Elevated α-methyl-γ-hydroxy-1,N2-propano-2'-deoxyguanosine levels in urinary samples from individuals exposed to urban air pollution

Evaluation of the adsorption properties of nucleobase-modified sorbents for a solid-phase extraction of water-soluble compounds

We developed hydrophilic interaction chromatography (HILIC)-type sorbents modified with nucleobases for solid phase extraction (SPE). The synthesized hydrophilic base resins were modified by each nucleobase (adenine, guanine, and cytosine). The measurement of the amount of water content indicated that each nucleobase-modified sorbent had a water layer. To evaluate the adsorption properties in the HILIC mode, we chose two nucleobases (uracil and adenine) and four nucleosides (uridine, adenosine, cytidine, guanosine) as water-soluble analytes, which were loaded into an SPE cartridge packed with the nucleobase-modified sorbent. Firstly, 95% acetonitrile (ACN) solutions were used in the process of conditioning and sample loading of the above polar analytes. High recoveries of the analytes were observed in each nucleobase-modified sorbent, and the Diol-type sorbent (no modification with any of the nucleobases) did not adsorb each water-soluble analyte. On the basis of this result, a 98% ACN solution was used during the process of conditioning and sample loading to decrease the concentration of water in the sample, which potentially inhibited the formation of hydrogen bonding between each analyte and the modified nucleobase. Considerable improvements of recoveries were observed in Adenine- and Cytosine-modified sorbents. These results were possibly attributed to the effective expression of hydrogen bonding by decreasing water concentration in the sample solution. Although a non-aqueous (100% ACN) sample solution can be expected to obtain higher recoveries compared with the 98% ACN solution, a decrease in recoveries was observed in Adenine-modified sorbent. From these results, the highest adsorption property was observed in Adenine-modified sorbent using 98% ACN as a sample condition, and the combination of this sample condition and sorbent is effective for high adsorption under HILIC condition. Moreover, we also revealed that a balance between the thickness of water layer and the modification amount of nucleobase is important for retention in the HILIC-type sorbent.

DNA Adducts as Biomarkers To Predict, Prevent, and Diagnose Disease-Application of Analytical Chemistry to Clinical Investigations

Characterization of the chemistry, structure, formation, and metabolism of DNA adducts has been one of the most significant contributions to the field of chemical toxicology. This work provides the foundation to develop analytical methods to measure DNA adducts, define their relationship to disease, and establish clinical tests. Monitoring exposure to environmental and endogenous toxicants can predict, diagnose, and track disease as well as guide therapeutic treatment. DNA adducts are one of the most promising biomarkers of toxicant exposure owing to their stability, appearance in numerous biological matrices, and characteristic analytical properties. In addition, DNA adducts can induce mutations to drive disease onset and progression and can serve as surrogate markers of chemical exposure. In this perspective, we highlight significant advances made within the past decade regarding DNA adduct quantitation using mass spectrometry. We hope to expose a broader audience to this field and encourage analytical chemistry laboratories to explore how specific adducts may be related to various pathologies. One of the limiting factors in developing clinical tests to measure DNA adducts is cohort size; ideally, the cohort would allow for model development and then testing of the model to the remaining cohort. The goals of this perspective article are to (1) provide a summary of analyte levels measured using state-of-the-art analytical methods, (2) foster collaboration, and (3) highlight areas in need of further investigation.

Resolution and Quantitation of Mercapturic Acids Derived from Crotonaldehyde, Methacrolein, and Methyl Vinyl Ketone in the Urine of Smokers and Nonsmokers

Using improved HPLC analysis conditions, we report the separation of three isomers of mercapturic acid conjugates previously assigned in the literature only to 3-hydroxy-1-methylpropylmercapturic acid (HMPMA-1), a human urinary metabolite of crotonaldehyde. The new conditions, employing a biphenyl column cooled to 5 °C and eluted with a gradient of formic acid, acetonitrile, and methanol, allow the analysis of human urinary mercapturic acids derived not only from crotonaldehyde but also from its isomers methacrolein (3-hydroxy-2-methylpropyl mercapturic acid, HMPMA-2) and methyl vinyl ketone (3-hydroxy-3-methylpropyl mercapturic acid, HMPMA-3). The mercapturic acids were detected and quantified by LC-ESI-MS/MS using the corresponding stable isotope labeled mercapturic acids as internal standards. The analysis was validated for accuracy and precision and applied to urine samples collected from cigarette smokers and nonsmokers. Smokers had significantly higher levels of all three mercapturic acids than did nonsmokers. The results demonstrated that HMPMA-3 from methyl vinyl ketone comprised the major portion of the peaks previously ascribed in multiple studies to HMPMA-1. HMPMA-1 had concentrations intermediate between those of HMPMA-2 and HMPMA-3 in both smokers and nonsmokers. This study reports the first quantitation of HMPMA-2 and HMPMA-3 in human urine. The observation of higher levels of HMPMA-3 than in the other two mercapturic acids suggests a previously unrecognized potential significance of methyl vinyl ketone as a toxicant in smokers and nonsmokers.

Effects of pendant-like hydrophilic monomers on the adsorption properties of reversed-phase-type sorbents for solid-phase extraction

Solid-phase extraction (SPE) has been extensively employed as a pretreatment method. In SPE, reversed-phase-type sorbents have been widely applied for the pretreatment of environmental or biological samples. Hydrophilic-lipophilic balance (HLB)-type sorbents, constituting the copolymers used as reversed-phase-type sorbents, have been applied for various sample pretreatment methods. In HLB-type sorbents, the hydrophilic monomer contributes to the improved wettability of sorbents and increase of polar interactions. In this study, three pendant-like hydrophilic monomers, viz. N-vinylpyrrolidone (NVP), 4-acryloylmorpholine (AMO), and 4-vinyl-1,3-dioxolan-2-one (VDO), respectively, exhibiting different Log P values and possibly causing different polar interactions, were selected to improve the adsorption properties of polar compounds, and divinylbenzene (DVB)-based HLB-type sorbents containing each hydrophilic monomer were synthesized and examined. By the optimization of the molar ratio of DVB and the hydrophilic monomer (i.e. HLB), the inert diluent, and the degree of cross-linking, the developed sorbents exhibited higher recoveries for various polar compounds (viz. cytosine, uracil, cytidine, uridine, 2'-deoxycytidine, 2'-deoxyguanosine, adenine, thymidine, adenosine, and 2'-deoxyadenosine) compared to commercially available HLB-type sorbents.

Recent Studies on DNA Adducts Resulting from Human Exposure to Tobacco Smoke

DNA adducts are believed to play a central role in the induction of cancer in cigarette smokers and are proposed as being potential biomarkers of cancer risk. We have summarized research conducted since 2012 on DNA adduct formation in smokers. A variety of DNA adducts derived from various classes of carcinogens, including aromatic amines, polycyclic aromatic hydrocarbons, tobacco-specific nitrosamines, alkylating agents, aldehydes, volatile carcinogens, as well as oxidative damage have been reported. The results are discussed with particular attention to the analytical methods used in those studies. Mass spectrometry-based methods that have higher selectivity and specificity compared to 32P-postlabeling or immunochemical approaches are preferred. Multiple DNA adducts specific to tobacco constituents have also been characterized for the first time in vitro or detected in vivo since 2012, and descriptions of those adducts are included. We also discuss common issues related to measuring DNA adducts in humans, including the development and validation of analytical methods and prevention of artifact formation.

Genotoxic and epigenotoxic effects in mice exposed to concentrated ambient fine particulate matter (PM2.5) from São Paulo city, Brazil

BACKGROUND

The Metropolitan Area of São Paulo has a unique composition of atmospheric pollutants, and positive correlations between exposure and the risk of diseases and mortality have been observed. Here we assessed the effects of ambient fine particulate matter (PM2.5) on genotoxic and global DNA methylation and hydroxymethylation changes, as well as the activities of antioxidant enzymes, in tissues of AJ mice exposed whole body to ambient air enriched in PM2.5, which was concentrated in a chamber near an avenue of intense traffic in São Paulo City, Brazil.

RESULTS

Mice exposed to concentrated ambient PM2.5 (1 h daily, 3 months) were compared to in situ ambient air exposed mice as the study control. The concentrated PM2.5 exposed group presented increased levels of the oxidized nucleoside 8-oxo-7,8-dihydro-2'-deoxyguanosine in lung and kidney DNA and increased levels of the etheno adducts 1,N6-etheno-2'-deoxyadenosine and 1,N2-etheno-2'-deoxyguanosine in kidney and liver DNA, respectively. Apart from the genotoxic effects, the exposure to PM2.5 led to decreased levels of the epigenetic mark 5-hydroxymethylcytosine (5-hmC) in lung and liver DNA. Changes in lung, liver, and erythrocyte antioxidant enzyme activities were also observed. Decreased glutathione reductase and increased superoxide dismutase (SOD) activities were observed in the lungs, while the liver presented increased glutathione S-transferase and decreased SOD activities. An increase in SOD activity was also observed in erythrocytes. These changes are consistent with the induction of local and systemic oxidative stress.

CONCLUSIONS

Mice exposed daily to PM2.5 at a concentration that mimics 24-h exposure to the mean concentration found in ambient air presented, after 3 months, increased levels of DNA lesions related to the occurrence of oxidative stress in the lungs, liver, and kidney, in parallel to decreased global levels of 5-hmC in lung and liver DNA. Genetic and epigenetic alterations induced by pollutants may affect the genes committed to cell cycle control, apoptosis, and cell differentiation, increasing the chance of cancer development, which merits further investigation.

Evaluation of Type-A Endonucleases for the Quantitative Analysis of DNA Damage due to Exposure to Acetaldehyde Using Capillary Electrophoresis

The substrate selectivities of three endonucleases were studied quantitatively using capillary zone electrophoresis to find one giving N²-ethyl(Et)-2'-deoxyguanosine-5'-monophosphate (5'-dGMP) and cyclic 1,N²-propano(CPr)-5'-dGMP from DNAs damaged by acetaldehyde (AA). Six 2'-deoxyribonucleoside-5'-monophosphates to be quantified in the hydrolysis solutions of DNAs, namely, Et-5'-dGMP, CPr-5'-dGMP, and four authentic ones, were completely separated using a 100 mM borate running buffer solution having an optimized pH of 9.67. Using the present method, nuclease reactions of nuclease S1 (NS1), nuclease P1 (NP1), and nuclease Bal 31 to 2'-deoxyribonucleoside-5'-monophosphates from damaged Calf thymus (CT-) DNAs were monitored. The CT-DNAs were prepared by treatment with AA to generate Et-guanine or CPr-guanine internally. Bal 31 hydrolyzed the damaged CT-DNAs to yield Et-5'-dGMP and CPr-5'-dGMP quantitatively. The two 5'-dGMP adducts were not detected in the hydrolysis solutions using NS1 or NP1. Bal 31 can be a suitable nuclease for analyzing DNA damages caused by AA.

DNA Adduct Formation in the Lungs and Brain of Rats Exposed to Low Concentrations of [13C2]-Acetaldehyde

Air pollution is a major environmental risk for human health. Acetaldehyde is present in tobacco smoke and vehicle exhaust. In this study, we show that [¹³C₂]-acetaldehyde induces DNA modification with the formation of isotopically labeled 1, N²-propano-2'-deoxyguanosine adducts in the brain and lungs of rats exposed to concentrations of acetaldehyde found in the atmosphere of megacities. The adduct, with the addition of two molecules of isotopically labeled acetaldehyde [¹³C₄]-1, N²-propano-dGuo, was detected in the lung and brain tissues of exposed rats by micro-HPLC/MS/MS. Structural confirmation of the products was unequivocally performed by nano-LC/ESI⁺-HRMS³ analyses. DNA modifications induced by acetaldehyde have been regarded as a key factor in the mechanism of mutagenesis and may be involved in the cancer risks associated with air pollution.

Progress in a selective method for the determination of the acetaldehyde-derived DNA adducts by using HILIC-ESI-MS/MS

Acetaldehyde (AA), which is present in tobacco smoke, automobile exhaust gases and alcohol beverage, is a mutagen and carcinogen. AA reacts with 2'-deoxyguanosine (dG) in DNA to form N²-ethyl-dG (EtdG) and cyclic, 1, N²-propano-dG (CPrdG), which are considered to have a critical role in carcinogenesis induced by AA. In this study, we have developed a highly sensitive method for the quantitation of the two AA-derived DNA adducts by using liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) in which hydrophilic interaction chromatography (HILIC) employing mobile phases of high organic solvent concentration was selected to improve the ionization efficiency in the ESI process. Fourteen times and 11 times larger peak areas for EtdG and CPrdG, respectively, in HILIC-ESI-MS/MS were obtained compared with those in reversed phase (RP)-LC-ESI-MS/MS. Furthermore, 6.9 times (for EtdG) and 2.4 times (for CPrdG) larger peak areas were also obtained as additional enhancement by varying additive compounds in the HILIC mobile phases from ammonium acetate to ammonium bicarbonate. In total, the enhancements in detected MS signal intensities by exchanging from the RP-LC system to the HILIC system are 97 times for EtdG and 26 times for CPrdG, respectively. Three commercially available HILIC columns with different polar functional groups were examined and sufficient separation between normal 2'-deoxynucleosides and the AA-derived DNA adducts was achieved by a carbamoyl-bonded HILIC column. Finally, we applied the established method to quantify EtdG and CPrdG in the damaged calf thymus DNA.

Formation and repair of oxidatively generated damage in cellular DNA

In this review article, emphasis is placed on the critical survey of available data concerning modified nucleobase and 2-deoxyribose products that have been identified in cellular DNA following exposure to a wide variety of oxidizing species and agents including, hydroxyl radical, one-electron oxidants, singlet oxygen, hypochlorous acid and ten-eleven translocation enzymes. In addition, information is provided about the generation of secondary oxidation products of 8-oxo-7,8-dihydroguanine and nucleobase addition products with reactive aldehydes arising from the decomposition of lipid peroxides. It is worth noting that the different classes of oxidatively generated DNA damage that consist of single lesions, intra- and interstrand cross-links were unambiguously assigned and quantitatively detected on the basis of accurate measurements involving in most cases high performance liquid chromatography coupled to electrospray ionization tandem mass spectrometry. The reported data clearly show that the frequency of DNA lesions generated upon severe oxidizing conditions, including exposure to ionizing radiation is low, at best a few modifications per 106 normal bases. Application of accurate analytical measurement methods has also allowed the determination of repair kinetics of several well-defined lesions in cellular DNA that however concerns so far only a restricted number of cases.