Mammalian glucose permease GLUT1 facilitates transport of arsenic trioxide and methylarsonous acid

Characterizing the toxicological responses to inorganic arsenicals and their metabolites in immortalized human bladder epithelial cells

Arsenic is highly toxic to the human bladder. In the present study, we established a human bladder epithelial cell line that closely mimics normal human bladder epithelial cells by immortalizing primary uroplakin 1B-positive human bladder epithelial cells with human telomerase reverse transcriptase (HBladEC-T). The uroplakin 1B-positive human bladder epithelial cell line was then used to evaluate the toxicity of seven arsenicals (iAsV, iAsIII, MMAV, MMAIII, DMAV, DMAIII, and DMMTAV). The cellular uptake and metabolism of each arsenical was different. Trivalent arsenicals and DMMTAV exhibited higher cellular uptake than pentavalent arsenicals. Except for MMAV, arsenicals were transported into cells by aquaglyceroporin 9 (AQP9). In addition to AQP9, DMAIII and DMMTAV were also taken up by glucose transporter 5. Microarray analysis demonstrated that arsenical treatment commonly activated the NRF2-mediated oxidative stress response pathway. ROS production increased with all arsenicals, except for MMAV. The activating transcription factor 3 (ATF3) was commonly upregulated in response to oxidative stress in HBladEC-T cells: ATF3 is an important regulator of necroptosis, which is crucial in arsenical-induced bladder carcinogenesis. Inorganic arsenics induced apoptosis while MMAV and DMAIII induced necroptosis. MMAIII, DMAV, and DMMTAV induced both cell death pathways. In summary, MMAIII exhibited the strongest cytotoxicity, followed by DMMTAV, iAsIII, DMAIII, iAsV, DMAV, and MMAV. The cytotoxicity of the tested arsenicals on HBladEC-T cells correlated with their cellular uptake and ROS generation. The ROS/NRF2/ATF3/CHOP signaling pathway emerged as a common mechanism mediating the cytotoxicity and carcinogenicity of arsenicals in HBladEC-T cells.

Multilevel Regulation of Membrane Proteins in Response to Metal and Metalloid Stress: A Lesson from Yeast

In the face of flourishing industrialization and global trade, heavy metal and metalloid contamination of the environment is a growing concern throughout the world. The widespread presence of highly toxic compounds of arsenic, antimony, and cadmium in nature poses a particular threat to human health. Prolonged exposure to these toxins has been associated with severe human diseases, including cancer, diabetes, and neurodegenerative disorders. These toxins are known to induce analogous cellular stresses, such as DNA damage, disturbance of redox homeostasis, and proteotoxicity. To overcome these threats and improve or devise treatment methods, it is crucial to understand the mechanisms of cellular detoxification in metal and metalloid stress. Membrane proteins are key cellular components involved in the uptake, vacuolar/lysosomal sequestration, and efflux of these compounds; thus, deciphering the multilevel regulation of these proteins is of the utmost importance. In this review, we summarize data on the mechanisms of arsenic, antimony, and cadmium detoxification in the context of membrane proteome. We used yeast Saccharomyces cerevisiae as a eukaryotic model to elucidate the complex mechanisms of the production, regulation, and degradation of selected membrane transporters under metal(loid)-induced stress conditions. Additionally, we present data on orthologues membrane proteins involved in metal(loid)-associated diseases in humans.

Microbial biochemical pathways of arsenic biotransformation and their application for bioremediation

Arsenic is a ubiquitous toxic metalloid, the concentration of which is beyond WHO safe drinking water standards in many areas of the world, owing to many natural and anthropogenic activities. Long-term exposure to arsenic proves lethal for plants, humans, animals, and even microbial communities in the environment. Various sustainable strategies have been developed to mitigate the harmful effects of arsenic which include several chemical and physical methods, however, bioremediation has proved to be an eco-friendly and inexpensive technique with promising results. Many microbes and plant species are known for arsenic biotransformation and detoxification. Arsenic bioremediation involves different pathways such as uptake, accumulation, reduction, oxidation, methylation, and demethylation. Each of these pathways has a certain set of genes and proteins to carry out the mechanism of arsenic biotransformation. Based on these mechanisms, various studies have been conducted for arsenic detoxification and removal. Genes specific for these pathways have also been cloned in several microorganisms to enhance arsenic bioremediation. This review discusses different biochemical pathways and the associated genes which play important roles in arsenic redox reactions, resistance, methylation/demethylation, and accumulation. Based on these mechanisms, new methods can be developed for effective arsenic bioremediation.

Type 2 diabetes affects arsenic metabolism via transporters in arsenic trioxide treated acute promyelocytic leukemia patients

Our study aimed to explore whether type 2 diabetes (T2DM) can affect arsenic metabolism in acute promyelocytic leukemia (APL) patients treated with arsenic trioxide. We found that compared with non-diabetic APL patients, the concentrations of arsenic metabolites in APL patients with T2DM increased significantly and positively correlated with blood glucose (P < 0.05). Meanwhile, APL patients with T2DM were more prone to liver injury and QTc interval prolongation due to altered arsenic methylation capacity. Then we cultured HEK293T cells at different glucose concentrations, and the results showed that the cells with high glucose had higher concentrations of arsenic metabolites compared to other cells. Meanwhile, the high glucose significantly increased the mRNA and protein expression levels of the arsenic uptake transporter AQP7 in HEK293T cells. Overall, our study demonstrated that T2DM can lead to elevated concentrations of arsenic metabolites in APL patients by increasing AQP7 expression.

Arsenic in medicine: past, present and future

Arsenicals are one of the oldest treatments for a variety of human disorders. Although infamous for its toxicity, arsenic is paradoxically a therapeutic agent that has been used since ancient times for the treatment of multiple diseases. The use of most arsenic-based drugs was abandoned with the discovery of antibiotics in the 1940s, but a few remained in use such as those for the treatment of trypanosomiasis. In the 1970s, arsenic trioxide, the active ingredient in a traditional Chinese medicine, was shown to produce dramatic remission of acute promyelocytic leukemia similar to the effect of all-trans retinoic acid. Since then, there has been a renewed interest in the clinical use of arsenicals. Here the ancient and modern medicinal uses of inorganic and organic arsenicals are reviewed. Included are antimicrobial, antiviral, antiparasitic and anticancer applications. In the face of increasing antibiotic resistance and the emergence of deadly pathogens such as the severe acute respiratory syndrome coronavirus 2, we propose revisiting arsenicals with proven efficacy to combat emerging pathogens. Current advances in science and technology can be employed to design newer arsenical drugs with high therapeutic index. These novel arsenicals can be used in combination with existing drugs or serve as valuable alternatives in the fight against cancer and emerging pathogens. The discovery of the pentavalent arsenic-containing antibiotic arsinothricin, which is effective against multidrug-resistant pathogens, illustrates the future potential of this new class of organoarsenical antibiotics.

Microbial remediation and plant-microbe interaction under arsenic pollution

Arsenic contamination in aquatic and terrestrial ecosystem is a serious environmental issue. Both natural and anthropogenic processes can introduce it into the environment. The speciation of the As determine the level of its toxicity. Among the four oxidation states of As (-3, 0, +3, and + 5), As(III) and As(V) are the common species found in the environment, As(III) being the more toxic with adverse impact on the plants and animals including human health. Therefore, it is very necessary to remediate arsenic from the polluted water and soil. Different physicochemical as well as biological strategies can be used for the amelioration of arsenic polluted soil. Among the microbial approaches, oxidation of arsenite, methylation of arsenic, biosorption, bioprecipitation and bioaccumulation are the promising transformation activities in arsenic remediation. The purpose of this review is to discuss the significance of the microorganisms in As toxicity amelioration in soil, factors affecting the microbial remediation, interaction of the plants with As resistant bacteria, and the effect of microorganisms on plant arsenic tolerance mechanism. In addition, the exploration of genetic engineering of the bacteria has a huge importance in bioremediation strategies, as the engineered microbes are more potent in terms of remediation activity along with quick adaptively in As polluted sites.

Arsenic and cancer: Evidence and mechanisms

Arsenic is a potent carcinogen and poses a significant health concern worldwide. Exposure occurs through ingestion of drinking water and contaminated foods and through inhalation due to pollution. Epidemiological evidence shows arsenic induces cancers of the skin, lung, liver, and bladder among other tissues. While studies in animal and cell culture models support arsenic as a carcinogen, the mechanisms of arsenic carcinogenesis are not fully understood. Arsenic carcinogenesis is a complex process due its ability to be metabolized and because of the many cellular pathways it targets in the cell. Arsenic metabolism and the multiple forms of arsenic play distinct roles in its toxicity and contribute differently to carcinogenic endpoints, and thus must be considered. Arsenic generates reactive oxygen species increasing oxidative stress and damaging DNA and other macromolecules. Concurrently, arsenic inhibits DNA repair, modifies epigenetic regulation of gene expression, and targets protein function due its ability to replace zinc in select proteins. While these mechanisms contribute to arsenic carcinogenesis, there remain significant gaps in understanding the complex nature of arsenic cancers. In the future improving models available for arsenic cancer research and the use of arsenic induced human tumors will bridge some of these gaps in understanding arsenic driven cancers.

Low-dose arsenic trioxide enhances membrane-GLUT1 expression and glucose uptake via AKT activation to support L-02 cell aberrant proliferation

Long term low dose exposure of arsenic has been reported to lead various cells proliferation and malignant transformation. GLUT1, as the key transporter of glucose, has been reported to have association with rapid proliferation of various cells or tumor cells. In our study, we found that low dose exposure to arsenic trioxide (0.1μmol/L As₂O₃) could induce an increase in glucose uptake and promote cell viability and DNA synthesis. And, 2-DG, a non-metabolized glucose analog, significantly decreased the glucose uptake and cell proliferation of 0.1μmol/L As₂O₃ treated L-02 cells. However, 4 mmol/L 2-DG was co-utilized with equal dose glucose had no significant effect on the cell proliferation of 0.1μmol/L As₂O₃ treated L-02 cells. Further studies showed that exposure to 0.1μmol/L As₂O₃ could promote the expression of GLUT1 on plasma membrane. Inhibition of GLUT1 expression by 5μmol/L BAY-876 significantly decreased the abilities of glucose uptake and cell proliferation in As₂O₃-treated L-02 cells. Moreover, 0.1μmol/L As₂O₃ induced the AKT activation indicated by increased the phospho-AKT (Ser473 and Thr308). Knockdown AKT by shRNA or inhibited AKT activation by LY294002 was followed by significantly decreased glucose uptake, GLUT1 plasma membrane expression and cell proliferation in As₂O₃-treated L-02 cells. All in all, these results demonstrated that arsenic trioxide-induced AKT activation contributed to the cells proliferation through upregulating expression of GLUT1 on plasma membrane that enhanced glucose uptake.

Availability, Toxicology and Medical Significance of Antimony

Antimony has been known and used since ancient times, but its applications have increased significantly during the last two centuries. Aside from its few medical applications, it also has industrial applications, acting as a flame retardant and a catalyst. Geologically, native antimony is rare, and it is mostly found in sulfide ores. The main ore minerals of antimony are antimonite and jamesonite. The extensive mining and use of antimony have led to its introduction into the biosphere, where it can be hazardous, depending on its bioavailability and absorption. Detailed studies exist both from active and abandoned mining sites, and from urban settings, which document the environmental impact of antimony pollution and its impact on human physiology. Despite its evident and pronounced toxicity, it has also been used in some drugs, initially tartar emetics and subsequently antimonials. The latter are used to treat tropical diseases and their therapeutic potential for leishmaniasis means that they will not be soon phased out, despite the fact the antimonial resistance is beginning to be documented. The mechanisms by which antimony is introduced into human cells and subsequently excreted are still the subject of research; their elucidation will enable us to better understand antimony toxicity and, hopefully, to improve the nature and delivery method of antimonial drugs.

Multiple Interactions of Glucose with the Extra-Membranous Loops of GLUT1 Aid Transport

Molecular dynamics simulations amounting to ≈8 μs demonstrate that the glucose transporter GLUT1 undergoes structural fluctuations mediated by the fluidity of the lipid bilayer and the proximity to glucose. The fluctuations of GLUT1 increase as the glucose concentration is raised. These fluctuations are more pronounced when the lipid bilayer is in the fluid compared to the gel phase. Glucose interactions are confined to the extra-membranous residues when the lipid is in the gel phase but diffuses into the transmembrane regions in the fluid phase. Proximity of glucose to GLUT1 causes asynchronous expansions of key bottlenecks at the internal and external openings of the central pore. This is accomplished only by small conformational changes at the single residue level that lower the resistance to glucose movements, thereby permitting unsteered glucose and water movements along the entire length of the pore. When glucose is near salt bridges located at the external and internal openings of the central pore, the distance separating the polar amino acid residues guarding these apertures tends to increase in both fluid and gel phases. It is evident that the multiplicity of glucose interactions, obtained with high concentrations, amplifies the structural fluctuations in GLUT1. The findings that most of the salt bridges and the bottlenecks appear to be operated by glucose proximity suggest that the main triggers to activation of transport are located within the solvent accessible linker regions in the extramembranous zones.

Hypoxia enhances the cytotoxic effect of As4S4 on rat ventricular H9c2 cells through activation of ubiquitin-proteasome system

BACKGROUND

As₄S₄ is widely used in Chinese traditional medicine compound. However, based on some recent studies, we found that the cardiotoxicity risk of using As₄S₄ in ischemic heart disease patients may be increased. To study this potential risk, we compared the effects of As₄S₄ on rat ventricular H9c2 cell line with or without hypoxic pretreatment, and to elucidate mechanisms of c-Cbl mediated ubiquitination/degradation of integrin β1.

METHODS

The present study was conducted on rat ventricular H9c2 cell line in the absence or presence of hypoxic pretreatment for 6 h followed by As₄S₄ treatment for 24 h. Following As₄S₄ treatment, cell viability assay, flow cytometric quantification of apoptotic cells, caspase-3 activity assay and DAPI staining were conducted. Western blotting was carried out to detect expressions of ubiquitination related proteins. In addition, the ubiquitination/degradation of integrin β1 and the role of c-Cbl in it was evaluated by immunoprecipitation and immunoblot assay.

RESULTS

The viability of cells with hypoxic pretreatment followed by As₄S₄ treatment was decreased significantly, apoptosis rate and the activity of caspase-3 were increased than As₄S₄ treatment alone. The ubiquitin-proteasome degradation pathway induced by As₄S₄ was further enhanced by hypoxic pretreatment. The results of IP and immunoblot assay showed hypoxic enhanced down-regulation effect of As₄S₄ on integrin β1 probably through c-Cbl activation.

CONCLUSIONS

This study demonstrated that the hypoxia enhanced cytotoxicity of As₄S₄ on H9c2 cells may through increasing the ubiquitin-proteasome degradation of integrin β1 mediated by the E3 ligase c-Cbl. The results provide an important clue that, in patients with ischemic heart disease, use of As₄S₄ may be associated with increased cardiotoxicity. We believe that the results worth to be further illuminated by in vivo and clinical research.

Crossing the blood-brain barrier with carbon dots: uptake mechanism and in vivo cargo delivery

The blood-brain barrier (BBB) is a major obstacle for drug delivery to the central nervous system (CNS) such that most therapeutics lack efficacy against brain tumors or neurological disorders due to their inability to cross the BBB. Therefore, developing new drug delivery platforms to facilitate drug transport to the CNS and understanding their mechanism of transport are crucial for the efficacy of therapeutics. Here, we report (i) carbon dots prepared from glucose and conjugated to fluorescein (GluCD-F) cross the BBB in zebrafish and rats without the need of an additional targeting ligand and (ii) uptake mechanism of GluCDs is glucose transporter-dependent in budding yeast. Glucose transporter-negative strain of yeast showed undetectable GluCD accumulation unlike the glucose transporter-positive yeast, suggesting glucose-transporter-dependent GluCD uptake. We tested GluCDs' ability to cross the BBB using both zebrafish and rat models. Following the injection to the heart, wild-type zebrafish showed GluCD-F accumulation in the central canal consistent with the transport of GluCD-F across the BBB. In rats, following intravenous administration, GluCD-F was observed in the CNS. GluCD-F was localized in the gray matter (e.g. ventral horn, dorsal horn, and middle grey) of the cervical spinal cord consistent with neuronal accumulation. Therefore, neuron targeting GluCDs hold tremendous potential as a drug delivery platform in neurodegenerative disease, traumatic injury, and malignancies of the CNS.

Effect of renal impairment on arsenic accumulation, methylation capacity, and safety in acute promyelocytic leukemia (APL) patients treated with arsenic trioxide

Background: Arsenic trioxide (ATO) was successfully applied to treat acute promyelocytic leukemia (APL).Methods: Inorganic arsenic (iAs), monomethylarsonic acid (MMA^V) and dimethyarsinic acid (DMA^V) in plasma of 143 APL patients with different renal function were determined. Arsenic methylation capacity was evaluated by iAs%, MMA^V%, DMA^V%, primary methylation index (PMI, MMA^V/iAs), and secondary methylated index (SMI, DMA^V/MMA^V). Arsenic accumulation with administration frequency were explored. Moreover, safety assessments were performed.Results: Compared with normal renal function, MMA^V and DMA^V concentrations increased 1.5-4 fold in moderate and severe renal impairment groups, iAs increased 1.3-1.7 fold. APL patients with renal impairment showed lower iAs%, but higher DMA^V% and PMI in plasma than those with normal renal function (P < 0.05). MMA^V, DMA^V, and tAs apparently accumulated with administration frequency in moderate and severe renal dysfunction groups. The incidence of QTc interval prolongation and liver injury increased with the increasing severity of renal impairment.Conclusion: Renal dysfunction may increase exposure to arsenic and arsenic accumulation and affect methylation capacity, then the clinical safety in APL patients treated with ATO. Arsenic-level monitoring and dosing regimen adjustment should be considered in APL patients with moderate and severe renal dysfunction.

Effects of heavy metals on reproduction owing to infertility

The reproductive performance of most of the species is adversely affected by hazardous heavy metals like lead, cadmium, mercury, arsenic, zinc, and copper. Heavy metals are liberated in the environment by natural sources like rock weathering, volcanic eruption, and other human activities like industrial discharge, mineral mining, automobile exhaust, and so forth. Heavy metals alter several reproductive functions in both males and females like a decrease in sperm count, motility, viability, spermatogenesis, hormonal imbalance, follicular atresia, and delay in oocyte maturation, and so forth, and thus, forms an important aspect of reproductive toxicology. The present review compiles toxicity aspects of various heavy metals and their efficacy and mechanism of action in mammals.

Metal-metal interaction and metal toxicity: a comparison between mammalian and D. melanogaster

1. Non-essential heavy metals such as mercury (Hg), arsenic (As), cadmium (Cd), and aluminium (Al) are useless to organisms and have shown extensive toxic effects. Previous studies show that two main molecular mechanisms of metal toxicity are oxidative stress and metal-metal interaction which can disrupt metal homeostasis.2. In this paper, we mainly illustrate metal toxicity and metal-metal interaction through examples in mammalians and D. melanogaster (fruit fly).3. We describe the interference of metal homeostasis by metal-metal interactions in three aspects including replacement, cellular transporter competition, and disruption of the regulation mechanism, and elaborate the mechanisms of metal toxicity to better deal with the challenges of heavy metal pollution and related health problems.

Environmental toxicants in the brain: A review of astrocytic metabolic dysfunction

Exposure to environmental toxicants is linked to long-term adverse outcomes in the brain and involves the dysfunction of glial and neuronal cells. Astrocytes, the most numerous cell type, are increasingly implicated in the pathogenesis of many diseases of the central nervous system, including neurodegenerative diseases. Astrocytes are critical for proper brain function in part due to their robust antioxidant and unique metabolic capabilities. Additionally, astrocytes are positioned both at the blood-brain barrier, where they are the primary responders to xenobiotic penetrance of the CNS, and at synapses where they are in close contact with neurons and synaptic machinery. While exposure to several classes of environmental toxicants, including chlorinated and fluorinated compounds, and trace metals, have been implicated in neurodegenerative diseases, their impact on astrocytes represents an important and growing field of research. Here, we review existing literature focused on the impact of a range of synthetic compounds on astrocytic function. We focus specifically on perturbed metabolic processes in response to these compounds and consider how perturbation of these pathways impacts disease pathogenesis.

Glucose transporters in brain in health and disease

Energy demand of neurons in brain that is covered by glucose supply from the blood is ensured by glucose transporters in capillaries and brain cells. In brain, the facilitative diffusion glucose transporters GLUT1-6 and GLUT8, and the Na⁺-d-glucose cotransporters SGLT1 are expressed. The glucose transporters mediate uptake of d-glucose across the blood-brain barrier and delivery of d-glucose to astrocytes and neurons. They are critically involved in regulatory adaptations to varying energy demands in response to differing neuronal activities and glucose supply. In this review, a comprehensive overview about verified and proposed roles of cerebral glucose transporters during health and diseases is presented. Our current knowledge is mainly based on experiments performed in rodents. First, the functional properties of human glucose transporters expressed in brain and their cerebral locations are described. Thereafter, proposed physiological functions of GLUT1, GLUT2, GLUT3, GLUT4, and SGLT1 for energy supply to neurons, glucose sensing, central regulation of glucohomeostasis, and feeding behavior are compiled, and their roles in learning and memory formation are discussed. In addition, diseases are described in which functional changes of cerebral glucose transporters are relevant. These are GLUT1 deficiency syndrome (GLUT1-SD), diabetes mellitus, Alzheimer’s disease (AD), stroke, and traumatic brain injury (TBI). GLUT1-SD is caused by defect mutations in GLUT1. Diabetes and AD are associated with changed expression of glucose transporters in brain, and transporter-related energy deficiency of neurons may contribute to pathogenesis of AD. Stroke and TBI are associated with changes of glucose transporter expression that influence clinical outcome.

Effects of oral exposure to arsenite on arsenic metabolism and transport in rat kidney

Nephrotoxicity is within the recognized toxic effects of arsenic. In this study we assessed the effect of arsenite on the renal capacity to metabolize and handle arsenicals in rats exposed to drinking water with 0, 1, 5, or 10 ppm sodium arsenite for ten days. Arsenite treatment did not affect the gene expression of the main enzyme catalyzing methylation of arsenite, As3mt, while it reduced the expression of GSTO1 mRNA and protein. Arsenite decreased the expression of Aqp3, Mrp1, Mrp4, and Mdr1b (i.e., transporters and channels used by arsenic), but not that of Aqp7, Glut1, Mrp2, and Mdr1a. The protein abundance of AQP3 was also reduced by arsenite. Arsenite increased urinary NGAL and FABP3 and decreased Klotho plasma levels, without alteration of creatinine, which evidenced early tubular damage. Renal Klotho mRNA and protein expressions were also downregulated, which may exacerbate renal damage. No effect was observed in selected miRNAs putatively associated with renal injury. Plasma PTH and FGF23 were similar between groups, but arsenite decreased the renal expression of Fgfr1 mRNA. In conclusion, exposure to arsenite alters the gene expression of proteins involved in the cellular handling of arsenical species and elicits tubular damage.

Human red blood cell uptake and sequestration of arsenite and selenite: Evidence of seleno-bis(S-glutathionyl) arsinium ion formation in human cells

Over 200 million people worldwide are exposed to the human carcinogen, arsenic, in contaminated drinking water. In laboratory animals, arsenic and the essential trace element, selenium, can undergo mutual detoxification through the formation of the seleno-bis(S-glutathionyl) arsinium ion [(GS)₂AsSe]^-, which undergoes biliary and fecal elimination. [(GS)₂AsSe]^-, formed in animal red blood cells (RBCs), sequesters arsenic and selenium, and slows the distribution of both compounds to peripheral tissues susceptible to toxic effects. In human RBCs, the influence of arsenic on selenium accumulation, and vice versa, is largely unknown. The study aims were to characterize arsenite (As^III) and selenite (Se^IV) uptake by human RBCs, to determine if Se^IV and As^III increase the respective accumulation of the other in human RBCs, and ultimately to determine if this occurs through the formation and sequestration of [(GS)₂AsSe]^-. ⁷⁵Se^IV accumulation was temperature and Cl^--dependent, inhibited by 4,4'-diisothiocyanatodihydrostilbene-2,2'-disulfonic acid (H₂DIDS) (IC₅₀ 1 ± 0.2 µM), and approached saturation at 30 µM, suggesting uptake is mediated by the erythrocyte anion-exchanger 1 (AE1 or Band 3, gene SLC4A1). HEK293 cells overexpressing AE1 showed concentration-dependent ⁷⁵Se^IV uptake. ⁷³As^III uptake by human RBCs was temperature-dependent, partly reduced by aquaglyceroporin 3 inhibitors, and not saturated. As^III increased ⁷⁵Se^IV accumulation (in the presence of albumin) and Se^IV increased ⁷³As^III accumulation in human RBCs. Near-edge X-ray absorption spectroscopy revealed the formation of [(GS)₂AsSe]^- in human RBCs exposed to both As^III and Se^IV. The sequestration of [(GS)₂AsSe]^- in human RBCs potentially slows arsenic distribution to susceptible tissues and could reduce arsenic-induced disease.

Altered neurotransmission and neuroimaging biomarkers of chronic arsenic poisoning in wild muskrats (Ondatra zibethicus) and red squirrels (Tamiasciurus hudsonicus) breeding near the City of Yellowknife, Northwest Territories (Canada)

Chronic arsenic poisoning has been shown to be a risk factor for the development of intellectual disability. Numerous human and animal studies have also confirmed that low-level arsenic exposure has deleterious effects on neurotransmission and brain structures which have been further linked to neurobehavioral disorders. The aim of this present work was to comparatively assess structural brain volume changes and alteration of two (2) neurotransmitters, specifically dopamine (DA) and serotonin (5-HT) in the brains of wild muskrats and squirrels breeding in arsenic endemic areas, near the vicinity of the abandoned Giant mine site in Yellowknife and in reference locations between 52 and 105 km from the city of Yellowknife. The levels of DA and 5-HT were measured in the brain tissues, and Magnetic Resonance Imaging (MRI) was used to attempt brain volume measurements. The results revealed that the concentrations of DA and 5-HT were slightly increased in the brains of squirrels from the arsenic endemic areas compared to the reference site. Further, DA and 5-HT were slightly reduced in the brains of muskrats from the arsenic endemic areas compared to the reference location. In general, no statistically significant neurotransmission changes and differences were observed in the brain tissues of muskrats and squirrels from both arsenic endemic areas and non-endemic sites. Although MRI results showed that the brain volumes of squirrels and muskrats were not statistically different between sites after multiple comparison correction; it was noted that core brain regions were substantially affected in muskrats, in particular the hippocampal memory circuit, striatum and thalamus. Squirrel brains showed more extensive neuroanatomical changes, likely due to their relatively smaller body mass, with extensive shrinkage of the core brain structures, and the cortex, even after accounting for differences in overall brain size. The results of this present study constitute the first observation of neuroanatomical changes in wild small mammal species breeding in arsenic endemic areas of Canada.

Arsenic exposure: A public health problem leading to several cancers

Arsenic, a metalloid and naturally occurring element, is one of the most abundant elements in the earth's crust. Water is contaminated by arsenic through natural sources (underground water, minerals and geothermal processes) and anthropogenic sources such as mining, industrial processes, and the production and use of pesticides. Humans are exposed to arsenic mainly by drinking contaminated water, and secondarily through inhalation and skin contact. Arsenic exposure is associated with the development of vascular disease, including stroke, ischemic heart disease and peripheral vascular disease. Also, arsenic increases the risk of tumors of bladder, lungs, kidneys and liver, according to the International Agency for Research on Cancer and the Food and Drug Administration. Once ingested, an estimated 70-90% of inorganic arsenic is absorbed by the gastrointestinal tract and widely distributed through the blood to different organs, primarily to the liver, kidneys, lungs and bladder and secondarily to muscle and nerve tissue. Arsenic accumulates in the organs, especially in the liver. Its excretion mostly takes place through urination. The toxicokinetics of arsenic depends on the duration of exposure, pathway of ingestion, physicochemical characteristics of the compound, and affected biological species. The present review outlines of arsenic toxic effects focusing on different cancer types whit highest prevalence's by exposure to this metalloid and signaling pathways of carcinogenesis.

Targeting Acr3 from Ensifer medicae to the plasma membrane or to the tonoplast of tobacco hairy roots allows arsenic extrusion or improved accumulation. Effect of acr3 expression on the root transcriptome

Transgenic tobacco hairy roots expressing the bacterial arsenite efflux pump Acr3 from Ensifer medicae were generated. The gene product was targeted either to the plasma membrane (ACR3 lines) or to the tonoplast by fusing the ACR3 protein to the tonoplast integral protein TIP1.1 (TIP-ACR3 lines). Roots expressing Acr3 at the tonoplast showed greater biomass than those expressing Acr3 at the plasma membrane. Furthermore, higher contents of malondialdehyde (MDA) and RNA degradation in ACR3 lines were indicative of higher oxidative stress. The determination of ROS-scavenging enzymes depicted the transient role of peroxidases in ROS detoxification, followed by the action of superoxide dismutase during both short- and medium-term exposure periods. Regarding As accumulation, ACR3 lines accumulated up to 20-30% less As, whereas TIP-ACR3 achieved a 2-fold increase in As accumulation in comparison to control hairy roots. Strategies that presumably induce As uptake, such as phosphate deprivation or dehydration followed by rehydration in the presence of As, fostered As accumulation up to 10 800 μg g-1. Finally, the effects of the heterologous expression of acr3 on the root transcriptome were assessed. Expression at the plasma membrane induced drastic changes in gene expression, with outstanding overexpression of genes related to electron transport, ATP synthesis and ATPases, suggesting that As efflux is the main detoxification mechanism in these lines. In addition, genes encoding heat shock proteins and those related to proline synthesis and drought tolerance were activated. On the other hand, TIP-ACR3 lines showed a similar gene expression profile to that of control roots, with overexpression of the glutathione and phytochelatin synthesis pathways, together with secondary metabolism pathways as the most important resistance mechanisms in TIP-ACR3, for which As allocation into the vacuole allowed better growth and stress management. Our results suggest that modulation of As accumulation can be achieved by subcellular targeting of Acr3: expression at the tonoplast enhances As accumulation in roots, whereas expression at the plasma membrane could promote As efflux. Thus, both approaches open the possibilities for developing safer crops when grown on As-polluted paddy soils, but expression at the tonoplast leads to better growth and less stressed roots, since the high energy cost of As efflux likely compromises growth in ACR3 lines.

Targeted Degradation of Glucose Transporters Protects against Arsenic Toxicity

The abundance of cell surface glucose transporters must be precisely regulated to ensure optimal growth under constantly changing environmental conditions. We recently conducted a proteomic analysis of the cellular response to trivalent arsenic, a ubiquitous environmental toxin and carcinogen. A surprising finding was that a subset of glucose transporters was among the most downregulated proteins in the cell upon arsenic exposure. Here we show that this downregulation reflects targeted arsenic-dependent degradation of glucose transporters. Degradation occurs in the vacuole and requires the E2 ubiquitin ligase Ubc4, the E3 ubiquitin ligase Rsp5, and K63-linked ubiquitin chains. We used quantitative proteomic approaches to determine the ubiquitinated proteome after arsenic exposure, which helped us to identify the ubiquitination sites within these glucose transporters. A mutant lacking all seven major glucose transporters was highly resistant to arsenic, and expression of a degradation-resistant transporter restored arsenic sensitivity to this strain, suggesting that this pathway represents a protective cellular response. Previous work suggests that glucose transporters are major mediators of arsenic import, providing a potential rationale for this pathway. These results may have implications for the epidemiologic association between arsenic exposure and diabetes.

Pathways of arsenic uptake and efflux

Arsenic is a non-essential, environmentally ubiquitous toxic metalloid. In response to this pervasive environmental challenge, organisms evolved mechanisms to confer resistance to arsenicals. Inorganic pentavalent arsenate is taken into most cells adventitiously by phosphate uptake systems. Similarly, inorganic trivalent arsenite is taken into most cells adventitiously, primarily via aquaglyceroporins or sugar permeases. The most common strategy for tolerance to both inorganic and organic arsenicals is by efflux that extrude them from the cytosol. These efflux transporters span across kingdoms and belong to various families such as aquaglyceroporins, major facilitator superfamily (MFS) transporters, ATP-binding cassette (ABC) transporters and potentially novel, yet to be discovered families. This review will outline the properties and substrates of known arsenic transport systems, the current knowledge gaps in the field, and aims to provide insight into the importance of arsenic transport in the context of the global arsenic biogeocycle and human health.

Chronic Oral Arsenic Exposure and Its Correlation with Serum S100B Concentration

Arsenic is one of the most important environmental pollutants especially in drinking water. The S100B protein is presented as a sensitive biomarker for assessment of the blood-brain barrier integrity previously. The objective of this study was to determine the impact of chronic arsenic exposure in drinking water and serum S100B correlation. Fifty-four male BALB/c mice were randomly divided into three groups. Group I and II subjects were treated with arsenic trioxide (1 ppm and 10 ppm, respectively), while the rest received normal drinking water. Arsenic concentration in serum and brain was measured by an atomic absorption spectrometer (Varian model 220-Z) conjugated with a graphite furnace atomizer (GTA-110). Also, a serum S100B protein concentration was determined using commercial ELISA kit during different times of exposure. It was observed that body weight gain was significantly lower from the 10th week onwards in arsenic-treated subjects. However, it did not induce any visible clinical signs of toxicity. Measured arsenic level in serum and brain was higher in espoused groups as compared to the control subjects (p < 0.001 and p < 0.0001, respectively). In addition, serum S100B content was increased over a period of 3 months and had significant differences as compared to the control and 1-ppm group especially after 3 months of exposure in the 10-ppm group (p < 0.0001). In conclusion, it could be inferred that long-term arsenic exposure via drinking water leads to brain arsenic accumulation with serum S100B elevated concentration as a probable BBB disruption consequence.

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.

Braving the Element: Pancreatic β-Cell Dysfunction and Adaptation in Response to Arsenic Exposure

Type 2 diabetes mellitus (T2DM) is a serious global health problem, currently affecting an estimated 451 million people worldwide. T2DM is characterized by hyperglycemia and low insulin relative to the metabolic demand. The precise contributing factors for a given individual vary, but generally include a combination of insulin resistance and insufficient insulin secretion. Ultimately, the progression to diabetes occurs only after β-cells fail to meet the needs of the individual. The stresses placed upon β-cells in this context manifest as increased oxidative damage, local inflammation, and ER stress, often inciting a destructive spiral of β-cell death, increased metabolic stress due to further insufficiency, and additional β-cell death. Several pathways controlling insulin resistance and β-cell adaptation/survival are affected by a class of exogenous bioactive compounds deemed endocrine disrupting chemicals (EDCs). Epidemiological studies have shown that, in several regions throughout the world, exposure to the EDC inorganic arsenic (iAs) correlates significantly with T2DM. It has been proposed that a lifetime of exposure to iAs may exacerbate problems with both insulin sensitivity as well as β-cell function/survival, promoting the development of T2DM. This review focuses on the mechanisms of iAs action as they relate to known adaptive and maladaptive pathways in pancreatic β-cells.

Blood-brain barrier development: Systems modeling and predictive toxicology

The blood-brain barrier (BBB) serves as a gateway for passage of drugs, chemicals, nutrients, metabolites, and hormones between vascular and neural compartments in the brain. Here, we review BBB development with regard to the microphysiology of the neurovascular unit (NVU) and the impact of BBB disruption on brain development. Our focus is on modeling these complex systems. Extant in silico models are available as tools to predict the probability of drug/chemical passage across the BBB; in vitro platforms for high-throughput screening and high-content imaging provide novel data streams for profiling chemical-biological interactions; and engineered human cell-based microphysiological systems provide empirical models with which to investigate the dynamics of NVU function. Computational models are needed that bring together kinetic and dynamic aspects of NVU function across gestation and under various physiological and toxicological scenarios. This integration will inform adverse outcome pathways to reduce uncertainty in translating in vitro data and in silico models for use in risk assessments that aim to protect neurodevelopmental health.

Molecular mechanism of the increased tissue uptake of trivalent inorganic arsenic in mice with type 1 diabetes mellitus

Arsenic is associated with several adverse health outcomes, and people with diabetes may be more susceptible to arsenic. In this study, we found that arsenic levels in some tissues such as liver, kidney, and heart but not lung of type 1 diabetes mellitus (T1DM) mice were higher than in those of normal mice after a single oral dose of arsenic trioxide for 2 h. However, little is known about the molecular mechanism of the increased tissue uptake of trivalent inorganic arsenic in mice with T1DM. This study aimed to investigate the expression of the mammalian arsenic transporters aquaglyceroporins (AQPs) and glucose transporter 1 (GLUT1) in T1DM mice and compare them with those in normal mice. Results showed that the levels of AQP9 and GLUT1 mRNA and protein were higher in T1DM mouse liver than in the normal one. The levels of AQP7 mRNA and protein were higher in T1DM mouse kidney. In the heart, we observed that the levels of AQP7 and GLUT1 mRNA and protein were higher in T1DM mice, but the levels of AQP9 mRNA and protein in the lung had no significant difference between both mice. These results suggested that T1DM may increase the expression of transporters of trivalent inorganic arsenic and thus increase the arsenic uptake in specific tissues.

Individual susceptibility to arsenic-induced diseases: the role of host genetics, nutritional status, and the gut microbiome

Arsenic (As) contamination in water or food is a global issue affecting hundreds of millions of people. Although As is classified as a group 1 carcinogen and is associated with multiple diseases, the individual susceptibility to As-related diseases is highly variable, such that a proportion of people exposed to As have higher risks of developing related disorders. Many factors have been found to be associated with As susceptibility. One of the main sources of the variability found in As susceptibility is the variation in the host genome, namely, polymorphisms of many genes involved in As transportation, biotransformation, oxidative stress response, and DNA repair affect the susceptibility of an individual to As toxicity and then influence the disease outcomes. In addition, lifestyles and many nutritional factors, such as folate, vitamin C, and fruit, have been found to be associated with individual susceptibility to As-related diseases. Recently, the interactions between As exposure and the gut microbiome have been of particular concern. As exposure has been shown to perturb gut microbiome composition, and the gut microbiota has been shown to also influence As metabolism, which raises the question of whether the highly diverse gut microbiota contributes to As susceptibility. Here, we review the literature and summarize the factors, such as host genetics and nutritional status, that influence As susceptibility, and we also present potential mechanisms of how the gut microbiome may influence As metabolism and its toxic effects on the host to induce variations in As susceptibility. Challenges and future directions are also discussed to emphasize the importance of characterizing the specific role of these factors in interindividual susceptibility to As-related diseases.

Chronic Kidney Disease and Exposure to Nephrotoxic Metals

Chronic kidney disease (CKD) is a common progressive disease that is typically characterized by the permanent loss of functional nephrons. As injured nephrons become sclerotic and die, the remaining healthy nephrons undergo numerous structural, molecular, and functional changes in an attempt to compensate for the loss of diseased nephrons. These compensatory changes enable the kidney to maintain fluid and solute homeostasis until approximately 75% of nephrons are lost. As CKD continues to progress, glomerular filtration rate decreases, and remaining nephrons are unable to effectively eliminate metabolic wastes and environmental toxicants from the body. This inability may enhance mortality and/or morbidity of an individual. Environmental toxicants of particular concern are arsenic, cadmium, lead, and mercury. Since these metals are present throughout the environment and exposure to one or more of these metals is unavoidable, it is important that the way in which these metals are handled by target organs in normal and disease states is understood completely.

Effects of phosphate binders on the gastrointestinal absorption of arsenate and of an SGLT2 inhibitor drug on the urinary excretion of arsenite in mice

Arsenate (As^V) and arsenite (As^III) are typical sources of acute and chronic arsenic poisoning. Therefore, reducing inner exposure to these arsenicals is a rational objective. Because As^V mimics phosphate, phosphate binder drugs may decrease the intestinal As^V absorption. Indeed, lanthanum and aluminium salts and sevelamer removed As^V from solution in vitro, especially at acidic pH. In mice gavaged with As^V, lanthanum chloride, lanthanum carbonate and aluminium hydroxide given orally also lowered the urinary excretion and tissue levels of As^V and its metabolites, indicating that they decreased the gastrointestinal As^V absorption. As some glucose transporters may carry As^III, the effect of the SGLT2 inhibitor dapagliflozin was investigated in As^III-injected mice. While producing extreme glucosuria, dapagliflozin barely affected the urinary excretion and tissue concentrations of As^III and its metabolites. Thus, phosphate binders (especially lanthanum compounds) can reduce the gastrointestinal absorption of As^V; however, SGLT2 inhibition cannot diminish the renal reabsorption of As^III.

Molecular insight into arsenic toxicity via the genome-wide deletion mutant screening of Saccharomyces cerevisiae

Arsenic is omnipresent in soil, air, food and water. Chronic exposure to arsenic is a serious problem to human health. In-depth understanding of this metalloid's toxicity is a fundamental step towards development of arsenic-free foods and measures for bioremediation. By screening the complete set of gene deletion mutants (4873) of Saccharomyces cerevisiae, this study uncovered 75 sensitive and 39 resistant mutants against arsenite [As(III)]. Functional analysis of the corresponding genes revealed the molecular details for its uptake, toxicity and detoxification. On the basis of the hypersensitivity of yap3Δ, the transcription factor, Yap3p, is for the first time linked to the cell's detoxification against As(III). Apart from confirming the previously described role of the mitogen-activated protein kinase (MAPK) Hog1 pathway in combating arsenic toxicity, the results show that the regulatory subunits (Ckb1p and Ckb2p) of protein kinase CK2 are also involved in the process, suggesting possible crosstalk between the two key protein kinases. The sensitivity to As(III) conferred by deletion of the genes involved in protein degradation and chromatin remodelling demonstrates protein damage is the key mode of toxicity for the metalloid. Furthermore, the resistant phenotype of fps1Δ, snf3Δ and pho81Δ against As(III) links arsenic uptake with the corresponding plasma membrane-bound transporters-aquaglyceroporin (Fps1p), hexose (Snf3p) and phosphate transporters. The molecular details obtained in this screen for As(III) uptake, detoxification and toxicity provide the basis for future investigations into arsenic-related problems in the environment, agriculture and human health.

Cellular arsenic transport pathways in mammals

Natural contamination of drinking water with arsenic results in the exposure of millions of people world-wide to unacceptable levels of this metalloid. This is a serious global health problem because arsenic is a Group 1 (proven) human carcinogen and chronic exposure is known to cause skin, lung, and bladder tumors. Furthermore, arsenic exposure can result in a myriad of other adverse health effects including diseases of the cardiovascular, respiratory, neurological, reproductive, and endocrine systems. In addition to chronic environmental exposure to arsenic, arsenic trioxide is approved for the clinical treatment of acute promyelocytic leukemia, and is in clinical trials for other hematological malignancies as well as solid tumors. Considerable inter-individual variability in susceptibility to arsenic-induced disease and toxicity exists, and the reasons for such differences are incompletely understood. Transport pathways that influence the cellular uptake and export of arsenic contribute to regulating its cellular, tissue, and ultimately body levels. In the current review, membrane proteins (including phosphate transporters, aquaglyceroporin channels, solute carrier proteins, and ATP-binding cassette transporters) shown experimentally to contribute to the passage of inorganic, methylated, and/or glutathionylated arsenic species across cellular membranes are discussed. Furthermore, what is known about arsenic transporters in organs involved in absorption, distribution, and metabolism and how transport pathways contribute to arsenic elimination are described.

Evaluation of the ability of arsenic species to traverse cell membranes by simple diffusion using octanol-water and liposome-water partition coefficients

Arsenic metabolism in living organisms is dependent on the ability of different arsenic species to traverse biological membranes. Simple diffusion provides an alternative influx and efflux route to mediated transport mechanisms that can increase the amount of arsenic available for metabolism in cells. Using octanol-water and liposome-water partition coefficients, the ability of arsenous acid, arsenate, methylarsonate, dimethylarsinate, thio-methylarsonate, thio-dimethylarsinic acid, arsenotriglutathione and monomethylarsonic diglutathione to diffuse through the lipid bilayer of cell membranes was investigated. Molecular modelling of arsenic species was used to explain the results. All arsenic species with the exception of arsenate, methylarsonate and thio-methylarsonate were able to diffuse through the lipid bilayer of liposomes, with liposome-water partition coefficients between 0.04 and 0.13. Trivalent arsenic species and thio-pentavalent arsenic species showed higher partition coefficients, suggesting that they can easily traverse cell membranes by passive simple diffusion. Given the higher toxicity of these species compared to oxo-pentavalent arsenic species, this study provides evidence supporting the risk associated with human exposure to trivalent and thio-arsenic species.

Overexpression of rice glutaredoxins (OsGrxs) significantly reduces arsenite accumulation by maintaining glutathione pool and modulating aquaporins in yeast

Arsenic (As) is an acute poison and class I carcinogen, can cause a serious health risk. Staple crops like rice are the primary source of As contamination in human food. Rice grown on As contaminated areas accumulates higher As in their edible parts. Based on our previous transcriptome data, two rice glutaredoxins (OsGrx_C7 and OsGrx_C2.1) were identified that showed up-regulated expression during As stress. Here, we report OsGrx_C7 and OsGrx_C2.1 from rice involved in the regulation of intracellular arsenite (AsIII). To elucidate the mechanism of OsGrx mediated As tolerance, both OsGrxs were cloned and expressed in Escherichia coli (Δars) and Saccharomyces cerevisiae mutant strains (Δycf1, Δacr3). The expression of OsGrxs increased As tolerance in E. coli (Δars) mutant strain (up to 4 mM AsV and up to 0.6 mM AsIII). During AsIII exposure, S. cerevisiae (Δacr3) harboring OsGrx_C7 and OsGrx_C2.1 have lower intracellular AsIII accumulation (up to 30.43% and 24.90%, respectively), compared to vector control. Arsenic accumulation in As-sensitive S. cerevisiae mutant (Δycf1) also reduced significantly on exposure to inorganic As. The expression of OsGrxs in yeast maintained intracellular GSH pool and increased extracellular GSH concentration. Purified OsGrxs displays in vitro GSH-disulfide oxidoreductase, glutathione reductase and arsenate reductase activities. Also, both OsGrxs are involved in AsIII extrusion by altering the Fps1 transcripts in yeast and protect the cell by maintaining cellular GSH pool. Thus, our results strongly suggest that OsGrxs play a crucial role in the maintenance of the intracellular GSH pool and redox status of the cell during both AsV and AsIII stress and might be involved in regulating intracellular AsIII levels by modulation of aquaporin expression and functions.

New mechanisms of bacterial arsenic resistance

Arsenic is the most pervasive environmental substance and is classified by the International Agency for Research on Cancer as a Group 1 human carcinogen. Nearly every organism has resistance pathways for inorganic arsenic, and in bacteria, their genes are found in arsenic resistance (ars) operons. Recently, a parallel pathway for organic arsenicals has been identified. The ars genes responsible for the organoarsenical detoxification includes arsM, which encodes an As(III) S-adenosylmethionine methyltransferase, arsI, which encodes a C–As bond lyase, and arsH, which encodes a methylarsenite oxidase. The identification and properties of arsM, arsI and arsH are described in this review.

The genome sequence of the popular hexose-transport-deficient Saccharomyces cerevisiae strain EBY.VW4000 reveals LoxP/Cre-induced translocations and gene loss

Saccharomyces cerevisiae harbours a large group of tightly controlled hexose transporters with different characteristics. Construction and characterization of S. cerevisiae EBY.VW4000, a strain devoid of glucose import, was a milestone in hexose-transporter research. This strain has become a widely used platform for discovery and characterization of transporters from a wide range of organisms. To abolish glucose uptake, 21 genes were knocked out, involving 16 successive deletion rounds with the LoxP/Cre system. Although such intensive modifications are known to increase the risk of genome alterations, the genome of EBY.VW4000 has hitherto not been characterized. Based on a combination of whole genome sequencing, karyotyping and molecular confirmation, the present study reveals that construction of EBY.VW4000 resulted in gene losses and chromosomal rearrangements. Recombinations between the LoxP scars have led to the assembly of four neo-chromosomes, truncation of two chromosomes and loss of two subtelomeric regions. Furthermore, sporulation and spore germination are severely impaired in EBY.VW4000. Karyotyping of the EBY.VW4000 lineage retraced its current chromosomal architecture to four translocations events occurred between the 6th and the 12th rounds of deletion. The presented data facilitate further studies on EBY.VW4000 and highlight the risks of genome alterations associated with repeated use of the LoxP/Cre system.

Toxic trace elements at gastrointestinal level

Many trace elements are considered essential [iron (Fe), zinc (Zn), copper (Cu)], whereas others may be harmful [lead (Pb), cadmium (Cd), mercury (Hg), arsenic (As)], depending on their concentration and chemical form. In most cases, the diet is the main pathway by which they enter our organism. The presence of toxic trace elements in food has been known for a long time, and many of the food matrices that carry them have been identified. This has led to the appearance of legislation and recommendations concerning consumption. Given that the main route of exposure is oral, passage through the gastrointestinal tract plays a fundamental role in their entry into the organism, where they exert their toxic effect. Although the digestive system can be considered to be of crucial importance in their toxicity, in most cases we do not know the events that occur during the passage of these elements through the gastrointestinal tract and of ascertaining whether they may have some kind of toxic effect on it. The aim of this review is to summarize available information on this subject, concentrating on the toxic trace elements that are of greatest interest for organizations concerned with food safety and health: Pb, Cd, Hg and As.

Prenatal Exposure to Sodium Arsenite Alters Placental Glucose 1, 3, and 4 Transporters in Balb/c Mice

Inorganic arsenic (iAs) exposure induces a decrease in glucose type 4 transporter (GLUT4) expression on the adipocyte membrane, which may be related to premature births and low birth weight infants in women exposed to iAs at reproductive age. The aim of this study was to analyze the effect of sodium arsenite (NaAsO2) exposure on GLUT1, GLUT3, and GLUT4 protein expression and on placental morphology. Female Balb/c mice (n = 15) were exposed to 0, 12, and 20 ppm of NaAsO2 in drinking water from 8th to 18th day of gestation. Morphological changes and GLUT1, GLUT3, and GLUT4 expression were evaluated in placentas by immunohistochemical and image analysis and correlated with iAs and arsenical species concentration, which were quantified by atomic absorption spectroscopy. NaAsO2 exposure induced a significant decrease in fetal and placental weight (P < 0.01) and increases in infarctions and vascular congestion. Whereas GLUT1 expression was unchanged in placentas from exposed group, GLUT3 expression was found increased. In contrast, GLUT4 expression was significantly lower (P < 0.05) in placentas from females exposed to 12 ppm. The decrease in placental GLUT4 expression might affect the provision of adequate fetal nutrition and explain the low fetal weight observed in the exposed groups.

Neurotoxicity of metals

Metals are frequently used in industry and represent a major source of toxin exposure for workers. For this reason governmental agencies regulate the amount of metal exposure permissible for worker safety. While essential metals serve physiologic roles, metals pose significant health risks upon acute and chronic exposure to high levels. The central nervous system is particularly vulnerable to metals. The brain readily accumulates metals, which under physiologic conditions are incorporated into essential metalloproteins required for neuronal health and energy homeostasis. Severe consequences can arise from circumstances of excess essential metals or exposure to toxic nonessential metal. Herein, we discuss sources of occupational metal exposure, metal homeostasis in the human body, susceptibility of the nervous system to metals, detoxification, detection of metals in biologic samples, and chelation therapeutic strategies. The neurologic pathology and physiology following aluminum, arsenic, lead, manganese, mercury, and trimethyltin exposures are highlighted as classic examples of metal-induced neurotoxicity.

Uptake and toxicity of arsenite and arsenate in cultured brain astrocytes

Inorganic arsenicals are environmental toxins that have been connected with neuropathies and impaired cognitive functions. To investigate whether such substances accumulate in brain astrocytes and affect their viability and glutathione metabolism, we have exposed cultured primary astrocytes to arsenite or arsenate. Both arsenicals compromised the cell viability of astrocytes in a time- and concentration-dependent manner. However, the early onset of cell toxicity in arsenite-treated astrocytes revealed the higher toxic potential of arsenite compared with arsenate. The concentrations of arsenite and arsenate that caused within 24h half-maximal release of the cytosolic enzyme lactate dehydrogenase were around 0.3mM and 10mM, respectively. The cellular arsenic contents of astrocytes increased rapidly upon exposure to arsenite or arsenate and reached after 4h of incubation almost constant steady state levels. These levels were about 3-times higher in astrocytes that had been exposed to a given concentration of arsenite compared with the respective arsenate condition. Analysis of the intracellular arsenic species revealed that almost exclusively arsenite was present in viable astrocytes that had been exposed to either arsenate or arsenite. The emerging toxicity of arsenite 4h after exposure was accompanied by a loss in cellular total glutathione and by an increase in the cellular glutathione disulfide content. These data suggest that the high arsenite content of astrocytes that had been exposed to inorganic arsenicals causes an increase in the ratio of glutathione disulfide to glutathione which contributes to the toxic potential of these substances.