Antimicrobial peptides as therapeutic agents: opportunities and challenges

Antimicrobial peptides: evolving soldiers in the battle against drug-resistant superbugs

The discovery of antibiotics was one of the greatest achievements in human history, however, antibiotic resistance evolved no later than the introduction of antibiotics. The rapid evolution of antibiotic-resistant pathogens soon became frightening and remained a global healthcare threat. There is an urgent need to have new alternatives or new strategies to combat the multi-drug resistant superbugs such as methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE), carbapenem-resistant Pseudomonas aeruginosa (CR-PA), extended-spectrum β-lactamases (ESBL) bearing multidrug-resistant Acinetobacter baumannii (MDR-AB), Escherichia coli (E. coli), and Klebsiella pneumoniae (K. pneumoniae). Antimicrobial peptides (AMPs) have been considered promising agents equipped with unique mechanisms of action along with several other benefits to fight the battle against drug-resistant superbugs. Overall, the current review summarizes the mechanisms of drug-resistant development, the mechanism of action adopted by AMPs to combat drug-resistant pathogens, and the immunomodulatory properties of AMPs. Additionally, we have also reviewed the synergistic potential of AMPs with conventional antibiotics along with the associated challenges and limitations of AMPs in the way of pharmacological development for therapeutic applications in clinical settings.

Rational design of synthetic antimicrobial peptides based on the Escherichia coli ShoB toxin

Antibiotic resistance is an escalating global concern, necessitating the development of novel antibiotics with unique mechanisms of action, and preferably also with a lowered propensity for resistance development. Type-I Toxin-Antitoxin (TA) systems that are ubiquitous in bacterial genomes consist of a genetic toxin element encoding a hydrophobic peptide and an antitoxin element producing an sRNA that inhibits the toxin translation. Although the biological roles of these membrane-associated toxins remain incompletely understood, their inherent lethality upon overexpression suggests a potential as antimicrobial agents. In this study, we explore the ShoB toxin from the shoB-ohsC TA system in Escherichia coli (E. coli) as a basis for designing synthetic antimicrobial peptides for exogenous delivery. We demonstrate that ShoB-derived peptides can retain antimicrobial efficacy when modified into shorter, cationic analogs with enhanced solubility. Our most promising hits exhibit rapid bactericidal action and frequency of resistance within E. coli cultures indicate a limited tendency for resistance development. These findings highlight that type-I TA systems constitute a novel source of potential peptide-based antibiotics, thereby offering an alternative largely unexplored strategy to combat antibiotic-resistant bacterial infections.

Antimicrobial action and mechanism of piscidin against Helicobacter pylori

BACKGROUND

The rise of antibiotic-resistant Helicobacter pylori (Hp) strains is complicating the management of common gastrointestinal conditions such as gastritis and ulcers. In search of effective treatment options, antimicrobial peptides are being explored as a promising strategy.

METHODS

Leveraging bioinformatics, we dissected structural and sequence profiles of piscidin, an antimicrobial peptide. We investigated whether long-term piscidin exposure induces resistance in Hp strains by measuring their minimum inhibitory concentration. The Oxford cup test was applied to measure inhibition zones of piscidin against Hp strains. Following piscidin treatment, we monitored morphological alterations in Hp strains using scanning electron microscopy, and changes in urease activity, expressions of virulence factors CagA and UreB, and adenosine triphosphate levels. Cytotoxicity of piscidin was evaluated in AGS and 293T cells.

RESULTS

Piscidin inhibited proliferation of Hp strains, with a low propensity of inducing resistance. Delving into underlying mechanisms, we observed piscidin could alter morphology of Hp strains, suppress urease activity, and downregulate expressions of virulence factors CagA and UreB, while also reducing intracellular ATP levels. Piscidin had good security.

CONCLUSION

Piscidin is a potent antibacterial agent against Hp with low resistance risk, making it a safe and effective treatment candidate.

Newly Identified Antimicrobial Peptide Scymicrosin7-26 from Scylla paramamosain Showing Potent Antimicrobial Activity Against Methicillin-Resistant Staphylococcus aureus In Vitro and In Vivo

Methicillin-resistant Staphylococcus aureus (MRSA) is a predominant pathogen causing skin and soft tissue infections, which significantly hinders the wound healing process and contributes to high mortality rates. The rise of multidrug-resistant bacteria, coupled with the limited availability of new antibiotics, underscores the pressing need for the development of innovative antimicrobial substances. Antimicrobial peptides (AMPs), with their multitargeted and rapid antimicrobial activity, are promising candidates to address this crisis. In this study, we identified a novel AMP, Scymicrosin7-26, derived from Scylla paramamosain, which demonstrated potent antimicrobial activity against a variety of MDR strains, particularly MRSA. Confocal microscopy and transmission electron microscopy observations showed that Scymicrosin7-26 bound to MRSA, and had a disruptive effect on cell walls and cell membranes, rapidly penetrating and killing MRSA. Notably, Scymicrosin7-26 exhibited good stability under various ionic conditions, thermal stresses and certain serum concentration, had no obvious toxic effects on HaCaT cells, and its ability to penetrate HaCaT cells indicated its potential for intracellular targeted therapy. In vitro, Scymicrosin7-26 significantly reduced the number of MRSA in HaCaT cells and inhibited intracellular MRSA proliferation. After verifying the low toxicity of Scymicrosin7-26 in vivo in the Marine model organism─marine medaka (Oryzias melastigma), a wound model of MRSA-infected mice was made, and topical administration of Scymicrosin7-26 in hypromellose gels could significantly reduce bacterial burden and promote wound closure. Histological analysis confirmed that Scymicrosin7-26 alleviated tissue damage and was comparable to the effect of vancomycin treatment. Collectively, Scymicrosin7-26 is promising for the treatment of MRSA wound infections and could be a valuable addition to the arsenal against antibiotic-resistant bacteria.

Lactoferrin-derived peptide PXL01 impacts nerve regeneration after sciatic nerve reconstruction in healthy and diabetic rats

Introduction

Although advanced surgical techniques are available, satisfactory functional outcomes after peripheral nerve injuries are uncommon. Hence, immune-modulating factors such as PXL01, a lactoferrin-derived peptide that improves axonal outgrowth in injured human digital nerves, have gained attention. We previously reported a short-term immunosuppressive effect of PXL01 after the repair of transected rat sciatic nerves, but it had no effect on nerve regeneration. Here, we investigated the potential of PXL01 to improve nerve regeneration in healthy rats and in a rat model of type 2 diabetes (Goto-Kakizaki [GK] rats).

Methods

A 10-mm sciatic nerve defect was created in healthy (n = 14) and diabetic GK rats (n = 14) and reconstructed using nerve autografts. Immediately after surgery, PXL01 or sodium chloride (control, placebo) (n = 7 for each treatment) was administered around the autograft. On day 8, immunohistochemical staining of the sciatic nerve and dorsal root ganglia (DRGs) was performed to analyze axonal outgrowth (neurofilament staining); inflammation (CD68 and CD206 macrophage staining in nerve); Schwann cell and sensory neuron activation (transcription factor ATF3 staining in nerve and DRGs) and apoptosis (cleaved caspase 3 staining in nerve); and neuroprotection (heat shock protein [HSP27] staining in nerve and DRGs).

Results

PXL01 had no impact on the macrophage response in the autografts but increased axonal outgrowth and HSP27 expression in the DRGs of healthy and diabetic rats, despite a lower number of activated Schwann cells in the autograft. Diabetes affected axonal outgrowth, Schwann cell and macrophage responses, and HSP27 expression. These effects were observed in the sciatic nerve as well as the DRG.

Discussion

Application of PXL01, despite having no impact on macrophages, may improve axonal outgrowth and affects Schwann cell activation in autograft-reconstructed sciatic nerves, as well as conveys neuroprotection (HSP27 expression) in the DRGs of healthy and diabetic GK rats. Diabetes influenced nerve regeneration in such autografts. Therefore, PXL01 is a promising candidate to improve nerve regeneration.

Single or double lipid-modified ultra-short antimicrobial peptides for treating infections caused by resistant bacteria

Unmodified ultra-short antimicrobial peptides (AMPs) have difficulty attaining high antimicrobial activity and low toxicity concurrently. Our previous studies have shown that single-site lipid modification can enhance the antimicrobial activity of AMPs. However, research on multi-site modification is scarce. This study designed and synthesized a series of single/double-site lipid-modified ultra-short AMPs. Particularly, the new single-site lipid-modified AMP C12 (C12-KKWW-NH2) and double-site lipid-modified AMP DC8 [(C8)2-KKKWW-NH2] showed high bacterial membrane selectivity and presented high stability. It is worth noting that C12 and DC8 exert excellent antibacterial effects on clinically resistant bacteria and have an extremely low resistance tendency. When combined with conventional antibiotics, they show synergistic antibacterial activity against resistant bacteria and curb the resistance of the antibiotics. Additionally, the novel ultra-short AMPs reveal non-receptor-mediated membrane bactericidal mechanisms and can kill the tested bacteria rapidly. Moreover, both C12 and DC8 have high antibacterial activity and low toxicity in vivo. These results suggest that both single-site and multi-site lipid modifications can produce highly efficient AMPs.

A novel function of short cationic peptide FP-CATH9 without antimicrobial activity reverses resistance to minocycline in common multidrug-resistant gram-negative bacteria

The increase in bacterial resistance to minocycline and other tetracyclines poses a serious threat to global public health. Because the development of new antibiotics has proven problematic, antibiotic sensitization therapy is now an effective coping strategy. While antimicrobial peptides generally exhibit broad-spectrum antibacterial activity and good biocompatibility, naturally truncated portions of antimicrobial peptides (such as snake cathelicidin) often do not exhibit antimicrobial activity, and their function remains unknown. FP-CATH9 is a short cationic peptide derived from FP-CATH (snake cathelicidin antimicrobial peptide) with an amphiphilic α-helical structure and no discernible antibacterial activity. However, FP-CATH9 was previously found to significantly enhance the activity of minocycline against gram-negative bacteria. In the present paper, clinically relevant minocycline-resistant gram-negative bacteria (Escherichia coli, Klebsiella pneumoniae, Acinetobacter baumannii, and Pseudomonas aeruginosa) were used as test bacteria for antibiotic sensitization screening. The sensitization activity of FP-CATH9 was found to be dose dependent in a double-dilution assay. The synergistic activity of FP-CATH9 on minocycline was subsequently determined using the checkerboard method. An ethidium bromide efflux test revealed that FP-CATH9 caused an accumulation of minocycline in bacteria. Additionally, FP-CATH9 exhibited low hemolytic activity on red blood cells and low cytotoxicity on Raw264.7 cells. In an in vivo model of bacterial infection, FP-CATH9 combined with minocycline exhibited an 80% protective effect on Galleria mellonella larvae infected with multidrug-resistant K. pneumoniae. In summary, FP-CATH9 is a new antibiotic adjuvant that reverses the resistance of gram-negative bacteria to minocycline by increasing intracellular accumulation of minocycline. This finding has broad application potential.IMPORTANCEThe existence of the efflux pump system enables bacteria to expel antibiotics, reduce the concentration of antibiotics in cells, and make antibiotics unable to effectively inhibit or kill bacteria, which is one of the main mechanisms of bacterial resistance to antibiotics. However, some efflux pumps are substrate specific, while others are with a wide range of substrates. In this study, FP-CATH9 as a new antibiotic adjuvant can specifically reverse the resistance of gram-negative bacteria to minocycline by increasing the intracellular accumulation of minocycline in bacteria and provides a new way to solve the increasing problem of bacterial drug resistance.

Optimizing the discovery bioanalysis strategy for macrocyclic peptides

Macrocyclic peptides (MCPs) have remained a compelling modality in drug discovery and development, with many successful marketed drugs. Their unique molecular structure and ADME properties have posed bioanalytical challenges that cannot be fully addressed with conventional small molecule LC-MRM assays. In this work, we developed and optimized a high-throughput discovery bioanalytical strategy for MCPs with 16 marketed MCP drugs. By evaluating ten different sample extraction methods based on the recovery and matrix effect, we identified that the protein precipitation extraction with MeOH/ACN (1/1 v/v) with 0.5% FA outperformed the other sample extraction methods, achieving 80% recovery for 80% of the MCP drugs and 90% matrix effect for 90% of the MCP drugs. By assessing the sensitivity of the targeted-selected ion monitoring (t-SIM) and parallel reaction monitoring (PRM) on the Orbitrap HRMS and comparing with the conventional LC-MRM, we concluded that the t-SIM provided comparable sensitivity with MRM (LOQ at 1~3 ng/mL for the majority of the MCP drugs), with the extra benefits of minimal method development and high post-acquisition flexibility in data processing. The optimized bioanalytical strategy was applied to various biological matrices and displayed performance that met the quantitation requirements for discovery bioanalysis.

Antimicrobial Peptides and Their Mimetics: Promising Candidates of Next-Generation Therapeutic Agents Combating Multidrug-Resistant Bacteria

The increasing morbidity and mortality caused by multidrug-resistant bacteria alerts human beings to the fact that conventional antibiotics are no longer reliable and effective alternatives are imperatively needed. Owing to wide range of sources, diverse structures, and unique mode of action, antimicrobial peptides have been highly anticipated and extensively studied in recent years. Besides, the integration of artificial intelligence helps researchers gain access to the vast unexplored chemical space, which opens more opportunities for the optimization and design of novel structures. Moreover, Due to advances in chemistry and synthetic biology, researchers have also begun to focus on the potential of chemical mimetics of antimicrobial peptides. In this review, a comprehensive discussion about natural and synthesized antimicrobial peptides as well as their chemical mimetics is made, so as to provide a comprehensive summary of this field and inspire follow-up research.

The importance role of central proline to the antimicrobial potency and selectivity of indolicidin

The increasing prevalence of multidrug-resistant pathogens urged the development of new therapeutic strategies, and antimicrobial peptides (AMPs) have emerged as promising candidates. Indolicidin, a proline-rich AMP, is effective against a wide range of pathogens by penetrating the membrane to disrupt the cytoplasmic membrane or inhibit DNA synthesis. This study investigates the impact of replacing the central proline residue in Indolicidin with glycine (IND-7G), D-proline (IND-7DP), or lysine (IND-7K). Results show that both glycine and D-proline substitutions significantly reduced antimicrobial activity with lower hemolysis than the parent peptide. Besides, the analog having lysine substitution (IND-7K) slightly increased activity against E. coli and C. albicans but reduced potency against S. aureus, E. faecalis, and K. pneumoniae. The hemolytic activity of IND-7K remained comparable to that of Indolicidin. These findings demonstrated the essential role of proline in maintaining the antimicrobial efficacy of Indolicidin.

Evolutionary trajectory of bacterial resistance to antibiotics and antimicrobial peptides in Escherichia coli

The global crisis of antimicrobial resistance poses a major threat to human health, underscoring the urgency of developing new antibacterial strategies. Antimicrobial peptides (AMPs) are promising alternatives to antibiotic therapy, yet potential microbial resistance is of great concern. Resistance is often accompanied by fitness costs, which may in turn influence the spread of drug-resistant bacteria and their susceptibility to other antimicrobial agents. Herein, we investigate the evolutionary trajectory of bacterial resistance to antibiotics and AMPs in Escherichia coli, and evaluate the fitness costs and collateral sensitivity of drug-resistant strains. We reveal that E. coli develops resistance to antibiotics, particularly ciprofloxacin and kanamycin, at a notably faster rate than to AMPs. Moreover, antibiotic-evolved strains exhibit slightly higher fitness costs than AMP-evolved bacteria, primarily manifested in reduced bacterial growth and swimming motility. Notably, we demonstrate that trimethoprim-resistant E. coli, with mutations in thyA gene, displays enhanced susceptibility to pexiganan, as evidenced by both in vitro and in vivo studies. Overall, our findings shed new insights for the clinical deployment of AMPs and propose innovative therapeutic strategies for combating antibiotic-resistant bacterial infections.IMPORTANCEThe global spread of antimicrobial resistance necessitates the development of innovative anti-infective strategies. Antimicrobial peptides (AMPs) represent promising alternatives in the post-antibiotic era. By monitoring the evolutionary trajectory of bacterial resistance to eight antibiotics and ten AMPs in Escherichia coli, we demonstrate that E. coli exhibits slower emergence of resistance against AMPs compared with antibiotics. Additionally, these antibiotic-resistant strains incur significant fitness costs, particularly in bacterial growth and motility. Most importantly, we find that some antibiotic-resistant strains show collateral sensitivity to specific AMPs in both in vitro and animal infection models, which is conducive to accelerating the development of AMP-based antibacterial treatment.

Harnessing bacterial antimicrobial peptides: a comprehensive review on properties, mechanisms, applications, and challenges in combating antimicrobial resistance

Antimicrobial resistance (AMR) is a significant global health concern due to the persistence of pathogens and the emergence of resistance in bacterial infections. Bacterial-derived antimicrobial peptides (BAMPs) have emerged as a promising strategy to combat these challenges. Known for their diversity and multifaceted nature, BAMPs are notable bioactive agents that exhibit potent antimicrobial activities against various pathogens. This review explores the intricate properties and underlying mechanisms of BAMPs, emphasizing their diverse applications in addressing AMR. Additionally, the review investigates the mechanisms, analyses the challenges in utilizing BAMPs effectively, and examines their potential applications and associated deployment challenges providing comprehensive insights into how BAMPs can be harnessed to combat AMR across different domains. The significance of this review lies in highlighting the potential of BAMPs as transformative agents in combating AMR, offering sustainable and eco-friendly solutions to this pressing global health challenge.

Natural peptides and their synthetic congeners acting against Acinetobacter baumannii through the membrane and cell wall: latest progress

Acinetobacter baumannii is one of the deadliest Gram-negative bacteria (GNB), responsible for 2-10% of hospital-acquired infections. Several antibiotics are used to control the growth of A. baumannii. However, in recent decades, the abuse and misuse of antibiotics to treat non-microbial diseases have led to the emergence of multidrug-resistant A. baumannii strains. A. baumannii possesses a complex cell wall structure. Cell wall-targeting agents remain the center of antibiotic drug discovery. Notably, the antibacterial drug discovery intends to target the membrane of the bacteria, offering several advantages over antibiotics targeting intracellular systems, as membrane-targeting agents do not have to travel through the plasma membrane to reach the cytoplasmic targets. Microorganisms, insects, and mammals produce antimicrobial peptides as their first line of defense to protect themselves from pathogens and predators. Importantly, antimicrobial peptides are considered potential alternatives to antibiotics. This communication summarises the recently identified peptides of natural origin and their synthetic congeners acting against the A. baumannii membrane by cell wall disruption.

Frontiers in superbug management: innovating approaches to combat antimicrobial resistance

Anti-microbial resistance (AMR) is a global health issue causing significant mortality and economic burden. Pharmaceutical companies' discontinuation of research hinders new agents, while MDR pathogens or "superbugs" worsen the problem. Superbugs pose a threat to common infections and medical procedures, exacerbated by limited antibiotic development and rapid antibiotic resistance. The rising tide of antimicrobial resistance threatens to undermine progress in controlling infectious diseases. This review examines the global proliferation of AMR, its underlying mechanisms, and contributing factors. The study explores various methodologies, emphasizing the significance of precise and timely identification of resistant strains. We discuss recent advancements in CRISPR/Cas9, nanoparticle technology, light-based techniques, and AI-powered antibiogram analysis for combating AMR. Traditional methods often fail to effectively combat multidrug-resistant bacteria, as CRISPR-Cas9 technology offers a more effective approach by cutting specific DNA sequences, precision targeting and genome editing. AI-based smartphone applications for antibiogram analysis in resource-limited settings face challenges like internet connectivity, device compatibility, data quality, energy consumption, and algorithmic limitations. Additionally, light-based antimicrobial techniques are increasingly being used to effectively kill antibiotic-resistant microbial species and treat localized infections. This review provides an in-depth overview of AMR covering epidemiology, evolution, mechanisms, infection prevention, control measures, antibiotic access, stewardship, surveillance, challenges and emerging non-antibiotic therapeutic approaches.

Microbial production systems and optimization strategies of antimicrobial peptides: a review

Antibiotic resistance has become a public safety issue of the twenty-first century, posing a growing threat and drawing increased attention. Compared to traditional antibiotics, antimicrobial peptides (AMPs), as naturally produced small peptides, can target multiple pathways within pathogens and render them less prone to developing resistance. This makes them promising alternatives to antibiotics. However, traditional chemical synthesis methods face challenges, such as high costs, low yields, and poor stability, limiting the large-scale industrial production of AMPs. Despite extensive research to improve AMP production efficiency, issues such as low yields and complex extraction processes continue to pose significant barriers to commercial application. Therefore, there is an urgent need for new biosynthesis strategies and optimization methods to enhance AMP production efficiency and quality. This review summarizes the sources, classification, mechanisms of action and recent advances in the microbial synthesis of AMPs. It also explores innovative production methods, including recombinant microbial expression systems, fusion tags, codon optimization, tandem multimer expression, and hybrid peptide expression. Furthermore, we review the applications of gene editing technologies and artificial intelligence in AMP production, providing new perspectives and strategies for efficient, large-scale AMP production.

Antimicrobials from endophytes as novel therapeutics to counter drug-resistant pathogens

The rapid increase in antimicrobial resistance (AMR) projects a "global emergency" and necessitates a need to discover alternative resources for combating drug-resistant pathogens or "superbugs." One of the key themes in "One Health Concept" is based on the fact that the interconnected network of humans, the environment, and animal habitats majorly contribute to the rapid selection and spread of AMR. Moreover, the injudicious and overuse of antibiotics in healthcare, the environment, and associated disciplines, further aggravates the concern. The prevalence and persistence of AMR contribute to the global economic burden and are constantly witnessing an upsurge due to fewer therapeutic options, rising mortality statistics, and expensive healthcare. The present decade has witnessed the extensive exploration and utilization of bio-based resources in harnessing antibiotics of potential efficacies. The discovery and characterization of diverse chemical entities from endophytes as potent antimicrobials define an important yet less-explored area in natural product-mediated drug discovery. Endophytes-produced antimicrobials show potent efficacies in targeting microbial pathogens and synthetic biology (SB) mediated engineering of endophytes for yield enhancement, forms a prospective area of research. In keeping with the urgent requirements for new/novel antibiotics and growing concerns about pathogenic microbes and AMR, this paper comprehensively reviews emerging trends, prospects, and challenges of antimicrobials from endophytes and their effective production via SB. This literature review would serve as the platform for further exploration of novel bioactive entities from biological organisms as "novel therapeutics" to address AMR.

Novel-designed antimicrobial peptides with dual antimicrobial and anti-inflammatory actions against Cutibacterium acnes for acne vulgaris therapy

Acne vulgaris is a prevalent skin condition among adolescents, primarily instigated by over-colonization and subsequent inflammation triggered by Cutibacterium acnes. Although topical and oral antibiotics are standard treatments, they often lead to the proliferation of antibiotic-resistant bacteria and are associated with undesirable side effects. Antimicrobial peptides (AMPs) are considered a promising solution to these challenges. In this study, we aimed to develop novel short AMPs to combat C. acnes. By comparing sequences and abstracting the distribution of residue types of established AMPs, we derived a sequence template. Using this template, we crafted novel anti-C. acnes peptides comprising 13 amino acid residues. To enhance their potential therapeutic application, we designed a series of peptides by varying the number and position of the tryptophan residues. Among these peptides, DAP-7 and DAP-10 demonstrated potent antimicrobial activity against both antibiotic-susceptible and -resistant strains of C. acnes, with minimal cytotoxicity. The antimicrobial action of these peptides was attributed to their ability to target the bacterial membrane, resulting in permeabilization and rupture. Moreover, DAP-7 and DAP-10 effectively reduced the expression of pro-inflammatory cytokines induced by C. acnes and remained stable for up to 12 h after exposure to proteases found in acne lesions. Notably, DAP-7 decreased the C. acnes colonies on the ears and significantly alleviated C. acnes-induced ear swelling in a mouse model. Our findings suggest that the DAP-7 and DAP-10 peptides hold promise as candidates for developing a new acne vulgaris treatment.

Decoding the Role of Antimicrobial Peptides in the Fight against Mycobacterium tuberculosis

Tuberculosis (TB), a leading infectious disease caused by the pathogen Mycobacterium tuberculosis, poses a significant treatment challenge due to its unique characteristics and resistance to existing drugs. The conventional treatment regimens, which are lengthy and involve multiple drugs, often result in poor patient adherence and subsequent drug resistance, particularly with multidrug-resistant (MDR) and extensively drug-resistant (XDR) strains. This highlights the urgent need for novel anti-TB therapies and new drug targets. Antimicrobial peptides (AMPs), which are natural host defense molecules present in all living organisms, offer a promising alternative to traditional small-molecule drugs. AMPs have several advantages, including their broad-spectrum activity and the potential to circumvent existing resistance mechanisms. However, their clinical application faces challenges such as stability, delivery, and potential toxicity. This review aims to provide essential information on AMPs, including their sources, classification, mode of action, induction within the host under stress, efficacy against M. tuberculosis, clinical status and hurdles to their use. It also highlights future research directions to address these challenges and advance the development of AMP-based therapies for TB.

Novel antimicrobial defensin peptides from different coleopteran insects (Coleoptera: Insecta): identification, characterisation and antimicrobial properties

Antimicrobial peptides are crucial components of the immune systems of both vertebrates and invertebrates. Here, defensins, the most studied class of antimicrobial molecules in arthropods were investigated in four coleopteran insect species: Harpalus rufipes (DeGeer, 1774), Mylabris quadripunctata (Linnaeus, 1767), Sphaeridium marginatum (Linnaeus, 1758), and Ocypus mus (Brullé, 1832). The peptides synthesized with over 95% purity and their antimicrobial activities were evaluated by MIC test method. As a result, it was determined that Mylabris quadripunctata defensin (MqDef) showed high antimicrobial activity against Staphylococcus aureus and MRSA, whereas Sphaeridium marginatum (SmDef) and Harpalus rufipes (HrDef) defensins against Candida tropicalis.

Enhancing the Therapeutic Potential of Peptide Antibiotics Using Bacteriophage Mimicry Strategies

The rise of antibiotic resistance, coupled with a dwindling antibiotic pipeline, presents a significant threat to public health. Consequently, there is an urgent need for novel therapeutics targeting antibiotic-resistant pathogens. Nisin, a promising peptide antibiotic, exhibits potent bactericidal activity through a mechanism distinct from that of clinically used antibiotics. However, its cationic nature leads to hemolysis and cytotoxicity, which has limited its clinical application. Here, nanodelivery systems have been developed by mimicking the mechanisms bacteriophages use to deliver their genomes to host bacteria. These systems utilize bacteriophage receptor-binding proteins conjugated to loading modules, enabling efficient targeting of bacterial pathogens. Peptide antibiotics are loaded via dynamic covalent bonds, allowing for infection microenvironment-responsive payload release. These nanodelivery systems demonstrate remarkable specificity against target pathogens and effectively localize to bacteria-infected lungs in vivo. Notably, they significantly reduce the acute toxicity of nisin, rendering it suitable for intravenous administration. Additionally, these bacteriophage-mimicking nanomedicines exhibit excellent therapeutic efficacy in a mouse model of MRSA-induced pneumonia. The facile synthesis, potent antimicrobial performance, and favorable biocompatibility of these nanomedicines highlight their potential as alternative therapeutics for combating antibiotic-resistant pathogens. This study underscores the effectiveness of bacteriophage mimicry as a strategy for transforming peptide antibiotics into viable therapeutics.

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.

Computational Approaches for Antimicrobial Peptide Delivery

Peptides constitute alternative molecules for the treatment of infections caused by bacteria, viruses, fungi, and protozoa. However, their therapeutic effectiveness is often limited by enzymatic degradation, chemical and physical instability, and toxicity toward healthy human cells. To improve their pharmacokinetic (PK) and pharmacodynamic (PD) profiles, novel routes of administration are being explored. Among these, nanoparticles have shown promise as potential carriers for peptides, although the design of delivery vehicles remains a slow and painstaking process, heavily reliant on trial and error. Recently, computational approaches have been introduced to accelerate the development of effective drug delivery systems for peptides. Here we present an overview of some of these computational strategies and discuss their potential to optimize drug development and delivery.

Assessment of Linear and Cyclic Peptides' Immobilization onto Cross-Linked, Poly(vinyl alcohol)/Cellulose Nanocrystal Nanofibers Electrospun over Quartz Crystal Microbalances with Dissipation Sensors

Immobilization of peptides onto nanofiber dressings holds significant potential for chronic wound treatment. However, it is necessary to understand the adsorptive capacity of the produced substrates and the binding affinity of the peptides to determine the interface success. This study aims at exploring for the first time the influence of electrospun poly(vinyl alcohol)-based nanofibers on the adsorption of a cyclic peptide, Tiger 17, and of a linear peptide, Pexiganan, using quartz crystal microbalance with dissipation monitoring (QCM-D). PVA fibers reinforced with 0, 10, and 20% w/v cellulose nanocrystals (CNC) were electrospun directly onto QCM-D sensors and, posteriorly, cross-linked by glutaraldehyde vapor. Adsorption levels of Pexiganan were the highest (∼7348 ng/cm2) on C80/20 PVA/CNC electrospun fibers, while the time to achieve equilibrium was the longest (∼235 min). In contrast, the adsorption mass with cyclic Tiger 17 was the highest (∼3428 ng/cm2) on C100/0 PVA, reaching equilibrium after nearly 123 min. In sequential deposition, the combination Tiger 17 + Pexiganan on C100/0 fibers attained the highest number of bound peptide molecules, with ∼55% of Tiger 17 and ∼45% of Pexiganan. Elastic shear modulus data on this peptide sequence, over the C80/20 electrospun mats, reported 220 and 249 kPa for each peptide, respectively, indicating the formation of stable bonds with the surface. The results contributed to the understanding of the immobilization of linear and cyclic peptides, never studied in combination, and their mutual influence on polymeric substrates for engineering potential wound treatment strategies.

Hyaluronan Scaffold Decorated with Bifunctional Peptide Promotes Wound Healing via Antibacterial and Anti-Inflammatory

The invasion of bacteria and inflammation impeded infected wounds heal. Here, a hyaluronan-based scaffold (HAG-g-C) was designed by cross-linking with gallic acid-modified gelatin to provide a protein microenvironment and decorated with cathelicidin-BF (CBF), a natural antimicrobial peptide, to remove bacterial infections and reverse the inflammatory environment. In vitro, HAG-g-C presented an antibacterial effect on Staphylococcus aureus and Escherichia coli. Meanwhile, it could drive the phenotypic switch of macrophage from M1 to M2 to accelerate tissue remodeling. In a mouse model of S. aureus-infected total skin defects, HAG-g-C inhibited the process of infection at the beginning of the wound and then regulated the M1 macrophage transformed to M2 phenotype on day 12. In addition, HAG-g-C induced collagen deposition, and reduced the expression of TNF-α, thereby significantly accelerating the reconstruction of infected wounds.

Unlocking microbial reservoirs for antimicrobial peptides and beyond

Recently, Santos-Júnior et al. utilized a machine learning approach to identify nearly a million novel antimicrobial peptides (AMPs) from the global microbiome. Here we explore the untapped potential of plant- and soil-associated microbiomes as a source of novel peptides, highlighting their promising applications in advancing agricultural innovation and sustainability.

The Wheel of Fortune: Helical Wheel Alanine Scanning of a Spider Venom Antimicrobial Peptide Reveals Residues Involved in Antimicrobial and Cytotoxic Activity

A preference for several amino acids is observed to occur at particular positions of cationic α-helical antimicrobial peptides (AMPs), which ensures the formation of amphipathic regions once they assume their correct secondary structure in membranes or membrane-mimicking environments and makes them active against pathogens. This study determined the effect of alanine mutations on the secondary structure and bioactivity of lyp1987 (GRLQAFLAKMKEIAAQTL-NH2), a cationic α-helical AMP obtained from the venom of Lycosa poonaensis which exhibits broad range activity against Gram-positive and Gram-negative bacteria with micromolar minimum inhibitory concentrations (MIC). CD spectroscopy revealed no significant difference in the secondary structure, with all alanine-substituted analogs exhibiting predominantly α-helical structure in buffered 2,2,2-trifluoroethanol solution. Alanine substitution at Glu12 and Thr17 increased the activity of lyp1987 against Gram-positive and -negative bacteria, while alanine substitution at Lys9 increased its selectivity against Gram-positive bacteria. Further investigation can be done to determine positions and substitutions that will give less cytotoxic analogs.

Host defense peptides at the crossroad of endothelial cell physiology: Insight into mechanistic and pharmacological implications

Antimicrobial peptides (AMPs), particularly host defense peptides (HDPs), have gained recognition for their role in host defense mechanisms, but they have also shown potential as a promising anticancer, antiviral, antiparasitic, antifungal and immunomodulatory agent. Research studies in recent years have shown HDPs play a crucial role in endothelial cell function and biology. The function of endothelial cells is impacted by HDPs' complex interplay between cytoprotective and cytotoxic actions as they are known to modulate barrier integrity, inflammatory response and angiogenesis. This biphasic response varies and depends on the peptide structure, its concentration, and the microenvironment. These effects are mediated through key signaling pathways, including MAPK, NF-κB, and PI3K/Akt, which controls responses such as cell proliferation, apoptosis, and migration. In the present review, we have discussed the significance of the intriguing relationship between HDPs and endothelial cell physiology which suggests it potential as a therapeutic agents for the treating wounds, cardiovascular diseases, and inflammation-related endothelial damage.

Discovery, development and optimisation of a novel frog antimicrobial peptide with combined mode of action against drug-resistant bacteria

Antimicrobial peptides (AMP) have emerged as promising candidates for addressing the clinical challenges posed by the rapid evolution of antibiotic-resistant microorganisms. Brevinins, a representative frog-derived AMP family, exhibited broad-spectrum antimicrobial activities, attacking great attentions in previous studies. However, their strong haemolytic activity and cytotoxicity, greatly limit their further development. In this work, we identified and characterised a novel brevinin-1 peptide, brevinin-1pl, from the skin secretions of the northern leopard frog, Rana pipiens. Like many brevinins, brevinin-1pl also displayed strong haemolytic activity, resulting in a lower therapeutic index. We employed several bioinformatics tools to analyse the structure and potential membrane interactions of brevinin-1pl, leading to a series of modifications. Among these analogues, des-Ala16-[Lys4]brevinin-1pl exhibited great enhanced therapeutic efficacy in both in vitro and in vivo tests, particularly against some antibiotics-resistant Escherichia coli strains. Mechanistic studies suggest that des-Ala16-[Lys4]brevinin-1pl may exert bactericidal effects through multiple mechanisms, including membrane disruption and DNA binding. Consequently, des-Ala16-[Lys4]brevinin-1pl holds promise as a candidate for the treatment of drug-resistant Escherichia coli infections.

Unveiling the roles of CaSDH8 in Candida albicans: Implications for virulence and azole resistance

Candida albicans is the most common pathogen in systemic fungal diseases, exhibits a complex pathogenic mechanism, and is increasingly becoming drug tolerant. Therefore, it is particularly important to study the genes associated with virulence and resistance of C. albicans. Here, we identified a gene (orf19.1588) that encodes a conserved mitochondrial protein known as CaSDH8, upon deletion of CaSdh8, the deleted strain (Casdh8Δ/Δ) experienced impaired growth, hyphal development, and virulence. Casdh8Δ/Δ displayed a reduced capacity to utilize alternative carbon sources, along with detrimental alterations in reactive oxygen species (ROS), mitochondrial membrane potential (MMP) depolarization, and adenosine triphosphate (ATP) levels. Interestingly, Casdh8Δ/Δ demonstrated resistance to azole drugs, and under the influence of fluconazole, the cell membrane permeability and mitochondrial function of Casdh8Δ/Δ were less compromised than those of the wild type, indicating a reduction in the detrimental effects of fluconazole on Casdh8Δ/Δ. These findings highlight the significance of CaSDH8 as a crucial gene for the maintenance of cellular homoeostasis. Our study is the first to document the effects of the CaSDH8 gene on the virulence and azole resistance of C. albicans at both the molecular and animal levels, providing new clues and directions for the antifungal infection and the discovery of antifungal drug targets.

Antimicrobial Peptides From Different Sources: Isolation, Purification, and Characterization to Potential Applications

Antimicrobial peptides (AMPs) are excellent promising candidates for biomedical applications owing to their structural properties, high biocompatibility, good biodegradability, and functional diversity. Unlike conventional antibiotics, AMPs have been shown to have broad-spectrum antimicrobial activity toward Gram-positive/negative bacteria, as well as antifungal and antiviral activity. These peptides have also been found to be cytotoxic to sperm and cancer cells. A range of AMPs has been isolated from various organisms, such as bacteria, fungi, plants, and animals. This review summarizes the latest studies on AMPs, covering their isolation, purification, and characterization as well as their potential biomedical applications and beyond.

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.

The proline-rich antimicrobial peptide B7-005: low bacterial resistance, safe for human cells and effective in zebrafish embryo bacteraemia model

Proline-rich antimicrobial peptides (PrAMPs) have gained attention due to their antimicrobial properties and low cytotoxicity. B7-005, a small optimized PrAMP, exhibits a broader spectrum of activity than native PrAMPs, due to an antimicrobial mechanism based on inhibiting prokaryotic protein synthesis and destabilizing bacterial membranes. However, the toxicity and the in vivo efficacy of B7-005 remain poorly understood, so in vitro and in vivo microbiology and toxicology experiments were used to assess its suitability as an anti-infective agent. The incidence of resistance towards B7-005 by E. coli was lower than for other PrAMPs and antibiotics; moreover, it maintained antimicrobial activity in the presence of human serum. B7-005 exerted its antimicrobial effect at a much lower concentration than those causing harmful effects on four different cell types, such as membrane permeabilization or non-lytic depolarization of mitochondria. The latter effect may be related to the inhibition of eukaryotic protein synthesis by B7-005 observed in vitro. In a zebrafish embryo model, B7-005 was well tolerated and reduced mortality from pre-existing E. coli bacteraemia. Overall, B7-005 was safe for human cells and effective against systemic infection in vivo, making it a promising lead for developing new antibiotics.

Classical Simulations on Quantum Computers: Interface-Driven Peptide Folding on Simulated Membrane Surfaces

BACKGROUND

Antimicrobial peptides (AMPs) are crucial in the fight against infections and play significant roles in various health contexts, including cancer, autoimmune diseases, and aging. A key aspect of AMP functionality is their selective interaction with pathogen membranes, which often exhibit altered lipid compositions. These interactions are thought to induce a conformational shift in AMPs from random coil to alpha-helical structures, essential for their lytic activity. Traditional computational approaches have faced challenges in accurately modeling these structural changes, especially in membrane environments, thereby opening and opportunity for more advanced approaches.

METHOD

This study extends an existing quantum computing algorithm, initially designed for peptide folding simulations in homogeneous environments, to address the complexities of AMP interactions at interfaces. Our approach enables the prediction of the optimal conformation of peptides located in the transition region between hydrophilic and hydrophobic phases, resembling lipid membranes. The new method was tested on three 10-amino-acid-long peptides, each characterized by distinct hydrophobic, hydrophilic, or amphipathic properties, across different media and at interfaces between solvents of different polarity.

RESULTS

The developed method successfully modeled the structure of the peptides without increasing the number of qubits required compared to simulations in homogeneous media, making it more feasible with current quantum computing resources. Despite the current limitations in computational power and qubit availability, the findings demonstrate the significant potential of quantum computing in accurately characterizing complex biomolecular processes, particularly AMP folding at membrane models.

CONCLUSIONS

This research highlights the promising applications of quantum computing in biomolecular simulations, paving the way for future advancements in the development of novel therapeutic agents. We aim to offer a new perspective on enhancing the accuracy and applicability of biomolecular simulations in the context of AMP interactions with membrane models.

Novel antimicrobial peptides based on Protegrin-1: In silico and in vitro assessments

The development of antibiotic resistance has caused significant health problems. Antimicrobial peptides (AMPs) are considered next-generation antibiotics. Protegrin-1 (PG-1) is a β-hairpin AMP with a membrane-binding capacity. This study used twelve PG-1 analogs with different amino acid substitutions. Coarse-grained molecular dynamics (MD) simulations were used to assess these analogs, and their physicochemical properties were computed using the Antimicrobial Peptide Database. Three AMPs, PEP-D, PEP-C, and PEP-H, were chosen and synthesized for antibacterial testing. The microbroth dilution technique and hemolytic assays evaluated the antimicrobial efficacy and cellular toxicity. The checkerboard method was used to test the combined activity of AMP and standard antibiotics. Cell membrane permeability and electron microscopy were used to evaluate the mode of action. The chemical stability of the selective AMP, PEP-D, was assessed by a validated HPLC method. PEP-D consists of 16-18 amino acid residues and has a charge of +7 and a hydrophobicity of 44 %, similar to PG-1. It can efficiently inactivate bacteria by disrupting cell membranes and significantly reducing hemolytic activity. Chemical stability studies indicated that AMP was stable at 40 °C for six months under autoclave conditions. This study could introduce the potential therapeutic application of selective AMP as an anti-infective agent.

ProT-Diff: A Modularized and Efficient Strategy for De Novo Generation of Antimicrobial Peptide Sequences by Integrating Protein Language and Diffusion Models

Antimicrobial peptides (AMPs) are a promising solution for treating antibiotic-resistant pathogens. However, efficient generation of diverse AMPs without prior knowledge of peptide structures or sequence alignments remains a challenge. Here, ProT-Diff is introduced, a modularized deep generative approach that combines a pretrained protein language model with a diffusion model for the de novo generation of AMPs sequences. ProT-Diff generates thousands of AMPs with diverse lengths and structures within a few hours. After silico physicochemical screening, 45 peptides are selected for experimental validation. Forty-four peptides showed antimicrobial activity against both gram-positive or gram-negative bacteria. Among broad-spectrum peptides, AMP_2 exhibited potent antimicrobial activity, low hemolysis, and minimal cytotoxicity. An in vivo assessment demonstrated its effectiveness against a drug-resistant E. coli strain in acute peritonitis. This study not only introduces a viable and user-friendly strategy for de novo generation of antimicrobial peptides, but also provides potential antimicrobial drug candidates with excellent activity. It is believed that this study will facilitate the development of other peptide-based drug candidates in the future, as well as proteins with tailored characteristics.

Peptide Dimerization as a Strategy for the Development of Antileishmanial Compounds

Leishmaniasis is recognized as a serious public health problem in Brazil and around the world. The limited availability of drugs for treatment, added to the diversity of side effects and the emergence of resistant strains, shows the importance of research focused on the development of new molecules, thus contributing to treatments. Therefore, this work aimed to identify leishmanicidal compounds using a peptide dimerization strategy, as well as to understand their mechanisms of action. Herein, it was demonstrated that the dimerization of the peptide TSHa, (TSHa)2K, presented higher potency and selectivity than its monomeric form when evaluated against Leishmania mexicana and Leishmania amazonensis. Furthermore, these compounds are capable of inhibiting the parasite cysteine protease, an important target explored for the development of antileishmanial compounds, as well as to selectively interact with the parasite membranes, as demonstrated by flow cytometry, permeabilization, and fluorescence microscopy experiments. Based on this, the identified molecules are candidates for use in in vivo studies with animal models to combat leishmaniasis.

Recent Progress in Terrestrial Biota Derived Antibacterial Agents for Medical Applications

Conventional antibiotic and multidrug treatments are becoming less and less effective and the discovery of new effective and safe antibacterial agents is becoming a global priority. Returning to a natural antibacterial product is a relatively new current trend. Terrestrial biota is a rich source of biologically active substances whose antibacterial potential has not been fully utilized. The aim of this review is to present the current state-of-the-art terrestrial biota-derived antibacterial agents inspired by natural treatments. It summarizes the most important sources and newly identified or modified antibacterial agents and treatments from the last five years. It focuses on the significance of plant- animal- and bacteria-derived biologically active agents as powerful alternatives to antibiotics, as well as the advantages of utilizing natural antibacterial molecules alone or in combination with antibiotics. The main conclusion is that terrestrial biota-derived antibacterial products and substances open a variety of new ways for modern improved therapeutic strategies. New terrestrial sources of known antibacterial agents and new antibacterial agents from terrestrial biota were discovered during the last 5 years, which are under investigation together with some long-ago known but now experiencing their renaissance for the development of new medical treatments. The use of natural antibacterial peptides as well as combinational therapy by commercial antibiotics and natural products is outlined as the most promising method for treating bacterial infections. In vivo testing and clinical trials are necessary to reach clinical application.

Enhancing Antimicrobial Peptide Activity through Modifications of Charge, Hydrophobicity, and Structure

Antimicrobial peptides (AMPs) are emerging as a promising alternative to traditional antibiotics due to their ability to disturb bacterial membranes and/or their intracellular processes, offering a potential solution to the growing problem of antimicrobial resistance. AMP effectiveness is governed by factors such as net charge, hydrophobicity, and the ability to form amphipathic secondary structures. When properly balanced, these characteristics enable AMPs to selectively target bacterial membranes while sparing eukaryotic cells. This review focuses on the roles of positive charge, hydrophobicity, and structure in influencing AMP activity and toxicity, and explores strategies to optimize them for enhanced therapeutic potential. We highlight the delicate balance between these properties and how various modifications, including amino acid substitutions, peptide tagging, or lipid conjugation, can either enhance or impair AMP performance. Notably, an increase in these parameters does not always yield the best results; sometimes, a slight reduction in charge, hydrophobicity, or structural stability improves the overall AMP therapeutic potential. Understanding these complex interactions is key to developing AMPs with greater antimicrobial activity and reduced toxicity, making them viable candidates in the fight against antibiotic-resistant bacteria.

Microscopic and metabolomics analysis of the anti-Listeria activity of natural and engineered cruzioseptins

Listeria monocytogenes is a human opportunistic foodborne pathogen that produces life-threatening infections with a high mortality rate. The control of Listeria in the food production environment and effective clinical management of human listeriosis are challenging due to the emergence of antibiotic resistance. Hence we evaluate the in vitro anti-Listeria activity of two synthetic cruzioseptins reproducing their natural sequences CZS-9, and CZS-12, and one engineered sequence based on CZS-1, named [K4K15]CZS-1. The assessment of the in vitro potential of cruzioseptins, highlighted the promising antibacterial effect of [K4K15]CZS-1 in very low concentrations (0.91 μM) and its thermal stability at high-temperature conditions, is compatible with the food industry. Microscopic and metabolomic analyses suggest cruzioseptin induces anti-Listeria bioactivity through membrane disruption and changes in the intracellular metabolome. We also report that [K4K15]CZS-1 is not resistant to peptidases/proteases emphasizing a key advantage for their use as a food preservative. However, there is a need for further structural and functional optimisations for the potential clinical application as an antibiotic. In conclusion, [K4K15]CZS-1 stand out as membrane-active peptides with the ability to induce shifts in the bacteria metabolome and inspire the development of strategies for the prevention of L. monocytogenes emergence and dissemination.

Understanding the Dynamics of Human Defensin Antimicrobial Peptides: Pathogen Resistance and Commensal Induction

Antimicrobial peptides (AMPs), also known as host defense peptides, are petite molecules with inherent microbicidal properties that are synthesized by the host's innate immune response. These peptides serve as an initial barrier against pathogenic microorganisms, effectively eliminating them. Human defensin (HD) AMPs represent a prominent group of peptides involved in the innate immune response of humans. These peptides are primarily produced by neutrophils and epithelial cells, serving as a crucial defense mechanism against invading pathogens. The extensive research conducted has focused on the broad spectrum of antimicrobial activities and multifaceted immunomodulatory functions exhibited by human defensin AMPs. During the process of co-evolution between hosts and bacterial pathogens, bacteria have developed the ability to recognize and develop an adaptive response to AMPs to counterattack their bactericidal activity by different antibiotic-resistant mechanisms. However, numerous non-pathogenic commensal bacteria elicit the upregulation of defensins as a means to surmount the resistance mechanisms implemented by pathogens. The precise mechanism underlying the induction of HD by commensal organisms remains to be fully understood. This review summarizes the most recent research on the expression of human defensin by pathogens and discusses the various defense mechanisms used by pathogens to counter host AMP production. We also mention recent developments in the commensal induction of defensin AMPs. A better knowledge of the pathogens' defensin AMP resistance mechanisms and commensals' induction of AMP expression may shed light on the creation of fresh antibacterial tactics to get rid of bacterial infection.

Chitosan/cellulose nanocrystals/graphene oxide scaffolds as a potential pH-responsive wound dressing: Tuning physico-chemical, pro-regenerative and antimicrobial properties

Chronic wounds (CWs) treatment still represents a demanding medical challenge. Several intrinsic physiological signals (i.e., pH) help to stimulate and support wound healing. CWs, in fact, are characterized by a predominantly alkaline pH of the exudate, which acidifies as the wound heals. Therefore, pH-responsive wound dressings hold great potential owing to their capability of tuning their functions according to the wound conditions. Herein, porous chitosan (CS)-based scaffolds loaded with cellulose nanocrystals (CNCs) and graphene oxide (GO) were successfully fabricated using a freeze-drying method. CNCs were extracted from bagasse pulps fibers through acid hydrolysis. GO was synthesised by Hummer's method. The scaffolds were then ionically cross-linked using the amino acid L-Arginine (Arg), as a bioactive agent, and tested as potential pH-responsive wound dressing. Notably, the effect of CNCs and GO singly and simultaneously loaded within the CS-Arg scaffolds was investigated. The modulation of CNCs and GO content within CS-Arg scaffolds facilitated the development of scaffolds with an optimal pH-dependent swelling ratio capability and extended degradation time. Furthermore, CS/CNC/GO-Arg scaffolds exhibited tuned biological features, in terms of antimicrobial activity, cellular proliferation/migration ability, and the expression of extracellular matrix specific markers (i.e., elastin and collagen I) related to wound healing in human dermal fibroblasts.

Exploration and Characterization of Antimicrobial Peptides from Shrimp Litopenaeus Vannamei by A Genomic and Transcriptomic Approach

Antimicrobial peptides (AMPs) are crucial in the humoral immunity aspect of invertebrates' innate immune systems. However, studies on AMP discovery in the Pacific white shrimp (Litopenaeus vannamei) using omics data have been limited. Addressing the growing concern of antibiotic resistance in aquaculture, this study focused on the identification and characterization of AMPs in L. vannamei using advanced genomic and transcriptomic techniques. The genome of L. vannamei was performed to predict and identify a total of 754 AMP-derived genes, distributed across most chromosomes and spanning 24 distinct AMP families, and further identified 236 AMP-derived genes at the mRNA level in hemocytes. A subset of 20 chemically synthesized peptides, derived from these genes, exhibited significant antimicrobial activity, with over 85% showing effectiveness against key bacterial strains such as Staphylococcus aureus and Vibrio parahaemolyticus. The expression patterns of these AMPs were also investigated in different shrimp tissues and at various infection stages, revealing dynamic responses to pathogenic challenges. These findings highlight the significant potential of AMPs in L. vannamei as novel, effective alternatives to traditional antibiotics in aquaculture, offering insights into their diverse structural properties and biological functions. Together, this comprehensive characterization of the AMP repertoire in L. vannamei demonstrates the efficacy of using omics data for AMP discovery and lays the groundwork for their potential applications.

High Therapeutic Index α-Helical AMPs and Their Therapeutic Potential on Bacterial Lung and Skin Wound Infections

Antimicrobial peptides (AMPs) possess strong antibacterial activity and low drug resistance, making them ideal candidates for bactericidal drugs for addressing the issue of traditional antibiotic resistance. In this study, a template (G(XXKK)nI, G = Gly; X = Leu, Ile, Phe, or Trp; n = 2, 3, or 4; K = Lys; I = Ile.) was employed for the devised of a variety of novel α-helical AMPs with a high therapeutic index. The AMP with the highest therapeutic index, WK2, was ultimately chosen following a thorough screening process. It demonstrates broad-spectrum and potent activity against both standard and multidrug-resistant bacteria, while also showing low hemolysis and rapid and efficient time-kill kinetics. Additionally, WK2 exhibits excellent efficacy in treating mouse models of Klebsiella pneumonia-induced lung infections and methicillin-resistant Staphylococcus aureus (MRSA)-induced skin wound infections while demonstrating good safety profiles in vivo. In conclusion, the template-based design methodology for novel AMPs with high therapeutic indices offers new insights into addressing antibiotic resistance problems. WK2 represents a promising antimicrobial agent.

Recent Insights into the Antimicrobial Properties of Phyllanthus emblica L.: A Comprehensive Review of Wonder Berry

Phyllanthus emblica L., or Amla, is known for its therapeutic properties and has been used as a medicinal plant. It is rich in vitamin C and other bioactive phytochemicals like polyphenols, gallic acid, chebulagic acid, leutolin, quercetin, etc. Different parts of this plant are used to treat various viral, bacterial, and fungal diseases. This review article summarizes the recent literature relevant to the antiviral, antibacterial, and antifungal effects of P. emblica. A variety of bacteria (Staphylococcus aureus, Bacillus subtillus, Enterococcus faecalis, Salmonella typhi, and Escherichia, etc.), fungi (Alternaria alternate Botroyodiplodia theobromae, Colletotrichum corcori, Curvularia lunata, Fusarium exquisite, Fusarium solanii, Aspergillus niger, Candida albicans, Colletotrichum gleosparoitis, and Macrophomina phaseolina) and viruses, like Influenza A virus strain H3N2, hepatitis B, Human Immunodeficiency virus type-1 (HIV-1), Simplex virus type 1 (HSV-1) and type 2 (HSV-2) have experimented. Different techniques were used based on the way of identification. 'For example, disc diffusion, dilution methods, sound diffusion, Immuno-peroxidase monolayer assay, serum HBV and HBsAg assay, enzyme immunoassay, etc. The present review analyzed and summarized the antimicrobial activities of P. emblica and possible mechanisms of action to provide future directions in translating these findings clinically.

Dual electro-/pH-responsive nanoparticle/hydrogel system for controlled delivery of anticancer peptide

An electro-chemo-responsive carrier has been engineered for the controlled release of a highly hydrophilic anticancer peptide, CR(NMe)EKA (Cys-Arg- N-methyl-Glu-Lys-Ala). Remotely controlled on demand release of CR(NMe)EKA, loaded in electro-responsive poly(3,4-ethylenedioxythiophene) (PEDOT) nanoparticles, has been achieved by applying electrical stimuli consisting of constant positive (+0.50 V) or negative voltages (-0.50 V) at pre-defined time intervals. In addition, after loading CR(NMe)EKA/PEDOT nanoparticles into an injectable pH responsive hydrogel formed by phenylboronic acid grafted to chitosan (PBA-CS), the efficiency of the controlled peptide release has increased approximately by a factor of 2.6. The hydration ratio of such hydrogel is significantly lower in acidic environments than in neutral and basic media, which has been attributed to the dissociation of the boronate bonds between polymer chains. Hence, the electro-controlled peptide release from PBA-CS/CR(NMe)EKA/PEDOT hydrogels, in the acidic environment of tumors, combines the effects of the oxidation and reduction of PEDOT chains on the interactions with the peptide and the carrier, with the peptide concentration gradient at the interface between the collapsed hydrogel and the release medium. Furthermore, the peptide released by electro-stimulation preserved its bioactivity assessed by promoting human prostate cancer cells death. Overall, this work is a promising attempt to develop a carrier platform for small hydrophilic anticancer peptides, which delivery rationale is synergistically regulated by the electrical and pH responsiveness of the carrier.

Genetically encoded libraries and spider venoms as emerging sources for crop protective peptides

Agricultural crops are targeted by various pathogens (fungi, bacteria, and viruses) and pests (herbivorous arthropods). Antimicrobial and insecticidal peptides are increasingly recognized as eco-friendly tools for crop protection due to their low propensity for resistance development and the fact that they are fully biodegradable. However, historical challenges have hindered their development, including poor stability, limited availability, reproducibility issues, high production costs, and unwanted toxicity. Toxicity is a primary concern because crop-protective peptides interact with various organisms of environmental and economic significance. This review focuses on the potential of genetically encoded peptide libraries like the use of two-hybrid-based methods for antimicrobial peptides identification and insecticidal spider venom peptides as two main approaches for targeting plant pathogens and pests. We discuss some key findings and challenges regarding the practical application of each strategy. We conclude that genetically encoded peptide library- and spider venom-derived crop protective peptides offer a sustainable and environmentally responsible approach for addressing modern crop protection needs in the agricultural sector.

Antimicrobial peptides: Opportunities and challenges in overcoming resistance

Antibiotic resistance represents a global health threat, challenging the efficacy of traditional antimicrobial agents and necessitating innovative approaches to combat infectious diseases. Among these alternatives, antimicrobial peptides have emerged as promising candidates against resistant pathogens. Unlike traditional antibiotics with only one target, these peptides can use different mechanisms to destroy bacteria, with low toxicity to mammalian cells compared to many conventional antibiotics. Antimicrobial peptides (AMPs) have encouraging antibacterial properties and are currently employed in the clinical treatment of pathogen infection, cancer, wound healing, cosmetics, or biotechnology. This review summarizes the mechanisms of antimicrobial peptides against bacteria, discusses the mechanisms of drug resistance, the limitations and challenges of AMPs in peptide drug applications for combating drug-resistant bacterial infections, and strategies to enhance their capabilities.

Proline, a unique amino acid whose polymer, polyproline II helix, and its analogues are involved in many biological processes: a review

Proline is a unique amino acid in that its side-chain is cyclised to the backbone, thus giving proline an exceptional rigidity and a considerably restricted conformational space. Polyproline forms two well-characterized helical structures: a left-handed polyproline helix (PPII) and a right-handed polyproline helix (PPI). Usually, sequences made only of prolyl residues are in PPII conformation, but even sequences not rich in proline but which are rich in glycine, lysine, glutamate, or aspartate have also a tendency to form PPII helices. Currently, the only way to study unambiguously PPII structure in solution is to use spectroscopies based on optical activity such as circular dichroism, vibrational circular dichroism and Raman optical activity. The importance of the PPII structure is emphasized by its ubiquitous presence in different organisms from yeast to human beings where proline-rich motifs and their binding domains are believed to be involved in vital biological processes. Some of the domains that are bound by proline-rich motifs include SH3 domains, WW domains, GYF domains and UEV domains, etc. The PPII structure has been demonstrated to be essential to biological activities such as signal transduction, transcription, cell motility, and immune response.

Antimicrobial Peptides and Their Biomedical Applications: A Review

The emergence of drug resistance genes and the detrimental health effects caused by the overuse of antibiotics are increasingly prominent problems. There is an urgent need for effective strategies to antibiotics or antimicrobial resistance in the fields of biomedicine and therapeutics. The pathogen-killing ability of antimicrobial peptides (AMPs) is linked to their structure and physicochemical properties, including their conformation, electrical charges, hydrophilicity, and hydrophobicity. AMPs are a form of innate immune protection found in all life forms. A key aspect of the application of AMPs involves their potential to combat emerging antibiotic resistance; certain AMPs are effective against resistant microbial strains and can be modified through peptide engineering. This review summarizes the various strategies used to tackle antibiotic resistance, with a particular focus on the role of AMPs as effective antibiotic agents that enhance the host's immunological functions. Most of the recent studies on the properties and impregnation methods of AMPs, along with their biomedical applications, are discussed. This review provides researchers with insights into the latest advancements in AMP research, highlighting compelling evidence for the effectiveness of AMPs as antimicrobial agents.