Does microbiota composition affect thyroid homeostasis?
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Does microbiota composition affect thyroid homeostasis? Camilla Virili • Marco Centanni
Received: 23 October 2014 / Accepted: 8 December 2014 Ó Springer Science+Business Media New York 2014
Abstract The intestinal microbiota is essential for the host to ensure digestive and immunologic homeostasis. When microbiota homeostasis is impaired and dysbiosis occurs, the malfunction of epithelial barrier leads to intestinal and systemic disorders, chiefly immunologic and metabolic. The role of the intestinal tract is crucial in the metabolism of nutrients, drugs, and hormones, including exogenous and endogenous iodothyronines as well as micronutrients involved in thyroid homeostasis. However, the link between thyroid homeostasis and microbiota composition is not yet completely ascertained. A pathogenetic link with dysbiosis has been described in different autoimmune disorders but not yet fully elucidated in autoimmune thyroid disease which represents the most frequent of them. Anyway, it has been suggested that intestinal dysbiosis may trigger autoimmune thyroiditis. Furthermore, hypo- and hyper-thyroidism, often of autoimmune origin, were respectively associated to small intestinal bacterial overgrowth and to changes in microbiota composition. Whether some steps of this thyroid network may be affected by intestinal microbiota composition is briefly discussed below. Keywords Intestinal microbiota Selenium Thyroxine malabsorption Autoimmune thyroiditis Deiodinase Dysbiosis
C. Virili M. Centanni (&) Endocrinology Section, Department of Medico-Surgical Sciences and Biotechnologies, ‘‘Sapienza’’ University of Rome, Latina, Italy e-mail: [email protected] C. Virili M. Centanni Endocrinology Unit, AUSL Latina, Latina, Italy
Introduction Intestinal tract contains about 800 bacteria species, both anaerobes and aerobes, and about one hundred of that characterize each human being. They are distributed in a progressive fashion in the gut being lesser represented in the stomach and duodenum, increased in jejunum and ileum, then reaching the maximum concentration in the colon. Along with bacteriophage viruses and fungal species, they constitute the intestinal microbiota [1]. Its composition is clustered in at least 3 enterotypes [2] depending on several features including genetic background, immune phenotype, dietary habits, etc. [3]. Relatively simple at birth, microbiota composition increases its complexity with time but remains substantially stable in adult life being modified, however, by long-term diet changes, drug interference (anti acid or immunosuppressive treatments), and regional or systemic pathologic conditions [1]. Microbiota is essential for the host to develop and to maintain immunologic and digestive homeostasis [4]. In fact, in germ-free (GF) rats, a model of microbiotafree animals, the lack of microbiota is associated to reduced intestinal surface areas with shorter villi, changes in mucus layer and permeability [5]. Also the immune system is compromised in GF animals with reduce
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