Plant-Derived Antimicrobial Peptides as Potential Antiviral Agents in Systemic Viral Infections

Small and Versatile Cyclotides as Anti-infective Agents

Plants provide an abundant source of potential therapeutic agents, including a diverse array of compounds, such as cyclotides, which are peptides known for their antimicrobial activity. Cyclotides are multifaceted molecules with a wide range of biological activities. Their unique topology forms a head-to-tail cyclic structure reinforced by a cysteine knot, which confers chemical and thermal stability. These molecules can directly target membranes of infectious agents by binding to phosphatidylethanolamine in lipid membranes, leading to membrane permeabilization. Additionally, they function as carriers and cell-penetrating molecules, demonstrating antiviral, antibacterial, antifungal, and nematicidal properties. The structure of cyclotides is also amenable to chemical synthesis, facilitating drug design through residue substitutions or grafting of bioactive epitopes within the cyclotide scaffold to enhance peptide stability. In this review, we explore the multifunctionality of these biomolecules as anti-infective agents, emphasizing their potential as a novel class of antimicrobial drugs.

Revisiting the potential of natural antimicrobial peptides against emerging respiratory viral disease: a review

This review assesses the antiviral capabilities of antimicrobial peptides (AMPs) against SARS-CoV-2 and other respiratory viruses, focussing on their therapeutic potential. AMPs, derived from natural sources, exhibit promising antiviral properties by disrupting viral membranes, inhibiting viral entry, and modulating host immune responses. Preclinical studies demonstrate that peptides such as defensins, cathelicidins, and lactoferrin can effectively reduce SARS-CoV-2 replication and inhibit viral spread. In addition, AMPs have shown potential in enhancing the host's antiviral immunity. Despite these promising outcomes, several challenges require assessments before transforming into clinical translation. Several issues related to peptide stability, cytotoxicity, and efficient delivery systems pose significant limitations to their therapeutic application. Recent advancements in peptide engineering, nanotechnology-based delivery systems, and peptide conjugation strategies have improved AMPs stability and bioavailability; however, further optimization is essential. Moreover, whilst AMPs are safe, their effects on host cells and tissues need a thorough investigation to minimise potential adverse reactions. This review concludes that whilst AMPs present a promising route for antiviral therapies, particularly in targeting SARS-CoV-2, extensive clinical trials and additional studies are required to overcome current limitations. Future research should focus on developing more stable, less toxic AMPs formulations with enhanced delivery mechanisms, aiming to integrate AMPs into viable therapeutic options for respiratory viral diseases, including COVID-19 and other emerging infections.

Antimicrobial Peptides Against Arboviruses: Mechanisms, Challenges, and Future Directions

This review delves into the potential of antimicrobial peptides (AMPs) as promising candidates for combating arboviruses, focusing on their mechanisms of antiviral activity, challenges, and future directions. AMPs have shown promise in preventing arbovirus attachment to host cells, inducing interferon production, and targeting multiple viral stages, illustrating their multifaceted impact on arbovirus infections. Structural elucidation of AMP-viral complexes is explored to deepen the understanding of molecular determinants governing viral neutralization, paving the way for structure-guided design. Furthermore, this review highlights the potential of AMP-based combination therapies to create synergistic effects that enhance overall treatment outcomes while minimizing the likelihood of resistance development. Challenges such as susceptibility to proteases, toxicity, and scalable production are discussed alongside strategies to address these limitations. Additionally, the expanding applications of AMPs as vaccine adjuvants and antiviral delivery systems are emphasized, underscoring their versatility beyond direct antiviral functions.

Plant Antimicrobial Peptides and Their Main Families and Roles: A Review of the Literature

Antimicrobial peptides (AMPs) are constituent molecules of the innate defense system and are naturally produced by all organisms. AMPs are characterized by a relatively low molecular weight (less than 10 kDa) and a variable number of cysteine residues that form disulfide bonds and contribute to the stabilization of the tertiary structure. In addition, there is a wide repertoire of antimicrobial agents against bacteria, viruses, fungi, and protozoa that can provide a large number of prototype peptides for study and biochemical manipulation. In this sense, plant AMPs stand out because they have a wide range of biological functions against microorganisms and potential applications in medicine and agriculture. Herein, we describe a mini-review of the principal AMP families, such as defensins, lipid transfer proteins (LTPs), thionins, heveins, and cyclotides. The objective of this work was to present the main discoveries regarding the biological activities of these plant AMP families, especially in the last 20 years. We also discuss the current knowledge of their biological activities, gene expression, and possible uses as antimicrobial molecules and in plant biotechnology.

A review on the diversity of antimicrobial peptides and genome mining strategies for their prediction

Antibiotic resistance has become one of the most serious threats to human health in recent years. In response to the increasing microbial resistance to the antibiotics currently available, it is imperative to develop new antibiotics or explore new approaches to combat antibiotic resistance. Antimicrobial peptides (AMPs) have shown considerable promise in this regard, as the microbes develop low or no resistance against them. The discovery and development of AMPs still confront numerous obstacles such as finding a target, developing assays, and identifying hits and leads, which are time-consuming processes, making it difficult to reach the market. However, with the advent of genome mining, new antibiotics could be discovered efficiently using tools such as BAGEL, antiSMASH, RODEO, etc., providing hope for better treatment of diseases in the future. Computational methods used in genome mining automatically detect and annotate biosynthetic gene clusters in genomic data, making it a useful tool in natural product discovery. This review aims to shed light on the history, diversity, and mechanisms of action of AMPs and the data on new AMPs identified by traditional as well as genome mining strategies. It further substantiates the various phases of clinical trials for some AMPs, as well as an overview of genome mining databases and tools built expressly for AMP discovery. In light of the recent advancements, it is evident that targeted genome mining stands as a beacon of hope, offering immense potential to expedite the discovery of novel antimicrobials.

The Influence of Cholesterol on Membrane Targeted Bioactive Peptides: Modulating Peptide Activity Through Changes in Bilayer Biophysical Properties

Cholesterol is a biological molecule that is essential for cellular life. It has unique features in terms of molecular structure and function, and plays an important role in determining the structure and properties of cell membranes. One of the most recognized functions of cholesterol is its ability to increase the level of lipid packing and rigidity of biological membranes while maintaining high levels of lateral mobility of the bulk lipids, which is necessary to sustain biochemical signaling events. There is increased interest in designing bioactive peptides that can act as effective antimicrobial agents without causing harm to human cells. For this reason, it becomes relevant to understand how cholesterol can affect the interaction between bioactive peptides and lipid membranes, in particular by modulating the peptides' ability to penetrate and disrupt the membranes through these changes in membrane rigidity. Here we discuss cholesterol and its role in modulating lipid bilayer properties and discuss recent evidence showing how cholesterol modulates bioactive peptides to different degrees.

A critical review of novel antibiotic resistance prevention approaches with a focus on postbiotics

Antibiotic resistance is a significant public health issue, causing illnesses that were once easily treatable with antibiotics to develop into dangerous infections, leading to substantial disability and even death. To help fight this growing threat, scientists are developing new methods and techniques that play a crucial role in treating infections and preventing the inappropriate use of antibiotics. These effective therapeutic methods include phage therapies, quorum-sensing inhibitors, immunotherapeutics, predatory bacteria, antimicrobial adjuvants, haemofiltration, nanoantibiotics, microbiota transplantation, plant-derived antimicrobials, RNA therapy, vaccine development, and probiotics. As a result of the activity of probiotics in the intestine, compounds derived from the structure and metabolism of these bacteria are obtained, called postbiotics, which include multiple agents with various therapeutic applications, especially antimicrobial effects, by using different mechanisms. These compounds have been chosen in particular because they don't promote the spread of antibiotic resistance and don't include substances that can increase antibiotic resistance. This manuscript provides an overview of the novel approaches to preventing antibiotic resistance with emphasis on the various postbiotic metabolites derived from the gut beneficial microbes, their activities, recent related progressions in the food and medical fields, as well as concisely giving an insight into the new concept of postbiotics as "hyperpostbiotic".

Strategies of plants to overcome abiotic and biotic stresses

In their environment, plants are exposed to a multitude of abiotic and biotic stresses that differ in intensity, duration and severity. As sessile organisms, they cannot escape these stresses, but instead have developed strategies to overcome them or to compensate for the consequences of stress exposure. Defence can take place at different levels and the mechanisms involved are thought to differ in efficiency across these levels. To minimise metabolic constraints and to reduce the costs of stress defence, plants prioritise first-line defence strategies in the apoplastic space, involving ascorbate, defensins and small peptides, as well as secondary metabolites, before cellular processes are affected. In addition, a large number of different symplastic mechanisms also provide efficient stress defence, including chemical antioxidants, antioxidative enzymes, secondary metabolites, defensins and other peptides as well as proteins. At both the symplastic and the apoplastic level of stress defence and compensation, a number of specialised transporters are thought to be involved in exchange across membranes that still have not been identified, and information on the regeneration of different defence compounds remains ambiguous. In addition, strategies to overcome and compensate for stress exposure operate not only at the cellular, but also at the organ and whole-plant levels, including stomatal regulation, and hypersensitive and systemic responses to prevent or reduce the spread of stress impacts within the plant. Defence can also take place at the ecosystem level by root exudation of signalling molecules and the emission of volatile organic compounds, either directly or indirectly into the rhizosphere and/or the aboveground atmosphere. The mechanisms by which plants control the production of these compounds and that mediate perception of stressful conditions are still not fully understood. Here we summarise plant defence strategies from the cellular to ecosystem level, discuss their advantages and disadvantages for plant growth and development, elucidate the current state of research on the transport and regeneration capacity of defence metabolites, and outline insufficiently explored questions for further investigation.

smAMPsTK: a toolkit to unravel the smORFome encoding AMPs of plant species

The pervasive repertoire of plant molecules with the potential to serve as a substitute for conventional antibiotics has led to obtaining better insights into plant-derived antimicrobial peptides (AMPs). The massive distribution of Small Open Reading Frames (smORFs) throughout eukaryotic genomes with proven extensive biological functions reflects their practicality as antimicrobials. Here, we have developed a pipeline named smAMPsTK to unveil the underlying hidden smORFs encoding AMPs for plant species. By applying this pipeline, we have elicited AMPs of various functional activity of lengths ranging from 5 to 100 aa by employing publicly available transcriptome data of five different angiosperms. Later, we studied the coding potential of AMPs-smORFs, the inclusion of diverse translation initiation start codons, and amino acid frequency. Codon usage study signifies no such codon usage biases for smORFs encoding AMPs. Majorly three start codons are prominent in generating AMPs. The evolutionary and conservational study proclaimed the widespread distribution of AMPs encoding genes throughout the plant kingdom. Domain analysis revealed that nearly all AMPs have chitin-binding ability, establishing their role as antifungal agents. The current study includes a developed methodology to characterize smORFs encoding AMPs, and their implications as antimicrobial, antibacterial, antifungal, or antiviral provided by SVM score and prediction status calculated by machine learning-based prediction models. The pipeline, complete package, and the results derived for five angiosperms are freely available at https://github.com/skbinfo/smAMPsTK.Communicated by Ramaswamy H. Sarma.

Antifungal Plant Defensins as an Alternative Tool to Combat Candidiasis

Currently, the spread of fungal infections is becoming an urgent problem. Fungi of the Candida genus are opportunistic microorganisms that cause superficial and life-threatening systemic candidiasis in immunocompromised patients. The list of antifungal drugs for the treatment of candidiasis is very limited, while the prevalence of resistant strains is growing rapidly. Therefore, the search for new antimycotics, including those exhibiting immunomodulatory properties, is of great importance. Plenty of natural compounds with antifungal activities may be extremely useful in solving this problem. This review evaluates the features of natural antimicrobial peptides, namely plant defensins as possible prototypes of new anticandidal agents. Plant defensins are important components of the innate immune system, which provides the first line of defense against pathogens. The introduction presents a brief summary regarding pathogenic Candida species, the pathogenesis of candidiasis, and the mechanisms of antimycotic resistance. Then, the structural features of plant defensins, their anticandidal activities, their mechanisms of action on yeast-like fungi, their ability to prevent adhesion and biofilm formation, and their combined action with conventional antimycotics are described. The possible mechanisms of fungal resistance to plant defensins, their cytotoxic activity, and their effectiveness in in vivo experiments are also discussed. In addition, for the first time for plant defensins, knowledge about their immunomodulatory effects is also presented.

Naturally Occurring Isorhamnetin Glycosides as Potential Agents Against Influenza Viruses: Antiviral and Molecular Docking Studies

Influenza remains one of the most widespread infections, causing an annual illness in adults and children. Therefore, the search for new antiviral drugs is one of the priorities of practical health care. Eight isorhamnetin glycosides were purified from Persicaria species, characterized by nuclear magnetic resonance spectroscopy and mass spectrometry and then evaluated as potential agents against influenza virus. A comprehensive in vitro and in vivo assessment of the compounds revealed that compound 5 displayed the most potent inhibitory activity with an EC50 value of 1.2-1.3 μM, better than standard drugs (isorhamnetin 28.0-56.0 μM and oseltamivir 1.3-9.1 μM). Molecular docking results also revealed that compound 5 has the lowest binding energy (-10.7 kcal/mol) among the tested compounds and isorhamnetin (-8.1 kcal/mol). The ability of the isorhamnetin glycosides to suppress the reproduction of the influenza virus was studied on a model of a cell culture and chicken embryos. The ability of active compounds to influence the structure of the virion, as well as the activity of hemagglutinin and neuraminidase, has been demonstrated. Compound 1, 5, and 6 demonstrated the most effective inhibition of virus replication for all tested viruses. Molecular dynamics simulation techniques were run for 100 ns for compound 5 with two protein receptors Hem (1RUY) and Neu (3BEQ). These results revealed that the Hem-complex system acquired a relatively more stable conformation and even better descriptors than the other Neu-complex studied systems, suggesting that it can be an effective inhibiting drug toward hemagglutinin than neuraminidase inhibition. Based on the reported results, compound 5 can be a good candidate to be evaluated for effectiveness in preclinical testing.

Peptides as Therapeutic Agents: Challenges and Opportunities in the Green Transition Era

Peptides are at the cutting edge of contemporary research for new potent, selective, and safe therapeutical agents. Their rise has reshaped the pharmaceutical landscape, providing solutions to challenges that traditional small molecules often cannot address. A wide variety of natural and modified peptides have been obtained and studied, and many others are advancing in clinical trials, covering multiple therapeutic areas. As the demand for peptide-based therapies grows, so does the need for sustainable and environmentally friendly synthesis methods. Traditional peptide synthesis, while effective, often involves environmentally draining processes, generating significant waste and consuming vast resources. The integration of green chemistry offers sustainable alternatives, prioritizing eco-friendly processes, waste reduction, and energy conservation. This review delves into the transformative potential of applying green chemistry principles to peptide synthesis by discussing relevant examples of the application of such approaches to the production of active pharmaceutical ingredients (APIs) with a peptide structure and how these efforts are critical for an effective green transition era in the pharmaceutical field.

Efficacy and safety of add-on Viola odorata L. in the treatment of COVID-19: A randomized double-blind controlled trial

ETHNOPHARMACOLOGICAL RELEVANCE

Severe Acute Respiratory Syndrome (SARS) due to the novel coronavirus has become the highest priority that threatens human health. This situation demands widespread vaccination and the innovation of new therapeutic methods. Despite drug discoveries, the need for approving new medicaments is felt because of adverse effects and lack of efficacy. Several medicinal plants including Viola odorata L. are recommended in traditional Persian medicine for alleviating respiratory infection symptoms. Recent studies showed anti-inflammatory, antioxidant, anti-asthmatic, antitussive, analgesic, and antibacterial activities of sweet violet. These enhance respiratory functions, reduce pulmonary inflammation, and decline mucous membrane edema. This study aimed to evaluate the efficacy of sweet violet syrup in alleviating the manifestations of COVID-19 infection.

MATERIAL AND METHODS

A randomized parallel-group double-blind controlled trial was conducted at Al-Zahra general hospital, Isfahan, Iran. A total of 108 outpatients were enrolled in the study. The patients were randomly allocated to intervention and placebo groups, with 54 patients in each group. The allocation was concealed using sealed opaque envelopes. The intervention group received violet syrup and the control group received placebo syrup, an add-on to the conventional treatment. The outcomes were COVID-19 manifestations, such as dyspnea, cough, myalgia, headache, and diarrhea, considered as outcomes of the study and were evaluated twice using a visual analog scale before the intervention and after 7 days, at the end of the study. Patients were followed daily by phone calls to monitor proper drug consumption and possible side effects.

RESULTS

No significant difference was between groups regarding demographic characteristics and vital signs before and after the treatment. Although all symptoms have improved significantly in both groups, patients who received violet syrup recovered faster and the mean severity scores of cough (P = 0.025), myalgia (P = 0.036), headache (P = 0.037), and diarrhea (P = 0.044) decreased greater in comparison to control group.

CONCLUSION

This study, the first clinical trial on the effectiveness of Viola odorata on SARS-CoV-2 patients, showed that Viola odorata L. effectively controls prevalent manifestations of COVID-19 including cough, myalgia, headache, and diarrhea. Regarding this survey, the violet syrup can be mentioned as a complementary treatment for viral influenza-like infections in which cough, myalgia, headache, and diarrhea are prominent.

Are Herbal-peptides Effective as Adjunctive Therapy in Coronavirus Disease COVID-19?

BACKGROUND

Plant antiviral peptides (AVP) are macromolecules that can inhibit the pathogenesis of viruses by affecting their pathogenic mechanism, but most of these peptides can bind to cell membranes, inhibit viral receptors, and prevent viruses. Recently, due to the coronavirus pandemic, the availability of appropriate drugs with low side effects is needed. In this article, the importance of plant peptides in viral inhibition, especially viral inhibition of the coronavirus family, will be discussed.

METHODS

By searching the databases of PubMed, Scopus, Web of Science, the latest articles on plant peptides effective on the COVID-19 virus were collected and reviewed.

RESULTS

Some proteins can act against the COVID-19 virus by blocking sensitive receptors in COVID-19, such as angiotensin-converting enzyme 2 (ACE2). The 23bp sequence of the ACE2 alpha receptor chain can be considered as a target for therapeutic peptides. Protease and RNAP inhibitors and other important receptors that are active against COVID-19 should also be considered.

CONCLUSION

Herbal medicines with AVP, especially those with a long history of antiviral effects, might be a good choice in complement therapy against the COVID-19 virus.

Crosstalk of nitro-oxidative stress and iron in plant immunity

Accumulation of oxygen and nitrogen radicals and their derivatives, known as reactive oxygen species (ROS) and reactive nitrogen species (RNS), occurs throughout various phases of plant growth in association with biotic and abiotic stresses. One of the consequences of environmental stresses is disruption of homeostasis between production and scavenging of ROS and RNS, which leads to nitro-oxidative burst and affects other defense-related mechanisms, such as polyamines levels, phenolics, lignin and callose as defense components related to plant cell wall reinforcement. Although this subject has attracted huge interest, the cross-talk between these signaling molecules and iron, as a main metal element involved in the activity of various enzymes and numerous vital processes in the living cells, remains largely unexplored. Therefore, it seems necessary to pay more in depth attention to the mechanisms of plant resistance against various environmental stimuli for designing novel and effective plant protection strategies. This review is focused on advances in recent knowledge related to the role of ROS, RNS, and association of these signaling molecules with iron in plant immunity. Furthermore, the role of cell wall fortification as a main physical barrier involved in plant defense have been discussed in association with reactive species and iron ions.

Antiviral Peptides as Anti-Influenza Agents

Influenza viruses represent a leading cause of high morbidity and mortality worldwide. Approaches for fighting flu are seasonal vaccines and some antiviral drugs. The development of the seasonal flu vaccine requires a great deal of effort, as careful studies are needed to select the strains to be included in each year's vaccine. Antiviral drugs available against Influenza virus infections have certain limitations due to the increased resistance rate and negative side effects. The highly mutative nature of these viruses leads to the emergence of new antigenic variants, against which the urgent development of new approaches for antiviral therapy is needed. Among these approaches, one of the emerging new fields of "peptide-based therapies" against Influenza viruses is being explored and looks promising. This review describes the recent findings on the antiviral activity, mechanism of action and therapeutic capability of antiviral peptides that bind HA, NA, PB1, and M2 as a means of countering Influenza virus infection.

The Updated Review on Plant Peptides and Their Applications in Human Health

Biologically active plant peptides, consisting of secondary metabolites, are compounds (amino acids) utilized by plants in their defense arsenal. Enzymatic processes and metabolic pathways secrete these plant peptides. They are also known for their medicinal value and have been incorporated in therapeutics of major human diseases. Nevertheless, its limitations (low bioavailability, high cytotoxicity, poor absorption, low abundance, improper metabolism, etc.) have demanded a need to explore further and discover other new plant compounds that overcome these limitations. Keeping this in mind, therapeutic plant proteins can be excellent remedial substitutes for bodily affliction. A multitude of these peptides demonstrates anti-carcinogenic, anti-microbial, anti-HIV, and neuro-regulating properties. This article's main aim is to list out and report the status of various therapeutic plant peptides and their prospective status as peptide-based drugs for multiple diseases (infectious and non-infectious). The feasibility of these compounds in the imminent future has also been discussed.

Therapeutic Potential of Marine Bioactive Peptides against Human Immunodeficiency Virus: Recent Evidence, Challenges, and Future Trends

Acquired immunodeficiency syndrome (AIDS) is a chronic and potentially fatal ailment caused by the human immunodeficiency virus (HIV) and remains a major health problem worldwide. In recent years, the research focus has shifted to a greater emphasis on complementing treatment regimens involving conventional antiretroviral (ARV) drug therapies with novel lead structures isolated from various marine organisms that have the potential to be utilized as therapeutics for the management of HIV-AIDS. The present review summarizes the recent developments regarding bioactive peptides sourced from various marine organisms. This includes a discussion encompassing the potential of these novel marine bioactive peptides with regard to antiretroviral activities against HIV, preparation, purification, and processing techniques, in addition to insight into the future trends with an emphasis on the potential of exploration and evaluation of novel peptides to be developed into effective antiretroviral drugs.

In vitro Inhibition of HIV-1 by Cyclotide-Enriched Extracts of Viola tricolor

Since viral infectious diseases continue to be a global health threat, new antiviral drugs are urgently needed. A unique class of therapeutic compounds are antimicrobial peptides (AMPs). They can be found in humans, bacteria and plants. Plants express a wide variety of such defense peptides as part of their innate immune system to protect from invading pathogens. Cyclotides are non-classical AMPs that share a similar structure. Their unique topology consists of a circular peptide backbone and disulfide bonds. In previous studies they have been attributed to a wide range of biological activities. To identify novel cyclotides with antiviral activity, we established a library of plant extracts largely consisting of cyclotide-rich species and screened them as inhibitors of HIV-1 infection. Subsequent extraction and fractionation revealed four cyclotide-containing subfractions from Viola tricolor with antiviral activity. These subfractions inhibited HIV-1 infection with IC50 values between 0.6 and 11.2 μg/ml, and selectivity indices of up to 8.1. The identification and characterization of antiviral cyclotides and the determination of the antiviral mechanisms may allow to develop novel agents to combat viral infections. Therefore, cyclotides represent a natural source of bioactive molecules with prospects for development as therapeutics.

Improved Database Filtering Technology Enables More Efficient Ab Initio Design of Potent Peptides against Ebola Viruses

The rapid mutations of viruses such as SARS-CoV-2 require vaccine updates and the development of novel antiviral drugs. This article presents an improved database filtering technology for a more effective design of novel antiviral agents. Different from the previous approach, where the most probable parameters were obtained stepwise from the antimicrobial peptide database, we found it possible to accelerate the design process by deriving multiple parameters in a single step during the peptide amino acid analysis. The resulting peptide DFTavP1 displays the ability to inhibit Ebola virus. A deviation from the most probable peptide parameters reduces antiviral activity. The designed peptides appear to block viral entry. In addition, the amino acid signature provides a clue to peptide engineering to gain cell selectivity. Like human cathelicidin LL-37, our engineered peptide DDIP1 inhibits both Ebola and SARS-CoV-2 viruses. These peptides, with broad antiviral activity, may selectively disrupt viral envelopes and offer the lasting efficacy required to treat various RNA viruses, including their emerging mutants.