Inhibitory effects of naturally occurring compounds on aflatoxin B-1 biotransformation

Effects of naturally occurring compounds from plants on biotransformation o f a mycotoxin, aflatoxin B-1, were evaluated. Among 77 naturally occurring compounds tested, anthraquinones, coumarins, and flavone-type flavonoids we re shown to be potent inhibitors of aflatoxin B-1-8,9-epoxide formation. Ad dition of the flavonoids galangin, rhamnetin, and flavone strongly inhibite d mouse liver microsomal conversion of aflatoxin B-1 to aflatoxin B-1-8,9-e poxide, a metabolically activated mutagenic product. In contrast to these r esults, addition of isoflavonoids, catechins,, terpenes, alkaloids, and qui nones 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 diferulo ylmethane 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 occurri ng compounds tested did not inhibit formation of aflatoxicol. These results demonstrate that dietary constituents in certain fruits, vegetables, and s pices may have significant inhibitory effects on metabolic transformation o f aflatoxins to their hepatotoxic or carcinogenic derivatives or, alternati vely, may promote their transformation into nontoxic products.