Analyses of oxidative DNA damage among coal vendors via single cell gel electrophoresis and quantification of 8-hydroxy-2'-deoxyguanosine

Looking at the development status of Nigeria and other developing nations, most low-income and rural households often use coal as a source of energy which necessitates its trade very close to the communities. Moreover, the effects of exposure to coal mining activities are rarely explored or yet to be studied, not to mention the numerous street coal vendors in Nigeria. This study investigated the oxidative stress levels in serum and urine through the biomarker 8-OHdG and DNA damage via single cell gel electrophoresis (alkaline comet assay). Blood and urine levels of 8-OHdG from 130 coal vendors and 130 population-based controls were determined by ELISA. Alkaline comet assay was also performed on white blood cells for DNA damage. The average values of 8-OHdG in serum and urine of coal vendors were 22.82 and 16.03 ng/ml respectively, which were significantly greater than those detected in controls (p < 0.001; 15.46 and 10.40 ng/ml of 8-OHdG in serum and urine respectively). The average tail length, % DNA in tail and olive tail moment were 25.06 μm, 18.71% and 4.42 respectively for coal vendors. However, for controls, the average values were 4.72 μm, 3.63% and 1.50 for tail length, % DNA in tail and olive tail moment respectively which were much lower than coal vendors (p < 0.001). Therefore, prolonged exposure to coal dusts could lead to higher serum and urinary 8-OHdG and significant DNA damage in coal vendors observed in tail length, % DNA in tail, and olive tail moment by single cell gel electrophoresis. It is therefore established that coal vendors exhibit a huge risk from oxidative stress and assessment of 8-OHdG with single cell gel electrophoresis has proven to be a feasible tool as biomarkers of DNA damage.

MicroRNAs as Regulators of Radiation-Induced Oxidative Stress

microRNAs (miRNAs) represent small RNA molecules involved in the regulation of gene expression. They are implicated in the regulation of diverse cellular processes ranging from cellular homeostasis to stress responses. Unintended irradiation of the cells and tissues, e.g., during medical uses, induces various pathological conditions, including oxidative stress. miRNAs may regulate the expression of transcription factors (e.g., nuclear factor erythroid 2 related factor 2 (Nrf2), nuclear factor kappa B (NF-κB), tumor suppressor protein p53) and other redox-sensitive genes (e.g., mitogen-activated protein kinase (MAPKs), sirtuins (SIRTs)), which trigger and modulate cellular redox signaling. During irradiation, miRNAs mainly act with reactive oxygen species (ROS) to regulate the cell fate. Depending on the pathway involved and the extent of oxidative stress, this may lead to cell survival or cell death. In the context of radiation-induced oxidative stress, miRNA-21 and miRNA-34a are among the best-studied miRNAs. miRNA-21 has been shown to directly target superoxide dismutase (SOD), or NF-κB, whereas miRNA-34a is a direct regulator of NADPH oxidase (NOX), SIRT1, or p53. Understanding the mechanisms underlying radiation-induced injury including the involvement of redox-responsive miRNAs may help to develop novel approaches for modulating the cellular response to radiation exposure.

Involvement of oxidative stress in orofacial mechanical pain hypersensitivity following neonatal maternal separation in rats

Patients with persistent pain have sometimes history of physical abuse or neglect during infancy. However, the pathogenic mechanisms underlying orofacial pain hypersensitivity associated with early-life stress remain unclear. The present study focused on oxidative stress and investigated its role in pain hypersensitivity in adulthood following early-life stress. To establish an early-life stress model, neonatal pups were separated with their mother in isolated cages for 2 weeks. The mechanical head-withdrawal threshold (MHWT) in the whisker pad skin of rats received maternal separation (MS) was lower than that of non-MS rats at postnatal week 7. In MS rats, the expression of 8-hydroxy-deoxyguanosine, a marker of DNA oxidative damage, was enhanced, and plasma antioxidant capacity, but not mitochondrial complex I activity, decreased compared with that in non-MS rats. Reactive oxygen species (ROS) inactivation and ROS-sensitive transient receptor potential ankyrin 1 (TRPA1) antagonism in the whisker pad skin at week 7 suppressed the decrease of MHWT. Corticosterone levels on day 14 increased in MS rats. Corticosterone receptor antagonism during MS periods suppressed the reduction in antioxidant capacity and MHWT. The findings suggest that early-life stress potentially induces orofacial mechanical pain hypersensitivity via peripheral nociceptor TRPA1 hyperactivation induced by oxidative stress in the orofacial region.

Myricetin causes site-specific DNA damage via reactive oxygen species generation by redox interactions with copper ions

Myricetin (MYR), found in tea and berries, may have preventive effects on diseases, including Alzheimer's disease and cancer. However, MYR is also a mutagen, inducing DNA damage in the presence of metal ions. We have studied the molecular mechanisms of DNA damage by MYR in the presence of Cu(II) (MYR+Cu). Using 32P-5'-end-labeled DNA fragments, we analyzed site-specific DNA damage caused by MYR+Cu. MYR+Cu caused concentration-dependent DNA strand breaks and base alterations, leading to cleavage of DNA at thymine, cytosine, and guanine nucleotides. Formation of the oxidative DNA damage indicator, 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), in calf thymus DNA was increased by MYR+Cu. The production of 8-oxodG in MYR-treated HL-60 cells was significantly higher than in HP100 cells, which are more resistant to H2O2 than are HL-60 cells. Reactive oxygen species (ROS) scavengers were used to elucidate the mechanism of DNA damage. DNA damage was not inhibited by typical free hydroxyl radical (•OH) scavengers such as ethanol, mannitol, or sodium formate. However, methional, catalase, and bathocuproine inhibited DNA damage induced by MYR+Cu. These results suggest that H2O2, Cu(I), and ROS other than •OH are involved in MYR+Cu-induced DNA damage. We conclude that the Cu(I)/Cu(II) redox cycle and concomitant H2O2 production via autoxidation of MYR generate a complex of H2O2 and Cu(I), probably Cu(I)-hydroperoxide, which induces oxidative DNA damage.

AOP report: Development of an adverse outcome pathway for oxidative DNA damage leading to mutations and chromosomal aberrations

The Genetic Toxicology Technical Committee (GTTC) of the Health and Environmental Sciences Institute (HESI) is developing adverse outcome pathways (AOPs) that describe modes of action leading to potentially heritable genomic damage. The goal was to enhance the use of mechanistic information in genotoxicity assessment by building empirical support for the relationships between relevant molecular initiating events (MIEs) and regulatory endpoints in genetic toxicology. Herein, we present an AOP network that links oxidative DNA damage to two adverse outcomes (AOs): mutations and chromosomal aberrations. We collected empirical evidence from the literature to evaluate the key event relationships between the MIE and the AOs, and assessed the weight of evidence using the modified Bradford-Hill criteria for causality. Oxidative DNA damage is constantly induced and repaired in cells given the ubiquitous presence of reactive oxygen species and free radicals. However, xenobiotic exposures may increase damage above baseline levels through a variety of mechanisms and overwhelm DNA repair and endogenous antioxidant capacity. Unrepaired oxidative DNA base damage can lead to base substitutions during replication and, along with repair intermediates, can also cause DNA strand breaks that can lead to mutations and chromosomal aberrations if not repaired adequately. This AOP network identifies knowledge gaps that could be filled by targeted studies designed to better define the quantitative relationships between key events, which could be leveraged for quantitative chemical safety assessment. We anticipate that this AOP network will provide the building blocks for additional genotoxicity-associated AOPs and aid in designing novel integrated testing approaches for genotoxicity.

Effects of smoking cessation on biological monitoring markers in urine

INTRODUCTION

Urinary nicotine and cotinine levels are often measured as biomarkers for tobacco smoke exposure. However, these biomarkers are not appropriate to evaluate the effects of quitting smoking for several days, because of their short half-lives. In this study, we focused on the changes in the urinary 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) levels of 55 patients in a smoking cessation program, because of the long half-life. At the same time, urinary 7-methylguanine (m7Gua) and 8-hydroxy-2'-deoxyguanosine (8-OHdG), as DNA damage markers of cigarette smoking, were also measured.

RESULTS

In the subjects who completed the quit-smoking program (18 subjects out of 55), the urinary nicotine and cotinine levels decreased to 1.7 and 0.2% at 8 weeks after the first visit to the clinic. By contrast, the NNAL levels decreased to 12.3% at 8 weeks after quitting smoking. During the same period, the urinary m7Gua levels significantly decreased, from 27.32 μg/mg creatinine to 14.17 μg/mg creatinine by the elimination of subjects who showed increased levels of NNAL during the smoking cessation program. The 8-OHdG levels were also reduced within the same period, but were not significantly different. From the all data analysis, the urinary levels of cotinine and NNAL positively correlated with the level of m7Gua.

CONCLUSIONS

NNAL may be an appropriate exposure marker for evaluating the smoking status of patients in a smoking cessation program. The urinary cotinine and NNAL levels positively correlated with the m7Gua levels.

Assessments of DNA Damage and Radiation Exposure Dose in Cattle Living in the Contaminated Area Caused by the Fukushima Nuclear Accident

Since the Fukushima nuclear accident in 2011, various abnormalities have been reported in animals living in the contaminated area. In the present study, we examined DNA damage in cattle living in the "difficult-to-return zone" by 8-hydroxy-2'-deoxyguanosine, comet, and micronucleus assays using their peripheral blood. The radiation exposure dose rate at the sampling time was approximately 0.25 or 0.38 mGy/day and the cumulative dose was estimated at approximately 1000 mGy. Significant increase in DNA damage was not detected by any of the three methods. As DNA damage is a stochastic effect of radiation, it might be occurring in animals living in the contaminated area. However, the present results suggest that radiation-induced DNA damage in the cattle did not increase to the level detectable by the assays we used due to the low dose rate in this area.

Serum 8-Hydroxy-2'-Deoxyguanosine Level as a Potential Biomarker of Oxidative DNA Damage Induced by Ionizing Radiation in Human Peripheral Blood

In this study, the effect of ionizing radiation on 8-hydroxy-2'-deoxyguanosine (8-OHdG) in human peripheral blood was investigated. Blood samples were collected from 230 radiation workers and 8 patients who underwent radiotherapy for population study. Blood samples from 2 healthy individuals were irradiated with different X-ray doses for in vitro experiment, and levels of 8-OHdG in serum and cell culture supernatants were assessed by enzyme-linked immunosorbent assay. Observations demonstrated the positive relationships between serum 8-OHdG level and radiation dose and working period were observed, and serum 8-OHdG levels were higher among interventional radiation workers than among other hospital radiation workers. In addition, 8-OHdG yields in supernatants increased, peaked at 3 Gy of radiation dose, and then decreased with further increases in radiation; the dose-response curve obtained fitted a polynomial function. By contrast, a similar trend was not found in radiotherapy patients. The present study suggests that 8-OHdG may be a useful biomarker reflecting oxidative damage among workers occupationally exposed to low-dose radiation.

Antioxidant properties of green tea aroma in mice

Green tea (‘Sencha’), made from the leaves of Camellia sinensis, is the most well-researched antioxidant beverage. The major source of its antioxidant activity is polyphenols, consisting mainly of catechins (flavan-3-ols). However, little is known about the physiological effects of green tea aroma, which lacks catechins. In the present study, we performed inhalation experiments with green tea aroma to evaluate its antioxidant activity in mice. As a result, the urinary 8-hydroxydeoxyguanosine levels were significantly decreased in comparison with those of the non-treated group, and the serum antioxidant capacity was significantly increased by the inhalation administration of green tea aroma. Furthermore, the increase in the urinary 8-hydroxydeoxyguanosine levels due to whole-body X-ray irradiation was significantly suppressed by the inhalation of green tea aroma. This is the first study to show the antioxidant activity of green tea aroma in vivo.

What causes human cancer? Approaches from the chemistry of DNA damage

To prevent human cancers, environmental mutagens must be identified. A common mechanism of carcinogenesis is DNA damage, and thus it is quite possible that environmental mutagens can be trapped as adducts by DNA components. It is also important to identify new types of DNA damaging reactions and clarify their mechanisms. In this paper, I will provide typical examples of our efforts to identify DNA damage by environmental agents, from chemistry-based studies. 1) Oxidative DNA damage: 8-Hydroxydeoxyguanosine (8-OHdG, 8-oxodG) was discovered during a structural study of DNA modifications caused in vitro by heating glucose, which was used as a model of cooked foods. We found that various oxygen radical-forming agents induced the formation of 8-OHdG in DNA, in vitro and in vivo. Analyses of the urinary 8-OHdG levels are useful to assess the extent of oxidative DNA damage in a human population. 2) Lipid peroxide-derived DNA adducts: We searched for mutagens that react with deoxynucleosides, in model systems of lipid peroxidation. The reaction mixtures were analyzed by high performance liquid chromatography (HPLC), and we discovered various lipid peroxide-derived mutagens, including new mutagens. Some of these adducts were detected in human DNA. These mutagens may be involved in lipid peroxide-related cancers. 3) Methylation of cytosine by free radicals: Methylation of the cytosine C-5 position is an important mechanism of carcinogenesis, in addition to gene mutations. However, the actual mechanisms of de novo methylation in relation to environmental agents are not clear. We found that cytosine C-5 methylation occurred by a free radical mechanism. The possible role of this radical-induced DNA methylation in carcinogenesis will be discussed, in relation to the presently accepted concept of cancer epigenetics. In these studies, chemical analyses of the adducts formed in model reactions led to the discoveries of new mutagens and important types of DNA modifications, which seem to be involved in human carcinogenesis.