Amphiphilic Antimicrobial Peptides Research Articles

Combination of a pH-responsive peptide amphiphile and a conventional antibiotic in treating Gram-negative bacteria

BackgroundClinical treatments ofgastric infections using antibiotics suffer from the undesired killing of commensal bacteria and emergence of antibiotic resistance. It is desirable to develop pH-responsive antimicrobial peptides (AMPs) that kill pathogenic bacteria such as H. pyloriand resistant E. coli under acidic environment with minimal impact to commensal bacteria whilst not causing antibiotic resistance. ExperimentsUsing a combined approach of cell assays, molecular dynamics (MD) simulations and membrane models facilitating biophysical and biochemical measurements including small angle neutron scattering (SANS), we have characterized the pH-responsive physiochemical properties and antimicrobial performance of two amphiphilic AMPs, GIIKDIIKDIIKDI-NH2 and GIIKKIIDDIIKKI-NH2 (denoted as 3D and 2D, respectively), that were designed by selective substitutions of cationic residues of Lys (K) in the extensively studied AMP G(IIKK)3I-NH2 with anionic residue Asp (D). FindingsWhilst 2D kept non-ordered coils across the entire pH range studied, 3D displayed a range of secondary structures when pH was shifted from basic to acidic, with distinct self-assembly into nanofibers in aqueous environment. Further experimental and modeling studies revealed that the AMPs interacted differently with the inner and outer membranes of Gram-negative bacteria in a pH-responsive manner and that the structural features characterized by membrane leakage and intramembrane nanoaggregates revealed from fluorescence spectroscopy and SANS were well linked to antimicrobial actions. Different antimicrobial efficacies of 2D and 3D were underlined by the interplay between their ability to bind to the outer membrane lipid LPS (lipopolysaccharide), outer membrane permeability change and inner membrane depolarization and leakage. Furthermore, AMP’s binding with the inner membrane under acidic condition caused both the dissipation of membrane potential (Δψ) and the continuous dissipation of transmembrane ΔpH, with Δψ and ΔpH being the key components of the proton motive force. Combinations of antibiotic (Minocycline) with the pH-responsive AMP generated the synergistic effects against Gram-negative bacteria only under acidic condition. These features are crucial to target applications to gastric infections, anti-acne and wound healing.

Encapsulation in oleyl-modified hyaluronic acid nanogels substantially improves the clinical potential of the antimicrobial peptides SAAP-148 and Ab-Cath

Antimicrobial peptides (AMPs) are promising alternatives to antibiotics for treatment of antimicrobial resistant (AMR) bacterial infections. However, their narrow therapeutic window due to in vivo toxicity and limited stability hampers their clinical use. Here, we evaluated encapsulation of two amphiphilic AMPs, SAAP-148 and snake cathelicidin Ab-Cath, into oleyl-modified hyaluronic acid (OL-HA) nanogels to improve their selectivity index. The AMP-loaded OL-HA nanogels ranged 181–206 nm in size with a PDI of 0.2, highly negative surface charge (−47 to −48 mV) and moderate encapsulation efficiency (53–63%). The AMP-loaded OL-HA nanogels displayed similar activity in vitro as AMP solutions against AMR Staphylococcus aureus and Acinetobacter baumannii, with a dose-dependent effect over time. Importantly, the AMP-loaded OL-HA nanogels showed decreased cytotoxicity towards human erythrocytes and primary skin fibroblast, thereby improving the selectivity index of SAAP-148 and Ab-Cath by 2- and 16.8-fold, respectively. Particularly, the selectivity of Ab-Cath-loaded OL-HA nanogels has great clinical potential, with an index that reached ≥ 300 for S. aureus and ≥ 3000 for A. baumannii. These findings indicate that OL-HA nanogels are a promising drug delivery system to reduce the cytotoxicity of AMPs without substantially affecting their antimicrobial activity, thereby increasing their selectivity index and potential as therapeutics to combat AMR bacterial infections.

Antimicrobial peptides fight against Pseudomonas aeruginosa at a sub-inhibitory concentration via anti-QS pathway

The broad-spectrum antimicrobial ability of de novo designed amphiphilic antimicrobial peptides (AMPs) G(IIKK)3I-NH2 (G3) and C8-G(IIKK)2I-NH2 (C8G2) have been demonstrated. Nonetheless, their potential as anti-quorum-sensing (anti-QS) agents, particularly against the opportunistic pathogen Pseudomonas aeruginosa at subinhibitory concentrations, has received limited attention. In this study, we proved that treating P. aeruginosa PAO1 with both AMPs at subinhibitory concentrations led to significant inhibition of QS-regulated virulence factors, including pyocyanin, elastase, proteases, and bacterial motility. Additionally, the AMPs exhibited remarkable capabilities in suppressing biofilm formation and their elimination rate of mature biofilm exceeded 95%. Moreover, both AMPs substantially downregulated the expression of QS-related genes. CD analysis revealed that both AMPs induced structural alterations in the important QS-related protein LasR in vitro. Molecular docking results indicated that both peptides bind to the hydrophobic groove of the LasR dimer. Notably, upon mutating key binding sites (D5, E11, and F87) to Ala, the binding efficiency of LasR to both peptides significantly decreased. We revealed the potential of antibacterial peptides G3 and C8G2 at their sub-MIC concentrations as QS inhibitors against P. aeruginosa and elucidated their action mechanism. These findings contribute to our understanding of the therapeutic potential of these peptides in combating P. aeruginosa infections by targeting the QS system.

Unique thermophoretic behavior of supramolecular assemblies of cationic antimicrobial peptides with anionic small molecule agents

Peptidic supramolecules formed via self- and co-assembly are intensively studied and exploited from materials chemistry to biomedicine. Recently we have demonstrated that cationic, amphiphilic antimicrobial peptides (AMPs) are able to form co-assemblies with various anionic, aromatic small molecule (SM) binding agents, which results in modulating their activity. Herein we investigated interactions of four selected AMPs (CM15, Dhvar4, LL-37, and FK-16) with four selected SMs (suramin, tartrazine, biliverdin, and bilirubin ditaurate) exploiting the sensitivity of microscale thermophoresis (MST). Interestingly, negative thermophoresis was frequently observed, and maximal MST responses were typically found at moderate SM concentrations. Besides substantial similarities, various scenarios of thermophoretic behaviors were revealed, contributing to understanding the factors driving their interaction, including variations in charge and hydration effects, oligomeric state of the individual components, and the dynamic nature of the association process, rationalized in turn in different affinities. Results demonstrate that the MST method could particularly be suitable for identifying and studying peptidic assemblies and expanded to interaction systems of highly charged compounds where binding is coupled to higher association.

An intrinsically disordered antimicrobial peptide dendrimer from stereorandomized virtual screening

Membrane-disruptive amphiphilic antimicrobial peptides behave as intrinsically disordered proteins by being unordered in water and becoming α-helical in contact with biological membranes. We recently discovered that synthesizing the α-helical antimicrobial peptide dendrimer L-T25 ((KL)8(KKL)4(KLL)2 KKLL) using racemic amino acids to form stereorandomized sr-T25, an analytically pure mixture of all possible diastereoisomers of L-T25, preserved antibacterial activity but abolished hemolysis and cytotoxicity, pointing to an intrinsically disordered antibacterial conformation and an α-helical cytotoxic conformation. In this study, to identify non-toxic intrinsically disordered homochiral antimicrobial peptide dendrimers (AMPDs), we surveyed sixty-three sr-analogs of sr-T25 selected by virtual screening. One of the analogs, sr-X18 ((KL)8(KLK)4(KLL)2 KLLL), lost antibacterial activity as L-enantiomer and became hemolytic due to α-helical folding. By contrast, the L- and D-enantiomers of sr-X22 ((KL)8(KL)4(KKLL)2 KLKK) were equally antibacterial, non-hemolytic, and non-toxic, implying an intrinsically disordered bioactive conformation. Screening stereorandomized libraries may be generally useful to identify or optimize intrinsically disordered bioactive peptides.

Влияние применения пробиотического препарата, содержащего штамм Lactobacillus rhamnosus GG, на уровни HbD-2 и LL-37 в секрете верхних дыхательных путей и респираторную заболеваемость у детей, больных бронхиальной астмой и аллергическим ринитом

Актуальность. На сегодняшний день аллергические заболевания респираторного тракта, в частности бронхиальная астма и аллергический ринит, у детей являются актуальной медико-социальной проблемой, ассоциированной с высоким риском инвалидизации, существенным снижением качества жизни пациентов и их семей, а также значительной финансовой нагрузкой на пациентов и государство. Бронхиальная астма и аллергический ринит часто сосуществуют, обременяя течение друг друга. Дети, больные респираторными аллергическими заболеваниями, являются особенно уязвимыми к развитию острой респираторной вирусной инфекции (ОРВИ), а респираторные вирусы, в свою очередь, играют важную роль в патогенезе бронхиальной астмы и аллергического ринита, способствуя развитию заболеваний и выступая триггерами их обострений. Одной из возможных причин склонности к частым ОРВИ у детей с аллергической патологией дыхательной системы может быть недостаточность неспецифических факторов мукозального иммунитета респираторного тракта — эндогенных катионоактивных амфифильных антимикробных пептидов, в частности кателицидина (LL-37) и человеческих дефензинов. По данным ряда исследований, эти антимикробные пептиды проявляют противовирусное, антимикробное и иммуномодулирующее действие. При этом данных о состоянии продукции антимикробных пептидов и их влиянии на респираторную заболеваемость у детей с аллергическими заболеваниями в современной литературе недостаточно. В то же время в ряде литературных источников описано положительное влияние отдельных пробиотических штаммов, в частности Lactobacillus rhamnosus GG, на общую резистентность к респираторной вирусной инфекции и профилактику атопических заболеваний. Целью нашей работы стало изучение уровней антимикробных пептидов (человеческого β-дефензина 2 (HbD-2) и LL-37) в секрете слизистых оболочек верхних дыхательных путей у детей с бронхиальной астмой и аллергическим ринитом, выяснение их роли в защите от респираторной вирусной инфекции у данного контингента больных и оценка эффективности применения пробиотического препарата, содержащего Lactobacillus rhamnosus GG, с целью профилактики ОРВИ и снижения частоты вирус-индуцированных обострений аллергической патологии. Материалы и методы. Нами было проведено клинико-лабораторное обследование 76 детей в возрасте от 7 до 17 лет, из которых у 24 был диагностирован аллергический ринит, у 28 детей — бронхиальная астма, а у 24 — бронхиальная астма и аллергический ринит. Группу контроля составили 20 клинически здоровых детей соответствующего возраста и пола. Кроме общепринятых клинических, методы исследования включали анализ паттернов респираторной заболеваемости, определение уровней антимикробных пептидов LL-37, HbD-2 в секрете верхних дыхательных путей методами иммуноферментного и статистического анализа. Результаты. Установлено, что дети с аллергическими заболеваниями респираторного тракта характеризуются большей частотой ОРВИ (на 30 %) с более частым вовлечением в воспалительный процесс нижних дыхательных путей (на 72 %), что обусловливает более длительную продолжительность заболеваний (на 95 %) по сравнению со здоровыми детьми. У детей с аллергическим ринитом и бронхиальной астмой обнаружено существенное снижение уровней антимикробных пептидов в секрете верхних дыхательных путей по сравнению с группой контроля. На уровни антимикробных пептидов в секрете верхних дыхательных путей в наибольшей степени негативно влияет степень активности аллергического воспаления, сопровождающегося отсутствием контроля симптомов, а положительно — прием препаратов базисной терапии и отсутствие симптомов. Вместе с тем даже при наличии полного контроля симптомов аллергических заболеваний, то есть при минимальном уровне аллергического воспаления в дыхательных путях, уровни антимикробных пептидов были достоверно ниже, чем у детей контрольной группы. Установлено, что существует обратная связь между уровнями антимикробных пептидов и частотой и продолжительностью ОРВИ у детей с аллергическими заболеваниями, которая в наибольшей степени выражена при бронхиальной астме. Выводы. Прием пробиотического препарата, содержащего штамм Lactobacillus rhamnosus GG, в течение 1 месяца дополнительно к базисной терапии аллергического ринита и бронхиальной астмы способствовал достоверному повышению уровней HbD-2 (в среднем на 27 %) и LL-37 (в среднем на 60 %) в секрете верхних дыхательных путей, что сопровождалось снижением частоты ОРВИ в среднем на 26 % (в том числе и эпизодов с привлечением нижних дыхательных путей), уменьшением средней продолжительности ОРВИ на 22 % в течение следующего года и снижением вирус-индуцированных обострений на 25,7 %.

An optimized analog of antimicrobial peptide Jelleine-1 shows enhanced antimicrobial activity against multidrug resistant P.aeruginosa and negligible toxicity invitro and invivo.

Due to the threat of escalating multi-drug resistant gram-negative bacteria to human health and life, novel antimicrobial agents against gram-negative pathogens are urgently needed. As antimicrobial peptides are not prone to induce bacteria resistance, they are believed to be one kind of promising class of potential antimicrobial agent candidates to combat multi-drug resistant bacteria for long-term use. Jelleine-1, first isolated from the royal jelly of honeybees, is a typical amphiphilic antimicrobial peptide and shows broad antimicrobial spectrum and negligible toxicity. To promote its antimicrobial activity and extend its potential of clinical use against multi-drug resistant gram-negative bacteria, novel analogs of jelleine-1 were designed, synthesized and their antimicrobial functions and toxicity were examined in this study. Our results showed that fine tuning of the cationic charge, polarity, and basicity of the sequence through amino acids substitution at position 3, 5, 7 and maintaining position 1, 4, 6, 8 unchanged could improve the bioactivity of jelleine-1 significantly. Meanwhile, we also found that the substitution of phenylalanine by tryptophan also could improve the antimicrobial activity of jelleine-1. Among all the analogs, analog 15, which is enriched in arginine and leucine, showed the most potent antimicrobial activity against both gram-negative and gram-positive bacteria, especially to multi-drug resistant Pseudomonas aeruginosa invivo and invitro. In addition, analog 15 also showed potent inhibition of the formation of multi-drug resistant P.aeruginosa biofilm and negligible toxicity, which was certified by MTT, hemolysis, blood assay, and biochemical analysis.

Structural Disruptions of the Outer Membranes of Gram-Negative Bacteria by Rationally Designed Amphiphilic Antimicrobial Peptides.

Gram-negative bacteria are covered by both an inner cytoplasmic membrane (IM) and an outer membrane (OM). Antimicrobial peptides (AMPs) must first permeate through the OM and cell wall before attacking the IM to cause cytoplasmic leakage and kill the bacteria. The bacterial OM is an asymmetric bilayer with the outer leaflet primarily composed of lipopolysaccharides (LPSs) and the inner leaflet composed of phospholipids (PLs). Two cationic α-helical AMPs were designed to target Gram-negative bacteria, a full peptide G(IIKK)3I-NH2 (G3), and a hydrophobic lipopeptide C8-G(IIKK)2I-NH2 (C8G2, with C8 denoting the octanoyl chain). LPS dominates OM functions as the first line of defense against antibiotics, thereby reducing drug susceptibility. This work explores how the two AMPs interact with LPS through several carefully chosen OM models that facilitated measurements from solid-state nuclear magnetic resonance (ss-NMR), small-angle neutron scattering (SANS), and neutron reflectivity (NR). The results revealed that G3 molecules bound preferably to the LPS head region and functioned as bridge molecules to reassemble the dislocated lipids into bilayer stacks. In contrast, C8G2 lipopeptides could quickly penetrate into the central region of the OM to cause direct removal of some membrane lipids. Different structural disruptions implicated different antimicrobial efficacies from these AMPs. The demonstration of the structural features underlying different susceptibilities of the OM to AMPs offers a useful route for the future development of strain-specific AMPs against antimicrobial-resistant pathogens.

The role of human β-defensin 2 (HbD-2) and cathelicidin (LL-37) in the local protection of the upper respiratory tract in children with allergic rhinitis and bronchial asthma

Allergic diseases of the respiratory system seriously affect the psychological, physical and social aspects of the live of sick children, morally and financially exhausting members of their families as well. It is known that exacerbations of allergic diseases of the respiratory tract occur due to interaction with numerous triggers, one of which is a respiratory viral infection. At the same time, it is widely known that patients with allergic respiratory diseases are more prone to to acute respiratory infections. One of the reasons for this tendency often is an insufficient activity of non-specific factors of local immunity of the respiratory system – endogenous amphiphilic antimicrobial peptides, in particular the most studied their representatives - the family of defensins and human cathelicidin. Current research proves that these antimicrobial peptides are characterized by broad antiviral, antimicrobial and immunomodulatory activity. The aim of this study was to study the concentrations of local immune factors - human HbD-2 and LL-37 - in the secretion of the mucous membranes of the upper respiratory tract in children with asthma and allergic rhinitis and to clarify their role in protection against respiratory viral infections in this contingent of patients. We performed laboratory and clinical examinations of 76 children aged 7 to 18 years, of whom 24 were diagnosed with allergic rhinitis, 28 children - bronchial asthma, and 24 - bronchial asthma and allergic rhinitis. The control group consisted of 20 healthy children of the appropriate sex and age. In addition to general clinical methods, patterns of respiratory morbidity were analyzed and concentrations of antimicrobial peptides were determined: by ELISA human cathelicidin (LL-37), β-defensin 2 (HbD-2) in the secretion of the upper respiratory tract, statistical analysis was performed. It was found that children with allergic diseases of the respiratory tract are characterized by a higher frequency of acute respiratory infections with more frequent involvement of the lower respiratory tract, which led to an increase in the duration of the disease compared to their healthy peers. In children with allergic rhinitis and bronchial asthma, there was revealed a significant decrease in the concentrations of antimicrobial peptides in the secretion of the upper respiratory tract compared with the control group.

Stereorandomization as a Method to Probe Peptide Bioactivity

Solid-phase peptide synthesis (SPPS) is usually performed with optically pure building blocks to prepare peptides as single enantiomers. Herein we report that SPPS using racemic amino acids provides stereorandomized (sr) peptides, containing up to billions of different stereoisomers, as well-defined single HPLC peaks, single mass products with high yield, which can be used to investigate peptide bioactivity. To exemplify our method, we show that stereorandomization abolishes the membrane-disruptive effect of α-helical amphiphilic antimicrobial peptides but preserves their antibiofilm effect, implying different mechanisms involving folded versus disordered conformations. For antimicrobial peptide dendrimers by contrast, stereorandomization preserves antibacterial, membrane-disruptive, and antibiofilm effects but reduces hemolysis and cytotoxicity, thereby increasing their therapeutic index. Finally, we identify partially stereorandomized analogues of the last resort cyclic peptide antibiotic polymyxin B with preserved antibacterial activity but lacking membrane-disruptive and lipopolysaccharide-neutralizing activity, pointing to the existence of additional targets.

A mixed chirality α-helix in a stapled bicyclic and a linear antimicrobial peptide revealed by X-ray crystallography.

The peptide α-helix is right-handed when containing amino acids with l-chirality, and left-handed with d-chirality, however mixed chirality peptides generally do not form α-helices unless a helix inducer such as the non-natural residue amino-isobutyric acid is used. Herein we report the first X-ray crystal structures of mixed chirality α-helices in short peptides comprising only natural residues as the example of a stapled bicyclic and a linear membrane disruptive amphiphilic antimicrobial peptide (AMP) containing seven l- and four d-residues, as complexes of fucosylated analogs with the bacterial lectin LecB. The mixed chirality α-helices are superimposable onto the homochiral α-helices and form under similar conditions as shown by CD spectra and MD simulations but non-hemolytic and resistant to proteolysis. The observation of a mixed chirality α-helix with only natural residues in the protein environment of LecB suggests a vast unexplored territory of α-helical mixed chirality sequences and their possible use for optimizing bioactive α-helical peptides.

The introduction of L-phenylalanine into antimicrobial peptide protonectin enhances the selective antibacterial activity of its derivative phe-Prt against Gram-positive bacteria.

Protonectin was a typical amphiphilic antimicrobial peptide with potent antimicrobial activity against Gram-positive and Gram-negative bacteria. In the present study, when its eleventh amino acid in the sequence was substituted by phenylalanine, the analog named phe-Prt showed potent antimicrobial activity against Gram-positive bacteria, but no antimicrobial activity against Gram-negative bacteria, indicating a significant selectivity between Gram-positive bacteria and Gram-negative bacteria. However, when Gram-negative bacteria were incubated with EDTA, the bacteria were susceptible to phe-Prt. Next, the binding effect of phe-Prt with LPS was determined. Our result showed that LPS could hamper the bactericidal activity of phe-Prt against Gram-positive bacteria. The result of zeta potential assay further confirmed the binding effect of phe-Prt with LPS for it could neutralize the surface charge of E. coli and LPS. Then, the effect of phe-Prt on the integrity of outer membrane of Gram-negative bacteria was determined. Our results showed that phe-Prt had a much weaker disturbance to the outer membrane of Gram-negative bacteria than the parent peptide protonectin. In summary, the introduction of L-phenylalanine into the sequence of antimicrobial peptide protonectin made phe-Prt show significant selectivity against Gram-positive bacteria, which could partly be attributed to the delay effect of LPS for phe-Prt to access to cell membrane. Although further study is still needed to clarify the exact mechanism of selectivity, the present study provided a strategy to develop antimicrobial peptides with selectivity toward Gram-positive and Gram-negative bacteria.

Aggregated Amphiphilic Antimicrobial Peptides Embedded in Bacterial Membranes.

Molecular dynamics (MD) simulations, stochastic optical reconstruction microscopy (STORM), and neutron reflection (NR) were combined to explore how antimicrobial peptides (AMPs) can be designed to promote the formation of nanoaggregates in bacterial membranes and impose effective bactericidal actions. Changes in the hydrophobicity of the designed AMPs were found to have a strong influence on their bactericidal potency and cytotoxicity. G(IIKK)3I-NH2 (G3) achieved low minimum inhibition concentrations (MICs) and effective dynamic kills against both antibiotic-resistant and -susceptible bacteria. However, a G3 derivative with weaker hydrophobicity, KI(KKII)2I-NH2 (KI), exhibited considerably lower membrane-lytic activity. In contrast, the more hydrophobic G(ILKK)3L-NH2 (GL) peptide achieved MICs similar to those observed for G3 but with worsened hemolysis. Both the model membranes studied by Brewster angle microscopy, zeta potential measurements, and NR and the real bacterial membranes examined with direct STORM contained membrane-inserted peptide aggregates upon AMP exposure. These structural features were well supported by MD simulations. By revealing how AMPs self-assemble in microbial membranes, this work provides important insights into AMP mechanistic actions and allows further fine-tuning of antimicrobial potency and cytotoxicity.

Novel Stapling by Lysine Tethering Provides Stable and Low Hemolytic Cationic Antimicrobial Peptides.

Cationic antimicrobial peptides (CAMPs) are potent therapeutics for drug-resistant bacterial infections. However, the clinical application of CAMPs is hampered by its poor proteolytic stability and hemolytic activity toward eukaryotic cells. Great efforts have been made to design and generate derivatives of CAMPs with improved pharmacological properties. Here, we report a novel stapling protocol, which tethers two ε-amino groups of the lysine residue by the N-alkylation reaction on the hydrophilic face of amphiphilic antimicrobial peptides. A series of lysine-tethered stapled CAMPs were synthesized, employing the antimicrobial peptide OH-CM6 as a model. Biological screening of the stapled CAMPs provided an analogue with strong antimicrobial activity, high proteolytic stability, and low hemolytic activity. This novel stapling approach offers an important chemical tool for developing CAMP-based antibiotics.

Turning a Killing Mechanism into an Adhesion and Antifouling Advantage

AbstractMild and universal methods to introduce functionality in polymeric surfaces remain a challenge. Herein, a bacterial killing mechanism based on amphiphilic antimicrobial peptides is turned into an adhesion advantage. Surface activity (surfactant) of the antimicrobial liquid chromatography peak I (LCI) peptide is exploited to achieve irreversible binding of a protein–polymer hybrid to surfaces via physical interactions. The protein–polymer hybrid consists of two blocks, a surface‐affine block (LCI) and a functional block to prevent protein fouling on surfaces by grafting antifouling polymers via single electron transfer‐living radical polymerization (SET‐LRP). The mild conditions of SET‐LRP of N‐2‐hydroxy propyl methacrylamide (HPMA) and carboxybetaine methacrylamide (CBMAA) preserve the secondary structure of the fusion protein. Adsorption kinetics and grafting densities are assessed using surface plasmon resonance and ellipsometry on model gold surfaces, while the functionalization of a range of artificial and natural surfaces, including teeth, is directly observed by confocal microscopy. Notably, the fusion protein modified with poly(HPMA) completely prevents the fouling from human blood plasma and thereby exhibits a resistance to protein fouling that is comparable to the best grafted‐from polymer brushes. This, combined with their simple application on a large variety of materials, highlights the universal and scalable character of the antifouling concept.

From Structure to Function: pH-Switchable Antimicrobial Nano-Self-Assemblies.

Stimuli-responsive nanocarriers based on lipid self-assemblies have the potential to provide targeted delivery of antimicrobial peptides, limiting their side effects while protecting them from degradation in the biological environments. In the present study, we design and characterize a simple pH-responsive antimicrobial nanomaterial, formed through the self-assembly of oleic acid (OA) with the human cathelicidin LL-37 as a model for an amphiphilic antimicrobial peptide. Colloidal transformations from core-shell cylindrical micelles with a cross-sectional diameter of ∼5.5 nm and a length of ∼23 nm at pH 7.0 to aggregates of branched threadlike micelles at pH 5.0 were detected using synchrotron small-angle X-ray scattering, cryogenic transmission electron microscopy, and dynamic light scattering. Biological in vitro assays using an Escherichia coli bacteria strain showed high antimicrobial activity of the positively charged LL-37/OA aggregates at pH 5.0, which was not caused by the pH conditions themselves. Contrary to that, negligible antimicrobial activity was observed at pH 7.0 for the negatively charged cylindrical micelles. The nanocarrier's ability to switch its biological activity "on" and "off" in response to changes in pH could be used to focus the antimicrobial peptides' action to areas of specific pH in the body. The presented findings contribute to the fundamental understanding of lipid-peptide self-assembly and may open up a promising strategy for designing simple pH-responsive delivery systems for antimicrobial peptides.

Behavior of a Peptide During a Langmuir–Blodgett Compression Isotherm: A Molecular Dynamics Simulation Study

A detailed characterization of the behavior of the amphiphilic antimicrobial peptide Trichogin GA IV (TRIC) at the air/water interface during a Langmuir–Blodgett (LB) isotherm is reported. By means of molecular dynamics simulations, experimental data are explained in terms of the conformational changes and aggregate features adopted by TRIC. We show that, due to compression, different structural changes occur: initially formed drop-like aggregates coalesce, forming nanofibers; on increasing the surface tension further, these nanofibers constitute a web-like structure in which meshes are filled by water pools. During these transitions, the peptide chains lie almost parallel to the surface mostly adopting a helical conformation. At high peptide concentration, reaching the maximum of the allowed surface pressure, a monolayer of TRICs in nonhelical conformation and vertically aligned with respect to the air/water interface is formed.

Differential Interaction of Antimicrobial Peptides with Lipid Structures Studied by Coarse-Grained Molecular Dynamics Simulations.

In this work; we investigated the differential interaction of amphiphilic antimicrobial peptides with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) lipid structures by means of extensive molecular dynamics simulations. By using a coarse-grained (CG) model within the MARTINI force field; we simulated the peptide–lipid system from three different initial configurations: (a) peptides in water in the presence of a pre-equilibrated lipid bilayer; (b) peptides inside the hydrophobic core of the membrane; and (c) random configurations that allow self-assembled molecular structures. This last approach allowed us to sample the structural space of the systems and consider cooperative effects. The peptides used in our simulations are aurein 1.2 and maculatin 1.1; two well-known antimicrobial peptides from the Australian tree frogs; and molecules that present different membrane-perturbing behaviors. Our results showed differential behaviors for each type of peptide seen in a different organization that could guide a molecular interpretation of the experimental data. While both peptides are capable of forming membrane aggregates; the aurein 1.2 ones have a pore-like structure and exhibit a higher level of organization than those conformed by maculatin 1.1. Furthermore; maculatin 1.1 has a strong tendency to form clusters and induce curvature at low peptide–lipid ratios. The exploration of the possible lipid–peptide structures; as the one carried out here; could be a good tool for recognizing specific configurations that should be further studied with more sophisticated methodologies.

Evaluation of the Immunomodulatory Activity of the Chicken NK-Lysin-Derived Peptide cNK-2

Chicken NK-lysin (cNK-lysin), the chicken homologue of human granulysin, is a cationic amphiphilic antimicrobial peptide (AMP) that is produced by cytotoxic T cells and natural killer cells. We previously demonstrated that cNK-lysin and cNK-2, a synthetic peptide incorporating the core α-helical region of cNK-lysin, have antimicrobial activity against apicomplexan parasites such as Eimeria spp., via membrane disruption. In addition to the antimicrobial activity of AMPs, the immunomodulatory activity of AMPs mediated by their interactions with host cells is increasingly recognized. Thus, in this study, we investigated whether cNK-lysin derived peptides modulate the immune response in the chicken macrophage cell line HD11 and in chicken primary monocytes by evaluating the induction of chemokines, anti-inflammatory properties, and activation of signalling pathways. cNK-2 induced the expression of CCL4, CCL5 and interleukin(IL)-1β in HD11 cells and CCL4 and CCL5 in primary monocytes. We also determined that cNK-2 suppresses the lipopolysaccharide-induced inflammatory response by abrogating IL-1β expression. The immunomodulatory activity of cNK-2 involves the mitogen-activated protein kinases-mediated signalling pathway, including p38, extracellular signal-regulated kinase 1/2 and c-Jun N-terminal kinases, as well as the internalization of cNK-2 into the cells. These results indicate that cNK-2 is a potential novel immunomodulating agent rather than an antimicrobial agent.

Sequence-defined bioactive macrocycles via an acid-catalysed cascade reaction.

Synthetic macrocycles derived from sequence-defined oligomers are a unique structural class whose ring size, sequence and structure can be tuned via precise organization of the primary sequence. Similar to peptides and other peptidomimetics, these well-defined synthetic macromolecules become pharmacologically relevant when bioactive side chains are incorporated into their primary sequence. In this article, we report the synthesis of oligothioetheramide (oligoTEA) macrocycles via a one-pot acid-catalysed cascade reaction. The versatility of the cyclization chemistry and modularity of the assembly process was demonstrated via the synthesis of >20 diverse oligoTEA macrocycles. Structural characterization via NMR spectroscopy revealed the presence of conformational isomers, which enabled the determination of local chain dynamics within the macromolecular structure. Finally, we demonstrate the biological activity of oligoTEA macrocycles designed to mimic facially amphiphilic antimicrobial peptides. The preliminary results indicate that macrocyclic oligoTEAs with just two-to-three cationic charge centres can elicit potent antibacterial activity against Gram-positive and Gram-negative bacteria.