The effects of gypenosides on the inhibition of N-acetyltransferase (NAT) activity, AF-DNA adduct formation and NAT gene expression in a human cervix cancer cell line (Ca Ski) were studied. Various concentrations of gypenosides were added to the cytosols or individually to the culture medium of human cervix cancer cells. The NAT activity was determined by high performance liquid chromatography, assaying for the amounts of acetylated 2-aminofluorene (AAF) and non-acetylated 2-aminofluorene (AF). The NAT activity in the human cervix intact cancer cells and cytosols was suppressed by gypenosides in a dose-dependent manner. The results also demonstrated that gene expression (NAT1 mRNA) in human cervix cancer cells was decreased by gypenosides in a dose-dependent manner. The apparent values of Km and Vmax of NAT of human cervix cancer cells were also decreased by gypenosides in cytosols. Gypenosides may act as noncompetitive inhibitors. After the incubation of human cervix cancer cells with 30 or 60 microM AF and with or without 350 micrograms/ml gypenosides co-treatment, the cells were recovered, DNA was prepared and hydrolyzed to nucleotides; adducted nucleotides were extracted in butanol and AF-DNA adducts were analyzed by HPLC. The results demonstrated that gypenosides decreased the levels of AF-DNA adduct formation in these cells. The NAT PCR and cDNA microarray also demonstrated that gypenosides inhibited NAT mRNA expression in human cervix cancer cells.