AFLATOXIN B1-2,3-OXIDE AS A PROBABLE INTERMEDIATE IN COVALENT BINDING OF AFLATOXINS B1 AND B2 TO RAT-LIVER DNA AND RIBOSOMAL-RNA INVIVO

Abstract

Administration of [3H]aflatoxin B2 (2,3-dihydroaflatoxin B1) (AFB2) to male rats resulted in levels of hepatic DNA- and rRNA-aflatoxin adducts that were about 1% of those rats given [3H]aflatoxin B1 (AFB1). The levels of hepatic protein-aflatoxin adducts were 35-70% as great for AFB2-treated as compared to AFB1-treated rats. Mild acid hydrolysis of hepatic DNA and rRNA from rats given [3H]AFB1 or [3H]AFB2 yielded 2,3-dihydro-2,3-dihydroxyaflatoxin B1 and 2 other major 3H products that were separable by high pressure liquid chromatography. With 2 h hydrolyses .apprx. 77 and 54% of the 3H from the hepatic DNA of rats given [3H]AFB1 or [3H]AFB2, respectively, and 40 and 32%, respectively, of the 3H from the rRNA of rats given [3H]AFB1 or [3H]AFB2 were isolated as these products. One of the 3H products was converted to 2,3-dihydro-2,3-dihydroxyaflatoxin B1 on further mild acid hydrolysis. The high levels of the dihydrodiol and its precursor in the hydrolysates, especially when the 35% loss of added 2,3-dihydro-2,3-dihydroxyaflatoxin B1 under the hydrolysis conditions is taken into account, indicate that aflatoxin B1-2,3-oxide is a major ultimate precursor of the nucleic acid bound derivatives formed from AFB1 and AFB2 in rat liver. AFB2 appears to be converted to AFB1 in the rat liver in vivo to an extent (about 1%) that is comparable to the ratio of hepatocarcinogenicities of these compounds in this species. The levels of hepatic DNA bound adducts from [3H]AFB1 were about 1/2 of the control level in hypophysectomized rats, while the levels of the rRNA- and protein aflatoxin adducts were similar to those of the controls. The levels of the hepatic macromolecule-bound adducts were 10-30% of the control levels in phenobarbital-treated rats. The levels of AFB1 in kidney, spleen and small intestine were lower than those of liver. The inhibitory action of phenobarbital on AFB1-induced hepatocarcinogenesis was confirmed. Administration of benz(a)anthracene or high levels of ascorbic acid with AFB1 did not alter the tumor incidence.