developed as temporary therapy for patients suffering from fulminant hepatic failure. Some of these devices contain porcine hepatocytes entrapped in collagen matrices. In order to improve the function of these BAL devices, there exists a need to optimize metabolic function of cultured hepatocytes. The goal of these investigations was to evaluate the effect of altering culture conditions on rifampin-mediated induction of CYP3A isoforms in cultured porcine hepatocytes. Midazolam metabolism was compared in porcine hepatocytes cultured in a monolayer configuration on collagen gels, in a sandwich configuration between collagen gels and a Matrigel overlay, and in spheroidal cultures. The effect of culture conditions was evaluated, by measuring CYP3A-mediated metabolism of midazolam and by immunoblotting to detect CYP3A proteins, in control cultures and in rifampin-treated cultures. Results obtained by normalizing the metabolism rate data to cell numbers (based on DNA content) present at the end of the culture experiment, showed that there was no difference between the different culture conditions tested. Our results suggest that culturing porcine hepatocytes as spheroids or in a sandwich configuration between collagen and Matrigel, offers no advantage in terms of CYP3A-mediated metabolic function on a per cell basis compared to culturing on collagen gels.