Identification and characterization of novel antimicrobial decapeptides generated by combinatorial chemistry

Stimuli-Responsive Delivery of Antimicrobial Peptides Using Polyelectrolyte Complexes

Antimicrobial peptides (AMPs) are antibiotics with the potential to address antimicrobial resistance. However, their translation to the clinic is hampered by issues such as off-target toxicity and low stability in biological media. Stimuli-responsive delivery from polyelectrolyte complexes offers a simple avenue to address these limitations, wherein delivery is triggered by changes occurring during microbial infection. The review first provides an overview of pH-responsive delivery, which exploits the intrinsic pH-responsive nature of polyelectrolytes as a mechanism to deliver these antimicrobials. The examples included illustrate the challenges faced when developing these systems, in particular balancing antimicrobial efficacy and stability, and the potential of this approach to prepare switchable surfaces or nanoparticles for intracellular delivery. The review subsequently highlights the use of other stimuli associated with microbial infection, such as the expression of degrading enzymes or changes in temperature. Polyelectrolyte complexes with dual stimuli-response based on pH and temperature are also discussed. Finally, the review presents a summary and an outlook of the challenges and opportunities faced by this field. This review is expected to encourage researchers to develop stimuli-responsive polyelectrolyte complexes that increase the stability of AMPs while providing targeted delivery, and thereby facilitate the translation of these antimicrobials.

Targeting collagen damage for sustained in situ antimicrobial activities

Antimicrobial peptides (AMPs) are promising anti-infective drugs, but their use is restricted by their short-term retention at the infection site, non-targeted uptake, and adverse effects on normal tissues. Since infection often follows an injury (e.g., in a wound bed), directly immobilizing AMPs to the damaged collagenous matrix of the injured tissues may help overcome these limitations by transforming the extracellular matrix microenvironment of the infection site into a natural reservoir of AMPs for sustained in situ release. Here, we developed and demonstrated an AMP-delivery strategy by conjugating a dimeric construct of AMP Feleucin-K3 (Flc) and a collagen hybridizing peptide (CHP), which enabled selective and prolonged anchoring of the Flc-CHP conjugate to the damaged and denatured collagen in the infected wounds in vitro and in vivo. We found that the dimeric Flc and CHP conjugate design preserved the potent and broad-spectrum antimicrobial activities of Flc while significantly enhancing and extending its antimicrobial efficacy in vivo and facilitating tissue repair in a rat wound healing model. Because collagen damage is ubiquitous in almost all injuries and infections, our strategy of targeting collagen damage may open up new avenues for antimicrobial treatments in a range of infected tissues.

Important Roles and Potential Uses of Natural and Synthetic Antimicrobial Peptides (AMPs) in Oral Diseases: Cavity, Periodontal Disease, and Thrush

Numerous epithelial cells and sometimes leukocytes release AMPs as their first line of defense. AMPs encompass cationic histatins, defensins, and cathelicidin to encounter oral pathogens with minimal resistance. However, their concentrations are significantly below the effective levels and AMPs are unstable under physiological conditions due to proteolysis, acid hydrolysis, and salt effects. In parallel to a search for more effective AMPs from natural sources, considerable efforts have focused on synthetic stable and low-cytotoxicy AMPs with significant activities against microorganisms. Using natural AMP templates, various attempts have been used to synthesize sAMPs with different charges, hydrophobicity, chain length, amino acid sequence, and amphipathicity. Thus far, sAMPs have been designed to target Streptococcus mutans and other common oral pathogens. Apart from sAMPs with antifungal activities against Candida albicans, future endeavors should focus on sAMPs with capabilities to promote remineralization and antibacterial adhesion. Delivery systems using nanomaterials and biomolecules are promising to stabilize, reduce cytotoxicity, and improve the antimicrobial activities of AMPs against oral pathogens. Nanostructured AMPs will soon become a viable alternative to antibiotics due to their antimicrobial mechanisms, broad-spectrum antimicrobial activity, low drug residue, and ease of synthesis and modification.

Peptide and non-peptide mimetics as potential therapeutics targeting oral bacteria and oral biofilms

The development of the oral biofilm requires a complex series of interactions between host tissues and the colonizing bacteria as well as numerous interspecies interactions between the organisms themselves. Disruption of normal host-microbe homoeostasis in the oral cavity can lead to a dysbiotic microbial community that contributes to caries or periodontal disease. A variety of approaches have been pursued to develop novel potential therapeutics that are active against the oral biofilm and/or target specific oral bacteria. The structure and function of naturally occurring antimicrobial peptides from oral tissues and secretions as well as external sources such as frog skin secretions have been exploited to develop numerous peptide mimetics and small molecule peptidomimetics that show improved antimicrobial activity, increased stability and other desirable characteristics relative to the parent peptides. In addition, a rational and minimalist approach has been developed to design small artificial peptides with amphipathic α-helical properties that exhibit potent antibacterial activity. Furthermore, with an increased understanding of the molecular mechanisms of beneficial and/or antagonistic interspecies interactions that contribute to the formation of the oral biofilm, new potential targets for therapeutic intervention have been identified and both peptide-based and small molecule mimetics have been developed that target these key components. Many of these mimetics have shown promising results in in vitro and pre-clinical testing and the initial clinical evaluation of several novel compounds has demonstrated their utility in humans.

Antimicrobial peptide KSL-W and analogues: Promising agents to control plant diseases

Recent strong restrictions on the use of pesticides has prompted the search for safer alternatives, being antimicrobial peptides promising candidates. Herein, with the aim of identifying new agents, 15 peptides reported as plant defense elicitors, promiscuous, multifunctional or antimicrobial were selected and tested against six plant pathogenic bacteria of economic importance. Within this set, KSL-W (KKVVFWVKFK-NH2) displayed high antibacterial activity against all the tested pathogens, low hemolysis and low phytotoxicity in tobacco leaves. This peptide was taken as a lead and 49 analogues were designed and synthesized, including N-terminal deletion sequences, peptides incorporating a d-amino acid and lipopeptides. The screening of these sequences revealed that a nine amino acid length was the minimum for activity. The presence of a d-amino acid significantly decreased the hemolysis and endowed KSL-W with the capacity to induce the expression of defense-related genes in tomato plants. The incorporation of an acyl chain led to sequences with high activity against Xanthomonas strains, low hemolysis and phytotoxicity. Therefore, this study demonstrates that KSL-W constitutes an excellent candidate as new agent to control plant diseases and can be considered as a lead to develop derivatives with multifunctional properties, including antimicrobial and plant defense elicitation.

Tryptophan-Rich and Proline-Rich Antimicrobial Peptides

Due to the increasing emergence of drug-resistant pathogenic microorganisms, there is a world-wide quest to develop new-generation antibiotics. Antimicrobial peptides (AMPs) are small peptides with a broad spectrum of antibiotic activities against bacteria, fungi, protozoa, viruses and sometimes exhibit cytotoxic activity toward cancer cells. As a part of the native host defense system, most AMPs target the membrane integrity of the microorganism, leading to cell death by lysis. These membrane lytic effects are often toxic to mammalian cells and restrict their systemic application. However, AMPs containing predominantly either tryptophan or proline can kill microorganisms by targeting intracellular pathways and are therefore a promising source of next-generation antibiotics. A minimum length of six amino acids is required for high antimicrobial activity in tryptophan-rich AMPs and the position of these residues also affects their antimicrobial activity. The aromatic side chain of tryptophan is able to rapidly form hydrogen bonds with membrane bilayer components. Proline-rich AMPs interact with the 70S ribosome and disrupt protein synthesis. In addition, they can also target the heat shock protein in target pathogens, and consequently lead to protein misfolding. In this review, we will focus on describing the structures, sources, and mechanisms of action of the aforementioned AMPs.

Fabrication of Antimicrobial Peptide-Loaded PLGA/Chitosan Composite Microspheres for Long-Acting Bacterial Resistance

An antimicrobial decapeptide, KSL-W (KKVVFWVKFK-CONH₂), which could maintain stable antimicrobial activity in saliva, has therefore been widely used to inhibit biofilm formation on teeth and prevent the growth of oral microorganisms for related infectious diseases treatment. In order to control the release of KSL-W for long-term bacterial resistance, KSL-W-loaded PLGA/chitosan composite microspheres (KSL/PLGA/CS MSs) were prepared by electrospraying and combined crosslinking-emulsion methods. Different formulations of microspheres were characterized as to surface morphology, size distribution, encapsulation efficiency, in vitro drug release, and antimicrobial activity. Antibacterial experiment demonstrated the prolonged antimicrobial and inhibitory effects of KSL/PLGA/CS MSs on oral bacteria. Moreover, the cell proliferation assay proved that the released KSL-W antibacterial dosage had no cytotoxicity to the growth of osteoblast MC3T3-E1. Thus, our study suggested that the KSL-W-loaded PLGA/CS composite microspheres may have potentially therapeutic applications as an effective drug delivery system in the treatment of oral infectious diseases such as periodontitis and periodontitis, and also within bone graft substitutes for alveolar bone augmentation.

Antimicrobial peptide KSL-W promotes gingival fibroblast healing properties in vitro

We investigated the effect of synthetic antimicrobial decapeptide KSL-W (KKVVFWVKFK) on normal human gingival fibroblast growth, migration, collagen gel contraction, and α-smooth muscle actin protein expression. Results show that in addition to promoting fibroblast adhesion by increasing F-actin production, peptide KSL-W promoted cell growth by increasing the S and G2/M cell cycle phases, and enhanced the secretion of metalloproteinase (MMP)-1 and MMP-2 by upregulating MMP inhibitors, such as tissue inhibitors of metalloproteinase (TIMP)-1 and TIMP-2 in fibroblasts. An in vitro wound healing assay confirmed that peptide KSL-W promoted fibroblast migration and contraction of a collagen gel matrix. We also demonstrated a high expression of α-smooth muscle actin by gingival fibroblasts being exposed to KSL-W. This work shows that peptide KSL-W enhances gingival fibroblast growth, migration, and metalloproteinase secretion, and the expression of α-smooth muscle actin, thus promoting wound healing.

Selection of Small Synthetic Antimicrobial Peptides Inhibiting Xanthomonas citri subsp. citri Causing Citrus Canker

Citrus canker disease decreases the fruit quality and yield significantly, furthermore, emerging of streptomycin-resistant pathogens threatens the citrus industry seriously because of a lack of proper control agents. Small synthetic antimicrobial peptides (AMPs) could be a promising alternative. Fourteen hexapeptides were selected by using positional scanning of synthetic peptide combinatorial libraries. Each hexapeptide showed different antimicrobial spectrum against Bacillus, Pseudomonas, Xanthomonas, and Candida species. Intriguingly, BHC10 showed bactericidal activity exclusively on Xanthomonas citri subsp. citri (Xcc), while BHC7 was none-active exclusively against two Pseudomonas spp. at concentration of 100 μg/ml suggesting potential selectivity constrained in hexapeptide frame. Three hexapeptides, BHC02, 06 and 11, showed bactericidal activities against various Xcc strains at concentration of 10 μg/ml. When they were co-infiltrated with pathogens into citrus leaves the disease progress was suppressed significantly. Further study would be needed to confirm the actual disease control capacity of the selected hexapeptides.

Design of a hydroxyapatite-binding antimicrobial peptide with improved retention and antibacterial efficacy for oral pathogen control

Controlling and reducing the formation of pathogenic biofilm on tooth surface is the key to the prevention and treatment of the biofilm-associated oral diseases. Antimicrobial peptides (AMPs), considered as possible future alternatives for conventional antibiotics, have been extensively studied for the control of bacterial infection. Due to the rapid dilution and degradation by human saliva, AMP preparations designed for oral use with longer retention and higher efficacy are in urgent need. To this end, a hydroxyapatite (HAp)-binding antimicrobial peptide (HBAMP), which is based on the fusion of a specific HAp-binding heptapeptide (HBP7) domain and a broad-spectrum antimicrobial peptide (KSLW) domain, has been developed in our laboratory. HBAMP was supposed to form a contact-active antibacterial interface on tooth surface to inhibit the formation of biofilms. In this study, we investigated its binding behaviour, antibacterial activity against bacteria in both planktonic and sessile states, enzymatic stability in human saliva, and cytocompatibility to human gingival fibroblasts (HGFs). Our findings suggest that HBAMP could adsorb on tooth surface to provide effective antibacterial activity with improved retention. This study provides a proof-of-concept on using conjugated molecules to promote antibacterial efficacy by synergistically actions of HBAMP free in solution and bound on tooth surface.

Antibacterial Peptides: Opportunities for the Prevention and Treatment of Dental Caries

Dental caries is a multifactorial disease that is a growing and costly global health concern. The onset of disease is a consequence of an ecological imbalance within the dental plaque biofilm that favors specific acidogenic and aciduric caries pathogens, namely Streptococcus mutans and Streptococcus sobrinus. It is now recognized by the scientific and medical community that it is neither possible nor desirable to totally eliminate dental plaque. Conversely, the chemical biocides most commonly used for caries prevention and treatment indiscriminately attack all plaque microorganisms. These treatments also suffer from other drawbacks such as bad taste, irritability, and staining. Furthermore, the public demand for safe and natural personal hygiene products continues to rise. Therefore, there are opportunities that exist to develop new strategies for the treatment of this disease. As an alternative to conventional antibiotics, antibacterial peptides have been explored greatly over the last three decades for many different therapeutic uses. There are currently tens of hundreds of antibacterial peptides characterized across the evolutionary spectrum, and among these, many demonstrate physical and/or biological properties that may be suitable for a more targeted approach to the selective control or elimination of putative caries pathogens. Additionally, many peptides, such as nisin, are odorless, colorless, and tasteless and do not cause irritation or staining. This review focuses on antibacterial peptides for their potential role in the treatment and prevention of dental caries and suggests candidates that need to be explored further. Practical considerations for the development of antibacterial peptides as oral treatments are also discussed.

Peptide KSL-W-Loaded Mucoadhesive Liquid Crystalline Vehicle as an Alternative Treatment for Multispecies Oral Biofilm

Decapeptide KSL-W shows antibacterial activities and can be used in the oral cavity, however, it is easily degraded in aqueous solution and eliminated. Therefore, we aimed to develop liquid crystalline systems (F1 and F2) for KSL-W buccal administration to treat multispecies oral biofilms. The systems were prepared with oleic acid, polyoxypropylene (5) polyoxyethylene (20) cetyl alcohol (PPG-5-CETETH-20), and a 1% poloxamer 407 dispersion as the oil phase (OP), surfactant (S), and aqueous phase (AP), respectively. We characterized them using polarized light microscopy (PLM), small-angle X-ray scattering (SAXS), rheology, and in vitro bioadhesion, and performed in vitro biological analysis. PLM showed isotropy (F1) or anisotropy with lamellar mesophases (F2), confirmed by peak ratio quantification using SAXS. Rheological tests demonstrated that F1 exhibited Newtonian behavior but not F2, which showed a structured AP concentration-dependent system. Bioadhesion studies revealed an AP concentration-dependent increase in the system’s bioadhesiveness (F2 = 15.50 ± 1.00 mN·s) to bovine teeth blocks. Antimicrobial testing revealed 100% inhibition of multispecies oral biofilm growth after KSL-W administration, which was incorporated in the F2 aqueous phase at a concentration of 1 mg/mL. Our results suggest that this system could serve as a potential vehicle for buccal administration of antibiofilm peptides.

[Antibacterial activity of synthetic antimicrobial decapeptide against oral bacteria]

OBJECTIVE

This study aims to evaluate the antimicrobial activity of decapeptide, a novel antimicrobial peptide, against several major cariogenic and periodontopathogenic bacteria in vitro. METHODS In this study, we investigated the antimicrobial activity of decapeptide against Streptococcus mutans (S. mutans), Streptococcus sobrinus, Lactobacillus acidophilus, Streptococcus sanguis, Streptococcus gordonii, Actinomyces viscosus, Actinomyces naeslundii, Porphyromonas gingivalis, Prevotella intermedia, Fusobacterium nucleatum, Actinobacillus actinomycetemcomitans, and Saccharomyces albicans in vitro using the agar diffusion method and broth dilution method. Furthermore, a time-kill kinetic study of decapeptide against S. mutans was performed.

RESULTS

The results showed that decapeptide exhibited antimicrobial activity against various oral bacteria and fungi. The minimum inhibitory concentration (MIC) of main cariogenic bacteria ranged from 62.5 μg · mL(-1) to 125 μg · mL(-1), and the MIC of periodontopathogenic bacteria tested ranged from 250 μg · mL(-1) to 1,000 μg · mL(-1). Among the bacteria tested, decapeptide had a strong inhibitory effect on cariogenic S. mutans. Results of the time-kill kinetic studies showed that decapeptide reduced the viable counts of S. mutans by more than one order of magnitude after 20 min of incubation, and thoroughly killed S. mutans after 30 min. No viable cells could be detected after 24 h of incubation.

CONCLUSION

This study suggest that decapeptide might have potential clinical application in treating dental caries by killing S. mutans within dental plaque.

Novel formulations for antimicrobial peptides

Peptides in general hold much promise as a major ingredient in novel supramolecular assemblies. They may become essential in vaccine design, antimicrobial chemotherapy, cancer immunotherapy, food preservation, organs transplants, design of novel materials for dentistry, formulations against diabetes and other important strategical applications. This review discusses how novel formulations may improve the therapeutic index of antimicrobial peptides by protecting their activity and improving their bioavailability. The diversity of novel formulations using lipids, liposomes, nanoparticles, polymers, micelles, etc., within the limits of nanotechnology may also provide novel applications going beyond antimicrobial chemotherapy.

C. albicans growth, transition, biofilm formation, and gene expression modulation by antimicrobial decapeptide KSL-W

Background

Antimicrobial peptides have been the focus of much research over the last decade because of their effectiveness and broad-spectrum activity against microbial pathogens. These peptides also participate in inflammation and the innate host defense system by modulating the immune function that promotes immune cell adhesion and migration as well as the respiratory burst, which makes them even more attractive as therapeutic agents. This has led to the synthesis of various antimicrobial peptides, including KSL-W (KKVVFWVKFK-NH₂), for potential clinical use. Because this peptide displays antimicrobial activity against bacteria, we sought to determine its antifungal effect on C. albicans. Growth, hyphal form, biofilm formation, and degradation were thus examined along with EFG1, NRG1, EAP1, HWP1, and SAP 2-4-5-6 gene expression by quantitative RT-PCR.

Results

This study demonstrates that KSL-W markedly reduced C. albicans growth at both early and late incubation times. The significant effect of KSL-W on C. albicans growth was observed beginning at 10 μg/ml after 5 h of contact by reducing C. albicans transition and at 25 μg/ml by completely inhibiting C. albicans transition. Cultured C. albicans under biofilm-inducing conditions revealed that both KSL-W and amphotericin B significantly decreased biofilm formation at 2, 4, and 6 days of culture. KSL-W also disrupted mature C. albicans biofilms. The effect of KSL-W on C. albicans growth, transition, and biofilm formation/disruption may thus occur through gene modulation, as the expression of various genes involved in C. albicans growth, transition and biofilm formation were all downregulated when C. albicans was treated with KSL-W. The effect was greater when C. albicans was cultured under hyphae-inducing conditions.

Conclusions

These data provide new insight into the efficacy of KSL-W against C. albicans and its potential use as an antifungal therapy.

Synthetic decapeptide reduces bacterial load and accelerates healing in the wounds of restraint-stressed mice

Wound healing is a complex process involving four transitional yet concurrent stages: coagulation, inflammation, cell proliferation/epithelialization and remodeling. These overlapping stages occur uneventfully in normal physiology. However, during psychological stress, the inflammatory response can become dysregulated and result in increased susceptibility to bacterial infection and delayed wound closure. In our restraint stress model, cutaneous wounds of stressed SKH-1 mice demonstrate significantly higher levels of bacterial load, and healing progresses at a rate 30% slower, than in non-stressed mice. The purpose of this study was to test the hypothesis that a synthetic antimicrobial decapeptide (KSLW) enhances bacterial clearance during stress-impaired healing in mice. Here, using a Pluronic block copolymer nanocarrier, we endeavored to identify an efficient drug delivery system for KSLW, which would enhance the stability, substantivity and function of the cationic peptide in delayed-healing wounds. In this study, intradermal treatment of excisional wounds of stressed mice with 2mg/ml KSLW loaded in Pluronic F68, resulted in a sustained antimicrobial effect through post-operative day 5, with a 2-log (p<0.01) reduction in bacterial load compared with other stressed mice. The demonstrated bacterial reduction in KSLW-treated stressed mice did not approach the levels observed among control mice. Furthermore, treatment of stressed mice with KSLW improved healing, resulting in significantly faster (p<0.05) wound closure from days 2 to 5 post-wounding, relative to untreated stressed mice and stressed mice treated with Pluronic alone. These findings suggest that Pluronic F68 is an efficient carrier for KSLW, which improves its stability and activity in impaired dermal wounds.

Antimicrobial decapeptide KSL-W enhances neutrophil chemotaxis and function

Mammalian cationic antimicrobial peptides have received increased attention over the last decade, due to their prokaryotic selectivity and decreased risk of microbial resistance. In addition, antimicrobial peptides display differential biological effects on mammalian immune cell function, such as migration, adhesion, and modulation of respiratory burst, which make them even more attractive as therapeutic agents. Synthetic combinatorial libraries provide a time-efficient and cost-effective source for these diverse molecules. The novel synthetic antimicrobial peptide, KSLW (KKVVFWVKFK-NH(2)), has been shown to display a broad spectrum of antimicrobial activity against Gram (+) and Gram (-) bacteria, fungi and viruses. In this study, we evaluated the alternative biological activity of the decapeptide on neutrophil migration and function. KSLW was demonstrated to be chemotactic for neutrophils in micromolar amounts, and neutrophil treatment with KSLW, after 1 min, resulted in significant increases in F-actin polymerization. KSLW was shown to inhibit oxygen radical production in PMA- and LPS-stimulated neutrophils. Future studies, to determine if KSLW regulates neutrophil phagocytosis, adhesion, and apoptosis, or examining the effect of KSLW on other mammalian cell types, such as cell populations of healing-impaired wounds, would provide significant insight for the potential therapeutic strategies offered by antimicrobial peptides.

Peptide and protein drugs: the study of their metabolism and catabolism by mass spectrometry

Peptide and protein drugs have evolved in recent years into mainstream therapeutics, representing a significant portion of the pharmaceutical market. Peptides and proteins exhibit highly diverse structures, broad biological activities as hormones, neurotransmitters, structural proteins, metabolic modulators and therefore have a significant role as both therapeutics and biomarkers. Understanding the metabolism of synthetic or biotechnologically derived peptide and protein drugs is critical for pharmaceutical development as metabolism has a significant impact on drug efficacy and safety. Although the same principles of pharmacokinetics and metabolism of small molecule drugs apply to peptide and protein drugs, there are few notable differences. Moreover, the study of peptide and protein drug metabolism is a rather complicated process which requires sophisticated analytical techniques, and mass spectrometry based approaches have provided the capabilities for efficient and reliable quantification, characterization, and metabolite identification. This review article will focus on the current use of mass spectrometry for the study of the metabolism of peptide and protein drugs.

Endocytosis-mediated vacuolar accumulation of the human ApoE apolipoprotein-derived ApoEdpL-W antimicrobial peptide contributes to its antifungal activity in Candida albicans

The 18-amino-acid cationic, tryptophan-rich ApoEdpL-W peptide derived from human ApoE apolipoprotein was shown to have antifungal activity against pathogenic yeasts of the Candida genus (except C. glabrata). ApoEdpL-W was active against planktonic cells and early-stage biofilms but less active against mature biofilms, possibly because of its affinity for extracellular matrix beta-glucans. Moreover, ApoEdpL-W absorbed to medically relevant materials partially prevented the formation of biofilms on these materials. The exposure of C. albicans cells to sublethal doses of ApoEdpL-W triggered a transcriptional response reminiscent of that associated with the inactivation of the MYO5 gene required for endocytosis as well as the upregulation of amino acid transporter genes. A fluorescent derivative of ApoEdpL-W accumulated at the cytoplasmic membrane and subsequently was translocated to the vacuole. Strikingly, the inactivation of MYO5 or addition of latrunculin, an inhibitor of endocytosis, prevented the vacuolar accumulation of fluorescein-labeled ApoEdpL-W and reduced the antifungal activity of ApoEdpL-W. This, together with the insensitivity of ApoEdpL-W to alterations in membrane fluidity and high salt, suggested that the ApoEdpL-W mode of action was dependent upon vacuolar targeting and differed significantly from that of other antifungal peptides, such as Histatin-5 and Magainin 2.

Cell selectivity and interaction with model membranes of Val/Arg-rich peptides

Antimicrobial peptides are major components of the innate self-defence system and a large number of peptides have been designed to study the mechanism of action. In the present study, a small combinatorial library was designed to study whether the biological activity of Val/Arg-rich peptides is associated with targeted cell membranes. The peptides were produced by segregating hydrophilic residues on the polar side and hydrophobic residues on the opposite side. The peptides displayed strong antimicrobial activity against Gram-negative and Gram-positive bacteria, but weak haemolysis even at a concentration of 256 µM. CD spectra showed that the peptides formed α-helical-rich structure in the presence of negatively charged membranes. The tryptophan fluorescence and quenching experiments indicated that the peptides bound preferentially to negatively charged phospholipids over zwitterionic phospholipids, which corresponds well with the biological activity data. In the in vivo experiment, the peptide G6 decreased the bacterial counts in the mouse peritoneum and increased survival after 7 days. Overall, a high binding affinity with negatively charged phospholipids correlated closely with the cell selectivity of the peptides and some peptides in this study may be likely candidates for the development of antibacterial agents.

Biophysical properties of membrane-active peptides based on micelle modeling: a case study of cell-penetrating and antimicrobial peptides

We investigated the molecular mechanisms of short peptides interacting with membrane-mimetic systems. Three short peptides were selected for this study: penetratin as a cell-penetrating peptide (CPP), and temporin A and KSL as antimicrobial peptides (AMP). We investigated the detailed interactions of the peptides with dodecylphosphocholine (DPC) and sodium dodecyl sulfate (SDS) micelles, and the subsequent peptide insertion based on free energy calculations by using all-atomistic molecular dynamics simulations with the united atom force field and explicit solvent models. First, we found that the free energy barrier to insertion for the three peptides is dependent on the chemical composition of the micelles. Because of the favorable electrostatic interactions between the peptides and the headgroups of lipids, the insertion barrier into an SDS micelle is less than a DPC micelle. Second, the peptides' secondary structures may play a key role in their binding and insertion ability, particularly for amphiphilic peptides such as penetratin and KSL. The secondary structures with a stronger ability to bind with and insert into micelles are the ones that account for a smaller surface area of hydrophobic core, thus offering a possible criterion for peptide design with specific functionalities.

Rare casbane diterpenoids from the Hainan soft coral Sinularia depressa

A series of nine casbane diterpenes, compounds 5-13, exhibiting either cis or trans ring junctions were isolated from the Hainan soft coral Sinularia depressa. The structures of this group of compounds, the basic member of which was named depressin (5), were established by detailed spectroscopic analysis. In addition, the absolute configuration of the main metabolite, 10-hydroxydepressin (7), and of its epimer, 1-epi-10-hydroxydepressin (8), was determined by a combination of conformational analysis and the modified Mosher's method. A stereochemical relationship between all isolated molecules was investigated by analyzing their circular dichroism profiles. Antiproliferative and antibacterial activities of the depressins were also evaluated.

KKKKPLFGLFFGLF: a cationic peptide designed to exert antibacterial activity

With 14 residues organized as two domains linked by a single proline, the de novo peptide called K4 was designed, using Antimicrobial Peptide Database, to exert antibacterial activity. The N-terminal domain is composed of four lysines enhancing membrane interactions, and the C-terminal domain is putatively folded into a hydrophobic alpha-helix. Following the synthesis, the purification and the structural checking, antibacterial assays revealed a strong activity against gram-positive and gram-negative bacteria including human pathogenic bacteria such as Staphylococcus aureus and some marine bacteria of the genus Vibrio. Scanning electron microscopy of Escherichia coli confirmed that K4 lyses bacterial cells. The cytotoxicity was tested against rabbit erythrocytes and chinese hamster ovary cells (CHO-K1). These tests revealed that K4 is non-toxic to mammalian cells for bacteriolytic concentrations. The peptide K4 could be a valuable candidate for future therapeutic applications.

Aromatic cyclic peroxides and related keto-compounds from the Plakortis sp. component of a sponge consortium

Six unreported aromatic compounds, 1-6, were isolated, along with the known compounds dehydrocurcuphenol and manoalide, from a sample of Plakortis sp., which was the main component of a Pacific sponge consortium. The new molecules were chemically characterized by spectroscopic methods. Compounds 1-4 contain a six-membered cyclic peroxide, whereas 5 and 6 display a terminal methyl ketone. The new metabolites were tested for antifungal and antibacterial properties. Compounds 1 and 4 were weakly active against S. aureus.

Synthetic antimicrobial peptides as agricultural pesticides for plant-disease control

There is a need of antimicrobial compounds in agriculture for plant-disease control, with low toxicity and reduced negative environmental impact. Antimicrobial peptides are produced by living organisms and offer strong possibilities in agriculture because new compounds can be developed based on natural structures with improved properties of activity, specificity, biodegradability, and toxicity. Design of new molecules has been achieved using combinatorial-chemistry procedures coupled to high-throughput screening systems and data processing with design-of-experiments (DOE) methodology to obtain QSAR equation models and optimized compounds. Upon selection of best candidates with low cytotoxicity and moderate stability to protease digestion, anti-infective activity has been evaluated in plant-pathogen model systems. Suitable compounds have been submitted to acute toxicity testing in higher organisms and exhibited a low toxicity profile in a mouse model. Large-scale production can be achieved by solution organic or chemoenzymatic procedures in the case of very small peptides, but, in many cases, production can be performed by biotechnological methods using genetically modified microorganisms (fermentation) or transgenic crops (plant biofactories).

Synthesis of bioinorganic antimicrobial peptide nanoparticles with potential therapeutic properties

Amphiphilicity and cationicity are properties shared between antimicrobial peptides and proteins that catalyze biomineralization reactions. Merging these two functionalities, we demonstrate a reaction where a cationic antimicrobial peptide catalyzes self-biomineralization within inorganic matrices. The resultant antimicrobial peptide nanoparticles retain biocidal activity, protect the peptide from proteolytic degradation, and facilitate a continuous release of the antibiotic over time. Taken together, these properties demonstrate the therapeutic potential of self-synthesizing biomaterials that retain the biocidal properties of antimicrobial peptides.

Synthesis and in vitro biological properties of novel cationic derivatives of amphotericin B

Novel cationic amphotericin B derivatives as highly potent antifungal agents are reported. These semi-synthetic derivatives of amphotericin B were elaborated through a series of modifications both on the nitrogen atom of the mycosamine and on the C-16 carboxylic acid moiety. The antifungal activity of the new conjugates was tested against Saccharomyces cerevisiae and also against nine different strains of Candida albicans and Candida glabrata, including an amphotericin resistant strain. High potency was observed in the case of polyamine derivatives bearing two 3-aminopropyl chains on the mycosamine. The evaluation of the biological properties also included the determination of the hemolytic activity of the compounds by measuring the EH50 values.

Design and synthesis of novel antibacterial peptide-resin conjugates

We synthesized a novel peptide-resin conjugate by immobilizing beta-sheet antibacterial peptide on PEG-PS resin. The peptide-resin conjugate, similar to cationic antimicrobial peptides, demonstrated unique properties such as potent antibacterial activity, no hemolytic activity, lipid membrane perturbation activity, and potent synergism with vancomycin. Specially, the peptide-resin conjugate showed a more increased lipid membrane perturbation activity in comparison to unbound beta-sheet antibacterial peptide.

An antifungal protein from Escherichia coli

A cytosolic protein was purified fromEscherichia coliBL21 that demonstrated potent antifungal activity against pathogenic strains ofAspergillus fumigatus,Aspergillus flavus,Aspergillus nigerandCandida albicans. The MIC of purified protein fromE. coliBL21 (PPEBL21) againstAspergillusspecies andC. albicanswas 1.95–3.98 and 15.62 μg ml−1, respectively.In vitrotoxicity tests demonstrated no cytotoxicity of PPEBL21 to human erythrocytes up to the tested concentrations of 1250 μg ml−1. Amphotericin B was lethal to 100 % of human erythrocytes at a concentration of 37.5 μg ml−1. The N-terminal amino acid sequence of PPEBL21 was found to be DLAEVASR, which showed 75 % sequence similarity with alcohol dehydrogenase of yeast. Mass fingerprinting by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry also substantiated these observations. The results suggested thatE. coliBL21 might be an important bioresource of lead molecules for developing new peptide-based therapies for treating fungal infections.

Stability of Antimicrobial Decapeptide (KSL) and Its Analogues for Delivery in the Oral Cavity

PURPOSE

To investigate the stability of KSL, an antimicrobial decapeptide, and its analogues, in human saliva and simulated gastric fluid for delivery in the oral cavity.

MATERIALS AND METHODS

The degradation products of KSL in human saliva and simulated gastric fluid were separated by reversed-phase HPLC and their structures were identified by electrospray ionization-mass spectrometry. Analogues of KSL were synthesized by solid-phase synthesis procedure. Their enzymatic stabilities and antimicrobial activities were studied.

RESULTS

KSL was degraded by the peptide bond cleavages at Lys(6)-Val(7) in the human saliva and Phe(5)-Lys(6) in simulated gastric fluids. Three analogues of KSL were synthesized; the Lys(6) residue was either methylated (KSL-M), or replaced with Trp (KSL-W), or the d-form of Lys (KSL-D). The KSL analogues were much more stable than the native KSL, with the rank order of stability being KSL-D > KSL-W > KSL-M > KSL in human saliva. However, in simulated gastric fluid, while KSL-D was still stable, KSL-W was significantly degraded. In addition, KSL-D significantly lost the antimicrobial activity, whereas KSL-W completely preserved the activity against several oral bacteria. In a chewing gum formulation, KSL-W showed a more sustained release profile as compared with the native KSL.

CONCLUSION

This study suggests that KSL-W could be used as an antiplaque agent in a chewing gum formulation.

In vitro system for high-throughput screening of random peptide libraries for antimicrobial peptides that recognize bacterial membranes

Antibacterial peptides have been isolated from a wide range of species. Some of these peptides act on microbial membranes, disrupting their barrier function. With the increasing development of antibiotic resistance by bacteria, these antibacterial peptides, which have a new mode of action, have attracted interest as antibacterial agents. To date, however, few effective high-throughput approaches have been developed for designing and screening peptides that act selectively on microbial membranes. In vitro display techniques are powerful tools to select biologically functional peptides from peptide libraries. Here, we used the ribosome display system to form peptide-ribosome-mRNA complexes in vitro from nucleotides encoding a peptide library, as well as immobilized model membranes, to select specific sequences that recognize bacterial membranes. This combination of ribosome display and immobilized model membranes was effective as an in vitro high-throughput screening system and enabled us to identify motif sequences (ALR, KVL) that selectively recognized the bacterial membrane. Owing to host toxicity, it was not possible to enrich any sequence expected to show antimicrobial activity using another in vitro system, e.g. phage display. The synthetic peptides designed from these enriched motifs acted selectively on the bacterial model membrane and showed antibacterial activity. Moreover, the motif sequence conferred selectivity onto native peptides lacking selectivity, and decreased mammalian cell toxicity of native peptides without decreasing their antibacterial activity.

pH-Dependent lytic peptides discovered by phage display

Lipid membranes compartmentalize eukaryotic cells and separate the cell interior from the extracellular milieu. So far, studies of peptide and protein interactions with membranes have largely been limited to naturally occurring peptides or to sequences designed on the basis of structural information and biophysical parameters. To expand on these studies, utilizing a system with minimal assumptions, we used phage-display technology to identify 12 amino acid-long peptides that bind to liposomes at pH 5.0 but not at pH 7.5. Of the nineteen peptides discovered, three were able to cause leakage of liposome contents. Multivalent presentation of these membrane-active peptides by conjugation onto poly(l-Lysine) enhanced their lytic potential. The secondary structures were analyzed by circular dichroism in aqueous 2,2,2-trifluoroethanol and in buffered aqueous solutions, both in the presence and absence of liposomes. Two of the three lytic peptides show alpha helical profiles, whereas none of the nonlytic peptides formed stable secondary structures. The diverse characteristics of the peptides identified in this study demonstrate that phage-displayed peptide library screens on lipid membranes result in the discovery of nonclassical membrane-active peptides, whose study will provide novel insights into peptide-membrane interactions.

Peptide-membrane interactions and mechanisms of membrane destruction by amphipathic alpha-helical antimicrobial peptides

Antimicrobial peptides (AMPs) have received considerable interest as a source of new antibiotics with the potential for treatment of multiple-drug resistant infections. An important class of AMPs is composed of linear, cationic peptides that form amphipathic alpha-helices. Among the most potent of these are the cecropins and synthetic peptides that are hybrids of cecropin and the bee venom peptide, mellitin. Both cecropins and cecropin-mellitin hybrids exist in solution as unstructured monomers, folding into predominantly alpha-helical structures upon membrane binding with their long helical axis parallel to the bilayer surface. Studies using model membranes have shown that these peptides intercalate into the lipid bilayer just below the level of the phospholipid glycerol backbone in a location that requires expansion of the outer leaflet of the bilayer, and evidence from a variety of experimental approaches indicates that expansion and thinning of the bilayer are common characteristics during the early stages of antimicrobial peptide-membrane interactions. Subsequent disruption of the membrane permeability barrier may occur by a variety of mechanisms, leading ultimately to loss of cytoplasmic membrane integrity and cell death.

Potent antibacterial lysine-peptoid hybrids identified from a positional scanning combinatorial library

In this paper, we describe the synthesis and screening of a biased positional scanning library made up of peptoids (N-alkylglycines) and lysines. The library consisted of 100 mixtures divided into four sub-libraries; OXXXKKK, XOXXKKK, XXOXKKK, and XXXOKKK, O being a defined peptoid building block and X a mixture of 25 peptoid building blocks. A theoretical number of 390,625 compounds were synthesized. The compound mixtures were screened against the American Type Culture Collection (ATCC) Staphylococcus aureus ATCC 25923 and Escherichia coli ATCC 25922 bacterial strains, and the cytotoxic activities were assessed using a human blood hemolytic assay. The results from each sub-library were examined to identify the most potent amine at each position. On the basis of this knowledge eight new lysine-peptoid hybrids were synthesized and tested in the biological assays. One compound in particular, [N-(cyclohexylmethyl)glycyl]-[N-(1-methylhexyl)glycyl]-[N-(4-methylbenzyl)glycyl]-[N-(2-(3-chlorophenyl)ethyl)glycyl]-lysyl-lysyl-lysine amide, showed high antibacterial activity and low toxicity toward red blood cells.

Cryptococcus gattii: in vitro susceptibility to the new antifungal albaconazole versus fluconazole and voriconazole

Minimal inhibitory concentrations (MIC) and minimal fungicidal activity of albaconazole, voriconazole and fluconazole against 55 strains of Cryptococcus gattii, clinically or environmentally isolated in Spain and some Latin American countries, were assessed. By means of the microbroth method (National Committee for Clinical Laboratory Standards; document M27-A2), the geometric mean value for fluconazole was 5.01 microg/ml; however, MIC for 12.7% of isolates ranged from 16 to 32 microg/ml, suggesting increased resistance against fluconazole. Geometric mean values of 0.02 and 0.03 microg/ml for albaconazole and voriconazole, respectively, were found, indicating not only a higher susceptibility to these new azoles but also a better performance of albaconazole (P = 0.003). Minimal fungicidal concentrations were also very low for albaconazole and voriconazole (P<0.001; geometric mean values of 0.023 microg/ml and 0.07 microg/ml, respectively). Both azoles may be good alternatives for the treatment of C. gattii cryptococcosis.

Pharmacological agents in development for invasive aspergillosis

The urgent medical need for new potent antifungal agents in the management of invasive aspergillosis (IA) has resulted in the development of several compounds which may be of value in the future for the treatment or prophylaxis of IA. In the past years, several novel types of drugs have been discovered and developed, some of which are already in late-stage clinical trials and ready to enter the market. This paper discusses the antifungal agents, classified by their mode of action, that are currently available and the agents which are still in development for treatment or prevention of IA.