Comparative analysis of biological aspects of Leishmania infantum strains.

Leishmania infantum infantum (LII) is one of the species that causes visceral leishmaniasis (VL) in the Old World, while L. infantum chagasi (LIC) is present in the New World. Few studies address biological differences or the behavior of these strains during infection. These parasites live inside cells of their hosts, continuously evading microbicidal mechanisms and modulating the immune responses of these cells. One of the mechanisms used by these protozoa involves the L-arginine metabolism. Understanding the differences between Leishmania species and establishing an improved murine model for study of leishmaniasis are matters of extreme importance. Thereby, the objectives of this work were to analyze the biological and molecular differences between two Leishmania infantum strains (LII and LIC) and the degree of susceptibility to infection of mice with different genetic backgrounds. The infectivity in vivo and in vitro of LII and LIC strains was evaluated in BALB/c and Swiss Webster mice, as well the NOS and ARG activities. The LII strain was more infective than the LIC strain both in vivo and in vitro. In animals infected by the LII and LIC strains, differences in NOS and ARG activities occurred. In vitro, promastigotes of LII isolated from BALB/c and Swiss Webster mice showed higher ARG activity than LIC promastigotes during the growth curve. However, no difference was observed in intracellular NO production by promastigotes of these strains. The ARG gene sequences were compared, and those of both strains were identical. However, despite the similarity, the strains showed different expression levels of this gene. It can be concluded that although L. chagasi strains are considered identical to L. infantum strains from a molecular point of view, these strains have different biological behavior.

Leishmaniasis treatment: update of possibilities for drug repurposing.

The leishmaniases represent a public health problem in under-developed countries and are considered a neglected disease by the World Health Organization (WHO). They are cuased by Leishmania  parasites with different clinical manifestations. Currently, there is no vaccine, and treatment is in-efficient and is associated with both serious side effects often leading to resistance to the parasites. Thus, it is essential to search for new treatment strategies, such as drug repurposing, i.e., the use of drugs that are already used for other diseases. The discovery of new clinical applications for approved drugs is strategic for lowering the cost of drug discovery since human toxicity assays are already conducted. Here, we review a broad analysis of the different aspects of this approach for anti-leishmanial treatment.

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

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

Benznidazole-resistance in Trypanosoma cruzi: evidence that distinct mechanisms can act in concert.

Benznidazole is the main drug used to treat Trypanosoma cruzi infections. However, frequent instances of treatment failure have been reported. To better understand potential resistance mechanisms, we analysed three clones isolated from a single parasite population that had undergone benznidazole-selection. These clones exhibited differing levels of benznidazole-resistance (varying between 9 and 26-fold), and displayed cross-resistance to nifurtimox (2 to 4-fold). Each clone had acquired a stop-codon-generating mutation in the gene which encodes the nitroreductase (TcNTR) that is responsible for activating nitroheterocyclic pro-drugs. In addition, one clone had lost a copy of the chromosome containing TcNTR. However, these processes alone are insufficient to account for the extent and diversity of benznidazole-resistance. It is implicit from our results that additional mechanisms must also operate and that T. cruzi has an intrinsic ability to develop drug-resistance by independent sequential steps, even within a single population. This has important implications for drug development strategies.

Effectiveness of novel 5-(5-amino-1-aryl-1H-pyrazol-4-yl)-1H-tetrazole derivatives against promastigotes and amastigotes of Leishmania amazonensis.

In this research, a series of substituted 5-(5-amino-1-aryl-1H-pyrazol-4-yl)-1H-tetrazoles were synthesized and evaluated for in vitro antileishmanial activity. Among the derivatives, examined compounds 3b and 3l exhibited promising activity against promastigotes and amastigotes forms of Leishmania amazonensis. The cytotoxicity of these compounds was evaluated on murine cells, giving access to the corresponding selectivity index (SI).

Synthesis and activity of novel tetrazole compounds and their pyrazole-4-carbonitrile precursors against Leishmania spp.

A new series of 5-(1-aryl-3-methyl-1H-pyrazol-4-yl)-1H-tetrazole derivatives (4a-m) and their precursor 1-aryl-3-methyl-1H-pyrazole-4-carbonitriles (3a-m) were synthesized and evaluated as antileishmanials against Leishmania braziliensis and Leishmania amazonensis promastigotes in vitro. In parallel, the cytotoxicity of these compounds was evaluated on the RAW 264.7 cell line. The results showed that among the assayed compounds the substituted 3-chlorophenyl (4a) (IC50/24h=15±0.14 µM) and 3,4-dichlorophenyl tetrazoles (4d) (IC50/24h=26±0.09 µM) were the most potent against L. braziliensis promastigotes, as compared the reference drug pentamidine, which presented IC50=13±0.04 µM. In addition, 4a and 4d derivatives were less cytotoxic than pentamidine. However, these tetrazole derivatives (4) and pyrazole-4-carbonitriles precursors (3) differ against each of the tested species and were more effective against L.braziliensis than on L. amazonensis.

Synthesis, antileishmanial activity and structure-activity relationship of 1-N-X-phenyl-3-N'-Y-phenyl-benzamidines.

Two series of N,N'-diphenyl-benzamidines were synthesized as part of a study to search potential new drugs with antileishmanial activity. These compounds were obtained by anilides in PCl5 halogenation reaction with generation in situ of the corresponding benzimidoyl chlorides, and subsequently treatment with adequate anilines. The series I showed expressive results of antileishmanial activity, highlighted the compounds 9a with IC50 = 81.28 µM (log IC50 = 1.91 µM) against Leishmania chagasi, 8e with IC50 = 26.30 (log IC50 = 1.52 µM) against Leishmania braziliensis. From the results obtained from SAR study (series I), the series II was planned from Craig 2-dimensional map, in which was possible the discovery of the potent compounds, 9v and 9j with IC50 = 12.60 µM (log IC50 = 1.10 µM) and 13.00 µM (log IC50 = 1.11 µM), respectively, against Leishmania amazonensis. The results obtained from the SAR and QSAR studies indicated the best results when electron-donor groups in the ring attached to amidinic carbon, unlike when electron-withdrawing groups at the phenyl-N ring showing inhibitory activity increased. Furthermore, the QSAR model obtained indicated the hydrophobicity as a fundamental property for antileishmanial activity presented by these series.

In vitro evaluation of 4-phenyl-5-(4'-X-phenyl)-1,3,4-thiadiazolium-2-phenylaminide chlorides and 3[N-4'-X-phenyl]-1,2,3-oxadiazolium-5-olate derivatives on nitric oxide synthase and arginase activities of Leishmania amazonensis.

Leishmaniasis is a spectrum of infectious diseases caused by Leishmania protozoan parasites. The purpose of this study was to perform, in vitro, a comparative analysis of the activity amastigotes. Results showed excellent efficacy of all compounds against axenic amastigotes, compared to pentamidine isethionate, the reference drug used. The cytotoxic effect of these mesoionic compounds of six mesoionic compounds (three 1,3,4-thiadiazolium-2-aminide and three 1,2,3-oxadiazolium-5-olate class compounds) was evaluated in mouse peritoneal macrophages using MTT assay, low toxicity (≈ 10%) for these mammalian cells being observed. In an attempt to define a potential drug target, the activities of nitric oxide synthase (NOS) and arginase of the parasites treated with the mesoionic derivatives were evaluated. NOS was purified from a cell-free extract of infective promastigotes and axenic amastigotes and all derivatives tested were able to inhibit the enzyme as monitored by the decrease of NADPH consumption. Arginase activity from both stages of the parasite was measured using urea production and none of the compounds inhibited the enzyme activity of axenic amastigotes. However, the compounds without substituents (MI-H and SID-H) were able to inhibit arginase activity of these parasites.

P-glycoprotein efflux pump plays an important role in Trypanosoma cruzi drug resistance.

Drug resistance in protozoan parasites has been associated with the P-glycoprotein (Pgp), an energy-dependent efflux pump that transports substances across the membrane. Interestingly, the genes TcPGP1 and TcPGP2 have been described in Trypanosoma cruzi, although the function of these genes has not been fully elucidated. The main goal of this work was to investigate Pgp efflux pump activity and expression in T. cruzi lines submitted to in vitro induced resistance to the compounds 4-N-(2-methoxy styryl)-thiosemicarbazone (2-Meotio) and benznidazole (Bz) and to verify the stability of the resistant phenotypes during the parasite life cycle. We observed that the EC50 values for the treatment of epimastigotes with 2-Meotio or Bz were increased at least 4.7-fold in resistant lines, and this phenotype was maintained in metacyclic trypomastigotes, cell-derived trypomastigotes, and intracellular amastigotes. However, in epimastigotes, 2-Meotio resistance is reversible, but Bz resistance is irreversible. When compared with the parental line, the resistant lines exhibited higher Pgp efflux activity, reversion of the resistant phenotypes in the presence of Pgp inhibitors, cross-resistance with Pgp modulators, higher basal Pgp ATPase activity, and overexpression of the genes TcPGP1 and TcPGP2. In conclusion, the resistance induced in T. cruzi by the compounds 2-Meotio and Bz is maintained during the entire parasite life cycle. Furthermore, our data suggest the participation of the Pgp efflux pump in T. cruzi drug resistance.

The histopathological and immunological pattern of CBA mice infected with Leishmania amazonensis after treatment with pyrazole carbohydrazide derivatives.

Because there is no vaccine in clinical use, control of Leishmaniasis relies almost exclusively on chemotherapy and the conventional treatments exhibit high toxicity for patients and emerging drug resistance. Recently, we showed that oral treatment with synthetic pyrazole carbohydrazide compounds induced lower parasite load in draining lymph nodes and reduced skin lesion size without causing any toxic effects in an experimental murine infection model with Leishmania amazonensis. In this study, CBA mice were infected in the footpad with L. amazonensis and then orally treated with pyrazole carbohydrazides derivatives, such as BrNO(2), NO(2)Cl and NO(2)Br and their histopathological and immunological effects were then investigated. Epidermis and dermis had lower levels of inflammatory infiltration compared to the infected untreated control mice. In the dermis of treated animals, the numbers of vacuolated macrophages containing intracellular parasites were far lower than in infected untreated animals. In addition to dermal macrophages, we also observed a mixed inflammatory infiltrate containing lymphocytes and granulocyte cells. Lower numbers of B cells (B220+) and T lymphocytes (CD3+) were identified in the lesions of treated mice compared with the untreated, infected mice. In draining lymph node cells, the number of T lymphocytes (CD3+) was decreased, and the numbers of B cells (CD19+) and CD8+ T cells were increased in infected mice, when compared with the non-infected control group. In additional, we have shown that infected treated and untreated lymph node cells had similar levels of TGF-ß and IFN-γ mRNA expression, whereas IL-4 was expressed at a lower level in the treated group. Increased levels of the specific anti-Leishmania IgG2a or IgG3 antibody subclass were observed in NO(2)Cl or BrNO(2)-treated group, respectively. Overall, our experimental findings suggest that pyrazole carbohydrazides exert modulation of IL-4 expression and B cell levels; however, further evaluation is required to determine the optimal treatment regime.

4-(1H-Pyrazol-1-yl) benzenesulfonamide derivatives: identifying new active antileishmanial structures for use against a neglected disease.

Leishmaniasis is a neglected disease responsible for about 56,000 deaths every year. Despite its importance, there are no effective, safe and proper treatments for leishmaniasis due to strain resistance and/or drug side-effects. In this work we report the synthesis, molecular modeling, cytotoxicity and the antileishmanial profile of a series of 4-(1H-pyrazol-1-yl)benzenesulfonamides. Our experimental data showed an active profile for some compounds against Leishmania infantum and Leishmania amazonensis. The profile of two compounds against L. infantum was similar to that of pentamidine, but with lower cytotoxicity. Molecular modeling evaluation indicated that changes in electronic regions, orientation as well as lipophilicity of the derivatives were areas to improve the interaction with the parasitic target. Overall the compounds represent feasible prototypes for designing new molecules against L. infantum and L. amazonensis.

Kinetoplastid membrane protein-11 exacerbates infection with Leishmania amazonensis in murine macrophages.

In Leishmania amazonensis, kinetoplastid membrane protein-11 (KMP-11) expression increases during meta-cyclogenesis and is higher in amastigotes than in promastigotes, suggesting a role for this protein in the infection of the mammalian host. We show that the addition of KMP-11 exacerbates L. amazonensis infection in peritoneal macrophages from BALB/c mice by increasing interleukin (IL)-10 secretion and arginase activity while reducing nitric oxide (NO) production. The doses of KMP-11, the IL-10 levels and the intracellular amastigote loads were strongly, positively and significantly correlated. The increase in parasite load induced by KMP-11 was inhibited by anti-KMP-11 or anti-IL-10 neutralising antibodies, but not by isotype controls. The neutralising antibodies, but not the isotype controls, were also able to significantly decrease the parasite load in macrophages cultured without the addition of KMP-11, demonstrating that KMP-11-induced exacerbation of the infection is not dependent on the addition of exogenous KMP-11 and that the protein naturally expressed by the parasite is able to promote it. In this study, the exacerbating effect of KMP-11 on macrophage infection with Leishmania is for the first time demonstrated, implicating it as a virulence factor in L. amazonensis. The stimulation of IL-10 production and arginase activity and the inhibition of NO synthesis are likely involved in this effect.

Kinetoplastid membrane protein-11 exacerbates infection with Leishmania amazonensis in murine macrophages

In Leishmania amazonensis, kinetoplastid membrane protein-11 (KMP-11) expression increases during metacyclogenesis and is higher in amastigotes than in promastigotes, suggesting a role for this protein in the infection of the mammalian host. We show that the addition of KMP-11 exacerbates L. amazonensis infection in peritoneal macrophages from BALB/c mice by increasing interleukin (IL)-10 secretion and arginase activity while reducing nitric oxide (NO) production. The doses of KMP-11, the IL-10 levels and the intracellular amastigote loads were strongly, positively and significantly correlated. The increase in parasite load induced by KMP-11 was inhibited by anti-KMP-11 or anti-IL-10 neutralising antibodies, but not by isotype controls. The neutralising antibodies, but not the isotype controls, were also able to significantly decrease the parasite load in macrophages cultured without the addition of KMP-11, demonstrating that KMP-11-induced exacerbation of the infection is not dependent on the addition of exogenous KMP-11 and that the protein naturally expressed by the parasite is able to promote it. In this study, the exacerbating effect of KMP-11 on macrophage infection with Leishmania is for the first time demonstrated, implicating it as a virulence factor in L. amazonensis. The stimulation of IL-10 production and arginase activity and the inhibition of NO synthesis are likely involved in this effect.

Anti-leishmanial activity of alkaloidal extracts obtained from different organs of Aspidosperma ramiflorum.

The present study was designated to evaluate semi-quantitative antileishmanial activity of alkaloidal extracts that were obtained from 1g of different parts of Aspidosperma ramiflorum (leaves, roots, seeds, and stem barks). Alkaloidal extracts of barks and leaves presented a good activity against the extracellular form (promastigotes) of Leishmania (L.) amazonensis. It is known that compounds responsible for the antileishmanial activity in the alkaloidal extracts from A. ramiflorum are the monoterpenoid indole alkaloids ramiflorine A and ramiflorine B, therefore extracts obtained from different plant parts were analyzed by electrospray ionization mass spectrometry (ESI-MS) in order to evidence the presence of these bioactive alkaloids. Based on these findings, alkaloidal extract from leaves was fractionated on preparative thin-layer chromatography in a bioassay-guided fractionation affording individual purified ramiflorines A and B. Both ramiflorines A and B showed significant activity against Leishmania (L.) amazonensis (LD(50) values of 18.5±6.5µg/ml and 12.63±5.52µg/ml, respectively). Our results are showing that alkaloidal extract from leaves is a promising alternative to the use of stem barks from A. ramiflorum.

Chemical and biological analyses of the essential oils and main constituents of Piper species.

The essential oils obtained from leaves of Piper duckei and Piper demeraranum by hydrodistillation were analyzed by gas chromatography-mass spectrometry. The main constituents found in P. demeraranum oil were limonene (19.3%) and ß-elemene (33.1%) and in P. duckei oil the major components found were germacrene D (14.7%) and trans-caryophyllene (27.1%). P. demeraranum and P. duckei oils exhibited biological activity, with IC(50) values between 15 to 76 µg mL(-1) against two Leishmania species, P. duckei oil being the most active. The cytotoxicity of the essential oils on mice peritoneal macrophage cells was insignificant, compared with the toxicity of pentamidine. The main mono- and sesquiterpene, limonene (IC(50) = 278 µM) and caryophyllene (IC(50) = 96 µM), were tested against the strains of Leishmania amazonensis, and the IC(50) values of these compounds were lower than those found for the essential oils of the Piper species. The HET-CAM test was used to evaluate the irritation potential of these oils as topical products, showing that these oils can be used as auxiliary medication in cases of cutaneous leishmaniasis, with less side effects and lower costs.

Investigation of trypanothione reductase inhibitory activity by 1,3,4-thiadiazolium-2-aminide derivatives and molecular docking studies.

The biological activities of a series of mesoionic 1,3,4-thiadiazolium-2-aminide derivatives have been studied. The most active compounds (MI-HH; MI-3-OCH(3); MI-4-OCH(3) and MI-4-NO(2)) were evaluated to determine their effect on trypanothione reductase (TryR) activity in Leishmania sp. and Trypanosoma cruzi. Among the assayed compounds, only MI-4-NO(2) showed enzyme inhibition effect on extracts from different cultures of parasites, which was confirmed using the recombinant enzyme from T. cruzi (TcTryR) and Leishmania infantum (LiTryR). The enzyme kinetics determined with LiTryR demonstrated a non-competitive inhibition profile of MI-4-NO(2). A molecular docking study showed that the mesoionic compounds could effectively dock into the substrate binding site together with the substrate molecule. The mesoionic compounds were also effective ligands of the NADPH and FAD binding sites and the NADPH binding site was predicted as the best of all three binding sites. Based on the theoretical results, an explanation at the molecular level is proposed for the MI-4-NO(2) enzyme inhibition effect. Given TryR as a molecular target, it is important to continue the study of mesoionic compounds as part of a drug discovery campaign against Leishmaniasis or Chagas' disease.

The in vivo activity of 1,3,4-thiadiazolium-2-aminide compounds in the treatment of cutaneous and visceral leishmaniasis.

OBJECTIVES: Researchers have recently investigated the biological activities of mesoionic (MI) compounds, which have shown in vitro activity against many species of Leishmania, as well as Trypanosoma cruzi. The main goal of this study was to evaluate and compare the activity of three MI compounds against Leishmania amazonensis and Leishmania infantum infection in vivo. METHODS: The experiments were carried out using BALB/c mice infected with L. amazonensis or L. infantum as a highly sensitive murine model. The infected mice were treated with MI-HH, MI-4-OCH(3), MI-4-NO(2) or meglumine antimoniate by different routes (intralesional, topical or intraperitoneal). RESULTS: Treatment with MI-4-OCH(3) and MI-4-NO(2) efficiently contained the progression of cutaneous and visceral leishmaniasis in comparison with the control group or mice treated with meglumine antimoniate. Interestingly, these MI compounds did not produce toxicological effects after treatment. Furthermore, treatment with these compounds led to a modulation of the immune response that was correlated with disease control. In this study, MI compounds, and MI-4-NO(2) in particular, exhibited high activity in the L. infantum murine model. In the L. amazonensis model, intralesional treatment with MI-4-OCH(3) or MI-4-NO(2) showed greater therapeutic efficacy than treatment with meglumine antimoniate, and the new topical formulations of these compounds also displayed great activity in the cutaneous leishmaniasis model. CONCLUSIONS: Upon comparison of each MI compound, MI-4-NO(2) was clearly the compound with the greatest activity in these two in vivo infection models by each administration route tested.

Synthesis and antileishmanial evaluation of 1-aryl-4-(4,5-dihydro-1H-imidazol-2-yl)-1H-pyrazole derivatives.

A series of 1-aryl-4-(4,5-dihydro-1H-imidazol-2-yl)-1H-pyrazoles (4a-g) and 5-amino-1-aryl-4-(4,5-dihydro-1H-imidazol-2-yl)-1H-pyrazoles (5a-g) were synthesized and evaluated in vitro against three Leishmania species: L. amazonensis, L. braziliensis and L. infantum (L. chagasi syn.). The cytotoxicity was assessed. Among the derivatives examined, six compounds emerged as the most active on promastigotes forms of L. amazonensis with IC(50) values ranging from 15 to 60 µM. The reference drug pentamidine presented IC(50)=10 µM. However, these new compounds were less cytotoxic than pentamidine. Based on these results, the more promising derivative 5d was tested further in vivo. This compound showed inhibition of the progression of cutaneous lesions in CBA mice infected with L. amazonensis relative to an untreated control.

Evaluation of thiosemicarbazones and semicarbazones as potential agents anti-Trypanosoma cruzi.

Synthetic thiosemicarbazones and semicarbazones were evaluated for their Trypanosoma cruzi trypomastigotes obtained from LLC-MK2 cell cultures. In general, thiosemicarbazone derivatives were most effective and among them the 4-N-(2'-methoxy styryl)-thiosemicarbazone was chosen, to compare the in vitro effect against amastigotes of T. cruzi lodged in mouse peritoneal and human macrophages. A potent trypanocidal effect was observed that was more pronounced against parasites internalized in human macrophages. A potential target for this compound was also evaluated by measuring the nitric oxide synthase activity through NADPH consumption. A significant decrease in enzyme activity was observed. In contrast to the cytotoxic effect observed with benznidazole, no macrophage toxicity was observed for any of the compounds, indicating that their activity was specific for the parasite forms investigated.

Rat models to investigate host macrophage defense against Trypanosoma cruzi.

Trypanosoma cruzi is the causal agent of Chagas' disease, an infection with a great impact on public health in Latin America. One of the challenges to understand Chagas' disease lies on the complex host-parasite interaction. The understanding of this interaction requires the use of appropriate experimental models that mimic the human disease. Here, we have used two lineages of rats (Wistar and Holtzman) to comparatively evaluate the course of the acute infection (Y strain). Infection was monitored by parasitemia, cardiac and skeletal muscle parasitism and inflammation, heart ultrastructure, recruitment of monocytes/macrophages and nitric oxide, and arginase production by these cells. Although both rats were able to infect, only Holtzman rats developed a marked infection in the cardiac and skeletal muscles, in parallel to a high recruitment of first-line defense cells. A high number of inflammatory macrophages directed parasite clearance. By the end of the acute phase, Holtzman rats showed consistent disease control. Interestingly, parasite killing was not related to nitric oxide production likely inhibited by an arginase-dependent mechanism. Our work demonstrates differential responses of Holtzman and Wistar rats to T. cruzi, and highlights the use of Holtzman rats as useful models for further studies of cardiac/skeletal muscle tropism and innate immune responses that protect the host against parasite replication. This is important for the development of proper therapeutic interventions.