Studies of selenium and arsenic mutual protection in human HepG2 cells

Emerging evidence on selenoneine and its public health relevance in coastal populations: a review and case study of dietary Se among Inuit populations in the Canadian Arctic

Selenium is an essential mineral yet both deficiency and excess are associated with adverse health effects. Dietary intake of Se in humans varies greatly between populations due to food availability, dietary preferences, and local geological and ecosystem processes impacting Se accumulation into agricultural products and animal populations. We argue there is a need to evaluate and reconsider the relevance of public health recommendations on Se given recent evidence, including the metabolic pathways and health implications of Se. This argument is particularly pertinent for Inuit populations in Northern Canada, who often exceed dietary tolerable upper intake levels and exhibit very high whole blood Se concentrations due to their dependence on local country foods high in the newly discovered Se compound, selenoneine. Since selenoneine appears to have lower toxicity compared to other Se species and does not contribute to the circulating pools of Se for selenoprotein synthesis, we argue that total dietary Se or total Se in plasma or whole blood are poor indicators of Se adequacy for human health in these populations. Overall, this review provides an overview of the current evidence of Se speciation, deficiency, adequacy, and excess and implications for human health and dietary recommendations, with particular reference to Inuit populations in the Canadian Arctic and other coastal populations consuming marine foods.

X-ray Fluorescence Microscopy Methods for Biological Tissues

Synchrotron-based X-ray fluorescence microscopy is a flexible tool for identifying the distribution of trace elements in biological specimens across a broad range of sample sizes. The technique is not particularly limited by sample type and can be performed on ancient fossils, fixed or fresh tissue specimens, and in some cases even live tissue and live cells can be studied. The technique can also be expanded to provide chemical specificity to elemental maps, either at individual points of interest in a map or across a large field of view. While virtually any sample type can be characterized with X-ray fluorescence microscopy, common biological sample preparation methods (often borrowed from other fields, such as histology) can lead to unforeseen pitfalls, resulting in altered element distributions and concentrations. A general overview of sample preparation and data acquisition methods for X-ray fluorescence microscopy is presented, along with outlining the general approach for applying this technique to a new field of investigation for prospective new-users. Considerations for improving data acquisition and quality are reviewed as well as the effects of sample preparation, with a particular focus on soft tissues. The effects of common sample pre-treatment steps as well as the underlying factors that govern which, and to what extent, specific elements are likely to be altered are reviewed along with common artifacts observed in X-ray fluorescence microscopy data.

Effects of Selenium on the Immunotoxicity of Subacute Arsenic Poisoning in Chickens

This study aimed to determine the effects of selenium on the immune toxicity of subacute arsenic poisoning in chickens. Two hundred 8-day-old broilers were randomly divided into 5 groups: the control group (0.1 mg/kg As + 0.2 mg/kg Se), the As group (3 mg/kg As + 0.2 mg/kg Se), As + Se group I (3 mg/kg As + 5 mg/kg Se), As + Se group II (3 mg/kg As + 10 mg/kg Se), and As + Se group III (3 mg/kg As + 15 mg/kg Se). The conclusions were drawn based on the following measurements: 3.0 mg/kg added to feed led to a decrease in the growth performance of the broilers, reduced the level and conversion rate of ANAE, reduced the blood protein content of the broilers but had no effect on the albumin/globulin ratio, and had an inhibitory effect on erythrocyte immunity. Selenium-added of 5 and 10 mg/kg in daily feed leads to increased growth performance, increases the positive rate and conversion rate of ANAE, increases the hemoglobin content of broilers, and promotes erythrocyte immunity, which indicates that the selenium-added reduces the toxic effects of arsenic; 3.0 mg/kg arsenic with 15 mg/kg selenium had the most severe toxic effects. Fifteen milligrams per kilogram of selenium added in daily feed increases the toxicity of arsenic to broilers. The dose of 10 mg/kg selenium showed the best inhibitory effect on subacute arsenic poisoning in the broilers.

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.

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.