Accumulation of 8-oxo-deoxyguanosine in cardiovascular tissues with the development of hypertension

Oxidative Stress: Role and Response of Short Guanine Tracts at Genomic Locations

Over the decades, oxidative stress has emerged as a major concern to biological researchers. It is involved in the pathogenesis of various lifestyle-related diseases such as hypertension, diabetes, atherosclerosis, and neurodegenerative diseases. The connection between oxidative stress and telomere shortening via oxidative guanine lesion is well documented. Telomeres are confined to guanine rich ends of chromosomes. Owing to its self-association properties, it adopts G-quadruplex structures and hampers the overexpression of telomerase in the cancer cells. Guanine, being the most oxidation prone nucleobase, when structured in G-quadruplex entity, is found to respond peculiarly towards oxidative stress. Interestingly, this non-Watson-Crick structural feature exists abundantly in promoters of various oncogenes, exons and other genomic locations. The involvement of G-quadruplex architecture in oncogene promoters is well recognized in gene regulation processes. Development of small molecules aimed to target G-quadruplex structures, have found to alter the overexpression of oncogenes. The interaction may lead to the obstruction of diseased cell having elevated level of reactive oxygen species (ROS). Thus, presence of short guanine tracts (Gn) forming G-quadruplexes suggests its critical role in oxidative genome damage. Present review is a modest attempt to gain insight on the association of oxidative stress and G-quadruplexes, in various biological processes.

The mechanism of RNA oxidation involved in the development of heart failure

Heart failure (HF) has become a global public health problem due to its unclear pathogenesis. Our previous studies have found that RNA oxidation is associated with the occurrence and development of a variety of chronic diseases in the elderly, but whether RNA oxidation is related to the pathogenesis of HF remains unclear. Male Dahl salt-sensitive rats (DSSR) were divided into 8% NaCl groups and 0.3% NaCl groups. The blood pressure of DSSR, HE staining of cardiac tissue, cardiac function index of colour Doppler echocardiography and plasma N-terminal probrain Natriuretic Peptide (NT-ProBNP) were used to evaluate the model making. The levels of 8-hydroxyguanosine (8-oxoGsn) and 8-hydroxydeoxyguanosine (8-oxodGsn) in myocardium and urine of DSSR were determined by high-performance liquid chromatography-mass spectrometry (LC-MS/MS). The expression of ERK-MAPK pathway and MTH1 was detected by Western blot (WB). Rats in the 8% NaCl group developed heart failure symptoms such as increased blood pressure, myocardial hypertrophy, decreased diastolic function, and increased plasma NT-ProBNP. The content of 8-oxoGsn in urine and heart tissue also increased, which was positively correlated with the related indicators of heart failure. This process is also accompanied by the sequential activation of ERK-MAPK pathway molecules and the increase of MTH1. The mechanism of RNA oxidation and inhibition is related to the occurrence and development of HF, which may be involved through ERK-MAPK pathway.

Disruption of xanthine oxidoreductase gene attenuates renal ischemia reperfusion injury in mice

AIMS

We examined the roles of xanthine oxidoreductase (XOR) in renal ischemia reperfusion (IR) injury.

MAIN METHODS

XOR+/+ and XOR+/- mice were subjected to 24-h reperfusion after a 45-min bilateral renal artery occlusion or sham operation. We evaluated the renal damage based on the concentrations of blood urea nitrogen (BUN) and serum creatinine (Cr), and histological changes were detected by PAS staining. Xanthine dehydrogenase, oxidase (XO) and XOR activities, amounts of blood and urine 8-OHdG, and expressions of TNF-α and MCP-1 mRNA were examined. F4/80 and nitrotyrosine-positive cells were assessed by immunohistochemical staining.

KEY FINDINGS

The BUN and Cr concentrations in the XOR+/+IR mice were increased significantly compared to those in XOR+/-IR and allopurinol-treated XOR+/+IR mice. XO and XOR activity, which were increased in IR mice, were reduced in the allopurinol-treated XOR+/+IR and XOR+/-IR mice compared to the XOR+/+IR mice. The concentrations of blood and urine 8-OHdG, and the expressions of MCP-1 and TNF-α mRNA were increased significantly in the XOR+/+IR mice compared to those in the XOR+/-IR mice. The histological analysis revealed that the XOR+/-IR and allopurinol-treated XOR+/+IR mice showed less tubular injury than the XOR+/+IR mice in the cortex regions, with the reduction of inflammation and oxidative stress assessed by the immunohistological staining for F4/80 and nitrotyrosine.

SIGNIFICANCE

Both the disruption of XOR gene in XOR+/- mice and the reduction of XOR activity in allopurinol-treated XOR+/+IR mice attenuated renal tissue injury in this IR model. Reduced XOR activity during renal IR could be a beneficial treatment target.

Oxidized DNA induces an adaptive response in human fibroblasts

Cell-free DNA (cfDNA) released from dying cells contains a substantial proportion of oxidized nucleotides, thus, forming cfDNA(OX). The levels of cfDNA(OX) are increased in the serum of patients with chronic diseases. Oxidation of DNA turns it into a stress signal. The samples of genomic DNA (gDNA) oxidized by Н2О2in vitro (gDNA(OX)) induce effects similar to that of DNA released from damaged cells. Here we describe the effects of gDNA(OX) on human fibroblasts cultivated in the stressful conditions of serum withdrawal. In these cells, gDNA(OX) evokes an adaptive response that leads to an increase in the rates of survival in serum starving cell populations as well as in populations irradiated at the dose of 1.2Gy. These effects are not seen in control populations of fibroblasts treated with non-modified gDNA. In particular, the exposure to gDNA(OX) leads to a decrease in the expression of the proliferation marker Ki-67 and an increase in levels of РСNА, a decrease in the proportion of subG1- and G2/M cells, a decrease in proportion of cells with double strand breaks (DSBs). Both gDNA(OX) and gDNA suppress the expression of DNA sensors TLR9 and AIM2 and up-regulate nuclear factor-erythroid 2 p45-related factor 2 (NRF2), while only gDNA(OX) inhibits NF-κB signaling. gDNA(OX) is a model for oxidized cfDNA(OX) that is released from the dying tumor cells and being carried to the distant organs. The systemic effects of oxidized DNA have to be taken into account when treating tumors. In particular, the damaged DNA released from irradiated cells may be responsible for an abscopal effects and a bystander mediated adaptive response seen in some cancer patients. These results indicate the necessity for the further study of the effects of oxidized DNA in both in vitro and in vivo systems.

Association of oxidative DNA damage and C-reactive protein in women at risk for cardiovascular disease

OBJECTIVE

The aim of the current study was to examine the relationship between clinical markers of inflammation and 8-oxo-7,8-dihydro-2'deoxyguanosine (8-oxodG), an oxidative stress marker, in middle-aged women drawn from the HANDLS study, a longitudinal epidemiological study.

METHODS AND RESULTS

We examined commonly assayed markers of inflammation, the DNA base adduct 8-oxodG, a marker of oxidative stress, and cardiovascular risk factors in a cohort of women matched on age and race in 3 groups (n=39 per group) who had low (<3 mg/L) high-sensitivity C-reactive protein (hsCRP), mid (>3-20 mg/L), and high (>20 mg/L) hsCRP. We found a significant relationship between hsCRP level and the oxidative stress marker, 8-oxodG. 8-oxodG was positively correlated with systolic blood pressure, pulse pressure, and interleukin-23. hsCRP was associated with obesity variables, high-density lipoprotein, serum insulin levels, interleukin-12p70 and intracellular adhesion molecule-1. Incubation of primary human endothelial cells with hsCRP generated reactive oxygen species in vitro. Furthermore, hsCRP specifically induced DNA base lesions, but not other forms of DNA damage, including single and double strand breaks.

CONCLUSIONS

These data suggest that in women 8-oxodG is associated with hsCRP and is independently related to select cardiovascular risk factors. Our data in women suggest that hsCRP may contribute to cardiovascular disease by increasing oxidative stress.

Immunochemical detection of oxidatively damaged DNA

Oxidatively damaged DNA is implicated in various diseases, including neurodegenerative disorders, cancer, diabetes, cardiovascular and inflammatory diseases as well as aging. Several methods have been developed to detect oxidatively damaged DNA. They include chromatographic techniques, the Comet assay, (32)P-postlabelling and immunochemical methods that use antibodies to detect oxidized lesions. In this review, we discuss the detection of 8-oxo-7,8-dihydro-29-deoxyguanosine (8-oxodG), the most abundant oxidized nucleoside. This lesion is frequently used as a marker of exposure to oxidants, including environmental pollutants, as well as a potential marker of disease progression. We concentrate on studies published between the years 2000 and 2011 that used enzyme-linked immunosorbent assay (ELISA) and immunohistochemistry to detect 8-oxodG in humans, laboratory animals and in cell lines. Oxidative damage observed in these organisms resulted from disease, exposure to environmental pollutants or from in vitro treatment with various chemical and physical factors.

Measurement of oxidatively generated base damage in cellular DNA

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

Superoxide anion and hydrogen peroxide-induced signaling and damage in angiotensin II and aldosterone action

The formation of reactive oxygen species (ROS) can be induced by xenobiotic substances, such as redox cycling molecules, but also by endogenous substances such as hormones and cytokines. Recent research shows the importance of ROS in cellular signaling. Here, the signaling pathways of the two blood pressure-regulating hormones angiotensin II and aldosterone are presented, focusing on both their physiological effects and the change of signaling owing to the action of increased concentrations or prolonged exposure. When present in high concentrations, both angiotensin II and aldosterone, as various other endogenous substances, activate NADPH oxidase, which produces superoxide. In this review the generation of superoxide anions and hydrogen peroxide in cells stimulated with angiotensin II or aldosterone, as well as the subsequently induced signaling processes and DNA damage is discussed.

The 8-oxoguanine glycosylase I (hOGG1) Ser326Cys variant affects the susceptibility to multi-vessel disease in Taiwan coronary artery disease patients

8-hydroxydeoxyguanosine, the key lesion of oxidative DNA damage, contributes to the development of coronary artery disease (CAD). In humans, 8-hydroxydeoxyguanosine is repaired by the enzyme 8-oxoguanine glycosylase I (hOGG1). We investigated the association between the hOGG1 Ser(326)Cys polymorphism and the presence and the severity of CAD in a Taiwan population. Genotypes of the hOGG1 Ser(326)Cys polymorphism were determined from 1397 participants enrolled in this study (378 CAD patients and 1019 controls). CAD severity was indicated both by number of vessels affected (single-vessel disease, SVD vs. multi-vessel disease, MVD), and by individual diffuse score. Real-time polymerase chain reaction was used to determine genotype, using allele-specific TaqMan probes. We found that presence of the hOGG1 Ser(326)Cys polymorphism was associated with a significantly increased risk of CAD and multi-vessel disease when assuming a dominant model of inheritance (OR: 1.52 [95%:1.082~2.133], p=0.015; OR: 2.26 [95%:1.232~4.156], p=0.007). This result was confirmed by multivariate analysis, after adjustment for age, gender, body-mass index, diabetes hypertension, hypercholesterolemia and smoking (OR: 1.78 [95%:1.127~2.806], p<0.005; OR: 2.44 [95%:1.276~4.651], p<0.001). In the present study, hOGG1 Ser(326)Cys polymorphism is a novel genetic marker to be independently associated with the development and severity of CAD in Taiwanese population.

Oxidation in the nucleotide pool, the DNA damage response and cellular senescence: Defective bricks build a defective house

Activation of persistent DNA damage response (DDR) signaling is associated with the induction of a permanent proliferative arrest known as cellular senescence, a phenomenon intrinsically linked to both tissue aging as well as tumor suppression. The DNA damage observed in senescent cells has been attributed to elevated levels of reactive oxygen species (ROS), failing DNA damage repair processes, and/or oncogenic activation. It is not clear how labile molecules such as ROS are able to damage chromatin-bound DNA to a sufficient extent to invoke persistent DNA damage and DDR signaling. Recent evidence suggests that the nucleotide pool is a significant target for oxidants and that oxidized nucleotides, once incorporated into genomic DNA, can lead to the induction of a DNA strand break-associated DDR that triggers senescence in normal cells and in cells sustaining oncogene activation. Evasion of this DDR and resulting senescence is a key step in tumor progression. This review will explore the role of oxidation in the nucleotide pool as a major effector of oxidative stress-induced genotoxic damage and DDR in the context of cellular senescence and tumorigenic transformation.

Programmed cell death triggered by nucleotide pool damage and its prevention by MutT homolog-1 (MTH1) with oxidized purine nucleoside triphosphatase

Accumulation of oxidized bases such as 8-oxoguanine in either nuclear or mitochondrial DNA triggers various cellular dysfunctions including mutagenesis, and programmed cell death or senescence. Recent studies have revealed that oxidized nucleoside triphosphates such as 8-oxo-dGTP in the nucleotide pool are the main source of oxidized bases accumulating in the DNA of cells under oxidative stress. To counteract such deleterious effects of nucleotide pool damage, mammalian cells possess MutT homolog-1 (MTH1) with oxidized purine nucleoside triphosphatase and related enzymes, thus minimizing the accumulation of oxidized bases in cellular DNA. Depletion or increased expression of the MTH1 protein have revealed its significant roles in avoiding programmed cell death or senescence as well as mutagenesis, and accumulating evidences indicate that MTH1 is involved in suppression of degenerative disorders such as neurodegeneration.

Stable-isotope dilution LC–MS for quantitative biomarker analysis

The ability to conduct validated analyses of biomarkers is critically important in order to establish the sensitivity and selectivity of the biomarker in identifying a particular disease. The use of stable-isotope dilution (SID) methodology in combination with LC–MS/MS provides the highest possible analytical specificity for quantitative determinations. This methodology is now widely used in the discovery and validation of putative exposure and disease biomarkers. This review will describe the application of SID LC–MS methodology for the analysis of small-molecule and protein biomarkers. It will also discuss potential future directions for the use of this methodology for rigorous biomarker analysis.

Vitamin C prevents DNA damage induced by renovascular hypertension in multiple organs of Wistar rats

The aim of this study was to investigate, through the single-cell gel (comet) assay, whether vitamin C is able to protect against renovascular hypertension-induced genotoxicity in multiple organs. A total of 32 male Wistar rats were divided into four groups: negative control (n = 6); animals treated with vitamin C (n = 6); hypertensive rats (n = 10) and hypertensive rats and treated with vitamin C (n = 10). Hypertension was induced as a result of partial obstruction of the left renal artery by means of a silver clip during 6 weeks. Vitamin C was administered at 150 mg/kg during 7 consecutive days before the end of the experimental period. The results showed that vitamin C was able to protect blood cells against hypertension-induced genotoxicity. Brain, liver and heart cells were also protected by vitamin C following hypertension-induced genotoxic damage. Regarding blood pressure, vitamin C reduced the hypertensive state. In conclusion, our results suggest that vitamin C can prevent hypertension-induced DNA damage in blood, liver, brain and heart cells as well as to normalize the blood pressure of rats.

Xanthine oxidoreductase depletion induces renal interstitial fibrosis through aberrant lipid and purine accumulation in renal tubules

Xanthine oxidoreductase (XOR) is an enzyme responsible for purine degradation, reactive oxygen species production, and adipogenesis. XOR gene-disrupted (XOR(-/-)) mice demonstrate renal failure and early death within several months. The aim of this study was to elucidate the mechanism of renal damage in XOR(-/-) mice and to determine the physiological role of XOR in the kidney. Histological analysis revealed that renal tubular damage in XOR(-/-) mice was accompanied by deposition of crystals and lipid-rich substances. Triglyceride content in renal homogenates was significantly increased in XOR(-/-) mice. The level of lipogenesis-related gene expression was comparable in XOR(+/+) and XOR(-/-) mice, whereas the expression of adipogenesis-related gene expression was significantly elevated in XOR(-/-) mice. Urinary excretions of xanthine and hypoxanthine were markedly elevated in XOR(-/-) mice. Immunohistochemical analysis, Western blotting, and real time RT-PCR revealed that various markers of fibrosis, inflammation, ischemia, and oxidative stress were increased in XOR(-/-) mice. Finally, we demonstrate that primary renal epithelial cells from XOR(-/-) mice are more readily transformed to myofibroblasts, which is a marker of increased epithelial mesenchymal transition. These results suggest that XOR gene disruption induced the depletion of uric acid and the accumulation of triglyceride-rich substances, xanthine, and hypoxanthine in the renal tubules. We believe that these changes contribute to a complex cellular milieu characterized by inflammation, tissue hypoxia, and reactive oxygen species production, ultimately resulting in renal failure through increased renal interstitial fibrosis.

Analysis of 7,8-dihydro-8-oxo-2'-deoxyguanosine in cellular DNA during oxidative stress

Analysis of cellular 7,8-dihydro-8-oxo-2′-deoxyguanosine (8-oxo-dGuo) as a biomarker of oxidative DNA damage has been fraught with numerous methodological problems. This is primarily due to artifactual oxidation of dGuo that occurs during DNA isolation and hydrolysis. Therefore, it has become necessary to rely on using the comet assay, which is not necessarily specific for 8-oxo-dGuo. A highly specific and sensitive method based on immunoaffinity purification and stable isotope dilution liquid chromatography (LC)-multiple reaction monitoring (MRM)/mass spectrometry (MS) that avoids artifact formation has now been developed. Cellular DNA was isolated using cold DNAzol (a proprietary product that contains guanidine thiocyanate) instead of chaotropic- or phenol-based methodology. Chelex-treated buffers were used to prevent Fenton chemistry-mediated generation of reactive oxygen species (ROS) and artifactual oxidation of DNA bases. Deferoxamine was also added to all buffers in order to complex any residual transition metal ions remaining after Chelex treatment. The LC-MRM/MS method was used to determine that the basal 8-oxo-dGuo level in DNA from human bronchoalveolar H358 cells was 2.2 ± 0.4 8-oxo-dGuo/10⁷ dGuo (mean ± standard deviation) or 5.5 ± 1.0 8-oxo-dGuo/10⁸ nucleotides. Similar levels were observed in human lung adenocarcinoma A549 cells, mouse hepatoma Hepa-1c1c7 cells, and human HeLa cervical epithelial adenocarcinoma cells. These values are an order of magnitude lower than is typically reported for basal 8-oxo-dGuo levels in DNA as determined by other MS- or chromatography-based assays. H358 cells were treated with increasing concentrations of potassium bromate (KBrO₃) as a positive control or with the methylating agent methyl methanesulfonate (MMS) as a negative control. A linear dose−response for 8-oxo-dGuo formation (r² = 0.962) was obtained with increasing concentrations of KBrO₃ in the range of 0.05 mM to 2.50 mM. In contrast, no 8-oxo-dGuo was observed in H358 cell DNA after treatment with MMS. At low levels of oxidative DNA damage, there was an excellent correlation between a comet assay that measured DNA single strand breaks (SSBs) after treatment with human 8-oxo-guanine glycosylase-1 (hOGG1) when compared with 8-oxo-dGuo in the DNA as measured by the stable isotope dilution LC-MRM/MS method. Availability of the new LC-MRM/MS assay made it possible to show that the benzo[a]pyrene (B[a]P)-derived quinone, B[a]P-7,8-dione, could induce 8-oxo-dGuo formation in H358 cells. This most likely occurred through redox cycling between B[a]P-7,8-dione and B[a]P-7,8-catechol with concomitant generation of DNA damaging ROS. In keeping with this concept, inhibition of catechol-O-methyl transferase (COMT)-mediated detoxification of B[a]P-7,8-catechol with Ro 410961 caused increased 8-oxo-dGuo formation in the H358 cell DNA.

5-Lipoxygenase-mediated endogenous DNA damage

Lipoxygenases (LOs) convert polyunsaturated fatty acids into lipid hydroperoxides. Homolytic decomposition of lipid hydroperoxides gives rise to endogenous genotoxins such as 4-oxo-2(E)-nonenal, which cause the formation of mutagenic DNA adducts. Chiral lipidomics analysis was employed to show that a 5-LO-derived lipid hydroperoxide was responsible for endogenous DNA-adduct formation. The study employed human lymphoblastoid CESS cells, which expressed both 5-LO and the required 5-LO-activating protein (FLAP). The major lipid peroxidation product was 5(S)-hydroperoxy-6,8,11,14-(E,Z,Z,Z)-eicosatetraenoic acid, which was analyzed as its reduction product, 5(S)-hydroxy-6,8,11,14-(E,Z,Z,Z)-eicosatetraenoic acid (5(S)-HETE)). Concentrations of 5(S)-HETE increased from 0.07 +/- 0.01 to 45.50 +/- 4.05 pmol/10(7) cells upon stimulation of the CESS cells with calcium ionophore A23187. There was a concomitant increase in the 4-oxo-2(E)-nonenal-derived DNA-adduct, heptanone-etheno-2'-deoxyguanosine (HepsilondGuo) from 2.41 +/- 0.35 to 6.31 +/- 0.73 adducts/10(7) normal bases. Biosynthesis of prostaglandins, 11(R)-hydroxy-5,8,12,14-(Z,Z,E,Z)-eicosatetraenoic acid, and 15(R,S)-hydroxy-5,8,11,13-(Z,Z,Z,E)-eicosatetraenoic acid revealed that there was cyclooxygenase (COX) activity in the CESS cells. Western blot analysis revealed that COX-1 was expressed by the cells, but there was no COX-2 or 15-LO-1. FLAP inhibitor reduced HepsilondGuo-adducts and 5(S)-HETE to basal levels. In contrast, aspirin, which had no effect on 5(S)-HETE, blocked the formation of prostaglandins, 15-HETE, and 11-HETE but did not inhibit HepsilondGuo-adduct formation. These data showed that 5-LO was the enzyme responsible for the generation of the HepsilondGuo DNA-adduct in CESS cells.

Chronic renal failure induces genetic instability in multiple organs of Wistar rats

BACKGROUND

Taking into consideration the strong evidence for a relationship between DNA damage and carcinogenesis, the aim of this study was to investigate whether blood, liver, heart, kidney and brain are particularly sensitive organs for DNA damaging during chronic renal disease by the single-cell gel (comet) assay to predict genetic instability induced by this pathological condition.

METHODS

A total of 18 male Wistar rats were divided into two groups: negative control (n = 8) and experimental (n = 10), in which was submitted to the 5/6 renal mass ablation by ligation of two or three branches of the left renal artery and total right nephrectomy during 8 weeks.

RESULTS

The results showed that chronic renal disease was able to induce genetic damage in blood, heart, liver and kidney cells as depicted by the mean tail moment. No genetic damage was induced in brain cells, i.e. no significant statistically differences (P > 0.05) were noticed when compared to negative control.

CONCLUSION

In conclusion, our results suggest that chronic renal failure could contribute to the damage of DNA at all organs evaluated, except to the brain cells. As DNA damage is an important step in events leading to carcinogenesis, this study represents a relevant contribution to the correct evaluation of the potential health risks associated with kidney disease.