Xenobiotic metabolism by cultured primary porcine hepatocytes

The effects of fenbendazole, flubendazole and mebendazole on activities of hepatic cytochromes P450 in pig

Fenbendazole (FBZ), flubendazole (FLBZ) and mebendazole (MBZ) are benzimidazole anthelmintics widely used in veterinary medicine. The effects of these drugs on cytochromes P450 (CYP) were investigated in primary cultures of swine (Sus scrofa f. domestica) hepatocytes. After 48-h incubation of hepatocytes with benzimidazoles (0.1-2.5 microm), ethoxyresorufin O-deethylation (EROD), benzoxyresorufin O-dearylation (BROD), testosterone hydroxylase (6beta-TOH) and testosterone oxidase (17-TO) activities were measured and the CYP1A and 3A protein levels were determined by Western blotting. FBZ produced a significant, concentration-dependent increase of CYP1A activity (EROD) and protein level. No enhancement of CYP1A was observed after exposure to FLBZ and MBZ. All benzimidazoles tested did not cause any induction of CYP3A (BROD, 6beta-TOH, 17-TO activities and protein content). On the other hand, MBZ produced a significant, concentration-dependent decrease of CYP3A (BROD, 6beta-TOH and 17-TO) activities. Pharmacological and toxicological consequences of CYP1A induction and CYP3A inhibition should be taken into account in treatment of pigs with FBZ and MBZ.

Long-term function of cryopreserved rat hepatocytes in a coculture system

The goal of this study was to investigate postpreservation long-term function of cryopreserved primary rat hepatocytes using the hepatocyte/3T3-J2 fibroblast coculture system. The long-term function of thawed hepatocytes cocultured with fibroblasts was evaluated and compared with hepatocytes cultured without fibroblasts. Fresh isolated primary rat hepatocytes were frozen at a controlled rate (-1 degrees C/min) up to -80 degrees C, and then stored in liquid nitrogen for up to 90 days. Thawed hepatocytes were thereafter cocultured with 3T3-J2 murine fibroblasts and cocultivation was monitored for 14 days. The viability of fresh isolated hepatocytes was 91.4%, and that of cryopreserved hepatocytes was 82.1%. Cellular morphology and polarity, which were determined by the localization of actin filaments and connexin-32, were successfully maintained in cryopreserved hepatocytes following cryopreservation. Albumin and urea synthesis reached the maximum level and became stable after day 7 in coculture in both fresh and cryopreserved hepatocytes. Urea synthesis of cryopreserved hepatocytes was maintained 89.0% of nonfrozen fresh control, and albumin production of cryopreserved hepatocytes was 63.7% of control in coculture. Cytochrome P450 activity, which was measured by deethylation of ethoxyresorufin, was also maintained in cryopreserved hepatocytes at 88.6% of nonfrozen fresh control in coculture. The retention of synthetic and detoxification activities was verified to be well preserved during extended low-temperature storage (90 days). Both fresh control and cryopreserved hepatocytes cultured without fibroblast did not retain their synthetic and detoxification functions in long-term culture. These data illustrate that, through the utilization of our cryopreservation procedure, primary hepatocyte function was successfully maintained when placed into coculture configuration following thawing.

The effects of albendazole and its metabolites on hepatic cytochromes P450 activities in mouflon and rat

Albendazole (ABZ) is a benzimidazole anthelmintic widely used in veterinary medicine. The effects of ABZ on cytochromes P450 were investigated in primary cultures of mouflon (Ovis musimon) and rat (Rattus norvegicus) hepatocytes. Besides ABZ, its two main metabolites (albendazole-sulphoxide, ABZSO and albendazole-sulphone, ABZSOO) were tested to clarify which compound is responsible for the induction potency of this benzimidazole drug. After 48 h incubation of hepatocytes with benzimidazoles (0.2-25 microM), ethoxyresorufin O-deethylation (EROD) and benzoxyresorufin O-dearylation (BROD) were measured and the P4501A and 3A protein levels were determined by Western blotting. All benzimidazoles provoked a significant increase of EROD and BROD activities in rat hepatocytes. ABZSO and ABZSOO seemed to be responsible for the induction effect of ABZ on P450s in rat. In mouflon, no pharmacologically significant induction of EROD and BROD activities by benzimidazoles tested was observed. From this point of view, anthelmintic therapy of mouflons with ABZ seems to be safe.

Efficacy of an extracorporeal flat-plate bioartificial liver in treating fulminant hepatic failure

BACKGROUND

Fulminant hepatic failure is associated with a high mortality rate. Orthotopic liver transplantation is the only established treatment for patients who do not respond to medical management. A major limitation of this treatment is a shortage of donor organs, resulting in many patients dying while waiting for a transplant. An extracorporeal bioartificial liver (BAL) has the potential to provide temporary support for patients with fulminant hepatic failure (FHF) and for patients awaiting orthotopic liver transplantation. We developed a flat-plate BAL with an internal membrane oxygenator in which porcine hepatocytes were cultured as a monolayer.

MATERIALS AND METHODS

Twenty-four hours after cannulation of the left carotid artery and right jugular vein, FHF was induced in rats by administering 2 intraperitoneal injections of D-galactosamine (GalN) (1.2 g/kg) at a 12-h interval. The rats were connected to a BAL device 24 h after the first GalN injection and underwent extracorporeal perfusion for a duration of 10 h. Liver histology, liver-specific markers, and animal survival up to 168 h (7 days) were examined.

RESULTS

Histologically, liver damage was reduced in the animal group treated with the hepatocyte-based BAL device. Significant reductions occurred in the plasma ammonia levels and prothrombin times in the group treated with the seeded BAL device. Animal survival in the group treated with the seeded BAL device was significantly higher (50.0%) than in the control animal group treated with an unseeded BAL device (11.1%).

CONCLUSIONS

This flat-plate BAL with an internal membrane oxygenator and cultured porcine hepatocytes has yielded encouraging results in the treatment of rats with GalN-induced FHF.

Engineering liver therapies for the future

Treatment of liver disease has been greatly improved by the advent and evolution of liver transplantation. However, as demand for donor organs continues to increase beyond their availability, the need for alternative liver therapies is clear. Several approaches including extracorporeal devices, cell transplantation, and tissue-engineered constructs have been proposed as potential adjuncts or even replacements for transplantation. Simultaneously, experience from the liver biology community have provided valuable insight into tissue morphogenesis and in vitro stabilization of the hepatocyte phenotype. The next generation of cellular therapies must therefore consider incorporating cell sources and cellular microenvironments that provide both a large population of cells and strategies to maintain liver-specific functions over extended time frames. As cell-based therapies evolve, their success will require contribution from many diverse disciplines including regenerative medicine, developmental biology, and transplant medicine.

Long-term maintenance of cytochrome P450 activities by rat hepatocyte/3T3 cell co-cultures in heparinized human plasma

Little information on the effect of plasma on hepatocyte cytochrome P450 (CYP) activities is currently available. We characterized the effect of plasma on CYPs of hepatocyte-mesenchymal cell co-cultures, which exhibit stable liver specific functions and may be potentially useful for bioartificial liver design. Rat hepatocyte-mouse 3T3-J2 cell co-cultures were maintained for 6 days in medium, and then switched to heparinized human plasma containing 3-methylcholanthrene (3MC; 2 microM), phenobarbital (PB; 1 mM), or no inducer for up to 7 days. CYP activities were measured in situ based on the o-dealkylation of ethoxy- (EROD), methoxy- (MROD), pentoxy- (PROD), or benzyloxy- (BROD) resorufin. Plasma alone increased PROD/BROD but not EROD/MROD. The endogenous inducer was in the high molecular weight fraction (>5 kD) of plasma and inhibited by >5 nM okadaic acid and >10 microM dibutyryl cyclic AMP, two inhibitors of PB-inducible CYPs. Furthermore, plasma increased CYP1A1 and CYP2B1/2 mRNA levels. In plasma, 3MC induced EROD/MROD to about 60% of the level induced in culture medium while PB induced PROD/BROD that were three- to 10-fold above levels induced in medium. CYP activities decreased between days 2 and 7 of plasma exposure, but were enhanced by plasma supplementation with amino acids, insulin, glucagon, and hydrocortisone.

In vitro and in vivo evaluation of albumin synthesis rate of porcine hepatocytes in a flat-plate bioreactor

Several configurations of extracorporeal bioartificial liver devices have been developed for the potential treatment of fulminant hepatic failure or as a bridge to liver transplantation. Recently, we developed a microchannel flat-plate bioreactor with an internal membrane oxygenator in which porcine hepatocytes are cultured as a monolayer on the bottom glass surface. In the present study, we investigated synthetic function of porcine hepatocytes in the bioreactor in both in vitro and in vivo flow circuit models. In vitro, albumin synthesis was stable in the bioreactor for up to 4 days of perfusion. In vivo, with the extracorporeal connection of the bioreactor to rat vasculature, porcine albumin was detectable for 24 h in the rat plasma. We also developed a simple mathematical model to predict the in vivo porcine albumin concentration in rat plasma. These results indicate that this configuration of a microchannel flat-plate bioreactor has potential as a liver support device and warrants further investigation.