Oligonucleotides in human urine do not contain 8-oxo-7,8-dihydrodeoxyguanosine

Genotoxicity of organic contaminants in the soil: A review based on bibliometric analysis and methodological progress

Organic contaminants (OCs) are ubiquitous in the environment, posing severe threats to human health and ecological balance. In particular, OCs and their metabolites could interact with genetic materials to induce genotoxicity, which has attracted considerable attention. In this review, bibliometric analysis was executed to analyze the publications on the genotoxicity of OCs in soil from 1992 to 2021. The result indicated that significant contributions were made by China and the United States in this field and the research hotspots were biological risks, damage mechanisms, and testing methods. Based on this, in this review, we summarized the manifestations and influencing factors of genotoxicity of OCs to soil organisms, the main damage mechanisms, and the most commonly utilized testing methods. OCs can induce genotoxicity and the hierarchical response of soil organisms, which could be influenced by the physicochemical properties of OCs and the properties of soil. Specific mechanisms of genotoxicity can be classified into DNA damage, epigenetic toxicity, and chromosomal aberrations. OCs with different molecular weights lead to genetic material damage by inducing the generation of ROS or forming adducts with DNA, respectively. The micronucleus test and the comet test are the most commonly used testing methods. Moreover, this review also pointed out that future studies should focus on the relationships between bioaccessibilities and genotoxicities, transcriptional regulatory factors, and potential metabolites of OCs to elaborate on the biological risks and mechanisms of genotoxicity from an overall perspective.

Comparison of therapeutic effects between topical 8-oxo-2'-deoxyguanosine and corticosteroid in ocular alkali burn model

We compared the therapeutic effects of topical 8-oxo-2'-deoxyguanosine (8-oxo-dG) and corticosteroid in a murine ocular alkali burn model. (n = 128) The corneal alkali burn model was established by applying 0.1 N sodium hydroxide (NaOH), followed by treatment with 8-oxo-dG, 0.1% fluorometholone (FML), 1% prednisolone acetate (PDE), or phosphate-buffered saline (PBS) twice daily. One week later, the clinical and histological status of the cornea were assessed. Transcript levels of inflammatory cytokines and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase as well as the levels of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in the cornea, were assayed. The 8-oxo-dG and PDE groups showed marked improvements in corneal integrity and clarity when compared with the PBS group (each p < 0.01). The numbers of cells stained for neutrophil elastase and F4/80-positive inflammatory cells were significantly decreased, with levels of interleukin(IL)-1β, IL-6, tumor necrosis factor(TNF)-α, and total ROS/RNS amounts markedly reduced in the 8-oxo-dG, FML, and PDE groups (each p < 0.05). Levels of NADPH oxidase type 2 and 4 were substantially more repressed in the 8-oxo-dG-treated group than in the PDE-treated group (each p < 0.05). Topical 8-oxo-dG showed excellent therapeutic effects that were comparable with those treated with topical PDE in a murine ocular alkali burn model.

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.

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.

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.

Oxidatively induced DNA damage: mechanisms, repair and disease

Endogenous and exogenous sources cause oxidatively induced DNA damage in living organisms by a variety of mechanisms. The resulting DNA lesions are mutagenic and, unless repaired, lead to a variety of mutations and consequently to genetic instability, which is a hallmark of cancer. Oxidatively induced DNA damage is repaired in living cells by different pathways that involve a large number of proteins. Unrepaired and accumulated DNA lesions may lead to disease processes including carcinogenesis. Mutations also occur in DNA repair genes, destabilizing the DNA repair system. A majority of cancer cell lines have somatic mutations in their DNA repair genes. In addition, polymorphisms in these genes constitute a risk factor for cancer. In general, defects in DNA repair are associated with cancer. Numerous DNA repair enzymes exist that possess different, but sometimes overlapping substrate specificities for removal of oxidatively induced DNA lesions. In addition to the role of DNA repair in carcinogenesis, recent evidence suggests that some types of tumors possess increased DNA repair capacity that may lead to therapy resistance. DNA repair pathways are drug targets to develop DNA repair inhibitors to increase the efficacy of cancer therapy. Oxidatively induced DNA lesions and DNA repair proteins may serve as potential biomarkers for early detection, cancer risk assessment, prognosis and for monitoring therapy. Taken together, a large body of accumulated evidence suggests that oxidatively induced DNA damage and its repair are important factors in the development of human cancers. Thus this field deserves more research to contribute to the development of cancer biomarkers, DNA repair inhibitors and treatment approaches to better understand and fight cancer.

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.

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 of biomarkers of oxidatively damaged DNA and RNA in hereditary hemochromatosis

Oxidatively generated damage to nucleic acids is considered to play a significant role in carcinogenesis, and it has been shown that people with hereditary hemochromatosis are at increased risk of cancer. In this study we used a new refined liquid chromatography-tandem mass spectrometry method to measure the urinary excretion of oxidatively generated 8-oxo-7,8-dihydroguanine and related 2'-deoxyribonucleoside and ribonucleoside derivatives in hereditary hemochromatosis patients, and we investigated the effect of treatment on the levels of these modifications. The study was carried out as a classical case-control study of 21 newly diagnosed, never treated hereditary hemochromatosis patients and 21 matched controls. We found that at baseline the urinary excretion of the RNA oxidation product 8-oxo-7,8-dihydroguanosine (8-oxoGuo) was 2.5-fold increased in patients compared with controls, and after phlebotomy treatment the excretion of the RNA oxidation product 8-oxoGuo returned to control values and the excretion of the DNA product 8-oxo-7,8-dihydro-2'-deoxyguanosine was reduced by 30%. In patients with hereditary hemochromatosis oxidative stress on nucleic acids is an important feature of the iron overload seen in this disease. By this mechanism cellular damage resulting in end organ damage, typically seen in the liver of such patients, may be mediated.

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.

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

Non-invasive monitoring of oxidative stress is highly desirable. Urinary 7,8-8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) is a biologically relevant and convenient analytical target. However, immunoassays can over-estimate levels of urinary 8-oxodG. Measurement of more than one DNA oxidation product in urine would be advantageous in terms of mechanistic information. Urines samples were analysed for 8-oxodG by solid-phase extraction/LC-MS/MS and ELISA. The solid-phase extraction/LC-MS/MS assay was also applied to the analysis of urinary 7,8-dihydro-8-oxo-2'-deoxyadenosine (8-oxodA). Concurring with previous reports, urinary 8-oxodG measured by ELISA was significantly higher than levels measured by LC-MS/MS. However, apparent improvement in the specificity of the commercially available Japanese Institute for the Control of Ageing (JaICA) ELISA brought mean LC-MS/MS and ELISA measurements of urinary 8-oxodG into agreement. Urinary 8-oxodA was undetectable in all urines, despite efficient recovery by solid phase extraction. Exploitation of the advantages of ELISA may be enhanced by a simple modification to the assay procedure, although chromatographic techniques still remain the 'gold standard' techniques for analysis of urinary 8-oxodG. Urinary 8-oxodA is either not present or below the limit of detection of the instrumentation.

8-hydroxydeoxyguanosine suppresses NO production and COX-2 activity via Rac1/STATs signaling in LPS-induced brain microglia

Free 8-hydroxydeoxyguanosine (oh(8)dG), a nucleoside of 8-hydroxyguanine (oh(8)Gua), present in cytosol is not incorporated into DNA. However, nothing is known about its biological function when it presents in cytosol as a free form. We demonstrate here for the first time that oh(8)dG inhibits lipopolysaccharide (LPS)-induced nitric oxide (NO) production and cyclooxygenase-2 (COX-2) activity, and both gene transcriptions in microglia. Furthermore, oh(8)dG reduced mRNA levels of pro-inflammatory cytokine, such as IL-1beta, IL-6, and TNF-alpha, in activated BV2 cells. We also found that oh(8)dG suppressed reactive oxygen species (ROS) production through reduction of NADPH oxidase activity and blocked Rac1/STATs signal cascade. Finally, oh(8)dG suppressed recruitment of STATs and p300 to the iNOS and COX-2 promoters, and inhibited H3 histone acetylation. Taken together, these results provide new aspects of oh(8)dG as an anti-inflammatory agent.

8-Oxo-7,8-dihydro-2'-deoxyguanosine is not salvaged for DNA synthesis in human leukemic U937 cells

8-Oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dG), the most common oxidatively modified nucleoside, is released from oxidized DNA and oxidized nucleotide pool. However, little information is available regarding the metabolic pathway of free 8-oxo-dG. In this study, we generated radiolabeled 8-oxo-dG to track its metabolic fate. We report that 8-oxo-dG is neither phosphorylated to 8-oxo-dGMP nor degraded to the free base, 8-oxo-7,8-dihydroguanine (8-oxo-Gua), indicating that 8-oxo-dG is not a substrate for nucleotide synthesis. This result was confirmed by the finding that no radioactivity was detected in the DNA of U937 cells after incubating the cells with radiolabeled 8-oxo-dG. These observations indicate that 8-oxo-dG produced by oxidative stress is not reutilized for DNA synthesis.

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.

Monitoring of 8-oxo-7,8-dihydro-2′-deoxyguanosine in urine by high-performance liquid chromatography after pre-column derivatization with glyoxal reagents

A new, simple and sensitive pre-column fluorescence derivatization high-performance liquid chromatographic method for the determination of the oxidative DNA stress marker, 8-oxo-7,8-dihydro-2'-deoxyguanosine, was developed. Solid-phase extraction using an Oasis HLB cartridge avoided troublesome sample preparation steps, interference from charged species and frequent and essential electrode maintenance in electrochemical procedures. 8-Oxo-7,8-dihydro-2'-deoxyguanosine and other guanine compounds were selectively derivatized with glyoxal reagents (phenylglyoxal, 3,4-methylenedioxyglyoxal, 2-naphtylglyoxal and 6-methoxynaphthylglyoxal) at 40-60 degrees C. Derivatization with 6-methoxynaphthylglyoxal at 40 degrees C for 30 min gave the strongest fluorescence product. The fluorescence derivatives from reaction with 6-methoxynaphthylglyoxal were separated on a Capcell Pak C18 SG 120A column (4.6 mm i.d. x 150 mm, 5 microm) with acetonitrile-5 mM phosphate buffer (pH 6.0; 3:7, v/v) as mobile phase. The detection wavelength of the fluorescence derivative of 8-oxo-7,8-dihydro-2'-deoxyguanosine was lambda(ex) 400 nm and lambda(em) 510 nm. The detection limit of 8-oxo-7,8-dihydro-2'-deoxyguanosine was 1 ng/mL using 50 mL of urine. The calibration graphs were linear up to 30 microg/mL for 8-oxo-7,8-dihydro-2'-deoxyguanosine. The relative standard deviation of 20 ng/mL of 8-oxo-7,8-dihydro-2'-deoxyguanosine was 7.0%. The proposed method was compared with the enzymatic ELISA 8-oxo-7,8-dihydro-2'-deoxyguanosine analysis method (8-OH-dG Check, JaICA, Shizuoka, Japan). The correlation coefficient was 0.79 (n = 20) and y = 0.85x + 5.34. The proposed method was applied to the monitoring of 8-oxo-7,8-dihydro-2'-deoxyguanosine in urine from male heavy smokers.

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.

DNA repair is responsible for the presence of oxidatively damaged DNA lesions in urine

The repair of oxidatively damaged DNA is integral to the maintenance of genomic stability, and hence prevention of a wide variety of pathological conditions, such as aging, cancer and cardiovascular disease. The ability to non-invasively assess DNA repair may provide information regarding repair pathways, variability in repair capacity, and susceptibility to disease. The development of assays to measure urinary DNA lesions offered this potential, although it rapidly became clear that possible contribution from diet and cell turnover may influence urinary lesion levels. Whilst early studies attempted to address these issues, up until now, much of the data appears conflicting. However, recent work from our laboratories, in which human volunteers were fed highly oxidatively modified 15N-labelled DNA demonstrates that diet does not appear to contribute to urinary levels of 8-hydroxyguanine and 7,8-dihydro-8-oxo-2'-deoxyguanosine. Furthermore, we propose that a number of literature reports form an argument against a contribution from cell death. Indeed we, and others, have presented evidence, which strongly suggests the involvement of cell death to be minimal. Taken together, these data would appear to rule out various confounding factors, leaving DNA repair pathways as the principal source of urinary purine, if not DNA, lesions enabling such measurements to be used as indicators of repair.

Generation of 8-hydroxydeoxyguanosine from DNA using rat liver homogenates

In relation to carcinogenesis, aging and other pathologic conditions, urinary 8-hydroxydeoxyguanosine (8OHdG) is widely used as a marker for evaluating the effect of oxidative stress on DNA. Because no reports have described how 8OHdG is generated from DNA in vivo or by biological materials, and how it is excreted into urine, the authors investigated the generation of 8OHdG from DNA, using rat liver homogenate. Oxidatively damaged DNA samples containing different levels of 8OHdG were prepared using ultraviolet irradiation with three different concentrations of riboflavin. Following incubation of damaged DNA samples with rat liver homogenates, the generation of 8OHdG from the DNA was determined using high-performance liquid chromatography with electrochemical detection after ultrafiltration of the incubation mixtures. The generation of 8OHdG was also tested with an anti-8OHdG antibody. The quantity of 8OHdG generated from the DNA by rat liver homogenates was dependent on the 8OHdG levels in the DNA: almost all 8OHdG in the DNA was released as 8OHdG by rat liver homogenates. Generation of 8OHdG correlated with the degradation of DNA. Interestingly, the generated 8OHdG was stable in the presence of rat liver homogenates, whereas deoxyguanosine (dG) rapidly disappeared in the same conditions. Less than 1/10,000 of dG was converted to 8OHdG when dG was incubated with rat liver homogenate. Incubation of 8-hydroxyguanine with rat liver homogenates did not generate 8OHdG. These findings suggest that most of the 8OHdG in DNA is released as 8OHdG during DNA degradation and that, because of its stability, 8OHdG is excreted into urine, thus providing a convenient measure of oxidative damage to DNA.