Antimicrobial peptides: natural effectors of the innate immune system

A critical view of antimicrobial peptides: exploring their potential and the barriers to realization

The global rise of multidrug-resistant infections highlights the urgent need for innovative therapeutic strategies beyond traditional antibiotics. Antimicrobial peptides (AMPs), naturally occurring in all forms of life and synthetically producible, have garnered significant attention for their broad-spectrum antimicrobial properties and diverse mechanisms of action, including membrane disruption, immune modulation, and biofilm formation inhibition and disruption. Despite great potential, the clinical deployment of AMPs faces significant challenges, including cytotoxicity, low chemical stability, high production costs, and stringent regulatory demands. Innovative strategies, such as AMP-antibiotic conjugation, offer potential solutions to some of these challenges by enhancing efficacy, reducing toxicity, and broadening antimicrobial activity. This review critically evaluates the promise and limitations of AMPs as therapeutic antibacterial agents. We also explore the potential of AMP-antibiotic conjugates, highlighting their potential synergistic effects and the obstacles to their clinical application. Antimicrobial self-assembling peptides are also discussed, with their ability to form nanostructures that may disrupt biofilms and inhibit bacterial communication, representing a promising but complex avenue. A critical evaluation of these emerging strategies, grounded in their practical applicability and translational challenges, is essential to drive meaningful progress in combating antimicrobial resistance.

An Analysis of Intrinsic Protein Disorder in Antimicrobial Peptides

Antibiotic resistance, driven by the rise of pathogens like VRE and MRSA, poses a global health threat, prompting the exploration of antimicrobial peptides (AMPs) as alternatives to traditional antibiotics. AMPs, known for their broad-spectrum activity and structural flexibility, share characteristics with intrinsically disordered proteins, which lack a rigid structure and play diverse roles in cellular processes. This study aims to quantify the intrinsic disorder and liquid-liquid phase separation (LLPS) propensity in AMPs, advancing our understanding of their antimicrobial mechanisms and potential therapeutic applications. To investigate the propensity for intrinsic disorder and LLPS in AMPs, we compared the AMPs to the human proteome. The AMP sequences were retrieved from the AMP database (APD3), while the human proteome was obtained from the UniProt database. We analyzed amino acid composition using the Composition Profiler tool and assessed intrinsic disorder using various predictors, including PONDR® and IUPred, through the Rapid Intrinsic Disorder Analysis Online (RIDAO) platform. For LLPS propensity, we employed FuzDrop, and FuzPred was used to predict context-dependent binding behaviors. Statistical analyses, such as ANOVA and χ2 tests, were performed to determine the significance of observed differences between the two groups. We analyzed over 3000 AMPs and 20,000 human proteins to investigate differences in amino acid composition, intrinsic disorder, and LLPS potential. Composition analysis revealed distinct differences in amino acid abundance, with AMPs showing an enrichment in both order-promoting and disorder-promoting amino acids compared to the human proteome. Intrinsic disorder analysis, performed using a range of predictors, consistently demonstrated that AMPs exhibit higher levels of predicted disorder than human proteins, with significant differences confirmed by statistical tests. LLPS analysis, conducted using FuzDrop, showed that AMPs had a lower overall propensity for LLPS compared to human proteins, although specific subsets of AMPs exhibited high LLPS potential. Additionally, redox-dependent disorder predictions highlighted significant differences in how AMP and human proteins respond to oxidative conditions, further suggesting functional divergences between the two proteomes. CH-CDF plot analysis revealed that AMPs and human proteins occupy distinct structural categories, with AMPs showing a greater proportion of highly disordered proteins compared to the human proteome. These findings underscore key molecular differences between AMPs and human proteins, with implications for their antimicrobial activity and potential therapeutic applications. Our study reveals that AMPs possess a significantly higher degree of intrinsic disorder and specific subsets exhibit LLPS potential, distinguishing them from the human proteome. These molecular characteristics likely contribute to their antimicrobial function and adaptability, offering valuable insights for developing novel therapeutic strategies to combat antibiotic resistance.

Antimicrobial Activity of the Peptide C14R Against Ab Initio Growing and Preformed Biofilms of Candida albicans, Candida parapsilosis and Candidozyma auris

Biofilms are the predominant lifeforms of microorganisms, contributing to over 80% of infections, including those caused by Candida species like C. albicans, C. parapsilosis and Candidozyma auris. These species form biofilms on medical devices, making infections challenging to treat, especially with the rise in drug-resistant strains. Candida infections, particularly hospital-acquired ones, are a significant health threat due to their resistance to antifungals and the risk of developing systemic infections (i.e., sepsis). We have previously shown that C14R reduces the viability of C. albicans and C. auris, but not of C. parapsilosis. Here, we show that C14R not only inhibits viability by pore formation, shown in a resazurin reduction assay, and in a C. parapsilosis and fluorescence-based permeabilization assay, but it also halts biofilm maturation and significantly reduces the biomass of preformed biofilms by over 70%. These findings suggest C14R could be an effective option for treating severe fungal infections, offering a potential new treatment approach for biofilm-related diseases. Further research is needed to fully understand its biofilm dispersal potential and to optimize its use for future applications as an antifungal in clinical settings.

Antischistosomal Potential of Animal-Derived Natural Products and Compounds

Schistosomiasis is a neglected tropical disease that affects over 240 million people worldwide. Currently, praziquantel is the only drug recommended by the World Health Organization for treatment. However, cases of drug resistance have been reported, which indicates an urgent need for new therapeutics. In this context, natural compounds represent valuable sources of pharmacological substances. Plant-derived natural products have been greatly explored for their potential antischistosomal activity, while animal-derived compounds have received little attention. Recent advances in the biotechnology field allow the wide exploration of animal-derived compounds in drug discovery, which may represent a cost-effective option to find bioactive molecules also against Schistosoma mansoni and other parasites. This review highlights the research into animal-derived products and compounds that have already been tested against schistosomes. Phenotypic effects on schistosomes have been observed upon incubation with some of these substances, which may, therefore, represent possible candidates to be used in the development of new drugs. Overall, these studies advance the discovery of antischistosomal compounds by exploring a yet understudied natural resource. The present review also discusses the challenges of testing animal-derived products and provides examples of the experimental in vitro testing of different selected animal natural products against S. mansoni.

Current developments and prospects of the antibiotic delivery systems

Antibiotics have remained the cornerstone for the treatment of bacterial infections ever since their discovery in the twentieth century. The uproar over antibiotic resistance among bacteria arising from genome plasticity and biofilm development has rendered current antibiotic therapies ineffective, urging the development of innovative therapeutic approaches. The development of antibiotic resistance among bacteria has further heightened the clinical failure of antibiotic therapy, which is often linked to its low bioavailability, side effects, and poor penetration and accumulation at the site of infection. In this review, we highlight the potential use of siderophores, antibodies, cell-penetrating peptides, antimicrobial peptides, bacteriophages, and nanoparticles to smuggle antibiotics across impermeable biological membranes to achieve therapeutically relevant concentrations of antibiotics and combat antimicrobial resistance (AMR). We will discuss the general mechanisms via which each delivery system functions and how it can be tailored to deliver antibiotics against the paradigm of mechanisms underlying antibiotic resistance.

Investigation of genes expression of the JAK/STAT signalling pathway and AMPs in the presence of Borrelia spirochetes in Ixodes ricinus

Multicellular animals need to control the spread of invading pathogens. This is a particular challenge for blood-feeding vectors such as ticks, which ingest large amounts of blood potentially laden with harmful microorganisms. Ticks have a basic innate immune system and protect themselves from infection through innate immune responses involving pathways such as Janus kinase (JAK) or the signalling transducer activator of transcription (STAT). Direct antimicrobial defence occurs through the rapid synthesis of numerous antimicrobial agents including antimicrobial peptides (AMPs). The tick Ixodes ricinus is one of the main vectors of the Lyme disease pathogen, the spirochete Borrelia burgdorferi sensu lato. Data suggest that the JAK/STAT signalling pathway controls the expression of AMPs and regulates the infection of the pathogen in the tick body. The innate immune system during the off-host period keeps the level of spirochete infection in check. Spirochetes may influence the innate immune response in ticks. Therefore, the aim of this study was to analyse the expression of the genes related to the JAK/STAT pathway and selected AMPs in questing ticks in which B. burgorferi s.l. was detected. In the ticks infected with spirochetes, overexpression of genes related to the JAK/STAT signalling pathway was observed in the case of STAM and SOCS genes. AMPs genes such as def1, ric, lzs were overexpressed with different expression patterns. The results obtained suggest that AMPs may be involved in infection management in ticks.

Inflammation and response to bacterial infection as potential drivers of equine odontoclastic tooth resorption and hypercementosis: A proteomics insight

BACKGROUND

Equine dental diseases significantly impact a horse's overall health, performance and quality of life. They can result in secondary infections and digestive disturbances, potentially leading to colic. A recently described disease affecting the incisors of horses is equine odontoclastic tooth resorption and hypercementosis (EOTRH). Understanding EOTRH is crucial for early diagnosis, effective management and prevention of its severe consequences.

OBJECTIVES

To determine proteomic differences in incisor cementum in horses with and without clinical EOTRH.

STUDY DESIGN

Comparative and observational clinical study.

METHODS

Teeth were extracted (N = 5) and cementum was isolated using a diamond wire. Proteins were extracted using an optimised sequential workflow, and trypsin was digested for mass spectrometry. Protein identification and label-free quantification were undertaken.

RESULTS

In total 1149 unique proteins were detected in cementum across all samples. We identified four proteins exclusively in EOTRH-affected cementum. EOTRH samples showed a higher heterogeneity than healthy samples. In total, 54 proteins were increased in EOTRH, and 64 proteins were reduced (adjusted p-value <0.05). Inflammatory proteins, such as cathepsin G (p = 0.004), neutrophil elastase (p = 0.003), bactericidal permeability-increasing protein (p = 0.002), azurocidin (p = 0.003) and lactotransferrin (p = 0.002) were all increased in EOTRH. Pathway analysis revealed that antimicrobial peptides (Z score 2.65, p = 1.93E-09) and neutrophil degranulation (Z-score 1.89, p = 1.7E-04) were commonly up-regulated canonical pathways.

MAIN LIMITATIONS

The sample size was limited. Lack of age-matched healthy controls.

CONCLUSION

EOTRH leads to biochemical changes within the cementum proteome, which are important in explaining the physiological changes occurring in disease. Differentially abundant proteins may represent promising biomarkers for earlier disease detection and the establishment of a cell-based model could provide further insight into the role these proteins play in hypercementosis and resorption.

Antimicrobial Peptides: A Promising Solution to the Rising Threat of Antibiotic Resistance

The demand for developing novel antimicrobial drugs has increased due to the rapid appearance and global spread of antibiotic resistance. Antimicrobial peptides (AMPs) offer distinct advantages over traditional antibiotics, such as broad-range efficacy, a delayed evolution of resistance, and the capacity to enhance human immunity. AMPs are being developed as potential medicines, and current computational and experimental tools aim to facilitate their preclinical and clinical development. Structural and functional constraints as well as a more stringent regulatory framework have impeded clinical translation of AMPs as possible therapeutic agents. Although around four thousand AMPs have been identified so far, there are some limitations of using these AMPs in clinical trials due to their safety in the host and sometimes limitations in the biosynthesis or chemical synthesis of some AMPs. Overcoming these obstacles may help to open a new era of AMPs to combat superbugs without using synthetic antibiotics. This review describes the classification, mechanisms of action and immune modulation, advantages, difficulties, and opportunities of using AMPs against multidrug-resistant pathogens and highlights the need and priorities for creating targeted development strategies that take into account the most cutting-edge tools currently available. It also describes the barriers to using these AMPs in clinical trials.

Characterization of Structural Properties and Antimicrobial Activity of the C3f Peptide of Complement System

The C3f peptide is a by-product of regulation of the activated complement system with no firmly established function of its own. We have previously shown that C3f exhibits moderate antimicrobial activity against some Gram-positive bacteria in vitro. Presence of two histidine residues in the amino acid sequence of the peptide suggests enhancement of its antimicrobial activity at lower pH and in the presence of metal cations, particularly zinc cations. Since such conditions could be realized in inflammatory foci, the study of dependence of C3f activity on pH and presence of metal cations could provide an opportunity to assess biological significance of antimicrobial properties of the peptide. The peptide C3f and its analogs with histidine residues substituted by lysines or serines, C3f[H/K] and C3f[H/S], were prepared by solid-phase synthesis. Using CD spectroscopy, we found that C3f contained a β-hairpin and unstructured regions; presence of Zn2+ did not affect conformation of the peptide. In the present work, it was shown that C3f could also exhibit antimicrobial activity against Gram-negative bacteria, in particular, Pseudomonas aeruginosa ATCC 27583. Exposure of P. aeruginosa and Listeria monocytogenes EGD to the peptide was accompanied by disruption of the barrier function of bacterial membranes. Zn2+ ions, unlike Cu2+ ions, enhanced antimicrobial activity of C3f against L. monocytogenes, with 4- and 8-fold molar excess of Zn2+ being no more effective than a 20% excess. Activity of the C3f analogs was also enhanced to some extent by the zinc ions. Thus, we hypothesize existence of the histidine-independent formation of C3f-Zn2+ complexes leading to increase in the total charge and antimicrobial activity of the peptide. In the presence of 0.15 M NaCl, C3f lost its antimicrobial activity regardless of the presence of Zn2+, indicating an insignificant role of C3f as an endogenous antimicrobial peptide. Presence of C3f eliminated bactericidal effect of Zn2+ against the zinc-sensitive Escherichia coli strain ESBL 521/17, indirectly confirming interaction of the peptide with Zn2+. Activity of C3f against Micrococcus luteus A270 increased with decreasing pH, while effect of pH on the C3f activity against L. monocytogenesis was more complex. In this work, we show significance of the factors such as pH and metal cations in realization of antimicrobial activity of peptides based on the example of C3f.

Unveiling mechanisms of antimicrobial peptide: Actions beyond the membranes disruption

Antimicrobial peptides (AMPs) are a critical component of the innate immune system, playing a key role in defending against a variety of pathogenic microorganisms. While many AMPs act primarily on the cell membrane of target pathogens, leading to lysis and subsequent cell death, less is known about their nonlytic membrane activity. This nonlytic activity allows AMPs to target and disrupt bacterial cells without causing lysis, leading to bacterial death through alternative mechanisms.Understanding these nonlytic properties of AMPs is crucial, as they present a promising alternative to traditional antibiotics, which can induce bacterial resistance and have adverse effects on human health and the environment. The mechanisms by which AMPs exhibit nonlytic membrane activity are still being explored. However, it is believed that AMPs penetrate the bacterial membrane and interact directly with internal cellular components such as DNA, RNA, and various enzymes essential for microbial survival and replication. This interaction disrupts metabolic homeostasis, ultimately resulting in bacterial death.The nonlytic activity of AMPs also results in minimal damage to host cells and tissues, making them attractive candidates for the development of new, more effective antibiotics. This review emphasizes the mechanisms by which AMPs nonlytically target cellular components, including DNA, proteins, RNA, and other biomolecules, and discusses their clinical significance. Understanding these mechanisms may pave the way for developing alternatives to conventional antibiotics, offering a solution to the growing issue of antibiotic resistance.

The Role of Autologous Platelet Concentrates as a Local Antibiotic Delivery System: A Systematic Scoping Review

OBJECTIVES

Ongoing research has begun to develop innovative approaches to deliver local antibiotics while minimizing systemic side effects, antimicrobial resistance, and limited tissue penetration. Autologous platelet concentrates (APCs) offer promise in delivering antibiotics directly to infection sites. Despite the interest, a comprehensive evaluation of their effectiveness is lacking. Therefore, this systematic scoping review aims to collect and appraise studies regarding the efficacy of APCs in delivering antibiotics.

METHODS

A systematic electronic search of PubMed, Scopus, and Web of Science, using a combination of keywords, was conducted up to February 2024. Articles addressing the use of APCs as a local antibiotic delivery system were included.

RESULTS

A total of 13 articles, including 10 in vitro studies, 1 in vitro and clinical study, 1 ex vivo study, and 1 clinical study, were selected. Antibiotic loading capacity and release was confirmed in all studies using doxycycline, gentamicin, linezolid, vancomycin, metronidazole, and penicillin. In addition, the antibacterial effect was obtained mainly against E. coli., P. aeruginosa, S. mitis, H. influenzae, S. pneumoniae, and S. aureus.

CONCLUSIONS

The incorporation of antibiotics into APCs has been proven to facilitate the effective release of antimicrobial agents at optimal concentrations, potentially reducing the incidence of post-operative infections, substituting, or augmenting systemic antibiotic treatment while retaining APCs' inherent healing properties.

Growth factor and cytokine characterization of canine platelet lysate with variable leukocyte concentration, plasma content, and heat-sensitive proteins

Background

Platelet lysate is an acellular platelet product containing factors released from secretory granules, including cytokines and growth factors. This study aimed to evaluate different centrifugation methods used to prepare canine platelet lysate with variable content of leukocytes, plasma, and heat-sensitive proteins.

Methods

Whole blood was collected from six dogs and two double-spin preparation methods were used to generate the platelet-rich plasma with reduced (PRP) and high (L-PRP) concentration of leukocytes. A portion of both methods underwent plasma depletion via centrifugation and platelet lysate was generated via freeze-thaw cycles. A portion of the generated platelet lysate underwent complement inactivation via heat treatment. Growth factors (TGF-β1, VEGF, TNF-α, PDGF-BB, HGF) were quantified in all different platelet lysate preparations using ELISAs.

Results

Both platelet-rich plasma preparations had a 6.7-fold increase in platelet concentration. White blood cell (WBC) concentration compared to whole blood increased 1.2-fold times in PRP and 1.9-fold times in L-PRP. Negligible concentrations of platelets, WBC, and hematocrit were identified in all lysate groups. Statistically significant differences were identified for PDGF, VEGF, and TNF-α, and not for TGF-β or HGF. No growth factor differences were noted between centrifugation methods. PDGF was significantly higher in platelet lysate that was plasma depleted. VEGF was significantly higher in heat-treated lysate groups. TNF-α concentrations were overall very low, though were noted to significantly increase following plasma depletion.

Conclusion

These results support that growth factors and cytokine release can be affected by the platelet lysate preparation and processing.

Revolutionizing orthopedic healthcare: a systematic review unveiling recombinant antimicrobial peptides

The increasing demand for orthopedic surgeries, including joint replacements, is driven by an aging population and improved diagnosis of joint conditions. Orthopedic surgeries carry a risk of infection, especially in patients with comorbidities. The rise of antibiotic resistance exacerbates this issue, necessitating alternatives like in vitro bioengineered antimicrobial peptides (AMPs), offering broad-spectrum activity and multiple action mechanisms. This review aimed to assess the prevalence of antimicrobial potential and the yield after purification among recombinant AMP families. The antimicrobial potential was evaluated using the Minimum Inhibitory Concentration (MIC) values against the most common bacteria involved in clinical infections. This systematic review adhered to PRISMA guidelines, focusing on in vitro studies of recombinant AMPs. The search strategy was run on PubMed, Scopus and Embase up to 30th March 2023. The Population, Exposure and Outcome model was used to extract the data from studies and ToxRTool for the risk of bias analysis. This review included studies providing peptide production yield data and MIC values against pathogenic bacteria. Non-English texts, reviews, conference abstracts, books, studies focusing solely on chemical synthesis, those reporting incomplete data sets, using non-standard MIC assessment methods, or presenting MIC values as ranges rather than precise concentrations, were excluded. From 370 publications, 34 studies on AMPs were analyzed. These covered 46 AMPs across 18 families, with Defensins and Hepcidins being most common. Yields varied from 0.5 to 2,700 mg/L. AMPs were tested against 23 bacterial genera, with MIC values ranging from 0.125 to >1,152 μg/mL. Arenicins showed the highest antimicrobial activity, particularly against common orthopedic infection pathogens. However, AMP production yields varied and some AMPs demonstrated limited effectiveness against certain bacterial strains. This systematic review emphasizes the critical role of bioengineered AMPs to cope infections and antibiotic resistance. It meticulously evaluates recombinant AMPs, focusing on their antimicrobial efficacy and production yields. The review highlights that, despite the variability in AMP yields and effectiveness, Arenicins and Defensins are promising candidates for future research and clinical applications in treating antibiotic-resistant orthopedic infections. This study contributes significantly to the understanding of AMPs in healthcare, underscoring their potential in addressing the growing challenge of antibiotic resistance. Systematic review registration:https://osf.io/2uq4c/.

Platelet-rich fibrin as an autologous biomaterial for bone regeneration: mechanisms, applications, optimization

Platelet-rich fibrin, a classical autologous-derived bioactive material, consists of a fibrin scaffold and its internal loading of growth factors, platelets, and leukocytes, with the gradual degradation of the fibrin scaffold and the slow release of physiological doses of growth factors. PRF promotes vascular regeneration, promotes the proliferation and migration of osteoblast-related cells such as mesenchymal cells, osteoblasts, and osteoclasts while having certain immunomodulatory and anti-bacterial effects. PRF has excellent osteogenic potential and has been widely used in the field of bone tissue engineering and dentistry. However, there are still some limitations of PRF, and the improvement of its biological properties is one of the most important issues to be solved. Therefore, it is often combined with bone tissue engineering scaffolds to enhance its mechanical properties and delay its degradation. In this paper, we present a systematic review of the development of platelet-rich derivatives, the structure and biological properties of PRF, osteogenic mechanisms, applications, and optimization to broaden their clinical applications and provide guidance for their clinical translation.

Recent advances in antimicrobial peptide-based therapy

Antimicrobial peptides (AMPs) are a group of polypeptide chains that have the property to target and kill a myriad of microbial organisms including viruses, bacteria, protists, etc. The first discovered AMP was named gramicidin, an extract of aerobic soil bacteria. Further studies discovered that these peptides are present not only in prokaryotes but in eukaryotes as well. They play a vital role in human innate immunity and wound repair. Consequently, they have maintained a high level of intrigue among scientists in the field of immunology, especially so with the rise of antibiotic-resistant pathogens decreasing the reliability of antibiotics in healthcare. While AMPs have promising potential to substitute for common antibiotics, their use as effective replacements is barred by certain limitations. First, they have the potential to be cytotoxic to human cells. Second, they are unstable in the blood due to action by various proteolytic agents and ions that cause their degradation. This review provides an overview of the mechanism of AMPs, their limitations, and developments in recent years that provide techniques to overcome those limitations. We also discuss the advantages and drawbacks of AMPs as a replacement for antibiotics as compared to other alternatives such as synthetically modified bacteriophages, traditional medicine, and probiotics.

An amphibian-derived cathelicidin accelerates cutaneous wound healing through its main regulatory effect on phagocytes

Cathelicidins are an important family of antimicrobial peptides (AMPs) involved in the innate immunity in vertebrates. The mammalian cathelicidins have been well characterized, but the relationship between structure and function in amphibian cathelicidins is still not well understood. In this study, a novel 29-residue cathelicidin antimicrobial peptide (BugaCATH) was identified from the skin of Bufo gargarizans. Unlike other AMPs, BugaCATH does not display any direct antimicrobial effects in vitro. However, it effectively promotes full-thickness wound repair in mice. Following injury, BugaCATH initiates and expedites the inflammatory stage by recruiting neutrophils and macrophages to the wound site. BugaCATH not only regulates neutrophil phagocytic activity but also stimulates the generation of cytokines (TNF-α, IL-6, and IL-1β) and chemokines (CXCL1, CXCL2, CCL2, and CCL3) in macrophages and in mice. Furthermore, it promotes macrophage M2 polarization that facilitates the conversion from a pro-inflammatory macrophage-dominated wound environment to an anti-inflammatory one during the mid to late stages, which is crucial for reducing inflammation and effective wound repair. The MAPK (ERK, JNK, and p38) and NF-κB-NLRP3 signaling pathways are involved in the activity. Moreover, BugaCATH directly enhances the migration of keratinocytes and vascular endothelial cells without affecting their proliferation. Notably, BugaCATH significantly improves the proliferation of keratinocytes and endothelial cells in the presence of macrophages. The current study revealed that in addition to proliferation of keratinocytes and endothelial cells, BugaCATH possesses the ability to modulate inflammatory processes during skin injury through its regulatory effect on phagocytes. The combination of these capabilities makes BugaCATH a potent candidate for skin wound therapy.

The Designed Pore-Forming Antimicrobial Peptide C14R Combines Excellent Activity against the Major Opportunistic Human Pathogen Pseudomonas aeruginosa with Low Cytotoxicity

The diminishing portfolio of mankind's available antibiotics urges science to develop novel potent drugs. Here, we present a peptide fitting the typical blueprint of amphipathic and membrane-active antimicrobial peptides, denominated C14R. This 2 kDa peptide consists of 16 amino acid residues, with seven being either hydrophobic, aromatic, or non-polar, and nine being polar or positively charged, strictly separated on opposite sides of the predicted α-helix. The affinity of the peptide C14R to P. aeruginosa membranes and its intrinsic tendency to productively insert into membranes of such composition were analyzed by dynamic simulations. Its biological impact on the viability of two different P. aeruginosa reference strains was demonstrated by determining the minimal inhibitory concentrations (MICs), which were found to be in the range of 10-15 µg/mL. C14R's pore-forming capability was verified in a permeabilization assay based on the peptide-triggered uptake of fluorescent dyes into the bacterial cells. Finally, the peptide was used in radial diffusion assays, which are commonly used for susceptibility testing of antimicrobial peptides in clinical microbiology. In comparison to reference strains, six clinical P. aeruginosa isolates were clearly affected, thereby paving the way for further in-depth analyses of C14R as a promising new AMP drug in the future.

Lipid-Centric Approaches in Combating Infectious Diseases: Antibacterials, Antifungals and Antivirals with Lipid-Associated Mechanisms of Action

One of the global challenges of the 21st century is the increase in mortality from infectious diseases against the backdrop of the spread of antibiotic-resistant pathogenic microorganisms. In this regard, it is worth targeting antibacterials towards the membranes of pathogens that are quite conservative and not amenable to elimination. This review is an attempt to critically analyze the possibilities of targeting antimicrobial agents towards enzymes involved in pathogen lipid biosynthesis or towards bacterial, fungal, and viral lipid membranes, to increase the permeability via pore formation and to modulate the membranes' properties in a manner that makes them incompatible with the pathogen's life cycle. This review discusses the advantages and disadvantages of each approach in the search for highly effective but nontoxic antimicrobial agents. Examples of compounds with a proven molecular mechanism of action are presented, and the types of the most promising pharmacophores for further research and the improvement of the characteristics of antibiotics are discussed. The strategies that pathogens use for survival in terms of modulating the lipid composition and physical properties of the membrane, achieving a balance between resistance to antibiotics and the ability to facilitate all necessary transport and signaling processes, are also considered.

Antimicrobial Peptide-Peptoid Hybrids with and without Membrane Disruption

Among synthetic analogues of antimicrobial peptides (AMPs) under investigation to address antimicrobial resistance, peptoids (N-alkylated oligoglycines) have been reported to act both by membrane disruption and on intracellular targets. Here we gradually introduced peptoid units into the membrane-disruptive undecapeptide KKLLKLLKLLL to test a possible transition toward intracellular targeting. We found that selected hybrids containing up to five peptoid units retained the parent AMP's α-helical folding, membrane disruption, and antimicrobial effects against Gram-negative bacteria including multidrug-resistant (MDR) strains of Pseudomonas aeruginosa and Klebsiella pneumoniae while showing reduced hemolysis and cell toxicities. Furthermore, some hybrids containing as few as three peptoid units as well as the full peptoid lost folding, membrane disruption, hemolysis, and cytotoxicity but displayed strong antibacterial activity under dilute medium conditions typical for proline-rich antimicrobial peptides (PrAMPs), pointing to intracellular targeting. These findings parallel previous reports that partially helical amphiphilic peptoids are privileged oligomers for antibiotic development.

Antimicrobial Effects of Platelet-Rich Plasma and Platelet-Rich Fibrin: A Scoping Review

Platelet-rich plasma (PRP), derived from the centrifugation and subsequent separation of whole blood, results in an unusually high concentration of platelets. A newer form of platelet concentrate, platelet-rich fibrin (PRF), has also been developed. There has been significant research into the therapeutic effects of PRP, particularly in enhancing wound healing and preventing infections in surgical wounds. This scoping review aims to thoroughly evaluate preclinical and clinical evidence regarding the antimicrobial effects of PRP and PRF. In conducting this review, 612 records were examined, and 36 articles were selected for inclusion. The studies reviewed include preclinical research, such as in-vitro and in-vivo studies, and clinical trials involving human participants. The current clinical evidence suggests a notable trend towards the antimicrobial capabilities of PRP and PRF, underscoring their potential benefits in treating wounds. The application of PRP and PRF in wound management shows encouraging outcomes, but further investigation is needed to optimize their use as antimicrobial agents. Additional research, particularly randomized controlled trials, is essential to substantiate their antimicrobial effectiveness in specific diseases and types of wounds, considering their potential impact on clinical results.

Determination of suitable reference genes for RT-qPCR normalisation in Bombyx mori (Lepidoptera: Bombycidae) infected by the parasitoid Exorista sorbillans (Diptera, Tachinidae)

The silkworm Bombyx mori (Lepidoptera: Bombycidae) is a lepidopteran model insect of great economic importance. The parasitoid Exorista sorbillans (Diptera, Tachinidae) is the major pest of B. mori and also a promising candidate for biological control. However, the molecular interactions between hosts and dipteran parasitoids have only partially been studied. Gene expression analysis by reverse-transcription quantitative real-time polymerase chain reaction (RT-qPCR) is indispensable to characterise their interactions. Accurate normalisation of RT-qPCR-based gene expression requires the use of reference genes that are constantly expressed irrespective of experimental conditions. In this study, the expression stability of 13 traditionally used reference genes was estimated by five statistical algorithms (ΔCt, geNorm, Normfinder, BestKeeper, and RefFinder) to determine the best reference genes for gene expression studies in different tissues of B. mori under E. sorbillans parasitism. Specifically, TATA-box-binding protein was the best reference gene in epidermis and testis, while elongation factor 1α was the most stable gene in prothoracic gland and midgut. Elongation factor 1γ, ribosomal protein L3, actin A1, ribosomal protein L40, glyceraldehyde-3-phosphate dehydrogenase and eukaryotic translation initiation factor 4A were the most suitable genes in head, silk gland, fat body, haemolymph, Malpighian tubule and ovary, respectively. Our study offers a set of suitable reference genes for gene expression normalisation in B. mori under the parasitic stress of E. sorbillans, which will benefit the in-depth exploration of host-dipteran parasitoid interactions, and also provide insights for further improvements of B. mori resistance against parasitoids and biocontrol efficacy of dipteran parasitoids.

Conformation Dependent Architectures of Assembled Antimicrobial Peptides with Enhanced Antimicrobial Ability

Antimicrobial peptides (AMPs) are a developing class of natural and synthetic oligopeptides with host defense mechanisms against a broad spectrum of microorganisms. With in-depth research on the structural conformations of AMPs, synthesis or modification of peptides has shown great potential in effectively obtaining new therapeutic agents with improved physicochemical and biological properties. Notably, AMPs with self-assembled properties have gradually become a hot research topic for various biomedical applications. Compared to monomeric peptides, these peptides can exist in diverse forms (e.g., nanoparticles, nanorods, and nanofibers) and possess several advantages, such as high stability, good biocompatibility, and potent biological functions, after forming aggregates under specific conditions. In particular, the stability and antibacterial property of these AMPs can be modulated by rationally regulating the peptide sequences to promote self-assembly, leading to the reconstruction of molecular structure and spatial orientation while introducing some peptide fragments into the scaffolds. In this work, four self-assembled AMPs are developed, and the relationship between their chemical structures and antibacterial activity is explored extensively through different experiments. Importantly, the evaluation of antibacterial performance in both in vitro and in vivo studies has provided a general guide for using self-assembled AMPs in subsequent treatments for combating bacterial infections.

Ag- but Not ZnO-Nanoparticles Disturb the Airway Epithelial Barrier at Subtoxic Concentrations

Inhalation is considered to be the most relevant source of human exposure to nanoparticles (NPs); however, only a few investigations have addressed the influence of exposing the respiratory mucosal barrier to subcytotoxic doses. In the nasal respiratory epithelium, cells of the mucosa represent one of the first contact points of the human organism with airborne NPs. Disruption of the epithelial barrier by harmful materials can lead to inflammation in addition to potential intrinsic toxicity of the particles. The aim of this study was to investigate whether subtoxic concentrations of zinc oxide (ZnO)- and silver (Ag)-NPs have an influence on upper airway barrier integrity. Nasal epithelial cells from 17 donors were cultured at the air-liquid interface and exposed to ZnO- and Ag-NPs. Barrier function, quantified by transepithelial electrical resistance (TEER), decreased after treatment with 10 µg/mL Ag-NPs, but FITC-dextran permeability remained stable and no change in mRNA levels of tight junction proteins and E-cadherin was detected by real-time quantitative PCR (RT-qPCR). The results indicate that subtoxic concentrations of Ag-NPs may already induce damage of the upper airway epithelial barrier in vitro. The lack of similar disruption by ZnO-NPs of similar size suggests a specific effect by Ag-NPs.

A peptide encoded by a highly conserved gene belonging to the genus Streptomyces shows antimicrobial activity against plant pathogens

The genus Streptomyces has been unceasingly highlighted for the versatility and diversity of the antimicrobial agents they produce. Moreover, it is a heavily sequenced taxon in the phylum Actinobacteria. In this study, 47 sequence profiles were identified as proteins highly conserved within the genus Streptomyces. Significant hits to the 38 profiles were found in more than 2000 Streptomyces genomes, 11 of which were further conserved in more than 90% of Actinobacterial genomes analyzed. Only a few genes corresponding to these sequence profiles were functionally characterized, which play regulatory roles in the morphology and biosynthesis of antibiotics. Here a highly conserved sequence, namely, SHC-AMP (Streptomyces highly conserved antimicrobial peptide), which exhibited antimicrobial activity against bacterial and fungal plant pathogens, was reported. In particular, Arabidopsis thaliana was effectively protected against infection with Pseudomonas syringae pv. tomato DC3000 by treatment with this peptide. Results indicated the potential application of this peptide as an antimicrobial agent for control of plant diseases. Our results suggest putative target genes for controlling Streptomyces spp., including the one exhibiting antimicrobial activity against a wide range of phytopathogens.

Filipendula glaberrima Nakai extract inhibits the bacterial infection by induction of HBD2 and HBD3 expression, and reduction of the inflammatory activity

Defensins and inflammation are innate immune barriers of the body against infectious pathogens. Searching for a compound that can inhibit infectious diseases by affecting human β-defensin (HBD) and proinflammatory cytokines is the new trend in research to control bacterial infection. The aim of this study is to provide a natural compound, Filipendula glaberrima Nakai extract (FGE), which is able to induce the expression of an antimicrobial defensin as well as reduce inflammation. FGE induced the expression of HBD2 and HBD3 through activating both p38 and NF-κB signaling pathways. Furthermore, FGE inhibited the expression of TNF-α and IL-6 via p38 and NF-κB pathways in Staphylococcus aureus-stimulated THP1 cells. Injection of FGE alleviated cutaneous erythema and swelling caused by S. aureus injection in mice ears. Taken together, FGE could reduce bacterial infection by inducing the expression of defensin and anti-inflammatory activity.

A Bioresponsive Genetically Encoded Antimicrobial Crystal for the Oral Treatment of Helicobacter Pylori Infection

Helicobacter pylori (H. pylori) causes infection in the stomach and is a major factor for gastric carcinogenesis. The application of antimicrobial peptides (AMPs) as an alternative treatment to traditional antibiotics is limited by their facile degradation in the stomach, their poor penetration of the gastric mucosa, and the cost of peptide production. Here, the design and characterization of a genetically encoded H. pylori-responsive microbicidal protein crystal Cry3Aa-MIIA-AMP-P17 is described. This designed crystal exhibits preferential binding to H. pylori, and when activated, promotes the targeted release of the AMP at the H. pylori infection site. Significantly, when the activated Cry3Aa-MIIA-AMP-P17 crystals are orally delivered to infected mice, the Cry3Aa crystal framework protects its cargo AMP against degradation, resulting in enhanced in vivo efficacy against H. pylori infection. Notably, in contrast to antibiotics, treatment with the activated crystals results in minimal perturbation of the mouse gut microbiota. These results demonstrate that engineered Cry3Aa crystals can serve as an effective platform for the oral delivery of therapeutic peptides to treat gastrointestinal diseases.

Characterizing the Interactions of Cell-Membrane-Disrupting Peptides with Lipid-Functionalized Single-Walled Carbon Nanotubes

Lipid-functionalized single-walled carbon nanotubes (SWNTs) have garnered significant interest for their potential use in a wide range of biomedical applications. In this work, we used molecular dynamics simulations to study the equilibrium properties of SWNTs surrounded by the phosphatidylcholine (POPC) corona phase and their interactions with three cell membrane disruptor peptides: colistin, TAT peptide, and crotamine-derived peptide. Our results show that SWNTs favor asymmetrical positioning within the POPC corona, so that one side of the SWNT, covered by the thinnest part of the corona, comes in contact with charged and polar functional groups of POPC and water. We also observed that colistin and TAT insert deeply into the POPC corona, while crotamine-derived peptide only adsorbs to the corona surface. In separate simulations, we show that three examined peptides exhibit similar insertion and adsorption behaviors when interacting with POPC bilayers, confirming that peptide-induced perturbations to POPC in conjugates and bilayers are similar in nature and magnitude. Furthermore, we observed correlations between the peptide-induced structural perturbations and the near-infrared emission of the lipid-functionalized SWNTs, which suggest that the optical signal of the conjugates transduces the morphological changes in the lipid corona. Overall, our findings indicate that lipid-functionalized SWNTs could serve as simplified cell membrane model systems for prescreening of new antimicrobial compounds that disrupt cell membranes.

Characterizing the Interactions of Cell Membrane-Disrupting Peptides with Lipid-Functionalized Single-Walled Carbon Nanotube Systems for Antimicrobial Screening

Lipid-functionalized single-walled carbon nanotubes (SWNTs) have garnered significant interest for their potential use in a wide range of biomedical applications. In this work, we used molecular dynamics simulations to study the equilibrium properties of SWNTs surrounded by the phosphatidylcholine (POPC) corona phase, and their interactions with three cell membrane disruptor peptides: colistin, TAT peptide, and crotamine-derived peptide. Our results show that SWNTs favor asymmetrical positioning within the POPC corona, so that one side of the SWNT, covered by the thinnest part of the corona, comes in contact with charged and polar functional groups of POPC and water. We also observed that colistin and TAT insert deeply into POPC corona, while crotamine-derived peptide only adsorbs to the corona surface. Compared to crotamine-derived peptide, colistin and TAT also induce larger perturbations in the thinnest region of the corona, by allowing more water molecules to directly contact the SWNT surface. In separate simulations, we show that three examined peptides exhibit similar insertion and adsorption behaviors when interacting with POPC bilayers, confirming that peptide-induced perturbations to POPC in conjugates and bilayers are similar in nature and magnitude. Furthermore, we observed correlations between the peptide-induced structural perturbations and the near-infrared emission of the lipid-functionalized SWNTs, which suggest that the optical signal of the conjugates transduces the morphological changes in the lipid corona. Overall, our findings indicate that lipid-functionalized SWNTs could serve as simplified cell membrane model systems for pre-screening of new antimicrobial compounds that disrupt cell membranes.

Immunological pathogenesis of Bovine E. coli infection in a model of C. elegans

BACKGROUND

Cattle industry is critical for China's livestock industry, whereas E. coli infection and relevant diseases could lead huge economic loss. Traditional mammalian models would be costly, time consuming and complicated to study pathological changes of bovine E. coli. There is an urgent need for a simple but efficient animal model to quantitatively evaluate the pathological changes of bovine-derived E. coli in vivo. Caenorhabditis elegans (C. elegans) has a broad host range of diverse E. coli strains with advantages, including a short life cycle, a simple structure, a transparent body which is easily visualized, a well-studied genetic map, an intrinsic immune system which is conservable with more complicated mammalians.

RESULTS

Here, we considered that O126 was the dominant serotype, and a total of 19 virulence factors were identified from 41 common E. coli virulence factors. Different E. coli strains with diverse pathogenicity strengths were tested in C. elegans in E. coli with higher pathogenicity (EC3/10), Nsy-1, Sek-1 and Pmk-1 of the p38 MAPK signaling pathway cascade and the expression of the antimicrobial peptides Abf-3 and Clec-60 were significantly up-regulated comparing with other groups. E. coli with lower pathogenicity (EC5/13) only activated the expression of Nsy-1 and Sek-1 genes in the p38 MAPK signaling pathway, Additionally, both groups of E. coli strains caused significant upregulation of the antimicrobial peptide Spp-1.

CONCLUSION

Thirteen E. coli strains showed diverse pathogenicity in nematodes and the detection rate of virulence factors did not corresponding to the virulence in nematodes, indicating complex pathogenicity mechanisms. We approved that C. elegans is a fast and convenient detection model for pathogenic bacteria virulence examinations.

Mesangial cell: A hub in lupus nephritis

Lupus nephritis (LN) is a severe renal disease caused by the massive deposition of the immune complexes (ICs) in renal tissue, acting as one of the significant organ manifestations of systemic lupus erythematosus (SLE) and a substantial cause of death in clinical patients. As mesangium is one of the primary sites for IC deposition, mesangial cells (MCs) constantly undergo severe damage, resulting in excessive proliferation and increased extracellular matrix (ECM) production. In addition to playing a role in organizational structure, MCs are closely related to in situ immunomodulation by phagocytosis, antigen-presenting function, and inflammatory effects, aberrantly participating in the tissue-resident immune responses and leading to immune-mediated renal lesions. Notably, such renal-resident immune responses drive a second wave of MC damage, accelerating the development of LN. This review summarized the damage mechanisms and the in situ immune regulation of MCs in LN, facilitating the current drug research for exploring clinical treatment strategies.

The Antimicrobial Peptide AMP-17 Derived from Musca domestica Inhibits Biofilm Formation and Eradicates Mature Biofilm in Candida albicans

The biofilm formation of C. albicans represents a major virulence factor during candidiasis. Biofilm-mediated drug resistance has necessitated the search for a new antifungal treatment strategy. In our previous study, a novel antimicrobial peptide named AMP-17 derived from Musca domestica was confirmed to have significant antifungal activity and suppress hyphal growth greatly in C. albicans. In the current work, we aimed to investigate the antibiofilm property of AMP-17 in C. albicans and explore the underlying mechanism. An antifungal susceptibility assay showed that AMP-17 exerted a strong inhibitory efficacy on both biofilm formation and preformed biofilms in C. albicans. Furthermore, AMP-17 was found to block the yeast-to-hypha transition and inhibit the adhesion of biofilm cells with a reduction in cellular surface hydrophobicity. A morphological analysis revealed that AMP-17 indeed suppressed typical biofilm formation and damaged the structures of the preformed biofilm. The RNA-seq showed that the MAPK pathway, biosynthesis of antibiotics, and essential components of the cell were mainly enriched in the biofilm-forming stage, while the citrate cycle (TCA cycle), phenylamine metabolism, and propanoate metabolism were enriched after the biofilm matured. Moreover, the co-expressed DEGs in the two pairwise comparisons highlighted the terms of transmembrane transporter activity, regulation of filamentation, and biofilm formation as important roles in the antibiofilm effect of AMP-17. Additionally, qRT-PCR confirmed that the level of the genes involved in cell adhesion, filamentous growth, MAPK, biofilm matrix, and cell dispersal was correspondingly altered after AMP-17 treatment. Overall, our findings reveal the underlying antibiofilm mechanisms of AMPs in C. albicans, providing an interesting perspective for the development of effective antifungal agents with antibiofilm efficacy in Candida spp.

Antibacterial and antibiofilm activities of novel antimicrobial peptide DP7 against the periodontal pathogen Porphyromonas gingivalis

AIMS

Accumulating evidence suggests that Porphyromonas gingivalis is closely associated with the development of various chronic inflammatory diseases, particularly periodontitis. This study investigated the antibacterial activity and action mechanism of a novel antimicrobial peptide (AMP), DP7, against P. gingivalis.

METHODS AND RESULTS

The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) for DP7 were determined via a broth microdilution method, revealing an MIC of 8 μg ml^-1 and MBC of 32 μg ml^-1 . Growth inhibition and killing assays confirmed the bactericidal effect of DP7, and treatment with DP7 at MBC eliminated P. gingivalis within 8 h. DP7 had a low cytotoxic effect against human cells. Transmission electron microscopy revealed that DP7 destroyed the bacterial membrane, and confocal laser scanning microscopy revealed its inhibitory effect on P. gingivalis biofilms. Quantitative reverse transcription-polymerase chain reaction revealed DP7-mediated inhibition of several virulence factor genes, partially explaining its antibacterial mechanism.

CONCLUSIONS

DP7, a novel AMP with low mammalian cytotoxicity, inhibits both planktonic and biofilm forms of P. gingivalis by destroying the bacterial membrane and reducing virulence factor gene expression.

SIGNIFICANCE AND IMPACT OF THE STUDY

DP7 has potential clinical application in the prevention and treatment of P. gingivalis-associated diseases.

Truncated analog Brevinin2-CE-N26V5K: Revelation the Augmentation of Antimicrobial Activity

Brevinin2-CE (B2CE), a natural peptide containing 37 amino acids, was first isolated from the skin secretions of the Chinese forest frog Rana chensinensis. B2CE shows good antibacterial activity. In this study, a series of B2CE analogs with differences in cationicity, α-helicity, hydrophobicity and amphipathic properties were designed through chain-length deletion and amino acid substitution. The most potent, nontoxic analog, B2CE-N26V5K, was identified by examination of its antibacterial activity, hemolytic activity, and stability under physiological conditions. The increased cationicity, hydrophobicity and more obvious hydrophilic and hydrophobic surface of B2CE-N26-N16WA18KG23K did not improve the antibacterial activity but increased the hemolytic activity of this modified peptide. The helicity might promote antibacterial activity for brevinin-2 peptides, as the 15-aa analogs with lower helicity show decreased potency against different test bacteria (approximately 2- to 72-fold) compared to B2CE-N26V5K. Additionally, the results indicated that the "Rana box" does not affect the antimicrobial activity of brevinin-2 peptides, as B2CE, B2CE-nonDS and B2CE-C31-37 S have similar strong inhibitory effects on both gram-positive and gram-negative bacteria. However, the "Rana box" does affect the hemolytic activity, as the HC₅₀ values of the 3 peptides range from 25 ~ 130 µM. Furthermore, B2CE-N26V5K caused obvious morphological alterations of the bacterial surfaces, as shown by atomic force microscopy. Additionally, B2CE-N26V5K exhibited strong membrane-disrupting activity when examined using the LIVE/DEAD Bac Light Bacterial Viability Kit. Thus, the antibacterial effect of B2CE-N26V5K on gram-negative and gram-positive bacteria may be caused by cell membrane attack. In conclusion, the excellent candidate B2CE-N26V5K was obtained and has application prospects as a novel anti-infective agent.

Combination of Six Individual Derivatives of the Pom-1 Antibiofilm Peptide Doubles Their Efficacy against Invasive and Multi-Resistant Clinical Isolates of the Pathogenic Yeast Candida albicans

In previous studies, derivatives of the peptide Pom-1, which was originally extracted from the freshwater mollusk Pomacea poeyana, showed an exceptional ability to specifically inhibit biofilm formation of the laboratory strain ATCC 90028 as a model strain of the pathogenic yeast Candida albicans. In follow-up, here, we demonstrate that the derivatives Pom-1A to Pom-1F are also active against biofilms of invasive clinical C. albicans isolates, including strains resistant against fluconazole and/or amphotericin B. However, efficacy varied strongly between the isolates, as indicated by large deviations in the experiments. This lack of robustness could be efficiently bypassed by using mixtures of all peptides. These mixed peptide preparations were active against biofilm formation of all the isolates with uniform efficacies, and the total peptide concentration could be halved compared to the original MIC of the individual peptides (2.5 µg/mL). Moreover, mixing the individual peptides restored the antifungal effect of fluconazole against fluconazole-resistant isolates even at 50% of the standard therapeutic concentration. Without having elucidated the reason for these synergistic effects of the peptides yet, both the gain of efficacy and the considerable increase in efficiency by combining the peptides indicate that Pom-1 and its derivatives in suitable formulations may play an important role as new antibiofilm antimycotics in the fight against invasive clinical infections with (multi-) resistant C. albicans.

Chemical Barrier Proteins in Human Body Fluids

Chemical barriers are composed of those sites of the human body where potential pathogens can contact the host cells. A chemical barrier is made up by different proteins that are part of the antimicrobial and immunomodulatory protein/peptide (AMP) family. Proteins of the AMP family exert antibacterial, antiviral, and/or antifungal activity and can modulate the immune system. Besides these proteins, a wide range of proteases and protease inhibitors can also be found in the chemical barriers maintaining a proteolytic balance in the host and/or the pathogens. In this review, we aimed to identify the chemical barrier components in nine human body fluids. The interaction networks of the chemical barrier proteins in each examined body fluid were generated as well.

β-defensin 118 attenuates inflammation and injury of intestinal epithelial cells upon enterotoxigenic Escherichia coli challenge

Background

Antimicrobial peptides including various defensins have been attracting considerable research interest worldwide, as they have potential to substitute for antibiotics. Moreover, AMPs also have immunomodulatory activity. In this study, we explored the role and its potential mechanisms of β-defensin 118 (DEFB118) in alleviating inflammation and injury of IPEC-J2 cells (porcine jejunum epithelial cell line) upon the enterotoxigenic Escherichia coli (ETEC) challenge.

Results

The porcine jejunum epithelial cell line (IPEC-J2) pretreated with or without DEFB118 (25 μg/mL) were challenged by ETEC (1×10⁶ CFU) or culture medium. We showed that DEFB118 pretreatment significantly increased the cell viability (P<0.05) and decreased the expressions of inflammatory cytokines such as the interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α) in IPEC-J2 cells exposure to ETEC (P<0.05). Interestingly, DEFB118 pretreatment significantly elevated the abundance of the major tight-junction protein zonula occludens-1 (ZO-1), but decreased the number of apoptotic cells upon ETEC challenge (P<0.05). The expression of caspase 3, caspase 8, and caspase 9 were downregulated by DEFB118 in the IPEC-J2 cells exposure to ETEC (P<0.05). Importantly, DEFB118 suppressed two critical inflammation-associated signaling proteins, nuclear factor-kappa-B inhibitor alpha (IκB-α) and nuclear factor-kappaB (NF-κB) in the ETEC-challenged IPEC-J2 cells.

Conclusions

DEFB118 can alleviate ETEC-induced inflammation in IPEC-J2 cells through inhibition of the NF-κB signaling pathway, resulting in reduced secretion of inflammatory cytokines and decreased cell apoptosis. Therefore, DEFB118 can act as a novel anti-inflammatory agent.

Pharmacokinetics and pharmacodynamics of peptide antibiotics

Antimicrobial resistance is a major global health challenge. As few new efficacious antibiotics will become available in the near future, peptide antibiotics continue to be major therapeutic options for treating infections caused by multidrug-resistant pathogens. Rational use of antibiotics requires optimisation of the pharmacokinetics and pharmacodynamics for the treatment of different types of infections. Toxicodynamics must also be considered to improve the safety of antibiotic use and, where appropriate, to guide therapeutic drug monitoring. This review focuses on the pharmacokinetics/pharmacodynamics/toxicodynamics of peptide antibiotics against multidrug-resistant Gram-negative and Gram-positive pathogens. Optimising antibiotic exposure at the infection site is essential for improving their efficacy and minimising emergence of resistance.

Peptidomic Analysis on Mouse Lung Tissue Reveals AGDP as a Potential Bioactive Peptide against Pseudorabies Virus Infection

Pseudorabies virus (PRV) infection could cause severe histopathological damage via releasing multiple factors, including cytokines, peptides, etc. Here, peptidomic results showed that 129 peptides were identified in PRV-infected mouse lungs and were highly involved in the process of PRV infection. The role of one down-regulated biological peptide (designated as AGDP) during PRV infection was investigated. To verify the expression profiles of AGDP in response to PRV infection, the expression level of the precursor protein of AGDP mRNA was significantly decreased in PRV-infected mouse lungs and cells. The synthesized AGDP-treating cells were less susceptible to PRV challenges than the controls, as demonstrated by the decreased virus production and gE expression. AGDP not only inhibited the expression of TNF-α and IL-8 but also appeared to suppress the extracellular release of high-mobility group box 1 (HMGB1) by inhibiting the output of nuclear HMGB1 in cells. AGDP could also inhibit the degradation of IκBα and the phosphorylation levels of P65 after PRV infection. In total, our results revealed many meaningful peptides involved in PRV infection, thereby enhancing the current understanding of the host response to PRV infection, and how AGDP may serve as a promising candidate for developing novel anti-PRV drugs.

Therapeutic Role of Antimicrobial Peptides in Diabetes Mellitus

Antimicrobial peptides (AMPs) have recently become widely publicized because they have the potential to function in alternative therapies as “natural” antibiotics, with their main advantage being a broad spectrum of activity. The potential for antimicrobial peptides to treat diabetes mellitus (DM) has been reported. In diabetes mellitus type I (T1D), cathelicidin-related antimicrobial peptide (CRAMP), cathelicidin antimicrobial peptide (CAMP) and mouse-β- defensin 14 (mBD14) are positively affected. Decreased levels of LL-37 and human neutrophil peptide 1-3 (HNP1-3) have been reported in diabetes mellitus type II (T2D) relative to healthy patients. Moreover, AMPs from amphibians and social wasps have antidiabetic effects. In infections occurring in patients with tuberculosis-diabetes or diabetic foot, granulysin, HNP1, HNP2, HNP3, human beta-defensin 2 (HBD2), and cathelicidins are responsible for pathogen clearance. An interesting alternative is also the use of modified M13 bacteriophages containing encapsulated AMPs genes or phagemids.

A non-bactericidal cathelicidin provides prophylactic efficacy against bacterial infection by driving phagocyte influx

The roles of bactericidal cathelicidins against bacterial infection have been extensively studied. However, the antibacterial property and mechanism of action of non-bactericidal cathelicidins are rarely known. Herein, a novel naturally occurring cathelicidin (PopuCATH) from tree frog (Polypedates puerensis) did not show any direct anti-bacterial activity in vitro. Intriguingly, intraperitoneal injection of PopuCATH before bacterial inoculation significantly reduced the bacterial load in tree frogs and mice, and reduced the inflammatory response induced by bacterial inoculation in mice. PopuCATH pretreatment also increased the survival rates of septic mice induced by a lethal dose of bacterial inoculation or cecal ligation and puncture (CLP). Intraperitoneal injection of PopuCATH significantly drove the leukocyte influx in both frogs and mice. In mice, PopuCATH rapidly drove neutrophil, monocyte/macrophage influx in mouse abdominal cavity and peripheral blood with a negligible impact on T and B lymphocytes, and neutrophils, monocytes/macrophages, but not T and B lymphocytes, were required for the preventive efficacy of PopuCATH. PopuCATH did not directly act as chemoattractant for phagocytes, but PopuCATH obviously drove phagocyte migration when it was cultured with macrophages. PopuCATH significantly elicited chemokine/cytokine production in macrophages through activating p38/ERK mitogen-activated protein kinases (MAPKs) and NF-κB p65. PopuCATH markedly enhanced neutrophil phagocytosis via promoting the release of neutrophil extracellular traps (NETs). Additionally, PopuCATH showed low side effects both in vitro and in vivo. Collectively, PopuCATH acts as a host-based immune defense regulator that provides prophylactic efficacy against bacterial infection without direct antimicrobial effects. Our findings reveal a non-bactericidal cathelicidin which possesses unique anti-bacterial action, and highlight the potential of PopuCATH to prevent bacterial infection.

Intracellular mechanism of antimicrobial peptide HJH-3 against Salmonella pullorum

To explore the potential intracellular mechanism of the antimicrobial peptide HJH-3 in killing Salmonella, a DNA blocking test and scanning electron microscopy (SEM) were used to determine the ability of the peptide to bind bacterial DNA in vitro. Laser confocal analysis and electron microscopy were used to observe the binding of antimicrobial peptide HJH-3 and Salmonella DNA, and flow cytometry was used to analyze the effect of antimicrobial peptides on cell division in vivo. The results showed that HJH-3 can bind to DNA to block the diffusion and migration of DNA in agarose gel. Laser confocal microscopy revealed that antimicrobial peptide HJH-3 penetrated the bacterial cell membrane and bound with bacterial DNA. Transmission electron microscopy showed that antimicrobial peptide HJH-3 aggregated in the nucleoid of Salmonella cells, and through a channel in the membrane destroyed by the antimicrobial peptide, DNA and other intracellular contents were excreted, and polymerized DNA was fragmented. The results of the flow cytometry analysis confirmed that the death rate of Salmonella increased significantly after exposure to antimicrobial peptide HJH-3 and increased with increasing antimicrobial peptide concentration. These results suggest that AMP HJH-3 may be a candidate antimicrobial agent to treat infectious diseases caused by Salmonella pullorum.

To explore the potential intracellular mechanism of the antimicrobial peptide HJH-3 in killing Salmonella, a DNA blocking test and scanning electron microscopy (SEM) were used to determine the ability of the peptide to bind bacterial DNA in vitro.

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

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

Bioactive cationic peptides as potential agents for breast cancer treatment

Breast cancer continues to affect millions of women worldwide, and the number of new cases dramatically increases every year. The physiological causes behind the disease are still not fully understood. One in every 100 cases can occur in men, and although the frequency is lower than among women, men tend to have a worse prognosis of the disease. Various therapeutic alternatives to combat the disease are available. These depend on the type and progress of the disease, and include chemotherapy, radiotherapy, surgery, and cancer immunotherapy. However, there are several well-reported side effects of these treatments that have a significant impact on life quality, and patients either relapse or are refractory to treatment. This makes it necessary to develop new therapeutic strategies. One promising initiative are bioactive peptides, which have emerged in recent years as a family of compounds with an enormous number of clinical applications due to their broad spectrum of activity. They are widely distributed in several organisms as part of their immune system. The antitumoral activity of these peptides lies in a nonspecific mechanism of action associated with their interaction with cancer cell membranes, inducing, through several routes, bilayer destabilization and cell death. This review provides an overview of the literature on the evaluation of cationic peptides as potential agents against breast cancer under different study phases. First, physicochemical characteristics such as the primary structure and charge are presented. Secondly, information about dosage, the experimental model used, and the mechanism of action proposed for the peptides are discussed.

Mechanism of Antimicrobial Peptides: Antimicrobial, Anti-Inflammatory and Antibiofilm Activities

Antimicrobial peptides (AMPs) are regarded as a new generation of antibiotics. Besides antimicrobial activity, AMPs also have antibiofilm, immune-regulatory, and other activities. Exploring the mechanism of action of AMPs may help in the modification and development of AMPs. Many studies were conducted on the mechanism of AMPs. The present review mainly summarizes the research status on the antimicrobial, anti-inflammatory, and antibiofilm properties of AMPs. This study not only describes the mechanism of cell wall action and membrane-targeting action but also includes the transmembrane mechanism of intracellular action and intracellular action targets. It also discusses the dual mechanism of action reported by a large number of investigations. Antibiofilm and anti-inflammatory mechanisms were described based on the formation of biofilms and inflammation. This study aims to provide a comprehensive review of the multiple activities and coordination of AMPs in vivo, and to fully understand AMPs to realize their therapeutic prospect.

Toward insights on antimicrobial selectivity of host defense peptides via machine learning model interpretation

Host defense peptides are promising candidates for the development of novel antibiotics. To realize their therapeutic potential, high levels of target selectivity is essential. This study aims to identify factors governing selectivity via the use of the random forest algorithm for correlating peptide sequence information with their bioactivity data. Satisfactory predictive models were achieved from out-of-bag prediction that yielded accuracies and Matthew's correlation coefficients in excess of 0.80 and 0.57, respectively. Model interpretation through the use of variable importance metrics and partial dependence plots indicated that the selectivity was heavily influenced by the composition and distribution patterns of molecular charge and solubility related parameters. Furthermore, the three investigated bacterial target species (Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus) likely had a significant influence on how selectivity was realized as there appears to be a similar underlying selectivity mechanism on the basis of charge-solubility properties (i.e. but which is tailored according to the target in question).

Reduced Level of Tear Antimicrobial and Immunomodulatory Proteins as a Possible Reason for Higher Ocular Infections in Diabetic Patients

(1) Background: Diabetes mellitus is one of the most common metabolic disorders and a risk factor for bacterial ocular infections. Our aim was to examine the antibacterial activity of tears from patients with diabetes mellitus with and without diabetic retinopathy and to link this activity to the level of tear proteins. (2) Methods: Non-stimulated basal tears were collected from 39 eyes of 35 subjects. The antibacterial activity of tear pools was tested against pathogenic Staphylococcus aureus ATCC 29213, Escherichia coli ATCC 26922 and Pseudomonas aeruginosa ATCC 27853 strains. The levels of 10 antimicrobial and immunomodulatory proteins were analyzed in the individual tear samples of the studied groups by SRM-based targeted mass spectrometry analysis. (3) Results: Disease stage-specific antimicrobial effect was observed in case of Staphylococcus aureus ATCC 29213 strain, and a non-disease specific inhibitory effect was observed in case of Pseudomonas aeruginosa ATCC 27853 strain. Changes in the levels of the studied antimicrobial and immunomodulatory proteins in the tears of the studied groups were also observed. (4) Conclusions: The higher ocular infection rate observed in diabetic patients may be the consequence of the decreased antimicrobial activity of tears possibly caused by the changes in the levels of antimicrobial and immunomodulatory proteins.

Mechanistic Insights into the Leishmanicidal and Bactericidal Activities of Batroxicidin, a Cathelicidin-Related Peptide from a South American Viper (Bothrops atrox)

Snake venoms are important sources of bioactive molecules, including those with antiparasitic activity. Cathelicidins form a class of such molecules, which are produced by a variety of organisms. Batroxicidin (BatxC) is a cathelicidin found in the venom of the common lancehead (Bothrops atrox). In the present work, BatxC and two synthetic analogues, BatxC(C-2.15Phe) and BatxC(C-2.14Phe)des-Phe1, were assessed for their microbicidal activity. All three peptides showed a broad-spectrum activity on Gram-positive and -negative bacteria, as well as promastigote and amastigote forms of Leishmania (Leishmania) amazonensis. Circular dichroism (CD) and nuclear magnetic resonance (NMR) data indicated that the three peptides changed their structure upon interaction with membranes. Biomimetic membrane model studies demonstrated that the peptides exert a permeabilization effect in prokaryotic membranes, leading to cell morphology distortion, which was confirmed by atomic force microscopy (AFM). The molecules considered in this work exhibited bactericidal and leishmanicidal activity at low concentrations, with the AFM data suggesting membrane pore formation as their mechanism of action. These peptides stand as valuable prototype drugs to be further investigated and eventually used to treat bacterial and protozoal infections.

Alignment-Free Antimicrobial Peptide Predictors: Improving Performance by a Thorough Analysis of the Largest Available Data Set

In the last two decades, a large number of machine-learning-based predictors for the activities of antimicrobial peptides (AMPs) have been proposed. These predictors differ from one another in the learning method and in the training and testing data sets used. Unfortunately, the training data sets present several drawbacks, such as a low representativeness regarding the experimentally validated AMP space, and duplicated peptide sequences between negative and positive data sets. These limitations give a low confidence to most of the approaches to be used in prospective studies. To address these weaknesses, we propose novel modeling and assessing data sets from the largest experimentally validated nonredundant peptide data set reported to date. From these novel data sets, alignment-free quantitative sequence-activity models (AF-QSAMs) based on Random Forest are created to identify general AMPs and their antibacterial, antifungal, antiparasitic, and antiviral functional types. An applicability domain analysis is carried out to determine the reliability of the predictions obtained, which, to the best of our knowledge, is performed for the first time for AMP recognition. A benchmarking is undertaken between the models proposed and several models from the literature that are freely available in 13 programs (ClassAMP, iAMP-2L, ADAM, MLAMP, AMPScanner v2.0, AntiFP, AMPfun, PEPred-suite, AxPEP, CAMPR3, iAMPpred, APIN, and Meta-iAVP). The models proposed are those with the best performance in all of the endpoints modeled, while most of the methods from the literature have weak-to-random predictive agreements. The models proposed are also assessed through Y-scrambling and repeated k-fold cross-validation tests, demonstrating that the outcomes obtained by them are not given by chance. Three chemometric analyses also confirmed the relevance of the peptides descriptors used in the modeling. Therefore, it can be concluded that the models built by fixing the drawbacks existing in the literature contribute to identifying antibacterial, antifungal, antiparasitic, and antiviral peptides with high effectivity and reliability. Models are freely available via the AMPDiscover tool at https://biocom-ampdiscover.cicese.mx/.

Internalization and membrane activity of the antimicrobial peptide CGA-N12

Antimicrobial peptides (AMPs) are conventional antibiotic alternatives due to their broad-spectrum antimicrobial activities and special mechanisms of action against pathogens. The antifungal peptide CGA-N12 was originally derived from human chromogranin A (CGA) and consists of the 65th to 76th amino acids of the CGA N-terminal region. In the present study, we found that CGA-N12 had fungicidal activity and exhibited time-dependent inhibition activity against Candida tropicalis. CGA-N12 entered the cells to exert its antagonist activity. The internalization of CGA-N12 was energy-dependent and accompanied by actin cytoskeleton-, clathrin-, sulfate proteoglycan-, endosome-, and lipid-depleting agent-mediated endocytosis. Moreover, the CGA-N12 internalization pathway was related to the peptide concentration. The effects of CGA-N12 on the cell membrane were investigated. CGA-N12 at a low concentration less than 4 × MIC100 did not destroy the cell membrane. While with increasing concentration, the damage to the cell membrane caused by CGA-N12 became more serious. At concentrations greater than 4 × MIC100, CGA-N12 destroyed the cell membrane integrity. Therefore, the membrane activity of CGA-N12 is concentration dependant.

Nasal Epithelial Barrier Integrity and Tight Junctions Disruption in Allergic Rhinitis: Overview and Pathogenic Insights

Allergic rhinitis (AR) is a common disorder affecting up to 40% of the population worldwide and it usually persists throughout life. Nasal epithelial barrier constitutes the first line of defense against invasion of harmful pathogens or aeroallergens. Cell junctions comprising of tight junctions (TJs), adherens junctions, desmosomes and hemidesmosomes form the nasal epithelial barrier. Impairment of TJ molecules plays causative roles in the pathogenesis of AR. In this review, we describe and discuss the components of TJs and their disruption leading to development of AR, as well as regulation of TJs expression by epigenetic changes, neuro-immune interaction, epithelial-derived cytokines (thymic stromal lymphopoietin, IL-25 and IL-33), T helper 2 (Th2) cytokines (IL-4, IL-5, IL-6 and IL-13) and innate lymphoid cells. These growing evidence support the development of novel therapeutic approaches to restore nasal epithelial TJs expression in AR patients.