Role of lipids in the interaction of antimicrobial peptides with membranes

Dead bacterial absorption of antimicrobial peptides underlies collective tolerance

The collective tolerance towards antimicrobial peptides (APs) is thought to occur primarily through mechanisms associated with live bacterial cells. In contrast to the focus on live cells, we discover that the LL37 antimicrobial peptide kills a subpopulation of Escherichia coli, forming dead cells that absorb the remaining LL37 from the environment. Combining mathematical modelling with population and single-cell experiments, we show that bacteria absorb LL37 at a timing that coincides with the permeabilization of their cytoplasmic membranes. Furthermore, we show that one bacterial strain can absorb LL37 and protect another strain from killing by LL37. Finally, we demonstrate that the absorption of LL37 by dead bacteria can be reduced using a peptide adjuvant. In contrast to the known collective tolerance mechanisms, we show that the absorption of APs by dead bacteria is a dynamic process that leads to emergent population behaviour.

Effect of dipole moment on amphiphile solubility and partition into liquid ordered and liquid disordered phases in lipid bilayers

Association of amphiphiles with biomembranes is important for their availability at specific locations in organisms and cells, being critical for their biological function. A prominent role is usually attributed to the hydrophobic effect, and to electrostatic interactions between charged amphiphiles and lipids. This work explores a closely related and complementary aspect, namely the contribution made by dipole moments to the strength of the interactions established. Two xanthene amphiphiles with opposite relative orientations of their dipole and amphiphilic moments have been selected (Rhodamine-C₁₄ and Carboxyfluorescein-C₁₄). The membranes studied have distinct lipid compositions, representing typical cell membrane pools, ranging from internal membranes to the outer and inner leaflet of the plasma membrane. A comprehensive study is reported, including the affinity of the amphiphiles for the different membranes, the stability of the amphiphiles as monomers and their tendency to form small clusters, as well as their transverse location in the membrane. The orientation of the amphiphile dipole moment, which determines whether its interaction with the membrane dipole potential is repulsive or attractive, is found to exert a large influence on the association of the amphiphile with ordered lipid membranes. These interactions are also responsible for the formation of small clusters or stabilization of amphiphile monomers in the membrane. The results obtained allow understanding the prevalence of protein lipidation at the N-terminal for efficient targeting to the plasma membrane, as well as the tendency of GPI-anchored proteins (usually lipidated at the C-terminal) to form small clusters in the membrane ordered domains.

The Epipeptide YydF Intrinsically Triggers the Cell Envelope Stress Response of Bacillus subtilis and Causes Severe Membrane Perturbations

The Gram-positive model organism and soil bacterium Bacillus subtilis naturally produces a variety of antimicrobial peptides (AMPs), including the ribosomally synthesized and post-translationally modified AMP YydF, which is encoded in the yydFGHIJ locus. The yydF gene encodes the pre-pro-peptide, which is, in a unique manner, initially modified at two amino acid positions by the radical SAM epimerase YydG. Subsequently, the membrane-anchored putative protease YydH is thought to cleave and release the mature AMP, YydF, to the environment. The AMP YydF, with two discreet epimerizations among 17 residues as sole post-translational modification, defines a novel class of ribosomally synthesized and post-translationally modified peptides (RiPPs) called epipeptides, for which the mode-of-action (MOA) is unknown. The predicted ABC transporter encoded by yydIJ was previously postulated as an autoimmunity determinant of B. subtilis against its own AMP. Here, we demonstrate that extrinsically added YydF^* kills B. subtilis cells by dissipating membrane potential via membrane permeabilization. This severe membrane perturbation is accompanied by a rapid reduction of membrane fluidity, substantiated by lipid domain formation. The epipeptide triggers a narrow and highly specific cellular response. The strong induction of liaIH expression, a marker for cell envelope stress in B. subtilis, further supports the MOA described above. A subsequent mutational study demonstrates that LiaIH—and not YydIJ—represents the most efficient resistance determinant against YydF^* action. Unexpectedly, none of the observed cellular effects upon YydF^* treatment alone are able to trigger liaIH expression, indicating that only the unique combination of membrane permeabilization and membrane rigidification caused by the epipetide, leads to the observed cell envelope stress response.

Study of mastoparan analog peptides against Candida albicans and safety in zebrafish embryos (Danio rerio)

Aim: In this work, mastoparan analog peptides from wasp venom were tested against Candida albicans and safety assays were performed using cell culture and model zebrafish. Materials & methods: Minimal inhibitory concentration was determined and toxicity was performed using human skin keratinocyte and embryo zebrafish. Also, permeation of peptides through embryo chorion was performed. Results: The peptides demonstrated anti-C. albicans activity, with low cytotoxicity and nonteratogenicity in Danio rerio. The compounds had different permeation through chorion, suggesting that this occurs due to modifications in their amino acid sequence. Conclusion: The results showed that the studied peptides can be used as structural study models for novel potential antifungal agents.

Conversion of Broad-Spectrum Antimicrobial Peptides into Species-Specific Antimicrobials Capable of Precisely Targeting Pathogenic Bacteria

Currently, the majority of antibiotics in clinical use have broad activity spectra, killing pathogenic and beneficial microorganisms indiscriminately. The disruption of the ecological balance of normal flora often results in secondary infections or other antibiotic-associated complications. Therefore, targeted antimicrobial therapies capable of specifically eliminating pathogenic bacteria while retaining the protective benefits of a normal microflora would be advantageous. In this study, we successfully constructed a series of Enterococcus faecalis-targeted antimicrobial peptides from wide-spectrum antimicrobial peptide precursors. These peptides are designed based on fusion of the species-specific peptide pheromone cCF10 and modification of the active region of the antimicrobial peptide. The results showed that cCF10-C4 possessed specific antimicrobial activity against E. faecalis and was not active against other types of bacteria tested. The specificity of this hybrid peptide was shown by the absence of antimicrobial effects in the pheromone-substituted derivative. Further studies indicated that cCF10-C4 and its parent peptide C4 exert their activities by damaging cytoplasmic membrane integrity. The present study reveals the application potential of these molecules as “probiotic” antimicrobials for the control of specific bacterial infections, and it also helps to elucidate the design and construction of species-specific antimicrobials with precise targeting specificity.

The Antifungal Peptide MCh-AMP1 Derived From Matricaria chamomilla Inhibits Candida albicans Growth via Inducing ROS Generation and Altering Fungal Cell Membrane Permeability

The rise of antifungal drug resistance in Candida species responsible for life threatening candidiasis is considered as an increasing challenge for the public health. MCh-AMP1 has previously been reported as a natural peptide from Matricaria chamomilla L. flowers with broad-spectrum antifungal activity against human pathogenic molds and yeasts. In the current study, the mode of action of synthetic MCh-AMP1 was investigated against Candida albicans, the major etiologic agent of life-threatening nosocomial candidiasis at cellular and molecular levels. Candida albicans ATCC 10231 was cultured in presence of various concentrations of MCh-AMP1 (16-64 μg/mL) and its mode of action was investigated using plasma membrane permeabilization assays, reactive oxygen species (ROS) induction, potassium ion leakage and ultrastructural analyses by electron microscopy. MCh-AMP1 showed fungicidal activity against Candida albicans at the concentrations of 32 and 64 μg/mL. The peptide increased fungal cell membrane permeability as evidenced by elevating of PI uptake and induced potassium leakage from the yeast cells. ROS production was induced by the peptide inside the fungal cells to a maximum of 64.8% at the concentration of 64 μg/mL. Scanning electron microscopy observations showed cell deformation as shrinkage and folding of treated yeast cells. Transmission electron microscopy showed detachment of plasma membrane from the cell wall, cell depletion and massive destruction of intracellular organelles and cell membrane of the fungal cells. Our results demonstrated that MCh-AMP1 caused Candida albicans cell death via increasing cell membrane permeability and inducing ROS production. Therefore, MCh-AMP1 could be considered as a promising therapeutic agent to combat Candida albicans infections.

The role of C-terminal amidation in the mechanism of action of the antimicrobial peptide aurein 1.2

C-terminal amidation is a common feature of wild type membrane disrupting antimicrobial peptides (AMPs). Empirical evidence suggests that this modification increases antimicrobial efficacy. However, the actual role of C-terminal amidation in the molecular mechanism of action of AMPs is not fully understood. Amidation alters two key properties simultaneously: the net charge and helicity of the peptide, both of which are implicated in the mechanism of action. However, the differences between the physicochemical properties of the carboxyl and amide moieties have been disregarded in former studies. In this study we assessed whether the difference in activity is only caused by changes in the helicity and overall charge of a peptide, i.e. whether the chemistry of the terminus is otherwise irrelevant. To do so, the membrane disrupting activity of a modified aurein 1.2 peptide was studied in which a secondary amide was formed with a terminal methyl group, instead of the primary amide as in the wild type peptide. Results of quartz crystal microbalance, dye leakage and circular dichroism experiments show that the activity of the modified peptide is substantially reduced compared to the wild type peptide, in particular that the modified peptide exhibited a much-reduced ability to bind to the membrane. Thus, the primary amide at the C-terminus is required to bind to the membrane, and a secondary amide cannot serve the same purpose. We hypothesize that this difference is related to the hydration state of the terminus. The lack of membrane binding ability of the modified peptide identifies the primary amide moiety at the C terminus as a specific membrane binding motif.

Profiling antimicrobial peptides from the medical maggot Lucilia sericata as potential antibiotics for MDR Gram-negative bacteria

Background

The ability of MDR Gram-negative bacteria to evade even antibiotics of last resort is a severe global challenge. The development pipeline for conventional antibiotics cannot address this issue, but antimicrobial peptides (AMPs) offer an alternative solution.

Objectives

Two insect-derived AMPs (LS-sarcotoxin and LS-stomoxyn) were profiled to assess their suitability for systemic application in humans.

Methods

The peptides were tested against an extended panel of 114 clinical MDR Gram-negative bacterial isolates followed by time–kill analysis, interaction studies and assays to determine the likelihood of emerging resistance. In further in vitro studies we addressed cytotoxicity, cardiotoxicity and off-target interactions. In addition, an in vivo tolerability and pharmacokinetic study in mice was performed.

Results

LS-sarcotoxin and LS-stomoxyn showed potent and selective activity against Gram-negative bacteria and no cross-resistance with carbapenems, fluoroquinolones or aminoglycosides. Peptide concentrations of 4 or 8 mg/L inhibited 90% of the clinical MDR isolates of Escherichia coli, Enterobacter cloacae, Acinetobacter baumannii and Salmonella enterica isolates tested. The ‘all-d’ homologues of the peptides displayed markedly reduced activity, indicating a chiral target. Pharmacological profiling revealed a good in vitro therapeutic index, no cytotoxicity or cardiotoxicity, an inconspicuous broad-panel off-target profile, and no acute toxicity in mice at 10 mg/kg. In mouse pharmacokinetic experiments LS-sarcotoxin and LS-stomoxyn plasma levels above the lower limit of quantification (1 and 0.25 mg/mL, respectively) were detected after 5 and 15 min, respectively.

Conclusions

LS-sarcotoxin and LS-stomoxyn are suitable as lead candidates for the development of novel antibiotics; however, their pharmacokinetic properties need to be improved for systemic administration.

Design of Heptad Repeat Amphiphiles Based on Database Filtering and Structure-Function Relationships to Combat Drug-Resistant Fungi and Biofilms

Due to the emergence of reports of multidrug-resistant fungi, infections caused by multidrug-resistant fungi and biofilms are considered to be a global threat to human health due to the lack of effective broad-spectrum drugs. Here, we developed a series heptad repeat sequences based on an antimicrobial peptide database (APD) and structure-function relationships. Among the developed peptides, the target peptide ACR3 exhibited good activity against all fungi and bacteria tested, including fluconazole-resistant Candida albicans (C. albicans) and methicillin-resistant Staphylococcu saureus (S. aureus), while demonstrating relatively low toxicity and good salt tolerance. The peptide ACR3 inhibits the formation of C. albicans biofilms and has a therapeutic effect on mature biofilms in vitro and in vivo. Moreover, we did not observe any resistance of C. albicans and E. coli against the peptide ACR3. A series of assays and microscopy were used to analyze the antimicrobial mechanism. These results showed that the antimicrobial activity of the peptide ACR3 utilizes a multimodal mechanism that degrades the cell wall barrier, alters the cytoplasmic membrane electrical potential, and induces intracellular reactive oxygen species (ROS) production. In general, the peptide ACR3 is a potent antibacterial agent that shows great potential for use in biomedical coatings and healthcare formulas to combat the growing threat of fungal and bacterial infection.

Ubiquicidin-Derived Peptides Selectively Interact with the Anionic Phospholipid Membrane

Ubiquicidin (UBI)/ribosomal protein S30 (RS30) is an intracellular protein with antimicrobial activities against various pathogens. UBI (29-41) and UBI (31-38) are two crucial peptides derived from Ubiquicidin, which have shown potential as infection imaging probes. Here, we report the interactions of UBI-derived peptides with anionic and zwitterionic phospholipid membranes. Our isothermal titration calorimetry results show that both peptides selectively interact with the anionic phospholipid membrane (a model bacterial membrane) and reside mainly on the membrane surface. The interaction of UBI-derived peptides with the anionic phospholipid membrane is exothermic and driven by both enthalpy (ΔH) and entropy (ΔS), with the entropic term TΔS being greater than ΔH. This large entropic term can be a result of the aggregation of the anionic vesicles, which is confirmed by dynamic light scattering (DLS) measurements. DLS data show that vesicle aggregation is enhanced with increasing peptide-to-lipid molar ratios (P/L) and is found to be more pronounced in the case of UBI (29-41). DLS results are found to be consistent with independent transmission measurements. To study the effects of UBI-derived peptides on the microscopic dynamics of the model bacterial membrane, quasielastic neutron scattering (QENS) measurements have been carried out. The QENS results show that both peptides restrict the lateral motion of the lipid within the leaflet. UBI (29-41) acts as a stronger stiffening agent, hindering the lateral diffusion of lipids more efficiently than UBI (31-38). To our knowledge, this is the first report illustrating the mechanism of interaction of UBI-derived peptides with model membranes. This study also has implications for the improvement and design of antimicrobial peptide-based infection imaging probes.

Cyclic Analogues of Horseshoe Crab Peptide Tachyplesin I with Anticancer and Cell Penetrating Properties

Tachyplesin-I (TI) is a host defense peptide from the horseshoe crab Tachypleus tridentatus that has outstanding potential as an anticancer therapeutic lead. Backbone cyclized TI (cTI) has similar anticancer properties to TI but has higher stability and lower hemolytic activity. We designed and synthesized cTI analogues to further improve anticancer potential and investigated structure-activity relationships based on peptide-membrane interactions, cellular uptake, and anticancer activity. The membrane-binding affinity and cytotoxic activity of cTI were found to be highly dependent on peptide hydrophobicity and charge. We describe two analogues with increased selectivity toward melanoma cells and one analogue with the ability to enter cells with high efficacy and low toxicity. Overall, the structure-activity relationship study shows that cTI can be developed as a membrane-active antimelanoma lead, or be employed as a cell penetrating peptide scaffold that can target and enter cells without damaging their integrity.

Multiple Strategy Optimization of Specifically Targeted Antimicrobial Peptide Based on Structure-Activity Relationships to Enhance Bactericidal Efficiency

Unlike traditional broad-spectrum antibacterial agents, specifically targeted antimicrobial peptides (STAMPs) are difficult for bacteria to develop resistance to due to their unique membrane lytic mechanism. Additionally, STAMPs can maintain a normal ecological balance and provide long-term protection to the body. However, therapeutic applications of STAMPS are hindered by their weak activity and imperfect specificity, as well as lack of knowledge in understanding their structure-activity relationships. To investigate the effects of different parameters on the biological activities of STAMPs, a peptide sequence, WKKIWK^DPGIKKWIK, was truncated, extended, and provided with an increased charge and altered amphipathicity. In addition, a novel template modification method for attaching a phage-displayed peptide, which recognized and bound to Escherichia coli (E. coli) cells, to the end of the sequence was introduced. Compared with the traditional template modification method, peptide 13, which contained a phage-displayed peptide at the C-terminus, exhibited superior narrow-spectrum antibacterial activity against E. coli compared to that of parental peptide 2, and the activity and specificity of peptide 13 were increased by 5.0 and 2.4 times, respectively. Additionally, peptide 13 showed low cytotoxicity and relatively desirable salt, serum, acid, alkaline and heat stability. In this study, peptide 13 specifically killed E. coli by causing cytoplasmic membrane rupture and cytosol leakage. In summary, these findings are useful for improving the activity and specificity of STAMPs and show that peptide 13 is able to combat the growing threat of E. coli infections.

Increases in Hydrophilicity and Charge on the Polar Face of Alyteserin 1c Helix Change its Selectivity towards Gram-Positive Bacteria

Recently, resistance of pathogens towards conventional antibiotics has increased, representing a threat to public health globally. As part of the fight against this, studies on alternative antibiotics such as antimicrobial peptides have been performed, and it has been shown that their sequence and structure are closely related to their antimicrobial activity. Against this background, we here evaluated the antibacterial activity of two peptides developed by solid-phase synthesis, Alyteserin 1c (WT) and its mutant derivative (ΔM), which shows increased net charge and reduced hydrophobicity. These structural characteristics were modified as a result of amino acid substitutions on the polar face of the WT helix. The minimum inhibitory concentration (MIC) of both peptides was obtained in Gram-positive and Gram-negative bacteria. The results showed that the rational substitutions of the amino acids increased the activity in Gram-positive bacteria, especially against Staphylococcus aureus, for which the MIC was one-third of that for the WT analog. In contrast to the case for Gram-positive bacteria, these substitutions decreased activity against Gram-negative bacteria, especially in Escherichia coli, for which the MIC was eight-fold higher than that exhibited by the WT peptide. To understand this, models of the peptide behavior upon interacting with membranes of E. coli and S. aureus created using molecular dynamics were studied and it was determined that the helical stability of the peptide is indispensable for antimicrobial activity. The hydrogen bonds between the His20 of the peptides and the phospholipids of the membranes should modulate the selectivity associated with structural stability at the carboxy-terminal region of the peptides.

Structural characterization of scorpion peptides and their bactericidal activity against clinical isolates of multidrug-resistant bacteria

Scorpion venom peptides represent a novel source of antimicrobial peptides (AMPs) with broad-spectrum activity. In this study, we determined the minimum bactericidal concentration (MBC) of three scorpion AMPs, Uy234, Uy17, and Uy192, which are found in the venomous glands of the Urodacus yaschenkoi scorpion, against the clinical isolates of multidrug-resistant (MDR) bacteria. In addition, we tested the activity of a consensus AMP designed in our laboratory based on some previously reported IsCT-type (cytotoxic linear peptide) AMPs with the aim of obtaining higher antimicrobial activity. All peptides tested showed high antimicrobial activity against MDR clinical isolates, with the highest activity against β-hemolytic Streptococcus strains. The hemolytic activity was determined against human red blood cells and was significantly lower than that of previously reported AMPs. The α-helical structure of the four AMPs was confirmed by circular dichroism (CD). These results suggest that the four peptides can be valuable tools for the design and development of AMPs for use in the inhibition of MDR pathogenic bacteria. A clear index of synergism and additivity was found for the combination of QnCs-BUAP + Uy234, which makes these peptides the most promising candidates against pathogenic bacteria.

Characterization of the Bioactivity and Mechanism of Bactenecin Derivatives Against Food-Pathogens

With the emergence of multidrug-resistant bacteria, antimicrobial peptides (AMPs) are regarded as potential alternatives to traditional antibiotics or chemicals. We designed and synthesized six derivatives of bactenecin (L₂C₃V₁₀C₁₁, RLCRIVVIRVCR), including R₂F₃W₁₀L₁₁ (RRFRIVVIRWLR), R₂W₃W₁₀R₁₁ (RRWRIVVIRWRR), K₂W₃V₁₀R₁₁ (RKWRIVVIRVRR), W₂R₃V₁₀R₁₁ (RWRRIVVIRVRR), W₂K₃K₁₀R₁₁ (RWKRIVVIRKRR), and K₂R₃R₁₀K₁₁ (RKRRIVVIRRKR), by amino acid substitution to increase the net charge and reduce hydrophobicity gradually. The bioactivity and mechanisms of action of the designed peptides were investigated. The results indicated that the antimicrobial activity of the designed peptides was higher than that of bactenecin. The hemolytic activity and cytotoxicity of the designed peptides were significantly lower than those of bactenecin. The designed peptides exhibited a wide range of antimicrobial activity against food-pathogens, particularly peptides K₂W₃V₁₀R₁₁ and W₂R₃V₁₀R₁₁; in addition, the activity was maintained under physiological salt and heat conditions. Mechanism studies indicated that AMPs interacted with negatively charged bacterial cell membranes, resulting in the destruction of cell membrane integrity by increasing membrane permeability and changing transmembrane potential, leading to cell death. The present study suggested that peptides K₂W₃V₁₀R₁₁ and W₂R₃V₁₀R₁₁ exhibited potential as alternatives to traditional antibiotics or chemicals for the treatment of food-pathogens. These findings lead to the development of a potential method for the design of novel AMPs.

Aggregation determines the selectivity of membrane-active anticancer and antimicrobial peptides: The case of killerFLIP

Host defense peptides selectively kill bacterial and cancer cells (including those that are drug-resistant) by perturbing the permeability of their membranes, without being significantly toxic to the host. Coulombic interactions between these cationic and amphipathic peptides and the negatively charged membranes of pathogenic cells contribute to the selective toxicity. However, a positive charge is not sufficient for selectivity, which can be achieved only by a finely tuned balance of electrostatic and hydrophobic driving forces. A common property of amphipathic peptides is the formation of aggregated structures in solution, but the role of this phenomenon in peptide activity and selectivity has received limited attention. Our data on the anticancer peptide killerFLIP demonstrate that aggregation strongly increases peptide selectivity, by reducing the effective peptide hydrophobicity and thus the affinity towards membranes composed of neutral lipids (like the outer layer of healthy eukaryotic cell membranes). Aggregation is therefore a useful tool to modulate the selectivity of membrane active peptides and peptidomimetics.

Cytotoxic Effects of Smp24 and Smp43 Scorpion Venom Antimicrobial Peptides on Tumour and Non-tumour Cell Lines

Smp24 and Smp43 are novel cationic AMPs identified from the venom of the Egyptian scorpion Scorpio maurus palmatus, having potent activity against both Gram-positive and Gram-negative bacteria as well as fungi. Here we describe cytotoxicity of these peptides towards three non-tumour cell lines (CD34+ (hematopoietic stem progenitor from cord blood), HRECs (human renal epithelial cells) and HACAT (human skin keratinocytes) and two acute leukaemia cell lines (myeloid (KG1a) and lymphoid (CCRF-CEM) leukaemia cell lines) using a combination of biochemical and imaging techniques. Smp24 and Smp43 (4–256 µg/mL) decreased the cell viability (as measured by intracellular ATP) of all cells tested, although keratinocytes were markedly less sensitive. Cell membrane leakage as evidenced by the release of lactate dehydrogenase was evident throughout and was confirmed by scanning electron microscope studies.

Studies on the Interaction of Alyteserin 1c Peptide and Its Cationic Analogue with Model Membranes Imitating Mammalian and Bacterial Membranes

Antimicrobial peptides (AMPs) are effector molecules of the innate immune system and have been isolated from multiple organisms. Their antimicrobial properties are due to the fact that they interact mainly with the anionic membrane of the microorganisms, permeabilizing it and releasing the cytoplasmic content. Alyteserin 1c (+2), an AMP isolated from Alytes obstetricans and its more cationic and hydrophilic analogue (+5) were synthesized using the solid phase method, in order to study the interaction with model membranes by calorimetric and spectroscopic assays. Differential scanning calorimetry (DSC) showed that both peptides had a strong effect when the membrane contained phosphatidylcholine (PC) alone or was mixed with phosphatidylglycerol (PG), increasing membrane fluidization. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) was used to study the secondary structure of the peptide. Peptide +2 exhibited a transition from β-sheet/turns to β-sheet/α-helix structures after binding with model membranes, whereas peptide +5 had a transition from aggregation/unordered to β-sheet/α-helix structures after binding with membrane-contained PC. Interestingly, the latter showed a β-sheet structure predominantly in the presence of PG lipids. Additionally, molecular dynamics (MD) results showed that the carboxy-terminal of the peptide +5 has the ability to insert into the surface of the PC/PG membranes, resulting in the increase of the membrane fluidity.

Solution structure of linear battacin lipopeptides - the effect of lengthening fatty acid chain

In recent years, lipopeptides have received attention for their enhanced antimicrobial activity, especially against multi-drug resistant (MDR) pathogens. We have previously reported that the bacterial soil extracted, novel cyclic lipopeptide, battacin, and its synthetic analogues have enhanced antimicrobial activity against various Gram negative, Gram positive and fungal pathogens. In particular, the modification of the hydrophobic fatty acid chain and molecular structure has improved its activity. We have used small angle X-ray scattering (SAXS) and circular dichroism (CD) to characterise the low resolution structure of battacin lipopeptides containing covalently bonded fatty acid chains and the one without it. In the absence of fatty acids or with short fatty acid chain, the peptides adopted an extended random coil structure that is best described barbell-like shape, while fatty acids that are sufficiently long induced an aggregation into a ∼4.0 nm diameter core shell sphere. While the kinked structure found within this barbell shape may have a role in antimicrobial activities, the self-assembly of the battacin analogue with the longest fatty acid chain may have a correlation to the declined antibacterial activities.

The innate immune system of kissing bugs, vectors of chagas disease

Kissing bugs have long served as models to study many aspects of insect physiology. They also serve as vectors for the parasite Trypanosoma cruzi that causes Chagas disease in humans. The overall success of insects is due, in part, to their ability to recognize parasites and pathogens as non-self and to eliminate them using their innate immune system. This immune system comprises physical barriers, cellular responses (phagocytosis, nodulation and encapsulation), and humoral factors (antimicrobial peptides and the prophenoloxidase cascade). Trypanosoma cruzi survives solely in the gastrointestinal (GI) tract of the vector; if it migrates to the hemocoel it is eliminated. Kissing bugs may not mount a vigorous immune response in the GI tract to avoid eliminating obligate symbiotic microbes on which they rely for survival. Here we describe the current knowledge of innate immunity in kissing bugs and new opportunities using genomic and transcriptomic approaches to study the complex triatomine-trypanosome-microbiome interactions.

Characterization of Tachyplesin Peptides and Their Cyclized Analogues to Improve Antimicrobial and Anticancer Properties

Tachyplesin I, II and III are host defense peptides from horseshoe crab species with antimicrobial and anticancer activities. They have an amphipathic β-hairpin structure, are highly positively-charged and differ by only one or two amino acid residues. In this study, we compared the structure and activity of the three tachyplesin peptides alongside their backbone cyclized analogues. We assessed the peptide structures using nuclear magnetic resonance (NMR) spectroscopy, then compared the activity against bacteria (both in the planktonic and biofilm forms) and a panel of cancerous cells. The importance of peptide-lipid interactions was examined using surface plasmon resonance and fluorescence spectroscopy methodologies. Our studies showed that tachyplesin peptides and their cyclic analogues were most potent against Gram-negative bacteria and melanoma cell lines, and showed a preference for binding to negatively-charged lipid membranes. Backbone cyclization did not improve potency, but improved peptide stability in human serum and reduced toxicity toward human red blood cells. Peptide-lipid binding affinity, orientation within the membrane, and ability to disrupt lipid bilayers differed between the cyclized peptide and the parent counterpart. We show that tachyplesin peptides and cyclized analogues have similarly potent antimicrobial and anticancer properties, but that backbone cyclization improves their stability and therapeutic potential.

Design and synthesis of new N-terminal fatty acid modified-antimicrobial peptide analogues with potent in vitro biological activity

Developing novel antimicrobial agents is a top priority in fighting against bacterial resistance. Thus, a series of new monomer and dimer peptides were designed and synthesized by conjugating fatty acids at the N-terminus of partial d-amino acid substitution analogues of anoplin and dimerization. The new peptides exhibited more efficient killing of gram-negative and gram-positive bacteria, including methicillin-resistant Staphylococcus aureus compared with the parent peptide anoplin, and the dimer peptides were superior to the monomer peptides. It was important that the new peptides displayed low impact on bacterial resistance development. In addition, the antimicrobial activities were not significantly influenced by a physiological salt environment. They also presented high stability in the presence of protease or serum. Almost all of the new peptides had better selectivity towards anionic bacterial membranes over zwitterionic mammalian cell membranes. Moreover, the new peptides displayed synergistic or additive effects when used together with the antibiotics rifampicin and polymyxin B. These results showed that the new peptides could also prevent the formation of bacterial biofilms. Furthermore, outer/inner membrane permeabilization and cytoplasmic membrane depolarization experiments revealed that the new peptides had strong membrane permeabilization and depolarization. Confocal laser scanning microscopy, flow cytometry analysis and scanning electron microscopy further demonstrated that the new peptides could damage the integrity of the bacterial membrane. Finally, a DNA-binding affinity assay showed that the new peptides could bind to bacterial DNA. In summary, the conjugation of fatty acids at the N-terminus of peptides and dimerization are promising strategies for obtaining potent antimicrobial agents.

Medicinal leech antimicrobial peptides lacking toxicity represent a promising alternative strategy to combat antibiotic-resistant pathogens

The rise of antibiotic resistance has necessitated the development of alternative strategies for the treatment of infectious diseases. Antimicrobial peptides (AMPs), components of the innate immune response in various organisms, are promising next-generation drugs against bacterial infections. The ability of the medicinal leech Hirudo medicinalis to store blood for months with little change has attracted interest regarding the identification of novel AMPs in this organism. In this study, we employed computational algorithms to the medicinal leech genome assembly to identify amino acid sequences encoding potential AMPs. Then, we synthesized twelve candidate AMPs identified by the algorithms, determined their secondary structures, measured minimal inhibitory concentrations against three bacterial species (Escherichia coli, Bacillus subtilis, and Chlamydia thrachomatis), and assayed cytotoxic and haemolytic activities. Eight of twelve candidate AMPs possessed antimicrobial activity, and only two of them, 3967 (FRIMRILRVLKL) and 536-1 (RWRLVCFLCRRKKV), exhibited inhibition of growth of all tested bacterial species at a minimal inhibitory concentration of 10 μmol. Thus, we evidence the utility of the developed computational algorithms for the identification of AMPs with low toxicity and haemolytic activity in the medicinal leech genome assembly.

Redesigning Arenicin-1, an Antimicrobial Peptide from the Marine Polychaeta Arenicola marina, by Strand Rearrangement or Branching, Substitution of Specific Residues, and Backbone Linearization or Cyclization

Arenicin-1, a β-sheet antimicrobial peptide isolated from the marine polychaeta Arenicola marina coelomocytes, has a potent, broad-spectrum microbicidal activity and also shows significant toxicity towards mammalian cells. Several variants were rationally designed to elucidate the role of structural features such as cyclization, a certain symmetry of the residue arrangement, or the presence of specific residues in the sequence, in its membranolytic activity and the consequent effect on microbicidal efficacy and toxicity. The effect of variations on the structure was probed using molecular dynamics simulations, which indicated a significant stability of the β-hairpin scaffold and showed that modifying residue symmetry and β-strand arrangement affected both the twist and the kink present in the native structure. In vitro assays against a panel of Gram-negative and Gram-positive bacteria, including drug-resistant clinical isolates, showed that inversion of the residue arrangement improved the activity against Gram-negative strains but decreased it towards Gram-positive ones. Variants with increased symmetry were somewhat less active, whereas both backbone-cyclized and linear versions of the peptides, as well as variants with R→K and W→F replacement, showed antimicrobial activity comparable with that of the native peptide. All these variants permeabilized both the outer and the inner membranes of Escherichia coli, suggesting that a membranolytic mechanism of action was maintained. Our results indicate that the arenicin scaffold can support a considerable degree of variation while maintaining useful biological properties and can thus serve as a template for the elaboration of novel anti-infective agents.

Mechanistic predictions of the influence of collagen-binding domain sequences on human LL37 interactions with model lipids using quartz crystal microbalance with dissipation

Modifications of human-derived antimicrobial peptide LL37 with collagen binding domains (CBD-LL37) hold promise as alternatives to antibiotics due to their wider therapeutic ratio than unmodified LL37 when interacting with collagen substrates such as commercial wound dressings. However, CBD-LL37 lipid membrane interaction mechanisms (against both mammalian and bacterial lipids) are not well understood. Our goal was to develop a mechanistic explanation of how CBDs modulate peptide-lipid interactions leading to their observed bioactivities, in order to better understand their potential for clinical applications. The authors studied time- and concentration-dependent interactions of CBD-LL37 modified with collagenase (cCBD) and fibronectin (fCBD) CBDs, with zwitterionic and anionic supported lipid bilayers, in order to model mammalian erythrocytes and bacterial cells, respectively. Quartz crystal microbalance with dissipation monitoring (QCM-D) was used to characterize peptide-lipid interactions at concentrations in the immunomodulatory (0.5-1.0 μM), antimicrobial (1.0-5.0 μM), and cytotoxic (5.0-10.0 μM) ranges. Their prior work with zwitterionic membranes demonstrated that cCBD-LL37 formed transmembrane pores while fCBD-LL37 underwent surface adsorption. Our goal in this study is to better interpret these results, by investigating the data at a wider concentration range and for two types of lipids, and by applying the Voigt-Kelvin viscoelastic model to calculate thickness and density changes of the peptide-lipid films as a function of time and concentration, thus providing information to help build detailed mechanisms of peptide/bilayer interactions. For pore-forming cCBD-LL37 and unmodified LL37, they found that there was a relationship between layer thicknesses and pore formation, which was attributed to different peptide orientation changes influenced by bilayer charge prior to pore formation. Specifically, cCBD-LL37 at 0.5 and 1.0 μM demonstrated higher thicknesses on zwitterionic than anionic membranes, indicating that prior to insertion into zwitterionic membranes, it orients perpendicular to the surface, which was also consistent with the higher dissipation changes observed on zwitterionic membranes. fCBD-LL37 demonstrated a bilayer adsorption mechanism with a preference toward anionic lipids. Adsorption of fCBD-LL37 onto anionic lipids demonstrated a rapid first adsorption step that transitioned depending on the number of fCBD-LL37 molecules on the bilayer. For this peptide at higher concentrations, greater dissipation changes were observed than for fCBD-LL37 physically adsorbed onto surfaces without bilayers. This suggests that peptide-peptide interactions promoted by the fCBD domain dominated after saturation. The development of a structure-function relationship for cCBD-LL37 and fCBD-LL37 demonstrates promise for using QCM-D predictions to inform the rational design of novel, antimicrobial, and noncytotoxic CBD-LL37 for clinical applications.

Application of Antimicrobial Peptides of the Innate Immune System in Combination With Conventional Antibiotics-A Novel Way to Combat Antibiotic Resistance?

Rapidly growing resistance of pathogenic bacteria to conventional antibiotics leads to inefficiency of traditional approaches of countering infections and determines the urgent need for a search of fundamentally new anti-infective drugs. Antimicrobial peptides (AMPs) of the innate immune system are promising candidates for a role of such novel antibiotics. However, some cytotoxicity of AMPs toward host cells limits their active implementation in medicine and forces attempts to design numerous structural analogs of the peptides with optimized properties. An alternative route for the successful AMPs introduction may be their usage in combination with conventional antibiotics. Synergistic antibacterial effects have been reported for a number of such combinations, however, the molecular mechanisms of the synergy remain poorly understood and little is known whether AMPs cytotoxicy for the host cells increases upon their application with antibiotics. Our study is directed to examination of a combined action of natural AMPs with different structure and mode of action (porcine protegrin 1, caprine bactenecin ChBac3.4, human alpha- and beta-defensins (HNP-1, HNP-4, hBD-2, hBD-3), human cathelicidin LL-37), and egg white lysozyme with varied antibiotic agents (gentamicin, ofloxacin, oxacillin, rifampicin, polymyxin B, silver nanoparticles) toward selected bacteria, including drug-sensitive and drug-resistant strains, as well as toward some mammalian cells (human erythrocytes, PBMC, neutrophils, murine peritoneal macrophages and Ehrlich ascites carcinoma cells). Using “checkerboard titrations” for fractional inhibitory concentration indexes evaluation, it was found that synergy in antibacterial action mainly occurs between highly membrane-active AMPs (e.g., protegrin 1, hBD-3) and antibiotics with intracellular targets (e.g., gentamicin, rifampcin), suggesting bioavailability increase as the main model of such interaction. In some combinations modulation of dynamics of AMP-bacterial membrane interaction in presence of the antibiotic was also shown. Cytotoxic effects of the same combinations toward normal eukaryotic cells were rarely synergistic. The obtained data approve that combined application of antimicrobial peptides with antibiotics or other antimicrobials is a promising strategy for further development of new approach for combating antibiotic-resistant bacteria by usage of AMP-based therapeutics. Revealing the conventional antibiotics that increase the activity of human endogenous AMPs against particular pathogens is also important for cure strategies elaboration.

Rational Design of Short Peptide Variants by Using Kunitzin-RE, an Amphibian-Derived Bioactivity Peptide, for Acquired Potent Broad-Spectrum Antimicrobial and Improved Therapeutic Potential of Commensalism Coinfection of Pathogens

Commensalism coinfection of pathogens has seriously jeopardized human health. Currently, Kunitzin-RE, as an amphibian-derived bioactivity peptide, is regarded as a potential antimicrobial candidate. However, its antimicrobial properties were unsatisfactory. In this study, a set of shortened variants of Kunitzin-RE was developed by the interception of a peptide fragment and single-site mutation to investigate the effect of chain length, positive charge, hydrophobicity, amphipathicity, and secondary structure on antimicrobial properties. Among them, W8 (AARIILRWRFR) significantly broadened the antimicrobial spectrum and showed the highest antimicrobial activity (GM_all = 2.48 μM) against all the fungi and bacteria tested. Additionally, W8 showed high cell selectivity and salt tolerance in vitro, whereas it showed high effectiveness against mice keratitis cause by infection by C. albicans 2.2086. Additionally, it also had obviously lipopolysaccharide-binding ability and a potent membrane-disruptive mechanism. Overall, these findings contributed to the design of short antimicrobial peptides and to combat the serious threat of commensalism coinfection of pathogens.

Drug delivery systems designed to overcome antimicrobial resistance

Antimicrobial resistance has emerged as a huge challenge to the effective treatment of infectious diseases. Aside from a modest number of novel anti-infective agents, very few new classes of antibiotics have been successfully developed for therapeutic use. Despite the research efforts of numerous scientists, the fight against antimicrobial (ATB) resistance has been a longstanding continued effort, as pathogens rapidly adapt and evolve through various strategies, to escape the action of ATBs. Among other mechanisms of resistance to antibiotics, the sophisticated envelopes surrounding microbes especially form a major barrier for almost all anti-infective agents. In addition, the mammalian cell membrane presents another obstacle to the ATBs that target intracellular pathogens. To negotiate these biological membranes, scientists have developed drug delivery systems to help drugs traverse the cell wall; these are called "Trojan horse" strategies. Within these delivery systems, ATB molecules can be conjugated with one of many different types of carriers. These carriers could include any of the following: siderophores, antimicrobial peptides, cell-penetrating peptides, antibodies, or even nanoparticles. In recent years, the Trojan horse-inspired delivery systems have been increasingly reported as efficient strategies to expand the arsenal of therapeutic solutions and/or reinforce the effectiveness of conventional ATBs against drug-resistant microbes, while also minimizing the side effects of these drugs. In this paper, we aim to review and report on the recent progress made in these newly prevalent ATB delivery strategies, within the current context of increasing ATB resistance.

Identification and expression of the hepcidin gene from brown trout (Salmo trutta) and functional analysis of its synthetic peptide

Hepcidin, a hepatic antimicrobial peptide, is a key player of the nonspecific immune system. The structure of hepcidin gene from brown trout (Bthepc) has been characterized at the molecular level. The 1158-bp mRNA generates a coding sequence (CDS) of 267 bp, which encodes an 88-amino acid protein. Molecular evolution analysis classified Bthepc to the family Salmonidae. Amino acid sequence homologies between Bthepc and hepcidin in other species such as Oncorhynchus mykiss, Salmo salar, and Hucho taimen were found to be 93.18%, 96.59%, and 92.05% respectively. The mature peptide and the signal peptide of Bthepc are made of 25 and 24 amino acids, respectively. Similar to the other species, eight conserved cysteines in the mature peptide of Bthepc are held together by four disulphide bonds. Expression profiling of Bthepc indicated its highest expression in the liver. Further, iron levels or inflammation did not induce the age-dependent expression of Bthepc. Bthepc mRNA expression analysis in six immune tissues (liver, gill, spleen, skin, head kidney and intestine) indicated different levels of increase when challenged with Aeromonas salmonicida and Aeromonas hydrophila. The antimicrobial activity of synthetic Bthepc to typical pathogens was verified in vitro. In addition, Bthepc showed moderate haemolytic activity to mammalian erythrocytes. The antimicrobial activity of Bthepc was attributed to the disruption of the bacterial outer membrane integrity, which was evident from our scanning electron microscopy results. In summary, hepcidin gene of brown trout was characterized, and its antimicrobial activity was verified on different levels.

Enhanced Expression and Functional Characterization of the Recombinant Putative Lysozyme-PMAP36 Fusion Protein

The porcine myeloid antimicrobial peptide (PMAP), one of the cathelicidin family members, contains small cationic peptides with amphipathic properties. We used a putative lysozyme originated from the bacteriophage P22 (P22 lysozyme) as a fusion partner, which was connected to the N-terminus of the PMAP36 peptide, to markedly increase the expression levels of recombinant PMAP36. The PMAP36-P22 lysozyme fusion protein with high solubility was produced in Escherichia coli. The final purified yield was approximately 1.8 mg/L. The purified PMAP36-P22 lysozyme fusion protein exhibited antimicrobial activity against both Gram-negative and Gram-positive bacteria (Staphylococcus aureus, Salmonella enterica serovar Typhimurium, Pseudomonas aeruginosa, and Bacillus subtilis). Furthermore, we estimated its hemolytic activity against pig erythrocytes as 6% at the high concentration (128 μM) of the PMAP36-P22 lysozyme fusion protein. Compared with the PMAP36 peptide (12%), our fusion protein exhibited half of the hemolytic activity. Overall, our recombinant PMAP36-P22 lysozyme fusion protein sustained the antimicrobial activity with the lower hemolytic activity associated with the synthetic PMAP36 peptide. This study suggests that the PMAP36-P22 lysozyme fusion system could be a crucial addition to the plethora of novel antimicrobials.

Symmetrical Modification of Minimized Dermaseptins to Extend the Spectrum of Antimicrobials with Endotoxin Neutralization Potency

Antimicrobial peptides (AMPs) have emerged as a promising class of antimicrobial agents that could potentially address the global antibiotic resistance. Generating mirror-like peptides by minimizing dermaseptin family sequences is an effective strategy for designing AMPs. However, the previous research still had some limitations such as lower effectiveness and a narrow spectrum of antibacterial activity. To further expand and hone this strategy, we designed a series of AMPs consisting of the WXMXW-NH₂ motif (X represents V, I, F, and W; M represents KAAAKAAAK). The peptides formed α-helices and displayed broad-spectrum antimicrobial activities against eleven types of clinical bacteria including both Gram-negative and Gram-positive bacteria. The optimized peptide WW exhibited high physical rupture by inducing membrane shrinkage, disruption, and lysis. Moreover, WW effectively neutralized endotoxins and inhibited the inflammatory response while having the highest therapeutic index. In conclusion, these results indicated that the peptide WW has potential as a broad-spectrum antimicrobial agent or preservative for overcoming the risk of multidrug resistance in localized or external therapeutic applications.

Characterization and Antimicrobial Activity of Amphiphilic Peptide AP3 and Derivative Sequences

The continued emergence of new antibiotic resistant bacterial strains has resulted in great interest in the development of new antimicrobial treatments. Antimicrobial peptides (AMPs) are one of many potential classes of molecules to help meet this emerging need. AMPs are naturally derived sequences, which act as part of the innate immune system of organisms ranging from insects through humans. We investigated the antimicrobial peptide AP3, which is originally isolated from the winter flounder Pleuronectes americanus. This peptide is of specific interest because it does not exhibit the canonical facially amphiphilic orientation of side chains when in a helical orientation. Different analogs of AP3 were synthesized in which length, charge identity, and Trp position were varied to investigate the sequence-structure and activity relationship. We performed biophysical and microbiological characterization using fluorescence spectroscopy, CD spectroscopy, vesicle leakage assays, bacterial membrane permeabilization assays, and minimal inhibitory concentration (MIC) assays. Fluorescence spectroscopy showed that the peptides bind to lipid bilayers to similar extents, while CD spectra show the peptides adopt helical conformations. All five peptides tested in this study exhibited binding to model lipid membranes, while the truncated peptides showed no measurable antimicrobial activity. The most active peptide proved to be the parent peptide AP3 with the highest degree of leakage and bacterial membrane permeabilization. Moreover, it was found that the ability to permeabilize model and bacterial membranes correlated most closely with the ability to predict antimicrobial activity.

Membrane disintegration by the antimicrobial peptide (P)GKY20: lipid segregation and domain formation

Antimicrobial peptides (AMPs) are membrane-active peptides with a broad spectrum of activity against different pathogenic organisms and they represent promising new drugs to overcome the emergence of resistance to antibiotics in bacteria. (P)GKY20 is an antimicrobial peptide with a low hemolytic effect on eukaryotic cells and a strong antimicrobial activity especially against Gram-negative bacteria. However, its mechanism of action is still unknown. Here, we use fluorescence spectroscopy and differential scanning calorimetry combined with atomic force microscopy to characterise the binding of (P)GKY20 with model biomembranes and its effect on the membrane's microstructure and thermotropic properties. We found that (P)GKY20 selectively perturbs the bacterial-like membrane via a carpet-like mechanism employing peptide conformational changes, lipid segregation and domain formation as key steps in promoting membrane disruption. These results shed a first light on the action mechanism of (P)GKY20 and could represent an important contribution to the development of new peptides serving as antimicrobial agents.

Elastic behavior of model membranes with antimicrobial peptides depends on lipid specificity and d-enantiomers

In an effort to provide new treatments for the global crisis of bacterial resistance to current antibiotics, we have used a rational approach to design several new antimicrobial peptides (AMPs). The present study focuses on 24-mer WLBU2 and its derivative, D8, with the amino acid sequence, RRWVRRVRRWVRRVVRVVRRWVRR. In D8, all of the valines are the d-enantiomer. We use X-ray low- and wide-angle diffuse scattering data to measure elasticity and lipid chain order. We show a good correlation between in vitro bacterial killing efficiency and both bending and chain order behavior in bacterial lipid membrane mimics; our results suggest that AMP-triggered domain formation could be the mechanism of bacterial killing in both Gram-positive and Gram-negative bacteria. In red blood cell lipid mimics, D8 stiffens and orders the membrane, while WLBU2 softens and disorders it, which correlate with D8's harmless vs. WLBU2's toxic behavior in hemolysis tests. These results suggest that elasticity and chain order behavior can be used to predict mechanisms of bactericidal action and toxicity of new AMPs.

Effects of Hydrophobic Amino Acid Substitutions on Antimicrobial Peptide Behavior

Antimicrobial peptides (AMPs) are naturally occurring components of the immune system that act against bacteria in a variety of organisms throughout the evolutionary hierarchy. There have been many studies focused on the activity of AMPs using biophysical and microbiological techniques; however, a clear and predictive mechanism toward determining if a peptide will exhibit antimicrobial activity is still elusive, in addition to the fact that the mechanism of action of AMPs has been shown to vary between peptides, targets, and experimental conditions. Nonetheless, the majority of AMPs contain hydrophobic amino acids to facilitate partitioning into bacterial membranes and a net cationic charge to promote selective binding to the anionic surfaces of bacteria over the zwitterionic host cell surfaces. This study explores the role of hydrophobic amino acids using the peptide C18G as a model system. These changes were evaluated for the effects on antimicrobial activity, peptide-lipid interactions using Trp fluorescence spectroscopy, peptide secondary structure formation, and bacterial membrane permeabilization. The results show that while secondary structure formation was not significantly impacted by the substitutions, antibacterial activity and binding to model lipid membranes were well correlated. The variants containing Leu or Phe as the sole hydrophobic groups bound bilayers with highest affinity and were most effective at inhibiting bacterial growth. Peptides with Ile exhibited intermediate behavior while those with Val or α-aminoisobutyric acid (Aib) showed poor binding and activity. The Leu, Phe, and Ile peptides demonstrated a clear preference for anionic bilayers, exhibiting significant emission spectrum shifts upon binding. Similarly, the Leu, Phe, and Ile peptides demonstrated greater ability to disrupt lipid vesicles and bacterial membranes. In total, the data indicate that hydrophobic moieties in the AMP sequence play a significant role in the binding and ability of the peptide to exhibit antibacterial activity.

Evaluation of the Antimicrobial Activity of Cationic Peptides Loaded in Surface-Modified Nanoliposomes against Foodborne Bacteria

Bacteria are a common group of foodborne pathogens presenting public health issues with a large economic burden for the food industry. Our work focused on a solution to this problem by evaluating antibiotic activity against two bacteria (Listeria monocytogenes and Escherichia coli) of relevance in the field of foodstuffs. We used two approaches: (i) structural modification of the antimicrobial peptides and (ii) nano-vehiculisation of the modified peptides into polymer-coated liposomes. To achieve this, two antimicrobial peptides, herein named ‘peptide +2′ and ‘peptide +5′ were synthesised using the solid phase method. The physicochemical characterisation of the peptides was carried out using measurements of surface tension and dynamic light scattering. Additionally, nanoliposomes were elaborated by the ethanol injection method and coated with a cationic polymer (Eudragit E-100) through the layer-by-layer process. Liposome characterisation, in terms of size, polydispersity and zeta potential, was undertaken using dynamic light scattering. The results show that the degree of hydrophilic modification in the peptide leads to different characteristics of amphipathicity and subsequently to different physicochemical behaviour. On the other hand, antibacterial activity against both bacteria was slightly altered after modifying peptide sequence. Nonetheless, after the encapsulation of the peptides into polymer-coated nano-liposomes, the antibacterial activity increased approximately 2000-fold against that of L. monocytogenes.

Inhibition of peptide BF-30 on influenza A virus infection in vitro/vivo by causing virion membrane fusion

Influenza A virus is a leading cause of mortality in humans and poses a global health emergency due to its newly adapted and resistant strains. Thus, there is an urgency to develop novel anti-influenza drugs. Peptides are a type of biological molecule having a wide range of inhibitory effects against bacteria, fungi, viruses and cancer cells. The prospects of several peptides and their mechanisms of action have received significant attention. BF-30, a 30 amino acid residue peptide isolated from the venom of the snake, Bungarus fasciatus, is reported to have antibacterial and antitumor activities. Here, we demonstrated that the 50% cytotoxic concentration (CC50) of the peptide to MDCK cells is 67.7 μM. While BF-30 could inhibit the influenza virus strains H1N1, H3N2 and the oseltamivir-resistant strain H1N1, in vitro, with 50% effective concentration (EC50) of 5.2, 7.4 and 18.9 μM, respectively. In animal experiments, mice treated with BF-30 showed 50% survival at a dosage of 4 μM, with an approximately 2 log viral titer decrease in the lung. However, further studies showed that BF-30 worked on only the virus invasion stage, and inhibited the influenza virus infection by causing virion membrane fusion rather than interacting with hemagglutinin or neuraminidase. These results demonstrated that the peptide BF-30 exhibited an effective inhibitory activity against the influenza A virus and could be a promising candidate for influenza virus therapy.