Selenomethionine protects against neuronal degeneration by methylmercury in the developing rat cerebrum

Protective effects of selenium on mercury induced immunotoxic effects in mice by way of concurrent drinking water exposure

Selenium (Se) has been recognized as one key to understanding mercury (Hg) exposure risks. To explore the effects of Se on Hg-induced immunotoxicity, female Balb/c mice were exposed to HgCl2- or MeHgCl-contaminated drinking water (0.001, 0.01, and 0.1 mM as Hg) with coexisting Na2SeO3 at different Se/Hg molar ratios (0:1, 1/3:1, 1:1 and 3:1). The potential immunotoxicity induced by Na2SeO3 exposure alone (by way of drinking water) was also determined within a wide range of concentrations. After 14 days' exposure, the effects of Hg or Se on the immune system of Balb/c mice were investigated by determining the proliferation of T and B lymphocytes and the activity of natural killer cells. Hg exposure alone induced a dose-dependent suppression effect, whereas Se provided promotion effects at low exposure level (<0.01 mM) and inhibition effects at high exposure level (>0.03 mM). Under Hg and Se coexposure condition, the effects on immunotoxicity depended on the Hg species, Se/Hg ratio, and exposure concentration. At low Hg concentration (0.001 mM), greater Se ingestion exhibited stronger protective effects on Hg-induced suppression effect mainly by way of decreasing Hg concentrations in target organs. At greater Hg concentration (0.01 and 0.1 mM), immunotoxicity induced by Se (>0.03 mM) became evident, and the protective effects appeared more significant at an Se/Hg molar ratio of 1:1. The complex antagonistic effects between Se and Hg suggested that both Se/Hg molar ratio and concentration should be considered when evaluating the potential health risk of Hg-contaminated biota.

New insights into traditional health risk assessments of mercury exposure: implications of selenium

There is increasing evidence that selenium (Se) has a significant effect on mercury (Hg) toxicology; however, Hg exposure risk assessments usually consider only the amount of Hg present in the environment or in food. On the basis of the present understanding of mechanisms of interaction between Se and Hg, the physiology/toxicology of Se, and the toxicology of Hg, we propose a new criterion for Se/Hg exposure assessment. This criterion, which is based on Se-Hg interactions, considers not only the toxicological consequences of Hg exposure but also the benefits and/or adverse effects of Se intake, especially the adverse effects related to a Se deficiency/excess. According to an illustrative assessment based on the new criterion and nine existing criteria, large knowledge gaps in the traditional assessments of exposure to Hg and/or Se were found, including those that assessed the interactions between Hg and Se. These results suggest that future assessments of Hg exposure (or Se intake) should include both Se and Hg.

Relationships between trace element concentrations in chorionic tissue of placenta and umbilical cord tissue: potential use as indicators for prenatal exposure

The role of the placenta was assessed by comparing the profiles of methylmercury (MeHg), inorganic mercury (I-Hg), lead (Pb), cadmium (Cd), selenium (Se), zinc (Zn), and copper (Cu) in freeze-dried chorionic tissue of the placenta and umbilical cord tissue. The significance of the placenta and cord tissue as predictors of prenatal exposure to these trace elements in pregnant women and newborns was also examined by comparing the element profiles among placenta and cord tissue, and maternal and cord blood red blood cells (RBCs). The samples were collected from 48 mother-child pairs at birth in the general population of Japanese. The concentrations of all elements, except for MeHg, were significantly higher in placenta than in cord tissue. In particular, the Cd showed the highest placenta vs. cord tissue ratio (59:1), followed by I-Hg (2.4:1), indicating that the placental barrier works most strongly against Cd among the examined toxic elements. Contrary to the other elements, the MeHg concentration in cord tissue was significantly higher (1.6 times) than that in placenta, indicating its exceptionally high placental transfer. The MeHg in placenta showed significant correlations with total mercury (T-Hg) in maternal and cord RBCs (rs=0.80 and 0.91, respectively). The MeHg in cord tissue also showed significant correlations with T-Hg in maternal and cord RBCs (rs=0.75 and 0.85, respectively). Therefore, both placenta and cord tissue are useful for predicting maternal and fetal exposure to MeHg. The Se concentration in placenta showed significant but moderate correlations with that in maternal and cord RBCs (rs=0.38 and 0.57, respectively). The Pb, Zn, and Cu concentrations in placenta and cord tissue showed no significant correlations with those in maternal and cord RBCs. As an exception, the Cd concentration in placenta showed a moderate but significant correlation (rs=0.41) with that in maternal RBCs, suggesting that the placenta is useful for predicting maternal exposure to Cd during gestation.