SARS-CoV-2 Main Protease Targets Host Selenoproteins and Glutathione Biosynthesis for Knockdown via Proteolysis, Potentially Disrupting the Thioredoxin and Glutaredoxin Redox Cycles.

Associations between dietary selenium status and the clinical outcome of many viral infections, including SARS-CoV-2, are well established. Multiple independent studies have documented a significant inverse correlation between selenium status and the incidence and mortality of COVID-19. At the molecular level, SARS-CoV-2 infection has been shown to decrease the expression of certain selenoproteins, both in vitro and in COVID-19 patients. Using computational methods, our group previously identified a set of six host proteins that contain potential SARS-CoV-2 main protease (Mpro) cleavage sites. Here we show experimentally that Mpro can cleave four of the six predicted target sites, including those from three selenoproteins: thioredoxin reductase 1 (TXNRD1), selenoprotein F, and selenoprotein P, as well as the rate-limiting enzyme in glutathione synthesis, glutamate-cysteine ligase catalytic subunit (GCLC). Cleavage was assessed by incubating recombinant SARS-CoV-2 Mpro with synthetic peptides spanning the proposed cleavage sites, and analyzing the products via UPLC-MS. Furthermore, upon incubation of a recombinant Sec498Ser mutant of the full TXNRD1 protein with SARS-CoV-2 Mpro, the predicted cleavage was observed, destroying the TXNRD1 C-terminal redox center. Mechanistically, proteolytic knockdown of both TXNRD1 and GCLC is consistent with a viral strategy to inhibit DNA synthesis, conserving the pool of ribonucleotides for increased virion production. Viral infectivity could also be enhanced by GCLC knockdown, given the ability of glutathione to disrupt the structure of the viral spike protein via disulfide bond reduction. These findings shed new light on the importance of dietary factors like selenium and glutathione in COVID-19 prevention and treatment.

Sodium Selenite As Potential Adjuvant Therapy for COVID-19.

The review considers the role that selenium plays in RNA virus infections and, in particular, COVID-19. Many RNA viruses are selenium dependent because antisense interactions arise between viral RNAs and host mRNA regions containing the selencysteine insertion sequence to cause selenium deficiency, oxidative stress, immune response impairment, etc. Sodium selenite is a licensed selenium-containing product and is widely used in medicine, veterinary, and agriculture. Its advantages include the following. Sodium selenite rapidly penetrates through cell membranes in all tissues of the body; is intensely involved in metabolic processes accompanied by oxidation of sulfur-containing cell proteins; exerts an antiaggregation effect by reducing thromboxane activity; interrupts the contact of a virion (SARS-CoV-1 and SARS-CoV-2) with the membrane of a healthy cell; and suppresses NF-κB activity, which significantly increases in coronavirus infections. Arguments supporting the use of sodium selenite as adjuvant therapy in COVID-19 are discussed.

Research advance on the important role of selenoprotein in human health

Selenium (Se) is an essential trace element for animal and human health. Se deficiency and Se excessive intake can lead to severe symptoms and are related to diseases. Se is mainly combined with protein in the form of selenocysteine (Sec) and selenomethionine (Se-Met) in the human body. Generally, proteins formed by incorporating Sec into them are called selenoproteins, while proteins bound in other forms are called Se-containing proteins. Selenoprotein is the main form of Se to exert its biological functions in the human body, and Se deficiency could reduce the content and activity of selenoproteins and disturb the normal physiological function. Researches on the relationship between selenoproteins and human health have received increasing attention, and a comprehensive understanding of the function of selenoproteins is helpful to explain the effects of Se on human health. Although the functions of selenoproteins are not yet fully understood, the critical role of many selenoproteins in human health has been revealed increasingly. So far, 25 kinds of selenoproteins have been found in the human body, and this review focuses on the structure and biological function of glutathione peroxidase (GPX), thioredoxin reductase (TrxR) and iodothyronine deiodinase (ID) families and their relationship with diseases. It shows that selenoproteins such as GPX, TrxR and ID families have biological functions of regulating cell oxidative stress, endoplasmic reticulum stress, antioxidant defense, immune response and inflammatory response. The single nucleotide polymorphism (SNP) and DNA methylation in the promoter region of selenoprotein are related to the risk of diseases. Selenoproteins play a vital role in the pathogenesis and prevention of diseases such as tumors, cardiovascular diseases, osteoarthritis (OA), Keshan disease (KSD), Kashin-Beck disease (KBD), and corona virus disease 2019 (COVID-19) through their genetic and epigenetic forms. This research will provide clues and basis for further revealing the role of Se and selenoprotein in human health and screening to prevent disease targets. However, due to the complexity and unknown biological functions of selenoproteins, the mechanism of selenoproteins in resisting diseases and promoting human health is still worthy of further exploration and research.

Eicosapentaenoic acid favorably modulates protein expression in pulmonary endothelial inflammation

INTRODUCTION: SARS-CoV-2 and other viruses can cause endothelial cell (EC) dysfunction in multiple vascular beds, including pulmonary tissue. Infected patients may then develop acute respiratory distress syndrome (ARDS) and cardiovascular (CV) complications. The omega-3 fatty acid eicosapentaenoic acid (EPA) and its bioactive metabolites favorably modulate inflammation and EC function. These benefits of EPA may contribute to reduced CV events as reported in outcome trials (REDUCE-IT). Currently, EPA is being tested in patients with or at risk for COVID-19. This study tested the effects of either EPA pre- or post-treatment on global protein expression in human pulmonary ECs under conditions of inflammation using the cytokine IL-6 to simulate conditions of advanced viral infections. METHODS: Human lung microvascular endothelial cells (HMVEC-L) were pre-treated with either EPA (40 μM) or IL-6 (12 ng/mL) for 2 hr and then treated with IL-6 or EPA, respectively, for 24 hr in media with 2% FBS. Proteomic analysis was performed using LC/MS to assess relative protein expression levels. Only significant (p< 0.05) changes in protein expression between treatment groups >1-fold were analyzed. Expression of soluble intercellular adhesion molecule-1 (sICAM-1) was separately measured with immunochemistry. RESULTS: HMVEC-L pre- and post-treated with EPA during challenge with IL-6 showed significant changes in 100 (49/51 up/down) and 441 (229/212 up/down) proteins, respectively, compared with IL-6 treatment alone. Among the 31 proteins that were significantly modulated by both EPA pre- and post-treatment, thioredoxin reductase 1 increased relative to IL-6 alone, while matrix metalloproteinase 1 and fibronectin both decreased. Other proteins, such as hypoxia up-regulated protein 1, were differentially modulated by EPA relative to IL-6 (increased in pre-treatment, decreased in post-treatment). Finally, EPA significantly reduced sICAM- 1expression by 41% and 12% compared with IL-6 alone in the pre- and post-treatment models, respectively. CONCLUSIONS: These findings indicate that EPA favorably modulates the expression of multiple inflammatory and cytoprotective proteins during inflammation. These studies support a broad anti-inflammatory effect of EPA on pulmonary ECs that may have therapeutic implications for patients at risk for ARDS due to infectious agents including SARS-CoV-2 or other viruses.

Role of Selenium in Viral Infections with a Major Focus on SARS-CoV-2.

Viral infections have afflicted human health and despite great advancements in scientific knowledge and technologies, continue to affect our society today. The current coronavirus (COVID-19) pandemic has put a spotlight on the need to review the evidence on the impact of nutritional strategies to maintain a healthy immune system, particularly in instances where there are limited therapeutic treatments. Selenium, an essential trace element in humans, has a long history of lowering the occurrence and severity of viral infections. Much of the benefits derived from selenium are due to its incorporation into selenocysteine, an important component of proteins known as selenoproteins. Viral infections are associated with an increase in reactive oxygen species and may result in oxidative stress. Studies suggest that selenium deficiency alters immune response and viral infection by increasing oxidative stress and the rate of mutations in the viral genome, leading to an increase in pathogenicity and damage to the host. This review examines viral infections, including the novel SARS-CoV-2, in the context of selenium, in order to inform potential nutritional strategies to maintain a healthy immune system.

Selenium and RNA Virus Interactions: Potential Implications for SARS-CoV-2 Infection (COVID-19).

SARS-CoV-2 is an RNA virus responsible for the COVID-19 pandemic that already claimed more than 340,000 lives worldwide as of May 23, 2020, the majority of which are elderly. Selenium (Se), a natural trace element, has a key and complex role in the immune system. It is well-documented that Se deficiency is associated with higher susceptibility to RNA viral infections and more severe disease outcome. In this article, we firstly present evidence on how Se deficiency promotes mutations, replication and virulence of RNA viruses. Next, we review how Se might be beneficial via restoration of host antioxidant capacity, reduction of apoptosis and endothelial cell damages as well as platelet aggregation. It also appears that low Se status is a common finding in conditions considered at risk of severe COVID-19, especially in the elderly. Finally, we present a rationale for Se use at different stages of COVID-19. Se has been overlooked but may have a significant place in COVID-19 spectrum management, particularly in vulnerable elderly, and might represent a game changer in the global response to COVID-19.

Understanding Selenium and Glutathione as Antiviral Factors in COVID-19: Does the Viral Mpro Protease Target Host Selenoproteins and Glutathione Synthesis?

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 with catalytically active wild-type Mpro. This seemingly anomalous result is what might be expected if GPX1 is a substrate for the active protease, leading to its fragmentation. We show that the GPX1 active site sequence is substantially similar to a known Mpro cleavage site, and is identified as a potential cysteine protease site by the Procleave algorithm. Proteolytic knockdown of GPX1 is highly consistent with previously documented effects of recombinant SARS-CoV Mpro in transfected cells, including increased reactive oxygen species and NF-κB activation. Because NF-κB in turn activates many pro-inflammatory cytokines, this mechanism could contribute to increased inflammation and cytokine storms observed in COVID-19. Using web-based protease cleavage site prediction tools, we show that Mpro may be targeting not only GPX1, but several other selenoproteins including SELENOF and thioredoxin reductase 1, as well as glutamate-cysteine ligase, the rate-limiting enzyme for glutathione synthesis. This hypothesized proteolytic knockdown of components of both the thioredoxin and glutaredoxin systems is consistent with a viral strategy to inhibit DNA synthesis, to increase the pool of ribonucleotides for RNA synthesis, thereby enhancing virion production. The resulting "collateral damage" of increased oxidative stress and inflammation would be exacerbated by dietary deficiencies of selenium and glutathione precursors.