Antileishmanial activity of a naphthoquinone derivate against promastigote and amastigote stages of Leishmania infantum and Leishmania amazonensis and its mechanism of action against L. amazonensis species

A phthalimide-triazole derivative obtained by click chemistry exhibits trypanocidal activity, induces autophagy and ameliorates Trypanosoma cruzi infection

Chagas disease (CD), caused by Trypanosoma cruzi, remains a leading cause of cardiomyopathy and heart failure in Latin America. Since the 1970s, benznidazole (BNZ) and nifurtimox (NFX) have been the only chemotherapeutic agents used to treat CD. However, their toxicity and low effectiveness in the chronic phase of the disease, make the development of more efficient chemotherapeutics imperative. Here, we investigated the effects of 1,2,3-triazole hybrids, synthesized via click chemistry, containing either phthalimide (FT1, FT2, FT3, FT4) or naphthoquinone (NT1) moieties on T. cruzi and their cytotoxicity on mammalian cells. NT1 and FT1 were the most effective against intracellular parasite with an IC50 = 31.1 and 189.2 µM, respectively. FT1-FT4 showed low cytotoxicity to mammalian cells (CC50 > 754 µM), while NT1 exhibited moderate toxicity (CC50 ≥ 96.1 µM). FT1 demonstrated the highest selectivity towards trypomastigotes and amastigotes with selectivity indexes (SeI) of 6.9 and 6.7, respectively. Ultrastructural analysis of trypomastigotes treated with FT1 revealed mitochondrial alterations, lipid accumulation and Golgi complex disorganization. FT1 also decreased the mitochondrial membrane potential, increased mitochondrial reactive oxygen species (ROS) production, and induced late apoptosis in trypomastigotes. In infected cardiac cells, FT1 treatment led to degradation of amastigotes and Golgi disruption. An increase in autophagosomes in treated host cells and their interaction with intracellular parasites suggest that FT1-induced host cell autophagy may play a role in mitigating the infection and protecting cardiac cells from its deleterious effects.

Evaluation of SB-83, a 2-amino-thiophene derivative, against Leishmania species that cause visceral leishmaniasis

Visceral leishmaniasis is a systemic disease that affects various internal organs and represents the most severe and fatal form of leishmaniasis. Conventional treatment presents significant challenges, such as prolonged management in hospital settings, high toxicity, and an increasing growing number of cases of resistance. In previous studies, our research group demonstrated the effective and selective activity of the 2-amino-thiophene derivative SB-83 in preclinical models of cutaneous leishmaniasis. Given the urgent need for new therapeutic alternatives for visceral leishmaniasis, and considering our previous promising results for SB-83, this study investigated the antileishmanial activity of the compound on the etiological agents of visceral leishmaniasis. SB-83 demonstrated efficacy in inhibiting the growth of promastigote forms of Leishmania (Leishmania) infantum (IC50 = 7.46 µM) and Leishmania (Leishmania) donovani (IC50 = 9.84 µM). In the cytotoxicity evaluation, in RAW 264.7 macrophages, the compound revealed a CC50 = 52.27 µM, being more toxic to the parasite, and respective selectivity indices (SI) of 7 and 5.31 against the previously mentioned species. Atomic force microscopy analysis showed that the compound causes alterations in surface roughness, formation of englobulations, and accumulation of lipids, all of which are indicative of cell death by apoptosis. This was confirmed by flow cytometry, which showed an increase in the number of cells labeled with Annexin V-FITC+/IP-, indicating apoptosis. SB-83 showed even greater efficacy against intramacrophagic amastigote forms (EC50 = 2.91 µM), which was associated with structural changes, such as increased lysosomal volume, and cellular mechanisms, including elevated levels of cytokines TNF-α and IL-12, reactive oxygen and nitrogen species, and reduced levels of cytokines IL-10 and IL-6, as well as decreased arginase activity. The results allow us to conclude that the 2-amino-thiophene derivative SB-83 is a promising compound for development of new treatments against visceral leishmaniasis.

Photoinactivation mechanism of hypericin nanoencapsulated in P123 against Microsporum canis

Aim: To evaluate the photodynamic mechanism of hypericin nanoencapsulated in P123 copolymer micelles against Microsporum canis in vitro.Material & methods: Antifungal susceptibility tests were performed, including the determination of the minimum fungicidal concentration and time-kill curve. Flow cytometry was used to evaluate the internalization of P123-Hyp in conidia and the activation of PDT type I and II mechanisms via the detection of reactive oxygen species (ROS), as well as to assess changes in the cell membrane using propidium iodide (PI) and cell morphology.Results: P123-Hyp-PDT exerted a fungistatic action on fungus, maintaining this action up to 24 h after exposure, corroborating the PS internalization results, which showed satisfactory uptake of P123-Hyp from a concentration of 3.125 μmol/l. Among the ROS studied, singlet oxygen was detected. Furthermore, the increased fluorescence intensity of PI in treated cells indicated necrotic cell death, while the size and granularity of the cells were also altered.Conclusion: Our results show, for the first time, a proposal for the mechanism of action of P123-Hyp-mediated PDT against M. canis, proving that it has a prolonged action on the fungus through activation of the type II photodynamic pathway, which resulted in disruption of the plasma membrane and cellular alterations.

Buparvaquone Induces Ultrastructural and Physiological Alterations Leading to Mitochondrial Dysfunction and Caspase-Independent Apoptotic Cell Death in Leishmania donovani

Leishmaniasis is a neglected tropical disease (endemic in 99 countries) caused by parasitic protozoa of the genus Leishmania. As treatment options are limited, there is an unmet need for new drugs. The hydroxynaphthoquinone class of compounds demonstrates broad-spectrum activity against protozoan parasites. Buparvaquone (BPQ), a member of this class, is the only drug licensed for the treatment of theileriosis. BPQ has shown promising antileishmanial activity but its mode of action is largely unknown. The aim of this study was to evaluate the ultrastructural and physiological effects of BPQ for elucidating the mechanisms underlying the in vitro antiproliferative activity in Leishmania donovani. Transmission and scanning electron microscopy analyses of BPQ-treated parasites revealed ultrastructural effects characteristic of apoptosis-like cell death, which include alterations in the nucleus, mitochondrion, kinetoplast, flagella, and the flagellar pocket. Using flow cytometry, laser scanning confocal microscopy, and fluorometry, we found that BPQ induced caspase-independent apoptosis-like cell death by losing plasma membrane phospholipid asymmetry and cell cycle arrest at sub-G0/G1 phase. Depolarization of the mitochondrial membrane leads to the generation of oxidative stress and impaired ATP synthesis followed by disruption of intracellular calcium homeostasis. Collectively, these findings provide valuable mechanistic insights and demonstrate BPQ's potential for development as an antileishmanial agent.

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.

Anti-Leishmania major activity of Calotropis procera extract by increasing ROS production and upregulating TNF-α, IFN-γ and iNOS mRNA expression under in vitro conditions

BACKGROUND

Leishmaniasis, caused by protozoan parasites of the genus Leishmania, is a neglected tropical disease with 700,000 to 1,000,000 global new cases annually. Adverse effects associated with expense, long-term treatment and drug resistance have made conventional therapies unfavorable, encouraging the search for alternative drugs based on plant products. In this study, the effect of Calotropis procera (Asclepiadaceae) extract against viability of promastigotes and amastigotes of Leishmania major was evaluated in vitro.

METHODS

The extract from the leaves of C. procera seedlings was prepared using a methanol maceration method. The colorimetric cell viability 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was used to determine the growth-inhibitory effect of the extract on promastigotes. The level of reactive oxygen species (ROS) in promastigote cultures was determined after treatment with the extract using the 2',7'-dichlorofluorescein diacetate (DCFH-DA) method and compared with untreated cultures (control). After exposure to the extract the expression levels of tumor necrosis factor-α (TNF-α), interferon gamma (IFN-γ) and inducible nitric oxide synthase (iNOS) genes were determined and compared to control in peripheral blood mononuclear cells (PBMCs) infected with L. major.

RESULTS

Based on the MTT assay, the C. procera extract significantly reduced the proliferation of L. major promastigotes with IC50 values of 377.28 and 222.44 μg/mL for 24 and 72 h, respectively (p < 0.01). After treatment with 222.44 and 377.28 μg/mL of C. procera extract, ROS production in L. major promastigote cultures increased 1.2- to 1.65-fold and 2- to 4-fold compared to the control, respectively (p < 0.05). C. procera extract induced significant increases in gene expression of TNF-α (2.76-14.83 fold), IFN-γ (25.63-threefold) and iNOS (16.32-3.97 fold) in infected PBMCs compared to control (p < 0.01).

CONCLUSIONS

On the basis of its anti-leishmanial activity, C. procera can be considered as a promising new plant source for the potential treatment of leishmaniasis.

Antileishmanial activity of 2-amino-thiophene derivative SB-200

Leishmaniasis, presenting the highest number of cases worldwide is one of the most serious Neglected Tropical Diseases (NTDs). Clinical manifestations are intrinsically related to the host's immune response making immunomodulatory substances the target of numerous studies on antileishmanial activity. The currently available drugs used for treatment present various problems including high toxicity, low efficacy, and associated drug resistance. The search for therapeutic alternatives is urgent, and in this context, thiophene derivatives appear to be a promising therapeutic alternative (many have shown promising anti-leishmanial activity). The objective of this study was to investigate the antileishmanial activity of the 2-amino-thiophenic derivative SB-200. The thiophenic derivative was effective in inhibiting the growth of Leishmania braziliensis, Leishmania major, and Leishmania infantum promastigotes, obtaining respective IC50 values of 4.25 μM, 4.65 μM, and 3.96 μM. For L. infantum, it was demonstrated that the antipromastigote effect of SB-200 is associated with cell membrane integrity losses, and with morphological changes observed during scanning and transmission electron microscopy. Cytotoxicity was performed for J774.A1 macrophages and VERO cells, to obtain a CC50 of 42.52 μM and a SI of 10.74 for macrophages and a CC50 of 39.2 μM and an SI of 9.89 for VERO cells. The anti-amastigote activity of SB-200 revealed an IC50 of 2.85 μM and an SI of 14.97 against macrophages and SI of 13.8 for VERO cells. The anti-amastigote activity of SB-200 is associated with in vitro immunomodulation. For acute toxicity, SB-200 against Zophobas morio larvae permitted 100% survival. We conclude that the 2-amino-thiophenic derivative SB-200 is a promising candidate for in vivo anti-leishmania drug tests to evaluate its activity, efficacy, and safety.

Antiprotozoal activity of natural products from Nigerien plants used in folk medicine

In the course of the screening of plants from Niger for antiprotozoal activity, the methanol extract of Cassia sieberiana, and the dichloromethane extracts of Ziziphus mauritiana and Sesamun alatum were found to be active against protozoan parasites, namely Trypanosoma brucei rhodesiense, Trypanosoma cruzi, Leishmania donovani and/or Plasmodium falciparum. Myricitrin (1), quercitrin (2) and 1-palmitoyl-lysolecithin (3) were isolated from C. sieberiana. From Z. mauritiana, the three triterpene derivatives 13, 15, and 16 are described here for the first time. Their chemical structures were determined by 1D and 2D NMR experiments, UV, IR and HRESIMS data. The absolute configurations were assigned via comparison of the experimental and calculated ECD spectra. In addition, eight known cyclopeptide alkaloids (4, 5, 7-12), and five known triterpenoids (6, 14, 17-19) were isolated. The antiprotozoal activity of the isolated compounds, as well as of eleven quinone derivatives (20-30) previously isolated from S. alatum was determined in vitro. The cytotoxicity in L6 rat myoblast cells was also evaluated. Compound 18 showed the highest antiplasmodial activity (IC₅₀ = 0.2 µm) and compound 24 inhibited T. b. rhodesiense with an IC₅₀ value of 0.007 µM. However, it also displayed significant cytotoxicity in L6 cells (IC₅₀ = 0.4 µm).

In vitro effects of lapachol and β-lapachone against Leishmania amazonensis

Leishmaniasis is a neglected disease that affects millions of people worldwide, and special attention should be given to treatment because the available drugs have limitations, which can lead to low therapeutic adherence and parasitic resistance. This study evaluated the activity of the bioactive naphthoquinones, lapachol and β-lapachone, against Leishmania amazonensis. The cell alterations were evaluated in vitro on promastigote and amastigote forms. The lethal dose (LD50) at 24, 48, and 72 h on the promastigote's forms using lapachol was 75.60, 72.82, and 58.85 μg/mL and for β-lapachone was 0.65, 1.24, and 0.71 μg/mL, respectively. The naphthoquinones significantly inhibited the survival rate of L. amazonensis amastigotes at 83.11, 57.59, and 34.95% for lapachol (82.28, 41.14, and 20.57 µg/mL), and 78.49, 83.25, and 80.22% for β-lapachone (3.26, 1.63, and 0.815 µg/mL). The compounds on the promastigote's forms led to the loss of mitochondrial membrane potential, induced changes in the integrity of the membrane, caused damage to cells suggestive of the apoptotic process, and showed inhibition of tumor necrosis factor (TNF)-α and interleukin (IL)-6 production. The results showed that these naphthoquinones are promising candidates for research on new drugs with anti-Leishmania activity derived from natural products.

In vitro evaluation of antileishmanial activity, mode of action and cellular response induced by vanillin synthetic derivatives against Leishmania species able to cause cutaneous and visceral leishmaniasis

The treatment against leishmaniasis presents problems, mainly due to their toxicity of the drugs, high cost and/or by the emergence of parasite resistant strains. In this context, new therapeutics should be searched. In this study, two novel synthetic derivatives from vanillin: [4-(2-hydroxy-3-(4-octyl-1H-1,2,3-triazol-1-yl)propoxy)-3-methoxybenzaldehyde] or 3s and [4-(3-(4-decyl-1H-1,2,3-triazol-1-yl)-2-hydroxypropoxy)-3-methoxybenzaldehyde] or 3t, were evaluated regarding their antileishmanial activity against distinct parasite species able to cause cutaneous and visceral leishmaniasis. Results showed that compounds 3s and 3t were effective against Leishmania infantum, L. amazonensis and L. braziliensis promastigote and amastigote-like forms, showing selectivity index (SI) of 25.1, 18.2 and 22.9, respectively, when 3s was used against promastigotes, and of 45.2, 7.5 and 15.0, respectively, against amastigote-like stage. Using the compound 3t, SI values were 45.2, 53.0 and 80.0, respectively, against promastigotes, and of 35.9, 46.0 and 58.4, respectively, against amastigote-like forms. Amphotericin B (AmpB) showed SI values of 5.0, 7.5 and 15.0, respectively, against promastigotes, and of 3.8, 5.0 and 7.5, respectively, against amastigote-like stage. The treatment of infected macrophages and inhibition of the infection upon pre-incubation with the molecules showed that they were effective in reducing the infection degree and inhibiting the infection in pre-incubated parasites, respectively, as compared to data obtained using AmpB. The mechanism of action of 3s and 3t was evaluated in L. infantum, revealing that both 3s and 3t altered the parasite mitochondrial membrane potential leading to reactive oxygen species production, increase in lipid corps and changes in the cell cycle, causing the parasite' death. A preliminary assay using the cell culture supernatant from treated and infected macrophages showed that 3s and 3t induced higher IL-12 and lower IL-10 values; suggesting the development of an in vitro Th1-type response in the treated cells. In this context, data indicated that 3s and 3t could be considered therapeutic agents to be tested in future studies against leishmaniasis.

Models for cytotoxicity screening of antileishmanial drugs: what has been done so far?

A growing number of studies have demonstrated the in vitro potential of an impressive number of antileishmanial candidates in the past years. However, the lack of uniformity regarding the choice of cell types for cytotoxicity assays may lead to uncomparable and inconclusive data. In vitro assays relying solely on non-phagocytic cell models may not represent a realistic result as the effect of an antileishmanial agent should ideally be presented based on its cytotoxicity profile against reticuloendothelial system cells. In the present review, we have assembled studies published in the scientific literature from 2015 to 2021 that explored leishmanicidal candidates, emphasising the main host cell models used for cytotoxicity assays. The pros and cons of different host cell types as well as primary cells and cell lines are discussed in order to draw attention to the need to establish standardised protocols for preclinical testing when assessing new antileishmanial candidates.

Gum-based nanocapsules comprising naphthoquinones enhance the apoptotic and trypanocidal activity against Trypanosoma evansi

Nanoencapsulation is a promising approach to enhance the therapeutic potential of a drug. Herein, three selected naphthoquinone (NTQ) derivatives, based on the IC₅₀ value against Trypanosoma evansi, were encapsulated using gum damar as biocompatible and biodegradable natural gum via nanoprecipitation method. Nanoformulation of NTQs (NNTQs) was less than 150 nm in size, was found to be stable and released the drug in a sustained manner. All the three NNTQs exhibited significant antitrypanosomal effect and morphological changes at approximately two to three times lesser drug concentrations. The nanoformulations exhibited enhanced production of reactive oxygen species (ROS) in the axenic culture of T. evansi and less cytotoxic effect on horse peripheral blood mononuclear cells relative to pure NTQs. As evidenced by flow cytometry, the NNTQs showed dose-dependent and time-dependent increased transition of live cells (AV^-PI^-) to early apoptotic cells (AV⁺PI^-), late apoptotic cells (AV^-PI⁺), and necrotic cells (AV⁺PI⁺) using annexin V/propidium iodide probe analysis. The results concluded that NNTQs induced more ROS, apoptosis and necrotic effects that exhibited more inhibitory effect on the growth of T. evansi with respect to respective NTQ by themselves.

Axenic amastigotes of Leishmania species as a suitable model for in vitro studies

Leishmania spp. are etiological agents of infection diseases, which in some cases can be fatal. The main forms of their biological cycle, promastigotes and amastigotes, can be maintained in vitro. While promastigotes are easier to maintain, amastigotes are more complex and can be obtained through different ways, including infection assays of tissues or in vitro cells, and differentiation from promastigotes to axenic amastigotes. Several protocols have been proposed for in vitro differentiation for at least 12 Leishmania spp. of both subgenera, Leishmania and Viannia. In this review we propose a critical summary of axenic amastigotes induction, as well as the impact of these strategies on metabolic pathways and regulatory networks analyzed by omics approaches. The parameters used by different research groups show considerable variations in temperature, pH and induction stages, as highlighted here for Leishmania (Viannia) braziliensis. Therefore, a consensus on strategies for inducing amastigogenesis is necessary to improve accuracy and even define stage-specific biomarkers. In fact, the axenic amastigote model has contributed to elucidate several aspects of the parasite cycle, however, since it does not reproduce the intracellular environment, its use requires several precautions. In addition, we present a discussion about using axenic amastigotes for drug screening, suggesting the need of a more sensitive methodology to verify cell viability in these tests. Collectively, this review explores the advantages and limitations found in studies with axenic amastigotes, done for more than 30 years, and discuss the gaps that impair their use as a suitable model for in vitro studies.

Naphthoquinones and Derivatives for Chemotherapy: Perspectives and Limitations of their Anti-trypanosomatids Activities

Chagas disease, Sleeping sickness and Leishmaniasis, caused by trypanosomatids Trypanosoma cruzi, Trypanosoma brucei and Leishmania spp., respectively, are considered neglected tropical diseases, and they especially affect impoverished populations in the developing world. The available chemotherapies are very limited, and a search for alternatives is still necessary. In folk medicine, natural naphthoquinones have been employed for the treatment of a great variety of illnesses, including parasitic infections. This review is focused on the anti-trypanosomatid activity and mechanistic analysis of naphthoquinones and derivatives. Among all the series of derivatives tested in vitro, naphthoquinone-derived 1,2,3-triazoles were very active on T. cruzi infective forms in blood bank conditions, as well as in amastigotes of Leishmania spp. naphthoquinones containing a CF₃ on a phenyl amine ring inhibited T. brucei proliferation in the nanomolar range, and naphthopterocarpanquinones stood out for their activity on a range of Leishmania species. Some of these compounds showed a promising selectivity index (SI) (30 to 1900), supporting further analysis in animal models. Indeed, high toxicity to the host and inactivation by blood components are crucial obstacles to be overcome to use naphthoquinones and/or their derivatives for chemotherapy. Multidisciplinary initiatives embracing medicinal chemistry, bioinformatics, biochemistry, and molecular and cellular biology need to be encouraged to allow the optimization of these compounds. Large scale automated tests are pivotal for the efficiency of the screening step, and subsequent evaluation of both the mechanism of action in vitro and pharmacokinetics in vivo is essential for the development of a novel, specific and safe derivative, minimizing adverse effects.

In Silico Insights into the Mechanism of Action of Epoxy-α-Lapachone and Epoxymethyl-Lawsone in Leishmania spp

Epoxy-α-lapachone (Lap) and Epoxymethyl-lawsone (Law) are oxiranes derived from Lapachol and have been shown to be promising drugs for Leishmaniases treatment. Although, it is known the action spectrum of both compounds affect the Leishmania spp. multiplication, there are gaps in the molecular binding details of target enzymes related to the parasite’s physiology. Molecular docking assays simulations were performed using DockThor server to predict the preferred orientation of both compounds to form stable complexes with key enzymes of metabolic pathway, electron transport chain, and lipids metabolism of Leishmania spp. This study showed the hit rates of both compounds interacting with lanosterol C-14 demethylase (−8.4 kcal/mol to −7.4 kcal/mol), cytochrome c (−10.2 kcal/mol to −8.8 kcal/mol), and glyceraldehyde-3-phosphate dehydrogenase (−8.5 kcal/mol to −7.5 kcal/mol) according to Leishmania spp. and assessed compounds. The set of molecular evidence reinforces the potential of both compounds as multi-target drugs for interrupt the network interactions between parasite enzymes, which can lead to a better efficacy of drugs for the treatment of leishmaniases.

In Vitro, In Vivo and In Silico Effectiveness of LASSBio-1386, an N-Acyl Hydrazone Derivative Phosphodiesterase-4 Inhibitor, Against Leishmania amazonensis

Leishmaniasis are group of neglected diseases with worldwide distribution that affect about 12 million people. The current treatment is limited and may cause severe adverse effects, and thus, the search for new drugs more effective and less toxic is relevant. We have previously investigated the immunomodulatory effects of LASSBio-1386, an N-acylhydrazone derivative. Here we investigated the in vitro and in vivo activity of LASSBio-1386 against L. amazonensis. LASSBio-1386 inhibited the proliferation of promastigotes of L. amazonensis (EC₅₀ = 2.4 ± 0.48 µM), while presenting low cytotoxicity to macrophages (CC₅₀ = 74.1 ± 2.9 µM). In vitro incubation with LASSBio-1386 reduced the percentage of Leishmania-infected macrophages and the number of intracellular parasites (EC₅₀ = 9.42 ± 0.64 µM). Also, in vivo treatment of BALB/c mice infected with L. amazonensis resulted in a decrease of lesion size, parasitic load and caused histopathological alterations, when compared to vehicle-treated control. Moreover, LASSBio-1386 caused ultrastructural changes, arrested cell cycle in G0/G1 phase and did not alter the membrane mitochondrial potential of L. amazonensis. Aiming to its possible molecular interactions, we performed docking and molecular dynamics studies on Leishmania phosphodiesterase B1 (PDB code: 2R8Q) and LASSBio-1386. The computational analyses suggest that LASSBio-1386 acts against Leishmania through the modulation of leishmanial PDE activity. In conclusion, our results indicate that LASSBio-1386 is a promising candidate for the development of new leishmaniasis treatment.

Digitoxigenin presents an effective and selective antileishmanial action against Leishmania infantum and is a potential therapeutic agent for visceral leishmaniasis

Treatment for visceral leishmaniasis (VL) is hampered mainly by drug toxicity, their high cost, and parasite resistance. Drug development is a long and pricey process, and therefore, drug repositioning may be an alternative worth pursuing. Cardenolides are used to treat cardiac diseases, especially those obtained from Digitalis species. In the present study, cardenolide digitoxigenin (DIGI) obtained from a methanolic extract of Digitalis lanata leaves was tested for its antileishmanial activity against Leishmania infantum species. Results showed that 50% Leishmania and murine macrophage inhibitory concentrations (IC₅₀ and CC₅₀, respectively) were of 6.9 ± 1.5 and 295.3 ± 14.5 μg/mL, respectively. With amphotericin B (AmpB) deoxycholate, used as a control drug, values of 0.13 ± 0.02 and 0.79 ± 0.12 μg/mL, respectively, were observed. Selectivity index (SI) values were of 42.8 and 6.1 for DIGI and AmpB, respectively. Preliminary studies suggested that the mechanism of action for DIGI is to cause alterations in the mitochondrial membrane potential, to increase the levels of reactive oxygen species and induce accumulation of lipid bodies in the parasites. DIGI was incorporated into Pluronic® F127-based polymeric micelles, and the formula (DIGI/Mic) was used to treat L. infantum–infected mice. Miltefosine was used as a control drug. Results showed that animals treated with either miltefosine, DIGI, or DIGI/Mic presented significant reductions in the parasite load in their spleens, livers, bone marrows, and draining lymph nodes, as well as the development of a specific Th1-type response, when compared with the controls. Results obtained 1 day after treatment were corroborated with data corresponding to 15 days after therapy. Importantly, treatment with DIGI/Mic induced better parasitological and immunological responses when compared with miltefosine- and DIGI-treated mice. In conclusion, DIGI/Mic has the potential to be used as a therapeutic agent to protect against L. infantum infection, and it is therefore worth of consideration in future studies addressing VL treatment.

Antileishmanial activity of cordiaquinone E towards Leishmania (Leishmania) amazonensis

Leishmaniasis is caused by several protozoan species of Leishmania, and being endemically present in 98 countries around the world, it is also a severe public-health problem. The available antileishmanial drugs are toxic and yet present risks of recurrent infection. Efforts to find new, effective, and safe oral agents for the treatment of leishmaniasis are continuing throughout the world. This work aimed to evaluate the antileishmania activity of cordiaquinone E (CORe), isolated from the roots of Cordia polycephala (Lam.) I. M. Johnston. Cytotoxicity, and possible mechanisms of action against promastigote and amastigote forms of Leishmania amazonensis were examined. CORe was effective in inhibiting promastigote (IC₅₀ 4.5 ± 0.3 µM) and axenic amastigote (IC₅₀ 2.89 ± 0.11 µM) growth in concentrations found non-toxic for the host cell (CC₅₀ 246.81 ± 14.5 µM). Our results revealed that CORe presents direct activity against the parasite, inducing cell death by apoptosis. CORe present greater activity against intracellular amastigotes (EC₅₀ 1.92 ± 0.2 µM), yet with much higher selectivity indexes than the reference drugs, being respectively more benign towards RAW 264.7 macrophages than meglumine antimoniate and amphotericin B, (respectively by 4.68 and 42.84 fold). The antiamastigote activity was associated with increased TNF-α, IL-12, NO, and ROS levels, as well as decreased IL-10 levels. These results encourage the progression of studies on this compound for the development of new leishmanicidal agents.

Biological activity of Morita-Baylis-Hillman adduct homodimers in L. infantum and L. amazonensis: anti-Leishmania activity and cytotoxicity

This study is a report on the anti-Leishmania activity of Morita-Baylis-Hillman (MBH) homodimers adducts against the promastigote and axenic amastigote forms of Leishmania (Leishmania) infantum and Leishmania (Leishmania) amazonensis and on the cytotoxicity of these adducts to human blood cells. Both studied homodimers, MBH 1 and MBH 2, showed activity against the promastigote forms of L. infantum and L. amazonensis, which are responsible for visceral and cutaneous leishmaniasis, respectively. Additionally, the homodimers presented biological activity against the axenic amastigote forms of these two Leishmania species. The adducts exhibited no hemolytic activity to human peripheral blood mononuclear cells or erythrocytes at the tested concentrations and achieved higher selectivity indices than amphotericin B. Evaluation of cell death by apoptosis revealed that the homodimers had better apoptosis/necrosis profiles than amphotericin B in the promastigote forms of both L. infantum and L. amazonensis. In conclusion, these Morita-Baylis-Hillman adducts had anti-Leishmania activity in an in vitro model and may thus be promising molecules in the search for new drugs to treat leishmaniasis.

A chloroquinoline derivate presents effective in vitro and in vivo antileishmanial activity against Leishmania species that cause tegumentary and visceral leishmaniasis

The identification of new therapeutics to treat leishmaniasis is desirable, since available drugs are toxic and present high cost and/or poor availability. Therefore, the discovery of safer, more effective and selective pharmaceutical options is of utmost importance. Efforts towards the development of new candidates based on molecule analogs with known biological functions have been an interesting and cost-effective strategy. In this context, quinoline derivatives have proven to be effective biological activities against distinct diseases. In the present study, a new chloroquinoline derivate, AM1009, was in vitro tested against two Leishmania species that cause leishmaniasis. The present study analyzed the necessary inhibitory concentration to preclude 50% of the Leishmania promastigotes and axenic amastigotes (EC₅₀ value), as well as the inhibitory concentrations to preclude 50% of the murine macrophages and human red blood cells (CC₅₀ and RBC₅₀ values, respectively). In addition, the treatment of infected macrophages and the inhibition of infection using pre-treated parasites were also investigated, as was the mechanism of action of the molecule in L. amazonensis. To investigate the in vivo therapeutic effect, BALB/c mice were infected with L. amazonensis and later treated with AM1009. Parasitological and immunological parameters were also evaluated. Clioquinol, a known antileishmanial quinoline derivate, and amphotericin B (AmpB), were used as molecule and drug controls, respectively. Results in both in vitro and in vivo experiments showed a better and more selective action of AM1009 to kill the in vitro parasites, as well as in treating infected mice, when compared to results obtained using clioquinol or AmpB. AM1009-treated animals presented significantly lower average lesion diameter and parasite burden in the infected tissue and organs evaluated in this study, as well as a more polarized antileishmanial Th1 immune response and low renal and hepatic toxicity. This result suggests that AM1009 should be considered a possible therapeutic target to be evaluated in future studies for treatment against leishmaniasis.

Diagnostic evaluation of the amastin protein from Leishmania infantum in canine and human visceral leishmaniasis and immunogenicity in human cells derived from patients and healthy controls

The diagnosis of visceral leishmaniasis (VL) presents problems due to the toxicity and/or high cost of drugs. In addition, no vaccine exists to protect against human disease. In this study, the antigenicity and immunogenicity of amastin protein were evaluated in L. infantum-infected dogs and humans. For the diagnosis, besides the recombinant protein, 1 linear B-cell epitope was synthetized and evaluated in serological assays. Results showed high sensitivity and specificity values to detect the disease when both antigens were employed against a canine and human serological panel. By contrast, when using rA2 and a soluble Leishmania antigenic preparation, sensitivity and specificity values proved to be lower. A preliminary immunogenicity study showed that the amastin protein induced high IFN-γ and low IL-10 production in stimulated PBMC derived from treated VL patients and healthy subjects, thus suggesting a potential use of this protein as an immunogen to protect against human disease.

Potential of Pluronics® P-123 and F-127 as nanocarriers of anti-Leishmania chemotherapy

Leishmaniasis is a neglected disease and drugs approved for its treatment often lead to abandonment, failure of therapy and even death. Photodynamic therapy (PDT) has been shown to be a promising, non-invasive and selective for a target region without requiring high-cost technology. Usually, it is employed a photosensitizing agent (PS) incorporated into nanoparticles (NP). Pluronics^® P-123 and F-127 micelles are very interesting aqueous NP promoting efficient and selective delivery and less adverse effects. This study aimed to detect the activity of Pluronics^® P-123 and F-127 themselves since there is a scarcity of data on these NP activities without drugs incorporation. This study evaluated, in vitro, the activity of Pluronics^® against promastigotes and amastigotes of Leishmania amazonensis and also their cytotoxicities. Additionally, the determination of the mitochondria membrane potential in promastigotes, internalization of these Pluronics^® in the parasite membrane and macrophages and its stability in the culture medium was evaluated. Results showed that Pluronics^® did not cause significant damage to human red cells and promastigotes. The P-123 and F-127 inhibited the survival rate of L. amazonensis amastigotes, and also presented loss of mitochondrial membrane potential on promastigotes. The Pluronics^® showed low cytotoxic activity on J774A.1 macrophages, while only P-123 showed moderate cytotoxicity for BALB/c macrophages. The stability of P-123 and F-127 in culture medium was maintained for ten days. In conclusion, the NP studied can be used for incorporating potent leishmanicidal chemotherapy, due to their selectivity towards macrophages, being a promising system for the treatment of cutaneous leishmaniasis.

Evaluation of the in vitro and in vivo antileishmanial activity of a chloroquinolin derivative against Leishmania species capable of causing tegumentary and visceral leishmaniasis

The treatment against leishmaniasis presents problems, since the currently used drugs are toxic and/or have high costs. In addition, parasite resistance has increased. As a consequence, in this study, a chloroquinolin derivative, namely 7-chloro-N,N-dimethylquinolin-4-amine or GF1059, was in vitro and in vivo tested against Leishmania parasites. Experiments were performed to evaluate in vitro antileishmanial activity and cytotoxicity, as well as the treatment of infected macrophages and the inhibition of infection using pre-treated parasites. This study also investigated the GF1059 mechanism of action in L. amazonensis. Results showed that the compound was highly effective against L. infantum and L. amazonensis, presenting a selectivity index of 154.6 and 86.4, respectively, against promastigotes and of 137.6 and 74.3, respectively, against amastigotes. GF1059 was also effective in the treatment of infected macrophages and inhibited the infection of these cells when parasites were pre-incubated with it. The molecule also induced changes in the parasites' mitochondrial membrane potential and cell integrity, and caused an increase in the reactive oxygen species production in L. amazonensis. Experiments performed in BALB/c mice, which had been previously infected with L. amazonensis promastigotes, and thus treated with GF1059, showed that these animals presented significant reductions in the parasite load when the infected tissue, spleen, liver, and draining lymph node were evaluated. GF1059-treated mice presented both lower parasitism and low levels of enzymatic markers, as compared to those receiving amphotericin B, which was used as control. In conclusion, data suggested that GF1059 can be considered a possible therapeutic target to be tested against leishmaniasis.

Novel organic salts based on quinoline derivatives: The in vitro activity trigger apoptosis inhibiting autophagy in Leishmania spp

Leishmaniases are infectious diseases, caused by protozoa of the Leishmania genus. These drugs present high toxicity, long-term administration, many adverse effects and are expensive, besides the identification of resistant parasites. In this work, the antileishmanial activity of quinoline derivative salts (QDS) was evaluated, as well as the toxicity on mammalian cells and the mechanism of action of the most promising compound. Among the compound tested, only the compound QDS3 showed activity against promastigotes and amastigotes of Leishmania spp., being more active against the intracellular amastigotes of L. amazonensis-GFP (IC₅₀ of 5.48 μM). This value is very close to the one observed for miltefosine (IC₅₀ of 4.05 μM), used as control drug. Furthermore, the compound QDS3 exhibited a selective effect, being 40.35 times more toxic to the amastigote form than to the host cell. Additionally, promastigotes of L. amazonensis treated with this compound exhibited characteristics of cells in the process of apoptosis such as mitochondrial membrane depolarization, mitochondrial swelling, increase of ROS production, phosphatidylserine externalization, reduced and rounded shape, and cell cycle alteration. The integrity of the plasma membrane remained unaltered, excluding necrosis in treated promastigotes. The compound QDS3 inhibited the formation of autophagic vacuoles, which may have contributed to parasite death by preventing autophagic mechanisms in the removal of damaged organelles, intensifying the damage caused by the treatment, highlighting the antileishmanial effect of this compound. In addition, treatment with QDS3 induced increased ROS levels in L. amazonensis-infected macrophages, but not in uninfected host cell. These data reinforce that the induction of oxidative stress is one of the main toxic effects caused by the treatment with the compound QDS3 in L. amazonensis, causing irreversible damage and triggering a selective death of intracellular parasites. Data shown here confirm the biological activity of quinoline derivatives and encourage future in vivo studies with this compound in the murine model.