Arsenic for the fool: an exponential connection

Metal Toxicity and Dementia Including Frontotemporal Dementia: Current State of Knowledge

Frontotemporal dementia (FTD) includes a number of neurodegenerative diseases, often with early onset (before 65 years old), characterized by progressive, irreversible deficits in behavioral, linguistic, and executive functions, which are often difficult to diagnose due to their similar phenotypic characteristics to other dementias and psychiatric disorders. The genetic contribution is of utmost importance, although environmental risk factors also play a role in its pathophysiology. In fact, some metals are known to produce free radicals, which, accumulating in the brain over time, can induce oxidative stress, inflammation, and protein misfolding, all of these being key features of FTD and similar conditions. Therefore, the present review aims to summarize the current evidence about the environmental contribution to FTD-mainly dealing with toxic metal exposure-since the identification of such potential environmental risk factors can lead to its early diagnosis and the promotion of policies and interventions. This would allow us, by reducing exposure to these pollutants, to potentially affect society at large in a positive manner, decreasing the burden of FTD and similar conditions on affected individuals and society overall. Future perspectives, including the application of Artificial Intelligence principles to the field, with related evidence found so far, are also introduced.

Arsenic exposure at environmentally relevant levels induced metabolic toxicity in development mice: Mechanistic insights from integrated transcriptome and metabolome

Emerging evidence has linked arsenic exposure and metabolic homeostasis, but the mechanism is incompletely understood, especially at relatively low concentrations. In this study, we used a mouse model to evaluate the health impacts and metabolic toxicity of arsenic exposure in drinking water at environmentally relevant levels (0.25 and 1.0 ppm). Our results indicated that arsenic damaged intestinal barrier and induced arsenic accumulation, oxidative stress, and pathological changes in the liver and illum. Interestingly, arsenic increased the hepatic triglyceride (TG) and total cholesterol (TC), while reduced serum TG and TC levels. The liver transcriptome found that arsenic exposure caused transcriptome perturbation and promoted hepatic lipid accumulation by regulating the exogenous fatty acids degradation and apolipoproteins related genes. The serum metabolomics identified 74 and 88 differential metabolites in 0.25 and 1.0 ppm, respectively. The KEGG disease and subcellular location analysis indicated that arsenic induced liver and intestinal diseases, and the mitochondrion might be the target organelle for arsenic-induced toxicity. Co-enrichment of transcriptome and metabolome identified 24 metabolites and 9 genes as metabolic toxicity biomarkers. Moreover, 40 male (20 nonalcoholic fatty liver disease (NAFLD) cases and 20 healthy controls) was further selected to validate our findings. Importantly, the significantly changed L-palmitoylcarnitine, 3-hydroxybutyric acid, 2-hydroxycaproic acid and 6 genes of Hadha, Acadl, Aldh3a2, Cpt1a, Cpt2, and Acox1 were found in the NAFLD cases. The results from integrated multi-omics and chemical-protein network analysis indicated that L-palmitoylcarnitine played a critical role in metabolic toxicity by regulating mitochondrial fatty acids β-oxidation genes (Cpt1a, Cpt2). In conclusion, these findings provided new clues for the metabolic toxicity of arsenic exposure at environmentally relevant levels, which involved in the late-life NAFLD development. Our results also contribute to understanding the human responses and phenotypic changes to this hazardous material exposure in the environment.

The Role of microRNAs in Arsenic-Induced Human Diseases: A Review

MicroRNAs (miRNAs) are noncoding RNAs with 20-22 nucleotides, which are encoded by endogenous genes and are capable of targeting the majority of human mRNAs. Arsenic is regarded as a human carcinogen, which can lead to many adverse health effects including diabetes, skin lesions, kidney disease, neurological impairment, male reproductive injury, and cardiovascular disease (CVD) such as cardiac arrhythmias, ischemic heart failure, and endothelial dysfunction. miRNAs can act as tumor suppressors and oncogenes via directly targeting oncogenes or tumor suppressors. Recently, miRNA dysregulation was considered to be an important mechanism of arsenic-induced human diseases and a potential biomarker to predict the diseases caused by arsenic exposure. Endogenic miRNAs such as miR-21, the miR-200 family, miR-155, and the let-7 family are involved in arsenic-induced human disease by inducing translational repression or RNA degradation and influencing multiple pathways, including mTOR/Arg 1, HIF-1α/VEGF, AKT, c-Myc, MAPK, Wnt, and PI3K pathways. Additionally, exogenous miRNAs derived from plants, such as miR-34a, miR-159, miR-2911, miR-159a, miR-156c, miR-168, etc., among others, can be transported from blood to specific tissue/organ systems in vivo. These exogenous miRNAs might be critical players in the treatment of human diseases by regulating host gene expression. This review summarizes the regulatory mechanisms of miRNAs in arsenic-induced human diseases, including cancers, CVD, and other human diseases. These special miRNAs could serve as potential biomarkers in the management and treatment of human diseases linked to arsenic exposure. Finally, the protective action of exogenous miRNAs, including antitumor, anti-inflammatory, anti-CVD, antioxidant stress, and antivirus are described.

Mechanisms of genotoxicity and proteotoxicity induced by the metalloids arsenic and antimony

Arsenic and antimony are metalloids with profound effects on biological systems and human health. Both elements are toxic to cells and organisms, and exposure is associated with several pathological conditions including cancer and neurodegenerative disorders. At the same time, arsenic- and antimony-containing compounds are used in the treatment of multiple diseases. Although these metalloids can both cause and cure disease, their modes of molecular action are incompletely understood. The past decades have seen major advances in our understanding of arsenic and antimony toxicity, emphasizing genotoxicity and proteotoxicity as key contributors to pathogenesis. In this review, we highlight mechanisms by which arsenic and antimony cause toxicity, focusing on their genotoxic and proteotoxic effects. The mechanisms used by cells to maintain proteostasis during metalloid exposure are also described. Furthermore, we address how metalloid-induced proteotoxicity may promote neurodegenerative disease and how genotoxicity and proteotoxicity may be interrelated and together contribute to proteinopathies. A deeper understanding of cellular toxicity and response mechanisms and their links to pathogenesis may promote the development of strategies for both disease prevention and treatment.

Among Gerontogens, Heavy Metals Are a Class of Their Own: A Review of the Evidence for Cellular Senescence

Advancements in modern medicine have improved the quality of life across the globe and increased the average lifespan of our population by multiple decades. Current estimates predict by 2030, 12% of the global population will reach a geriatric age and live another 3-4 decades. This swelling geriatric population will place critical stress on healthcare infrastructures due to accompanying increases in age-related diseases and comorbidities. While much research focused on long-lived individuals seeks to answer questions regarding how to age healthier, there is a deficit in research investigating what aspects of our lives accelerate or exacerbate aging. In particular, heavy metals are recognized as a significant threat to human health with links to a plethora of age-related diseases, and have widespread human exposures from occupational, medical, or environmental settings. We believe heavy metals ought to be classified as a class of gerontogens (i.e., chemicals that accelerate biological aging in cells and tissues). Gerontogens may be best studied through their effects on the "Hallmarks of Aging", nine physiological hallmarks demonstrated to occur in aged cells, tissues, and bodies. Evidence suggests that cellular senescence-a permanent growth arrest in cells-is one of the most pertinent hallmarks of aging and is a useful indicator of aging in tissues. Here, we discuss the roles of heavy metals in brain aging. We briefly discuss brain aging in general, then expand upon observations for heavy metals contributing to age-related neurodegenerative disorders. We particularly emphasize the roles and observations of cellular senescence in neurodegenerative diseases. Finally, we discuss the observations for heavy metals inducing cellular senescence. The glaring lack of knowledge about gerontogens and gerontogenic mechanisms necessitates greater research in the field, especially in the context of the global aging crisis.

Bioaccessible arsenic in soil of thermal areas of Viterbo, Central Italy: implications for human health risk

Thermal waters near the city of Viterbo (Central Italy) are known to show high As contents (up to 600 µg/l). Travertine is precipitated by these waters, forming extended plateau. In this study, we determine the As content, speciation and bioaccessibility in soil and travertine samples collected near a recreational area highly frequented by local inhabitants and tourists to investigate the risk of As exposure through accidental ingestion of soil particles. (Pseudo)total contents in the studied soils range from 17 to 528 mg/kg, being higher in soil developed on a travertine substrate (197 ± 127 mg/kg) than on volcanic rocks (37 ± 13 mg/kg). In travertines, most As is bound to the carbonatic fraction, whereas in soil the semimetal is mostly associated with the oxide and residual fractions. Accordingly, bioaccessibility (defined here by the simplified bioaccessibility extraction test, SBET; Oomen et al., 2002.) is maximum (up to 139 mg/kg) for soil developed on a travertine substrate, indicating a control of calcite dissolution on As bioaccessibility. On the other hand, risk analysis suggests a moderate carcinogenic risk associated with accidental soil ingestion, while dermal contact is negligible. By contrast, ingestion of thermal water implies a higher carcinogenic and systemic health risk.

Association of urinary arsenic and sleep disorder in the US population: NHANES 2015-2016

Arsenic is a known carcinogen and neurotoxin and is found in the natural earth crust. Arsenic exposure can develop depression, memory dysfunction, and neurodegenerative disorder. The mechanism of arsenic toxicity on the nervous system is not known. There is a lack of research on the association between arsenic exposure and sleep disturbance in humans. This study aims to investigate the relationship between six types of urinary speciated arsenic exposure and sleep disturbance in adults from the general population using the National Health and Nutrition Examination Survey (NHANES) 2015-2016 dataset. Sleep disturbance was measured using self-reported questionnaires, asking participants if they had ever told a doctor they had trouble sleeping. We utilized multivariate logistic regression analysis using complex survey procedures to examine the association between six types of urinary arsenic concentration and trouble sleeping. The total sample included 1,611 adults who were 20 years and older. Of the study participants, 30.0% had trouble sleeping. Compared to individuals with urinary arsenous acid below the lower level of detection (LLOD), those with urinary arsenous acid at or above the detection limit had lower odds of trouble sleeping [odds ratio: 0.72 (95% confidence interval 0.51-1.00, p-value: 0.05)]. The other five types of urinary speciated arsenic studied (arsenic acid, arsenobetaine, arsenocholine, dimethylarsinic acid, monomethylarsonic acid) were not associated with a sleep disorder. More studies are required to confirm or refute these findings.

[The role of mercury and arsenic in the etiology and pathogenesis of Parkinson's and Alzheimer's diseases]

A critical review of literature data on the toxic effects of mercury and arsenic on the human brain and their relationship with the etiology and pathogenesis of neurodegenerative diseases such as Parkinson's and Alzheimer's diseases is presented. In the first case, the toxic effect of mercury and arsenic on the brain stimulates oxidative stress, which leads to the formation of free oxygen species and a decrease in the antioxidant defense of neurons. In the second case, the harmful effect of mercury changes the structure and properties of β-amyloid, and the toxic effect of arsenic contributes to its accumulation. In the pathogenesis of the diseases under consideration, particular importance is attached to the reaction of astrocytes that initiate neuroinflammation, which is also characteristic of mercury and arsenic intoxication. Considering that the symptoms recorded during intoxication with mercury and arsenic are in many respects similar to those of Parkinson's and Alzheimer's diseases, and their pathogenetic mechanisms (oxidative stress and neuroinflammation) coincide, then the toxic effects of mercury and arsenic in neurodegenerative diseases analyzed in this review can be characterized as the influence of the most significant risk factors.

Behaviour and distribution of arsenic in seawater and suspended particulate matter in the adjacent area of the Changjiang Estuary during summer and autumn

Water and suspended particulate matter (SPM) were collected from the Changjiang Estuary and its adjacent areas during summer (July) and autumn (October) to study the distributions and partitioning of arsenic. The dissolved arsenic (DAs) and particulate arsenic (PAs) concentration distributions were strongly affected by inputs from riverine discharge and water masses in the East China Sea, generally exhibiting a decreasing trend from inshore to offshore. The DAs concentration was higher in the surface water due to the influence of seawater stratification in summer, but it was not obvious in autumn. DAs and PAs concentrations in the estuary were significantly higher in autumn than in summer. Seasonal variations in arsenic were due to seasonal differences in riverine input (mainly the Changjiang River) and the intrusion of water masses. PAs showed a positive correlation with both SPM and turbidity. The highest PAs concentration was observed in the northern Changjiang Estuary affected by the YSCC, with higher turbidity during autumn. The higher concentration of PAs in autumn was affected by the high SPM input and resuspension of sediment. The water-particulate distribution coefficient of As in summer showed an increasing tendency with salinity, which might be caused by the decrease in the diameter of suspended particles in the open sea.

Changes in metabolomics and lipidomics in brain tissue and their correlations with the gut microbiome after chronic food-derived arsenic exposure in mice

Arsenic can cause neurodegenerative diseases of the brain, but the definite mechanism is still unknown. In this study, to discuss the disturbances on brain metabolome and lipidome under subchronic arsenic exposure, we treated mice with the arsenic-containing feed (concentration of total arsenic = 30 mg/kg) prepared in accordance with the proportion of rice arsenicals for 16 weeks and performed metabolomics and lipidomics studies respectively using UHPLC-Triple-TOF-MS/MS and UHPLC-Q Exactive Focus MS/MS on mice brain. In addition, the distributions of arsenical metabolites along the feed-gut-blood-brain chain were analyzed by ICP-MS and HPLC-ICP-MS, and fecal microbial variations were investigated by 16 s sequencing. The data showed that although only a tiny amount of arsenic (DMA=0.101 mg/kg, uAs=0.071 mg/kg) enters the brain through the blood-brain barrier, there were significant changes in brain metabolism, including 118 metabolites and 17 lipids. These different metabolites were involved in 30 distinct pathways, including glycometabolism, and metabolisms of lipid, nucleic acid, and amino acid were previously reported to be correlated with neurodegenerative diseases. Additionally, these different metabolites were significantly correlated with 12 gut bacterial OTUs, among which Lachnospiraceae, Muribaculaceae, Ruminococcaceae, and Erysipelotrichaceae were also previously reported to be related to the distortion of metabolism, indicating that the disturbance of metabolism in the brain may be associated with the disturbance of gut microbes induced by arsenic. Thus, the current study demonstrated that the brain metabolome and lipidome were significantly disturbed under subchronic arsenic exposure, and the disturbances also significantly correlated with some gut microbiome and may be associated with neurodegenerative diseases. Although preliminary, the results shed some light on the pathophysiology of arsenic-caused neurodegenerative diseases.

Exposure to Environmental Arsenic and Emerging Risk of Alzheimer's Disease: Perspective Mechanisms, Management Strategy, and Future Directions

Alzheimer’s disease (AD) is one of the most prevailing neurodegenerative diseases, characterized by memory dysfunction and the presence of hyperphosphorylated tau and amyloid β (Aβ) aggregates in multiple brain regions, including the hippocampus and cortex. The exact etiology of AD has not yet been confirmed. However, epidemiological reports suggest that populations who were exposed to environmental hazards are more likely to develop AD than those who were not. Arsenic (As) is a naturally occurring environmental risk factor abundant in the Earth’s crust, and human exposure to As predominantly occurs through drinking water. Convincing evidence suggests that As causes neurotoxicity and impairs memory and cognition, although the hypothesis and molecular mechanism of As-associated pathobiology in AD are not yet clear. However, exposure to As and its metabolites leads to various pathogenic events such as oxidative stress, inflammation, mitochondrial dysfunctions, ER stress, apoptosis, impaired protein homeostasis, and abnormal calcium signaling. Evidence has indicated that As exposure induces alterations that coincide with most of the biochemical, pathological, and clinical developments of AD. Here, we overview existing literature to gain insights into the plausible mechanisms that underlie As-induced neurotoxicity and the subsequent neurological deficits in AD. Prospective strategies for the prevention and management of arsenic exposure and neurotoxicity have also been discussed.

Risk of neurodegenerative disease due to tau phosphorylation changes and arsenic exposure via drinking water

It is estimated that around 140 million people are drinking highly contaminated water with arsenic (As) as a natural earth's crust component. On the other hand, the prevalence of neurodegenerative disorders, especially Alzheimer's disease, is constantly increasing. The aim of the present study was to investigate the correlation between oral arsenic trioxide exposure and its impact on tau protein phosphorylation at Ser262. Fifty-four male mice were randomly divided into three groups and were freely accessed to food and contaminated water of 1 and 10 ppm arsenic trioxide for 3 months, except for control subjects. At the end of each month, As concentration and tau phosphorylation were checked with graphite furnace atomic absorption spectrometer and western blot analysis, respectively. Surprisingly, it was observed that the amount of measured brain arsenic in 10 ppm-exposed subjects was significantly increased after 3 months (P-value ˂ 0.0001). The significant changes in tau phosphorylation were not seen in the 1 ppm-exposed subjects, and it was observed that Ser262 phosphorylation significantly increased after 2 and 3 months in the 10 ppm group (P-value < 0.05). Our results demonstrated that arsenic accumulated in the brain time-dependently and increased Ser262 tau phosphorylation, which is very important in several tauopathies. In conclusion, it could be inferred that environmental arsenic exposure even at very low concentrations could be considered as a reason for increasing the risk of developing neurodegenerative disease.

Selective removal of arsenic in water: A critical review

Selective removal of arsenic (As) is the key challenge for any of As removal mechanisms as this not only increases the efficiency of removal of the main As species (neutral As(III) and As(V) hydroxyl-anions) but also allows for a significant reduction of waste as it does not co-remove other solutes. Selective removal has a number of benefits: it increases the capacity and lifetime of units while lowering the cost of the process. Therefore, a sustainable selective mitigation method should be considered concerning the economic resources available, the ability of infrastructure to sustain water treatment, and the options for reuse and/or safe disposal of treatment residuals. Several methods of selective As removal have been developed, such as precipitation, adsorption and modified iron and ligand exchange. The biggest challenge in selective removal of As is the presence of phosphate in water which is chemically comparable with As(V). There are two types of mechanisms involved with As removal: Coulombic or ion exchange; and Lewis acid-base interaction. Solution pH is one of the major controlling factors limiting removal efficiency since most of the above-mentioned methods depend on complexation through electrostatic effects. The different features of two different As species make the selective removal process more difficult, especially under natural conditions. Most of the selective As removal methods involve hydrated Fe(III) oxides through Lewis acid-base interaction. Microbiological methods have been studied recently for selective removal of As, and although there have been only a small number of studies, the method shows remarkable results and indicates positive prospects for the future.

Role of environmental pollutants in Alzheimer's disease: a review

Neurodegenerative disorders are commonly erratic influenced by various factors including lifestyle, environmental, and genetic factors. In recent observations, it has been hypothesized that exposure to various environmental factors enhances the risk of Alzheimer's disease (AD). The exact etiology of Alzheimer's disease is still unclear; however, the contribution of environmental factors in the pathology of AD is widely acknowledged. Based on the available literature, the review aims to culminate in the prospective correlation between the various environmental factors and AD. The prolonged exposure to the various well-known environmental factors including heavy metals, air pollutants (particulate matter), pesticides, nanoparticles containing metals, industrial chemicals results in accelerating the progression of AD. Common mechanisms have been documented in the field of environmental contaminants for enhancing amyloid-β (Aβ) peptide along with tau phosphorylation, resulting in the initiation of senile plaques and neurofibrillary tangles, which results in the death of neurons. This review offers a compilation of available data to support the long-suspected correlation between environmental risk factors and AD pathology. Graphical abstract .

Effect of environmental toxicants on neuronal functions

In the last few years, neurodegenerative diseases like Alzheimer's disease (AD) and Parkinson's disease (PD) have attracted attention due to their high prevalence worldwide. Environmental factors may be one of the biggest reasons for these diseases related to neuronal dysfunctions. Most of neuronal disorders are strongly associated with pre- and postnatal exposure to environmental toxins released from industries. Some of the neurotoxic metals such as lead, aluminum, mercury, manganese, cadmium, and arsenic as well as some pesticides and metal-based nanoparticles have been involved in AD and PD due to their ability to produce senile/amyloid plaques and NFTs which are the main feature of these neuronal dysfunctions. Exposure to solvents is also majorly responsible for neurodegenerative disorders. The present review highlights the impact of omnipresent heavy metals with some other neurotoxins on human health and how they give rise to neuronal dysfunctions which in turn causes socio-economic consequences due to increasing pollution worldwide. Graphical abstract.

Treatment of aqueous arsenic - A review of biosorbent preparation methods

Arsenic (As) is a worldwide human health issue with the major exposure route being the consumption of As-contaminated drinking water. Sorption is considered to be an efficient treatment method, among other technologies, for As removal from various water and wastewater matrices. There are common commercially available sorbents, however, the use of locally or regionally available biomasses have recently been of interest as potentially cost-effective and environmentally friendly alternatives. Despite these benefits, untreated biomasses often show low sorption capacity, can be too fragile, and can lead to coloration of waters when used in treatment processes. Treatment methods of biomasses can include chemical processes using acid or alkaline solutions, developing of biomass composite by deposition of activating agents, and preparation of biochars. This review includes an overview of 53 recent studies that assess a variety of biomass modification methods meant to overcome these issues such as activation with acids or bases and biomass-based composites. Furthermore, future perspectives have been provided to assist in the further optimization of methods for biomass modifications to enhance their As sorption capacities.

Positive association between soil arsenic concentration and mortality from alzheimer's disease in mainland China

OBJECTIVES

The current study was designed to investigate the relationship between the soil arsenic (As) concentration and the mortality from Alzheimer's disease (AD) in mainland China.

STUDY DESIGN

Ecological study.

METHODS

Twenty-two provinces and 3 municipal districts in mainland China were included in this study. The As concentrations in soil in 1990 was obtained from the China State Environmental Protection Bureau; the data on annual mortality of AD from 1991 to 2000 were obtained from the National Death Cause Surveillance Database of China. Using these data, we calculated the spearman correlation coefficient between soil As concentration and AD mortality, and the relative risk (RR) between soil As levels and AD mortality by quartile-dividing study groups.

RESULTS

The spearman correlation coefficient between As concentration and AD mortality was 0.552 (p = 0.004), 0.616 (p = 0.001) and 0.622 (p = 0.001) in the A soil As (eluvial horizon), the C soil As (parent material horizon), and the Total soil As (A soil As + C soil As), respectively. When the A soil As concentration was over 9.05 mg/kg, 10.40 mg/kg and 13.10 mg/kg, the relative risk was 0.835 (95 % CI: 0.832, 0.838), 1.969 (95 %CI: 1.955, 1.982), and 2.939 (95 % CI: 2.920, 2.958), respectively; when the C soil As reached 9.45 mg/kg, 11.10 mg/kg and 13.55 mg/kg, the relative risk was 4.349 (95 % CI: 4.303, 4.396), 6.108 (95 % CI: 6.044, 6.172), and 9.125 (95 %CI: 9.033, 9.219), respectively. No correlation was found between lead, cadmium, and mercury concentration in the soil and AD mortality.

CONCLUSION

There was an apparent soil As concentration dependent increase in AD mortality. Results of this study may provide evidence for a possible causal linkage between arsenic exposure and the death risk from AD.

Nanomaterial-based aptamer sensors for arsenic detection

Arsenic (As) is a highly toxic contaminant in the environment and a serious carcinogen for the human being. The toxicity of arsenic significantly threatens environmental and human health. The effective removing technology for arsenic remains challenging, and one of the reasons is due to the lack of powerful detection method in the complex environmental matrix. There is thus an urgent need to develop novel analytical methods for arsenic, preferably with the potential for the field-testing. To combat arsenic pollution and maintain a healthy environment and eco-system, many analytical methods have been developed for arsenic detection in various samples. Among these strategies, biosensors hold great promise for rapid detection of arsenic, in particular, nanomaterials-based aptamer sensors have attracted significant attention due to their simplicity, high sensitivity and rapidness. In this paper, we reviewed the recent development and applications of aptamer sensors (aptasensors) based-on nanomaterial for arsenic detection, in particular with emphasis on the works using optical and electrochemical technologies. We also discussed the recent novel technology in aptasensors development for arsenic detection, including nucleic acid amplification for signal enhancement and device integration for the portability of arsenic sensors. We are hoping this review could inspire further researches in developing novel nanotechnologies based aptasensors for possible on-site detection of arsenic.

Gas chromatography-mass spectrometry based metabolomics profile of hippocampus and cerebellum in mice after chronic arsenic exposure

Intake of arsenic (As) via drinking water has been a serious threat to global public health. Though there are numerous reports of As neurotoxicity, its pathogenesis mechanisms remain vague especially its chronic effects on metabolic network. Hippocampus is a renowned area in relation to learning and memory, whilst recently, cerebellum is argued to be involved with process of cognition. Therefore, the study aimed to explore metabolomics alternations in these two areas after chronic As exposure, with the purpose of further illustrating details of As neurotoxicity. Twelve 3-week-old male C57BL/6J mice were divided into two groups, receiving deionized drinking water (control group) or 50 mg/L of sodium arsenite (via drinking water) for 24 weeks. Learning and memory abilities were tested by Morris water maze (MWM) test. Pathological and morphological changes of hippocampus and cerebellum were captured via transmission electron microscopy (TEM). Metabolic alterations were analyzed by gas chromatography-mass spectrometry (GC-MS). MWM test confirmed impairments of learning and memory abilities of mice after chronic As exposure. Metabolomics identifications indicated that tyrosine increased and aspartic acid (Asp) decreased simultaneously in both hippocampus and cerebellum. Intermediates (succinic acid) and indirect involved components of tricarboxylic acid cycle (proline, cysteine, and alanine) were found declined in cerebellum, indicating disordered energy metabolism. Our findings suggest that these metabolite alterations are related to As-induced disorders of amino acids and energy metabolism, which might therefore, play an important part in mechanisms of As neurotoxicity.

Arsenic Exposure Contributes to the Bioenergetic Damage in an Alzheimer's Disease Model

Worldwide, every year there is an increase in the number of people exposed to inorganic arsenic (iAs) via drinking water. Human populations present impaired cognitive function as a result of prenatal and childhood iAs exposure, while studies in animal models demonstrate neurobehavioral deficits accompanied by neurotransmitter, protein, and enzyme alterations. Similar impairments have been observed in close association with Alzheimer's disease (AD). In order to determine whether iAs promotes the pathophysiological progress of AD, we used the 3xTgAD mouse model. Mice were exposed to iAs in drinking water from gestation until 6 months (As-3xTgAD group) and compared with control animals without arsenic (3xTgAD group). We investigated the behavior phenotype on a test battery (circadian rhythm, locomotor behavior, Morris water maze, and contextual fear conditioning). Adenosine triphosphate (ATP), reactive oxygen species, lipid peroxidation, and respiration rates of mitochondria were evaluated, antioxidant components were detected by immunoblots, and immunohistochemical studies were performed to reveal AD markers. As-3xTgAD displayed alterations in their circadian rhythm and exhibited longer freezing time and escape latencies compared to the control group. The bioenergetic profile revealed decreased ATP levels accompanied by the decline of complex I, and an oxidant state in the hippocampus. On the other hand, the cortex showed no changes of oxidant stress and complex I; however, the antioxidant response was increased. Higher immunopositivity to amyloid isoforms and to phosphorylated tau was observed in frontal cortex and hippocampus of exposed animals. In conclusion, mitochondrial dysfunction may be one of the triggering factors through which chronic iAs exposure exacerbates brain AD-like pathology.

Revisiting the biogeochemistry of arsenic in the Baltic Sea: Impact of anthropogenic activity

With the increase in anthropogenic environmental disruption, the behavior of arsenic in the Baltic Sea has received more scientific attention because of its complex forms and toxicity, and was re-visited to determine if there have been measurable changes recently. A cruise was conducted in 10-19 May 2011 to investigate the species and distribution of total dissolved inorganic arsenic (TDIAs: [TDIAs]=[As(V)]+[As(III)]) revealing links between the hydrographic dynamics and biological/chemical reactions in the Baltic Sea. In addition, long-term (2002-2010) time-series investigations of particulate arsenic in the Gotland Basin were also conducted in February every year for monitoring purposes. The behavior of TDIAs was non-conservative due to the removal and regeneration processes occurring in the Baltic Sea. Biological scavenging plays a dominant role as sink for TDIAs, with removal amount of 3.1±1.6nmol/L above the pycnocline of the Baltic Sea. Significant regeneration of TDIAs was observed below the pycnocline of the Baltic Sea, which was closely related to hypoxia. The decomposition of organic arsenic and release from the sediment by desorption of As-bearing Fe and Mn oxides were thought to be two major sources for TDIAs regeneration. The median concentration of TDIAs (8.4nmol/L) was much lower than in most marginal seas and oceans, including the near-bottom water around a chemical weapon dumpsite (13.9nmol/L). The hypoxia in the deep water contributed to the increase in As(III) concentrations based on the relationship between As(III)/TDIAs ratio and apparent oxygen utilization. If the difference of As(III) profiles (1981 and 2011) actually represents a long-term increase in As(III) concentrations and a shoaling of the As(III) chemocline, these factors could enhance the toxic effects and extend the residence time of arsenic and, hence, potentially have negative impacts on fisheries and ecosystem health in the Baltic Sea.

Water Quality and Brain Function

In the United States, regulations are in place to ensure the quality of drinking water. Such precautions are intended to safeguard the health of the population. However, regulatory guidelines may at times fail to achieve their purpose. This may be due to lack of sufficient data regarding the health hazards of chronic low dose exposure to contaminants or the introduction of new substances that pose a health hazard risk that has yet to be identified. In this review, examples of different sources of contaminants in drinking water will be discussed, followed by an evaluation of some select individual toxicants with known adverse neurological impact. The ability of mixtures to potentially cause additive, synergistic, or antagonistic neurotoxic responses will be briefly addressed. The last section of the review will provide examples of select mechanisms by which different classes of contaminants may lead to neurological impairments. The main objective of this review is to bring to light the importance of considering trace amounts of chemicals in the drinking water and potential brain abnormalities. There is continued need for toxicology studies to better understand negative consequences of trace amounts of toxins and although it is beyond the scope of this brief overview it is hoped that the review will underscore the paucity of studies focused on determining how long-term exposure to minute levels of contaminants in drinking water may pose a significant health hazard.

Metals and neurodegenerative diseases. A systematic review

Neurodegenerative processes encompass a large variety of diseases with different pathological patterns and clinical presentation such as Amyotrophic Lateral Sclerosis (ALS), Alzheimer Disease (AD) and Parkinson's disease (PD). Genetic mutations have a known causative role, but the majority of cases are likely to be probably caused by a complex gene-environment interaction. Exposure to metals has been hypothesized to increase oxidative stress in brain cells leading to cell death and neurodegeneration. Neurotoxicity of metals has been demonstrated by several in vitro and in vivo experimental studies and it is likely that each metal could be toxic through specific pathways. The possible pathogenic role of different metals has been supported by some epidemiological evidences coming from occupational and ecological studies. In order to assess the possible association between metals and neurodegenerative disorders, several case-control studies have also been carried out evaluating the metals concentration in different biological specimens such as blood/serum/plasma, cerebrospinal fluid (CSF), nail and hair, often reporting conflicting results. This review provides an overview of our current knowledge on the possible association between metals and ALS, AD and PD as main neurodegenerative disorders.

Trace metal concentrations in hair and nails from Alzheimer's disease patients: Relations with clinical severity

BACKGROUND AND OBJECTIVES

Metals, especially transition metals, seem to be important in the pathogenesis of Alzheimer disease. This study aims to determine the relationship of trace metal elements to the pathogenesis and/or course of Alzheimer Disease in terms of clinical severity.

METHODS

The hair and nail trace metal levels of 62 Alzheimer Disease patients at different clinical stages (21 mild, 20 moderate, 21 severe) and 60 healthy control subjects were measured by using inductively coupled plasma-mass spectrometry. The statistical comparisons were performed with regards to the study groups, clinical stages, disease duration and age.

RESULTS

The patient and control groups were significantly different from each other in regards to Mn, Fe, Cu, Cd, Hg (p<0.001), Zn (p<0.01) in nail concentrations and, Na, Al, Pb, Co (p<0.001), Fe, Mn (p=0.001), Hg, Cu, Cd, K in hair concentrations (p<0.01). No difference was detected in the levels of Mg and Ca. Nail Na level showed differences among different clinical stages of the disease (p<0.01). In comparing the mild degree Alzheimer patients to the control group; significant differences were detected in nail Mn, Fe, Cu, Co (p<0.001), Hg, Zn (p<0.01) and, hair Pb, Al (p<0.001), Na, K levels (p<0.01).

CONCLUSIONS

Our results have shown that transition and posttransition metals are especially important metals for the disease process. The relation of nail Na level with clinical stages of AD is an interesting new finding, making someone to think that alkali metals may be important in the progression of the disease.

Environmental risk factors for dementia: a systematic review

BACKGROUND

Dementia risk reduction is a major and growing public health priority. While certain modifiable risk factors for dementia have been identified, there remains a substantial proportion of unexplained risk. There is evidence that environmental risk factors may explain some of this risk. Thus, we present the first comprehensive systematic review of environmental risk factors for dementia.

METHODS

We searched the PubMed and Web of Science databases from their inception to January 2016, bibliographies of review articles, and articles related to publically available environmental data. Articles were included if they examined the association between an environmental risk factor and dementia. Studies with another outcome (for example, cognition), a physiological measure of the exposure, case studies, animal studies, and studies of nutrition were excluded. Data were extracted from individual studies which were, in turn, appraised for methodological quality. The strength and consistency of the overall evidence for each risk factor identified was assessed.

RESULTS

We screened 4784 studies and included 60 in the review. Risk factors were considered in six categories: air quality, toxic heavy metals, other metals, other trace elements, occupational-related exposures, and miscellaneous environmental factors. Few studies took a life course approach. There is at least moderate evidence implicating the following risk factors: air pollution; aluminium; silicon; selenium; pesticides; vitamin D deficiency; and electric and magnetic fields.

CONCLUSIONS

Studies varied widely in size and quality and therefore we must be circumspect in our conclusions. Nevertheless, this extensive review suggests that future research could focus on a short list of environmental risk factors for dementia. Furthermore, further robust, longitudinal studies with repeated measures of environmental exposures are required to confirm these associations.

Climate change enhances the mobilisation of naturally occurring metals in high altitude environments

Manmade climate change has expressed a plethora of complex effects on Earth's biogeochemical compartments. Climate change may also affect the mobilisation of natural metal sources, with potential ecological consequences beyond mountains' geographical limits; however, this question has remained largely unexplored. We investigated this by analysing a number of key climatic factors in relationship with trace metal accumulation in the sediment core of a Pyrenean lake. The sediment metal contents showed increasing accumulation trend over time, and their levels varied in step with recent climate change. The findings further revealed that a rise in the elevation of freezing level, a general increase in the frequency of drier periods, changes in the frequency of winter freezing days and a reducing snow cover since the early 1980s, together are responsible for the observed variability and augmented accumulation of trace metals. Our results provide clear evidence of increased mobilisation of natural metal sources - an overlooked effect of climate change on the environment. With further alterations in climate equilibrium predicted over the ensuing decades, it is likely that mountain catchments in metamorphic areas may become significant sources of trace metals, with potentially harmful consequences for the wider environment.

Environmental pollutants as risk factors for neurodegenerative disorders: Alzheimer and Parkinson diseases

Neurodegenerative diseases including Alzheimer (AD) and Parkinson (PD) have attracted attention in last decades due to their high incidence worldwide. The etiology of these diseases is still unclear; however the role of the environment as a putative risk factor has gained importance. More worryingly is the evidence that pre- and post-natal exposures to environmental factors predispose to the onset of neurodegenerative diseases in later life. Neurotoxic metals such as lead, mercury, aluminum, cadmium and arsenic, as well as some pesticides and metal-based nanoparticles have been involved in AD due to their ability to increase beta-amyloid (Aβ) peptide and the phosphorylation of Tau protein (P-Tau), causing senile/amyloid plaques and neurofibrillary tangles (NFTs) characteristic of AD. The exposure to lead, manganese, solvents and some pesticides has been related to hallmarks of PD such as mitochondrial dysfunction, alterations in metal homeostasis and aggregation of proteins such as α-synuclein (α-syn), which is a key constituent of Lewy bodies (LB), a crucial factor in PD pathogenesis. Common mechanisms of environmental pollutants to increase Aβ, P-Tau, α-syn and neuronal death have been reported, including the oxidative stress mainly involved in the increase of Aβ and α-syn, and the reduced activity/protein levels of Aβ degrading enzyme (IDE)s such as neprilysin or insulin IDE. In addition, epigenetic mechanisms by maternal nutrient supplementation and exposure to heavy metals and pesticides have been proposed to lead phenotypic diversity and susceptibility to neurodegenerative diseases. This review discusses data from epidemiological and experimental studies about the role of environmental factors in the development of idiopathic AD and PD, and their mechanisms of action.

Arsenic mobility and speciation in contaminated kitchen garden and lawn soils: an evaluation of water for assessment of As phytoavailability

Emissions from primary lead smelters have been recognized as one of the mainly factor which has contributed to the contamination of soils by metals. Less attention has been paid to volatile metalloids such as arsenic (As) which accompanies lead (Pb) smelting activities. One of the objectives of this study was to determine the As concentrations in various extracting solutions using a collection of urban soils located no far away from two former Pb and zinc plants in the North of France. The procedure for the determination of As, As(III), and As(V) with hydride vapor generator atomic absorption spectrometry was described in details. Pseudo-total concentrations of As in the studied soils ranged from 5.3 to 65.9 mg kg(-1). Good correlations were found between As and lead, zinc, and cadmium concentrations in soils. These depended on the soil uses and the soil distance from the source of contamination. Because the form of As may pose a health risk to human population, its speciation was determined in each urban top soils. Very good correlations were found between As(III) and As(V) versus As concentrations in soils studied, but the results did no permit to establish a relation between the location of soils and their uses. In contrast, it was shown that the highest mobility factor and lowest partitioning index values were related to the location. The mobilty of As depended on the assimilated phosphorus (P), carbonate contents, and pH. The percentages of the water-extractable As concentrations ranged from 0.3 to 3.0% of the As concentrations in soils. Very good positive correlations between water-extractable As(III) and As(V) versus water-extractable As concentrations were obtained. It was shown that the water-extractable As(III) concentrations depended on the soil uses. The results revealed that soils for which the As was the most mobile presented the highest water-extractable As concentrations. Principal component analysis indicated that mechanisms related to the release of As depended on the physico-chemical parameters of the soils, particularly on the assimilated P, organic matter, and/or iron oxides/hydroxides contents. Finally, the glasshouse experiments using ryegrass as plant model and three soils with similar physico-chemical parameters with regard to the PCA analysis showed that the water extracting solution could be a good indicator to evaluate the As phytoavailability.

Role of environmental contaminants in the etiology of Alzheimer's disease: a review

Alzheimer's dis ease (AD) is a leading cause of mortality in the developed world with 70% risk attributable to genetics. The remaining 30% of AD risk is hypothesized to include environmental factors and human lifestyle patterns. Environmental factors possibly include inorganic and organic hazards, exposure to toxic metals (aluminium, copper), pesticides (organochlorine and organophosphate insecticides), industrial chemicals (flame retardants) and air pollutants (particulate matter). Long term exposures to these environmental contaminants together with bioaccumulation over an individual's life-time are speculated to induce neuroinflammation and neuropathology paving the way for developing AD. Epidemiologic associations between environmental contaminant exposures and AD are still limited. However, many in vitro and animal studies have identified toxic effects of environmental contaminants at the cellular level, revealing alterations of pathways and metabolisms associated with AD that warrant further investigations. This review provides an overview of in vitro, animal and epidemiological studies on the etiology of AD, highlighting available data supportive of the long hypothesized link between toxic environmental exposures and development of AD pathology.

Serum trace metal levels in Alzheimer's disease and normal control groups

OBJECTIVE

To determine whether serum trace metals are related to abnormal cognition in Alzheimer's disease (AD).

METHODS

We studied serum lead (Pb), cadmium (Cd), mercury (Hg), and arsenic(As) in 89 patients with AD and in 118 cognitively normal individuals. We analyzed the results of the blood tests and the food intake.

RESULTS

Serum Pb levels correlated with word list recall (P = .039) and word list recognition (P = .037). Without age adjustment, serum Cd levels (P = .044) were significantly higher in the AD group. After stratified age adjustment, the levels of selected trace metals did not differ significantly between AD and normal individuals. Food intakes regarding selected trace metals were not significantly different between the 2 groups.

CONCLUSIONS

In this study, serum Pb, Cd, Hg, and As levels were not directly related to abnormal cognition in AD. Serum Pb levels were significantly negatively correlated with verbal memory scores.

Bacterial metabolism of environmental arsenic--mechanisms and biotechnological applications

Arsenic causes threats for environmental and human health in numerous places around the world mainly due to its carcinogenic potential at low doses. Removing arsenic from contaminated sites is hampered by the occurrence of several oxidation states with different physicochemical properties. The actual state of arsenic strongly depends on its environment whereby microorganisms play important roles in its geochemical cycle. Due to its toxicity, nearly all organisms possess metabolic mechanisms to resist its hazardous effects, mainly by active extrusion, but also by extracellular precipitation, chelation, and intracellular sequestration. Some microbes are even able to actively use various arsenic compounds in their metabolism, either as an electron donor or as a terminal electron acceptor for anaerobic respiration. Some microorganisms can also methylate inorganic arsenic, probably as a resistance mechanism, or demethylate organic arsenicals. Bioavailability of arsenic in water and sediments is strongly influenced by such microbial activities. Therefore, understanding microbial reactions to arsenic is of importance for the development of technologies for improved bioremediation of arsenic-contaminated waters and environments. This review gives an overview of the current knowledge on bacterial interactions with arsenic and on biotechnologies for its detoxification and removal.

Osteoresorptive arsenic intoxication

A 47-year-old woman consulted her dermatologist complaining whole body dermatitis, urticaria and irritating bullous eruptions on the plantar and side surfaces of her feet. She had had multiple hypopigmented spots on her skin since her early adulthood. The patient was treated with topical medication without significant improvement of symptoms. One year later she suffered a myocardial infarction, accompanied by refractory anaemia. At the age of 49, a breast cancer was diagnosed and shortly thereafter her last menstruation occurred. At age 50years, upon complaint of weight loss despite normal food intake, Hashimoto thyroiditis with latent hyperthyroidism, vitamin D insufficiency with secondary hyperparathyroidism, and poikilocytic anaemia with anisochromia, hypochromia, anisocytosis, elliptocytes, drepanocytes, dacryocytes, acanthocytes, echinocytes, schizocytes, stomatocytes and target cells were diagnosed. The osteodensitometric and laboratory examinations revealed osteoporosis with sustained elevation of urinary Dipyridinolin-crosslinks (u-Dpd), and urinary arsenic (u-As) of 500μg/l (equivalent to 0.5 parts per million-ppm, 2.5μg/mg creatinine/dl, u-As: Phosphate of 26μg/mmol; the estimated bone As:P and As/kg body weight were 500μg/g and 11.3mg/kg, respectively). Thalassemia, immunoglobinopathy and iron deficiency were excluded. Supplementation with oral vitamin D and calcium, and antiresorptive therapy with intravenous zolendronate normalised the u-Dpd, significantly decreased the urinary arsenic concentration, and cured the anemia and the urticaria. A diagnosis of osteoresorptive arsenic intoxication (ORAI) was established.

Arsenic affects expression and processing of amyloid precursor protein (APP) in primary neuronal cells overexpressing the Swedish mutation of human APP

Arsenic poisoning due to contaminated water and soil, mining waste, glass manufacture, select agrochemicals, as well as sea food, affects millions of people world wide. Recently, an involvement of arsenic in Alzheimer's disease (AD) has been hypothesized (Gong and O'Bryant, 2010). The present study stresses the hypothesis whether sodium arsenite, and its main metabolite, dimethylarsinic acid (DMA), may affect expression and processing of the amyloid precursor protein (APP), using the cholinergic cell line SN56.B5.G4 and primary neuronal cells overexpressing the Swedish mutation of APP, as experimental approaches. Exposure of cholinergic SN56.B5.G4 cells with either sodium arsenite or DMA decreased cell viability in a concentration- and exposure-time dependent manner, and affected the activities of the cholinergic enzymes acetylcholinesterase and choline acetyltransferase. Both sodium arsenite and DMA exposure of SN56.B5.G4 cells resulted in enhanced level of APP, and sAPP in the membrane and cytosolic fractions, respectively. To reveal any effect of arsenic on APP processing, the amounts of APP cleavage products, sAPPβ, and β-amyloid (Aβ) peptides, released into the culture medium of primary neuronal cells derived from transgenic Tg2576 mice, were assessed by ELISA. Following exposure of neuronal cells by sodium arsenite for 12h, the membrane-bound APP level was enhanced, the amount of sAPPβ released into the culture medium was slightly higher, while the levels of Aβ peptides in the culture medium were considerably lower as compared to that assayed in the absence of any drug. The sodium arsenite-induced reduction of Aβ formation suggests an inhibition of the APP γ-cleavage step by arsenite. In contrast, DMA exposure of neuronal cells considerably increased formation of Aβ and sAPPβ, accompanied by enhanced membrane APP level. The DMA-induced changes in APP processing may be the result of the enhanced APP expression. Alternatively, increased Aβ production may also be due to stimulation of caspase activity by arsenic compounds, or failure in Aβ degradation. In summary, the present report clearly demonstrates that sodium arsenite and DMA affect processing of APP in vitro.