Analysis of urinary 8-oxo-7,8-dihydro-purine-2'-deoxyribonucleosides by LC-MS/MS and improved ELISA

Potential contribution of ELISA and LFI assays to assessment of the oxidative stress condition based on 8-oxodG biomarker

Immunoassays have been extensively applied in the medical diagnostic field. Enzyme-Linked Immunosorbent Assay (ELISA) and Lateral Flow Immunochemical Assay (LFIA) are methods that have been well established to analysis of clinical substances such as protein, hormones, drugs, identification of antibodies and in the quantification of antigen. Over the past years, the application of these methods has been extended to assess the clinical oxidative stress condition based on monitoring of the 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) biomarker levels. The present manuscript provides an overview of the current immunoassays based on ELISA and LFIA technologies applied for a quantitative analysis of the 8-oxodG. The discussion focuses on the principles of development, improvement and analytical performance of these assays. The relationship of the molecule 8-oxodG as a clinical biomarker of the assessment of the oxidative stress condition is also discussed. Commercially available products to 8-oxodG analysis are also presented.

Biomarkers of nucleic acid oxidation - A summary state-of-the-art

Oxidatively generated damage to DNA has been implicated in the pathogenesis of a wide variety of diseases. Increasingly, interest is also focusing upon the effects of damage to the other nucleic acids, RNA and the (2′-deoxy-)ribonucleotide pools, and evidence is growing that these too may have an important role in disease. LC-MS/MS has the ability to provide absolute quantification of specific biomarkers, such as 8-oxo-7,8-dihydro-2′-deoxyGuo (8-oxodG), in both nuclear and mitochondrial DNA, and 8-oxoGuo in RNA. However, significant quantities of tissue are needed, limiting its use in human biomonitoring studies. In contrast, the comet assay requires much less material, and as little as 5 μL of blood may be used, offering a minimally invasive means of assessing oxidative stress in vivo, but this is restricted to nuclear DNA damage only. Urine is an ideal matrix in which to non-invasively study nucleic acid-derived biomarkers of oxidative stress, and considerable progress has been made towards robustly validating these measurements, not least through the efforts of the European Standards Committee on Urinary (DNA) Lesion Analysis. For urine, LC-MS/MS is considered the gold standard approach, and although there have been improvements to the ELISA methodology, this is largely limited to 8-oxodG. Emerging DNA adductomics approaches, which either comprehensively assess the totality of adducts in DNA, or map DNA damage across the nuclear and mitochondrial genomes, offer the potential to considerably advance our understanding of the mechanistic role of oxidatively damaged nucleic acids in disease.

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Oxidatively damaged nucleic acids are implicated in the pathogenesis of disease.

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LC-MS/MS, comet assay and ELISA are often used to study oxidatively damaged DNA.

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Urinary oxidatively damaged nucleic acids non-invasively reflect oxidative stress.

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DNA adductomics will aid understanding the role of ROS damaged DNA in disease.

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.

Comparison of an HPLC-MS/MS Method with Multiple Commercial ELISA Kits on the Determination of Levels of 8-oxo-7,8-Dihydro-2'-Deoxyguanosine in Human Urine

Introduction: Analysis of 8-oxodG is usually conducted by either chromatography-based methods or by immunochemical methods commonly used based upon their low cost and high-throughput. However, concern regarding the accuracy of ELISA methods has complicated their use. We directly compare the levels of urinary 8-oxodG obtained by HPLC-MS/MS with three commercially available ELISA kits in this report. Methods: In the current study, a total of 9 human urine samples were analyzed by LC-MS/MS and three commonly used commercial available ELISA kits. Results: We found that urinary 8-oxodG levels analyzed by HPLC-MS/MS [1.4 ± 0.3 nmol/mmol creatinine) were 7.6- to 23.5-fold lower than those detected by ELISA. Overall, the correlations between ELISA and HPLC-MS/MS were poor but were improved after SPE purification for kits from ENZO (P = 0.2817 without SPE; P = 0.0086 with SPE) and Abcam (P = 0.0596 without SPE; P = 0.0473 with SPE). Discussion and conclusion: While we confirmed that SPE purification can improve the correlation between the selected ELISA kits and HPLC-MS/MS, HPLC-MS/MS is still the method of choice to accurately assess the levels of 8-oxodG in human urine.

Measurement of 8-oxo-7,8-dihydro-2'-deoxyguanosine and 8-oxo-7,8-dihydro-guanosine in cerebrospinal fluid by ultra performance liquid chromatography-tandem mass spectrometry

Increased levels of nucleosides modified by oxidation in human cerebrospinal fluid (CSF) have several times been reported in Alzheimer patients and patients suffering from Parkinson's disease. The focus has especially been on nucleosides containing the 8-hydroxylation of guanine. Only few reports on quantification of the ribonucleoside 8-oxo-7,8-dihydro-guanosine (8oxoGuo) in CSF have been published, whereas more have been published on the quantification of the deoxy-ribonucleoside 8-oxo-7,8-dihydro-2'-deoxyguanosine (8oxodGuo). The reports on the quantification of 8oxodGuo concentrations in CSF report absolute concentrations varying by a factor >10⁵ in healthy humans. This could indicate that there is a serious specificity problem in some of the methods. In this paper an isotope-dilution UPLC-MS/MS method with high specificity and sensitivity for the quantification of 8oxoGuo and 8oxodGuo in CSF is presented. LLOQ for the two analytes is determined to 4pM and 2pM, respectively. The calibration curves has been tested to be linear in the range from 4 to 3,000pM for 8oxoGuo and between 2 and 3,000pM for 8oxodGuo. Using a weighting factor of 1/x the correlation coefficient "r" for both analytes is >0.999.

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.

Oxidative damage and the pathogenesis of menopause related disturbances and diseases

The postmenopausal phase of life is frequently associated in women with subjective symptoms (e.g. vasomotor) and real diseases (atherosclerosis with coronary ischemia, osteoporosis, Alzheimer-type neurodegeneration, urogenital dystrophy), which together determine the post-menopausal syndrome. Observations that oxidative damage by reactive oxygen/nitrogen species in experimental models can contribute to the pathogenesis of these disturbances stimulated research on the relationships between menopause, its endocrine deficiency, oxidative balance and the "wellness" in postmenopausal life. The connection among these events is probably due to the loss of protective actions exerted by estrogens during the fertile life. Most recent studies have revealed that estrogens exert an antioxidant action not by direct chemical neutralization of reactants as it was expected until recently but by modulating the expression of antioxidant enzymes that control levels of biological reducing agents. Also nutritional antioxidants apparently act by a similar mechanism. From this perspective it is conceivable that a cumulative control of body oxidant challenges and biological defenses could help in monitoring between "normal" and "pathological" menopause. However, as clinical studies failed to confirm this scenario in vivo, we have decided to review the existing literature to understand the causes of this discrepancy and whether this was due to methodologic reasons or to real failure of the basic hypothesis.

Urinary 8-oxo-7,8-dihydro-2'-deoxyguanosine analysis by an improved ELISA: An inter-laboratory comparison study

ELISA is commonly used for the detection of urinary 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), a marker of whole body oxidative stress. However, the method has been criticized for high inter-laboratory variability and poor agreement with chromatographic techniques. We performed an inter-laboratory comparison of 8-oxodG assessed in 30 urine samples and a urine spiked with four different concentrations of 8-oxodG by ELISA using standardized experimental conditions, including: sample pre-treatment with solid-phase extraction (SPE), performing analysis using a commercial kit from a single manufacturer and strict temperature control during the assay. We further compared the ELISA results with high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) and performed tentative identification of compounds that may contribute to the discrepancy between both methods. For all but one participating laboratory (Data 1) we observed consistent ELISA results lying mostly within 1SD of the mean 8-oxodG concentration. Mean 8-oxodG levels assessed by ELISA correlated with the data obtained by HPLC-MS/MS (R=0.679, p<0.001). The correlation improved when Data 1 were excluded from the analysis (R=0.749, p<0.001). We identified three outlying urine samples; one with an ELISA 8-oxodG concentration lower, and two with 8-oxodG levels higher, than those measured by HPLC-MS/MS. Omitting these samples further improved inter-methodology agreement (R=0.869, p<0.001). In the outliers with high 8-oxodG estimates various aromatic and heterocyclic compounds were tentatively identified using gas chromatography-mass spectrometry (GC-MS). Application of authentic standards revealed the presence of saccharides, including d-glucose and d-galactose as putative interfering substances. In summary, assay standardization improved ELISA inter-laboratory agreement, although some variability is still observed. There are still compounds contributing to overestimation of 8-oxodG by ELISA, but only in some urine samples. Thus, despite significant improvement, ELISA still should not be considered a robust alternative to chromatographic techniques.

Higher Urinary Levels of 8-Hydroxy-2'-deoxyguanosine Are Associated with a Worse RANKL/OPG Ratio in Postmenopausal Women with Osteopenia

Postmenopausal osteoporosis (PO) is a major public health issue which affects a large fraction of elderly women. Emerging in vitro evidence suggests a central role of oxidative stress (OxS) in postmenopausal osteoporosis (PO) development. Contrariwise, the human studies on this topic are still scarce and inconclusive. In the attempt to address this issue, we sought to determine if OxS, as assessed by 8-hydroxy-2-deoxyguanosine (8-OHdG), may influence the level of receptor activator of nuclear factor-κb ligand (RANKL)/osteoprotegerin (OPG) ratio (a central regulator of bone metabolism) in a sample (n = 124), including postmenopausal women with osteoporosis, osteopenia and normal bone mass density (BMD). The most striking result that emerged in our study was the independent and positive (beta = 0.449, p = 0.004, and R² = 0.185) association between the OxS marker and RANKL/OPG ratio which was found in osteopenic but not in the other 2 sample groups. If confirmed by longitudinal studies, our findings would suggest that OxS is implicated in the derangement of bone homeostasis which precedes PO development. In line with these considerations, antioxidant treatment of postmenopausal women with moderately low BMD might contribute to preventing PO and related complications.

Improvement in Depressive Symptoms Is Associated with Reduced Oxidative Damage and Inflammatory Response in Type 2 Diabetic Patients with Subsyndromal Depression: The Results of a Randomized Controlled Trial Comparing Psychoeducation, Physical Exercise, and Enhanced Treatment as Usual

Aims. To examine one-year changes in oxidative damage and inflammation level in type 2 diabetic patients undergoing behavioral treatment for subsyndromal depression. Materials and Methods. A randomized controlled comparison of psychoeducation (A), physical exercise (B), and enhanced treatment as usual (C) was performed in 209 eligible subjects in a tertiary diabetes care setting. Depressive symptoms (primary outcome) and selected biomarkers of oxidative damage and inflammation (secondary outcomes) were assessed at baseline and six- and twelve-month follow-up. Results. Out of the 74, 67, and 68 patients randomised into groups A, B, and C, respectively, 201 completed the interventions, and 179 were analysed. Participants in all three groups equally improved in depressive symptoms from baseline to one-year follow-up (repeated measures ANOVA; F = 12.51, p < 0.0001, η (2) = 0.07). Urinary 8-oxo-deoxyguanosine (u-8-oxodG) decreased (F = 10.66, p < 0.0001, η (2) = 0.06), as did sialic acid and leukocytes (F = 84.57, η (2) = 0.32 and F = 12.61, η (2) = 0.07, resp.; p < 0.0001), while uric acid increased (F = 12.53, p < 0.0001, η (2) = 0.07) in all subjects during one year. Improvement of depressive symptoms at 6 months significantly predicted one-year reduction in u-8-oxodG (β = 0.15, p = 0.044). Conclusion. Simple behavioral interventions are capable not only of alleviating depressive symptoms, but also of reducing the intensity of damaging oxidative/inflammatory processes in type 2 diabetic patients with subsyndromal depression. This trial is registered with ISRCTN05673017.

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.

Associations of job stress indicators with oxidative biomarkers in Japanese men and women

Some researchers have suggested that oxidative damage may be one of the mechanisms linking job stress with coronary heart disease. The aim of this study was to investigate the association between job stress indicators and oxidative biomarkers. The study included 567 subjects (272 men, 295 women) who answered questionnaires related to their work and underwent a medical examination. Job stress evaluated using the demands-control-support model was measured using the Job Content Questionnaire. Effort-reward imbalance was measured using the Effort-Reward Imbalance Questionnaire. Urinary hydrogen peroxide (H₂O₂) and 8-hydroxy-2'-deoxyguanosine (8-OHdG) were measured by the modified ferrous ion oxidation xylenol orange version-1 method and enzyme-linked immunosorbent assay, respectively. In men, the changes in the odds ratios for high urinary H₂O₂ associated with a 1-standard-deviation (SD) increase in worksite social support were 0.69 (95% confidence interval (CI) 0.53, 0.91) univariately and 0.68 (95%CI 0.51, 0.90) after adjustment for covariates. The change in the odds ratio for high urinary H₂O₂ associated with a 1-SD increase in effort-reward ratio was 1.35 (95% CI 1.03, 1.78) after adjustment for covariates. In women, there were no significant associations of the two job stress indicators with urinary H₂O₂ and 8-OHdG levels after adjustment for covariates (p > 0.05).

Evaluation of serum arginase I as an oxidative stress biomarker in a healthy Japanese population using a newly established ELISA

OBJECTIVE

We reported previously that serum arginase I increased in asthmatic patients and was associated with oxidative stress in a small healthy population. However, the exact association of arginase I with oxidative stress is not known. The present study aimed to analyze the association of arginase I with oxidative stress in a larger healthy population by a newly established ELISA.

DESIGN AND METHODS

The new ELISA for the measurement of human arginase I was established by generating recombinant arginase I protein in human arginase I gene-transfected Escherichia coli via an ARG1 cDNA fragment-inserted vector and -specific antibody in rabbits. Serum arginase I was evaluated in a cross-sectional study on a healthy population (n=721) by comparing a commercial ELISA kit with the new ELISA.

RESULTS

The mean levels of serum arginase I were 20.3 ± 0.7 ng/mL and 4.7 ± 0.2 ng/mL using the commercial ELISA kit and the new ELISA, respectively. Arginase I was correlated with WBC, RBC, hs-CRP, 8-OHdG, HDL-c, ALT, and BMI. Logistic regression analysis showed independent positive associations of arginase I with WBC, RBC, and urinary 8-OHdG and inverse independent associations with serum insulin and age. The association of arginase I with hs-CRP was not independent.

CONCLUSION

The independent associations of arginase I with urinary 8-OHdG and serum insulin may reflect its involvement in oxidative stress and diabetes mellitus.

Human and methodological sources of variability in the measurement of urinary 8-oxo-7,8-dihydro-2'-deoxyguanosine

AIMS

Urinary 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) is a widely used biomarker of oxidative stress. However, variability between chromatographic and ELISA methods hampers interpretation of data, and this variability may increase should urine composition differ between individuals, leading to assay interference. Furthermore, optimal urine sampling conditions are not well defined. We performed inter-laboratory comparisons of 8-oxodG measurement between mass spectrometric-, electrochemical- and ELISA-based methods, using common within-technique calibrants to analyze 8-oxodG-spiked phosphate-buffered saline and urine samples. We also investigated human subject- and sample collection-related variables, as potential sources of variability.

RESULTS

Chromatographic assays showed high agreement across urines from different subjects, whereas ELISAs showed far more inter-laboratory variation and generally overestimated levels, compared to the chromatographic assays. Excretion rates in timed 'spot' samples showed strong correlations with 24 h excretion (the 'gold' standard) of urinary 8-oxodG (rp 0.67-0.90), although the associations were weaker for 8-oxodG adjusted for creatinine or specific gravity (SG). The within-individual excretion of 8-oxodG varied only moderately between days (CV 17% for 24 h excretion and 20% for first void, creatinine-corrected samples).

INNOVATION

This is the first comprehensive study of both human and methodological factors influencing 8-oxodG measurement, providing key information for future studies with this important biomarker.

CONCLUSION

ELISA variability is greater than chromatographic assay variability, and cannot determine absolute levels of 8-oxodG. Use of standardized calibrants greatly improves intra-technique agreement and, for the chromatographic assays, importantly allows integration of results for pooled analyses. If 24 h samples are not feasible, creatinine- or SG-adjusted first morning samples are recommended.

Quantitation of DNA adducts by stable isotope dilution mass spectrometry

Exposure to endogenous and exogenous chemicals can lead to the formation of structurally modified DNA bases (DNA adducts). If not repaired, these nucleobase lesions can cause polymerase errors during DNA replication, leading to heritable mutations and potentially contributing to the development of cancer. Because of their critical role in cancer initiation, DNA adducts represent mechanism-based biomarkers of carcinogen exposure, and their quantitation is particularly useful for cancer risk assessment. DNA adducts are also valuable in mechanistic studies linking tumorigenic effects of environmental and industrial carcinogens to specific electrophilic species generated from their metabolism. While multiple experimental methodologies have been developed for DNA adduct analysis in biological samples, including immunoassay, HPLC, and ³²P-postlabeling, isotope dilution high performance liquid chromatography-electrospray ionization-tandem mass spectrometry (HPLC-ESI-MS/MS) generally has superior selectivity, sensitivity, accuracy, and reproducibility. As typical DNA adduct concentrations in biological samples are between 0.01-10 adducts per 10⁸ normal nucleotides, ultrasensitive HPLC-ESI-MS/MS methodologies are required for their analysis. Recent developments in analytical separations and biological mass spectrometry, especially nanoflow HPLC, nanospray ionization MS, chip-MS, and high resolution MS, have pushed the limits of analytical HPLC-ESI-MS/MS methodologies for DNA adducts, allowing researchers to accurately measure their concentrations in biological samples from patients treated with DNA alkylating drugs and in populations exposed to carcinogens from urban air, drinking water, cooked food, alcohol, and cigarette smoke.

8-Oxo-2'-deoxyguanosine as a biomarker of tobacco-smoking-induced oxidative stress

7,8-Dihydro-8-oxo-2'-deoxyguanosine (8-oxo-dGuo) is a useful biomarker of oxidative stress. However, its analysis can be challenging because 8-oxo-dGuo must be quantified in the presence of dGuo, without artifactual conversion to 8-oxo-dGuo. Urine is the ideal biological fluid for population studies, because it can be obtained noninvasively and it is less likely that artifactual oxidation of dGuo can occur because of the relatively low amounts that are present compared with hydrolyzed DNA. Stable isotope dilution liquid chromatography-selected reaction monitoring/mass spectrometry (LC-SRM/MS) with 8-oxo-[(15)N(5)]dGuo as internal standard provided the highest possible specificity for 8-oxo-dGuo analysis. Furthermore, artifact formation was determined by addition of [(13)C(10)(15)N(5)]dGuo and monitoring of its conversion to 8-oxo-[(13)C(10)(15)N(5)]dGuo during the analytical procedure. 8-Oxo-dGuo concentrations were normalized for interindividual differences in urine flow by analysis of creatinine using stable isotope dilution LC-SRM/MS. A significant increase in urinary 8-oxo-dGuo was observed in tobacco smokers compared with nonsmokers either using simple urinary concentrations or after normalization for creatinine excretion. The mean levels of 8-oxo-dGuo were 1.65ng/ml and the levels normalized to creatinine were 1.72μg/g creatinine. Therefore, stable isotope dilution LC-SRM/MS analysis of urinary 8-oxo-dGuo complements urinary isoprostane (isoP) analysis for assessing tobacco-smoking-induced oxidative stress. This method will be particularly useful for studies that employ polyunsaturated fatty acids, in which a reduction in arachidonic acid precursor could confound isoP measurements.

Rapid measurement of 8-oxo-7,8-dihydro-2'-deoxyguanosine in human biological matrices using ultra-high-performance liquid chromatography-tandem mass spectrometry

Interaction of reactive oxygen species with DNA results in a variety of modifications, including 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), which has been extensively studied as a biomarker of oxidative stress. Oxidative stress is implicated in a number of pathophysiological processes relevant to obstetrics and gynecology; however, there is a lack of understanding as to the precise role of oxidative stress in these processes. We aimed to develop a rapid, validated assay for the accurate quantification of 8-oxodG in human urine using solid-phase extraction and ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) and then investigate the levels of 8-oxodG in several fluids of interest to obstetrics and gynecology. Using UHPLC-MS/MS, 8-oxodG eluted after 3.94 min with an RSD for 15 injections of 0.07%. The method was linear between 0.95 and 95 nmol/L with LOD and LOQ of 5 and 25 fmol on-column, respectively. Accuracy and precision were 98.7-101.0 and <10%, respectively, over three concentrations of 8-oxodG. Recovery from urine was 88% with intra- and interday variations of 4.0 and 10.2%, respectively. LOQ from urine was 0.9 pmol/ml. Rank order from the greatest to lowest 8-oxodG concentration was urine>seminal plasma>amniotic fluid>plasma>serum>peritoneal fluid, and it was not detected in saliva. Urine concentrations normalized to creatinine (n=15) ranged between 0.55 and 1.95 pmol/μmol creatinine. We describe, for the first time, 8-oxodG concentrations in human seminal plasma, peritoneal fluid, amniotic fluid, and breast milk, as well as in urine, plasma, and serum, using a rapid UHPLC-MS/MS method that will further facilitate biomonitoring of oxidative stress.

Assays for urinary biomarkers of oxidatively damaged nucleic acids

The analysis of oxidized nucleic acid metabolites can be performed by a variety of methodologies: liquid chromatography coupled with electrochemical or mass-spectrometry detection, gas chromatography coupled with mass spectrometry, capillary electrophoresis and ELISA (Enzyme-linked immunosorbent assay). The major analytical challenge is specificity. The best combination of selectivity and speed of analysis can be obtained by liquid chromatography coupled with tandem mass spectrometric detection. This, however, is also the most demanding technique with regard to price, complexity and skills requirement. The available ELISA methods present considerable specificity problems and cannot be recommended at present. The oxidized nucleic acid metabolites in urine are assumed to originate from the DNA and RNA. However, direct evidence is not available. A possible contribution from the nucleotide pools is most probably minimal, if existing. Recent investigation on RNA oxidation has shown conditions where RNA oxidation but not DNA oxidation is prominent, and while investigation on DNA is of huge interest, RNA oxidation may be overlooked. The methods for analyzing oxidized deoxynucleosides can easily be expanded to analyze the oxidized ribonucleosides. The urinary measurement of oxidized nucleic acid metabolites provides a non-invasive measurement of oxidative stress to DNA and RNA.

UKEMS/Dutch EMS-sponsored workshop on biomarkers of exposure and oxidative DNA damage & 7th GUM-32P-postlabelling workshop, University of Münster, Münster, Germany, 28-29 March 2011

Environmental exposures are a major concern for human cancer. However, the precise contribution of specific risk factors and their interactions, both with each other and with genotype, continue to be difficult to elucidate. The exposome is the comprehensive characterisation of an individual's lifetime exposure history (Wild, C. P. (2009) Environmental exposure measurement in cancer epidemiology. Mutagenesis, 24, 117-125). Unravelling complex environmental and genetic aetiologies in order to plan effective public health interventions demands that both environmental exposures and genetic variations are reliably measured. The development, validation and application of biomarkers of exposure are manifestly critical to the future of cancer epidemiology. The aim of this workshop at the University of Münster was to discuss the current status of exposure biomarkers in cancer molecular epidemiology as well as new findings achieved by applying the methods to studies of mechanisms of human cancer. Day 1 focused on biomarkers of exposure (i.e. carcinogen DNA adducts), effect and susceptibility to gain greater understanding of environmental cancer risks and their modulation. Day 2 focused on the role of oxidative stress and DNA damage in human carcinogenesis including methodologies used for the measurement of oxidatively induced DNA lesions in human cells or tissues and the possible use of these lesions as cancer biomarkers.

Measurement of oxidatively generated base damage in cellular DNA

This survey focuses on the critical evaluation of the main methods that are currently available for monitoring single and complex oxidatively generated damage to cellular DNA. Among chromatographic methods, HPLC-ESI-MS/MS and to a lesser extent HPLC-ECD which is restricted to a few electroactive nucleobases and nucleosides are appropriate for measuring the formation of single and clustered DNA lesions. Such methods that require optimized protocols for DNA extraction and digestion are sensitive enough for measuring base lesions formed under conditions of severe oxidative stress including exposure to ionizing radiation, UVA light and high intensity UVC laser pulses. In contrast application of GC-MS and HPLC-MS methods that are subject to major drawbacks have been shown to lead to overestimated values of DNA damage. Enzymatic methods that are based on the use of DNA repair glycosylases in order to convert oxidized bases into strand breaks are suitable, even if they are far less specific than HPLC methods, to deal with low levels of single modifications. Several other methods including immunoassays and (32)P-postlabeling methods that are still used suffer from drawbacks and therefore are not recommended. Another difficult topic is the measurement of oxidatively generated clustered DNA lesions that is currently achieved using enzymatic approaches and that would necessitate further investigations.

High-sensitivity capillary electrophoresis method for monitoring purine nucleoside phosphorylase and adenosine deaminase reactions by a reversed electrode polarity switching mode

A simple, efficient, and highly sensitive in-line CE method was developed for the characterization and for inhibition studies of the nucleoside-metabolizing enzymes purine nucleoside phosphorylase (PNP) and adenosine deaminase (ADA) present in membrane preparations of human 1539 melanoma cells. After filling the running buffer (50 mM borate buffer, 100 mM SDS, pH 9.10) into a fused-silica capillary (50 cm effective length × 75 μm), a large sample volume was loaded by hydrodynamic injection (5 psi, 36 s), followed by the removal of the large plug of sample matrix from the capillary using polarity switching (-20 kV). The current was monitored and the polarity was reversed when 95% of the current had been recovered. The separation of the neutral analytes (nucleosides and nucleobases) was performed by applying a voltage of 15 kV. An about 10-fold improvement of sensitivity for the five investigated analytes (adenosine, inosine, adenine, hypoxanthine, xanthine) was achieved by large-volume stacking with polarity switching when compared with CE without stacking. For inosine and adenine detection limits as low as 60 nM were achieved. To the best of our knowledge, this represents the highest sensitivity for nucleoside and nucleobase analysis using CE with UV detection reported so far. The Michaelis-Menten constants (K(m)) for PNP and ADA and the inhibition constants (K(i)) for standard inhibitors determined with the new method were consistent with literature data.

Models of accelerated sarcopenia: critical pieces for solving the puzzle of age-related muscle atrophy

Sarcopenia, the age-related loss of skeletal muscle mass, is a significant public health concern that continues to grow in relevance as the population ages. Certain conditions have the strong potential to coincide with sarcopenia to accelerate the progression of muscle atrophy in older adults. Among these conditions are co-morbid diseases common to older individuals such as cancer, kidney disease, diabetes, and peripheral artery disease. Furthermore, behaviors such as poor nutrition and physical inactivity are well-known to contribute to sarcopenia development. However, we argue that these behaviors are not inherent to the development of sarcopenia but rather accelerate its progression. In the present review, we discuss how these factors affect systemic and cellular mechanisms that contribute to skeletal muscle atrophy. In addition, we describe gaps in the literature concerning the role of these factors in accelerating sarcopenia progression. Elucidating biochemical pathways related to accelerated muscle atrophy may allow for improved discovery of therapeutic treatments related to sarcopenia.

Salvage of oxidized guanine derivatives in the (2'-deoxy)ribonucleotide pool as source of mutations in DNA

Recent evidence suggests that salvage of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) and 8-oxo-7,8-dihydro-guanine (8-oxoGua) can contribute substantially to levels of 8-oxoGua in DNA and RNA. However, it remains to be determined if this mechanism contributes to mutagenesis and disease. This review covers the predominant methods for detecting 8-oxoGua and its derivatives, summarizes some of the relevant recent DNA repair studies and discusses the mechanisms for metabolism of oxidized guanine derivatives in the (2'-deoxy)ribonucleoside and (2'-deoxy)ribonucleotide pools.

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

Monitoring oxidative stress in vivo is made easier by the ability to use samples obtained non-invasively, such as urine. The analysis of DNA oxidation, by measurement of oxidized 2'-deoxyribonucleosides in urine, particularly 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), has been reported extensively in the literature in many situations relating to various pathologies, populations and environmental exposures. Understanding the origins of urinary 8-oxodG, other than it simply being a marker of DNA oxidation or its synthetic precursors, is important to being able to effectively interpret differences in baseline urinary 8-oxodG levels between subject groups and changes in excretion. Diet and cell turnover play negligible roles in contributing to urinary 8-oxodG levels, leaving DNA repair as a primary source of this lesion. However, which repair processes contribute, and to what extent, to urinary 8-oxodG is still open to question. The most rational source would be the activity of selected members of the Nudix hydrolase family of enzymes, sanitizing the deoxyribonucleotide pool via the degradation of 8-oxo-7,8-dihydro-2'-deoxyguanosine-5'-triphosphate and 8-oxo-7,8-dihydro-2'-deoxyguanosine-5'-diphosphate, yielding mononucleotide products that can then be dephosphorylated to 8-oxodG and excreted. However, nucleotide excision repair (NER), transcription-coupled repair, nucleotide incision repair (NIR), mismatch repair and various exonuclease activities, such as proofreading function associated with DNA polymerases, can all feasibly generate initial products that could yield 8-oxodG after further metabolism. A recent study implying that a significant proportion of genomic 8-oxodG exists in the context of tandem lesions, refractory to repair by glycosylases, suggests the roles of NER and/or NIR remain to be further examined and defined as a source of 8-oxodG. 8-OxodG has been the primary focus of investigation, but other oxidized 2'-deoxyribonucleosides have been detected in urine, 2'-deoxythymidine glycol and 5-hydroxymethyl-2'-deoxyuridine; the origins of these compounds in urine, however, are presently even more speculative than for 8-oxodG.

Interpretation of urinary 8-oxo-7,8-dihydro-2'-deoxyguanosine is adversely affected by methodological inaccuracies when using a commercial ELISA

The DNA lesion 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), a urinary marker of oxidative stress, is produced from reactions of reactive oxygen species with host DNA 2'-deoxyribonucleotides. The current gold-standard assessment is by complex chromatographic methods using HPLC or LC-MS/MS. Several studies have reported that commercial 8-oxodG ELISA kits correlate sufficiently with chromatographic techniques to be an easier alternative for laboratories without access to gold-standard techniques. However, the assumption that significant correlation translates into a similar ability to differentiate disease categories or treatment groups is yet to be tested. Using LC-MS/MS and two variants of a commercial ELISA, we measured urinary 8-oxodG and creatinine concentrations in young children with cystic fibrosis, a disease associated with oxidative stress, and age-matched controls. We show that, despite significant correlation, both ELISAs overestimate the levels of 8-oxodG, and neither ELISA accurately depicted the difference in group means that was observed by gold-standard LC-MS/MS. The implications of these findings for study outcomes add further support for chromatographic techniques, despite their cost and complexity, to remain the gold standard in urinary 8-oxodG assessment.

Urinary analysis of 8-oxo-7,8-dihydroguanine and 8-oxo-7,8-dihydro-2'-deoxyguanosine by isotope-dilution LC-MS/MS with automated solid-phase extraction: Study of 8-oxo-7,8-dihydroguanine stability

A highly sensitive quantitative method based on LC-MS/MS was developed to simultaneously and directly measure 8-oxo-7,8-dihydroguanine (8-oxoGua) and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo) in urine. It was found that 8-oxoGua could be artifactually generated from 8-oxodGuo during the ionization process by both in-source thermolysis and collisionally induced dissociation. Our method applied a two-stage wash procedure in the online solid-phase extraction system that not only eliminated ion suppression but also prevented artifactual interference with 8-oxoGua by 8-oxodGuo by eluting the analytes individually. With the use of isotope internal standards, the detection limits of 8-oxoGua and 8-oxodGuo were estimated to be 30 and 3.5 fmol, respectively. The 8-oxoGua stability under common storage conditions was first investigated. Dissolved 8-oxoGua in NaOH (pH 12) was quite fragile and stable for only <1 day at room temperature. When pH and temperature were reduced, the 8-oxoGua stability at -20 degrees C was significantly increased to approximately 87 days in water (pH approximately 7) and approximately 112 days when diluted in 5% methanol. This method was further applied to measure urinary samples of healthy subjects. A molar ratio of 8-oxoGua to 8-oxodGuo of approximately 4.6 was found, supporting the hypothesis that oxidatively damaged DNA is primarily repaired by the base excision repair pathway.

Sources of extracellular, oxidatively-modified DNA lesions: implications for their measurement in urine

There is a robust mechanistic basis for the role of oxidation damage to DNA in the aetiology of various major diseases (cardiovascular, neurodegenerative, cancer). Robust, validated biomarkers are needed to measure oxidative damage in the context of molecular epidemiology, to clarify risks associated with oxidative stress, to improve our understanding of its role in health and disease and to test intervention strategies to ameliorate it. Of the urinary biomarkers for DNA oxidation, 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) is the most studied. However, there are a number of factors which hamper our complete understanding of what meausrement of this lesion in urine actually represents. DNA repair is thought to be a major contributor to urinary 8-oxodG levels, although the precise pathway(s) has not been proven, plus possible contribution from cell turnover and diet are possible confounders. Most recently, evidence has arisen which suggests that nucleotide salvage of 8-oxodG and 8-oxoGua can contribute substantially to 8-oxoG levels in DNA and RNA, at least in rapidly dividing cells. This new observation may add an further confounder to the conclusion that 8-oxoGua or 8-oxodG, and its nucleobase equivalent 8-oxoguanine, concentrations in urine are simply a consequence of DNA repair. Further studies are required to define the relative contributions of metabolism, disease and diet to oxidised nucleic acids and their metabolites in urine in order to develop urinalyis as a better tool for understanding human disease.

Urea, the most abundant component in urine, cross-reacts with a commercial 8-OH-dG ELISA kit and contributes to overestimation of urinary 8-OH-dG

Urinary 8-OH-dG is commonly analyzed as a marker of oxidative stress. For its analysis, ELISA and HPLC methods are generally used, although discrepancies in the data obtained by these methods have often been discussed. To clarify this problem, we fractionated human urine by reverse-phase HPLC and assayed each fraction by the ELISA method. In addition to the 8-OH-dG fraction, a positive reaction was observed in the first eluted fraction. The components in this fraction were examined by the ELISA. Urea was found to be the responsible component in this fraction. Urea is present in high concentrations in the urine of mice, rats, and humans, and its level is influenced by many factors. Therefore, certain improvements, such as a correction based on urea content or urease treatment, are required for the accurate analysis of urinary 8-OH-dG by the ELISA method. In addition, performance of the ELISA at 4 degrees C reduced the recognition of urea considerably and improved the 8-OH-dG analysis.