Complex effects of retinol on the metabolic activation of 2-aminofluorene

It has been reported that vitamin A alcohol (retinol) inhibits the mutagenicity of certain carcinogenic agents requiring metabolic activation by mammalian microsomal enzymes in the Ames Salmonella assay. We have found that the effect of retinol on the mutagenicity of 2-aminofluorene (2AF), a carcinogen requiring metabolic activation, is complex and dependent both on the ratio of retinol (microgram per plate) to S9 (microgram of protein per plate), as well as the absolute concentration of retinol. Retinol had no effect on the mutagenicity of 4-nitro-o-phenylenediamine (4NPDA), a direct-acting mutagen. However, the mutagenicity of 4NPDA was inhibited by S9 and this inhibition was not affected by retinol.