Abstract
Ethanolic extracts from Agaricus bisporus, the most extensively cultivated and consumed type of mushroom in the Western hemisphere, displayed a direct-acting mutagenic response in various Salmonella typhimurium strains, TA 104 being clearly the most sensitive. Ethanolic extracts from two other edible mushrooms, namely Pleurotus ostreatus and Lentinus edodes, were also screened for mutagenic activity in the Ames test. Pleurotus ostreatus extracts exhibited weak, direct-acting mutagenicity towards all bacterial strains studied. Extracts from Lentinus edodes were bacteriocidal when tested at concentrations similar to those of Pleurotus ostreatus extracts. Incorporation of hepatic S9 activation systems (i.e., microsomes and soluble fractions) from laboratory animals, control or induced, did not alter the mutagenic response of the extracts from Agaricus bisporus. The mutagenic potential was also unaffected by purified prostaglandin H synthase. The mutagenicity was, however, markedly enhanced in the presence of a rat activation system containing hepatic cytosolic fraction, i.e., in the absence of microsomes. This cytosol-mediated potentiation in mutagenicity was dependent on NADPH, was inhibited by NADH and was abolished by heat-treatment. Moreover, the cytosolic-mediated mutagenic response was inhibited by dicoumarol and menadione, implicating the cytosolic enzyme, DT-diaphorase, in the cytosolic activation of the mushroom extracts. Factors such as mushroom strain, break, and time of harvest did not have any significant effect on the mutagenic potential of the extracts from Agaricus bisporus. In contrast, the mutagenicity decreased with the age of the fruit body and enhanced with storage. Moreover, cooking of mushrooms resulted in a reduction of the mutagenic response. Non-polar solvents such as chloroform and ethyl acetate failed to extract the mushroom mutagens whereas methanolic and water extracts from Agaricus bisporus exhibited mutagenicity of the same magnitude as the ethanolic extracts. Agaritine, the postulated mutagenic/carcinogenic component of Agaricus bisporus, was mutagenic in a narrower range of Salmonella strains than the ethanolic extracts from the mushroom. Moreover, the mutagenic potency of ethanolic extracts from various types of mushroom containing markedly different amounts of agaritine did not correlate with the agaritine content. Finally, γ-glutamyl transpeptidase, did not enhance the mutagenic response. It is, therefore concluded that agaritine does not mediate the mutagenicity of the fungal extracts to TA 104. Incubation of the ethanolic extracts from Agaricus bisporus with purified mushroom tyrosinase, the enzyme responsible for the conversion of phenols to quinones within the mushroom, markedly enhanced the mutagenic activity. The enzymes superoxide dismutase and catalase, that detoxicate O2- and H2O2 respectively, glutathione, which breaks down H2O2 to H2O, and the OH- scavenger DMSO, significantly decreased mutagenicity. These findings indicate that the fungal phenols/quinones and reactive oxygen species make important contributions in the mushroom mutagenicity.