Discovery of Novel N-(4-Hydroxybenzyl)valine Hemoglobin Adducts in Human Blood

Amanda Degner, Henrik Carlsson, Isabella Karlsson, Johan Eriksson, Suresh S. Pujari, Natalia Y. Tretyakova, Margareta Törnqvist

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12 Scopus citations

Abstract

Humans are exposed to a wide range of electrophilic compounds present in our diet and environment or formed endogenously as part of normal physiological processes. These electrophiles can modify nucleophilic sites of proteins and DNA to form covalent adducts. Recently, powerful untargeted adductomic approaches have been developed for systematic screening of these adducts in human blood. Our earlier untargeted adductomics study detected 19 unknown adducts to N-terminal valine in hemoglobin (Hb) in human blood. We now describe a full characterization of one of these adducts, which corresponds to the addition of a 4-hydroxybenzyl (4-OHBn) group to N-terminal valine in Hb to form N(4-hydroxybenzyl)valine (4-OHBn-Val). The adduct structure was determined by comparison of its accurate mass, HPLC retention time, and MS/MS fragmentation to that of authentic standards prepared by chemical synthesis. Average 4-OHBn-Val adduct concentrations in 12 human blood samples were estimated to 380 ± 160 pmol/g Hb. Two possible routes of 4-OHBnVal adduct formation are proposed using two different precursor electrophiles: 4-quinone methide (4-QM) and 4-hydroxybenzaldehyde (4-OHBA). We found that 4-QM reacts rapidly with valine to form the 4-OHBn-Val adduct; however, the quinone methide is unstable under physiological conditions due to hydrolysis. It was shown that 4-OHBA forms reversible Schiff base adducts with valine, which can be stabilized via reduction in blood generating the 4-OHBn-Val adduct. In addition, trace amounts of isomeric 2-hydroxybenzyl-valine (2-OHBn-Val) adducts were detected in 12 human blood samples (estimated mean adduct level, 5.0 ± 1.4 pmol/g Hb). Further studies are needed to quantify the contributions from identified possible precursor electrophiles to the observed hydroxybenzyl adducts in humans.

Original languageEnglish (US)
Pages (from-to)1305-1314
Number of pages10
JournalChemical research in toxicology
Volume31
Issue number12
DOIs
StatePublished - Dec 17 2018

Bibliographical note

Funding Information:
*E-mail: margareta.tornqvist@aces.su.se. ORCID Suresh S. Pujari: 0000-0002-0246-3362 Natalia Y. Tretyakova: 0000-0002-0621-6860 Margareta Törnqvist: 0000-0002-5626-1125 Author Contributions §These authors contributed equally to this work. Funding We acknowledge Sw. Research Council and Stockholm University for financial support. A.D. was partially supported by the American Chemistry Council and a grant from the National Cancer Institute (P01 CA138338). Notes The authors declare no competing financial interest.

Publisher Copyright:
© 2018 American Chemical Society.

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