Developmental toxicity of aflatoxin B1 in the rodent embryo in vitro: contribution of exogenous biotransformation systems to toxicity.

Abstract

Aflatoxin B1 (AFB1) is a known carcinogen and developmental toxin in various species of mammals, birds, amphibians, and fish. AFB1 requires metabolic activation (biotransformation) to the 2,3-epoxide metabolite for carcinogenicity; however, it is unknown if biotransformation is a prerequisite for AFB1 embryotoxicity. Cultured day 10 rat embryos were exposed to AFB1 alone and AFB1 in the presence of cofactors and hepatic S9 fractions from adult male rats induced with either phenobarbital or 3-methylcholanthrene. Under these different culture conditions qualitatively similar patterns of malformation were seen in all embryos exposed to AFB1. At culture concentrations of 15 microM or greater, AFB1 produced abnormalities in neural tube development in a concentration-dependent manner. The presence of hepatic S9 fractions had no effect on the ability of AFB1 to produce dysmorphogenesis in vitro or on the spectrum of malformations elicited. However, the addition of hepatic S9 fractions did greatly enhance the embryolethality of AFB1. This enhancement was greater with phenobarbital- than 3-methylcholanthrene-preinduced hepatic S9 fractions. Our results suggest that separate chemical mediators may be responsible for the embryolethal and dysmorphogenic effects of AFB1 observed in day 10 rat embryos in vitro. We found that the embryolethality of AFB1, but not the dysmorphogenicity, could be greatly modulated by exogenous biotransformation.