Cathelicidin antimicrobial peptides suppress EV71 infection via regulating antiviral response and inhibiting viral binding

Litopeidin28-51, a novel antimicrobial peptide from Litopenaeus vannamei, combats white spot syndrome virus infection through direct virus lysis and immunomodulatory effects

White spot syndrome virus (WSSV) poses a critical threat to crustacean aquaculture, particularly shrimp, causing widespread pandemics. In crustaceans, hemocytes function as a key component of the innate immune system and play a pivotal role in both cellular and humoral immune responses by producing various immune factors, such as antimicrobial peptides (AMPs), to defend against pathogenic microorganisms. In this study, an uncharacterized functional gene named Litopeidin was identified in Pacific white shrimp (Litopenaeus vannamei). It exhibited heightened expression in hemocytes and demonstrated a significant response to WSSV infection. Further, a truncated peptide, Litopeidin28-51, derived from this gene, was characterized and identified as a novel AMP with robust antibacterial and antifungal properties, especially against common aquatic pathogens, including Vibrio spp. Moreover, Litopeidin28-51 significantly suppressed the expression of viral genes (IE1 and VP28, WSSV replication-related genes) and the VP28 protein, as well as reduced viral copy numbers in hematopoietic tissue (Hpt) cells following WSSV infection. Mechanistic studies revealed that Litopeidin28-51 exhibited a direct virucidal effect on WSSV and significantly upregulated immune-related gene expression (including Relish, ALF, Crustin, and LYZ1) in Hpt cells. Notably, in Cherax quadricarinatus and L. vannamei, either co- or pre-treatment with Litopeidin28-51 markedly reduced animal mortality and viral replication in tissues. Collectively, the findings suggest that Litopeidin28-51, a newly identified AMP with potent antibacterial activity, effectively inhibits WSSV replication by disrupting the viral envelope and regulating the cellular antiviral responses, making it a promising candidate for developing anti-infective agents or immunostimulants in aquaculture.

Molecular characterization and immunological functions of the antimicrobial peptide theromacin from razor clam Sinonovacula constricta

Antimicrobial peptides are natural immune effector molecules that protect the host from pathogenic microorganisms and play crucial roles in the innate immune system. Herein, the functions of theromacin from the razor clam Sinonovacula constricta (ScTM) were identified. Multiple sequence alignment revealed that the structure of ScTM was similar to that of a theromacin homolog with a signal peptide and conserved Macin domain. Tissue distribution analysis indicated that ScTM mRNA was expressed in all tested tissues. Moreover, ScTM transcripts were upregulated in hemocytes and hepatopancreas after challenge with Vibrio parahaemolyticus. Importantly, interfering with ScTM expression through siRNA transfection reduced hemocyte clearance ability and razor clam survival rates. Further functional analysis indicated that recombinant ScTM protein possessed considerable binding abilities to pathogens and PAMPs, showing the strongest binding ability to LPS. Minimum inhibitory concentration assays revealed that rScTm exerted stronger antimicrobial activities against Gram-negative bacteria than against Gram-positive bacteria. Moreover, rScTM exhibited antimicrobial activity against V. parahaemolyticus by increasing extracellular membrane permeability, impairing inner membrane integrity, and binding to genomic DNA, leading to cytoplasmic efflux and bacterial death. All of the results of this work provide a new perspective for the development of an effective strategy to control razor clam bacterial infection.

Harnessing Non-Antibiotic Strategies to Counter Multidrug-Resistant Clinical Pathogens with Special Reference to Antimicrobial Peptides and Their Coatings

Antimicrobial resistance is a critical global challenge in the 21st century, validating Sir Alexander Fleming's warning about the misuse of antibiotics leading to resistant microbes. With a dwindling arsenal of effective antibiotics, it is imperative to concentrate on alternative antimicrobial strategies. Previous studies have not comprehensively discussed the advantages and limitations of various strategies, including bacteriophage therapy, probiotics, immunotherapies, photodynamic therapy, essential oils, nanoparticles and antimicrobial peptides (AMPs) within a single review. This review addresses that gap by providing an overview of these various non-antibiotic antimicrobial strategies, highlighting their pros and cons, with a particular emphasis on antimicrobial peptides (AMPs). We explore the mechanism of action of AMPs against bacteria, viruses, fungi and parasites. While these peptides hold significant promise, their application in mainstream drug development is hindered by challenges such as low bioavailability and potential toxicity. However, advancements in peptide engineering and chemical modifications offer solutions to enhance their clinical utility. Additionally, this review presents updates on strategies aimed at improving the cost, stability and selective toxicity of AMPs through the development of peptidomimetics. These molecules have demonstrated effective activity against a broad range of pathogens, making them valuable candidates for integration into surface coatings to prevent device-associated infections. Furthermore, we discuss various approaches for attaching and functionalising these peptides on surfaces. Finally, we recommend comprehensive in vivo studies to evaluate the efficacy of AMPs and their mimetics, investigate their synergistic combinations with other molecules and assess their potential as coatings for medical devices.

Antimicrobial peptide Mt 5 inhibits human hepatocellular carcinoma cell HepG2 proliferation

The Mt 5 peptide is an antimicrobial peptide, its effect on hepatocellular carcinoma (HCC) and its underlying mechanism is not understood. Therefore, this study aimed to investigate the effects of the Mt 5 peptide in a human HCC cell line, namely HepG2, in vitro. Notably, Mt 5 markedly reduced the growth of HepG2 cells by disrupting the cell membrane while exhibiting minimal toxicity to healthy liver cells. Furthermore, Mt 5 treatment increased intracellular reactive oxygen species levels and decreased the mitochondria membrane potential, suggesting the induction of mitochondrial damage-mediated apoptosis. Additionally, Mt 5-mediated cytoskeleton disruption suggested the potential inhibition of cell metastasis. Altogether, the findings of this study indicate the potential of the Mt 5 peptide as a drug candidate against HCC.

Antiviral activity of cathelicidins against porcine epidemic diarrhea virus (PEDV): Mechanisms, and efficacy

Porcine epidemic diarrhea virus (PEDV) is a harmful coronavirus infecting pigs, which is resulting in substantial financial losses in the global pig industry. The lack of effective vaccines or treatments underscores the pressing need for new antiviral strategies. Antimicrobial peptides (AMPs), specifically cathelicidins such as LL-37, have demonstrated promising activity against a range of viruses. This study aims to elucidate the antiviral mechanisms of cathelicidins by examining their inhibitory capabilities against PEDV in vitro. Four pig-derived antimicrobial peptides (PMAP-36, PMAP-23, PR-39, and PG-1), together with chicken-derived CATH-B1 and human-derived LL-37 were analyzed for their anti-PEDV activity. Flow cytometry and fluorescent microscopy confirmed that LL-37 and CATH-B1 had strong inhibitory effects at non-toxic concentrations of 5 and 10 µM, significantly reducing GFP-PEDV infection of Vero cells both in co- and pre-incubation setups. In contrast, none of the porcine peptides exhibited any inhibitory effects, even at higher doses. Fluorogenic LL-37 was shown to enter VERO cells, indicative of a possible immunomodulatory antiviral mode of action. However, transmission electron microscopy clearly indicated that both LL-37 and CATH-B1 affected virus morphology and caused aggregation of viral particles, showing that peptide-virus interaction caused reduced virus infectivity. In conclusion, this analysis highlights the potential of LL-37 and CATH-B1 as inhibitors against PEDV, suggesting promising directions for innovative therapeutic antiviral strategies.

Recombinant Lactococcus lactis Expressing Human LL-37 Prevents Deaths from Viral Infections in Piglets and Chicken

Novel antibiotic substitutes are increasingly in demand in the animal husbandry industry. An oral recombinant Lactococcus lactis (L. lactis) expressing human LL-37 (oral LL-37) was developed and its safety and antiviral effectiveness in vivo was tested. In addition to impairing liposome integrity, LL-37 polypeptide from recombinant L. lactis could prevent the host cell infection by a variety of viruses, including recombinant SARS, SARS-CoV-2, Ebola virus, and vesicular stomatitis virus G. Subchronic toxicity studies performed on Sprague-Dawley rats showed that no cumulative toxicity was found during short-term intervention. Oral LL-37 treatment after the onset of fever could reduce mortality in piglets infected with porcine reproductive and respiratory syndrome virus. Moreover, body weight gain of piglets receiving treatment was progressively restored, and nucleic acid positive rebound was not undetected after discontinuation. Oral LL-37 consistently increased the lifespan of chickens infected with Newcastle viruses. These findings suggested a potential use of recombinantly modified microorganisms in veterinary medicine.

A Cyclic Peptide Based on Pheasant Cathelicidin Inhibits Influenza A H1N1 Virus Infection

Influenza viruses are the leading cause of upper respiratory tract infections, leading to several global pandemics and threats to public health. Due to the continuous mutation of influenza A viruses, there is a constant need for the development of novel antiviral therapeutics. Recently, natural antimicrobial peptides have provided an opportunity for the discovery of anti-influenza molecules. Here, we designed several peptides based on pheasant cathelicidin and tested their antiviral activities and mechanisms against the H1N1 virus. Of note, the designed peptides Pc-4 and Pc-5 were found to inhibit replication of the H1N1 virus with an IC50 = 8.14 ± 3.94 µM and 2.47 ± 1.95 µM, respectively. In addition, the cyclic peptide Pc-5 was found to induce type I interferons and the expression of interferon-induced genes. An animal study showed that the cyclic peptide Pc-5 effectively inhibited H1N1 virus infection in a mouse model. Taken together, our work reveals a strategy for designing cyclic peptides and provides novel molecules with therapeutic potential against influenza A virus infection.

Recent advances in the therapeutic potential of cathelicidins

The alarming increase in antimicrobial resistance in the last decades has prompted the search for alternatives to control infectious diseases. Antimicrobial peptides (AMPs) represent a heterogeneous class of molecules with ample antibacterial, antiviral, and antifungal effects. They can be found in many organisms, including all classes of vertebrates, providing a valuable source of new antimicrobial agents. The unique properties of AMPs make it harder for microbes develop resistance, while their immunomodulatory properties and target diversity reinforce their translational use in multiple diseases, from autoimmune disorders to different types of cancer. The latest years have witnessed a vast number of studies evaluating the use of AMPs in therapy, with many progressing to clinical trials. The present review explores the recent developments in the medicinal properties of cathelicidins, a vast family of AMPs with potent antimicrobial and immunomodulatory effects. Cathelicidins from several organisms have been tested in disease models of viral and bacterial infections, inflammatory diseases, and tumors, with encouraging results. Combining nanomaterials with active, natural antimicrobial peptides, including LL-37 and synthetic analogs like ceragenins, leads to the creation of innovative nanoagents with significant clinical promise. However, there are still important limitations, such as the toxicity of many cathelicidins to healthy host cells and low stability in vivo. The recent advances in nanomaterials and synthetic biology may help overcome the current limitations, enabling the use of cathelicidins in future therapeutics. Furthermore, a better understanding of the mechanisms of cathelicidin action in vivo and their synergy with other host molecules will contribute to the development of safer, highly effective therapies.

A Reliable Multifaceted Solution against Foodborne Viral Infections: The Case of RiLK1 Decapeptide

Food-borne transmission is a recognized route for many viruses associated with gastrointestinal, hepatic, or neurological diseases. Therefore, it is essential to identify new bioactive compounds with broad-spectrum antiviral activity to exploit innovative solutions against these hazards. Recently, antimicrobial peptides (AMPs) have been recognized as promising antiviral agents. Indeed, while the antibacterial and antifungal effects of these molecules have been widely reported, their use as potential antiviral agents has not yet been fully investigated. Herein, the antiviral activity of previously identified or newly designed AMPs was evaluated against the non-enveloped RNA viruses, hepatitis A virus (HAV) and murine norovirus (MNV), a surrogate for human norovirus. Moreover, specific assays were performed to recognize at which stage of the viral infection cycle the peptides could function. The results showed that almost all peptides displayed virucidal effects, with about 90% of infectivity reduction in HAV or MNV. However, the decapeptide RiLK1 demonstrated, together with its antibacterial and antifungal properties, a notable reduction in viral infection for both HAV and MNV, possibly through direct interaction with viral particles causing their damage or hindering the recognition of cellular receptors. Hence, RiLK1 could represent a versatile antimicrobial agent effective against various foodborne pathogens including viruses, bacteria, and fungi.

Scorpion Venom Antimicrobial Peptide Derivative BmKn2-T5 Inhibits Enterovirus 71 in the Early Stages of the Viral Life Cycle In Vitro

Enterovirus 71 (EV71), a typical representative of unenveloped RNA viruses, is the main pathogenic factor responsible for hand, foot, and mouth disease (HFMD) in infants. This disease seriously threatens the health and lives of humans worldwide, especially in the Asia-Pacific region. Numerous animal antimicrobial peptides have been found with protective functions against viruses, bacteria, fungi, parasites, and other pathogens, but there are few studies on the use of scorpion-derived antimicrobial peptides against unenveloped viruses. Here, we investigated the antiviral activities of scorpion venom antimicrobial peptide BmKn2 and five derivatives, finding that BmKn2 and its derivative BmKn2-T5 exhibit a significant inhibitory effect on EV71. Although both peptides exhibit characteristics typical of amphiphilic α-helices in terms of their secondary structure, BmKn2-T5 displayed lower cellular cytotoxicity than BmKn2. BmKn2-T5 was further found to inhibit EV71 in a dose-dependent manner in vitro. Moreover, time-of-drug-addition experiments showed that BmKn2-T5 mainly restricts EV71, but not its virion or replication, at the early stages of the viral cycle. Interestingly, BmKn2-T5 was also found to suppress the replication of the enveloped viruses DENV, ZIKV, and HSV-1 in the early stages of the viral cycle, which suggests they may share a common early infection step with EV71. Together, the results of our study identified that the scorpion-derived antimicrobial peptide BmKn2-T5 showed valuable antiviral properties against EV71 in vitro, but also against other enveloped viruses, making it a potential new candidate therapeutic molecule.

Construction of exosome-loaded LL-37 and its protection against zika virus infection

Zika virus (ZIKV) is an enveloped, single-stranded and positive-stranded RNA virus of the genus Flavivirus in the family Flaviviridae. ZIKV can cross the placental barrier and infect the fetus, causing microcephaly, congenital ZIKV syndrome, and even fetal death. ZIKV infection can also lead to testicular damage and male sterility. But no effective drugs and vaccines are available up to now. Previous studies have shown that the cathelicidin antimicrobial peptide LL-37 can protect against ZIKV infection. However, LL-37 is a secreted peptide, which can be easily degraded in vivo. We herein constructed exosome-loaded LL-37 (named LL-37-TM-exo and TM-LL-37-exo) using the transmembrane protein TM to load LL-37 onto the membrane of exosome. We found that exosome-loaded LL-37 could significantly inhibit ZIKV infection in vitro and in vivo, and LL-37-TM-exo had stronger antiviral activity than that of TM-LL-37-exo, which could significantly reduce ZIKV-induced testicular injury and sperm injury, and had broad-spectrum antiviral effect. Compared to free LL-37, exosome-loaded LL-37 showed a better serum stability, higher efficiency to cross the placental barrier, and stronger antiviral activity. The mechanism of exosome-loaded LL-37 against ZIKV infection was consistent with that of free LL-37, which could directly inactivate viral particles, reduce the susceptibility of host cells, and act on viral replication stage. Our study provides a novel strategy for the development of LL-37 against viral infection.

Function and Mechanism of Antiviral Wasp Venom Peptide Protopolybia-MP III and Its Derivatives against HSV-1

Viruses are one of the leading causes of human disease, and many highly pathogenic viruses still have no specific treatment drugs. Therefore, producing new antiviral drugs is an urgent matter. In our study, we first found that the natural wasp venom peptide Protopolybia-MP III had a significant inhibitory effect on herpes simplex virus type 1 (HSV-1) replication in vitro by using quantitative real-time PCR (qPCR), Western blotting, and plaque-forming assays. Immunofluorescence analysis showed Protopolybia-MP III could enter cells, and it inhibited multiple stages of the HSV-1 life cycle, including the attachment, entry/fusion, and post-entry stages. Furthermore, ultracentrifugation and electron microscopy detected that Protopolybia-MP III significantly suppressed HSV-1 virion infectivity at different temperatures by destroying the integrity of the HSV-1 virion. Finally, by comparing the antiviral activity of Protopolybia-MP III and its mutants, a series of peptides with better anti-HSV-1 activity were identified. Overall, this work found the function and mechanism of the antiviral wasp venom peptide Protopolybia-MP III and its derivatives against HSV-1 and laid the foundation for the research and development of wasp venom-derived antiviral candidate peptide drugs.

Role of protein Post-translational modifications in enterovirus infection

Enteroviruses (EVs) are the main cause of a number of neurological diseases. Growing evidence has revealed that successful infection with enteroviruses is highly dependent on the host machinery, therefore, host proteins play a pivotal role in viral infections. Both host and viral proteins can undergo post-translational modification (PTM) which can regulate protein activity, stability, solubility and interactions with other proteins; thereby influencing various biological processes, including cell metabolism, metabolic, signaling pathways, cell death, and cancer development. During viral infection, both host and viral proteins regulate the viral life cycle through various PTMs and different mechanisms, including the regulation of host cell entry, viral protein synthesis, genome replication, and the antiviral immune response. Therefore, protein PTMs play important roles in EV infections. Here, we review the role of various host- and virus-associated PTMs during enterovirus infection.

Oral administration of LfcinB alleviates DSS-induced colitis by improving the intestinal barrier and microbiota

Ulcerative colitis (UC) is a kind of inflammatory bowel disease (IBD) that often recurs and is difficult to cure, and no drugs with few side effects are available to treat this disease. LfcinB is a small molecular peptide obtained by the hydrolysis of bovine lactoferrin in the digestive tract of animals. It has strong antibacterial and anti-inflammatory activities. However, direct evidence that LfcinB improves the condition of colitis in mice is rarely reported. In this study, UC was induced in mice by adding 2.5% dextran sulfate (DSS) to drinking water and LfcinB was orally administered. The results showed that oral administration of LfcinB improved colonic tissue damage and inflammatory cell infiltration, increased the expression of tight junction proteins, and down-regulated the phosphorylation of proteins related to the NF-κB/MAPK inflammatory signalling pathway in mice. It also significantly suppressed the relative abundance of potentially pathogenic bacteria (Bacteroides, Barnesiella and Escherichia) in the intestinal flora. In conclusion, oral administration of LfcinB significantly alleviated DSS-induced UC. This may be related to the regulation of inflammatory signalling pathways and gut microbial composition by LfcinB.

Advances in anti-EV-A71 drug development research

BACKGROUND

Enterovirus A71 (EV-A71) is capable of causing hand, foot and mouth disease (HFMD), which may lead to neurological sequelae and even death. As EV-A71 is resistant to environmental changes and mutates easily, there is still a lack of effective treatments or globally available vaccines.

AIM OF REVIEW

For more than 50 years since the HFMD epidemic, related drug research has been conducted. Progress in this area can promote the further application of existing potential drugs and develop more efficient and safe antiviral drugs, and provide useful reference for protecting the younger generation and maintaining public health security.

KEY SCIENTIFIC CONCEPTS OF REVIEW

At present, researchers have identified hundreds of EV-A71 inhibitors based on screening repurposed drugs, targeted structural design, and rational modification of previously effective drugs as the main development strategies. This review systematically introduces the current potential drugs to inhibit EV-A71 infection, including viral inhibitors targeting key sites such as the viral capsid, RNA-dependent RNA polymerase (RdRp), 2C protein, internal ribosome entry site (IRES), 3C proteinase (3Cpro), and 2A proteinase (2Apro), starting from each stage of the viral life cycle. Meanwhile, the progress of host-targeting antiviral drugs and their development are summarized in terms of regulating host immunity, inhibiting autophagy or apoptosis, and regulating the cellular redox environment. In addition, the current clinical methods for the prevention and treatment of HFMD are summarized and discussed with the aim of providing support and recommendations for the treatment of enterovirus infections including EV-A71.

Melittin-Related Peptides Interfere with Sandfly Fever Naples Virus Infection by Interacting with Heparan Sulphate

Emerging viruses pose an important global public health challenge, and early action is needed to control their spread. The Bunyaviridae family contains a great number of arboviruses which are potentially pathogenic for humans. For example, phleboviruses affect a large range of hosts, including humans and animals. Some infections usually have an asymptomatic course, but others lead to severe complications, such as Toscana virus, which is able to cause meningitis and encephalitis. Unfortunately, to date, no vaccines or antiviral treatments have been found. In the present study, we evaluated the effect of melittin-related peptides, namely the frog-derived RV-23 and AR-23, on sandfly fever Naples virus infection in vitro. Both peptides exhibited a strong antiviral activity by targeting the viral particles and blocking the virus-cell interaction. Their action was directed to an early phase of SFNV infection, in particular at viral adsorption on host cells, by interfering with the binding of common glycosaminoglycan receptors. Given the better antimicrobial behavior of AR-23 and RV-23 compared to melittin in terms of selectivity, our studies expand our understanding of the potential of these peptides as antimicrobials and stimulate further investigations in the direction of novel antiviral strategies against phlebovirus infection.

A review of the antiviral activity of cationic antimicrobial peptides

Viral epidemics are occurring frequently, and the COVID-19 viral pandemic has resulted in at least 6.5 million deaths worldwide. Although antiviral therapeutics are available, these may not have sufficient effect. The emergence of resistant or novel viruses requires new therapies. Cationic antimicrobial peptides are agents of the innate immune system that may offer a promising solution to viral infections. These peptides are gaining attention as possible therapies for viral infections or for use as prophylactic agents to prevent viral spread. This narrative review examines antiviral peptides, their structural features, and mechanism of activity. A total of 156 cationic antiviral peptides were examined for information of their mechanism of action against both enveloped and non-enveloped viruses. Antiviral peptides can be isolated from various natural sources or can be generated synthetically. The latter tend to be more specific and effective and can be made to have a broad spectrum of activity with minimal side effects. Their unique properties of being positively charged and amphipathic enable their main mode of action which is to target and disrupt viral lipid envelopes, thereby inhibiting viral entry and replication. This review offers a comprehensive summary of the current understanding of antiviral peptides, which could potentially aid in the design and creation of novel antiviral medications.

Role of antimicrobial peptide cathelicidin in thrombosis and thromboinflammation

Thrombosis is a frequent cause of cardiovascular mortality and hospitalization. Current antithrombotic strategies, however, target both thrombosis and physiological hemostasis and thereby increase bleeding risk. In recent years the pathophysiological understanding of thrombus formation has significantly advanced and inflammation has become a crucial element. Neutrophils as most frequent immune cells in the blood and their released mediators play a key role herein. Neutrophil-derived cathelicidin next to its strong antimicrobial properties has also shown to modulates thrombosis and thus presents a potential therapeutic target. In this article we review direct and indirect (immune- and endothelial cell-mediated) effects of cathelicidin on platelets and the coagulation system. Further we discuss its implications for large vessel thrombosis and consecutive thromboinflammation as well as immunothrombosis in sepsis and COVID-19 and give an outlook for potential therapeutic prospects.

Cathelicidins Target HSP60 To Restrict CVB3 Transmission via Disrupting the Exosome and Reducing Cardiomyocyte Apoptosis

Cathelicidin antimicrobial peptides (mouse, CRAMP; human, LL-37) have broad-spectrum antiviral activities against enveloped viruses, but their mechanisms of action against nonenveloped viruses remain to be elucidated. Coxsackievirus B3 (CVB3), a member of nonenveloped virus belonging to the Enterovirus genus of Picornaviridae, is an important pathogen of viral myocarditis and dilated cardiomyopathy. Here, we observed that cardiac CRAMP expression was significantly upregulated in mice after CVB3 infection. The administration of CRAMP or LL-37 markedly suppressed CVB3 infection in mice, and CRAMP deficiency increased the susceptibility of mice to CVB3. CRAMP and LL-37 inhibited CVB3 replication in primary cardiomyocytes. However, they did not inactivate CVB3 particles and did not regulate the response of cardiomyocytes against CVB3 infection. Intriguingly, they inhibited CVB3 transmission through the exosome, but not virus receptor. In detail, CRAMP and LL-37 directly induced the lysis of exosomes by interfering with exosomal heat shock protein 60 (HSP60) and then blocked the diffusion of exosomes to recipient cells and inhibited the establishment of productive infection by exosomes. In addition, the interaction of CRAMP and LL-37 with HSP60 simultaneously inhibited HSP60-induced apoptosis in cardiomyocytes and reduced HSP60-enhanced CVB3 replication. Our findings reveal a novel mechanism of cathelicidins against viral infection and provide a new therapeutic strategy for CVB3-induced viral myocarditis. IMPORTANCE The relative mechanisms that cathelicidin antimicrobial peptides use to influence nonenveloped virus infection are unclear. We show here that cathelicidin antimicrobial peptides (CRAMP and LL-37) directly target exosomal HSP60 to destroy exosomes, which in turn block the diffusion of exosomes to recipient cardiomyocytes and reduced HSP60-induced apoptosis, thus restricting coxsackievirus B3 infection. Our results provide new insights into the mechanisms cathelicidin antimicrobial peptides use against viral infection.

Berberine prevents lethal EV71 neurological infection in newborn mice

Enterovirus 71 (EV71) is the major pathogen causing fatal neurological complications of hand, foot, and mouth disease (HFMD) in young children. Currently no effective antiviral therapy is available. In the present study, we found that natural compound Berberine (BBR) displayed potent inhibitory effects on EV71 replication in various neural cells (IC₅₀ of 2.79–4.03 μM). In a newborn mouse model of lethal EV71 infection, Berberine at 2–5 mg/kg markedly reduced mortality and clinical scores. Consistently, the replication of EV71 and pathological changes were attenuated in various infected organs including brain and lung with BBR treatment. Interestingly, EV71 infection in the brain mainly localized in the peripheral zone of brainstem and largely in astrocytes. Primary culture of astrocytes from newborn mouse brain confirmed the efficient EV71 replication that was mostly inhibited by BBR treatment at 5 μM. Further investigations revealed remarkably elevated cellular reactive oxygen species (ROS) levels that coincided with EV71 replication in primary cultured astrocytes and various cell lines. BBR largely abolished the virus-elevated ROS production and greatly diminished EV71 replication by up-regulating NFE2 like bZIP transcription factor 2 (Nrf2) via the kelch like ECH associated protein 1 (Keap)-Nrf2 axis. The nuclear localization of Nrf2 and expression of downstream antioxidant enzymes heme oxygenase 1 (HO-1) and NAD(P)H quinone dehydrogenase 1 (NQO1) were increased significantly by BBR treatment. Collectively, our findings revealed that BBR prevents lethal EV71 neurological infection via inhibiting virus replication through regulating Keap-Nrf2 axis and ROS generation in astrocytes of brainstem, thus providing a potential antiviral treatment for severe EV71 infection associated with neurological complications.

A cathelicidin antimicrobial peptide from Hydrophis cyanocinctus inhibits Zika virus infection by downregulating expression of a viral entry factor

Zika virus (ZIKV) is a re-emerging flavivirus that causes conditions such as microcephaly and testis damage. The spread of ZIKV has become a major public health concern. Recent studies indicated that antimicrobial peptides are an ideal source for screening antiviral candidates with broad-spectrum antiviral activities, including against ZIKV. We herein found that Hc-CATH, a cathelicidin antimicrobial peptide identified from the sea snake Hydrophis cyanocinctus in our previous work, conferred protection against ZIKV infection in host cells and showed preventative efficacy and therapeutic efficacy in C57BL/6J mice, Ifnar1^−/− mice, and pregnant mice. Intriguingly, we revealed that Hc-CATH decreased the susceptibility of host cells to ZIKV by downregulating expression of AXL, a TAM (TYRO3, AXL and MERTK) family kinase receptor that mediates ZIKV infection, and subsequently reversed the negative regulation of AXL on host’s type I interferon response. Furthermore, we showed that the cyclo-oxygenase-2/prostaglandin E2/adenylyl cyclase/protein kinase A pathway was involved in Hc-CATH-mediated AXL downregulation, and Hc-CATH in addition directly inactivated ZIKV particles by disrupting viral membrane. Finally, while we found Hc-CATH did not act on the late stage of ZIKV infection, structure–function relationship studies revealed that α-helix and phenylalanine residues are key structural requirements for its protective efficacy against initial ZIKV infection. In summary, we demonstrate that Hc-CATH provides prophylactic and therapeutic efficacy against ZIKV infection via downregulation of AXL, as well as inactivating the virion. Our findings reveal a novel mechanism of cathelicidin against viral infection and highlight the potential of Hc-CATH to prevent and treat ZIKV infection.

Nanocarriers for effective delivery: modulation of innate immunity for the management of infections and the associated complications

Innate immunity is the first line of defense against invading pathogens. Innate immune cells can recognize invading pathogens through recognizing pathogen-associated molecular patterns (PAMPs) via pattern recognition receptors (PRRs). The recognition of PAMPs by PRRs triggers immune defense mechanisms and the secretion of pro-inflammatory cytokines such as TNF-α, IL-1β, and IL-6. However, sustained and overwhelming activation of immune system may disrupt immune homeostasis and contribute to inflammatory disorders. Immunomodulators targeting PRRs may be beneficial to treat infectious diseases and their associated complications. However, therapeutic performances of immunomodulators can be negatively affected by (1) high immune-mediated toxicity, (2) poor solubility and (3) bioactivity loss after long circulation. Recently, nanocarriers have emerged as a very promising tool to overcome these obstacles owning to their unique properties such as sustained circulation, desired bio-distribution, and preferred pharmacokinetic and pharmacodynamic profiles. In this review, we aim to provide an up-to-date overview on the strategies and applications of nanocarrier-assisted innate immune modulation for the management of infections and their associated complications. We first summarize examples of important innate immune modulators. The types of nanomaterials available for drug delivery, as well as their applications for the delivery of immunomodulatory drugs and vaccine adjuvants are also discussed.

Antiviral Effect of hBD-3 and LL-37 during Human Primary Keratinocyte Infection with West Nile Virus

West Nile virus (WNV) is an emerging flavivirus transmitted through mosquito bites and responsible for a wide range of clinical manifestations. Following their inoculation within the skin, flaviviruses replicate in keratinocytes of the epidermis, inducing an innate immune response including the production of antimicrobial peptides (AMPs). Among them, the cathelicidin LL-37 and the human beta-defensin (hBD)-3 are known for their antimicrobial and immunomodulatory properties. We assessed their role during WNV infection of human primary keratinocytes. LL-37 reduced the viral load in the supernatant of infected keratinocytes and of the titer of a viral inoculum incubated in the presence of the peptide, suggesting a direct antiviral effect of this AMP. Conversely, WNV replication was not inhibited by hBD-3. The two peptides then demonstrated immunomodulatory properties whether in the context of keratinocyte stimulation by poly(I:C) or infection by WNV, but not alone. This study demonstrates the immunostimulatory properties of these two skin AMPs at the initial site of WNV replication and the ability of LL-37 to directly inactivate West Nile viral infectious particles. The results provide new information on the multiple functions of these two peptides and underline the potential of AMPs as new antiviral strategies in the fight against flaviviral infections.

Antimicrobial peptides and their potential application in antiviral coating agents

Coronavirus pandemic has evidenced the importance of creating bioactive materials to mitigate viral infections, especially in healthcare settings and public places. Advances in antiviral coatings have led to materials with impressive antiviral performance; however, their application may face health and environmental challenges. Bio-inspired antimicrobial peptides (AMPs) are suitable building blocks for antimicrobial coatings due to their versatile design, scalability, and environmentally friendly features. This review presents the advances and opportunities on the AMPs to create virucidal coatings. The review first describes the fundamental characteristics of peptide structure and synthesis, highlighting the recent findings on AMPs and the role of peptide structure (α-helix, β-sheet, random, and cyclic peptides) on the virucidal mechanism. The following section presents the advances in AMPs coating on medical devices with a detailed description of the materials coated and the targeted pathogens. The use of peptides in vaccine formulations is also reported, emphasizing the molecular interaction of peptides with different viruses and the current clinical stage of each formulation. The role of several materials (metallic particles, inorganic materials, and synthetic polymers) in the design of antiviral coatings is also presented, discussing the advantages and the drawbacks of each material. The final section offers future directions and opportunities for using AMPs on antiviral coatings to prevent viral outbreaks.

An in silico scientific basis for LL-37 as a therapeutic for Covid-19

A multi-pronged approach with help in all forms possible is essential to completely overcome the Covid-19 pandemic. There is a requirement to research as many new and different types of approaches as possible to cater to the entire world population, complementing the vaccines with promising results. The need is also because SARS-CoV-2 has several unknown or variable facets which get revealed from time to time. In this work, in silico scientific findings are presented, which are indicative of the potential for the use of the LL-37 human anti-microbial peptide as a therapeutic against SARS-CoV-2. This indication is based on the high structural similarity of LL-37 to the N-terminal helix, with which the virus interacts, of the receptor for SARS-CoV-2, Angiotensin Converting Enzyme 2. Moreover, there is positive prediction of binding of LL-37 to the receptor-binding domain of SARS-CoV-2; this is the first study to have described this interaction. In silico data on the safety of LL-37 are also reported. As Vitamin D is known to upregulate the expression of LL-37, the vitamin is a candidate preventive molecule. This work provides the possible basis for an inverse correlation between Vitamin D levels in the body and the severity of or susceptibility to Covid-19, as widely reported in literature. With the scientific link put forth herein, Vitamin D could be used at an effective, medically prescribed, safe dose as a preventive. The information in this report would be valuable in bolstering the worldwide efforts to eliminate the pandemic as early as possible.

Endogenous cathelicidin is required for protection against ZIKV-caused testis damage via inactivating virons

Cathelicidins have been shown to effectively inhibit flavivirus replication in vitro. However, the effects of mouse and human endogenous cathelicidins on flavivirus infection in vivo are rarely known. We herein found that mouse endogenous cathelicidin CRAMP was significantly up-regulated upon Zika virus (ZIKV) infection. CRAMP deficiency markedly exacerbated ZIKV replication in testis, and aggravated ZIKV-induced testicular damage and ZIKV-induced spermatic damage in mice, indicating that endogenous cathelicidin is required for protection against ZIKV-caused male infertility in mice. In vitro antiviral assay showed that both mouse cathelidin CRAMP and human cathelicidin LL-37 obviously reduced ZIKV-caused cytopathic effect and inhibited ZIKV replication in Vero cells. Antiviral mechanism revealed that they both directly inactivated ZIKV virons by binding to ZIKV virons and inducing the leakage of ZIKV genomic RNA, consequently inactivated ZIKV virons. In vivo antiviral assay indicated that both of them effectively inhibited ZIKV replication in C57BL/6J and IFNα/β receptor-deficient (Ifnar1^-/-) mice when CRAMP or LL-37 was intravenously injected in parallel with or at 1 h after intravenous injection of ZIKV, implying that mouse cathelidin CRAMP and human cathelicidin LL-37 effectively inactivated ZIKV particles and exhibited therapeutic potential against ZIKV infection in vivo. Our findings reveal that endogenous cahtelicidin CRAMP and LL-37 act as inactivators of ZIKV, and effectively protect against ZIKV replication and ZIKV-induced male infertility, highlighting their potential for therapy of ZIKV infection.

Antimicrobial peptides: mechanism of action, activity and clinical potential

The management of bacterial infections is becoming a major clinical challenge due to the rapid evolution of antibiotic resistant bacteria. As an excellent candidate to overcome antibiotic resistance, antimicrobial peptides (AMPs) that are produced from the synthetic and natural sources demonstrate a broad-spectrum antimicrobial activity with the high specificity and low toxicity. These peptides possess distinctive structures and functions by employing sophisticated mechanisms of action. This comprehensive review provides a broad overview of AMPs from the origin, structural characteristics, mechanisms of action, biological activities to clinical applications. We finally discuss the strategies to optimize and develop AMP-based treatment as the potential antimicrobial and anticancer therapeutics.

Natural antimicrobial peptides as a source of new antiviral agents

Current antiviral drugs are limited because of their adverse side effects and increased rate of resistance. In recent decades, much scientific effort has been invested in the discovery of new synthetic and natural compounds with promising antiviral properties. Among this new generation of compounds, antimicrobial peptides with antiviral activity have been described and are attracting attention due to their mechanism of action and biological properties. To understand the potential of antiviral peptides (AVPs), we analyse the antiviral activity of well-known AVP families isolated from different natural sources, discuss their physical-chemical properties, and demonstrate how AVP databases can guide us to design synthetic AVPs with better therapeutic properties. All considerations in this sphere of antiviral therapy clearly demonstrate the remarkable contribution that AVPs may make in conquering old as well as newly emerging viruses that plague humanity.