Autoantibodies targeting G protein-coupled receptors: An evolving history in autoimmunity. Report of the 4th international symposium.

G protein-coupled receptors (GPCR) are involved in various physiological and pathophysiological processes. Functional autoantibodies targeting GPCRs have been associated with multiple disease manifestations in this context. Here we summarize and discuss the relevant findings and concepts presented in the biennial International Meeting on autoantibodies targeting GPCRs (the 4th Symposium), held in Lübeck, Germany, 15-16 September 2022. The symposium focused on the current knowledge of these autoantibodies' role in various diseases, such as cardiovascular, renal, infectious (COVID-19), and autoimmune diseases (e.g., systemic sclerosis and systemic lupus erythematosus). Beyond their association with disease phenotypes, intense research related to the mechanistic action of these autoantibodies on immune regulation and pathogenesis has been developed, underscoring the role of autoantibodies targeting GPCRs on disease outcomes and etiopathogenesis. The observation repeatedly highlighted that autoantibodies targeting GPCRs could also be present in healthy individuals, suggesting that anti-GPCR autoantibodies play a physiologic role in modeling the course of diseases. Since numerous therapies targeting GPCRs have been developed, including small molecules and monoclonal antibodies designed for treating cancer, infections, metabolic disorders, or inflammatory conditions, anti-GPCR autoantibodies themselves can serve as therapeutic targets to reduce patients' morbidity and mortality, representing a new area for the development of novel therapeutic interventions.

α1-Adrenergic Receptors: Insights into Potential Therapeutic Opportunities for COVID-19, Heart Failure, and Alzheimer's Disease.

α1-Adrenergic receptors (ARs) are members of the G-Protein Coupled Receptor superfamily and with other related receptors (ß and α2), they are involved in regulating the sympathetic nervous system through binding and activation by norepinephrine and epinephrine. Traditionally, α1-AR antagonists were first used as anti-hypertensives, as α1-AR activation increases vasoconstriction, but they are not a first-line use at present. The current usage of α1-AR antagonists increases urinary flow in benign prostatic hyperplasia. α1-AR agonists are used in septic shock, but the increased blood pressure response limits use for other conditions. However, with the advent of genetic-based animal models of the subtypes, drug design of highly selective ligands, scientists have discovered potentially newer uses for both agonists and antagonists of the α1-AR. In this review, we highlight newer treatment potential for α1A-AR agonists (heart failure, ischemia, and Alzheimer's disease) and non-selective α1-AR antagonists (COVID-19/SARS, Parkinson's disease, and posttraumatic stress disorder). While the studies reviewed here are still preclinical in cell lines and rodent disease models or have undergone initial clinical trials, potential therapeutics discussed here should not be used for non-approved conditions.

ß-arrestins and G protein-coupled receptor kinases in viral entry: A graphical review.

Viruses rely on host-cell machinery in order to invade host cells and carry out a successful infection. G-protein coupled receptor (GPCR)-mediated signaling pathways are master regulators of cellular physiological processing and are an attractive target for viruses to rewire cells during infection. In particular, the GPCR-associated scaffolding proteins ß-arrestins and GPCR signaling effectors G-protein receptor kinases (GRKs) have been identified as key cellular factors that mediate viral entry and orchestrate signaling pathways that reprogram cells for viral replication. Interestingly, a broad range of viruses have been identified to activate and/or require GPCR-mediated pathways for infection, including polyomaviruses, flaviviruses, influenza virus, and SARS-CoV-2, demonstrating that these viruses may have conserved mechanisms of host-cell invasion. Thus, GPCR-mediated pathways highlight an attractive target for the development of broad antiviral therapies.

Post-COVID-19 Syndrome: Retinal Microcirculation as a Potential Marker for Chronic Fatigue.

Post-COVID-19 syndrome (PCS) is characterized by persisting sequelae after infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). PCS can affect patients with all COVID-19 disease severities. As previous studies have revealed impaired blood flow as a provoking factor triggering PCS, it was the aim of the present study to investigate the potential association between self-reported chronic fatigue and retinal microcirculation in patients with PCS, potentially indicating an objective biomarker. A prospective study was performed, including 201 subjects: 173 patients with PCS and 28 controls. Retinal microcirculation was visualized by OCT angiography (OCT-A) and quantified using the Erlangen-Angio-Tool as macula and peripapillary vessel density (VD). Chronic fatigue (CF) was assessed according to the variables of Bell's score, age and gender. VDs in the superficial vascular plexus (SVP), intermediate capillary plexus (ICP) and deep capillary plexus (DCP) were analyzed, considering the repetitions (12 times). Seropositivity for autoantibodies targeting G protein-coupled receptors (GPCR-AAbs) was determined by an established cardiomyocyte bioassay. Taking account of the repetitions, a mixed model was performed to detect possible differences in the least square means between the different groups included in the analysis. An age effect in relation to VD was observed between patients and controls (p < 0.0001). Gender analysis showed that women with PCS showed lower VD levels in the SVP compared to male patients (p = 0.0015). The PCS patients showed significantly lower VDs in the ICP as compared to the controls (p = 0.0001 (CI: 0.32; 1)). Moreover, considering PCS patients, the mixed model revealed a significant difference between those with chronic fatigue (CF) and those without CF with respect to VDs in the SVP (p = 0.0033 (CI: -4.5; -0.92)). The model included variables of age, gender and Bell's score, representing a subjective marker for CF. Consequently, retinal microcirculation might serve as an objective biomarker in subjectively reported chronic fatigue in patients with PCS.

In Silico Discovery of GPCRs and GnRHRs as Novel Binding Receptors of SARS-CoV-2 Spike Protein Could Explain Neuroendocrine Disorders in COVID-19.

Despite the intense research work since the beginning of the pandemic, the pathogenesis of COVID-19 is not yet clearly understood. The previous mechanism of COVID-19, based on ACE2 tropism and explained through a single receptor, is insufficient to explain the pathogenesis due to the absence of angiotensin-converting enzyme 2 (ACE2) receptors in most of the affected organs. In the current study, we used the PatchDock server to run a molecular docking study of both the gonadotropin-releasing hormone receptor (GnRHR) and G-protein-coupled-receptor (GPCR) with the SARS-CoV-2 spike protein. Molecular Dynamics (MD) simulations were run to analyze the stability of the complexes using the GROMACS package. The docking results showed a high affinity between the spike protein with the GnRHR (-1424.9 kcal/mol) and GPCR (-1451.8 kcal/mol). The results of the MD simulations revealed the significant stability of the spike protein with the GnRHR and GPCR up to 100 ns. The SARS-CoV-2 spike protein had strong binding interactions with the GPCRs and GnRHRs, which are highly expressed in the brain, endocrine organs, and olfactory neurons. This study paves the way towards understanding the complex mechanism of neuroendocrine involvement and peripheral organ involvement, may explain the changing symptoms in patients due to new variants, and may lead to the discovery of new drug targets for COVID-19. In vitro studies involving genetic engineering or gene knockdown of the GPCRs and GnRHRs are needed to further investigate the role of these receptors in COVID-19 pathogenesis.

OA Biology

Purpose: The field of osteoarthritis (OA) biology is rapidly evolving and brilliant progress has been made this year as well. Methods: Landmark studies of OA biology published in 2021 and early 2022 were selected through PubMed searches and classified by their molecular mechanisms, and it was largely divided into the intra-cellular mechanisms and the inter-compartment or inter-cellular interaction in OA progression. Results: The intra-cellular mechanisms involving OA progression included 1) Piezo1/TRPV4-mediated calcium signaling, 2) low grade inflammation by TLR-CD14-LBP complex and IKKβ-NFkB signaling, 3) PGRN/TNFR2/14-3-3ε/Elk-1 anabolic cascade, 4) G protein-coupled receptor (GPCR) signaling, 5) mechanical loading-cilia/Ift88-hedgehog signaling, 6) mitochondrial fission by ERK1/2-DRP1 pathway, and 7) hypoxia-DOT1L-H3K79 methylation pathway. The studies on inter-compartment or inter-cellular interaction in OA progression included the following subjects: 1) the anabolic role of Lubricin, a proteoglycan from superficial zone cells, 2) osteoclast-chondrocyte interaction via exosomal miRNA and sphingosine 1-phosphate (S1P), 3) αV integrin-mediated TGFβ activation by mechanical loading, 4) TGFβ-mediated suppression of sclerostin in osteocytes, 5) catabolic role of Flightless I as a DAMPs-triggering molecule, and 6) catabolic role of paracrine signaling from fat. Conclusions: Despite the disastrous Covid-19 pandemic situation, many outstanding studies have expanded the boundary of OA biology. They give us not only critical insight on pathophysiology, but also clue for the treatment of OA.

Long COVID: Association of Functional Autoantibodies against G-Protein-Coupled Receptors with an Impaired Retinal Microcirculation.

Long COVID (LC) describes the clinical phenotype of symptoms after infection with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Diagnostic and therapeutic options are limited, as the pathomechanism of LC is elusive. As the number of acute SARS-CoV-2 infections was and is large, LC will be a challenge for the healthcare system. Previous studies revealed an impaired blood flow, the formation of microclots, and autoimmune mechanisms as potential factors in this complex interplay. Since functionally active autoantibodies against G-protein-coupled receptors (GPCR-AAbs) were observed in patients after SARS-CoV-2 infection, this study aimed to correlate the appearance of GPCR-AAbs with capillary microcirculation. The seropositivity of GPCR-AAbs was measured by an established cardiomyocyte bioassay in 42 patients with LC and 6 controls. Retinal microcirculation was measured by OCT-angiography and quantified as macula and peripapillary vessel density (VD) by the Erlangen-Angio Tool. A statistical analysis yielded impaired VD in patients with LC compared to the controls, which was accentuated in female persons. A significant decrease in macula and peripapillary VD for AAbs targeting adrenergic ß2-receptor, MAS-receptor angiotensin-II-type-1 receptor, and adrenergic α1-receptor were observed. The present study might suggest that a seropositivity of GPCR-AAbs can be linked to an impaired retinal capillary microcirculation, potentially mirroring the systemic microcirculation with consecutive clinical symptoms.

Disruption of transport regulation of ions and fluid in the lungs with COVID-19

The article discusses scientific data on impaired transport of ions and fluids in the lungs with COVID-19. The authors of the study believe that inhibition of TRPV4 has important therapeutic benefits in COVID-19 patients in particular, powerful prospects for the protection of the alveolar-capillary barrier and even for the regeneration of a damaged barrier. A phase I of the clinical trial using a selective TRPV4 inhibitor demonstrated a favorable safety profile in healthy control volunteers and in patients with cardiogenic pulmonary edema. The protection of the alveolar-capillary barrier with a selective TRPV4 inhibitor would also be useful in eliminating possible pulmonary fibrosis as a late consequence of COVID-19.

Case Report: Neutralization of Autoantibodies Targeting G-Protein-Coupled Receptors Improves Capillary Impairment and Fatigue Symptoms After COVID-19 Infection.

Clinical features of Coronavirus disease 2019 (COVID-19) are caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Acute infection management is a substantial healthcare issue, and the development of long-Covid syndrome (LCS) is extremely challenging for patients and physicians. It is associated with a variety of characteristics as impaired capillary microcirculation, chronic fatigue syndrome (CFS), proinflammatory cytokines, and functional autoantibodies targeting G-protein-coupled receptors (GPCR-AAbs). Here, we present a case report of successful healing of LCS with BC 007 (Berlin Cures, Berlin, Germany), a DNA aptamer drug with a high affinity to GPCR-AAbs that neutralizes these AAbs. A patient with a documented history of glaucoma, recovered from mild COVID-19, but still suffered from CFS, loss of taste, and impaired capillary microcirculation in the macula and peripapillary region. He was positively tested for various targeting GPCR-AAbs. Within 48 h after a single BC 007 treatment, GPCR-AAbs were functionally inactivated and remained inactive during the observation period of 4 weeks. This observation was accompanied by constant improvement of the fatigue symptoms of the patient, taste, and retinal capillary microcirculation. Therefore, the removal of GPCR-AAb might ameliorate the characteristics of the LCD, such as capillary impairment, loss of taste, and CFS.

Adenosine: a partially discovered medicinal agent.

BACKGROUND: A plethora of chemicals exists in human body which can alter physiology in one way or other. Scientists have always been astounded by such abilities of chemicals but as the technology advances, even the chemical which was once expected to be well known changes its status to not really well known. Adenosine is one of the chemicals which is in consonance with the aforementioned statements, although previous articles have covered vast information on role of adenosine in cardiovascular physiology, bacterial pathophysiology and inflammatory diseases. In this review we have discussed adenosine and its congeners as potential promising agents in the treatment of Huntington's disease, post-traumatic stress disorder, erectile dysfunction, viral infections (SARS-CoV) and anxiety. MAIN TEXT: Adenosine is a unique metabolite of ATP; which serves in signalling as well. It is made up of adenine (a nitrogenous base) and ribo-furanose (pentose) sugar linked by ß-N9-glycosidic bond. Adenosine on two successive phosphorylation forms ATP (Adenosine Triphosphate) which is involved in several active processes of cell. It is also one of the building blocks (nucleotides) involved in DNA (Deoxy-ribonucleic Acid) and RNA (Ribonucleic Acid) synthesis. It is also a component of an enzyme called S-adenosyl-L-methionine (SAM) and cyano-cobalamin (vitamin B-12). Adenosine acts by binding to G protein-coupled receptor (GPCR: A1, A2A, A2B and A3) carries out various responses some of which are anti-platelet function, hyperaemic response, bone remodelling, involvement in penile erection and suppression of inflammation. On the other hand, certain microorganisms belonging to genus Candida, Staphylococcus and Bacillus utilize adenosine in order to escape host immune response (phagocytic clearance). These microbes evade host immune response by synthesizing and releasing adenosine (with the help of an enzyme: adenosine synthase-A), at the site of infection. CONCLUSION: With the recent advancement in attribution of adenosine in physiology and pathological states, adenosine and its congeners are being looked forward to bringing a revolution in treatment of inflammation, viral infections, psychiatric and neurodegenerative disorders.

Greek gods and the double-edged sword of liver regeneration.

In the current issue of the Biomedical Journal we gain an insight into the regeneration of liver tissue and how an over-the-counter supplement, stem cells and two plant extracts counteract liver damage. Furthermore the advances against hepatitis C virus are presented, the role of long non-coding RNA elucidated as well as the potential of an adhesion G protein-coupled receptor. In another contribution, the definition and evolutionary impact of copy number variants is clarified. Also, the polymorphism of a scaffolding caspase is investigated. We furthermore learn about the relation between SARS-CoV2 mutants in dependence of geography and explore the challenges of telemedicine in a complex healthcare field. A novel approach to engineering artificial grafts is presented, the challenges of total knee arthroplasty discussed as well as a possible mean of sinus floor elevation for dental implants. At last the concept of flipped classroom is scrutinized in terms of usefulness for a hospital in Taiwan.

Receptor-Loaded Virion Endangers GPCR Signaling: Mechanistic Exploration of SARS-CoV-2 Infections and Pharmacological Implications.

SARS-CoV-2 exploits the respiratory tract epithelium including lungs as the primary entry point and reaches other organs through hematogenous expansion, consequently causing multiorgan injury. Viral E protein interacts with cell junction-associated proteins PALS1 or ZO-1 to gain massive penetration by disrupting the inter-epithelial barrier. Conversely, receptor-mediated viral invasion ensures limited but targeted infections in multiple organs. The ACE2 receptor represents the major virion loading site by virtue of its wide tissue distribution as demonstrated in highly susceptible lung, intestine, and kidney. In brain, NRP1 mediates viral endocytosis in a similar manner to ACE2. Prominently, PDZ interaction involves the entire viral loading process either outside or inside the host cells, whereas E, ACE2, and NRP1 provide the PDZ binding motif required for interacting with PDZ domain-containing proteins PALS1, ZO-1, and NHERF1, respectively. Hijacking NHERF1 and ß-arrestin by virion loading may impair specific sensory GPCR signalosome assembling and cause disordered cellular responses such as loss of smell and taste. PDZ interaction enhances SARS-CoV-2 invasion by supporting viral receptor membrane residence, implying that the disruption of these interactions could diminish SARS-CoV-2 infections and be another therapeutic strategy against COVID-19 along with antibody therapy. GPCR-targeted drugs are likely to alleviate pathogenic symptoms-associated with SARS-CoV-2 infection.

Mechanism deconvolution of Qing Fei Pai Du decoction for treatment of Coronavirus Disease 2019 (COVID-19) by label-free integrative pharmacology assays.

ETHNOPHARMACOLOGICAL RELEVANCE: Traditional Chinese medicine (TCM) has a long history in the prevention and treatment of pandemics. The TCM formula Lung Cleansing and Detoxifying Decoction (LCDD), also known as Qing Fei Pai Du Decoction, has been demonstrated effective against Coronavirus Disease 2019 (COVID-19). AIM OF THE STUDY: This work aimed to elucidate the active ingredients, targets and pathway mechanism of LCDD related to suppression of inflammatory, immunity regulation and relaxation of airway smooth muscle for the treatment of COVID-19. MATERIALS AND METHODS: Mining chemical ingredients reported in LCDD, 144 compounds covering all herbs were selected and screened against inflammatory-, immunity- and respiratory-related GPCRs including GPR35, H1, CB2, B2, M3 and ß2-adrenoceptor receptor using a label-free integrative pharmacology method. Further, all active compounds were detected using liquid chromatography-tandem mass spectrometry, and an herb-compound-target network based on potency and content of compounds was constructed to elucidate the multi-target and synergistic effect. RESULTS: Thirteen compounds were identified as GPR35 agonists, including licochalcone B, isoliquiritigenin, etc. Licochalcone B, isoliquiritigenin and alisol A exhibited bradykinin receptor B2 antagonism activities. Atractyline and shogaol showed as a cannabinoid receptor CB2 agonist and a histamine receptor H1 antagonist, respectively. Tectorigenin and aristofone acted as muscarinic receptor M3 antagonists, while synephrine, ephedrine and pseudoephedrine were ß2-adrenoceptor agonists. Pathway deconvolution assays suggested activation of GPR35 triggered PI3K, MEK, JNK pathways and EGFR transactivation, and the activation of ß2-adrenoceptor mediated MEK and Ca2+. The herb-compound-target network analysis found that some compounds such as licochalcone B acted on multiple targets, and multiple components interacted with the same target such as GPR35, reflecting the synergistic mechanism of Chinese medicine. At the same time, some low-abundance compounds displayed high target activity, meaning its important role in LCDD for anti-COVID-19. CONCLUSIONS: This study elucidates the active ingredients, targets and pathways of LCDD. This is useful for elucidating multitarget synergistic action for its clinical therapeutic efficacy.

Mini-review: antibody therapeutics targeting G protein-coupled receptors and ion channels.

Antibodies are now well established as therapeutics with many additional advantages over small molecules and peptides relative to their selectivity, bioavailability, half-life and effector function. Major classes of membrane-associated protein targets include G protein-coupled receptors (GPCRs) and ion channels that are linked to a wide range of disease indications across all therapeutic areas. This mini-review summarizes the antibody target landscape for both GPCRs and ion channels as well as current progress in the respective research and development pipelines with some example case studies highlighted from clinical studies, including those being evaluated for the treatment of symptoms in COVID-19 infection.

Functional autoantibodies against G-protein coupled receptors in patients with persistent Long-COVID-19 symptoms.

Impairment of health after overcoming the acute phase of COVID-19 is being observed more and more frequently. Here different symptoms of neurological and/or cardiological origin have been reported. With symptoms, which are very similar to the ones reported but are not caused by SARS-CoV-2, the occurrence of functionally active autoantibodies (fAABs) targeting G-protein coupled receptors (GPCR-fAABs) has been discussed to be involved. We, therefore investigated, whether GPCR-fAABs are detectable in 31 patients suffering from different Long-COVID-19 symptoms after recovery from the acute phase of the disease. The spectrum of symptoms was mostly of neurological origin (29/31 patients), including post-COVID-19 fatigue, alopecia, attention deficit, tremor and others. Combined neurological and cardiovascular disorders were reported in 17 of the 31 patients. Two recovered COVID-19 patients were free of follow-up symptoms. All 31 former COVID-19 patients had between 2 and 7 different GPCR-fAABs that acted as receptor agonists. Some of those GPCR-fAABs activate their target receptors which cause a positive chronotropic effect in neonatal rat cardiomyocytes, the read-out in the test system for their detection (bioassay for GPCR-fAAB detection). Other GPCR-fAABs, in opposite, cause a negative chronotropic effect on those cells. The positive chronotropic GPCR-fAABs identified in the blood of Long-COVID patients targeted the ß2-adrenoceptor (ß2-fAAB), the α1-adrenoceptor (α1-fAAB), the angiotensin II AT1-receptor (AT1-fAAB), and the nociceptin-like opioid receptor (NOC-fAAB). The negative chronotropic GPCR-fAABs identified targeted the muscarinic M2-receptor (M2-fAAB), the MAS-receptor (MAS-fAAB), and the ETA-receptor (ETA-fAAB). It was analysed which of the extracellular receptor loops was targeted by the autoantibodies.

COVID-19: Famotidine, Histamine, Mast Cells, and Mechanisms.

SARS-CoV-2 infection is required for COVID-19, but many signs and symptoms of COVID-19 differ from common acute viral diseases. SARS-CoV-2 infection is necessary but not sufficient for development of clinical COVID-19 disease. Currently, there are no approved pre- or post-exposure prophylactic COVID-19 medical countermeasures. Clinical data suggest that famotidine may mitigate COVID-19 disease, but both mechanism of action and rationale for dose selection remain obscure. We have investigated several plausible hypotheses for famotidine activity including antiviral and host-mediated mechanisms of action. We propose that the principal mechanism of action of famotidine for relieving COVID-19 symptoms involves on-target histamine receptor H2 activity, and that development of clinical COVID-19 involves dysfunctional mast cell activation and histamine release. Based on these findings and associated hypothesis, new COVID-19 multi-drug treatment strategies based on repurposing well-characterized drugs are being developed and clinically tested, and many of these drugs are available worldwide in inexpensive generic oral forms suitable for both outpatient and inpatient treatment of COVID-19 disease.

SARS-CoV-2 may hijack GPCR signaling pathways to dysregulate lung ion and fluid transport.

The tropism of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a virus responsible for the ongoing coronavirus disease 2019 (COVID-19) pandemic, toward the host cells is determined, at least in part, by the expression and distribution of its cell surface receptor, angiotensin-converting enzyme 2 (ACE2). The virus further exploits the host cellular machinery to gain access into the cells; its spike protein is cleaved by a host cell surface transmembrane serine protease 2 (TMPRSS2) shortly after binding ACE2, followed by its proteolytic activation at a furin cleavage site. The virus primarily targets the epithelium of the respiratory tract, which is covered by a tightly regulated airway surface liquid (ASL) layer that serves as a primary defense mechanism against respiratory pathogens. The volume and viscosity of this fluid layer is regulated and maintained by a coordinated function of different transport pathways in the respiratory epithelium. We argue that SARS-CoV-2 may potentially alter evolutionary conserved second-messenger signaling cascades via activation of G protein-coupled receptors (GPCRs) or by directly modulating G protein signaling. Such signaling may in turn adversely modulate transepithelial transport processes, especially those involving cystic fibrosis transmembrane conductance regulator (CFTR) and epithelial Na+ channel (ENaC), thereby shifting the delicate balance between anion secretion and sodium absorption, which controls homeostasis of this fluid layer. As a result, activation of the secretory pathways including CFTR-mediated Cl- transport may overwhelm the absorptive pathways, such as ENaC-dependent Na+ uptake, and initiate a pathophysiological cascade leading to lung edema, one of the most serious and potentially deadly clinical manifestations of COVID-19.

Inflammation and thrombosis in COVID-19 pathophysiology: proteinase-activated and purinergic receptors as drivers and candidate therapeutic targets.

Evolving information has identified disease mechanisms and dysregulation of host biology that might be targeted therapeutically in coronavirus disease 2019 (COVID-19). Thrombosis and coagulopathy, associated with pulmonary injury and inflammation, are emerging clinical features of COVID-19. We present a framework for mechanisms of thrombosis in COVID-19 that initially derive from interaction of SARS-CoV-2 with ACE2, resulting in dysregulation of angiotensin signaling and subsequent inflammation and tissue injury. These responses result in increased signaling by thrombin (proteinase-activated) and purinergic receptors, which promote platelet activation and exert pathological effects on other cell types (e.g., endothelial cells, epithelial cells, and fibroblasts), further enhancing inflammation and injury. Inhibitors of thrombin and purinergic receptors may, thus, have therapeutic effects by blunting platelet-mediated thromboinflammation and dysfunction in other cell types. Such inhibitors include agents (e.g., anti-platelet drugs) approved for other indications, and that could be repurposed to treat, and potentially improve the outcome of, COVID-19 patients. COVID-19, caused by the SARS-CoV-2 virus, drives dysregulation of angiotensin signaling, which, in turn, increases thrombin-mediated and purinergic-mediated activation of platelets and increase in inflammation. This thromboinflammation impacts the lungs and can also have systemic effects. Inhibitors of receptors that drive platelet activation or inhibitors of the coagulation cascade provide opportunities to treat COVID-19 thromboinflammation.

Melatonin controversies, an update.

Melatonin was discovered more than 60 years ago. Since then, several seminal discoveries have allowed us to define its function as a neuroendocrine hormone and its molecular targets in mammals and many other species. However, many fundamental issues have not yet been solved such as the subcellular localization of melatonin synthesis and the full spectrum of its molecular targets. In addition, a considerable number of controversies persist in the field, mainly concerning how many functions melatonin has. Altogether, this illustrates how "immature" the field still is. The intention of this opinion article is to note the controversies and limitations in the field, to initiate a discussion and to make proposals/guidelines to overcome them and move the field forward.