Mutagenicity of aflatoxin B1: observations in vivo and their relation to in vitro activation.

Aflatoxin B1 (AFB1) was shown to be clastogenic in vivo on the basis of its capacity to produce micronucleated cells and chromosomal aberrations in mouse bone marrow cells. On the other hand, in vitro studies on cultured human lymphocytes suggested only a slight mutagenic action of AFB1. If, however, a microsomal extract isolated from rat liver was added together with the AFB1 (1.92 X 10(-5) M) to the lymphocytes before the incubation period, the yield of chromosomal aberrations and of sister chromatid exchanges (SCE) increased markedly indicating that AFB1 must be metabolically converted before it can act as an active mutagen. The use of microsomal extracts for in vitro tests can thus considerably improve the reliability of such tests of mutagenicity although studies in vitro will not be able to entirely replace those in vitro.