Antimicrobial activity of the Naja atra cathelicidin and related small peptides

Discovery of Ll-CATH: a novel cathelicidin from the Chong'an Moustache Toad (Leptobrachium liui) with antibacterial and immunomodulatory activity

BACKGROUND

Cathelicidins are vital antimicrobial peptides expressed in diverse vertebrates, crucial for immunity. Despite being a new field, amphibian cathelicidin research holds promise.

RESULTS

We isolated the cDNA sequence of the cathelicidin (Ll-CATH) gene from the liver transcriptome of the Chong'an Moustache Toad (Leptobrachium liui). We confirmed the authenticity of the cDNA sequence by rapid amplification of cDNA ends and reverse transcription PCR, and obtained the Ll-CATH amino acid sequence using the Open Reading Frame Finder, an online bioinformatics tool. Its translated protein contained a cathelin domain, signal peptide, and mature peptide, confirmed by amino acid sequence. The comparative analysis showed that the mature peptides were variable between the amphibian species, while the cathelin domain was conserved. The concentration of Ll-CATH protein and the expression of its gene varied in the tissues, with the spleen showing the highest levels. The expression levels of Ll-CATH in different tissues of toads was significantly increased post infection with Aeromonas hydrophila. Chemically synthesized Ll-CATH effectively combated Proteus mirabilis, Staphylococcus epidermidis, Vibrio harveyi, V. parahaemolyticus, and V. vulnificus; disrupted the membrane of V. harveyi, hydrolyzed its DNA. Ll-CATH induced chemotaxis and modulated the expression of pro-inflammatory cytokine genes in RAW264.7 macrophages.

CONCLUSIONS

This study unveiled the antibacterial and immunomodulatory potential of amphibian cathelicidin, implying its efficacy against infections. Ll-CATH characterization expands our knowledge, emphasizing its in a bacterial infection therapy.

Candida auris from the Egyptian cobra: Role of snakes as potential reservoirs

Candida auris represents one of the most urgent threats to public health, although its ecology remains largely unknown. Because amphibians and reptiles may present favorable conditions for C. auris colonization, cloacal and blood samples (n = 68), from several snake species, were cultured and molecularly screened for C. auris using molecular amplification of glycosylphosphatidylinositol protein-encoding genes and ribosomal internal transcribed spacer sequencing. Candida auris was isolated from the cloacal swab of one Egyptian cobra (Naja haje legionis) and molecularly identified in its cloaca and blood. The isolation of C. auris from wild animals is herein reported for the first time, thus suggesting the role that these animals could play as reservoirs of this emerging pathogen. The occurrence of C. auris in blood requires further investigation, although the presence of cationic antimicrobial peptides in the plasma of reptiles could play a role in reducing the vitality of the fungus.

Development of a defibrinated human blood hemolysis assay for rapid testing of hemolytic activity compared to computational prediction

Cytotoxicity studies determining hemolytic properties of antimicrobial peptides or other drugs are an important step in the development of novel therapeutics for clinical use. Hemolysis is an affordable, accessible, and rapid method for initial assessment of cellular toxicity for all drugs under development. However, variability in species of red blood cells and protocols used may result in significant differences in results. AMPs generally possess higher selectivity for bacterial cells but can have toxicity against host cells at high concentrations. Knowing the hemolytic activity of the peptides we are developing contributes to our understanding of their potential toxicity. Computational approaches for predicting hemolytic activity of AMPs exist and were tested head-to-head with our experimental results.

RESULTS

Starting with an observation of high hemolytic activity of LL-37 peptide against human red blood cells that were collected in EDTA, we explored alternative approaches to develop a more robust, accurate and simple hemolysis assay using defibrinated human blood. We found significant differences between the sensitivity of defibrinated red blood cells and EDTA treated red blood cells.

SIGNIFICANCE

Accurately determining the hemolytic activity using human red blood cells will allow for a more robust calculation of the therapeutic index of our potential antimicrobial compounds, a critical measure in their pre-clinical development.

CONCLUSION

We introduce a standardized, more accurate protocol for assessing hemolytic activity using defibrinated human red blood cells. This approach, facilitated by the increased commercial availability of de-identified human blood and defibrination methods, offers a robust tool for evaluating toxicity of emerging drug compounds, especially AMPs.

Aquiluscidin, a Cathelicidin from Crotalus aquilus, and the Vcn-23 Derivative Peptide, Have Anti-Microbial Activity against Gram-Negative and Gram-Positive Bacteria

Anti-microbial peptides play a vital role in the defense mechanisms of various organisms performing functions that range from the elimination of microorganisms, through diverse mechanisms, to the modulation of the immune response, providing protection to the host. Among these peptides, cathelicidins, a well-studied family of anti-microbial peptides, are found in various animal species, including reptiles. Due to the rise in anti-microbial resistance, these compounds have been suggested as potential candidates for developing new drugs. In this study, we identified and characterized a cathelicidin-like peptide called Aquiluscidin (Aq-CATH) from transcripts obtained from the skin and oral mucosa of the Querétaro's dark rattlesnake, Crotalus aquilus. The cDNA was cloned, sequenced, and yielded a 566-base-pair sequence. Using bioinformatics, we predicted that the peptide precursor contains a signal peptide, a 101-amino-acid conserved cathelin domain, an anionic region, and a 34-amino-acid mature peptide in the C-terminal region. Aq-CATH and a derived 23-amino-acid peptide (Vcn-23) were synthesized, and their anti-microbial activity was evaluated against various species of bacteria in in vitro assays. The minimal inhibitory concentrations against bacteria ranged from 2 to 8 μg/mL for both peptides. Furthermore, at concentrations of up to 50 μM, they exhibited no significant hemolytic activity (<2.3% and <1.2% for Aquiluscidin and Vcn-23, respectively) against rat erythrocytes and displayed no significant cytotoxic activity at low concentrations (>65% cell viability at 25 µM). Finally, this study represents the first identification of an antimicrobial peptide in Crotalus aquilus, which belongs to the cathelicidin family and exhibits the characteristic features of these peptides. Both Aq-CATH and its derived molecule, Vcn-23, displayed remarkable inhibitory activity against all tested bacteria, highlighting their potential as promising candidates for further antimicrobial research.

The anti-infective crotalicidin peptide analog RhoB-Ctn[1-9] is harmless to bovine oocytes and able to induce parthenogenesis in vitro

Crotalicidin is a cathelicidin-related anti-infective (antimicrobial) peptide expressed in the venom glands of the South American rattlesnake Crotalus durissus terrificus. Congener peptides of crotalicidin, named vipericidins, are found in other pit vipers inhabiting South America. Crotalicidin is active against bacteria and pathogenic yeasts and has anti-proliferative activity for some cancer cells. The structural dissection of crotalicidin produced fragments (e.g., Ctn [15-34]) with multiple biological functionalities that mimic the native peptide. Another structural characteristic of crotalidicin and congeners is a unique repetitive stretch of amino acid sequences in tandem embedded in their primary structures. One of the encrypted vipericidn peptides (Ctn [1-9]) was synthesized, and the analog covalently conjugated with rhodamine B (RhoB-Ctn [1-9]) displayed considerable antimicrobial activity and selective cytotoxicity. Methods to evaluate antimicrobial peptides' toxicity include lysis of red blood cells (hemolysis) in vitro and cytotoxicity of healthy cultured cells (e.g., fibroblasts). Here, as a non-conventional model of toxicity, the bovine oocytes were exposed to two standardized concentrations of RhoB-Ctn [1-9], and embryo viability and development at its first stage of cleavage (division of cells) and blastocyst formation were evaluated. Oocytes treated with peptide at 10 and 40 μM induced cleavage rates of 44.94% and 51.53%, resulting in the formation of blastocysts of 7.07% and 11.73%, respectively. Light sheet microscopy and in silico prediction analysis indicated that RhoB-Ctn [1-9] peptide interacts with zona pellucida and internalizes into bovine oocytes and developing embryos. The ADMET prediction estimated good bioavailability of RhoB-Ctn [1-9]. In conclusion, the peptide appeared harmless to bovine oocytes and, remarkably, activated the parthenogenesis in vitro.

Drug discovery efforts at George Mason University

With over 39,000 students, and research expenditures in excess of $200 million, George Mason University (GMU) is the largest R1 (Carnegie Classification of very high research activity) university in Virginia. Mason scientists have been involved in the discovery and development of novel diagnostics and therapeutics in areas as diverse as infectious diseases and cancer. Below are highlights of the efforts being led by Mason researchers in the drug discovery arena. To enable targeted cellular delivery, and non-biomedical applications, Veneziano and colleagues have developed a synthesis strategy that enables the design of self-assembling DNA nanoparticles (DNA origami) with prescribed shape and size in the 10 to 100 nm range. The nanoparticles can be loaded with molecules of interest such as drugs, proteins and peptides, and are a promising new addition to the drug delivery platforms currently in use. The investigators also recently used the DNA origami nanoparticles to fine tune the spatial presentation of immunogens to study the impact on B cell activation. These studies are an important step towards the rational design of vaccines for a variety of infectious agents. To elucidate the parameters for optimizing the delivery efficiency of lipid nanoparticles (LNPs), Buschmann, Paige and colleagues have devised methods for predicting and experimentally validating the pKa of LNPs based on the structure of the ionizable lipids used to formulate the LNPs. These studies may pave the way for the development of new LNP delivery vehicles that have reduced systemic distribution and improved endosomal release of their cargo post administration. To better understand protein-protein interactions and identify potential drug targets that disrupt such interactions, Luchini and colleagues have developed a methodology that identifies contact points between proteins using small molecule dyes. The dye molecules noncovalently bind to the accessible surfaces of a protein complex with very high affinity, but are excluded from contact regions. When the complex is denatured and digested with trypsin, the exposed regions covered by the dye do not get cleaved by the enzyme, whereas the contact points are digested. The resulting fragments can then be identified using mass spectrometry. The data generated can serve as the basis for designing small molecules and peptides that can disrupt the formation of protein complexes involved in disease processes. For example, using peptides based on the interleukin 1 receptor accessory protein (IL-1RAcP), Luchini, Liotta, Paige and colleagues disrupted the formation of IL-1/IL-R/IL-1RAcP complex and demonstrated that the inhibition of complex formation reduced the inflammatory response to IL-1B. Working on the discovery of novel antimicrobial agents, Bishop, van Hoek and colleagues have discovered a number of antimicrobial peptides from reptiles and other species. DRGN-1, is a synthetic peptide based on a histone H1-derived peptide that they had identified from Komodo Dragon plasma. DRGN-1 was shown to disrupt bacterial biofilms and promote wound healing in an animal model. The peptide, along with others, is being developed and tested in preclinical studies. Other research by van Hoek and colleagues focuses on in silico antimicrobial peptide discovery, screening of small molecules for antibacterial properties, as well as assessment of diffusible signal factors (DFS) as future therapeutics. The above examples provide insight into the cutting-edge studies undertaken by GMU scientists to develop novel methodologies and platform technologies important to drug discovery.

Computationally Designed AMPs with Antibacterial and Antibiofilm Activity against MDR Acinetobacter baumannii

The discovery of new antimicrobials is necessary to combat multidrug-resistant (MDR) bacteria, especially those that infect wounds and form prodigious biofilms, such as Acinetobacter baumannii. Antimicrobial peptides (AMPs) are a promising class of new therapeutics against drug-resistant bacteria, including gram-negatives. Here, we utilized a computational AMP design strategy combining database filtering technology plus positional analysis to design a series of novel peptides, named HRZN, designed to be active against A. baumannii. All of the HRZN peptides we synthesized exhibited antimicrobial activity against three MDR A. baumannii strains with HRZN-15 being the most active (MIC 4 µg/mL). This peptide also inhibited and eradicated biofilm of A. baumannii strain AB5075 at 8 and 16 µg/mL, which is highly effective. HRZN-15 permeabilized and depolarized the membrane of AB5075 rapidly, as demonstrated by the killing kinetics. HRZN 13 and 14 peptides had little to no hemolysis activity against human red blood cells, whereas HRZN-15, -16, and -17 peptides demonstrated more significant hemolytic activity. HRZN-15 also demonstrated toxicity to waxworms. Further modification of HRZN-15 could result in a new peptide with an improved toxicity profile. Overall, we successfully designed a set of new AMPs that demonstrated activity against MDR A. baumannii using a computational approach.

Cardiolipin Strongly Inhibits the Leakage Activity of the Short Antimicrobial Peptide ATRA-1 in Comparison to LL-37, in Model Membranes Mimicking the Lipid Composition of Staphylococcus aureus

Cardiolipin is one of the main phospholipid components of Staphylococcus aureus membranes. This lipid is found at varying concentrations in the bilayer, depending on the growth stage of the bacteria, and as a response to environmental stress. Cardiolipin is an anionic phospholipid with four acyl chains, which modulates the bending properties of the membrane due to its inverted conical shape. It has been shown to inhibit the pore forming activity of several antimicrobial peptides, in general doubling the peptide concentration needed to induce leakage. Here we find that the short snake-derived antimicrobial peptide ATRA-1 is inhibited by several orders of magnitude in the presence of cardiolipin in saturated membranes (DMPG) compared to the human cathelicidin LL-37, which is only inhibited two-fold in its leakage-inducing concentration. The ATRA-1 is too short to span the membrane and its leakage activity is likely related to detergent-like alterations of bilayer structure. Fluorescence spectroscopy shows only a minor effect on ATRA-1 binding to DMPG membranes due to the presence of cardiolipin. However, FTIR spectroscopy shows that the acyl chain structure of DMPG membranes, containing cardiolipin, become more organized in the presence of ATRA-1, as reflected by an increase in the gel to liquid-crystalline phase transition temperature. Instead, a depression in the melting temperature is induced by ATRA-1 in DMPG in the absence of cardiolipin. In comparison, LL-37 induces a depression of the main phase transition of DMPG even in the presence of cardiolipin. These data suggest that cardiolipin inhibits the penetration of ATRA-1 into the membrane core, impeding its capacity to disrupt lipid packing.

Past, Present, and Future of Naturally Occurring Antimicrobials Related to Snake Venoms

This review focuses on proteins and peptides with antimicrobial activity because these biopolymers can be useful in the fight against infectious diseases and to overcome the critical problem of microbial resistance to antibiotics. In fact, snakes show the highest diversification among reptiles, surviving in various environments; their innate immunity is similar to mammals and the response of their plasma to bacteria and fungi has been explored mainly in ecological studies. Snake venoms are a rich source of components that have a variety of biological functions. Among them are proteins like lectins, metalloproteinases, serine proteinases, L-amino acid oxidases, phospholipases type A₂, cysteine-rich secretory proteins, as well as many oligopeptides, such as waprins, cardiotoxins, cathelicidins, and β-defensins. In vitro, these biomolecules were shown to be active against bacteria, fungi, parasites, and viruses that are pathogenic to humans. Not only cathelicidins, but all other proteins and oligopeptides from snake venom have been proteolyzed to provide short antimicrobial peptides, or for use as templates for developing a variety of short unnatural sequences based on their structures. In addition to organizing and discussing an expressive amount of information, this review also describes new β-defensin sequences of Sistrurus miliarius that can lead to novel peptide-based antimicrobial agents, using a multidisciplinary approach that includes sequence phylogeny.

Lipidation of Naturally Occurring α-Helical Antimicrobial Peptides as a Promising Strategy for Drug Design

In this paper, we describe the chemical synthesis, preliminary evaluation of antimicrobial properties and mechanisms of action of a novel group of lipidated derivatives of three naturally occurring α-helical antimicrobial peptides, LL-I (VNWKKVLGKIIKVAK-NH₂), LK6 (IKKILSKILLKKL-NH₂), ATRA-1 (KRFKKFFKKLK-NH₂). The obtained results showed that biological properties of the final compounds were defined both by the length of the fatty acid and by the structural and physico-chemical properties of the initial peptide. We consider C₈-C₁₂ length of the hydrocarbon chain as the optimal for antimicrobial activity improvement. However, the most active analogues exerted relatively high cytotoxicity toward keratinocytes, with the exception of the ATRA-1 derivatives, which had a higher selectivity for microbial cells. The ATRA-1 derivatives had relatively low cytotoxicity against healthy human keratinocytes but high cytotoxicity against human breast cancer cells. Taking into account that ATRA-1 analogues carry the highest positive net charge, it can be assumed that this feature contributes to cell selectivity. As expected, the studied lipopeptides showed a strong tendency to self-assembly into fibrils and/or elongated and spherical micelles, with the least cytotoxic ATRA-1 derivatives forming apparently smaller assemblies. The results of the study also confirmed that the bacterial cell membrane is the target for the studied compounds.

Rational Design of RN15m4 Cathelin Domain-Based Peptides from Siamese Crocodile Cathelicidin Improves Antimicrobial Activity

Antimicrobial peptides are becoming a new generation of antibiotics due to their therapeutic potential and ability to decrease drug-resistant bacteria development. Cathelicidins are known as effective peptides of vertebrate immunity that play crucial roles in the defensive strategy against pathogens. To improve its potency, the RN15 antibacterial peptide derived from the cathelin domain of Crocodylus siamensis cathelicidin has been modified and its antimicrobial properties investigated. Peptides were derived by template-based and physicochemical designation. The RN15 derivative peptides were predicted through their structure modeling, antimicrobial potency, and peptide-membrane calculation. The antimicrobial and cytotoxic activities of candidate peptides were investigated. Simultaneous consideration of physicochemical characteristics, secondary structure modeling, and the result of antimicrobial peptide tools prediction indicated that RN15m4 peptide was a candidate derivative antimicrobial peptide. The RN15m4 peptide expresses antimicrobial activity against most Gram-positive and Gram-negative bacteria and fungi with a lower minimum inhibition concentration (MIC) than the parent peptide. Besides, the time-killing assay shows that the designed peptide performed its ability to quickly kill bacteria better than the original peptide. Scanning electron microscopy (SEM) displayed the destruction of the bacterial cell membrane caused by the RN15m4 peptide. In addition, the RN15m4 peptide exhibits low hemolytic activity and low cytotoxic activity as good as the template peptide. The RN15m4 peptide performs a range of antimicrobial activities with low cell toxicity. Our study has illustrated the combination approach to peptide design for potent antibiotic peptide discovery.

In pursuit of next-generation therapeutics: Antimicrobial peptides against superbugs, their sources, mechanism of action, nanotechnology-based delivery, and clinical applications

Antimicrobial peptides (AMPs) attracted attention as potential source of novel antimicrobials. Multi-drug resistant (MDR) infections have emerged as a global threat to public health in recent years. Furthermore, due to rapid emergence of new diseases, there is pressing need for development of efficient antimicrobials. AMPs are essential part of the innate immunity in most living organisms, acting as the primary line of defense against foreign invasions. AMPs kill a wide range of microorganisms by primarily targeting cell membranes or intracellular components through a variety of ways. AMPs can be broadly categorized based on their physico-chemical properties, structure, function, target and source of origin. The synthetic analogues produced either with suitable chemical modifications or with the use of suitable delivery systems are projected to eliminate the constraints of toxicity and poor stability commonly linked with natural AMPs. The concept of peptidomimetics is gaining ground around the world nowadays. Among the delivery systems, nanoparticles are emerging as potential delivery tools for AMPs, amplifying their utility against a variety of pathogens. In the present review, the broad classification of various AMPs, their mechanism of action (MOA), challenges associated with AMPs, current applications, and novel strategies to overcome the limitations have been discussed.

Machine Learning Prediction of Antimicrobial Peptides

Antibiotic resistance constitutes a global threat and could lead to a future pandemic. One strategy is to develop a new generation of antimicrobials. Naturally occurring antimicrobial peptides (AMPs) are recognized templates and some are already in clinical use. To accelerate the discovery of new antibiotics, it is useful to predict novel AMPs from the sequenced genomes of various organisms. The antimicrobial peptide database (APD) provided the first empirical peptide prediction program. It also facilitated the testing of the first machine-learning algorithms. This chapter provides an overview of machine-learning predictions of AMPs. Most of the predictors, such as AntiBP, CAMP, and iAMPpred, involve a single-label prediction of antimicrobial activity. This type of prediction has been expanded to antifungal, antiviral, antibiofilm, anti-TB, hemolytic, and anti-inflammatory peptides. The multiple functional roles of AMPs annotated in the APD also enabled multi-label predictions (iAMP-2L, MLAMP, and AMAP), which include antibacterial, antiviral, antifungal, antiparasitic, antibiofilm, anticancer, anti-HIV, antimalarial, insecticidal, antioxidant, chemotactic, spermicidal activities, and protease inhibiting activities. Also considered in predictions are peptide posttranslational modification, 3D structure, and microbial species-specific information. We compare important amino acids of AMPs implied from machine learning with the frequently occurring residues of the major classes of natural peptides. Finally, we discuss advances, limitations, and future directions of machine-learning predictions of antimicrobial peptides. Ultimately, we may assemble a pipeline of such predictions beyond antimicrobial activity to accelerate the discovery of novel AMP-based antimicrobials.

The Rhodamine B-encrypted vipericidin peptide, RhoB-Ctn[1-9], displays in vitro antimicrobial activity against opportunistic bacteria and yeasts

BACKGROUND

Crotalicidin (Ctn), a snake venom cathelicidin-related antimicrobial peptide, is a 34-residue-long linear lysine-rich vipericidin obtained from the South American rattlesnake, Crotalus durissus terrificus. Ctn contains tandem repeats of nine amino acid residues (1KRFKKFFKK9 and 16KRLKKIFKK24; consensus: 1KRhKKhFKK9, h = hydrophobic amino acid) as an integral part of its structure.

OBJECTIVE

The aim of this study was to evaluate the antimicrobial activity of the encrypted vipericidin nonapeptide KRFKKFFKK, designated as Ctn[1-9], and its structural analogue, rhodamine-B‒conjugated Ctn[1-9], designated as RhoB-Ctn[1-9].

METHOD

The susceptibility of representative pathogenic bacteria and yeasts to antimicrobial agents was determined using the broth microdilution minimum inhibitory concentration (MIC) method. Cytotoxicity was estimated using a hemolytic assay. The accumulation of RhoB-Ctn[1-9] in microbial cells was observed by fluorescence microscopy. The antimicrobial synergism of RhoB-Ctn[1-9] with antimicrobials was evaluated using a checkerboard analysis.

RESULTS

RhoB-conjugated Ctn[1-9] displayed selective antimicrobial activity against infectious gram-negative bacteria such as Escherichia coli, Pseudomonas aeruginosa, and pathogenic species of Candida with low hemolytic effects on human erythrocytes which was not observed with unconjugated Ctn[1-9]. RhoB-Ctn[1-9] could permeate cell membranes and accumulate intracellularly in microbial cells. RhoB-Ctn[1-9] exhibits synergistic effects when used with antibiotics or antifungal agents and reduced the MICs of the peptide and antimicrobials.

CONCLUSION

These findings indicate the potential of crotalicidin-related short peptides as structural motifs for the diversification of biological functionalities. Further, they set the stage to investigate the molecular mechanisms by which chemically modified vipericidin repeats modulate cell fate.

Cell-Penetrating Peptides Derived from Animal Venoms and Toxins

Cell-penetrating peptides (CPPs) comprise a class of short polypeptides that possess the ability to selectively interact with the cytoplasmic membrane of certain cell types, translocate across plasma membranes and accumulate in the cell cytoplasm, organelles (e.g., the nucleus and mitochondria) and other subcellular compartments. CPPs are either of natural origin or de novo designed and synthesized from segments and patches of larger proteins or designed by algorithms. With such intrinsic properties, along with membrane permeation, translocation and cellular uptake properties, CPPs can intracellularly convey diverse substances and nanomaterials, such as hydrophilic organic compounds and drugs, macromolecules (nucleic acids and proteins), nanoparticles (nanocrystals and polyplexes), metals and radionuclides, which can be covalently attached via CPP N- and C-terminals or through preparation of CPP complexes. A cumulative number of studies on animal toxins, primarily isolated from the venom of arthropods and snakes, have revealed the cell-penetrating activities of venom peptides and toxins, which can be harnessed for application in biomedicine and pharmaceutical biotechnology. In this review, I aimed to collate examples of peptides from animal venoms and toxic secretions that possess the ability to penetrate diverse types of cells. These venom CPPs have been chemically or structurally modified to enhance cell selectivity, bioavailability and a range of target applications. Herein, examples are listed and discussed, including cysteine-stabilized and linear, α-helical peptides, with cationic and amphipathic character, from the venom of insects (e.g., melittin, anoplin, mastoparans), arachnids (latarcin, lycosin, chlorotoxin, maurocalcine/imperatoxin homologs and wasabi receptor toxin), fish (pardaxins), amphibian (bombesin) and snakes (crotamine and cathelicidins).

Komodo-dragon cathelicidin-inspired peptides are antibacterial against carbapenem-resistant Klebsiella pneumoniae

Introduction.The rise of carbapenem-resistant enterobacteriaceae (CRE) is a growing crisis that requires development of novel therapeutics.

Hypothesis.To this end, cationic antimicrobial peptides (CAMPs) represent a possible source of new potential therapeutics to treat difficult pathogens such as carbapenem-resistantKlebsiella pneumoniae(CRKP), which has gained resistance to many if not all currently approved antibiotics, making treatment difficult.

Aim.To examine the anti-CRKP antimicrobial activity of the predicted cathelicidins derived fromVaranus komodoensis(Komodo dragon) as well as synthetic antimicrobial peptides that we created.

Methodology.We determined the minimum inhibitory concentrations of the peptides against CRKP. We also characterized the abilities of these peptides to disrupt the hyperpolarization of the bacterial membrane as well as their ability to form pores in the membrane.

Results.We did not observe significant anti-CRKP activity for the predicted native Komodo cathelicidin peptides. We found that the novel peptides DRGN-6,-7 and -8 displayed significant antimicrobial activity against CRKP with MICs of 4–8 µg ml−1. DRGN-6 peptide was the most effective peptide against CRKP. Unfortunately, these peptides showed higher than desired levels of hemolysis, althoughin vivotesting in the waxwormGalleria mellonellashowed no mortality associated with treatment by the peptide; however, CRKP-infected waxworms treated with peptide did not show an improvement in survival.

Conclusion.Given the challenges of treating CRKP, identification of peptides with activity against it represents a promising avenue for further research. Given DRGN-6′s similar level of activity to colistin, DRGN-6 is a promising template for the development of novel antimicrobial peptide-based therapeutics.

Physicochemical-guided design of cathelicidin-derived peptides generates membrane active variants with therapeutic potential

The spread of multi-drug resistance and the slow pace at which antibiotics come onto the market are undermining our ability to treat human infections, leading to high mortality rates. Aiming to overcome this global crisis, antimicrobial peptides are considered promising alternatives to counter bacterial infections with multi-drug resistant bacteria. The cathelicidins comprise a well-studied class of AMPs whose members have been used as model molecules for sequence modifications, aiming at enhanced biological activities and stability, along with reduced toxic effects on mammalian cells. Here, we describe the antimicrobial activities, modes of action and structural characterization of two novel cathelicidin-like peptides, named BotrAMP14 and CrotAMP14, which were re-designed from snake batroxicidin and crotalicidin, respectively. BotrAMP14 and CrotAMP14 showed broad-spectrum antibacterial activity against susceptible microorganisms and clinical isolates with minimal inhibitory concentrations ranging from 2–35.1 μM. Moreover, both peptides had low cytotoxicity against Caco-2 cells in vitro. In addition, in vivo toxicity against Galleria mellonella moth larvae revealed that both peptides led to>76% larval survival after 144 h. Microscopy studies suggest that BotrAMP14 and CrotAMP14 destabilize E. coli membranes. Furthermore, circular dichroism and molecular dynamics simulations indicate that, in a membrane-like environment, both peptides adopt α-helical structures that interact with bilayer phospholipids through hydrogen bonds and electrostatic interaction. Thus, we concluded that BotrAMP14 and CrotAMP14 are helical membrane active peptides, with similar antibacterial properties but lower cytotoxicity than the larger parent peptides batroxicidin and crotalicidin, having advantages for drug development strategies.

Hitchhiking with Nature: Snake Venom Peptides to Fight Cancer and Superbugs

Abstract

For decades, natural products in general and snake venoms (SV) in particular have been a rich source of bioactive compounds for drug discovery, and they remain a promising substrate for therapeutic development. Currently, a handful of SV-based drugs for diagnosis and treatment of various cardiovascular disorders and blood abnormalities are on the market. Likewise, far more SV compounds and their mimetics are under investigation today for diverse therapeutic applications, including antibiotic-resistant bacteria and cancer. In this review, we analyze the state of the art regarding SV-derived compounds with therapeutic potential, focusing on the development of antimicrobial and anticancer drugs. Specifically, information about SV peptides experimentally validated or predicted to act as antimicrobial and anticancer peptides (AMPs and ACPs, respectively) has been collected and analyzed. Their principal activities both in vitro and in vivo, structures, mechanisms of action, and attempts at sequence optimization are discussed in order to highlight their potential as drug leads.

Key Contribution

This review describes the state of the art in snake venom-derived peptides and their therapeutic applications. This work reinforces the potential of snake venom components as therapeutic agents, particularly in the quest for new antimicrobial and anticancer drugs.

Recent advances: peptides and self-assembled peptide-nanosystems for antimicrobial therapy and diagnosis

Bacterial infections, especially the refractory treatment of drug-resistant bacteria, are one of the greatest threats to human health. Self-assembling peptide-based strategies can specifically detect the bacteria at the site of infection in the body and kill it.

Snake Venom Cathelicidins as Natural Antimicrobial Peptides

Bioactive small molecules isolated from animals, plants, fungi and bacteria, including natural antimicrobial peptides, have shown great therapeutic potential worldwide. Among these peptides, snake venom cathelicidins are being widely exploited, because the variation in the composition of the venom reflects a range of biological activities that may be of biotechnological interest. Cathelicidins are short, cationic, and amphipathic molecules. They play an important role in host defense against microbial infections. We are currently facing a strong limitation on pharmacological interventions for infection control, which has become increasingly complex due to the lack of effective therapeutic options. In this review, we will focus on natural snake venom cathelicidins as promising candidates for the development of new antibacterial agents to fight antibiotic-resistant bacteria. We will highlight their antibacterial and antibiofilm activities, mechanism of action, and modulation of the innate immune response.

Differential presentation of a single antimicrobial peptide is sufficient to identify LPS from distinct bacterial samples

Rapid detection and identification of bacteria is important for human health, biodefense, and food safety. Small arrays of different antimicrobial peptides (AMPs) enable the identification of lipopolysaccharide (LPS) samples from a variety of bacterial species and strains. A model system for examining how peptide presentation affects LPS detection is the sheep myeloid antimicrobial peptide (SMAP-29), which contains a helix-turn-helix motif. Varying the cysteine attachment site on SMAP-29 controls the three-dimensional presentation of the peptide on the surface, altering the ability of the peptide to discriminate between LPS samples. A small array of only SMAP-29 variants-and no other peptides-is capable of discriminating among LPS samples from multiple bacterial species, as well as between different strains within the same species, with high accuracy.

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.

Nanostructural Differentiation and Toxicity of Amyloid-β25-35 Aggregates Ensue from Distinct Secondary Conformation

Amyloid nanostructures are originated from protein misfolding and aberrant aggregation, which is associated with the pathogenesis of many types of degenerative diseases, such as Alzheimer’s disease (AD), Parkinson’s disease (PD) and Huntington’s disease. The secondary conformation of peptides is of a fundamental importance for aggregation and toxicity of amyloid peptides. In this work, Aβ25-35, a fragment of amyloid β(1-42) (Aβ42), was selected to investigate the correlation between secondary structures and toxicity of amyloid fibrils. Furthermore, each aggregation assemblies show different cell membrane disruption and cytotoxicity. The structural analysis of amyloid aggregates originated from different secondary structure motifs is helpful to understand the mechanism of peptides/cell interactions in the pathogenesis of amyloid diseases.

Antimicrobial peptides as an alternative to anti-tuberculosis drugs

Tuberculosis (TB) presently accounts for high global mortality and morbidity rates, despite the introduction four decades ago of the affordable and efficient four-drugs (isoniazid, rifampicin, pyrazinamide and ethambutol). Thus, a strong need exists for new drugs with special structures and uncommon modes of action to effectively overcome M. tuberculosis. Within this scope, antimicrobial peptides (AMPs), which are small, cationic and amphipathic peptides that comprise a section of the innate immune system, are currently the leading potential agents for the treatment of TB. Many studies have recently illustrated the capability of anti-mycobacterial peptides to disrupt the normal mycobacterial cell wall function through various modes, thereby interacting with the intracellular targets, as well as encompassing nucleic acids, enzymes and organelles. This review presents a wide array of antimicrobial activities, alongside the associated properties of the AMPs that could be utilized as potential agents in therapeutic tactics for TB treatment.

The SpTransformer Gene Family (Formerly Sp185/333) in the Purple Sea Urchin and the Functional Diversity of the Anti-Pathogen rSpTransformer-E1 Protein

The complex innate immune system of sea urchins is underpinned by several multigene families including the SpTransformer family (SpTrf; formerly Sp185/333) with estimates of ~50 members, although the family size is likely variable among individuals of Strongylocentrotus purpuratus. The genes are small with similar structure, are tightly clustered, and have several types of repeats in the second of two exons and that surround each gene. The density of repeats suggests that the genes are positioned within regions of genomic instability, which may be required to drive sequence diversification. The second exon encodes the mature protein and is composed of blocks of sequence called elements that are present in mosaics of defined element patterns and are the major source of sequence diversity. The SpTrf genes respond swiftly to immune challenge, but only a single gene is expressed per phagocyte. Many of the mRNAs appear to be edited and encode proteins with altered and/or missense sequence that are often truncated, of which some may be functional. The standard SpTrf protein structure is an N-terminal glycine-rich region, a central RGD motif, a histidine-rich region, and a C-terminal region. Function is predicted from a recombinant protein, rSpTransformer-E1 (rSpTrf-E1), which binds to Vibrio and Saccharomyces, but not to Bacillus, and binds tightly to lipopolysaccharide, β-1,3-glucan, and flagellin, but not to peptidoglycan. rSpTrf-E1 is intrinsically disordered but transforms to α helical structure in the presence of binding targets including lipopolysaccharide, which may underpin the characteristics of binding to multiple targets. SpTrf proteins associate with coelomocyte membranes, and rSpTrf-E1 binds specifically to phosphatidic acid (PA). When rSpTrf-E1 is bound to PA in liposome membranes, it induces morphological changes in liposomes that correlate with PA clustering and leakage of luminal contents, and it extracts or removes PA from the bilayer. The multitasking activities of rSpTrf-E1 infer multiple and perhaps overlapping activities for the hundreds of native SpTrf proteins that are produced by individual sea urchins. This likely generates a flexible and highly protective immune system for the sea urchin in its marine habitat that it shares with broad arrays of microbes that may be pathogens and opportunists.

Cathelicidin antimicrobial peptide from Alligator mississippiensis has antibacterial activity against multi-drug resistant Acinetobacter baumanii and Klebsiella pneumoniae

Alligator mississippiensis (American alligator), a member of order Crocodilia, lives in bacteria-laden environments but is not often known to succumb to bacterial infections. Their serum has been shown to have antibacterial activity beyond that of human serum, and it is believed that this activity is partially due to cationic antimicrobial peptides (CAMPs). CAMPs are produced by many organisms as part of the innate immune system. CAMPs are attractive possible therapies against multi-drug resistant bacteria, such as those found in biofilm-infected war wounds, because they seldom cause genetic resistance in bacteria and are effective against antibiotic resistant bacteria. In this work, we identified, synthesized, and characterized a cathelicidin and two shorter fragments from the American alligator. We discovered the cathelicidin using Basic Local Alignment Search Tool (BLAST) alignment and by comparing A. mississippiensis expressed sequence tags (ESTs) with propeptide cathelicidins of other reptiles. We analyzed the structure using bioinformatics tools and circular dichroism and predicted that the full-length cathelicidin peptide has a mixed structure, with an N-terminal α-helix and a center Pro hinge. In minimal inhibitory concentration (MIC) assays, it was determined that the cathelicidin and the two shorter fragments have strong activity against multiple Gram-negative bacteria, including clinical isolates of multi-drug resistant (MDR) Acinetobacter baumannii and carbapenem-resistant Klebsiella pneumoniae. Using the ethidium bromide uptake assay, it was found that these peptides permeabilize the bacterial membrane and are less sensitive to salt inhibition than many other known CAMPs. The alligator cathelicidin peptides were not hemolytic against sheep red blood cells at 300 μg/ml and were not significantly cytotoxic against A549 human lung epithelial cells after 24 h exposure in 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays. These alligator cathelicidin peptides have activity similar to other CAMPs from reptiles such as NA-CATH. It is possible that the alligator cathelicidins play an important role in the innate immune response of A. mississippiensis, similar to LL-37 in humans. In addition, due to their activities against MDR bacteria and lack of cytotoxicity, the AM-CATH peptides could be an attractive platform for further development as a potential therapeutic.

Komodo dragon-inspired synthetic peptide DRGN-1 promotes wound-healing of a mixed-biofilm infected wound

Cationic antimicrobial peptides are multifunctional molecules that have a high potential as therapeutic agents. We have identified a histone H1-derived peptide from the Komodo dragon (Varanus komodoensis), called VK25. Using this peptide as inspiration, we designed a synthetic peptide called DRGN-1. We evaluated the antimicrobial and anti-biofilm activity of both peptides against Pseudomonas aeruginosa and Staphylococcus aureus. DRGN-1, more than VK25, exhibited potent antimicrobial and anti-biofilm activity, and permeabilized bacterial membranes. Wound healing was significantly enhanced by DRGN-1 in both uninfected and mixed biofilm (Pseudomonas aeruginosa and Staphylococcus aureus)-infected murine wounds. In a scratch wound closure assay used to elucidate the wound healing mechanism, the peptide promoted the migration of HEKa keratinocyte cells, which was inhibited by mitomycin C (proliferation inhibitor) and AG1478 (epidermal growth factor receptor inhibitor). DRGN-1 also activated the EGFR-STAT1/3 pathway. Thus, DRGN-1 is a candidate for use as a topical wound treatment. Wound infections are a major concern; made increasingly complicated by the emerging, rapid spread of bacterial resistance. The novel synthetic peptide DRGN-1 (inspired by a peptide identified from Komodo dragon) exhibits pathogen-directed and host-directed activities in promoting the clearance and healing of polymicrobial (Pseudomonas aeruginosa & Staphylococcus aureus) biofilm infected wounds. The effectiveness of this peptide cannot be attributed solely to its ability to act upon the bacteria and disrupt the biofilm, but also reflects the peptide’s ability to promsote keratinocyte migration. When applied in a murine model, infected wounds treated with DRGN-1 healed significantly faster than did untreated wounds, or wounds treated with other peptides. The host-directed mechanism of action was determined to be via the EGFR-STAT1/3 pathway. The pathogen-directed mechanism of action was determined to be via anti-biofilm activity and antibacterial activity through membrane permeabilization. This novel peptide may have potential as a future therapeutic for treating infected wounds.

A synthetic peptide based on a natural molecule found in the Komodo dragon promotes healing of biofilm-infected wounds. Peptides are small protein-like molecules. Monique van Hoek, Barney Bishop and colleagues at George Mason University in Virginia, USA, isolated a natural peptide with some antimicrobial properties from Komodo dragon plasma. They designed a modified synthetic version with rearranged amino acids, named DRGN-1 in recognition of the “Komodo dragon” peptide that inspired it. In preliminary trials, DRGN-1 enhanced the healing of biofilm-infected wounds in mice, and was more effective than the natural peptide. This may be due to both bacterial- and host-directed effects. DRGN-1 reduced biofilm and bacterial number while increasing wound closure. The authors suggest DRGN-1 could be developed into a therapeutic agent that may treat the biofilm-infected wounds that are increasingly resistant to conventional antibiotics.

Multitasking Immune Sp185/333 Protein, rSpTransformer-E1, and Its Recombinant Fragments Undergo Secondary Structural Transformation upon Binding Targets

The purple sea urchin, Strongylocentrotus purpuratus, expresses a diverse immune response protein family called Sp185/333. A recombinant Sp185/333 protein, previously called rSp0032, shows multitasking antipathogen binding ability, suggesting that the protein family mediates a flexible and effective immune response to multiple foreign cells. Bioinformatic analysis predicts that rSp0032 is intrinsically disordered, and its multiple binding characteristic suggests structural flexibility to adopt different conformations depending on the characteristics of the target. To address the flexibility and structural shifting hypothesis, circular dichroism analysis of rSp0032 suggests that it transforms from disordered (random coil) to α helical structure. This structural transformation may be the basis for the strong affinity between rSp0032 and several pathogen-associated molecular patterns. The N-terminal Gly-rich fragment of rSp0032 and the C-terminal His-rich fragment show unique transformations by either intensifying the α helical structure or changing from α helical to β strand depending on the solvents and molecules added to the buffer. Based on these results, we propose a name change from rSp0032 to rSpTransformer-E1 to represent its flexible structural conformations and its E1 element pattern. Given that rSpTransformer-E1 shifts its conformation in the presence of solvents and binding targets and that all Sp185/333 proteins are predicted to be disordered, many or all of these proteins may undergo structural transformation to enable multitasking binding activity toward a wide range of targets. Consequently, we also propose an overarching name change for the entire family from Sp185/333 proteins to SpTransformer proteins.

Membrane phase characteristics control NA-CATH activity

Our studies presented in this report focus on the behavior of NA-CATH, an α-helical cathelicidin antimicrobial peptide, originally discovered in the Naja atra snake. It has demonstrated high potency against gram-positive and gram-negative bacteria with minimal hemolysis. Here we examine the kinetics, behaviors and potential mechanisms of the peptide in the presence of membrane liposome, modeling Escherichia coli, whose membrane exhibits distinct lipid phases. To understand NA-CATH interactions, the role of lipid phases is critical. We test three different lipid compositions to detangle the effect of phase on NA-CATH's activity using a series of leakage experiments. From these studies, we observe that NA-CATH changes from membrane disruption to pore-based lysing, depending on phases and lipid composition. This behavior also plays a major role in its kinetics.

Characterization and performance of short cationic antimicrobial peptide isomers

Cationic antimicrobial peptides (CAMPs) represent an ancient defense mechanism against invading bacteria, with peptides such as the cathelicidins being essential elements of vertebrate innate immunity. CAMPs are typically associated with broad-spectrum antimicrobial potency and limited bacterial resistance. The cathelicidin identified from the elapid snake Naja atra (NA-CATH) contains a semi-conserved repeated 11-residue motif (ATRA motif) with a sequence pattern consistent with formation of an amphipathic helical conformation. Short peptide amides (ATRA-1, -1A, -1P, and -2) generated based on the pair of ATRA motifs in NA-CATH exhibited varied antimicrobial potencies. The small size of the ATRA peptides, coupled with their varied antimicrobial performances, make them interesting models to study the impact various physico-chemical properties have on antimicrobial performance in helical CAMPs. Accordingly, the D- and L-enantiomers of the peptide ATRA-1A, which in earlier studies had shown both good antimicrobial performance and strong helical character, were investigated in order to assess the impact peptide stereochemistry has on antimicrobial performance and interaction with chiral membranes. The ATRA-1A isomers exhibit varied potencies against four bacterial strains, and their conformational properties in the presence of mixed zwitterionic/anionic liposomes are influenced by anionic lipid content. These studies reveal subtle differences in the properties of the peptide isomers. Differences are also seen in the abilities of the ATRA-1A isomers to induce liposome fusion/aggregation, bilayer rearrangement and lysing through turbidity studies and fluorescence microscopy. The similarities and differences in the properties of the ATRA-1A isomers could aid in efforts to develop D-peptide-based therapeutics using high-performing L-peptides as templates.

Effect of substituting arginine and lysine with alanine on antimicrobial activity and the mechanism of action of a cationic dodecapeptide (CL(14-25)), a partial sequence of cyanate lyase from rice

The antimicrobial activity of analogs obtained by substituting arginine and lysine in CL(14-25), a cationic α-helical dodecapeptide, with alanine against Porphyromonas gingivalis, a periodontal pathogen, varied significantly depending on the number and position of cationic amino acids. The alanine-substituted analogs had no hemolytic activity, even at a concentration of 1 mM. The antimicrobial activities of CL(K20A) and CL(K20A, K25A) were 3.8-fold and 9.1-fold higher, respectively, than that of CL(14-25). The antimicrobial activity of CL(R15A) was slightly lower than that of CL(14-25), suggesting that arginine at position 15 is not essential but is important for the antimicrobial activity. The experiments in which the alanine-substituted analogs bearing the replacement of arginine at position 24 and/or lysine at position 25 were used showed that arginine at position 24 was crucial for the antimicrobial activity whenever lysine at position 25 was substituted with alanine. Helical wheel projections of the alanine-substituted analogs indicate that the hydrophobicity in the vicinity of leucine at position 16 and alanines at positions 18 and/or 21 increased by substituting lysine at positions 20 and 25 with alanine, respectively. The degrees of diSC3 -5 release from P. gingivalis cells and disruption of GUVs induced by the alanine-substituted analogs with different positive charges were not closely related to their antimicrobial activities. The enhanced antimicrobial activities of the alanine-substituted analogs appear to be mainly attributable to the changes in properties such as hydrophobicity and amphipathic propensity due to alanine substitution and not to their extents of positive charge (cationicity).

Short, Synthetic Cationic Peptides Have Antibacterial Activity against Mycobacterium smegmatis by Forming Pores in Membrane and Synergizing with Antibiotics

Multicellular organisms are constantly exposed to a multitude of pathogenic microbes. Infection is inhibited in vivo by the innate and adaptive immune system. Mycobacterium species have emerged that are resistant to most antibiotics. We identified several naturally occurring cationic antimicrobial peptides that were active at low micromolar concentrations against Mycobacterium smegmatis. Human-derived cathelicidin LL-37 is well characterized and studied against M. smegmatis; we compared LL-37 with Chinese cobra-derived cathelicidin NA-CATH and mouse cathelicidin (mCRAMP). Two synthetic 11-residue peptides (ATRA-1A and ATRA-2) containing variations of a repeated motif within NA-CATH were tested for their activity against M. smegmatis along with a short synthetic peptide derivative from the human beta-defensin hBD3 (hBD3-Pep4). We hypothesized that these smaller synthetic peptides may demonstrate antimicrobial effectiveness with shorter length (and at less cost), making them strong potential candidates for development into broad-spectrum antimicrobial compounds or use in combination with antibiotics. These peptides have antimicrobial activity with EC50 ranging from 0.05 to 1.88 μg/mL against Mycobacterium smegmatis. The ATRA-1A short peptide was found to be the most effective antimicrobial peptide (AMP) (EC50 = 0.05 μg/mL). High bactericidal activity correlated with bacterial membrane depolarization and permeabilization activities. The efficacy of the peptides was further analyzed through Minimal Inhibitory Concentration (MIC) assays. The MICs were determined by the microdilution method. The peptide mCRAMP showed the best MIC activity at 15.6 μg/mL. Neither of the effective short synthetic peptides demonstrated synergy with the antibiotic rifampicin, although both demonstrated synergy with the cyclic peptide antibiotic polymyxin B. The peptides LL-37 and mCRAMP displayed synergism with rifampicin in MIC assays, whereas antibiotic polymyxin B displayed synergism with LL-37, ATRA-1A, and hBD3-Pep4. In further studies, polymyxin B synergized with LL-37, ATRA-1A, and hBD3-Pep4 while Rifampicin synergized with LL-37 and mCRAMP for intracellular killing of mycobacteria residing inside macrophages. These studies provide the foundation for the potential development of synthetic cationic antimicrobial peptides with activity against mycobacteria.

Snake Cathelicidin NA-CATH and Smaller Helical Antimicrobial Peptides Are Effective against Burkholderia thailandensis

Burkholderia thailandensis is a Gram-negative soil bacterium used as a model organism for B. pseudomallei, the causative agent of melioidosis and an organism classified category B priority pathogen and a Tier 1 select agent for its potential use as a biological weapon. Burkholderia species are reportedly “highly resistant” to antimicrobial agents, including cyclic peptide antibiotics, due to multiple resistance systems, a hypothesis we decided to test using antimicrobial (host defense) peptides. In this study, a number of cationic antimicrobial peptides (CAMPs) were tested in vitro against B. thailandensis for both antimicrobial activity and inhibition of biofilm formation. Here, we report that the Chinese cobra (Naja atra) cathelicidin NA-CATH was significantly antimicrobial against B. thailandensis. Additional cathelicidins, including the human cathelicidin LL-37, a sheep cathelicidin SMAP-29, and some smaller ATRA peptide derivatives of NA-CATH were also effective. The D-enantiomer of one small peptide (ATRA-1A) was found to be antimicrobial as well, with EC50 in the range of the L-enantiomer. Our results also demonstrate that human alpha-defensins (HNP-1 & -2) and a short beta-defensin-derived peptide (Peptide 4 of hBD-3) were not bactericidal against B. thailandensis. We also found that the cathelicidin peptides, including LL-37, NA-CATH, and SMAP-29, possessed significant ability to prevent biofilm formation of B. thailandensis. Additionally, we show that LL-37 and its D-enantiomer D-LL-37 can disperse pre-formed biofilms. These results demonstrate that although B. thailandensis is highly resistant to many antibiotics, cyclic peptide antibiotics such as polymyxin B, and defensing peptides, some antimicrobial peptides including the elapid snake cathelicidin NA-CATH exert significant antimicrobial and antibiofilm activity towards B. thailandensis.

Burkholderia species such as B. pseudomallei, which causes melioidosis, and the model organism B. thailandensis are extremely resistant to antibiotics, including cyclic peptide antibiotics such as polymyxin B. Treatment for Burkholderia infections is impeded by this resistance, and new approaches are needed. We hypothesized that the cathelicidin NA-CATH from the Chinese cobra, Naja atra, and smaller derivative peptides (ATRA peptides) may have antimicrobial activity against Burkholderia. We therefore tested the bactericidal effects of the cathelicidin and its derivative peptides. We also wanted to determine whether the antimicrobial peptides exert anti-biofilm activity, although the role of biofilm as a critical virulence factor of Burkholderia has not yet been established. We found that the peptide ATRA-1A, as well as the stereo-isomer D-ATRA-1A, were able to kill B. thailandensis, and the full-length snake cathelicidin NA-CATH was able to both kill B. thailandensis and inhibit its biofilm formation, unlike the human-alpha defensin peptides HNP-1 and HNP-2, and the small peptide derived from hBD3. These results show that the NA-CATH antimicrobial peptide possess bactericidal and anti-biofilm activity against B. thailandensis, and suggest that these compounds should be tested for their effect against the more virulent strains of Burkholderia.

SarA based novel therapeutic candidate against Staphylococcus aureus associated with vascular graft infections

Staphylococcus aureus is a common pathogen seen in prosthetic vascular graft, leading to high morbidity and mortality. The virulence genes for severity of infections are under the control of global regulators. Staphylococcal accessory regulator A (SarA) a known master controller of biofilm formation is an attractive target for the drug development. A structure based screening of lead compounds was employed for the identification of novel small molecule inhibitors targeted to interact to the DNA binding domain of the transcriptional activator, SarA and hinder its response over the control of genes that up-regulate the phenotype, biofilm. The top-hit SarA selective inhibitor, 4-[(2,4-diflurobenzyl)amino] cyclohexanol (SarABI) was further validated in-vitro for its efficacy. The SarABI was found to have MBIC₅₀value of 200 μg/ml and also down-regulated the expression of the RNA effector, (RNAIII), Hemolysin (hld), and fibronectin-binding protein (fnbA). The anti-adherence property of SarABI on S. aureus invasion to the host epithelial cell lines (Hep-2) was examined where no significant attachment of S. aureus was observed. The SarABI inhibits the colonization of MDR S. aureus in animal model experiment significantly cohere to the molecular docking studies and in vitro experiments. So, we propose that the SarABI could be a novel substitute to overcome a higher degree of MDR S. aureus colonization on vascular graft.

Rhodamine B-conjugated encrypted vipericidin nonapeptide is a potent toxin to zebrafish and associated with in vitro cytotoxicity

BACKGROUND

Animal venoms contain a diverse array of proteins and enzymes that are toxic toward various physiological systems. However, there are also some practical medicinal uses for these toxins including use as anti-bacterial and anti-tumor agents.

METHODS

In this study, we identified a nine-residue cryptic oligopeptide, KRFKKFFKK (EVP50) that is repeatedly encoded in tandem within vipericidin sequences.

RESULTS

EVP50 displayed in vivo potent lethal toxicity to zebrafish larvae (LD50=6 μM) when the peptide's N-terminus was chemically conjugated to rhodamine B (RhoB). In vitro, RhoB-conjugated EVP50 (RhoB-EVP50) exhibited a concentration-dependent cytotoxic effect toward MCF-7 and MDA-MB-231 breast cancer cells. In MCF-7 cells, the RhoB-EVP50 nonapeptide accumulated inside the cells within minutes. In the cytoplasm, the RhoB-EVP50 induced extracellular calcium influx and intracellular calcium release. Membrane budding was also observed after incubation with micromolar concentrations of the fluorescent EVP50 conjugate.

CONCLUSIONS

The conjugate's interference with calcium homeostasis, its intracellular accumulation and its induced membrane dysfunction (budding and vacuolization) seem to act in concert to disrupt the cell circuitry. Contrastively, unconjugated EVP50 peptide did not display neither toxic nor cytotoxic activities in our in vivo and in vitro models.

GENERAL SIGNIFICANCE

The synergic mechanism of toxicity was restricted to the structurally modified encrypted vipericidin nonapeptide.

Antimicrobial peptides in reptiles

Reptiles are among the oldest known amniotes and are highly diverse in their morphology and ecological niches. These animals have an evolutionarily ancient innate-immune system that is of great interest to scientists trying to identify new and useful antimicrobial peptides. Significant work in the last decade in the fields of biochemistry, proteomics and genomics has begun to reveal the complexity of reptilian antimicrobial peptides. Here, the current knowledge about antimicrobial peptides in reptiles is reviewed, with specific examples in each of the four orders: Testudines (turtles and tortosises), Sphenodontia (tuataras), Squamata (snakes and lizards), and Crocodilia (crocodilans). Examples are presented of the major classes of antimicrobial peptides expressed by reptiles including defensins, cathelicidins, liver-expressed peptides (hepcidin and LEAP-2), lysozyme, crotamine, and others. Some of these peptides have been identified and tested for their antibacterial or antiviral activity; others are only predicted as possible genes from genomic sequencing. Bioinformatic analysis of the reptile genomes is presented, revealing many predicted candidate antimicrobial peptides genes across this diverse class. The study of how these ancient creatures use antimicrobial peptides within their innate immune systems may reveal new understandings of our mammalian innate immune system and may also provide new and powerful antimicrobial peptides as scaffolds for potential therapeutic development.

The effect of an adding histidine on biological activity and stability of Pc-pis from Pseudosciaena crocea

Pc-pis is a novel piscidin-like antimicrobial polypeptide that was identified in Pseudosciaena crocea. Although active against most bacteria tested, Pc-pis was inactive against Aeromonas hydrophila and Pseudomonas aeruginosa. The Pc-pis analogue Pc-pis-His was designed by adding a histidine residue at the carboxyl terminal. Pc-pis-His demonstrated a more broad-spectrum and stronger antimicrobial activity against a representative set of microorganisms and more potent antiparasitic activity against Cryptocaryon irritans trophonts than Pc-pis. The stability assay revealed that Pc-pis-His was active against Staphylococcus aureus not only in acidic (pH 5.5-7.3) and relatively low concentration monovalent cation (0-160 mM NaCl) environments but also in alkaline (pH 7.5-9.5), divalent cation (1.25-160 mM MgCl2 and 1.25-40 mM CaCl2) and high concentration monovalent cation (320-2560 mM NaCl) environments, which indicates that the added histidine residue conferred better salt-, acid- and alkali-tolerance to Pc-pis-His. Pc-pis-His also possessed the desired heat-tolerance, which was reflected by the antimicrobial activity of the peptide after being boiled for 10-60 minutes. Hemolytic activity analysis revealed that Pc-pis-His at concentrations up to 6 µM exhibited no hemolysis against human erythrocytes, with 6 µM being a concentration that is highly active against most of the microorganisms tested, although the hemolytic activity of Pc-pis-His was enhanced compared to Pc-pis. These results provide a unique, reasonable basis for designing novel piscidins with potent, broad-spectrum and stable antimicrobial activity and new insight into the future development of piscidins as potential therapeutic agents against microbial and external protozoan parasite infections.

The Human Cathelicidin Antimicrobial Peptide LL-37 as a Potential Treatment for Polymicrobial Infected Wounds

Diabetic patients often have ulcers on their lower-limbs that are infected by multiple biofilm-forming genera of bacteria, and the elimination of the biofilm has proven highly successful in resolving such wounds in patients. To that end, antimicrobial peptides have shown potential as a new anti-biofilm approach. The single human cathelicidin peptide LL-37 has been shown to have antimicrobial and anti-biofilm activity against multiple Gram-positive and Gram-negative human pathogens, and have wound-healing effects on the host. The combination of the anti-biofilm effect and wound-healing properties of LL-37 may make it highly effective in resolving polymicrobially infected wounds when topically applied. Such a peptide or its derivatives could be a platform from which to develop new therapeutic strategies to treat biofilm-mediated infections of wounds. This review summarizes known mechanisms that regulate the endogenous levels of LL-37 and discusses the anti-biofilm, antibacterial, and immunological effects of deficient vs. excessive concentrations of LL-37 within the wound environment. Here, we review recent advances in understanding the therapeutic potential of this peptide and other clinically advanced peptides as a potential topical treatment for polymicrobial infected wounds.

Ancient antimicrobial peptides kill antibiotic-resistant pathogens: Australian mammals provide new options

Background

To overcome the increasing resistance of pathogens to existing antibiotics the 10×^'20 Initiative declared the urgent need for a global commitment to develop 10 new antimicrobial drugs by the year 2020. Naturally occurring animal antibiotics are an obvious place to start. The recently sequenced genomes of mammals that are divergent from human and mouse, including the tammar wallaby and the platypus, provide an opportunity to discover novel antimicrobials. Marsupials and monotremes are ideal potential sources of new antimicrobials because they give birth to underdeveloped immunologically naïve young that develop outside the sterile confines of a uterus in harsh pathogen-laden environments. While their adaptive immune system develops innate immune factors produced either by the mother or by the young must play a key role in protecting the immune-compromised young. In this study we focus on the cathelicidins, a key family of antimicrobial peptide genes.

Principal Finding

We identified 14 cathelicidin genes in the tammar wallaby genome and 8 in the platypus genome. The tammar genes were expressed in the mammary gland during early lactation before the adaptive immune system of the young develops, as well as in the skin of the pouch young. Both platypus and tammar peptides were effective in killing a broad range of bacterial pathogens. One potent peptide, expressed in the early stages of tammar lactation, effectively killed multidrug-resistant clinical isolates of Pseudomonas aeruginosa, Klebsiella pneumoniae and Acinetobacter baumannii.

Conclusions and Significance

Marsupial and monotreme young are protected by antimicrobial peptides that are potent, broad spectrum and salt resistant. The genomes of our distant relatives may hold the key for the development of novel drugs to combat multidrug-resistant pathogens.

Susceptibility of Pseudomonas aeruginosa Biofilm to Alpha-Helical Peptides: D-enantiomer of LL-37

Pseudomonas aeruginosa is a highly versatile opportunistic pathogen and its ability to produce biofilms is a direct impediment to the healing of wounds and recovery from infection. Interest in anti-microbial peptides (AMPs) has grown due to their potential therapeutic applications and their possible use against antibiotic resistant bacteria. LL-37 is the only cathelicidin expressed by humans. In this study, we tested LL-37 and the effect of a protease-resistant LL-37 peptide mimetic, the peptide enantiomer D-LL-37, for anti-microbial and anti-biofilm activity against P. aeruginosa. Both forms of the peptide were equally effective as AMPs with similar killing kinetics. Circular dichroism spectra were obtained to demonstrate the chirality of D- and L-LL-37, and the trypsin resistance of D-LL-37 was confirmed. The helical cathelicidin from the cobra Naja atra (NA-CATH), and synthetic peptide variations (ATRA-1, ATRA-2, NA-CATH:ATRA1-ATRA1) were also tested. Although the cobra cathelicidin and related peptides had strong anti-microbial activity, those tested did not inhibit Pseudomonas biofilm formation, neither did control peptides. Both D- and L-LL-37 inhibited the attachment of Pseudomonas to a 96-well plate and decreased the amount of pre-formed (established) biofilm. D-LL-37 is able to promote Pseudomonas motility and decrease biofilm formation by altering the rate of twitching as well as by downregulating the expression of the biofilm-related genes, rhlA and rhlB, similar to L-LL-37. Both L- and D-LL-37 protected Galleria mellonella in vivo against Pseudomonas infection, while NA-CATH:ATRA1-ATRA1 peptide did not. This study demonstrates the ability and equivalence of D-LL-37 compared to L-LL-37 to promote bacterial twitching motility and inhibit biofilm formation, and protect against in vivo infection, and suggests that this peptide could be a critical advancement in the development of new treatments for P. aeruginosa infection.

Natural and synthetic cathelicidin peptides with anti-microbial and anti-biofilm activity against Staphylococcus aureus

BACKGROUND

Chronic, infected wounds typically contain multiple genera of bacteria, including Staphylococcus aureus, many of which are strong biofilm formers. Bacterial biofilms are thought to be a direct impediment to wound healing. New therapies that focus on a biofilm approach may improve the recovery and healing rate for infected wounds. In this study, cathelicidins and related short, synthetic peptides were tested for their anti-microbial effectiveness as well as their ability to inhibit the ability of S. aureus to form biofilms.

RESULTS

The helical human cathelicidin LL-37 was tested against S. aureus, and was found to exhibit effective anti-microbial, anti-attachment as well as anti-biofilm activity at concentrations in the low μg/ml range. The effect of peptide chirality and associated protease-resistance was explored through the use of an all-D amino acid peptide, D-LL-37, and in turn compared to scrambled LL-37. Helical cathelicidins have been identified in other animals such as the Chinese cobra, Naja atra (NA-CATH). We previously identified an 11-residue imperfectly repeated pattern (ATRA motif) within the sequence of NA-CATH. A series of short peptides (ATRA-1, -2, -1A), as well as a synthetic peptide, NA-CATH:ATRA1-ATRA1, were designed to explore the significance of the conserved residues within the ATRA motif for anti-microbial activity. The CD spectrum of NA-CATH and NA-CATH:ATRA1-ATRA1 revealed the structural properties of these peptides and suggested that helicity may factor into their anti-microbial and anti-biofilm activities.

CONCLUSIONS

The NA-CATH:ATRA1-ATRA1 peptide inhibits the production of biofilm by S. aureus in the presence of salt, exhibiting anti-biofilm activity at lower peptide concentrations than NA-CATH, LL-37 and D-LL-37; and demonstrates low cytoxicity against host cells but does not affect bacterial attachment. The peptides utilized in this anti-biofilm approach may provide templates for a new group of anti-microbials and potential future topical therapeutics for treating chronic wound infections.