Optimising conditions for induction of cytochrome P450 in primary hepatocyte cultures

Isolated hepatocytes undergo rapid dedifferentiation in primary culture, one of the indices of this dedifferentiation being differential loss of the isoforms of cytochrome P450 (CYP) [1]. The loss of CYPs occurs to varying extents and at different rates across species. The most extensively investigated species and the one in which there is the most marked loss of CYPs is the rat [2]. Chapter 24 describes some strategies and mechanisms involved in the maintenance of CYP in rat hepatocyte cultures. Some of the same strategies have been used to enhance induction of CYP in culture. However, there is no correlation between maintenance of constitutive CYPs and optimising induction of CYPs. Since the inducible CYP isoforms are differently regulated [3], there is unlikely to be one set of conditions where all CYPs can be maximally induced. Similarly species differences in CYP induction necessitate different culture conditions across species [4]. The focus of this chapter will be optimisation of conditions for induction of CYP in rat hepatocyte cultures i.e. such that the extent of induction reflects that seen in vivo. It will also refer to human hepatocyte cultures and to dog and rabbit hepatocyte cultures where data are available. Although there is pressure to decrease the use of dogs in research, the dog is still used in toxicology studies for regulatory purposes and validation of the use of cultured dog hepatocytes could reduce the use of this species in research.