Selenium and at-risk pregnancy: challenges and controversies
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REVIEW
Open Access
Selenium and at-risk pregnancy: challenges and controversies Leonidas H. Duntas
Abstract Selenium (Se), an essential trace element, is inserted as selenocysteine into an array of functional proteins and forms the core of various enzymes that play a cardinal role in antioxidant defense mechanisms, in redox regulation, and in thyroid hormone metabolism. Variations in plasma Se are due to nutritional habits, geographic and ethnic differences, and probably to genetic polymorphisms, the latter still to be conclusively established. Se concentrations were reported to be low in women of reproductive age in the UK, decreasing further during pregnancy, this resulting in low plasma and placental antioxidant enzyme activities. Since low serum Se levels have been found in women with preeclampsia, it has been hypothesized that low maternal Se status during early gestation may be an indicator of preterm birth. Moreover, it is documented that Se administration during pregnancy tendentially reduced the markers of thyroid autoimmunity and the incidence of maternal hypothyroidism in the postpartum period. Importantly, low Se levels in pregnant women affect fetal growth and augment the risk of delivering a small-for-gestational age infant by reducing placental antioxidant defense, while low Se in the third trimester is thought to indicate increased demands by the placenta, an issue which requires further confirmation. There is evidently a need for double-blind, placebo-controlled studies to better determine the efficacy and safety of Se supplementation in pregnancy at high risk for complications, and for measurement of Se levels or of selenoprotein P, the most reliable parameter of Se status, particularly in selenopenic regions. Keywords: Selenium, Selenoproteins, Selenomethionine, Selenoprotein-P, Thyroid autoimmunity, Pregnancy, Miscarriage, Preeclampsia, Premature birth
Introduction Selenium (Se), in the form of the 21st proteinogenic amino acid selenocysteine (SeCyS), is incorporated in specific proteins called selenoproteins, the most important being the deiodinases (DIOs), gluthathione peroxidases (GPXs), thioredoxin reductases (TRXR), SeCys insertion binding protein 2 (SECISBP2), and the Se transport protein (SELENOP) [1, 2]. DIOs, by regulating the conversion of thyroxine (T4) to triiodothyronine (T3) and reversing triiodothyronine (rT3) and thyroidonamines, control thyroid hormone turnover [3]. Correspondence: [email protected] Evgenideion Hospital, Unit of Endocrinology, Metabolism and Diabetes, Thyroid Section, University of Athens, 20 Papadiamantopoulou Str, 11528 Athens, Greece
Meanwhile, Se-dependent GPXs and TRXR are implicated in thyroid gland protection through modulating redox activities [4] (Fig. 1). Se deficiency has been associated with autoimmune thyroid diseases (AITD) and sepsis, arteriosclerosis, cardiovascular disease, cancer, increased mortality among the elderly and hemodialysis patients, and cognitive decline [5, 6]. Importantly, low Se status has been associated with adverse pregn
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