Human Endogenous Metabolite; synthetic form of the thyroid hormone thyroxine (T4)

Thyroid stimulating hormone (TSH) levels are linked to deiodinases (DIOs), which catalyze the transformation of thyroxine (pro-hormone) to the active thyroid hormone. While DIO3 plays a role in inactivating the secretion, DIO1 and DIO2 catalyze the activation of thyroid hormone secretion. The negative feedback regulation of pituitary TSH secretion is largely dependent on the activities of DIO1 and DIO2[1]. Ionic channels, pumps, and regulatory contractile proteins are known to have their expression modulated by the hormones triiodothyronine (T3) and levothyroxine (T4). Additionally, it has been demonstrated that thyroid hormones affect the calcium flux and homeostasis that are in charge of excitation and contractility, with L-thyroxine and triiodothyronine influencing the pharmacological regulation and secretion of this process. Rats fed an iodine-free diet for 12 weeks showed a significant reduction in their levels of L-thyroxine and triiodothyronine compared to the control group fed a standard diet (p<0.001). L-thyroxine levels rise (p=0.02) in the group receiving low doses of the medication, but triiodothyronine levels essentially stay the same (p=0.19) as in the control group. Rats given large doses of L-thyroxine show a significant increase in circulating concentrations of both triiodothyronine and L-thyroxine relative to the hypothyroid group that was not treated (p<0.001 and p=0.004, respectively), as well as a significant increase in L-thyroxine levels relative to the control values (p=0.03)[2].

Thyroid-stimulating hormone (TSH) levels are correlated with the catalysis of thyroxine (prohormone) conversion to active thyroid hormone by deiodinase (DIO). Thyroid hormone secretion is activated by DIO1 and DIO2, whereas secretion is inactivated by DIO3. The regulation of pituitary TSH secretion by negative feedback is largely dependent on the actions of DIO1 and DIO2 [1]. The expression of ion channels, pumps, and regulating contractile proteins is regulated by the hormones triiodothyronine (T3) and L-thyroxine (T4). Moreover, it has been demonstrated that thyroid hormones affect calcium homeostasis and flux, which are in charge of excitation and contraction. Triiodothyronine and L-thyroxine are known to modify the pharmacological regulation and secretion of calcium. Triiodothyronine and L-thyroxine levels significantly decreased (p<0.001) in rats given an iodine-free diet for 12 weeks as compared to controls given a regular diet. Triiodothyronine levels were essentially comparable to those in the control group (p=0.19), but an increase in L-thyroxine was noted in the low-dose L-thyroxine treatment group (p=0.02). Rats treated with high-dose L-thyroxine showed significantly higher circulating concentrations of both triiodothyronine and L-thyroxine compared to the untreated hypothyroid group (p<0.001 and p=0.004, respectively), and L-thyroxine levels were significantly higher than the control value (p=0.03)[2].

Biochemical techniques[2] ELISA assays were performed using a standard rat Thyroxine (T4) and T3 ELISA kit according to the manufacturer's protocol. Western blot analysis was performed exactly as previously described.

Rats: The experiment uses 22 female Sprague-Dawley rats. There are four groups of non-pregnant rats: 1) No thyroid function, 2) hypothyroidism, 3) hypothyroidism treated with low doses of L-thyroxine (20 μg/kg/day), and 4) high doses of L-thyroxine (100 μg/kg/day). While the intervention rats (groups 2-4) are fed an iodine-free diet for 12 weeks to induce hypothyroidism, the control group (group 1) is fed a standard diet. This is followed by an additional 4 weeks of feeding to allow for L-thyroxine treatment and screening for hypothyroidism. You have unlimited access to food and water (iodine-free diet). Groups 3 and 4, which represent the hypothyroid group, receive intraperitoneal injections of 20 μg/kg and 100 μg/kg of L-thyroxine per day, respectively, every 24 hours. Within weeks 12 and 16 of starting the iodine-free or control diet, blood samples are taken for thyroid function screening. After treatment, a hysterectomy is performed under general anesthesia (isoflurane 2%), and the two uterine horns are kept in physiological Krebs' solution until isometric tension measurements are taken, which should take no longer than an hour.

bsorption is increased in the fasting state and decreased in malabsorption states (e.g., sprue); absorption also may decrease with age. American Society of Health-System Pharmacists 2015; Drug Information 2015. Bethesda, MD. 2015, p. 3230

For more Absorption, Distribution and Excretion (Complete) data for LEVOTHYROXINE (7 total), please visit the HSDB record page.

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Metabolism / Metabolites
Approximately 70% of secreted T4 is deiodinated to equal amounts of T3 and reverse triiodothyronine (rT3), which is calorigenically inactive. T4 is slowly eliminated through its major metabolic pathway to T3 via sequential deiodination, where approximately 80% of circulating T3 is derived from peripheral T4. The liver is the major site of degradation for both T4 and T3, with T4 deiodination also occurring at a number of additional sites, including the kidney and other tissues. Elimination of T4 and T3 involves hepatic conjugation to glucuronic and sulfuric acids. The hormones undergo enterohepatic circulation as conjugates are hydrolyzed in the intestine and reabsorbed. Conjugated compounds that reach the colon are hydrolyzed and eliminated as free compounds in the feces. Other minor T4 metabolites have been identified.

Yields l-tyrosine in rabbit, in rat /From table/ Goodwin, B.L. Handbook of Intermediary Metabolism of Aromatic Compounds. New York: Wiley, 1976., p. T-14

Yields 3,3',5-triiodo-L-thyronine in man, rat, dog, rabbit. /From table/ Goodwin, B.L. Handbook of Intermediary Metabolism of Aromatic Compounds. New York: Wiley, 1976., p. T-14

Yields l-thyroxine-4'-beta-d-glucuronide in dog, in man, in rat. Yields l-thyroxine-4'-sulfate in dog. /From table/ Goodwin, B.L. Handbook of Intermediary Metabolism of Aromatic Compounds. New York: Wiley, 1976., p. T-14

Yields 3,3',5,5'-tetraiodothyropyruvic acid in rat. Yields l-thyronine in rat. /From table/ Goodwin, B.L. Handbook of Intermediary Metabolism of Aromatic Compounds. New York: Wiley, 1976., p. T-14

Yields 3,3'-diiodo-l-thyronine in dog. Yields 3,3',5,5'-tetraiodothyroacetic acid in man, in rat. /From table/ Goodwin, B.L. Handbook of Intermediary Metabolism of Aromatic Compounds. New York: Wiley, 1976., p. T-14

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Biological Half-Life
T₄ half-life is 6 to 7 days. T₃ half-life is 1 to 2 days.

In dogs orally administered levothyroxine has relatively ... short elimination half life when compared to humans. ... The serum half life is approximately 12-16 hours. Plumb D.C. Veterinary Drug Handbook. 8th ed. (pocket). Ames, IA: Wiley-Blackwell, 2015., p. 842

The usual plasma half-lives of thyroxine and triiodothyronine are 6-7 days and approximately 1-2 days, respectively. The plasma half-lives of thyroxine and triiodothyronine are decreased in patients with hyperthyroidism and increased in those with hypothyroidism.

Effects During Pregnancy and Lactation
◉ Summary of Use during Lactation
Levothyroxine (T4) is a normal component of human milk. Limited data on exogenous replacement doses of levothyroxine during breastfeeding indicate no adverse effects in infants. The American Thyroid Association recommends that subclinical and overt hypothyroidism should be treated with levothyroxine in lactating women seeking to breastfeed. Adequate levothyroxine treatment during lactation may normalize milk production in hypothyroid lactating mothers with low milk supply. Levothyroxine dosage requirement may be increased in the postpartum period compared to prepregnancy requirements in patients with Hashimoto's thyroiditis.
◉ Effects in Breastfed Infants
Effects of exogenous thyroid hormone administration to mothers on their infant have not been reported. One case of apparent mitigation of cretinism in hypothyroid infants by breastfeeding has been reported, but the amounts of thyroid hormones in milk are not optimal, and this result has been disputed. The thyroid hormone content of human milk from the mothers of very preterm infants appears not to be sufficient to affect the infants' thyroid status. The amounts of thyroid hormones in milk are apparently not sufficient to interfere with diagnosis of hypothyroidism.
In a telephone follow-up study, 5 nursing mothers reported taking levothyroxine (dosage unspecified). The mothers reported no adverse reactions in their infants.
One mother who had undergone a thyroidectomy was taking levothyroxine 100 mcg daily as well as calcium carbonate and calcitriol. Her breastfed infant was reportedly "thriving" at 3 months of age.
A woman with propionic acidemia took levothyroxine 50 mcg daily as well as biotin, carnitine, and various amino acids while exclusively breastfeeding her infant for 2 months and nonexclusively for 10 months. At that time, the infant had normal growth and development.
◉ Effects on Lactation and Breastmilk
Adequate thyroid hormone serum levels are required for normal lactation. Replacing deficient thyroid levels should improve milk production caused by hypothyroidism. Supraphysiologic doses would not be expected to further improve lactation.

[1]. Arici M, et al. Association between genetic polymorphism and levothyroxine bioavailability in hypothyroid patients. Endocr J. 2018 Mar 28;65(3):317-323.
[2]. Corriveau S, et al. Levothyroxine treatment generates an abnormal uterine contractility patterns in an in vitro animalmodel. J Clin Transl Endocrinol. 2015 Sep 9;2(4):144-149.

Levothyroxine Sodium is the sodium salt of levothyroxine, a synthetic levoisomer of thyroxine (T4) that is similar to the endogenous hormone produced by the thyroid gland. In peripheral tissues, levothyroxine is deiodinated by 5'-deiodinase to form triiodothyronine (T3). T3 enters the cell and binds to nuclear thyroid hormone receptors; the activated hormone-receptor complex in turn triggers gene expression and produces proteins required in the regulation of cellular respiration; thermogenesis; cellular growth and differentiation; and the metabolism of proteins, carbohydrates and lipids. T3 also exhibits cardiostimulatory effects.
The major hormone derived from the thyroid gland. Thyroxine is synthesized via the iodination of tyrosines (MONOIODOTYROSINE) and the coupling of iodotyrosines (DIIODOTYROSINE) in the THYROGLOBULIN. Thyroxine is released from thyroglobulin by proteolysis and secreted into the blood. Thyroxine is peripherally deiodinated to form TRIIODOTHYRONINE which exerts a broad spectrum of stimulatory effects on cell metabolism.

C15H12I4NNAO5

816.87

816.679

C, 22.06; H, 1.48; I, 62.14; N, 1.71; Na, 2.81; O, 9.79

25416-65-3

Thyroxine sulfate;77074-49-8;L-Thyroxine sodium salt pentahydrate;6106-07-6;L-Thyroxine sodium;55-03-8;L-Thyroxine-13C6-1;1217780-14-7;Biotin-(L-Thyroxine);149734-00-9;Biotin-hexanamide-(L-Thyroxine);2278192-78-0;Thyroxine hydrochloride-13C6;1421769-38-1;L-Thyroxine-13C6;720710-30-5;L-Thyroxine-13C6,15N;1431868-11-9

23665037

Typically exists as solid at room temperature

576.3ºC at 760 mmHg

207 °C

302.3ºC

3.922

7

10

5

30

426

1

C1=C(C=C(C(=C1I)OC2=CC(=C(C(=C2)I)O)I)I)C[C@@H](C(=O)[O-])N.O.O.O.O.O.[Na+]

JMHCCAYJTTWMCX-QWPJCUCISA-M

InChI=1S/C15H11I4NO4.Na.5H2O/c16-8-4-7(5-9(17)13(8)21)24-14-10(18)1-6(2-11(14)19)3-12(20)15(22)23;;;;;;/h1-2,4-5,12,21H,3,20H2,(H,22,23);;5*1H2/q;+1;;;;;/p-1/t12-;;;;;;/m0....../s1

sodium;(2S)-2-amino-3-[4-(4-hydroxy-3,5-diiodophenoxy)-3,5-diiodophenyl]propanoate;pentahydrate

25416-65-3; Levothyroxine sodium; Levothyroxine sodium monohydrate; L-Thyroxine sodium xhydrate; Levothyroxine sodium hydrate; L-Thyroxine sodium hydrate; Monosodium L-thyroxine hydrate; 31178-59-3;

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

May dissolve in DMSO (in most cases), if not, try other solvents such as H2O, Ethanol, or DMF with a minute amount of products to avoid loss of samples

Note: Listed below are some common formulations that may be used to formulate products with low water solubility (e.g. < 1 mg/mL), you may test these formulations using a minute amount of products to avoid loss of samples.

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Injection Formulation 1: DMSO : Tween 80： Saline = 10 : 5 : 85 (i.e. 100 μL DMSO stock solution → 50 μL Tween 80 → 850 μL Saline)
*Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH ₂ O to obtain a clear solution.
Injection Formulation 2: DMSO : PEG300 ：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL DMSO → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)
Injection Formulation 3: DMSO : Corn oil = 10 : 90 (i.e. 100 μL DMSO → 900 μL Corn oil)
Example: Take the Injection Formulation 3 (DMSO : Corn oil = 10 : 90) as an example, if 1 mL of 2.5 mg/mL working solution is to be prepared, you can take 100 μL 25 mg/mL DMSO stock solution and add to 900 μL corn oil, mix well to obtain a clear or suspension solution (2.5 mg/mL, ready for use in animals).

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Injection Formulation 4: DMSO : 20% SBE-β-CD in saline = 10 : 90 [i.e. 100 μL DMSO → 900 μL (20% SBE-β-CD in saline)]
*Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.
Injection Formulation 5: 2-Hydroxypropyl-β-cyclodextrin : Saline = 50 : 50 (i.e. 500 μL 2-Hydroxypropyl-β-cyclodextrin → 500 μL Saline)
Injection Formulation 6: DMSO : PEG300 : castor oil : Saline = 5 : 10 : 20 : 65 (i.e. 50 μL DMSO → 100 μLPEG300 → 200 μL castor oil → 650 μL Saline)
Injection Formulation 7: Ethanol : Cremophor : Saline = 10： 10 : 80 (i.e. 100 μL Ethanol → 100 μL Cremophor → 800 μL Saline)
Injection Formulation 8: Dissolve in Cremophor/Ethanol (50 : 50), then diluted by Saline
Injection Formulation 9: EtOH : Corn oil = 10 : 90 (i.e. 100 μL EtOH → 900 μL Corn oil)
Injection Formulation 10: EtOH : PEG300：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL EtOH → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)

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Oral Formulation 1: Suspend in 0.5% CMC Na (carboxymethylcellulose sodium)
Oral Formulation 2: Suspend in 0.5% Carboxymethyl cellulose
Example: Take the Oral Formulation 1 (Suspend in 0.5% CMC Na) as an example, if 100 mL of 2.5 mg/mL working solution is to be prepared, you can first prepare 0.5% CMC Na solution by measuring 0.5 g CMC Na and dissolve it in 100 mL ddH2O to obtain a clear solution; then add 250 mg of the product to 100 mL 0.5% CMC Na solution, to make the suspension solution (2.5 mg/mL, ready for use in animals).

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Oral Formulation 3: Dissolved in PEG400
Oral Formulation 4: Suspend in 0.2% Carboxymethyl cellulose
Oral Formulation 5: Dissolve in 0.25% Tween 80 and 0.5% Carboxymethyl cellulose
Oral Formulation 6: Mixing with food powders

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Note: Please be aware that the above formulations are for reference only. InvivoChem strongly recommends customers to read literature methods/protocols carefully before determining which formulation you should use for in vivo studies, as different compounds have different solubility properties and have to be formulated differently.

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 (Please use freshly prepared in vivo formulations for optimal results.)