Antimicrobial host defence peptides: functions and clinical potential

On-demand imidazolidinyl urea-based tissue-like, self-healable, and antibacterial hydrogels for infectious wound care

Bacterial wound infections are a growing challenge in healthcare, posing severe risks like systemic infection, organ failure, and sepsis, with projections predicting over 10 million deaths annually by 2050. Antibacterial hydrogels, with adaptable extracellular matrix-like features, are emerging as promising solutions for treating infectious wounds. However, the antibacterial properties of most of these hydrogels are largely attributed to extrinsic agents, and their mechanisms of action remain poorly understood. Herein we introduce for the first time, modified imidazolidinyl urea (IU) as the polymeric backbone for developing tissue-like antibacterial hydrogels. As-designed hydrogels behave tissue-like mechanical features, outstanding antifreeze behavior, and rapid self-healing capabilities. Molecular dynamics (MD) simulation and density functional theory (DFT) calculation were employed to well-understand the extent of H-bonding and metal-ligand coordination to finetune hydrogels' properties. In vitro studies suggest good biocompatibility of hydrogels against mouse fibroblasts & human skin, lung, and red blood cells, with potential wound healing capacity. Additionally, the hydrogels exhibit good 3D printability and remarkable antibacterial activity, attributed to concentration dependent ROS generation, oxidative stress induction, and subsequent disruption of bacterial membrane. On top of that, in vitro biofilm studies confirmed that developed hydrogels are effective in preventing biofilm formation. Therefore, these tissue-mimetic hydrogels present a promising and effective platform for accelerating wound healing while simultaneously controlling bacterial infections, offering hope for the future of wound care.

Categorizing interaction modes of antimicrobial peptides with extracellular vesicles: Disruption, membrane trespassing, and clearance of the protein corona

Host antimicrobial peptides (AMPs) and extracellular vesicles (EVs) are known to play important roles as part of the immune system, from antimicrobial actions to immune regulation. Recent results also demonstrate that EVs could serve as carriers for AMPs. Related, it was shown that some AMPs can remove the protein corona (PC), the externally adsorbed layer of proteins, from EVs which can be exploited for subtractive proteomics strategies. The interaction of these compounds is thus interesting for multiple reasons from better insight to natural processes to direct applications in EV-based bioengineering. However, we have only limited information on the various ways these species may interact with each other. To reach a broader overview, here we selected twenty-six AMPs, including cell-penetrating peptides (CPPs), and investigated their interactions with red blood cell-derived vesicles (REVs). For this, we employed a complex lipid biophysics including linearly polarized light spectroscopy, flow cytometry, nanoparticle tracking analysis, electron microscopy and also zeta-potential measurements. This enabled the categorization of these peptides into distinct groups. At specific low concentrations, peptides such as LL-37 and lasioglossin-III were effective in PC elimination with minimal disruption of the membrane. In contrast, AMPs like KLA, bradykinin, histatin-5, and most of the tested CPPs (e.g. octa-arginine, penetratin, and buforin II), demonstrate cell-penetrating mechanisms as they could sustain large peptide concentrations with minimal membrane damage. The systematic overview presented here shows the potential mechanism of how AMPs and EVs could interact in vivo, and also how certain peptides may be employed to manipulate EVs for specific applications.

Cubosome lipid nanocarriers for delivery of ultra-short antimicrobial peptides

HYPOTHESIS

Although antimicrobial peptides (AMPs) are a promising class of new antibiotics, their inherent susceptibility to degradation requires nanocarrier-mediated delivery. While cubosome nanocarriers have been extensively studied for delivery of AMPs, we do not currently understand why cubosome encapsulation improves antimicrobial efficacy for some compounds but not others. This study therefore aims to investigate the link between the mechanism of action and permeation efficiency of the peptides, their encapsulation efficacy, and the antimicrobial activity of these systems.

EXPERIMENTS

Encapsulation and delivery of Indolicidin, and its ultra-short derivative, Priscilicidin, were investigated using SAXS, cryo-TEM and circular dichroism. Molecular dynamics simulations were used to understand the loading of these peptides within cubosomes. The antimicrobial efficacy was assessed against gram-negative (E. coli) and gram-positive (MRSA) bacteria.

FINDINGS

A high ionic strength solution was required to facilitate high loading of the cationic AMPs, with bilayer encapsulation driven by tryptophan and Fmoc moieties. Cubosome encapsulation did not improve the antimicrobial efficacy of the AMPs consistent with their high permeation, as explained by a recent 'diffusion to capture model'. This suggests that cubosome encapsulation may not be an effective strategy for all antimicrobial compounds, paving the way for improved selection of nanocarriers for AMPs, and other antimicrobial compounds.

Bacillus subtilis fermented shrimp waste isolated peptide, PVQ9, and its antimicrobial mechanism on four Gram-positive foodborne bacteria

Bacillus subtilis produces proteases that hydrolyze proteins to produce bioactive peptides. Given the mounting waste from processed shrimp, the antimicrobial potential of peptides isolated from B. subtilis fermented shrimp waste was explored. Among the five peptides screened using molecular docking prediction, PVQ9 (AVFPSIVGRPR) had strong antibacterial activity against four common foodborne Gram-positive bacteria, i.e., Staphylococcus aureus, Bacillus cereus, Mammaliicoccus sciuri, and Kurthia gibsonii. The minimum bactericidal concentrations (MBCs) were 62.5 μg/mL for S. aureus and B. cereus, and 31.3 μg/mL for both M. sciuri and K. gibsonii, with a time-kill of 3 h observed for all strains. Mechanistically, it was demonstrated that PVQ9 could destroy bacterial cell walls, change bacteria cell membrane permeability, bind to bacteria DNA, and cause cell apoptosis. Most importantly, peptide PVQ9 could inhibit the spoilage of bean curd or tofu contaminated with K. gibsonii. These findings suggest that PVQ9 could be a useful preservative in controlling foodborne pathogenic bacteria in soy products and other processed foods.

Antimicrobial peptide Mt 5 inhibits human hepatocellular carcinoma cell HepG2 proliferation

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

Human coronaviruses: activation and antagonism of innate immune responses

SUMMARYHuman coronaviruses cause a range of respiratory diseases, from the common cold (HCoV-229E, HCoV-NL63, HCoV-OC43, and SARS-CoV-2) to lethal pneumonia (SARS-CoV, SARS-CoV-2, and MERS-CoV). Coronavirus interactions with host innate immune antiviral responses are an important determinant of disease outcome. This review compares the host's innate response to different human coronaviruses. Host antiviral defenses discussed in this review include frontline defenses against respiratory viruses in the nasal epithelium, early sensing of viral infection by innate immune effectors, double-stranded RNA and stress-induced antiviral pathways, and viral antagonism of innate immune responses conferred by conserved coronavirus nonstructural proteins and genus-specific accessory proteins. The common cold coronaviruses HCoV-229E and -NL63 induce robust interferon signaling and related innate immune pathways, SARS-CoV and SARS-CoV-2 induce intermediate levels of activation, and MERS-CoV shuts down these pathways almost completely.

Current Advances in Viral Nanoparticles for Biomedicine

Viral nanoparticles (VNPs) have emerged as crucial tools in the field of biomedicine. Leveraging their biological and physicochemical properties, VNPs exhibit significant advantages in the prevention, diagnosis, and treatment of human diseases. Through techniques such as chemical bioconjugation, infusion, genetic engineering, and encapsulation, these VNPs have been endowed with multifunctional capabilities, including the display of functional peptides or proteins, encapsulation of therapeutic drugs or inorganic particles, integration with imaging agents, and conjugation with bioactive molecules. This review provides an in-depth analysis of VNPs in biomedicine, elucidating their diverse types, distinctive features, production methods, and complex design principles behind multifunctional VNPs. It highlights recent innovative research and various applications, covering their roles in imaging, drug delivery, therapeutics, gene delivery, vaccines, immunotherapy, and tissue regeneration. Additionally, the review provides an assessment of their safety and biocompatibility and discusses challenges and future opportunities in the field, underscoring the vast potential and evolving nature of VNP research.

Investigating How Lysophosphatidylcholine and Lysophosphatidylethanolamine Enhance the Membrane Permeabilization Efficacy of Host Defense Peptide Piscidin 1

Lysophospholipids (LPLs) and host defense peptides (HDPs) are naturally occurring membrane-active agents that disrupt key membrane properties, including the hydrocarbon thickness, intrinsic curvature, and molecular packing. Although the membrane activity of these agents has been widely examined separately, their combined effects are largely unexplored. Here, we use experimental and computational tools to investigate how lysophosphatidylcholine (LPC) and lysophosphatidylethanolamine (LPE), an LPL of lower positive spontaneous curvature, influence the membrane activity of piscidin 1 (P1), an α-helical HDP from fish. Four membrane systems are probed: 75:25 C16:0-C18:1 PC (POPC)/C16:0-C18:1 phosphoglycerol (POPG), 50:25:25 POPC/POPG/16:0 LPC, 75:25 C16:0-C18:1 PE (POPE)/POPG, and 50:25:25 POPE/POPG/14:0 LPE. Dye leakage, circular dichroism, and NMR experiments demonstrate that while the presence of LPLs alone does not induce leakage-proficient defects, it boosts the permeabilization capability of P1, resulting in an efficacy order of POPC/POPG/16:0 LPC > POPE/POPG/14:0 LPE > POPC/POPG > POPE/POPG. This enhancement occurs without altering the membrane affinity and conformation of P1. Molecular dynamics simulations feature two types of asymmetric membranes to represent the imbalanced ("area stressed") and balanced ("area relaxed") distribution of lipids and peptides in the two leaflets. The simulations capture the membrane thinning effects of P1, LPC, and LPE, and the positive curvature strain imposed by both LPLs is reflected in the lateral pressure profiles. They also reveal a higher number of membrane defects for the P1/LPC than P1/LPE combination, congruent with the permeabilization experiments. Altogether, these results show that P1 and LPLs disrupt membranes in a concerted fashion, with LPC, the more disruptive LPL, boosting the permeabilization of P1 more than LPE. This mechanistic knowledge is relevant to understanding biological processes where multiple membrane-active agents such as HDPs and LPLs are involved.

Host-directed therapies modulating innate immunity against infection in hematologic malignancies

Patients with hematologic malignancies (HM) are highly susceptible to bloodstream infection (BSI), particularly those undergoing treatments such as chemotherapy. A common and debilitating side effect of chemotherapy is oral and intestinal mucositis. These Patients are also at high risk of developing sepsis, which can arise from mucosal barrier injuries and significantly increases mortality in these patients. While conventional antibiotics are effective, their use can lead to antimicrobial resistance (AMR) and disrupt the gut microbiota (dysbiosis). In this review, we discuss utilizing host defense peptides (HDPs), key components of the innate immune system, and immune system inducers (ISIs) to maintain mucosal barrier integrity against infection, an underexplored host-directed therapy (HDT) approach to prevent BSI and sepsis. We advocate for the discovery of potent and safe ISIs for clinical use and call for further research into the mechanisms by which these ISIs induce HDPs and strengthen mucosal barriers.

Use of adjuvants to improve antibiotic efficacy and reduce the burden of antimicrobial resistance

INTRODUCTION

The increase of antibiotic resistance, together with the absence of novel antibiotics, makes mandatory the introduction of novel strategies to optimize the use of existing antibiotics. Among them, the use of molecules that increase their activity looks promising.

AREAS COVERED

Different categories of adjuvants were reviewed. Anti-resistance adjuvants increase the activity of antibiotics by inhibiting antibiotic resistance determinants. Anti-virulence approaches focus on the infection process itself; reducing virulence in combination with an antibiotic can improve therapeutic efficacy. Combination of phages with antibiotics can also be useful, since they present different mechanisms of action and targets. Finally, combining antibiotics with adjuvants in the same molecule may serve to improve antibiotics' efficacy and overcome potential problems of differential pharmacokinetics/pharmacodynamics.

EXPERT OPINION

The successful combination of inhibitors of β-lactamases with β-lactams has shown that adjuvants can improve the efficacy of current antibiotics. In this sense, novel anti-resistance adjuvants able to inhibit efflux pumps are still needed, as well as anti-virulence compounds that improve the efficacy of antibiotics by interfering with the infection process. Although adjuvants may present different pharmacodynamics/pharmacokinetics than antibiotics, conjugates containing both compounds can solve this problem. Finally, already approved drugs can be a promising source of antibiotic adjuvants.

A Universal Method for Fingerprinting Multiplexed Bacteria: Evolving Pruned Sensor Arrays via Machine Learning-Driven Combinatorial Group-Specificity Strategy

Array-based sensing technology holds immense potential for discerning the intricacies of biological systems. Nevertheless, developing a universal strategy for simultaneous identification of diverse types of multianalytes and meeting the diagnostic needs of a range of multiclassified clinical diseases poses substantial challenges. Herein, we introduce a combination method for constructing sensor arrays by assembling two types of group-specific elements. Such a method enables the rapid generation of a library of 100 sensing units, each with dual bacterial targeting capabilities. By employing a three-step screening strategy optimized by machine learning algorithms, various optimal five-element arrays were rapidly obtained for diverse clinical infectious models. Moreover, the pruned arrays successfully identified disparate mixing ratios and quantitative detection of clinically prevalent bacterial strains. Optimized through nine multiclassification algorithms, the top-performing multilayer perceptron (MLP) model demonstrated impressive recognition capabilities, achieving 100% accuracy for diagnosing clinical urinary tract infection (UTI) and 99.4% accuracy for clinical sepsis detection in the test models we collected. Such a combinatorial library construction and screening process should be standard and provides insights into successfully generating powerful high-recognition sensor elements and configuring them into highly discriminative mini-sensor arrays.

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.

The novel β-hairpin antimicrobial peptide D-G(RF)3 demonstrates exceptional antibacterial efficacy

The clinical application of most natural antimicrobial peptides (AMPs) is hindered by their lack of a synergistic combination of high antibacterial efficacy, low toxicity, and stability, necessitating frequent complex modifications that incur significant labor and economic costs. Therefore, it is imperative to optimize the antibacterial properties of AMPs using some simplified approach. In this study, we designed a library of β-hairpin AMPs with identical β-turn sequences (-D-Pro-Gly-) and varying repetition units (IR, FR, and WK). Ultimately, candidate peptide G(RF)3 exhibited high antibacterial activity and low toxicity; however, its stability was compromised. Moreover, we synthesized the new analogue D-G(RF)3 by D-type amino acid substitution of G(RF)3, and D-G(RF)3 demonstrated concurrent high antibacterial activity, low toxicity, and remarkable stability. Interestingly, both G(RF)3 and D-G(RF)3 exerted bactericidal effects by disrupting the bacterial membrane. However, D-G(RF)3 displayed superior antibiofilm activity with a faster bactericidal rate compared to G(RF)3 and also showed enhanced synergy with antibiotics. Furthermore, D-G(RF)3 exhibited potent in vivo bactericidal activity without inducing drug resistance and has the potential to be a novel antibiotic alternative or adjuvant.

SAMP: Identifying antimicrobial peptides by an ensemble learning model based on proportionalized split amino acid composition

It is projected that 10 million deaths could be attributed to drug-resistant bacteria infections in 2050. To address this concern, identifying new-generation antibiotics is an effective way. Antimicrobial peptides (AMPs), a class of innate immune effectors, have received significant attention for their capacity to eliminate drug-resistant pathogens, including viruses, bacteria, and fungi. Recent years have witnessed widespread applications of computational methods especially machine learning (ML) and deep learning (DL) for discovering AMPs. However, existing methods only use features including compositional, physiochemical, and structural properties of peptides, which cannot fully capture sequence information from AMPs. Here, we present SAMP, an ensemble random projection (RP) based computational model that leverages a new type of feature called proportionalized split amino acid composition (PSAAC) in addition to conventional sequence-based features for AMP prediction. With this new feature set, SAMP captures the residue patterns like sorting signals at both the N-terminal and the C-terminal, while also retaining the sequence order information from the middle peptide fragments. Benchmarking tests on different balanced and imbalanced datasets demonstrate that SAMP consistently outperforms existing state-of-the-art methods, such as iAMPpred and AMPScanner V2, in terms of accuracy, Matthews correlation coefficient (MCC), G-measure, and F1-score. In addition, by leveraging an ensemble RP architecture, SAMP is scalable to processing large-scale AMP identification with further performance improvement, compared to those models without RP. To facilitate the use of SAMP, we have developed a Python package that is freely available at https://github.com/wan-mlab/SAMP.

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.

Novel active Trp- and Arg-rich antimicrobial peptides with high solubility and low red blood cell toxicity designed using machine learning tools

Given the rising number of multidrug-resistant (MDR) bacteria, there is a need to design synthetic antimicrobial peptides (AMPs) that are highly active, non-hemolytic, and highly soluble to act as alternatives to antibiotics that are either no longer effective or used as drugs of last resort. Machine learning tools allow the straightforward in silico identification of non-hemolytic antimicrobial peptides. Here, we utilized a number of these tools to rank the best peptides from two libraries: 1) 8192 peptides with sequence bhxxbhbGAL, where b is the basic amino acid R or K, h is a hydrophobic amino acid, i.e. G, A, L, F, I, V, Y, or W and x is Q, S, A, or V; and 2) 512 peptides with sequence RWhxbhRGWL, where b and h are as for the first library and x is Q, S, A, or G. The top 100 sequences from each library, as well as 10 peptides predicted to be active but hemolytic (for a total of 220 peptides), were SPOT synthesized and their IC50 values were determined against S. aureus USA 300 (MRSA). Of these, 6 AMPs with low IC50's were characterized further in terms of: MICs against MRSA, E. faecalis, K. pneumoniae, E.coli and P. aeruginosa; RBC lysis; secondary structure in mammalian and bacterial model membranes; and activity against cancer cell lines HepG2, CHO, and PC-3. Overall, the approach yielded a large family of active antimicrobial peptides with high solubility and low red blood cell toxicity. It also provides a framework for future designs and improved machine learning tools.

Aggregation-prone antimicrobial peptides target gram-negative bacterial nucleic acids and protein synthesis

Aggregation of antimicrobial peptides (AMPs) enhances their efficacy by destabilising the bacterial cell wall, membrane, and cytosolic proteins. Developing aggregation-prone AMPs offers a promising strategy to combat antibiotic resistance, though predicting such AMPs and understanding bacterial responses remain challenging. Octopus bimaculoides, a cephalopod species, lacks known AMP gene families, yet its protein fragments were used to predict AMPs via artificial intelligence tools. Four peptides (Oct-P1, Oct-P2, Oct-P3, and Oct-P4) were identified based on their aggregation propensity. Among them, Oct-P2 reduced the viability of Escherichia coli and Staphylococcus aureus by up to 90 %, confirmed by confocal laser scanning microscopy and scanning electron microscopy. It further aggregated plasmid DNA in vitro, and the presence of extracellular DNA reduced their antibacterial activity. With knockout mutants, it revealed that Oct-P2 was internalized into bacterial cells, possibly through membrane transport proteins, enhancing its antibacterial effect. Aggregation-induced emission assays and molecular dynamics simulations revealed that Oct-P2 aggregates with transcription promoter DNA, inhibiting transcription and translation in vitro. This dual-target mechanism not only highlights the potential of Oct-P2 as a lead template for new antimicrobial drug development, but also opens a new window for discovering AMPs from protein fragments against the upcoming challenge of bacterial infections. STATEMENT OF SIGNIFICANCE: A popular strategy for identifying antimicrobial peptides (AMPs) in specific genomes uses the conserved regions of AMP families, but this strategy has limitations in organisms lacking classical AMP gene families, such as Octopus. Fragments from non-antimicrobial proteins serve as a rich source for the identification of new AMPs. In this study, we used artificial intelligence tools to search for potential candidate AMP sequences from non-antimicrobial proteins in Octopus bimaculoides. The successful identification of aggregation-prone AMPs was shown to decrease bacterial viability, increase permeability, and reduce biomass. One candidate, Oct-P2, kills the gram-negative bacteria E. coli by aggregating with DNA and inhibiting transcription and translation, suggesting a new intracellular mechanism of AMP activity.

The limits of prediction: Why intrinsically disordered regions challenge our understanding of antimicrobial peptides

Antimicrobial peptides (AMPs) are molecules found in most organisms, playing a vital role in innate immune defense against pathogens. Their mechanism of action involves the disruption of bacterial cell membranes, causing leakage of cellular contents and ultimately leading to cell death. While AMPs typically lack a defined structure in solution, they often assume a defined conformation when interacting with bacterial membranes. Given this structural flexibility, we investigated whether intrinsically disordered regions (IDRs) with AMP-like properties could exhibit antimicrobial activity. We tested 14 peptides from different IDRs predicted to have antimicrobial activity and found that nearly all of them did not display the anticipated effects. These peptides failed to adopt a defined secondary structure and had compromised membrane interactions, resulting in a lack of antimicrobial activity. We hypothesize that evolutionary constraints may prevent IDRs from folding, even in membrane-like environments, limiting their antimicrobial potential. Moreover, our research reveals that current antimicrobial predictors fail to accurately capture the structural features of peptides when dealing with intrinsically unstructured sequences. Hence, the results presented here may have far-reaching implications for designing and improving antimicrobial strategies and therapies against infectious diseases.

Peptides for microbe-induced cancers: latest therapeutic strategies and their advanced technologies

Cancer is a significant global health concern associated with multiple distinct factors, including microbial and viral infections. Numerous studies have elucidated the role of microorganisms, such as Helicobacter pylori (H. pylori), as well as viruses for example human papillomavirus (HPV), hepatitis B virus (HBV), and hepatitis C virus (HCV), in the development of human malignancies. Substantial attention has been focused on the treatment of these microorganism- and virus-associated cancers, with promising outcomes observed in studies employing peptide-based therapies. The current paper provides an overview of microbe- and virus-induced cancers and their underlying molecular mechanisms. We discuss an assortment of peptide-based therapies which are currently being developed, including tumor-targeting peptides and microbial/viral peptide-based vaccines. We describe the major technological advancements that have been made in the design, screening, and delivery of peptides as anticancer agents. The primary focus of the current review is to provide insight into the latest research and development in this field and to provide a realistic glimpse into the future of peptide-based therapies for microbe- and virus-induced neoplasms.

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

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

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.

De novo design of Na+-activated lipopeptides with selective antifungal activity: A promising strategy for antifungal drug discovery

In recent years, invasive fungal infections have posed a significant threat to human health, particularly due to the limited availability of effective antifungal medications. This study responds to the urgent need for powerful and selective antifungal agents by designing and synthesizing a series of lipopeptides with lipoylation at the N-terminus of the antimicrobial peptide I6. Compared to the parent peptide I6, lipopeptides exhibited selective antifungal efficacy in the presence of Na+. Among the variants tested, C8-I6 emerged as the most effective, with an average effective concentration of 5.3 μM against 12 different fungal species. C8-I6 combated fungal infections by disrupting both cytoplasmic and mitochondrial membranes, impairing the proton motive force, generating reactive oxygen species, and triggering apoptosis in fungal cells. Importantly, C8-I6 exhibited minimal hemolysis and cytotoxicity while effectively inhibiting fungal biofilm formation. In vivo experiments further validated the safety and therapeutic potential of C8-I6 in treating fungal skin infections. These findings underscore the significance of lipoylation in enhancing the efficacy of antimicrobial peptides, positioning C8-I6 as a promising candidate in fighting against drug-resistant fungal infections.

Intranasal B5 promotes mucosal defence against Actinobacillus pleuropneumoniae via ameliorating early immunosuppression

Actinobacillus pleuropneumoniae (APP) is an important pathogen of the porcine respiratory disease complex, which leads to huge economic losses worldwide. We previously demonstrated that Pichia pastoris-producing bovine neutrophil β-defensin-5 (B5) could resist the infection by the bovine intracellular pathogen Mycobacterium bovis. In this study, the roles of synthetic B5 in regulating mucosal innate immune response and protecting against extracellular APP infection were further investigated using a mouse model. Results showed that B5 promoted the production of tumour necrosis factor (TNF)-α, interleukin (IL)-1β, and interferon (IFN)-β in macrophages as well as dendritic cells (DC) and enhanced DC maturation in vitro. Importantly, intranasal B5 was safe and conferred effective protection against APP via reducing the bacterial load in lungs and alleviating pulmonary inflammatory damage. Furthermore, in the early stage of APP infection, we found that intranasal B5 up-regulated the secretion of TNF-α, IL-1β, IL-17, and IL-22; enhanced the rapid recruitment of macrophages, neutrophils, and DC; and facilitated the generation of group 3 innate lymphoid cells in lungs. In addition, B5 activated signalling pathways associated with cellular response to IFN-β and activation of innate immune response in APP-challenged lungs. Collectively, B5 via the intranasal route can effectively ameliorate the immune suppression caused by early APP infection and provide protection against APP. The immunization strategy may be applied to animals or human respiratory bacterial infectious diseases. Our findings highlight the potential importance of B5, enhancing mucosal defence against intracellular bacteria like APP which causes early-phase immune suppression.

Fabrication of ZnO/Gypsum/Gelatine nanocomposites films and their antibacterial mechanism against Staphylococcus aureus

Staphylococcus aureus (S. aureus) has long been acknowledged as being one of the most harmful bacteria for human civilization. It is the main contributor to skin and soft tissue infections. The gram positive pathogen also contributes to bloodstream infections, pneumonia, or bone and joint infections. Hence, developing an efficient and targeted treatment for these illnesses is greatly desired. Recently, studies on nanocomposites (NCs) have significantly increased due to their potent antibacterial and antibiofilm properties. These NCs provide an intriguing way to control the growth of bacteria without causing the development of resistance strains that come from improper or excessive use of the conventional antibiotics. In this context, we have demonstrated the synthesis of a NC system by precipitation of ZnO nanoparticles (NPs) on Gypsum followed by encapsulation with Gelatine, in the present study. Fourier transform infrared (FTIR) spectroscopy was used to validate the presence of ZnO NPs and Gypsum. The film was characterized by X-ray diffraction (XRD) spectroscopy and scanning electron microscopy (SEM). The system exhibited promising antibiofilm action and was effective in combating S. aureus and MRSA in concentrations between 10 and 50 ug/ml. The bactericidal mechanism by release of reactive oxygen species (ROS) was anticipated to be induced by the NC system. Studies on cell survival and in-vitro infection support the film's notable biocompatibility and its potential for treating Staphylococcus infections in the future.

Unlocking lysosomal acidity to activate membranolytic module for accurately cancer theranostics

Chemotherapy drug efflux, toxic side effects, and low efficacy against drug-resistant cells have plagued safe and efficient cancer theranostics. However, the materials or methods that resolve these defects all-in-one are scarce. Here, a new cancer theranostics strategy is proposed by utilizing changes in lysosomal acidity in cancer cells to activate the membranolytic model to overcome these obstacles together. Therefore, a simple fluorescent anthracene derivative Lyso-Mito is developed, which has a perfect pKa (4.62) value that falls between the pH of lysosomes in cancer and normal cells. Lyso-Mito itself can precisely target and convert the pH perturbation of lysosomes in cancer cells to fluorescent response and membranolytic module activity to accomplish the low drug efflux, weak toxic side effects, and low drug-resistant cancer diagnosis and treatment without linking other functional units or any additional assistance. Hereby, a new cancer theranostics strategy of integrating organelle microenvironment and the membranolytic model is realized.

A novel cathelicidin TS-CATH derived from Thamnophis sirtalis combats drug-resistant gram-negative bacteria in vitro and in vivo

Antimicrobial peptides are promising therapeutic agents for treating drug-resistant bacterial disease due to their broad-spectrum antimicrobial activity and decreased susceptibility to evolutionary resistance. In this study, three novel cathelicidin antimicrobial peptides were identified from Thamnophis sirtalis, Balaenoptera musculus, and Lipotes vexillifer by protein database mining and sequence alignment and were subsequently named TS-CATH, BM-CATH, and LV-CATH, respectively. All three peptides exhibited satisfactory antibacterial activity and broad antibacterial spectra against clinically isolated E. coli, P. aeruginosa, K. pneumoniae, and A. baumannii in vitro. Among them, TS-CATH displayed the best antimicrobial/bactericidal activity, with a rapid elimination efficiency against the tested drug-resistant gram-negative bacteria within 20 min, and exhibited the lowest cytotoxicity toward mammalian cells. Furthermore, TS-CATH effectively enhanced the survival rate of mice with ceftazidime-resistant E. coli bacteremia and promoted wound healing in meropenem-resistant P. aeruginosa infection. These results were achieved through the eradication of bacterial growth in target organs and wounds, further inhibiting the systemic dissemination of bacteria and the inflammatory response. TS-CATH exhibited direct antimicrobial activity by damaging the inner and outer membranes, resulting in leakage of the bacterial contents at super-MICs. Moreover, TS-CATH disrupted the bacterial respiratory chain, which inhibited ATP synthesis and induced ROS formation, significantly contributing to its antibacterial efficacy at sub-MICs. Overall, TS-CATH has potential for use as an antibacterial agent.

Identification of a Novel β-Defensin Gene in Gilthead Seabream (Sparus aurata)

The excessive use of antibiotics in aquaculture favors the natural selection of multidrug-resistant bacteria, and antimicrobial peptides (AMPs) could be a promising alternative to this problem. The most studied AMPs in teleost fish are piscidins, hepcidins, and β-defensins. In this work, we have found a new gene (defb2) encoding a type 2 β-defensin in the genome of gilthead seabream, a species chosen for its economic interest in aquaculture. Its open reading frame (192 bp) encodes a protein (71 amino acids) that undergoes proteolytic cleavage to obtain the functional mature peptide (42 amino acids). The genetic structure in three exons and two introns and the six characteristic cysteines are conserved as the main signature of this protein family. In the evolutionary analysis, synteny shows a preservation of chromosomal localization and the phylogenetic tree constructed exposes the differences between both types of β-defensin as well as the similarities between seabream and European seabass. In relation to its basal expression, β-defensin 2 is mostly expressed in the intestine, thymus, skin, and gonads of the gilthead seabream (Sparus aurata). In head kidney leucoytes (HKLs), the expression was very low and did not change significantly when stimulated with various immunocompetent agents. However, the expression was significantly down-regulated in the liver, head-kidney, and blood 4 h post-injection with the fish pathogen Vibrio harveyi. When infected with nodavirus, the expression was downregulated in brain at 7 days post-infection. These results denote a possible complementarity between the expression patterns of β-defensins and hepcidins. Further studies are needed to analyze gene duplications and expression patterns of β-defensins and describe their mechanism of action in seabream and other teleost fish.

High-yield, plant-based production of an antimicrobial peptide with potent activity in a mouse model

Plants offer a promising chassis for the large-scale, cost-effective production of diverse therapeutics, including antimicrobial peptides (AMPs). However, key advances will reduce production costs, including simplifying the downstream processing and purification steps. Here, using Nicotiana benthamiana plants, we present an improved modular design that enables AMPs to be secreted via the endomembrane system and sequestered in an extracellular compartment, the apoplast. Additionally, we translationally fused an AMP to a mutated small ubiquitin-like modifier sequence, thereby enhancing peptide yield and solubilizing the peptide with minimal aggregation and reduced occurrence of necrotic lesions in the plant. This strategy resulted in substantial peptide accumulation, reaching around 2.9 mg AMP per 20 g fresh weight of leaf tissue. Furthermore, the purified AMP demonstrated low collateral toxicity in primary human skin cells, killed pathogenic bacteria by permeabilizing the membrane and exhibited anti-infective efficacy in a preclinical mouse (Mus musculus) model system, reducing bacterial loads by up to three orders of magnitude. A base-case techno-economic analysis demonstrated the economic advantages and scalability of our plant-based platform. We envision that our work can establish plants as efficient bioreactors for producing preclinical-grade AMPs at a commercial scale, with the potential for clinical applications.

Unraveling the Applicability of LbL Coatings for Drug Delivery in Dental Implant-Related Infection Treatment

Peri-implantitis is an inflammatory condition caused by bacterial biofilms adhered on dental implant surfaces that cause progressive tissue destruction from the host's inflammatory response. The adverse effects of peri-implantitis progression can go beyond just losing the implant. This highlights the importance of implementing strategies to stabilize disease in the short term. Layer-by-layer (LbL) assembly is a promising avenue in the field of peri-implantitis management due to its applicability with a variety of substances, in addition to being an easy, versatile, and flexible process for multilayer formation to act directly in the affected site. In this Review, our objective is to offer comprehensive chemical and biological insights into the LbL system, clarifying its specific application as antimicrobial coatings, with concern for the physical site and purpose. Additionally, we delve deeper into the concepts of onset and progression of peri-implantitis, aiming to elucidate the precise indications for employing the LbL system as a coating for implant abutments in peri-implantitis treatment. Finally, we correlate the chemical composition of the LbL system with its functionality while also addressing the challenges posed by the uncontrolled environment of the oral cavity, which ultimately restricts its clinical applicability.

Microbiome interactions: Acinetobacter baumannii biofilms as a co-factor in oral cancer progression

Acinetobacter baumannii (A. baumannii) has long been recognized primarily as a hospital-acquired pathogen. However, recent studies have uncovered a potential link between this bacterium and oral cancer, necessitating a deeper exploration of this relationship. This review examines the relevance of A. baumannii biofilms in the context of oral cancer development. By synthesizing current knowledge, we seek to provide a comprehensive understanding of this emerging area of research and identify critical directions for future investigations. The review emphasizes the remarkable adaptability, environmental resilience, and antibiotic resistance of A. baumannii, delves into the molecular mechanisms of biofilm formation, and their potential connection to oral cancer progression. The review also evaluates how biofilm colonization on oral surfaces and medical devices, along with its role in chronic infections, inflammation, and increased antimicrobial resistance, could contribute to creating a microenvironment favourable for tumor development. This review underscores the broader healthcare implications of A. baumannii biofilms, evaluates current strategies for their prevention and eradication, and calls for interdisciplinary research in this emerging field. By shedding light on the complex interactions between A. baumannii biofilms and oral cancer, it aims to stimulate further research and guide the development of new diagnostic, preventive, and therapeutic strategies in both microbiology and oncology.

Hyaluronic acid based nanoparticles that mediate sustained thanatin release protect against NDM-1-resistant bacterial infections in a murine model

Thanatin, a potent cationic antimicrobial peptide, has demonstrated remarkable efficacy against new NDM-1 producing bacteria. However, its clinical application is hampered by suboptimal stability in circulation and limited bioavailability in the human body. To overcome these challenges, a novel thanatin nanomedicine has been developed, which encapsulated thanatin in nanoparticles formed by electrostatic interactions between negatively charged HA and PLGA. The obtained ThaNPs demonstrated good stability, low cytotoxicity, and good metabolic ratio. ThaNPs significantly improve the stability of thanatin in the circulation, increasing its half-life in 50 % serum from 0.6 h to 3.2 h. Notably, the protective effect of ThaNPs against sepsis induced by NDM-1-producing Escherichia coli. Was 10-fold higher than that of unencapsulated thanatin. These findings suggest that hyaluronic acid-based nanoparticles have the potentiality to overcome the clinical limitations associated with cationic antimicrobial peptides, thereby providing a novel and effective strategy for treating severe infections caused by antibiotic-resistant bacteria.

Antimicrobial Peptide CATH-2 Attenuates Avian Pathogenic E. coli-Induced Inflammatory Response via NF-κB/NLRP3/MAPK Pathway and Lysosomal Dysfunction in Macrophages

Cathelicidins have anti-inflammatory activity and chicken cathelicidin-2 (CATH-2) has shown to modulate immune response, but the underlying mechanism of its anti-inflammation is still unclear. Therefore, in this study, we investigated the anti-inflammatory activity of CATH-2 on murine peritoneal macrophages during avian pathogenic E. coli (APEC) infection. The results showed that CATH-2 priming significantly reduced the production of IL-1β, IL-6, IL-1α, and IL-12. In addition, CATH-2 significantly attenuated APEC-induced caspase-1 activation and the formation of an adaptor (ASC) of NLRP3 inflammasome, indicating that CATH-2 inhibits APEC-induced NLRP3 inflammasome activation. Furthermore, CATH-2 remarkably inhibited NF-κB and MAPK signaling pathways activation. Moreover, CATH-2 significantly inhibited mRNA expression of cathepsin B and inhibited lysosomal acidification, demonstrating that CATH-2 disrupts lysosomal function. In addition, promoting lysosomal acidification using ML-SA1 hampered the anti-inflammatory effect of CATH-2 on APEC-infected cells. In conclusion, our study reveals that CATH-2 inhibits APEC-induced inflammation via the NF-κB/NLRP3/MAPK pathway through the dysfunction of lysosome.

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.

Antimicrobial Peptides: The Game-Changer in the Epic Battle Against Multidrug-Resistant Bacteria

The rapid progress of antibiotic resistance among bacteria has prompted serious medical concerns regarding how to manage multidrug-resistant (MDR) bacterial infections. One emerging strategy to combat antibiotic resistance is the use of antimicrobial peptides (AMPs), which are amino acid chains that act as broad-spectrum antimicrobial molecules and are essential parts of the innate immune system in mammals, fungi, and plants. AMPs have unique antibacterial mechanisms that offer benefits over conventional antibiotics in combating drug-resistant bacterial infections. Currently, scientists have conducted multiple studies on AMPs for combating drug-resistant bacterial infections and found that AMPs are a promising alternative to conventional antibiotics. On the other hand, bacteria can develop several tactics to resist and bypass the effect of AMPs. Therefore, it is like a battle between the bacterial community and the AMPs, but who will win? This review provides thorough insights into the development of antibiotic resistance as well as detailed information about AMPs in terms of their history and classification. Furthermore, it addresses the unique antibacterial mechanisms of action of AMPs, how bacteria resist these mechanisms, and how to ensure AMPs win this battle. Finally, it provides updated information about FDA-approved AMPs and those that were still in clinical trials. This review provides vital information for researchers for the development and therapeutic application of novel AMPs for drug-resistant bacterial infections.

Interplay between Antimicrobial Peptides and Amyloid Proteins in Host Defense and Disease Modulation

The biological properties of antimicrobial peptides (AMPs) and amyloid proteins and their cross-talks have gained increasing attention due to their potential implications in both host defense mechanisms and amyloid-related diseases. However, complex interactions, molecular mechanisms, and physiological applications are not fully understood. The interplay between antimicrobial peptides and amyloid proteins is crucial for uncovering new insights into immune defense and disease mechanisms, bridging critical gaps in understanding infectious and neurodegenerative diseases. This review provides an overview of the cross-talk between AMPs and amyloids, highlighting their intricate interplay, mechanisms of action, and potential therapeutic implications. The dual roles of AMPs, which not only serve as key components of the innate immune system, combating microbial infections, but also exhibit modulatory effects on amyloid formation and toxicity, are discussed. The diverse mechanisms employed by AMPs to modulate amyloid aggregation, fibril formation, and toxicity are also discussed. Additionally, we explore emerging evidence suggesting that amyloid proteins may possess antimicrobial properties, adding a new dimension to the intricate relationship between AMPs and amyloids. This review underscores the importance of understanding the cross-talk between AMPs and amyloids to better understand the molecular processes underlying infectious diseases and amyloid-related disorders and to aid in the development of therapeutic avenues to treat them.

Modification of Antibacterial Copolymers on the Surface of PVA-Based Microfibers via Thermal Cross-Linking and Their Antibacterial Properties

Bacterial infections on material surfaces are a serious public health concern worldwide. Although poly(vinyl alcohol) (PVA)-based materials have great potential as medical devices, they lack antibacterial properties on their surfaces and pose bacterial infection risks during implantation surgery. Copolymers containing antibacterial [2-(methacryloyloxy)ethyl]trimethylammonium chloride (METAC) units were used to modify the surfaces of chemically cross-linked water-insoluble PVA-based microfibers. The copolymers also had carboxy units that were used to react with the hydroxy group of the PVA-based microfibers via a simple thermal treatment at 135 °C. PVA-based materials containing METAC units exhibit significant swelling due to electrostatic repulsions. Because the copolymers were modified on the extreme surface of the microfibers, no difference in the diameters between unmodified microfibers (PM-fiber) and copolymers with METAC unit-modified microfibers (PM-METAC-fiber), in both the dry and swollen states, was observed. The viable bacterial cell numbers, which were evaluated by colony counting, decreased by exposure to the poly(METAC-co-methacrylic acid (MAAc)) aqueous solution or PM-METAC-fibers. The value of CFU/mL decreased to 0.1% (against B. subtilis) and 3.9% (against E. coli) after contact with the PM-METAC-fibers compared to the PM-fibers. The percentage of hemolysis against rabbit red blood cells was equivalent to that of the negative control, suggesting that PM-METAC-fibers can selectively exhibit antibacterial properties. This modification method can be applied to various PVA-based materials if hydroxy groups are present on their surface. This study provides a facile, cost-effective, and promising strategy to impart antibacterial properties to the surface of PVA-based materials without significantly affecting their physicochemical properties.

Tissue nano-transfection of antimicrobial genes drives bacterial biofilm killing in wounds and is potentially mediated by extracellular vesicles

The emergence of bacteria that are resistant to antibiotics is on track to become a major global health crisis. Therefore, there is an urgent need for new treatment options. Here, we studied the implementation of tissue-nanotransfection (TNT) to treat Staphylococcus aureus-infected wounds by delivering gene cargos that boost the levels of naturally produced antimicrobial peptides. The Cathelicidin Antimicrobial Peptide gene (CAMP), which produces the antimicrobial peptide LL-37, was used as model gene cargo. In vitro evaluation showed successful transfection and an increase in the transcription and translation of CAMP-coding plasmid in mouse primary epithelial cells. Moreover, we found that the extracellular vesicles (EVs) derived from the transfected cells (in vitro and in vivo) carried significantly higher concentrations of CAMP transcripts and LL-37 peptide compared to control EVs, possibly mediating the trafficking of the antimicrobial contents to other neighboring cells. The TNT platform was then used in vivo on an excisional wound model in mice to nanotransfect the CAMP-coding plasmid on the edge of infected wounds. After 4 days of daily treatment, we observed a significant decrease in the bacterial load in the CAMP-treated group compared to the sham group. Moreover, histological analysis and bacterial load quantification also revealed that TNT of CAMP on S. aureus-infected wounds was effective in treating biofilm progression by reducing the bacterial load. Lastly, we observed a significant increase in macrophage recruitment to the infected tissue, a robust increase in vascularization, as well as and an increased expression of IL10 and Fli1. Our results demonstrate that TNT-based delivery of gene cargos coding for antimicrobial compounds to the wound is a promising approach for combating biofilm infections in wounds.

Antimicrobial Peptide Pro10-1D Exhibits Anti-Allergic Activity: A Promising Therapeutic Candidate

Although antimicrobial peptides (AMPs) exhibit a range of biological functions, reports on AMPs with therapeutic effects in allergic disorders are limited. In this study, we investigated the anti-allergic effects of Pro10-1D, a 10-meric AMP derived from insect defensin protaetiamycine. Our findings demonstrate that Pro10-1D effectively inhibits antigen-induced degranulation of mast cells (MCs) with IC50 values of approximately 11.6 μM for RBL-2H3 cells and 2.7 μM for bone marrow-derived MCs. Furthermore, Pro10-1D suppressed the secretion of cytokines with IC50 values of approximately 2.8 μM for IL-4 and approximately 8.6 μM for TNF-α. Mechanistically, Pro10-1D inhibited the Syk-LAT-PLCγ1 signaling pathway in MCs and decreased the activation of mitogen-activated protein kinases (MAPKs). Pro10-1D demonstrated a dose-dependent reduction in IgE-mediated passive cutaneous anaphylaxis in mice with an ED50 value of approximately 7.6 mg/kg. Further investigation revealed that Pro10-1D significantly reduced the activity of key kinases Fyn and Lyn, which are critical in the initial phase of the FcεRI-mediated signaling pathway, with IC50 values of approximately 22.6 μM for Fyn and approximately 1.5 μM for Lyn. Collectively, these findings suggest that Pro10-1D represents a novel therapeutic candidate for the treatment of IgE-mediated allergic disorders by targeting the Lyn/Fyn Src family kinases in MCs.

Novel Tree Shrew-Derived Antimicrobial Peptide with Broad-Spectrum Antibacterial Activity

The number of cationic residues and net charge are critical for the activity of antimicrobial peptides (AMPs) due to their role in facilitating initial electrostatic interactions with negatively charged bacterial membranes. A cathelicidin AMP (TC-33) has been identified from the Chinese tree shrew in our previous work, which exhibited weak antimicrobial activity, likely due to its moderately cationic nature. In the current study, based on TC-33, we designed a novel AMP by peptide truncation and Glu substitutions to increase its net cationic charge from +4 to +8. The resulting peptide, TC-LAR-18, showed 4-128-fold enhanced antimicrobial activity relative to TC-33 without causing hemolysis and cytotoxicity within 100 μg/mL. TC-LAR-18 effectively eliminated both planktonic and biofilm-associated bacteria, demonstrating rapid bactericidal effects due to its ability to quickly penetrate and disrupt bacterial cell membranes with a low propensity to induce resistance. Notably, TC-LAR-18 provided substantial protection against skin bacterial infection in mice, underscoring its therapeutic potential. These findings not only highlight the importance of positively charged residues for the antibacterial activity of AMPs but also present a useful drug candidate for combating multidrug-resistant bacteria.

Antimicrobial Peptides: A Promising Alternative to Conventional Antimicrobials for Combating Polymicrobial Biofilms

Polymicrobial biofilms adhere to surfaces and enhance pathogen resistance to conventional treatments, significantly contributing to chronic infections in the respiratory tract, oral cavity, chronic wounds, and on medical devices. This review examines antimicrobial peptides (AMPs) as a promising alternative to traditional antibiotics for treating biofilm-associated infections. AMPs, which can be produced as part of the innate immune response or synthesized therapeutically, have broad-spectrum antimicrobial activity, often disrupting microbial cell membranes and causing cell death. Many specifically target negatively charged bacterial membranes, unlike host cell membranes. Research shows AMPs effectively inhibit and disrupt polymicrobial biofilms and can enhance conventional antibiotics' efficacy. Preclinical and clinical research is advancing, with animal studies and clinical trials showing promise against multidrug-resistant bacteria and fungi. Numerous patents indicate increasing interest in AMPs. However, challenges such as peptide stability, potential cytotoxicity, and high production costs must be addressed. Ongoing research focuses on optimizing AMP structures, enhancing stability, and developing cost-effective production methods. In summary, AMPs offer a novel approach to combating biofilm-associated infections, with their unique mechanisms and synergistic potential with existing antibiotics positioning them as promising candidates for future treatments.

Antimicrobial Peptides: Mechanism, Expressions, and Optimization Strategies

Antimicrobial peptides (AMPs) are favoured because of their broad-spectrum antimicrobial properties and because they do not easily develop microbial resistance. However, the low yield and difficult extraction processes of AMPs have become bottlenecks in large-scale industrial applications and scientific research. Microbial recombinant production may be the most economical and effective method of obtaining AMPs in large quantities. In this paper, we review the mechanism, summarize the current status of microbial recombinant production, and focus on strategies to improve the yield and activity of AMPs, in order to provide a reference for their large-scale production.

Quaternized 1,2,3-Triazolyl Content and Modulation Potentiate Antibacterial and Antifungal Activities of Amphipathic Peptoids

Bioinspired from cationic antimicrobial peptides, sequence-defined triazolium-grafted peptoid oligomers (6- to 12-mer) were designed to adopt an amphipathic helical polyproline I-type structure. Their evaluation on a panel of bacterial strains (Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Enterococcus faecalis), pathogenic fungi (Candida albicans, Cryptococcus neoformans, and Aspergillus fumigatus), and human cells (hRBC, BEAS-2B, Caco-2, HaCaT, and HepG2) enabled the identification of two heptamers with improved activity to selectively fight Staphylococcus aureus pathogens. Modulation of parameters such as the nature of the triazolium and hydrophobic/lipophilic side chains, the charge content, and the sequence length drastically potentiates activity and selectivity. Besides, the ability to block the proinflammatory effect induced by lipopolysaccharide or lipoteichoic acid was also explored. Finally, biophysical studies by circular dichroism and fluorescence spectroscopies strongly supported that the bactericidal effect of these triazolium-grafted oligomers was primarily due to the selective disruption of the bacterial membrane.

The Equilibrium of Bacterial Microecosystem: Probiotics, Pathogenic Bacteria, and Natural Antimicrobial Substances in Semen

Semen is a complex fluid that contains spermatozoa and also functions as a dynamic bacterial microecosystem, comprising probiotics, pathogenic bacteria, and natural antimicrobial substances. Probiotic bacteria, such as Lactobacillus and Bifidobacterium, along with pathogenic bacteria like Pseudomonas aeruginosa and Escherichia coli, play significant roles in semen preservation and reproductive health. Studies have explored the impact of pathogenic bacteria on sperm quality, providing insights into the bacterial populations in mammalian semen and their influence on sperm function. These reviews highlight the delicate balance between beneficial and harmful bacteria, alongside the role of natural antimicrobial substances that help maintain this equilibrium. Moreover, we discuss the presence and roles of antimicrobial substances in semen, such as lysozyme, secretory leukocyte peptidase inhibitors, lactoferrin, and antimicrobial peptides, as well as emerging antibacterial substances like amyloid proteins. Understanding the interactions among probiotics, pathogens, and antimicrobial agents is crucial for elucidating semen preservation and fertility mechanisms. Additionally, the potential for adding probiotic bacteria with recombinant antibacterial properties presents a promising avenue for the development of new semen extenders. This review offers updated insights to understand the equilibrium of the bacterial microecosystem in semen and points toward innovative approaches for improving semen preservation.

Effect of Nk-lysin peptides on bacterial growth, MIC, antimicrobial resistance, and viral activities

NK-lysins from chicken, bovine and human are used as antiviral and antibacterial agents. Gram-negative and gram-positive microorganisms, including Streptococcus pyogenes, Streptococcus mutans, Escherichia coli, Pseudomonas aeruginosa, Klebsiella oxytoca, Shigella sonnei, Klebsiella pneumoniae and Salmonella typhimurium, are susceptible to NK-lysin treatment. The presence of dominant TEM-1 gene was noted in all untreated and treated bacteria, while TOHO-1 gene was absent in all bacteria. Importantly, β-lactamase genes CTX-M-1, CTX-M-8, and CTX-M-9 genes were detected in untreated bacterial strains; however, none of these were found in any bacterial strains following treatment with NK-lysin peptides. NK-lysin peptides are also used to test for inhibition of infectivity, which ranged from 50 to 90% depending on NK-lysin species. Chicken, bo vine and human NK-lysin peptides are demonstrated herein to have antibacterial activity and antiviral activity against Rotavirus (strain SA-11). On the basis of the comparison between these peptides, potent antiviral activity of bovine NK-lysin against Rotavirus (strain SA-11) is particularly evident, inhibiting infection by up to 90%. However, growth was also significantly inhibited by chicken and human NK-lysin peptides, restricted by 80 and 50%, respectively. This study provided a novel treatment using NK-lysin peptides to inhibit expression of β-lactamase genes in β-lactam antibiotic-resistant bacterial infections.

The Human Mitochondrial Genome Encodes for an Interferon-Responsive Host Defense Peptide

The mitochondrial DNA (mtDNA) can trigger immune responses and directly entrap pathogens, but it is not known to encode for active immune factors. The immune system is traditionally thought to be exclusively nuclear-encoded. Here, we report the identification of a mitochondrial-encoded host defense peptide (HDP) that presumably derives from the primordial proto-mitochondrial bacteria. We demonstrate that MOTS-c (mitochondrial open reading frame from the twelve S rRNA type-c) is a mitochondrial-encoded amphipathic and cationic peptide with direct antibacterial and immunomodulatory functions, consistent with the peptide chemistry and functions of known HDPs. MOTS-c targeted E. coli and methicillin-resistant S. aureus (MRSA), in part, by targeting their membranes using its hydrophobic and cationic domains. In monocytes, IFNγ, LPS, and differentiation signals each induced the expression of endogenous MOTS-c. Notably, MOTS-c translocated to the nucleus to regulate gene expression during monocyte differentiation and programmed them into macrophages with unique transcriptomic signatures related to antigen presentation and IFN signaling. MOTS-c-programmed macrophages exhibited enhanced bacterial clearance and shifted metabolism. Our findings support MOTS-c as a first-in-class mitochondrial-encoded HDP and indicates that our immune system is not only encoded by the nuclear genome, but also by the co-evolved mitochondrial genome.

Function of immune cells and effector molecules of the innate immune system in the establishment and maintenance of pregnancy in mammals - A review

In mammalian species, pregnancy is a complex process that involves the maternal recognition of pregnancy, implantation, decidualization, placentation, and parturition. The innate immune system is composed of cellular components, such as natural killer cells, neutrophils, monocytes, and macrophages, and effector molecules, such as cytokines, interferons, antimicrobial peptides, and complement components. The innate immune system plays a critical role as the first line of defense against infection or inflammation to maintain homeostasis and activate the adaptive immunity. During pregnancy, innate immune cells and effector molecules act on the regulation of innate immunity for host defense and processes such as embryo development, implantation, and placentation at the maternal-conceptus interface. In this review, we describe the components of the innate immune system and their functions at the maternal-conceptus interface to establish and maintain pregnancy in animal species that form hemochorial- or epitheliochorial-type placentas, including humans, rodents, ruminants, and pigs.

Evolutionary trends indicate a coherent organization of sap operons

Human hosts possess a complex network of immune responses against microbial pathogens. The production of antimicrobial peptides (AMPs), which target the pathogen cell membranes and inhibit them from inhabiting the hosts, is one such mechanism. However, pathogens have evolved systems that encounter these host-produced AMPs. The Sap (sensitivity to antimicrobial peptides) transporter uptakes AMPs inside the microbial cell and proteolytically degrades them. The Sap transporters comprise five subunits encoded by genes in an operon. Despite its ubiquitous nature, its subunits are not found to be in tandem with many organisms. In this study, a total of 421 Sap transporters were analyzed for their operonic arrangement. Out of 421, a total of 352 operons were found to be in consensus arrangement, while the remaining 69 show a varying arrangement of genes. The analysis of the intergenic distance between the subunits of the sap operon suggests a signature pattern with sapAB (-4), sapBC (-14), sapCD (-1), and sapDF (-4 to 1). An evolutionary analysis of these operons favors the consensus arrangement of the Sap transporter systems, substantiating its prevalence in most of the Gram-negative pathogens. Overall, this study provides insight into bacterial evolution, favoring the maintenance of the genetic organization of essential pathogenicity factors.

A potent antimicrobial glycolipopeptide GLIP and its promising combined antimicrobial effect

Here, the glycolipopeptide GLIP was obtained by coupling IL-C8 and the monosaccharide molecule D-(+)-glucosamine to the N-terminal and C-terminal of the peptide P, which was designed on the basis of the biological characteristics of the antimicrobial peptides. In vitro bioactivity and physicochemical properties assays confirmed that GLIP had excellent antimicrobial activity against Gram-negative E. coli ATCC 25922 and Gram-positive S. aureus ATCC 29213, as well as good stability in serum and trypsin, low hemolysis, and good bacterial membrane-disrupting ability. In addition, the glycolipopeptide GLIP could self-assembly in aqueous solution to form spherical nano-aggregates, which could encapsulate the small molecule antibiotic TC to form the nanomedicine GLIP@TC and release the TC continuously and slowly in a sustained-release manner, exerting the combined antimicrobial effect of both. The results of animal experiments demonstrated the excellent in vivo antimicrobial activities of GLIP and nanomedicine GLIP@TC. Finally, molecular docking experiment showed that the GLIP could effectively bind to penicillin-binding protein 5 (PBP5) of E. coli and possibly inhibit its D-Ala carboxypeptidase (CPase) activity. All these results may imply the great potential of GLIP for clinical application against bacterial drug resistance.

Functional antimicrobial peptide-loaded 3D scaffolds for infected bone defect treatment with AI and multidimensional printing

Infection is the most prevalent complication of fractures, particularly in open fractures, and often leads to severe consequences. The emergence of bacterial resistance has significantly exacerbated the burden of infection in clinical practice, making infection control a significant treatment challenge for infectious bone defects. The implantation of a structural stent is necessary to treat large bone defects despite the increased risk of infection. Therefore, there is a need for the development of novel antibacterial therapies. The advancement in antibacterial biomaterials and new antimicrobial drugs offers fresh perspectives on antibacterial treatment. Although antimicrobial 3D scaffolds are currently under intense research focus, relying solely on material properties or antibiotic action remains insufficient. Antimicrobial peptides (AMPs) are one of the most promising new antibacterial therapy approaches. This review discusses the underlying mechanisms behind infectious bone defects and presents research findings on antimicrobial peptides, specifically emphasizing their mechanisms and optimization strategies. We also explore the potential prospects of utilizing antimicrobial peptides in treating infectious bone defects. Furthermore, we propose that artificial intelligence (AI) algorithms can be utilized for predicting the pharmacokinetic properties of AMPs, including absorption, distribution, metabolism, and excretion, and by combining information from genomics, proteomics, metabolomics, and clinical studies with computational models driven by machine learning algorithms, scientists can gain a comprehensive understanding of AMPs' mechanisms of action, therapeutic potential, and optimizing treatment strategies tailored to individual patients, and through interdisciplinary collaborations between computer scientists, biologists, and clinicians, the full potential of AI in accelerating the discovery and development of novel AMPs will be realized. Besides, with the continuous advancements in 3D/4D/5D/6D technology and its integration into bone scaffold materials, we anticipate remarkable progress in the field of regenerative medicine. This review summarizes relevant research on the optimal future for the treatment of infectious bone defects, provides guidance for future novel treatment strategies combining multi-dimensional printing with new antimicrobial agents, and provides a novel and effective solution to the current challenges in the field of bone regeneration.

Water-medicated specifically targeting the S1 pockets among serine proteases using an arginine analogue

Because of the high similarity in structure and sequence, it is challenging to distinguish the S1 pocket among serine proteases, primarily due to the only variability at residue 190 (A190 and S190). Peptide or protein-based inhibitors typically target the negatively charged S1 pocket using lysine or arginine as the P1 residue, yet neither discriminates between the two S1 pocket variants. This study introduces two arginine analogues, L-4-guanidinophenylalanine (12) and L-3-(N-amidino-4-piperidyl)alanine (16), as novel P1 residues in peptide inhibitors. 16 notably enhances affinities across all tested proteases, whereas 12 specifically improved affinities towards proteases possessing S190 in the S1 pocket. By crystallography and molecular dynamics simulations, we discovered a novel mechanism involving a water exchange channel at the bottom of the S1 pocket, modulated by the variation of residue 190. Additionally, the specificity of 12 towards the S190-presenting S1 pocket is dependent on this water channel. This study not only introduces novel P1 residues to engineer inhibitory potency and specificity of peptide inhibitors targeting serine proteases, but also unveils a water-mediated molecular mechanism of targeting serine proteases.