title: ApoB-100-containing lipoproteins are major carriers of 3-iodothyronamine in circulation.
abstract: 3-Iodothyronamine (T(1)AM) is a biogenic amine derivative of thyroid hormone present in tissue and blood of vertebrates. Approximately 99% of the circulating thyroid hormones are bound to plasma proteins, including three major thyroid hormone-binding proteins, and the question arises as to whether circulating T(1)AM is also bound to serum factors. We report here that T(1)AM is largely bound to a single protein component of human serum. Using T(1)AM-affinity chromatography, we isolated this protein, and sequence analysis identified it as apolipoprotein B-100 (apoB-100), the protein component of several low density lipoprotein particles. Consistent with this finding, we demonstrate that >90% of specifically bound T(1)AM in human serum resides in the apoB-100-containing low density lipoprotein fraction. T(1)AM reversibly binds to apoB-100-containing lipoprotein particles with an equilibrium dissociation constant (K(D)) of 17 nm and a T(1)AM/apoB-100 stoichiometry of 1:1. Competition binding assays demonstrate that this binding site is highly selective for T(1)AM. Intracellular T(1)AM uptake is significantly enhanced by apoB-100-containing lipoprotein particles. Modest enhancements to apoB-100 cellular uptake and secretion by T(1)AM were observed; however, multidose T(1)AM treatment did not affect lipid or lipoprotein inventory in vivo. Thus, it appears that apoB-100 serves as a carrier of circulating T(1)AM and affords a novel mechanism by which T(1)AM gains entry to cells.
authors: Department of Physiology and Pharmacology, Oregon Health and Science University, Portland, Oregon 97239-3098, USA.
authors: Gouriprassana
authors: G
authors: Roy
authors: Ekaterina
authors: E
authors: Placzek
authors: Thomas S
authors: TS
authors: Scanlan
mesh_terms: D000818:Animals; D053299:Apolipoprotein B-100 / Q000737:chemistry / Q000378:metabolism*; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D056945:Hep G2 Cells; D006801:Humans; D011485:Protein Binding / Q000502:physiology; D051381:Rats; D013970:Thyronines / Q000737:chemistry / Q000378:metabolism*
chemical_list: C487948:3-iodothyronamine; D053299:Apolipoprotein B-100; D002352:Carrier Proteins; D013970:Thyronines