The aim of our study is to modify the Ames test used for human risk assessment of genotoxic carcinogens to render it sensitive for the environmental factors. In the present protocols of the Ames test rat S9 fraction has to be used for metabolic activation of precarcinogens. These protocols allow the investigation of just a part of the whole metabolic process, mediated by phase I enzymes, disregarding the role of phase II enzymes and transport proteins resulting in false negative and positive outcome. In our work human S9 fraction or rat primer hepatocyte culture substitute for rat S9 fraction. Addition of cofactors of phase II enzymes to the reaction mixture assures the activity of these enzymes.

The metabolism of xenobiotics in rats is not always identical with that in human. By using human preparation the extrapolation from rat to human can be eliminated. Modelling the in vivo situation by primer hepatocyte culture reduces the frequency of false results since intact cells contain all of the necessary cofactors for the entire metabolic pathways. The modified method makes it possible to study the role of individual variance in enzyme activities and the effect of chemical environment on mutagenicity of xenobiotics.