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Comparison of known and predicted Mpro cleavage sites.  The most relevant positions P4-P1′ of the 11 known SARS coronavirus Mpro cleavage sites in nonstructural proteins are shown (for nsp4 through nsp16), aligned with predicted sites in several human selenoproteins (GPX1, SelenoF, SelenoP, and TXNRD1), as well as glutaredoxin-1 (GLRX-1) and the rate-limiting enzyme for glutathione synthesis, glutamate-cysteine ligase catalytic subunit (GCLC, with 2 predicted cleavage sites a and b). The known nsp cleavage sites shown are all from SARS-CoV-2, with the addition of the nsp5/6 site from SARS-CoV (marked *). The sites identified in human proteins are displayed next to the known Mpro cleavage site to which they are most similar, highlighted in matching color. The experimentally determined catalytic efficiencies of SARS-CoV Mpro at each of the known nsp cleavage sites are shown as relative kcat/Km ([10]). Three different methods for prediction of cysteine protease cleavage sites were used: PROSPER, with numbers in parenthesis showing the score for the predicted site, any score > 0.8 being significant; NetCorona, where scores > 0.5 are considered positive, and ProCleave, where every possible P4-P4′ octamer in a protein sequence is evaluated, scored and ranked. Some aligned non-identical residues highlighted in italics are nonetheless chemically and structually similar to residues found in the same position in the known cleavage sites, e.g., serine (S) vs. threonine (T), Leucine  (L) or isoleucine (I) vs. valine (V), and glutamine (Q) vs. asparagine (N); all of these pairs differ only by a single carbon atom (CH3 or CH2 unit). The predicted Mpro cleavage sites in human proteins labeled A to G are discussed in the text.

Comparison of known and predicted Mpro cleavage sites. The most relevant positions P4-P1′ of the 11 known SARS coronavirus Mpro cleavage sites in nonstructural proteins are shown (for nsp4 through nsp16), aligned with predicted sites in several human selenoproteins (GPX1, SelenoF, SelenoP, and TXNRD1), as well as glutaredoxin-1 (GLRX-1) and the rate-limiting enzyme for glutathione synthesis, glutamate-cysteine ligase catalytic subunit (GCLC, with 2 predicted cleavage sites a and b). The known nsp cleavage sites shown are all from SARS-CoV-2, with the addition of the nsp5/6 site from SARS-CoV (marked *). The sites identified in human proteins are displayed next to the known Mpro cleavage site to which they are most similar, highlighted in matching color. The experimentally determined catalytic efficiencies of SARS-CoV Mpro at each of the known nsp cleavage sites are shown as relative kcat/Km ([10]). Three different methods for prediction of cysteine protease cleavage sites were used: PROSPER, with numbers in parenthesis showing the score for the predicted site, any score > 0.8 being significant; NetCorona, where scores > 0.5 are considered positive, and ProCleave, where every possible P4-P4′ octamer in a protein sequence is evaluated, scored and ranked. Some aligned non-identical residues highlighted in italics are nonetheless chemically and structually similar to residues found in the same position in the known cleavage sites, e.g., serine (S) vs. threonine (T), Leucine (L) or isoleucine (I) vs. valine (V), and glutamine (Q) vs. asparagine (N); all of these pairs differ only by a single carbon atom (CH3 or CH2 unit). The predicted Mpro cleavage sites in human proteins labeled A to G are discussed in the text.

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Glutathione peroxidases (GPX), a family of antioxidant selenoenzymes, functionally link selenium and glutathione, which both show correlations with clinical outcomes in COVID-19. Thus, it is highly significant that cytosolic GPX1 has been shown to interact with an inactive C145A mutant of Mpro , the main cysteine protease of SARS-CoV-2, but not wit...

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... So, boosting the intracellular glutathione redox status and 25(OH)D level may constitute a novel therapeutic alternative for overcoming impaired immunity and inflammation in COVID-19 subjects. 38 By employing web-based predictive strategies that are relative to molecular interactions and focused on protease cleavage sites, it has been proved that the viral main protease targets glutamate−cysteine ligase involved in the rate-limiting step of glutathione synthesis, glutathione peroxidase (GPX1), and other selenoproteins like selenoprotein F (SELENOF) or thioredoxin reductase 1. 57 These observations showed consistency with the viral ability to interfere with DNA synthesis and to promote RNA synthesis via increase in the ribonucleotide profile by that enhancing multiplication. Moreover, these findings are confirmatory for the correlation between oxidative stress, associated inflammatory response, and the impairment in glutathione precursors and dietary selenium. ...
... Moreover, these findings are confirmatory for the correlation between oxidative stress, associated inflammatory response, and the impairment in glutathione precursors and dietary selenium. 43,57 Endogenous glutathione impairment can enhance the oxidative damage of the lungs induced by SARS-CoV-2, leading to acute respiratory distress syndrome, organ failure, and even death. With respect to the antiviral activity of glutathione, individuals with low glutathione levels seem to present a greater susceptibility for uncontrolled replication of the virus and, therefore, increased viral load. ...
Article
Viral pathologies encompass activation of pro-oxidative pathways and inflammatory burst. Alleviating overproduction of reactive oxygen species and cytokine storm in COVID-19 is essential to counteract the immunogenic damage in endothelium and alveolar membranes. Antioxidants alleviate oxidative stress, cytokine storm, hyperinflammation, and diminish the risk of organ failure. Direct antiviral roles imply: impact on viral spike protein, interference with the ACE2 receptor, inhibition of dipeptidyl peptidase 4, transmembrane protease serine 2 or furin, and impact on of helicase, papain-like protease, 3-chyomotrypsin like protease, and RNA-dependent RNA polymerase. Prooxidative environment favors conformational changes in the receptor binding domain, promoting the affinity of the spike protein for the host receptor. Viral pathologies imply a vicious cycle, oxidative stress promoting inflammatory responses, and vice versa. The same was noticed with respect to the relationship antioxidant impairment-viral replication. Timing, dosage, pro-oxidative activities, mutual influences, and interference with other antioxidants should be carefully regarded. Deficiency is linked to illness severity.
... Although GSH adduct formation might lower the efficacy of both wifA and win, it should be mentioned here that the host protein involved in the biosynthesis of GSH, glutamate-cysteine ligase, is a proposed substrate of M pro . 42 Hence, the attenuated levels of GSH in the infected cells would allow wifA and win to inhibit M pro , while the normal level of GSH in noninfected cells would play a protective role against any toxic effect of wifA and win. Additionally, depletion of GSH in SARS-CoV-2-infected cells may also occur due to excessive ROS production due to acute inflammation. ...
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The current COVID-19 pandemic caused by the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) created a global health crisis. The ability of vaccines to protect immunocompromised individuals and from emerging new strains are major concerns. Hence antiviral drugs against SARS-CoV-2 are essential. The SARS-CoV-2 main protease Mpro is vital for replication and an important target for antivirals. Using CMap analysis and docking studies, withaferin A (wifA) and withanone (win), two natural products from the medicinal herb Withania somnifera (ashwagandha), were identified as promising candidates that can covalently inhibit the viral protease Mpro. Cell culture, enzymatic, LC-MS/MS, computational, and equilibrium dialysis based assays were performed. DFT calculations indicated that wifA and win can form stable adducts with thiols. The cytotoxicity of Mpro was significantly reduced by wifA and win. Both wifA and win were found to irreversibly inhibit 0.5 μM Mpro with IC50 values of 0.54 and 1.8 μM, respectively. LC-MS/MS analysis revealed covalent adduct formation with wifA at cysteines 145 and 300 of Mpro. The natural products wifA and win can irreversibly inhibit the SARS-CoV-2 main protease Mpro. Based on the work presented here we propose that both wifA and win have the potential to be safely used as preventative and therapeutic interventions for COVID-19.
... GSH interacts and, in certain conditions, decreases the main SARS-CoV-2 protease activity [100]. Bioinformatic tools predicted that SARS-CoV-2 main protease targets GPX1, an enzyme involved in neutralizing lipid peroxides and hydrogen peroxide in organisms [101], as well as a glutamate-cysteine ligase, an enzyme involved in GSH synthesis [102]. In a study on 60 hospitalized COVID-19 patients, GSH deficiency was observed compared to healthy controls. ...
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The coronavirus disease (COVID-19) pandemic is a leading global health and economic challenge. What defines the disease’s progression is not entirely understood, but there are strong indications that oxidative stress and the defense against reactive oxygen species are crucial players. A big influx of immune cells to the site of infection is marked by the increase in reactive oxygen and nitrogen species. Our article aims to highlight the critical role of oxidative stress in the emergence and severity of COVID-19 and, more importantly, to shed light on the underlying molecular and genetic mechanisms. We have reviewed the available literature and clinical trials to extract the relevant genetic variants within the oxidative stress pathway associated with COVID-19 and the anti-oxidative therapies currently evaluated in the clinical trials for COVID-19 treatment, in particular clinical trials on glutathione and N-acetylcysteine.
... Note that high doses of oral NAC could result in intolerable gastrointestinal adverse effects such as nausea, vomiting, and diarrhoea [159]. Other micronutrients, such as zinc [194], selenium [106,195,196], magnesium, vitamins A, C, and D [113,116,197], should form part of a successful integrative protocol [110], while sulfur-donors such as MSM, allicin [157], or marine-derived sulfated PSs can also be considered. MSM is entirely safe and effective, taken at daily dosages of up to 4 g to prevent infection and modulate the immune response [136]. ...
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The airway epithelial glycocalyx plays an important role in preventing severe acute respiratory syndrome coronavirus 2 entry into the epithelial cells, while the endothelial glycocalyx contributes to vascular permeability and tone, as well as modulating immune, inflammatory, and coagulation responses. With ample evidence in the scientific literature that coronavirus disease 2019 (COVID19) is related to epithelial and endothelial dysfunction, preserving the glycocalyx should be the main focus of any COVID-19 treatment protocol. The most studied functional unit of the glycocalyx is the glycosaminoglycan heparan sulfate, where the degree and position of the sulfate groups determine the biological activity. N-acetylcysteine (NAC) and other sulfur donors contribute to the inorganic sulfate pool, the rate-limiting molecule in sulfation. NAC is not only a precursor to glutathione but also converts to hydrogen sulfide, inorganic sulfate, taurine, Coenzyme A, and albumin. By optimising inorganic sulfate availability, and therefore sulfation, it is proposed that COVID-19 can be prevented or at least most of the symptoms attenuated. A comprehensive COVID19 treatment protocol is needed to preserve the glycocalyx in both the prevention and treatment of COVID-19. The use of NAC at a dosage of 600 mg bid for the prevention of COVID-19 is proposed, but a higher dosage of NAC (1200 mg bid) should be administered upon the first onset of symptoms. In the severe to critically ill, it is advised that IV NAC should be administered immediately upon hospital admission, and in the late stage of the disease, IV sodium thiosulfate should be considered. Doxycycline as a protease inhibitor will prevent shedding and further degradation of the glycocalyx.
... Superoxide dismutase (SOD) [131], heme oxygenase-1 (HO-1) [90], catalase (CAT) [154], glutathione peroxidase (GPX) [243], glutathione S-transferase (GST) [210], peroxiredoxin (PrxI) [112], and nuclear factor erythroid 2-related factor 2 (Nrf2) [55] are enzymes that mitigate oxidative stress and are implicated in the pathogenesis of COVID-19. The correlation between decreased expression of SOD3 in lungs and severity of COVID-19 has been reported in elderly patients [131]. ...
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The Coronavirus Disease-2019 (COVID-19) pandemic urges researching possibilities for prevention and management of the effects of the virus. Carotenoids are natural phytochemicals of anti-oxidant, anti-inflammatory and immunomodulatory properties and may exert potential in aiding in combatting the pandemic. This review presents the direct and indirect evidence of the health benefits of carotenoids and derivatives based on in vitro and in vivo studies, human clinical trials and epidemiological studies and proposes possible mechanisms of action via which carotenoids may have the capacity to protect against COVID-19 effects. The current evidence provides a rationale for considering carotenoids as natural supportive nutrients via antioxidant activities, including scavenging lipid-soluble radicals, reducing hypoxia-associated superoxide by activating antioxidant enzymes, or suppressing enzymes that produce reactive oxygen species (ROS). Carotenoids may regulate COVID-19 induced over-production of pro-inflammatory cytokines, chemokines, pro-inflammatory enzymes and adhesion molecules by nuclear factor kappa B (NF-κB), renin-angiotensin-aldosterone system (RAS) and interleukins-6- Janus kinase-signal transducer and activator of transcription (IL-6-JAK/STAT) pathways and suppress the polarization of pro-inflammatory M1 macrophage. Moreover, carotenoids may modulate the peroxisome proliferator-activated receptors γ by acting as agonists to alleviate COVID-19 symptoms. They also may potentially block the cellular receptor of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), human angiotensin-converting enzyme 2 (ACE2). These activities may reduce the severity of COVID-19 and flu-like diseases. Thus, carotenoid supplementation may aid in combatting the pandemic, as well as seasonal flu. However, further in vitro, in vivo and in particular long-term clinical trials in COVID-19 patients are needed to evaluate this hypothesis.
... Proteolysis of GPx-1 increases ROS and NF-κB activation. Since NF-κB activates numerous pro-inflammatory cytokines, this mechanism seems to contribute to both enhancing virion production and cytokine storm in COVID-19 (Taylor and Radding, 2020). As stated above, the increased production of ROS in host cells by viral infection leads to oxidative stress, if not balanced by antioxidant defense mechanisms. ...
... As a Sedependent antioxidant, the optimal function of the GPxs also depends upon adequate intracellular J o u r n a l P r e -p r o o f concentrations of the cofactor GSH. COVID-19 patients with low GSH and selenoprotein levels are more vulnerable to the harmful effects of virus-induced proteolysis (Taylor and Radding, 2020). ...
Article
In severe COVID-19, the levels of iron (Fe), copper (Cu), zinc (Zn) and selenium (Se), do not only regulate host immune responses, but modify the viral genome, as well. While low serum Fe concentration is an independent risk factor for the increased death rate, Zn controls oxidative stress, synthesis of inflammatory cytokines and viral replication. Therefore, Zn deficiency associates with a worse prognosis. Although Cu exposure inactivates the viral genome and exhibits spike protein dispersal, increase in Cu/Zn due to high serum Cu levels, are correlated with enhanced risk of infections. Se levels are significantly higher in surviving COVID-19 patients. Meanwhile, both Zn and Se suppress the replication of SARS-CoV-2. Since the balance between the deficiency and oversupply of these metals due to a reciprocal relationship, has decisive effect on the prognosis of the SARS-CoV-2 infection, monitoring their concentrations may facilitate improved outcomes for patients suffering from COVID-19.
... Both its dietary restriction and the suppression in the expression of selenoproteins have been associated with higher levels of pro-inflammatory cytokines, IL-1β, IL-6, and TNF-α, in a variety of tissues, including the gastrointestinal tract, uterus, mammary gland tissues, and lung tissue [70]. Therefore, Se appears to play an important role in fighting viral diseases, such as COVID-19 [27,71]. ...
... To date, twenty-five genes encoding selenoproteins have been identified [71], such as selenoprotein F, K, M, N, and S that fold proteins and protect against oxidative stress from the endoplasmic reticulum [72]. There is also the SELENOP antioxidant defense role, which, as it is the most abundant, is used as a biomarker of Se status [73]. ...
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The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes coronavirus disease 2019 (COVID-19). SARS-CoV-2 infection can activate innate and adaptive immune responses and result in massive inflammatory responses in the disease. A comprehensive understanding of the participation of micronutrients in the immune response to COVID-19 will allow the creation of prevention and supplementation scenarios in malnutrition states. Microelement deficiency can be decisive in the progression of diseases and their optimal levels can act as protective factors, helping to maintain homeostasis. Vitamin A, B, D, selenium, zinc, and copper, through their complementary and synergistic effects, allow the components of innate and adaptive immunity to counteract infections like those occurring in the respiratory tract. Thus, alterations in nutritional status are related to metabolic diseases, systemic inflammation, and deterioration of the immune system that alter the response against viral infections, such as COVID-19. The aim of this review is to describe the micronutrients that play an important role as immunomodulators and its relationship between malnutrition and the development of respiratory infections with an emphasis on severe and critical COVID-19. We conclude that although an unbalanced diet is not the only risk factor that predisposes to COVID-19, a correct and balanced diet, which provides the optimal amount of micronutrients and favors an adequate nutritional status, could confer beneficial effects for prevention and improvement of clinical results. The potential usefulness of micronutrient supplementation in special cases is highlighted.
... The hypothesis proposed on the role of Se in SARS-CoV-2 infection is mainly based on the increase in oxidative stress, a severe reduction in blood Se levels, and decreased concentration of SELENOP and GPx3 in COVID-19 patients [95]. Of note, GPx1, and possibly also TrxR1 and selenoprotein F, are substrates of M pro , the main cysteine protease of SARS-CoV-2, and the proteolytic cleavage of these antioxidant molecules results in increased oxidative stress, NF-κB activation, and proapoptotic signaling [96]. ...
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COVID-19 represents a worldwide public health emergency, and, beyond the respiratory symptoms characterizing the classic viral disease, growing evidence has highlighted a possible reciprocal relationship between SARS-CoV-2 infection and thyroid dysfunction. The updated data discussed in this review suggests a role of SARS-CoV-2 infection on the thyroid gland, with multiple thyroid pictures described. Conversely, no conclusion can be drawn on the association between pre-existing thyroid disease and increased risk of SARS-CoV-2 infection. In this scenario, selenium (Se), an essential trace element critical for thyroid function and known as an effective agent against viral infections, is emerging as a potential novel therapeutic option for the treatment of COVID-19. Large multicentre cohort studies are required to elucidate the mechanisms underlying thyroid dysfunction during or following recovery from COVID-19, including Se status. Meanwhile, clinical trials should be performed to evaluate whether adequate intake of Se can help address COVID-19 in Se-deficient patients, also avoiding thyroid complications that can contribute to worsening outcomes during infection.
... Another example of COVID-19's mitochondrial-related impacts is the over-production of cellular ROS [63]. ROS and reactive nitrogen species have diverse functions in biological systems; oxidatively attacking pathogens, regulating cell proliferation, and key signaling functions [64]. However, dysregulation of ROS is implicated in many diseases, including the hyper-inflammatory late phase of COVID-19 [65]. ...
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COVID-19, the disease caused by SARS-CoV-2, has claimed approximately 5 million lives and 257 million cases reported globally. This virus and disease have significantly affected people worldwide, whether directly and/or indirectly, with a virulent pathogen that continues to evolve as we race to learn how to prevent, control, or cure COVID-19. The focus of this review is on the SARS-CoV-2 virus’ mechanism of infection and its proclivity at adapting and restructuring the intracellular environment to support viral replication. We highlight current knowledge and how scientific communities with expertize in viral, cellular, and clinical biology have contributed to increase our understanding of SARS-CoV-2, and how these findings may help explain the widely varied clinical observations of COVID-19 patients.
... Verma et al. [86] showed that selenium may be a key ingredient to protect cells infected with West Nile Virus (WNV) from death. Taylor and Radding [87] reported that the SARS-CoV-2 virus reduces the biosynthesis of glutathione (GSH) and selenoproteins in infected cells. The consequence of this is a decrease in the level of these antioxidant molecules, which leads to an increase in oxidative stress and the activation of the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB). ...
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