Broad-spectrum antiviral activity of chebulagic acid and punicalagin against viruses that use glycosaminoglycans for entry

Potentiated virucidal activity of pomegranate rind extract (PRE) and punicalagin against Herpes simplex virus (HSV) when co-administered with zinc (II) ions, and antiviral activity of PRE against HSV and aciclovir-resistant HSV

Background

There is a clinical need for new therapeutic products against Herpes simplex virus (HSV). The pomegranate, fruit of the tree Punica granatum L, has since ancient times been linked to activity against infection. This work probed the activity of pomegranate rind extract (PRE) and co-administered zinc (II) ions.

Materials and methods

PRE was used in conjunction with zinc (II) salts to challenge HSV-1 and aciclovir-resistant HSV in terms of virucidal plaque assay reduction and antiviral activities in epithelial Vero host cells. Cytotoxicity was determined by the MTS assay using a commercial kit.

Results

Zinc sulphate, zinc citrate, zinc stearate and zinc gluconate demonstrated similar potentiated virucidal activity with PRE against HSV-1 by up to 4-fold. A generally parabolic relationship was observed when HSV-1 was challenged with PRE and varying concentrations of ZnSO₄, with a maximum potentiation factor of 5.5. Punicalagin had 8-fold greater virucidal activity than an equivalent mass of PRE. However, antiviral data showed that punicalagin had significantly lower antiviral activity compared to the activity of PRE (EC₅₀ = 0.56 μg mL^-1) a value comparable to aciclovir (EC₅₀ = 0.18 μg mL^-1); however, PRE also demonstrated potency against aciclovir-resistant HSV (EC₅₀ = 0.02 μg mL^-1), whereas aciclovir showed no activity. Antiviral action of PRE was not influenced by ZnSO₄. No cytotoxicity was detected with any test solution.

Conclusions

The potentiated virucidal activity of PRE by coadministered zinc (II) has potential as a multi-action novel topical therapeutic agent against HSV infections, such as coldsores.

Anti-HSV-2 activity of Terminalia chebula Retz extract and its constituents, chebulagic and chebulinic acids

Background

Development of new and effective therapeutics for sexually transmitted herpes simplex virus-2 (HSV-2) infection is important from public health perspective. With an aim to identify natural products from medicinal plants, in the present study, the potential of Terminalia chebula Retz was investigated for its activity against HSV-2.

Methods

Fruits of Terminalia chebula Retz were used to prepare 50% ethanolic extract. In addition, chebulagic acid and chebulinic acid both purified from T. chebula were also used. The extract as well as purified compounds were first used to determine their in vitro cytotoxicity on Vero cells by MTT assay. T. chebula extract, chebulagic acid, chebulinic acid along with acyclovir were subsequently assessed for direct anti-viral activity, and their ability to inhibit attachment and penetration of HSV-2 to the Vero cells. In addition, their anti-HSV-2 activity was also determined by in vitro post-infection plaque reduction assay.

Results

Cytotoxicity assay using Vero cells revealed CC₅₀ = 409.71 ± 47.70 μg/ml for the extract whereas chebulagic acid and chebulinic acid showed more than 95% cell viability up to 200 μg/ml. The extract from T. chebula (IC₅₀ = 0.01 ± 0.0002 μg/ml), chebulagic (IC₅₀ = 1.41 ± 0.51 μg/ml) and chebulinic acids (IC₅₀ = 0.06 ± 0.002 μg/ml) showed dose dependent potent in vitro direct anti-viral activity against HSV-2. These also effectively prevented the attachment as well as penetration of the HSV-2 to Vero cells. In comparison, acyclovir showed poor direct anti-viral activity and failed to significantly (p > 0.05) prevent the attachment as well as penetration of HSV-2 to Vero cells when tested upto 50 μg/ml. However, in post-infection plaque reduction assay, T. chebula extract, chebulagic and chebulinic acids showed IC₅₀ values of 50.06 ± 6.12, 31.84 ± 2.64, and 8.69 ± 2.09 μg/ml, respectively, which were much lower than acyclovir (71.80 ± 19.95 ng/ml).

Conclusions

The results presented herein suggest that T. chebula extract, chebulagic and chebulinic acids have higher direct antiviral activity against HSV-2 and efficacy to inhibit virus attachment and penetration to the host cells as compared to acyclovir. However, acyclovir is more potent to inhibit post-infection virus replication. Hence, T. chebula may be a useful candidate for developing alternative therapy for prevention of sexually transmitted HSV-2 infection.

Graphical abstract

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High-throughput screening for the identification of small-molecule inhibitors of the flaviviral protease

The mosquito-borne dengue virus serotypes 1-4 (DENV1-4) and West Nile virus (WNV) cause serious illnesses worldwide associated with considerable morbidity and mortality. According to the World Health Organization (WHO) estimates, there are about 390 million infections every year leading to ∼500,000 dengue haemorrhagic fever (DHF) cases and ∼25,000 deaths, mostly among children. Antiviral therapies could reduce the morbidity and mortality associated with flaviviral infections, but currently there are no drugs available for treatment. In this study, a high-throughput screening assay for the Dengue protease was employed to screen ∼120,000 small molecule compounds for identification of inhibitors. Eight of these inhibitors have been extensively analyzed for inhibition of the viral protease in vitro and cell-based viral replication using Renilla luciferase reporter replicon, infectivity (plaque) and cytotoxicity assays. Three of these compounds were identified as potent inhibitors of DENV and WNV proteases, and viral replication of DENV2 replicon and infectious RNA. Fluorescence quenching, kinetic analysis and molecular modeling of these inhibitors into the structure of NS2B-NS3 protease suggest a mode of inhibition for three compounds that they bind to the substrate binding pocket.

(4R,6S)-2-Dihydromenisdaurilide is a Butenolide that Efficiently Inhibits Hepatitis C Virus Entry

Without a vaccine, hepatitis C virus (HCV) remains a significant threat, putting 170–300 million carriers worldwide at risk of cirrhosis and hepatocellular carcinoma. Although the direct-acting antivirals targeting HCV replication have revolutionized the treatment of hepatitis C, several obstacles persist, including resistance development, potential side-effects, and the prohibitive cost that limits their availability. Furthermore, treatment of HCV re-infection in liver transplantation remains a significant challenge. Developing novel antivirals that target viral entry could help expand the scope of HCV therapeutics and treatment strategies. Herein, we report (4R,6S)-2-dihydromenisdaurilide (DHMD), a natural butenolide, as an efficient inhibitor of HCV entry. Specifically, DHMD potently inhibited HCV infection at non-cytotoxic concentration. Examination on the viral life cycle demonstrated that DHMD selectively targeted the early steps of infection while leaving viral replication/translation and assembly/release unaffected. Furthermore, DHMD did not induce an antiviral interferon response. Mechanistic dissection of HCV entry revealed that DHMD could inactivate cell-free virus, abrogate viral attachment, and inhibit viral entry/fusion, with the most pronounced effect observed against the viral adsorption phase as validated using ELISA and confocal microscopy. Due to its potency, DHMD may be of value for further development as an entry inhibitor against HCV, particularly for application in transplant setting.

Hepato-protective effects and chemical constituents of a bioactive fraction of the traditional compound medicine-Gurigumu-7

BACKGROUND

Gurigumu-7 is an important traditional Mongolian medicine frequently used for liver diseases. However, the pharmacological effects and the bioactive constituents are not well understood.

METHOD

This research was to use CCl4-induced liver damage in mice to investigate the hepatoprotective effects of Gurigumu-7 and the methanol eluted fraction from a DIAION column of an extract of Gurigumu-7 (MF). The chemical constituents of MF were analyzed by UPLC-MS.

RESULTS

Pretreated orally with MF (66, 132 and 264 mg/kg) once a day for 4 days dose-dependently suppressed CCl4-induced mice liver histopathological changes and serum aminotransferase activities (alanine transaminase: 1144.0 ± 787.2 v.s. 2461.8 ± 1072.7 U/L, p < 0.05; aspartate transaminase: 1173 ± 785.3 v.s. 2506.6 ± 1140.7 U/L, p < 0.01). MF treated group demonstrated increased levels of SOD (108.19 ± 30.32 v.s. 75.75 ± 5.37 U/mg protein, p < 0.01) but decreased levels of malonyldialdehyde (7.68 ± 1.95 v.s. 44.32 ± 16.68 nmol/mg protein, p < 0.01) compared to the CCl4 control group. More than 30 chemical constituents were quantified, and MF was found to be rich in ellagic acid (297.97 mg/g), luteolin and its glucosides (35.10 mg/g), apigenin and its glucosides (>30 mg/g), ursolic acid (14.91 mg/g), bidenoside C (8.75 mg/g), and proanthocyanidins (15.64 mg/g in proanthocyanidin A2 equivalent).

CONCLUSION

The methanol eluted fraction (MF) from a DIAION column of an extract of the Mongolian medicine-Gurigumu-7 was found to be more hepatoprotective than Gurigumu-7. The results suggested that MF is a promising bioactive fraction for the development of new hepatoprotective medicine with better formulation and quality control properties.

Comparison of pharmacokinetic profiles of Terminalia phenolics after intragastric administration of the aqueous extracts of the fruit of Terminalia chebula and a Mongolian compound medicine-Gurigumu-7

ETHNOPHARMACOLOGICAL RELEVANCE

The dried fruit of Terminalia chebula (fructus chebulae) is an important Traditional Medicine used for intestinal and hepatic detoxification. Gurigumu-7 which is made of fructus chebulae and 6 other traditional medicines is one of the most frequently used compound Mongolian and Tibet medicines for liver diseases. Terminalia phenolics are considered as the bioactive constituents of fructus chebulae and consequently of Gurigumu-7.

AIM OF THE STUDY

To compare the pharmacokinetic profiles of Terminalia phenolics after intragastric administration of the aqueous extracts of fructus chebulae and Gurigumu-7 and to evaluate the possible influence of intestinal bacterial metabolism on these pharmacokinetic profiles.

MATERIALS AND METHODS

An ultra performance liquid chromatography with triple quadrupole mass spectrometry method was established and validated for simultaneously determining the pharmacokinetic profiles of seven Terminalia phenolics after intragastric administration of pure compounds, fructus chebulae extract, and Gurigumu-7 extract. In vitro rat fecal lysates experiments were carried out to explore the metabolic discrepancy between fructus chebulae and Gurigumu-7.

RESULTS

Seven Terminalia phenolics were detected in rat plasma after intragastric administration of the aqueous extracts of fructus chebulae and Gurigumu-7. Administration of Gurigumu-7 could promote the absorption and increase the Cmax and AUC values of these phenolic constituents compared to fructus chebulae administration. The fecal lysates studies showed that the Terminalia phenolics in Gurigumu-7 were less rapidly bio-transformed than those in fructus chebulae. This may be a contributing factor to the pharmacokinetic discrepancy between the phenolics in fructus chebulae and Gurigumu-7.

CONCLUSION

Administration of Gurigumu-7 could increase the absorption of Terminalia phenolics through slowing down the intestinal bacteria metabolism. These results provide, in part, an in vivo rationale for the formulation of the traditional Mongolia / Tibet medicine, Gurigumu-7.

Scope of Hydrolysable Tannins as Possible Antimicrobial Agent

Hydrolysable tannins (HTs) are secondary metabolites from plants, which are roughly classified into gallotannins and ellagitannins having gallic acid and ellagic acid residues respectively attached to the hydroxyl group of glucose by ester linkage. The presence of hexahydroxydiphenoyl and nonahydroxyterphenoyl moieties is considered to render antimicrobial property to HTs. HTs also show considerable synergy with antibiotics. Nevertheless, they have low pharmacokinetic property. The present review presents the scope of HTs as future antimicrobial agent. Copyright © 2016 John Wiley & Sons, Ltd.

Activity-based and fraction-guided analysis of Phyllanthus urinaria identifies loliolide as a potent inhibitor of hepatitis C virus entry

Without a vaccine, hepatitis C virus (HCV) remains a global medical and socio-economic burden, predisposing about 170 million carriers worldwide to end-stage liver diseases including cirrhosis and hepatocellular carcinoma. Although the recently developed direct-acting antivirals (DAAs) have revolutionized hepatitis C treatment, most of them are unsuitable for monotherapy due to risks of resistance, thus necessitating combination with interferon (IFN)-alpha, ribavirin, or additional DAAs. More importantly, the high cost associated with the DAAs restricts their accessibility to most parts of the world. Developing novel cost-effective anti-HCV therapeutics may help expand the scope of antivirals and treatment strategies against hepatitis C. Herein, we applied an activity-based and fraction-guided analysis of extracts from the medicinal plant Phyllanthus urinaria (P. urinaria), which yielded fraction 13 (F13) as possessing the most potent inhibitory activity against early viral entry of cell-culture HCV infection. Chemical analysis (silica gel chromatography followed by ESI LC-MS plus (1)H and (13)C NMR) of F13 identified loliolide (LOD), a monoterpenoid lactone, as a novel inhibitor of HCV entry. Specifically, LOD could efficiently inactivate HCV free virus particles, abrogate viral attachment, and impede viral entry/fusion, with minimal effect on viral replication/translation, particle production, and induction of type I IFN host antiviral immune response. ELISA-based binding analysis confirmed the monoterpenoid's ability in efficiently blocking HCV particle attachment to the host cell surface. Furthermore, LOD could inhibit infection by several genotypic strains of HCV. This is the first report characterizing P. urinaria and its bioactive compound LOD as potent HCV entry inhibitors, which merit further evaluation for development as candidate antiviral agents against hepatitis C.

CD36 is a co-receptor for hepatitis C virus E1 protein attachment

The cluster of differentiation 36 (CD36) is a membrane protein related to lipid metabolism. We show that HCV infection in vitro increased CD36 expression in either surface or soluble form. HCV attachment was facilitated through a direct interaction between CD36 and HCV E1 protein, causing enhanced entry and replication. The HCV co-receptor effect of CD36 was independent of that of SR-BI. CD36 monoclonal antibodies neutralized the effect of CD36 and reduced HCV replication. CD36 inhibitor sulfo-N-succinimidyl oleate (SSO), which directly bound CD36 but not SR-BI, significantly interrupted HCV entry, and therefore inhibited HCV replication. SSO’s antiviral effect was seen only in HCV but not in other viruses. SSO in combination with known anti-HCV drugs showed additional inhibition against HCV. SSO was considerably safe in mice. Conclusively, CD36 interacts with HCV E1 and might be a co-receptor specific for HCV entry; thus, CD36 could be a potential drug target against HCV.

Chinese herbal medicines as a source of molecules with anti-enterovirus 71 activity

Enterovirus 71 (EV71) is one of the causative agents of hand, foot, and mouth disease (HFMD), which sometimes leads to severe neurological disease and death in the Asia-Pacific region. In Chinese medicine, HFMD is caused mainly by an accumulation of damp-heat and toxicity in the body. No effective drugs are currently available for the treatment and prevention of EV71 infection. This review summarizes the potential Chinese herbal extracts and isolated compounds with antiviral activity against EV71 and their clinical applications, especially those categorized as heat-clearing and detoxifying.

Punicalagin induces apoptosis-independent autophagic cell death in human papillary thyroid carcinoma BCPAP cells

Punicalagin induces apoptosis-independent autophagic cell death in BCPAP cells.

Activities of Tannins – from in Vitro Studies to Clinical Trials

Tannins are considered as valuable plant secondary metabolites providing many benefits for human health. In this review information was gathered about bioactivity in vitro and in vivo, as well as about conducted clinical trials. The literature research was based on ScienceDirect, Scopus, and Cochrane databases and presents a wide range of tested activities of tannins. The described clinical trials verify laboratory tests and show the effective health benefits taken from supplementation with tannins.

Early Viral Entry Assays for the Identification and Evaluation of Antiviral Compounds

Cell-based systems are useful for discovering antiviral agents. Dissecting the viral life cycle, particularly the early entry stages, allows a mechanistic approach to identify and evaluate antiviral agents that target specific steps of the viral entry. In this report, the methods of examining viral inactivation, viral attachment, and viral entry/fusion as antiviral assays for such purposes are described, using hepatitis C virus as a model. These assays should be useful for discovering novel antagonists/inhibitors to early viral entry and help expand the scope of candidate antiviral agents for further drug development.

Herbal plants and plant preparations as remedial approach for viral diseases

Herbal plants, plant preparations and phytoconstituents have proved useful in attenuating infectious conditions and were the only remedies available, till the advent of antibiotics (many being of plant origin themselves). Among infectious diseases, viral diseases in particular, remain the leading cause of death in humans globally. A variety of phytoconstituents derived from medicinal herbs have been extensively studied for antiviral activity. Based on this rationale, an online search was performed, which helped to identify a large number of plant species harboring antiviral molecules. These herbal sources have been reported individually or in combinations across a large number of citations studied. Activities against rabies virus, Human immunodeficiency virus, Chandipura virus, Japanese Encephalitis Virus, Enterovirus, Influenza A/H1N1 and other influenza viruses were discovered during the literature search. This review includes all such plant species exhibiting antiviral properties. The review also encompasses composition and methodologies of preparing various antiviral formulations around the globe. An elaborate section on the formulations filed for patent registration, along with non-patented formulations, has also been included in this article. To conclude, herbal sources provide researchers enormous scope to explore and bring out viable alternatives against viral diseases, considering non-availability of suitable drug candidates and increasing resistance to existing drug molecules for many emerging and re-emerging viral diseases.

Tannic Acid Inhibits Hepatitis C Virus Entry into Huh7.5 Cells

Chronic infection with the hepatitis C virus (HCV) is a cause of cirrhosis and hepatocellular carcinoma worldwide. Although antiviral therapy has dramatically improved recently, a number of patients remain untreated and some do not clear infection with treatment. Viral entry is an essential step in initiating and maintaining chronic HCV infections. One dramatic example of this is the nearly 100% infection of newly transplanted livers in patients with chronic hepatitis C. HCV entry inhibitors could play a critical role in preventing HCV infection of newly transplanted livers. Tannic acid, a polymer of gallic acid and glucose molecules, is a plant-derived polyphenol that defends some plants from insects and microbial infections. It has been shown to have a variety of biological effects, including antiviral activity, and is used as a flavoring agent in foods and beverages. In this study, we demonstrate that tannic acid is a potent inhibitor of HCV entry into Huh7.5 cells at low concentrations (IC₅₀ 5.8 μM). It also blocks cell-to-cell spread in infectious HCV cell cultures, but does not inhibit HCV replication following infection. Moreover, experimental results indicate that tannic acid inhibits an early step of viral entry, such as the docking of HCV at the cell surface. Gallic acid, tannic acid’s structural component, did not show any anti-HCV activity including inhibition of HCV entry or replication at concentrations up to 25 μM. It is possible the tannin structure is related on the effect on HCV inhibition. Tannic acid, which is widely distributed in plants and foods, has HCV antiviral activity in cell culture at low micromolar concentrations, may provide a relative inexpensive adjuvant to direct-acting HCV antivirals and warrants future investigation.

Therapeutic and prevention strategies against human enterovirus 71 infection

Human enterovirus 71 (HEV71) is the cause of hand, foot and mouth disease and associated neurological complications in children under five years of age. There has been an increase in HEV71 epidemic activity throughout the Asia-Pacific region in the past decade, and it is predicted to replace poliovirus as the extant neurotropic enterovirus of highest global public health significance. To date there is no effective antiviral treatment and no vaccine is available to prevent HEV71 infection. The increase in prevalence, virulence and geographic spread of HEV71 infection over the past decade provides increasing incentive for the development of new therapeutic and prevention strategies against this emerging viral infection. The current review focuses on the potential, advantages and disadvantages of these strategies. Since the explosion of outbreaks leading to large epidemics in China, research in natural therapeutic products has identified several groups of compounds with anti-HEV71 activities. Concurrently, the search for effective synthetic antivirals has produced promising results. Other therapeutic strategies including immunotherapy and the use of oligonucleotides have also been explored. A sound prevention strategy is crucial in order to control the spread of HEV71. To this end the ultimate goal is the rapid development, regulatory approval and widespread implementation of a safe and effective vaccine. The various forms of HEV71 vaccine designs are highlighted in this review. Given the rapid progress of research in this area, eradication of the virus is likely to be achieved.

Dengue virus entry and trafficking: perspectives as antiviral target for prevention and therapy

ABSTRACT 

Dengue virus (DENV) is the etiological agent of the most important human viral infection transmitted by mosquitoes in the world. In spite of the serious health threat that dengue represents, at present there are no vaccine or antiviral agents available and treatment of patients consists of supportive therapy. This review will focus on the process of DENV entry into the host cell as a potential target for antiviral therapy. The recent advances in the knowledge of viral and cellular molecules and mechanisms involved in binding, internalization and trafficking of DENV into the host cell until virion uncoating are discussed, together with an overview of the strategies and compounds evaluated for development of antiviral agents targeted to DENV entry.

TnBP⁄Triton X-45 treatment of plasma for transfusion efficiently inactivates hepatitis C virus

Risk of transmission of hepatitis C virus (HCV) by clinical plasma remains high in countries with a high prevalence of hepatitis C, justifying the implementation of viral inactivation treatments. In this study, we assessed the extent of inactivation of HCV during minipool solvent/detergent (SD; 1% TnBP / 1% Triton X-45) treatment of human plasma. Luciferase-tagged infectious cell culture-derived HCV (HCVcc) particles were used to spike human plasma prior to treatment by SD at 31 ± 0.5°C for 30 min. Samples were taken before and after SD treatment and filtered on a Sep-Pak Plus C18 cartridge to remove the SD agents. Risk of cytotoxicity was assessed by XTT cell viability assay. Viral infectivity was analyzed based on the luciferase signals, 50% tissue culture infectious dose viral titer, and immunofluorescence staining for HCV NS5A protein. Total protein, cholesterol, and triglyceride contents were determined before and after SD treatment and C18 cartridge filtration. Binding analysis, using patient-derived HCV clinical isolates, was also examined to validate the efficacy of the inactivation by SD. SD treatment effectively inactivated HCVcc within 30 min, as demonstrated by the baseline level of reporter signals, total loss of viral infectivity, and absence of viral protein NS5A. SD specifically targeted HCV particles to render them inactive, with essentially no effect on plasma protein content and hemostatic function. More importantly, the efficacy of the SD inactivation method was confirmed against various genotypes of patient-derived HCV clinical isolates and against HCVcc infection of primary human hepatocytes. Therefore, treatment by 1% TnBP / 1% Triton X-45 at 31°C is highly efficient to inactivate HCV in plasma for transfusion, showing its capacity to enhance the safety of therapeutic plasma products. We propose that the methodology used here to study HCV infectivity can be valuable in the validation of viral inactivation and removal processes of human plasma-derived products.

Antiviral drug discovery: broad-spectrum drugs from nature

Covering: up to April 2014. The development of drugs with broad-spectrum antiviral activities is a long pursued goal in drug discovery. It has been shown that blocking co-opted host-factors abrogates the replication of many viruses, yet the development of such host-targeting drugs has been met with scepticism mainly due to toxicity issues and poor translation to in vivo models. With the advent of new and more powerful screening assays and prediction tools, the idea of a drug that can efficiently treat a wide range of viral infections by blocking specific host functions has re-bloomed. Here we critically review the state-of-the-art in broad-spectrum antiviral drug discovery. We discuss putative targets and treatment strategies, with particular focus on natural products as promising starting points for antiviral lead development.

The anti-infective activity of punicalagin against Salmonella enterica subsp. enterica serovar typhimurium in mice

Punicalagin, a major bioactive component of pomegranate peel, has an anti-infective effect againstS. typhimuriuminfection in mice.

The mechanism of HCV entry into host cells

Hepatitis C virus (HCV) is an enveloped, positive strand RNA virus classified within the Flaviviridae family and is a major cause of liver disease worldwide. HCV life cycle and propagation are tightly linked to several aspects of lipid metabolism. HCV propagation depends on and also shapes several aspects of lipid metabolism such as cholesterol uptake and efflux through different lipoprotein receptors during its entry into cells, lipid metabolism modulating HCV genome replication, lipid droplets acting as a platform for recruitment of viral components, and very low density lipoprotein assembly pathway resulting in incorporation of neutral lipids and apolipoproteins into viral particles. During the first steps of infection, HCV enters hepatocytes through a multistep and slow process. The initial capture of HCV particles by glycosaminoglycans and/or lipoprotein receptors is followed by coordinated interactions with the scavenger receptor class B type I, a major receptor of high-density lipoprotein, the CD81 tetraspanin, and the tight junction proteins Claudin-1 and Occludin. This tight concert of receptor interactions ultimately leads to uptake and cellular internalization of HCV through a process of clathrin-dependent endocytosis. Over the years, the identification of the HCV entry receptors and cofactors has led to a better understanding of HCV entry and of the narrow tropism of HCV for the liver. Yet, the role of the two HCV envelope glycoproteins, E1 and E2, remains ill-defined, particularly concerning their involvement in the membrane fusion process. Here, we review the current knowledge and advances addressing the mechanism of HCV cell entry within hepatocytes and we highlight the challenges that remain to be addressed.

Tannic acid modified silver nanoparticles show antiviral activity in herpes simplex virus type 2 infection

The interaction between silver nanoparticles and herpesviruses is attracting great interest due to their antiviral activity and possibility to use as microbicides for oral and anogenital herpes. In this work, we demonstrate that tannic acid modified silver nanoparticles sized 13 nm, 33 nm and 46 nm are capable of reducing HSV-2 infectivity both in vitro and in vivo. The antiviral activity of tannic acid modified silver nanoparticles was size-related, required direct interaction and blocked virus attachment, penetration and further spread. All tested tannic acid modified silver nanoparticles reduced both infection and inflammatory reaction in the mouse model of HSV-2 infection when used at infection or for a post-infection treatment. Smaller-sized nanoparticles induced production of cytokines and chemokines important for anti-viral response. The corresponding control buffers with tannic acid showed inferior antiviral effects in vitro and were ineffective in blocking in vivo infection. Our results show that tannic acid modified silver nanoparticles are good candidates for microbicides used in treatment of herpesvirus infections.

Punicalagin inhibits Salmonella virulence factors and has anti-quorum-sensing potential

Punicalagin, an essential component of pomegranate rind, has been demonstrated to possess antimicrobial activity against several food-borne pathogens, but its activity on the virulence of pathogens and its anti-quorum-sensing (anti-QS) potential have been rarely reported. This study investigated the efficacy of subinhibitory concentrations of punicalagin on Salmonella virulence factors and QS systems. A broth microdilution method was used to determine the MICs of punicalagin for 10 Salmonella strains. Motility assay and quantitative reverse transcription (RT)-PCR were performed to evaluate the effects of punicalagin on the virulence attributes and QS-related genes of Salmonella. The MICs of punicalagin for several Salmonella strains ranged from 250 to 1,000 μg/ml. Motility assays showed that punicalagin, at 1/16× MIC and 1/32× MIC, significantly decreased bacterial swimming and swarming motility, which corresponded to downregulation of the motility-related genes (fliA, fliY, fljB, flhC, and fimD) in RT-PCR assays. RT-PCR also revealed that punicalagin downregulated the expression of most of the selected genes involved in Salmonella virulence. Moreover, a QS inhibition assay indicated that punicalagin dose dependently inhibited the production of violacein by Chromobacterium violaceum and repressed the expression of QS-related genes (sdiA and srgE) in Salmonella. In addition, punicalagin significantly reduced Salmonella invasion of colonic cells (P<0.01) with no impact on adhesion. These findings suggest that punicalagin has the potential to be developed as an alternative or supplemental agent for prevention of Salmonella infection.

Progress in the identification of dengue virus entry/fusion inhibitors

Dengue fever, a reemerging disease, is putting nearly 2.5 billion people at risk worldwide. The number of infections and the geographic extension of dengue fever infection have increased in the past decade. The disease is caused by the dengue virus, a flavivirus that uses mosquitos Aedes sp. as vectors. The disease has several clinical manifestations, from the mild cold-like illness to the more serious hemorrhagic dengue fever and dengue shock syndrome. Currently, there is no approved drug for the treatment of dengue disease or an effective vaccine to fight the virus. Therefore, the search for antivirals against dengue virus is an active field of research. As new possible receptors and biological pathways of the virus biology are discovered, new strategies are being undertaken to identify possible antiviral molecules. Several groups of researchers have targeted the initial step in the infection as a potential approach to interfere with the virus. The viral entry process is mediated by viral proteins and cellular receptor molecules that end up in the endocytosis of the virion, the fusion of both membranes, and the release of viral RNA in the cytoplasm. This review provides an overview of the targets and progress that has been made in the quest for dengue virus entry inhibitors.

Antiviral natural products and herbal medicines

Viral infections play an important role in human diseases, and recent outbreaks in the advent of globalization and ease of travel have underscored their prevention as a critical issue in safeguarding public health. Despite the progress made in immunization and drug development, many viruses lack preventive vaccines and efficient antiviral therapies, which are often beset by the generation of viral escape mutants. Thus, identifying novel antiviral drugs is of critical importance and natural products are an excellent source for such discoveries. In this mini-review, we summarize the antiviral effects reported for several natural products and herbal medicines.

A small molecule inhibits virion attachment to heparan sulfate- or sialic acid-containing glycans

Primary attachment to cellular glycans is a critical entry step for most human viruses. Some viruses, such as herpes simplex virus type 1 (HSV-1) and hepatitis C virus (HCV), bind to heparan sulfate, whereas others, such as influenza A virus (IAV), bind to sialic acid. Receptor mimetics that interfere with these interactions are active against viruses that bind to either heparan sulfate or to sialic acid. However, no molecule that inhibits the attachment of viruses in both groups has yet been identified. Epigallocatechin gallate (EGCG), a green tea catechin, is active against many unrelated viruses, including several that bind to heparan sulfate or to sialic acid. We sought to identify the basis for the broad-spectrum activity of EGCG. Here, we show that EGCG inhibits the infectivity of a diverse group of enveloped and nonenveloped human viruses. EGCG acts directly on the virions, without affecting the fluidity or integrity of the virion envelopes. Instead, EGCG interacts with virion surface proteins to inhibit the attachment of HSV-1, HCV, IAV, vaccinia virus, adenovirus, reovirus, and vesicular stomatitis virus (VSV) virions. We further show that EGCG competes with heparan sulfate for binding of HSV-1 and HCV virions and with sialic acid for binding of IAV virions. Therefore, EGCG inhibits unrelated viruses by a common mechanism. Most importantly, we have identified EGCG as the first broad-spectrum attachment inhibitor. Our results open the possibility for the development of small molecule broad-spectrum antivirals targeting virion attachment. Importance: This study shows that it is possible to develop a small molecule antiviral or microbicide active against the two largest groups of human viruses: those that bind to glycosaminoglycans and those that bind to sialoglycans. This group includes the vast majority of human viruses, including herpes simplex viruses, cytomegalovirus, influenza virus, poxvirus, hepatitis C virus, HIV, and many others.

Antiviral effects of Phyllanthus urinaria containing corilagin against human enterovirus 71 and Coxsackievirus A16 in vitro

Human enterovirus 71 (EV71) and Coxsackievirus A16 (CA16) are major causative agents of hand, foot, and mouth disease (HFMD) especially in infants and children under 5 years of age. Despite recent outbreaks of HFMD, there are no approved therapeutics against EV71 and CA16 infection. Moreover, in a small percentage of cases, the disease progression can lead to serious complications of the central nervous system. In this study, we investigated the antiviral effect of corilagin and Phyllanthus urinaria extract, which contains corilagin as a major component, on EV71 and CA16 infection in vitro. Our results indicate that corilagin reduces the cytotoxicity induced by EV71 or CA16 on Vero cells with and IC50 value of 5.6 and 32.33 μg/mL, respectively. We confirmed the presence of corilagin in EtOAc and BuOH fractions from P. urinaria extract and this correlated with antiviral activity of the fractions against EV71 or CA16. Future studies will be required to confirm the antiviral activity of corilagin and P. urinaria extract in vivo. Challenging a model with a lethal dose of viral infection will be required to test this. Collectively, our work provides potential candidates for the development of novel drugs to treat HFMD.

Tannins from Hamamelis virginiana bark extract: characterization and improvement of the antiviral efficacy against influenza A virus and human papillomavirus

Antiviral activity has been demonstrated for different tannin-rich plant extracts. Since tannins of different classes and molecular weights are often found together in plant extracts and may differ in their antiviral activity, we have compared the effect against influenza A virus (IAV) of Hamamelis virginiana L. bark extract, fractions enriched in tannins of different molecular weights and individual tannins of defined structures, including pseudotannins. We demonstrate antiviral activity of the bark extract against different IAV strains, including the recently emerged H7N9, and show for the first time that a tannin-rich extract inhibits human papillomavirus (HPV) type 16 infection. As the best performing antiviral candidate, we identified a highly potent fraction against both IAV and HPV, enriched in high molecular weight condensed tannins by ultrafiltration, a simple, reproducible and easily upscalable method. This ultrafiltration concentrate and the bark extract inhibited early and, to a minor extent, later steps in the IAV life cycle and tannin-dependently inhibited HPV attachment. We observed interesting mechanistic differences between tannin structures: High molecular weight tannin containing extracts and tannic acid (1702 g/mol) inhibited both IAV receptor binding and neuraminidase activity. In contrast, low molecular weight compounds (<500 g/mol) such as gallic acid, epigallocatechin gallate or hamamelitannin inhibited neuraminidase but not hemagglutination. Average molecular weight of the compounds seemed to positively correlate with receptor binding (but not neuraminidase) inhibition. In general, neuraminidase inhibition seemed to contribute little to the antiviral activity. Importantly, antiviral use of the ultrafiltration fraction enriched in high molecular weight condensed tannins and, to a lesser extent, the unfractionated bark extract was preferable over individual isolated compounds. These results are of interest for developing and improving plant-based antivirals.