Determination of CYP activity in precision-cut liver slices: whether to use intact slices or slice homogenate.

Despite CYP induction in vitro in precision-cut liver slices (LS) is well documented, there are no standardised assays for determining CYP activity as a major end-point. In this paper, short-term assays with intact and homogenised LS from male and female rats were directly compared. We obtained similar results for 7-ethoxycoumarine O-deethylation (ECOD) with LS from both sexes: higher basal activities were measured in LS homogenate, whereas slightly stronger induction by BNF was found with intact LS. CYP3A-dependent basal and dexamethasone (Dex)-induced 2beta-, 15beta- and 6beta-testosterone hydroxylation (TH) rates were higher in both intact and homogenised LS from male compared to female rats. CYP3A induction in vitro could likewise be detected in intact and homogenised LS preferentially by determining 2beta- and 15beta-TH, with higher induction factors observed in LS from females. 6beta-TH seems to be less inducible in intact LS of males. In vivo pretreatment of liver donors with BNF and Dex did not substantially disturb the subsequent in vitro induction of ECOD and TH, respectively.