Measurement of adducts of benzoquinone with hemoglobin and albumin.
Benzoquinones (BQ) are genotoxic species that stem from metabolism of phenolic compounds. We have developed a method for measuring adducts of 1,2- and 1,4-benzoquinone (1,2-BQ and 1,4-BQ) with cysteine residues of hemoglobin (Hb) and albumin (Alb). The method employs a reductive catalyst (Raney nickel) to selectively cleave sulfur-bound adducts so that they may be extracted with an organic solvent, derivatized with heptafluorobutyrylimidazole and measured by GC-ECD or GC-MS. Reactions of 1,4-BQ (0-300 microM) with whole blood of both F344 rats and humans resulted in linear formation of adducts with Hb and Alb. Adducts of 1,2-BQ with human Alb were formed by activation of catechol (0-300 microM) in situ with horseradish peroxidase. The mean half lives in vitro of 1,4-BQ in blood from humans and rats were 3.5 and 0.68 h, respectively. Second-order rate constants for reaction of 1,4-BQ with Hb and Alb in whole blood were estimated to be 18 and 76 l/mol/h for humans and 180 and 74 l/mol/h for rats respectively. Interestingly, the following high background levels of 1,2-BQ and 1,4-BQ adducts were observed in the proteins: 1,2-BQ-human Hb = 1.5 nmol/g, rat Hb = 25.1 nmol/g; human Alb = 8.0 nmol/g; 1,4-BQ-human Hb = 27.2 nmol/g, rat Hb = 11.5 nmol/g; human Alb = 20.5 nmol/g. These large background levels of BQ adducts suggest that significant exposure to BQ precursors occurs from dietary and/or endogenous sources. Given current evidence regarding the genotoxicity of BQ, such exposures and their health consequences should be investigated.
McDonald
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Department of Environmental Sciences and Engineering, University of North Carolina at Chapel Hill 27599.
Waidyanatha
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Rappaport
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D000818:Animals; D016227:Benzoquinones / Q000378:metabolism*; D001798:Blood Proteins / Q000378:metabolism; D002396:Catechols / Q000378:metabolism*; D006441:Hemoglobin A / Q000378:metabolism*; D006801:Humans; D009532:Nickel; D051381:Rats; D011916:Rats, Inbred F344; D012709:Serum Albumin / Q000378:metabolism*
D016227:Benzoquinones; D001798:Blood Proteins; D002396:Catechols; D012709:Serum Albumin; C004532:quinone; D009532:Nickel; D006441:Hemoglobin A; C034221:catechol; C025225:2-benzoquinone