Activity of Temporin A and Short Lipopeptides Combined with Gentamicin against Biofilm Formed by Staphylococcus aureus and Pseudomonas aeruginosa

The formation of biofilms on biomaterials causes biofilm-associated infections. Available treatments often fail to fight the microorganisms in the biofilm, creating serious risks for patient well-being and life. Due to their significant antibiofilm activities, antimicrobial peptides are being intensively investigated in this regard. A promising approach is a combination therapy that aims to increase the efficacy and broaden the spectrum of antibiotics. The main goal of this study was to evaluate the antimicrobial efficacy of temporin A and the short lipopeptides (C10)2-KKKK-NH2 and (C12)2-KKKK-NH2 in combination with gentamicin against biofilm formed by Staphylococcus aureus (SA) and Pseudomonas aeruginosa (PA). Peptides were synthesized with solid-phase temperature-assisted synthesis methodology. The minimum inhibitory concentrations (MICs), fractional inhibitory concentrations (FICs), minimum biofilm eradication concentrations (MBECs), and the influence of combinations of compounds with gentamicin on bacterial biofilm were determined for reference strains of SA (ATCC 25923) and PA (ATCC 9027). The peptides exhibited significant potential to enhance the antibacterial activity of gentamicin against SA biofilm, but there was no synergy in activity against planktonic cells. The antibiotic applied alone demonstrated strong activity against planktonic cells and poor effectiveness against SA biofilm. Biofilm formed by PA was much more sensitive to gentamicin, but some positive influences of supplementation with peptides were noticed. The results of the performed experiments suggest that the potential application of peptides as adjuvant agents in the treatment of biofilm-associated infections should be studied further.

Ultrashort Cationic Lipopeptides-Effect of N-Terminal Amino Acid and Fatty Acid Type on Antimicrobial Activity and Hemolysis

Ultrashort cationic lipopeptides (USCLs) are promising antimicrobial agents that hypothetically may be alternatively used to combat pathogens such as bacteria and fungi. In general, USCLs consist of fatty acid chains and a few basic amino acid residues. The main shortcoming of USCLs is their relatively high cytotoxicity and hemolytic activity. This study focuses on the impact of the hydrophobic fatty acid chain, on both antimicrobial and hemolytic activities. To learn more about this region, a series of USCLs with different straight-chain fatty acids (C8, C10, C12, C14) attached to the tripeptide with two arginine residues were synthesized. The amino acid at the N-terminal position was exchanged for proteinogenic and non-proteinogenic amino acid residues (24 in total). Moreover, the branched fatty acid residues were conjugated to N-terminus of a dipeptide with two arginine residues. All USCLs had C-terminal amides. USCLs were tested against reference bacterial strains (including ESKAPE group) and Candida albicans. The hemolytic potential was tested on human erythrocytes. Hydrophobicity of the compounds was evaluated by RP-HPLC. Shortening of the fatty acid chain and simultaneous addition of amino acid residue at N-terminus were expected to result in more selective and active compounds than those of the reference lipopeptides with similar lipophilicity. Hypothetically, this approach would also be beneficial to other antimicrobial peptides where N-lipidation strategy was used to improve their biological characteristics.

Synergistic combinations of antimicrobial peptides against biofilms of methicillin-resistant Staphylococcus aureus (MRSA) on polystyrene and medical devices

OBJECTIVES

Antimicrobial research is being focused to look for more effective therapeutics against antibiotic-resistant infections such as those caused by methicillin-resistant Staphylococcus aureus (MRSA). In this regard, antimicrobial peptides (AMPs) appear to be a promising solution. The aim of the present study was to investigate the potential activity of temporin A, citropin 1.1, CA(1-7)M(2-9)NH₂ and Pal-KGK-NH₂ in synergistic activity against MRSA biofilms developed on polystyrene surface (PSS) and central venous catheter (CVC).

METHODS

The study was subdivided into distinct phases to assess the ability of AMPs to inhibit biofilm formation, to identify possible synergy between AMPs, and to eradicate preformed biofilms on PSS and CVC using AMPs alone or in combination.

RESULTS

Activity of the AMPs was particularly evident in the inhibition of biofilm formation on PSS and CVC, whilst the eradication of preformed biofilms was more difficult and was reached only after 24h of contact. The synergistic activity of AMP combinations, selected by their fractional inhibitory concentration index (FICI), led to an improvement in the performance of all of the molecules in the removal of different biofilms.

CONCLUSION

Overall, AMPs could represent the next generation of antimicrobial agents for a prophylactic or therapeutic tool to control biofilms of antibiotic-resistant bacteria and/or biofilm-associated infections on different medical devices.

Influence of Short Cationic Lipopeptides with Fatty Acids of Different Chain Lengths on Bacterial Biofilms Formed on Polystyrene and Hydrogel Surfaces

Nowadays, biomaterials are applied in many different branches of medicine. They significantly improve the patients' comfort and quality of life, but also constitute a significant risk factor for biofilm-associated infections. Currently, intensive research on the development of novel materials resistant to microbial colonization as well as new compounds that are active against biofilms is being carried out. Within this research, antimicrobial peptides (AMPs) and their analogues are being intensively investigated due to their promising antimicrobial activities. The main goal of this study was to synthesize and evaluate the antimicrobial efficacy of short cationic lipopeptides that were designed to imitate the features of AMPs responsible for antimicrobial activities: positive net charge and amphipacity. The positive charge of the molecules results from the presence of basic amino acid residues: arginine and lysine. Amphipacity is provided by the introduction of decanoic, dodecanoic, tetradecanoic, and hexadecanoic acid chains to the molecules. Lipopeptides (C16-KR-NH2, C16-KKK-NH2, C16-KKC-NH2, C16-KGK-NH2, C14-KR-NH2, C14-KKC-NH2, C12-KR-NH2, C12-KKC-NH2, and (C10)2-KKKK-NH2) were synthesized using a novel solid-phase temperature-assisted methodology. The minimum inhibitory concentrations (MICs), minimum biofilm eradication concentrations (MBECs), and minimum biofilm formation inhibitory concentrations (MBFICs) were determined for the following bacterial strains: Staphylococcus aureus ATCC 25923, Staphylococcus epidermidis ATCC 14990, Enterococcus faecalis ATCC 29212, Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 9027, and Proteus mirabilis PCM 543. The biofilms were cultured on two types of surfaces: polystyrene plates (PS) and contact lenses (CL). The lipopeptides exhibited the ability to inhibit the growth of bacteria in a liquid medium as well as on the PS and CL. The compounds also eliminated the bacterial biofilm from the surface of both materials. In general, the activity against gram-positive bacteria was stronger in comparison to that against gram-negative strains. There were certain discrepancies between the activity of compounds against the biofilm cultured on PS and CL. This was especially noticeable for staphylococci-the lipopeptides presented much higher activity against biofilm formed on the PS surface. It is worth noting that the obtained MBEC values for lipopeptides were usually only a few times higher than the MICs. The results of the performed experiments suggest that further studies on lipopeptides and their potential application in the treatment and prophylaxis of biofilm-associated infections should be conducted.

Antibacterial Activities of Lipopeptide (C10)₂-KKKK-NH₂ Applied Alone and in Combination with Lens Liquids to Fight Biofilms Formed on Polystyrene Surfaces and Contact Lenses

The widespread use of biomaterials such as contact lenses is associated with the development of biofilm-related infections which are very difficult to manage with standard therapies. The formation of bacterial biofilms on the surface of biomaterials is associated with increased antibiotic resistance. Owing to their promising antimicrobial potential, lipopeptides are being intensively investigated as novel antimicrobials. However, due to the relatively high toxicity exhibited by numerous compounds, a lot of attention is being paid to designing new lipopeptides with optimal biological activities. The principal aim of this study was to evaluate the potential ophthalmic application of lipopeptide (C₁₀)₂-KKKK-NH₂. This lipopeptide was synthesized according to Fmoc chemistry using the solid-phase method. The antibiofilm activities of the lipopeptide, antibiotics used in ocular infections, and commercially available lens liquids were determined using the broth dilution method on polystyrene 96-well plates and contact lenses. Resazurin was applied as the cell-viability reagent. The effectiveness of the commercially available lens liquids supplemented with the lipopeptide was evaluated using the same method and materials. (C₁₀)₂-KKKK-NH₂ exhibited stronger anti-biofilm properties compared to those of the tested conventional antimicrobials and showed the ability to enhance the activity of lens liquids at relatively low concentrations (4–32 mg/L). Estimation of the eye irritation potential of the lipopeptide using Toxtree software 2.6.13 suggests that the compound could be safely applied on the human eye. The results of performed experiments encourage further studies on (C₁₀)₂-KKKK-NH₂ and its potential application in the prophylaxis of contact lens-related eye infections.

In Vitro Evaluation of Cytotoxicity and Permeation Study on Lysine- and Arginine-Based Lipopeptides with Proven Antimicrobial Activity

Owing to their excellent antimicrobial activities with a relatively low cost of production, lipopeptides are being intensively investigated as potential alternatives to popular antimicrobials. However, a critical obstacle for their application is a relatively high toxicity, hence a lot of attention has been paid to designing new molecules with optimal properties. In this study we synthesized the following lipopeptides: C₁₆-KK-NH₂, C₁₆-KεK-NH₂, C₁₆-KKK-NH₂, C₁₆-KRK-NH₂, C₁₆-RR-NH₂, C₁₆-RRR-NH₂, (C₁₀)₂-KKKK-NH₂ and (C₁₂)₂-KKKK-NH₂. Their antimicrobial activity against representative strains of Gram-positive bacteria, Gram-negative bacteria and fungi has been confirmed. The compounds have been evaluated with regard to the safety of their application in dermatology. The cytotoxicity was determined in HaCaT keratinocytes using MTT assay, whereas Strat M membranes placed in Franz diffusion cells were used to assess their ability to skin permeation. The compounds containing one hexadecanoic acid chain turned out to be very toxic towards human keratinocytes, while lipopeptides containing two fatty acid chains (decanoic and dodecanoic) demonstrated much lower cytotoxicity. For the most promising lipopeptide, (C₁₀)₂-KKKK-NH₂, the measured IC₅₀ on HaCaT keratinocytes was few times higher as compared to MICs obtained for the tested bacteria. Both groups of lipopeptides did not permeate the model membranes and therefore lack of permeation through human skin could be expected. The results of this work encourage further research on the potential application of lipopeptides with two fatty acids as novel antimicrobials.

Comparative Study on Antistaphylococcal Activity of Lipopeptides in Various Culture Media

Staphylococcus aureus bacteria are one of the leading microorganisms responsible for nosocomial infections as well as being the primary causative pathogen of skin and wound infections. Currently, the therapy of staphylococcal diseases faces many difficulties, due to a variety of mechanisms of resistance and virulence factors. Moreover, a number of infections caused by S. aureus are connected with biofilm formation that impairs effectiveness of the therapy. Short cationic lipopeptides that are designed on the basis of the structure of antimicrobial peptides are likely to provide a promising alternative to conventional antibiotics. Many research groups have proved a high antistaphylococcal potential of lipopeptides, however, the use of different protocols for determination of antimicrobial activity may be the reason for inconsistency of the results. The aim of this study was to learn how the use of various bacteriological media as well as solvents may affect activity of lipopeptides and their cyclic analogs. Obtained results showed a great impact of these variables. For example, cyclic analogs were more effective when dissolved in an aqueous solution of acetic acid and bovine serum albumin (BSA). The greater activity against planktonic cultures was found in brain-heart infusion broth (BHI) and tryptic-soy broth (TSB), while the antibiofilm activity was higher in the Mueller-Hinton medium.

Influence of Amphibian Antimicrobial Peptides and Short Lipopeptides on Bacterial Biofilms Formed on Contact Lenses

The widespread use of contact lenses is associated with several complications, including ocular biofilm-related infections. They are very difficult to manage with standard antimicrobial therapies, because bacterial growth in a biofilm is associated with an increased antibiotic resistance. The principal aim of this study was to evaluate the efficacy of antimicrobial peptides (AMPs) in eradication of bacterial biofilms formed on commercially available contact lenses. AMPs were synthesized according to Fmoc/tBu chemistry using the solid-phase method. Minimum inhibitory concentration (MIC) and minimum biofilm eradication concentration (MBEC) of the compounds were determined. Anti-biofilm activity of the antimicrobial peptides determined at different temperatures (25 °C and 37 °C) were compared with the effectiveness of commercially available contact lens solutions. All of the tested compounds exhibited stronger anti-biofilm properties as compared to those of the tested lens solutions. The strongest activity of AMPs was noticed against Gram-positive strains at a temperature of 25 °C. Conclusions: The results of our experiments encourage us toward further studies on AMPs and their potential application in the prophylaxis of contact lens-related eye infections.

The Antistaphylococcal Activity of Citropin 1.1 and Temporin A against Planktonic Cells and Biofilms Formed by Isolates from Patients with Atopic Dermatitis: An Assessment of Their Potential to Induce Microbial Resistance Compared to Conventional Antimicrobials

Staphylococcus aureus (SA) colonizes the vast majority of patients with atopic dermatitis (AD). Its resistance to antibiotics and ability to form biofilms are the main origins of therapeutic complications. Endogenous antimicrobial peptides (AMPs) exhibit strong activity against SA, including antibiotic resistant strains as well as bacteria existing in biofilm form. The purpose of the present work was to determine the antistaphylococcal activity of two amphibian peptides against SA isolated from patients with AD. The AMPs demonstrated permanent activity towards strains exposed to sublethal concentrations of the compounds and significantly stronger antibiofilm activity in comparison to that of conventional antimicrobials. The results suggest the potential application of amphibian AMPs as promising antistaphylococcal agents for the management of skin infections.

Small lipopeptides possess anti-biofilm capability comparable to daptomycin and vancomycin

Antibiotic resistance, to a large extent, is related to the formation of bacterial biofilms. Thus, compounds with anti-biofilm capability are of practical importance. Inspired by the recent discovery of two amino acid lipopeptides from marine bacteria, we constructed a family of small lipopeptides with 2-3 amino acids. While no antimicrobial activity was found for anionic lipopeptides, cationic candidates are potent against Staphylococcus strains, such as methicillin-resistant Staphylococcus aureus (MRSA) USA200, USA300, USA400, UAMS-1, Newman, and Mu50. In the simplest design, two lysines (C14-KK) or three arginines (C14-RRR) attached to an acyl chain of 14 carbons were sufficient to make the compounds antimicrobial. These simple lipopeptides are inherently stable towards S. aureus V8 proteinase and fungal proteinase K, more soluble in water, and more selective than other lipopeptides containing a mixture of hydrophobic and cationic amino acids. Furthermore, the activity of C14-RRR was not compromised by salts, serum, or a change in pH. Live cell experiments revealed that these lipopeptides, with a detergent-like structure, killed bacteria rapidly by targeting cell membranes. Importantly, these compounds were also able to inhibit biofilm formation and could even disrupt preformed biofilms of clinically relevant MRSA strains with an in vitro efficacy comparable to daptomycin and vancomycin. These results indicate that small lipopeptides are potentially useful candidates for preventing or eliminating bacterial biofilms alone or in combination with daptomycin or vancomycin.

Influence of Dimerization of Lipopeptide Laur-Orn-Orn-Cys-NH2 and an N-terminal Peptide of Human Lactoferricin on Biological Activity

Lactoferrin (LF) is a naturally occurring antimicrobial peptide that is cleaved by pepsin to lactoferricin (LFcin). LFcin has an enhanced antimicrobial activity as compared to that of LF. Recently several hetero- and homodimeric antimicrobial peptides stabilized by a single disulfide bond linking linear polypeptide chains have been discovered. We have demonstrated that the S–S bond heterodimerization of lipopeptide Laur-Orn-Orn-Cys–NH₂ (peptide III) and the synthetic N-terminal peptide of human lactoferricin (peptide I) yields a dimer (peptide V), which is almost as microbiologically active as the more active monomer and at the same time it is much less toxic. Furthermore, it has been found that the S–S bond homodimerization of both peptide I and peptide III did not affect antimicrobial and haemolytic activity of the compounds. The homo- and heterodimerization of peptides I and III resulted in either reduction or loss of antifungal activity. This work suggests that heterodimerization of antimicrobial lipopeptides via intermolecular disulfide bond might be a powerful modification deserving consideration in the design of antimicrobial peptides.

Self-assembly and interactions of short antimicrobial cationic lipopeptides with membrane lipids: ITC, FTIR and molecular dynamics studies

In this work, the self-organization and the behavior of the surfactant-like peptides in the presence of biological membrane models were studied. The studies were focused on synthetic palmitic acid-containing lipopeptides, C16-KK-NH2 (I), C16-KGK-NH2 (II) and C16-KKKK-NH2 (III). The self-assembly was explored by molecular dynamics simulations using a coarse-grained force field. The critical micellar concentration was estimated by the surface tension measurements. The thermodynamics of the peptides binding to the anionic and zwitterionic lipids were established using isothermal titration calorimetry (ITC). The influence of the peptides on the lipid acyl chain ordering was determined using FTIR spectroscopy. The compounds studied show surface-active properties with a distinct CMC over the millimolar range. An increase in the steric and electrostatic repulsion between polar head groups shifts the CMC toward higher values and reduces the aggregation number. An analysis of the peptide-membrane binding revealed a unique interplay between the initial electrostatic and the subsequent hydrophobic interactions enabling the lipopeptides to interact with the lipid bilayer. In the case of C16-KKKK-NH2 (III), compensation of the electrostatic and hydrophobic interactions upon binding to the anionic membrane has been suggested and consequently no overall binding effects were noticed in ITC thermograms and FTIR spectra.

Chemical methods for peptide and protein production

Since the invention of solid phase synthetic methods by Merrifield in 1963, the number of research groups focusing on peptide synthesis has grown exponentially. However, the original step-by-step synthesis had limitations: the purity of the final product decreased with the number of coupling steps. After the development of Boc and Fmoc protecting groups, novel amino acid protecting groups and new techniques were introduced to provide high quality and quantity peptide products. Fragment condensation was a popular method for peptide production in the 1980s, but unfortunately the rate of racemization and reaction difficulties proved less than ideal. Kent and co-workers revolutionized peptide coupling by introducing the chemoselective reaction of unprotected peptides, called native chemical ligation. Subsequently, research has focused on the development of novel ligating techniques including the famous click reaction, ligation of peptide hydrazides, and the recently reported α-ketoacid-hydroxylamine ligations with 5-oxaproline. Several companies have been formed all over the world to prepare high quality Good Manufacturing Practice peptide products on a multi-kilogram scale. This review describes the advances in peptide chemistry including the variety of synthetic peptide methods currently available and the broad application of peptides in medicinal chemistry.