A comparison of activity, toxicity, and conformation of tritrpticin and two TOAC-labeled analogues. Effects on the mechanism of action

Antibiofilm Activities of Tritrpticin Analogs Against Pathogenic Pseudomonas aeruginosa PA01 Strains

In our previous work, we showed that short antimicrobial hexapeptides (AMPs) containing three Trp and three Arg residues had a potent antibiofilm activity against a pathogenic Gram-positive Staphylococcus aureus MRSA strain. However, the activity of these hexapeptides against a Gram-negative Pseudomonas aeruginosa PA01 strain was relatively poor. Herein, we tested the longer 13-residue synthetic AMP tritrpticin-NH2 (Tritrp) and several of its analogs as potential antibiofilm agents that can prevent biofilm formation (MBIC) and/or cause biofilm dissolution (MBEC) for two P. aeruginosa PA01 strains, one of which expressed the GFP protein. Tritrp, a porcine cathelicidin, is currently the only known naturally occurring cationic AMP that has three Trp in sequence (WWW), a feature that was found to be important in our previous study. Our results show that several Tritrp analogs were effective. In particular, analogs with Pro substitutions that had altered peptide backbone structures compared to the naturally occurring amphipathic two-turn structure showed more potent MBIC and MBEC antibiofilm activities. Selectivity of the peptides towards P. aeruginosa could be improved by introducing the non-proteinogenic amino acid 2,3-diaminopropionic acid, rather than Arg or Lys, as the positively charged residues. Using 1H NMR spectroscopy, we also reinvestigated the role of the two Pro residues in cis-trans isomerism of the peptide in aqueous solution. Overall, our results show that the WWW motif embedded in longer cationic AMPs has considerable potential to combat biofilm formation in pathogenic Gram-negative strains.

Comparative Properties of Helical and Linear Amphipathicity of Peptides Composed of Arginine, Tryptophan, and Valine

BACKGROUND

The persistence of antibiotic resistance has incited a strong interest in the discovery of agents with novel antimicrobial mechanisms. The direct killing of multidrug-resistant bacteria by cationic antimicrobial peptides (AMPs) underscores their importance in the fight against infections associated with antibiotic resistance. Despite a vast body of AMP literature demonstrating a plurality in structural classes, AMP engineering has been largely skewed toward peptides with idealized amphipathic helices (H-amphipathic). In contrast to helical amphipathicity, we designed a series of peptides that display the amphipathic motifs in the primary structure. We previously developed a rational framework for designing AMP libraries of H-amphipathic peptides consisting of Arg, Trp, and Val (H-RWV, with a confirmed helicity up to 88% in the presence of membrane lipids) tested against the most common MDR organisms.

METHODS

In this study, we re-engineered one of the series of the H-RWV peptides (8, 10, 12, 14, and 16 residues in length) to display the amphipathicity in the primary structure by side-by-side (linear) alignment of the cationic and hydrophobic residues into the 2 separate linear amphipathic (L-amphipathic) motifs. We compared the 2 series of peptides for antibacterial activity, red blood cell (RBC) lysis, killing and membrane-perturbation properties.

RESULTS

The L-RWV peptides achieved the highest antibacterial activity at a minimum length of 12 residues (L-RWV12, minimum optimal length or MOL) with the lowest mean MIC of 3-4 µM, whereas the MOL for the H-RWV series was reached at 16 residues (H-RWV16). Overall, H-RWV16 displayed the lowest mean MIC at 2 µM but higher levels of RBC lysis (25-30%), while the L-RWV series displayed minor RBC lytic effects at the test concentrations. Interestingly, when the S. aureus strain SA719 was chosen because of its susceptibility to most of the peptides, none of the L-RWV peptides demonstrated a high level of membrane perturbation determined by propidium iodide incorporation measured by flow cytometry, with <50% PI incorporation for the L-RWV peptides. By contrast, most H-RWV peptides displayed almost up to 100% PI incorporation. The results suggest that membrane perturbation is not the primary killing mechanism of the L-amphipathic RWV peptides, in contrast to the H-RWV peptides.

CONCLUSIONS

Taken together, the data indicate that both types of amphipathicity may provide different ideal pharmacological properties that deserve further investigation.

Important structural features of antimicrobial peptides towards specific activity: Trends in the development of efficient therapeutics

Proteins and peptides, as polypeptide chains, have usually got unique conformational structures for effective biological activity. Antimicrobial peptides (AMPs) are a group of bioactive peptides, which have been increasingly studied during recent years for their promising antibacterial, antifungal, antiviral and anti-inflammatory activity, as well as, other esteemed bioactivities. Numerous AMPs have been separated from a wide range of natural resources, or produced in vitro through chemical synthesis and recombinant protein expression. Natural AMPs have had limited clinical application due to several drawbacks, such as their short half-life due to protease degradation, lack of activity at physiological salt concentrations, toxicity to mammalian cells, and the absence of suitable methods of delivery for the AMPs that are targeted and sustained. The creation of synthetic analogs of AMPs would both avoid the drawbacks of the natural analogs and maintain or even increase the antimicrobial effectiveness. The structure-activity relationship of discovered AMPs or their derivatives facilitates the development of synthetic AMPs. This review discovered that the relationship between the activity of AMPs and their positive net charge, hydrophobicity, and amino acid sequence and the relationship between AMPs' function and other features like their topology, glycosylation, and halogenation.

Spatial Distribution Control of Antimicrobial Peptides through a Novel Polymeric Carrier for Safe and Efficient Cancer Treatment

Antimicrobial peptides (AMPs) hold great potential for use in tumor treatment. However, developing AMP-based antitumor therapies is challenging due to circulatory instability, hemolytic toxicity, low selectivity, and poor cell permeability of AMPs. In this study, a polymeric carrier for AMPs (denoted as PAMP_m -co-PPBE_n /PCA) is presented that effectively enhances their anticancer efficacy while minimizing their potential side effects. By integrating multiple responsive structures at the molecular level, the carrier finely controls the spatial distribution of AMPs in different biological microenvironments, thereby effectively modulating their membranolytic ability. Upon employing KLA as the model AMP, the polymeric carrier's hemolytic toxicity during blood circulation is suppressed, its cellular internalization when reaching tumor tissues facilitated, and its membranolytic toxicity toward the mitochondria upon entering cancer cells restored and further enhanced. Animal studies indicate that this approach significantly improves the antitumor efficacy of KLA and reduces its toxicity. Considering that the loading method for most AMPs is identical to that of KLA, the polymeric carrier reported in this study may provide a feasible approach for the development of AMP-based cancer treatments.

Challenge in the Discovery of New Drugs: Antimicrobial Peptides against WHO-List of Critical and High-Priority Bacteria

Bacterial resistance has intensified in recent years due to the uncontrolled use of conventional drugs, and new bacterial strains with multiple resistance have been reported. This problem may be solved by using antimicrobial peptides (AMPs), which fulfill their bactericidal activity without developing much bacterial resistance. The rapid interaction between AMPs and the bacterial cell membrane means that the bacteria cannot easily develop resistance mechanisms. In addition, various drugs for clinical use have lost their effect as a conventional treatment; however, the synergistic effect of AMPs with these drugs would help to reactivate and enhance antimicrobial activity. Their efficiency against multi-resistant and extensively resistant bacteria has positioned them as promising molecules to replace or improve conventional drugs. In this review, we examined the importance of antimicrobial peptides and their successful activity against critical and high-priority bacteria published in the WHO list.

Light-Emitting Probes for Labeling Peptides

Peptides are versatile biopolymers composed of 2-100 amino acid residues that present a wide range of biological functions and constitute potential therapies for numerous diseases, partly due to their ability to penetrate cell membranes. However, their mechanisms of action have not been fully elucidated due to the lack of appropriate tools. Existing light-emitting probes are limited by their cytotoxicity and large size, which can alter peptide structure and function. Here, we describe the available fluorescent, bioluminescent, and chemiluminescent probes for labeling peptides, with a focus on minimalistic options.

The Best Peptidomimetic Strategies to Undercover Antibacterial Peptides

Health-care systems that develop rapidly and efficiently may increase the lifespan of humans. Nevertheless, the older population is more fragile, and is at an increased risk of disease development. A concurrently growing number of surgeries and transplantations have caused antibiotics to be used much more frequently, and for much longer periods of time, which in turn increases microbial resistance. In 1945, Fleming warned against the abuse of antibiotics in his Nobel lecture: "The time may come when penicillin can be bought by anyone in the shops. Then there is the danger that the ignorant man may easily underdose himself and by exposing his microbes to non-lethal quantities of the drug make them resistant". After 70 years, we are witnessing the fulfilment of Fleming's prophecy, as more than 700,000 people die each year due to drug-resistant diseases. Naturally occurring antimicrobial peptides protect all living matter against bacteria, and now different peptidomimetic strategies to engineer innovative antibiotics are being developed to defend humans against bacterial infections.

Membrane activity of two short Trp-rich amphipathic peptides

Short linear antimicrobial peptides are attractive templates for developing new antibiotics. Here, it is described a study of the interaction between two short Trp-rich peptides, horine and verine-L, and model membranes. Isothermal titration calorimetry studies showed that the affinity of these peptides towards large unilamellar vesicles (LUV) having a lipid composition mimicking the lipid composition of S. aureus membranes is ca. 30-fold higher than that towards E. coli mimetics. The former interaction is driven by enthalpy and entropy, while the latter case is driven by entropy, suggesting differences in the forces that play a role in the binding to the two types of model membranes. Upon membrane binding the peptides acquired different conformations according to circular dichroism (CD) studies; however, in both cases CD studies indicated stacked W-residues. Peptide-induced membrane permeabilization, lipid flip-flop, molecular packing at the membrane-water interface, and lateral lipid segregation were observed in all cases. However, the extent of these peptide-induced changes on membrane properties was always higher in S. aureus than E. coli mimetics. Both peptides seem to act via a similar mechanism of membrane permeabilization of S. aureus membrane mimetics, while their mechanisms seem to differ in the case of E. coli. This may be the result of differences in both the peptides´ structure and the membrane lipid composition between both types of bacteria.