Oxidative DNA damage and repair in children exposed to low levels of arsenic in utero and during early childhood: Application of salivary and urinary biomarkers

The present study aimed to assess arsenic exposure and its effect on oxidative DNA damage and repair in young children exposed in utero and continued to live in arsenic-contaminated areas. To address the need for biological specimens that can be acquired with minimal discomfort to children, we used non-invasive urinary and salivary-based assays for assessing arsenic exposure and early biological effects that have potentially serious health implications. Levels of arsenic in nails showed the greatest magnitude of difference between exposed and control groups, followed by arsenic concentrations in saliva and urine. Arsenic levels in saliva showed significant positive correlations with other biomarkers of arsenic exposure, including arsenic accumulation in nails (r = 0.56, P < 0.001) and arsenic concentration in urine (r = 0.50, P < 0.05). Exposed children had a significant reduction in arsenic methylation capacity indicated by decreased primary methylation index and secondary methylation index in both urine and saliva samples. Levels of salivary 8-OHdG in exposed children were significantly higher (~ 4-fold, P < 0.01), whereas levels of urinary 8-OHdG excretion and salivary hOGG1 expression were significantly lower in exposed children (~ 3-fold, P < 0.05), suggesting a defect in hOGG1 that resulted in ineffective cleavage of 8-OHdG. Multiple regression analysis results showed that levels of inorganic arsenic (iAs) in saliva and urine had a significant positive association with salivary 8-OHdG and a significant negative association with salivary hOGG1 expression.     

Oxidative DNA damage and inflammatory responses in cultured human cells and in humans exposed to traffic-related particles

Particulate pollution is a major public health concern because epidemiological studies have demonstrated that exposure to particles is associated with respiratory diseases and lung cancer. Diesel exhaust particles (DEP), which is classified as a human carcinogen (IARC, 2012), are considered a major contributor to traffic-related particulate matter (PM) in urban areas. DEP consists of various compounds, including PAHs and metals which are the principal components that contribute to the toxicity of PM. The present study aimed to investigate effects of PM on induction of oxidative DNA damage and inflammation by using lymphocytes in vitro and in human exposed to PM in the environment. Human lymphoblasts (RPMI 1788) were treated with DEP (SRM 2975) at various concentrations (25–100 μg/ml) to compare the extent of responses with alveolar epithelial cells (A549). ROS generation was determined in each cell cycle phase of DEP-treated cells in order to investigate the influence of the cell cycle stage on induction of oxidative stress. The oxidative DNA damage was determined by measurement of 8-hydroxy-deoxyguanosine (8-OHdG) whereas the inflammatory responses were determined by mRNA expression of interleukin-6 and -8 (IL-6 and IL-8), Clara cell protein (CC16), and lung surfactant protein-A (SP-A). The results showed that RPMI 1788 and A549 cells had a similar pattern of dose-dependent responses to DEP in terms of particle uptake, ROS generation with highest level found in G2/M phase, 8-OHdG formation, and induction of IL-6 and IL-8 expression. The human study was conducted in 51 healthy subjects residing in traffic-congested areas. The effects of exposure to PM_2.5 and particle-bound PAHs and toxic metals on the levels of 8-OHdG in lymphocyte DNA, IL-8 expression in lymphocytes, and serum CC16 were evaluated. 8-OHdG levels correlated with the exposure levels of PM_2.5 (P < 0.01) and PAHs (P < 0.05), but this was not the case with IL-8. Serum CC16 showed significantly negative correlations with B[a]P equivalent (P < 0.05) levels, but positive correlation with Pb (P < 0.05). In conclusion, a similar pattern of the dose-dependent responses to DEP in the lymphoblasts and lung cells suggests that circulating lymphocytes could be used as a surrogate for assessing PM-induced oxidative DNA damage and inflammatory responses in the lung. Human exposure to PM leads to oxidative DNA damage whereas PM-induced inflammation was not conclusive and should be further investigated.     

Evaluation of free radical scavenging and antityrosinase activities of standardized longan fruit extract.

The protective effects of fruits and vegetables against chronic diseases have been attributed to the antioxidant properties of some secondary metabolites present in these foods. Plant polyphenols have been reported to exhibit bioactive properties, and in particular antioxidant activities. Longan seeds are found to contain high levels of some beneficial polyphenolic compounds such as corilagin, gallic acid and ellagic acid. The present study examined the free radical scavenging activity of longan seed extract by using three different assay methods. Longan extracts contained corilagin ranging from zero to 50.64 mg/g DW, gallic acid from 9.18 to 23.04 mg/g DW, and ellagic acid from 8.13 to 12.65 mg/g DW depending on the cultivars. Dried longan seed extracts of cultivar Edor contained high levels of gallic acid and ellagic acid and also exhibited the highest radical scavenging activities when comparing fresh seed and dried pulp extracts. For scavenging activity of DPPH and superoxide radicals, longan seed extract was found to be as effective as Japanese green tea extract while dried longan pulp and mulberry green tea extracts showed the least scavenging activities. In the ORAC assay, both fresh and dried longan seed also had higher activity than dried pulp and whole fruit. However, the results demonstrate that three polyphenolics may not be the major contributors of the high antioxidant activity of longan water extracts but this high activity may be due to other phenolic/flavonoid glycosides and ellagitannins present in longan fruit. In addition, longan seed also showed tyrosinase inhibitory activity with IC(50) values of 2.9-3.2 mg/ml. Therefore, the preliminary observations suggest that longan seed extract could be another potential source of potent natural dietary antioxidants and also in an application as a new natural skin-whitening agent.     

Inhibitory effects of carbon tetrachloride on dimethylnitrosamine metabolism and DNA alkylation

The effect of CCl₄ pretreatment (dose range from 0.5 to 2.0ml/kg body weight) on the pathways of dimethylnitrosamine (DMN)metabolism was investigated. The oxidative-N-demethylation bythe enzymes, DMN-demethylase I and II operating at low (4 mM)and high (200 mM) substrate concentration, respectively, wasgreatly reduced in a dose-dependent manner. In addition, thegeneration of an electrophilic intermediate capable of methylatingDNA, specifically at the N-7 and O-6 positions of guanine, wascompletely inhibited by CCl₄ (0.5 ml/kg body weight) pretreatment.When indole feeding (1% in the diet for 8 days prior to CCl₄administration) was employed as a means to enhance DMN-demethylaseactivities, it was found that the reduction of DMN-demethylaseactivities was more pronounced in these rats than in the controls.In agreement with earlier findings, 7-methylguanine and O⁶-methylguaninewere not detectable in the CCl₄ pretreated group. These resultssuggest that CCl₄ exerts a strong inhibitory action on hepaticDMN metabolism, in particular on the pathway leading to alkylationof DNA guanine. This phenomenon may explain the protective roleof CCl₄ against DMN-induced hepatotoxicity and perhaps, carcinogenicity,believed to be closely associated with the abnormal modificationsof DNA.     

Increased health risk in Bangkok children exposed to polycyclic aromatic hydrocarbons from traffic-related sources

The aim of this study is to assess potential health risk of exposure to particle-associated polycyclic aromatic hydrocarbons (PAHs) in children living in a megacity with traffic congestion such as Bangkok. The study population comprised 184 Thai schoolboys (aged 8-13 years) attending schools adjacent to high-density traffic areas in Bangkok and schools located in the provincial area of Chonburi. The ambient concentration of total PAHs at roadsides in proximity to the Bangkok schools was 30-fold greater than at roadsides in proximity to the provincial schools (30.39 +/- 5.80 versus 1.50 +/- 0.28 ng/m(3); P < 0.001). Benzo(g,h,i)perylene (BghiP), an indicator of automobile exhaust emission, was the predominant PAH. Personal exposure to total PAHs and the corresponding benzo(a)pyrene (BaP) equivalent concentrations in Bangkok schoolchildren were 3.5-fold higher than in provincial schoolchildren (4.13 +/- 0.21 versus 1.18 +/- 0.09 ng/m(3); P < 0.001 and 1.50 +/- 0.12 versus 0.43 +/- 0.05 ng/m(3); P < 0.001, respectively). The concentration of urinary 1-hydroxypyrene (1-HOP) was significantly higher in Bangkok schoolchildren. Bulky carcinogen-DNA adduct levels in peripheral lymphocytes were also significantly higher (0.45 +/- 0.03 versus 0.09 +/- 0.00 adducts/10(8) nt; P < 0.001). Finally, a significantly higher level of DNA strand breaks and a significantly lower level of DNA repair capacity were observed in Bangkok schoolchildren (P < 0.001). This study indicates that Bangkok schoolchildren exposed to a high level of genotoxic PAHs in ambient air may be more vulnerable to the health impacts associated with the exposure to genotoxic pollutants than children in provincial areas and may have increased health risks for the development of certain diseases such as cancer.     

Effects of the El Ni?o-Southern Oscillation on dengue epidemics in Thailand, 1996-2005

Background  

Despite intensive vector control efforts, dengue epidemics continue to occur throughout Southeast Asia in multi-annual cycles. Weather is considered an important factor in these cycles, but the extent to which the El Ni?o-Southern Oscillation (ENSO) is a driving force behind dengue epidemics remains unclear.     

Low level occupational exposure to styrene: its effects on DNA damage and DNA repair

The present study aimed to evaluate the effects of styrene exposure at levels below the recommended standards of the Threshold Limit Value (TLV-TWA(8)) of 20 ppm (ACGIH, 2004) in reinforced-fiberglass plastics workers. Study subjects comprised 50 exposed workers and 40 control subjects. The exposed workers were stratified by styrene exposure levels, i.e. group I (<10 ppm, <42.20 mg/m(3)), group II (10-20 ppm, 42.20-84.40 mg/m(3)), and group III (>20 ppm, >84.40 mg/m(3)). The mean styrene exposure levels of exposed workers were significantly higher than those of the control workers. Biomarkers of exposure to styrene, including blood styrene and the urinary metabolites, mandelic acid (MA) and phenylglyoxylic acid (PGA), were significantly increased with increasing levels of styrene exposure, but were not detected in the control group. DNA damage, such as DNA strand breaks, 8-hydroxydeoxyguanosine (8-OHdG), and DNA repair capacity, were used as biomarkers of early biological effects. DNA strand breaks and 8-OHdG/10(5)dG levels in peripheral leukocytes of exposed groups were significantly higher compared to the control group (P<0.05). In addition, DNA repair capacity, determined by the cytogenetic challenge assay, was lower in all exposed groups when compared to the control group (P<0.05). The expression of CYP2E1, which is involved in styrene metabolism, in all styrene exposed groups, was higher than that of the control group at a statistically significant level (P<0.05). Levels of expression of the DNA repair genes hOGG1 and XRCC1 were significantly higher in all exposed groups than in the control group (P<0.05). In addition to styrene contamination in ambient air, a trace amount of benzene was also found but, the correlation between benzene exposure and DNA damage or DNA repair capacity was not statistically significant. The results obtained from this study indicate an increase in genotoxic effects and thus health risk from occupational styrene exposure, even at levels below the recommended TLV-TWA(8) of 20 ppm.     

Challenge assay: A functional biomarker for exposure-induced DNA repair deficiency and for risk of cancer

A variety of biomarkers have been used to monitor exposed populations to determine potential health hazards from their exposure to environmental toxic agents. However, the majority of these biomarkers have been focused onto the identification of biological damage from the exposure. Therefore, there is a need to develop functional biomarkers that can identify exposure-induced functional deficiencies. More importantly, these deficiencies should be positioned along pathways that are responsible for the development of specific diseases. One of such pathways belongs to the extensive and complex DNA-repair machinery. The machinery thus becomes a large target for damage from environmental toxic agents. The hypothesis is that damage to any component of a repair pathway will interfere with the pathway-specific repair activities. Therefore, when cells from exposed populations are challenged with a DNA-damaging agent in vitro, the in vivo exposure-induced repair deficiency will be dramatically amplified and the deficiency will be detectable in a challenge assay as increased chromosome aberrations, micronuclei or un-repaired DNA strand breaks. The challenge assay has been used in different laboratories to show that a variety of exposed populations (with exposure to air pollutants, arsenic, benzene, butadiene, cigarette smoke, incense smoke, lead, mercury, pesticides, uranium or xylene but not to low concentrations of air pollutants or butadiene) expressed abnormal challenge response. The predicted health consequences of some of these studies have also been validated. Therefore, the challenge assay is a useful functional biomarker for population studies. Details of the challenge assay and its application will be presented in this review.     

The protective role of thiol reducing agents in the in vitro inhibition of rat liver DNA methylase by direct acting carcinogens

The direct-acting carcinogens N-acetoxy-N-acetyl-2-aminofluorene(AcAAF), methyl nitrosourea (MNU), and N-methyl-N'-nitro-N-nitrosoguanidine(MNNG) were tested for their ability to inhibit highly purified,rat liver DNA methylase in vitro. Fifty percent inhibition ofDNA methylase ativity was achieved with 4.3 mM AcAAF, 47 mMMNU and 2.8 mM MNNG. When the enzyme was reassayed in the presenceand absence of dithiothreitol, it was shown that DNA methylasewas protected by increasing amounts of the thiol reducing agent.When other thiol reducing agents were tested for their abilityto protect DNA methylase from carcinogen damage, a differentialprotective ability was observed. Dithiothreitol, ß-mercaptoethanol,and reduced glutathione were effective in protecting DNA methylasefrom carcinogen inhibition, while the effect of cysteine wasintermediary and the effect of ergothioneine was minimal. Theseresults may be related to the hypomethylation of DNA observedin several cancers, suggesting that the carcinogens achievethis effect at least in part by inhibiting crucial sulfhydrylgroup(s) in the methylase molecule. These data also suggestthat various intracellular thiols may play an important rolein protecting DNA-modifying enzymes from carcinogen damage.