Does serotonin deficiency lead to anosmia, ageusia, dysfunctional chemesthesis and increased severity of illness in COVID-19?

5-HT/CGRP pathway and Sumatriptan role in Covid-19

Coronavirus disease 2019 (Covid-19) is a pandemic caused by severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2). In Covid-19, there is uncontrolled activation of immune cells with a massive release of pro-inflammatory cytokines and the development of cytokine storm. These inflammatory changes induce impairment of different organ functions, including the central nervous system (CNS), leading to acute brain injury and substantial changes in the neurotransmitters, including serotonin (5-HT) and calcitonin gene-related peptide (CGRP), which have immunomodulatory properties through modulation of central and peripheral immune responses. In Covid-19, 5-HT neurotransmitters and CGRP could contribute to abnormal and atypical vascular reactivity. Sumatriptan is a pre-synaptic 5-HT (5-HT1D and 5-HT1B) agonist and inhibits the release of CGRP. Both 5-HT and CGRP seem to be augmented in Covid-19 due to underlying activation of inflammatory signaling pathways and hyperinflammation. In virtue of its anti-inflammatory and antioxidant properties with inhibition release of 5-HT and CGRP, Sumatriptan may reduce Covid-19 hyperinflammation. Therefore, Sumatriptan might be a novel potential therapeutic strategy in managing Covid-19. In conclusion, Sumatriptan could be an effective therapeutic strategy in managing Covid-19 through modulation of 5-HT neurotransmitters and inhibiting CGRP.

SARS-CoV-2 propagation to the TPH2-positive neurons in the ventral tegmental area induces cell death via GSK3β-dependent accumulation of phosphorylated tau

COVID-19, an infectious disease caused by SARS-CoV-2, was declared a pandemic by the WHO in 2020. Psychiatric symptoms including sleep disturbance, memory impairment, and depression are associated with SARS-CoV-2 infection. These symptoms are causes long-term mental and physical distress in recovering patients; however, the underlying mechanism is unclear. In this study, we determined the effects of SARS-CoV-2 infection on brain tissue using k18hACE2 mice. Using brain tissue from 18hACE2 mice infected with SARS-CoV-2 through intranasal administration, SARS-CoV-2 spike protein and RNA were analyzed by immunohistochemical staining and in-situ hybridization. Immunohistochemical analysis revealed that Tryptophan hydroxylase 2 (TPH2)-positive cells and SARS-CoV-2 spike protein were co-localized in the ventral tegmental area of SARS-CoV-2-infected mice. We observed decreased TPH2 expression and increased accumulation of phosphorylated tau protein and Phospho-Histone H2A.X (γH2AX) expression in the ventral tegmental region. In addition, activation of glycogen synthase kinase 3β (GSK3β) was induced by SARS-CoV-2 infection. Overall, our results suggest that SARS-CoV-2 infection of TPH2-positive cells in the ventral tegmental area induces neuronal cell death through increased accumulation of phosphorylated tau. Attenuation of the GSK3β pathway and decreased serotonin synthesis through suppression of TPH2 expression may contribute to the development of neurological symptoms.

Precision nutrition to reset virus-induced human metabolic reprogramming and dysregulation (HMRD) in long-COVID

SARS-CoV-2, the etiological agent of COVID-19, is devoid of any metabolic capacity; therefore, it is critical for the viral pathogen to hijack host cellular metabolic machinery for its replication and propagation. This single-stranded RNA virus with a 29.9 kb genome encodes 14 open reading frames (ORFs) and initiates a plethora of virus-host protein-protein interactions in the human body. These extensive viral protein interactions with host-specific cellular targets could trigger severe human metabolic reprogramming/dysregulation (HMRD), a rewiring of sugar-, amino acid-, lipid-, and nucleotide-metabolism(s), as well as altered or impaired bioenergetics, immune dysfunction, and redox imbalance in the body. In the infectious process, the viral pathogen hijacks two major human receptors, angiotensin-converting enzyme (ACE)-2 and/or neuropilin (NRP)-1, for initial adhesion to cell surface; then utilizes two major host proteases, TMPRSS2 and/or furin, to gain cellular entry; and finally employs an endosomal enzyme, cathepsin L (CTSL) for fusogenic release of its viral genome. The virus-induced HMRD results in 5 possible infectious outcomes: asymptomatic, mild, moderate, severe to fatal episodes; while the symptomatic acute COVID-19 condition could manifest into 3 clinical phases: (i) hypoxia and hypoxemia (Warburg effect), (ii) hyperferritinemia ('cytokine storm'), and (iii) thrombocytosis (coagulopathy). The mean incubation period for COVID-19 onset was estimated to be 5.1 days, and most cases develop symptoms after 14 days. The mean viral clearance times were 24, 30, and 39 days for acute, severe, and ICU-admitted COVID-19 patients, respectively. However, about 25-70% of virus-free COVID-19 survivors continue to sustain virus-induced HMRD and exhibit a wide range of symptoms that are persistent, exacerbated, or new 'onset' clinical incidents, collectively termed as post-acute sequelae of COVID-19 (PASC) or long COVID. PASC patients experience several debilitating clinical condition(s) with >200 different and overlapping symptoms that may last for weeks to months. Chronic PASC is a cumulative outcome of at least 10 different HMRD-related pathophysiological mechanisms involving both virus-derived virulence factors and a multitude of innate host responses. Based on HMRD and virus-free clinical impairments of different human organs/systems, PASC patients can be categorized into 4 different clusters or sub-phenotypes: sub-phenotype-1 (33.8%) with cardiac and renal manifestations; sub-phenotype-2 (32.8%) with respiratory, sleep and anxiety disorders; sub-phenotype-3 (23.4%) with skeleto-muscular and nervous disorders; and sub-phenotype-4 (10.1%) with digestive and pulmonary dysfunctions. This narrative review elucidates the effects of viral hijack on host cellular machinery during SARS-CoV-2 infection, ensuing detrimental effect(s) of virus-induced HMRD on human metabolism, consequential symptomatic clinical implications, and damage to multiple organ systems; as well as chronic pathophysiological sequelae in virus-free PASC patients. We have also provided a few evidence-based, human randomized controlled trial (RCT)-tested, precision nutrients to reset HMRD for health recovery of PASC patients.

Treatment of 95 post-Covid patients with SSRIs

After Covid-19 infection, 12.5% develops post-Covid-syndrome (PCS). Symptoms indicate numerous affected organ systems. After a year, chronic fatigue, dysautonomia and neurological and neuropsychiatric complaints predominate. In this study, 95 PCS patients were treated with selective serotonin reuptake inhibitors (SSRIs). This study used an exploratory questionnaire and found that two-thirds of patients had a reasonably good to strong response on SSRIs, over a quarter of patients had moderate response, while 10% reported no response. Overall, patients experienced substantial improved well-being. Brainfog and sensory overload decreased most, followed by chronic fatigue and dysautonomia. Outcomes were measured with three different measures that correlated strongly with each other. The response to SSRIs in PCS conditions was explained by seven possible neurobiological mechanisms based on recent literature on PCS integrated with already existing knowledge. Important for understanding these mechanisms is the underlying biochemical interaction between various neurotransmitter systems and parts of the immune system, and their dysregulation in PCS. The main link appears to be with the metabolic kynurenine pathway (KP) which interacts extensively with the immune system. The KP uses the same precursor as serotonin: tryptophan. The KP is overactive in PCS which maintains inflammation and which causes a lack of tryptophan. Finally, potential avenues for future research to advance this line of clinical research are discussed.

Three Cases of Reported Improvement in Microsmia and Anosmia Following Naturalistic Use of Psilocybin and LSD

Cultural awareness of anosmia and microsmia has recently increased due to their association with COVID-19, though treatment for these conditions is limited. A growing body of online media claims that individuals have noticed improvement in anosmia and microsmia following classic psychedelic use. We report what we believe to be the first three cases recorded in the academic literature of improvement in olfactory impairment after psychedelic use. In the first case, a man who developed microsmia after a respiratory infection experienced improvement in smell after the use of 6 g of psilocybin containing mushrooms. In the second case, a woman with anosmia since childhood reported olfactory improvement after ingestion of 100 µg of lysergic acid diethylamide (LSD). In the third case, a woman with COVID-19-related anosmia reported olfactory improvement after microdosing 0.1 g of psilocybin mushrooms three times. Following a discussion of these cases, we explore potential mechanisms for psychedelic-facilitated improvement in olfactory impairment, including serotonergic effects, increased neuroplasticity, and anti-inflammatory effects. Given the need for novel treatments for olfactory dysfunction, increasing reports describing improvement in these conditions following psychedelic use and potential biological plausibility, we believe that the possible therapeutic benefits of psychedelics for these conditions deserve further investigation.

Selective serotonin reuptake inhibitors: New hope in the fight against COVID-19

The emerging COVID-19 pandemic led to a dramatic increase in global mortality and morbidity rates. As in most infections, fatal complications of coronavirus affliction are triggered by an untrammeled host inflammatory response. Cytokine storms created by high levels of interleukin and other cytokines elucidate the pathology of severe COVID-19. In this respect, repurposing drugs that are already available and might exhibit anti-inflammatory effects have received significant attention. With the in vitro and clinical investigation of several studies on the effect of antidepressants on COVID-19 prognosis, previous data suggest that selective serotonin reuptake inhibitors (SSRIs) might be the new hope for the early treatment of severely afflicted patients. SSRIs' low cost and availability make them potentially eligible for COVID-19 repurposing. This review summarizes current achievements and literature about the connection between SSRIs administration and COVID-19 prognosis.

The Role of Tryptophan Metabolites in Neuropsychiatric Disorders

In recent decades, neuropsychiatric disorders such as major depressive disorder, schizophrenia, bipolar, etc., have become a global health concern, causing various detrimental influences on patients. Tryptophan is an important amino acid that plays an indisputable role in several physiological processes, including neuronal function and immunity. Tryptophan’s metabolism process in the human body occurs using different pathways, including the kynurenine and serotonin pathways. Furthermore, other biologically active components, such as serotonin, melatonin, and niacin, are by-products of Tryptophan pathways. Current evidence suggests that a functional imbalance in the synthesis of Tryptophan metabolites causes the appearance of pathophysiologic mechanisms that leads to various neuropsychiatric diseases. This review summarizes the pharmacological influences of tryptophan and its metabolites on the development of neuropsychiatric disorders. In addition, tryptophan and its metabolites quantification following the neurotransmitters precursor are highlighted. Eventually, the efficiency of various biomarkers such as inflammatory, protein, electrophysiological, genetic, and proteomic biomarkers in the diagnosis/treatment of neuropsychiatric disorders was discussed to understand the biomarker application in the detection/treatment of various diseases.

Psychological and Biochemical Effects of an Online Pilates Intervention in Pregnant Women during COVID-19: A Randomized Pilot Study

The purpose of this study was to analyze the effect of real-time online Pilates exercise during COVID-19 on women's body composition, blood lipids, and psychological health after childbirth. The participants were 16 pregnant women (24-28 weeks pregnant) enrolled at the C Women's Culture Center in Seoul, South Korea, classified into online Pilates groups and non-exercise groups (PE, n = 8; CON, n = 8). The online Pilates program was conducted for 8 weeks, twice a week, and 50 min a day using a real-time video chat app. Participants visited the hospital twice for body composition and blood tests. Questionnaires on postpartum depression, sleep disorder, and stress were conducted at 6 weeks and 12 weeks after childbirth. We found a significant difference between groups in body composition. The weight, percentage of body fat, body fat mass, and BMI of the PE group decreased. Blood lipids showed significant differences between the groups in TC, TG, LDL and CRP, while insulin and HDL showed no difference. All blood lipids, insulin, and CRP in the PE group were reduced. There were significant differences between the groups in postpartum depression, sleep disorders, and perceived stress indices performed in the post-test, and the serotonin concentration in the PE group increased. Serotonin levels were significantly correlated with postpartum depression, body fat mass, and body fat rate. Pregnant women's online Pilates in this study was effective at reducing weight and depression in women after childbirth and should be used to promote women's mental health during COVID-19.

Severe COVID-19 Is Characterised by Perturbations in Plasma Amines Correlated with Immune Response Markers, and Linked to Inflammation and Oxidative Stress

The COVID-19 pandemic raised a need to characterise the biochemical response to SARS-CoV-2 infection and find biological markers to identify therapeutic targets. In support of these aims, we applied a range of LC-MS platforms to analyse over 100 plasma samples from patients with varying COVID-19 severity and with detailed clinical information on inflammatory responses (>30 immune markers). The first publication in a series reports the results of quantitative LC-MS/MS profiling of 56 amino acids and derivatives. A comparison between samples taken from ICU and ward patients revealed a notable increase in ten post-translationally modified amino acids that correlated with markers indicative of an excessive immune response: TNF-alpha, neutrophils, markers for macrophage, and leukocyte activation. Severe patients also had increased kynurenine, positively correlated with CRP and cytokines that induce its production. ICU and ward patients with high IL-6 showed decreased levels of 22 immune-supporting and anti-oxidative amino acids and derivatives (e.g., glutathione, GABA). These negatively correlated with CRP and IL-6 and positively correlated with markers indicative of adaptive immune activation. Including corresponding alterations in convalescing ward patients, the overall metabolic picture of severe COVID-19 reflected enhanced metabolic demands to maintain cell proliferation and redox balance, alongside increased inflammation and oxidative stress.

Could melatonin have a potential adjuvant role in the treatment of the lasting anosmia associated with COVID-19? A review

INTRODUCTION

Anosmia, the loss of the sense of smell, is usually associated with rhinopathies and has been reported as a common symptom of COVID-19. There is no specific drug to treat this condition, although some evidence suggests that melatonin could promote the recovery of olfactory sensory neurons.

METHODS

We set out to perform a narrative review to synthesize the current evidence in this area in respect of our hypothesis that melatonin may be linked with anosmia and play a part in oxidative stress and the regulation of inflammation. The main electronic databases (MEDLINE/PubMed, Embase, and Cochrane) were searched.

RESULTS

The search produced 26 articles related to our hypothesis. Some studies examined issues related to melatonin's effects and its use as adjuvant therapy for COVID-19. Despite some studies suggesting that melatonin may have potential in the treatment of COVID-19, to the best of our knowledge, there have been no trials that have used it to treat anosmia associated with the disease. Few articles identified proposed that melatonin might have an effect on olfactory cells.

DISCUSSION

Further experimental and clinical research on the role of circadian melatonin in the olfactory system is warranted. This will provide evidence of the use of melatonin in the management of anosmia. A number of identified studies suggest that the imbalanced release of melatonin by the pineal gland associated with sleep disturbance may play a role in anosmia, although the specific pathway is not yet entirely clear. This may be a base for further research into the potential role of melatonin as adjuvant treatment of anosmia.

Unbalanced IDO1/IDO2 Endothelial Expression and Skewed Keynurenine Pathway in the Pathogenesis of COVID-19 and Post-COVID-19 Pneumonia

Despite intense investigation, the pathogenesis of COVID-19 and the newly defined long COVID-19 syndrome are not fully understood. Increasing evidence has been provided of metabolic alterations characterizing this group of disorders, with particular relevance of an activated tryptophan/kynurenine pathway as described in this review. Recent histological studies have documented that, in COVID-19 patients, indoleamine 2,3-dioxygenase (IDO) enzymes are differentially expressed in the pulmonary blood vessels, i.e., IDO1 prevails in early/mild pneumonia and in lung tissues from patients suffering from long COVID-19, whereas IDO2 is predominant in severe/fatal cases. We hypothesize that IDO1 is necessary for a correct control of the vascular tone of pulmonary vessels, and its deficiency in COVID-19 might be related to the syndrome’s evolution toward vascular dysfunction. The complexity of this scenario is discussed in light of possible therapeutic manipulations of the tryptophan/kynurenine pathway in COVID-19 and post-acute COVID-19 syndromes.

The relationship between the serotonergic system and COVID-19 disease: A review

COVID-19 is an infectious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which led to a pandemic started in Wuhan, China, in 2019. The rapid spread of the disease in the world, unprecedented mortality rate, and lack of definitive treatment for the disease have led to a global effort to develop effective vaccines as well as new therapeutic interventions. Immune cells activation with excessive inflammation is an important pathophysiological feature of COVID-19 that may impair the various organs functions. Accordingly, these could cause dysfunction in the brain with some symptoms such as respiratory failure, headache, impaired consciousness, olfactory and taste disorders, and severe neurological disorders such as encephalitis. It was found that there is a two-way communication between the immune system and the nervous system through classical neurotransmitters, hormones, and cytokines. Among neurotransmitters, serotonin plays important roles in the immune system and in regulating inflammatory responses by central and peripheral mechanisms. This article aimed to review the two-way relationship between the immune and the nervous systems by focusing on the serotonergic system and the emerging COVID-19 disease.

Mechanisms and clinical evidence to support melatonin's use in severe COVID-19 patients to lower mortality

The fear of SARS-CoV-2 infection is due to its high mortality related to seasonal flu. To date, few medicines have been developed to significantly reduce the mortality of the severe COVID-19 patients, especially those requiring tracheal intubation. The severity and mortality of SARS-CoV-2 infection not only depend on the viral virulence, but are primarily determined by the cytokine storm and the destructive inflammation driven by the host immune reaction. Thus, to target the host immune response might be a better strategy to combat this pandemic. Melatonin is a molecule with multiple activities on a virus infection. These include that it downregulates the overreaction of innate immune response to suppress inflammation, promotes the adaptive immune reaction to enhance antibody formation, inhibits the entrance of the virus into the cell as well as limits its replication. These render it a potentially excellent candidate for treatment of the severe COVID-19 cases. Several clinical trials have confirmed that melatonin when added to the conventional therapy significantly reduces the mortality of the severe COVID-19 patients. The cost of melatonin is a small fraction of those medications approved by FDA for emergency use to treat COVID-19. Because of its self-administered, low cost and high safety margin, melatonin could be made available to every country in the world at an affordable cost. We recommend melatonin be used to treat severe COVID-19 patients with the intent of reducing mortality. If successful, it would make the SARS-CoV-2 pandemic less fearful and help to return life back to normalcy.

Ongoing Use of SSRIs Does Not Alter Outcome in Hospitalized COVID-19 Patients: A Retrospective Analysis

SARS-CoV-2 continues to have devastating consequences worldwide. Though vaccinations have helped reduce spread, new strains still pose a threat. Therefore, it is imperative to identify treatments that prevent severe COVID-19 infection. Recently, acute use of SSRI antidepressants in COVID+ patients was shown to reduce symptom severity. The aim of this retrospective observational study was to determine whether COVID+ patients already on SSRIs upon hospital admission had reduced mortality compared to COVID+ patients not on chronic SSRI treatment. Electronic medical records of 9044 patients with laboratory-confirmed COVID-19 from six hospitals were queried for demographic and clinical information. Using R, a logistic regression model was run with mortality as the outcome and SSRI status as the exposure. In this sample, no patients admitted on SSRIs had them discontinued. There was no significant difference in the odds of dying between COVID+ patients on chronic SSRIs vs. those not taking SSRIs, after controlling for age category, gender, and race. This study shows the utility of large clinical databases in determining what commonly prescribed drugs might be useful in treating COVID-19. During pandemics due to novel infectious agents, it is critical to evaluate safety and efficacy of drugs that might be repurposed for treatment.

Deficient synthesis of melatonin in COVID-19 can impair the resistance of coronavirus patients to mucormycosis

In addition to uncontrolled diabetes and the excess use of corticosteroids, it is believed that other factors may be responsible for the recent spurt of COVID-19 associated mucormycosis (CAM). In the present paper it is argued that COVID-19 increases the susceptibility of the patients to mucormycosis by augmenting the virulence factors of the mucor species, where deficient synthesis of melatonin plays a key role. Melatonin is synthesized from tryptophan via the serotonin pathway and melatonin deficiency in COVID-19 arises from the faulty absorption of tryptophan from the food because SARS-CoV-2 downregulates angiotensin-converting enzyme-2, the chaperone of the transporter of tryptophan. The enhanced fungal virulence in COVID-19 can be mitigated by correcting the melatonin deficiency as melatonin can prevent iron acquisition of the mucor species and inhibit their morphological transition from the yeast to the virulent hyphal form, given the fact that melatonin is an iron chelator, calmodulin blocker and inhibitor of myeloperoxidase as well as inhibitor of ferroptosis and pyroptosis. Also, by lowering the expression of glucose-regulated protein 78 and by inhibiting the suppression of T-cell immunity, melatonin can further increase the resistance of the patients to mucormycosis. Accordingly, clinical trials should be carried out on tryptophan supplementation, administration of selective serotonin reuptake inhibitors (to increase serotonin, the precursor of melatonin), and exogenous melatonin to find out how they perform in eliminating or reducing the propensity of the coronavirus patients to CAM.

TRP channels in COVID-19 disease: Potential targets for prevention and treatment

Coronavirus disease 2019 [COVID-19] is a global health threat caused by severe acute respiratory syndrome coronavirus 2 [SARS-CoV2] that requires two proteins for entry: angiotensin-converting enzyme 2 [ACE2] and -membrane protease serine 2 [TMPRSS2]. Many patients complain from pneumonia, cough, fever, and gastrointestinal (GI) problems. Notably, different TRP channels are expressed in various tissues infected by SARS-CoV-2. TRP channels are cation channels that show a common architecture with high permeability to calcium [Ca²⁺] in most sub-families. Literature review shed light on the possible role of TRP channels in COVID-19 disease. TRP channels may take part in inflammation, pain, fever, anosmia, ageusia, respiratory, cardiovascular, GI and neurological complications related to COVID-19. Also, TRP channels could be the targets for many active compounds that showed effectiveness against SARS-CoV-2. Desensitization or blocking TRP channels by antibodies, aptamers, small molecules or venoms can be an option for COVID-19 prevention and future treatment. This review provides insights into the involvement of TRP channels in different symptoms and mechanisms of SARS-CoV-2 , potential treatments targeting these channels and highlights missing gaps in literature.