Leishmaniasis treatment—a challenge that remains: a review

In vitro leishmanicidal activity of 1,3-disubstituted 5-nitroindazoles

The antiprotozoal activity of some indazole-derived amines (2, 3, 5-8) as well as that of some simple structurally related 3-alkoxy-1-alkyl-5-nitroindazoles (1, 4) against promastigote and amastigote forms of Leishmania infantum and Leishmania braziliensis is reported. In some cases, these compounds showed in vitro activities against the different morphological forms of Leishmania similar to or higher than those of the reference drug glucantime; this fact, along with low unspecific cytotoxicities against macrophages shown by some of them, led to good selectivity indexes (SI). The high efficiency of some 5-nitroindazoles against the mentioned protozoa was confirmed by further in vitro studies on infection rates. Complementary analyses by (1)H NMR of the changes on the metabolites excreted by parasites after treatment with the more active indazole derivatives in many cases showed the decreased excretion of succinate and increased levels of acetate, lactate and alanine, as well as, in some cases, the appearance of glycine and pyruvate as new metabolites. Damage caused by indazoles at the glycosomal or mitochondrial level are consistent with these metabolic changes as well as with the huge ultrastructural alterations observed by transmission electron microscopy (TEM), especially affecting the mitochondria and other cytoplasmic organelles.

Leishmanicidal and cytotoxic activities of Nigella sativa and its active principle, thymoquinone

CONTEXT

Leishmaniasis is a complex disease with a broad spectrum of clinical presentations.

OBJECTIVE

We evaluated the anti-leishmanial effects of Nigella sativa L. (Ranunculaceae) against Leishmania tropica and Leishmania infantum with an in vitro model.

MATERIALS AND METHODS

Antileishmanial effects of essential oil and methanolic extract of N. sativa (0-200 µg/mL) and thymoquinone (0-25 µg/mL) on promastigotes of both species and their cytotoxicity activities against murine macrophages were evaluated using the MTT assay at 24, 48, and 72 h. Moreover, their leishmanicidal effects against amastigotes were investigated in a macrophage model, for 48 and 72 h.

RESULTS

The findings showed that essential oil (L. tropica IC50 9.3 μg/mL and L. infantum IC50 11.7 μg/mL) and methanolic extract (L. tropica IC50 14.8 μg/mL and L. infantum IC50 15.7 μg/mL) of N. sativa, particularly thymoquinone (L. tropica IC50 1.16 μg/mL and L. infantum IC50 1.47 μg/mL), had potent antileishmanial activity on promastigotes of both species after 72 h. In addition, essential oil (L. tropica IC50 21.4 μg/mL and L. infantum IC50 26.3 μg/mL), methanolic extract (L. tropica IC50 30.8 μg/mL and L. infantum IC50 34.6 μg/mL), and thymoquinone (L. tropica IC50 2.1 μg/mL and L. infantum IC50 2.6 μg/mL) mediated a significant decrease in the growth rate of amastigote forms of both species. Thymoquinone (CC50 38.8 μg/mL) exhibited higher cytotoxic effects against murine macrophages than the other extracts.

CONCLUSION

N. sativa, especially its active principle, thymoquinone, showed a potent leishmanicidal activity against L. tropica and L.infantum with an in vitro model.

(-)-α-Bisabolol, a Promising Oral Compound for the Treatment of Visceral Leishmaniasis

The aim of the present study was to assess the in vitro and in vivo activity of (-)-α-bisabolol (1) against the etiological agents of visceral leishmaniasis. Bone-marrow-derived macrophages were infected with Leishmania infantum or L. donovani promastigotes and incubated with (-)-α-bisabolol at different concentrations. Pentamidine isethionate and meglumine antimoniate were used as reference drugs. Inhibitory concentration 50% (IC50) and cytotoxic concentration 50% (CC50) were calculated. Balb/c mice were infected intraperitoneally with stationary-phase promastigotes. They were treated with (-)-α-bisabolol at different doses orally, meglumine antimoniate at 104 mg Sb(V)/kg, or a combination of both. (-)-α-Bisabolol proved to be innocuous to mammal cells and active against L. infantum and L. donovani intracellular amastigotes (IC50 55 and 39 μM, respectively). Compound 1 also proved to be active in an in vivo model of visceral leishmaniasis due to L. infantum, as it reduced parasite load in the spleen and liver by 71.60% and 89.22%, respectively, at 200 mg/kg without showing toxicity. (-)-α-Bisabolol (1) is a nontoxic compound that was proven to be active against visceral leishmaniasis in an in vivo murine model orally. It was more effective than meglumine antimoniate at reducing spleen parasite load and as effective as this antimonial drug in the liver.

Antileishmanial activity of some Brazilian plants, with particular reference to Casearia sylvestris

Leishmaniasis is a complex of diseases caused by Leishmania protozoa which treatment is restricted to a limited number of drugs that exhibit high toxicity, collateral effects and are often costly. There are a variety of tropical plants distributed in Brazil, and for many poor people the therapy for several diseases is based mainly on the use of traditional herbal remedies. In this work, the cytotoxic activity of 17 plant methanol extracts was evaluated on several Leishmania species and murine macrophages. Among them, the extract of Casearia sylvestris, Piptocarpha macropoda, Trembleya parviflora, Samanea tubulosa and Plectranthus neochilus showed a promissing leishmanicidal activity, exhibiting IC50 values below of 20 µg/mL against at least one species of Leishmania. Casearia sylvestris showed the most expressive activity against all promastigote forms of Leishmania species (IC50 values of 5.4 µg/mL, 5.0 µg/mL, 8.5 µg/mL and 7.7 µg/mL for L. amazonensis, L. braziliensis, L. chagasi and L. major, respectively), being more effective than the reference drug miltefosine. In spite of the cytotoxic effect on macrophages (CC50 value of 5.2 µg/mL), C. sylvestris exhibited a strong inhibition against intracellular amastigotes of L. braziliensis (IC50 value of 1.3 µg/mL). Further studies, including bio-guided fractionation will be conducted to identify the active compounds.

Natural products as inhibitors of recombinant cathepsin L of Leishmania mexicana

Cysteine proteinases (cathepsins) from Leishmania spp. are promising molecular targets against leishmaniasis. Leishmania mexicana cathepsin L is essential in the parasite life cycle and a pivotal in virulence factor in mammals. Natural products that have been shown to display antileishmanial activity were screened as part of our ongoing efforts to design inhibitors against the L. mexicana cathepsin L-like rCPB2.8. Among them, agathisflavone (1), tetrahydrorobustaflavone (2), 3-oxo-urs-12-en-28-oic acid (3), and quercetin (4) showed significant inhibitory activity on rCPB2.8 with IC50 values ranging from 0.43 to 18.03 µM. The mechanisms of inhibition for compounds 1-3, which showed Ki values in the low micromolar range (Ki = 0.14-1.26 µM), were determined. The biflavone 1 and the triterpene 3 are partially noncompetitive inhibitors, whereas biflavanone 2 is an uncompetitive inhibitor. The mechanism of action established for these leishmanicidal natural products provides a new outlook in the search for drugs against Leishmania.

In silico search of energy metabolism inhibitors for alternative leishmaniasis treatments

Leishmaniasis is a complex disease that affects mammals and is caused by approximately 20 distinct protozoa from the genus Leishmania. Leishmaniasis is an endemic disease that exerts a large socioeconomic impact on poor and developing countries. The current treatment for leishmaniasis is complex, expensive, and poorly efficacious. Thus, there is an urgent need to develop more selective, less expensive new drugs. The energy metabolism pathways of Leishmania include several interesting targets for specific inhibitors. In the present study, we sought to establish which energy metabolism enzymes in Leishmania could be targets for inhibitors that have already been approved for the treatment of other diseases. We were able to identify 94 genes and 93 Leishmania energy metabolism targets. Using each gene's designation as a search criterion in the TriTrypDB database, we located the predicted peptide sequences, which in turn were used to interrogate the DrugBank, Therapeutic Target Database (TTD), and PubChem databases. We identified 44 putative targets of which 11 are predicted to be amenable to inhibition by drugs which have already been approved for use in humans for 11 of these targets. We propose that these drugs should be experimentally tested and potentially used in the treatment of leishmaniasis.

In Vitro and In Vivo Antileishmanial Effects of Pistacia khinjuk against Leishmania tropica and Leishmania major

The present study aims to evaluate the in vitro and in vivo antileishmanial activities of Pistacia khinjuk Stocks (Anacardiaceae) alcoholic extract and to compare its efficacy with a reference drug, meglumine antimoniate (MA, Glucantime), against Leishmania tropica and Leishmania major. This extract (0-100 µg/mL) was evaluated in vitro against promastigote and intracellular amastigote forms of L. tropica (MRHO/IR/75/ER) and then tested on cutaneous leishmaniasis (CL) in male BALB/c mice with L. major to reproduce the antileishmanial activity topically. In vitro, P. khinjuk extract significantly (P < 0.05) inhibited the growth rate of promastigote (IC50 58.6 ± 3.2 µg/mL) and intramacrophage amastigotes (37.3 ± 2.5 µg/mL) of L. tropica as a dose-dependent response. In the in vivo assay, after 30 days of treatment, 75% recovery was observed in the infected mice treated with 30% extract. After treatment of the subgroups with the concentration of 20 and 30% of P. khinjuk extract, mean diameter of lesions was significantly (P < 0.05) reduced. To conclude, the present investigation demonstrated that P. vera extract had in vitro and in vivo effectiveness against L. major. Obtained findings also provide the scientific evidences that natural plants could be used in the traditional medicine for the prevention and treatment of CL.

Antileishmanial and cytotoxic effects of essential oil and methanolic extract of Myrtus communis L

Plants used for traditional medicine contain a wide range of substances that can be used to treat various diseases such as infectious diseases. The present study was designed to evaluate the antileishmanial effects of the essential oil and methanolic extract of Myrtus communis against Leishmania tropica on an in vitro model. Antileishmanial effects of essential oil and methanolic extract of M. communis on promastigote forms and their cytotoxic activities against J774 cells were evaluated using MTT assay for 72 hr. In addition, their leishmanicidal activity against amastigote forms was determined in a macrophage model, for 72 hr. Findings showed that the main components of essential oil were α-pinene (24.7%), 1,8-cineole (19.6%), and linalool (12.6%). Findings demonstrated that M. communis, particularly its essential oil, significantly (P<0.05) inhibited the growth rate of promastigote and amastigote forms of L. tropica based on a dose-dependent response. The IC₅₀ values for essential oil and methanolic extract was 8.4 and 28.9 μg/ml against promastigotes, respectively. These values were 11.6 and 40.8 μg/ml against amastigote forms, respectively. Glucantime as control drug also revealed IC₅₀ values of 88.3 and 44.6 μg/ml for promastigotes and amastigotes of L. tropica, respectively. The in vitro assay demonstrated no significant cytotoxicity in J774 cells. However, essential oil indicated a more cytotoxic effect as compared with the methanolic extract of M. communis. The findings of the present study demonstrated that M. communis might be a natural source for production of a new leishmanicidal agent.

In vitro anti-leishmanial activity of methanolic extracts of Calendula officinalis flowers, Datura stramonium seeds, and Salvia officinalis leaves

AIM

The anti-leishmanial activity of methanolic extracts of Calendula officinalis flowers, Datura stramonium seeds, and Salvia officinalis leaves against extracellular (promastigote) and intracellular (amastigote) forms of Leishmania major were evaluated in this study.

METHOD

In the first stage, promastigote forms of L. major, were treated with different doses of the plant extracts in a 96-well tissue-culture microplate and IC50 values for each extract were measured with colorimetric MTT assay. In the second stage, macrophage cells were infected with L. major promastigotes. Infected macrophages were treated with plant extracts. Then the macrophages were stained with Gimsa and the number of infected macrophages and amastigotes were counted with a light microscope.

RESULTS

The results indicated that the plant extracts inhibited the growth of promastigotes and amastigotes of L. major. Inhibitory concentrations (IC50) for promastigote assay were 108.19, 155.15, and 184.32 μgmL(-1) for C. officinalis flowers, D. stramonium seeds and S. officinalis, respectively. The extracts also reduced the number of amastigotes in macrophage cells from 264 for control group to 88, 97, and 102 for test groups. Although the anti-leishmanial activity of the extracts were not comparable with the standard drug, miltefosine; but they showed significant efficiency in reducing the number of amastigotes in macrophages, in comparison with the control group (P < 0.001). These plant extracts had lower toxicity compared with miltefosine.

CONCLUSION

This study demonstrates the potential efficacy of the methanolic extracts of C. officinalis flowers, D. stramonium seeds, and S. officinalis leaves to control of cutaneous leishmaniasis.

In vitro sensitivity of paired Leishmania (Viannia) braziliensis samples isolated before meglumine antimoniate treatment and after treatment failure or reactivation of cutaneous leishmaniasis

This study evaluated the in vitro sensitivity of paired Leishmania braziliensis samples isolated from the same patient before pentavalent antimonial treatment (Sample A) and after treatment failure or cutaneous leishmaniasis reactivation (Sample B) in patients undergoing intralesional administration or injections (5 mgSb(V)/kg/d) of meglumine antimoniate. Fourteen samples from 7 patients were studied. After 24 h of drug exposure, 50% lethal dose (LD50) values for promastigotes ranged from 0.37 mg/mL to 5.86 mg/mL for samples obtained before treatment (A) and 0.89 mg/mL to 7.80 mg/mL for samples obtained after treatment (B). After 48 h, LD50 values ranged from 0.37 mg/mL to 5.75 mg/mL and 0.70 mg/mL to 7.68 mg/mL for A and B samples, respectively. After 48 h, LD50 values for amastigotes ranged from 11.7 to 44.3 μg/mL for A samples and 13.7 to 52.7 μg/mL for B samples. Of 7 patients, 1 discontinued treatment and 6 were cured after retreatment with amphotericin B (4 cases) or meglumine antimoniate (2 cases). Overall the B samples had higher LD50 values than A samples; however the difference was not significant. These results do not support the hypothesis that low-dose and intralesional treatments induce selection of resistant parasites in vitro and suggest that other factors may influence therapeutic outcome in patients with poor response to initial treatment.

Intranasal vaccination with leishmanial antigens protects golden hamsters (Mesocricetus auratus) against Leishmania (Viannia) Braziliensis infection

Background

Previous results have shown that oral and intranasal administration of particulate Leishmania (Leishmania) amazonensis antigens (LaAg) partially protects mice against L. amazonensis infection. However, vaccination studies on species of the subgenus Viannia, the main causative agent of cutaneous and mucosal leishmaniasis in the Americas, have been hampered by the lack of easy-to-handle bio-models that accurately mimic the human disease. Recently, we demonstrated that the golden hamster is an appropriate model for studying the immunopathogenesis of cutaneous leishmaniasis caused by L. (Viannia) braziliensis. Using the golden hamster model, our current study investigated whether the protective effect of intranasal immunisation with LaAg can be extended to L. braziliensis infection.

Methodology/Principal Findings

Golden hamsters vaccinated with either two intranasal (IN) doses of LaAg (10 µg) or two intramuscular doses of LaAg (20 µg) were challenged 2 weeks post-vaccination with L. braziliensis. The results showed that IN immunisation with LaAg significantly reduced lesion growth and parasitic load as well as serum IgG and IgG2 levels. At the experimental endpoint on day 114 post-infection, IN-immunised hamsters that were considered protected expressed IFN-γ and IL10 mRNA levels that returned to uninfected skin levels. In contrast to the nasal route, intramuscular (IM) immunisation failed to provide protection.

Conclusions/Significance

These results demonstrate for the first time that the nasal route of immunisation can induce cross protection against L. braziliensis infection.

Leishmaniasis is a disease that is common in most tropical countries. In Brazil, the cutaneous form of the disease is highly prevalent, with approximately 28,000 new cases reported annually. L. (Viannia) braziliensis is the main causative agent of cutaneous leishmaniasis; however, vaccine studies against protozoans of the subgenus Viannia have been largely neglected, mainly due to the high resistance of most mouse strains to the infection. Here, the authors used the golden hamster, which is highly susceptible to dermotropic Leishmania spp infection. It was previously shown that oral and intranasal vaccination with whole L. (Leishmania) amazonensis antigens (LaAg) protected mice against L. amazonensis infection. In the present study, the authors investigated whether the protective effect of intranasal immunisation with LaAg can be extended to L. braziliensis infection using the golden hamster model. The results showed that intranasal immunisation with LaAg significantly reduced lesion growth and parasitic load as well as IgG and IgG2 serum levels. At the endpoint of the experiment, intranasally immunised hamsters that were considered protected expressed IFN-γ and IL10 mRNA at levels similar to those in uninfected skin. These data show that the use of a proper animal model and/or different vaccination strategies may facilitate the development of an effective vaccine against L. braziliensis.

Antileishmanial drug discovery: comprehensive review of the last 10 years

This review covers the current aspects of leishmaniasis including marketed drugs, new antileishmanial agents, and possible drug targets of antileishmanial agents.

PEGylated silver doped zinc oxide nanoparticles as novel photosensitizers for photodynamic therapy against Leishmania

We describe daylight responsive silver (Ag) doped semiconductor nanoparticles of zinc oxide (DSNs) for photodynamic therapy (PDT) against Leishmania. The developed materials were characterized by X-ray diffraction analysis (XRD), Rutherford backscattering (RBS), diffused reflectance spectroscopy (DRS), and band-gap analysis. The Ag doped semiconductor nanoparticles of zinc oxide were PEGylated to enhance their biocompatibility. The DSNs demonstrated effective daylight response in the PDT of Leishmania protozoans, through the generation of reactive oxygen species (ROS) with a quantum yield of 0.13 by nondoped zinc oxide nanoparticles (NDSN) whereas 0.28 by DSNs. None of the nanoparticles have shown any antileishmanial activity in dark, confirming that only ROS produced in the daylight were involved in the killing of leishmanial cells. Furthermore, the synthesized nanoparticles were found biocompatible. Using reactive oxygen species scavengers, cell death was attributable mainly to 77-83% singlet oxygen and 18-27% hydroxyl radical. The nanoparticles caused permeability of the cell membrane, leading to the death of parasites. Further, the uptake of nanoparticles by Leishmania cells was confirmed by inductively coupled plasma atomic emission spectroscopy (ICP-AES). We believe that these DSNs are widely applicable for the PDT of leishmaniasis, cancers, and other infections due to daylight response.

Evidences for leishmanicidal activity of the naphthoquinone derivative epoxy-α-lapachone

In this work, we analyze the leishmanicidal effects of epoxy-α-lapachone on Leishmania (Viannia) braziliensis and Leishmania (Leishmania) amazonensis. Promasigotes and amastigotes (inhabiting human macrophages) from both species were assayed to verify the compound's activity over the distinct morphological stages. The incubation with epoxy-α-lapachone led to a significant decrease in the numbers of promastigotes from both species in the cultures, in a dose-and time-dependent fashion. The survival of amastigotes inhabiting human macrophages was also drastically affected by the compound, as shown by the variations in the endocytic index. Our results indicate that the epoxy-α-lapachone has an antiparasitic effect over Leishmania in both morphological stages and may potentially affect a range of species in two distinct subgenera of this parasite.

Reactive oxygen species regulates expression of iron-sulfur cluster assembly protein IscS of Leishmania donovani

The cysteine desulfurase, IscS, is a highly conserved and essential component of the mitochondrial iron-sulfur cluster (ISC) system that serves as a sulfur donor for Fe-S clusters biogenesis. Fe-S clusters are versatile and labile cofactors of proteins that orchestrate a wide array of essential metabolic processes, such as energy generation and ribosome biogenesis. However, no information regarding the role of IscS or its regulation is available in Leishmania, an evolving pathogen model with rapidly developing drug resistance. In this study, we characterized LdIscS to investigate the ISC system in AmpB-sensitive vs resistant isolates of L. donovani and to understand its regulation. We observed an upregulated Fe-S protein activity in AmpB-resistant isolates but, in contrast to our expectations, LdIscS expression was upregulated in the sensitive strain. However, further investigations showed that LdIscS expression is positively correlated with ROS level and negatively correlated with Fe-S protein activity, independent of strain sensitivity. Thus, our results suggested that LdIscS expression is regulated by ROS level with Fe-S clusters/proteins acting as ROS sensors. Moreover, the direct evidence of a mechanism, in support of our results, is provided by dose-dependent induction of LdIscS-GFP as well as endogenous LdIscS in L. donovani promastigotes by three different ROS inducers: H2O2, menadione, and Amphotericin B. We postulate that LdIscS is upregulated for de novo synthesis or repair of ROS damaged Fe-S clusters. Our results reveal a novel mechanism for regulation of IscS expression that may help parasite survival under oxidative stress conditions encountered during infection of macrophages and suggest a cross talk between two seemingly unrelated metabolic pathways, the ISC system and redox metabolism in L. donovani.

Resveratrol is active against Leishmania amazonensis: in vitro effect of its association with Amphotericin B

Resveratrol is a polyphenol found in black grapes and red wine and has many biological activities. In this study, we evaluated the effect of resveratrol alone and in association with amphotericin B (AMB) against Leishmania amazonensis. Our results demonstrate that resveratrol possesses both antipromastigote and antiamastigote effects, with 50% inhibitory concentrations (IC50s) of 27 and 42 μM, respectively. The association of resveratrol with AMB showed synergy for L. amazonensis amastigotes, as demonstrated by the mean sums of fractional inhibitory index concentration (mean ΣFIC) of 0.483, although for promastigotes, this association was indifferent. Treatment with resveratrol increased the percentage of promastigotes in the sub-G0/G1 phase of the cell cycle, reduced the mitochondrial potential, and showed an elevated choline peak and CH2-to-CH3 ratio in the nuclear magnetic resonance (NMR) spectroscopy analysis; all these features indicate parasite death. Resveratrol also decreased the activity of the enzyme arginase in uninfected and infected macrophages with and without stimulation with interleukin-4 (IL-4), also implicating arginase inhibition in parasite death. The anti-Leishmania effect of resveratrol and its potential synergistic association with AMB indicate that these compounds should be subjected to further studies of drug association therapy in vivo.

Antileishmanial, toxicity, and phytochemical evaluation of medicinal plants collected from Pakistan

Leishmaniasis is an important parasitic problem and is in focus for development of new drugs all over the world. Objective of the present study was to evaluate phytochemical, toxicity, and antileishmanial potential of Jurinea dolomiaea, Asparagus gracilis, Sida cordata, and Stellaria media collected from different areas of Pakistan. Dry powder of plants was extracted with crude methanol and fractionated with n-hexane, chloroform, ethyl acetate, n-butanol, and water solvents in escalating polarity order. Qualitative phytochemical analysis of different class of compounds, that is, alkaloids, saponins, terpenoids, anthraquinones, cardiac glycosides, coumarins, phlobatannins, flavonoids, phenolics, and tannins, was tested. Its appearance was observed varying with polarity of solvent used for fractionation. Antileishmanial activity was performed against Leishmania tropica KWH23 promastigote. Potent antileishmanial activity was observed for J. dolomiaea methanol extract (IC50 = 10.9 ± 1.1 μ g/mL) in comparison to other plant extracts. However, J. dolomiaea "ethyl acetate fraction" was more active (IC50 = 5.3 ± 0.2 μ g/mL) against Leishmania tropica KWH23 among all plant fractions as well as standard Glucantime drug (6.0 ± 0.1 μ g/mL). All the plants extract and its derived fraction exhibited toxicity in safety range (LC50 > 100) in brine shrimp toxicity evaluation assay.

Antifungal, Antileishmanial, and Cytotoxicity Activities of Various Extracts of Berberis vulgaris (Berberidaceae) and Its Active Principle Berberine

In this study, in vitro antidermatophytic activity against Trichophyton mentagrophytes, Trichophyton rubrum, Microsporum canis, and Microsporum gypseum was studied by disk diffusion test and assessment of minimum inhibitory concentration (MIC) using CLSI broth macrodilution method (M38-A2). Moreover, antileishmanial and cytotoxicity activity of B. vulgaris and berberine against promastigotes of Leishmania major and Leishmania tropica were evaluated by colorimetric MTT assay. The findings indicated that the various extracts of B. vulgaris particularly berberine showed high potential antidermatophytic against pathogenic dermatophytes tested with MIC values varying from 0.125 to >4 mg/mL. The results revealed that B. vulgaris extracts as well as berberine were effective in inhibiting L. major and L. tropica promastigotes growth in a dose-dependent manner with IC50 (50% inhibitory concentration) values varying from 2.1 to 26.6  μ g/mL. Moreover, it could be observed that berberine as compared with B. vulgaris exhibited more cytotoxicity against murine macrophages with CC50 (cytotoxicity concentration for 50% of cells) values varying from 27.3 to 362.6  μ g/mL. Results of this investigation were the first step in the search for new antidermatophytic and antileishmanial drugs. However, further works are required to evaluate exact effect of these extracts in animal models as well as volunteer human subjects.

Isolation of arginase inhibitors from the bioactivity-guided fractionation of Byrsonima coccolobifolia leaves and stems

Byrsonima coccolobifolia leaf and stem extracts were studied in the search for possible leishmanicidal compounds using arginase (ARG) from Leishmania amazonensis as a molecular target. Flavonoids 1b, 1e-1g, 2a, 2b, and 2d-2f showed significant inhibitory activity, with IC50 values ranging from 0.9 to 4.8 μM. The kinetics of the most active compounds were determined. Flavonoids 1e, 1f, 2a, 2b, and 2e were characterized as noncompetitive inhibitors of ARG with dissociation constants (Ki) ranging from 0.24 to 3.8 μM, demonstrating strong affinity. Structure-activity relationship studies revealed some similarities in the structural features of flavonoids related to ARG activity.

Treatment with triterpenic fraction purified from Baccharis uncinella leaves inhibits Leishmania (Leishmania) amazonensis spreading and improves Th1 immune response in infected mice

The current medications used to treat leishmaniasis have many side effects for patients; in addition, some cases of the disease are refractory to treatment. Therefore, the search for new leishmanicidal compounds is indispensable. Recently, it was demonstrated that oleanolic- and ursolic-containing fraction from Baccharis uncinella leaves eliminated the promastigote and amastigote forms of Leishmania (Leishmania) amazonensis and L. (Viannia) braziliensis without causing toxic effects for J774 macrophages. Thus, the aim of the present work was to characterize the therapeutic effect of the triterpenic fraction in L. (L.) amazonensis-infected BALB/c mice. Oleanolic- and ursolic acid-containing fraction was extracted from B. uncinella leaves using organic solvents and chromatographic procedures. L. (L.) amazonensis-infected BALB/c mice were treated intraperitoneally with triterpenic fraction during five consecutive days with 1.0 and 5.0 mg/kg of triterpenic fraction, or with 10.0 mg/kg of amphotericin B drug. Groups of mice treated with the triterpenic fraction, presented with decreased lesion size and low parasitism of the skin-both of which were associated with high amounts of interleukin-12 and interferon gamma. The curative effect of this fraction was similar to amphotericin B-treated mice; however, the final dose, required to eliminate amastigotes, was lesser than amphotericin B. Moreover, triterpenic fraction did not cause microscopic alterations in liver, spleen, heart, lung, and kidney of experimental groups. This work suggests that this fraction possesses compounds that are characterized by leishmanicidal and immunomodulatory activities. From this perspective, the triterpenic fraction can be explored as a new therapeutic agent for use against American Tegumentar Leishmaniasis.

Leishmanicidal activity of synthetic chalcones in Leishmania (Viannia) braziliensis

The treatment of American cutaneous leishmaniasis (ACL) is based on a small group of compounds that were developed decades ago, all of which are highly toxic and have a high rate of treatment failure. The chalcones show leishmanicidal activity, yet few studies have evaluated this activity against Leishmania (Viannia) braziliensis, one of the most important species of Leishmania across Latin America. Four new synthetic chalcones (1-4) were evaluated for inhibitory activity in vitro against promastigotes and intracellular parasites 24h post infection of L. (V.) braziliensis, cytotoxicity for macrophages J774.A1 and red blood cells, and the ability to stimulate nitric oxide production. The results for the inhibitory concentration for 50% of the promastigotes (IC50) (1.38±1.09-6.36±2.04μM), cytotoxic concentration for 50% of the macrophages (CC50) (13.49±3.13-199.43±4.11μM), and selectivity index (SI) (3.76 to 33.94) indicate that all chalcones (1-4) showed an effect on promastigotes of L. (V.) braziliensis; chalcone 2 had the highest SI. The haemolytic assay with chalcones 1 (301.93μM), 2 (534.18μM), 3 (419.46μM) and 4 (381.11μM) showed 0.00%, 2.33%, 0.57% and 1.74% haemolysis, respectively. All chalcones significantly reduced the infection index of macrophages by parasites; for chalcones (1-3) this effect may be dependent on nitric-oxide production by macrophages. The chalcones tested exhibited inhibitory activity for promastigotes and intracellular parasites of L. (V.) braziliensis, with low toxicity for macrophages and red blood cells. The anti-Leishmania activity of chalcones (1-3) may depend on the stimulation of nitric-oxide production in the initial stage of infection. These results show an initially encouraging potential for the use of chalcones (1-4) to treat ACL.

Leishmania amazonensis promastigotes present two distinct modes of nucleus and kinetoplast segregation during cell cycle

Here, we show the morphological events associated with organelle segregation and their timing in the cell cycle of a reference strain of Leishmania (L.) amazonensis promastigotes, the main causative agent of Tegumentary leishmaniasis in the Americas. We show evidences that during the cell cycle, L. amazonensis promastigotes present two distinct modes of nucleus and kinetoplast segregation, which occur in different temporal order in different proportions of cells. We used DAPI-staining and EdU-labeling to monitor the segregation of DNA-containing organelles and DNA replication in wild-type parasites. The emergence of a new flagellum was observed using a specific monoclonal antibody. The results show that L. amazonensis cell cycle division is peculiar, with 65% of the dividing cells duplicating the kinetoplast before the nucleus, and the remaining 35% doing the opposite or duplicating both organelles concomitantly. In both cases, the new flagellum appeared during S to G2 phase in 1N1K cells and thus before the segregation of both DNA-containing organelles; however, we could not determine the exact timing of flagellar synthesis. Most of these results were confirmed by the synchronization of parasites using hydroxyurea. Altogether, our data show that during the cell cycle of L. amazonensis promastigotes, similarly to L. donovani, the segregation of nucleus and kinetoplast do not follow a specific order, especially when compared to other trypanosomatids, reinforcing the idea that this characteristic seems to be species-specific and may represent differences in cellular biology among members of the Leishmania genus.

Triazino indole-quinoline hybrid: a novel approach to antileishmanial agents

A novel series of 1,2,4-triazino-[5,6b]indole-3-thione covalently linked to 7-chloro-4-aminoquinoline have been synthesized and evaluated for their in vitro activity against extracellular promastigote and intracellular amastigote form of Leishmania donovani. Among all tested compounds, compounds 7a and 7b were found to be the most active with IC50 values 1.11, 0.36μM and selectivity index (SI) values 67, >1111, respectively, against amastigote form of L. donovani which is several folds more potent than the standard drugs, miltefosine (IC50=8.10μM, SI=7) and sodium stibo-gluconate (IC50=54.60μM, SI⩾7).

Sphingosine kinase A is a pleiotropic and essential enzyme for Leishmania survival and virulence

Sphingosine kinase is a key enzyme in sphingolipid metabolism, catalysing the conversion of sphingosine or dihydrosphingosine into sphingosine-1-phosphate or dihydrosphingosine-1-phosphate respectively. In mammals, sphingosine-1-phosphate is a powerful signalling molecule regulating cell growth, differentiation, apoptosis and immunity. Functions of sphingosine kinase or sphingosine-1-phosphate in pathogenic protozoans are virtually unknown. While most organisms possess two closely related sphingosine kinases, only one sphingosine kinase homologue (SKa) can be identified in Leishmania, which are vector-borne protozoan parasites responsible for leishmaniasis. Leishmania SKa is a large, cytoplasmic enzyme capable of phosphorylating both sphingosine and dihydrosphingosine. Remarkably, deletion of SKa leads to catastrophic defects in both the insect stage and mammalian stage of Leishmania parasites. Genetic and biochemical analyses demonstrate that proper expression of SKa is essential for Leishmania parasites to remove toxic metabolites, to survive stressful conditions, and to cause disease in mice. Therefore, SKa is a pleiotropic enzyme with vital roles throughout the life cycle of Leishmania. The essentiality of SKa and its apparent divergence from mammalian counterparts suggests that this enzyme can be selectively targeted to reduce Leishmania infection.

7-Chloro-4-quinolinyl hydrazones: a promising and potent class of antileishmanial compounds

In this work, we report the antileishmanial evaluation of twenty 7-chloro-4-quinolinyl hydrazone derivatives (1-20). Firstly, the compounds were tested against promastigotes of four different Leishmania species. After that, all derivatives were assayed against L. braziliensis amastigotes and murine macrophages. Furthermore, it was investigated whether the antiamastigote L. braziliensis effect of the compounds could be associated with nitric oxide production. Compounds 6 and 7 showed a strong leishmanicidal activity against intracellular parasite with IC50 in nanogram levels (30 and 20 ng/mL, respectively). Appreciable activity of three compounds tested can be considered an important finding for the rational design of new leads for antileishmanial compounds.

In vitro and in vivo effects of (-)-epigallocatechin 3-O-gallate on Leishmania amazonensis

(-)-Epigallocatechin 3-O-gallate (1), the most abundant flavanol in green tea, has been reported to have antiproliferative effects on Trypanosoma cruzi. The present study reports the effects in vitro and in vivo of 1 on Leishmania amazonensis. L. amazonensis-infected macrophages treated with 1 exhibited a significant reduction of the infection index in a dose-dependent manner, with an IC50 value of 1.6 μM. Oral administration of 1 on L. amazonensis-infected BALB/c mice (30 mg/kg/day) resulted in a decrease in the lesion size and parasite burden, without altering serological markers of toxicity. These data demonstrate the in vitro and in vivo leishmanicidal effects of compound 1.

Drug resistance in leishmaniasis: current drug-delivery systems and future perspectives

Leishmaniasis is a complex of diseases with numerous clinical manifestations for instance harshness from skin lesions to severe disfigurement and chronic systemic infection in the liver and spleen. So far, the most classical leishmaniasis therapy, despite its documented toxicities, remains pentavalent antimonial compounds. The arvailable therapeutic modalities for leishmaniasis are overwhelmed with resistance to leishmaniasis therapy. Mechanisms of classical drug resistance are often related with the lower drug uptake, increased efflux, the faster drug metabolism, drug target modifications and over-expression of drug transporters. The high prevalence of leishmaniasis and the appearance of resistance to classical drugs reveal the demand to develop and explore novel, less toxic, low cost and more promising therapeutic modalities. The review describes the mechanisms of classical drug resistance and potential drug targets in Leishmania infection. Moreover, current drug-delivery systems and future perspectives towards Leishmaniasis treatment are also covered.

Efficacy of biogenic selenium nanoparticles against Leishmania major: in vitro and in vivo studies

PROJECT

This study investigated the in vitro and in vivo effectiveness of biogenic selenium nanoparticles (Se NPs), biosynthesized by Bacillus sp. MSh-1, against Leishmania major (MRHO/IR/75/ER).

PROCEDURE

The 3-(4,5-dimethylthiozol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) assay was used to evaluate the cytotoxicity effects of the biogenic Se NPs against both promastigote and amastigote forms of L. major. In a separate in vivo experiment, we also determined the preventive and therapeutic effects of biogenic Se NPs in BALB/c mice following subcutaneous infected with L. major.

RESULTS

The MTT assays showed that the highest toxicity occurred after 72 h against both promastigote and amastigote forms of L. major. The cytotoxicity of Se NPs was higher at all incubation times (24, 48, and 72 h) against the promastigote than the amastigote form (p<0.05). The 50% inhibitory concentrations (IC50) of the Se NPs were 1.62±0.6 and 4.4±0.6 μg ml(-1) against the promastigote and amastigote forms, respectively, after a 72-h incubation period. Apoptosis assays showed DNA fragmentation in promastigotes treated with Se NPs. In an animal challenge, prophylactic doses of biogenic Se NPs delayed the development of localized cutaneous lesions. Moreover, daily administration of Se NPs (5 or 10 mg kg(-1) day(-1)) in similarly infected BALB/c mice that had not received prophylactic doses of Se NPs also abolished the localized lesions after 14 days.

CONCLUSION

Based on these in vitro and in vivo studies, biogenic Se NPs can be considered as a novel therapeutic agent for treatment of the localized lesions typical of cutaneous leishmaniasis.

LABCG2, a new ABC transporter implicated in phosphatidylserine exposure, is involved in the infectivity and pathogenicity of Leishmania

Leishmaniasis is a neglected disease produced by the intracellular protozoan parasite Leishmania. In the present study, we show that LABCG2, a new ATP-binding cassette half-transporter (ABCG subfamily) from Leishmania, is involved in parasite virulence. Down-regulation of LABCG2 function upon expression of an inactive mutant version of this half-transporter (LABCG2(K/M)) is shown to reduce the translocation of short-chain analogues of phosphatidylserine (PS). This dominant-negative phenotype is specific for the headgroup of the phospholipid, as the movement of phospholipid analogues of phosphatidylcholine, phosphatidylethanolamine or sphingomyelin is not affected. In addition, promastigotes expressing LABCG2(K/M) expose less endogenous PS in the stationary phase than control parasites. Transient exposure of PS at the outer leaflet of the plasma membrane is known to be one of the mechanisms used by Leishmania to infect macrophages and to silence their immune response. Stationary phase/metacyclic promastigotes expressing LABCG2(K/M) are less infective for macrophages and show decreased pathogenesis in a mouse model of cutaneous leishmaniasis. Thus, mice infected with parasites expressing LABCG2(K/M) did not develop any lesion and showed significantly lower inflammation and parasite burden than mice infected with control parasites. Our results indicate that LABCG2 function is required for the externalization of PS in Leishmania promastigotes, a process that is involved in the virulence of the parasite.

DNA aptamers selectively target Leishmania infantum H2A protein

Parasites of the genus Leishmania produce leishmaniasis which affects millions people around the world. Understanding the molecular characteristics of the parasite can increase the knowledge about the mechanisms underlying disease development and progression. Thus, the study of the molecular features of histones has been considered of particular interest because Leishmania does not condense the chromatin during mitosis and, consequently, a different role for these proteins in the biology of the parasite can be expected. Furthermore, the sequence divergences in the amino and in the carboxy-terminal domains of the kinetoplastid core histones convert them in potential diagnostic and/or therapeutics targets. Aptamers are oligonucleotide ligands that are selected in vitro by their affinity and specificity for the target as a consequence of the particular tertiary structure that they are able to acquire depending on their sequence. Development of high-affinity molecules with the ability to recognize specifically Leishmania histones is essential for the progress of this kind of study. Two aptamers which specifically recognize Leishmania infantum H2A histone were cloned from a previously obtained ssDNA enriched population. These aptamers were sequenced and subjected to an in silico analysis. ELONA, slot blot and Western blot were performed to establish aptamer affinity and specificity for LiH2A histone and ELONA assays using peptides corresponding to overlapped sequences of LiH2A were made mapping the aptamers:LiH2A interaction. As "proofs of concept", aptamers were used to determine the number of parasites in an ELONA platform and to purify LiH2A from complex mixtures. The aptamers showed different secondary structures among them; however, both of them were able to recognize the same peptides located in a side of the protein. In addition, we demonstrate that these aptamers are useful for LiH2A identification and also may be of potential application as diagnostic system and as a laboratory tool with purification purpose.

The stepwise selection for ketoconazole resistance induces upregulation of C14-demethylase (CYP51) in Leishmania amazonensis

Ketoconazole is a clinically safe antifungal agent that also inhibits the growth of Leishmania spp. A study was undertaken to determine whether Leishmania parasites are prone to becoming resistant to ketoconazole by upregulating C14-demethylase after stepwise pharmacological pressure. Leishmania amazonensis promastigotes [inhibitory concentration (IC)₅₀ = 2 µM] were subjected to stepwise selection with ketoconazole and two resistant lines were obtained, La8 (IC₅₀ = 8 µM) and La10 (IC₅₀ = 10 µM). As a result, we found that the resistance level was directly proportional to the C14-demethylase mRNA expression level; we also observed that expression levels were six and 12 times higher in La8 and La10, respectively. This is the first demonstration that L. amazonensis can up-regulate C14-demethylase in response to drug pressure and this report contributes to the understanding of the mechanisms of parasite resistance.

RFLPs of ITS, ITS1 and hsp70 amplicons and sequencing of ITS1 of recent clinical isolates of Kala-azar from India and Bangladesh confirms the association of L. tropica with the disease

Visceral Leishmaniasis or Kala-azar (KA) is a serious health concern in India. In the present study, Restriction Fragment Length Polymorphism (RFLP) of three genetic markers viz., Internal Transcribed Spacer (ITS), ITS1 and heat shock protein 70 (hsp70) have been employed for typing the clinical isolates [n=15] of KA and post Kala-azar Dermal Leishmaniosis (PKDL) collected from India and Bangladesh in the period of 2006-2010. Experimentally, ITS, ITS1 and hsp70 regions of genomes of all the clinical isolates were separately amplified by PCR and then digested with restriction enzymes: ITS with Alu1, EcoR1 and Msp1, ITS1 with Hae III and Rsa1 and hsp70 with Hae III. The resultant fragments were analyzed by agarose gel electrophoresis and the RFLP profiles of the clinical isolates were compared with that of the WHO reference strains for Leishmania donovani (DD8) and Leishmania tropica (K27), respectively. Also, the ITS1 regions of all the clinical isolates along with the two WHO reference strains were sequenced and a phylogram was constructed to ascertain the extent of similarity or dissimilarity. Interestingly, the RFLP profiles of one of the isolates showed a significant homology with K27 and the phylogram revealed its closeness with the same putting credence to our earlier typing of isolates by RAPD method. This observation also supported an earlier report claiming that both the species are responsible for KA in India and thus, emphasizes urgent need for thorough systematic characterization of the clinical isolates of Indian KA as appropriate treatment regime relies primarily on proper diagnosis.