Neurosensory effects of chronic human exposure to arsenic associated with body burden and environmental measures

Examining carcinogenic and noncarcinogenic health risks related to arsenic exposure in Ethiopia: A longitudinal study

Background

The carcinogenic properties of arsenic make it one of the most hazardous chemicals globally. Nevertheless, the exact level of human exposure to arsenic and the associated risks of cancer and non-cancer effects through different pathways in Ethiopia are still uncertain.

Objective

The primary aim of this study was to evaluate the risk of both cancer and non-cancer outcomes among children and adults who have been exposed to arsenic through drinking water in the Adami Tulu Jido Kombolcha district of Ethiopia.

Methods

For this study, a longitudinal study design was employed. A total of 45 groundwater sources were sampled using the census sampling method. The concentrations of total arsenic were measured using Agilent 7900 series inductively coupled plasma mass spectrometry. Carcinogenic and noncarcinogenic risk assessments were conducted by calculating lifetime cancer risk and hazard quotients. Microsoft Office Excel was utilized to calculate human health risk indices, and descriptive statistical analysis were performed using SPSS software.

Results

Our findings revealed that during the dry season, the mean arsenic concentration in the groundwater samples was 11.15 ± 9.38 µg/L, while during the rainy season, it was 10.67 ± 8.16 µg/L. The total cancer risk for children, resulting from oral ingestion and skin contact, was 1.15 × 10-2 and 1.07 × 10-2 during the dry and rainy seasons, respectively. For adults, the total cancer risk from oral ingestion and skin contact during the dry and rainy seasons was 4.95 × 10-3 and 4.59 × 10-3, respectively. Furthermore, the total hazard quotients for children via oral ingestion and skin absorption were 25.9 and 24.0 during the dry and rainy seasons, respectively. For adults, the total hazard quotients from ingestion and dermal contact during the dry and rainy seasons were 11 and 10, respectively.

Conclusions

The findings indicate that the risks of cancer and non-cancer effects resulting from arsenic exposure through ingestion and dermal exposure were found to exceed the acceptable thresholds in both seasons. These results emphasize the urgent need for focused attention on the study population in the study area due to the high likelihood of experiencing adverse health outcomes.

Assessing Acute and Chronic Risks of Human Exposure to Arsenic: A Cross-Sectional Study in Ethiopia Employing Body Biomarkers

Background

Arsenic, a widely recognized and highly toxic carcinogen, is regarded as one of the most hazardous metalloids globally. However, the precise assessment of acute and chronic human exposure to arsenic and its contributing factors remains unclear in Ethiopia.

Objective

The primary goal of this study was to assess the levels of acute and chronic arsenic exposure, as well as the contributing factors, using urine and nail biomarkers.

Methods

A community-based analytical cross-sectional study design was employed for this study. Agilent 7900 series inductively coupled plasma mass spectrometry was used to measure the concentrations of arsenic in urine and nail samples. We performed a multiple linear regression analysis to assess the relationships between multiple predictors and outcome variables.

Results

The concentration of arsenic in the urine samples ranged from undetectable (<0.01) to 126.13, with a mean and median concentration of 16.02 and 13.5 μg/L, respectively. However, the mean and median concentration of arsenic in the nails was 1.01, ranging from undetectable (<0.01 μg/g) to 2.54 μg/g. Furthermore, Pearson's correlation coefficient analysis showed a significant positive correlation between arsenic concentrations in urine and nail samples (r = 0.432, P < .001). Also, a positive correlation was observed between urinary (r = 0.21, P = .007) and nail (r = 0.14, P = .044) arsenic concentrations and the arsenic concentration in groundwater. Groundwater sources and smoking cigarettes were significantly associated with acute arsenic exposure. In contrast, groundwater sources, cigarette smoking, and the frequency of showers were significantly associated with chronic arsenic exposure.

Conclusions

The study's findings unveiled the widespread occurrence of both acute and chronic arsenic exposure in the study area. Consequently, it is crucial to prioritize the residents in the study area and take further measures to prevent both acute and chronic arsenic exposure.

Toenails as a biomarker of exposure to arsenic: A review

This systematic review summarizes the current evidence related to the reliability of toenail total arsenic concentrations (thereafter "arsenic") as a biomarker of long-term exposure. Specifically, we reviewed literature on consistency of repeated measures over time, association with other biomarkers and metal concentrations, factors influencing concentrations, and associations with health effects. We identified 129 papers containing quantitative original data on arsenic in toenail samples covering populations from 29 different countries. We observed geographic differences in toenail arsenic concentrations, with highest median or mean concentrations in Asian countries. Arsenic-contaminated drinking water, occupational exposure or living in specific industrial areas were associated with an increased toenail arsenic content. The effects of other potential determinants and sources of arsenic exposure including diet, gender and age on the concentrations in toenails need further investigations. Toenail arsenic was correlated with the concentrations in hair and fingernails, and with urine arsenic mainly among highly exposed populations with a toenail mean or median ≥1 μg/g. Overall, there is a growing body of evidence suggesting that arsenic content from a single toenail sample may reflect long-term internal dose-exposure. Toenail arsenic can serve as a reliable measure of toxic inorganic arsenic exposure in chronic disease research, particularly promising for cancer and cardiovascular conditions.

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.

Environmental toxins and Alzheimer's disease progression

Alzheimer's disease (AD) is the most common form of dementia, which causes progressive memory loss and cognitive decline. Effective strategies to treat or prevent remains one of the most challenging undertakings in the medical field. AD is a complex and multifactorial disease that involves several risk factors. Aging and genetic factors both play important roles in the onset of the AD, however; certain environmental factors have been reported to increase the risk of AD. Chronic exposure to toxins has been seen as an environmental factor that may increase the risk of developing a neurodegenerative disease such as AD. Exposure to metals and biotoxins produced by bacteria, molds, and viruses may contribute to the cognitive decline and pathophysiology associated with AD. Toxins may contribute to the pathology of the disease through various mechanisms such as deposition of amyloid-beta (Aβ) plaques and tangles in the brain, induction of apoptosis, inflammation, or oxidative damage. Here, we will review how toxins affect brain physiology with a focus on mechanisms by which toxins may contribute to the development and progression of AD. A better understanding of these mechanisms may help contribute towards the development of an effective strategy to slow the progression of AD.

Influence of age on arsenic-induced behavioral and cholinergic perturbations: Amelioration with zinc and α-tocopherol

This study was planned to determine arsenic (As) (10 mg/kg body weight given through oral gavage) induced behavioral and cholinergic perturbations in three different age groups of rats; young (postnatal day 21), adult (3 months), and aged (18 months) at 7 days post-acute exposure ( n = 6 for each of the four groups of all three age points). Further, we also evaluated the ameliorative effect of essential metal zinc (Zn; 0.02% through drinking water) and an antioxidant, α-tocopherol (vitamin E; 125 mg/kg body weight through oral gavage) against As-induced neurotoxicity. As exposure showed significant alterations in behavioral functions (open-field behavior, total locomotor activity, grip strength, exploratory behavior, and water maze learning). Cholinergic studies in three brain regions (cerebral cortex, cerebellum, and hippocampus) of different age groups also showed significant increase in acetylcholine levels and a decrease in acetylcholinesterase activity. These effects were more pronounced in hippocampus followed by cerebral cortex and cerebellum. Among the three different age points, aged animals were found to be more vulnerable to the As-induced toxicity as compared to young and adult animals suggesting that As neurotoxicity is age dependent. These As-induced alterations were significantly reversed following supplementation with Zn or vitamin E. However, vitamin E was found to elicit greater protection as compared to Zn in restoring the altered behavioral and cholinergic perturbations, providing evidence for As-induced oxidative damage.

Monoisoamyl 2,3-dimercaptosuccinic acid attenuates arsenic induced toxicity: behavioral and neurochemical approach

Chronic exposure to arsenic in drinking water is associated with skin lesions, neurological effects, hypertension and high risk of cancer. The treatment in use at present employs administration of thiol chelators, such as meso-2,3-dimercaptosuccinic acid (DMSA) which are compromised with number of limitations due to their lipophobic nature. To address this problem, therapeutic efficacy of monoisoamyl meso-2,3-dimercaptosuccinic acid (MiADMSA), an analog of DMSA having lipophilic character, was examined against chronic arsenic poisoning in rats. Adult male Wistar rats were orally exposed to arsenic (2mg sodium arsenite/kg body weight) for 10 weeks followed by treatment with MiADMSA (50mg/kg, orally, once daily for 5 consecutive days). As-exposed rats showed significant differences in behavioral functions (open field behavior, total locomotor activity, grip strength and exploratory behavior) and water maze learning. Further, the biochemical studies performed on three brain regions (cerebellum, cortex and hippocampus) also showed significant elevation in malondialdehyde (MDA) levels with a concomitant decrease in the oxidative stress marker enzymes Mn-superoxide dismutase (Mn-SOD), Cu/Zn-superoxide dismutase (Cu/Zn-SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR) and glutathione-S-transferase (GST). The alterations were more pronounced in cortex compared to cerebellum and hippocampus. The results showed that MiADMSA significantly reversed the As-induced alterations in behavior and biochemical variables suggestive of oxidative injury.

Arsenic-induced alteration in intracellular calcium homeostasis induces head kidney macrophage apoptosis involving the activation of calpain-2 and ERK in Clarias batrachus

We had earlier shown that exposure to arsenic (0.50 μM) caused caspase-3 mediated head kidney macrophage (HKM) apoptosis involving the p38-JNK pathway in Clarias batrachus. Here we examined the roles of calcium (Ca(2+)) and extra-cellular signal-regulated protein kinase (ERK), the other member of MAPK-pathway on arsenic-induced HKM apoptosis. Arsenic-induced HKM apoptosis involved increased expression of ERK and calpain-2. Nifedipine, verapamil and EGTA pre-treatment inhibited the activation of calpain-2, ERK and reduced arsenic-induced HKM apoptosis as evidenced from reduced caspase-3 activity, Annexin V-FITC-propidium iodide and Hoechst 33342 staining. Pre-incubation with ERK inhibitor U 0126 inhibited the activation of calpain-2 and interfered with arsenic-induced HKM apoptosis. Additionally, pre-incubation with calpain-2 inhibitor also interfered with the activation of ERK and inhibited arsenic-induced HKM apoptosis. The NADPH oxidase inhibitor apocynin and diphenyleneiodonium chloride also inhibited ERK activation indicating activation of ERK in arsenic-exposed HKM also depends on signals from NADPH oxidase pathway. Our study demonstrates the critical role of Ca(2+) homeostasis on arsenic-induced HKM apoptosis. We suggest that arsenic-induced alteration in intracellular Ca(2+) levels initiates pro-apoptotic ERK and calpain-2; the two pathways influence each other positively and induce caspase-3 mediated HKM apoptosis. Besides, our study also indicates the role of ROS in the activation of ERK pathway in arsenic-induced HKM apoptosis in C. batrachus.

Arsenic-induced oxidative stress and its reversibility

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

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

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

Arsenic speciation in clinical samples: urine analysis using fast micro-liquid chromatography ICP-MS

Arsenic speciation is a subject that is developing all the time both from improvements in analytical techniques and from increases in toxicological understanding. Despite speciation methods being widely developed, arsenic speciation is not routinely offered as an analysis in clinical laboratory. The work in this paper describes a simple routine method for arsenic speciation that could be easily implemented in clinical laboratories. The method described, a new, fast analytical method for arsenic speciation, is reported using micro-liquid chromatography hyphenated to an inductively coupled plasma mass spectrometer (μLC-ICP-MS). The method uses a low-pressure delivery six-port valve with a 5 cm anion exchange column, which allows a fully resolved separation of five arsenic species (arsenobetaine [AB], arsenite [As(3+)], arsenate [As(5+)], mono-methylarsonic acid [MMA(5+)] and dimethylarsinic acid [DMA(5+)]) in urine in just 6 min. This fast analytical method offers an arsenic speciation method that is feasible for a laboratory that does not have the capability for a dedicated arsenic speciation LC-ICP-MS instrument. The micro-LC system is small, easy to install and is fully integrated with the ICP-MS software. The results reported here are from urine samples from 65 workers in a semiconductor work providing a sample for their routine biological monitoring to assess workplace exposure. Control samples from 20 unexposed people were also determined. Results show that the semiconductor workers exhibit very low levels of arsenic in their urine samples, similar to the levels in the controls, and thus are not significantly exposed to arsenic. Care must be taken when interpreting urinary arsenic species results because it is not always possible to differentiate between dietary and other external sources of exposure.

Arsenic neurotoxicity--a review

Arsenic (As) is one of the oldest poisons known to men. Its applications throughout history are wide and varied: murder, make-up, paint and even as a pesticide. Chronic As toxicity is a global environmental health problem, affecting millions of people in the USA and Germany to Bangladesh and Taiwan. Worldwide, As is released into the environment by smelting of various metals, combustion of fossil fuels, as herbicides and fungicides in agricultural products. The drinking water in many countries, which is tapped from natural geological resources, is also contaminated as a result of the high level of As in groundwater. The environmental fate of As is contamination of surface and groundwater with a contaminant level higher than 10 particle per billion (ppb) as set by World Health Organization (WHO). Arsenic exists in both organic and inorganic species and either form can also exist in a trivalent or pentavalent oxidation state. Long-term health effects of exposure to these As metabolites are severe and highly variable: skin and lung cancer, neurological effects, hypertension and cardiovascular diseases. Neurological effects of As may develop within a few hours after ingestion, but usually are seen in 2-8 weeks after exposure. It is usually a symmetrical sensorimotor neuropathy, often resembling the Guillain-Barré syndrome. The predominant clinical features of neuropathy are paresthesias, numbness and pain, particularly in the soles of the feet. Electrophysiological studies performed on patients with As neuropathy have revealed a reduced nerve conduction velocity, typical of those seen in axonal degeneration. Most of the adverse effects of As, are caused by inactivated enzymes in the cellular energy pathway, whereby As reacts with the thiol groups of proteins and enzymes and inhibits their catalytic activity. Furthermore, As-induced neurotoxicity, like many other neurodegenerative diseases, causes changes in cytoskeletal protein composition and hyperphosphorylation. These changes may lead to disorganization of the cytoskeletal framework, which is a potential mechanism of As-induced neurotoxicity.