Novel antimicrobial peptides that exhibit activity against select agents and other drug resistant bacteria

Study of the Antioxidant, Antimicrobial, and Wound Healing Properties of Raw Hydrolyzed Extract from Nile Tilapia Skin (Oreochromis niloticus)

Oreochromis niloticus (Nile tilapia) skin is a by-product of Brazilian fish farming, rich in collagen. The present study aims to evaluate the wound healing, antioxidant, and antimicrobial potential of the raw hydrolyzed extract of Nile tilapia skin, as well as the identification of the main compounds. The in vitro activity was performed using antioxidant, antimicrobial and scratch wound healing assays. An in vivo experiment was performed to evaluate the wound healing potential. On days 1, 7, 14 and 21, the lesions were photographed to assess wound retraction and on the 7th , 14th and 21st  days the skins were removed for histological evaluation and the blood of the animals was collected for glutamic oxaloacetic transaminase and glutamic pyruvic transaminase determination. The chemical study was carried out through liquid chromatography-tandem mass spectrometry and de novo sequencing of peptides. The in vitro assays showed a reduction of the gap area in 24 h, dose-dependent antimicrobial activity for both bacteria, and antioxidant activity. The chemical analysis highlighted the presence of active biopeptides. The histological evaluation showed that the raw hydrolyzed extract of Nile tilapia skin has a healing potential, and does not present toxicological effects; therefore, is promising for the treatment of wounds.

Recent advances and applications of peptide-agent conjugates for targeting tumor cells

BACKGROUND

Cancer, being a complex disease, presents a major challenge for the scientific and medical communities. Peptide therapeutics have played a significant role in different medical practices, including cancer treatment.

METHOD

This review provides an overview of the current situation and potential development prospects of anticancer peptides (ACPs), with a particular focus on peptide vaccines and peptide-drug conjugates for cancer treatment.

RESULTS

ACPs can be used directly as cytotoxic agents (molecularly targeted peptides) or can act as carriers (guiding missile) of chemotherapeutic agents and radionuclides by specifically targeting cancer cells. More than 60 natural and synthetic cationic peptides are approved in the USA and other major markets for the treatment of cancer and other diseases. Compared to traditional cancer treatments, peptides exhibit anticancer activity with high specificity and the ability to rapidly kill target cancer cells. ACP's target and kill cancer cells via different mechanisms, including membrane disruption, pore formation, induction of apoptosis, necrosis, autophagy, and regulation of the immune system. Modified peptides have been developed as carriers for drugs, vaccines, and peptide-drug conjugates, which have been evaluated in various phases of clinical trials for the treatment of different types of solid and leukemia cancer.

CONCLUSIONS

This review highlights the potential of ACPs as a promising therapeutic option for cancer treatment, particularly through the use of peptide vaccines and peptide-drug conjugates. Despite the limitations of peptides, such as poor metabolic stability and low bioavailability, modified peptides show promise in addressing these challenges. Various mechanism of action of anticancer peptides. Modes of action against cancer cells including: inducing apoptosis by cytochrome c release, direct cell membrane lysis (necrosis), inhibiting angiogenesis, inducing autophagy-mediated cell death and immune cell regulation.

Anti-Cancer Peptides: Status and Future Prospects

The dramatic rise in cancer incidence, alongside treatment deficiencies, has elevated cancer to the second-leading cause of death globally. The increasing morbidity and mortality of this disease can be traced back to a number of causes, including treatment-related side effects, drug resistance, inadequate curative treatment and tumor relapse. Recently, anti-cancer bioactive peptides (ACPs) have emerged as a potential therapeutic choice within the pharmaceutical arsenal due to their high penetration, specificity and fewer side effects. In this contribution, we present a general overview of the literature concerning the conformational structures, modes of action and membrane interaction mechanisms of ACPs, as well as provide recent examples of their successful employment as targeting ligands in cancer treatment. The use of ACPs as a diagnostic tool is summarized, and their advantages in these applications are highlighted. This review expounds on the main approaches for peptide synthesis along with their reconstruction and modification needed to enhance their therapeutic effect. Computational approaches that could predict therapeutic efficacy and suggest ACP candidates for experimental studies are discussed. Future research prospects in this rapidly expanding area are also offered.

Incorporation of Non-Canonical Amino Acids into Antimicrobial Peptides: Advances, Challenges, and Perspectives

The emergence of antimicrobial resistance is a global health concern and calls for the development of novel antibiotic agents. Antimicrobial peptides seem to be promising candidates due to their diverse sources, mechanisms of action, and physicochemical characteristics, as well as the relatively low emergence of resistance. The incorporation of noncanonical amino acids into antimicrobial peptides could effectively improve their physicochemical and pharmacological diversity. Recently, various antimicrobial peptides variants with improved or novel properties have been produced by the incorporation of single and multiple distinct noncanonical amino acids. In this review, we summarize strategies for the incorporation of noncanonical amino acids into antimicrobial peptides, as well as their features and suitabilities. Recent applications of noncanonical amino acid incorporation into antimicrobial peptides are also presented. Finally, we discuss the related challenges and prospects.

Selected Antimicrobial Peptides Inhibit In Vitro Growth of Campylobacter spp

Campylobacter is a major cause of acute human diarrheal illness. Broiler chickens constitute a primary reservoir for C. jejuni leading to human infection. Consequently, there is a need for developing novel intervention methods. Antimicrobial peptides (AMP) are small proteins which have evolved in most lifeforms to provide defense against microbial infections. To date, over 3000 AMP have been discovered; however, few of them have been analyzed specifically for ability to kill campylobacters. We selected and evaluated a set of 11 unique chemically synthesized AMP for ability to inhibit growth of C. jejuni. Six of the AMP we tested produced zones of inhibition on lawns of C. jejuni. These AMP included: NRC-13, RL-37, Temporin L, Cecropin–Magainin, Dermaseptin, and C12K-2β12. In addition, MIC were determined for Cecropin–Magainin, RL-37 and C12K-2β12 against 15 isolates of Campylobacter representing the three most common pathogenic strains. MIC for campylobacters were approximately 3.1 µg/mL for AMP RL-37 and C12K-2β12. MIC were slightly higher for the Cecropin–Magainin AMP in the range of 12.5 to 100 µg/mL. These AMP are attractive subjects for future study and potential in vivo delivery to poultry to reduce Campylobacter spp. populations.

Antibacterial effect of synthetic ultra-short lipopeptide on Streptococcus agalactiae and its active on bacterial mastitis in mice

Streptococcus agalactiae mastitis is one of the significant threats to the milk industry. The traditional antibiotic treatment method is easy to cause the emergence of resistant strains, and the problem of drug residue is increasingly severe. In this study, we designed and synthesized five lipopeptides. The antibacterial activity of different molecular structure lipopeptides against Streptococcus agalactiae was detected. Furthermore, the mouse mastitis model was established using Streptococcus agalactiae. The lipopeptides with better antibacterial effect were selected for the treatment experiment to evaluate the application value in the treatment of mastitis. The results showed that 4 of the synthesized lipopeptides had specific antibacterial activity. SLP3 and SLP4 have an excellent antibacterial effect and can treat murine mastitis caused by Streptococcus agalactiae infection within the safe concentration range. The results of this study can provide an excellent experimental basis for new antibiotics and clinical application in the treatment of dairy cow mastitis.

Peptidomimetics - An infinite reservoir of metal binding motifs in metabolically stable and biologically active molecules

The involvement of metal ions in interactions with therapeutic peptides is inevitable. They are one of the factors able to fine-tune the biological properties of antimicrobial peptides, a promising group of drugs with one large drawback - a problematic metabolic stability. Appropriately chosen, proteolytically stable peptidomimetics seem to be a reasonable solution of the problem, and the use of D-, β-, γ-amino acids, unnatural amino acids, azapeptides, peptoids, cyclopeptides and dehydropeptides is an infinite reservoir of metal binding motifs in metabolically stable, well-designed, biologically active molecules. Below, their specific structural features, metal-chelating abilities and antimicrobial potential are discussed.

Anti-cancer peptides: classification, mechanism of action, reconstruction and modification

Anti-cancer peptides (ACPs) are a series of short peptides composed of 10-60 amino acids that can inhibit tumour cell proliferation or migration, or suppress the formation of tumour blood vessels, and are less likely to cause drug resistance. The aforementioned merits make ACPs the most promising anti-cancer candidate. However, ACPs may be degraded by proteases, or result in cytotoxicity in many cases. To overcome these drawbacks, a plethora of research has focused on reconstruction or modification of ACPs to improve their anti-cancer activity, while reducing their cytotoxicity. The modification of ACPs mainly includes main chain reconstruction and side chain modification. After summarizing the classification and mechanism of action of ACPs, this paper focuses on recent development and progress about their reconstruction and modification. The information collected here may provide some ideas for further research on ACPs, in particular their modification.

The application of DOSY NMR and molecular dynamics simulations to explore the mechanism(s) of micelle binding of antimicrobial peptides containing unnatural amino acids

Anionic and zwitterionic micelles are often used as simple models for the lipids found in bacterial and mammalian cell membranes to investigate antimicrobial peptide-lipid interactions. In our laboratory we have employed a variety of 1D, 2D, and diffusion ordered (DOSY) NMR experiments to investigate the interactions of antimicrobial peptides containing unnatural amino acids with SDS and DPC micelles. Complete assignment of the proton spectra of these peptides is prohibited by the incorporation of a high percentage of unnatural amino acids which don't contain amide protons into the backbone. However preliminary assignment of the TOCSY spectra of compound 23 in the presence of both micelles indicated multiple conformers are present as a result of binding to these micelles. Chemical Shift Indexing agreed with previously collected CD spectra that indicated on binding to SDS micelles compound 23 adopts a mixture of α-helical structures and on binding to DPC micelles this peptide adopts a mixture of helical and β-turn/sheet like structures. DOSY NMR experiments also indicated that the total positive charge and the relative placement of that charge at the N-terminus or C-terminus are important in determining the mole fraction of the peptide that will bind to the different micelles. DOSY and (1) H-NMR experiments indicated that the length of Spacer #1 plays a major role in defining the binding conformation of these analogs with SDS micelles. Results obtained from molecular simulations studies of the binding of compounds 23 and 36 with SDS micelles were consistent with the observed NMR results.

Synthetic Antimicrobial Peptides Exhibit Two Different Binding Mechanisms to the Lipopolysaccharides Isolated from Pseudomonas aeruginosa and Klebsiella pneumoniae

Circular dichroism and ¹H NMR were used to investigate the interactions of a series of synthetic antimicrobial peptides (AMPs) with lipopolysaccharides (LPS) isolated from Pseudomonas aeruginosa and Klebsiella pneumoniae. Previous CD studies with AMPs containing only three Tic-Oic dipeptide units do not exhibit helical characteristics upon interacting with small unilamellar vesicles (SUVs) consisting of LPS. Increasing the number of Tic-Oic dipeptide units to six resulted in five analogues with CD spectra that exhibited helical characteristics on binding to LPS SUVs. Spectroscopic and in vitro inhibitory data suggest that there are two possible helical conformations resulting from two different AMP-LPS binding mechanisms. Mechanism one involves a helical binding conformation where the AMP binds LPS very strongly and is not efficiently transported across the LPS bilayer resulting in the loss of inhibitory activity. Mechanism two involves a helical binding conformation where the AMP binds LPS very loosely and is efficiently transported across the LPS bilayer resulting in an increase in inhibitory activity. Mechanism three involves a nonhelical binding conformation where the AMP binds LPS very loosely and is efficiently transported across the LPS bilayer resulting in an increase in inhibitory activity.

Spectroscopic investigations of the binding mechanisms between antimicrobial peptides and membrane models of Pseudomonas aeruginosa and Klebsiella pneumoniae

CD spectroscopy was used to investigate the interactions of a series of synthetic AMPs with LPS isolated from Pseudomonas aeruginosa and Klebsiella pneumoniae, as well as with various phospholipids to better approximate the chemical composition of the membranes of these two strains of Gram-negative bacteria. This investigation was conducted in order to probe how the contributions of key physicochemical properties of an AMP vary in different regions of the membranes of these two bacteria. The conclusions from this study are as follows. (1) The binding interactions between the AMP and the membranes are defined by the complementarity of delocalization of positive charge density of the basic amino side chains (i.e., electrostatics), molecular flexibility of the peptide backbone, and overall hydrophobicity. (2) The binding interactions of these AMPs to LPS seem to be predominantly with the lipid A region of the LPS. (3) Incorporation of phospholipids into the LPS containing SUVs resulted in dramatic changes in the conformational equilibrium of the bound AMPs. (4) For the LPS-phospholipid models of Pseudomonas aeruginosa, delocalization of the side chain positive charge plays a major role in determining the number of conformers that contribute to the binding conformational equilibrium. This relationship was not observed for the models of the outer and inner membranes of Klebsiella pneumoniae.

Inhibitory effect of short cationic homopeptides against gram-positive bacteria

In the selection or design of antimicrobial peptides, the key role played by cationic amino acids and chain length on the inhibitory potency and specificity is not clear. A fundamental study was conducted using chemically synthesized homopeptides of L-Lys and L-Arg ranging from 7 to 14 residues. Their effect on growth inhibition was evaluated over a wide range of Gram-positive bacteria at different levels of concentration. Interestingly, at lower concentrations (10 μM), Lys homopeptides with odd number of residues, especially with 11 residues, showed a broader inhibitory activity than those with even number of residues. At higher peptide concentrations (>20 μM), the inhibitory activity of Lys homopeptides was directly related to the number of residues in the chain. In contrast, Arg homopeptides, at lower concentrations, did not exhibit a defined pattern of bacterial inhibition related to the number of residues; however, at higher concentrations (>20 μM), the inhibitory effects were more pronounced. Lys homopeptides at concentrations up to 300 μM showed a remarkably lower toxicity against CHSE-214 cells. Arg homopeptides exhibited negligible cytotoxicity up to chain length of 11 residues at concentrations lower than 100 μM, but an abrupt increase in toxicity resulted when the peptide chain length reached 12 amino acid residues and higher concentrations. All synthesized homopeptides displayed characteristic polyproline II helix conformation in both buffer and liposomes, as shown by CD spectroscopy. This result suggests that short Lys homopeptides with an odd number of residues (9 and 11) have a broad spectrum of activity against Gram-positive bacterial cells compared with Arg homopeptides, which in turn showed a considerably higher selectivity toward those cells. By investigating the differences between Lys and Arg homopeptides, this study contributes to the understanding of their mechanism of growth inhibition and selectivity. Thus, it provides further guidelines for a rational design of short antimicrobial peptides.

Actinopyga lecanora hydrolysates as natural antibacterial agents

Actinopyga lecanora, a type of sea cucumber commonly known as stone fish with relatively high protein content, was explored as raw material for bioactive peptides production. Six proteolytic enzymes, namely alcalase, papain, pepsin, trypsin, bromelain and flavourzyme were used to hydrolyze A. lecanora at different times and their respective degrees of hydrolysis (DH) were calculated. Subsequently, antibacterial activity of the A. lecanora hydrolysates, against some common pathogenic Gram positive bacteria (Bacillus subtilis and Staphylococcus aureus) and Gram negative bacteria (Escherichia coli, Pseudomonas aeruginosa, and Pseudomonas sp.) were evaluated. Papain hydrolysis showed the highest DH value (89.44%), followed by alcalase hydrolysis (83.35%). Bromelain hydrolysate after one and seven hours of hydrolysis exhibited the highest antibacterial activities against Pseudomonas sp., P. aeruginosa and E. coli at 51.85%, 30.07% and 30.45%, respectively compared to the other hydrolysates. Protein hydrolysate generated by papain after 8 h hydrolysis showed maximum antibacterial activity against S. aureus at 20.19%. The potent hydrolysates were further fractionated using RP-HPLC and antibacterial activity of the collected fractions from each hydrolysate were evaluated, wherein among them only three fractions from the bromelain hydrolysates exhibited inhibitory activities against Pseudomonas sp., P. aeruginosa and E. coli at 24%, 25.5% and 27.1%, respectively and one fraction of papain hydrolysate showed antibacterial activity of 33.1% against S. aureus. The evaluation of the relationship between DH and antibacterial activities of papain and bromelain hydrolysates revealed a meaningful correlation of four and six order functions.

Antimicrobial peptides containing unnatural amino acid exhibit potent bactericidal activity against ESKAPE pathogens

A series of 36 synthetic antimicrobial peptides containing unnatural amino acids were screened to determine their effectiveness to treat Enterococcus faecium, Staphylococcus aureus, Klebsiella pnemoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species (ESKAPE) pathogens, which are known to commonly infect chronic wounds. The primary amino acid sequences of these peptides incorporate either three or six dipeptide units consisting of the unnatural amino acids Tetrahydroisoquinolinecarboxylic acid (Tic) and Octahydroindolecarboxylic acid (Oic). The Tic-Oic dipeptide units are separated by SPACER amino acids with specific physicochemical properties that control how these peptides interact with bacterial cell membranes of different chemical compositions. These peptides exhibited minimum inhibitory concentrations (MIC) against these pathogens in the range from >100 to 6.25 μg/mL. The observed diversity of MIC values for these peptides against the various bacterial strains are consistent with our hypothesis that the complementarity of the physicochemical properties of the peptide and the lipid of the bacteria's cell membrane determines the resulting antibacterial activity of the peptide.

Application of unnatural amino acids to the de novo design of selective antibiotic peptides

Because of their unique mechanism of cytotoxicity against bacteria and other microorganisms, antimicrobial peptides have received a great deal of attention as possible therapeutic agents. Incorporation of unnatural amino acids into the peptide sequences has the potential to improve the organism selectivity and potency of these peptides as well as increase their metabolic stability. This protocol outlines the logic used to selectively incorporate unnatural amino acid into a peptide sequence in an attempt to obtain peptides with increased therapeutic potential as antibiotic agents.

Synthesis and characterization of the 47-residue heterodimeric antimicrobial peptide distinctin, featuring directed disulfide bridge formation

Distinctin, a 47-residue heterodimeric peptide with potent antimicrobial activity, comprises two monomeric units linked covalently by a disulfide bond between Cys19 from the 22-residue A chain and Cys23 from the 25-residue B chain. Previous synthetic strategies involved assemblies of the two individual chains, followed by their co-oxidation to form the connecting disulfide bridge, and resulted in a mixture of three species: two homodimers and one heterodimer. Here, we report synthesis of exclusively heterodimeric distinctin, using recently developed tactics for directed disulfide bridge formation. Material prepared this way was characterized and found to be suitable for more detailed structural studies.

The effect of the placement and total charge of the basic amino acid clusters on antibacterial organism selectivity and potency

Extensive circular dichroism, isothermal titration calorimetry and induced calcein leakage studies were conducted on a series of antimicrobial peptides (AMPs), with a varying number of Lys residues located at either the C-terminus or the N-terminus to gain insight into their effect on the mechanisms of binding with zwitterionic and anionic membrane model systems. Different CD spectra were observed for these AMPs in the presence of zwitterionic DPC and anionic SDS micelles indicating that they adopt different conformations on binding to the surfaces of zwitterionic and anionic membrane models. Different CD spectra were observed for these AMPs in the presence of zwitterionic POPC and anionic mixed 4:1 POPC/POPG LUVs and SUVs, indicating that they adopt very different conformations on interaction with these two types of LUVs and SUVs. In addition, ITC and calcein leakage data indicated that all the AMPs studied interact via very different mechanisms with anionic and zwitterionic LUVs. ITC data suggest these peptides interact primarily with the surface of zwitterionic LUVs while they insert into and form pores in anionic LUVs. CD studies indicated that these compounds adopt different conformations depending on the ratio of POPC to POPG lipids present in the liposome. There are detectable spectroscopic and thermodynamic differences between how each of these AMPs interacts with membranes, that is position and total charge density defines how these AMPs interact with specific membrane models and thus partially explain the resulting diversity of antibacterial activity of these compounds.

Determining the effect of the incorporation of unnatural amino acids into antimicrobial peptides on the interactions with zwitterionic and anionic membrane model systems

Circular Dichroism (CD), isothermal calorimetry (ITC) and calcein fluorescence leakage experiments were conducted to provide insight into the mechanisms of binding of a series of antimicrobial peptides containing unnatural amino acids (Ac-XF-Tic-Oic-XK-Tic-Oic-XF-Tic-Oic-XK-Tic-KKKK-CONH(2)) to zwitterionic and anionic micelles, SUVs and LUVs; where X (Spacer# 1) is either Gly, β-Ala, Gaba or 6-aminohexanoic acid. It is the intent of this investigation to correlate these interactions with the observed potency and selectivity against several different strains of bacteria. The CD spectra of these compounds in the presence of zwitterionic DPC micelles and anionic SDS micelles are very different indicating that these compounds adopt different conformations on binding to the surface of anionic and zwitterionic membrane models. These compounds also exhibited very different CD spectra in the presence of zwitterionic POPC and anionic mixed 4:1 POPC/POPG SUVs and LUVs, indicating the formation of different conformations on interaction with the two membrane types. This observation is also supported by ITC and calcein leakage data. ITC data suggested these peptides interact primarily with the surface of zwitterionic LUVs and was further supported by fluorescence experiments where the interactions do not appear to be concentration dependent. In the presence of anionic membranes, the interactions appear more complex and the calorimetric and fluorescence data both imply pore formation is dependent on peptide concentration. Furthermore, evidence suggests that as the length of Spacer# 1 increases the mechanism of pore formation also changes. Based on the observed differences in the mechanisms of interactions with zwitterionic and anionic LUVs these AMPs are potential candidates for further drug development.