Therapeutic potential of flavonoids and their mechanism of action against microbial and viral infections—A review

Natural biflavonoids as potential therapeutic agents against microbial diseases

Microbes broadly constitute several organisms like viruses, protozoa, bacteria, and fungi present in our biosphere. Fast-paced environmental changes have influenced contact of human populations with newly identified microbes resulting in diseases that can spread quickly. These microbes can cause infections like HIV, SARS-CoV2, malaria, nosocomial Escherichia coli, methicillin-resistant Staphylococcus aureus (MRSA), or Candida infection for which there are no available vaccines/drugs or are less efficient to prevent or treat these infections. In the pursuit to find potential safe agents for therapy of microbial infections, natural biflavonoids like amentoflavone, tetrahydroamentoflavone, ginkgetin, bilobetin, morelloflavone, agathisflavone, hinokiflavone, Garcinia biflavones 1 (GB1), Garcinia biflavones 2 (GB2), robustaflavone, strychnobiflavone, ochnaflavone, dulcisbiflavonoid C, tetramethoxy-6,6″-bigenkwanin and other derivatives isolated from several species of plants can provide effective starting points and become a source of future drugs. These biflavonoids show activity against influenza, severe acute respiratory syndrome (SARS), dengue, HIV-AIDS, coxsackieviral, hepatitis, HSV, Epstein-Barr virus (EBV), protozoal (Leishmaniasis, Malaria) infections, bacterial and fungal infections. Some of the biflavonoids can provide antiviral and protozoal activity by inhibition of neuraminidase, chymotrypsin-like protease, DV-NS5 RNA dependant RNA polymerase, reverse transcriptase (RT), fatty acid synthase, DNA polymerase, UL54 gene expression, Epstein-Barr virus early antigen activation, recombinant cysteine protease type 2.8 (r-CPB2.8), Plasmodium falciparum enoyl-acyl carrier protein (ACP) reductase or cause depolarization of parasitic mitochondrial membranes. They may also provide anti-inflammatory therapeutic activity against the infection-induced cytokine storm. Considering the varied bioactivity of these biflavonoids against these organisms, their structure-activity relationships are derived and wherever possible compared with monoflavones. Overall, this review aims to highlight these natural biflavonoids and briefly discuss their sources, reported mechanism of action, pharmacological uses, and comment on resistance mechanism, flavopiridol repurposing and the bioavailability aspects to provide a starting point for anti-microbial research in this area.

Heavy metals analysis, GCMS-QP quantification of flavonoids, amino acids and saponins, analysis of tannins and organoleptic properties of powder and tincture of Echinacea purpurea (L.) and Rhapónticum carthamoídes

Medicinal plants are one of the main sources of vitamins, minerals salts, macro-and microelements, and other biologically active substances that have a health and protective effect on the human body. The current study was aimed to appraise the heavy metals contents in the powder materials of two medicinally important plants Echinacea purpurea (L.)  and Rhapónticum carthamoídes collected from the Semipalatinsk nuclear test site using atomic absorption spectrophotometer. Flavonoids, saponins, amino acid contents quantification were done both in raw materials as well as tincture prepared from both plants via GCMS-QP 2010 Ultra chromatomass spectrometer. Further, tannins concentrations and organoleptic properties of the tincture were elucidated using previously reported standard procedures. In the current study, the concentrations of heavy metals were within the permitted range i.e. lead (0.0027 mg.100g-1), cadmium (0.00012 mg.100g-1), arsenic (ND), mercury (ND). In the crude powder, flavonoids were observed to be in the highest concentration in E. purpurea (L.) (5.5 ±0.20 mg.100g-1), whereas, its concentration was 3.1 ±0.346 mg.100g-1 in R. carthamoídes powder. Tannin concentration was higher in R. carthamoídes (5.5 ±0.115 mg.100g-1) and 3.1 ±0.46 mg.100g-1 in E. purpurea. Likewise, saponins concentrations were 4.1 ±0.40 mg.100g-1 and 5.6 ±0.17 mg.100g-1 in E. purpurea and R. carthamoídes powder respectively. Concentrations of these active metabolites in the resultant tincture were flavonoids (7.6 ±0.23), tannins (7.5  ±0.28), and saponins (8.5 ±0.16) mg.100g-1. In the current study, we observed highest concentrations of these essential amino acids in the tincture including leucine/isoleucine (78.00 ±1.15 mg.100g-1), histidine (14.00 ±1.44 mg.100g-1), lysine (49.33 ±2.02 mg.100g-1), methionine (18.66 ±2.90 mg.100g-1), cystine (29.00 ±0.57 mg.100g-1), phenylalanine (24.16 ±1.87 mg.100g-1) and threonine (32.50 ±1.22 mg.100g-1) respectively. The resultant tincture has a pleasant agreeable taste coupled with acceptable herbal flavor which are important organoleptic properties for any product.

Review of the Applications of Biomedical Compositions Containing Hydroxyapatite and Collagen Modified by Bioactive Components

Regenerative medicine is becoming a rapidly evolving technique in today's biomedical progress scenario. Scientists around the world suggest the use of naturally synthesized biomaterials to repair and heal damaged cells. Hydroxyapatite (HAp) has the potential to replace drugs in biomedical engineering and regenerative drugs. HAp is easily biodegradable, biocompatible, and correlated with macromolecules, which facilitates their incorporation into inorganic materials. This review article provides extensive knowledge on HAp and collagen-containing compositions modified with drugs, bioactive components, metals, and selected nanoparticles. Such compositions consisting of HAp and collagen modified with various additives are used in a variety of biomedical applications such as bone tissue engineering, vascular transplantation, cartilage, and other implantable biomedical devices.

A Review on the Biological Activity of Camellia Species

Medicinal plants have been used since antiquity to cure illnesses and injuries. In the last few decades, natural compounds extracted from plants have garnered the attention of scientists and the Camellia species are no exception. Several species and cultivars are widespread in Asia, namely in China, Japan, Vietnam and India, being also identified in western countries like Portugal. Tea and oil are the most valuable and appreciated Camellia subproducts extracted from Camellia sinensis and Camellia oleifera, respectively. The economic impact of these species has boosted the search for additional information about the Camellia genus. Many studies can be found in the literature reporting the health benefits of several Camellia species, namely C. sinensis, C. oleifera and Camellia japonica. These species have been highlighted as possessing antimicrobial (antibacterial, antifungal, antiviral) and antitumoral activity and as being a huge source of polyphenols such as the catechins. Particularly, epicatechin (EC), epigallocatechin (EGC), epicatechin-3-gallate (ECG), and specially epigallocatechin-3-gallate (EGCG), the major polyphenols of green tea. This paper presents a detailed review of Camellia species’ antioxidant properties and biological activity.

Phytochemical characterization and biological activities of Plectranthus barbatus Andrews

Plectranthus barbatus Andrews (Lamiaceae) is widely distributed in the world and has a range of popular therapeutic indications. This work aimed to evaluate the phytochemical characterization of two leaf extracts of P. barbatus, and their antimicrobial, antineoplastic and immunomodulatory potential. After collection, herborization and obtainment of the P. barbatus aqueous extract (PBA) and acetone:water 7:3 P. barbatus organic extract (PBO), the phytochemical characterization was performed by high-performance liquid chromatography (HPLC). The antimicrobial activity was performed to determine the minimum inhibitory concentration (MIC) against eight bacterial strains using the microdilution test and the fungus Trichophyton rubrum by disc diffusion assay and microdilution test. Cytotoxicity was assessed by MTT and trypan blue methods in normal peripheral blood mononuclear cells (PBMCs) at concentrations ranged between 0.1 to 100 µg.mL-1 and in neoplastic cell lines Toledo, K562, DU-145 and PANC-1 at 1, 10 and 100 µg.mL-1 . Immunomodulatory activity, was evaluated by sandwich ELISA of proinflammatory cytokines at BALB/c mice splenocytes cultures supernatant. Both extracts presented flavonoids, cinnamic derivatives, steroids and ellagic acid. PBO showed bacteriostatic activity against Acinetobacter baumannii (MIC = 250 µg.mL-1) clinical isolate and PBA fungistatic activity against Trichophyton rubrum (MIC = 800 µg.mL-1). The extracts did not exhibit toxicity to PBMCs and neoplastic cells (IC50 > 100 µg.mL-1). Additionally, PBO at 100 µg.mL-1 significantly inhibited IFN-γ and IL-17A cytokines (p = 0.03). Plectranthus barbatus is a potential candidate for therapeutic use due to its low toxicity in healthy human cells and exhibits biological activities of medical interest as bacteriostatic, fungistatic and immunomodulatory.

Exploitation of polyphenols and proteins using nanoencapsulation for anti-viral and brain boosting properties - Evoking a synergistic strategy to combat COVID-19 pandemic

The world is currently under the threat of COVID pandemic and has focused every dimension of research in finding a cure to this novel disease. In this current situation, people are facing mental stress, agony, fear, depression and other associated symptoms which are taking a toll on their overall mental health. Nanoencapsulation of certain brain boosting polyphenols including quercetin, caffeine, cocoa flavanols and proteins like lectins can become new area of interest in the present scenario. Besides the brain boosting benefits, we have also highlighted the anti- viral activities of these compounds which we assume can play a possible role in combating COVID-19 given to their previous history of action against certain viruses. This review outlines the nanoencapsulation approaches of such synergistic compounds as a novel strategy to take the ongoing research a step ahead and also provides a new insight in bringing the role of nanotechnology in addressing the issues related to COVID pandemic.

Antimetastatic effects of VOflavonoid complexes on A549 cell line

BACKGROUND

Non-small-cell lung cancer (NSCLC) is the most frequent type of lung cancer and more than 90 % of mortality is due to metastasis-related deaths. Flavonoids are considered nutraceuticals due to the variety of pharmacological properties. In this paper, we studied the effects of baicalin, silibinin, apigenin, luteolin, and its oxidovanadium(IV) cation complexes on the viability, adhesion to fibronectin, invasion, and migration on human lung cancer cell line A549. In addition, in order to complete the study of the interaction of VOflavonoids and bovine serum albumin (BSA), the binding ability of silibinin and VOsil to the protein was evaluated.

METHOD

To establish the non-cytotoxic concentration range of the tested compounds, the cancer cell viability was evaluated using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) assay. Cell migration and invasion assays were performed using Boyden chambers and adhesion assay using MTT method. The interaction of compounds with BSA were investigated in physiological buffer (pH = 7.4) by fluorescence spectroscopy.

RESULTS

All complexes inhibited the metastatic cascade steps to a greater extent than their respective ligands. Likewise, based on binding constant values (K_b) for BSA-silibinin and BSA-VOsil, we can suggest that both compounds can interact with the protein.

CONCLUSION

Although all the complexes suppressed cell adhesion, invasion and migration, VOlut can be considered as a good candidate to continue the trials because it presented encouraging results as a potential antitumor and antimetastatic agent, and can be transported by BSA.

Ameliorative potentials of Persea americana leaf extract on toxicants - induced oxidative assault in multiple organs of wistar albino rat

Background

Persea americana (PA) is a popular medicinal plant in folkloric medicines. The present study therefore investigates the ameliorative potentials of its leaves extract on carbon tetrachloride and rifampicin-induced toxicity in the liver, kidney and heart of albino rat. This was aimed at assessing the potentials of the plant in the management of liver, kidney and heart diseases.

Methodology

Forty (40) rats were randomly divided into eight (8) groups of five animals each. Groups I and II were administered with only distilled water and carbon tetrachloride (CCl4) respectively. Groups III and IV animals received 3.0 ml/kg bw of CCl4 and were treated with the extract at 50 mg/kg bw and 100 mg/kg respectively, while group V received 100 mg/kg bw. of silymarin orally for 14 days. Groups VI animals were administered with rifampicin (250 mg/kg bw.) only, while groups VII and VIII animals received rifampicin and were treated with 50 mg and 100 mg/kg bw of the extract respectively. Activities of creatine kinase, aspartate amino transferase, alanine amino transferase, alkaline phosphatase, superoxide dismutase, catalase as well as levels of urea, uric acid, bilirubin and malonidialdehyde (MDA) were assayed. Lipid profiles and histopathological examination of liver and kidney slices were also performed.

Result

Treatment with P. americana significantly (p < 0.05) restored all deranged biochemical parameters (creatine kinase, aspartate amino transferase, alanine amino transferase, alkaline phosphatase, urea, uric acid, bilirubin, MDA, lipid profile as well as superoxide dismutase and catalase) in a dose-dependent manner. Normal hepatic and renal histoarchitecture were also restored following treatment with P. americana.

Conclusion

Amelioration of distorted cardiac, hepatic and renal histoarchitecture as well as restoration of lipid profile, biomarkers of liver and kidney injury and antioxidant enzymes (catalase and superoxide dismutase) affirm the potential usefulness of P. americana in the management of liver, kidney and heart diseases.

Investigation of the inhibitory activity of some dietary bioactive flavonoids against SARS-CoV-2 using molecular dynamics simulations and MM-PBSA calculations

Eventhough the development of vaccine against COVID-19 pandemic is progressing in different part of the world a well-defined treatment plan is not yet developed. Therefore, we investigate the inhibitory activity of a group of dietary bioactive flavonoids against SARS-CoV-2 main protease (M^pro), which are identified as one of the potential targets in the drug discovery process of COVID-19. After the initial virtual screening of a number of bioactive flavonoids, the binding affinity of three compounds - Naringin, Naringenin and Amentoflavone - at the active site of M^pro was investigated through MD Simulations, MM-PBSA and DFT Binding Energy calculations. From the MD trajectory analysis, Amentoflavone and Naringin showed consistent protein-ligand interactions with the aminoacid residues of the active site domains of M^pro. The excellent inhibitory activity of Amentoflavone and Naringin was established from its MM-PBSA binding energy values of -190.50 and -129.87 kJ/mol respectively. The MET165 residue of M^pro is identified as one of the key residue which contributed significantly to MM-PBSA binding energy through hydrophobic interactions. Furthermore, the DFT binding energy values of Amentoflavone (-182.92 kJ/mol) and Naringin (-160.67 kJ/mol) in active site molecular clusters with hydrogen bonds confirmed their potential inhibitory activity. These compounds are of high interest because of their wide availability, low cost, no side effects, and long history of use. We can prevent the severity of this disease for home care patients using these effective dietary supplements. We are hopeful that our results have implications for the development of prophylaxis of COVID-19.Communicated by Ramaswamy H. Sarma.

Computational and network pharmacology analysis of bioflavonoids as possible natural antiviral compounds in COVID-19

Bioflavonoids are the largest group of plant-derived polyphenolic compounds with diverse biological potential and have also been proven efficacious in the treatment of Severe Acute Respiratory Syndrome (SARS) and Middle East Respiratory Syndrome (MERS). The present investigation validates molecular docking, simulation, and MM-PBSA studies of fifteen bioactive bioflavonoids derived from plants as a plausible potential antiviral in the treatment of COVID-19. Molecular docking studies for 15 flavonoids on the three SARS CoV-2 proteins, non-structural protein-15 Endoribonuclease (NSP15), the receptor-binding domain of spike protein (RBD of S protein), and main protease (Mpro/3CLpro) were performed and selected protein-ligand complexes were subjected to Molecular Dynamics simulations. The molecular dynamics trajectories were subjected to free energy calculation by the MM-PBSA method. All flavonoids were further assessed for their effectiveness as adjuvant therapy by network pharmacology analysis on the target proteins. The network pharmacology analysis suggests the involvement of selected bioflavonoids in the modulation of multiple signaling pathways like p53, FoxO, MAPK, Wnt, Rap1, TNF, adipocytokine, and leukocyte transendothelial migration which plays a significant role in immunomodulation, minimizing the oxidative stress and inflammation. Molecular docking and molecular dynamics simulation studies illustrated the potential of glycyrrhizic acid, amentoflavone, and mulberroside in inhibiting key SARS-CoV-2 proteins and these results could be exploited further in designing future ligands from natural sources.

Ethanolic extract of Artemisia campestris subsp. glutinosa (Besser) Batt. inhibits HIV-1 replication in vitro through the activity of terpenes and flavonoids on viral entry and NF-κB pathway

ETHNO-PHARMACOLOGICAL RELEVANCE

The genus Artemisia spp. is well known for its anti-infectious properties and its high content in anti-infectious compounds, like the well-known sweet wormwood (Artemisia annua L.). Another Artemisia species, Artemisia campestris subsp. glutinosa (Besser) Batt., field wormwood, has been traditionally used as medicinal plant in the Mediterranean region.

AIM OF THE STUDY

The aim of this study is to investigate the anti-HIV activity of field wormwood, to identify the compounds responsible for this activity and their structure and mechanism of action.

MATERIALS AND METHODS

Antiviral activity of isolated compounds and extracts was evaluated in HIV-1 infections of lymphoblastoid cells. We also evaluated the mechanism of action of isolated compounds. Viral entry was studied comparing the inhibitory effect of isolated compounds on wild type HIV-1 and VSV pseudotyped HIV-1. To assess the viral transcriptional effect, plasmids encoding luciferase reporter genes under the control of the whole genome of HIV-1 or NF-κB or Sp1 transcription factors were transfected in the presence of the compounds under evaluation. Finally, antioxidant activity was assessed by quantitation of reduced and total glutathione in treated cell cultures.

RESULTS

Ethanolic and aqueous extracts of Artemisia campestris subsp. glutinosa (Besser) Batt. subsp. glutinosa displayed anti-HIV activity in vitro, although ethanolic extract was more powerful (IC₅₀ 14.62 μg/mL). Bio-guided ethanolic extract fractionation leads to the isolation and characterization of two terpenes, damsin and canrenone, and four flavonoids, 6, 2', 4'-trimethoxyflavone, acerosin, cardamonin and xanthomicrol. All the isolated compounds inhibited HIV-1 replication in vitro with IC₅₀ values between the middle nanomolar and the low micromolar range. Their anti-HIV mechanism of action is due to the bloking of viral entry and/or transcription inhibition, without correlation with the antioxidant activity, through interference with the cellular transcription factors NF-κB and Sp1, which are targets that are not currently reached by antiretroviral therapy.

CONCLUSION

We describe here the anti-HIV activity of field wormwood, Artemisia campestris subsp. glutinosa (Besser) Batt., and the isolation and study of the mechanism of action of two terpenes and four flavonoids, responsible, at least in part, for its activity, through the inhibition of two different cellular targets affecting the HIV replication cycle. The activity of these compounds in cellular targets could explain why plant extracts can be used in the treatment of different diseases. Besides, the presence of several compounds with dual and different mechanisms of action could prove useful in the treatment of HIV-1 infection, since it could aid to overcome drug resistances and simplify drug therapy. This work is a further step in understanding the anti-infectious activity of wormwood species and their use in treating infectious diseases.

Important Flavonoids and Their Role as a Therapeutic Agent

Flavonoids are phytochemical compounds present in many plants, fruits, vegetables, and leaves, with potential applications in medicinal chemistry. Flavonoids possess a number of medicinal benefits, including anticancer, antioxidant, anti-inflammatory, and antiviral properties. They also have neuroprotective and cardio-protective effects. These biological activities depend upon the type of flavonoid, its (possible) mode of action, and its bioavailability. These cost-effective medicinal components have significant biological activities, and their effectiveness has been proved for a variety of diseases. The most recent work is focused on their isolation, synthesis of their analogs, and their effects on human health using a variety of techniques and animal models. Thousands of flavonoids have been successfully isolated, and this number increases steadily. We have therefore made an effort to summarize the isolated flavonoids with useful activities in order to gain a better understanding of their effects on human health.

Honey: Another Alternative in the Fight against Antibiotic-Resistant Bacteria?

Antibacterial resistance has become a challenging situation worldwide. The increasing emergence of multidrug-resistant pathogens stresses the need for developing alternative or complementary antimicrobial strategies, which has led the scientific community to study substances, formulas or active ingredients used before the antibiotic era. Honey has been traditionally used not only as a food, but also with therapeutic purposes, especially for the topical treatment of chronic-infected wounds. The intrinsic characteristics and the complex composition of honey, in which different substances with antimicrobial properties are included, make it an antimicrobial agent with multiple and different target sites in the fight against bacteria. This, together with the difficulty to develop honey-resistance, indicates that it could become an effective alternative in the treatment of antibiotic-resistant bacteria, against which honey has already shown to be effective. Despite all of these assets, honey possesses some limitations, and has to fulfill a number of requirements in order to be used for medical purposes.

Antibiofilm activity of flavonoids on staphylococcal biofilms through targeting BAP amyloids

The opportunistic pathogen Staphylococcus aureus is responsible for causing infections related to indwelling medical devices, where this pathogen is able to attach and form biofilms. The intrinsic properties given by the self-produced extracellular biofilm matrix confer high resistance to antibiotics, triggering infections difficult to treat. Therefore, novel antibiofilm strategies targeting matrix components are urgently needed. The Biofilm Associated Protein, Bap, expressed by staphylococcal species adopts functional amyloid-like structures as scaffolds of the biofilm matrix. In this work we have focused on identifying agents targeting Bap-related amyloid-like aggregates as a strategy to combat S. aureus biofilm-related infections. We identified that the flavonoids, quercetin, myricetin and scutellarein specifically inhibited Bap-mediated biofilm formation of S. aureus and other staphylococcal species. By using in vitro aggregation assays and the cell-based methodology for generation of amyloid aggregates based on the Curli-Dependent Amyloid Generator system (C-DAG), we demonstrated that these polyphenols prevented the assembly of Bap-related amyloid-like structures. Finally, using an in vivo catheter infection model, we showed that quercetin and myricetin significantly reduced catheter colonization by S. aureus. These results support the use of polyphenols as anti-amyloids molecules that can be used to treat biofilm-related infections.

Malus hupehensis leaves extract attenuates obesity, inflammation, and dyslipidemia by modulating lipid metabolism and oxidative stress in high-fat diet-induced obese mice

Malus hupehensis leaves (MHL) are used to make traditional Chinese tea. In this study, MHL extract was shown to improve metabolic disorders and inflammatory response in high-fat diet-induced obese mice. MHL extract could reduce body weight, and significantly alleviate liver damage and fat accumulation. MHL extract caused a decrease in the levels of ALT, AST, AKP, TC, TG, LDL-C, and an increase in the level of HDL-C. It also caused a decrease in inflammatory cytokines, including TNF-α, IFN-γ, IL-1β, IL-6, and an increase in the anti-inflammatory cytokine IL-10 and IL-4. MHL extract could upregulate mRNA expression of PPAR-α, LPL, CPT1, CYP7A1, SOD1, SOD2, CAT, GSH1, and GSH-Px and downregulate that of PPAR-γ and C/EBP-α in the liver of obese mice. In conclusion, our work represents the first study demonstrating that MHL extract possesses an anti-obesity effect and alleviates obesity-related symptoms, including dyslipidemia, chronic low-grade inflammatory, and liver damage. PRACTICAL APPLICATIONS: The research may contribute to the development and application of MHL as functional foods or dietary supplement to fight against obesity.

Flavonoids: A complementary approach to conventional therapy of COVID-19?

COVID-19, the highly contagious novel disease caused by SARS-CoV-2, has become a major international concern as it has spread quickly all over the globe. However, scientific knowledge and therapeutic treatment options for this new coronavirus remain limited. Although previous outbreaks of human coronaviruses (CoVs) such as SARS and MERS stimulated research, there are, to date, no antiviral therapeutics available that specifically target these kinds of viruses. Natural compounds with a great diversity of chemical structures may provide an alternative approach for the discovery of new antivirals. In fact, numerous flavonoids were found to have antiviral effects against SARS-and MERS-CoV by mainly inhibiting the enzymes 3-chymotrypsin-like protease (3CLpro) and papain-like protease (PLpro). In this review, we specifically focused on the search for flavonoids, polyphenolic compounds, which are proven to be effective against human CoVs. We therefore summarized and analyzed the latest progress in research to identify flavonoids for antiviral therapy and proposed strategies for future work on medicinal plants against coronaviruses such as SARS-CoV-2. We discovered quercetin, herbacetin, and isobavachalcone as the most promising flavonoids with anti-CoV potential.

Unraveling the anti-influenza effect of flavonoids: Experimental validation of luteolin and its congeners as potent influenza endonuclease inhibitors

The biological effects of flavonoids on mammal cells are diverse, ranging from scavenging free radicals and anti-cancer activity to anti-influenza activity. Despite appreciable effort to understand the anti-influenza activity of flavonoids, there is no clear consensus about their precise mode-of-action at a cellular level. Here, we report the development and validation of a screening assay based on AlphaScreen technology and illustrate its application for determination of the inhibitory potency of a large set of polyols against PA N-terminal domain (PA-Nter) of influenza RNA-dependent RNA polymerase featuring endonuclease activity. The most potent inhibitors we identified were luteolin with an IC₅₀ of 72 ± 2 nM and its 8-C-glucoside orientin with an IC₅₀ of 43 ± 2 nM. Submicromolar inhibitors were also evaluated by an in vitro endonuclease activity assay using single-stranded DNA, and the results were in full agreement with data from the competitive AlphaScreen assay. Using X-ray crystallography, we analyzed structures of the PA-Nter in complex with luteolin at 2.0 Å resolution and quambalarine B at 2.5 Å resolution, which clearly revealed the binding pose of these polyols coordinated to two manganese ions in the endonuclease active site. Using two distinct assays along with the structural work, we have presumably identified and characterized the molecular mode-of-action of flavonoids in influenza-infected cells.

Prolonging the Shelf Life of Cherry Tomatoes by Pullulan Coating with Ethanol Extract of Propolis During Refrigerated Storage

Cherry tomatoes are one of the most popular tomato varieties known for their bioactive compounds and sensory properties. One way to reduce the contamination of tomato is to coat them with natural or antimicrobial substances. In this study, an ethanolic extract of propolis (EEP) was obtained, and its chemical composition was analyzed using high-performance liquid chromatography with diode array detector (HPLC-DAD), and minimum inhibitory concentration (MIC) and the minimum bactericidal/fungicidal concentration (MBC/MFC) were determined using the serial microdilution method. The antimicrobial activity of 5 and 10% EEP and pullulan films containing EEP (5 and 10%) against Listeria monocytogenes, Salmonella Typhimurium, Escherichia coli O157, Penicillium chrysogenum, Fusarium solani, and Botrytis cinerea were compared. The influence of a pullulan coating containing EEP (5 and 10%) on reducing the number of bacteria and molds, physicochemical properties (weight loss (WL), total soluble solids (TSS), titratable acidity (TA), maturity index, pH, and color), and sensory properties (color and brightness of skin, aroma, flavor, overall quality, and general preference) of cherry tomatoes during refrigerated storage was evaluated. Pullulan films with EEP inhibited the growth of microorganisms on cherry tomatoes. These coatings did not affect the TSS and pH values of tomatoes, but a slight decrease in TA and WL was observed. Cherry tomatoes coated with pullulan coatings containing EEP did not show any adverse changes in their sensory properties. It was found that the addition of EEP to the pullulan coatings enriched them with antimicrobial properties and enhanced their action while reducing the WL and maturation time of cherry tomatoes.

Separation Processes to Provide Pure Enantiomers and Plant Ingredients

Enantiomer separation and the isolation of natural products from plants pose challenging separation problems resulting from the similarity of molecules and the number of compounds present in synthesis or extract mixtures. Furthermore, limited theory is available to predict productivities for possible alternative separation techniques. The application and performance of chromatography- and crystallization-based processes are demonstrated for various case studies devoted to isolating valuable target compounds from complex initial mixtures. In all cases, the first emphasis is set to determine the process-specific phase equilibria to identify feasible process options. For all examples considered, yields and productivities are evaluated and compared for different scenarios. Guidelines to approach and solve similar separation tasks are given.

State of the Art of Anthocyanins: Antioxidant Activity, Sources, Bioavailability, and Therapeutic Effect in Human Health

The antioxidant activity of anthocyanins in food is well known. Numerous antioxidant assays have been proposed to measure the capacity of anthocyanins to prevent the oxidation process that naturally occurs. Different solvents, temperatures, and pH levels are applied in each assay, and these factors should be taken into account in order to obtain useful and reproducible results. The concentration and the structure of these compounds are directly related to their antioxidant capacity and their environment. However, the effectiveness of the anthocyanin ingestion against diseases is also influenced by its bioavailability. Novel methodologies that simulate the digestion process have been developed in order to facilitate the current knowledge of anthocyanins bioavailability. Studies highlight the potential synergy effect between parent compounds and their derivatives (metabolites, conjugated products, and microbe-generated metabolites). The aim of this review is to provide an overview of advantages and disadvantages of the most common methods to determine the antioxidant activity of anthocyanins, chemical structure, and concentration of these compounds in different edible fruits, vegetables, and plants; their bioavailability after intake; as well as the main therapeutic effect described in the scientific literature.

Silver ion bioreduction in nanoparticles using Artemisia annua L. extract: characterization and application as antibacterial agents

The biological synthesis of metal nanoparticles using plant extracts with defined size and morphology is a simple, nontoxic and environmentally friendly method. The present study focused on the synthesis of silver nanoparticles (Ag NPs) by Artemisia annua L. extract as reducing and stabilising agent. The Ag NPs function, as antibacterial agents, is with that they are further used in human therapy. The effects of pH and temperature on the synthesis of NPs were characterized by UV-absorption spectroscopy and shown by surface plasmon resonance (SPR) band at 410 nm. NPs' size and morphology were measured by transmission electron microscopy (TEM) and dynamic light scattering (DLS). TEM images showed that Ag NPs were in a nano-sized range (20-90 nm) and had spherical shape. Our findings demonstrated that lower concentration (100 µg mL-1) of the biogenic Ag NPs exhibited antibacterial activity against Gram-negative Escherichia coli BW 25113 and Gram-positive Enterococcus hirae ATCC 9790.

Polo-like kinase 1 as a promising diagnostic biomarker and potential therapeutic target for hepatocellular carcinoma

Hepatocellular carcinoma is a major cause of cancer mortality worldwide. The outcome of hepatocellular carcinoma depends mainly on its early diagnosis. To date, the performance of traditional biomarkers is unsatisfactory. Polo-like kinase 1 is a serine/threonine kinase that plays essential roles in cell cycle progression and deoxyribonucleic acid damage. Moreover, polo-like kinase 1 knockdown decreases the survival of hepatocellular carcinoma cells; therefore, polo-like kinase 1 is an attractive target for anticancer treatments. Nobiletin, a natural polymethoxy flavonoid, exhibits a potential antiproliferative effect against a wide variety of cancers. This study targets to identify a reliable diagnostic biomarker for hepatocellular carcinoma and provide a potential therapeutic target for its treatment. Polo-like kinase 1 levels were analyzed in 44 hepatocellular carcinoma patients, 33 non-hepatocellular carcinoma liver cirrhosis patients and 15 healthy controls using the enzyme-linked immunosorbent assay method. Receiver operating characteristics curve analysis was used to establish a predictive model for polo-like kinase 1 relative to α-fetoprotein in hepatocellular carcinoma diagnosis. Furthermore, in the in vitro study, gene expressions were assessed by quantitative polymerase chain reaction in two human hepatocellular carcinoma cell lines after treatment with doxorubicin and polo-like kinase 1 inhibitor volasertib (Vola) either alone or in combination with nobiletin. Cell viability was also determined using the crystal violet assay.: Serum polo-like kinase 1 levels in hepatocellular carcinoma patients were significantly higher than liver cirrhosis and control groups (p < 0.0001). Polo-like kinase 1 showed a reasonable sensitivity, specificity, positive predictive value, and negative predictive value in hepatocellular carcinoma diagnosis. Moreover, nobiletin improved inhibition of cell growth induced by Vola and doxorubicin. Regarding reverse transcription polymerase chain reaction results, nobiletin suppressed expressions of polo-like kinase 1 and proliferating cell nuclear antigen and elevated expressions of P53, poly (ADPribose) polymerase 1, and caspase-3. Nobiletin/doxorubicin and nobiletin/Vola showed a significant increase in caspase-3 activity indicating cell apoptosis. Polo-like kinase 1 may be a potential biomarker for hepatocellular carcinoma diagnosis and follow-up during treatment with chemotherapies. In addition, nobiletin synergistically potentiates the doxorubicin and Vola-mediated anticancer effect that may be attributed partly to suppression of polo-like kinase 1 and proliferating cell nuclear antigen expression and enhancement of chemotherapy-induced apoptosis.

Estevinho L, Teixeira-Santos R, G. Rodrigues A, Pina-Vaz C, Fresno JM, Tornadijo ME. Antibacterial Action Mechanisms of Honey: Physiological Effects of Avocado, Chestnut, and Polyfloral Honey upon Staphylococcus aureus and Escherichia coli

Numerous studies have explored the antibacterial properties of different types of honey from all around the world. However, the data available describing how honey acts against bacteria are few. The aim of this study was to apply a flow cytometry (FC) protocol to examine and characterize the primary effects of three varieties of honey (avocado, chestnut and polyfloral) upon physiological status of Staphylococcus aureus and Escherichia coli cells to reveal their antibacterial action mechanisms. The effects of honey samples on membrane potential, membrane integrity, and metabolic activity were assessed using different fluorochromes, in a 180 min time course assay. Time-kill experiments were also carried out under similar conditions. Exposure of S. aureus and E. coli to the distinct honey samples resulted in physiological changes related to membrane polarization and membrane integrity. Moreover, honey induced a remarkable metabolic disruption as primary physiological effect upon S. aureus. The different honey samples induced quite similar effects on both bacteria. However, the depth of bacteria response throughout the treatment varied depending on the concentration tested and among honey varieties, probably due to compositional differences in the honey.

Discovery of small molecule inhibitors of chikungunya virus proteins (nsP2 and E1) using in silico approaches

Chikungunya virus (CHIKV) has emerged as a major viral threat, affecting over a million people worldwide per year. It is a vector borne disease transmitted to the human by Ades mosquitoes and primarily affect people by causing viral fever, severe joint pain and other symptoms, like rash, joint swelling, muscle pain and in rare cases can be fatal. CHIKV is a deadly virus, with its mutation rate found to be significantly higher as compared to other viruses. To date, there has been no reported FDA approved drug against this virus. Thus, keeping in mind the urgent need to scrutinize potential therapies against CHIKV, the present study identified twenty plant bioactive compounds that are available at low price and do not have associated adverse effect. For identification of active potentials molecules the pharmacoinformatics-based perspective was applied against CHIKV structural (E1) and non-structural (nsP2) proteins using molecular docking and scoring. The selected compounds were further studied for pharmacokinetics (PK) and pharmacodynamics (PD) associated parameters such as initial absorption, then distribution and later on metabolism excretion and toxicity (ADMET) profiles based on in silico study. The results reveal five potential lead compounds having high binding energy that can help in the development of commercial drugs with favorable ADMET characteristic.Communicated by Ramaswamy H. Sarma.

Ethnopharmacology, phytochemistry and biological activity of Erodium species: A review

Erodium spp. is a genus that can be found in all continents that has been traditionally used in folk medicine to treat many diseases such as hemorrhage, dermatological disorders, indigestion, and inflammatory diseases. Moreover, Erodium leaves have been used for the preparation of salads, omelets, sandwiches, sauces and soups, among other food products. The objective of this review was to show the recent and relevant studies about extraction of bioactive compounds, the phytochemical characterization, the potential biological activities and toxicological evidence reported in both in vitro and in vivo studies from Erodium spp. In addition, the use of Erodium spp. as natural compounds against the development of diseases were also showed. This review highlights the traditional use of Erodium species in several countries as a therapeutic agent to treat several diseases (such as constipation, dermatological disorders, diabetes, indigestion, urinary inflammations, and as carminative agent), the factors influencing the extraction of bioactive compounds (mainly species and solvent composition on phenolic compounds) and phytochemical profile (presence of essential oils and alkaloids), the scientific evidence about its anti-inflammatory, antimicrobial (against both spoilage and pathogenic microorganisms), antiviral and other health-related activities (anti-protozoal and anti-viral activity) as well as the toxicological evidence. Erodium spp. is a relevant source of compounds with antioxidant, antimicrobial, and biological activity, which support its potential exploration in pharmacological and food area. Major efforts are necessary to advance the knowledge about Erodium genus regarding the relation between traditional use and scientific evidence, optimization of extraction conditions, the influence on biological mechanisms at animal and clinical levels, and bioaccessibility and bioavailability of bioactive compounds.

Structure-Dependent Inhibition of Stenotrophomonas maltophilia by Polyphenol and Its Impact on Cell Membrane

As natural occurring antimicrobial substances, phenolic compounds have been used to inhibit various bacteria. Stenotrophomonas maltophilia 4–1, a strain isolated from food, exhibited spoilage potential in vitro with proteolysis and lipolysis at 25°C. The present study evaluated the antibacterial properties of 13 polyphenols on S. maltophilia 4–1, and selected 6 compounds (ferulic acid, p-coumaric acid, caffeic acid, chlorogenic acid, (−)-epigallocatechin, and phloretin) for binary combination treatments. The results revealed that antibacterial activities of polyphenols were structure-dependent, and cinnamic acid showed strong inhibitory effects, with a minimum inhibitory concentration (MIC) of 0.125 mg/mL. Importantly, we did not observe any obvious synergistic effects across all binary combinations. The antibacterial mechanism of cinnamic acid was related to membrane damage, caused by the loss of cell membrane integrity and alteration of cell morphology. These findings suggest that cinnamic acid is a promising candidate for the control of spoilage bacteria in food.

α-Glucosidase inhibitory, antibacterial, and antioxidant activities of natural substances from the wood of Derris reticulata Craib

Derris reticulata (Leguminosae-Papilionoideae) has been used for the treatment of diabetes in Thai folk remedies. The phytochemical investigation of the wood of D. reticulata revealed the isolation of two new pyranoflavanones, 4'-methoxydereticulatin (1) and 2'''-hydroxy,3'''-ethoxylupinifolin (2), along with five known compounds namely lupinifolin (3), 2''',3'''-dihydroxylupinifolin (4), genistein (5), lupeol (6), and β-sitosterol (7). Compounds 1-4 were selected for antibacterial assay using broth microdilution method, and displayed good activity against four out of five tested pathogenic bacterial strains, with MIC values ranging from 0.78 to 128 μg/mL. The result from spectrophotometric assay of α-glucosidase inhibition showed that 5 exhibited promising α-glucosidase inhibitory activity, compared with the positive control acarbose. Additionally, it was found that compounds 4 and 5 showed moderate DPPH and NO radicals scavenging activity. Modeling studies were also performed to suggest the interaction modes of compounds 3-5 in the α-glucosidase enzyme active site.

Ultrasound-Assisted Phytochemical Extraction Condition Optimization Using Response Surface Methodology from Perlette Grapes (Vitis vinifera)

In the current study, bioactive compounds of Vitis vinifera (Perlette) were extracted using an ultrasound-assisted extraction technique. The central composite design of response surface methodology (RSM) was used to determine the effect of time, temperature, and concentration of acetic acid on response variables that include extract yield, total phenolic content (TPC), total flavonoid content (TFC), and antioxidant activity of Vitis vinifera extracts. The results of the central composite design of RSM revealed that the quadratic polynomial model is best fitted to experimental results, with all the responses having a regression coefficient greater than 0.9. Optimized extraction levels include 26.5 min, an extraction temperature of 59 °C, and an acetic acid concentration of 62.9% with good extraction yield results of 34.95 g/100 g dry weight (DW) of grapes, TPC 34.38 mg gallic acid equivalent per gram (GAE/g) DW, flavonoid content 10.21 mg quercetin equivalents per gram (QEQ/g) DW, and antioxidant activity of 9.11 mg/100 mL ascorbic acid equivalent. The present study showed that acetic acid can be effectively used for the ultrasound-assisted extraction of polyphenols, flavonoids, and antioxidants of Vitis vinifera. These optimized conditions can be used for the extraction of bioactive compounds that can be for the development of nutraceutical products.

Review on Natural Preservatives for Extending Fish Shelf Life

Fish is extremely perishable as a result of rapid microbial growth naturally present in fish or from contamination. Synthetic preservatives are widely used in fish storage to extend shelf life and maintain quality and safety. However, consumer preferences for natural preservatives and concerns about the safety of synthetic preservatives have prompted the food industry to search natural preservatives. Natural preservatives from microorganisms, plants, and animals have been shown potential in replacing the chemical antimicrobials. Bacteriocins and organic acids from bacteria showed good antimicrobial activities against spoilage bacteria. Plant-derived antimicrobials could prolong fish shelf life and decrease lipid oxidation. Animal-derived antimicrobials also have good antimicrobial activities; however, their allergen risk should be paid attention. Moreover, some algae and mushroom species can also provide a potential source of new natural preservatives. Obviously, the natural preservatives could perform better in fish storage by combining with other hurdles such as non-thermal sterilization processing, modified atmosphere packaging, edible films and coatings.

Antimicrobial Activity of a New Class of Phosphorylated and Modified Flavonoids

The surge of resistant food pathogens is a major threat worldwide. Previous research conducted on phytochemicals has shown their antibacterial activity against pathogenic bacteria. The design of antimicrobial agents to curb pathogenic disease remains a challenge demanding critical attention. Flavonoids such as apigenin and quercetin were evaluated against Gram-positive and Gram-negative bacteria. The results indicated that the antibacterial activity of each flavonoid occurred at a different minimum inhibitory concentration. However, the antimicrobial activity results of the modified flavonoids were also reported, and it was observed that the Gram-positive bacteria were more susceptible in comparison to the Gram-negative bacteria. The cell wall structure of the Gram-positive and Gram-negative bacteria could be the main reason for the bacteria susceptibility. Modified flavonoids could be used as a suitable alternative antimicrobial agent for the treatment of infectious diseases. Our results indicated 100% inhibition of Listeria monocytogenes, Pseudomonas aeruginosa, and Aeromonas hydrophila with modified flavonoids.

Synthesis of a Series of Chalcones and Related Flavones and Evaluation of their Antibacterial and Antifungal Activities

Background:

A series of chalcones and flavones were synthesized from 2’-hydroxyacetophenone and substituted aromatic aldehydes via Simmons-Schmidt condensation followed by oxidative cyclization.

Methods:

Characterization of the obtained structures was established on the basis of their spectroscopic data. The synthesized compounds were screened for their antimicrobial activities against five bacterial strains (Citrobacter freundii, Staphylococcus aureus, Listeria monocytogenes, Salmonella braenderup, Escherichia coli.) and two fungal strains (Candida albicans, Candida krusei).

Results:

The in vitro bioassay results indicated that some target compounds displayed moderate (4d, 4e) to high (4a) antifungal activity against the pathogenic fungi C. albicans and C. krusei.

Conclusion:

For the antibacterial activity, only products 3d and 4d showed a weak antibacterial activity. These compounds can lead to the design of new drugs with specific antifungal activity.

Chemical Composition of Selected Commercial Herbal Remedies in Relation to Geographical Origin and Inter-Species Diversity

Infusions prepared from medicinal herbs that are rich in flavonoids are very popular herbal remedies in societies of Eastern Europe. Therefore, the content of essential elements together with total flavonoids was analyzed in 65 commercially available samples of herbal drugs originating from Ukraine, Romania, and Belarus. The results showed that metallic elements (in mg kg^-1 d.w.) have occurred in the following order: Fe > Mn > Zn > Cu, both for total and water-extractable species. Total flavonoids were determined in the range from 10.0 to 191.8 mg g^-1 d.w. Several significant correlations have been found between the analytes, especially among water-extractable Fe with other metals, and total flavonoids and Fe, Zn, and Mn. Analysis of variance has revealed significant differences among studied samples due to their origin from different countries, especially between Belarussian samples and others. Differences owing to belonging to various plant species were also found, as it was noticed in the case of Polygoni aviculare herba in comparison with other botanical plant species. Moreover, multivariate statistical techniques, such as cluster analysis (CA) and principal component analysis (PCA) were used to gather herbal drugs based on similarity of chemical composition. CA grouped the samples into clusters with similar level of elements and total flavonoid contents, and PCA has indicated Hyperici herba, Tiliae flores, and Crataegi fructus as herbal remedies with close concentration of studied elements and flavonoids.

Phenolic compounds and biological effects of edible Rumex scutatus and Pseudosempervivum sempervivum: potential sources of natural agents with health benefits

The present study outlines a chemical characterization and further effects beneficial to health of edible Rumex scutatus and Pseudosempervivum sempervivum, in addition to presenting the antioxidant, enzyme inhibitory effects and antimicrobial properties of different extracts. The phenolic compounds composition of the extracts was assessed by RP-HPLC-DAD, outlining benzoic acid and rutin as major constituents in P. sempervivum and rutin and hesperidin in R. scutatus. Moreover, further biological effects were tested on key enzymes involved in diabetes mellitus, Alzheimer's disease and skin melanogenesis revealing an important tyrosinase inhibitory effect of Pseudosempervivum water extract. Moreover, both species possessed antimicrobial properties towards bacteria and fungi relevant to public health. Accordingly, we find that R. scutatus and P. sempervivum can be considered as novel functional foods because they are rich sources of biologically active compounds that provide health benefits.

Pharmacological and phytochemical screening of Palestinian traditional medicinal plants Erodium laciniatum and Lactuca orientalis

BACKGROUND

Various epidemiological studies showed that herbal remedies containing polyphenols may protect against various diseases such as cancers, vascular diseases and inflammatory pathologies. Currently, such groups of bioactive compounds have become a subject of many antimicrobials and antioxidant investigations. Accordingly, the current study aimed to conduct biological and phytochemical screening for two Palestinian traditional medicinal plants, Erodium laciniatum and Lactuca orientalis.

METHODS

Current plants phytoconstituents and their antioxidant activities were evaluated by using standard phytochemical methods; meanwhile, antimicrobial activities were estimated by using several types of American Type Culture Collection and multidrug resistant clinical isolates by using agar diffusion well-variant, agar diffusion disc-variant and broth microdilution methods.

RESULTS

Phytochemical screenings showed that L. orientalis and E. laciniatum contain mixtures of secondary and primary metabolites Moreover, total flavonoid, tannins and phenols content in E. laciniatum extract were higher than the L. orientalis extracts with almost the same antioxidant potentials. Additionally, both plants organic and aqueous extracts showed various potentials of antimicrobial activity Conclusions: Overall, the studied species have a mixture of phytochemicals, flavonoids, phenols and tannins also have antioxidant and antimicrobial activities which approved their folk uses in treatments of infectious and Alzheimer diseases and simultaneously can be used as therapeutic agents in the pharmaceutical industries.

Modulation of the growth and metabolic response of cyanobacteria by the multifaceted activity of naringenin

The interactions between the plant-derived bioflavonoid, naringenin, and prokaryotic microalgae representatives (cyanobacteria), were investigated with respect to its influence on the growth and metabolic response of these microorganisms. To achieve reliable results, the growth of cyanobacteria was determined based on measurements of chlorophyll content, morphological changes were assessed through microscopic observations, and the chemical response of cells was determined using liquid and gas chromatography (HPLC; GC-FID). The results show that micromolar levels of naringenin stimulated the growth of cyanobacteria. Increased growth was observed for halophilic strains at naringenin concentrations below 40 mg L-1, and in freshwater strains at concentrations below 20 mg L-1. The most remarkable stimulation was observed for the freshwater species Nostoc muscorum, which had a growth rate that was up to 60% higher than in the control. When naringenin was examined at concentrations above 40 mg L-1, the growth of the tested microorganisms was inhibited. Simultaneously, an intensive excretion of exopolysaccharides was observed. Microscopic observations strongly suggest that these effects resulted from a structural disturbance of cyanobacterial cell walls that was exerted by naringenin. This phenomenon, in combination with the absorption of naringenin into cell wall structures, influenced cell permeability and thus the growth of bacteria. Fortunately, almost all the naringenin added to the culture was incorporated into to cell substructures and could be recovered through extraction, raising the possibility that this modulator could be recycled.

A structural mechanism of flavonoids in inhibiting serine proteases

The crystal structure of quercerin:uPA reveals that catechol serves as the functional group in inhibiting serine proteases.

Anti-HSV-1 and HSV-2 Flavonoids and a New Kaempferol Triglycoside from the Medicinal Plant Kalanchoe daigremontiana

Kalanchoe daigremontiana (Crassulaceae) is a medicinal plant native to Madagascar. The aim of this study was to investigate the flavonoid content of an aqueous leaf extract from K. daigremontiana (Kd), and assess its antiherpetic potential. The major flavonoid, kaempferol 3-O-β-d-xylopyranosyl-(1 → 2)-α-l-rhamnopyranoside (1), was isolated from the AcOEt fraction (Kd-AC). The BuOH-soluble fraction afforded quercetin 3-O-β-d-xylopyranosyl-(1 → 2)-α-l-rhamnopyranoside (2) and the new kaempferol 3-O-β-d-xylopyranosyl-(1 → 2)-α-l-rhamnopyranoside-7-O-β-d-glucopyranoside (3), named daigremontrioside. The crude extract, Kd-AC fraction, flavonoids 1 and 2 were evaluated using acyclovir-sensitive strains of HSV-1 and HSV-2. Kd-AC was highly active against HSV-1 (EC₅₀  = 0.97 μg/ml, SI > 206.1) and HSV-2 (EC₅₀  = 0.72 μg/ml, SI > 277.7). Flavonoids 1 and 2 showed anti-HSV-1 (EC₅₀  = 7.4 μg/ml; SI > 27 and EC₅₀  = 5.8 μg/ml; SI > 8.6, respectively) and anti-HSV-2 (EC₅₀  = 9.0 μg/ml; SI > 22.2 and EC₅₀  = 36.2 μg/ml; SI > 5.5, respectively) activities, suggesting the contribution of additional substances to the antiviral activity.