Short KR-12 analogs designed from human cathelicidin LL-37 possessing both antimicrobial and antiendotoxic activities without mammalian cell toxicity

LL37 Microspheres Loaded on Activated Carbon-chitosan Hydrogel: Anti-bacterial and Anti-toxin Wound Dressing for Chronic Wound Infections

Antimicrobial peptide LL37 is a promising antibacterial candidate due to its potent antimicrobial activity with no known bacterial resistance. However, intrinsically LL37 is susceptible to degradation in wound fluids limits its effectiveness. Bacterial toxins which are released after cell lysis are found to hinder wound healing. To address these challenges, encapsulating LL37 in microspheres (MS) and loading the MS onto activated carbon (AC)-chitosan (CS) hydrogel. This advanced wound dressing not only protects LL37 from degradation but also targets bacterial toxins, aiding in the healing of chronic wound infections. First, LL37 MS and LL37-AC-CS hydrogel were prepared and characterised in terms of physicochemical properties, drug release, and peptide-polymer compatibility. Antibacterial and antibiofilm activity, bacterial toxin elimination, cell migration, and cell cytotoxicity activities were investigated. LL37-AC-CS hydrogel was effective against Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus. LL37-AC-CS hydrogel bound more endotoxin than AC with CS hydrogel alone. The hydrogel also induced cell migration after 72 h and showed no cytotoxicity towards NHDF after 72 h of treatment. In conclusion, the LL37-AC-CS hydrogel was shown to be a stable, non-toxic advanced wound dressing method with enhanced antimicrobial and antitoxin activity, and it can potentially be applied to chronic wound infections to accelerate wound healing.

Methods to improve antibacterial properties of PEEK: A review

As a thermoplastic and bioinert polymer, polyether ether ketone (PEEK) serves as spine implants, femoral stems, cranial implants, and joint arthroplasty implants due to its mechanical properties resembling the cortical bone, chemical stability, and radiolucency. Although there are standards and antibiotic treatments for infection control during and after surgery, the infection risk is lowered but can not be eliminated. The antibacterial properties of PEEK implants should be improved to provide better infection control. This review includes the strategies for enhancing the antibacterial properties of PEEK in four categories: immobilization of functional materials and functional groups, forming nanocomposites, changing surface topography, and coating with antibacterial material. The measuring methods of antibacterial properties of the current studies of PEEK are explained in detail under quantitative, qualitative, andin vivomethods. The mechanisms of bacterial inhibition by reactive oxygen species generation, contact killing, trap killing, and limited bacterial adhesion on hydrophobic surfaces are explained with corresponding antibacterial compounds or techniques. The prospective analysis of the current studies is done, and dual systems combining osteogenic and antibacterial agents immobilized on the surface of PEEK are found the promising solution for a better implant design.

Functionalization of Bacterial Cellulose with the Antimicrobial Peptide KR-12 via Chimerical Cellulose-Binding Peptides

Bacterial-derived cellulose (BC) has been studied as a promising material for biomedical applications, including wound care, due to its biocompatibility, water-holding capacity, liquid/gas permeability, and handleability properties. Although BC has been studied as a dressing material for cutaneous wounds, to date, BC inherently lacks antibacterial properties. The current research utilizes bifunctional chimeric peptides containing carbohydrate binding peptides (CBP; either a short version or a long version) and an antimicrobial peptide (AMP), KR-12. The secondary structure of the chimeric peptides was evaluated and confirmed that the α-helix structure of KR-12 was retained for both chimeric peptides evaluated (Long-CBP-KR12 and Short-CBP-KR12). Chimeric peptides and their individual components were assessed for cytotoxicity, where only higher concentrations of Short-CBP and longer timepoints of Short-CBP-KR12 exposure exhibited negative effects on metabolic activity, which was attributed to solubility issues. All KR-12-containing peptides exhibited antibacterial activity in solution against Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa). The lipopolysaccharide (LPS) binding capability of the peptides was evaluated and the Short-CBP-KR12 peptide exhibited enhanced LPS-binding capabilities compared to KR-12 alone. Both chimeric peptides were able to bind to BC and were observed to be retained on the surface over a 7-day period. All functionalized materials exhibited no adverse effects on the metabolic activity of both normal human dermal fibroblasts (NHDFs) and human epidermal keratinocyte (HaCaT) epithelial cells. Additionally, the BC tethered chimeric peptides exhibited antibacterial activity against E. coli. Overall, this research outlines the design and evaluation of chimeric CBP-KR12 peptides for developing antimicrobial BC membranes with potential applications in wound care.

Turning cationic antimicrobial peptide KR-12 into self-assembled nanobiotics with potent bacterial killing and LPS neutralizing activities

Gram-negative sepsis has become a substantial and escalating global healthcare challenge due to the growing antibiotic resistance crisis and the sluggish development of new antibiotics. LL-37, a unique Cathelicidin species found in humans, exhibits a wide range of bioactive properties, including direct bactericidal effects, inflammation regulation, and LPS neutralization. KR-12, the smallest yet potent peptide fragment of LL-37, has been modified to create more effective antimicrobials. In this study, we designed two myristoylated derivatives of KR-12, referred to as Myr-KR-12N and Myr-KR-12C. These derivatives displayed remarkable ability to spontaneously assemble into nanoparticles when mixed with deionized water. Myristoylated KR-12 derivatives exhibited broad-spectrum and intensified bactericidal activity by disrupting bacterial cell membranes. In particular, Myr-KR-12N showed superior capability to rescue mice from lethal E. coli-induced sepsis in comparison with the conventional antibiotic meropenem. We also confirmed that the myristoylated KR-12 nanobiotic possesses significant LPS binding capacity and effectively reduces inflammation in vitro. In an in vivo context, Myr-KR-12N outperformed polymyxin B in rescuing mice from LPS-induced sepsis. Crucially, toxicological assessments revealed that neither Myr-KR-12N nor Myr-KR-12C nanobiotics induced meaningful hemolysis or caused damage to the liver and kidneys. Collectively, our study has yielded an innovative nanobiotic with dual capabilities of bactericidal action and LPS-neutralization, offering substantial promise for advancing the clinical translation of antimicrobial peptides and the development of novel antibiotics. This addresses the critical need for effective solutions to combat Gram-negative sepsis, a pressing global medical challenge.

Self-Entrapment of Antimicrobial Peptides in Silica Particles for Stable and Effective Antimicrobial Peptide Delivery System

Antimicrobial peptides (AMPs) have emerged as a promising solution to tackle bacterial infections and combat antibiotic resistance. However, their vulnerability to protease degradation and toxicity towards mammalian cells has hindered their clinical application. To overcome these challenges, our study aims to develop a method to enhance the stability and safety of AMPs applicable to effective drug-device combination products. The KR12 antimicrobial peptide was chosen, and in order to further enhance its delivery and efficacy the human immunodeficiency virus TAT protein-derived cell-penetrating peptide (CPP) was fused to form CPP-KR12. A new product, CPP-KR12@Si, was developed by forming silica particles with self-entrapped CPP-KR12 peptide using biomimetic silica precipitability because of its cationic nature. Peptide delivery from CPP-KR12@Si to bacteria and cells was observed at a slightly delivered rate, with improved stability against trypsin treatment and a reduction in cytotoxicity compared to CPP-KR12. Finally, the antimicrobial potential of the CPP-KR12@Si/bone graft substitute (BGS) combination product was demonstrated. CPP-KR12 is coated in the form of submicron-sized particles on the surface of the BGS. Self-entrapped AMP in silica nanoparticles is a safe and effective AMP delivery method that will be useful for developing a drug-device combination product for tissue regeneration.

Why to target G-quadruplexes using peptides: Next-generation G4-interacting ligands

Guanine-rich oligonucleotides existing in both DNA and RNA are able to fold into four-stranded DNA secondary structures via Hoogsteen type hydrogen-bonding, where four guanines self-assemble into a square planar arrangement, which, when stacked upon each other, results in the formation of higher-order structures called G-quadruplexes. Their distribution is not random; they are more frequently present at telomeres, proto-oncogenic promoters, introns, 5'- and 3'-untranslated regions, stem cell markers, ribosome binding sites and so forth and are associated with various biological functions, all of which play a pivotal role in various incurable diseases like cancer and cellular ageing. Several studies have suggested that G-quadruplexes could not regulate biological processes by themselves; instead, various proteins take part in this regulation and can be important therapeutic targets. There are certain limitations in using whole G4-protein for therapeutics purpose because of its high manufacturing cost, laborious structure prediction, dynamic nature, unavailability for oral administration due to its degradation in the gut and inefficient penetration to reach the target site because of the large size. Hence, biologically active peptides can be the potential candidates for therapeutic intervention instead of the whole G4-protein complex. In this review, we aimed to clarify the biological roles of G4s, how we can identify them throughout the genome via bioinformatics, the proteins interacting with G4s and how G4-interacting peptide molecules may be the potential next-generation ligands for targeting the G4 motifs located in biologically important regions.

Antimicrobial and Antibiofilm Activity of Synthetic Peptide [W7]KR12-KAEK Against Enterococcus faecalis Strains

The emergence of infections caused by microorganisms in the oral cavity and increasing concerns regarding the use of antibiotics have resulted in the development of novel antimicrobial molecules, such as antimicrobial synthetic peptides. The purpose of this study was to evaluate the antimicrobial and antibiofilm activities of the native peptide KR-12 and its derivative, the synthetic peptide [W7]KR12-KAEK, against planktonic and biofilms Enterococcus faecalis strains. The methods used to evaluate the antimicrobial activity in planktonic cultures include minimum inhibitory concentration and minimum bactericidal concentration assays. The effects of [W7]KR12-KAEK on biofilm formation and mature biofilms were evaluated by quantifying biomass (crystal violet staining) and counting colony-forming units. Structural assessments of the biofilms and cellular morphological changes were performed using scanning electron microscopy. Peptide [W7]KR12-KAEK showed potential antimicrobial activity against planktonic cells. Interestingly, the native peptide KR-12 showed no antimicrobial activity. Moreover, it inhibited biofilm formation and disrupted the mature biofilms of E. faecalis strains. These results suggest that [W7]KR12-KAEK may be a potential molecule for the development of auxiliary antimicrobial therapies against oral infections.

Dual functional therapeutics: mitigating bacterial infection and associated inflammation

The emergence of antimicrobial resistance, coupled with the occurrence of persistent systemic infections, has already complicated clinical therapy efforts. Moreover, infections are also accompanied by strong inflammatory responses, generated by the host's innate and adaptive immune systems. The closely intertwined relationship between bacterial infection and inflammation has multiple implications on the ability of antibacterial therapeutics to tackle infection and inflammation. Particularly, uncontrolled inflammatory responses to infection can lead to sepsis, a life-threatening physiological condition. In this review, we discuss dual-functional antibacterial therapeutics that have potential to be developed for treating inflammation associated with bacterial infections. Immense research is underway that aims to develop new therapeutic agents that, when administered, regulate the excess inflammatory response, i.e. they have immunomodulatory properties along with the desired antibacterial activity. The classes of antibiotics that have immunomodulatory function in addition to antibacterial activity have been reviewed. Host defense peptides and their synthetic mimics are amongst the most sought-after solutions to develop such dual-functional therapeutics. This review also highlights the important classes of peptidomimetics that exhibit both antibacterial and immunomodulatory properties.

Phosphorylcholine and KR12-Containing Corneal Implants in HSV-1-Infected Rabbit Corneas

Severe HSV-1 infection can cause blindness due to tissue damage from severe inflammation. Due to the high risk of graft failure in HSV-1-infected individuals, cornea transplantation to restore vision is often contraindicated. We tested the capacity for cell-free biosynthetic implants made from recombinant human collagen type III and 2-methacryloyloxyethyl phosphorylcholine (RHCIII-MPC) to suppress inflammation and promote tissue regeneration in the damaged corneas. To block viral reactivation, we incorporated silica dioxide nanoparticles releasing KR12, the small bioactive core fragment of LL37, an innate cationic host defense peptide produced by corneal cells. KR12 is more reactive and smaller than LL37, so more KR12 molecules can be incorporated into nanoparticles for delivery. Unlike LL37, which was cytotoxic, KR12 was cell-friendly and showed little cytotoxicity at doses that blocked HSV-1 activity in vitro, instead enabling rapid wound closure in cultures of human epithelial cells. Composite implants released KR12 for up to 3 weeks in vitro. The implant was also tested in vivo on HSV-1-infected rabbit corneas where it was grafted by anterior lamellar keratoplasty. Adding KR12 to RHCIII-MPC did not reduce HSV-1 viral loads or the inflammation resulting in neovascularization. Nevertheless, the composite implants reduced viral spread sufficiently to allow stable corneal epithelium, stroma, and nerve regeneration over a 6-month observation period.

KR-12 Derivatives Endow Nanocellulose with Antibacterial and Anti-Inflammatory Properties: Role of Conjugation Chemistry

This work combines the wound-healing-related properties of the host defense peptide KR-12 with wood-derived cellulose nanofibrils (CNFs) to obtain bioactive materials, foreseen as a promising solution to treat chronic wounds. Amine coupling through carbodiimide chemistry, thiol-ene click chemistry, and Cu(I)-catalyzed azide-alkyne cycloaddition were investigated as methods to covalently immobilize KR-12 derivatives onto CNFs. The effects of different coupling chemistries on the bioactivity of the KR12-CNF conjugates were evaluated by assessing their antibacterial activities against Escherichia coli and Staphylococcus aureus. Potential cytotoxic effects and the capacity of the materials to modulate the inflammatory response of lipopolysaccharide (LPS)-stimulated RAW 245.6 macrophages were also investigated. The results show that KR-12 endowed CNFs with antibacterial activity against E. coli and exhibited anti-inflammatory properties and those conjugated by thiol-ene chemistry were the most bioactive. This finding is attributed to a favorable peptide conformation and accessibility (as shown by molecular dynamics simulations), driven by the selective chemistry and length of the linker in the conjugate. The results represent an advancement in the development of CNF-based materials for chronic wound care. This study provides new insights into the effect of the conjugation chemistry on the bioactivity of immobilized host defense peptides, which we believe to be of great value for the use of host defense peptides as therapeutic agents.

Recent Advances in Antimicrobial Peptide Hydrogels

Advances in the number and type of available biomaterials have improved medical devices such as catheters, stents, pacemakers, prosthetic joints, and orthopedic devices. The introduction of a foreign material into the body comes with a risk of microbial colonization and subsequent infection. Infections of surgically implanted devices often lead to device failure, which leads to increased patient morbidity and mortality. The overuse and improper use of antimicrobials has led to an alarming rise and spread of drug-resistant infections. To overcome the problem of drug-resistant infections, novel antimicrobial biomaterials are increasingly being researched and developed. Hydrogels are a class of 3D biomaterials consisting of a hydrated polymer network with tunable functionality. As hydrogels are customizable, many different antimicrobial agents, such as inorganic molecules, metals, and antibiotics have been incorporated or tethered to them. Due to the increased prevalence of antibiotic resistance, antimicrobial peptides (AMPs) are being increasingly explored as alternative agents. AMP-tethered hydrogels are being increasingly examined for antimicrobial properties and practical applications, such as wound-healing. Here, we provide a recent update, from the last 5 years of innovations and discoveries made in the development of photopolymerizable, self-assembling, and AMP-releasing hydrogels.

A novel designed membrane-active peptide for the control of foodborne Salmonella enterica serovar Typhimurium

The main cause of non-typhoidal Salmonella (NTS) infection in humans is ingestion of contaminated animal-derived foods such as eggs, poultry and dairy products. These infections highlight the need to develop new preservatives to increase food safety. Antimicrobial peptides (AMPs) have the potential to be further developed as food preservative agents and join nisin, the only AMP currently approved, for use as a preservative in food. Acidocin J1132β, a bacteriocin produced by probiotic Lactobacillus acidophilus, displays no toxicity to humans, however it exhibits only low and narrow-spectrum antimicrobial activity. Accordingly, four peptide derivatives (A5, A6, A9, and A11) were modified from acidocin J1132β by truncation and amino acid substitution. Among them, A11 showed the most antimicrobial activity, especially against S. Typhimurium, as well as a favorable safety profile. It tended to form an α-helix structure upon encountering negatively charged-mimicking environments. A11 caused transient membrane permeabilization and killed bacterial cells through membrane depolarization and/or intracellular interactions with bacterial DNA. A11 maintained most of its inhibitory effects when heated, even when exposed to temperatures up to 100 °C. Notably, it inhibited drug-resistant S. Typhimurium and its monophasic variant strains. Furthermore, the combination of A11 and nisin was synergistic against drug-resistant strains in vitro. Taken together, this study indicated that a novel antimicrobial peptide derivative (A11), modified from acidocin J1132β, has the potential to be a bio-preservative to control S. Typhimurium contamination in the food industry.

Transforming Cross-Linked Cyclic Dimers of KR-12 into Stable and Potent Antimicrobial Drug Leads

Is it possible to enhance structural stability and biological activity of KR-12, a truncated antimicrobial peptide derived from the human host defense peptide LL-37? Based on the mapping of essential residues in KR-12, we have designed backbone-cyclized dimers, cross-linked via a disulfide bond to improve peptide stability, while at the same time improving on-target activity. Circular dichroism showed that each of the dimers adopts a primarily alpha-helical conformation (55% helical content) when bound to lyso-phosphatidylglycerol micelles, indicating that the helical propensity of the parent peptide is maintained in the new cross-linked cyclic form. Compared to KR-12, one of the cross-linked dimers showed 16-fold more potent antimicrobial activity against human pathogens Pseudomonas aeruginosa, Staphylococcus aureus, and Candida albicans and 8-fold increased activity against Escherichia coli. Furthermore, these peptides retained antimicrobial activity at physiologically relevant conditions, including in the presence of salts and in human serum, and with selective Gram-negative antibacterial activity in rich growth media. In addition to giving further insight into the structure-activity relationship of KR-12, the current work demonstrates that by combining peptide stabilization strategies (dimerization, backbone cyclization, and cross-linking via a disulfide bond), KR-12 can be engineered into a potent antimicrobial peptide drug lead with potential utility in a therapeutic context.

Synergy by Perturbing the Gram-Negative Outer Membrane: Opening the Door for Gram-Positive Specific Antibiotics

New approaches to target antibacterial agents toward Gram-negative bacteria are key, given the rise of antibiotic resistance. Since the discovery of polymyxin B nonapeptide as a potent Gram-negative outer membrane (OM)-permeabilizing synergist in the early 1980s, a vast amount of literature on such synergists has been published. This Review addresses a range of peptide-based and small organic compounds that disrupt the OM to elicit a synergistic effect with antibiotics that are otherwise inactive toward Gram-negative bacteria, with synergy defined as a fractional inhibitory concentration index (FICI) of <0.5. Another requirement for the inclusion of the synergists here covered is their potentiation of a specific set of clinically used antibiotics: erythromycin, rifampicin, novobiocin, or vancomycin. In addition, we have focused on those synergists with reported activity against Gram-negative members of the ESKAPE family of pathogens namely, Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, and/or Acinetobacter baumannii. In cases where the FICI values were not directly reported in the primary literature but could be calculated from the published data, we have done so, allowing for more direct comparison of potency with other synergists. We also address the hemolytic activity of the various OM-disrupting synergists reported in the literature, an effect that is often downplayed but is of key importance in assessing the selectivity of such compounds for Gram-negative bacteria.

Linearized teixobactin is inactive and after sequence enhancement, kills methicillin-resistant Staphylococcus aureus via a different mechanism

Staphylococcus aureus is a highly adaptable pathogen that can rapidly develop resistance to conventional antibiotics such as penicillin. Recently, teixobactin was discovered from uncultivated soil bacteria by using the i-chip technology. This depsipeptide forms an ester bond between the backbone C-terminal isoleucine carboxylic acid and the hydroxyl group of threonine at position 8. Also, it contains multiple nonstandard amino acids, making it costly to synthesize. This study reports new peptides designed by linearizing teixobactin. After linearization and conversion to normal amino acids, teixobactin lost its antibacterial activity. Using this inactive template, a series of peptides were designed via hydrophobic patching and residue replacements. Three out of the five peptides were active. YZ105, only active against Gram-positive bacteria, however, showed the highest cell selectivity index. Different from teixobactin, which inhibits cell wall synthesis, YZ105 targeted the membranes of methicillin-resistant S. aureus (MRSA) based on kinetic killing, membrane permeation, depolarization, and scanning electron microscopy studies. Moreover, YZ105 could kill nafcillin-resistant MRSA, Staphylococcal clinical strains, and disrupted preformed biofilms. Taken together, YZ105, with a simpler sequence, is a promising lead for developing novel anti-MRSA agents.

Atomic-Resolution Structures and Mode of Action of Clinically Relevant Antimicrobial Peptides

Global rise of infections and deaths caused by drug-resistant bacterial pathogens are among the unmet medical needs. In an age of drying pipeline of novel antibiotics to treat bacterial infections, antimicrobial peptides (AMPs) are proven to be valid therapeutics modalities. Direct in vivo applications of many AMPs could be challenging; however, works are demonstrating encouraging results for some of them. In this review article, we discussed 3-D structures of potent AMPs e.g., polymyxin, thanatin, MSI, protegrin, OMPTA in complex with bacterial targets and their mode of actions. Studies on human peptide LL37 and de novo-designed peptides are also discussed. We have focused on AMPs which are effective against drug-resistant Gram-negative bacteria. Since treatment options for the infections caused by super bugs of Gram-negative bacteria are now extremely limited. We also summarize some of the pertinent challenges in the field of clinical trials of AMPs.

A novel hybrid peptide composed of LfcinB6 and KR-12-a4 with enhanced antimicrobial, anti-inflammatory and anti-biofilm activities

Hybridizing two known antimicrobial peptides (AMPs) is a simple and effective strategy for designing antimicrobial agents with enhanced cell selectivity against bacterial cells. Here, we generated a hybrid peptide Lf-KR in which LfcinB6 and KR-12-a4 were linked with a Pro hinge to obtain a novel AMP with potent antimicrobial, anti-inflammatory, and anti-biofilm activities. Lf-KR exerted superior cell selectivity for bacterial cells over sheep red blood cells. Lf-KR showed broad-spectrum antimicrobial activities (MIC: 4–8 μM) against tested 12 bacterial strains and retained its antimicrobial activity in the presence of salts at physiological concentrations. Membrane depolarization and dye leakage assays showed that the enhanced antimicrobial activity of Lf-KR was due to increased permeabilization and depolarization of microbial membranes. Lf-KR significantly inhibited the expression and production of pro-inflammatory cytokines (nitric oxide and tumor necrosis factor‐α) in LPS-stimulated mouse macrophage RAW264.7 cells. In addition, Lf-KR showed a powerful eradication effect on preformed multidrug-resistant Pseudomonas aeruginosa (MDRPA) biofilms. We confirmed using confocal laser scanning microscopy that a large portion of the preformed MDRPA biofilm structure was perturbed by the addition of Lf-KR. Collectively, our results suggest that Lf-KR can be an antimicrobial, anti-inflammatory, and anti-biofilm candidate as a pharmaceutical agent.

How to Combat Gram-Negative Bacteria Using Antimicrobial Peptides: A Challenge or an Unattainable Goal?

Antimicrobial peptides (AMPs) represent a promising and effective alternative for combating pathogens, having some advantages compared to conventional antibiotics. However, AMPs must also contend with complex and specialised Gram-negative bacteria envelops. The variety of lipopolysaccharide and phospholipid composition in Gram-negative bacteria strains and species are decisive characteristics regarding their susceptibility or resistance to AMPs. Such biological and structural barriers have created delays in tuning AMPs to deal with Gram-negative bacteria. This becomes even more acute because little is known about the interaction AMP–Gram-negative bacteria and/or AMPs’ physicochemical characteristics, which could lead to obtaining selective molecules against Gram-negative bacteria. As a consequence, available AMPs usually have highly associated haemolytic and/or cytotoxic activity. Only one AMP has so far been FDA approved and another two are currently in clinical trials against Gram-negative bacteria. Such a pessimistic panorama suggests that efforts should be concentrated on the search for new molecules, designs and strategies for combating infection caused by this type of microorganism. This review has therefore been aimed at describing the currently available AMPs for combating Gram-negative bacteria, exploring the characteristics of these bacteria’s cell envelop hampering the development of new AMPs, and offers a perspective regarding the challenges for designing new AMPs against Gram-negative bacteria.

Targeted Delivery of Miconazole Employing LL37 Fragment Mutant Peptide CKR12-Poly (Lactic-Co-Glycolic) Acid Polymeric Micelles

We previously reported that conjugates of antimicrobial peptide fragment analogues and poly (lactic-co-glycolic) acid (PLGA) enhance antimicrobial activity and that the conjugated micelle structure is an effective tool for antimicrobial drug delivery. In recent years, the delivery of antimicrobial peptides to targets for antimicrobial activity has attracted attention. In this study, we targeted Candida albicans, a causative organism of catheter-related bloodstream infections, which is refractory to antimicrobial agents and is currently a problem in medical practice. We evaluated the antifungal activity of CKR12 (a mutant fragment of the human cathelicidin peptide, LL-37)-PLGA-miconazole (MCZ) micelles using nanotechnology with MCZ delivery. The prepared CKR12-PLGA-MCZ micelles were characterised by measuring dynamic light scattering, zeta potential, dilution stability, and drug release. CKR12-PLGA-MCZ micelles showed higher antifungal activity than CKR12-PLGA micelles and MCZ solution. Furthermore, scanning and transmission electron microscopy suggested that CKR12-PLGA-MCZ micelles disrupted both cell wall and cell membrane of C. albicans. Our results revealed a synergistic effect of antifungal activity using a combination of antimicrobial peptide fragment analogues and MCZ, and that MCZ is a promising tool for the delivery to target microorganisms.

Designed Trp-Cage Proteins with Antimicrobial Activity and Enhanced Stability

α-Helical antimicrobial peptides (αAMPs) are among the potential candidates for new anti-infectives to tackle the global crisis in antibiotic resistance, but they suffer from low bioavailability due to high susceptibility to enzymatic degradation. Here, we describe a strategy to increase the resistance of αAMPs against proteases. Fusing the 12-residue αAMP KR-12 with a Trp-cage domain induces an α-helical structure in the otherwise unfolded KR-12 moiety in solution. The resulting antimicrobial Trp-cage exhibits higher proteolytic resistance due to its stable fold as evidenced by correlating sequence-resolved digest data with structural analyses. In addition, the antimicrobial Trp-cage displays increased activity against bacteria in the presence of physiologically relevant concentrations of NaCl, while the hemolytic activity remains negligible. In contrast to previous strategies, the presented approach is not reliant on artificial amino acids and is therefore applicable to biosynthetic procedures. Our study aims to improve the pharmacokinetics of αAMPs to facilitate their use as therapeutics.

Physical behavior of KR-12 peptide on solid surfaces and Langmuir-Blodgett lipid films: Complementary approaches to its antimicrobial mode against S. aureus

Biophysical characterization of antimicrobial peptides helps to understand the mechanistic aspects of their action. The physical behavior of the KR-12 antimicrobial peptide (e.g. orientation and changes in secondary structure), was analyzed after interactions with a Staphylococcus aureus membrane model and solid surfaces. We performed antimicrobial tests using Gram-positive S. aureus (ATCC 25923) bacteria. Moreover, Langmuir-Blodgett experiments showed that the synthetic peptide can disturb the lipidic membrane at a concentration lower than the Minimum Inhibitory Concentration, thus confirming that KR-12/lipid interactions are involved. Partially- and fully-deactivated KR-12 hybrid samples were obtained by physisorption and covalent immobilization in chitosan/silica and glyoxal-rich solid supports. The correlation of Langmuir-Blodgett data with the α-helix formation, followed by FTIR-ATR in a frozen-like state, and the antimicrobial activity showed the importance of these interactions and conformation changes on the first step action mode of this peptide. This is the first time that material science (immobilization in solid surfaces assisted by FTIR-ATR analysis in frozen-like state) and physical (Langmuir-Blodgett/Schaefer) approaches are combined for exploring mechanistic aspects of the primary action mode of the KR-12 antimicrobial peptide against S. aureus.

Elucidating the mechanism by which synthetic helper peptides sensitize Pseudomonas aeruginosa to multiple antibiotics

The emergence and rapid spread of multi-drug resistant (MDR) bacteria pose a serious threat to the global healthcare. There is an urgent need for new antibacterial substances or new treatment strategies to deal with the infections by MDR bacterial pathogens, especially the Gram-negative pathogens. In this study, we show that a number of synthetic cationic peptides display strong synergistic antimicrobial effects with multiple antibiotics against the Gram-negative pathogen Pseudomonas aeruginosa. We found that an all-D amino acid containing peptide called D-11 increases membrane permeability by attaching to LPS and membrane phospholipids, thereby facilitating the uptake of antibiotics. Subsequently, the peptide can dissipate the proton motive force (PMF) (reducing ATP production and inhibiting the activity of efflux pumps), impairs the respiration chain, promotes the production of reactive oxygen species (ROS) in bacterial cells and induces intracellular antibiotics accumulation, ultimately resulting in cell death. By using a P. aeruginosa abscess infection model, we demonstrate enhanced therapeutic efficacies of the combination of D-11 with various antibiotics. In addition, we found that the combination of D-11 and azithromycin enhanced the inhibition of biofilm formation and the elimination of established biofilms. Our study provides a realistic treatment option for combining close-to-nature synthetic peptide adjuvants with existing antibiotics to combat infections caused by P. aeruginosa.

Cytocompatibility and Synergy of EGCG and Cationic Peptides Against Bacteria Related to Endodontic Infections, in Planktonic and Biofilm Conditions

This study evaluated the cytocompatibility and antimicrobial/antibiofilm effects of epigallocatechin-3-gallate (EGCG) associated with peptide LL-37 and its analogue KR-12-a5 against oral pathogens. The effect of the compounds on metabolism of fibroblasts was evaluated by methyltetrazolium assays. Antimicrobial activity of the compounds was evaluated on Streptococcus mutans, Enterococcus faecalis, Actinomyces israelii, and Fusobacterium nucleatum under planktonic conditions, on single- and dual-species biofilms and E. faecalis biofilms in dentinal tubules and analyzed by bacterial counts and confocal microscopy. Data were statistically analyzed considering p < 0.05. EGCG and peptide combinations were not toxic to fibroblasts. KR-12-a5 showed synergistic or addictive effects with EGCG and LL-37 against all bacteria tested. However, EGCG associated with KR-12-a5 demonstrated the highest bactericidal activity on all bacteria tested, at lower concentrations. In single-species biofilms, EGCG + KR-12-a5 eliminated S. mutans and A. israelii and reduced E. faecalis and F. nucleatum counts around 5 log CFU/mL. EGCG + KR-12-a5 reduced E. faecalis (-3.93 log CFU/mL) and eliminated S. mutans in dual-species biofilms. No growth of E. faecalis and significant reduction in A. israelii (-6.24 log CFU/mL) and F. nucleatum (-4.62 log CFU/mL) counts were detected in dual-species biofilms. The combination of EGCG and KR-12-a5 led to 88% of E. faecalis dead cells inside dentin tubules. The association of EGCG and KR-12-a5 was cytocompatible and promoted synergistic effect against biofilms of bacteria associated with endodontic infections.

The Impact of Lung Proteases on Snake-Derived Antimicrobial Peptides

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

Enhancing the anticancer efficacy of a LL-37 peptide fragment analog using peptide-linked PLGA conjugate micelles in tumor cells

LL-37, a well-known antimicrobial human peptide, is a cationic peptide that provides an important antimicrobial defense mechanism in damaged skin. Accumulating evidence indicates that LL-37 also displays an anticancer effect in colon cancer, gastric cancer, hematologic malignancy and oral squamous cell carcinoma. However, anticancer activity of LL-37 peptide fragment analogs has not been reported. Poor intercellular translocation may be one of the causes for this lack of observed anticancer activity. In this study, a LL-37 peptide fragment analog with cysteine at the N-terminus was conjugated with the biodegradable polymer, lactic acid/glycolic acid copolymer (PLGA), using the thiol group of cysteine. The purpose of this study was to improve the cell permeability of the peptide using a micellar system and then evaluate the anticancer activity. Cell proliferation, migration, and invasion assays were performed to evaluate the anticancer activity in four cancer cell lines with high metastasis, HM-1, B16/BL6, HeLa, and HepG2. The LL-37 fragment peptide analog-linked PLGA conjugate was shown to effectively inhibit cell proliferation, migration, and invasion and had increased cell permeability in all the cancer cell lines, compared with the peptide alone. These results suggested that LL-37 fragment peptide analog (CKR12)-linked PLGA conjugate micelles could be useful in the development of cancer therapeutics.

Short and Robust Anti-Infective Lipopeptides Engineered Based on the Minimal Antimicrobial Peptide KR12 of Human LL-37

This study aims to push the frontier of the engineering of human cathelicidin LL-37, a critical antimicrobial innate immune peptide that wards off invading pathogens. By sequential truncation of the smallest antibacterial peptide (KR12) of LL-37 and conjugation with fatty acids, with varying chain lengths, a library of lipopeptides is generated. These peptides are subjected to antibacterial activity and hemolytic assays. Candidates (including both forms made of l- and d-amino acids) with the optimal cell selectivity are subsequently fed to the second layer of in vitro filters, including salts, pH, serum, and media. These practices lead to the identification of a miniature LL-37 like peptide (d-form) with selectivity, stability, and robust antimicrobial activity in vitro against both Gram-positive and negative bacteria. Proteomic studies reveal far fewer serum proteins that bind to the d-form than the l-form peptide. C10-KR8d targets bacterial membranes to become helical, making it difficult for bacteria to develop resistance in a multiple passage experiment. In vivo, C10-KR8d is able to reduce bacterial burden of methicillin-resistant Staphylococcus aureus (MRSA) USA300 LAC in neutropenic mice. In addition, this designer peptide prevents bacterial biofilm formation in a catheter-associated mouse model. Meanwhile, C10-KR8d also recruits cytokines to the vicinity of catheters to clear infection. Thus, based on the antimicrobial region of LL-37, this study succeeds in identifying the smallest anti-infective peptide C10-KR8d with both robust antimicrobial, antibiofilm, and immune modulation activities.

The Potential of Human Peptide LL-37 as an Antimicrobial and Anti-Biofilm Agent

The rise in antimicrobial resistant bacteria threatens the current methods utilized to treat bacterial infections. The development of novel therapeutic agents is crucial in avoiding a post-antibiotic era and the associated deaths from antibiotic resistant pathogens. The human antimicrobial peptide LL-37 has been considered as a potential alternative to conventional antibiotics as it displays broad spectrum antibacterial and anti-biofilm activities as well as immunomodulatory functions. While LL-37 has shown promising results, it has yet to receive regulatory approval as a peptide antibiotic. Despite the strong antimicrobial properties, LL-37 has several limitations including high cost, lower activity in physiological environments, susceptibility to proteolytic degradation, and high toxicity to human cells. This review will discuss the challenges associated with making LL-37 into a viable antibiotic treatment option, with a focus on antimicrobial resistance and cross-resistance as well as adaptive responses to sub-inhibitory concentrations of the peptide. The possible methods to overcome these challenges, including immobilization techniques, LL-37 delivery systems, the development of LL-37 derivatives, and synergistic combinations will also be considered. Herein, we describe how combination therapy and structural modifications to the sequence, helicity, hydrophobicity, charge, and configuration of LL-37 could optimize the antimicrobial and anti-biofilm activities of LL-37 for future clinical use.

Antimicrobial Activities of LL-37 Fragment Mutant-Poly (Lactic-Co-Glycolic) Acid Conjugate against Staphylococcus aureus, Escherichia coli, and Candida albicans

Various peptides and their derivatives have been reported to exhibit antimicrobial activities. Although these activities have been examined against microorganisms, novel methods have recently emerged for conjugation of the biomaterials to improve their activities. Here, we prepared CKR12-PLGA, in which CKR12 (a mutated fragment of human cathelicidin peptide, LL-37) was conjugated with poly (lactic-co-glycolic) acid (PLGA), and compared the antimicrobial and antifungal activities of the conjugated peptide with those of FK13 (a small fragment of LL-37) and CKR12 alone. The prepared CKR12-PLGA was characterized by dynamic light scattering and measurement of the zeta potential, critical micellar concentration, and antimicrobial activities of the fragments and conjugate. Although CKR12 showed higher antibacterial activities than FK13 against Staphylococcus aureus and Escherichia coli, the antifungal activity of CKR12 was lower than that of FK13. CKR12-PLGA showed higher antibacterial activities against S. aureus and E. coli and higher antifungal activity against Candida albicans compared to those of FK13. Additionally, CKR12-PLGA showed no hemolytic activity in erythrocytes, and scanning and transmission electron microscopy suggested that CKR12-PLGA killed and disrupted the surface structure of microbial cells. Conjugation of antimicrobial peptide fragment analogues was a successful approach for obtaining increased microbial activity with minimized cytotoxicity.

Cytotoxicity and antimicrobial activity of synthetic peptides alone or in combination with conventional antimicrobials against fish pathogenic bacteria

AIMS

This study aimed to evaluate the in vitro cytotoxicity and efficacy of synthetic host defence peptides (HDPs), alone or in combination with florfenicol (FFC), oxytetracycline (OTC) or thiamphenicol (TAP), against different pathogenic bacteria isolated from diseased fish.

METHODS AND RESULTS

Solid-phase synthesis, purification and characterization of several HDPs were performed manually, using the fluorenylmethyloxycarbonyl protecting group in different resins and via high-performance liquid chromatography-mass spectrometry, respectively. The in vitro cytotoxicity and antimicrobial activity of HDPs, FFC, OTC and TAP against Nile tilapia red blood cells (RBCs) and relevant fish pathogenic bacteria (Aeromonas, Citrobacter, Edwardsiella, Streptococcus, Lactococcus and Vibrio) was determined using the haemolysis assay and broth microdilution method, respectively. The checkerboard assay was used to evaluate the synergy between the most active HDPs and other antimicrobials against the tested strains. MUC 7 12-mer, FFC, OTC and TAP were not cytotoxic to Nile tilapia RBCs, in all tested concentrations. LL-37, (p-BthTX-I)₂ and Hylin-a1 were not cytotoxic at concentrations up to 78·13, 19·53 and 9·77 μg ml^-1 , respectively. HDPs demonstrated potent antimicrobial activity (minimum inhibitory concentration ≤31·25 µg ml^-1 ) against Aeromonas jandaei (KR-12-a5), Citrobacter freundii (Kr-12-a5; (p-BthTX-I)₂ ; LL-37; and Hylin a1), Streptococcus agalactiae (Hylin a1; (p-BthTX-I)₂ and LL-37), Lactococcus garviae (Hylin a1), and Vibrio fluvialis (KR-12-a5). The combinations of (p-BthTX-I)₂ with TAP and LL-37 with FFC showed synergistic activity against C. freundii (fractional inhibitory concentration index of 0·25 and 0·50, respectively).

CONCLUSIONS

Synthetic HDPs have the potential as a good treatment option for bacterial diseases in aquaculture.

SIGNIFICANCE AND IMPACT OF THE STUDY

The in vivo effectiveness of synthetic HDPs such as KR-12-a5; LL-37; (p-BthTX-I)₂ and Hylin a1 can be tested alone or in combination with conventional antimicrobials as a treatment option to reduce the use of antimicrobials in aquaculture.

Outer-membrane-acting peptides and lipid II-targeting antibiotics cooperatively kill Gram-negative pathogens

The development and dissemination of antibiotic-resistant bacterial pathogens is a growing global threat to public health. Novel compounds and/or therapeutic strategies are required to face the challenge posed, in particular, by Gram-negative bacteria. Here we assess the combined effect of potent cell-wall synthesis inhibitors with either natural or synthetic peptides that can act on the outer-membrane. Thus, several linear peptides, either alone or combined with vancomycin or nisin, were tested against selected Gram-negative pathogens, and the best one was improved by further engineering. Finally, peptide D-11 and vancomycin displayed a potent antimicrobial activity at low μM concentrations against a panel of relevant Gram-negative pathogens. This combination was highly active in biological fluids like blood, but was non-hemolytic and non-toxic against cell lines. We conclude that vancomycin and D-11 are safe at >50-fold their MICs. Based on the results obtained, and as a proof of concept for the newly observed synergy, a Pseudomonas aeruginosa mouse infection model experiment was also performed, showing a 4 log₁₀ reduction of the pathogen after treatment with the combination. This approach offers a potent alternative strategy to fight (drug-resistant) Gram-negative pathogens in humans and mammals.

Anti-inflammatory and antibacterial effects of human cathelicidin active fragment KR-12 in the mouse models of colitis: a novel potential therapy of inflammatory bowel diseases

Introduction

Inflammatory bowel diseases (IBD) are a group of chronic gastrointestinal tract disorders with complex etiology, with intestinal dysbiosis as the most prominent factor. In this study, we assessed the anti-inflammatory and antibacterial actions of the human cathelicidin LL-37 and its shortest active fragment, KR-12 in the mouse models of colitis.

Materials and methods

Mouse models of colitis induced by 2,4,6-trinitrobenzenesulfonic acid (TNBS) and dextran sulfate sodium (DSS) were used in the study. The extent of inflammation was evaluated based on the macro- and microscopic scores, quantification of myeloperoxidase (MPO) activity and microbiological analysis of stool samples.

Results

A preliminary study with LL-37 and KR-12 (1 mg/kg, ip, twice daily) showed a decrease in macroscopic and ulcer scores in the acute TNBS-induced model of colitis. We observed that KR-12 (5 mg/kg, ip, twice daily) reduced microscopic and ulcer scores in the semi-chronic and chronic TNBS-induced models of colitis compared with inflamed mice. Furthermore, qualitative and quantitative changes in colonic microbiota were observed: KR-12 (5 mg/kg, ip, twice daily) decreased the overall number of bacteria, Escherichia coli and coli group bacteria. In the semi-chronic DSS-induced model, KR-12 attenuated intestinal inflammation as demonstrated by a reduction in macroscopic score and colon damage score and MPO activity.

Conclusions

We demonstrated that KR-12 alleviates inflammation in four different mouse models of colitis what suggests KR-12 and cathelicidins as a whole are worth being considered as a potential therapeutic option in the treatment of IBD.

Harnessing biomolecules for bioinspired dental biomaterials

Dental clinicians have relied for centuries on traditional dental materials (polymers, ceramics, metals, and composites) to restore oral health and function to patients. Clinical outcomes for many crucial dental therapies remain poor despite many decades of intense research on these materials. Recent attention has been paid to biomolecules as a chassis for engineered preventive, restorative, and regenerative approaches in dentistry. Indeed, biomolecules represent a uniquely versatile and precise tool to enable the design and development of bioinspired multifunctional dental materials to spur advancements in dentistry. In this review, we survey the range of biomolecules that have been used across dental biomaterials. Our particular focus is on the key biological activity imparted by each biomolecule toward prevention of dental and oral diseases as well as restoration of oral health. Additional emphasis is placed on the structure-function relationships between biomolecules and their biological activity, the unique challenges of each clinical condition, limitations of conventional therapies, and the advantages of each class of biomolecule for said challenge. Biomaterials for bone regeneration are not reviewed as numerous existing reviews on the topic have been recently published. We conclude our narrative review with an outlook on the future of biomolecules in dental biomaterials and potential avenues of innovation for biomaterial-based patient oral care.

Antimicrobial Peptides with Enhanced Salt Resistance and Antiendotoxin Properties

A strategy was described to design antimicrobial peptides (AMPs) with enhanced salt resistance and antiendotoxin activities by linking two helical AMPs with the Ala-Gly-Pro (AGP) hinge. Among the designed peptides, KR12AGPWR6 demonstrated the best antimicrobial activities even in high salt conditions (NaCl ~300 mM) and possessed the strongest antiendotoxin activities. These activities may be related to hydrophobicity, membrane-permeability, and α-helical content of the peptide. Amino acids of the C-terminal helices were found to affect the peptide-induced permeabilization of LUVs, the α-helicity of the designed peptides under various LUVs, and the LPS aggregation and size alternation. A possible model was proposed to explain the mechanism of LPS neutralization by the designed peptides. These findings could provide a new approach for designing AMPs with enhanced salt resistance and antiendotoxin activities for potential therapeutic applications.

Polydopamine Linking Substrate for AMPs: Characterisation and Stability on Ti6Al4V

Infections are common complications in joint replacement surgeries. Eradicated infections can lead to implant failure. In this paper, analogues of the peptide KR-12 derived from the human cathelicidin LL-37 were designed, synthesised, and characterised. The designed antimicrobial peptides (AMPs) were attached to the surface of a titanium alloy, Ti6Al4V, by conjugation to a polydopamine linking substrate. The topography of the polydopamine coating was evaluated by electron microscopy and coating thickness measurements were performed with ellipsometry and Atomic Force Microscopy (AFM). The subsequently attached peptide stability was investigated with release profile studies in simulated body fluid, using both fluorescence imaging and High-Performance Liquid Chromatography (HPLC). Finally, the hydrophobicity of the coating was characterised by water contact angle measurements. The designed AMPs were shown to provide long-term bonding to the polydopamine-coated Ti6Al4V surfaces.

Antimicrobial Peptides Display Strong Synergy with Vancomycin Against Vancomycin-Resistant E. faecium, S. aureus, and Wild-Type E. coli

There is an urgent and imminent need to develop new antimicrobials to fight against antibiotic-resistant bacterial and fungal strains. In this study, a checkerboard method was used to evaluate the synergistic effects of the antimicrobial peptide P-113 and its bulky non-nature amino acid substituted derivatives with vancomycin against vancomycin-resistant Enterococcus faecium, Staphylococcus aureus, and wild-type Escherichia coli. Boron-dipyrro-methene (BODIPY) labeled vancomycin was used to characterize the interactions between the peptides, vancomycin, and bacterial strains. Moreover, neutralization of antibiotic-induced releasing of lipopolysaccharide (LPS) from E. coli by the peptides was obtained. Among these peptides, Bip-P-113 demonstrated the best minimal inhibitory concentrations (MICs), antibiotics synergism, bacterial membrane permeabilization, and supernatant LPS neutralizing activities against the bacteria studied. These results could help in developing antimicrobial peptides that have synergistic activity with large size glycopeptides such as vancomycin in therapeutic applications.

Synergism between Host Defence Peptides and Antibiotics Against Bacterial Infections

Background:

Antimicrobial resistance (AMR) to conventional antibiotics is becoming one of the main global health threats and novel alternative strategies are urging. Antimicrobial peptides (AMPs), once forgotten, are coming back into the scene as promising tools to overcome bacterial resistance. Recent findings have attracted attention to the potentiality of AMPs to work as antibiotic adjuvants.

Methods:

In this review, we have tried to collect the currently available information on the mechanism of action of AMPs in synergy with other antimicrobial agents. In particular, we have focused on the mechanisms of action that mediate the inhibition of the emergence of bacterial resistance by AMPs.

Results and Conclusion:

We find in the literature many examples where AMPs can significantly reduce the antibiotic effective concentration. Mainly, the peptides work at the bacterial cell wall and thereby facilitate the drug access to its intracellular target. Complementarily, AMPs can also contribute to permeate the exopolysaccharide layer of biofilm communities, or even prevent bacterial adhesion and biofilm growth. Secondly, we find other peptides that can directly block the emergence of bacterial resistance mechanisms or interfere with the community quorum-sensing systems. Interestingly, the effective peptide concentrations for adjuvant activity and inhibition of bacterial resistance are much lower than the required for direct antimicrobial action. Finally, many AMPs expressed by innate immune cells are endowed with immunomodulatory properties and can participate in the host response against infection. Recent studies in animal models confirm that AMPs work as adjuvants at non-toxic concentrations and can be safely administrated for novel combined chemotherapies.

The Critical Role of Tryptophan in the Antimicrobial Activity and Cell Toxicity of the Duck Antimicrobial Peptide DCATH

Antimicrobial peptides (AMPs) have attracted more attention for their potential candidates for new antibiotic drugs. As a novel identified cathelicidin AMP from duck, dCATH owns broad-spectrum antimicrobial activities but with a noticeable toxicity. To explore dCATH-derived AMPs with reduced cell toxicity and improved cell selectivity, a series of truncated and tryptophan-replaced peptides of dCATH were designed. Two truncated peptides containing one of the two tryptophan (Trp) residues at the positions of 4 and 17 (W4 and W17) of dCATH, dCATH(1-16) and dCATH(5-20), showed strong antibacterial activity, but didn't show obvious hemolytic activity and cytotoxicity. The derived peptides not containing Trp didn't possess obvious antimicrobial activity, and their hemolytic and cytotoxic effect was also diminished. Also as evidence by Trp fluorescence experiment that existence of W4 and W17 was crucially important to the antimicrobial activity, hemolysis and cytotoxicity of dCATH, and one of the two Trp residues was competent and necessary to retain its antimicrobial activity. Antibacterial mechanism analysis showed that dCATH(1-16) and dCATH(5-20) killed bacterial cells by increasing permeability and causing a loss of membrane integrity. dCATH(1-16) and dCATH(5-20) possessed insignificant inhibitory activity against levels of IL-6, TNF-α, and NO in RAW 264.7 cells treated with LPS. In vivo, intraperitoneal administration of the two peptides significantly decreased mortality and provided protection against LPS-induced inflammation in mice challenged with lethal dose of LPS. The two peptides, dCATH(1-16) and dCATH(5-20), which possessed high antibacterial activity and cell selectivity, may herald development prospects as new antibacterial agents in the future.

Strategies in Translating the Therapeutic Potentials of Host Defense Peptides

The golden era of antibiotics, heralded by the discovery of penicillin, has long been challenged by the emergence of antimicrobial resistance (AMR). Host defense peptides (HDPs), previously known as antimicrobial peptides, are emerging as a group of promising antimicrobial candidates for combatting AMR due to their rapid and unique antimicrobial action. Decades of research have advanced our understanding of the relationship between the physicochemical properties of HDPs and their underlying antimicrobial and non-antimicrobial functions, including immunomodulatory, anti-biofilm, and wound healing properties. However, the mission of translating novel HDP-derived molecules from bench to bedside has yet to be fully accomplished, primarily attributed to their intricate structure-activity relationship, toxicity, instability in host and microbial environment, lack of correlation between in vitro and in vivo efficacies, and dwindling interest from large pharmaceutical companies. Based on our previous experience and the expanding knowledge gleaned from the literature, this review aims to summarize the novel strategies that have been employed to enhance the antimicrobial efficacy, proteolytic stability, and cell selectivity, which are all crucial factors for bench-to-bedside translation of HDP-based treatment. Strategies such as residues substitution with natural and/or unnatural amino acids, hybridization, L-to-D heterochiral isomerization, C- and N-terminal modification, cyclization, incorporation with nanoparticles, and "smart design" using artificial intelligence technology, will be discussed. We also provide an overview of HDP-based treatment that are currently in the development pipeline.

Lipidated Analogs of the LL-37-Derived Peptide Fragment KR12-Structural Analysis, Surface-Active Properties and Antimicrobial Activity

An increasing number of multidrug-resistant pathogens is a serious problem of modern medicine and new antibiotics are highly demanded. In this study, different n-alkyl acids (C2-C14) and aromatic acids (benzoic and trans-cinnamic) were conjugated to the N-terminus of KR12 amide. The effect of this modification on antimicrobial activity (ESKAPE bacteria and biofilm of Staphylococcus aureus) and cytotoxicity (human red blood cells and HaCaT cell line) was examined. The effect of lipophilic modifications on helicity was studied by CD spectroscopy, whereas peptide self-assembly was studied by surface tension measurements and NMR spectroscopy. As shown, conjugation of the KR12-NH2 peptide with C4-C14 fatty acid chains enhanced the antimicrobial activity with an optimum demonstrated by C8-KR12-NH2 (MIC 1-4 μg/mL against ESKAPE strains; MBEC of S. aureus 4-16 μg/mL). Correlation between antimicrobial activity and self-assembly behavior of C14-KR12-NH2 and C8-KR12-NH2 has shown that the former self-assembled into larger aggregated structures, which reduced its antimicrobial activity. In conclusion, N-terminal modification can enhance antimicrobial activity of KR12-NH2; however, at the same time, the cytotoxicity increases. It seems that the selectivity against pathogens over human cells can be achieved through conjugation of peptide N-terminus with appropriate n-alkyl fatty and aromatic acids.

KR‑12‑a6 promotes the osteogenic differentiation of human bone marrow mesenchymal stem cells via BMP/SMAD signaling

Considering the increased resistance to antibiotics in the clinic and the ideal antibacterial properties of KR‑12, the effects of KR‑12‑a6, an important analogue of KR‑12, on the osteogenic differentiation of human bone marrow mesenchymal stem cells (hBMSCs) were investigated. Osteogenic differentiation‑associated experiments were conducted in hBMSCs, and KR‑12‑a6 was used as an additional stimulating factor during osteogenic induction. Quantitative analysis of alkaline phosphatase (ALP) and alizarin red staining, and reverse transcription‑quantitative PCR analysis of the expression of osteogenesis‑associated genes were performed to determine the effects of KR‑12‑a6 on the osteogenic differentiation of hBMSCs. LDN‑212854 was selected to selectively suppress BMP/SMAD signaling. Western blotting was performed to investigate the underlying mechanisms. The intensity of ALP and alizarin red staining gradually increased with increasing KR‑12‑a6 concentrations. KR‑12‑a6 induced the strongest staining at 40 µg/ml, whereas 60 µg/ml and 80 µg/ml concentrations did not further increase the intensity of staining. The mRNA expression levels of RUNX2 and ALP increased in a dose‑dependent manner as early as 3 days post‑KR‑12‑a6 treatment. The mRNA expression of COL1A1, BSP and BMP2 exhibited significant upregulation from day 7 post‑KR‑12‑a6 treatment. In contrast, the mRNA levels of OSX, OCN and OPN were enhanced dramatically at day 14 following KR‑12‑a6 stimulation. Additionally, KR‑12‑a6 significantly promoted the phosphorylation of Smad1/5. Furthermore, LDN‑212854 suppressed the activation of Smad1/5 and inhibited the upregulation of several osteogenic differentiation‑associated genes in KR‑12‑a6‑treated hBMSCs. KR‑12‑a6 promoted the osteogenic differentiation of hBMSCs via BMP/SMAD signaling.

KR-12 coating of polyetheretherketone (PEEK) surface via polydopamine improves osteointegration and antibacterial activity in vivo

KR-12 was grafted onto the surface of PEEK, which improved the hydrophilicity of the material surface, promoted cell adhesion, osteogenic differentiation and osseointegration, while also endowing the appreciable antibacterial activity on the material surface.

Approaches based on passive and active antibacterial coating on titanium to achieve antibacterial activity

Titanium (Ti) and its alloys are widely applied as orthopedic implants for hip and knee prosthesis, fixation, and dental implants. However, Ti and its alloys are bioinert and susceptible to bacteria and biofilm formation. Strategies for improving the antibacterial properties of Ti can be divided into two approaches, namely, passive coating and active coating on the Ti surface. Passive coating on Ti mainly kills the bacteria in contact but does not kill plankton or bacteria dwell in the bone tissue around the Ti implant. Active coating mainly involves the release of antibacterial agents to kill the bacteria, but this may result in the development of bacterial resistance. Both strategies include advantages and disadvantages. This article reviews the current and potential future approaches for improving antibacterial activity on Ti. We mainly focus on current approaches for fabricating antibacterial Ti and its limitations and countermeasures, and provide direction for further studies of biofunctionalization of Ti with antibacterial properties. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A:2531-2539, 2018.

Modulation of antimicrobial potency of human cathelicidin peptides against the ESKAPE pathogens and in vivo efficacy in a murine catheter-associated biofilm model

Antimicrobial peptides are essential components of innate immune systems that protect hosts from infection. They are also useful candidates for developing a new generation of antibiotics to fight antibiotic-resistant pathogens. Human innate immune peptide LL-37 can inhibit biofilm formation, but suffers from high cost due to a long peptide length and rapid protease degradation. To improve the peptide, we previously identified the major active region and changed the peptide backbone structure. This study designed two families of new peptides by altering peptide side chains. Interestingly, these peptides displayed differential potency against various ESKAPE pathogens in vitro and substantially reduced hemolysis. Further potency test in vivo revealed that 17tF-W eliminated the burden of methicillin-resistant Staphylococcus aureus (MRSA) USA300 in both mouse-embedded catheters and their surrounding tissues. In addition, peptide treatment suppressed the level of chemokine TNFα, and boosted the levels of chemokines MCP-1, IL-17A and IL-10 in the surrounding tissues of the infected catheter embedded in mice. In conclusion, we have designed a set of new LL-37 peptides with varying antimicrobial activities, opening the door to potential topical treatment of infections involving different drug-resistant pathogens.