Urinary 8-oxo-7,8-dihydro-2′-deoxyguanosine values determined by a modified ELISA improves agreement with HPLC–MS/MS

Comparative evaluation of salivary, serum and urinary 8-OHdG in gutka-associated oral submucous fibrosis

Background

Gutka chewing is the most common deleterious oral habit prevalent in the geographical distribution of the Indian subcontinent. Gutka leads to the production of numerous free radicals, which causes oxidative stress in regional oral tissues. Oxidative stress brings about the oxidation of guanine bases of DNA that generates 8-OHdG as its main byproduct. The presence of 8-OHdG can be evaluated not only in tissue but also in saliva, blood and urine. The availability of 8-OHdG in these samples is quite documented. In addition, a comparative assay of 8-ohdg DNA damage marker in multiple samples is yet to be done.

Material and Methodology

A sample size of 60 was divided into two groups, i.e., gutka consumers without any lesion and gutka consumers with OSMF. Ten samples each of saliva, serum and urine were collected from these two groups and healthy controls. Samples were centrifuged at 1000 RPM at 2-8°C for 15-20 minutes. A volume of 1.5 ml resultant supernatant was pipetted out in labelled Eppendorf tubes and stored at -80°C. The ELISA test was performed to measure the concentration of 8-OHdG protein in different samples at 450 nm after adding stop solution in 96-well microplate.

Results

8-OHdG concentration was found to be highest in saliva followed by urine and serum. 8-OHdG concentration in serum was significantly less than that in saliva and urine (P-value <0.05). Intergroup difference in concentration of 8-OHdG of urine, saliva and serum was significant (P-value <0.05). Post hoc analysis revealed that concentration of 8-OHdG in saliva and urine was non-significantly different (P-value >0.05).

Conclusion

Saliva appears to be the most appropriate sample type as compared to serum and urine for the evaluation of 8-OHdG in OSMF subjects.

Association of urinary arsenic with the oxidative DNA damage marker 8-hydroxy-2 deoxyguanosine: A meta-analysis

BACKGROUND

The International Agency for Research on Cancer has classified arsenic as a class I carcinogen. Oxidative DNA damage is a typical early precursor to recognized malignancies. The most sensitive early independent marker of oxidative DNA damage is believed to be 8-hydroxy-2 deoxyguanosine (8-OHdG). To date, research on the link between urinary arsenic and 8-OHdG has not been consistent.

OBJECTIVE

This study was aimed at exploring the effects of urinary arsenic on 8-OHdG in human urine.

METHODS

A literature search until January 2023 was performed on the PubMed, Cochrane Library, Web of Science, Embase, and Scopus databases through a combination of computer and manual retrieval. Stata 12.0 was used to examine the degree of heterogeneity among included studies. The percentage change and 95 % confidence interval (95 % CI) of 8-OHdG were calculated between populations exposed to different doses. We used a random effect model because the degree of heterogeneity exceeded 50 %. Sensitivity analysis and testing for publication bias were performed.

RESULTS

This meta-analysis included nine studies, most of which were performed in China. After exposure to arsenic, urinary arsenic (per 10 μg/g creatinine increase) was associated with the increased 8-OHdG (% change = 41.49 %, 95 % CI: 19.73 %, 63.25 %). Subgroup analysis indicated that the percentage change in 8-OHdG in urine was more pronounced in people exposed to arsenic <50 μg/L (% change = 24.60 %, 95 % CI: 17.35 %, 37.85 %). In studies using total urinary arsenic content as an indicator, the percentage change in 8-OHdG in urine was more significant (% change = 60.38 %, 95 % CI: 15.08 %, 105.68 %).

CONCLUSION

The 8-OHdG levels in human urine significantly increased after exposure to environmental arsenic, thus suggesting that arsenic exposure is correlated with oxidative DNA damage.

Analyses of oxidative DNA damage among coal vendors via single cell gel electrophoresis and quantification of 8-hydroxy-2'-deoxyguanosine

Looking at the development status of Nigeria and other developing nations, most low-income and rural households often use coal as a source of energy which necessitates its trade very close to the communities. Moreover, the effects of exposure to coal mining activities are rarely explored or yet to be studied, not to mention the numerous street coal vendors in Nigeria. This study investigated the oxidative stress levels in serum and urine through the biomarker 8-OHdG and DNA damage via single cell gel electrophoresis (alkaline comet assay). Blood and urine levels of 8-OHdG from 130 coal vendors and 130 population-based controls were determined by ELISA. Alkaline comet assay was also performed on white blood cells for DNA damage. The average values of 8-OHdG in serum and urine of coal vendors were 22.82 and 16.03 ng/ml respectively, which were significantly greater than those detected in controls (p < 0.001; 15.46 and 10.40 ng/ml of 8-OHdG in serum and urine respectively). The average tail length, % DNA in tail and olive tail moment were 25.06 μm, 18.71% and 4.42 respectively for coal vendors. However, for controls, the average values were 4.72 μm, 3.63% and 1.50 for tail length, % DNA in tail and olive tail moment respectively which were much lower than coal vendors (p < 0.001). Therefore, prolonged exposure to coal dusts could lead to higher serum and urinary 8-OHdG and significant DNA damage in coal vendors observed in tail length, % DNA in tail, and olive tail moment by single cell gel electrophoresis. It is therefore established that coal vendors exhibit a huge risk from oxidative stress and assessment of 8-OHdG with single cell gel electrophoresis has proven to be a feasible tool as biomarkers of DNA damage.

A robust LC-MS/MS method to measure 8-oxoGuo, 8-oxodG, and NMN in human serum and urine

OBJECTIVE

To establish and validate a robust LC-MS/MS method for simultaneously measuring 8-oxoGuo, 8-oxodG, and NMN in serum and urine to evaluate the oxidative stress status.

METHODS

A Waters TQ-XS triple quadrupole mass spectrometer system coupled with an Acquity UPLC Primer HSS T3 column was chosen. The clinical performance was verified according to the CLSI C62-A and EP-15 guidelines. Furthermore, matched serum and urine samples from 22 apparently healthy check-ups, 20 patients with atherosclerosis, and 18 individuals with dementia were evaluated.

RESULTS

The recovery for serum 8-oxoGuo, urine 8-oxoGuo, serum 8-oxodG, urine 8-oxodG, serum NMN, and urine NMN was 88.8-112.4%, 102.4-114.1%, 88.5-107.7%, 94.9-102.6%, 98.4-108.9%, and 88.5-108.6%, respectively. Based on the inter-assay results, total coefficient of variation, matrix effect, and carryover, the LC-MS/MS method was deemed robust. The limit of quantification was 0.017, 0.018, and 0.150 nmol/L for 8-oxoGuo, 8-oxodG, and NMN, respectively, which are suitable for accurate measurements in human serum and urine samples. Higher 8-oxoGuo and 8-oxodG levels and lower NMN levels, indicative of significantly higher oxidative stress status, were found in patients with dementia compared to healthy subjects.

CONCLUSION

We established and validated a robust LC-MS/MS method to simultaneously measure 8-oxoGuo, 8-oxodG, and NMN in serum and urine.

Oxidative Stress and Antioxidant Response in Populations of the Czech Republic Exposed to Various Levels of Environmental Pollutants

We aimed to identify the variables that modify levels of oxidatively damaged DNA and lipid peroxidation in subjects living in diverse localities of the Czech Republic (a rural area, a metropolitan locality, and an industrial region). The sampling of a total of 126 policemen was conducted twice in two sampling seasons. Personal characteristics, concentrations of particulate matter of aerodynamic diameter <2.5 µm and benzo[a]pyrene in the ambient air, activities of antioxidant mechanisms (superoxide dismutase, catalase, glutathione peroxidase, and antioxidant capacity), levels of pro-inflammatory cytokines (TNF-α, IL-1β, and IL-6), concentrations of persistent organic pollutants in blood plasma, and urinary levels of polycyclic aromatic hydrocarbon metabolites were investigated as parameters potentially affecting the markers of DNA oxidation (8-oxo-7,8-dihydro-2′-deoxyguanosine) and lipid peroxidation (15-F2t-isoprostane). The levels of oxidative stress markers mostly differed between the localities in the individual sampling seasons. Multivariate linear regression analysis revealed IL-6, a pro-inflammatory cytokine, as a factor with the most pronounced effects on oxidative stress parameters. The role of other variables, including environmental pollutants, was minor. In conclusion, our study showed that oxidative damage to macromolecules was affected by processes related to inflammation; however, we did not identify a specific environmental factor responsible for the pro-inflammatory response in the organism.

How Robust is the Evidence for a Role of Oxidative Stress in Autism Spectrum Disorders and Intellectual Disabilities?

Growing interest in the pathogenesis of autism spectrum disorders (ASDs) and other intellectual and developmental disabilities (IDD) has led to emerging evidence implicating a role for oxidative stress. However, understanding the strength of this association is made challenging by the use of a variety of purported biomarkers of oxidative stress, many of which have either uncertain specificity or flawed methods of analysis. This review aims to address this issue, which is widespread in the ASD and IDD literature, by providing readers with information concerning the strengths and limitations of the choice and analysis of biomarkers of oxidative stress. We highlight that biomarkers and assays should be specific, sensitive, reproducible, precise, robust, and chosen with careful consideration. Future studies should be sufficiently powered and address sample collection, processing, and storage which are, additionally, poorly considered, sources of bad practice, and potential errors. Only with these issues considered, will the data lead to conclusions as to the precise role of oxidative stress in ASDs and IDD.

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.

Development of Low-Cost AuNP-Based Aptasensors with Truncated Aptamer for Highly Sensitive Detection of 8-Oxo-dG in Urine

8-Oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dG), an oxidized form of guanosine residues, is a critical biomarker for various cancers. Herein, a sensitive citrate-capped gold nanoparticle-based aptasensor device has been developed for the detection of 8-oxo-dG in urine. We previously designed a 38-nt anti-8-oxo-dG-aptamer by a computer simulation and the experimental validation has been performed in the present work. The analytical performance of the 38-nt aptamer from the in silico design was compared with the parent 66-nt aptamer. This assay is based on the principle of salt-induced aggregation of citrate-capped gold nanoparticles. Based on this sensing mechanism, the difference between the absorbance in the presence and absence of 8-oxo-dG at λ = 525 nm (ΔA525) increased linearly as a function of 8-oxo-dG concentrations in the ranges of 10-100 and 15-100 nM for 38-nt and 66-nt aptasensors, respectively. This method can provide detection limits of 6.4 nM for 8-oxo-dG in the 38-nt aptasensor and 13.2 nM in the 66-nt aptasensor. Similar to the 66-nt aptamer, the shortened aptamer, 38-nt long, can provide high sensitivity and selectivity with rapid detection time. In addition, using the 38-nt aptamer as a recognition component in the developed portable low-cost device showed high sensitivity in the detection range of 15-100 nM with a detection limit of 12.9 nM, which is much lower than the threshold value (280 nM) for normal human urine. This easy-to-use device could effectively and economically be utilized for monitoring 8-oxo-dG in real urine samples and potentially serve as a prototype for a commercial device.

Urinary 8-OHdG as a Biomarker for Oxidative Stress: A Systematic Literature Review and Meta-Analysis

Oxidative stress reflects a disturbance in the balance between the production and accumulation of reactive oxygen species (ROS). ROS are scavenged by the antioxidant system, but when in excess concentration, they can oxidize proteins, lipids, and DNA. DNA damage is usually repaired, and the oxidized products are excreted in urine. 8-hydroxy-2-deoxyguanosine is considered a biomarker for oxidative damage of DNA. It is needed to define background ranges for 8-OHdG, to use it as a measure of oxidative stress overproduction. We established a standardized protocol for a systematic review and meta-analysis to assess background ranges for urinary 8-OHdG concentrations in healthy populations. We computed geometric mean (GM) and geometric standard deviations (GSD) as the basis for the meta-analysis. We retrieved an initial 1246 articles, included 84 articles, and identified 128 study subgroups. We stratified the subgroups by body mass index, gender, and smoking status reported. The pooled GM value for urinary 8-OHdG concentrations in healthy adults with a mean body mass index (BMI) ≤ 25 measured using chemical methods was 3.9 ng/mg creatinine (interquartile range (IQR): 3 to 5.5 ng/mg creatinine). A significant positive association was observed between smoking and urinary 8-OHdG concentrations when measured by chemical analysis. No gender effect was observed.

Interventions targeted at oxidatively generated modifications of nucleic acids focused on urine and plasma markers

Oxidative stress is associated with the development and progression of numerous diseases. However, targeting oxidative stress has not been established in the clinical management of any disease. Several methods and markers are available to measure oxidative stress, including direct measurement of free radicals, antioxidants, redox balance, and oxidative modifications of cellular macromolecules. Oxidatively generated nucleic acid modifications have attracted much interest due to the pre-mutagenic oxidative modification of DNA into 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), associated with cancer development. During the last decade, the perception of RNA has changed from that of a 'silent messenger' to an 'active contributor', and, parallelly oxidatively generated RNA modifications measured as 8-oxo-7,8-dihydro-guanosine (8-oxoGuo), has been demonstrated as a prognostic factor for all-caused and cardiovascular related mortality in patients with type 2 diabetes. Several attempts have been made to modify the amount of oxidative nucleic acid modifications. Thus, this review aims to introduce researchers to the measurement of oxidatively generated nucleic acid modifications as well as critically review previous attempts and provide future directions for targeting oxidatively generated nucleic acid modifications.

Serum cholesterol positively associated with oxidative DNA damage: a propensity score-matched analysis

Oxidative DNA damage pathogenically links to some major diseases. This study aimed to comprehensively assess the association between serum total cholesterol (TC) and oxidative DNA damage based on propensity score matching (PSM) method. A total of 407 participants chronically exposed to arsenic via drinking water from China were enrolled. Oxidative DNA damage was determined with urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG). Serum TC was classified into favourable TC (FTC, TC <5.18 mmol/L) and unfavourable TC (NFTC, TC ≥5.18 mmol/L) categories. Multivariable generalised linear regression model was applied to examine the association. Of 407 participants, 125 pairs with FTC and NFTC subjects were matched using PSM. Urinary 8-OHdG/creatinine levels in NFTC were significantly higher than those in FTC category (p = .002). As compared to the counterparts, additional adjusted log-transformed 8-OHdG/creatinine increase was observed in NFTC for unmatched (β = 0.12, p = .052) and matched (β = 0.17, p < .001) participants, respectively. We also detected obviously increased log-transformed urinary 8-OHdG/creatinine with per interquartile range raise of serum TC either in unmatched (β = 0.10, p = .007) or matched (β = 0.16, p = .003) subjects. In conclusion, serum TC was independently associated with oxidative DNA damage. Our findings provided new insights on the health promotion of lipids relevant to the early warning of diseases due to oxidative DNA damage.

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.

Resonance light scattering aptasensor for urinary 8-hydroxy-2'-deoxyguanosine based on magnetic nanoparticles: a preliminary study of oxidative stress association with air pollution

An aptamer based method is described for the determination of 8-hydroxy-2'-deoxyguanosine (8-OHdG) using resonance light scattering (RLS). Magnetic nanoparticles (MNPs) were employed as RLS probes. The probe DNA was placed on the surface of MNPs, which produces a rather low RLS signal. If, however, probe DNA hybridizes with the aptamer against 8-OHdG, a sandwich structure will be formed. This results in a significant enhancement of RLS intensity. The aptamer was used as the recognition element to capture 8-OHdG. 8-OHdG has a stronger affinity for the aptamer than probe DNA, and the conformation of the aptamer therefore switches from a double-stranded to a G-quadruplex structure. As a result, MNPs labeled with probe DNA are released, and RLS intensity decreases. The method allows 8-OHdG to be detected with a linear response in the 32 pM - 12.0 nM concentration range and an 11 pM limit of detection (at 3.29S_B/m, according to the recent recommendation of IUPAC). The MNPs can be reused 5 times by applying an external magnetic field for collection. The method was successfully applied to analyze human urine samples for its content of 8-OHdG. It was also found that the levels of 8-OHdG noticeably increased with the increase of the Air Quality Index. Conceivably, the method is a viable tool to investigate the relationship between 8-OHdG levels and the effect of air pollution. Graphical abstract A reusable sensing strategy was constructed to detect urinary 8-OHdG based on "turn-off" resonance light scattering. The LOD was as low as 11 pM. This study showed some preliminary data for the association between oxidative stress and air pollution.

European contribution to the study of ROS: A summary of the findings and prospects for the future from the COST action BM1203 (EU-ROS)

The European Cooperation in Science and Technology (COST) provides an ideal framework to establish multi-disciplinary research networks. COST Action BM1203 (EU-ROS) represents a consortium of researchers from different disciplines who are dedicated to providing new insights and tools for better understanding redox biology and medicine and, in the long run, to finding new therapeutic strategies to target dysregulated redox processes in various diseases. This report highlights the major achievements of EU-ROS as well as research updates and new perspectives arising from its members. The EU-ROS consortium comprised more than 140 active members who worked together for four years on the topics briefly described below. The formation of reactive oxygen and nitrogen species (RONS) is an established hallmark of our aerobic environment and metabolism but RONS also act as messengers via redox regulation of essential cellular processes. The fact that many diseases have been found to be associated with oxidative stress established the theory of oxidative stress as a trigger of diseases that can be corrected by antioxidant therapy. However, while experimental studies support this thesis, clinical studies still generate controversial results, due to complex pathophysiology of oxidative stress in humans. For future improvement of antioxidant therapy and better understanding of redox-associated disease progression detailed knowledge on the sources and targets of RONS formation and discrimination of their detrimental or beneficial roles is required. In order to advance this important area of biology and medicine, highly synergistic approaches combining a variety of diverse and contrasting disciplines are needed.

Assessing Free-Radical-Mediated DNA Damage during Cardiac Surgery: 8-Oxo-7,8-dihydro-2'-deoxyguanosine as a Putative Biomarker

Coronary artery bypass grafting (CABG), one of the most common cardiac surgical procedures, is characterized by a burst of oxidative stress. 8-Oxo-7,8-dihydro-2′-deoxyguanosine (8-oxodG), produced following DNA repairing, is used as an indicator of oxidative DNA damage in humans. The effect of CABG on oxidative-induced DNA damage, evaluated through the measurement of urinary 8-oxodG by a developed and validated liquid chromatography-tandem mass spectrometry (LC-MS/MS) method in 52 coronary artery disease (CAD) patients, was assessed before (T0), five days (T1), and six months (T2) after CABG procedure. These results were compared with those obtained in 40 subjects with cardiovascular risk factors and without overt cardiovascular disease (CTR). Baseline (T0) 8-oxodG was higher in CAD than in CTR (p = 0.035). A significant burst was detected at T1 (p = 0.019), while at T2, 8-oxodG levels were significantly lower than those measured at T0 (p < 0.0001) and comparable to those found in CTR (p = 0.73). A similar trend was observed for urinary 8-iso-prostaglandin F_2α (8-isoPGF_2α), a reliable marker of oxidative stress. In the whole population baseline, 8-oxodG significantly correlated with 8-isoPGF_2α levels (r = 0.323, p = 0.002). These data argue for CABG procedure in CAD patients as inducing a short-term increase in oxidative DNA damage, as revealed by 8-oxodG concentrations, and a long-term return of such metabolite toward physiological levels.

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.

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.

Protective Effect of Folic Acid on Oxidative DNA Damage: A Randomized, Double-Blind, and Placebo Controlled Clinical Trial

Although previous reports have linked DNA damage with both transmissions across generations as well as our own survival, it is unknown how to reverse the lesion. Based on the data from a Randomized, Double-blind, Placebo Controlled Clinical Trial, this study aimed to assess the efficacy of folic acid supplementation (FAS) on DNA oxidative damage reversal.In this randomized clinical trial (RCT), a total of 450 participants were enrolled and randomly assigned to 3 groups to receive folic acid (FA) 0.4 mg/day (low-FA), 0.8 mg/day (high-FA), or placebo (control) for 8 weeks. The urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG) and creatinine (Cr) concentration at pre- and post-FAS were measured with modified enzyme-linked immunosorbent assay (ELISA) and high-performance liquid chromatography (HPLC), respectively. A multivariate general linear model was applied to assess the individual effects of FAS and the joint effects between FAS and hypercholesterolemia on oxidative DNA damage improvement. This clinical trial was registered with ClinicalTrials.gov, number NCT02235948.Of the 438 subjects that received FA fortification or placebo, the median (first quartile, third quartile) of urinary 8-OHdG/Cr for placebo, low-FA, and high-FA groups were 58.19 (43.90, 82.26), 53.51 (38.97, 72.74), 54.73 (39.58, 76.63) ng/mg at baseline and 57.77 (44.35, 81.33), 51.73 (38.20, 71.30), and 50.65 (37.64, 76.17) ng/mg at the 56th day, respectively. A significant decrease of urinary 8-OHdG was observed after 56 days FA fortification (P < 0.001). Compared with the placebo, after adjusting for some potential confounding factors, including the baseline urinary 8-OHdG/Cr, the urinary 8-OHdG/Cr concentration significantly decreased after 56 days FAS [β (95% confidence interval) = -0.88 (-1.62, -0.14) and P = 0.020 for low-FA; and β (95% confidence interval) = -2.68 (-3.42, -1.94) and P < 0.001 for high-FA] in a dose-response fashion (Ptrend < 0.001). Test of interaction between hypercholesterolemia and FA supplementation on urinary 8-OHdG reduction was significant (P = 0.001).The present study demonstrates that FA fortification is independently linked to the reduction of urinary 8-OHdG/Cr in a dose-related pattern, which suggests that FA is beneficial to protect against oxidative damage to DNA. This effect is apparently stronger in those with hypercholesterolemia. The authors provide a new insight into the prevention and reversal of oxidative DNA damage.

Measurement of a Urinary Marker (8-hydroxydeoxy­Guanosine, 8-OHdG) of DNA Oxidative Stress in Epidemiological Surveys: A Pilot Study

Background

8-Hydroxydeoxyguanosine (8-OHdG) is a commonly used marker of DNA oxidative stress in epidemiological studies. The aim of this study was to establish whether the urinary concentration of 8-OHdG varies during the first part of the day, when clinical tests are usually performed, and whether it can therefore be measured without bias in spot urine samples.

Material and methods

Spot urine samples were collected using a convenience sample. A linear mixed-effects model for repeated measurements was used to analyze 8-OHdG levels.

Results

A significant increasing trend in time in the 8-OHdG concentration was found among smokers, but not in the case of nonsmokers.

Conclusions

In epidemiological studies on oxidative stress, all participants should collect their early morning urine specimens – before their first cigarette if they are smokers – to gather information on individual background oxidation levels.

Association of low GLP-1 with oxidative stress is related to cardiac disease and outcome in patients with type 2 diabetes mellitus: a pilot study

Oxidative stress (OS) contributes to cardiovascular damage in type 2 diabetes mellitus (T2DM). The peptide glucagon-like peptide-1 (GLP-1) inhibits OS and exerts cardiovascular protective actions. Our aim was to investigate whether cardiac remodeling (CR) and cardiovascular events (CVE) are associated with circulating GLP-1 and biomarkers of OS in T2DM patients. We also studied GLP-1 antioxidant effects in a model of cardiomyocyte lipotoxicity. We examined 72 T2DM patients with no coronary or valve heart disease and 14 nondiabetic subjects. A median of 6 years follow-up information was obtained in 60 patients. Circulating GLP-1, dipeptidyl peptidase-4 activity, and biomarkers of OS were quantified. In T2DM patients, circulating GLP-1 decreased and OS biomarkers increased, compared with nondiabetics. Plasma GLP-1 was inversely correlated with serum 3-nitrotyrosine in T2DM patients. Patients showing high circulating 3-nitrotyrosine and low GLP-1 levels exhibited CR and higher risk for CVE, compared to the remaining patients. In palmitate-stimulated HL-1 cardiomyocytes, GLP-1 reduced cytosolic and mitochondrial oxidative stress, increased mitochondrial ATP synthase expression, partially restored mitochondrial membrane permeability and cytochrome c oxidase activity, blunted leakage of creatine to the extracellular medium, and inhibited oxidative damage in total and mitochondrial DNA. These results suggest that T2DM patients with reduced circulating GLP-1 and exacerbated OS may exhibit CR and be at higher risk for CVE. In addition, GLP-1 exerts antioxidant effects in HL-1 palmitate-overloaded cardiomyocytes. It is proposed that therapies aimed to increase GLP-1 may counteract OS, protect from CR, and prevent CVE in patients with T2DM.

Measurement of oxidatively induced DNA damage and its repair, by mass spectrometric techniques

Oxidatively induced damage caused by free radicals and other DNA-damaging agents generate a plethora of products in the DNA of living organisms. There is mounting evidence for the involvement of this type of damage in the etiology of numerous diseases including carcinogenesis. For a thorough understanding of the mechanisms, cellular repair, and biological consequences of DNA damage, accurate measurement of resulting products must be achieved. There are various analytical techniques, with their own advantages and drawbacks, which can be used for this purpose. Mass spectrometric techniques with isotope dilution, which include gas chromatography (GC) and liquid chromatography (LC), provide structural elucidation of products and ascertain accurate quantification, which are absolutely necessary for reliable measurement. Both gas chromatography-mass spectrometry (GC-MS) or liquid chromatography-mass spectrometry (LC-MS), in single or tandem versions, have been used for the measurement of numerous DNA products such as sugar and base lesions, 8,5'-cyclopurine-2'-deoxynucleosides, base-base tandem lesions, and DNA-protein crosslinks, in vitro and in vivo. This article reviews these techniques and their applications in the measurement of oxidatively induced DNA damage and its repair.

Oxidatively induced DNA damage and its repair in cancer

Oxidatively induced DNA damage is caused in living organisms by endogenous and exogenous reactive species. DNA lesions resulting from this type of damage are mutagenic and cytotoxic and, if not repaired, can cause genetic instability that may lead to disease processes including carcinogenesis. Living organisms possess DNA repair mechanisms that include a variety of pathways to repair multiple DNA lesions. Mutations and polymorphisms also occur in DNA repair genes adversely affecting DNA repair systems. Cancer tissues overexpress DNA repair proteins and thus develop greater DNA repair capacity than normal tissues. Increased DNA repair in tumors that removes DNA lesions before they become toxic is a major mechanism for development of resistance to therapy, affecting patient survival. Accumulated evidence suggests that DNA repair capacity may be a predictive biomarker for patient response to therapy. Thus, knowledge of DNA protein expressions in normal and cancerous tissues may help predict and guide development of treatments and yield the best therapeutic response. DNA repair proteins constitute targets for inhibitors to overcome the resistance of tumors to therapy. Inhibitors of DNA repair for combination therapy or as single agents for monotherapy may help selectively kill tumors, potentially leading to personalized therapy. Numerous inhibitors have been developed and are being tested in clinical trials. The efficacy of some inhibitors in therapy has been demonstrated in patients. Further development of inhibitors of DNA repair proteins is globally underway to help eradicate cancer.