Small hepatocytes in primary cultures

Abstract

Recently, we and other investigators have made significant advances toward the development of culture conditions that promote proliferation of primary hepatocytes isolated from normal adult rats [1–6]. Inoue et al. [1] first showed that the number of hepatic nuclei increased more than twofold in a medium supplemented with 5% calf serum, 10 mM nicotinamide, and 10 ng/ml epidermal growth factor (EGF)*. The cultured hepatocytes maintained a high level of albumin mRNA expression and had the potential to express tryptophan 2,3-dioxygenase (TO) mRNA, which is thought to be a differentiated function of mature hepatocytes. Thereafter, we reported that primary rat hepatocytes cultured in a serum-free chemically defined medium could repeatedly replicate their DNA [2]. This was the first report proving that many hepatocytes that maintained hepatic differentiated functions and structures can complete the cell cycle more than twice in a serum-free medium. In this culture we found a remarkable increase of small mononucleate cells amongst mature hepatocytes. Although the size of these cells is about 1/2 to 1/3 that of typical hepatocytes in culture, the phenotypic appearance is close to that of mature hepatocytes [7–9]. Therefore, we call the cells small hepatocytes. In this review article we show that the small hepatocytes appear in primary culture and discuss the role of the cells in liver growth and hepatic diseases.