Mass spectrometric identification of a candidate biomarker peptide from the in vitro interaction of epichlorohydrin with red blood cells

Globin monoadducts and cross-links provide evidence for the presence of S-(1,2-dichlorovinyl)-L-cysteine sulfoxide, chlorothioketene, and 2-chlorothionoacetyl chloride in the circulation in rats administered S-(1,2-dichlorovinyl)-L-cysteine

S-(1,2-Dichlorovinyl)-L-cysteine (DCVC), a mutagenic and nephrotoxic metabolite of trichloroethylene, is bioactivated to S-(1,2-dichlorovinyl)-L-cysteine sulfoxide (DCVCS) and chlorothioketene and/or 2-chlorothionoacetyl chloride by cysteine conjugate S-oxidase (S-oxidase) and cysteine conjugate beta-lyase (beta-lyase), respectively. Previously, we identified DCVCS-globin monoadducts and cross-links upon treating rats with DCVCS or incubating erythrocytes with DCVCS. In this study, the formation of DCVC-derived reactive intermediates was investigated after rats were given a single (230 or 460 micromol/kg, i.p.) or multiple (3 or 30 micromol/kg daily for 5 days) DCVC doses. LC/ESI/MS of trypsin-digested globin peptides revealed both S-oxidase and beta-lyase-derived globin monoadducts and cross-links consistent with in vivo DCVC bioactivation by both pathways. MS/MS analyses of trypsin-digested fractions of globin from one of the rats treated with multiple 30 micromol/kg DCVC doses led to identification of beta-lyase-derived monoadducts on both Cys93 and Cys125 of the beta-chains. While rats dosed with the 230 micromol/kg DCVC dose exhibited beta-lyase-dependent monoadducts and cross-links only (four out of four rats), rats given the 460 micromol/kg DCVC dose (two out of four) and rats administered the multiple DCVC doses (two out of four) exhibited both beta-lyase- and S-oxidase-derived monoadducts and cross-links. Because previous incubations of erythrocytes with DCVC did not result in detection of DCVCS-derived monoadducts or cross-links and had only resulted in detection of beta-lyase-derived monoadducts and cross-links, the DCVCS-globin monoadducts and cross-links detected in this study are likely the result of DCVC bioactivation outside the circulation and subsequent translocation of DCVCS and N-acetylated DCVCS into the erythrocytes.

Toward an "omic" physiopathology of reactive chemicals: thirty years of mass spectrometric study of the protein adducts with endogenous and xenobiotic compounds

Cancer and degenerative diseases are major causes of morbidity and death, derived from the permanent modification of key biopolymers such as DNA and regulatory proteins by usually smaller, reactive molecules, present in the environment or generated from endogenous and xenobiotic components by the body's own biochemical mechanisms (molecular adducts). In particular, protein adducts with organic electrophiles have been studied for more than 30 [see, e.g., Calleman et al., 1978] years essentially for three purposes: (a) as passive monitors of the mean level of individual exposure to specific chemicals, either endogenously present in the human body or to which the subject is exposed through food or environmental contamination; (b) as quantitative indicators of the mean extent of the individual metabolic processing which converts a non-reactive chemical substance into its toxic products able to damage DNA (en route to cancer induction through genotoxic mechanisms) or key proteins (as in the case of several drugs, pesticides or otherwise biologically active substances); (c) to relate the extent of protein modification to that of biological function impairment (such as enzyme inhibition) finally causing the specific health damage. This review describes the role that contemporary mass spectrometry-based approaches employed in the qualitative and quantitative study of protein-electrophile adducts play in the discovery of the (bio)chemical mechanisms of toxic substances and highlights the future directions of research in this field. A particular emphasis is given to the measurement of often high levels of the protein adducts of several industrial and environmental pollutants in unexposed human populations, a phenomenon which highlights the possibility that a number of small organic molecules are generated in the human organism through minor metabolic processes, the imbalance of which may be the cause of "spontaneous" cases of cancer and of other degenerative diseases of still uncharacterized etiology. With all this in mind, it is foreseen that a holistic description of cellular functions will take advantage of new analytical methods based on time-integrated metabolomic measurements of a new biological compartment, the "adductome," aimed at better understanding integrated organism response to environmental and endogenous stressors.

Novel lipid hydroperoxide-derived hemoglobin histidine adducts as biomarkers of oxidative stress

Hemoglobin (Hb) adducts have long been used as dosimeters of exposure to xenobiotics and endogenously formed reactive metabolites. In this study, hemoglobin chains were separated from each other and their prosthetic heme groups and reacted with 4-oxo-2-nonenal, a major breakdown product of lipid hydroperoxides. The adducts were characterized by matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-TOF/MS) analysis of the intact proteins and by a combination of liquid chromatography/electrospray ionization/tandem MS (MS/MS) and MALDI-TOF/MS/MS analysis of the tryptic peptides. Covalent modifications were found on both hemoglobin chains. The location was determined to be on H20 of the alpha-hemoglobin chain and on H(63) of the beta-hemoglobin chain. Molecular modeling revealed that these two residues were two most solvent accessible H residues present in intact Hb. The proposed reaction mechanism is based on that described for the reaction of 4-hydroxy-2-nonenal with proteins. Initial nucleophilic Michael addition is followed by hydration of the resulting aldehyde, cyclization, and two sequential dehydration reactions to give stable furan derivatives. This results in the addition of 136 Da from 4-oxo-2-nonenal to give adducts corresponding to (17)VGAH(.) AGEYGAEALER(31) from alpha-hemoglobin and (62)AH(.) GK(65) from beta-hemoglobin. These hemoglobin modifications can potentially serve as biomarkers of lipid hydroperoxide-mediated macromolecule damage and may reflect an indirect measurement of the potential for DNA damage in vivo.

Hemoglobin Adduct Levels in Rat and Mouse Treated with 1,2:3,4-Diepoxybutane

For cancer risk assessment of 1,3-butadiene from rodent cancer test data, the in vivo doses of formed 1,2:3,4-diepoxybutane (DEB) should be known. In vivo doses of DEB were measured through a specific reaction product with hemoglobin (Hb), a ring-closed adduct, N,N-(2,3-dihydroxy-1,4-butadiyl)valine (Pyr-Val), to N-terminal valines. An analytical method based on tryptic digestion of Hb and quantification of Pyr-modified heptapeptides by LC-MS/MS has been further developed and applied in vivo to DEB-treated rats. Furthermore, N-(2,3,4-trihydroxybutyl)valine adducts (THB-Val) to the N-terminal valine in Hb were measured in rats and mice treated with DEB and in a complementary experiment with 1,2-epoxy-3,4-butanediol (EBdiol), using a modified Edman degradation method and GC-MS/MS. In vitro reactions of hemolysate with DEB and EBdiol were used to measure reaction rates for adduct formation needed for calculation of doses and rates elimination in vivo. The results showed that the level of the Pyr-Val adduct per administered dose of DEB was approximately the same in rats as had earlier been observed in mice [Kautiainen et al. (2000) Rapid Commun. Mass Spectrom. 14, 1848-1853]. Levels of the THB-Val adduct after DEB treatment were 3-4 times higher in rat than in mouse, probably reflecting an enhanced hydrolysis of DEB to EBdiol catalyzed by epoxide hydrolase. After EBdiol treatment, the THB-Val adduct levels were about the same in rat and mouse. Calculations from in vitro data show that the Pyr-Val adduct is a relevant monitor for the in vivo dose of DEB and that THB-Val primarily reflects doses to EBdiol. The calculated rates of formation of adducts and rates of elimination agree with expectations. Procedures for quantification of Hb adducts as modified peptides as well as preparation and characterization of peptide standards have been evaluated.

Structural analysis of styrene oxide/haemoglobin adducts by mass spectrometry: identification of suitable biomarkers for human exposure evaluation

The structural characterisation of adducts formed by the in vitro reaction of haemoglobin (Hb) with styrene oxide (SO), the most reactive metabolite of the industrial reagent styrene, was obtained by liquid chromatography/electrospray ionisation mass spectrometry (LC/ES-MS) analysis of modified tryptic peptides of human Hb chains. The reactive sites of human Hb towards SO were identified through characterisation of alkylated tryptic peptides by matrix-assisted laser desorption/ionisation with tandem mass spectrometry (MALDI-MS/MS). A procedure was set up based on this characterisation, allowing Hb modification to be assessed by monitoring SO/Hb adducts using HPLC with selected ion recording (SIR) mass spectrometry. By this methodology it was also possible to compare advantages and disadvantages of presently available strategies for the measurement of Hb adducts with SO. The results obtained could most plausibly lead to the optimisation of molecular dosimetry of SO adducts, and the analytical procedure described herein could be applied to the biological monitoring of styrene exposure in the workplace.

Ion trap mass spectrometry in the structural analysis of haemoglobin peptides modified by epichlorohydrin and diepoxybutane

Ion trap mass spectrometry has been shown to be particularly suitable for the structural analysis of high molecular weight peptides directly fragmented in the mass analyser without needing further sub-digestion reactions. Here we report the advantages of using multi-stage ion trap mass spectrometry in the structural characterisation of haemoglobin alkylated with epichlorohydrin and diepoxybutane. Alkylated globins were digested with trypsin and the peptide mixtures were analysed by MS(3). This technique allows the sequential fragmentation of peptides under analysis, giving rise to MS(3) product ion spectra with additional information with respect to MS(2) mass spectra. The results obtained complete the previously reported structural characterisation of alkylated haemoglobin, demonstrating the potential of ion trap mass spectrometry.