A wide variety of phenolic compounds are constituents of the human diet. These include synthetic antioxidants, such as butylated hydroxytoluene (BHT) and butylated hydroxyanisole, together with naturally occurring substances such as vitamin E and hydroxylated flavonoids. Many of these produce diverse biochemical effects that range from tumor prevention to tumor initiation or promotion. Mutagenicity and cytotoxicity are also associated with certain dietary phenols. Much evidence indicates that phenols undergo metabolic activation to reactive species which can affect essential cellular processes. A common chemical feature of these compounds is their susceptibility to one-electron oxidation to produce phenoxy radicals. These radicals readily undergo further one-electron oxidation to quininoid species and also combine with molecular oxygen to produce hydroperoxy derivatives (peroxyquinols). This latter pathway has received very little attention, partly due to the high reactivity of peroxyquinols in biological systems, and also to a lack of knowledge concerning the transformation products formed. Cytochrome P-450 is a potent peroxidase, but its mechanism of action remains unclear. Studies have shown that BHT is converted to hydroperoxide in hepatic microsomes and that this peroxyquinol is rapidly degraded by P-450. Results of detailed product studies indicated the existance of three distinct pathways involving free radical formation, isomerization and electrophilic rearrangements. The proposed project will address three related issues, the role of hydroperoxide pathways in phenol metabolism, the mechanisms of cytochrome P-450 degradation of peroxyquinols and the relationships of these processes to phenol toxicity.
The specific aims are as follows. (1) Synthesize hydroperoxide derivatives of alkylated phenols, and (2) investigate mechanisms of the cytochrome P-450-catalyzed transformations of the hydroperoxides. Peroxyquinols of varying structures will be incubated with hepatic microsomes and purified P-450, and the products identified. This information will facilitate elucidation of the mechanisms involved. (3) Evaluate the contribution of hydroperoxide formation to the biotransformations of phenolic antioxidants and their analogs. (4) Investigate influences of enzyme origin on the formation and degradation of hydroperoxides. (5) Investigate the effects of peroxyquinols on lipid peroxidation, destruction of cytochrome P-450, oxidations of cosubstrates, and on biological macromolecules via covalent binding.
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