Modes of action of Leishmanicidal antimicrobial peptides

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.

Neglected Zoonotic Diseases: Advances in the Development of Cell-Penetrating and Antimicrobial Peptides against Leishmaniosis and Chagas Disease

In 2020, the WHO established the road map for neglected tropical diseases 2021-2030, which aims to control and eradicate 20 diseases, including leishmaniosis and Chagas disease. In addition, since 2015, the WHO has been developing a Global Action Plan on Antimicrobial Resistance. In this context, the achievement of innovative strategies as an alternative to replace conventional therapies is a first-order socio-sanitary priority, especially regarding endemic zoonoses in poor regions, such as those caused by Trypanosoma cruzi and Leishmania spp. infections. In this scenario, it is worth highlighting a group of natural peptide molecules (AMPs and CPPs) that are promising strategies for improving therapeutic efficacy against these neglected zoonoses, as they avoid the development of toxicity and resistance of conventional treatments. This review presents the novelties of these peptide molecules and their ability to cross a whole system of cell membranes as well as stimulate host immune defenses or even serve as vectors of molecules. The efforts of the biotechnological sector will make it possible to overcome the limitations of antimicrobial peptides through encapsulation and functionalization methods to obtain approval for these treatments to be used in clinical programs for the eradication of leishmaniosis and Chagas disease.

Membrane-acting biomimetic peptoids against visceral leishmaniasis

Visceral leishmaniasis (VL) is among the most neglected tropical diseases in the world. Drug cell permeability is essential for killing the intracellular residing parasites responsible for VL, making cell-permeating peptides a logical choice to address VL. Unfortunately, the limited biological stability of peptides restricts their usage. Sequence-specific oligo-N-substituted glycines ('peptoids') are a class of peptide mimics that offers an excellent alternative to peptides in terms of ease of synthesis and good biostability. We tested peptoids against the parasite Leishmania donovani in both forms, that is, intracellular amastigotes and promastigotes. N-alkyl hydrophobic chain addition (lipidation) and bromination of oligopeptoids yielded compounds with good antileishmanial activity against both forms, showing the promise of these antiparasitic peptoids as potential drug candidates to treat VL.

Biological Functions and Applications of Antimicrobial Peptides

Abstract:

Despite antimicrobial resistance, which is attributed to the misuse of broad-spectrum antibiotics, antibiotics can indiscriminately kill pathogenic and beneficial microorganisms. These events disrupt the delicate microbial balance in both humans and animals, leading to secondary infections and other negative effects. Antimicrobial peptides (AMPs) are functional natural biopolymers in plants and animals. Due to their excellent antimicrobial activities and absence of microbial resistance, AMPs have attracted enormous research attention. We reviewed the antibacterial, antifungal, antiviral, antiparasitic, as well as antitumor properties of AMPs and research progress on AMPs. In addition, we highlighted various recommendations and potential research areas for their progress and challenges in practical applications.

Anti-leishmanial compounds from microbial metabolites: a promising source

Leishmania is a complex disease caused by the protozoan parasites and transmitted by female phlebotomine sandfly. The disease affects some of the poorest people on earth with an estimated 700,000 to 1 million new cases annually. The current treatment for leishmaniasis is toxic, long, and limited, in view of the high resistance rate presented by the parasite, necessitating new perspectives for treatment. The discovery of new compounds with different targets can be a hope to make the treatment more efficient. Microbial metabolites and their structural analogues with enormous scaffold diversity and structural complexity have historically played a key role in drug discovery. We found thirty-nine research articles published between 1999 and 2021 in the scientific database (PubMed, Science Direct) describing microbes and their metabolites with activity against leishmanial parasites which is the focus of this review. KEY POINTS: • Leishmania affects the poorest regions of the globe • Current treatments for leishmaniasis are toxic and of limited efficacy • Microbial metabolites are potential sources of antileishmania drugs.

Dissection of phospholipases A2 reveals multifaceted peptides targeting cancer cells, Leishmania and bacteria

Cationic peptides bio-inspired by natural toxins have been recognized as an efficient strategy for the treatment of different health problems. Due to the specific interaction with substrates from biological membranes, snake venom phospholipases (PLA2s) represent valuable scaffolds for the research and development of short peptides targeting parasites, bacteria, and cancer cells. Considering this, we evaluated the in vitro therapeutic potential of three biomimetic peptides (pCergo, pBmTxJ and pBmje) based on three different amino acid sequences from Asp49 PLA2s. First, short amino acid sequences (12-17 in length) derived from these membranolytic toxins were selected using a combination of bioinformatics tools, including AntiCP, AMPA, PepDraw, ToxinPred, and HemoPI. The peptide, from each polypeptide sequence, with the greatest average antimicrobial index, no toxicity, and no hemolysis predicted was synthesized, purified, and characterized. According to in vitro assays performed, pBmje showed moderate cytotoxicity specifically against MCF-7 (breast cancer cells) with an EC50 of 464.85 µM, whereas pBmTxJ showed an antimicrobial effect against Staphylococcus aureus (ATCC 25923) with an MIC of 37.5 µM, and pCergo against E. coli (ATCC 25922) with an MIC of 75 µM. In addition, pCergo showed antileishmanial activity with an EC50 of 93.69 µM and 110.40 µM against promastigotes of Leishmania braziliensis and L. amazonensis, respectively. Altogether, these results confirmed the versatility of PLA2-derived synthetic peptides, highlighting the relevance of the use of these membrane-interacting toxins as specific archetypes for drug design focused on public health problems.

Current status of nanoscale drug delivery and the future of nano-vaccine development for leishmaniasis - A review

The study of tropical diseases like leishmaniasis, a parasitic disease, has not received much attention even though it is the second-largest infectious disease after malaria. As per the WHO report, a total of 0.7-1.0 million new leishmaniasis cases, which are spread by 23 Leishmania species in more than 98 countries, are estimated with an alarming 26,000-65,000 death toll every year. Lack of potential vaccines along with the cost and toxicity of amphotericin B (AmB), the most common drug for the treatment of leishmaniasis, has raised the interest significantly for new formulations and drug delivery systems including nanoparticle-based delivery as anti-leishmanial agents. The size, shape, and high surface area to volume ratio of different NPs make them ideal for many biological applications. The delivery of drugs through liposome, polymeric, and solid-lipid NPs provides the advantage of high biocomatibilty of the carrier with reduced toxicity. Importantly, NP-based delivery has shown improved efficacy due to targeted delivery of the payload and synergistic action of NP and payload on the target. This review analyses the advantage of NP-based delivery over standard chemotherapy and natural product-based delivery system. The role of different physicochemical properties of a nanoscale delivery system is discussed. Further, different ways of nanoformulation delivery ranging from liposome, niosomes, polymeric, metallic, solid-lipid NPs were updated along with the possible mechanisms of action against the parasite. The status of current nano-vaccines and the future potential of NP-based vaccine are elaborated here.

Cruzioseptins, antibacterial peptides from Cruziohyla calcarifer skin, as promising leishmanicidal agents

Screenings of natural products have significantly contributed to the discovery of novel leishmanicidal agents. In this study, three known cruzioseptins-antibacterial peptides from Cruziohyla calcarifer skin-were synthesized and evaluated against promastigotes and amastigotes stages of Leishmania (L.) amazonensis and L. (V.) braziliensis. EC50 ranged from 9.17 to 74.82 μM, being cruzioseptin-1 the most active and selective compound, with selectivity index > 10 for both promastigotes and amastigotes of L. (V.) braziliensis. In vitro infections incubated with cruzioseptins at 50 μM showed up to ∼86% reduction in the amastigote number. Cruzioseptins were able to destabilize the parasite's cell membrane, allowing the incorporation of a DNA-fluorescent dye. Our data also demonstrated that hydrophobicity and charge appear to be advantageous features for enhancing parasiticidal activity. Antimicrobial cruzioseptins are suitable candidates and alternative molecules that deserve further in vivo investigation focusing on the development of novel antileishmanial therapies.

Small Molecule-Peptide Conjugates as Dimerization Inhibitors of Leishmania infantum Trypanothione Disulfide Reductase

Trypanothione disulfide reductase (TryR) is an essential homodimeric enzyme of trypanosomatid parasites that has been validated as a drug target to fight human infections. Using peptides and peptidomimetics, we previously obtained proof of concept that disrupting protein-protein interactions at the dimer interface of Leishmania infantum TryR (LiTryR) offered an innovative and so far unexploited opportunity for the development of novel antileishmanial agents. Now, we show that linking our previous peptide prototype TRL38 to selected hydrophobic moieties provides a novel series of small-molecule-peptide conjugates that behave as good inhibitors of both LiTryR activity and dimerization.

Peptide-mediated leishmaniasis management strategy: Tachyplesin emerges as an effective anti-leishmanial peptide against Leishmania donovani

Visceral leishmaniasis is one of the neglected tropical diseases caused by an intracellular parasite, Leishmania donovani. Drug resistance, adverse side effects and long treatment regimes are important limitations in achieving the effective elimination of visceral leishmaniasis. In the absence of any vaccine, chemotherapy remains a viable treatment for leishmaniasis. For effective killing of leishmania parasite, the drug molecule needs to cross the cell membrane. In the present study, marine membrane-active peptide Tachyplesin has been used against Leishmania donovani. Further, the mechanism of action and importance of cysteine amino acids of Tachyplesin in anti-leishmanial activity has been assessed. The cargo-carrying ability of Tachyplesin in L. donovani has been established. Thus, dual-use of Tachyplesin as an anti-leishmanial peptide as well as a cargo delivery vehicle makes the marine peptide an attractive therapeutic target against visceral leishmaniasis.

Peptides to Tackle Leishmaniasis: Current Status and Future Directions

Peptide-based drugs are an attractive class of therapeutic agents, recently recognized by the pharmaceutical industry. These molecules are currently being used in the development of innovative therapies for diverse health conditions, including tropical diseases such as leishmaniasis. Despite its socioeconomic influence on public health, leishmaniasis remains long-neglected and categorized as a poverty-related disease, with limited treatment options. Peptides with antileishmanial effects encountered to date are a structurally heterogeneous group, which can be found in different natural sources—amphibians, reptiles, insects, bacteria, marine organisms, mammals, plants, and others—or inspired by natural toxins or proteins. This review details the biochemical and structural characteristics of over one hundred peptides and their potential use as molecular frameworks for the design of antileishmanial drug leads. Additionally, we detail the main chemical modifications or substitutions of amino acid residues carried out in the peptide sequence, and their implications in the development of antileishmanial candidates for clinical trials. Our bibliographic research highlights that the action of leishmanicidal peptides has been evaluated mainly using in vitro assays, with a special emphasis on the promastigote stage. In light of these findings, and considering the advances in the successful application of peptides in leishmaniasis chemotherapy, possible approaches and future directions are discussed here.

In Vitro Modulator Effect of Total Extract from the Endophytic Paenibacillus polymyxa RNC-D in Leishmania (Leishmania) amazonensis and Macrophages

Leishmaniases are diseases with high epidemiological relevance and wide geographical distribution. In Brazil, Leishmania (Leishmania) amazonensis is related to the tegumentary form of leishmaniasis. The treatment for those diseases is problematic as the available drugs promote adverse effects in patients. Therefore, it is important to find new therapeutic targets. In this regard, one alternative is the study of biomolecules produced by endophytic microorganisms. In this study, the total extract produced by the endophytic Paenibacillus polymyxa RNC-D was used to evaluate the leishmanicidal, nitric oxide, and cytokines production using RAW 264.7 macrophages. The results showed that, in the leishmanicidal assay with L. amazonensis, EC50 values at the periods of 24 and 48 hours were 0.624 mg/mL and 0.547 mg/mL, respectively. Furthermore, the cells treated with the extract presented approximately 25% of infected cells with an average of 3 amastigotes/cell in the periods of 24 and 48 hours. Regarding the production of cytokines in RAW 264.7 macrophages infected/treated with the extract, a significant increase in TNF-α was observed at the periods of 24 and 48 hours in the treated cells. The concentrations of IFN-γ and IL-12 showed significant increase in 48 hours. A significant decrease in IL-4 was observed in all cells treated with the extract in 24 hours. It was observed in the treated cells that the NO production by RAW 264.7 macrophages increased between 48 and 72 hours. The endophytic Paenibacillus polymyxa RNC-D extract modulates the mediators of inflammation produced by RAW 264.7 macrophages promoting L. amazonensis death. The immunomodulatory effects might be a promising target to develop new immunotherapeutic and antileishmanial drugs.

Potential use of 13-mer peptides based on phospholipase and oligoarginine as leishmanicidal agents

Phospholipase A₂ toxins present in snake venoms interact with biological membranes and serve as structural models for the design of small peptides with anticancer, antibacterial and antiparasitic properties. Oligoarginine peptides are capable of increasing cell membrane permeability (cell penetrating peptides), and for this reason are interesting delivery systems for compounds of pharmacological interest. Inspired by these two families of bioactive molecules, we have synthesized two 13-mer peptides as potential antileishmanial leads gaining insights into structural features useful for the future design of more potent peptides. The peptides included p-Acl, reproducing a natural segment of a Lys49 PLA₂ from Agkistrodon contortrix laticinctus snake venom, and its p-AclR7 analogue where all seven lysine residues were replaced by arginines. Both peptides were active against promastigote and amastigote forms of Leishmania (L.) amazonensis and L. (L.) infantum, while displaying low cytotoxicity for primary murine macrophages. Spectrofluorimetric studies suggest that permeabilization of the parasite's cell membrane is the probable mechanism of action of these biomolecules. Relevantly, the engineered peptide p-AclR7 was more active in both life stages of Leishmania and induced higher rates of ethidium bromide incorporation than its native template p-Acl. Taken together, the results suggest that short peptides based on phospholipase toxins are potential scaffolds for development of antileishmanial candidates. Moreover, specific amino acid substitutions, such those herein employed, may enhance the antiparasitic action of these cationic peptides, encouraging their future biomedical applications.

Natural Occurrence in Venomous Arthropods of Antimicrobial Peptides Active against Protozoan Parasites

Arthropoda is a phylum of invertebrates that has undergone remarkable evolutionary radiation, with a wide range of venomous animals. Arthropod venom is a complex mixture of molecules and a source of new compounds, including antimicrobial peptides (AMPs). Most AMPs affect membrane integrity and produce lethal pores in microorganisms, including protozoan pathogens, whereas others act on internal targets or by modulation of the host immune system. Protozoan parasites cause some serious life-threatening diseases among millions of people worldwide, mostly affecting the poorest in developing tropical regions. Humans can be infected with protozoan parasites belonging to the genera Trypanosoma, Leishmania, Plasmodium, and Toxoplasma, responsible for Chagas disease, human African trypanosomiasis, leishmaniasis, malaria, and toxoplasmosis. There is not yet any cure or vaccine for these illnesses, and the current antiprotozoal chemotherapeutic compounds are inefficient and toxic and have been in clinical use for decades, which increases drug resistance. In this review, we will present an overview of AMPs, the diverse modes of action of AMPs on protozoan targets, and the prospection of novel AMPs isolated from venomous arthropods with the potential to become novel clinical agents to treat protozoan-borne diseases.

A Comparative Study on Interactions of Antimicrobial Peptides L- and D-phenylseptin with 1,2-dimyristoyl-sn-glycero-3-phosphocholine

L-phenylseptin (L-Phes) and D-phenylseptin (D-Phes) are amphibian antimicrobial peptides isolated from the skin secretion of Hypsiboas punctatus. In the N-termini, L-Phes and D-Phes contain three consecutive phenylalanine residues, l-Phe-l-Phe-l-Phe and l-Phe-d-Phe-l-Phe, respectively. They are known to exhibit antimicrobial activity against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Xanthomonas axonopodis pv. Glycines. However, their mechanism of action and the role of the D-amino acid residue have not been elucidated yet. In this study, the interactions of both peptides with 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) were investigated by means of quartz crystal microbalance, circular dichroism, vibrational circular dichroism, 31P solid-state NMR, and molecular dynamics simulation. Both peptides have similar binding constants to the DMPC lipid bilayers, in the order of 106 M−1, and form an α-helix structure in the DMPC lipid bilayers. Both the peptides induce similar changes in the dynamics of DMPC lipids. Thus, in spite of the difference in the conformations caused by the chirality at the N-terminus, the peptides showed similar behavior in the membrane-bound state, experimentally and computationally.

Co-delivery of buparvaquone and polymyxin B in a nanostructured lipid carrier for leishmaniasis treatment

OBJECTIVES

This study aimed to describe the preparation and in vitro evaluation of a surface-modified nanostructured lipid carrier (NLC) using chitosan and dextran for co-delivery of buparvaquone (BPQ) and polymyxin B (PB) against leishmaniasis.

METHODS

The NLC was prepared using high-pressure homogenisation. Polymyxin B binding and surface modification with biopolymers were achieved by electrostatic interaction. In vitro cytotoxicity was assessed in mouse peritoneal macrophages, and leishmanicidal activity in amastigotes of Leishmania infantum.

RESULTS

The performance attributes of BPQ-NLC, BPQ-NLC-PB[A^-] (anionic) and BPQ-NLC-PB[C⁺] (cationic) were respectively: Z-average 173.9 ± 1.6, 183.8 ± 4.5 and 208.8 ± 2.6 nm; zeta potential -19.6 ± 1.5, -20.1 ± 1.1 and 31.1 ± 0.8 mV; CC₅₀ 583.4 ± 0.10, 203.1 ± 0.04 and 5.7 ± 0.06 μM; IC₅₀ 229.0 ± 0.04, 145.7 ± 0.04 and 150.5 ± 0.02 nM. The NLC in vitro leishmanicidal activity showed up to 3.1-fold increase when compared with free BPQ (P <  0.05, α = 0.05).

CONCLUSIONS

The developed NLC proved to be a promising formulation with which to overcome the drawbacks of current leishmaniasis treatment by the co-delivery of two alternative drugs and a macrophage targeting modified surface.

Prospects for antimicrobial peptide-based immunotherapy approaches in Leishmania control

INTRODUCTION

Leishmaniasis is one of the neglected tropical diseases and is highly endemic in many countries. Currently, there is no adequate human vaccine and treatment to control the disease. Areas covered: As a result of the failure of chemotherapy and toxicity, it is necessary to find another approach for the treatment of leishmaniasis. Recently, antimicrobial peptides (AMPs), originating from natural resources, have attracted much attention for their use as a new antibiotics for many infectious and noninfectious diseases. Natural AMPs are named interchangeably as host defense peptides. They are naturally active in the innate immune system as a primary defense mechanism in most species all over the world. Several AMPs have been tested in in vitro and in vivo experiments against leishmaniasis. Expert commentary: Most AMPs require proper conformation to be active. Leishmania (L.) tarentolae as a nonpathogenic strain, is an effective tool not only for vaccine development but also for therapy. Recombinant L. tarentolae expressing selective or combined AMPs is a suggestive approach for leishmaniasis or any other infectious disease treatment.

Nanosilver: new ageless and versatile biomedical therapeutic scaffold

Silver nanotechnology has received tremendous attention in recent years, owing to its wide range of applications in various fields and its intrinsic therapeutic properties. In this review, an attempt is made to critically evaluate the chemical, physical, and biological synthesis of silver nanoparticles (AgNPs) as well as their efficacy in the field of theranostics including microbiology and parasitology. Moreover, an outlook is also provided regarding the performance of AgNPs against different biological systems such as bacteria, fungi, viruses, and parasites (leishmanial and malarial parasites) in curing certain fatal human diseases, with a special focus on cancer. The mechanism of action of AgNPs in different biological systems still remains enigmatic. Here, due to limited available literature, we only focused on AgNPs mechanism in biological systems including human (wound healing and apoptosis), bacteria, and viruses which may open new windows for future research to ensure the versatile application of AgNPs in cosmetics, electronics, and medical fields.

The role of d-allo-isoleucine in the deposition of the anti-Leishmania peptide bombinin H4 as revealed by 31P solid-state NMR, VCD spectroscopy, and MD simulation

Bombinin H4 is an antimicrobial peptide that was isolated from the toad Bombina variegata. Bombinin H family peptides are active against gram-positive, gram-negative bacteria, and fungi as well as the parasite Leishmania. Among them, bombinin H4 (H4), which contains d-allo-isoleucine (d-allo-Ile) as the second residue in its sequence, is the most active, and its l-isomer is bombinin H2 (H2). H4 has a significantly lower LC50 than H2 against Leishmania. However, the atomic-level mechanism of the membrane interaction and higher activity of H4 has not been clarified. In this work, we investigated the behavior of the conformations and interactions of H2 and H4 with the Leishmania membrane using ³¹P solid-state nuclear magnetic resonance (NMR), vibrational circular dichroism (VCD) spectroscopy, and molecular dynamics (MD) simulations. The generation of isotropic ³¹P NMR signals depending on the peptide concentration indicated the abilities of H2 and H4 to exert antimicrobial activity via membrane disruption. The VCD experiment and density functional theory calculation confirmed the different stability and conformations of the N-termini of H2 and H4. MD simulations revealed that the N-terminus of H4 is more stable than that of H2 in the membrane, in line with the VCD experiment data. VCD and MD analyses demonstrated that the first l-Ile and second d-allo-Ile of H4 tend to take a cis conformation. These residues function as an anchor and facilitate the easy winding of the helical conformation of H4 in the membrane. It may assist to quickly reach to the threshold concentration of H4 on the Leishmania membrane. This article is part of a Special Issue entitled: d-Amino acids: biology in the mirror, edited by Dr. Loredano Pollegioni, Dr. Jean-Pierre Mothet and Dr. Molla Gianluca.

Perspectives on the evolutionary ecology of arthropod antimicrobial peptides

Antimicrobial peptides (AMPs) are important elements of the innate immune defence in multicellular organisms that target and kill microbes. Here, we reflect on the various points that are raised by the authors of the 11 contributions to a special issue of Philosophical Transactions on the 'evolutionary ecology of arthropod antimicrobial peptides'. We see five interesting topics emerging. (i) AMP genes in insects, and perhaps in arthropods more generally, evolve much slower than most other immune genes. One explanation refers to the constraints set by AMPs being part of a finely tuned defence system. A new view argues that AMPs are under strong stabilizing selection. Regardless, this striking observation still invites many more questions than have been answered so far. (ii) AMPs almost always are expressed in combinations and sometimes show expression patterns that are dependent on the infectious agent. While it is often assumed that this can be explained by synergistic interactions, such interactions have rarely been demonstrated and need to be studied further. Moreover, how to define synergy in the first place remains difficult and needs to be addressed. (iii) AMPs play a very important role in mediating the interaction between a host and its mutualistic or commensal microbes. This has only been studied in a very small number of (insect) species. It has become clear that the very same AMPs play different roles in different situations and hence are under concurrent selection. (iv) Different environments shape the physiology of organisms; especially the host-associated microbial communities should impact on the evolution host AMPs. Studies in social insects and some organisms from extreme environments seem to support this notion, but, overall, the evidence for adaptation of AMPs to a given environment is scant. (v) AMPs are considered or already developed as new drugs in medicine. However, bacteria can evolve resistance to AMPs. Therefore, in the light of our limited understanding of AMP evolution in the natural context, and also the very limited understanding of the evolution of resistance against AMPs in bacteria in particular, caution is recommended. What is clear though is that study of the ecology and evolution of AMPs in natural systems could inform many of these outstanding questions, including those related to medical applications and pathogen control.This article is part of the themed issue 'Evolutionary ecology of arthropod antimicrobial peptides'.

Nanostructured delivery systems with improved leishmanicidal activity: a critical review

Leishmaniasis is a vector-borne zoonotic disease caused by protozoan parasites of the genus Leishmania, which are responsible for numerous clinical manifestations, such as cutaneous, visceral, and mucocutaneous leishmaniasis, depending on the site of infection for particular species. These complexities threaten 350 million people in 98 countries worldwide. Amastigotes living within macrophage phagolysosomes are the principal target of antileishmanial treatment, but these are not an easy target as drugs must overcome major structural barriers. Furthermore, limitations on current therapy are related to efficacy, toxicity, and cost, as well as the length of treatment, which can increase parasitic resistance. Nanotechnology has emerged as an attractive alternative as conventional drugs delivered by nanosized carriers have improved bioavailability and reduced toxicity, together with other characteristics that help to relieve the burden of this disease. The significance of using colloidal carriers loaded with active agents derives from the physiological uptake route of intravenous administered nanosystems (the phagocyte system). Nanosystems are thus able to promote a high drug concentration in intracellular mononuclear phagocyte system (MPS)-infected cells. Moreover, the versatility of nanometric drug delivery systems for the deliberate transport of a range of molecules plays a pivotal role in the design of therapeutic strategies against leishmaniasis. This review discusses studies on nanocarriers that have greatly contributed to improving the efficacy of antileishmaniasis drugs, presenting a critical review and some suggestions for improving drug delivery.

Melittin-Induced Lipid Extraction Modulated by the Methylation Level of Phosphatidylcholine Headgroups

Protein- and peptide-induced lipid extraction from membranes is a critical process for many biological events, including reverse cholesterol transport and sperm capacitation. In this work, we examine whether such processes could display specificity for some lipid species. Melittin, the main component of dry bee venom, was used as a model amphipathic α-helical peptide. We specifically determined the modulation of melittin-induced lipid extraction from membranes by the change of the methylation level of phospholipid headgroups. Phosphatidylcholine (PC) bilayers were demethylated either by substitution with phosphatidylethanolamine (PE) or chemically by using mono- and dimethylated PE. It is shown that demethylation reduces the association of melittin with membranes, likely because of the resulting tighter chain packing of the phospholipids, which reduces the capacity of the membranes to accommodate inserted melittin. This reduced binding of the peptide is accompanied by an inhibition of the lipid extraction caused by melittin. We demonstrate that melittin selectively extracts PC from PC/PE membranes. This selectivity is proposed to be a consequence of a PE depletion in the surroundings of bound melittin to minimize disruption of the interphospholipid interactions. The resulting PC-enriched vicinity of melittin would be responsible for the observed formation of PC-enriched lipid/peptide particles resulting from the lipid efflux. These findings reveal that modulating the methylation level of phospholipid headgroups is a simple way to control the specificity of lipid extraction from membranes by peptides/proteins and thereby modulate the lipid composition of the membranes.

Insect antimicrobial peptides act synergistically to inhibit a trypanosome parasite

The innate immune system provides protection from infection by producing essential effector molecules, such as antimicrobial peptides (AMPs) that possess broad-spectrum activity. This is also the case for bumblebees, Bombus terrestris, when infected by the trypanosome, Crithidia bombi Furthermore, the expressed mixture of AMPs varies with host genetic background and infecting parasite strain (genotype). Here, we used the fact that clones of C. bombi can be cultivated and kept as strains in medium to test the effect of various combinations of AMPs on the growth rate of the parasite. In particular, we used pairwise combinations and a range of physiological concentrations of three AMPs, namely Abaecin, Defensin and Hymenoptaecin, synthetized from the respective genomic sequences. We found that these AMPs indeed suppress the growth of eight different strains of C. bombi, and that combinations of AMPs were typically more effective than the use of a single AMP alone. Furthermore, the most effective combinations were rarely those consisting of maximum concentrations. In addition, the AMP combination treatments revealed parasite strain specificity, such that strains varied in their sensitivity towards the same mixtures. Hence, variable expression of AMPs could be an alternative strategy to combat highly variable infections.This article is part of the themed issue 'Evolutionary ecology of arthropod antimicrobial peptides'.

Role of the Cationic C-Terminal Segment of Melittin on Membrane Fragmentation

The widespread distribution of cationic antimicrobial peptides capable of membrane fragmentation in nature underlines their importance to living organisms. In the present work, we determined the impact of the electrostatic interactions associated with the cationic C-terminal segment of melittin, a 26-amino acid peptide from bee venom (net charge +6), on its binding to model membranes and on the resulting fragmentation. In order to detail the role played by the C-terminal charges, we prepared a melittin analogue for which the four cationic amino acids in positions 21-24 were substituted with the polar residue citrulline, providing a peptide with the same length and amphiphilicity but with a lower net charge (+2). We compared the peptide bilayer affinity and the membrane fragmentation for bilayers prepared from 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC)/1,2-dipalmitoyl-sn-glycero-3-phospho-l-serine (DPPS) mixtures. It is shown that neutralization of the C-terminal considerably increased melittin affinity for zwitterionic membranes. The unfavorable contribution associated with transferring the cationic C-terminal in a less polar environment was reduced, leaving the hydrophobic interactions, which drive the peptide insertion in bilayers, with limited counterbalancing interactions. The presence of negatively charged lipids (DPPS) in bilayers increased melittin binding by introducing attractive electrostatic interactions, the augmentation being, as expected, greater for native melittin than for its citrullinated analogue. The membrane fragmentation power of the peptide was shown to be controlled by electrostatic interactions and could be modulated by the charge carried by both the membrane and the lytic peptide. The analysis of the lipid composition of the extracted fragments from DPPC/DPPS bilayers revealed no lipid specificity. It is proposed that extended phase separations are more susceptible to lead to the extraction of a lipid species in a specific manner than a specific lipid-peptide affinity. The present work on the lipid extraction by melittin and citrullinated melittin with model membranes emphasizes the complex relation between the affinity, the lipid extraction/membrane fragmentation, and the lipid specificity.

Identification of Synthetic and Natural Host Defense Peptides with Leishmanicidal Activity

Leishmaniaparasites are a major public health problem worldwide. Effective treatment of leishmaniasis is hampered by the high incidence of adverse effects to traditional drug therapy and the emergence of resistance to current therapeutics. A vaccine is currently not available. Host defense peptides have been investigated as novel therapeutic agents against a wide range of pathogens. Here we demonstrate that the antimicrobial peptide LL-37 and the three synthetic peptides E6, L-1018, and RI-1018 exhibit leishmanicidal activity against promastigotes and intramacrophage amastigotes ofLeishmania donovaniandLeishmania major We also report that theLeishmaniaprotease/virulence factor GP63 confers protection toLeishmaniafrom the cytolytic properties of alll-form peptides (E6, L-1018, and LL-37) but not thed-form peptide RI-1018. The results suggest that RI-1018, E6, and LL-37 are promising peptides to develop further into components for antileishmanial therapy.

Attenuated Leishmania induce pro-inflammatory mediators and influence leishmanicidal activity by p38 MAPK dependent phagosome maturation in Leishmania donovani co-infected macrophages

Promastigote form of Leishmania, an intracellular pathogen, delays phagosome maturation and resides inside macrophages. But till date limited study has been done to manipulate the phagosomal machinery of macrophages to restrict Leishmania growth. Attenuated Leishmania strain exposed RAW 264.7 cells showed a respiratory burst and enhanced production of pro-inflammatory mediators. The augmentation of pro-inflammatory activity is mostly attributed to p38 MAPK and p44/42 MAPK. In our study, these activated macrophages are found to induce phagosome maturation when infected with pathogenic Leishmania donovani. Increased co-localization of carboxyfluorescein succinimidyl ester labeled pathogenic L. donovani with Lysosome was found. Moreover, increased co-localization was observed between pathogenic L. donovani and late phagosomal markers viz. Rab7, Lysosomal Associated Membrane Protein 1, Cathepsin D, Rab9, and V-ATPase which indicate phagosome maturation. It was also observed that inhibition of V-type ATPase caused significant hindrance in attenuated Leishmania induced phagosome maturation. Finally, it was confirmed that p38 MAPK is the key player in acidification and maturation of phagosome in attenuated Leishmania strain pre-exposed macrophages. To our knowledge, this study for the first time reported an approach to induce phagosome maturation in L. donovani infected macrophages which could potentiate short-term prophylactic response in future.

Anti-parasitic Peptides from Arthropods and their Application in Drug Therapy

Africa, Asia, and Latin America are regions highly affected by endemic diseases, such as Leishmaniasis, Malaria, and Chagas' disease. They are responsible for the death of 1000s of patients every year, as there is not yet a cure for them and the drugs used are inefficient against the pathogenic parasites. During the life cycle of some parasitic protozoa, insects become the most important host and disseminator of the diseases triggered by these microorganisms. As infected insects do not develop nocive symptoms, they can carry the parasites for long time inside their body, enabling their multiplication and life cycle completion. Eventually, parasites infect human beings after insect's transmission through their saliva and/or feces. Hence, host insects and general arthropods, which developed a way to coexist with such parasites, are a promising source for the prospection of anti-parasitic compounds, as alternative methods for the treatment of protozoa-related diseases. Among the molecules already isolated and investigated, there are proteins and peptides with high activity against parasites, able to inhibit parasite activity in different stages of development. Although, studies are still taking their first steps, initial results show new perspectives on the treatment of parasitic diseases. Therefore, in this report, we describe about peptides from host insect sources with activity against the three most endemic parasites: Leishmania sp., Plasmodium sp., and Trypanosomes. Moreover, we discuss the future application insect peptides as anti-parasitic drugs and the use of non-hosts insect transcriptomes on the prospection of novel molecules for the treatment of parasitic neglected diseases.

Design of protease-resistant pexiganan enhances antileishmanial activity

Antimicrobial peptides are increasingly being explored as alternative agents for therapy against the parasitic protozoan Leishmania. Previously, we reported that the synthetic magainin analog, pexiganan, induced apoptosis of surface protease-deficient Leishmania. Here, we report the development of an arginine-rich variant of this peptide which has reduced protease susceptibility and enhanced activity against wild type Leishmania in vitro. This peptide induces calcium delocalization and caspase 3/7 activity indicative of apoptosis, demonstrating that structural modification of pexiganan leads to drastic changes in biologic activity against Leishmania.

Synthesis, leishmanicidal activity and theoretical evaluations of a series of substituted bis-2-hydroxy-1,4-naphthoquinones

A series of eight substituted bis-2-hydroxy-1,4-naphthoquinone derivatives was synthesized through lawsone condensation with various aromatic and aliphatic aldehydes under mild acidic conditions. The title compounds were evaluated for antileishmanial activity in vitro against Leishmania amazonensis and Leishmania braziliensis promastigotes; six compounds showed good activity without significant toxic effects. The compound with the highest activity was used for an in vivo assay with Leishmania amazonensis.

Oral azithromycin versus its combination with miltefosine for the treatment of experimental Old World cutaneous leishmaniasis

Leishmaniasis is one of the neglected infectious diseases included in the World Health Organization's list of the top guns of antimicrobial resistance. Miltefosine is the first and the only available oral effective therapy for leishmaniasis. For fear of its potential resistance, identification of alternative, effective and safe drugs is urgently needed. Therefore, in view of azithromycin promising activity against a number of Leishmania species, this work was carried out to evaluate the efficacy of oral azithromycin alone versus its combination with miltefosine against experimental Old World Cutaneous leishmaniasis thus, can provide another alternative oral therapy or for the first time an oral combination therapy for leishmaniasis. The experiment were carried out on Swiss strain albino mice which were treated either with miltefosine for 20 days, Azithromycin for 20 days or both drugs in combination therapy for shorter duration of 10 days. Efficacy of azithromycin mono and combination therapy with miltefosine was evaluated clinically, parasitologically and by examination of the cutaneous lesions by Transmission Electron Microscopy. The current work demonstrated superior activity of oral azithromycin over oral miltefosine in the treatment of experimentally infected mice with Leishmania major (MHOM/IL/81/FEBNI). Unfortunately, oral combination therapy of azithromycin and miltefosine for short duration though, induced dramatic clinical improvement yet, relapse rapidly developed after cessation of therapy. Oral azithromycin could be a promising oral antileishmanial agent. Further research is recommended to investigate its leishmanicidal activity against other Leishmania species thus; another alternative oral therapy for leishmaniasis can be rapidly available.

Antiparasitic activity and effect of casearins isolated from Casearia sylvestris on Leishmania and Trypanosoma cruzi plasma membrane

Leishmaniasis and Chagas disease are infectious diseases caused by parasite Leishmania sp. and Trypanosoma cruzi, respectively, and are included among the most neglected diseases in several underdeveloped and developing countries, with an urgent demand for new drugs. Considering the antiparasitic potential of MeOH extract from leaves of Casearia sylvestris Sw. (Salicaceae), a bioguided fractionation was conducted and afforded four active clerodane diterpenes (casearins A, B, G, and J). The obtained results indicated a superior efficacy of tested casearins against trypomastigotes of T. cruzi, with IC50 values ranging from 0.53 to 2.77 μg/ml. Leishmania infantum promastigotes were also susceptible to casearins, with IC50 values in a range between 4.45 and 9.48 μg/ml. These substances were also evaluated for mammalian cytotoxicity against NCTC cells resulting in 50% cytotoxic concentrations (CC50) ranging from 1.46 to 13.76 μg/ml. Additionally, the action of casearins on parasite membranes was investigated using the fluorescent probe SYTOX Green. The obtained results demonstrated a strong interaction of casearins A and B to the plasma membrane of T. cruzi parasites, corroborating their higher efficacy against these parasites. In contrast, the tested casearins induced no alteration in the permeability of plasma membrane of Leishmania parasites, suggesting that biochemical differences between Leishmania and T. cruzi plasma membrane might have contributed to the target effect of casearins on trypomastigotes. Thus, considering the importance of studying novel and selective drug candidates against protozoans, casearins A, B, G, and J could be used as tools to future drug design studies.

Nanoparticles as multifunctional devices for the topical treatment of cutaneous leishmaniasis

INTRODUCTION

Cutaneous and mucocutaneous leishmaniasis are major tropical skin diseases. Topical treatment is currently limited to the least severe forms of cutaneous leishmaniasis (CL) without risk of dissemination. It is also recommended in combination with systemic therapy for more severe forms. Progresses in this modality of treatment are hindered by the heterogeneity of the disease and shortcomings in the clinical trials.

AREAS COVERED

This review overlooks three major modalities of topical therapies in use or under investigation against CL: chemotherapy, photodynamic therapy and immunotherapy; either with older compounds such as paramomycin or more recent nitric oxide donors, antimicrobial peptides or silver derivatives. The advantages and limitations of their administration with newer formulation strategies such as nanoparticles (NPs) are discussed.

EXPERT OPINION

The efficacy of a topical treatment against CL depends not only on the intrinsic antileishmanial activity of the drug but also on the amount of drug available in the dermis. NPs as sustained release systems and permeation enhancers could favour the creation of a drug reservoir in the dermis. Additionally, certain NPs have immunomodulatory properties or wound healing capabilities of benefit in CL treatment. Pending task is the selective delivery of active compounds to intracellular amastigotes, because even small NPs are unable to penetrate deeply into the skin to encounter infected macrophages (except in ulcerative lesions).

Broad-spectrum bioactivities of silver nanoparticles: the emerging trends and future prospects

There are alarming reports of growing microbial resistance to all classes of antimicrobial agents used against different infections. Also the existing classes of anticancer drugs used against different tumours warrant the urgent search for more effective alternative agents for treatment. Broad-spectrum bioactivities of silver nanoparticles indicate their potential to solve many microbial resistance problems up to a certain extent. The antibacterial, antifungal, antiviral, antiprotozoal, acaricidal, larvicidal, lousicidal and anticancer activities of silver nanoparticles have recently attracted the attention of scientists all over the world. The aim of the present review is to discuss broad-spectrum multifunctional activities of silver nanoparticles and stress their therapeutic potential as smart nanomedicine. Much emphasis has been dedicated to the antimicrobial and anticancer potential of silver nanoparticles showing their promising characteristics for treatment, prophylaxis and control of infections, as well as for diagnosis and treatment of different cancer types.

Spinigerin induces apoptotic like cell death in a caspase independent manner in Leishmania donovani

Antimicrobial peptides (AMPs) are multifunctional components of the innate immune system. Chemotherapeutic agents used for treatment of visceral leishmaniasis (VL) are now threatened due to the emergence of acquired drug resistance and toxicity. AMPs are attractive alternative to conventional pharmaceuticals. In this study, first time we explored the antileishmanial activity of spinigerin originally derived from Pseudacanthotermes spiniger. Leishmania donovani promastigotes present apoptosis-like cell death upon exposure to spinigerin (IC50, 150 μM). The infection rate was reduced by 20% upon exposure to 150 μM spinigerin but no cytotoxicity on host macrophages was observed. Elevation of intracellular ROS level and down-regulation of two ROS detoxifying enzymes, ascorbate peroxidase (APx) and trypanothione reductase (TR) suggested essential role of ROS machinery during spinigerin mediated cell death. About 97% cell population was found to be Annexin-V positive; 44% cells being highly Annexin-V positive. Moreover, we observed morphological changes like cell rounding, nuclear condensation, oligonucleosomal DNA degradation and TUNEL positive cells without loss of membrane integrity upon spinigerin exposure, suggests apoptosis-like death. Interestingly, collapse in mitochondrial membrane potential and increased level of intracellular ROS and calcium were not associated with caspase like activity. Computational analysis suggests spiningerin interacts with trypanothione reductase and thus probably interferes its function to detoxify the toxic ROS level. Therefore, spinigerin induces apoptosis-like cell death in L. donovani in a caspase-independent manner. The study elucidates the antileishmanial property of spinigerin that may be considered for future chemotherapeutic option alone or adjunct with other drug regimens for improved treatment of visceral leishmaniasis.