DNA damage in arsenite- and cadmium-treated bovine aortic endothelial cells

Combined exposure to multiple metals on cardiovascular disease in NHANES under five statistical models

BACKGROUND

It is well-documented that heavy metals are associated with cardiovascular disease (CVD). However, there is few studies exploring effect of metal mixture on CVD. Therefore, the primary objective of present study was to investigate the joint effect of heavy metals on CVD and to identify the most influential metals in the mixture.

METHODS

Original data for study subjects were obtained from the National Health and Nutrition Examination Survey. In this study, adults with complete data on 12 kinds of urinary metals (antimony, arsenic, barium, cadmium, cobalt, cesium, molybdenum, mercury, lead, thallium, tungsten, and uranium), cardiovascular disease, and core covariates were enrolled. We applied five different statistical strategies to examine the CVD risk with metal exposure, including multivariate logistic regression, adaptive elastic net combined with Environmental Risk Score, Quantile g-computation, Weighted Quantile Sum regression, and Bayesian kernel machine regression.

RESULTS

Higher levels of cadmium, tungsten, cobalt, and antimony were significantly associated with Increased risk of CVD when covariates were adjusted for multivariate logistic regression. The results from multi-pollutant strategies all indicated that metal mixture was positively associated with the risk of CVD. Based on the results of multiple statistical strategies, it was determined that cadmium, tungsten, cobalt, and antimony exhibited the strongest positive correlations, whereas barium, lead, molybdenum, and thallium were most associated with negative correlations.

CONCLUSION

Overall, our study demonstrates that exposure to heavy metal mixture is linked to a higher risk of CVD. Meanwhile, this association may be driven primarily by cadmium, tungsten, cobalt, and antimony. Further prospective studies are warranted to validate or refute our primary findings as well as to identify other important heavy metals linked with CVD.

Environmental Contaminants Acting as Endocrine Disruptors Modulate Atherogenic Processes: New Risk Factors for Cardiovascular Diseases in Women?

The number of aged individuals is increasing worldwide, rendering essential the comprehension of pathophysiological mechanisms of age-related alterations, which could facilitate the development of interventions contributing to “successful aging” and improving quality of life. Cardiovascular diseases (CVD) include pathologies affecting the heart or blood vessels, such as hypertension, peripheral artery disease and coronary heart disease. Indeed, age-associated modifications in body composition, hormonal, nutritional and metabolic factors, as well as a decline in physical activity are all involved in the increased risk of developing atherogenic alterations that raise the risk of CVD development. Several factors have been reported to play a role in the alterations observed in muscle and endothelial cells and that lead to increased CVD, such as genetic pattern, smoking and unhealthy lifestyle. Moreover, a difference in the risk of these diseases in women and men has been reported. Interestingly, in the past decades attention has been focused on a potential role of several pollutants that disrupt human health by interfering with hormonal pathways, and more specifically in non-communicable diseases such as obesity, diabetes and CVD. This review will focus on the potential alteration induced by Endocrine Disruptors (Eds) in the attempt to characterize a potential role in the cellular and molecular mechanisms involved in the atheromatous degeneration process and CVD progression.

The endocrine disruptor cadmium: a new player in the pathophysiology of metabolic diseases

Cadmium (Cd), a highly toxic heavy metal, is found in soil, environment and contaminated water and food. Moreover, Cd is used in various industrial activities, such as electroplating, batteries production, fertilizers, while an important non-occupational source is represented by cigarette smoking, as Cd deposits in tobacco leaves. Since many years it is clear a strong correlation between Cd body accumulation and incidence of many diseases. Indeed, acute exposure to Cd can cause inflammation and affect many organs such as kidneys and liver. Furthermore, the attention has focused on its activity as environmental pollutant and endocrine disruptor able to interfere with metabolic and energy balance of living beings. Both in vitro and in vivo experiments have demonstrated that the Cd-exposure is related to metabolic diseases such as obesity, diabetes and osteoporosis even if human studies are still controversial. Recent data show that Cd-exposure is associated with atherosclerosis, hypertension and endothelial damage that are responsible for cardiovascular diseases. Due to the large environmental diffusion of Cd, in this review, we summarize the current knowledge concerning the role of Cd in the incidence of metabolic and cardiovascular diseases.

BCRP/ABCG2 Transporter Regulates Accumulation of Cadmium in Kidney Cells: Role of the Q141K Variant in Modulating Nephrotoxicity

Exposure to the environmental pollutant cadmium is ubiquitous, as it is present in cigarette smoke and the food supply. Over time, cadmium enters and accumulates in the kidneys, where it causes tubular injury. The breast cancer resistance protein (BCRP, ATP-Binding Cassette G2 ABCG2) is an efflux transporter that mediates the urinary secretion of pharmaceuticals and toxins. The ABCG2 genetic variant Q141K exhibits altered membrane trafficking that results in reduced efflux of BCRP substrates. Here, we sought to 1) evaluate the in vitro and in vivo ability of BCRP to transport cadmium and protect kidney cells from toxicity and 2) determine whether this protection is impaired by the Q141K variant. Cadmium concentrations, cellular stress, and toxicity were quantified in human embryonic kidney 293 cells expressing an empty vector (EV), BCRP wild-type (WT), or variant (Q141K) gene. Treatment with CdCl₂ resulted in greater accumulation of cadmium and apoptosis in EV cells relative to WT cells. Exposure to CdCl₂ induced expression of stress-related genes and proteins including MT-1A/MT-2A, NAD(P)H quinone dehydrogenase 1, and heme oxygenase-1 to a higher extent in EV cells compared with WT cells. Notably, the Q141K variant protected against CdCl₂-induced activation of stress genes and cytotoxicity, but this protection was to a lesser magnitude than observed with WT BCRP. Lastly, concentrations of cadmium in the kidneys of Bcrp knockout mice were 40% higher than in WT mice, confirming that cadmium is an in vivo substrate of BCRP. In conclusion, BCRP prevents the accumulation of cadmium and protects against toxicity, a response that is impaired by the Q141K variant. SIGNIFICANCE STATEMENT: The breast cancer resistance protein transporter lowers cellular accumulation of the toxic heavy metal cadmium. This protective function is partially attenuated by the Q141K genetic variant in the ABCG2 gene.

Non-enzymatic antioxidant responses of Mytilus galloprovincialis: Insights into the physiological role against metal-induced oxidative stress

The exposure to metals is known to generate oxidative stress in living organisms, which can result in the induction of protective antioxidant defences, both enzymatic and non-enzymatic. This work aims to obtain new data on the existing links among several non-enzymatic components of the antioxidant system, that are physiologically related to both metal sequestration and defense against metal-induced oxidative stress, using the blue mussels (Mytilus galloprovincialis) as a model organism. Specimens of this marine bivalve were experimentally exposed to cadmium (Cd), used as oxidative stress inducer. Cd, metallothionein (MT), glutathione (GSH), malondialdehyde (MDA) contents, and glutathione reductase (GR) activity in gills and in digestive glands were assessed at 0, 12, 24, 48, 72 and 96 h. The obtained results provide new data about the relationships among the non-enzymatic antioxidant cellular components considered in this study. These constitute the prompt physiological responses to the oxidative stress in blue mussels exposed to Cd in controlled laboratory conditions.

Oncogenic transformation of human benign prostate hyperplasia with chronic cadmium exposure

Experimentally, it has been proved that cadmium served as an effective carcinogen and able to induce tumors in rodents in a dose-specific manner. However, systemic evaluation of cadmium exposure for the transformation of prostatic hyperplasia into prostate cancer (PCa) is still unclear. In the present study, an attempt has been made to establish cadmium-induced human prostate carcinogenesis using an in vitro model of BPH cells. Wide range of cadmium concentrations, i.e., 1 nM, 10 nM, 100 nM and 1μM, were chronically exposed to the human BPH cells for transformation into PCa and monitored using cell and molecular biology approaches. After eight weeks of exposure, the cells showed subtle morphological changes and shifts of cell cycle in the G2M phase. Significant increase in expression of prostatic genes AR, PSA, ER-β, and 5αR with increased nuclear localization of AR and pluripotency markers Cmyc, Klf4 indicated the carcinogenic effect of Cd. Further, the BPH cells exposed to Cd showed a substantial increase in the secretion of MMP-2 and MMP-9, influencing migratory potential of the cells along with decreased expression of the p63 protein which further strengthen the progression towards carcinogenesis and aggressive tumor studies. Data from the present study state that Cd exhibited marked invasiveness in BPH cells. These observations established a connecting link of BPH towards PCa pathogenesis. Further, the study will also help in investigating the intricate pathways involved in cancer progression.

Protection from Ultraviolet Damage and Photocarcinogenesis by Vitamin D Compounds

Exposure of skin cells to UV radiation results in DNA damage, which if inadequately repaired, may cause mutations. UV-induced DNA damage and reactive oxygen and nitrogen species also cause local and systemic suppression of the adaptive immune system. Together, these changes underpin the development of skin tumours. The hormone derived from vitamin D, calcitriol (1,25-dihydroxyvitamin D₃) and other related compounds, working via the vitamin D receptor and at least in part through endoplasmic reticulum protein 57 (ERp57), reduce cyclobutane pyrimidine dimers and oxidative DNA damage in keratinocytes and other skin cell types after UV. Calcitriol and related compounds enhance DNA repair in keratinocytes, in part through decreased reactive oxygen species, increased p53 expression and/or activation, increased repair proteins and increased energy availability in the cell when calcitriol is present after UV exposure. There is mitochondrial damage in keratinocytes after UV. In the presence of calcitriol, but not vehicle, glycolysis is increased after UV, along with increased energy-conserving autophagy and changes consistent with enhanced mitophagy. Reduced DNA damage and reduced ROS/RNS should help reduce UV-induced immune suppression. Reduced UV immune suppression is observed after topical treatment with calcitriol and related compounds in hairless mice. These protective effects of calcitriol and related compounds presumably contribute to the observed reduction in skin tumour formation in mice after chronic exposure to UV followed by topical post-irradiation treatment with calcitriol and some, though not all, related compounds.

Protective effect of Tualang honey against cadmium-induced morphological abnormalities and oxidative stress in the ovary of rats

BACKGROUND

To investigate the protective effects of Tualang honey against the toxicity effects induced by cadmium (Cd) on the ovary.

METHODS

A total of 32 female Sprague Dawley rats were taken and randomly divided into four groups (n = 8). Throughout the experimental period of 6 weeks, negative control-NC (vehicle deionized water), positive control-CD (Cd at 5 mg/kg), Tualang honey followed by Cd exposure-TH (Tualang honey at 200 mg/kg and Cd at 5 mg/kg) and Tualang honey control-THC (Tualang honey at 200 mg/kg) groups, were administered orally on a daily basis.

RESULTS

Rats exposed to Cd were significantly higher in ovarian weight, number of antral and atretic follicles as compared to the NC group. The disruptive effects of Cd on ovarian follicles were associated with a disruption in gonadotropin hormones and decreases in follicular stimulating hormone (FSH) and luteinizing hormone (LH). Moreover, a significant formation of oxidative stress in ovarian Cd-exposed rats has been proven by increasing the level of lipid peroxidation products (malondialdehyde) and decreasing the levels of enzymatic antioxidant (catalase). Interestingly, a daily supplementation of high antioxidant agents such as Tualang honey in these animals, caused significant improvements in the histological changes. Additionally, less atretic follicles were observed, restoring the normal level of LH and FSH (P < 0.001), and normalizing the ovarian malondialdehyde (P < 0.05) and catalase levels in comparison with CD group (P < 0.05).

CONCLUSIONS

Tualang honey has protective effects against Cd-induced ovarian toxicity by reducing morphological abnormalities, restoring the normal levels of gonadotropin hormones and stabilizing equilibrium levels of lipid peroxidation and antioxidant enzyme in ovaries of rats.

Subchronic Exposure to Cadmium Causes Persistent Changes in the Reproductive System in Female Wistar Rats

Cadmium (Cd) is an environmental toxicant and endocrine disruptor in humans and animals, and recent studies have illustrated that the uterus is exceedingly sensitive to Cd toxicity. The aim of the study was to investigate the influence of subchronic (90 days) oral Cd exposure in daily doses of 0.09-4.5 mg/kg b.w. on the balance of sex hormones by estimating estradiol (E₂) and progesterone (P) concentrations in the uterus and plasma in comparison with the effects of 17β-E₂. Additionally, the uterine weight, histopathological changes in the uterus and ovaries, the regularity of the estrous cycle, Cd bioaccumulation in uterine tissue, and selected biochemical parameters of oxidative stress were determined. A long period of observation (three and six months following the administration period) was used to assess whether the existing effects are reversible. The lowest dose of Cd caused effects similar to 17β-E₂: an increase of E₂ concentration in the uterus, endometrial epithelium thickness, and disturbed estrous cycle with estrus phase prolongation. The obtained results suggest that Cd causes nonlinear response. Higher doses of Cd caused a significant decrease in E₂ concentration in the uterus and plasma, estrous cycle disturbances, endometrium atrophy, and structural damage in the ovaries. This dose additionally induces lipid peroxidation in the uterine tissues. It is noteworthy that a prolonged time of observation after terminating the exposure showed persistent changes in the concentration of E₂ in uterine tissue, as well as alterations in estrous cycle phases, and an increase in lipid peroxidation in the uterus. Moreover, significant positive correlations between the plasma E₂ concentration and endometrial epithelium thickness in all studied groups were found. In summary, subchronic oral Cd exposure of female rats may result in impaired fertility processes.

Seasonal dependence of cadmium molecular effects on Mytilus galloprovincialis (Lamarck, 1819) protamine-like protein properties

Mussels have a seasonal reproduction and cadmium is a common stressor in estuarine and coastal environments. In previous studies, we have shown that exposure to subtoxic doses of cadmium produced alterations in the properties of winter Mytilus galloprovincialis sperm protamine-like (PL) proteins. In this study, it was analyzed the possibility that these cadmium effects may be seasonal. Winter and summer mussels were exposed to CdCl₂ , and it was tested the PL-proteins for cadmium bioaccumulation, electrophoretic pattern, DNA binding, and potentiality to induce DNA oxidative damage. It was found that cadmium exposure did not produce the same effects on PL-proteins of summer mussels that were produced on PL-proteins of winter mussels, that is: cadmium bioaccumulation, alterations in the acetic acid-urea polyacrylamide gels (AU-PAGE) and sodium dodecyl sulfate-PAGE pattern, a reduced DNA binding affinity and the ability to induce DNA oxidative damage. PL-proteins from summer mussels, apart from not being affected by all the abovementioned effects of cadmium, also showed a very low DNA binding affinity, independent of cadmium exposure. This study reveals clock-associated seasonal responses to cadmium in M. galloprovincialis. Understanding the mechanisms through which environmental signals guide biological rhythms is fundamental to understanding the seasonal sensitivity of this bioindicator, to use M. galloprovincialis in appropriate seasonal periods.

PI3K/Akt/mTOR Signaling Pathway and the Biphasic Effect of Arsenic in Carcinogenesis

Arsenic is a naturally occurring, ubiquitous metalloid found in the Earth’s crust. In its inorganic form, arsenic is highly toxic and carcinogenic and is widely found across the globe and throughout the environment. As an International Agency for Research on Cancer–defined class 1 human carcinogen, arsenic can cause multiple human cancers, including liver, lung, urinary bladder, skin, kidney, and prostate. Mechanisms of arsenic-induced carcinogenesis remain elusive, and this review focuses specifically on the role of the PI3K/AKT/mTOR pathway in promoting cancer development. In addition to exerting potent carcinogenic responses, arsenic is also known for its therapeutic effects against acute promyelocytic leukemia. Current literature suggests that arsenic can achieve both therapeutic as well as carcinogenic effects, and this review serves to examine the paradoxical effects of arsenic, specifically through the PI3K/AKT/mTOR pathway. Furthermore, a comprehensive review of current literature reveals an imperative need for future studies to establish and pinpoint the exact conditions for which arsenic can, and through what mechanisms it is able to, differentially regulate the PI3K/AKT/mTOR pathway to maximize the therapeutic and minimize the carcinogenic properties of arsenic.

Arsenite induces DNA damage via mitochondrial ROS and induction of mitochondrial permeability transition

Arsenite is an established DNA-damaging agent and human carcinogen. We initially selected conditions in which the metalloid causes DNA strand scission in the absence of detectable apoptotic DNA degradation in U937 cells. This response was suppressed by catalase and by treatments (rotenone and ascorbic acid), or manipulations (respiration-deficient phenotype), preventing the mitochondrial formation of O2-. ( mitoO2-.). MitoO2-., and its dismutation product, H₂ O₂ , are therefore critically involved in the arsenite-dependent DNA-damaging response. We then established a link between mitoO2-./H₂ O₂ and mitochondrial permeability transition (MPT), and found that this second event also promoted the formation of DNA-damaging species. As a consequence, the DNA damage induced by arsenite, in addition to being abolished by the aforementioned treatments/manipulations, was also significantly reduced by the MPT inhibitor cyclosporin A (CsA). A CsA-sensitive induction of p53 mRNA expression was also detected. Finally, evidence of CsA-sensitive DNA strand scission was also obtained in MCF-7, HT22, and NCTC-2544 cells. MitoO2-./H₂ O₂ therefore directly mediates DNA damage induced by arsenite and indirectly promotes the formation of additional DNA-damaging species via the induction of MPT. © 2017 BioFactors, 43(5):673-684, 2017.

Effects of cadmium on Bcl-2/Bax expression ratio in rat cortex brain and hippocampus

To investigate the underlying mechanism of neurotoxicity of cadmium, we examined the effects of intraperitoneal injection of cadmium on messenger RNA (mRNA) expression of Bcl-2 (B-cell lymphoma 2) and Bax (Bcl2-associated x) genes and caspase-3/7 activation in rat hippocampus and frontal cortex. Twenty-eight male Wistar rats weighing 200–250 g were randomly divided into four groups. Control group received saline and three other groups received cadmium at doses of 1, 2 and 4 mg/kg (body weight) for 15 successive days. One day after the last injection, the hippocampus and frontal cortex were dissected and removed and then the expression of Bcl-2 and Bax genes was evaluated using real-time polymerase chain reaction and apoptotic studies was done using caspase-3/7 activation assay. Cadmium reduced the mRNA level of Bcl-2 in the control group at doses of 1 ( p < 0.01), 2 and 4 mg/kg ( p < 0.001) in rat hippocampus and cortex cells. The mRNA level of Bax increased significantly compared to the control group at the doses of 1 ( p < 0.05), 2 and 4 mg/kg ( p < 0.001) in rat hippocampus. The mRNA level of Bax was increased significantly compared to the control group at the doses of 2 and 4 mg/kg ( p < 0.001) in rat cortex cells. Cadmium increased caspase-3/7 activity at doses of 1, 2 and 4 mg/kg in rat hippocampus. Caspase-3/7 activity was increased significantly at dose of 4 mg/kg in rat cortex. This decreased Bcl-2/Bax mRNA ratio induces cell apoptosis. Apoptotic effect of cadmium may be through the mitochondrial pathway by the activation of caspase-3/7.

Possible antioxidant effect of Lycium barbarum polysaccharides on hepatic cadmium-induced oxidative stress in rats

The aim of this study was to investigate the potential protective effect of Lycium barbarum polysaccharides (LBP) pretreatment against cadmium (Cd)-induced hepatotoxicity in rats. Wistar rats were divided into control group, LBP group (300 mg/kg orally, once a day, for 30 days), Cd group (CdCl₂ 4 mg/kg i.p. once), and LBP + Cd group (LBP 300 mg/kg orally, once a day, for 30 days + CdCl₂ 4 mg/kg i.p. 24 h after the last treatment). Cd liver injury was examined by morphological/histological changes, transaminases, total protein concentration, and oxidative stress evaluated by MDA, 3NT, GSH, SOD, and TEAC activities. Cd intoxication caused gross morphological changes with hyperemia of the parenchyma, increased volume, and disappearance of the anatomical limits of the lobes associated with an increase of ALT, GSH, and TEAC in plasma and a decrease of MDA, GSH, and TEAC in liver, SOD, and total proteins in plasma. LBP pretreatment caused a slight improvement in the histological architecture and in the 3NT amount together with a significant improvement of hematic parameters. On the basis of the obtained results, we can affirm that LBP pretreatment can ameliorate liver conditions, but further studies are needed to better evaluate the protective antioxidant effects of LBP against Cd-induced toxicity.

Dithiothreitol enhanced arsenic-trioxide-induced cell apoptosis in cultured oral cancer cells via mitochondrial dysfunction and endoplasmic reticulum stress

Arsenic is naturally occurring toxic metalloid and drinking As₂ O₃ containing water are recognized to be related to increased risk of neurotoxicity, liver injury, blackfoot disease, hypertension, and cancer. On the contrary, As₂ O₃ has been an ancient drug used in traditional Chinese medicine with substantial anticancer activities, especially in the treatment of acute promyelocytic leukemia as well as chronic wound healing. However, the cytotoxicity and detail mechanisms of As₂ O₃ action in solid cancer cells, such as oral cancer cells, are largely unknown. In this study, we have primarily cultured four pairs of tumor and nontumor cells from the oral cancer patients and treated the cells with As₂ O₃ alone or combined with dithiothreitol (DTT). The results showed that 0.5 μM As₂ O₃ plus 20 μM DTT caused a significant cell death of oral cancer cells but not the nontumor cells. Also As₂ O₃ plus DTT upregulated Bax and Bak, downregulated Bcl-2 and p53, caused a loss of mitochondria membrane potential in oral cancer cells. On the other way, As₂ O₃ also triggered endoplasmic reticulum stress and increased the levels of glucose-regulated protein 78, calpain 1 and 2. Our results suggest that DTT could synergistically enhance the effects of As₂ O₃ on killing oral cancer cells while nontoxic to the nontumor cells. The combination is promising for clinical practice in oral cancer therapy and worth further investigations. © 2015 Wiley Periodicals, Inc. Environ Toxicol 32: 17-27, 2017.

Effects of single and combined heavy metals and their chelators on aphid performance and preferences

When present at elevated levels in the environment, heavy metals are toxic for most organisms. However, so-called hyperaccumulator plants tolerate heavy metals and use chelators for their internal long-distance transport. Thus, phloem-sucking insects may come in contact with the chelated metals. In the present study, the effects of individual and combined heavy metals, zinc (Zn) and cadmium (Cd), as well as of common chelators, nicotianamine and phytochelatin, were investigated on the performance, preferences, and metal accumulation of the generalist aphid Myzus persicae, using artificial diets. Added Zn increased aphid growth, whereas Cd reduced the survival of aphids. Chelators had neither protective nor negative effects on aphids. The combination of the 2 heavy metals in chelated or nonchelated form caused a potentiation effect that led to an extinction of the aphids within less than 2 wk, before they could reproduce. Both Cd and Zn accumulated in the aphids, indicating a possible biomagnification. In choice assays, aphids preferred diets amended with Zn with or without nicotianamine compared to a control diet. In contrast, a Cd-containing diet led to neither attraction nor aversion. The present study provides insight into how mixtures of heavy metals and their chelators influence the life history of a generalist aphid. The results have implications for the use of phytoremediation to remove heavy metals from contaminated soils. Environ Toxicol Chem 2016;35:3023-3030. © 2016 SETAC.

Possible antioxidant effect of Lycium barbarum polysaccharides on hepatic cadmium-induced oxidative stress in rats

The aim of this study was to investigate the potential protective effect of Lycium barbarum polysaccharides (LBP) pretreatment against cadmium (Cd)-induced hepatotoxicity in rats. Wistar rats were divided into control group, LBP group (300 mg/kg orally, once a day, for 30 days), Cd group (CdCl₂ 4 mg/kg i.p. once), and LBP + Cd group (LBP 300 mg/kg orally, once a day, for 30 days + CdCl₂ 4 mg/kg i.p. 24 h after the last treatment). Cd liver injury was examined by morphological/histological changes, transaminases, total protein concentration, and oxidative stress evaluated by MDA, 3NT, GSH, SOD, and TEAC activities. Cd intoxication caused gross morphological changes with hyperemia of the parenchyma, increased volume, and disappearance of the anatomical limits of the lobes associated with an increase of ALT, GSH, and TEAC in plasma and a decrease of MDA, GSH, and TEAC in liver, SOD, and total proteins in plasma. LBP pretreatment caused a slight improvement in the histological architecture and in the 3NT amount together with a significant improvement of hematic parameters. On the basis of the obtained results, we can affirm that LBP pretreatment can ameliorate liver conditions, but further studies are needed to better evaluate the protective antioxidant effects of LBP against Cd-induced toxicity.

Toxic effects of cadmium on flatworm stem cell dynamics: A transcriptomic and ultrastructural elucidation of underlying mechanisms

Stem cells or undifferentiated cells can cope more easily with external stresses. To evaluate the impact of toxic compounds on stem cell dynamics in vivo, in relation to other biological responses, we use the carcinogenic element cadmium and the regenerating model organism Macrostomum lignano. Through both BrdU and anti-histone H3 immunostainings, cadmium-induced effects were investigated at different stages of the stem cell cycle. A 24-h exposure to 100 and 250 μM CdCl2 significantly decreased the number of stem cells (neoblasts) in mitosis, whereas the number of cells in the S phase remained unchanged. After this short-term exposure, the ultrastructure of the neoblasts was minimally affected in contrast to the epidermal tissues. These results were supported by gene expression data: transcripts of cdc2 and pig3 were significantly upregulated during all treatments. Both genes are involved in the cell cycle progression and are transcribed in the gonadal region, where stem cells are highly represented. Based on a substantial increase in gene expression of heat shock proteins (HSP) and their high activity in the gonadal region, we hypothesize that these proteins are key players in the protection of stem cells against external stresses. Apart from the strong HSP induction, other protective processes including cell division, apoptosis and anti-oxidative defence, were also activated. We, therefore, conclude that the protection of stem cells against external stressors may be based on the interplay between stem cell maintenance, i.e. repair and recovery through division, on one hand and apoptosis on the other hand. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 1217-1228, 2016.

Combined Incubation of Cadmium, Docosahexaenoic and Eicosapentaenoic Acid Affecting the Oxidative Stress and Antioxidant Response in Human Hepatocytes In Vitro

Human hepatocellular cells Hep G2 were used to investigate the effects of the intake of contaminated fish on oxidative stress. Uptake of heavy metal contaminated fish was mimicked by incubating the cells with a combination of cadmium chloride (Cd2+) as possible contaminant and a combination of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) as important fatty acids (FA) specific for fish. The main aim of this study was to determine the effects of these co-incubations (FA, Cd2+) on lipid and protein oxidation. In addition we also evaluated the antioxidant response of the cells using two different methods (SOD and TAC). Pre-incubation with the chosen FA significantly reduced the oxidative stress caused by incubation with Cd2+. We measured an increased level of carbonyl proteins (CP) in the cells pre-incubated with bovine serum albumin (BSA) and post-incubated with Cd2+.

The impact of subchronic cadmium poisoning on the vascular effect of nitric oxide in rats

The aim of this study was to evaluate the impact of poisoning with cadmium in hypertensive doses (50 or 200 ppm in drinking water for three months) on the basal and stimulated release NO effect in the isolated and perfused rat mesenteric bed. Mesenteric artery preparation preconstricted by norepinephrine (0.5 μg/mL) was used to determine changes in its vascular resistance induced by e-NOS synthase blocker, N-ω-nitro-L-arginine (L-NOARG) injected in increasing doses from 1.0 to 200.0 μg or acetylcholine (ACh) administered in doses from 0.05 × 10-10 to 5.0 × 10-10 mol before and during L-NOARG infusion (1.0 μg/mL). Vascular reactivity was measured as an increase or decrease in perfusion pressure in the constant flow system.

Rats poisoned with 50 or 200 ppm of cadmium demonstrated a significant decrease (P < 0.05) in vascular response to L-NOARG used in doses of 50 or 100 μg. The dose-response curve obtained for L-NOARG was shifted to the right and ED50 value was greater in the group of rats given cadmium in a dose of 200 ppm than in the controls (70.39 ± 10.7 versus 25.79 ± 4.8 μg, P < 0.01). These rats reacted with lower expressed vasodilatation to ACh in doses to 0.2 ± 10-10 mol. In all poisoned rats, L-NOARG enhanced the effect of ACh used in doses from 0.05 to 0.5 ± 10-10 mol, whereas in the control group this effect was only achieved at 0.1 ± 10-10 mol. The serum nitric oxide concentration was decreased (P B < 0.05) in both groups of cadmium-treated rats. These results suggest that cadmium in hypertensive doses modifies the vascular effect of NO in basal conditions and after stimulation by ACh.

Subchronic Exposure to Arsenic Through Drinking Water Alters Expression of Cancer-Related Genes in Rat Liver

Although arsenic exposure causes liver disease and/or hepatoma, little is known about molecular mechanisms of arsenic-induced liver toxicity or carcinogenesis. We investigated the effects of arsenic on expression of cancer-related genes in a rat liver following subchronic exposure to sodium arsenate (1, 10, 100 ppm in drinking water), by using real-time quantitative RT-PCR and immunohistochemical analyses. Arsenic accumulated in the rat liver dose-dependently and caused hepatic histopathological changes, such as disruption of hepatic cords, sinusoidal dilation, and fatty infiltration. A 1-month exposure to arsenic significantly increased hepatic mRNA levels of cyclin D1 (10 ppm), ILK (1 ppm), and p27Kip1 (10 ppm), whereas it reduced mRNA levels of PTEN (1 ppm) and β-catenin (100 ppm). In contrast, a 4-month arsenic exposure showed increased mRNA expression of cyclin D1 (100 ppm), ILK (1 ppm), and p27Kip1 (1 and 10 ppm), and decreased expression of both PTEN and β-catenin at all 3 doses. An immunohistochemical study revealed that each protein expression accords closely with each gene expression of mRNA level. In conclusion, subchronic exposure to inorganic arsenate caused pathological changes and altered expression of cyclin D1, p27Kip1, ILK, PTEN, and β-catenin in the liver. This implies that arsenic liver toxicity involves disturbances of some cancer-related molecules.

Oxidative Stress and Cardiovascular Dysfunction Associated with Cadmium Exposure: Beneficial Effects of Curcumin and Tetrahydrocurcumin

Cadmium (Cd) is a non-essential heavy metal with high toxicity potential. Humans are exposed to Cd present in diet, polluted air, and cigarette smoke. Cd exposure has been associated with increased risk of chronic diseases, including hypertension, atherosclerosis, diabetes, and nephropathy, all of which could be attributable to dysfunctional endothelial and smooth muscle cells. Cd toxicity is correlated with increased reactive oxygen formation and depletion of antioxidants, resulting in an oxidative stress. Chelation of Cd has proved useful in the removal of the Cd burden. However, several chelating agents cause side effects in clinical usage. Recent studies have shown that the antioxidant compounds curcumin and tetrahydrocurcumin can alleviate vascular dysfunction and high blood pressure caused by Cd toxicity. In chronic Cd exposure, these antioxidants protect vascular endothelium by increasing nitric oxide (NO•) bioavailability and improving vascular function. Antioxidant activity against Cd intoxication results directly and/or indirectly through free radical scavenging, metal chelation, enhanced expression of the antioxidant defense system, regulation of inflammatory enzymes, increase in NO• bioavailability, and reduction of gastrointestinal absorption and tissue Cd accumulation. This review summarizes current knowledge of Cd-induced oxidative stress and cardiovascular dysfunction and a possible protective effect conferred by the antioxidants curcumin and tetrahydrocurcumin.

Role and mechanism of miR-222 in arsenic-transformed cells for inducing tumor growth

High levels of arsenic in drinking water, soil, and air are associated with the higher incidences of several kinds of cancers worldwide, but the mechanism is yet to be fully discovered. Recently, a number of evidences show that dysregulation of microRNAs (miRNAs) induces carcinogenesis. In this study, we found miR-222 was upregulated in arsenic-transformed human lung epithelial BEAS-2B cells (As-T cells). Anti-miR-222 inhibitor treatment decreased cell proliferation, migration, tube formation, and induced apoptosis. In addition, anti-miR-222 inhibitor expression decreased tumor growth in vivo. We also found that inhibition of miR-222 induced the expression of its direct targets ARID1A and phosphatase and tensin homolog deleted on chromosome 10 (PTEN), and activated apoptosis of As-T cells in part through ARID1A downregulation. These results indicate that miR-222 plays an important role in arsenic-induced tumor growth.

Cadmium overkill: autophagy, apoptosis and necrosis signalling in endothelial cells exposed to cadmium

Apoptosis, necrosis, or autophagy-it is the mode of cell demise that defines the response of surrounding cells and organs. In case of one of the most toxic substances known to date, cadmium (Cd), and despite a large number of studies, the mode of cell death induced is still unclear. As there exists conflicting data as to which cell death mode is induced by Cd both across various cell types and within a single one, we chose to analyse Cd-induced cell death in primary human endothelial cells by investigating all possibilities that a cell faces in undergoing cell death. Our results indicate that Cd-induced death signalling starts with the causation of DNA damage and a cytosolic calcium flux. These two events lead to an apoptosis signalling-related mitochondrial membrane depolarisation and a classical DNA damage response. Simultaneously, autophagy signalling such as ER stress and phagosome formation is initiated. Importantly, we also observed lysosomal membrane permeabilization. It is the integration of all signals that results in DNA degradation and a disruption of the plasma membrane. Our data thus suggest that Cd causes the activation of multiple death signals in parallel. The genotype (for example, p53 positive or negative) as well as other factors may determine the initiation and rate of individual death signals. Differences in the signal mix and speed may explain the differing results recorded as to the Cd-induced mode of cell death thus far. In human endothelial cells it is the sum of most if not all of these signals that determine the mode of Cd-induced cell death: programmed necrosis.

Heme oxygenase-1 attenuates cadmium-induced mitochondrial-caspase 3- dependent apoptosis in human hepatoma cell line

Background

Cadmium (Cd) is a well known environmental and industrial toxicant causing damaging effects in numerous organs. In this study, we examined the role of heme oxygenase-1 (HO-1) in modulating the Cd-induced apoptosis in human hepatoma (HepG2) cells after 24 h exposure.

Methods

HepG2 cells were exposed to 5 and 10 μM Cd as CdCl₂ for 24 h while other sets of cells were pre-treated with either 10 μM Cobalt protoporphyrin (CoPPIX) or 10 μM Tin protoporphyrin (SnPPIX) for 24 h, or 50 μM Z-DEVD-FMK for 1 h before exposure to 5 and 10 μM CdCl₂ for 24 h. Expressions of caspase 3, cytosolic cytochrome c, mitochondrial Bax and anti-apoptotic BCL-xl proteins were assessed by western blot. Intracellular reactive oxygen species (ROS) production was determined using the dihydrofluorescein diacetate (H₂DFA) method. Cell viability was assessed by MTT assay, while a flow cytometry method was used to assess the level of apoptosis in the cell populations.

Results

Our results show that there were a significant increase in the expression of cytosolic cytochrome c, mitochondrial Bax protein, and caspase 3 at 5 and 10 μM compared to the control, but these increases were attenuated by the presence of CoPPIX. The presence of SnPPIX significantly enhanced Cd-induced caspase 3 activities. CoPPIX significantly decreased the level of ROS production by 24.6 and 22.2 % in 5 and 10 μM CdCl_2, respectively, but SnPPIX caused a significant increase in ROS production in the presence of CdCl₂. HepG2 cell viability was also significantly impaired by 13.89 and 32.53 % in the presence of 5 and 10 μM CdCl₂, respectively, but the presence of CoPPIX and Z-DEVD-FMK significantly enhanced cell survival, while SnPPIX enhanced Cd-impaired cell viability. The presence of CoPPIX and Z-DEVD-FMK also significantly decreased the population of apoptotic and necrotic cells compared with Cd.

Conclusion

In summary, the present study showed that HO-1 attenuates the Cd-induced caspase 3 dependent pathway of apoptosis in HepG2 cells, probably by modulating Cd-induced oxidative stress.

Arsenic-Induced Antioxidant Depletion, Oxidative DNA Breakage, and Tissue Damages are Prevented by the Combined Action of Folate and Vitamin B12

Arsenic is a grade I human carcinogen. It acts by disrupting one-carbon (1C) metabolism and cellular methyl (-CH3) pool. The -CH3 group helps in arsenic disposition and detoxification of the biological systems. Vitamin B12 and folate, the key promoters of 1C metabolism were tested recently (daily 0.07 and 4.0 μg, respectively/100 g b.w. of rat for 28 days) to evaluate their combined efficacy in the protection from mutagenic DNA-breakage and tissue damages. The selected tissues like intestine (first-pass site), liver (major xenobiotic metabolizer) and lung (major arsenic accumulator) were collected from arsenic-ingested (0.6 ppm/same schedule) female rats. The hemo-toxicity and liver and kidney functions were monitored. Our earlier studies on arsenic-exposed humans can correlate carcinogenesis with DNA damage. Here, we demonstrate that the supplementation of physiological/therapeutic dose of vitamin B12 and folate protected the rodents significantly from arsenic-induced DNA damage (DNA fragmentation and comet assay) and hepatic and renal tissue degeneration (histo-architecture, HE staining). The level of arsenic-induced free-radical products (TBARS and conjugated diene) was significantly declined by the restored actions of several antioxidants viz. urate, thiol, catalase, xanthine oxidase, lactoperoxidase, and superoxide dismutase in the tissues of vitamin-supplemented group. The alkaline phosphatase, transaminases, urea and creatinine (hepatic and kidney toxicity marker), and lactate dehydrogenase (tissue degeneration marker) were significantly impaired in the arsenic-fed group. But a significant protection was evident in the vitamin-supplemented group. In conclusion, the combined action of folate and B12 results in the restitution in the 1C metabolic pathway and cellular methyl pool. The cumulative outcome from the enhanced arsenic methylation and antioxidative capacity was protective against arsenic induced mutagenic DNA breakages and tissue damages.

Arsenic-induced S phase cell cycle lengthening is associated with ROS generation, p53 signaling and CDC25A expression

Cellular response to arsenic is strongly dependent on p53 functional status. Primarily arresting the cell cycle in G1 or G2/M phases, arsenic treatment also induces an increase in the S-phase time in wild-type p53 cells. In contrast, cells with a non-functional p53 display only a subtle increase in the S phase, indicating arsenic differentially affects the cell cycle depending on p53 status. Importantly, it has been reported that arsenic induces reactive oxygen species (ROS), a process counteracted by p53. To evaluate the participation of p53 in the lengthening of the S phase and the connection between the transient cell cycle arrest and oxidative stress, we evaluated the cell response to arsenic in MCF-7 and H1299 cells, and analyzed p53's role as a transcription factor in regulating genes involved in ROS reduction and S phase transition. Herein, we discovered that arsenic induced an increase in the population of S phase cells that was dependent on the presence and transcriptional activity of p53. Furthermore, for the first time, we demonstrate that arsenic activates p53-dependent transcription of ROS detoxification genes, such as SESN1, and by an indirect mechanism involving ATF3, genes that could be responsible for the S phase cell cycle arrest, such as CDC25A.

Combination of cadmium and high cholesterol levels as a risk factor for heart fibrosis

The deleterious effects of increased cadmium (Cd) serum levels on the cardiovascular system are proven by epidemiological and basic science studies. Cd exposure of animals and humans is known to impair myocardial function, possibly leading to heart failure. This study aims at investigating the effect of Cd treatment on the cardiac system with emphasis on the combined effect of Cd and high serum cholesterol levels as an important cardiovascular risk factor. Detailed analyses of Cd-induced effects on the heart of ApoE-/- mice fed a high fat diet (HFD), ApoE-/- mice fed a normal diet (ND), and C57BL/6J mice fed a ND revealed proinflammatory and fibrotic changes in the presence of cellular hypertrophy but in the absence of organ hypertrophy. Hypercholesterolemia in ApoE-/- mice alone and in combination with Cd treatment resulted in significant cardiomyocyte cell death. Based on further analyses of heart sections, we conclude that severe hypercholesterolemia in combination with ApoE-/- genotype as well as Cd treatment results in necrotic cardiomyocyte death. These data were supported by in vitro experiments showing a Cd-induced depolarization of the mitochondrial membrane and the permeabilization of the plasma membrane arguing for the occurrence of Cd-induced necrotic cell death. In summary, we were able to show for the first time that the combination of high cholesterol and Cd levels increase the risk for heart failure through cardiac fibrosis. This observation could in part be explained by the dramatically increased deposition of Cd in the hearts of ApoE-/- mice fed a HFD.

Effects of cadmium and 17β-estradiol on Mytilus galloprovincialis redox status. Prooxidant-antioxidant balance (PAB) as a novel approach in biomonitoring of marine environments

Cadmium and 17β-estradiol are rapidly accumulated in mussel tissues, making mussels excellent pollution sentinel organisms. The aim of the present study was to compare the oxidative responses of the mussels after 1, 3 and 7 days of exposure to cadmium with those to 17β-estradiol and subsequently, to suggest a multi-parametric approach for biomonitoring studies. Our results showed that environmentally relevant concentrations of either cadmium or 17β-estradiol for 1, 3 and 7 days induced oxidative stress in hemocytes of exposed mussels. The latter was determined by significantly increased ROS levels and apoptosis, by suppression of antioxidant enzymes catalase (CAT), superoxide dismutase (SOD) and glutathione-S-transferase (GST) expression levels and subsequent increased prooxidant levels, as measured by prooxidant-antioxidant balance (PAB) assay. To our knowledge this is the first time that prooxidant-antioxidant balance is evaluated in invertebrates as an index of oxidative stress. The simultaneous use of the parameters of prooxidant-antioxidant balance and antioxidant enzymes expression patterns, in combination with ROS production levels and apoptosis, in mussel hemocytes is suggested as an approach that may help to better evaluate the impact of environmental pollution on marine organisms and thereupon ecosystems.

Arsenite Acutely Decreases Nitric Oxide Production via the ROS-Protein Phosphatase 1-Endothelial Nitric Oxide Synthase-Thr(497) Signaling Cascade

Chronic (>24 h) exposure of arsenite, an environmental toxicant, has shown the decreased nitric oxide (NO) production in endothelial cells (EC) by decreasing endothelial NO synthase (eNOS) expression and/or its phosphorylation at serine 1179 (eNOS-Ser¹¹⁷⁹ in bovine sequence), which is associated with increased risk of vascular diseases. Here, we investigated the acute (<24 h) effect of arsenite on NO production using bovine aortic EC (BAEC). Arsenite acutely increased the phosphorylation of eNOS-Thr⁴⁹⁷, but not of eNOS-Ser¹¹⁶ or eNOS-Ser¹¹⁷⁹, which was accompanied by decreased NO production. The level of eNOS expression was unaltered under this condition. Treatment with arsenite also induced reactive oxygen species (ROS) production, and pretreatment with a ROS scavenger N-acetyl-L-cysteine (NAC) completely reversed the observed effect of arsenite on eNOS-Thr⁴⁹⁷ phosphorylation. Although protein kinase C (PKC) and protein phosphatase 1 (PP1) were reported to be involved in eNOS-Thr⁴⁹⁷ phosphorylation, treatment with PKC inhibitor, Ro318425, and overexpression of various PKC isoforms did not affect the arsenite-stimulated eNOS-Thr⁴⁹⁷ phosphorylation. In contrast, treatment with PP1 inhibitor, calyculin A, mimicked the observed effect of arsenite on eNOS-Thr⁴⁹⁷ phosphorylation. Lastly, we found decreased cellular PP1 activity in arsenite-treated cells, which was reversed by NAC. Overall, our study demonstrates firstly that arsenite acutely decreases NO production at least in part by increasing eNOS-Thr⁴⁹⁷ phosphorylation via ROS-PP1 signaling pathway, which provide the molecular mechanism underlying arsenite-induced increase in vascular disease.

Assessment of arsenic-induced DNA damage in goldfish by a polymerase chain reaction-based technique using random amplified polymorphic DNA markers

Arsenic is a groundwater contaminant of global concern. It is a potent human carcinogen, and its marked genotoxic effects have been reported in several human and animal studies. The present work investigates the applicability of the random amplified polymorphic DNA (RAPD) assay to study the DNA-damaging effects of arsenic at low-level exposure in goldfish Carassius auratus. Four experimental groups of fish, A, B, C and D, were exposed to 0, 10, 50, and 1,000 µg L(-1) of arsenic, respectively, in aquaria water for 15 consecutive days. Genomic DNA extraction was followed by RAPD-polymerase chain reaction amplification for each fish separately. One arbitrary decamer primer (PUZ-19) of 33 primers used appeared as the most informative and was capable of exhibiting marked alterations in RAPD profiles between arsenic-exposed and unexposed (control) samples. Different sets of 11 loci were amplified in various experimental groups with four clear polymorphic bands by the primer PUZ-19. The X and XIII amplification loci, which were prominent in the unexposed group, failed to appear in the arsenic-exposed groups. In contrast, the I and XI RAPD bands appeared as new amplification loci in all of the exposed groups. Such alterations in genomic DNA, however, did not exhibit a clear dose-dependent tendency. The RAPD assay, because of its efficacy to unmask alterations in genomic DNA induced by arsenic at low exposure level of 10 µg L(-1), appears to be a sensitive and potential tool for detecting arsenic genotoxicity.

Arsenic-induced genotoxicity and genetic susceptibility to arsenic-related pathologies

The arsenic (As) exposure represents an important problem in many parts of the World. Indeed, it is estimated that over 100 million individuals are exposed to arsenic, mainly through a contamination of groundwaters. Chronic exposure to As is associated with adverse effects on human health such as cancers, cardiovascular diseases, neurological diseases and the rate of morbidity and mortality in populations exposed is alarming. The purpose of this review is to summarize the genotoxic effects of As in the cells as well as to discuss the importance of signaling and repair of arsenic-induced DNA damage. The current knowledge of specific polymorphisms in candidate genes that confer susceptibility to arsenic exposure is also reviewed. We also discuss the perspectives offered by the determination of biological markers of early effect on health, incorporating genetic polymorphisms, with biomarkers for exposure to better evaluate exposure-response clinical relationships as well as to develop novel preventative strategies for arsenic- health effects.

Nitric oxide protects endothelium from cadmium mediated leakiness

Cadmium targets the vascular endothelium causing endothelial dysfunction and leakiness of endothelial barrier. Nitric oxide plays a major role in mediating endothelial functions including angiogenesis, migration and permeability. The present study investigates the nitric oxide effects on cadmium induced endothelial leakiness. Results of ex vivo and in vitro permeability assays showed that even a sub-lethal dose of cadmium chloride (1 µM) was sufficient to induce leakiness of endothelial cells. Cadmium drastically altered the actin polymerisation pattern and membrane tension of these cells compared to controls. Addition of nitric oxide donor Spermine NONOate (SP) significantly blunted cadmium-mediated effects and recover endothelial cells integrity. Cadmium-induced cytoskeletal rearrangements and membrane leakiness are associated with the low nitric oxide availability and high reactive oxygen species generation. In brief, we show the protective role of nitric oxide against cadmium-mediated endothelial leakiness.

Arsenic metabolism and thioarsenicals

Arsenic has received considerable attention in the world, since it can lead to a multitude of toxic effects and has been recognized as a human carcinogen causing cancers. Here, we focus on the current state of knowledge regarding the proposed mechanisms of arsenic biotransformation, with a little about cellular uptake, toxicity and clinical utilization of arsenicals. Since pentavalent methylated metabolites were found in animal urine after exposure to iAs(III), methylation was considered to be a detoxification process, but the discovery of methylated trivalent intermediates and thioarsenicals in urine has diverted the view and gained much interest regarding arsenic biotransformation. To further investigate the partially understood phenomena relating to arsenic toxicity and the uses of arsenic as a drug, it is important to elucidate the exact pathways involved in metabolism of this metalloid, as the toxicity and the clinical uses of arsenic can be best recognized in context of its biotransformation. Thereby, in this perspective, we have focused on arsenic metabolic pathways including three proposed mechanisms: a classic pathway by Challenger in 1945, followed by a new metabolic pathway proposed by Hayakawa in 2005 involving arsenic-glutathione complexes, while the third is a new reductive methylation pathway that is proposed by our group involving As-protein complexes. According to previous and present in vivo and in vitro experiments, we conclude that the methylation reaction takes place with simultaneous reductive rather than stepwise oxidative methylation. In addition, production of pentavalent methylated arsenic metabolites are suggested to be as the end product of metabolism, rather than intermediates.

Mouse micronucleus assay as a surrogate to assess genotoxic potential of arsenic at its human reference dose

Exposure to high contents of arsenic (a genotoxic carcinogen) in humans through drinking water is one of the most serious concerns in many parts of the world including India. The United States Environmental Protection Agency (USEPA) has recommended a permissible limit of daily exposure in humans to arsenic as its reference dose (0.3 μg kg(-1) d(-1)) with almost no likelihood of any adverse effect. The present work was a quantitative assessment of the genotoxic potential of arsenic at the exposure level of its human reference dose through micronucleus (MN) assay in mice. The animals were exposed to various doses of arsenic through oral gavaging for 15 consecutive days. Significant increases in the frequency of micronucleated erythrocytes were observed in mice upon exposure to arsenic which occurred even at its human reference dose and in a dose-dependent manner. The study of the genotoxic potential of arsenic in humans at lower exposure levels (including its human reference dose) is, therefore, highly desirable for risk assessment and hazard identification.

Mechanisms of cadmium induced genomic instability

Cadmium is an ubiquitous environmental contaminant that represents hazard to humans and wildlife. It is found in the air, soil and water and, due to its extremely long half-life, accumulates in plants and animals. The main source of cadmium exposure for non-smoking human population is food. Cadmium is primarily toxic to the kidney, but has been also classified as carcinogenic to humans by several regulatory agencies. Current evidence suggests that exposure to cadmium induces genomic instability through complex and multifactorial mechanisms. Cadmium dose not induce direct DNA damage, however it induces increase in reactive oxygen species (ROS) formation, which in turn induce DNA damage and can also interfere with cell signalling. More important seems to be cadmium interaction with DNA repair mechanisms, cell cycle checkpoints and apoptosis as well as with epigenetic mechanisms of gene expression control. Cadmium mediated inhibition of DNA repair mechanisms and apoptosis leads to accumulation of cells with unrepaired DNA damage, which in turn increases the mutation rate and thus genomic instability. This increases the probability of developing not only cancer but also other diseases associated with genomic instability. In the in vitro experiments cadmium induced effects leading to genomic instability have been observed at low concentrations that were comparable to those observed in target organs and tissues of humans that were non-occupationally exposed to cadmium. Therefore, further studies aiming to clarify the relevance of these observations for human health risks due to cadmium exposure are needed.

Oxidative and non-oxidative DNA damage and cardiovascular disease

Evidence for the association of DNA damage with cardiovascular disease has been obtained from in vitro cell culture models, experimental cardiovascular disease and analysis of samples obtained from humans with disease. There is general acceptance that several factors associated with the risk of developing cardiovascular disease cause oxidative damage to DNA in cell culture models with both nuclear and mitochondrial DNA as targets. Moreover, evidence obtained over the past 10 years points to a possible mechanistic role for DNA damage in experimental atherosclerosis culminating in recent studies challenging the assumption that DNA damage is merely a biomarker of the disease process. This kind of mechanistic insight provides a renewed impetus for further studies in this area.

Arsenite promotes apoptosis and dysfunction in microvascular endothelial cells via an alteration of intracellular calcium homeostasis

Vascular endothelium has been considered as a target for arsenic-induced cardiovascular toxicity. The present study demonstrated that arsenite caused slow and sustained elevation of intracellular free calcium levels ([Ca2+]i) in HMEC-1, a human microvessel-derived endothelial cell line, in a concentration-dependent manner. Pretreatment with U-73122 (a specific PLC inhibitor) or 2-APB (a specific IP3 receptor antagonist) attenuated this effect, suggesting that PLC/IP3 signaling cascade is involved in arsenite-induced elevation of [Ca2+]i. Cytotoxic concentrations of arsenite (5 and 10 μM) significantly enhanced endothelial nitric oxide synthase (eNOS) phosphorylation, nitric oxide (NO) production and apoptosis after 24-h exposure. Additionally, 2-APB attenuated eNOS phosphorylation and apoptosis induced by arsenite, indicating that Ca2+ -mediated eNOS activation participates in arsenite-induced endothelial cell apoptosis. Moreover, we also found that non-apoptotic concentrations of arsenite (0.5 and 1 μM) dramatically mitigated thrombin-induced rapid transient rise of [Ca2+]i, eNOS phosphorylation and NO production, suggesting functional disruption of endothelial by arsenite, and these effects occurred without an alteration of PLC-β1 and thrombin receptor levels. Altogether, the results reveal that arsenite induces apoptotic cell death and endothelial dysfunction as indicated by the reduction of thrombin responses, particularly related to an alteration of intracellular Ca2+ homeostasis.

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 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.

A Mechanistic Approach for Modulation of Arsenic Toxicity in Human Lymphocytes by Curcumin, an Active Constituent of Medicinal Herb Curcuma longa Linn

Chronic exposure of humans to high concentrations of arsenic in drinking water is associated with skin lesions, peripheral vascular disease, hypertension, blackfoot disease and a high risk of cancer. Arsenic induces single strand breaks, DNA-protein crosslinks and apurinic sites in DNA, which are prerequisites for induction of cancer. Amelioration of such damages with natural compounds could be an effective strategy to combat arsenic toxicity. Curcumin is the active ingredient of turmeric, a common household spice, which is a rich source of polyphenols and this compound has been extensively studied as a chemopreventive agent against many types of cancer. The present study investigates whether curcumin could counteract the DNA damage caused by arsenic as assessed by single cell gel electrophoresis (SCGE) using peripheral blood lymphocytes, from healthy donors. It was observed that DNA damage induced by arsenic could be efficiently reduced by curcumin and the effect was more pronounced when lymphocytes were pre-incubated with curcumin prior to arsenic insult. Arsenic caused DNA damage by generation of reactive oxygen species (ROS) and enhancement of lipid peroxidation levels. Curcumin counteracted the damage by quenching ROS, decreasing the level of lipid peroxidation and increasing the level of phase II detoxification enzymes like catalase, superoxide dismutase and glutathione peroxidase. Curcumin also enhanced the DNA repair activity against arsenic induced damage. The expression of polymerase, a repair enzyme, was found to be highly elevated when arsenite induced damaged cells were allowed to repair in presence of curcumin. Results indicate that curcumin has significant role in confronting the deleterious effect caused by arsenic, which could be an economic mode of arsenic mitigation among rural population in West Bengal, India.

Role of DNA polymerase beta in the genotoxicity of arsenic

Arsenic, an important hazard in the environment, is associated with human cancer and other degenerative diseases. However, the mechanisms underlying arsenic hazardous effects remain unclear. It has been reported arsenic exposure can result in increased cellular reactive oxygen species and oxidative DNA damage. This suggests DNA base excision repair (BER), the major pathway for repairing oxidative DNA damage, may be involved in combating arsenic hazardous effects. As a critical repair enzyme in BER, DNA polymerase beta (Pol β) might play an essential role in reducing arsenic toxicity. To test this hypothesis, we evaluated arsenic-induced cytotoxic and genotoxic effects under Pol β deficiency. Our results demonstrated that the viability of Pol β-deficient mouse embryonic fibroblasts was much lower than that of Pol β wild-type cells after treatment with arsenite (As(3+) ). An increased level of DNA damage and significantly delayed arsenite-induced DNA damage repair in Pol β-deficient cells indicated reduced repair of DNA lesions under Pol β deficiency. This was consistent with the increase in the frequency of micronuclei (MN), an indicator of chromosomal breakage, which was also observed in Pol β-deficient cells treated with arsenite. In contrast, cells harboring overexpressed Pol β resulted in a lower level of DNA damage and MN than Pol β wild-type cells, indicating overexpression of the enzyme can combat arsenic-induced genotoxic effects. In conclusion, our results indicate an important role for Pol β in repairing arsenite-induced DNA damage and maintaining chromosomal integrity and further suggest deficiency of BER may be involved in arsenic genotoxicity and carcinogenicity.

Mitochondria are the main target organelle for trivalent monomethylarsonous acid (MMA(III))-induced cytotoxicity

Excessive generation of reactive oxygen species (ROS) is considered to play an important role in arsenic-induced carcinogenicity in the liver, lungs, and urinary bladder. However, little is known about the mechanism of ROS-based carcinogenicity, including where the ROS are generated, and which arsenic species are the most effective ROS inducers. In order to better understand the mechanism of arsenic toxicity, rat liver RLC-16 cells were exposed to arsenite (iAs(III)) and its intermediate metabolites [i.e., monomethylarsonous acid (MMA(III)) and dimethylarsinous acid (DMA(III))]. MMA(III) (IC(50) = 1 μM) was found to be the most toxic form, followed by DMA(III) (IC(50) = 2 μM) and iAs(III) (IC(50) = 18 μM). Following exposure to MMA(III), ROS were found to be generated primarily in the mitochondria. DMA(III) exposure resulted in ROS generation in other organelles, while no ROS generation was seen following exposures to low levels of iAs(III). This suggests the mechanisms of induction of ROS are different among the three arsenicals. The effects of iAs(III), MMA(III), and DMA(III) on activities of complexes I-IV in the electron transport chain (ETC) of rat liver submitochondrial particles and on the stimulation of ROS production in intact mitochondria were also studied. Activities of complexes II and IV were significantly inhibited by MMA(III), but only the activity of complexes II was inhibited by DMA(III). Incubation with iAs(III) had no inhibitory effects on any of the four complexes. Generation of ROS in intact mitochondria was significantly increased following incubation with MMA(III), while low levels of ROS generation were observed following incubation with DMA(III). ROS was not produced in mitochondria following exposure to iAs(III). The mechanism underlying cell death is different among As(III), MMA(III), and DMA(III), with mitochondria being one of the primary target organelles for MMA(III)-induced cytotoxicity.