DNA repair and the origins of urinary oxidized 2'-deoxyribonucleosides

An integrated LC-MS/MS platform for noninvasive urinary nucleus acid adductomics: A pilot study for tobacco exposure

Tobacco smoke exposure significantly increases the level of global nucleoside damage. To evaluate all aspects of nucleic acid (NA) modifications, NA adductomics analyzes DNA, RNA and nucleobase adducts and provides comprehensive data. Liquid chromatography-tandem triple quadrupole mass spectrometry (LC-QQQ-MS/MS) and LC-Zeno-TOF-MS/MS were employed to screen for DNA, RNA and nucleobase adducts, as part of the analytical platform that was designed to combine high sensitivity and high resolution detection. We identified and distinguished urine nucleoside adducts via precursor ion and neutral loss scanning. A total of 245 potential adducts were detected, of which 28 were known adducts. The smoking group had significantly higher concentrations of nucleoside adducts in rat urine than the control group, based on MRM scanning, which was then used to perform relative quantitative analysis of these adducts. Urine nucleoside adducts were further confirmed using LC-Zeno-TOF-MS/MS. This highlights the potential of untargeted detection methods to provide comprehensive data on both known and unknown adducts. These approaches can be used to investigate the interactions among oxidative and alkylation stresses, and epigenetic modifications caused by exposure to tobacco smoke.

DNA modifications: Biomarkers for the exposome?

The concept of the exposome is the encompassing of all the environmental exposures, both exogenous and endogenous, across the life course. Many, if not all, of these exposures can result in the generation of reactive species, and/or the modulation of cellular processes, that can lead to a breadth of modifications of DNA, the nature of which may be used to infer their origin. Because of their role in cell function, such modifications have been associated with various major human diseases, including cancer, and so their assessment is crucial. Historically, most methods have been able to only measure one or a few DNA modifications at a time, limiting the information available. With the development of DNA adductomics, which aims to determine the totality of DNA modifications, a far more comprehensive picture of the DNA adduct burden can be gained. Importantly, DNA adductomics can facilitate a "top-down" investigative approach whereby patterns of adducts may be used to trace and identify the originating exposure source. This, together with other 'omic approaches, represents a major tool for unraveling the complexities of the exposome and hence allow a better a understanding of the environmental origins of disease.

Identifying metabolic adaptations characteristic of cardiotoxicity using paired transcriptomics and metabolomics data integrated with a computational model of heart metabolism

Improvements in the diagnosis and treatment of cancer have revealed long-term side effects of chemotherapeutics, particularly cardiotoxicity. Here, we present paired transcriptomics and metabolomics data characterizing in vitro cardiotoxicity to three compounds: 5-fluorouracil, acetaminophen, and doxorubicin. Standard gene enrichment and metabolomics approaches identify some commonly affected pathways and metabolites but are not able to readily identify metabolic adaptations in response to cardiotoxicity. The paired data was integrated with a genome-scale metabolic network reconstruction of the heart to identify shifted metabolic functions, unique metabolic reactions, and changes in flux in metabolic reactions in response to these compounds. Using this approach, we confirm previously seen changes in the p53 pathway by doxorubicin and RNA synthesis by 5-fluorouracil, we find evidence for an increase in phospholipid metabolism in response to acetaminophen, and we see a shift in central carbon metabolism suggesting an increase in metabolic demand after treatment with doxorubicin and 5-fluorouracil.

Isotope Labeling Mass Spectrometry to Quantify Endogenous and Exogenous DNA Adducts and Metabolites of 1,3-Butadiene In Vivo

Human exposure to known carcinogen 1,3-butadiene (BD) is common due to its high concentrations in automobile exhaust, cigarette smoke, and forest fires, as well as its widespread use in the polymer industry. The adverse health effects of BD are mediated by epoxide metabolites such as 3,4-epoxy-1-butene (EB), which reacts with DNA to form 1-hydroxyl-3-buten-1-yl adducts on DNA nucleobases. EB-derived mercapturic acids (1- and 2-(N-acetyl-l-cysteine-S-yl)-1-hydroxybut-3-ene (MHBMA) and N-acetyl-S-(3,4-dihydroxybutyl)-l-cysteine (DHBMA)) and urinary N7-(1-hydroxyl-3-buten-1-yl) guanine DNA adducts (EB-GII) have been used as biomarkers of BD exposure and cancer risk in smokers and occupationally exposed workers. However, low but significant levels of MHBMA, DHBMA, and EB-GII have been reported in unexposed cultured cells, animals, and humans, suggesting that these metabolites and adducts may form endogenously and complicate risk assessment of butadiene exposure. In the present work, stable isotope labeling in combination with high-resolution mass spectrometry was employed to accurately quantify endogenous and exogenous butadiene metabolites and DNA adducts in vivo. Laboratory rats were exposed to 0.3, 0.5, or 3 ppm of BD-d6 by inhalation, and the amounts of endogenous (d0) and exogenous (d6) DNA adducts and metabolites were quantified in tissues and urine by isotope dilution capillary liquid chromatography/high resolution electrospray ionization tandem mass spectrometry (capLC-ESI-HRMS/MS). Our results reveal that EB-GII adducts and MHBMA originate exclusively from exogenous exposure to BD, while substantial amounts of DHBMA are formed endogenously. Urinary EB-GII concentrations were associated with genomic EB-GII levels in tissues of the same animals. Our findings confirm that EB-GII and MHBMA are specific biomarkers of exposure to BD, while endogenous DHBMA predominates at sub-ppm exposures to BD.

Specific prediction of mortality by oxidative stress-induced damage to RNA vs. DNA in humans

Modifications of nucleic acids (DNA and RNA) from oxidative stress is a potential driver of aging per se and of mortality in age-associated medical disorders such as type 2 diabetes (T2D). In a human cohort, we found a strong prediction of all-cause mortality by a marker of systemic oxidation of RNA in patients with T2D (n = 2672) and in nondiabetic control subjects (n = 4079). The finding persisted after the adjustment of established modifiers of oxidative stress (including BMI, smoking, and glycated hemoglobin). In contrast, systemic levels of DNA damage from oxidation, which traditionally has been causally linked to both T2D and aging, failed to predict mortality. Strikingly, these findings were subsequently replicated in an independent general population study (n = 3649). The data demonstrate a specific importance of RNA damage from oxidation in T2D and general aging.

Nucleic acid adductomics - The next generation of adductomics towards assessing environmental health risks

This Discussion article aims to explore the potential for a new generation of assay to emerge from cellular and urinary DNA adductomics which brings together DNA-RNA- and, to some extent, protein adductomics, to better understand the role of the exposome in environmental health. Components of the exposome have been linked to an increased risk of various, major diseases, and to identify the precise nature, and size, of risk, in this complex mixture of exposures, powerful tools are needed. Modification of nucleic acids (NA) is a key consequence of environmental exposures, and a goal of cellular DNA adductomics is to evaluate the totality of DNA modifications in the genome, on the basis that this will be most informative. Consequently, an approach which encompasses modifications of all nucleic acids (NA) would be potentially yet more informative. This article focuses on NA adductomics, which brings together the assessment of both DNA and RNA modifications, including modified (2'-deoxy)ribonucleosides (2'-dN/rN), modified nucleobases (nB), plus: DNA-DNA, RNA-RNA, DNA-RNA, DNA-protein, and RNA-protein crosslinks (DDCL, RRCL, DRCL, DPCL, and RPCL, respectively). We discuss the need for NA adductomics, plus the pros and cons of cellular vs. urinary NA adductomics, and present some evidence for the feasibility of this approach. We propose that NA adductomics provides a more comprehensive approach to the study of nucleic acid modifications, which will facilitate a range of advances, including the identification of novel, unexpected modifications e.g., RNA-RNA, and DNA-RNA crosslinks; key modifications associated with mutagenesis; agent-specific mechanisms; and adductome signatures of key environmental agents, leading to the dissection of the exposome, and its role in human health/disease, across the life course.

Assessment of the association of exposure to polycyclic aromatic hydrocarbons, oxidative stress, and inflammation: A cross-sectional study in Augsburg, Germany

BACKGROUND

Exposure to polycyclic aromatic hydrocarbons (PAHs) has been linked to acute and chronic health effects through the suggested pathways of oxidative stress and inflammation. However, evidence is still limited. We aimed to investigate jointly the relationship of PAHs, oxidative stress, and inflammation.

METHODS

We measured 13 biomarkers of PAH exposure (n = 6: hydroxylated polycyclic aromatic hydrocarbons, [OH-PAHs]), oxidative stress (n = 6: malondialdehyde (MDA); 8-hydroxy-2'-deoxyguanosine (8-OHdG); and 4 representatives of the compound class of F_2α-isoprostanes) in urine, and inflammation (n = 1: high-sensitivity C-reactive protein, [hs-CRP]) in serum from 400 participants at the second follow-up (2013/2014) of the German KORA survey S4. Multiple linear regression models were applied to investigate the interplay between biomarkers.

RESULTS

Concentrations of biomarkers varied according to sex, age, smoking status, season, and a history of obesity, diabetes, or chronic kidney disease. All OH-PAHs were significantly and positively associated with oxidative stress biomarkers. An interquartile range (IQR) increase in sum OH-PAHs was associated with a 13.3% (95% CI: 9.9%, 16.9%) increase in MDA, a 6.5% (95% CI: 3.5%, 9.6%) increase in 8-OHdG, and an 8.4% (95% CI: 6.6%, 11.3%) increase in sum F_2α-isoprostanes. Associations were more pronounced between OH-PAHs and F_2α-isoprostanes but also between OH-PAHs and 8-OHdG for participants with potential underlying systemic inflammation (hs-CRP ≥ 3 mg/L). We observed no association between OH-PAHs and hs-CRP levels. While 8-OHdG was significantly positively associated with hs-CRP (13.7% [95% CI: 2.2%, 26.5%] per IQR increase in 8-OHdG), F_2α-isoprostanes and MDA indicated only a positive or null association, respectively.

CONCLUSION

The results of this cross-sectional study suggest, at a population level, that exposure to PAHs is associated with oxidative stress even in a low exposure setting. Oxidative stress markers, but not PAHs, were associated with inflammation. Individual risk factors were important contributors to these processes and should be considered in future studies. Further longitudinal studies are necessary to investigate the causal chain of the associations.

Systemic DNA and RNA damage from oxidation after serotonergic treatment of unipolar depression

Previous studies have indicated that antidepressants that inhibit the serotonin transporter reduces oxidative stress. DNA and RNA damage from oxidation is involved in aging and a range of age-related pathophysiological processes. Here, we studied the urinary excretion of markers of DNA and RNA damage from oxidation, 8-oxodG and 8-oxoGuo, respectively, in the NeuroPharm cohort of 100 drug-free patients with unipolar depression and in 856 non-psychiatric community controls. Patients were subsequently treated for 8 weeks with escitalopram in flexible doses of 5-20 mg; seven of these switched to duloxetine by week 4, as allowed by the protocol. At week 8, 82 patients were followed up clinically and with measurements of 8-oxodG/8-oxoGuo. Contextual data were collected in patients, including markers of cortisol excretion and low-grade inflammation. The intervention was associated with a substantial reduction in both 8-oxodG/8-oxoGuo excretion (25% and 10%, respectively). The change was not significantly correlated to measures of clinical improvement. Both markers were strongly and negatively correlated to cortisol, as measured by the area under the curve for the full-day salivary cortisol excretion. Surprisingly, patients had similar levels of 8-oxodG excretion and lower levels of 8-oxoGuo excretion at baseline compared to the controls. We conclude that intervention with serotonin reuptake inhibitors in unipolar depression is associated with a reduction in systemic DNA and RNA damage from oxidation. To our knowledge, this to date the largest intervention study to characterize this phenomenon, and the first to include a marker of RNA oxidation.

Elevated Levels of Soluble CTLA-4, PD-1, PD-L1, LAG-3 and TIM-3 and Systemic Inflammatory Stress as Potential Contributors to Immune Suppression and Generalized Tumorigenesis in a Cohort of South African Xeroderma Pigmentosum Patients

Xeroderma Pigmentosum (XP), an autosomal recessive disorder characterized by ultraviolet radiation-induced abnormalities of DNA excision and repair pathways is associated with early development of cutaneous cancers. Intracellular oxidative stress has also been proposed as a contributor to the occurrence of skin cancers. However, little is known about the possible augmentative contributions of chronic inflammation, immune suppression and oxidative stress to the pathogenesis of malignancies associated with other subtypes of XP. This has been addressed in the current study, focused on the measurement of systemic biomarkers of inflammation, immune dysfunction and oxidative damage in XP patients, consisting of XP-C, XP-D and XP-E cases, including those XP-C cases who had already developed multiple skin malignancies. The inflammatory biomarker profile measured in XP patients and healthy control subjects included the cytokines, interleukins (ILs)-2, -4, -6, -10, interferon-γ (IFN- γ) and tumor-necrosis factor-α (TNF-α), the acute phase reactant, C-reactive protein (CRP), and cotinine (as an objective indicator of smoking status). Immune suppression was detected according to the levels of five soluble inhibitory immune checkpoint proteins (CTLA-4, PD-1, PD-L1, LAG-3 and TIM-3), as well as those of vitamin D, while oxidative stress was determined according to the circulating levels of the DNA adduct, 8-hydroxy-2-deoxyguanosine (8-OH-dG). These various biomarkers were measured in plasma using immunofluorimetric, nephelometric and ELISA procedures. Significant elevations in IL-6 (P<0.01) and TNF-α (P<0.0001), but none of the other cytokines, as well as increased levels of all five soluble inhibitory immune checkpoints (P=0.032-P=0.0001) were detected in the plasma of the XP patients. C-reactive protein and vitamin D were increased and decreased, respectively (both P<0.0001), while only one participant had an elevated level of plasma cotinine. Surprisingly, the levels of 8-OH-dG were significantly (P=0.0001) lower in the group of XP patients relative to a group of healthy control subjects. The findings of increased levels of pro-inflammatory cytokines and, in particular, those of the soluble immune checkpoints, in the setting of decreased vitamin D and moderately elevated levels of CRP in XP patients suggest a possible secondary role of ongoing, inflammatory stress and immune suppression in the pathogenesis of XP-associated malignancies.

An in silico kinetic model of 8-oxo-7,8-dihydro-2-deoxyguanosine and 8-oxo-7,8-dihydroguanosine metabolism from intracellular formation to urinary excretion

Oxidatively generated DNA damage is of paramount importance in a wide range of physiological and pathophysiological processes. Urinary 8-oxo-7,8-dihydro-2-deoxyguanosine (8-oxodG) is often used as an outcome marker in studies on the role of oxidatively generated DNA damage, but its exact relation to intracellular damage levels and variations in DNA repair have been unclear. Using a new approach of quantitative kinetic modeling inspired by pharmacokinetics, we find evidence that in steady state - i.e. when systemic consequences of given change in damage or cellular removal rates have stabilized - the urinary excretion of 8-oxodG is closely correlated to rates of damage and intracellular 8-oxodG levels, but independent of the rate of cellular removal. Steady state was calculated to occur within approximately 12 h. A similar pattern was observed in a model of the corresponding RNA marker 8-oxo-7,8-dihydroguanosine (8-oxoGuo), but with steady-state occurring slower (up to 5 d). These data have significant implications for the planning of studies and interpretation of data involving urinary 8-oxodG/8-oxoGuo excretion as outcome.HighlightsThe kinetics of 8-oxodG/8-oxoGuo formation, removal and excretion were simulated in silico.The model was based on existing data on 8-oxodG/8-oxoGuo levels and removal/excretion rates.Intracellular 8-oxodG/8-oxoGuo was closely correlated with urinary excretion in steady state.Changes in removal rates did not influence urinary excretion of 8-oxodG/8-oxoGuo.

Oxidative Stress Biomarkers in Urine of Metal Carpentry Workers Can Be Diagnostic for Occupational Exposure to Low Level of Welding Fumes from Associated Metals

Urinary concentrations of 16 different exposure biomarkers to metals were determined at the beginning and at the end of a working shift on a group of workers in the metal carpentry industry. Five different oxidative stress biomarkers were also measured, such as the oxidation products of RNA and DNA metabolized and excreted in the urine. The results of workers exposed to metals were compared to those of a control group. The metal concentrations found in these workers were well below the occupational exposure limit values and exceeded the mean concentrations of the same metals in the urine of the control group by a factor of four at maximum. Barium (Ba), mercury (Hg), lead (Pb) and strontium (Sr) were correlated with the RNA oxidative stress biomarker, 8-oxo-7, 8-dihydroguanosine (8-oxoGuo), which was found able to discriminate exposed workers from controls with a high level of specificity and sensitivity. The power of this early diagnostic technique was assessed by means of the ROC curve. Ba, rubidium (Rb), Sr, tellurium (Te), and vanadium (V) were correlated with the level of the protein oxidation biomarker 3-Nitrotyrosine (3-NO₂Tyr), and Ba, beryllium (Be), copper (Cu), and Rb with 5-methylcytidine (5-MeCyt), an epigenetic marker of RNA damage. These effect biomarkers can help in identifying those workers that can be defined as "occupationally exposed" even at low exposure levels, and they can provide information about the impact that such doses have on their health.

Diurnal and day-to-day variation of urinary oxidative stress marker 8-hydroxy-2'-deoxyguanosine

The urinary 8-hydroxy-2'-deoxyguanosine levels have been widely used as a biomarker of oxidative stress. The purpose of this study is to investigate the diurnal and day-to-day variations of urinary 8-hydroxy-2'-deoxyguanosine levels. For the diurnal variation, the urine samples were collected at the time of awakening and every 2 h, from 10:00 to 22:00, from 6 healthy participants. For the day-to-day variation, the urine samples were collected at the time of awakening for 35 consecutive days, from 27 healthy participants. As a result, no differences were observed in the diurnal urinary 8-hydroxy-2'-deoxyguanosine levels, and each subject had a characteristic 8-hydroxy-2'-deoxyguanosine level. On the other hand, the daily 8-hydroxy-2'-deoxyguanosine values showed a certain range of variation reflecting lifestyle factors, such as stress status, exercise, sleep time, drinking and diet. In conclusion, urinary 8-hydroxy-2'-deoxyguanosine may be a useful biomarker to control and prevent oxidative stress-related diseases, if the certain range of day-to-day variations of urinary 8-hydroxy-2'-deoxyguanosine is known. Even with only one measurement per year, the baseline urinary 8-hydroxy-2'-deoxyguanosine level could be achieved in a few years by incorporating the 8-hydroxy-2'-deoxyguanosine measurement as part of an annual health check. As the number of subjects was limited, further studies are needed for practical applications.

Influence of pubertal development on urinary oxidative stress biomarkers in adolescent girls in the New York LEGACY cohort

Puberty is a time of intense growth and differentiation of breast tissue and a window of susceptibility (WOS) for breast cancer. Although oxidative stress markers have been associated with breast cancer risk, it is unclear whether oxidative stress levels are different during the pubertal WOS, and if so, whether these differences are related to breast cancer susceptibility. We measured urinary biomarkers of whole body oxidative stress (urinary F2-Isoprostanes and 8-oxodeoxyguanosine (8-oxodG)) in 158 girls (ages 6-13 years), 71 with and 87 without a breast cancer family history (BCFH) from a cohort of adolescent girls from the New York site of the LEGACY cohort (Lessons in Epidemiology and Genetics in Adults Cancer from Youth). We compared levels of urinary oxidative stress biomarkers (F2-Isoprostanes and 8-oxodG) across the pubertal window, defined by Tanner Stage (TS) of breast development, both cross-sectionally and longitudinally within girls over an 18-month follow up period. Urinary oxidative stress biomarkers were unrelated to pubertal stages in cross-sectional analyses after considering adjustments for body mass index (BMI) and BCFH. In our longitudinal analysis, we found that urinary 8-oxodG levels, but not F2-Isoprostane levels, increased with age in BCFH + girls (β = 6.12, 95% CI = 0.08-12.16) compared to BCFH-girls. Higher BMI was associated with higher level of F2-Isoprostane in both cross-sectional (β = 0.02, 95% CI = 0.0004-0.05) and longitudinal analysis (β = 0.02, 95% CI = 0.0002-0.05). These findings support that higher BMI increases oxidative stress biomarkers over the pubertal window and that there are changes in 8-oxodG oxidative stress biomarkers in girls with a BCFH compared to girls without a BCFH.

Quantification of DNA Double Strand Breaks and Oxidation Response in Children and Adults Undergoing Dental CBCT Scan

Assessing the possible biological effects of exposure to low doses of ionizing radiation (IR) is one of the prime challenges in radiation protection, especially in medical imaging. Today, radiobiological data on cone beam CT (CBCT) related biological effects are scarce. In children and adults, the induction of DNA double strand breaks (DSBs) in buccal mucosa cells and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dG) and antioxidant capacity in saliva samples after CBCT examination were examined. No DNA DSBs induction was observed in children nor adults. In children only, an increase in 8-oxo-dG levels was observed 30 minutes after CBCT. At the same time an increase in antioxidant capacity was observed in children, whereas a decrease was observed in adults. Our data indicate that children and adults react differently to IR doses associated with CBCT. Fully understanding these differences could lead to an optimal use of CBCT in different age categories as well as improved radiation protection guidelines.

Levels of Urinary Biomarkers of Oxidatively Generated Damage to DNA and RNA in Different Groups of Workers Compared to General Population

(1) Background: The products of guanine oxidation in DNA and RNA excreted in urine are 8-oxo-7,8-dihydroguanine (8-oxoGua), 8-oxo-7,8-dihydroguanosine (8-oxoGuo), and 8-oxo-7,8-dihydro-2’-deoxyguanosine (8-oxodGuo). Despite intra and inter-individual variability, it is possible to identify situations that significantly increase the levels of these compounds when comparing urinary concentrations of some workers to those of the general population. (2) Methods: urines from gasoline pump attendants (58 from Saudi Arabia and 102 from Italy), 24 workers of a fiberglass reinforced plastics plant, 17 painters and 6 divers were analyzed by HPLC/MS-MS. To test the individual variability, two subjects provided daily samples for one month, and 132 urine samples from the general population were analyzed. (3) Results: We summarized the results for each biomarker, and found the following were statistically higher than in the general population: 8-oxoGua in fiberglass and Italian gasoline workers; 8-oxodGuo in fiberglass and both Saudi Arabian and Italian gasoline workers; 8-oxoGuo in fiberglass workers, both Saudi Arabian and Italian gasoline workers, and painters after the working shift. (4) Conclusions: these results confirm that both 8-oxodGuo and 8-oxoGuo are valuable biomarkers for occupational exposures to dangerous chemicals and seem to suggest that 8-oxoGuo, related to RNA oxidation, is a suitable biomarker to evaluate short term, reversible effects of occupational exposures even within the health-based limit values.

Associations between polychlorinated dibenzo-dioxins and polychlorinated dibenzo-furans exposure and oxidatively generated damage to DNA and lipid

Polychlorinated dibenzo-dioxins and polychlorinated dibenzo-furans (PCDD/Fs) have been reported to induce reactive oxygen species and oxidative stress, but the dose-response relationships have not been explored in molecular epidemiological studies. In this study, a total of 602 participants were recruited, comprising of 215 foundry workers, 171 incineration workers and 216 residents living more than 5 km away from the plants as the reference group. Individual PCDD/Fs exposures were estimated according to PCDD/Fs levels of working and living ambient air and daily foods. Urinary 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) and 8-iso-prostaglandin-F2α (8-isoPGF2α) were determined to reflect oxidatively generated damage to DNA and lipid. Generalized linear models were used to access the associations between PCDD/Fs exposure and oxidative stress biomarkers. We found that PCDD/Fs exposure and urinary oxidative stress biomarkers of workers were all higher than those of the reference group. Significantly positive exposure-response relationships between individual PCDD/Fs exposures and urinary 8-oxodG and 8-iso-PGF2α were found. Each 1-unit increase in ln-transformed levels of PCDD/Fs exposure generated a 0.78 nmol/mmol creatinine increase in ln-transformed 8-oxodG and a 0.50 ng/mmol creatinine increase in ln-transformed 8-isoPGF2α in foundry workers, a 0.49 nmol/mmol creatinine increase in ln-transformed 8-oxodG and a 0.26 ng/mmol creatinine increase in ln-transformed 8-isoPGF2α in incineration workers, compared with the reference group. And such associations were not modified by tobacco use. Our findings could help to understand the dose-response relationships between PCDD/Fs and oxidatively generated damage to DNA and lipid, and provide an epidemiologic basis for conducting research on the carcinogenesis and other toxicity mechanisms of PCDD/Fs.

Circulating microRNAs as potential biomarkers of occupational exposure to low dose organic solvents

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Circulating miRNAs can be used as sensitive biomarkers of low dose exposure to organic solvents at workplace.

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The miRNA response to organic chemicals elucidates molecular mechanisms occurring after specific occupational exposures.

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Associations between miRNAs, dose and oxidative stress biomarkers contribute to prevent and promote workers’ health.

Circulating microRNAs (miRNAs) have been recently acknowledged as novel and non-invasive biomarkers of exposure to environmental and occupational hazardous substances. This preliminary study investigates the potential role of blood miRNAs as molecular biomarkers of exposure to the most common organic solvents (ethylbenzene, toluene, xylene) used in the shipyard painting activity. Despite the low number of recruited workers, a two-tail standard Students’ test with Holm-Bonferroni adjusted p-value shows a significant up-regulation of two miRNAs (miR_6819_5p and miR_6778_5p) in exposed workers with respect to controls. A correlation analysis between miRNA, differentially expressed in exposed workers and in controls and urinary dose biomarkers i.e. methylhyppuric acid (xylenes metabolite), phenylglyoxylic and mandelic acid (ethylbenzene metabolites) S-benzyl mercapturic acid (toluene metabolite) and S-phenylmercapturic acid (benzene metabolite) measured at the end of the work-shift, allowed the identification of high correlation (0.80-0.99) of specific miRNAs with their respective urinary metabolites. MiRNA_671_5p correlated with methylhippuric, S-phenylmercapturic and S-benzyl mercapturic acid while the miRNA best correlating with the phenylglioxylic acid was miRNA_937_5p. These findings suggest miRNA as sensitive biomarkers of low dose exposure to organic chemicals used at workplace. Urinary DNA and RNA repair biomarkers coming from the oxidation product of guanine have been also associated to the different miRNAs. A significant negative association was found between 8-oxo-7,8-dihydroguanine (8-oxoGua) urinary concentration and miR_6778_5p. The findings of the present pilot study deserve to be tested on a larger population with the perspective of designing a miRNA based test of low dose exposure to organic solvents.

Effect of Benzene Exposure on the Urinary Biomarkers of Nucleic Acid Oxidation in Two Cohorts of Gasoline Pump Attendants

(1) Background: The oxidized guanine derivatives excreted into urine, products of DNA and RNA oxidation and repair, are used as biomarkers of oxidative damage in humans. This study aims to evaluate oxidative damage in gasoline pump attendants occupationally exposed to benzene. Benzene is contained in the gasoline but it is also produced from traffic and from smoking. (2) Methods: Twenty-nine gasoline pump attendants from two major cities of Saudi Arabia and 102 from Italy were studied for urinary 8-oxo-7,8-dihydroguanine (8-oxoGua), 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxodGuo), 8-oxo-7,8-dihydroguanosine (8-oxoGuo), and S-phenyl-mercapturic acid (SPMA) for benzene exposure and urinary cotinine for smoking status assessment by liquid chromatography-tandem mass spectrometry. Airborne benzene was also assessed in the Italian group by gas-chromatography with flame ionization detector (GC-FID). (3) Results: The results suggest that high levels of benzene exposure can cause an accumulation of SPMA and bring about the formation of the oxidation biomarkers studied to saturation. At low exposure levels, SPMA and oxidation biomarker levels were correlated among them and were associated with the smoking habit. (4) Conclusions: The study confirms the association between benzene exposure and the excretion of nucleic acid oxidation biomarkers and enhances the importance of measuring the smoking habit, as it can significantly influence oxidative damage, especially when the exposure levels are low.

Combinedin silicoandin vitrostudy of an aptasensor based on citrate-capped AuNPs for naked-eye detection of a critical biomarker of oxidative stress

An elevated level of 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxo-dG) in biosamples has been found to correlate to oxidative stress, and it has been assigned as a critical biomarker of various diseases. Herein, insights into the mechanisms of an aptasensor, based on citrate-capped gold nanoparticles (AuNPs), for 8-oxo-dG detection were elucidated using molecular dynamics (MD) simulations and validated experimentally. We found that the binding mechanism for binding between the anti-8-oxo-dG aptamer and 8-oxo-dG has the following characteristic stages: (i) adsorption stage, (ii) binding stage, and (iii) complex stabilization stage. Our simulations also reveal the binding sites between the anti-8-oxo-dG aptamer and 8-oxo-dG formed through hydrogen bonding during complex formation. A shortened anti-8-oxo-dG-aptamer was also engineered using in silico design, which was expected to improve the analytical performance of the colorimetric aptasensor. The mechanisms of the colorimetric aptasensor in the presence and absence of 8-oxo-dG were also investigated, and found to be in good agreement with the experiments. Complete understanding of the mechanism of the colorimetric aptasensor would open the door for development of novel naked-eye aptasensors.

A visual strategy for 8-oxo-dG monitoring based upon the dispersion of citrate-capped gold nanoparticles has been developed.

Statin treatment, oxidative stress and inflammation in a Danish population

Background

While statins may have anti-inflammatory effects, anti-oxidative effects are controversial. We investigated if statin treatment is associated with differences in oxidatively generated nucleotide damage and chronic inflammation, and the relationship between nucleotide damage and chronic inflammation.

Methods

We included 19,795 participants from the Danish General Suburban Population Study. In 3420 participants, we measured urinary 8-oxodG and 8-oxoGuo by liquid chromatography-tandem mass spectrometry as markers of oxidatively generated damage to DNA and RNA, respectively. We used a composite score for chronic inflammation (INFLA score) of hsCRP, WBC, platelet count, and neutrophil granulocyte to lymphocyte ratio. Associations were assessed using multivariate linear regression models.

Results

Compared with non-users, statin users had 4.3–6.0% lower 8-oxodG in three separate models (p < 0.05); there were no differences in 8-oxoGuo. Among participants aged > 60 y, statin users had 11.4% lower 8-oxodG (95%CI: 6.7–15.9%, p_interaction<0.001) and 3.9% lower 8-oxoGuo (95%CI: 0.1–7.5%, p_interaction = 0.002), compared with non-users. Compared with non-users, statin users had 11.1% (95%CI: 5.4–16.5%, p_interaction<0.001) lower 8-oxodG in participants treated for hypertension, and 18.6% (95%CI: 6.8–28.9%, p_interaction<0.001) lower 8-oxodG in participants with decreased renal function. Compared with non-users, statin users had significantly lower INFLA score (p < 0.001). 8-oxodG and 8-oxoGuo associated positively with markers of chronic inflammation.

Conclusions

Oxidatively generated DNA damage and inflammatory burden are lower in statin users compared with non-users. Together, anti-oxidative and anti-inflammatory effects may contribute to the beneficial effects of statins.

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Statin users have lower oxidatively generated DNA damage than non-users.

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The protective effect of statins is more pronounced in high-risk groups.

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Statin users have lower levels of chronic inflammation than non-users.

Urinary DNA adductomics - A novel approach for exposomics

The exposome is a concept that encompasses the totality of internal and external environmental exposures, from conception onwards. Evaluation of the exposome, across the lifecourse represents a significant challenge, e.g., methods/technology may simply not exist to comprehensively assess all exposures, or they may not be applicable to human populations, or may have insufficient sensitivity. Cellular DNA adductomics aims to determine the totality of DNA adducts in the cellular genome. However, application to human populations requires the necessarily invasive sampling of tissue, to obtain sufficient DNA for sensitive analysis, which can represent a logistical and IRB challenge, particularly when investigating vulnerable populations. To circumvent this, we recently applied DNA adductomics to urine, detecting a range of expected and unexpected 2'-deoxyribonucleoside DNA adducts. However, base excision repair, the main DNA repair pathway for non-bulky DNA adducts, and processes such as spontaneous depurination, generate nucleobase adducts. Herein we propose a strategy to simultaneously assess 2'-deoxyribonucleoside and nucleobase adducts, using a widely used mass spectrometic platform (i.e., triple quadrupole tandem mass spectrometry). This will provide a much needed DNA adductomic approach for non-invasively, biomonitoring environmental exposures, through assessing the totality of DNA adducts; contributing to the evaluation of the exposome, across the life-course.

Clinical relevance of guanine-derived urinary biomarkers of oxidative stress, determined by LC-MS/MS

A reliable and fast liquid chromatography-tandem mass spectrometry method has been developed for the simultaneous determination of three oxidized nucleic acid damage products in urine, 8-oxoguanine (8-oxoGua), 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo) and 8-oxo-7,8-dihydroguanosine (8-oxoGuo). We applied this method to assess the effect of various urine workup procedures on the urinary concentrations of the oxidized nucleic acid products. Our results showed that frozen urine samples must be warmed (i.e., to 37 °C) to re-dissolve any precipitates prior to analysis. We showed that common workup procedures, such as thawing at room temperature or dilution with deionized water, are not capable of releasing fully the oxidized nucleic acid products from the precipitates, and result in significant underestimation (up to ~ 100% for 8-oxoGua, ~ 86% for both 8-oxodGuo and 8-oxoGuo). With this method, we further assessed and compared the ability of the three oxidized nucleic acid products, as well as malondialdehyde (MDA, a product of lipid peroxidation), to biomonitor oxidative stress in vivo. We measured a total of 315 urine samples from subjects with burdens of oxidative stress from low to high, including healthy subjects, patients with chronic obstructive pulmonary disease (COPD), and patients on mechanical ventilation (MV). The results showed that both the MV and COPD patients had significantly higher urinary levels of 8-oxoGua, 8-oxodGuo, and 8-oxoGuo (P < 0.001), but lower MDA levels, compared to healthy controls. Receiver operating characteristic curve analysis revealed that urinary 8-oxoGuo is the most sensitive biomarker for oxidative stress with area under the curve (AUC) of 0.91, followed by 8-oxodGuo (AUC: 0.80) and 8-oxoGua (AUC: 0.76). Interestingly, MDA with AUC of 0.34 failed to discriminate the patients from healthy controls. Emerging evidence suggests a potential clinical utility for the measurement of urinary 8-oxoGuo, and to a lesser extent 8-oxodGuo, which is strongly supported by our findings.

Luminescent europium sensors for specific detection of 8-oxo-dGTP by time-gated fluorescence

The 9-hydroxy-1,3-diazaphenoxazine-2-one unit was conjugated with the Eu³⁺-cyclen complex through a linker. This diazaphenoxazine group was expected as an antenna unit for the excitation of europium ion, and a selective recognition site for 8-oxo-dGTP base. Among the synthesized three derivatives, the highest fluorescence emission was obtained by the complex constructed of an ethylene linker and the cyclen unit with three N,N-dimethylacetamide groups. The Eu³⁺-cyclen complex exhibited a selective response to the 8-oxo-dGTP in aqueous media by a time-resolved fluorescence assay.

Elevated Levels of Urinary 8-oxodG Correlate with Persistent Periductal Fibrosis after Praziquantel Treatment in Chronic Opisthorchiasis

Previous studies demonstrated that urinary 8-oxodG is a predictive biomarker for Opisthorchis viverrini (OV)-associated hepatobiliary disease (HBD) and cholangiocarcinoma (CCA). This study examined the effects of praziquantel treatment on the profile of urinary 8-oxodG in relation to HBD status. Infection with OV, levels of urinary 8-oxodG, and HBD status in terms of periductal fibrosis (PDF) assessed by abdominal ultrasonography (US) were monitored and compared in cohorts of participants in Khon Kaen, Thailand, before and 1 year after praziquantel treatment. Urinary 8-oxodG levels significantly decreased after treatment compared with the baseline level in OV-infected participants who had no HBD (PDF negative; PDF-ve) (N = 14). Levels of 8-oxodG were unchanged after treatment in OV-infected subjects (OV+ve) who had positive PDF (N = 52). Within the positive PDF (PDF+ve) group who became PDF-ve after treatment, there was no significant change in 8-oxodG levels between pre-and posttreatment (reversible PDF = 65.3%). In those who had persistent PDF+ve at both ultrasound sampling points, there was no significant difference in urinary 8-oxodG levels between pre- and posttreatment (persistent PDF = 34.6%). Based on a logistic regression model and receiver operation curve analysis, the increase of 8-oxodG levels was found to be associated with increasing risk of PDF. Measurement of urinary 8-oxodG and US increased the likelihood of discovering persistent PDF, which is a predictable condition for the patients at risk of OV-associated CCA. To identify high-risk individuals for CCA, it is useful to perform US in combination with urinary 8-oxodG measurement.

Iron induced RNA-oxidation in the general population and in mouse tissue

Iron promotes formation of hydroxyl radicals by the Fenton reaction, subsequently leading to potential oxidatively generated damage of nucleic acids. Oxidatively generated damage to RNA, measured as 8-oxo-7,8-dihydroguanosine (8-oxoGuo) in urine, is increased in patients with genetic iron overload, which have led us to test the hypothesis that high iron status, assessed by iron biomarkers and genetic disposition, increases urinary excretion of 8-oxoGuo. In a general Danish population study we used a Mendelian randomization design with HFE genotypes as a proxy for iron status and supplemented with ex vivo experiments in mice muscle tissue exposed to iron(II) sulfate to attempt to clarify this hypothesis. The biomarkers ferritin, transferrin, and transferrin saturation (TS) were associated with 8-oxoGuo (in linear univariable and multivariable regression analyses: P < 0.001). Mendelian randomization indicated a causal pathway between genetically elevated iron biomarkers (assessed by ferritin and TS) and high levels of 8-oxoGuo. The ex vivo experiments showed a monotonically increase in 8-oxoGuo with increased iron concentration (ANOVA: P = 0.0008) that was prevented with iron chelation (P = 0.01). Our results indicate a causal relationship between iron biomarkers and 8-oxoGuo. Furthermore, the ex vivo experiment shows a mechanistic link between iron and 8-oxoGuo formation. Both iron overload and the biomarker 8-oxoGuo have been linked to e.g. diabetes, which merits future studies to investigate if iron induced 8-oxoGuo is involved in disease development.

Perceived Stress, Depressive Symptoms, and Oxidative DNA Damage

OBJECTIVE

Psychosocial stress may influence the risk of disease through its association with oxidative DNA damage. We examined whether perceived stress and depressive symptoms were associated with urinary excretion of 8-hydroxydeoxyguanosine (8-OHdG), with mutual interaction on 8-OHdG.

METHODS

This cross-sectional study included 6517 individuals aged 45 to 74 years who participated, between 2010 and 2012, in a follow-up survey of an ongoing cohort study. Perceived stress during the past year was measured using a self-report questionnaire. Depressive symptoms were evaluated using the Zung Self-Rating Depression Scale. Urinary 8-OHdG concentrations were measured using a column switching high-pressure liquid chromatography system coupled to an electrochemical detector.

RESULTS

Higher perceived stress was significantly associated with higher 8-OHdG (2.1% increase per one-category increase of stress; ptrend = .025), even after adjusting for sex, age, supplement use, psychosocial factors, psychotropic medication use, smoking, and body mass index. This association was modestly attenuated after further adjustment for physical activity, suggesting possible mediation or confounding by this factor. Depressive symptoms were not significantly associated with 8-OHdG. No significant interaction was detected between perceived stress and depressive symptoms on 8-OHdG.

CONCLUSIONS

In a general Japanese population, we found a weak positive association between perceived stress and urinary excretion of 8-OHdG, whereas no association was observed between depressive symptoms and 8-OHdG. Further studies are needed to examine whether the association between perceived stress and 8-OHdG is modified by depressive symptoms.

Cardiovascular and All-Cause Mortality Risk Associated With Urinary Excretion of 8-oxoGuo, a Biomarker for RNA Oxidation, in Patients With Type 2 Diabetes: A Prospective Cohort Study

OBJECTIVE

Cardiovascular mortality risk remains high among patients with type 2 diabetes. Oxidative stress indicated by high urinary excretion of the biomarker for RNA oxidation, 8-oxo-7,8-dihydroguanosine (8-oxoGuo), is associated with an increased risk of death in newly diagnosed and treated patients. We assessed whether 8-oxoGuo is associated with specific cardiovascular and all-cause mortality risk.

RESEARCH DESIGN AND METHODS

Urinary biomarkers for nucleic acid oxidation were measured in a cohort of patients with type 2 diabetes aged ≥60 years (n = 1,863), along with biochemical measurements, questionnaire findings, and Central Person Registry information to estimate the hazard ratios (HRs) for log2-transformed RNA oxidation using Cox regression.

RESULTS

During the 5-year follow-up, 173 of 1,863 patients had died (9.3%), including 73 patients who died of cardiovascular disease (42.2%). Doubling of RNA oxidation was associated with an HR of all-cause mortality of 2.10 (95% CI 1.63-2.71; P < 0.001) and an HR of cardiovascular death of 1.82 (95% CI 1.20-2.77; P = 0.005) after multiple adjustments. The 5-year absolute risks (ARs) of all-cause mortality (AR 13.9 [95% CI 10.8-17.0] vs. AR 6.10 [95% CI 4.00-8.30]) and cardiovascular mortality (AR 5.49 [95% CI 3.44-7.55] vs. AR 3.16 [95% CI 1.59-4.73]) were approximately two times higher in the highest quartile of RNA oxidation than in the lowest quartile.

CONCLUSIONS

We conclude that high RNA oxidation is associated with all-cause and cardiovascular mortality risk in patients with type 2 diabetes. Targeting oxidative stress via interventions with long-term follow-up may reveal the predictive potential of the biomarker 8-oxoGuo.

Potential application of the oxidative nucleic acid damage biomarkers in detection of diseases

Reactive oxygen species (ROS) are generated after exposure to harmful environmental factors and during normal cellular metabolic processes. The balance of the generating and scavenging of ROS plays a significant role in living cells. The accumulation of ROS will lead to oxidative damage to biomolecules including nucleic acid. Although many types of oxidative nucleic acid damage products have been identified, 8-oxo-7,8-dihydro-2’-deoxyguanosine (8-oxodG) and 8-oxo-7,8-dihydroguanosine (8-oxoG) has been commonly chosen as the biomarkers of oxidative damage to DNA and RNA, respectively. It has been demonstrated that oxidative damage to nucleic acid is an initiator in pathogenesis of numerous diseases. Thus, oxidative nucleic acid damage biomarkers have the potential to be utilized for detection of diseases. Herein, we reviewed the relationship of oxidative nucleic acid damage and development of various diseases including cancers (colorectal cancer, gastrointestinal cancer, breast cancer, lung cancer, epithelial ovarian carcinoma, esophageal squamous cell carcinoma), neurodegenerative disorders and chronic diseases (diabetes and its complications, cardiovascular diseases). The potential of oxidative nucleic acid damage biomarkers for detection of diseases and drug development were described. Moreover, the approaches for detection of these biomarkers were also summarized.

Exposure to polycyclic aromatic hydrocarbons and volatile organic compounds among recently pregnant rural Guatemalan women cooking and heating with solid fuels

BACKGROUND

Household air pollution is a major contributor to death and disability worldwide. Over 95% of rural Guatemalan households use woodstoves for cooking or heating. Woodsmoke contains carcinogenic or fetotoxic polycyclic aromatic hydrocarbons (PAHs) and volatile organic compounds (VOCs). Increased PAHs and VOCs have been shown to increase levels of oxidative stress.

OBJECTIVE

We examined PAH and VOC exposures among recently pregnant rural Guatemalan women exposed to woodsmoke and compared exposures to levels seen occupationally or among smokers.

METHODS

Urine was collected from 23 women who were 3 months post-partum three times over 72h: morning (fasting), after lunch, and following dinner or use of wood-fired traditional sauna baths (samples=68). Creatinine-adjusted urinary concentrations of metabolites of four PAHs and eight VOCs were analyzed by liquid chromatography-mass spectrometry. Creatinine-adjusted urinary biomarkers of oxidative stress, 8-isoprostane and 8-OHdG, were analyzed using enzyme-linked immunosorbent assays (ELISA). Long-term (pregnancy through 3 months prenatal) exposure to particulate matter and airborne PAHs were measured.

RESULTS

Women using wood-fueled chimney stoves are exposed to high levels of particulate matter (median 48h PM2.5 105.7μg/m3; inter-quartile range (IQR): 77.6-130.4). Urinary PAH and VOC metabolites were significantly associated with woodsmoke exposures: 2-naphthol (median (IQR) in ng/mg creatinine: 295.9 (74.4-430.9) after sauna versus 23.9 (17.1-49.5) fasting; and acrolein: 571.7 (429.3-1040.7) after sauna versus 268.0 (178.3-398.6) fasting. Urinary PAH (total PAH: ρ=0.89, p<0.001) and VOC metabolites of benzene (ρ=0.80, p<0.001) and acrylonitrile (ρ=0.59, p<0.05) were strongly correlated with long-term exposure to particulate matter. However urinary biomarkers of oxidative stress were not correlated with particulate matter (ρ=0.01 to 0.05, p>0.85) or PAH and VOC biomarkers (ρ=-0.20 to 0.38, p>0.07). Urinary metabolite concentrations were significantly greater than those of heavy smokers (mean cigarettes/day=18) across all PAHs. In 15 (65%) women, maximum 1-hydroxypyrene concentrations exceeded the occupational exposure limit of coke-oven workers.

CONCLUSIONS

The high concentrations of urinary PAH and VOC metabolites among recently pregnant women is alarming given the detrimental fetal and neonatal effects of prenatal PAH exposure. As most women used chimney woodstoves, cleaner fuels are critically needed to reduce smoke exposure.

Clarithromycin, trimethoprim, and penicillin and oxidative nucleic acid modifications in humans: randomised, controlled trials

AIMS

In vitro studies have demonstrated that formation of reactive oxygen species (ROS) contributes to the effect of bactericidal antibiotics. The formation of ROS is not restricted to bacteria, but also occurs in mammalian cells. Oxidative stress is linked to several diseases. This study investigates whether antibiotic drugs induce oxidative stress in healthy humans as a possible mechanism for adverse reactions to the antibiotic drugs.

METHODS

This study contains information from two randomised, controlled trials. Participants underwent 1 week treatment with clarithromycin, trimethoprim, phenoxymethylpenicillin (penicillin V), or placebo. Oxidative modifications were measured as 24-h urinary excretion of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) and 8-oxo-7,8-dihydroguanosine (8-oxoGuo), and plasma levels of malondialdehyde before and after treatment as a measurement of DNA oxidation, RNA oxidation, and lipid peroxidation, respectively.

RESULTS

Clarithromycin significantly increased urinary excretion of 8-oxodG by 22.0% (95% confidence interval (CI): 3.6-40.4%) and 8-oxoGuo by 14.9% (95% CI: 3.7-26.1%). Further, we demonstrated that trimethoprim significantly lowered urinary excretion of 8-oxodG by 21.7% (95% CI: 5.8-37.6%), but did not influence urinary excretion of 8-oxoGuo. Penicillin V did not influence urinary excretion of 8-oxodG or 8-oxoGuo. None of the antibiotic drugs influenced plasma levels of malondialdehyde.

CONCLUSION

Clarithromycin significantly increases oxidative nucleic acid modifications. Increased oxidative modifications might explain some of clarithromycin's known adverse reactions. Trimethoprim significantly lowers DNA oxidation but not RNA oxidation. Penicillin V had no effect on oxidative nucleic acid modifications.

Aging with higher fractional exhaled nitric oxide levels are associated with increased urinary 8-oxo-7,8-dihydro-2'-deoxyguanosine concentrations in elder females

Indoor air pollutants from environmental tobacco smoke and cooking fume can induce oxidative stress and inflammatory response, which generate oxidatively damaged DNA in human body. Among 2224 adults, levels of FENO and urinary 8-oxodG were measured using a nano coulomb nitric oxide analyzer and a high performance liquid chromatography system with electrochemical detector, respectively. Association between aging with higher FENO levels and urinary 8-oxodG levels were analyzed using multiple linear regression analysis. Nonsmoking women aged 64 years and over, with higher FENO (≥ 25 part per billion) and self-catering but without passive smoking had a higher risk of increased urinary 8-oxodG (△% of urinary 8-oxodG: 81.3 %, 95 % CI: 27.4-158.0 %) levels, particularly these elderly women with using liquefied petroleum gas for cooking, had a higher risk for increased urinary 8-oxodG levels (△% of urinary 8-oxodG: 100.2 %, 95 % CI: 95 % CI: 35.3-196.3 %), compared with those aged less than 64 years, with lower FENO (< 25 part per billion). Cooking activity aggravated aging-related the aging-induced in urinary 8-oxodG excretion among nonsmoking women aged 64 years and over but without passive smoking.

The NUTRAOLEOUM Study, a randomized controlled trial, for achieving nutritional added value for olive oils

Background

Virgin olive oil, a recognized healthy food, cannot be consumed in great quantities. We aim to assess in humans whether an optimized virgin olive oil with high phenolic content (OVOO, 429 mg/Kg) and a functional one (FOO), both rich in phenolic compounds (429 mg/Kg) and triterpenic acids (389 mg/kg), could provide health benefits additional to those supplied a by a standard virgin olive oil (VOO).

Methods/design

A randomized, double-blind, crossover, controlled study will be conducted. Healthy volunteers (aged 20 to 50) will be randomized into one of three groups of daily raw olive oil consumption: VOO, OVOO, and FOO (30 mL/d). Olive oils will be administered over 3-week periods preceded by 2-week washout ones. The main outcomes will be markers of lipid and DNA oxidation, inflammation, and vascular damage. A bioavailability and dose-response study will be nested within this sustained- consumption one. It will be made up of 18 volunteers and be performed at two stages after a single dose of each olive oil. Endothelial function and nitric oxide will be assessed at baseline and at 4 h and 6 h after olive oil single dose ingestion.

Discussion

For the first time the NUTRAOLEUM Study will provide first level evidence on the health benefits in vivo in humans of olive oil triterpenes (oleanolic and maslinic acid) in addition to their bioavailability and disposition.

Trial registration

The Trial has been registered in ClinicalTrials.gov ID: NCT02520739.

Nucleotide excision repair of oxidised genomic DNA is not a source of urinary 8-oxo-7,8-dihydro-2'-deoxyguanosine

Urinary 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo) is a widely measured biomarker of oxidative stress. It has been commonly assumed to be a product of DNA repair, and therefore reflective of DNA oxidation. However, the source of urinary 8-oxodGuo is not understood, although potential confounding contributions from cell turnover and diet have been ruled out. Clearly it is critical to understand the precise biological origins of this important biomarker, so that the target molecule that is oxidised can be identified, and the significance of its excretion can be interpreted fully. In the present study we aimed to assess the contributions of nucleotide excision repair (NER), by both the global genome NER (GG-NER) and transcription-coupled NER (TC-NER) pathways, and sanitisation of the dGTP pool (e.g. via the activity of the MTH1 protein), on the production of 8-oxodGuo, using selected genetically-modified mice. In xeroderma pigmentosum A (XPA) mice, in which GG-NER and TC-NER are both defective, the urinary 8-oxodGuo data were unequivocal in ruling out a contribution from NER. In line with the XPA data, the production of urinary 8-oxodGuo was not affected in the xeroderma pigmentosum C mice, specifically excluding a role of the GG-NER pathway. The bulk of the literature supports the mechanism that the NER proteins are responsible for removing damage to the transcribed strand of DNA via TC-NER, and on this basis we also examined Cockayne Syndrome mice, which have a functional loss of TC-NER. These mice showed no difference in urinary 8-oxodGuo excretion, compared to wild type, demonstrating that TC-NER does not contribute to urinary 8-oxodGuo levels. These findings call into question whether genomic DNA is the primary source of urinary 8-oxodGuo, which would largely exclude it as a biomarker of DNA oxidation. The urinary 8-oxodGuo levels from the MTH1 mice (both knock-out and hMTH1-Tg) were not significantly different to the wild-type mice. We suggest that these findings are due to redundancy in the process, and that other enzymes substitute for the lack of MTH1, however the present study cannot determine whether or not the 2'-deoxyribonucleotide pool is the source of urinary 8-oxodGuo. On the basis of the above, urinary 8-oxodGuo is most accurately defined as a non-invasive biomarker of oxidative stress, derived from oxidatively generated damage to 2'-deoxyguanosine.

Association between Oxidative DNA Damage and Risk of Colorectal Cancer: Sensitive Determination of Urinary 8-Hydroxy-2'-deoxyguanosine by UPLC-MS/MS Analysis

Oxidative DNA damage plays crucial roles in the pathogenesis of numerous diseases including cancer. 8-hydroxy-2′-deoxyguanosine (8-OHdG) is the most representative product of oxidative modifications of DNA, and urinary 8-OHdG is potentially the best non-invasive biomarker of oxidative damage to DNA. Herein, we developed a sensitive, specific and accurate method for quantification of 8-OHdG in human urine. The urine samples were pretreated using off-line solid-phase extraction (SPE), followed by ultrahigh performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) analysis. By the use of acetic acid as an additive to the mobile phase, we improved the UPLC-MS/MS detection of 8-OHdG by 2.7−5.3 times. Using the developed strategy, we measured the contents of 8-OHdG in urine samples from 142 healthy volunteers and 84 patients with colorectal cancer (CRC). We observed increased levels of urinary 8-OHdG in patients with CRC and patients with tumor metastasis, compared to healthy controls and patients without tumor metastasis, respectively. Additionally, logistic regression analysis and receiver operator characteristic (ROC) curve analysis were performed. Our findings implicate that oxidative stress plays important roles in the development of CRC and the marked increase of urinary 8-OHdG may serve as a potential liquid biomarker for the risk estimation, early warning and detection of CRC.

Systemic oxidative DNA and RNA damage are not increased during early phases of psychosis: A case control study

It has been suggested that patients with schizophrenia develop higher levels of oxidative stress, which may contribute to deteriorating mental illness. In order to examine oxidative stress in the early stages of severe mental illness, we examined the levels of systemic Deoxyribonucleic Acid (DNA) and Ribonucleic Acid (RNA) oxidation, 8-oxo-7,8-dihydro-2'-deoxyguanosine and 8-oxo-7,8-dihydroguanosine, perceived stress and recent life events in patients at ultra high-risk (UHR) of developing psychosis, in antipsychotic naïve patients with first-episode schizophrenia (FES), and in healthy controls. We included 41 UHR patients, 35 FES patients, and 29 healthy controls. There was no difference in the level of DNA/RNA oxidative damage between UHR patients and FES patients compared with healthy controls. We found no association between levels of DNA/RNA oxidative damage and perceived stress/life events. Based on the results, we suggest that DNA and RNA oxidative markers are not increased during the early stages of illness, but further longitudinal studies in first-episode psychosis should be carried out to examine whether DNA and RNA oxidative damage are potential markers of severe illness.

What causes human cancer? Approaches from the chemistry of DNA damage

To prevent human cancers, environmental mutagens must be identified. A common mechanism of carcinogenesis is DNA damage, and thus it is quite possible that environmental mutagens can be trapped as adducts by DNA components. It is also important to identify new types of DNA damaging reactions and clarify their mechanisms. In this paper, I will provide typical examples of our efforts to identify DNA damage by environmental agents, from chemistry-based studies. 1) Oxidative DNA damage: 8-Hydroxydeoxyguanosine (8-OHdG, 8-oxodG) was discovered during a structural study of DNA modifications caused in vitro by heating glucose, which was used as a model of cooked foods. We found that various oxygen radical-forming agents induced the formation of 8-OHdG in DNA, in vitro and in vivo. Analyses of the urinary 8-OHdG levels are useful to assess the extent of oxidative DNA damage in a human population. 2) Lipid peroxide-derived DNA adducts: We searched for mutagens that react with deoxynucleosides, in model systems of lipid peroxidation. The reaction mixtures were analyzed by high performance liquid chromatography (HPLC), and we discovered various lipid peroxide-derived mutagens, including new mutagens. Some of these adducts were detected in human DNA. These mutagens may be involved in lipid peroxide-related cancers. 3) Methylation of cytosine by free radicals: Methylation of the cytosine C-5 position is an important mechanism of carcinogenesis, in addition to gene mutations. However, the actual mechanisms of de novo methylation in relation to environmental agents are not clear. We found that cytosine C-5 methylation occurred by a free radical mechanism. The possible role of this radical-induced DNA methylation in carcinogenesis will be discussed, in relation to the presently accepted concept of cancer epigenetics. In these studies, chemical analyses of the adducts formed in model reactions led to the discoveries of new mutagens and important types of DNA modifications, which seem to be involved in human carcinogenesis.

Effects of a dietary intervention with conjugated linoleic acid on immunological and metabolic parameters in children and adolescents with allergic asthma--a placebo-controlled pilot trial

Background

Circumstantial evidence suggests that conjugated linoleic acid (CLA) beneficially modulates immune function in allergic subjects. C9,t11-CLA, naturally occurring in ruminant fats, is suggested to be the effective isomer. In contrast, for the t10,c12-CLA isomer, which is naturally found only in traces but usually constitutes a relevant part in commercial CLA mixtures, adverse effects have been reported. Aim of this study was to assess putative immunomodulatory effects of highly enriched c9,t11-CLA in allergic subjects. To our best knowledge, our study is the first in that a CLA preparation was used for such purpose which was free of t10,c12-CLA.

Design

Twenty-nine asthmatic children and adolescents (age 6–18 y) with diagnosed allergic sensitization against grass pollen, house dust mite, or cat hair/epithelia consumed daily a portion of yoghurt containing either 3 g CLA (75 % c9,t11-CLA, 87 % purity) or placebo (safflower oil) over a period of 12 weeks. At study start and end, lung function parameters, specific IgE, in vitro allergen-induced cytokine production in peripheral blood mononuclear cells (PBMC), plasma ECP, urinary 8-oxodG as marker of oxidation, fatty acid profiles of erythrocytes, and routine haematological parameters were determined. Prior to blood samplings, 3-days dietary records were requested. Throughout the study, the participants documented daily their peak expiratory flow and kept protocol about their allergy symptoms and usage of demand medication.

Results

In contrast to the CLA group, PBMC-produced IFN-γ and IL-4 increased significantly and by trend, respectively, in the placebo group. Moreover, plasma ECP tended to increase in the placebo group. In the pollen subgroup, FEV1 improved upon both CLA and placebo oil supplementation. In both intervention groups, the n-6/n-3 PUFA ratio in red blood cells decreased, mainly due to an increase in n-3 PUFA. Moreover, 8-oxodG excretion increased in both groups. No changes occurred regarding specific IgE concentrations, allergy symptoms, and volume parameters.

Conclusion

Our results indicate that CLA modestly dampens the inflammatory response on the cellular level. A clinically relevant amelioration of the symptoms could not be proved in atopic manifest patients.

Trial registration

NCT01026506.

Strong Associations Exist among Oxidative Stress and Antioxidant Biomarkers in the Circulating, Cellular and Urinary Anatomical Compartments in Guatemalan Children from the Western Highlands

BACKGROUND

A series of antioxidant enzymes and non-enzymatic compounds act to protect cells from uncontrolled propagation of free radicals. It is poorly understood, though, to what extent and how their interaction is harmonized.

OBJECTIVES

To explore associative interactions among a battery of urinary and blood biomarkers of oxidative stress and enzymatic and non-enzymatic markers of the antioxidant defense system in children from low income households.

METHODS

For this cross-sectional descriptive study, urine, red cells, and plasma were sampled in 82 preschool children attending three daycare centers in Quetzaltenango Guatemala. The urinary oxidative stress biomarkers studied were F2-isoprostanes and 8-hydroxy-deoxy-guanosine. Red cell enzyme activities measured were: catalase, superoxide dismutase, glutathione peroxidase and glutathione reductase. Circulating non-enzymatic antioxidants selected were: retinol, tocopherols, β-carotene and coenzymes Q9 and Q10.

RESULTS

In a Spearman rank-order correlation hemi-matrix, of 55 paired combinations of the 11 biomarkers, 28 (51%) were significantly correlated among each other (p ≤ 0.05), with the strongest association being retinol and tocopherols (r = 0.697, p<0.001), and 4 associations (9%) showed a trend (p> 0.5 to ≤ 0.10). F2-isoprostanes showed the greatest number of cross-associations, having significant interactions with 8 of the 10 remaining biomarkers. Goodness-of-fit modeling improved or maintained the r value for 24 of the significant interactions and for one of the 5 borderline associations. Multiple regression backward stepwise analysis indicated that plasma retinol, β-carotene and coenzyme Q10 were independent predictors of urinary F2-isoprostanes.

CONCLUSION

Numerous significant associations resulted among biomarkers of oxidation and responders to oxidation. Interesting findings were the apparent patterns of harmonious interactions among the elements of the oxidation-antioxidation systems in this population.

Gender-related differences in susceptibility to oxidative stress in healthy middle-aged Serbian adults

Gender-related differences in the association between polymorphism of xenobiotic-metabolising enzymes or non-genetic biomarkers and susceptibility to oxidative stress was assessed in healthy middle-aged Serbian adults, by urinary 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG/creatinine) and total antioxidant status in serum (TAOS). Females were more susceptible to oxidative stress. In both genders, positive predictor of the antioxidative protection was serum triglyceride, while BMI <25 kg/m(2) was associated with oxidative stress. Susceptibility to oxidative stress in males was associated with GSTT1*null allele and increased serum iron, but in females, it was decreased serum bilirubin. Early identification of the risk factors could be important in the prevention of oxidative stress-related diseases.

Redox Imbalance in Lung Cancer of Patients with Underlying Chronic Respiratory Conditions

Chronic respiratory diseases such as obstructive pulmonary disease (COPD) and oxidative stress may underlie lung cancer (LC). We hypothesized that the profile of oxidative and antioxidant events may differ in lung tumors and blood compartments of patients with non-small cell LC (NSCLC) with and without COPD. Redox markers (immunoblotting, ELISA, chemiluminescence, 2D electrophoresis and proteomics) were analyzed in blood samples of 17 control subjects and 80 LC patients (59 LC-COPD and 21 LC) and lung specimens (tumor and nontumor) from those undergoing thoracotomy (35 patients: 23 LC-COPD and 12 LC). As smoking history was more prevalent in LC-COPD patients, these were further analyzed post hoc as heavy and moderate smokers (cutoff, 60 pack-years). Malondialdehyde (MDA)-protein adducts and SOD1 levels were higher in tumor and nontumor samples of LC-COPD than in LC. In tumors compared with nontumors, SOD2 protein content was greater, whereas catalase levels were decreased in both LC and LC-COPD patients. Blood superoxide anion levels, protein carbonylation and nitration were greater in LC and LC-COPD patients than in the controls, and in the latter patients compared with the former. Systemic superoxide anion, protein carbonyls and nitrotyrosine above specific cutoff values best identified underlying COPD among all patients. Smoking did not influence the study results. A differential expression profile of oxidative stress markers exists in blood and, to a lesser extent, in the tumors of LC-COPD patients. These findings suggest that systemic oxidative stress and lung antioxidants (potential biomarkers) may predispose patients with chronic respiratory diseases to a higher risk for LC.

Ionizing radiation-induced DNA injury and damage detection in patients with breast cancer

Breast cancer is the most common malignancy in women. Radiotherapy is frequently used in patients with breast cancer, but some patients may be more susceptible to ionizing radiation, and increased exposure to radiation sources may be associated to radiation adverse events. This susceptibility may be related to deficiencies in DNA repair mechanisms that are activated after cell-radiation, which causes DNA damage, particularly DNA double strand breaks. Some of these genetic susceptibilities in DNA-repair mechanisms are implicated in the etiology of hereditary breast/ovarian cancer (pathologic mutations in the BRCA 1 and 2 genes), but other less penetrant variants in genes involved in sporadic breast cancer have been described. These same genetic susceptibilities may be involved in negative radiotherapeutic outcomes. For these reasons, it is necessary to implement methods for detecting patients who are susceptible to radiotherapy-related adverse events. This review discusses mechanisms of DNA damage and repair, genes related to these functions, and the diagnosis methods designed and under research for detection of breast cancer patients with increased radiosensitivity.

Levels of 8-OxodG Predict Hepatobiliary Pathology in Opisthorchis viverrini Endemic Settings in Thailand

Opisthorchis viverrini is distinct among helminth infections as it drives a chronic inflammatory response in the intrahepatic bile duct that progresses from advanced periductal fibrosis (APF) to cholangiocarcinoma (CCA). Extensive research shows that oxidative stress (OS) plays a critical role in the transition from chronic O. viverrini infection to CCA. OS also results in the excision of a modified DNA lesion (8-oxodG) into urine, the levels of which can be detected by immunoassay. Herein, we measured concentrations of urine 8-oxodG by immunoassay from the following four groups in the Khon Kaen Cancer Cohort study: (1) O. viverrini negative individuals, (2) O. viverrini positive individuals with no APF as determined by abdominal ultrasound, (3) O. viverrini positive individuals with APF as determined by abdominal ultrasound, and (4) O. viverrini induced cases of CCA. A logistic regression model was used to evaluate the utility of creatinine-adjusted urinary 8-oxodG among these groups, along with demographic, behavioral, and immunological risk factors. Receiver operating characteristic (ROC) curve analysis was used to evaluate the predictive accuracy of urinary 8-oxodG for APF and CCA. Elevated concentrations of 8-oxodG in urine positively associated with APF and CCA in a strongly dose-dependent manner. Urinary 8-oxodG concentrations also accurately predicted whether an individual presented with APF or CCA compared to O. viverrini infected individuals without these pathologies. In conclusion, urinary 8-oxodG is a robust ‘candidate’ biomarker of the progression of APF and CCA from chronic opisthorchiasis, which is indicative of the critical role that OS plays in both of these advanced hepatobiliary pathologies. The findings also confirm our previous observations that severe liver pathology occurs early and asymptomatically in residents of O. viverrini endemic regions, where individuals are infected for years (often decades) with this food-borne pathogen. These findings also contribute to an expanding literature on 8-oxodG in an easily accessible bodily fluid (e.g., urine) as a biomarker in the multistage process of inflammation, fibrogenesis, and infection-induced cancer.

Opisthorchis viverrini is a food-borne helminth infection that drives a strong inflammatory response in the bile duct that can result in bile duct fibrosis and bile duct cancer (intrahepatic cholangiocarcinoma). Extensive research shows that oxidative stress (OS) plays a critical role in chronic O. viverrini infection transitioning to cancer in the bile duct. OS also results in a modified DNA lesion, referred to as 8-oxodG, excreted in the urine, where it can be detected by an antibody-based test. We measured the concentrations of 8-oxodG in the urine of O. viverrini-infected individuals who had developed bile duct fibrosis or bile duct cancer and compared levels of this metabolite in urine to O. viverrini infected individuals who did not have bile duct fibrosis or cancer in Northeastern Thailand. We determined bile duct fibrosis by ultrasonography and bile duct cancer by immunohistochemistry on resected liver tissue. We then built a statistical model to quantify how well urinary 8-oxodG predicted bile duct fibrosis and bile duct cancer in O. viverrini-infected individuals. We found that individuals with elevated levels of 8-oxodG in urine had a greater probability of developing bile duct fibrosis or bile duct cancer from O. viverrini infection. This association occurred in a strongly dose-dependent manner: in other words, the O. viverrini-infected individuals who had the highest concentration of urinary 8-oxodG also had the highest risk of presenting with bile duct fibrosis or bile duct cancer. In summary, measuring levels of 8-oxodG in the urine offers a unique opportunity to develop a candidate biomarker for advanced O. viverrini induced hepatobiliary pathologies such as fibrosis and cancer. The findings also confirm our previous observations that severe liver pathology occurs early and asymptomatically in residents of O. viverrini endemic regions, where individuals are infected for years (often decades) with this food-borne neglected tropical diseases (NTD) pathogen.

Analysis of Nucleosides in Municipal Wastewater by Large-Volume Liquid Chromatography Tandem Mass Spectrometry

Nucleosides are components of both DNA and RNA, and contain either a ribose (RNA) or 2deoxyribose (DNA) sugar and a purine or pyrimidine base. In addition to DNA and RNA turnover, modified nucleosides found in urine have been correlated to a diminished health status associated with AIDS, cancers, oxidative stress and age. Nucleosides found in municipal wastewater influent are potentially useful markers of community health status, and as of now, remain uninvestigated. A method was developed to quantify nucleosides in municipal wastewater using large-volume injection, liquid chromatography, and mass spectrometry. Method accuracy ranged from 92 to 139% when quantified by using isotopically labeled internal standards. Precision ranged from 6.1 to 19% of the relative standard deviation. The method's utility was demonstrated by the analysis of twenty-four hour composite wastewater influent samples that were collected over a week to investigate community nucleoside excretion. Nucleosides originating from RNA were more abundant that DNA over the study period, with total loads of nucleosides ranging from 2 to 25 kg/day. Given this relatively high amount of nucleosides found over the study period they present an attractive analyte for the investigation of community health.

BRCA1 and BRCA2 protect against oxidative DNA damage converted into double-strand breaks during DNA replication

BRCA1 and BRCA2 mutation carriers are predisposed to develop breast and ovarian cancers, but the reasons for this tissue specificity are unknown. Breast epithelial cells are known to contain elevated levels of oxidative DNA damage, triggered by hormonally driven growth and its effect on cell metabolism. BRCA1- or BRCA2-deficient cells were found to be more sensitive to oxidative stress, modeled by treatment with patho-physiologic concentrations of hydrogen peroxide. Hydrogen peroxide exposure leads to oxidative DNA damage induced DNA double strand breaks (DSB) in BRCA-deficient cells causing them to accumulate in S-phase. In addition, after hydrogen peroxide treatment, BRCA deficient cells showed impaired Rad51 foci which are dependent on an intact BRCA1-BRCA2 pathway. These DSB resulted in an increase in chromatid-type aberrations, which are characteristic for BRCA1 and BRCA2-deficient cells. The most common result of oxidative DNA damage induced processing of S-phase DSB is an interstitial chromatid deletion, but insertions and exchanges were also seen in BRCA deficient cells. Thus, BRCA1 and BRCA2 are essential for the repair of oxidative DNA damage repair intermediates that persist into S-phase and produce DSB. The implication is that oxidative stress plays a role in the etiology of hereditary breast cancer.

Potential survival markers in cancer patients undergoing chemotherapy

Due to the importance of the identification of chemotherapy outcome prognostic factors, we attempted to establish the potential of oxidative stress/DNA damage parameters such as prognostic markers. The aim of the study was to determine whether platinum derivative-based chemotherapy in cancer patients (n = 66) is responsible for systemic oxidatively damaged DNA and whether damage biomarkers, such as 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dG) and the modified base 8-oxo-7,8-dihydroguanine (8-oxo-Gua), in urine and DNA may be used as a prognostic factor for the outcome of chemotherapy. All the aforementioned modifications were analyzed using techniques involving high-performance liquid chromatography/electrochemical detection (HPLC/EC) or HPLC/gas chromatography-mass spectrometry (GC-MS). Among all the analyzed parameters, the significantly decreased levels of 8-oxo-Gua in urine collected from a subgroup of patients 24 h after the first infusion of the drug, as compared with the baseline levels, correlated with a significantly longer overall survival (OS) (60 months after therapy) than in the subgroup without any decrease of this parameter after therapy (median OS = 24 months, p = 0.007). Moreover, a significantly longer OS was also observed in a group with increased urine levels of 8-oxo-dG after chemotherapy (38.6 vs. 20.5 months, p = 0.03). The results of our study suggest that patients with decreased 8-oxo-Gua levels and increased 8-oxo-dG levels in urine 24 h after the first dose should be considered as better responders to the administered chemotherapy, with a lower risk of death. The conclusion may permit the use of these parameters as markers for predicting the clinical outcome of platinum derivative-based chemotherapy.

8-Oxo-7,8-dihydroguanine and 8-oxo-7,8-dihydro-2'-deoxyguanosine concentrations in various human body fluids: implications for their measurement and interpretation

8-Oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo) is the most investigated product of oxidatively damaged DNA lesion that has been associated with the development of aging, cancer and some degenerative diseases. Here, we present the first liquid chromatography-tandem mass spectrometry method that enables the simultaneous measurement of its repair products in plasma and saliva, namely 8-oxo-7,8-dihydroguanine (8-oxoGua) and 8-oxodGuo. Using this method, we investigated the underlying transport mechanism of the repair products of oxidatively damaged DNA between cellular compartments and biological matrices. Plasma, saliva and urine samples were collected concurrently from 57 healthy subjects. Various deproteinization methods were evaluated, and the precipitants acetonitrile and sodium hydroxide-methanol were, respectively, selected for plasma and saliva samples due to their effect on recovery efficiencies and chromatography. The mean baseline concentrations of 8-oxoGua and 8-oxodGuo in plasma were demonstrated to be 0.21 and 0.016 ng/mL, respectively, while in saliva they were 0.85 and 0.010 ng/mL, respectively. A relatively high concentration of 8-oxoGua was found in saliva with a concentration factor (CF, concentration ratio of saliva to plasma) of 4 as compared to that of 8-oxodGuo (CF: 0.6), implying that 8-oxoGua in plasma may be actively transported to saliva, whereas 8-oxodGuo was most dependent on a passive diffusion. Good correlations between urine and plasma concentrations were observed for 8-oxoGua and 8-oxodGuo, suggesting that blood was a suitable matrix in addition to urine. Significant correlation between 8-oxoGua and 8-oxodGuo in urine was only observed when the concentrations were not corrected for urinary creatinine, raising the issue of applicability of urinary creatinine to adjust 8-oxoGua concentrations.