Modulation of the embryotoxicity in vitro of reactive metabolites of 2-acetylaminofluorene by reduced glutathione and ascorbate and via sulfation.

To provide insights into mechanisms whereby reactive intermediary metabolites of foreign chemicals elicit teratogenic and embryotoxic effects, we initiated investigations of the capacity of physiologic factors to modulate the effects of embryotoxic metabolites of 2-acetylaminofluorene (AAF). The whole embryo culture system was utilized in order to avoid potentially confounding maternal factors. Reduced glutathione (GSH) effectively protected cultured embryos from the embryolethal effects of N-acetoxy-2-AAF (AAAF) and also reduced the severity of AAAF-elicited malformations although the percentage of embryos exhibiting malformations was not affected significantly. GSH also reduced the embryolethality of 2-nitrosofluorene (NF) as well as the percentage of NF-elicited axial rotation defects. Ascorbate protected against the embryolethality of both AAAF and NF and exhibited significant protection in terms of the capacity of NF to cause flexure abnormalities. However, significant protection against NF-elicited prosencephalic deformities was not detected. N-Acetylcysteine and alpha-tocopherol each failed to produce significant protection, even at the highest concentrations utilized. Enzymatic sulfation of N-hydroxy-AAF (N-OH-AAF) markedly increased the incidence of observable malformations. Synthesized N-sulfonyloxy-AAF also elicited a high incidence of malformations at relatively low concentrations when added to the culture medium. Malformations elicited, however, resembled those produced by NF rather than by AAAF. The results suggest that endogenous metabolic systems can play a critical role as determinants of both the quantitative and the qualitative capacity of foreign organic chemicals to produce embryotoxic or teratogenic effects via the generation of reactive intermediates.