Lutz Schomburg

On the importance of selenium and iodine metabolism for thyroid hormone biosynthesis and human health.

The trace elements iodine and selenium (Se) are essential for thyroid gland functioning and thyroid hormone biosynthesis and metabolism. While iodine is needed as the eponymous constituent of the two major thyroid hormones triiodo-L-thyronine (T3), and tetraiodo-L-thyronine (T4), Se is essential for the biosynthesis and function of a small number of selenocysteine (Sec)-containing selenoproteins implicated in thyroid hormone metabolism and gland function. The Se-dependent iodothyronine deiodinases control thyroid hormone turnover, while both intracellular and secreted Se-dependent glutathione peroxidases are implicated in gland protection. Recently, a number of clinical supplementation trials have indicated positive effects of increasing the Se status of the participants in a variety of pathologies. These findings enforce the notion that many people might profit from improving their Se status, both as a means to reduce the individual health risk as well as to balance a Se deficiency which often develops during the course of illness. Even though the underlying mechanisms are still largely uncharacterised, the effects of Se appear to be exerted via multiple different mechanisms that impact most pronounced on the endocrine and the immune systems.

Role of Selenium Intake for Risk and Development of Hyperthyroidism.

PurposenTo investigate the importance of dietary selenium (Se) for hyperthyroidism.nnnMethodsnWe performed a more in-depth analysis of a large cross-sectional study of 6152 participants from two counties within the Shaanxi Province, China. These counties are characterized by different habitual Se intake. We investigated the effects of a different dietary Se supply (0.02, 0.18, 0.6, or 2.0 ppm Se) on disease development in a mouse model of Graves disease (GD).nnnResultsnThe cross-sectional study revealed a comparable prevalence of hyperthyroidism, irrespective of Se intake, in both counties. However, an unexpected sex-specific difference was noted, and Se deficiency might constitute a risk factor for hyperthyroidism, especially in males. In a mouse model, pathological thyroid morphology was affected, and greater Se intake exerted some protecting effects on the pathological distortion. Circulating thyroid hormone levels, malondialdehyde concentrations, total antioxidant capacity, and the titer of GD-causing TSH receptor autoantibodies were not affected by Se. Expression analysis of the transcripts in the spleen indicated regulatory effects on genes implicated in the immune response, erythropoiesis, and oxygen status. However, the humoral immune response, including the CD4/CD8 or T-helper 1/T-helper 2 cell ratio and the concentration of regulatory T cells, was similar between the experimental groups, despite the difference in Se intake.nnnConclusionsnOur data have highlighted a sexual dimorphism for the interaction of Se and thyroid disease risk in humans, with indications of a local protective effects of Se on thyroid gland integrity, which appears not to be reflected in the circulating biomarkers tested.

Steroidhormone – Produkte von Nebennierenrinde und Keimdrüsen

Steroidhormone bilden eine umfangreiche Gruppe von Hormonen, die sich vom Cholesterin ableiten. Sie werden v. a. in der Nebennierenrinde, den Hoden sowie den Ovarien synthetisiert. Alle Steroidhormone wirken uber nucleare Rezeptoren. Ihr Wirkungsspektrum reicht von der Beeinflussung des Intermediar- und Knochenstoffwechsels bis zur Regulation der mannlichen bzw. weiblichen Sexualentwicklung und -funktion.

Wachstumshormon und Prolactin

In den vorangegangenen Kapiteln wurden die glandotropen Hypophysenhormone besprochen, nun wenden wir uns den Proteohormonen Wachstumshormon (GH, growth hormone) und Prolactin (PRL) zu. GH stimuliert das Korperwachstum, viele anabole und regenerative Vorgange und den Energiestoffwechsel.

Schilddrüsenhormone – Zentrale Regulatoren von Entwicklung, Wachstum, Grundumsatz, Stoffwechsel und Zelldifferenzierung

Die Schilddrusenhormone Thyroxin (T4) und Triiodthyronin (T3) steuern Entwicklung, Wachstum, Zelldifferenzierung, die meisten anabolen und katabolen Stoffwechselwege sowie viele Reaktionen des Struktur- und Funktionsstoffwechsels. Das biologisch aktive Hormon der Schilddruse ist das T3. Es entsteht aus dem als Prohormon dienenden T4 durch enzymatische Deiodierung. Seine Wirkungen werden uberwiegend durch nucleare T3-Rezeptoren (TRα, TRβ) vermittelt, die als ligandenabhangige Transkriptionsfaktoren die Transkription vieler Gene regulieren.

Hormone des Hypothalamus und der Hypophyse

Der Hypothalamus ist mit der Hypophyse uber das Infundibulum verbunden; hieraus ergibt sich eine anatomische und funktionale Einheit, die als ubergeordnetes Zentrum die hierarchisch organisierten Hormonachsen steuert.