MUTATIONAL SPECIFICITY OF AFLATOXIN-B1 - COMPARISON OF IN-VIVO HOST-MEDIATED ASSAY WITH IN-VITRO S9 METABOLIC-ACTIVATION

An intrasanguineous host-mediated assay was used to determine the patt ern of mutagenesis induced by the carcinogen aflatoxin B1 in the lacI gene of Escherichia coli recovered from rat liver, To investigate the influence of different types of metabolic activation, the mutation spe ctrum induced by AFB1 activated in vitro by a commercially prepared S9 microsomal fraction from Aroclor 1254-treated rats was also obtained, A total of 281 forward mutations affecting the N-terminal region of t he lacI gene were characterized by DNA sequencing analysis, AFB1 induc ed similar type of mutations with similar site specificity when activa ted by the standard S9 fraction or by employing a rat host-mediated as say, These results indicate the ability of the in vitro S9 fraction to mimic the in vivo metabolism, suggesting that the same active metabol ite, presumably AFB1 8,9-epoxide, is responsible for generating a simi lar pattern of DNA damage, as reflected in the similarity of mutationa l spectra, For both activation systems, most mutations (>90%) were bas e substitutions that occurred primarily at G:C pairs, Somewhat over on e-half of G:C targeted substitutions were GC>TA transversions, other m utations being evenly divided between G:C>AT transitions and GC>CG tra nsversions, The mutational specificity exhibited by activated AFB1 can be explained by incorporation of different bases opposite a single ty pe of non-instructive lesion during error-prone DNA synthesis, To what extent the mutations are due to the main adduct (AFB1-N7-Gua), its im idazole-ring-opened derivative or an apurinic site remains unknown.