A Metabolic Link between Arsenite and Selenite: The Seleno-bis(S-glutathionyl) Arsinium Ion

Arsenic bioaccumulation and biotransformation in different tissues of Nile tilapia (Oreochromis niloticus): A comparative study between As(III) and As(V) exposure and evaluation of antagonistic effects of selenium

The speciation of arsenic in fish has been widely investigated, but bioaccumulation and biotransformation of inorganic As in different tissues of Nile tilapia (Oreochromis niloticus) are not fully understood. The present study aimed to investigate the bioaccumulation of As in Nile tilapia, as well as to evaluate the distribution of the main arsenic species (As(III), As(V), MMA, DMA, and AsB) in liver, stomach, gill, and muscle, after controlled exposures to As(III) and As(V) at concentrations of 5.0 and 10.0 mg L-1 during periods of 1 and 7 days. Total As was determined by inductively coupled plasma mass spectroscopy (ICP-MS). For both exposures (As(III) and As(V)), the total As levels after 7-day exposure were highest in the liver and lowest in the muscle. Overall, the Nile tilapia exposed to As(III) showed higher tissue levels of As after the treatments, compared to As(V) exposure. Speciation of arsenic present in the tissues employed liquid chromatography coupled to ICP-MS (LC-ICP-MS), revealing that the biotransformation of As included As(V) reduction to As(III), methylation to monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA), and subsequent conversion to nontoxic arsenobetaine (AsB), which was the predominant arsenic form. Finally, the interactions and antagonistic effects of selenium in the bioaccumulation processes were tested by the combined exposure to As(III), the most toxic species of As, together with tetravalent selenium (Se(IV)). The results indicated a 4-6 times reduction of arsenic toxicity in the tilapia.

Elements in Serum, Muscle, Liver, and Kidney of Rabbits Fed Macroalgae-Supplemented Diets

The addition of marine macroalgae to animal feed has garnered interest due to the demonstrated benefits of gut health in many livestock species. Most macroalgae have a higher mineral content than terrestrial vegetables, making them an attractive, sustainable source of minerals. However, some macroalgae contain elevated concentrations of iodine and arsenic, which may be transferred to the meat of livestock fed with macroalgae. This study evaluated the mineral profile of rabbit serum, muscle, liver, and kidney of rabbits fed diets supplemented with different marine macroalgae, with the goal of improving post-weaning gut health and reducing reliance on antibiotics. We found increased deposition of iodine in muscle, liver, and kidney due to macroalgae supplementation, which is particularly promising for regions with low iodine endemicity. Higher, though relatively low arsenic concentrations, compared to those in other animal meats and food sources, were also detected in the muscle, liver, and kidney of macroalgae-fed rabbits. The absence of apparent interactions with other micronutrients, particularly selenium, suggests that the inclusion of macroalgae in rabbit diets will not affect the overall mineral content. Enhanced bioavailability of elements such as phosphorus and iron may provide additional benefits, potentially reducing the need for mineral supplementation.

In vitro study on the competitive reactions between arsenite and selenite with glutathione

Exposure to arsenic can cause various biological effects by increasing the production of reactive oxygen species (ROS). Selenium acts as a beneficial element by regulating ROS and limiting heavy metal uptake and translocation. There are studies on the interactive effects of As and Se in plants, but the antagonistic and synergistic effects of these elements based on their binding to glutathione (GSH) molecules have not been studied yet. In this study, we aimed to investigate the antagonistic or synergistic effects of As and Se on the binding mechanism of Se and As with GSH at pH 3.0, 5.0, or 6.5. The interaction of As and Se in Se(SG)2 + As(III) or As(SG)3 + Se(IV) binary systems and As(III) + Se(IV) + GSH ternary system were examined depending on their ratios via liquid chromatography diode array detector/electrospray mass spectrometry (LC-DAD/MS) and liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS). The results showed that the formation of As(GS)3 was not detected in the As(III) + Se(SG)2 binary system, indicating that As(III) did not affect the stability of Se(SG)2 complex antagonistically. However, in the Se(IV) + As(SG)3 binary system, the addition of Se(IV) to As(SG)3 affected the stability of As(SG)3 antagonistically. Se(IV) reacted with GSH, disrupting the As(SG)3 complex, and consequently, Se(SG)2 formation was measured using LC-MS/DAD. In the Se(IV) + GSH + As(III) ternary system, Se(SG)2 formation was detected upon mixing As(III), Se(IV), and GSH. The increase in the concentration of As(III) did not influence the stability of the Se(SG)2 complex. Additionally, Se(IV) has a higher affinity than As(III) to the GSH, regardless of the pH of the solution. In both binary and ternary systems, the formation of the by-product glutathione trisulfide (GSSSG) was detected using LC-ESI-MS/MS.

Integrative Metallomics Studies of Toxic Metal(loid) Substances at the Blood Plasma–Red Blood Cell–Organ/Tumor Nexus

Globally, an estimated 9 million deaths per year are caused by human exposure to environmental pollutants, including toxic metal(loid) species. Since pollution is underestimated in calculations of the global burden of disease, the actual number of pollution-related deaths per year is likely to be substantially greater. Conversely, anticancer metallodrugs are deliberately administered to cancer patients, but their often dose-limiting severe adverse side-effects necessitate the urgent development of more effective metallodrugs that offer fewer off-target effects. What these seemingly unrelated events have in common is our limited understanding of what happens when each of these toxic metal(loid) substances enter the human bloodstream. However, the bioinorganic chemistry that unfolds at the plasma/red blood cell interface is directly implicated in mediating organ/tumor damage and, therefore, is of immediate toxicological and pharmacological relevance. This perspective will provide a brief synopsis of the bioinorganic chemistry of AsIII, Cd2+, Hg2+, CH3Hg+ and the anticancer metallodrug cisplatin in the bloodstream. Probing these processes at near-physiological conditions and integrating the results with biochemical events within organs and/or tumors has the potential to causally link chronic human exposure to toxic metal(loid) species with disease etiology and to translate more novel anticancer metal complexes to clinical studies, which will significantly improve human health in the 21st century.

Natural Dietary Compounds in the Treatment of Arsenic Toxicity

Chronic exposure to arsenic (As) compounds leads to its accumulation in the body, with skin lesions and cancer being the most typical outcomes. Treating As-induced diseases continues to be challenging as there is no specific, safe, and efficacious therapeutic management. Therapeutic and preventive measures available to combat As toxicity refer to chelation therapy, antioxidant therapy, and the intake of natural dietary compounds. Although chelation therapy is the most commonly used method for detoxifying As, it has several side effects resulting in various toxicities such as hepatotoxicity, neurotoxicity, and other adverse consequences. Drugs of plant origin and natural dietary compounds show efficient and progressive relief from As-mediated toxicity without any particular side effects. These natural compounds have also been found to aid the elimination of As from the body and, therefore, can be more effective than conventional therapeutic agents in ameliorating As toxicity. This review provides an overview of the recently updated knowledge on treating As poisoning through natural dietary compounds. This updated information may serve as a basis for defining novel prophylactic and therapeutic formulations.

Biliary excretion of arsenic by human HepaRG cells is stimulated by selenide and mediated by the multidrug resistance protein 2 (MRP2/ABCC2)

Millions of people worldwide are exposed to unacceptable levels of arsenic, a proven human carcinogen, in drinking water. In animal models, arsenic and selenium are mutually protective through formation and biliary excretion of seleno-bis (S-glutathionyl) arsinium ion [(GS)₂AsSe]^-. Selenium-deficient humans living in arsenic-endemic regions are at increased risk of arsenic-induced diseases, and may benefit from selenium supplementation. The influence of selenium on human arsenic hepatobiliary transport has not been studied using optimal human models. HepaRG cells, a surrogate for primary human hepatocytes, were used to investigate selenium (selenite, selenide, selenomethionine, and methylselenocysteine) effects on arsenic hepatobiliary transport. Arsenite + selenite and arsenite + selenide at different molar ratios revealed mutual toxicity antagonism, with the latter being higher. Significant levels of arsenic biliary excretion were detected with a biliary excretion index (BEI) of 14 ± 8%, which was stimulated to 32 ± 7% by selenide. Consistent with the formation and biliary efflux of [(GS)₂AsSe]^-, arsenite increased the BEI of selenide from 0% to 24 ± 5%. Arsenic biliary excretion was lost in the presence of selenite, selenomethionine, and methylselenocysteine. Sinusoidal export of arsenic was stimulated ∼1.6-fold by methylselenocysteine, but unchanged by other selenium forms. Arsenic canalicular and sinusoidal transport (±selenide) was temperature- and GSH-dependent and inhibited by MK571. Knockdown experiments revealed that multidrug resistance protein 2 (MRP2/ABCC2) accounted for all detectable biliary efflux of arsenic (±selenide). Overall, the chemical form of selenium and human MRP2 strongly influenced arsenic hepatobiliary transport, information critical for human selenium supplementation in arsenic-endemic regions.

Dietary Selenium Deficiency Partially Mimics the Metabolic Effects of Arsenic

Chronic arsenic exposure via drinking water is associated with diabetes in human pop-ulations throughout the world. Arsenic is believed to exert its diabetogenic effects via multiple mechanisms, including alterations to insulin secretion and insulin sensitivity. In the past, acute arsenicosis has been thought to be partially treatable with selenium supplementation, though a potential interaction between selenium and arsenic had not been evaluated under longer-term exposure models. The purpose of the present study was to explore whether selenium status may augment arsenic's effects during chronic arsenic exposure. To test this possibility, mice were exposed to arsenic in their drinking water and provided ad libitum access to either a diet replete with selenium (Control) or deficient in selenium (SelD). Arsenic significantly improved glucose tolerance and decreased insulin secretion and β-cell function in vivo. Dietary selenium deficiency resulted in similar effects on glucose tolerance and insulin secretion, with significant interactions between arsenic and dietary conditions in select insulin-related parameters. The findings of this study highlight the complexity of arsenic's metabolic effects and suggest that selenium deficiency may interact with arsenic exposure on β-cell-related physiological parameters.

High Energy Resolution Fluorescence Detected X-ray Absorption Spectroscopy: An Analytical Method for Selenium Speciation

Selenium is in many ways an enigmatic element. It is essential for health but toxic in excess, with the difference between the two doses being narrower than for any other element. Environmentally, selenium is of concern due to its toxicity. As the rarest of the essential elements, its low levels often provide challenges to the analytical chemist. X-ray absorption spectroscopy (XAS) provides a powerful tool for in situ chemical speciation but is severely limited by poor spectroscopic resolution arising from core-hole lifetime broadening. Here we explore selenium Kα1 high energy resolution fluorescence detected XAS (HERFD-XAS) as a novel approach for chemical speciation of selenium, in comparison with conventional Se K-edge XAS. We present spectra of a range of selenium species relevant to environmental and life science studies, including spectra of seleno-amino acids, which show strong similarities with S K-edge XAS of their sulfur congeners. We discuss strengths and limitations of HERFD-XAS, showing improvements in both speciation performance and low concentration detection. We also develop a simple method to correct fluorescence self-absorption artifacts, which is generally applicable to any HERFD-XAS experiment.

Evaluating the cytotoxicity of Ge–Sb–Se chalcogenide glass optical fibres on 3T3 mouse fibroblasts

In vivo cancer detection based on the mid-infrared molecular fingerprint of tissue is promising for the fast diagnosis and treatment of suspected cancer patients. Few materials are mid-infrared transmissive, even fewer, which can be converted into functional, low-loss optical fibres for in vivo non-invasive testing. Chalcogenide-based glass optical fibres are, however, one of the few. These glasses are transmissive in the mid-infrared and are currently under development for use in molecular sensing devices. The cytotoxicity of these materials is however unknown. The cytotoxicity of Ge–Sb–Se chalcogenide optical glass fibres on 3T3 mouse fibroblast cells is here investigated. Fibres exposed to four different pre-treatment conditions are used: as-drawn (AD), propylamine-etched (PE), oxidised-and-washed (OW) and oxidised (Ox). To achieve the latter two conditions, fibres are treated with H₂O₂(aqueous (aq.)) and dried to produce a surface oxide layer; this is either washed off (OW) or left on the glass surface (Ox). Cellular response is investigated via 3 day elution and 14 day direct contact trials. The concentration of the metalloids (Ge, Sb and Se) in each leachate was measured via inductively coupled plasma mass spectrometry. Cell viability is assessed using the neutral red assay and scanning electron microscopy. The concentration of Ge, Sb and Se ions after a 3 day dissolution was as follows. In AD leachates, Ge: 0.40 mg L⁻¹, Sb: 0.17 mg L⁻¹, and Se: 0.06 mg L⁻¹. In PE leachates, Ge: 0.22 mg L⁻¹, Sb: 0.15 mg L⁻¹, and Se: 0.02 mg L⁻¹. In Ox leachates, Ge: 823.8 mg L⁻¹, Sb: 2586.6 mg L⁻¹, and Se: 3750 mg L⁻¹. Direct contact trials show confluent cell layers on AD, PE and OW fibres after 14 days, while no cells are observed on the Ox surfaces. A >50% cell viability is observed in AD, PE and OW eluates after 3 days, when compared with Ox eluates (<10% cell viability). Toxicity in Ox is attributed to the notable pH change, from neutral pH 7.49 to acidic pH 2.44, that takes place on dissolution of the surface oxide layer in the growth media. We conclude, as-prepared Ge–Sb–Se glasses are cytocompatible and toxicity arises when an oxide layer is forced to develop on the glass surface.

We present a study that aims to evaluate the cytotoxicity of Ge₂₀Sb10Se₇₀ at% glass optical fibres on 3T3 mouse fibroblast cells. To observe the toxicity of these optical fibres, 3T3 fibroblast proliferation was investigated.

Linking molecular targets of Cd in the bloodstream to organ-based adverse health effects

The chronic exposure of human populations to toxic metals remains a global public health concern. Although chronic Cd exposure is linked to kidney damage, osteoporosis and cancer, the underlying biomolecular mechanisms remain incompletely understood. Since other diseases could also be causally linked to chronic Cd exposure, a systems toxicology-based approach is needed to gain new insight into the underlying exposure-disease relationship. This approach requires one to integrate the cascade of dynamic bioinorganic chemistry events that unfold in the bloodstream after Cd enters with toxicological events that unfold in target organs over time. To this end, we have conducted a systematic literature search to identify all molecular targets of Cd in plasma and in red blood cells (RBCs). Based on this information it is impossible to describe the metabolism of Cd and the toxicological relevance of it binding to molecular targets in/on RBCs is elusive. Perhaps most importantly, the role that peptides, amino acids and inorganic ions, including HCO₃^-, Cl^- and HSeO₃^- play in terms of mediating the translocation of Cd to target organs and its detoxification is poorly understood. Causally linking human exposure to this metal with diseases requires a much better integration of the bioinorganic chemistry of Cd that unfolds in the bloodstream with target organs. This from a public health point of view important goal will require collaborations between scientists from different disciplines to untangle the complex mechanisms which causally link Cd exposure to disease.

Effects of selenium on antioxidant enzyme activity and bioaccessibility of arsenic in arsenic-stressed radish

Consuming arsenic (As)-contaminated vegetables is the main route of As exposure in humans. The present study focused on the alterations in antioxidant enzymatic activities and As bioaccessibility in As-contaminated radish subjected to Se. Compared to the CK group, the total As content in raw radish was reduced by 27.5 ± 1.3%, and the bioaccessibility of As was reduced by 21.9 ± 2.3% in the 6 mg Se kg^-1 treatment group. The total As content in the treatment groups decreased first but then increased with increasing Se application in raw radish, gastric (G) fraction and gastrointestinal (GI) fraction, while the antioxidant activity exhibited the opposite trend. The results revealed that a low amount of Se effectively blocks the accumulation of As in radish, improves the antioxidant activity in radish and reduces the bioaccessibility of As. These findings provide new ideas for effectively alleviating the spread of As to the human body through the food chain.

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.

Studies of selenium and arsenic mutual protection in human HepG2 cells

Hundreds of millions of people worldwide are exposed to unacceptable levels of carcinogenic inorganic arsenic. Animal models have shown that selenium and arsenic are mutually protective through the formation and elimination of the seleno-bis(S-glutathionyl) arsinium ion [(GS)₂AsSe]^-. Consistent with this, human selenium deficiency in arsenic-endemic regions is associated with arsenic-induced disease, leading to the initiation of human selenium supplementation trials. In contrast to the protective effect observed in vivo, in vitro studies have suggested that selenite increases arsenite cellular retention and toxicity. This difference might be explained by the rapid conversion of selenite to selenide in vivo. In the current study, selenite did not protect the human hepatoma (HepG2) cell line against the toxicity of arsenite at equimolar concentrations, however selenide increased the IC₅₀ by 2.3-fold. Cytotoxicity assays of arsenite + selenite and arsenite + selenide at different molar ratios revealed higher overall mutual antagonism of arsenite + selenide toxicity than arsenite + selenite. Despite this protective effect, in comparison to ⁷⁵Se-selenite, HepG2 cells in suspension were at least 3-fold more efficient at accumulating selenium from reduced ⁷⁵Se-selenide, and its accumulation was further increased by arsenite. X-ray fluorescence imaging of HepG2 cells also showed that arsenic accumulation, in the presence of selenide, was higher than in the presence of selenite. These results are consistent with a greater intracellular availability of selenide relative to selenite for protection against arsenite, and the formation and retention of a less toxic product, possibly [(GS)₂AsSe]^-.

Selenium intake from tuna in Galicia (Spain): Health risk assessment and protective role against exposure to mercury and inorganic arsenic

This study aims to quantify the selenium contribution from tuna to the Spanish diet and evidence the Se protective role against mercury and inorganic arsenic toxicity. Selenium concentrations in tuna were determined by ICP-MS spectrometry (expressed as mg kg^-1), and the risk assessment was evaluated joined to Hg and iAs contrasting criteria of regulatory agencies with those that consider the Se protective role. Differences between Se average concentrations in fresh (1.24) and preserved (1.17) tuna were not statistically significant. In canned tuna species, Se presented higher mean levels in Thunnus albacares (1.28) than Thunnus alalunga (1.01) with statistically significant differences (p = 0.002), and among canned preparations a decreasing sequence was observed in different preparation-packaging media: oil (1.42) > natural (1.01) > pickled (0.92). Statistical study showed Hg-iAs as the only pair significantly correlated in all samples. The HI (sum of individual target hazard quotients -THQs-) on the consumption of tuna in Spain, due to exposure to Se, Hg and iAs, revealed the possibility of risk of adverse chronic effects in the six-year-old children group (1.09). According to the maximum allowable tuna consumption rate in meals/week (CR_mw) and the THQs obtained, tuna intake, especially in children, should be moderated. The health benefit values (HBV_Se) were positive in all samples, 14.53 and 15.65 in fresh and preserved tuna, respectively, which allows tuna to be considered safe. The benefit-risk value (BRV) evidenced the Se molar excess with respect to Hg that reached a surplus of 14.32% on Se AI in adults. Since iAs reduces the Se bioavailability, applying a new BRV criterion, the aforementioned percentage decreased to 13.49% of Se AI. In conclusion, tuna offers high levels of selenium to counteract adverse effects by the presence of Hg and iAs, and to provide consumers an important source of this essential element safely.

Comprehensive analysis of renal arsenic accumulation using images based on X-ray fluorescence at the tissue, cellular, and subcellular levels

Exposure to arsenic (As) through drinking water results in accumulation of As and its methylated metabolites in several organs, promoting adverse health effects, particularly potential development of cancer. Arsenic toxicity is a serious global health concern since over 200 million people are chronically exposed worldwide. Abundant biochemical and epidemiological evidence indicates that the kidney is an important site of uptake and accumulation of As, and mitochondrial damage plays a crucial role in arsenic toxicity. However, non-destructive analyses and in situ images revealing As fate in renal cells and tissue are scarce or almost non-existent. In this work, kidney tissue from exposed rats was analyzed by EDXRF (Energy dispersive X-ray fluorescence), micro-SRXRF (micro X-ray Fluorescence using Synchrotron Radiation), SRTXRF (SRXRF in total reflection condition), SEM-EDX (Scanning Electron Microscope in combination with EDXRF) and SRXRF-XANES (SRXRF in combination with X-ray Absorption Near Edge Spectroscopy). Our results provide evidence of renal cortex distribution of As with periglomerular localization, co-localization of S, Cu and As in subcellular compartment of proximal tubule cells, mono-methylarsonous acid accumulation in renal cortex mitochondria, and altered subcellular concentration and distribution of other elements.

Selenium and zinc protections against metal-(loids)-induced toxicity and disease manifestations: A review

Metals are ubiquitous in the environment due to huge industrial applications in the form of different chemicals and from extensive mining activities. The frequent exposures to metals and metalloids are crucial for the human health. Trace metals are beneficial for health whereas non-essential metals are dangerous for the health and some are proven etiological factors for diseases including cancers and neurological disorders. The interactions of essential trace metals such as selenium (Se) and zinc (Zn) with non-essential metals viz. lead (Pb), cadmium (Cd), arsenic (As), and mercury (Hg) in biological system are very critical and complex. A huge number of studies report the protective role of Se and Zn against metal toxicity, both in animal and cellular levels, and also explain the numerous mechanisms involved. However, it has been considered that a tiny dyshomeostasis in the metals/trace metals status in biological system could induce severe deleterious effects that can manifest to numerous diseases. Thus, in this particular review, we have demonstrated the critical protection mechanism/s of Se and Zn against Cd, Pb, As and Hg toxicity in a one by one manner to clarify the up-to-date findings and perspectives. Furthermore, biomolecular consequences are comprehensively presented in light of particular cellular/biomolecular events which are somehow linked to a subsequent disease. The analyzed reports support significant protection potential of Se and Zn, either alone or in combination with other agents, against each of the abovementioned non-essential metals. However, Se and Zn are still not being used as detoxifying agents due to some unexplained reasons. We hypothesized that Se could be a potential candidate for detoxifying As and Hg regardless of their chemical speciations, but requires intensive clinical trials. However, particularly Zn-Hg interaction warrants more investigations both in animal and cellular level.

X-ray spectroscopy and imaging of selenium in living systems

BACKGROUND

Selenium is an essential element with a rich and varied chemistry in living organisms. It plays a variety of important roles ranging from being essential in enzymes that are critical for redox homeostasis to acting as a deterrent for herbivory in hyperaccumulating plants. Despite its importance there are many open questions, especially related to its chemistry in situ within living organisms.

SCOPE OF REVIEW

This review discusses X-ray spectroscopy and imaging of selenium in biological samples, with an emphasis on the methods, and in particular the techniques of X-ray absorption spectroscopy (XAS) and X-ray fluorescence imaging (XFI). We discuss the experimental methods and capabilities of XAS and XFI, and review their advantages and their limitations. A perspective on future possibilities and next-generation of experiments is also provided.

MAJOR CONCLUSIONS

XAS and XFI provide powerful probes of selenium chemistry, together with unique in situ capabilities. The opportunities and capabilities of the next generation of advanced X-ray spectroscopy experiments are particularly exciting.

GENERAL SIGNIFICANCE

XAS and XFI provide versatile tools that are generally applicable to any element with a convenient X-ray absorption edge, suitable for investigating complex systems essentially without pre-treatment.

The effect of dietary selenium addition on the concentrations of heavy metals in the tissues of fallow deer (Dama dama L.) in Croatia

The aim of this research was to determine the concentrations of cadmium, lead, mercury, and arsenic and the essential elements iron and selenium in the tissues (muscle, kidney, liver, spleen, and fat) of fallow deer (Dama dama L.) without and with supplemental selenium addition. Another aim was to determine the effect of selenium addition on the indicators of oxidative stress, namely, the levels of superoxide dismutase, glutathione peroxidase, glutathione, and vitamin E. The research was carried out with 40 fallow deer during two research periods. Supplemental feed without selenium addition was provided during the first research period, and supplemental feed with added selenium (3 mg/kg) was provided for 60 days during the second research period. The concentration of selenium in tissues was higher in the second research period than in the first research period (in kidney tissue, 0.957 vs. 0.688 mg/kg, P < 0.05). The dietary addition of selenium decreased (P < 0.05) the concentrations of some heavy metals (lead in the spleen = 0.06 vs. 0.27 mg/kg and in the fatty tissue = 0.17 vs. 0.69 mg/kg; arsenic in the muscle tissue = 0.005 vs. 0.014 mg/kg, liver = 0.003 vs. 0.009 mg/kg, spleen = 0.004 vs. 0.013 mg/kg, and fat = 0.008 vs. 0.016 mg/kg). The activity of glutathione peroxidase was significantly higher (P < 0.05) in the second research period than in the first research period (1375.36 vs. 933.23 U/L).

Ameliorative effects of selenium on arsenic-induced cytotoxicity in PC12 cells via modulating autophagy/apoptosis

Arsenic is well known toxicant responsible for human diseases including cancers. On the other hand, selenium is an essential trace element with significant chemopreventive effects, anticancer potentials and antioxidant properties. Although previous studies have reported antagonism/synergism between arsenic and selenium in biological systems, the biomolecular mechanism/s is still inconclusive. Therefore, to elucidate the molecular phenomena in cellular level, we hypothesized that co-exposure of selenium with arsenic may have suppressive effects on arsenic-induced cytotoxicity. We found that selenium in co-exposure with arsenic increases cell viability, and suppresses oxidative stress induced by arsenic in PC12 cells. Consequently, DNA fragmentation due to arsenic exposure was also reduced by arsenic and selenium co-exposure. Furthermore, western blot analyses revealed that simultaneous exposure of both metals significantly inhibited autophagy which further suppressed apoptosis through positively regulation of key proteins; p-mTOR, p-Akt, p-Foxo1A, p62, and expression of ubiquitin, Bax, Bcl2, NFкB, and caspases 3 and 9, although those are negatively regulated by arsenic. In addition, reverse transcriptase PCR analysis confirmed the involvement of caspase cascade in cell death process induced by arsenic and subsequent inhibition by co-exposure of selenium with arsenic. The cellular accumulation study of arsenic in presence/absence of selenium via inductively coupled plasma mass spectrometry confirmed that selenium effectively retarded the uptake of arsenic in PC12 cells. Finally, these findings imply that selenium is capable to modulate arsenic-induced intrinsic apoptosis pathway via enhancement of mTOR/Akt autophagy signaling pathway through employing antioxidant potentials and through inhibiting the cellular accumulation of arsenic in PC12 cells.

Selenium-mediated arsenic excretion in mammals: a synchrotron-based study of whole-body distribution and tissue-specific chemistry

Arsenicosis, a syndrome caused by ingestion of arsenic contaminated drinking water, currently affects millions of people in South-East Asia and elsewhere. Previous animal studies revealed that the toxicity of arsenite essentially can be abolished if selenium is co-administered as selenite. Although subsequent studies have provided some insight into the biomolecular basis of this striking antagonism, many details of the biochemical pathways that ultimately result in the detoxification and excretion of arsenic using selenium supplements have yet to be thoroughly studied. To this end and in conjunction with the recent Phase III clinical trial "Selenium in the Treatment of Arsenic Toxicity and Cancers", we have applied synchrotron X-ray techniques to elucidate the mechanisms of this arsenic-selenium antagonism at the tissue and organ levels using an animal model. X-ray fluorescence imaging (XFI) of cryo-dried whole-body sections of laboratory hamsters that had been injected with arsenite, selenite, or both chemical species, provided insight into the distribution of both metalloids 30 minutes after treatment. Co-treated animals showed strong co-localization of arsenic and selenium in the liver, gall bladder and small intestine. X-ray absorption spectroscopy (XAS) of freshly frozen organs of co-treated animals revealed the presence in liver tissues of the seleno bis-(S-glutathionyl) arsinium ion, which was rapidly excreted via bile into the intestinal tract. These results firmly support the previously postulated hepatobiliary excretion of the seleno bis-(S-glutathionyl) arsinium ion by providing the first data pertaining to organs of whole animals.

Environmental Toxicant Exposures and Type 2 Diabetes Mellitus: Two Interrelated Public Health Problems on the Rise

Rates of type 2 diabetes mellitus (T2DM) are rising rapidly across the globe and the impact of this devastating disease threatens to plague the 21^st century. While some contributing factors are well-recognized (e.g. sedentary lifestyles and caloric excess), others diabetes-promoting risk factors are less established or poorly appreciated. The latter category includes environmental exposures to diabetogenic contaminants. Herein we review some of the latest concepts and mechanisms by which environmental exposures may contribute to rising rates of T2DM with a particular focus on mechanisms involving mitochondrial dysfunction and imbalances in reactive oxygen species (ROS). Furthermore, while the pathogenesis of diabetes includes impairments in insulin sensitivity as well as insulin secretion, we will specifically delve into the links between environmental exposures to toxicants such as arsenic and disruptions in insulin release from pancreatic β-cells. Since β-cell death or dysfunction lies at the heart of both T2DM as well as type 1 diabetes mellitus (T1DM), environmental endocrine disrupting chemicals (EDCs) that disrupt the production or regulated release of the glucose-lowering hormone insulin are likely contributors to diabetes risk. Importantly, understanding the contribution of toxicants to diabetes risk as well as improved understanding of their mechanisms of action offer unique opportunities to modulate diabetes risk via targeted therapeutics or public policy interventions to reduce and remediate exposures.

Dietary compounds as modulators of metals and metalloids toxicity

A large part of the population is exposed to metals and metalloids through the diet. Most of the in vivo studies on its toxicokinetics and toxicity are conducted by means of exposure through drinking water or by intragastric or intraperitoneal administration of aqueous standards, and therefore they do not consider the effect of the food matrix on the exposure. Numerous studies show that some components of the diet can modulate the toxicity of these food contaminants, reducing their effect on a systemic level. Part of this protective role may be due to a reduction of intestinal absorption and subsequent tissue accumulation of the toxic element, although it may also be a consequence of their ability to counteract the toxicity directly by their antioxidant and/or anti-inflammatory activity, among other factors. The present review provides a compilation of existing information about the effect that certain components of the diet have on the toxicokinetics and toxicity of the metals and metalloids of greatest toxicological importance that are present in food (arsenic, cadmium, lead, and mercury), and of their most toxic chemical species.

Relationship between arsenic and selenium in workers occupationally exposed to inorganic arsenic

The interaction between arsenic (As) and selenium (Se) has been one of the most extensively studied. The antagonism between As and Se suggests that low Se status plays an important role in aggravating arsenic toxicity in diseases development. The objective of this study was to assess the Se contents in biological samples of inorganic As exposed workers (n=61) and in non-exposed subjects (n=52). Median (Me) total arsenic concentration in urine of exposed workers was 21.83μg/g creat. (interquartile range (IQR) 15.49-39.77) and was significantly higher than in the control group - (Me 3.75μg/g creat. (IQR 2.52-9.26), p<0.0001). The median serum Se concentrations in the study group and the control were: 54.20μg/l (IQR 44.2-73.10μg/l) and 55.45μg/l (IQR 38.5-69.60μg/l) respectively and did not differ significantly between the groups. In the exposed group we observed significantly higher urine concentrations of selenosugar 1 (SeSug 1) and selenosugar 3 (SeSug3) than in the control group Me: 1.68μg/g creat. (IQR 1.25-2.97 vs Me: 1.07μg/g creat. (IQR 0.86-1.29μg/g), p<0.0001 for SeSug1; Me: 0.45μg/g creat. (IQR 0.26-0.69) vs Me: 0.28μg/g creat. (IQR 0.17-0.45μg/g), p=0.0021). In the multivariate model, after adjusting to cofounders (age, BMI, job seniority time, consumption of fish and seafood and smoking habits) the high rate of arsenic urine wash out (measured as a sum of iAs+MMA+DMA) was significantly associated with the high total selenium urine excretion (B=0.14 (95%CI (confidence interval) 0.05-0.23)). Combination of both arsenic and selenium status to assess the risk of arsenic-induced diseases requires more studies with regard to both the analysis of speciation, genetics and the influence of factors such as nutritional status.

Assessing arsenic and selenium in a single nail clipping using portable X-ray fluorescence

The feasibility of measuring arsenic and selenium contents in a single nail clipping was investigated using a small-focus portable X-ray fluorescence (XRF) instrument with monochromatic excitation beams. Nail clipping phantoms supplemented with arsenic and selenium to produce materials with 0, 5, 10, 15, and 20µg/g were used for calibration purposes. In total, 10 different clippings were analyzed at two different measurement positions. Energy spectra were fit with detection peaks for arsenic K_α, selenium K_α, arsenic K_β, selenium K_β, and bromine K_α characteristic X-rays. Data analysis was performed under two distinct conditions of fitting constraint. Calibration lines were established from the amplitude of each of the arsenic and selenium peaks as a function of the elemental contents in the clippings. The slopes of the four calibration lines were consistent between the two conditions of analysis. The calculated minimum detection limit (MDL) of the method, when considering the K_α peak only, ranged from 0.210±0.002µg/g selenium under one condition of analysis to 0.777±0.009µg/g selenium under another. Compared with previous portable XRF nail clipping studies, MDLs were substantially improved for both arsenic and selenium. The new measurement technique had the additional benefits of being short in duration (~3min) and requiring only a single nail clipping. The mass of the individual clipping used did not appear to play a major role in signal strength, but positioning of the clipping is important.

Kinetics and thermodynamics of zinc(II) and arsenic(III) binding to XPA and PARP-1 zinc finger peptides

Inhibition of DNA repair is an established mechanism of arsenic co-carcinogenesis, and may be perpetuated by the binding of As(III) to key zinc finger (zf) DNA repair proteins. Validated molecular targets of As(III) include the first zinc finger domain of Poly (ADP-Ribose) Polymerase 1 (PARP-1), and the zinc finger domain of Xeroderma Pigmentosum Complementation Group A (XPA). In order to gain an understanding of the thermodynamic and kinetic parameters of the interaction of As(III) with these two zinc finger motifs, a fluorescence based approach was used to investigate Zn(II) and As(III) binding to synthetic model peptides corresponding to the zf motif of XPA and first zf motif of PARP-1, referred to in this paper as XPAzf and PARP-1zf-1, respectively. While XPAzf and PARP-1zf-1 display similar relative affinities for As(III), PARP-1zf-1 shows a potential kinetic advantage over XPAzf for As(III) binding, with a rate constant for the fast phase of formation of As(III)-PARP-1zf-1 approximately 4-fold higher than for As(III)-XPAzf. However, the binding of Zn(II) with either peptide proceeds at a faster rate than As(III). Notably, XPAzf demonstrates comparable affinities for binding both metals, while PARP-1zf-1 shows a slightly higher affinity for Zn(II), suggesting that the relative concentrations of Zn(II) and As(III) in a system may significantly influence which species predominates in zinc finger occupancy. These results provide insight into the mechanisms underlying interactions between zinc finger structures and As(III), and highlight the potential utility of zinc supplementation in mitigating adverse effects of As(III) on zinc finger functions in vivo.

Small mammals as sentinels of oil sands related contaminants and health effects in northeastern Alberta, Canada

The extraction of bitumen in areas of northeastern Alberta (Canada) has been associated with the release of complex mixtures of metals, metalloids, and polycyclic aromatic compounds (PACs) to the environment. To mitigate effects on ecosystems, Canadian legislation mandates that disturbed areas be reclaimed to an ecologically sustainable state after active operations. However, as part of reclamation activities, exposure to, and effects on wildlife living in these areas is not generally assessed. To support successful reclamation, the development of efficient methods to assess exposure and health effects in potentially exposed wildlife is required. In the present study, we investigated the usefulness of two native mammalian species (deer mouse Peromyscus maniculatus, and meadow vole Microtus pennsylvanicus) as sentinels of oil sands related contaminants by examining biomarkers of exposure and indicators of biological costs. Tissue residues of 31 metals and metalloids in kidneys and muscle, activity of the hepatic detoxification enzyme EROD (as a biomarker of exposure to organic contaminants), body condition, and the relative mass of liver, kidney, spleen, and testes were compared in animals from one reclaimed area and a reference site. Deer mice from the reclaimed site had higher renal levels of Co, Se and Tl compared to animals from the reference site, which was associated with reduced body condition. Lower testis mass was another feature that distinguished mice from the reclaimed site in comparison to those from the reference site. One mouse and one vole from the reclaimed site also showed increased hepatic EROD activity. In marked contrast, no changes were evident for these variables in meadow voles. Our results show that deer mouse is a sensitive sentinel species and that the biomarkers and indicators used here are efficient means to detect local contamination and associated biological effects in native mammals inhabiting reclaimed areas on active oil sands mine sites. These field-derived findings can be used by risk assessors to fill possible data gaps for mammalian wildlife in science-based environmental risk assessments for oil and gas projects.

Biochanin A Ameliorates Arsenic-Induced Hepato- and Hematotoxicity in Rats

Biochanin A (BCA) is a natural organic compound of the phytoestrogenic isoflavone class that has antioxidant and metal chelator properties in the presence of transition metal ions, however, its efficacy in animal models is still obscure. Therefore, the objective of this study was to investigate the protective effects of BCA against arsenic-induced hepatic injury and hematotoxicity in rats. The results suggest that arsenic intoxicated rats showed significantly higher levels of plasma hepatic markers than normal control rats. Furthermore, an increase in lipid peroxidation with depletion of reduced glutathione (GSH) and activities of superoxide dismutase (SOD) and catalase (CAT) occurred in the livers of rats exposed to arsenic. Administration of BCA (20 mg/kg·bw/day) and selenium (3 mg/kg·bw/day) resulted in a significant reversal of hepatic and oxidative stress markers in arsenic-intoxicated rats. A low dose of BCA (10 mg/kg·bw/day) did not show any preventive effect, while a high dose of BCA (40 mg/kg·bw/day) partially prevented all hepatotoxicity events. These biochemical perturbations were supported by histopathological observations of the liver. Our results suggest that administration of BCA (20 mg/kg·bw/day) attenuated the arsenic hepatotoxicity, a property that could contribute to the therapeutic approaches for chronic liver diseases.

High-selenium lentil diet protects against arsenic-induced atherosclerosis in a mouse model

BACKGROUND

Cardiovascular disease (CVD) is a major cause of death worldwide, and arsenic (As) intake, mainly through drinking water, is a well-known risk factor for CVD as well as other health problems. Selenium (Se) is a known antagonist to As toxicity.

OBJECTIVE

We tested the potential of high-Se lentils from the Canadian prairies as a therapeutic food to alter the outcome of As-enhanced atherosclerosis.

MATERIALS AND METHODS

Male ApoE(-/-) mice exposed to a moderate level of As (200ppb) in their drinking water, and control mice on tap water received one of three lentil diets: Se-deficient (0.009mg/kg), Se-adequate (0.16mg/kg) or Se-high (0.3mg/kg). After 13weeks, lesion formation in the aortic arch and sinus were assessed. Intralesional cellular composition, serum lipid levels and hepatic oxidative stress were assessed as well.

RESULTS

Arsenic-exacerbated plaque formation was reduced in the sinus and completely abolished in the aortic arch of mice on the Se-fortified lentil diet, whereas lesions were increased in As-exposed mice on both the Se-deficient and Se-adequate diets. Notably, Se deficiency contributed to proatherogenic composition of serum lipids in As-exposed mice as indicated by high-density lipoprotein:low-density lipoprotein. At least adequate Se status was crucial for counteracting As-induced oxidative stress.

CONCLUSION

This study is the first to show the potential of high-Se lentils to protect against As-triggered atherosclerosis, and this invites further investigations in human populations at risk from As contamination of their drinking water.

Selenium distribution and speciation in plant parts of wheat (Triticum aestivum) and Indian mustard (Brassica juncea) from a seleniferous area of Punjab, India

The concentration, distribution, and speciation of selenium in different parts of wheat and Indian mustard, grown in a seleniferous area in Punjab, were investigated using synchrotron based (XAS) and classical acid digestion and extraction methods. The analyses revealed a high Se enrichment in all investigated plant parts, with Se levels in the range of 133-931 mg/kg (dry weight, dw). Such high Se enrichment is mainly due to the considerable amounts of easily available Se detected in the soil, which are renewed on a yearly basis to some extent via irrigation. Speciation analysis in soil and plants indicated selenate and organic Se as major Se species taken up by plants, with a minor presence of selenite. The analyses also revealed that the highest Se enrichment occurs in the upper plant parts, in agreement with the high uptake rate and mobility of selenate within plants. In both wheat and mustard, highest Se enrichments were found in leaves (387 mg/kg·dw in wheat and 931 mg/kg·dw in mustard). Organic species (dimethylselenide and methylselenocysteine) were found in different parts of both plants, indicating that an active detoxification response to the high Se uptake is taking place through methylation and/or volatilization. The high proportion of selenate in wheat and mustard leaves (47% and 70%, respectively) is the result of the inability of the plant metabolism to completely transform selenate to non-toxic organic forms, if oversupplied. Methylselenocysteine, a common Se species in accumulating plants, was detected in wheat, suggesting that, in the presence of high Se concentration, this plant develops similar response mechanisms to accumulator plants.

Efficient interface for online coupling of capillary electrophoresis with inductively coupled plasma-mass spectrometry and its application in simultaneous speciation analysis of arsenic and selenium

A simple and highly efficient online system coupling of capillary electrophoresis to inductively coupled plasma-mass spectrometry (CE-ICP-MS) for simultaneous separation and determination of arsenic and selenium compounds was developed. CE was coupled to an ICP-MS system by a sprayer with a novel direct-injection high-efficiency nebulizer (DIHEN) chamber as the interface. By using this interface, six arsenic species, including arsenite (As(III), arsenate (As(V)), monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), arsenobetaine (AsB), and arsenocholine (AsC) and five selenium species (such as sodium selenite (Se(IV)), sodium selenate (Se(VI)), selenocysteine (SeCys), selenomethionine (SeMet), and Se-methylselenocysteine (MeSeCys)) were baseline-separated and determined in a single run within 9 min under the optimized conditions. Minimum dead volume, low and steady sheath flow liquid, high nebulization efficiency, and high sample transport efficiency were obtained by using this interface. Detection limits were in the range of 0.11-0.37 μg L(-1) for the six arsenic compounds (determined as (75)As at m/z 75) and 1.33-2.31 μg L(-1) for the five selenium species (determined as (82)Se at m/z 82). Repeatability expressed as the relative standard deviations (RSD, n = 6) of both migration time and peak area were better than 2.68% for arsenic compounds and 3.28% for selenium compounds, respectively. The proposed method had been successfully applied for the determination of arsenic and selenium species in the certified reference materials DORM-3, water, urine, and fish samples.

Arsenic and selenium toxicity and their interactive effects in humans

Arsenic (As) and selenium (Se) are unusual metalloids as they both induce and cure cancer. They both cause carcinogenesis, pathology, cytotoxicity, and genotoxicity in humans, with reactive oxygen species playing an important role. While As induces adverse effects by decreasing DNA methylation and affecting protein 53 expression, Se induces adverse effects by modifying thioredoxin reductase. However, they can react with glutathione and S-adenosylmethionine by forming an As-Se complex, which can be secreted extracellularly. We hypothesize that there are two types of interactions between As and Se. At low concentration, Se can decrease As toxicity via excretion of As-Se compound [(GS3)2AsSe](-), but at high concentration, excessive Se can enhance As toxicity by reacting with S-adenosylmethionine and glutathione, and modifying the structure and activity of arsenite methyltransferase. This review is to summarize their toxicity mechanisms and the interaction between As and Se toxicity, and to provide suggestions for future investigations.

Simultaneous speciation analysis of inorganic arsenic, chromium and selenium in environmental waters by 3-(2-aminoethylamino) propyltrimethoxysilane modified multi-wall carbon nanotubes packed microcolumn solid phase extraction and ICP-MS

Speciation analysis of inorganic arsenic, chromium and selenium in environmental waters is of great significance for the monitoring of environmental pollution. In this work, 3-(2-aminoethylamino) propyltrimethoxysilane (AAPTS) functionalized multi-wall carbon nanotubes (MWCNTs) were synthesized and employed as the adsorbent for simultaneous speciation analysis of inorganic arsenic, chromium and selenium in environmental waters by microcolumn solid-phase extraction (SPE)-inductively coupled plasma mass spectrometry (ICP-MS). It was found that As(V), Cr(VI) and Se(VI) could be selectively adsorbed on the microcolumn packed with AAPTS-MWCNTs adsorbent at pH around 2.2, while As(III), Cr(III) and Se(IV) could not be retained at this pH and passed through the microcolumn directly. Total inorganic arsenic, chromium and selenium was determined after the oxidation of As(III), Cr(III) and Se(IV) to As(V), Cr(VI) and Se(VI) with 10.0 μmol L(-1) KMnO4. The assay of As(III), Cr(III) and Se(IV) was based on subtracting As(V), Cr(VI) and Se(VI) from the total As, Cr and Se, respectively. Under the optimized conditions, the detection limits of 15, 38 and 16 ng L(-1) with the relative standard deviations (RSDs) of 7.4, 2.4 and 6.2% (c=1 µg L(-1), n=7) were obtained for As(V), Cr(VI) and Se(VI), respectively. The developed method was validated by analyzing four Certified Reference Materials, rainwater, Yangtze River and East Lake waters.

A cross-sectional study of the impact of blood selenium on blood and urinary arsenic concentrations in Bangladesh

BACKGROUND

Arsenic can naturally occur in the groundwater without an anthropogenic source of contamination. In Bangladesh over 50 million people are exposed to naturally occurring arsenic concentrations exceeding the World Health Organization's guideline of 10 μg/L. Selenium and arsenic have been shown to facilitate the excretion of each other in bile. Recent evidence suggests that selenium may play a role in arsenic elimination by forming a selenium-arsenic conjugate in the liver before excretion into the bile.

METHODS

A cross-sectional study of 1601 adults and 287 children was conducted to assess the relationship between blood selenium and urinary and blood arsenic in a study population residing in a moderately arsenic-contaminated rural area in Bangladesh.

RESULTS

The results of this study indicate a statistically significant inverse relationship between blood selenium and urinary arsenic concentrations in both adult and pediatric populations in rural Bangladesh after adjustment for age, sex, Body Mass Index, plasma folate and B12 (in children), and ever smoking and current betel nut use (in adults). In addition, there appears to be a statistically significant inverse relationship between blood selenium and blood arsenic in children.

CONCLUSIONS

Our results suggest that selenium is inversely associated with biomarkers of arsenic burden in both adults and children. These findings support the hypothesis that Se facilitates the biliary elimination of As, possibly via the putative formation of a Se-As conjugate using a glutathione complex. However, laboratory based studies are needed to provide further evidence to elucidate the presence of Se-As conjugate and its role in arsenic elimination in humans.

Treating chronic arsenic toxicity with high selenium lentil diets

Arsenic (As) toxicity causes serious health problems in humans, especially in the Indo-Gangetic plains and mountainous areas of China. Selenium (Se), an essential micronutrient is a potential mitigator of As toxicity due to its antioxidant and antagonistic properties. Selenium is seriously deficient in soils world-wide but is present at high, yet non-toxic levels in the great plains of North America. We evaluate the potential of dietary Se in counteracting chronic As toxicity in rats through serum biochemistry, blood glutathione levels, immunotoxicity (antibody response), liver peroxidative stress, thyroid response and As levels in tissues and excreta. To achieve this, we compare diets based on high-Se Saskatchewan (SK) lentils versus low-Se lentils from United States. Rats drank control (0ppm As) or As (40ppm As) water while consuming SK lentils (0.3ppm Se) or northwestern USA lentils (<0.01ppm Se) diets for 14weeks. Rats on high Se diets had higher glutathione levels regardless of As exposure, recovered antibody responses in As-exposed group, higher fecal and urinary As excretion and lower renal As residues. Selenium deficiency caused greater hepatic peroxidative damage in the As exposed animals. Thyroid hormones, triiodothyronine (T3) and thyroxine (T4), were not different. After 14weeks of As exposure, health indicators in rats improved in response to the high Se lentil diets. Our results indicate that high Se lentils have a potential to mitigate As toxicity in laboratory mammals, which we hope will translate into benefits for As exposed humans.

Metal Species in Biology: Bottom-Up and Top-Down LC Approaches in Applied Toxicological Research

Since the inception of liquid chromatography (LC) more than 100 years ago this separation technique has been developed into a powerful analytical tool that is frequently applied in life science research. To this end, unique insights into the interaction of metal species (throughout this manuscript “metal species” refers to “toxic metals, metalloid compounds, and metal-based drugs” and “toxic metals” to “toxic metals and metalloid compounds”) with endogenous ligands can be obtained by using LC approaches that involve their hyphenation with inductively coupled plasma-based element specific detectors. This review aims to provide a synopsis of the different LC approaches which may be employed to advance our understanding of these interactions either in a “bottom-up” or a “top-down” manner. In the “bottom-up” LC-configuration, endogenous ligands are introduced into a physiologically relevant mobile phase buffer, and the metal species of interest is injected. Subsequent “interrogation” of the on-column formed complex(es) by employing a suitable separation mechanism (e.g., size exclusion chromatography or reversed-phase LC) while changing the ligand concentration(s), the column temperature or the pH can provide valuable insight into the formation of complexes under near physiological conditions. This approach allows to establish the relative stability and hydrophobicity of metal-ligand complexes as well as the dynamic coordination of a metal species (injected) to two ligands (dissolved in the mobile phase). Conversely, the “top-down” analysis of a biological fluid (e.g., blood plasma) by LC (e.g., using size exclusion chromatography) can be used to determine the size distribution of endogenous metalloproteins which are collectively referred to as the “metalloproteome”. This approach can provide unique insight into the metabolism and the plasma protein binding of metal species, and can simultaneously visualize the dose-dependent perturbation of the metalloproteome by a particular metal species. The concerted application of these LC approaches is destined to provide new insight into biochemical processes which represent an important starting point to advance human health in the 21st century.

Production and separation of no-carrier-added 73 As and 75 Se from 7 Li irradiated germanium oxide target

This work reports for the first time 7Li-induced accelerator based production of 71,72,73,74As, 75,76,77Br and 73,75Se radionuclides in their no-carrier-added (nca) state. After the decay of all short-lived radionuclides 75Se and 73As were only existing radionuclides in germanium oxide target, which were subsequently separated by liquid-liquid extraction (LLX) using trioctylamine (TOA) dissolved in cyclohexane as liquid ion exchanger. The presence of stable germanium in various fractions was examined by Inductively Coupled Plasma Optical Spectrometry (ICP-OES). At 0.1 M TOA and 10 M HCl concentration, 75Se and stable Ge were extracted into the organic phase leaving 73As in the aqueous phase. The bulk Ge was stripped back to the aqueous phase by 1 M NaOH, keeping 75Se in the organic phase. Therefore complete separation between 73As, 75Se and bulk Ge was achieved.

Probing the bioinorganic chemistry of toxic metals in the mammalian bloodstream to advance human health

The etiology of numerous grievous human diseases, including Alzheimer's and Parkinson's Disease is not well understood. Conversely, the concentration toxic metals and metalloids, such as As, Cd, Hg and Pb in human blood of the average population is well established, yet we know strikingly little about the role that they might play in the etiology of disease processes. Establishing functional connections between the chronic exposure of humans to these and other inorganic pollutants and the etiology of certain human diseases is therefore viewed by many as one of the greatest challenges in the post-genomic era. Conceptually, this task requires us to uncover hitherto unknown biomolecular mechanisms which must explain how small doses of a toxic metal/metalloid compound (low μg per day) - or mixtures thereof - may eventually result in a particular human disease. The biological complexity that is inherently associated with mammals, however, makes the discovery of these mechanisms a truly monumental task. Recent findings suggest that a better understanding of the bioinorganic chemistry of inorganic pollutants in the mammalian bloodstream represents a fruitful strategy to unravel relevant biomolecular mechanisms. The adverse effect(s) that toxic metals/metalloid compounds exert on the transport of essential ultratrace elements to internal organs appear particularly pertinent. A brief overview of the effect that arsenite and Hg(2+) exert on the mammalian metabolism of selenium is presented.

Liquid chromatography-inductively coupled plasma-based metallomic approaches to probe health-relevant interactions between xenobiotics and mammalian organisms

In mammals, the transport of essential elements from the gastrointestinal tract to organs is orchestrated by biochemical mechanisms which have evolved over millions of years. The subsequent organ-based assembly of sufficient amounts of metalloproteins is a prerequisite to maintain mammalian health and well-being. The chronic exposure of various human populations to environmentally abundant toxic metals/metalloid compounds and/or the deliberate administration of medicinal drugs, however, can adversely affect these processes which may eventually result in disease. A better understanding of the perturbation of these processes has the potential to advance human health, but their visualization poses a major problem. Nonetheless, liquid chromatography-inductively coupled plasma-based 'metallomics' methods, however, can provide much needed insight. Size-exclusion chromatography-inductively coupled plasma atomic emission spectrometry, for example, can be used to visualize changes that toxic metals/medicinal drugs exert at the metalloprotein level when they are added to plasma in vitro. In addition, size-exclusion chromatography-inductively coupled plasma mass spectrometry can be employed to analyze organs from toxic metal/medicinal drug-exposed organisms for metalloproteins to gain insight into the biochemical changes that are associated with their acute or chronic toxicity. The execution of such studies-from the selection of an appropriate model organism to the generation of accurate analytical data-is littered with potential pitfalls that may result in artifacts. Drawing on recent lessons that were learned by two research groups, this tutorial review is intended to provide relevant information with regard to the experimental design and the practical application of these aforementioned metallomics tools in applied health research.