Commentary: Euthyroid Sick Syndrome in Patients With COVID-19

Recent data from case reports and small clinical studies indicates thyroid disorders characterized by reduction of T3 levels are found associated with adverse events and all causes of mortality in Covid-19 patients (1–7). In this scenario the paper from Zuo et al. (4) consistently describes the presence of the euthyroid sick syndrome (EES) correlating with Covid-19 disease severity but not with non-invasive or invasive ventilation. None of these reports clarify the clinical meaning of these endocrine disturbances, and their pathogenesis remains elusive. In this respect, hypotheses include they represent a stress-evoked response or are generated by a direct attack of the virus to the gland. This latter hypothesis is sustained by findings demonstrating gland cell types can be target of viruses from bat origin. Consistently, it has been reported that i) human thyrocytes express the mRNA for ACE2 (8), the host receptor of the virus Spike protein, ii) viral particles were detected in the follicular epithelium of patients who died of SARS and also of Covid-19 presenting subacute thyroiditis (9) iii) Covid-19 patients may present, where measured, high levels of pro-calcitonin (PCT). Overall, these intriguing data would need to be confirmed by larger clinical studies to establish conclusively the causal relationship, if any, among thyroid diseases and virus infection, and, more importantly, their clinical relevance as possible prognostic indicators of mortality and of severe cardiovascular events (10). However, in the light of the present data, we like to share some considerations on the possibility that reduced serum T3 levels, as observed in EES, because they are not representative of its tissue-specific levels, coincide with accumulation of T3 metabolites, i.e. thyromimetics. The accumulation of such compounds in the olfactory epithelium and skeletal muscle could offer a pathogenic hypothesis for the onset of anosmia and sarcopenia, two fingerprint manifestations of Covid-19 infection. In extra thyroid tissues, T3 levels are controlled by type 1, 2, and 3 deiodinases (DIO1, DIO2, and DIO3 respectively), enzymes removing iodide ions with respect to their position on the aromatic rings and that have a high specific tissue expression. In particular, DIO2 and DIO3 are the main isoforms expressed in neurons and skeletal muscle, and they are rapidly modulated at inflammatory conditions, including ESS (4) and, in general, infective agent attacks (11, 12). At conditions of reduced DIO2 activity, T4 metabolism is mainly driven towards revT3, the alternative metabolite with a very low intrinsic activity at thyroid hormone receptors and considered among the source of other iodinated metabolites belonging to three different chemical classes including thyronamines and thyroacetic acids. These metabolites are indicated as endogenous thyromimetics accumulating in thyroid hormone target tissues and sharing the same but not all the biological effects of T3 (13). Among these compounds, the 3-iodothyronamine (T1AM) is the more characterized in term of pharmacokinetic and pharmacodynamics features (13). Pharmacologically administered T1AM elicited neurological and metabolic effects with high potency. The mechanism of several of these effects remains to be clarified, and possible targets have been described including the trace amine associated receptors (TAAR1-5), while its affinity at thyroid hormone receptors is negligible. TAARs are evolutionarily conserved in vertebrates including humans, exerting an indispensable role in olfaction (14). T1AM, and possibly other thyronamines by the means of their nature as “amines in trace”, is a high affinity ligand for TAAR1 and is described as an inverse agonist at the TAAR5 (15). The olfactory epithelium expresses several TAAR isoforms including TAAR5 but also ACE2 and TMPRSS2, the host virus receptors. According to its pharmacodynamics, T1AM is expected to reduce the basal activity of TAAR5. Down-regulation of TAARs (and anosmia) is reported as a secondary event to immune innate signaling activation induced by virus infection (16). It is then possible to postulate accumulation of T1AM, as result of an increase of revT3 concentration, might have a role in increasing the threshold of olfactory receptor activation thus participating to Covid-19 induced anosmia. The fast recovery from this adverse event experienced by some Covid-19 patients would be consistent with the short half-life of T1AM. In those where anosmia persists even after infection resolution, desensitization effects could add to more complex damages at neurological circuits. Sarcopenia associated with Covid-19 is likely secondary to the cytokine storm and of a long bed rest even if a direct attack of the virus to the skeletal myocytes cannot be excluded since satellite cells and adult myofibers express ACE2 (17). Sarcopenia has a negative impact on patient recovery (18), and it represents a negative prognostic factor for cardiovascular complications (19). Since T3 strongly controls skeletal muscle regenerative capacity and metabolic functions (20), reduced levels of T3 together with vascular inflammation and cachexia, might trigger skeletal muscle catabolism and an incorrect myogenic program of satellite cells. In addition, a role for calcitonin in controlling satellite cell quiescence and their escape from fiber niche, a condition exposing satellite cells to aging and a fibrotic fate, has been described recently (21). In the skeletal muscle, Ju et al. (2017) reported T1AM activated catabolic pathways involved in sarcopenia including AMPK activation (22). Overall, anosmia and sarcopenia have an inflammatory ground which includes a crucial balance between DIO2/DIO3, thus controlling T3 local production (23, 24). Accumulation of revT3 and of T1AM may act in concert as pathogenic events in these Covid-19 clinical manifestations. The role of thyromimetics in Covid-19 related anosmia and sarcopenia is a hypothesis which needs to be confirmed by clinical data. In this respect we launched the opportunity to include the evaluation of thyromimetics among the biomarkers of the thyroid function. Covid-19 pandemic might offer an extraordinary opportunity for investigating the role of the thyroid and to assign a physiopathological role to endogenous thyromimetics

3-iodothyronamine (T1AM), a novel antagonist of muscarinic receptors.

3-iodothyronamine (T1AM) is a trace amine suspected to derive from thyroid hormone metabolism. T1AM was described as a ligand of G-protein coupled monoaminergic receptors, including trace amine associated receptors, suggesting the amine may exert a modulatory role on the monoaminergic transmission. Nothing is known on the possibility that T1AM could also modulate the cholinergic transmission interacting with muscarinic receptors. We evaluated whether T1AM (10 nM\u2013100 \u3bcM) was able to i) displace [3H]-NMS (0.20 nM) binding to membrane preparations from CHO cells stably transfected with human muscarinic receptor subtypes (M1-M5); ii) modify basal or acetylcholine induced pERK1/2 levels in CHO expressing the human muscarinic type 3 receptor subtype by Western blot iii) modify basal and carbachol-induced contraction of isolated rat urinary bladder. T1AM fitting within rat muscarinic type 3 receptor was simulated by Docking studies. T1AM recognized all muscarinic receptor subtypes (pKi values in the micromolar range). Interacting at type 3, T1AM reduced acetylcholine-increased pERK1/2 levels. T1AM reduced carbachol-induced contraction of the rat urinary bladder. The fenoxyl residue and the iodide ion were found essential for establishing contacts with the active site of the rat muscarinic type 3 receptor subtype. Our results indicate that T1AM binds at muscarinic receptors behaving as a weak, not selective, antagonist. This finding adds knowledge on the pharmacodynamics features of T1AM and it may prompt investigation on novel pharmacological effects of T1AM at conditions of hyper-activation of the muscarinic tone including the overactive urinary bladder

Pharmacological perspectives in sarcopenia: A potential role for renin-angiotensin system blockers?

Sarcopenia represents a major health problem highly prevalent in elderly and age-related chronic diseases. Current pharmacological strategies available to prevent and reverse sarcopenia are largely unsatisfactory thus raising the need to identify novel targets for pharmacological intervention and possibly more effective and safe drugs. This review highlights the current knowledge of the potential benefits of renin-angiotensin system blockade in sarcopenia and discuss the main mechanisms underlying the effects

Thyroid Hormone, Thyroid Hormone Metabolites and Mast Cells: A Less Explored Issue

Mast cells are primary players in immune and inflammatory diseases. In the brain, mast cells are located at the brain side of the blood brain barrier (BBB) exerting a crucial role in protecting the brain from xenobiotic invasion. Furthermore, recent advances in neuroscience indicate mast cells may play an important role in glial cell-neuron communication through the release of mediators, including histamine. Interestingly, brain mast cells contain not only 50% of the brain histamine but also hormones, proteases and lipids or amine mediators; and cell degranulation may be triggered by different stimuli activating membrane bound receptors including the four types of histaminergic receptors. Among hormones, mast cells can store thyroid hormone (T3) and express membrane-bound thyroid stimulating hormone receptors (TSHRs), thus suggesting from one side that thyroid function may affect mast cells function, from the other that mast cell degranulation may impact on thyroid function. In this respect, the research on hormones in mast cells is scarce. Recent pharmacological evidence indicates the existence of a non-genomic portion of the thyroid secretion including thyroid hormone metabolites. Among which the 3,5 diiodothyronine (3,5-T2), 3-iodothyroanamine (T1AM) and 3-iodothyroacetic acid (TA1) are the most studied. All these compounds are endogenously occurring and found to be increased in inflammatory-based diseases involving mast cells. T1AM and TA1 induce, as T3, neuroprotective effects and itch but also hyperalgesia in rodents with a mechanism largely unknown but mediated by the release of histamine. Due to the rapid onset of their effectiveness they may trigger histamine release from a cell where it is “ready-to-be released,” i.e., mast cells. Following a very thin path which passes through old experimental and clinical evidence, at the light of novel acquisitions on endogenous T3 metabolites, we aim to stimulate the attention on the possibility that mast cell histamine may be the connector of a novel (neuro) endocrine pathway linking the thyroid with mast cells

D-Tagatose Feeding Reduces the Risk of Sugar-Induced Exacerbation of Myocardial I/R Injury When Compared to Its Isomer Fructose

It is known that fructose may contribute to myocardial vulnerability to ischemia/reperfusion (I/R) injury. D-tagatose is a fructose isomer with less caloric value and used as low-calorie sweetener. Here we compared the metabolic impact of fructose or D-tagatose enriched diets on potential exacerbation of myocardial I/R injury. Wistar rats were randomizedly allocated in the experimental groups and fed with one of the following diets: control (CTRL), 30% fructose-enriched (FRU 30%) or 30% D-tagatose-enriched (TAG 30%). After 24 weeks of dietary manipulation, rats underwent myocardial injury caused by 30 min ligature of the left anterior descending (LAD) coronary artery followed by 24 h′ reperfusion. Fructose consumption resulted in body weight increase (49%) as well as altered glucose, insulin and lipid profiles. These effects were associated with increased I/R-induced myocardial damage, oxidative stress (36.5%) and inflammation marker expression. TAG 30%-fed rats showed lower oxidative stress (21%) and inflammation in comparison with FRU-fed rats. Besides, TAG diet significantly reduced plasmatic inflammatory cytokines and GDF8 expression (50%), while increased myocardial endothelial nitric oxide synthase (eNOS) expression (59%). Overall, we demonstrated that D-tagatose represents an interesting sugar alternative when compared to its isomer fructose with reduced deleterious impact not only on the metabolic profile but also on the related heart susceptibility to I/R injury

Brain Histamine Modulates the Antidepressant-Like Effect of the 3-Iodothyroacetic Acid (TA1)

3-iodothyroacetic acid (TA1), an end metabolite of thyroid hormone, has been shown to produce behavioral effects in mice that are dependent on brain histamine. We now aim to verify whether pharmacologically administered TA1 has brain bioavailability and is able to induce histamine-dependent antidepressant-like behaviors. TA1 brain, liver and plasma levels were measured by LC/MS-MS in male CD1 mice, sacrificed 15 min after receiving a high TA1 dose (330 μgkg–1). The hypothalamic mTOR/AKT/GSK-β cascade activation was evaluated in mice treated with 0.4, 1.32, 4 μgkg–1 TA1 by Western-blot. Mast cells were visualized by immuno-histochemistry in brain slices obtained from mice treated with 4 μgkg–1 TA1. Histamine release triggered by TA1 (20–1000 nM) was also evaluated in mouse peritoneal mast cells. After receiving TA1 (1.32, 4 or 11 μgkg–1; i.p.) CD1 male mice were subjected to the forced swim (FST) and the tail suspension tests (TST). Spontaneous locomotor and exploratory activities, motor incoordination, and anxiolytic or anxiogenic effects, were evaluated. Parallel behavioral tests were also carried out in mice that, prior to receiving TA1, were pre-treated with pyrilamine (10 mgkg–1; PYR) or zolantidine (5 mgkg–1; ZOL), histamine type 1 and type 2 receptor antagonists, respectively, or with p-chloro-phenylalanine (100 mgkg–1; PCPA), an inhibitor of serotonin synthesis. TA1 given i.p. to mice rapidly distributes in the brain, activates the hypothalamic mTOR/AKT and GSK-3β cascade and triggers mast cells degranulation. Furthermore, TA1 induces antidepressant effects and stimulates locomotion with a mechanism that appears to depend on the histaminergic system. TA1 antidepressant effect depends on brain histamine, thus highlighting a relationship between the immune system, brain inflammation and the thyroid

Dual-beam confocal light-sheet microscopy via flexible acousto-optic deflector

Confocal detection in digital scanned laser light-sheet fluorescence microscopy (DSLM) has been established as a gold standard method to improve image quality. The selective line detection of a complementary metal-oxide-semiconductor camera (CMOS) working in rolling shutter mode allows the rejection of out-of-focus and scattered light, thus reducing background signal during image formation. Most modern CMOS have two rolling shutters, but usually only a single illuminating beam is used, halving the maximum obtainable frame rate. We report on the capability to recover the full image acquisition rate via dual confocal DSLM by using an acousto-optic deflector. Such a simple solution enables us to independently generate, control and synchronize two beams with the two rolling slits on the camera. We show that the doubling of the imaging speed does not affect the confocal detection high contrast

New Insights into the Potential Roles of 3-Iodothyronamine (T1AM) and Newly Developed Thyronamine-Like TAAR1 Agonists in Neuroprotection

3-Iodothyronamine (T1AM) is an endogenous high-affinity ligand of the trace amine-associated receptor 1 (TAAR1), detected in mammals in many organs, including the brain. Recent evidence indicates that pharmacological TAAR1 activation may offer a novel therapeutic option for the treatment of a wide range of neuropsychiatric and metabolic disorders. To assess potential neuroprotection by TAAR1 agonists, in the present work, we initially investigated whether T1AM and its corresponding 3-methylbiaryl-methane analog SG-2 can improve learning and memory when systemically administered to mice at submicromolar doses, and whether these effects are modified under conditions of MAO inhibition by clorgyline. Our results revealed that when i.p. injected to mice, both T1AM and SG-2 produced memory-enhancing and hyperalgesic effects, while increasing ERK1/2 phosphorylation and expression of transcription factor c-fos. Notably, both compounds appeared to rely on the action of ubiquitous enzymes MAO to produce the corresponding oxidative metabolites that were then able to activate the histaminergic system. Since autophagy is key for neuronal plasticity, in a second line of experiments we explored whether T1AM and synthetic TAAR1 agonists SG1 and SG2 were able to induce autophagy in human glioblastoma cell lines (U-87MG). After treatment of U-87MG cells with 1 μM T1AM, SG-1, SG-2 transmission electron microscopy (TEM) and immunofluorescence (IF) showed a significant time-dependent increase of autophagy vacuoles and microtubule-associated protein 1 light chain 3 (LC3). Consistently, Western blot analysis revealed a significant increase of the LC3II/LC3I ratio, with T1AM and SG-1 being the most effective agents. A decreased level of the p62 protein was also observed after treatment with T1AM and SG-1, which confirms the efficacy of these compounds as autophagy inducers in U-87MG cells. In the process to dissect which pathway induces ATG, the effects of these compounds were evaluated on the PI3K-AKT-mTOR pathway. We found that 1 μM T1AM, SG-1 and SG-2 decreased pAKT/AKT ratio at 0.5 and 4 h after treatment, suggesting that autophagy is induced by inhibiting mTOR phosphorylation by PI3K-AKT-mTOR pathway. In conclusion, our study shows that T1AM and thyronamine-like derivatives SG-1 and SG-2 might represent valuable tools to therapeutically intervene with neurological disorder

Hit-to-Lead Optimization of Mouse Trace Amine Associated Receptor 1 (mTAAR1) Agonists with a Diphenylmethane-Scaffold: Design, Synthesis, and Biological Study

The trace amine-associated receptor 1 (TAAR1) is a G-protein-coupled receptors (GPCR) potently activated by a variety of molecules besides trace amines (TAs), including thyroid hormone-derivatives like 3-iodothyronamine (T1AM), catechol-O-methyltransferase products like 3-methoxytyramine, and amphetamine-related compounds. Accordingly, TAAR1 is considered a promising target for medicinal development. To gain more insights into TAAR1 physiological functions and validation of its therapeutic potential we recently developed a new class of thyronamine-like derivatives. Among them compound SG2 showed high affinity and potent agonist activity at mouse TAAR1. In the present work we describe design, the synthesis and SAR study of a new series of compounds (1-16) obtained by introducing specific structural changes at key points of our lead-compound SG2 skeleton. Five of the newly synthesized compounds displayed mTAAR1 agonist activity higher than both SG2 and T1AM. Selected diphenylmethane analogs, namely 1 and 2, showed potent functional activity in in vitro and in vivo models