1. Directional thyroid hormone distribution via the blood stream to target sites
- Author
-
Onno E. Janssen and Susanne T. Janssen
- Subjects
0301 basic medicine ,Thyroid Hormones ,endocrine system ,medicine.medical_specialty ,endocrine system diseases ,Thyroxine-Binding Globulin ,Serum Albumin, Human ,030209 endocrinology & metabolism ,Biochemistry ,Thyroid function tests ,Thyroid hormone receptor beta ,03 medical and health sciences ,Thyroxine-binding globulin ,Dogs ,0302 clinical medicine ,Endocrinology ,Hyperthyroxinemia ,Internal medicine ,Thyronines ,medicine ,Animals ,Humans ,Prealbumin ,Promoter Regions, Genetic ,Molecular Biology ,Thyroid hormone transport ,Mammals ,Binding Sites ,Thyroid hormone receptor ,biology ,medicine.diagnostic_test ,Thyroid ,medicine.disease ,Protein Transport ,030104 developmental biology ,medicine.anatomical_structure ,biology.protein ,Hormone - Abstract
Thyroid hormones are bound to three major serum transport proteins, thyroxin-binding globulin (TBG), transthyretin (TTR) and human serum albumin (HSA). TBG has the strongest affinity for thyroid hormones, TTR is also found in the cerebrospinal fluid and HSA is the most abundant protein in plasma. Combination defects of either a high affinity TTR or HSA variant do not compensate TBG deficiency, underscoring the dominant role of TBG among the thyroid hormone transport proteins. On the other hand, coexistence of raised affinity TTR and HSA variants causes an augmented hyperthyroxinemia. Variations in thyroid hormone transport proteins may alter thyroid function tests to mimic hypo- or hyperthyroidism. As affected individuals are clinically euthyroid and do not require treatment, identification of thyroid hormone transport protein defects is important to avoid unnecessary diagnostic and therapeutic interventions. Mammals share the multilayered system of thyroid hormone binding proteins with humans. Some of them, especially carnivores, do not express TBG. In dogs, this defect has been shown to be caused by a defective hepatocyte nuclear factor-1 binding site in the TBG promoter, preventing TBG synthesis in the liver. The major endogenous thyroid hormone metabolite 3-iodothyronamine (3-T1AM) exerts marked cryogenic, metabolic, cardiac and central nervous system actions. It is bound to apolipoproteinB-100 (ApoB100), possibly facilitating its cellular uptake via interaction with the low density lipoprotein-receptor. This review summarizes the handling of hydrophobic charged thyroid hormone signaling molecules and their metabolite 3-T1AM in aqueous body fluids and the advantages and limits of their serum distributor proteins.
- Published
- 2017