Endogenous formation and significance of 1,N2-propanodeoxyguanosine adducts

The Cooked Meat Carcinogen 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine Hair Dosimeter, DNA Adductomics Discovery, and Associations with Prostate Cancer Pathology Biomarkers

Well-done cooked red meat consumption is linked to aggressive prostate cancer (PC) risk. Identifying mutation-inducing DNA adducts in the prostate genome can advance our understanding of chemicals in meat that may contribute to PC. 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), a heterocyclic aromatic amine (HAA) formed in cooked meat, is a potential human prostate carcinogen. PhIP was measured in the hair of PC patients undergoing prostatectomy, bladder cancer patients under treatment for cystoprostatectomy, and patients treated for benign prostatic hyperplasia (BPH). PhIP hair levels were above the quantification limit in 123 of 205 subjects. When dichotomizing prostate pathology biomarkers, the geometric mean PhIP hair levels were higher in patients with intermediate and elevated-risk prostate-specific antigen values than lower-risk values <4 ng/mL (p = 0.03). PhIP hair levels were also higher in patients with intermediate and high-risk Gleason scores ≥7 compared to lower-risk Gleason score 6 and BPH patients (p = 0.02). PC patients undergoing prostatectomy had higher PhIP hair levels than cystoprostatectomy or BPH patients (p = 0.02). PhIP-DNA adducts were detected in 9.4% of the patients assayed; however, DNA adducts of other carcinogenic HAAs, and benzo[a]pyrene formed in cooked meat, were not detected. Prostate specimens were also screened for 10 oxidative stress-associated lipid peroxidation (LPO) DNA adducts. Acrolein 1,N²-propano-2'-deoxyguanosine adducts were detected in 54.5% of the patients; other LPO adducts were infrequently detected. Acrolein adducts were not associated with prostate pathology biomarkers, although DNA adductomic profiles differed between PC patients with low and high-grade Gleason scores. Many DNA adducts are of unknown origin; however, dG adducts of formaldehyde and a series of purported 4-hydroxy-2-alkenals were detected at higher abundance in a subset of patients with elevated Gleason scores. The PhIP hair biomarker and DNA adductomics data support the paradigm of well-done cooked meat and oxidative stress in aggressive PC risk.

Metabolic Activation and DNA Interactions of Carcinogenic N-Nitrosamines to Which Humans Are Commonly Exposed

Carcinogenic N-nitrosamine contamination in certain drugs has recently caused great concern and the attention of regulatory agencies. These carcinogens-widely detectable in relatively low levels in food, water, cosmetics, and drugs-are well-established and powerful animal carcinogens. The electrophiles resulting from the cytochrome P450-mediated metabolism of N-nitrosamines can readily react with DNA and form covalent addition products (DNA adducts) that play a central role in carcinogenesis if not repaired. In this review, we aim to provide a comprehensive and updated review of progress on the metabolic activation and DNA interactions of 10 carcinogenic N-nitrosamines to which humans are commonly exposed. Certain DNA adducts such as O⁶-methylguanine with established miscoding properties play central roles in the cancer induction process, whereas others have been linked to the high incidence of certain types of cancers. We hope the data summarized here will help researchers gain a better understanding of the bioactivation and DNA interactions of these 10 carcinogenic N-nitrosamines and facilitate further research on their toxicologic and carcinogenic properties.

Evolutionary Origins of DNA Repair Pathways: Role of Oxygen Catastrophe in the Emergence of DNA Glycosylases

It was proposed that the last universal common ancestor (LUCA) evolved under high temperatures in an oxygen-free environment, similar to those found in deep-sea vents and on volcanic slopes. Therefore, spontaneous DNA decay, such as base loss and cytosine deamination, was the major factor affecting LUCA’s genome integrity. Cosmic radiation due to Earth’s weak magnetic field and alkylating metabolic radicals added to these threats. Here, we propose that ancient forms of life had only two distinct repair mechanisms: versatile apurinic/apyrimidinic (AP) endonucleases to cope with both AP sites and deaminated residues, and enzymes catalyzing the direct reversal of UV and alkylation damage. The absence of uracil–DNA N-glycosylases in some Archaea, together with the presence of an AP endonuclease, which can cleave uracil-containing DNA, suggests that the AP endonuclease-initiated nucleotide incision repair (NIR) pathway evolved independently from DNA glycosylase-mediated base excision repair. NIR may be a relic that appeared in an early thermophilic ancestor to counteract spontaneous DNA damage. We hypothesize that a rise in the oxygen level in the Earth’s atmosphere ~2 Ga triggered the narrow specialization of AP endonucleases and DNA glycosylases to cope efficiently with a widened array of oxidative base damage and complex DNA lesions.

Crotonaldehyde-induced vascular relaxation and toxicity: Role of endothelium and transient receptor potential ankyrin-1 (TRPA1)

INTRODUCTION

Crotonaldehyde (CR) is an electrophilic α,β-unsaturated aldehyde present in foods and beverages and is a minor metabolite of 1,3-butadiene. CR is a product of incomplete combustion, and is at high levels in smoke of cigarettes and structural fires. Exposure to CR has been linked to cardiopulmonary toxicity and cardiovascular disease.

OBJECTIVE

The purpose of this study was to examine the direct effects of CR in murine blood vessels (aorta and superior mesenteric artery, SMA) using an in vitro system.

METHODS AND RESULTS

CR induced concentration-dependent (1-300 μM) relaxations (75-80%) in phenylephrine (PE) precontracted aorta and SMA. Because the SMA was 20× more sensitive to CR than aorta (SMA EC50 3.8 ± 0.5 μM; aorta EC50 76.0 ± 2.0 μM), mechanisms of CR relaxation were studied in SMA. The CR-induced relaxation at low concentrations (1-30 μM) was inhibited by: 1) mechanically-impaired endothelium; 2) Nω-Nitro-L-arginine methyl ester hydrochloride (L-NAME); 3) guanylyl cyclase (GC) inhibitor (ODQ); 4) transient receptor potential ankyrin-1 (TRPA1) antagonist (A967079); and, 5) by non-vasoactive level of nicotine (1 μM). Similarly, a TRPA1 agonist, allyl isothiocyanate (AITC; mustard oil), stimulated SMA relaxation dependent on TRPA1, endothelium, NO, and GC. Consistent with these mechanisms, TRPA1 was present in the SMA endothelium. CR, at higher concentrations (100-300 μM), induced tension oscillations (spasms) and irreversibly impaired contractility (a vasotoxic effect enhanced by impaired endothelium).

CONCLUSIONS

CR relaxation depends on a functional endothelium and TRPA1, whereas vasotoxicity is enhanced by endothelium dysfunction. Thus, CR is both vasoactive and vasotoxic along a concentration continuum.

N-(Hydroxybenzyl)benzamide Derivatives: Aqueous pH-Dependent Kinetics and Mechanistic Implications for the Aqueous Reactivity of Carbinolamides

The rate constants for the aqueous reaction, between pH 0 and 14, have been determined for a series of amide substituted N-(hydroxybenzyl)benzamide derivatives, in H₂O, at 25 °C, I = 1.0 M (KCl). The N-(hydroxybenzyl)benzamide derivatives were found to react via three distinct mechanisms with the kinetically dominant mechanism being dependent on the pH of the reaction solution. It has been shown that the carbinolamides react via a specific-base-catalyzed mechanism (E1cB-like) under basic and pH neutral conditions. At lower pH values, an acid-catalyzed mechanism was kinetically dominant and, last, a water reaction was postulated at pH values where neither the hydroxide-dependent nor the general-acid-catalyzed mechanism was dominant. Contrary to earlier studies with N-(hydroxymethyl)benzamide compounds, no evidence for mechanistic variation based upon the nature of the amidic substituent was observed for any of the N-(hydroxybenzyl)benzamide derivatives studied between pH values of 0-14. The rate for the acid-catalyzed reaction (k_H, ρ = -1.17), the apparent second-order hydroxide rate constant (k₁^', ρ = 0.87), the hydroxide-independent rate (k₁, ρ = 0.65), and the pK_a's of the hydroxyl group of the carbinolamide (ρ = 0.23) are reported.

Scientific Opinion on Flavouring Group Evaluation 200, Revision 1 (FGE.200 Rev.1): 74 α,β-unsaturated aliphatic aldehydes and precursors from chemical subgroup 1.1.1 of FGE.19

The Panel on Food Additives and Flavourings of the European Food Safety Authority was requested to evaluate the genotoxic potential of 74 flavouring substances from subgroup 1.1.1 of FGE.19 in the Flavouring Group Evaluation 200 Revision 1 (FGE.200 Rev1). In FGE.200, genotoxicity studies were provided for one representative substance, namely hex-2(trans)-enal [FL-no: 05.073], and for other two substances in the same subgroup, namely 2-dodecenal [FL-no: 05.037] and 2-nonenal [FL-no: 05.171]. The Panel concluded that the concern still remains with respect to genotoxicity for the substances of this subgroup and requested an in vivo Comet assay performed in duodenum and liver for hex-2(trans)-enal [FL-no: 05.073]. For the two other representative substances of subgroup 1.1.1 (nona-2(trans),6(cis)-dienal [FL-no: 05.058] and oct-2-enal [FL-no: 05.060]), the Panel requested a combined in vivo Comet assay and micronucleus assay. These data have been provided and are evaluated in the present opinion FGE.200 Rev1. Industry submitted genotoxicity studies on trans-2-octenal [FL-no: 05.190], instead of oct-2-enal [FL-no: 05.060]. Based on the available data, the Panel concluded that the concern for genotoxicity can be ruled out for hex-2(trans)-enal [FL-no: 05.073], trans-2-octenal [FL-no: 05.190] and nona-2(trans),6(cis)-dienal [FL-no: 05.058], therefore all the 74 substances [FL-no: 02.020, 02.049, 02.050, 02.090, 02.112, 02.137, 02.156, 02.192, 02.210, 02.231, 05.037, 05.058, 05.060, 05.070, 05.072, 05.073, 05.076, 05.078, 05.102, 05.109, 05.111, 05.114, 05.120, 05.144, 05.150, 05.171, 05.172, 05.179, 05.184, 05.189, 05.190, 05.191, 05.195, 06.025, 06.031, 06.072, 09.054, 09.097, 09.109, 09.119, 09.146, 09.233, 09.244, 09.247, 09.276, 09.277, 09.303, 09.312, 09.385, 09.394, 09.395, 09.396, 09.397, 09.398, 09.399, 09.400, 09.410, 09.411, 09.469, 09.482, 09.489, 09.492, 09.493, 09.498, 09.678, 09.701, 09.719, 09.741, 09.790, 09.841, 09.866, 09.947, 09.948, 13.004] can be evaluated through the Procedure for flavouring substances.

On the misincorporation of nucleotides opposite mutagenic cyclic 1,N2-propanoguanine: A computational investigation

The misincorporation properties of exocyclic DNA adduct, cyclic 1,N²-propanoguanine with nucleobases have been investigated using DFT and DFT-D methods. Number of possible and stable mispairing conformations of cyclic 1,N²-propanoguanine with A,T,G and C have been considered for our investigation. The single point energy calculations have been carried out at the M06/6-311++G**, ωB97XD/6-311++G** and MP2/6-311++G** levels on corresponding optimized geometries. The reaction enthalpy values were employed at the M06/6-31 + G* and ωB97XD/6-31 + G* levels. The energies have been compared among the cyclic 1,N²-propanoguanine adduct with nucleobases to find the most stable conformer. The CPCM model was utilized on account of solvent phase and overall polarizability. The computed binding energies follow the order as CPr-Gua-G(2)(-23.2 kcal/mol) > CPr-Gua-C(1) (-16.1 kcal/mol) > CPr-Gua-A(2)(-10.6 kcal/mol) > CPr-Gua-T(2)(-9.6 kcal/mol) in the gas phase at M06 level, which indicates the guanine and cytosine are favorable for mispairing with the cyclic 1,N²-propanoguanine adduct. The obtained results using computational tools are in good agreement with the experimental observation.

Modulation of the Oxidative Stress and Lipid Peroxidation by Endocannabinoids and Their Lipid Analogues

Growing evidence supports the pivotal role played by oxidative stress in tissue injury development, thus resulting in several pathologies including cardiovascular, renal, neuropsychiatric, and neurodegenerative disorders, all characterized by an altered oxidative status. Reactive oxygen and nitrogen species and lipid peroxidation-derived reactive aldehydes including acrolein, malondialdehyde, and 4-hydroxy-2-nonenal, among others, are the main responsible for cellular and tissue damages occurring in redox-dependent processes. In this scenario, a link between the endocannabinoid system (ECS) and redox homeostasis impairment appears to be crucial. Anandamide and 2-arachidonoylglycerol, the best characterized endocannabinoids, are able to modulate the activity of several antioxidant enzymes through targeting the cannabinoid receptors type 1 and 2 as well as additional receptors such as the transient receptor potential vanilloid 1, the peroxisome proliferator-activated receptor alpha, and the orphan G protein-coupled receptors 18 and 55. Moreover, the endocannabinoids lipid analogues N-acylethanolamines showed to protect cell damage and death from reactive aldehydes-induced oxidative stress by restoring the intracellular oxidants-antioxidants balance. In this review, we will provide a better understanding of the main mechanisms triggered by the cross-talk between the oxidative stress and the ECS, focusing also on the enzymatic and non-enzymatic antioxidants as scavengers of reactive aldehydes and their toxic bioactive adducts.

Aldehydes are the predominant forces inducing DNA damage and inhibiting DNA repair in tobacco smoke carcinogenesis

Tobacco smoke (TS) contains numerous cancer-causing agents, with polycyclic aromatic hydrocarbons (PAHs) and nitrosamines being most frequently cited as the major TS human cancer agents. Many lines of evidence seriously question this conclusion. To resolve this issue, we determined DNA adducts induced by the three major TS carcinogens: benzo(a)pyrene (BP), 4-(methylnitrosamine)-1-(3-pyridyl)-1-butanoe (NNK), and aldehydes in humans and mice. In mice, TS induces abundant aldehyde-induced γ-hydroxy-propano-deoxyguanosine (γ-OH-PdG) and α-methyl-γ-OH-PdG adducts in the lung and bladder, but not in the heart and liver. TS does not induce the BP- and NNK-DNA adducts in lung, heart, liver, and bladder. TS also reduces DNA repair activity and the abundance of repair proteins, XPC and OGG1/2, in lung tissues. These TS effects were greatly reduced by diet with polyphenols. We found that γ-OH-PdG and α-methyl-γ-OH-PdG are the major adducts formed in tobacco smokers' buccal cells as well as the normal lung tissues of tobacco-smoking lung cancer patients, but not in lung tissues of nonsmokers. However, the levels of BP- and NNK-DNA adducts are the same in lung tissues of smokers and nonsmokers. We found that while BP and NNK can induce BPDE-dG and O6-methyl-dG adducts in human lung and bladder epithelial cells, these inductions can be inhibited by acrolein. Acrolein also can reduce DNA repair activity and repair proteins. We propose a TS carcinogenesis paradigm. Aldehydes are major TS carcinogens exerting dominant effect: Aldehydes induce mutagenic PdG adducts, impair DNA repair functions, and inhibit many procarcinogens in TS from becoming DNA-damaging agents.

Mitochondria and Reactive Oxygen Species in Aging and Age-Related Diseases

Aging has been linked to several degenerative processes that, through the accumulation of molecular and cellular damage, can progressively lead to cell dysfunction and organ failure. Human aging is linked with a higher risk for individuals to develop cancer, neurodegenerative, cardiovascular, and metabolic disorders. The understanding of the molecular basis of aging and associated diseases has been one major challenge of scientific research over the last decades. Mitochondria, the center of oxidative metabolism and principal site of reactive oxygen species (ROS) production, are crucial both in health and in pathogenesis of many diseases. Redox signaling is important for the modulation of cell functions and several studies indicate a dual role for ROS in cell physiology. In fact, high concentrations of ROS are pathogenic and can cause severe damage to cell and organelle membranes, DNA, and proteins. On the other hand, moderate amounts of ROS are essential for the maintenance of several biological processes, including gene expression. In this review, we provide an update regarding the key roles of ROS-mitochondria cross talk in different fundamental physiological or pathological situations accompanying aging and highlighting that mitochondrial ROS may be a decisive target in clinical practice.

Recent technical and biological development in the analysis of biomarker N-deoxyguanosine-C8-4-aminobiphenyl

4-Aminobiphenyl (4-ABP) which is primarily formed during tobacco combustion and overheated meat is a major carcinogen responsible for various cancers. Its adducted form, N-deoxyguanosine-C8-4-aminobiphenyl (dG-C8-4-ABP), has long been employed as a biomarker for assessment of the risk for cancer. In this review, the metabolism and carcinogenisity of 4-ABP will be discussed, followed by a discussion of the current common approaches of analyzing dG-C8-4-ABP. The major part of this review will be on the history and recent development of key methods for detection and quantitation of dG-C8-4-ABP in complex biological samples and their biological applications, from the traditional ²P-postlabelling and immunoassay methods to modern liquid chromatography-mass spectrometry (LC-MS) with the latter as the focus. Many vital biological discoveries based on dG-C8-4-ABP have been published by using the nanoLC-MS with column switching platform in our laboratory, which has also been adopted and further improved by many other researchers. We hope this review can provide a perspective of the challenges that had to be addressed in reaching our present goals and possibly bring new ideas for those who are still working on the frontline of DNA adducts area.

Acute exposure to crotonaldehyde induces dysfunction of immune system in male Wistar rats

Crotonaldehyde is a ubiquitous air pollutant in the environment. It is reported to be harmful to the biosystems in vivo and in vitro. The exposure to crotonaldehyde irritates the mucous membranes and induces edema, hyperemia, cell necrosis, inflammation, and acute respiratory distress syndrome in the lungs. However, the effects of crotonaldehyde on the immune system have not been reported. In the present study, 6-8 weeks old male Wistar rats were exposed to crotonaldehyde by intratracheal instillation at doses of 4, 8, and 16 μL/kg body weight (b.w.). The general damage in the animals was investigated; the cell counting and the biochemical analysis in the peripheral blood were tested. Furthermore, we investigated the functions of alveolar macrophages (AMs), the alterations of the T-lymphocyte subsets, and the cell composition in the bronchoalveolar lavage fluid (BALF). We found that the activities of the animals were changed after exposure to crotonaldehyde, the cellular ratios and the biochemical components in the peripheral blood were altered, the ratio of mononuclear phagocytes decreased, and the ratios of lymphocytes and granulocytes elevated significantly in BALF. Meanwhile, crotonaldehyde altered the ratio of the T-lymphocyte subsets, and the phagocytic rates and indices of AMs increased obviously. In conclusion, crotonaldehyde induces dysfunction of immune system in male Wistar rats.

Genetic control of predominantly error-free replication through an acrolein-derived minor-groove DNA adduct

Acrolein, an α,β-unsaturated aldehyde, is generated in vivo as the end product of lipid peroxidation and from metabolic oxidation of polyamines, and it is a ubiquitous environmental pollutant. The reaction of acrolein with the N2 of guanine in DNA leads to the formation of γ-hydroxy-1-N²-propano-2' deoxyguanosine (γ-HOPdG), which can exist in DNA in a ring-closed or a ring-opened form. Here, we identified the translesion synthesis (TLS) DNA polymerases (Pols) that conduct replication through the permanently ring-opened reduced form of γ-HOPdG ((r) γ-HOPdG) and show that replication through this adduct is mediated via Rev1/Polη-, Polι/Polκ-, and Polθ-dependent pathways, respectively. Based on biochemical and structural studies, we propose a role for Rev1 and Polι in inserting a nucleotide (nt) opposite the adduct and for Pols η and κ in extending synthesis from the inserted nt in the respective TLS pathway. Based on genetic analyses and biochemical studies with Polθ, we infer a role for Polθ at both the nt insertion and extension steps of TLS. Whereas purified Rev1 and Polθ primarily incorporate a C opposite (r) γ-HOPdG, Polι incorporates a C or a T opposite the adduct; nevertheless, TLS mediated by the Polι-dependent pathway as well as by other pathways occurs in a predominantly error-free manner in human cells. We discuss the implications of these observations for the mechanisms that could affect the efficiency and fidelity of TLS Pols.

Abundance of DNA adducts of 4-oxo-2-alkenals, lipid peroxidation-derived highly reactive genotoxins

Reactive oxygen species and their reaction products can damage DNA to form mutagenic lesions. Among the reactive species, lipid peroxidation-derived aldehydes react with nucleobases and form bulky exocyclic adducts. Many types of aldehyde-derived DNA adducts have been characterized, identified and detected in vitro and in vivo, whereas relative quantitative and pathophysiological contributions of each adduct still remain unclear. In recent years, an abundant class of DNA adducts derived from 4-oxo-2-alkenals have been identified, in addition to classic aldehyde-derived adducts. The presence of 4-oxo-2-alkenal-derived DNA adducts associated with age-related diseases has been revealed in rodents and humans. In vitro studies have demonstrated that 4-oxo-2-alkenals, as compared with other classes of lipid peroxidation-derived aldehydes, are highly reactive with nucleobases. It has been generally recognized that 4-oxo-2-alkenals are generated through oxidative degradation of the corresponding 4-hydroperoxy-2-alkenals, homolytic degradation products of polyunsaturated fatty acid hydroperoxides. Our recent results have also shown an alternative pathway for the formation of 4-oxo-2-alkenals, in which 2-alkenals could undergo the metal-catalyzed autoxidation resulting in the formation of the corresponding 4-oxo-2-alkenals. This review summarizes the basis of the formation of lipid peroxidation-derived genotoxic aldehydes and their covalent adduction to nucleobases, especially focusing on the abundance of 4-oxo-2-alkenal-derived DNA adducts.

DNA damage by lipid peroxidation products: implications in cancer, inflammation and autoimmunity

Oxidative stress and lipid peroxidation (LPO) induced by inflammation, excess metal storage and excess caloric intake cause generalized DNA damage, producing genotoxic and mutagenic effects. The consequent deregulation of cell homeostasis is implicated in the pathogenesis of a number of malignancies and degenerative diseases. Reactive aldehydes produced by LPO, such as malondialdehyde, acrolein, crotonaldehyde and 4-hydroxy-2-nonenal, react with DNA bases, generating promutagenic exocyclic DNA adducts, which likely contribute to the mutagenic and carcinogenic effects associated with oxidative stress-induced LPO. However, reactive aldehydes, when added to tumor cells, can exert an anticancerous effect. They act, analogously to other chemotherapeutic drugs, by forming DNA adducts and, in this way, they drive the tumor cells toward apoptosis. The aldehyde-DNA adducts, which can be observed during inflammation, play an important role by inducing epigenetic changes which, in turn, can modulate the inflammatory process. The pathogenic role of the adducts formed by the products of LPO with biological macromolecules in the breaking of immunological tolerance to self antigens and in the development of autoimmunity has been supported by a wealth of evidence. The instrumental role of the adducts of reactive LPO products with self protein antigens in the sensitization of autoreactive cells to the respective unmodified proteins and in the intermolecular spreading of the autoimmune responses to aldehyde-modified and native DNA is well documented. In contrast, further investigation is required in order to establish whether the formation of adducts of LPO products with DNA might incite substantial immune responsivity and might be instrumental for the spreading of the immunological responses from aldehyde-modified DNA to native DNA and similarly modified, unmodified and/or structurally analogous self protein antigens, thus leading to autoimmunity.

Determination of two mercapturic acids related to crotonaldehyde in human urine: influence of smoking

Crotonaldehyde, an αβ-unsaturated aldehyde, and a potent alkylating agent, is present in many foods and beverages, ambient air and tobacco smoke. A previous study indicated that two metabolites, 3-hydroxy-1- methylpropylmercapturic acid (HMPMA) and 2-carboxy1-1-methylethylmercapturic acid (CMEMA), were excreted in rat urine after subcutaneous injection of crotonaldehyde. Herein, we report the development of a method based on liquid chromatography with tandem mass spectrometry (LC-MS/MS) and deuterated analytes as internal standards, for the determination of HMPMA and CMEMA in human urine. The limits of quantification of the method were 92 and 104 ng/mL for HMPMA and CMEMA, respectively. The calibration curves for both compounds were linear up to 7500 ng/mL with R2 >0.99. It was found that cigarette smokers excreted about three to five-fold more HMPMA, and only slightly elevated amounts of CMEMA, in their urine compared to non-smokers. In smokers, we also found significant correlations between the urinary excretion levels of HMPMA (but not CMEMA) and several markers of exposure for smoking, including the daily cigarette consumption, carbon monoxide in exhaled breath, salivary cotinine, and nicotine plus five of its major metabolites in urine. Smoking cessation or switching from smoking conventional cigarettes to experimental cigarettes with lower crotonaldehyde delivery led to significant reductions of urinary HMPMA excretion, but not CMEMA excretion. Alcohol consumption did not influence either urinary HMPMA or CMEMA excretion. We conclude that HMPMA is a potentially useful biomarker for smoking-related exposure to crotonaldehyde.

Detection of 1,N(2)-propano-2'-deoxyguanosine adducts in genomic DNA by ultrahigh performance liquid chromatography-electrospray ionization-tandem mass spectrometry in combination with stable isotope dilution

Crotonaldehyde (Cro) is one of widespread and genotoxic α,β-unsaturated aldehydes and can react with the exocyclic amino group of 2'-deoxyguanosine (dG) in genomic DNA to form 1,N(2)-propano-2'-deoxyguanosine (ProdG) adducts. In this study, two diastereomers of high purity were prepared, including non-isotope and stable isotope labeled ProdG adducts, and exploited stable isotope dilution-based calibration method. By taking advantage of synthesized ProdG standards, we developed a sensitive ultrahigh performance liquid chromatography-electrospray ionization-tandem mass spectrometry (UHPLC-ESI-MS/MS) method for accurate quantification of two diastereomers of ProdG adducts. In addition to optimization of the UHPLC separation, ammonium bicarbonate (NH4HCO3) was used as additive in the mobile phase for enhancing the ionization efficiency to ProdG adducts and facilitating MS detection. The limits of detection (LODs, S/N=3) and the limits of quantification (LOQs, S/N=10) are estimated about 50 amol and 150 amol, respectively. By the use of the developed method, both diastereomers of ProdG adducts can be detected in untreated human MRC5 cells with a frequency of 2.4-3.5 adducts per 10(8) nucleotides. Crotonaldehyde treatment dramatically increases the levels of ProdG adducts in human MRC5 in a concentration-dependent manner.

Application of DNA adductomics to soil bacterium Sphingobium sp. strain KK22

Toward the development of ecotoxicology methods to investigate microbial markers of impacts of hydrocarbon processing activities, DNA adductomic analyses were conducted on a sphingomonad soil bacterium. From growing cells that were exposed or unexposed to acrolein, a commonly used biocide in hydraulic fracturing processes, DNA was extracted, digested to 2'-deoxynucleosides and analyzed by liquid chromatography-positive ionization electrospray-tandem mass spectrometry in selected reaction monitoring mode transmitting the [M + H](+) > [M + H - 116](+) transition over 100 transitions. Overall data shown as DNA adductome maps revealed numerous putative DNA adducts under both conditions with some occurring specifically for each condition. Adductomic analyses of triplicate samples indicated that elevated levels of some targeted putative adducts occurred in exposed cells. Two exposure-specific adducts were identified in exposed cells as 3-(2'-deoxyribosyl)-5,6,7,8-tetrahydro-6-hydroxy-(and 8-hydroxy-)pyrimido[1,2-a]- purine-(3H)-one (6- and 8-hydroxy-PdG) following synthesis of authentic standards of these compounds and subsequent analyses. A time course experiment showed that 6- and 8-hydroxy-PdG were detected in bacterial DNA within 30 min of acrolein exposure but were not detected in unexposed cells. This work demonstrated the first application of DNA adductomics to examine DNA damage in a bacterium and sets a foundation for future work.

Mercapturic Acids Derived from the Toxicants Acrolein and Crotonaldehyde in the Urine of Cigarette Smokers from Five Ethnic Groups with Differing Risks for Lung Cancer

The Multiethnic Cohort epidemiology study has clearly demonstrated that, compared to Whites and for the same number of cigarettes smoked, African Americans and Native Hawaiians have a higher risk for lung cancer whereas Latinos and Japanese Americans have a lower risk. Acrolein and crotonaldehyde are two important constituents of cigarette smoke which have well documented toxic effects and could play a role in lung cancer etiology. Their urinary metabolites 3-hydroxypropylmercapturic acid (3-HPMA) and 3-hydroxy-1-methylpropylmercapturic acid (HMPMA), respectively, are validated biomarkers of acrolein and crotonaldehyde exposure. We quantified levels of 3-HPMA and HMPMA in the urine of more than 2200 smokers from these five ethnic groups, and also carried out a genome wide association study using blood samples from these subjects. After adjusting for age, sex, creatinine, and total nicotine equivalents, geometric mean levels of 3-HPMA and HMPMA were significantly different in the five groups (P < 0.0001). Native Hawaiians had the highest and Latinos the lowest geometric mean levels of both 3-HPMA and HMPMA. Levels of 3-HPMA and HMPMA were 3787 and 2759 pmol/ml urine, respectively, in Native Hawaiians and 1720 and 2210 pmol/ml urine in Latinos. These results suggest that acrolein and crotonaldehyde may be involved in lung cancer etiology, and that their divergent levels may partially explain the differing risks of Native Hawaiian and Latino smokers. No strong signals were associated with 3-HPMA in the genome wide association study, suggesting that formation of the glutathione conjugate of acrolein is mainly non-enzymatic, while the top significant association with HMPMA was located on chromosome 12 near the TBX3 gene, but its relationship to HMPMA excretion is not clear.

DNA adductomics

Systems toxicology is a broad-based approach to describe many of the toxicological features that occur within a living system under stress or subjected to exogenous or endogenous exposures. The ultimate goal is to capture an overview of all exposures and the ensuing biological responses of the body. The term exposome has been employed to refer to the totality of all exposures, and systems toxicology investigates how the exposome influences health effects and consequences of exposures over a lifetime. The tools to advance systems toxicology include high-throughput transcriptomics, proteomics, metabolomics, and adductomics, which is still in its infancy. A well-established methodology for the comprehensive measurement of DNA damage resulting from every day exposures is not fully developed. During the past several decades, the ³²P-postlabeling technique has been employed to screen the damage to DNA induced by multiple classes of genotoxicants; however, more robust, specific, and quantitative methods have been sought to identify and quantify DNA adducts. Although triple quadrupole and ion trap mass spectrometry, particularly when using multistage scanning (LC–MSⁿ), have shown promise in the field of DNA adductomics, it is anticipated that high-resolution and accurate-mass LC–MSⁿ instrumentation will play a major role in assessing global DNA damage. Targeted adductomics should also benefit greatly from improved triple quadrupole technology. Once the analytical MS methods are fully mature, DNA adductomics along with other -omics tools will contribute greatly to the field of systems toxicology.

Ring-opening of the γ-OH-PdG adduct promotes error-free bypass by the Sulfolobus solfataricus DNA polymerase Dpo4

Acrolein, a mutagenic aldehyde, reacts with deoxyguanosine (dG) to form 3-(2'-deoxy-β-d-erythro-pentofuranosyl)-5,6,7,8-tetrahydro-8-hydroxypyrimido[1,2-a] purin-10(3H)-one (γ-OH-PdG). When placed opposite deoxycytosine (dC) in DNA, γ-OH-PdG undergoes ring-opening to the N(2)-(3-oxopropyl)-dG. Ring-opening of the adduct has been hypothesized to facilitate nonmutagenic bypass, particularly by DNA polymerases of the Y family. This study examined the bypass of γ-OH-PdG by Sulfolobus solfataricus Dpo4, the prototypic Y-family DNA polymerase, using templates that contained the adduct in either the 5'-CXG-3' or the 5'-TXG-3' sequence context. Although γ-OH-PdG partially blocked Dpo4-catalyzed DNA synthesis, full primer extension was observed, and the majority of bypass products were error-free. Conversion of the adduct into an irreversibly ring-opened derivative prior to reaction facilitated bypass and further improved the fidelity. Structures of ternary Dpo4·DNA·dNTP complexes were determined with primers that either were positioned immediately upstream of the lesion (preinsertion complexes) or had a 3'-terminal dC opposite the lesion (postinsertion complexes); the incoming nucleotides, either dGTP or dATP, were complementary to the template 5'-neighbor nucleotide. In both postinsertion complexes, the adduct existed as ring-opened species, and the resulting base-pair featured Watson-Crick hydrogen bonding. The incoming nucleotide paired with the 5'-neighbor template, while the primer 3'-hydroxyl was positioned to facilitate extension. In contrast, γ-OH-PdG was in the ring-closed form in both preinsertion complexes, and the overall structure did not favor catalysis. These data provide insights into γ-OH-PdG chemistry during replication bypass by the Dpo4 DNA polymerase and may explain why γ-OH-PdG-induced mutations due to primer-template misalignment are uncommon.

Patterns and mutational signatures of tandem base substitutions causing human inherited disease

Tandem base substitutions (TBSs) are multiple mutations that comprise two or more contiguous nucleotide substitutions without any net gain or loss of bases. They have recently become recognized as a distinct category of human genomic variant. However, their role in causing human inherited disease so far has not been studied methodically. Here, using data from the Human Gene Mutation Database (http://www.hgmd.org), we identified 477 events to be TBSs (doublets, 448; triplets, 16; and quadruplets to octuplets, 13). A comprehensive sequence pattern and context analysis implied the likely fundamental importance of translesion synthesis (TLS) DNA polymerases in generating these diverse TBSs but revealed that TLS polymerases may operate differently in generating TBSs of ≤ 3 bases (bypass of endogenous DNA lesions) than those of ≥ 4 bases (serial replication slippage). Moreover, GC was found to be the most frequently affected dinucleotide with GC/GC>AA/TT being the most frequent double TBS. Comparison with cancer genome mutational spectra allowed us to conclude that human germline TBSs arise predominantly through the action of endogenous mechanisms of mutagenesis rather than through exposure to exogenous mutagens. Finally, the rates of double and triple TBSs were estimated to be 0.2-1.2 × 10(-10) and 0.8-4.8 × 10(-12) per base per generation, respectively.

Translesion synthesis past acrolein-derived DNA adducts by human mitochondrial DNA polymerase γ

Acrolein, a mutagenic aldehyde, is produced endogenously by lipid peroxidation and exogenously by combustion of organic materials, including tobacco products. Acrolein reacts with DNA bases forming exocyclic DNA adducts, such as γ-hydroxy-1,N(2)-propano-2'-deoxyguanosine (γ-HOPdG) and γ-hydroxy-1,N(6)-propano-2'-deoxyadenosine (γ-HOPdA). The bulky γ-HOPdG adduct blocks DNA synthesis by replicative polymerases but can be bypassed by translesion synthesis polymerases in the nucleus. Although acrolein-induced adducts are likely to be formed and persist in mitochondrial DNA, animal cell mitochondria lack specialized translesion DNA synthesis polymerases to tolerate these lesions. Thus, it is important to understand how pol γ, the sole mitochondrial DNA polymerase in human cells, acts on acrolein-adducted DNA. To address this question, we investigated the ability of pol γ to bypass the minor groove γ-HOPdG and major groove γ-HOPdA adducts using single nucleotide incorporation and primer extension analyses. The efficiency of pol γ-catalyzed bypass of γ-HOPdG was low, and surprisingly, pol γ preferred to incorporate purine nucleotides opposite the adduct. Pol γ also exhibited ∼2-fold lower rates of excision of the misincorporated purine nucleotides opposite γ-HOPdG compared with the corresponding nucleotides opposite dG. Extension of primers from the termini opposite γ-HOPdG was accomplished only following error-prone purine nucleotide incorporation. However, pol γ preferentially incorporated dT opposite the γ-HOPdA adduct and efficiently extended primers from the correctly paired terminus, indicating that γ-HOPdA is probably nonmutagenic. In summary, our data suggest that acrolein-induced exocyclic DNA lesions can be bypassed by mitochondrial DNA polymerase but, in the case of the minor groove γ-HOPdG adduct, at the cost of unprecedented high mutation rates.

Mutagenic/recombinogenic effects of four lipid peroxidation products in Drosophila

The human diet is an important factor in the development of different diseases. Lipid peroxidation during frying in edible vegetable liquid oils of food components is a mechanism leading to the formation of free radicals. Such radicals induce tissue damage and are implicated in diverse pathological conditions, including aging, atherosclerosis, brain disorders, cancer, lung disorders and various liver disorders. In the present study, we decided to investigate the genotoxic effects of four lipid peroxidation products in the in vivo Drosophila wing somatic mutation and recombination test. In this test, point mutation, chromosome breakage and mitotic recombination produce single spots; while twin spots are produced only by mitotic recombination. Drosophila is a suitable eukaryotic organism for mutagenicity studies and also its metabolism is quite similar to that of mammalians. Since conflicting data exist on the possible risk of several lipid peroxidation products for humans, we have selected four of them, namely acrolein, crotonaldehyde, 4-hydroxy-hexenal (4-HHE) and 4-oxo-2-nonenal (4-ONE). Especially at the highest concentrations tested all exert both mutagenic and recombinogenic effects in the Drosophila SMART assay, showing a direct dose-effect relationship. This is the first study reporting genotoxicity data in Drosophila for these compounds.

Oxidatively damaged DNA and its repair in colon carcinogenesis

Inflammation, high fat, high red meat and low fiber consumption have for long been known as the most important etiological factors of sporadic colorectal cancers (CRC). Colon cancer originates from neoplastic transformation in a single layer of epithelial cells occupying colonic crypts, in which migration and apoptosis program becomes disrupted. This results in the formation of polyps and metastatic cancers. Mutational program in sporadic cancers involves APC gene, in which mutations occur most abundantly in the early phase of the process. This is followed by mutations in RAS, TP53, and other genes. Progression of carcinogenic process in the colon is accompanied by augmentation of the oxidative stress, which manifests in the increased level of oxidatively damaged DNA both in the colon epithelium, and in blood leukocytes and urine, already at the earliest stages of disease development. Defence mechanisms are deregulated in CRC patients: (i) antioxidative vitamins level in blood plasma declines with the development of disease; (ii) mRNA level of base excision repair enzymes in blood leukocytes of CRC patients is significantly increased; however, excision rate is regulated separately, being increased for 8-oxoGua, while decreased for lipid peroxidation derived ethenoadducts, ɛAde and ɛCyt; (iii) excision rate of ɛAde and ɛCyt in colon tumors is significantly increased in comparison to asymptomatic colon margin, and ethenoadducts level is decreased. This review highlights mechanisms underlying such deregulation, which is the driving force to colon carcinogenesis.

Replication bypass of N2-deoxyguanosine interstrand cross-links by human DNA polymerases η and ι

DNA-interstrand cross-links (ICLs) can be repaired by biochemical pathways requiring DNA polymerases that are capable of translesion DNA synthesis (TLS). The anticipated function of TLS polymerases in these pathways is to insert nucleotides opposite and beyond the linkage site. The outcome of these reactions can be either error-free or mutagenic. TLS-dependent repair of ICLs formed between the exocyclic nitrogens of deoxyguanosines (N(2)-dG) can result in low-frequency base substitutions, predominantly G to T transversions. Previously, we demonstrated in vitro that error-free bypass of a model acrolein-mediated N(2)-dG ICL can be accomplished by human polymerase (pol) κ, while Rev1 can contribute to this bypass by inserting dC opposite the cross-linked dG. The current study characterized two additional human DNA polymerases, pol η and pol ι, with respect to their potential contributions to either error-free or mutagenic bypass of these lesions. In the presence of individual dNTPs, pol η could insert dA, dG, and dT opposite the cross-linked dG, but incorporation of dC was not apparent. Further primer extension was observed only from the dC and dG 3' termini, and the amounts of products were low relative to the matched undamaged substrate. Analyses of bypass products beyond the adducted site revealed that dG was present opposite the cross-linked dG in the majority of extended primers, and short deletions were frequently detected. When pol ι was tested for its ability to replicate past this ICL, the correct dC was preferentially incorporated, but no further extension was observed. Under the steady-state conditions, the efficiency of dC incorporation was reduced ~500-fold relative to the undamaged dG. Thus, in addition to pol κ-catalyzed error-free bypass of N(2)-dG ICLs, an alternative, albeit low-efficiency, mechanism may exist. In this pathway, either Rev1 or pol ι could insert dC opposite the lesion, while pol η could perform the subsequent extension.

Chemistry and structural biology of DNA damage and biological consequences

The formation of adducts by the reaction of chemicals with DNA is a critical step for the initiation of carcinogenesis. The structural analysis of various DNA adducts reveals that conformational and chemical rearrangements and interconversions are a common theme. Conformational changes are modulated both by the nature of adduct and the base sequences neighboring the lesion sites. Equilibria between conformational states may modulate both DNA repair and error-prone replication past these adducts. Likewise, chemical rearrangements of initially formed DNA adducts are also modulated both by the nature of adducts and the base sequences neighboring the lesion sites. In this review, we focus on DNA damage caused by a number of environmental and endogenous agents, and biological consequences.

Genotoxic analysis of four lipid-peroxidation products in the mouse lymphoma assay

Lipid-peroxidation products are formed by the thermal treatment of foodstuffs, as well as by endogenous processes. In addition, they are also common environmental pollutants originating from many different sources. Since conflicting data exist on their possible risk for humans, we have selected four lipid-peroxidation products namely acrolein, crotonaldehyde, 4-hydroxy-hexenal (4-HHE) and 4-oxo-2-nonenal (4-ONE) to determine their ability to induce mutagenicity in mammalian cells. There is an important lack of mutagenicity data on mammalian cells for such products, which presents an important gap for any risk-assessment estimation. We have used the mouse lymphoma assay (MLA) to determine the mutagenic potential of these four compounds. This assay detects a broad spectrum of mutational events, from point mutations to chromosome alterations. The results obtained indicate that the four selected compounds are mutagenic in the MLA assay, showing a direct dose-effect relationship. The relative mutagenic potencies according to the induced mutant frequency (IMF) are as follows: crotonaldehyde (IMF=758.5×10(-6)), 4-ONE (IMF=700.5×10(-6)), acrolein (IMF=660.5×10(-6)) and 4-HHE (IMF=572×10(-6)). Although the differences between the induced mutant frequencies for these compounds are not very large, the α,β-unsaturated aldehyde 4-oxo-2-nonenal turned out to be the agent most mutagenic. This is because its induced mutant frequency was reached after treatment with 10μM, while 50μM of the other compounds was needed to reach the reported frequencies.

Effects of potential dietary inhibitors of endogenous DNA damage on mutagenesis and lipid peroxidation in lacZ mice

The effects of a nine month administration of dietary: (1) 3H-1,2-dithiole-3-thione (D3T), (2) N-acetylcysteine (NAC), (3) antioxidant vitamin mix, (vitamin C+E), (4) free radical scavenger, amifostine, and (5) calorie restriction, (CR), on mutagenesis and lipid peroxidation in lung, kidney, spleen and liver of lacZ transgenic mice were examined. These agents/diets were chosen because they might inhibit certain proposed mechanisms of endogenous damage to DNA. The agents were added to a high fat, reduced antioxidant AIN-76 diet, to better approximate a Western style diet than the conventional AIN-76 diet. As the lacZ gene is not expressed, mutations in that gene are neutral, and simply accumulate over time. The mutant fractions in control mice increased about 50-100%. Most of the agents inhibited to various extents the age-related increase in mutagenesis in lung, kidney, and/or spleen, but no inhibition was observed in liver. There was no significant effect of age on lipid peroxidation levels in controls, possibly reflecting steady state turnover of lipid peroxidation products. Almost all of the treatments except D3T inhibited lipid peroxidation in most organs to different degrees. The vitamin C+E mix was the most effective at inhibiting lipid peroxidation, but a single most effective inhibitor of mutagenesis could not be discerned. Some associations were observed between the reduction in lipid peroxidation and the inhibition of mutagenesis. The results are consistent with a partial role for oxidative stress in the age-related increase in mutagenesis. These observations may have implications for chemoprevention of carcinogenesis.

Acrolein scavengers: reactivity, mechanism and impact on health

Acrolein (ACR) is an α,β-unsaturated aldehyde that exists extensively in the environment and (thermally processed) foods. It can also be generated through endogenous metabolism. Its high electrophilicity makes this aldehyde notorious for its facile reaction with biological nucleophiles, leading to the modification of proteins/DNA and depletion of glutathione. Recent studies also have revealed its roles in disturbing various cell signing pathways in biological systems. With growing evidences of ACR's implication in human diseases, strategies to eliminate its hazardous impacts are of great importance. One of the intervention strategies is the application of reactive scavengers to directly trap ACR. Some known ACR scavengers include sulfur (thiol)-containing and nitrogen (amino)-containing compounds as well as the newly emerging natural polyphenols. In this review, the interactions between ACR and its scavengers are highlighted. The discussion about ACR scavengers is mainly focused on their chemical reactivity, trapping mechanisms as well as their roles extended to biological relevance. In addition to their direct trapping effect on ACR, these scavengers might possess multiple functions and offer additional benefits against ACR-induced toxicity. A comprehensive understanding of the mechanism involved may help to establish ACR scavenging as a novel therapeutic intervention against human diseases that are associated with ACR and/or oxidative stress.

Reactive species and DNA damage in chronic inflammation: reconciling chemical mechanisms and biological fates

Chronic inflammation has long been recognized as a risk factor for many human cancers. One mechanistic link between inflammation and cancer involves the generation of nitric oxide, superoxide and other reactive oxygen and nitrogen species by macrophages and neutrophils that infiltrate sites of inflammation. Although pathologically high levels of these reactive species cause damage to biological molecules, including DNA, nitric oxide at lower levels plays important physiological roles in cell signaling and apoptosis. This raises the question of inflammation-induced imbalances in physiological and pathological pathways mediated by chemical mediators of inflammation. At pathological levels, the damage sustained by nucleic acids represents the full spectrum of chemistries and likely plays an important role in carcinogenesis. This suggests that DNA damage products could serve as biomarkers of inflammation and oxidative stress in clinically accessible compartments such as blood and urine. However, recent studies of the biotransformation of DNA damage products before excretion point to a weakness in our understanding of the biological fates of the DNA lesions and thus to a limitation in the use of DNA lesions as biomarkers. This review will address these and other issues surrounding inflammation-mediated DNA damage on the road to cancer.

γ-Hydroxy-1,N2-propano-2'-deoxyguanosine DNA adduct conjugates the N-terminal amine of the KWKK peptide via a carbinolamine linkage

The γ-hydroxy-1,N(2)-propano-2'-deoxyguanosine adduct (γ-OH-PdG) was introduced into 5'-d(GCTAGCXAGTCC)-3'·5'-d(GGACTCGCTAGC)-3' (X = γ-OH-PdG). In the presence of excess peptide KWKK, (13)C isotope-edited NMR revealed the formation of two spectroscopically distinct DNA-KWKK conjugates. These involved the reaction of the KWKK N-terminal amino group with the N(2)-dG propylaldehyde tautomer of the γ-OH-PdG lesion. The guanine N1 base imino resonance at the site of conjugation was observed in isotope-edited (15)N NMR experiments, suggesting that the conjugated guanine was inserted into the duplex and that the guanine imino proton was protected from exchange with water. The conjugates could be reduced in the presence of NaCNBH(3), suggesting that they existed, in part, as imine (Schiff base) linkages. However, (13)C isotope-edited NMR failed to detect the imine linkages, suggesting that these KWKK conjugates existed predominantly as diastereomeric carbinolamines, in equilibrium with trace amounts of the imines. The structures of the diastereomeric DNA-KWKK conjugates were predicted from potential energy minimization of model structures derived from the refined structure of the fully reduced cross-link [ Huang, H., Kozekov, I. D., Kozekova, A., Rizzo, C. J., McCullough, A., Lloyd, R. S., and Stone, M. P. ( 2010 ) Biochemistry , 49 , 6155 -6164 ]. Molecular dynamics calculations carried out in explicit solvent suggested that the conjugate bearing the S-carbinolamine linkage was the major species due to its potential for intramolecular hydrogen bonding. These carbinolamine DNA-KWKK conjugates thermally stabilized duplex DNA. However, the DNA-KWKK conjugates were chemically reversible and dissociated when the DNA was denatured. In this 5'-CpX-3' sequence, the DNA-KWKK conjugates slowly converted to interstrand N(2)-dG:N(2)-dG DNA cross-links and ring-opened γ-OH-PdG derivatives over a period of weeks.

Ultrasensitive simultaneous quantification of 1,N2-etheno-2'-deoxyguanosine and 1,N2-propano-2'-deoxyguanosine in DNA by an online liquid chromatography-electrospray tandem mass spectrometry assay

Exocyclic DNA adducts produced by exogenous and endogenous compounds are emerging as potential tools to study a variety of human diseases and air pollution exposure. A highly sensitive method involving online reverse-phase high performance liquid chromatography with electrospray tandem mass spectrometry detection in the multiple reaction monitoring mode and employing stable isotope-labeled internal standards was developed for the simultaneous quantification of 1,N(2)-etheno-2'-deoxyguanosine (1,N(2)-epsilondGuo) and 1,N(2)-propano-2'-deoxyguanosine (1,N(2)-propanodGuo) in DNA. This methodology permits direct online quantification of 2'-deoxyguanosine and ca. 500 amol of adducts in 100 microg of hydrolyzed DNA in the same analysis. Using the newly developed technique, accurate determinations of 1,N(2)-etheno-2'-deoxyguanosine and 1,N(2)-propano-2'-deoxyguanosine levels in DNA extracts of human cultured cells (4.01 +/- 0.32 1,N(2)-epsilondGuo/10(8) dGuo and 3.43 +/- 0.33 1,N(2)-propanodGuo/10(8) dGuo) and rat tissue (liver, 2.47 +/- 0.61 1,N(2)-epsilondGuo/10(8) dGuo and 4.61 +/- 0.69 1,N(2)-propanodGuo/10(8) dGuo; brain, 2.96 +/- 1.43 1,N(2)-epsilondGuo/10(8) dGuo and 5.66 +/- 3.70 1,N(2)-propanodGuo/10(8) dGuo; and lung, 0.87 +/- 0.34 1,N(2)-epsilondGuo/10(8) dGuo and 2.25 +/- 1.72 1,N(2)-propanodGuo/10(8) dGuo) were performed. The method described herein can be used to study the biological significance of exocyclic DNA adducts through the quantification of different adducts in humans and experimental animals with pathological conditions and after air pollution exposure.

Formation of deoxyguanosine cross-links from calf thymus DNA treated with acrolein and 4-hydroxy-2-nonenal

Acrolein (AC) and 4-hydroxy-2-nonenal (HNE) are endogenous bis-electrophiles that arise from the oxidation of polyunsaturated fatty acids. AC is also found in high concentrations in cigarette smoke and automobile exhaust. These reactive α,β-unsaturated aldehyde (enal) covalently modify nucleic acids, to form exocyclic adducts, where the three-carbon hydroxypropano unit bridges the N1 and N(2) positions of deoxyguanosine (dG). The bifunctional nature of these enals allows them to undergo reaction with a second nucleophilic group and form DNA cross-links. These cross-linked enal adducts are likely to contribute to the genotoxic effects of both AC and HNE. We have developed a sensitive mass spectrometric method to detect cross-linked adducts of these enals in calf thymus DNA (CT DNA) treated with AC or HNE. The AC and HNE cross-linked adducts were measured by the stable isotope dilution method, employing a linear quadrupole ion trap mass spectrometer and consecutive reaction monitoring at the MS(3) or MS(4) scan stage. The lower limit of quantification of the cross-linked adducts is ∼1 adduct per 10(8) DNA bases, when 50 μg of DNA is assayed. The cross-linked adducts occur at levels that are ∼1-2% of the levels of the monomeric 1,N(2)-dG adducts in CT DNA treated with either enal.

Detection of 7-(2'-carboxyethyl)guanine but not 7-carboxymethylguanine in human liver DNA

7-Carboxymethylguanine (7-CMGua) and 7-(2'-carboxyethyl)guanine (7-CEGua) are DNA adducts that potentially could be formed upon the metabolism of the carcinogenic nitrosamines N-nitrososarcosine (NSAR) and 3-(methylnitrosamino)propionic acid (MNPA), respectively, or from other sources such as nitrosation of glycine (7-CMGua) or reaction of DNA with acrylic acid (7-CEGua). Since both NSAR and MNPA have been detected in human urine and there are plausible sources of exposure to other precursors to these adducts, we analyzed human liver DNA for 7-CMGua and 7-CEGua, using liquid chromatography-electrospray ionization-tandem mass spectrometry-selected reaction monitoring (LC-ESI-MS/MS-SRM). Human hepatic DNA was mixed with [15N5]7-CMGua and [15N5]7-CEGua as internal standards and enzymatically hydrolyzed. The hydrolysate was partially purified by solid-phase extraction, and the resulting fraction was treated with acetyl chloride in methanol to convert 7-CMGua and 7-CEGua to their methyl esters. After a second solid-phase extraction, LC-ESI-MS/MS-SRM analysis was carried out using the transitions m/z 224 [M + H](+) --> m/z 164 [(M + H)-HCOOCH3]+ and m/z 238 [M + H]+ --> m/z 152 [BH]+ for the methyl esters of 7-CMGua and 7-CEGua, respectively. The method was sensitive, accurate, precise, and apparently free from artifact formation. 7-CEGua, as its methyl ester, was detected in all 24 human liver samples analyzed, mean +/- SD, 373 +/- 320 fmol/mumol Gua (74.6 adducts per 10(9) nucleotides), range 17-1189 fmol/mumol Gua, but the methyl ester of 7-CMGua was not detected in any sample. These results demonstrate the ubiquitous presence of 7-CEGua in human liver DNA. Acrylic acid may be a likely endogenous precursor to 7-CEGua.

Challenges in developing DNA and RNA biomarkers of inflammation

Inflammation is now a proven cause of human diseases such as cancer and cardiovascular disease. One potential link between inflammation and disease involves secretion of reactive chemical species by immune cells, with chronic damage to host epithelial cells leading to disease. This suggests pathophysiologically that DNA and RNA damage products are candidate biomarkers of inflammation, both for mechanistic understanding of the process and for risk assessment. Of the current approaches to quantifying DNA damage products, mass spectrometry-based methods provide the most rigorous quantification needed for biomarker development, while antibody-based approaches provide the most practical way to implement biomarkers in a clinical setting. Nonetheless, all approaches are biased by adventitious formation of DNA and RNA damage products during sample processing. Recent studies of tissue-derived DNA biomarkers in mouse models of inflammation reveal significant changes only in DNA adducts derived from lipid peroxidation. These and other observations raise the question of the most appropriate sampling compartment for DNA biomarker studies and highlight the emerging role of lipid damage in inflammation.

Elevated levels of volatile organic carcinogen and toxicant biomarkers in Chinese women who regularly cook at home

BACKGROUND

Epidemiologic studies associate lung cancer in nonsmoking Chinese women with Chinese-style wok cooking. Our goal was to quantify carcinogen and toxicant biomarkers in Chinese women who reported regularly doing home cooking compared with women randomly selected from the Singapore Chinese Health Study as controls.

METHODS

Biomarkers were quantified by high-performance liquid chromatography-mass spectrometry, high-performance liquid chromatography with fluorescence detection, and gas chromatography-mass spectrometry.

RESULTS

Compared with controls, women who engaged in regular home cooking had significantly higher levels of mercapturic acids of acrolein {geometric mean, 1,959 pmol/mg creatinine [95% confidence interval (95% CI), 1,554-2,467] versus 1,370 (95% CI, 1,077-1,742); P=0.038}, crotonaldehyde [geometric mean, 232 pmol/mg creatinine (95% CI, 193-277) versus 142 (95% CI, 118-171); P=0.0004], and benzene [geometric mean, 0.58 pmol/mg creatinine (95% CI, 0.44-0.78) versus 0.18 (95% CI, 0.14-0.24); P<0.0001]. No significant differences were found in levels of mercapturic acids of 1,3-butadiene, metabolites of pyrene and phenanthrene, or acetaldehyde-leukocyte DNA adduct levels between the groups. Levels of the ethylene oxide mercapturic acid were significantly higher in the controls.

CONCLUSIONS

The higher levels of the mercapturic acid of benzene, a multiorgan carcinogen, in the women who cooked are particularly notable. Overall, the results showing increased exposure to the volatile toxicants and carcinogens acrolein, crotonaldehyde, and benzene in Chinese women who regularly cook provide a plausible lead for further investigating the role of volatile compounds generated during high-temperature cooking with oils as causes of lung cancer.

IMPACT

A new direction for research on lung cancer etiology is suggested.

Mutagenicity of acrolein and acrolein-induced DNA adducts

Acrolein mutagenicity relies on DNA adduct formation. Reaction of acrolein with deoxyguanosine generates alpha-hydroxy-1, N(2)-propano-2'-deoxyguanosine (alpha-HOPdG) and gamma-hydroxy-1, N(2)-propano-2'-deoxyguanosine (gamma-HOPdG) adducts. These two DNA adducts behave differently in mutagenicity. gamma-HOPdG is the major DNA adduct and it can lead to interstrand DNA-DNA and DNA-peptide/protein cross-links, which may induce strong mutagenicity; however, gamma-HOPdG can be repaired by some DNA polymerases complex and lessen its mutagenic effects. alpha-HOPdG is formed much less than gamma-HOPdG, but difficult to be repaired, which contributes to accumulation in vivo. Results of acrolein mutagenicity studies haven't been confirmed, which is mainly due to the conflicting mutagenicity data of the major acrolein adduct (gamma-HOPdG). The minor alpha-HOPdG is mutagenic in both in vitro and in vivo test systems. The role of alpha-HOPdG in acrolein mutagenicity needs further investigation. The inconsistent result of acrolein mutagenicity can be attributed, at least partially, to a variety of acrolein-DNA adducts formation and their repair in diverse detection systems. Recent results of detection of acrolein-DNA adduct in human lung tissues and analysis of P53 mutation spectra in acrolein-treated cells may shed some light on mechanisms of acrolein mutagenicity. These aspects are covered in this mini review.

NMR structure of duplex DNA containing the alpha-OH-PdG.dA base pair: a mutagenic intermediate of acrolein

Acrolein, a cell metabolic product and main component of cigarette smoke, reacts with DNA generating alpha-OH-PdG lesions, which have the ability to pair with dATP during replication thereby causing G to T transversions. We describe the solution structure of an 11-mer DNA duplex containing the mutagenic alpha-OH-PdG.dA base pair intermediate, as determined by solution nuclear magnetic resonance (NMR) spectroscopy and retrained molecular dynamics (MD) simulations. The NMR data support a mostly regular right-handed helix that is only perturbed at its center by the presence of the lesion. Undamaged residues of the duplex are in anti orientation, forming standard Watson-Crick base pairs alignments. Duplication of proton signals at and near the damaged base pair reveals the presence of two enantiomeric duplexes, thus establishing the exocyclic nature of the lesion. The alpha-OH-PdG adduct assumes a syn conformation pairing to its partner dA base that is protonated at pH 6.6. The three-dimensional structure obtained by restrained molecular dynamics simulations show hydrogen bond interactions that stabilize alpha-OH-PdG in a syn conformation and across the lesion containing base pair. We discuss the implications of the structures for the mutagenic bypass of acrolein lesions.

Simultaneous quantification of 1,N2-propano-2'-deoxyguanosine adducts derived from acrolein and crotonaldehyde in human placenta and leukocytes by isotope dilution nanoflow LC nanospray ionization tandem mass spectrometry

Humans are exposed to acrolein and crotonaldehyde due to environmental pollution and endogenous lipid peroxidation. These aldehydes react with the 2'-deoxyguanosine moiety of DNA, forming the exocyclic 1,N2-propano-2'-deoxyguanosine adducts AdG and CdG. These adducts are mutagenic lesions, and they play an important role in cancer and neurodegenerative diseases. In this study, a highly sensitive and quantitative assay was developed for simultaneous detection and quantification of AdG and CdG isomers in human placenta and leukocyte DNA by isotope dilution nanoflow LC with nanospray ionization tandem mass spectrometry (nanoLC-NSI/MS/MS). The on-column detection limits (S/N > or = 3) of AdG and CdG were 15 and 8.9 amol, respectively. The quantification limits of AdG and CdG for the entire assay were 619 and 297 amol, respectively, corresponding to 9.8 and 4.7 adducts in 10(9) normal nucleotides, respectively, starting with 20 microg of DNA. Different enzyme hydrolysis methods were compared, and the optimal hydrolysis conditions were employed for the assay. Levels of AdG and CdG in human placental DNA (20 microg) were 108 and 26 in 10(8) normal nucleotides, respectively, with the respective relative standard deviation (RSD) of 2.6% and 3.1% (n = 3). Levels of AdG and CdG in 9 human leukocyte DNA samples were 78 +/- 23 (mean +/- SD) and 6.2 +/- 3.8 (mean +/- SD) in 10(8) normal nucleotides, respectively, starting from 30 microg of DNA. Using this assay, only 4-6 microg of DNA sample was subjected to this nanoLC-NSI/MS/MS system for analysis. Only 1-1.5 mL of blood is needed for measuring AdG and CdG levels in leukocyte DNA. Thus, it is clinically feasible using this highly sensitive assay to investigate the potential of using these adducts as noninvasive biomarkers for DNA damage resulting from acrolein and crotonaldehyde and to study their roles in cancer development and prevention.

Differential base stacking interactions induced by trimethylene interstrand DNA cross-links in the 5'-CpG-3' and 5'-GpC-3' sequence contexts

Synthetically derived trimethylene interstrand DNA cross-links have been used as surrogates for the native cross-links that arise from the 1,N²-deoxyguanosine adducts derived from α,β-unsaturated aldehydes. The native enal-mediated cross-linking occurs in the 5′-CpG-3′ sequence context but not in the 5′-GpC-3′ sequence context. The ability of the native enal-derived 1,N²-dG adducts to induce interstrand DNA cross-links in the 5′-CpG-3′ sequence as opposed to the 5′-GpC-3′ sequence is attributed to the destabilization of the DNA duplex in the latter sequence context. Here, we report higher accuracy solution structures of the synthetically derived trimethylene cross-links, which are refined from NMR data with the AMBER force field. When the synthetic trimethylene cross-links are placed into either the 5′-CpG-3′ or the 5′-GpC-3′ sequence contexts, the DNA duplex maintains B-DNA geometry with structural perturbations confined to the cross-linked base pairs. Watson−Crick hydrogen bonding is conserved throughout the duplexes. Although different from canonical B-DNA stacking, the cross-linked and the neighbor base pairs stack in the 5′-CpG-3′ sequence. In contrast, the stacking at the cross-linked base pairs in the 5′-GpC-3′ sequence is greatly perturbed. The π-stacking interactions between the cross-linked and the neighbor base pairs are reduced. This is consistent with remarkable chemical shift perturbations of the C⁵ H5 and H6 nucleobase protons that shifted downfield by 0.4−0.5 ppm. In contrast, these chemical shift perturbations in the 5′-CpG-3′ sequence are not remarkable, consistent with the stacked structure. The differential stacking of the base pairs at the cross-linking region probably explains the difference in stabilities of the trimethylene cross-links in the 5′-CpG-3′ and 5′-GpC-3′ sequence contexts and might, in turn, account for the sequence selectivity of the interstrand cross-link formation induced by the native enal-derived 1,N²-dG adducts.

Chemistry and biology of DNA containing 1,N(2)-deoxyguanosine adducts of the alpha,beta-unsaturated aldehydes acrolein, crotonaldehyde, and 4-hydroxynonenal

The α,β-unsaturated aldehydes (enals) acrolein, crotonaldehyde, and trans-4-hydroxynonenal (4-HNE) are products of endogenous lipid peroxidation, arising as a consequence of oxidative stress. The addition of enals to dG involves Michael addition of the N²-amine to give N²-(3-oxopropyl)-dG adducts, followed by reversible cyclization of N1 with the aldehyde, yielding 1,N²-dG exocyclic products. The 1,N²-dG exocyclic adducts from acrolein, crotonaldehyde, and 4-HNE exist in human and rodent DNA. The enal-induced 1,N²-dG lesions are repaired by the nucleotide excision repair pathway in both Escherichia coli and mammalian cells. Oligodeoxynucleotides containing structurally defined 1,N²-dG adducts of acrolein, crotonaldehyde, and 4-HNE were synthesized via a postsynthetic modification strategy. Site-specific mutagenesis of enal adducts has been carried out in E. coli and various mammalian cells. In all cases, the predominant mutations observed are G→T transversions, but these adducts are not strongly miscoding. When placed into duplex DNA opposite dC, the 1,N²-dG exocyclic lesions undergo ring opening to the corresponding N²-(3-oxopropyl)-dG derivatives. Significantly, this places a reactive aldehyde in the minor groove of DNA, and the adducted base possesses a modestly perturbed Watson−Crick face. Replication bypass studies in vitro indicate that DNA synthesis past the ring-opened lesions can be catalyzed by pol η, pol ι, and pol κ. It also can be accomplished by a combination of Rev1 and pol ζ acting sequentially. However, efficient nucleotide insertion opposite the 1,N²-dG ring-closed adducts can be carried out only by pol ι and Rev1, two DNA polymerases that do not rely on the Watson−Crick pairing to recognize the template base. The N²-(3-oxopropyl)-dG adducts can undergo further chemistry, forming interstrand DNA cross-links in the 5′-CpG-3′ sequence, intrastrand DNA cross-links, or DNA−protein conjugates. NMR and mass spectrometric analyses indicate that the DNA interstand cross-links contain a mixture of carbinolamine and Schiff base, with the carbinolamine forms of the linkages predominating in duplex DNA. The reduced derivatives of the enal-mediated N²-dG:N²-dG interstrand cross-links can be processed in mammalian cells by a mechanism not requiring homologous recombination. Mutations are rarely generated during processing of these cross-links. In contrast, the reduced acrolein-mediated N²-dG peptide conjugates can be more mutagenic than the corresponding monoadduct. DNA polymerases of the DinB family, pol IV in E. coli and pol κ in human, are implicated in error-free bypass of model acrolein-mediated N²-dG secondary adducts, the interstrand cross-links, and the peptide conjugates.

Stereospecific formation of the (R)-gamma-hydroxytrimethylene interstrand N2-dG:N2-dG cross-link arising from the gamma-OH-1,N2-propano-2'-deoxyguanosine adduct in the 5'-CpG-3' DNA sequence

Acrolein reacts with dG to form hydroxylated 1,N(2)-propanodeoxyguanosine (OH-PdG) adducts. Most abundant are the epimeric 3-(2-deoxy-beta-D-erythro-pentofuranosyl)-5,6,7,8-tetrahydro-8-hydroxypyrimido[1,2a] purin-10(3H)-ones, commonly referred to as the gamma-OH-PdG adducts. When placed complementary to deoxycytosine in duplex DNA, these undergo rearrangement to the N(2)-(3-oxopropyl)-dG aldehyde. The latter forms diastereomeric interstrand N(2)-dG:N(2)-dG cross-links in the 5'-CpG-3' sequence. Here we report the structure of the stereochemically favored (R)-gamma-hydroxytrimethylene N(2)-dG:N(2)-dG interstrand DNA cross-link in 5'-d(G(1)C(2)T(3)A(4)G(5)C(6)X(7)A(8)G(9)T(10)C(11)C(12))-3' x 5'-d(G(13)G(14)A(15)C(16)T(17)C(18)Y(19)C(20)T(21)A(22)G(23)C(24))-3' (X(7) is the dG linked to the alpha-carbon of the carbinolamine linkage, and Y(19) is the dG linked to the gamma-carbon of the carbinolamine linkage; the cross-link is in the 5'-CpG-3' sequence). The structure was characterized using isotope-edited (15)N nuclear Overhauser enhancement spectroscopy heteronuclear single quantum correlation (NOESY-HSQC) NMR, in which the exocyclic amines at X(7) or Y(19) were (15)N-labeled. Analyses of NOE intensities involving Y(19) N(2)H indicated that the (R)-gamma-hydroxytrimethylene linkage was the major cross-link species, constituting 80-90% of the cross-link. The X(7) and Y(19) imino resonances were observed at 65 degrees C. Additionally, for the 5'-neighbor base pair G(5) x C(20), the G(5) imino resonance remained sharp at 55 degrees C but broadened at 65 degrees C. In contrast, for the 3'-neighbor A(8) x T(17) base pair, the T(17) imino resonance was severely broadened at 55 degrees C. Structural refinement using NOE distance restraints obtained from isotope-edited (15)N NOESY-HSQC data indicated that the (R)-gamma-hydroxytrimethylene linkage maintained the C(6) x Y(19) and X(7) x C(18) base pairs with minimal structural perturbations. The (R)-gamma-hydroxytrimethylene linkage was located in the minor groove. The X(7) N(2) and Y(19) N(2) atoms were in the gauche conformation with respect to the linkage, which maintained Watson-Crick hydrogen bonding of the cross-linked base pairs. The anti conformation of the hydroxyl group with respect to C(alpha) of the tether minimized steric interaction and, more importantly, allowed the formation of a hydrogen bond between the hydroxyl group and C(20) O(2) located in the 5'-neighboring base pair G(5) x C(20). The formation of this hydrogen bond may, in part, explain the thermal stability of this carbinolamine interstrand cross-link and the stereochemical preference for the (R) configuration of the cross-link.

Solution structure of DNA containing alpha-OH-PdG: the mutagenic adduct produced by acrolein

Acrolein is a cell metabolic product and a main component of cigarette smoke. Its reaction with DNA produces two guanine lesions γ-OH-PdG, a major adduct that is nonmutagenic in mammalian cells, and the positional isomer α-OH-PdG. We describe here the solution structure of a short DNA duplex containing a single α-OH-PdG lesion, as determined by solution NMR spectroscopy and restrained molecular dynamics simulations. The spectroscopic data show a mostly regular right-handed helix, locally perturbed at its center by the presence of the lesion. All undamaged residues of the duplex are in anti orientation, forming standard Watson–Crick base-pair alignments. Duplication of proton signals near the damaged site differentiates two enantiomeric duplexes, thus establishing the exocyclic nature of the lesion. At the lesion site, α-OH-PdG rotates to a syn conformation, pairing to its counter cytosine residue that is protonated at pH 5.9. Three-dimensional models produced by restrained molecular dynamics simulations show different hydrogen-bonding patterns between the lesion and its cytosine partner and identify further stabilization of α-OH-PdG in a syn conformation by intra-residue hydrogen bonds. We compare the α-OH-PdG•dC duplex structure with that of duplexes containing the analogous lesion propano-dG and discuss the implications of our findings for the mutagenic bypass of acrolein lesions.

Screening for DNA adducts by data-dependent constant neutral loss-triple stage mass spectrometry with a linear quadrupole ion trap mass spectrometer

A two-dimensional linear quadrupole ion trap mass spectrometer (LIT/MS) was employed to simultaneously screen for DNA adducts of environmental, dietary, and endogenous genotoxicants, by data-dependent constant neutral loss scanning followed by triple-stage mass spectrometry (CNL-MS3). The loss of the deoxyribose (dR) from the protonated DNA adducts ([M + H - 116]+) in the MS/MS scan mode triggered the acquisition of MS3 product ion spectra of the aglycone adducts [BH2]+. Five DNA adducts of the tobacco carcinogen 4-aminobiphenyl (4-ABP) were detected in human hepatocytes treated with 4-ABP, and three DNA adducts of the cooked-meat carcinogen 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) were identified in the livers of rats exposed to MeIQx, by the CNL-MS3 scan mode. Buccal cell DNA from tobacco smokers was screened for DNA adducts of various classes of carcinogens in tobacco smoke including 4-ABP, 2-amino-9H-pyrido[2,3-b]indole (AalphaC), and benzo[a]pyrene (BaP); the cooked-meat carcinogens MeIQx, AalphaC, and 2-amino-1-methyl-6-phenylmidazo[4,5-b]pyridine (PhIP); and the lipid peroxidation products acrolein (AC) and trans-4-hydroxynonenal (HNE). The CNL-MS3 scanning technique can be used to simultaneously screen for multiple DNA adducts derived from different classes of carcinogens, at levels of adduct modification approaching 1 adduct per 108 unmodified DNA bases, when 10 microg of DNA is employed for the assay.