Influence of lipid bilayer composition on the activity of antimicrobial quaternary ammonium ionenes, the interplay of intrinsic lipid curvature and polymer hydrophobicity, the role of cardiolipin

Effect of cardiolipin on the lamellarity and elongation of liposomes hydrated in PBS

Lamellarity and shape are important factors in the formation of vesicles and determine their role in biological systems and pharmaceutical applications. Cardiolipin (CL) is a major lipid in many biological membranes and exerts a great influence on their structural organization due to its particular structure and physico-chemical properties. Here, we used small-angle X-ray and neutron scattering to study the effects of CL with different acyl chain lengths and saturations (CL14:0, CL18:1, CL18:2) on vesicle morphology and lamellarity in membrane models containing mixtures of phosphatidylcholine and phosphatidylethanolamine with different acyl chain lengths and saturations (C14:0 and C 18:1). Measurements were performed in the presence of Phosphate Buffer Saline (PBS), at 37°C, to better reflect physiological conditions, which resulted in strong effects on vesicle morphology, depending on the type and amount of CL used. The presence of small quantities of CL (from 2.5%) reduced inter-membrane correlations and increased perturbation of the membrane, an effect which is enhanced in the presence of matched shorter saturated acyl chains, and mainly unilamellar vesicles (ULV) are formed. In extruded vesicles, employed for SANS experiments, flattened vesicles are observed partly due to the hypertonic effect of PBS, but also influenced by the type of CL added. Our experimental data from SAXS and SANS revealed a strong dependence on CL content in shaping the membrane microstructure, with an apparent optimum in the PC:CL mixture in terms of promoting reduced correlations, preferred curvature and elongation. However, the use of PBS caused distinct differences from previously published studies in water in terms of vesicle shape, and highlights the need to investigate vesicle formation under physiological conditions in order to be able to draw conclusions about membrane formation in biological systems.

LEGO-lipophosphonoxins: length of hydrophobic module affects permeabilizing activity in target membranes of different phospholipid composition

In the past few decades, society has faced rapid development and spreading of antimicrobial resistance due to antibiotic misuse and overuse and the immense adaptability of bacteria. Difficulties in obtaining effective antimicrobial molecules from natural sources challenged scientists to develop synthetic molecules with antimicrobial effect. We developed modular molecules named LEGO-Lipophosphonoxins (LEGO-LPPO) capable of inducing cytoplasmic membrane perforation. In this structure-activity relationship study we focused on the role of the LEGO-LPPO hydrophobic module directing the molecule insertion into the cytoplasmic membrane. We selected three LEGO-LPPO molecules named C9, C8 and C7 differing in the length of their hydrophobic chain and consisting of an alkenyl group containing one double bond. The molecule with the long hydrophobic chain (C9) was shown to be the most effective with the lowest MIC and highest perforation rate both in vivo and in vitro. We observed high antimicrobial activity against both G+ and G- bacteria with significant differences in LEGO-LPPOs mechanism of action on these two cell types. We observed a highly cooperative mechanism of LEGO-LPPO action on G- bacteria as well as on liposomes resembling G- bacteria. LEGO-LPPO action on G- bacteria was significantly slower compared to G+ bacteria suggesting the role of the outer membrane in affecting the LEGO-LPPOs perforation rate. This notion was supported by the higher sensitivity of the E. coli strain with a compromised outer membrane. Finally, we noted that the composition of the cytoplasmic membrane affects the activity of LEGO-LPPOs since the presence of phosphatidylethanolamine increases their membrane disrupting activity.

Recent Progress in antibacterial hydrogel coatings for targeting biofilm to prevent orthopedic implant-associated infections

The application of orthopedic implants for bone tissue reconstruction and functional restoration is crucial for patients with severe bone fractures and defects. However, the abiotic nature of orthopedic implants allows bacterial adhesion and colonization, leading to the formation of bacterial biofilms on the implant surface. This can result in implant failure and severe complications such as osteomyelitis and septic arthritis. The emergence of antibiotic-resistant bacteria and the limited efficacy of drugs against biofilms have increased the risk of orthopedic implant-associated infections (OIAI), necessitating the development of alternative therapeutics. In this regard, antibacterial hydrogels based on bacteria repelling, contact killing, drug delivery, or external assistance strategies have been extensively investigated for coating orthopedic implants through surface modification, offering a promising approach to target biofilm formation and prevent OIAI. This review provides an overview of recent advancements in the application of antibacterial hydrogel coatings for preventing OIAI by targeting biofilm formation. The topics covered include: (1) the mechanisms underlying OIAI occurrence and the role of biofilms in exacerbating OIAI development; (2) current strategies to impart anti-biofilm properties to hydrogel coatings and the mechanisms involved in treating OIAI. This article aims to summarize the progress in antibacterial hydrogel coatings for OIAI prevention, providing valuable insights and facilitating the development of prognostic markers for the design of effective antibacterial orthopedic implants.

Membrane lytic activity of antibacterial ionenes, critical role of phosphatidylcholine (PC) and cardiolipin (CL)

Understanding the mechanism by which an antibacterial agent interacts with a model membrane provides vital information for better design of future antibiotics. In this study, we investigated two antibacterial polymers, hydrophilic C0-T-p and hydrophobic C8-T-p ionenes, known for their potent antimicrobial activity and ability to disrupt the integrity of lipid bilayers. Our hypothesize is that the composition of a lipid bilayer alters the mechanism of ionenes action, potentially providing an explanation for the observed differences in their bioactivity and selectivity. Calcein release experiments utilizing a range of liposomes to examine the impact of (i) cardiolipin (CL) to phosphatidylglycerol (PG) ratio, (ii) overall vesicle charge, and (iii) phosphatidylethanolamine (PE) to phosphatidylcholine (PC) ratio on the activity of ionenes were performed. Additionally, polymer-bilayer interactions were also investigated through vesicle fusion assay and the black lipid membrane (BLM) technique The activity of C0-T-p is strongly influenced by the amount of cardiolipin, while the activity of C8-T-p primarily depends on the overall vesicle charge. Consequently, C0-T-p acts through interactions with CL, whereas C8-T-p modifies the bulk properties of the membrane in a less-specific manner. Moreover, the presence of a small amount of PC in the membrane makes the vesicle resistant to permeabilization by tested molecules. Intriguingly, more hydrophilic C0-T-p retains higher membrane activity compared to the hydrophobic C8-T-p. However, both ionenes induce vesicle fusion and increase lipid bilayer ion permeability.

Polytrimethylenimines: Highly Potent Antibacterial Agents with Activity and Toxicity Modulated by the Polymer Molecular Weight

Cationic polymers have been extensively investigated as a potential replacement for traditional antibiotics. Here, we examined the effect of molecular weight (MW) on the antimicrobial, cytotoxic, and hemolytic activity of linear polytrimethylenimine (L-PTMI). The results indicate that the biological activity of the polymer sharply increases as MW increases. Thanks to a different position of the antibacterial activity and toxicity thresholds, tuning the MW of PTMI allows one to achieve a therapeutic window between antimicrobial activity and toxicity concentrations. L-PTMI presents significantly higher antimicrobial activity against model microorganisms than linear polyethylenimine (L-PEI) when polymers with a similar number of repeating units are compared. For the derivatives of L-PTMI and L-PEI, obtained through N-monomethylation and partial N,N-dimethylation of linear polyamines, the antimicrobial activity and toxicity were both reduced; however, resulting selectivity indices were higher. Selected materials were tested against clinical isolates of pathogens from the ESKAPE group and Mycobacteria, revealing good antibacterial properties of L-PTMI against antibiotic-resistant strains of Gram-positive and Gram-negative bacteria but limited antibacterial properties against Mycobacteria.

Isolation, identification, and mode of action of antibacterial peptides derived from egg yolk hydrolysate

Egg yolk is a coproduct of egg white processing. The protein hydrolysis of egg yolks to exhibit antimicrobial activity is a strategy for its valorization. The objective of this study is to fractionate antibacterial peptides from pepsin-hydrolyzed egg yolks using flash chromatography. In addition, the mode of actions of the fractionated peptides were elucidated and plausible antibacterial peptides were reported. The fraction 6 (F6) obtained from a C18-flash column exhibited antibacterial activity against Staphylococcus aureus ATCC 29213 and Salmonella typhimurium TISTR 292 at minimal inhibitory concentration (MIC) values of 0.5 to 1 mmol/L (Leucine equivalent). The fractionated peptides induced DNA leakage as monitored by 260 nm. Propidium iodide and SYTO9 staining observed under a confocal microscope suggested the disintegration of cell membranes. Synchrotron-based Fourier-transform infrared spectroscopy analysis revealed that the egg yolk peptides at 1 × MIC induced an alteration of phospholipids at cell membranes and modified conformation of intracellular proteins and nucleic acids. Scanning electron microscopy revealed obvious cell ruptures when S. aureus was treated at 1 × MIC for 4 h, whereas damage of cell membranes and leakage of intracellular components were also observed for the transmission electron microscopy. Egg yolk peptides showed no hemolytic activity in human erythrocytes at concentrations up to 4 mmol/L. Peptide identification by LC-MS/MS revealed 3 cationic and 10 anionic peptides with 100% sequence similarity to apolipoprotein-B of Gallus gallus with hydrophobicity ranging from 27 to 75%. The identified peptide KGGDLGLFEPTL exhibited the highest antibacterial activity toward S. aureus at MIC of 2 mmol/L. Peptides derived from egg yolk hydrolysate present significant potential as antistaphylococcal agents for food and/or pharmaceutical application.

Cardiolipin Strongly Inhibits the Leakage Activity of the Short Antimicrobial Peptide ATRA-1 in Comparison to LL-37, in Model Membranes Mimicking the Lipid Composition of Staphylococcus aureus

Cardiolipin is one of the main phospholipid components of Staphylococcus aureus membranes. This lipid is found at varying concentrations in the bilayer, depending on the growth stage of the bacteria, and as a response to environmental stress. Cardiolipin is an anionic phospholipid with four acyl chains, which modulates the bending properties of the membrane due to its inverted conical shape. It has been shown to inhibit the pore forming activity of several antimicrobial peptides, in general doubling the peptide concentration needed to induce leakage. Here we find that the short snake-derived antimicrobial peptide ATRA-1 is inhibited by several orders of magnitude in the presence of cardiolipin in saturated membranes (DMPG) compared to the human cathelicidin LL-37, which is only inhibited two-fold in its leakage-inducing concentration. The ATRA-1 is too short to span the membrane and its leakage activity is likely related to detergent-like alterations of bilayer structure. Fluorescence spectroscopy shows only a minor effect on ATRA-1 binding to DMPG membranes due to the presence of cardiolipin. However, FTIR spectroscopy shows that the acyl chain structure of DMPG membranes, containing cardiolipin, become more organized in the presence of ATRA-1, as reflected by an increase in the gel to liquid-crystalline phase transition temperature. Instead, a depression in the melting temperature is induced by ATRA-1 in DMPG in the absence of cardiolipin. In comparison, LL-37 induces a depression of the main phase transition of DMPG even in the presence of cardiolipin. These data suggest that cardiolipin inhibits the penetration of ATRA-1 into the membrane core, impeding its capacity to disrupt lipid packing.

Influence of PEG Subunit on the Biological Activity of Ionenes: Synthesis of Novel Polycations, Antimicrobial and Toxicity Studies

An alarming increase of antibiotic resistance among pathogens creates an urgent need to develop new antimicrobial agents. Many reported polycations show high antimicrobial activity along with low hemolytic activity. Unfortunately, most of those molecules remain highly cytotoxic against various mammalian cells. In this work, we present a systematic study on the impact of triethylene glycol monomethyl ether side groups (short PEG analog) on antimicrobial, hemolytic, and cytotoxic properties of novel amphiphilic ionenes. A detailed description of synthesis, leading to well-defined alternating polymers, which differ in structural elements responsible for hydrophilicity (PEG) and hydrophobicity (alkyl chain), is presented. Obtained results show that the PEG moiety and fine-tuned hydrophilic-lipophilic balance of ionenes synergistically lead to low-cytotoxic, low-hemolytic molecules with high activity against S. aureus, including methicillin-resistant strains (MRSA). Additionally, the results of mechanistic studies on bacterial cells and fluorescently labeled liposomes are also discussed. This article is protected by copyright. All rights reserved.

Main-chain flexibility and hydrophobicity of ionenes strongly impact their antimicrobial activity: an extended study on drug resistance strains and Mycobacterium

The spread of antibiotic-resistant pathogens and the resurgence of tuberculosis disease are major motivations to search for novel antimicrobial agents. Some promising candidates in this respect are cationic polymers, also known as synthetic mimics of antimicrobial peptides (SMAMPs), which act through the membrane-lytic mechanism. Development of resistance toward SMAMPs is less likely than toward currently employed antibiotics; however, further studies are needed to better understand their structure–activity relationship. The main objective of this work is to understand the cross-influence of hydrophobicity, main-chain flexibility, and the topology of ionenes (polycations containing a cationic moiety within the main-chain) on activity. To fulfill this goal, a library of ionenes was developed and compared with previously investigated molecules. The obtained compounds display promising activity against the model microorganisms and drug-resistance clinical isolates, including Mycobacterium tuberculosis. The killing efficiency was also investigated, and results confirm a strong effect of hydrophobicity, revealing higher activity for molecules possessing the flexible linker within the polymer main-chain.

A high significance of the main chain flexibility and an unexpected effect of hydrophobicity on the biological activity in series of ionenes was observed. The most potent among the tested polycations showed high activity toward clinical bacterial isolates.