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Skin melanisation ranges widely across human populations. Melanin has antioxidant properties and also acts as a filter to solar ultraviolet radiation (UVR) incident upon the skin. In this study we firstly examined whether melanin level might influence baseline levels of systemic oxidative stress, in 65 humans in vivo from the same geographical area ranging from the lightest to darkest skin type (phototype I-VI). This was examined in winter-time (latitude 53.5°N). Remarkably, we found that urinary biomarkers of oxidatively-generated DNA damage (8-oxodG) and RNA damage (8-oxoGuo) were significantly correlated with skin lightness (L*), such that 14–15% of the variation in their baseline levels could be explained by skin colour. Next we exposed 15 humans at the extremes of skin melanisation to a simulated summer-time exposure of solar UVR (95% UVA, 5% UVB; dose standardised to sunburn threshold), following which they provided a sample of every urine void over the next five days. We found that UVR induced a small but significant increase in urinary 8-oxodG and 8-oxoGuo, with differing kinetics between skin types. Thus greater melanisation is associated with protection against systemic oxidative stress, which may reflect melanin's antioxidant properties, and solar UVR exposure also influences systemic oxidative stress levels in humans. These novel findings may have profound implications for human physiology and health., Graphical abstract Image 1, Highlights • Biomarkers of systemic oxidative stress correlate with human skin lightness level. • Skin colour contributes 14–15% variation in baseline urinary 8-oxodG and 8-oxoGuo. • UVR exposure of the skin elevates biomarkers of systemic oxidative stress. • Both oxidatively-damaged DNA (8-oxodG) and RNA (8-oxoGuo) increase post-UVR. • Kinetics of urinary biomarker responses following UVR differ between skin types.

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., Graphical abstract Image 1, Highlights • Oxidatively damaged nucleic acids are implicated in the pathogenesis of disease. • LC-MS/MS, comet assay and ELISA are often used to study oxidatively damaged DNA. • Urinary oxidatively damaged nucleic acids non-invasively reflect oxidative stress. • DNA adductomics will aid understanding the role of ROS damaged DNA in disease.

The objective of this study was to investigate DNA damage and adducts in sperm from coke oven workers who have been exposed to polycyclic aromatic hydrocarbons. A longitudinal study was conducted with repeated measurements during spermatogenesis. Coke-oven workers (n=112) from a coke-oven plant served the PAH-exposed group, while administrators and security personnel (n=67) served the control. Routine semen parameters (concentration, motility, vitality, and morphology) were analyzed simultaneously; the assessment of sperm DNA integrity endpoints included DNA fragmentation, bulky DNA adducts, and 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxo-dGuo). The degree of sperm DNA fragmentation was measured using the terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) assay and sperm chromatin structure assay (SCSA). The PAH-exposed group had a significant increase in bulky DNA adducts and 8-oxo-dGuo compared to the control subjects (Ps = 0.002 and 0.045, respectively). Coke oven workers' percentages of DNA fragmentation and denaturation from the PAH-exposed group were not significantly different from those of the control subjects (Ps = 0.232 and 0.245, respectively). Routine semen parameters and DNA integrity endpoints were not correlated. Concentrations of 8-oxo-dGuo were positively correlated with percentages of DNA fragmentation measured by both TUNEL and SCSA (Ps = 0.045 and 0.034, respectively). However, the concentrations of 8-oxo-dGuo and percentages of DNA fragmentation did not correlate with concentrations of bulky DNA adducts. In summary, coke oven workers with chronic exposure to PAHs experienced decreased sperm DNA integrity. Oxidative stress could contribute to the degree of DNA fragmentation. Bulky DNA adducts may be independent of the formation of DNA fragmentation and oxidative adducts in sperm. Monitoring sperm DNA integrity is recommended as a part of the process of assessing the impact of occupational and environmental toxins on sperm.

We measured the levels of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo), a useful biomarker of oxidative injury, in liver (or urine) of maternal mice and their offspring, that were treated with humic acid (HA) and arsenic (As) alone, or their combination during pregnancy. A highly sensitive and specific isotope-dilution LC-MS/MS method was used for 8-oxodGuo quantification. Total arsenic accumulated in the offspring was also measured using ICP-MS. This study demonstrated, for the first time in an animal model, that HA alone treatment led to a significant increase of 8-oxodGuo levels both in liver and urine of maternal mice. No enhanced effect was observed when HA was combined with As, compared with the As alone treatment. With regard to the associated offspring, elevated levels of 8-oxodGuo and total arsenic were observed in offspring only when mother mice were treated with As and its combination with HA, but not for the HA-treated alone. It was worthy to note that the offspring from maternal combined treatment with HA and As had a significantly lower 8-oxodGuo than those of maternal treatment with As alone. This could be explained by that part of As formed complexes with HA and these macromolecules of HA-As complexes may not readily cross the placenta to the fetus, as evidenced by the lower accumulated total As observed in the offspring livers. Overall, it seems that HA may be detrimental to the maternal mice, but in the meantime it can be beneficial to the offspring by reducing free As.

Growing scientific evidence suggests that oxidative stress plays an important role in human health and disease. Under oxidative stress, the excess levels of reactive oxygen species (ROS) may lead to modification of cellular nucleic acids. Oxidatively damaged DNA has been recognized in association with the development of aging, cancer, and some degenerative diseases. The topics covered in this special edition give some insight into how oxidatively damaged DNA is involved in human disease and its health impacts. This special issue contains five papers. Two papers are related to human disease, including Keshan disease and chronic kidney disease, while two papers cover the underlying mechanisms of inflammation-related carcinogenesis and the association between DNA damage and antioxidant capacity in humans. Finally, a paper summarizes the literature regarding the effect of phytoagents on nucleic acid oxidation in cancer cells. Keshan disease (KD) is an endemic cardiomyopathy of unknown etiology affecting inhabitants of a narrow belt between Northeast China and Southwest China. This region is known for low levels of selenium in the environment as well as in food. In an original research article entitled “Oxidative stress is involved in the pathogenesis of Keshan disease (an endemic dilated cardiomyopathy) in China,” J. Pei et al. demonstrate that oxidative stress in the myocardium may play a crucial role in KD. The authors found elevated 8-oxodG levels in myocardial nuclei of the KD patients. Moreover, the expression of glutathione peroxidase 1 and thioredoxin reductases 1 (selenoproteins) was important in the antioxidant system of the organism and higher in the control group than in patients suffering from KD. In a review article entitled “Oxidative stress and nucleic acid oxidation in patients with chronic kidney disease,” C.-C. Sung et al. provide a systematic review of the role of oxidative stress in chronic kidney disease (CKD). It begins with the mechanisms of radical production, antioxidant defense, pathogenesis, and recent biomarkers of oxidative stress in CKD patients. The authors also summarized and evaluated the potential benefit of antioxidant therapies in CKD patients, although their value as useful therapeutic tools is being tested and future studies are necessary to validate their prospective beneficial effects on CKD. Infectious agents (e.g., parasites and viruses) have been identified as carcinogenic to humans (IARC, group 1). The underlying mechanism of their carcinogenicity includes inflammation accompanied by generation of reactive oxygen (ROS) and nitrogen species (RNS). In a review article entitled “DNA damage in inflammation-related carcinogenesis and cancer stem cells,” S. Ohnishi et al. propose a model by which chronic inflammation by infectious agents induces generation of cancer stem cells. The authors suggest that tissue injury caused by ROS/RNS may activate progenitor/stem cells for regeneration. Oxidative stress may then cause multiple mutations which may result in the formation of mutant stem cells and cancer stem cells thus leading to carcinogenesis. In an original research article entitled “Is the oxidative DNA damage level of human lymphocyte correlated with the antioxidant capacity of serum or the base excision repair activity of lymphocyte?,” Y.-C. Tsai et al. investigate the individual levels of oxidative DNA base damage in the human lymphocyte from different donors (healthy and infected patients) and its correlation with total antioxidant levels in the serum and the DNA base excision repair capacity. The most important finding is that antioxidant serum levels may not change the steady state levels of the oxidative base damage in the DNA. One should also consider that antioxidants in our body protect us in acute and highly stressful situations when we have high levels of ROS in a short time period rather than decrease the steady state levels. In a review article entitled “Phytoagents for cancer management: regulation of nucleic acid oxidation, ROS, and related mechanisms,” W.-L. Lee et al. present a detailed review of the role of phytoagents as redox regulators of nucleic acid oxidation in carcinogenesis. On the concept of genetic heterogeneity caused by nucleic acid oxidation as a major driving force of cancer progression, the authors highlight how and why phytoagents induce or prevent oxidative stress and their potential use in cancer prevention or therapy.

Of the DNA-derived biomarkers of oxidative stress, urinary 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) is the most frequently measured. However, there is significant discrepancy between chromatographic and immunoassay approaches, and intratechnique agreement among all available chromatography-based assays and ELISAs is yet to be established. This is a significant obstacle to their use in large molecular epidemiological studies. To evaluate the accuracy of intra/intertechnique and interlaboratory measurements, samples of phosphate buffered saline and urine, spiked with different concentrations of 8-oxoG, together with a series of urine samples from healthy individuals were distributed to ESCULA members. All laboratories received identical samples, including 2 negative controls that contained no added 8-oxodG. Data were returned from 17 laboratories, representing 20 methods, broadly classified as mass spectrometric (MS), electrochemical detection (EC), or enzyme-linked immunosorbant assay (ELISA). Overall, there was good within-technique agreement, with the majority of laboratories' results lying within 1 sd of their consensus mean. However, ELISA showed more within-technique variation than did the chromatographic techniques and, for the urine samples, reported higher values. Bland-Altman plots revealed good agreement between MS and EC methods but concentration-dependent deviation for ELISA. All methods ranked urine samples according to concentration similarly. Creatinine levels are routinely used as a correction factor for urine concentration, and therefore we also conducted an interlaboratory comparison of methods for urinary creatinine determination, in which the vast majority of values lay within 1 sd of the consensus value, irrespective of the analysis procedure. This study reveals greater consensus than previously expected, although concern remains over ELISA.-ESCULA [European Standards Committee on Urinary (DNA) Lesion Analysis], Evans, M. D., Olinski, R., Loft, S., Cooke, M. S. Toward consensus in the analysis of urinary 8-oxo-7,8-dihydro-2'-deoxyguanosine as a noninvasive biomarker of oxidative stress. Some of the authors of this paper are partners in, and this work was partly supported by, ECNIS (Environmental Cancer Risk, Nutrition and Individual Susceptibility), a Network of Excellence operating within the European Union 6th Framework Program, Priority 5: Food Quality and Safety (contract 513943)