AFLATOXIN-B1 METABOLISM TO AFLATOXICOL AND DERIVATIVES LETHAL TO BACILLUS-SUBTILIS GSY 1057 BY RAINBOW-TROUT (SALMO-GAIRDNERI) LIVER

Abstract

Aflatoxicol, R0, was isolated from Mt. Shasta strain rainbow trout (S. gairdneri), and liver homogenates were incubated with aflatoxin B1. Its identity was confirmed by mass, IR and UV spectrometry. The structure was identical to 1 of the diastereomers prepared by chemical reduction of aflatoxin B1. Aflatoxicol was apparently formed by a NADPH-dependent soluble enzyme of the 105,000 .times. g supernatant from rainbow trout. Aflatoxicol was not lethal in phosphate buffer to B. subtilis GSY 1057 (metB4, hisA1, uvr-1) nor were aflatoxins B1, Q1 and B2. In the presence of NADPH and trout liver microsomes, aflatoxicol reduced the viability of B. subtilis. Aflatoxin B2, which lacks the vinyl ether present in the other compounds, could not be activated. The product of aflatoxin B1 activation by trout liver microsomes was sought after incubation of 14C-labeled aflatoxin B1. The radioactivity was found in unaltered aflatoxin B1 and in 3 extremely polar metabolites. The quantity of the new metabolites and the level of microbial lethality was reduced by addition of cytosine and cysteine to the incubation medium. The vinyl ether configuration was a structural requirement for activation, and this finding the nature of the enzymatic reaction were consistent with the hypothesis that the compounds were metabolized to highly reactive and unstable electrophilic products which bound to nucleophiles such as cytosine and were lethal to B. subtilis. The formation of aflatoxicol as the major product of trout liver metabolism is of great significance considering that it could be activated to a lethal compound and rainbow trout are 1 of the most sensitive species to aflatoxin B1-induced [liver] carcinoma.