Selenium deficiency and thyroid function in acute renal failure

Se deficiency induces renal pathological changes by regulating selenoprotein expression, disrupting redox balance, and activating inflammation

Selenium (Se) is closely associated with kidney disease, and renal injury often occurs together with hyposelenemia. This study was designed to reveal the mechanism underlying renal injury induced by Se deficiency in pigs. Twenty-four castrated male Yorkshire pigs were divided into two groups fed either a Se-deficient diet (0.007 mg Se per kg) or a Se-adequate diet (0.3 mg Se per kg). Serum and kidney samples were collected at the 16th week of the trial, processed, and analyzed for serum biochemistry, Se concentration, kidney index markers, histology, selenoprotein mRNA expression, redox status, and inflammatory cytokines. Dietary Se deficiency induced kidney injury, decreased (P < 0.05) Se concentrations, and increased (P < 0.05) kidney index and serum blood urea nitrogen, creatinine, and carbon dioxide values. Histological analysis indicated that Se deficiency induced inflammatory lesions and renal tubular atrophy in the renal medulla. Se deficiency downregulated (P < 0.05) nine selenoprotein genes (GPX1, SELENOW, SELENOH, SELENOP, GPX3, TXNRD2, SELENOI, SELENON, and SELENOM) and upregulated (P < 0.05) SEPHS2 in the kidneys. Se deficiency decreased (P < 0.05) the activity of glutathione peroxidase, thioredoxin reductase, and catalase, as well as the hydroxyl radical inhibition capacity, and increased (P < 0.05) the content of malondialdehyde and nitric oxide. Se deficiency increased (P < 0.05) the expression of the transcription factors NF-κB and HIF-1α, and regulated inflammatory cytokines. Se deficiency increased (P < 0.05) the expression of IL-6, IL-8, IL-12, IL-17, and cyclooxygenase-2, and decreased (P < 0.05) the expression of IL-10, IL-13, and TGF-β. These results indicated that Se deficiency induces kidney injury through the regulation of selenoproteins, oxidative stress, and inflammation.

The effect of selenium supplementation on acute phase reactants and thyroid function tests in hemodialysis patients

BACKGROUND

Selenium deficiency is a common problem in patients with chronic kidney disease (CKD). This micronutrient has anti-inflammatory and anti-oxidant effects. Selenium is also found in high concentrations in the thyroid gland.

OBJECTIVES

To determine the effect of selenium supplementation on thyroid function tests and acute phase reactants in hemodialysis patients.

PATIENTS AND METHODS

In this double-blinded randomized clinical in 3 months, 64 hemodialysis patients with selenium deficiency were divided into experimental (received selenium supplementation; 32 cases) or control group (received placebo; 32 cases). Erythrocyte sedimentation rate (ESR), ferritin, quantitative C-reactive protein (CRP) and thyroid function tests (TFTs) including thyroid stimulating hormone (TSH), T3 resin uptake (T3RU), and free T4 were measured before and after the intervention and compared between experimental and control groups.

RESULTS

At baseline, no significant difference was found between experimental and control groups regarding CRP, ESR and ferritin serum levels. Likewise, after intervention, no significant difference was found between experimental and control groups for CRP (14.77 ± 17.93 vs. 18.29 ± 21.56 mg/L), ESR (32.90 ± 32.62 vs. 33.91 ± 31.15 mm/h) and ferritin (528.6 ± 423.07 vs. 519.52 ± 345.59 ng/mL). At baseline, no significant difference was found between experimental and control groups regarding TFTs. Likewise, after intervention, no significant difference was found between experimental and control groups for TSH (3.7 ± 2.22 vs. 2.84 ± 1.88 µU/mL), free T4 (7.19 ± 1.98 vs. 7.02 ± 1.87 µg/dL) and T3RU (30.04 ± 2.28% vs. 29.2 ± 1.98%).

CONCLUSIONS

Oral selenium supplementation for three months did not have any significant effect on thyroid function tests or acute phase reactants.

The heart of the matter on breastmilk and environmental chemicals: essential points for healthcare providers and new parents

Abstract The increasing number of environmental chemicals measured in breastmilk is a consequence of improved analytical capabilities and the increased interest in biomonitoring. It has been generally concluded that the benefits to the infant from breastfeeding outweigh potential risks associated with environmental chemical exposures associated with breastfeeding. However, there have been reports of subtle effects on infants associated with chemicals in breastmilk. Associations between concentrations of chemicals in breastmilk and a biochemical or other change in infants may signal the need for further study or regulatory action, whereas on an individual level, these changes may not be considered adverse. For healthcare providers, this distinction is critical, as many in the field are being asked for nuanced information on risks and benefits associated with breastfeeding, and this information is not readily available. Recognizing the challenge faced by healthcare providers, we have explored and developed a case study on dioxins in breastmilk. The essential conclusion for healthcare providers and new parents is that in studies of breastfed versus formula-fed infants across time, including times when levels of environmental chemicals such as dioxins were higher, beneficial effects associated with breastfeeding have been found. The current evidence does not support altering the World Health Organization recommendations promoting and supporting breastfeeding.

Selenium, the thyroid, and the endocrine system

Recent identification of new selenocysteine-containing proteins has revealed relationships between the two trace elements selenium (Se) and iodine and the hormone network. Several selenoproteins participate in the protection of thyrocytes from damage by H(2)O(2) produced for thyroid hormone biosynthesis. Iodothyronine deiodinases are selenoproteins contributing to systemic or local thyroid hormone homeostasis. The Se content in endocrine tissues (thyroid, adrenals, pituitary, testes, ovary) is higher than in many other organs. Nutritional Se depletion results in retention, whereas Se repletion is followed by a rapid accumulation of Se in endocrine tissues, reproductive organs, and the brain. Selenoproteins such as thioredoxin reductases constitute the link between the Se metabolism and the regulation of transcription by redox sensitive ligand-modulated nuclear hormone receptors. Hormones and growth factors regulate the expression of selenoproteins and, conversely, Se supply modulates hormone actions. Selenoproteins are involved in bone metabolism as well as functions of the endocrine pancreas and adrenal glands. Furthermore, spermatogenesis depends on adequate Se supply, whereas Se excess may impair ovarian function. Comparative analysis of the genomes of several life forms reveals that higher mammals contain a limited number of identical genes encoding newly detected selenocysteine-containing proteins.

Selenium and the control of thyroid hormone metabolism

Thyroid hormone synthesis, metabolism and action require adequate availability of the essential trace elements iodine and selenium, which affect homeostasis of thyroid hormone-dependent metabolic pathways. The three selenocysteine-containing iodothyronine deiodinases constitute a novel gene family. Selenium is retained and deiodinase expression is maintained at almost normal levels in the thyroid gland, the brain and several other endocrine tissues during selenium deficiency, thus guaranteeing adequate local and systemic levels of the active thyroid hormone T(3). Due to their low tissue concentrations and their mRNA SECIS elements deiodinases rank high in the cellular and tissue-specific hierarchy of selenium distribution among various selenoproteins. While systemic selenium status and expression of abundant selenoproteins (glutathione peroxidase or selenoprotein P) is already impaired in patients with cancer, disturbed gastrointestinal resorption, unbalanced nutrition or patients requiring intensive care treatment, selenium-dependent deiodinase function might still be adequate. However, disease-associated alterations in proinflammatory cytokines, growth factors, hormones and pharmaceuticals modulate deiodinase isoenzyme expression independent from altered selenium status and might thus pretend causal relationships between systemic selenium status and altered thyroid hormone metabolism. Limited or inadequate supply of both trace elements, iodine and selenium, leads to complex rearrangements of thyroid hormone metabolism enabling adaptation to unfavorable conditions.

The impact of cardiopulmonary bypass on selenium status, thyroid function, and oxidative defense in children

Selenium has important functions for oxidative defense and thyroid hormone metabolism. Selenium-dependent enzymes include 5'-iodothyronine deiodinase and glutathione peroxidase (GPX). The objective of this study was to investigate the relationship between plasma selenium, GPX activity, and thyroid hormone status in pediatric cardiac surgical patients. Plasma concentrations of selenium, free triiodothyronine (fT3), free thyroxin (fT4), and c-reactive protein as well as plasma activity of GPX were prospectively evaluated at anesthetic induction and 48 hours postoperatively in 59 children requiring cardiopulmonary bypass (CPB). GPX was measured at additional time points at 6, 12, and 24 hours postoperatively. There was a significant reduction in the plasma selenium concentration after cardiopulmonary bypass with obtained median measurements of 0.61 micromol/L (induction) and 0.51 micromol/L (48 hours postoperatively). The fT3/fT4 ratio decreased significantly from 0.28 at anesthetic induction to 0.22 at 48 hours postoperatively. There were no significant changes of GPX activity. 48 hours fT3 concentration, fT3/fT4 ratio, and selenium concentration were significantly negatively correlated with the time spent in intensive care. The concentration of plasma selenium in children undergoing cardiopulmonary bypass significantly decreases, resulting in diminished deiodinase activity, and a subsequent reduction in the conversion of T4 to T3.

Selenium status in Saudi Arabia

Selenium (Se) is a naturally occurring trace element that is essential for animal and human nutrition, but the range between dietary requirements and toxic levels is relatively narrow. In this review, we are interested in the beneficial effects of selenium and we report on a number of studies of the selenium status of different populations in Saudi Arabia. The Status reflects the geographical area inhabited by the populations. Apart from the few available studies reviewed here, no data on the human status of Se in Saudi Arabia has been obtained. A further objective of this paper is throw some the light on the direction of future studies.