Toxicological effects of selenium nanoparticles in laboratory animals: A review

This paper provides a comprehensive summary of the main toxicological studies conducted on selenium nanoparticles (NPs) using laboratory animals, up until February 28, 2023. A literature search revealed 17 articles describing experimental studies conducted on warm-blooded animals. Despite some uncertainties, in vivo studies have demonstrated that selenium NPs have an adverse effect on laboratory animals, as evidenced by several indicators of general toxic action. These effects include reductions of body mass, changes in hepatotoxicity indices (increased enzyme activity and accumulation of selenium in the liver), and the possibility of impairment of fatty acid, protein, lipid, and carbohydrate metabolisms. However, no specific toxic action attributable solely to selenium has been identified. The LOAEL and NOAEL values are contradictory. The NOAEL was 0.22 mg/kg body weight per day for males and 0.33 mg/kg body weight per day for females, while the LOAEL was assumed to be a dose of 0.05 mg/kg of nanoselenium. This LOAEL value is much higher for rats than for humans. The relationship between the adverse effects of selenium NPs and exposure dose is controversial and presents a wide typological diversity. Further research is needed to clarify the absorption, metabolism, and long-term toxicity of selenium NPs, which is critical to improving the risk assessment of these compounds.

Selenium deficiency inhibits differentiation and immune function and imbalances the Th1/Th2 of dendritic cells

Selenium (Se) deficiency inhibits immune cell differentiation, affects immune response, and leads to cellular and humoral immune dysfunction. However, the impact of Se deficiency on the differentiation and Th1/Th2 balance of dendritic cells is still unclear. In this study, we replicated a model of Se-deficient chickens by feeding the chickens with a low-Se diet (i.e., the content of Se is 0.008 mg per kg diet). On this basis, we explored the effect of Se deficiency on the differentiation of chicken dendritic cells by induction culture of peripheral blood monocyte cells. We induced chicken dendritic cells by incubating mononuclear cells with a 100 ng mL-1 recombinant chicken granulocyte-macrophage colony-stimulating factor and 20 ng mL-1 recombinant chicken IL-4 for total 7 days. The results showed that Se deficiency decreased the expression of cell-surface markers including CD11c, CD40, CD86, and MHC II. Furthermore, we analyzed the cytokine profiles using real-time quantitative PCR and ELISA. The results indicated that Se deficiency inhibited the expression of selenoproteins and changed the secretion of IL-10, IL-12p40, and IFN-γ. Additionally, Se deficiency weakened the ability of dendritic cells to stimulate the proliferation of mixed allogeneic lymphocytes. In conclusion, Se deficiency suppressed the differentiation and immune function of chicken dendritic cells by down-regulating the expression of CD11c, CD40, CD86, MHC II, and selenoproteins. The result also showed that the Th1/Th2 imbalance was induced by enhancing the secretion of Th1-type cytokine IL-12p40 and IFN-γ and reducing that of Th2-type cytokine IL-10. Our findings contribute to understanding the mechanism of Se deficiency in the differentiation and immune function of chicken dendritic cells.

Toxicity of selenium nanoparticles in male Sprague-Dawley rats at supranutritional and nonlethal levels

AIMS

We synthesized selenium nanoparticles (SeNPs) and examined their toxicity in male rats at supranutritional and nonlethal doses.

MAIN METHODS

The SeNPs were administered daily by gavage at doses of 0.0, 0.2, 0.4, 0.8, 2.0, 4.0, or 8.0 mg Se/kg-body weight (bw) in 2 mL of 0.9% saline for 14 consecutive days. Body weight, viscera index and blood biochemical parameters were measured. Histopathological examination was performed on selected tissues, and liver tissue was examined for apoptotic cells.

KEY FINDINGS

Body weight decreased considerably in the groups given doses of 2.0, 4.0, and 8.0 mg Se/kg-bw, but increased in the groups given doses of 0.2 and 0.4 mg Se/kg-bw. The viscera index and some biochemical parameters in the 8.0 mg Se/kg-bw group differed from the control group. Lesions in the liver, kidneys, lungs, and thymus, and apoptotic liver cells were observed in the 4.0 and 8.0 mg Se/kg-bw groups.

SIGNIFICANCE

From this study, we conclude that supranutritional levels of SeNPs had no obvious toxic effects in rats, and could be used as potential candidates for cancer chemoprevention, although doses greater than 2.0 mg Se/kg-bw induced chronic toxicity.

Effects of sodium selenite on aflatoxin B1-induced decrease of ileal IgA+ cell numbers and immunoglobulin contents in broilers

This study was aimed to assess the protective effect of sodium selenite on the ileum mucosal immunologic injury induced by AFB1. One hundred eighty-one-day-old healthy male Avian broilers were divided into four groups of three replicates and 15 birds per replicate and fed with basal diet (control group), 0.3 mg/kg AFB1 (AFB1 group), 0.4 mg/kg Se (+Se group), and 0.3 mg/kg AFB1 + 0.4 mg/kg Se (AFB1 + Se group) respectively. The numbers of IgA(+) cells of ileum were determined by immunohistochemistry as well as the contents of sIgA, IgA, IgG, and IgM in the mucosa of ileum by ELISA. Compared with those in the control group, the numbers of IgA(+) cells as well as the sIgA, IgA, IgG, and IgM contents were decreased in the AFB1 group. However, compared with those in the AFB1 group, the numbers of IgA(+) cells as well as the sIgA, IgA, IgG, and IgM contents were increased in the AFB1 + Se group, and these data had no difference between AFB1 + Se group and control group. It was concluded that 0.3 mg/kg AFB1 could reduce the humoral immune function of the ileum mucosa, but 0.4 mg/kg supplemented dietary selenium could protect the mucosal humoral immune function from AFB1-induced impairment.

Effects of sodium selenite on aflatoxin B1-induced decrease of ileac T cell and the mRNA contents of IL-2, IL-6, and TNF-α in broilers

The aim of this work was to assess the protective effect of sodium selenite on the ileum mucosal immunologic toxicity induced by aflatoxin B1 (AFB1). One hundred and eighty one-day-old healthy male avian broilers were divided into four groups of three replicates and 15 birds per replicate and fed with basal diet (control group), 0.3 mg/kg AFB1 (AFB1 group), 0.4 mg/kg Se (+Se group), and 0.3 mg/kg AFB1+0.4 mg/kg Se (AFB1+Se group), respectively. The ileac T-cell subsets were determined by the methods of flow cytometry (FCM), and the mRNA contents of interleukin-2 (IL-2), interleukin-6(IL-6), and tumor necrosis factor-alpha (TNF-α) by quantitative real-time PCR. Compared with those in control group, the percentages of CD3+, CD3+CD4+, CD3+CD8+ intraepithelial lymphocytes (IELs) and LPLs, the CD4+/CD8+ ratio of IELs, and the mRNA contents of IL-2, IL-6, and TNF-α were decreased in AFB1 group. However, compared with those in AFB1 group, these parameters of AFB1+Se group were increased to be close to those in control group. It was concluded that 0.3 mg/kg AFB1 could reduce the cellular immune function of the ileum mucosa, but 0.4 mg/kg supplemented dietary selenium showed protective effects on AFB1-induced immunologic injury.

Dietary selenium supplementation and whole blood gene expression in healthy North American men

Selenium (Se) is a trace nutrient required in microgram amounts, with a recommended dietary allowance of 55 μg/day in humans. The nutritional functions of Se are performed by a group of 25 selenoproteins containing the unusual amino acid selenocysteine at their active sites. The selenoproteins with known activities are oxidation-reduction enzymes with roles in antioxidant protection, redox homeostasis and signaling, and thyroid hormone metabolism. Both deficiencies and excesses of Se are associated with impaired innate and adaptive immune responses. We supplemented 16 healthy men for 1 year with 300 μg Se/day as high-Se yeast or placebo yeast and measured whole blood gene expression with DNA microarrays before and after supplementation. Protein phosphorylation was the main biological process in common among the Se-responsive genes, which included a prominent cluster of protein kinases, suggesting that protein phosphorylation in leukocytes is sensitive to Se supplementation. We found highly ranked clusters of genes associated with RNA processing and protein transport, suggesting that dietary Se may regulate protein expression in leukocytes at both the posttranscriptional and posttranslational levels. The main functional pathway affected by Se supplementation was FAS apoptosis signaling, and expression of genes associated with T cell and natural killer cell cytotoxicity was increased. At the same time, the numbers of circulating natural killer and T cells expressing activation markers decreased. These changes are consistent with an anti-inflammatory effect of Se supplementation exerted through regulation of protein phosphorylation.

Protective role of sodium selenite on histopathological lesions, decreased T-cell subsets and increased apoptosis of thymus in broilers intoxicated with aflatoxin B₁

For evaluating the ability of selenium (Se) in counteracting the adverse effects of aflatoxin B₁ (AFB₁), two hundred 1-day-old male Avian broilers, divided into five groups, were fed with basal diet (control group), 0.3 mg/kg AFB₁ (AFB₁ group), 0.3 mg/kg AFB₁+0.2 mg/kg Se (+Se group I), 0.3mg/kg AFB₁+0.4 mg/kg Se (+Se group II) and 0.3mg/kg AFB₁+0.6 mg/kg Se (+Se group III), respectively. Compared with control group, the decreased relative weight of thymus and percentages of mature thymocytes, congestion in medulla and much debris in cortex of thymus, and the increased apoptotic thymocytes were observed in AFB1 group. However, supplied dietary sodium selenite could increase the relative weight of thymus and percentages of mature thymocytes, and alleviate histopathological lesions. Compared with AFB1 group, the percentages of apoptotic thymocytes detected by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling method and flow cytometry method in three +Se groups were decreased, the expression of Caspase-3 and Bax, through quantitative real-time PCR and immunohistochemical method, in three +Se groups were decreased, while the expression of Bcl-2 was increased. The results indicate that sodium selenite supplied in the diet, through a mechanism of apoptosis regulation, may ameliorated AFB₁-induced lesions of thymus and accordingly improve the impaired cellular immune function.

Excess dietary sodium selenite alters apoptotic population and oxidative stress markers of spleens in broilers

Three hundred 1-day-old avian broilers were fed on a basic diet (0.2 mg/kg selenium) or the same diet amended to contain 1, 5, 10, and 15 mg/kg selenium supplied as sodium selenite (n = 60/group). In comparison with those of 0.2 mg/kg selenium group, the percentages of annexin V-positive splenocytes were increased in 5, 10, and 15 mg/kg selenium groups. TUNEL assay revealed that apoptotic cells with brown-stained nuclei distributed within the red pulp and white pulp of the spleens with increased frequency of occurrence in 10 and 15 mg/kg selenium groups in comparison with that of 0.2 mg/kg Se group. Sodium selenite-induced oxidative stress in spleens of chickens was evidenced by decrease in glutathione peroxidase, superoxide dismutase, and catalase activities and increase in malondialdehyde contents. The results indicate that excess dietary selenium in the range of 5-15 mg/kg of feed causes oxidative stress, which may be mainly responsible for the increased apoptosis of splenocytes in chickens.