Exposure to indoor background radiation and urinary concentrations of 8-hydroxydeoxyguanosine, a marker of oxidative DNA damage

Oxidative genomic damage in humans exposed to high indoor radon levels in Northeast Brazil

Radon gas inhalation is the main source of exposure to ionizing radiation by humans. There is still lack in knowledge concerning the chronic and indirect effects of exposure to this carcinogenic factor. Therefore, the aim of this work is to analyze the levels of oxidative genomic damage in inhabitants of a medium-high background radiation area (HBRA) (N = 82) in Northeastern Brazil and compare them with people living in a low background radiation area (LBRA) (N = 46). 8-hydroxy-2-deoxyguanosine (8-OHdG) was quantified in urine, Ser326Cys polymorphism was determined in the hOGG1 gene and indoor radon was measured. HBRA houses had 6.5 times higher indoor radon levels than those from LBRA (p-value < 0.001). The 8-OHdG mean (95% confidence interval) were significantly different, 8.42 (5.98-11.9) ng/mg creatinine and 29.91 (23.37-38.30) ng/mg creatinine for LBRA and HBRA, respectively. The variables representing lifestyle and environmental and occupational exposures did not have a significant association with oxidized guanosine concentrations. On the other hand, lower 8-OHdG values were observed in subjects that had one mutant allele (326Cys) in the hOGG1 gene than those who had both wild alleles (Ser/Ser (p-value < 0.05). It can be concluded that high radon levels have significantly influenced the genome oxidative metabolism and hOGG1 gene polymorphism would mediate the observed biological response.

A comparative study of genotoxicity endpoints for women exposed to different levels of indoor radon concentrations

BACKGROUND AND PURPOSE

Radon and its radioactive progenies are the most important source of ionizing radiation of natural origin, being classified as a Group 1 carcinogen. The aim of this study is to investigate the genotoxic effects of a wide range of indoor radon concentrations, as well as the kinetics of the process of repairing DNA-induced lesions by a challenging dose of gamma irradiation.

MATERIAL AND METHODS

Female subjects residing in the Băiţa-Ştei radon priority area were selected as the exposed group. The reference group was comprised of women from the same county (Bihor), but located in an area with an average indoor radon concentration typical of the county from which they were taken. Radon concentration values of 300 Bq/m³ and 148 Bq/m³, respectively, were chosen as a threshold in order to capture the impact of radon exposure between the groups. The alkaline comet assay was used in order to measure the DNA damage, as well as the repair kinetics at 2 and 24 h after 2 Gy challenging doses of gamma irradiation using peripheral blood lymphocytes. From the serum of the subjects, the oxidative damage by 8-hydroxydeoxyguanosine as well as the PARP induction was evaluated. The chromosomal aberrations were evaluated using the Cytokinesis Block MicroNucleus Assay.

RESULTS

A statistically significant increase was observed in terms of DNA-induced lesions assessed by comet assay for the exposed group compared to the reference group. A positive correlation was obtained between DNA damage and the annual effective dose, respectively with the radon progenies concentrations. A statistically significant difference was also observed for the frequency of the micronuclei between the exposed - reference groups. Significantly faster repair kinetics of DNA-induced lesions was recorded for the first 2 h after gamma irradiation in the reference group compared to the exposed group. Using the threshold of 300 Bq/m³ for radon concentration, faster kinetics of DNA damage repair for people exposed to low radon concentrations, compared to those exposed to higher concentrations for the second phase of DNA repair kinetics was observed.

CONCLUSION

An increased radiosensitivity of lymphocytes, as well as slower repair kinetics, may be associated with exposure to higher indoor radon concentrations.

Toxic Feedback Loop Involving Iron, Reactive Oxygen Species, α-Synuclein and Neuromelanin in Parkinson's Disease and Intervention with Turmeric

Parkinson's disease (PD) is a movement disorder associated with severe loss of mainly dopaminergic neurons in the substantia nigra. Pathological hallmarks include Lewy bodies, and loss of neuromelanin, due to degeneration of neuromelanin-containing dopaminergic neurons. Despite being described over 200 years ago, the etiology of PD remains unknown. Here, we highlight the roles of reactive oxygen species (ROS), iron, alpha synuclein (α-syn) and neuromelanin in a toxic feedback loop culminating in neuronal death and spread of the disease. Dopaminergic neurons are particularly vulnerable due to decreased antioxidant concentration with aging, constant exposure to ROS and presence of neurotoxic compounds (e.g. ortho-quinones). ROS and iron increase each other's levels, creating a state of oxidative stress. α-Syn aggregation is influenced by ROS and iron but also increases ROS and iron via its induced mitochondrial dysfunction and ferric-reductase activity. Neuromelanin's binding affinity is affected by increased ROS and iron. Furthermore, during neuronal death, neuromelanin is degraded in the extracellular space, releasing its bound toxins. This cycle of events continues to neighboring neurons in the form of a toxic loop, causing PD pathology. The increase in ROS and iron may be an important target for therapies to disrupt this toxic loop, and therefore diets rich in certain 'nutraceuticals' may be beneficial. Turmeric is an attractive candidate, as it is known to have anti-oxidant and iron chelating properties. More studies are needed to test this theory and if validated, this would be a step towards development of lifestyle-based therapeutic modalities to complement existing PD treatments.

The protective role of antioxidants in the defence against ROS/RNS-mediated environmental pollution

Overproduction of reactive oxygen and nitrogen species can result from exposure to environmental pollutants, such as ionising and nonionising radiation, ultraviolet radiation, elevated concentrations of ozone, nitrogen oxides, sulphur dioxide, cigarette smoke, asbestos, particulate matter, pesticides, dioxins and furans, polycyclic aromatic hydrocarbons, and many other compounds present in the environment. It appears that increased oxidative/nitrosative stress is often neglected mechanism by which environmental pollutants affect human health. Oxidation of and oxidative damage to cellular components and biomolecules have been suggested to be involved in the aetiology of several chronic diseases, including cancer, cardiovascular disease, cataracts, age-related macular degeneration, and aging. Several studies have demonstrated that the human body can alleviate oxidative stress using exogenous antioxidants. However, not all dietary antioxidant supplements display protective effects, for example, β-carotene for lung cancer prevention in smokers or tocopherols for photooxidative stress. In this review, we explore the increases in oxidative stress caused by exposure to environmental pollutants and the protective effects of antioxidants.

Influence of aroclor 1254 on benzo(a)pyrene-induced DNA breakage, oxidative DNA damage, and cytochrome P4501A activity in human hepatoma cell line

Both polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) are important environmental pollutants. They coexist widely in the environment at very low levels. Numerous studies indicated that aroclor1254 (one of PCBs mixture) is the inducer of cytochrome P450 1A enzyme acitivity. Benzo(a)pyrene (BaP) can cause a variety of toxicities in vitro, such as oxidative DNA damage and genotoxicity. In the present study, HepG2 cells were treated with either BaP (50 microM) or aroclor1254 at concentrations of 11.5 (low), 23.0 (medium), and 46.0 microM (high) alone, or pretreated the cells with aroclor1254 (11.5, 23.0, and 46.0 microM), followed by BaP (50 microM). It was found that 7-ethoxyresorufin-O-deetylase (EROD) activities of HepG2 cells exposed to either BaP or aroclor 1254 increased. DNA damage measured by DNA migration and the formation of 8-hydroxy-2'-deoxyguanosine (8-OHdG) also increased in cells exposed to BaP, but not in cells exposed to aroclor1254. Under the Aroclor 1254 pretreatment condition, BaP-induced EROD activities was enhanced in cells exposed to the medium and high concentrations of aroclor1254 (P < 0.01 for both), whereas in all pretreatment groups aroclor1254 significantly increased BaP-induced DNA migration (P < 0.01 for all) and the 8-OHdG formation (P < 0.05 for all). In addition, there was positive correlation between the EROD induction activity and Olive tail moment (r(2) = 0.958, P < 0.01) or the levels of 8-OHdG (r(2) = 0.992, P < 0.01). The findings suggest that under the experimental conditions aroclor1254 may enhance BaP-induced DNA migration and oxidative DNA damage in HepG2, due to inducing CYP1A enzyme activity.

Proteomic analysis of lung tissue of rats exposed to cigarette smoke and radon

This study examined the protein expression in lung tissues of rats exposed to radon and cigarette smoke using a proteomic approach. Male Wistar rats were exposed daily to radon at a concentration of 100,000 Bq/m(3) for 16 h, and then exposed to 20% cigarette smoke for 1 h for a period of 75 d, with the radon cumulative dose reaching 200 WLM (working level months). Proteins from rat lung tissue were separated by two-dimensional gel electrophoresis (2-DE), stained with Coomassie blue, and analyzed with ImageMaster two-dimensional (2D) platinum software. Differentially expressed proteins were analyzed by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MALDI-time of flight [TOF] MS or MALDI TOF/TOF-MS). Twenty prominent proteins that were correlated with signal transduction, metabolism, heat shock and stress, and cytoskeleton construction were identified. Some of the differential expression proteins were verified by Western blot analysis and immunohistochemical staining, and the results were consistent with 2-DE analysis. The identified proteins and peptides might be potential diagnostic markers of lung impairment induced by radon and cigarette smoke exposure.

Urinary 8-hydroxydeoxyguanosine in Belarussian children relates to urban living rather than radiation dose after the chernobyl accident: a pilot study

As a result of the Chernobyl accident in 1986, exposure to radioactive cesium is still a concern in the contaminated regions of Belarus. We tested the hypothesis that long-term radiation exposure from the Chernobyl accident might increase the urinary excretion of the oxidative stress marker, 8-hydroxydeoxyguanosine (8-OHdG), in Belarussian children. Urinary 8-OHdG was determined in two groups of children (-n = 31 and n = 46) -living in contaminated and uncontaminated areas of Belarus, respectively (the majority of the unexposed children lived in the capital Minsk). The children from the contaminated areas had a significantly higher annual summary effective dose but significantly lower urinary 8-OHdG levels than the children from the uncontaminated areas. Unexpectedly, children living in uncontaminated urban areas had significantly higher urinary 8-OHdG levels than children living in uncontaminated rural areas. There was no statistically significant effect of sex or body mass index on urinary 8-OHdG, but there was a weak significant inverse correlation to age as well as to the annual summary effective dose. These findings suggest that radiation from the Chernobyl accident is now a less important contributor to oxidative stress in Belarussian children than urban living.

Leukemia in childhood and adolescence and exposure to ionizing radiation in homes built from uranium-containing alum shale concrete

Concerns in Sweden about indoor radon around 1980 prompted measurements of gamma-radiation from the facades of houses to identify those constructed of uranium-containing alum shale concrete, with potentially high radon concentrations. To evaluate any possible risk of acute lymphocytic leukemia from exposure to elevated gamma-radiation in these homes, we identified the acute lymphocytic leukemia cases less than 20 years of age in Sweden during 1980-1989 as well as eight controls per case from the population registry, matching on age, gender, and county. Using the existing measurements, exposure was assessable for 312 cases and 1,418 controls from 151 properly measured municipalities. A conditional logistic odds ratio of 1.4 (95% confidence interval = 1.0-1.9) was obtained for those ever having lived in alum shale concrete houses, with the average exposure exceeding 0.10 microsieverts per hour. Comparing those who ever lived in alum shale concrete houses (divided by higher and lower annual average exposure) with those who never lived in such houses, we found a weak dose-response relation. The results suggest some risk of acute lymphocytic leukemia from indoor ionizing radiation among children and young adults.

Lack of direct involvement of 8-hydroxy-2'-deoxyguanosine in hypoxanthine-guanine phosphoribosyltransferase mutagenesis in V79 cells treated with N,N'-bis(2-hydroxyperoxy-2-methoxyethyl)-1,4,5,8-naphthalenetetracarboxylic-diimide (NP-III) or riboflavin

The object of this study is to investigate the relationship between a typical product of oxidative DNA damage, 8-hydroxy-2'-deoxyguanosine (8OHdG), and mutagenesis in V79 cells through a molecular analysis of hypoxanthine-guanine phosphoribosyltransferase (hprt) gene mutants. We performed a direct sequencing analysis of the cDNA of mutants obtained after treatment with N,N'-bis(2-hydroxyperoxy-2-methoxyethyl)-1,4,5,8-naphthalenetetracarboxylic-diimide (NP-III) or riboflavin, each of which induces the formation of 8OHdG in cellular DNA upon UVA irradiation. The frequency of mutation after both treatments was no more than 2 to 5 times the control value. A considerable number of the mutants could not be amplified by RT-PCR, and this was also the case for the control mutants. Among the mutants analyzed, deletions and a TA-->AT transversion occurred predominantly. The reasons for the weak association of induction of 8OHdG with frequency of mutation and the possible mechanism of oxidative-stress-derived mutagenesis are discussed.