Correlation between Glyoxal-Induced DNA Cross-Links and Hemoglobin Modifications in Human Blood Measured by Mass Spectrometry

Stable Interstrand Cross-Links Generated from the Repair of 1,N6-Ethenoadenine in DNA by α-Ketoglutarate/Fe(II)-Dependent Dioxygenase ALKBH2

DNA cross-links severely challenge replication and transcription in cells, promoting senescence and cell death. In this paper, we report a novel type of DNA interstrand cross-link (ICL) produced as a side product during the attempted repair of 1,N6-ethenoadenine (εA) by human α-ketoglutarate/Fe(II)-dependent enzyme ALKBH2. This stable/nonreversible ICL was characterized by denaturing polyacrylamide gel electrophoresis analysis and quantified by high-resolution LC-MS in well-matched and mismatched DNA duplexes, yielding 5.7% as the highest level for cross-link formation. The binary lesion is proposed to be generated through covalent bond formation between the epoxide intermediate of εA repair and the exocyclic N6-amino group of adenine or the N4-amino group of cytosine residues in the complementary strand under physiological conditions. The cross-links occur in diverse sequence contexts, and molecular dynamics simulations rationalize the context specificity of cross-link formation. In addition, the cross-link generated from attempted εA repair was detected in cells by highly sensitive LC-MS techniques, giving biological relevance to the cross-link adducts. Overall, a combination of biochemical, computational, and mass spectrometric methods was used to discover and characterize this new type of stable cross-link both in vitro and in human cells, thereby uniquely demonstrating the existence of a potentially harmful ICL during DNA repair by human ALKBH2.

Connecting chemical exposome to human health using high-resolution mass spectrometry-based biomonitoring: Recent advances and future perspectives

Compared with the rapid advances in genomics leading to broad understanding of human disease, the linkage between chemical exposome and diseases is still under investigation. High-resolution mass spectrometry (HRMS) is expected to accelerate the process via relatively accurate and precise biomonitoring of human exposome. This review covers recent advancements in biomonitoring of exposed environmental chemicals (chemical exposome) using HRMS described in the 124 articles that resulted from a systematic literature search on Medline and Web of Science databases. The analytical strategic aspects, including the selection of specimens, sample preparation, instrumentation, untargeted versus targeted analysis, and workflows for MS-based biomonitoring to explore the environmental chemical space of human exposome, are deliberated. Applications of HRMS in human exposome investigation are presented by biomonitoring (1) exposed chemical compounds and their biotransformation products; (2) DNA/protein adducts; and (3) endogenous compound perturbations. Challenges and future perspectives are also discussed.

Mass Spectrometry Analysis of DNA and Protein Adducts as Biomarkers in Human Exposure to Cigarette Smoking: Acrolein as an Example

Acrolein is a major component in cigarette smoke and a product of endogenous lipid peroxidation. It is difficult to distinguish human exposure to acrolein from exogenous sources versus endogenous causes, as components in cigarette smoke can stimulate lipid peroxidation in vivo. Therefore, analysis of acrolein-induced DNA and protein adducts by the highly accurate, sensitive, and specific mass spectrometry-based methods is vital to estimate the degree of damage by this IARC Group 2A carcinogen. This Perspective reviews the analyses of acrolein-induced DNA and protein adducts in humans by mass spectrometry focusing on samples accessible for biomonitoring, including DNA from leukocytes and oral cells and abundant proteins from blood, i.e., hemoglobin and serum albumin.

Malondialdehyde-Induced Post-translational Modifications in Hemoglobin of Smokers by NanoLC-NSI/MS/MS Analysis

Malondialdehyde (MDA) is the most abundant α,β-unsaturated aldehyde generated from endogenous peroxidation of polyunsaturated fatty acids and is present in cigarette smoke. Post-translational modifications of blood hemoglobin can serve as biomarkers for exposure to chemicals. In this study, two types of MDA-induced modifications, the N-propenal and the dihydropyridine (DHP), were identified at multiple sites in human hemoglobin digest by the high-resolution mass spectrometry. The N-propenal and the DHP types of modification led to the increase of 54.0106 and 134.0368 amu, respectively, at the N-terminal and lysine residues. Among the 21 MDA-modified peptides, 14 with dose-response to MDA concentrations were simultaneously quantified in study subjects by the nanoflow liquid chromatography nanoelectrospray ionization tandem mass spectrometry under selected reaction monitoring (nanoLC-NSI-MS/MS-SRM) without prior enrichment. The results showed that the modifications of the N-propenal-type at α-Lys-11, α-Lys-16, α-Lys-61, β-Lys-8, and β-Lys-17, as well as the DHP-type at the α-N-terminal valine, are significantly higher in hemoglobin isolated from the blood of smokers than in nonsmoking individuals. This is the first report to identify and quantify multiple sites of MDA-induced modifications in human hemoglobin from peripheral blood. Our results suggest that the MDA-derived modifications on hemoglobin might represent valuable biomarkers for MDA-induced protein damage.

Quantitation of Nitration, Chlorination, and Oxidation in Hemoglobin of Breast Cancer Patients by Nanoflow Liquid Chromatography Tandem Mass Spectrometry

Cells are continually exposed to endogenous reactive oxygen, nitrogen, and halogen species, causing damage to biomolecules. Among them, peroxynitrite and hypochlorous acid are not only oxidants but also biological nitrating and chlorinating agents, leading to the formation of 3-nitrotyrosine and 3-chlorotyrosine, respectively, in proteins. 3-Nitrotyrosine has been detected in vivo under several pathophysiological conditions, including breast cancer. Studies show that the concentrations of 3-nitrotyrosine in plasma proteins and platelets were significantly elevated in breast cancer patients. Compared to blood serum albumin, hemoglobin adducts represent biomonitoring of exposure with a longer lifetime. In this study, human hemoglobin was freshly isolated from blood and digested into peptides with trypsin, and the levels of protein adducts, including nitration, nitrosylation, and chlorination of tyrosine as well as oxidation of methionine residues, were simultaneously quantified by nanoflow liquid chromatography nanoelectrospray ionization tandem mass spectrometry (nanoLC-NSI/MS/MS) with selected reaction monitoring. The results demonstrated that the relative extents of nitration at α-Tyr-42 and β-Tyr-130, nitrosylation at α-Tyr-24, and chlorination at α-Tyr-24 and β-Tyr-130 are significantly higher in globin of 25 breast cancer patients compared to those in 25 healthy subjects (p < 0.05). In particular, nitration at α-Tyr-42 and chlorination at α-Tyr-24 showed the area under the receiver operating characteristic curve of >0.8. While the age of the subjects is correlated with the extents of some of these adducts, the body mass index does not have an effect on any of them. Starting with 1 drop of blood, our results indicated that this highly sensitive and specific nanoLC-NSI/MS/MS is useful in investigating the role of reactive nitrogen oxide species and reactive chlorine species in the etiology of breast cancer.

Formation and repair of unavoidable, endogenous interstrand cross-links in cellular DNA

Genome integrity is essential for life and, as a result, DNA repair systems evolved to remove unavoidable DNA lesions from cellular DNA. Many forms of life possess the capacity to remove interstrand DNA cross-links (ICLs) from their genome but the identity of the naturally-occurring, endogenous substrates that drove the evolution and retention of these DNA repair systems across a wide range of life forms remains uncertain. In this review, we describe more than a dozen chemical processes by which endogenous ICLs plausibly can be introduced into cellular DNA. The majority involve DNA degradation processes that introduce aldehyde residues into the double helix or reactions of DNA with endogenous low molecular weight aldehyde metabolites. A smaller number of the cross-linking processes involve reactions of DNA radicals generated by oxidation.

Effect of Glyoxal Modification on a Critical Arginine Residue (Arg-31α) of Hemoglobin: Physiological Implications of Advanced Glycated end Product an in vitro Study

BACKGROUND

Non-enzymatic protein glycation is involved in structure and stability changes that impair protein functionality, resulting in several human diseases, such as diabetes and amyloidotic neuropathies (Alzheimer's disease, Parkinson's disease and Andrade's syndrome). Glyoxal, an endogenous reactive oxoaldehyde, increases in diabetes and reacts with several proteins to form advanced glycation end products through Maillard-like reaction.

OBJECTIVE

Human hemoglobin, the most abundant protein in blood cells is subjected to nonenzymatic modification by reactive oxoaldehydes in diabetic condition. In the present study, the effect of a low concentration of glyoxal (5 μM) on hemoglobin (10 μM) has been investigated following a period of 30 days incubation in vitro.

METHODS

Different techniques, mostly biophysical and spectroscopic (e.g. circular dichroism, differential scanning calorimetric study, dynamic light scattering, mass spectrometry, etc.) were used to study glyoxal-induced changes of hemoglobin.

RESULTS

Glyoxal-treated hemoglobin exhibits decreased absorbance around 280 nm, decreased fluorescence and reduced surface hydrophobicity compared to normal hemoglobin. Glyoxal treatment enhances the stability of hemoglobin and lowers its susceptibility to thermal aggregation compared to control hemoglobin as seen by different studies. Finally, peptide mass fingerprinting study showed glyoxal to modify an arginine residue of α-chain of hemoglobin (Arg-31α) to hydroimidazolone.

CONCLUSION

Increased level of glyoxal in diabetes mellitus as well as its high reactivity may cause modifications of the heme protein. Thus, considering the significance of glyoxal-induced protein modification under physiological conditions, the observation appears clinically relevant in terms of understanding hydroimidazolone-mediated protein modification under in vivo conditions.

Unhooking of an interstrand cross-link at DNA fork structures by the DNA glycosylase NEIL3

Interstrand DNA-DNA cross-links (ICLs) are generated by endogenous processes, drugs, and environmental toxins. Understanding the cellular pathways by which various ICLs are repaired is critical to understanding their biological effects. Recent studies showed that replication-dependent repair of an ICL derived from the reaction of an abasic (AP) site with an adenine residue (dA) on the opposing strand of duplex DNA proceeds via a novel mechanism in which the DNA glycosylase NEIL3 unhooks the ICL. Here we examined the ability of the glycosylase domain of murine NEIL3 (MmuNEIL3-GD) to unhook dA-AP ICLs. The enzyme selectively unhooks the dA-AP ICL located at the duplex/single-strand junction of splayed duplexes that model the strand-separated DNA at the leading edge of a replication fork. We show that the ability to unhook the dA-AP ICL is a specialized function of NEIL3 as this activity is not observed in other BER enzymes. Importantly, NEIL3 only unhooks the dA-AP ICL when the AP residue is located on what would be the leading template strand of a model replication fork. The same specificity for the leading template strand was observed with a 5,6-dihydrothymine monoadduct, demonstrating that this preference is a general feature of the glycosylase and independent of the type of DNA damage. Overall, the results show that the glycosylase domain of NEIL3, lacking the C-terminal NPL4 and GRF zinc finger motifs, is competent to unhook the dA-AP ICL in splayed substrates and independently enforces important substrate preferences on the repair process.