The Experts below are selected from a list of 3555 Experts worldwide ranked by ideXlab platform

Cady P - One of the best experts on this subject based on the ideXlab platform.

Dillman Ro - One of the best experts on this subject based on the ideXlab platform.

Doris Rosenthal - One of the best experts on this subject based on the ideXlab platform.

  • Effects of aging on thyroidal function and proliferation.
    Current aging science, 2008
    Co-Authors: V M Corrêa Da Costa, Doris Rosenthal
    Abstract:

    The endocrine system is as affected by aging as are other systems. The effect of aging on the hypothalamus-pituitary-thyroid function is still controversial. Human aging was reported as associated with a decrease in thyrotropin (TSH) secretion, but increased TSH levels in relatively healthy elders are also reported. The main point discussed is whether this increase in the immunoreactive TSH of aged subjects, and related changes in thyroid function, are "physiologic" consequences of aging on the hypothalamus-pituitary-thyroid axis or are induced by non-thyroid illnesses and/or drug use, frequent in the elderly. There are strong evidences of decreased hypothalamus-pituitary-thyroid axis activity as well as decreased Thyroxine Metabolism (5'-deiodination) in humans, and other mammals. For now, we must consider that the hypothalamus-pituitary-thyroid axis is affected at all three levels by normal aging, and the mild state of "total" hypothyroidism during aging is completed by a reduced response of target cells/tissues to thyroid hormones. Despite the decreased response of the old rat thyroid to TSH there is no decrease in the glands mass. Ras proteins are involved in the transduction of growth factor signals by surface receptors, in thyroid as well as in other tissues, and are key components of downstream signaling through several pathways. Ras activation of Raf, and of extracellular-signal-regulated kinases (ERK) is an important signaling pathway for many Ras effects. Very little is known about the modulation of Ras expression in the aging thyroid. We detected an increase in Ras expression in thyroids of old rats, but the signal transduction by pERK was decreased, suggesting that another RAS-signaling pathway could be activated and responsible for the maintenance of the thyroid volume.

Ling Gao - One of the best experts on this subject based on the ideXlab platform.

  • Relation of Gut Microbes and L-Thyroxine Through Altered Thyroxine Metabolism in Subclinical Hypothyroidism Subjects.
    Frontiers in cellular and infection microbiology, 2020
    Co-Authors: Zhenyu Yao, Meng Zhao, Ying Gong, Chen Wenbin, Qian Wang, Tian Guo, Zhao Jiajun, Ling Gao
    Abstract:

    Thyroxine Metabolism is an important topic of pathogenesis research and treatment schedule of subclinical hypothyroidism (SCH). L-Thyroxine replacement therapy (LRT) is usually recommended for severe SCH patients only. Our previous studies reported that disordered serum lipid of mild SCH people could also benefit from LRT. However, the benefits were different among individuals, as shown by the variations in drug dosage that required to maintain thyroid-stimulating hormone (TSH) stability. Alternative pathways, such as sulfation and glucuronidation of iodothyronine, may play a role in thyroid hormones Metabolism in peripheral tissues aside from thyroid. Conjugated Thyroxine can be hydrolyzed and reused in tissues including gastrointestinal tract, in which gut microbiota are one of the most attractive physiological components. On this site, the roles of gut microbiota in thyroidal Metabolism should be valued. In this study, a cross-sectional study was performed by analyzing 16S rDNA of gut microbiota in mild SCH patients treated with L-Thyroxine or not. Subjects were divided by serum lipid level, L-Thyroxine treatment, or L-Thyroxine dosage, respectively. Relationship between gut microbiome and serum profile, L-Thyroxine treatment, and dose were discussed. Other metabolic disorders such as type 2 diabetes and hypertension were also taken into consideration. It turned out that microbiome varied among individuals divided by dose and the increment of L-Thyroxine but not by serum lipid profile. Relative abundance of certain species that were associated with Thyroxine Metabolism were found varied among different L-Thyroxine doses although in relatively low abundance. Moreover, serum cholesterol may perform relevance effects with L-Thyroxine in shaping microbiome. Our findings suggested that the differences in L-Thyroxine dosage required to maintain TSH level stability, as well as the SCH development, which was displayed by the increased L-Thyroxine doses in subsequent follow-up, had relationship with gut microbial composition. The reason may due to the differences in Thyroxine metabolic capacity in gut. In addition, the metabolic similarity of iodothyronines and bile acid in gut also provides possibilities for the correlation between host's Thyroxine and cholesterol levels. This study was registered with ClinicalTrials.gov as number NCT01848171.

  • SAT-553 Gut Microbiota Involved in Thyroxine Metabolism and Development of Subclinical Hypothyroidism
    Journal of the Endocrine Society, 2019
    Co-Authors: Meng Zhao, Wenbin Chen, Ling Gao
    Abstract:

    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.

Maria João Saraiva - One of the best experts on this subject based on the ideXlab platform.

  • The binding of xanthone derivatives to transthyretin
    Biochemical Pharmacology, 2005
    Co-Authors: Filipe R. N. C. Maia, Maria Rosário Almeida, Luís Gales, Anake Kijjoa, Madalena Pinto, Maria João Saraiva, Ana M. Damas
    Abstract:

    A series of xanthone derivatives, isolated from Calophyllum teysmannii var. inophylloide, have been evaluated for their binding affinity to transthyretin. Transthyretin is a plasma protein involved in the transport of Thyroxine (T4) and also implicated in amyloid diseases. Using competition-binding studies with the protein natural ligand T4, we have identified one prenylated xanthone with a very strong affinity to transthyretin. Molecular docking simulations show that the flexible tail of the prenylated xanthone could allow favorable molecular interactions. Since this xanthone may play a role in the Thyroxine Metabolism and/or over the pathogenic process associated with the amyloid disease, these results may be explored for the design of new ligands.

  • Transthyretin is not essential for Thyroxine to reach the brain and other tissues in transthyretin-null mice
    American Journal of Physiology-Endocrinology and Metabolism, 1997
    Co-Authors: Joana Almeida Palha, M. T. Hays, G. Moreale De Escobar, Vasso Episkopou, Max E. Gottesman, Maria João Saraiva
    Abstract:

    As part of a study on tissue uptake of Thyroxine (T4) in a transthyretin (TTR)-null mouse strain, kinetic parameters of Thyroxine Metabolism in wild-type mice under normal physiological conditions are presented. Kinetic analysis of injected [(125)I]T4 showed that TTR-null mutants have markedly increased [(125)I]T4 transfer rate constants from plasma to the fast-exchange compartments of liver and kidney and from fast to slow kidney compartments. Transfer rates from plasma to brain, testes, and fat were little affected. The T4 tissue content in the mutants was greatly reduced in brain but relatively normal in liver and kidney. No major changes were observed in brain 3,3',5-triiodothyronine concentrations, suggesting that availability of this hormone is not markedly altered in the mutant mice. The low T4 brain content probably reflects the absence of T4-TTR complexes in the mutant choroid plexus and cerebrospinal fluid. This study indicates that TTR is not essential for T4 tissue uptake or for T4 to reach the brain across the choroid plexus-cerebrospinal fluid and/or blood-brain barriers.