Use of Natural Products in Leishmaniasis Chemotherapy: An Overview

Evaluation of Immunopharmacological efficacy of live Leishmania donovani overexpressing Ld_ζ1domain for protection against experimental human visceral Leishmaniasis

OBJECTIVE

To evaluate the efficacy and immunogenicity of the zeta domain over-expressing Leishmania donovani (Ld_ζ1domain) as a vaccination candidate against visceral leishmaniasis (VL).

METHODS

In this study, Leishmania overexpressor Ld_ζ1domain (OE) were transformed by electroporation using a GFP-tagged Ld_ζ1domain recombinant plasmid. The resulting overexpressing cells were analysed in vitro to assess their growth dynamics and infectivity. We also investigated the immune-protective potential of these overexpressor in a mouse model challenged with Leishmania donovani. The immune response, including Th1 and Th2 pathways, was thoroughly characterized using RT-PCR and ELISA assays. In addition, the study conducted a thorough evaluation of the mouse's spleen and liver parasites, as well as quantitative evaluation of tissue pathological changes.

RESULTS

Ld_ζ1 domain (OE) parasites exhibited significantly lower viability and replication rates than WT parasites, and in vivo studies showed that mice immunized with the Ld_ζ1(OE) domain had lower parasite numbers than mice infected with LdWT. Spleen and liver showed significant histological changes suggestive of protection. Parasite load in the spleen and liver of vaccinated mice were significantly reduced. The immune response showed increased IFN-γ levels and lower IL-10 production, resulting in a greater IFN-γ/IL-10 ratio, indicating parasite elimination. The vaccination also caused a significant IgG humoral response and increased nitric oxide production in immunized mice.

CONCLUSION

Our findings demonstrated that overexpressing the zeta toxin resulted in controlled parasite attenuation, lowering pathogenicity while retaining immunogenic features. Our work established the zeta over-expressor's protective efficacy, immunogenicity, and proliferation in response to a Leishmania challenge in vitro and in vivo. This preliminary prototype study suggested that Ld_ζ1domain (OE) parasites may be suitable for developing an attenuated vaccine against leishmaniasis.

Topical Application of Oxylipin (3S)-16,17-Didehydrofalcarinol in Mice Infected with Leishmania mexicana: A Possible Treatment for Localized Cutaneous Leishmaniasis

Pentavalent antimonials are the first-line treatment for localized cutaneous leishmaniasis. However, they have disadvantages such as their elevated toxicity, high costs, and parenteral application. Plant-derived compounds may be an alternative treatment against this disease. Previous in vitro studies have shown that (3S)-16,17-didehydrofalcarinol (1), a polyacetylene oxylipin isolated from Tridax procumbens, is active against Leishmania mexicana. We have analyzed the mechanism of action of compound 1, evaluating reactive oxygen species production, apoptosis of L. mexicana, cytotoxicity in murine macrophages, and its efficacy in controlling the disease progression and parasite load when applied topically in C57BL/6 mice infected with L. mexicana. Results show that parasites incubated with 1.6 μM compound 1 significantly increased reactive oxygen species production (p ≤ 0.05). The percentage of apoptosis also increased significantly (p ≤ 0.05) and did not affect the viability of macrophages. The application of the topical formulations with 0.5% and 0.75% compound 1 for 7 weeks reduced disease progression and parasite load. We demonstrate that compound 1 generates the death of L. mexicana by apoptosis through reactive oxygen species production. We conclude that compound 1 can be used a possible alternative treatment for localized cutaneous leishmaniasis, enabling a less painful and more accessible therapy.

Antileishmanial activity of hesperetin on Leishmania donovani, in vitro and in silico inhibition of acetylcholinesterase and investigation of the targets sterol C-24 reductase and N-myristoyltransferase

The current treatment of leishmaniasis is confronted with significant challenges, including limited efficacy, adverse effects, and parasite resistance to drugs. The search for alternative therapeutic options, including the utilisation of natural products, has demonstrated considerable promise. In this study, the antileishmanial activity of the flavonoid hesperetin against Leishmania donovani, the causative agent of visceral leishmaniasis, was reported for the first time. Hesperetin was obtained through the hydrolysis of hesperidin and subsequently subjected to chemical characterisation via Infrared and NMR spectroscopy. The antileishmanial activity and cytotoxicity against RAW 264.7 macrophages were evaluated using the MTT colorimetric assay. In order to investigate the potential mechanisms of action, in vitro acetylcholinesterase inhibition assays and molecular docking analyses were conducted. Hesperetin showed an antipromastigote effect (IC50: 62.89 μM) with no evidence of cytotoxicity (CC50: 612.8 μM), with a selectivity index (SI) of 9.74, being 5.4 times more effective than trivalent antimony. In comparison, antimony showed an IC50 of 80.16 μM, a CC50 of 145.04 μM and a SI of 1.8, indicating a limited safety margin. The compound was observed to inhibit acetylcholinesterase (IC50 of 18.44 μg/mL), present in mitochondrial and plasma membrane of the parasite. Molecular docking and dynamic simulations indicated that hesperetin inhibit sterol C-24 reductase, essential for ergosterol biosynthesis and membrane integrity of L. donovani and shows activity against N-myristoyl transferase, responsible for parasite proliferation cycle. These findings open promising avenues for the development of effective antileishmanial therapies.

Structure-based Virtual Screening and Drug Design Development of Leishmanicidal Pyrimidines

Leishmaniasis is a neglected disease caused by parasites of the genus Leishmania sp. that causes approximately 1 million cases and 650,000 deaths annually worldwide. Its treatment has several limitations mainly due to high toxicity and clinical resistance, and the search for alternatives is highly desirable. The present work aimed to design new antileishmanial compounds through a virtual screening of a small in-house library of pyrimidine compounds, never tested against Leishmania, using the active site of trypanothione reductase (TR) as a target model. The compounds showed favorable affinity with the amino acid residues of the active site of TR. Pyr 1-9 were synthesized and tested against Leishmania amazonensis strain. Four derivatives demonstrated activity against promastigote (IC50 value between 11.23 and 91.5 µM) and three other compounds demonstrated discreet activity against amastigote, IC50 value between 81.29 and 153.21 µM. Based on the results obtained in the screening, three new pyrimidines Pyr 10-12 were designed to optimize activity, cytotoxicity, and selectivity. Pyr 10 and Pyr 11 demonstrated good activity against promastigotes, with IC50 of 11.38 ± 9.7 and 20.01 ± 13.55 µM, respectively, and improved cytotoxicity and selectivity. No activity was obtained against amastigotes. Thus, this study contributes important information for the development of new pyrimidines active against Leishmania.

In Vitro and In Vivo Leishmanicidal Activity of Beauvericin

Leishmaniasis is a worldwide disease caused by more than 20 species of Leishmania parasites. Leishmania amazonensis and L. braziliensis are among the main causative agents of cutaneous leishmaniasis, presenting a broad spectrum of clinical forms. As these pathologies lead to unsatisfactory treatment outcomes, the discovery of alternative chemotherapeutic options is urgently required. In this investigation, a leishmanicidal bioassay-guided fractionation of the growth media extract produced by Aspergillus terreus P63 led to the isolation of the cyclic depsipeptide beauvericin (1). The viability of L. amazonensis, L. braziliensis and mammalian cells (macrophages and L929 fibroblasts) was assessed in 1 incubated cultures. Leishmania promastigotes were sensitive to 1, with EC50 values ranging from 0.7 to 1.3 μM. Microscopy analysis indicated that Leishmania spp. parasites showed morphological abnormalities in a dose-dependent manner in the presence of 1. L. amazonensis intracellular amastigotes were more sensitive to 1 than promastigotes (EC50 = 0.8 ± 0.1 μM), with a good selectivity index (22-30). 1 reduced the infectivity index at very low concentrations, maintaining the integrity of the primary murine host cell for up to the highest concentration tested for 1. In vivo assays of 1 conducted using BALB/c mice infected with stationary-phase promastigotes of L. amazonensis in the tail base presented a significant reduction in the lesion parasite load. A second round of in vivo assays was performed to assess the efficacy of the topical use of 1. The results demonstrated a significant decrease in the total ulcerated area of mice treated with 1 when compared with untreated animals. Our results present promising in vitro and in vivo leishmanicidal effects of beauvericin, emphasizing that systemic inoculation of 1 led to a decrease in the parasite load at the lesion site, whereas topical administration of 1 delayed the progression of leishmaniasis ulcers, a cure criterion established for cutaneous leishmaniasis management.

Anti-leishmanial activity of Hypericum Scabrum extract against Leishmania major

Leishmaniasis is a vector-borne disease and one of the most significant neglected tropical diseases. Current anti-leishmanial treatments are often ineffective over extended periods and are associated with toxic side effects, highlighting the urgent need for new, effective, and safe alternative treatments for this infectious disease. The objective of this study was to evaluate the anti-leishmanial effects of a hydroalcoholic extract of Hypericum scabrum (H. scabrum), comparing its efficacy to that of the control drug glucantime against the standard strain of Leishmania major. The H. scabrum plants were collected from the western regions of Iran. A hydroalcoholic extract was prepared from the flower and stem of the plant using a maceration method. High-performance liquid chromatography analysis was conducted to identify the chemical compounds present in the extract. Promastigotes of L. major were cultured, and the anti-leishmanial activity of the extracts was assessed at concentrations ranging from 12.5 to 800 µg/ml using the MTT [3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide] assay. The half-maximal inhibitory concentration (IC50) values for the H. scabrum plant extract at 24, 48, and 72 h were 245.47, 141.25 and 85.11 μg/ml, respectively. The IC50 values for glucantime (the control drug) at 24 h, 48 h, and 72 h were 30.19, 21.37, and 12.58 μg/ml, respectively. While the H. scabrum extract exhibited a lower effect compared to the control drug, it still demonstrated a significant inhibitory effect on the promastigote form of L. major. Given that the plant extract of H. scabrum has demonstrated promising anti-leishmanial effects against L. major promastigotes, further studies are warranted to evaluate the efficacy of these extracts in animal models of leishmaniasis.

In Vitro Evaluation of the Combinatorial Effect of Naringenin and Miltefosine against Leishmania amazonensis

Leishmania amazonensis causes a clinical form called diffuse cutaneous leishmaniasis (DCL) with challenges to treatment, like low efficiency and drug toxicity. Therefore, it is necessary to investigate new therapies using less toxic leishmanicidal compounds, such as flavonoids like naringenin, and their combination with conventional drugs, such as miltefosine. Antileishmanial dose/response activity, isobologram, calculation of dose reduction index (DRI), and fractional inhibitory concentration index (FICI) tests were performed on in vitro assays using reference promastigote forms of L. amazonensis (IFLA/BR/67/PH8) to assess the combinatorial effect between naringenin and miltefosine. The in vitro results of isobologram, DRI, and FICI calculations showed that the combination of the compounds had an additive effect and was able to reduce the half maximal inhibitory concentration (IC50) of miltefosine in the promastigote forms of the parasite compared to the treatment of the drug alone. This study demonstrated in vitro the viability of a combination action of the flavonoid with the treatment with miltefosine, opening space for further investigations on the association of natural compounds with the drugs used for the treatment of L. amazonensis.

New synthetic molecules incorporated into polymeric micelles used for treatment against visceral leishmaniasis

Treatment against visceral leishmaniasis (VL) presents problems, mainly related to drug toxicity, high cost and/or by emergence of resistant strains. In the present study, two vanillin synthetic derivatives, 3 s [4-(2-hydroxy-3-(4-octyl-1H-1,2,3-triazol-1-yl)propoxy)-3-methoxybenzaldehyde] and 3 t [4-(3-(4-decyl-1H-1,2,3-triazol-1-yl)-2-hydroxypropoxy)-3-methoxybenzaldehyde], were evaluated as therapeutic candidates in a murine model against Leishmania infantum infection. Molecules were used pure (3 s and 3 t) or incorporated into Poloxamer 407-based micelles (3 s/M and 3 t/M) in the infected animals, which also received amphotericin B (AmpB) or Ambisome® as control. Results showed that 3 s/M and 3 t/M compositions induced a Th1-type immune response in treated animals, with higher levels of IFN-γ, IL-2, TNF-α, IL-12, nitrite, and IgG2a antibodies. Animals presented also low toxicity and significant reductions in the parasite load in their spleens, livers, bone marrows and draining lymph nodes, as compared as control groups mice, with the evaluations performed one and 30 days after the application of the therapeutics. In conclusion, preliminary data suggest that 3 s/M and 3 t/M could be considered for future studies as therapeutic agents against VL.

Piperine, quercetin, and curcumin identified as promising natural products for topical treatment of cutaneous leishmaniasis

Leishmania braziliensis (L. braziliensis) causes cutaneous leishmaniasis (CL) in the New World. The costs and the side effects of current treatments render imperative the development of new therapies that are affordable and easy to administer. Topical treatment would be the ideal option for the treatment of CL. This underscores the urgent need for affordable and effective treatments, with natural compounds being explored as potential solutions. The alkaloid piperine (PIP), the polyphenol curcumin (CUR), and the flavonoid quercetin (QUE), known for their diverse biological properties, are promising candidates to address these parasitic diseases. Initially, the in vitro cytotoxicity activity of the compounds was evaluated using U-937 cells, followed by the assessment of the leishmanicidal activity of these compounds against amastigotes of L. braziliensis. Subsequently, a golden hamster model with stationary-phase L. braziliensis promastigote infections was employed. Once the ulcer appeared, hamsters were treated with QUE, PIP, or CUR formulations and compared to the control group treated with meglumine antimoniate administered intralesionally. We observed that the three organic compounds showed high in vitro leishmanicidal activity with effective concentrations of less than 50 mM, with PIP having the highest activity at a concentration of 8 mM. None of the compounds showed cytotoxic activity for U937 macrophages with values between 500 and 700 mM. In vivo, topical treatment with QUE daily for 15 days produced cured in 100% of hamsters while the effectiveness of CUR and PIP was 83% and 67%, respectively. No failures were observed with QUE. Collectively, our data suggest that topical formulations mainly for QUE but also for CUR and PIP could be a promising topical treatment for CL. Not only the ease of obtaining or synthesizing the organic compounds evaluated in this work but also their commercial availability eliminates one of the most important barriers or bottlenecks in drug development, thus facilitating the roadmap for the development of a topical drug for the management of CL caused by L. braziliensis.

Overview of Research on Leishmaniasis in Africa: Current Status, Diagnosis, Therapeutics, and Recent Advances Using By-Products of the Sargassaceae Family

Leishmaniasis in Africa, which has been designated as a priority neglected tropical disease by various global organizations, exerts its impact on millions of individuals, primarily concentrated within this particular region of the world. As a result of the progressively grave epidemiological data, numerous governmental sectors and civil organizations have concentrated their endeavors on this widespread outbreak with the objective of devising appropriate remedies. This comprehensive examination delves into multiple facets of this parasitic ailment, scrutinizing the associated perils, diagnostic intricacies, and deficiencies within the existing therapeutic protocols. Despite the established efficacy of current treatments, they are not immune to deleterious incidents, particularly concerning toxicity and the emergence of parasitic resistance, thus accentuating the necessity of exploring alternative avenues. Consequently, this research not only encompasses conventional therapeutic approaches, but also extends its scope to encompass complementary and alternative medicinal techniques, thereby striving to identify innovative solutions. A particularly auspicious dimension of this study lies in the exploration of natural substances and by-products derived from some brown algae of the Sargassaceae family. These resources possess the potential to assume a pivotal role in the management of leishmaniasis.

Identification of Novel Flavonoids and Ansa-Macrolides with Activities against Leishmania donovani through Natural Product Library Screening

The protozoan parasite Leishmania donovani is the causative agent of visceral leishmaniasis (VL), a potentially fatal disease if left untreated. Given the limitations of current therapies, there is an urgent need for new, safe, and effective drugs. To discover novel antileishmanial compounds from previously unexplored chemical spaces, we conducted a high-throughput screening (HTS) of 2562 natural compounds, assessing their activity against L. donovani promastigotes and intracellular amastigotes. Utilizing the criteria of ≥70% parasite growth inhibition and ≥70% host cell (THP-1) viability, we selected 100 inhibitors for half-maximal inhibitory concentration (IC50) value determination. Twenty-six compounds showed activities in both forms of Leishmania with a selectivity index of over 3. Clustering analysis resulted in four chemical clusters with scaffolds of lycorine (cluster 1), 5-hydroxy-9,10-dihydro-4H,8H-pyrano[2,3-f]chromene-4,8-dione (cluster 2), and semi-synthetic derivatives of ansamycin macrolide (cluster 4). The enantiomer of lycorine, BMD-NP-00820, showed the highest anti-amastigote activity with an IC50 value of 1.74 ± 0.27 μM and a selectivity index (SI) > 29. In cluster 3, the most potent compound had an IC50 value of 2.20 ± 0.29 μM with an SI > 23, whereas in cluster 4, with compounds structurally similar to the tuberculosis drug rifapentine, BMD-NP-02085 had an IC50 value of 1.76 ± 0.28 μM, but the SI value was 7.5. Taken together, the natural products identified from this study are a potential source for the discovery of antileishmanial chemotypes for further development.

Targeting with Structural Analogs of Natural Products the Purine Salvage Pathway in Leishmania (Leishmania) infantum by Computer-Aided Drug-Design Approaches

Visceral Leishmaniasis (VL) has a high death rate, with 500,000 new cases and 50,000 deaths occurring annually. Despite the development of novel strategies and technologies, there is no adequate treatment for the disease. Therefore, the purpose of this study is to find structural analogs of natural products as potential novel drugs to treat VL. We selected structural analogs from natural products that have shown antileishmanial activities, and that may impede the purine salvage pathway using computer-aided drug-design (CADD) approaches. For these, we started with the vastly studied target in the pathway, the adenine phosphoribosyl transferase (APRT) protein, which alone is non-essential for the survival of the parasite. Keeping this in mind, we search for a substance that can bind to multiple targets throughout the pathway. Computational techniques were used to study the purine salvage pathway from Leishmania infantum, and molecular dynamic simulations were used to gather information on the interactions between ligands and proteins. Because of its low homology to human proteins and its essential role in the purine salvage pathway proteins network interaction, the findings further highlight the significance of adenylosuccinate lyase protein (ADL) as a therapeutic target. An analog of the alkaloid Skimmianine, N,N-diethyl-4-methoxy-1-benzofuran-6-carboxamide, demonstrated a good binding affinity to APRT and ADL targets, no expected toxicity, and potential for oral route administration. This study indicates that the compound may have antileishmanial activity, which was granted in vitro and in vivo experiments to settle this finding in the future.

Eugenol-Rich Essential Oil from Pimenta dioica: In Vitro and In Vivo Potentialities against Leishmania amazonensis

Pimenta dioica L. is one the most recognized species with diverse biological activities. In this study, in vitro activity and in vivo efficacy of essential oil from P. dioica (EO-Pd) was evaluated. The main compound was also included in the animal studies and its in silico prediction related to biological activities, molecular ligands, drug likeness, and ADME (absorption, distribution, metabolism, and excretion) properties are listed. The chemical composition analyzed by GC-MS retrieved 45 components, which the most abundant compound was the eugenol (80.1%). The EO-Pd was able to inhibit the growth of L. amazonensis (IC50 = 9.7 ± 0.7 and 11.3 ± 2.1 µg/mL, promastigotes and amastigotes, respectively). The cytotoxicity assay showed a CC50 of 104.5 ± 0.9 µg/mL and a selectivity index of 9. In the model of cutaneous leishmaniasis in BALB/c mice, the effect of EO-Pd and eugenol was observed after treatment at 30 mg/kg by intralesional route with 5 administrations every 4 days. In the in silico predictions, some targets that justified the antileishmanial activity of eugenol and good drug like properties for this compound, were obtained. This study showed for first time the potential of EO-Pd to inhibit L. amazonensis, which could be linked to the activity of major compound eugenol.

Nanotechnology-Based Strategies in Parasitic Disease Management: From Prevention to Diagnosis and Treatment

Parasitic infections are a major global health issue causing significant mortality and morbidity. Despite substantial advances in the diagnostics and treatment of these diseases, the currently available options fall far short of expectations. From diagnosis and treatment to prevention and control, nanotechnology-based techniques show promise as an alternative approach. Nanoparticles can be designed with specific properties to target parasites and deliver antiparasitic medications and vaccines. Nanoparticles such as liposomes, nanosuspensions, polymer-based nanoparticles, and solid lipid nanoparticles have been shown to overcome limitations such as limited bioavailability, poor cellular permeability, nonspecific distribution, and rapid drug elimination from the body. These nanoparticles also serve as nanobiosensors for the early detection and treatment of these diseases. This review aims to summarize the potential applications of nanoparticles in the prevention, diagnosis, and treatment of parasitic diseases such as leishmaniasis, malaria, and trypanosomiasis. It also discusses the advantages and disadvantages of these applications and their market values and highlights the need for further research in this field.

Prosopis juliflora (Sw.) DC.induces apoptotic-like programmed cell death in Leishmania donovani via over production of oxidative stress, mitochondrial dysfunction and ATP depletion

Background

Leishmaniasis is endemic in more than 60 countries with a large number of mortality cases. The current chemotherapy approaches employed for managing the leishmaniasis is associated with severe side effects. Therefore there is a need to develop effective, safe, and cost affordable antileishmanial drug candidates.

Purpose of the study

This study was designed to evaluate the in vitro antileishmanial activity of a Prosopis juliflora leaves extract (PJLME) towards the Leishmania donovani parasites.

Material and methods

PJLME was evaluated for its cytotoxicity against the L. donovani parasites and the mouse macrophage cells. Further, various in vitro experiments like ROS assay, mitochondrial membrane potential assay, annexin v assay, cell cycle assay, and caspase 3/7 assay were performed to understand the mechanism of cell death. Phytochemical profiling of P. juliflorawas performed by utilizing HPTLC and GC-MS analysis.

Results

PJLME demonstrated antileishmanial activity at a remarkably lower concentration of IC50 6.5 μg/mL. Of note, interestingly PJLME IC50 concentration has not demonstrated cytotoxicity against the mouse macrophage cell line. Performed experiments confirmed ROS inducing potential of PJLME which adversely affected the mitochondrial membrane potential and caused loss of mitochondrial membrane potential and thereby ATP levels. PJLME also arrested the cell cycle and induced apoptotic-like cell death in PJLME treated L. donovani promastigotes.

Conclusion

The results clearly established the significance of Prosopis juliflora as an effective and safe natural resource for managing visceral leishmaniasis. The findings can be used as a baseline reference for developing novel leads/formulations for effective management of visceral leishmaniasis.

Nitazoxanide and quercetin co-loaded nanotransfersomal gel for topical treatment of cutaneous leishmaniasis with macrophage targeting and enhanced anti-leishmanial effect

Purpose

Anti-leishmanial medications administered by oral and parenteral routes are less effective for treatment of cutaneous leishmaniasis (CL) and cause toxicity, hence targeted drug delivery is an efficient way to improve drug availability for CL with reduced toxicity. This study aimed to develop, characterize and evaluate nitazoxanide and quercetin co-loaded nanotransfersomal gel (NTZ-QUR-NTG) for the treatment of CL.

Methods

NTZ-QUR-NT were prepared by thin film hydration method and were statistically optimized using Box-Behnken design. To ease the topical delivery and enhance the retention time, the NTZ-QUR-NT were dispersed in 2 % chitosan gel. Moreover, in-vitro drug release, ex-vivo permeation, macrophage uptake, cytotoxicity and anti-leishmanial assays were performed.

Results

The optimized formulation indicated mean particle size 210 nm, poly dispersity index (PDI) 0.16, zeta potential (ZP) -15.1 mV and entrapment efficiency (EE) of NTZ and QUR was 88 % and 85 %, respectively. NTZ-QUR-NT and NTZ-QUR-NTG showed sustained release of the incorporated drugs as compared to the drug dispersions. Skin permeation of NTZ and QUR in NTZ-QUR-NTG was 4 times higher in comparison to the plain gels. The NTZ-QUR-NT cell internalization was almost 10-folds higher than NTZ-QUR dispersion. The cytotoxicity potential (CC50) of NTZ-QUR-NT (71.95 ± 3.32 μg/mL) was reduced as compared to NTZ-QUR dispersion (49.77 ± 2.15 μg/mL. A synergistic interaction was found between NTZ and QUR. Moreover, in-vitro anti-leishmanial assay presented a lower IC50 value of NTZ-QUR-NT as compared to NTZ-QUR dispersion. Additionally, a significantly reduced lesion size was observed in NTZ-QUR-NTG treated BALB/c mice, indicating its antileishmanial potential.

Conclusion

It can be concluded that nanotransfersomal gel has the capability to retain and permeate the incorporated drugs through stratum corneum and induce synergetic anti-leishmanial effect of NTZ and QUR against cutaneous leishmaniasis.

Exploring the leishmanicidal potential of terpenoids: a comprehensive review on mechanisms of cell death

Leishmaniasis is a neglected tropical disease with a wide spectrum of clinical manifestations, ranging from visceral to cutaneous, with millions of new cases and thousands of deaths reported each year. The species of Leishmania and the immune response of the host determine the severity of the disease. Leishmaniasis remains challenging to diagnose and treat, and there is no vaccine available. Several studies have been conducted on the use of herbal medicines for the treatment of leishmaniasis. Natural products can provide an inexhaustible source of chemical diversity with therapeutic potential. Terpenes are a class of natural products derived from a single isoprene unit, a five-carbon compound that forms the basic structure of isoprenoids. This review focuses on the most important and recent advances in the treatment of parasites of the genus Leishmania with different subclasses of terpenes. Several mechanisms have been proposed in the literature, including increased oxidative stress, immunomodulatory role, and induction of different types of parasite cell death. However, this information needs to be brought together to provide an overview of how these compounds can be used as therapeutic tools for drug development and as a successful adjuvant strategy against Leishmania sp.

(-)-5-Demethoxygrandisin B a New Lignan from Virola surinamensis (Rol.) Warb. Leaves: Evaluation of the Leishmanicidal Activity by In Vitro and In Silico Approaches

Leishmaniasis is a complex disease caused by infection with different Leishmania parasites. The number of medications used for its treatment is still limited and the discovery of new drugs is a valuable approach. In this context, here we describe the in vitro leishmanicidal activity and the in silico interaction between trypanothione reductase (TryR) and (-)-5-demethoxygrandisin B from the leaves of Virola surinamensis (Rol.) Warb. The compound (-)-5-demethoxygrandisin B was isolated from V. surinamensis leaves, a plant found in the Brazilian Amazon, and it was characterized as (7R,8S,7'R,8'S)-3,4,5,3',4'-pentamethoxy-7,7'-epoxylignan. In vitro antileishmanial activity was examined against Leishmania amazonensis, covering both promastigote and intracellular amastigote phases. Cytotoxicity and nitrite production were gauged using BALB/c peritoneal macrophages. Moreover, transmission electron microscopy was applied to probe ultrastructural alterations, and flow cytometry assessed the shifts in the mitochondrial membrane potential. In silico methods such as molecular docking and molecular dynamics assessed the interaction between the most stable configuration of (-)-5-demethoxygrandisin B and TryR from L. infantum (PDB ID 2JK6). As a result, the (-)-5-demethoxygrandisin B was active against promastigote (IC50 7.0 µM) and intracellular amastigote (IC50 26.04 µM) forms of L. amazonensis, with acceptable selectivity indexes. (-)-5-demethoxygrandisin B caused ultrastructural changes in promastigotes, including mitochondrial swelling, altered kDNA patterns, vacuoles, vesicular structures, autophagosomes, and enlarged flagellar pockets. It reduced the mitochondria membrane potential and formed bonds with important residues in the TryR enzyme. The molecular dynamics simulations showed stability and favorable interaction with TryR. The compound targets L. amazonensis mitochondria via TryR enzyme inhibition.

Synthesis of 1,2,3-Triazole-Containing Methoxylated Cinnamides and Their Antileishmanial Activity against the Leishmania braziliensis Species

Leishmaniasis is a group of infectious diseases caused by protozoan parasites that belong to the genus Leishmania. Currently, there is no human vaccine, and the available treatments are associated with toxicity, high cost, and the emergence of resistant strains. These factors highlight the need to identify new antileishmanial candidates. In this study, we synthesized twenty-four methoxylated cinnamides containing 1,2,3-triazole fragments and evaluated their antileishmanial activity against the Leishmania braziliensis species, which is the main etiological agent responsible for American Tegumentary Leishmaniasis (ATL). The cinnamides were synthetically prepared using nucleophilic acyl substitution and copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reactions. The compounds were characterized using infrared, nuclear magnetic resonance, and high-resolution mass spectrometry techniques. We performed preliminary studies to evaluate the biological activity of these compounds against L. braziliensis promastigotes and axenic amastigotes. Compound 28, N-((1-(7-(diethylamino)-2-oxo-2H-chromen-3-yl)-1H-1,2,3-triazole-4-yl) methyl)-3,4-dimethoxy cinnamide, demonstrated relevant antileishmanial activity with low toxicity in murine cells. The selectivity index values for this compound were superior compared with data obtained using amphotericin B. Furthermore, this cinnamide derivative reduced the infection percentage and number of recovered amastigotes in L. braziliensis-infected macrophages. It also induced an increase in reactive oxygen species production, depolarization of the mitochondrial potential, and disruption of the parasite membrane. Taken together, these findings suggest that this synthetic compound holds potential as an antileishmanial candidate and should be considered for future studies in the treatment of ATL.

Synthesis, antileishmanial activity and molecular modeling of new 1-aryl/alkyl-3-benzoyl/cyclopropanoyl thiourea derivatives

Due to the lack of effective vaccine(s) against leishmania and also pharmacokinetics issues of current drugs, it is necessary to discover new antileishmanial agents. Within this particular study, a series of novel 1-aryl/alkyl-3-benzoyl/cyclopropanoyl thiourea derivatives were synthesized (yields 69-84%) and evaluated as antileishmanial compounds (1-11). Synthetic derivatives were subjected to in vitro antileishmanial assessment against Leishmania major promastigotes by colorimetric MTT assay. Compounds 3 (IC50 38.54 µg/mL), 5 (IC50 84.75 µg/mL) and 10 (IC50 70.31 µg/mL) exhibited higher activities after 48 h but were less potent than amphotericin B (IC50 0.19 µg/mL). Antileishmanial activities indicated priority of 5-methyl-4-phenyl thiazole over furyl methyl substituents and 4-phenyl thiazole on thiourea nitrogen. N-myristoyltransferase (NMT) was selected as a validated L. major target for molecular docking studies. In silico results indicated the contribution of hydrophobic, π-stacking and H-bond interactions in binding to target. Most of the synthesized derivatives had lower binding affinities to human NMT (hNMT) than leishmanial enzyme. Docking conformations of top-ranked selective binders (compounds 3 and 5) were subjected to 50 ns MD simulations inside L. major HMT (LmNMT) active site. MD trajectories were used to extract RMSD, RMSF, Rg and durability of intramolecular/intermolecular H-bonds of the complex. It was observed that compound 3 escaped from LmNMT binding site during simulation period and no stable complex could be envisaged. Unlike 3, compound 5 attained stable binding conformation with converged stability parameters. Although mechanistic details for antileishmanial effects of synthesized derivatives are to be explored, current results may be implicated in further structure-guided approach toward potent antileishmanial agents.

Promising natural products for the treatment of cutaneous leishmaniasis: A review of in vitro and in vivo studies

Although there are available treatments for cutaneous leishmaniasis (CL), the drugs used are far from ideal, toxic, and costly, in addition to the challenge faced by the development of resistance. Plants have been used as a source of natural compounds with antileishmanial action. However, few have reached the market and become phytomedicines with registration in regulatory agencies. Difficulties related to the extraction, purification, chemical identification, efficacy, safety, and production in sufficient quantity for clinical studies, hinder the emergence of new effective phytomedicines against leishmaniasis. Despite the difficulties reported, the major research centers in the world see that natural products are a trend concerning the treatment of leishmaniasis. The present work consists of a literature review of articles with in vivo studies, covering the period from January 2011 to December 2022, providing an overview of promising natural products for CL treatment. The papers show encouraging antileishmanial action of natural compounds with reduced parasite load and lesion size in animal models, suggesting new strategies for the treatment of the disease. The results reported in this review show advances in using natural products as safe and effective formulations, which can stimulate clinical studies to establish clinical therapy. In conclusion, the information in this review article serves as a preliminary basis for establishing a therapeutic protocol for future clinical trials that can validate the safety and efficacy of natural compounds, providing the development of affordable and safe phytomedicines for the treatment of CL.

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.

Computer-aided drug design approaches applied to screen natural product's structural analogs targeting arginase in Leishmania spp

Introduction: Leishmaniasis is a disease with high mortality rates and approximately 1.5 million new cases each year. Despite the new approaches and advances to fight the disease, there are no effective therapies. Methods: Hence, this study aims to screen for natural products' structural analogs as new drug candidates against leishmaniasis. We applied Computer-aided drug design (CADD) approaches, such as virtual screening, molecular docking, molecular dynamics simulation, molecular mechanics-generalized Born surface area (MM-GBSA) binding free estimation, and free energy perturbation (FEP) aiming to select structural analogs from natural products that have shown anti-leishmanial and anti-arginase activities and that could bind selectively against the Leishmania arginase enzyme. Results: The compounds 2H-1-benzopyran, 3,4-dihydro-2-(2-methylphenyl)-(9CI), echioidinin, and malvidin showed good results against arginase targets from three parasite species and negative results for potential toxicities. The echioidinin and malvidin ligands generated interactions in the active center at pH 2.0 conditions by MM-GBSA and FEP methods. Conclusions: This work suggests the potential anti-leishmanial activity of the compounds and thus can be further in vitro and in vivo experimentally validated.

Analysis of 2′-hydroxyflavanone (2HF) in mouse whole blood by HPLC–MS/MS for the determination of pharmacokinetic parameters

Given the lack of investments, structure, and difficulty of metabolite isolation, promising natural product studies do not progress to preclinical studies, such as pharmacokinetics. 2′-Hydroxyflavanone (2HF) is a flavonoid that has shown promising results in different types of cancer and leishmaniasis. For accurate quantification of 2HF in BALB/c mouse blood, a validated HPLC-MS/MS method was developed. Chromatographic analysis was performed using C18 (5μm, 150 mm × 4.6 mm). The mobile phase consisted of water containing 0.1% formic acid, acetonitrile, and methanol (35/52/13 v/v/v) at a flow rate and total running time of 0.8 mL/min and 5.50 min, respectively, with an injection volume of 20 µL. 2HF was detected by electrospray ionization in negative mode (ESI-) using multiple reaction monitoring (MRM). The validated bioanalytical method showed satisfactory selectivity without significant interference for the 2HF and IS. In addition, the concentration range between 1 and 250 ng/mL showed good linearity (r = 0.9969). The method showed satisfactory results for the matrix effect. Precision and accuracy intervals varied between 1.89% and 6.76% and 95.27% and 100.77%, respectively, fitting the criteria. No degradation of 2HF in the biological matrix was observed since stability under freezing and thawing conditions, short duration, postprocessing, and long duration showed deviations less than 15%. Once validated, the method was successfully applied in a 2HF oral pharmacokinetic study with mouse blood, and the pharmacokinetic parameters were determined. 2HF demonstrated a Cmax of 185.86 ng/mL, a Tmax of 5 min, and a half-life (T1/2) of 97.52 min.

Identification of potential novel inhibitors against glutamine synthetase enzyme of Leishmania major by using computational tools

Glutamine Synthetase (GS) is functionally important in many pathogens, so its viability as a drug target has been widely investigated. We identified Leishmania major glutamine synthetase (Lm-GS) as an appealing target for developing potential leishmaniasis inhibitors. Comparative modeling, virtual screening, MD simulations along with MM-PBSA analyses were performed and two FDA approved compounds namely Chlortalidone (id ZINC00020253) and Ciprofloxacin (id ZINC00020220) were identified as potential inhibitor among the screened library. These compounds may be used as a lead molecule, although additional in vitro and in vivo testing is required to establish its anti-leishmanial effect. Hence, the goal of this study was to locate and identify certain medications that were previously FDA-approved for definite disorders and that might show anti-leishmanial effect. Due to GS's presence in additional Leishmania species, a novel medication docked with Lm-GS may have broad anti-leishmania efficacy.Communicated by Ramaswamy H. Sarma.

Capparis spinosa inhibits Leishmania major growth through nitric oxide production in vitro and arginase inhibition in silico

Cutaneous leishmaniasis is an infectious disease, considered as a major public health problem in different regions of the world. The current treatments are limited due to their toxicity and treatment failures, which have increased the search for new substances of natural origin to control this infection. Capparis spinosa is an important medicinal plant, rich in biochemical compounds with a broad range of activities including antimicrobial effects. Nevertheless, more investigations are still needed to determine its effect on Leishmania parasites. This study aimed to evaluate the effect of C. spinosa' extracts on Leishmania major promastigotes and amastigotes growth as well as on L-arginine metabolic pathways, especially the production of leishmanicidal molecules such as nitric oxide. Our results showed that C. spinosa' methanolic and aqueous extracts contained polyphenols and flavonoids at different concentrations. The methanolic extract of C. spinosa, compared to the aqueous extract, showed significantly higher amounts of total polyphenols (21.23 ± 1.08) mg GAE/g of dw (P < 0.05), as well as a higher antioxidant activity evaluated respectively by Reducing Power and DPPH (EC₅₀: 0.31 ± 0.02 and 7.69 ± 1.28) mg/ml. Both extracts significantly inhibited L. major promastigotes and intra-macrophagic amastigotes growth in vitro in a dose-dependent manner (P < 0.001) and induced NO production not only in Leishmania-infected macrophages but also in uninfected macrophages, without showing any cytotoxicity in vitro. Furthermore, in silico docking studies showed that C. spinosa compounds identified by RP-HPLC exhibited inhibitory activity against the arginase enzyme. The leishmanicidal effect of C. spinosa may be due to its phenolic content and its mechanism of action may be mediated by an increase in NO production and by the inhibition of arginase enzyme in silico. These findings support the hypothesis that C. spinosa might be a valuable source of new biomolecules for leishmaniasis treatment.

Emerging strategies and challenges of molecular therapeutics in antileishmanial drug development

Molecular therapy refers to targeted therapies based on molecules which have been intelligently directed towards specific biomolecular structures and include small molecule drugs, monoclonal antibodies, proteins and peptides, DNA or RNA-based strategies, targeted chemotherapy and nanomedicines. Molecular therapy is emerging as the most effective strategy to combat the present challenges of life-threatening visceral leishmaniasis, where the successful human vaccine is currently unavailable. Moreover, current chemotherapy-based strategies are associated with the issues of ineffective targeting, unavoidable toxicities, invasive therapies, prolonged treatment, high treatment costs and the development of drug-resistant strains. Thus, the rational approach to antileishmanial drug development primarily demands critical exploration and exploitation of biochemical differences between host and parasite biology, immunocharacteristics of parasite homing, and host-parasite interactions at the molecular/cellular level. Following this, the novel technology-based designing and development of host and/or parasite-targeted therapeutics having leishmanicidal and immunomodulatory activity is utmost essential to improve treatment efficacy. Thus, the present review is focused on immunological and molecular checkpoint targets in host-pathogen interaction, and molecular therapeutic prospects for Leishmania intervention, and the challenges ahead.

Computational studies on potential small molecule inhibitors of Leishmania pteridine reductase 1

Leishmaniasis is a neglected tropical disease of major public health concern. Challenges with current therapeutics have led to the exploration of plant medicine for potential antileishmanial agents. Despite the promising activity of some antileishmanial natural products, their protein targets have not been explored. The relevance of folate metabolism in the Leishmania parasite's existence presents crucial targets for the development of antileishmanial chemotherapy. Pteridine reductase 1 (PTR1), a crucial enzyme involved in DNA biosynthesis, is a validated target of the Leishmania parasite. Unearthing inhibitors of this enzyme is therefore an active research area. The goal of this work is to unearth small molecule inhibitors of PTR1 using molecular docking and molecular dynamic simulations. Thus, the interactions between selected antileishmanial natural products and PTR1 were examined. The binding affinities obtained from molecular docking ranged from -6.2 to -9.8 kcal/mol. When compared to the natural PTR1 substrate biopterin, compounds such as anonaine, chimanine D, corynantheine, grifolin, licochalcone A, piperogalin and xylopine produced better binding affinities, making interactions catalytic residues - Tyr194, Asp181, Phe113, Arg17 and Ser111. The PTR1- xylopine, -piperogalin, -grifolin, and -licochalcone A complexes exhibited remarkable stability under dynamic conditions during the entire 200 ns simulation period. The overall binding free energy of grifolin, piperogalin, and licochalcone A were observed to be -105.711, -103.567, and -105.646 kJ/mol respectively. The binding of these complexes was observed to be favorable and spontaneous and as such capable of inhibiting Leishmania PTR1. They could therefore be considered as candidates in the development of antileishmanial chemotherapy.Communicated by Ramaswamy H. Sarma.

Apigenin is a promising molecule for treatment of visceral leishmaniasis

Current treatment for visceral leishmaniasis is based on drugs such as pentavalent antimony and amphotericin B. However, this treatment remains mostly ineffective and expensive, resulting in several side effects and generating resistance. Apigenin, a flavonoid present in fruits and vegetables, has demonstrated several biological functions. In the present study, we observed a concentration-dependent inhibition of the L. infantum promastigote in the presence of apigenin, exhibiting an IC₅₀ value of 29.9 µM. Its effect was also evaluated in L. infantum-infected murine peritoneal macrophages, presenting an C₅₀ value against intracellular amastigotes of 2.3 µM and a selectivity index of 34.3. In a murine model of visceral leishmaniasis, the in vivo effect of apigenin was measured using short-term and long-term treatment schemes. Treatment with apigenin demonstrated 99.7% and 94% reductions in the liver parasite load in the short-term and long-term treatment schemes, respectively. Furthermore, no alterations in serological and hematological parameters were observed. Taken together, these results suggest that apigenin is a potential candidate for visceral leishmaniasis chemotherapy by oral administration.

Leishmanicidal and cytotoxic activity of essential oil from the fruit peel of Myrciaria floribunda (H. West ex Willd.) O. Berg: Molecular docking and molecular dynamics simulations of its major constituent onto Leishmania enzyme targets

Cutaneous Leishmaniasis (CL) is a neglected disease characterized by highest morbidity rates worldwide. The available treatment for CL has several limitations including serious side effects and resistance to the treatment. Herein we aimed to evaluate the activity of essential oil from the peel of Myrciaria floribunda fruits (MfEO) on Leishmania amazonensis. The cytotoxic potential of MfEO on host mammalian cells was evaluated by MTT. The in vitro leishmanicidal effects of MfEO were investigated on the promastigote and intracellular amastigote forms. The ultrastructural changes induced by MfEO were evaluated by Scanning Electron Microscopy (SEM). The molecular docking of the major compounds δ-Cadinene, γ-Cadinene, γ-Muurolene, α-Selinene, α-Muurolene and (E)-Caryophyllene onto the enzymes trypanothione reductase (TreR) and sterol 14-alpha demethylase (C14DM) were performed. Our results showed that MfEO presented moderate cytotoxicity for Vero cells and macrophages. The MfEO inhibited the growth of promastigote and the survival of intracellular amastigotes, in a dose- and time- dependent way. The MfEO presented high selectivity towards amastigote forms, being 44.1 times more toxic for this form than to macrophages. Molecular docking analysis showed that the major compounds of MfEO interact with Leishmania enzymes and that δ-Cadinene (δ-CAD) presented favorable affinity energy values over TreR and C14DM enzymes, when compared with the other major constituents. Molecular dynamics (MD) simulation studies revealed a stable binding of δ-CAD with lowest binding free energy values in MMGBSA assay. Our results suggested that δ-CAD may be a potent inhibitor of TreR and C14DM enzymes. Communicated by Ramaswamy H. Sarma.

Antileishmanial Activities of Medicinal Herbs and Phytochemicals In Vitro and In Vivo: An Update for the Years 2015 to 2021

Leishmaniasis is one of the most neglected tropical diseases that present areal public health problems worldwide. Chemotherapy has several limitations such as toxic side effects, high costs, frequent relapses, the development of resistance, and the requirement for long-term treatment. Effective vaccines or drugs to prevent or cure the disease are not available yet. Therefore, it is important to dissect antileishmanial molecules that present selective efficacy and tolerable safety. Several studies revealed the antileishmanial activity of medicinal plants. Several organic extracts/essential oils and isolated natural compounds have been tested for their antileishmanial activities. Therefore, the aim of this review is to update and summarize the investigations that have been undertaken on the antileishmanial activity of medicinal plants and natural compounds derived, rom plants from January 2015 to December 2021. In this review, 94 plant species distributed in 39 families have been identified with antileishmanial activities. The leaves were the most commonly used plant part (49.5%) followed by stem bark, root, and whole plant (21.9%, 6.6%, and 5.4%, respectively). Other plant parts contributed less (<5%). The activity was reported against amastigotes and/or promastigotes of different species (L. infantum, L. tropica, L. major, L. amazonensis, L. aethiopica, L. donovani, L. braziliensis, L. panamensis, L. guyanensis, and L. mexicana). Most studies (84.2%) were carried out in vitro, and the others (15.8%) were performed in vivo. The IC50 values of 103 plant extracts determined in vitro were in a range of 0.88 µg/mL (polar fraction of dichloromethane extract of Boswellia serrata) to 98 µg/mL (petroleum ether extract of Murraya koenigii). Among the 15 plant extracts studied in vivo, the hydroalcoholic leaf extract of Solanum havanense reduced parasites by 93.6% in cutaneous leishmaniasis. Voacamine extracted from Tabernaemontana divaricata reduced hepatic parasitism by ≈30 times and splenic parasitism by ≈15 times in visceral leishmaniasis. Regarding cytotoxicity, 32.4% of the tested plant extracts against various Leishmania species have a selectivity index higher than 10. For isolated compounds, 49 natural compounds have been reported with anti-Leishmania activities against amastigotes and/or promastigotes of different species (L. infantum, L. major, L. amazonensis, L. donovani and L. braziliensis). The IC50 values were in a range of 0.2 µg/mL (colchicoside against promastigotes of L. major) to 42.4 µg/mL (dehydrodieuginol against promastigotes of L. amazonensis). In conclusion, there are numerous medicinal plants and natural compounds with strong effects (IC50 < 100 µg/mL) against different Leishmania species under in vitro and in vivo conditions with good selectivity indices (SI > 10). These plants and compounds may be promising sources for the development of new drugs against leishmaniasis and should be investigated in randomized clinical trials.

HAS 1: A natural product from soil-isolated Streptomyces species with potent activity against cutaneous leishmaniasis caused by Leishmania tropica

Cutaneous Leishmaniasis (CL) is a neglected tropical disease, classified by the World Health Organization (WHO) as one of the most unrestrained diseases. The Syrian war and the significant displacement of refugees aggravated the spread of this ailment into several neighboring countries in the Eastern Mediterranean Region (EMR). In Syria, Leishmania tropica is identified as one of the most aggressive and endemic identified species, causing localized or generalized lesions, often chronic or relapsing. Pentavalent antimonial drugs are currently used as first line treatment against CL. Nonetheless, these drugs exhibit several limitations, including the repetitive painful injections, high cost, poor availability, and mainly systemic toxicity. Besides, the emergence of acquired parasitic resistance hinders their potency, stressing the need for new therapies to combat CL. Natural products (NPs) epitomize a valuable source in drug discovery. NPs are secondary metabolites (SMs) produced by plants, sponges, or a wide variety of organisms, including environmental microorganisms. The EMR is characterized by its immense biodiversity, yet it remains a relatively untapped area in drug discovery. NPs of the region were explored over the last 2 decades, but their discoveries lack biogeographical diversity and are limited to the Red Sea. Here, we isolated previously uncultured environmental soil-dwelling Streptomyces sp. HAS1, from Hasbaya region in southeast Lebanon. When fermented in one of our production media named INA, HAS1 produced a crude extract with significant potency against a clinical Leishmania tropica isolate. Using bio-guided fractionation, the bioactive compound was purified and the structure was elucidated by NMR and LC-HRMS. Our findings establish NPs as strong candidates for treating Leishmania tropica and further dwells on the importance of these natural sources to combat microbial infections.

Mechanistic insight into the role of mevalonate kinase by a natural fatty acid-mediated killing of Leishmania donovani

We evaluated the anti-leishmanial efficacy of different saturated medium-chain fatty acids (FAs, C8–C18) where FA containing C8 chain, caprylic acid (CA), was found to be most potent against Leishmania donovani, the causative agent for visceral leishmaniasis (VL). Different analogs of CA with C8 linear chain, but not higher, along with a carboxyl/ester group showed a similar anti-leishmanial effect. Ergosterol depletion was the major cause of CA-mediated cell death. Molecular docking and molecular dynamic simulation studies indicated the enzyme mevalonate kinase (MevK) of the ergosterol biosynthesis pathway as a possible target of CA. Enzyme assays with purified recombinant MevK and CA/CA analogs confirmed the target with a competitive inhibition pattern. Using biochemical and biophysical studies; strong binding interaction between MevK and CA/CA analogs was established. Further, using parasites with overexpressed MevK and proteomics studies of CA-treated parasites the direct role of MevK as the target was validated. We established the mechanism of the antileishmanial effect of CA, a natural product, against VL where toxicity and drug resistance with current chemotherapeutics demand an alternative. This is the first report on the identification of an enzymatic target with kinetic parameters and mechanistic insights against any organism for a natural medium-chain FA.

Direct In Vitro Comparison of the Anti-Leishmanial Activity of Different Olive Oil Total Polyphenolic Fractions and Assessment of Their Combined Effects with Miltefosine

The bioactive compounds present in the edible products of the olive tree have been extensively studied and their favorable effects on various disease risk factors have been demonstrated. The aim of this study was to perform a comparative analysis of the anti-leishmanial effects of total phenolic fractions (TPFs) derived from extra virgin olive oil with different phenolic contents and diverse quantitative patterns. Moreover, the present study investigated their association with miltefosine, a standard anti-leishmanial drug, against both extracellular promastigotes and intracellular amastigotes of a viscerotropic and a dermotropic Leishmania strain. The chemical compositions of TPFs were determined by high performance liquid chromatography with diode array detection (HPLC-DAD). Analysis of parasite growth kinetics, reactive oxygen species production and apoptotic events were determined by microscopy and flow cytometry. Our results revealed that the presence of oleacein (OLEA) and oleocanthal (OLEO) secoiridoids enhances the anti-leishmanial effect of TPF. The association between TPFs and miltefosine was suggested as being additive in Leishmania infantum and Leishmania major promastigotes, and as antagonistic in intracellular amastigotes, as was evaluated with the modified isobologram method. The obtained data verified that TPFs are bioactive dietary extracts with a strong anti-leishmanial activity and highlighted that fractions that are richer in OLEA and OLEO phenolic compounds possess stronger inhibitory effects against parasites. This study may contribute to improving the therapeutic approaches against leishmaniasis.

Effects of anti-Leishmania compounds in the behavior of the sand fly vector Lutzomyia longipalpis

BACKGROUND

Leishmaniasis is an infectious parasitic disease caused by pathogens of the genus Leishmania transmitted through the bite of adult female sand flies. To reduce case numbers, it is necessary to combine different control approaches, especially those aimed at the sand fly vectors. Innovative forms of control with the use of attractive sugar baits explored the fact that adult sand flies need to feed on sugars of plant origin. Leishmania parasites develop in the gut of sand flies, interacting with the sugars in the diet of adults. Recent studies have shown that sugar baits containing plant-derived compounds can reduce sand fly survival, the number of parasites per gut, and the percentage of infected sand flies. Several synthetic compounds produced from naphthoquinones and pterocarpans have anti-parasitic activity on Leishmania amazonensis and/or Leishmania infantum in cell culture. This work aimed to assess the inclusion of these compounds in sugar baits for blocking transmission, targeting the development of the Leishmania parasite inside the sand fly vector.

RESULTS

We evaluated the attractant or repellent properties of these compounds, as well as of the reference compound N,N'-diethyl-m-toluamide (DEET), in sugar baits. We also observed changes in feeding preference caused by these compounds, looking for anti-feeding or stimulation of ingestion. Pterocarpanquinone L4 and pentamidine showed attractant and repellent properties, respectively.

CONCLUSION

Based on the effects in feeding preference and intake volume, pterocarpanquinone L6, and the pyrazole-derived compound P8 were chosen as the most promising compounds for the future development of anti-Leishmania sugar baits. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Stellaria media Linn.: A comprehensive review highlights the nutritional, phytochemistry, and pharmacological activities

Stellaria media Linn., a member of the family Caryophyllaceae, is generally known by the name of Chickweed. This plant is extensively cultivated globally and is inherent to Africa, Asia, China, Europe, and North America. It is a well-known medicinal plant with immense therapeutic uses. Nutritional studies have revealed the presence of protein, especially 16 amino acids, vitamins, and minerals such as calcium, iron, phosphorus, and zinc. Phytochemicals, mainly flavonoids, isoflavonoids, saponins, tannins, alkaloids, phenolic acids, triterpenoids, phenolic compounds, and anthraquinone are present in chickweed. It has multiple therapeutic potentials like anti-obesity, anti-diabetic, anti-fungal, anti-bacterial, anti-inflammatory, anti-leishmanial, anti-anxiety, and toxicity profiles. The crude extracts and their metabolites did not show any toxicity in the experimental animal. This review summarizes the nutritional, phytochemical, pharmacological, and toxicity studies on this plant concerning its future use in pharmacological drugs.

Carajurin Induces Apoptosis in Leishmania amazonensis Promastigotes through Reactive Oxygen Species Production and Mitochondrial Dysfunction

Carajurin is the main constituent of Arrabidaea chica species with reported anti-Leishmania activity. However, its mechanism of action has not been described. This study investigated the mechanisms of action of carajurin against promastigote forms of Leishmania amazonensis. Carajurin was effective against promastigotes with IC₅₀ of 7.96 ± 1.23 μg.mL⁻¹ (26.4 µM), and the cytotoxic concentration for peritoneal macrophages was 258.2 ± 1.20 μg.mL⁻¹ (856.9 µM) after 24 h of treatment. Ultrastructural evaluation highlighted pronounced swelling of the kinetoplast with loss of electron-density in L. amazonensis promastigotes induced by carajurin treatment. It was observed that carajurin leads to a decrease in the mitochondrial membrane potential (p = 0.0286), an increase in reactive oxygen species production (p = 0.0286), and cell death by late apoptosis (p = 0.0095) in parasites. Pretreatment with the antioxidant NAC prevented ROS production and significantly reduced carajurin-induced cell death. The electrochemical and density functional theory (DFT) data contributed to support the molecular mechanism of action of carajurin associated with the ROS generation, for which it is possible to observe a correlation between the LUMO energy and the electroactivity of carajurin in the presence of molecular oxygen. All these results suggest that carajurin targets the mitochondria in L. amazonensis. In addition, when assessed for its drug-likeness, carajurin follows Lipinski’’s rule of five, and the Ghose, Veber, Egan, and Muegge criteria.

Therapeutic effect of Prosopis strombulifera (LAM) BENTH aqueous extract on a murine model of cutaneous leishmaniasis

Background and aim

Prosopis strombulifera (Lam.) Benth is a rhizomatous shrub native from different zones of Argentine Republic. P. strombulifera aqueous extract (PsAE) has different effects and several biological activities have been reported. The goal of this study was to analyze the activity of PsAE on a murine model of cutaneous leishmaniasis caused by Leishmania amazonensis.

Experimental procedure

PsAE was orally administered at 150 mg/animal/day on BALB/c mice infected in the right footpad (RFP) with 1 × 10⁵ promastigotes of L. amazonensis. As a chemotherapeutic control of treatment, animals receive a commercial form of meglumine antimoniate (MA) (Glucantime®, Aventis, Paris, France).

Results and conclusion

We observe that the size of RFP lesions of infected mice without treatment showed a grade of inflammation, ulceration and necrosis at the site of infection much greater than that observed with PsAE or MA treatment. Moreover, PsAE was capable of decreasing parasite burden and splenic index. Furthermore, PsAE treated mice showed a significant decrease in O.D. of total anti-Leishmania IgG antibody responses against L. amazonensis. This decrease was similar to those observed when the reference drug, MA, was used. This would indicate that PsAE treatment inhibits or delays disease progression in mice. In conclusion, our findings suggest that PsAE could be a potential candidate to be used, as a new therapeutic strategy, to treat cutaneous leishmaniasis caused by L. amazonensis.

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Prosopis strombulifera aqueous extract (PsAE) has antileishmanial effect.

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PsAE treatment reduces inflammation and ulceration at the site of infection.

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PsAE decreased parasite burden and splenic index.

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PsAE decreased total anti-Leishmania IgG antibody responses against L. amazonensis.

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PsAE produces a switch to Th1 humoral immune response after infection.

Analysis of the mechanisms of action of isopentenyl caffeate against Leishmania

Leishmaniasis is a neglected parasitic disease for which the conventional treatment can be considered inefficient and extremely aggressive, generating several and severe side effects. Therefore, the discovery of new drug candidates is important for the improvement in the quality of life of patients. Previously, we reported the promising results of isopentyl caffeate (ICaf) against Leishmania chagasi (agent of visceral leishmaniasis) and Leishmania amazonensis (agent of cutaneous leishmaniasis) promastigotes, displaying IC₅₀ of 1.56 and 1.71 μM, respectively. Herein, we aimed to decipher the mechanisms of anti-Leishmania action of ICaf. Light and scanning electron microscopy assays showed relevant morphological changes in promastigotes when treated with ICaf, including rounding of the parasite body, shortening of the flagellum, blebs on the plasma membrane and cellular aggregation. The parasite mitochondrion was targeted by ICaf, resulting in a significant reduction in its metabolic activity and electric membrane potential followed by an increase in the production of reactive oxygen species, which culminated in the loss of plasma membrane integrity and parasite death. Relevantly, ICaf also had a potent anti-amastigote action. The IC₅₀ values calculated for intracellular amastigotes of L. amazonensis were 3.27, 1.60 and 1.52 μM, while for L. chagasi the values were 2.48, 1.84 and 1.60 μM, respectively, after treating the infected macrophages with ICaf for 24, 48 and 72 h. ICaf was well tolerated by THP-1 macrophages, which gave rise to excellent selectivity indexes considering both Leishmania species. The current results suggest that ICaf may emerge as a chemotherapeutic alternative for the treatment of leishmaniasis.

Identification of Kaurane-Type Diterpenes as Inhibitors of Leishmania Pteridine Reductase I

The current treatments against Leishmania parasites present high toxicity and multiple side effects, which makes the control and elimination of leishmaniasis challenging. Natural products constitute an interesting and diverse chemical space for the identification of new antileishmanial drugs. To identify new drug options, an in-house database of 360 kauranes (tetracyclic diterpenes) was generated, and a combined ligand- and structure-based virtual screening (VS) approach was performed to select potential inhibitors of Leishmania major (Lm) pteridine reductase I (PTR1). The best-ranked kauranes were employed to verify the validity of the VS approach through LmPTR1 enzyme inhibition assay. The half-maximal inhibitory concentration (IC₅₀) values of selected bioactive compounds were examined using the random forest (RF) model (i.e., 2β-hydroxy-menth-6-en-5β-yl ent-kaurenoate (135) and 3α-cinnamoyloxy-ent-kaur-16-en-19-oic acid (302)) were below 10 μM. A compound similar to 302, 3α-p-coumaroyloxy-ent-kaur-16-en-19-oic acid (302a), was also synthesized and showed the highest activity against LmPTR1. Finally, molecular docking calculations and molecular dynamics simulations were performed for the VS-selected, most-active kauranes within the active sites of PTR1 hybrid models, generated from three Leishmania species that are known to cause cutaneous leishmaniasis in the new world (i.e., L. braziliensis, L. panamensis, and L. amazonensis) to explore the targeting potential of these kauranes to other species-dependent variants of this enzyme.

Epigallocathechin-O-3-Gallate Inhibits Trypanothione Reductase of Leishmania infantum, Causing Alterations in Redox Balance and Leading to Parasite Death

Leishmania infantum is a protozoan parasite that causes a vector borne infectious disease in humans known as visceral leishmaniasis (VL). This pathology, also caused by L. donovani, presently impacts the health of 500,000 people worldwide, and is treated with outdated anti-parasitic drugs that suffer from poor treatment regimens, severe side effects, high cost and/or emergence of resistant parasites. In previous works we have disclosed the anti-Leishmania activity of (-)-Epigallocatechin 3-O-gallate (EGCG), a flavonoid compound present in green tea leaves. To date, the mechanism of action of EGCG against Leishmania remains unknown. This work aims to shed new light into the leishmanicidal mode of action of EGCG. Towards this goal, we first confirmed that EGCG inhibits L. infantum promastigote proliferation in a concentration-dependent manner. Second, we established that the leishmanicidal effect of EGCG was associated with i) mitochondria depolarization and ii) decreased concentration of intracellular ATP, and iii) increased concentration of intracellular H₂O₂. Third, we found that the leishmanicidal effect and the elevated H₂O₂ levels induced by of EGCG can be abolished by PEG-catalase, strongly suggesting that this flavonoid kills L. infantum promastigotes by disturbing their intracellular redox balance. Finally, we gathered in silico and in vitro evidence that EGCG binds to trypanothione reductase (TR), a central enzyme of the redox homeostasis of Leishmania, acting as a competitive inhibitor of its trypanothione substrate.

Amentoflavone as an Ally in the Treatment of Cutaneous Leishmaniasis: Analysis of Its Antioxidant/Prooxidant Mechanisms

Treatment of leishmaniasis is a challenging subject. Although available, chemotherapy is limited, presenting toxicity and adverse effects. New drugs with antileishmanial activity are being investigated, such as antiparasitic compounds derived from plants. In this work, we investigated the antileishmanial activity of the biflavonoid amentoflavone on the protozoan Leishmania amazonensis. Although the antileishmanial activity of amentoflavone has already been reported in vitro, the mechanisms involved in the parasite death, as well as its action in vivo, remain unknown. Amentoflavone demonstrated activity on intracellular amastigotes in macrophages obtained from BALB/c mice (IC₅₀ 2.3 ± 0.93 μM). No cytotoxicity was observed and the selectivity index was estimated as greater than 10. Using BALB/c mice infected with L. amazonensis we verified the effect of an intralesional treatment with amentoflavone (0.05 mg/kg/dose, in a total of 5 doses every 4 days). Parasite quantification demonstrated that amentoflavone reduced the parasite load in treated footpads (46.3% reduction by limiting dilution assay and 56.5% reduction by Real Time Polymerase Chain Reaction). Amentoflavone decreased the nitric oxide production in peritoneal macrophages obtained from treated animals. The treatment also increased the expression of ferritin and decreased iNOS expression at the site of infection. Furthemore, it increased the production of ROS in peritoneal macrophages infected in vitro. The increase of ROS in vitro, associated with the reduction of NO and iNOS expression in vivo, points to the antioxidant/prooxidant potential of amentoflavone, which may play an important role in the balance between inflammatory and anti-inflammatory patterns at the infection site. Taken together these results suggest that amentoflavone has the potential to be used in the treatment of cutaneous leishmaniasis, working as an ally in the control and development of the lesion.