Structural Dissection of Crotalicidin, a Rattlesnake Venom Cathelicidin, Retrieves a Fragment with Antimicrobial and Antitumor Activity

A review on the diversity of antimicrobial peptides and genome mining strategies for their prediction

Antibiotic resistance has become one of the most serious threats to human health in recent years. In response to the increasing microbial resistance to the antibiotics currently available, it is imperative to develop new antibiotics or explore new approaches to combat antibiotic resistance. Antimicrobial peptides (AMPs) have shown considerable promise in this regard, as the microbes develop low or no resistance against them. The discovery and development of AMPs still confront numerous obstacles such as finding a target, developing assays, and identifying hits and leads, which are time-consuming processes, making it difficult to reach the market. However, with the advent of genome mining, new antibiotics could be discovered efficiently using tools such as BAGEL, antiSMASH, RODEO, etc., providing hope for better treatment of diseases in the future. Computational methods used in genome mining automatically detect and annotate biosynthetic gene clusters in genomic data, making it a useful tool in natural product discovery. This review aims to shed light on the history, diversity, and mechanisms of action of AMPs and the data on new AMPs identified by traditional as well as genome mining strategies. It further substantiates the various phases of clinical trials for some AMPs, as well as an overview of genome mining databases and tools built expressly for AMP discovery. In light of the recent advancements, it is evident that targeted genome mining stands as a beacon of hope, offering immense potential to expedite the discovery of novel antimicrobials.

Antiparasitic Evaluation of Aquiluscidin, a Cathelicidin Obtained from Crotalus aquilus, and the Vcn-23 Derivative Peptide against Babesia bovis, B. bigemina and B. ovata

Babesiosis is a growing concern due to the increased prevalence of this infectious disease caused by Babesia protozoan parasites, affecting various animals and humans. With rising worries over medication side effects and emerging drug resistance, there is a notable shift towards researching babesiacidal agents. Antimicrobial peptides, specifically cathelicidins known for their broad-spectrum activity and immunomodulatory functions, have emerged as potential candidates. Aquiluscidin, a cathelicidin from Crotalus aquilus, and its derivative Vcn-23, have been of interest due to their previously observed antibacterial effects and non-hemolytic activity. This work aimed to characterize the effect of these peptides against three Babesia species. Results showed Aquiluscidin's significant antimicrobial effects on Babesia species, reducing the B. bigemina growth rate and exhibiting IC50 values of 14.48 and 20.70 μM against B. ovata and B. bovis, respectively. However, its efficacy was impacted by serum presence in culture, and it showed no inhibition against a B. bovis strain grown in serum-supplemented medium. Conversely, Vcn-23 did not demonstrate babesiacidal activity. In conclusion, Aquiluscidin shows antibabesia activity in vitro and its efficacy is affected by the presence of serum in the culture medium. Nevertheless, this peptide represents a candidate for further investigation of its antiparasitic properties and provides insights into potential alternatives for the treatment of babesiosis.

Exploring the Potential of Bioactive Peptides: From Natural Sources to Therapeutics

Bioactive peptides, specific protein fragments with positive health effects, are gaining traction in drug development for advantages like enhanced penetration, low toxicity, and rapid clearance. This comprehensive review navigates the intricate landscape of peptide science, covering discovery to functional characterization. Beginning with a peptidomic exploration of natural sources, the review emphasizes the search for novel peptides. Extraction approaches, including enzymatic hydrolysis, microbial fermentation, and specialized methods for disulfide-linked peptides, are extensively covered. Mass spectrometric analysis techniques for data acquisition and identification, such as liquid chromatography, capillary electrophoresis, untargeted peptide analysis, and bioinformatics, are thoroughly outlined. The exploration of peptide bioactivity incorporates various methodologies, from in vitro assays to in silico techniques, including advanced approaches like phage display and cell-based assays. The review also discusses the structure-activity relationship in the context of antimicrobial peptides (AMPs), ACE-inhibitory peptides (ACEs), and antioxidative peptides (AOPs). Concluding with key findings and future research directions, this interdisciplinary review serves as a comprehensive reference, offering a holistic understanding of peptides and their potential therapeutic applications.

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.

Biophysical Insights into the Antitumoral Activity of Crotalicidin against Breast Cancer Model Membranes

Bioactive peptides have emerged as promising therapeutic agents with antimicrobial, antifungal, antiparasitic, and, recently, antitumoral properties with a mechanism of action based on membrane destabilization and cell death, often involving a conformational change in the peptide. This biophysical study aims to provide preliminary insights into the membrane-level antitumoral mode of action of crotalicidin, a cationic host defense peptide from rattlesnake venom, toward breast cancer cell lines. The lipid composition of breast cancer cell lines was obtained after lipid extraction and quantification to prepare representative cell membrane models. Membrane-peptide interaction studies were performed using differential scanning calorimetry and Fourier-transform infrared spectroscopy. The outcome evidences the potential antitumoral activity and selectivity of crotalicidin toward breast cancer cell lines and suggests a mechanism initiated by the electrostatic interaction of the peptide with the lipid bilayer surface and posterior conformation change with membrane intercalation between the acyl chains in negatively charged lipid systems. This research provides valuable information that clears up the antitumoral mode of action of crotalicidin.

Topoisomeric Membrane-Active Peptides: A Review of the Last Two Decades

In recent decades, bioactive peptides have been gaining recognition in various biomedical areas, such as intracellular drug delivery (cell-penetrating peptides, CPPs) or anti-infective action (antimicrobial peptides, AMPs), closely associated to their distinct mode of interaction with biological membranes. Exploiting the interaction of membrane-active peptides with diverse targets (healthy, tumoral, bacterial or parasitic cell membranes) is opening encouraging prospects for peptides in therapeutics. However, ordinary peptides formed by L-amino acids are easily decomposed by proteases in biological fluids. One way to sidestep this limitation is to use topoisomers, namely versions of the peptide made up of D-amino acids in either canonic (enantio) or inverted (retroenantio) sequence. Rearranging peptide sequences in this fashion provides a certain degree of native structure mimicry that, in appropriate contexts, may deliver desirable biological activity while avoiding protease degradation. In this review, we will focus on recent accounts of membrane-active topoisomeric peptides with therapeutic applications as CPP drug delivery vectors, or as antimicrobial and anticancer candidates. We will also discuss the most common modes of interaction of these peptides with their membrane targets.

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.

Biodegradable Polymers and Polymer Composites with Antibacterial Properties

Antibiotic resistance is one of the greatest threats to global health and food security today. It becomes increasingly difficult to treat infectious disorders because antibiotics, even the newest ones, are becoming less and less effective. One of the ways taken in the Global Plan of Action announced at the World Health Assembly in May 2015 is to ensure the prevention and treatment of infectious diseases. In order to do so, attempts are made to develop new antimicrobial therapeutics, including biomaterials with antibacterial activity, such as polycationic polymers, polypeptides, and polymeric systems, to provide non-antibiotic therapeutic agents, such as selected biologically active nanoparticles and chemical compounds. Another key issue is preventing food from contamination by developing antibacterial packaging materials, particularly based on degradable polymers and biocomposites. This review, in a cross-sectional way, describes the most significant research activities conducted in recent years in the field of the development of polymeric materials and polymer composites with antibacterial properties. We particularly focus on natural polymers, i.e., polysaccharides and polypeptides, which present a mechanism for combating many highly pathogenic microorganisms. We also attempt to use this knowledge to obtain synthetic polymers with similar antibacterial activity.

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.

Examining Topoisomers of a Snake-Venom-Derived Peptide for Improved Antimicrobial and Antitumoral Properties

Ctn[15-34], the C-terminal section of crotalicidin (Ctn), a cathelicidin from a South American pit viper, is an antimicrobial and antitumoral peptide with remarkably longer stability in human serum than the parent Ctn. In this work, a set of topoisomers of both Ctn and Ctn[15-34], including the retro, enantio, and retroenantio versions, were synthesized and tested to investigate the structural requirements for activity. All topoisomers were as active as the cognate sequences against Gram-negative bacteria and tumor cells while slightly more toxic towards normal cells. More importantly, the enhanced serum stability of the D-amino-acid-containing versions suggests that such topoisomers must be preferentially considered as future antimicrobial and anticancer peptide leads.

Antimicrobial peptides: On future antiprotozoal and anthelminthic applications

Control and elimination of parasitic diseases are nowadays further complicated by emergence of drug resistance. Drug resistance is a serious threat as there are not many effective antiparasitic drugs available. Aside from drug resistance, it is also favorable to look for alternative therapeutics that have lesser adverse effects. Antimicrobial peptides (AMPs) were found to address these issues. Some of its desirable traits are they are fast-acting, it has broad action that the pathogen will have difficulty developing resistance to, it has high specificity, and most importantly there are extensive sources such as bacteria; invertebrate and vertebrate animals as well as plants. Aside from this, AMPs are also found to modulate the immune response. This review would like to describe AMPs that have been studied for their antiparasitic activities especially on parasitic diseases that causes high mortality and exhibits drug resistance like malaria and leishmaniasis and to discuss the mechanism of action of these AMPS.

Renovation as innovation: Repurposing human antibacterial peptide LL-37 for cancer therapy

In many organisms, antimicrobial peptides (AMPs) display wide activities in innate host defense against microbial pathogens. Mammalian AMPs include the cathelicidin and defensin families. LL37 is the only one member of the cathelicidin family of host defense peptides expressed in humans. Since its discovery, it has become clear that they have pleiotropic effects. In addition to its antibacterial properties, many studies have shown that LL37 is also involved in a wide variety of biological activities, including tissue repair, inflammatory responses, hemotaxis, and chemokine induction. Moreover, recent studies suggest that LL37 exhibits the intricate and contradictory effects in promoting or inhibiting tumor growth. Indeed, an increasing amount of evidence suggests that human LL37 including its fragments and analogs shows anticancer effects on many kinds of cancer cell lines, although LL37 is also involved in cancer progression. Focusing on recent information, in this review, we explore and summarize how LL37 contributes to anticancer effect as well as discuss the strategies to enhance delivery of this peptide and selectivity for cancer cells.

Antitumor and antiparasitic activity of antimicrobial peptides derived from snake venom: a systematic review approach

BACKGROUND

In a scenario of increased pathogens with multidrug resistance phenotypes, it is necessary to seek new pharmacological options. This fact is responsible for an increase in neoplasms and multiresistant parasitic diseases. In turn, snake venom-derived peptides exhibited cytotoxic action on fungal and bacterial strains, possibly presenting activities in resistant tumor cells and parasites. Therefore, the aim of this work is to verify an antitumor and antiparasitic activity of antimicrobial peptides derived from snake venom.

METHODS

For this purpose, searches were performed in the Pubmed, Embase and Virtual Health Library databases by combining the descriptors peptides, venom and snake with antitumor/ antiparasitic agent and in silico. The inclusion criteria: in vitro and in vivo experimental articles in addition to in silico studies. The exclusion criteria: articles that were out of scope, review articles, abstracts, and letters to the reader. Data extracted: peptide name, peptide sequence, semi-maximal inhibitory concentration, snake species, tumor lineage or parasitic strain, cytotoxicity, in vitro and in vivo activity.

RESULTS

In total 164 articles were found, of which 14 were used. A total of ten peptides with antiproliferative activity on tumor cells were identified. Among the articles, seven peptides addressed the antiparasitic activity.

CONCLUSION

In conclusion, snake venom-derived peptides can be considered as potential pharmacological options for parasites and tumors, however more studies are needed to prove their specific activity.

The Impact of Lung Proteases on Snake-Derived Antimicrobial Peptides

Respiratory infections are a leading cause of global morbidity and mortality and are of significant concern for individuals with chronic inflammatory lung diseases. There is an urgent need for novel antimicrobials. Antimicrobial peptides (AMPs) are naturally occurring innate immune response peptides with therapeutic potential. However, therapeutic development has been hindered by issues with stability and cytotoxicity. Availing of direct drug delivery to the affected site, for example the lung, can reduce unwanted systemic side effects and lower the required dose. As cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD) lungs typically exhibit elevated protease levels, the aim of this study was to assess their impact on snake-derived AMPs. Peptide cleavage was determined using SDS-PAGE and antimicrobial and anti-inflammatory activities of neutrophil elastase (NE)-incubated peptides were assessed using a radial diffusion assay (RDA) and an in vitro LPS-induced inflammation model, respectively. Although the snake-derived AMPs were found to be susceptible to cleavage by lung proteases including NE, several retained their function following NE-incubation. This facilitated the design of novel truncated derivatives that retained functionality following NE incubation. Snake-derived AMPs are tractable candidate treatments for use in environments that feature elevated NE levels, such as the CF airways.

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).

DRACP: a novel method for identification of anticancer peptides

Background

Millions of people are suffering from cancers, but accurate early diagnosis and effective treatment are still tough for all doctors. Common ways against cancer include surgical operation, radiotherapy and chemotherapy. However, they are all very harmful for patients. Recently, the anticancer peptides (ACPs) have been discovered to be a potential way to treat cancer. Since ACPs are natural biologics, they are safer than other methods. However, the experimental technology is an expensive way to find ACPs so we purpose a new machine learning method to identify the ACPs.

Results

Firstly, we extracted the feature of ACPs in two aspects: sequence and chemical characteristics of amino acids. For sequence, average 20 amino acids composition was extracted. For chemical characteristics, we classified amino acids into six groups based on the patterns of hydrophobic and hydrophilic residues. Then, deep belief network has been used to encode the features of ACPs. Finally, we purposed Random Relevance Vector Machines to identify the true ACPs. We call this method ‘DRACP’ and tested the performance of it on two independent datasets. Its AUC and AUPR are higher than 0.9 in both datasets.

Conclusion

We developed a novel method named ‘DRACP’ and compared it with some traditional methods. The cross-validation results showed its effectiveness in identifying ACPs.

Tumor Cell Attack by Crotalicidin (Ctn) and Its Fragment Ctn[15-34]: Insights into Their Dual Membranolytic and Intracellular Targeting Mechanism

Crotalicidin (Ctn) and its fragment Ctn[15-34] are snake-venom-derived, cathelicidin-related peptides outstanding for their promising antimicrobial, antifungal, and antitumoral properties. In this study, we describe their membranolytic mechanisms as well as their putative interference with intracellular targets, both contributing to their antitumoral action against a pro-monocytic leukemia cell line. Initial flow cytometry assays demonstrated peptide ability to induce tumor cell membrane permeabilization and caspase-dependent apoptosis, without total activity reduction by serum proteases up to 24 h (Ctn) and 18 h (Ctn[15-34]). In addition, both Ctn and Ctn[15-34] showed preference for tumor cells rather than healthy cells, with selectivity ratios (tumoral vs healthy cells) of 17 and 7, respectively. Further microscopy and flow cytometry studies suggested their preferential accumulation in the cytoplasmic membrane and nucleus and proposed multiple predominant routes of peptide uptake, including direct entry and endocytosis. Affinity purification followed by proteomic identification experiments revealed both peptides to interact with proteins involved in DNA and protein metabolism, cell cycles, signal transduction, and/or programmed cell death, among others. These results suggest a putative role of Ctn and Ctn[15-34] to interact with key intracellular pathways, ultimately contributing to tumor cell death by necrosis/apoptosis. Altogether, this work proposes a dual mechanism underlying the antitumoral activity of Ctn and Ctn[15-34] and reinforces their potential as future therapeutic drugs.

Antibiofilm Activity on Candida albicans and Mechanism of Action on Biomembrane Models of the Antimicrobial Peptide Ctn[15-34]

Ctn[15–34], the C-terminal fragment of crotalicidin, an antimicrobial peptide from the South American rattlesnake Crotalus durissus terrificus venom, displays remarkable anti-infective and anti-proliferative activities. Herein, its activity on Candida albicans biofilms and its interaction with the cytoplasmic membrane of the fungal cell and with a biomembrane model in vitro was investigated. A standard C. albicans strain and a fluconazole-resistant clinical isolate were exposed to the peptide at its minimum inhibitory concentration (MIC) (10 µM) and up to 100 × MIC to inhibit biofilm formation and its eradication. A viability test using XTT and fluorescent dyes, confocal laser scanning microscopy, and atomic force microscopy (AFM) were used to observe the antibiofilm effect. To evaluate the importance of membrane composition on Ctn[15–34] activity, C. albicans protoplasts were also tested. Fluorescence assays using di-8-ANEPPS, dynamic light scattering, and zeta potential measurements using liposomes, protoplasts, and C. albicans cells indicated a direct mechanism of action that was dependent on membrane interaction and disruption. Overall, Ctn[15–34] showed to be an effective antifungal peptide, displaying antibiofilm activity and, importantly, interacting with and disrupting fungal plasma membrane.

The Addition of a Synthetic LPS-Targeting Domain Improves Serum Stability While Maintaining Antimicrobial, Antibiofilm, and Cell Stimulating Properties of an Antimicrobial Peptide

Multi-drug resistant (MDR) bacteria and their biofilms are a concern in veterinary and human medicine. Protegrin-1 (PG-1), a potent antimicrobial peptide (AMP) with antimicrobial and immunomodulatory properties, is considered a potential alternative for conventional antibiotics. AMPs are less stable and lose activity in the presence of physiological fluids, such as serum. To improve stability of PG-1, a hybrid peptide, SynPG-1, was designed. The antimicrobial and antibiofilm properties of PG-1 and the PG-1 hybrid against MDR pathogens was analyzed, and activity after incubation with physiological fluids was compared. The effects of these peptides on the IPEC-J2 cell line was also investigated. While PG-1 maintained some activity in 25% serum for 2 h, SynPG-1 was able to retain activity in the same condition for up to 24 h, representing a 12-fold increase in stability. Both peptides had some antibiofilm activity against Escherichia coli and Salmonella typhimurium. While both peptides prevented biofilm formation of methicillin-resistant Staphylococcus aureus (MRSA), neither could destroy MRSA's pre-formed biofilms. Both peptides maintained activity after incubation with trypsin and porcine gastric fluid, but not intestinal fluid, and stimulated IPEC-J2 cell migration. These findings suggest that SynPG-1 has much better serum stability while maintaining the same antimicrobial potency as PG-1.

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.

DPepH3, an Improved Peptide Shuttle for Receptor-independent Transport Across the Blood-Brain Barrier

Background:

The use of peptides as drug carriers across the blood-brain barrier (BBB) has increased significantly during the last decades. PepH3, a seven residue sequence (AGILKRW) derived from the α-helical domain of the dengue virus type-2 capsid protein, translocates across the BBB with very low toxicity. Somehow predictably from its size and sequence, PepH3 is degraded in serum relatively fast. Among strategies to increase peptide half-life (t1/2), the use of the enantiomer (wholly made of D-amino acid residues) can be quite successful if the peptide interacts with a target in non-stereospecific fashion.

Methods:

The goal of this work was the development of a more proteolytic-resistant peptide, while keeping the translocation properties. The serum stability, cytotoxicity, in vitro BBB translocation, and internalization mechanism of DPepH3 was assessed and compared to the native peptide.

Results:

DPepH3 demonstrates a much longer t1/2 compared to PepH3. We also confirm that BBB translocation is receptor-independent, which fully validates the enantiomer strategy chosen. In fact, we demonstrate that internalization occurs trough macropinocytosis. In addition, the enantiomer demonstrates to be non-cytotoxic towards endothelial cells as PepH3.

Conclusion:

DPepH3 shows excellent translocation and internalization properties, safety, and improved stability. Taken together, our results place DPepH3 at the forefront of the second generation of BBB shuttles.

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.

Crotamine and crotalicidin, membrane active peptides from Crotalus durissus terrificus rattlesnake venom, and their structurally-minimized fragments for applications in medicine and biotechnology

A global public health crisis has emerged with the extensive dissemination of multidrug-resistant microorganisms. Antimicrobial peptides (AMPs) from plants and animals have represented promising tools to counteract those resistant pathogens due to their multiple pharmacological properties such as antimicrobial, anticancer, immunomodulatory and cell-penetrating activities. In this review, we will focus on crotamine and crotalicidin, which are two interesting examples of membrane active peptides derived from the South America rattlesnake Crotalus durrisus terrificus venom. Their full-sequences and structurally-minimized fragments have potential applications, as anti-infective and anti-proliferative agents and diagnostics in medicine and in pharmaceutical biotechnology.

Potent antibacterial activity of MSI-1 derived from the magainin 2 peptide against drug-resistant bacteria

The structural modification of existing AMPs is an effective strategy to develop antimicrobial agents with high-efficiency, low-cost and low-toxicity antimicrobial agents. Methods: Here, we truncated 14-amino-acids at the N-terminus of MSI-78 to obtain MSI and further modified MSI to obtain four peptide analogs: MSI-1, MSI-2, MSI-3 and MSI-4. These peptide mutants were evaluated regarding their antibacterial activity against various sensitive or resistant bacteria; toxicity against mammalian cells or mice; and stability against violent pH, temperature variations and high NaCl concentrations. Finally, we also elucidated the possible mechanisms underlying its mode of action. Results: The results showed that MSI-1 and MSI-3 displayed activity that was superior to that of MSI-78 with MICs of 4-16 μg/ml and MBCs of 8-64 μg/ml, respectively, especially against drug-resistant bacteria, due to the increase in percent helicity and amphiphilicity. However, MSI-3, with higher hydrophobicity and antibacterial activity, had a relatively higher hemolysis rate and toxicity than MSI-1. MSI-1 exerted rapid bactericidal activity and effectively improved the survival rate and wound closure in penicillin-resistant E. coli-infected mice by eliminating bacterial counts in mouse organs or subeschar, further inhibiting the systemic dissemination of bacteria. Additionally, MSI-1 displayed perfect stability against violent pH, temperature variations and high NaCl concentrations and has the ability to circumvent the development of drug resistance. In terms of the mode of action, we found that at the super-MIC level, MSI-1 exhibited direct antimicrobial activity by disrupting the integrity of the bacterial cell membrane, while at the sub-MIC level, it bound to bacterial DNA to inhibit DNA replication and protein expression and ultimately disrupted bacterial biological function. Conclusions: This novel peptide MSI-1 could be a potential candidate for drug development against infection induced by drug-resistant bacteria.

Curved or linear? Predicting the 3-dimensional structure of α-helical antimicrobial peptides in an amphipathic environment

α-Helical membrane-active antimicrobial peptides (AMPs) are known to act via a range of mechanisms, including the formation of barrel-stave and toroidal pores and the micellisation of the membrane (carpet mechanism). Different mechanisms imply that the peptides adopt different 3D structures when bound at the water-membrane interface, a highly amphipathic environment. Here, an evolutionary algorithm is used to predict the 3D structure of a range of α-helical membrane-active AMPs at the water-membrane interface by optimising amphipathicity. This amphipathic structure prediction (ASP) is capable of distinguishing between curved and linear peptides solved experimentally, potentially allowing the activity and mechanism of action of different membrane-active AMPs to be predicted. The ASP algorithm is accessible via a web interface at http://atb.uq.edu.au/asp/.

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.

The antiproliferative peptide Ctn[15-34] is active against multidrug-resistant yeasts Candida albicans and Cryptococcus neoformans

AIMS

Crotalicidin (Ctn), a cathelicidin-related antimicrobial peptide from the South American rattlesnake venom gland, and its C-terminal Ctn[15-34] fragment, have exhibited important activities against micro-organisms, trypanosomatid protozoa and certain lines of tumour cells. Herein, the activity against clinical strains of fluconazole-resistant Candida albicans and of amphotericin B and fluconazole-resistant Cryptococcus neoformans was investigated.

METHODS AND RESULTS

Microdilution and luminescent cell viability tests were used to evaluate and compare the susceptibility of pathogenic yeasts to these peptides. The time-kill curves of the most active Ctn[15-34] alone or in combination with fluconazole against drug-resistant yeasts were determined. Concomitantly, the fungicidal and/or fungistatic effects of Ctn[15-34] were visualized by the spotting test. The peptides were active against all strains, including those resistant to antifungal agents. The association of fluconazole with both Ctn and Ctn[15-34], although not synergic, was additive. In contrast, such pattern was not observed for C. neoformans.

CONCLUSIONS

Overall, Ctn and Ctn[15-34] are potential antifungal leads displaying anti-yeast activities against clinical isolates endowed with drug resistance mechanisms.

SIGNIFICANCE AND IMPACT OF THE STUDY

The effective peptide activity against resistant strains of pathogenic yeasts demonstrates that crotalicidin-derived peptides are promising templates to develop new antifungal pharmaceuticals.

The Place for Enzymes and Biologically Active Peptides from Marine Organisms for Application in Industrial and Pharmaceutical Biotechnology

Since the beginning of written history, diverse texts have reported the use of enzymatic preparations in food processing and have described the medicinal properties of crude and fractionated venoms to treat various diseases and injuries. With the biochemical characterization of enzymes from distinct sources and bioactive polypeptides from animal venoms, the last sixty years have testified the advent of industrial enzymology and protein therapeutics, which are currently applicable in a wide variety of industrial processes, household products, and pharmaceuticals. Bioprospecting of novel biocatalysts and bioactive peptides is propelled by their unsurpassed properties that are applicable for current and future green industrial processes, biotechnology, and biomedicine. The demand for both novel enzymes with desired characteristics and novel peptides that lead to drug development, has experienced a steady increase in response to the expanding global market for industrial enzymes and peptidebased drugs. Moreover, although largely unexplored, oceans and marine realms, with their unique ecosystems inhabited by a large variety of species, including a considerable number of venomous animals, are recognized as untapped reservoirs of molecules and macromolecules (enzymes and bioactive venom-derived peptides) that can potentially be converted into highly valuable biopharmaceutical products. In this review, we have focused on enzymes and animal venom (poly)peptides that are presently in biotechnological use, and considering the state of prospection of marine resources, on the discovery of useful industrial biocatalysts and drug leads with novel structures exhibiting selectivity and improved performance.

Nanoparticles Functionalized with Venom-Derived Peptides and Toxins for Pharmaceutical Applications

Venom-derived peptides display diverse biological and pharmacological activities, making them useful in drug discovery platforms and for a wide range of applications in medicine and pharmaceutical biotechnology. Due to their target specificities, venom peptides have the potential to be developed into biopharmaceuticals to treat various health conditions such as diabetes mellitus, hypertension, and chronic pain. Despite the high potential for drug development, several limitations preclude the direct use of peptides as therapeutics and hamper the process of converting venom peptides into pharmaceuticals. These limitations include, for instance, chemical instability, poor oral absorption, short halflife, and off-target cytotoxicity. One strategy to overcome these disadvantages relies on the formulation of bioactive peptides with nanocarriers. A range of biocompatible materials are now available that can serve as nanocarriers and can improve the bioavailability of therapeutic and venom-derived peptides for clinical and diagnostic application. Examples of isolated venom peptides and crude animal venoms that have been encapsulated and formulated with different types of nanomaterials with promising results are increasingly reported. Based on the current data, a wealth of information can be collected regarding the utilization of nanocarriers to encapsulate venom peptides and render them bioavailable for pharmaceutical use. Overall, nanomaterials arise as essential components in the preparation of biopharmaceuticals that are based on biological and pharmacological active venom-derived peptides.

Decoding the human serum interactome of snake-derived antimicrobial peptide Ctn[15-34]: Toward an explanation for unusually long half-life

The inherent propensity to enzymatic degradation of most peptides remains a bottleneck in their therapeutic development. Efficient, early screening methods are necessary for in vitro characterization of the molecular events occurring when peptides get in contact with biological fluids such us plasma. Herein we present an affinity purification/MS approach for mapping peptide serum interactors. We have applied this methodology to identify the serum partners of antibiotic peptide Ctn [15-34], aiming to ascertain the molecular interactions underlying its unusually long half-life (~ 12 h) in human serum. From 42 proteins captured in pull-downs with biotinylated Ctn [15-34] as bait, five are of special interest for their transport/binding properties hence alleged peptide arresting potential. The subset contains two members of the albumin superfamily, two apolipoproteins and a globulin. All five share a binding ability for hydrophobic species, and also bind Ctn [15-34], presumably via its C-terminal hydrophobic section, with affinities in the μM range as shown by surface plasmon resonance. Additionally, our functional enrichment reveals several significant immune-related processes suggesting an immunomodulatory role of Ctn [15-34]. Taken together, this study exemplifies how pharmacoproteomics can be used to analyze bioavailability issues and shed light on the serum interactors ultimately conferring protection to Ctn [15-34] against proteolytic events. SIGNIFICANCE: The affinity purification/MS identification methodology reported here can be viewed as a routine pharmacoproteomic approach to investigate the serum interactome of peptide drugs, identifying proteins affecting bioavailability and thus assisting the peptide drug development process. The specific results described here enlighten the serum stability issues of peptide Ctn [15-34] and ratify its promising future as an anti-infective lead.

In-Depth Venome of the Brazilian Rattlesnake Crotalus durissus terrificus: An Integrative Approach Combining Its Venom Gland Transcriptome and Venom Proteome

Snake venoms are complex mixtures mainly composed of proteins and small peptides. Crotoxin is one of the most studied components from Crotalus venoms, but many other components are less known due to their low abundance. The venome of Crotalus durissus terrificus, the most lethal Brazilian snake, was investigated by combining its venom gland transcriptome and proteome to create a holistic database of venom compounds unraveling novel toxins. We constructed a cDNA library from C. d. terrificus venom gland using the Illumina platform and investigated its venom proteome through high resolution liquid chromotography-tandem mass spectrometry. After integrating data from both data sets, more than 30 venom components classes were identified by the transcriptomic analysis and 15 of them were detected in the venom proteome. However, few of them (PLA₂, SVMP, SVSP, and VEGF) were relatively abundant. Furthermore, only seven expressed transcripts contributed to ∼82% and ∼73% of the abundance in the transcriptome and proteome, respectively. Additionally, novel venom proteins are reported, and we highlight the importance of using different databases to perform the data integration and discuss the structure of the venom components-related transcripts identified. Concluding, this research paves the way for novel investigations and discovery of future pharmacological agents or targets in the antivenom therapy.

An acidic model pro-peptide affects the secondary structure, membrane interactions and antimicrobial activity of a crotalicidin fragment

In order to study how acidic pro-peptides inhibit the antimicrobial activity of antimicrobial peptides, we introduce a simple model system, consisting of a 19 amino-acid long antimicrobial peptide, and an N-terminally attached, 10 amino-acid long acidic model pro-peptide. The antimicrobial peptide is a fragment of the crotalicidin peptide, a member of the cathelidin family, from rattlesnake venom. The model pro-peptide is a deca (glutamic acid). Attachment of the model pro-peptide only leads to a moderately large reduction in the binding to- and induced leakage of model liposomes, while the antimicrobial activity of the crotalicidin fragment is completely inhibited by attaching the model pro-peptide. Attaching the pro-peptide induces a conformational change to a more helical conformation, while there are no signs of intra- or intermolecular peptide complexation. We conclude that inhibition of antimicrobial activity by the model pro-peptide might be related to a conformational change induced by the pro-peptide domain, and that additional effects beyond induced changes in membrane activity must also be involved.

In Silico Structural Evaluation of Short Cationic Antimicrobial Peptides

Cationic peptides with antimicrobial properties are ubiquitous in nature and have been studied for many years in an attempt to design novel antibiotics. However, very few molecules are used in the clinic so far, sometimes due to their complexity but, mostly, as a consequence of the unfavorable pharmacokinetic profile associated with peptides. The aim of this work is to investigate cationic peptides in order to identify common structural features which could be useful for the design of small peptides or peptido-mimetics with improved drug-like properties and activity against Gram negative bacteria. Two sets of cationic peptides (AMPs) with known antimicrobial activity have been investigated. The first reference set comprised molecules with experimentally-known conformations available in the protein databank (PDB), and the second one was composed of short peptides active against Gram negative bacteria but with no significant structural information available. The predicted structures of the peptides from the first set were in excellent agreement with those experimentally-observed, which allowed analysis of the structural features of the second group using computationally-derived conformations. The peptide conformations, either experimentally available or predicted, were clustered in an “all vs. all” fashion and the most populated clusters were then analyzed. It was confirmed that these peptides tend to assume an amphipathic conformation regardless of the environment. It was also observed that positively-charged amino acid residues can often be found next to aromatic residues. Finally, a protocol was evaluated for the investigation of the behavior of short cationic peptides in the presence of a membrane-like environment such as dodecylphosphocholine (DPC) micelles. The results presented herein introduce a promising approach to inform the design of novel short peptides with a potential antimicrobial activity.

A novel synthetic peptide inspired on Lys49 phospholipase A2 from Crotalus oreganus abyssus snake venom active against multidrug-resistant clinical isolates

Currently, the evolving and complex mechanisms of bacterial resistance to conventional antibiotics are increasing, while alternative medicines are drying up, which urges the need to discover novel agents able to kill antibiotic-resistant bacteria. Lys49 phospholipase A₂s (PLA₂s) from snake venoms are multifunctional toxins able to induce a huge variety of therapeutic effects and consequently serve as templates for new drug leads. Hence, the present study was aimed at the synthesis of oligopeptides mimicking regions of the antibacterial Lys49 PLA₂ toxin (CoaTx-II), recently isolated from Crotalus oreganus abyssus snake venom, to identify small peptides able to reproduce the therapeutic action of the toxin. Five peptides, representing major regions of interest within CoaTx-II, were synthesized and screened for their antibacterial properties. The 13-mer peptide pC-CoaTxII, corresponding to residues 115-129 of CoaTx-II, was able to reproduce the promising bactericidal effect of the toxin against multi-resistant clinical isolates. Peptide pC-CoaTxII is mainly composed by positively charged and hydrophobic amino acids, a typical trait in most antimicrobial peptides, and presented no defined secondary structure in aqueous environment. The physicochemical properties of pC-CoaTxII are favorable towards a strong interaction with anionic lipid membranes as those in bacteria. Additional in silico studies suggest formation of a water channel across the membrane upon peptide insertion, eventually leading to bacterial cell disruption and death. Overall, our findings confirm the valuable potential of snake venom toxins towards design and synthesis of novel antimicrobials, thus representing key insights towards development of alternative efficient antimicrobials to fight bacterial resistance to current antibiotics.

Antimicrobial Peptides: Diversity, Mechanism of Action and Strategies to Improve the Activity and Biocompatibility In Vivo

Antibiotic resistance is projected as one of the greatest threats to human health in the future and hence alternatives are being explored to combat resistance. Antimicrobial peptides (AMPs) have shown great promise, because use of AMPs leads bacteria to develop no or low resistance. In this review, we discuss the diversity, history and the various mechanisms of action of AMPs. Although many AMPs have reached clinical trials, to date not many have been approved by the US Food and Drug Administration (FDA) due to issues with toxicity, protease cleavage and short half-life. Some of the recent strategies developed to improve the activity and biocompatibility of AMPs, such as chemical modifications and the use of delivery systems, are also reviewed in this article.

The dinoponeratoxin peptides from the giant ant Dinoponera quadriceps display in vitro antitrypanosomal activity

The crude venom of the giant ant Dinoponera quadriceps is a cocktail of polypeptides and organic compounds that shows antiparasitic effects against Trypanosoma cruzi, the causative agent of Chagas disease. In order to investigate the venom-derived components responsible for such antitrypanosomal activity, four dinoponeratoxins (DnTxs) were identified, namely M-PONTX-Dq3a, -Dq3b, -Dq3c and -Dq4e, that are diverse in size, net charge, hydrophobicity and propensity to interact with eukaryote cell membranes. These peptides were tested against epimastigote, trypomastigote and amastigote forms of benznidazole (Bz)-resistant Y strain of T. cruzi and in mammalian host cells. The M-PONTX-Dq3a and -Dq4e inhibited all developmental forms of T. cruzi, including amastigotes, the responsible form for the maintenance of infection on chronic phase of the disease. The M-PONTX-Dq3a showed the highest selectivity index (SI) (80) and caused morphological alterations in T. cruzi, as observed by scanning electron microscopy (SEM), and induced cell death through necrosis, as seen by multiparametric flow cytometry analysis with specific biochemical markers. Altogether, the D. quadriceps venom appears as a source for the prospection of trypanocidal peptides and the M-PONTX-Dq3a arises as a candidate among the dinoponeratoxin-related peptides in the development of compounds against Chagas disease.

Mechanisms of bacterial membrane permeabilization by crotalicidin (Ctn) and its fragment Ctn(15-34), antimicrobial peptides from rattlesnake venom

Crotalicidin (Ctn), a cathelicidin-related peptide from the venom of a South American rattlesnake, possesses potent antimicrobial, antitumor, and antifungal properties. Previously, we have shown that its C-terminal fragment, Ctn(15-34), retains the antimicrobial and antitumor activities but is less toxic to healthy cells and has improved serum stability. Here, we investigated the mechanisms of action of Ctn and Ctn(15-34) against Gram-negative bacteria. Both peptides were bactericidal, killing ∼90% of Escherichia coli and Pseudomonas aeruginosa cells within 90-120 and 5-30 min, respectively. Studies of ζ potential at the bacterial cell membrane suggested that both peptides accumulate at and neutralize negative charges on the bacterial surface. Flow cytometry experiments confirmed that both peptides permeabilize the bacterial cell membrane but suggested slightly different mechanisms of action. Ctn(15-34) permeabilized the membrane immediately upon addition to the cells, whereas Ctn had a lag phase before inducing membrane damage and exhibited more complex cell-killing activity, probably because of two different modes of membrane permeabilization. Using surface plasmon resonance and leakage assays with model vesicles, we confirmed that Ctn(15-34) binds to and disrupts lipid membranes and also observed that Ctn(15-34) has a preference for vesicles that mimic bacterial or tumor cell membranes. Atomic force microscopy visualized the effect of these peptides on bacterial cells, and confocal microscopy confirmed their localization on the bacterial surface. Our studies shed light onto the antimicrobial mechanisms of Ctn and Ctn(15-34), suggesting Ctn(15-34) as a promising lead for development as an antibacterial/antitumor agent.

Antichagasic effect of crotalicidin, a cathelicidin-like vipericidin, found in Crotalus durissus terrificus rattlesnake's venom gland

Cathelicidins are antimicrobial peptides produced by humans and animals in response to various pathogenic microbes. Crotalicidin (Ctn), a cathelicidin-related vipericidin from the South American Crotalus durissus terrificus rattlesnake's venom gland, and its fragments have demonstrated antimicrobial and antifungal activity, similarly to human cathelicidin LL-37. In order to provide templates for the development of modern trypanocidal agents, the present study evaluated the antichagasic effect of these four peptides (Ctn, Ctn[1-14], Ctn[15-34] and LL-37). Herein, Ctn and short derived peptides were tested against the epimastigote, trypomastigote and amastigote forms of Trypanosoma cruzi Y strain (benznidazole-resistant strain) and cytotoxicity in mammalian cells was evaluated against LLC-MK2 lineage cells. Ctn inhibited all T. cruzi developmental forms, including amastigotes, which is implicated in the burden of infection in the chronic phase of Chagas disease. Moreover, Ctn showed a high selective index against trypomastigote forms (>200). Ctn induced cell death in T. cruzi through necrosis, as determined by flow cytometry analyses with specific molecular probes and morphological alterations, such as loss of membrane integrity and cell shrinkage, as observed through scanning electron microscopy. Overall, Ctn seems to be a promising template for the development of antichagasic agents.