Co-Cultivation of Liver Epithelial Cells with Hepatocytes

Primary hepatocytes from rat and other species maintained in pure monolayer culture undergo phenotypic changes within a few days (1 -3 ). This is particularly pronounced with respect to the cytochrome P450-dependent biotransformation capacity, but may also involve other metabolic pathways and, eventually, the switch from adult to fetal isozymes and proteins (4 -6 ). Many such changes are due to nutritional and/or hormonal deficiencies of the culture media and to inadequate extracellular matrix conditions (7 ,8 ). In 1983, Guguen-Guillouzo and coworkers, in an attempt to create a more liver-like environment, observed that co-cultivation of rat hepatocytes with rat liver epithelial cells stimulated maintenance and reversibility of hepatocellular albumin secretion (9 ). Subsequently, it became well documented through many studies that co-cultivation provides a promising culture approach for extending the life span and for maintaining the differentiated phenotype of liver parenchymal cells (10 ,11 ). This not only concerns the capacity of hepatocytes for carrying out complex biotransformation reactions of xenobiotics (12 -15 ), but also many other features, such as production of acute phase proteins, transport phenomena, and proliferation (16 -18 ). Thus, co-cultured hepatocytes can be considered as a valuable equivalent to hepatocytes in situ with respect to many metabolic and regulatory aspects and can be used in various biological and toxicological fields (19 ). However, it should be noted that certain functions or enzymes may still deviate from normal. For instance, epoxide hydratase activity remains diminished (12 ). On the other hand, the spontaneous induction of glutamine synthetase has been noted in hepatocytes co-cultured with some, but not all, epithelial cell lines (20 ,21 ), reflecting that there is a specific exchange of signals between hepatocytes and epithelial cells (22 ). Such signals and cell interactions may provide a clue to the heterogeneity of hepatocytes in liver parenchyma (23 ).