Epigallocatechin Gallate Inhibits the Uridylate-Specific Endoribonuclease Nsp15 and Efficiently Neutralizes the SARS-CoV-2 Strain

How many organic small molecules might be used to treat COVID-19? From natural products to synthetic agents

A large scale of pandemic coronavirus disease (COVID-19) in the past five years motivates a great deal of endeavors donating to the exploration on therapeutic drugs against COVID-19 as well as other diseases caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Herein is an overview on the organic small molecules that are potentially employed to treat COVID-19 and other SARS-CoV-2-related diseases. These organic small molecules are accessed from both natural resources and synthetic strategies. Notably, typical natural products presented herein consist of polyphenols, lignans, alkaloids, terpenoids, and peptides, which exert an advantage for the further discovery of novel anti-COVID-19 drugs from plant herbs. On the other hand, synthetic prodrugs are composed of a series of inhibitors towards RNA-dependent RNA polymerase (RdRp), main protease (Mpro), 3-chymotrypsin-like cysteine protease (3CLpro), spike protein, papain-like protease (PLpro) of the SARS-CoV-2 as well as the angiotensin-converting enzyme 2 (ACE2) in the host cells. Synthetic strategies are worth taken into consideration because they are beneficial for designing novel anti-COVID-19 drugs in the coming investigations. Although examples collected herein are just a drop in the bucket, developments of organic small molecules against coronavirus infections are believed to pave a promising way for the discovery of multi-targeted therapeutic drugs against not only COVID-19 but also other virus-mediated diseases.

A comprehensive overview on antiviral effects of baicalein and its glucuronide derivative baicalin

Natural product-based antiviral candidates have received significant attention. However, there is a lack of sufficient research in the field of antivirals to effectively combat patterns of drug resistance. Baicalein and its glucuronide derivative baicalin are two main components extracted from Scutellaria baicalensis Georgi. They have proven to be effective against a broad range of viruses by directly killing virus particles, protecting infected cells, and targeting viral antigens on their surface, among other mechanisms. As natural products, they both possess the advantage of lower toxicity, enhanced therapeutic efficacy, and even antagonistic effects against drug-resistant viral strains. Baicalein and baicalin exhibit promising potential as potent pharmacophore scaffolds, demonstrating their antiviral properties. However, to date, no review on the antiviral effects of baicalein and baicalin has been published. This review summarizes the recent research progress on antiviral effects of baicalein and baicalin against various types of viruses both in vitro and in vivo with a focus on the dosages and underlying mechanisms. The aim is to provide a basis for the rational development and utilization of baicalein and baicalin, as well as to promote antiviral drug research. Please cite this article as: Liu XY, Xie W, Zhou HY, Zhang HQ, Jin YS. A comprehensive overview on antiviral effects of baicalein and its glucuronide derivative baicalin. J Integr Med. 2024; 22(6): 621-636.

A structural-based virtual screening and in vitro validation reveals novel effective inhibitors for SARS-CoV-2 helicase and endoribonuclease

Researchers worldwide are looking for molecules that might disrupt the COVID-19 life cycle. Endoribonuclease, which is responsible for processing viral RNA to avoid detection by the host defense system, and helicase, which is responsible for unwinding the RNA helices for replication, are two key non-structural proteins. This study performs a hierarchical structure-based virtual screening approach for NSP15 and helicase to reach compounds with high binding probabilities. In this investigation, we incorporated a variety of filtering strategies for predicting compound interactions. First, we evaluated 756,275 chemicals from four databases using a deep learning method (NCI, Drug Bank, Maybridge, and COCONUT). Following that, two docking techniques (extra precision and induced fit) were utilized to evaluate the compounds' binding affinity, followed by molecular dynamic simulation supported by the MM-GBSA free binding energy calculation. Remarkably, two compounds (90616 and CNP0111740) exhibited high binding affinity values of -66.03 and -12.34 kcal/mol for helicase and NSP15, respectively. The VERO-E6 cell line was employed to test their in vitro therapeutic impact. The CC50 for CNP0111740 and 90616 were determined to be 102.767 μg/ml and 379.526 μg/ml, while the IC50 values were 140.176 μg/ml and 5.147 μg/ml, respectively. As a result, the selectivity index for CNP0111740 and 90616 is 0.73 and 73.73, respectively. Finally, these compounds were found to be novel, effective inhibitors for the virus; however, further in vivo validation is needed.Communicated by Ramaswamy H. Sarma.

Influence of EGCG oxidation on inhibitory activity against the SARS-CoV-2 main protease

SARS-CoV-2 main protease (Mpro) is a well-recognized target for COVID-19 therapy. Green tea (-)-epigallocatechin-3-gallate (EGCG) possesses Mpro-inhibitory activity; however, the influence of EGCG oxidation on its inhibition activity remains obscure, given its high oxidation propensity. This study reveals that prolonged EGCG oxidation in the presence of Mpro dramatically increases its inhibitory activity with an IC50 of 0.26 μM. The inhibitory mechanism is that EGCG-quinone preferentially binds the active site Mpro-Cys145-SH, which forms a quinoprotein. Though Mpro is present in the cell lysate, EGCG preferentially depletes its thiols. Non-cytotoxic EGCG effectively generates a quinoprotein in living cells, thus EGCG might selectively inhibit Mpro in SARS-CoV-2 infected cells. Chlorogenic acid facilitates EGCG oxidation. Together, they synergistically deplete multiple Mpro thiols though this is not more beneficial than EGCG alone. By contrast, excessive EGCG oxidation prior to incubation with Mpro largely compromises its inhibitory activity. Overall, the low IC50 and the high selectivity imply that EGCG is a promising dietary Mpro inhibitor. While EGCG oxidation in the presence of Mpro has a pivotal role in inhibition, enhancing EGCG oxidation by chlorogenic acid no longer increases its inhibitory potential. EGCG oxidation in the absence of Mpro should be avoided to maximize its Mpro-inhibitory activity.

The coronavirus nsp15 endoribonuclease: A puzzling protein and pertinent antiviral drug target

The SARS-CoV-2 pandemic has bolstered unprecedented research efforts to better understand the pathogenesis of coronavirus (CoV) infections and develop effective therapeutics. We here focus on non-structural protein nsp15, a hexameric component of the viral replication-transcription complex (RTC). Nsp15 possesses uridine-specific endoribonuclease (EndoU) activity for which some specific cleavage sites were recently identified in viral RNA. By preventing accumulation of viral dsRNA, EndoU helps the virus to evade RNA sensors of the innate immune response. The immune-evading property of nsp15 was firmly established in several CoV animal models and makes it a pertinent target for antiviral therapy. The search for nsp15 inhibitors typically proceeds via compound screenings and is aided by the rapidly evolving insight in the protein structure of nsp15. In this overview, we broadly cover this fascinating protein, starting with its structure, biochemical properties and functions in CoV immune evasion. Next, we summarize the reported studies in which compound screening or a more rational method was used to identify suitable leads for nsp15 inhibitor development. In this way, we hope to raise awareness on the relevance and druggability of this unique CoV protein.

Therapeutic implications of quercetin and its derived-products in COVID-19 protection and prophylactic

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a novel human coronavirus, which has triggered a global pandemic of the coronavirus infectious disease 2019 (COVID-19). Outbreaks of emerging infectious diseases continue to challenge human health worldwide. The virus conquers human cells through the angiotensin-converting enzyme 2 receptor-driven pathway by mostly targeting the human respiratory tract. Quercetin is a natural flavonoid widely represented in the plant kingdom. Cumulative evidence has demonstrated that quercetin and its derivatives have various pharmacological properties including anti-cancer, anti-hypertension, anti-hyperlipidemia, anti-hyperglycemia, anti-microbial, antiviral, neuroprotective, and cardio-protective effects, because it is a potential treatment for severe inflammation and acute respiratory distress syndrome. Furthermore, it is the main life-threatening condition in patients with COVID-19. This article provides a comprehensive review of the primary literature on the predictable effectiveness of quercetin and its derivatives docked to multi-target of SARS-CoV-2 and host cells via in silico and some of validation through in vitro, in vivo, and clinically to fight SARS-CoV-2 infections, contribute to the reduction of inflammation, which suggests the preventive and therapeutic latency of quercetin and its derived-products against COVID-19 pandemic, multisystem inflammatory syndromes (MIS), and long-COVID.

Improved antioxidative and antibacterial activity of epigallocatechin gallate derivative complexed by zinc cations and chitosan

Epigallocatechin gallate (EGCG) has attracted increasing attention thanks to its multi-bioactivities, and people are keen on improving the antioxidative and antibacterial performance of EGCG. Based on the favorable biofunctionality of Zn2+ and chitosan (CS), an EGCG derivative with a novel formula, i.e., EGCG-Zn-CS, is presented in this study. The structure of EGCG-Zn-CS was characterized by FT-IR, UV-vis, TGA, XPS, and SEM-EDS. The radical elimination results indicate that 0.1 mg mL-1 of EGCG-Zn-CS demonstrates DPPH radical and hydroxyl radical scavenging activities of 94.8% and 92.3%, while 0.1 mg mL-1 of EGCG exhibits only 78.5% and 75.6%, respectively, which means improved antioxidative activity of EGCG-Zn-CS was obtained. Inhibitory experiments against Staphylococcus aureus and Escherichia coli reveal that the minimal inhibitory concentrations (MICs) of EGCG-Zn-CS were 15.625 μg mL-1 and 187.5 μg mL-1, whereas the minimal bactericide concentrations (MBCs) were 46.875 μg mL-1 and 750 μg mL-1, respectively, which indicate that EGCG-Zn-CS exerts much higher antibacterial activity than EGCG. It can be concluded that the complexing of zinc cations and CS could amazingly improve both the antioxidative and antibacterial activity of EGCG, and it is expected that an exploration of EGCG-Zn-CS may inspire the development of simultaneous effective antioxidant and antibacterial agents.

The Potential of Anti-coronavirus Plant Secondary Metabolites in COVID-19 Drug Discovery as an Alternative to Repurposed Drugs: A Review

In early 2020, a global pandemic was announced due to the emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), known to cause COVID-19. Despite worldwide efforts, there are only limited options regarding antiviral drug treatments for COVID-19. Although vaccines are now available, issues such as declining efficacy against different SARS-CoV-2 variants and the aging of vaccine-induced immunity highlight the importance of finding more antiviral drugs as a second line of defense against the disease. Drug repurposing has been used to rapidly find COVID-19 therapeutic options. Due to the lack of clinical evidence for the therapeutic benefits and certain serious side effects of repurposed antivirals, the search for an antiviral drug against SARS-CoV-2 with fewer side effects continues. In recent years, numerous studies have included antiviral chemicals from a variety of plant species. A better knowledge of the possible antiviral natural products and their mechanism against SARS-CoV-2 will help to develop stronger and more targeted direct-acting antiviral agents. The aim of the present study was to compile the current data on potential plant metabolites that can be investigated in COVID-19 drug discovery and development. This review represents a collection of plant secondary metabolites and their mode of action against SARS-CoV and SARS-CoV-2.

Docking and other computing tools in drug design against SARS-CoV-2

The use of computer simulation methods has become an indispensable component in identifying drugs against the SARS-CoV-2 coronavirus. There is a huge body of literature on application of molecular modelling to predict inhibitors against target proteins of SARS-CoV-2. To keep our review clear and readable, we limited ourselves primarily to works that use computational methods to find inhibitors and test the predicted compounds experimentally either in target protein assays or in cell culture with live SARS-CoV-2. Some works containing results of experimental discovery of corresponding inhibitors without using computer modelling are included as examples of a success. Also, some computational works without experimental confirmations are also included if they attract our attention either by simulation methods or by databases used. This review collects studies that use various molecular modelling methods: docking, molecular dynamics, quantum mechanics, machine learning, and others. Most of these studies are based on docking, and other methods are used mainly for post-processing to select the best compounds among those found through docking. Simulation methods are presented concisely, information is also provided on databases of organic compounds that can be useful for virtual screening, and the review itself is structured in accordance with coronavirus target proteins.

Plant-derived strategies to fight against severe acute respiratory syndrome coronavirus 2

The coronavirus disease 2019 (COVID-19) pandemic has caused an unprecedented crisis, which has been exacerbated because specific drugs and treatments have not yet been developed. In the post-pandemic era, humans and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) will remain in equilibrium for a long time. Therefore, we still need to be vigilant against mutated SARS-CoV-2 variants and other emerging human viruses. Plant-derived products are increasingly important in the fight against the pandemic, but a comprehensive review is lacking. This review describes plant-based strategies centered on key biological processes, such as SARS-CoV-2 transmission, entry, replication, and immune interference. We highlight the mechanisms and effects of these plant-derived products and their feasibility and limitations for the treatment and prevention of COVID-19. The development of emerging technologies is driving plants to become production platforms for various antiviral products, improving their medicinal potential. We believe that plant-based strategies will be an important part of the solutions for future pandemics.

Inhibition of SARS-CoV-2 NSP-15 by Uridine-5'-Monophosphate Analogues Using QSAR Modelling, Molecular Dynamics Simulations, and Free Energy Landscape

SARS-CoV-2 is accountable for severe social and economic disruption around the world causing COVID-19. Non-structural protein-15 (NSP15) possesses a domain that is vital to the viral life cycle and is known as uridylate-specific endoribonuclease (EndoU). This domain binds to the uridine 5'-monophosphate (U5P) so that the protein may carry out its native activity. It is considered a vital drug target to inhibit the growth of the virus. Thus, in this current study, ML-based QSAR and virtual screening of U5P analogues targeting Nsp15 were performed to identify potential molecules against SARS-CoV-2. Screening of 816 unique U5P analogues using ML-based QSAR identified 397 compounds ranked on their predicted bioactivity (pIC50). Further, molecular docking and hydrogen bond interaction analysis resulted in the selection of the top three compounds (53309102, 57398422, and 76314921). Molecular dynamics simulation of the most promising compounds showed that two molecules 53309102 and 57398422 acted as potential binders of Nsp15. The compound was able to inhibit nsp15 activity as it was successfully bound to the active site of the nsp15 protein. This was achieved by the formation of relevant contacts with enzymatically critical amino acid residues (His235, His250, and Lys290). Principal component analysis and free energy landscape studies showed stable complex formation while MM/GBSA calculation showed lower binding energies for 53309102 (ΔGTOTAL = -29.4 kcal/mol) and 57398422 (ΔGTOTAL = -39.4 kcal/mol) compared to the control U5P (ΔGTOTAL = -18.8 kcal/mol). This study aimed to identify analogues of U5P inhibiting the NSP15 function that potentially could be used for treating COVID-19.

Animal efficacy study of a plant extract complex (BEN815) as a potential treatment for COVID-19

In a short time, several types of injectable and oral therapeutics have been developed and used to effectively manage patients with coronavirus disease 2019 (COVID-19). BEN815 is an improved mixture of three extracts (Psidium guajava, Camellia sinensis, and Rosa hybrida) recognized by the Ministry of Food and Drug Safety of Korea as a health food ingredient that alleviates allergic rhinitis. The current animal efficacy study was performed to assess its probability of improving COVID-19 symptoms. BEN815 treatment significantly increased the survival of K18-hACE2 transgenic mice and reduced viral titers in the lungs at 5 days post infection (DPI). Furthermore, the lungs of the treated mice showed mild tissue damage at 5 DPI and nearly complete recovery from COVID-19 at 14 DPI. BEN815 appears to be an effective and minimally toxic anti-SARS-CoV-2 agent in mice and has potential for clinical applications.

Health benefits, mechanisms of interaction with food components, and delivery of tea polyphenols: a review

Tea polyphenols (TPs) are the most important active component of tea and have become a research focus among natural products, thanks to their antioxidant, lipid-lowering, liver-protecting, anti-tumor, and other biological activities. Polyphenols can interact with other food components, such as protein, polysaccharides, lipids, and metal ions to further improve the texture, flavor, and sensory quality of food, and are widely used in food fields, such as food preservatives, antibacterial agents and food packaging. However, the instability of TPs under conditions such as light or heat and their low bioavailability in the gastrointestinal environment also hinder their application in food. In this review, we summarized the health benefits of TPs. In order to better use TPs in food, we analyzed the form and mechanism of interaction between TPs and main food components, such as polysaccharides and proteins. Moreover, we reviewed research into optimizing the applications of TPs in food by bio-based delivery systems, such as liposomes, nanoemulsions, and nanoparticles, so as to improve the stability and bioactivity of TPs in food application. As an effective active ingredient, TPs have great potential to be applied in functional food to produce benefits for human health.

Atovaquone and Pibrentasvir Inhibit the SARS-CoV-2 Endoribonuclease and Restrict Infection In Vitro but Not In Vivo

The emergence of SARS-CoV-1 in 2003 followed by MERS-CoV and now SARS-CoV-2 has proven the latent threat these viruses pose to humanity. While the SARS-CoV-2 pandemic has shifted to a stage of endemicity, the threat of new coronaviruses emerging from animal reservoirs remains. To address this issue, the global community must develop small molecule drugs targeting highly conserved structures in the coronavirus proteome. Here, we characterized existing drugs for their ability to inhibit the endoribonuclease activity of the SARS-CoV-2 non-structural protein 15 (nsp15) via in silico, in vitro, and in vivo techniques. We have identified nsp15 inhibition by the drugs pibrentasvir and atovaquone which effectively inhibit SARS-CoV-2 and HCoV-OC43 at low micromolar concentrations in cell cultures. Furthermore, atovaquone, but not pibrentasvir, is observed to modulate HCoV-OC43 dsRNA and infection in a manner consistent with nsp15 inhibition. Although neither pibrentasvir nor atovaquone translate to clinical efficacy in a murine prophylaxis model of SARS-CoV-2 infection, atovaquone may serve as a basis for the design of future nsp15 inhibitors.

Targeting SARS-CoV-2 Non-Structural Proteins

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is an enveloped respiratory β coronavirus that causes coronavirus disease (COVID-19), leading to a deadly pandemic that has claimed millions of lives worldwide. Like other coronaviruses, the SARS-CoV-2 genome also codes for non-structural proteins (NSPs). These NSPs are found within open reading frame 1a (ORF1a) and open reading frame 1ab (ORF1ab) of the SARS-CoV-2 genome and encode NSP1 to NSP11 and NSP12 to NSP16, respectively. This study aimed to collect the available literature regarding NSP inhibitors. In addition, we searched the natural product database looking for similar structures. The results showed that similar structures could be tested as potential inhibitors of the NSPs.

The Therapeutic Potential of Natural Dietary Flavonoids against SARS-CoV-2 Infection

The exploration of non-toxic and cost-effective dietary components, such as epigallocatechin 3-gallate and myricetin, for health improvement and disease treatment has recently attracted substantial research attention. The recent COVID-19 pandemic has provided a unique opportunity for the investigation and identification of dietary components capable of treating viral infections, as well as gathering the evidence needed to address the major challenges presented by public health emergencies. Dietary components hold great potential as a starting point for further drug development for the treatment and prevention of SARS-CoV-2 infection owing to their good safety, broad-spectrum antiviral activities, and multi-organ protective capacity. Here, we review current knowledge of the characteristics-chemical composition, bioactive properties, and putative mechanisms of action-of natural bioactive dietary flavonoids with the potential for targeting SARS-CoV-2 and its variants. Notably, we present promising strategies (combination therapy, lead optimization, and drug delivery) to overcome the inherent deficiencies of natural dietary flavonoids, such as limited bioavailability and poor stability.

COVID-19 associated thyroid dysfunction and other comorbidities and its management using phytochemical-based therapeutics: a natural way

The present severe acute respiratory syndrome-2 (SARS-CoV-2) mediated Coronavirus pandemic (COVID-19) and post-COVID-19 complications affect human life drastically. Patients who have been cured of COVID-19 infection are now experiencing post-COVID-19 associated comorbidities, which have increased mortality rates. The SARS-CoV-2 infection distresses the lungs, kidneys, gastrointestinal tract, and various endocrine glands, including the thyroid. The emergence of variants which includes Omicron (B.1.1.529) and its lineages threaten the world severely. Among different therapeutic approaches, phytochemical-based therapeutics are not only cost-effective but also have lesser side effects. Recently a plethora of studies have shown the therapeutic efficacy of various phytochemicals for the treatment of COVID-19. Besides this, various phytochemicals have been found efficacious in treating several inflammatory diseases, including thyroid-related anomalies. The method of the phytochemical formulation is quick and facile and the raw materials for such herbal preparations are approved worldwide for human use against certain disease conditions. Owing to the advantages of phytochemicals, this review primarily discusses the COVID-19-related thyroid dysfunction and the role of key phytochemicals to deal with thyroid anomaly and post-COVID-19 complications. Further, this review shed light on the mechanism via which COVID-19 and its related complication affect organ function of the body, along with the mechanistic insight into the way by which phytochemicals could help to cure post-COVID-19 complications in thyroid patients. Considering the advantages offered by phytochemicals as a safer and cost-effective medication they can be potentially used to combat COVID-19-associated comorbidities.

An overview of anti-SARS-CoV-2 and anti-inflammatory potential of baicalein and its metabolite baicalin: Insights into molecular mechanisms

The current Coronavirus Disease 2019 (COVID-19) pandemic, caused by the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), is highly contagious infection that breaks the healthcare systems of several countries worldwide. Till to date, no effective antiviral drugs against COVID-19 infection have reached the market, and some repurposed drugs and vaccines are prescribed for the treatment and prevention of this disease. The currently prescribed COVID-19 vaccines are less effective against the newly emergent variants of concern of SARS-CoV-2 due to several mutations in viral spike protein and obviously there is an urgency to develop new antiviral drugs against this disease. In this review article, we systematically discussed the anti-SARS-CoV-2 and anti-inflammatory efficacy of two flavonoids, baicalein and its 7-O-glucuronide, baicalin, isolated from Scutellaria baicalensis, Oroxylum indicum, and other plants as well as their pharmacokinetics and oral bioavailability, for development of safe and effective drugs for COVID-19 treatment. Both baicalein and baicalin target the activities of viral S-, 3CL-, PL-, RdRp- and nsp13-proteins, and host mitochondrial OXPHOS for suppression of viral infection. Moreover, these compounds prevent sepsis-related inflammation and organ injury by modulation of host innate immune responses. Several nanoformulated and inclusion complexes of baicalein and baicalin have been reported to increase oral bioavailability, but their safety and efficacy in SARS-CoV-2-infected transgenic animals are not yet evaluated. Future studies on these compounds are required for use in clinical trials of COVID-19 patients.

Chitosan hydrogel modified with lanthanum as a drug delivery system for epigallocatechin gallate: Investigation of hydrogel - drug interaction by FT-IR and Raman spectroscopy

In the presented work, chitosan hydrogel modified with lanthanum was obtained for the first time. The hydrogel was used as a carrier in the controlled release of epigallocatechin gallate. The work proved the effectiveness of drug sorption by hydrogel and controlled release in simulated body fluids. The drug was released slowly and in a controlled manner from the carrier. The research techniques used in this work (FT-IR spectroscopy and imaging, Raman spectroscopy, SEM/EDS) allowed to confirm the successful retention of EGCG on the hydrogel surface. On the basis of the EDS mapping, it was possible to confirm the even distribution of the lanthanum ions. Using FT-IR imaging, we verified that the drug was evenly distributed on the entire surface of the prepared material. The antifungal effectiveness of the material has been proven on several types of fungi. The research proved that the prepared material is capable of long-term release of the active substance and has antifungal properties. As a result, the prepared material can be successfully used as an implantable hydrogel or a coating in, e.g. titanium implants.

Green Tea Consumption and the COVID-19 Omicron Pandemic Era: Pharmacology and Epidemiology

In spite of the development of numerous vaccines for the prevention of COVID-19 and the approval of several drugs for its treatment, there is still a great need for effective and inexpensive therapies against this disease. Previously, we showed that green tea and tea catechins interfere with coronavirus replication as well as coronavirus 3CL protease activity, and also showed lower COVID-19 morbidity and mortality in countries with higher green tea consumption. However, it is not clear whether green tea is still effective against the newer SARS-CoV-2 variants including omicron. It is also not known whether higher green tea consumption continues to contribute to lower COVID-19 morbidity and mortality now that vaccination rates in many countries are high. Here, we attempted to update the information regarding green tea in relation to COVID-19. Using pharmacological and ecological approaches, we found that EGCG as well as green tea inhibit the activity of the omicron variant 3CL protease efficiently, and there continues to be pronounced differences in COVID-19 morbidity and mortality between groups of countries with high and low green tea consumption as of December 6, 2022. These results collectively suggest that green tea continues to be effective against COVID-19 despite the new omicron variants and increased vaccination.

A Comprehensive Review of Natural Flavonoids with Anti-SARS-CoV-2 Activity

The COVID-19 pandemic caused by SARS-CoV-2 has majorly impacted public health and economies worldwide. Although several effective vaccines and drugs are now used to prevent and treat COVID-19, natural products, especially flavonoids, showed great therapeutic potential early in the pandemic and thus attracted particular attention. Quercetin, baicalein, baicalin, EGCG (epigallocatechin gallate), and luteolin are among the most studied flavonoids in this field. Flavonoids can directly or indirectly exert antiviral activities, such as the inhibition of virus invasion and the replication and inhibition of viral proteases. In addition, flavonoids can modulate the levels of interferon and proinflammatory factors. We have reviewed the previously reported relevant literature researching the pharmacological anti-SARS-CoV-2 activity of flavonoids where structures, classifications, synthetic pathways, and pharmacological effects are summarized. There is no doubt that flavonoids have great potential in the treatment of COVID-19. However, most of the current research is still in the theoretical stage. More studies are recommended to evaluate the efficacy and safety of flavonoids against SARS-CoV-2.

Targeting viral proteins for restraining SARS-CoV-2: focusing lens on viral proteins beyond spike for discovering new drug targets

INTRODUCTION

Emergence of highly infectious SARS-CoV-2 variants are reducing protection provided by current vaccines, requiring constant updates in antiviral approaches. The virus encodes four structural and sixteen nonstructural proteins which play important roles in viral genome replication and transcription, virion assembly, release , entry into cells, and compromising host cellular defenses. As alien proteins to host cells, many viral proteins represent potential targets for combating the SARS-CoV-2.

AREAS COVERED

Based on literature from PubMed and Web of Science databases, the authors summarize the typical characteristics of SARS-CoV-2 from the whole viral particle to the individual viral proteins and their corresponding functions in virus life cycle. The authors also discuss the potential and emerging targeted interventions to curb virus replication and spread in detail to provide unique insights into SARS-CoV-2 infection and countermeasures against it.

EXPERT OPINION

Our comprehensive analysis highlights the rationale to focus on non-spike viral proteins that are less mutated but have important functions. Examples of this include: structural proteins (e.g. nucleocapsid protein, envelope protein) and extensively-concerned nonstructural proteins (e.g. NSP3, NSP5, NSP12) along with the ones with relatively less attention (e.g. NSP1, NSP10, NSP14 and NSP16), for developing novel drugs to overcome resistance of SARS-CoV-2 variants to preexisting vaccines and antibody-based treatments.

Therapeutic potential of green tea catechin, (-)-epigallocatechin-3-O-gallate (EGCG) in SARS-CoV-2 infection: Major interactions with host/virus proteases

BACKGROUND

The current COVID-19 pandemic from the human pathogenic virus SARS-CoV-2 has resulted in a major health hazard globally. The morbidity and transmission modality of this disease are severe and uncontrollable. As no effective clinical drugs are available for treatment of COVID-19 infection till to date and only vaccination is used as prophylaxis and its efficacy is restricted due to emergent of new variants of SARS-CoV-2, there is an urgent need for effective drugs for its treatment.

PURPOSE

The aim of this review was to provide a detailed analysis of anti-SARS-CoV-2 efficacy of (-)-epigallocatechin-3-O-gallate (EGCG), a major catechin constituent of green tea (Camellia sinensis (L.) Kuntze) beverage to highlight the scope of EGCG in clinical medicine as both prophylaxis and treatment of present COVID-19 infection. In addition, the factors related to poor oral bioavailabilty of EGCG was also analysed for a suggestion for future research in this direction.

STUDY DESIGN

We collected the published articles related to anti-SARS-CoV-2 activity of EGCG against the original strain (Wuhan type) and its newly emerged variants of SARS-CoV-2 virus.

METHODS

A systematic search on the published literature was conducted in various databases including Google Scholar, PubMed, Science Direct and Scopus to collect the relevant literature.

RESULTS

The findings of this search demonstrate that EGCG shows potent antiviral activity against SARS-CoV-2 virus by preventing viral entry and replication in host cells in vitro models. The studies on the molecular mechanisms of EGCG in inhibition of SARS-CoV-2 infection in host cells reveal that EGCG blocks the entry of the virus particles by interaction with the receptor binding domain (RBD) of viral spike (S) protein to host cell surface receptor protease angiotensin-converting enzyme 2 (ACE2) as well as suppression of the expressions of host proteases, ACE2, TMPRSS2 and GRP78, required for viral entry, by Nrf2 activation in host cells. Moreover, EGCG inhibits the activities of SARS-CoV-2 main protease (Mpro), papain-like protease (PLpro), endoribonuclease Nsp15 in vitro models and of RNA-dependent RNA polymerase (RdRp) in molecular docking model for suppression of viral replication. In addition, EGCG significantly inhibits viral inflammatory cytokine production by stimulating Nrf2- dependent host immune response in virus-infected cells. EGCG significantly reduces the elevated levels of HMGB1, a biomarker of sepsis, lung fibrosis and thrombotic complications in viral infections. EGCG potentially inhibits the infection of original (Wuhan type) strain of SARS-CoV-2 and other newly emerged variants as well as the infections of SARS-CoV-2 virus spike-protein of WT and its mutants-mediated pseudotyped viruses . EGCG shows maximum inhibitory effect against SARS-CoV-2 infection when the host cells are pre-incubated with the drug prior to viral infection. A sorbitol/lecithin-based throat spray containing concentrated green tea extract rich in EGCG content significantly reduces SARS-CoV-2 infectivity in oral mucosa. Several factors including degradation in gastrointestinal environment, low absorption in small intestine and extensive metabolism of EGCG are responsible for its poor bioavailability in humans. Pharmacokinetic and metabolism studies of EGCG in humans reveal poor bioavailability of EGCG in human plasma and EGCG-4"-sulfate is its major metabolite. The concentration of EGCG-4"-sulfate in human plasma is almost equivalent to that of free EGCG (Cmax 177.9 vs 233.5 nmol/L). These findings suggest that inhibition of sulfation of EGCG is a crucial factor for improvement of its bioavailability. In vitro study on the mechanism of EGCG sulfonation indicates that sulfotransferases, SULT1A1 and SULT1A3 are responsible for sulfonation in human liver and small intestine, respectively. Some attempts including structural modifications, and nanoformulations of EGCG and addition of nutrients with EGCG have been made to improve the bioavailability of EGCG.

CONCLUSIONS

The findings of this study suggest that EGCG has strong antiviral activity against SARS-CoV-2 infection independent of viral strains (Wuhan type (WT), other variants) by inhibition of viral entry and replication in host cells in vitro models. EGCG may be useful in reduction of this viral load in salivary glands of COVID-19 patients, if it is applied in mouth and throat wash formulations in optimal concentrations. EGCG could be a promising candidate in the development of effective vaccine for prevention of the infections of newly emergent strains of SARS-CoV-2 virus. EGCG might be useful also as a clinical medicine for treatment of COVID-19 patients if its bioavailability in human plasma is enhanced.

Potential of green tea EGCG in neutralizing SARS-CoV-2 Omicron variant with greater tropism toward the upper respiratory tract

Background

COVID-19 due to SARS-CoV-2 infection has had an enormous adverse impact on global public health. As the COVID-19 pandemic evolves, the WHO declared several variants of concern (VOCs), including Alpha, Beta, Gamma, Delta, and Omicron. Compared with earlier variants, Omicron, now a dominant lineage, exhibits characteristics of enhanced transmissibility, tropism shift toward the upper respiratory tract, and attenuated disease severity. The robust transmission of Omicron despite attenuated disease severity still poses a great challenge for pandemic control. Under this circumstance, its tropism shift may be utilized for discovering effective preventive approaches.

Scope and approach

This review aims to estimate the potential of green tea epigallocatechin gallate (EGCG), the most potent antiviral catechin, in neutralizing SARS-CoV-2 Omicron variant, based on current knowledge concerning EGCG distribution in tissues and Omicron tropism.

Key findings and conclusions

EGCG has a low bioavailability. Plasma EGCG levels are in the range of submicromolar concentrations following green tea drinking, or reach at most low μM concentrations after pharmacological intervention. Nonetheless, its levels in the upper respiratory tract could reach concentrations as high as tens or even hundreds of μM following green tea consumption or pharmacological intervention. An approach for delivering sufficiently high concentrations of EGCG in the pharynx has been developed. Convincing data have demonstrated that EGCG at tens to hundreds of μM can dramatically neutralize SARS-CoV-2 and effectively eliminate SARS-CoV-2-induced cytopathic effects and plaque formation. Thus, EGCG, which exhibits hyperaccumulation in the upper respiratory tract, deserves closer investigation as an antiviral in the current global battle against COVID-19, given Omicron's greater tropism toward the upper respiratory tract.

Modeling of SARS-CoV-2 Virus Proteins: Implications on Its Proteome

COronaVIrus Disease 19 (COVID-19) is a severe acute respiratory syndrome (SARS) caused by a group of beta coronaviruses, SARS-CoV-2. The SARS-CoV-2 virus is similar to previous SARS- and MERS-causing strains and has infected nearly six hundred and fifty million people all over the globe, while the death toll has crossed the six million mark (as of December, 2022). In this chapter, we look at how computational modeling approaches of the viral proteins could help us understand the various processes in the viral life cycle inside the host, an understanding of which might provide key insights in mitigating this and future threats. This understanding helps us identify key targets for the purpose of drug discovery and vaccine development.

A little less aggregation a little more replication: Viral manipulation of stress granules

Recent exciting studies have uncovered how membrane-less organelles, also known as biocondensates, are providing cells with rapid response pathways, allowing them to re-organize their cellular contents and adapt to stressful conditions. Their assembly is driven by the phase separation of their RNAs and intrinsically disordered protein components into condensed foci. Among these, stress granules (SGs) are dynamic cytoplasmic biocondensates that form in response to many stresses, including activation of the integrated stress response or viral infections. SGs sit at the crossroads between antiviral signaling and translation because they concentrate signaling proteins and components of the innate immune response, in addition to translation machinery and stalled mRNAs. Consequently, they have been proposed to contribute to antiviral activities, and therefore are targeted by viral countermeasures. Equally, SGs components can be commandeered by viruses for their own efficient replication. Phase separation processes are an important component of the viral life cycle, for example, driving the assembly of replication factories or inclusion bodies. Therefore, in this review, we will outline the recent understanding of this complex interplay and tug of war between viruses, SGs, and their components. This article is categorized under: RNA in Disease and Development > RNA in Disease Translation > Regulation RNA Interactions with Proteins and Other Molecules > RNA-Protein Complexes.

Small molecules in the treatment of COVID-19

The outbreak of COVID-19 has become a global crisis, and brought severe disruptions to societies and economies. Until now, effective therapeutics against COVID-19 are in high demand. Along with our improved understanding of the structure, function, and pathogenic process of SARS-CoV-2, many small molecules with potential anti-COVID-19 effects have been developed. So far, several antiviral strategies were explored. Besides directly inhibition of viral proteins such as RdRp and Mpro, interference of host enzymes including ACE2 and proteases, and blocking relevant immunoregulatory pathways represented by JAK/STAT, BTK, NF-κB, and NLRP3 pathways, are regarded feasible in drug development. The development of small molecules to treat COVID-19 has been achieved by several strategies, including computer-aided lead compound design and screening, natural product discovery, drug repurposing, and combination therapy. Several small molecules representative by remdesivir and paxlovid have been proved or authorized emergency use in many countries. And many candidates have entered clinical-trial stage. Nevertheless, due to the epidemiological features and variability issues of SARS-CoV-2, it is necessary to continue exploring novel strategies against COVID-19. This review discusses the current findings in the development of small molecules for COVID-19 treatment. Moreover, their detailed mechanism of action, chemical structures, and preclinical and clinical efficacies are discussed.

Interaction of Epigallocatechin Gallate and Quercetin with Spike Glycoprotein (S-Glycoprotein) of SARS-CoV-2: In Silico Study

Severe acute respiratory syndrome (SARS)-CoV-2 from the family Coronaviridae is the cause of the outbreak of severe pneumonia, known as coronavirus disease 2019 (COVID-19), which was first recognized in 2019. Various potential antiviral drugs have been presented to hinder SARS-CoV-2 or treat COVID-19 disease. Side effects of these drugs are among the main complicated issues for patients. Natural compounds, specifically primary and secondary herbal metabolites, may be considered as alternative options to provide therapeutic activity and reduce cytotoxicity. Phenolic materials such as epigallocatechin gallate (EGCG, polyphenol) and quercetin have shown antibacterial, antifungal, antiviral, anticancer, and anti-inflammatory effects in vitro and in vivo. Therefore, in this study, molecular docking was applied to measure the docking property of epigallocatechin gallate and quercetin towards the transmembrane spike (S) glycoprotein of SARS-CoV-2. Results of the present study showed Vina scores of -9.9 and -8.3 obtained for EGCG and quercetin by CB-Dock. In the case of EGCG, four hydrogen bonds of OG1, OD2, O3, and O13 atoms interacted with the Threonine (THR778) and Aspartic acid (ASP867) amino acids of the spike glycoprotein (6VSB). According to these results, epigallocatechin gallate and quercetin can be considered potent therapeutic compounds for addressing viral diseases.

A Review of In Silico Research, SARS-CoV-2, and Neurodegeneration: Focus on Papain-Like Protease

Since the appearance of SARS-CoV-2 and the COVID-19 pandemic, the search for new approaches to treat this disease took place in the scientific community. The in silico approach has gained importance at this moment, once the methodologies used in this kind of study allow for the identification of specific protein-ligand interactions, which may serve as a filter step for molecules that can act as specific inhibitors. In addition, it is a low-cost and high-speed technology. Molecular docking has been widely used to find potential viral protein inhibitors for structural and non-structural proteins of the SARS-CoV-2, aiming to block the infection and the virus multiplication. The papain-like protease (PLpro) participates in the proteolytic processing of SARS-CoV-2 and composes one of the main targets studied for pharmacological intervention by in silico methodologies. Based on that, we performed a systematic review about PLpro inhibitors from the perspective of in silico research, including possible therapeutic molecules in relation to this viral protein. The neurological problems triggered by COVID-19 were also briefly discussed, especially relative to the similarities of neuroinflammation present in Alzheimer's disease. In this context, we focused on two molecules, curcumin and glycyrrhizinic acid, given their PLpro inhibitory actions and neuroprotective properties and potential therapeutic effects on COVID-19.

Promising natural products against SARS-CoV-2: Structure, function, and clinical trials

The corona virus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus type 2 (SARS-COV-2) poses a severe threat to human health and still spreads globally. Due to the high mutation ratio and breakthrough infection rate of the virus, vaccines and anti-COVID-19 drugs require continual improvements. Drug screening research has shown that some natural active products can target the critical proteins of SARS-CoV-2, including 3CLpro, ACE2, FURIN, and RdRp, which could produce great inhibitory effects on SARS-COV-2. In addition, some natural products have displayed activities of immunomodulation, antiinflammatory, and antihepatic failure in COVID-19 clinical trials, which may relate to their non-monomeric structures. However, further evaluation and high-quality assessments, including safety verification tests, drug interaction tests, and clinical trials, are needed to substantiate natural products' multi-target and multi-pathway effects on COVID-19. Here, we review the literature on several promising active natural products that may act as vaccine immune enhancers or provide targeted anti-COVID-19 drugs. The structures, mechanisms of action, and research progress of these natural products are analyzed, to hopefully provide effective ideas for the development of targeted drugs that possess better structure, potency, and safety.

SARS-CoV-2 Non-Structural Proteins and Their Roles in Host Immune Evasion

Coronavirus disease 2019 (COVID-19) has caused an unprecedented global crisis and continues to threaten public health. The etiological agent of this devastating pandemic outbreak is the severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2). COVID-19 is characterized by delayed immune responses, followed by exaggerated inflammatory responses. It is well-established that the interferon (IFN) and JAK/STAT signaling pathways constitute the first line of defense against viral and bacterial infections. To achieve viral replication, numerous viruses are able to antagonize or hijack these signaling pathways to attain productive infection, including SARS-CoV-2. Multiple studies document the roles of several non-structural proteins (NSPs) of SARS-CoV-2 that facilitate the establishment of viral replication in host cells via immune escape. In this review, we summarize and highlight the functions and characteristics of SARS-CoV-2 NSPs that confer host immune evasion. The molecular mechanisms mediating immune evasion and the related potential therapeutic strategies for controlling the COVID-19 pandemic are also discussed.

Targeting SARS-CoV-2 endoribonuclease: a structure-based virtual screening supported by in vitro analysis

Researchers are focused on discovering compounds that can interfere with the COVID-19 life cycle. One of the important non-structural proteins is endoribonuclease since it is responsible for processing viral RNA to evade detection of the host defense system. This work investigates a hierarchical structure-based virtual screening approach targeting NSP15. Different filtering approaches to predict the interactions of the compounds have been included in this study. Using a deep learning technique, we screened 823,821 compounds from five different databases (ZINC15, NCI, Drug Bank, Maybridge, and NCI Diversity set III). Subsequently, two docking protocols (extra precision and induced fit) were used to assess the binding affinity of the compounds, followed by molecular dynamic simulation supported by the MM-GBSA free binding energy. Interestingly, one compound (ZINC000104379474) from the ZINC15 database has been found to have a good binding affinity of − 7.68 kcal/Mol. The VERO-E6 cell line was used to investigate its therapeutic effect in vitro. Half-maximal cytotoxic concentration and Inhibitory concentration 50 were determined to be 0.9 mg/ml and 0.01 mg/ml, respectively; therefore, the selectivity index is 90. In conclusion, ZINC000104379474 was shown to be a good hit for targeting the virus that needs further investigations in vivo to be a drug candidate.

Structure-guided pharmacophore based virtual screening, docking, and molecular dynamics to discover repurposed drugs as novel inhibitors against endoribonuclease Nsp15 of SARS-CoV-2

COVID-19 (Corona Virus Disease of 2019) caused by the novel 'Severe Acute Respiratory Syndrome Coronavirus-2' (SARS-CoV-2) has wreaked havoc on human health and the global economy. As a result, for new medication development, it's critical to investigate possible therapeutic targets against the novel virus. 'Non-structural protein 15' (Nsp15) endonuclease is one of the crucial targets which helps in the replication of virus and virulence in the host immune system. Here, in the current study, we developed the structure-based pharmacophore model based on Nsp15-UMP interactions and virtually screened several databases against the selected model. To validate the screening process, we docked the top hits obtained after secondary filtering (Lipinski's rule of five, ADMET & Topkat) followed by 100 ns molecular dynamics (MD) simulations. Next, to revalidate the MD simulation studies, we have calculated the binding free energy of each complex using the MM-PBSA procedure. The discovered repurposed drugs can aid the rational design of novel inhibitors for Nsp15 of the SARS-CoV-2 enzyme and may be considered for immediate drug development.

Potential Application of Tea Polyphenols to the Prevention of COVID-19 Infection: Based on the Gut-Lung Axis

Coronavirus disease 2019 (COVID-19) disrupts the intestinal micro-ecological balance, and patients often develop the intestinal disease. The gut is the largest immune organ in the human body; intestinal microbes can affect the immune function of the lungs through the gut-lung axis. It has been reported that tea polyphenols (TPs) have antiviral and prebiotic activity. In this review, we discussed TPs reduced lung-related diseases through gut-lung axis by inhibiting dysbiosis. In addition, we also highlighted the preventive and therapeutic effects of TPs on COVID-19 complications, further demonstrating the importance of research on TPs for the prevention and treatment of COVID-19 in humans. Based on this understanding, we recommend using TPs to regulate the gut microbiota to prevent or alleviate COVID-19 through the gut-lung axis.

Coronavirus enzyme inhibitors-experimentally proven natural compounds from plants

Coronavirus disease (COVID-19) can cause critical conditions that require efficient therapeutics. Several medicines are derived from plants, and researchers are seeking natural compounds to ameliorate the symptoms of COVID-19. Viral enzymes are popular targets of antiviral medicines; the genome of coronaviruses encodes several enzymes, including RNA-dependent RNA polymerase and viral proteases. Various screening systems have been developed to identify potential inhibitors. In this review, we describe the natural compounds that have been shown to exert inhibitory effects on coronavirus enzymes. Although computer-aided molecular structural studies have predicted several antiviral compound candidates, the current review focuses on experimentally proven natural compounds.

Antiviral plant-derived natural products to combat RNA viruses: Targets throughout the viral life cycle

There is a need for new effective antivirals, particularly in response to the development of antiviral drug resistance and emerging RNA viruses such as SARS‐CoV‐2. Plants are a significant source of structurally diverse bioactive compounds for drug discovery suggesting that plant‐derived natural products could be developed as antiviral agents. This article reviews the antiviral activity of plant‐derived natural products against RNA viruses, with a focus on compounds targeting specific stages of the viral life cycle. A range of plant extracts and compounds have been identified with antiviral activity, often against multiple virus families suggesting they may be useful as broad‐spectrum antiviral agents. The antiviral mechanism of action of many of these phytochemicals is not fully understood and there are limited studies and clinical trials demonstrating their efficacy and toxicity in vivo. Further research is needed to evaluate the therapeutic potential of plant‐derived natural products as antiviral agents.

Epigallocatechin Gallate (EGCG), a Green Tea Polyphenol, Reduces Coronavirus Replication in a Mouse Model

The COVID-19 pandemic has resulted in a huge number of deaths from 2020 to 2021; however, effective antiviral drugs against SARS-CoV-2 are currently under development. Recent studies have demonstrated that green tea polyphenols, particularly EGCG, inhibit coronavirus enzymes as well as coronavirus replication in vitro. Herein, we examined the inhibitory effect of green tea polyphenols on coronavirus replication in a mouse model. We used epigallocatechin gallate (EGCG) and green tea polyphenols containing more than 60% catechin (GTP60) and human coronavirus OC43 (HCoV-OC43) as a surrogate for SARS-CoV-2. Scanning electron microscopy analysis results showed that HCoV-OC43 infection resulted in virion particle production in infected cells. EGCG and GTP60 treatment reduced coronavirus protein and virus production in the cells. Finally, EGCG- and GTP60-fed mice exhibited reduced levels of coronavirus RNA in mouse lungs. These results demonstrate that green tea polyphenol treatment is effective in decreasing the level of coronavirus in vivo.

Are Antiviral Flavonoids Part of the Solution to the COVID-19 Pandemic?

The relentless continuation of the COVID-19 (coronavirus disease 2019) pandemic clearly indicates the need to broaden our approach to this serious, worldwide problem. An important factor that has received little attention is the protective role of dietary antiviral flavonoids. Many flavonoids have been shown through molecular docking assays, as well as in silico studies, and in vitro and in vivo studies to inhibit virtually every mechanism needed by SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) to penetrate cells and hijack molecular processes. These inhibitory effects have shown clinical benefit in a few preliminary studies. In this editorial I present research which makes the case for dietary flavonoids as part of the solution to the COVID-19 pandemic.

The intestinal microbiota and improving the efficacy of COVID-19 vaccinations

Most COVID-19 cases are mild or asymptomatic and recover well, suggesting that effective immune responses ensue, which successfully eliminate SARS-CoV-2 viruses. However, a small proportion of patients develop severe COVID-19 with pathological immune responses. This indicates that a strong immune system balanced with anti-inflammatory mechanisms is critical for the recovery from SARS-CoV-2 infections. Many vaccines against SARS-CoV-2 have now been developed for eliciting effective immune responses to protect from SARS-CoV-2 infections or reduce the severity of the disease if infected. Although uncommon, serious morbidity and mortality have resulted from both COVID-19 vaccine adverse reactions and lack of efficacy, and further improvement of efficacy and prevention of adverse effects are urgently warranted. Many factors could affect efficacy of these vaccines to achieve optimal immune responses. Dysregulation of the gut microbiota (gut dysbiosis) could be an important risk factor as the gut microbiota is associated with the development and maintenance of an effective immune system response. In this narrative review, we discuss the immune responses to SARS-CoV-2, how COVID-19 vaccines elicit protective immune responses, gut dysbiosis involvement in inefficacy and adverse effects of COVID-19 vaccines and the modulation of the gut microbiota by functional foods to improve COVID-19 vaccine immunisations.

Phytochemicals for the treatment of COVID-19

The coronavirus disease 2019 (COVID-19) pandemic has underscored the lack of approved drugs against acute viral diseases. Plants are considered inexhaustible sources of drugs for several diseases and clinical conditions, but plant-derived compounds have seen little success in the field of antivirals. Here, we present the case for the use of compounds from vascular plants, including alkaloids, flavonoids, polyphenols, and tannins, as antivirals, particularly for the treatment of COVID-19. We review current evidence for the use of these phytochemicals against SARS-CoV-2 infection and present their potential targets in the SARS-CoV-2 replication cycle.

Promising Antiviral Activities of Natural Flavonoids against SARS-CoV-2 Targets: Systematic Review

The ongoing COVID-19 pandemic, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) became a globally leading public health concern over the past two years. Despite the development and administration of multiple vaccines, the mutation of newer strains and challenges to universal immunity has shifted the focus to the lack of efficacious drugs for therapeutic intervention for the disease. As with SARS-CoV, MERS-CoV, and other non-respiratory viruses, flavonoids present themselves as a promising therapeutic intervention given their success in silico, in vitro, in vivo, and more recently, in clinical studies. This review focuses on data from in vitro studies analyzing the effects of flavonoids on various key SARS-CoV-2 targets and presents an analysis of the structure-activity relationships for the same. From 27 primary papers, over 69 flavonoids were investigated for their activities against various SARS-CoV-2 targets, ranging from the promising 3C-like protease (3CLpro) to the less explored nucleocapsid (N) protein; the most promising were quercetin and myricetin derivatives, baicalein, baicalin, EGCG, and tannic acid. We further review promising in silico studies featuring activities of flavonoids against SARS-CoV-2 and list ongoing clinical studies involving the therapeutic potential of flavonoid-rich extracts in combination with synthetic drugs or other polyphenols and suggest prospects for the future of flavonoids against SARS-CoV-2.

Recent insights on tea metabolites, their biosynthesis and chemo-preventing effects: A review

Tea manufactured from the cultivated shoots of Camellia sinensis (L.) O. Kuntze is the most commonly consumed nonalcoholic drink around the world. Tea is an agro-based, environmentally sustainable, labor-intensive, job-generating, and export-oriented industry in many countries. Tea includes phenolic compounds, flavonoids, alkaloids, vitamins, enzymes, crude fibers, protein, lipids, and carbohydrates, among other biochemical constituents. This review described the nature of tea metabolites, their biosynthesis and accumulation with response to various factors. The therapeutic application of various metabolites of tea against microbial diseases, cancer, neurological, and other metabolic disorders was also discussed in detail. The seasonal variation, cultivation practices and genetic variability influence tea metabolite synthesis. Tea biochemical constituents, especially polyphenols and its integral part catechin metabolites, are broadly focused on potential applicability for their action against various diseases. In addition to this, tea also contains bioactive flavonoids that possess health-beneficial effects. The catechin fractions, epigallocatechin 3-gallate and epicatechin 3-gallate, are the main components of tea that has strong antioxidant and medicinal properties. The synergistic function of natural tea metabolites with synthetic drugs provides effective protection against various diseases. Furthermore, the application of nanotechnologies enhanced bioavailability, enhancing the therapeutic potential of natural metabolites against numerous diseases and pathogens.

Catechins: Therapeutic Perspectives in COVID-19-Associated Acute Kidney Injury

Data obtained from several intensive care units around the world have provided substantial evidence of the strong association between impairment of the renal function and in-hospital deaths of critically ill COVID-19 patients, especially those with comorbidities and requiring renal replacement therapy (RRT). Acute kidney injury (AKI) is a common renal disorder of various etiologies characterized by a sudden and sustained decrease of renal function. Studies have shown that 5-46% of COVID-19 patients develop AKI during hospital stay, and the mortality of those patients may reach up to 100% depending on various factors, such as organ failures and RRT requirement. Catechins are natural products that have multiple pharmacological activities, including anti-coronavirus and reno-protective activities against kidney injury induced by nephrotoxic agents, obstructive nephropathies and AKI accompanying metabolic and cardiovascular disorders. Therefore, in this review, we discuss the anti-SARS-CoV-2 and reno-protective effects of catechins from a mechanistic perspective. We believe that catechins may serve as promising therapeutics in COVID-19-associated AKI due to their well-recognized anti-SARS-CoV-2, and antioxidant and anti-inflammatory properties that mediate their reno-protective activities.

Anticoronavirus and Immunomodulatory Phenolic Compounds: Opportunities and Pharmacotherapeutic Perspectives

In 2019, COVID-19 emerged as a severe respiratory disease that is caused by the novel coronavirus, Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2). The disease has been associated with high mortality rate, especially in patients with comorbidities such as diabetes, cardiovascular and kidney diseases. This could be attributed to dysregulated immune responses and severe systemic inflammation in COVID-19 patients. The use of effective antiviral drugs against SARS-CoV-2 and modulation of the immune responses could be a potential therapeutic strategy for COVID-19. Studies have shown that natural phenolic compounds have several pharmacological properties, including anticoronavirus and immunomodulatory activities. Therefore, this review discusses the dual action of these natural products from the perspective of applicability at COVID-19.

A computational study of cooperative binding to multiple SARS-CoV-2 proteins

Structure-based drug design targeting the SARS-CoV-2 virus has been greatly facilitated by available virus-related protein structures. However, there is an urgent need for effective, safe small-molecule drugs to control the spread of the virus and variants. While many efforts are devoted to searching for compounds that selectively target individual proteins, we investigated the potential interactions between eight proteins related to SARS-CoV-2 and more than 600 compounds from a traditional Chinese medicine which has proven effective at treating the viral infection. Our original ensemble docking and cooperative docking approaches, followed by a total of over 16-micorsecond molecular simulations, have identified at least 9 compounds that may generally bind to key SARS-CoV-2 proteins. Further, we found evidence that some of these compounds can simultaneously bind to the same target, potentially leading to cooperative inhibition to SARS-CoV-2 proteins like the Spike protein and the RNA-dependent RNA polymerase. These results not only present a useful computational methodology to systematically assess the anti-viral potential of small molecules, but also point out a new avenue to seek cooperative compounds toward cocktail therapeutics to target more SARS-CoV-2-related proteins.

Natural Products, Alone or in Combination with FDA-Approved Drugs, to Treat COVID-19 and Lung Cancer

As a public health emergency of international concern, the highly contagious coronavirus disease 2019 (COVID-19) pandemic has been identified as a severe threat to the lives of billions of individuals. Lung cancer, a malignant tumor with the highest mortality rate, has brought significant challenges to both human health and economic development. Natural products may play a pivotal role in treating lung diseases. We reviewed published studies relating to natural products, used alone or in combination with US Food and Drug Administration-approved drugs, active against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and lung cancer from 1 January 2020 to 31 May 2021. A wide range of natural products can be considered promising anti-COVID-19 or anti-lung cancer agents have gained widespread attention, including natural products as monotherapy for the treatment of SARS-CoV-2 (ginkgolic acid, shiraiachrome A, resveratrol, and baicalein) or lung cancer (daurisoline, graveospene A, deguelin, and erianin) or in combination with FDA-approved anti-SARS-CoV-2 agents (cepharanthine plus nelfinavir, linoleic acid plus remdesivir) and anti-lung cancer agents (curcumin and cisplatin, celastrol and gefitinib). Natural products have demonstrated potential value and with the assistance of nanotechnology, combination drug therapies, and the codrug strategy, this "natural remedy" could serve as a starting point for further drug development in treating these lung diseases.

An efficient chemical screening method for structure-based inhibitors to nucleic acid enzymes targeting the DNA repair-replication interface and SARS CoV-2

We present a Chemistry and Structure Screen Integrated Efficiently (CASSIE) approach (named for Greek prophet Cassandra) to design inhibitors for cancer biology and pathogenesis. CASSIE provides an effective path to target master keys to control the repair-replication interface for cancer cells and SARS CoV-2 pathogenesis as exemplified here by specific targeting of Poly(ADP-ribose) glycohydrolase (PARG) and ADP-ribose glycohydrolase ARH3 macrodomains plus SARS CoV-2 nonstructural protein 3 (Nsp3) Macrodomain 1 (Mac1) and Nsp15 nuclease. As opposed to the classical massive effort employing libraries with large numbers of compounds against single proteins, we make inhibitor design for multiple targets efficient. Our compact, chemically diverse, 5000 compound Goldilocks (GL) library has an intermediate number of compounds sized between fragments and drugs with predicted favorable ADME (absorption, distribution, metabolism, and excretion) and toxicological profiles. Amalgamating our core GL library with an approved drug (AD) library, we employ a combined GLAD library virtual screen, enabling an effective and efficient design cycle of ranked computer docking, top hit biophysical and cell validations, and defined bound structures using human proteins or their avatars. As new drug design is increasingly pathway directed as well as molecular and mechanism based, our CASSIE approach facilitates testing multiple related targets by efficiently turning a set of interacting drug discovery problems into a tractable medicinal chemistry engineering problem of optimizing affinity and ADME properties based upon early co-crystal structures. Optimization efforts are made efficient by a computationally-focused iterative chemistry and structure screen. Thus, we herein describe and apply CASSIE to define prototypic, specific inhibitors for PARG vs distinct inhibitors for the related macrodomains of ARH3 and SARS CoV-2 Nsp3 plus the SARS CoV-2 Nsp15 RNA nuclease.