Linoleate-dependent co-oxygenation of benzo(a)pyrene and benzo(a)pyrene-7,8-dihydrodiol by rat cytosolic lipoxygenase

1. Co-oxygenation of ¹⁴C-labelled benzo(a)pyrene and benzo(a)pyrene-7,8-dihydrodiol was studied in rat lung cytosol, using linoleic acid as a co-substrate. Covalently bound and soluble metabolites were quantified by radiometry and?h.p.l.c., respectively.

2. The co-oxygenation resulted in the production of reactive metabolites capable of protein binding as well as a series of soluble derivatives.

3. Co-oxygenation of benzo(a)pyrene yielded primarily a significant amount of benzo(a)pyrene-6,12-dione while benzo(a)pyrene-7,8-dihydrodiol led to a significant amount of benzo(a)pyrene-trans-anti-tetrol.

4. Their production was abolished by addition of 25 μM of the lipoxygenase inhibitor and antioxidant NDGA.

5. It is postulated that the lineoleic acid peroxyl radicals, formed by rat lung lipoxygenase, initiate the one-electron oxidation of benzo(a)pyrene to its quinones, and epoxidation of benzo(a)pyrene-7,8-diol to the ultimate carcinogenic benzo(a)pyrene-7,8-dihydrodiol-9,10-epoxide.