Chronic arsenic exposure and oxidative stress: OGG1 expression and arsenic exposure, nail selenium, and skin hyperkeratosis in Inner Mongolia

Intrauterine arsenic exposure induces glucose metabolism disorders in adult offspring by targeting TET2-mediated DNA hydroxymethylation reprogramming of HNF4α in developing livers, an effect alleviated by ascorbic acid

Exposure to arsenic during gestation has lasting health-related effects on the developing fetus, including an increase in the risk of metabolic disease later in life. Epigenetics is a potential mechanism involved in this process. Ten-eleven translocation 2 (TET2) has been widely considered as a transferase of 5-hydroxymethylcytosine (5hmC). Here, mice were exposed, via drinking water, to arsenic or arsenic combined with ascorbic acid (AA) during gestation. For adult offspring, intrauterine arsenic exposure exhibited disorders of glucose metabolism, which are associated with DNA hydroxymethylation reprogramming of hepatic nuclear factor 4 alpha (HNF4α). Further molecular structure analysis, by SEC-UV-DAD, SEC-ICP-MS, verified that arsenic binds to the cysteine domain of TET2. Mechanistically, arsenic reduces the stability of TET2 by binding to it, resulting in the decrease of 5hmC levels in Hnf4α and subsequently inhibiting its expression. This leads to the disorders of expression of its downstream key glucose metabolism genes. Supplementation with AA blocked the reduction of TET2 and normalized the 5hmC levels of Hnf4α, thus alleviating the glucose metabolism disorders. Our study provides targets and methods for the prevention of offspring glucose metabolism abnormalities caused by intrauterine arsenic exposure.

H3K18 lactylation promotes the progression of arsenite-related idiopathic pulmonary fibrosis via YTHDF1/m6A/NREP

As epigenetic modifications, lactylation and N6-methyladenosine (m6A) have attracted wide attention. Arsenite is an environmental pollutant that has been proven to induce idiopathic pulmonary fibrosis (IPF). However, the molecular mechanisms of lactylation and m6A methylation are unclear in arsenite-related IPF (As-IPF). In view of the limited understanding of molecular mechanism of m6A and lactylation in As-IPF, MeRIP-seq, RNA-seq and ChIP-seq were analyzed to verify the target gene regulated by m6A and H3K18 lactylation (H3K18la). We found that, for As-IPF, the global levels of m6A, levels of YTHDF1 and m6A-modified neuronal protein 3.1 (NREP) were elevated in alveolar epithelial cells (AECs). The secretion levels of TGF-β1 were increased via YTHDF1/m6A/NREP, which promoted the fibroblast-to-myofibroblast transition (FMT). Further, extracellular lactate from myofibroblasts elevated levels of the global lactylation (Kla) and H3K18la via the lactate monocarboxylate transporter 1 (MCT1), and, in AECs, H3K18la facilitated the transcription of Ythdf1. This report highlights the role of crosstalk between AECs and myofibroblasts via lactylation and m6A and the significance of H3K18la regulation of YTHDF1 in the progression of As-IPF, which may be useful for finding effective therapeutic targets.

Urinary arsenic and spontaneous pregnancy loss - a hypothesis-generating case-control investigation in western Romania

Arsenic occurs as a natural contaminant of drinking water supplies in arsenic endemic areas, posing a threat to public health. Our aim was to evaluate the relationship between urinary arsenic concentrations and spontaneous pregnancy loss in a population with low-moderate level drinking water arsenic exposure (mostly <10 μg/L). We enrolled 150 women with incident spontaneous pregnancy losses and 150 controls with ongoing pregnancies matched by gestational age. We measured arsenic species in urine using high performance liquid chromatography paired to inductively coupled plasma mass spectrometry. Urinary arsenic was not related to spontaneous pregnancy loss in conditional logistic regression models adjusted for confounding factors. However, a 10 μg/L increase in urinary arsenic (III + V) salt concentrations was associated with 8.00-fold (95% CI: 0.68, 3.35 × 105) greater odds of spontaneous loss among women using prenatal vitamins in an interaction model (P for interaction = 0.07), although the effect estimate was imprecise. In an additional interaction model, prenatal vitamin use was associated with lower odds of loss (OR = 0.30; 95% CI: 0.13, 0.66), although the association was diminished in the presence of a 10 μg/L increase in urinary inorganic arsenic (OR = 0.44; 95% CI: 0.70, 3.22). Total urinary arsenic was associated with 1.48-fold (95% CI: 0.20, 11.35) greater odds for loss among women with urinary cotinine >50 μg/L in another interaction model (P for interaction = 0.07). These results suggest a potential modest increase in the odds of pregnancy loss associated with increased total urinary arsenic among women smoking during pregnancy (urinary cotinine >50 μg/L). Prenatal vitamin use may act as a protective factor for arsenic exposure associated pregnancy loss, but appears to be less protective with increasing urinary inorganic arsenic concentrations.

Evaluation of low-to-moderate arsenic exposure, metabolism and skin lesions in a Turkish rural population exposed through drinking water

BACKGROUND

There is no human data regarding the exposure, metabolism and potential health effects of arsenic (As) contamination in drinking water in the Central Anatolian region of Turkey.

METHODS

Residents in ten villages with drinking water of total As (T-As) level >50 μg L^-1 and 10-50 μg L^-1 were selected as an exposed group (n = 420) and <10 μg L^-1 as an unexposed group (n = 185). Time-weighted average-As (TWA-As) intake was calculated from T-As analysis of drinking water samples. Concentrations of T-As in urine and hair samples, urinary As species [i.e., As(III), As(V), MMA(V) and DMA(V], and some micronutrients in serum samples of residents of the study area were determined. Primary and secondary methylation indices (PMI and SMI, respectively) were assessed from urinary As species concentrations and the presence of skin lesion was examined.

RESULTS

TWA-As intake was found as 75 μg L^-1 in the exposed group. Urinary and hair T-As and urinary As species concentrations were significantly higher in the exposed group (P < 0.05). The PMI and SMI values revealed that methylation capacities of the residents were efficient and that there was no saturation in As metabolism. No significant increase was observed in the frequency of skin lesions (hyperpigmentation, hypopigmentation, keratosis) of the exposed group (P > 0.05). Only frequency of keratosis either at the hand or foot was higher in individuals with hair As concentration >1 μg g^-1 (P < 0.05).

CONCLUSIONS

Individuals living in the study area were chronically exposed to low-to-moderate As due to geological contamination in drinking water. No significant increase was observed in the frequency of skin lesions. Because of the controversy surrounding the health risks of low-to-moderate As exposure, it is critical to initiate long-term follow-up studies on health effects in this region.

Tocopherol Enhances the Antioxidant Defense System and Histomorphometric Parameters in The Gastrointestinal Tract of Rats Treated with Sodium Arsenite

Arsenic compromises the gastrointestinal integrity and function via the body's anti-oxidative system breakdown.  Hence, this study aimed to investigate the effects of tocopherol on redox imbalance and histoarchitectural alterations in rats' gastrointestinal tract exposed to sodium arsenite. Sodium arsenite and graded doses of tocopherol were administered orally into experimental rats assigned to different groups for four weeks concurrently. Redox status assay was done in homogenized samples by spectrophotometry. Parietal cell mass and mucous cell density (stomach), villus height and crypt depth (ileum), goblet cells count, and crypt depth (colon) were evaluated by histomorphometry. Inflammatory cells infiltration was also assessed using a semi-quantitative procedure. Sodium arsenite caused a significant increase in Malondialdehyde and Myeloperoxidase but, decreased Superoxide dismutase, Catalase, Nitric oxide, Glutathione peroxidase, Glutathione, and Glutathione-S-Transferase. Tocopherol treatment reversed the changes (p<0.05) though not largely dose-dependent. Furthermore, tocopherol annulled sodium arsenite-induced increase in parietal cell mass and decrease in mucous cell density in the stomach, decrease in villus height and villus height/crypt depth ratio in the ileum, and decrease in goblets cells and increase in crypt depth in the colon. Moreover, activated inflammatory cell infiltration by sodium arsenite was mitigated by tocopherol. Sodium arsenite provokes not only marked inflammatory cellular infiltration but a focal loss of glands, hyperplasia of crypts, atrophic villi, and hypertrophy of Peyer's patches in the intestines, which are all lessened with tocopherol treatment.  These findings underscore the anti-oxidative properties of tocopherol as a potent dietary factor against sodium arsenite toxicity in the gastrointestinal tract. Keywords: Tocopherol, arsenic, stomach, ileum, colon.

Arsenic co-carcinogenesis: Inhibition of DNA repair and interaction with zinc finger proteins

Arsenic is widely present in the environment and is associated with various population health risks including cancers. Arsenic exposure at environmentally relevant levels enhances the mutagenic effect of other carcinogens such as ultraviolet radiation. Investigation on the molecular mechanisms could inform the prevention and intervention strategies of arsenic carcinogenesis and co-carcinogenesis. Arsenic inhibition of DNA repair has been demonstrated to be an important mechanism, and certain DNA repair proteins have been identified to be extremely sensitive to arsenic exposure. This review will summarize the recent advances in understanding the mechanisms of arsenic carcinogenesis and co-carcinogenesis, including DNA damage induction and ROS generation, particularly how arsenic inhibits DNA repair through an integrated molecular mechanism which includes its interactions with sensitive zinc finger DNA repair proteins.

From environmental bioavailability of metal(loid)s to their ecogenotoxicological effects in land snails

To date, no study has linked the environmental and the ecogenotoxicological bioavailability of contaminants to land snails. Yet, understanding the specific ecotoxicological mechanisms from bioaccumulation to genotoxicity is necessary e.g., to build an adverse outcome pathway relevant to risk assessment. Consequently, the aim of our study is to look for relationships between accumulated concentrations of As, Cd and Hg in sub-adult snails and ecotoxicological effects at the individual (survival and growth) and molecular (genomic stability) levels. This study combines random amplified polymorphic DNA (RAPD) coupled with high-resolution capillary electrophoresis system (HRS) and micronucleus (MN) assay on haemocytes to consider various types of cytogenomic damage, such as chromosomal aberrations, breakages, adducts and mutations. The results showed alteration of the individual endpoints at higher accumulation quotients (AQs) that reflect the excess of transfers to snails, especially with decreased survival for As. In addition, genotoxic effects were observed with an increased occurrence of MN in haemocytes for the three meta(loid)s considered (R² from 0.57 to 0.61 as a function of the meta(loid)s). No concentration-dependent decrease in genome stability was highlighted by RAPD-HRS in snails exposed to As and Cd but not Hg. Our results demonstrate the complementarity of the RAPD-HRS and the MN assay for understanding the different genotoxic mechanisms of the three metal(loid)s studied in land snails. They show a way to better assess environmental risks of contaminated soils by associating ecotoxicity, genotoxicity and bioaccumulation assays (ISO 24032), i.e., ecogenotoxicological bioavailability. Convergences highlighted here between the bioaccumulation of metal(loid)s in viscera and genotoxic effects in haemocytes constitute a way to better assess the bioavailability of contaminants in soils to the land snail and the subsequent environmental risk.

Exposure characteristics of antimony and coexisting arsenic from multi-path exposure in typical antimony mine area

In this study, samples of daily foods, drinking waters, surface waters, and soils were collected and screened to investigate the external exposure of Sb and As from various intake pathways in typical Sb mining area. Biomarker samples of residents were analyzed to monitor internal exposure characteristic of Sb and As in human body. Exposure dosages of As and Sb and transfer of Sb and As from environment to human body were estimated based on the external and internal exposure. The following results were obtained: daily intakes of food accounted for major intakes of both Sb and As, and highlighted the significance of foods intakes from rice and vegetable. The results of Monte Carlo simulations showed that total daily intake of Sb(n = 1444)and As(n = 1131) approximately reached 1.08 × 10^-2 mg/kg/d and 1.19 × 10^-3 mg/kg/d, in which 98.82% and 63.07% of residents have exceeded the threshold dosages of Sb and As. The contaminants contents in biomarkers indicated that Sb exhibited the similar internal exposure as As, while the total transfer rate of Sb from environment to human were estimated as approximately 2.04-2.40 times lower than As. This study also suggested that drinking water is another important pathway with high bioavailability and male resident may present higher priority than female in uptake of Sb and As. The paper suggested the similarity and difference on bioavailability existed in Sb and its group V elements, As, that would provide the essential information on exposure of Sb and As in the typical Sb mine area.

External environmental agents influence telomere length and telomerase activity by modulating internal cellular processes: Implications in human aging

External environment affects cellular physiological processes and impact the stability of our genome. The most important structural components of our linear chromosomes which endure the impact by these agents, are the chromosomal ends called telomeres. Telomeres preserve the integrity of our genome by preventing end to end fusions and telomeric loss through by inhibiting DNA damage response (DDR) activation. This is accomplished by the presence of a six membered shelterin complex at telomeres. Further, telomeres cannot be replicated by normal DNA polymerase and require a special enzyme called telomerase which is expressed only in stem cells, few immune cells and germ cells. Telomeres are rich in guanine content and thus become extremely prone to damage arising due to physiological processes like oxidative stress and inflammation. External environmental factors which includes various physical, biological and chemical agents also affect telomere homeostasis by increasing oxidative stress and inflammation. In the present review, we highlight the effect of these external factors on telomerase activity and telomere length. We also discuss how the external agents affect the physiological processes, thus modulating telomere stability. Further, we describe its implication in the development of aging and its related pathologies.

Associations between and risks of trace elements related to skin and liver damage induced by arsenic from coal burning

Long-term exposure to high levels of arsenic has been documented to induce skin and liver damage, affecting hundreds of millions of people. While arsenic-induced skin and liver damage and trace element alterations have been studied, their correlations and risks have not been explained. Based on the above premise, this study included a total of 172 subjects from a coal-burning arsenic poisoning area. The levels of 18 trace elements in hair and six liver function indices in serum were detected, and the associations between and risks of trace elements related to skin and liver damage were analyzed. Finally, the receiver operating characteristic (ROC) curve and areas under the curve (AUC) were used to analyze the diagnostic values of certain trace elements for arsenic-induced skin and liver damage. The results found that a decrease in Se was a risk factor for arsenic-induced skin and liver damage (OR = 8.33 and 1.92, respectively). Furthermore, increases in Al and V were risk factors for arsenic-induced skin damage (OR = 1.05) and liver damage (OR = 13.16), respectively. In addition, the results found that Se and Al possessed certain diagnostic values for arsenic-induced skin damage (AUC = 0.93, 0.80), that Se possessed a diagnostic value for liver damage (AUC = 0.93), and that the combination of Se and Al increased the diagnostic value for skin damage (AUC = 0.96). This study provides an important research basis for further understanding the reasons for arsenic-induced skin and liver damage, for screening and identifying candidate diagnostic biomarkers, and for improving prevention and control strategies for arsenism.

Thyroid disrupting effects of perfluoroundecanoic acid and perfluorotridecanoic acid in zebrafish (Danio rerio) and rat pituitary (GH3) cell line

Due to global restriction on perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA), the use of long-chain perfluoroalkyl substances (PFASs, C > 8) and their environmental occurrences have increased. PFOS and PFOA have been known for thyroid disruption, however, knowledge is still limited on thyroid disrupting effects of long-chain PFASs (C > 10). In this study, two long-chain perfluorinated carboxylic acids (PFCAs), i.e., perfluoroundecanoic acid (PFUnDA) and perfluorotridecanoic acid (PFTrDA), were chosen and investigated for thyroid disrupting effects, using zebrafish embryo/larvae and rat pituitary cell line (GH3). For comparison, PFOA was also added as a test chemical and also investigated for its thyroid disruption potential. Following a 5 d exposure to PFTrDA, zebrafish larvae showed upregulation of the genes responsible for thyroid hormone synthesis (tshβ, nkx2.1, nis, tpo, mct8) and (de)activation (dio1, dio2). In contrast, both PFUnDA and PFOA induced no regulatory changes except for upregulation of a thyroid metabolism related gene (ugt1ab). Morphological changes such as decreased eyeball size, increased yolk sac size, or deflated swim bladder, occurred following exposure to PFUnDA, PFTrDA, and PFOA. In GH3 cells, exposure to PFUnDA and PFTrDA upregulated Tshβ gene, suggesting that these PFCAs increase thyroid hormone synthesis through stimulation by Tsh. In summary, both long-chain PFCAs could cause transcriptional changes of thyroid regulating genes that may lead to increased malformation of the zebrafish larvae, but the pathway of thyroid disruption appears to be different by the chain length. Confirmation and validation in adult fish following long term exposure are warranted.

Phytoremedial effect of Tinospora cordifolia against arsenic induced toxicity in Charles Foster rats

Arsenic poisoning is one of the most serious health hazards of recent times. It has been estimated that more than 200 million people of about 105 countries in the world are affected due to arsenic poisoning. Except mitigation, there is no such mode by which the population can be prevented from being exposed to arsenic. Tinospora cordifolia (T. cordifolia) is widely used in the folk medicine system for the treatment of various diseases. Hence, the aim of the present study was to investigate the antidote effects of ethanolic extract of T. cordifolia stem against arsenic induced hepato-renal toxicity in rat model. Twenty-four male Charles Foster rats (weighing 160-180 g) were randomly divided into two groups, where six rats were used as control group. Eighteen rats were orally treated with arsenic at the dose of 8 mg/kg body weight for 90 days daily and then further divided into three sub groups (n = 6 each). Sub group I-arsenic treated rats, were sacrificed after treatment; sub group II rats were used as arsenic control and the sub group III rats were administrated with T. cordifolia at the dose of 400 mg/kg body weight/day for 90 days. After the completion of dose duration, all the control and treatment group rats were sacrificed to evaluate the various parameters. Arsenic induced rats had significantly (p < 0.0001) altered biochemical serum levels of SGPT, SGOT, ALP, total bilirubin, urea, uric acid, creatinine and albumin; But, after the administration of T. cordifolia there was significant (p < 0.0001) restoration observed in these liver and kidney function parameters. The T. cordifolia administration also significantly (p < 0.0001) restored the serum MDA levels and arsenic concentration in blood, liver and kidney tissues, as well as significant (p < 0.0001) improvement in haematological variables. In histopathological study, the arsenic treated rats showed degenerative changes in the liver and kidney tissues such as lesions and vacuolizations in hepatocytes and nephrocytes respectively. However, after the administration with T. cordifolia rats, there was considerably significant restoration in liver and kidney tissues. The entire study suggests that arsenic caused severe damage to the liver and kidney at haematological, biochemical and histopathological levels in rats. However, T. cordifolia played the vital role to combat the arsenic induced toxicity in rats. Hence, T. cordifolia might be used as a nutritional supplement to combat the arsenic led toxicity among the exposed population.

Epigallocatechin gallate attenuates arsenic induced genotoxicity via regulation of oxidative stress in balb/C mice

Arsenic is well known genotoxicant which causes the excessive generation of reactive oxygen species (ROS) and inhibition of antioxidant enzyme systems leading to cell damage through the activation of oxidative sensitive signaling pathways. Epigallocatechin gallate (EGCG), the main and active polyphenolic catechin present in green tea, has shown potent antioxidant, free radical scavenging and genoprotective activity in vivo. The present study attempted to investigate antioxidant and geno-protective efficacy of EGCG by regulating arsenic induced oxidative stress in mice. Animals received prophylactic and therapeutic treatments at two different doses (25 and 50 mg/kg b.wt.) of EGCG orally for 15 days and administered arsenic intraperitoneally at dose of 1.5 mg/kg b.wt (1/10th of LD₅₀) for 10 days. Arsenic intoxication revealed enhanced ROS production (114%) in lymphocytes; elevated levels of LPO (2-4 fold); reduced levels of hepato-renal antioxidants (approx. 45%) and augmented genomic fragmentation in hepato-renal tissues; increased chromosomal anomalies (78%) and micronucleation (21.93%) in bone marrow cells and comet tailing (25%) in lymphocytes of mice. Both pre and post treatments of EGCG decreased ROS production, restored lipid peroxidation (LPO) and reduced hepato-renal antioxidants levels, reduced the DNA fragmentation, number of chromosomal aberrations (CA), micronucleation (MN), and comet tailing but prophylactic treatment of 50 mg/kg b.wt was the most effective treatment in regulating arsenic induced oxidative stress. The effectiveness of this dose was furthermore validated by calculating the inhibitory index. Thus, results of present work empirically demonstrate free radical scavenging, anti-oxidative and genoprotective efficacy of EGCG against arsenic toxicity.

Substantial Evidences Indicate That Inorganic Arsenic Is a Genotoxic Carcinogen: a Review

Arsenic is one of the most toxic environmental toxicants. More than 150 million people worldwide are exposed to arsenic through ground water contamination. It is an exclusive human carcinogen. Although the hallmarks of arsenic toxicity are skin lesions and skin cancers, arsenic can also induce cancers in the lung, liver, kidney, urinary bladder, and other internal organs. Arsenic is a non-mutagenic compound but can induce significant cytogenetic damage as measured by chromosomal aberrations, sister chromatid exchanges, and micronuclei formation in human systems. These genotoxic end points are extensively used to predict genotoxic potentials of different environmental chemicals, drugs, pesticides, and insecticides. These cytogenetic end points are also used for evaluating cancer risk. Here, by critically reviewing and analyzing the existing literature, we conclude that inorganic arsenic is a genotoxic carcinogen.

Blood concentrations of lead, cadmium, mercury and their association with biomarkers of DNA oxidative damage in preschool children living in an e-waste recycling area

Reactive oxygen species (ROS)-induced DNA damage occurs in heavy metal exposure, but the simultaneous effect on DNA repair is unknown. We investigated the influence of co-exposure of lead (Pb), cadmium (Cd), and mercury (Hg) on 8-hydroxydeoxyguanosine (8-OHdG) and human repair enzyme 8-oxoguanine DNA glycosylase (hOGG1) mRNA levels in exposed children to evaluate the imbalance of DNA damage and repair. Children within the age range of 3-6 years from a primitive electronic waste (e-waste) recycling town were chosen as participants to represent a heavy metal-exposed population. 8-OHdG in the children's urine was assessed for heavy metal-induced oxidative effects, and the hOGG1 mRNA level in their blood represented the DNA repair ability of the children. Among the children surveyed, 88.14% (104/118) had a blood Pb level >5 μg/dL, 22.03% (26/118) had a blood Cd level >1 μg/dL, and 62.11% (59/95) had a blood Hg level >10 μg/dL. Having an e-waste workshop near the house was a risk factor contributing to high blood Pb (r _s  = 0.273, p < 0.01), while Cd and Hg exposure could have come from other contaminant sources. Preschool children of fathers who had a college or university education had significantly lower 8-OHdG levels (median 242.76 ng/g creatinine, range 154.62-407.79 ng/g creatinine) than did children of fathers who had less education (p = 0.035). However, we did not observe a significant difference in the mRNA expression levels of hOGG1 between the different variables. Compared with children having low lead exposure (quartile 1), the children with high Pb exposure (quartiles 2, 3, and 4) had significantly higher 8-OHdG levels (β _Q2 = 0.362, 95% CI 0.111-0.542; β _Q3 = 0.347, 95% CI 0.103-0.531; β _Q4 = 0.314, 95% CI 0.087-0.557). Associations between blood Hg levels and 8-OHdG were less apparent. Compared with low levels of blood Hg (quartile 1), elevated blood Hg levels (quartile 2) were associated with higher 8-OHdG levels (β _Q2 = 0.236, 95% CI 0.039-0.406). Compared with children having low lead exposure (quartile 1), the children with high Pb exposure (quartiles 2, 3, and 4) had significantly higher 8-OHdG levels.

Arsenic exposure and risk of preeclampsia in a Mexican mestizo population

BACKGROUND

Exposure to arsenic in drinking water has been associated with various complications of pregnancy including fetal loss, low birth weight, anemia, gestational diabetes and spontaneous abortion. However, to date, there are no studies evaluating its possible association with preeclampsia.

METHODS

This case-control study involved 104 preeclamptic and 202 healthy pregnant women. The concentrations of arsenic in drinking water and urine were measured using a Microwave Plasma-Atomic Emission Spectrometer.

RESULTS

We found relatively low levels of arsenic in household tap water (range of 2.48-76.02 μg/L) and in the urine of the participants (7.1 μg/L vs 6.78 μg/L in cases and controls, respectively).

CONCLUSIONS

The analysis between groups showed for the first time that at these lower levels of exposure there is no association with preeclampsia.

When Parasites Are Good for Health: Cestode Parasitism Increases Resistance to Arsenic in Brine Shrimps

Parasites and pollutants can both affect any living organism, and their interactions can be very important. To date, repeated studies have found that parasites and heavy metals or metalloids both have important negative effects on the health of animals, often in a synergistic manner. Here, we show for the first time that parasites can increase host resistance to metalloid arsenic, focusing on a clonal population of brine shrimp from the contaminated Odiel and Tinto estuary in SW Spain. We studied the effect of cestodes on the response of Artemia to arsenic (acute toxicity tests, 24h LC50) and found that infection consistently reduced mortality across a range of arsenic concentrations. An increase from 25°C to 29°C, simulating the change in mean temperature expected under climate change, increased arsenic toxicity, but the benefits of infection persisted. Infected individuals showed higher levels of catalase and glutathione reductase activity, antioxidant enzymes with a very important role in the protection against oxidative stress. Levels of TBARS were unaffected by parasites, suggesting that infection is not associated with oxidative damage. Moreover, infected Artemia had a higher number of carotenoid-rich lipid droplets which may also protect the host through the "survival of the fattest" principle and the antioxidant potential of carotenoids. This study illustrates the need to consider the multi-stress context (contaminants and temperature increase) in which host-parasite interactions occur.

Protective Effects of Combined Selenium and Punica granatum Treatment on Some Inflammatory and Oxidative Stress Markers in Arsenic-Induced Hepatotoxicity in Rats

Oxidative stress is one of the major mechanisms implicated in inorganic arsenic poisoning. Punica granatum is known by its free radical scavenging properties. The aim of this study was to evaluate the protective role of combined selenium and P. granatum against arsenic-induced liver injury. Seventy-five female albino rats were divided into five groups (of 15 rats each). Toxicity was induced by oral sodium arsenite (5.5 mg/kg body weight (bw) daily) (group ІІ). Treatment of arsenic-intoxicated rats was induced by daily oral administration of sodium selenite (3 mg/kg bw) (group ІІІ), 100 mg of P. granatum ethanol extract per kilogram body weight dissolved in 300 mL distilled water in three divided doses (100 mL of this suspension every 8 h) (group IV), and combined daily oral treatment with both selenite and P. granatum ethanol extract (group V). After 3 weeks, serum and liver tissues were obtained from the decapitated rats for different estimations. Hepatotoxicity was demonstrated by significant elevation in liver weights and activities of liver enzymes, alanine aminotransferase (ALT) and aspartate aminotransferase (AST), and decrease in serum total proteins and albumin (p < 0.05) which were confirmed by histopathological examination. Additionally, arsenic hepatotoxicity led to an increased values of malondialdehyde, advanced oxidation protein products, nitric oxide, and interleukin-6 (IL-6) (p < 0.05) and decreased activity of thioredoxin reductase, values of total anti-oxidant capacity, and nuclear factor erythroid 2-related factor 2 (Nrf2) gene expression. Significant improvement in all assessed parameters was observed in rat group treated with both P. granatum and selenium. It was concluded that combined P. granatum and selenium treatment had a synergistic hepatoprotective effect against arsenic toxicity through activation of Nrf2 anti-oxidant pathway.

Antioxidative effect of rice bran oil and medium chain fatty acid rich rice bran oil in arsenite induced oxidative stress in rats

The present study was adopted to evaluate the antioxidant efficacy of medium chain fatty acid (caprylic, capric and lauric) rich rice bran oils in comparison to rice bran oil in terms of altered biochemical parameters of oxidative stress following sodium arsenite treatment in rats. Animals were divided into ten groups; five normal groups and five arsenite treated groups. Results showed that activities of antioxidant enzymes in liver, brain and erythrocyte membrane increased with the administration of rice bran oil and MCFA rich rice bran oils both in normal and arsenite treated cases. Lipid peroxidation increased with the administration of sodium arsenite, but again administration of rice bran oil and MCFA rich rice bran oils decreased the lipid peroxidation. Caprylic acid rich rice bran oil showed the best ameliorative effects.

Cardiovascular disease and arsenic exposure in Inner Mongolia, China: a case control study

BACKGROUND

Millions of people are at risk from the adverse effects of arsenic exposure through drinking water. Increasingly, non-cancer effects such as cardiovascular disease have been associated with drinking water arsenic exposures. However, most studies have been conducted in highly exposed populations and lacked individual measurements.

OBJECTIVE

To evaluate the association between cardiovascular disease and well-water arsenic exposure.

METHODS

We conducted a hospital based case control study in Inner Mongolia, China. Cases and controls were prospectively identified and enrolled from a large hospital in the Hangjin Hou area. Cases were patients diagnosed with cardiovascular disease and controls were patients free from cardiovascular disease, admitted for conditions unrelated to arsenic exposure. Water from the primary water source and toenail samples were collected from each subject and tested for inorganic arsenic.

RESULTS

Arsenic exposures were moderate with mean and median arsenic exposures of 8.9 μg/L and 13.1 μg/L, respectively. A total of 298 cases and 275 controls were enrolled. The adjusted odds ratio (AOR) and corresponding 95% confidence interval (95% CI) for a 10 μg/L increase in water arsenic were 1.19 (95% CI: 1.03, 1.38). Compared to exposures less than 10 μg/L, the AOR for water arsenic exposures above 40 μg/L was 4.05 (95% CI: 1.1-14.99, p = 0.04). Nail arsenic above 1.38 μg/g was also associated with an increased risk of cardiovascular disease.

CONCLUSIONS

By using standardized case definitions and collecting individual measurements of arsenic, this study addressed several limitations of previous studies. The results provide further evidence of the association between cardiovascular disease and arsenic at moderate exposures.

β-Carotene ameliorates arsenic-induced toxicity in albino mice

The present study evaluated the ameliorative potential of β-carotene (BCT) against experimentally induced arsenic toxicity in Swiss albino mice. BCT (5 and 10 mg/kg) was administered orally to mice 30 min before oral administration of arsenic trioxide (3 mg/kg) for 14 consecutive days. On 15th day, the body weights, organ weights, hematological profiles, serum biochemical profile; hepatic and renal antioxidative parameters viz. lipid peroxidation, reduced and oxidized glutathione, glutathione-S-transferase, glutathione peroxidase, glutathione reductase, superoxide dismutase, catalase; and DNA fragmentation were evaluated. Co-treatment with BCT markedly and significantly normalized body weights, organ weights, hematological profiles, serum biochemical profile and significantly modulated all the hepatic and renal biochemical parameters and DNA fragmentation in arsenic-intoxicated mice. The present findings conclude that β-carotene possessed remarkable ameliorative effect against arsenic-induced toxicity in albino mice mediated by its antioxidant and antigenotoxic properties.

Arsenic exposure, telomere length, and expression of telomere-related genes among Bangladeshi individuals

BACKGROUND

Inorganic arsenic is a carcinogen whose mode of action may involve telomere dysfunction. Recent epidemiological studies suggest that chronic arsenic exposure is associated with longer telomeres and altered expression of telomere-related genes in peripheral blood. In this study, we evaluated the association of urinary arsenic concentration with expression of telomere-related genes and telomere length in Bangladeshi individuals with a wide range of arsenic exposure through naturally contaminated drinking water.

METHODS

We used linear regression models to estimate associations between urinary arsenic and array-based expression measures for 69 telomere related genes using mononuclear cell RNA samples from 1799 individuals. Association between arsenic exposure and a qPCR-based telomere length measure was assessed among 167 individuals.

RESULTS

Urinary arsenic was positively associated with expression of WRN, and negatively associated with TERF2, DKC1, TERF2IP and OBFC1 (all P<0.00035, Bonferroni-corrected threshold). We detected interaction between urinary arsenic and arsenic metabolism efficiency in relation to expression of WRN (P for interaction =0.00008). In addition, we observed that very high arsenic exposure was associated with longer telomeres compared to very low exposure (P=0.02).

DISCUSSION

Our findings suggest that arsenic's carcinogenic mode of action may involve alteration of telomere maintenance and/or telomere damage. This study extends our knowledge regarding the effect of arsenic on telomere length and expression of telomere-related genes.

Colorimetric Au nanoparticle probe for speciation test of arsenite and arsenate inspired by selective interaction between phosphonium ionic liquid and arsenite

The exposure of millions of people to unsafe levels of arsenite (AsIII) and arsenate (AsV) in drinking waters calls for the development of low-cost methods for on-site monitoring these two arsenic species in waters. Herein, for the first time, tetradecyl (trihexyl) phosphonium chloride ionic liquid was found to selectively bind with AsIII via extended X-ray absorption fine structure (EXAFS) analysis. Based on the finding, an AsIII-specific probe was developed by modifying gold nanoparticles with the ionic liquid. Futhermore, Hofmeister effect was primarily observed to significantly affect the sensitivity of gold nanoparticle probe. With the colorimetric probe, we developed a protocol for naked eye speciation test of AsIII and AsV at levels below the World Health Organization (WHO) guideline of 10 μg L(-1). This method featured with high tolerance to common coexisting ions such as 10 mM PO4(3-), and was validated by assaying certified reference and environmental water samples.

Triphlorethol-A from Ecklonia cava up-regulates the oxidant sensitive 8-oxoguanine DNA glycosylase 1

This study investigated the protective mechanisms of triphlorethol-A, isolated from Ecklonia cava, against oxidative stress-induced DNA base damage, especially 8-oxoguanine (8-oxoG), in Chinese hamster lung fibroblast V79-4 cells. 8-Oxoguanine DNA glycosylase-1 (OGG1) plays an important role in the removal of 8-oxoG during the cellular response to DNA base damage. Triphlorethol-A significantly decreased the levels of 8-oxoG induced by H2O2, and this correlated with increases in OGG1 mRNA and OGG1 protein levels. Furthermore, siOGG1-transfected cell attenuated the protective effect of triphlorethol-A against H2O2 treatment. Nuclear factor erythroid 2-related factor 2 (Nrf2) is a transcription factor for OGG1, and Nrf2 combines with small Maf proteins in the nucleus to bind to antioxidant response elements (ARE) in the upstream promoter region of the OGG1 gene. Triphlorethol-A restored the expression of nuclear Nrf2, small Maf protein, and the Nrf2-Maf complex, all of which were reduced by oxidative stress. Furthermore, triphlorethol-A increased Nrf2 binding to ARE sequences and the resulting OGG1 promoter activity, both of which were also reduced by oxidative stress. The levels of the phosphorylated forms of Akt kinase, downstream of phosphatidylinositol 3-kinase (PI3K), and Erk, which are regulators of OGG1, were sharply decreased by oxidative stress, but these decreases were prevented by triphlorethol-A. Specific PI3K, Akt, and Erk inhibitors abolished the cytoprotective effects of triphlorethol-A, suggesting that OGG1 induction by triphlorethol-A involves the PI3K/Akt and Erk pathways. Taken together, these data indicate that by activating the DNA repair system, triphlorethol-A exerts protective effects against DNA base damage induced by oxidative stress.

In vivo study on the effects of curcumin on the expression profiles of anti-tumour genes (VEGF, CyclinD1 and CDK4) in liver of rats injected with DEN

In this study we investigated the effects of curcumin, derived from plant Curcuma longa, on oxidative toxicity, and the possible molecular mechanism of antitumour of curcumin in liver cancer rats. Results showed that blood levels of Gamma-glutamyltransferase, aspartate aminotransferase, alanine aminotransferase, glutathione S-transferase, and liver level of MD were significantly decreased after curcumin feeding. Levels of the liver malondialdehyde MDA, nitric oxide and antioxidant enzymes were significantly increased. Moreover, RT-PCR and Western blot analysis results showed that curcumin treatment significantly decreased liver vascular endothelial growth factor (VEGF), CyclinD1 and CDK4 mRNA expression levels and CyclinD1 and CDK4 proteins levels in liver cancer rats. These findings were confirmed by histopathology. It is concluded that curcumin can protect the liver from the damage caused by N-nitrosodiethylamine. Moreover, curcumin has the potential to be used in a therapy for liver cancer. The present data provide evidence to support the presence of free radicals and VEGF, CyclinD1 and CDK4 mRNA in rat tumour cells. Studies are in progress in order to further characterize the role of VEGF, CyclinD1 and CDK4 mRNA in liver cancer cells and in hepatic therapeutics.

7,8-Dihydroxyflavone suppresses oxidative stress-induced base modification in DNA via induction of the repair enzyme 8-oxoguanine DNA glycosylase-1

The modified guanine base 8-oxoguanine (8-oxoG) is abundantly produced by oxidative stress, can contribute to carcinogenesis, and can be removed from DNA by 8-oxoguanine DNA glycosylase-1 (OGG1), which acts as an 8-oxoG glycosylase and endonuclease. This study investigated the mechanism by which 7,8-dihydroxyflavone (DHF) inhibits oxidative stress-induced 8-oxoG formation in hamster lung fibroblasts (V79-4). DHF significantly reduced the amount of 8-oxoG induced by hydrogen peroxide (H₂O₂) and elevated the levels of OGG1 mRNA and protein. DHF increased the binding of nuclear factor erythroid 2-related factor 2 (Nrf2) to antioxidant response element sequences in the upstream promoter region of OGG1. Moreover, DHF increased the nuclear levels of Nrf2, small Maf proteins, and the Nrf2/small Maf complex, all of which are decreased by H₂O₂ treatment. Likewise, the level of phosphorylated Akt, which activates Nrf2, was decreased by H₂O₂ treatment but restored by DHF treatment. The levels of OGG1 and nuclear translocation of Nrf2 protein were decreased upon treatment with PI3K inhibitor or Akt inhibitor, and DHF treatment did not restore OGG1 and nuclear Nrf2 levels in these inhibitor-treated cells. Furthermore, PI3K and Akt inhibitors abolished the protective effects of DHF in cells undergoing oxidative stress. These data indicate that DHF induces OGG1 expression via the PI3K-Akt pathway and protects cells against oxidative DNA base damage by activating DNA repair systems.

Environmental and occupational exposure to chemicals and telomere length in human studies

Telomeres are complexes of tandem repeats of DNA (5'-TTAGGG-3') and protein that cap eukaryotic chromosomes and play a critical role in chromosome stability. Telomeres shorten with aging and this process can be accelerated by increased oxidative stress and episodes of inflammation. Evidence is rapidly growing that telomere length (TL) may be affected by environmental chemicals that have frequently been associated with chronic diseases. In this article, we review the published data on TL in relation to environmental and occupational exposure to several chemicals based on our own and others' studies. The environmental and occupational exposures associated with shorter TL include traffic-related air pollution (ie, particulate matter (PM), black carbon (BC), and benzene and toluene), polycyclic aromatic hydrocarbons (PAHs), N-nitrosamines, pesticides, lead, exposure in car mechanical workshops, and hazardous waste exposure. Arsenic, persistent organic pollutants (POPs) and short-term exposure to PM are associated with longer TL. We discuss the possible reasons for the differences in results, including time- and dose-related issues, study design, and possible mechanisms involved in telomere regulation. We also discuss the future directions and challenges for TL-related environmental and occupational health research, such as investigation of TL in subpopulations of blood leukocytes, and the study of genetic and epigenetic factors that may regulate telomere integrity using longitudinal designs.

Arsenic levels and speciation from ingestion exposures to biomarkers in Shanxi, China: implications for human health

Chronic exposure to arsenic (As) threatens human health. To systematically understand the health risks induced by As ingestion, we explored water and diet contributions to As exposure, and compared As in biomarkers and the arsenicosis in a geogenic As area in China. In this study, high percentages of water (77% of n = 131 total samples), vegetables (92%, n = 120), cereals (32%, n = 25), urine (70%, n = 99), nails (76%, n = 176), and hair (62%, n = 61) contained As higher than the acceptable levels. Dietary As contributed 92% of the average daily dose (ADD) when the water As concentration was less than 10 μg/L, for which 5 out of 30 examined participants were diagnosed with arsenicosis symptoms. The distinct positive correlation between ADD and As concentrations in urine, nails, and hair suggests different applicability for these biomarkers. Methylated As as the predominant urinary As species confirms that the ingested inorganic As is methylated and is excreted through urine. In situ microdistribution and speciation analysis indicates that As is mainly associated with sulfur in nails and hair. Nails, rather than hair and urine, could be used as a proper biomarker for arsenicosis. High ADD from the environment and low excretion could result in As toxicity to humans.

The dietary acrylamide intake adversely affects the serum trace element status

Acrylamide is an organic chemical which occurs in foods widespreadly consumed in diets worldwide. The purpose of this study was to evaluate the serum trace element levels (Fe, Cu, Zn, Mn, Cr, Se, Co, Ni, V, As, Mg, P, Li, K, Al) in Wistar rats exposed to acrylamide. Acrylamide was administered to the treatment groups at 2 and 5 mg/kg body weight (bw)/day via drinking water for 90 days. Inductively coupled plasma mass spectrometry was used for the determination of serum trace element concentrations. Serum Zn, Se, Co, V and Mg concentrations of 5 mg/kg bw/day acrylamide-treated male rats were lower, whereas serum As concentration was higher than the same parameters of the controls rats. Similarly, serum Zn, Se, Co, V and Mg concentrations were decreased in 5 mg/kg bw/day acrylamide-treated female rats compared with control rats. On the other hand, there were no significant differences between serum Fe, Cu, Mn, Cr, Ni, P, Li, K and Al concentrations of all groups. The results from this study provide evidence that dietary acrylamide intake adversely affects the serum trace elements status.

Protective effect of conjugated linolenic acid isomers present in vegetable oils against arsenite-induced renal toxicity in rat model

OBJECTIVE

The aim of the present study was to investigate the protective effect of conjugated linolenic acid (CLnA), present in vegetable oils against arsenite-induced renal oxidative stress.

METHODS

Albino rats were divided into six groups. Group 1 was control and group 2 was treated with sodium arsenite (Sa; 10 mg/kg BW). Rats in groups 3 and 4 were treated with mixture of α-eleostearic acid and punicic acid (1:1) (0.5% and 1.0%, respectively), whereas rats in the groups 5 and 6 were treated with 0.5% of α-eleostearic acid and 0.5% of punicic acid, respectively, along with Sa by oral gavage once daily.

RESULTS

Results revealed that activity of antioxidant enzymes and total reduced glutathione content, total protein content, and phospholipid content in kidney were decreased significantly in arsenite-treated group compared with control. Activity of nitric oxide synthase, peroxidation of lipid, protein oxidation, total cholesterol content, total lipid content of kidney, and plasma creatinine level were increased significantly (P < 0.05) in arsenite-treated rats compared with control. Fatty-acid composition of renal lipids showed significant decrease in monounsaturated fatty acid, polyunsaturated fatty acid (PUFA) content, and increase in saturated fatty acid content due to oxidative stress. PUFA such as γ-linolenic acid, eicosapentaenoic acid, and docosahexaenoic acid decreased significantly with significant (P < 0.05) increase in arachidonic acid content after Sa treatment. Administration of blended product of both the isomers caused better restoration of renal fatty acids and other altered parameters.

CONCLUSION

CLnA isomers caused amelioration of renal oxidative stress and the isomers showed synergistic activity.

Trichosanthes dioica fruit ameliorates experimentally induced arsenic toxicity in male albino rats through the alleviation of oxidative stress

The present work was focused to evaluate the ameliorative property of aqueous extract of Trichosanthes dioica fruit (AQ T. dioica fruit) against arsenic-induced toxicity in male Wistar albino rats. AQ T. dioica fruit was administered orally to rats at 50 and 100 mg/kg body weight for 20 consecutive days prior to oral administration of sodium arsenite (10 mg/kg) for 10 days. Then the rats were sacrificed for the evaluation of body weights, organ weights, hematological profile, serum biochemical profile, and hepatic and renal antioxidative parameters viz. lipid peroxidation, reduced and oxidized glutathione, glutathione-S-transferase, glutathione peroxidase, glutathione reductase, superoxide dismutase, catalase, and DNA fragmentation. Pretreatment with AQ T. dioica fruit at both doses markedly and significantly normalized body weights, organ weights, hematological profiles, and serum biochemical profile in arsenic-treated animals. Further, AQ T. dioica fruit pretreatment significantly modulated all the aforesaid hepatic and renal biochemical perturbations and reduced DNA fragmentation in arsenic-intoxicated rats. Therefore, from the present findings, it can be concluded that T. dioica fruit possessed remarkable value in amelioration of arsenic-induced hepatic and renal toxicity, mediated by alleviation of arsenic-induced oxidative stress by multiple mechanisms in male albino rats.

Ameliorative effect Trichosanthes dioica root against experimentally induced arsenic toxicity in male albino rats

The present study evaluated the ameliorative potential of hydroalcoholic extract of Trichosanthes dioica root (TDA) against arsenic induced toxicity in male albino rats. TDA (5 and 10mg/kg) was administered orally to rats for 20 consecutive days before oral administration of sodium arsenite (10mg/kg) for 8 days. Then the body weights, organ weights, haematological profiles, serum biochemical profile; hepatic and renal antioxidative parameters viz. lipid peroxidation, reduced and oxidized glutathione, glutathione-S-transferase, glutathione peroxidase, glutathione reductase, superoxide dismutase, catalase and DNA fragmentation were evaluated. Pretreatment with TDA markedly and significantly normalized body weights, organ weights, haematological profiles, serum biochemical profile and significantly modulated all the hepatic and renal biochemical parameters and reduced DNA fragmentation in arsenic intoxicated rats. The present findings conclude that T. dioica root possessed remarkable ameliorative effect against arsenic induced organ toxicity in male albino rats mediated by alleviation of arsenic induced oxidative stress by multiple mechanisms.

Molecular mechanisms for age-associated mitochondrial deficiency in skeletal muscle

The abundance, morphology, and functional properties of mitochondria decay in skeletal muscle during the process of ageing. Although the precise mechanisms remain to be elucidated, these mechanisms include decreased mitochondrial DNA (mtDNA) repair and mitochondrial biogenesis. Mitochondria possess their own protection system to repair mtDNA damage, which leads to defects of mtDNA-encoded gene expression and respiratory chain complex enzymes. However, mtDNA mutations have shown to be accumulated with age in skeletal muscle. When damaged mitochondria are eliminated by autophagy, mitochondrial biogenesis plays an important role in sustaining energy production and physiological homeostasis. The capacity for mitochondrial biogenesis has shown to decrease with age in skeletal muscle, contributing to progressive mitochondrial deficiency. Understanding how these endogenous systems adapt to altered physiological conditions during the process of ageing will provide a valuable insight into the underlying mechanisms that regulate cellular homeostasis. Here we will summarize the current knowledge about the molecular mechanisms responsible for age-associated mitochondrial deficiency in skeletal muscle. In particular, recent findings on the role of mtDNA repair and mitochondrial biogenesis in maintaining mitochondrial functionality in aged skeletal muscle will be highlighted.

8-Oxoguanine DNA glycosylase 1 (OGG1) from the copepod Tigriopus japonicus: molecular characterization and its expression in response to UV-B and heavy metals

8-Oxoguanine DNA glycosylase 1 (EC 3.2.2.23) is encoded by OGG1 gene and plays a key role in removing 8-oxo-7,8-dihydroguanine (8-oxoG) base in DNA lesion by reactive oxygen species (ROS). To identify and characterize OGG1 gene (TJ-OGG1) in the copepod Tigriopus japonicus, the full-length cDNA sequence, genomic structure, and promoter region was analyzed. In addition, to investigate transcriptional change of TJ-OGG1 mRNA under oxidative stress conditions, T. japonicus were exposed to environmental oxidative inducers, H(2)O(2), UV-B, and heavy metals (Cd, Cu, and Zn), respectively. The full-length cDNA of TJ-OGG1 gene was 1708 bp in length, encoding 343 amino acid residues. The deduced amino acid sequences of TJ-OGG1 showed a 56% similarity with human. Two conserved motifs (HhH and PVD loop) and two conserved residues (lysine and aspartic acid) in active sites were also observed. TJ-OGG1 genome structure contained six exons and five introns and putative transcription factor binding sites such as Nrf-2, p53, ERE-half sites, and XRE were detected on the promoter region. TJ-OGG1 mRNA level was increased at approximately three-fold (P<0.05) at 1mM and approximately 4-fold (P<0.01) at 10mM of H(2)O(2), respectively. UV-B enhanced the expression of TJ-OGG1 mRNA at 15kJ/m(2) (P<0.05) and more (P<0.001). In a time-course experiment, TJ-OGG1 gene was highly transcribed within 12h after exposure of 10 kJ/m(2) (P<0.01) and 20 kJ/m(2) (P<0.001). The expression of TJ-OGG1 mRNA after exposure to Cu and Cd for 96 h was significantly up-regulated at 0.1 μg/L and then remarkably reduced in a dose-dependent manner. Their transcript levels did not change at low dose (0.1 and 1 μg/L) but were dose-dependently down-regulated at high dose (10 and 100 μg/L). These findings suggest that H(2)O(2), UV-B, and heavy metals induce oxidative stress and generate oxidatively damaged DNA. Consequently, the enhanced TJ-OGG1 gene expression would be associated with active involvement of TJ-OGG1 gene in DNA repair process as a cellular protection mechanism. This is the first report on the cloning and characterization of OGG1 gene in aquatic animals. This study is helpful for a better understanding of the molecular mechanisms of cellular protection against various environmental oxidative stress inducers such as UV-B and heavy metals in aquatic invertebrates.

Influence of the OGG1 Ser326Cys polymorphism on oxidatively damaged DNA and repair activity

Oxidatively damaged DNA base lesions are considered to be mainly repaired by 8-oxoguanine DNA glycosylase (OGG1) mediated pathways. We investigated the effect of the OGG1 Ser326Cys polymorphism on the level and repair of oxidatively damaged DNA in mononuclear blood cells (MNBC) by means of the comet assay. We collected blood samples from 1,019 healthy subjects and genotyped for the OGG1 Ser326Cys polymorphism. We found 49 subjects homozygous for the variant genotype (Cys/Cys) and selected same numbers of age-matched subjects with the heterozygous (Ser/Cys) and homozygous wild-type genotype (Ser/Ser). Carriers of the Cys/Cys genotype had higher levels of formamidopyrimidine DNA glycosylase (FPG) sensitive sites in MNBC (0.31 ± 0.03 lesions/10(6)bp) compared to Ser/Ser (0.19 ± 0.02 lesions/10(6)bp, P<0.01). The level of hOGG1 sensitive sites in MNBC from the Ser326Cys carriers (0.19 ± 0.16 lesions/10(6) bp) was also higher compared to the Ser/Ser genotype (0.11 ± 0.09 lesions/10(6) bp, P<0.05). Still, there was no genotype-related difference in DNA repair incision activity of MNBC extracts on nucleoids with oxidatively damaged DNA induced by Ro19-8022/white light (P=0.20). In addition, there were no differences in the expression of OGG1 (P=0.69), ERCC1 (P=0.62), MUTYH (P=0.85), NEIL1 (P=0.17) or NUDT1 (P=0.48) in whole blood. Our results indicate that the OGG1 Ser326Cys polymorphism has limited influence on the DNA repair incisions by extracts of MNBC, whereas the apparent increased risk of cancer in subjects with the Cys/Cys genotype may be because of higher levels of oxidatively damaged DNA.

Arsenic biotransformation as a cancer promoting factor by inducing DNA damage and disruption of repair mechanisms

Chronic exposure to arsenic in drinking water poses a major global health concern. Populations exposed to high concentrations of arsenic-contaminated drinking water suffer serious health consequences, including alarming cancer incidence and death rates. Arsenic is biotransformed through sequential addition of methyl groups, acquired from s-adenosylmethionine (SAM). Metabolism of arsenic generates a variety of genotoxic and cytotoxic species, damaging DNA directly and indirectly, through the generation of reactive oxidative species and induction of DNA adducts, strand breaks and cross links, and inhibition of the DNA repair process itself. Since SAM is the methyl group donor used by DNA methyltransferases to maintain normal epigenetic patterns in all human cells, arsenic is also postulated to affect maintenance of normal DNA methylation patterns, chromatin structure, and genomic stability. The biological processes underlying the cancer promoting factors of arsenic metabolism, related to DNA damage and repair, will be discussed here.

Arsenicals affect base excision repair by several mechanisms

Inorganic arsenic is a strong, widespread human carcinogen. How exactly inorganic arsenic exerts carcinogenicity in humans is as yet unclear, but it is thought to be closely related to its metabolism. At exposure-relevant concentrations arsenic is neither directly DNA reactive nor mutagenic. Thus, more likely epigenetic and indirect genotoxic effects, among others a modulation of the cellular DNA damage response and DNA repair, are important molecular mechanisms contributing to its carcinogenicity. In the present study, we investigated the impact of arsenic on several base excision repair (BER) key players in cultured human lung cells. For the first time gene expression, protein level and in case of human 8-oxoguanine DNA glycosylase 1 (hOGG1) protein function was examined in one study, comparing inorganic arsenite and its trivalent and pentavalent mono- and dimethylated metabolites, also taking into account their cellular bioavailability. Our data clearly show that arsenite and its metabolites can affect several cellular endpoints related to DNA repair. Thus, cellular OGG activity was most sensitively affected by dimethylarsinic acid (DMA(V)), DNA ligase IIIα (LIGIIIα) protein level by arsenite and X-ray cross complementing protein 1 (XRCC1 protein) content by monomethylarsonic acid (MMA(V)), with significant effects starting at ≥3.2μM cellular arsenic. With respect to MMA(V), to our knowledge these effects are the most sensitive endpoints, related to DNA damage response, that have been identified so far. In contrast to earlier nucleotide excision repair related studies, the trivalent methylated metabolites exerted strong effects on the investigated BER key players only at cytotoxic concentrations. In summary, our data point out that after mixed arsenic species exposure, a realistic scenario after oral inorganic arsenic intake in humans, DNA repair might be affected by different mechanisms and therefore very effectively, which might facilitate the carcinogenic process of inorganic arsenic.

Arsenic biotransformation as a cancer promoting factor by inducing DNA damage and disruption of repair mechanisms

Chronic exposure to arsenic in drinking water poses a major global health concern. Populations exposed to high concentrations of arsenic-contaminated drinking water suffer serious health consequences, including alarming cancer incidence and death rates. Arsenic is biotransformed through sequential addition of methyl groups, acquired from s-adenosylmethionine (SAM). Metabolism of arsenic generates a variety of genotoxic and cytotoxic species, damaging DNA directly and indirectly, through the generation of reactive oxidative species and induction of DNA adducts, strand breaks and cross links, and inhibition of the DNA repair process itself. Since SAM is the methyl group donor used by DNA methyltransferases to maintain normal epigenetic patterns in all human cells, arsenic is also postulated to affect maintenance of normal DNA methylation patterns, chromatin structure, and genomic stability. The biological processes underlying the cancer promoting factors of arsenic metabolism, related to DNA damage and repair, will be discussed here.

Arsenic-induced oxidative stress and its reversibility

This review summarizes the literature describing the molecular mechanisms of arsenic-induced oxidative stress, its relevant biomarkers, and its relation to various diseases, including preventive and therapeutic strategies. Arsenic alters multiple cellular pathways including expression of growth factors, suppression of cell cycle checkpoint proteins, promotion of and resistance to apoptosis, inhibition of DNA repair, alterations in DNA methylation, decreased immunosurveillance, and increased oxidative stress, by disturbing the pro/antioxidant balance. These alterations play prominent roles in disease manifestation, such as carcinogenicity, genotoxicity, diabetes, cardiovascular and nervous systems disorders. The exact molecular and cellular mechanisms involved in arsenic toxicity are rather unrevealed. Arsenic alters cellular glutathione levels either by utilizing this electron donor for the conversion of pentavalent to trivalent arsenicals or directly binding with it or by oxidizing glutathione via arsenic-induced free radical generation. Arsenic forms oxygen-based radicals (OH(•), O(2)(•-)) under physiological conditions by directly binding with critical thiols. As a carcinogen, it acts through epigenetic mechanisms rather than as a classical mutagen. The carcinogenic potential of arsenic may be attributed to activation of redox-sensitive transcription factors and other signaling pathways involving nuclear factor κB, activator protein-1, and p53. Modulation of cellular thiols for protection against reactive oxygen species has been used as a therapeutic strategy against arsenic. N-acetylcysteine, α-lipoic acid, vitamin E, quercetin, and a few herbal extracts show prophylactic activity against the majority of arsenic-mediated injuries in both in vitro and in vivo models. This review also updates the reader on recent advances in chelation therapy and newer therapeutic strategies suggested to treat arsenic-induced oxidative damage.

Altered gene expression by low-dose arsenic exposure in humans and cultured cardiomyocytes: assessment by real-time PCR arrays

Chronic arsenic exposure results in higher risk of skin, lung, and bladder cancer, as well as cardiovascular disease and diabetes. The purpose of this study was to investigate the effects on expression of selected genes in the blood lymphocytes from 159 people exposed chronically to arsenic in their drinking water using a novel RT-PCR TaqMan low-density array (TLDA). We found that expression of tumor necrosis factor-α (TNF-α), which activates both inflammation and NF-κB-dependent survival pathways, was strongly associated with water and urinary arsenic levels. Expression of KCNA5, which encodes a potassium ion channel protein, was positively associated with water and toe nail arsenic levels. Expression of 2 and 11 genes were positively associated with nail and urinary arsenic, respectively. Because arsenic exposure has been reported to be associated with long QT intervals and vascular disease in humans, we also used this TLDA for analysis of gene expression in human cardiomyocytes exposed to arsenic in vitro. Expression of the ion-channel genes CACNA1, KCNH2, KCNQ1 and KCNE1 were down-regulated by 1-μM arsenic. Alteration of some common pathways, including those involved in oxidative stress, inflammatory signaling, and ion-channel function, may underlay the seemingly disparate array of arsenic-associated diseases, such as cancer, cardiovascular disease, and diabetes.