Deficiency of Brummer lipase disturbs lipid mobilization and locomotion, and impairs reproduction due to defects in the eggshell ultrastructure in the insect vector Rhodnius prolixus.

Rhodnius prolixus is a hematophagous insect, which feeds on large and infrequent blood meals, and is a vector of trypanosomatids that cause Chagas disease. After feeding, lipids derived from blood meal are stored in the fat body as triacylglycerol, which is recruited under conditions of energy demand by lipolysis, where the first step is catalyzed by the Brummer lipase (Bmm), whose orthologue in mammals is the adipose triglyceride lipase (ATGL). Here, we investigated the roles of Bmm in adult Rhodnius prolixus under starvation, and after feeding. Its gene (RhoprBmm) was expressed in all the analyzed insect organs, and its transcript levels in the fat body were not altered by nutritional status. RNAi-mediated knockdown of RhoprBmm caused triacylglycerol retention in the fat body during starvation, resulting in larger lipid droplets and lower ATP levels compared to control females. The silenced females showed decreased flight capacity and locomotor activity. When RhoprBmm knockdown occurred before the blood meal and the insects were fed, the females laid fewer eggs, which collapsed and showed low hatching rates. Their hemolymph had reduced diacylglycerol content and vitellogenin concentration. The chorion (eggshell) of their eggs had no difference in hydrocarbon amounts or in dityrosine crosslinking levels compared to control eggs. However, it showed ultrastructural defects. These results demonstrated that Bmm activity is important not only to guarantee lipid mobilization to maintain energy homeostasis during starvation, but also for the production of viable eggs after a blood meal, by somehow contributing to the right formation of the egg chorion.

Acanthamoeba castellanii trophozoites escape killing by neutrophil extracellular traps using their 3'-nucleotidase/nuclease activity.

Acanthamoeba castellanii is a free-living amoeba that acts as an opportunistic pathogen for humans and is the pathogenic agent of Acanthamoeba keratitis (AK). A. castellanii may present as proliferative and infective trophozoites or as resistant cysts during their life cycle. The immune response against AK is still poorly explored; however, it is well established that macrophages and neutrophils play essential roles in controlling corneal infection during the disease outcome. The release of NETs is one of the innate immune strategies to prevent parasite infection, especially when neutrophils interact with microorganisms that are too large to be phagocytosed, which is the case for amoeba species. The present work demonstrated that A. castellanii trophozoites can trigger NET formation upon in vitro interaction with neutrophils. Using DNase as a control, we observed increased parasite survival after coinciding with neutrophils, which may be correlated with NET degradation. Indeed, A. castellanii trophozoites degrade the NET DNA scaffold. Molecular analysis confirmed the occurrence of a 3'-nucleotidase/nuclease (3'-NT/NU) in the A. castellanii genome. We also demonstrated that trophozoites exhibit significantly higher 3'-NT/NU activity than cysts, which cannot trigger NET release. Considering that previous studies indicated the pathological role of 3'-NT-/NU in parasite infection, we suggest that this enzyme may act as the mechanism of escape of A. castellanii trophozoites from NETs.

Synthesis of new non-natural L-glycosidic flavonoid derivatives and their evaluation as inhibitors of Trypanosoma cruzi ecto-nucleoside triphosphate diphosphohydrolase 1 (TcNTPDase1).

Trypanosoma cruzi is the pathogen of Chagas disease, a neglected tropical disease that affects more than 6 million people worldwide. There are no vaccines to prevent infection, and the therapeutic arsenal is very minimal and toxic. The unique E-NTPDase of T. cruzi (TcNTPDase1) plays essential roles in adhesion and infection and is a virulence factor. Quercetin is a flavonoid with antimicrobial, antiviral, and antitumor activities. Its potential as a partial inhibitor of NTPDases has also been demonstrated. In this work, we synthesized the non-natural L-glycoside derivatives of quercetin and evaluated them as inhibitors of recombinant TcNTPDase1 (rTcNTPDase1). These compounds, and quercetin and miquelianin, a natural quercetin derivative, were also tested. Compound 16 showed the most significant inhibitory effect (94%). Quercetin, miquelianin, and compound 14 showed inhibition close to 50%. We thoroughly investigated the inhibitory effect of 16. Our data suggested a competitive inhibition with a Ki of 8.39 µM (± 0.90). To better understand the interaction of compound 16 and rTcNTPDase1, we performed molecular dynamics simulations of the enzyme and docking analyses with the compounds. Our predictions show that compound 16 binds to the enzyme's catalytic site and interacts with important residues for NTPDase activity. As an inhibitor of a critical T. cruzi enzyme, (16) could be helpful as a starting point in the developing of a future treatment for Chagas disease. Furthermore, the discovery of (16) as an inhibitor of TcNTPDase1 may open new avenues in the study and development of new inhibitors of E-NTPDases.

Identification and characterization of an ectophosphatase activity involved in Acanthamoeba castellanii adhesion to host cells.

Acanthamoeba castellanii is a free-living amoeba and an opportunistic pathogen for humans that can cause encephalitis and, more commonly, Acanthamoeba keratitis. During its life cycle, A. castellanii may present as proliferative and infective trophozoites or resistant cysts. The adhesion of trophozoites to host cells is a key first step in the pathogenesis of infection. A major virulence protein of Acanthamoeba is a mannose-binding protein (MBP) that mediates the adhesion of amoebae to cell surfaces. Ectophosphatases are ecto-enzymes that can dephosphorylate extracellular substrates and have already been described in several microorganisms. Regarding their physiological roles, there is consistent evidence that ectophosphatase activities play an important role in parasite-host interactions. In the present work, we identified and biochemically characterized the ectophosphatase activity of A. castellanii. The ectophosphatase activity is acidic, stimulated by magnesium, cobalt and nickel, and presents the following apparent kinetic parameters: Km = 2.12 ± 0.54 mM p-NPP and Vmax = 26.12 ± 2.53 nmol p-NP × h-1 × 10-6 cells. We observed that sodium orthovanadate, ammonium molybdate, sodium fluoride, and inorganic phosphate are able to inhibit ectophosphatase activity. Comparing the two stages of the A. castellanii lifecycle, ectophosphatase activity is significantly higher in trophozoites than in cysts. The ectophosphatase activity is stimulated by mannose residues and is significantly increased when trophozoites interact with LLC-MK2 cells. The inhibition of ectophosphatase by pretreatment with sodium orthovanadate also inhibits the adhesion of trophozoites to epithelial cells. These results allow us to conclude that the ectophosphatase activity of A. castellanii is somehow important for the adhesion of trophozoites to their host cells. According to our data, we believe that the activation of MBP by mannose residues triggers the stimulation of ectophosphatase activity to facilitate the adhesion process.

Euglena gracilis: Biochemical properties of a membrane bound ecto-phosphatase activity modulated by fluoroaluminate complexes and different trophic conditions.

The ecto-phosphatases belong to a group of enzymes closely associated with the cell surface that has its catalytic site facing the extracellular environment, where different phosphorylated substrates can be hydrolyzed. In the present work, we biochemically characterized the ecto-phosphatase activity of the freshwater microalgae Euglena gracilis, a model microorganism, ubiquitously distributed and resistant to several environmental stressors. The ecto-phosphatase activity is acidic, stimulated by copper and presents the following apparent kinetic parameters: Km = 2.52 ± 0.12 mM p-NPP and Vmax = 3.62 ± 0.06 nmol p-NP × h-1 × 106 cells. We observed that zinc, orthovanadate, molybdate, fluoride, and inorganic phosphate inhibit the ecto-phosphatase activity with different magnitudes. Fluoroaluminate complexes are also inhibitors of this ecto-phosphatase activity. They can be formed in the enzyme reaction conditions and are likely to occur in a natural environment where E. gracilis can be found. The ecto-phosphatase activity is constant through the culture growth phases and is negatively modulated after continuous subculturing in the dark when a shift from phototrophic to the heterotrophic metabolism is likely. The analysis of those biochemical parameters may contribute to understanding the role of E. gracilis ecto-phosphatase activity in natural environments.

ATP synthase affects lipid metabolism in the kissing bug Rhodnius prolixus beyond its role in energy metabolism.

ATP synthase plays an essential role in mitochondrial metabolism, being responsible for the production of ATP in oxidative phosphorylation. However, recent results have shown that it may also be present in the cell membrane, involved in lipophorin binding to its receptors. Here, we used a functional genetics approach to investigate the roles of ATP synthase in lipid metabolism in the kissing bug Rhodnius prolixus. The genome of R. prolixus encodes five nucleotide-binding domain genes of the ATP synthase α and ß family, including the α and ß subunits of ATP synthase (RpATPSynα and RpATPSynß), and the catalytic and non-catalytic subunits of the vacuolar ATPase (RpVha68 and RpVha55). These genes were expressed in all analyzed organsn highest in the ovaries, fat body and flight muscle. Feeding did not regulate the expression of ATP synthases in the posterior midgut or fat body. Furthermore, ATP synthase is present in the fat body's mitochondrial and membrane fractions. RpATPSynß knockdown by RNAi impaired ovarian development and reduced egg-laying by approximately 85%. Furthermore, the lack of RpATPSynß increased the amount of triacylglycerol in the fat body due to increased de novo fatty acid synthesis and reduced transfer of lipids to lipophorin. RpATPSynα knockdown had similar effects, with altered ovarian development, reduced oviposition, and triacylglycerol accumulation in the fat body. However, ATP synthases knockdown had only a slight effect on the amount of ATP in the fat body. These results support the hypothesis that ATP synthase has a direct role in lipid metabolism and lipophorin physiology, which are not directly due to changes in energy metabolism.

Anaerobic energy metabolism in human microaerophile parasites.

Mucosal-associated parasites, such as Giardia intestinalis, Entamoeba histolytica, and Trichomonas vaginalis, have significant clinical relevance. The pathologies associated with infection by these parasites are among those with the highest incidence of gastroenteritis (giardiasis and amoebiasis) and sexually transmitted infections (trichomoniasis). The treatment of these diseases is based on drugs that act on the anaerobic metabolism of these parasites, such as nitroimidazole and benzimidazole derivatives. One interesting feature of parasites is their ability to produce ATP under anaerobic conditions. Due to the absence of enzymes capable of producing ATP under anaerobic conditions in the vertebrate host, they have become interesting therapeutic targets. This review discusses anaerobic energy metabolism in mucosal-associated parasites, focusing on the anaerobic metabolism of pyruvate, the importance of these enzymes as therapeutic targets, and the importance of treating their infections.

Inorganic Phosphate (Pi) in the Breast Cancer Microenvironment: Production, Transport and Signal Transduction as Potential Targets for Anticancer Strategies.

Tumor cells develop a high demand for inorganic phosphate (Pi) due to their high growth rates and energy requirements. Serum Pi concentrations in cancer patients have been found to be two to four times higher than baseline levels in healthy individuals. Twofold Pi accumulation was observed in breast cancer cells in the mouse tumor microenvironment. In the breast tumoral microenvironment, ectonucleotidases and ectophosphatases-presenting catalytic sites facing the extracellular environment-could be involved in the extracellular release of Pi to be internalized by Pi transporters to fuel the high energy requirement typical of cancer cells. Two Pi transporters were characterized in breast cancer cells (Na+-dependent and H+-dependent) with strong associations with tumor processes such as proliferation, migration, adhesion, and epithelium-mesenchymal transition (EMT). Moreover, a high extracellular Pi concentration stimulates ROS production in triple-negative breast cancer cells by Pi transport stimulation. Several compounds show a potent ability to inhibit ectonucleotidases, ectophosphatases, Pi transporters, and Pi-modulated signal pathways in breast cancer cells and regulate proliferation, migration, adhesion, and EMT. This review article aimed to gather the relevant experimental records regarding Pi's effects on the breast cancer microenvironment and points to possible inhibitors for ectonucleotidases, ectophosphatases, Pi transporters, and Pi-modulated signal pathways as potential chemotherapeutic agents or Pi acting as a potent enhancer of classical chemical-induced cytotoxicity in triple-negative breast cancer cells.

Inorganic phosphate transporter in Giardia duodenalis and its possible role in ATP synthesis.

Giardia duodenalis is a flagellated protozoan that inhabits vertebrate host intestines, causing the disease known as giardiasis. Similar to other parasites, G. duodenalis must take advantage of environmental resources to survive, such as inorganic phosphate (Pi) availability. Pi is an anionic molecule and an essential nutrient for all organisms because it participates in the biosynthesis of biomolecules, energy storage, and cellular structure formation. The first step in Pi metabolism is its uptake through specific transporters on the plasma membrane. We identified a symporter H+:Pi-type ORF sequence in the G. duodenalis genome (GenBank ID: GL50803_5164), named GdPho84, which is homologous to Saccharomyces cerevisiae PHO84. In trophozoites, Pi transport was linear for up to 15 min, and the cell density was 3 × 107 cells/ml. Physiological variations in pH (6.4-8.0) did not influence Pi uptake. This Pi transporter had a high affinity, with K0.5 = 67.7 ± 7.1 µM Pi. SCH28080 (inhibitor of H+, K+-ATPase), bafilomycin A1 (inhibitor of vacuolar H+-ATPase), and FCCP (H+ ionophore) were able to inhibit Pi transport, indicating that an H+ gradient in the cell powered uphill Pi movement. PAA, an H+-dependent Pi transport inhibitor, reduced cell proliferation, Pi transport activity, and GdPHO48 mRNA levels. Pi starvation stimulated membrane potential-sensitive Pi uptake coupled to H+ fluxes, increased GdPho84 expression, and reduced intracellular ATP levels. These events indicate that these cells had an increased capacity to internalize Pi as a compensatory mechanism compared to cells maintained in control medium conditions. Internalized Pi can be used in glycolytic metabolism once iodoacetamide (GAPDH inhibitor) inhibits Pi influx. Together, these results reinforce the hypothesis that Pi is a crucial nutrient for G. duodenalis energy metabolism.

Anaerobic ATP synthesis pathways and inorganic phosphate transport and their possible roles in encystment in Acanthamoeba castellanii.

Acanthamoeba castellanii is the etiological agent of amoebic keratitis and is present in the environment in trophozoite or cyst forms. Both forms can infect the vertebrate host and colonize different tissues. The high resistance of cysts to standard drugs used in clinics contributes to the lack of effective treatments. Therefore, in this context, studies have emerged to understand cyst physiology and metabolism. Phosphate transporters are proteins responsible for the uptake of extracellular inorganic phosphate and transport to the cytosol. This work aims to verify the relationship between Pi transport and energetic metabolism in cysts of A. castellanii. The phosphate uptake ratio was higher in cysts compared with trophozoites. Recently, three sequences related to phosphate transporters have been identified in the A. castellanii genome (AcPHS1, AcPHS2, and AcPHS3); the messenger RNA expression levels of which differ depending on the amoeba life form. Pi uptake in cysts displayed peak activity at alkaline pH, whereas Pi transport in trophozoites was not affected in the same pH ranges. Cysts harbor a low-affinity Pi transport system (K0,5 and Vmax values of 1.76 ± 0.26 mM and 104.6 ± 6.3 nmol Pi × h-1 × 106 cells) compared to the trophozoite phosphate transport system. Pi transport seems important for anaerobic adenosine triphosphate synthesis in cysts, which initially occurs through the glycolytic pathway and subsequently through the pyruvate ferredoxin oxidoreductase pathway. Altogether, these results suggest that contrary to that previously postulated, cysts are active metabolic forms, and, as noted in trophozoites, phosphate uptake is important for energetic metabolism.

The Role of Inorganic Phosphate Transporters in Highly Proliferative Cells: From Protozoan Parasites to Cancer Cells.

In addition to their standard inorganic phosphate (Pi) nutritional function, Pi transporters have additional roles in several cells, including Pi sensing (the so-called transceptor) and a crucial role in Pi metabolism, where they control several phenotypes, such as virulence in pathogens and tumour aggressiveness in cancer cells. Thus, intracellular Pi concentration should be tightly regulated by the fine control of intake and storage in organelles. Pi transporters are classified into two groups: the Pi transporter (PiT) family, also known as the Pi:Na+ symporter family; and the Pi:H+ symporter (PHS) family. Highly proliferative cells, such as protozoan parasites and cancer cells, rely on aerobic glycolysis to support the rapid generation of biomass, which is equated with the well-known Warburg effect in cancer cells. In protozoan parasite cells, Pi transporters are strongly associated with cell proliferation, possibly through their action as intracellular Pi suppliers for glyceraldehyde-3-phosphate dehydrogenase (GAPDH) activity. Similarly, the growth rate hypothesis (GRH) proposes that the high Pi demands of tumours when achieving accelerated proliferation are mainly due to increased allocation to P-rich nucleic acids. The purpose of this review was to highlight recent advances in understanding the role of Pi transporters in unicellular eukaryotes and tumorigenic cells, correlating these roles with metabolism in these cells.

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.

Stage-Specific Class I Nucleases of Leishmania Play Important Roles in Parasite Infection and Survival.

Protozoans of the genus Leishmania are the causative agents of an important neglected tropical disease referred to as leishmaniasis. During their lifecycle, the parasites can colonize the alimentary tract of the sand fly vector and the parasitophorous vacuole of the mammalian host, differentiating into distinct stages. Motile promastigotes are found in the sand fly vector and are transmitted to the mammalian host during the insect blood meal. Once in the vertebrate host, the parasites differentiate into amastigotes and multiply inside macrophages. To successfully establish infection in mammalian hosts, Leishmania parasites exhibit various strategies to impair the microbicidal power of the host immune system. In this context, stage-specific class I nucleases play different and important roles related to parasite growth, survival and development. Promastigotes express 3'-nucleotidase/nuclease (3'-NT/NU), an ectoenzyme that can promote parasite escape from neutrophil extracellular traps (NET)-mediated death through extracellular DNA hydrolysis and increase Leishmania-macrophage interactions due to extracellular adenosine generation. Amastigotes express secreted nuclease activity during the course of human infection that may be involved in the purine salvage pathway and can mobilize extracellular nucleic acids available far from the parasite. Another nuclease expressed in amastigotes (P4/LmC1N) is located in the endoplasmic reticulum of the parasite and may be involved in mRNA stability and DNA repair. Homologs of this class I nuclease can induce protection against infection by eliciting a T helper 1-like immune response. These immunogenic properties render these nucleases good targets for the development of vaccines against leishmaniasis, mainly because amastigotes are the form responsible for the development and progression of the disease. The present review aims to present and discuss the roles played by different class I nucleases during the Leishmania lifecycle, especially regarding the establishment of mammalian host infection.

Higher expression of proline dehydrogenase altered mitochondrial function and increased Trypanosoma cruzi differentiation in vitro and in the insect vector.

The pathogenic protist Trypanosoma cruzi uses kissing bugs as invertebrate hosts that vectorize the infection among mammals. This parasite oxidizes proline to glutamate through two enzymatic steps and one nonenzymatic step. In insect vectors, T. cruzi differentiates from a noninfective replicating form to nonproliferative infective forms. Proline sustains this differentiation, but to date, a link between proline metabolism and differentiation has not been established. In T. cruzi, the enzymatic steps of the proline-glutamate oxidation pathway are catalyzed exclusively by the mitochondrial enzymes proline dehydrogenase [TcPRODH, EC: 1.5.5.2] and Δ1-pyrroline-5-carboxylate dehydrogenase [TcP5CDH, EC: 1.2.1.88]. Both enzymatic steps produce reducing equivalents that are able to directly feed the mitochondrial electron transport chain (ETC) and thus produce ATP. In this study, we demonstrate the contribution of each enzyme of the proline-glutamate pathway to ATP production. In addition, we show that parasites overexpressing these enzymes produce increased levels of H2O2, but only those overexpressing TcP5CDH produce increased levels of superoxide anion. We show that parasites overexpressing TcPRODH, but not parasites overexpressing TcP5CDH, exhibit a higher rate of differentiation into metacyclic trypomastigotes in vitro. Finally, insect hosts infected with parasites overexpressing TcPRODH showed a diminished parasitic load but a higher percent of metacyclic trypomastigotes, when compared with controls. Our data show that parasites overexpressing both, PRODH and P5CDH had increased mitochondrial functions that orchestrated different oxygen signaling, resulting in different outcomes in relation to the efficiency of parasitic differentiation in the invertebrate host.

Hydrogen Peroxide Generation as an Underlying Response to High Extracellular Inorganic Phosphate (Pi) in Breast Cancer Cells.

According to the growth rate hypothesis (GRH), tumour cells have high inorganic phosphate (Pi) demands due to accelerated proliferation. Compared to healthy individuals, cancer patients present with a nearly 2.5-fold higher Pi serum concentration. In this work, we show that an increasing concentration of Pi had the opposite effect on Pi-transporters only in MDA-MB-231 when compared to other breast cell lines: MCF-7 or MCF10-A (non-tumoural breast cell line). Here, we show for the first time that high extracellular Pi concentration mediates ROS production in TNBC (MDA-MB-231). After a short-time exposure (1 h), Pi hyperpolarizes the mitochondrial membrane, increases mitochondrial ROS generation, impairs oxygen (O2) consumption and increases PKC activity. However, after 24 h Pi-exposure, the source of H2O2 seems to shift from mitochondria to an NADPH oxidase enzyme (NOX), through activation of PKC by H2O2. Exogenous-added H2O2 modulated Pi-transporters the same way as extracellular high Pi, which could be reversed by the addition of the antioxidant N-acetylcysteine (NAC). NAC was also able to abolish Pi-induced Epithelial-mesenchymal transition (EMT), migration and adhesion of MDA-MB-231. We believe that Pi transporters support part of the energy required for the metastatic processes stimulated by Pi and trigger Pi-induced H2O2 production as a signalling response to promote cell migration and adhesion.

3-Bromopyruvate: A new strategy for inhibition of glycolytic enzymes in Leishmania amazonensis.

The compound 3-bromopyruvate (3-BrPA) is well-known and studies from several researchers have demonstrated its involvement in tumorigenesis. It is an analogue of pyruvic acid that inhibits ATP synthesis by inhibiting enzymes from the glycolytic pathway and oxidative phosphorylation. In this work, we investigated the effect of 3-BrPA on energy metabolism of L. amazonensis. In order to verify the effect of 3-BrPA on L. amazonensis glycolysis, we measured the activity level of three glycolytic enzymes located at different points of the pathway: (i) glucose kinases, step 1, (ii) glyceraldehyde 3-phosphate dehydrogenase (GAPDH), step 6, and (iii) enolase, step 9. 3-BrPA, in a dose-dependent manner, significantly reduced the activity levels of all the enzymes. In addition, 3-BrPA treatment led to a reduction in the levels of phosphofruto-1-kinase (PFK) protein, suggesting that the mode of action of 3-BrPA involves the downregulation of some glycolytic enzymes. Measurement of ATP levels in promastigotes of L. amazonensis showed a significant reduction in ATP generation. The O2 consumption was also significantly inhibited in promastigotes, confirming the energy depletion effect of 3-BrPA. When 3-BrPA was added to the cells at the beginning of growth cycle, it significantly inhibited L. amazonensis proliferation in a dose-dependent manner. Furthermore, the ability to infect macrophages was reduced by approximately 50% when promastigotes were treated with 3-BrPA. Taken together, these studies corroborate with previous reports which suggest 3-BrPA as a potential drug against pathogenic microorganisms that are reliant on glucose catabolism for ATP supply.

Extracellular Inorganic Phosphate-Induced Release of Reactive Oxygen Species: Roles in Physiological Processes and Disease Development.

Inorganic phosphate (Pi) is an essential nutrient for living organisms and is maintained in equilibrium in the range of 0.8-1.4 mM Pi. Pi is a source of organic constituents for DNA, RNA, and phospholipids and is essential for ATP formation mainly through energy metabolism or cellular signalling modulators. In mitochondria isolated from the brain, liver, and heart, Pi has been shown to induce mitochondrial reactive oxygen species (ROS) release. Therefore, the purpose of this review article was to gather relevant experimental records of the production of Pi-induced reactive species, mainly ROS, to examine their essential roles in physiological processes, such as the development of bone and cartilage and the development of diseases, such as cardiovascular disease, diabetes, muscle atrophy, and male reproductive system impairment. Interestingly, in the presence of different antioxidants or inhibitors of cytoplasmic and mitochondrial Pi transporters, Pi-induced ROS production can be reversed and may be a possible pharmacological target.

Candida Extracellular Nucleotide Metabolism Promotes Neutrophils Extracellular Traps Escape.

Host innate immunity is fundamental to the resistance against Candida albicans and Candida glabrata infection, two of the most important agents contributing to human fungal infections. Phagocytic cells, such as neutrophils, constitute the first line of host defense mechanisms, and the release of neutrophil extracellular traps (NETs) represent an important strategy to immobilize and to kill invading microorganisms, arresting the establishment of infection. The purinergic system operates an important role in the homeostasis of immunity and inflammation, and ectophosphatase and ectonucleotidase activities are recognized as essential for survival strategies and infectious potential of several pathogens. The expression and unique activity of a 3'-nucleotidase/nuclease (3'NT/NU), able to hydrolyze not only AMP but also nucleic acids, has been considered as part of a possible mechanism of microbes to escape from NETs. The aim of the present study was to evaluate if yeasts escape from the NET-mediated killing through their 3'NT/NU enzymatic activity contributing to NET-hydrolysis. After demonstrating the presence of 3'NT/NU activity in C. albicans, C. glabrata, and Saccharomyces cerevisiae, we show that, during neutrophils-Candida interaction, when NETs formation and release are triggered, NETs digestion occurs and this process of NETs disruption promoted by yeast cells was prevented by ammonium tetrathiomolybdate (TTM), a 3'NT/NU inhibitor. In conclusion, although the exact nature and specificity of yeasts ectonucleotidases are not completely unraveled, we highlight the importance of these enzymes in the context of infection, helping yeasts to overcome host defenses, whereby C. albicans and C. glabrata can escape NET-mediate killing through their 3'NT/NU activity.

Differential regulation of E-NTPdases during Leishmania amazonensis lifecycle and effect of their overexpression on parasite infectivity and virulence.

Infections caused by Leishmania amazonensis are characterized by a persistent parasitemia due to the ability of the parasite to modulate the immune response of macrophages. It has been proposed that ecto-nucleoside triphosphate diphosphohydrolase (E-NTPDases) could be able to suppress the host immune defense by reducing the ATP and ADP levels. The AMP generated from E-NTPDase activity can be subsequently hydrolyzed by ecto-nucleotidases, increasing the levels of adenosine, which can reduce the inflammatory response. In the present work, we provide new information about the role of E-NTPDases on infectivity and virulence of L. amazonensis. Our data demonstrate that not only the E-NTPDase activity is differentially regulated during the parasite development but also the expression of the genes ntpd1 and ntpd2. E-NTPDase activity increases significantly in axenic amastigotes and metacyclic promastigotes, both infective forms in mammalian host. A similar profile was found for mRNA levels of the ntpd1 and ntpd2 genes. Using parasites overexpressing the genes ntpd1 and ntpd2, we could demonstrate that L. amazonensis promastigotes overexpressing ntpd2 gene show a remarkable increase in their ability to interact with macrophages compared to controls. In addition, both ntpd1 and ntpd2-overexpressing parasites were more infective to macrophages than controls. The kinetics of lesion formation by transfected parasites were similar to controls until the second week. However, twenty days post-infection, mice infected with ntpd1 and ntpd2-overexpressing parasites presented significantly reduced lesions compared to controls. Interestingly, parasite load reached similar levels among the different experimental groups. Thus, our data show a non-linear relationship between higher E-NTPDase activity and lesion formation. Previous studies have correlated increased ecto-NTPDase activity with virulence and infectivity of Leishmania parasites. Based in our results, we are suggesting that the induced overexpression of E-NTPDases in L. amazonensis could increase extracellular adenosine levels, interfering with the balance of the immune response to promote the pathogen clearance and maintain the host protection.

Involvement of Leishmania Phosphatases in Parasite Biology and Pathogeny.

In the Leishmania lifecycle, the motile promastigote form is transmitted from the sand fly vector to a mammalian host during a blood meal. Inside vertebrate host macrophages, the parasites can differentiate into the amastigote form and multiply, causing leishmaniasis, one of the most significant neglected tropical diseases. Leishmania parasites face different conditions throughout their development inside sand flies. Once in the mammalian host, the parasites have to overcome the microbicide repertoire of the cells of the immune system to successfully establish the infection. In this context, the expression of protein phosphatases is of particular interest. Several members of the serine/threonine-specific protein phosphatase (STP), protein tyrosine phosphatase (PTP), and histidine acid phosphatase (HAcP) families have been described in different Leishmania species. Although their physiological roles have not been fully elucidated, many studies suggest they have an involvement with parasite biology and pathogeny. Phosphatases play a role in adaptation to nutrient starvation during parasite passage through the sand fly midgut. They are also important to parasite virulence, mainly due to the modulation of host cytokine production and impairment of the microbiocidal potential of macrophages. Furthermore, recent whole-genome expression analyses have shown that different phosphatases are upregulated in metacyclic promastigotes, the infective form of the mammalian host. Leishmania phosphatases are also upregulated in drug-resistant strains, probably due to the increase in drug efflux related to the activation of ABC transporters. Throughout this review, we will describe the physiological roles that have been attributed to Leishmania endogenous phosphatases, including their involvement in the adaptation, survival, and proliferation of the parasites inside their hosts.