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 Nterminal
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 Nterminal
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 Nsubstitutions
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