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Comparison of Protein Adducts of Benzene Oxide and Benzoquinone in the Blood and Bone Marrow of Rats and Mice Exposed to [¹⁴C/¹³C₆]Benzene¹

Department of Environmental Sciences and Engineering, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7400

Protein binding of hemoglobin (Hb) and bone marrow was used to compare in vivo reactions of 3 electrophilic metabolites of benzene, i.e., benzene oxide and 1,2- and 1,4-benzoquinone (1, 2-BQ and 1, 4-BQ), in F344 rats and B6C3F₁ mice. Following a single p.o. administration of a mixture of [¹⁴C]- and [¹³C₆]benzene between 50 and 400 mg/kg body weight, cysteine adducts of benzene oxide, 1,2-BQ, and 1,4-BQ were assayed, and the proportions of cysteine-bound adducts to total protein binding were estimated. Although dose-related production of each adduct was seen, large differences were observed between species and tissues. With rat Hb, benzene oxide adducts represented 27% of the total Hb binding and 73% of the cysteinyl binding, whereas quinone adducts represented relatively small proportions. However, with mouse Hb, the 1,4-BQ adducts accounted for 5.5% of the total Hb binding and 12.2% of the cysteinyl binding, while 1,2-BQ and benzene oxide each accounted for less than 3% of the total. In the bone marrow of both rats and mice, BQ adducts were more abundant than those of benzene oxide. However, adducts of 1,2-BQ predominated in rat marrow (9% of binding), whereas adducts of 1,4-BQ were more abundant in the mouse (21% of binding). The average blood concentrations of 1,4-BQ were estimated from the adduct levels and reaction-rate constants to be 2–5-fold higher in the mouse than in the rat. This work suggests that BQ binding is favored over that of benzene oxide in the bone marrow; however, high background levels of BQ adducts, observed with Hb and bone marrow proteins, suggest that any toxic effects of the quinones should only arise from high exposures to benzene.

¹ This work was supported by the National Institute of Environmental Health Sciences through Grant P42ES05948.

² To whom requests for reprints should be addressed, at Department of Environmental Sciences and Engineering, CB 7400, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7400.

Received 3/10/94. Accepted 7/13/94.

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