Expression and amplification of glutamine synthetase gene endows HepG2 cells with ammonia-metabolizing activity for bioartificial liver support system

Double-Compartment Cell Culture Apparatus: Construction and Biochemical Evaluation for Bioartificial Liver Support

Functional demands on a bioartificial liver support (BAL) device are not limited to biosynthetic activities, but must also encompass metabolic removal of potentially toxic substances. For most BALs, however, the concept and design are exclusively directed to biosynthetic support. To add the ability to metabolize and remove toxic substances, we designed a double-compartment cell culture apparatus (DCCA). Two compartments are separated from each other by a compact epithelial cell sheet spread over a synthetic microporous membrane. When a renal proximal convoluted tubular cell line that had been transduced with the human multidrug-resistant (MDR) gene, PCTL-MDR, was introduced into one of the compartments (hereafter referred to as the “inner” compartment) of the DCCA, a compact cellular monolayer was formed on the membrane. Ammonium ions passed across the membrane, but glucose and its metabolite lactate could not, indicating that the DCCA allowed selective transportation of cellular metabolites. In addition to PCTL-MDR, HepG2, a cell line of hepatic-origin, transduced with CYP3A4 (designated GS-3A4-HepG2), was seeded on the opposite side of the membrane, and the metabolism and transportation of lidocaine were studied. The lidocaine metabolite, monoethylglycinexylidide, was detected in the inner compartment across the PCTL-MDR cell layered membrane, indicating that metabolism and the selective transportation of metabolites between the two compartments occurred by cooperation of renal and hepatic cells. These results suggest that this type of DCCA represents a novel BAL that possesses biotransporting activities, as well as biosynthetic and metabolic activities.

Consideration of a Safe Protocol for Hepatocyte Transplantation Using Infantile Pigs

Hepatocyte transplantation is hoped to be an alternative treatment to certain cases of liver transplantation. The most promising indication is for congenital metabolic diseases, especially in infants. To establish a safe protocol for hepatocyte transplantation into infants, we examined physiological changes during treatment using infantile pigs. Recipient pigs (domestic, crossbred with Large-Yorkshire, Landrace, and Duroc; 2.5 kg; 7-14 days old) were anesthetized with isoflurane; a midline incision of minimum length provided access to the superior mesenteric vein. A double lumen catheter was inserted through the vein to within 1 cm of the hepatic portal region. Physiological parameters such as heart rate, systemic blood pressure, and portal pressure were monitored. Cryopreserved porcine hepatocytes isolated from the same strain were suspended in physiological saline and transfused through the catheter. In experiments requiring tracing, cells were stained with fluorescent dye prior to transfusion. Recipient pigs were kept for 1 day and sacrificed for histological liver examination. After preliminary experiments, the optimized number and concentration for hepatocyte transplantation were determined to be 1 × 10⁸ cells/kg and 1 × 10⁷ cells/ml. The cell suspension was transfused at a rate of 0.67 ml/min. No marked anomaly of physiological parameters was observed, whereas light tachycardia occurred in preliminary trials when the transfusion rate was faster than our standard protocol. All five pigs transfused with the established method recovered from anesthesia and survived with good vital signs. Histology revealed that the transfused hepatocytes were integrated in the hepatic tissue.

Construction and Evaluation of Drug-Metabolizing Cell Line for Bioartificial Liver Support System

Focusing on drug metabolism in liver, we constructed and evaluated a drug-metabolizing bioartificial liver (BAL) support system. In a previous study, we constructed ammonia-metabolizing CHO and hepatoma-derived HepG2 cell lines by recombination of the glutamine synthetase (GS) gene. For further mimicking of liver metabolism, the human hepatoma-derived cell line HepG2 was transformed by the pBudCE-GS-CYP3A4 vector, which contains GS and drug-metabolizing CYP 3A4 genes. The constructed GS-3A4-HepG2 cell line showed 3A4 activity higher than that of human primary hepatocytes. The drug-metabolizing activity of BAL (BAL clearance) was evaluated using this cell line. The estimated clearance was higher than that of the human hepatocyte system.

The significant improvement of survival times and pathological parameters by bioartificial liver with recombinant HepG2 in porcine liver failure model

We developed a bioartificial liver (BAL) containing human hepatoblastoma cell line, HepG2, with the addition of ammonia removal activity by transfecting a glutamine synthetase (GS) gene and estimated the efficacy using pigs with ischemic liver failure. GS-HepG2 cells showed 15% ammonia removal activity of porcine hepatocytes, while unmodified HepG2 had no such activity. The established GS-HepG2 cells were grown in a circulatory flow bioreactor to 3.5-4.1 x 10(9) cells. Survival time of the animals treated with GS-HepG2 BAL was significantly prolonged compared to the cell-free control (14.52 +/- 5.24 h vs. 8.53 +/- 2.52 h) and the group treated with the BAL consisting of unmodified wild-type HepG2 (9.58 +/- 4.52 h). Comparison showed the cell-containing BAL groups to have significantly fewer incidences of increased brain pressure. Thus, the GS-HepG2 BAL treatment resulted in a significant improvement of survival time and pathological parameters in pigs with ischemic liver failure.