Inhibitory effects of ellagic acid on the direct-acting mutagenicity of aflatoxin B₁ in the Salmonella microsuspension assay

Ellagic acid (EA) is a phenolic compound that exhibits both antimutagenic and anticarcinogenic activity in a wide range of assays in vitro and in vivo. It occurs naturally in some foods such as strawberries, raspberries, and grapes. In the previous work, we used the Salmonella microsuspension assay to examine the antimutagenicity of EA against the potent mutagen aflatoxin B₁ (AFB₁) using tester strains TA98 and TA100. Briefly, the microsuspension assay was approximately 10 times more sensitive than the standard Salmonella/microsome (Ames) test in detecting AFB₁ mutagenicity, and EA significantly inhibited mutagenicity of all AFB₁ doses in both tester strains with the addition of S9. The greatest inhibitory effect of EA on AFB₁ mutagenicity occurred when EA and AFB₁ were incubated together (with metabolic enzymes). Lower inhibition was apparent when the cells were first incubated with EA followed by a second incubation with AFB₁ or when the cells were first incubated with AFB₁ followed by a second incubation with EA alone, all with metabolic enzymes. The result of these sequential incubation studies indicates that one mechanism of inhibition could involve the formation of an AFB₁-EA chemical complex, In the present study, we further examine the effect of EA on AFB₁ mutagenicity, but without the addition of exogenous metabolic enzymes. We report the mutagenicity of AFB₁ in the microsuspension assay using TA98 and TA100 without the addition of S9. Neither the concentrations of AFB₁ (0.6, 1.2, and 2.4 μg/tube) nor the concentrations of EA (0.3, 1.5, 3, 10, and 20 μg/tube) were toxic to the bacteria, The results indicate that AFB₁ is a direct-acting mutagen, and that EA inhibits AFB₁ direct-acting mutagenicity.