Effect of Apigenin on Leishmania amazonensis Is Associated with Reactive Oxygen Species Production Followed by Mitochondrial Dysfunction.

Leishmaniasis is an important neglected disease caused by protozoa of the genus Leishmania that affects more than 12 million people worldwide. Leishmaniasis treatment requires the administration of toxic and poorly tolerated drugs, and parasite resistance greatly reduces the efficacy of conventional medications. Apigenin (1), a naturally occurring plant flavone, has a wide range of reported biological effects. In this study, antileishmanial activity of 1 in vitro was investigated, and its mechanism of action against Leishmania amazonensis promastigotes was described. Treatment with 1 for 24 h resulted in concentration-dependent inhibition of cellular proliferation (IC50 = 23.7 µM) and increased reactive oxygen species (ROS) generation. Glutathione and N-acetyl-l-cysteine protected L. amazonensis from the effects of 1 and reduced ROS levels after the treatment. By contrast, oxidized glutathione did not reduce the levels of ROS caused by 1 by not preventing the proliferation inhibition. Apigenin 1 also induced an extensive swelling in parasite mitochondria, leading to an alteration of the mitochondrial membrane potential, rupture of the trans-Golgi network, and cytoplasmic vacuolization. These results demonstrate the leishmanicidal effect of 1 and suggest the involvement of ROS leading to mitochondrial collapse as part of the mechanism of action.

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.

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

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

Reactive oxygen species production by quercetin causes the death of Leishmania amazonensis intracellular amastigotes.

The present study reports the mechanism of the antileishmanial activity of quercetin against the intracellular amastigote form of Leishmania amazonensis. Treatment with 1 reduced the infection index in L. amazonensis-infected macrophages in a dose-dependent manner, with an IC50 value of 3.4 µM and a selectivity index of 16.8, and additionally increased ROS generation also in a dose-dependent manner. Quercetin has been described as a pro-oxidant that induces the production of reactive oxygen species, which can cause cell death. Taken together, these results suggest that ROS production plays a role in the mechanism of action of 1 in the control of intracellular amastigotes of L. amazonensis.

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.

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.

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.

Mitochondrial damage contribute to epigallocatechin-3-gallate induced death in Leishmania amazonensis.

Epigallocatechin-3-gallate (EGCG), the most abundant flavonoid in green tea, has been reported to have antiproliferative effects on Trypanosoma cruzi however, the mechanism of protozoan action of EGCG has not been studied. In the present study, we demonstrate the mechanism for the antileishmanial activity of EGCG against Leishmania amazonensis promastigotes. Incubation with EGCG significantly inhibited L. amazonensis promastigote proliferation in a time- and dose-dependent manner. The IC(50) for EGCG at 120 h was 0.063 mM. Ultrastructural alterations of the mitochondria were observed in promastigote treated with EGCG, being the organelle injury reinforced by the decrease in rhodamine 123 fluorescence. The effects of several drugs that interfere directly with mitochondrial physiology in parasites such as Leishmania have been described. The unique mitochondrial features of Leishmania make this organelle an ideal drug target while minimizing toxicity. These data suggest mitochondrial collapse as a part of the EGCG mechanism of action and demonstrate the leishmanicidal effect of EGCG.

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.

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.

A review of antimalarial plants used in traditional medicine in communities in Portuguese-speaking countries: Brazil, Mozambique, Cape Verde, Guinea-Bissau, São Tomé and Príncipe and Angola.

The isolation of bioactive compounds from medicinal plants, based on traditional use or ethnomedical data, is a highly promising potential approach for identifying new and effective antimalarial drug candidates. The purpose of this review was to create a compilation of the phytochemical studies on medicinal plants used to treat malaria in traditional medicine from the Community of Portuguese-Speaking Countries (CPSC): Angola, Brazil, Cape Verde, Guinea-Bissau, Mozambique and São Tomé and Príncipe. In addition, this review aimed to show that there are several medicinal plants popularly used in these countries for which few scientific studies are available. The primary approach compared the antimalarial activity of native species used in each country with its extracts, fractions and isolated substances. In this context, data shown here could be a tool to help researchers from these regions establish a scientific and technical network on the subject for the CPSC where malaria is a public health problem.

Antileishmanial activity of 1,3,4-thiadiazolium-2-aminide in mice infected with Leishmania amazonensis.

The efficacy of two mesoionic derivatives (MI-H-H and MI-4-OCH(3)) was evaluated in CBA/J mice infected with Leishmania amazonensis. Treatment with these compounds demonstrated that the MI-4-OCH(3) derivative and the reference drug meglumine antimoniate (Glucantime) presented significant activity relative to an untreated control. No apparent hepatic or renal toxicity due to these mesoionic compounds was found.

Synthesis and evaluation of new difluoromethyl azoles as antileishmanial agents.

Several compounds of great pharmacological interest contain the triazole and imidazole rings. In order to find new drugs with antileishmanial activity we have synthesized and evaluated new imidazole and triazole compounds carrying either the carbaldehyde or the difluoromethylene functionalities against promastigote forms of Leishmania amazonensis. Among the compounds tested difluoromethylene azoles 4b and 8f have inhibited the parasite growth significantly. Our results show that the introduction of the difluoromethylene moieties has turned the inactive carbaldehydes into active antileishmanial compounds.

A comparative study of mesoionic compounds in Leishmania sp. and toxicity evaluation.

In this first study, a series of mesoionic compounds like 1,3,4-thiadiazolium-2-phenylamine derivatives were synthesized and studied in Leishmania amazonensis. The cytotoxic effects of these compounds on the host cells were investigated and the antileishmanial in vitro activity was compared with other species of Leishmania (Leishmania chagasi and Leishmania braziliensis). The compounds presented lower toxicity in murine macrophages than the reference drug pentamidine. The halogen derivatives 5, 6, 8 and 13 (4-F, 4-Cl, 4-Br and 3-Cl) were the most active compounds among all the species tested.

Synthesis and leishmanicidal activities of 1-(4-X-phenyl)-N'-[(4-Y-phenyl)methylene]-1H-pyrazole-4-carbohydrazides.

1H-pyrazole-4-carbohydrazides were synthesized and their leishmanicidal in vitro activities and cytotoxic effects were investigated. The drugs prototypes of these new compounds (ketoconazole, benznidazole, allopurinol and pentamidine) were also tested. It was found that among all the 1H-pyrazole-4-carbohydrazides derivatives examined, the most active compounds were those with X = Br, Y = NO2 (27) and X = NO2, Y = Cl (15) derivatives which showed to be most effective on promastigotes forms of L. amazonensis than on L. chagasi and L. braziliensis species. When tested against murine peritoneal macrophages as mammalian host cell controls of toxicity, 1-(4-Br-phenyl)-N'-[(4-NO(2)-phenyl)methylene]-1H-pyrazole-4-carbohydrazides (27) (EC50 = 50 microM l(-1)) and 1-(4-NO2-phenyl)-N'-[(4-Cl-phenyl)methylene]-1H-pyrazole-4-carbohydrazides (15) EC50 = 80 microM l(-1))] was reasonably toxic. However, both compounds were less toxic than pentamidine and ketoconazole. These results provide new perspectives on the development of drugs with activities against Leishmania parasite.

Oral Efficacy of Apigenin against Cutaneous Leishmaniasis: Involvement of Reactive Oxygen Species and Autophagy as a Mechanism of Action.

BACKGROUND: The treatment for leishmaniasis is currently based on pentavalent antimonials and amphotericin B; however, these drugs result in numerous adverse side effects. The lack of affordable therapy has necessitated the urgent development of new drugs that are efficacious, safe, and more accessible to patients. Natural products are a major source for the discovery of new and selective molecules for neglected diseases. In this paper, we evaluated the effect of apigenin on Leishmania amazonensis in vitro and in vivo and described the mechanism of action against intracellular amastigotes of L. amazonensis. METHODOLOGY/PRINCIPAL FINDING: Apigenin reduced the infection index in a dose-dependent manner, with IC50 values of 4.3 µM and a selectivity index of 18.2. Apigenin induced ROS production in the L. amazonensis-infected macrophage, and the effects were reversed by NAC and GSH. Additionally, apigenin induced an increase in the number of macrophages autophagosomes after the infection, surrounding the parasitophorous vacuole, suggestive of the involvement of host autophagy probably due to ROS generation induced by apigenin. Furthermore, apigenin treatment was also effective in vivo, demonstrating oral bioavailability and reduced parasitic loads without altering serological toxicity markers. CONCLUSIONS/SIGNIFICANCE: In conclusion, our study suggests that apigenin exhibits leishmanicidal effects against L. amazonensis-infected macrophages. ROS production, as part of the mechanism of action, could occur through the increase in host autophagy and thereby promoting parasite death. Furthermore, our data suggest that apigenin is effective in the treatment of L. amazonensis-infected BALB/c mice by oral administration, without altering serological toxicity markers. The selective in vitro activity of apigenin, together with excellent theoretical predictions of oral availability, clear decreases in parasite load and lesion size, and no observed compromises to the overall health of the infected mice encourage us to supports further studies of apigenin as a candidate for the chemotherapeutic treatment of leishmaniasis.

Synthesis, and biological evaluation of new 1,3,4-thiadiazolium-2-phenylamine derivatives against Leishmania amazonensis promastigotes and amastigotes.

1,3,4-thiadiazolium-2-aminide, which is a class of mesoionic compounds, were tested against promastigote and amastigote forms of Leishmania amazonensis. Parasites were assayed with or without the drugs in axenic media, using pentamidine isethionate as a reference drug. The very promising results showed us the most active compounds were the 4'- and 3'-methoxy derivatives against promastigote forms, while the highest activity against the amastigote forms was obtained with the 4'-fluor and 3'-bromo derivatives.

The effect of (-)-epigallocatechin 3-O--gallate in vitro and in vivo in Leishmania braziliensis: involvement of reactive oxygen species as a mechanism of action.

BACKGROUND: Leishmaniasis is a parasitic disease associated with extensive mortality and morbidity. The treatment for leishmaniasis is currently based on pentavalent antimonials and amphotericin B; however, these drugs result in numerous adverse side effects. Natural compounds have been used as novel treatments for parasitic diseases. In this paper, we evaluated the effect of (-)-epigallocatechin 3-O-gallate (EGCG) on Leishmania braziliensis in vitro and in vivo and described the mechanism of EGCG action against L. braziliensis promastigotes and intracellular amastigotes. METHODOLOGY/PRINCIPAL FINDING: In vitro activity and reactive oxygen species (ROS) measurements were determined during the promastigote and intracellular amastigote life stages. The effect of EGCG on mitochondrial membrane potential (ΔΨm) was assayed using JC-1, and intracellular ATP concentrations were measured using a luciferin-luciferase system. The in vivo experiments were performed in infected BALB/c mice orally treated with EGCG. EGCG reduced promastigote viability and the infection index in a time- and dose-dependent manner, with IC50 values of 278.8 µM and 3.4 µM, respectively, at 72 h and a selectivity index of 149.5. In addition, EGCG induced ROS production in the promastigote and intracellular amastigote, and the effects were reversed by polyethylene glycol (PEG)-catalase. Additionally, EGCG reduced ΔΨm, thereby decreasing intracellular ATP concentrations in promastigotes. Furthermore, EGCG treatment was also effective in vivo, demonstrating oral bioavailability and reduced parasitic loads without altering serological toxicity markers. CONCLUSIONS/SIGNIFICANCE: In conclusion, our study demonstrates the leishmanicidal effects of EGCG against the two forms of L. braziliensis, the promastigote and amastigote. In addition, EGCG promotes ROS production as a part of its mechanism of action, resulting in decreased ΔΨm and reduced intracellular ATP concentrations. These actions ultimately culminate in parasite death. Furthermore, our data suggest that EGCG is orally effective in the treatment of L. braziliensis-infected BALB/c mice without altering serological toxicity markers.

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).