Expression and Amplification of Glutamine Synthetase Gene for Constructing Ammonia-Metabolizing Cell Lines in Hybrid Bioartificial Liver Support System

Recently, a hybrid bioartificial liver support (BAL) system, composed of artificial materials and living cells, was developed for stopgap use in patients with hepatic failure in the U.S.A [1,2]. Primary xenogeneic hepatocytes have heretofore been the predominant cell type used to support human liver functions in BAL systems [1]. BAL systems that use these cells are extremely effective for short-term use (a few days), but are unsuitable for long-term use (more than one week), because of the short life-span of the primary hepatocyte. However, in Japan, the BAL system is required for long-term rather than short-term use because of the severe limitations on transplantation. In designing a BAL system for a long-term use, the most important factor is the use of a highly functional and stable liver cell. Hepatoma-derived cell lines are suitable for longterm use because of their infinite capacity for proliferation [2]. On the other hand, the cell line frequently loses some of the liver cell functions, especially its’ ammonia-metabolizing activity [3]. Ammonia is considered to be one of the major causes of hepatic encephalopathy, which is among the most serious pathophysiological features of fulminant hepatic failure. Hemodialysis and/or plasmapheresis have been used for ammonia removal but neither can effect selective removal of ammonia. In this study, we constructed ammonia-removing CHO and hepatoma- derived HepG2 cell lines by recombination and gene amplification of the GS gene, and constructed a BAL system for long-term usage.