Effects of 4,4'-diisothyocyanatostilbene-2,2'-disulfonic acid on Trypanosoma cruzi proliferation and Ca(2+) homeostasis

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

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

Potential of sulfur-selenium isosteric replacement as a strategy for the development of new anti-chagasic drugs

Current treatment for Chagas disease is based on only two drugs: benznidazole and nifurtimox. Compounds containing sulfur (S) in their structure have shown promising results in vitro and in vivo against Trypanosoma cruzi, the parasite causing Chagas disease. Notably, some reports show that the isosteric replacement of S by selenium (Se) could be an interesting strategy for the development of new compounds for the treatment of Chagas disease. To date, the activity against T. cruzi of three Se- containing groups has been compared with their S counterparts: selenosemicarbazones, selenoquinones, and selenocyanates. More studies are needed to confirm the positive results of Se compounds. Therefore, we have investigated S compounds described in the literature tested against T. cruzi. We focused on those tested in vivo that allowed isosteric replacement to propose their Se counterparts as promising compounds for the future development of new drugs against Chagas disease.

E-NTPDases: Possible Roles on Host-Parasite Interactions and Therapeutic Opportunities

Belonging to the GDA1/CD39 protein superfamily, nucleoside triphosphate diphosphohydrolases (NTPDases) catalyze the hydrolysis of ATP and ADP to the monophosphate form (AMP) and inorganic phosphate (Pi). Several NTPDase isoforms have been described in different cells, from pathogenic organisms to animals and plants. Biochemical characterization of nucleotidases/NTPDases has revealed the existence of isoforms with different specificities regarding divalent cations (such as calcium and magnesium) and substrates. In mammals, NTPDases have been implicated in the regulation of thrombosis and inflammation. In parasites, such as Trichomonas vaginalis, Trypanosoma spp., Leishmania spp., Schistosoma spp. and Toxoplasma gondii, NTPDases were found on the surface of the cell, and important processes like growth, infectivity, and virulence seem to depend on their activity. For instance, experimental evidence has indicated that parasite NTPDases can regulate the levels of ATP and Adenosine (Ado) of the host cell, leading to the modulation of the host immune response. In this work, we provide a comprehensive review showing the involvement of the nucleotidases/NTPDases in parasites infectivity and virulence, and how inhibition of NTPDases contributes to parasite clearance and the development of new antiparasitic drugs.

DIDS inhibits Vibrio vulnificus cytotoxicity by interfering with TolC-mediated RtxA1 toxin secretion

Vibrio vulnificus (V. vulnificus) infection, frequently resulting in fatal septicemia, has become a growing health concern worldwide. The present study aimed to explore the potential agents that could protect against V. vulnificus cytotoxicity, and to analyze the possible underlying mechanisms. First, we observed that 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid disodium salt hydrate (DIDS) significantly suppressed V. vulnificus cytotoxicity to host cells by using a lactate dehydrogenase (LDH) assay. DIDS did not exhibit any effect on host cell viability, bacterial growth, microbial adhesion and swarming motility. DIDS effectively lowered V. vulnificus RtxA1 toxin-induced calcium influx into host mitochondria and RtxA1 binding to host cells. To further elucidate the underlying mechanism, the synthesis and secretion of RtxA1 toxin were investigated by Western blotting. Intriguingly, DIDS selectively inhibited the secretion of RtxA1 toxin, but did not influence its synthesis. Consequently, the outer membrane portal TolC, a key conduit for RtxA1 export coupled with tripartite efflux pumps, was examined by RT-PCR and Western blotting. We found that DIDS significantly reduced the expression of TolCV1 protein at the transcriptional level. Taken together, these results suggest that DIDS is a promising new paradigm as an antimicrobial drug that targets TolC-mediated toxin.

Knocking Down TcNTPDase-1 Gene Reduces in vitro Infectivity of Trypanosoma cruzi

Ecto-Nucleoside Triphosphate Diphosphohydrolases are enzymes that hydrolyze tri- and/or diphosphate nucleosides. Evidences pointed out to their participation in Trypanosoma cruzi virulence, infectivity, and purine acquisition. In this study, recombinant T. cruzi knocking out or overexpressing the TcNTPDase-1 gene were built, and the role of TcNTPDase-1 in the in vitro interaction with VERO cells was investigated. Results show that epimastigote forms of hemi-knockout parasites showed about 50% lower level of TcNTPDase-1 gene expression when compared to the wild type, while the T. cruzi overexpressing this gene reach 20 times higher gene expression. In trypomastigote forms, the same decreasing in TcNTPDase-1 gene expression was observed to the hemi-knockout parasites. The in vitro infection assays showed a reduction to 51.6 and 59.9% at the adhesion and to 25.2 and 26.4% at the endocytic indexes to the parasites knockout to one or other allele (Hygro and Neo hemi-knockouts), respectively. In contrast, the infection assays with T. cruzi overexpressing TcNTPDase-1 from the WT or Neo hemi-knockout parasites showed an opposite result, with the increasing to 287.7 and 271.1% at the adhesion and to 220.4 and 186.7% at the endocytic indexes, respectively. The parasitic load estimated in infected VERO cells by quantitative real time PCR corroborated these findings. Taken together, the partial silencing and overexpression of the TcNTPDase-1 gene generated viable parasites with low and high infectivity rates, respectively, corroborating that the enzyme encoded for this gene plays an important role to the T. cruzi infectivity.

ATP-Diphosphohydrolases in Parasites: Localization, Functions and Recent Developments in Drug Discovery

ATP-diphosphohydrolases (EC 3.6.1.5), also known as ATPDases, NTPases, NTPDases, EATPases or apyrases, are enzymes that hydrolyze a variety of nucleoside tri- and diphosphates to their respective nucleosides, being their activities dependent on the presence of divalent cations, such as calcium and magnesium. Recently, ATP-diphosphohydrolases were identified on the surface of several parasites, such as Trypanosoma sp, Leishmania sp and Schistosoma sp. In parasites, the activity of ATPdiphosphohydrolases has been associated with the purine recuperation and/or as a protective mechanism against the host organism under conditions that involve ATP or ADP, such as immune responses and platelet activation. These proteins have been suggested as possible targets for the development of new antiparasitic drugs. In this review, we will comprehensively address the main aspects of the location and function of ATP-diphosphohydrolase in parasites. Also, we performed a detailed research in scientific database of recent developments in new natural and synthetic inhibitors of the ATPdiphosphohydrolases in parasites.

Leishmania amazonensis: Increase in ecto-ATPase activity and parasite burden of vinblastine-resistant protozoa

Leishmania amazonensis is a protozoan parasite that induces mucocutaneous and diffuse cutaneous lesions upon infection. An important component in treatment failure is the emergence of drug-resistant parasites. It is necessary to clarify the mechanism of resistance that occurs in these parasites to develop effective drugs for leishmaniasis treatment. Promastigote forms of L. amazonensis were selected by gradually increasing concentrations of vinblastine and were maintained under continuous drug pressure (resistant cells). Vinblastine-resistant L. amazonensis proliferated similarly to control parasites. However, resistant cells showed changes in the cell shape, irregular flagella and a decrease in rhodamine 123 accumulation, which are factors associated with the development of resistance, suggesting the MDR phenotype. The Mg-dependent-ecto-ATPase, an enzyme located on cell surface of Leishmania parasites, is involved in the acquisition of purine and participates in the adhesion and infectivity process. We compared control and resistant L. amazonensis ecto-enzymatic activities. The control and resistant Leishmania ecto-ATPase activities were 16.0 ± 1.5 nmol Pi × h(-1) × 10(-7) cells and 40.0 ± 4.4 nmol Pi × h(-1) × 10(-7)cells, respectively. Interestingly, the activity of other ecto-enzymes present on the L. amazonensis cell surface, the ecto-5' and 3'-nucleotidases and ecto-phosphatase, did not increase. The level of ecto-ATPase modulation is related to the degree of resistance of the cell. Cells resistant to 10 μM and 60 μM of vinblastine have ecto-ATPase activities of 22.7 ± 0.4 nmol Pi × h(-1) × 10(-7) cells and 33.8 ± 0.8 nmol Pi × h(-1) × 10(-7)cells, respectively. In vivo experiments showed that both lesion size and parasite burden in mice infected with resistant parasites are greater than those of L. amazonensis control cells. Furthermore, our data established a relationship between the increase in ecto-ATPase activity and greater infectivity and severity of the disease caused by vinblastine-resistant L. amazonensis promastigotes. Taken together, these data suggest that ecto-enzymes could be potential therapeutic targets in the struggle against the spread of leishmaniasis, a neglected world-wide public health problem.

Trypanosoma cruzi nucleoside triphosphate diphosphohydrolase 1 (TcNTPDase-1) biochemical characterization, immunolocalization and possible role in host cell adhesion

Previous work has suggested that Trypanosoma cruzi diphosphohydrolase 1 (TcNTPDase-1) may be involved in the infection of mammalian cells and serve as a potential target for rational drug design. In this work, we produced recombinant TcNTPDase-1 and evaluated its nucleotidase activity, cellular localization and role in parasite adhesion to mammalian host cells. TcNTPDase-1 was able to utilize a broad range of triphosphate and diphosphate nucleosides. The enzyme's Km for ATP (0.096 mM) suggested a capability to influence the host's ATP-dependent purinergic signaling. The use of specific polyclonal antibodies allowed us to confirm the presence of TcNTPDase-1 at the surface of parasites by confocal and electron microscopy. In addition, electron microscopy revealed that TcNTPDase-1 was also found in the flagellum, flagellum insertion region, kinetoplast, nucleus and intracellular vesicles. The presence of this enzyme in the flagellum insertion region and vesicles suggests that it may have a role in nutrient acquisition, and the widespread distribution of TcNTPDase-1 within the parasite suggests that it may be involved in other biological process. Adhesion assays using anti-TcNTPDase-1 polyclonal antibodies as a blocker or purified recombinant TcNTPDase-1 as a competitor revealed that the enzyme has a role in parasite-host cell adhesion. These data open new frontiers to future studies on this specific parasite-host interaction and other unknown functions of TcNTPDase-1 related to its ubiquitous localization.

Effects of metronidazole analogues on Giardia lamblia: experimental infection and cell organization

The chemotherapeutic agents used for the treatment of giardiasis are often associated with adverse side effects and are refractory cases, due to the development of resistant parasites. Therefore the search for new drugs is required. We have previously reported the giardicidal effects of metronidazole (MTZ) and its analogues (MTZ-Ms, MTZ-Br, MTZ-N(3), and MTZ-I) on the trophozoites of Giardia lamblia. Now we evaluated the activity of some giardicidal MTZ analogues in experimental infections in gerbils and its effects on the morphology and ultrastructural organization of Giardia. The giardicidal activity in experimental infections showed ED(50) values significantly lower for MTZ-I and MTZ-Br when compared to MTZ. Transmission electron microscopy was employed to approach the mechanism(s) of action of MTZ analogues upon the protozoan. MTZ analogues were more active than MTZ in changing significantly the morphology and ultrastructure of the parasite. The analogues affected parasite cell vesicle trafficking, autophagy, and triggered differentiation into cysts. These results coupled with the excellent giardicidal activity and lower toxicity demonstrate that these nitroimidazole derivates may be important therapeutic alternatives for combating giardiasis. In addition, our results suggest a therapeutic advantage in obtaining synthetic metronidazole analogues for screening of activities against other infectious agents.

DIDS (4,4-diisothiocyanatostilbenedisulphonic acid) induces apoptotic cell death in a hippocampal neuronal cell line and is not neuroprotective against ischemic stress

DIDS is a commonly used anion channel antagonist that is putatively cytoprotective against ischemic insult. However, recent reports indicate potentially deleterious secondary effects of DIDS. To assess the impact of DIDS on cellular viability comprehensively we examined neuronal morphology and function through 24 hours treatment with ACSF ± DIDS (40 or 400 µM). Control cells were unchanged, whereas DIDS induced an apoptotic phenotype (chromatin condensation, nuclear fragmentation and cleavage of the nuclear membrane protein lamin A, expression of pro-apoptotic proteins c-Jun N-terminal kinase 3, caspase 3, and cytochrome C, Annexin V staining, RNA degradation, and oligonucleosomal DNA cleavage). These deleterious effects were mediated by DIDS in a dose- and time-dependant manner, such that higher [DIDS] induced apoptosis more rapidly while apoptosis was observed at lower [DIDS] with prolonged exposure. In an apparent paradox, despite a clear overall apoptotic phenotype, certain hallmarks of apoptosis were not present in DIDS treated cells, including mitochondrial fission and loss of plasma membrane integrity. We conclude that DIDS induces apoptosis in cultured hippocampal neurons, in spite of the fact that some common hallmarks of cell death pathways are prevented. These contradictory effects may cause false-positive results in certain assays and future evaluations of DIDS as a neuroprotective agent should incorporate multiple viability assays.

Trypanosoma cruzi: effects of heat shock on ecto-ATPase activity

In this work, we demonstrate that Trypanosoma cruzi Y strain epimastigotes exhibit Mg2+-dependent ecto-ATPase activity that is stimulated by heat shock. When the epimastigotes were incubated at 37°C for 2h, the ecto-ATPase activity of the cells was 43.95±0.97 nmol Pi/h×10(7) cells, whereas the ecto-ATPase activity of cells that were not exposed to heat shock stress was 16.97±0.30 nmol Pi/h×10(7) cells. The ecto-ATPase activities of cells, that were exposed or not exposed to heat shock stress had approximately the same Km values (2.25±0.26 mM ATP and 1.55±0.23 mM ATP, respectively) and different Vmax values. The heat-shocked cells had higher Vmax values (54.38±3.07 nmol Pi/h×10(7) cells) than the cells that were not exposed to heat shock (19.38±1.76 nmol Pi/h×10(7) cells). We also observed that the ecto-phosphatase and ecto-5'nucleotidase activities of cells that had been incubated at 28°C or 37°C were the same. Interestingly, cycloheximide, an inhibitor of protein synthesis, suppressed the heat shock effect of ecto-ATPase activity on T. cruzi. The Mg2+-dependent ecto-ATPase activity from the Y strain (high virulence) was approximately 2-fold higher than that of Dm28c (a clone with low virulence). In addition, these two strains presented different responses to heat shock with regard to their ecto-ATPase activities; Y strain epimastigotes had a stimulation of 2.52-fold while the Dm28c strain had a 1.71-fold stimulation. In this context, the virulent trypomastigote form of T. cruzi, Dm28c, had an ecto-ATPase activity that was more than 7-fold higher (66.67±5.98 nmol Pi/h×10(7) cells) than that of the insect epimastigote forms (8.91±0.76 nmol Pi/h×10(7) cells). This difference increased to approximately 10-fold when both forms were subjected to heat shock stress (181.14±16.48 nmol Pi/h×10(7) cells for trypomastigotes and 16.71±1.17 nmol Pi/h×10(7) cells for epimastigotes at 37°C). The ecto-ATPase activity of a plasma membrane-enriched fraction obtained from T. cruzi epimastigotes was not increased by heat treatment, which suggested that cytoplasmic components had an influence on enzyme activation by heat shock stress.

Ecto-nucleotidase activities of promastigotes from Leishmania (Viannia) braziliensis relates to parasite infectivity and disease clinical outcome

Background

Leishmania (Viannia) braziliensis has been associated with a broad range of clinical manifestations ranging from a simple cutaneous ulcer to destructive mucosal lesions. Factors leading to this diversity of clinical presentations are not clear, but parasite factors have lately been recognized as important in determining disease progression. Given the fact that the activity of ecto-nucleotidases correlates with parasitism and the development of infection, we evaluated the activity of these enzymes in promastigotes from 23 L. braziliensis isolates as a possible parasite-related factor that could influence the clinical outcome of the disease.

Methodology/Principal Findings

Our results show that the isolates differ in their ability to hydrolyze adenine nucleotides. Furthermore, we observed a positive correlation between the time for peak of lesion development in C57BL/6J mice and enzymatic activity and clinical manifestation of the isolate. In addition, we found that L. (V.) braziliensis isolates obtained from mucosal lesions hydrolyze higher amounts of adenine nucleotides than isolates obtained from skin lesions. One isolate with high (PPS6m) and another with low (SSF) ecto-nucleotidase activity were chosen for further studies. Mice inoculated with PPS6m show delayed lesion development and present larger parasite loads than animals inoculated with the SSF isolate. In addition, PPS6m modulates the host immune response by inhibiting dendritic cell activation and NO production by activated J774 macrophages. Finally, we observed that the amastigote forms from PPS6m and SSF isolates present low enzymatic activity that does not interfere with NO production and parasite survival in macrophages.

Conclusions/Significance

Our data suggest that ecto-nucleotidases present on the promastigote forms of the parasite may interfere with the establishment of the immune response with consequent impaired ability to control parasite dissemination and this may be an important factor in determining the clinical outcome of leishmaniasis.

Cutaneous leishmaniasis is a widespread tropical disease caused by different species of Leishmania protozoa that are transmitted by infected sandflies. Clinical presentations are extremely diverse and dependent on a variety of parasite and host factors that are poorly understood. Leishmania (V.) braziliensis infection may result in a devastating disease manifestation characterized by the development of destructive lesions in the oral, nasal, and pharyngeal mucosal. Ecto-nucleotidases are enzymes that are involved in the hydrolysis of extracellular nucleotides. These enzymes have been shown to correlate with virulence of Leishmania parasites. In this work, we evaluated the ecto-nucleotidase activity of promastigotes from the twenty three different L. braziliensis isolates. We demonstrated that isolates obtained from mucosal lesions present higher levels of ecto-nucleotidase activity than those from cutaneous lesions. In addition, we show that in the murine model of cutaneous leishmaniasis, promastigote forms of parasite with higher activity induce a delayed/decreased immune response that may correlate with spreading of the parasites throughout the body. Thus, we propose that the level of ecto-nucleotidase activity of promastigotes may be a marker for the development of severe clinical forms of cutaneous leishmaniasis and also a possible target for future therapeutic intervention.

The role of the NTPDase enzyme family in parasites: what do we know, and where to from here?

Nucleoside triphosphate diphosphohydrolases (NTPDases, GDA1_CD39 protein superfamily) play a diverse range of roles in a number of eukaryotic organisms. In humans NTPDases function in regulating the inflammatory and immune responses, control of vascular haemostasis and purine salvage. In yeast NTPDases are thought to function primarily in the Golgi, crucially involved in nucleotide sugar transport into the Golgi apparatus and subsequent protein glycosylation. Although rare in bacteria, in Legionella pneumophila secreted NTPDases function as virulence factors. In the last 2 decades it has become clear that a large number of parasites encode putative NTPDases, and the functions of a number of these have been investigated. In this review, the available evidence for NTPDases in parasites and the role of these NTPDases is summarized and discussed. Furthermore, the processes by which NTPDases could function in pathogenesis, purine salvage, thromboregulation, inflammation and glycoconjugate formation are considered, and the data supporting such putative roles reviewed. Potential future research directions to further clarify the role and importance of NTPDases in parasites are proposed. An attempt is also made to clarify the nomenclature used in the parasite field for the GDA1_CD39 protein superfamily, and a uniform system suggested.

CrATP interferes in the promastigote-macrophage interaction in Leishmania amazonensis infection

Recent have shown the relationship between Ecto-Nucleoside-Triphosphate-Diphosphohydrolases (Ecto-NTPDases or ecto-nucleotidases) and virulence and infectivity in trypanosomatids. In this work, the inhibition of the ecto-ATPase activities and promastigote growth of Leishmania amazonensis by CrATP was characterized. Furthermore, this compound was used to investigate the role of ecto-nucleotidase in the interaction of L. amazonensis with resident peritoneal macrophages obtained from BALB/c mice. CrATP partially inhibits the ecto-ATPase activity, presenting Ki values of 575·7±199·1 and 383·5±79·0 μm, in the presence or absence of 5 mm MgCl2, respectively. The apparent Kms for ATP (2·9±0·5 mm to Mg2+-dependent ecto-ATPase and 0·4±0·2 mm to Mg2+-independent ecto-ATPase activities) are not significantly altered by CrATP, suggesting a reversible non-competitive inhibition of both enzymes. When CrATP was added to the cultivation medium at 500 μm, it drastically inhibited the cellular growth. The interaction of promastigote forms of L. amazonensis with BALB/c peritoneal macrophages is strongly affected by CrATP. When the parasites were treated with 500 μm CrATP before interacting with macrophages, the adhesion and endocytic indices were strongly reduced to 53·0±14·8% and 39·8±1·1%, respectively. These results indicate that ecto-nucleotidase plays an important role in the infection process caused by Leishmania amazonensis.

Biochemical characterization of an ecto-ATP diphosphohydrolase activity in Candida parapsilosis and its possible role in adenosine acquisition and pathogenesis

In this work, we describe the ability of intact cells of Candida parapsilosis to hydrolyze extracellular ATP. ATP hydrolysis was stimulated by MgCl(2) in a dose-dependent manner. The ecto-ATPase activity was increased in the presence of 5 mM MgCl(2), with values of V(max) and apparent K(m) for Mg-ATP(2-) increasing to 33.80 +/- 1.2 nmol Pi h(-1) 10(-8) cells and 0.6 +/- 0.06 mM, respectively. Inhibitors of phosphatases, mitochondrial Mg(2+)-ATPases and Na(+)-ATPases had no effect on the C. parapsilosis Mg(2+)-stimulated ATPase activity, but extracellular impermeant compounds, 4,4'-diisothiocyanatostilbene-2,2'disulfonic acid and suramin, reduced enzyme activity in yeast living cells by 83.1% and 81.9%, respectively. ARL 67156 (6-N,N'-diethyl-d-beta-gamma-dibromomethylene ATP), a nucleotide analogue, also inhibited the ecto-ATPase activity in a dose-dependent manner. ATP was the best substrate for the yeast Mg(2+)-stimulated ecto-enzyme, but ADP, ITP, CTP, GTP and UTP were also hydrolyzed. A direct relationship between ecto-ATPase activity and adhesion to host cells was observed. In these assays, inhibition of enzyme activity resulted in decreased levels of yeast adhesion to epithelial cells. Based also on the differential expression of ecto-ATPase activities in the different isolates of C. parapsilosis, the possible role of this enzyme in fungal biology is discussed.

Trichomonas vaginalis nucleoside triphosphate diphosphohydrolase and ecto-5'-nucleotidase activities are inhibited by lycorine and candimine

Drug discovery from plants plays an important role in the pharmaceutical therapy field and the alkaloids lycorine and candimine are candidates for this purpose. Trichomonas vaginalis is a parasite that infects the human urogenital tract and causes trichomonosis, the most prevalent non-viral sexually transmitted disease. Ecto-nucleotidases including nucleoside triphosphate diphosphohydrolase (NTPDase) members, which hydrolyses extracellular ATP (adenosine triphosphate) and ADP (adenosine diphosphate), and ecto-5'-nucleotidase, which hydrolyses AMP (adenosine monophosphate), have been characterized in T. vaginalis. Because purine nucleotides are released from cells under physiological and stress conditions, the goal of this study was to evaluate the effect of lycorine and candimine on T. vaginalis NTPDase and ecto-5'-nculeotidase activities. The alkaloids (50 to 250microM) were tested against both long-term-grown and clinical isolates. Specific enzymatic activities were expressed as nmolPi released/min/mg protein. The effect of both alkaloids at NTPDase A and B expression levels was investigated. When the alkaloids were added directly to the reaction mixture, no effect on ATP, ADP or AMP hydrolysis was observed. NTPDase and ecto-5'-nucleotidase activities were strongly inhibited by candimine and lycorine on 24h-treated parasites. This effect was abolished when 24-treated parasites were innoculated in a culture medium without alkaloid. Transcript levels of NTPDase A or B were not altered by the alkaloids. Considering the cytotoxic and proinflammatory roles of ATP besides the anti-inflammatory effects of adenosine, the regulation of extracellular nucleotide levels could be relevant in increasing susceptibility of T. vaginalis to host immune response in the presence of lycorine and candimine.

Demonstration and partial characterization of ecto-ATPase in Balamuthia mandrillaris and its possible role in the host-cell interactions

AIMS

To investigate the presence and partial characterization of ecto-ATPase in Balamuthia mandrillaris.

METHODS AND RESULTS

In vitro assays were used to demonstrate that live B. mandrillaris hydrolyses extracellular AtP. Using nondenaturing polyacrylamide gel electrophoresis, B. mandrillaris exhibited a single ecto-ATPase band of molecular mass of more than 545 kDa. This ecto-ATPase was insensitive to ouabain, levamisole, sodium azide and sodium orthovanadate but stimulated by MgCl2. The ecto-ATPase was heat stable, but labile to detergent, sodium dodecyl sulphate. Suramin, an antagonist of P2 purinoreceptors and an inhibitor of some ecto-ATPases, inhibited B. mandrillaris binding to and cytotoxicity of HBMEC (human brain microvascular endothelial cello), in vitro.

CONCLUSIONS

For the first time, we describe that live B. mandrillaris hydrolyses extracellular ATP and exhibits a > 545kDa ecto-ATPase.

SIGNIFICANCE AND IMPACT OF THE STUDY

This surface enzyme may play a role in the salvage of purines from the extracellular medium and may be important for the pathogenesis of B. mandrillaris.

Influence of Ecto-nucleoside triphosphate diphosphohydrolase activity on Trypanosoma cruzi infectivity and virulence

Background

The protozoan Trypanosoma cruzi is the causative agent of Chagas disease. There are no vaccines or effective treatment, especially in the chronic phase when most patients are diagnosed. There is a clear necessity to develop new drugs and strategies for the control and treatment of Chagas disease. Recent papers have suggested the ecto-nucleotidases (from CD39 family) from pathogenic agents as important virulence factors. In this study we evaluated the influence of Ecto-Nucleoside-Triphosphate-Diphosphohydrolase (Ecto-NTPDase) activity on infectivity and virulence of T. cruzi using both in vivo and in vitro models.

Methodology/Principal Findings

We followed Ecto-NTPDase activities of Y strain infective forms (trypomastigotes) obtained during sequential sub-cultivation in mammalian cells. ATPase/ADPase activity ratios of cell-derived trypomastigotes decreased 3- to 6-fold and infectivity was substantially reduced during sequential sub-cultivation. Surprisingly, at third to fourth passages most of the cell-derived trypomastigotes could not penetrate mammalian cells and had differentiated into amastigote-like parasites that exhibited 3- to 4-fold lower levels of Ecto-NTPDase activities. To evidence the participation of T. cruzi Ecto-NTPDase1 in the infective process, we evaluated the effect of known Ecto-ATPDase inhibitors (ARL 67156, Gadolinium and Suramin), or anti-NTPDase-1 polyclonal antiserum on ATPase and ADPase hydrolytic activities in recombinant T. cruzi NTPDase-1 and in live trypomastigotes. All tests showed a partial inhibition of Ecto-ATPDase activities and a marked inhibition of trypomastigotes infectivity. Mice infections with Ecto-NTPDase-inhibited trypomastigotes produced lower levels of parasitemia and higher host survival than with non-inhibited control parasites.

Conclusions/Significance

Our results suggest that Ecto-ATPDases act as facilitators of infection and virulence in vitro and in vivo and emerge as target candidates in chemotherapy of Chagas disease.

The protozoan Trypanosoma cruzi is the causative agent of Chagas disease, an endemic zoonosis present in some countries of South and Central Americas. The World Health Organization estimates that 100 million people are at risk of acquiring this disease. The infection affects mainly muscle tissues in the heart and digestive tract. There are no vaccines or effective treatment, especially in the chronic phase when most patients are diagnosed, which makes a strong case for the development of new drugs to treat the disease. In this work we evaluate a family of proteins called Ecto-Nucleoside-Triphosphate-Diphosphohydrolase (Ecto-NTPDase) as new chemotherapy target to block T. cruzi infection in mammalian cells and in mice. We have used inhibitors and antibodies against this protein and demonstrated that T. cruzi Ecto-NTPDases act as facilitators of infection in mammalian cells and virulence factors in mice model. Two of the drugs used in this study (Suramin and Gadolinium) are currently used for other diseases in humans, supporting the possibility of their use in the treatment of Chagas disease.

CrATP as a new inhibitor of ecto-ATPases of trypanosomatids

Trypanosomatid protozoa include heteroxenic species some of them pathogenic for men, animals and plants. Parasite membrane contains ecto-enzymes whose active sites face the external medium rather than the cytoplasm. Herpetomonas sp. displayed a Mg2+-dependent ecto-ATPase activity, a Mg-independent ecto-ADPase and an ecto-phosphatase activity. Both, the ecto-ADPase and phosphatase activities were insensitive to CrATP (chromium(III) adenosine 5'-triphosphate complex). Ecto-ATPase activity was reversibly inhibited. At 2 mm ATP the apparent Ki was 4 x 7+/-1 x 0 microm but a fraction of about 40-50% was insensitive to CrATP. Remarkably, at low substrate concentration (0 x 2 mm) more than 90% of the ecto-ATPase was inhibited with Ki=0 x 33+/-0 x 10 microm. These parameter dependences are interpreted as the presence of 2 ecto-ATPases activities, one of them with high ATP apparent affinity and sensitivity to CrATP. DIDS (4,4 diisothiocyanatostilbene 2,2' disulfonic acid), suramin and ADP were also effective as inhibitors. Only ADP presented no additive inhibition with CrATP. The pattern of partial inhibition by CrATP was also observed for the ecto-ATPase activities of Leishmania amazonensis, Trypanosoma cruzi and Trypanosoma rangeli. CrATP emerges as a new inhibitor of ecto-ATPases and as a tool for a better understanding of properties and role of ecto-ATPases in the biology of parasites.

Sterol methenyl transferase inhibitors alter the ultrastructure and function of the Leishmania amazonensis mitochondrion leading to potent growth inhibition

We describe here the effects of Delta(24(25)) sterol methenyl transferase inhibitors (SMTI) on promastigote and axenic amastigote forms of Leishmania amazonensis. When these cells were exposed to 20-piperidin-2-yl-5alpha-pregnan-3beta-20-diol (22,26-azasterol; AZA), hydrazone-imidazol-2-yl-5alpha-pregnan-3beta-ol (IMI), 20-hydrazone-pyridin-2-yl-5alpha-pregnan-3beta-ol (PYR) or 24(R,S),25-epiiminolanosterol (EIL), a concentration- and time-dependent inhibition of growth was observed, with IC(50) values in the sub-micromolar range. Ultrastructural alterations in treated cells were mainly observed in the mitochondrion, which displayed an intense swelling and a reduction of the electron density of the matrix with remarkable changes in the inner mitochondrial membranes. Mitochondrial transmembrane electric potential (DeltaPsi) was measured using spectrophotometric methods in control and treated promastigotes permeabilized with digitonin. After energization with the substrates for complexes I, II or IV of the respiratory chain, it was possible to detect marked changes of DeltaPsi in promastigotes treated with 1 microM of the SMTI for 48 or 72 h when compared with normal cells, indicating that these compounds led to the loss of the energy-transducing properties of the mitochondrial inner membrane, probably related to the alteration of its lipid composition. The present study confirms these findings, showing that in Leishmania amazonensis the mitochondrial complex appears to be the first organelle affected after treatment with different SMTI.

Leishmania amazonensis: Characterization of an ecto-phosphatase activity

We have characterized a phosphatase activity present on the external surface of Leishmania amazonensis, using intact living parasites. This enzyme hydrolyzes the substrate p-nitrophenylphosphate (p-NPP) at the rate of 25.70+/-1.17 nmol Pi x h(-1) x 10(-7)cells. The dependence on p-NPP concentration shows a normal Michaelis-Menten kinetics for this ecto-phosphatase activity present a V(max) of 31.93+/-3.04 nmol Pi x h(-1) x 10(-7)cells and apparent K(m) of 1.78+/-0.32 mM. Inorganic phosphate inhibited the ecto-phoshatase activity in a dose-dependent manner with the K(i) value of 2.60 mM. Experiments using classical inhibitor of acid phosphatase, such as ammonium molybdate, as well as inhibitors of phosphotyrosine phosphatase, such as sodium orthovanadate and [potassiumbisperoxo(1,10-phenanthroline)oxovanadate(V)] (bpV-PHEN), inhibited the ecto-phosphatase activity, with the K(i) values of 0.33 microM, 0.36 microM and 0.25 microM, respectively. Zinc chloride, another classical phosphotyrosine phosphatase inhibitor, also inhibited the ecto-phosphatase activity in a dose-dependent manner with K(i) 2.62 mM. Zinc inhibition was reversed by incubation with reduced glutathione (GSH) and cysteine, but not serine, showing that cysteine residues are important for enzymatic activity. Promastigote growth in a medium supplemented with 1mM sodium orthovanadate was completely inhibited as compared to the control medium. Taken together, these results suggest that L. amazonensis express a phosphohydrolase ectoenzyme with phosphotyrosine phosphatase activity.

An intracellular calcium store is present in Leishmania donovani glycosomes

A fourth intracellular Ca2+ pool in Leishmania donovani was identified by permeabilizing plasma membrane with digitonin. In Fura 2 loaded cells Ca2+ was released synergistically when mitochondrial function was blocked by antimycin and oligomycin. Vanadate did not have any effect if applied before incorporation of these mitochondrial poisons. However, the same inhibitor which inhibits Ca2+-ATPase activity of endoplasmic reticulum was able to release Ca2+ at a slow rate when added after antimycin and oligomycin. Alkalization of cytoplasmic pH allowed further release of Ca2+ essentially from the acidocalcisome. Purified glycosomes could mediate Ca2+ uptake mechanism in presence of vanadate whereas bafilomycin, a specific and potent inhibitor of vacuolar proton pump did not have any effect. Glycosomal Ca2+-ATPase activity was optimum at pH 7.5. The apparent Km for calciumin presence of vanadate was 12 nM. Taken together, it may be suggested that a vanadate-insensitive Ca2+-ATPase is present in the membrane of this microbody. Presence of glycosomal Ca2+ was further confirmed by imaging of Ca2+ activity in the Fura 2 loaded purified organelle using confocal laser. Results reveal that newly localized glycosomal calcium may essentially be an effective candidate to play a significant role in cellular function.

Characterization of an ecto-ATPase activity in Fonsecaea pedrosoi

In this work, we characterized an ecto-ATPase activity in intact mycelial forms of Fonsecaea pedrosoi, the primary causative agent of chromoblastomycosis. In the presence of 1 mM EDTA, fungal cells hydrolyzed adenosine-5'-triphosphate (ATP) at a rate of 84.6 +/- 11.3 nmol Pi h(-1) mg(-1) mycelial dry weight. The ecto-ATPase activity was increased at about five times (498.3 +/- 27.6 nmol Pi h(-1) mg(-1)) in the presence of 5 mM MgCl2, with values of Vmax and apparent Km for Mg-ATP(2-) corresponding to 541.9 +/- 48.6 nmol Pi h(-1) mg(-1) cellular dry weight and 1.9 +/- 0.2 mM, respectively. The Mg2+-stimulated ecto-ATPase activity was insensitive to inhibitors of intracellular ATPases such as vanadate (P-ATPases), bafilomycin A1(V-ATPases), and oligomycin (F-ATPases). Inhibitors of acid phosphatases (molybdate, vanadate, and fluoride) or alkaline phosphatases (levamizole) had no effect on the ecto-ATPase activity. The surface of the Mg2+ -stimulated ATPase in F. pedrosoi was confirmed by assays in which 4,4'-diisothiocyanostylbene-2,2'-disulfonic acid (DIDS), a membrane impermeant inhibitor, and suramin, an inhibitor of ecto-ATPase and antagonist of P2 purinoreceptors. Based on the differential expression of ecto-ATPases in the different morphological stages of F. pedrosoi, the putative role of this enzyme in fungal biology is discussed.

Different subunit location of the inhibition and transport sites in the mitochondrial calcium uniporter

The mitochondrial calcium uniporter behaves as a cooperative mechanism, where the velocity is dependent on [Ca2+]ex. Transport kinetics follows a sigmoidal behavior with a Hill coefficient near 2.0, indicating the binding of at least two calcium molecules. Calcium transport in mitochondria is dependent on a negative inner membrane potential and is inhibited by policationic ruthenium compounds. In this study, calcium uptake activity was reconstituted into cytochrome oxidase vesicles by incorporating solubilized mitochondrial proteins. Calcium accumulation plotted against increasing Ca2+ concentrations followed a sigmoidal behavior with a Hill coefficient of 1.53. The uptake was sensitive to ruthenium policationic inhibitors, e.g. ruthenium red and Ru360. After mitochondrial proteins were separated by preparative isoelectrofocusing and incorporated into cytochrome oxidase vesicles, two peaks of calcium uptake activity were recovered. One of the activities was inhibited by Ru360, while the second activity was insensitive to Ru360 and was associated with proteins focused at very acidic isoelectric points. By using a thiol-group crosslinker and radiolabeled Ru360, we proposed a scheme of partial dissociation of the uniporter inhibitor-binding subunit under acidic conditions.

A Mg-dependent ecto-ATPase is increased in the infective stages of Trypanosoma cruzi

In this work, we describe the ability of living epimastigotes of Trypanosoma cruzi to hydrolyze extracellular ATP. In these intact parasites, there was a low level of ATP hydrolysis in the absence of any divalent metal (2.42 +/- 0.31 nmol Pi/h x 10(8) cells). ATP hydrolysis was stimulated by MgCl2, and the Mg-dependent ecto-ATPase activity was 27.15 +/- 2.91 nmol Pi/h x 10(8) cells. The addition of MgCl2 to the extracellular medium increased the ecto-ATPase activity in a dose-dependent manner. This stimulatory activity was also observed when MgCl2 was replaced by MnCl2, but not by CaCl2 or SrCl2. The apparent Km for Mg-ATP2- was 0.61 mM, and free Mg2+ did not increase the ecto-ATPase activity. This ecto-ATPase activity was insensitive to the inhibitors of other ATPase and phosphatase activities. To confirm that this Mg-dependent ATPase was an ecto-ATPase, we used an impermeant inhibitor, DIDS (4, 4'.diisothiocyanostylbene 2'-2'-disulfonic acid) as well as suramin, an antagonist of P2 purinoreceptors and inhibitor of some ecto-ATPases. These two reagents inhibited the Mg2+-dependent ATPase activity in a dose-dependent manner. A comparison among the Mg2+-ecto-ATPase activities of the three forms of T. cruzi showed that the noninfective epimastigotes were less efficient at hydrolyzing ATP than the infective trypomastigote and amastigote stages.

Characterization and immunolocalization of an NTP diphosphohydrolase of Trypanosoma cruzi

An ecto-NTP diphosphohydrolase (NTPDase) activity, insensitive to inhibitors of ATPases and phosphatases, was characterized on the surface of live Trypanosoma cruzi intact parasites. The enzyme exhibits broad substrate specificity, typical of NTPDases, and a high hydrolysis rate for GTP. A 2282 bp message encoding a full-length NTPDase was cloned by RT-PCR using epimastigote mRNA. A single protein was immunoprecipitated from [(35)S]methionine-labeled parasites using antibodies against Toxoplasma gondii NTPase I. This antibody localized an NTPDase on the external surface of all forms of T. cruzi, as seen by confocal immuno-fluorescence microscopy. The NTPDase could be part of the parasite's purine salvage pathway. Additionally, trypomastigotes (infective form) presented a 2:1 ATP/ADP hydrolysis ratio, while epimastigotes (non-infective form) presented a 1:1 ratio, suggesting a possible role for the NTPDase in the parasite's virulence mechanisms.

Ecto-ATPases in protozoa parasites: looking for a function

The plasma membrane of cells contains enzymes whose active sites face the external medium rather than the cytoplasm. The activities of these enzymes, referred to as ecto-enzymes, can be measured using living cells. Cell membrane ecto-ATPases are integral membrane glycoproteins that are millimolar divalent cation-dependent, low specificity enzymes that hydrolyze all nucleoside triphosphates. Their physiological role is still unknown. However, several hypotheses have been suggested such as; (i). protection from cytolytic effects of extracellular ATP, (ii). regulation of ectokinase substrate concentration, (iii). termination of purinergic signaling, (iv). involvement in signal transduction, and (v). involvement in cellular adhesion. In this review, the biochemical properties and possible functions of the ecto-ATPases of different protozoa are summarized.

Characterization of an ecto-ATPase of Tritrichomonas foetus

In this work, we describe the ability of living Tritrichomonas foetus to hydrolyze extracellular ATP. The addition of MgCl(2) to the assay medium increased the ecto-ATPase activity in a dose-dependent manner. At 5mM ATP, half maximal stimulation of ATP hydrolysis was obtained with 0.46mM MgCl(2). The ecto-ATPase activity was also stimulated by MnCl(2) and CaCl(2), but not by SrCl(2). The Mg(2+)-dependent ATPase presents two apparent K(m) values for Mg-ATP(2-) (K(m1)=0.03 mM and K(m2)=2.01 mM). ATP was the best substrate for this enzyme, although other nucleotides such as ITP, CTP, UTP also produced high reaction rates. GTP produced a low reaction rate and ADP was not a substrate for this enzyme. The Mg(2+)-dependent ecto-ATPase activity was insensitive to inhibitors of other ATPase and phosphatase activities, such as oligomycin, sodium azide, bafilomycin A(1), ouabain, furosemide, vanadate, molybdate, sodium fluoride and levamizole. The acid phosphatase inhibitors (vanadate and molybdate) inhibited about 60-70% of the Mg(2+)-independent ecto-ATPase activity, suggesting that the ATP hydrolysis measured in the absence of any metal divalent could, at least in part, also be catalyzed by an ecto-phosphatase present in this cell. In order to confirm the observed Mg(2+)-dependent activity as an ecto-ATPase, we used an impermeant inhibitor, 4,4'-diisothiocyanostylbene-2',2'-disulfonic acid (DIDS) as well as suramin, an antagonist of P(2) purinoreceptors and inhibitor of some ecto-ATPases. These two reagents inhibited the Mg(2+)-dependent ATPase activity in a dose-dependent manner. This ecto-ATPase was stimulated by more than 90% by 50mM D-galactose. Since previous results showed that D-galactose exposed on the surface of host cells is involved with T. foetus adhesion, the Mg(2+)-dependent ecto-ATPase may be involved with cellular adhesion and possible pathogenicity.

A Mg-dependent ecto-ATPase in Leishmania amazonensis and its possible role in adenosine acquisition and virulence

The plasma membrane of cells contains enzymes whose active sites face the external medium rather than the cytoplasm. The activities of these enzymes, referred to as ectoenzymes, can be measured using living cells. In this work we describe the ability of living promastigotes of Leishmania amazonensis to hydrolyze extracellular ATP. In these intact parasites whose viability was assessed before and after the reactions by motility and by trypan blue dye exclusion, there was a low level of ATP hydrolysis in the absence of any divalent metal (5.39 +/- 0.71 nmol P(i)/h x 10(7) cells). The ATP hydrolysis was stimulated by MgCl(2) and the Mg-dependent ecto-ATPase activity was 30.75 +/- 2.64 nmol P(i)/h x 10(7) cells. The Mg-dependent ecto-ATPase activity was linear with cell density and with time for at least 60 min. The addition of MgCl(2) to extracellular medium increased the ecto-ATPase activity in a dose-dependent manner. At 5 mM ATP, half-maximal stimulation of ATP hydrolysis was obtained with 1.21 mM MgCl(2). This stimulatory activity was also observed when MgCl(2) was replaced by MnCl(2), but not by CaCl(2) or SrCl(2). The apparent K(m) for Mg-ATP(2-) was 0.98 mM and free Mg(2+) did not increase the ecto-ATPase activity. In the pH range from 6.8 to 8.4, in which the cells were viable, the acid phosphatase activity decreased, while the Mg(2+)-dependent ATPase activity increased. This ecto-ATPase activity was insensitive to inhibitors of other ATPase and phosphatase activities, such as oligomycin, sodium azide, bafilomycin A(1), ouabain, furosemide, vanadate, molybdate, sodium fluoride, tartrate, and levamizole. To confirm that this Mg-dependent ATPase was an ecto-ATPase, we used an impermeant inhibitor, 4,4'-diisothiocyanostylbene 2',2'-disulfonic acid as well as suramin, an antagonist of P(2) purinoreceptors and inhibitor of some ecto-ATPases. These two reagents inhibited the Mg(2+)-dependent ATPase activity in a dose-dependent manner. A comparison between the Mg(2+)-dependent ATPase activity of virulent and avirulent promastigotes showed that avirulent promastigotes were less efficient than the virulent promastigotes in hydrolyzing ATP.