3-Iodothyronamine Affects Thermogenic Substrates' Mobilization in Brown Adipocytes

Adipose Tissue Remodeling in Obesity: An Overview of the Actions of Thyroid Hormones and Their Derivatives

Metabolic syndrome and obesity have become important health issues of epidemic proportions and are often the cause of related pathologies such as type 2 diabetes (T2DM), hypertension, and cardiovascular disease. Adipose tissues (ATs) are dynamic tissues that play crucial physiological roles in maintaining health and homeostasis. An ample body of evidence indicates that in some pathophysiological conditions, the aberrant remodeling of adipose tissue may provoke dysregulation in the production of various adipocytokines and metabolites, thus leading to disorders in metabolic organs. Thyroid hormones (THs) and some of their derivatives, such as 3,5-diiodo-l-thyronine (T2), exert numerous functions in a variety of tissues, including adipose tissues. It is known that they can improve serum lipid profiles and reduce fat accumulation. The thyroid hormone acts on the brown and/or white adipose tissues to induce uncoupled respiration through the induction of the uncoupling protein 1 (UCP1) to generate heat. Multitudinous investigations suggest that 3,3',5-triiodothyronine (T3) induces the recruitment of brown adipocytes in white adipose depots, causing the activation of a process known as "browning". Moreover, in vivo studies on adipose tissues show that T2, in addition to activating brown adipose tissue (BAT) thermogenesis, may further promote the browning of white adipose tissue (WAT), and affect adipocyte morphology, tissue vascularization, and the adipose inflammatory state in rats receiving a high-fat diet (HFD). In this review, we summarize the mechanism by which THs and thyroid hormone derivatives mediate adipose tissue activity and remodeling, thus providing noteworthy perspectives on their efficacy as therapeutic agents to counteract such morbidities as obesity, hypercholesterolemia, hypertriglyceridemia, and insulin resistance.

Substantial impact of 3-iodothyronamine (T1AM) on the regulations of fluorescent thermoprobe-measured cellular temperature and natriuretic peptide expression in cardiomyocytes

There is growing interest in 3-iodothyronamine (T1AM), an active thyroid hormone metabolite, that induces negative inotropic and chronotropic actions in the heart and exerts systemic hypothermic action. We explored the direct impact of T1AM on cardiomyocytes with a focus on the regulation of the intracellular temperature and natriuretic peptide (NP) expression. A thermoprobe was successfully introduced into neonatal rat cardiomyocytes, and the temperature-dependent changes in the fluorescence intensity ratio were measured using a fluorescence microscope. After one-hour incubation with T1AM, the degree of change in the fluorescence intensity ratio was significantly lower in T1AM-treated cardiomyocytes than in equivalent solvent-treated controls (P < 0.01), indicating the direct hypothermic action of T1AM on cardiomyocytes. Furthermore, T1AM treatment upregulated B-type NP (BNP) gene expression comparable to treatment with endothelin-1 or phenylephrine. Of note, ERK phosphorylation was markedly increased after T1AM treatment, and inhibition of ERK phosphorylation by an MEK inhibitor completely cancelled both T1AM-induced decrease in thermoprobe-measured temperature and the increase in BNP expression. In summary, T1AM decreases fluorescent thermoprobe-measured temperatures (estimated intracellular temperatures) and increases BNP expression in cardiomyocytes by activating the MEK/ERK pathway. The present findings provide new insight into the direct myocardial cellular actions of T1AM in patients with severe heart failure.

Redox Properties of 3-Iodothyronamine (T1AM) and 3-Iodothyroacetic Acid (TA1)

3-iodothyronamine (T1AM) and 3-iodothyroacetic acid (TA1) are thyroid-hormone-related compounds endowed with pharmacological activity through mechanisms that remain elusive. Some evidence suggests that they may have redox features. We assessed the chemical activity of T1AM and TA1 at pro-oxidant conditions. Further, in the cell model consisting of brown adipocytes (BAs) differentiated for 6 days in the absence (M cells) or in the presence of 20 nM T1AM (M + T1AM cells), characterized by pro-oxidant metabolism, or TA1 (M + TA1 cells), we investigated the expression/activity levels of pro- and anti-oxidant proteins, including UCP-1, sirtuin-1 (SIRT1), mitochondrial monoamine (MAO-A and MAO-B), semicarbazide-sensitive amine oxidase (SSAO), and reactive oxygen species (ROS)-dependent lipoperoxidation. T1AM and TA1 showed in-vitro antioxidant and superoxide scavenging properties, while only TA1 acted as a hydroxyl radical scavenger. M + T1AM cells showed higher lipoperoxidation levels and reduced SIRT1 expression and activity, similar MAO-A, but higher MAO-B activity in terms of M cells. Instead, the M + TA1 cells exhibited increased levels of SIRT1 protein and activity and significantly lower UCP-1, MAO-A, MAO-B, and SSAO in comparison with the M cells, and did not show signs of lipoperoxidation. Our results suggest that SIRT1 is the mediator of T1AM and TA1 pro-or anti-oxidant effects as a result of ROS intracellular levels, including the hydroxyl radical. Here, we provide evidence indicating that T1AM and TA1 administration impacts on the redox status of a biological system, a feature that indicates the novel mechanism of action of these two thyroid-hormone-related compounds.

The 3-iodothyronamine (T1AM) and the 3-iodothyroacetic acid (TA1) indicate a novel connection with the histamine system for neuroprotection

The 3-iodothyronamine (T1AM) and 3-iodothryoacetic acid (TA1), are endogenous occurring compounds structurally related with thyroid hormones (THs, the pro-hormone T4 and the active hormone T3) initially proposed as possible mediators of the rapid effects of T3. However, after years from their identification, the physio-pathological meaning of T1AM and TA1 tissue levels remains an unsolved issue while pharmacological evidence indicates both compounds promote in rodents central and peripheral effects with mechanisms which remain mostly elusive. Pharmacodynamics of T1AM includes the recognition of G-coupled receptors, ion channels but also biotransformation into an active metabolite, i.e. the TA1. Furthermore, long term T1AM treatment associates with post-translational modifications of cell proteins. Such array of signaling may represent an added value, rather than a limit, equipping T1AM to play different functions depending on local expression of targets and enzymes involved in its biotransformation. Up to date, no information regarding TA1 mechanistic is available. We here review some of the main findings describing effects of T1AM (and TA1) which suggest these compounds interplay with the histaminergic system. These data reveal T1AM and TA1 are part of a network of signals involved in neuronal plasticity including neuroprotection and suggest T1AM and TA1 as lead compounds for a novel class of atypical psychoactive drugs.