Aflatoxin B-1 epoxidation catalysed by partially purified human liver lipoxygenase

(1) This study demonstrates for the first time the human liver lipoxygenase-mediated co-oxidation of aflatoxin B-1 to the reactive metabolite, aflatoxin B-1-8,9-epoxide, which rapidly hydrolyzes to dihydrodiol and preferentially binds to Tris. (2) The Tris-diol complex formed was quantitated fluorimetrically, based on its characteristic excitation at lambda(ex) = 395 nm and emission at lambda(em) = 435 nm. (3) The incubation of partially purified human liver lipoxygenase for 30 min under optimum assay conditions (3.5 mM linoleic acid and 50 mu M aflatoxin B-1 in Tris buffer at pH 7.2) resulted in the formation of 10.6+/-1.7 nmol Tris-diol/mg protein. (4) In addition to linoleic acid, other unsaturated fatty acids namely gamma-linolenic acid, cis-11,14-eicosadienoic acid and arachidonic acid also supported the lipoxygenase mediated epoxidation of aflatoxin B-1. (5) The enzymatic Tris-diol formation was significantly inhibited by all the lipoxygenase inhibitors tested in a concentration-dependent manner. (6) These results strongly suggest that lipoxygenase is capable of aflatoxin B-1 metabolism and this may represent yet another pathway for the bioactivation of this hepatocarcinogen in the human liver.