Chicken cathelicidin-2-derived peptides with enhanced immunomodulatory and antibacterial activities against biological warfare agents

Immunomodulatory properties of chicken cathelicidin-2 investigated on an ileal explant culture

As the threat posed by antimicrobial resistance grows more crucial, the development of compounds that can replace antibiotics becomes increasingly vital. Chicken cathelicidin-2 (Cath-2) belongs to the group of Host Defense Peptides (HDPs), which could provide a feasible solution for the treatment of gastrointestinal infections in poultry. It is a small peptide produced by the heterophil granulocytes of chickens as part of the innate immune response, and its immunomodulatory activity has already been demonstrated in several cell types. In this study, the effects of Cath-2 on the intestinal immune response were examined using ileal explant cultures isolated from chicken. Regarding our results, Cath-2 displayed a potent anti-inflammatory effect as it alleviated the LTA-caused elevation of interleukin (IL)-6 and IL-2 concentrations, and that of the IFN-γ/IL-10 ratio, furthermore, it increased the concentration of IL-10, alleviating the LTA-evoked decreased level of the anti-inflammatory cytokine. Moreover, when applied alone, it elevated the concentrations of IL-6, CXCLi2, and IL-2, providing evidence of its complex immunomodulatory mechanisms. In summary, Cath-2 was able to modulate the immune response of the intestinal wall not only by reducing pro-inflammatory cytokine release, but also through immune stimulation, demonstrating that it has the ability to improve innate immunity via a complex mechanism that may make it a suitable candidate for the control of intestinal infections.

Designing the antimicrobial peptide with centrosymmetric and amphipathic characterizations for improving antimicrobial activity

Antibiotic-resistant bacterial infections are becoming a serious health issue and will cause 10 million deaths per year by 2050. As a result, the development of new antimicrobial agents is urgently needed. Antimicrobial peptides (AMPs) are found in the innate immune systems of various organisms to effectively fend off invading pathogens. In this study, we designed a series of AMPs (THL-2-1 to THL-2-9) with centrosymmetric and amphipathic properties, through substituting different amino acids on the hydrophobic side and at the centrosymmetric position to improve their antimicrobial activity. The results showed that leucine as a residue on the hydrophobic side of the peptide could enhance its antimicrobial activity and that glutamic acid as a centrosymmetric residue could increase the salt resistance of the peptide. Thus, the THL-2-3 peptide (KRLLRELKRLL-NH2 ) showed the greatest antimicrobial activity (MIC90 of 16 μM) against Gram-negative bacteria and had the highest salt resistance and cell selectivity among all the designed peptides. In summary, the results of this study provide useful references for the design of AMPs to enhance antimicrobial activity.

The current research status and strategies employed to modify food-derived bioactive peptides

The ability of bioactive peptides to exert biological functions has mainly contributed to their exploitation. The exploitation and utilization of these peptides have grown tremendously over the past two decades. Food-derived peptides from sources such as plant, animal, and marine proteins and their byproducts constitute a more significant portion of the naturally-occurring peptides that have been documented. Due to their high specificity and biocompatibility, these peptides serve as a suitable alternative to pharmacological drugs for treating non-communicable diseases (such as cardiovascular diseases, obesity, and cancer). They are helpful as food preservatives, ingredients in functional foods, and dietary supplements in the food sector. Despite their unique features, the application of these peptides in the clinical and food sector is to some extent hindered by their inherent drawbacks such as toxicity, bitterness, instability, and susceptibility to enzymatic degradation in the gastrointestinal tract. Several strategies have been employed to eliminate or reduce the disadvantages of peptides, thus enhancing the peptide bioactivity and broadening the opportunities for their applications. This review article focuses on the current research status of various bioactive peptides and the strategies that have been implemented to overcome their disadvantages. It will also highlight future perspectives regarding the possible improvements to be made for the development of bioactive peptides with practical uses and their commercialization.

d-enantiomers of CATH-2 enhance the response of macrophages against Streptococcus suis serotype 2

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D-CATH-2 has strong antimicrobial activities towards multiple S.suis strains.

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D-CATH-2 ameliorates macrophage function.

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DCATH-2 binds LTA.

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DCATH-2 has prophylactic effect against S. suis infection in vivo.

Introduction

Due to the increase of antibiotic resistant bacterial strains, there is an urgent need for development of alternatives to antibiotics. Cathelicidins can be such an alternative to antibiotics having both a direct antimicrobial capacity as well as an immunomodulatory function. Previously, the full d-enantiomer of chicken cathelicidin-2 (d-CATH-2) has shown to prophylactically protect chickens against infection 7 days post hatch when administered in ovo three days before hatch.

Objectives

To further evaluate d-CATH-2 in mammals as a candidate for an alternative to antibiotics.

In this study, the prophylactic capacity of d-CATH-2 and two truncated derivatives, d-C(1–21) and d-C(4–21), was determined in mammalian cells.

Methods

Antibacterial assays; immune cell differentiation and modulation; cytotoxicity, isothermal titration calorimetry; in vivo prophylactic capacity of peptides in an S. suis infection model.

Results

d-CATH-2 and its derivatives were shown to have a strong direct antibacterial capacity against four different S. suis serotype 2 strains (P1/7, S735, D282, and OV625) in bacterial medium and even stronger in cell culture medium. In addition, d-CATH-2 and its derivatives ameliorated the efficiency of mouse bone marrow-derived macrophages (BMDM) and skewed mouse bone marrow-derived dendritic cells (BMDC) towards cells with a more macrophage-like phenotype. The peptides directly bind lipoteichoic acid (LTA) and inhibit LTA-induced activation of macrophages. In addition, S. suis killed by the peptide was unable to further activate mouse macrophages, which indicates that S. suis was eliminated by the previously reported silent killing mechanism. Administration of d-C(1–21) at 24 h or 7 days before infection resulted in a small prophylactic protection with reduced disease severity and reduced mortality of the treated mice.

Conclusion

d-enantiomers of CATH-2 show promise as anti-infectives against pathogenic S. suis for application in mammals.

Targeting the TLR2 Receptor With a Novel Thymopentin-Derived Peptide Modulates Immune Responses

The innate and adaptive immune systems act in concert to protect us from infectious agents and other harmful substances. As a state of temporary or permanent immune dysfunction, immunosuppression can make an organism more susceptible to infection, organ injury, and cancer due to damage to the immune system. It takes a long time to develop new immunomodulatory agents to prevent and treat immunosuppressive diseases, with slow progress. Toll-like receptor 2 (TLR2) agonists have been reported as potential immunomodulatory candidates due to their effective activation of immune responses. It has been demonstrated that thymopentin (TP5) could modulate immunity by binding to the TLR2 receptor. However, the fairly short half-life of TP5 greatly reduces its pharmacological potential for immunosuppression therapy. Although peptide cathelicidin 2 (CATH2) has a long half-life, it shows poor immunomodulatory activity and severe cytotoxicity, which seriously hampers its clinical development. Peptide hybridization is an effective approach for the design and engineering of novel functional peptides because hybrid peptides combine the advantages and benefits of various native peptides. In this study, to overcome all these challenges faced by the parental peptides, six hybrid peptides (CaTP, CbTP, CcTP, TPCa, TPCb, and TPCc) were designed by combining the full-length TP5 with different active fragments of CATH2. CbTP, the most potent TLR2 agonist among the six hybrid peptides, was effectively screened through in silico analysis and in vitro experiments. The CbTP peptide exhibited lower cytotoxicity than either CATH2 or TP5. Furthermore, the immunomodulatory effects of CbTP were confirmed in a CTX-immunosuppressed mouse model, which showed that CbTP has increased immunopotentiating activity and physiological stability compared to the parental peptides. CbTP successfully inhibited immunosuppression and weight loss, increased immune organ indices, and improved CD4⁺/CD8⁺ T lymphocyte subsets. In addition, CbTP significantly increased the production of the cytokine TNF-α and IL-6, and the immunoglobulins IgA, IgM, and IgG. The immunoenhancing effects of CbTP were attributed to its TLR2-binding activity, promoting the formation of the TLR2 cluster, the activation of the TLR2 receptor, and thus activation of the downstream MyD88-NF-кB signaling pathway.

Genetic diversity of Japanese quail cathelicidins

Japanese quail is a low-fat, meat-bird species exhibiting high disease resistance. Cathelicidins (CATHs) are host defense peptides conserved across numerous vertebrate species that play an important role in innate immunity. The activity of host defense peptides can be affected by amino acid substitutions. However, no polymorphisms in avian CATH genes have been reported to date. The aim of this study was to clarify the polymorphisms in CATHs in Japanese quail. DNA for genomic analyses was extracted from the peripheral blood of 99 randomly selected quail from 6 inbred lines. A total of 6, 4, 6, and 4 CjCATH1, -2, -3, and -B1 alleles were identified, respectively. Nine haplotypes, including 4 strain-specific haplotypes, were identified by combining alleles at the CjCATH1, -2, -3, and -B1 loci. In addition, 2 and 1 amino acid substitutions (I145F, Q148H, and P245H) predicted by PROVEAN and PolyPhen-2 to have deleterious effects were detected in CjCATH2 and -B1, respectively. Synthetic CjCATH2 and -B1 peptides exhibited greater antibacterial activity against Escherichia coli than chicken CATH2 and -B1, respectively. Furthermore, the CjCATHB1∗04 peptide exhibited less potent antimicrobial activity than other CjCATHB1 peptides examined. This is the first report of amino acid substitutions accompanied by changes in antibacterial activity in avian CATHs. These findings could be employed as indicators of improvements in innate immune response in poultry.

Insights into antimicrobial peptides in fighting anthrax: A review

Anthrax is an infectious disease occurring worldwide and is a threat to global society due to its possible misuse as a biological weapon. Bacillus anthracis is the etiologic agent of this disease which can be transmitted via inhalation, ingestion, and skin contact. Globally, it is estimated around 2000 anthrax cases occur per year. Upon infection, the organism can cause cytolysis of macrophage and produce exotoxin capable of inducing edema and lymphatic blockage. Another challenge posed by the organism is the ability to form spores in harsh conditions. Various antibiotics have been used to fight the disease. However, like many other microbes, B. anthracis may develop resistance, thus the discovery of new therapeutics is urgently required. Antimicrobial peptides (AMPs) have been discovered since 1980s and attracted researchers in the antimicrobial field. In this review, the work and studies on the attempts to discover potent AMPs to treat anthrax together with the brief overview of the synthesis and modification pathways of several AMPs have been presented.

The effect of structural modification of antimicrobial peptides on their antimicrobial activity, hemolytic activity, and plasma stability

In this article, a series of modifications were made on an antimicrobial peptide F_2,5,12 W, including altering the amino acid sequence, introducing cysteine and other typical amino acids, developing peptide dimers via disulfide bonds, and conjugating with mPEG, in order to enhance the antimicrobial activity, plasma stability, and reduce the hemolytic activity of peptides. The results showed that mPEG conjugation could significantly improve the plasma stability and reduce the hemolytic activity of peptides, while the antimicrobial activity decreased meanwhile. However, altering the sequence of the peptide without changing its amino acid composition had little impact on its antimicrobial activity and plasma stability. The introduction of cysteine enhanced the plasma stability of peptides conspicuously, but at the same time, the increased hydrophobicity of peptides increased their hemolysis. The antimicrobial mechanism and cytotoxicity of the peptides with relatively high antimicrobial activity were also studied. In general, this study provided some ideas for the rational design and structure optimization of antimicrobial peptides.

Cathelicidins Modulate TLR-Activation and Inflammation

Cathelicidins are short cationic peptides that are part of the innate immune system. At first, these peptides were studied mostly for their direct antimicrobial killing capacity, but nowadays they are more and more appreciated for their immunomodulatory functions. In this review, we will provide a comprehensive overview of the various effects cathelicidins have on the detection of damage- and microbe-associated molecular patterns, with a special focus on their effects on Toll-like receptor (TLR) activation. We review the available literature based on TLR ligand types, which can roughly be divided into lipidic ligands, such as LPS and lipoproteins, and nucleic-acid ligands, such as RNA and DNA. For both ligand types, we describe how direct cathelicidin-ligand interactions influence TLR activation, by for instance altering ligand stability, cellular uptake and receptor interaction. In addition, we will review the more indirect mechanisms by which cathelicidins affect downstream TLR-signaling. To place all this information in a broader context, we discuss how these cathelicidin-mediated effects can have an impact on how the host responds to infectious organisms as well as how these effects play a role in the exacerbation of inflammation in auto-immune diseases. Finally, we discuss how these immunomodulatory activities can be exploited in vaccine development and cancer therapies.

Combinations of early generation antibiotics and antimicrobial peptides are effective against a broad spectrum of bacterial biothreat agents

The misuse of infectious disease pathogens as agents of deliberate attack on civilians and military personnel is a serious national security concern, which is exacerbated by the emergence of natural or genetically engineered multidrug resistant strains. In this study, the therapeutic potential of combinations of an antibiotic and a broad-spectrum antimicrobial peptide (AMP) was evaluated against five bacterial biothreats, the etiologic agents of glanders (Burkholderia mallei), melioidosis (Burkholderia pseudomallei), plague (Yersinia pestis), tularemia (Francisella tularensis), and anthrax (Bacillus anthracis). The therapeutics included licensed early generation antibiotics which are now rarely used. Three antibiotics and one 24- amino acid AMP were selected based on MIC assay data. Combinations of the AMP and tigecycline, minocycline, or novobiocin were screened for synergistic activity by checkerboard MIC assay. The combinations each enhanced the susceptibility of several strains. The tetracycline-peptide combinations increased the sensitivities of Y. pestis, F. tularensis, B. anthracis and B. pseudomallei, and the novobiocin-AMP combination augmented the sensitivity of all five. In time-kill assays, down-selected combinations of the peptide and minocycline or tigecycline enhanced killing of B. anthracis, Y. pestis, F. tularensis, and Burkholderia mallei but not B. pseudomallei. The novobiocin-AMP pair significantly reduced viability of all strains except B. mallei, which was very sensitive to the antibiotic alone. The results suggested that antibiotic-AMP combinations are useful tools for combating diverse pathogens. Future studies employing cell culture and animal models will utilize virulent strains of the agents to investigate the in vivo availability, host cytotoxicity, and protective efficacy of these therapeutics.

Antibacterial, anti-biofilm and in vivo activities of the antimicrobial peptides P5 and P6.2

Cationic antimicrobial peptides (AMPs) are short linear amino acid sequences, which display antimicrobial activity against a wide range of bacterial species. They are promising novel antimicrobials since they have shown bactericidal effects against multiresistant bacteria. Their amphiphilic structure with hydrophobic and cationic regions drives their interaction with anionic bacterial cytoplasmic membranes, which leads to their disruption. In this work two synthetic designed AMPs, P5 and P6.2, which have been previously analyzed in their ability to interact with bacterial or eukaryotic membranes, were evaluated in their anti-biofilm and in vivo antibacterial activity. In a first step, a time-kill kinetic assay against P. aeruginosa and S. aureus and a curve for hemolytic activity were performed in order to determine the killing rate and the possible undesirable toxic effect, respectively, for both peptides. The biofilm inhibitory activity was quantified at sub MIC concentrations of the peptides and the results showed that P5 displayed antibiofilm activity on both strains while P6.2 only on S. aureus. Scanning electron microscopy (SEM) of bacteria treated with peptides at their MIC revealed protruding blisters on Gam-negative P. aeruginosa strain, but almost no visible surface alteration on Gram-positive S. aureus. These micrographs highlighted different manifestations of the membrane-disrupting activity that these kinds of peptides possess. Finally, both peptides were analyzed in vivo, in the lungs of neutropenic mice previously instilled with P. aeruginosa. Mice lungs were surgically extracted and bacteria and pro-inflammatory cytokines (IL-β, IL-6 and TNF-α) were quantified by colony forming units and ELISA, respectively. Results showed that instillation of the peptides produced a significant decrease in the number of living bacteria in the lungs, concomitant with a decrease in pro-inflammatory cytokines. Overall, the results presented here suggest that these two new peptides could be good candidates for future drug development for anti-biofilm and anti-infective therapy.

The Komodo dragon (Varanus komodoensis) genome and identification of innate immunity genes and clusters

Background

We report the sequencing, assembly and analysis of the genome of the Komodo dragon (Varanus komodoensis), the largest extant lizard, with a focus on antimicrobial host-defense peptides. The Komodo dragon diet includes carrion, and a complex milieu of bacteria, including potentially pathogenic strains, has been detected in the saliva of wild dragons. They appear to be unaffected, suggesting that dragons have robust defenses against infection. While little information is available regarding the molecular biology of reptile immunity, it is believed that innate immunity, which employs antimicrobial host-defense peptides including defensins and cathelicidins, plays a more prominent role in reptile immunity than it does in mammals. .

Results

High molecular weight genomic DNA was extracted from Komodo dragon blood cells. Subsequent sequencing and assembly of the genome from the collected DNA yielded a genome size of 1.6 Gb with 45x coverage, and the identification of 17,213 predicted genes. Through further analyses of the genome, we identified genes and gene-clusters corresponding to antimicrobial host-defense peptide genes. Multiple β-defensin-related gene clusters were identified, as well as a cluster of potential Komodo dragon ovodefensin genes located in close proximity to a cluster of Komodo dragon β-defensin genes. In addition to these defensins, multiple cathelicidin-like genes were also identified in the genome. Overall, 66 β-defensin genes, six ovodefensin genes and three cathelicidin genes were identified in the Komodo dragon genome.

Conclusions

Genes with important roles in host-defense and innate immunity were identified in this newly sequenced Komodo dragon genome, suggesting that these organisms have a robust innate immune system. Specifically, multiple Komodo antimicrobial peptide genes were identified. Importantly, many of the antimicrobial peptide genes were found in gene clusters. We found that these innate immunity genes are conserved among reptiles, and the organization is similar to that seen in other avian and reptilian species. Having the genome of this important squamate will allow researchers to learn more about reptilian gene families and will be a valuable resource for researchers studying the evolution and biology of the endangered Komodo dragon.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-6029-y) contains supplementary material, which is available to authorized users.

In vitro immunomodulatory activities of peptides derived from Salmo salar NK-lysin and cathelicidin in fish cells

Antimicrobial peptides (AMPs) are amphipathic peptides, which play an important role in innate defence. These peptides are gene-encoded and either constitutively expressed and/or upregulated during an infection. NK-lysins are AMPs with a three-dimensional globular structure. They are larger molecules, which comprise 74-78 amino acid residues and six conserved cysteine residues forming three disulphide bonds. Cathelicidins are a family of antimicrobial peptides that act as important components of the innate immune system with a broad spectrum of antimicrobial activity and immunomodulatory properties. Although they are widely studied in mammals, little is known about their immunomodulatory function. In the present study, we identified and characterized for the first time four NK-lysin-like transcripts from Atlantic salmon (Salmo salar) based on EST reported sequences. In vitro, NK-lysin derived peptides were able to induce the expression of IL-1β and IL-8 in Salmo salar head kidney leukocytes. We also tested Salmo salar cathelicidin 1 derived peptide in a similar assay, showing its ability to induce the expression of IFN-γ. These results indicate that NK-lysin and cathelicidin 1 derived peptides are able to modulated immune response, suggesting their potential use to enhance immune response in fish.

Cathelicidins PMAP-36, LL-37 and CATH-2 are similar peptides with different modes of action

Host defense peptides (HDPs) play a pivotal role in innate immunity and have, in addition to antimicrobial activity, also important immunomodulatory functions. Bacteria are less likely to develop resistance against HDPs because these peptides target and kill bacteria in multiple ways, as well as modulate the immune system. Therefore, HDPs, and derivatives thereof, are promising alternatives to traditional antibiotics. Hardly anything is known about the immunomodulatory functions of porcine cathelicidin PMAP-36. In this study, we aimed to determine both antibacterial and immunomodulatory activities of PMAP-36 comparing the properties of PMAP-36 analogs with two well-studied peptides, human LL-37 and chicken CATH-2. Transmission electron microscopy revealed different killing mechanisms of E. coli for PMAP-36, CATH-2 and LL-37. LL-37 binds LPS very weakly in contrast to PMAP-36, but it inhibits LPS activation of macrophages the strongest. The first 11 amino acids of the N-terminal side of PMAP-36 are dispensable for E. coli killing, LPS-neutralization and binding. Deletion of four additional amino acids resulted in a strong decrease in activity. The activity of full length PMAP-36 was not affected by monomerization, whereas the shorter analogs require dimerization for proper immunomodulatory activity but not for their antibacterial activity.

Imaging the Antistaphylococcal Activity of CATH-2: Mechanism of Attack and Regulation of Inflammatory Response

Chicken cathelicidin-2 (CATH-2) is a broad-spectrum antimicrobial host defense peptide (HDP) that may serve as a paradigm for the development of new antimicrobial agents. While previous studies have elucidated the mechanism by which CATH-2 kills Escherichia coli, its mode of action against Gram-positive bacteria remains to be determined. In this study, we explored the underlying antibacterial mechanism of CATH-2 against a methicillin-resistant strain of Staphylococcus aureus and the effect of CATH-2-mediated S. aureus killing on immune activation. Visualization of the antimicrobial activity of CATH-2 against S. aureus with live-imaging confocal microscopy demonstrated that CATH-2 directly binds the bacteria, which is followed by membrane permeabilization and cell shrinkage. Transmission electron microscopy (TEM) studies further showed that CATH-2 initiated pronounced morphological changes of the membrane (mesosome formation) and ribosomal structures (clustering) in a dose-dependent manner. Immunolabeling of these sections demonstrated that CATH-2 binds and passes the bacterial membrane at subminimal bactericidal concentrations (sub-MBCs). Furthermore, competition assays and isothermal titration calorimetry (ITC) analysis provided evidence that CATH-2 directly interacts with lipoteichoic acid and cardiolipin. Finally, stimulation of macrophages with S. aureus and CATH-2 showed that CATH-2 not only kills S. aureus but also has the potential to limit S. aureus-induced inflammation at or above the MBC. Taken together, it is concluded that at sub-MBCs, CATH-2 perturbs the bacterial membrane and subsequently enters the cell and binds intracellular S. aureus components, while at or above the MBC, CATH-2 causes disruption of membrane integrity and inhibits S. aureus-induced macrophage activation. IMPORTANCE Due to the high use of antibiotics in both human and veterinary settings, many bacteria have become resistant to those antibiotics that we so heavily rely on. Methicillin-resistant S. aureus (MRSA) is one of these difficult-to-treat resistant pathogens for which novel antimicrobial therapies will be required in the near future. One novel approach could be the utilization of naturally occurring antimicrobial peptides, such as chicken CATH-2, which have been show to act against a wide variety of bacteria. However, before these peptides can be used clinically, more knowledge of their functions and mechanisms of action is required. In this study, we used live imaging and electron microscopy to visualize in detail how CATH-2 kills S. aureus, and we investigated how CATH-2 affects immune activation by S. aureus. Together, these results give a better understanding of how CATH-2 kills S. aureus and what the potential immunological consequences of this killing can be.

Tryptophan-Containing Cyclic Decapeptides with Activity against Plant Pathogenic Bacteria

A library of 66 cyclic decapeptides incorporating a Trp residue was synthesized on solid phase and screened against the phytopathogenic bacteria Pseudomonas syringae pv. syringae, Xanthomonas axonopodis pv. vesicatoria, and Erwinia amylovora. The hemolytic activity of these peptides was also evaluated. The results obtained were compared with those of a collection of Phe analogues previously reported. The analysis of the data showed that the presence of the Trp improved the antibacterial activity against these three pathogens. In particular, 40 to 46 Trp analogues displayed lower minimum inhibitory concentration (MIC) values than their corresponding Phe counterparts. Interestingly, 26 Trp-containing sequences exhibited MIC of 0.8 to 3.1 μM against X. axonopodis pv. vesicatoria, 21 peptides MIC of 1.6 to 6.2 μM against P. syringae pv. syringae and six peptides MIC of 6.2 to 12.5 μM against E. amylovora. Regarding the hemolysis, in general, Trp derivatives displayed a percentage of hemolysis comparable to that of their Phe analogues. Notably, 49 Trp-containing cyclic peptides showed a hemolysis ≤ 20% at 125 μM. The peptides with the best biological activity profile were c(LKKKLWKKLQ) (BPC086W) and c(LKKKKWLLKQ) (BPC108W), which displayed MIC values ranging from 0.8 to 12.5 μM and a hemolysis ≤ 8% at 125 μM. Therefore, it is evident that these Trp sequences constitute promising candidates for the development of new agents for use in plant protection.

Chicken cathelicidins as potent intrinsically disordered biocides with antimicrobial activity against infectious pathogens

This study was performed to identify the expression patterns of the cathelicidin genes in a local chicken breed and to evaluate the antimicrobial activities of the cathelicidin peptides against pathogenic bacteria. This analysis revealed that the coding regions of CATH-1, -2, and -3 genes contain 447 bp, 465 bp, and 456 bp, respectively, and encode proteins of 148, 154, 151 amino acids, respectively. The complete amino acid sequences of the cathelicidin peptides are similar to those found in Meleagris gallopavo, Phasianus colchicus, and Coturnix coturnix, and show high sequence identity to their Columba livia and Anas platyrhynchos counterparts. In contrast, these avian peptides shared a very low sequence identity with the mammalian cathelicidins. The analysis further revealed that the cathelicidin genes are expressed in various organ and tissues. We also show that the CATH peptides 1, 2, 3 and their amide-modified structures possess potent antimicrobial activities against both Gram-positive and Gram-negative pathogens, with these bacteria being affected to different extents. The antimicrobial activities of the peptides are slightly lower than those of their amide analogs. Computational analysis revealed that pre-pro-cathelicidins are hybrid proteins that contain ordered domains and functional intrinsically disordered regions. Furthermore, high structural and sequence variability of mature cathelicidins is a strong indication of their rather disordered nature. It is likely that intrinsic disorder is needed for the multifarious functionality of these antimicrobial peptides. Our analyses indicated that cathelicidin peptides require further study to better understand their full potentials in the treatment of diseases in both humans and animals. The data obtained for synthetic avian peptides will help elucidating of their potential applications in the pharmaceutical industry.

Influence of Cysteine and Tryptophan Substitution on DNA-Binding Activity on Maize α-Hairpinin Antimicrobial Peptide

For almost four decades, antimicrobial peptides have been studied, and new classes are being discovered. However, for therapeutic use of these molecules, issues related to the mechanism of action must be answered. In this work, the antimicrobial activity of the hairpinin MBP-1 was studied by the synthesis of two variants, one replacing cysteines and one tryptophan with alanine. Antibacterial activity was abolished in both variants. No membrane disturbance, even in concentrations higher than those required to inhibit the bacteria, was observed in SEM microscopy. The gel retardation assay showed that MBP-1 possesses a higher DNA-binding ability than variants. Finally, molecular modelling showed that the lack of cysteines resulted in structure destabilization and lack of tryptophan resulted in a less flexible peptide, with less solvent assessable surface area, both characteristics that could contribute to absence of activity. In summary, the data here reported add more information about the multiple mechanisms of action of α-hairpinins.

Cationic host defense peptides; novel antimicrobial therapeutics against Category A pathogens and emerging infections

Cationic Host Defense Peptides (HDP, also known as antimicrobial peptides) are crucial components of the innate immune system and possess broad-spectrum antibacterial, antiviral, and immunomodulatory activities. They can contribute to the rapid clearance of biological agents through direct killing of the organisms, inhibition of pro-inflammatory mediators such as lipopolysaccharide, and by modulating the inflammatory response to infection. Category A biological agents and materials, as classified by the United States National Institutes for Health, the US Centers for Disease Control and Prevention, and the US Department of Homeland Security, carry the most severe threat in terms of human health, transmissibility, and preparedness. As such, there is a pressing need for novel frontline approaches for prevention and treatment of diseases caused by these organisms, and exploiting the broad antimicrobial activity exhibited by cationic host defense peptides represents an exciting priority area for clinical research. This review will summarize what is known about the antimicrobial and antiviral effects of the two main families of cationic host defense peptides, cathelicidins, and defensins in the context of Category A biological agents which include, but are not limited to; anthrax (Bacillus anthracis), plague (Yersinia pestis), smallpox (Variola major), tularemia (Francisella tularensis). In addition, we highlight priority areas, particularly emerging viral infections, where more extensive research is urgently required.

Protective effect of in ovo treatment with the chicken cathelicidin analog D-CATH-2 against avian pathogenic E. coli

Increasing antibiotic resistance and ever stricter control on antibiotic use are a driving force to develop alternatives to antibiotics. One such strategy is the use of multifunctional Host Defense Peptides. Here we examined the protective effect of prophylactic treatment with the D analog of chicken cathelicidin-2 (D-CATH-2) against a respiratory E. coli infection. Chickens were treated with D-CATH-2 in ovo at day 18 of embryonic development or intramuscularly at days 1 and 4 after hatch. At 7 days of age, birds were challenged intratracheally with avian pathogenic E. coli. Protection was evaluated by recording mortality, morbidity (Mean Lesion Score) and bacterial swabs of air sacs at 7 days post-infection. In ovo D-CATH-2 treatment significantly reduced morbidity (63%) and respiratory bacterial load (>90%), while intramuscular treatment was less effective. D-CATH-2 increased the percentage of peripheral blood lymphocytes and heterophils by both administration routes. E. coli specific IgM levels were lower in in ovo treated animals compared to intramuscular D-CATH-2 treatment. In short, in ovo treatment with the Host Defense Peptide derived D-CATH-2 can partially protect chickens from E. coli infection, making this peptide an interesting starting point to develop alternatives to antibiotics for use in the poultry sector.

Immunomodulatory and Anti-Inflammatory Activities of Chicken Cathelicidin-2 Derived Peptides

Host Defence Peptides and derived peptides are promising classes of antimicrobial and immunomodulatory lead compounds. For this purpose we examined whether chicken cathelicidin-2 (CATH-2)-derived peptides modulate the function and inflammatory response of avian immune cells. Using a chicken macrophage cell line (HD11) we found that full-length CATH-2 dose-dependently induced transcription of chemokines CXCLi2/IL-8, MCP-3 and CCLi4/RANTES, but not of pro-inflammatory cytokine IL-1β. In addition, CATH-2 efficiently inhibited IL-1β and nitric oxide production by HD11 cells induced by different sources of lipopolysaccharides (LPS). N-terminal truncated CATH-2 derived peptides maintained the capacity to selectively induce chemokine transcription, but despite their high LPS affinity several analogs lacked LPS-neutralizing capacity. Substitution of phenylalanine residues by tryptophan introduced endotoxin neutralization capacity in inactive truncated CATH-2 derived peptides. In contrast, amino acid substitution of phenylalanine by tyrosine abrogated endotoxin neutralization activity of CATH-2 analogs. These findings support a pivotal role for aromatic residues in peptide-mediated endotoxin neutralization by CATH-2 analogs and were shown to be independent of LPS affinity. The capacity to modulate chemokine production and dampen endotoxin-induced pro-inflammatory responses in chicken immune cells implicates that small CATH-2 based peptides could serve as leads for the design of CATH-2 based immunomodulatory anti-infectives.

Determination of changes in bovine plasma and milk proteins during naturally occurring Escherichia coli mastitis by comparative proteomic analysis

The aim of this study was to investigate changes in plasma and milk proteins in response to Escherichia coli infection in cows. Plasma and milk were collected from healthy cows, cows suffering from mild E. coli mastitis, and cows suffering from severe E. coli mastitis. Protein composition was examined by two-dimensional gel electrophoresis coupled with mass spectrometry. Plasma haptoglobin and α-1 acid glycoprotein demonstrated greater expression in mastitic cows compared with controls, but there were no difference between mildly and severely mastitic cows. Milk from mildly mastitic cows showed increased albumin and casein variants. Severely mastitic cows showed lower casein levels and increased anti-microbial and acute phase proteins. Milk α-1 acid glycoprotein and cathelicidins were associated with severe mastitis. A greater number of β-casein fragments that corresponded to β-casein isoforms were found in milk from mildly mastitic cows. These results suggest that caseins levels decreased and the concentrations of anti-microbial and acute phase proteins increased corresponding to the degree of E. coli mastitis. Nevertheless, further studies are needed to determine whether cathelicidin could serve as a diagnostic marker for mastitis.

Avian antimicrobial host defense peptides: from biology to therapeutic applications

Host defense peptides (HDPs) are an important first line of defense with antimicrobial and immunomoduatory properties. Because they act on the microbial membranes or host immune cells, HDPs pose a low risk of triggering microbial resistance and therefore, are being actively investigated as a novel class of antimicrobials and vaccine adjuvants. Cathelicidins and β-defensins are two major families of HDPs in avian species. More than a dozen HDPs exist in birds, with the genes in each HDP family clustered in a single chromosomal segment, apparently as a result of gene duplication and diversification. In contrast to their mammalian counterparts that adopt various spatial conformations, mature avian cathelicidins are mostly α-helical. Avian β-defensins, on the other hand, adopt triple-stranded β-sheet structures similar to their mammalian relatives. Besides classical β-defensins, a group of avian-specific β-defensin-related peptides, namely ovodefensins, exist with a different six-cysteine motif. Like their mammalian counterparts, avian cathelicidins and defensins are derived from either myeloid or epithelial origin expressed in a majority of tissues with broad-spectrum antibacterial and immune regulatory activities. Structure-function relationship studies with several avian HDPs have led to identification of the peptide analogs with potential for use as antimicrobials and vaccine adjuvants. Dietary modulation of endogenous HDP synthesis has also emerged as a promising alternative approach to disease control and prevention in chickens.

Avian host defense peptides

Host defense peptides (HDPs) are important effector molecules of the innate immune system of vertebrates. These antimicrobial peptides are also present in invertebrates, plants and fungi. HDPs display broad-spectrum antimicrobial activities and fulfill an important role in the first line of defense of many organisms. It is becoming increasingly clear that in the animal kingdom the functions of HDPs are not confined to direct antimicrobial actions. Research in mammals has indicated that HDPs have many immunomodulatory functions and are also involved in other physiological processes ranging from development to wound healing. During the past five years our knowledge about avian HDPs has increased considerably. This review addresses our current knowledge on the evolution, regulation and biological functions of HDPs of birds.

Improved proteolytic stability of chicken cathelicidin-2 derived peptides by D-amino acid substitutions and cyclization

A truncated version of host defense peptide chicken cathelicidin-2, C1-15, possesses potent, broad spectrum antibacterial activity. A variant of this peptide, F(2,5,12)W, which contains 3 phenylalanine to tryptophan substitutions, possesses improved antibacterial activity and lipopolysaccharide (LPS) neutralizing activity compared to C1-15. In order to improve the proteolytic resistance of both peptides we engineered novel chicken cathelicidin-2 analogs by substitution of l- with D-amino acids and head-to-tail cyclization. Both cyclic and D-amino acid variants showed enhanced stability in human serum compared to C1-15 and F(2,5,12)W. The D-amino acid variants were fully resistant to proteolysis by trypsin and bacterial proteases. Head-to-tail cyclization of peptide F(2,5,12)W resulted in a 3.5-fold lower cytotoxicity toward peripheral blood mononuclear cells. In general, these modifications did not influence antibacterial and LPS neutralization activities. It is concluded that for the development of novel therapeutic compounds based on chicken cathelicidin-2 D-amino acid substitutions and cyclization must be considered. These modifications increase the stability and lower cytotoxicity of the peptides without altering their antimicrobial potency.

A cathelicidin-2-derived peptide effectively impairs Staphylococcus epidermidis biofilms

Staphylococcus epidermidis is a major cause of nosocomial infections owing to its ability to form biofilms on the surface of medical devices. Biofilms are surface-adhered bacterial communities. In mature biofilms these communities are encased in an extracellular matrix composed of bacterial polysaccharides, proteins and DNA. The antibiotic resistance of bacteria present in biofilms can be up to 1000-fold higher compared with the planktonic phenotype. Host defence peptides (HDPs) are considered to be excellent candidates for the development of novel antibiotics. Recently, we demonstrated that a short variant of the HDP chicken cathelicidin-2, peptide F(2,5,12)W, has potent antibacterial and lipopolysaccharide-neutralising activities. This study reports on the antibiofilm activity of peptide F(2,5,12)W against two strains of S. epidermidis, including a multiresistant strain. Peptide F(2,5,12)W potently inhibited the formation of bacterial biofilms in vitro at a low concentration of 2.5 μM, which is below the concentration required to kill or inhibit growth (minimal inhibitory concentration=10 μM). Moreover, peptide F(2,5,12)W also impaired existing S. epidermidis biofilms. A 4-h challenge of pre-grown biofilms with 40 μM F(2,5,12)W reduced the metabolic activity of the wild-type strain biofilm completely and reduced that of the multiresistant strain biofilm by >50%. It is concluded that F(2,5,12)W prevents biofilm formation and impairs mature S. epidermidis biofilms.