Biol. Pharm. Bull. 30(12) 2308—2311 (2007)

porcine hepatocytes have been submitted for clinical trials as a “bridge” for liver transplantations in patients with fulminant hepatic failure. But the possibility of zoonosis is of concern and the use of xenogeneic cells for human therapy has severe practical limitations. Therefore, mass culture of human hepatocytes, about 10 cells, at high cell density in the bioreactor and their functional expression are very important subjects for the development of bioartificial liver. However, since primary human hepatocytes from adult liver lack the ability to proliferate in vitro, it is essential to establish a culture method for proliferation of human hepatic stem cells as a cell source and for differentiation of the cells to hepatocytes in vitro. Recently, a transformation of the cultured stem cells, such as ES cells, has been reported and a risk of tumorigenesis by using the cells should be discussed in the research field of regenerative medicine and bioartificial organs. Therefore, a proliferation of the stem cells in vitro without transformation is also a very important subject. In our previous papers, we focused on the use of human fetal hepatocytes as a cell source for the bioartificial liver development. The cells could proliferate in monolayer along with lowering hepatic functions such as cytochrome P450 (CYP) activity and ammonia metabolizing activity, but the activities of the cells could be enhanced by the formation of spheroid on poly-L-glutamic acid coated dish. In general, fetal hepatocytes include hepatoblasts which are kinds of hepatic stem cells. Therefore, in this study, we examined the induction and proliferation of human hepatoblasts from fetal hepatocytes by the treatment of sodium butyrate (SB), which is well known as a differentiation-promoting agent of ES cells and so on, along with suppressing transformation. Furthermore, we investigated the functional expression of the cells at high cell density using porous hydroxyapatite carriers for the development of bioartificial liver.