Primary Hepatocyte Culture: Is It Home Away from Home?
Primary hepatocyte culture is one of many techniques which simplify the analysis of liver function. The advantage of a culture approach over alternative methods such as isolated liver perfusion is that it permits evaluation of hepatocytes as pure isolates in a controlled environment. Cultures have proven applicable to a variety of experiments, including studies of protein synthesis, intermediary metabolism and enzyme function [reviewed in Ref.
(l)], and, more recently, membrane potential and electrical coupling (2, 3). The utility of cultures for intermediate-and long-term studies has been limited, however, by morphologic and functional alteration of cells during the first few days after plating and ultimately the deterioration and death of hepatocytes within 1 to 2 weeks (4-6). Loss of liver-specific characteristics reflects the absence in culture of elements that are present and support hepatocellular function in uiuo. Research directed at this problem has involved manipulation of the cell culture environment in an effort to define the appropriate conditions under which hepatocytes will maintain a differentiated phenotype for extended periods. Initial studies demonstrated that medium supplements such as nutrients (7,8) and hormones (9-12) promote increased protein synthesis and secretion by hepatocyte monolayers. Similarly, introduction of an organic substratum, such as Type I collagen, in place of plain tissue culture plastic, enhanced viability and cell attachment (13). In general, though, simple culture additions have resulted only in improvements which are quantitatively minor or transient. Currently under development are more sophisticated culture methods which introduce factors that may play a role in hepatocellular differentiation in uiuo (14) (Table 1). Those which rely on medium supplements alone fail to support liver-specific functions for more than 1 to 2 weeks (15-17). On the other hand, cultures that make use of complex extracellular matrix substrata (18-20) or incorporate cell-cell interactions in the form of coculture (24-29) have provided dramatic results. In this issue of Hepatology, Goulet and colleagues (30) demonstrate that liver-specific morphology and function can be successfully maintained by hepatocytes for up to 4 weeks when established in coculture with a variety of epithelial or mesenchymal cell lines. The following discussion will review the rationale for a coculture technique and assess its benefits in relation to alternative methods.