Mechanisms underlying arsenic carcinogenesis: hypersensitivity of mice exposed to inorganic arsenic during gestation

Dose-Dependent Hepatotoxicity in Wistar Rat Neonates From Early-Life Arsenic Exposure

Arsenic, a highly toxic heavy metal widely found in the environment, is a known carcinogen and toxin. Our study examined the effects of sodium arsenite on Wistar rat neonates exposed during gestation and weaning periods. The pregnant and weaning rats were given the low dose (LDG), median dose (MDG), and high dose (HDG) daily as 8.2, 12.3, and 16.4 mg/kgbw of NaAsO2, respectively. The results revealed that despite not affecting litter size, gestation index, or immediate postnatal observations, prolonged exposure to high doses of sodium arsenite led to increased liver weights, indicating potential liver stress or damage. Arsenic accumulation in liver tissues was significant, and histological examinations revealed liver damage, vascular congestion, and inflammation. Elevated levels of ALT, AST, ALP, and GGT were observed in arsenic-exposed groups during liver function tests, indicating hepatocellular injury and impaired function. Exposure to arsenic led to a dose-dependent decline in the mRNA expression levels and activity of antioxidant enzymes, including GST, GR, GPx, SOD, and CAT, showing that oxidative stress is present. Furthermore, LPx levels were increased. Metallothionein gene expression was upregulated, indicating a protective response against arsenic toxicity. Our findings underscore the risks associated with gestational and weaning exposure to sodium arsenite, providing insight into potential mechanisms behind arsenic-induced health issues and highlighting the importance of understanding these risks during critical developmental stages.

Cell Cycle dysregulation on prenatal and postnatal Arsenic exposure in skin of Wistar rat neonates

This study explores the effects of prenatal and postnatal (until weaning period) arsenic exposure given via pregnant females on Wistar rat neonates. Pregnant female rats were divided in four groups - control, low dose, moderate dose and high dose groups of sodium arsenite exposure during gestation and weaning period. Half of the neonates were sacrificed at day 1 of birth and other half at day 21 of birth. Cell cycle analysis in epidermal keratinocytes using flowcytometer revealed that there was a consistent increase in number of cells in G2/M phase from 0.04% in control group to 0.88%, 1.59% and 2.77% in low, moderate and high dose groups respectively for neonates sacrificed at day-1. Whereas, the increase in number of cells with increasing doses in G2/M phase of neonates sacrificed at day-21 was from 3.44% to 5.1%, 6.82%, and 9.17%. At postnatal day 21, mRNA expression of Cyclin A and B1, p53, Caspases 3, 7 and 9, and Bax were found to be up-regulated. Whereas that of Cyclin E, CDK 1 and 2 and Bcl2 were down regulated consistently in skin tissues of arsenic exposed groups.

Heavy metals in paired samples of hair and nails in China: occurrence, sources and health risk assessment

The occurrence of heavy metals including chromium (Cr), nickel (Ni), copper (Cu), zinc (Zn), arsenic (As), cadmium (Cd) and lead (Pb) was investigated in paired samples of hair and nails collected from 121 volunteers in 16 cities, China. Results showed that the mean concentrations of Zn, Cu, As, Pb, Cr, Ni and Cd were 205, 18.0, 7.79, 6.18, 3.54, 2.02, 0.533 μg g^-1 in hair and 103, 8.09, 0.760, 7.27, 6.07, 8.81, 0.485 μg g^-1 in nails, respectively. The concentrations of Zn, Ni, Cr, Cd and Pb were positively correlated in paired samples of hair and nails, whereas a negative correlation was found for Cu and As between hair and nails. Higher concentrations of heavy metals were found in northern China than southern China. The multivariate analysis of variance revealed that dwelling environment was the dominant factor influencing the levels of Cd in hair (p < 0.05), while age was the dominant factor influencing the levels of Cr in nails (p < 0.05). Moreover, industrial pollution and smoking were also the important factors leading to the accumulation of heavy metals in human body. Principal component analysis (PCA) showed that industrial pollution and decoration material immersion were the main factors for the high concentrations of Cr and Ni in hair, accounting for 62.9% of the total variation; As in hair was dominantly related to groundwater pollution. The concentrations of heavy metals were within the recommended ranges in nails from this study. However, the mean levels of Cr, Ni and As in hair exceeded their recommended reference values, indicating potential health risks from heavy metals for residents in China.

The Multiple Functions of Melatonin: Applications in the Military Setting

The aim of this review is to provide the reader with a general overview on the rationale for the use of melatonin by military personnel. This is a technique that is being increasingly employed to manage growing psycho-physical loads. In this context, melatonin, a pleotropic and regulatory molecule, has a potential preventive and therapeutic role in maintaining the operational efficiency of military personnel. In battlefield conditions in particular, the time to treatment after an injury is often a major issue since the injured may not have immediate access to medical care. Any drug that would help to stabilize a wounded individual, especially if it can be immediately administered (e.g., per os) and has a very high safety profile over a large range of doses (as melatonin does) would be an important asset to reduce morbidity and mortality. Melatonin may also play a role in the oscillatory synchronization of the neuro-cardio-respiratory systems and, through its epigenetic action, poses the possibility of restoring the main oscillatory waves of the cardiovascular system, such as the Mayer wave and RSA (respiratory sinus arrhythmia), which, in physiological conditions, result in the oscillation of the heartbeat in synchrony with the breath. In the future, this could be a very promising field of investigation.

A review on sources, identification and treatment strategies for the removal of toxic Arsenic from water system

Arsenic liberation and accumulation in the groundwater environment are both affected by the presence of primary ions and soluble organic matter. The most important influencing role in the co-occurrence is caused by human activity, which includes logging, agricultural runoff stream, food, tobacco, and fertilizers. Furthermore, it covers a wide range of developed and emerging technologies for removing arsenic impurities from the ecosystem, including adsorption, ion exchangers, bio sorption, coagulation and flocculation, membrane technology and electrochemical methods. This review thoroughly explores various arsenic toxicity to the atmosphere and the removal methods involved with them. To begin, the analysis focuses on the general context of arsenic outbreaks in the area, health risks associated with arsenic, and measuring techniques. The utilization of innovative functional substances such as graphite oxides, metal organic structures, carbon nanotubes, and other emerging types of composite materials, as well as the ease, reduced price, and simple operating method of the adsorbent material, are better potential alternatives for arsenic removal. The aim of this article is to examine the origins of arsenic, as well as identification and treatment methods. It also addressed recent advancements in Arsenic removal using graphite oxides, carbon nanotubes, metal organic structures, magnetic nano composites, and other novel types of usable materials. Under ideal conditions for the above methods, the arsenic removal will achieve nearly 99% in lab scale.

Environmental and Health Hazards of Chromated Copper Arsenate-Treated Wood: A Review

Copper chrome arsenate (CCA) water-borne solution used to be widely used to make timber highly resistant to pests and fungi, in particular, wood products designed for outdoor use. Nowadays, CCA is a restricted chemical product in most countries, since potential environmental and health risks were reported due to dermal contact with CCA residues from treated structures and the surrounding soil, as well as the contamination of soils. However, large quantities of CCA-treated timber are still in use in framings, outdoor playground equipment, landscaping, building poles, jetty piles, and fencing structures around the world, thus CCA remains a source of pollutants to the environment and of increasing toxic metal/metalloid exposure (mainly in children). International efforts have been dedicated to the treatment of materials impregnated with CCA, however not only does some reuse of CCA-treated timber still occur, but also existing structures are leaking the toxic compounds into the environment, with impacts on the environment and animal and human health. This study highlights CCA mechanisms and the documented consequences in vivo of its exposure, as well as the adverse environmental and health impacts.

Magnesium Isoglycyrrhizinate Alleviates Arsenic Trioxide-Induced Cardiotoxicity: Contribution of Nrf2 and TLR4/NF-κB Signaling Pathway

PURPOSE

Magnesium isoglycyrrhizinate (MgIG), a single stereoisomer magnesium salt of glycyrrhizic acid, has beneficial effects on the cardiovascular system through anti-inflammatory, anti-oxidation, and anti-apoptotic actions. However, MgIG has not been shown to provide protection against cardiotoxicity induced by arsenic trioxide (ATO). This study aims to demonstrate the protection of MgIG against ATO-induced cardiac toxicity in mice and to investigate the underlying mechanism.

METHODS

A mouse cardiotoxicity model was established by administering 5 mg/kg ATO for 7 days. MgIG used in conjunction with the ATO to assess its cardioprotection.

RESULTS

MgIG administration could significantly reduce reactive oxygen species generation and the changes in tissue morphology. Also, MgIG administration increased the activity of antioxidase, such as superoxide dismutase, catalase, and glutathione peroxidase, and reduced malondialdehyde content and pro-inflammatory cytokine levels. Western blotting showed decreased expression of Bcl-2 associated X protein and Caspase-3, with increased expression of B-cell lymphoma 2. Importantly, MgIG administration increased nuclear factor-erythroid-2-related factor 2 (Nrf2) expression, while the expressions of nuclear factor kappa-B (NF-κB) and toll-like receptor-4 (TLR4) were significantly decreased.

CONCLUSION

Our data showed that MgIG alleviates ATO-induced cardiotoxicity, which is associated to the anti-inflammation, anti-oxidation, and anti-apoptosis action, potentially through activation of the Nrf2 pathway and suppression of the TLR4/NF-κB pathway.

Tannic acid ameliorates arsenic trioxide-induced nephrotoxicity, contribution of NF-κB and Nrf2 pathways

BACKGROUND AND PURPOSE

Tannic acid (TA), a group of polyphenolic compounds, has multiple anticancer, antimutagenic, antioxidant and anti-inflammatory activities. However, the effects of TA on arsenic trioxide (ATO)-induced nephrotoxicity are still relatively unknown. This study investigated the protective effects and potential mechanisms of TA on ATO-induced nephrotoxicity in rats.

METHODS

Rats were intragastrically administered TA with concurrent ATO infused intraperitoneally over 10 days. Renal morphology changes were observed through light microscopy. The levels of antioxidants and pro-inflammatory factors were measured in the serum and renal tissue, respectively. Further, expression of B-cell lymphoma-2, B-cell lymphoma-extra large, p53, and Bcl-2-associated X protein were measured using an immunohistochemical method. The protein expression of nuclear factor kappa B (NF-κB), nuclear factor-erythroid-2-related factor 2 (Nrf2), and kelch-like ECH-associated protein 1 (Keap1) were measured by Western blot.

RESULTS

The data showed that ATO exposure significantly increased the serum nephritic, oxidative stress, apoptosis and inflammatory markers in the renal tissue of rats. Conversely, pretreatment with TA reversed these changes. Furthermore, TA treatment caused a significant decrease in NF-κB expression (P < 0.05), while increasing Nrf2 and Keap1 expressions (P < 0.05).

CONCLUSION

TA ameliorates ATO-induced nephrotoxicity, which is related to the inhibition of oxidative stress, inflammation and apoptosis, potentially through the NF-κB/Nrf2 pathway.

Chinese Medicine Might Be A Promising Way for A Solution to Arsenic Nephrotoxicity

Arsenic from environmental contamination is a risk factor for kidney disease, and the clinical use of arsenic also triggers a new concern that the potential kidney damage caused by exposure to clinical doses of arsenic trivalent. So far, the undergoing mechanisms contributing to arsenic nephrotoxicity mostly remain unclear, and universally accepted methods for preventing this complication are limited too. Ancient Chinese medical scientists recognized the toxicity of arsenic long ago, and there were some records of Chinese herbs against arsenic poisoning in ancient books of Chinese medicine. In the past decade, several herbal formulations, as well as some potentially active compounds extracted from Chinese herbs, have been employed to prevent arsenic nephrotoxicity both in vivo and in vitro and showed better therapeutic effects. The present paper thus summarizes and discusses these Chinese medicine methods in preventing such a public health problem. In addition, we call for large, well-designed, randomized, and controlled clinical trials to be performed to further assess the efficacy and safety of these potential methods of Chinese medicine against arsenic nephrotoxicity.

Bioaccumulation and human health implications of essential and toxic metals in freshwater products of Northeast China

Bioaccumulation and human health risks of essential and toxic metals in ten species of freshwater products from Northeast China were investigated in this study. The concentrations (mg/kg wet weight) of target metals in aquatic products were: Fe (4.6-165.4), Zn (4.1-33.4), Mn (0.28-80.0), Cu (0.24-15.8), Cr (0.074-0.80), As (0.0068-0.72), Hg (0.016-0.58), Ni (0.019-0.58), Pb (0.017-0.27) and Cd (0.0004-0.058). There was no significant regional difference of target metal levels in fish samples between Liaoning province and Inner Mongolia Autonomous Region according to matched sample t-test. Every daily intakes (EDI) of target metals from freshwater products were far below their corresponding limits. However, health risk assessment of individual metal in freshwater products showed methyl mercury (MeHg) and Mn could pose potential noncarcinogenic risk to human, and inorganic arsenic (iAs) would cause potential carcinogenic risk to consumers at the level of 1 in 100,000. Furthermore, freshwater product species-specific bioaccumulation characteristics for different metals are quite different. The total hazard quotients of target metals in different aquatic product species demonstrated that co-exposure of target metals by consumption of these six species (C. auratus, E. sinensis, C. erythropterus, C. carpio, M. anguillicaudatus and O. cantor) from Northeast China could cause potential noncarcinogenic risk to human, and the pollution of toxic metals in E. sinensis and C. auratus were most serious among all investigated aquatic species.

Sulforaphane potentially attenuates arsenic-induced nephrotoxicity via the PI3K/Akt/Nrf2 pathway in albino Wistar rats

Oxidative stress plays a significant role in the pathophysiology of numerous kidney diseases, generally mediated by reactive oxygen species (ROS). Arsenic (Ar) is known to exert its toxicity through the generation of ROS and inflammation. The current study investigates the protective effects of sulforaphane (SFN) against arsenic-induced renal damage via PI3K/Akt-mediated Nrf2 pathway signaling. Thirty-two male albino Wistar rats were randomly divided into four groups of eight animals each, designated as control, arsenic (Ar), sulforaphane plus Ar (SFN+Ar), and sulforaphane alone (SFN), with oral administration of Ar (5 mg/kg BW) and SFN (80 mg/kg BW) daily for 28 days. Ar administration significantly (P < 0.05) increased the levels of ROS, OHdG, Ar accumulation, and lipid peroxidation, and decreased levels of enzymatic and nonenzymatic antioxidants. Notably, a significant (P < 0.05) increase was observed in markers of apoptosis, DNA damage, TUNEL-positive cells, and dark staining of ICAM-1 in renal tissue with decreased PI3K/Akt/Nrf2 gene expression. The biochemical findings were supported by histopathological and electron microscopy evaluation, which showed severe renal damage in rats treated with Ar. Pretreatment with SFN significantly (P < 0.05) attenuated renal ROS, OHdG, lipid peroxidation, and DNA damage, and increased phase II antioxidants via PI3K/Akt-mediated Nrf2 activation in renal tissue. These results show that dietary supplementation with SFN protects against Ar-induced nephrotoxicity via the PI3K/Akt-mediated Nrf2 signaling pathway in the rat kidney.

Epigenetic mechanisms underlying the toxic effects associated with arsenic exposure and the development of diabetes

BACKGROUND

Exposure to inorganic arsenic (iAs) is a major threat to the human health worldwide. The consumption of arsenic in drinking water and other food products is associated with the risk of development of type-2 diabetes mellitus (T2DM). The available experimental evidence indicates that epigenetic alterations may play an important role in the development of diseases that are linked with exposure to environmental toxicants. iAs seems to be associated with the epigenetic modifications such as alterations in DNA methylation, histone modifications, and micro RNA (miRNA) abundance.

OBJECTIVE

This article reviewed epigenetic mechanisms underlying the toxic effects associated with arsenic exposure and the development of diabetes.

METHOD

Electronic databases such as PubMed, Scopus and Google scholar were searched for published literature from 1980 to 2017. Searched MESH terms were "Arsenic", "Epigenetic mechanism", "DNA methylation", "Histone modifications" and "Diabetes".

RESULTS

There are various factors involved in the pathogenesis of T2DM but it is assumed that arsenic consumption causes the epigenetic alterations both at the gene-specific level and generalized genome level.

CONCLUSION

The research indicates that exposure from low to moderate concentrations of iAs is linked with the epigenetic effects. In addition, it is evident that, arsenic can change the components of the epigenome and hence induces diabetes through epigenetic mechanisms, such as alterations in glucose transport and/or metabolism and insulin expression/secretion.

Effects of in Utero Exposure to Arsenic during the Second Half of Gestation on Reproductive End Points and Metabolic Parameters in Female CD-1 Mice

BACKGROUND

Mice exposed to high levels of arsenic in utero have increased susceptibility to tumors such as hepatic and pulmonary carcinomas when they reach adulthood. However, the effects of in utero arsenic exposure on general physiological functions such as reproduction and metabolism remain unclear.

OBJECTIVES

We evaluated the effects of in utero exposure to inorganic arsenic at the U.S. Environmental Protection Agency (EPA) drinking water standard (10 ppb) and at tumor-inducing levels (42.5 ppm) on reproductive end points and metabolic parameters when the exposed females reached adulthood.

METHODS

Pregnant CD-1 mice were exposed to sodium arsenite [none (control), 10 ppb, or 42.5 ppm] in drinking water from gestational day 10 to birth, the window of organ formation. At birth, exposed offspring were fostered to unexposed dams. We examined reproductive end points (age at vaginal opening, reproductive hormone levels, estrous cyclicity, and fertility) and metabolic parameters (body weight changes, hormone levels, body fat content, and glucose tolerance) in the exposed females when they reached adulthood.

RESULTS

Arsenic-exposed females (10 ppb and 42.5 ppm) exhibited early onset of vaginal opening. Fertility was not affected when females were exposed to the 10-ppb dose. However, the number of litters per female was decreased in females exposed to 42.5 ppm of arsenic in utero. In both 10-ppb and 42.5-ppm groups, arsenic-exposed females had significantly greater body weight gain, body fat content, and glucose intolerance.

CONCLUSION

Our findings revealed unexpected effects of in utero exposure to arsenic: exposure to both a human-relevant low dose and a tumor-inducing level led to early onset of vaginal opening and to obesity in female CD-1 mice.

Therapeutic efficacy of biochanin A against arsenic-induced renal and cardiac damage in rats

The present study was investigated the effects of biochanin A (BCA) on arsenic toxicity in rats. For this purpose, rats were orally treated with arsenic in the form of sodium meta-arsenite alone (10mg/kg body weight (bw)/day) and co-administered selenium (10mg/kgbw/day) and BCA at different doses (10, 20 and 40mg/kgbw/day) for 6 weeks. Arsenic altered the oxidative stress indices in both renal and cardiac tissues. There was an increase in plasma renal markers, triglyceride, lipoproteins with no alterations in cholesterol levels were noted in arsenic-intoxicated rats. Non-significant changes of phospholipids and free fatty acids levels in the tissues of arsenic-exposed rats. The biochemical disturbances were well correlated with the histological findings in the kidney, but not in the heart. The administration of BCA and selenium significantly reversed the alterations in the above-mentioned parameters in arsenic-intoxicated rats. Our findings revealed the beneficial effects of BCA against arsenic toxicity.

Biomedical implications of heavy metals induced imbalances in redox systems

Several workers have extensively worked out the metal induced toxicity and have reported the toxic and carcinogenic effects of metals in human and animals. It is well known that these metals play a crucial role in facilitating normal biological functions of cells as well. One of the major mechanisms associated with heavy metal toxicity has been attributed to generation of reactive oxygen and nitrogen species, which develops imbalance between the prooxidant elements and the antioxidants (reducing elements) in the body. In this process, a shift to the former is termed as oxidative stress. The oxidative stress mediated toxicity of heavy metals involves damage primarily to liver (hepatotoxicity), central nervous system (neurotoxicity), DNA (genotoxicity), and kidney (nephrotoxicity) in animals and humans. Heavy metals are reported to impact signaling cascade and associated factors leading to apoptosis. The present review illustrates an account of the current knowledge about the effects of heavy metals (mainly arsenic, lead, mercury, and cadmium) induced oxidative stress as well as the possible remedies of metal(s) toxicity through natural/synthetic antioxidants, which may render their effects by reducing the concentration of toxic metal(s). This paper primarily concerns the clinicopathological and biomedical implications of heavy metals induced oxidative stress and their toxicity management in mammals.

A review of metal-catalyzed molecular damage: protection by melatonin

Metal exposure is associated with several toxic effects; herein, we review the toxicity mechanisms of cadmium, mercury, arsenic, lead, aluminum, chromium, iron, copper, nickel, cobalt, vanadium, and molybdenum as these processes relate to free radical generation. Free radicals can be generated in cells due to a wide variety of exogenous and endogenous processes, causing modifications in DNA bases, enhancing lipid peroxidation, and altering calcium and sulfhydryl homeostasis. Melatonin, an ubiquitous and pleiotropic molecule, exerts efficient protection against oxidative stress and ameliorates oxidative/nitrosative damage by a variety of mechanisms. Also, melatonin has a chelating property which may contribute in reducing metal-induced toxicity as we postulate here. The aim of this review was to highlight the protective role of melatonin in counteracting metal-induced free radical generation. Understanding the physicochemical insights of melatonin related to the free radical scavenging activity and the stimulation of antioxidative enzymes is of critical importance for the development of novel therapeutic strategies against the toxic action of these metals.

Genotoxic and epigenetic mechanisms in arsenic carcinogenicity

Arsenic is a human carcinogen with weak mutagenic properties that induces tumors through mechanisms not yet completely understood. People worldwide are exposed to arsenic-contaminated drinking water, and epidemiological studies showed a high percentage of lung, bladder, liver, and kidney cancer in these populations. Several mechanisms by which arsenical compounds induce tumorigenesis were proposed including genotoxic damage and chromosomal abnormalities. Over the past decade, a growing body of evidence indicated that epigenetic modifications have a role in arsenic-inducing adverse effects on human health. The main epigenetic mechanisms are DNA methylation in gene promoter regions that regulate gene expression, histone tail modifications that regulate the accessibility of transcriptional machinery to genes, and microRNA activity (noncoding RNA able to modulate mRNA translation). The "double capacity" of arsenic to induce mutations and epimutations could be the main cause of arsenic-induced carcinogenesis. The aim of this review is to better clarify the mechanisms of the initiation and/or the promotion of arsenic-induced carcinogenesis in order to understand the best way to perform an early diagnosis and a prompt prevention that is the key point for protecting arsenic-exposed population. Studies on arsenic-exposed population should be designed in order to examine more comprehensively the presence and consequences of these genetic/epigenetic alterations.

Studies on the effect of sodium arsenate on the enzymes of carbohydrate metabolism, brush border membrane, and oxidative stress in the rat kidney

Arsenic is an environmental pollutant and its contamination in drinking water poses serious world wide environmental health threats. It produces multiple adverse effects in various tissues, including the kidney. However, biochemical mechanism and renal response to its toxic insult are not completely elucidated. We hypothesized that sodium arsenate (ARS) induces oxidative stress and alters the structure and metabolic functions of kidney. Male Wistar rats were administered ARS (10 mg/kg body weight/day), intraperitoneally daily for 10 days. ARS administration increased blood urea nitrogen, serum creatinine, cholesterol, glucose, and phospholipids but decreased inorganic phosphate, indicating kidney toxicity. The activity of brush border membrane (BBM) enzymes significantly lowered in both cortex and medulla. Activity of hexokinase, lactate dehydrogenase, glucose-6-phosphate dehydrogenases, and NADP-malic enzyme significantly increased whereas malate dehydrogenase, glucose-6-phosphatase, and fructose 1,6 bis phosphatase decreased by ARS exposure. The activity of superoxide dismutase, GSH-peroxidase, and catalase were selectively altered in renal tissues along with an increase in lipid peroxidation. The present results indicated that ARS induced oxidative stress caused severe renal damage that resulted in altered levels of carbohydrate metabolism and BBM enzymes.

In utero and early life arsenic exposure in relation to long-term health and disease

BACKGROUND

There is a growing body of evidence that prenatal and early childhood exposure to arsenic from drinking water can have serious long-term health implications.

OBJECTIVES

Our goal was to understand the potential long-term health and disease risks associated with in utero and early life exposure to arsenic, as well as to examine parallels between findings from epidemiological studies with those from experimental animal models.

METHODS

We examined the current literature and identified relevant studies through PubMed by using combinations of the search terms "arsenic", "in utero", "transplacental", "prenatal" and "fetal".

DISCUSSION

Ecological studies have indicated associations between in utero and/or early life exposure to arsenic at high levels and increases in mortality from cancer, cardiovascular disease and respiratory disease. Additional data from epidemiologic studies suggest intermediate effects in early life that are related to risk of these and other outcomes in adulthood. Experimental animal studies largely support studies in humans, with strong evidence of transplacental carcinogenesis, atherosclerosis and respiratory disease, as well as insight into potential underlying mechanisms of arsenic's health effects.

CONCLUSIONS

As millions worldwide are exposed to arsenic and evidence continues to support a role for in utero arsenic exposure in the development of a range of later life diseases, there is a need for more prospective studies examining arsenic's relation to early indicators of disease and at lower exposure levels.

Morpho-mechanical intestinal remodeling in type 2 diabetic GK rats--is it related to advanced glycation end product formation?

Little is known about the mechanisms for the biomechanical remodeling in diabetes. The histomorphology, passive biomechanical properties and expression of advanced glycation end product (N epsilon-(carboxymethyl) lysine, AGE) and its receptor (RAGE) were studied in jejunal segments from 8 GK diabetic rats (GK group) and 10 age-matched normal rats (Normal group). The mechanical test was done by using a ramp distension of fluid into the jejunal segments in vitro. Circumferential stress and strain were computed from the length, diameter and pressure data and from the zero-stress state geometry. AGE and RAGE were detected by immunohistochemistry staining. Linear regression analysis was done to study association between the glucose level and AGE/RAGE expression with the histomorphometric and biomechanical parameters. The blood glucose level, the jejunal weight per length, wall thickness, wall area and layer thickness significantly increased in the GK group compared with the Normal group (P<0.05, P<0.01 and P<0.001). The opening angle and absolute values of residual strain decreased whereas the circumferential stiffness of the jejunal wall increased in the GK group (P<0.05 and P<0.01). Furthermore, stronger AGE expression in the villi and crypt and RAGE expression in the villi were found in the GK group (P<0.05 and P<0.01). Most histomorphometric and biomechanical changes were associated with blood glucose level and AGE/RAGE expression. In conclusion, histomorphometric and biomechanical remodeling occurred in type 2 diabetic GK rats. The increasing blood glucose level and the increased AGE/RAGE expression were associated with the remodeling, indicating a causal relationship.

Cytotoxic and Genotoxic effects of Arsenic and Lead on Human Adipose Derived Mesenchymal Stem Cells (AMSCs)

Arsenic and lead, known to have genotoxic and mutagenic effects, are ubiquitously distributed in the environment. The presence of arsenic in drinking water has been a serious health problem in many countries. Human exposure to these metals has also increased due to rapid industrialization and their use in formulation of many products. Liposuction material is a rich source of stem cells. In the present study cytotoxic and genotoxic effects of these metals were tested on adipose derived mesenchymal stem cells (AMSCs). Cells were exposed to 1-10 μg/ml and 10-100 μg/ml concentration of arsenic and lead, respectively, for 6, 12, 24 and 48 h. The cytotoxic effects were measured by neutral red uptake assay, while the genotoxic effects were tested by comet assay. The growth of cells decreased with increasing concentration and the duration of exposure to arsenic. Even the morphology of cells was changed; they became round at 10 μg /ml of arsenic. The cell growth was also decreased after exposure to lead, though it proved to be less toxic when cells were exposed for longer duration. The cell morphology remained unchanged. DNA damage was observed in the metal treated cells. Different parameters of comet assay were investigated for control and treated cells which indicated more DNA damage in arsenic treated cells compared to that of lead. Intact nuclei were observed in control cells. Present study clearly demonstrates that both arsenic and lead have cytotoxic and genotoxic effects on AMSCs, though arsenic compared to lead has more deleterious effects on AMSCs.

Hematological effects of arsenic in rats after subchronical exposure during pregnancy and lactation: the protective role of antioxidants

Free radicals production is involved in the toxicity of arsenic. The aim of this study was to determine whether biochemical changes occurred in the blood of arsenic-exposed pups during gestation and lactation, and additionally to investigate the potential beneficial role of the administration of certain antioxidants against arsenic exposure damage. Pregnant wistar rats received the following treatments as drinking water: (1) distilled water; (2) arsenic (50 mg/L); (3) antioxidants: zinc (20 mg/L)+vitamin C (2 g/L)+vitamin E (500 mg/L); (4) arsenic (50 mg/L)+antioxidants: zinc (20 mg/L)+vitamin C (2 g/L)+vitamin E (500 mg/L). We found a normocytic and normochromic anemia as well as a significant increase in hemolysis, TBARS production and catalase activity in the blood of arsenic intoxicated pups. Moreover, this metalloid produced a significant increase of serum cholesterol, triglicerids and urea levels whereas the proteins diminished. These effects were palliated in some extent by the coadministration of vitamins and zinc. Our findings suggest that administration of antioxidants during gestation and lactation could prevent some of the negative effects of arsenic.

Oxidative stress and antioxidant defense

Reactive oxygen species (ROS) are produced by living organisms as a result of normal cellular metabolism and environmental factors, such as air pollutants or cigarette smoke. ROS are highly reactive molecules and can damage cell structures such as carbohydrates, nucleic acids, lipids, and proteins and alter their functions. The shift in the balance between oxidants and antioxidants in favor of oxidants is termed “oxidative stress.” Regulation of reducing and oxidizing (redox) state is critical for cell viability, activation, proliferation, and organ function. Aerobic organisms have integrated antioxidant systems, which include enzymatic and nonenzymatic antioxidants that are usually effective in blocking harmful effects of ROS. However, in pathological conditions, the antioxidant systems can be overwhelmed. Oxidative stress contributes to many pathological conditions and diseases, including cancer, neurological disorders, atherosclerosis, hypertension, ischemia/perfusion, diabetes, acute respiratory distress syndrome, idiopathic pulmonary fibrosis, chronic obstructive pulmonary disease, and asthma. In this review, we summarize the cellular oxidant and antioxidant systems and discuss the cellular effects and mechanisms of the oxidative stress.

Reactive oxygen species mediate arsenic induced cell transformation and tumorigenesis through Wnt/β-catenin pathway in human colorectal adenocarcinoma DLD1 cells

Long term exposure to arsenic can increase incidence of human cancers, such as skin, lung, and colon rectum. The mechanism of arsenic induced carcinogenesis is still unclear. It is generally believed that reactive oxygen species (ROS) may play an important role in this process. In the present study, we investigate the possible linkage between ROS, β-catenin and arsenic induced transformation and tumorigenesis in human colorectal adenocarcinoma cell line, DLD1 cells. Our results show that arsenic was able to activate p47(phox) and p67(phox), two key proteins for activation of NADPH oxidase. Arsenic was also able to generate ROS in DLD1 cells. Arsenic increased β-catenin expression level and its promoter activity. ROS played a major role in arsenic-induced β-catenin activation. Treatment of DLD1 cells by arsenic enhanced both transformation and tumorigenesis of these cells. The tumor volumes of arsenic treated group were much larger than those without arsenic treatment. Addition of either superoxide dismutase (SOD) or catalase reduced arsenic induced cell transformation and tumor formation. The results indicate that ROS are involved in arsenic induced cell transformation and tumor formation possible through Wnt/β-catenin pathway in human colorectal adenocarcinoma cell line DLD1 cells.

Advances in metal-induced oxidative stress and human disease

Detailed studies in the past two decades have shown that redox active metals like iron (Fe), copper (Cu), chromium (Cr), cobalt (Co) and other metals undergo redox cycling reactions and possess the ability to produce reactive radicals such as superoxide anion radical and nitric oxide in biological systems. Disruption of metal ion homeostasis may lead to oxidative stress, a state where increased formation of reactive oxygen species (ROS) overwhelms body antioxidant protection and subsequently induces DNA damage, lipid peroxidation, protein modification and other effects, all symptomatic for numerous diseases, involving cancer, cardiovascular disease, diabetes, atherosclerosis, neurological disorders (Alzheimer's disease, Parkinson's disease), chronic inflammation and others. The underlying mechanism of action for all these metals involves formation of the superoxide radical, hydroxyl radical (mainly via Fenton reaction) and other ROS, finally producing mutagenic and carcinogenic malondialdehyde (MDA), 4-hydroxynonenal (HNE) and other exocyclic DNA adducts. On the other hand, the redox inactive metals, such as cadmium (Cd), arsenic (As) and lead (Pb) show their toxic effects via bonding to sulphydryl groups of proteins and depletion of glutathione. Interestingly, for arsenic an alternative mechanism of action based on the formation of hydrogen peroxide under physiological conditions has been proposed. A special position among metals is occupied by the redox inert metal zinc (Zn). Zn is an essential component of numerous proteins involved in the defense against oxidative stress. It has been shown, that depletion of Zn may enhance DNA damage via impairments of DNA repair mechanisms. In addition, Zn has an impact on the immune system and possesses neuroprotective properties. The mechanism of metal-induced formation of free radicals is tightly influenced by the action of cellular antioxidants. Many low-molecular weight antioxidants (ascorbic acid (vitamin C), alpha-tocopherol (vitamin E), glutathione (GSH), carotenoids, flavonoids, and other antioxidants) are capable of chelating metal ions reducing thus their catalytic activity to form ROS. A novel therapeutic approach to suppress oxidative stress is based on the development of dual function antioxidants comprising not only chelating, but also scavenging components. Parodoxically, two major antioxidant enzymes, superoxide dismutase (SOD) and catalase contain as an integral part of their active sites metal ions to battle against toxic effects of metal-induced free radicals. The aim of this review is to provide an overview of redox and non-redox metal-induced formation of free radicals and the role of oxidative stress in toxic action of metals.

The involvement of hypophyseal-gonadal and hypophyseal-adrenal axes in arsenic-mediated ovarian and uterine toxicity: modulation by hCG

This study evaluated the involvement of hypophyseal-gonadal and hypophyseal-adrenal axes as a possible mechanism of sodium arsenite toxicity in ovary and uterus by the coadministration of hCG. Subchronic treatment of 0.4 ppm of sodium arsenite/(100 g body weight day) via drinking water for seven estrous cycles significantly suppressed the plasma levels of leutinizing hormone, follicle-stimulating hormone, and estradiol along with sluggish ovarian activities of Delta(5),3beta-hydroxysteroid dehydrogenase and 17beta-hydroxysteroid dehydrogenase followed by a reduction in gonadal tissue peroxidase activities in mature female rats at diestrous phase. Noticeable weight loss of the ovary and uterus along with prolonged diestrous phase and increased deposition of arsenic in the plasma and in these reproductive organs were also demonstrated following the ingestion of arsenic. Follicular atresia and thinning of the uterine luminal diameter were evident after sodium arsenite treatment. Effective protection of gonadal weight loss, suppressed ovarian steroidogenesis, and altered ovarian and uterine peroxidase activities were noticed when 1.0 IU hCG/(100 g body weight day) is given in arsenic-intoxicated rats. Normal estrous cyclicity was restored toward the control level after hCG coadministration, though the elimination of elementary arsenic from the plasma and gonadal tissues was impossible. A significant recovery in the restoration of ovarian and uterine histoarchitecture was prominent after hCG treatment. Adrenal hypertrophy and steroidogenic arrest of the adrenal gland along with altered level of brain monoamines in the midbrain and diencephalons following arsenic intoxication were also ameliorated after hCG coadministration.

Ascorbic acid improves mitochondrial function in liver of arsenic-treated rat

Arsenic is an ubiquitous and well-documented carcinogenic metalloid. The most common source of arsenic is drinking water. The mechanism of arsenic toxicity in a cell has historically been centered around its inhibitory effects on cellular respiration and mitochondrial injury. Ascorbic acid, a low molecular weight, water-soluble antioxidant, improves the reduced glutathione (GSH) status by recycling oxidized glutathione. Ascorbic acid can improve mitochondrial function by improving the thiol status; thereby preventing reactive oxygen species- mediated damage to liver as well as kidney. Ascorbic acid has been shown to protect membrane and other cellular compartments by regenerating vitamin E. Therefore, ascorbic acid seems to be a suitable protective factor against arsenic toxicity. Present reports describe the effect of ascorbic acid on oxidative phosphorylation, adenosine triphosphatase (ATPase), succinic dehydrogenase, caspase-3 and apoptosis in the liver of rats treated with arsenic trioxide (As(III)). Ultrastructural changes in the mitochondria have also been reported. We show that cotreatments with ascorbic acid and As(III) improve mitochondrial structure and function. We attribute these improvements mainly to antioxidative role of ascorbic acid. Apoptosis was restricted due to caspase-3 inhibition. Ascorbic acid could protect DNA from the attack of reactive oxygen species generated by As(III). Consequently its events led to improved ADP:O ratio, normalized ATPase activity and restored the activity of succinic dehydrogenase. Overall, results support the protective role of ascorbic acid against As( III)-induced liver injury.

Effects of arsenic exposure on DNA methylation and epigenetic gene regulation

Arsenic is a nonmutagenic human carcinogen that induces tumors through unknown mechanisms. A growing body of evidence suggests that its carcinogenicity results from epigenetic changes, particularly in DNA methylation. Changes in gene methylation status, mediated by arsenic, have been proposed to activate oncogene expression or silence tumor suppressor genes, leading to long-term changes in the activity of genes controlling cell transformation. Mostly descriptive, and often contradictory, studies have demonstrated that arsenic exposure is associated with both hypo- and hyper-methylation at various genetic loci in vivo or in vitro. This ambiguity has made it difficult to assess whether the changes induced by arsenic are causally involved in the transformation process or are simply a reflection of the altered physiology of rapidly dividing cancer cells. Here, we discuss the evidence supporting changes in DNA methylation as a cause of arsenic carcinogenesis and highlight the strengths and limitations of these studies, as well as areas where consistencies and inconsistencies exist.

Transition metal ions and selenite modulate the methylation of arsenite by the recombinant human arsenic (+3 oxidation state) methyltransferase (hAS3MT)

This report demonstrates that transition metal ions and selenite affect the arsenite methylation by the recombinant human arsenic (+3 oxidation state) methyltransferase (hAS3MT) in vitro. Co(2+), Mn(2+), and Zn(2+) inhibited the arsenite methylation by hAS3MT in a concentration-dependent manner and the kinetics indicated Co(2+) and Mn(2+) to be mixed (competitive and non-competitive) inhibitors while Zn(2+) to be a competitive inhibitor. However, only a high concentration of Fe(2+) could restrain the methylation. UV-visible, CD and fluorescence spectroscopy were used to study the interactions between the metal ions above and hAS3MT. Further studies showed that neither superoxide anion nor hydrogen peroxide was involved in the transition metal ion or selenite inhibition of hAS3MT activity. The inhibition of arsenite methylating activity of hAS3MT by selenite was reversed by 2mM DTT (dithiothreitol) but neither by cysteine nor by beta-mercaptoethanol. Whereas, besides DTT, cysteine can also prevent the inhibition of hAS3MT activity by Co(2+), Mn(2+), and Zn(2+). Free Cys residues were involved in the interactions of transition metal ions or selenite with hAS3MT. It is proposed that the inhibitory effect of the ions (Co(2+), Mn(2+), and Zn(2+)) or selenite on hAS3MT activity might be via the interactions of them with free Cys residues in hAS3MT to form inactive protein adducts.

Respiratory effects in people exposed to arsenic via the drinking water and tobacco smoking in southern part of Pakistan

In this study, a survey has been conducted during 2005-2007 on surface and groundwater arsenic (As) contamination and its impact on the health of local population, of villages located on the banks of Manchar lake, southern part of Sindh, Pakistan. We have also assessed the relationship between arsenic exposure through respiratory disorders in male subjects with drinking water and smoking cigarettes made from tobacco grown in agricultural land irrigated with As contaminated lake water. The biological samples (blood and scalp hair) were collected from As exposed subjects (100% smokers) and age matched healthy male subjects (40.2% smoker and 59.8% non smokers) belong to unexposed areas for comparison purposes. The As concentration in drinking water (surface and underground water), agricultural soil, cigarette tobacco and biological samples were determined by electrothermal atomic absorption spectrometry. The range of As concentrations in lake water was 35.2-158 microg/L (average 97.5 microg/L), which is 3-15 folds higher than permissible limit of World Health Organization (WHO, 2004). While the As level in local cigarette tobacco was found to be 3-6 folds higher than branded cigarettes (0.37-0.79 microg/g). Arsenic exposed subjects (with and without RD) had significantly elevated levels of As in their biological samples as compared to referent male subject of unexposed area. These respiratory effects were more pronounced in individuals who had also As induced skin lesions. The linear regressions showed good correlations between As concentrations in water versus hair and blood samples of exposed subjects with and without respiratory problems.

Structural, chemical and biological aspects of antioxidants for strategies against metal and metalloid exposure

Oxidative stress contributes to the pathophysiology of exposure to heavy metals/metalloid. Beneficial renal effects of some medications, such as chelation therapy depend at least partially on the ability to alleviate oxidative stress. The administration of various natural or synthetic antioxidants has been shown to be of benefit in the prevention and attenuation of metal induced biochemical alterations. These include vitamins, N-acetylcysteine, alpha-lipoic acid, melatonin, dietary flavonoids and many others. Human studies are limited in this regard. Under certain conditions, surprisingly, the antioxidant supplements may exhibit pro-oxidant properties and even worsen metal induced toxic damage. To date, the evidence is insufficient to recommend antioxidant supplements in subject with exposure to metals. Prospective, controlled clinical trials on safety and effectiveness of different therapeutic antioxidant strategies either individually or in combination with chelating agent are indispensable. The present review focuses on structural, chemical and biological aspects of antioxidants particularly related to their chelating properties.

Enhanced ROS production and redox signaling with combined arsenite and UVA exposure: contribution of NADPH oxidase

Solar ultraviolet radiation (UVR) is the major etiological factor in skin carcinogenesis. However, in vivo studies demonstrate that mice exposed to arsenic and UVR exhibit significantly more tumors and oxidative DNA damage than animals treated with either agent alone. Interactions between arsenite and UVR in the production of reactive oxygen species (ROS) and stress-associated signaling may provide a basis for the enhanced carcinogenicity. In this study keratinocytes were pretreated with arsenite (3 microM) and then exposed to UVA (10 kJ/m(2)). We report that exposure to UVA after arsenite pretreatment enhanced ROS production, p38 MAP kinase activation, and induction of a redox-sensitive gene product, heme oxygenase-1, compared to either stimulus alone. UVR exposure resulted in rapid and transient NADPH oxidase activation, whereas the response to arsenite was more pronounced and persistent. Inhibition of NADPH oxidase decreased ROS production in arsenite-treated cells but had little impact on UVA-exposed cells. Furthermore, arsenite-induced, but not UVA-induced, p38 activation and HO-1 expression were dependent upon NADPH oxidase activity. These findings indicate differences in the mechanisms of ROS production by arsenite and UVA that may provide an underlying basis for the observed enhancement of redox-related cellular responses upon combined UVA and arsenite exposure.

Trace metals and over-expression of metallothioneins in bladder tumoral lesions: a case-control study

BACKGROUND

Previous studies have provided some evidence of a possible association between cancer and metallothioneins. Whether this relates to an exposure to carcinogenic metals remains unclear.

METHODS

In order to examine the association between the expression of metallothioneins and bladder tumors, and to compare the levels of arsenic, cadmium, chromium, lead and nickel in animals with bladder tumors and animals without bladder tumors, 37 cases of bovine bladder tumors and 17 controls were collected. The detection and quantification of metallothioneins in bladder tissue of both cases and controls was performed by immunohistochemistry. And the quantification of metals in tissue and hair was assessed by inductively coupled plasma - mass spectrometry.

RESULTS

Increased expression of metallothioneins was associated with bladder tumors when compared with non-tumoral bladder tissue (OR = 9.3, 95% CI: 1.0 - 480). The concentrations of cadmium, chromium, lead and nickel in hair of cases were significantly higher than those of controls. However, as for the concentration of metals in bladder tissue, the differences were not significant.

CONCLUSION

Though the sample size was small, the present study shows an association between bladder tumors and metallothioneins. Moreover, it shows that concentrations of metals such as cadmium, chromium, lead and nickel in hair may be used as a biomarker of exposure.

Strategies for addressing global environmental health concerns

While each region of the world faces unique public health challenges, environmental threats to vulnerable populations in Asia constitute a significant global public health challenge. Environmental threats to health are widespread and are increasing as nations in the region undergo rapid industrial development. One of the major predictors of ill health is poverty. Regional poverty puts large populations at risk for ill health, which exacerbates poverty and increases the exposure risk to environmental factors, such as pollution and disease. Patterns of illness have changed dramatically in the last century, and will continue to change in this century. Chemical toxicants in the environment, poverty, and little or no access to health care are all factors contributing to life-threatening diseases. Therefore, it is vital that we develop a better understanding of the mechanisms and interactions between nutrition, infectious disease, environmental exposures, and genetic predisposition in order to develop better prevention methods.

Identification of Genes Responding to Low-Dose Arsenite Using HiCEP

ABSTRACT Chronic ingestion of arsenic in polluted food and water can cause various human disorders including skin and lung cancers. Sensitive biomarkers from human tissue/cells could help to prevent chronic intoxication with low-dose arsenite. Using High-Coverage Expression Profiling (HiCEP), an Amplified Fragment Length Polymorphism (AFLP)-based gene expression profiling technique, we analyzed the expression of approximately 11,000 genes in human lung fibroblasts (HFLIII) and compared the profiles between cells, treated and untreated with 1 muM sodium arsenite (NaAsO(2)). Hundreds of genes appeared upregulated and downregulated more than two-fold, 2 h after the treatment. Marked induction was found (>4.4-fold) in a few genes including HMOX1, INHBA, and ANKRD11. Induction of the HMOX1 was detected with a dose of arsenite at as low as 0.3 muM (0.04 ppm) and reached its maximum at 4 h after the treatment. The arsenite-induced HMOX1 expression was attenuated by the promoted glutathione (GSH) synthesis by N-acetyl-L-cysteine (NAC). However, it was not affected by pretreating the cells with general radical scavengers, consistent with the fact that ionizing radiation at either high-or low-doses has never induced HMOX1 in the same assay system. Thus, induction of HMOX1 gene is highly sensitive and also selective against arsenite in the cells. The present process could provide a useful strategy for exploring biomarkers that might help in assessing the known and unknown risks of any natural and artificial toxic reagents.

Epigenetic reprogramming and imprinting in origins of disease

The traditional view that gene and environment interactions control disease susceptibility can now be expanded to include epigenetic reprogramming as a key determinant of origins of human disease. Currently, epigenetics is defined as heritable changes in gene expression that do not alter DNA sequence but are mitotically and transgenerationally inheritable. Epigenetic reprogramming is the process by which an organism's genotype interacts with the environment to produce its phenotype and provides a framework for explaining individual variations and the uniqueness of cells, tissues, or organs despite identical genetic information. The main epigenetic mediators are histone modification, DNA methylation, and non-coding RNAs. They regulate crucial cellular functions such as genome stability, X-chromosome inactivation, gene imprinting, and reprogramming of non-imprinting genes, and work on developmental plasticity such that exposures to endogenous or exogenous factors during critical periods permanently alter the structure or function of specific organ systems. Developmental epigenetics is believed to establish "adaptive" phenotypes to meet the demands of the later-life environment. Resulting phenotypes that match predicted later-life demands will promote health, while a high degree of mismatch will impede adaptability to later-life challenges and elevate disease risk. The rapid introduction of synthetic chemicals, medical interventions, environmental pollutants, and lifestyle choices, may result in conflict with the programmed adaptive changes made during early development, and explain the alarming increases in some diseases. The recent identification of a significant number of epigenetically regulated genes in various model systems has prepared the field to take on the challenge of characterizing distinct epigenomes related to various diseases. Improvements in human health could then be redirected from curative care to personalized, preventive medicine based, in part, on epigenetic markings etched in the "margins" of one's genetic make-up.

Implications of gender differences for human health risk assessment and toxicology

This paper from The Human Health working group of SGOMSEC 16 examines a broad range of issues on gender effects in toxicology. Gender differences in toxicology begin at the gamete and embryo stage, continuing through development and maturation and into old age. Sex influences exposure, toxicokinetics, and toxicodynamics. The effects of sex have often been overlooked in both epidemiology and toxicology. In addition to the obvious modifying effects of the sex hormones and conditions affecting the male and female reproductive organs and sex roles, both genetic and hormonal effects influence many aspects of life and toxic responses. All aspects of toxicology should consider gender-balanced designs so that a more comprehensive understanding of differences and similarities can be obtained. Differential gene expression is a new frontier in toxicology. Risk assessment should account for gender and life cycle differences. The biological basis for altered sex ratios observed in several populations should be sought in animal models, and expanded to other compounds that might exert sex-selective effects. Wherever possible and feasible, toxicologic and environmental epidemiological studies should be designed and have sufficient statistical power to quantify differential gender-based exposures and outcomes.

Benzene-induced cancers: abridged history and occupational health impact

Benzene-induced cancer in humans was first reported in the late 1920s. Carcinogenesis findings in animals were not reported conclusively until 1979. Industry exploited this "discrepancy" to discredit the use of animal bioassays as surrogates for human exposure experience. The cardinal reason for the delay between first recognizing leukemia in humans and sought-after neoplasia in animals centers on poor design and conduct of experimental studies. The first evidence of carcinogenicity in animals manifested as malignant tumors of the zymbal glands (sebaceous glands in the ear canal) of rats, and industry attempted to discount this as being irrelevant to humans, as this organ is vestigial and not present per se in humans. Nonetheless, shortly thereafter benzene was shown to be carcinogenic to multiple organ sites in both sexes of multiple strains and multiple species of laboratory animals exposed via various routes. This paper presents a condensed history of the benzene bioassay story with mention of benzene-associated human cancers.

Arsenic exposure and age and sex-specific risk for skin lesions: a population-based case-referent study in Bangladesh

BACKGROUND

The objective of this population-based case-referent study in Matlab, Bangladesh, was to assess the susceptibility to arsenic-induced skin lesions by age and sex, in a population drinking water from As-contaminated tube wells.

METHODS

Identification of As-related skin lesions was carried out in three steps: a) screening of the entire population > 4 years of age (n = 166,934) by trained field teams; b) diagnosis of suspected As-related cases by physicians; and c) confirmation by experts based on physicians' records and photographs. A total of 504 cases with skin lesions were confirmed. We randomly selected 2,201 referents from the Matlab health and demographic surveillance system; 1,955 were eligible, and 1,830 (94%) were available for participation in the study. Individual history of As exposure was based on information obtained during interviews and included all drinking-water sources used since 1970 and concentrations of As (assessed by atomic absorption spectrophotometry) in all the tube wells used.

RESULTS

Cases had been exposed to As more than referents (average exposure since 1970: male cases, 200 microg/L; female cases, 211 microg/L; male referents, 143 microg/L; female referents, 155 microg/L). We found a dose-response relationship for both sexes (p < 0.001) and increased risk with increasing socioeconomic status. Males had a higher risk of obtaining skin lesions than females (odds ratio 10.9 vs. 5.78) in the highest average exposure quintile (p = 0.005). Start of As exposure (cumulative exposure) before 1 year of age was not associated with higher risk of obtaining skin lesions compared to start of As exposure later in life.

CONCLUSIONS

The results demonstrate that males are more susceptible than females to develop skin lesions when exposed to As in water from tube wells.

Long term low-dose arsenic exposure induces loss of DNA methylation

Arsenic ranks as the number one toxic environmental contaminant. In humans, arsenic exposure is associated with various forms of cancer, cardiovascular and skin diseases, neuropathies of the central nervous system, and genotoxic and immunotoxic effects. Although a well recognized human carcinogen, arsenic itself is not a potent mutagen and has been thought to act through epigenetic mechanisms that modify DNA methylation patterns, perhaps in conjunction with DNA-damaging agents. To develop preliminary support for a more thorough examination of this hypothesis, we have measured the effect of submicromolar and low-micromolar concentrations of arsenite on the methylation status of DNA and the biochemical reactions that regulate it. We find that arsenic causes the depletion of S-adenosylmethionine, the main cellular methyl donor, and represses the expression of the DNA methyltransferase genes DNMT1 and DNMT3A. Possibly as a consequence of these two complementary mechanisms, long-term exposure to arsenic results in DNA hypomethylation.