Selenium deficiency, thyroid hormone metabolism, and thyroid hormone deiodinases

Physiology and pharmacology of iodized oil in goiter prophylaxis

Thyroid complications resulting from excess iodide such as thyrotoxicosis, thyroiditis, sialadenitis, or hypothyroidism are much rarer after iodine supplementation with Lipiodol than with KI. They do not militate against its widespread use in endemic goiter populations, especially in pregnant women. However, patients with multinodular goiter should not be treated or should be treated only under careful observation. When Lipiodol-induced thyrotoxicosis occurs it tends to be mild or even subclinical and self-limited. If treatment is required, potassium perchlorate with or without thionamides is recommended. Iodide goiter has not been seen after Lipiodol supplementation, nor has thyroiditis. Sialadenitis occurs rarely. Iodide derived from Lipiodol readily enters the fetus, possibly by active transport, and theoretically endangers the fetus because autoregulation of the fetal thyroid occurs late during gestation. Despite the difficulty in distinguishing iodide goiter from iodide deficiency goiter of the newborn, no cases of neonatal iodide goiter have been reported. Possible mechanisms of thyroid inhibition by excess iodide are briefly discussed. The use of locally produced iodized plant oils is recommended for financial reasons as well as for the benefits derived from local participation.

Laboratory support of the clinical nutrition service

This article critically reviews the role of the laboratory services in assessment, monitoring and management of complications in patients requiring nutritional support. It has broadly been divided into three sections. (i) Assessment of protein and energy status: whilst it is stressed that clinical judgement and anthropometric measurements are the most effective methods of evaluation of nutritional requirements, laboratory tests which can be of use in assessment of protein energy status are discussed in detail, including an appraisal of the value of each test in various clinical situations. (ii) Assessment of micronutrient and electrolyte status: the clinical justification for assessment of the various micronutrients and electrolytes is considered. A few selected examples are discussed in detail including an evaluation of the tests of status available and examples of situations where measurement may be clinically helpful. (iii) Effective use of the laboratory: this section attempts to guide the clinician in the most appropriate use of laboratory tests, firstly in the assessment of requirement for aspects of nutritional support, secondly in the continued monitoring and evaluation of the support provided, and thirdly in prevention and treatment of metabolic complications. It is emphasised that clinical nutrition is a multidisciplinary topic requiring input from the laboratory in conjunction with other specialities to provide the best available patient care.

The diverse role of selenium within selenoproteins: a review

Selenium functions within mammalian systems primarily in the form of selenoproteins. Selenoproteins contain selenium as selenocysteine and perform a variety of physiological roles. Eleven selenoproteins have been identified: cellular or classical glutathione peroxidase; plasma (or extracellular) glutathione peroxidase; phospholipid hydroperoxide glutathione peroxidase; gastrointestinal glutathione peroxidase; selenoprotein P; types 1, 2, and 3 iodothyronine deiodinase; selenoprotein W; thioredoxin reductase; and selenophosphate synthetase. Of these, cellular and plasma glutathione peroxidase are the functional parameters used for the assessment of selenium status. Glutathione peroxidases catalyze the reduction of peroxides that can cause cellular damage. Thioredoxin reductase provides reducing power for several biochemical processes and defends against oxidative stress. Selenoprotein P appears to play a role in oxidant defense. Selenoprotein W may play a role in oxidant defense and be involved with muscle metabolism. Thyroid deiodinases function in the formation and regulation of active thyroid hormone. Selenophosphate synthetase is an enzyme required for the incorporation of selenocysteine into selenoproteins. In addition, a protein in the sperm mitochondrial capsule, which is vital to the integrity of sperm flagella, may be a unique selenoprotein. Recommended intakes, food sources, and status assessment of selenium, as well as selenium's role in health and disease processes, are reviewed.

Influence of dietary selenium and vitamin E on the levels of fatty acids in brain and liver tissues of lambs

In this study, the effects of dietary vitamin E, selenium, and their combination on the levels of fatty acid composition of the brain and liver tissues were examined. In brain tissue, the amounts of most fatty acids increased in vitamin E, combination and selenium groups compared with control group values. While the proportions of myristic, pentadecanoic, palmitic, linoleic, and total saturated fatty acids were decreased in vitamin E, Se and combination groups, eicosapentaenoic, total unsaturated and MUFA were increased in the same groups. In addition, the proportions arachidonic, eicosapentaenoic, total unsaturated, omega 6 and MUFA in the combination group were higher than in the control group. In liver tissue, the amounts of myristic, pentadecanoic, palmitic, eicosedienoic, eicosapentaenoic, docosahexaenoic, omega 3 and PUFA were higher in the combination group than in the control group. Also the proportions of eicosapentaenoic, docosahexaenoic acids in supplemented groups were higher than those in the control group. We conclude that dietary vitamin E and selenium have an influence on the levels of fatty acids in the brain and liver.

Single and multiple selenium-zinc-iodine deficiencies affect rat thyroid metabolism and ultrastructure

This study was conducted to evaluate the effects of single and combined deficiencies of Se, Zn and I on thyroid function in rats. Rats were fed amino acid-based diets for 6 wk starting from weaning. The diets contained either low or adequate amounts of these minerals. In addition to the control and control pair-fed groups, seven experimental groups were formed: Se deficient (Se-); I deficient (I-); Zn deficient (Zn-); Se and I deficient (Se-I-); Zn and I deficient (Zn-I-); Se and Zn deficient (Se-Zn); and Se, I and Zn deficient (Se-I-Zn-). Serum triiodothyronine (T3) was significantly lower than in controls in Zn-, Se-Zn- and Se-I- groups. Serum total thyroxine (T4) and free T4 were significantly lower and thyroid-stimulating hormone (TSH) greater in all iodine-deficient groups, regardless of Se or Zn status. Thyroid glutathione peroxidase activity was significantly reduced in Se- and Se-Zn- groups. Nevertheless, in the groups with a concurrent I deficiency, the activity of this enzyme was significantly greater than in controls. Severe alterations of the follicle cellular architecture, including signs compatible with apoptosis, were observed in the Zn- and Se-Zn- groups. These alterations appeared to be less severe when iodine deficiency was simultaneously present. Single and multiple deficiencies of Se, Zn and I have distinct effects on thyroid metabolism and structure.

Serum selenium levels in multinodular goitre

Serum selenium levels were measured in 22 patients with a multinodular goitre and compared to 15 normal controls using atomic absorption spectrophotometry. The serum selenium was significantly low in these patients (patients' mean = 9.6 +/- 1.24 mcg/l, versus control mean = 11.7 +/- 1.64 mcg/l and P < 0.005). Serum T4 and T3 were within the normal range in all patients and controls. Their levels correlated positively, though weakly, with the serum selenium levels (r = 0.4 and 0.36, respectively). The control selenium levels in this study were lower than the reported figures from some European countries, but they were close to those from other studies in Egypt. It seems that Egypt is a low selenium area. A wide-scale epidemiological study is recommended, together with the examination of the possible preventive role of selenium supplementation in areas of endemic goitre.

Expression pattern of mitochondrial capsule selenoprotein mRNA in the hamster testis

Mitochondrial capsule selenoprotein (MCS) has been known as a structural protein of the mitochondrial sheath in spermatozoa. In the present study, to determine the expression pattern of MCS mRNA in the hamster testis, northern blot and in situ hybridization analyses using digoxigenin-labeled riboprobes for the hamster MCS were performed in the testes of 10-week-old golden hamsters. According to the northern blot analysis, hamster MCS was detected as a single transcript of about 1 kb in the testis. During spermatogenesis, the hamster MCS mRNA first appeared in step 6 spermatids, gradually increased in round spermatids during spermiogenesis, reached a peak in step 8 spermatids, and persisted a high level until step 13 spermatids. After step 14, the signal began to show a progressive decline in the spermatids and was weakly detected in the tails of step 17 spermatids. However, the signal was not observed in spermatogonia, spermatocytes, Sertoli cells, peritubular myoid cells, and interstitial cells. These findings indicate that hamster MCS is mainly related to the spermiogenesis during spermatogenesis.

Cloning and expression of mitochondrial capsule selenoprotein gene in the golden hamster

Mitochondrial capsule selenoprotein (MCS) has been known as a structural protein of the mitochondrial sheath in spermatoza. In the present study, a full-length cDNA encoding the MCS was first isolated from the testes of 10-week-old golden hamsters using a RACE (rapid amplification of cDNA ends) technique and its mRNA expression pattern was investigated from the hamster tissues by reverse transcription-polymerase chain reaction (RT-PCR) analysis. Hamster MCS cDNA was 820 bp long, including 24 bp of the 5'-untranslated region (UTR) and 243 bp of the 3'-UTR, and showed identity of 75.6% and 73.9% with mouse and rat MCS. According to the deduced amino acid (aa) sequence analysis, hamster MCS encoded a polypeptide of 184 aa, including a cysteine- and proline-rich domain which is the characteristic sequences of MCS, and contained 2 in-frame UGA codons for selenocysteine. Hamster MCS also shared aa identity of 64.4% with mouse MCS and contained an Arg-Lys-Ser-Thr-rich region in the N-terminus similar to the mitochondrial targeting signal. On the other hand, according to the RT-PCR analysis using the specific primers for hamster MCS, hamster MCS mRNA was expressed in various tissues as well as the testes. This finding indicates that MCS in hamster may have more than just a function of mitochondrial sheath formation of spermatozoa.

Mice deficient in cellular glutathione peroxidase develop normally and show no increased sensitivity to hyperoxia

Glutathione peroxidase, a selenium-containing enzyme, is believed to protect cells from the toxicity of hydroperoxides. The physiological role of this enzyme has previously been implicated mainly using animals fed with a selenium-deficient diet. Although selenium deficiency also affects the activity of several other cellular selenium-containing enzymes, a dramatic decrease of glutathione peroxidase activity has been postulated to play a role in the pathogenesis of a number of diseases, particularly those whose progression is associated with an overproduction of reactive oxygen species, found in selenium-deficient animals. To further clarify the physiological relevance of this enzyme, a model of mice deficient in cellular glutathione peroxidase (GSHPx-1), the major isoform of glutathione peroxidase ubiquitously expressed in all types of cells, was generated by gene-targeting technology. Mice deficient in this enzyme were apparently healthy and fertile and showed no increased sensitivity to hyperoxia. Their tissues exhibited neither a retarded rate in consuming extracellular hydrogen peroxide nor an increased content of protein carbonyl groups and lipid peroxidation compared with those of wild-type mice. However, platelets from GSHPx-1-deficient mice incubated with arachidonic acid generated less 12-hydroxyeicosatetraenoic acid and more polar products relative to control platelets at a higher concentration of arachidonic acid, presumably reflecting a decreased ability to reduce the 12-hydroperoxyeicosatetraenoic acid intermediate. These results suggest that the contribution of GSHPx-1 to the cellular antioxidant mechanism under normal animal development and physiological conditions and to the pulmonary defense against hyperoxic insult is very limited. Nevertheless, the potential antioxidant role of this enzyme in protecting cells and animals against the pathogenic effect of reactive oxygen species in other disorders remains to be defined. The knockout mouse model described in this report will also provide a new tool for future study to distinguish the physiological role of this enzyme from other selenium-containing proteins in mammals under normal and disease states.

Influences of intraperitoneally and dietary administered vitamin E and selenium on the lipid composition in reproductive organs of male animals

The aim of this work was to determine the protective effect of intraperitoneally and dietary administered vitamin E and selenium (Se) on the total lipid, cholesterol, and fatty acid composition in rat and lamb testes. The level of total lipid in rat testes was significantly decreased (p < 0.001) in the combination group as compared to the control group but slightly decreased in lamb testes (p < 0.05). In addition, the level of total lipid in lamb testes was significantly decreased (p < 0.001) by the Se alone. The content of total cholesterol in rats was higher in the Se group and its level in lamb testes was higher in the vitamin E groups than in the control group (p < 0.001). In rats testes, the amounts of palmitic, oleic, arachidonic acids, the total fatty acid, total unsaturated and total omega 6 acids were higher (p < 0.001) in the Se group. The proportions of palmitic and arachidonic acids were reduced in the vitamin E group and linoleic acid, total unsaturated, and total omega 6 fatty acids were high (p < 0.05) in the vitamin E and combination groups. In lamb testis tissues, the amounts of palmitic, arachidonic, total unsaturated and total omega 6 fatty acids were decreased in the vitamin E group in comparison to the control (p < 0.05). However, the amounts of arachidonic and total omega 6 fatty acids increased (p < 0.05) in the Se group. The proportions of arachidonic acid, total unsaturated fatty acid and total omega 6 fatty acids were high (p < 0.05) in the Se and combination groups. We concluded that the level of total lipid in testis tissues was reduced by dietary and intraperitoneally administered vitamin E and Se together. In contrast, it seems that the proportions of unsaturated and essential fatty acids in examined tissues are increased by vitamin E and Se.

Determination of bromine and iodine in normal tissues from Beijing healthy adults

The contents of bromine and iodine in samples of heart, liver, spleen, lung, muscle, and hair from healthy adults living in Beijing, China, were determined using epithermal neutron activation analysis. The results indicate that the contents of bromine in lung and iodine in liver are higher than those in other tissues, except human hair. The bromine contents in Beijing human tissues are significantly lower than those in other countries. The contents of iodine are slightly lower than those in other countries, but the difference is not significant. Three biological standard reference materials were simultaneously determined with the samples, and our results agree well with the certified values.

Thyroid hormones and selenium status in breast cancer

Within a case-control study of postmenopausal breast cancer patients (n = 99) and matched healthy controls (n = 105), thyroid hormone levels were compared and correlated with toenail selenium concentrations. Plasma triiodothyronine (T3) was significantly lower in cases (1.4 +/- 0.4 nmol/l) than in controls (1.6 +/- 0.4 nmol/l), and a strong inverse relationship with breast cancer was observed with an odds ratio of 0.17 (95% CI = 0.08-0.36) in the highest compared with the lowest tertile of T3. Plasma thyroxine and thyroid-stimulating hormone concentrations were similar between cases and controls. Plasma T3 concentration was positively associated with toenail selenium in cases (age-adjusted regression coefficient = 0.049) and controls (age-adjusted regression coefficient = 0.036). Toenail selenium concentrations tended to be lower in cases than in controls, but the differences did not reach statistical significance. Although the disease process per se may explain the lower plasma T3 concentrations, it is also possible, inasmuch as these patients were in early-stage breast cancer, that selenium status may be influencing T3 levels via changes in the activity of the selenoenzyme type 1 iodothyronine deiodinase.

Diets deficient in selenium and vitamin E affect plasma lipoprotein and apolipoprotein concentrations in the rat

The present study examined the effects of Se, vitamin E and combined Se and vitamin E deficiencies in rats on plasma lipid, lipoprotein and apolipoprotein (apo) concentrations. Deficiencies were induced by feeding rats the respective diets for 6 weeks. The study shows that Se deficiency results in increased concentrations of plasma cholesterol and apo E. Both could be explained by an increase in the HDL1 fraction. Vitamin E deficiency alone had no significant effect on plasma lipid, lipoprotein and apo concentrations. Se deficiency in combination with vitamin E deficiency leads to an increase in plasma LDL and apo B concentrations. These results point to the need for further investigations on the mechanism by which Se deficiency affects lipoprotein metabolism.

Changed serum trace element profile in Down's syndrome

Being cofactors of important antioxidant enzymes superoxide dismutase (SOD) and glutathione peroxidase (GPx), which are significantly modified in Down's syndrome (trisomy 21), serum levels of microtrace elements zinc, copper, and selenium and of macroelement magnesium are reported in 16 subjects with Down's syndrome (DS) and their respective well age- and sex-matched controls. Serum zinc and selenium levels were significantly lowered in DS subjects, whereas copper levels were elevated. Consequently, a marked increase (40%) of the copper/zinc ratio in DS persons was observed. There were no differences in serum levels of magnesium between DS and control subjects.

Sudden infant death syndrome: near-weightlessness and delayed neural transformation

Dilation of the pulmonary arteries and increased pulmonary blood volume are recorded in sudden infant death syndrome and in infants living at low barometric pressures (high altitude). Low barometric pressure leads to chronic alveolar hypoxia (1,2). There is diversion and loss of body-fluid under conditions of microgravity (near-weightlessness) encountered in human space-travel and prolonged bedrest (3). The condition mimics shock and oligemia (4,5). The human neonate has underdeveloped postural mechanisms and low muscle-power. A transformation begins at about two months of age, which enables the human infant to adapt to the extrauterine environment (6). The neonate resembles the space traveller who, in a near-weightlessness antigravity environment, develops baroreceptor incompetence, visceral and venous congestion and oliguria. The low birthweight infant displays many of the disorders of the space traveller, viz. poor circulation, high blood-glucose, insulin resistance, weak muscles, slow gut absorption and bone demineralization (7-10). These conditions are virtually identical with the internal adjustments the body makes on lying down (negative gravity or near-weightlessness). We discuss the similarities of sudden infant death syndrome to low barometric pressure environment, orthostatic intolerance, the Pickwickian syndrome and X disease.

Selenium, zinc, and thyroid hormones in healthy subjects: low T3/T4 ratio in the elderly is related to impaired selenium status

Iodothyronine 5' deiodinase, which is mainly responsible for peripheral T3 production, has recently been demonstrated to be a selenium (Se)-containing enzyme. The structure of nuclear thyroid hormone receptors contains Zinc (Zn) ions, crucial for the functional properties of the protein. In the elderly, reduced peripheral conversion of T4 to T3 with a lower T3/T4 ratio and overt hypothyroidism are frequently observed. We measured serum Se and RBC GSH-Px (as indices of Se status), circulating and RBC Zinc (as indices of Zn status), thyroid hormones and TSH in 109 healthy euthyroid subjects (52 women, 57 men), carefully selected to avoid abnormally low thyroid hormone levels induced by acute or chronic diseases or calorie restriction. The subjects were subdivided into three age groups. To avoid under- or malnutrition conditions, dietary records were obtained for a sample of 24 subjects, randomly selected and representative of the whole population for age and sex. Low T3/T4 ratios and reduced Se and RBC GSH-Px activity were observed only in the older group. A highly significant linear correlation between the T3/T4 ratio and indices of Se status was observed in the older group of subjects (r = 0.54; p < 0.002, for Se; r = 0.50; p < 0.002, for RBC GSH-Px). Indices of Zn status did not correlate with thyroid hormones, but RBC Zn was decreased in older as compared with younger subjects. We concluded that reduced peripheral T4 conversion is related to impaired Se status in the elderly.

Thyroid function parameters during a selenium repletion/depletion study in phenylketonuric subjects

Phenylketonuric (PKU) subjects have a limited supply of selenium (Se) in their phenylalanine-restricted diet. A Se repletion (1 microgram Se/kg/day)/depletion study was conducted in PKU children to determine the effect of Se on thyroid function parameters. The initial plasma Se concentration (mean +/- SD: 0.26 +/- 0.12 mumol/L, p < 0.00003, n = 10) and glutathione peroxidase (GSH-Px) activity (140 +/- 58 U/L, p < 0.00003, n = 10) were significantly lower compared to age-matched controls. After 14 weeks of supplementation, the plasma Se concentration (mean +/- SD: 0.74 +/- 0.20 mumol/L) normalized (normal range: 0.57-1.15 mumol/L, mean +/- SD: 0.76 +/- 0.13 mumol/L, n = 32) and remained stable thereafter during repletion. Plasma GSH-Px activity reached normal values after 18 weeks of supplementation (312 +/- 57 U/L; normal range: 238-492 U/L, mean +/- SD: 345 +/- 54 U/L, n = 32) and increased significantly for up to eight weeks thereafter (332 +/- 52 U/L). Individual and mean thyroid parameters were initially normal in all cases. The mean concentrations of plasma thyroxine (T4: p < 0.025), free T4 (FT4: p < 0.01) and reverse triiodothyronine (rT3: p < 0.005) decreased to 75% of their initial value within three weeks of Se supplementation and remained stable thereafter, within a normal physiological range during selenium supplementation. They increased back to their initial values three weeks (T4: p < 0.05, FT4: p < 0.05) and six weeks (rT3: p < 0.025) respectively, after the end of the supplementation. In conclusion, Se supplementation modifies thyroid function parameters in Se-deficient PKU subjects most likely by an increase in activity of type I 5'-deiodinase (5'-DIase I).

Correlations between parameters of body selenium status and peripheral thyroid parameters in the low selenium region

The following were measured in 380 male and female inhabitants of Prague (n the age range 6-65 years):selenium in serum and urine, iodine in urine, thyroid-stimulating hormone, thyroid volume, thyroxine (T4), triiodothyronine (T3), ankle jerk time, pulse rate and body fat. Correlations were calculated to assess the influence of Se upon the thyroid hormone parameters and their peripheral effects in Se-deficient regions both by using the linear correlation analysis and by using the multiple linear correlation analysis and the analysis of variance. Many significant linear correlations were found for whole groups of examined persons, for the individual groups (boys, men, girls and women) as well as for subgroups, according to the age and sex. We conclude, from the analytical results of Se indices (serum, hair, urine) reported previously, and on the basis of the statistical demonstration of the influence of selenium upon thyroid hormone levels and the peripheral effects in the group of Prague inhabitants in connection with the previously documented role of Se in pathways resulting in the synthesis of physiologically active thyroid hormone, that inhabitants of Prague are selenium deficient. Concurrent deficiency of selenium may modify and even worsen iodine deficiency disorders of various stages. Multiple linear correlation analysis followed by analysis of variance of subgroups indicated a coincidence of the effects of some measured parameters upon the peripheral manifestation of thyroid hormone state as well as highlighting the effect of other independent variables of thyroid hormone metabolism than those measured in the study.(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of trace amounts of selenium in poultry feedstuffs by gas chromatography

In view of the importance of establishing reliable selenium concentration levels in different kinds of feedstuffs, the purpose of this work was to develop optimum experimental conditions for the isolation and GC determination of selenium as its chelate with 4-nitro-1,2-diaminobenzene. It was shown that ignition of the sample in an oxygen flask followed by reduction of Se(VI) to Se(IV) and the formation of 5-nitro-2,1,3-benzoselenadiazole chelate in HCl medium is a relatively rapid procedure giving a low blank value and allowing the determination of selenium in commercial feedstuffs and similar biological samples. The method was validated by the analysis of suitable certified or standard reference materials.