Aflatoxin B1epoxidation catalysed by partially purified human liver lipoxygenase

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Abstract
(1) This study demonstrates for the first time the human liver lipoxygenase-mediated co-oxidation of aflatoxin B1 to the reactive metabolite, aflatoxin B1-8,9-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 λex 395 nm and emission at λem 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 μM aflatoxin B1 in Tris buffer atpH 7.2) resulted in the formation of 10 ± 1.7 nmol Tris- diol/mg protein. (4) In addition to linoleic acid, other unsaturated fatty acids namely γ-linolenic acid, cis-11,14-eicosadienoic acid and arachidonic acid also supported the lipoxygenase mediated epoxidation of aflatoxin B1. (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 B1 metabolism and this may represent yet another pathway for the bioactivation of this hepatocarcinogen in the human liver.

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