Monoclonal Antibody to Single-Stranded DNA: A Potential Tool for DNA Repair Studies

Oral 8-aminoguanine against age-related retinal degeneration

Vision decline in the elderly, often due to retinal aging, predisposes individuals to pathologies like age-related macular degeneration. Currently, there are few effective oral treatments for this condition. Our study introduces an oral agent, 8-aminoguanine (8-AG), which targets age-related retinal degeneration using an aged Fischer 344 rat model. When administered in drinking water at a low dose for 8 weeks starting at 22 months of age, 8-AG significantly preserves retinal structure and function, as evidenced by increased retinal thickness, enhanced photoreceptor integrity, and improved electroretinogram responses. 8-AG reduces apoptosis, oxidative damage, and microglial/macrophage activation in aging retinae. 8-AG also mitigates retinal inflammation at transcriptional and cytokine levels. Extending treatment to 17 weeks further amplifies these protective effects. Given its efficacy in various disease models, 8-AG shows great promise as an anti-aging compound with the potential to mitigate common hallmarks of aging.

Oral 8-aminoguanine against age-related retinal degeneration

Visual decline in the elderly is often attributed to retinal aging, which predisposes the tissue to pathologies such as age-related macular degeneration. Currently, effective oral pharmacological interventions for retinal degeneration are limited. We present a novel oral intervention, 8-aminoguanine (8-AG), targeting age-related retinal degeneration, utilizing the aged Fischer 344 rat model. A low-dose 8-AG regimen (5 mg/kg body weight) via drinking water, beginning at 22 months for 8 weeks, demonstrated significant retinal preservation. This was evidenced by increased retinal thickness, improved photoreceptor integrity, and enhanced electroretinogram responses. 8-AG effectively reduced apoptosis, oxidative damage, and microglial/macrophage activation associated with aging retinae. Age-induced alterations in the retinal purine metabolome, characterized by elevated levels of inosine, hypoxanthine, and xanthine, were partially mitigated by 8-AG. Transcriptomics highlighted 8-AG's anti-inflammatory effects on innate and adaptive immune responses. Extended treatment to 17 weeks further amplified the retinal protective effects. Moreover, 8-AG showed temporary protective effects in the RhoP23H/+ mouse model of retinitis pigmentosa, reducing active microglia/macrophages. Our study positions 8-AG as a promising oral agent against retinal aging. Coupled with previous findings in diverse disease models, 8-AG emerges as a promising anti-aging compound with the capability to reverse common aging hallmarks.

Oxidative RNA Damage in the Pathogenesis and Treatment of Type 2 Diabetes

Excessive production of free radicals can induce cellular damage, which is associated with many diseases. RNA is more susceptible to oxidative damage than DNA due to its single-stranded structure, and lack of protective proteins. Yet, oxidative damage to RNAs received little attention. Accumulating evidence reveals that oxidized RNAs may be dysfunctional and play fundamental role in the occurrence and development of type 2 diabetes (T2D) and its complications. Oxidized guanine nucleoside, 8-oxo-7, 8-dihydroguanine (8-oxoGuo) is a biomarker of RNA oxidation that could be associated with prognosis in patients with T2D. Nowadays, some clinical trials used antioxidants for the treatment of T2D, though the pharmacological effects remained unclear. In this review, we overview the cellular handling mechanisms and the consequences of the oxidative RNA damage for the better understanding of pathogenesis of T2D and may provide new insights to better therapeutic strategy.

In Situ Detection of Complex DNA Damage Using Microscopy: A Rough Road Ahead

Complexity of DNA damage is considered currently one if not the primary instigator of biological responses and determinant of short and long-term effects in organisms and their offspring. In this review, we focus on the detection of complex (clustered) DNA damage (CDD) induced for example by ionizing radiation (IR) and in some cases by high oxidative stress. We perform a short historical perspective in the field, emphasizing the microscopy-based techniques and methodologies for the detection of CDD at the cellular level. We extend this analysis on the pertaining methodology of surrogate protein markers of CDD (foci) colocalization and provide a unique synthesis of imaging parameters, software, and different types of microscopy used. Last but not least, we critically discuss the main advances and necessary future direction for the better detection of CDD, with important outcomes in biological and clinical setups.

Ionizing Radiation and Complex DNA Damage: From Prediction to Detection Challenges and Biological Significance

Biological responses to ionizing radiation (IR) have been studied for many years, generally showing the dependence of these responses on the quality of radiation, i.e., the radiation particle type and energy, types of DNA damage, dose and dose rate, type of cells, etc. There is accumulating evidence on the pivotal role of complex (clustered) DNA damage towards the determination of the final biological or even clinical outcome after exposure to IR. In this review, we provide literature evidence about the significant role of damage clustering and advancements that have been made through the years in its detection and prediction using Monte Carlo (MC) simulations. We conclude that in the future, emphasis should be given to a better understanding of the mechanistic links between the induction of complex DNA damage, its processing, and systemic effects at the organism level, like genomic instability and immune responses.

Elevation in and persistence of multiple urinary biomarkers indicative of oxidative DNA stress and inflammation: Toxicological implications of maleic acid consumption using a rat model

Maleic acid (MA), an intermediate reagent used in many industrial products, instigated public health concerns in Taiwan when it was used to adulterate an array of starch-based delicacies to improve texture and storage time. Established studies reported that exposure to high concentrations of MA induce renal injury; little is known whether oxidative stress is induced at a relative low dose. This study aims to investigate the effect of oral single dose exposure of MA on the status of oxidative stress and inflammation. Single dose of MA at 0, 6 and 60 mg/kg (control, low- and high-dose groups, respectively) were orally administered to adult male and female rats. Urine samples were collected and analyzed to measure 8-hydroxy-2’-deoxyguanosine (8-OHdG), 8-iso-prostaglandin F_2α (8-IsoPGF_2α), 8-nitroguanine (8-NO₂Gua) and N-acetyl-S-(tetrahydro-5-hydroxy-2-pentyl-3-furanyl)-L-cysteine (HNE-MA) using LC-MS/MS. Results revealed that oral consumption of MA induced oxidative DNA damage and lipid peroxidation, as demonstrated by the statistically significant increases in urinary levels of 8-NO₂Gua, 8-OHdG, and 8-isoPGF_2α, in high-dosed male rats within 12 h of oral gavage (p < 0.05). Additionally, increases in concentration of these biomarkers persist for days after consumption; male rats appear to be more sensitive to oxidative burden compared to their counterparts. The aforementioned findings could help elucidate the mechanisms through which nephrotoxicity occur.

Quantification of ultraviolet radiation-induced DNA damage in the urine of Swedish adults and children following exposure to sunlight

CONTEXT

DNA damage following exposure to ultraviolet radiation (UVR) is important in skin cancer development. The predominant photoproduct, cyclobutane thymine dimer (T=T), is repaired and excreted in the urine, where it provides a biomarker of exposure.

OBJECTIVE

To quantify urinary T=T levels after recreational sunlight exposure in adults and children.

METHODS

Average UVR doses were measured with personal dosimeters. Urinary T=T was analysed with (32)P-postlabelling.

RESULTS

Background levels of T=T increased significantly following exposure to sunlight. Amounts of T=T in urine of children and adults were not significantly different after adjusting for area of skin exposed and physiological differences. UVR dose and amounts of T=T correlated for both adults and children.

CONCLUSION

Recreational exposure to sunlight in Sweden induces levels of DNA damage, clearly detectable in urine.

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.

Detection of extracellular 8-oxo-7,8-dihydro-2'-deoxyguanosine as a biomarker of oxidative damage in X-irradiated fibroblast cultures: optimization of analytical procedure

We have developed a simple methodology, based on single-step solid-phase extraction followed by isocratic high-performance liquid chromatography coupled with electrochemical detection (HPLC-ECD), to determine extracellular 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) in culture supernatants of normal human dermal fibroblasts. A standard addition method, using externally added 8-oxodG (0.5 and 1 pmol) was employed to eliminate matrix effects arising from the chemically complex, protein-rich medium. Secondly, applying this procedure to X-ray irradiated fibroblasts, we report a significant twofold increase in the levels of 8-oxodG at the radiobiologically relevant dose of 6 Gy. This suggests that extracellular 8-oxodG might be a useful biomarker for oxidative stress following moderate doses of X-irradiation.

Role of dietary antioxidants in the prevention of in vivo oxidative DNA damage

Epidemiological evidence consistently shows that diets high in fresh fruit and vegetables significantly lower cancer risk. Given the postulated role of oxidative DNA damage in carcinogenesis, the assumption has been made that it is the antioxidant properties of food constituents, such as vitamin C, E and carotenoids, which confer protection. However, epidemiological studies with specific antioxidants, either singly or in combination, have not, on the whole, supported this hypothesis. In contrast, studies examining the in vitro effect of antioxidants upon oxidative DNA damage have generally been supportive, in terms of preventing damage induction. The same, however, cannot be said for the in vivo intervention studies where overall the results have been equivocal. Nevertheless, recent work has suggested that some dietary antioxidants may confer protective properties through a novel mechanism, unrelated to their conventional free-radical scavenging abilities. Upregulation of antioxidant defence, xenobiotic metabolism, or DNA-repair genes may all limit cellular damage and hence promote maintenance of cell integrity. However, until further work has clarified whether dietary supplementation with antioxidants confers a reduced risk of cancer and the mechanism by which this effect is exerted, the recommendation for a diet rich in fruit and vegetables remains valid empirically.

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.

Urinary excretion rates of 8-oxoGua and 8-oxodG and antioxidant vitamins level as a measure of oxidative status in healthy, full-term newborns

The aim of the present study was to evaluate the oxidative status in healthy full-term children and piglets. Urinary excretion of 8-oxoGua (8-oxoguanine) and 8-oxodG (8-oxo-2'-deoxyguanosine) were determined using HPLC/GS/MS methodology and concentrations of vitamins A, C and E with HPLC technique. The levels of 8-oxoGua in urine samples were about 7-8 times higher in newborn children and piglets when compared with the level of adult subjects, while in the case of 8-oxodG the difference was about 2.5 times. The levels of vitamin C and E in umbilical cord blood of newborn children significantly depend on the concentration of these compounds in their mother's blood. However, the values of vitamin C in human's cord blood were about 2-times higher than in respective mother blood, while the level of vitamin E showed an opposite trend. The results suggest that: (i) healthy, full-term newborns are under potential oxidative stress; (ii) urinary excretion of 8-oxoGua and 8-oxodG may be a good marker of oxidative stress in newborns; and (iii) antioxidant vitamins, especially vitamin C, play an important role in protecting newborns against oxidative stress.

Inhibition of Rac and Rac-linked functions by 8-oxo-2'-deoxyguanosine in murine macrophages

Rac is a protein involved in the various functions of macrophages (Mphi), including the production of reactive oxygen species (ROS), phagocytosis, chemotaxis and the secretion of cytokines (such as gamma-INF). This study tested the effects of nucleosides containing 8-oxoguanine(8-hydroxyguanine) such as 8-oxo-2'-guanosine (8-oxoG) or 8-oxo-2'-deoxyguanosine (8-oxodG), on Rac and the above-listed Rac-associated functions of Mphi using mouse peritoneal Mphi (MpMphi). It is reported that 8-oxodG was able to effectively inhibit Rac and the Rac-associated functions of MpMphi. Compared to 8-oxodG, 8-oxoG showed negligible effects. Furthermore, normal nucleosides such as deoxyguanosine (dG), guanosine (G) and adenosine (A) did not exert any effects. These results suggest that 8-oxodG could be used as a potential tool to modulate the functions of Mphi that are intimately related to various pathological processes.

Anti-inflammatory effects of 8-hydroxy-2'-deoxyguanosine on lipopolysaccharide-induced inflammation via Rac suppression in Balb/c mice

Recently, we observed that 8-hydroxyguanosine triphosphate and 8-hydroxy-2'-deoxyguanosine (oh(8)dG) inactivate Rac and consequently down-regulate the Rac-linked NADPH oxidase, iNOS, and Cox2. Based on these observations, we tested whether oh(8)dG has anti-inflammatory activity in vivo in lipopolysaccharide (LPS)-treated mice. LPS (1 mg/kg, ip)-treated mice exhibit marked inflammatory responses, including increases in proinflammatory cytokines (TNF-alpha, IL-6, IL-18, and IL-12p70) in serum and infiltration of neutrophils, increased translocation of NF-kappaB p50 from the cytosol to the nucleus, and phosphorylation of c-Jun in lung tissues. Mice were pretreated with oh(8)dG (up to 60 mg/kg, ip) 4 h before LPS injection, and this pretreatment dose-dependently inhibited the inflammatory responses; the inhibitions observed with 60 mg/kg oh(8)dG were statistically significant. At the same time, oh(8)dG pretreatment inactivated Rac in lung tissues. Oh(8)dG pretreatment (50 mg/kg, ip) also significantly protected against LPS-induced septic death. Furthermore, oh(8)dG was more effective than acetyl salicylic acid in inhibiting these inflammatory responses. 8-Hydroxyguanosine also had some effect but was much weaker than oh(8)dG. The effects of normal nucleosides (dG, G, and A) were negligible or not significant. These results support an anti-inflammatory activity for oh(8)dG, which could be ascribed to its Rac-inactivating action.

Evidence for attenuated cellular 8-oxo-7,8-dihydro-2'-deoxyguanosine removal in cancer patients

Measurement of the products of oxidatively damaged DNA in urine is a frequently used means by which oxidative stress may be assessed non-invasively. We believe that urinary DNA lesions, in addition to being biomarkers of oxidative stress, can potentially provide more specific information, for example, a reflection of repair activity. We used high-performance liquid chromatography prepurification, with gas chromatography-mass spectrometry (LC-GC-MS) and ELISA to the analysis of a number of oxidative [e.g., 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), 8-oxo-7,8-dihydro-guanine, 5-(hydroxymethyl)uracil], non-oxidative (cyclobutane thymine dimers) and oligomeric DNA products in urine. We analysed spot urine samples from 20 healthy subjects, and 20 age- and sex-matched cancer patients. Mononuclear cell DNA 8-oxodG levels were assessed by LC-EC. The data support our proposal that urinary DNA lesion products are predominantly derived from DNA repair. Furthermore, analysis of DNA and urinary 8-oxodG in cancer patients and controls suggested reduced repair activity towards this lesion marker in these patients.

Urinary measurement of 8-OxodG, 8-OxoGua, and 5HMUra: a noninvasive assessment of oxidative damage to DNA

Numerous DNA repair pathways exist to prevent the persistence of damage, and are integral to the maintenance of genome stability, and hence prevention of disease. Excised lesions arising from repair may ultimately appear in the urine where their measurement has been acknowledged to be reflective of overall oxidative stress. The development of reliable assays to measure urinary DNA lesions, such as HPLC prepurification followed by gas chromatography/mass spectrometry, offers the potential to assess whole body oxidative DNA damage. However, some studies suggest a possibility that confounding factors may contribute to urinary levels of 7,8-dihydro-8-oxoguanine (8-oxoGua) and 7,8-dihydro-8-oxo-2 -deoxyguanosine (8-oxodG). This article considers several possible sources of urinary lesions: (a) the repair of oxidatively damaged DNA; (b) a possible dietary influence; and (c) cell death. The authors conclude that data from their laboratories, along with a number of literature reports, form an argument against a contribution from cell death and diet. In the absence of these confounding factors, urinary measurements may be attributed entirely to the repair of DNA damage and suggests their possible use in studying associations between DNA repair and disease.

Helicobacter pylori infection is associated with oxidatively damaged DNA in human leukocytes and decreased level of urinary 8-oxo-7,8-dihydroguanine

Helicobacter pylori infection is responsible for inflammation, increased production of reactive oxygen species and oxidatively damaged DNA in the gastric mucosa. There is also evidence which suggests that H.pylori infection may lead to the development of several extragastroduodenal pathologies with reactive oxygen species involvement. In order to assess whether the infection may impose oxidatively damaged DNA not only in the target organ (stomach) but in other organs as well we decided, for the first time, to analyse the two kinds of oxidatively damaged DNA biomarkers: urinary excretion of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) and 8-oxo-7,8-dihydroguanine (8-oxoGua) as well as the level of oxidatively damaged DNA in leukocytes. Using high performance liquid chromatography prepurification/gas chromatography with isotope dilution mass detection methodology, we examined the amount of oxidatively damaged DNA products excreted into urine and the amount of 8-oxodG in the DNA of leukocytes' (with the the HPLC/EC technique) in three groups of children: (i) control group, (ii) H.pylori infected children and (iii) children with gastritis where H.pylori infection was excluded. The levels of 8-oxodG in DNA isolated from leukocytes of H.pylori infected patients and in the group with gastritis without H.pylori infection were significantly higher than in DNA isolated from the control group. The mean level of 8-oxoGua in urine samples of children infected with H.pylori was significantly lower than in the urine of the group with gastritis without H.pylori infection. The data suggest that inflammation itself, not just H.pylori infection, is responsible for the observed rise of 8-oxodG level in leukocytes. However, the observed decrease in the level of modified base in urine seems to be specific for H.pylori infection and possibly linked with nitric oxide mediated inhibition of a key base excision repair enzyme (human 8-oxo-7, 8-dihydroguanine glycosylase) responsible for the repair of 8-oxo-7,8-dihydroguanine.

Oxidative DNA damage and disease: induction, repair and significance

The generation of reactive oxygen species may be both beneficial to cells, performing a function in inter- and intracellular signalling, and detrimental, modifying cellular biomolecules, accumulation of which has been associated with numerous diseases. Of the molecules subject to oxidative modification, DNA has received the greatest attention, with biomarkers of exposure and effect closest to validation. Despite nearly a quarter of a century of study, and a large number of base- and sugar-derived DNA lesions having been identified, the majority of studies have focussed upon the guanine modification, 7,8-dihydro-8-oxo-2'-deoxyguanosine (8-OH-dG). For the most part, the biological significance of other lesions has not, as yet, been investigated. In contrast, the description and characterisation of enzyme systems responsible for repairing oxidative DNA base damage is growing rapidly, being the subject of intense study. However, there remain notable gaps in our knowledge of which repair proteins remove which lesions, plus, as more lesions identified, new processes/substrates need to be determined. There are many reports describing elevated levels of oxidatively modified DNA lesions, in various biological matrices, in a plethora of diseases; however, for the majority of these the association could merely be coincidental, and more detailed studies are required. Nevertheless, even based simply upon reports of studies investigating the potential role of 8-OH-dG in disease, the weight of evidence strongly suggests a link between such damage and the pathogenesis of disease. However, exact roles remain to be elucidated.

Spontaneous DNA repair in human peripheral blood mononuclear cells

DNA molecules are constantly damaged during mitosis and by oxygen-free radicals produced by either cellular metabolism or by external factors. Populations at risk include patients with cancer-prone disease, patients under enhanced oxidative stress, and those treated with immunosuppressive/cytotoxic therapy. The DNA repair process is crucial in maintaining the genomal DNA integrity. The aim of this study was to evaluate spontaneous DNA repair capacity of peripheral blood mononuclear cells (PBMC) from normal blood donors. PBMC DNA repair ability represents DNA repair by other tissues as well. It is shown in the present study that in vitro incorporation of [3H]thymidine in non-stimulated PBMC expresses the ability of the cells to repair DNA damage. This method was validated by double-stranded DNA measurements. Both catalase and Fe2+ increased DNA repair, the former by preventing re-breakage of newly repaired DNA and the latter by introducing additional DNA damage, which enhanced DNA repair. Better understanding of DNA repair processes will enable to minimize DNA damage induced by oxidative stress.

Urinary 8-OHdG: a marker of oxidative stress to DNA and a risk factor for cancer, atherosclerosis and diabetics

Reactive oxygen species (ROS) produced either endogenously or exogenously can attack lipid, protein and nucleic acid simultaneously in the living cells. In nuclear and mitochondrial DNA, 8-hydroxydeoxyguanosine (8-OHdG), an oxidized nucleoside of DNA, is the most frequently detected and studied DNA lesion. Upon DNA repair, 8-OHdG is excreted in the urine. Numerous evidences have indicated that urinary 8-OHdG not only is a biomarker of generalized, cellular oxidative stress but might also be a risk factor for cancer, atherosclerosis and diabetes. For example, elevated level of urinary 8-OHdG has been detected in patients with various cancers. In human atherosclerotic plaques, there were increased amounts of oxidatively modified DNA and 8-OHdG. Elevated urinary 8-OHdG and leukocyte DNA were also detected in diabetic patients with hyperglycemia, and the level of urinary 8-OHdG in diabetes correlated with the severity of diabetic nephropathy and retinopathy. We have discussed various methods for determining 8-OHdG in the tissue and urine, including HPLC with and without extraction, and ELISA. Using the ELISA we developed, we found that the normal range of urinary 8-OHdG for females was 43.9 +/- 42.1 ng/mg creatinine and 29.6 +/- 24.5 ng/mg creatinine for males, respectively. We found that the normal value between females and males is significantly different (p < 0.001).

Oxidative DNA damage: mechanisms, mutation, and disease

Oxidative DNA damage is an inevitable consequence of cellular metabolism, with a propensity for increased levels following toxic insult. Although more than 20 base lesions have been identified, only a fraction of these have received appreciable study, most notably 8-oxo-2'deoxyguanosine. This lesion has been the focus of intense research interest and been ascribed much importance, largely to the detriment of other lesions. The present work reviews the basis for the biological significance of oxidative DNA damage, drawing attention to the multiplicity of proteins with repair activities along with a number of poorly considered effects of damage. Given the plethora of (often contradictory) reports describing pathological conditions in which levels of oxidative DNA damage have been measured, this review critically addresses the extent to which the in vitro significance of such damage has relevance for the pathogenesis of disease. It is suggested that some shortcomings associated with biomarkers, along with gaps in our knowledge, may be responsible for the failure to produce consistent and definitive results when applied to understanding the role of DNA damage in disease, highlighting the need for further studies.

Progress in the analysis of urinary oxidative DNA damage

Oxidative DNA damage has been implicated to be important in the pathogenesis of many diseases, including cancer and heart disease. The assessment of damage in various biological matrices, such as DNA, serum, and urine, is vital to understanding this role and subsequently devising intervention strategies. Despite the numerous techniques to measure oxidative DNA damage products in urine, it remains unclear what these measurements truly represent. Sources of urinary lesions may include the diet, cell death, and, of most interest, DNA repair. Were it possible to exclude the two former contributions, a noninvasive assay for DNA repair would be invaluable in the study of DNA damage and disease. This review highlights that, although progress has been made, significant work remains. Diet, cell death, and repair need continued examination to further elucidate the kinetics of lesion formation and clearance in vivo. Studies from our laboratory and others are making appreciable progress towards the interpretation of urinary lesion measurements along with the development of urinary assays to evaluate DNA repair. Upon establishment of these details, urinary oxidative DNA damage measurements may become more than a reflection of generalized oxidative stress.

Urinary 8-oxo-2'-deoxyguanosine: redox regulation of DNA repair in vivo?

DNA is susceptible to damage by reactive oxygen species (ROS). ROS are produced during normal and pathophysiological processes in addition to ionizing radiation, environmental mutagens, and carcinogens. 8-oxo-2'-deoxyguanosine (8-oxodG) is probably one of the most abundant DNA lesion formed during oxidative stress. This potentially mutagenic lesion causes G --> T transversions and is therefore an important candidate lesion for repair, particularly in mammalian cells. Several pathways exist for the removal, or repair, of this lesion from mammalian DNA. The most established is via the base excision repair enzyme, human 8-oxoguanine glycosylase (hOgg1), which acts in combination with the human apurinic endonuclease (hApe). The latter is known to respond to regulation by redox reactions and may act in combination with hOgg1. We discuss evidence in this review article concerning alternative pathways in humans, such as nucleotide excision repair (NER), which could possibly remove the 8-oxodG lesion. We also propose that redox-active components of the diet, such as vitamin C, may promote such repair, affecting NER specifically.