Arsenic induced neuronal apoptosis in guinea pigs is Ca2+ dependent and abrogated by chelation therapy: role of voltage gated calcium channels

Endocrine disrupting effects on morphological synaptic plasticity

Neural regulation of the homeostasis depends on healthy synaptic function. Adaptation of synaptic functions to physiological needs manifests in various forms of synaptic plasticity (SP), regulated by the normal hormonal regulatory circuits. During the past several decades, the hormonal regulation of animal and human organisms have become targets of thousands of chemicals that have the potential to act as agonists or antagonists of the endogenous hormones. As the action mechanism of these endocrine disrupting chemicals (EDCs) came into the focus of research, a growing number of studies suggest that one of the regulatory avenues of hormones, the morphological form of SP, may well be a neural mechanism affected by EDCs. The present review discusses known and potential effects of some of the best known EDCs on morphological synaptic plasticity (MSP). We highlight molecular mechanisms altered by EDCs and indicate the growing need for more research in this area of neuroendocrinology.

Analysis of arsenic-modulated expression of hypothalamic estrogen receptor, thyroid receptor, and peroxisome proliferator-activated receptor gamma mRNA and simultaneous mitochondrial morphology and respiration rates in the mouse

Arsenic has been identified as an environmental toxicant acting through various mechanisms, including the disruption of endocrine pathways. The present study assessed the ability of a single intraperitoneal injection of arsenic, to modify the mRNA expression levels of estrogen- and thyroid hormone receptors (ERα,β; TRα,β) and peroxisome proliferator-activated receptor gamma (PPARγ) in hypothalamic tissue homogenates of prepubertal mice in vivo. Mitochondrial respiration (MRR) was also measured, and the corresponding mitochondrial ultrastructure was analyzed. Results show that ERα,β, and TRα expression was significantly increased by arsenic, in all concentrations examined. In contrast, TRβ and PPARγ remained unaffected after arsenic injection. Arsenic-induced dose-dependent changes in state 4 mitochondrial respiration (St4). Mitochondrial morphology was affected by arsenic in that the 5 mg dose increased the size but decreased the number of mitochondria in agouti-related protein- (AgRP), while increasing the size without affecting the number of mitochondria in pro-opiomelanocortin (POMC) neurons. Arsenic also increased the size of the mitochondrial matrix per host mitochondrion. Complex analysis of dose-dependent response patterns between receptor mRNA, mitochondrial morphology, and mitochondrial respiration in the neuroendocrine hypothalamus suggests that instant arsenic effects on receptor mRNAs may not be directly reflected in St3-4 values, however, mitochondrial dynamics is affected, which predicts more pronounced effects in hypothalamus-regulated homeostatic processes after long-term arsenic exposure.

Nanoplastics promote arsenic-induced ROS accumulation, mitochondrial damage and disturbances in neurotransmitter metabolism of zebrafish (Danio rerio)

As a carrier, nanoplastics (NPs) can adsorb other toxic substances and thus modify their biological toxicity. Numerous studies have investigated the neurotoxic of high concentrations of arsenic (As, 2.83 mg/L-5 mg/L). However, it is still unknown whether the relatively low environmentally relevant concentrations of As (200 μg/L) can damage the structure and function of fish brains with the presence of NPs. In this study, zebrafish were exposed to polystyrene NPs, As and their mixture for 30 days respectively. Firstly, we found that the presence of NPs promoted the accumulation of As in zebrafish brains. Thereby the co-exposure of NPs and As further promoted the production of reactive oxygen species (ROS) in zebrafish brains compared with the single exposure of NPs or As, resulting in severe oxidative stress. Moreover, accumulated ROS directly damaged the mitochondrial membrane and mtDNA in zebrafish brains. Moreover, the mitochondrial damage was further aggravated due to inhibited mitochondrial fusion and activated mitochondrial division and mitophagy. Ultimately, the co-exposure led to mitochondrial damage in the zebrafish brain. Damaged mitochondria may not meet the high energy metabolic requirement for neuronal function. As a result, the normal function of nerve cells was adversely affected and eventually cell apoptosis may occur. Besides, the co-exposure caused more significant structural alterations in zebrafish brain tissue. Finally, the co-exposure of NPs and As caused abnormal biosynthesis and degradation of dopamine and acetylcholine. These resulted in decreased dopamine levels and increased acetylcholine levels in zebrafish brains. In conclusion, the presence of NPs promoted the accumulation of As, thereby inducing severe oxidative stress, which caused structural alterations and mitochondrial damage in the zebrafish brain, thus disordering neuromodulation, which may ultimately cause neurological dysfunction in zebrafish. This study will provide a risk assessment for evaluating the biotoxicity of NPs and As to fish and even other animals.

The protective effect of natural or chemical compounds against arsenic-induced neurotoxicity: Cellular and molecular mechanisms

Arsenic is a notorious metalloid that exists in the earth's crust and is considered toxic for humans and the environment. Both cancerous and non-cancerous complications are possible after arsenic exposure. Target organs include the liver, lungs, kidney, heart, and brain. Arsenic-induced neurotoxicity, the main focus of our study, can occur in central and peripheral nervous systems. Symptoms can develop in a few hours, weeks, or years depending on the quantity of arsenic and the duration of exposure. In this review, we aimed to gather all the compounds, natural and chemical, that have been studied as protective agents in cellular, animal, and human reports. Oxidative stress, apoptosis, and inflammation are frequently described as destructive mechanisms in heavy metal toxicity. Moreover, reduced activity of acetylcholinesterase, the altered release of monoamine neurotransmitters, down-regulation of N-methyl-D-aspartate receptors, and decreased brain-derived neurotrophic factor are important underlying mechanisms of arsenic-induced neurotoxicity. As for neuroprotection, though some compounds have yet limited data, there are others, such as curcumin, resveratrol, taurine, or melatonin which have been studied more deeply and might be closer to a reliable protective agent. We collected the available information on all protective agents and the mechanisms by which they fight against arsenic-induced neurotoxicity.

Mechanistic insight into the protective effects of fisetin against arsenic-induced reproductive toxicity in male rats

Arsenic is one of the most hazardous environmental contaminants, which adversely affects the dynamics of male reproductive system. Fisetin (FIS) is a bioactive flavonoid, which is known to exert strong antioxidative effects. Therefore, the current research was planned to evaluate the alleviative efficacy of FIS against arsenic-induced reproductive damages. Forty-eight male albino rats were divided into 4 groups (n = 12), which were treated as follows: (1) Control, (2) Arsenic-intoxicated group (8 mg kg-1), (3) Arsenic + FIS-treated group (8 mg kg-1 + 10 mg kg-1), and (4) FIS-treated group (10 mgkg-1). After 56 days of treatment, the biochemical, lipidemic, steroidogenic, hormonal, spermatological, apoptotic and histoarchitectural profiles of rats were analyzed. Arsenic intoxication reduced the enzymatic activities of catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx) and glutathione reductase (GSR), in addition to glutathione (GSH) level. Conversely, the levels of thiobarbituric acid reactive substance (TBARS) and reactive oxygen species (ROS) were increased. Moreover, it escalated the level of low-density lipoprotein (LDL), triglycerides and total cholesterol, while declining the level of high-density lipoprotein (HDL). Furthermore, steroidogenic enzymes expressions, 3β-hydroxysteroid dehydrogenase (HSD), 17β-HSD, steroidogenic acute regulatory protein (StAR), cholesterol side-chain cleavage enzyme (CYP11A1) and 17α-hydroxylase/17, 20-lyase (CYP17A1), were found to be reduced, which brought down the level of testosterone. Besides, the levels of gonadotropins (LH and FSH) were decreased. Additionally, a decline in sperm mitochondrial membrane potential (MMP), motility, epididymal sperm count and hypo-osmotic swelling (HOS) coil-tailed sperms was observed, whereas the dead sperms and structural damages (head, midpiece and tail) of sperms were escalated. Moreover, arsenic exposure up-regulated the mRNA expressions of apoptotic markers, namely Bax and caspase-3, whereas lowered the expression of anti-apoptotic marker, Bcl-2. In addition, it induced histoarchitectural changes in testes of rats. However, FIS treatment resulted in remarkable improvements in testicular and sperm parameters. Therefore, it was inferred that FIS could serve as a therapeutic candidate against arsenic-generated male reproductive toxicity attributing to its anti-oxidant, anti-lipoperoxidative, anti-apoptotic, and androgenic efficacy.

The role of Shunaoxin pills in the treatment of chronic cerebral hypoperfusion and its main pharmacodynamic components

Chronic cerebral hypoperfusion (CCH) is a frequent ischemic cerebrovascular disease that induces brain dysfunction. Shunaoxin pills (SNX) are traditional Chinese medicines (TCM), frequently used for the treatment of CCH. The purpose of this study was to develop an activity-based screening system to identify the active ingredients of SNX. We developed a model of CCH and revealed that SNX induces cerebrovascular dilatation and protects against CCH-induced nerve cell injury in rats. Using the transcriptome analysis, we found that Ca2+-related signaling pathways play a major role in the effect of SNX against CCH. We developed an activity-based screening system based on the ultra-high performance liquid chromatography with quadrupole time-of-flight mass spectrometry coupled with a dual-luciferase reporter calcium assay to identify the active components of SNX. As a result, SNX dilates cerebral blood vessels, increasing cerebral blood flow by modulating calcium-related signaling pathways and regulating calcium homeostasis. Two calcium antagonists, ligustilide and senkyunolide I, were identified as active ingredients in SNX. In conclusion, we developed a rapid screening method suitable for the discovery of active natural products in TCM by integrating genomics and target pathway-oriented spectroscopic analysis.

Ex vivo exposures to arsenite and its methylated trivalent metabolites alter gene transcription in mouse sperm cells

We have previously reported that preconception exposure to iAs may contribute to the development of diabetes in mouse offspring by altering gene expressions in paternal sperm. However, the individual contributions of iAs and its methylated metabolites, monomethylated arsenic (MAs) and dimethylated arsenic (DMAs), to changes in the sperm transcriptome could not be determined because all three As species are present in sperm after in vivo iAs exposure. The goal of the present study was to assess As species-specific effects using an ex vivo model. We exposed freshly isolated mouse sperm to either 0.1 or 1 μM arsenite (iAsIII) or the methylated trivalent arsenicals, MAsIII and DMAsIII, and used RNA-sequencing to identify differentially expressed genes, enriched pathways, and associated protein networks. For all arsenicals tested, the exposures to 0.1 μM concentrations had greater effects on gene expression than 1 μM exposures. Transcription factor AP-1 and B cell receptor complexes were the most significantly enriched pathways in sperm exposed to 0.1 μM iAsIII. The Mre11 complex and Antigen processing were top pathways targeted by exposure to 0.1 μM MAsIII and DMAsIII, respectively. While there was no overlap between gene transcripts altered by ex vivo exposures in the present study and those altered by in vivo exposure in our prior work, several pathways were shared, including PI3K-Akt signaling, Focal adhesion, and Extracellular matrix receptor interaction pathways. Notably, the protein networks associated with these pathways included those with known roles in diabetes. This study is the first to assess the As species-specific effects on sperm transcriptome, linking these effects to the diabetogenic effects of iAs exposure.

Chemistry, Pharmacology, and Toxicology of Monoisoamyl Dimercaptosuccinic Acid: A Chelating Agent for Chronic Metal Poisoning

Arsenic, a metalloid, is known to cause deleterious effects in various body organs, particularly the liver, urinary bladder, and brain, and these effects are primarily mediated through oxidative stress. Chelation therapy has been considered one of the promising medical treatments for arsenic poisoning. Meso 2,3- dimercaptosuccinic acid (DMSA) has been recognized as one of the most effective chelating drugs to treat arsenic poisoning. However, the drug is compromised with a number of shortcomings, including the inability to treat chronic arsenic poisoning due to its extracellular distribution. Monoisoamyl 2,3-dimercaptosuccinic acid, one of the analogues of meso 2,3-dimeraptosuccinic acid (DMSA), is a lipophilic chelator and has shown promise to be considered as a potential future chelating agent/antidote not only for arsenic but also for a few other heavy metals like lead, mercury, cadmium, and gallium arsenide. The results from numerous studies carried out in the recent past, mainly from our group, strongly support the clinical application of MiADMSA. This review paper summarizes most of the scientific details including the chemistry, pharmacology, and safety profile of MiADMSA. The efficacy of MiADMSA mainly against arsenic toxicity but also a few other heavy metals was also discussed. We also reviewed a few other strategies in order to achieve the optimum effects of MiADMSA, like combination therapy using two chelating agents or coadministration of a natural and synthetic antioxidant (including phytomedicine) along with MiADMSA for treatment of metal/metalloid poisoning. We also briefly discussed the use of nanotechnology (nano form of MiADMSA i.e. nano-MiADMSA) and compared it with bulk MiADMSA. All these strategies have been shown to be beneficial in getting more pronounced therapeutic efficacy of MiADMSA, as an adjuvant or as a complementary agent, by significantly increasing the chelating efficacy of MiADMSA.

Mitochondrial ROS, ER Stress, and Nrf2 Crosstalk in the Regulation of Mitochondrial Apoptosis Induced by Arsenite

Long-term ingestion of arsenicals, a heterogeneous group of toxic compounds, has been associated with a wide spectrum of human pathologies, which include various malignancies. Although their mechanism of toxicity remains largely unknown, it is generally believed that arsenicals mainly produce their effects via direct binding to protein thiols and ROS formation in different subcellular compartments. The generality of these mechanisms most probably accounts for the different effects mediated by different forms of the metalloid in a variety of cells and tissues. In order to learn more about the molecular mechanisms of cyto- and genotoxicity, there is a need to focus on specific arsenic compounds under tightly controlled conditions. This review focuses on the mechanisms regulating the mitochondrial formation of ROS after exposure to low concentrations of a specific arsenic compound, NaAsO₂, and their crosstalk with the nuclear factor (erythroid-2 related) factor 2 antioxidant signaling and the endoplasmic reticulum stress response.

Phytochemicals in the Management of Arsenic Toxicity

Arsenic toxicity is a major concern due to its deleterious consequences for human health. Rapid industrialization also has weakened the quality of the environment by introducing pollutants that may disrupt balanced ecosystems, adversely and irreversibly impacting humans, plants, and animals. Arsenic, an important toxicant among all environmental hazards, can lead to several detrimental effects on cells and organs, impacting the overall quality of life. Nevertheless, arsenic also has a rich history as a chemotherapeutic agent used in ancient days for the treatment of diseases such as malaria, cancer, plague, and syphilis when other chemotherapeutic agents were yet to be discovered. Arsenicosis-mediated disorders remain a serious problem due to the lack of effective therapeutic options. Initially, chelation therapy was used to metabolically eliminate arsenic by forming a complex, but adverse effects limited their pharmacological use. More recently, plant-based products have been found to provide significant relief from the toxic effects of arsenic poisoning. They act by different mechanisms affecting various cellular processes. Phytoconstituents such as curcumin, quercetin, diallyl trisulfide, thymoquinone, and others act via various molecular pathways, primarily by attenuating oxidative damage, membrane damage, DNA damage, and proteinopathies. Nonetheless, most of the phytochemicals reviewed here protect against the adverse effects of metal or metalloid exposure, supporting their consideration as alternatives to chelation therapy. These agents, if used prophylactically and in conjunction with other chemotherapeutic agents, may provide an effective approach for management of arsenic toxicity. In a few instances, such strategies like coadministration of phytochemicals with a known chelating agent have led to more pronounced elimination of arsenic from the body with lesser off-site adverse effects. This is possible because combination treatment ensures the use of a reduced dose of chelating agent with a phytochemical without compromising treatment. Thus, these therapies are more practical than conventional therapeutic agents in ameliorating arsenic-mediated toxicity. This review summarizes the potential of phytochemicals in alleviating arsenic toxicity on the basis of available experimental and clinical evidence.

BioNet: a large-scale and heterogeneous biological network model for interaction prediction with graph convolution

Motivation

Understanding chemical–gene interactions (CGIs) is crucial for screening drugs. Wet experiments are usually costly and laborious, which limits relevant studies to a small scale. On the contrary, computational studies enable efficient in-silico exploration. For the CGI prediction problem, a common method is to perform systematic analyses on a heterogeneous network involving various biomedical entities. Recently, graph neural networks become popular in the field of relation prediction. However, the inherent heterogeneous complexity of biological interaction networks and the massive amount of data pose enormous challenges. This paper aims to develop a data-driven model that is capable of learning latent information from the interaction network and making correct predictions.

Results

We developed BioNet, a deep biological networkmodel with a graph encoder–decoder architecture. The graph encoder utilizes graph convolution to learn latent information embedded in complex interactions among chemicals, genes, diseases and biological pathways. The learning process is featured by two consecutive steps. Then, embedded information learnt by the encoder is then employed to make multi-type interaction predictions between chemicals and genes with a tensor decomposition decoder based on the RESCAL algorithm. BioNet includes 79 325 entities as nodes, and 34 005 501 relations as edges. To train such a massive deep graph model, BioNet introduces a parallel training algorithm utilizing multiple Graphics Processing Unit (GPUs). The evaluation experiments indicated that BioNet exhibits outstanding prediction performance with a best area under Receiver Operating Characteristic (ROC) curve of 0.952, which significantly surpasses state-of-theart methods. For further validation, top predicted CGIs of cancer and COVID-19 by BioNet were verified by external curated data and published literature.

Mitochondrial bioenergetic, oxidative stress and burrowing responses in earthworm exposed to roxarsone in soil

The eco-risk of roxarsone (ROX) was evaluated using multiple responses of earthworm biomarkers under different ROX concentrations for 28 d. With the increasing total arsenic accumulation (TAs-E), biological responses in earthworm generally showed a two-stage changes of homeostasis dysregulation and dose-dependent alterations. At the early periods, ROX stress increased the reactive oxygen species (ROS) and lipid peroxidation (LPO) in a similar manner, and apparently disrupted mitochondrial calcium ([Ca2+]m). But earthworms regulated their mitochondrial and redox homeostasis through stable mitochondrial membrane potential (MMP) and increase of ATP level, superoxide dismutase (SOD) and catalase (CAT). After 14 d, the positively correlated mitochondrial effects of ROS, [Ca2+]m, MMP and ATP were related to the behavioral inhibition of burrow length, depth and reuse rate as well as antioxidant up-regulation of Nrf2, HO-1, sod1 and cat. These results contributed possible biomarkers from the dose-dependent relationship between mitochondrial, antioxidant and behavioral responses. Multiple biological detection in earthworms can better reflect the sub-chronic ecotoxicity of phenylarsenic pollutants in soil.

ANXA11 mutations in ALS cause dysregulation of calcium homeostasis and stress granule dynamics

Dysregulation of calcium ion homeostasis and abnormal protein aggregation have been proposed as major pathogenic hallmarks underpinning selective degeneration of motor neurons in amyotrophic lateral sclerosis (ALS). Recently, mutations in annexin A11 (ANXA11), a gene encoding a Ca²⁺-dependent phospholipid-binding protein, have been identified in familial and sporadic ALS. However, the physiological and pathophysiological roles of ANXA11 remain unknown. Here, we report functions of ANXA11 related to intracellular Ca²⁺ homeostasis and stress granule dynamics. We analyzed the exome sequences of 500 Korean patients with sALS and identified nine ANXA11 variants in 13 patients. The amino-terminal variants p.G38R and p.D40G within the low-complexity domain of ANXA11 enhanced aggregation propensity, whereas the carboxyl-terminal ANX domain variants p.H390P and p.R456H altered Ca²⁺ responses. Furthermore, all four variants in ANXA11 underwent abnormal phase separation to form droplets with aggregates and led to the alteration of the biophysical properties of ANXA11. These functional defects caused by ALS-linked variants induced alterations in both intracellular Ca²⁺ homeostasis and stress granule disassembly. We also revealed that p.G228Lfs*29 reduced ANXA11 expression and impaired Ca²⁺ homeostasis, as caused by missense variants. Ca²⁺-dependent interaction and coaggregation between ANXA11 and ALS-causative RNA-binding proteins, FUS and hnRNPA1, were observed in motor neuron cells and brain from a patient with ALS-FUS. The expression of ALS-linked ANXA11 variants in motor neuron cells caused cytoplasmic sequestration of endogenous FUS and triggered neuronal apoptosis. Together, our findings suggest that disease-associated ANXA11 mutations can contribute to ALS pathogenesis through toxic gain-of-function mechanisms involving abnormal protein aggregation.

Arsenite impinges on endoplasmic reticulum-mitochondria crosstalk to elicit mitochondrial ROS formation and downstream toxicity

Arsenite is an important carcinogen and toxic compound, causing various deleterious effects through multiple mechanisms. In this review, we focused on mitochondrial ROS (mitoROS) and discussed on the mechanisms mediating their formation. The metalloid promotes direct effects in mitochondria, resulting in superoxide formation only under conditions of increased mitochondrial Ca²⁺ concentration ([Ca²⁺]_m). In this perspective, the time of exposure and concentration requirements for arsenite were largely conditioned by other effects of the metalloid in specific sites of the endoplasmic reticulum (ER). Arsenite induced a slow and limited mobilization of Ca²⁺ from IP₃R via a saturable mechanism, failing to increase the [Ca²⁺]_m. This effect was however associated with the triggering of an intraluminal crosstalk between the IP₃R and the ryanodine receptor (RyR), causing a large and concentration dependent release of Ca²⁺ from RyR and a parallel increase in [Ca²⁺]_m. Thus, the Ca²⁺-dependent mitoO₂^-. formation appears to be conditioned by the spatial/functional organization of the ER/mitochondria network and RyR expression. We also speculate on the possibility that the ER stress response might regulate the above effects on the intraluminal crosstalk between the IP₃R and the RyR via oxidation of critical thiols mediated by the H₂O₂ locally released by oxidoreductin 1α.

MiADMSA abrogates chronic copper-induced hepatic and immunological changes in Sprague Dawley rats

Wilson disease (WD) is an autosomal-recessive disorder associated with the impaired copper metabolism, resulting in hepatic and neurologic manifestations. D-Pencillamine (DPA) is a first-line of treatment however, monoisoamyl 2, 3-dimercaptosuccinic acid (MiADMSA), is gaining recognition recently as a future chelating agent of choice. We evaluated the effects of MiADMSA against copper-induced (20 mg/kg, orally, once, daily for 16 weeks) hepatic and immunological changes in the male Sprague Dawley (SD) rats. Copper overload increased the levels of pro-oxidant and concurrently decreased the levels of antioxidant enzymes in the liver. Increased oxidative stress triggered the up-regulation of pro-inflammatory cytokines (TNF-α, IL-1β, IL-6) in the liver and down-regulated the anti-inflammatory cytokine IL-4. Altered liver function parameters as well as serum immunoglobulins' (IgG, IgA, IgE, and IgM) levels, were also noted. MiADMSA treatment restored most of copper altered biochemical and immunological changes. Further, the histopathological changes proved that MiADMSA treatment ameliorated copper induced hepatic injury. Infra red spectra of liver tissue indicated shift in the characteristic -OH peak during copper exposure while the shifting came to normal in MiADMSA administered rat liver. We conclude that MiADMSA could be a promising antidote for the chronic copper toxicity and possibly in the clinical management of WD.

MiADMSA ameliorate arsenic induced urinary bladder carcinogenesis in vivo and in vitro

BACKGROUND AND PURPOSE

Arsenicosis is a major threat to public health and is a major cause of the development of urinary bladder cancer. Oxidative/ nitrosative stress is one of the key factors for these effects but the involvement of other associated factors is less known. There is a lack of data for the efficacy of chelator against urinary bladder carcinogenesis. The present study demonstrates the early signs of arsenic exposed urinary bladder carcinogenesis and its attenuation by Monoisoamyl dimercaptosuccinic acid (MiADMSA).

METHODS

Male rats were exposed to 50 ppm of sodium arsenite and dimethylarsinic acid (DMA) via drinking water for 18 weeks and treated with MiADMSA (50 mg/kg, orally once daily for 5 days) for 3 weeks with a gap one week between the two courses of treatments. We compared in vivo data with in vitro by co-exposing 100 nM of sodium arsenite and DMA to rat (NBT-II) as well as human transitional epithelial carcinoma (T-24) cells with 100 nM of MiADMSA.

RESULTS

The data showed that sodium arsenite and DMA exposure significantly increased the tissue arsenic contents, ROS, TBARS levels, catalase, SOD activities and significantly decreased GSH level which might be responsible for an increased 8-OHdG level. These changes might have increased pro-oncogenic biomarkers like MMP-9 and survivin in serum, bladder tissues, NBT-II, and T-24 cells. High cell migration and clonogenic potential in NBT-II and T-24 cells exposed to arsenic suggest pronounced carcinogenic potential. Significant recovery in these biomarkers was noted on treatment with MiADMSA.

CONCLUSION

Early signs of urinary bladder carcinogenesis were observed in arsenic and DMA exposed rats which were linked to metal accumulation, oxidative/ nitrosative stress, 8-OHdG, MMP-9 and survivin which were reduced by MiADMSA possibly via its efficient chelation abilities in vivo and in vitro.

Arsenic intoxication: general aspects and chelating agents

Arsenic (As) is widely used in the modern industry, especially in the production of pesticides, herbicides, wood preservatives, and semiconductors. The sources of As such as contaminated water, air, soil, but also food, can cause serious human diseases. The complex mechanism of As toxicity in the human body is associated with the generation of free radicals and the induction of oxidative damage in the cell. One effective strategy in reducing the toxic effects of As is the usage of chelating agents, which provide the formation of inert chelator–metal complexes with their further excretion from the body. This review discusses different aspects of the use of metal chelators, alone or in combination, in the treatment of As poisoning. Consideration is given to the therapeutic effect of thiol chelators such as meso-2,3-dimercaptosuccinic acid, sodium 2,3-dimercapto-1-propanesulfonate, 2,3-dimercaptopropanol, penicillamine, ethylenediaminetetraacetic acid, and other recent agents against As toxicity. The review also considers the possible role of flavonoids, trace elements, and herbal drugs as promising natural chelating and detoxifying agents.

Gestational Arsenic Trioxide Exposure Acts as a Developing Neuroendocrine-Disruptor by Downregulating Nrf2/PPARγ and Upregulating Caspase-3/NF-ĸB/Cox2/BAX/iNOS/ROS

The goal of this investigation was to evaluate the effects of gestational administrations of arsenic trioxide (ATO; As₂O₃) on fetal neuroendocrine development (the thyroid-cerebrum axis). Pregnant Wistar rats were orally administered ATO (5 or 10 mg/kg) from gestation day (GD) 1 to 20. Both doses of ATO diminished free thyroxine and free triiodothyronine levels and augmented thyrotropin level in both dams and fetuses at GD 20. Also, the maternofetal hypothyroidism in both groups caused a dose-dependent reduction in the fetal serum growth hormone, insulin growth factor-I (IGF-I), and IGF-II levels at embryonic day (ED) 20. These disorders perturbed the maternofetal body weight, fetal brain weight, and survival of pregnant and their fetuses. In addition, destructive degeneration, vacuolation, hyperplasia, and edema were observed in the fetal thyroid and cerebrum of both ATO groups at ED 20. These disruptions appear to depend on intensification in the values of lipid peroxidation, nitric oxide, and H₂O₂, suppression of messenger RNA (mRNA) expression of nuclear factor erythroid 2-related factor 2 and peroxisome proliferator-activated receptor gamma, and activation of mRNA expression of caspase-3, nuclear factor kappa-light-chain-enhancer of activated B cells, cyclooxygenase-2, Bcl-2–associated X protein, and inducible nitric oxide synthase in the fetal cerebrum. These data suggest that gestational ATO may disturb thyroid-cerebrum axis generating fetal neurodevelopmental toxicity.

Exposure to mixtures of mercury, cadmium, lead, and arsenic alters the disposition of single metals in tissues of Wistar rats

Humans throughout the world are exposed regularly to mixtures of environmental toxicants. Four of the most common heavy metal toxicants in the environment are mercury (Hg), cadmium (Cd), lead (Pb), and arsenic (As). Numerous studies have assessed the effects and disposition of individual metals in organ systems; however, humans are usually exposed to mixtures of toxicants or metals rather than to a single toxicant. Therefore, the purpose of the current study was to test the hypothesis that exposure to a mixture of toxic heavy metals alters the disposition of single metals in target organs. Wistar rats (Rattus norvegicus) were exposed to Hg, Cd, Pb, or As as a single metal or as a mixture of metals. Rats were injected intravenously for three days, following which kidneys, liver, brain, and blood were harvested. Samples were analyzed for content of Hg, Cd, Pb, and As via inductively coupled plasma mass spectrometry. In general, exposure to a mixture of metals reduced accumulation of single metals in target organs. Interestingly, exposure to mixtures of metals with Pb and/or As increased the concentration of these metals specifically in the liver. The findings from this study indicate that exposure to mixtures of toxic heavy metals may alter significantly the distribution and accumulation of these metals in target organs and tissues.

An overview of plant-based interventions to ameliorate arsenic toxicity

The industrial and technological advancements in the world have also contributed to the rapid deterioration in the environment quality through introduction of obnoxious pollutants that threaten to destroy the subtle balance in the ecosystem. The environment contaminants cause severe adverse effects to humans, flora and fauna that are mostly irreversible. Chief among these toxicants is arsenic, a metalloid, which is considered among the most dangerous environmental toxins that leads to various diseases which affect the quality of life even when present in small quantities. Treatment of arsenic-mediated disorders still remains a challenge due to lack of effective options. Chelation therapy has been the most widely used method to detoxify arsenic. But this method is associated with deleterious effects leading various toxicities such as hepatotoxicity, neurotoxicity and other adverse effects. It has been discovered that indigenous drugs of plant origin display effective and progressive relief from arsenic-mediated toxicity without any side-effects. Further, these phytochemicals have also been found to aid the elimination of arsenic from the biological system and therefore can be more effective than conventional therapeutic agents in ameliorating arsenic-mediated toxicity. This review presents an overview of the toxic effects of arsenic and the therapeutic strategies that are available to mitigate the toxic effects with emphasis on chelation as well as protective and detoxifying activities of different phytochemicals and herbal drugs against arsenic. This information may serve as a primer in identifying novel prophylactic as well as therapeutic formulations against arsenic-induced toxicity.

Calcium signals between the ryanodine receptor- and mitochondria critically regulate the effects of arsenite on mitochondrial superoxide formation and on the ensuing survival vs apoptotic signaling

A low concentration of arsenite (6 h), selectively stimulating the intraluminal crosstalk between the inositol-1, 4, 5-triphosphate receptor and the ryanodine receptor (RyR), increased the mitochondrial transport of RyR-derived Ca²⁺ through the mitochondrial Ca²⁺ uniporter. This event was characterized in intact and permeabilized cells, and was shown to be critical for mitochondrial superoxide (mitoO₂^.-) formation. Inhibition of mitochondrial Ca²⁺ accumulation therefore prevented the effects of arsenite, in both the mitochondrial (e.g., cardiolipin oxidation) and extramitochondrial (e.g., DNA single- strand breakage) compartments, and suppressed the Nrf2/GSH survival signaling. The effects of arsenite on Ca²⁺ homeostasis and mitoO₂^.- formation were reversible, as determined after an additional 10 h incubation in fresh culture medium and by measuring long-term viability. A 16 h continuous exposure to arsenite instead produced a sustained increase in the cytosolic and mitochondrial Ca²⁺ concentrations, a further increased mitoO₂^.- formation and mitochondrial permeability transition. These events, followed by delayed apoptosis (48 h), were sensitive to treatments/manipulations preventing mitochondrial Ca²⁺ accumulation. Interestingly, cells remained viable under conditions in which the deregulated Ca²⁺ homeostasis was not accompanied by mitoO₂^.-formation.

In conclusion, we report that the fraction of Ca²⁺ taken up by the mitochondria in response to arsenite derives from the RyR. Mitochondrial Ca²⁺ appears critical for mitoO₂^.- formation and for the triggering of both the cytoprotective and apoptotic signaling. The effects of arsenite were reversible, whereas its prolonged exposure caused a sustained increase in mitochondrial Ca²⁺ and mitoO₂^.- formation, and the prevalence of the apoptotic vs survival signaling.

Low Concentrations of Arsenite Target the Intraluminal Inositol 1, 4, 5-Trisphosphate Receptor/Ryanodine Receptor Crosstalk to Significantly Elevate Intracellular Ca2

Arsenite is an established human carcinogen that induces cytotoxic and genotoxic effects through poorly defined mechanisms involving the formation of reactive oxygen species (ROS) and deregulated Ca2+ homeostasis. We used variants of the U937 cell line to address the central issue of the mechanism whereby arsenite affects Ca2+ homeostasis. We found that 6-hour exposure to the metalloid (2.5 μM), although not associated with an immediate or delayed toxicity, causes a significant increase in the intracellular Ca2+ concentration ([Ca2+]i) through a mechanism characterized by the following components: 1) it was not affected by ROS produced under the same conditions; 2) a small amount of Ca2+ was mobilized from the inositol-1,4,5-trisphosphate receptor (IP3R), and this response was not augmented by greater concentrations of the metalloid; 3) large amounts of Ca2+ were instead dose dependently mobilized from the ryanodine receptor (RyR) in response to IP3R stimulation; 4) the cells maintained an intact responsiveness to agonist-stimulated Ca2+ mobilization from both channels; 5) arsenite, even at 5-10 µM, failed to directly mobilize Ca2+ from the RyR; and 6) arsenite failed to enhance Ca2+ release from the RyR under conditions in which the [Ca2+]i was increased by either RyR agonists or ionophore-stimulated Ca2+ uptake. We therefore conclude that arsenite elevates the [Ca2+]i by directly targeting the IP3R and its intraluminal crosstalk with the RyR. This mechanism likely mediates mitochondrial superoxide formation, downstream damage on various biomolecules (including genomic DNA), and mitochondrial dysfunction/apoptosis eventually occurring after longer incubation to, or exposure to greater concentrations of, arsenite.

WITHDRAWN: Toxic effects of gestational arsenic trioxide on the neuroendocrine axis of developing rats

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Ferroptosis is newly characterized form of neuronal cell death in response to arsenite exposure

Ferroptosis is a novel iron-dependent form of cell death implicated in brain pathology. However, whether arsenite is an inducer of ferroptosis in the neuron remains completely unknown. In this study, the seven-week-old healthy C57BL/6 J male mice were treated with environmental related doses (0.5, 5 and 50 mg/L) of arsenite for 6 months via drinking water, and the ferroptosis-related indicators were further determined. Our results demonstrated for the first time that, arsenite exposure significantly reduced the number of neuron and caused the pathological changes of mitochondria in the cerebral cortex of mice. We further revealed that arsenite induced ferroptotic cell death in neuron by accumulation of reactive oxygen species and lipid peroxidation products, disruption of Fe²⁺ homeostasis, depletion of glutathione and adenosine triphosphate, inhibition of cysteine/glutamate antiporter, activation of mitogen-activated protein kinases and mitochondrial voltage-dependent anion channels pathways, up-regulation of endoplasmic reticulum stress, all of which were involved in the process of ferroptosis. These findings were also verified in the cultured PC-12 cells by using ferropotosis inhibitor, desferoxamine. Taken together, our results not only reveal a novel mechanism that chronic arsenite exposure may trigger the new form of cell death, ferroptosis, but also shed a new light on a potential clue for the intervention and prevention against arsenite-related neurodegenerative diseases.

A β-carboline derivative-based nickel(ii) complex as a potential antitumor agent: synthesis, characterization, and cytotoxicity

A novel nickel(ii) complex of 6-methoxy-1-pyridine-β-carboline (4a) was synthesized and characterized. The cytotoxicities of the complex towards six cancer cell lines, including MGC-803, Hep G2, T24, OS-RC-2, NCI-H460, and SK-OV-3, and human normal liver cell line HL-7702 were investigated. The IC50 values for MGC-803, Hep G2, T24, OS-RC-2, NCI-H460 and SK-OV-3 were generally in the micromolar range (3.77-15.10 μM), lower than those of ligand 4 and cisplatin. Furthermore, 4a (6 μM) significantly induced cell cycle arrest at the S phase, and caused the down-regulation of p-AKT, cyclin E, cyclin A and CDK2 and the up-regulation of p27. Various experiments showed that 4a induced apoptosis, activated caspase-3, increased the levels of reactive oxygen species (ROS) and enhanced the intracellular [Ca2+]c levels in MGC-803. In addition, the expression of intrinsic apoptotic proteins, including cytochrome c and apaf-1, increased. Further intrinsic apoptosis was triggered via executive molecular caspase-9 and caspase-3. In short, 4a exerted its cytotoxic activity primarily through inducing cell cycle arrest at the S phase and intrinsic apoptosis.

Deciphering the molecular events during arsenic induced transcription signal cascade activation in cellular milieu

Anthropogenic sources of arsenic poses and creates unintentional toxico-pathological concerns to humans in many parts of the world. The understanding of toxicity of this metalloid, which shares properties of both metal and non-metal is principally structured on speciation types and holy grail of toxicity prevention. Visible symptoms of arsenic toxicity include nausea, vomiting, diarrhea and abdominal pain. In this review, we focused on the dermal cell stress caused by trivalent arsenic trioxide and pentavalent arsanilic acid. Deciphering the molecular events involved during arsenic toxicity and signaling cascade interaction is key in arsenicosis prevention. FoxO1 and FoxO2 transcription factors, members of the Forkhead/Fox family, play important roles in this aspect. Like Foxo family proteins, ATM/CHK signaling junction also plays important role in DNA nuclear factor guided cellular development. This review will summarize and discuss current knowledge about the interplay of these pathways in arsenic induced dermal pathogenesis.

Oxidative Damage Induced by Arsenic in Mice or Rats: A Systematic Review and Meta-Analysis

In this meta-analysis, studies reporting arsenic-induced oxidative damage in mouse models were systematically evaluated to provide a scientific understanding of oxidative stress mechanisms associated with arsenic poisoning. Fifty-eight relevant peer-reviewed publications were identified through exhaustive database searching. Oxidative stress indexes assessed included superoxide dismutase (SOD), catalase (CAT), glutathione (GSH), glutathione peroxidase (GPx), glutathione-s-transferase (GST), glutathione reductase (GR), oxidized glutathione (GSSG), malondialdehyde (MDA), and reactive oxygen species (ROS). Our meta-analysis showed that arsenic exposure generally suppressed measured levels of the antioxidants, SOD, CAT, GSH, GPx, GST, and GR, but increased levels of the oxidants, GSSG, MDA, and ROS. Arsenic valence was important and GR and MDA levels increased to a significantly (P < 0.05) greater extent upon exposure to As³⁺ than to As⁵⁺. Other factors that contributed to a greater overall oxidative effect from arsenic exposure included intervention time, intervention method, dosage, age of animals, and the sample source from which the indexes were estimated. Our meta-analysis effectively summarized a wide range of studies and detected a positive relationship between arsenic exposure and oxidative damage. These data provide a scientific basis for the prevention and treatment of arsenic poisoning.

Curcumin Inhibits The Adverse Effects of Sodium Arsenite in Mouse Epididymal Sperm

Background

The aim of this study was to investigate the effects of curcumin on epididy- mal sperm parameters in adult male Navel Medical Research Institute (NMRI) mice ex- posed to sodium arsenite.

Materials and Methods

In this experimental study, we divided the animals into four groups: control, sodium arsenite (5 mg/kg), curcumin (100 mg/kg) and curcumin+sodium arsenite. Exposures were performed by intraperitoneal injections for a 5-week period. After the exposure period, we recorded the animals’ body and left testes weights. The left caudal epididymis was used to count the sperm number and analyze motility, viability, morphological abnormalities, acrosome reaction, DNA integrity, and histone-protamine replacement in the spermatozoa. One-way analysis of variance (ANOVA) followed by the Tukey’s test was used to assess the statistical significance of the data with SPSS 16.0. P<0.05 was considered significant.

Results

Mice exposed to sodium arsenite showed a significant decrease in the num- ber, motility, viability, normal sperm morphology and acrosome integrity of spermato- zoa compared to the control group. In the curcumin+sodium arsenite group, curcumin significantly reversed these adverse effects to the point where they approximated the control. In addition, the application of curcumin alone had no significant difference in these parameters compared to the control and curcumin+sodium arsenite groups. However, we observed no significant differences in the body and the testis weight as well as the DNA integrity and histone-protamine replacement in the spermatozoa of the four groups.

Conclusion

Curcumin compensated for the toxic effects of sodium arsenite on a number of sperm parameters in adult mice.

Inorganic Arsenic Induces NRF2-Regulated Antioxidant Defenses in Both Cerebral Cortex and Hippocampus in Vivo

Inorganic arsenic is reported to induce the reactive oxygen species-mediated oxidative stress, which is supposed to be one of the main mechanisms of arsenic-related neurological diseases. Nuclear factor erythroid 2-related factor 2 (NRF2), a master regulator of antioxidant defense systems, up-regulates the expression of target genes to fight against oxidative damages caused by harmful substances, including metals. In the present study, mice were used as a model to investigate the oxidative stress levels and the expressions of NRF2-regulated antioxidant substances in both cerebral cortex and hippocampus with 5, 10 and 20 mg/kg NaAsO2 exposure intra-gastrically. Our results showed that acute NaAsO2 treatment resulted in decreased total anti-oxidative capacity (T-AOC) and increased maleic dialdehyde production in the nervous system. We also detected rapidly elevation of NRF2 protein levels by enhancement of Nrf2 transcription, especially at 20 mg/kg NaAsO2 exposure group. In the meantime, mRNA and protein levels of Nrf2 encoding antioxidant enzymes heme oxygenase-1 (HO-1), NAD(P)H: quinine oxidoreductase 1 (NQO1) and glutathione S-transferase (GST) were consistently elevated time- and dose-dependently both in the cerebral cortex and hippocampus. Taken together, the presence study demonstrated the activation of NRF2 pathway, an early antioxidant defensive response, in both cerebral cortex and hippocampus upon inorganic arsenic (iAs) exposure in vivo. A better knowledge on the roles of NRF2 pathway in maintaining cellular redox homeostasis would be helpful for the strategies on improvement of neurotoxicity related to this metalloid.

Protective effect of telmisartan treatment against arsenic-induced testicular toxicity in rats

Oxidative/nitrosative stress, inflammation, and apoptosis play a crucial role in the pathogenesis of arsenic-induced testicular injury. Telmisartan, the angiotensin II-receptor antagonist, possesses antioxidant and anti-inflammatory activities. The protective effect of telmisartan against arsenic-induced testicular damage was investigated in rats. Testicular damage was induced by sodium arsenite (10 mg kg-1/day, p.o., for 2 consecutive days). Telmisartan (10 mg kg-1/day, i.p.) was given for 3 consecutive days, starting 1 day before sodium arsenite administration. Telmisartan significantly attenuated the arsenic-induced decrease in the levels of serum testosterone and testicular reduced glutathione, and significantly decreased the elevation of the levels of testicular malondialdehyde, nitric oxide, and arsenic levels, as well as myeloperoxidase activity resulting from sodium arsenite administration. Histopathological and immunohistochemical examination revealed that telmisartan markedly attenuated testicular tissue changes, and decreased the arsenic-induced expression of vascular endothelial growth factor, inducible nitric oxide synthase, tumor necrosis factor-α, cyclooxygenase-2, nuclear factor-κB, and caspase-3. Telmisartan, via its antioxidant and/or anti-inflammatory effects, may represent a potential candidate to protect against the deleterious effects of arsenic on testicular tissue.

Arsenic and nicotine co-exposure lead to some synergistic effects on oxidative stress and apoptotic markers in young rat blood, liver, kidneys and brain

Arsenic and nicotine exposure has been a major health concern globally. Individually both these toxicants increase the risk to various diseases including cancers. However, limited information exists on the co-exposure. In this study, we evaluate the effects of their individual and combined exposure and if co-exposure to these toxicants might have a synergism or antagonism. Male rats were exposed to a very low dose of arsenic (25 ppm in drinking water) or nicotine (0.25 mg/kg, sub-cutaneously) for a period of 5 months and post exposure various biochemical variables indicative of oxidative stress and apoptosis evaluated. Almost all glutathione linked enzymes showed marked alteration in individual as well as co-exposure treated groups. While serum creatinine and apoptosis indicator, lactate dehydrogenase (LDH) were significantly increased in both treatments, an additive effect was noted in co-exposure group. A similar trend was also seen in brain and liver but not in kidneys. Gene expression studies showed marked reduction in catalase, Cu-Zn SOD, GST, there was a significant up regulation in Bax, caspase 3 in various tissues along with urinary 8-OHdG levels, indicative of DNA damage and apoptosis. Interestingly, a decrease in liver arsenic concentration was noted in co-exposed group compared to arsenic alone exposed group. In conclusion, the present study suggests that arsenic and nicotine exhibited significant toxicity during individual exposure whereas co-exposure to these toxins showed variable conditions (indicative of both synergism and antagonism) in male rats.

Biochemical and Molecular Alterations Following Arsenic-Induced Oxidative Stress and Mitochondrial Dysfunction in Rat Brain

Oxidative stress is associated with the generation of reactive oxygen species (ROS), which is supposed to be one of the mechanisms of arsenic-induced neurodegeneration. Mitochondria, being the major source of ROS generation may present an important target of arsenic-mediated neurotoxicity. Hence, we planned the study to elucidate the possible biochemical and molecular alterations induced by arsenic exposure in rat brain mitochondria. Chronic sodium arsenite treatment (25 ppm for 12 weeks) resulted in decreased activity of mitochondrial complexes I, II, and IV followed by increased ROS generation. There was decrease in mitochondrial superoxide dismutase (MnSOD) activity in arsenic-treated rat brain further showing increased superoxide radical generation in mitochondria. The decrease in MnSOD activity might be responsible for the increased protein and lipid oxidation as observed in our study. Protein and messenger RNA (mRNA) levels of MnSOD and mitochondrial uncoupling protein 2 (UCP-2) were downregulated suggesting decreased removal of ROS in rat brain. Fourier transform infrared (FTIR) spectroscopy analysis revealed significant decrease in amide A, amide I, amide II, and Olefinic = CH stretching band area suggesting molecular alteration in proteins and lipids after arsenic treatment. The results of present study indicate that arsenic-induced disturbed mitochondrial metabolism, decreased removal of ROS, decrease in protein synthesis, and altered membrane lipid polarity and fluidity may be responsible for the mitochondrial oxidative damage in rat brain that may further be implicated as contributing factor in arsenic-induced neurodegeneration.

Cytotoxicity, DNA binding and cell apoptosis induction of a zinc(ii) complex of HBrQ

A zinc(ii) complex of HBrQ showed higher in vitro antitumor activity. It induced cell apoptosis in BEL-7404 cells via G₂ phase arrest, led to mitochondria dysfunction and activation of caspase cascade. The central zinc(ii) should play a key role to enhance the antitumor effect

A review with recent advancements on bioremediation-based abolition of heavy metals

There has been a significant rise in the levels of heavy metals (Pb, As, Hg and Cd) due to their increased industrial usage causing a severe concern to public health. The accumulation of heavy metals generates oxidative stress in the body causing fatal effects to important biological processes leading to cell death. Therefore, there is an imperative need to explore efficient and effective methods for the eradication of these heavy metals as against the conventionally used uneconomical and time consuming strategies that have numerous environmental hazards. One such eco-friendly, low cost and efficient alternative to target heavy metals is bioremediation technology that utilizes various microorganisms, green plants or enzymes for the abolition of heavy metals from polluted sites. This review comprehensively discusses toxicological manifestations of heavy metals along with the detailed description of bioremediation technologies employed such as phytoremediation and biosorption for the potential removal of these metals. It also updates readers about recent advances in bioremediation technologies like the use of nanoparticles, non-living biomass and transgenic crops.

Alpha-lipoic acid protects oxidative stress, changes in cholinergic system and tissue histopathology during co-exposure to arsenic-dichlorvos in rats

We investigated protective efficacy of α-lipoic acid (LA), an antioxidant against arsenic and DDVP co-exposed rats. Biochemical variables suggestive of oxidative stress, neurological dysfunction, and tissue histopathological alterations were determined. Male rats were exposed either to 50 ppm sodium arsenite in drinking water or in combination with DDVP (4 mg/kg, subcutaneously) for 10 weeks. α-Lipoic acid (50mg/kg, pos) was also co-administered in above groups. Arsenic exposure led to significant oxidative stress along, hepatotoxicity, hematotoxicity and altered brain biogenic amines levels accompanied by increased arsenic accumulation in blood and tissues. These altered biochemical variables were supported by histopathological examinations leading to oxidative stress and cell death. These biochemical alterations were significantly restored by co-administration of α-lipoic acid with arsenic and DDVP alone and concomitantly. The results indicate that arsenic and DDVP induced oxidative stress and cholinergic dysfunction can be significantly protected by the supplementation of α-lipoic acid.