On the evolution of programmed cell death: apoptosis of the unicellular eukaryote Leishmania major involves cysteine proteinase activation and mitochondrion permeabilization

Apoptotic proteins in Leishmania donovani: in silico screening, modeling, and validation by knock-out and gene expression analysis

Visceral leishmaniasis, a life-threatening vector-borne illness that disproportionately affects children and elderly immunocompromised people, is a primary tropical neglected disease. No apoptotic partner proteins have yet been reported in Leishmania donovani, while their identification could contribute to knowledge on parasite cell death and the establishment of alternative therapeutics. We searched for mammalian Bcl-2 family protein orthologs and found one anti-apoptotic and two pro-apoptotic orthologs in L. donovani. A pro-death aquaporin protein, due to its characteristic BH3 domain known to interact with pro-apoptotic proteins in mammalian Bcl-2 family proteins, was also included in this study. Molecular docking and molecular dynamics simulations were conducted to assess protein-protein interactions between the identified apoptotic proteins and mimic mammalian intrinsic apoptotic pathways. The results showed that both pro-apoptotic proteins interacted with the hydrophobic pocket of the anti-apoptotic ortholog, forming a stable complex. This interaction may represent a critical event in an apoptotic pathway in L. donovani. To further characterise it, we used CRISPR-Cas9 approaches to target the identified proteins. Pure knocked population mutants, and episomal over-expressing mutant cells were exposed to apoptotic stimuli. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay and quantitative expression profiling suggested that these proteins are involved in the parasite's apoptosis and could play a role in its survival.

Iris setosa Pall. ex Link Extract Reveals Amoebicidal Activity against Acanthamoeba castellanii and Acanthamoeba polyphaga with Low Toxicity to Human Corneal Cells

Acanthamoeba keratitis (AK) is a sight-threatening and difficult-to-treat ocular infection. The significant side effects of current AK treatments highlight the urgent need to develop a safe and effective AK medication. In this study, the amoebicidal activity of Iris setosa Pall. ex Link extract (ISE) against Acanthamoeba was examined and its specific amoebicidal mechanism was explored. ISE induced significant morphological changes in Acanthamoeba trophozoites and exhibited amoebicidal activity against A. castellanii and A. polyphaga. ISE was further fractionated into five subfractions by sequential extraction with n-hexane, chloroform, ethyl acetate, n-butanol, and water, and their amoebicidal activities and underlying amoebicidal mechanisms were investigated. The n-butanol subfraction of ISE (ISE-BuOH) displayed selective amoebicidal activity against the Acanthamoeba species with minimal cytotoxicity in human corneal cells (HCE-2). ISE-BuOH triggered apoptosis-like programmed cell death (PCD) in amoebae, characterized by DNA fragmentation, increased ROS production, and caspase-3 activity elevation. ISE-BuOH also demonstrated a partial cysticidal effect against the amoeba species. ISE-BuOH could be a promising candidate in the development of therapeutic drugs for AK.

Cell Death of P. vivax Blood Stages Occurs in Absence of Classical Apoptotic Events and Induces Eryptosis of Parasitized Host Cells

Elucidation of pathways regulating parasite cell death is believed to contribute to identification of novel therapeutic targets for protozoan diseases, and in this context, apoptosis-like cell death has been reported in different groups of protozoa, in which metacaspases seem to play a role. In the genus Plasmodium, apoptotic markers have been detected in P. falciparum and P. berghei, and no study focusing on P. vivax cell death has been reported so far. In the present study, we investigated the susceptibility of P. vivax to undergo apoptotic cell death after incubating mature trophozoites with the classical apoptosis inducer staurosporine. As assessed by flow cytometry assays, staurosporine inhibited parasite intraerythrocytic development, which was accompanied by a decrease in cell viability, evidenced by reduced plasmodial mitochondrial activity. However, typical signs of apoptosis, such as DNA fragmentation, chromatin condensation, and nuclear segregation, were not detected in the parasites induced to cell death, and no significant alteration in metacaspase gene expression (PvMCA1) was observed under cell death stimulus. Interestingly, dying parasites positively modulated cell death (eryptosis) of host erythrocytes, which was marked by externalization of phosphatidylserine and cell shrinkage. Our study shows for the time that P. vivax blood stages may not be susceptible to apoptosis-like processes, while they could trigger eryptosis of parasitized cells by undergoing cell death. Further studies are required to elucidate the cellular machinery involved in cell death of P. vivax parasites as well as in the modulation of host cell death.

Cell death of Acanthamoeba castellanii following exposure to antimicrobial agents commonly included in contact lens disinfecting solutions

Several antimicrobial agents are commonly included in contact lens disinfectant solutions including chlorhexidine diacetate (CHX), polyhexamethylene biguanide (PHMB) or myristamidopropyl dimethylamine (MAPD); however, their mode of action, i.e. necrosis versus apoptosis is incompletely understood. Here, we determined whether a mechanism of cell death resembling that of apoptosis was present in Acanthamoeba castellanii of the T4 genotype (NEFF) following exposure to the aforementioned antimicrobials using the anticoagulant annexin V that undergoes rapid high affinity binding to phosphatidylserine in the presence of calcium, making it a sensitive probe for phosphatidylserine exposure. The results revealed that under the conditions employed in this study, an apoptotic pathway of cell death in this organism at the tested conditions does not occur. Our findings suggest that necrosis is the likely mode of action; however, future mechanistic studies should be accomplished in additional experimental conditions to further comprehend the molecular mechanisms of cell death in Acanthamoeba.

Multi-target withaferin-A analogues as promising anti-kinetoplastid agents through the programmed cell death

Leishmaniasis and Chagas disease, two of the most prevalent neglected tropical diseases, are a world health problem. The harsh reality of these infective diseases is the absence of effective and safe therapies. In this framework, natural products play an important role in overcoming the current need to development new antiparasitic agents. The present study reports the synthesis, antikinetoplastid screening, mechanism study of fourteen withaferin A derivatives (2-15). Nine of them (2-6, 8-10 and 12) showed a potent dose-dependent inhibitory effect on the proliferation of Leishmania amazonensis and L. donovani promastigotes and Trypanosoma cruzi epimastigotes with IC₅₀ values ranging from 0.19 to 24.01 µM. Outstandingly, the fully acetylated derivative 10 (4,27-diacetylwithaferin A) was the most potent compound showing IC₅₀ values of 0.36, 2.82 and 0.19 µM against L. amazonensis, L. donovani and T. cruzi, respectively. Furthermore, analogue 10 exhibited approximately 18 and 36-fold greater antikinetoplastid activity, on L. amazonensis and T. cruzi, than the reference drugs. The activity was accompanied by significantly lower cytotoxicity on the murine macrophage cell line. Moreover, compounds 2, 3, 5-7, 9 and 10 showed more potent activity than the reference drug against the intracellular amastigotes forms of L. amazonensis and T.cruzi, with a good selectivity index on a mammalian cell line. In addition, withaferin A analogues 3, 5-7, 9 and 10 induce programmed cell death through a process of apoptosis-like and autophagy. These results strengthen the anti-parasitic potential of withaferin A-related steroids against neglected tropical diseases caused by Leishmania spp. and T. cruzi parasites.

Parasite Metalo-aminopeptidases as Targets in Human Infectious Diseases

BACKGROUND

Parasitic human infectious diseases are a worldwide health problem due to the increased resistance to conventional drugs. For this reason, the identification of novel molecular targets and the discovery of new chemotherapeutic agents are urgently required. Metalo- aminopeptidases are promising targets in parasitic infections. They participate in crucial processes for parasite growth and pathogenesis.

OBJECTIVE

In this review, we describe the structural, functional and kinetic properties, and inhibitors, of several parasite metalo-aminopeptidases, for their use as targets in parasitic diseases.

CONCLUSION

Plasmodium falciparum M1 and M17 aminopeptidases are essential enzymes for parasite development, and M18 aminopeptidase could be involved in hemoglobin digestion and erythrocyte invasion and egression. Trypanosoma cruzi, T. brucei and Leishmania major acidic M17 aminopeptidases can play a nutritional role. T. brucei basic M17 aminopeptidase down-regulation delays the cytokinesis. The inhibition of Leishmania basic M17 aminopeptidase could affect parasite viability. L. donovani methionyl aminopeptidase inhibition prevents apoptosis but not the parasite death. Decrease in Acanthamoeba castellanii M17 aminopeptidase activity produces cell wall structural modifications and encystation inhibition. Inhibition of Babesia bovis growth is probably related to the inhibition of the parasite M17 aminopeptidase, probably involved in host hemoglobin degradation. Schistosoma mansoni M17 aminopeptidases inhibition may affect parasite development, since they could participate in hemoglobin degradation, surface membrane remodeling and eggs hatching. Toxoplasma gondii M17 aminopeptidase inhibition could attenuate parasite virulence, since it is apparently involved in the hydrolysis of cathepsin Cs- or proteasome-produced dipeptides and/or cell attachment/invasion processes. These data are relevant to validate these enzymes as targets.

Apoptosis-Like Cell Death in Leishmania major Treated with HESA-A: An Herbal Marine Compound

Background: The first drug for the treatment of leishmaniasis is pentavalent antimony compounds which have great side effects. Objectives: This study aimed to assess apoptosis induction by HESA-A, an herbal marine compound in Leishmania major promastigotes. Methods: Leishmania major promastigotes were treated with HESA-A in different increasing concentrations ranged 1.625 - 120 µg/mL, and amphotericin B and the phenomenon of apoptosis in the parasite were evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), flow cytometry, and DNA fragmentation tests. Results: The IC50 value of the compound and amphotericin B at 72 h were estimated at 2.81 µg/mL and 40 µg/mL, respectively. After 72 h of the adjacency of Leishmania major promastigotes with IC50 dose (2.81 µg/mL), the percentage of promastigotes in early and late apoptosis phases in the treated group was 5.4% and 60.4%, respectively. DNA fragmentation of Leishmania major promastigotes treated with 2.81 µg/mL for 72 h was observed. Conclusions: HESA-A, with significant induction of apoptosis in Leishmania major promastigotes, can be plausible in the treatment of cutaneous Leishmaniasis.

Identification of Potential Kinase Inhibitors within the PI3K/AKT Pathway of Leishmania Species

Leishmaniasis is a public health disease that requires the development of more effective treatments and the identification of novel molecular targets. Since blocking the PI3K/AKT pathway has been successfully studied as an effective anticancer strategy for decades, we examined whether the same approach would also be feasible in Leishmania due to their high amount and diverse set of annotated proteins. Here, we used a best reciprocal hits protocol to identify potential protein kinase homologues in an annotated human PI3K/AKT pathway. We calculated their ligandibility based on available bioactivity data of the reported homologues and modelled their 3D structures to estimate the druggability of their binding pockets. The models were used to run a virtual screening method with molecular docking. We found and studied five protein kinases in five different Leishmania species, which are AKT, CDK, AMPK, mTOR and GSK3 homologues from the studied pathways. The compounds found for different enzymes and species were analysed and suggested as starting point scaffolds for the design of inhibitors. We studied the kinases’ participation in protein–protein interaction networks, and the potential deleterious effects, if inhibited, were supported with the literature. In the case of Leishmania GSK3, an inhibitor of its human counterpart, prioritized by our method, was validated in vitro to test its anti-Leishmania activity and indirectly infer the presence of the enzyme in the parasite. The analysis contributes to improving the knowledge about the presence of similar signalling pathways in Leishmania, as well as the discovery of compounds acting against any of these kinases as potential molecular targets in the parasite.

Efficient photodynamic inactivation of Leishmania parasites mediated by lipophilic water-soluble Zn(II) porphyrin ZnTnHex-2-PyP4

BACKGROUND

Photodynamic inactivation (PDI) is emerging as a promising alternative for cutaneous leishmaniasis (CL). The chemotherapy currently used presents adverse effects and cases of drug resistance have been reported. ZnTnHex-2-PyP4+ is a porphyrin with a high potential as a photosensitizer (PS) for PDI, due to its photophysical properties, structural stability, and cationic/amphiphilic character that can enhance interaction with cells. This study aimed to investigate the photodynamic effects mediated by ZnTnHex-2-PyP4+ on Leishmania parasites.

METHODS

ZnTnHex-2-PyP4+ stability was evaluated using accelerated solvolysis conditions. The photodynamic action on promastigotes was assessed by (i) viability assays, (ii) mitochondrial membrane potential evaluation, and (iii) morphological analysis. The PS-promastigote interaction was studied. PDI on amastigotes and the cytotoxicity on macrophages were also analyzed.

RESULTS

ZnTnHex-2-PyP4+, under submicromolar concentration, led to immediate inactivation of more than 95% of promastigotes. PDI promoted intense mitochondrial depolarization, loss of the fusiform shape, and plasma membrane wrinkling in promastigotes. Fluorescence microscopy revealed a punctate PS labeling in the parasite cytoplasm. PDI also led to reductions of ca. 64% in the number of amastigotes/macrophage and 70% in the infection index after a single treatment session. No noteworthy toxicity was observed on mammalian cells.

CONCLUSIONS

ZnTnHex-2-PyP4+ is stable against demetallation and more efficient as PS than the ethyl analogue ZnTE-2-PyP4+, indicating readiness for evaluation in in vivo studies as an alternative approach to CL.

GENERAL SIGNIFICANCE

This report highlighted promising photodynamic effects mediated by ZnTnHex-2-PyP4+ on Leishmania parasites, opening up perspectives for applications in CL pre-clinical assays and PDI of other microorganisms.

Can the iron content of culture media impact on the leishmanicidal effect of artemisinin?

Endoperoxides (EPs) like artemisinin following cleavage of their EP bridge can kill parasites via generation of carbon-centered radicals. As the presence of low molecular mass iron and/or heme is crucial, this study aimed to establish the influence of iron on the leishmanicidal action of artemisinin when present in differing amounts in culture media. In promastigotes cultured in Schneiders insect medium (SIM), that had a 8.0-fold higher amount of iron as compared to Medium 199 (M199), the impact of artemisinin on cell viability, redox status, labile iron pool (LIP), and Annexin-V positivity was evaluated. In SIM, the IC50 of artemisinin was 25.50-fold lower than M199, and in both media its cytotoxicity was decreased by the addition of hemin or following chelation of Fe2+ by Deferoxamine (DFO). In SIM vis-a-vis M199, artemisinin caused a greater redox imbalance which translated into a higher degree of externalization of phosphatidylserine and depletion of the LIP. The presence of a higher proportion of iron in SIM as compared to M199 significantly enhanced the cytotoxicity of artemisinin in Leishmania promastigotes, and was attributed to a higher degree of iron-mediated cleavage of its EP bridge that led to a higher generation of free radicals.

Related Pentacyclic Triterpenes Have Immunomodulatory Activity in Chronic Experimental Visceral Leishmaniasis

Leishmaniasis is a neglected tropical disease caused by the flagellated protozoa of the genus Leishmania that affects millions of people around the world. Drugs employed in the treatment of leishmaniasis have limited efficacy and induce local and systemic side effects to the patients. Natural products are an interesting alternative to treat leishmaniasis, because some purified molecules are selective toward parasites and not to the host cells. Thus, the aim of the present study was to compare the in vitro antileishmanial activity of the triterpenes betulin (Be), lupeol (Lu), and ursolic acid (UA); analyze the physiology and morphology of affected organelles; analyze the toxicity of selected triterpenes in golden hamsters; and study the therapeutic activity of triterpenes in hamsters infected with L. (L.) infantum as well as the cellular immunity induced by studied molecules. The triterpenes Lu and UA were active on promastigote (IC₅₀ = 4.0 ± 0.3 and 8.0 ± 0.2 μM, respectively) and amastigote forms (IC₅₀ = 17.5 ± 0.4 and 3.0 ± 0.2 μM, respectively) of L. (L.) infantum, and their selectivity indexes (SI) toward amastigote forms were higher (≥13.4 and 14, respectively) than SI of miltefosine (2.7). L. (L.) infantum promastigotes treated with Lu and UA showed cytoplasmic degradation, and in some of these areas, cell debris were identified, resembling autophagic vacuoles, and parasite mitochondria were swelled, fragmented, and displayed membrane potential altered over time. Parasite cell membrane was not affected by studied triterpenes. Studies of toxicity in golden hamster showed that Lu did not alter blood biochemical parameters associated with liver and kidney functions; however, a slight increase of aspartate aminotransferase level in animals treated with 2.5 mg/kg of UA was detected. Lu and UA triterpenes eliminated amastigote forms in the spleen (87.5 and 95.9% of reduction, respectively) and liver of infected hamster (95.9 and 99.7% of reduction, respectively); and UA showed similar activity at eliminating amastigote forms in the spleen and liver than amphotericin B (99.2 and 99.8% of reduction). The therapeutic activity of both triterpenes was associated with the elevation of IFN-γ and/or iNOS expression in infected treated animals. This is the first comparative work showing the in vitro activity, toxicity, and therapeutic activity of Lu and UA in the chronic model of visceral leishmaniasis caused by L. (L.) infantum; additionally, both triterpenes activated cellular immune response in the hamster model of visceral leishmaniasis.

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.

Gene regulation underpinning increased thermal tolerance in a laboratory-evolved coral photosymbiont

Small increases in ocean temperature can disrupt the obligate symbiosis between corals and dinoflagellate microalgae, resulting in coral bleaching. Little is known about the genes that drive the physiological and bleaching response of algal symbionts to elevated temperature. Moreover, many studies to-date have compared highly divergent strains, making it challenging to accredit specific genes to contrasting traits. Here, we compare transcriptional responses at ambient (27°C) and bleaching-relevant (31°C) temperatures in a monoclonal, wild-type (WT) strain of Symbiodiniaceae to those of a selected-strain (SS), derived from the same monoclonal culture and experimentally evolved to elevated temperature over 80 generations (2.5 years). Thousands of genes were differentially expressed at a log fold-change of >8 between the WT and SS over a 35 days temperature treatment period. At 31°C, WT cells exhibited a temporally unstable transcriptomic response upregulating genes involved in the universal stress response such as molecular chaperoning, protein repair, protein degradation and DNA repair. Comparatively, SS cells exhibited a temporally stable transcriptomic response and downregulated many stress response genes that were upregulated by the WT. Among the most highly upregulated genes in the SS at 31°C were algal transcription factors and a gene probably of bacterial origin that encodes a type II secretion system protein, suggesting interactions with bacteria may contribute to the increased thermal tolerance of the SS. Genes and functional pathways conferring thermal tolerance in the SS could be targeted in future genetic engineering experiments designed to develop thermally resilient algal symbionts for use in coral restoration and conservation.

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.

The role of Bax in the apoptosis of Leishmania-infected macrophages

BACKGROUND

Leishmania is a protozoan parasite that nests in macrophages and is responsible for the Leishmaniasis disease. In spite of different defense pathways, last strategy of macrophage for killing parasite is apoptosis process. By permeableizing the mitochondrial outer membrane (MOM). As breaching MOM releases apoptogenic factors like cytochrome-c which activate caspases that result in the destruction of the cell. In this review, we summarized the appropriate manuscripts regarding the bax includes, its different types and the effect of bax on the apoptosis of Leishmania and parasite-infected macrophages.

METHODS

Information about the role of BAX in the apoptosis of parasite-infected macrophage of recent articles were surveyed by searching computerized bibliographic database PubMed and Google Scholar entering the keywords BAX and leishmaniasis.

RESULTS

The common studies revealed Leishmania use different survival strategies for inhibiting macrophage apoptosis. As Leishmania by preventing homooligomerization or upregulating the anti-apoptotic molecule Bcl-2 can prohibits proteins of host-cell apoptosis such as Bax that is required for mitochondrial permeabilisation during apoptosis.

CONCLUSION

With regard to the supportive role of bax in apoptosis and the preventive role of Leishmania in its function, it seems that expression of bax gene in parasite by technologies like transgenic or down regulating of anti-apoptotic molecule Bcl-2 by miRNA could be prompted the apoptosis process of infected-macrophages and inhibited extensive spread of Leishmania and the resulting lesions.

Lavandula Luisieri and Lavandula Viridis Essential Oils as Upcoming Anti-Protozoal Agents: A Key Focus on Leishmaniasis

Background and objectives: Leishmania species is the causative agent of leishmaniasis, a broad-spectrum clinical condition that can even be life-threatening when neglected. Current therapeutic strategies, despite beings highly cost-effective, have been increasingly associated with the appearance of drug-resistant microorganisms. Thus, an increasing number of thorough studies are needed towards upcoming drug discovery. This study aims to reveal the anti-protozoa activity of Lavandula luisieri and Lavandula viridis essential oils (EO) and their main components (1,8-cineole, linalool, and borneol). Materials and Methods: L. luisieri and L. viridis EO and their main components’ leishmanicidal effects were tested in vitro against Leishmania infantum, Leishmania major, and Leishmania tropica strains. Cell viability effects were estimated by using the tetrazolium-dye (MTT) colorimetric method, morphological changes were assessed by scanning electron microscopy (SEM) and ultrastructural investigation by transmission electronic microscopy (TEM). Phosphatidylserine externalization, mitochondrial membrane potential (MMP), and cathepsin D activity assessment were also carried out. Finally, cytotoxic activity of the studied matrices was also determined in mammalian cells. Results: Plant-studied EO exhibited prominent anti-Leishmania effects (IC50 = 31–263 µg/mL), with L. luisieri being the most active one. At concentrations corresponding to IC50 values, EO-exposed L. infantum promastigotes suffered marked ultrastructural modifications. The presence of aberrant-shaped cells, mitochondrial and kinetoplast swelling, and autophagosomal structures were the most common evidenced changes. L. luisieri EO exerted its leishmanicidal activity through different mechanisms, but mainly through unleashing apoptosis. Phosphatidylserine externalization, mitochondrial membrane potential loss, and cell-cycle arrest at G(0)/G(1) phase were the most remarkable apoptosis-mediated aspects. Inhibition of cathepsin D activity was also observed. No toxic effects were found on macrophage cells. Conclusions: L. luisieri seems to be an upcoming source of bioactive molecules for leishmaniasis control and to find leading molecules for new drugs formulation against Leishmania infections.

Arab world's growing contribution to global leishmaniasis research (1998-2017): a bibliometric study

BACKGROUND

Leishmaniasis is a parasitic disease caused by a protozoan of the Leishmania genus, and is considered a neglected tropical disease. It still remains a main public health concern at global level and in Arab world mainly in low-income countries. Therefore, this study was designed to evaluate the Arab world's growing contribution to global leishmaniasis research.

METHODS

This study describes a bibliometric review of all leishmaniasis research publications published between January 1998 and December 2017 indexed on the Scopus database.

RESULTS

The total number of publications published at global level was 17,570 papers, which achieves an average annual productivity of 878.50 papers publications. Brazil was responsible for the greatest output with the total number of publications of 3865 followed by the Unites States (n = 2729), India (n = 2119), the United Kingdom (n = 1363), and Spain (n = 1274). By limiting the analysis to the publications that have been published by Arab world, the research productivity was 993 papers, which represents 5.65% of total research output at global level in research regarding leishmaniasis. Tunisia was responsible for the greatest output from Arab world with the total number of publications of 297 followed by Sudan (n = 192), Saudi Arabia (n = 131), Morocco (n = 119) and Egypt (n = 67). Since 1998, the growth of publications on leishmaniasis fluctuates, overall showing a rising trend in both global and Arab world. There is a highly significant correlation between publication productivity related to leishmaniasis at global level and the Arab world (r = 0.936; p-value< 0.001). Leishmaniasis treatment, intracellular mechanism of infection, and lifecycle of leishmania are the major current hot topics for the research in this subject at global level and the Arab world.

CONCLUSIONS

The current study presents a novel review of the current Arab leishmaniasis-related research, and how these results are related to worldwide output. In comparison to the global research output, the Arab world produced less leishmaniasis research. The data presented in the current study by this innovative approach may serve relevant researchers to direct the global leishmaniasis research to Arab counties in which leishmaniasis is endemic.

Efficacy of lapachol on treatment of cutaneous and visceral leishmaniasis

Leishmaniasis is one of the most important neglected diseases worldwide. It is a life-threatening disease and causes significant morbidity, long-term disability, and early death. Treatment involves disease control or use of intervention measures, although the currently used drugs require long-lasting therapy, and display toxicity and reduced efficacy. The use of natural products isolated from plants, such as lapachol, an abundant naphthoquinone naturally occurring in South American Handroanthus species (Tabebuia, Bignoniaceae), is a promising option for the treatment of leishmaniasis. In this study, we investigated the leishmanicidal activity of lapachol in vitro and in vivo against Leishmania infantum and L. amazonensis, causative agents of visceral and cutaneous leishmaniasis, respectively. Low cytotoxicity in HepG2 cells (3405.8 ± 261.33 μM), good anti-Leishmania activity, and favorable selectivity indexes (SI) against promastigotes of both L. amazonensis (IC₅₀ = 79.84 ± 9.10 μM, SI = 42.65) and L. infantum (IC₅₀ = 135.79 ± 33.04 μM, SI = 25.08) were observed. Furthermore, anti-Leishmania activity assays performed on intracellular amastigotes showed good activity for lapachol (IC₅₀ = 191.95 μM for L. amazonensis and 171.26 μM for L. infantum). Flow cytometric analysis demonstrated that the cytotoxic effect of lapachol in Leishmania promastigotes was caused by apoptosis-like death. Interestingly, the in vitro leishmanicidal effect of lapachol was confirmed in vivo in murine models of visceral and cutaneous leishmaniasis, as lapachol (25 mg/kg oral route for 24 h over 10 days) was able to significantly reduce the parasitic load in skin lesions, liver, and spleen, similar to amphotericin B, the reference drug. These results reinforce the therapeutic potential of lapachol, which warrants further investigations as an anti-leishmaniasis therapeutic.

Emerging role of amiodarone and dronedarone, as antiarrhythmic drugs, in treatment of leishmaniasis

Leishmaniasis is a group of human and animal diseases causing 20,000-40,000 annual deaths and its etiological agents belong to the Leishmania genus. The most current treatment against leishmaniasis is chemotherapy. Pentavalent antimonials such as glucantime and pentostam have been administrated as the first-line drugs in treatment of various forms of leishmaniasis. The second-line drugs such as amphotericin B, liposomal amphotericin B, miltefosine, pentamidine, azole drugs and paromomycin are used in resistant cases to pentavalent antimonials. Because of drawbacks of the first-line and second-line drugs including adverse side effects on different organs, increasing resistance, high cost, need to hospitalization and long-term treatment, it is necessary to find an alternative drug for leishmaniasis treatment. Several investigations have reported the effectiveness of amiodarone, the most commonly used antiarrhythmic drug, against fungi, Trypanosomes and Leishmania spp. in vitro, in vivo and clinical conditions. Moreover, the beneficial effects of dronedarone, amiodarone analogues, against Trypanosoma cruzi and Leishmania mexicana have recently been demonstrated and such treatment regimens resulted in lower side effects. The anti- leishmanial and anti- trypanosomal effectiveness of amiodarone and dronedarone has been attributed to destabilization of intracellular Ca²⁺ homeostasis, inhibition of sterol biosynthesis and collapse of mitochondrial membrane potential. Because of relative low cost, excellent pharmacokinetic properties, easy accessibility and beneficial effects of amiodarone and dronedarone on leishmaniasis, they are proper candidates to replace the current drugs used in leishmaniasis treatment.

Temporal analysis of the autophagic and apoptotic phenotypes in Leishmania parasites

The leishmaniases are worldwide neglected tropical diseases caused by parasitic protozoa of the Leishmania genus. Different stimuli induce Leishmania cell death, but the proteins involved remain poorly understood. Furthermore, confusion often appears between cell death and the cell survival process autophagy, whose phenotype is not clearly defined. In this article, we present a comprehensive and temporal analysis of the cellular events occurring during miltefosine-induced cell death and autophagy in L. major. We also provide a list of features in order to clearly identify apoptotic cells, autophagic cells and to distinguish both processes. Furthermore, we demonstrate that autophagy is followed by apoptosis in the absence of nutrients. Finally, we show that cells treated with the generic kinase inhibitor staurosporine express apoptotic as well as autophagic markers and therefore cannot be used as an apoptosis inducer in Leishmania. These descriptions lead to a better recognition and understanding of apoptosis and autophagy, enabling their targeting in the development of new anti-leishmanial drugs. These researches also make it possible to better understand these processes in general, through the study of an ancestral eukaryote.

A3K2A3-induced apoptotic cell death of Leishmania amazonensis occurs through caspase- and ATP-dependent mitochondrial dysfunction

Leishmaniasis is a neglected tropical disease that affects millions of people worldwide. Current therapies mainly rely on antimonial drugs that are inadequate because of their high toxicity and increased drug resistance. An urgent need exists to discover new, more effective, more affordable, and more target-specific drugs. Pathways that are associated with apoptosis-like cell death have been identified in unicellular eukaryotes, including protozoan parasites. In the present study, we studied the mechanism of cell death that is induced by A3K2A3 against L. amazonensis. A3K2A3 is a dibenzylideneacetone that has an acyclic dienone that is attached to aryl groups in both β-positions, which is similar to curcuminoids and chalcone structures. This compound was previously shown to be safe with regard to cytotoxicity and active against the parasite. Biochemical and morphological approaches were used in the present study. The results suggested that A3K2A3 caused mitochondrial dysfunction in L. amazonensis promastigotes, leading to mechanisms of cell death that share some common phenotypic features with metazoan apoptosis, such as an increase in reactive oxygen species production, a decrease in the adenosine triphosphate ratio, phosphatidylserine exposure, a decrease in cell volume, caspase production, and DNA fragmentation. Altogether, these findings indicate that apoptosis can indeed be triggered by chemotherapeutic agents.

Moroccan strains of Leishmania major and Leishmania tropica differentially impact on nitric oxide production by macrophages

BACKGROUND

Cutaneous leishmaniasis (CL) is a vector-borne parasitic disease caused by protozoa of the genus Leishmania. In Morocco, CL is a public health problem mainly caused by Leishmania major and Leishmania tropica, which are responsible for zoonotic and anthroponotic CL, respectively. Macrophages are the primary cells infected by Leishmania parasites and their capacity to produce nitric oxide (NO) is of critical importance for parasite elimination. To our knowledge, the role of NO on autochthonous infections has never been investigated before. In this study, we evaluated in vitro the capacity of autochthonous primary dermotropic strains of L. major and L. tropica to modulate NO production by J774-macrophages and determine the sensitivity of both species to exogenous NO.

METHODS

The infectivity of the J774 cell line was analyzed by optical microscopy. NO production by macrophages was measured by the Griess method. The sensitivity to NO by the two strains was assessed by the MTT assay using NO donors.

RESULTS

Our results show that the percentage of infected macrophages and the average number of parasites per macrophage were similar for L. major and L. tropica strains. While L. tropica significantly inhibited NO production induced by LPS and IFN-γ stimulation in J774 macrophages, L. major did not affect it. However, soluble Leishmania antigens (SLAs) from both autochthonous primary strains significantly inhibited the production of NO by J774-macrophages in a dose-dependent manner. Finally, our results demonstrated that promastigotes and amastigotes from both strains are sensitive to SNAP NO donor in a dose-dependent manner, although L. tropica demonstrated an increased sensitivity.

CONCLUSIONS

Our results suggest a differential ability of L. major and L. tropica strains to modulate the capacity of macrophages to produce NO. The increased ability of L. tropica to inhibit NO production by macrophages might come as a necessity due to its higher sensitivity to NO donor. Our results provide one explanation for the tendency of L. tropica to cause chronic lesions and may contribute to the different physiopathology of CL in Morocco.

Zinc depletion promotes apoptosis-like death in drug-sensitive and antimony-resistance Leishmania donovani

Micronutrients are essential for survival and growth for all the organisms including pathogens. In this manuscript, we report that zinc (Zn) chelator N,N,N’,N’-tetrakis(2-pyridinylmethyl)-1,2-ethylenediamine (TPEN) affects growth and viability of intracellular pathogen Leishmania donovani (LD) by a concentration and time dependent manner. Simultaneous addition of zinc salt reverses the effect of TPEN. Further experiments provide evidence of apoptosis-like death of the parasite due to Zn-depletion. TPEN treatment enhances caspase-like activity suggesting increase in apoptosis-like events in LD. Specific inhibitors of cathepsin B and Endoclease G block TPEN-induced leishmanial death. Evidences show involvement of reactive oxygen species (ROS) potentially of extra-mitochondrial origin in TPEN-induced LD death. Pentavalent antimonials remained the prime source of treatment against leishmaniasis for several decades; however, antimony-resistant Leishmania is now common source of the disease. We also reveal that Zn-depletion can promote apoptosis-like death in antimony-resistant parasites. In summary, we present a new finding about the role of zinc in the survival of drug sensitive and antimony-resistant LD.

Calcium sensing receptor protects high glucose-induced energy metabolism disorder via blocking gp78-ubiquitin proteasome pathway

Diabetic cardiomyopathy (DCM) is a major complication and fatal cause of the patients with diabetes. The calcium sensing receptor (CaSR) is a G protein-coupled receptor, which is involved in maintaining calcium homeostasis, regulating cell proliferation and apoptosis, and so on. In our previous study, we found that CaSR expression, intracellular calcium levels and cardiac function were all significantly decreased in DCM rats; however, the exact mechanism are not clear yet. The present study revealed the protective role of CaSR in myocardial energy metabolism disorder induced by high glucose (HG) as well as the underlying mechanism. Here, we demonstrated that HG decreased the expression of CaSR, mitochondrial fusion proteins (Mfn1, Mfn2), cell gap junction related proteins (Cx43, β-catenin, N-cadherin), and intracellular ATP concentration. In contrast, HG increased extracellular ATP concentration, the expression of gp78, mitochondrial fission proteins (Fis1, Drp1), and the ubiquitination levels of Mfn1, Mfn2 and Cx43. Moreover, CaSR agonist and gp78-siRNA significantly reduced the above changes. Taken together, these results suggest that HG induces myocardial energy metabolism disorder via decrease of CaSR expression, and activation of gp78-ubiquitin proteasome system. In turn, these effects disrupt the structure and function of the mitochondria and the cell gap junction, result in the reduced ATP synthesis and the increased ATP leakage. Stimulation of CaSR significantly attenuates HG-induced abnormal myocardial energy metabolism, suggesting CaSR would be a promising potential therapeutic target for DCM.

Evolution of caspase-mediated cell death and differentiation: twins separated at birth

The phenotypic and biochemical similarities between caspase-mediated apoptosis and cellular differentiation are striking. They include such diverse phenomenon as mitochondrial membrane perturbations, cytoskeletal rearrangements and DNA fragmentation. The parallels between the two disparate processes suggest some common ancestry and highlight the paradoxical nature of the death-centric view of caspases. That is, what is the driving selective pressure that sustains death-inducing proteins throughout eukaryotic evolution? Plausibly, caspase function may be rooted in a primordial non-death function, such as cell differentiation, and was co-opted for its role in programmed cell death. This review will delve into the links between caspase-mediated apoptosis and cell differentiation and examine the distinguishing features of these events. More critically, we chronicle the evolutionary origins of caspases and propose that caspases may have held an ancient role in mediating the fidelity of cell division/differentiation through its effects on proteostasis and protein quality control.

Methionine aminopeptidase 2 is a key regulator of apoptotic like cell death in Leishmania donovani

We investigate the role of methionine aminopeptidase 2 (MAP2) in miltefosine induced programmed cell death (PCD) in promastigote form of L. donovani. We report that TNP-470, an inhibitor of MAP2, inhibits programmed cell death in miltefosine treated promastigotes. It inhibits the biochemical features of metazoan apoptosis, including caspase3/7 protease like activity, oligonucleosomal DNA fragmentation, collapse of mitochondrial transmembrane potential, and increase in cytosolic pool of calcium ions but did not prevent the cell death and phosphatidyl serine externalization. The data suggests that the MAP2 is involved in the regulation of PCD in parasite. Moreover, TNP-470 shows the leishmanicidal activity (IC₅₀ = 15 µM) and in vitro inhibition of LdMAP2 activity (K_i = 13.5 nM). Further studies on MAP2 and identification of death signaling pathways provide valuable information that could be exploited to understand the role of non caspase proteases in PCD of L. donovani.

DDX3 DEAD-box RNA helicase plays a central role in mitochondrial protein quality control in Leishmania

DDX3 is a highly conserved member of ATP-dependent DEAD-box RNA helicases with multiple functions in RNA metabolism and cellular signaling. Here, we describe a novel function for DDX3 in regulating the mitochondrial stress response in the parasitic protozoan Leishmania. We show that genetic inactivation of DDX3 leads to the accumulation of mitochondrial reactive oxygen species (ROS) associated with a defect in hydrogen peroxide detoxification. Upon stress, ROS production is greatly enhanced, causing mitochondrial membrane potential loss, mitochondrial fragmentation, and cell death. Importantly, this phenotype is exacerbated upon oxidative stress in parasites forced to use the mitochondrial oxidative respiratory machinery. Furthermore, we show that in the absence of DDX3, levels of major components of the unfolded protein response as well as of polyubiquitinated proteins increase in the parasite, particularly in the mitochondrion, as an indicator of mitochondrial protein damage. Consistent with these findings, immunoprecipitation and mass-spectrometry studies revealed potential interactions of DDX3 with key components of the cellular stress response, particularly the antioxidant response, the unfolded protein response, and the AAA-ATPase p97/VCP/Cdc48, which is essential in mitochondrial protein quality control by driving proteosomal degradation of polyubiquitinated proteins. Complementation studies using DDX3 deletion mutants lacking conserved motifs within the helicase core support that binding of DDX3 to ATP is essential for DDX3's function in mitochondrial proteostasis. As a result of the inability of DDX3-depleted Leishmania to recover from ROS damage and to survive various stresses in the host macrophage, parasite intracellular development was impaired. Collectively, these observations support a central role for the Leishmania DDX3 homolog in preventing ROS-mediated damage and in maintaining mitochondrial protein quality control.

Amiodarone triggers induction of apoptosis in cutaneous leishmaniasis agents

Leishmaniasis is a parasitic disease that is an important problem of public health worldwide. The aim of this study was to assess the cytotoxic effects of amiodarone (AMD) on Leishmania tropica (MHOM/AF/88/KK27) and L. major (MRHO/IR/75/ER) promastigotes and to observe the programmed cell death features. The colorimetric MTT assay was used to find L. tropica and L. major viability and the obtained results were expressed as 50% inhibitory concentration (IC50). Annexin-V FLUOS staining was performed to study the cell death properties of AMD using fluorescence-activated cell-sorting analysis. Qualitative analysis of the total genomic DNA fragmentation was performed by agarose gel electrophoresis. Furthermore, to observe changes in cell morphology, promastigotes were examined using light microscopy. The IC50 was achieved at 55 and 81 μM for L. tropica and L. major after 48 h of incubation, respectively. In both strains, AMD induced death with features of apoptosis, including externalization of phosphatidylserine, DNA laddering, and cell shrinkage. Our findings indicate that AMD may induce apoptosis on the causative agents of cutaneous leishmaniasis.

The antifungal compound butenafine eliminates promastigote and amastigote forms of Leishmania (Leishmania) amazonensis and Leishmania (Viannia) braziliensis

The production of ergosterol lipid, important for the Leishmania membrane homeostasis, involves different enzymes. This pathway can be blocked to azoles and allylamines drugs, such as Butenafine. The aim of the present work was to evaluate the anti-leishmanicidal activity of this drug in 2 major species of Leishmania responsible for causing the American tegumentar leishmaniasis (L. (L.) amazonensis and L. (V.) braziliensis). Butenafine eliminated promastigote forms of L. amazonensis and L. braziliensis with efficacy similar to miltefosine, a standard anti-leishmania drug. In addition, butenafine induced alterations in promastigote forms of L. amazonensis that resemble programmed cell death. Butenafine as well as miltefosine presented mild toxicity in peritoneal macrophages, however, butenafine was more effective to eliminate intracellular amastigotes of both L. amazonensis and L. braziliensis, and this effect was not associated with elevated levels of nitric oxide or hydrogen peroxide. Taken together, data presented herein suggests that butenafine can be considered as a prototype drug able to eliminate L. amazonensis and L. braziliensis, etiological agents of anergic diffuse and mucocutaneous leishmaniasis, respectively.

A functional BH3 domain in an aquaporin from Leishmania infantum

Despite the absence of sequences showing significant similarity to any of the members of the Bcl-2 family of proteins in protozoa, experiments carried out in yeast or trypanosomatids have demonstrated that ectopic expression of some of these members alters their response to different death stimuli. Because the BH3 domain is the smallest common signature in all the proteins of this family of apoptosis regulators and also because they are essential for molecular interactions between antagonistic members, we looked for sequences with significant similarity to the BH3 motif in the Leishmania infantum genome. Among the top scoring ones, we found the MYLALQNLGDEV amino-acid stretch at the C terminus of a previously described aquaporin, now renamed as Li-BH3AQP. This motif is highly conserved in homologous proteins from other species of the Leishmania genus. The association of Li-BH3AQP with human Bcl-XL was demonstrated by both co-immunoprecipitation and yeast two-hybrid experiments. Ectopic expression of Li-BH3AQP reduced viability of HeLa cells and this deleterious effect was abrogated by the simultaneous overexpression of Bcl-XL. Although we were not able to demonstrate a reduction in parasite viability when the protein was overexpressed in Leishmania promastigotes, a prodeath effect could be observed when the parasites overexpressing Li-BH3AQP were treated with staurosporine or antimycin A. Surprisingly, these parasites were more resistant, compared with wild-type parasites, to hypotonic stress or nutrient deprivation. The prodeath activity was abolished upon replacement of two highly conserved amino acids in this BH3 domain. Taken together, these results point to Li-BH3AQP as the first non-enzymatic protein ever described in trypanosomatids that is involved in cell death.

Deprivation of L-Arginine Induces Oxidative Stress Mediated Apoptosis in Leishmania donovani Promastigotes: Contribution of the Polyamine Pathway

The growth and survival of intracellular parasites depends on the availability of extracellular nutrients. Deprivation of nutrients viz glucose or amino acid alters redox balance in mammalian cells as well as some lower organisms. To further understand the relationship, the mechanistic role of L-arginine in regulation of redox mediated survival of Leishmania donovani promastigotes was investigated. L-arginine deprivation from the culture medium was found to inhibit cell growth, reduce proliferation and increase L-arginine uptake. Relative expression of enzymes, involved in L-arginine metabolism, which leads to polyamine and trypanothione biosynthesis, were downregulated causing decreased production of polyamines in L-arginine deprived parasites and cell death. The resultant increase in reactive oxygen species (ROS), due to L-arginine deprivation, correlated with increased NADP+/NADPH ratio, decreased superoxide dismutase (SOD) level, increased lipid peroxidation and reduced thiol content. A deficiency of L-arginine triggered phosphatidyl serine externalization, a change in mitochondrial membrane potential, release of intracellular calcium and cytochrome-c. This finally led to DNA damage in Leishmania promastigotes. In summary, the growth and survival of Leishmania depends on the availability of extracellular L-arginine. In its absence the parasite undergoes ROS mediated, caspase-independent apoptosis-like cell death. Therefore, L-arginine metabolism pathway could be a probable target for controlling the growth of Leishmania parasites and disease pathogenesis.

Implication of different domains of the Leishmania major metacaspase in cell death and autophagy

Metacaspases (MCAs) are cysteine peptidases expressed in plants, fungi and protozoa, with a caspase-like histidine–cysteine catalytic dyad, but differing from caspases, for example, in their substrate specificity. The role of MCAs is subject to debate: roles in cell cycle control, in cell death or even in cell survival have been suggested. In this study, using a Leishmania major MCA-deficient strain, we showed that L. major MCA (LmjMCA) not only had a role similar to caspases in cell death but also in autophagy and this through different domains. Upon cell death induction by miltefosine or H₂O₂, LmjMCA is processed, releasing the catalytic domain, which activated substrates via its catalytic dyad His/Cys and a proline-rich C-terminal domain. The C-terminal domain interacted with proteins, notably proteins involved in stress regulation, such as the MAP kinase LmaMPK7 or programmed cell death like the calpain-like cysteine peptidase. We also showed a new role of LmjMCA in autophagy, acting on or upstream of ATG8, involving Lmjmca gene overexpression and interaction of the C-terminal domain of LmjMCA with itself and other proteins. These results allowed us to propose two models, showing the role of LmjMCA in the cell death and also in the autophagy pathway, implicating different protein domains.

A putative role for inosine 5' monophosphate dehydrogenase (IMPDH) in Leishmania amazonensis programmed cell death

Leishmania amazonensis undergoes apoptosis-like programmed cell death (PCD) under heat shock conditions. We identified a potential role for inosine 5' monophosphate dehydrogenase (IMPDH) in L. amazonensis PCD. Trypanosomatids do not have a "de novo" purine synthesis pathway, relying on the salvage pathway for survival. IMPDH, a key enzyme in the purine nucleotide pathway, is related to cell growth and apoptosis. Since guanine nucleotide depletion triggers cell cycle arrest and apoptosis in several organisms we analyzed the correlation between IMPDH and apoptosis-like death in L. amazonensis. The L. amazonensis IMPDH inhibition effect on PCD was evaluated through gene expression analysis, mitochondrial depolarization and detection of Annexin-V labeled parasites. We demonstrated a down-regulation of impdh expression under heat shock treatment, which mimics the natural mammalian host infection. Also, IMPDH inhibitors ribavirin and mycophenolic acid (MPA) prevented cell growth and generated an apoptosis-like phenotype in sub-populations of L. amazonensis promastigotes. Our results are in accordance with previous results showing that a subpopulation of parasites undergoes apoptosis-like cell death in the nutrient poor environment of the vector gut. Here, we suggest the involvement of purine metabolism in previously observed apoptosis-like cell death during Leishmania infection.

The molecular ecophysiology of programmed cell death in marine phytoplankton

Planktonic, prokaryotic, and eukaryotic photoautotrophs (phytoplankton) share a diverse and ancient evolutionary history, during which time they have played key roles in regulating marine food webs, biogeochemical cycles, and Earth's climate. Because phytoplankton represent the basis of marine ecosystems, the manner in which they die critically determines the flow and fate of photosynthetically fixed organic matter (and associated elements), ultimately constraining upper-ocean biogeochemistry. Programmed cell death (PCD) and associated pathway genes, which are triggered by a variety of nutrient stressors and are employed by parasitic viruses, play an integral role in determining the cell fate of diverse photoautotrophs in the modern ocean. Indeed, these multifaceted death pathways continue to shape the success and evolutionary trajectory of diverse phytoplankton lineages at sea. Research over the past two decades has employed physiological, biochemical, and genetic techniques to provide a novel, comprehensive, mechanistic understanding of the factors controlling this key process. Here, I discuss the current understanding of the genetics, activation, and regulation of PCD pathways in marine model systems; how PCD evolved in unicellular photoautotrophs; how it mechanistically interfaces with viral infection pathways; how stress signals are sensed and transduced into cellular responses; and how novel molecular and biochemical tools are revealing the impact of PCD genes on the fate of natural phytoplankton assemblages.

Induction of mitochondrial dysfunction and oxidative stress in Leishmania donovani by orally active clerodane diterpene

This study was performed to investigate the mechanistic aspects of cell death induced by a clerodane diterpene (K-09) in Leishmania donovani promastigotes that was previously demonstrated to be safe and orally active against visceral leishmaniasis (VL). K-09 caused depolarization of the mitochondrion and the generation of reactive oxygen species, triggering an apoptotic response in L. donovani promastigotes. Mitochondrial dysfunction subsequently resulted in the release of cytochrome c into the cytosol, impairing ATP production. Oxidative stress caused the depletion of reduced glutathione, while pretreatment with antioxidant N-acetyl cysteine (NAC) was able to abrogate oxidative stress. However, NAC failed to restore the mitochondrial membrane potential or intracellular calcium homeostasis after K-09 treatment, suggesting that the generation of oxidative stress is a downstream event relative to the other events. Caspase-3/-7-like protease activity and genomic DNA fragmentation were observed. Electron microscopy studies revealed gross morphological alterations typical of apoptosis, including severe mitochondrial damage, pyknosis of the nucleus, structural disruption of the mitochondrion-kinetoplast complex, flagellar pocket alterations, and the displacement of organelles. Moreover, an increased number of lipid droplets was detected after K-09 treatment, which is suggestive of altered lipid metabolism. Our results indicate that K-09 induces mitochondrial dysfunction and oxidative stress-mediated apoptotic cell death in L. donovani promastigotes, sharing many features with metazoan apoptosis. These mechanistic insights provide a basis for further investigation toward the development of K-09 as a potential drug candidate for VL.

Activity of melatonin against Leishmania infantum promastigotes by mitochondrial dependent pathway

Visceral leishmaniasis, a potentially fatal disease, remains a major international health problem. Only a limited number of effective antileishmanial agents are available for chemotherapy, and many of them are expensive with severe side effects or have a markedly reduced effectiveness due to the development of drug resistance. Hence, there is a genuine need to develop a novel effective and less toxic antileishmanial drug. Melatonin, a neurohormone found in animals, plants, and microbes, can participate in various biological and physiological functions. Several in vitro or in vivo studies have reported the inhibitory effect of melatonin against many parasites via various mechanisms, including modulation of intracellular concentrations of calcium in the parasite and/or any other suggested mechanism. Importantly, many of available antileishmanial drugs have been reported to exert their effects by disrupting calcium homeostasis in the parasite. The objective of the present study was to test the efficacy of exogenous melatonin against Leishmania infantum promastigotes in vitro. Interestingly, melatonin not only demonstrated a significant antileishmanial activity of against promastigote viability in tested cultures but was also accompanied by an alteration of the calcium homeostasis of parasite mitochondrion, represented by earlier mitochondrial permeability transition pore opening, and by changes in some mitochondrial parameters are critical to parasite survival. These pioneering findings suggest that melatonin may be a candidate for the development of novel effective antileishmanial agents either alone or in associations with other drugs.

Trypanosoma cruzi cell death induced by the Morita-Baylis-Hillman adduct 3-Hydroxy-2-methylene-3-(4-nitrophenylpropanenitrile)

Chagas disease, caused by the protozoan Trypanosoma cruzi, remains a serious health concern due to the lack of effective vaccines or satisfactory treatment. In the search for new compounds against this neglected disease, we have previously demonstrated that the compound 3-Hydroxy-2-methylene-3-(4-nitrophenylpropanenitrile) (MBHA3), derived from the Morita-Baylis-Hillman reaction, effectively caused a loss of viability in both the epimastigote and trypomastigote forms. However, the mechanisms of parasite death elicited by MBHA3 remain unknown. The aim of this study was to better understand the morphophysiological changes and the mechanism of cell death induced by MBHA3 treatment on T. cruzi. To perform this analysis, we used confocal microscopy and flow cytometry to monitor the fluorescent probes such as annexin-V/propidium iodide (AV/PI), calcein-AM/ethidium homodimer (CA/EH), acridine orange (AO) and rhodamine 123 (Rho 123). Lower concentrations of MBHA3 led to alterations in the mitochondrial membrane potential and AO labeling, but did not decrease the viability of the epimastiogote forms, as determined by the CA/EH and AV/PI assays. Conversely, treatment with higher concentrations of MBHA3 led to extensive plasma membrane damage, loss of mitochondrion membrane potential, DNA fragmentation and acidification of the cytoplasm. Our findings suggest that at higher concentrations, MBHA3 induces T. cruzi epimastigote death by necrosis in a mitochondrion-dependent manner.

Auranofin is an apoptosis-simulating agent with in vitro and in vivo anti-leishmanial activity

Cutaneous leishmaniasis remains ignored in therapeutic drug discovery programs worldwide. This is mainly because cutaneous leishmaniasis is frequently a disease of impoverished populations in countries where funds are limited for research and patient care. However, the health burden of individuals in endemic areas mandates readily available, effective, and safe treatments. Of the existing cutaneous leishmaniasis therapeutics, many are growth inhibitory to Leishmania parasites, potentially creating dormant parasite reservoirs that can be activated when host immunity is compromised, enabling the reemergence of cutaneous leishmaniasis lesions or worse spread of Leishmania parasites to other body sites. To accelerate the identification and development of novel cutaneous leishmaniasis therapeutics, we designed an integrated in vitro and in vivo screening platform that incorporated multiple Leishmania life cycles and species and probed a focused library of pharmaceutically active compounds. The objective of this phenotypic drug discovery platform was the identification and prioritization of bona fide cytotoxic chemotypes toward Leishmania parasites. We identified the Food and Drug Administration-approved drug auranofin, a known inhibitor of Leishmania promastigote growth, as a potent cytotoxic anti-leishmanial agent and inducer of apoptotic-like death in promastigotes. Significantly, the anti-leishmanial activity of auranofin transferred to cell-based amastigote assays as well as in vivo murine models. With appropriate future investigation, these data may provide the foundation for potential exploitation of gold(I)-based complexes as chemical tools or the basis of therapeutics for leishmaniasis. Thus, auranofin may represent a prototype drug that can be used to identify signaling pathways within the parasite and host cell critical for parasite growth and survival.

Activity of Thymus capitellatus volatile extract, 1,8-cineole and borneol against Leishmania species

In the search for new leishmanicidal agents, Thymus capitellatus Hoffmanns. & Link (family Lamiaceae) volatile extract and its major compounds, 1,8-cineole and borneol, were tested against Leishmania infantum, Leishmania tropica and Leishmania major. Plant volatile extract (essential oil) was analysed by GC and GC-MS and the activity of essential oil on Leishmania promastigotes viability was assessed using tetrazolium-dye colorimetric method (MTT). The MTT test was also used to assess the cytotoxicity of essential oil on macrophages and bovine aortic endothelial cells. Effects on parasites were also analyzed by flow cytometry in order to assess mitochondrial transmembrane electrochemical gradient (JC-1), analyze phosphatidylserine externalization (annexin V-FITC, propidium iodide) and evaluate cell cycle (DNase-free, RNase, PI). Morphological and ultrastructural studies were performed by light, scanning and transmission electron microscopy. T. capitellatus volatile extract exhibited anti-parasite activity on Leishmania species, with IC50 values ranging from 35 to 62 μg/ml. However, major compounds 1,8-cineole and borneol did not showed biological activity suggesting that these monoterpenes are not responsible for the antileishmanial activity of T. capitellatus essential oil. Appearance of aberrant-shaped cells, mitochondrial swelling and autophagosomal structures were some of the ultrastructural alterations exhibited among treated promastigote cells. T. capitellatus promoted leishmanicidal effect by triggering a programmed cell death as evidenced by externalization of phosphatidylserine, loss of mitochondrial membrane potential, and cell-cycle arrest at the G(0)/G(1) phase. The volatile extract did not induced cytotoxic effects on mammalian cells. Taken together, these results suggest that T. capitellatus may represent a valuable source for therapeutic control of leishmaniasis in humans and animals.

Apoptosis-like cell death pathways in the unicellular parasite Toxoplasma gondii following treatment with apoptosis inducers and chemotherapeutic agents: a proof-of-concept study

Ancient pathways of an apoptosis-like cell death have been identified in unicellular eukaryotes including protozoan parasites. Here, we examined programmed cell death in the apicomplexan Toxoplasma gondii which is a common intracellular pathogen of humans and warm-blooded animals. Treatment of extracellular T. gondii with various pro-apoptotic stimuli significantly induced DNA strand breaks as revealed by TUNEL and flow cytometry. Using staurosporine or miltefosine as pro-apoptotic stimuli, parasites also presented a reduced cell size, i.e. pyknosis and externalized phosphatidylserine while the plasma membrane remained intact. Importantly, staurosporine also induced DNA strand breaks in intracellular T. gondii. Data mining of the Toxoplasma genome resource identified 17 putative cell death-associated genes encoding proteases, a nuclease and several apoptosis regulators. Staurosporine-treated parasites but not controls strongly up-regulated several of these genes in a time-dependent fashion with a putative PDCD2 protein being more than 100-fold up-regulated. However, the mitochondrial membrane potential (ΔΨ_m) remained intact and caspase-like activity increased only slightly during staurosporine-triggered cell death. As compared to staurosporine, the transcriptional response of parasites to miltefosine was more restricted but PDCD2 was again strongly induced. Furthermore, T. gondii lost their ΔΨ_m and rapidly presented strong caspase-like activity during miltefosine treatment. Consequently, protease inhibitors abrogated miltefosine-induced but not staurosporine-induced Toxoplasma cell death. Finally, toxoplasmacidal drugs triggered DNA strand breaks in extracellular T. gondii. Interestingly, clindamycin also induced markers of an apoptosis-like cell death in intracellular parasites. Together, the data indicate that T. gondii possesses ancient apoptosis-like cell death machinery which can be triggered by chemotherapeutic agents.

The first suicides: a legacy inherited by parasitic protozoans from prokaryote ancestors

It is more than 25 years since the first report that a protozoan parasite could die by a process resulting in a morphological phenotype akin to apoptosis. Since then these phenotypes have been observed in many unicellular parasites, including trypanosomatids and apicomplexans, and experimental evidence concerning the molecular pathways that are involved is growing. These observations support the view that this form of programmed cell death is an ancient one that predates the evolution of multicellularity. Here we review various hypotheses that attempt to explain the origin of apoptosis, and look for support for these hypotheses amongst the parasitic protists as, with the exception of yeast, most of the work on death mechanisms in unicellular organisms has focussed on them. We examine the role that addiction modules may have played in the original eukaryote cell and the part played by mitochondria in the execution of present day cells, looking for examples from Leishmania spp. Trypanosoma spp. and Plasmodium spp. In addition, the expanding knowledge of proteases, nucleases and other molecules acting in protist execution pathways has enabled comparisons to be made with extant Archaea and bacteria and with biochemical pathways that evolved in metazoans. These comparisons lend support to the original sin hypothesis but also suggest that present-day death pathways may have had multifaceted beginnings.

Eupomatenoid-5 Isolated from Leaves of Piper regnellii Induces Apoptosis in Leishmania amazonensis

Leishmania spp. are protozoa responsible for leishmaniasis, a neglected disease that kills up to 50,000 people every year. Current therapies mainly rely on antimonial drugs that are inadequate because of their poor efficacy and safety and increased drug resistance. An urgent need exists to find new and more affordable drugs. Our previous study demonstrated the antileishmanial activity of eupomatenoid-5, a neolignan obtained from leaves of Piper regnellii var. pallescens. The aim of the present study was to clarify the mode of action of eupomatenoid-5 against L. amazonensis. We used biochemical and morphological techniques and demonstrated that eupomatenoid-5 induced cell death in L. amazonensis promastigotes, sharing some phenotypic features observed in metazoan apoptosis, including increased reactive oxygen species production, hypopolarization of mitochondrial potential, phosphatidylserine exposure, decreased cell volume, and G0/G1 phase cell cycle arrest.