Antimicrobial peptides: old molecules with new ideas

Staphylococcus aureus Exploits Epidermal Barrier Defects in Atopic Dermatitis to Trigger Cytokine Expression

Patients with atopic dermatitis (AD) have an abnormal skin barrier and are frequently colonized by S. aureus. In this study we investigated if S. aureus penetrates the epidermal barrier of subjects with AD and sought to understand the mechanism and functional significance of this entry. S. aureus was observed to be more abundant in the dermis of lesional skin from AD patients. Bacterial entry past the epidermis was observed in cultured human skin equivalents and in mice but was found to be increased in the skin of cathelicidin knockout and ovalbumin-sensitized filaggrin mutant mice. S. aureus penetration through the epidermis was dependent on bacterial viability and protease activity, because killed bacteria and a protease-null mutant strain of S. aureus were unable to penetrate. Entry of S. aureus directly correlated with increased expression of IL-4, IL-13, IL-22, thymic stromal lymphopoietin, and other cytokines associated with AD and with decreased expression of cathelicidin. These data illustrate how abnormalities of the epidermal barrier in AD can alter the balance of S. aureus entry into the dermis and provide an explanation for how such dermal dysbiosis results in increased inflammatory cytokines and exacerbation of disease.

Sustained Release of Antibacterial Lipopeptides from Biodegradable Polymers against Oral Pathogens

The development of antibacterial drugs to overcome various pathogenic species, which inhabit the oral cavity, faces several challenges, such as salivary flow and enzymatic activity that restrict dosage retention. Owing to their amphipathic nature, antimicrobial peptides (AMPs) serve as the first line of defense of the innate immune system. The ability to synthesize different types of AMPs enables exploitation of their advantages as alternatives to antibiotics. Sustained release of AMPs incorporated in biodegradable polymers can be advantageous in maintaining high levels of the peptides. In this study, four potent ultra-short lipopeptides, conjugated to an aliphatic acid chain (16C) were incorporated in two different biodegradable polymers: poly (lactic acid co castor oil) (PLACO) and ricinoleic acid-based poly (ester-anhydride) (P(SA-RA)) for sustained release. The lipopeptide and polymer formulations were tested for antibacterial activity during one week, by turbidometric measurements of bacterial outgrowth, anti-biofilm activity by live/dead staining, biocompatibility by hemolysis and XTT colorimetric assays, mode of action by fluorescence-activated cell sorting (FACS) and release profile by a fluorometric assay. The results show that an antibacterial and anti-biofilm effect, as well as membrane disruption, can be achieved by the use of a formulation of lipopeptide incorporated in biodegradable polymer.

Peptides from American alligator plasma are antimicrobial against multi-drug resistant bacterial pathogens including Acinetobacter baumannii

BACKGROUND

Our group has developed a new process for isolating and identifying novel cationic antimicrobial peptides from small amounts of biological samples. Previously, we identified several active antimicrobial peptides from 100 μl of plasma from Alligator mississippiensis. These peptides were found to have in vitro antimicrobial activity against Pseudomonas aeruginosa and Staphylococcus aureus. In this work, we further characterize three of the novel peptides discovered using this process: Apo5, Apo6, and A1P.

RESULTS

We examined the activity of these peptides against multi-drug resistant strains and clinical isolates of common human pathogens. We investigated their structural characteristics using circular dichroism and tested for membrane disruption and DNA binding. These peptides were found to have strong in vitro activity against multi-drug resistant and clinically isolated strains of S. aureus, Escherichia coli, P. aeruginosa, and Acinetobacter baumannii. Apo5 and Apo6, peptides derived from alligator apolipoprotein C-1, depolarized the bacterial membrane. A1P, a peptide from the serpin proteinase inhibitor, did not permeabilize membranes. Performing circular dichroism analysis, Apo5 and Apo6 were found to be predominantly helical in SDS and TFE buffer, while A1P has significantly different structures in phosphate buffer, SDS, and TFE. None of these peptides were found to be hemolytic to sheep red blood cells or significantly cytotoxic up to 100 μg/ml after 24 h exposure.

CONCLUSIONS

Overall, we suggest that Apo5 and Apo6 have a different mode of action than A1P, and that all three peptides make promising candidates for the treatment of drug-resistant bacteria, such as A. baumannii.

Mutation of the Enterohemorrhagic Escherichia coli Core LPS Biosynthesis Enzyme RfaD Confers Hypersusceptibility to Host Intestinal Innate Immunity In vivo

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 is an important foodborne pathogen causing severe diseases in humans worldwide. Currently, there is no specific treatment available for EHEC infection and the use of conventional antibiotics is contraindicated. Therefore, identification of potential therapeutic targets and development of effective measures to control and treat EHEC infection are needed. Lipopolysaccharides (LPS) are surface glycolipids found on the outer membrane of gram-negative bacteria, including EHEC, and LPS biosynthesis has long been considered as potential anti-bacterial target. Here, we demonstrated that the EHEC rfaD gene that functions in the biosynthesis of the LPS inner core is required for the intestinal colonization and pathogenesis of EHEC in vivo. Disruption of the EHEC rfaD confers attenuated toxicity in Caenorhabditis elegans and less bacterial colonization in the intestine of C. elegans and mouse. Moreover, rfaD is also involved in the control of susceptibility of EHEC to antimicrobial peptides and host intestinal immunity. It is worth noting that rfaD mutation did not interfere with the growth kinetics when compared to the wild-type EHEC cells. Taken together, we demonstrated that mutations of the EHEC rfaD confer hypersusceptibility to host intestinal innate immunity in vivo, and suggested that targeting the RfaD or the core LPS synthesis pathway may provide alternative therapeutic regimens for EHEC infection.

Activation of Molecular Signatures for Antimicrobial and Innate Defense Responses in Skin with Transglutaminase 1 Deficiency

Mutations of the transglutaminase 1 gene (TGM1) are a major cause of autosomal recessive congenital ichthyoses (ARCIs) that are associated with defects in skin barrier structure and function. However, the molecular processes induced by the transglutaminase 1 deficiency are not fully understood. The aim of the present study was to uncover those processes by analysis of cutaneous molecular signatures. Gene expression profiles of wild-type and Tgm1-/-epidermis were assessed using microarrays. Gene ontology analysis of the data showed that genes for innate defense responses were up-regulated in Tgm1-/-epidermis. Based on that result, the induction of Il1b and antimicrobial peptide genes, S100a8, S100a9, Defb14, Camp, Slpi, Lcn2, Ccl20 and Wfdc12, was confirmed by quantitative real-time PCR. A protein array revealed that levels of IL-1β, G-CSF, GM-CSF, CXCL1, CXCL2, CXCL9 and CCL2 were increased in Tgm1-/-skin. Epidermal growth factor receptor (EGFR) ligand genes, Hbegf, Areg and Ereg, were activated in Tgm1-/-epidermis. Furthermore, the antimicrobial activity of an epidermal extract from Tgm1-/-mice was significantly increased against both Escherichia coli and Staphylococcus aureus. In the epidermis of ichthyosiform skins from patients with TGM1 mutations, S100A8/9 was strongly positive. The expression of those antimicrobial and defense response genes was also increased in the lesional skin of an ARCI patient with TGM1 mutations. These results suggest that the up-regulation of molecular signatures for antimicrobial and innate defense responses is characteristic of skin with a transglutaminase 1 deficiency, and this autonomous process might be induced to reinforce the defective barrier function of the skin.

The Cutaneous Microbiome and Aspects of Skin Antimicrobial Defense System Resist Acute Treatment with Topical Skin Cleansers

The human skin microbiome has been suggested to play an essential role in maintaining health by contributing to innate defense of the skin. These observations have inspired speculation that the use of common skin washing techniques may be detrimental to the epidermal antibacterial defense system by altering the microbiome. In this study, several common skin cleansers were used to wash human forearms and the short-term effect on the abundance of the antimicrobial peptide LL-37 and the abundance and diversity of bacterial DNA was measured. Despite small but significant decreases in the amount of LL-37 on the skin surface shortly after washing, no significant change in the bacterial community was detected. Furthermore, Group A Streptococcus did not survive better on the skin after washing. In contrast, the addition of antimicrobial compounds such as benzalkonium chloride or triclocarban to soap before washing decreased the growth of Group A Streptococcus applied after rinse. These results support prior studies that hand washing techniques in the health care setting are beneficial and should be continued. Additional research is necessary to better understand the effects of chronic washing and the potential impact of skin care products on the development of dysbiosis in some individuals.

Colonisation with methicillin-resistant Staphylococcus aureus and associated factors among nurses with occupational skin diseases

OBJECTIVES

To evaluate the prevalence of colonisation with methicillin-resistant Staphylococcus aureus (MRSA), associated factors and the effectiveness of decolonisation procedures among nurses with occupational skin diseases (OSD).

METHODS

In a retrospective cohort study, the medical records of 319 nurses from Germany who were screened consecutively for MRSA when participating in a tertiary individual prevention programme (TIP) for severe OSD between July 2009 and December 2014 were evaluated.

RESULTS

90.3% of nurses with severe OSD suffered from hand eczema. 43 were colonised with MRSA on admission (13.5%), mainly in the nose (n=35, 81.4%). However, the hands were affected in more than half of the MRSA carriers (n=24, 55.8%). Risk factors for MRSA colonisation were atopic skin diathesis (OR 2.01, 95% CI 1.03 to 3.92, p=0.049) and presence of atopic dermatitis on other body parts than the hands (OR 4.33, 95% CI 2.23 to 8.43, p<0.001). Hand eczema was significantly more severe in MRSA carriers than in non-carriers (OR 1.23, 95% CI 1.10 to 1.37, p<0.001) and showed a higher prevalence of vesicles, erosions or fissures. MRSA eradication was successful in 67.4% after the first attempt.

CONCLUSIONS

Nurses with OSD have a twofold to threefold higher prevalence of MRSA colonisation than what has been reported for point-prevalence screenings among healthcare workers in Germany. Atopic skin diathesis, atopic dermatitis and severe hand eczema are the main risk factors. Thus, prevention and treatment of OSD could be important elements in reduction of colonisation with MRSA among nurses and transmission to others.

Pleurocidin congeners demonstrate activity against Streptococcus and low toxicity on gingival fibroblasts

OBJECTIVES

Fish epidermal antimicrobial peptides, such as pleurocidin, are cathelicidins with broad-spectrum antimicrobial activity against gram negative and gram-positive bacteria, as well as fungi. In the current study, we attempted to optimize peptide bioactivity by sequence modification and assess the antimicrobial activities.

METHODS

Fifteen pleurocidin analogues were designed, and the efficacy of pleurocidin congeners against common cariogenic microorganisms was tested; furthermore, we performed a preliminary study of the antimicrobial mechanism. We assayed the minimal inhibitory concentration (MIC), minimal bactericide concentration (MBC) and bactericidal kinetics to determine the cell killing activity. Scanning electron microscopy (SEM) was used to observe the bacterial membrane after treatment with congeners' peptides. Human gingival fibroblasts (HGFs) were also used in toxicity studies.

RESULTS

The MIC and MBC results indicated that peptide congeners had different antimicrobial activities against the tested oral strains. Toxicity studies indicated that several congener peptides had little effect on human gingival fibroblasts (HGFs) with 5min of in vitro treatment.

CONCLUSION

Our findings suggested that several pleurocidin congeners had the antimicrobial effect against Streptococcus mutans, Streptococcus sanguinis and Streptococcus sobrinus.

A pH-dependent charge reversal peptide for cancer targeting

Naturally occurring cationic antimicrobial peptides exhibit not only antimicrobial activity, but also anticancer activity and are expected to be new weapons in cancer treatment. The selectivity for cancer cells over normal cells is at least partly due to the more negative surface of cancer cells. A lower pH in tumor tissue (pH 6.2-6.9) than that in normal tissues (pH 7.3-7.4) has also been utilized to develop anticancer agents. However, cytotoxicity against normal cells at physiological pH is often an issue. Furthermore, acidic regions can be found in some normal tissues such as the kidneys. Therefore, existing approaches to cancer targeting are not fully satisfactory. In this study, we designed a peptide, HE (GIHHWLHSAHEFGEHFVHHIMNS-amide), with a charge that reverses from -1.5 at pH 7.4 to +6 at pH 5.5 for cancer targeting at low pH based on the antimicrobial peptide magainin 2 by introducing 6 His, an additional Glu, and an amidated terminal. HE interacted with cancer-mimicking negatively charged liposomes in a pH-dependent fashion with a midpoint with a pH of 6.5 just above the membrane surface. The peptide killed human renal adenocarcinoma ACHN cells at pH 6.0, but not at pH 7.4, and was nontoxic against human normal glomerular mesangial cells even at this low pH. Thus, the novel peptide may be a promising lead peptide for cancer therapy, although this derivatization resulted in weakened cytotoxicity.

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.

Intrinsic Defect in Keratinocyte Function Leads to Inflammation in Hidradenitis Suppurativa

Hidradenitis suppurativa (HS) is a chronic, inflammatory, debilitating, follicular disease of the skin. Despite a high prevalence in the general population, the physiopathology of HS remains poorly understood. The use of antibiotics and immunosuppressive agents for therapy suggests a deregulated immune response to microflora. Using cellular and gene expression analyses, we found an increased number of infiltrating CD4(+) T cells secreting IL-17 and IFN-γ in perilesional and lesional skin of patients with HS. By contrast, IL-22-secreting CD4(+) T cells are not enriched in HS lesions contrasting with increased number of those cells in the blood of patients with HS. We showed that keratinocytes isolated from hair follicles of patients with HS secreted significantly more IL-1β, IP-10, and chemokine (C-C motif) ligand 5 (RANTES) either constitutively or on pattern recognition receptor stimulations. In addition, they displayed a distinct pattern of antimicrobial peptide production. These findings point out a functional defect of keratinocytes in HS leading to a balance prone to inflammatory responses. This is likely to favor a permissive environment for bacterial infections and chronic inflammation characterizing clinical outcomes in patients with HS.

Angiogenic peptide (AG)-30/5C activates human keratinocytes to produce cytokines/chemokines and to migrate and proliferate via MrgX receptors

BACKGROUND

In addition to their antimicrobial activities, antimicrobial peptides, also known as host defense peptides (HDPs) activate keratinocytes; promote wound healing; and improve the skin barrier. AG-30/5C is a novel angiogenic HDP that activates various functions of fibroblasts and endothelial cells, including cytokine/chemokine production and wound healing.

OBJECTIVES

To investigate whether AG-30/5C activates human keratinocytes and to examine the underlying mechanisms.

METHODS

Production of cytokines/chemokines was assessed by ELISA. Expression of Mas-related G-protein coupled receptors X (MrgXs) in keratinocytes was determined by real-time PCR and Western blot. MAPK and NF-κB activation was analysed by Western blot. Cell migration was assessed by chemotaxis microchamber and in vitro wound closure assay, whereas cell proliferation was analysed using an XTT assay.

RESULTS

We found that AG-30/5C was more efficient than its parent peptide AG-30 in increasing the production of various cytokines/chemokines and promoting keratinocyte migration and proliferation. Furthermore, MrgX3 and MrgX4 receptors were constitutively expressed in keratinocytes at higher levels than MrgX1 and MrgX2, and were up-regulated upon stimulation with TLR ligands. Because MrgX3 and MrgX4 siRNAs suppressed AG-30/5C-mediated cytokine/chemokine production, keratinocyte migration and proliferation, we propose that AG-30/5C utilizes these MrgXs to stimulate keratinocytes. In addition, AG-30/5C-induced activation of keratinocytes was controlled by MAPK and NF-κB pathways, as evidenced by the inhibitory effects of ERK-, JNK-, p38- and NF-κB-specific inhibitors. Indeed, we confirmed that AG-30/5C enhanced phosphorylation of MAPKs and IκB.

CONCLUSIONS

Our findings provide novel evidence that AG-30/5C may be a useful therapeutic agent for wound healing by activating human keratinocytes.

Alternatives to overcoming bacterial resistances: State-of-the-art

Worldwide, bacterial resistance to chemical antibiotics has reached such a high level that endangers public health. Presently, the adoption of alternative strategies that promote the elimination of resistant microbial strains from the environment is of utmost importance. This review discusses and analyses several (potential) alternative strategies to current chemical antibiotics. Bacteriophage (or phage) therapy, although not new, makes use of strictly lytic phage particles as an alternative, or a complement, in the antimicrobial treatment of bacterial infections. It is being rediscovered as a safe method, because these biological entities devoid of any metabolic machinery do not possess any affinity whatsoever to eukaryotic cells. Lysin therapy is also recognized as an innovative antimicrobial therapeutic option, since the topical administration of preparations containing purified recombinant lysins with amounts in the order of nanograms, in infections caused by Gram-positive bacteria, demonstrated a high therapeutic potential by causing immediate lysis of the target bacterial cells. Additionally, this therapy exhibits the potential to act synergistically when combined with certain chemical antibiotics already available on the market. Another potential alternative antimicrobial therapy is based on the use of antimicrobial peptides (AMPs), amphiphilic polypeptides that cause disruption of the bacterial membrane and can be used in the treatment of bacterial, fungal and viral infections, in the prevention of biofilm formation, and as antitumoral agents. Interestingly, bacteriocins are a common strategy of bacterial defense against other bacterial agents, eliminating the potential opponents of the former and increasing the number of available nutrients in the environment for their own growth. They can be applied in the food industry as biopreservatives and as probiotics, and also in fighting multi-resistant bacterial strains. The use of antibacterial antibodies promises to be extremely safe and effective. Additionally, vaccination emerges as one of the most promising preventive strategies. All these will be tackled in detail in this review paper.

Interactions of Aspergillus fumigatus Conidia with Airway Epithelial Cells: A Critical Review

Aspergillus fumigatus is an environmental filamentous fungus that also acts as an opportunistic pathogen able to cause a variety of symptoms, from an allergic response to a life-threatening disseminated fungal infection. The infectious agents are inhaled conidia whose first point of contact is most likely to be an airway epithelial cell (AEC). The interaction between epithelial cells and conidia is multifaceted and complex, and has implications for later steps in pathogenesis. Increasing evidence has demonstrated a key role for the airway epithelium in the response to respiratory pathogens, particularly at early stages of infection; therefore, elucidating the early stages of interaction of conidia with AECs is essential to understand the establishment of infection in cohorts of at-risk patients. Here, we present a comprehensive review of the early interactions between A. fumigatus and AECs, including bronchial and alveolar epithelial cells. We describe mechanisms of adhesion, internalization of conidia by AECs, the immune response of AECs, as well as the role of fungal virulence factors, and patterns of fungal gene expression characteristic of early infection. A clear understanding of the mechanisms involved in the early establishment of infection by A. fumigatus could point to novel targets for therapy and prophylaxis.

Nanoparticles Suitable for BCAA Isolation Can Serve for Use in Magnetic Lipoplex-Based Delivery System for L, I, V, or R-rich Antimicrobial Peptides

This paper investigates the synthesis of paramagnetic nanoparticles, which are able to bind branched chain amino acids (BCAAs)—leucine, valine, and isoleucine and, thus, serve as a tool for their isolation. Further, by this, we present an approach for encapsulation of nanoparticles into a liposome cavity resulting in a delivery system. Analyses of valine and leucine in entire complex show that 31.3% and 32.6% recoveries are reached for those amino acids. Evaluation of results shows that the success rate of delivery in Escherichia coli (E. coli) is higher in the case of BCAAs on nanoparticles entrapped in liposomes (28.7% and 34.7% for valine and leucine, respectively) when compared to nanoparticles with no liposomal envelope (18.3% and 13.7% for valine and leucine, respectively). The nanoparticles with no liposomal envelope exhibit the negative zeta potential (−9.1 ± 0.3 mV); however, their encapsulation results in a shift into positive values (range of 28.9 ± 0.4 to 33.1 ± 0.5 mV). Thus, electrostatic interactions with negatively-charged cell membranes (approx. −50 mV in the case of E. coli) leads to a better uptake of cargo. Our delivery system was finally tested with the leucine-rich antimicrobial peptide (FALALKALKKALKKLKKALKKAL) and it is shown that hemocompatibility (7.5%) and antimicrobial activity of the entire complex against E. coli, Staphylococcus aureus (S. aureus), and methicilin-resistant S. aureus (MRSA) is comparable or better than conventional penicillin antibiotics.

Mechanisms of Antimicrobial Peptide Resistance in Gram-Negative Bacteria

Cationic antimicrobial peptides (CAMPs) are important innate immune defenses that inhibit colonization by pathogens and contribute to clearance of infections. Gram-negative bacterial pathogens are a major target, yet many of them have evolved mechanisms to resist these antimicrobials. These resistance mechanisms can be critical contributors to bacterial virulence and are often crucial for survival within the host. Here, we summarize methods used by Gram-negative bacteria to resist CAMPs. Understanding these mechanisms may lead to new therapeutic strategies against pathogens with extensive CAMP resistance.

Nanotechnology Formulations for Antibacterial Free Fatty Acids and Monoglycerides

Free fatty acids and monoglycerides have long been known to possess broad-spectrum antibacterial activity that is based on lytic behavior against bacterial cell membranes. Considering the growing challenges of drug-resistant bacteria and the need for new classes of antibiotics, the wide prevalence, affordable cost, and broad spectrum of fatty acids and monoglycerides make them attractive agents to develop for healthcare and biotechnology applications. The aim of this review is to provide a brief introduction to the history of antimicrobial lipids and their current status and challenges, and to present a detailed discussion of ongoing research efforts to develop nanotechnology formulations of fatty acids and monoglycerides that enable superior in vitro and in vivo performance. Examples of nano-emulsions, liposomes, solid lipid nanoparticles, and controlled release hydrogels are presented in order to highlight the potential that lies ahead for fatty acids and monoglycerides as next-generation antibacterial solutions. Possible application routes and future directions in research and development are also discussed.

Antimicrobial peptides and wound healing: biological and therapeutic considerations

Repair of tissue wounds is a fundamental process to re-establish tissue integrity and regular function. Importantly, infection is a major factor that hinders wound healing. Multicellular organisms have evolved an arsenal of host-defense molecules, including antimicrobial peptides (AMPs), aimed at controlling microbial proliferation and at modulating the host's immune response to a variety of biological or physical insults. In this brief review, we provide the evidence for a role of AMPs as endogenous mediators of wound healing and their promising therapeutic potential for the treatment of non-life-threatening skin and other epithelial injuries.

ER stress stimulates production of the key antimicrobial peptide, cathelicidin, by forming a previously unidentified intracellular S1P signaling complex

We recently identified a previously unidentified sphingosine-1-phosphate (S1P) signaling mechanism that stimulates production of a key innate immune element, cathelicidin antimicrobial peptide (CAMP), in mammalian cells exposed to external perturbations, such as UVB irradiation and other oxidative stressors that provoke subapoptotic levels of endoplasmic reticulum (ER) stress, independent of the well-known vitamin D receptor-dependent mechanism. ER stress increases cellular ceramide and one of its distal metabolites, S1P, which activates NF-κB followed by C/EBPα activation, leading to CAMP production, but in a S1P receptor-independent fashion. We now show that S1P activates NF-κB through formation of a previously unidentified signaling complex, consisting of S1P, TRAF2, and RIP1 that further associates with three stress-responsive proteins; i.e., heat shock proteins (GRP94 and HSP90α) and IRE1α. S1P specifically interacts with the N-terminal domain of heat shock proteins. Because this ER stress-initiated mechanism is operative in both epithelial cells and macrophages, it appears to be a universal, highly conserved response, broadly protective against diverse external perturbations that lead to increased ER stress. Finally, these studies further illuminate how ER stress and S1P orchestrate critical stress-specific signals that regulate production of one protective response by stimulating production of the key innate immune element, CAMP.

Protein aggregation as an antibiotic design strategy

Taking advantage of the xenobiotic nature of bacterial infections, we tested whether the cytotoxicity of protein aggregation can be targeted to bacterial pathogens without affecting their mammalian hosts. In particular, we examined if peptides encoding aggregation-prone sequence segments of bacterial proteins can display antimicrobial activity by initiating toxic protein aggregation in bacteria, but not in mammalian cells. Unbiased in vitro screening of aggregating peptide sequences from bacterial genomes lead to the identification of several peptides that are strongly bactericidal against methicillin-resistant Staphylococcus aureus. Upon parenteral administration in vivo, the peptides cured mice from bacterial sepsis without apparent toxic side effects as judged from histological and hematological evaluation. We found that the peptides enter and accumulate in the bacterial cytosol where they cause aggregation of bacterial polypeptides. Although the precise chain of events that leads to cell death remains to be elucidated, the ability to tap into aggregation-prone sequences of bacterial proteomes to elicit antimicrobial activity represents a rich and unexplored chemical space to be mined in search of novel therapeutic strategies to fight infectious diseases.

Opposing Effects of Zac1 and Curcumin on AP-1-Regulated Expressions of S100A7

ZAC, an encoding gene mapped at chromosome 6q24-q25 within PSORS1, was previously found over-expressed in the lower compartment of the hyperplastic epidermis in psoriatic lesions. Cytokines produced in the inflammatory dermatoses may drive AP-1 transcription factor to induce responsive gene expressions. We demonstrated that mZac1 can enhance AP-1-responsive S100A7 expression of which the encoding gene was located in PSORS4 with HaCaT keratinocytes. However, the mZac1-enhanced AP-1 transcriptional activity was suppressed by curcumin, indicating the anti-inflammatory property of this botanical agent and is exhibited by blocking the AP-1-mediated cross-talk between PSORS1 and PSORS4. Two putative AP-1-binding sites were found and demonstrated to be functionally important in the regulation of S100A7 promoter activity. Moreover, we found curcumin reduced the DNA-binding activity of AP-1 to the recognition element located in the S100A7 promoter. The S100A7 expression was found to be upregulated in the lesioned epidermis of atopic dermatitis and psoriasis, which is where this keratinocyte-derived chemoattractant engaged in the pro-inflammatory feedback loop. Understanding the regulatory mechanism of S100A7 expression will be helpful to develop therapeutic strategies for chronic inflammatory dermatoses via blocking the reciprocal stimuli between the inflammatory cells and keratinocytes.

Self-assembling lipopeptides with a potent activity against Gram-positive bacteria, including multidrug resistant strains

Aim: To explore the potential of de novo designed cyclic lipopeptides and its linear counterparts as antibacterial agents. Materials & methods: The lipopeptides were synthesized via solid-phase peptide synthesis and the cyclization was achieved by using succinic acid linker. The antimicrobial activities of the lipopeptides were evaluated in vitro against a variety selection of Gram-negative and Gram-positive bacteria including clinical isolates of multidrug-resistant strains. Results: The synthesized lipopeptides were able to self-assemble into nanoparticles in an aqueous environment, with three exhibiting potent antibacterial activity against Gram-positive bacteria, including clinically relevant multidrug-resistant bacteria. Conclusion: The lead compounds have the potential to be developed as new antibacterials that are effective against Gram-positive bacteria, including multidrug-resistant isolates.

A novel antimicrobial peptide derived from fish goose type lysozyme disrupts the membrane of Salmonella enterica

In aquaculture, accumulation of antibiotics resulted in development of resistance among bacterial pathogens. Consequently, it became mandatory to find alternative to synthetic antibiotics. Antimicrobial peptides (AMPs) which are described as evolutionary ancient weapons have been considered as promising alternates in recent years. In this study, a novel antimicrobial peptide had been derived from goose type lysozyme (LyzG) which was identified from the cDNA library of freshwater fish Channa striatus (Cs). The identified lysozyme cDNA contains 585 nucleotides which encodes a protein of 194 amino acids. CsLyzG was closely related to Siniperca chuatsi with 92.8% homology. The depicted protein sequence contained a GEWL domain with conserved GLMQ motif, 7 active residues and 2 catalytic residues. Gene expression analysis revealed that CsLyzG was distributed in major immune organs with highest expression in head kidney. Results of temporal expression analysis after bacterial (Aeromonas hydrophila) and fungal (Aphanomyces invadans) challenges indicated a stimulant-dependent expression pattern of CsLyzG. Two antimicrobial peptides IK12 and TS10 were identified from CsLyzG and synthesized. Antibiogram showed that IK12 was active against Salmonella enterica, a major multi-drug resistant (MDR) bacterial pathogen which produces beta lactamase. The IK12 induced loss of cell viability in the bacterial pathogen. Flow cytometry assay revealed that IK12 disrupt the membrane of S. enterica which is confirmed by scanning electron microscope (SEM) analysis that reveals blebs around the bacterial cell membrane. Conclusively, CsLyzG is a potential innate immune component and the identified antimicrobial peptide has great caliber to be used as an ecofriendly antibacterial substance in aquaculture.

Barrier function and microbiotic dysbiosis in atopic dermatitis

Atopic dermatitis (AD) or atopic eczema is the common inflammatory skin disorder, the prevalence of which has considerably increased during the last 30 years. It affects 15%-30% of children and 2%-10% of adults. AD characteristically alternates between periods of exacerbation or flares and periods of remission, which may be therapeutically induced or spontaneous. Current knowledge about AD includes abnormalities of the skin barrier (physical and chemical), the immune barrier, and more recently, the microbial barrier or microbiota. There is growing evidence for a tight relationship between them. To obtain satisfactory control of this condition, the clinical strategy to manage AD involves prescribing both anti-inflammatory medications and dermocosmetic products. The role of the physician is therefore to advise the patient with regard to hygiene measures aimed to help to improve these three barriers or to prevent any further deterioration.

Antifungal activity of cathelicidin peptides against planktonic and biofilm cultures of Candida species isolated from vaginal infections

Vulvovaginal candidiasis (VVC) is a frequent gynecological condition caused by Candida albicans and a few non-albicans Candida spp. It has a significant impact on the quality of life of the affected women also due to a considerable incidence of recurrent infections that are difficult to treat. The formation of fungal biofilm may contribute to the problematic management of recurrent VVC due to the intrinsic resistance of sessile cells to the currently available antifungals. Thus, alternative approaches for the prevention and control of biofilm-related infections are urgently needed. In this regard, the cationic antimicrobial peptides (AMPs) of the innate immunity are potential candidates for the development of novel antimicrobials as many of them display activity against biofilm formed by various microbial species. In the present study, we investigated the in vitro antifungal activities of the cathelicidin peptides LL-37 and BMAP-28 against pathogenic Candida spp. also including C. albicans, isolated from vaginal infections, and against C. albicans SC5314 as a reference strain. The antimicrobial activity was evaluated against planktonic and biofilm-grown Candida cells by using microdilution susceptibility and XTT [2,3-bis(2-methoxy-4-nitro-5-sulfo-phenyl)-2H-tetrazolium-5-carboxanilide] reduction assays and, in the case of established biofilms, also by CFU enumeration and fluorescence microscopy. BMAP-28 was effective against planktonically grown yeasts in standard medium (MIC range, 2-32μM), and against isolates of C. albicans and Candida krusei in synthetic vaginal simulated fluid (MIC range 8-32μM, depending on the pH of the medium). Established 48-h old biofilms formed by C. albicans SC5314 and C. albicans and C. krusei isolates were 70-90% inhibited within 24h incubation with 16μM BMAP-28. As shown by propidium dye uptake and CFU enumeration, BMAP-28 at 32μM killed sessile C. albicans SC5314 by membrane permeabilization with a faster killing kinetics compared to 32μM miconazole (80-85% reduced biofilm viability in 90min vs 48h). In addition, BMAP-28 at 16μM prevented Candida biofilm formation on polystyrene and medical grade silicone surfaces by causing a >90% reduction in the viability of planktonic cells in 30min. LL-37 was overall less effective than BMAP-28 against planktonic Candida spp. (MIC range 4-≥64μM), and was ineffective against established Candida biofilms. However, LL-37 at 64μM prevented Candida biofilm development by inhibiting cell adhesion to polystyrene and silicone surfaces. Finally, Candida adhesion was strongly inhibited when silicone was pre-coated with a layer of BMAP-28 or LL-37, encouraging further studies for the development of peptide-based antimicrobial coatings.

Highly abundant defense proteins in human sweat as revealed by targeted proteomics and label-free quantification mass spectrometry

BACKGROUND

The healthy human skin with its effective antimicrobial defense system forms an efficient barrier against invading pathogens. There is evidence suggesting that the composition of this chemical barrier varies between diseases, making the easily collected sweat an ideal candidate for biomarker discoveries.

OBJECTIVE

Our aim was to provide information about the normal composition of the sweat, and to study the chemical barrier found at the surface of skin.

METHODS

Sweat samples from healthy individuals were collected during sauna bathing, and the global protein panel was analysed by label-free mass spectrometry. SRM-based targeted proteomic methods were designed and stable isotope labelled reference peptides were used for method validation.

RESULTS

Ninety-five sweat proteins were identified, 20 of them were novel proteins. It was shown that dermcidin is the most abundant sweat protein, and along with apolipoprotein D, clusterin, prolactin-inducible protein and serum albumin, they make up 91% of secreted sweat proteins. The roles of these highly abundant proteins were reviewed; all of which have protective functions, highlighting the importance of sweat glands in composing the first line of innate immune defense system, and maintaining the epidermal barrier integrity.

CONCLUSION

Our findings with regard to the proteins forming the chemical barrier of the skin as determined by label-free quantification and targeted proteomics methods are in accordance with previous studies, and can be further used as a starting point for non-invasive sweat biomarker research.

Effects of adalimumab, etanercept and ustekinumab on the expression of psoriasin (S100A7) in psoriatic skin

BACKGROUND

Psoriasis is a chronic inflammatory skin disease. It is characterized by immune cell activation and altered epidermal differentiation. S100A7 (psoriasin) is overexpressed in psoriasis, suggesting a determinant role of this protein in inflammation and keratinocyte differentiation.

OBJECTIVE

The purpose of this study was to investigate the expression of S100A7 in the skin from psoriatic patients undergoing biological therapy with adalimumab, etanercept or ustekinumab.

METHODS

S100A7 expression and distribution were analyzed by immunohistochemistry.

RESULTS

S100A7, overexpressed in epidermal keratinocytes of psoriatic lesions, was downregulated, under the biological therapy with adalimumab, etanercept or ustekinumab, only in patients achieving a PASI score<15.

CONCLUSIONS

Dysregulation of S100A7 may represent a non-negligible player in the maintenance of psoriasis and the relative epidermal changes. Blockage of S100A7 may represent an additional therapeutic approach in the treatment of psoriasis.

Anti-Inflammatory Action of an Antimicrobial Model Peptide That Suppresses the TRIF-Dependent Signaling Pathway via Inhibition of Toll-Like Receptor 4 Endocytosis in Lipopolysaccharide-Stimulated Macrophages

Antimicrobial peptides (AMPs), also called host defense peptides, particularly those with amphipathic helical structures, are emerging as target molecules for therapeutic development due to their immunomodulatory properties. Although the antimicrobial activity of AMPs is known to be exerted primarily by permeation of the bacterial membrane, the mechanism underlying its anti-inflammatory activity remains to be elucidated. We report potent anti-inflammatory activity of WALK11.3, an antimicrobial model peptide with an amphipathic helical conformation, in lipopolysaccharide (LPS)-stimulated RAW264.7 cells. This peptide inhibited the expression of inflammatory mediators, including nitric oxide, COX-2, IL-1β, IL-6, INF-β, and TNF-α. Although WALK11.3 did not exert a major effect on all downstream signaling in the MyD88-dependent pathway, toll-like receptor 4 (TLR4)- mediated pro-inflammatory signals were markedly attenuated in the TRIF-dependent pathway due to inhibition of the phosphorylation of STAT1 by attenuation of IRF3 phosphorylation. WALK11.3 specifically inhibited the endocytosis of TLR4, which is essential for triggering TRIF-mediated signaling in macrophage cells. Hence, we suggest that specific interference with TLR4 endocytosis could be one of the major modes of the anti-inflammatory action of AMPs. Our designed WALK11 peptides, which possess both antimicrobial and anti-inflammatory activities, may be promising molecules for the development of therapies for infectious inflammation.

Identification and Characterization of the First Cathelicidin from Sea Snakes with Potent Antimicrobial and Anti-inflammatory Activity and Special Mechanism

Cathelicidins are a family of gene-encoded peptide effectors of innate immunity found exclusively in vertebrates. They play pivotal roles in host immune defense against microbial invasions. Dozens of cathelicidins have been identified from several vertebrate species. However, no cathelicidin from marine reptiles has been characterized previously. Here we report the identification and characterization of a novel cathelicidin (Hc-CATH) from the sea snake Hydrophis cyanocinctus. Hc-CATH is composed of 30 amino acids, and the sequence is KFFKRLLKSVRRAVKKFRKKPRLIGLSTLL. Circular dichroism spectroscopy and structure modeling analysis indicated that Hc-CATH mainly assumes an amphipathic α-helical conformation in bacterial membrane-mimetic solutions. It possesses potent broad-spectrum and rapid antimicrobial activity. Meanwhile, it is highly stable and shows low cytotoxicity toward mammalian cells. The microbial killing activity of Hc-CATH is executed through the disruption of cell membrane and lysis of bacterial cells. In addition, Hc-CATH exhibited potent anti-inflammatory activity by inhibiting the LPS-induced production of nitric oxide (NO) and pro-inflammatory cytokines such as TNF-α, IL-1β, and IL-6. Hc-CATH directly binds with LPS to neutralize its toxicity, and it also binds to Toll-like receptor 4 (TLR4/MD2 complex), which therefore inhibits the binding of LPS to TLR4/MD2 complex and the subsequent activation of LPS-induced inflammatory response pathways. Taken together, our study demonstrates that Hc-CATH, the first cathelicidin from sea snake discovered to have both antimicrobial and anti-inflammatory activity, is a potent candidate for the development of peptide antibiotics.

NKCS, a Mutant of the NK-2 Peptide, Causes Severe Distortions and Perforations in Bacterial, But Not Human Model Lipid Membranes

NKCS is an improved mutant of the bioactive peptide NK-2, which shows strong activity against Escherichia coli and low toxicity towards human cells. The different activity demonstrates the relevance of the physico-chemical nature of the target membrane for the biological effect of this peptide. We studied the effect of this potent antimicrobial peptide on model membranes by activity studies, differential scanning calorimetry, single molecule tracking and tracer efflux experiments. We found that NKCS severely distorted, penetrated and perforated model lipid membranes that resembled bacterial membranes, but not those that were similar to human cell membranes. The interactions of NKCS with phosphatidylethanolamine, which is abundant in bacterial membranes, were especially strong and are probably responsible for its antimicrobial activity.

Epidermal tight junctions in health and disease

The skin, the largest organ of the body, is an essential barrier that under homeostatic conditions efficiently protects and/or minimizes damage from both environmental (e.g. microorganisms, physical trauma, ultraviolet radiation) and endogenous (e.g., cancers, inflammation) factors. This formidable barrier function resides mainly in the epidermis, a dynamic, highly-stratified epithelium. The epidermis has 2 major barrier structures: stratum corneum, the outmost layer and tight junctions, intercellular junctions that seal adjacent keratinocytes in the stratum granulosum, found below the stratum corneum. In recent years there have been significant advances in our understanding of tight junction function, composition and regulation. Herein we review what is known about tight junctions in healthy skin and keratinocyte culture systems and highlight the dynamic crosstalk observed between tight junctions and the cutaneous immune system. Finally we discuss the preliminary observations suggesting that tight junction function or protein expression may be relevant for the pathogenesis of a number of common cutaneous inflammatory and neoplastic conditions.

Antimicrobial benzodiazepine-based short cationic peptidomimetics

Antimicrobial peptides (AMPs) appear to be good candidates for the development of new antibiotic drugs. We describe here the synthesis of peptidomimetic compounds that are based on a benzodiazepine scaffold flanked with positively charged and hydrophobic amino acids. These compounds mimic the essential properties of cationic AMPs. The new design possesses the benzodiazepine scaffold that is comprised of two glycine amino acids and which confers flexibility and aromatic hydrophobic 'back', and two arms used for further synthesis on solid phase for incorporation of charged and hydrophobic amino acids. This approach allowed us a better understanding of the influence of these features on the antimicrobial activity and selectivity. A novel compound was discovered which has MICs of 12.5 µg/ml against Staphylococcus aureus and 25 µg/ml against Escherichia coli, similar to the well-known antimicrobial peptide MSI-78. In contrast to MSI-78, the above mentioned compound has lower lytic effect against mammalian red blood cells. These peptidomimetic compounds will pave the way for future design of potent synthetic mimics of AMPs for therapeutic and biomedical applications.

In vitro approaches to pharmacological screening in the field of atopic dermatitis

In vitro models are valuable for evaluating potential active ingredients and other molecules used in medications for atopic dermatitis (AD). However, finding appropriate in vitro models can be problematic. Our strategy was to set up different in vitro models that would mimic the pathomechanisms of AD. We describe five such models - the AD keratinocyte model, the AD reconstructed human epidermis model, the adaptive immunity model, the innate immunity model and the pruritus model - which we have used to evaluate a new ingredient for emollients derived from a biological extract. The models chosen provide useful data for the pharmacological characterization of active ingredients in adjunctive treatments for AD.

Endogenous intracellular cathelicidin enhances TLR9 activation in dendritic cells and macrophages

Cathelicidins are a gene family best known for their antimicrobial action, but the diverse mature peptides they encode also have other host defense functions. The human cathelicidin peptide LL-37 enhances recognition of nucleic acids, an action whose significance is seen in human diseases such as psoriasis where it is associated with increased type 1 IFN production. This function has been attributed to the extracellular action of the peptide to facilitate uptake of nucleic acids. In this study, we demonstrate that the murine mature cathelicidin peptide (CRAMP), encoded by the mouse gene (Camp), is functionally distinct from the human mature peptide (LL-37), as it does not facilitate CpG entry. However, mouse cathelicidin does influence recognition of CpG as bone marrow-derived dendritic cells from Camp(-/-) mice have impaired CpG responses and Camp(-/-) mice had impaired response to CpG given i.v. or s.c. We show that cathelicidin concentrates in Lamp1 positive compartments, is colocalized with CpG in the endolysosome, can be immunoprecipitated with TLR9, and binds to CpG intracellulary. Collectively, these results indicate that the functions of cathelicidin in control of TLR9 activation may include both intracellular and extracellular effects.

Augmentation of Cationic Antimicrobial Peptide Production with Histone Deacetylase Inhibitors as a Novel Epigenetic Therapy for Bacterial Infections

The emergence of antibiotic resistance seriously threatens our ability to treat many common and medically important bacterial infections. Novel therapeutics are needed that can be used alone or in conjunction with antibiotics. Cationic antimicrobial peptides (CAMPs) are important effectors of the host innate defense that exhibit broad-spectrum activity against a wide range of microorganisms. CAMPs are carried within phagocytic granules and are constitutively or inducibly expressed by multiple cell types, including epithelial cells. The role of histone modification enzymes, specifically the histone deacetylases (HDAC), in down-regulating the transcription of CAMP-encoding genes is increasingly appreciated as is the capacity of HDAC inhibitors (HDACi) to block the action of HDACs to increase CAMP expression. The use of synthetic and natural HDACi molecules to increase CAMPs on mucosal surfaces, therefore, has potential therapeutic applications. Here, we review host and pathogen regulation of CAMP expression through the induction of HDACs and assess the therapeutic potential of natural and synthetic HDACi based on evidence from tissue culture systems, animal models, and clinical trials.

Chemical aspects of the preservation and safety control of sea foods

The interest in biopreservation of food has prompted the quest for new natural antimicrobial compounds from different origins.

Detection of antimicrobial (poly)peptides with acid urea polyacrylamide gel electrophoresis followed by Western immunoblot

Antimicrobial (poly)peptides (AMPs) are ancient key effector molecules of innate host defense and have been identified in mammals, insects, plants, and even fungi (Nakatsuji and Gallo, J Invest Dermatol, 132: 887-895, 2012). They exhibit a cationic net charge at physiological pH and are rich in hydrophobic amino acids (Dufourc et al., Curr Protein Pept Sci, 13: 620-631, 2012). Their mode of action has been best investigated in bacteria. When assuming secondary structure the cationic and hydrophobic amino acids are sequestered creating a bipartitioned molecule in which the cationic amino acids mediate initial electrostatic interaction with the negatively charged bacterial surface and the hydrophobic amino acids mediate embedding into the bacterial membranes followed by a multitude of effects interfering with bacterial viability (Nicolas, FEBS J, 276: 6483-6496, 2009; Padovan et al., Curr Protein Pept Sci, 11: 210-219, 2010). However, immunomodulatory, antitumor, and other effects have been added to the ever increasing list of AMP functions (Pushpanathan et al., Int J Pept, 2013: 675391, 2013). Several classes of AMPs have been distinguished based on structure, namely anti-parallel beta-sheet, alpha-helical, circular, as well as disulfide bridge connectivity (Bond and Khalid, Protein Pept Lett, 17: 1313-1327, 2010). Many of the AMPs undergo posttranslational modification including further proteolysis. Biochemical analysis at the protein level is of great interest for a wide range of scientists and important when studying host-pathogen interaction, for example Salmonella invasion of the small intestine. Acid-urea polyacrylamide gel electrophoresis (AU-PAGE) followed by Western immunoblotting is an important tool for the identification and quantification of cationic AMPs. The protocol for these procedures outlined here describes, in detail, the necessary steps; including pouring the AU-gels, preparing the test samples, performing the electrophoretic separation and protein transfer to the membrane, and conducting the immunodetection using an alkaline phosphatase/NBT/BCIP system. A standard SDS-PAGE in comparison with AU-PAGE and the corresponding Western immunoblot are depicted in Fig. 1.

Dynamic Role of Host Stress Responses in Modulating the Cutaneous Microbiome: Implications for Wound Healing and Infection

Significance: Humans are under constant bombardment by various stressors, including psychological anxiety and physiologic injury. Understanding how these stress responses influence the innate immune system and the skin microbiome remains elusive due to the complexity of the neuroimmune and stress response pathways. Both animal and human studies have provided critical information upon which to further elucidate the mechanisms by which mammalian stressors impair normal wound healing and/or promote chronic wound progression. Recent Advances: Development of high-throughput genomic and bioinformatic approaches has led to the discovery of both an epidermal and dermal microbiome with distinct characteristics. This technology is now being used to identify statistical correlations between specific microbiota profiles and clinical outcomes related to cutaneous wound healing and the response to pathogenic infection. Studies have also identified more prominent roles for typical skin commensal organisms in maintaining homeostasis and modulating inflammatory responses. Critical Issues: It is well-established that stress-induced factors, including catecholamines, acetylcholine, and glucocorticoids, increase the risk of impaired wound healing and susceptibility to infection. Despite the characterization of the cutaneous microbiome, little is known regarding the impact of these stress-induced molecules on the development and evolution of the cutaneous microbiome during wound healing. Future Directions: Further characterization of the mechanisms by which stress-induced molecules influence microbial proliferation and metabolism in wounds is necessary to identify altered microbial phenotypes that differentially influence host innate immune responses required for optimal healing. These mechanisms may yield beneficial as targets for manipulation of the microbiome to further benefit the host after cutaneous injury.

Cationic membrane-active peptides - anticancer and antifungal activity as well as penetration into human skin

Cationic antimicrobial peptides are ancient natural broad-spectrum antibiotics, and several compounds also exhibit anticancer activity. However, most applications pertain to bacterial infections, and treatment for skin cancer is less frequently considered. The cytotoxicity of melittin, cecropin A, protegrin-1 and histatin 5 against squamous skin cancer cell lines and normal human keratinocytes was evaluated and compared to established drugs. The results show that melittin clearly outperforms 5-fluorouracil regarding antitumor activity. Importantly, combined melittin and 5-fluorouracil enhanced cytotoxic effects on cancer cells and reduced toxicity on normal keratinocytes. Additionally, minimum inhibitory concentrations indicate that melittin also shows superior activity against clinical and laboratory strains of Candida albicans compared to amphotericin B. To evaluate its potential for topical applications, human skin penetration of melittin was investigated ex vivo and compared to two non-toxic cell-penetrating peptides (CPPs), low molecular weight protamine (LMWP) and penetratin. The stratum corneum prevents penetration into viable epidermis over 6 h; however, the peptides gain access to the viable skin after 24 h. Inhibition of digestive enzymes during skin penetration significantly enhances the availability of intact peptide. In conclusion, melittin may represent an innovative agent for non-melanoma skin cancer and infectious skin diseases. In order to develop a drug candidate, skin absorption and proteolytic digestion by skin enzymes need to be addressed.

Antimicrobial peptides and their analogs: searching for new potential therapeutics

Antimicrobial peptides (AMPs) are an essential part of innate immunity. These compounds have been considered as potential therapeutics because of their broad-spectrum activities and proven ability to avoid antimicrobial resistance, but their clinical and commercial developments have some limitations, such as susceptibility to proteases and a high cost of peptide production. To overcome these problems, many researchers have tried to develop short active peptides, their modifications and mimics with better properties while retaining their basic features of natural AMPs such as cationic charge and the amphipathic structure.