title: Investigation of the cumulative tissue doses of naphthoquinones in human serum using protein adducts as biomarker of exposure.
abstract: Both 1,2-naphthoquinone (1,2-NPQ) and 1,4-naphthoquinone (1,4-NPQ) are reactive metabolites of naphthalene that are thought to be responsible for the naphthalene-induced cytotoxicity and genotoxicity. The aim of this study was to investigate the cumulative tissue dose of 1,2-NPQ and 1,4-NPQ in human serum derived from blood donors in Taiwan via measurements of albumin adducts by a methodology, which employs trifluoroacetic acid anhydride and methanesulfonic acid to selectively cleave cysteinyl adducts on proteins. Both 1,2-NPQ and 1,4-NPQ adducts were detected in all male and female subjects (n=22). The median levels of 1,2-NPQ adduct in human subjects were estimated to be 268 (range 139-857) and 203 (range 128-1352) (pmol/g) in male (n=11) and female (n=11) subjects, respectively. In contrast, the median levels of 1,4-NPQ adduct were estimated to be 45.0 (range 22.0-117) and 38.9 (range 21.5-172) (pmol/g) in male and female subjects, respectively. We noticed that levels of 1,2-NPQ adduct were significantly correlated with those of 1,4-NPQ adduct (correlation coefficient r=0.643, p<0.01). Results from in vitro experiments confirmed that the production of naphthoquinones-derived adducts on serum albumin increased with increased concentration of naphthoquinones (0-100 microM). Linear relationships were observed over the range of concentration. Time-course experiments suggested that both 1,2-NPQ and 1,4-NPQ-derived adducts rapidly reached maximum values at 10 min mark and remained constant thereafter. The reaction rate constant analyses indicated that the second-order rate constants, representing in vitro reactions between naphthoquinones and cysteine residues of serum albumin, were estimated to be 0.0044/0.0002L(gprotein)(-1)h(-1), respectively. Overall, the cumulative tissue doses of 1,4-NPQ (217-316 nM h) in male and female subjects were approximately 3-fold greater than those of 1,2-NPQ (76-98 nM h) in the study population. The initial concentrations of serum 1,2-NPQ and 1,4-NPQ in the study population were estimated to be between 145-188 and 807-1175 nM, respectively. We conclude that the relatively large amounts of naphthoquinones present in human serum may point to toxicological consequences.
authors.affiliation: Department of Environmental Engineering, National Chung Hsing University, Taichung 402, Taiwan. pohsiunglin@yahoo.com
authors.forename: Po-Hsiung
authors.initials: PH
authors.lastname: Lin
authors.forename: Dar-Ren
authors.initials: DR
authors.lastname: Chen
authors.forename: Tzu-Wen
authors.initials: TW
authors.lastname: Wang
authors.forename: Chia-Hua
authors.initials: CH
authors.lastname: Lin
authors.forename: Ming-Chieh
authors.initials: MC
authors.lastname: Chuang
mesh_terms: D000328:Adult; D015415:Biomarkers / Q000097:blood*; D001782:Blood Donors; D004781:Environmental Exposure; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009285:Naphthoquinones / Q000097:blood*; D013624:Taiwan
chemical_list: D015415:Biomarkers; D009285:Naphthoquinones