Inhibitory effects of naturally occurring compounds on aflatoxin B1 biotransformation

Effects of naturally occurring compounds from plants on biotransformation of a mycotoxin, aflatoxin B-1, were evaluated. Among 77 naturally occurring compounds tested, anthraquinones, coumarins, and flavone-type flavonoids were shown to be potent inhibitors of aflatoxin B-1-8,9-epoxide formation. Addition of the flavonoids galangin, rhamnetin, and flavone strongly inhibited mouse liver microsomal conversion of aflatoxin B-1 to aflatoxin B-1-8,9-epoxide, a metabolically activated mutagenic product. In contrast to these results, addition of isoflavonoids, catechins,, terpenes, alkaloids, and quinones to mouse liver microsomes did not inhibit formation of aflatoxin B-1-8,9-epoxide. Formation of the aflatoxin B-1 reductase product, aflatoxicol, by chicken liver cytosols was strongly inhibited by curcumin, the diferuloylmethane present in turmeric and other Curcuma species. Curcumin analogues also showed inhibitory effects, and a structure-activity study established that beta -diketone groups linked with two benzyl moieties were essential for inhibition of aflatoxicol formation. An additional 37 naturally occurring compounds tested did not inhibit formation of aflatoxicol. These results demonstrate that dietary constituents in certain fruits, vegetables, and spices may have significant inhibitory effects on metabolic transformation of aflatoxins to their hepatotoxic or carcinogenic derivatives or, alternatively, may promote their transformation into nontoxic products.