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Development of an adductomic approach to identify electrophiles in vivo through their hemoglobin adducts
Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Stockholms Universitet, MMK. (Margareta Törnqvist)
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Humans are exposed to electrophilically reactive compounds, both formed endogenously and from exogenous exposure. Such compounds could react and form stable reaction products, adducts, at nucleophilic sites in proteins and DNA. The formation of adducts constitutes a risk for effects, such as cancer and contact allergy, and plays a role in ageing processes. Adducts to proteins offer a possibility to measure electrophilic compounds in vivo.

Adductomic approaches aim to study the totality of adducts, to specific biomolecules, by mass spectrometric screening. This thesis describes the development and application of an adductomic approach for the screening of unknown adducts to N-terminal valine (Val) in hemoglobin (Hb) by liquid chromatography tandem mass spectrometry (LC/MS/MS).

The adductomic approach is based on the FIRE procedure, a modified Edman procedure for the analysis of adducts to N-terminal Val in Hb by LC/MS/MS. The adduct screening was performed by stepwise scanning of precursor ions in small mass increments and monitoring four fragments common for derivatives of detached Val adducts, in the multiple reaction monitoring mode. Samples from 12 smokers/nonsmokers were screened with the adductomic approach, and seven previously identified adducts and 19 unknown adducts were detected. A semiquantitative approach was applied for approximate quantification of adduct levels.

A strategy for identifying unknown Hb adducts using adductome LC/MS/MS data was formulated and applied for the identification of unknown adducts. Identifications were based on the observed m/z of precursor ions and retention times combined with databases and Log P calculations. Hypothesized adducts were generated in vitro for comparison and matching with the corresponding unknown adducts. Five identified adducts correspond to the precursor electrophiles ethyl vinyl ketone (EVK), glyoxal, methylglyoxal, acrylic acid, and 1-octen-3-one. These adducts, except the adducts corresponding to glyoxal and methylglyoxal, have not been observed as protein adducts before.  Probable exposure sources to these electrophiles are diet and/or endogenous formation. The observation of these adducts motivate further studies to evaluate possible contributions to health risks, as well as their potential as biomarkers of exposure.

The adduct from EVK was quantitatively assessed through different experiments to estimate the daily internal dose (area under the concentration-time-curve, AUC). EVK is about 2 × 103 more reactive than the reference compound acrylamide. The EVK adduct was shown to be unstable, with a relatively short half-life. The daily AUC in humans of EVK was estimated to be about 20 times lower than the corresponding AUC of acrylamide from intake via food.

To confirm the observation of the detected unknown adducts and obtain a statistical foundation, analysis of unknown adducts were performed in large sets of blood samples (n = 50–120) from human cohorts. The majority of the previously detected unknown adducts were found in all analyzed samples, and the levels of many adducts showed large variations between individuals. The cause and significance of these observed variations are not yet clarified, but are of importance for the directions of future studies.

In conclusion, a new approach for identification of unknown human exposure to electrophiles was developed and successfully applied. 

Place, publisher, year, edition, pages
Stockholm: Department of Environmental Science and Analytical Chemistry , 2016. , 87 p.
Keyword [en]
Adductomics, Hemoglobin adducts, LC/MS/MS, Ethyl vinyl ketone, Glyoxal, Methylglyoxal, Acrylic acid, 1-Octen-3-one
National Category
Other Chemistry Topics Analytical Chemistry
Research subject
Environmental Chemistry
Identifiers
URN: urn:nbn:se:su:diva-129248ISBN: 978-91-7649-348-9 (print)OAI: oai:DiVA.org:su-129248DiVA: diva2:920520
Public defence
2016-06-10, William-Olssonsalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Cancer and Allergy FoundationSwedish Research Council
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Submitted.

Available from: 2016-05-18 Created: 2016-04-18 Last updated: 2017-02-17Bibliographically approved
List of papers
1. LC–MS/MS Screening Strategy for Unknown Adducts to N-Terminal Valine in Hemoglobin Applied to Smokers and Nonsmokers
Open this publication in new window or tab >>LC–MS/MS Screening Strategy for Unknown Adducts to N-Terminal Valine in Hemoglobin Applied to Smokers and Nonsmokers
2014 (English)In: Chemical Research in Toxicology, ISSN 0893-228X, E-ISSN 1520-5010, Vol. 27, no 12, 2062-2070 p.Article in journal (Refereed) Published
Abstract [en]

Electrophilically reactive compounds have the ability to form adducts with nucleophilic sites in DNA and proteins, constituting a risk for toxic effects. Mass spectrometric detection of adducts to N-terminal valine in hemoglobin (Hb) after detachment by modified Edman degradation procedures is one approach for in vivo monitoring of exposure to electrophilic compounds/metabolites. So far, applications have been limited to one or a few selected reactive species, such as acrylamide and its metabolite glycidamide. This article presents a novel screening strategy for unknown Hb adducts to be used as a basis for an adductomic approach. The method is based on a modified Edman procedure, FIRE, specifically developed for LC-MS/MS analysis of N-terminal valine adducts in Hb detached as fluorescein thiohydantoin (FTH) derivatives. The aim is to detect and identify a priori unknown Hb adducts in human blood samples. Screening of valine adducts was performed by stepwise scanning of precursor ions in small mass increments, monitoring four fragments common for the FTH derivative of valine with different N-substitutions in the multiple-reaction mode, covering a mass range of 135 Da (m/z 503-638). Samples from six smokers and six nonsmokers were analyzed. Control experiments were performed to compare these results with known adducts and to check for artifactual formation of adducts. In all samples of smokers and nonsmokers, seven adducts were identified, of which six have previously been studied. Nineteen unknown adducts were observed, and 14 of those exhibited fragmentation patterns similar to earlier studied FTH derivatives of adducts to valine. Identification of the unknown adducts will be the focus of future work. The presented methodology is a promising screening tool using Hb adducts to indicate exposure to potentially toxic electrophilic compounds and metabolites.

National Category
Chemical Sciences
Research subject
Environmental Chemistry
Identifiers
urn:nbn:se:su:diva-112092 (URN)10.1021/tx5002749 (DOI)000346543900008 ()
Available from: 2015-01-09 Created: 2015-01-09 Last updated: 2017-12-05Bibliographically approved
2. Characterization of a Hemoglobin Adduct from Ethyl Vinyl Ketone Detected in Human Blood Samples
Open this publication in new window or tab >>Characterization of a Hemoglobin Adduct from Ethyl Vinyl Ketone Detected in Human Blood Samples
2015 (English)In: Chemical Research in Toxicology, ISSN 0893-228X, E-ISSN 1520-5010, Vol. 28, no 11, 2120-2129 p.Article in journal (Refereed) Published
Abstract [en]

Electrophiles have the ability to form adducts to nudeophilic sites in proteins and DNA. Internal exposure to such compounds thus constitutes a risk for toxic effects. Screening of adducts using mass spectrometric methods by adductomic approaches offers possibilities to detect unknown electrophiles present in tissues. Previously, we employed untargeted adductomics to detect 19 unknown adducts to N-terminal valine in hemoglobin (Hb) in human blood. This article describes the characterization of one of these adducts, which was identified as the adduct from ethyl vinyl ketone (EVK). The mean adduct level was 40 +/- 12 pmol/g Hb in 12 human blood samples; adduct levels from acrylamide (AA) and methyl vinyl ketone (MVK) were quantified for comparison. Using L-valine p-nitroanilide (Val-pNA), introduced as a model of the N-terminal valine, the rate of formation of the EVK adduct was studied, and the rate constant determined to 200 M(-1)h(-1) at 37 degrees C. In blood, the reaction rate was too fast to be feasibly measured, EVK showing a half-life <1 min. Parallel experiments with AA and MVK showed that the two vinyl ketones react approximately 2 x 10(3) times faster than AA. The EVK-Hb adduct was found to be unstable, with a half-life of 7.6 h. From the mean adduct level measured in human blood, a daily dose (area under the concentration-time-curve, AUC) of 7 nMh EVK was estimated. The AUC of AA from intake via food is about 20 times higher. EVK is naturally present in a wide range of foods and is also used as a food additive. Most probably, naturally formed EVK is a major source to observed adducts. Evaluation of available toxicological data and information on occurrence of EVK indicate that further studies of EVK are motivated. This study illustrates a quantitative strategy in the initial evaluation of the significance of an adduct detected through adduct screening.

National Category
Chemical Sciences Pharmacology and Toxicology
Research subject
Environmental Chemistry
Identifiers
urn:nbn:se:su:diva-125010 (URN)10.1021/acs.chemrestox.5b00287 (DOI)000364980800008 ()26447499 (PubMedID)
Available from: 2016-01-12 Created: 2016-01-07 Last updated: 2017-11-30Bibliographically approved
3. Strategy for identifying unknown hemoglobin adducts using adductome LC-MS/MS data: Identification of adducts corresponding to acrylic acid, glyoxal, methylglyoxal, and 1-octen-3-one
Open this publication in new window or tab >>Strategy for identifying unknown hemoglobin adducts using adductome LC-MS/MS data: Identification of adducts corresponding to acrylic acid, glyoxal, methylglyoxal, and 1-octen-3-one
2016 (English)In: Food and Chemical Toxicology, ISSN 0278-6915, E-ISSN 1873-6351, Vol. 92, 94-103 p.Article in journal (Refereed) Published
Abstract [en]

Electrophilic compounds have the ability to form adducts with nucleophilic sites in proteins and DNA in tissues, and thereby constitute risks for toxic effects. Adductomic approaches are developed for systematic screening of adducts to DNA and blood proteins, with the aim to detect unknown internal exposures to electrophiles. In a previous adductomic screening of adducts to N-terminals in hemoglobin, using LC-MS/MS, 19 unknown adducts were detected in addition to seven previously identified adducts. The present paper describes the identification of four of these unknown adducts, as well as the strategy used to identify them. Using LC-MS data from the screening, hypotheses about adduct identities were formulated: probable precursor electrophiles with matching molecular weights were suggested based on the molecular weights of the modifications and the retention times of the analytes, in combination with comparisons of theoretical Log P calculations and databases. Reference adducts were generated by incubation of blood samples with the hypothesized precursor electrophiles. The four identified precursor electrophiles, corresponding to the observed unknown adducts, were glyoxal, methylglyoxal, acrylic acid and 1-octen-3-one. Possible origins/exposure sources and toxicological information concerning the electrophilic precursors are discussed. The identified adducts could be explored as possible biomarkers for exposure.

Keyword
Adductomics, Hemoglobin adducts, Glyoxal, Methylglyoxal, Acrylic acid, 1-Octen-3-one
National Category
Chemical Sciences
Research subject
Environmental Chemistry
Identifiers
urn:nbn:se:su:diva-129040 (URN)10.1016/j.fct.2016.03.028 (DOI)000376804400011 ()
Funder
Swedish Research CouncilCancer and Allergy Foundation
Available from: 2016-04-13 Created: 2016-04-13 Last updated: 2017-11-30Bibliographically approved
4. Adductomic Screening of N-terminal Hemoglobin Adducts and Measurement of Micronuclei in Blood Samples from Swedish School Children
Open this publication in new window or tab >>Adductomic Screening of N-terminal Hemoglobin Adducts and Measurement of Micronuclei in Blood Samples from Swedish School Children
Show others...
(English)Article in journal (Refereed) Submitted
Keyword
Adductomics, LC/MS/MS, micronuclei, hemoglobin adducts
National Category
Chemical Sciences
Research subject
Environmental Chemistry
Identifiers
urn:nbn:se:su:diva-129247 (URN)
Available from: 2016-04-18 Created: 2016-04-18 Last updated: 2016-04-29Bibliographically approved

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