Safety and efficacy of antimicrobial peptides against naturally acquired leishmaniasis

Compounds with potentialities as novel chemotherapeutic agents in leishmaniasis at preclinical level

Leishmaniasis are neglected infectious diseases caused by kinetoplastid protozoan parasites from the genus Leishmania. These sicknesses are present mainly in tropical regions and almost 1 million new cases are reported each year. The absence of vaccines, as well as the high cost, toxicity or resistance to the current drugs determines the necessity of new treatments against these pathologies. In this review, several compounds with potentialities as new antileishmanial drugs are presented. The discussion is restricted to the preclinical level and molecules are organized according to their chemical nature, source and molecular targets. In this manner, we present antimicrobial peptides, flavonoids, withanolides, 8-aminoquinolines, compounds from Leish-Box, pyrazolopyrimidines, and inhibitors of tubulin polymerization/depolymerization, topoisomerase IB, proteases, pteridine reductase, N-myristoyltransferase, as well as enzymes involved in polyamine metabolism, response against oxidative stress, signaling pathways, and sterol biosynthesis. This work is a contribution to the general knowledge of these compounds as antileishmanial agents.

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.

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.

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.

Chlorin, Phthalocyanine, and Porphyrin Types Derivatives in Phototreatment of Cutaneous Manifestations: A Review

Recent scientific research has shown the use of chlorin, phthalocyanines, and porphyrins derivatives as photosensitizers in photodynamic therapy in the treatment of various pathologies, including some of the major skin diseases. Thus, the main goal of this critical review is to catalog the papers that used these photosensitizers in the treatment of acne vulgaris, psoriasis, papillomavirus infections, cutaneous leishmaniasis, and skin rejuvenation, and to explore the photodynamic therapy mechanisms against these conditions alongside their clinical benefits.

Efflux pumps and antimicrobial resistance: Paradoxical components in systems genomics

Efflux pumps play a major role in the increasing antimicrobial resistance rendering a large number of drugs of no use. Large numbers of pathogens are becoming multidrug resistant due to inadequate dosage and use of the existing antimicrobials. This leads to the need for identifying new efflux pump inhibitors. Design of novel targeted therapies using inherent complexity involved in the biological network modeling has gained increasing importance in recent times. The predictive approaches should be used to determine antimicrobial activities with high pathogen specificity and microbicidal potency. Antimicrobial peptides, which are part of our innate immune system, have the ability to respond to infections and have gained much attention in making resistant strain sensitive to existing drugs. In this review paper, we outline evidences linking host-directed therapy with the efflux pump activity to infectious disease.

Control of Citrus Post-harvest Green Molds, Blue Molds, and Sour Rot by the Cecropin A-Melittin Hybrid Peptide BP21

In this study, the activity of the cecropin A-melittin hybrid peptide BP21 (Ac-FKLFKKILKVL-NH₂) in controlling of citrus post-harvest green and blue molds and sour rot and its involved mechanism was studied. The minimum inhibitory concentrations of BP21 against Penicillium digitatum, Penicillium italicum, and Geotrichum candidum were 8, 8, and 4 μmol L^-1, respectively. BP21 could inhibit the growth of mycelia, the scanning electron microscopy results clearly showed that the mycelia treated with BP21 shrank, formed a rough surface, became distorted and collapsed. Fluorescent staining with SYTOX Green (SG) indicated that BP21 could disintegrate membranes. Membrane permeability parameters, including extracellular conductivity, the leakage of potassium ions, and the release of cellular constituents, visibly increased as the BP21 concentration increased. Gross and irreversible damage to the cytoplasm and membranes was observed. There was a positive correlation between hemolytic activity and the concentration of BP21. These results suggest peptide BP21 could be used to control citrus post-harvest diseases.

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.

Emerging therapeutic targets for treatment of leishmaniasis

INTRODUCTION

Parasitic diseases that pose a threat to human life include leishmaniasis - caused by protozoan parasite Leishmania species. Existing drugs have limitations due to deleterious side effects like teratogenicity, high cost and drug resistance. This calls for the need to have an insight into therapeutic aspects of disease. Areas covered: We have identified different drug targets via. molecular, imuunological, metabolic as well as by system biology approaches. We bring these promising drug targets into light so that they can be explored to their maximum. In an effort to bridge the gaps between existing knowledge and prospects of drug discovery, we have compiled interesting studies on drug targets, thereby paving the way for establishment of better therapeutic aspects. Expert opinion: Advancements in technology shed light on many unexplored pathways. Further probing of well established pathways led to the discovery of new drug targets. This review is a comprehensive report on current and emerging drug targets, with emphasis on several metabolic targets, organellar biochemistry, salvage pathways, epigenetics, kinome and more. Identification of new targets can contribute significantly towards strengthening the pipeline for disease elimination.

Current status on prevention and treatment of canine leishmaniasis

Canine leishmaniasis (CanL) is a parasite-borne disease mainly induced by Leishmania infantum in the Old World and Leishmania chagasi (infantum) in the New World. CanL is a zoonosis transmitted by the bite of infected Phlebotominae flies that act as vectors. CanL is a very serious disease that usually produces death when remains untreated and can be a focus of transmission to other dogs or humans. Infected dogs and other domestic and wild animals act as reservoirs and are a real threat to uninfected/healthy dogs and humans in endemic areas where the sand flies are present. Prevention of new infections in dogs can help to stop the current increase of the disease in humans, reinforcing the concept of "One Health" approach. The management of CanL is being performed using prophylactic measures in healthy dogs - insecticides impregnated in collars or immunostimulants applied by spot-on devices - and chemotherapy in animals that suffer from the disease. Antimonials as first-line monotherapy have proven efficacy in reducing most of the clinical signs of CanL, but they need to be administered during several days, and no complete parasite clearance is achieved, favouring the presence of relapses among treated dogs. Therefore, new drugs, such as miltefosine, or combinations of this drug or antimonials with allopurinol are in the pipeline of clinical treatment of CanL. Recently, there has been an emergence of protective - prophylactic - and curative - autogenous vaccines - immunotherapy tools to face CanL, whose results are still under study. This review highlights the current use of preventive and eradicative weapons to fight against this disease, which is a scourge for dogs and a continuous threat to human beings.

Antiparasitic peptides

: The most important parasitic diseases, malaria, leishmaniasis, trypanosomiasis, and schistosomiasis, are a great burden to mankind, threatening the life of millions of people worldwide and mostly affecting the poorest. Because drug resistance is increasing and vaccines are rarely available, novel chemotherapeutic compounds are necessary in order to treat these devastating diseases. Insects serve as vectors of many human parasitic diseases and have been shown to express a huge variety of antimicrobial peptides (AMPs). Therefore, research activity on insect-derived AMPs has been increasing in the last 40 years. This chapter summarizes the current state of research on the possible role of AMPs as potential chemotherapeutic compounds against human parasitic diseases. As a representative antimicrobial peptide with antiparasitic activity, the structure of insect defensin A is shown [PDB accession code: 1ICA]. The molecule is surrounded by schematic representations of the human pathogenic parasites Plasmodium, Leishmania and Trypanosoma.

Killing of Trypanozoon Parasites by the Equine Cathelicidin eCATH1

Trypanozoon parasites infect both humans, causing sleeping sickness, and animals, causing nagana, surra, and dourine. Control of nagana and surra depends to a great extent on chemotherapy. However, drug resistance to several of the front-line drugs is rising. Furthermore, there is no official treatment for dourine. Therefore, there is an urgent need to develop antiparasitic agents with novel modes of action. Host defense peptides have recently gained attention as promising candidates. We have previously reported that one such peptide, the equine antimicrobial peptide eCATH1, is highly active against equine Gram-positive and Gram-negative bacteria, without cytotoxicity against mammalian cells at bacteriolytic concentrations. In the present study, we show that eCATH1 exhibits an in vitro 50% inhibitory concentration (IC50) of 9.5 μM against Trypanosoma brucei brucei, Trypanosoma evansi, and Trypanosoma equiperdum Its trypanocidal mechanism involves plasma membrane permeabilization and mitochondrial alteration based on the following data: (i) eCATH1 induces the rapid influx of the vital dye SYTOX Green; (ii) it rapidly disrupts mitochondrial membrane potential, as revealed by immunofluorescence microscopy using the fluorescent dye rhodamine 123; (iii) it severely damages the membrane and intracellular structures of the parasites as early as 15 min after exposure at 9.5 μM and 5 min after exposure at higher concentrations (19 μM), as evidenced by scanning and transmission electron microscopy. We also demonstrate that administration of eCATH1 at a dose of 10 mg/kg to T. equiperdum-infected mice delays mortality. Taken together, our findings suggest that eCATH1 is an interesting template for the development of novel therapeutic agents in the treatment of trypanosome infections.

Melittin induces in vitro death of Leishmania (Leishmania) infantum by triggering the cellular innate immune response

BACKGROUND

Apis mellifera venom, which has already been recommended as an alternative anti-inflammatory treatment, may be also considered an important source of candidate molecules for biotechnological and biomedical uses, such as the treatment of parasitic diseases.

METHODS

Africanized honeybee venom from Apis mellifera was fractionated by RP-C18-HPLC and the obtained melittin was incubated with promastigotes and intracellular amastigotes of Leishmania (L.) infantum. Cytotoxicity to mice peritoneal macrophages was evaluated through mitochondrial oxidative activity. The production of anti- and pro-inflammatory cytokines, NO and H2O2 by macrophages was determined.

RESULTS

Promastigotes and intracellular amastigotes were susceptible to melittin (IC50 28.3 μg.mL(-1) and 1.4 μg.mL(-1), respectively), but also showed mammalian cell cytotoxicity with an IC50 value of 5.7 μg.mL(-1). Uninfected macrophages treated with melittin increased the production of IL-10, TNF-α, NO and H2O2. Infected melittin-treated macrophages increased IL-12 production, but decreased the levels of IL-10, TNF-α, NO and H2O2.

CONCLUSIONS

The results showed that melittin acts in vitro against promastigotes and intracellular amastigotes of Leishmania (L.) infantum. Furthermore, they can act indirectly on intracellular amastigotes through a macrophage immunomodulatory effect.

Antimicrobial peptides

The rapid increase in drug-resistant infections has presented a serious challenge to antimicrobial therapies. The failure of the most potent antibiotics to kill “superbugs” emphasizes the urgent need to develop other control agents. Here we review the history and new development of antimicrobial peptides (AMPs), a growing class of natural and synthetic peptides with a wide spectrum of targets including viruses, bacteria, fungi, and parasites. We summarize the major types of AMPs, their modes of action, and the common mechanisms of AMP resistance. In addition, we discuss the principles for designing effective AMPs and the potential of using AMPs to control biofilms (multicellular structures of bacteria embedded in extracellular matrixes) and persister cells (dormant phenotypic variants of bacterial cells that are highly tolerant to antibiotics).

Melittin peptide kills Trypanosoma cruzi parasites by inducing different cell death pathways

Antimicrobial peptides (AMPs) are components of the innate immune response that represent desirable alternatives to conventional pharmaceuticals, as they have a fast mode of action, a low likelihood of resistance development and can act in conjunction with existing drug regimens. AMPs exhibit strong inhibitory activity against both Gram-positive and Gram-negative bacteria, fungi, viruses, metazoans and other parasites, such as the protozoan Leishmania. Melittin is a naturally occurring AMP, which comprises 40-50% of the dry weight of Apis mellifera venom. Our group has recently shown that crude A. mellifera venom is lethal to Trypanosoma cruzi, the Chagas disease etiologic agent, and generates a variety of cell death phenotypes among treated parasites. Here, we demonstrate that the melittin affected all of T. cruzi developmental forms, including the intracellular amastigotes. The ultrastructural changes induced by melittin suggested the occurrence of different programmed cell death pathways, as was observed in A. mellifera-treated parasites. Autophagic cell death appeared to be the main death mechanism in epimastigotes. In contrast, melittin-treated trypomastigotes appeared to be dying via an apoptotic mechanism. Our findings confirm the great potential of AMPs, including melittin, as a potential source of new drugs for the treatment of neglected diseases, such as Chagas disease.

Apis mellifera venom induces different cell death pathways in Trypanosoma cruzi

Chagas disease chemotherapy is based on drugs that exhibit toxic effects and have limited efficacy, such as Benznidazole. Therefore, research into new chemotherapeutic agents from natural sources needs to be exploited. Apis mellifera venom consists of many biologically active molecules and has been reported to exhibit remarkable anti-cancer effects, often promoting an apoptosis-like death phenotype. This study demonstrates that A. mellifera venom can affect the growth, viability and ultrastructure of all Trypanosoma cruzi developmental forms, including intracellular amastigotes, at concentrations 15- to 100-fold lower than those required to cause toxic effects in mammalian cells. The ultrastructural changes induced by the venom in the different developmental forms led us to hypothesize the occurrence of different programmed cell death pathways. Autophagic cell death, characterized by the presence of autophagosomes-like organelles and a strong monodansyl cadaverine labelling, appears to be the main death mechanism in epimastigotes. In contrast, increased TUNEL staining, abnormal nuclear chromatin condensation and kDNA disorganization was observed in venom-treated trypomastigotes, suggesting cell death by an apoptotic mechanism. On the other hand, intracellular amastigotes presented a heterogeneous cell death phenotype profile, where apoptosis-like death seemed to be predominant. Our findings confirm the great potential of A. mellifera venom as a source for the development of new drugs for the treatment of neglected diseases such as Chagas disease.

Modes of action of Leishmanicidal antimicrobial peptides

Leishmaniasis is one of the major neglected tropical diseases of the world. It is present in 88 countries with an estimated number of 500,000 cases of visceral leishmaniasis and 1.5 million cases of cutaneous disease. No effective vaccinations are available against leishmaniasis and the efficacy of existing treatments is compromised due to the emergence of drug resistance. Thus, there is an urgent need to develop new compounds with antileishmanial activity. Antimicrobial peptides have potential as novel antileishmanial therapy, either for use alone or in combination with current drug regimens. The modes of action of these peptides against Leishmania includes: membrane disruption leading to necrotic cell death; induction of apoptosis; binding to intracellular target(s); and indirect effects via immunomodulation of host immune cells. This article reviews the mechanisms of action of antimicrobial peptides with leishmanicidal activity.

Head-to-head comparison of three vaccination strategies based on DNA and raw insect-derived recombinant proteins against Leishmania

Parasitic diseases plague billions of people among the poorest, killing millions annually, and causing additional millions of disability-adjusted life years lost. Leishmaniases affect more than 12 million people, with over 350 million people at risk. There is an urgent need for efficacious and cheap vaccines and treatments against visceral leishmaniasis (VL), its most severe form. Several vaccination strategies have been proposed but to date no head-to-head comparison was undertaken to assess which is the best in a clinical model of the disease. We simultaneously assayed three vaccination strategies against VL in the hamster model, using KMPII, TRYP, LACK, and PAPLE22 vaccine candidate antigens. Four groups of hamsters were immunized using the following approaches: 1) raw extracts of baculovirus-infected Trichoplusia ni larvae expressing individually one of the four recombinant proteins (PROT); 2) naked pVAX1 plasmids carrying the four genes individually (DNA); 3) a heterologous prime-boost (HPB) strategy involving DNA followed by PROT (DNA-PROT); and 4) a Control including empty pVAX1 plasmid followed by raw extract of wild-type baculovirus-infected T. ni larvae. Hamsters were challenged with L. infantum promastigotes and maintained for 20 weeks. While PROT vaccine was not protective, DNA vaccination achieved protection in spleen. Only DNA-PROT vaccination induced significant NO production by macrophages, accompanied by a significant parasitological protection in spleen and blood. Thus, the DNA-PROT strategy elicits strong immune responses and high parasitological protection in the clinical model of VL, better than its corresponding naked DNA or protein versions. Furthermore, we show that naked DNA coupled with raw recombinant proteins produced in insect larvae biofactories -the cheapest way of producing DNA-PROT vaccines- is a practical and cost-effective way for potential "off the shelf" supplying vaccines at very low prices for the protection against leishmaniases, and possibly against other parasitic diseases affecting the poorest of the poor.

Efficacy of synthetic peptides RP-1 and AA-RP-1 against Leishmania species in vitro and in vivo

Host defense peptides are naturally occurring molecules that play essential roles in innate immunity to infection. Based on prior structure-function knowledge, we tested two synthetic peptides (RP-1 and AA-RP-1) modeled on the conserved, microbicidal α-helical domain of mammalian CXCL4 platelet kinocidins. These peptides were evaluated for efficacy against Leishmania species, the causative agents of the group of diseases known as leishmaniasis. In vitro antileishmanial activity was assessed against three distinct Leishmania strains by measuring proliferation, metabolic activity and parasite viability after exposure to various concentrations of peptides. We demonstrate that micromolar concentrations of RP-1 and AA-RP-1 caused dose-dependent growth inhibition of Leishmania promastigotes. This antileishmanial activity correlated with rapid membrane disruption, as well as with a loss of mitochondrial transmembrane potential. In addition, RP-1 and AA-RP-1 demonstrated distinct and significant in vivo antileishmanial activities in a mouse model of experimental visceral leishmaniasis after intravenous administration. These results establish efficacy of RP-1 lineage synthetic peptides against Leishmania species in vitro and after intravenous administration in vivo and provide further validation of proof of concept for the development of these and related systemic anti-infective peptides targeting pathogens that are resistant to conventional antibiotics.

Lysine N(epsilon)-trimethylation, a tool for improving the selectivity of antimicrobial peptides

The effects of lysine N(epsilon)-trimethylation at selected positions of the antimicrobial cecropin A-melittin hybrid peptide KWKLFKKIGAVLKVL-amide have been studied. All five monotrimethylated, four bis-trimethylated plus the per-trimethylated analogues have been synthesized and tested for antimicrobial activity on Leishmania parasites and on Gram-positive and -negative bacteria, as well as for hemolysis of sheep erythrocytes as a measure of cytotoxicity. The impact of trimethylation on the solution conformation of selected analogues has been evaluated by NMR, which indicates a slight decrease in the alpha-helical content of the modified peptides, particularly in the N-terminal region. Trimethylation also enhances the proteolytic stability of mono- and bis-trimethylated analogues by 2-3-fold. Although it tends to lower antimicrobial activity in absolute terms, trimethylation causes an even higher decrease in hemolytic activity and therefore results in improved selectivity for several analogues. The monotrimethylated analogue at position 6 shows the overall best selectivity against both the Leishmania donovani protozoan and Acinetobacter baumannii, a Gram-negative bacterium of increasing clinical concern.

Anti-trypanosomatid activity of ceragenins

Cationic steroid antibiotics (CSAs), or ceragenins, are amphiphilic compounds consisting of a cholic acid backbone that is attached to several cationic amines. In this study, we tested the hypothesis that CSAs possess antiparasitic activities with minimal to no effects on mammalian cells, and thus could be used as potential therapeutic agents against pathogenic trypanosomatids. To investigate this notion, we synthesized CSAs and determined their trypanocidal and leishmanicidal activities in vitro. The 3 ceragenins assayed, i.e., CSA-8, CSA-13, and CSA-54, showed several degrees of parasiticidal activity. CSA-13 was the most effective compound against Leishmania major promastigotes and Trypanosoma cruzi trypomastigotes, at LD(50) 4.9 and 9 microM, respectively. The trypanocidal activities of these ceragenins were also assessed by infectivity experiments. We found CSA-8 was more effective on T. cruzi intracellular amastigotes when the infected host cells were treated for 24 hr (LD(50), 6.7 microM). Macrophages and LLC-MK(2) (treated for 72 hr) showed relative low susceptibility to these compounds. Our results suggest that ceragenins are indeed promising chemotherapeutic agents against trypanosomatids, but they require further investigation.

Leishmania infection: laboratory diagnosing in the absence of a "gold standard"

There is no gold standard for diagnosing leishmaniases. Our aim was to assess the operative validity of tests used in detecting Leishmania infection using samples from experimental infections, a reliable equivalent to the classic definition of gold standard. Without statistical differences, the highest sensitivity was achieved by protein A (ProtA), immunoglobulin (Ig)G2, indirect fluorescenece antibody test (IFAT), lymphocyte proliferation assay, quantitative real-time polymerase chain reaction of bone marrow (qPCR-BM), qPCR-Blood, and IgG; and the highest specificity by IgG1, IgM, IgA, qPCR-Blood, IgG, IgG2, and qPCR-BM. Maximum positive predictive value was obtained simultaneously by IgG2, qPCR-Blood, and IgG; and maximum negative predictive value by qPCR-BM. Best positive and negative likelihood ratios were obtained by IgG2. The test having the greatest, statistically significant, area under the receiver operating characteristics curve was IgG2 enzyme-linked immunosorbent assay (ELISA). Thus, according to the gold standard used, IFAT and qPCR are far from fulfilling the requirements to be considered gold standards, and the test showing the highest potential to detect Leishmania infection is Leishmania-specific ELISA IgG2.

Interactions of antimicrobial peptides with Leishmania and trypanosomes and their functional role in host parasitism

Antimicrobial peptides (AMPs) are multifunctional components of the innate systems of both insect and mammalian hosts of the pathogenic trypanosomatids Leishmania and Trypanosoma species. Structurally diverse AMPs from a wide range of organisms have in vitro activity against these parasites acting mainly to disrupt surface-membranes. In some cases AMPs also localize intracellularly to affect calcium levels, mitochondrial function and induce autophagy, necrosis and apoptosis. In this review we discuss the work done in the area of AMP interactions with trypanosomatid protozoa, propose potential targets of AMP activity at the cellular level and discuss how AMPs might influence parasite growth and differentiation in their hosts to determine the outcome of natural infection.

Kahalalide F, an antitumor depsipeptide in clinical trials, and its analogues as effective antileishmanial agents

Leishmaniasis is a human parasitic disease caused by infection by the protozoan Leishmania spp. Chemotherapy is currently the only treatment available, but its efficacy is increasingly challenged by the rising incidence of resistance and the frequent severe side effects associated with first-line drugs. Thus the development of leads with distinct mechanisms of action is urgently needed. A strategy often used for this purpose consists of assaying for leishmanicidal activity drugs formerly developed for other applications, such as amphotericin B (antifungal) or miltefosine (antitumor), among others, to profit from previous pharmacological and toxicological studies. Kahalalide F (KF) is a tumoricidal cyclic depsipeptide currently under phase II clinical trials for several types of cancer and psoriasis. Its mechanism of action has not been fully elucidated. Here we report the leishmanicidal activity of KF and its synthetic analogues at a micromolar range of concentrations. Its lethality is strongly linked to the alteration of the plasma membrane (PM) of the parasite based on (i) a rapid depolarization of the PM and uptake of the vital dye SYTOX Green upon its addition; (ii) evidence of severe morphological damage to the membrane of the parasite, as shown by transmission electron microscopy; and (iii) a rapid drop in the intracellular ATP levels, which correlates significantly with the leishmanicidal activity for active analogues, some of them with significant improvement of their therapeutic index with respect to the parental molecule. In addition to the basic knowledge obtained, this class of lethal mechanism is considerably less prone to the induction of resistance than classical drugs. All together, these observations foster further studies for the optimization of KF and its analogues as new anti-Leishmania leads with a new mode of action.

Synergistic effects of the membrane actions of cecropin-melittin antimicrobial hybrid peptide BP100

BP100 (KKLFKKILKYL-NH(2)) is a short cecropin A-melittin hybrid peptide, obtained through a combinatorial chemistry approach, which is highly effective in inhibiting both the in vitro and in vivo growth of economically important plant pathogenic Gram-negatives. The intrinsic Tyr fluorescence of BP100 was taken advantage of to study the peptide's binding affinity and damaging effect on phospholipid bilayers modeling the bacterial and mammalian cytoplasmic membranes. In vitro cytotoxic effects of this peptide were also studied on mammalian fibroblast cells. Results show a stronger selectivity of BP100 toward anionic bacterial membrane models as indicated by the high obtained partition constants, one order of magnitude greater than for the neutral mammalian membrane models. For the anionic systems, membrane saturation was observed at high peptide/lipid ratios and found to be related with BP100-induced vesicle permeabilization, membrane electroneutrality, and vesicle aggregation. Occurrence of BP100 translocation was unequivocally detected at both high and low peptide/lipid ratios using a novel and extremely simple method. Moreover, cytotoxicity against mammalian models was reached at a concentration considerably higher than the minimum inhibitory concentration. Our findings unravel the relationships among the closely coupled processes of charge neutralization, permeabilization, and translocation in the mechanism of action of antimicrobial peptides.

Lysine-enriched cecropin-mellitin antimicrobial peptides with enhanced selectivity

Lysine-enriched analogs of the cecropin-mellitin hybrid peptide, CA(1-7) M(2-9) (designated CM15), designed with optimized amphipathicity, retained antimicrobial activities similar to that of wild-type CM15 and had substantially reduced levels of hemolytic activity and cytotoxicity toward cultured macrophages, resulting in enhanced selectivity. These lysine-enriched analogs provide templates for improved CM15 peptide or peptidomimetic antibiotics.

Synthesis and antimicrobial activity of dermaseptin S1 analogues

Dermaseptins are peptides found in the skin secretions of Phyllomedusinae frogs. These peptides exert lytic action on some microorganisms without substantial haemolysis. In an attempt to understand the antimicrobial activity of these peptides we designed several dermaseptin S1 (ALWKTMLKKLGTMALHAGKAALGAAADTISQGTQ) (DS1) analogues. All peptides were tested on the growth of prokaryotic (Gram-positive and Gram-negative bacteria) and eukaryotic (the yeast Candida albicans and the protozoon Leishmania major) organisms. Our data showed a dose-dependent killing effect by most DS1 derivatives. Maximal antibacterial activity was displayed by a 16-mer peptide that was more active than native DS1.

Efficacy of different treatment regimens of marbofloxacin in canine visceral leishmaniosis: a pilot study

This phase II, randomized, open-label field trial was designed to evaluate and compare the safety and efficacy of four treatment durations (10, 20, 28 or 40 days) with marbofloxacin administered orally at the dosage of 2mg/kg once a day for canine visceral leishmaniosis. Twenty-four dogs naturally infected with visceral leishmaniosis and without biochemical disorder evidences of renal insufficiency, were recruited by two Greek veterinarian clinics. They were also randomly assigned to one of the four treatment duration groups, and have been clinically, haematologically, biochemically and parasitologically followed-up regularly for 9 months. Efficacy was achieved for 5/6 dogs treated for 28 days, 4/6 dogs treated for 10 or 20 days and for 3/6 dogs treated for 40 days. Moreover, efficacy was reached more quickly (58.4 days) in dogs treated for 28 days. Improvement of clinical signs tended to be better and faster in the 28 days treatment group too. After 9 months of follow-up, a total of three cases could be considered as relapsing (two dogs treated for 40 days and one dog treated for 28 days). There was a significant reduction in amastigotes density in macrophages after 3 months in the four groups when compared with the parasite density at inclusion. No adverse effects were noticed during this 9 months study. Results obtained with marbofloxacin at the dosage of 2mg/kg once a day for 28 days seem encouraging and may offer a safe alternative for treating canine visceral leishmaniosis.

A library of linear undecapeptides with bactericidal activity against phytopathogenic bacteria

A 125-member library of synthetic linear undecapeptides was prepared based on a previously described peptide H-K(1)KLFKKILKF(10)L-NH(2) (BP76) that inhibited in vitro growth of the plant pathogenic bacteria Erwinia amylovora, Xanthomonas axonopodis pv. vesicatoria, and Pseudomonas syringae pv. syringae at low micromolar concentrations. Peptides were designed using a combinatorial chemistry approach by incorporating amino acids possessing various degrees of hydrophobicity and hydrophilicity at positions 1 and 10 and by varying the N-terminus. Library screening for in vitro growth inhibition identified 27, 40 and 113 sequences with MIC values below 7.5 microM against E. amylovora, P. syringae and X. axonopodis, respectively. Cytotoxicity, bactericidal activity and stability towards protease degradation of the most active peptides were also determined. Seven peptides with a good balance between antibacterial and hemolytic activities were identified. Several analogues displayed a bactericidal effect and low susceptibility to protease degradation. The most promising peptides were tested in vivo by evaluating their preventive effect of inhibition of E. amylovora infection in detached apple and pear flowers. The peptide H-KKLFKKILKYL-NH(2) (BP100) showed efficacies in flowers of 63-76% at 100 microM, being more potent than BP76 and only less effective than streptomycin, currently used for fire blight control.

Trypanocidal and leishmanicidal activities of different antimicrobial peptides (AMPs) isolated from aquatic animals

Most of the available animal antimicrobial peptides (AMPs) have been tested against bacteria and fungi, but very few against protozoan parasites. In the present study, we investigated the antiparasitic activity of different AMPs isolated from aquatic animals: tachyplesin (Tach, from Tachypleus tridentatus), magainin (Mag, from Xenopus laevis), clavanin (Clav, from Styela clava), penaeidin (Pen, from Litopenaeus vannamei), mytilin (Myt, from Mytilus edulis) and anti-lipopolysaccharide factor (ALF, from Penaeus monodon). The antiparasitic activity was evaluated against the promastigote form of Leishmania braziliensis and epi and trypomastigote forms of Trypanosoma cruzi, through the MTT method. Tach was the most potent peptide, killing completely L. braziliensis and trypomastigote T. cruzi from 12.5microM, whereas Pen and Clav were weakly active against trypomastigotes and Myt against L. braziliensis, only at a high concentration (100microM). Tach and Mag were markedly hemolytic at high concentrations, whereas the other peptides caused only a slight hemolysis (<10% up to 50microM). Our results point to Tach as the only potential candidate for further investigation and potential application as a therapeutic agent.

A long term experimental study of canine visceral leishmaniasis

Previous studies on Leishmania infantum and the canine immune response are derived mainly from short-term studies. To date, there have been no longitudinal studies that perform a serial analysis of the intensity of infection in conjunction with immunological parameters and clinical signs in Leishmania-infected dogs. For this purpose, six dogs were infected experimentally by the i.v. route and were monitored for 1 year. Clinical, immunological (humoral and cellular response) and parasitological (parasitaemia) parameters were evaluated monthly. Four dogs developed clinico-pathological signs compatible with leishmaniasis, whereas two dogs showed few abnormalities during the study. Evaluation of clinical, immunological and parasitological parameters showed that the intensity of Leishmania infection in blood samples, as indicated by the amount of Leishmania DNA, was correlated significantly with IgG, IgG1, IgG2, IgA, and IgM concentrations and with clinical signs. Parasitaemia and Leishmania-specific cell-mediated immunity were inversely correlated. Moreover, higher quantities of Leishmania DNA were detected in the liver, spleen, lymph node, skin and bone marrow of dogs exhibiting clinical signs than those exhibiting few such signs. These findings suggest that progressive disease in experimental canine leishmaniasis is associated with specific T-cell unresponsiveness and unprotective humoral responses which allow the dissemination and multiplication of L. infantum in different tissues.

Peptide antimicrobial agents

Antimicrobial host defense peptides are produced by all complex organisms as well as some microbes and have diverse and complex antimicrobial activities. Collectively these peptides demonstrate a broad range of antiviral and antibacterial activities and modes of action, and it is important to distinguish between direct microbicidal and indirect activities against such pathogens. The structural requirements of peptides for antiviral and antibacterial activities are evaluated in light of the diverse set of primary and secondary structures described for host defense peptides. Peptides with antifungal and antiparasitic activities are discussed in less detail, although the broad-spectrum activities of such peptides indicate that they are important host defense molecules. Knowledge regarding the relationship between peptide structure and function as well as their mechanism of action is being applied in the design of antimicrobial peptide variants as potential novel therapeutic agents.

Antimicrobial peptides: therapeutic potential

A significant component of the innate immune system of a wide variety of animals and plants is arbitrated by cationic host defence peptides. In man, these peptides, in addition to exhibiting a direct antimicrobial activity, seems to provide a range of non-antimicrobial bioactivities related to defence, inflammation and wound healing. Despite the fact that such peptides have so far failed to reach the market, there are continued initiatives to advance such potential therapeutics to, and through, the clinic. The reasons behind such initiatives include: reduced manufacturing costs for peptides; allowing entry into therapeutic areas previously inaccessible due to cost; the continued identification of previously unknown bioactivities of such peptides; and the resurgence of interest in peptide therapeutics. As a result, clinical programmes based on cationic host defence peptides exist in the areas of infection, dermatology, cancer and inflammation. The probability of clinical success for host defence peptide-based therapeutics is on the rise as options for a wider range of clinical indications emerge.

Peptide-membrane interactions and mechanisms of membrane destruction by amphipathic alpha-helical antimicrobial peptides

Antimicrobial peptides (AMPs) have received considerable interest as a source of new antibiotics with the potential for treatment of multiple-drug resistant infections. An important class of AMPs is composed of linear, cationic peptides that form amphipathic alpha-helices. Among the most potent of these are the cecropins and synthetic peptides that are hybrids of cecropin and the bee venom peptide, mellitin. Both cecropins and cecropin-mellitin hybrids exist in solution as unstructured monomers, folding into predominantly alpha-helical structures upon membrane binding with their long helical axis parallel to the bilayer surface. Studies using model membranes have shown that these peptides intercalate into the lipid bilayer just below the level of the phospholipid glycerol backbone in a location that requires expansion of the outer leaflet of the bilayer, and evidence from a variety of experimental approaches indicates that expansion and thinning of the bilayer are common characteristics during the early stages of antimicrobial peptide-membrane interactions. Subsequent disruption of the membrane permeability barrier may occur by a variety of mechanisms, leading ultimately to loss of cytoplasmic membrane integrity and cell death.

Inhibition of plant-pathogenic bacteria by short synthetic cecropin A-melittin hybrid peptides

Short peptides of 11 residues were synthesized and tested against the economically important plant pathogenic bacteria Erwinia amylovora, Pseudomonas syringae, and Xanthomonas vesicatoria and compared to the previously described peptide Pep3 (WKLFKKILKVL-NH(2)). The antimicrobial activity of Pep3 and 22 analogues was evaluated in terms of the MIC and the 50% effective dose (ED(50)) for growth. Peptide cytotoxicity against human red blood cells and peptide stability toward protease degradation were also determined. Pep3 and several analogues inhibited growth of the three pathogens and had a bactericidal effect at low micromolar concentrations (ED(50) of 1.3 to 7.3 microM). One of the analogues consisting of a replacement of both Trp and Val with Lys and Phe, respectively, resulted in a peptide with improved bactericidal activity and minimized cytotoxicity and susceptibility to protease degradation compared to Pep3. The best analogues can be considered as potential lead compounds for the development of new antimicrobial agents for use in plant protection either as components of pesticides or expressed in transgenic plants.

Advantages of real-time PCR assay for diagnosis and monitoring of canine leishmaniosis

The aim of the present study is to highlight the advantages of real-time quantitative PCR intended to aid in the diagnosis and monitoring of canine leishmaniosis. Diagnosis of canine leishmaniosis is extremely challenging, especially in endemic areas, due to the diverse and non-specific clinical manifestations, and due to the high seroprevalence rate in sub-clinical dogs. Veterinarian clinicians are usually confronted with cases that are compatible with the disease, and with several diagnostic tests, sometimes with contradictory results. We have developed a new TaqMan assay, targeting the kinetoplast, applied to 44 samples of bone marrow aspirate or peripheral blood. The dynamic range of detection of Leishmania DNA was established in 7 logs and the limit of detection is 0.001 parasites in the PCR reaction. At the time of diagnosis parasitemia ranges from less than 1 to 10(7)parasites/ml. The ability to quantify the parasite burden allowed: (i) to elucidate the status of positive dogs by conventional PCR, although larger studies are necessary to clarify the dividing line between infection and disease, (ii) to estimate the kinetics of the parasite load and the different response to the treatment in a follow-up and (iii) to validate blood as less invasive sample for qPCR. The continuous data provided by real-time qPCR could solve the dilemma for the clinician managing cases of canine leishmaniosis by differentiating between Leishmania-infected dogs or dogs with active disease of leishmaniosis.

Enhanced resistance to the rice blast fungus Magnaporthe grisea conferred by expression of a cecropin A gene in transgenic rice

Cecropins are a family of antimicrobial peptides, which constitute an important key component of the immune response in insects. Here, we demonstrate that transgenic rice (Oryza sativa L.) plants expressing the cecropin A gene from the giant silk moth Hyalophora cecropia show enhanced resistance to Magnaporthe grisea, the causal agent of the rice blast disease. Two plant codon-optimized synthetic cecropin A genes, which were designed either to retain the cecropin A peptide in the endoplasmic reticulum, the ER-CecA gene, or to secrete cecropin A to the extracellular space, the Ap-CecA gene, were prepared. Both cecropin A genes were efficiently expressed in transgenic rice. The inhibitory activity of protein extracts prepared from leaves of cecropin A-expressing plants on the in vitro growth of M. grisea indicated that the cecropin A protein produced by the transgenic rice plants was biologically active. Whereas no effect on plant phenotype was observed in ER-CecA plants, most of the rice lines expressing the Ap-CecA gene were non-fertile. Cecropin A rice plants exhibited resistance to rice blast at various levels. Transgene expression of cecropin A genes was not accompanied by an induction of pathogenesis-related (PR) gene expression supporting that the transgene product itself is directly active against the pathogen. Taken together, the results presented in this study suggest that the cecropin A gene, when designed for retention of cecropin A into the endoplasmic reticulum, could be a useful candidate for protection of rice plants against the rice blast fungus M. grisea.

The induction of NOS2 expression by the hybrid cecropin A-melittin antibiotic peptide CA(1-8)M(1-18) in the monocytic line RAW 264.7 is triggered by a temporary and reversible plasma membrane permeation

There is an increasing awareness of immune cell modulation by antimicrobial peptides. While this process often requires specific receptors for the peptides involved, several reports point out to a receptor-independent process. The cecropin A-melittin hybrid peptide CA(1-8)M(1-18) (KWKLFKKIGIGAVLKVLTTGLPALIS-amide) modifies gene expression in the macrophage line RAW 264.7 in the absence of any previous macrophage priming, suggesting a membrane permeation process. To further analyze the initial steps of this mechanism, we have studied the interaction of the peptide with these cells. Below 2 microM, CA(1-8)M(1-18) causes a concentration-dependent membrane depolarization partially reversible with time. At 2 microM, the accumulation of the SYTOX green vital dye is one half of that achieved with 0.05% Triton X-100. The binding level, as assessed by fluorescein-labeled CA(1-8)M(1-18), varies from 7.7+/-1.2 to 37.4+/-3.9 x 10(6) molecules/cell over a 0.5-4.0 microM concentration range. Electrophysiological experiments with 0.5 microM CA(1-8)M(1-18), a concentration that triggers maximal NOS2 expression and minimal toxicity, show a reversible current induction in the RAW 264.7 plasma membrane that is maintained as far as peptide is present. This activation of the macrophage involves the production of nitric oxide, a metabolite lethal for many pathogens that results from unspecific membrane permeation by antimicrobial peptides, and represents a new mode of action that may open new therapeutic possibilities for these compounds against intracellular pathogens.