triiodothyronine--reverse and tetraiodothyroacetic-acid

Thyroid hormones (THs) are produced by the thyroid gland and converted in peripheral organs by deiodinases. THs regulate cell functions through two distinct mechanisms: genomic (nuclear) and nongenomic (non-nuclear). Many TH effects are mediated by the genomic pathway--a mechanism that requires TH activation of nuclear thyroid hormone receptors. The overall nongenomic processes, emerging as important accessory mechanisms in TH actions, have been observed at the plasma membrane, in the cytoplasm and cytoskeleton, and in organelles. Some products of peripheral TH metabolism (besides triiodo-L-thyronine), now termed 'nonclassical THs', were previously considered as inactive breakdown products. However, several reports have recently shown that they may have relevant biological effects. The recent accumulation of knowledge on how classical and nonclassical THs modulate the activity of membrane receptors, components of the mitochondrial respiratory chain, kinases and deacetylases, opened the door to the discovery of new pathways through which they act. We reviewed the current state-of-the-art on the actions of the nonclassical THs, discussing the role that these endogenous TH metabolites may have in the modulation of thyroid-related effects in organisms with differing complexity, ranging from nonmammals to humans.

Topics: Animals; Diiodothyronines; Humans; Signal Transduction; Thyroid Gland; Thyroid Hormones; Thyronines; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

Topics: Chemical Phenomena; Chemistry; Diiodothyronines; Diiodotyrosine; Glucuronates; Humans; Hyperthyroidism; Iodine; Kinetics; Phenyl Ethers; Radioimmunoassay; Sulfates; Thyronines; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

Thyroid hormones (THs) operate numerous physiological processes through modulation of the nuclear thyroid hormone receptors and several other proteins. We report direct activation of the nuclear peroxisome proliferator-activated receptor gamma (PPARγ) and retinoid X receptor (RXR) by classical and nonclassical THs as another molecular activity of THs. The T4 metabolite TETRAC was the most active TH on PPARγ with nanomolar potency and binding affinity. We demonstrate that TETRAC promotes PPARγ/RXR signaling in cell-free, cellular, and

Topics: Amino Acid Sequence; Animals; Drug Evaluation, Preclinical; Male; Mice; Models, Molecular; PPAR gamma; Protein Conformation; Thyroxine

We have investigated the mechanism by which thyroid hormone potentiates IFN-gamma-induced HLA-DR expression. IFN-gamma-induced HLA-DR expression requires activation of STAT1alpha and induction of the Class II trans-activator, CIITA. HeLa and CV-1 cells treated only with L-thyroxine (T4) demonstrated increased tyrosine phosphorylation and nuclear translocation (= activation) of STAT1alpha; this hormone effect on signal transduction, and T4 potentiation of IFN-gamma-induced HLA-DR expression, were blocked by the inhibitors CGP 41251 (PKC) and genistein (tyrosine kinase). Treatment of cells with T4-agarose also caused activation of STAT1alpha. In the presence of IFN-gamma, T4 enhanced cytokine-induced STAT1alpha activation. Potentiation by T4 of IFN-gamma action was associated with increased mRNA for both CIITA and HLA-DR, with peak enhancement at 16 h (CIITA), and 2 d (HLA-DR). T4 increased IFN-gamma-induced HLA-DR protein 2.2-fold and HLA-DR mRNA fourfold after 2 d. Treatment with actinomycin D after induction of HLA-DR mRNA with IFN-gamma, with or without T4, showed that thyroid hormone decreased the t(1/2) of mRNA from 2.4 to 1.1 h. HeLa and CV-1 cells lack functional nuclear thyroid hormone receptor. Tetraiodothyroacetic acid (tetrac) and 3,5,3'-triiodo-thyroacetic acid (triac) blocked T4 potentiation of IFN-gamma-induced HLA-DR expression and T4 activation of STAT1alpha. These studies define an early hormone recognition step at the cell surface that is novel, distinct from nuclear thyroid hormone receptor, and blocked by tetrac and triac. Thus, thyroid hormone potentiation of IFN-gamma-induced HLA-DR transcription is mediated by a cell membrane hormone binding site, enhanced activation of STAT1alpha, and increased CIITA induction.

Topics: Biological Transport; Cell Nucleus; Dextrothyroxine; Diiodothyronines; Drug Synergism; Genistein; HeLa Cells; HLA-DR Antigens; Humans; Interferon-gamma; Interferon-Stimulated Gene Factor 3; Nuclear Proteins; Phosphorylation; Protein Kinase C; Protein-Tyrosine Kinases; RNA, Messenger; Thyroxine; Time Factors; Trans-Activators; Transcription Factors; Triiodothyronine; Triiodothyronine, Reverse; Tyrosine

The uptake of [125I]T4 was investigated in cultured anterior pituitary cells isolated from adult fed Wistar rats and cultured for 3 days in medium containing 10% fetal calf serum. Experiments were performed with [125I]T4 (10(5) to 2 x 10(6) cpm; 0.35-7 nM) in medium containing 0.5% or 0.1% BSA. The uptake of [125I]T4 increased with time and showed equilibrium after around 1 h of incubation. The presence of 10 microM unlabeled T4 during incubation decreased the uptake of [125I]T4 by 65-70% at all time intervals. After 24 h of incubation, 1.5% iodide and 3.2% conjugates were detected in the medium, whereas around 20% of cellular radioactivity represented [125I]T3. The 15-min uptake of [125I]T4 was significantly reduced by simultaneous incubation with 100 nM T4 (by 24%; P < 0.05), 100 nM T3 (by 38%; P < 0.001), or 10 microM rT3 (by 32%; P < 0.001), whereas 10 microM tetraiodothyroacetic acid (Tetrac) had no effect. Furthermore, preincubation (30 min) and incubation (15 min) with 10 microM monodansylcadaverine, oligomycin, or monensin reduced the uptake of [125I]T4 by 30%, 50%, and 40%, respectively (all P < 0.001). Substitution of Na+ in the buffer by K+ diminished the uptake of [125I]T4 by 39% (P < 0.005); 2 mM phenylalanine, tyrosine, or tryptophan reduced [125I]T4 uptake by 18% (P < 0.05), 18% (P = NS), and 33% (P < 0.005), respectively. Our data suggest that the pituitary contains a specific carrier-mediated energy-requiring mechanism for [125I]T4 uptake that is partly dependent on the Na+ gradient. In addition, part of [125I]T4 uptake in the pituitary might occur through an amino acid transport system. When expressed per pM of free hormone, the 15-min uptake of [125I]T4 was approximately as high as that of [125I]T3. Because the reduction of [125I]T4 uptake by T4, T3, monodansylcadaverine, oligomycin, and monensin was roughly the same as the previously reported reduction of [125I]T3 uptake by the same compounds, it is further suggested that T4 and T3 share a common carrier in cultured anterior pituitary cells.

Topics: Animals; Binding, Competitive; Cadaverine; Cell Membrane; Cells, Cultured; Iodine Radioisotopes; Kinetics; Male; Monensin; Oligomycins; Pituitary Gland, Anterior; Rats; Rats, Wistar; Serum Albumin, Bovine; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

Photolysis of thyroxine and its analogs in the near UV permitted synthesis in good yield of picogram to gram quantities of thyroid hormone metabolites. Preparation of the same metabolites by classical chemical synthesis requires multistep procedures. Specifically labeled metabolites of high specific activity (e.g., those carrying the label in the nonphenolic ring) were obtained by photolysis of appropriately labeled thyroxine or 3',3',5'-triiodothyronine (reverse triiodothyronine). Some of these labeled metabolites, which are required for metabolic studies (3-iodothyronine and 3,3'-diiodothyronine, labeled in the nonphenolic ring), had not previously been obtained by other methods. Irradiation of thyroxine and reverse triiodothyronine in 150 mM methanolic ammonium hydroxide with greater than 340-nm light caused removal of one iodine atom from the phenolic ring with formation of 3,5,3'-triiodothyronine and 3,3'-diiodothyronine, respectively. Irradiation with higher-energy light (greater than 300 nm) led to stepwise removal of additional iodine atoms. Those in the phenolic ring were removed preferentially, so that 3,5-diiodothyronine and 3-iodothyronine, respectively, were formed. The iodine atoms in the nonphenolic ring were lost more slowly. Tetraiodothyroacetic acid followed a similar photodeiodination pattern. Photolysis with light in the near UV is a simple method for the synthesis of thyroid hormone metabolites.

Topics: Diiodothyronines; Kinetics; Photolysis; Thyroxine; Triiodothyronine, Reverse; Ultraviolet Rays

The metabolism of 3, 5-[3'-125I]triiodothyronin (T3) and 3-[3', 5'-125I]triiodothyronine (rT3) was studied in cultured monkey hepatocarcinoma cells (NCLP-6E), and the deiodinations of these iodothyronines were also investigated in cultured cell homogenates and in rat liver homogenates. The metabolites were analyzed by ion exchange column chromatography. For nonphenolic ring deiodination of 3, 5-[3'-125I]triiodothyronine, the order of the inhibitory effect of excess unlabeled iodothyronine or its analog was as follows: 3,3',5-triiodothyroinine greater than triiodothyroacetic acid greater than tetraiodothyroacetic acid greater than thyroxine. This order did not differ between in the intact cells (NCLP-6E) and their homogenates. The order of effectiveness of the excess unlabeled compounds on phenolic ring deiodination of 3-[3', 5'-125I]triiodothyronine in the intact cells was as follows: tetraiodothyroacetic acid greater than triiodothyroacetic acid, 3, 3', 5-triiodothyronine greater than thyroxine. This order was the same among monkey hepatocarcinoma cell homogenates, rat hepatoma cell homogenates and rat liver homogenates, and triiodothyroacetic acid was obviously more effective than 3, 3', 5-triiodothyronine. It was concluded that 3, 3', 5-triiodothyronine had the highest affinity for nonphenolic ring deiodinase among iodothyronines and their analogs used in the present study and that tetraiodothyroacetic acid and the highest affinity for phenolic ring deiodinase. It seems, therefore, that the metabolites derived from the thyroid hormones might contribute to deiodinations which involve activation and inactivation of the hormones.

Topics: Animals; Cell Line; Chromatography, Ion Exchange; Haplorhini; Iodide Peroxidase; Liver; Liver Neoplasms; Peroxidases; Rats; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

Complete turnover studies of T4, T3, rT3, and 3,5,3',5-tetriodothyroacetic acid (TA4) were carried out in normal subjects given T4 (0.2 mg, by mouth daily) by the integration method. When compared to the five fed controls, the four fasting subjects showed a decrease of mean T3 disposal from 41 to 18 micrograms/day, an increase of mean rT3 disposal from 49 to 61 micrograms/day. The mean serum TA4 concentration rose from 53 to 112 ng/dl, while the TA4 metabolic clearance remained unchanged. The fraction of T4 metabolized by deiodination changed from 79.0% to 77.5% in the fasting subjects as the fraction of T4 metabolized by deamination changed from 1.1% to 2.2%. Therefore, fasting induces a significant shunting of T4 away from T3 production into rT3 and TA4 production. However, oxidative deamination remains a minor metabolic pathway of T4 in man during both normal and fasting conditions. Given its low disposal rate and low biological potency, the increased TA4 production during fasting is probably not the inhibitory factor of TSH response to the lowered T3 production during fasting.

Topics: Adult; Fasting; Humans; Kinetics; Reference Values; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

Topics: Animals; Bile; Chromatography, High Pressure Liquid; Diiodothyronines; Male; Rats; Starvation; Thyronines; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse