Flavonols and dihydroflavonols inhibit the main protease activity of SARS-CoV-2 and the replication of human coronavirus 229E

Dual Functionality of Papaya Leaf Extracts: Anti-Coronavirus Activity and Anti-Inflammation Mechanism

Papaya leaves have been used as food and traditional herbs for the treatment of cancer, diabetes, asthma, and virus infections, but the active principle has not been understood. We hypothesized that the anti-inflammatory activity could be the predominant underlying principle. To test this, we extracted papaya leaf juice with different organic solvents and found that the ethyl acetate (EA) fraction showed the most outstanding anti-inflammatory activity by suppressing the production of nitric oxide (NO, IC50 = 24.94 ± 2.4 μg/mL) and the expression of pro-inflammatory enzymes, such as inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX-2), and cytokines including interleukins (IL-1β and IL-6), and a tumor necrosis factor (TNF-α) in lipopolysaccharide (LPS)-induced RAW 264.7 cells. Transcriptomic analysis and Western blot results revealed its anti-inflammatory mechanisms were through the MAPK signaling pathway by inhibiting the phosphorylation of ERK1/2, JNKs, and p38 and the prevention of the cell surface expression of TLR4. Furthermore, we discovered that the EA fraction could inhibit the replication of alpha-coronavirus (HCoV-229E) and beta-coronavirus (HCoV-OC43 and SARS-CoV-2) and might be able to prevent cytokine storms caused by the coronavirus infection. From HPLC-QTOF-MS data, we found that the predominant phytochemicals that existed in the EA fraction were quercetin and kaempferol glycosides and carpaine. Counter-intuitively, further fractionation resulted in a loss of activity, suggesting that the synergistic effect of different components in the EA fraction contribute to the overall potent activity. Taken together, our results provide preliminary evidence for papaya leaf as a potential anti-inflammatory and anti-coronavirus agent, warranting further study for its use for human health promotion.

In vitro analysis of quercetin-like compounds from mistletoe Dendrophthoe pentandra (L.) Miq as a potential antiviral agent for Newcastle disease

Background

Recent evidence suggests that some flavonoid compounds obtained from crude methanol extract of mistletoe leaves ( Dendrophthoe pentandra L. Miq), also known as Benalu Duku (BD), have antimicrobial effects. Thus, the plant has the potential to eliminate viruses that may cause outbreaks in chicken farms. This study aimed to prove the in vitro ability of flavonoid compounds, namely quercetin-like compounds (QLCs), to eliminate field viruses, specifically the Newcastle disease virus (NDV).

Methods

This research was performed in two stages. An in vitro test was used with a post-test of the control groups designed at a significance of 0.05. BD leaves (5 kg) were extracted using a maceration method with methanol and then separated into hexane, chloroform, ethyl acetate, and methanol fractions. The final extracted products were separated using semi-preparative high-performance liquid chromatography (HPLC) to obtain QLCs. The QLCs were identified and compared with quercetin using HPLC, proton and carbon nuclear magnetic resonance spectrometry, Fourier transform infrared spectrophotometry and ultra-performance liquid chromatography-mass spectrometry. The activity of QLCs was tested in vitro against the NDV at a virulence titter of 10 -5 Tissue Culture Infectious Dose 50% (TCID50) in chicken kidney cell culture.

Results

Solutions of 0.05% (w/v) QLCs were discovered to have antiviral activity against NDVs, with an average cytopathogenic effect antigenicity at a 10 -5 dilution (p<0.05).

Conclusions

QLCs from flavonoids from the leaves of BD have in vitro antiviral bioactivity against NDV at a virulence titter of 10-5 Tissue Culture Infectious Dose 50% (TCID50) in chicken kidney cell culture. QLCs may have the potential to be developed as medicinal compounds for the treatment of other human or animal viral infections.

A BSL-2 compliant mouse model of SARS-CoV-2 infection for efficient and convenient antiviral evaluation

Animal models of authentic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection require operation in biosafety level 3 (BSL-3) containment. In the present study, we established a mouse model employing a single-cycle infectious virus replicon particle (VRP) system of SARS-CoV-2 that can be safely handled in BSL-2 laboratories. The VRP [ΔS-VRP(G)-Luc] contains a SARS-CoV-2 genome in which the spike gene was replaced by a firefly luciferase (Fluc) reporter gene (Rep-Luci), and incorporates the vesicular stomatitis virus glycoprotein on the surface. Intranasal inoculation of ΔS-VRP(G)-Luc can successfully transduce the Rep-Luci genome into mouse lungs, initiating self-replication of Rep-Luci and, accordingly, inducing acute lung injury mimicking the authentic SARS-CoV-2 pathology. In addition, the reporter Fluc expression can be monitored using a bioluminescence imaging approach, allowing a rapid and convenient determination of viral replication in ΔS-VRP(G)-Luc-infected mouse lungs. Upon treatment with an approved anti-SARS-CoV-2 drug, VV116, the viral replication in infected mouse lungs was significantly reduced, suggesting that the animal model is feasible for antiviral evaluation. In summary, we have developed a BSL-2-compliant mouse model of SARS-CoV-2 infection, providing an advanced approach to study aspects of the viral pathogenesis, viral-host interactions, as well as the efficacy of antiviral therapeutics in the future.IMPORTANCESevere acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is highly contagious and pathogenic in humans; thus, research on authentic SARS-CoV-2 has been restricted to biosafety level 3 (BSL-3) laboratories. However, due to the scarcity of BSL-3 facilities and trained personnel, the participation of a broad scientific community in SARS-CoV-2 research had been greatly limited, hindering the advancement of our understanding on the basic virology as well as the urgently necessitated drug development. Previously, our colleagues Jin et al. had generated a SARS-CoV-2 replicon by replacing the essential spike gene in the viral genome with a Fluc reporter (Rep-Luci), which can be safely operated under BSL-2 conditions. By incorporating the Rep-Luci into viral replicon particles carrying vesicular stomatitis virus glycoprotein on their surface, and via intranasal inoculation, we successfully transduced the Rep-Luci into mouse lungs, developing a mouse model mimicking SARS-CoV-2 infection. Our model can serve as a useful platform for SARS-CoV-2 pathological studies and antiviral evaluation under BSL2 containment.

Insights into the stereoisomerism of dihydroquercetin: analytical and pharmacological aspects

Dihydroquercetin (DHQ) is a representative of flavonoids that is available on the market as a food supplement and registered as an active pharmaceutical ingredient. The structure of this compound is characterized by the presence of two chiral centers in positions 2 and 3 of the pyranone ring. Current regulatory documentation on DHQ lacks quantitative analysis of the stereoisomers of this flavanonol. This poses potential risks for consumers of DHQ-based dietary supplements and developers of new drugs. This review was conducted to systematize data on the pharmacology of DHQ stereoisomers and the possible methods of controlling them in promising chiral drugs. We found that relying on literature data of polarimetry for the identification of DHQ stereoisomers is currently impossible due to these heterogeneities. NMR spectroscopy allows to distinguishing between trans- and cis-DHQ using chemical shifts values. Only HPLC is currently characterized by sufficient enantioselectivity. Regarding pharmacology, the most active stereoisomer of DHQ should be identified, if the substituents in chiral centers both take part in binding with the biological target. The significant impact of stereochemical structure on the pharmacokinetics of DHQ isomers was reported. The question about these toxicity of these compounds remains open. The results of the conducted review of scientific literature indicate the necessity of revising the pharmacology of DHQ taking into account its stereoisomerism.

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.

Exploring the Antiviral Potential of Esters of Cinnamic Acids with Quercetin

Severe acute respiratory syndrome-related Coronavirus 2 (SARS-CoV-2) has infected more than 762 million people to date and has caused approximately 7 million deaths all around the world, involving more than 187 countries. Although currently available vaccines show high efficacy in preventing severe respiratory complications in infected patients, the high number of mutations in the S proteins of the current variants is responsible for the high level of immune evasion and transmissibility of the virus and the reduced effectiveness of acquired immunity. In this scenario, the development of safe and effective drugs of synthetic or natural origin to suppress viral replication and treat acute forms of COVID-19 remains a valid therapeutic challenge. Given the successful history of flavonoids-based drug discovery, we developed esters of substituted cinnamic acids with quercetin to evaluate their in vitro activity against a broad spectrum of Coronaviruses. Interestingly, two derivatives, the 3,4-methylenedioxy 6 and the ester of acid 7, have proved to be effective in reducing OC43-induced cytopathogenicity, showing interesting EC50s profiles. The ester of synaptic acid 7 in particular, which is not endowed with relevant cytotoxicity under any of the tested conditions, turned out to be active against OC43 and SARS-CoV-2, showing a promising EC50. Therefore, said compound was selected as the lead object of further analysis. When tested in a yield reduction, assay 7 produced a significant dose-dependent reduction in viral titer. However, the compound was not virucidal, as exposure to high concentrations of it did not affect viral infectivity, nor did it affect hCoV-OC43 penetration into pre-treated host cells. Additional studies on the action mechanism have suggested that our derivative may inhibit viral endocytosis by reducing viral attachment to host cells.

Metabolic profiling of milk thistle different organs using UPLC-TQD-MS/MS coupled to multivariate analysis in relation to their selective antiviral potential

INTRODUCTION

Silybum marianum commonly known as milk thistle is one of the most imperative medicinal plants due to its remarkable pharmacological activities. Lately, the antiviral activities of S. marianum extract have been studied and it showed effectiveness against many viruses.

OBJECTIVE

Although most previous studies were concerned mainly with silymarin content of the fruit, the present study provides comprehensive comparative evaluation of S. marianum different organs' chemical profiles using UPLC-MS/MS coupled to chemometrics to unravel potentially selective antiviral compounds against human coronavirus (HCoV-229E).

METHODOLOGY

UPLC-ESI-TQD-MS/MS analysis was utilized to establish metabolic fingerprints for S. marianum organs namely fruits, roots, stems and seeds. Multivariate analysis, using OPLS-DA and HCA-heat map was applied to explore the main discriminatory phytoconstituents between organs. Selective virucidal activity of organs extracts against coronavirus (HCoV-229E) was evaluated for the first time using cytopathic effect (CPE) inhibition assay. Correlation coefficient analysis was implemented for detection of potential constituents having virucidal activity.

RESULTS

UPLC-MS/MS analysis resulted in 87 identified metabolites belonging to different classes. OPLS-DA revealed in-between class discrimination between milk thistle organs proving their significantly different metabolic profiles. The results of CPE assay showed that all tested organ samples exhibited dose dependent inhibitory activity in nanomolar range. Correlation analysis disclosed that caffeic acid-O-hexoside, gadoleic and linolenic acids were the most potentially selective antiviral phytoconstituents.

CONCLUSION

This study valorizes the importance of different S. marianum organs as wealthy sources of selective and effective antiviral candidates. This approach can be extended to unravel potentially active constituents from complex plant matrices.

Quercetin inhibits SARS-CoV-2 infection and prevents syncytium formation by cells co-expressing the viral spike protein and human ACE2

BACKGROUND

Several in silico studies have determined that quercetin, a plant flavonol, could bind with strong affinity and low free energy to SARS-CoV-2 proteins involved in viral entry and replication, suggesting it could block infection of human cells by the virus. In the present study, we examined the ex vivo ability of quercetin to inhibit of SARS-CoV-2 replication and explored the mechanisms of this inhibition.

METHODS

Green monkey kidney Vero E6 cells and in human colon carcinoma Caco-2 cells were infected with SARS-CoV-2 and incubated in presence of quercetin; the amount of replicated viral RNA was measured in spent media by RT-qPCR. Since the formation of syncytia is a mechanism of SARS-CoV-2 propagation, a syncytialization model was set up using human embryonic kidney HEK293 co-expressing SARS-CoV-2 Spike (S) protein and human angiotensin converting enzyme 2 (ACE2), [HEK293(S + ACE2) cells], to assess the effect of quercetin on this cytopathic event by microscopic imaging and protein immunoblotting.

RESULTS

Quercetin inhibited SARS-CoV-2 replication in Vero E6 cells and Caco-2 cells in a concentration-dependent manner with a half inhibitory concentration (IC50) of 166.6 and 145.2 µM, respectively. It also inhibited syncytialization of HEK293(S + ACE2) cells with an IC50 of 156.7 µM. Spike and ACE2 co-expression was associated with decreased expression, increased proteolytic processing of the S protein, and diminished production of the fusogenic S2' fragment of S. Furin, a proposed protease for this processing, was inhibited by quercetin in vitro with an IC50 of 116 µM.

CONCLUSION

These findings suggest that at low 3-digit micromolar concentrations of quercetin could impair SARS-CoV-2 infection of human cells partly by blocking the fusion process that promotes its propagation.

Exploring Scoring Function Space: Developing Computational Models for Drug Discovery

BACKGROUND

The idea of scoring function space established a systems-level approach to address the development of models to predict the affinity of drug molecules by those interested in drug discovery.

OBJECTIVE

Our goal here is to review the concept of scoring function space and how to explore it to develop machine learning models to address protein-ligand binding affinity.

METHODS

We searched the articles available in PubMed related to the scoring function space. We also utilized crystallographic structures found in the protein data bank (PDB) to represent the protein space.

RESULTS

The application of systems-level approaches to address receptor-drug interactions allows us to have a holistic view of the process of drug discovery. The scoring function space adds flexibility to the process since it makes it possible to see drug discovery as a relationship involving mathematical spaces.

CONCLUSION

The application of the concept of scoring function space has provided us with an integrated view of drug discovery methods. This concept is useful during drug discovery, where we see the process as a computational search of the scoring function space to find an adequate model to predict receptor-drug binding affinity.

Identification and biosynthesis of plant papanridins, a group of novel oligomeric flavonoids

The discovery of novel flavonoids and elucidation of their biosynthesis are fundamental to understanding their roles in plants and their benefits for human and animal health. Here, we report a new pathway for polymerization of a group of novel oligomeric flavonoids in plants. We engineered red cells for discovering genes of interest involved in the flavonoid pathway and identified a gene encoding a novel flavanol polymerase (FP) localized in the central vacuole. FP catalyzes the polymerization of flavanols, such as epicatechin and catechin, to produce yellowish dimers or oligomers. Structural elucidation shows that these compounds feature a novel oligomeric flaven-flavan (FF) skeleton linked by interflavan-flaven and interflaven bonds, distinguishing them from proanthocyanidins and dehydrodicatechins. Detailed chemical and physical characterizations further confirmed the novel FFs as flavonoids. Mechanistic investigations demonstrated that FP polymerizes flavan-3-ols and flav-2-en-3-ol carbocation, forming dimeric or oligomeric flaven-4→8-flavans, which we term "papanridins." Data from transgenic experiments, mutant analysis, metabolic profiling, and phylogenetic analyses show that the biosynthesis of papanridins is prevalent in cacao, grape, blueberry, corn, rice, Arabidopsis, and other species in the plant kingdom. In summary, our study discoveries a group of novel oligomeric flavonoids, namely papanridins, and reveals that a novel FP-mediated polymerization mechanism for the biosynthesis of papanridins in plants.

A potential Chinese medicine monomer against influenza A virus and influenza B virus: isoquercitrin

BACKGROUND

Influenza viruses, especially Influenza A virus and Influenza B virus, are respiratory pathogens and can cause seasonal epidemics and pandemics. Severe influenza viruses infection induces strong host-defense response and excessive inflammatory response, resulting in acute lung damage, multiple organ failure and high mortality. Isoquercitrin is a Chinese medicine monomer, which was reported to have multiple biological activities, including antiviral activity against HSV, IAV, SARS-CoV-2 and so on. Aims of this study were to assess the in vitro anti-IAV and anti-IBV activity, evaluate the in vivo protective efficacy against lethal infection of the influenza virus and searched for the more optimal method of drug administration of isoquercitrin.

METHODS

In vitro infection model (MDCK and A549 cells) and mouse lethal infection model of Influenza A virus and Influenza B virus were used to evaluate the antiviral activity of isoquercitrin.

RESULTS

Isoquercitrin could significantly suppress the replication in vitro and in vivo and reduced the mortality of mouse lethal infection models. Compared with virus infection group, isoquercitrin mitigated lung and multiple organ damage. Moreover, isoquercitrin blocked hyperproduction of cytokines induced by virus infection via inactivating NF-κB signaling. Among these routes of isoquercitrin administration, intramuscular injection is a better drug delivery method.

CONCLUSION

Isoquercitrin is a potential Chinese medicine monomer Against Influenza A Virus and Influenza B Virus infection.

Jinhua Qinggan Granule UHPLC-Q-extractive-Orbitrap-MS assay: Putative identification of 45 potential anti-Covid-19 constituents, confidential addition, and pharmacopoeia quality-markers recommendation

The study combined UHPLC-Q-Orbitrap-MS analysis with authentic standards, to create a novel strategy for isomers recognition and putative identification. Through the strategy, anti-Covid-19 Jinhua Qinggan Granule was found to comprise 28 isomers and 45 potential anti-Covid-19 constituents. The detection of three constituents (Danshensu, cryptotanshin, and tanshinone IIA) suggests Danshen as confidential additive. Based on this, 6 constituents are recommended as quality-marker candidates, including chlorogenic acid, acteoside, peimisine, baicalein, licoricesaponin H2, and tanshinone IIA. Obviously, the study can not only help the public to really understand the Granule's formula and chemistry, but also facilitate its Pharmacopoeia collection in future.

In vitro and in vivo effects of Pelargonium sidoides DC. root extract EPs® 7630 and selected constituents against SARS-CoV-2 B.1, Delta AY.4/AY.117 and Omicron BA.2

The occurrence of immune-evasive SARS-CoV-2 strains emphasizes the importance to search for broad-acting antiviral compounds. Our previous in vitro study showed that Pelargonium sidoides DC. root extract EPs® 7630 has combined antiviral and immunomodulatory properties in SARS-CoV-2-infected human lung cells. Here we assessed in vivo effects of EPs® 7630 in SARS-CoV-2-infected hamsters, and investigated properties of EPs® 7630 and its functionally relevant constituents in context of phenotypically distinct SARS-CoV-2 variants. We show that EPs® 7630 reduced viral load early in the course of infection and displayed significant immunomodulatory properties positively modulating disease progression in hamsters. In addition, we find that EPs® 7630 differentially inhibits SARS-CoV-2 variants in nasal and bronchial human airway epithelial cells. Antiviral effects were more pronounced against Omicron BA.2 compared to B.1 and Delta, the latter two preferring TMPRSS2-mediated fusion with the plasma membrane for cell entry instead of receptor-mediated low pH-dependent endocytosis. By using SARS-CoV-2 Spike VSV-based pseudo particles (VSVpp), we confirm higher EPs® 7630 activity against Omicron Spike-VSVpp, which seems independent of the serine protease TMPRSS2, suggesting that EPs® 7630 targets endosomal entry. We identify at least two molecular constituents of EPs® 7630, i.e., (-)-epigallocatechin and taxifolin with antiviral effects on SARS-CoV-2 replication and cell entry. In summary, our study shows that EPs® 7630 ameliorates disease outcome in SARS-CoV-2-infected hamsters and has enhanced activity against Omicron, apparently by limiting late endosomal SARS-CoV-2 entry.

Repositioned Natural Compounds and Nanoformulations: A Promising Combination to Counteract Cell Damage and Inflammation in Respiratory Viral Infections

Respiratory viral diseases are among the most important causes of disability, morbidity, and death worldwide. Due to the limited efficacy or side effects of many current therapies and the increase in antiviral-resistant viral strains, the need to find new compounds to counteract these infections is growing. Since the development of new drugs is a time-consuming and expensive process, numerous studies have focused on the reuse of commercially available compounds, such as natural molecules with therapeutic properties. This phenomenon is generally called drug repurposing or repositioning and represents a valid emerging strategy in the drug discovery field. Unfortunately, the use of natural compounds in therapy has some limitations, due to their poor kinetic performance and consequently reduced therapeutic effect. The advent of nanotechnology in biomedicine has allowed this limitation to be overcome, showing that natural compounds in nanoform may represent a promising strategy against respiratory viral infections. In this narrative review, the beneficial effects of some promising natural molecules, curcumin, resveratrol, quercetin, and vitamin C, which have been already studied both in native form and in nanoform, against respiratory viral infections are presented and discussed. The review focuses on the ability of these natural compounds, analyzed in in vitro and in vivo studies, to counteract inflammation and cellular damage induced by viral infection and provide scientific evidence of the benefits of nanoformulations in increasing the therapeutic potential of these molecules.

Cytotoxicity and Biomineralization Potential of Flavonoids Incorporated into PNVCL Hydrogels

This study aimed to evaluate the effects of flavonoids incorporated into poly(N-vinylcaprolactam) (PNVCL) hydrogel on cell viability and mineralization markers of odontoblast-like cells. MDPC-23 cells were exposed to ampelopsin (AMP), isoquercitrin (ISO), rutin (RUT) and control calcium hydroxide (CH) for evaluation of cell viability, total protein (TP) production, alkaline phosphatase (ALP) activity and mineralized nodule deposition by colorimetric assays. Based on an initial screening, AMP and CH were loaded into PNVCL hydrogels and had their cytotoxicity and effect on mineralization markers determined. Cell viability was above 70% when MDPC-23 cells were treated with AMP, ISO and RUT. AMP showed the highest ALP activity and mineralized nodule deposition. Extracts of PNVCL+AMP and PNVCL+CH in culture medium (at the dilutions of 1/16 and 1/32) did not affect cell viability and stimulated ALP activity and mineralized nodules’ deposition, which were statistically higher than the control in osteogenic medium. In conclusion, AMP and AMP-loaded PNVCL hydrogels were cytocompatible and able to induce bio-mineralization markers in odontoblast-cells.

Natural Flavonoid Derivatives Have Pan-Coronavirus Antiviral Activity

The SARS-CoV-2 protease (3CLpro) is one of the key targets for the development of efficacious drugs for COVID-19 treatment due to its essential role in the life cycle of the virus and exhibits high conservation among coronaviruses. Recent studies have shown that flavonoids, which are small natural molecules, have antiviral activity against coronaviruses (CoVs), including SARS-CoV-2. In this study, we identified the docking sites and binding affinity of several natural compounds, similar to flavonoids, and investigated their inhibitory activity towards 3CLpro enzymatic activity. The selected compounds were then tested in vitro for their cytotoxicity, for antiviral activity against SARS-CoV-2, and the replication of other coronaviruses in different cell lines. Our results showed that Baicalein (100 μg/mL) exerted strong 3CLpro activity inhibition (>90%), whereas Hispidulin and Morin displayed partial inhibition. Moreover, Baicalein, up to 25 μg/mL, hindered >50% of SARS-CoV-2 replication in Vero E6 cultures. Lastly, Baicalein displayed antiviral activity against alphacoronavirus (Feline-CoV) and betacoronavirus (Bovine-CoV and HCoV-OC43) in the cell lines. Our study confirmed the antiviral activity of Baicalein against SARS-CoV-2 and demonstrated clear evidence of its pan-coronaviral activity.

The Main Protease of SARS-CoV-2 as a Target for Phytochemicals against Coronavirus

In late December 2019, the first cases of COVID-19 emerged as an outbreak in Wuhan, China that later spread vastly around the world, evolving into a pandemic and one of the worst global health crises in modern history. The causative agent was identified as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Although several vaccines were authorized for emergency use, constantly emerging new viral mutants and limited treatment options for COVID-19 drastically highlighted the need for developing an efficient treatment for this disease. One of the most important viral components to target for this purpose is the main protease of the coronavirus (Mpro). This enzyme is an excellent target for a potential drug, as it is essential for viral replication and has no closely related homologues in humans, making its inhibitors unlikely to be toxic. Our review describes a variety of approaches that could be applied in search of potential inhibitors among plant-derived compounds, including virtual in silico screening (a data-driven approach), which could be structure-based or fragment-guided, the classical approach of high-throughput screening, and antiviral activity cell-based assays. We will focus on several classes of compounds reported to be potential inhibitors of Mpro, including phenols and polyphenols, alkaloids, and terpenoids.

Genetic Diversity for Quercetin, Myricetin, Cyanidin, and Delphinidin Concentrations in 38 Blackeye Pea (Vigna unguiculata L. Walp.) Genotypes for Potential Use as a Functional Health Vegetable

Blackeye peas (Vigna unguiculata L. Walp.) are mainly used as a vegetable throughout the world, however they may contain significant concentrations of quercetin, myricetin, cyanidin, and delphinidin for potential use as a functional vegetable. Thirty-eight blackeye pea genotypes were selected from the core collection in the USDA, ARS, Plant Genetic Resources Conservation Unit's cold storage at 4 °C during 2016. Information regarding concentrations of quercetin, myricetin, cyanidin, delphindin, and correlations among these as well as additional seed traits including seed coat color, seed pattern color, seed pattern, seed texture, and years in storage would add value to the blackeye pea genotypes for use as a functional vegetable. Using high performance liquid chromatography (HPLC), the red seeded accession originating from Mozambique, PI 367927 produced the highest quercetin (469.53 µg/g) and myricetin (212.23 µg/g) concentrations. The black seeded genotype, PI 353236, originating from India, produced the highest cyanidin (1,388.82 µg/g) concentration. However, PI 353236 and the brown seeded genotype, PI 353352 from India produced the highest concentrations of delphinidin (1,343.27 and 1,353.94 µg/g), respectively. Several correlations were observed and interestingly only delphinidin showed a significant negative correlation (r = -0.293*) with years in cold storage indicating that delphinidin declined in the seeds stored the longest (from 4-45 years) at 4 °C. Principal component analysis (PCA) explained how the flavonols, anthocyanidins, and the additional seed traits contributed to the variation of the blackeye pea genotypes. The cluster analysis showed six clusters representing low to high phytochemical concentrations. The genetic parameters including σ2g, σ2p, GCV, PCV, h2h, and GG indicate that improvement in these phytochemical traits is possible through selection. The genotypic and phenotypic correlations showed that improving one phytochemical significantly improved the other except for cyanidin with delphinidin. These results can be used by scientists to develop blackeye pea cultivars with high flavonol and anthocyanidin concentrations.

The emerging role of miRNAs in the pathogenesis of COVID-19: Protective effects of nutraceutical polyphenolic compounds against SARS-CoV-2 infection

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection can cause immunosuppression and cytokine storm, leading to lung damage and death. The clinical efficacy of anti-SARS-CoV-2 drugs in preventing viral entry into host cells and suppressing viral replication remains inadequate. MicroRNAs (miRNAs) are crucial to the immune response to and pathogenesis of coronaviruses, such as SARS-CoV-2. However, the specific roles of miRNAs in the life cycle of SARS-CoV-2 remain unclear. miRNAs can participate in SARS-CoV-2 infection and pathogenesis through at least four possible mechanisms: 1. host cell miRNA expression interfering with SARS-CoV-2 cell entry, 2. SARS-CoV-2-derived RNA transcripts acting as competitive endogenous RNAs (ceRNAs) that may attenuate host cell miRNA expression, 3. host cell miRNA expression modulating SARS-CoV-2 replication, and 4. SARS-CoV-2-encoded miRNAs silencing the expression of host protein-coding genes. SARS-CoV-2-related miRNAs may be used as diagnostic or prognostic biomarkers for predicting outcomes among patients with SARS-CoV-2 infection. Furthermore, accumulating evidence suggests that dietary polyphenolic compounds may protect against SARS-CoV-2 infection by modulating host cell miRNA expression. These findings have major implications for the future diagnosis and treatment of COVID-19.