No abstract

Adducts of styrene 7,8-oxide (SO) with the blood proteins, Hb and albumin (Alb), were measured following treatment of the proteins with Raney nickel (Ra-Ni) to cleave 2-phenylethanol, which was subsequently assayed. Internal standards were prepared by modifying Hb and Alb with 4-methyl-SO to produce similar adducts. In a preliminary experiment with human blood, which had been modified with [14C]SO in vitro, it was determined that Ra-Ni released 6% of the total binding to globin and 76% of the total binding to Alb. Since Ra-Ni primarily cleaves covalently-bound sulfur species, this suggests that much more binding to human serum Alb occurred at a free cysteine residue than to human Hb. The overall rate of reaction of SO at 37 degrees C in vitro had a half-time of 0.70 h in human blood and of 0.36 h in blood from Sprague-Dawley rats. Adducts of SO with Hb and Alb were measured following SO modification of blood from humans and rats in vitro at 37 degrees C. Slopes of the linear relationships between adduct level and SO concentration allowed the following second-order rate constants [(L/mol of protein)/h] to be estimated: rat Hb, 72; human Hb, 2.4; rat Alb, 63; human Alb, 32. These rate constants show that intrinsic reactivity of SO toward the cysteine residue of human Hb is much lower than that of rat Hb or of Alb from either species. Adducts of Hb and Alb were also measured following administration of both SO and styrene to rats.(ABSTRACT TRUNCATED AT 250 WORDS)

No abstract

Little is known about the formation and disposition of benzene oxide (BO), the initial metabolite arising from oxidation of benzene by cytochrome P450. In this study, reactions of BO with hemoglobin (Hb) and albumin (Alb) were investigated in blood from B6C3F1 mice, F344 rats, and humans in vitro. The estimated half-lives of BO in blood were 6.6 min (mice), 7.9 min (rats), and 7.2 min (humans). The following second-order rate constants were estimated for reactions between BO and cysteinyl residues of Hb and Alb [in units of L (g of Hb- or Alb-h)-1]: mouse Hb = 1.16 x 10(-)4, rat Hb = 15.4 x 10(-)4, human Hb = 0.177 x 10(-)4, mouse Alb = 2.68 x 10(-)4, rat Alb = 4.96 x 10(-)4, and human Alb = 5.19 x 10(-)4. These rate constants were used with BO-adduct measurements to assess the systemic doses of BO arising from benzene in vivo in published animal and human studies. Among rats receiving a single gavage dose of 400 mg of benzene/kg of body weight, the BO dose of 2.62 x 10(3) nM BO-h, predicted from Alb adducts, was quite similar to the reported AUC0-infinity = 1.09 x 10(3) nM BO-h of BO in blood. Interestingly, assays of Hb adducts in the same rats predicted a much higher dose of 14.7 x 10(3) nM BO-h, suggesting possible in situ generation of adducts within the erythrocyte. Doses of BO predicted from Alb adducts were similar in workers exposed to benzene [13.3 nM BO-h (mg of benzene/kg of body weight)-1] and in rats following a single gavage dose of benzene [8. 42 nM BO-h (mg of benzene/kg of body weight)-1]. Additional experiments indicated that crude isolates of Hb and Alb had significantly higher levels of BO adducts than dialyzed proteins, suggesting that conjugates of low-molecular-weight species were abundant in these isolates.