Cell death in parasitic protozoa: regulated or incidental?

The function of the ATG8 in the cilia and cortical microtubule maintenance of Euplotes amieti

Autophagy regulates the formation of primary cilia, which in turn affects autophagy. The relationship between autophagy and cilia is known to be bidirectional although the specific mechanisms involved have yet to be elucidated. In this study, we found for the first time that ATG8 protein localizes in the basal body of the dorsal kineties and the base of the ventral cirri in Euplotes amieti. ATG8 protein maintains the structural integrity of cilia and plays a role in the construction of the cortical ciliature and microtubule cytoskeleton associated with cilia. ATG8 gene interference leads to the degradation of IFT88, the transport protein in cilia, thus inhibiting the generation of cilia, and affecting the swing of cilia. This influences the swimming speed and cilia pattern, leading to death in Euplotes amieti.

4-Quinolinylhydrazone analogues kill Leishmania (Leishmania) amazonensis by inducing apoptosis and mitochondria-dependent pathway cell death

Despite efforts, available alternatives for the treatment of leishmaniasis are still scarce. In this work we tested a class of 15 quinolinylhydrazone analogues and presented data that support the use of the most active compound in cutaneous leishmaniasis caused by Leishmania amazonensis. In general, the compounds showed activity at low concentrations for both parasitic forms (5.33-37.04 μM to promastigotes, and 14.31-61.98 μM to amastigotes). In addition, the best compound (MHZ15) is highly selective for the parasite. Biochemical studies indicate that the treatment of promastigotes with MHZ15 leads the loss of mitochondrial potential and increase in ROS levels as the primary effects, which triggers accumulation of lipid droplets, loss of plasma membrane integrity and apoptosis hallmarks, including DNA fragmentation and phosphatidylserine exposure. These effects were similar in the intracellular form of the parasite. However, in this parasitic form there is no change in plasma membrane integrity in the observed treatment time, which can be attributed to metabolic differences and the resilience of the amastigote. Also, ultrastructural changes such as vacuolization suggesting autophagy were observed. The in vivo effectiveness of MHZ15 in the experimental model of cutaneous leishmaniasis was carried out in mice of the BALB/c strain infected with L. amazonensis. The treatment by intralesional route showed that MHZ15 acted with great efficiency with significantly reduction in the parasite load in the injured paws and draining lymph nodes, without clinical signs of distress or compromise of animal welfare. In vivo toxicity was also evaluated and null alterations in the levels of hepatic enzymes aspartate aminotransferase, and alanine aminotransferase was observed. The data presented herein demonstrates that MHZ15 exhibits a range of favorable characteristics conducive to the development of an antileishmanial agent.

Triethyl phosphine decorated cerium oxide nanoparticles exhibit selective killing of the unicellular protozoan parasite Leishmania donovani

Globally, Leishmaniasis affects underprivileged communities of the nations and chemotherapy remains one of the preferred treatment options. However, the cytotoxicity, side effects, and cost of the present chemotherapies limit their utilization. Auranofin [an organogold compound having significant structural similarity with triethyl-phosphine (TEP)] has been reported as an effective therapy for Leishmaniasis treatment. Considering the high cost of gold and the strong affinity of cerium oxide nanoparticles (CeNPs) to phosphine ligands, we designed TEP-decorated CeNPs (CeNPs-TEP) and used them as a novel antileishmanial agent. The hydrodynamic size of synthesized CeNPs and CeNPs-TEP was observed to be 22.2 ± 3.7 nm and 92.11 ± 6.2 nm, respectively. CeNPs-TEP provided aqueous stability to TEP as TEP alone is extremely unstable in water. Exposure of CeNPs-TEP showed ~ 60 and ~ 82% cell death in Leishmania donovani Ag83 promastigotes after 24 and 48 h, respectively. The same concentration of CeNPs-TEP did not affect the cellular viability of RAW 264.7 macrophage cells significantly. The oxidative stress and depolarization of the mitochondrial membrane were also observed after the treatment of CeNPs-TEP. Exposure of CeNPs-TEP induced a ~ 2.2-fold increase in ROS generation inside Leishmania donovani Ag83 cells. Dual staining with ethidium bromide and acridine orange reveals that these processes ultimately result in cell death. The results conclude that a combination of CeNPs and TEP could open the door for developing novel antileishmanial therapeutics in the future.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03813-7.

Repurposing of Nitroxoline as an Alternative Primary Amoebic Meningoencephalitis Treatment

Among the pathogenic free-living amoebae (FLA), Naegleria fowleri is the etiological agent of a fatal disease known as primary amoebic meningoencephalitis (PAM). Once infection begins, the lesions generated in the central nervous system (CNS) result in the onset of symptoms leading to death in a short period of time. Currently, there is no standardized treatment against the infection, which, due to the high virulence of the parasite, results in a high case fatality rate (>97%). Therefore, it is essential to search for new therapeutic sources that can generate a rapid elimination of the parasite. In recent years, there have already been several successful examples of drug repurposing, such as Nitroxoline, for which, in addition to its known bioactive properties, anti-Balamuthia activity has recently been described. Following this approach, the anti-Naegleria activity of Nitroxoline was tested. Nitroxoline displayed low micromolar activity against two different strains of N. fowleri trophozoites (IC50 values of 1.63 ± 0.37 µM and 1.17 ± 0.21 µM) and against cyst stages (IC50 of 1.26 ± 0.42 μM). The potent anti-parasitic activity compared to the toxicity produced (selectivity index of 3.78 and 5.25, respectively) in murine macrophages and human cell lines (reported in previous studies), together with the induction of programmed cell death (PCD)-related events in N. fowleri make Nitroxoline a great candidate for an alternative PAM treatment.

Perillaldehyde Functions as a Potential Antifungal Agent by Triggering Metacaspase-Independent Apoptosis in Botrytis cinerea

Botrytis cinerea, the causal agent of gray mold, is an important plant pathogen causing preharvest and postharvest diseases. Due to the extensive use of commercial fungicides, fungicide-resistant strains have emerged. Natural compounds with antifungal properties are widely present in various kinds of organisms. Perillaldehyde (PA), derived from the plant species Perilla frutescens, is generally recognized as a potent antimicrobial substance and to be safe to humans and the environment. In this study, we demonstrated that PA could significantly inhibit the mycelial growth of B. cinerea and reduced its pathogenicity on tomato leaves. We also found that PA had a significant protective effect on tomato, grape, and strawberry. The antifungal mechanism of PA was investigated by measuring the reactive oxygen species (ROS) accumulation, the intracellular Ca2+ level, the mitochondrial membrane potential, DNA fragmentation, and phosphatidylserine exposure. Further analyses revealed that PA promoted protein ubiquitination and induced autophagic activities and then triggered protein degradation. When the two metacaspase genes, BcMca1 and BcMca2, were knocked out from B. cinerea, all mutants did not exhibit reduced sensitivity to PA. These findings demonstrated that PA could induce metacaspase-independent apoptosis in B. cinerea. Based on our results, we proposed that PA could be used as an effective control agent for gray mold management. IMPORTANCE Botrytis cinerea causes gray mold disease, is considered one of the most important dangerous pathogens worldwide, and leads to severe economic losses worldwide. Due to the lack of resistant varieties of B. cinerea, gray mold control has mainly relied on application of synthetic fungicides. However, long-term and extensive use of synthetic fungicides has increased fungicide resistance in B. cinerea and is harmful to humans and the environment. In this study, we found that perillaldehyde has a significant protective effect on tomato, grape, and strawberry. We further characterized the antifungal mechanism of PA on B. cinerea. Our results indicated that PA induced apoptosis that was independent of metacaspase function.

The concepts and origins of cell mortality

Organismal death is foundational to the evolution of life, and many biological concepts such as natural selection and life history strategy are so fashioned only because individuals are mortal. Organisms, irrespective of their organization, are composed of basic functional units-cells-and it is our understanding of cell death that lies at the heart of most general explanatory frameworks for organismal mortality. Cell death can be exogenous, arising from transmissible diseases, predation, or other misfortunes, but there are also endogenous forms of death that are sometimes the result of adaptive evolution. These endogenous forms of death-often labeled programmed cell death, PCD-originated in the earliest cells and are maintained across the tree of life. Here, we consider two problematic issues related to PCD (and cell mortality generally). First, we trace the original discoveries of cell death from the nineteenth century and place current conceptions of PCD in their historical context. Revisions of our understanding of PCD demand a reassessment of its origin. Our second aim is thus to structure the proposed origin explanations of PCD into coherent arguments. In our analysis we argue for the evolutionary concept of PCD and the viral defense-immunity hypothesis for the origin of PCD. We suggest that this framework offers a plausible account of PCD early in the history of life, and also provides an epistemic basis for the future development of a general evolutionary account of mortality.

In vitro effects of lapachol and β-lapachone against Leishmania amazonensis

Leishmaniasis is a neglected disease that affects millions of people worldwide, and special attention should be given to treatment because the available drugs have limitations, which can lead to low therapeutic adherence and parasitic resistance. This study evaluated the activity of the bioactive naphthoquinones, lapachol and β-lapachone, against Leishmania amazonensis. The cell alterations were evaluated in vitro on promastigote and amastigote forms. The lethal dose (LD50) at 24, 48, and 72 h on the promastigote's forms using lapachol was 75.60, 72.82, and 58.85 μg/mL and for β-lapachone was 0.65, 1.24, and 0.71 μg/mL, respectively. The naphthoquinones significantly inhibited the survival rate of L. amazonensis amastigotes at 83.11, 57.59, and 34.95% for lapachol (82.28, 41.14, and 20.57 µg/mL), and 78.49, 83.25, and 80.22% for β-lapachone (3.26, 1.63, and 0.815 µg/mL). The compounds on the promastigote's forms led to the loss of mitochondrial membrane potential, induced changes in the integrity of the membrane, caused damage to cells suggestive of the apoptotic process, and showed inhibition of tumor necrosis factor (TNF)-α and interleukin (IL)-6 production. The results showed that these naphthoquinones are promising candidates for research on new drugs with anti-Leishmania activity derived from natural products.

Leishmaniasis: Immune Cells Crosstalk in Macrophage Polarization

Leishmaniasis is a complex infectious parasitic disease caused by protozoa of the genus Leishmania, belonging to a group of neglected tropical diseases. It establishes significant global health challenges, particularly in socio-economically disadvantaged regions. Macrophages, as innate immune cells, play a crucial role in initiating the inflammatory response against the pathogens responsible for this disease. Macrophage polarization, the process of differentiating macrophages into pro-inflammatory (M1) or anti-inflammatory (M2) phenotypes, is essential for the immune response in leishmaniasis. The M1 phenotype is associated with resistance to Leishmania infection, while the M2 phenotype is predominant in susceptible environments. Notably, various immune cells, including T cells, play a significant role in modulating macrophage polarization by releasing cytokines that influence macrophage maturation and function. Furthermore, other immune cells can also impact macrophage polarization in a T-cell-independent manner. Therefore, this review comprehensively examines macrophage polarization's role in leishmaniasis and other immune cells' potential involvement in this intricate process.

Cyanomethyl Vinyl Ethers Against Naegleria fowleri

Naegleria fowleri is a pathogenic amoeba that causes a fulminant and rapidly progressive disease affecting the central nervous system called primary amoebic meningoencephalitis (PAM). Moreover, the disease is fatal in more than 97% of the reported cases, mostly affecting children and young people after practicing aquatic activities in nontreated fresh and warm water bodies contaminated with these amoebae. Currently, the treatment of primary amoebic meningoencephalitis is based on a combination of different antibiotics and antifungals, which are not entirely effective and lead to numerous side effects. In the recent years, research against PAM is focused on the search of novel, less toxic, and fully effective antiamoebic agents. Previous studies have reported the activity of cyano-substituted molecules in different protozoa. Therefore, the activity of 46 novel synthetic cyanomethyl vinyl ethers (QOET-51 to QOET-96) against two type strains of N. fowleri (ATCC 30808 and ATCC 30215) was determined. The data showed that QOET-51, QOET-59, QOET-64, QOET-67, QOET-72, QOET-77, and QOET-79 were the most active molecules. In fact, the selectivity index (CC₅₀/IC₅₀) was sixfold higher when compared to the activities of the drugs of reference. In addition, the mechanism of action of these compounds was studied, with the aim to demonstrate the induction of a programmed cell death process in N. fowleri.

Transcriptome profile of halofuginone resistant and sensitive strains of Eimeria tenella

The antiparasitic drug halofuginone is important for controlling apicomplexan parasites. However, the occurrence of halofuginone resistance is a major obstacle for it to the treatment of apicomplexan parasites. Current studies have identified the molecular marker and drug resistance mechanisms of halofuginone in Plasmodium falciparum. In this study, we tried to use transcriptomic data to explore resistance mechanisms of halofuginone in apicomplexan parasites of the genus Eimeria (Apicomplexa: Eimeriidae). After halofuginone treatment of E. tenella parasites, transcriptome analysis was performed using samples derived from both resistant and sensitive strains. In the sensitive group, DEGs associated with enzymes were significantly downregulated, whereas the DNA damaging process was upregulated after halofuginone treatment, revealing the mechanism of halofuginone-induced parasite death. In addition, 1,325 differentially expressed genes (DEGs) were detected between halofuginone resistant and sensitive strains, and the DEGs related to translation were significantly downregulated after halofuginone induction. Overall, our results provide a gene expression profile for further studies on the mechanism of halofuginone resistance in E. tenella.

Autophagy in protists and their hosts: When, how and why?

Pathogenic protists are a group of organisms responsible for causing a variety of human diseases including malaria, sleeping sickness, Chagas disease, leishmaniasis, and toxoplasmosis, among others. These diseases, which affect more than one billion people globally, mainly the poorest populations, are characterized by severe chronic stages and the lack of effective antiparasitic treatment. Parasitic protists display complex life-cycles and go through different cellular transformations in order to adapt to the different hosts they live in. Autophagy, a highly conserved cellular degradation process, has emerged as a key mechanism required for these differentiation processes, as well as other functions that are crucial to parasite fitness. In contrast to yeasts and mammals, protist autophagy is characterized by a modest number of conserved autophagy-related proteins (ATGs) that, even though, can drive the autophagosome formation and degradation. In addition, during their intracellular cycle, the interaction of these pathogens with the host autophagy system plays a crucial role resulting in a beneficial or harmful effect that is important for the outcome of the infection. In this review, we summarize the current state of knowledge on autophagy and other related mechanisms in pathogenic protists and their hosts. We sought to emphasize when, how, and why this process takes place, and the effects it may have on the parasitic cycle. A better understanding of the significance of autophagy for the protist life-cycle will potentially be helpful to design novel anti-parasitic strategies.

Silver and copper-benznidazole derivatives as potential antiparasitic metallodrugs: Synthesis, characterization, and biological evaluation

Currently the only drug available to treat Chagas disease in Brazil is benznidazole (BZN). Therefore, there is an urgent need to discover and develop new anti- Trypanosoma cruzi candidates. In our continuous effort to enhance clinical antiparasitic drugs using synergistic strategy, BZN was coordinated to silver and copper ions to enhance its effectiveness to treat that illness. In this work, the syntheses of four novel metal-BZN complexes, [Ag(BZN)₂]NO₃·H₂O (1), [CuCl₂(BZN)(H₂O)]·1/2CH₃CN (2), [Ag(PPh₃)₂(BZN)₂]NO₃·H₂O (3), and [Cu(PPh₃)₂(BNZ)₂]NO₃·2H₂O (4), and their characterization using multiple analytical and spectroscopic techniques such as Infrared (FTIR), Nuclear Magnetic Resonance (¹H, ¹³C, ³¹P), UV-Visible (UV-Vis), Electron Paramagnetic Resonance (EPR), conductivity and elemental analysis are described. IC₅₀ (Half-maximal inhibitory concentration) values of Ag-BZN compounds are about five to ten times lower than benznidazole itself in both proliferation stages of the parasite (epimastigotes and amastigotes). The cytotoxicity of both compounds in human cells (fibroblasts and hepatocytes) are comparable to BZN, indicating that Ag-BZN complexes can be more selective than BZN.

Current Landscape of Methods to Evaluate Antimicrobial Activity of Natural Extracts

Natural extracts have been and continue to be used to treat a wide range of medical conditions, from infectious diseases to cancer, based on their convenience and therapeutic potential. Natural products derived from microbes, plants, and animals offer a broad variety of molecules and chemical compounds. Natural products are not only one of the most important sources for innovative drug development for animal and human health, but they are also an inspiration for synthetic biology and chemistry scientists towards the discovery of new bioactive compounds and pharmaceuticals. This is particularly relevant in the current context, where antimicrobial resistance has risen as a global health problem. Thus, efforts are being directed toward studying natural compounds' chemical composition and bioactive potential to generate drugs with better efficacy and lower toxicity than existing molecules. Currently, a wide range of methodologies are used to analyze the in vitro activity of natural extracts to determine their suitability as antimicrobial agents. Despite traditional technologies being the most employed, technological advances have contributed to the implementation of methods able to circumvent issues related to analysis capacity, time, sensitivity, and reproducibility. This review produces an updated analysis of the conventional and current methods to evaluate the antimicrobial activity of natural compounds.

Withaferin A-silyl ether analogs as potential anti-kinetoplastid agents targeting the programmed cell death

Current therapies of leishmaniasis and Chagas disease, two of the most widespread neglected tropical diseases, have limited efficacy and toxic side effects. In this regard, natural products play an important role in overcoming the current need for new antiparasitic agents. The present study reports the leishmanicidal and trypanocidal activities of twenty-four known silyl-ether derivatives of withaferin A. Eleven compounds from this series (4, 7, 8, 10, 12, 15, 17, 18, 20, 22 and 25) showed a potent dose-dependent inhibitory effect on the proliferation of Leishmania amazonensis promastigotes and Trypanosoma cruzi epimastigotes respectively, even higher than the references drugs, miltefosine and benznidazole. Among them, the most promising compound, derivative 10, exhibited approximately 34-fold higher leishmanicidal activity and 49-fold higher trypanocidal activity compared to the reference drugs, as well as lower cytotoxicity. Moreover, compounds 4, 7, 10, 12 and 15 were more active than the reference drugs against the amastigote forms of L. amazonensis, presenting a high selectivity index. Assays performed to study the ATP levels, mitochondrial membrane potential, plasma membrane permeability, chromatin condensation, reactive oxygen species and autophagy indicated that these withaferin A-silyl analogs appear to induce events characteristic of apoptosis-like and also autophagy leading to programmed cell death. These findings support the therapeutic potential of withaferin A-related steroids as anti-Leishmania and Trypanosoma agents.

Dinuclear and mononuclear metal(II) polypyridyl complexes against drug-sensitive and drug-resistant Plasmodium falciparum and their mode of action

BACKGROUND

Malaria remains one of the most virulent and deadliest parasitic disease in the world, particularly in Africa and Southeast Asia. Widespread occurrence of artemisinin-resistant Plasmodium falciparum strains from the Greater Mekong Subregion is alarming. This hinders the national economies, as well as being a major drawback in the effective control and elimination of malaria worldwide. Clearly, an effective anti-malarial drug is urgently needed.

METHODS

The dinuclear and mononuclear copper(II) and zinc(II) complexes were synthesized in ethanolic solution and characterized by various physical measurements (FTIR, CHN elemental analysis, solubility, ESI-MS, UV-Visible, conductivity and magnetic moment, and NMR). X-ray crystal structure of the dicopper(II) complex was determined. The in vitro haemolytic activities of these metal complexes were evaluated spectroscopically on B+ blood while the anti-malarial potency was performed in vitro on blood stage drug-sensitive Plasmodium falciparum 3D7 (Pf3D7) and artemisinin-resistant Plasmodium falciparum IPC5202 (Pf5202) with fluorescence dye. Mode of action of metal complexes were conducted to determine the formation of reactive oxygen species using PNDA and DCFH-DA dyes, JC-1 depolarization of mitochondrial membrane potential, malarial 20S proteasome inhibition with parasite lysate, and morphological studies using Giemsa and Hoechst stains.

RESULTS

Copper(II) complexes showed anti-malarial potency against both Pf3D7 and Pf5202 in sub-micromolar to micromolar range. The zinc(II) complexes were effective against Pf3D7 with excellent therapeutic index but encountered total resistance against Pf5202. Among the four, the dinuclear copper(II) complex was the most potent against both strains. The zinc(II) complexes caused no haemolysis of RBC while copper(II) complexes induced increased haemolysis with increasing concentration. Further mechanistic studies of both copper(II) complexes on both Pf3D7 and Pf5202 strains showed induction of ROS, 20S malarial proteasome inhibition, loss of mitochondrial membrane potential and morphological features indicative of apoptosis.

CONCLUSION

The dinuclear [Cu(phen)-4,4'-bipy-Cu(phen)](NO₃)₄ is highly potent and can overcome the total drug-resistance of Pf5202 towards chloroquine and artemisinin. The other three copper(II) and zinc(II) complexes were only effective towards the drug-sensitive Pf3D7, with the latter causing no haemolysis of RBC. Their mode of action involves multiple targets.

In silico insight of cell-death-related proteins in photosynthetic cyanobacteria

Cyanobacteria are a large group of ubiquitously found photosynthetic prokaryotes that are constantly exposed to different kinds of stressors of varying intensities and seem to overcome these in a precise and regulated manner. However, a high dose and duration of given stress induce cell death in a few select cyanobacteria, mainly to protect other cells (altruism). Despite the recent findings for the presence of biochemical and molecular hallmarks of cell death in cyanobacteria, it is yet a sketchily understood phenomenon. Regulation of metacaspase-like genes during Programmed Cell Death suggests it to be a genetically controlled mechanism like other eukaryotes. In addition to providing a comprehensive understanding of the current status of cell death in cyanobacteria, this review has used in silico analyses to directly compare the existence of some important molecular players operating in the intrinsic and extrinsic apoptotic pathways. Phylogenetic trees for all sequences indicate a cluster with a common ancestry and also a divergence from sequences of eukaryotic origin. To the best of our knowledge, such a comparison (except for orthocaspases) has not been attempted earlier and hopes to encourage workers in the field to investigate this altruistic phenomenon in detail.

A new adenine nucleotide transporter located in the ER is essential for maintaining the growth of Toxoplasma gondii

The lumen of the endoplasmic reticulum (ER) is the subcellular site where secretory protein folding, glycosylation and sulfation of membrane-bound proteins, proteoglycans, and lipids occur. The protein folding and degradation in the lumen of the ER require high levels of energy in the form of ATP. Biochemical and genetic approaches show that ATP must first be translocated across ER membrane by particular transporters before serving as substrates and energy sources in the lumenal reactions. Here we describe an ATP/ADP transporter residing in the ER membranes of T.gondii. Immunofluorescence (IFA) assay in transgenic TgANT1-HA tag revealed that TgANT1 is a protein specifically expressed in the ER. In vitro assays, functional integration of TgANT in the cytoplasmic membrane of intact E. coli cells reveals high specificity for an ATP/ADP antiport. The depletion of TgANT leads to fatal growth defects in T.gondii, including a significant slowdown in replication, no visible plaque formation, and reduced ability to invade. We also found that the amino acid mutations in two domains of TgANT lead to the complete loss of its function. Since these two domains are conserved in multiple species, they may share the same transport mechanism. Our results indicate that TgANT is the only ATP/ADP transporter in the ER of T. gondii, and the lack of ATP in the ER is the cause of the death of T. gondii.

The secretory protein of T. gondii is essential for its invasion and normal growth in host cells, all the secretory proteins are synthesized in the ER before being destined for these distinct organelles, such as apicoplast, microneme, dense granule and rhoptry. ER ATP is demanded to support secretory protein folding and trafficking, and the level of ER ATP determines which proteins are able to be directed to the distinct organelles. In theory, the supply of ATP in the ER is necessary for T. gondii. However, the transport mechanism and importance of the ER ATP in T. gondii are still unclear. In our study, we identified an ATP/ADP transporter (TgANT) located in the ER and verified its function through various methods. Unlike the ER ATP/ADP transporter in mammals, we proved that TgANT is functionally specific; the deletion of TgANT caused the interruption of the supply of ATP in the ER, which leads to fatal phenotypic defects of T. gondii. Our research further expands the understanding of the growth regulation in T. gondii.

Mitochondrial Ca2+ and Reactive Oxygen Species in Trypanosomatids

Significance: Millions of people are infected with trypanosomatids and new therapeutic approaches are needed. Trypanosomatids possess one mitochondrion per cell and its study has led to discoveries of general biological interest. These mitochondria, as in their animal counterparts, generate reactive oxygen species (ROS) and have evolved enzymatic and nonenzymatic defenses against them. Mitochondrial calcium ion (Ca2+) overload leads to generation of ROS and its study could lead to relevant information on the biology of trypanosomatids and to novel drug targets. Recent Advances: Mitochondrial Ca2+ is normally involved in maintaining the bioenergetics of trypanosomes, but when Ca2+ overload occurs, it is associated with cell death. Trypanosomes lack key players in the mechanism of cell death described in mammalian cells, although mitochondrial Ca2+ overload results in collapse of their membrane potential, production of ROS, and cytochrome c release. They are also very resistant to mitochondrial permeability transition, and cell death after mitochondrial Ca2+ overload depends on generation of ROS. Critical Issues: In this review, we consider the mechanisms of mitochondrial oxidant generation and removal and the involvement of Ca2+ in trypanosome cell death. Future Directions: More studies are required to determine the reactions involved in generation of ROS by the mitochondria of trypanosomatids, their enzymatic and nonenzymatic defenses against ROS, and the occurrence and composition of a mitochondrial permeability transition pore. Antioxid. Redox Signal. 36, 969-983.

Different Drugs, Same End: Ultrastructural Hallmarks of Autophagy in Pathogenic Protozoa

Protozoan parasites interact with a wide variety of organisms ranging from bacteria to humans, representing one of the most common causes of parasitic diseases and an important public health problem affecting hundreds of millions of people worldwide. The current treatment for these parasitic diseases remains unsatisfactory and, in some cases, very limited. Treatment limitations together with the increased resistance of the pathogens represent a challenge for the improvement of the patient’s quality of life. The continuous search for alternative preclinical drugs is mandatory, but the mechanisms of action of several of these compounds have not been described. Electron microscopy is a powerful tool for the identification of drug targets in almost all cellular models. Interestingly, ultrastructural analysis showed that several classes of antiparasitic compounds induced similar autophagic phenotypes in trypanosomatids, trichomonadids, and apicomplexan parasites as well as in Giardia intestinalis and Entamoeba spp. with the presence of an increased number of autophagosomes as well as remarkable endoplasmic reticulum profiles surrounding different organelles. Autophagy is a physiological process of eukaryotes that maintains homeostasis by the self-digestion of nonfunctional organelles and/or macromolecules, limiting redundant and damaged cellular components. Here, we focus on protozoan autophagy to subvert drug effects, discussing its importance for successful chemotherapy.

The Ancient Origins of Death Domains Support the 'Original Sin' Hypothesis for the Evolution of Programmed Cell Death

The discovery of caspase homologs in bacteria highlighted the relationship between programmed cell death (PCD) evolution and eukaryogenesis. However, the origin of PCD genes in prokaryotes themselves (bacteria and archaea) is poorly understood and a source of controversy. Whether archaea also contain C14 peptidase enzymes and other death domains is largely unknown because of a historical dearth of genomic data. Archaeal genomic databases have grown significantly in the last decade, which allowed us to perform a detailed comparative study of the evolutionary histories of PCD-related death domains in major archaeal phyla, including the deepest branching phyla of Candidatus Aenigmarchaeota, Candidatus Woesearchaeota, and Euryarchaeota. We identified death domains associated with executioners of PCD, like the caspase homologs of the C14 peptidase family, in 321 archaea sequences. Of these, 15.58% were metacaspase type I orthologues and 84.42% were orthocaspases. Maximum likelihood phylogenetic analyses revealed a scattered distribution of orthocaspases and metacaspases in deep-branching bacteria and archaea. The tree topology was incongruent with the prokaryote 16S phylogeny suggesting a common ancestry of PCD genes in prokaryotes and subsequent massive horizontal gene transfer coinciding with the divergence of archaea and bacteria. Previous arguments for the origin of PCD were philosophical in nature with two popular propositions being the "addiction" and 'original sin' hypotheses. Our data support the 'original sin' hypothesis, which argues for a pleiotropic origin of the PCD toolkit with pro-life and pro-death functions tracing back to the emergence of cellular life-the Last Universal Common Ancestor State.

β-carbolines RCC and C5 induce death of Leishmania amazonensis intracellular amastigotes

Background: Cutaneous leishmaniasis is caused by Leishmania spp., and its treatment is limited. The β-carbolines have shown activity against kinetoplastids. Aim: To evaluate the activity and effects of the β-carbolines, N-{2-[(4,6-bis(isopropylamino)-1,3,5-triazin-2-yl)amino]ethyl}-1-(4-methoxyphenyl)-β-carboline-3-carboxamide (RCC) and N-benzyl-1-(4-methoxy)phenyl-9H-beta-carboline-3-carboxamide (C5), against L. amazonensis intracellular amastigotes and to suggest their mechanism of action. Methods: We analyzed the activity and cytotoxicity of β-carbolines and the morphological alterations by electron microscopy. Mitochondrial membrane potential, production nitric oxide, reactive oxygen species, lipidic bodies, autophagic vacuoles and ATP were also evaluated. Results & conclusion: The results showed that RCC and C5 are active against intracellular amastigotes and were able to induce oxidative stress and ultrastructural alterations such as accumulation of lipid bodies and autophagic vacuoles, leading to parasite death.

Nanoliposomes increases Anti-Trichomonas vaginalis and apoptotic activities of metronidazole

Trichomoniasis, caused by Trichomonas vaginalis (T. vaginalis), is the most common non-viral sexually transmitted disease worldwide. As current trichomoniasis chemotherapies have many side effects, we examined the Anti-Trichomonas effects of nano-liposomal metronidazole (NLMTZ) compared to metronidazole (MTZ) in vitro. Liposomes were produced using the thin film hydration-sonication technique with a slight modification coated with MTZ. The average hydrodynamic diameter of monodispersed NLMTZ was evaluated by DLS and the morphological measurements were performed by scanning electron microscopy (SEM). The effects of NLMTZ and MTZ (5, 10, 20 and 40 µg/mL) on T. vaginalis trophozoites (10⁵ cells/mL) in trypticase-yeast extract-maltose (TYM) medium were evaluated in different exposure times. Then, cell viability, IC₅₀, SEM analysis and the expression of the metacaspase gene were assessed by qRT-PCR. Growth inhibition of MTZ in a concentration of 40 μg/mL was 39.34% after 3 h, whereas NLMTZ caused 51% growth inhibition after 3 h and lysed Trichomonas completely after 12 h. The IC₅₀ values were estimated at 31.51 and 15.90 μg/mL after a 6 h exposure for MTZ and NLMTZ, respectively. Moreover, both T. vaginalis treated with MTZ and NLMTZ had high levels of metacaspase mRNA expression relative to the control groups (P< 0.05). A significant difference was observed between the apoptotic intensities of T. vaginalis treated with MTZ and NLMTZ (P< 0.05). This study showed that nano-liposomal MTZ is a potentially excellent approach for the treatment of trichomoniasis in vitro, although further studies are needed before consideration of clinical trials.

Discovery of New Chemical Tools against Leishmania amazonensis via the MMV Pathogen Box

The protozoan parasite Leishmania causes a spectrum of diseases and there are over 1 million infections each year. Current treatments are toxic, expensive, and difficult to administer, and resistance to them is emerging. In this study, we screened the antileishmanial activity of the Pathogen Box compounds from the Medicine for Malaria Venture against Leishmania amazonensis, and compared their structures and cytotoxicity. The compounds MMV676388 (3), MMV690103 (5), MMV022029 (7), MMV022478 (9) and MMV021013 (10) exerted a significant dose-dependent inhibition effect on the proliferation of L. amazonensis promastigotes and intracellular amastigotes. Moreover, studies on the mechanism of cell death showed that compounds 3 and 5 induced an apoptotic process while the compounds 7, 9 and 10 seem to induce an autophagic mechanism. The present findings underline the potential of these five molecules as novel therapeutic leishmanicidal agents.

Investigation of the antileishmanial activity and mechanisms of action of acetyl-thiohydantoins

The currently available treatment options for leishmaniasis are associated with high costs, severe side effects, and high toxicity. In previous studies, thiohydantoins demonstrated some pharmacological activities and were shown to be potential hit compounds with antileishmanial properties. The present study further explored the antileishmanial effect of acetyl-thiohydantoins against Leishmania amazonensis and determined the main processes involved in parasite death. We observed that compared to thiohydantoin nuclei, acetyl-thiohydantoin treatment inhibited the proliferation of promastigotes. This treatment caused alterations in cell cycle progression and parasite size and caused morphological and ultrastructural changes. We then investigated the mechanisms involved in the death of the protozoan; there was an increase in ROS production, phosphatidylserine exposure, and plasma membrane permeabilization and a loss of mitochondrial membrane potential, resulting in an accumulation of lipid bodies and the formation of autophagic vacuoles on these parasites and confirming an apoptosis-like process. In intracellular amastigotes, selected acetyl-thiohydantoins reduced the percentage of infected macrophages and the number of amastigotes/macrophages by increasing ROS production and reducing TNF-α levels. Moreover, thiohydantoins did not induce cytotoxicity in murine macrophages (J774A.1), human monocytes (THP-1), or sheep erythrocytes. In silico and in vitro analyses showed that acetyl-thiohydantoins exerted in vitro antileishmanial effects on L. amazonensis promastigotes in apoptosis-like and amastigote forms by inducing ROS production and reducing TNF-α levels, indicating that they are good candidates for drug discovery studies in leishmaniasis treatment. Additionally, we carried out molecular docking analyses of acetyl-thiohydantoins on two important targets of Leishmania amazonensis: arginase and TNF-alpha converting enzyme. The results suggested that the acetyl groups in the N1-position of the thiohydantoin ring and the ring itself could be pharmacophoric groups due to their affinity for binding amino acid residues at the active site of both enzymes via hydrogen bond interactions. These results demonstrate that thiohydantoins are promising hit compounds that could be used as antileishmanial agents.

CELLULAR AND METABOLIC CHANGES AFTER PHOTODYNAMIC THERAPY IN LEISHMANIA PROMASTIGOTES

Leishmaniasis is a zoonotic disease, regarded by WHO as a public health problem that has presented a significant increase in the recent years. Conventional treatment is toxic and leads to serious side effects. Photodynamic therapy has been studied as a treatment to cutaneous leishmaniasis. This study aimed to evaluate the cell viability, morphological changes, type of cell death, production of reactive oxygen species, and changes in the mitochondrial membrane and DNA fragmentation in Leishmania braziliensis and Leishmania major promastigotes. Confocal microscopy was used to quantify the fluorescence emitted by JC-1, Annexin V, and propidium iodide reagents. The trypan blue exclusion test was used to evaluate the viability of the cells, the mitochondrial activity was verified with MTT, and the morphological changes were analyzed for SEM and DNA damage using the comet assay. PDT using curcumin at 500, 125, and 31,25 μg/mL decreased the viability of the parasites and induced changes in the mitochondrial membrane potential. The production of reactive oxygen species was dose-dependent and was observed only in the groups submitted to PDT. DNA damage was also observed in the parasite cells. The morphology of the cells was affected mainly at the highest curcumin concentration, resulting in rounded cells with a shortened flagellum. When the type of cell death was analyzed, the prevalence of apoptosis was noted. The results support the use of curcumin as photosensitizer in PDT against Leishmania promastigotes in the treatment for cutaneous leishmaniasis.

In vitro study of the trypanocidal activity of anilinophenanthrolines against Trypanosoma cruzi

Chagas disease is present in Latin America, North America, Europe, and Asia, where between 6 and 7 million people are infected. This illness is transmitted mainly by the insect vector during blood feeding and by oral transmission. Chagas disease is treated with benznidazole and its effectiveness depends on which phase of the disease the treatment starts. Therefore, the identification of new compounds with anti-Chagas activities is important. Protozoan parasites present cysteine proteases, important for host cell infection and differentiation, which have been explored as valid targets against pathogenic parasites. In the present study, the effects of 10 new 1,10-phenanthroline derivatives were evaluated on T. cruzi. Three of them were effective against amastigotes (IC₅₀ from 0.5 to 3 μM), epimastigotes (IC₅₀ from 0.5 to at least 10 μM) and trypomastigotes (and LD₅₀ from 1 to 10 μM), and they were not toxic to mammalian cells (CC₅₀ ≥ 20 μM). These compounds also promoted the formation of autophagosomes, alter the level of heterochromatin condensation, caused the loss of kDNA topology, and the elongated cell body shape. Apart from ultrastructural alterations, an increased generation of ROS and decreased mitochondrial membrane potential were observed. Therefore, these drugs revealed potential trypanocidal effects and warrant further antiparasitic studies against Chagas disease.

Anti-proliferative and apoptosis induction activities of curcumin on Leishmania major

Leishmaniasis is a major vector-borne disease triggered by an obligate intracellular protozoan parasite of the genus Leishmania and transmitted by the bite of phlebotomine female sand flies. This parasite causes a wide range of human diseases, from localized self-healing cutaneous lesions to fatal visceral infections. The aim of this study was to investigate the cytotoxic, antiproliferative, and apoptotic effects of curcumin on Leishmania major promastigotes (MHOM/SA/84/JISH) and to assess these effects on the cell cycle of promastigotes. The MTT colorimetric assay was used to evaluate the cytotoxicity and proliferation of promastigotes. Additionally, flow cytometry was used to analyze the cell cycle. The Annexin V/propidium iodide staining technique followed by flow cytometry was used to study the cell death induced by curcumin. In this study curcumin showed a potent antileishmanial effect, exhibiting cytotoxicity against L. major promastigotes. At 80μM, the survival in curcumin treated promastigotes reached 22%; however, the median lethal concentration of curcumin (LC₅₀) was 35μM. The drug exerted its cytotoxic effect by inducing apoptosis. Curcumin-induced cell death in promastigotes reached 82.5% at 80μM concentration. In addition, curcumin delayed the cell cycle in the S-phase inhibiting cell proliferation. Thus, curcumin was shown to be effective against L. major promastigotes. Therefore, curcumin merits further research studies to demonstrate its efficacy in treating cutaneous leishmaniasis.

PF-429242, a Subtilisin Inhibitor, Is Effective in vitro Against Leishmania infantum

PF-429242 is an inhibitor of subtilisin, an important protease found in Leishmania. However, studies regarding the effect of PF-429242 on Leishmania are scarce. In this work we evaluated the antileishmanial effect of PF-429242 against Leishmania infantum and the mechanism involved in the death of the parasite. PF-429242 had low toxicity against mammalian cells (peritoneal macrophages) (CC₅₀ = 189.07 μM) and presented activity against L. infantum promastigotes (IC₅₀ = 2.78 μM) and intracellular amastigotes (IC₅₀ = 14.07 μM), indicating selectivity toward the parasite. Transmission electron microscopy (TEM), as well as staining of L. infantum promastigotes with MitoTracker^® Red, rhodamine 123 and MitoSOX, revealed that the mitochondria was a potential target of PF-429242. In addition, PF-429242 caused an accumulation of neutral lipids in promastigotes, which was demonstrated by Nile Red staining and TEM, and induced oxidative stress (H₂DCFDA staining). Furthermore the formation of autophagic vacuoles in L. infantum promastigotes was observed by MDC staining and TEM. However, the killing induced by PF-429242 in L. infantum promastigotes appeared to be unrelated to apoptosis and/or necrosis as there was no phosphatidylserine externalization, DNA fragmentation or alterations in the permeability of the parasite plasma membrane, as assessed by annexin V-FITC, TUNEL and propidium iodide staining, respectively. The morphological and ultrastructural evaluation of the promastigotes by optical microscopy, scanning electron microscopy (SEM) and TEM, revealed the presence of parasites with flagellar defects. TEM analysis of the intracellular amastigotes indicated that mitochondrial damage and autophagy could also be involved in the death of these forms after treatment with PF-429242. In addition, PF-429242 treatment stimulated NO production from infected macrophage, but only at a high concentration (100 μM), as well as an increase of TNF levels after treatment with 10 μM of PF-429242. The compound did not stimulate ROS or IL-10 production. Together, these data highlight the antileishmanial potential of PF-429242, inducing several cellular alterations in the parasite, such as mitochondrial damage, neutral lipids accumulation, oxidative stress and autophagy which culminate in the death of L. infantum, as well as modulating host cellular responses that favor the development of an immune response against the parasite.

Programmed cell death as a black queen in microbial communities

Programmed cell death (PCD) in unicellular organisms is in some instances an altruistic trait. When the beneficiaries are clones or close kin, kin selection theory may be used to explain the evolution of the trait, and when the trait evolves in groups of distantly related individuals, group or multilevel selection theory is invoked. In mixed microbial communities, the benefits are also available to unrelated taxa. But the evolutionary ecology of PCD in communities is poorly understood. Few hypotheses have been offered concerning the community role of PCD despite its far-reaching effects. The hypothesis we consider here is that PCD is a black queen. The Black Queen Hypothesis (BQH) outlines how public goods arising from a leaky function are exploited by other taxa in the community. Black Queen (BQ) traits are essential for community survival, but only some members bear the cost of possessing them, while others lose the trait In addition, BQ traits have been defined in terms of adaptive gene loss, and it is unknown whether this has occurred for PCD. Our conclusion is that PCD fulfils the two most important criteria of a BQ (leakiness and costliness), but that more empirical data are needed for assessing the remaining two criteria. In addition, we hold that for viewing PCD as a BQ, the original BQH needs to include social traits. Thus, despite some empirical and conceptual shortcomings, the BQH provides a helpful avenue for investigating PCD in microbial communities.

Anti-Leishmania amazonensis activity of the terpenoid fraction from Eugenia pruniformis leaves

Leishmaniasis is caused by protozoan parasites belonging to the genus Leishmania and includes cutaneous, mucocutaneous and visceral clinical forms. Drugs currently available for leishmaniasis treatment present high toxicity, and development of parasite resistance. Plants constitute an important source of compounds with leishmanicidal potential. This study aimed to evaluate the anti-Leishmania amazonensis activity of the terpenoid fraction of Eugenia pruniformis leaves (TF-EpL). TF-EpL was active against the promastigote and intracellular amastigote forms of L. amazonensis with IC50(24h) value of 43.60μg/mL and 44.77μg/mL, respectively. TF-EpL altered the cell cycle of the parasite, increasing 2.32-fold the cells in the Sub-G0/G1 phase. TF-EpL also changed the ΔΨm and increased ROS and the number of annexin-V-PI positive promastigotes, which suggests incidental death. β-sitosterol, ursolic acid, corosolic acid and asiatic acid were isolated from TF-EpL. The results showed the antileishmanial activity of E. pruniformis terpenoids and its potential for further studies as a source of new drugs for leishmaniasis.

Update on relevant trypanosome peptidases: Validated targets and future challenges

Trypanosoma cruzi, the agent of the American Trypanosomiasis, Chagas disease, and Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense, the agents of Sleeping sickness (Human African Trypanosomiasis, HAT), as well as Trypanosoma brucei brucei, the agent of the cattle disease nagana, contain cysteine, serine, threonine, aspartyl and metallo peptidases. The most abundant among these enzymes are the cysteine proteases from the Clan CA, the Cathepsin L-like cruzipain and rhodesain, and the Cathepsin B-like enzymes, which have essential roles in the parasites and thus are potential targets for chemotherapy. In addition, several other proteases, present in one or both parasites, have been characterized, and some of them are also promising candidates for the developing of new drugs. Recently, new inhibitors, with good selectivity for the parasite proteasomes, have been described and are very promising as lead compounds for the development of new therapies for these neglected diseases. This article is part of a Special Issue entitled: "Play and interplay of proteases in health and disease".

Dual Parasiticidal Activities of Phthalimides: Synthesis and Biological Profile against Trypanosoma cruzi and Plasmodium falciparum

Chagas disease and malaria are two neglected tropical diseases (NTDs) that prevail in tropical and subtropical regions in 149 countries. Chagas is also present in Europe, the US and Australia due to immigration of asymptomatic infected individuals. In the absence of an effective vaccine, the control of both diseases relies on chemotherapy. However, the emergence of parasite drug resistance is rendering currently available drugs obsolete. Hence, it is crucial to develop new molecules. Phthalimides, thiosemicarbazones, and 1,3-thiazoles have been used as scaffolds to obtain antiplasmodial and anti-Trypanosoma cruzi agents. Herein we present the synthesis of 24 phthalimido-thiosemicarbazones (3 a-x) and 14 phthalimido-thiazoles (4 a-n) and the corresponding biological activity against T. cruzi, Plasmodium falciparum, and cytotoxicity against mammalian cell lines. Some of these compounds showed potent inhibition of T. cruzi at low cytotoxic concentrations in RAW 264.7 cells. The most active compounds, 3 t (IC₅₀ =3.60 μM), 3 h (IC₅₀ =3.75 μM), and 4 j (IC₅₀ =4.48 μM), were more active than the control drug benznidazole (IC₅₀ =14.6 μM). Overall, the phthalimido-thiosemicarbazone derivatives were more potent than phthalimido-thiazole derivatives against T. cruzi. Flow cytometry assay data showed that compound 4 j was able to induce necrosis and apoptosis in trypomastigotes. Analysis by scanning electron microscopy showed that T. cruzi trypomastigote cells treated with compounds 3 h, 3 t, and 4 j at IC₅₀ concentrations promoted changes in the shape, flagella, and surface of the parasite body similar to those observed in benznidazole-treated cells. The compounds with the highest antimalarial activity were the phthalimido-thiazoles 4 l (IC₅₀ =1.2 μM), 4 m (IC₅₀ =1.7 μM), and 4 n (IC₅₀ =2.4 μM). Together, these data revealed that phthalimido derivatives possess a dual antiparasitic profile with potential effects against T. cruzi and lead-like characteristics.

Antiproliferative activity of the dibenzylideneacetone derivate (E)-3-ethyl-4-(4-nitrophenyl)but‑3-en-2-one in Trypanosoma cruzi

Chagas disease is one of the most prevalent neglected diseases in the world. The illness is caused by Trypanosoma cruzi, a protozoan parasite with a complex life cycle and three morphologically distinct developmental stages. Nowadays, the only treatment is based on two nitro-derivative drugs, benznidazole and nifurtimox, which cause serious side effects. Since the treatment is limited, the search for new treatment options for patients with Chagas disease is highly necessary. In this study we analyzed the substance A11K3, a dibenzylideneacetone (DBA). DBAs have an acyclic dienone attached to aryl groups in both β-positions and studies have shown that they have biological activity against tumors cells, bacteria, and protozoa such as T. cruzi and Leishmania spp. Here we show that A11K3 is active against all three T. cruzi evolutionary forms: the epimastigote (IC₅₀ = 3.3 ± 0.8), the trypomastigote (EC₅₀ = 24 ± 4.3) and the intracellular amastigote (IC₅₀ = 9.3 ± 0.5 µM). A cytotoxicity assay in LLCMK₂ cells showed a CC₅₀ of 239.2 ± 15.7 µM giving a selectivity index (CC₅₀/IC₅₀) of 72.7 for epimastigotes, 9.9 for trypomastigotes and 25.9 for intracellular amastigotes. Morphological and ultrastructural analysis of the parasites treated with A11K3 by TEM and SEM revealed alterations in the Golgi complex, mitochondria, plasma membrane and cell body, with an increase of autophagic vacuoles and lipid bodies. Biochemical assays of A11K3-treated T. cruzi showed an increase of ROS, plasma membrane ruptures, lipid peroxidation, mitochondrial membrane depolarization with a decrease in ATP and accumulation of autophagic vacuoles. The results lead to the hypothesis that A11K3 causes death of the protozoan through events such as plasma membrane and mitochondrial alterations and autophagy, characteristic of cell collapse.

The terpenic diamine GIB24 inhibits the growth of Trypanosoma cruzi epimastigotes and intracellular amastigotes, with proteomic analysis of drug-resistant epimastigotes

The effect of N-geranyl-ethane-1,2-diamine dihydochloride (GIB24), a synthetic diamine, was assayed against different developmental forms of the parasitic protozoan Trypanosoma cruzi (strain Dm28c). The compound was effective against culture epimastigote forms (IC₅₀/24h = 5.64 μM; SI = 16.4) and intracellular amastigotes (IC₅₀/24h = 12.89 μM; SI = 7.18), as detected by the MTT methodology and by cell counting, respectively. Incubation of epimastigotes for 6h with 6 μM GIB24 (IC₅₀/24h value) resulted in significant dissipation of the mitochondrial membrane potential, prior to permeabilization of the plasma membrane. Rounded epimastigotes with cell size reduction were observed by scanning electron microscopy. These morpho-physiological changes induced by GIB24 suggest an incidental death process. Treatment of infected Vero cells did not prevent the intracellular amastigotes from completing the intracellular cycle. However, there was a decrease in the number of released parasites, increasing the ratio amastigotes/trypomastigotes. Proteomic analysis of 15 μM GIB24 resistant epimastigotes indicated that the compound acts mainly on mitochondrial components involved in the Krebs cycle and in maintaining the oxidative homeostasis of the parasites. Our data suggest that GIB24 is active against the main morphological forms of T. cruzi.

Venom alkaloids against Chagas disease parasite: search for effective therapies

Chagas disease is an important disease affecting millions of patients in the New World and is caused by a protozoan transmitted by haematophagous kissing bugs. It can be treated with drugs during the early acute phase; however, effective therapy against the chronic form of Chagas disease has yet to be discovered and developed. We herein tested the activity of solenopsin alkaloids extracted from two species of fire ants against the protozoan parasite Trypanosoma cruzi, the aetiologic agent of Chagas disease. Although IC₅₀ determinations showed that solenopsins are more toxic to the parasite than benznidazole, the drug of choice for Chagas disease treatment, the ant alkaloids presented a lower selectivity index. As a result of exposure to the alkaloids, the parasites became swollen and rounded in shape, with hypertrophied contractile vacuoles and intense cytoplasmic vacuolization, possibly resulting in osmotic stress; no accumulation of multiple kinetoplasts and/or nuclei was detected. Overexpressing phosphatidylinositol 3-kinase-an enzyme essential for osmoregulation that is a known target of solenopsins in mammalian cells-did not prevent swelling and vacuolization, nor did it counteract the toxic effects of alkaloids on the parasites. Additional experimental results suggested that solenopsins induced a type of autophagic and programmed cell death in T. cruzi. Solenopsins also reduced the intracellular proliferation of T. cruzi amastigotes in infected macrophages in a concentration-dependent manner and demonstrated activity against Trypanosoma brucei rhodesiense bloodstream forms, which is another important aetiological kinetoplastid parasite. The results suggest the potential of solenopsins as novel natural drugs against neglected parasitic diseases caused by kinetoplastids.

Of Drugs and Trypanosomatids: New Tools and Knowledge to Reduce Bottlenecks in Drug Discovery

Leishmaniasis (Leishmania species), sleeping sickness (Trypanosoma brucei), and Chagas disease (Trypanosoma cruzi) are devastating and globally spread diseases caused by trypanosomatid parasites. At present, drugs for treating trypanosomatid diseases are far from ideal due to host toxicity, elevated cost, limited access, and increasing rates of drug resistance. Technological advances in parasitology, chemistry, and genomics have unlocked new possibilities for novel drug concepts and compound screening technologies that were previously inaccessible. In this perspective, we discuss current models used in drug-discovery cascades targeting trypanosomatids (from in vitro to in vivo approaches), their use and limitations in a biological context, as well as different examples of recently discovered lead compounds.

Extracellular Vesicles Could Carry an Evolutionary Footprint in Interkingdom Communication

Extracellular vesicles (EVs) are minute particles secreted by the cells of living organisms. Although the functional role of EVs is not yet clear, recent work has highlighted their role in intercellular communication. Here, we expand on this view by suggesting that EVs can also mediate communication among interacting organisms such as hosts, pathogens and vectors. This inter-kingdom communication via EVs is likely to have important evolutionary consequences ranging from adaptation of parasites to specialized niches in the host, to host resistance and evolution and maintenance of parasite virulence and transmissibility. A potential system to explore these consequences is the interaction among the human host, the mosquito vector and Plasmodium parasite involved in the malaria disease. Indeed, recent studies have found that EVs derived from Plasmodium infected red blood cells in humans are likely mediating the parasite's transition from the asexual to sexual stage, which might facilitate transmission to the mosquito vector. However, more work is needed to establish the adaptive consequences of this EV signaling among different taxa. We suggest that an integrative molecular approach, including a comparative phylogenetic analysis of the molecules (e.g., proteins and nucleic acids) derived from the EVs of interacting organisms (and their closely-related species) in the malaria system will prove useful for understanding interkingdom communication. Such analyses will also shed light on the evolution and persistence of host, parasite and vector interactions, with implications for the control of vector borne infectious diseases.

Repositioning of HIV Aspartyl Peptidase Inhibitors for Combating the Neglected Human Pathogen Trypanosoma cruzi

Chagas disease, caused by the flagellate parasite Trypanosoma cruzi, is a wellknown neglected tropical disease. This parasitic illness affects 6-7 million people and can lead to severe myocarditis and/or complications of the digestive tract. The changes in its epidemiology facilitate co-infection with the Human Immunodeficiency Virus (HIV), making even more difficult the diagnosis and prognosis. The parasitic infection is reactivated in T. cruzi/HIV co-infection, with the appearance of unusual manifestations in the chronic phase and the exacerbation of classical clinical signs. The therapeutic arsenal to treat Chagas disease, in all its clinical forms, is restricted basically to two drugs, benznidazole and nifurtimox. Both drugs are extremely toxic and the therapeutic efficacy is still unclear, making the clinical treatment a huge issue to be solved. Therefore, it seems obvious the necessity of new tangible approaches to combat this illness. In this sense, the repositioning of approved drugs appears as an interesting and viable strategy. The discovery of Human Immunodeficiency Virus Aspartyl Peptidase Inhibitors (HIV-PIs) represented a milestone in the treatment of Acquired Immune Deficiency Syndrome (AIDS) and, concomitantly, a marked reduction in both the incidence and prevalence of important bacterial, fungal and parasitic co-infections was clearly observed. Taking all these findings into consideration, the present review summarizes the promising and beneficial data concerning the effects of HIV-PIs on all the evolutionary forms of T. cruzi and in important steps of the parasite's life cycle, which highlight their possible application as alternative drugs to treat Chagas disease.

A Triazole Hybrid of Neolignans as a Potential Antileishmanial Agent by Triggering Mitochondrial Dysfunction

In the search for new compounds with antileishmanial activity, we synthesized a triazole hybrid analogue of the neolignans grandisin and machilin G (LASQUIM 25), which was previously found highly active against both promastigotes and intracellular amastigote forms of Leishmania amazonensis. In this work, we investigated the leishmanicidal effects of LASQUIM 25 to identify the mechanisms involved in the cell death of L. amazonensis promastigotes. Transmission electron microscopy (TEM) analysis showed marked effects of LASQUIM 25 (IC₅₀ = 7.2 µM) on the morphology of promastigote forms, notably on mitochondria. The direct action of the triazole derivative on the parasite was noticed over time from 2 h to 48 h, and cells displayed several ultrastructural alterations characteristic of apoptotic cells. Also, flow cytometric analysis (FACS) after TMRE staining detected changes in mitochondrial membrane potential after LASQUIM 25 treatment (64.83% labeling versus 83.38% labeling in nontreated cells). On the other hand, FACS after PI staining in 24 h-treatment showed a slight alteration in the integrity of the cell membrane, a necrotic event (16.76% necrotic cells versus 3.19% staining in live parasites). An abnormal secretion of lipids was observed, suggesting an exocytic activity. Another striking finding was the presence of autophagy-related lysosome-like vacuoles, suggesting an autophagic cell death that may arise as consequence of mitochondrial stress. Taken together, these results suggest that LASQUIM 25 leishmanicidal mechanisms involve some degree of mitochondrial dysregulation, already evidenced by the treatment with the IC₅₀ of this compound. This effect may be due to the presence of a methylenedioxy group originated from machilin G, whose toxicity has been associated with the capacity to generate electrophilic intermediates.

Cell death in Leishmania

Leishmaniases still represent a global scourge and new therapeutic tools are necessary to replace the current expensive, difficult to administer treatments that induce numerous adverse effects and for which resistance is increasingly worrying. In this context, the particularly original organization of the Leishmania parasite in comparison to higher eukaryotes is a great advantage. It allows for the development of new, very specific, and thus non-cytotoxic treatments. Among these originalities, Leishmania cell death can be cited. Despite a classic pattern of apoptosis, key mammalian apoptotic proteins are not present in Leishmania, such as caspases, cell death receptors, and anti-apoptotic molecules. Recent studies have helped to develop a better understanding of parasite cell death, identifying new proteins or even new apoptotic pathways. This review provides an overview of the current knowledge on Leishmania cell death, describing its physiological roles and its phenotype, and discusses the involvement of various proteins: endonuclease G, metacaspase, aquaporin Li-BH3AQP, calpains, cysteine proteinase C, LmjHYD36 and Lmj.22.0600. From these data, potential apoptotic pathways are suggested. This review also offers tools to identify new Leishmania cell death effectors. Lastly, different approaches to use this knowledge for the development of new therapeutic tools are suggested: either inhibition of Leishmania cell death or activation of cell death for instance by treating cells with proteins or peptides involved in parasite death fused to a cell permeant peptide or encapsulated into a lipidic vector to target intra-macrophagic Leishmania cells.

Novel indol-3-yl-thiosemicarbazone derivatives: Obtaining, evaluation of in vitro leishmanicidal activity and ultrastructural studies

Parasitic diseases still represent serious public health problems, since the high and steady emergence of resistant strains is evident. Because parasitic infections are distributed predominantly in developing countries, less toxic, more efficient, safer and more accessible drugs have become desirable in the treatment of the infected population. This is the case of leishmaniasis, an infectious disease caused by a protozoan of the genus Leishmania sp., responsible for triggering pathological processes from the simplest to the most severe forms leading to high rates of morbidity and mortality throughout the world. In the search for new leishmanicidal drugs, the thiosemicarbazones and the indole fragments have been identified as promising structures for leishmanicidal activity. The present study proposes the synthesis and structural characterization of new indole-thiosemicarbazone derivatives (2a-j), in addition to performing in vitro evaluations through cytotoxicity assays using macrophages (J774) activity against forms of Leishmania infantum and Leishmania amazonensis promastigote as well as ultrastructural analyzes in promastigotes of L. infantum. Results show that the indole-thiosemicarbazone derivatives were obtained with yield values varying from 32.09 to 94.64%. In the evaluation of cytotoxicity, the indole-thiosemicarbazone compounds presented CC₅₀ values between 53.23 and 357.97 μM. Concerning the evaluation against L. amazonensis promastigote forms, IC₅₀ values ranged between 12.31 and  > 481.52 μM, while the activity against L. infantum promastigotes obtained IC₅₀ values between 4.36 and 23.35 μM. The compounds 2d and 2i tested against L. infantum were the most promising in the series, as they showed the lowest IC₅₀ values: 5.60 and 4.36 respectively. The parasites treated with the compounds 2d and 2i showed several structural alterations, such as shrinkage of the cell body, shortening and loss of the flagellum, intense mitochondrial swelling and vacuolization of the cytoplasm leading the parasite to cellular unviability. Therefore, the indole-thiosemicarbazone compounds are promising because they yield considerable synthesis, have low cytotoxicity to mammalian cells and act as leishmanicidal agents.

A potential acetyltransferase involved in Leishmania major metacaspase-dependent cell death

BACKGROUND

Currently, there is no satisfactory treatment for leishmaniases, owing to the cost, mode of administration, side effects and to the increasing emergence of drug resistance. As a consequence, the proteins involved in Leishmania apoptosis seem a target of choice for the development of new therapeutic tools against these neglected tropical diseases. Indeed, Leishmania cell death, while phenotypically similar to mammalian apoptosis, is very peculiar, involving no homologue of the key mammalian apoptotic proteins such as caspases and death receptors. Furthermore, very few proteins involved in Leishmania apoptosis have been identified.

RESULTS

We identified a protein involved in Leishmania apoptosis from a library of genes overexpressed during Leishmania differentiation during which autophagy occurs. Indeed, the gene was overexpressed when L. major cell death was induced by curcumin or miltefosine. Furthermore, its overexpression increased L. major curcumin- and miltefosine-induced apoptosis. This gene, named LmjF.22.0600, whose expression is dependent on the expression of the metacaspase, another apoptotic protein, encodes a putative acetyltransferase.

CONCLUSIONS

This new protein, identified as being involved in Leishmania apoptosis, will contribute to a better understanding of Leishmania death, which is needed owing to the absence of a satisfactory treatment against leishmaniases. It will also allow a better understanding of the original apoptotic pathways of eukaryotes in general, while evidence of the existence of such pathways is accumulating.

(De)glutamylation and cell death in Leishmania parasites

Trypanosomatids are flagellated protozoan parasites that are very unusual in terms of cytoskeleton organization but also in terms of cell death. Most of the Trypanosomatid cytoskeleton consists of microtubules, forming different substructures including a subpellicular corset. Oddly, the actin network appears structurally and functionally different from other eukaryotic actins. And Trypanosomatids have an apoptotic phenotype under cell death conditions, but the pathways involved are devoid of key mammal proteins such as caspases or death receptors, and the triggers involved in apoptotic induction remain unknown. In this article, we have studied the role of the post-translational modifications, deglutamylation and polyglutamylation, in Leishmania. We have shown that Leishmania apoptosis was linked to polyglutamylation and hypothesized that the cell survival process autophagy was linked to deglutamylation. A balance seems to be established between polyglutamylation and deglutamylation, with imbalance inducing microtubule or other protein modifications characterizing either cell death if polyglutamylation was prioritized, or the cell survival process of autophagy if deglutamylation was prioritized. This emphasizes the role of post-translational modifications in cell biology, inducing cell death or cell survival of infectious agents.

Leishmania are unique unicellular organisms in terms of cytoskeleton organization and mechanisms of cell death. For example, the major cytoskeletal components of these parasites are microtubules, which form a subpellicular corset. In terms of cell death, an apoptotic phenotype has been characterized in Leishmania but the pathways remain unknown, being devoid of key mammal cell death proteins. In a previous article, we demonstrated that the cytoskeleton of this parasite is extensively glutamylated but, paradoxically, overexpression or inhibition of polyglutamylase expression have limited visible cellular consequences. In this manuscript, we have highlighted the link between polyglutamylation and Leishmania cell death, suggesting the importance of the polyglutamylation/deglutamylation balance in this parasite. Further, we have identified, for the first time in Leishmania, deglutamylases, among which one that, in an original manner, deglutamylates glutamates at branching points but also long glutamate side chains. This work emphasizes the role of post-translational modifications as essential regulators of protein function, not only of mammal cells such as neurons or ciliated/flagellated cells, but also of infectious agents. This work suggests an important and discernible “live or die”—“cell death or autophagy” balance pathway and the conceptual mechanism that is involved in cellular decision making.

Semicarbazone derivatives as promising therapeutic alternatives in leishmaniasis

In the present study, we investigated the in vitro and in vivo leishmanicidal activity of synthetic compounds, containing a semicarbazone scaffold as a peptide mimetic framework. The leishmanicidal effect against amastigotes of Leishmania amazonensis was also evaluated at concentration of 100 μM-0.01 nM. The derivatives 2e, 2f, 2g and 1g, beyond the standards miltefosine and pentamidine, significantly diminished the number of L. amazonensis amastigotes in macrophages. These derivatives were also active against amastigotes of L. braziliensis. As 2g presented potent leishmanicidal activity against the amastigotes of L. amazonensis in macrophages, we also investigated the in vivo leishmanicidal activity of this compound against L. amazonensis. Approximately 10⁵L. amazonensis promastigotes were subcutaneously inoculated into the dermis of the right ear of BALB/c mice, which were subsequently treated with 2g (p.o. or i.p.), miltefosine (p.o.) or glucantime (i.p.) at 30 μmol/kg/day x 28 days. Thus, a similar reduction in the lesion size was observed after the administration of 2g through oral (63.7 ± 10.1%) and intraperitoneal (61.8 ± 3.7%) routes. A larger effect was observed after treatment with miltefosine (97.7 ± 0.4%), and glucantime did not exhibit activity at the dose administered. With respect to the ear parasite load, 2g diminished the number of parasites by p.o. (30.5 ± 5.1%) and i.p. (33.3 ± 4.3%) administration. In addition, 2g induced in vitro apoptosis, autophagy and cell cycle alterations on L. amazonensis promastigotes. In summary, the derivative 2g might represent a lead candidate for antileishmanial drugs, as this compound displayed pronounced leishmanicidal activity.

In vitro and in vivo antileishmanial activity of a fluoroquinoline derivate against Leishmania infantum and Leishmania amazonensis species

New therapeutics against leishmaniasis are desirable, since the current drugs applied against this disease complex presents problems, such as the toxicity, high cost and/or parasite resistance. In the present study, a new fluoroquinoline derivate, namely 7-chloro-N-(4-fluorophenethyl)quinolin-4-amine or GF1061, was evaluated regarding to its in vitro antileishmanial action against Leishmania infantum and L. amazonensis species, as well as by its toxicity in mammalian cells and efficacy in the treatment of infected macrophages. The mechanism of action of this molecule in L. amazonensis and the therapeutic efficacy in infected BALB/c mice were also evaluated. Results showed that GF1061 was effective against both parasite species, showing selectivity index (SI) of 38.7 and 42.7 against L. infantum and L. amazonensis promastigotes, respectively, and of 45.0 and 48.9 against the amastigotes, respectively. Amphotericin B (AmpB), used as control, showed SI values of 6.6 and 8.8 against L. infantum and L. amazonensis promastigotes, respectively, and of 2.2 and 2.7 against the amastigotes, respectively. The molecule was effective in treat infected macrophages, as well as it induced alterations in the mitochondrial membrane potential, increase in the reactive oxygen species production, and in the cell integrity of the parasites. Regarding to the in vivo experiments, BALB/c mice (n = 8 per group) were subcutaneously infected with 10⁶L. amazonensis stationary promastigotes and, 60 days post-infection, they received saline or were treated during 10 days, once a day, with AmpB (1 mg/kg body weight) or GF1061 (5 mg/kg body weight). One day after the treatment, the infected tissue, spleen, liver, and draining lymph node (dLN) of the animals were collected, and the parasite load was evaluated. GF1061-treated mice, as compared to the saline and AmpB groups, showed significant reductions in the parasitism in the infected tissue (66% and 62%, respectively), liver (69% and 44%, respectively), spleen (71% and 38%, respectively), and dLN (72% and 48%, respectively). In conclusion, results suggested that GF1061 may be considered as a possible therapeutic target to be evaluated against leishmaniasis in other mammalian hosts.

Cell death pathways in pathogenic trypanosomatids: lessons of (over)kill

Especially in tropical and developing countries, the clinically relevant protozoa Trypanosoma cruzi (Chagas disease), Trypanosoma brucei (sleeping sickness) and Leishmania species (leishmaniasis) stand out and infect millions of people worldwide leading to critical social-economic implications. Low-income populations are mainly affected by these three illnesses that are neglected by the pharmaceutical industry. Current anti-trypanosomatid drugs present variable efficacy with remarkable side effects that almost lead to treatment discontinuation, justifying a continuous search for alternative compounds that interfere with essential and specific parasite pathways. In this scenario, the triggering of trypanosomatid cell death machinery emerges as a promising approach, although the exact mechanisms involved in unicellular eukaryotes are still unclear as well as the controversial biological importance of programmed cell death (PCD). In this review, the mechanisms of autophagy, apoptosis-like cell death and necrosis found in pathogenic trypanosomatids are discussed, as well as their roles in successful infection. Based on the published genomic and proteomic maps, the panel of trypanosomatid cell death molecules was constructed under different experimental conditions. The lack of PCD molecular regulators and executioners in these parasites up to now has led to cell death being classified as an unregulated process or incidental necrosis, despite all morphological evidence published. In this context, the participation of metacaspases in PCD was also not described, and these proteases play a crucial role in proliferation and differentiation processes. On the other hand, autophagic phenotype has been described in trypanosomatids under a great variety of stress conditions (drugs, starvation, among others) suggesting that this process is involved in the turnover of damaged structures in the protozoa and is not a cell death pathway. Death mechanisms of pathogenic trypanosomatids may be involved in pathogenesis, and the identification of parasite-specific regulators could represent a rational and attractive alternative target for drug development for these neglected diseases.