Potential Antivirals: Natural Products Targeting Replication Enzymes of Dengue and Chikungunya Viruses

Ethyl palmitate, an anti-chikungunya virus principle from Sauropus androgynus, a medicinal plant used to alleviate fever in ethnomedicine

ETHNOPHARMACOLOGICAL RELEVANCE

Sauropus androgynus is a medicinal shrub used for the treatment of fever in ethnomedical traditions in various Southeast Asian countries.

AIM OF THE STUDY

This study was aimed to identify antiviral principles from S. androgynus against Chikungunya virus (CHIKV), a major mosquito-borne pathogen that re-emerged in the last decade, and to unravel their mechanism of action.

MATERIALS AND METHODS

Hydroalcoholic extract of S. androgynus leaves was screened for anti-CHIKV activity using cytopathic effect (CPE) reduction assay. The extract was subjected to activity guided isolation and the resultant pure molecule was characterized by GC-MS, Co-GC and Co-HPTLC. The isolated molecule was further evaluated for its effect by plaque reduction assay, Western blot and immunofluorescence assays. In silico docking with CHIKV envelope proteins and molecular dynamics simulation (MD) analyses were used to elucidate its possible mechanism of action.

RESULTS

S. androgynus hydroalcoholic extract showed promising anti-CHIKV activity and its active component, obtained by activity guided isolation, was identified as ethyl palmitate (EP), a fatty acid ester. At 1 μg/mL, EP led to 100% inhibition of CPE and a significant 3 log₁₀ reduction in CHIKV replication in Vero cells at 48 h post-infection. EP was highly potent with an EC₅₀ of 0.0019 μg/mL (0.0068 μM) and a very high selectivity index. EP treatment significantly reduced viral protein expression, and time of addition studies revealed that it acts at the stage of viral entry. A strong binding to the viral envelope protein E1 homotrimer during entry, thus preventing viral fusion, was identified as a possible mechanism by which EP imparts its antiviral effect.

CONCLUSIONS

S. androgynus contains EP as a potent antiviral principle against CHIKV. This justifies the use of the plant against febrile infections, possibly caused by viruses, in various ethnomedical systems. Our results also prompt more studies on fatty acids and their derivatives against viral diseases.

Effect of BaltPLA2, a phospholipase A2 from Bothrops alternatus snake venom, on the viability of cells infected with dengue virus

Dengue fever is considered a major public health problem in tropical and subtropical regions. Our study analyzed the effect of BaltPLA_2, a phospholipase A₂ from Bothrops alternatus snake venom, on the viability of cells infected with Dengue virus. In presence of BaltPLA₂, the viability of infected cells increased significantly in virucidal, post-treatment, and adsorption assays. Although preliminary these results reveal the need for further studies to investigated whether BaltPLA₂ has antiviral activity against Dengue virus.

Recent advances in natural products as potential inhibitors of dengue virus with a special emphasis on NS2b/NS3 protease

Dengue virus (DENV) is an arbovirus widespread through tropical and subtropical areas. It is transmitted to humans through Aedes mosquitoes. Infections with DENV can lead to a series of complications, including dengue fever, dengue haemorrhagic fever, or dengue shock syndrome, which might manifest through secondary infections because of a vulnerable immune system. To date, only one tetravalent DENV vaccine is approved to be administered to children whom have been previously DENV-infected and between 9 and 16 years of age. One of the key targets in discovering DENV antiviral agents is the NS2b/NS3 protease. This protease is a crucial enzyme complex for the proteolytic and cleavage activities of the translated polyprotein during DENV life cycle. Several studies were conducted to discover potential antivirals from natural sources or synthetic compounds and peptides. In this review, we describe the recent studies from the past five years dealing with isolated natural products as potential inhibitors of DENV with a greater focus on inhibiting the NS2b/NS3 protease. This review describes recent discoveries in anti-DENV potential of isolated phytochemicals belonging to different groups including fatty acids, glucosides, terpenes and terpenoids, flavonoids, phenolics, chalcones, acetamides, and peptides. Curcumin, quercetin, and myricetin were found to act as non-competitive inhibitors for the NS2b/NS3 protease enzyme. In some studies, the molecular targets of some of these compounds are yet to be identified using in-silico and in-vitro approaches. So far, none of the isolated natural products was tested clinically for the management of DENV infections. The discussed studies demonstrate that natural products are a rich source of potential anti-DENV compounds. However, not all of these compounds were studied for their kinetic molecular mechanism and type of inhibition. In-silico studies provided an ample number of phytochemical hits to be tested experimentally as DENV protease inhibitors. In conclusion, derivatives of these natural products can be designed and synthesised, which could enhance their specificity and efficacy towards the protease. Other sources of natural products, such as fungi, bacterial toxins, marine organisms, and animals, should also be explored towards discovering more potential and effective DENV NS2b/NS3 protease inhibitors.

In vitro antiviral activity of piperidine alkaloids from Senna spectabilis flowers on Chikungunya virus infection

BACKGROUND

Chikungunya fever is an endemic disease caused by the Chikungunya virus (CHIKV). To date there is no antiviral treatment against this infection or licensed vaccine to prevent it. Our study aims to evaluate whether (-)-cassine (1) and (-)-spectaline (2), the main alkaloids of Senna spectabilis, display anti-CHIKV activity. Both compounds have been described to be biologically active against neglected tropical diseases, including malaria, leishmaniasis, and schistosomiasis, which emphasizes that these molecules could be repurposed for chikungunya fever treatment.

METHODS

The structures of the isolated compounds 1 and 2 were identified by NMR and HRESIMS analyses, and their antiviral activity against CHIKV was assessed by a dose-response assay employing BHK-21 cells and CHIKV-nanoluc, a recombinant virus carrying the nanoluciferase gene reporter.

RESULTS

Compound 1 presented CC₅₀ of 126.5 µM and EC₅₀ of 14.9 µM, while compound 2 presented CC₅₀ of 91.9 µM and EC₅₀ of 8.3 µM. The calculated selectivity index (SI) was 8.5 for 1 and 11.3 for 2.

CONCLUSION

The data presented herein show that compounds 1 and 2 have potential for being repurposed as anti-CHIKV drug. Our promising in vitro results encourage further in vitro and in vivo assays. This is the first description of the antiviral activity of compounds 1 and 2 against CHIKV infection, which can impact the development of antiviral drug candidates against chikungunya fever, which sometimes can be debilitating.

Therapeutic Potential of Medicinal Plants against Dengue Infection: A Mechanistic Viewpoint

Dengue is a tropical disease caused by the Dengue virus (DENV), a positive-sense, single stranded RNA virus of the family Flaviviridae, which is transmitted by Aedes mosquitoes. The occurrence of dengue has grown dramatically around the globe in recent decades, and it is rapidly becoming a global burden. Furthermore, all four DENV serotypes cocirculate and create a problematic hyperendemic situation. Characteristic symptoms range from being asymptomatic, dengue fever to life-threatening complications such as hemorrhagic fever and shock. Apart from the inherent virulence of the virus strain, a dysregulated host immune response makes the condition worse. Currently, there is no highly recommended vaccine or therapeutic agent against dengue. With the advent of virus strains resistant to antiviral agents, there is a constant need for new therapies to be developed. Since time immemorial, human civilization has utilized plants in traditional medicine to treat various diseases, including infectious viral diseases. With the advancement in molecular biology, cell biology techniques, and bioinformatics, recent studies have tried to provide scientific evidence and determine the mechanism of anti-dengue activity of various plant extracts and plant-derived agents. The current Review consolidates the studies on the last 20 years of in vitro and in vivo experiments on the ethnomedicinal plants used against the dengue virus. Several active phytoconstituents like quercetin, castanospermine, α-mangostin, schisandrin-A, hirsutin have been found to be promising to inhibition of all the four DENV serotypes. However, novel therapeutics need to be reassessed in relevant cells using high-throughput techniques. Further, in vivo dose optimization for the immunomodulatory and antiviral activity should be examined on a vast sample size. Such a Review should help take the knowledge forward, validate it, and use medicinal plants in different combinations targeting multiple stages of virus infection for more effective multipronged therapy against dengue infection.

In Silico Elucidation of Potent Inhibitors from Natural Products for Nonstructural Proteins of Dengue Virus

Medicinal plants have been used from the beginning of human civilization against various health complications. Dengue virus (DENV) has emerged as one of the most widespread viruses in tropical and subtropical countries. Yet no clinically approved antiviral drug is available to combat DENV infection. Consequently, the search for novel antidengue agents from medicinal plants has assumed more insistence than in previous days. This study has focused on 31 potential antidengue molecules from secondary metabolites to examine their inhibitory activity against DENV nonstructural proteins through molecular docking and pharmacokinetics studies. In this research, the wet lab experiments were tested on a computational platform. Agathisflavone and pectolinarin are the top-scored inhibitors of DENV NS2B/NS3 protease and NS5 polymerase, respectively. Epigallocatechin gallate, Pinostrobin, Panduratin A, and Pectolinarin could be potential lead compounds against NS2B/NS3 protease, while acacetin-7-O-rutinoside against NS5 polymerase. Moreover, agathisflavone (LD50= 1430 mg/kg) and pectolinarin (LD50= 5000 mg/kg) exhibited less toxicity than nelfinavir (LD50= 600 mg/kg) and balapiravir (LD50 = 824 mg/kg), and the reference drugs. Further research on clinical trials is required to analyze the therapeutic efficacy of these metabolites to develop new potential drug candidates against different serotypes of DENV.

Anti-Dengue Screening on Several Vietnamese Medicinal Plants: Experimental Evidences and Computational Analyses

Worldwide, medicinal plants have been known for economic and geographical advantages, thus possibly holding potentiality against dengue hemorrhagic fever. The methanol/water extracts from different parts of fourteen Vietnam-based plant species were subjected for experimental screening on anti-dengue activity using baby hamster kidney cells (BHK21) and plaque reduction neutralisation test (PRNT). Firstly, the methanol/water extracts were tested against serotype dengue virus DENV-1. Seven out from nineteen extracts show the PRNT₅₀ values less than 31.25 μg/mL. Four of the above extracts namely from Euphorbia hirta, Cordyline terminalis, Carica papaya, and Elaeagnus latifolia were chosen for testing against the serotype DENV-2. All of them exhibit good activity with the PRNT₅₀ values less than 31.25 μg/ml, which were further fractionated to obtain hexane, ethyl acetate and butanol fractions. Anti-dengue virus activity of the fractions against four serotypes DENV-1, -2, -3 and -4 was evaluated. As results, the ethyl acetate fraction of Elaeagnus latifolia is highly active against all four serotype viruses. The structural formulae of its nine constituents were input for molecular docking simulation. The docking-based order for static inhibitability is 6-3L6P>7-3L6P>9-3L6P>2-3L6P>3-3L6P≈5-3L6P>9-3L6P>1-3L6P>8-3L6P; QSARIS-based analysis reveals the biocompatibility of the most promising ligands (4-7); ADMET-based analysis expects their pharmacological suitability. Exceptional finding on 2-3LKW hydrophilic interaction at Lys43 (with the associated Gibbs free energy of -10.3 kcal mol^-1 ) raises an open explanation for inhibitory effects. The results encourage further investigations for more in-depth mechanisms and drug development, such as in vitro enzyme assays or in vitro clinical trials with natural substances from E. latifolia.

In silico and in vitro evaluation of silibinin: a promising anti-Chikungunya agent

Chikungunya virus (CHIKV) infection and subsequent high patient morbidity is a global threat. The present study aimed to identify the potent antiviral agent against Chikungunya virus, with minimum in vitro cytotoxicity. CHIKV nsP4 3D structure was determined using the I-TASSER server followed by its refinement and pocket determination. Furthermore, high-throughput molecular docking was employed to identify candidate CHIKV nsP4 inhibitors in a library containing 214 compounds. The top ranked compound was evaluated further with various assays, including cytotoxicity, antiviral activity, time of drug addition, viral entry attachment, and microneutralization assays. High-throughput computational screening indicated silibinin to have the best interaction with CHIKV nsP4 protein, immature and mature glycoproteins with highest negative free binding energy, - 5.24 to - 5.86 kcal/mol, and the lowest inhibitory constant, 50.47 to 143.2 µM. Further in vitro analysis demonstrated silibinin could exhibit statistically significant (p < 0.05) dose-dependent anti-CHIKV activity within 12.5-100-µM concentrations with CC₅₀ as 50.90 µM. In total, 50 µM silibinin interfered with both CHIKV attachment (75%) and entry (82%) to Vero cells. Time of addition assay revealed silibinin interfered with late phase of the CHIKV replication cycle. Microneutralization assay revealed that silibinin could inhibit clearing of 50% Vero cell monolayer caused by CHIKV-induced CPE at a minimum dose of 25 µM. These data indicated silibinin to be a promising candidate drug against CHIKV infection.

Challenges, Advances and Opportunities in Exploring Natural Products to Control Arboviral Disease Vectors

Natural products constitute an important source of molecules for product development. However, despite numerous reports of compounds and active extracts from biodiversity, poor and developing countries continue to suffer with endemic diseases caused by arboviral vectors, including dengue, Zika, chikungunya and urban yellow fever. Vector control remains the most efficient disease prevention strategy. Wide and prolonged use of insecticides has resulted in vector resistance, making the search for new chemical prototypes imperative. Considering the potential of natural products chemistry for developing natural products-based products, including insecticides, this contribution discusses the general aspects and specific characteristics involved in the development of drug leads for vector control. Throughout this work, we highlight the obstacles that need to be overcome in order for natural products compounds to be considered promising prototypes. Moreover, we analyze the bottlenecks that should be addressed, together with potential strategies, to rationalize and improve the efficiency of the drug discovery process.

Immunomodulatory effects of Allium Sativum L. and its constituents against viral infections and metabolic diseases

BACKGROUND

Allium sativum L., or garlic, is one of the most studied plants worldwide within the field of traditional medicine. Current interests lie in the potential use of garlic as a preventive measure and adjuvant treatment for viral infections, e.g., SARS-CoV-2. Even though it cannot be presented as a single treatment, its beneficial effects are beyond doubt. The World Health Organization has deemed it an essential part of any balanced diet with immunomodulatory properties.

OBJECTIVE

The aim of the study was to review the literature on the effects of garlic compounds and preparations on immunomodulation and viral infection management, with emphasis on SARS-CoV-2.

METHOD

Exhaustive literature search has been carried out on electronic databases.

CONCLUSION

Garlic is a fundamental part of a well-balanced diet which helps maintain general good health. The reported information regarding garlic's ability to beneficially modulate inflammation and the immune system is encouraging. Nonetheless, more efforts must be made to understand the actual medicinal properties and mechanisms of action of the compounds found in this plant to inhibit or diminish viral infections, particularly SARS-CoV-2. Based on our findings, we propose a series of innovative strategies to achieve such a challenge in the near future.

Flavonoids as Molecules With Anti-Zika virus Activity

Zika virus (ZIKV) is an arthropod-born virus that is mainly transmitted to humans by mosquitoes of the genus Aedes spp. Since its first isolation in 1947, only a few human cases had been described until large outbreaks occurred on Yap Island (2007), French Polynesia (2013), and Brazil (2015). Most ZIKV-infected individuals are asymptomatic or present with a self-limiting disease and nonspecific symptoms such as fever, myalgia, and headache. However, in French Polynesia and Brazil, ZIKV outbreaks led to the diagnosis of congenital malformations and microcephaly in newborns and Guillain-Barré syndrome (GBS) in adults. These new clinical presentations raised concern from public health authorities and highlighted the need for anti-Zika treatments and vaccines to control the neurological damage caused by the virus. Despite many efforts in the search for an effective treatment, neither vaccines nor antiviral drugs have become available to control ZIKV infection and/or replication. Flavonoids, a class of natural compounds that are well-known for possessing several biological properties, have shown activity against different viruses. Additionally, the use of flavonoids in some countries as food supplements indicates that these molecules are nontoxic to humans. Thus, here, we summarize knowledge on the use of flavonoids as a source of anti-ZIKV molecules and discuss the gaps and challenges in this area before these compounds can be considered for further preclinical and clinical trials.

Natural-Product-Based Solutions for Tropical Infectious Diseases

About half of the world's population and 80% of the world's biodiversity can be found in the tropics. Many diseases are specific to the tropics, with at least 41 diseases caused by endemic bacteria, viruses, parasites, and fungi. Such diseases are of increasing concern, as the geographic range of tropical diseases is expanding due to climate change, urbanization, change in agricultural practices, deforestation, and loss of biodiversity. While traditional medicines have been used for centuries in the treatment of tropical diseases, the active natural compounds within these medicines remain largely unknown. In this review, we describe infectious diseases specific to the tropics, including their causative pathogens, modes of transmission, recent major outbreaks, and geographic locations. We further review current treatments for these tropical diseases, carefully consider the biodiscovery potential of the tropical biome, and discuss a range of technologies being used for drug development from natural resources. We provide a list of natural products with antimicrobial activity, detailing the source organisms and their effectiveness as treatment. We discuss how technological advancements, such as next-generation sequencing, are driving high-throughput natural product screening pipelines to identify compounds with therapeutic properties. This review demonstrates the impact natural products from the vast tropical biome have in the treatment of tropical infectious diseases and how high-throughput technical capacity will accelerate this discovery process.

Efficacy and sustainability of natural products in COVID-19 treatment development: opportunities and challenges in using agro-industrial waste from Citrus and apple

Natural products have been used in the treatment of illnesses throughout the history of humankind. Exploitation of bioactive compounds from natural sources can aid in the discovery of new drugs, provide the scaffold of new medicines. In the face of challenging diseases, such as the COVID-19 pandemic, for which there was no effective treatment, nature could offer insights as to novel therapeutic options for control measures. However, the environmental impact and supply chain of bioactive production must be carefully evaluated to ensure the detrimental effects will not outweigh the potential benefits gained. History has already proven that highly bioactive compounds can be rare and not suitable for medicinal exploitation; therefore, the sustainability must be accessed before expensive, time-demanding, and large trials can be initialized. A sustainable option to readily produce a phytotherapy with minimal environmental stress is the use of agro-industry wastes, a by-product produced in high quantities. In this review we evaluate the sustainability issues associated with the production of phytotherapy as a readily available tool for pandemic control.

Anti-SARS-CoV-2 Natural Products as Potentially Therapeutic Agents

Severe acute respiratory syndrome-related coronavirus-2 (SARS-CoV-2), a β-coronavirus, is the cause of the recently emerged pandemic and worldwide outbreak of respiratory disease. Researchers exchange information on COVID-19 to enable collaborative searches. Although there is as yet no effective antiviral agent, like tamiflu against influenza, to block SARS-CoV-2 infection to its host cells, various candidates to mitigate or treat the disease are currently being investigated. Several drugs are being screened for the ability to block virus entry on cell surfaces and/or block intracellular replication in host cells. Vaccine development is being pursued, invoking a better elucidation of the life cycle of the virus. SARS-CoV-2 recognizes O-acetylated neuraminic acids and also several membrane proteins, such as ACE2, as the result of evolutionary switches of O-Ac SA recognition specificities. To provide information related to the current development of possible anti-SARS-COV-2 viral agents, the current review deals with the known inhibitory compounds with low molecular weight. The molecules are mainly derived from natural products of plant sources by screening or chemical synthesis via molecular simulations. Artificial intelligence-based computational simulation for drug designation and large-scale inhibitor screening have recently been performed. Structure-activity relationship of the anti-SARS-CoV-2 natural compounds is discussed.

Quercetin can reduce viral RNA level of O'nyong-nyong virus and resulting innate immune cytokine responses in cultured human synovial fibroblasts

O’nyong-nyong virus is an alphavirus closely related to chikungunya virus, causing arthralgia, rash and fever. Alphaviruses mainly target synovial fibroblasts and persists in the joints of patients, possibly leading to chronic arthritis. To date, no specific antiviral treatment is available for ONNV infection and induced-inflammation. Primary human synovial fibroblasts cells were used to assess infection by ONNV and the resulting cytokine responses. Phenolics (gallic acid, caffeic acid and chlorogenic acid, curcumin and quercetin) and a curcuminoids-rich extract from turmeric were tested for their antiviral and anti-inflammatory capacities. We showed that infection occurred in HSF cells and increased gene expression and protein secretion of two major proinflammatory CCL-2 and IL-1β markers. In ONNV-infected HSF cells (MOI 1), we found that non-cytotoxic concentrations of phenolics (10 µM) reduced the level of viral RNA (E1, E2, nsP1, nsP2) and downregulated CCL-2 and IL-1β expression and secretion. These results highlighted the high value of the flavonol quercetin to reduce viral RNA levels and inflammatory status induced by ONNV in HSF cells.

Antiviral potential of garlic (Allium sativum) and its organosulfur compounds: A systematic update of pre-clinical and clinical data

BACKGROUND

Garlic (Allium sativum L.) is a common herb consumed worldwide as functional food and traditional remedy for the prevention of infectious diseases since ancient time. Garlic and its active organosulfur compounds (OSCs) have been reported to alleviate a number of viral infections in pre-clinical and clinical investigations. However, so far no systematic review on its antiviral effects and the underlying molecular mechanisms exists.

SCOPE AND APPROACH

The aim of this review is to systematically summarize pre-clinical and clinical investigations on antiviral effects of garlic and its OSCs as well as to further analyse recent findings on the mechanisms that underpin these antiviral actions. PubMed, Cochrane library, Google Scholar and Science Direct databases were searched and articles up to June 2020 were included in this review.

KEY FINDINGS AND CONCLUSIONS

Pre-clinical data demonstrated that garlic and its OSCs have potential antiviral activity against different human, animal and plant pathogenic viruses through blocking viral entry into host cells, inhibiting viral RNA polymerase, reverse transcriptase, DNA synthesis and immediate-early gene 1(IEG1) transcription, as well as through downregulating the extracellular-signal-regulated kinase (ERK)/mitogen activated protein kinase (MAPK) signaling pathway. The alleviation of viral infection was also shown to link with immunomodulatory effects of garlic and its OSCs. Clinical studies further demonstrated a prophylactic effect of garlic in the prevention of widespread viral infections in humans through enhancing the immune response. This review highlights that garlic possesses significant antiviral activity and can be used prophylactically in the prevention of viral infections.

Current approaches for target-specific drug discovery using natural compounds against SARS-CoV-2 infection

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The pandemic of COVID-19 remains to affect the whole world.

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Current remedies for COVID-19 is not satisfactory/available.

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The therapeutic efficacy of Natural Compounds is well explored in various viral infections.

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Natural Compounds could be explored as target specific therapeutic agents against COVID-19 infection.

The severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) recently caused a pandemic outbreak called coronavirus disease 2019 (COVID-19). This disease has initially been reported in China and also now it is expeditiously spreading around the globe directly among individuals through coughing and sneezing. Since it is a newly emerging viral disease and obviously there is a lack of anti-SARS-CoV-2 therapeutic agents, it is urgently required to develop an effective anti-SARS-CoV-2-agent.Through recent advancements in computational biology and biological assays, several natural compounds and their derivatives have been reported to confirm their target specific antiviral potential against Middle East respiratory syndrome coronavirus (MERS-CoV) or Severe Acute Respiratory Syndrome(SARS-CoV).These targets including an important host cell receptor, i.e., angiotensin-converting enzyme ACE2 and several viral proteins e.g. spike glycoprotein (S) containing S1 and S2 domains, SARS CoV Chymotrypsin-like cysteine protease (3CL^pro), papain-like cysteine protease (PL^pro), helicases and RNA-dependent RNA polymerase (RdRp). Due to physical, chemical, and some genetic similarities of SARS CoV-2 with SARS−COV and MERS−COV, repurposing various anti-SARS−COV or anti-MERS−COV natural therapeutic agents could be helpful for the development of anti−COVID-19 herbal medicine. Here we have summarized various drug targets in SARS−COV and MERS−COV using several natural products and their derivatives, which could guide researchers to design and develop a safe and cost-effective anti-SARS−COV-2 drugs.

Review of Phytochemical Compounds as Antiviral Agents Against Arboviruses from the Genera Flavivirus and Alphavirus

Arboviruses are a diverse group of viruses that are among the major causes of emerging infectious diseases. Arboviruses from the genera flavivirus and alphavirus are the most important human arboviruses from a public health perspective. During recent decades, these viruses have been responsible for millions of infections and deaths around the world. Over the past few years, several investigations have been carried out to identify antiviral agents to treat these arbovirus infections. The use of synthetic antiviral compounds is often unsatisfactory since they may raise the risk of viral mutation; they are costly and possess either side effects or toxicity. One attractive strategy is the use of plants as promising sources of novel antiviral compounds that present significant inhibitory effects on these viruses. In this review, we describe advances in the exploitation of compounds and extracts from natural sources that target the vital proteins and enzymes involved in arbovirus replication.

Antiviral Natural Products for Arbovirus Infections

Over the course of the last 50 years, the emergence of several arboviruses have resulted in countless outbreaks globally. With a high proportion of infections occurring in tropical and subtropical regions where arthropods tend to be abundant, Asia in particular is a region that is heavily affected by arboviral diseases caused by dengue, Japanese encephalitis, West Nile, Zika, and chikungunya viruses. Major gaps in protection against the most significant emerging arboviruses remains as there are currently no antivirals available, and vaccines are only available for some. A potential source of antiviral compounds could be discovered in natural products—such as vegetables, fruits, flowers, herbal plants, marine organisms and microorganisms—from which various compounds have been documented to exhibit antiviral activities and are expected to have good tolerability and minimal side effects. Polyphenols and plant extracts have been extensively studied for their antiviral properties against arboviruses and have demonstrated promising results. With an abundance of natural products to screen for new antiviral compounds, it is highly optimistic that natural products will continue to play an important role in contributing to antiviral drug development and in reducing the global infection burden of arboviruses.

Natural products' role against COVID-19

COVID-19 is a viral disease caused by a new severe acute respiratory syndrome (SARS-CoV-2), which has quickly resulted in a pandemic. As a great threat to global public health, the development of a treatment has become vital, and a rush to find a cure has mobilized researchers from all areas across the world. Synthetic drugs, such as hydroxychloroquine, have gained attention. However, the efficacy of repositioned drugs is still under evaluation, and besides, some severe side effects are a cause for concern. This emphasizes the urgency for treatment options, which can be both safe and effective. With this in mind, natural products could be an important resource in the development of COVID-19 treatment, as they have already contributed in the past to treatments against other viruses, such as HIV, MERS-CoV, and influenza. Natural products are described long term as bioactive substances and some phytochemical classes such as flavonoids, alkaloids, and peptides are known antiviral bioproducts, and have been virtually tested with success against COVID-19. However, important issues still need to be addressed as to their bioavailability and true efficacy in vivo. This review intends to systematically evaluate the natural metabolites that could potentially be used against this new disease looking at their natural sources, mechanism of action and previous pharmacological usages. The aim is to provide a starting point for this research area in order to speed up the establishment of anti-SARS-CoV-2 bioproducts.

Natural products and their derivatives against coronavirus: A review of the non-clinical and pre-clinical data

Several corona viral infections have created serious threats in the last couple of decades claiming the death of thousands of human beings. Recently, corona viral epidemic raised the issue of developing effective antiviral agents at the earliest to prevent further losses. Natural products have always played a crucial role in drug development process against various diseases, which resulted in screening of such agents to combat emergent mutants of corona virus. This review focuses on those natural compounds that showed promising results against corona viruses. Although inhibition of viral replication is often considered as a general mechanism for antiviral activity of most of the natural products, studies have shown that some natural products can interact with key viral proteins that are associated with virulence. In this context, some of the natural products have antiviral activity in the nanomolar concentration (e.g., lycorine, homoharringtonine, silvestrol, ouabain, tylophorine, and 7-methoxycryptopleurine) and could be leads for further drug development on their own or as a template for drug design. In addition, a good number of natural products with anti-corona virus activity are the major constituents of some common dietary supplements, which can be exploited to improve the immunity of the general population in certain epidemics.

Antiviral therapeutics for chikungunya virus

Introduction: Chikungunya virus (CHIKV), a reemerging human arthropod borne virus, can causes global epidemic outbreaks and has become a serious health concern due to the unavailability of any antiviral therapy/vaccine. Extensive research has been conducted to target different proteins from CHIKV to curtail the spread of virus.Areas covered: This review provides an overview of the granted patents including the current status of antiviral strategies targeting CHIKV.Expert opinion: Under the current scenario, potential molecules and different approaches have been utilized to suppress CHIKV infection. MV-CHIKV and VRC-CHKVLP059-00-VP vaccine candidates have successfully completed phase I clinical trials and ribavirin (inhibitor) has shown significant inhibition of CHIKV replication and could be the most promising candidates. The drug resistance and toxicity can be modulated by using the inhibitors/drugs in combination. Moreover, nanoparticle formulations can improve the efficacy and bioavailability of drugs.

MCP-1 LEVELS AND ATYPICAL LYMPHOCYTES IN EARLY FEVER OF DENGUE VIRUS INFECTION WITH NON-STRUCTURAL PROTEIN 1 (NS-1) ANTIGEN TEST IN dr DARSONO HOSPITAL, PACITAN

Dengue infection caused by DENV and transmitted by mosquitoes Aedes aegypti and Aedes albopictus is a major health problem in the world, including Indonesia. Clinical manifestations of dengue infection are very widely, from asymptomatic until dengue shock syndrome (DSS). DENV will attack macrophages and dendritic cells (DC) and replicate them. Monocytes are macrophages in the blood (±10% leukocytes). Macrophages produce cytokines and chemokines such as monocyte chemotactic protein-1 (MCP-1)/CCL2. The monocytes that are infected with DENV will express MCP-1, which will increase the permeability of vascular endothelial cells so that they have a risk of developing DHF/DSS. Macrophages and DC secrete NS1 proteins, which are the co-factors that are needed for viral replication and can be detected in the early phase of fever. The increased MCP-1 levels in dengue infection followed by an increase in the number of atypical lymphocytes indicate the arrival of macrophages and monocytes to the site of inflammation which triggers proliferation rather than lymphocytes. This is an observational analytical study with a cross-sectional design to determine the MCP-1 level in dengue infection patients with 1st until the 4th day of fever and the presence of atypical lymphocytes. Dengue infection was determined by rapid tests NS1 positive or negative and MCP-1 levels were measured using by ELISA sandwich method.MCP-1 level of sixty patients dengue infection NS-1 rapid positive or negative with 2nd until 4rt fever were significantly higher than healthy subjects (420.263±158,496vs29, 475±23.443;p=0.000), but there was no significant difference in subjects with DF, DHF or DSS (436,47±225,59 vs422,77±170,55vs 448,50±117,39; p =0.844). Atypicallymphosite differs significantly in healthy  subjects than subjects infected with DENV an average of 2% (p= 0,000). In conclusion, this shows the arrival of macrophages and monocytes to the site of inflammation, which triggers the proliferation of lymphocytes.

In silico drug repurposing for the identification of potential candidate molecules against arboviruses infection

Arboviral diseases caused by dengue (DENV), Zika (ZIKV) and chikungunya (CHIKV) viruses represent a major public health problem worldwide, especially in tropical areas where millions of infections occur every year. The aim of this research was to identify candidate molecules for the treatment of these diseases among the drugs currently available in the market, through in silico screening and subsequent in vitro evaluation with cell culture models of DENV and ZIKV infections. Numerous pharmaceutical compounds from antibiotics to chemotherapeutic agents presented high in silico binding affinity for the viral proteins, including ergotamine, antrafenine, natamycin, pranlukast, nilotinib, itraconazole, conivaptan and novobiocin. These five last compounds were tested in vitro, being pranlukast the one that exhibited the best antiviral activity. Further in vitro assays for this compound showed a significant inhibitory effect on DENV and ZIKV infection of human monocytic cells and human hepatocytes (Huh-7 cells) with potential abrogation of virus entry. Finally, intrinsic fluorescence analyses suggest that pranlukast may have some level of interaction with three viral proteins of DENV: envelope, capsid, and NS1. Due to its promising results, suitable accessibility in the market and reduced restrictions compared to other pharmaceuticals; the anti-asthmatic pranlukast is proposed as a drug candidate against DENV, ZIKV, and CHIKV, supporting further in vitro and in vivo assessment of the potential of this and other lead compounds that exhibited good affinity scores in silico as therapeutic agents or scaffolds for the development of new drugs against arboviral diseases.

Molecular characteristics and replication mechanism of dengue, zika and chikungunya arboviruses, and their treatments with natural extracts from plants: An updated review

Viruses transmitted by arthropods (arboviruses) are the etiological agents of several human diseases with worldwide distribution; including dengue (DENV), zika (ZIKV), yellow fever (YFV), and chikungunya (CHIKV) viruses. These viruses are especially important in tropical and subtropical regions; where, ZIKV and CHIKV are involved in epidemics worldwide, while the DENV remains as the biggest problem in public health. Factors, such as, environmental conditions promote the distribution of vectors, deficiencies in health services, and lack of effective vaccines, guarantee the presence of these vector-borne diseases. Treatment against these viral diseases is only palliative since available therapies formulated lack to demonstrate specific antiviral activity and vaccine candidates fail to demonstrate enough effectiveness. The use of natural products, as therapeutic tools, is an ancestral practice in different cultures. According to WHO 80 % of the population of some countries from Africa and Asia depend on the use of traditional medicines to deal with some diseases. Molecular characteristics of these viruses are important in determining its cellular pathogenesis, emergence, and dispersion mechanisms, as well as for the development of new antivirals and vaccines to control strategies. In this review, we summarize the current knowledge of the molecular structure and replication mechanisms of selected arboviruses, as well as their mechanism of entry into host cells, and a brief overview about the potential targets accessed to inhibit these viruses in vitro and a summary about their treatment with natural extracts from plants.

Computer-Assisted and Data Driven Approaches for Surveillance, Drug Discovery, and Vaccine Design for the Zika Virus

Human life has been at the edge of catastrophe for millennia due diseases which emerge and reemerge at random. The recent outbreak of the Zika virus (ZIKV) is one such menace that shook the global public health community abruptly. Modern technologies, including computational tools as well as experimental approaches, need to be harnessed fast and effectively in a coordinated manner in order to properly address such challenges. In this paper, based on our earlier research, we have proposed a four-pronged approach to tackle the emerging pathogens like ZIKV: (a) Epidemiological modelling of spread mechanisms of ZIKV; (b) assessment of the public health risk of newly emerging strains of the pathogens by comparing them with existing strains/pathogens using fast computational sequence comparison methods; (c) implementation of vaccine design methods in order to produce a set of probable peptide vaccine candidates for quick synthesis/production and testing in the laboratory; and (d) designing of novel therapeutic molecules and their laboratory testing as well as validation of new drugs or repurposing of drugs for use against ZIKV. For each of these stages, we provide an extensive review of the technical challenges and current state-of-the-art. Further, we outline the future areas of research and discuss how they can work together to proactively combat ZIKV or future emerging pathogens.

ANTI-DENGUE TYPE 2 VIRUS ACTIVITIES OF ZINC (II) COMPLEX COMPOUNDS WITH 2-(2,4 -DIHYDROXYPHENYL)-3,5,7-TRIHYDROXYCROMEN-4-ONE LIGANDS IN VERO CELLS

Dengue virus (DENV) is a disease that is transmitted through Aedes aegypti and Aedes albopictus mosquitoes, and is spread in tropical and sub-tropical regions. Now, dengue or antiviral vaccines for humans do not yet exist, but there are great efforts to achieve this goal. Complex compounds are reported to fungicidal, bactericidal and antiviral activity. Antiviral activity against DENV is an important alternative to the characterization and development of drugs candidate. The purpose of this study was to study zinc(II) compounds with 2-(2,4-dihydroxyphenyl)-3,5,7-trihydroxycromen-4-one ligand on DENV-2 replication in Vero cells. Vero cell lines (African green monkey kidney) was used in this study, maintained and propagated in Minimum Essential Eagle Medium containing 10% fetal bovine serum at 37°C in 5% CO2. The activity of dengue virus was carried out by enzyme-immunosorbent assay (ELISA) method and CellTiter96® Non-Radioactive Proliferation. The value of activity inhibition (IC50) of complex compounds with variations of mol metal: ligand 1:2, 1:3, and 1:4 against dengue virus type 2 (DENV2) was 2.44 μg/ml, 2.75 μg/ml, respectively and 2.00 μg/ml, also the toxicity value (CC50) of complex compounds with variation mol metal: ligand 1:4 for Vero cells is 3.59 μg/ml. The results of this study were indicate that these properties have been shown to inhibit anti-dengue type 2 virus (DENV-2), but are also toxic in Vero cells. Including previous study about complex compound interaction with dengue virus type 2 activity, Zn(II) more reactive compound then Cu(II), and Co(II). The comparison with Cu(II) complex compound, it has been revealed that Co(II) and Zn(II) is more toxic, was found to be nontoxic to human erythrocyte cells even at a concentration of 500 μg/ml.

Investigational drugs for the treatment of Zika virus infection: a preclinical and clinical update

INTRODUCTION

The Zika virus (ZIKV) infection results in severe neurological complications and has emerged as a threat to public health worldwide. No drugs or vaccines are available for use in the clinic and the need for novel and effective therapeutic agents is urgent.

AREAS COVERED

This review describes the latest progress of antiviral development for the treatment of ZIKV infection; it primarily focuses on the literature describing 20 potential anti-ZIKV drugs/agents currently being tested in vivo or in clinical trials. The paper also discusses the need for novel ZIKV inhibitors and the critical issues for successful antiviral drug development.

EXPERT OPINION

So far, 20 compounds have been tested in vivo and three in the clinical trials; progressing these compounds to the clinic is a challenge. Novel ZIKV inhibitors that target virus or host factors are urgently needed. Knowledge-driven drug repurposing, structure-based discovery, RNA interference, long noncoding RNAs, miRNAs, and peptide inhibitors may pave the way for the discovery of such novel agents.

Lucidone suppresses dengue viral replication through the induction of heme oxygenase-1

Dengue virus (DENV) infection causes life-threatening diseases such as dengue hemorrhagic fever and dengue shock syndrome. Currently, there is no effective therapeutic agent or vaccine against DENV infection; hence, there is an urgent need to discover anti-DENV agents. The potential therapeutic efficacy of lucidone was first evaluated in vivo using a DENV-infected Institute of Cancer Research (ICR) suckling mouse model by monitoring body weight, clinical score, survival rate, and viral titer. We found that lucidone effectively protected mice from DENV infection by sustaining survival rate and reducing viral titers in DENV-infected ICR suckling mice. Then, the anti-DENV activity of lucidone was confirmed by western blotting and quantitative-reverse-transcription-polymerase chain reaction analysis, with an EC₅₀ value of 25 ± 3 μM. Lucidone significantly induced heme oxygenase-1 (HO-1) production against DENV replication by inhibiting DENV NS2B/3 protease activity to induce the DENV-suppressed antiviral interferon response. The inhibitory effect of lucidone on DENV replication was attenuated by silencing of HO-1 gene expression or blocking HO-1 activity. In addition, lucidone-stimulated nuclear factor erythroid 2-related factor 2 (Nrf2), which is involved in transactivation of HO-1 expression for its anti-DENV activity. Taken together, the mechanistic investigations revealed that lucidone exhibits significant anti-DENV activity in in vivo and in vitro by inducing Nrf2-mediated HO-1 expression, leading to blockage of viral protease activity to induce the anti-viral interferon (IFN) response. These results suggest that lucidone is a promising candidate for drug development.

Taking a bite out of nutrition and arbovirus infection

Nutrition is a key factor in host–pathogen defense. Malnutrition can increase both host susceptibility and severity of infection through a number of pathways, and infection itself can promote nutritional deterioration and further susceptibility. Nutritional status can also strongly influence response to vaccination or therapeutic pharmaceuticals. Arthropod-borne viruses (arboviruses) have a long history of infecting humans, resulting in regular pandemics as well as an increasing frequency of autochthonous transmission. Interestingly, aside from host-related factors, nutrition could also play a role in the competence of vectors required for transmission of these viruses. Nutritional status of the host and vector could even influence viral evolution itself. Therefore, it is vital to understand the role of nutrition in the arbovirus lifecycle. This Review will focus on nutritional factors that could influence susceptibility and severity of infection in the host, response to prophylactic and therapeutic strategies, vector competence, and viral evolution.

As the old adage goes, you are what you eat. Proper nutrition is a cornerstone of health, and malnutrition can seriously impair the function of the immune system, resulting in increased infections or a more severe disease. Imbalanced or inadequate nutrition can also affect responses to vaccines or drugs that are vital for protection and treatment against viruses. A mosquito is also a product of what it eats. Nutrition during development and adult lifecycle can affect the feeding behavior of mosquitoes, thereby affecting transmission of viral diseases. Arthropod-borne viruses (arboviruses) are a major global health concern, especially in areas impacted by malnutrition. Understanding how nutrition can affect both humans and mosquitoes in the context of these viruses is vital to combating these diseases.

Hirsutine, an Indole Alkaloid of Uncaria rhynchophylla, Inhibits Late Step in Dengue Virus Lifecycle

Dengue virus (DENV) is transmitted to humans by Aedes mosquitoes and is a public health issue worldwide. No antiviral drugs specific for treating dengue infection are currently available. To identify novel DENV inhibitors, we analyzed a library of 95 compounds and 120 extracts derived from crude drugs (herbal medicines). In the primary screening, A549 cells infected with DENV-1 were cultured in the presence of each compound and extract at a final concentration of 10 μM (compound) and 100 μg/mL (extract), and reduction of viral focus formation was assessed. Next, we eliminated compounds and extracts which were cytotoxic using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Hirsutine, an indole alkaloid of Uncaria rhynchophylla, was identified as a potent anti-DENV compound exhibiting high efficacy and low cytotoxicity. Hirsutine showed antiviral activity against all DENV serotypes. Time-of-drug-addition and time-of-drug-elimination assays indicated that hirsutine inhibits the viral particle assembly, budding, or release step but not the viral translation and replication steps in the DENV lifecycle. A subgenomic replicon system was used to confirm that hirsutine does not restrict viral genome RNA replication. Hirsutine is a novel DENV inhibitor and potential candidate for treating dengue fever.

In silico analysis of natural compounds targeting structural and nonstructural proteins of chikungunya virus

Background: Chikungunya fever presents as a high-grade fever during its acute febrile phase and can be prolonged for months as chronic arthritis in affected individuals. Currently, there are no effective drugs or vaccines against this virus. The present study was undertaken to evaluate protein-ligand interactions of all chikungunya virus (CHIKV) proteins with natural compounds from a MolBase library in order to identify potential inhibitors of CHIKV. Methods: Virtual screening of the natural compound library against four non-structural and five structural proteins of CHIKV was performed. Homology models of the viral proteins with unknown structures were created and energy minimized by molecular dynamic simulations. Molecular docking was performed to identify the potential inhibitors for CHIKV. The absorption, distribution, metabolism and excretion (ADME) toxicity parameters for the potential inhibitors were predicted for further prioritization of the compounds. Results: Our analysis predicted three compounds, Catechin-5-O-gallate, Rosmarinic acid and Arjungenin, to interact with CHIKV proteins; two (Catechin-5-O-gallate and Rosmarinic acid) with capsid protein, and one (Arjungenin) with the E3. Conclusion: The compounds identified show promise as potential antivirals, but further in vitro studies are required to test their efficacy against CHIKV.