The Use of Intact Mammalian Cells as Metabolic Activation Systems in Mutagenicity Tests

Test systems for mutagenicity have three different components: (1) genetic endpoint; (2) target cell; and (3) metabolizing system. Concerning the former two aspects, clear conceptions have been developed for requirements in routine testing. However, metabolization of premutagens has been insufficiently considered up to now, although it can be assumed that most mutagens act indirectly, namely after metabolic transformation (see Parke 1987; Venitt et al. 1986). In routine in vitro mutagenicity testing, so-called S-9 mix from rat liver, a supernatant of liver homogenates centrifuged at 9000 x g supplemented with NADPH2 and Glucose 6-P as cofactors to maintain the activity of cytochrome P450-dependent mixed-function oxygenases is used. The use of freshly isolated hepatocytes for the detection of DNA repair monitored as unscheduled DNA synthesis (UDS) is the only exception of a routine system which considers the metabolism of intact mammalian cells.