Differential effects of polyamine derivative compounds against Leishmania infantum promastigotes and axenic amastigotes

A "Core-Linker-Polyamine (CLP)" strategy enabling rapid discovery of antileishmanial aminoalkyl-quinoline-carboxamides that target oxidative stress mechanism

A "Core-Linker-Polyamine (CLP)" strategy has been exploited to develop new antileishmanial agents. It involves the linker-based assembly of alkyl-polyamine side chain as a potential pharmacophore motif with a privileged heterocyclic motif, 4-arylquinoline. A series of aminoalkyl 4-arylquinoline-2-carboxamides and their analogs were synthesized and tested against L. donovani promastigotes. Among all synthesized derivatives, 10 compounds showed significant antipromastigote activities with more efficacy (IC 50 : 4.75-8 µ M) than an antileishmanial oral drug Miltefosine (IC 50 : 8.9±1.55 µ M). Most active compounds 9a and 9b , displayed negligible cytotoxicity towards human monocytic (THP-1) macrophages. The compounds show antileishmanial activity by generating mitochondrial superoxide radicals. However, they did not show interference with trypanothione reductase, a redox enzyme of Leishmania. Significant change in the morphology of the L. donovani promastigote by the compounds was observed. The Structure-activity relationship analysis suggest the pharmacophoric importance of alkylpolyamine and carboxamide motifs.  In silico evaluation  indicated that the investigated active molecules 9a and 9b possess important drug-likeness, physicochemical and pharmacokinetic-relevant properties.

Polyamine Metabolism in Leishmania Parasites: A Promising Therapeutic Target

Parasites of the genus Leishmania cause a variety of devastating and often fatal diseases in humans and domestic animals worldwide. The need for new therapeutic strategies is urgent because no vaccine is available, and treatment options are limited due to a lack of specificity and the emergence of drug resistance. Polyamines are metabolites that play a central role in rapidly proliferating cells, and recent studies have highlighted their critical nature in Leishmania. Numerous studies using a variety of inhibitors as well as gene deletion mutants have elucidated the pathway and routes of transport, revealing unique aspects of polyamine metabolism in Leishmania parasites. These studies have also shed light on the significance of polyamines for parasite proliferation, infectivity, and host-parasite interactions. This comprehensive review article focuses on the main polyamine biosynthetic enzymes: ornithine decarboxylase, S-adenosylmethionine decarboxylase, and spermidine synthase, and it emphasizes recent discoveries that advance these enzymes as potential therapeutic targets against Leishmania parasites.

Antileishmanial Activity of BNIPDaoct- and BNIPDanon-loaded Emulsomes on Leishmania infantum Parasites

Among bisnaphthalimidopropyl (BNIP) derivatives, BNIPDaoct and BNIPDanon recently came forward with antileishmanial activities beyond the standard, commercialized antileishmanial therapies. However, high-level toxicity on macrophages plus poor aqueous solubility and poor bioavailability of the compounds limit their application in therapies. Addressing these limitations, the present study introduces BNIPDaoct- and BNIPDanon-loaded emulsomes as lipid-based nanocarrier systems. Accordingly, emulsome formulations were prepared with the presence of BNIP compounds. The average diameters of BNIPDaoct- and BNIPDanon-loaded emulsomes were found as 363.1 and 337.4 nm, respectively; while empty emulsomes differed with a smaller average particle diameter, i.e., 239.1 nm. All formulations exhibited a negative zeta potential value. The formulations achieved the encapsulation of BNIPDaoct and BNIPDanon at approximately 0.31 mg/ml (501 µM) and 0.24 mg/ml (387 µM), respectively. The delivery of BNIP within the emulsomes improved the antileishmanial activity of the compounds. BNIPDaoct-loaded emulsome with 50% inhibitory concentration (IC50) value of 0.59 ± 0.08 µM was in particular effective against Leishmania infantum promastigotes compared to free BNIPDaoct (0.84 ± 0.09 µM), free BNIPDanon (1.85 ± 0.01 µM), and BNIPDanon-loaded emulsome (1.73 ± 0.02 µM). Indicated by at least ≥ 2-fold higher 50% cytotoxic concentration (CC50) values, the incorporation of BNIP into emulsomes significantly reduced the toxicity of BNIPs against macrophages, corresponding to up to 16-fold improvement in selectivity index (CC50/IC50) for L. infantum promastigotes. The infection rates of macrophages were determined using dual-fluorescent flow cytometry as 68.6%. Both BNIP formulations at concentration of 1.87 µM reduced the parasitic load nearly to 40%, whereas BNIPDaoct-loaded emulosmes could further decrease the parasitic load below 20% at 7.5 µM and above. In conclusion, the incorporation of BNIPDaoct and BNIPDanon into emulsomes results in water-soluble dispersed emulsome formulations that do not only successfully facilitate the delivery of BNIP compounds into the parasites and the Leishmania-infected macrophages in vitro but also enhance antileishmanial efficacy as proven by the decline in IC50 values. The selectivity of the formulation for L. infantum parasites further contributes to the challenging safety profile of the compounds. The promising in vitro antileishmanial efficacy of BNIP-loaded emulsomes highlights the potential of the system for the future in vivo studies.

Metabolomics reveal alterations in arachidonic acid metabolism in Schistosoma mekongi after exposure to praziquantel

BACKGROUND

Mekong schistosomiasis is a parasitic disease caused by the blood-dwelling fluke Schistosoma mekongi. This disease contributes to human morbidity and mortality in the Mekong region, posing a public health threat to people in the area. Currently, praziquantel (PZQ) is the drug of choice for the treatment of Mekong schistosomiasis. However, the molecular mechanisms of PZQ action remain unclear, and Schistosoma PZQ resistance has been reported occasionally. Through this research, we aimed to use a metabolomic approach to identify the potentially altered metabolic pathways in S. mekongi associated with PZQ treatment.

METHODOLOGY/PRINCIPAL FINDINGS

Adult stage S. mekongi were treated with 0, 20, 40, or 100 μg/mL PZQ in vitro. After an hour of exposure to PZQ, schistosome metabolites were extracted and studied with mass spectrometry. The metabolomic data for the treatment groups were analyzed with the XCMS online platform and compared with data for the no treatment group. After low, medium (IC50), and high doses of PZQ, we found changes in 1,007 metabolites, of which phosphatidylserine and anandamide were the major differential metabolites by multivariate and pairwise analysis. In the pathway analysis, arachidonic acid metabolism was found to be altered following PZQ treatment, indicating that this pathway may be affected by the drug and potentially considered as a novel target for anti-schistosomiasis drug development.

CONCLUSIONS/SIGNIFICANCE

Our findings suggest that arachidonic acid metabolism is a possible target in the parasiticidal effects of PZQ against S. mekongi. Identifying potential targets of the effective drug PZQ provides an interesting viewpoint for the discovery and development of new agents that could enhance the prevention and treatment of schistosomiasis.

More than just protein building blocks: how amino acids and related metabolic pathways fuel macrophage polarization

Macrophages represent the first line of defence in innate immune responses and additionally serve important functions for the regulation of host inflammation and tissue homeostasis. The M1/M2 model describes the two extremes of macrophage polarization states, which can be induced by multiple stimuli, most notably by LPS/IFN‐γ and IL‐4/IL‐13. Historically, the expression of two genes encoding for enzymes, which use the same amino acid as their substrate, iNOS and ARG1, has been used to define classically activated M1 (iNOS) and alternatively activated M2 (ARG1) macrophages. This ‘arginine dichotomy’ has recently become a matter of debate; however, in parallel with the emerging field of immunometabolism there is accumulating evidence that these two enzymes and their related metabolites are fundamentally involved in the intrinsic regulation of macrophage polarization and function. The aim of this review is to highlight recent advances in macrophage biology and immunometabolism with a specific focus on amino acid metabolism and their related metabolic pathways: iNOS/ARG1 (arginine), TCA cycle and OXPHOS (glutamine) as well as the one‐carbon metabolism (serine, glycine).

Novel Synthetic Approaches for Bisnaphthalimidopropyl (BNIP) Derivatives as Potential Anti-Parasitic Agents for the Treatment of Leishmaniasis

Leishmaniasis is a neglected parasitic disease that is widely seen in more than 60 countries worldwide, including Turkey and its subcontinental region. There are several chemotherapy agents for the treatment of leishmaniasis, including pentavalent antimonials—i.e., sodium stibogluconate (Pentostan) and meglumine antimoniate (Glucantim), pentamidine, conventional amphotericin B deoxycholate, miltefosine, paramomycin (aminosidine), and liposomal amphotericin B. However, these therapies are usually unsatisfactory due to dose-limiting toxicity issues and limited efficacy. Furthermore, resistance gained by parasites endangers future success of these therapies. Addressing these issues, the development of novel drugs with high efficacy has a vital importance. Latest studies have shown that bisnaphthalimidopropyl (BNIP) derivatives display high activity against Leishmaniasis parasites by selectively targeting parasitic sirtuin proteins and interacting with DNA. Despite the promising anti-parasitic activity, the low solubility and toxicity on human macrophages are the limitations to overcome. This study describes the new synthesis strategies for existing—i.e., BNIPDaoct and BNIPDanon—and novel BNIP derivatives differing in respect of their alkyl linker chain lengths. The new synthesis approach provides certain advantages compared to its existing alternatives reported in the literature. The proposed methodology does not only decrease the number of synthesis steps and production time of BNIPDaoct and BNIPDanon, but also provides higher yields, thereby making the synthesis highly cost-effective.

KH-TFMDI, a novel sirtuin inhibitor, alters the cytoskeleton and mitochondrial metabolism promoting cell death in Leishmania amazonensis

Treatment of leishmaniasis involves the use of antimonials, miltefosine, amphotericin B or pentamidine. However, the side effects of these drugs and the reports of drug-resistant parasites demonstrate the need for new treatments that are safer and more efficacious. Histone deacetylase inhibitors are a new class of compounds with potential to treat leishmaniasis. Herein, we evaluated the effects of KH-TFMDI, a novel histone deacetylase inhibitor, on Leishmania amazonensis promastigotes and intracellular amastigotes. The IC₅₀ values of this compound for promastigotes and intracellular amastigotes were 1.976 and 1.148 μM, respectively, after 72 h of treatment. Microscopic analyses revealed that promastigotes became elongated and thinner in response to KH-TFMDI, indicating changes in cytoskeleton organization. Immunofluorescence microscopy, western blotting and flow cytometry using an anti-acetylated tubulin antibody revealed an increase in the expression of acetylated tubulin. Furthermore, transmission electron microscopy revealed several ultrastructural changes, such as (a) mitochondrial swelling, followed by the formation of many vesicles inside the matrix; (b) presence of lipid bodies randomly distributed through the cytoplasm; (c) abnormal chromatin condensation; and (d) formation of blebs on the plasma membrane. Physiological studies for mitochondrial function, flow cytometry with propidium iodide and TUNEL assay confirmed the alterations in the mitochondrial metabolism, cell cycle, and DNA fragmentation, respectively, which could result to cell death by mechanisms related to apoptosis-like. All these together indicate that histone deacetylases are promising targets for the development of new drugs to treat Leishmania, and KH-TFMDI is a promising drug candidate that should be tested in vivo.

Development of monoclonal antibodies against axenic amastigotes of Leishmania infantum strain in Iran: implication for diagnosis of Kala-azar

OBJECTIVES

Leishmaniasis is endemic in 88 countries. Amastigote forms of Leishmania are experts at exploiting host cell processes to establish infection. Monoclonal antibodies are key reagents used in the diagnosis of infectious and non-infectious diseases. The aim of this study was to produce monoclonal antibodies against axenic amastigotes of the Leishmaniainfantum strain in Iran.

MATERIALS AND METHODS

First, standard strains were cultured and axenic amastigote antigens of L. infantum were obtained. Since then, BALB/c smice were immunized and antibody titers were determined. For hybridoma cell formation, lymphocytes isolated from spleen of immunized mice and myeloma cells were fused at a ratio of 10 to 1 in the presence of polyethylene glycol, followed by limiting dilution for the isolation of monoclones. Subsequently, antibody isotypes were determined by using the isotyping kit. The best clone was injected intraperitoneally to pristane-primed mice for large scale production of monoclonal antibodies. The specificity of antibody was determined with Western blotting.

RESULTS

Approximately 25 positive monoclones were obtained, of which four hybrids producing anti-amastigotes L. infantum monoclonal antibodies with high optical density (OD), selected and designated as 8D2 FVI6, 8D2 FVI3, 6G2 FV4 and 6G2 FV3. Results from isotype determination showed the IgG2b sub-class in 6G2FV2 and 8D2FVI6 monoclones.

CONCLUSION

This study produced monoclonal antibody against amastigotes of Iranian strain of L. infantum for the first time. These antibodies have reactivity against Iranian strain of L. infantum and can be used in the diagnosis of Kala-azar.

The first successful report of the in vitro life cycle of Chinese Leishmania: the in vitro conversion of Leishmania amastigotes has been raised to 94% by testing 216 culture medium compound

Chinese Leishmania isolate MHOM/CN/90/SC10H2 (L. H2), which was obtained from the spinal cords of patients from the Sichuan province of China, is an uncharacterized, pathogenic species closely related to Leishmania tarentolae. The in vitro transformation rate of L. H2 promastigotes into amastigotes has not been studied. This study is the first to successfully define the in vitro life cycle of L. H2 by investigating the percent conversion of L.H2 promastigotes to amastigotes in vitro under 216 different culture conditions. The highest proportion of L. H2 amastigotes observed (94%) was significantly higher than that previously reported. After conversion, the axenic amastigotes remained viable as verified by the levels of stage-specific genes (Gp46, A2 and β-tubulin) detected by RT-PCR. Meanwhile, morphological and protein characterizations of these axenic amastigotes were carried out in order to confirm the successful conversion. Specific antibodies were only able to detect 46 kDa, 52 kDa and 75 kDa proteins in samples isolated from axenic amastigotes. Afterward, these converted axenic amastigotes were transformed into the promastigote form by altering the culture condition. These converted axenic promastigotes still have the ability to infect macrophages, and their morphology changed back to the amastigote form following infection. These findings will assist further investigations into the biological characteristics of the host-parasite relationship and the process of pathogenesis.

Activity of Bisnaphthalimidopropyl Derivatives against Trypanosoma brucei

Current treatments for African trypanosomiasis are either toxic, costly, difficult to administer, or prone to elicit resistance. This study evaluated the activity of bisnaphthalimidopropyl (BNIP) derivatives againstTrypanosoma brucei BNIPDiaminobutane (BNIPDabut), the most active of these compounds, showedin vitroinhibition in the single-unit nanomolar range, similar to the activity in the reference drug pentamidine, and presented low toxicity and adequate metabolic stability. Additionally, using a murine model of acute infection and live imaging, a significant decrease in parasite load in BNIPDabut-treated mice was observed. However, cure was not achieved. BNIPDabut constitutes a new scaffold for antitrypanosomal drugs that deserves further consideration.

Development and validation of HPLC method with fluorometric detection for quantification of bisnaphthalimidopropyldiaminooctane in animal tissues following administration in polymeric nanoparticles

A simple, sensitive and specific high-performance liquid chromatography method for the quantification of bisnaphthalimidopropyldiaminooctane (BNIPDaoct), a potent anti-Leishmania compound, incorporated into poly(d,l-lactide-co-glycolic acid) (PLGA) nanoparticles was developed and validated toward bioanalysis application. Biological tissue extracts were injected into a reversed-phase monolithic column coupled to a fluorimetric detector (λexc=234nm, λem=394nm), using isocratic elution with aqueous buffer (acetic acid/acetate 0.10M, pH 4.5, 0.010M octanesulfonic acid) and acetonitrile, 60:40 (v/v) at a flow rate of 1.5mLmin(-1). The run time was 6min, with a BNIPDaoct retention time of 3.3min. Calibration curves were linear for BNIPDaoct concentrations ranging from 0.002 to 0.100μM. Matrix effects were observed and calibration curves were performed using the different organ (spleen, liver, kidney, heart and lung) extracts. The method was found to be specific, accurate (97.3-106.8% of nominal values) and precise for intra-day (RSD<1.9%) and inter-day assays (RSD<7.2%) in all matrices. Stability studies showed that BNIPDaoct was stable in all matrices after standing for 24h at room temperature (20°C) or in the autosampler, and after three freeze-thaw cycles. Mean recoveries of BNIPDaoct spiked in mice organs were >88.4%. The LOD and LOQ for biological matrices were ≤0.8 and ≤1.8nM, respectively, corresponding to values ≤4 and ≤9nmolg(-1) in mice organs. The method developed was successfully applied to biodistribution assessment following intravenous administration of BNIPDaoct in solution or incorporated in PLGA nanoparticles.

Antileishmanial drug discovery: comprehensive review of the last 10 years

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

Macrophage arginase-1 controls bacterial growth and pathology in hypoxic tuberculosis granulomas

Lung granulomas develop upon Mycobacterium tuberculosis (Mtb) infection as a hallmark of human tuberculosis (TB). They are structured aggregates consisting mainly of Mtb-infected and -uninfected macrophages and Mtb-specific T cells. The production of NO by granuloma macrophages expressing nitric oxide synthase-2 (NOS2) via l-arginine and oxygen is a key protective mechanism against mycobacteria. Despite this protection, TB granulomas are often hypoxic, and bacterial killing via NOS2 in these conditions is likely suboptimal. Arginase-1 (Arg1) also metabolizes l-arginine but does not require oxygen as a substrate and has been shown to regulate NOS2 via substrate competition. However, in other infectious diseases in which granulomas occur, such as leishmaniasis and schistosomiasis, Arg1 plays additional roles such as T-cell regulation and tissue repair that are independent of NOS2 suppression. To address whether Arg1 could perform similar functions in hypoxic regions of TB granulomas, we used a TB murine granuloma model in which NOS2 is absent. Abrogation of Arg1 expression in macrophages in this setting resulted in exacerbated lung granuloma pathology and bacterial burden. Arg1 expression in hypoxic granuloma regions correlated with decreased T-cell proliferation, suggesting that Arg1 regulation of T-cell immunity is involved in disease control. Our data argue that Arg1 plays a central role in the control of TB when NOS2 is rendered ineffective by hypoxia.

Triazolopyrimidine compounds containing first-row transition metals and their activity against the neglected infectious Chagas disease and leishmaniasis

Leishmaniasis and Chagas disease remain a significant global problem. Current treatments have serious disadvantage due to cost, toxicity, long therapy duration and resistance. In the last years increasing interest has arisen in drug development to fight both diseases. Recently, metal-based drugs have revealed as promising drugs in a variety of therapeutic areas. Herein we describe six newly synthesized transition metal complexes with a bioactive molecule 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine (dmtp). All of them have been characterized by X-ray, spectroscopic and thermal methods. In vitro and in vivo studies (murine model) on the antiproliferative activity of these complexes against Leishmania spp. (Leishmania infantum, Leishmania braziliensis) and Trypanosoma cruzi have been carried out. Our results reveal a strong potential of three of the assayed compounds as antiparasitic agents against the above-mentioned infectious diseases.

Natural product based leads to fight against leishmaniasis

The growing incidence of parasitic resistance against generic pentavalent antimonials, specifically for visceral disease in Indian subcontinent, is a serious issue in Leishmania control. Notwithstanding the two treatment alternatives, that is amphotericin B and miltefosine are being effectively used but their high cost and therapeutic complications limit their use in endemic areas. In the absence of a vaccine candidate, identification, and characterization of novel drugs and targets is a major requirement of leishmanial research. This review describes current drug regimens, putative drug targets, numerous natural products that have shown promising antileishmanial activity alongwith some key issues and strategies for future research to control leishmaniasis worldwide.

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

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

In vitro antileishmanial, trypanocidal, and Mammalian cell activities of diverse n,n' -dihetaryl substituted diamines and related compounds

The leishmaniasis and Chagas diseases constitute a serious public health problem worldwide with few and ineffective treatment options. The search for new antiparasitic candidates at the initial steps of drug discovery and development is still necessary. The synthesis of 22 de novo synthetized N,N′-dihetaryl-alkyldiamine derivatives and in vitro antiparasitic activity were evaluated for the first time against intracellular and extracellular forms of Leishmania (Leishmania) infantum, L. (Viannia) panamensis, L. (Leishmania) amazonensis, and Trypanosoma cruzi. Additionally, the toxicity on mammalian cells was determined. Some of these substituted N,N′-diamines (25–35 % of the tested compounds) showed interesting results against free-living forms of parasites with activities at the inhibitory concentration (IC₅₀) level of 1.96 to 28.83 μM for L. (L.) infantum promastigotes and IC₅₀ of 0.02 to 5.31 μM for T. cruzi epimastigotes. No activity at the IC₅₀ level on intracellular amastigotes of T. cruzi was observed. However, N¹,N²-dibenzylethane-1,2-diamine 5a revealed an important activity against the intracellular amastigotes of L. infantum (IC₅₀ 25.42 μM ±0.33) and L. panamensis (IC₅₀ 58.20 μM ±3.23), while their analogue N¹,N⁴-dibenzylbutane-1,4-diamine 5c resulted in activity only against L. panamensis (IC₅₀ 11.19 μM ±0.20) without toxicity on Vero and THP-1 mammalian cells. The active compounds against intracellular parasites with low toxicity in mammalian cells may be considered for future studies in experimental models.

Characterization and evaluation of BNIPDaoct-loaded PLGA nanoparticles for visceral leishmaniasis: in vitro and in vivo studies

OBJECTIVE

To overcome the limitation of bisnaphthalimidopropyldiaaminooctane (BNIPDaoct) low physiological solubility and potentially increase its efficiency against visceral leishmaniasis (VL), a delivery system based on poly(d,l-lactide-co-glycolide) (PLGA) nanoparticles was developed.

MATERIALS & METHODS

BNIPDaoct-PLGA nanoparticles were prepared by nanoprecipitation and characterized. Anti-Leishmania activity was evaluated using in vitro and in vivo VL infection models.

RESULTS

BNIPDaoct-PLGA nanoparticles were successfully produced and were sized at 156.0 ± 2.8 nm with an encapsulation efficiency of approximately 85%. The PLGA nanoparticles reduced BNIPDaoct cellular toxicity, retained its in vitro anti-leishmanial activity and led to a significant reduction (∼80%) in the parasite burden in the infected mice spleen when compared with the free drug or amphotericin B. In the liver the effect was less pronounced, with a 30-50% reduction observed between the nanoformulation and the BNIPDaoct per se or the amphotericin B, respectively.

CONCLUSION

PLGA nanoparticles provide controlled and effective delivery of BNIPDaoct for treatment of VL.

Leishmaniasis: current status of available drugs and new potential drug targets

The control of Leishmania infection relies primarily on chemotherapy till date. Resistance to pentavalent antimonials, which have been the recommended drugs to treat cutaneous and visceral leishmaniasis, is now widespread in Indian subcontinents. New drug formulations like amphotericin B, its lipid formulations, and miltefosine have shown great efficacy to treat leishmaniasis but their high cost and therapeutic complications limit their usefulness. In addition, irregular and inappropriate uses of these second line drugs in endemic regions like state of Bihar, India threaten resistance development in the parasite. In context to the limited drug options and unavailability of either preventive or prophylactic candidates, there is a pressing need to develop true antileishmanial drugs to reduce the disease burden of this debilitating endemic disease. Notwithstanding significant progress of leishmanial research during last few decades, identification and characterization of novel drugs and drug targets are far from satisfactory. This review will initially describe current drug regimens and later will provide an overview on few important biochemical and enzymatic machineries that could be utilized as putative drug targets for generation of true antileishmanial drugs.

In vitro leishmanicidal activity of N-dodecyl-1,2-ethanediamine

Polyamine biosynthesis and inhibition in parasites have been an attractive chemotherapeutic approach in the design of novel antiparasitic drugs. We study in this work the effect of N-dodecyl-1,2-ethylenediamine (NDDE) on the morphology and replication of Leishmania using macrophages cultured from the peritoneal exudate of mice infected in vitro with three species of Leishmania: Leishmania (Leishmania) amazonensis, Leishmania (Viannia) brasiliensis and Leishmania (Leishmania) chagasi. The results showed that NDDE inhibited Leishmania amastigotes multiplication into inflammatory peritoneal cells in concentrations which were not toxic to mammalian cells (0.5-1μg/mL). An intracellular disorganization of the promastigote forms was observed by transmission electron microscopy after 3 to 24h of treatment with 1μg/mL NDDE, suggesting that this compound affects the viability of the parasite by an autophagy pathway.

In vitro leishmanicidal activity of imidazole- or pyrazole-based benzo[g]phthalazine derivatives against Leishmania infantum and Leishmania braziliensis species

OBJECTIVES

To evaluate the in vitro leishmanicidal activity of imidazole-based (1-4) and pyrazole-based (5-6) benzo[g]phthalazine derivatives against Leishmania infantum and Leishmania braziliensis.

METHODS

The in vitro activity of compounds 1-6 was assayed on extracellular promastigote and axenic amastigote forms, and on intracellular amastigote forms of the parasites. Infectivity and cytotoxicity tests were performed on J774.2 macrophage cells using meglumine antimoniate (Glucantime) as the reference drug. The mechanisms of action were analysed by iron superoxide dismutase (Fe-SOD) and copper/zinc superoxide dismutase (CuZn-SOD) inhibition, metabolite excretion and transmission electronic microscopy (TEM).

RESULTS

Compounds 1-6 were more active and less toxic than meglumine antimoniate. Data on infection rates and amastigote mean numbers showed that 2, 4 and 6 were more active than 1, 3 and 5 in both L. infantum and L. braziliensis. The inhibitory effect of these compounds on the antioxidant enzyme Fe-SOD of promastigote forms of the parasites was remarkable, whereas inhibition of human CuZn-SOD was negligible. The ultrastructural alterations observed in treated promastigote forms confirmed the greater cell damage caused by the most active compounds 2, 4 and 6. The modifications observed by (1)H-NMR in the nature and amounts of catabolites excreted by the parasites after treatment with 1-6 suggested that the catabolic mechanisms could depend on the structure of the side chains linked to the benzo[g]phthalazine moiety.

CONCLUSIONS

All the compounds assayed were active in vitro against the two Leishmania species and were less toxic against mammalian cells than the reference drug, but the monosubstituted compounds were significantly more effective and less toxic than their disubstituted counterparts.

Targeting essential pathways in trypanosomatids gives insights into protozoan mechanisms of cell death

Apoptosis is a normal component of the development and health of multicellular organisms. However, apoptosis is now considered a prerogative of unicellular organisms, including the trypanosomatids of the genera Trypanosoma spp. and Leishmania spp., causative agents of some of the most important neglected human diseases. Trypanosomatids show typical hallmarks of apoptosis, although they lack some of the key molecules contributing to this process in metazoans, like caspase genes, Bcl-2 family genes and the TNF-related family of receptors. Despite the lack of these molecules, trypanosomatids appear to have the basic machinery to commit suicide. The components of the apoptotic execution machinery of these parasites are slowly coming into light, by targeting essential processes and pathways with different apoptogenic agents and inhibitors. This review will be confined to the events known to drive trypanosomatid parasites to apoptosis.

Polyamine metabolism in Leishmania: from arginine to trypanothione

Polyamines (PAs) are essential metabolites in eukaryotes, participating in a variety of proliferative processes, and in trypanosomatid protozoa play an additional role in the synthesis of the critical thiol trypanothione. The PAs are synthesized by a metabolic process which involves arginase (ARG), which catalyzes the enzymatic hydrolysis of L-arginine (L-Arg) to L-ornithine and urea, and ornithine decarboxylase (ODC), which catalyzes the enzymatic decarboxylation of L-ornithine in putrescine. The S-adenosylmethionine decarboxylase (AdoMetDC) catalyzes the irreversible decarboxylation of S-adenosylmethionine (AdoMet), generating the decarboxylated S-adenosylmethionine (dAdoMet), which is a substrate, together with putrescine, for spermidine synthase (SpdS). Leishmania parasites and all the other members of the trypanosomatid family depend on spermidine for growth and survival. They can synthesize PAs and polyamine precursors, and also scavenge them from the microenvironment, using specific transporters. In addition, Trypanosomatids have a unique thiol-based metabolism, in which trypanothione (N1-N8-bis(glutathionyl)spermidine, T(SH)(2)) and trypanothione reductase (TR) replace many of the antioxidant and metabolic functions of the glutathione/glutathione reductase (GR) and thioredoxin/thioredoxin reductase (TrxR) systems present in the host. Trypanothione synthetase (TryS) and TR are necessary for the protozoa survival. Consequently, enzymes involved in spermidine synthesis and its utilization, i.e. ARG, ODC, AdoMetDC, SpdS and, in particular, TryS and TR, are promising targets for drug development.

Bisnaphthalimidopropyl derivatives as inhibitors of Leishmania SIR2 related protein 1

The NAD(+)-dependent deacetylases, namely sirtuins, are involved in the regulation of a variety of biological processes such as gene silencing, DNA repair, longevity, metabolism, apoptosis, and development. An enzyme from the parasite Leishmania infantum that belongs to this family, LiSIR2RP1, is a NAD(+)-dependent tubulin deacetylase and an ADP-ribosyltransferase. This enzyme's involvement in L. infantum virulence and survival underscores its potential as a drug target. Our search for selective inhibitors of LiSIR2RP1 has led, for the first time, to the identification of the antiparasitic and anticancer bisnaphthalimidopropyl (BNIP) alkyl di- and triamines (IC(50) values in the single-digit micromolar range for the most potent compounds). Structure-activity studies were conducted with 12 BNIP derivatives that differ in the length of the central alkyl chain, which links the two naphthalimidopropyl moieties. The most active and selective compound is the BNIP diaminononane (BNIPDanon), with IC(50) values of 5.7 and 97.4 microM against the parasite and human forms (SIRT1) of the enzyme, respectively. Furthermore, this compound is an NAD(+)-competitive inhibitor that interacts differently with the parasite and human enzymes, as determined by docking analysis, which might explain its selectivity toward the parasitic enzyme.

In vitro susceptibilities of Leishmania donovani promastigote and amastigote stages to antileishmanial reference drugs: practical relevance of stage-specific differences

The in vitro susceptibilities of the reference strain Leishmania donovani MHOM/ET/67/L82 to sodium stibogluconate, amphotericin B, miltefosine, and the experimental compound PX-6518 were determined for extracellular log-phase promastigotes, established axenic amastigotes, fresh spleen-derived amastigotes, and intracellular amastigotes in primary mouse peritoneal macrophages. Susceptibility to amphotericin B did not differ across the various axenic models (50% inhibitory concentrations [IC50], 0.6 to 0.7 microM), and amphotericin B showed slightly higher potency against intracellular amastigotes (IC50, 0.1 to 0.4 microM). A similar trend was observed for miltefosine, with comparable efficacies against the extracellular (IC50, 0.4 to 3.8 microM) and intracellular (IC50, 0.9 to 4.3 microM) stages. Sodium stibogluconate, used either as Pentostam or as a crystalline substance, was inactive against all axenic stages (IC50, >64 microg SbV/ml) but showed good efficacy against intracellular amastigotes (IC50, 22 to 28 microg SbV/ml); the crystalline substance was about two to three times more potent (IC50, 9 to 11 microg SbV/ml). The activity profile of PX-6518 was comparable to that of sodium stibogluconate, but at a much higher potency (IC50, 0.1 microg/ml). In conclusion, the differential susceptibility determines which in vitro models are appropriate for either drug screening or resistance monitoring of clinical field isolates. Despite the more complex and labor-intensive protocol, the current results support the intracellular amastigote model as the gold standard for in vitro Leishmania drug discovery research and for evaluation of the resistance of field strains, since it also includes host cell-mediated effects. Axenic systems can be recommended only for compounds for which no cellular mechanisms are involved, for example, amphotericin B and miltefosine.

Fast high yield of pure Leishmania (Leishmania) infantum axenic amastigotes and their infectivity to mouse macrophages

Leishmania (L.) infantum (syn. Leishmania chagasi) is a dimorphic protozoan parasite that lives in promastigote and amastigote form in its sandfly vector and mammalian hosts, respectively. Here, we describe an in vitro culture system for the generation of a pure population of L. infantum axenic amastigotes after only 4 days incubation in culture medium supplemented with fetal calf serum, human urine, L: -glutamine, and HEPES at 37 masculineC (pH 5.5). Ultrastrutural analysis and infection assays in two macrophage populations (Kupffer cells (KUP) and peritoneal macrophages (PM)) infected with axenic amastigotes demonstrated that they maintained morphological and biochemical (A2 expression) features and a similar infection pattern to tissue-derived L. infantum amastigotes. The susceptibility of the macrophage lines to axenic or tissue-derived amastigotes and promastigotes was investigated. We found a completely different susceptibility profile for KUP and PM. Liver macrophages, both KUP and immigrant macrophages, are intimately involved in the response to L. infantum infection; this difference in susceptibility is probably related to their capacity to eliminate these parasites. Our in vitro system was thus able to generate axenic amastigotes that resemble tissue-derived amastigotes both in morphology and infectivity pattern; this will help in further investigation of the biological characteristics of the host-parasite relationship as well as the process of pathogenesis.

Characterization of the anti-Leishmania effect induced by cisplatin, an anticancer drug

The cis-diamminedichloroplatinum(II), known as cis-DDP or cisplatin is a widely used drug in cancer chemotherapy. Although a recent study has shown the anti-Leishmania activity of some cis-DDP derivatives, the cytotoxic properties were measured only on promastigotes, the insect vector form of the parasite. In this study the effect of cis-DDP on promastigotes and amastigotes, the vertebrate stage of the parasite is reported. The IC50, determined by flow cytometry, after 72 h of drug incubation was four times higher, 7.73+/-1.03 microM in the case of promastigotes compared to axenic amastigotes, 1.88+/-0.10 microM. In intracellular amastigotes the IC50, determined by counting the parasite index was 1.85+/-0.22 microM. By using flow cytometry, two patterns of cell cycle changes was observed: cis-DDP treated promastigotes and amastigotes accumulated in S phase and G2 phase, respectively. The cis-DDP response was also found to involve an "apoptosis-like" death of both promastigotes and amastigotes. However, DNA fragmentation was only detected in promastigote forms. In contrast mitochondrial transmembrane potential loss was observed for both stages of the parasite. Upon incubation of parasites with the drug an increase on GSH and GSSG levels and reactive oxygen species could be detected in the case of promastigote. Moreover, a slight increase of GSH level was detected on amastigote form. Taken together, these observations indicate that amastigotes are more sensitive to cis-DDP when compared to promastigotes. However, the signaling pathways leading to cell death could be different.

Phenotypical characteristics, biochemical pathways, molecular targets and putative role of nitric oxide-mediated programmed cell death in Leishmania

Nitric oxide (NO) has been demonstrated to be the principal effector molecule mediating intracellular killing of Leishmania, both in vitro and in vivo. We investigated the type of cell death process induced by NO for the intracellular amastigote stage of the protozoa Leishmania. Specific detection methods revealed a rapid and extensive cell death with morphological features of apoptosis in axenic amastigotes exposed to NO donors, in intracellular amastigotes inside in vitro - activated mouse macrophages and also in activated macrophages of regressive lesions in a leishmaniasis-resistant mouse model. We extended our investigations to the dog, a natural host-reservoir of Leishmania parasites, by demonstrating that co-incubation of infected macrophages with autologous lymphocytes derived from dogs immunised with purified excreted-secreted antigens of Leishmania resulted in a significant NO-mediated apoptotic cell death of intracellular amastigotes. From the biochemical point of view, NO-mediated Leishmania amastigotes apoptosis did not seem to be controlled by caspase activity as indicated by the lack of effect of cell permeable inhibitors of caspases and cysteine proteases, in contrast to specific proteasome inhibitors, such as lactacystin or calpain inhibitor I. Moreover, addition of the products of two NO molecular targets, cis-aconitase and glyceraldehyde-3-phosphate dehydrogenase, also had an inhibitory effect on the cell death induced by NO. Interestingly, activities of these two enzymes plus 6-phosphogluconate dehydrogenase, parasitic enzymes involved in both glycolysis and respiration processes, are overexpressed in amastigotes selected for their NO resistance. This review focuses on cell death of the intracellular stage of the pathogen Leishmania induced by nitrogen oxides and gives particular attention to the biochemical pathways and the molecular targets potentially involved. Questions about the role of Leishmania amastigotes NO-mediated apoptosis in the overall infection process are raised and discussed.