Selenium and the control of thyroid hormone metabolism

The Impact of Sodium Selenite and Seleno-L-Methionine on Stress Erythropoiesis in a Murine Model of Hemolytic Anemia

BACKGROUND

Selenium (Se) is an essential trace element that exerts most biological activities through selenoproteins. Dietary selenium is a key regulator of red cell homeostasis and stress erythropoiesis. However, it is unknown whether the form and increasing doses of Se supplementation in the diet impact stress erythropoiesis under anemic conditions.

OBJECTIVES

If inorganic (sodium selenite; Na2SeO3) or organic [seleno-L-methionine (Se-Met)] forms of Se in different amounts (deficient, adequate, supplemented, and supranutritional) support stress erythropoiesis in anemic mice.

METHODS

Three-wk-old male C57BL/6 mice were subjected to graded amounts of Se in the form of <0.01 mg/kg Se [Se-deficiency (Se-D)], 0.1 mg/kg Na2SeO3 (adequacy), 0.4 mg/kg Na2SeO3 (supplemented), 3 mg/kg Na2SeO3 (supranutritional), 0.4 mg/kg Se-Met (supplemented), or 3 mg/kg Se-Met (supranutritional), for 10-12 wk before intraperitoneal phenylhydrazine administration to induce hemolytic anemia. Following 3 d of phenylhydrazine injection, spleen and blood samples were used to assess the impact of form and graded amounts of Se in the diet on stress erythropoiesis.

RESULTS

Phenotypic parameters showed that supplementing the diet with Se in the form of Na2SeO3 or Se-Met alleviated hemolytic anemia and promoted stress erythropoiesis by supporting the formation of erythroblastic islands. Se-Met at 0.4 mg/kg enhanced erythroid progenitor differentiation by 2-fold compared with Se-D, while Na2SeO3 at 0.4 mg/kg and 3 mg/kg significantly (P < 0.05) aided monocyte recruitment and macrophage differentiation within erythroblastic islands. Additionally, 3 mg/kg of Se-Met triggered a stronger inflammatory response than the same dose of Na2SeO3. CONCLUSIONS: While both Se-Met and Na2SeO3 effectively aid in stress erythropoiesis, Na2SeO3 supplementation effectively support stress erythropoiesis with a minimal inflammatory response, while Se-Met at supranutritional dosage lead to increased inflammation despite its support for stress erythropoiesis. These results indicate diverse mechanisms of action of Se on the alleviation of anemia by stress erythropoiesis, which should be considered for further studies to complement existing therapies.

Serum iodine concentration in pregnant women and its association with thyroid function

OBJECTIVE

This study aims to investigate the association of serum iodine concentration (SIC) with thyroid function-associated parameters in pregnant women in mild iodine deficient area, and explore its potential to predict individual iodine nutrition status in pregnant women.

METHODS

A total of 741 pregnant women undergoing prenatal examinations in their second trimester at the Women's Hospital, Zhejiang University School of Medicine, from March 2021 to May 2022 were finally recruited into the study. Venous blood and morning urine were collected. Serum free triiodothyronine (FT3), free thyroxine (FT4), thyro-stimulating hormone (TSH), total thyroxine (TT4), total triiodothyronine (TT3), thyroid peroxidase antibody (TPOAb), thyroglobulin antibody (TgAb), UIC (urinary iodine concentration) and SIC were measured.

RESULTS

The median SIC was 54.44 μg/L. SIC was linearly and positively associated with concentrations of FT4 [ β = 0.10, 95 % CI: (0.07, 0.12), TT4 [ β = 0.29, 95 % CI: (0.26, 0.33), TT3 [ β = 0.14, 95 % CI: (0.09, 0.18). There was an inverted "U" shaped relationship between SIC and FT3. The associations between SIC and thyroid hormones remained robust when participants taking specific drug were excluded.

CONCLUSIONS

SIC is associated with thyroid function-related parameters in pregnant women in their second trimester, indicating that the SIC may have the potential to predict individual iodine nutrition status in pregnant women.

Rapid Determination of Organic and Inorganic Selenium in Poultry Tissues by Internal Extractive Electrospray Ionization Mass Spectrometry

An online reactive internal extraction electrospray ionization (iEESI) method was developed for the rapid determination of organic and inorganic speciation information for selenium in poultry tissue samples without complex sample pretreatment. The addition of citric acid as a reducing agent to the internal extraction solvent of methanol/acetic acid (99:1, V/V) for iEESI resulted in the reduction of selenate in the sample to selenite, accompanied by the production of malic acid as an oxidation product. The quantitative analysis of selenate was conducted by using malic acid. By addition of o-phenylenediamine (OPD) to the extractant, inorganic selenium including selenite and selenite reduced from selenate was immediately extracted and converted into 1,3-dihydro-2,1,3-benzoselenadiazole after an in situ reaction. The methanol in the reagent extracted organic selenium compounds from the samples, enabling a rapid quantitative analysis of organic and inorganic selenium in chicken tissue. The concentrations of selenomethionine (SeMet), l-selenocystine (SeCys(2)), selenite, and selenate in different tissue samples were examined, showing strong linearity in the range of 1.00-100.00 μg/kg with the limit of detection (LOD) ranging from 0.36 to 0.84 μg/kg. The results were validated by two conventional methods with an accuracy of 84.2-107.6%. The quantitative analysis of three chicken visceral samples revealed that the highest concentration of organic selenium was present in chicken livers, while the highest concentration of inorganic selenium was observed in gizzards. The findings may provide a reliable method for studying selenium metabolism pathways in organisms.

Selenium in cancer management: exploring the therapeutic potential

Selenium (Se) is important and plays significant roles in many biological processes or physiological activities. Prolonged selenium deficiency has been conclusively linked to an elevated risk of various diseases, including but not limited to cancer, cardiovascular disease, inflammatory bowel disease, Keshan disease, and acquired immunodeficiency syndrome. The intricate relationship between selenium status and health outcomes is believed to be characterized by a non-linear U-shaped dose-response curve. This review delves into the significance of maintaining optimal selenium levels and the detrimental effects that can arise from selenium deficiency. Of particular interest is the important role that selenium plays in both prevention and treatment of cancer. Finally, this review also explores the diverse classes of selenium entities, encompassing selenoproteins, selenium compounds and selenium nanoparticles, while examining the mechanisms and molecular targets of their anticancer efficacy.

Association between multipollutant exposure and thyroid hormones in elderly people: A cross-sectional study in China

Environmental chemicals have been indicated to cause disruption of thyroid homeostasis in human populations. However, previous studies mostly focused on single group of chemicals. Herein, we investigate the independent and combined effects of multiple pollutants on thyroid homeostasis, including thyroid-stimulating hormone (TSH), total and free thyroxine (tT4 and fT4) and total and free triiodothyronine (tT3 and fT3) in elderly people. These environmental pollutants (n = 144) are from ten categories, including phenols, parabens, perfluoroalkyl substances (PFASs), polychlorinated biphenyls (PCBs), phthalate esters (PAEs), polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OCPs), organophosphate pesticides (OPPs), synthetic pyrethroids (SPs), herbicides, and metals. Few studies have evaluated the health risks of these 144 chemicals, especially their joint effects. In single-pollutant evaluations, multiple linear regression (MLR) models were used to estimate the independent associations between multiple exposures and thyroid biomarkers. In multi-pollutant evaluations, elastic net regression and Bayesian kernel machine regression (BKMR) models were used to estimate the combined associations. The MLR models showed that 41 chemicals were significantly related to THs levels. BKMR models revealed the most important chemical groups: metals for TSH, PAHs, SPs and PCBs for tT4, herbicides and SPs for tT3. This study will contribute to the understanding of multipollutant exposure and help prioritize specific chemical groups related to thyroid hormone disruption.

Assessment of Individual and Mixed Effects of Six Minerals on Thyroid Hormones in Chinese Pregnant Women

The biosynthesis of thyroid hormones is essential for brain and neurological development. It requires iodine as a key component but is also influenced by other nutrients. Evidence for the combined nutrient status in relation to thyroid hormones during pregnancy is limited. We aimed to investigate the joint associations of iodine, selenium, zinc, calcium, magnesium and iron with maternal thyroid functions in 489 pregnant women from Hangzhou, China. Serum levels of six essential minerals and thyroid function parameters were measured during the first antenatal visit. Linear regression, quantile g-computation and Bayesian kernel machine regression were used to explore the individual and joint relationships between the six minerals and thyroid hormones. Linear regression analyses revealed that calcium was positively associated with free triiodothyronine (FT3). Zinc was positively associated with free thyroxine (FT4). Iodine was negatively associated with thyroid-stimulating hormone (TSH) and positively associated with FT3 and FT4. The quantile g-computation and BKMR models indicated that the joint nutrient concentration was negatively associated with TSH and positively associated with FT3 and FT4. Among the six minerals, iodine contributed most to thyroid function. The findings suggested that maintaining the appropriate concentration of minerals, either as individuals or a mixture, is important for thyroid health during pregnancy.

Efficacy of selenium supplementation for mild-to-moderate Graves' ophthalmopathy in a selenium-sufficient area (SeGOSS trial): study protocol for a phase III, multicenter, open-label, randomized, controlled intervention trial

BACKGROUND

The therapeutic effect of selenium has been demonstrated in mild Graves' ophthalmopathy (GO) in a European region where selenium status is suboptimal. However, there is a lack of evidence to support selenium use in selenium-sufficient areas. The aim of this study is to evaluate the therapeutic effect of selenium in mild-to-moderate GO in selenium-sufficient South Korea.

METHODS

The SeGOSS trial is a multicenter, prospective, randomized, open-label trial in South Korea. Eighty-four patients aged 19 years or older with mild-to-moderate GO will be randomized to receive either vitamin B complex alone or vitamin B complex with selenium for 6 months with three monthly follow-up visits. The primary outcome is comparison of the improvement in quality of life at 6 months from baseline between the control and selenium groups. The secondary outcomes are intergroup differences in changes in quality of life at 3 months, clinical activity of GO at 3 and 6 months, thyroid autoantibody titers at 3 and 6 months, and the response rate at 3 and 6 months from baseline. Quality of life will be measured by questionnaire for patients with GO, and the clinical activity of GO will be evaluated by the clinical activity score (CAS). A positive response is defined as either changes in the CAS < 0 or the changes in the GO-QOL score ≥ 6.

DISCUSSION

The SeGOSS study will evaluate the therapeutic potential of selenium for mild-to-moderate GO in a selenium-sufficient area and provide support in tailoring better treatment for GO.

TRIAL REGISTRATION

KCT0004040. Retrospectively registered on 5 June 2019. https://cris.nih.go.kr/cris/search/detailSearch.do/14160 .

Selenium, Iodine and Iron-Essential Trace Elements for Thyroid Hormone Synthesis and Metabolism

The adequate availability and metabolism of three essential trace elements, iodine, selenium and iron, provide the basic requirements for the function and action of the thyroid hormone system in humans, vertebrate animals and their evolutionary precursors. Selenocysteine-containing proteins convey both cellular protection along with H₂O₂-dependent biosynthesis and the deiodinase-mediated (in-)activation of thyroid hormones, which is critical for their receptor-mediated mechanism of cellular action. Disbalances between the thyroidal content of these elements challenge the negative feedback regulation of the hypothalamus-pituitary-thyroid periphery axis, causing or facilitating common diseases related to disturbed thyroid hormone status such as autoimmune thyroid disease and metabolic disorders. Iodide is accumulated by the sodium-iodide-symporter NIS, and oxidized and incorporated into thyroglobulin by the hemoprotein thyroperoxidase, which requires local H₂O₂ as cofactor. The latter is generated by the dual oxidase system organized as 'thyroxisome' at the surface of the apical membrane facing the colloidal lumen of the thyroid follicles. Various selenoproteins expressed in thyrocytes defend the follicular structure and function against life-long exposure to H₂O₂ and reactive oxygen species derived therefrom. The pituitary hormone thyrotropin (TSH) stimulates all processes required for thyroid hormone synthesis and secretion and regulates thyrocyte growth, differentiation and function. Worldwide deficiencies of nutritional iodine, selenium and iron supply and the resulting endemic diseases are preventable with educational, societal and political measures.

Relationship between selenium status, selenoproteins and COVID-19 and other inflammatory diseases: A critical review

The antioxidant effects of selenium as a component of selenoproteins has been thought to modulate host immunity and viral pathogenesis. Accordingly, the association of low dietary selenium status with inflammatory and immunodeficiency has been reported in the literature; however, the causal role of selenium deficiency in chronic inflammatory diseases and viral infection is still undefined. The COVID-19, characterized by acute respiratory syndrome and caused by the novel coronavirus 2, SARS-CoV-2, has infected millions of individuals worldwide since late 2019. The severity and mortality from COVID-19 have been associated with several factor, including age, sex and selenium deficiency. However, available data on selenium status and COVID-19 are limited, and a possible causative role for selenium deficiency in COVID-19 severity has yet to be fully addressed. In this context, we review the relationship between selenium, selenoproteins, COVID-19, immune and inflammatory responses, viral infection, and aging. Regardless of the role of selenium in immune and inflammatory responses, we emphasize that selenium supplementation should be indicated after a selenium deficiency be detected, particularly, in view of the critical role played by selenoproteins in human health. In addition, the levels of selenium should be monitored after the start of supplementation and discontinued as soon as normal levels are reached. Periodic assessment of selenium levels after supplementation is a critical issue to avoid over production of toxic metabolites of selenide because under normal conditions, selenoproteins attain saturated expression levels that limits their potential deleterious metabolic effects.

Maternal supplementation of nano-selenium in a plant-based diet improves antioxidant competence of female Arabian yellowfin sea bream (Acanthopagrus arabicus) breeders and their progeny

Antioxidants such as selenium (Se) play vital roles in reproduction success and larval development in fish. A three-month feeding experiment was conducted to examine the impact of enriching a plant-based diet (60% of fishmeal was substituted with a blend of plant ingredients) with nano-selenium (nano-Se) on antioxidant metabolism in female brooders and the progeny of Arabian yellowfin sea bream (Acanthopagrus arabicus). At this point, the plant-based diet was supplemented with graded levels of nano-Se at 0, 0.5, 1, 2, and 4 mg/Kg diet. Moreover, a fishmeal-based diet served as a positive control (FMD-Control). Broodfish were randomly distributed into eighteen 10 m³ rectangular concrete tanks (8 males and 8 females in each tank). Each experimental diet was subjected to three replications. Selenium retention increased in the serum, liver, ovary, eggs, and three-day larvae with increasing dietary nano-Se levels (P < 0.05). Supplementing the plant-based diet with 2-4 mg nano-Se/Kg significantly enhanced normal embryogenesis, fertilization, hatching, and larval survival rates. Generally, fish fed on plant-based diets with lower nano-Se supplementation (0-0.5 mg/Kg) had higher catalase and superoxide dismutase activities in the liver, ovaries, eggs, and larvae compared to the other groups. Glutathione peroxidase activity and total antioxidant capacity markedly increased, whereas lipid peroxidation decreased in the liver, ovary, serum, eggs, and progeny of broodfish fed with nano-Se supplemented diets (P < 0.05). In conclusion, supplementation of 2-4 mg nano-Se /Kg in a plan-based feed is recommended for the improvement of antioxidant defense in female A. arabicus brooders and their progeny.

Selenocompounds and Sepsis-Redox Bypass Hypothesis: Part B-Selenocompounds in the Management of Early Sepsis

Significance: Endothelial barrier damage, which is in part caused by excess production of reactive oxygen, halogen and nitrogen species (ROHNS), especially peroxynitrite (ONOO^-), is a major event in early sepsis and, with leukocyte hyperactivation, part of the generalized dysregulated immune response to infection, which may even become a complex maladaptive state. Selenoenzymes have major antioxidant functions. Their synthesis is related to the need to limit deleterious oxidant redox cycling by small selenocompounds, which may be of therapeutic cytotoxic interest. Plasma selenoprotein-P is crucial for selenium transport from the liver to the tissues and for antioxidant endothelial protection, especially against ONOO^-. Above micromolar concentrations, sodium selenite (Na₂SeO₃) becomes cytotoxic, with a lower cytotoxicity threshold in activated cells, which has led to cancer research. Recent Advances: Plasma selenium (<2% of total body selenium) is mainly contained in selenoprotein-P, and concentrations decrease rapidly in the early phase of sepsis, because of increased selenoprotein-P binding and downregulation of hepatic synthesis and excretion. At low concentrations, Na₂SeO₃ acts as a selenium donor, favoring selenoprotein-P synthesis in physiology, but probably not in the acute phase of sepsis. Critical Issues: The cytotoxic effects of Na₂SeO₃ against hyperactivated leukocytes, especially the most immature forms that liberate ROHNS, may be beneficial, but they may also be harmful for activated endothelial cells. Endothelial protection against ROHNS by selenoprotein-P may reduce Na₂SeO₃ toxicity, which is increased in sepsis. Future Direction: The combination of selenoprotein-P for endothelial protection and the cytotoxic effects of Na₂SeO₃ against hyperactivated leukocytes may be a promising intervention for early sepsis. Antioxid. Redox Signal. 37, 998-1029.

Natural Compounds and Products from an Anti-Aging Perspective

Aging is a very complex process that is accompanied by a degenerative impairment in many of the major functions of the human body over time. This inevitable process is influenced by hereditary factors, lifestyle, and environmental influences such as xenobiotic pollution, infectious agents, UV radiation, diet-borne toxins, and so on. Many external and internal signs and symptoms are related with the aging process and senescence, including skin dryness and wrinkles, atherosclerosis, diabetes, neurodegenerative disorders, cancer, etc. Oxidative stress, a consequence of the imbalance between pro- and antioxidants, is one of the main provoking factors causing aging-related damages and concerns, due to the generation of highly reactive byproducts such as reactive oxygen and nitrogen species during the metabolism, which result in cellular damage and apoptosis. Antioxidants can prevent these processes and extend healthy longevity due to the ability to inhibit the formation of free radicals or interrupt their propagation, thereby lowering the level of oxidative stress. This review focuses on supporting the antioxidant system of the organism by balancing the diet through the consumption of the necessary amount of natural ingredients, including vitamins, minerals, polyunsaturated fatty acids (PUFA), essential amino acids, probiotics, plants' fibers, nutritional supplements, polyphenols, some phytoextracts, and drinking water.

Dietary selenium intake and thyroid cancer risk in postmenopausal women

OBJECTIVE

It has been suggested that higher selenium intake and consumption of supplements protect against several cancers. To our knowledge, epidemiologic evidence is rare and inconsistent on the association of selenium level and the risk for thyroid cancer. Therefore, the aim of this study was to examine the association between selenium intake and thyroid cancer risk in postmenopausal women using the Women's Health Initiative (WHI) database.

METHODS

The WHI recruited 161 808 postmenopausal women 50 to 79 y of age between September 1, 1993 and December 31, 1998. The present study included 147 348 women 63.15 y of age (SD = 7.21) at baseline. The main exposure was baseline total selenium intake including dietary selenium measured by food frequency questionnaire (FFQ) and supplemental selenium. The outcome was thyroid cancer, which was adjudicated by trained physicians. Cox proportional hazard models were used to analyze the association.

RESULTS

During a mean follow-up of 16.4 y until September 30, 2020, 442 thyroid cancer cases were identified. There was no significant association between total selenium intake and thyroid cancer risk after adjusting for multiple covariates (highest versus lowest quartile: hazard ratio [HR], 0.88; 95% confidence interval [CI], 0.60-1.29). Association between total selenium intake and the risk for papillary thyroid cancer was also not significant (highest versus lowest quartile: HR, 1.02; 95% CI, 0.66-1.52).

CONCLUSIONS

The present data did not support that either total or dietary selenium intake was associated with the risk for thyroid cancer or the papillary subtype in postmenopausal women ages 50 to 79 y in the United States.

Relationship between Serum Levels of Selenium and Thyroid Cancer: A Systematic Review and Meta-Analysis

Thyroid cancer is one of the most malignant tumors and a serious threat to human health. Selenium (Se) is an essential trace element that is critical for thyroid function. Since the relationship between Se and thyroid cancer remains unclear, a meta-analysis was performed to clarify the relationship. A total of five databases (PubMed, Web of Science, Scopus, Embase and Cochrane library) were searched for case-control studies and cohort studies on serum levels of Se and thyroid cancer published up to 13 July 2022. Seven articles consisting of 10 case-control studies and comprised of 2,205 subjects met the inclusion criteria for meta-analysis. From the 10 selected studies, pooled analysis indicated that thyroid cancer patients had lower serum levels of Se than healthy controls [standardized mean difference = -1.25, 95% confidence interval = (-2.07, -0.44), P = 0.003]. Our meta-analysis supports a significant relationship between serum levels of Se and thyroid cancer.

Function and regulation of GPX4 in the development and progression of fibrotic disease

Fibrosis is a common feature of fibrotic diseases that poses a serious threat to global health due to high morbidity and mortality in developing countries. There exist some chemical compounds and biomolecules associated with the development of fibrosis, including cytokines, hormones, and enzymes. Among them, glutathione peroxidase 4 (GPX4), as a selenoprotein antioxidant enzyme, is widely found in the embryo, testis, brain, liver, heart, and photoreceptor cells. Moreover, it is shown that GPX4 elicits diverse biological functions by suppressing phospholipid hydroperoxide at the expense of decreased glutathione (GSH), including loss of neurons, autophagy, cell repair, inflammation, ferroptosis, apoptosis, and oxidative stress. Interestingly, these processes are intimately related to the occurrence of fibrotic disease. Recently, GPX4 has been reported to exhibit a decline in fibrotic disease and inhibit fibrosis, suggesting that alterations of GPX4 can change the course or dictate the outcome of fibrotic disease. In this review, we summarize the role and underlying mechanisms of GPX4 in fibrosis diseases such as lung fibrosis, liver fibrosis, kidney fibrosis, cardiac fibrosis, and myelofibrosis.

The Antioxidant Role of Selenium via GPx1 and GPx4 in LPS-Induced Oxidative Stress in Bovine Endometrial Cells

This study investigated the antioxidant role of selenium (Se) in the form of selenomethionine (SLM) in LPS-induced oxidative stress via the glutathione peroxidase (GPx) enzymes and the Nrf2/HO-1 transcription factor. The impact of serum supplementation in culture media on GPxs was also studied. The bovine uterus is constantly exposed to exogenous pathogens postpartum, and the endometrium is the first contact against bacteria invasion. Endometritis is an inflammation of the endometrium and is brought about by bacterial lipopolysaccharide capable of inducing oxidative stress. The BEND cells were supplemented at the point of seeding with the following SLM concentrations 0, 100, 500, and 1000 nM for 48 h. BEND cells, cultured with or without SLM (100 nM), were initially incubated for 48 h, and then, we serum starved the SLM group for 24, 48, and 72 h. Similarly, an assay involving serum volume (0, 2, 5, and 10%) supplementation in culture media (v/v) with or without SLM (100 nM) was performed for 48 h. The BEND cells were also seeded into four experimental groups and cultured for an initial 48 h as follows: control, LPS (20 μg/mL), SLM (100 nM), and SLM + LPS groups followed by 6-h LPS treatment. The role of SLM in modulating the expressions of GPx1 and GPx4 and the Nrf2 transcription factor-related genes was assessed using qRT-PCR and Western blot techniques. The results showed serum starvation in the presence of SLM supplementation decreased the expression of GPx1 enzyme but increased GPx4 compared to the control. The addition of SLM to cell culture media in an FBS limiting condition improved the expressions of both GPx1 and GPx4. SLM supplementation promoted GPx enzymes' expressions in a serum-free media (0%) and at 2% FBS in media. However, it did not improve their expressions at 10% FBS in media than the untreated groups. Together, our data show the protective role of Se by regulating the expressions of GPx1 and GPx4 enzymes in BEND cells. It also shows that SLM promoted the expression of Nrf2 transcription factor-related genes at both the mRNA and protein levels in BEND cells during LPS stimulation.

Selected Essential and Toxic Chemical Elements in Hypothyroidism-A Literature Review (2001-2021)

Thyroid hormones are known for controlling metabolism of lipids, carbohydrates, proteins, minerals, and electrolytes and for regulating body temperature. Normal thyroid status depends on the chemical/elemental composition of body fluids and tissues, which changes depending on physiological state, lifestyle and environment. A deficiency or excess of certain essential chemical elements (selenium, zinc, copper, iron or fluorine) or exposure to toxic (cadmium or lead) or potentially toxic elements (manganese or chromium) interacts with thyroid hormone synthesis and may disturb thyroid homeostasis. In our review, accessible databases (Scopus, PubMed and Web of Science) were searched for articles from 2001-2021 on the influence of selected chemical elements on the development of hypothyroidism. Our review adopted some of the strengths of a systematic review. After non-eligible reports were rejected, 29 remaining articles were reviewed. The review found that disruption of the physiological levels of elements in the body adversely affects the functioning of cells and tissues, which can lead to the development of disease.

Emerging roles for non-selenium containing ER-resident glutathione peroxidases in cell signaling and disease

Maintenance of cellular redox control is pivotal for normal cellular functions and cell fate decisions including cell death. Among the key cellular redox systems in mammals, the glutathione peroxidase (GPX) family of proteins is the largest conferring multifaceted functions and affecting virtually all cellular processes. The endoplasmic reticulum (ER)-resident GPXs, designated as GPX7 and GPX8, are the most recently added members of this family of enzymes. Recent studies have provided exciting insights how both enzymes support critical processes of the ER including oxidative protein folding, maintenance of ER redox control by eliminating H₂O₂, and preventing palmitic acid-induced lipotoxicity. Consequently, numerous pathological conditions, such as neurodegeneration, cancer and metabolic diseases have been linked with altered GPX7 and GPX8 expression. Studies in mice have demonstrated that loss of GPX7 leads to increased differentiation of preadipocytes, increased tumorigenesis and shortened lifespan. By contrast, GPX8 deficiency in mice results in enhanced caspase-4/11 activation and increased endotoxic shock in colitis model. With the increasing recognition that both types of enzymes are dysregulated in various tumor entities in man, we deem a review of the emerging roles played by GPX7 and GPX8 in health and disease development timely and appropriate.

[Iodine-rich thermal water in cure and rehabilitation from the perspective of the thyroid gland]

Bei einzelnen Schilddrüsenerkrankungen (Immunthyreopathie Morbus Basedow, Immunthyreopathie Hashimoto, Struma mit Autonomie) sollte eine übermäßige Jodzufuhr vermieden werden. Betreffend alimentärer Jodzufuhr gibt es dazu reichliches Informationsmaterial. Kuranwendungen werden zu einem breiten Indikationsspektrum eingesetzt und tragen einen wichtigen Teil zur Therapie gerade chronisch degenerativen Erkrankungen, zur Rehabilitation nach Traumen oder Tumorerkrankungen bei. Eine Jodzufuhr ist auch bei Kuranwendungen mit jodhaltigem Thermalwasser möglich, das Ausmaß der Jodzufuhr ist dabei abhängig von der Applikationsform und der Expositionsdauer. Informationsmaterial dazu ist nur spärlich in der Literatur zu finden. Der Artikel betrachtet jodhaltige Kuranwendungen aus thyreologischer Sicht im Spannungsfeld von positiven und möglichen negativen Auswirkungen einer jodhaltigen Kuranwendung. Neben einem Einblick in die Physiologie und Pathophysiologie des Jodstoffwechsels und Auswirkungen auf einzelne Schilddrüsenerkrankungen wird die Intensität einer Jodaufnahme bei unterschiedlichen Kuranwendungen dargestellt. Eine Übersicht von Kurorten/Thermen mit jodhaltigem Wasser in Österreich und seinen Nachbarstaaten ergänzt von einem Algorithmus zur Selektion von Patienten für eine Kur in Kurorten mit jodhaltigem Wasser wird präsentiert, um mögliche negative jodinduzierte Schilddrüsenfehlfunktionen schon vor Kurantritt zu vermeiden. Dem klinisch tätigen Arzt wird damit eine Unterstützung in der Entscheidungsfindung bei der Auswahl bzw. Ablehnung einer jodhaltigen Kuranwendung für seine Patienten zur Verfügung gestellt.

Selenium and selenoproteins in viral infection with potential relevance to COVID-19

Selenium is a trace element essential to human health largely because of its incorporation into selenoproteins that have a wide range of protective functions. Selenium has an ongoing history of reducing the incidence and severity of various viral infections; for example, a German study found selenium status to be significantly higher in serum samples from surviving than non-surviving COVID-19 patients. Furthermore, a significant, positive, linear association was found between the cure rate of Chinese patients with COVID-19 and regional selenium status. Moreover, the cure rate continued to rise beyond the selenium intake required to optimise selenoproteins, suggesting that selenoproteins are probably not the whole story. Nonetheless, the significantly reduced expression of a number of selenoproteins, including those involved in controlling ER stress, along with increased expression of IL-6 in SARS-CoV-2 infected cells in culture suggests a potential link between reduced selenoprotein expression and COVID-19-associated inflammation. In this comprehensive review, we describe the history of selenium in viral infections and then go on to assess the potential benefits of adequate and even supra-nutritional selenium status. We discuss the indispensable function of the selenoproteins in coordinating a successful immune response and follow by reviewing cytokine excess, a key mediator of morbidity and mortality in COVID-19, and its relationship to selenium status. We comment on the fact that the synthetic redox-active selenium compound, ebselen, has been found experimentally to be a strong inhibitor of the main SARS-CoV-2 protease that enables viral maturation within the host. That finding suggests that redox-active selenium species formed at high selenium intake might hypothetically inhibit SARS-CoV-2 proteases. We consider the tactics that SARS-CoV-2 could employ to evade an adequate host response by interfering with the human selenoprotein system. Recognition of the myriad mechanisms by which selenium might potentially benefit COVID-19 patients provides a rationale for randomised, controlled trials of selenium supplementation in SARS-CoV-2 infection.

Association Between Thyroid Hormone Status and Trace Elements in Serum of Patients with Nodular Goiter

The present study investigated the status of calcium and magnesium as well as essential trace elements including iodine, selenium, copper, iron, and zinc in adults residing in the Zhytomyr region of Ukraine. In addition, the relative risk of goiter occurrence was evaluated. In this comparative study, 40 adults without goiter (control group) and 16 adults with diagnosed nodular goiter (NG) were examined. Inductively coupled plasma optical emission spectrometry (ICP-OES) was used for the measurements of Mg, Ca, Se, Zn, Cu, and Fe in serum of patients with NG and control group. Patients with nodular goiter had lower serum values of Ca, Mg, Se, Cu, Fe, and Zn than those in the control group. The presence of mild iodine deficiency was evident in both groups with the median urinary iodine excretion (UIE) 80.5 μg/L in the control group and 64.5 μg/L in goiter group. There was a positive association between goiter presence and low concentration of Ca in serum (odds ratio (OR) = 2.29 (1.26-3.55), p < 0.05) in the NG group. High relative risk of goiter was observed at low concentrations of magnesium (OR = 3.33 (1.39-7.62), p < 0.05) and selenium (OR = 1.63, (1.16-1.78), p < 0.05) in comparison with OR values in the control group. Low concentrations of Ca, Mg, Zn, and Se in serum combined with reduced UIE resulted in the highest risk of goiter (OR = 12.5, (2.15-79.42), p < 0.01). This study proved that Thyroglobulin concentration in serum is the reliable indicator of nodular goiter. We also suggest that a combination of low concentrations of Ca, Mg, Zn, Cu, and Se in blood serum, and reduced iodine concentration in urine resulted in the highest risk of nodular goiter development.

Selenium supplementation during pregnancy and lactation promotes metabolic changes in Wistar rats' offspring

Epidemiological and animal studies have demonstrated a strong association between selenium (Se) supplementation and metabolic disorders, we aimed to evaluate whether maternal Se supplementation was able to change metabolic parameters in rats' offspring. Moreover, as Se is a deiodinase (DIO) cofactor, we decided to investigate how thyroid hormones (THs) would be involved in such metabolic changes. Thereby, two groups (n = 6, ~250 g) of female Wistar rats underwent isotonic saline or sodium selenite (1 mg/kg, p.o.) treatments. Although there were no significant differences in body weight between groups, the Se treatment during pregnancy and lactation increased milk intake and the visceral white adipose tissue (WAT) in offspring. The rats whose mothers were treated with Se also presented an improvement in the glucose tolerance test and in the glucose-stimulated insulin secretion. Regarding the lipid metabolism, the Se group had a reduction of triglycerides in the liver and in WAT. These metabolic changes were accompanied by an increase in serum triiodothyronine (T3 ) and in DIO 2 expression in brown adipose tissue (BAT). We further demonstrate an increased expression of peroxisome proliferator-activated receptor-gamma coactivator 1-alpha (PGC-1α) and nuclear respiratory factor-1 (NRF-1) mRNA in the liver. In adulthood offspring, Se supplementation programs thyroid function, glucose homeostasis, and feeding behaviour. Taken together, there is no indication that Se programming causes insulin resistance. Moreover, we conjecture that these metabolic responses are induced by increased thyroxine (T4 ) to T3 conversion by DIO2 in BAT and mediated by altered transcription factors expression associated with oxidative metabolism control in the liver.

A Feedforward Loop within the Thyroid-Brown Fat Axis Facilitates Thermoregulation

Thyroid hormones (TH) control brown adipose tissue (BAT) activation and differentiation, but their subsequent homeostatic response following BAT activation remains obscure. This study aimed to investigate the relationship between cold- and capsinoids-induced BAT activation and TH changes between baseline and 2 hours post-intervention. Nineteen healthy subjects underwent ¹⁸F-fluorodeoxyglucose positron-emission tomography (¹⁸F-FDG PET) and whole-body calorimetry (WBC) after 2 hours of cold exposure (~14.5 °C) or capsinoids ingestion (12 mg) in a crossover design. Standardized uptake values (SUV-mean) of the region of interest and energy expenditure (EE) were measured. Plasma free triiodothyronine (FT3), free thyroxine (FT4) and thyroid stimulating hormone (TSH) were measured before and 2 hours after each intervention. Subjects were divided into groups based on the presence (n = 12) or absence (n = 7) of BAT after cold exposure. 12 of 19 subjects were classified as BAT-positive. Subjects with BAT had higher baseline FT3 concentration, baseline FT3/FT4 ratio compared with subjects without BAT. Controlling for body fat percentage, FT3 concentration at baseline was associated with EE change from baseline after cold exposure (P = 0.037) and capsinoids (P = 0.047). Plasma FT4 level significantly increased associated with reciprocal decline in TSH after acute cold exposure and capsinoids independently of subject and treatment status. Circulating FT3 was higher in BAT-positive subjects and was a stronger predictor of EE changes after cold exposure and capsinoids in healthy humans. BAT activation elevates plasma FT4 acutely and may contribute towards augmentation of thermogenesis via a positive feedback response.

Identifying a critical window of maternal metal exposure for maternal and neonatal thyroid function in China: A cohort study

BACKGROUND

China, a developing country, has a particularly serious problem with metal pollution. We evaluated the association of metal exposure during pregnancy with maternal and neonatal thyroid function, and identified the critical window for maternal metal exposure effects on maternal and neonatal thyroid functions.

METHODS

The maternal urinary concentrations of mercury (Hg), cadmium (Cd), arsenic (As) and cesium (Cs) were determined in pregnant women during their first (n = 389) or third (n = 257) trimesters in a prospective cohort from 2014 to 2015 in Nanjing, China, using an inductively coupled plasma mass spectrometry (ICP-MS) instrument. Maternal serum-free thyroxine (FT4) and thyroid-stimulating hormone (TSH) were measured by electrochemiluminescent microparticle immunoassays in the second and third trimesters. Neonatal TSH levels were detected 72 h after birth.

RESULTS

Hg (>0.162 µg/L), Cd (>0.084 µg/L), As (>0.348 µg/L) and Cs (>0.093 µg/L) were detectable in 76.9%, 90.1%, 100% and 100% of maternal urine samples from women in the first trimester of pregnancy. In the multiple adjusted linear regression models, maternal exposures to Hg and Cd in the first trimester were positively associated with maternal TSH levels in the second trimester (P < 0.01, P = 0.02). Moreover, maternal exposures to Cd and Cs in the first trimester were positively associated with neonatal TSH levels (P = 0.04, P = 0.02). In the Bayesian kernel machine regression (BKMR) model, the results were stable and consistent with the linear regression model.

CONCLUSIONS

Maternal exposure to Hg, Cd and Cs in the first trimester was related to TSH levels in mothers and newborns. Efforts to identify maternal and neonatal thyroid disruptors should carefully consider the effects of exposure to these metals.

Disruption of selenium transport and function is a major contributor to mercury toxicity in zebrafish larvae

Mercury is one of the most toxic elements threatening the biosphere, with levels steadily rising due to both natural and human activities. Selenium is an essential micronutrient, required for normal development and functioning of many organisms. While selenium is known to counteract mercury's toxicity under some conditions, to date information about the mercury-selenium relationship is fragmented and often controversial. As part of a systematic study of mercury and selenium interactions, zebrafish (Danio rerio) larvae (a model verterbrate) were exposed to methylmercury chloride or mercuric chloride. The influence of pre- and post-treatment of selenomethionine on the level and distribution of mercury and selenium in the brain and eye sections, as well as on toxicity, were examined. Selenomethionine treatment decreased the amount of maternally transfered mercury in the larval brain. Selenomethionine treatment prior to exposure to mercuric chloride increased both mercury and selenium levels in the brain but decreased their toxic effects. Conversely, methylmercury levels were not changed as a result of selenium pre-treatment, while toxicity was increased. Strikingly, both forms of mercury severely disrupted selenium metabolism, not only by depleting selenium levels due to formation of Hg-Se complexes, but also by blocking selenium transport into and out of tissues, suggesting that restoring normal selenium levels by treating the organism with selenium after mercury exposure may not be possible. Disruption of selenium metabolism by mercury may lead to disruption in function of selenoproteins. Indeed, the production of thyroid hormones by selenoprotein deiodinases was found to be severely impaired as a result of mercury exposure, with selenomethionine not always being a suitable source of selenium to restore thyroid hormone levels.

Maternal Selenium Deficiency in Mice Alters Offspring Glucose Metabolism and Thyroid Status in a Sexually Dimorphic Manner

Selenium is an essential micronutrient commonly deficient in human populations. Selenium deficiency increases the risks of pregnancy complications; however, the long-term impact of selenium deficiency on offspring disease remains unclear. This study investigates the effects of selenium deficiency during pregnancy on offspring metabolic function. Female C57BL/6 mice were allocated to control (>190 μg selenium/kg, n = 8) or low selenium (<50 μg selenium/kg, n = 8) diets prior to mating and throughout gestation. At postnatal day (PN) 170, mice underwent an intraperitoneal glucose tolerance test and were culled at PN180 for biochemical analysis. Mice exposed to selenium deficiency in utero had reduced fasting blood glucose but increased postprandial blood glucose concentrations. Male offspring from selenium-deficient litters had increased plasma insulin levels in conjunction with reduced plasma thyroxine (tetraiodothyronine or T4) concentrations. Conversely, females exposed to selenium deficiency in utero exhibited increased plasma thyroxine levels with no change in plasma insulin. This study demonstrates the importance of adequate selenium intake around pregnancy for offspring metabolic health. Given the increasing prevalence of metabolic disease, this study highlights the need for appropriate micronutrient intake during pregnancy to ensure a healthy start to life.

Maternal selenium deficiency during pregnancy in mice increases thyroid hormone concentrations, alters placental function and reduces fetal growth

KEY POINTS

Inappropriate intake of key micronutrients in pregnancy is known to alter maternal endocrine status, impair placental development and induce fetal growth restriction. Selenium is an essential micronutrient required for the function of approximately 25 important proteins. However, the specific effects of selenium deficiency during pregnancy on maternal, placental and fetal outcomes are poorly understood. The present study demonstrates that maternal selenium deficiency increases maternal triiodothyronine and tetraiodothyronine concentrations, reduces fetal blood glucose concentrations, and induces fetal growth restriction. Placental expression of key selenium-dependent thyroid hormone converting enzymes were reduced, whereas the expression of key placental nutrient transporters was dysregulated. Selenium deficiency had minimal impact on selenium-dependent anti-oxidants but increased placental copper concentrations and expression of superoxide dismutase 1. These results highlight the idea that selenium deficiency during pregnancy may contribute to thyroid dysfunction, causing reduced fetal growth, that may precede programmed disease outcomes in offspring.

ABSTRACT

Selenium is a trace element fundamental to diverse homeostatic processes, including anti-oxidant regulation and thyroid hormone metabolism. Selenium deficiency in pregnancy is common and increases the risk of pregnancy complications including fetal growth restriction. Although altered placental formation may contribute to these poor outcomes, the mechanism by which selenium deficiency contributes to complications in pregnancy is poorly understood. Female C57BL/6 mice were randomly allocated to control (>190 µg kg-1 , n = 8) or low selenium (<50 µg kg-1 , n = 8) diets 4 weeks prior to mating and throughout gestation. Pregnant mice were killed at embryonic day 18.5 followed by collection of maternal and fetal tissue. Maternal and fetal plasma thyroid hormone concentrations were analysed, as was placental expression of key selenoproteins involved in thyroid metabolism and anti-oxidant defences. Selenium deficiency increased plasma tetraiodothyronine and triiodothyronine concentrations. This was associated with a reduction in placental expression of key selenodependent deiodinases, DIO2 and DIO3. Placental expression of selenium-dependent anti-oxidants was unaffected by selenium deficiency. Selenium deficiency reduced fetal glucose concentrations, leading to reduced fetal weight. Placental glycogen content was increased within the placenta, as was Slc2a3 mRNA expression. This is the first study to demonstrate that selenium deficiency may reduce fetal weight through increased maternal thyroid hormone concentrations, impaired placental thyroid hormone metabolism and dysregulated placental nutrient transporter expression. The study suggests that the magnitude of selenium deficiency commonly reported in pregnant women may be sufficient to impair thyroid metabolism but not placental anti-oxidant concentrations.

Atorvastatin potentiates the effect of selenomethionine on thyroid autoimmunity in euthyroid women with Hashimoto's thyroiditis

OBJECTIVE

In many studies, selenium supplementation decreased serum titers of thyroid antibodies. The aim of the study was to investigate whether statin therapy determines selenium action on thyroid autoimmunity.

METHODS

This prospective case-control study enrolled 42 euthyroid women with Hashimoto's thyroiditis and normal vitamin D status, 20 of whom had been treated with atorvastatin (40 mg daily) for at least 6 months. All patients received selenomethionine (200 µg daily) for 6 months. Plasma levels of lipids, serum titers of thyroid peroxidase (TPOAb) and thyroglobulin (TgAb) antibodies, as well as serum levels of thyrotropin, free thyroid hormones, and 25-hydroxyvitamin D were determined at the beginning and at the end of the study.

RESULTS

At baseline, there were no differences between both treatment arms in plasma lipids, titers of thyroid antibodies, serum levels of thyrotropin, free thyroid hormones, and 25-hydroxyvitamin D. Selenometionine decreased titers of TPOAb (from 843 ± 228 to 562 ± 189 U/mL) and TgAb (from 795 ± 286 to 501 ± 216 U/mL) in atorvastatin-treated women, as well as titers of TPOAb (from 892 ± 247 to 705 ± 205 U/mL) and TgAb (from 810 ± 301 to 645 ± 224 U/mL) in statin-naive women. The changes in antibody titers were more pronounced in women receiving atorvastatin (between-group difference: 94 [32-156] [TPOAb]; 129 [52-206] [TgAb]). Treatment-induced changes in TPOAb and TgAb correlated positively with baseline thyroid antibody titers. Circulating levels of lipids, free thyroxine, free triiodothyronine, and 25-hydroxyvitamin D remained at similar levels throughout the study.

CONCLUSIONS

The obtained results indicate that the decrease in titers of thyroid antibodies was potentiated by atorvastatin use.

Effects of Selenium Supplementation on Graves' Disease: A Systematic Review and Meta-Analysis

Low selenium status is associated with increased risk of Graves' disease (GD). While several trials have discussed the efficacy of selenium supplementation for thyroid function, in GD patients, the effectiveness of selenium intake as adjuvant therapy remains unclear. In this systematic review and meta-analysis, we aimed to determine the efficacy of selenium supplementation on thyroid function in GD patients. Two reviewers searched PubMed, Web of Science, the Cochrane Central Register of Controlled Trials, and four Chinese databases for studies published up to October 31, 2017. RCTs comparing the effect of selenium supplementation on thyroid hyperfunction in GD patients on antithyroid medication to placebo were included. Serum free thyroxine (FT4), free triiodothyronine (FT3), thyrotrophic hormone receptor antibody (TRAb), and thyroid-stimulating hormone (TSH) levels were assessed. Ten trials involving 796 patients were included. Random-effects meta-analyses in weighted mean difference (WMD) were performed for 3, 6, and 9 months of supplementation and compared to placebo administration. Selenium supplementation significantly decreased FT4 (WMD=-0.86 [confidence interval (CI)-1.20 to -0.53]; p=0.756; I2=0.0%) and FT3 (WMD=-0.34 [CI-0.66 to -0.02]; p=0.719; I2=0.0%) levels at 3 months, compared to placebo administration; these findings were consistent at 6 but not 9 months. TSH levels were more elevated in the group of patients taking selenium than in the control group at 3 and 6, but not 9 months. TRAb levels decreased at 6 but not 9 months. At 6 months, patients on selenium supplementation were more likely than controls to show improved thyroid function; however, the effect disappeared at 9 months. Whether these effects correlate with clinically relevant measures remains to be demonstrated.

The Effect of Levothyroxine and Selenium versus Levothyroxine Alone on Reducing the Level of Anti-thyroid Peroxidase Antibody in Autoimmune Hypothyroid Patients

Background:

Due to the prevalence of autoimmune hypothyroidism and its effects on physical and mental health it is necessary to provide a treatment which is also effective in preventing the progression of sub-clinical hypothyroidism in these patients. This study aims to investigate the effect of selenium supplementation on of anti-thyroid hormone antibodies in these patients.

Materials and Methods:

In a randomized clinical trial, 70 patients with autoimmune hypothyroidism randomly divided into two groups of 35 each, the first group was treated with oral selenium treatment with levothyroxine (LT4) and to the second group along with LT4, placebo was also prescribed. Serum selenium level, thyroid hormones and anti-thyroid hormone antibodies before and after 3 months of treatment in both groups, were determined, and the results were analyzed using SPSS software.

Results:

The mean of the serum anti-thyroid peroxidase serum level in the intervention group before and after treatment was 682.18 ± 87.25 and 522.96 ± 47.21 and the difference before and after treatment was statistically significant (P = 0.021). The level of this antibody before and after treatment in the control group was 441 ± 53.54 and 501.18 ± 77.68, and no significant differences between two groups were observed before and after treatment (P = 0.42).

Conclusion:

Selenium supplementation may help to reduce the levels of antibodies in patients with autoimmune hypothyroidism.

Association of Iodine and Iron with Thyroid Function

Iodine and iron are essential elements for healthy thyroid function. However, little is known about the association of iron and iodine with thyroid function in the general US population. We investigated iron and iodine status in relation to concentrations of thyroid hormones. We included 7672 participants aged 20 and older from three surveys (2007-2008, 2009-2010, and 2011-2012) of the National Health and Nutrition Examination Survey. Serum thyroid measures (including free and total T3 and T4, and TSH), serum iron concentration, and urinary iodine concentrations were measured. Multivariate linear regression models were conducted with serum thyroid measures as dependent variables and combinations of serum iron concentration and urinary iodine concentration as predictors with covariate adjustment. Logistic regression models were performed with TSH levels (low, normal, and high) and combinations of serum iron concentration and urinary iodine concentration. Overall, 10.9% of the study population had low iron; 32.2 and 18.8% had low or high iodine levels, respectively. Compared with normal levels of iron and iodine, normal iron and high iodine were associated with reduced free T3 and increased risk of abnormal high TSH. Combined low iron and low iodine was associated with reduced free T3 and increased TSH. In addition, high iodine was associated with increased risk of abnormal high TSH in females but not in males. Thyroid function may be disrupted by low levels of iron or abnormal iodine, and relationships are complex and sex-specific. Large prospective studies are needed to understand the mechanisms by which iron interacts with iodine on thyroid function.

Crossreactivity of an Antiserum Directed to the Gram-Negative Bacterium Neisseria gonorrhoeae with the SNARE-Complex Protein Snap23 Correlates to Impaired Exocytosis in SH-SY5Y Cells

Early maternal infections with Neisseria gonorrhoeae (NG) correlate to an increased lifetime schizophrenia risk for the offspring, which might be due to an immune-mediated mechanism. Here, we investigated the interactions of polyclonal antisera to NG (α-NG) with a first trimester prenatal brain multiprotein array, revealing among others the SNARE-complex protein Snap23 as a target antigen for α-NG. This interaction was confirmed by Western blot analysis with a recombinant Snap23 protein, whereas the closely related Snap25 failed to interact with α-NG. Furthermore, a polyclonal antiserum to the closely related bacterium Neisseria meningitidis (α-NM) failed to interact with both proteins. Functionally, in SH-SY5Y cells, α-NG pretreatment interfered with both insulin-induced vesicle recycling, as revealed by uptake of the fluorescent endocytosis marker FM1-43, and insulin-dependent membrane translocation of the glucose transporter GluT4. Similar effects could be observed for an antiserum raised directly to Snap23, whereas a serum to Snap25 failed to do so. In conclusion, Snap23 seems to be a possible immune target for anti-gonococcal antibodies, the interactions of which seem at least in vitro to interfere with vesicle-associated exocytosis. Whether these changes contribute to the correlation between maternal gonococcal infections and psychosis in vivo remains still to be clarified.

Selenoproteins are involved in antioxidant defense systems in thalassemia

Thalassemia major (TM) is a hereditary blood disease that affects the production of hemoglobin, resulting in severe anemia.

The Association Between Serum Levels of Selenium, Copper, and Magnesium with Thyroid Cancer: a Meta-analysis

There are conflicting reports on the correlation between serum levels of selenium (Se), copper (Cu), and magnesium (Mg) with thyroid cancer. The purpose of the present study is to clarify the association between Se, Cu, and Mg levels with thyroid cancer using a meta-analysis approach. We searched articles indexed in PubMed published as of January 2015 that met our predefined criteria. Eight eligible articles involving 1291 subjects were identified. Overall, pooled analysis indicated that subjects with thyroid cancer had lower serum levels of Se and Mg, but higher levels of Cu than the healthy controls [Se: standardized mean difference (SMD) = -0.485, 95% confidence interval (95%CI) = (-0.878, -0.092), p = 0.016; Cu: SMD = 2.372, 95%CI = (0.945, 3.799), p = 0.001; Mg: SMD = -0.795, 95%CI = (-1.092, -0.498), p < 0.001]. Further subgroup analysis found lower serum levels of Se in thyroid cancer in Norway [SMD = -0.410, 95%CI = (-0.758, -0.062), p = 0.021] and Austria [SMD = -0.549, 95%CI = (-0.743, -0.355), p < 0.001], but not in Poland (SMD = -0.417, 95%CI = (-1.724, 0.891), p = 0.532]. Further subgroup analysis also found that patients with thyroid cancer had higher serum levels of Cu in China [SMD = 1.571, 95%CI = (1.121, 2.020), p < 0.001] and Turkey [SMD = 0.977, 95%CI = (0.521, 1.432), p < 0.001], but not in Poland [SMD = 3.471, 95%CI = (-0.056, 6.997], p = 0.054]. In conclusion, this meta-analysis supports a significant association between serum levels of Se, Cu, and Mg with thyroid cancer. However, the subgroup analysis found that there was significant effect modification of Se, Cu levels by ethnic, like China and Poland. Thus, this finding needs further confirmation by a trans-regional multicenter study to obtain better understanding of causal relationship between Se, Cu, and Mg with thyroid cancer of different human races or regions.

Sodium selenite supplementation during pregnancy and lactation promotes anxiolysis and improves mnemonic performance in wistar rats' offspring

Selenium is a micronutrient which is part of selenoprotein molecules and participates in a vast number of physiological roles and, among them,we have fetal and neonatal development. Therefore, the aimof this studywas to evaluate possible behavioral changes in offspring of female rats supplemented during pregnancy and lactation with sodium selenite. To address that, we treated two groups of female rats by saline or sodium selenite at a dose of 1mg/kg through oral route and performed neurochemical and behavioral tests. In the offspring, the thyroid profile and hippocampal neurochemistrywere evaluated. Behavioral testswere performed in pups both during childhood and adulthood. We found out that selenium (Se) supplementation increased serum levels of triiodothyronine (25%, p b 0.001) and thyroxine (18%, p b 0.05) and promoted a tryptophan hydroxylase 2 (TPH 2) expression decrease (17%, p b 0.01) and tyrosine hydroxylase (TH) expression increase (202%, p b 0.01) in the hippocampus. The cholinesterase activity was decreased (28%, p b 0.01) in Se supplemented rats, suggesting a neurochemical modulation in the hippocampal activity. During childhood, the Sesupplemented offspring had a reduction in anxiety-like behavior both in elevated plus maze test and in light–dark box test. In adulthood, Se-treated pups had an increase in the locomotor activity (36%, p b 0.05) and in rearing episodes (77%, p b 0.001) in the open field test, while in the elevated plus maze test they also exhibited an increase in the time spent in the open arms (243%, p b 0.01). For the object recognition test, Se-treated offspring showed increase in the absolute (230.16%, p b 0.05) and relative index discrimination (234%, p b 0.05). These results demonstrate that maternal supplementation by sodium selenite promoted psychobiological changes both during childhood and adulthood. Therefore, the behavioral profile observed possibly can be explained by neurochemical changes induced by thyroid hormones during the critical period of the central nervous system ontogeny.

A novel upregulation of glutathione peroxidase 1 by knockout of liver-regenerating protein Reg3β aggravates acetaminophen-induced hepatic protein nitration

Murine regenerating islet-derived 3β (Reg3β) represents a homologue of human hepatocarcinoma-intestine-pancreas/pancreatic-associated protein and enhances mouse susceptibility to acetaminophen (APAP)-induced hepatotoxicity. Our objective was to determine if and how knockout of Reg3β (KO) affects APAP (300 mg/kg, ip)-mediated protein nitration in mouse liver. APAP injection produced greater levels of hepatic protein nitration in the KO than in the wild-type mice. Their elevated protein nitration was alleviated by a prior injection of recombinant mouse Reg3β protein and was associated with an accelerated depletion of the peroxynitrite (ONOO(-)) scavenger glutathione by an upregulated hepatic glutathione peroxidase-1 (GPX1) activity. The enhanced GPX1 production in the KO mice was mediated by an 85% rise (p<0.05) in the activity of selenocysteine lyase (Scly), a key enzyme that mobilizes Se for selenoprotein biosynthesis. Knockout of Reg3β enhanced AP-1 protein and its binding activity to the Scly gene promoter, upregulating its gene transcription. However, knockout of Reg3β did not affect gene expression of other key factors for selenoprotein biosynthesis. In conclusion, our findings unveil a new metabolic role for Reg3β in protein nitration and a new biosynthesis control of GPX1 by a completely "unrelated" regenerating protein, Reg3β, via transcriptional activation of Scly in coping with hepatic protein nitration. Linking selenoproteins to tissue regeneration will have profound implications in understanding the mechanism of Se functions and physiological coordination of tissue regeneration with intracellular redox control.

A comprehensive metabolic modeling of thyroid pathway in relation to thyroid pathophysiology and therapeutics

The thyroid pathway represents a complex interaction of different glands for thyroid hormone synthesis. Thyrotropin releasing hormone is synthesized in the hypothalamus and regulates thyrotropin stimulating hormone gene expression in the pituitary gland. In order to understand the complexity of the thyroid pathways, and using experimental data retrieved from the biomedical literature (e.g., NCBI, HuGE Navigator, Protein Data Bank, and KEGG), we constructed a metabolic map of the thyroid hormone pathway at a molecular level and analyzed it topologically. A total of five hub nodes were predicted in regards to the transcription thyroid receptor (TR), cAMP response element-binding protein (CREB), signal transducer and activator of transcription 3 (STAT 3), nuclear factor kappa-light-chain-enhancer of activated B cells (NFkB), and activator protein 1 (AP-1) as being potentially important in study of thyroid disorders and as novel putative therapeutic drug targets. Notably, the thyroid receptor is a highly connected hub node and currently used as a therapeutic target in hypothyroidism. Our analysis represents the first comprehensive description of the thyroid pathway, which pertains to understanding the function of the protein and gene interaction networks. The findings from this study are therefore informative for pathophysiology and rational therapeutics of thyroid disorders.

A pilot study of serum selenium, vitamin D, and thyrotropin concentrations in patients with thyroid cancer

BACKGROUND

Low serum selenium concentrations have been associated with a diagnosis of differentiated thyroid cancer in small studies in selenium deficient areas. We conducted a pilot study to explore associations between selenium concentrations and the diagnosis of thyroid cancer in an area of selenium sufficiency in the United States. As low 25-hydroxyvitamin D concentrations have been associated with several malignancies, we also examined 25-hydroxyvitamin D levels.

METHODS

This study was designed as a pilot study of prediagnostic selenium and 25-hydroxyvitamin D concentrations. We identified 65 euthyroid patients at an academic medical center who were scheduled for thyroidectomy for thyroid cancer, suspicion of thyroid cancer, or nodular disease. Blood samples were obtained two to four weeks prior to thyroidectomy. Samples were analyzed for thyrotropin (TSH), free thyroxine, total triiodothyronine, selenium, and 25 hydroxyvitamin D levels. Concentrations of these analytes were correlated with whether the patient was diagnosed with benign or malignant disease following their thyroidectomy. In patients with thyroid cancer, the concentrations of selenium and 25-hydroxyvitamin D were correlated with various prognostic features.

RESULTS

Although selenium concentrations were not significantly lower in patients with thyroid cancer, serum selenium concentrations were inversely correlated with disease stage (p = 0.011). There were no associations between vitamin D concentration and a diagnosis of thyroid cancer. Within the thyroid cancer patients, vitamin D concentrations were not associated with disease stage or any other prognostic features. In contrast, TSH concentrations were significantly higher in patients with thyroid cancer, and were positively correlated with the number of involved lymph nodes (p = 0.011) and disease stage (p = 0.022).

CONCLUSION

These data confirm the association between serum TSH and advanced thyroid cancer. In addition, they also suggest a potential association between selenium concentrations and higher thyroid cancer stage. No such association was seen for 25-hydroxyvitamin D concentrations. Larger prospective studies will be required to confirm this association. If confirmed, future studies would need to determine if the association is causative in nature. If causation exists, it seems likely that selenium concentrations would influence thyroid cancer development via an independent mechanism from that of TSH.

Sodium selenite increases the transcript levels of iodothyronine deiodinases I and II in ovine and bovine fetal thyrocytes in vitro

Selenium is essential for thyroid hormone homeostasis. Selenium is co-translationally incorporated into the protein backbone of 5' deiodinase enzymes, which are responsible for the intra- and extra-thyroidal activation of thyroid hormones. The objective of this study was to evaluate the effects of sodium selenite on the transcript levels of type I (DIO1) and II (DIO2) deiodinases in the primary culture of ovine and bovine fetal thyroid. By culture of fetal thyrocytes in the presence or absence of sodium selenite, and quantification of DIO1 and DIO2 transcripts using real-time reverse transcription polymerase chain reaction (RT-qPCR), we found that sodium selenite is able to increase the abundance of transcripts for DIO1 and DIO2 genes. We also found that cultured thyrocytes in the presence of sodium selenite compared to control cultured thyrocytes release more T3 into the culture medium. This indicates that in the presence of sodium selenite higher levels of DIO1 and DIO2 enzymes are produced, which are able to convert T4 to T3. In conclusion, we have shown that sodium selenite is increasing the abundance of DIO1 and DIO2 transcripts and increasing the production and release of T3 from cultured fetal thyrocytes. This finding emphasizes the role of selenium in transcriptional and expression processes during development and suggests that selenium deficiency during pregnancy in sheep and cattle may lead to the lower levels of DIO1 and DIO2 transcription in fetal thyroid, and thus, lower level of thyroidal T3 release into the fetal serum.

Postnatal toxic and acquired disorders

To develop and function optimally, the brain requires a balanced environment of electrolytes, amino acids, neurotransmitters, and metabolic substrates. As a consequence, organ dysfunction has the potential to induce brain disorders and toxic-metabolic encephalopathies, particularly when occurring during early stages of cerebral maturation. Induced toxicity of three different organ systems that are commonly associated with brain complications are discussed. First, thyroid hormone deficiency caused by intrinsic or extrinsic factors (e.g., environmental toxins) may induce severe adverse effects on child neurological development from reversible impairments to permanent mental retardation. Second, inadequate removal of wastes due to chronic renal failure leads to the accumulation of endogenous toxins that are harmful to brain function. In uremic pediatric patients, the brain becomes more vulnerable to exogenous substances such as aluminum, which can induce aluminum encephalopathy. Following surgical procedures, neurological troubles including focal defects and severe epileptic seizures may result from hypertensive encephalopathy combined with toxicity of immunomodulating substances, or from the delayed consequences of cardiovascular defect. Taken together, this illustrates that organ disorders clearly have an impact on child brain function in various ways.

Selenium homeostasis and antioxidant selenoproteins in brain: implications for disorders in the central nervous system

The essential trace element selenium, as selenocysteine, is incorporated into antioxidant selenoproteins such as glutathione peroxidases (GPx), thioredoxin reductases (TrxR) and selenoprotein P (Sepp1). Although comparatively low in selenium content, the brain exhibits high priority for selenium supply and retention under conditions of dietary selenium deficiency. Liver-derived Sepp1 is the major transport protein in plasma to supply the brain with selenium, serving as a "survival factor" for neurons in culture. Sepp1 expression has also been detected within the brain. Presumably, astrocytes secrete Sepp1, which is subsequently taken up by neurons via the apolipoprotein E receptor 2 (ApoER2). Knock-out of Sepp1 or ApoER2 as well as neuron-specific ablation of selenoprotein biosynthesis results in neurological dysfunction in mice. Astrocytes, generally less vulnerable to oxidative stress than neurons, are capable of up-regulating the expression of antioxidant selenoproteins upon brain injury. Occurrence of neurological disorders has been reported occasionally in patients with inadequate nutritional selenium supply or a mutation in the gene encoding selenocysteine synthase, one of the enzymes involved in selenoprotein biosynthesis. In three large trials carried out among elderly persons, a low selenium status was associated with faster decline in cognitive functions and poor performance in tests assessing coordination and motor speed. Future research is required to better understand the role of selenium and selenoproteins in brain diseases including hepatic encephalopathy.

Selenium and the thyroid gland: more good news for clinicians

The thyroid is the organ with the highest selenium content per gram of tissue because it expresses specific selenoproteins. Since the discovery of myxoedematous cretinism and thyroid destruction following selenium repletion in iodine- and selenium-deficient children, data on links between thyroid metabolism and selenium have multiplied. Although very minor amounts of selenium appear sufficient for adequate activity of deiodinases, thus limiting the impact of its potential deficiency on synthesis of thyroid hormones, selenium status appears to have an impact on the development of thyroid pathologies. The value of selenium supplementation in autoimmune thyroid disorders has been emphasized. Most authors attribute the effect of supplementation on the immune system to the regulation of the production of reactive oxygen species and their metabolites. In patients with Hashimoto's disease and in pregnant women with anti-TPO antibodies, selenium supplementation decreases anti-thyroid antibody levels and improves the ultrasound structure of the thyroid gland. Although clinical applications still need to be defined for Hashimoto's disease, they are very interesting for pregnant women given that supplementation significantly decreases the percentage of postpartum thyroiditis and definitive hypothyroidism. In Graves' disease, selenium supplementation results in euthyroidism being achieved more rapidly and appears to have a beneficial effect on mild inflammatory orbitopathy. A risk of diabetes has been reported following long-term selenium supplementation, but few data are available on the side effects associated with such supplementation and further studies are required.

Glutathione peroxidases

BACKGROUND

With increasing evidence that hydroperoxides are not only toxic but rather exert essential physiological functions, also hydroperoxide removing enzymes have to be re-viewed. In mammals, the peroxidases inter alia comprise the 8 glutathione peroxidases (GPx1-GPx8) so far identified.

SCOPE OF THE REVIEW

Since GPxs have recently been reviewed under various aspects, we here focus on novel findings considering their diverse physiological roles exceeding an antioxidant activity.

MAJOR CONCLUSIONS

GPxs are involved in balancing the H2O2 homeostasis in signalling cascades, e.g. in the insulin signalling pathway by GPx1; GPx2 plays a dual role in carcinogenesis depending on the mode of initiation and cancer stage; GPx3 is membrane associated possibly explaining a peroxidatic function despite low plasma concentrations of GSH; GPx4 has novel roles in the regulation of apoptosis and, together with GPx5, in male fertility. Functions of GPx6 are still unknown, and the proposed involvement of GPx7 and GPx8 in protein folding awaits elucidation.

GENERAL SIGNIFICANCE

Collectively, selenium-containing GPxs (GPx1-4 and 6) as well as their non-selenium congeners (GPx5, 7 and 8) became key players in important biological contexts far beyond the detoxification of hydroperoxides. This article is part of a Special Issue entitled Cellular functions of glutathione.