3,5-diiodo-L-thyronine (t2) in dietary supplements: what are the physiological effects?

Effects of Prenatal Exposure to Bisphenol A Substitutes, Bisphenol S and Bisphenol F, on Offspring's Health: Evidence from Epidemiological and Experimental Studies

Pregnancy and lactation are critical periods for human well-being and are sensitive windows for pollutant exposure. Bisphenol A (BPA) is well demonstrated as a toxicant and has been replaced in the plastic industry with other bisphenol analogs that share similarities in structure and characteristics, most commonly Bisphenol S (BPS) and Bisphenol F (BPF). Maternal exposure to BPS or BPF can result in their accumulation in the fetal compartment, leading to chronic exposure and potentially limiting normal fetal growth and development. This review summarizes considerable findings of epidemiological or experimental studies reporting associations between BPS or BPF and impaired fetal growth and development. Briefly, the available findings indicate that exposure to the two bisphenol analogs during pregnancy and lactation can result in multiple disturbances in the offspring, including fetal growth restrictions, neurological dysfunctions, and metabolic disorders with the potential to persist throughout childhood. The occurrence of premature births may also be attributed to exposure to the two bisphenols. The possible mechanisms of actions by which the two bisphenols can induce such effects can be attributed to a complex of interactions between the physiological mechanisms, including impaired placental functioning and development, dysregulation of gene expression, altered hormonal balance, and disturbances in immune responses as well as induced inflammations and oxidative stress. In conclusion, the available evidence suggests that BPS and BPF have a toxic potential in a compartment level to BPA. Future research is needed to provide more intensive information; long-term studies and epidemiological research, including a wide scale of populations with different settings, are recommended. Public awareness regarding the safety of BPA-free products should also be enhanced, with particular emphasis on educating individuals responsible for the well-being of children.

Determination of thyroid hormones in dietary supplements using liquid chromatography-tandem mass spectrometry

More than 27 million Americans have some kind of thyroid disease. Numerous dietary supplements claiming to support healthy thyroid function and healthy metabolism and balance or promote weight loss are available for purchase in retail stores and on the internet. In the literature, there have been reports of adverse events associated with the consumption of thyroid hormone-containing products. In this study, an LC-MS/MS method was developed and validated for the analysis of thyroxine (T4), 3,3',5-triiodo-l-thyronine (T3), 3,3',5'-triiodothyronine (rT3), 3,5-diiodothyronine (3,5-T2) and 3,3'-diiodothyronine (3,3'-T2) in dietary supplements. Sonication with methanol was used for the extraction of free hormones from nonglandular products. The tissue-bound hormones from glandular thyroid products were extracted using a modified enzymatic digestion, in which the matrix was first extracted by sonication with methanol and then by enzymatic digestion with proteases. Both extraction methods provided acceptable recovery values between 78% and 116%. Fifty-eight products making claims related to thyroid management were purchased over the internet from 2017-2018 and quantitatively analyzed for five hormones using the validated methods. Eleven out of 19 glandular products were found to contain quantifiable amounts of hormones. Maximum daily servings were also calculated for each product based on label information. The maximum amount of T4, T3, and rT3 per daily serving in the glandular products were up to 210, 32, and 7.6 μg/day, respectively. In the case of nonglandular products, which were labeled to contain plant extracts, vitamins, minerals, diiodo compounds, and so forth, the amounts of 3,5-T2 and 3,3'-T2 were up to 740 and 2700 μg/day, respectively.

Physiological Role and Use of Thyroid Hormone Metabolites - Potential Utility in COVID-19 Patients

Thyroxine and triiodothyronine (T3) are classical thyroid hormones and with relatively well-understood actions. In contrast, the physiological role of thyroid hormone metabolites, also circulating in the blood, is less well characterized. These molecules, namely, reverse triiodothyronine, 3,5-diiodothyronine, 3-iodothyronamine, tetraiodoacetic acid and triiodoacetic acid, mediate both agonistic (thyromimetic) and antagonistic actions additional to the effects of the classical thyroid hormones. Here, we provide an overview of the main factors influencing thyroid hormone action, and then go on to describe the main effects of the metabolites and their potential use in medicine. One section addresses thyroid hormone levels in corona virus disease 19 (COVID-19). It appears that i) the more potently-acting molecules T3 and triiodoacetic acid have shorter half-lives than the less potent antagonists 3-iodothyronamine and tetraiodoacetic acid; ii) reverse T3 and 3,5-diiodothyronine may serve as indicators for metabolic dysregulation and disease, and iii) Nanotetrac may be a promising candidate for treating cancer, and resmetirom and VK2809 for steatohepatitis. Further, the use of L-T3 in the treatment of severely ill COVID-19 patients is critically discussed.

Immunohistochemical Analysis of Intestinal and Central Nervous System Morphology in an Obese Animal Model (Danio rerio) Treated with 3,5-T2: A Possible Farm Management Practice?

Simple Summary

The obesity induced by overconsumption of nutrients leads to systemic inflammation and alters metabolic homeostasis by acting on central nervous system and peripheral tissues such as intestine. The 3,5-diiodo-L-thyronine (3,5-T2) is well-known for its positive role on fat mass and lipid metabolism, and at date, it is widely used as a drug for the treatment of obesity. However, the safe and effective dose as well as the possible adverse effects of this molecule have not been sufficiently explored. In this study, we analyzed the role of 3,5-T2 in regulating central and peripheral inflammation in diet-induced obese (D.I.O.) model of zebrafish. We found that 3,5-T2 sustained the intestinal alteration caused by D.I.O., as indicated by the high levels of pro-inflammatory cytokines, accompanied by a significant effect of 3,5-T2 on body weight and central inflammation in D.I.O. zebrafish. Therefore, the suggested potential use of 3,5-T2 to contrast obesity should be viewed with caution. We conclude that the zebrafish model can help to better understand the fundamental beneficial and side effects of 3,5-T2, which is of great importance to define the possible use of this metabolite of thyroid hormones as a drug in different diseases including obesity.

Abstract

The 3,5-diiodo-L-thyronine (3,5-T2) is an endogenous metabolite of thyroid hormones, whose administration to rodents fed high-fat diet (HFD) prevents body weight increase and reverts the expression pattern of pro-inflammatory factors associated to HFD. The diet-induced obese (D.I.O.) zebrafish (Danio rerio) has been recently used as an experimental model to investigate fundamental processes underlying central and peripheral obesity-driven inflammation. Herein, we aim to understand the role of 3,5-T2 in regulating central and peripheral inflammation in D.I.O. model of zebrafish. 3,5-T2 (10 nM and 100 nM) was administered with the obesity-inducing diet (D.I.O. with 3,5-T2) or after 4 weeks of obesity-inducing diet (D.I.O. flw 3,5-T2). 3,5-T2 significantly increased the body weight and serum triglyceride levels in D.I.O. zebrafish in both conditions. Moreover, 3,5-T2 sustained or increased inflammation in the anterior (AI) and mid (MI) intestine when administered with the obesity-inducing diet, as indicated by the immunoexpression of the inflammatory markers tumor-necrosis factor-α (TNFα), cyclooxygenase 2 (COX2), calnexin, caspase 3, and proliferating cell nuclear antigen (PCNA). On the contrary, when 3,5-T2 was administered after the obesity-inducing diet, partly reverted the intestinal alteration induced by D.I.O. In addition, brain inflammation, as indicated by the increase in the activation of microglia, was detected in D.I.O. zebrafish and D.I.O. treated with 3,5-T2. These findings reveal that the effects of 3,5-T2 on fish intestine and brain can deviate from those shown in obese mammals, opening new avenues to the investigation of the potential impact of this thyroid metabolite in different diseases including obesity.

Obesity Therapy: How and Why?

Background:

Obesity represents the second preventable mortality cause worldwide, and is very often associated with type 2 Diabetes Mellitus (T2DM). The first line treatment is lifestyle modification to weight-loss, but for those who fail to achieve the goal or have difficulty in maintaining achieved results, pharmacological treatment is needed. Few drugs are available today, because of their side effects.

Objective:

We aim to review actual pharmacological management of obese patients, highlighting differences between Food and Drug Administration - and European Medicine Agency-approved molecules, and pointing out self-medications readily obtainable and widely distributed.

Methods:

Papers on obesity, weight loss, pharmacotherapy, self- medication and diet-aid products were selected using Medline. Research articles, systematic reviews, clinical trials and meta-analyses were screened.

Results:

Anti-obesity drugs with central mechanisms, such as phentermine and lorcaserin, are available in USA, but not in Europe. Phentermine/topiramate and naltrexone/bupropion combinations are now available, even though the former is still under investigation from EMA. Orlistat, with peripheral mechanisms, represents the only drug approved for weight reduction in adolescents. Liraglutide has been approved at higher dose for obesity. Anti-obesity drugs, readily obtainable from the internet, include crude-drug products and supplements for which there is often a lack of compliance to national regulatory standards.

Conclusion:

Mechanisms of weight loss drugs include the reduction of energy intake or the increase in energy expenditure and sense of satiety as well as the decrease of hunger or the reduction in calories absorption. Few drugs are approved, and differences exist between USA and Europe. Moreover, herbal medicines and supplements often sold on the internet and widely used by obese patients, present a risk of adverse effects.

Thyroid Hormones and Derivatives: Endogenous Thyroid Hormones and Their Targets

More than a century after the discovery of L-Thyroxine, the main thyroid hormone secreted solely by the thyroid gland, several metabolites of this iodinated, tyrosine-derived ancestral hormone have been identified. These are utilized as hormones during development, differentiation, metamorphosis, and regulation of most biochemical reactions in vertebrates and their precursor species. Among those metabolites are the thyromimetically active 3,3',5-Triiodo-L-thyronine (T3) and 3,5-Diiodo-L-thronine, reverse-T3 (3,3',5'-Triiodo-L-thyronine) with still unclear function, the recently re-discovered thyronamines (e.g., 3-Iodo-thyronamine), which exert in part T3-antagonistic functions, the thyroacetic acids (e.g., Tetrac and Triac), as well as various sulfated or glucuronidated metabolites of this panel of iodinated signaling compounds. In the blood most of these hydrophobic metabolites are tightly bound to the serum distributor proteins thyroxine binding globulin (TBG), transthyretin (TTR), albumin or apolipoprotein B100. Cellular import and export of these charged, highly hydrophobic amino acid derivatives requires a number of cell-membrane transporters or facilitators such as MCT8 or MCT10 and members of the OATP and LAT families of transporters. Depending on their structure, the thyroid hormone metabolites exert their cellular action by binding and thus modulating the function of various receptors systems (e.g., ανβ3 integrin receptor and transient receptor potential channels (TRPM8) of the cell membrane), in part linked to intracellular downstream kinase signaling cascades, and several isoforms of membrane-associated, mitochondrial or nuclear thyroid hormone receptors (TR), which are members of the c-erbA family of ligand-modulated transcription factors. Intracellular deiodinase selenoenzymes, which obligatory are membrane integrated enzymes, ornithine decarboxylase and monoamine oxidases control local availability of biologically active thyroid hormone metabolites. Inactivation of thyroid hormone metabolites occurs mainly by deiodination, sulfation or glucuronidation, reactions which favor their renal or fecal elimination.

Emerging role of thyroid hormone metabolites

Thyroid hormones (THs) are essential for the regulation of development and metabolism in key organs. THs produce biological effects both by directly affecting gene expression through the interaction with nuclear receptors (genomic effects) and by activating protein kinases and/or ion channels (short-term effects). Such activations can be either direct, in the case of ion channels, or mediated by membrane or cytoplasmic receptors. Short-term-activated signalling pathways often play a role in the regulation of genomic effects. Several TH intermediate metabolites, which were previously considered without biological activity, have now been associated with a broad range of actions, mostly attributable to short-term effects. Here, we give an overview of the physiological roles and mechanisms of action of THs, focusing on the emerging position that TH metabolites are acquiring as important regulators of physiology and metabolism.

Serum Thyrotropin Concentrations Are Not Associated with the Ankle-Brachial Index: Results from Three Population-Based Studies

BACKGROUND

There is only limited data on the potential association between thyroid dysfunction and peripheral arterial disease (PAD).

OBJECTIVE

The aim of our study was to investigate the potential association of thyroid function, as defined by serum concentrations of the clinically used primary thyroid function marker thyrotropin [i.e. thyroid-stimulating hormone (TSH)] and 3,5-diiodothyronine (3,5-T2), with the ankle-brachial index (ABI) as a marker of PAD.

METHODS

We used data from 5,818 individuals from three cross-sectional population-based studies conducted in Northeast (SHIP-2 and SHIP-TREND) and Central Germany (CARLA). Measurement of serum TSH concentrations was conducted in one central laboratory for all three studies. In a randomly selected subpopulation of 750 individuals of SHIP-TREND, serum 3,5-T2 concentrations were measured with a recently developed immunoassay. ABI was measured either by a hand-held Doppler ultrasound using the Huntleigh Dopplex D900 or palpatorily by the OMRON HEM-705CP device.

RESULTS

Serum TSH concentrations were not significantly associated with ABI values in any of the three studies. Likewise, groups of individuals with a TSH <0.3 mIU/l or with a TSH ≥3.0 mIU/l had no significantly different ABI values in comparison with individuals with a TSH in the reference range. Analyses regarding TSH within the reference range or serum 3,5-T2 concentrations did not reveal consistent significant associations with the ABI. No sex-specific associations were detected.

CONCLUSIONS

The results of our study do not substantiate evidence for an association between thyroid function and PAD, but further studies are needed to investigate the associations of overt forms of thyroid dysfunction with PAD.