Peptide antimicrobial agents

A Pleurocidin-Like Peptide from Poecilia Mexicana Fish Induces Selective Cytotoxicity in Leukemia Jurkat Cells Through The Apoptosis Pathway

OBJECTIVE

Some cationic anti-microbial peptides show a wide range of cytotoxic action versus malignant cells, which may lead to developing a novel group of antitumor medications. In the present study, the anticancer activity of pleurocidin-like peptide WF3 isoform X2 (AMP-WF3), from the Poecilia Mexicana fish, against leukemic cell line Jurkat was evaluated, and the cytotoxicity compared with the effects on normal cells, including peripheral blood mononuclear cells (PBMCs) and human dermal fibroblast (HDF) cells.

MATERIALS AND METHODS

In this experimental study, cells were treated with various dosages of AMP-WF3 for 24 hours. Using methyl thiazole tetrazolium salt reduction (MTT test), the effects of the AMP-WF3 on cell viability and toxicity were evaluated. The impact of this peptide on apoptotic pathways was examined using flow cytometry and Annexin V-PI stains. Additionally, the relative expression of the P53, P21 and BCL-2 genes was evaluated using a real-time polymerase chain reaction.

RESULTS

The Jurkat cell line was more susceptible to AMP-WF3 cytotoxicity [half-maximal inhibitory concentration (IC₅₀)=50 μM], while normal cells (PBMCs and HDF) were less susceptible. Flow cytometry verified that the apoptotic activity of AMP-WF3 on Jurkat cells was significantly higher than that of HDF and PBMCs. Peptide-treated Jurkat cells were associated with increased expression of P21, and P53 genes. In contrast, the changes in P21, P53, and BCL-2 genes differed in PBMCs and HDF cells. In HDF cells, simultaneous increase of P21, P53, and BCL-2, and in PBMCs, only the increase of BCL-2 was observed.

CONCLUSION

Our research showed that AMP-WF3 could be developed as a novel treatment agent with minimum side effects for ALL patients.

A review of potential antibacterial activities of nisin against Listeria monocytogenes: the combined use of nisin shows more advantages than single use

Listeria monocytogenes is a foodborne pathogen causing serious public health problems. Nisin is a natural antimicrobial agent produced by Lactococcus lactis and widely used in the food industry. However, the anti-L. monocytogenes efficiency of nisin might be decreased due to natural or acquired resistance of L. monocytogenes to nisin, or complexity of the food environment. The limitation of nisin as a bacteriostatic agent in food could be improved using a combination of methods. In this review, the physiochemical characteristics, species, bioengineered mutants, and antimicrobial mechanism of nisin are reviewed. Strategies of nisin combined with other antibacterial methods, including physical, chemical, and natural substances, and nanotechnology to enhance antibacterial effect are highlighted and discussed. Additionally, the antibacterial efficiency of nisin applied in real meat, dairy, and aquatic products is evaluated and analyzed. Among the various binding treatments, the combination with natural substances is more effective than the combination with physical and chemical methods. However, the combination of nisin and nanotechnology has more potential in terms of the impact on food quality.

Advancements, challenges and future perspectives on peptide-based drugs: Focus on antimicrobial peptides

Among other health related issues, the rising concerns on drug resistance led to look for alternative pharmaceutical drugs that are effective both against infectious and noninfectious diseases. Antimicrobial peptides (AMPs) emerged as potential therapeutic molecule with wide range of applications. With their limitations, AMPs have gained reputable attentions in research as well as in the pharmaceutical industry. This review highlighted the historical background, research trends, technological advancements, challenges, and future perspectives in the development and applications of peptide drugs. Some vital questions related with the need for pharmaceutical production, factors for the slow and steady journey, the importance of oral bioavailability, and the drug resistance possibilities of AMPs were raised and addressed accordingly. Therefore, the current study is believed to provide a profound understanding in the past and current scenarios and future directions on the therapeutic impacts of peptide drugs.

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.

Botryllin, a Novel Antimicrobial Peptide from the Colonial Ascidian Botryllus schlosseri

By mining the transcriptome of the colonial ascidian Botryllus schlosseri, we identified a transcript for a novel styelin-like antimicrobial peptide, which we named botryllin. The gene is constitutively transcribed by circulating cytotoxic morula cells (MCs) as a pre-propeptide that is then cleaved to mature peptide. The synthetic peptide, obtained from in silico translation of the transcript, shows robust killing activity of bacterial and unicellular yeast cells, causing breakages of both the plasma membrane and the cell wall. Specific monoclonal antibodies were raised against the epitopes of the putative amino acid sequence of the propeptide and the mature peptide; in both cases, they label the MC granular content. Upon MC degranulation induced by the presence of nonself, the antibodies recognise the extracellular nets with entrapped bacteria nearby MC remains. The obtained results suggest that the botryllin gene carries the information for the synthesis of an AMP involved in the protection of B. schlosseri from invading foreign cells.

In Vitro Pharmacokinetics of LL-37 and Oncorhyncin II Combination Against Acinetobacter baumannii

Background: Multidrug-resistant (MDR) Acinetobacter baumannii is one of the most common nosocomial pathogens. Antimicrobial peptides (AMPs) have been introduced as a viable alternative to antibiotics in the treatment of MDR pathogens. Objectives: This study was designed to assess the in vitro pharmacokinetics of the combination of two potent AMPs, LL-37 and oncorhyncin II, against A. baumannii (ATCC19606). Methods: The synthesized genes of oncorhyncin II and LL-37 were introduced into Escherichia coli BL21 as the expression host. The minimum inhibitory concentration (MIC), time-kills, and growth kinetics of these peptides were used to evaluate their antimicrobial efficiencies against A. baumannii (ATCC19606). Results: LL-37 and oncorhyncin II recombinant peptides showed MIC of 30.6 and 95.87 µg/mL against A. baumannii, respectively. Additive action was confirmed by combining the generated AMPs at the checkerboard approach. The combination of LL-37 and oncorhyncin II at 2 × MIC resulted in a rapid drop in log10 CFU/mL of A. baumannii in the time-kill and growth kinetic findings studies. Conclusions: The combination of the produced LL-37 and oncorhyncin II synergizes the bioactivity of the individual peptides. Therefore, these peptides or their combinations might function as novel antibiotics and be used to develop and produce new antimicrobial drugs for the treatment of infections caused by A. baumannii.

Exclusion of Anchor-Matched Peptide Nucleic Acid from Liquid-Ordered Domains by Hybridization with Complementary Flavin-Labeled DNA

Membrane-anchored proteins and their mimics, such as peptide nucleic acids (PNAs), are known to partition preferentially into either lipid raft/liquid-ordered (lo) domains or into non-raft/liquid-disordered (ld) domains, depending on their lipophilic anchors. Here, anchor-matched PNA was demonstrated to be excluded from the lo microdomains of giant unilamellar vesicles by hybridization with the complementary flavin-labeled DNA. As shown in control experiments using Alexa Fluor 488-labeled DNA, which showed that the preferential partitioning was the lo domain, the domain distribution of PNA was not only dependent on the lipophilic anchor but also on the structure of the hybridized DNA or PNA pair. In such systems, the main factors that influence changes in the domain selectivity of the probes are most likely to also be interactivity (i.e., steric bulkiness), hydrophilicity, and self-assembling ability. These findings may have the potential to contribute to the elucidation of membrane-active peptides, the method of their activation, and their applications in medicine such as antimicrobial use, especially with regard to their actions at the interface between the lo and ld domains in cells.

Efficacy and Safety of PL-5 (Peceleganan) Spray for Wound Infections: A Phase IIb Randomized Clinical Trial

OBJECTIVE

To assess the safety and efficacy of antimicrobial peptide PL-5 (Peceleganan) spray in the treatment of wound infections.

BACKGROUND

Antimicrobial peptide PL-5 spray is a novel topical antimicrobial agent.

METHODS

We conducted a multicenter, open-label, randomized, controlled phase IIb clinical trial to evaluate the efficacy and safety of PL-5 spray, as compared with silver sulfadiazine, in patients with skin wound infections. The primary efficacy outcome was the clinical efficacy rate on the first day after ending the treatment (D8). The secondary efficacy outcome was the clinical efficacy rate on the fifth day posttreatment (D5), the bacteria clearance rate, and the overall efficacy rate at the mentioned 2 time points. The safety outcomes included adverse reactions and pharmacokinetic analysis posttreatment.

RESULTS

A total of 220 patients from 27 hospitals in China were randomly assigned to 4 groups. On D8, the efficacy rate was 100.0%, 96.7%, 96.7% for the 1‰ PL-5, 2‰ PL-5, 4‰ PL-5 groups, respectively, as compared with 87.5% for the control group. The efficacy rate among the 4 groups was significantly different ( P <0.05). On D5, the efficacy rate was 100.0%, 93.4%, 98.3% for the 1‰ PL-5, 2‰ PL-5, 4‰ PL-5 groups, respectively, as compared with 82.5% for the control group. The efficacy rate among the 4 groups was significantly different ( P <0.05). The blood concentration of PL-5 was not detectable in pharmacokinetic analysis. No severe adverse event related to the application of PL-5 was reported.

CONCLUSIONS

Antimicrobial peptide PL-5 spray is safe and effective for the treatment of skin wound infections.

TRIAL REGISTRATION

ChiCTR2000033334.

Antimicrobial Proteins: Structure, Molecular Action, and Therapeutic Potential

Second- and third-line treatments of patients with antibiotic-resistant infections can have serious side effects, such as organ failure with prolonged care and recovery. As clinical practices such as cancer therapies, chronic disease treatment, and organ transplantation rely on the ability of available antibiotics to fight infection, the increased resistance of microbial pathogens presents a multifaceted, serious public health concern worldwide. The pipeline of traditional antibiotics is exhausted and unable to overcome the continuously developing multi-drug resistance. To that end, the widely observed limitation of clinically utilized antibiotics has prompted researchers to find a clinically relevant alternate antimicrobial strategy. In recent decades, the discovery of antimicrobial peptides (AMPs) as an excellent candidate to overcome antibiotic resistance has received further attention, particularly from scientists, health professionals, and the pharmaceutical industry. Effective AMPs are characterized by a broad spectrum of antimicrobial activities, high pathogen specificity, and low toxicity. In addition to their antimicrobial activity, AMPs have been found to be involved in a variety of biological functions, including immune regulation, angiogenesis, wound healing, and antitumor activity. This review provides a current overview of the structure, molecular action, and therapeutic potential of AMPs.

Antimicrobial Peptides Therapy: An Emerging Alternative for Treating Drug-Resistant Bacteria

Microbial resistance to antibiotics is an ancient and dynamic issue that has brought a situation reminiscent of the pre-antibiotic era to the limelight. Currently, antibiotic resistance and the associated infections are widespread and pose significant global health and economic burden. Thus, the misuse of antibiotics, which has increased resistance, has necessitated the search for alternative therapeutic agents for combating resistant pathogens. Antimicrobial peptides (AMPs) hold promise as a viable therapeutic approach against drug-resistant pathogens. AMPs are oligopeptides with low molecular weight. They have broad-spectrum antimicrobial activities against pathogenic microorganisms. AMPs are nonspecific and target components of microbes that facilitate immune response by acting as the first-line defense mechanisms against invading pathogenic microbes. The diversity and potency of AMPs make them good candidates for alternative use. They could be used alone or in combination with several other biomaterials for improved therapeutic activity. They can also be employed in vaccine production targeting drug-resistant pathogens. This review covers the opportunities and advances in AMP discovery and development targeting antimicrobial resistance (AMR) bacteria. Briefly, it presents an overview of the global burden of the antimicrobial resistance crisis, portraying the global magnitude, challenges, and consequences. After that, it critically and comprehensively evaluates the potential roles of AMPs in addressing the AMR crisis, highlighting the major potentials and prospects.

Network Science and Group Fusion Similarity-Based Searching to Explore the Chemical Space of Antiparasitic Peptides

Antimicrobial peptides (AMPs) have appeared as promising compounds to treat a wide range of diseases. Their clinical potentialities reside in the wide range of mechanisms they can use for both killing microbes and modulating immune responses. However, the hugeness of the AMPs' chemical space (AMPCS), represented by more than 10⁶⁵ unique sequences, has represented a big challenge for the discovery of new promising therapeutic peptides and for the identification of common structural motifs. Here, we introduce network science and a similarity searching approach to discover new promising AMPs, specifically antiparasitic peptides (APPs). We exploited the network-based representation of APPs' chemical space (APPCS) to retrieve valuable information by using three network types: chemical space (CSN), half-space proximal (HSPN), and metadata (METN). Some centrality measures were applied to identify in each network the most important and nonredundant peptides. Then, these central peptides were considered as queries (Qs) in group fusion similarity-based searches against a comprehensive collection of known AMPs, stored in the graph database StarPepDB, to propose new potential APPs. The performance of the resulting multiquery similarity-based search models (mQSSMs) was evaluated in five benchmarking data sets of APP/non-APPs. The predictions performed by the best mQSSM showed a strong-to-very-strong performance since their external Matthews correlation coefficient (MCC) values ranged from 0.834 to 0.965. Outstanding MCC values (>0.85) were attained by the mQSSM with 219 Qs from both networks CSN and HSPN with 0.5 as similarity threshold in external data sets. Then, the performance of our best mQSSM was compared with the APPs prediction servers AMPDiscover and AMPFun. The proposed model showed its relevance by outperforming state-of-the-art machine learning models to predict APPs. After applying the best mQSSM and additional filters on the non-APP space from StarPepDB, 95 AMPs were repurposed as potential APP hits. Due to the high sequence diversity of these peptides, different computational approaches were applied to identify relevant motifs for searching and designing new APPs. Lastly, we identified 11 promising APP lead candidates by using our best mQSSMs together with diversity-based network analyses, and 24 web servers for activity/toxicity and drug-like properties. These results support that network-based similarity searches can be an effective and reliable strategy to identify APPs. The proposed models and pipeline are freely available through the StarPep toolbox software at http://mobiosd-hub.com/starpep.

Incorporation of Non-Canonical Amino Acids into Antimicrobial Peptides: Advances, Challenges, and Perspectives

The emergence of antimicrobial resistance is a global health concern and calls for the development of novel antibiotic agents. Antimicrobial peptides seem to be promising candidates due to their diverse sources, mechanisms of action, and physicochemical characteristics, as well as the relatively low emergence of resistance. The incorporation of noncanonical amino acids into antimicrobial peptides could effectively improve their physicochemical and pharmacological diversity. Recently, various antimicrobial peptides variants with improved or novel properties have been produced by the incorporation of single and multiple distinct noncanonical amino acids. In this review, we summarize strategies for the incorporation of noncanonical amino acids into antimicrobial peptides, as well as their features and suitabilities. Recent applications of noncanonical amino acid incorporation into antimicrobial peptides are also presented. Finally, we discuss the related challenges and prospects.

Antimicrobial activity of the recombinant peptide Melittin-Thanatin with three glycine to tryptophan mutations

The antimicrobial peptide was considered an important target for developing novel antibacterial drugs. However, the unstable biological activity and the low antibacterial activity are challenges for the application of recombinant proteins. In this study, the fusion peptide of Melittin-Thanatin (MT) was designed and produced, and its derivative sequence (MT-W) was obtained by replacing three glycines (Gly, G) with tryptophan (Trp, W). The MT-W peptide were synthesized in Bacillus subtilis WB700 by EDDIE self-cleavage protein fusion. Compared with MT, MT-W exhibited 2-4 times higher antibacterial rate against Escherichia coli K88. In addition, MT-W showed lower cytotoxicity (IC50 > 300 mg·L^-1) to the red blood cell, and more stable biological activities under the conditions of different temperatures (20, 30, 40, 50, 60, 70, 80, and 90 °C), pH values (2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, and 9.0) and different proteases. Especially, MT-W showed a broader antibacterial effect on three drug-resistant strains than florfenicol and oxytetracycline calcium. In conclusion, compared with MT, the MT-W showed increased antibacterial activity, stability, lower cytotoxicity, and broader antimicrobial effect. Therefore, it would become a promising alternative to conventional antibiotics.

Disparate Regions of the Human Chemokine CXCL10 Exhibit Broad-Spectrum Antimicrobial Activity against Biodefense and Antibiotic-Resistant Bacterial Pathogens

CXCL10 is a pro-inflammatory chemokine produced by the host in response to microbial infection. In addition to canonical, receptor-dependent actions affecting immune-cell migration and activation, CXCL10 has also been found to directly kill a broad range of pathogenic bacteria. Prior investigations suggest that the bactericidal effects of CXCL10 occur through two distinct pathways that compromise the cell envelope. These observations raise the intriguing notion that CXCL10 features a separable pair of antimicrobial domains. Herein, we affirm this possibility through peptide-based mapping and structure/function analyses, which demonstrate that discrete peptides derived from the N- and C-terminal regions of CXCL10 mediate bacterial killing. The N-terminal derivative, peptide P1, exhibited marked antimicrobial activity against Bacillus anthracis vegetative bacilli and spores, as well as antibiotic-resistant clinical isolates of Klebsiella pneumoniae, Acinetobacter baumannii, Enterococcus faecium, and Staphylococcus aureus, among others. At bactericidal concentrations, peptide P1 had a minimal degree of chemotactic activity, but did not cause red blood cell hemolysis or cytotoxic effects against primary human cells. The C-terminal derivative, peptide P9, exhibited antimicrobial effects, but only against Gram-negative bacteria in low-salt medium─conditions under which the peptide can adopt an α-helical conformation. The introduction of a hydrocarbon staple induced and stabilized α-helicity; accordingly, stapled peptide P9 displayed significantly improved bactericidal effects against both Gram-positive and Gram-negative bacteria in media containing physiologic levels of salt. Together, our findings identify and characterize the antimicrobial regions of CXCL10 and functionalize these novel determinants as discrete peptides with potential therapeutic utility against difficult-to-treat pathogens.

Short, mirror-symmetric antimicrobial peptides centered on "RRR" have broad-spectrum antibacterial activity with low drug resistance and toxicity

The increasingly severe bacterial resistance worldwide pushes people to discover and design potential antibacterial drugs unavoidably. In this work, a series of short, mirror-symmetric peptides were designed and successfully synthesized, centered on "RRR" and labeled with hydrophobic amino acids at both ends. Based on the structure-activity relationship analysis, LWWR (LWWRRRWWL-NH₂) was screened as a desirable mirror-symmetric peptide for further study. As expected, LWWR displayed broad-spectrum antibacterial activity against the standard bacteria and antibiotic-resistant strains. Undoubtedly, the high stability of LWWR in a complex physiological environment was an essential guarantee to maximizing its antibacterial activity. Indeed, LWWR also exhibited a rapid bactericidal speed and a low tendency to develop bacterial resistance, based on the multiple actions of non-receptor-mediated membrane actions and intra-cellular mechanisms. Surprisingly, although LWWR showed similar in vivo antibacterial activity compared with Polymyxin B and Melittin, the in vivo safety of LWWR was far higher than that of them, so LWWR had better therapeutic potential. In summary, the desirable mirror-symmetric peptide LWWR was promised as a potential antibacterial agent to confront the antibiotics resistance crisis. STATEMENT OF SIGNIFICANCE: Witnessing the growing problem of antibiotic resistance, a series of short, mirror-symmetric peptides based on the symmetric center "RRR" and hydrophobic terminals were designed and synthesized in this study. Among, LWWR (LWWRRRWWL-NH₂) presented broad-spectrum antibacterial activity both in vitro and in vivo due to its multiple mechanisms and good stability. Meanwhile, the low drug resistance and toxicity of LWWR also suggested its potential for clinical application. The findings of this study will provide some inspiration for the design and development of potential antibacterial agents, and contribute to the elimination of bacterial infections worldwide as soon as possible.

Target-AMP: Computational prediction of antimicrobial peptides by coupling sequential information with evolutionary profile

Antimicrobial peptides (AMPs) are gaining a lot of attention as cutting-edge treatments for many infectious disorders. The effectiveness of AMPs against bacteria, fungi, and viruses has persisted for a long period, making them the greatest option for addressing the growing problem of antibiotic resistance. Due to their wide-ranging actions, AMPs have become more prominent, particularly in therapeutic applications. The prediction of AMPs has become a difficult task for academics due to the explosive increase of AMPs documented in databases. Wet-lab investigations to find anti-microbial peptides are exceedingly costly, time-consuming, and even impossible for some species. Therefore, in order to choose the optimal AMPs candidate before to the in-vitro trials, an efficient computational method must be developed. In this study, an effort was made to develop a machine learning-based classification system that is effective, accurate, and can distinguish between anti-microbial peptides. The position-specific-scoring-matrix (PSSM), Pseudo Amino acid composition, di-peptide composition, and combination of these three were utilized in the suggested scheme to extract salient aspects from AMPs sequences. The classification techniques K-nearest neighbor (KNN), Random Forest (RF), and Support Vector Machine (SVM) were employed. On the independent dataset and training dataset, the accuracy levels achieved by the suggested predictor (Target-AMP) are 97.07% and 95.71%, respectively. The results show that, when compared to other techniques currently used in the literature, our Target-AMP had the best success rate.

Antimicrobial peptides: natural or synthetic defense peptides against HBV and HCV infections

According to the literature, treatment of HCV and HBV infections faces challenges due to problems such as the emergence of drug-resistant mutants, the high cost of treatment, and the side effects of current antiviral therapy. Antimicrobial peptides (AMPs), a group of small peptides, are a part of the immune system and are considered as an alternative treatment for microbial infections. These peptides are water-soluble with amphiphilic (hydrophilic and hydrophobic surfaces) characteristics. AMPs are produced by a wide range of organisms including both prokaryotic and eukaryotic cells. The antiviral mechanisms of AMPs include inhibiting virus entry, inhibiting intracellular virus replication, inhibiting intracellular viral packaging, and inducing immune responses. In addition, AMPs are a new generation of antiviral biomolecules that have very low toxicity for human host cells, particularly liver cell lines. AMPs can be considered as one of the most important strategies for developing new adjuvant drugs in the treatment of HBV and HCV infections. In the present study, several groups of AMPs (with a net positive charge) such as Human cathelicidin, Claudin-1, Defensins, Hepcidin, Lactoferrin, Casein, Plectasin, Micrococcin P1, Scorpion venom, and Synthetic peptides were reviewed with antiviral properties against HBV and HCV.

Tachyplesin I and its derivatives: A pharmaco-chemical perspective on their antimicrobial and antitumor potential

INTRODUCTION

Increasing evidence suggests that intratumor microbiota are an intrinsic component in the tumor microenvironment across multiple cancer types, and that there is a close relationship between microbiota and tumor progression. Therefore, how to address the interaction between bacteria and malignances has become a growing concern. Tachyplesin I (TPI), a peptide with dual antimicrobial and antitumor effects, holds great promise as a therapeutic alternative for the aforementioned diseases, with the advantage of broad-spectrum activities, quick killing efficacy, and a low tendency to induce resistance.

AREAS COVERED

This review comprehensively summarizes the pharmacological mechanisms of TPI with an emphasis on its antimicrobial and antitumor potential. Furthermore, it presents advances in TPI derivatives and gives a perspective on their future development. The article is based on literature searches using PubMed and SciFinder to retrieve the most up-to-date information of TPI.

EXPERT OPINION

Bacterial infections and cancer both pose a serious threat to health due to their symbiotic interactions and drug resistance. TPI is anticipated to be a novel agent to control pathogenic bacteria and various tumors through multiple mechanisms of action. Indeed, the continuous advancements in chemical modification and innovative applications of TPI give hope for future improvements in therapeutic efficacy.

Novel antimicrobial agents targeting the Streptococcus mutans biofilms discovery through computer technology

Dental caries is one of the most prevalent and costly biofilm-associated infectious diseases worldwide. Streptococcus mutans (S. mutans) is well recognized as the major causative factor of dental caries due to its acidogenicity, aciduricity and extracellular polymeric substances (EPSs) synthesis ability. The EPSs have been considered as a virulent factor of cariogenic biofilm, which enhance biofilms resistance to antimicrobial agents and virulence compared with planktonic bacterial cells. The traditional anti-caries therapies, such as chlorhexidine and antibiotics are characterized by side-effects and drug resistance. With the development of computer technology, several novel approaches are being used to synthesize or discover antimicrobial agents. In this mini review, we summarized the novel antimicrobial agents targeting the S. mutans biofilms discovery through computer technology. Drug repurposing of small molecules expands the original medical indications and lowers drug development costs and risks. The computer-aided drug design (CADD) has been used for identifying compounds with optimal interactions with the target via silico screening and computational methods. The synthetic antimicrobial peptides (AMPs) based on the rational design, computational design or high-throughput screening have shown increased selectivity for both single- and multi-species biofilms. These methods provide potential therapeutic agents to promote targeted control of the oral microbial biofilms in the near future.

Efficacy of natural antimicrobial peptides versus peptidomimetic analogues: a systematic review

Aims: This systematic review was carried out to determine whether synthetic peptidomimetics exhibit significant advantages over antimicrobial peptides in terms of in vitro potency. Structural features - molecular weight, charge and length - were examined for correlations with activity. Methods: Original research articles reporting minimum inhibitory concentration  values against Escherichia coli, indexed until 31 December 2020, were searched in PubMed/ScienceDirect/Google Scholar and evaluated using mixed-effects models. Results: In vitro antimicrobial activity of peptidomimetics resembled that of antimicrobial peptides. Net charge significantly affected minimum inhibitory concentration values (p < 0.001) with a trend of 4.6% decrease for increments in charge by +1. Conclusion: AMPs and antibacterial peptidomimetics exhibit similar potencies, providing an opportunity to exploit the advantageous stability and bioavailability typically associated with peptidomimetics.

Could artificial intelligence revolutionize the development of nanovectors for gene therapy and mRNA vaccines?

Gene therapy enables the introduction of nucleic acids like DNA and RNA into host cells, and is expected to revolutionize the treatment of a wide range of diseases. This growth has been further accelerated by the discovery of CRISPR/Cas technology, which allows accurate genomic editing in a broad range of cells and organisms in vitro and in vivo. Despite many advances in gene delivery and the development of various viral and non-viral gene delivery vectors, the lack of highly efficient non-viral systems with low cellular toxicity remains a challenge. The application of cutting-edge technologies such as artificial intelligence (AI) has great potential to find new paradigms to solve this issue. Herein, we review AI and its major subfields including machine learning (ML), neural networks (NNs), expert systems, deep learning (DL), computer vision and robotics. We discuss the potential of AI-based models and algorithms in the design of targeted gene delivery vehicles capable of crossing extracellular and intracellular barriers by viral mimicry strategies. We finally discuss the role of AI in improving the function of CRISPR/Cas systems, developing novel nanobots, and mRNA vaccine carriers.

Chickpea Peptide: A Nutraceutical Molecule Corroborating Neurodegenerative and ACE-I Inhibition

Chickpea seeds are the source of proteins in human nutrition and attribute some nutraceutical properties. Herein, we report the effects of chickpea seed bioactive peptide on albumin, insulin, lactoglobulin and lysozyme amyloid fibril formation. Employing thioflavin T (ThT) assays and circular dichroism (CD), amyloid structural binding transition was experimented to analyze the inhibition of amyloid fibril formation. The purified active peptide with a molecular mass of 934.53 Da was evaluated in vitro for its ACE-I inhibitory, antibacterial, antifungal and antidiabetic activities. Further, in vivo animal studies were carried out in wistar rats for blood pressure lowering action. In hypertensive rats, chickpea peptide decreased 131 ± 3.57 mm of Hg for systolic blood pressure and 86 ± 1.5 mm of Hg for diastolic blood pressure after 8 h intraperitoneal administration. Additionally, the peptide suppressed the fibrillation of amyloid and destabilized the preformed mature fibrils. Data emphasize efficacy of chickpea peptide vis-a-vis ACE-Inhibitory, antibacterial, antifungal, antidiabetic and anti-amyloidogenic activities, allowing us to propose this novel peptide as a suitable candidate for nutraceutical-based drugs and seems the first kind of its nature.

sAMPpred-GAT: prediction of antimicrobial peptide by graph attention network and predicted peptide structure

MOTIVATION

Antimicrobial peptides (AMPs) are essential components of therapeutic peptides for innate immunity. Researchers have developed several computational methods to predict the potential AMPs from many candidate peptides. With the development of artificial intelligent techniques, the protein structures can be accurately predicted, which are useful for protein sequence and function analysis. Unfortunately, the predicted peptide structure information has not been applied to the field of AMP prediction so as to improve the predictive performance.

RESULTS

In this study, we proposed a computational predictor called sAMPpred-GAT for AMP identification. To the best of our knowledge, sAMPpred-GAT is the first approach based on the predicted peptide structures for AMP prediction. The sAMPpred-GAT predictor constructs the graphs based on the predicted peptide structures, sequence information and evolutionary information. The Graph Attention Network (GAT) is then performed on the graphs to learn the discriminative features. Finally, the full connection networks are utilized as the output module to predict whether the peptides are AMP or not. Experimental results show that sAMPpred-GAT outperforms the other state-of-the-art methods in terms of AUC, and achieves better or highly comparable performance in terms of the other metrics on the eight independent test datasets, demonstrating that the predicted peptide structure information is important for AMP prediction.

AVAILABILITY AND IMPLEMENTATION

A user-friendly webserver of sAMPpred-GAT can be accessed at http://bliulab.net/sAMPpred-GAT and the source code is available at https://github.com/HongWuL/sAMPpred-GAT/.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

A Novel Antimicrobial Peptide Spampcin56-86 from Scylla paramamosain Exerting Rapid Bactericidal and Anti-Biofilm Activity In Vitro and Anti-Infection In Vivo

The abuse of antibiotics leads to the increase of bacterial resistance, which seriously threatens human health. Therefore, there is an urgent need to find effective alternatives to antibiotics, and antimicrobial peptides (AMPs) are the most promising antibacterial agents and have received extensive attention. In this study, a novel potential AMP was identified from the marine invertebrate Scylla paramamosain and named Spampcin. After bioinformatics analysis and AMP database prediction, four truncated peptides (Spa31, Spa22, Spa20 and Spa14) derived from Spampcin were screened, all of which showed potent antimicrobial activity with different antibacterial spectrum. Among them, Spampcin_56-86 (Spa31 for short) exhibited strong bactericidal activity against a variety of clinical pathogens and could rapidly kill the tested bacteria within minutes. Further analysis of the antibacterial mechanism revealed that Spa31 disrupted the integrity of the bacterial membrane (as confirmed by scanning electron microscopy observation, NPN, and PI staining assays), leading to bacterial rupture, leakage of cellular contents (such as elevated extracellular ATP), increased ROS production, and ultimately cell death. Furthermore, Spa31 was found to interact with LPS and effectively inhibit bacterial biofilms. The antibacterial activity of Spa31 had good thermal stability, certain ion tolerance, and no obvious cytotoxicity. It is worth noting that Spa31 could significantly improve the survival rate of zebrafish Danio rerio infected with Pseudomonas aeruginosa, indicating that Spa31 played an important role in anti-infection in vivo. This study will enrich the database of marine animal AMPs and provide theoretical reference and scientific basis for the application of marine AMPs in medical fields.

Genomic Variant in NK-Lysin Gene Is Associated with T Lymphocyte Subpopulations in Pigs

As an antimicrobial peptide, NK-lysin (NKL) plays an important role in the innate immune system of organisms. In this study, 300 piglets (68 Landrace pigs, 158 Large White pigs and 74 Songliao Black pigs) were used to further explore the function of NLK gene in porcine immune system. The quantitative real-time PCR analysis detected the NKL gene's expression, and the result demonstrated that NKL mRNA was expressed in lung, spleen, stomach, kidney, liver and heart, and the expression level decreased sequentially. A single-nucleotide polymorphism (SNP, g.59070355 G > A) in intron 3 of the NKL gene was detected by PCR amplification and sequencing. The results of the Chi-square (χ2) test showed that the genotype of the SNP was consistent with the Hardy-Weinberg equilibrium. What's more, association analysis results showed the SNP in NKL gene was significantly associated with T lymphocyte subpopulations. Different genotypes had significant effects on the proportion of CD4-CD8-, CD4-CD8+, CD4+CD8+, CD8+, CD4+/CD8+ in peripheral blood (p < 0.05). These results further suggested that NKL could be recognized as a promising immune gene for swine disease resistance breeding.

Growing Global Research Interest in Antimicrobial Peptides for Caries Management: A Bibliometric Analysis

Objective: Researchers are studying the use of antimicrobial peptides as functional biomaterials to prevent and treat dental caries. This study aims to investigate the global research interest in antimicrobial peptides for caries management. Methods: Two independent investigators systematically searched with keywords ('Caries' OR 'Dental caries') AND ('Antimicrobial peptide' OR 'AMP' OR 'Statherin' OR 'Histatin' OR 'Defensin' OR 'Cathelicidin') on Web of Science, PubMed and Scopus. They removed duplicate publications and screened the titles and abstracts to identify relevant publications. The included publications were summarized and classified as laboratory studies, clinical trials or reviews. The citation count and citation density of the three publication types were compared using a one-way analysis of variance. The publications' bibliometric data were analyzed using the Bibliometrix program. Results: This study included 163 publications with 115 laboratory studies (71%), 29 clinical trials (18%) and 19 reviews (11%). The number of publications per year have increased steadily since 2002. The citation densities (mean ± SD) of laboratory study publications (3.67 ± 2.73) and clinical trial publications (2.63 ± 1.85) were less than that of review articles (5.79 ± 1.27) (p = 0.002). The three publication types had no significant difference in citation count (p = 0.54). Most publications (79%, 129/163) reported the development of a novel antimicrobial peptide. China (52/163, 32%) and the US (29/163, 18%) contributed to 50% (81/163) of the publications. Conclusion: This bibliometric analysis identified an increasing trend in global interest in antimicrobial peptides for caries management since 2002. The main research topic was the development of novel antimicrobial peptides. Most publications were laboratory studies, as were the three publications with the highest citation counts. Laboratory studies had high citation counts, whereas reviews had high citation density.

A Non-Canonical Teleost NK-Lysin: Antimicrobial Activity via Multiple Mechanisms

NK-lysin (NKL) is a family of antimicrobial proteins with an important role in innate and adaptive immunity. In this study, a non-canonical NK-lysin (NKLnc) was identified in the Japanese flounder (Paralichthys olivaceus), which shares low sequence identities (15.8-20.6%) with previously reported fish NKLs and was phylogenetically separated from the canonical NKLs in teleost. NKLnc expression was upregulated in flounder tissues during bacterial infection, and interference with NKLnc expression impaired the ability of flounder cells to eliminate invading bacteria. When expressed in Escherichia coli, NKLnc was detrimental to the host cells. P35, a peptide derived from the saposin B domain (SapB) of NKLnc, bound major bacterial surface molecules and killed both Gram-negative and Gram-positive bacteria by inflicting damage to bacterial cell structure and genomic DNA. The bactericidal activity, but not the bacteria-binding capacity, of P35 required the structural integrity of the alpha 2/3 helices in SapB. Furthermore, P35 induced the migration of flounder peripheral blood leukocytes, inhibited bacterial dissemination in fish tissues, and facilitated fish survival after bacterial challenge. Together our study reveals that NKLnc plays an important part in flounder immune defense, and that NKLnc peptide exerts an antimicrobial effect via multiple mechanisms by targeting both bacteria and fish cells.

Antimicrobial Activity of Apidermin 2 from the Honeybee Apis mellifera

Apidermins (APDs) are known as structural cuticular proteins in insects, but their additional roles are poorly understood. In this study, we characterized the honeybee, Apis mellifera, APD 2 (AmAPD 2), which displays activity suggesting antimicrobial properties. In A. mellifera worker bees, the AmAPD 2 gene is transcribed in the epidermis, hypopharyngeal glands, and fat body, and induced upon microbial ingestion. Particularly in the epidermis of A. mellifera worker bees, the AmAPD 2 gene showed high expression and responded strongly to microbial challenge. Using a recombinant AmAPD 2 peptide, which was produced in baculovirus-infected insect cells, we showed that AmAPD 2 is heat-stable and binds to live bacteria and fungi as well as carbohydrates of microbial cell wall molecules. This binding action ultimately induced structural damage to microbial cell walls, which resulted in microbicidal activity. These findings demonstrate the antimicrobial role of AmAPD 2 in honeybees.

Advancements in antimicrobial nanoscale materials and self-assembling systems

Antimicrobial resistance is directly responsible for more deaths per year than either HIV/AIDS or malaria and is predicted to incur a cumulative societal financial burden of at least $100 trillion between 2014 and 2050. Already heralded as one of the greatest threats to human health, the onset of the coronavirus pandemic has accelerated the prevalence of antimicrobial resistant bacterial infections due to factors including increased global antibiotic/antimicrobial use. Thus an urgent need for novel therapeutics to combat what some have termed the 'silent pandemic' is evident. This review acts as a repository of research and an overview of the novel therapeutic strategies being developed to overcome antimicrobial resistance, with a focus on self-assembling systems and nanoscale materials. The fundamental mechanisms of action, as well as the key advantages and disadvantages of each system are discussed, and attention is drawn to key examples within each field. As a result, this review provides a guide to the further design and development of antimicrobial systems, and outlines the interdisciplinary techniques required to translate this fundamental research towards the clinic.

Atypical Viral Infections in Gastroenterology

Enteric viruses are commonly found obligate parasites in the gastrointestinal (GI) tract. These viruses usually follow a fecal-oral route of transmission and are characterized by their extraordinary stability as well as resistance in high-stress environments. Most of them cause similar symptoms including vomiting, diarrhea, and abdominal pain. In order to come in contract with mucosal surfaces, these viruses need to pass the three main lines of defense: mucus layer, innate immune defenses, and adaptive immune defenses. The following atypical gastrointestinal infections are discussed: SARS-CoV2, hantavirus, herpes simplex virus I, cytomegalovirus, and calicivirus. Dysbiosis represents any modification to the makeup of resident commensal communities from those found in healthy individuals and can cause a patient to become more susceptible to bacterial and viral infections. The interaction between bacteria, viruses, and host physiology is still not completely understood. However, with growing research on viral infections, dysbiosis, and new methods of detection, we are getting closer to understanding the nature of these viruses, their typical and atypical characteristics, long-term effects, and mechanisms of action in different organ systems.

Effect of Lipid Length and Cationic Residues on the Antibacterial and Hemolytic Activities of Paenibacterin

Paenibacterin A1 (PA1) is a broad-spectrum, cationic cyclic lipodepsipeptide antibiotic isolated from Paenibacillus thiaminolyticus. In this study, the roles of the cationic residues and lipid tail length on the in vitro antibacterial and hemolytic activities of PA1 was examined in the context of an active PA1 analogue, called PAK, in which the two D-Orn residues in PA1 were converted to D-Lys residues. The effect of reducing the length of the lipid tail in PAK from 15 to 12-10 carbons on the minimum inhibitory concentration (MIC) depended upon the bacteria. This change had little effect on the MIC against Escherichia coli and Bacillus subtilis but resulted in a reduction in activity against most of the ESKAPE pathogens tested with the exception of Klebsiella pneumoniae. Any one of the four cationic residues in PAK could be replaced with alanine with only a minimal effect on its MIC against B. subtilis, E.coli, K. pneumoniae, Acinetobacter baumannii, and MSSA. For Pseudomonas aeruginosa and the two MRSA strains tested, the presence of cationic residues at positions 7 and 12 are not important for activity, while the cationic residues at positions 1 and 4 are important. While PAK exhibited some hemolysis at 8 μg/mL and 70% hemolysis at 128 μg/mL, its C-12 and C-10 analogues were not hemolytic up to 128 μg/mL. All PAK analogues that had one or two cationic residues replaced with alanine were as hemolytic as or more hemolytic than PAK.

One-step synthesized antimicrobial peptide-functionalized gold nanoclusters for selective imaging and killing of pathogenic bacteria

The development of multifunctional nanomaterials with bacterial imaging and killing activities is of great importance for the rapid diagnosis and timely treatment of bacterial infections. Herein, peptide-functionalized gold nanoclusters (CWR11-AuNCs) with high-intensity red fluorescence were successfully synthesized via a one-step method using CWR11 as a template and by optimizing the ratio of CWR11 to HAuCl4, reaction time, pH, and temperature. The CWR11-AuNCs bound to bacteria and exhibited selective fluorescence microscopy imaging properties, which is expected to provide a feasible method for locating and imaging bacteria in complex in vivo environments. In addition, CWR11-AuNCs not only retained the antibacterial and bactericidal activities of CWR11 but also exhibited certain inhibitory or killing effects on gram-negative and gram-positive bacteria and biofilms. The MICs of CWR11-AuNCs against Escherichia coli and Staphylococcus aureus were 178 and 89 μg/ml, respectively. Surprisingly, cell viability in the CWR11-AuNC-treated group was greater than that in the CWR11-treated group, and the low cytotoxicity exhibited by the CWR11-AuNCs make them more promising for clinical applications.

Recombinant phage displaying ToAP2D peptide with antifungal activity against Sporothrix globosa

We designed and synthesized recombinant phage nanofibers displaying ToAP2D peptide and investigated their antifungal effect on Sporothrix and the corresponding mechanism. Antimicrobial peptide, ToAP2D, was used as the template. The effect of synthesized recombinant phages on the immune function of CD4+ T lymphocytes in mice was tested using an enzyme-linked immunosorbent assay. The therapeutic effect and safety of recombinant phage administration on Sporothrix-infected BALB/c mice were evaluated based on survival analysis, histopathological changes, and renal and liver functions. The successfully prepared recombinant phage displaying ToAP2D peptides significantly inhibited Sporothrix growth. According to the scanning electron microscopy results, the recombinant phage caused shrinkage and rupture of Sporothrix globosa, leading to leakage of the contents. The Hoechst/propidium iodide double staining test indicated that the recombinant phage could induce cell apoptosis of Sporothrix globosa. The apoptotic pathway might be due to the accumulation of reactive oxygen species in large quantities in cells, activating caspase dependence; this reduced inflammation, prolonged the survival time, and enhanced levels of IFN-γ and IL-17 in mice. We believe that recombinant phage inhibits Sporothrix growth by adjusting the immune response of mice, inducing Sporothrix apoptosis and improving animal survival. This study offers a new approach to preparing antimicrobial peptides.

Microcin MccI47 selectively inhibits enteric bacteria and reduces carbapenem-resistant Klebsiella pneumoniae colonization in vivo when administered via an engineered live biotherapeutic

The gastrointestinal (GI) tract is the reservoir for multidrug resistant (MDR) pathogens, specifically carbapenem-resistant (CR) Klebsiella pneumoniae and other Enterobacteriaceae, which often lead to the spread of antimicrobial resistance genes, severe extraintestinal infections, and lethal outcomes. Selective GI decolonization has been proposed as a new strategy for preventing transmission to other body sites and minimizing spreading to susceptible individuals. Here, we purify the to-date uncharacterized class IIb microcin I47 (MccI47) and demonstrate potent inhibition of numerous Enterobacteriaceae, including multidrug-resistant clinical isolates, in vitro at concentrations resembling those of commonly prescribed antibiotics. We then genetically modify the probiotic bacterium Escherichia coli Nissle 1917 (EcN) to produce MccI47 from a stable multicopy plasmid by using MccI47 toxin production in a counterselection mechanism to engineer one of the native EcN plasmids, which renders provisions for inducible expression and plasmid selection unnecessary. We then test the clinical relevance of the MccI47-producing engineered EcN in a murine CR K. pneumoniae colonization model and demonstrate significant MccI47-dependent reduction of CR K. pneumoniae abundance after seven days of daily oral live biotherapeutic administration without disruption of the resident microbiota. This study provides the first demonstration of MccI47 as a potent antimicrobial against certain Enterobacteriaceae, and its ability to significantly reduce the abundance of CR K. pneumoniae in a preclinical animal model, when delivered from an engineered live biotherapeutic product. This study serves as the foundational step toward the use of engineered live biotherapeutic products aimed at the selective removal of MDR pathogens from the GI tract.

Tilted State Population of Antimicrobial Peptide PGLa Is Coupled to the Transmembrane Potential

Cationic antimicrobial peptide PGLa gets into close contact with the anionic bacterial cell membrane, facilitating cross-membrane transport phenomena and membrane disruption depending on the concentration. The mechanisms of action are closely associated with the tilted insertion geometry of PGLa. Therefore, we aimed to understand the interaction between the transmembrane potential (TMP) and the orientation of the membrane-bound PGLa helix. Molecular dynamics simulations were performed with TMP, and we found that the PGLa tilt angle relative to the membrane is coupled with the TMP. Elevated TMP increases the population of the tilted state. We observed positive feedback between the tilt angle and the TMP, which occurs due to the electrostatic interaction between the peptidic helix and the Na⁺ cations at the membrane-water interface. These TMP coupled phenomena can contribute to understanding the direct antimicrobial and adjuvant effects of PGLa in combination with regular antibiotics.

Strategies for improving antimicrobial peptide production

Antimicrobial peptides (AMPs) found in a wide range of animal, insect, and plant species are host defense peptides forming an integral part of their innate immunity. Although the exact mode of action of some AMPs is yet to be deciphered, many exhibit membrane lytic activity or interact with intracellular targets. The ever-growing threat of antibiotic resistance has brought attention to research on AMPs to enhance their clinical use as a therapeutic alternative. AMPs have several advantages over antibiotics such as broad range of antimicrobial activities including anti-fungal, anti-viral and anti-bacterial, and have not reported to contribute to resistance development. Despite the numerous studies to develop efficient production methods for AMPs, limitations including low yield, degradation, and loss of activity persists in many recombinant approaches. In this review, we outline available approaches for AMP production and various expression systems used to achieve higher yield and quality. In addition, recent advances in recombinant strategies, suitable fusion protein partners, and other molecular engineering strategies for improved AMP production are surveyed.

Dual function of a bumblebee (Bombus ignitus) serine protease inhibitor that acts as a microbicidal peptide and anti-fibrinolytic venom toxin

In bee venoms, low-molecular-weight peptides, including serine protease inhibitors (SPIs), exhibit multifunctional activities. Although SPIs in bee venoms are relatively well known, those that function in both the body and secreted venom of bees are not well-characterized. In this study, we identified a bumblebee (Bombus ignitus) SPI (BiSPI) that displays microbicidal and anti-fibrinolytic activities. BiSPI was found to consist of a trypsin inhibitor-like domain containing a P1 site and ten cysteine residues. We observed that the BiSPI gene was ubiquitously transcribed in the body, including the venom glands. In correlation, the BiSPI protein was detected both in the body and secreted venom by using an antibody against a recombinant BiSPI peptide produced in baculovirus-infected insect cells. Recombinant BiSPI exhibited inhibitory activity against trypsin but not chymotrypsin and inhibited microbial serine proteases and plasmin but not elastase or thrombin. Moreover, recombinant BiSPI recognized carbohydrates and bound to fungi and gram-negative and gram-positive bacteria. Consistent with these properties, recombinant BiSPI exhibited microbicidal activities against bacteria and fungi through induction of structural damage by binding to the microbial surfaces. Additionally, recombinant BiSPI inhibited the plasmin-mediated degradation of human fibrin and was thus concluded to exhibit anti-fibrinolytic activity. Moreover, the peptide showed no effect on hemolysis. These findings demonstrate the dual function of BiSPI, which acts as a microbicidal peptide and anti-fibrinolytic venom toxin.

The Remarkable Innate Resistance of Burkholderia bacteria to Cationic Antimicrobial Peptides: Insights into the Mechanism of AMP Resistance

Gram-negative bacteria belonging to the genus Burkholderia are remarkably resistant to broad-spectrum, cationic, antimicrobial peptides (AMPs). It has been proposed that this innate resistance is related to changes in the outer membrane lipopolysaccharide (OM LPS), including the constitutive, essential modification of outer membrane Lipid A phosphate groups with cationic 4-amino-4-deoxy-arabinose. This modification reduces the overall negative charge on the OM LPS which may change the OM structure and reduce the binding, accumulation, and permeation of cationic AMPs. Similarly, the Gram-negative pathogen Pseudomonas aeruginosa can quickly become resistant to many AMPs by multiple mechanisms, frequently, including activation of the arn operon, which leads, transiently, to the same modification of Lipid A. We recently discovered a set of synthetically evolved AMPs that do not invoke any resistance in P. aeruginosa over multiple passages and thus are apparently not inhibited by aminorabinosylation of Lipid A in P. aeruginosa. Here we test these resistance-avoiding peptides, within a set of 18 potent AMPs, against Burkholderia thailandensis. We find that none of the AMPs tested have measurable activity against B. thailandensis. Some were inactive at concentrations as high as 150 μM, despite all having sterilizing activity at ≤ 10 μM against a panel of common, human bacterial pathogens, including P. aeruginosa. We speculate that the constitutive modification of Lipid A in members of the Burkholderia genus is only part of a broader set of modifications that change the architecture of the OM to provide such remarkable levels of resistance to cationic AMPs.

The capsule of Bacillus anthracis protects it from the bactericidal activity of human defensins and other cationic antimicrobial peptides

During infection, Bacillus anthracis bacilli encounter potent antimicrobial peptides (AMPs) such as defensins. We examined the role that B. anthracis capsule plays in protecting bacilli from defensins and other cationic AMPs by comparing their effects on a fully virulent encapsulated wild type (WT) strain and an isogenic capsule-deficient capA mutant strain. We identified several human defensins and non-human AMPs that were capable of killing B. anthracis. The human alpha defensins 1–6 (HNP-1-4, HD-5-6), the human beta defensins 1–4 (HBD-1-4), and the non-human AMPs, protegrin, gramicidin D, polymyxin B, nisin, and melittin were all capable of killing both encapsulated WT and non-encapsulated capA mutant B. anthracis. However, non-encapsulated capA mutant bacilli were significantly more susceptible than encapsulated WT bacilli to killing by nearly all of the AMPs tested. We demonstrated that purified capsule bound HBD-2, HBD-3, and HNP-1 in an electrophoretic mobility shift assay. Furthermore, we determined that the capsule layer enveloping WT bacilli bound and trapped HBD-3, substantially reducing the amount reaching the cell wall. To assess whether released capsule might also play a protective role, we pre-incubated HBD-2, HBD-3, or HNP-1 with purified capsule before their addition to non-encapsulated capA mutant bacilli. We found that free capsule completely rescued the capA mutant bacilli from killing by HBD-2 and -3 while killing by HNP-1 was reduced to the level observed with WT bacilli. Together, these results suggest an immune evasion mechanism by which the capsule, both that enveloping the bacilli and released fragments, contributes to virulence by binding to and inhibiting the antimicrobial activity of cationic AMPs.

Bacillus anthracis causes anthrax after spores infect the skin, respiratory tract, or gastrointestinal tract. Antimicrobial peptides (AMPs), such as defensins, are a first line of host defense that B. anthracis encounters in all of these tissues. B. anthracis bacteria are covered by a capsule that protects them from being engulfed and destroyed by phagocytic immune cells. In this study, we found that the capsule also provides protection from AMPs. An encapsulated B. anthracis strain is resistant to killing by multiple AMPs from humans and other species compared to an otherwise identical strain that is not encapsulated. By binding defensins the capsule surrounding the bacilli reduces the amount that gets to the bacterial cell wall where it can do damage. B. anthracis bacteria release large fragments of capsule in the host during infection and during growth in culture. We found that purified released capsule can bind defensins and reduce killing of non-encapsulated B. anthracis. Thus, both capsule covering the bacteria and capsule shed by the bacteria can contribute to the pathogenicity of B. anthracis by providing protection from AMPs. Our study reveals a new mechanism by which B. anthracis capsule contributes to virulence.

Role of Antimicrobial Peptides in Treatment and Prevention of Mycobacterium Tuberculosis: A Review

Tuberculosis (TB) is one of the leading cause of death worldwide, and the world is fighting with this global health emergency from the past 25 year. The current clinical interventions for the management of TB face a number of inherent challenges which includes low patient compliance due to the long therapy regimen, and emerging antimicrobial resistance. Therefore, there is an unmet need of new anti-TB therapeutic agent with enhanced safety profile, which can reduce the duration of therapy, enhanced bioavailability and efficacy against drug resistant forms of TB. Bacteriocins or anti microbial peptides (AMPs) occurring in microbes, human beings and other life forms have been investigated as host defense peptides. Structurally AMPs are short and ionized and play crucial role in innate immunity of host. Some AMPs can kill microbial infections directly while others function indirectly by altering the host defense mechanisms. Amidst rising issue of antibiotic resistance, AMPs are being tested in clinical research as potential antibiotics and novel therapeutics to fight against infections and non-infectious diseases. Studies have also highlighted the ability of AMPs to act against the bacteria spreading tuberculosis. The present review provides information on antimicrobial peptides, highlights their biological role, classification and mode of action in treatment and prevention of tuberculosis. It further mentions the prospects and challenges of developing peptides for their therapeutic applications against mycobacterium tuberculosis.

Structural analysis of the peptides temporin-Ra and temporin-Rb and interactions with model membranes

The skin of amphibians is widely exploited as rich sources of membrane active peptides that differ in chain size, polypeptide net charge, secondary structure, target selectivity and toxicity. In this study, two small antimicrobial peptides, temporin-Ra and temporin-Rb, originally isolated from the skin of the European marsh frog (Rana ridibunda), described as active against pathogen bacteria and presenting low toxicity to eukaryotic cells were synthesized and had their physicochemical properties and mechanism of action investigated. The temporin peptides were examined in aqueous solution and in the presence of membrane models (lipid monolayers, micelles, lipid bilayers and vesicles). A combined approach of bioinformatics analyses, biological activity assays, surface pressure measurements, synchrotron radiation circular dichroism spectroscopy, and oriented circular dichroism spectroscopy were employed. Both peptides were able to adsorb at a lipid-air interface with a negative surface charge density, and efficiently disturb the lipid surface packing. A disorder-to-helix transition was observed on the secondary structure of both peptides when either in a non-polar environment or interacting with model membranes containing a negative net charge density. The binding of both temporin-Ra and temporin-Rb to membrane models is modulated by the presence of negatively charged lipids in the membrane. The amphipathic helix induced in temporin-Ra is oriented parallel to the membrane surface in negatively charged or in zwitterionic lipid bilayers, with no tendency for realignment after binding. Temporin-Rb, instead, assumes a β-sheet conformation when deposited into oriented stacked lipid bilayers. Due to their short size and simple composition, both peptides are quite attractive for the development of new classes of peptide-based anti-infective drugs.

Antimicrobial Peptides in Early-Life Host Defense, Perinatal Infections, and Necrotizing Enterocolitis—An Update

Host defense against early-life infections such as chorioamnionitis, neonatal sepsis, or necrotizing enterocolitis (NEC) relies primarily on innate immunity, in which antimicrobial peptides (AMPs) play a major role. AMPs that are important for the fetus and neonate include α and β defensins, cathelicidin LL-37, antiproteases (elafin, SLPI), and hepcidin. They can be produced by the fetus or neonate, the placenta, chorioamniotic membranes, recruited neutrophils, and milk-protein ingestion or proteolysis. They possess antimicrobial, immunomodulating, inflammation-regulating, and tissue-repairing properties. AMPs are expressed as early as the 13th week and increase progressively through gestation. Limited studies are available on AMP expression and levels in the fetus and neonate. Nevertheless, existing evidence supports the role of AMPs in pathogenesis of chorioamnionitis, neonatal sepsis, and NEC, and their association with disease severity. This suggests a potential role of AMPs in diagnosis, prevention, prognosis, and treatment of sepsis and NEC. Herein, we present an overview of the antimicrobial and immunomodulating properties of human AMPs, their sources in the intrauterine environment, fetus, and neonate, and their changes during pre- and post-natal infections and NEC. We also discuss emerging data regarding the potential utility of AMPs in early-life infections, as diagnostic or predictive biomarkers and as therapeutic alternatives or adjuncts to antibiotic therapy considering the increase of antibiotic resistance in neonatal intensive care units.

Examining Topoisomers of a Snake-Venom-Derived Peptide for Improved Antimicrobial and Antitumoral Properties

Ctn[15-34], the C-terminal section of crotalicidin (Ctn), a cathelicidin from a South American pit viper, is an antimicrobial and antitumoral peptide with remarkably longer stability in human serum than the parent Ctn. In this work, a set of topoisomers of both Ctn and Ctn[15-34], including the retro, enantio, and retroenantio versions, were synthesized and tested to investigate the structural requirements for activity. All topoisomers were as active as the cognate sequences against Gram-negative bacteria and tumor cells while slightly more toxic towards normal cells. More importantly, the enhanced serum stability of the D-amino-acid-containing versions suggests that such topoisomers must be preferentially considered as future antimicrobial and anticancer peptide leads.

Antibacterial properties of lactoferrin: A bibliometric analysis from 2000 to early 2022

Background

Here, a bibliometric and knowledge map analysis are used to analyze the research hot spots and development trends regarding the antibacterial effect of lactoferrin (LF). By looking for research hot spots and new topics, we provide new clues and research directions for future research.

Methods

Articles and reviews regarding the antibacterial effect of LF were retrieved and from the Web of Science Core Collection (WoSCC) on 25 June 2022. CiteSpace and VOSviewer were used to conduct the bibliometric and knowledge map analysis.

Results

In total, 8,292 authors at 2,151 institutions from 86 countries published 1,923 articles in 770 academic journals. The United States was the leader regarding research on the antibacterial effects of LF, while the Netherlands was a pioneer in conducting research in this field. The University of California system contributed the most publications. Bolscher JGM published most articles, while Wayne Bellamy had most cocitations. However, there was insufficient cooperation among the various institutions and authors. BioMetals published most LF-antibacterial activity-related articles, whereas Infection and Immunity was most commonly cocited journal. The most influential research hot spots about the antibacterial effect of LF focused on antimicrobial peptides, casein, human milk, expression, and Escherichia coli-related research. The latest hot spots and research frontier included COVID-19, antibiofilm activity, and immune defense.

Conclusions

LF is a multifunctional protein with a broad spectrum of antimicrobial activities. The related field of antibacterial properties of LF will remain a research hot spot in future.