Oxidative DNA damage in peripheral leukocytes and its association with expression and polymorphisms of hOGG1: A study of adolescents in a high risk region for hepatocellular carcinoma in China

Urinary 8-hydroxydeoxyguanosine in relation to XRCC1 rs25487 G/A (Arg399Gln) and OGG1 rs1052133 C/G (Ser326Cys) DNA repair genes polymorphisms in patients with chronic hepatitis C and related hepatocellular carcinoma

Background and aim: DNA repair represents a protective mechanism against cell injury and cancer. 8-hydroxy-deoxyguanosine (8-OHdG) is the main ROS-induced DNA mutation. The current study aimed to evaluate urinary 8-OHdG levels in patients with chronic hepatitis C virus (HCV) and its related hepatocellular (HCC) and correlate its level to XRCC1 rs25487 G/A and OGG1 rs1052133 C/G gene polymorphisms.

Materials and methods: Urinary 8-OHdG assays were performed using HPLC technique, and XRCC1 rs25487 G/A and OGG1 rs1052133 C/G gene polymorphisms were analyzed by PCR using confronting two-pair primer method (PCR-CTPP) in 200 subjects allocated into 50 chronic HCV patients, 50 HCV-related HCC patients, and 100 controls.

Results: There were significantly increased urinary 8-OHdG levels in HCV-related HCC and chronic HCV patients when compared with the controls (P<0.05 for all). Urinary 8-OHdG was associated with the tumor spread. Regarding, XRCC1 (Arg399Gln), AA (Gln/Gln) genotype and A-allele were more frequent in HCC and chronic HCV patients than in the controls (P<0.05). ORs (95%CI) using the dominant and the recessive genetic models were; 2.1 (1.1–4.1), P=0.032 and 1.9 (1–3.6), P=0.043 respectively. For OGG1 (Ser326Cys), GG (Cys/Cys) genotype and G-allele were increased significantly in chronic HCV and HCC patients compared to the controls (P<0.05). ORs (95%CI) under the dominant and the recessive genetic models were; 2.1 (1.1–4.1), P=0.032 and 1.9 (1–3.8), P=0.049 respectively. Additionally, XRCC1 (AA) and OGG1 (GG) genotypes had significantly increased urinary 8-OHdG levels among patients (P<0.05).

Conclusions: XRCC1 (AA) and OGG1 (GG) could be considered as possible genotypic risk factors for HCV- related HCC development which were associated with significantly high urinary 8-hydroxy-deoxyguanosine levels, thus urinary 8-OHdG could be considered as non-invasive marker in follow-up chronic HCV progression into HCC.

Stress-induced DNA damage biomarkers: applications and limitations

A variety of environmental stresses like chemicals, UV and ionizing radiation and organism's endogenous processes such as replication stress and metabolism can lead to the generation of reactive oxygen and nitrogen species (ROS/RNS) that can attack cellular vital components like DNA, proteins and lipid membranes. Among them, much attention has been focused on DNA since DNA damage plays a role in several biological disorders and aging processes. Thus, DNA damage can be used as a biomarker in a reliable and accurate way to quantify for example radiation exposure and can indicate its possible long term effects and cancer risk. Based on the type of DNA lesions detected one can hypothesize on the most probable mechanisms involved in the formation of these lesions for example in the case of UV and ionizing radiation (e.g., X- or α-, γ-rays, energetic ions, neutrons). In this review we describe the most accepted chemical pathways for DNA damage induction and the different types of DNA lesions, i.e., single, complex DNA lesions etc. that can be used as DNA damage biomarkers. We critically compare DNA damage detection methods and their limitations. In addition, we suggest the use of DNA repair gene products as biomarkes for identification of different types of stresses i.e., radiation, oxidative, or replication stress, based on bioinformatic approaches and meta-analysis of literature data.

A functional Ser326Cys polymorphism in hOGG1 is associated with noise-induced hearing loss in a Chinese population

DNA damage to cochlear hair cells caused by 8-oxoguanine (8-oxoG) is essential for the development of noise-induced hearing loss (NIHL). Human 8-oxoG DNA glycosylase1 (hOGG1) is a key enzyme in the base excision repair (BER) pathway that eliminates 8-oxoG. Many epidemiological and functional studies have suggested that the hOGG1 Ser326Cys polymorphism (rs1052133) is associated with many diseases. The purpose of this investigation was to investigate whether the hOGG1 Ser326Cys polymorphism in the human BER pathway is associated with genetic susceptibility to NIHL in a Chinese population. This polymorphism was genotyped among 612 workers with NIHL and 615 workers with normal hearing. We found that individuals with the hOGG1 Cys/Cys genotype had a statistically significantly increased risk of NIHL compared with those who carried the hOGG1 Ser/Ser genotype (adjusted OR=1.59, 95% CI=1.13-2.25) and this increased risk was more pronounced among the workers in the 15- to 25- and >25-year noise exposure time, 85-92 dB(A) noise exposure level, ever smoking, and ever drinking groups, similar effects were also observed in a recessive model. In summary, our data suggested that the hOGG1 Cys/Cys genotype may be a genetic susceptibility marker for NIHL in the Chinese Han population.

hOGG1 Ser326Cys polymorphism and risk of hepatocellular carcinoma among East Asians: a meta-analysis

Background

The hOGG1 gene encodes a DNA glycosylase enzyme responsible for DNA repair. The Ser326Cys polymorphism in this gene may influence its repair ability and thus plays a role in carcinogenesis. Several case-control studies have been conducted on this polymorphism and its relationship with the risk of hepatocellular carcinoma (HCC) among East Asians. However, their results are inconsistent.

Methods

We performed a meta-analysis of published case-control studies assessing the association of the hOGG1 Ser326Cys polymorphism with HCC risk among East Asians. PubMed, EMBASE, SCI, BIOSIS, CNKI and WanFang databases were searched. A random-effect model was used to calculate odds ratios (ORs) and 95% confidence intervals (95% CIs). Analyses were conducted for additive, dominant and recessive genetic models.

Results

Eight studies were identified involving 2369 cases and 2442 controls assessing the association of the hOGG1 Ser326Cys polymorphism with HCC risk among East Asians. Applying a dominant genetic model, only in the Chinese population, the Cys allele was significantly associated with increased risk of HCC (OR 1.56, 95% CI 1.12–2.17). However, two studies influenced this finding according to sensitivity analysis. Furthermore, considerable heterogeneity and bias existed among Chinese studies.

Conclusion

There is limited evidence to support that the hOGG1 Ser326Cys polymorphism is associated with HCC risk among East Asians. Well-designed and large-sized studies are required to determine this relationship.

Microsomal triglyceride transfer protein gene -493G/T polymorphism and its association with serum lipid levels in Bama Zhuang long-living families in China

BACKGROUND

The -493G/T polymorphism in the microsomal triglyceride transfer protein (MTP) gene is associated with lower serum low-density lipoprotein cholesterol (LDL-C) and triglyceride (TG) levels and longevity in several populations, but the results are inconsistent in different racial/ethnic groups. The current study was to investigate the plausible association of MTP -493G/T polymorphism with serum lipid levels and longevity in Zhuang long-lived families residing in Bama area, a famous home of longevity in Guangxi, China.

METHODS

The MTP -493G/T was genotyped by PCR-restriction fragment length polymorphism in 391 Bama Zhuang long-lived families (BLF, n = 1467, age 56.60 ± 29.43 years) and four control groups recruited from Bama and out-of-Bama area with or without a familial history of exceptional longevity: Bama non-long-lived families (BNLF, n = 586, age 44.81 ± 26.83 years), Bama non-Zhuang long-lived families (BNZLF, n = 444, age 52.09 ± 31.91 years), Pingguo long-lived families (PLF, n = 658, age 50.83 ± 30.30 years), and Pingguo non-long-lived families (PNLF, n = 539, age 38.74 ± 24.69 years). Correlation analyses between genotypes and serum lipid levels and longevity were then performed.

RESULTS

No particularly favorable lipoprotein and clinical phenotypes were seen in BLF as compared to general families in the same area. Instead, the levels of total cholesterol (TC), TG, LDL-C, and the prevalence of dyslipidemia were significantly higher in the three Bama families as compared to the two non-Bama families (P < 0.01 for all). There were no differences in the allelic and genotypic frequencies among the tested cohorts (P > 0.05 for all), but the TT genotype tended to enrich in the three long-lived cohorts from both areas. In addition, the individuals harboring TT genotype exhibited lower LDL-C and TC levels in the overall populations and Bama populations with a region- and sex-specific pattern. Multiple linear regression analyses unraveled that LDL-C levels were correlated with genotypes in Bama combined population, BNLF, and the total population (P < 0.05 for each) but not in Pingguo populations; TC and HDL-C levels were correlated with genotypes in Bama combined population and BLF, respectively (P < 0.05 for each).

CONCLUSIONS

MTP -493G/T polymorphism may play an important role in fashioning the serum lipid profiles of Bama populations, despite no direct association between MTP -493G/T and longevity was detected.

Micronucleus frequency in lymphocytes and 8-hydroxydeoxyguanosine level in plasma of women with polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) has recently been linked with genomic instability and DNA damage. The aim of this study was to test genomic damage in women PCOS, using two different methods for assessing damage in both chromosome and base level. The study was performed on 36 newly diagnosed women with PCOS and 29 healthy women as controls. The micronucleus (MN) analysis used as a biomarker of chromosomal/DNA damage was performed in peripheral lymphocytes by cytokinesis-block method. 8-hydroxydeoxyguanosine (8-OHdG) levels used as a reliable marker of oxidative DNA damage were measured in plasma using an ELISA kit. We found that MN frequencies obtained from lymphocytes of the women with PCOS were significantly higher than those of controls (4.1 +/- 1.0 vs. 2.1 +/- 0.6, P = 0.001), whereas, no differences in 8-OHdG level were found between the patients with PCOS and controls (0.5 +/- 0.3 vs. 0.5 +/- 0.2, P = 0.858). These findings indicate that women with PCOS seem to have increased genomic instability, but do not appear to have oxidative DNA damage despite the increased oxidative stress associated with PCOS.

The effect of ranibizumab versus photodynamic therapy on DNA damage in patients with exudative macular degeneration

PURPOSE

To compare the effect of ranibizumab treatment versus photodynamic therapy (PDT) on single-stranded DNA damage in circulating leukocytes in patients with exudative age-related macular degeneration (AMD).

METHODS

A comparative quantification of single-stranded DNA breaks was performed in circulating leukocytes of AMD patients before and 30 min, 45 min, 60 min, and 24 h after two different modes of therapy: a) PDT; and b) intravitreal ranibizumab injection. DNA breaks lead to smaller pieces of DNA, which in an electrical field, migrate out of the nucleus forming a tail. Damage of an individual cell was quantified as a comet tail moment. The proportion of non-zero values compared to the total number of observations was referred to as "amount of DNA damage" expressed in arbitrary units (AU). Comparisons between time points and study groups were assessed using a linear mixed-effect model.

RESULTS

PDT induced an increase in the amount of single-stranded DNA damage in the circulating leukocytes from 0.2 AU (before treatment) to 0.53 AU (30 min after treatment). This increase was significant (p=0.004). In contrast, after ranibizumab treatment, the DNA damage in the circulating leukocytes remained unchanged.

CONCLUSIONS

PDT purposely induces a local oxidative stress to damage the newly formed vessels. Our results indicate an additional systemic oxidative stress, apparent as amount of single-stranded DNA damage in the circulating leukocytes, for at least 30 min after treatment.

Single nucleotide polymorphisms in DNA repair genes and prostate cancer risk

The specific causes of prostate cancer are not known. However, multiple etiologic factors, including genetic profile, metabolism of steroid hormones, nutrition, chronic inflammation, family history of prostate cancer, and environmental exposures are thought to play significant roles. Variations in exposure to these risk factors may explain interindividual differences in prostate cancer risk. However, regardless of the precise mechanism(s), a robust DNA repair capacity may mitigate any risks conferred by mutations from these risk factors. Numerous single nucleotide polymorphisms (SNPs) in DNA repair genes have been found, and studies of these SNPs and prostate cancer risk are critical to understanding the response of prostate cells to DNA damage. A few SNPs in DNA repair genes are associated with significantly increased risk of prostate cancer; however, in most cases, the effects are moderate and often depend upon interactions among the risk alleles of several genes in a pathway or with other environmental risk factors. This report reviews the published epidemiologic literature on the association of SNPs in genes involved in DNA repair pathways and prostate cancer risk.

The LEC rat: a useful model for studying liver carcinogenesis related to oxidative stress and inflammation

Growing evidence indicates oxidative stress as a mechanism of several diseases including cancer. Oxidative stress can be defined as the imbalance between cellular oxidant species production and antioxidant capability shifted towards the former. Lipid peroxidation is one of the processes that takes place during oxidative stress. Lipid peroxidation products, such as malondialdehyde (MDA) and 4-hydroxy-2-nonenal (HNE), are closely related to carcinogenesis as they are potent mutagens and they have been suggested as modulators of signal pathways related to proliferation and apoptosis, two processes implicated in cancer development. Mechanisms by which oxidative stress leads to tumor formation are still under investigation. The need of suitable in vivo models that could reflect that inflammation-related human carcinogenesis is evident. In this regard, the mutant strain Long Evans Cinnamon-like (LEC) rat provides a promising model for investigation of the relationship between hepatitis induced by oxidative stress and hepatocarcinogenesis because it has been demonstrated to develop spontaneous liver tumor formation related to copper accumulation and oxidative stress. In this review, the findings regarding oxidative stress and its relation with liver pathologies in LEC rats are discussed; we focus on the mechanisms proposed for HNE carcinogenesis.

Estimating the effect of human base excision repair protein variants on the repair of oxidative DNA base damage

Epidemiologic studies have revealed a complex association between human genetic variance and cancer risk. Quantitative biological modeling based on experimental data can play a critical role in interpreting the effect of genetic variation on biochemical pathways relevant to cancer development and progression. Defects in human DNA base excision repair (BER) proteins can reduce cellular tolerance to oxidative DNA base damage caused by endogenous and exogenous sources, such as exposure to toxins and ionizing radiation. If not repaired, DNA base damage leads to cell dysfunction and mutagenesis, consequently leading to cancer, disease, and aging. Population screens have identified numerous single-nucleotide polymorphism variants in many BER proteins and some have been purified and found to exhibit mild kinetic defects. Epidemiologic studies have led to conflicting conclusions on the association between single-nucleotide polymorphism variants in BER proteins and cancer risk. Using experimental data for cellular concentration and the kinetics of normal and variant BER proteins, we apply a previously developed and tested human BER pathway model to (i) estimate the effect of mild variants on BER of abasic sites and 8-oxoguanine, a prominent oxidative DNA base modification, (ii) identify ranges of variation associated with substantial BER capacity loss, and (iii) reveal nonintuitive consequences of multiple simultaneous variants. Our findings support previous work suggesting that mild BER variants have a minimal effect on pathway capacity whereas more severe defects and simultaneous variation in several BER proteins can lead to inefficient repair and potentially deleterious consequences of cellular damage.

Targeting of mutant hogg1 in mammalian mitochondria and nucleus: effect on cellular survival upon oxidative stress

Background

Oxidative damage to mitochondrial DNA has been implicated as a causative factor in a wide variety of degenerative diseases, aging and cancer. The modified guanine, 7,8-dihydro-8-oxoguanine (also known as 8-hydroxyguanine) is one of the major oxidized bases generated in DNA by reactive oxygen species and has gained most of the attention in recent years as a marker of oxidative DNA injury and its suspected role in the initiation of carcinogenesis. 8-hydroxyguanine is removed by hOgg1, a DNA glycosylase/AP lyase involved in the base excision repair pathway.

Methods

We over-expressed wild type and R229Q mutant hOGG1 in the nucleus and mitochondria of cells lacking mitochondrial hOGG1 expression through an expression vector containing nuclear and mitochondrial targeting sequence respectively. We used quantitative real time PCR to analyze mtDNA integrity after exposure to oxidative damaging agents, in cells transfected with or without mitochondrially-targeted mutant hogg1.

Result

Over-expression of wild type hOgg1 in both nucleus and mitochondria resulted in increased cellular survival when compared to vector or mutant over-expression of hOGG1. Interestingly, mitochondrially-targeted mutant hogg1 resulted in more cell death than nuclear targeted mutant hogg1 upon exposure of cells to oxidative damage. Additional we examined mitochondrial DNA integrity after oxidative damage exposure using real-time quantitative PCR. The presence of mutant hogg1 in the mitochondria resulted in reduced mitochondrial DNA integrity when compared to the wild type. Our work indicates that the R229Q hOGG1 mutation failed to protect cells from oxidative damage and that such mutations in cancer may be more detrimental to cellular survival when present in the mitochondria than in the nucleus.

Conclusion

These findings suggest that deficiencies in hOGG1, especially in the mitochondria may lead to reduced mitochondrial DNA integrity, consequently resulting in decreased cell viability.

The changes of oxidative stress and human 8-hydroxyguanine glycosylase1 gene expression in depressive patients with acute leukemia

The results of several recent studies indicated that free radicals are involved in the biochemical mechanisms that underlie neuropsychiatric disorders. In the present study, we evaluated changes in oxidative stress and human 8-hydroxyguanine glycosylase1 gene (hOGG1) expression in depressive patients with acute leukemia. Ninety two cases were assessed using the Zung self-rating depression scale (SDS) and multiple-item questionnaires. We measured total antioxidant capacity (T-AOC) and the concentrations of reactive oxygen species (ROS), superoxide dismutase (SOD), malondialdehyde (MDA) and nitric oxide (NO) during a pre-treatment period. The steady-state expression of hOGG1 mRNA transcripts was monitored. The incidence of depression was 47.83%. There was a significant decrease in serum T-AOC and SOD concentrations in depressive patients compared to the control subjects, whereas the opposite was the case for serum concentrations of ROS, NO and MDA. Real-time polymerase chain reaction (PCR) revealed that hOGG1 mRNA expression was greater in depressive patients than in the controls. Person correlation analysis revealed that depression was correlated positively with sex, the course of the disease and hOGG1 mRNA expression; depression was correlated negatively with T-AOC. Based on these results, we conclude that the antioxidant system is impaired in leukemic patients with affective disorders. Therefore, oxidative stress may play an important role in the pathophysiology of depression.

Monocyte telomere shortening and oxidative DNA damage in type 2 diabetes

OBJECTIVE

Telomeres are DNA sequences necessary for DNA replication, which shorten at cell division at a rate related to levels of oxidative stress. Once shortened to a critical length, cells are triggered into replicative senescence. Type 2 diabetes is associated with oxidative DNA damage, and we hypothesized that telomere shortening would characterize type 2 diabetes.

RESEARCH DESIGN AND METHODS

We studied 21 male type 2 diabetic subjects (mean age 61.2 years, mean HbA(1c) 7.9%) selected to limit confounding effects on telomere length and 29 matched control subjects. Telomere length was measured in peripheral venous monocyte and T-cells (naïve and memory) by fluorescent in situ hybridization and oxidative DNA damage by flow cytometry of oxidized DNA bases. Peripheral insulin resistance (homeostasis model assessment) and high-sensitivity C-reactive protein (hsCRP) were measured.

RESULTS

Mean monocyte telomere length in the diabetic group was highly significantly lower than in control subjects (4.0 [1.1] vs. 5.5 [1.1]; P < 0.0001), without significant differences in lymphocyte telomere length. There was a trend toward increased oxidative DNA damage in all diabetes cell types examined and a significant inverse relationship between oxidative DNA damage and telomere length (r = -0.55; P = 0.018) in the diabetic group. Telomere length was unrelated to plasma CRP concentration or insulin resistance.

CONCLUSIONS

Monocyte telomere shortening in type 2 diabetes could be due to increased oxidative DNA damage to monocyte precursors during cell division. This data suggests that monocytes adhering to vascular endothelium and entering the vessel wall in type 2 diabetes are from a population with shorter telomeres and at increased risk of replicative senescence within vascular plaque.

Polymorphic variation in hOGG1 and risk of cancer: a review of the functional and epidemiologic literature

The gene encoding human 8-oxoguanine glycosylase 1 (hOGG1) is involved in DNA base excision repair. The encoded DNA glycosylase excises 7,8-dihydro-8-oxoguanine (8-OHdG), a highly mutagenic base produced in DNA as a result of exposure to reactive oxygen species (ROS). Polymorphisms in this gene may alter glycosylase function and an individual's ability to repair damaged DNA, possibly resulting in genetic instability that can foster carcinogenesis. In order to elucidate the possible impact of polymorphisms in hOGG1, we performed a literature review of both functional and epidemiologic studies that assessed the effects of these polymorphisms on repair function, levels of oxidative DNA damage, or associations with cancer risk. Fourteen functional studies and 19 epidemiologic studies of breast, colon, esophageal, head and neck, lung, nasopharyngeal, orolaryngeal, prostate, squamous cell carcinoma of the head and neck (SCCHN), and stomach cancers were identified. Although the larger functional studies suggest reduced repair function with variant alleles in hOGG1, the evidence is generally inconclusive. There is some epidemiologic evidence that risk for esophageal, lung, nasopharyngeal, orolaryngeal, and prostate is related to hOGG1 genotype, whereas risk of breast cancer does not appear related. In studies that explored potential interactions with environmental factors, cancer risk for hOGG1 genotypes differed depending on exposure, especially for colon cancer. In summary, there is limited evidence that polymorphisms in hOGG1 affect repair function and carcinogenesis. Larger, well-designed functional and epidemiologic studies are needed to clarify these relationships, especially with respect to interactions with other DNA repair enzymes and interactions with environmental factors that increase carcinogenic load.