Inhibition of bacterial mutagenesis by Citrus flavonoids

The antimutaqenicity of the Citrus flavonoids naringin, hesperidin, nobiletin, and tangeretin against the mutagens benza[a]pyrene, 2-aminofluorene, quercetin, and nitroquinoline N-oxide was investigated in the Salmonella/microsome assay. Naringin and hesperidin showed a weak antimutagenic activity against benzo[a]pyrene. Tangeretin was antimutagenic against all indirectly-acting mutagens tested, but in general a large molar excess was necessary. Liquid preincubation increased the antimutagenicity of tangeretin against 2-aminofluorene. Nobiletin acted as an antimutagen against benzo[a]pyrene, but it enhanced the mutagenicity of 2-aminofluorene. However, in a liquid preincubation assay nobiletin also exhibited antimutagenicity against 2-aminofluorene. Both tangeretin and nobiletin inhibited the mutagenicity of quercetin. Quercetin itself acted as an antimutagen against 2-aminofluorene in a Salmonella strain (TA1538) where its mutagenicity was not expressed. Quercetin should not merely be regarded as a genotoxic risk factor in the human diet, since its mutagenicity may be inhibited by accompanying compounds including other flavonoids, and since quercetin itself also exhibits an antimutagenic action. Because of the antimutagenic properties the Citrus flavonoids tested, especially tangeretin and nobiletin, might play a role in the chemoprevention of cancer.