Identification and Characterization of the First Cathelicidin from Sea Snakes with Potent Antimicrobial and Anti-inflammatory Activity and Special Mechanism

Cathelicidin-BF: A Potent Antimicrobial Peptide Leveraging Charge and Phospholipid Recruitment against Multidrug-Resistant Clinical Bacterial Isolates

Cathelicidin-BF (CatBF) is a LL-37 homologous antimicrobial peptide (AMP) isolated from Bungarus fasciatus with an exceptional portfolio of antimicrobial, antiviral, antifungal, and anticancer activities. Contrary to many AMPs, it showed a good pharmacological profile with a half-life of at least 1 h in serum and efficacy against bacterial infections in mice. To evaluate its potential against resistant nosocomial infections, we assessed its activity against 81 clinically relevant resistant bacterial isolates. CatBF exhibited minimum inhibitory concentrations (MICs) as low as 0.5 μM against carbapenem-resistant Acinetobacter baumannii, Klebsiella pneumoniae, and Escherichia coli. Its wide-ranging activity, unaffected by resistance mechanisms or Gram phenotype, prompted us to investigate its molecular mode of action. NMR spectroscopy, paramagnetic probes, and molecular dynamics (MD) simulations were employed to define its structure, penetration depth, and orientation in various membrane models, including micelles, bicelles, oriented bilayers, and vesicles. We found that CatBF's potent activity relies on its strong charge, allowing membrane neutralization at low peptide/lipid ratios and selective recruitment of charged phospholipids. At higher concentrations, a change in peptide orientation reveals membrane invagination and the formation of transient pores possibly leading to bacterial death. Our findings highlight the potential of CatBF as a model for developing resistance-independent agents to combat multidrug-resistant (MDR) bacterial infections.

Identification and Characterization of a Novel GAPDH-Derived Antimicrobial Peptide From Jellyfish

Marine organisms serve as a rich source of bioactive natural compounds, including antimicrobial agents. Jellyfish, which are ancient marine invertebrates with hundreds of millions of years of evolutionary history, have been in continuous contact with a diverse array of pathogenic microorganisms from seawater, which may give rise to a distinctive innate immune system and related defensive molecules. However, it is difficult and inefficient to isolate active ingredients directly from jellyfish for enrichment, though few jellyfish-sourced antimicrobial peptides (AMPs) have been reported. In this study, we utilized transcriptomic big data with bioinformatic tools to dig deeper into potential antimicrobial components in jellyfish, and identified a new AMP JFP-2826 from Rhopilema esculentum. The 20-mer peptide exhibited an alpha-helix structure and showed antimicrobial activity against selected bacterial strains; more importantly, JFP-2826 demonstrated good selectivity for marine-specific Vibrio including Vibrio vulnificus. Sequence analysis of the full-length protein of JFP-2826 revealed that it is derived from the housekeeping gene glyceraldehyde-3-phosphate dehydrogenase (GAPDH), which is probably produced through enzymatic cleavage of the N-terminal fragment. This suggests that GAPDH of jellyfish might have a newly discovered antimicrobial-related function that is conducted by releasing JFP-2826-like cryptic peptides. JFP-2826 can be subjected to further structural modifications and optimizations to potentially become a potent lead peptide for the development of novel antimicrobial drugs treating infections of marine pathogens.

Harnessing marine antimicrobial peptides for novel therapeutics: A deep dive into ocean-derived bioactives

Marine antimicrobial peptides (AMPs) are potent bioactive compounds with broad-spectrum activity against bacteria, viruses, and fungi, offering a promising alternative to traditional antibiotics. These small, cationic, and amphiphilic peptides (3-50 amino acids) are key components of marine organisms' immune defenses, adapted to harsh oceanic environments. Discovered in the 1980s, marine AMPs have garnered interest for their unique structures and potential applications in human health. However, despite the ocean's vast biodiversity, they remain underexplored compared to land-based AMPs. This review emphasizes the therapeutic potential of marine AMPs, including their modes of action, structural variety, and applications in drug development, tissue regeneration, and cancer treatment. Moreover, it discusses their antibacterial, antiviral, antifungal, and antiparasitic properties. Additionally, the review addresses strategies to enhance the therapeutic potential of marine AMPs and the challenges associated with their development. By examining the promising future of marine AMPs, this review aims to pave the way for new approaches to combat antimicrobial resistance and develop innovative treatments for various infectious diseases. The potential of marine AMPs as the "medicine bank of the new millennium" remains vast, providing a valuable resource for future drug discovery and sustainable practices across industries.

Nature's Arsenal: Uncovering Antibacterial Agents Against Antimicrobial Resistance

Background/Objectives: Antimicrobial resistance (AMR) poses a significant public health threat, leading to increased mortality. The World Health Organization has established a priority list highlighting critical multidrug-resistant (MDR) pathogens that demand urgent research on antimicrobial treatments. Considering this and the fact that new antibiotics are only sporadically approved, natural antibacterial agents have seen a resurgence in interest as potential alternatives to conventional antibiotics and chemotherapeutics. Natural antibacterials, derived from microorganisms, higher fungi, plants, animals, natural minerals, and food sources, offer diverse mechanisms of action against MDR pathogens. Here, we present a comprehensive summary of antibacterial agents from natural sources, including a brief history of their application and highlighting key strategies for using microorganisms (microbiopredators, such as bacteriophages), plant extracts and essential oils, minerals (e.g., silver and copper), as well as compounds of animal origin, such as milk or even venoms. The review also addresses the role of prebiotics, probiotics, and antimicrobial peptides, as well as novel formulations such as nanoparticles. The mechanisms of action of these compounds, such as terpenoids, alkaloids, and phenolic compounds, are explored alongside the challenges for their application, e.g., extraction, formulation, and pharmacokinetics. Conclusions: Future research should focus on developing eco-friendly, sustainable antimicrobial agents and validating their safety and efficacy through clinical trials. Clear regulatory frameworks are essential for integrating these agents into clinical practice. Despite challenges, natural sources offer transformative potential for combating AMR and promoting sustainable health solutions.

Improving the Stability and Anti-Infective Activity of Sea Turtle AMPs Using Multiple Structural Modification Strategies

Antimicrobial peptides (AMPs) are regarded as promising candidates for combating antimicrobial resistance. Previously we identified an AMP named Cm-CATH2 from the green sea turtle, which exhibited potent antibacterial activity and attractive potential in application. However, natural AMPs including Cm-CATH2 frequently suffer from structural instability and sensitivity to physiological conditions, limiting their effectiveness. Herein, we explored various strategies to enhance the efficacy and stability of Cm-CATH2, including peptide truncation, non-natural amino acid substitutions, disulfide bond-based cyclization, and stapled peptide techniques. The results demonstrated that the truncated NCM4 significantly improved the antimicrobial capability of Cm-CATH2 while also enhancing its anti-inflammatory and antibiofilm activities with minimal cytotoxicity. Further ornithine-substituted peptide oNCM markedly enhanced the stability of NCM4 without compromising its antimicrobial efficacy. This study successfully designed a lead peptide oNCM with significant development potential, while providing valuable insights into the advantages and limitations associated with diverse strategies for enhancing the stability of AMPs.

Cath-HG improves the survival rates and symptoms in LPS-induced septic mice due to its multifunctional properties

The clinical syndrome of sepsis arises from severe infection, triggering an abnormal immune response that can lead to multiple organ dysfunction and ultimately the death of the host. Current therapies for sepsis are often limited in efficacy and fail to target the complex interplay of infection, inflammation and coagulation, leading to high mortality rates, which underscores the urgent need for novel therapeutics to combat sepsis. We previously identified Cath-HG, a compound capable of alleviating platelet dysfunction by suppressing GPVI-mediated platelet activation, thereby improving the survival of septic mice subjected to cecal ligation and puncture. Here, we further explored the antimicrobial, anti-inflammatory, LPS-neutralizing and anticoagulant properties of Cath-HG, as well as its protective effects in LPS-induced septic mice. Our results demonstrated that Cath-HG can bind to LPS, aggregate bacteria, and disrupt bacterial cell membranes, subsequently resulting in microbial death. Unlike most other Cathelicidins, Cath-HG displayed anticoagulation properties by regulating the enzymes plasmin, thrombin, β-tryptase, chymase and tissue plasminogen activator. In septic mice, Cath-HG provided protection against sepsis induced by LPS injection and exhibited bactericidal killing, LPS neutralization and inhibition of coagulation and MAPK signal transduction. Furthermore, Cath-HG obviously reduced the expression of pro-inflammatory cytokines and improved the pathological manifestations of tissue injury across multiple organs. Thus, Cath-HG emerges as a promising drug candidate for protecting against sepsis.

Cathelicidins: Opportunities and Challenges in Skin Therapeutics and Clinical Translation

Cathelicidins are a group of cationic, amphipathic peptides that play a vital role in the innate immune response of many vertebrates, including humans. Produced by immune and epithelial cells, they serve as natural defenses against a wide range of pathogens, including bacteria, viruses, and fungi. In humans, the cathelicidin LL-37 is essential for wound healing, maintaining skin barrier integrity, and combating infections. Cathelicidins of different origins have shown potential in treating various skin conditions, including melanoma, acne, and diabetic foot ulcers. Despite their promising therapeutic potential, cathelicidins face significant challenges in clinical application. Many peptide-based therapies have failed in clinical trials due to unclear efficacy and safety concerns. Additionally, the emergence of bacterial resistance, which contradicts initial claims of non-resistance, further complicates their development. To successfully translate cathelicidins into effective clinical treatments, therefore, several obstacles must be addressed, including a better understanding of their mechanisms of action, sustainable large-scale production, optimized formulations for drug delivery and stability, and strategies to overcome microbial resistance. This review examines the current knowledge of cathelicidins and their therapeutic applications and discusses the challenges that hinder their clinical use and must be overcome to fully exploit their potential in medicine.

A Tachyplesin Antimicrobial Peptide from Theraphosidae Spiders with Potent Antifungal Activity Against Cryptococcus neoformans

The venoms of Theraphosidae spiders have evolved into diverse natural pharmacopeias through selective pressures. Cryptococcus neoformans is a global health threat that frequently causes life-threatening meningitis and fungemia, particularly in immunocompromised patients. In this study, we identify a novel anti-C. neoformans peptide, QS18 (QCFKVCFRKRCFTKCSRS), from the venom gland of China's native spider species Chilobrachys liboensis by utilizing bioinformatic tools. QS18 shares over 50% sequence similarity with tachyplesin peptides, previously identified only in horseshoe crab hemocytes, expanding the known repertoire of the tachyplesin family to terrestrial arachnids. The oxidative folding of QS18 notably enhances its antifungal activity and stability, resulting in a minimum inhibitory concentration of 1.4 µM. The antimicrobial mechanism of QS18 involves cell membrane disruption. QS18 exhibits less than 5% hemolysis in human erythrocytes, indicating microbial selectivity and a favorable safety profile for therapeutic use. Furthermore, mouse model studies highlight QS18's ability as an antifungal agent with notable anti-inflammatory activity. Our study demonstrates QS18 as both a promising template for spider venom peptide research and a novel candidate for the development of peptide antifungals.

Immunomodulatory peptides: new therapeutic horizons for emerging and re-emerging infectious diseases

The emergence and re-emergence of multi-drug-resistant (MDR) infectious diseases have once again posed a significant global health challenge, largely attributed to the development of bacterial resistance to conventional anti-microbial treatments. To mitigate the risk of drug resistance globally, both antibiotics and immunotherapy are essential. Antimicrobial peptides (AMPs), also referred to as host defense peptides (HDPs), present a promising therapeutic alternative for treating drug-resistant infections due to their various mechanisms of action, which encompass antimicrobial and immunomodulatory effects. Many eukaryotic organisms produce HDPs as a defense mechanism, for example Purothionin from Triticum aestivum plant, Defensins, Cathelicidins, and Histatins from humans and many such peptides are currently the focus of research because of their antibacterial, antiviral and anti-fungicidal properties. This article offers a comprehensive review of the immunomodulatory activities of HDPs derived from eukaryotic organisms including humans, plants, birds, amphibians, reptiles, and marine species along with their mechanisms of action and therapeutic benefits.

Host defense peptides in crocodilians - A comprehensive review

Amphibians and reptiles, like all animals, are prone to periodic infections. However, crocodilians stand out for their remarkable ability to remain generally healthy and infection-free despite frequent exposure to a wide variety of microorganisms in their habitats and often sustaining significant injuries. These animals have evolved highly active immune mechanisms that provide rapid and effective defense. This is evidenced by the superior hemolytic capacity of their plasma compared to that of other organisms. To date, several host defense peptides (HDPs) have been identified in crocodilians, including cathelicidins, beta-defensins, hepcidins, leucrocins, hemocidins, and omwaprins. These peptides exhibit potent and broad-spectrum antimicrobial, antibiofilm, antifungal, and anticancer activities. Due to the relatively low but diverse evolutionary rate of crocodilians, the HDPs found in this species offer valuable insights into proteins and mechanisms of action that are highly conserved across many animals related to immune defense. The potential applications of HDPs in modern medicine represent a promising strategy for developing new therapeutic agents. Their novelty and the vast variability with which peptide sequences can be designed and modified expand the field of application for HDPs almost infinitely. This review addresses the urgent need for innovative and more effective drugs to combat the rise of antimicrobialresistant infections and evaluates the potential of crocodilian HDPs. It presents recent advances in the identification of crocodilian HDPs, particularly antimicrobial peptides (AMPs), including previously underexplored topics such as the sequential and structural conformation of different peptide types in crocodilians and the use of bioinformatics tools to enhance native peptides.

Discovery and characterization of a novel Lepidoptera-specific antimicrobial peptide from the fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae)

Antimicrobial peptides (AMPs) are critical components of innate immunity in diverse organisms, including plants, vertebrates, and insects. This study identified and characterized a novel Lepidoptera-specific AMP, named lepidoptin, from the invasive pest Spodoptera frugiperda (Lepidoptera: Noctuidae). Lepidoptin is a 116-amino acid protein containing a signal peptide and a novel β-sandwich domain that is distinct from previously reported AMPs. Temporal and spatial expression analyses revealed a significant upregulation of the lepidoptin gene in vivo and in cultured SF9 cells in response to pathogens. Molecular docking analysis identified a specific binding cavity. Enzyme-linked immunosorbent assay and binding assays confirmed that lepidoptin can bind to pathogen-associated molecular patterns, bacteria, and fungi. Recombinant lepidoptin exhibited potent antibacterial activity by inducing bacterial agglutination, inhibiting bacterial growth, increasing bacterial membrane permeability, and preventing biofilm formation. Lepidoptin also showed antifungal activity against the entomopathogenic fungus Beauveria bassiana by inhibiting spore germination, increasing fungal cell permeability, and increasing reactive oxygen species. Injection of recombinant lepidoptin into S. frugiperda larvae increased survival after B. bassiana infection, whereas knockdown of lepidoptin by RNA interference decreased larval survival. In addition, lepidoptin showed antimicrobial activity against the plant pathogen Fusarium graminearum by inhibiting spore germination and alleviating disease symptoms in wheat seedlings and cherry tomatoes. This study demonstrates the remarkable dual functionality of lepidoptin in enhancing S. frugiperda immunity and controlling plant pathogens, making it a promising candidate for biocontrol strategies in both pest management and plant disease prevention.

Venom: A Promising Avenue for Antimicrobial Therapeutics

Venom in medicine is well documented in the chronicles of ancient Greece and the Roman Empire and persisted into the Renaissance and even into the modern era. Venoms were not always associated with detrimental consequences. Since ancient times, the curative capacity of venom has been recognized, portraying venom as a metaphor for pharmacy and medicine. Venom proteins and peptides' antimicrobial potential has not undergone systematic exploration despite the huge literature on natural antimicrobials. In light of the escalating challenge of antimicrobial resistance and the diminishing effectiveness of antibiotics, there is a pressing need for innovative antimicrobials capable of effectively addressing illnesses caused by multidrug-resistant microorganisms. This review adds to our understanding of the effectiveness of different venom components against a host of pathogenic microorganisms. The aim is to illuminate the various antimicrobials present in venom and venom peptides, thereby emphasizing the unexplored medicinal potential for antimicrobial properties. We have presented a concise summary of the molecular examination of the venom peptides' functioning processes, as well as the current clinical and preclinical progress of venom antimicrobial peptides.

Synergistic collaboration between AMPs and non-direct antimicrobial cationic peptides

Non-direct antimicrobial cationic peptides (NDACPs) are components of the animal innate immune system. But their functions and association with antimicrobial peptides (AMPs) are incompletely understood. Here, we reveal a synergistic interaction between the AMP AW1 and the NDACP AW2, which are co-expressed in the frog Amolops wuyiensis. AW2 enhances the antibacterial activity of AW1 both in vitro and in vivo, while mitigating the development of bacterial resistance and eradicating biofilms. AW1 and AW2 synergistically damage bacterial membranes, facilitating cellular uptake and interaction of AW2 with the intracellular target bacterial genomic DNA. Simultaneously, they trigger the generation of ROS in bacteria, contributing to cell death upon reaching a threshold level. Moreover, we demonstrate that this synergistic antibacterial effect between AMPs and NDACPs is prevalent across diverse animal species. These findings unveil a robust and previously unknown correlation between AMPs and NDACPs as a widespread antibacterial immune defense strategy in animals.

Antiparasitic Evaluation of Aquiluscidin, a Cathelicidin Obtained from Crotalus aquilus, and the Vcn-23 Derivative Peptide against Babesia bovis, B. bigemina and B. ovata

Babesiosis is a growing concern due to the increased prevalence of this infectious disease caused by Babesia protozoan parasites, affecting various animals and humans. With rising worries over medication side effects and emerging drug resistance, there is a notable shift towards researching babesiacidal agents. Antimicrobial peptides, specifically cathelicidins known for their broad-spectrum activity and immunomodulatory functions, have emerged as potential candidates. Aquiluscidin, a cathelicidin from Crotalus aquilus, and its derivative Vcn-23, have been of interest due to their previously observed antibacterial effects and non-hemolytic activity. This work aimed to characterize the effect of these peptides against three Babesia species. Results showed Aquiluscidin's significant antimicrobial effects on Babesia species, reducing the B. bigemina growth rate and exhibiting IC50 values of 14.48 and 20.70 μM against B. ovata and B. bovis, respectively. However, its efficacy was impacted by serum presence in culture, and it showed no inhibition against a B. bovis strain grown in serum-supplemented medium. Conversely, Vcn-23 did not demonstrate babesiacidal activity. In conclusion, Aquiluscidin shows antibabesia activity in vitro and its efficacy is affected by the presence of serum in the culture medium. Nevertheless, this peptide represents a candidate for further investigation of its antiparasitic properties and provides insights into potential alternatives for the treatment of babesiosis.

Cathelicidin AS-12W Derived from the Alligator sinensis and Its Antimicrobial Activity Against Drug-Resistant Gram-Negative Bacteria In Vitro and In Vivo

Antimicrobial peptides (AMPs) have the potential to treat multidrug-resistant bacterial infections. Cathelicidins are a class of cationic antimicrobial peptides that are found in nearly all vertebrates. Herein, we determined the mature peptide region of Alligator sinensis cathelicidin by comparing its cathelicidin peptide sequence with those of other reptiles and designed nine peptide mutants based on the Alligator sinensis cathelicidin mature peptide. According to the antibacterial activity and cytotoxicity screening, the peptide AS-12W demonstrated broad-spectrum antibacterial activity and exhibited low erythrocyte hemolytic activity. In particular, AS-12W exhibited strong antibacterial activity and rapid bactericidal activity against carbapenem-resistant Pseudomonas aeruginosa in vitro. Additionally, AS-12W effectively removed carbapenem-resistant P. aeruginosa from blood and organs in vivo, leading to improved survival rates in septic mice. Furthermore, AS-12W exhibited good stability and tolerance to harsh conditions such as high heat, high salt, strong acid, and strong alkali, and it also displayed high stability toward trypsin and simulated gastric fluid (SGF). Moreover, AS-12W showed significant anti-inflammatory effects in vitro by inhibiting the production of proinflammatory factors induced by lipopolysaccharide (LPS). Due to its antibacterial mechanism against Escherichia coli, we found that this peptide could neutralize the negative charge on the surface of the bacteria and disrupt the integrity of the bacterial cell membrane. In addition, AS-12W has the ability to bind to the genomic DNA of bacteria and stimulate the production of reactive oxygen species (ROS) within bacteria, which is believed to be the reason for the good antibacterial activity of AS-12W. These results demonstrated that AS-12W exhibits remarkable antibacterial activity, particularly against carbapenem-resistant P. aeruginosa. Therefore, it is a potential candidate for antibacterial drug development.

Marine Antimicrobial Peptides: An Emerging Nightmare to the Life-Threatening Pathogens

The emergence of multidrug-resistant pathogens due to improper usage of conventional antibiotics has created a global health crisis. Alternatives to antibiotics being an urgent need, the scientific community is forced to search for new antimicrobials. This exploration has led to the discovery of antimicrobial peptides, a group of small peptides occurring in different phyla such as Porifera, Cnidaria, Annelida, Arthropoda, Mollusca, Echinodermata, and Chordata, as a component of their innate immune system. The marine environment, possessing immense diversity of organisms, is undoubtedly one of the richest sources of unique potential antimicrobial peptides. The distinctiveness of marine antimicrobial peptides lies in their broad-spectrum activity, mechanism of action, less cytotoxicity, and high stability, which form the benchmark for developing a potential therapeutic. This review aims to (1) synthesise the available information on the distinctive antimicrobial peptides discovered from marine organisms, particularly over the last decade, and (2) discuss the distinctiveness of marine antimicrobial peptides and their prospects.

Engineering Enhanced Antimicrobial Properties in α-Conotoxin RgIA through D-Type Amino Acid Substitution and Incorporation of Lysine and Leucine Residues

Antimicrobial peptides (AMPs), acknowledged as host defense peptides, constitute a category of predominant cationic peptides prevalent in diverse life forms. This study explored the antibacterial activity of α-conotoxin RgIA, and to enhance its stability and efficacy, D-amino acid substitution was employed, resulting in the synthesis of nine RgIA mutant analogs. Results revealed that several modified RgIA mutants displayed inhibitory efficacy against various pathogenic bacteria and fungi, including Candida tropicalis and Escherichia coli. Mechanistic investigations elucidated that these polypeptides achieved antibacterial effects through the disruption of bacterial cell membranes. The study further assessed the designed peptides' hemolytic activity, cytotoxicity, and safety. Mutants with antibacterial activity exhibited lower hemolytic activity and cytotoxicity, with Pep 8 demonstrating favorable safety in mice. RgIA mutants incorporating D-amino acids exhibited notable stability and adaptability, sustaining antibacterial properties across diverse environmental conditions. This research underscores the potential of the peptide to advance innovative oral antibiotics, offering a novel approach to address bacterial infections.

Asymmetric disturbance and permeabilization of bilayer membranes by 3-nm carbon dots

Small-sized fluorescent carbon dots (CDs) are gaining increasing attention in the field of biomedical applications. The environmental and biological compatibility of positively charged CDs has been extensively investigated; however, the potential cytotoxicity caused by negatively and particularly neutrally charged small CDs has been significantly overlooked. In this study, we conducted a comprehensive investigation into the cellular membrane disruption effect of weakly negatively charged 3-nm CDs using a combination of various biophysical techniques. Our findings demonstrate that even at a low concentration of 0.5 μg mL-1, these CDs induce significant perturbations on the cellular membrane, resulting in increased membrane permeability due to asymmetric disruption of the bilayer structure. Furthermore, CDs exhibit distinct mechanisms at different concentrations, including prompt insertion into the bilayer at low concentrations (<20 μg mL-1) and a synergistic effect after a threshold time at high concentrations (e.g., 25-200 μg mL-1). Moreover, these CDs possess specific antibacterial properties against Acinetobacter baumannii (with a minimum inhibitory concentration of 50 μg mL-1) while showing minimal hemolytic or cytotoxic effects on mammalian cells. This study provides comprehensive insights into the biophysical aspects of cellular membrane toxicity caused by small weakly negatively charged CDs and contributes to assessing their potential biomedical applications.

Marine natural products and human immunity: novel biomedical resources for anti-infection of SARS-CoV-2 and related cardiovascular disease

Marine natural products (MNPs) and marine organisms include sea urchin, sea squirts or ascidians, sea cucumbers, sea snake, sponge, soft coral, marine algae, and microalgae. As vital biomedical resources for the discovery of marine drugs, bioactive molecules, and agents, these MNPs have bioactive potentials of antioxidant, anti-infection, anti-inflammatory, anticoagulant, anti-diabetic effects, cancer treatment, and improvement of human immunity. This article reviews the role of MNPs on anti-infection of coronavirus, SARS-CoV-2 and its major variants (such as Delta and Omicron) as well as tuberculosis, H. Pylori, and HIV infection, and as promising biomedical resources for infection related cardiovascular disease (irCVD), diabetes, and cancer. The anti-inflammatory mechanisms of current MNPs against SARS-CoV-2 infection are also discussed. Since the use of other chemical agents for COVID-19 treatment are associated with some adverse effects in cardiovascular system, MNPs have more therapeutic advantages. Herein, it's time to protect this ecosystem for better sustainable development in the new era of ocean economy. As huge, novel and promising biomedical resources for anti-infection of SARS-CoV-2 and irCVD, the novel potential mechanisms of MNPs may be through multiple targets and pathways regulating human immunity and inhibiting inflammation. In conclusion, MNPs are worthy of translational research for further clinical application.

The Cell Envelope Integrity Protein Homologue D0Y85_RS06240 of Stenotrophomonas Confers Multiantibiotic Resistance

Background

The potential role of cell envelope integrity proteins in mediating antibiotic resistance is not well understood. In this study, we investigated whether the cell envelope integrity protein D0Y85_RS06240 from the multiantibiotic resistant strain Stenotrophomonas sp. G4 mediates antibiotic resistance.

Methods

Bioinformatics analysis was conducted to identify proteins related to the D0Y85_RS06240 protein. The D0Y85_RS06240 gene was heterologously expressed in Escherichia coli, both antibiotic MICs and the effect of efflux pump inhibitors on antibiotic MICs were determined by the broth microdilution method. A combination of antibiotic and efflux pump inhibitor was used to investigate bacterial killing kinetics, and binding of D0Y85_RS06240 to antibiotic molecules was predicted by molecular docking analysis.

Results

Sequence homology analysis revealed that D0Y85_RS06240 was related to cell envelope integrity proteins. The D0Y85_RS06240 heterologous expression strains were resistant to multiple antibiotics, including colistin, tetracycline, and cefixime. However, the efflux pump inhibitor N-methylpyrrolidone (NMP) reduced the antibiotic MICs of the D0Y85_RS06240 heterologous expression strain, and bacterial killing kinetics revealed that NMP enhanced the bactericidal rate of tetracycline to the drug-resistant bacteria. Molecular docking analysis indicated that D0Y85_RS06240 could bind colistin, tetracycline, and cefixime.

Conclusion

The cell envelope integrity protein D0Y85_RS06240 in Stenotrophomonas sp. G4 mediates multiantibiotic resistance. This study lays the foundation for an in-depth analysis of D0Y85_RS06240-mediated antibiotic resistance mechanisms and the use of D0Y85_RS06240 as a target for the treatment of multiantibiotic-resistant bacterial infections.

Aquiluscidin, a Cathelicidin from Crotalus aquilus, and the Vcn-23 Derivative Peptide, Have Anti-Microbial Activity against Gram-Negative and Gram-Positive Bacteria

Anti-microbial peptides play a vital role in the defense mechanisms of various organisms performing functions that range from the elimination of microorganisms, through diverse mechanisms, to the modulation of the immune response, providing protection to the host. Among these peptides, cathelicidins, a well-studied family of anti-microbial peptides, are found in various animal species, including reptiles. Due to the rise in anti-microbial resistance, these compounds have been suggested as potential candidates for developing new drugs. In this study, we identified and characterized a cathelicidin-like peptide called Aquiluscidin (Aq-CATH) from transcripts obtained from the skin and oral mucosa of the Querétaro's dark rattlesnake, Crotalus aquilus. The cDNA was cloned, sequenced, and yielded a 566-base-pair sequence. Using bioinformatics, we predicted that the peptide precursor contains a signal peptide, a 101-amino-acid conserved cathelin domain, an anionic region, and a 34-amino-acid mature peptide in the C-terminal region. Aq-CATH and a derived 23-amino-acid peptide (Vcn-23) were synthesized, and their anti-microbial activity was evaluated against various species of bacteria in in vitro assays. The minimal inhibitory concentrations against bacteria ranged from 2 to 8 μg/mL for both peptides. Furthermore, at concentrations of up to 50 μM, they exhibited no significant hemolytic activity (<2.3% and <1.2% for Aquiluscidin and Vcn-23, respectively) against rat erythrocytes and displayed no significant cytotoxic activity at low concentrations (>65% cell viability at 25 µM). Finally, this study represents the first identification of an antimicrobial peptide in Crotalus aquilus, which belongs to the cathelicidin family and exhibits the characteristic features of these peptides. Both Aq-CATH and its derived molecule, Vcn-23, displayed remarkable inhibitory activity against all tested bacteria, highlighting their potential as promising candidates for further antimicrobial research.

Antibacterial properties of peptides from chia (Salvia hispanica L.) applied to pork meat preservation

Chia-derived peptides might represent a novel alternative to conventional preservatives in food. Despite the antibacterial potential of these molecules, their food application is still limited. This study aimed to evaluate chia-derived peptides' antibacterial and antibiofilm potential in food preservation. The peptides YACLKVK, KLKKNL, KLLKKYL, and KKLLKI were synthesized, and their antibacterial activity against Listeria monocytogenes, Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, and Salmonella Enteritidis was evaluated through microdilution tests. A bacterial killing kinetic assay determined bacterial growth over time. The ability to prevent and eradicate S. aureus biofilm was assessed by crystal violet staining. The hemolytic and cytotoxic activities were determined in human red blood cells and fibroblasts using free hemoglobin detection and (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assays, respectively. Finally, a microbial challenge was performed on meat samples inoculated with L. monocytogenes and S. Enteritidis to determine their inhibitory effects on pork meat. Results showed the potential antibacterial activity of these peptides, with minimum inhibitory concentrations ranging from 0.23 to 5.58 mg/mL. Biofilm inhibition percentages were above 40%, and eradication percentages were lower than 20%. In vitro assays in human red blood cells and fibroblasts demonstrated that peptides are not hemolytic or cytotoxic agents. In microbiological challenge testing, KKLLKI showed the most promising antibacterial effects against S. Enteritidis on refrigerated pork meat samples. These findings suggest that chia-derived peptides have the potential as natural food preservatives due to their antibacterial and antibiofilm properties. Notably, KKLLKI demonstrated promising antibacterial effects against Salmonella spp. on a complex food matrix, such as pork meat. PRACTICAL APPLICATION: Chia-derived peptides can be a safer alternative to synthetic preservatives in the food industry because the latter may be detrimental to human health. Salmonella spp. growth on chilled pork meat was shown to be inhibited by the peptide KKLLKI, indicating that the use of these peptides may offer a more secure and natural alternative to synthetic preservatives.

Identification and Characterization of RK22, a Novel Antimicrobial Peptide from Hirudinaria manillensis against Methicillin Resistant Staphylococcus aureus

Staphylococcus aureus (S. aureus) infections are a leading cause of morbidity and mortality, which are compounded by drug resistance. By manipulating the coagulation system, S. aureus gains a significant advantage over host defense mechanisms, with hypercoagulation induced by S. aureus potentially aggravating infectious diseases. Recently, we and other researchers identified that a higher level of LL-37, one endogenous antimicrobial peptide with a significant killing effect on S. aureus infection, resulted in thrombosis formation through the induction of platelet activation and potentiation of the coagulation factor enzymatic activity. In the current study, we identified a novel antimicrobial peptide (RK22) from the salivary gland transcriptome of Hirudinaria manillensis (H. manillensis) through bioinformatic analysis, and then synthesized it, which exhibited good antimicrobial activity against S. aureus, including a clinically resistant strain with a minimal inhibitory concentration (MIC) of 6.25 μg/mL. The RK22 peptide rapidly killed S. aureus by inhibiting biofilm formation and promoting biofilm eradication, with good plasma stability, negligible cytotoxicity, minimal hemolytic activity, and no significant promotion of the coagulation system. Notably, administration of RK22 significantly inhibited S. aureus infection and the clinically resistant strain in vivo. Thus, these findings highlight the potential of RK22 as an ideal treatment candidate against S. aureus infection.

Dual-targeted and dual-sensitive self-assembled protein nanocarrier delivering hVEGI-192 for triple-negative breast cancer

Breast cancer is a highly prevalent malignancy worldwide among women with an increasing incidence in recent years. Triple-negative breast cancer (TNBC), a specific type of breast cancer, occurs primarily in young women and exhibits large tumor size, high clinical stage, and extremely poor prognosis with a high rate of lymph node, liver, and lung metastases. TNBC is insensitive to endocrine therapy and trastuzumab treatment, and there is an urgent need for effective therapeutics and treatment guidelines. However, investigations into antiangiogenic agents for the treatment of TNBC are ongoing. In this study, we successfully engineered a self-assembled protein nanocarrier TfRBP9-hVEGI-192-ELP fusion protein (TVEFP) to deliver the therapeutic protein, human vascular endothelial growth inhibitor (hVEGI-192). This was found to be effective in inhibiting tumor angiogenesis in vivo. The protein nanocarrier effectively inhibited the progression of TNBC in vivo and showed the behavior of self-assembly, thermoresponsiveness, enzyme stimulation-responsiveness, tumor-targeting, biocompatibility, and biodegradability. Near-infrared imaging studies showed that fluorescent dye-stained TVEFP effectively aggregated at the tumor site. The TVEFP nanocarrier significantly expands the application of the therapeutic protein hVEGI-192 and improves the imaging and biotherapeutic effects in TNBC, chiefly based on anti-angiogenesis effects.

Blapstin, a Diapause-Specific Peptide-Like Peptide from the Chinese Medicinal Beetle Blaps rhynchopetera, Has Antifungal Function

Drug resistance against bacteria and fungi has become common in recent years, and it is urgent to discover novel antimicrobial peptides to manage this problem. Many antimicrobial peptides from insects have been reported to have antifungal activity and are candidate molecules in the treatment of human diseases. In the present study, we characterized an antifungal peptide named blapstin that was isolated from the Chinese medicinal beetle Blaps rhynchopetera used in folk medicine. The complete coding sequence was cloned from the cDNA library prepared from the midgut of B. rhynchopetera. It is a 41-amino-acid diapause-specific peptide (DSP)-like peptide stabilized by three disulfide bridges and shows antifungal activity against Candida albicans and Trichophyton rubrum with MICs of 7 μM and 5.3 μM, respectively. The C. albicans and T. rubrum treated with blapstin showed irregular and shrunken cell membranes. In addition, blapstin inhibited the activity of C. albicans biofilm and showed little hemolytic or toxic activity on human cells and it is highly expressed in the fat body, followed by the hemolymph, midgut, muscle, and defensive glands. These results indicate that blapstin may help insects fight against fungi and showed a potential application in the development of antifungal reagents. IMPORTANCE Candida albicans is one of the conditional pathogenic fungi causing severe nosocomial infections. Trichophyton rubrum and other skin fungi are the main pathogens of superficial cutaneous fungal diseases, especially in children and the elderly. At present, antibiotics such as amphotericin B, ketoconazole, and fluconazole are the main drugs for the clinical treatment of C. albicans and T. rubrum infections. However, these drugs have certain acute toxicity. Long-term use can increase kidney damage and other side effects. Therefore, obtaining broad-spectrum antifungal drugs with high efficiency and low toxicity for the treatment of C. albicans and T. rubrum infections is a top priority. Blapstin is an antifungal peptide which shows activity against C. albicans and T. rubrum. The discovery of blapstin provides a novel clue for our understanding of the innate immunity of Blaps rhynchopetera and provides a template for designing antifungal drugs.

Past, Present, and Future of Naturally Occurring Antimicrobials Related to Snake Venoms

This review focuses on proteins and peptides with antimicrobial activity because these biopolymers can be useful in the fight against infectious diseases and to overcome the critical problem of microbial resistance to antibiotics. In fact, snakes show the highest diversification among reptiles, surviving in various environments; their innate immunity is similar to mammals and the response of their plasma to bacteria and fungi has been explored mainly in ecological studies. Snake venoms are a rich source of components that have a variety of biological functions. Among them are proteins like lectins, metalloproteinases, serine proteinases, L-amino acid oxidases, phospholipases type A₂, cysteine-rich secretory proteins, as well as many oligopeptides, such as waprins, cardiotoxins, cathelicidins, and β-defensins. In vitro, these biomolecules were shown to be active against bacteria, fungi, parasites, and viruses that are pathogenic to humans. Not only cathelicidins, but all other proteins and oligopeptides from snake venom have been proteolyzed to provide short antimicrobial peptides, or for use as templates for developing a variety of short unnatural sequences based on their structures. In addition to organizing and discussing an expressive amount of information, this review also describes new β-defensin sequences of Sistrurus miliarius that can lead to novel peptide-based antimicrobial agents, using a multidisciplinary approach that includes sequence phylogeny.

Exploring Oceans for Curative Compounds: Potential New Antimicrobial and Anti-Virulence Molecules against Pseudomonas aeruginosa

Although several antibiotics are already widely used against a large number of pathogens, the discovery of new antimicrobial compounds with new mechanisms of action is critical today in order to overcome the spreading of antimicrobial resistance among pathogen bacteria. In this regard, marine organisms represent a potential source of a wide diversity of unique secondary metabolites produced as an adaptation strategy to survive in competitive and hostile environments. Among the multidrug-resistant Gram-negative bacteria, Pseudomonas aeruginosa is undoubtedly one of the most important species due to its high intrinsic resistance to different classes of antibiotics on the market and its ability to cause serious therapeutic problems. In the present review, we first discuss the general mechanisms involved in the antibiotic resistance of P. aeruginosa. Subsequently, we list the marine molecules identified up until now showing activity against P. aeruginosa, dividing them according to whether they act as antimicrobial or anti-virulence compounds.

A Frog-Derived Cathelicidin Peptide with Dual Antimicrobial and Immunomodulatory Activities Effectively Ameliorates Staphylococcus aureus-Induced Peritonitis in Mice

As antimicrobial resistance poses an increasing threat to public health, it is urgent to develop new antimicrobial agents. In this paper, we identify a novel 30-residue peptide (Nv-CATH, NCNFLCKVKQRLRSVSSTSHIGMAIPRPRG) from the skin of the frog Nanorana ventripunctata, which belongs to the cathelicidin family. Nv-CATH exhibited broad-spectrum antimicrobial activity against Gram-positive and Gram-negative bacteria. Nv-CATH significantly protected mice from lethal infections caused by Staphylococcus aureus. Furthermore, the peptide suppressed excessive and harmful inflammatory responses by repressing the production of NO, IL-6, TNF-α, and IL-1β. The NF-κB-NLRP3 and MAPK inflammatory signaling pathways were involved in the protection in vitro and in vivo. Nv-CATH also modulated macrophage/monocyte and neutrophil trafficking to the infection site by stimulating CXCL1, CXCL2, and CCL2 production in macrophages. Nv-CATH augmented immunocyte-mediated bacterial killing by modestly promoting neutrophils' phagocytosis and PMA-induced NET formation. Thus, Nv-CATH protects mice against bacterial infection by antimicrobial-immunomodulatory duality. The combination of these two characteristics makes Nv-CATH a promising molecule template for the development of novel antimicrobial and antibiotic-resistant agents.

The dual antimicrobial and immunomodulatory roles of host defense peptides and their applications in animal production

Host defense peptides (HDPs) are small molecules with broad-spectrum antimicrobial activities against infectious bacteria, viruses, and fungi. Increasing evidence suggests that HDPs can also indirectly protect hosts by modulating their immune responses. Due to these dual roles, HDPs have been considered one of the most promising antibiotic substitutes to improve growth performance, intestinal health, and immunity in farm animals. This review describes the antimicrobial and immunomodulatory roles of host defense peptides and their recent applications in animal production.

Novel Alligator Cathelicidin As-CATH8 Demonstrates Anti-Infective Activity against Clinically Relevant and Crocodylian Bacterial Pathogens

Host defense peptides (HDPs) represent an alternative way to address the emergence of antibiotic resistance. Crocodylians are interesting species for the study of these molecules because of their potent immune system, which confers high resistance to infection. Profile hidden Markov models were used to screen the genomes of four crocodylian species for encoded cathelicidins and eighteen novel sequences were identified. Synthetic cathelicidins showed broad spectrum antimicrobial and antibiofilm activity against several clinically important antibiotic-resistant bacteria. In particular, the As-CATH8 cathelicidin showed potent in vitro activity profiles similar to the last-resort antibiotics vancomycin and polymyxin B. In addition, As-CATH8 demonstrated rapid killing of planktonic and biofilm cells, which correlated with its ability to cause cytoplasmic membrane depolarization and permeabilization as well as binding to DNA. As-CATH8 displayed greater antibiofilm activity than the human cathelicidin LL-37 against methicillin-resistant Staphylococcus aureus in a human organoid model of biofilm skin infection. Furthermore, As-CATH8 demonstrated strong antibacterial effects in a murine abscess model of high-density bacterial infections against clinical isolates of S. aureus and Acinetobacter baumannii, two of the most common bacterial species causing skin infections globally. Overall, this work expands the repertoire of cathelicidin peptides known in crocodylians, including one with considerable therapeutic promise for treating common skin infections.

Synergistic Membrane Disturbance Improves the Antibacterial Performance of Polymyxin B

Drug-resistant Gram-negative bacteria pose a serious threat to public health, and polymyxin B (PMB) is clinically used as a last-line therapy for the treatment of infections caused by these pathogens. However, the appearance of PMB resistance calls for an effort to develop new approaches to improve its antibacterial performance. In this work, a new type of nanocomposite, composed of PMB molecules being chemically decorated on the surface of graphene oxide (GO) nanosheets, was designed, which showed potent antibacterial ability through synergistically and physically disturbing the bacterial membrane. The as-fabricated PMB@GO nanocomposites demonstrated an enhanced bacterial-killing efficiency, with a minimum inhibitory concentration (MIC) value half of that of free PMB (with an MIC value as low as 0.5 μg mL^-1 over Escherichia coli), and a bacterial viability less than one fourth of that of PMB (with a bacterial reduction of 60% after 3 h treatment, and 90% after 6 h incubation). Furthermore, the nanocomposite displayed moderate cytotoxicity or hemolysis effect, with cellular viabilities over 85% at concentrations up to 16 times the MIC value. Studies on antibacterial mechanism revealed that the synergy between PMB molecules and GO nanosheets greatly facilitated the vertical insertion of the nanocomposite into the lipid membrane, leading to membrane disturbance and permeabilization. Our results demonstrate a physical mechanism for improving the antibacterial performance of PMB and developing advanced antibacterial agents for better clinic uses.

A designed antimicrobial peptide with potential ability against methicillin resistant Staphylococcus aureus

Staphylococcus aureus (S. aureus) is a Gram-positive pathogenic bacterium, which persistently colonizes the anterior nares of approximately 20-30% of the healthy adult population, and up to 60% is intermittently colonized. With the misuse and overuse of antibiotics, large-scale drug-resistant bacteria, including methicillin-resistant S. aureus (MRSA), have been appeared. MRSA is among the most prevalent pathogens causing community-associated infections. Once out of control, the number of deaths caused by antimicrobial resistance may exceed 10 million annually by 2050. Antimicrobial peptides (AMPs) are regarded as the best solution, for they are not easy to develop drug resistance. Based on our previous research, here we designed a new antimicrobial peptide named GW18, which showed excellent antimicrobial activity against S. aureus, even MRSA, with the hemolysis less than 5%, no cytotoxicity, and no acute toxicity. Notably, administration of GW18 significantly decreased S. aureus infection in mouse model. These findings identify GW18 as the ideal candidate against S. aureus infection.

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.

Hunting for Novel Routes in Anticancer Drug Discovery: Peptides against Sam-Sam Interactions

Among the diverse protein binding modules, Sam (Sterile alpha motif) domains attract attention due to their versatility. They are present in different organisms and play many functions in physiological and pathological processes by binding multiple partners. The EphA2 receptor contains a Sam domain at the C-terminus (EphA2-Sam) that is able to engage protein regulators of receptor stability (including the lipid phosphatase Ship2 and the adaptor Odin). Ship2 and Odin are recruited by EphA2-Sam through heterotypic Sam-Sam interactions. Ship2 decreases EphA2 endocytosis and consequent degradation, producing chiefly pro-oncogenic outcomes in a cellular milieu. Odin, through its Sam domains, contributes to receptor stability by possibly interfering with ubiquitination. As EphA2 is upregulated in many types of tumors, peptide inhibitors of Sam-Sam interactions by hindering receptor stability could function as anticancer therapeutics. This review describes EphA2-Sam and its interactome from a structural and functional perspective. The diverse design strategies that have thus far been employed to obtain peptides targeting EphA2-mediated Sam-Sam interactions are summarized as well. The generated peptides represent good initial lead compounds, but surely many efforts need to be devoted in the close future to improve interaction affinities towards Sam domains and consequently validate their anticancer properties.

Screening of TNFR1 Binding Peptides from Deinagkistrodon acutus Venom through Phage Display

The venomous species Deinagkistrodon acutus has been used as anti-inflammatory medicine in China for a long time. It has been proven to have anti-inflammatory activity, but its specific anti-inflammatory components have not yet been fully elucidated. Tumor necrosis factor receptor-1 (TNFR1), which participates in important intracellular signaling pathways, mediates apoptosis, and functions as a regulator of inflammation, is often used as the target to develop anti-inflammatory drugs. The small peptides of snake venom have the advantages of weak immunogenicity and strong activity. To obtain the specific TNFR1 binding peptides, we constructed a T7 phage library of D. acutus venom glands, and then performed biopanning against TNFR1 on the constructed library. After biopanning three times, several sequences with potential binding capacity were obtained and one 41-amino acid peptide was selected through a series of biological analyses including sequence length, solubility, and simulated affinity, named DAvp-1. After synthesis, the binding capacity of DAvp-1 and TNFR1 was verified using surface plasmon resonance technology (SPR). Conclusively, by applying phage display technology, this work depicts the successful screening of a promising peptide DAvp-1 from D. acutus venom that binds to TNFR1. Additionally, our study emphasizes the usefulness of phage display technology for studies on screening natural product components.

Antimicrobial peptides, conventional antibiotics, and their synergistic utility for the treatment of drug-resistant infections

Antimicrobial peptides (AMPs), also known as host defense peptides (HDPs), are important effector immune defense molecules in multicellular organisms. AMPs exert their antimicrobial activities through several mechanisms; thus far, induction of drug resistance through AMPs has been regarded as unlikely. Therefore, they have great potential as new generation antimicrobial agents. To date, more than 30 AMP-related drugs are in the clinical trial phase. In recent years, studies show that some AMPs and conventional antibiotics have synergistic effects. The combined use of AMPs and antibiotics can kill drug-resistant pathogens, prevent drug resistance, and significantly improve the therapeutic effects of antibiotics. In this review, we discuss the progress in synergistic studies on AMPs and conventional antibiotics. An overview of the current understanding of the functional scope of AMPs, ongoing clinical trials, and challenges in the development processes are also presented.

The Protective Effects of Cath-MH With Anti-Propionibacterium Acnes and Anti-Inflammation Functions on Acne Vulgaris

Acne vulgaris is a common adolescent skin condition which is mainly caused by Propionibacterium acnes overcolonization and subsequent inflammation. Our previous studies have demonstrated that Cath-MH, an antimicrobial peptide from the skin of the frog Microhyla heymonsivogt, possesses potential antimicrobial, LPS-binding, and anti-septicemic properties. However, its protective effects and potential mechanisms against acne vulgaris are still unclear. In the present study, its anti-P. acnes effects were measured by two-fold broth dilution method, agglutination assay, scanning electron microscopy and confocal laser scanning microscopy experiments. Its treatment potential for acne vulgaris was further evaluated in mice ear inoculated by P. acnes. In addition, the binding ability between Cath-MH and LTA was measured by the Circular Dichroism and antibacterial assay. Moreover, the anti-inflammatory efficiency of Cath-MH was evaluated in LTA- and LPS-induced RAW 264.7 macrophage cells. Cath-MH was found to kill P. acnes with a MIC value of about 1.56 μM by membrane disruption mechanism. It also exhibited agglutination activity against P. acnes. Cath-MH was able to bind LTA as well as LPS, inhibit LTA/LPS-stimulated TLR2/4 expression, and subsequently decreased the inflammatory response in RAW 264.7 cells. As expected, Cath-MH alleviated the formation of edema and the infiltration of inflammatory cells in acne mouse model with concurrent suppression of P. acnes growth and inflammatory cytokines expression in vivo. The potent P. acnes inhibition activity combined with powerful anti-inflammatory effect of Cath-MH indicates its potential as a novel therapeutic option for acne vulgaris.

Defensing role of novel piscidins from largemouth bass (Micropterus salmoides) with evidence of bactericidal activities and inducible expressional delineation

Micropterus salmoides is an economical important species of freshwater-cultured fish, the in-depth knowledge of its immune system is in urgent development to cope with serious infectious diseases. Piscidin is an important antimicrobial peptide (AMP) family existing in almost all teleosts. However, no piscidin has been reported in largemouth bass. In this study, three novel piscidins (MSPiscidin-1, -2, and -3) were firstly identified and characterized from the largemouth bass. The predicted mature peptides of MSPiscidin-1, -2, and -3 (consists of 24, 27, 25 amino acid residues, respectively) all adopted an amphipathic α-helical conformation representative of cationic AMPs that are important for membrane permeabilization and antibacterial activity. MSPiscidin-2 and -3 indeed displayed strong, broad-spectrum, and highly efficient antimicrobial activities in vitro against aquatic pathogens, but MSPiscidin-1 didn't show direct antimicrobial activity. MSPiscidin-2 and -3 killed bacteria mainly by inducing membrane permeabilization, in addition, they also can interact with bacterial genomic DNA, which might influence the DNA replication and transcription. Besides, MSPiscidin-2 and -3 could effectively inhibit the formation of the bacterial biofilm and eliminate the preformed biofilms. In vivo, MSPiscidin-1-3 genes showed an inducible expression pattern in the tested tissues upon Vibrio harveyi infection, which further indicated the key roles of piscidins in innate immunity in largemouth bass. Overall, this study will supplement the understanding of M. salmoides innate immune system and provide candidates for the design of novel peptide antibacterial agents used in aquaculture.

Antimicrobial Activity of Snake β-Defensins and Derived Peptides

β-defensins are antimicrobial peptides presenting in vertebrate animals. They participate in innate immunity, but little is known about them in reptiles, including snakes. Although several β-defensin genes were described in Brazilian snakes, their function is still unknown. The peptide sequence from these genes was deduced, and synthetic peptides (with approximately 40 amino acids and derived peptides) were tested against pathogenic bacteria and fungi using microbroth dilution assays. The linear peptides, derived from β-defensins, were designed applying the bioisosterism strategy. The linear β-defensins were more active against Escherichia coli, Micrococcus luteus, Citrobacter freundii, and Staphylococcus aureus. The derived peptides (7–14 mer) showed antibacterial activity against those bacteria and on Klebsiella pneumoniae. Nonetheless, they did not present activity against Candida albicans, Cryptococcus neoformans, Trychophyton rubrum, and Aspergillus fumigatus showing that the cysteine substitution to serine is deleterious to antifungal properties. Tryptophan residue showed to be necessary to improve antibacterial activity. Even though the studied snake β-defensins do not have high antimicrobial activity, they proved to be attractive as template molecules for the development of antibiotics.

Biomaterials from the sea: Future building blocks for biomedical applications

Marine resources have tremendous potential for developing high-value biomaterials. The last decade has seen an increasing number of biomaterials that originate from marine organisms. This field is rapidly evolving. Marine biomaterials experience several periods of discovery and development ranging from coralline bone graft to polysaccharide-based biomaterials. The latter are represented by chitin and chitosan, marine-derived collagen, and composites of different organisms of marine origin. The diversity of marine natural products, their properties and applications are discussed thoroughly in the present review. These materials are easily available and possess excellent biocompatibility, biodegradability and potent bioactive characteristics. Important applications of marine biomaterials include medical applications, antimicrobial agents, drug delivery agents, anticoagulants, rehabilitation of diseases such as cardiovascular diseases, bone diseases and diabetes, as well as comestible, cosmetic and industrial applications.

Brevinin-2GHk, a Peptide Derived from the Skin of Fejervarya limnocharis, Inhibits Zika Virus Infection by Disrupting Viral Integrity

Several years have passed since the Zika virus (ZIKV) pandemic reoccurred in 2015–2016. However, there is still a lack of proved protective vaccines or effective drugs against ZIKV. The peptide brevinin-2GHk (BR2GK), pertaining to the brevinin-2 family of antimicrobial peptides, has been reported to exhibit only weak antibacterial activity, and its antiviral effects have not been investigated. Thus, we analyzed the effect of BR2GK on ZIKV infection. BR2GK showed significant inhibitory activity in the early and middle stages of ZIKV infection, with negligible cytotoxicity. Furthermore, BR2GK was suggested to bind with ZIKV E protein and disrupt the integrity of the envelope, thus directly inactivating ZIKV. In addition, BR2GK can also penetrate the cell membrane, which may contribute to inhibition of the middle stage of ZIKV infection. BR2GK blocked ZIKV E protein expression with an IC₅₀ of 3.408 ± 0.738 μΜ. In summary, BR2GK was found to be a multi-functional candidate and a potential lead compound for further development of anti-ZIKV drugs.

Effectiveness of Cathelicidin Antimicrobial Peptide against Ictalurid Catfish Bacterial Pathogens

One of the major goals in aquaculture is to protect fish against infectious diseases as disease outbreaks could lead to economic losses if not controlled. Antimicrobial peptides (AMPs), a class of highly conserved peptides known to possess direct antimicrobial activities against invading pathogens, were evaluated for their ability to protect Channel Catfish Ictalurus punctatus and hybrid catfish (female Channel Catfish × male Blue Catfish I. furcatus) against infection caused by the fish pathogen Aeromonas hydrophila ML09-119. To identify effective peptides, the minimum inhibitory concentrations against bacterial pathogens Edwardsiella ictaluri S97-773, Edwardsiella piscicida E22-10, A. hydrophila ML09-119, Aeromonas veronii 03X03876, and Flavobacterium columnare GL-001 were determined in vitro. In general and overall, cathelicidins derived from alligator and sea snake exhibited more potent and rapid antimicrobial activities against the tested catfish pathogens as compared to cecropin and pleurocidin AMPs and ampicillin, the antibiotic control. When the peptides (2.5 µg of peptide/g of fish) were injected into fish and simultaneously challenged with A. hydrophila through immersion, increased survival rates in Channel Catfish and hybrid catfish were observed in both cathelicidin (alligator and sea snake) treatments as compared to other peptides and the infected control (P < 0.001) with alligator cathelicidin being the overall best treatment. Bacterial numbers in the kidney and liver of Channel Catfish and hybrid catfish also decreased (P < 0.05) for cathelicidin-injected groups at 24 and 48 h after challenge infection. These results show the potential of cathelicidin to protect catfish against bacterial infections and suggest that an approach overexpressing the peptide in transgenic fish, which is the long-term goal of this research program, may provide a method of decreasing bacterial disease problems in catfish as delivering the peptides via individual injection or feeding would not be economically feasible.

A novel anionic cathelicidin lacking direct antimicrobial activity but with potent anti-inflammatory and wound healing activities from the salamander Tylototriton kweichowensis

Cathelicidin is a family of antimicrobial peptides (AMPs) existing in vertebrates, which play multiple functions in host responses against environmental stresses. All cathelicidins identified to date are cationic, no anionic member with net negative charges has been reported. In the present study, a novel anionic cathelicidin (TK-CATH) with a net charge of -3 was identified from the skin of the salamander, T. kweichowensis. Unlike most other cathelicidin members, it didn't exhibit direct antimicrobial activity. However, it demonstrated strong anti-inflammatory activity. It effectively inhibited the LPS-induced pro-inflammatory cytokine gene expression and protein production in amphibian leukocytes and mouse macrophages by inhibiting the LPS-activated mitogen-activated protein kinase (MAPK) signaling pathways. Besides, TK-CATH showed potent wound healing activity. It could effectively induce the production of several cytokines, chemokines and growth factors relating to wound healing, promote the motility and proliferation of keratinocytes, and accelerate the skin wound healing in a mouse full-thickness wound model. These results imply that TK-CATH participates in both the inflammatory phase and new tissue formation phase of wound repair process. Meanwhile, TK-CATH exhibited weak but effective free radical scavenging activity and low cytotoxicity. All the results above indicate that TK-CATH is a multifunctional peptide in the skin of the salamander T. kweichowensis. It may play important roles in host immune responses against bacterial infection and skin wound repair.

The Impact of Lung Proteases on Snake-Derived Antimicrobial Peptides

Respiratory infections are a leading cause of global morbidity and mortality and are of significant concern for individuals with chronic inflammatory lung diseases. There is an urgent need for novel antimicrobials. Antimicrobial peptides (AMPs) are naturally occurring innate immune response peptides with therapeutic potential. However, therapeutic development has been hindered by issues with stability and cytotoxicity. Availing of direct drug delivery to the affected site, for example the lung, can reduce unwanted systemic side effects and lower the required dose. As cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD) lungs typically exhibit elevated protease levels, the aim of this study was to assess their impact on snake-derived AMPs. Peptide cleavage was determined using SDS-PAGE and antimicrobial and anti-inflammatory activities of neutrophil elastase (NE)-incubated peptides were assessed using a radial diffusion assay (RDA) and an in vitro LPS-induced inflammation model, respectively. Although the snake-derived AMPs were found to be susceptible to cleavage by lung proteases including NE, several retained their function following NE-incubation. This facilitated the design of novel truncated derivatives that retained functionality following NE incubation. Snake-derived AMPs are tractable candidate treatments for use in environments that feature elevated NE levels, such as the CF airways.

Recent developments on production, purification and biological activity of marine peptides

Marine peptides are one of the richest sources of structurally diverse bioactive compounds and a considerable attention has been drawn towards their production and bioactivity. However, there is a paucity in consolidation of emerging trends encompassing both production techniques and biological application. Herein, we intend to review the recent advancements on different production, purification and identification technologies used for marine peptides along with presenting their potential health benefits. Bibliometric analysis revealed a growing number of scientific publications on marine peptides (268 documents per year) with both Asia (37.2%) and Europe (33.1%) being the major contributors. Extraction and purification by ultrafiltration and enzymatic hydrolysis, followed by identification by chromatographic techniques coupled with an appropriate detector could yield a high content of peptides with improved bioactivity. Moreover, the multifunctional health benefits exerted by marine peptides including anti-microbial, antioxidant, anti-hypertension, anti-diabetes and anti-cancer along with their structure-activity relationship were presented. The future perspective on marine peptide research should focus on finding improved separation and purification technologies with enhanced selectivity and resolution for obtaining more novel peptides with high yield and low cost. In addition, by employing encapsulation strategies such as nanoemulsion and nanoliposome, oral bioavailability and bioactivity of peptides can be greatly enhanced. Also, the potential health benefits that are demonstrated by in vitro and in vivo models should be validated by conducting human clinical trials for a technology transfer from bench to bedside.

EGCG Induces Pro-inflammatory Response in Macrophages to Prevent Bacterial Infection through the 67LR/p38/JNK Signaling Pathway

Extensive studies focused on the therapeutic efficacy of epigallocatechin-3-gallate (EGCG) against bacterial infection. However, little is known about its prophylactic efficacy against bacterial infection. Herein, we found that EGCG showed an effective prophylactic efficacy against bacterial infection with a broad spectrum, including Gram-negative, Gram-positive, and drug-resistant bacteria. Pretreatment with EGCG through intraperitoneal injection, intravenous injection, or intragastric administration significantly reduced the bacterial load, inflammatory response, and mortality in mouse abdominal infection models induced by bacterial inoculation or cecal ligation and puncture. Pretreatment with EGCG by intraperitoneal injection significantly increased the numbers of neutrophils and monocytes/macrophages in the abdominal cavity and peripheral blood of mice, and depletion of neutrophils and monocytes/macrophages by specific antibodies or chemical drugs obviously increased the bacterial load in mice. Of note, EGCG did not directly induce neutrophil and macrophage migration, and it just induced phagocyte migration in the presence of macrophages in a co-cultured system, implying that EGCG-induced phagocyte migration relies on its immunoregulatory effects on macrophages. EGCG markedly induced the production of cytokines and chemokines in macrophages and mouse peritoneal lavage, including tumor necrosis factor-α (TNF-α), interleukin-1 β (IL-1β), IL-6, CXC chemokine ligands 1 and 2 (CXCL1 and 2), and monocyte chemotactic protein-1 (MCP-1). EGCG significantly induced the phosphorylation of p38 and JNK mitogen-activated protein kinases (MAPKs) in macrophages, and inhibition of p38 and JNK MAPKs markedly reduced EGCG-induced chemokine and cytokine production. Anti-67-kDa laminin receptor (67LR) antibody treatment significantly reduced EGCG-induced chemokine production and p38 and JNK phosphorylation in macrophages. Together, EGCG showed an obvious prophylactic efficacy against bacterial infection by inducing a pro-inflammatory response in macrophages through the 67LR/p38/JNK signaling pathway, supporting the further development of EGCG as a potent prophylaxis for bacterial infection and providing new clues to understand the healthcare function of green tea.