Antiviral and Possible Prophylactic Significance of Myricetin for COVID-19*

Myricetin (3,5,7,3 ',4 ',5 ' -hexahydroxyflavone), a common dietary flavonoid, has been reported for its roles in improving health due to various pharmacological activities, such as antioxidant, antimicrobial, anti-inflammatory, analgesic, antitumor, hepatoprotective, and antidiabetic. Myricetin has also been shown to have a broad spectrum of antiviral effects against a variety of viruses including Rauscher murine leukemia virus (RLV), human immunodeficiency virus (HIV), Coxsackie virus, Ebolavirus, Zika virus, herpes simplex virus (HSV-1 and HSV-2), dengue virus, murine norovirus, infectious bronchitis virus, African swine fever virus, and both DNA polymerase alpha and DNA polymerase I. Intensive research suggests that the remarkable potential of myricetin in promoting either the prevention or overcoming of SARS-CoV-2 infection is due to the wide range of its effects on SARS-COV-2 proteases, including modulation of inflammatory processes and immune responses. In silico and in vitro studies demonstrated that myricetin can effectively interfere at various stages of viral infection, including the coronavirus entry and replication cycle due to its high-binding affinity with S-protein, ACE2 receptor, PLpro, Mpro, RdRp, exonuclease, and endoribonuclease. Based on the findings discussed in this review, myricetin, its glycosides, and dihydromyricetin, can be considered as multi-targeted agents having beneficial effects in combatting COVID-19.

Rhamnetin is a better inhibitor of SARS-CoV-2 2'-O-methyltransferase than Dolutegravir: a computational prediction

Background: The 2'-O-methyltransferase is responsible for the capping of SARS-CoV-2 mRNA and consequently the evasion of the host's immune system. This study aims at identifying prospective natural inhibitors of the active site of SARS-CoV-2 2'O-methyltransferase (2'-OMT) through an in silico approach. Materials and Method: The target was docked against a library of natural compounds obtained from edible African plants using PyRx - virtual screening software. The antiviral agent, Dolutegravir which has a binding affinity score of -8.5 kcal mol-1 with the SARS-CoV-2 2'-OMT was used as a standard. Compounds were screened for bioavailability through the SWISSADME web server using their molecular descriptors. Screenings for pharmacokinetic properties and bioactivity were performed with PKCSM and Molinspiration web servers respectively. The PLIP and Fpocket webservers were used for the binding site analyses. The Galaxy webserver was used for simulating the time-resolved motions of the apo and holo forms of the target while the MDWeb web server was used for the analyses of the trajectory data.

Investigation on chemical composition, antioxidant activity and SARS-CoV-2 nucleocapsid protein of endemic Ferula longipedunculata pesmen

The essential and fatty oils were investigated and a quantitative analysis of the root, green and stem parts of F. Longipedunculata was performed by GC-MS and HPLC-TOF/MS and their antioxidant (DPPH method) activities and potential binding of phytochemicals against SARS-CoV-2 nucleocapsid were determined using Molegro Virtual Docker software. In the root part of the plant, the prominent components of oil were beta-phellandrene (53.46%), ocimene (6.79%), 4-terpineol (5.94%) and santalol (5.03%). According to the quantitative results, vanillic acid (141.35 mg/kg), ferulic acid (126.19 mg/kg) and 4-hydroxybenzoic acid (119.92 mg/kg) were found in the roots;quercetin-3-beta-O-glycoside (1737.70 mg/kg), quercetin (531.35 mg/kg) and ferulic acid (246.22 mg/kg) were found in the in the green part;and fumaric acid (2100.21 mg/kg), quercetin-3-beta-O-glycoside (163.24 mg/kg), vanillic acid (57.59 mg/kg) were detected in the stem part. The antioxidant activity of all parts of the plant was higher than the control with BHT. Silibinin, rutin, and neohesperidin exhibited a stronger affinity than nucleotides. In the silico analysis, many of the phytochemicals were attached with strong hydrogen-bonds and electrostatic effects to the amino acids to which nucleotides are bound. The results indicated that the plant showed antioxidant effects and can be effective against SARS-CoV-2 thanks to the different phytochemical compounds it contains.

Molecular docking studies of Apigenin, Kaempferol, and Quercetin as potential target against spike receptor protein of SARS CoV

COVID-19 has been categorized as a pandemic in early 2020 and is known to cause by Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV2). Numerous investigators and people in the scientific community are trying to find a superlative way to avert and cure the ailment by using phytochemicals. Abundant studies have revealed that flavonoids can be very operative in averting virus-mediated infection. The purpose of this study was to accomplish molecular docking studies among plant-derived flavonoids (Apigenin, Kaempferol, and Quercetin) and spike receptor (PDB ID: 2AJF) protein of coronavirus. Pyrx virtual screening tool and biovia discovery studio visualizer were utilized in the current molecular docking investigations. Outcomes of docking studies exposed that selected phytochemicals have interacted with targeted spike receptor protein with binding energies in the range of -6.3 to -7.3 kcal. In conclusion among the various selected ligands, quercetin may be a better inhibitor for the deactivation of SARS-Coronavirus.

Molecular docking, molecular dynamic and drug-likeness studies of natural flavonoids as inhibitors for SARS-CoV-2 main protease (Mpro). (COVID-19 dedicated issue.)

The emergence of the global pandemic COVID-19 lead to a huge demand for the therapeutic agent to combat the disease. Since the FDA approval of some of HIV-1 main protease inhibitors such as ritonavir lopinavir to treat COVID-19, the investigation of anti-HIV inhibitor to inhibit SARS-CoV-2 main protease (Mpro) is getting considerably much attention. This study evaluates the potency of sixteen selected natural flavonoids which were previously reported active to block HIV-1 protease as potential inhibitors of SARS-CoV-2 Mpro. The molecular docking and dynamic study were completed to know the binding affinity and stability of the protein-ligand complex via docking study along with molecular dynamic simulations. Moreover, drug-likeness was also evaluated through via ADMET evaluation. This study revealed robinin (6), a flavonol molecule with linked to galactose-rhamnose at C3 and rhamnose molecule at C7, exhibited the highest binding affinity (-9 kcal/mol) among others. The amino acids that interacted with robinin were Asn142;Gly143;Arg188;Thr190. The binding affinity of robinin surpassed the binding affinity of ritonavir (-7.7 kcal/mol) and lopinavir (-8.2 kcal/mol). The replacement of the hydroxyl group from the flavonoid skeleton at C-7, C-4' was proposed to affect the binding affinity. The free hydroxyl group particularly in A ring and the position of the hydroxyl group were important to improve the binding affinity. The molecular dynamic simulation showed the stability of Mpro-robinin during the simulation period. The ADME evaluation referring to Lipinski's rule of 5 revealed that the flavonoids (2,5,6,9,10,13,14,15) show low oral bioavailability and absorption. Robinin exhibited a good drug-likeness score (value:1) with an unconcerned level of acute toxicity. From this study, it was concluded that robinin showed the most potent natural flavonoids studied to inhibit SASR-CoV-2 Mpro by both docking study and ADME/tox properties evaluation.

Effect of Extraction Methodology on the Phytochemical Composition for Camelia sinensis “Powdered Tea Extracts” from Different Provenances

(1) Background: beverages based on extracts from Camellia sinensis are popular worldwide. Due to an increasing number of processed teas on the market, there is a need to develop unified classification standards based on chemical analysis. Meanwhile, phytochemical characterizations are mainly performed on tea samples from China (~80%). Hence, data on teas of other provenances is recommended. (2) Methods: in the present investigation, we characterized lyophilised extracts obtained by infusion, maceration and methanolic extraction derived from tea samples from China, Japan, Sri Lanka and Portugal by phytochemistry (catechins, oxyaromatic acids, flavonols, alkaloids and theanine). The real benefits of drinking the tea were analysed based on the bioavailability of the determined phytochemicals. (3) Results: the infusions revealed the highest total phenolic contents (TPC) amounts, while methanolic extracts yielded the lowest. The correlation matrix indicated that the levels of phenolic compounds were similar in the infusions and methanolic samples, while extractions made by maceration were significantly different. The differences could be partially explained by the different amounts of (-)-epigallocatechin gallate (EGCG), (-)-epicatechin gallate (ECG) and gallic acids (GA). The catechin percentages were significantly lower in the macerations, especially the quantity of EGCG decreases by 4- to 5-fold after this process. (4) Conclusions: the results highlight the importance of the processing methodology to obtain “instant tea”;the composition of the extracts obtained with the same methodology is not significantly affected by the provenance of the tea. However, attention should be drawn to the specificities of the Japanese samples (the tea analysed in the present work was of Sencha quality). In contrast, the extraction methodology significantly affects the phytochemical composition, especially concerning the content of polyphenols. As such, our results indicate that instant tea classification based on chemical composition is sensible, but there is a need for a standard extraction methodology, namely concerning the temperature and time of contact of the tea leaves with the extraction solvent.

Biotechnological Applications and Health-Promoting Properties of Flavonols: An Updated View.

Flavonols are a subclass of natural flavonoids characterized by a remarkable number of biotechnological applications and health-promoting properties. They attract researchers' attention due to many epidemiological studies supporting their usage. They are phytochemicals commonly present in our diet, being ubiquitous in the plant kingdom and, in particular, relatively very abundant in fruits and vegetables. All these aspects make flavonols candidates of choice for the valorization of products, based on the presence of a remarkable number of different chemical structures, each one characterized by specific chemical features capable of influencing biological targets inside the living organisms in very different manners. In this review, we analyzed the biochemical and physiological characteristics of flavonols focalizing our attention on the most promising compounds to shed some light on their increasing utilization in biotechnological applications in processing industries, as well as their suitable employment to improve the overall wellness of the humankind.

Development of Effective Therapeutic Molecule from Natural Sources against Coronavirus Protease.

The SARS-CoV-2 main protease (Mpro) is one of the molecular targets for drug design. Effective vaccines have been identified as a long-term solution but the rate at which they are being administered is slow in several countries, and mutations of SARS-CoV-2 could render them less effective. Moreover, remdesivir seems to work only with some types of COVID-19 patients. Hence, the continuous investigation of new treatments for this disease is pivotal. This study investigated the inhibitory role of natural products against SARS-CoV-2 Mpro as repurposable agents in the treatment of coronavirus disease 2019 (COVID-19). Through in silico approach, selected flavonoids were docked into the active site of Mpro. The free energies of the ligands complexed with Mpro were computationally estimated using the molecular mechanics-generalized Born surface area (MM/GBSA) method. In addition, the inhibition process of SARS-CoV-2 Mpro with these ligands was simulated at 100 ns in order to uncover the dynamic behavior and complex stability. The docking results showed that the selected flavonoids exhibited good poses in the binding domain of Mpro. The amino acid residues involved in the binding of the selected ligands correlated well with the residues involved with the mechanism-based inhibitor (N3) and the docking score of Quercetin-3-O-Neohesperidoside (-16.8 Kcal/mol) ranked efficiently with this inhibitor (-16.5 Kcal/mol). In addition, single-structure MM/GBSA rescoring method showed that Quercetin-3-O-Neohesperidoside (-87.60 Kcal/mol) is more energetically favored than N3 (-80.88 Kcal/mol) and other ligands (Myricetin 3-Rutinoside (-87.50 Kcal/mol), Quercetin 3-Rhamnoside (-80.17 Kcal/mol), Rutin (-58.98 Kcal/mol), and Myricitrin (-49.22 Kcal/mol). The molecular dynamics simulation (MDs) pinpointed the stability of these complexes over the course of 100 ns with reduced RMSD and RMSF. Based on the docking results and energy calculation, together with the RMSD of 1.98 ± 0.19 Å and RMSF of 1.00 ± 0.51 Å, Quercetin-3-O-Neohesperidoside is a better inhibitor of Mpro compared to N3 and other selected ligands and can be repurposed as a drug candidate for the treatment of COVID-19. In addition, this study demonstrated that in silico docking, free energy calculations, and MDs, respectively, are applicable to estimating the interaction, energetics, and dynamic behavior of molecular targets by natural products and can be used to direct the development of novel target function modulators.

Flavonoids as an effective sensitizer for anti-cancer therapy: insights into multi-faceted mechanisms and applicability towards individualized patient profiles.

Cost-efficacy of currently applied treatments is an issue in overall cancer management challenging healthcare and causing tremendous economic burden to societies around the world. Consequently, complex treatment models presenting concepts of predictive diagnostics followed by targeted prevention and treatments tailored to the personal patient profiles earn global appreciation as benefiting the patient, healthcare economy, and the society at large. In this context, application of flavonoids as a spectrum of compounds and their nano-technologically created derivatives is extensively under consideration, due to their multi-faceted anti-cancer effects applicable to the overall cost-effective cancer management, primary, secondary, and even tertiary prevention. This article analyzes most recently updated data focused on the potent capacity of flavonoids to promote anti-cancer therapeutic effects and interprets all the collected research achievements in the frame-work of predictive, preventive, and personalized (3P) medicine. Main pillars considered are: - Predictable anti-neoplastic, immune-modulating, drug-sensitizing effects; - Targeted molecular pathways to improve therapeutic outcomes by increasing sensitivity of cancer cells and reversing their resistance towards currently applied therapeutic modalities.

Quercetin as a Natural Therapeutic Candidate for the Treatment of Influenza Virus.

The medical burden caused by respiratory manifestations of influenza virus (IV) outbreak as an infectious respiratory disease is so great that governments in both developed and developing countries have allocated significant national budget toward the development of strategies for prevention, control, and treatment of this infection, which is seemingly common and treatable, but can be deadly. Frequent mutations in its genome structure often result in resistance to standard medications. Thus, new generations of treatments are critical to combat this ever-evolving infection. Plant materials and active compounds have been tested for many years, including, more recently, active compounds like flavonoids. Quercetin is a compound belonging to the flavonols class and has shown therapeutic effects against influenza virus. The focus of this review includes viral pathogenesis as well as the application of quercetin and its derivatives as a complementary therapy in controlling influenza and its related symptoms based on the targets. We also touch on the potential of this class of compounds for treatment of SARS-COV-2, the cause of new pandemic.

Flavonol morin targets host ACE2, IMP-α, PARP-1 and viral proteins of SARS-CoV-2, SARS-CoV and MERS-CoV critical for infection and survival: a computational analysis.

A sudden outbreak of a novel coronavirus SARS-CoV-2 in 2019 has now emerged as a pandemic threatening to efface the existence of mankind. In absence of any valid and appropriate vaccines to combat this newly evolved agent, there is need of novel resource molecules for treatment and prophylaxis. To this effect, flavonol morin which is found in fruits, vegetables and various medicinal herbs has been evaluated for its antiviral potential in the present study. PASS analysis of morin versus reference antiviral drugs baricitinib, remdesivir and hydroxychloroquine revealed that morin displayed no violations of Lipinski's rule of five and other druglikeness filters. Morin also displayed no tumorigenic, reproductive or irritant effects and exhibited good absorption and permeation through GI (clogP <5). In principal component analysis, morin appeared closest to baricitinib in 3D space. Morin displayed potent binding to spike glycoprotein, main protease 3CLPro and papain-like protease PLPro of SARS-CoV-2, SARS-CoV and MERS-CoV using molecular docking and significant binding to three viral-specific host proteins viz. human ACE2, importin-α and poly (ADP-ribose) polymerase (PARP)-1, further lending support to its antiviral efficacy. Additionally, morin displayed potent binding to pro-inflammatory cytokines IL-6, 8 and 10 also supporting its anti-inflammatory activity. MD simulation of morin with SARS-CoV-2 3CLPro and PLPro displayed strong stability at 300 K. Both complexes exhibited constant RMSDs of protein side chains and Cα atoms throughout the simulation run time. In conclusion, morin might hold considerable therapeutic potential for the treatment and management of not only COVID-19, but also SARS and MERS if studied further. Communicated by Ramaswamy H. Sarma.

Flavonols as potential antiviral drugs targeting SARS-CoV-2 proteases (3CLpro and PLpro), spike protein, RNA-dependent RNA polymerase (RdRp) and angiotensin-converting enzyme II receptor (ACE2).

The novel coronavirus outbreak (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) represents the actual greatest global public health crisis. The lack of efficacious drugs and vaccines against this viral infection created a challenge for scientific researchers in order to find effective solutions. One of the promising therapeutic approaches is the search for bioactive molecules with few side effects that display antiviral properties in natural sources like medicinal plants and vegetables. Several computational and experimental studies indicated that flavonoids especially flavonols and their derivatives constitute effective viral enzyme inhibitors and possess interesting antiviral activities. In this context, the present study reviews the efficacy of many dietary flavonols as potential antiviral drugs targeting the SARS-CoV-2 enzymes and proteins including Chymotrypsin-Like Protease (3CLpro), Papain Like protease (PLpro), Spike protein (S protein) and RNA-dependent RNA polymerase (RdRp), and also their ability to interact with the angiotensin-converting enzyme II (ACE2) receptor. The relationship between flavonol structures and their SARS-CoV-2 antiviral effects were discussed. On the other hand, the immunomodulatory, the anti-inflammatory and the antiviral effects of secondary metabolites from this class of flavonoids were reported. Also, their bioavailability limitations and toxicity were predicted.

Synthetic flavonoids as potential antiviral agents against SARS-CoV-2 main protease.

The COVID-19 pandemic has claimed more than a million lives worldwide within a short time span. Due to the unavailability of specific antiviral drugs or vaccine, the infections are causing panic both in general public and among healthcare providers. Therefore, an urgent discovery and development of effective antiviral drug for the treatment of COVID-19 is highly desired. Targeting the main protease (Mpro) of the causative agent, SARS-CoV-2 has great potential for drug discovery and drug repurposing efforts. Published crystal structures of SARS-CoV-2 Mpro further facilitated in silico investigations for discovering new inhibitors against Mpro. The present study aimed to screen several libraries of synthetic flavonoids and benzisothiazolinones as potential SARS-CoV-2 Mpro inhibitors using in silico methods. The short-listed compounds after virtual screening were filtered through SwissADME modeling tool to remove molecules with unfavorable pharmacokinetics and medicinal properties. The drug-like molecules were further subjected to iterative docking for the identification of top binders of SARS-CoV-2 Mpro. Finally, molecular dynamic (MD) simulations and binding free energy calculations were performed for the evaluation of the dynamic behavior, stability of protein-ligand complex, and binding affinity, resulting in the identification of thioflavonol, TF-9 as a potential inhibitor of Mpro. The computational studies further revealed the binding of TF-9 close to catalytic dyad and interactions with conserved residues in the S1 subsite of the substrate binding site. Our in-silico study demonstrated that synthetic analogs of flavonoids, particularly thioflavonols, have a strong tendency to inhibit the main protease Mpro, and thereby inhibit the reproduction of SARS-CoV-2. Communicated by Ramaswamy H. Sarma.