SAT-553 Gut Microbiota Involved in Thyroxine Metabolism and Development of Subclinical Hypothyroidism

The diversity, structure, and stability of the gut microbiota can influence hosts’ nutrition, energy, metabolism, and immunity through intestinal nutrient-sensing mechanisms, the gut-brain axis, or changes in intestinal permeability. It was reported that gut microbiota can influence hosts’ selenium concentration and 3,5,3’-triiodothyronine (T3) conversion, therefore participating in thyroid hormone metabolism. The detailed relationship of microbiota and thyroid disorder is not clear yet. In our study, an open-level randomized clinical trail (RCT) was performed in 100 people with subclinical hypothyroidism (SCH) in July 2017. Patients were randomly divided into L-thyroxine treated group (dosage was depended on thyroid function test) or untreated group. Fecal sample were collected and microbiome were analyzed by 16S rDNA high-throughput sequencing. The discrepancy of the microbiome community structure were obvious between not only the two groups, but also individuals with different drug dose within L-thyroxine group, as calculated by principle components analysis (PCA), principle coordinate analysis (PCoA) and non-metric multi-dimensional scaling (NMDS). Moreover, the microbial profile of certain patients, who were diagnosed to need to adjust their drug dose after nine months (March, 2018), showed same tendencies in PCA and NMDS analysis, which means microbiota may have correlation with the development of SCH. The abundance of some species (eg., Bacteroides, Lactobacillus, Streptococcus) showed a positive correlation with the drug dose. Those species were reported with sulfatase or glucuronidase activities, which could participate in the hydrolysis process of thyroid hormone and secondary bile acid. These results indicated that microbiota attributed in thyroxine absorption process in gut, and cholesterol or bile acid level might have correlation with thyroid dysfunction. However, in our test, we did not observe the obvious correlation between drug dose and serum cholesterol level. Taken together, these results indicated that gut microbiota may act as an important factor in influencing the occurrence, development and prognosis of thyroid dysfunction, and may partially responsible for the high risk of SCH in patients with hypercholesterolemia. The casual relationship between gut microbiota and thyroid dysfunction need to be further discussing.