Disruption of Intracellular Calcium Homeostasis as a Therapeutic Target Against Trypanosoma cruzi

Unmasking the Mechanism behind Miltefosine: Revealing the Disruption of Intracellular Ca2+ Homeostasis as a Rational Therapeutic Target in Leishmaniasis and Chagas Disease

Originally developed as a chemotherapeutic agent, miltefosine (hexadecylphosphocholine) is an inhibitor of phosphatidylcholine synthesis with proven antiparasitic effects. It is the only oral drug approved for the treatment of Leishmaniasis and American Trypanosomiasis (Chagas disease). Although its precise mechanisms are not yet fully understood, miltefosine exhibits broad-spectrum anti-parasitic effects primarily by disrupting the intracellular Ca2+ homeostasis of the parasites while sparing the human hosts. In addition to its inhibitory effects on phosphatidylcholine synthesis and cytochrome c oxidase, miltefosine has been found to affect the unique giant mitochondria and the acidocalcisomes of parasites. Both of these crucial organelles are involved in Ca2+ regulation. Furthermore, miltefosine has the ability to activate a specific parasite Ca2+ channel that responds to sphingosine, which is different to its L-type VGCC human ortholog. Here, we aimed to provide an overview of recent advancements of the anti-parasitic mechanisms of miltefosine. We also explored its multiple molecular targets and investigated how its pleiotropic effects translate into a rational therapeutic approach for patients afflicted by Leishmaniasis and American Trypanosomiasis. Notably, miltefosine's therapeutic effect extends beyond its impact on the parasite to also positively affect the host's immune system. These findings enhance our understanding on its multi-targeted mechanism of action. Overall, this review sheds light on the intricate molecular actions of miltefosine, highlighting its potential as a promising therapeutic option against these debilitating parasitic diseases.

Molecular, immunological, and physiological evidences of a sphingosine-activated plasma membrane Ca2+-channel in Trypanosoma equiperdum

The hemoparasite Trypanosoma equiperdum belongs to the Trypanozoon subgenus and includes several species that are pathogenic to animals and humans in tropical and subtropical areas across the world. As with all eukaryotic organisms, Ca2+ is essential for these parasites to perform cellular processes thus ensuring their survival across their life cycle. Despite the established paradigm to study proteins related to Ca2+ homeostasis as potential drug targets, so far little is known about Ca2+ entry into trypanosomes. Therefore, in the present study, the presence of a plasma membrane Ca2+-channel in T. equiperdum (TeCC), activated by sphingosine and inhibited by verapamil, is described. The TeCC was cloned and analyzed using bioinformatic resources, which confirmed the presence of several domains, motifs, and a topology similar to the Ca2+ channels found in higher eukaryotes. Biochemical and confocal microscopy assays using antibodies raised against an internal region of human L-type Ca2+ channels indicate the presence of a protein with similar predicted molar mass to the sequence analyzed, located at the plasma membrane of T. equiperdum. Physiological assays based on Fura-2 signals and Mn2+ quenching performed on whole parasites showed a unidirectional Ca2+ entry, which is activated by sphingosine and blocked by verapamil, with the distinctive feature of insensitivity to nifedipine and Bay K 8644. This suggests a second Ca2+ entry for T. equiperdum, different from the store-operated Ca2+ entry (SOCE) previously described. Moreover, the evidence presented here for the TeCC indicates molecular and pharmacological differences with their mammal counterparts, which deserve further studies to evaluate the potential of this channel as a drug target.

Synthesis, Antimalarial, Antileishmanial, and Cytotoxicity Activities and Preliminary In Silico ADMET Studies of 2-(7-Chloroquinolin-4-ylamino)ethyl Benzoate Derivatives

A series of heterocyclic chloroquine hybrids, containing a chain of two carbon atoms at position four of the quinolinic chain and acting as a link between quinoline and several benzoyl groups, is synthesized and screened in vitro as an inhibitor of β-hematin formation and in vivo for its antimalarial activity against chloroquine-sensitive strains of Plasmodium berghei ANKA in this study. The compounds significantly reduced haeme crystallization, with IC50 values < 10 µM. The values were comparable to chloroquine's, with an IC50 of 1.50 ± 0.01 µM. The compounds 4c and 4e prolonged the average survival time of the infected mice to 16.7 ± 2.16 and 14.4 ± 1.20 days, respectively. We also studied the effect of the compounds 4b, 4c, and 4e on another important human parasite, Leishmania mexicana, which is responsible for cutaneous leishmaniasis, demonstrating a potential leishmanicidal effect against promasigotes, with an IC50 < 10 µM. Concerning the possible mechanism of action of these compounds on Lesihmania mexicana, we performed experiments demonstrating that these three compounds could induce the collapse of the parasite mitochondrial electrochemical membrane potential (Δφ). The in vitro cytotoxicity assays against mammalian cancerous and noncancerous human cell lines showed that the studied compounds exhibit low cytotoxic effects. The ADME/Tox analysis predicted moderate lipophilicity values, low unbound fraction values, and a poor distribution for these compounds. Therefore, moderate bioavailability was expected. We calculated other molecular descriptors, such as the topological polar surface area, according to Veber's rules, and except for 2 and 4i, the rest of the compounds violated this descriptor, demonstrating the low antimalarial activity of our compounds in vivo.

Effects of SQ109 on Trichomonas vaginalis

Trichomonas vaginalis is a protozoan that causes human trichomoniasis, a sexually transmitted infection (STI) that affects approximately 278 million people worldwide. The current treatment for human trichomoniasis is based on 1-(2-hydroxyethyl)-2-methyl-5-nitroimidazole, known as Metronidazole (MTZ). Although effective in eliminating parasitic infection, MTZ is related to serious adverse effects and is not recommended during pregnancy. In addition, some strains are resistant to 5'-nitroimidazoles, prompting the development of alternative drugs for trichomoniasis. Here we show that SQ109 [N-adamantan-2-yl-N'-((E)-3,7-dimethyl-octa- 2,6-dienyl)-ethane-1,2-diamine], a drug under development (antitubercular drug candidate that completed Phase IIb/III) for the treatment of tuberculosis, and previously tested in Trypanosoma cruzi and Leishmania. SQ109 inhibited T.vaginalis growth with an IC50 of 3.15 μM. We used scanning and transmission electron microscopy to visualize the ultrastructural alterations induced by SQ109. The microscopy analysis showed morphological changes on the protozoan surface, where the cells became rounded with increasing surface projections. In addition, the hydrogenosomes increased their size and area occupied in the cell. Furthermore, the volume and a significant association of glycogen particles with the organelle were seen to be altered. A bioinformatics search was done about the compound to find its possible targets and mechanisms of action. Our observations identify SQ109 as a promising compound against T. vaginalis in vitro, suggesting its potential utility as an alternative chemotherapy for trichomoniasis.

Trypanosoma cruzi dysregulates expression profile of piRNAs in primary human cardiac fibroblasts during early infection phase

Trypanosoma cruzi, the etiological agent of Chagas Disease, causes severe morbidity, mortality, and economic burden worldwide. Though originally endemic to Central and South America, globalization has led to increased parasite presence in most industrialized countries. About 40% of infected individuals will develop cardiovascular, neurological, and/or gastrointestinal pathologies. Accumulating evidence suggests that the parasite induces alterations in host gene expression profiles in order to facilitate infection and pathogenesis. The role of regulatory gene expression machinery during T. cruzi infection, particularly small noncoding RNAs, has yet to be elucidated. In this study, we aim to evaluate dysregulation of a class of sncRNAs called piRNAs during early phase of T. cruzi infection in primary human cardiac fibroblasts by RNA-Seq. We subsequently performed in silico analysis to predict piRNA-mRNA interactions. We validated the expression of these selected piRNAs and their targets during early parasite infection phase by stem loop qPCR and qPCR, respectively. We found about 26,496,863 clean reads (92.72%) which mapped to the human reference genome. During parasite challenge, 441 unique piRNAs were differentially expressed. Of these differentially expressed piRNAs, 29 were known and 412 were novel. In silico analysis showed several of these piRNAs were computationally predicted to target and potentially regulate expression of genes including SMAD2, EGR1, ICAM1, CX3CL1, and CXCR2, which have been implicated in parasite infection, pathogenesis, and various cardiomyopathies. Further evaluation of the function of these individual piRNAs in gene regulation and expression will enhance our understanding of early molecular mechanisms contributing to infection and pathogenesis. Our findings here suggest that piRNAs play important roles in infectious disease pathogenesis and can serve as potential biomarkers and therapeutic targets.

Synthetic Analogues of Gibbilimbol B Induce Bioenergetic Damage and Calcium Imbalance in Trypanosoma cruzi

Chagas disease is an endemic tropical disease caused by the protozoan Trypanosoma cruzi, which affects around 7 million people worldwide, mostly in development countries. The treatment relies on only two available drugs, with severe adverse effects and a limited efficacy. Therefore, the search for new therapies is a legitimate need. Within this context, our group reported the anti-Trypanosoma cruzi activity of gibbilimbol B, a natural alkylphenol isolated from the plant Piper malacophyllum. Two synthetic derivatives, LINS03018 (1) and LINS03024 (2), demonstrated a higher antiparasitic potency and were selected for mechanism of action investigations. Our studies revealed no alterations in the plasma membrane potential, but a rapid alkalinization of the acidocalcisomes. Nevertheless, compound 1 exhibit a pronounced effect in the bioenergetics metabolism, with a mitochondrial impairment and consequent decrease in ATP and reactive oxygen species (ROS) levels. Compound 2 only depolarized the mitochondrial membrane potential, with no interferences in the respiratory chain. Additionally, no macrophages response of nitric oxide (NO) was observed in both compounds. Noteworthy, simple structure modifications in these derivatives induced significant differences in their lethal effects. Thus, this work reinforces the importance of the mechanism of action investigations at the early phases of drug discovery and support further developments of the series.

Down the membrane hole: Ion channels in protozoan parasites

Parasitic diseases caused by protozoans are highly prevalent around the world, disproportionally affecting developing countries, where coinfection with other microorganisms is common. Control and treatment of parasitic infections are constrained by the lack of specific and effective drugs, plus the rapid emergence of resistance. Ion channels are main drug targets for numerous diseases, but their potential against protozoan parasites is still untapped. Ion channels are membrane proteins expressed in all types of cells, allowing for the flow of ions between compartments, and regulating cellular functions such as membrane potential, excitability, volume, signaling, and death. Channels and transporters reside at the interface between parasites and their hosts, controlling nutrient uptake, viability, replication, and infectivity. To understand how ion channels control protozoan parasites fate and to evaluate their suitability for therapeutics, we must deepen our knowledge of their structure, function, and modulation. However, methodological approaches commonly used in mammalian cells have proven difficult to apply in protozoans. This review focuses on ion channels described in protozoan parasites of clinical relevance, mainly apicomplexans and trypanosomatids, highlighting proteins for which molecular and functional evidence has been correlated with their physiological functions.

Lethal action of Licarin A derivatives in Leishmania (L.) infantum: Imbalance of calcium and bioenergetic metabolism

Natural metabolites present an extraordinary chemo-diversity and have been used as the inspiration for new drugs. Considering the need for new treatments against the neglected parasitic disease leishmaniasis, three semi-synthetic derivatives of natural neolignane licarin A were prepared: O-acetyl (1a), O-allyl (1b), and 5-allyl (1c). Using an ex vivo assay, compounds 1a, 1b, and 1c showed activity against the intracellular amastigotes of Leishmania (L.) infantum, with IC₅₀ values of 9, 13, and 10 μM, respectively. Despite no induction of hemolytic activity, only compound 1b resulted in mammalian cytotoxicity (CC₅₀ = 64 μM). The most potent compounds (1a and 1c) resulted in selectivity indexes >18. The mechanism of action of compound 1c was evaluated by fluorescent/luminescent based techniques and MALDI-TOF/MS. After a short incubation period, increased levels of the cytosolic calcium were observed in the parasites, with alkalinization of the acidocalcisomes. Compound 1c also induced mitochondrial hyperpolarization, resulting in decreased levels of ATP without altering the reactive oxygen species (ROS). Neither plasma membrane damages nor DNA fragmentation were observed after the treatment, but a reduction in the cellular proliferation was detected. Using MALDI-TOF/MS, mass spectral alterations of promastigote proteins were observed when compared to untreated and miltefosine-treated groups. This chemically modified neolignan induced lethal alterations of the bioenergetic and protein metabolism of Leishmania. Future PKPD and animal efficacy studies are needed to optimize this promising natural-derived compound.

The endoplasmic reticulum of trypanosomatids: An unrevealed road for chemotherapy

The endoplasmic reticulum (ER) of higher eukaryotic cells forms an intricate membranous network that serves as the main processing facility for folding and assembling of secreted and membrane proteins. The ER is a highly dynamic organelle that interacts with other intracellular structures, as well as endosymbiotic pathogenic and non-pathogenic microorganisms. A strict ER quality control (ERQC) must work to ensure that proteins entering the ER are folded and processed correctly. Unfolded or misfolded proteins are usually identified, selected, and addressed to Endoplasmic Reticulum-Associated Degradation (ERAD) complex. Conversely, when there is a large demand for secreted proteins or ER imbalance, the accumulation of unfolded or misfolded proteins activates the Unfold Protein Response (UPR) to restore the ER homeostasis or, in the case of persistent ER stress, induces the cell death. Pathogenic trypanosomatids, such as Trypanosoma cruzi, Trypanosoma brucei and Leishmania spp are the etiological agents of important neglected diseases. These protozoans have a complex life cycle alternating between vertebrate and invertebrate hosts. The ER of trypanosomatids, like those found in higher eukaryotes, is also specialized for secretion, and depends on the ERAD and non-canonical UPR to deal with the ER stress. Here, we reviewed the basic aspects of ER biology, organization, and quality control in trypanosomatids. We also focused on the unusual way by which T. cruzi, T. brucei, and Leishmania spp. respond to ER stress, emphasizing how these parasites' ER-unrevealed roads might be an attractive target for chemotherapy.

The old and the new about the contractile vacuole of Trypanosoma cruzi

Osmoregulation is a conserved cellular process required for the survival of all organisms. In protists, the need for robust compensatory mechanisms that can maintain cell volume and tonicity within physiological range is even more relevant, as their life cycles are often completed in different environments. Trypanosoma cruzi, the protozoan pathogen responsible for Chagas disease, is transmitted by an insect vector to multiple types of mammalian hosts. The contractile vacuole complex (CVC) is an organelle that senses and compensates osmotic changes in the parasites, ensuring their survival upon ionic and osmotic challenges. Recent work shows that the contractile vacuole is also a key component of the secretory and endocytic pathways, regulating the selective targeting of surface proteins during differentiation. Here we summarize our current knowledge of the mechanisms involved in the osmoregulatory processes that take place in the vacuole, and we explore the new and exciting functions of this organelle in cell trafficking and signaling.

The repositioned drugs disulfiram/diethyldithiocarbamate combined to benznidazole: Searching for Chagas disease selective therapy, preventing toxicity and drug resistance

Chagas disease (CD) affects at least 6 million people in 21 South American countries besides several thousand in other nations all over the world. It is estimated that at least 14,000 people die every year of CD. Since vaccines are not available, chemotherapy remains of pivotal relevance. About 30% of the treated patients cannot complete the therapy because of severe adverse reactions. Thus, the search for novel drugs is required. Here we tested the benznidazole (BZ) combination with the repositioned drug disulfiram (DSF) and its derivative diethyldithiocarbamate (DETC) upon Trypanosoma cruzi in vitro and in vivo. DETC-BZ combination was synergistic diminishing epimastigote proliferation and enhancing selective indexes up to over 10-fold. DETC was effective upon amastigotes of the BZ- partially resistant Y and the BZ-resistant Colombiana strains. The combination reduced proliferation even using low concentrations (e.g., 2.5 µM). Scanning electron microscopy revealed membrane discontinuities and cell body volume reduction. Transmission electron microscopy revealed remarkable enlargement of endoplasmic reticulum cisternae besides, dilated mitochondria with decreased electron density and disorganized kinetoplast DNA. At advanced stages, the cytoplasm vacuolation apparently impaired compartmentation. The fluorescent probe H2-DCFDA indicates the increased production of reactive oxygen species associated with enhanced lipid peroxidation in parasites incubated with DETC. The biochemical measurement indicates the downmodulation of thiol expression. DETC inhibited superoxide dismutase activity on parasites was more pronounced than in infected mice. In order to approach the DETC effects on intracellular infection, peritoneal macrophages were infected with Colombiana trypomastigotes. DETC addition diminished parasite numbers and the DETC-BZ combination was effective, despite the low concentrations used. In the murine infection, the combination significantly enhanced animal survival, decreasing parasitemia over BZ. Histopathology revealed that low doses of BZ-treated animals presented myocardial amastigote, not observed in combination-treated animals. The picrosirius collagen staining showed reduced myocardial fibrosis. Aminotransferase de aspartate, Aminotransferase de alanine, Creatine kinase, and urea plasma levels demonstrated that the combination was non-toxic. As DSF and DETC can reduce the toxicity of other drugs and resistance phenotypes, such a combination may be safe and effective.

Energy metabolism as a target for cyclobenzaprine: A drug candidate against Visceral Leishmaniasis

Leishmaniases have a broad spectrum of clinical manifestations, ranging from a cutaneous to a progressive and fatal visceral disease. Chemotherapy is nowadays the almost exclusive way to fight the disease but limited by its scarce therapeutic arsenal, on its own compromised by adverse side effects and clinical resistance. Cyclobenzaprine (CBP), an FDA-approved oral muscle relaxant drug has previously demonstrated in vitro and in vivo activity against Leishmania sp., but its targets were not fully unveiled. This study aimed to define the role of energy metabolism as a target for the leishmanicidal mechanisms of CBP. Methodology to assess CBP leishmanicidal mechanism variation of intracellular ATP levels using living Leishmania transfected with a cytoplasmic luciferase. Induction of plasma membrane permeability by assessing depolarization with DiSBAC(2)3 and entrance of the vital dye SYTOX® Green. Mitochondrial depolarization by rhodamine 123 accumulation. Mapping target site within the respiratory chain by oxygen consumption rate. Reactive oxygen species (ROS) production using MitoSOX. Morphological changes by transmission electron microscopy. CBP caused on L. infantum promastigotes a decrease of intracellular ATP levels, with irreversible depolarization of plasma membrane, the collapse of the mitochondrial electrochemical potential, mild uncoupling of the respiratory chain, and ROS production, with ensuing intracellular Ca²⁺ imbalance and DNA fragmentation. Electron microscopy supported autophagic features but not a massive plasma membrane disruption. The severe and irreversible mitochondrial damage induced by CBP endorsed the bioenergetics metabolism as a relevant target within the lethal programme induced by CBP in Leishmania. This, together with the mild-side effects of this oral drug, endorses CBP as an appealing novel candidate as a leishmanicidal drug under a drug repurposing strategy.

Miltefosine and Benznidazole Combination Improve Anti-Trypanosoma cruzi In Vitro and In Vivo Efficacy

Drug repurposing and combination therapy have been proposed as cost-effective strategies to improve Chagas disease treatment. Miltefosine (MLT), a synthetic alkylphospholipid initially developed for breast cancer and repositioned for leishmaniasis, is a promising candidate against Trypanosoma cruzi infection. This study evaluates the efficacy of MLT as a monodrug and combined with benznidazole (BZ) in both in vitro and in vivo models of infection with T. cruzi (VD strain, DTU TcVI). MLT exhibited in vitro activity on amastigotes and trypomastigotes with values of IC_{50 =} 0.51 µM (0.48 µM; 0,55 µM) and LC_{50 =} 31.17 µM (29.56 µM; 32.87 µM), respectively. Drug interaction was studied with the fixed-ration method. The sum of the fractional inhibitory concentrations (ΣFICs) resulted in ∑FIC= 0.45 for trypomastigotes and ∑FIC= 0.71 for amastigotes, suggesting in vitro synergistic and additive effects, respectively. No cytotoxic effects on host cells were observed. MLT efficacy was also evaluated in a murine model of acute infection alone or combined with BZ. Treatment was well tolerated with few adverse effects, and all treated animals displayed significantly lower mean peak parasitemia and mortality than infected non-treated controls (p<0.05). The in vivo studies showed that MLT led to a dose-dependent parasitostatic effect as monotherapy which could be improved by combining with BZ, preventing parasitemia rebound after a stringent immunosuppression protocol. These results support MLT activity in clinically relevant stages from T. cruzi, and it is the first report of positive interaction with BZ, providing further support for evaluating combined schemes using MLT and exploring synthetic alkylphospholipids as drug candidates.

The Kinetoplastid-Specific Protein TcCAL1 Plays Different Roles During In Vitro Differentiation and Host-Cell Invasion in Trypanosoma cruzi

In the pathogen Typanosoma cruzi, the calcium ion (Ca2+) regulates key processes for parasite survival. However, the mechanisms decoding Ca2+ signals are not fully identified or understood. Here, we investigate the role of a hypothetical Ca2+-binding protein named TcCAL1 in the in vitro life cycle of T. cruzi. Results showed that the overexpression of TcCAL1 fused to a 6X histidine tag (TcCAL1-6xHis) impaired the differentiation of epimastigotes into metacyclic trypomastigotes, significantly decreasing metacyclogenesis rates. When the virulence of transgenic metacyclic trypomastigotes was explored in mammalian cell invasion assays, we found that the percentage of infection was significantly higher in Vero cells incubated with TcCAL1-6xHis-overexpressing parasites than in controls, as well as the number of intracellular amastigotes. Additionally, the percentage of Vero cells with adhered metacyclic trypomastigotes significantly increased in samples incubated with TcCAL1-6xHis-overexpressing parasites compared with controls. In contrast, the differentiation rates from metacyclic trypomastigotes to axenic amastigotes or the epimastigote proliferation in the exponential phase of growth have not been affected by TcCAL1-6xHis overexpression. Based on our findings, we speculate that TcCAL1 exerts its function by sequestering intracellular Ca2+ by its EF-hand motifs (impairing metacyclogenesis) and/or due to an unknown activity which could be amplified by the ion binding (promoting cell invasion). This work underpins the importance of studying the kinetoplastid-specific proteins with unknown functions in pathogen parasites.

Bioactivity of Natural Polyphenols as Antiparasitic Agents and their Biochemical Targets

BACKGROUND

Leishmaniasis and trypanosomiasis are diseases that affect public health worldwide due to their high incidence, morbidity, and mortality. Available treatments are costly, prolonged, and toxic, not to mention the problem of parasite resistance. The development of alternative treatments is justified and polyphenols show promising activity.

OBJECTIVE

The main aim of this mini-review was to analyze the most promising phenolic compounds with reported antileishmanial and antitrypanosomal activity as well as their mechanisms of action.

RESULTS

We found that the mode of action of these natural compounds mainly lignans, neolignans, and flavonoids depends on the organism they act on and includes, macrophage activation, induction of morphological changes such as chromatin condensation, DNA fragmentation, accumulation of acidocalcisomes, and glycosomes, Golgi damage and mitochondrial dysfunction as well as negative regulation of mitochondrial enzymes and other essential enzymes for parasite survival such as arginase. This gives a wide scope for future research towards the rational development of anti-kinetoplastid drugs.

CONCLUSION

Although the specific molecular targets, bioavailability, route of administration, and dosages of some of these natural compounds need to be determined, polyphenols and their combinations represent a very promising and safe strategy to be considered for use against Leishmania spp and Trypanosoma spp. In addition, these compounds may provide a scaffold for developing new, more potent, and more selective antiprotozoal agents.

In Vivo Efficacy of SQ109 against Leishmania donovani, Trypanosoma spp. and Toxoplasma gondii and In Vitro Activity of SQ109 Metabolites

SQ109 is an anti-tubercular drug candidate that has completed Phase IIb/III clinical trials for tuberculosis and has also been shown to exhibit potent in vitro efficacy against protozoan parasites including Leishmania and Trypanosoma cruzi spp. However, its in vivo efficacy against protozoa has not been reported. Here, we evaluated the activity of SQ109 in mouse models of Leishmania, Trypanosoma spp. as well as Toxoplasma infection. In the T. cruzi mouse model, 80% of SQ109-treated mice survived at 40 days post-infection. Even though SQ109 did not cure all mice, these results are of interest since they provide a basis for future testing of combination therapies with the azole posaconazole, which acts synergistically with SQ109 in vitro. We also found that SQ109 inhibited the growth of Toxoplasma gondii in vitro with an IC50 of 1.82 µM and there was an 80% survival in mice treated with SQ109, whereas all untreated animals died 10 days post-infection. Results with Trypanosoma brucei and Leishmania donovani infected mice were not promising with only moderate efficacy. Since SQ109 is known to be extensively metabolized in animals, we investigated the activity in vitro of SQ109 metabolites. Among 16 metabolites, six mono-oxygenated forms were found active across the tested protozoan parasites, and there was a ~6× average decrease in activity of the metabolites as compared to SQ109 which is smaller than the ~25× found with mycobacteria.

Experimental Combination Therapy with Amiodarone and Low-Dose Benznidazole in a Mouse Model of Trypanosoma cruzi Acute Infection

Chagas disease (CD), caused by Trypanosoma cruzi, affects approximately 6 to 7 million people in Latin America, with cardiomyopathy being the clinical manifestation most commonly associated with patient death during the acute phase. The etiological treatment of CD is restricted to benznidazole (Bz) and nifurtimox (Nif), which involve long periods of administration, frequent side effects, and low efficacy in the chronic phase. Thus, combined therapies emerge as an important tool in the treatment of CD, allowing the reduction of Bz dose and treatment duration. In this sense, amiodarone (AMD), the most efficient antiarrhythmic drug currently available and prescribed to CD patients, is a potential candidate for combined treatment due to its known trypanocidal activity. However, the efficacy of AMD during the acute phase of CD and its interaction with Bz or Nif are still unknown. In the present study, using a well-established murine model of the acute phase of CD, we observed that the Bz/AMD combination was more effective in reducing the peak parasitemia than both monotherapy treatments. Additionally, the Bz/AMD combination reduced (i) interleukin-6 (IL-6) levels in cardiac tissue, (ii) P-wave duration, and (iii) frequency of arrhythmia in infected animals and (iv) restored gap junction integrity in cardiac tissue. Therefore, our study validates AMD as a promising candidate for combined therapy with Bz, reinforcing the strategy of combined therapy for CD.

IMPORTANCE Chagas disease affects approximately 6 to 7 million people worldwide, with cardiomyopathy being the clinical manifestation that most commonly leads to patient death. The etiological treatment of Chagas disease is limited to drugs (benznidazole and nifurtimox) with relatively high toxicity and therapeutic failures. In this sense, amiodarone, the most effective currently available antiarrhythmic drug prescribed to patients with Chagas disease, is a potential candidate for combined treatment due to its known trypanocidal effect. In the present study, we show that combined treatment with benznidazole and amiodarone improves the trypanocidal effect and reduces cardiac damage in acutely T. cruzi-infected mice.

(-)-T-Cadinol-a Sesquiterpene Isolated From Casearia sylvestris (Salicaceae)-Displayed In Vitro Activity and Causes Hyperpolarization of the Membrane Potential of Trypanosoma cruzi

Chagas disease is caused by the protozoan parasite Trypanosoma cruzi and affects 6-8 million people worldwide, mainly from developing countries. The treatment is limited to two approved nitro-derivatives, nifurtimox and benznidazole, with several side effects and reduced efficacy. Casearia sylvestris has been used in folk medicine as an antiseptic and cicatrizing in skin diseases. In the present work, the hexane phase from the MeOH extract from the leaves of Casearia sylvestris afforded a fraction composed by the sesquiterpene T-cadinol, which was chemically characterized by NMR and HRMS. The activity of T-cadinol was evaluated against T. cruzi, and IC₅₀ values of 18 (trypomastigotes) and 15 (amastigotes) µM were established. The relation between the mammalian toxicity and the antiparasitic activity resulted in a selectivity index >12. Based on this promising activity, the mechanism of action was investigated by different approaches using fluorescent-based techniques such as plasma membrane permeability, plasma membrane electric potential, mitochondrial membrane electric potential, reactive oxygen species, and the intracellular calcium (Ca²⁺) levels. The obtained results demonstrated that T-cadinol affected neither the parasite plasma membrane nor the electric potential of the membrane. Nevertheless, this compound induced a mitochondrial impairment, resulting in a hyperpolarization of the membrane potential, with decreased levels of reactive oxygen species. No alterations in Ca²⁺ levels were observed, suggesting that T-cadinol may affect the single mitochondria of the parasite. This is the first report about the occurrence of T-cadinol in C. sylvestris, and our data suggest this sesquiterpene as an interesting hit compound for future optimizations in drug discovery studies for Chagas disease.

The antimicrobial and immunomodulatory effects of Ionophores for the treatment of human infection

Ionophores are a diverse class of synthetic and naturally occurring ion transporter compounds which demonstrate both direct and in-direct antimicrobial properties against a broad panel of bacterial, fungal, viral and parasitic pathogens. In addition, ionophores can regulate the host-immune response during communicable and non-communicable disease states. Although the clinical use of ionophores such as Amphotericin B, Bedaquiline and Ivermectin highlight the utility of ionophores in modern medicine, for many other ionophore compounds issues surrounding toxicity, bioavailability or lack of in vivo efficacy studies have hindered clinical development. The antimicrobial and immunomodulating properties of a range of compounds with characteristics of ionophores remain largely unexplored. As such, ionophores remain a latent therapeutic avenue to address both the global burden of antimicrobial resistance, and the unmet clinical need for new antimicrobial therapies. This review will provide an overview of the broad-spectrum antimicrobial and immunomodulatory properties of ionophores, and their potential uses in clinical medicine for combatting infection.

Calcium Signaling Involves Na+/H+ Exchanger and IP3 Receptor Activation in T. cruzi Epimastigotes

The calcium ion (Ca2+) plays a fundamental role in the metabolism and cell physiology of eukaryotic cells. In general, increases in cytosolic Ca2+ may come from both of the extracellular environment through specific channels and/or calcium release from intracellular stores. The mechanism by which the ion calcium (Ca2+) is released from intracellular stores in higher eukaryotes is well known; however, in lower eukaryotes is still a subject of study. In the present work, it was elucidated that Trypanosoma cruzi epimastigotes can release Ca2+ from intracellular stores in response to high osmolarity, in a process involving a protein kinase-regulated Na+/H+ exchanger present in the acidocalsisomes of the parasite. In addition, we demonstrated that epimastigote membranes are able to release Ca2+ in response to exogenous activators of both inositol 1,4,5-triphosphate (IP3) and Ryanodine receptors. Furthermore, we also summarize the involvement of calcium-related signaling pathways in biochemical and morphological changes triggered by hyperosmotic stress in T. cruzi epimastigotes.

Kaempferol-3-O-α-(3,4-di-E-p-coumaroyl)-rhamnopyranoside from Nectandra oppositifolia releases Ca2+ from intracellular pools of Trypanosoma cruzi affecting the bioenergetics system

Phytochemical analysis of EtOH extract from leaves of Nectandra oppositifolia afforded three flavonoids: kaempferol (1), kaempferol-3-O-α-rhamnopyranoside (2) and kaempferol-3-O-α-(3,4-di-E-p-coumaroyl)-rhamnopyranoside (3), which were characterized by NMR and ESI-HRMS. When tested against the protozoan parasite Trypanosoma cruzi, the etiologic agent of Chagas disease, flavonoids 1 and 3 were effective to kill the trypomastigotes with IC₅₀ values of 32.0 and 6.7 μM, respectively, while flavonoid 2 was inactive. Isolated flavonoids 1-3 were also tested in mammalian fibroblasts and showed CC₅₀ values of 24.8, 48.7 and 153.1 μM, respectively. Chemically, these results suggested that the free aglycone plays an important role in the bioactivity while the presence of p-coumaroyl unities linked in the rhamnoside unity is important to enhance the antitrypanosomal activity and reduce the mammalian cytotoxicity. The mechanism of cellular death was investigated for the most potent flavonoid 3 in the trypomastigotes using fluorescent and luminescent-based assays. It indicated that this compound induced neither permeabilization of the plasma membrane nor depolarization of the membrane electric potential. However, early time incubation (20 min) with flavonoid 3 resulted in a constant elevation of the Ca²⁺ levels inside the parasite. This effect was followed by a mitochondrial imbalance, leading to a hyperpolarization and depolarization of the mitochondrial membrane potential, with reduction of the ATP levels. During this time, the levels of reactive oxygen species levels (ROS) were unaltered. The leakage of Ca²⁺ from the intracellular pools can affect the bioenergetics system of T. cruzi, leading to the parasite death. Therefore, flavonoid 3 can be a useful tool for future studies against T. cruzi parasites.

Pan-phylum genome-wide identification of sodium calcium exchangers reveal heterogeneous expansions and possible roles in nematode parasitism

Calcium signaling is ubiquitous in nematode development from fertilization to cell specification to apoptosis. Calcium also regulates dauer entry in Caenorhabditis elegans, which corresponds to the infective stage of parasitic nematodes. In diverse parasites such as Trypanosoma cruzi and Toxoplasma gondii calcium has been shown to regulate host cell entry and egress, and perturbing calcium signaling represents a possible route to inhibit infection and parasitism in these species. Sodium calcium exchangers are considered the most important mechanism of calcium efflux, and our lab has previously characterized the sodium calcium exchanger gene family in C. elegans and studied the diversity of this family across a subset of specific nematode species. Here we build upon these data and explore sodium calcium exchangers across 108 species of nematodes. Our data reveal substantial differences in sodium calcium exchanger counts across the Phylum and detail expansions and contractions of specific exchanger subtypes within certain nematode clades. Finally, we also provide evidence for a role of sodium calcium exchangers in parasite activation by examining differentially expressed genes in non-activated versus activated infective stage larvae. Taken together our findings paint a heterogeneous picture of sodium calcium exchanger evolution across the Phylum Nematoda that may reflect unique adaptations to free-living and parasitic lifestyles.

Interaction With the Extracellular Matrix Triggers Calcium Signaling in Trypanosoma cruzi Prior to Cell Invasion

Trypanosoma cruzi, the etiological agent of Chagas disease in humans, infects a wide variety of vertebrates. Trypomastigotes, the parasite infective forms, invade mammalian cells by a still poorly understood mechanism. Adhesion of tissue culture- derived trypomastigotes to the extracellular matrix (ECM) prior to cell invasion has been shown to be a relevant part of the process. Changes in phosphorylation, S-nitrosylation, and nitration levels of proteins, in the late phase of the interaction (2 h), leading to the reprogramming of both trypomastigotes metabolism and the DNA binding profile of modified histones, were described by our group. Here, the involvement of calcium signaling at a very early phase of parasite interaction with ECM is described. Increments in the intracellular calcium concentrations during trypomastigotes-ECM interaction depends on the Ca²⁺ uptake from the extracellular medium, since it is inhibited by EGTA or Nifedipine, an inhibitor of the L-type voltage gated Ca²⁺ channels and sphingosine-dependent plasma membrane Ca²⁺ channel, but not by Vanadate, an inhibitor of the plasma membrane Ca²⁺-ATPase. Furthermore, Nifedipine inhibits the invasion of host cells by tissue culture- derived trypomastigotes in a dose-dependent manner, reaching 95% inhibition at 100 µM Nifedipine. These data indicate the importance of both Ca²⁺ uptake from the medium and parasite-ECM interaction for host-cell invasion. Previous treatment of ECM with protease abolishes the Ca²⁺ uptake, further reinforcing the possibility that these events may be connected. The mitochondrion plays a relevant role in Ca²⁺ homeostasis in trypomastigotes during their interaction with ECM, as shown by the increment of the intracellular Ca²⁺ concentration in the presence of Antimycin A, in contrast to other calcium homeostasis disruptors, such as Cyclopiazonic acid for endoplasmic reticulum and Bafilomycin A for acidocalcisome. Total phosphatase activity in the parasite decreases in the presence of Nifedipine, EGTA, and Okadaic acid, implying a role of calcium in the phosphorylation level of proteins that are interacting with the ECM in tissue culture- derived trypomastigotes. In summary, we describe here the increment of Ca²⁺ at an early phase of the trypomastigotes interaction with ECM, implicating both nifedipine-sensitive Ca²⁺ channels in the influx of Ca²⁺ and the mitochondrion as the relevant organelle in Ca²⁺ homeostasis. The data unravel a complex sequence of events prior to host cell invasion itself.

A store-operated Ca2+-entry in Trypanosoma equiperdum: Physiological evidences of its presence

The Trypanosomatidae family encompasses many unicellular organisms responsible of several tropical diseases that affect humans and animals. Livestock tripanosomosis caused by Trypanosoma brucei brucei (T. brucei), Trypanosoma equiperdum (T. equiperdum) and Trypanosoma evansi (T. evansi), have a significant socio-economic impact and limit animal protein productivity throughout the intertropical zones of the world. Similarly, to all organisms, the maintenance of Ca²⁺ homeostasis is vital for these parasites, and the mechanism involved in the intracellular Ca²⁺ regulation have been widely described. However, the evidences related to the mechanisms responsible for the Ca²⁺ entry are scarce. Even more, to date the presence of a store-operated Ca²⁺ channel (SOC) has not been reported. Despite the apparent absence of Orai and STIM-like proteins in these parasites, in the present work we demonstrate the presence of a store-operated Ca²⁺-entry (SOCE) in T. equiperdum, using physiological techniques. This Ca²⁺-entry is induced by thapsigargin (TG) and 2,5-di-t-butyl-1,4-benzohydroquinone (BHQ), and inhibited by 2-aminoethoxydiphenyl borate (2APB). Additionally, the use of bioinformatics techniques allowed us to identify putative transient receptor potential (TRP) channels, present in members of the Trypanozoon family, which would be possible candidates responsible for the SOCE described in the present work in T. equiperdum.

The Rationale for Use of Amiodarone and its Derivatives for the Treatment of Chagas' Disease and Leishmaniasis

The repurposing or repositioning of previously-approved drugs has become an accepted strategy for the expansion of the pharmacopeia for neglected diseases. Accordingly, amiodarone, an inexpensive and extensively- used class III antiarrhythmic has been proposed as a treatment for Chagas' disease and leishmaniasis. Amiodarone has a potent trypanocidal and leishmanicidal action, mainly acting through the disruption of parasite intracellular Ca²⁺ homeostasis, which is a recognized target of different drugs that have activity against trypanosomatids. Amiodarone collapses the mitochondrial electrochemical potential (Δφm) and induces the rapid alkalinization of parasite acidocalcisomes, driving a large increase in the intracellular Ca²⁺ concentration. Amiodarone also inhibits oxidosqualene cyclase activity, a key enzyme in the ergosterol synthesis pathway that is essential for trypanosomatid survival. In combination, these three effects lead to parasite death. Dronedarone, a drug synthesized to minimize some of the adverse effects of amiodarone, displays trypanocidal and leishmanicidal activity through the same mechanisms, but curiously, being more potent on Leishmaniasis than its predecessor. In vitro studies suggest that other recently-synthesized benzofuran derivatives can act through the same mechanisms, and produce similar effects on different trypanosomatid species. Recently, the combination of amiodarone and itraconazole has been used successfully to treat 121 dogs naturally-infected by T. cruzi, strongly supporting the potential therapeutic use of this combination against human trypanosomatid infections.

Antitrypanosomal Lactones from Nectandra barbellata

Twigs of Nectandra barbellata were extracted using a solution of the ionic liquid 1-butyl-3-methylimidazolium bromide (BMImBr) in H₂O, assisted by microwave (MAE). After successive chromatographic steps, one sesquiterpene, costic acid, and three new related lactones, (R)-3(7)-Z-3-hexadec-21-enylidene-5-(hydroxymethyl)tetrahydrofuran-2-one (1), (R)-3(7)-Z-3-hexadecylidene-5-(hydroxymethyl)tetrahydrofuran-2-one (2), and (R)-3(7)-Z-3-docosylidene-5-(hydroxymethyl)tetrahydrofuran-2-one (3), were isolated. After structural elucidation using IR, UV, HRESIMS, NMR, ECD, and VCD, compounds 1-3 were tested against trypomastigote forms of Trypanosoma cruzi. The mechanism of action of bioactive isolated compounds was studied using different fluorescent-based approaches to investigate alterations of the plasma membrane, permeability/electric potential (ΔΨ_p), reactive oxygen species levels, mitochondria (electric membrane potential, ΔΨ_m/ATP levels), Ca²⁺ levels, and pH of the acidocalcisomes. In addition, in silico studies predicted no resemblance to pan assay interference compounds (PAINS).

Melittin as a promising anti-protozoan peptide: current knowledge and future prospects

Protozoan diseases such as malaria, leishmaniasis, Chagas disease, and sleeping sickness still levy a heavy toll on human lives. Deplorably, only few classes of anti-protozoan drugs have thus far been developed. The problem is further compounded by their intrinsic toxicity, emergence of drug resistance, and the lack of licensed vaccines. Thus, there is a genuine exigency to develop novel anti-protozoan medications. Over the past years, melittin, the major constituent in the venom of European honeybee Apis mellifera, has gathered the attention of researchers due to its potential therapeutic applications. Insofar as we are aware, there has been no review pertinent to anti-protozoan properties of melittin. The present review outlines the current knowledge about anti-protozoan effects of melittin and its underlying mechanisms. The peptide has proven to be efficacious in killing different protozoan parasites such as Leishmania, Plasmodium, Toxoplasma, and Trypanosoma in vitro. Apart from direct membrane-disruptive activity, melittin is capable of destabilizing calcium homeostasis, reducing mitochondrial membrane potential, disorganizing kinetoplast DNA, instigating apoptotic cell death, and induction of autophagy in protozoan pathogens. Emerging evidence suggests that melittin is a promising candidate for future vaccine adjuvants. Transmission-blocking activity of melittin against vector-borne pathogens underscores its potential utility for both transgenic and paratransgenic manipulations. Nevertheless, future research should focus upon investigating anti-microbial activities of melittin, alone or in combination with the current anti-protozoan medications, against a far broader spectrum of protozoan parasites as well as pre-clinical testing of the peptide in animal models.

The emerging paradigm of calcium homeostasis as a new therapeutic target for protozoan parasites

Calcium channels (CCs), a group of ubiquitously expressed membrane proteins, are involved in many pathophysiological processes of protozoan parasites. Our understanding of CCs in cell signaling, organelle function, cellular homeostasis, and cell cycle control has led to improved insights into their structure and functions. In this article, we discuss CCs characteristics of five major protozoan parasites Plasmodium, Leishmania, Toxoplasma, Trypanosoma, and Cryptosporidium. We provide a comprehensive review of current antiparasitic drugs and the potential of using CCs as new therapeutic targets. Interestingly, previous studies have demonstrated that human CC modulators can kill or sensitize parasites to antiparasitic drugs. Still, none of the parasite CCs, pumps, or transporters has been validated as drug targets. Information for this review draws from extensive data mining of genome sequences, chemical library screenings, and drug design studies. Parasitic resistance to currently approved therapeutics is a serious and emerging threat to both disease control and management efforts. In this article, we suggest that the disruption of calcium homeostasis may be an effective approach to develop new anti-parasite drug candidates and reduce parasite resistance.

Review on Experimental Treatment Strategies Against Trypanosoma cruzi

Chagas disease is a neglected tropical disease caused by the protozoan Trypanosoma cruzi. Currently, only nitroheterocyclic nifurtimox (NFX) and benznidazole (BNZ) are available for the treatment of Chagas disease, with limitations such as variable efficacy, long treatment regimens and toxicity. Different strategies have been used to discover new active molecules for the treatment of Chagas disease. Target-based and phenotypic screening led to thousands of compounds with anti-T. cruzi activity, notably the nitroheterocyclic compounds, fexinidazole and its metabolites. In addition, drug repurposing, drug combinations, re-dosing regimens and the development of new formulations have been evaluated. The CYP51 antifungal azoles, as posaconazole, ravuconazole and its prodrug fosravuconazole presented promising results in experimental Chagas disease. Drug combinations of nitroheterocyclic and azoles were able to induce cure in murine infection. New treatment schemes using BNZ showed efficacy in the experimental chronic stage, including against dormant forms of T. cruzi. And finally, sesquiterpene lactone formulated in nanocarriers displayed outstanding efficacy against different strains of T. cruzi, susceptible or resistant to BNZ, the reference drug. These pre-clinical results are encouraging and provide interesting evidence to improve the treatment of patients with Chagas disease.

Identification of Trypanosoma cruzi Growth Inhibitors with Activity In Vivo within a Collection of Licensed Drugs

Chagas disease, caused by the parasite Trypanosoma cruzi (T. cruzi), affects more than six million people worldwide, with its greatest burden in Latin America. Available treatments present frequent toxicity and variable efficacy at the chronic phase of the infection, when the disease is usually diagnosed. Hence, development of new therapeutic strategies is urgent. Repositioning of licensed drugs stands as an attractive fast-track low-cost approach for the identification of safer and more effective chemotherapies. With this purpose we screened 32 licensed drugs for different indications against T. cruzi. We used a primary in vitro assay of Vero cells infection by T. cruzi. Five drugs showed potent activity rates against it (IC₅₀ < 4 µmol L⁻¹), which were also specific (selectivity index >15) with respect to host cells. T. cruzi inhibitory activity of four of them was confirmed by a secondary anti-parasitic assay based on NIH-3T3 cells. Then, we assessed toxicity to human HepG2 cells and anti-amastigote specific activity of those drugs progressed. Ultimately, atovaquone-proguanil, miltefosine, and verapamil were tested in a mouse model of acute T. cruzi infection. Miltefosine performance in vitro and in vivo encourages further investigating its use against T. cruzi.

Bioenergetics impairment of Trypanosoma cruzi by the antihypertensive manidipine: A drug repurposing strategy

Considering the lack of effective and safe therapy for the treatment of Chagas disease, the antihypertensive drug manidipine (MDP) was in vitro evaluated against Trypanosoma cruzi. The bioenergetics of trypomastigotes was studied in the presence of the drug using fluorimetric and luminescent assays. Manidipine showed a potent antiparasitic activity, with IC₅₀ values of 0.1 μM (intracellular amastigotes) and 3 μM (trypomastigotes), resulting in a promising selectivity index against the amastigotes (>1459). Using fluorimetric analysis, the drug showed depolarisation of the electric potential of the plasma membrane with no alteration of the permeability. A decrease in ATP levels suggested a bioenergetic alteration of the mitochondria, which was confirmed by the depolarisation of the mitochondrial membrane potential and a slight increase of the ROS levels. This is the first study to show the promising in vitro effectiveness of the antihypertensive MDP against T. cruzi, which may represent a candidate for future investigations in animal models.

Role of anti-filarial drugs in inducing ER stress mediated signaling in bovine filarial parasitosis Setaria cervi

In this ex vivo study, S. cervi parasitoses were treated with Ivermectin (50 μM), Albendazole (200 μM) alone and Ivermectin + Albendazole (50 + 200 μM) at 37°C for 8 h and the motility and viability of the parasitoses were evaluated. Individually both drugs Ivermectin (Iver) and Albendazole (Alb) are reported to affect the function and integrity of ER, however till date, no reports are available on the functional changes in ER due to a combined Iver and Alb treatment of bovine helminth parasitosis. Here, we report the lethal effect of a combination treatment of Iver and Alb against adult bovine filarial parasitosis Setaria cervi. The underlying mechanism of drug action was elucidated by performing a systematic biochemical, molecular and proteomics based study. Altered calcium homeostasis in drug treated parasitoses lead to reduction in levels of total Endoplasmic Reticulum (ER) calcium by 50 % and 61 % and elevation by 50 % and 63 % in cytosol in Iver alone and Iver + Alb treated parasitoses respectively. Further, it was found that upregulated expression of ER localized GRP94, galactosyltransferase and glycosyltransferase activity in addition to reduction in activity of PDI indicated ER stress mechanisms being operative under combined drug treatment. Marked rise of 79 % reactive oxygen species and reduced antioxidant levels induced oxidative stress in drug treated parasitosis. The collective effect of both ER and oxidative stress might have triggered apoptosis, as evidenced by the elevated calpain activity, reduction of 67 % in cytochrome c oxidase and 83 % rise in caspase-3 activity in the Iver + Alb treated parasitoses respectively. The ER proteome analysis by 2D gel electrophoresis revealed 76 spots in the control and 56 spots in the treated proteome. A MALDI-MS/MS analysis of some of the differentially expressed spots of the combination drug treated parasitoses identified glucuronosyltransferase as a major upregulated protein with a fold change of 1.81. Trafficking protein, acyl transferase, MATH involved in protein folding were also found to be downregulated. Thus, this study based on biochemical and proteomic approaches indicates that a combination of anti-filarial drugs Iver and Alb can alter calcium homeostasis in bovine filarial parasitosis leading to induction of ER stress culminating into apoptosis.

Trypanosoma cruzi Modulates PIWI-Interacting RNA Expression in Primary Human Cardiac Myocytes during the Early Phase of Infection

Trypanosoma cruzi dysregulates the gene expression profile of primary human cardiomyocytes (PHCM) during the early phase of infection through a mechanism which remains to be elucidated. The role that small non-coding RNAs (sncRNA) including PIWI-interacting RNA (piRNA) play in regulating gene expression during the early phase of infection is unknown. To understand how T. cruzi dysregulate gene expression in the heart, we challenged PHCM with T. cruzi trypomastigotes and analyzed sncRNA, especially piRNA, by RNA-sequencing. The parasite induced significant differential expression of host piRNAs, which can target and regulate the genes which are important during the early infection phase. An average of 21,595,866 (88.40%) of clean reads mapped to the human reference genome. The parasite induced 217 unique piRNAs that were significantly differentially expressed (q ≥ 0.8). Of these differentially expressed piRNAs, 6 were known and 211 were novel piRNAs. In silico analysis showed that some of the dysregulated known and novel piRNAs could target and potentially regulate the expression of genes including NFATC2, FOS and TGF-β1, reported to play important roles during T. cruzi infection. Further evaluation of the specific functions of the piRNAs in the regulation of gene expression during the early phase of infection will enhance our understanding of the molecular mechanism of T. cruzi pathogenesis. Our novel findings constitute the first report that T. cruzi can induce differential expression of piRNAs in PHCM, advancing our knowledge about the involvement of piRNAs in an infectious disease model, which can be exploited for biomarker and therapeutic development.

Determination of Intracellular Ca2+ Concentration in the Human Pathogens Trypanosomatids Leishmania mexicana and Trypanosoma cruzi by the Use of the Fluorescent Ca2+ Indicator Fura-2

Ca²⁺ is an essential signaling messenger in all eukariotic cells, playing a pivotal role in many cellular functions as cell growth control (differentiation, fertilization and apoptosis), secretion, gene expression, enzyme regulation, among many others. This basic premise includes trypanosomatids as Trypanosoma cruzi and various species of Leishmania, the causative agents of Chagas disease and leishmaniasis respectively, where intracellular Ca²⁺ concentration ([Ca²⁺]_i) has been demonstrated to be finely regulated. Nevertheless [Ca²⁺]_i has been difficult to measure because of its very low cytoplasmic concentration (typically around 50-100 nM), when compared to the large concentration in the outside milieu (around 2 mM in blood). The development of intracellular fluorescent Ca²⁺-sensitive indicators has been of paramount importance to achieve this goal. The success was based on the synthesis of acetoximethylated derivative precursors, which allow the fluorescent molecules typically composed of many hydrophilic carboxyl groups responsible for its high affinity Ca²⁺-binding (and therefore very hydrophilic), to easily cross the plasma membrane. Once in the cell interior, unspecific esterases split the hydrophobic moiety from the fluorescent backbone structure, releasing the carboxyl groups, transforming it in turn to the acid form of the molecule, which remain trapped in the cytoplasm and regain its ability to fluoresce in a Ca²⁺-dependent manner. Among them, Fura-2 is by far the most used, because it is a ratiometric (two different wavelength excitation and one emission) Ca²⁺ indicator with a Ca²⁺ affinity compatible with the [Ca²⁺]_i. This protocol essentially consists in loading exponential phase parasites with Fura-2 and recording changes in [Ca²⁺]_i by mean of a double wavelength spectrofluorometer. This technique allows the acquisition of valuable information about [Ca²⁺]_i changes in real time, as a consequence of diverse stimuli or changes in conditions, as addition of drugs or different natural modulators.

Ethanolic Extract of the Fungus Trichoderma asperelloides Induces Ultrastructural Effects and Death on Leishmania amazonensis

The Trichoderma genus comprises several species of fungi whose diversity of secondary metabolites represents a source of potential molecules with medical application. Because of increased pathogen resistance and demand for lower production costs, the search for new pharmacologically active molecules effective against pathogens has become more intense. This is particularly evident in the case of American cutaneous leishmaniasis due to the high toxicity of current treatments, parenteral administration, and increasing rate of refractory cases. We have previously shown that a fungus from genus Trichoderma can be used for treating cerebral malaria in mouse models and inhibit biofilm formation. Here, we evaluated the effect of the ethanolic extract of Trichoderma asperelloides (Ext-Ta) and its fractions on promastigotes and amastigotes of Leishmania amazonensis, a major causative agent of cutaneous leishmaniasis in the New World. Ext-Ta displayed leishmanicidal action on L. amazonensis parasites, and its pharmacological activity was associated with the low-molecular-weight fraction (LMWF) of Ext-Ta. Ultrastructural analysis demonstrated morphological alterations in the mitochondria and the flagellar pocket of promastigotes, with increased lipid body and acidocalcisome formation, microtubule disorganization of the cytoplasm, and intense vacuolization of the cytoplasm when amastigotes were present. We suggest the antiparasitic activity of Trichoderma fungi as a promising tool for developing chemotherapeutic leishmanicidal agents.