Protozoan parasites: programmed cell death as a mechanism of parasitism

Acrylonitrile derivatives: In vitro activity and mechanism of cell death induction against Trypanosoma cruzi and Leishmania amazonensis

Leishmaniasis and Chagas disease are parasitic infections that affect millions of people worldwide, producing thousands of deaths per year. The current treatments against these pathologies are not totally effective and produce some side effects in the patients. Acrylonitrile derivatives are a group of compounds that have shown activity against these two diseases. In this work, four novels synthetic acrylonitriles were evaluated against the intracellular form and extracellular forms of L. amazonensis and T. cruzi. The compounds 2 and 3 demonstrate to have good selectivity indexes against both parasites, specifically the compound 3 against the amastigote form (SI = 6 against L. amazonensis and SI = 7.4 against T. cruzi). In addition, the parasites treated with these two compounds demonstrate to produce a programmed cell death, since they were positive for the events studied related to this type of death, including chromatin condensation, accumulation of reactive oxygen species and alteration of the mitochondrial membrane potential. In conclusion, this work confirms that acrylonitriles is a source of possible new compounds against kinetoplastids, however, more studies are needed to corroborate this activity.

Honokiol induces apoptosis-like death in Cryptocaryon irritans Tomont

BACKGROUND

Cryptocaryon irritans, a common parasite in tropical and subtropical marine teleost fish, has caused serious harm to the marine aquaculture industry. Honokiol was proven to induce C. irritans tomont cytoplasm shrinkage and death in our previous study, but the mechanism by which it works remains unknown.

METHODS

In this study, the changes of apoptotic morphology and apoptotic ratio were detected by microscopic observation and AnnexinV-FITC/PI staining. The effects of honokiol on intracellular calcium ([Ca2+]i) concentration, mitochondrial membrane potential (ΔΨm), reactive oxygen species (ROS), quantity of DNA fragmentations (QDF) and caspase activities were detected by Fluo-3 staining, JC-1 staining, DCFH-DA staining, Tunel method and caspase activity assay kit. The effects of honokiol on mRNA expression levels of 61 apoptosis-related genes in tomonts of C. irritans were detected by real-time PCR.

RESULTS

The results of the study on the effects of honokiol concentration on C. irritans tomont apoptosis-like death showed that the highest levels of prophase apoptosis-like death rate (PADR), [Ca2+]i concentration, ROS, the activities of caspase-3/9 and the lowest necrosis ratio (NER) were obtained at a concentration of 1 μg/ml, which was considered the most suitable for inducing C. irritans tomont apoptosis-like death. When C. irritans tomonts were treated with 1 μg/ml honokiol, the [Ca2+]i concentration began to increase significantly at 1 h. Following this, the ROS, QDF and activities of caspase-3/9 began to increase significantly, and the ΔΨm began to decrease significantly at 2 h; the highest PADR was obtained at 4 h. The mRNA expression of 14 genes was significantly upregulated during honokiol treatment. Of these genes, itpr2, capn1, mc, actg1, actb, parp2, traf2 and fos were enriched in the pathway related to apoptosis induced by endoplasmic reticulum (ER) stress.

CONCLUSIONS

This article shows that honokiol can induce C. irritans tomont apoptosis-like death. These results suggest that honokiol may disrupt [Ca2+]i homeostasis in ER and then induce C. irritans tomont apoptosis-like death by caspase cascade or mitochondrial pathway, which might represent a novel therapeutic intervention for C. irritans infection.

Ultrastructural Alterations of the Human Pathogen Giardia intestinalis after Drug Treatment

This review presents the main cell characteristics altered after in vitro incubation of the parasite with commercial drugs used to treat the disease caused by Giardia intestinalis. This important intestinal parasite primarily causes diarrhea in children. Metronidazole and albendazole are the primary compounds used in therapy against Giardia intestinalis. However, they provoke significant side effects, and some strains have developed resistance to metronidazole. Benzimidazole carbamates, such as albendazole and mebendazole, have shown the best activity against Giardia. Despite their in vitro efficacy, clinical treatment with benzimidazoles has yielded conflicting results, demonstrating lower cure rates. Recently, nitazoxanide has been suggested as an alternative to these drugs. Therefore, to enhance the quality of chemotherapy against this parasite, it is important to invest in developing other compounds that can interfere with key steps of metabolic pathways or cell structures and organelles. For example, Giardia exhibits a unique cell structure called the ventral disc, which is crucial for host adhesion and pathogenicity. Thus, drugs that can disrupt the adhesion process hold promise for future therapy against Giardia. Additionally, this review discusses new drugs and strategies that can be employed, as well as suggestions for developing novel drugs to control the infection caused by this parasite.

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.

The potential role and apoptotic profile of three medicinal plant extracts on Leishmania tropica by MTT assay, macrophage model and flow cytometry analysis

Introduction

Treatment of leishmaniasis with conventional synthetic drugs is a major global challenge. This study was designed to explore the leishmanicidal activity and apoptotic profile of three leaf extracts on Leishmania tropica stages.

Methods

The plants of Quercus velutina, Calotropis procera and Nicotiana tabacum were gathered from Anbarabbad county, in the southeastern part of Kerman province and extracted by maceration method using methanol alcohol. Various concentrations of the extracts (1, 10, 100 and 1000 μg/mL) were used against L. tropica stages to evaluate the inhibitory effect by colorimetric assay, macrophage model and flow cytometry. The MTT assay was conducted to determine the IC₅₀ and CC₅₀ values in promastigotes and J774-A1 macrophages, respectively. For intra-macrophage amastigotes, the leishmanicidal activity was evaluated by calculating the mean number of amastigotes in each macrophage and also IC₅₀ values. The promastigote or amastigote stages with no drug and complete medium without organisms were considered as positive and negative controls, respectively. Meglumine antimoniate (Glucantime) was also used as standard drug. Also, annexin V was used to assess the apoptotic profile. All treatment settings were incubated for a standard time of 72 h in triplicates. Data were analyzed by t-test and ANOVA.

Results

The findings showed that all plant extracts inhibited the proliferation rate of promastigotes and amastigotes (P ˂ 0.001); especially, Q. velutina represented the lowest IC₅₀ in both stages. Besides, Q. velutina showed the least number of amastigotes in each macrophage compared to the other groups (4.5 μg/mL). The percentage of parasitic apoptosis at 1000 μg/mL of Q. velutina, C. procera, N. tabacum and Glucantime® were 37.4, 18.6, 8.5 and 52.4, respectively. Amastigotes (clinical stage) were significantly more susceptible to extracts and also Glucantime® than promastigotes (P < 0.001).

Conclusions

This study revealed that all three extracts of Q. velutina, C. procera and N. tabacum exhibited an effective antileishmanial activity and induced apoptosis against the L. tropica promastigotes. Further investigations are essential to isolate and analyze the chemical compositions and their biological properties.

Identification of immune-related proteins of Dreissena polymorpha hemocytes and plasma involved in host-microbe interactions by differential proteomics

Biological responses of zebra mussel Dreissena polymorpha are investigated to assess the impact of contaminants on aquatic organisms and ecosystems. In addition to concentrate chemical contaminants in their tissues, zebra mussels accumulate several microorganisms such as viruses, protozoa and bacteria. In order to understand the molecular mechanisms involved in the defence against microorganisms this study aims at identifying immune proteins from D. polymorpha hemolymph involved in defence against protozoa and viruses. For this purpose, hemolymph were exposed ex vivo to Cryptosporidium parvum and RNA poly I:C. Differential proteomics on both hemocytes and plasma revealed immune proteins modulated under exposures. Different patterns of response were observed after C. parvum and RNA poly I:C exposures. The number of modulated proteins per hemolymphatic compartments suggest that C. parvum is managed in cells while RNA poly I:C is managed in plasma after 4 h exposure. BLAST annotation and GO terms enrichment analysis revealed further characteristics of immune mechanisms. Results showed that many proteins involved in the recognition and destruction of microorganisms were modulated in both exposure conditions, while proteins related to phagocytosis and apoptosis were exclusively modulated by C. parvum. This differential proteomic analysis highlights in zebra mussels modulated proteins involved in the response to microorganisms, which reflect a broad range of immune mechanisms such as recognition, internalization and destruction of microorganisms. This study paves the way for the identification of new markers of immune processes that can be used to assess the impact of both chemical and biological contaminations on the health status of aquatic organisms.

Apoptotic mimicry as a strategy for the establishment of parasitic infections: parasite- and host-derived phosphatidylserine as key molecule

The establishment of parasitic infection is dependent on the development of efficient strategies to evade the host defense mechanisms. Phosphatidylserine (PS) molecules are pivotal for apoptotic cell recognition and clearance by professional phagocytes. Moreover, PS receptors are able to trigger anti-inflammatory and immunosuppressive responses by phagocytes, either by coupled enzymes or through the induction of regulatory cytokine secretion. These PS-dependent events are exploited by parasites in a mechanism called apoptotic mimicry. Generally, apoptotic mimicry refers to the effects of PS recognition for the initiation and maintenance of pathogenic infections. However, in this context, PS molecules can be recognized on the surface of the infectious agent or in the surface of apoptotic host debris, leading to the respective denomination of classical and non-classical apoptotic mimicry. In this review, we discuss the role of PS in the pathogenesis of several human infections caused by protozoan parasites.

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.

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.

Alterations on growth and cell organization of Giardia intestinalis trophozoites after treatment with KH-TFMDI, a novel class III histone deacetylase inhibitor

Giardia trophozoites have developed resistance mechanisms to currently available compounds, leading to treatment failures. In this context, the development of new additional agents is mandatory. Sirtuins, which are class III NAD⁺-dependent histone deacetylases, have been considered important targets for the development of new anti-parasitic drugs. Here, we evaluated the activity of KH-TFMDI, a novel 3-arylideneindolin-2-one-type sirtuin inhibitor, on G. intestinalis trophozoites. This compound decreased the trophozoite growth presenting an IC₅₀ value lower than nicotinamide, a moderately active inhibitor of yeast and human sirtuins. Light and electron microscopy analysis showed the presence of multinucleated cell clusters suggesting that the cytokinesis could be compromised in treated trophozoites. Cell rounding, concomitantly with the folding of the ventro-lateral flange and flagella internalization, was also observed. These cells eventually died by a mechanism which lead to DNA/nuclear damage, formation of multi-lamellar bodies and annexin V binding on the parasite surface. Taken together, these data show that KH-TFMDI has significant effects against G. intestinalis trophozoites proliferation and structural organization and suggest that histone deacetylation pathway should be explored on this protozoon as target for chemotherapy.

Encephalitozoon cuniculi and Vittaforma corneae (Phylum Microsporidia) inhibit staurosporine-induced apoptosis in human THP-1 macrophages in vitro

Obligately intracellular microsporidia regulate their host cell life cycles, including apoptosis, but this has not been evaluated in phagocytic host cells such as macrophages that can facilitate infection but also can be activated to kill microsporidia. We examined two biologically dissimilar human-infecting microsporidia species, Encephalitozoon cuniculi and Vittaforma corneae, for their effects on staurosporine-induced apoptosis in the human macrophage-differentiated cell line, THP1. Apoptosis was measured after exposure of THP-1 cells to live and dead mature organisms via direct fluorometric measurement of Caspase 3, colorimetric and fluorometric TUNEL assays, and mRNA gene expression profiles using Apoptosis RT2 Profiler PCR Array. Both species of microsporidia modulated the intrinsic apoptosis pathway. In particular, live E. cuniculi spores inhibited staurosporine-induced apoptosis as well as suppressed pro-apoptosis genes and upregulated anti-apoptosis genes more broadly than V. corneae. Exposure to dead spores induced an opposite effect. Vittaforma corneae, however, also induced inflammasome activation via Caspases 1 and 4. Of the 84 apoptosis-related genes assayed, 42 (i.e. 23 pro-apoptosis, nine anti-apoptosis, and 10 regulatory) genes were more affected including those encoding members of the Bcl2 family, caspases and their regulators, and members of the tumour necrosis factor (TNF)/TNF receptor R superfamily.

Apoptosis inhibition of Atlantic salmon (Salmo salar) peritoneal macrophages by Piscirickettsia salmonis

To improve the understanding of the piscirickettsiosis pathogenesis, the in vivo apoptosis modulation of peritoneal macrophages and lymphocytes was studied in juvenile Salmo salar intraperitoneally injected with Piscirickettsia salmonis. Five fish were sampled at post-exposure days 1, 5, 8 (preclinical), 20 (clinical) and 40 (post-clinical period of the disease), and the leucocytes of their coelomic washings were analysed by flow cytometry (using the JC-1 cationic dye), TUNEL and cytology to detect apoptotic cells. A selective and temporal pattern of apoptosis modulation by P. salmonis infection was observed. Apoptosis in lymphocytes was not affected, whereas it was inhibited in macrophages but only during the preclinical stage of the induced piscirickettsiosis. Hence, it is postulated that P. salmonis inhibits macrophage apoptosis at the beginning of the disease development to survive, multiply and probably be transported inside these phagocytes; once this process is complete, macrophage apoptosis is no longer inhibited, thus facilitating the exit of the bacteria from the infected cells for continuing their life cycle.

Isopropyl quinoxaline-7-carboxylate 1,4-di-N-oxide derivatives induce regulated necrosis-like cell death on Leishmania (Leishmania) mexicana

Leishmaniasis is a neglected tropical disease caused by the parasite of the genus Leishmania. About 13 million people are infected worldwide, and it is estimated that 350 million are at risk of infection. Clinical manifestations depend on the parasite species and factors related to the host such as the immune system, nutrition, housing, and financial resources. Available treatments have severe side effects; therefore, research currently focuses on finding more active and less toxic compounds. Quinoxalines have been described as promising alternatives. In this context, 17 isopropyl quinoxaline-7-carboxylate 1,4-di-N-oxide derivatives were evaluated as potential leishmanicidal agents. Their effect on the cell metabolism of Leishmania mexicana promastigotes and their cytotoxic effects on the J774.A1 cell line and on erythrocytes were evaluated, and their selectivity index was calculated. Compounds T-069 (IC₅₀ = 1.49 μg/mL), T-070 (IC₅₀ = 1.71 μg/mL), T-072 (IC₅₀ = 6.62 μg/mL), T-073 (IC₅₀ = 1.25 μg/mL), T-085 (IC₅₀ = 0.74 μg/mL), and T-116 (IC₅₀ = 0.88 μg/mL) were the most active against L. mexicana promastigotes and their mechanism of action was characterized by flow cytometry and microscopy. Compound T-073, the most selective quinoxaline derivative, induced cell membrane damage, phosphatidylserine exposition, reactive oxygen species production, disruption of the mitochondrion membrane potential, and DNA fragmentation, all in a dose-dependent manner, indicating the induction of regulated necrosis. Light and transmission electron microscopy showed the drastic morphological changes induced and the mitochondrion as the most sensitive organelle in response to T-073. This study describes the mechanism by which active isopropyl quinoxaline-7-carboxylate 1,4-di-N-oxide quinoxalines affect the parasite.

Amphotericin B induces apoptosis-like programmed cell death in Naegleria fowleri and Naegleria gruberi

Naegleria fowleri and Naegleria gruberi belong to the free-living amoebae group. It is widely known that the non-pathogenic species N. gruberi is usually employed as a model to describe molecular pathways in this genus, mainly because its genome has been recently described. However, N. fowleri is an aetiological agent of primary amoebic meningoencephalitis, an acute and fatal disease. Currently, the most widely used drug for its treatment is amphotericin B (AmB). It was previously reported that AmB has an amoebicidal effect in both N. fowleri and N. gruberi trophozoites by inducing morphological changes that resemble programmed cell death (PCD). PCD is a mechanism that activates morphological, biochemical and genetic changes. However, PCD has not yet been characterized in the genus Naegleria. The aim of the present work was to evaluate the typical markers to describe PCD in both amoebae. These results showed that treated trophozoites displayed several parameters of apoptosis-like PCD in both species. We observed ultrastructural changes, an increase in reactive oxygen species, phosphatidylserine externalization and a decrease in intracellular potassium, while DNA degradation was evaluated using the TUNEL assay and agarose gels, and all of these parameters are related to PCD. Finally, we analysed the expression of apoptosis-related genes, such as sir2 and atg8, in N. gruberi. Taken together, our results showed that AmB induces the morphological, biochemical and genetic changes of apoptosis-like PCD in the genus Naegleria.

Perifosine Mechanisms of Action in Leishmania Species

Here the mechanism by which perifosine induced cell death in Leishmania donovani and Leishmania amazonensis is described. The drug reduced Leishmania mitochondrial membrane potential and decreased cellular ATP levels while increasing phosphatidylserine externalization. Perifosine did not increase membrane permeabilization. We also found that the drug inhibited the phosphorylation of Akt in the parasites. These results highlight the potential use of perifosine as an alternative to miltefosine against Leishmania.

Genetic diversity of Plasmodium vivax metacaspase 1 and Plasmodium vivax multi-drug resistance 1 genes of field isolates from Mauritania, Sudan and Oman

BACKGROUND

Plasmodium vivax is the second most important human malaria parasite, widely spread across the world. This parasite is associated with important issues in the process toward malaria elimination, including potential for relapse and increased resistance to chloroquine. Plasmodium vivax multi-drug resistant (pvmdr1) is suspected to be a marker of resistance although definitive evidence is lacking. Progress has been made in knowledge of biological factors affecting parasite growth, including mechanisms of regulated cell death and the suspected role of metacaspase. Plasmodium vivax metacaspase1 (PvMCA1-cd) has been described with a catalytic domain composed of histidine (H372) and cysteine (C428) residues. The aim of this study was to test for a link between the conserved histidine and cysteine residues in PvMCA1-cd, and the polymorphism of the P. vivax multi-drug resistant gene (pvmdr1).

RESULTS

Thirty P. vivax isolates were collected from Mauritania, Sudan, and Oman. Among the 28 P. vivax isolates successfully sequenced, only 4 samples showed the conserved His (372)-Cys (428) residues in PvMCA1-cd. Single nucleotide polymorphisms observed were H372T (46.4%), H372D (39.3%), and C428R (85.7%). A new polymorphic catalytic domain was observed at His (282)-Cys (305) residues. Sequences alignment analysis of pvmdr1 showed SNP in the three codons 958, 976 and 1076. A single SNP was identified at the codon M958Y (60%), 2 SNPs were found at the position 976: Y976F (13%) and Y976V (57%), and 3 SNPs were identified at the position 1076: F1076L (40%), F1076T (53%) and F1076I (3%). Only one isolate was wildtype in all three codons (MYF), 27% were single MYL mutants, and 10% were double MFL mutants. Three new haplotypes were also identified: the triple mutant YVT was most prevalent (53.3%) distributed in the three countries, while triple YFL and YVI mutants (3%), were only found in samples from Sudan and Mauritania.

CONCLUSIONS

Triple or quadruple mutants for metacaspase genes and double or triple mutants for Pvmdr1 were observed in 24/28 and 19/28 samples. There was no difference in the frequency of mutations between PvMCA1-cd and Pvmdr1 (P > 0.2). Histidine and cysteine residues in PvMCA1-cd are highly polymorphic and linkage disequilibrium with SNPs of Pvmdr1 gene may be expected from these three areas with different patterns of P. vivax transmission.

Microsporidia infection impacts the host cell's cycle and reduces host cell apoptosis

Intracellular parasites can alter the cellular machinery of host cells to create a safe haven for their survival. In this regard, microsporidia are obligate intracellular fungal parasites with extremely reduced genomes and hence, they are strongly dependent on their host for energy and resources. To date, there are few studies into host cell manipulation by microsporidia, most of which have focused on morphological aspects. The microsporidia Nosema apis and Nosema ceranae are worldwide parasites of honey bees, infecting their ventricular epithelial cells. In this work, quantitative gene expression and histology were studied to investigate how these two parasites manipulate their host’s cells at the molecular level. Both these microsporidia provoke infection-induced regulation of genes involved in apoptosis and the cell cycle. The up-regulation of buffy (which encodes a pro-survival protein) and BIRC5 (belonging to the Inhibitor Apoptosis protein family) was observed after infection, shedding light on the pathways that these pathogens use to inhibit host cell apoptosis. Curiously, different routes related to cell cycle were modified after infection by each microsporidia. In the case of N. apis, cyclin B1, dacapo and E2F2 were up-regulated, whereas only cyclin E was up-regulated by N. ceranae, in both cases promoting the G1/S phase transition. This is the first report describing molecular pathways related to parasite-host interactions that are probably intended to ensure the parasite’s survival within the cell.

Differential proteomics reveals novel insights into Nosema-honey bee interactions

Host manipulation is a common strategy by parasites to reduce host defense responses, enhance development, host exploitation, reproduction and, ultimately, transmission success. As these parasitic modifications can reduce host fitness, increased selection pressure may result in reciprocal adaptations of the host. Whereas the majority of studies on host manipulation have explored resistance against parasites (i.e. ability to prevent or limit an infection), data describing tolerance mechanisms (i.e. ability to limit harm of an infection) are scarce. By comparing differential protein abundance, we provide evidence of host-parasite interactions in the midgut proteomes of N. ceranae-infected and uninfected honey bees from both Nosema-tolerant and Nosema-sensitive lineages. We identified 16 proteins out of 661 protein spots that were differentially abundant between experimental groups. In general, infections of Nosema resulted in an up-regulation of the bee's energy metabolism. Additionally, we identified 8 proteins that were differentially abundant between tolerant and sensitive honey bees regardless of the Nosema infection. Those proteins were linked to metabolism, response to oxidative stress and apoptosis. In addition to bee proteins, we also identified 3 Nosema ceranae proteins. Interestingly, abundance of two of these Nosema proteins were significantly higher in infected Nosema-sensitive honeybees relative to the infected Nosema-tolerant lineage. This may provide a novel candidate for studying the molecular interplay between N. ceranae and its honey bee host in more detail.

Parasiticidal effect of synthetic bovine lactoferrin peptides on the enteric parasite Giardia intestinalis

Giardia intestinalis is the most common infectious protozoan parasite in children. Despite the effectiveness of some drugs, the disease remains a major worldwide problem. Consequently, the search for new treatments is important for disease eradication. Biological molecules with antimicrobial properties represent a promising alternative to combat pathogens. Bovine lactoferrin (bLF) is a key component of the innate host defense system, and its peptides have exhibited strong antimicrobial activity. Based on these properties, we evaluated the parasiticidal activity of these peptides on G. intestinalis. Trophozoites were incubated with different peptide concentrations for different periods of time, and the growth or viability was determined by carboxyfluorescein-succinimidyl-diacetate-ester (CFDA) and propidium iodide (PI) staining. Endocytosis of peptides was investigated by confocal microscopy, damage was analyzed by transmission and scanning electron microscopy, and the type of programmed cell death was analyzed by flow cytometry. Our results showed that the LF peptides had giardicidal activity. The LF peptides interacted with G. intestinalis and exposure to LF peptides correlated with an increase in the granularity and vacuolization of the cytoplasm. Additionally, the formation of pores, extensive membrane disruption, and programmed cell death was observed in trophozoites treated with LF peptides. Our results demonstrate that LF peptides exhibit potent in vitro antigiardial activity.

C-Geranylated flavonoids from Paulownia tomentosa fruits with antimicrobial potential and synergistic activity with antibiotics

Context C-6-Geranylated flavonoids possess promising biological activities. These substances could be a source of lead compounds for the development of therapeutics. Objective The study was designed to evaluate their antibacterial and antileishmanial activity. Materials and methods C-6-Geranylated flavanones were tested in micromolar concentrations against promastigote forms of Leishmania brazilensis, L. donovani, L. infantum, and L. panamensis against methicillin-resistant Staphylococcus aureus (MRSA); and synergistic potential with antibiotics was analyzed. IC50 values (after 72 h) were calculated and compared with that of miltefosine. Flow cytometry and DNA fragmentation analysis were used the mechanism of the effect. Geranylated flavanones or epigallocatechin gallate were combined with oxacillin, tetracycline, and ciprofloxacin, and the effects of these two-component combinations were evaluated. Minimal inhibitory concentrations (MICs) and minimal bactericidal concentrations (MBCs) were established (after 24 h), the synergy was measured by the checkerboard titration technique, and the sums of the fractional inhibitory concentrations (∑FICs) were computed. Results 3'-O-Methyl-5'-O-methyldiplacone and 3'-O-methyldiplacone showed good antileishmanial activities (IC50 8-42 μM). 3'-O-Methyl-5'-hydroxydiplacone activates the apoptotic death at leishmanias, the effect of 3'-O-methyl-5'-O-methyldiplacone has another mechanism. The test of the antibacterial activity showed good effects of 3'-O-methyldiplacol and mimulone against MRSA (MIC 2-16 μg/mL), and in six cases, the results showed synergistic effects when combined with oxacillin. Synergistic effects were also found for the combination of epigallocatechin gallate with tetracycline or oxacillin. Conclusion This work demonstrates anti-MRSA and antileishmanial potential of geranylated flavanones and uncovers their promising synergistic activities with antibiotics. In addition, the mechanism of antileishmanial effect is proposed.

Does Leishmaniasis disease alter the parenchyma and protein expression in salivary glands?

Leishmaniasis is considered a serious public health problem in several regions in Brazil and worldwide. This research aimed to perform a histopathological and proteomic study of parotid, submandibular and sublingual glands of BALB/c mice infected by Leishmania (L) infantum chagasi using histological, immunohistochemical and epifluorescence techniques. Twelve isogenic BALB/c male mice, around six- to eight-weeks old, were separated into two groups: the animals of the control group were injected with 0.15 ml of NaCl, while those in the experimental group were inoculated with 5 × 10(6) amastigote forms of Leishmania (L) infantum chagasi by the ip route. After 50 days, animals were euthanized and major salivary glands were collected to perform histological, immunohistochemical and epifluorescence techniques using anti-Caspase-2, anti-Ki-67 and anti-β-catenin antibodies, respectively. The histological and morphometric evaluation showed clusters of mononuclear inflammatory cells and a higher area and perimeter of the parotid gland. However, none of the salivary glands had morphophysiological impairment. There was no immunoreactivity to the anti-caspase-2 antibody and Ki67 expression in acinar and ductal cells in both groups. According to the immunofluorescence staining, the β-catenin antibodies did not show nuclear expression, suggesting no uncontrolled proliferation. The data obtained in this study showed population and morphological stability of major salivary glands after 50 days post-infection by Leishmania (L) infantum chagasi.

The Apoptotic Role of Metacaspase in Toxoplasma gondii

Toxoplasma gondii is a major opportunistic pathogen that spreads in a range of animal species and human beings. Quite a few characterizations of apoptosis have been identified in T. gondii treated with apoptosis inducers, but the molecular mechanisms of the pathway are not clearly understood. Metacaspases are caspase-like cysteine proteases that can be found in plants, fungi, and protozoa in which caspases are absent. Metacaspases are multifunctional proteases involved in apoptosis-like cell death, insoluble protein aggregate clearance, and cell proliferation. To investigate whether T. gondii metacaspase (TgMCA) is involved in the apoptosis of the parasites, we generated TgMCA mutant strains. Western blot analysis indicated that the autoproteolytic processing of TgMCA was the same as that for metacaspases of some other species. Indirect immunofluorescence assay (IFA) showed that TgMCA was dispersed throughout the cytoplasm and relocated to the nucleus when the parasites were exposed to the extracellular environment, which indicated the execution of its function in the nucleus. The number of apoptosis parasites was significantly diminished in the TgMCA knockout strain and increased in the TgMCA overexpression strain after treatment with extracellular buffer, as determined by the terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay. The lack of TgMCA did not affect the parasite propagation in vitro and virulence in vivo, suggesting that it is probably redundant in parasite propagation. But overexpression of TgMCA reduced the intracellular parasites growth in vitro. The TgMCA knockout strain showed more viability in extracellular buffer compared to the parental and overexpression lines. In this study, we demonstrated that TgMCA contributes to the apoptosis of T. gondii.

Nosema Tolerant Honeybees (Apis mellifera) Escape Parasitic Manipulation of Apoptosis

Apoptosis is not only pivotal for development, but also for pathogen defence in multicellular organisms. Although numerous intracellular pathogens are known to interfere with the host’s apoptotic machinery to overcome this defence, its importance for host-parasite coevolution has been neglected. We conducted three inoculation experiments to investigate in the apoptotic respond during infection with the intracellular gut pathogen Nosema ceranae, which is considered as potential global threat to the honeybee (Apis mellifera) and other bee pollinators, in sensitive and tolerant honeybees. To explore apoptotic processes in the gut epithelium, we visualised apoptotic cells using TUNEL assays and measured the relative expression levels of subset of candidate genes involved in the apoptotic machinery using qPCR. Our results suggest that N. ceranae reduces apoptosis in sensitive honeybees by enhancing inhibitor of apoptosis protein-(iap)-2 gene transcription. Interestingly, this seems not be the case in Nosema tolerant honeybees. We propose that these tolerant honeybees are able to escape the manipulation of apoptosis by N. ceranae, which may have evolved a mechanism to regulate an anti-apoptotic gene as key adaptation for improved host invasion.

In vitro activities of hexaazatrinaphthylenes against Leishmania spp

The in vitro activity of a novel group of compounds, hexaazatrinaphthylene derivatives, against two species of Leishmania is described in this study. These compounds showed a significant dose-dependent inhibition effect on the proliferation of the parasites, with 50% inhibitory concentrations (IC(50)s) ranging from 1.23 to 25.05 μM against the promastigote stage and 0.5 to 0.7 μM against intracellular amastigotes. Also, a cytotoxicity assay was carried out to in order to evaluate the possible toxic effects of these compounds. Moreover, different assays were performed to determine the type of cell death induced after incubation with these compounds. The obtained results highlight the potential use of hexaazatrinaphthylene derivatives against Leishmania species, and further studies should be undertaken to establish them as novel leishmanicidal therapeutic agents.

Stress management in cyst-forming free-living protists: programmed cell death and/or encystment

In the face of harsh conditions and given a choice, a cell may (i) undergo programmed cell death, (ii) transform into a cancer cell, or (iii) enclose itself into a cyst form. In metazoans, the available evidence suggests that cellular machinery exists only to execute or avoid programmed cell death, while the ability to form a cyst was either lost or never developed. For cyst-forming free-living protists, here we pose the question whether the ability to encyst was gained at the expense of the programmed cell death or both functions coexist to counter unfavorable environmental conditions with mutually exclusive phenotypes.

Virus infection of Haptolina ericina and Phaeocystis pouchetii implicates evolutionary conservation of programmed cell death induction in marine haptophyte-virus interactions

The mechanisms by which phytoplankton cope with stressors in the marine environment are neither fully characterized nor understood. As viruses are the most abundant entities in the global ocean and represent a strong top-down regulator of phytoplankton abundance and diversity, we sought to characterize the cellular response of two marine haptophytes to virus infection in order to gain more knowledge about the nature and diversity of microalgal responses to this chronic biotic stressor. We infected laboratory cultures of the haptophytes Haptolina ericina and Phaeocystis pouchetii with CeV-01B or PpV-01B dsDNA viruses, respectively, and assessed the extent to which host cellular responses resemble programmed cell death (PCD) through the activation of diagnostic molecular and biochemical markers. Pronounced DNA fragmentation and activation of cysteine aspartate-specific proteases (caspases) were only detected in virus-infected cultures of these phytoplankton. Inhibition of host caspase activity by addition of the pan-caspase inhibitor z-VAD-fmk did not impair virus production in either host-virus system, differentiating it from the Emiliania huxleyi-Coccolithovirus model of haptophyte-virus interactions. Nonetheless, our findings point to a general conservation of PCD-like activation during virus infection in ecologically diverse haptophytes, with the subtle heterogeneity of cell death biochemical responses possibly exerting differential regulation on phytoplankton abundance and diversity.

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.

Over-expression of 60s ribosomal L23a is associated with cellular proliferation in SAG resistant clinical isolates of Leishmania donovani

BACKGROUND

Sodium antimony gluconate (SAG) unresponsiveness of Leishmania donovani (Ld) had effectively compromised the chemotherapeutic potential of SAG. 60s ribosomal L23a (60sRL23a), identified as one of the over-expressed protein in different resistant strains of L.donovani as observed with differential proteomics studies indicates towards its possible involvement in SAG resistance in L.donovani. In the present study 60sRL23a has been characterized for its probable association with SAG resistance mechanism.

METHODOLOGY AND PRINCIPAL FINDINGS

The expression profile of 60s ribosomal L23a (60sRL23a) was checked in different SAG resistant as well as sensitive strains of L.donovani clinical isolates by real-time PCR and western blotting and was found to be up-regulated in resistant strains. Ld60sRL23a was cloned, expressed in E.coli system and purified for raising antibody in swiss mice and was observed to have cytosolic localization in L.donovani. 60sRL23a was further over-expressed in sensitive strain of L.donovani to check its sensitivity profile against SAG (Sb V and III) and was found to be altered towards the resistant mode.

CONCLUSION/SIGNIFICANCE

This study reports for the first time that the over expression of 60sRL23a in SAG sensitive parasite decreases the sensitivity of the parasite towards SAG, miltefosine and paramomycin. Growth curve of the tranfectants further indicated the proliferative potential of 60sRL23a assisting the parasite survival and reaffirming the extra ribosomal role of 60sRL23a. The study thus indicates towards the role of the protein in lowering and redistributing the drug pressure by increased proliferation of parasites and warrants further longitudinal study to understand the underlying mechanism.

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.

Strategies of Echinococcus species responses to immune attacks: implications for therapeutic tool development

Echinococcus species have been studied as a model to investigate parasite-host interactions. Echinococcus spp. can actively communicate dynamically with a host to facilitate infection, growth and proliferation partially via secretion of molecules, especially in terms of harmonization of host immune attacks. This review systematically outlines our current knowledge of how the Echinococcus species have evolved to adapt to their host's microenvironment. This understanding of parasite-host interplay has implications in profound appreciation of parasite plasticity and is informative in designing novel and effective tools including vaccines and drugs for the treatment of echinococcosis and other diseases.

Involvement of apoptosis in host-parasite interactions in the zebra mussel

The question of whether cell death by apoptosis plays a biological function during infection is key to understanding host-parasite interactions. We investigated the involvement of apoptosis in several host-parasite systems, using zebra mussels Dreissena polymorpha as test organisms and their micro- and macroparasites. As a stress response associated with parasitism, heat shock proteins (Hsp) can be induced. In this protein family, Hsp70 are known to be apoptosis inhibitors. Mussels were diagnosed for their respective infections by standard histological methods; apoptosis was detected using the TUNEL methods on paraffin sections and Hsp70 by immunohistochemistry on cryosections. Circulating hemocytes were the main cells observed in apoptosis whereas infected tissues displayed no or few apoptotic cells. Parasitism by intracellular bacteria Rickettsiales-like and the trematode Bucephalus polymorphus were associated with the inhibition of apoptosis whereas ciliates Ophryoglena spp. or the trematode Phyllodistomum folium did not involve significant differences in apoptosis. Even if some parasites were able to modulate apoptosis in zebra mussels, we did not see evidence of any involvement of Hsp70 on this mechanism.

Features of autophagic cell death in Plasmodium liver-stage parasites

Analyzing molecular determinants of Plasmodium parasite cell death is a promising approach for exploring new avenues in the fight against malaria. Three major forms of cell death (apoptosis, necrosis and autophagic cell death) have been described in multicellular organisms but which cell death processes exist in protozoa is still a matter of debate. Here we suggest that all three types of cell death occur in Plasmodium liver-stage parasites. Whereas typical molecular markers for apoptosis and necrosis have not been found in the genome of Plasmodium parasites, we identified genes coding for putative autophagy-marker proteins and thus concentrated on autophagic cell death. We characterized the Plasmodium berghei homolog of the prominent autophagy marker protein Atg8/LC3 and found that it localized to the apicoplast. A relocalization of PbAtg8 to autophagosome-like vesicles or vacuoles that appear in dying parasites was not, however, observed. This strongly suggests that the function of this protein in liver-stage parasites is restricted to apicoplast biology.

Trypanosoma cruzi response to sterol biosynthesis inhibitors: morphophysiological alterations leading to cell death

The protozoan parasite Trypanosoma cruzi displays similarities to fungi in terms of its sterol lipid biosynthesis, as ergosterol and other 24-alkylated sterols are its principal endogenous sterols. The sterol pathway is thus a potential drug target for the treatment of Chagas disease. We describe here a comparative study of the growth inhibition, ultrastructural and physiological changes leading to the death of T. cruzi cells following treatment with the sterol biosynthesis inhibitors (SBIs) ketoconazole and lovastatin. We first calculated the drug concentration inhibiting epimastigote growth by 50% (EC(50)/72 h) or killing all cells within 24 hours (EC(100)/24 h). Incubation with inhibitors at the EC(50)/72 h resulted in interesting morphological changes: intense proliferation of the inner mitochondrial membrane, which was corroborated by flow cytometry and confocal microscopy of the parasites stained with rhodamine 123, and strong swelling of the reservosomes, which was confirmed by acridine orange staining. These changes to the mitochondria and reservosomes may reflect the involvement of these organelles in ergosterol biosynthesis or the progressive autophagic process culminating in cell lysis after 6 to 7 days of treatment with SBIs at the EC(50)/72 h. By contrast, treatment with SBIs at the EC(100)/24 h resulted in rapid cell death with a necrotic phenotype: time-dependent cytosolic calcium overload, mitochondrial depolarization and reservosome membrane permeabilization (RMP), culminating in cell lysis after a few hours of drug exposure. We provide the first demonstration that RMP constitutes the "point of no return" in the cell death cascade, and propose a model for the necrotic cell death of T. cruzi. Thus, SBIs trigger cell death by different mechanisms, depending on the dose used, in T. cruzi. These findings shed new light on ergosterol biosynthesis and the mechanisms of programmed cell death in this ancient protozoan parasite.

Activation of autophagic programmed cell death and innate immune gene expression reveals immuno-competence of integumental epithelium in Bombyx mori infected by a dipteran parasitoid

In insects, the integument forms the primary barrier between the environment and internal milieu, but cellular and immune responses of the integumental epithelium to infection by micro- and macro-parasites are mostly unknown. We elucidated cellular and immune responses of the epithelium induced through infection by a dipteran endoparasitoid, Exorista bombycis in the economically important silkworm Bombyx mori. Degradative autophagic vacuoles, lamella-like bodies, a network of cytoplasmic channels with cellular cargo, and an RER network that opened to vacuoles were observed sequentially with increase in age after infection. This temporal sequence culminated in apoptosis, accompanied by the upregulation of the caspase gene and fragmentation of DNA. The infection significantly enhanced the tyrosine level and phenol oxidase activity in the integument. Proteomic analysis revealed enhanced expression of innate immunity components of toll and melanization pathways, cytokines, signaling molecules, chaperones, and proteolytic enzymes demonstrating diverse host responses. qPCR analysis revealed the upregulation of spatzle, BmToll, and NF kappa B transcription factors Dorsal and BmRel. NF kappa B inhibitor cactus showed diminished expression when Dorsal and BmRel were upregulated, revealing a negative correlation (R = (-)0.612). During melanization, prophenol oxidase 2 was expressed, a novel finding in integumental epithelium. The integument showed a low level of melanin metabolism and localized melanism in order to prevent the spreading of cytotoxic quinones. The gene-encoding proteolytic enzyme, beta-N-acetylglucosaminidase, was activated at 24 h post-infection, whereas chitinase, was activated at 96 h post-infection; however, most of the immune genes enhanced their expression in the early stages of infection. Thus the integument contributes to humoral immune responses that enhance resistance against macroparasite invasion.

Apoptotic-like activity of staurosporine in axenic cultures of Trypanosoma evansi

Trypanosoma evansi is a blood protozoan parasite of the genus Trypanosoma which is responsible for surra (Trypanosomosis) in domestic and wild animals. This study addressed apoptotic-like features in Trypanosoma evansi in vitro. The mechanism of parasite death was investigated using staurosporine as an inducing agent. We evaluated its effects through several cytoplasmic features of apoptosis, including cell shrinkage, phosphatidylserine exposure, maintenance of plasma membrane integrity, and mitochondrial trans-membrane potential. For access to these features we have used the flow cytometry and fluorescence microscopy with cultures in the stationary phase and adjusted to a density of 10(6) cells/mL. The apoptotic effect of staurosporine in T. evansi was evaluated at 20 nM final concentration. There was an increase of phosphatidylserine exposure, whereas mitochondrial potential was decreased. Moreover, no evidence of cell permeability increasing with staurosporine was observed in this study, suggesting the absence of a necrotic process. Additional studies are needed to elucidate the possible pathways associated with this form of cell death in this hemoparasite.

Molecular and structural insight into plasmodium falciparum RIO2 kinase

Among approximately 65 kinases of the malarial genome, RIO2 (right open reading frame) kinase belonging to the atypical class of kinase is unique because along with a kinase domain, it has a highly conserved N-terminal winged helix (wHTH) domain. The wHTH domain resembles the wing like domain found in DNA binding proteins and is situated near to the kinase domain. Ligand binding to this domain may reposition the kinase domain leading to inhibition of enzyme function and could be utilized as a novel allosteric site to design inhibitor. In the present study, we have generated a model of RIO2 kinase from Plasmodium falciparum utilizing multiple modeling, simulation approach. A novel putative DNA-binding site is identified for the first time in PfRIO2 kinase to understand the DNA binding events involving wHTH domain and flexible loop. Induced fit DNA docking followed by minimization, molecular dynamics simulation, energetic scoring and binding mode studies are used to reveal the structural basis of PfRIO2-ATP-DNA complex. Ser105 as a potential site of phosphorylation is revealed through the structural studies of ATP binding in PfRIO2. Overall the present study discloses the structural facets of unknown PfRIO2 complex and opens an avenue toward exploration of novel drug target.

Apoptosis-like programmed cell death induces antisense ribosomal RNA (rRNA) fragmentation and rRNA degradation in Leishmania

Few natural antisense (as) RNAs have been reported as yet in the unicellular protozoan Leishmania. Here, we describe that Leishmania produces natural asRNAs complementary to all ribosomal RNA (rRNA) species. Interestingly, we show that drug-induced apoptosis-like programmed cell death triggers fragmentation of asRNA complementary to the large subunit gamma (LSU-γ) rRNA, one of the six 28S rRNA processed fragments in Leishmania. Heat and oxidative stress also induce fragmentation of asrRNA, but to a lesser extent. Extensive asrRNA cleavage correlates with rRNA breakdown and translation inhibition. Indeed, overexpression of asLSU-γ rRNA accelerates rRNA degradation upon induction of apoptosis. In addition, we provide mechanistic insight into the regulation of apoptosis-induced asrRNA fragmentation by a 67 kDa ATP-dependent RNA helicase of the DEAD-box subfamily. This helicase binds both sense (s)LSU-γ and asLSU-γ rRNAs, and appears to have a key role in protecting rRNA from degradation by preventing asrRNA cleavage and thus cell death. Remarkably, the asrRNA fragmentation process operates not only in trypanosomatid protozoa but also in mammals. Our findings uncover a novel mechanism of regulation involving asrRNA fragmentation and rRNA breakdown, that is triggered by apoptosis and conditions of reduced translation under stress, and seems to be evolutionary conserved.

Programmed cell death in Giardia

Programmed cell death (PCD) has been observed in many unicellular eukaryotes; however, in very few cases have the pathways been described. Recently the early divergent amitochondrial eukaryote Giardia has been included in this group. In this paper we investigate the processes of PCD in Giardia. We performed a bioinformatics survey of Giardia genomes to identify genes associated with PCD alongside traditional methods for studying apoptosis and autophagy. Analysis of Giardia genomes failed to highlight any genes involved in apoptotic-like PCD; however, we were able to induce apoptotic-like morphological changes in response to oxidative stress (H2O2) and drugs (metronidazole). In addition we did not detect caspase activity in induced cells. Interestingly, we did observe changes resembling autophagy when cells were starved (staining with MDC) and genome analysis revealed some key genes associated with autophagy such as TOR, ATG1 and ATG 16. In organisms such as Trichomonas vaginalis, Entamoeba histolytica and Blastocystis similar observations have been made but no genes have been identified. We propose that Giardia possess a pathway of autophagy and a form of apoptosis very different from the classical known mechanism; this may represent an early form of programmed cell death.

On Programmed Cell Death in Plasmodium falciparum: Status Quo

Conflicting arguments and results exist regarding the occurrence and phenotype of programmed cell death (PCD) in the malaria parasite Plasmodium falciparum. Inconsistencies relate mainly to the number and type of PCD markers assessed and the different methodologies used in the studies. In this paper, we provide a comprehensive overview of the current state of knowledge and empirical evidence for PCD in the intraerythrocytic stages of P. falciparum. We consider possible reasons for discrepancies in the data and offer suggestions towards more standardised investigation methods in this field. Furthermore, we present genomic evidence for PCD machinery in P. falciparum. We discuss the potential adaptive or nonadaptive role of PCD in the parasite life cycle and its possible exploitation in the development of novel drug targets. Lastly, we pose pertinent unanswered questions concerning the PCD phenomenon in P. falciparum to provide future direction.

The meaning of death: evolution and ecology of apoptosis in protozoan parasites

The discovery that an apoptosis-like, programmed cell death (PCD) occurs in a broad range of protozoan parasites offers novel therapeutic tools to treat some of the most serious infectious diseases of humans, companion animals, wildlife, and livestock. Whilst apoptosis is an essential part of normal development, maintenance, and defence in multicellular organisms, its occurrence in unicellular parasites appears counter-intuitive and has proved highly controversial: according to the Darwinian notion of “survival of the fittest”, parasites are expected to evolve strategies to maximise their proliferation, not death. The prevailing, and untested, opinion in the literature is that parasites employ apoptosis to “altruistically” self-regulate the intensity of infection in the host/vector. However, evolutionary theory tells us that at most, this can only be part of the explanation, and other non-mutually exclusive hypotheses must also be tested. Here, we explain the evolutionary concepts that can explain apoptosis in unicellular parasites, highlight the key questions, and outline the approaches required to resolve the controversy over whether parasites “commit suicide”. We highlight the need for integration of proximate and functional approaches into an evolutionary framework to understand apoptosis in unicellular parasites. Understanding how, when, and why parasites employ apoptosis is central to targeting this process with interventions that are sustainable in the face of parasite evolution.

Anti-amoebic properties of a Malaysian marine sponge Aaptos sp. on Acanthamoeba castellanii

Crude methanol extracts of a marine sponge, Aaptos aaptos, collected from three different localities namely Kapas, Perhentian and Redang Islands, Terengganu, Malaysia, were tested in vitro on a pathogenic Acanthamoeba castellanii (IMR isolate) to examine their anti-amoebic potential. The examination of anti-Acanthamoebic activity of the extracts was conducted in 24 well plates for 72 h at 30 °C. All extracts possessed anti-amoebic activity with their IC(50) values ranging from 0.615 to 0.876 mg/mL. The effect of the methanol extracts on the surface morphology of A. castellanii was analysed under scanning electron microscopy. The ability of the extracts to disrupt the amoeba cell membrane was indicated by extensive cell's blebbing, changes in the surface morphology, reduced in cell size and with cystic appearance of extract-treated Acanthamoeba. Number of acanthapodia and food cup was also reduced in this Acanthamoeba. Morphological criteria of apoptosis in Acanthamoeba following treatment with the sponge's extracts was determined by acridine orange-propidium iodide staining and observed by fluorescence microscopy. By this technique, apoptotic and necrotic cells can be visualized and quantified. The genotoxic potential of the methanol extracts was performed by the alkaline comet assay. All methanol extracts used were significantly induced DNA damage compared to untreated Acanthamoeba by having high percentage of scores 1, 2, and 3 of the DNA damage. Results from cytotoxicity and genotoxicity studies carried out in the present study suggest that all methanol extracts of A. aaptos have anti-amoebic properties against A. castellanii.

Caspase dependent programmed cell death in developing embryos: a potential target for therapeutic intervention against pathogenic nematodes

Background

Successful embryogenesis is a critical rate limiting step for the survival and transmission of parasitic worms as well as pathology mediated by them. Hence, blockage of this important process through therapeutic induction of apoptosis in their embryonic stages offers promise for developing effective anti-parasitic measures against these extra cellular parasites. However, unlike in the case of protozoan parasites, induction of apoptosis as a therapeutic approach is yet to be explored against metazoan helminth parasites.

Methodology/Principal Findings

For the first time, here we developed and evaluated flow cytometry based assays to assess several conserved features of apoptosis in developing embryos of a pathogenic filarial nematode Setaria digitata, in-vitro as well as ex-vivo. We validated programmed cell death in developing embryos by using immuno-fluorescence microscopy and scoring expression profile of nematode specific proteins related to apoptosis [e.g. CED-3, CED-4 and CED-9]. Mechanistically, apoptotic death of embryonic stages was found to be a caspase dependent phenomenon mediated primarily through induction of intracellular ROS. The apoptogenicity of some pharmacological compounds viz. DEC, Chloroquine, Primaquine and Curcumin were also evaluated. Curcumin was found to be the most effective pharmacological agent followed by Primaquine while Chloroquine displayed minimal effect and DEC had no demonstrable effect. Further, demonstration of induction of apoptosis in embryonic stages by lipid peroxidation products [molecules commonly associated with inflammatory responses in filarial disease] and demonstration of in-situ apoptosis of developing embryos in adult parasites in a natural bovine model of filariasis have offered a framework to understand anti-fecundity host immunity operational against parasitic helminths.

Conclusions/Significance

Our observations have revealed for the first time, that induction of apoptosis in developing embryos can be a potential approach for therapeutic intervention against pathogenic nematodes and flow cytometry can be used to address different issues of biological importance during embryogenesis of parasitic worms.

Pathogenic nematodes currently infect billions of people around the world and pose serious challenges to the economic welfare and public health in most developing countries. At present, limitations of existing therapies warrant identification of new anti-parasitic drugs/drug targets to effectively treat and control neglected tropical diseases [NTD] caused by nematode pathogens. The current gold standard for measuring/screening drug effectiveness against most helminth parasites is in-vitro assessment of motility of parasites/larvae and larval development assays which fails to provide any conclusive idea about the precise mechanism of death of parasitic worms or their larval stages. Given the huge load of parasites or their larval stages in an infected host, a compound which shows promise in in-vitro/motility screening assays but induces necrotic death in parasites/larvae will be of limited use, as it may elicit severe inflammatory response in infected hosts. In this context, the present study, which demonstrates induction of apoptotic death in developing embryos of a pathogenic nematode as a potential drug target for the first time, and provides scope for high throughput screening of pharmacological agents for their apoptogenicity against nematode embryos, is a step forward to develop novel anti-parasitic measures to challenge NTD caused by nematode pathogens.

Copper exposure affects hemocyte apoptosis and Perkinsus marinus infection in eastern oysters Crassostrea virginica (Gmelin)

Dermo disease in the eastern oyster (Crassostrea virginica) is caused by an intracellular protistan parasite Perkinsus marinus. The progression and outcome of this disease is determined by a complex interplay between the host's immunity and parasite's escape mechanisms, both of which can be influenced by environmental pollutants including heavy metals such as copper (Cu). The goal of the present study was to determine the effects of Cu on the levels of apoptosis (which can serve as an important host defense mechanism) in oyster immune cells (hemocytes) in vitro and in vivo as well as on the establishment of P. marinus infections in vivo. Surprisingly, Cu exerted opposing effects on apoptosis levels of hemocytes in vitro and in vivo, stimulating apoptosis in isolated hemocytes but suppressing it during Cu exposure of whole oysters. The mechanisms of this effect are presently unknown and may be related to the different bioavailability of the metal in vitro and in vivo. As expected, Cu accumulated in oyster soft tissues during in vitro exposure. Unexpectedly, this metal also strongly accumulated in hemolymph plasma which is classically considered isoionic with the surrounding seawater, likely reflecting the presence of soluble Cu-binding proteins in oyster plasma. Cu reduced growth of P. marinus in vitro and greatly reduced infection levels of hemocytes in vivo, presumably by direct toxic effects on the parasite. As a possible parasitic counterbalance, Cu accumulation in the hemocytes was reduced by P. marinus infection, although this reduction was not sufficient to prevent the parasiticidal effects of the heavy metal in vivo. This effect of Cu may be useful as a potential therapeutic against Dermo disease in aquaculture conditions. Overall, this study provides important new insights into the potential role of environmental metals in host-parasite relationships and disease dynamics in C. virginica.

Platelet activation attracts a subpopulation of effector monocytes to sites of Leishmania major infection

Leishmania infection triggers the recruitment of Gr1⁺ monocytes to the site of infection via platelet-derived PDGF and subsequent CCL2 production.

Leishmania species trigger a brisk inflammatory response and efficiently induce cell-mediated immunity. We examined the mechanisms whereby leukocytes were recruited into lesions after Leishmania major infection of mice. We found that a subpopulation of effector monocytes expressing the granulocyte marker GR1 (Ly6C) is rapidly recruited into lesions, and these monocytes efficiently kill L. major parasites. The recruitment of this subpopulation of monocytes depends on the chemokine receptor CCR2 and the activation of platelets. Activated platelets secrete platelet-derived growth factor, which induces the rapid release of CCL2 from leukocytes and mesenchymal cells. This work points to a new role for platelets in host defense involving the selective recruitment of a subpopulation of effector monocytes from the blood to efficiently kill this intracellular parasite.

Impact of protozoan cell death on parasite-host interactions and pathogenesis

PCD in protozoan parasites has emerged as a fascinating field of parasite biology. This not only relates to the underlying mechanisms and their evolutionary implications but also to the impact on the parasite-host interactions within mammalian hosts and arthropod vectors. During recent years, common functions of apoptosis and autophagy in protozoa and during parasitic infections have emerged. Here, we review how distinct cell death pathways in Trypanosoma, Leishmania, Plasmodium or Toxoplasma may contribute to regulation of parasite cell densities in vectors and mammalian hosts, to differentiation of parasites, to stress responses, and to modulation of the host immunity. The examples provided indicate crucial roles of PCD in parasite biology. The existence of PCD pathways in these organisms and the identification as being critical for parasite biology and parasite-host interactions could serve as a basis for developing new anti-parasitic drugs that take advantage of these pathways.

Targeting essential pathways in trypanosomatids gives insights into protozoan mechanisms of cell death

Apoptosis is a normal component of the development and health of multicellular organisms. However, apoptosis is now considered a prerogative of unicellular organisms, including the trypanosomatids of the genera Trypanosoma spp. and Leishmania spp., causative agents of some of the most important neglected human diseases. Trypanosomatids show typical hallmarks of apoptosis, although they lack some of the key molecules contributing to this process in metazoans, like caspase genes, Bcl-2 family genes and the TNF-related family of receptors. Despite the lack of these molecules, trypanosomatids appear to have the basic machinery to commit suicide. The components of the apoptotic execution machinery of these parasites are slowly coming into light, by targeting essential processes and pathways with different apoptogenic agents and inhibitors. This review will be confined to the events known to drive trypanosomatid parasites to apoptosis.

Investigating the evolution of apoptosis in malaria parasites: the importance of ecology

Apoptosis is a precisely regulated process of cell death which occurs widely in multicellular organisms and is essential for normal development and immune defences. In recent years, interest has grown in the occurrence of apoptosis in unicellular organisms. In particular, as apoptosis has been reported in a wide range of species, including protozoan malaria parasites and trypanosomes, it may provide a novel target for intervention. However, it is important to understand when and why parasites employ an apoptosis strategy before the likely long- and short-term success of such an intervention can be evaluated. The occurrence of apoptosis in unicellular parasites provides a challenge for evolutionary theory to explain as organisms are expected to have evolved to maximise their own proliferation, not death. One possible explanation is that protozoan parasites undergo apoptosis in order to gain a group benefit from controlling their density as this prevents premature vector mortality. However, experimental manipulations to examine the ultimate causes behind apoptosis in parasites are lacking. In this review, we focus on malaria parasites to outline how an evolutionary framework can help make predictions about the ecological circumstances under which apoptosis could evolve. We then highlight the ecological considerations that should be taken into account when designing evolutionary experiments involving markers of cell death, and we call for collaboration between researchers in different fields to identify and develop appropriate markers in reference to parasite ecology and to resolve debates on terminology.