Mechanisms of cellular invasion by intracellular parasites

Effect of Leishmania infantum infection on B cell lymphopoiesis and memory in the bone marrow and spleen

Visceral leishmaniasis (VL) is characterized by an uncontrolled infection of internal organs such as the spleen, liver and bone marrow (BM) and can be lethal when left untreated. No effective vaccination is currently available for humans. The importance of B cells in infection and VL protective immunity has been controversial, with both detrimental and protective effects described. VL infection was found in this study to increase not only all analyzed B cell subsets in the spleen but also the B cell progenitors in the BM. The enhanced B lymphopoiesis aligns with the clinical manifestation of polyclonal hypergammaglobulinemia and the occurrence of autoantibodies. In line with earlier reports, flow cytometric and microscopic examination identified parasite attachment to B cells of the BM and spleen without internalization, and transformation of promastigotes into amastigote morphotypes. The interaction appears independent of IgM expression and is associated with an increased detection of activated lysosomes. Furthermore, the extracellularly attached amastigotes could be efficiently transferred to infect macrophages. The observed interaction underscores the potentially crucial role of B cells during VL infection. Additionally, using immunization against a fluorescent heterologous antigen, it was shown that the infection does not impair immune memory, which is reassuring for vaccination campaigns in VL endemic areas.

Endocytosis at the maternal-fetal interface: balancing nutrient transport and pathogen defense

Endocytosis represents a category of regulated active transport mechanisms. These encompass clathrin-dependent and -independent mechanisms, as well as fluid phase micropinocytosis and macropinocytosis, each demonstrating varying degrees of specificity and capacity. Collectively, these mechanisms facilitate the internalization of cargo into cellular vesicles. Pregnancy is one such physiological state during which endocytosis may play critical roles. A successful pregnancy necessitates ongoing communication between maternal and fetal cells at the maternal-fetal interface to ensure immunologic tolerance for the semi-allogenic fetus whilst providing adequate protection against infection from pathogens, such as viruses and bacteria. It also requires transport of nutrients across the maternal-fetal interface, but restriction of potentially harmful chemicals and drugs to allow fetal development. In this context, trogocytosis, a specific form of endocytosis, plays a crucial role in immunological tolerance and infection prevention. Endocytosis is also thought to play a significant role in nutrient and toxin handling at the maternal-fetal interface, though its mechanisms remain less understood. A comprehensive understanding of endocytosis and its mechanisms not only enhances our knowledge of maternal-fetal interactions but is also essential for identifying the pathogenesis of pregnancy pathologies and providing new avenues for therapeutic intervention.

Effective factors in the pathogenesis of Toxoplasmagondii

Toxoplasma gondii (T. gondii) is a cosmopolitan protozoan parasite in humans and animals. It infects about 30 % of the human population worldwide and causes potentially fatal diseases in immunocompromised hosts and neonates. For this study, five English-language databases (ScienceDirect, ProQuest, Web of Science, PubMed, and Scopus) and the internet search engine Google Scholar were searched. This review was accomplished to draw a global perspective of what is known about the pathogenesis of T. gondii and various factors affecting it. Virulence and immune responses can influence the mechanisms of parasite pathogenesis and these factors are in turn influenced by other factors. In addition to the host's genetic background, the type of Toxoplasma strain, the routes of transmission of infection, the number of passages, and different phases of parasite life affect virulence. The identification of virulence factors of the parasite could provide promising insights into the pathogenesis of this parasite. The results of this study can be an incentive to conduct more intensive research to design and develop new anti-Toxoplasma agents (drugs and vaccines) to treat or prevent this infection. In addition, further studies are needed to better understand the key agents in the pathogenesis of T. gondii.

Peptide selection via phage display to inhibit Leishmania-macrophage interactions

Introduction

Leishmaniasis comprises a complex group of diseases caused by protozoan parasites from the Leishmania genus, presenting a significant threat to human health. Infection starts by the release into the skin of metacyclic promastigote (MP) form of the parasite by an infected sand fly. Soon after their release, the MPs enter a phagocytic host cell. This study focuses on finding peptides that can inhibit MP-phagocytic host cell interaction.

Methods

We used a phage display library to screen for peptides that bind to the surface of L. amazonensis (causative agent for cutaneous leishmaniasis) and L. infantum (causative agent for cutaneous and visceral leishmaniasis) MPs. Candidate peptide binding to the MP surface and inhibition of parasite-host cell interaction were tested in vitro. Peptide Inhibition of visceral leishmaniasis development was assessed in BALB/c mice.

Results

The selected L. amazonensis binding peptide (La1) and the L. infantum binding peptide (Li1) inhibited 44% of parasite internalization into THP-1 macrophage-like cells in vitro. While inhibition of internalization by La1 was specific to L. amazonensis, Li1 was effective in inhibiting internalization of both parasite species. Importantly, Li1 inhibited L. infantum spleen and liver infection of BALB/c mice by 84%.

Conclusion

We identified one peptide that specifically inhibits L. amazonensis MP infection of host cells and another that inhibits both, L. amazonensis and L. infantum, MP infection. Our findings suggest a promising path for the development of new treatments and prevention of leishmaniasis.

Antimicrobial Peptides (AMP) in the Cell-Free Culture Media of Xenorhabdus budapestensis and X. szentirmaii Exert Anti-Protist Activity against Eukaryotic Vertebrate Pathogens including Histomonas meleagridis and Leishmania donovani Species

Anti-microbial peptides provide a powerful toolkit for combating multidrug resistance. Combating eukaryotic pathogens is complicated because the intracellular drug targets in the eukaryotic pathogen are frequently homologs of cellular structures of vital importance in the host organism. The entomopathogenic bacteria (EPB), symbionts of entomopathogenic-nematode species, release a series of non-ribosomal templated anti-microbial peptides. Some may be potential drug candidates. The ability of an entomopathogenic-nematode/entomopathogenic bacterium symbiotic complex to survive in a given polyxenic milieu is a coevolutionary product. This explains that those gene complexes that are responsible for the biosynthesis of different non-ribosomal templated anti-microbial protective peptides (including those that are potently capable of inactivating the protist mammalian pathogen Leishmania donovanii and the gallinaceous bird pathogen Histomonas meleagridis) are co-regulated. Our approach is based on comparative anti-microbial bioassays of the culture media of the wild-type and regulatory mutant strains. We concluded that Xenorhabdus budapestensis and X. szentirmaii are excellent sources of non-ribosomal templated anti-microbial peptides that are efficient antagonists of the mentioned pathogens. Data on selective cytotoxicity of different cell-free culture media encourage us to forecast that the recently discovered "easy-PACId" research strategy is suitable for constructing entomopathogenic-bacterium (EPB) strains producing and releasing single, harmless, non-ribosomal templated anti-microbial peptides with considerable drug, (probiotic)-candidate potential.

cGAS-STING signaling pathway in intestinal homeostasis and diseases

The intestinal mucosa is constantly exposed to commensal microbes, opportunistic pathogens, toxins, luminal components and other environmental stimuli. The intestinal mucosa consists of multiple differentiated cellular and extracellular components that form a critical barrier, but is also equipped for efficient absorption of nutrients. Combination of genetic susceptibility and environmental factors are known as critical components involved in the pathogenesis of intestinal diseases. The innate immune system plays a critical role in the recognition and elimination of potential threats by detecting pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs). This host defense is facilitated by pattern recognition receptors (PRRs), in which the cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway has gained attention due to its role in sensing host and foreign double-stranded DNA (dsDNA) as well as cyclic dinucleotides (CDNs) produced by bacteria. Upon binding with dsDNA, cGAS converts ATP and GTP to cyclic GMP-AMP (cGAMP), which binds to STING and activates TANK binding kinase 1 (TBK1) and interferon regulatory factor 3 (IRF3), inducing type I interferon (IFN) and nuclear factor kappa B (NF-κB)-mediated pro-inflammatory cytokines, which have diverse effects on innate and adaptive immune cells and intestinal epithelial cells (IECs). However, opposite perspectives exist regarding the role of the cGAS-STING pathway in different intestinal diseases. Activation of cGAS-STING signaling is associated with worse clinical outcomes in inflammation-associated diseases, while it also plays a critical role in protection against tumorigenesis and certain infections. Therefore, understanding the context-dependent mechanisms of the cGAS-STING pathway in the physiopathology of the intestinal mucosa is crucial for developing therapeutic strategies targeting the cGAS-STING pathway. This review aims to provide insight into recent findings of the protective and detrimental roles of the cGAS-STING pathway in intestinal diseases.

The hows and whys of amastigote flagellum motility in Trypanosoma cruzi

The protist Trypanosoma cruzi exhibits several extracellular stages characterized by the presence of a long and motile flagellum and one intracellular life cycle stage termed amastigote, which possesses a tiny flagellum barely exiting the flagellar pocket. This stage was so far described as replicative but immotile cells. Unexpectedly, the recent work of M. M. Won, T. Krüger, M. Engstler, and B. A. Burleigh (mBio 14:e03556-22, 2023, https://doi.org/10.1128/mbio.03556-22) revealed that this short flagellum actually displays beating activity. This commentary explores how such a short flagellum could be constructed and why it could affect the parasite's survival inside the mammalian host.

Malaria Elimination in Africa: Rethinking Strategies for Plasmodium vivax and Lessons from Botswana

The global malaria community has picked up the theme of malaria elimination in more than 90% of the world's population in the next decade. Recent reports of Plasmodium vivax (P. vivax) in sub-Saharan Africa, including in Duffy-negative individuals, threaten the efforts aimed at achieving elimination. This is not only in view of strategies that are tailored only to P. falciparum elimination but also due to currently revealed biological characteristics of P. vivax concerning the relapse patterns of hypnozoites and conservation of large biomasses in cryptic sites in the bone marrow and spleen. A typical scenario was observed in Botswana between 2008 and 2018, which palpably projects how P. vivax could endanger malaria elimination efforts where the two parasites co-exist. The need for the global malaria community, national malaria programs (NMPs), funding agencies and relevant stakeholders to engage in a forum to discuss and recommend clear pathways for elimination of malaria, including P. vivax, in sub-Saharan Africa is warranted.

Cryptosporidium parvum hijacks a host's long noncoding RNA U90926 to evade intestinal epithelial cell-autonomous antiparasitic defense

Cryptosporidium is a zoonotic apicomplexan parasite that infects the gastrointestinal epithelium and other mucosal surfaces in humans. It is an important opportunistic pathogen in AIDS patients and a leading cause of infectious diarrhea and diarrheal-related death in children worldwide. The intestinal epithelial cells provide the first line of defense against Cryptosporidium infection and play a central role in activating and regulating the host's antiparasitic response. Increasing evidence suggests that long noncoding RNAs (lncRNAs) participate in host-pathogen interactions and play a regulatory role in the pathogenesis of diseases but the underlying molecular mechanisms are not fully understood. We previously identified a panel of host lncRNAs that are upregulated in murine intestinal epithelial cells following Cryptosporidium infection, including U90926. We demonstrate here that U90926 is acting in a pro-parasitic manner in regulating intestinal epithelial cell-autonomous antiparasitic defense. Inhibition of U90926 resulted in a decreased infection burden of the parasite while overexpression of U90926 showed an increase in infection burden in cultured murine intestinal epithelial cells. Induction of U90926 suppressed transcription of epithelial defense genes involved in controlling Cryptosporidium infection through epigenetic mechanisms. Specifically, transcription of Aebp1, which encodes the Aebp1 protein, a potent modulator of inflammation and NF-κB signaling, was suppressed by U90926. Gain- or loss-of-function of Aebp1 in the host's epithelial cells caused reciprocal alterations in the infection burden of the parasite. Interestingly, Cryptosporidium carries the Cryptosporidium virus 1 (CSpV1), a double-stranded (ds) RNA virus coding two dsRNA fragments, CSpV1-dsRdRp and CSpV1-dsCA. Both CSpV1-dsRdRp and CSpV1-dsCA can be delivered into infected cells as previously reported. We found that cells transfected with in vitro transcribed CSpV1-dsCA or CSpV1-dsRdRp displayed an increased level of U90926, suggesting that CSpV1 is involved in the upregulation of U90926 during Cryptosporidium infection. Our study highlights a new strategy by Cryptosporidium to hijack a host lncRNA to suppress epithelial cell-autonomous antiparasitic defense and allow for a robust infection.

The most prominent modulated annexins during parasitic infections

Annexins (ANXs) exert different functions in cell biological and pathological processes and are thus known as double or multi-faceted proteins. These sophisticated proteins might express on both parasite structure and secretion and in parasite-infected host cells. In addition to the characterization of these pivotal proteins, describing their mechanism of action can be also fruitful in recognizing their roles in the pathogenesis of parasitic infections. Accordingly, this study presents the most prominent ANXs thus far identified and their relevant functions in parasites and infected host cells during pathogenesis, especially in the most important intracellular protozoan parasitic infections including leishmaniasis, toxoplasmosis, malaria and trypanosomiasis. The data provided in this study demonstrate that the helminth parasites most probably express and secret ANXs to develop pathogenesis while the modulation of the host-ANXs could be employed as a crucial strategy by intracellular protozoan parasites. Moreover, such data highlight that the use of analogs of both parasite and host ANX peptides (which mimic or regulate ANXs physiological functions through various strategies) might suggest novel therapeutic insights into the treatment of parasitic infections. Furthermore, due to the prominent immunoregulatory activities of ANXs during most parasitic infections and the expression levels of these proteins in some parasitic infected tissues, such multifunctional proteins might be also potentially relevant as vaccine and diagnostic biomarkers. We also suggest some prospects and insights that could be useful and applicable to form the basis of future experimental studies.

Design and synthesis of N-acyl and dimeric N-Arylpiperazine derivatives as potential antileishmanial agents

The current regime for leishmaniasis is associated with several adverse effects, expensive, parenteral treatment for longer periods and the emergence of drug resistance. To develop affordable and potent antileishmanial agents, a series of N-acyl and homodimeric aryl piperazines were synthesized with high purity, predicted druggable properties by in silico methods and investigated their antileishmanial activity. The in vitro biological activity of synthesized compounds against clinically validated intracellular amastigote and extracellular promastigote form of Leishmania donovani parasite showed eight compounds inhibited 50% amastigotes growth below 25 µM. The half maximal inhibitory concentration (IC₅₀) and cytotoxicity assessment of eight active compounds, 4a, 4d and 4e demonstrated activity with an IC₅₀ 2.0 - 9.1 µM and selectivity index 10 - 42. Compound 4d (IC₅₀ 2.0 µM, SI = 42) found to be the best among them with four-folds more potent and eight-folds less toxic than the control drug miltefosine. Overall, results demonstrated that compound 4d is a promising lead candidate for further development as antileishmanial drug.

In-vitro biological evaluation of 3,3',5,5'-tetramethoxy-biphenyl-4,4'-diol and molecular docking studies on trypanothione reductase and Gp63 from Leishmania amazonensis demonstrated anti-leishmania potential

Available treatments for leishmaniasis have been widely used since the 1940s but come at a high cost, variable efficacy, high toxicity, and adverse side-effects. 3,3',5,5'-Tetramethoxy-biphenyl-4,4'-diol (TMBP) was synthesized through laccase-catalysis of 2,6-dimethoxyphenol and displayed antioxidant and anticancer activity, and is considered a potential drug candidate. Thus, this study aimed to evaluate the anti-leishmanial effect of TMBP against promastigote and amastigote forms of Leishmania (L.) amazonensis and investigated the mechanisms involved in parasite death. TMBP treatment inhibited the proliferation (IC₅₀ 0.62-0.86 µM) and induced the death of promastigote forms by generating reactive oxygen species and mitochondrial dysfunction. In intracellular amastigotes, TMBP reduced the percentage of infected macrophages, being 62.7 times more selective to the parasite (CC₅₀ 53.93 µM). TMBP did not hemolyze sheep erythrocytes; indicative of low cytotoxicity. Additionally, molecular docking analysis on two enzyme targets of L. amazonensis: trypanothione reductase (TR) and leishmanolysin (Gp63), suggested that the hydroxyl group could be a pharmacophoric group due to its binding affinity by hydrogen bonds with residues at the active site of both enzymes. TMBP was more selective to the Gp63 target than TR. This is the first report that TMBP is a promising compound to act as an anti-leishmanial agent.

Cultivation of Protozoa Parasites In Vitro: Growth Potential in Conventional Culture Media versus RPMI-PY Medium

The in vitro cultivation of Leishmania and Trypanosoma parasites plays an important role in the diagnosis and treatment of parasitic diseases. Although Evans’s modified Tobie and Novy–MacNeal–Nicolle media, for Leishmania spp. and Trypanosoma cruzi, respectively, are the two commonly used media for both isolation and maintenance of strains in vitro, their preparation is expensive and laborious and requires fresh rabbit blood from housed animals. The purpose of this study was to evaluate the in vitro growth of both parasites with an alternative monophasic, blood-free, easy, and affordable medium called RPMI-PY, which was previously demonstrated suitable for the in vitro growth of Leishmania infantum. The potential growth of different Leishmania species and Trypanosoma cruzi was evaluated in traditional culture media versus RPMI-PY medium, and we recorded the protozoa parasites’ morphology via orange acridine–ethidium bromide staining. The results of our study show that RPMI-PY medium can be used for Trypanosoma cruzi, Leishmania amazonensis, Leishmania major, and Leishmania tropica species since in all the species except Leishmania braziliensis, the exponential growth of the parasite was observed, in many cases higher than conventional media. The staining confirmed not only their growth during the 72 h investigation but also the optimal morphology and viability of the protozoa in the RPMI-PY medium.

Unrevealing the Mystery of Latent Leishmaniasis: What Cells Can Host Leishmania?

Leishmania spp. (Kinetoplastida) are unicellular parasites causing leishmaniases, neglected tropical diseases of medical and veterinary importance. In the vertebrate host, Leishmania parasites multiply intracellularly in professional phagocytes, such as monocytes and macrophages. However, their close relative with intracellular development-Trypanosoma cruzi-can unlock even non-professional phagocytes. Since Leishmania and T. cruzi have similar organelle equipment, is it possible that Leishmania can invade and even proliferate in cells other than the professional phagocytes? Additionally, could these cells play a role in the long-term persistence of Leishmania in the host, even in cured individuals? In this review, we provide (i) an overview of non-canonical Leishmania host cells and (ii) an insight into the strategies that Leishmania may use to enter them. Many studies point to fibroblasts as already established host cells that are important in latent leishmaniasis and disease epidemiology, as they support Leishmania transformation into amastigotes and even their multiplication. To invade them, Leishmania causes damage to their plasma membrane and exploits the subsequent repair mechanism via lysosome-triggered endocytosis. Unrevealing the interactions between Leishmania and its non-canonical host cells may shed light on the persistence of these parasites in vertebrate hosts, a way to control latent leishmaniasis.

Autophagy induced macrophages by α-alumina(α-AL2O3) conjugated cysteine peptidase, enhances the cytotoxic activity of CD8+ T lymphocytes against Leishmania major

Introduction

Induction of a protective immune response against Leishmania major requires the activation of both TH1 and CD8+ T lymphocytes. Because L. major is an intra-phagosomal parasite, its antigens do not have access to MHC-I. The present study aimed to evaluate the effect of cysteine peptidase A (CPA)/cysteine peptidase B (CPB) conjugated to α-AL2O3 on autophagy induction in L. major infected macrophages and subsequent activation of cytotoxic CD8+ T lymphocytes.

Methods

Recombinant CPA and CPB of L. major were produced in expression vectors and purified. Aldehyde functionalized α-AL2O3 were conjugated to hydrazine-modified CPA/CPB by a chemical bond was confirmed by Fourier-transform infrared spectroscopy (FTIR). The High efficient internalization of α-AL2O3 conjugated CPA/CPB to macrophages was confirmed using a fluorescence microscope and flowcytometry. Induction of the acidic autophagosome and LC3 conversion in macrophages was determined by acridine orange (AO) staining and western blot. Autophagy-activated macrophages were used for CD8+ T cell priming. Cytotoxic activity of the primed CD8+ T cell against L. major infected macrophages was measured using apoptosis assay.

Results

α-AL2O3 conjugated CPA/CPB enhances macrophages antigen uptake and increases acidic vacuole formation and LC-3I to LC-3II conversion. Co-culture of autophagy-activated macrophages with CD8+ T cells augmented CD8+ T cells priming and proliferation more than in other study groups. These primed CD8+ T cells induce significant apoptotic death of L. major infected macrophages compared with non-primed CD8+ T cells.

Conclusion

α-AL2O3 nanoparticles enhance the cross-presentation of L. major antigens to CD8+ T cells by inducing autophagy. This finding supports the positive role of autophagy and encourages the use of α-AL2O3 in vaccine design.

Unraveling the role of natural killer cells in leishmaniasis

NK cells are known as frontline responders that are efficient in combating several maladies as well as leishmaniasis caused by Leishmania spp. As such they are being investigated to be used for adoptive transfer therapy and vaccine. In spite of the lack of antigen-specific receptors at their surface, NK cells can selectively recognize pathogens, accomplished by the activation of the receptors on the NK cell surface and also as the result of their effector functions. Activation of NK cells can occur through interaction between TLR-2 expressed on NK cells and. LPG of Leishmania parasites. In addition, NK cell activation can occur by cytokines (e.g., IFN-γ and IL-12) that also lead to producing cytokines and chemokines and lysis of target cells. This review summarizes several evidences that support NK cells activation for controlling leishmaniasis and the potentially lucrative roles of NK cells during leishmaniasis. Furthermore, we discuss strategies of Leishmania parasites in inhibiting NK cell functions. Leishmania LPG can utilizes TLR2 to evade host-immune responses. Also, Leishmania GP63 can directly binds to NK cells and modulates NK cell phenotype. Finally, this review analyzes the potentialities to harness NK cells effectiveness in therapy regimens and vaccinations.

Deciphering the mechanism and function of Hsp100 unfoldases from protein structure

Hsp100 chaperones, also known as Clp proteins, constitute a family of ring-forming ATPases that differ in 3D structure and cellular function from other stress-inducible molecular chaperones. While the vast majority of ATP-dependent molecular chaperones promote the folding of either the nascent chain or a newly imported polypeptide to reach its native conformation, Hsp100 chaperones harness metabolic energy to perform the reverse and facilitate the unfolding of a misfolded polypeptide or protein aggregate. It is now known that inside cells and organelles, different Hsp100 members are involved in rescuing stress-damaged proteins from a previously aggregated state or in recycling polypeptides marked for degradation. Protein degradation is mediated by a barrel-shaped peptidase that physically associates with the Hsp100 hexamer to form a two-component system. Notable examples include the ClpA:ClpP (ClpAP) and ClpX:ClpP (ClpXP) proteases that resemble the ring-forming FtsH and Lon proteases, which unlike ClpAP and ClpXP, feature the ATP-binding and proteolytic domains in a single polypeptide chain. Recent advances in electron cryomicroscopy (cryoEM) together with single-molecule biophysical studies have now provided new mechanistic insight into the structure and function of this remarkable group of macromolecular machines.

Trypanosoma cruzi pathogenicity involves virulence factor expression and upregulation of bioenergetic and biosynthetic pathways

The molecular repertoire of Trypanosoma cruzi effects its virulence and impacts the clinical course of the resulting Chagas disease. This study aimed to determine the mechanism underlying the pathogenicity of T. cruzi. Two T. cruzi cell lines (C8C3hvir and C8C3lvir), obtained from the clone H510 C8C3 and exhibiting different virulence phenotypes, were used to evaluate the parasite's infectivity in mice. The organ parasite load was analysed by qPCR. The proteomes of both T. cruzi cell lines were compared using nLC-MS/MS. Cruzipain (Czp), complement regulatory protein (CRP), trans-sialidase (TS), Tc-85, and sialylated epitope expression levels were evaluated by immunoblotting. High-virulence C8C3hvir was highly infectious in mice and demonstrated three to five times higher infectivity in mouse myocardial cells than low-virulence C8C3lvir. qPCR revealed higher parasite loads in organs of acute as well as chronically C8C3hvir-infected mice than in those of C8C3lvir-infected mice. Comparative quantitative proteomics revealed that 390 of 1547 identified proteins were differentially regulated in C8C3hvir with respect to C8C3lvir. Amongst these, 174 proteins were upregulated in C8C3hvir and 216 were downregulated in C8C3lvir. The upregulated proteins in C8C3hvir were associated with the tricarboxylic acid cycle, ribosomal proteins, and redoxins. Higher levels of Czp, CRP, TS, Tc-85, and sialylated epitopes were expressed in C8C3hvir than in C8C3lvir. Thus, T. cruzi virulence may be related to virulence factor expression as well as upregulation of bioenergetic and biosynthetic pathways proteins.

Enhancement of immune responses by vaccine potential of three antigens, including ROP18, MIC4, and SAG1 against acute toxoplasmosis in mice

Toxoplasma gondii (T. gondii) causes considerable financial losses in the livestock industry and can present serious threats to pregnant women, as well as immunocompromised patients. Therefore, it is required to design and produce an efficient vaccine for controlling toxoplasmosis. The present study aimed to evaluate the protective immunity induced by RMS protein (ROP18, MIC4, and SAG1) with Freund adjuvant, calcium phosphate nanoparticles (CaPNs), and chitosan nanoparticles (CNs) in BALB/c mice. The RMS protein was expressed in Escherichia coli (E. coli) and purified using a HisTrap HP column. Thereafter, cellular and humoral immunity was assessed by injecting RMS protein on days 0, 21, and 35 into four groups [RMS, RMS-chitosan nanoparticles (RMS-CNs), RMS-calcium phosphate nanoparticles (RMS-CaPNs), and RMS-Freund]. Phosphate buffered saline (PBS), CNs, CaPNs, and Freund served as the four control groups. The results displayed that vaccination with RMS protein and adjuvants significantly elicited the levels of specific IgG antibodies and cytokines against toxoplasmosis. There were high levels of total IgG, IgG2a, and IFN-γ in vaccinated mice, compared to those in the control groups, especially in the RMS-Freund, indicating a Th-1 type response. The vaccinated and control mice were challenged intraperitoneally with 1 × 10³ tachyzoites of the T. gondii RH strain four weeks after the last injection, and in RMS-Freund and RMS-CaPNs groups, the highest increase in survival time was observed (15 days). The RMS can significantly increase Th1 and Th2 responses; moreover, multi-epitope vaccines with adjuvants can be a promising strategy for the production of a vaccine against toxoplasmosis.

Evaluation of anti-parasitic activities of new quinolones containing nitrofuran moiety against Toxoplasma gondii

Toxoplasmosis is a disease with a worldwide prevalence that is caused by Toxoplasma gondii. Pyrimethamine and sulfadiazine are two pharmacological agents commonly used to treat of this infection. However, they are accompanied by some side effects. Therefore, the identifying of new drugs with low toxocytosis seems to be a matter of vital importance. Quinolones are DNA replication inhibitors, exerting inhibitory effects against many pathogens, including bacteria, mycoplasma, and protozoa. Given the importance of quinolones and their efficacy, the present in vitro study was conducted to investigate the antiparasitic activities of new quinolones (NFQ-2, NFQ-5, and NFQ-6) containing nitrofuran moiety against T. gondii. To this end, Vero cells were incubated with various concentrations of new quinolones and pyrimethamine (positive control) to determine their viability. Subsequently, they were infected with T. gondii (RH strain) and then subjected to drug treatment. The obtained IC₅₀ values were 3.60, 4.84, 5.59, 3.44 and 2.75 μg/mL for NFQ-2, NFQ-5, NFQ-6, ciprofloxacin and pyrimethamine, respectively. The CC₅₀ values for the NFQ-2, NFQ-5, and NFQ-6 were 25.20, 29.89, and 28.43 μg/mL, indicating the selectivity indexes more than 5 for these compounds. The anti-Toxoplasma efficiency was determined by evaluating infection index, number and size of plaques, and T. gondii intracellular proliferation. As the results indicated, the administration of new quinolone derivatives resulted in the reduction of intracellular proliferation, infection index, and the number and size of plaques in comparison to uninfected treated cells (P < 0.05). The results were indicative of a considerable synergetic effect when each of the derivatives was used in combination with pyrimethamine, compared to when used alone. Based on our results, the nitrofuran-derived quinolones can be considered as new leads for the design of new anti-Toxoplasma agents.

Oxidative Stress and High-Mobility Group Box 1 Assay in Dogs with Gastrointestinal Parasites

This study aimed to evaluate the concentration of reactive oxidative metabolites, the antioxidant barrier, thiol groups of plasma compounds, and high-mobility group box 1 in shelter dogs naturally infected with helminths. In addition, the correlation between clinical signs and oxidative stress was investigated. Sixty-six (41 male and 25 female) adult mixed-breed dogs housed in a shelter with the diagnosis of gastrointestinal nematodes (i.e., Ancylostoma spp., Uncinaria stenocephala, Toxocara canis, Toxascaris leonina, or Trichuris vulpis) were enrolled in Group 1 (G1) and twenty healthy adult dogs were included in Group 2 (G2), which served as the control. A clinical assessment was performed using a physician-based scoring system. Oxidative stress variables and high-mobility group box 1 were assessed and compared by the means of unpaired t-tests (p < 0.05). Spearman’s rank correlation was performed to calculate the correlation between oxidative stress variables, high-mobility group box 1, hematological parameters, and clinical signs. The results showed statistically significant values for reactive oxidative metabolites, thiol groups of plasma compounds, and high-mobility group box 1 in G1. Negative correlations between thiol groups and the number of red cells and hemoglobin were recorded. These preliminary results support the potential role of oxidative stress and HGMB-1 in the pathogenesis of gastrointestinal helminthiasis in dogs.

Regulated necrosis, a proinflammatory cell death, potentially counteracts pathogenic infections

Since the discovery of cell apoptosis, other gene-regulated cell deaths are gradually appreciated, including pyroptosis, ferroptosis, and necroptosis. Necroptosis is, so far, one of the best-characterized regulated necrosis. In response to diverse stimuli (death receptor or toll-like receptor stimulation, pathogenic infection, or other factors), necroptosis is initiated and precisely regulated by the receptor-interacting protein kinase 3 (RIPK3) with the involvement of its partners (RIPK1, TRIF, DAI, or others), ultimately leading to the activation of its downstream substrate, mixed lineage kinase domain-like (MLKL). Necroptosis plays a significant role in the host's defense against pathogenic infections. Although much has been recognized regarding modulatory mechanisms of necroptosis during pathogenic infection, the exact role of necroptosis at different stages of infectious diseases is still being unveiled, e.g., how and when pathogens utilize or evade necroptosis to facilitate their invasion and how hosts manipulate necroptosis to counteract these detrimental effects brought by pathogenic infections and further eliminate the encroaching pathogens. In this review, we summarize and discuss the recent progress in the role of necroptosis during a series of viral, bacterial, and parasitic infections with zoonotic potentials, aiming to provide references and directions for the prevention and control of infectious diseases of both human and animals.

In vivo transcriptional analysis of mice infected with Leishmania major unveils cellular heterogeneity and altered transcriptomic profiling at single-cell resolution

Leishmania parasites cause cutaneous leishmaniasis (CL), a disease characterized by disfiguring, ulcerative skin lesions. Both parasite and host gene expression following infection with various Leishmania species has been investigated in vitro, but global transcriptional analysis following L. major infection in vivo is lacking. Thus, we conducted a comprehensive transcriptomic profiling study combining bulk RNA sequencing (RNA-Seq) and single-cell RNA sequencing (scRNA-Seq) to identify global changes in gene expression in vivo following L. major infection. Bulk RNA-Seq analysis revealed that host immune response pathways like the antigen processing and presentation pathway were significantly enriched amongst differentially expressed genes (DEGs) upon infection, while ribosomal pathways were significantly downregulated in infected mice compared to naive controls. scRNA-Seq analyses revealed cellular heterogeneity including distinct resident and recruited cell types in the skin following murine L. major infection. Within the individual immune cell types, several DEGs indicative of many interferon induced GTPases and antigen presentation molecules were significantly enhanced in the infected ears including macrophages, resident macrophages, and inflammatory monocytes. Ingenuity Pathway Analysis of scRNA-Seq data indicated the antigen presentation pathway was increased with infection, while EIF2 signaling is the top downregulated pathway followed by eIF4/p70S6k and mTOR signaling in multiple cell types including macrophages, blood and lymphatic endothelial cells. Altogether, this transcriptomic profile highlights known recruitment of myeloid cells to lesions and recognizes a potential role for EIF2 signaling in murine L. major infection in vivo.

Immune Responses in Leishmaniases: An Overview

Leishmaniasis is a parasitic, widespread, and neglected disease that affects more than 90 countries in the world. More than 20 Leishmania species cause different forms of leishmaniasis that range in severity from cutaneous lesions to systemic infection. The diversity of leishmaniasis forms is due to the species of parasite, vector, environmental and social factors, genetic background, nutritional status, as well as immunocompetence of the host. Here, we discuss the role of the immune system, its molecules, and responses in the establishment, development, and outcome of Leishmaniasis, focusing on innate immune cells and Leishmania major interactions.

Leishmania survives by exporting miR-146a from infected to resident cells to subjugate inflammation

Leishmania donovani, the causative agent of visceral leishmaniasis, infects and resides within tissue macrophage cells. It is not clear how the parasite infected cells crosstalk with the noninfected cells to regulate the infection process. During infection, Leishmania adopts a dual strategy for its survival by regulating the intercellular transport of host miRNAs to restrict inflammation. The parasite, by preventing mitochondrial function of host cells, restricts the entry of liver cell derived miR-122-containing extracellular vesicles in infected macrophages to curtail the inflammatory response associated with miR-122 entry. On contrary, the parasite up-regulates the export of miR-146a from the infected macrophages. The miR-146a, associated with the extracellular vesicles released by infected cells, restricts miR-122 production in hepatocytes while polarizing neighbouring naïve macrophages to the M2 state by affecting the cytokine expression. On entering the recipient macrophages, miR-146a dominates the miRNA antagonist RNA-binding protein HuR to inhibit the expression of proinflammatory cytokine mRNAs having HuR-interacting AU-rich elements whereas up-regulates anti-inflammatory IL-10 by exporting the miR-21 to polarize the recipient cells to M2 stage.

Three-dimensional Architecture of Cyrilia lignieresi Gametocyte-stage Development Inside Red Blood Cells

The Haemogregarinidae family (Apicomplexa: Adeleina) comprises hemoprotozoa that infect mammals, birds, amphibians, fish and reptiles. Some morphological characteristics of the Cyrilia lignieresi have been described previously, but the parasite-erythrocyte relationship is still poorly understood. In order to understand the structural architecture of Cyrilia lignieresi-infected red blood cells, electron microscopy-based three-dimensional reconstruction was carried out using TEM as well as FIB-SEM tomography. Results showed that development of the macrogametocyte-stage inside the red blood cell is related to an increase in cleft-like structures in the host cell cytoplasm. Furthermore, other aspects related to parasite intraerythrocytic development were explored by 3D visualization techniques. We observed the invagination of a large extension of the Inner Membrane Complex on the parasite body, which results from or induces a folding of the posterior end of the parasite. Small tubular structures were seen associated with areas related to Inner Membrane Complex folding. Taken together, results provide new information on the remodeling of erythrocytes induced by the protozoan C. lignieresi.

Interleukin-32γ in the Control of Acute Experimental Chagas Disease

Chagas disease (CD) is an important parasitic disease caused by Trypanosoma cruzi. Interleukin-32 (IL-32) plays an important role in inflammation and in the development of Th1/Th17 acquired immune responses. We evaluated the influence of IL-32γ on the immune response profile, pathogenesis of myocarditis in acute experimental CD, and control of the disease. For this, C57BL/6 wild-type (WT) and IL-32γTg mice were infected subcutaneously with 1,000 forms of Colombian strain of T. cruzi. In the histopathological analyzes, T. cruzi nests, myocarditis, and collagen were quantified in cardiac tissue. Cytokine productions (IL-32, IFN-γ, TNF-α, IL-10, and IL-17) were measured in cardiac homogenate by ELISA. The IL-32γTg mice showed a better control of parasitemia and T. cruzi nests in the heart than WT mice. Infected-WT and -IL-32γTg mice showed similar levels of IFN-γ, TNF-α, and IL-17, but IL-10 was significantly higher expressed in IL-32γTg than in WT mice. The cytokine profile found in IL-32γTg animals contributed to body weight maintenance, parasitemia control, and survival. Our results indicate that the presence of human IL-32γ in mice infected with the Colombian strain of T. cruzi is important for infection control during the acute phase of Chagas disease.

CD300a Receptor Blocking Enhances Early Clearance of Leishmania donovani From Its Mammalian Host Through Modulation of Effector Functions of Phagocytic and Antigen Experienced T Cells

The parasites of the genus Leishmania survive and proliferate in the host phagocytic cells by taking control over their microbicidal functions. The parasite also promotes differentiation of antigen-specific anti-inflammatory cytokines producing effector T cells, which eventually results in disease pathogenesis. The mechanisms that parasites employ to dominate host adaptive immunity are largely unknown. For the first time, we report that L. donovani, which causes visceral leishmaniasis in the Indian subcontinent, upregulates the expression of an immune inhibitory receptor i.e., CD300a on antigen presenting and phagocytic cells to dampen their effector functions. The blocking of CD300a signals in leishmania antigens activated macrophages and dendritic cells enhanced the production of nitric oxide, pro-inflammatory cytokines along with MHCI/II genes expression, and reduced parasitic uptake. Further, the abrogation of CD300a signals in Leishmania infected mice benefited antigen-experienced, i.e., CD4⁺CD44⁺ and CD8⁺CD44⁺ T cells to acquire more pro-inflammatory cytokines producing phenotypes and helped in the early clearance of parasites from their visceral organs. The CD300a receptor blocking also enhanced the conversion of CD4⁺ T effectors cells to their memory phenotypes i.e., CCR7^high CD62L^high up to 1.6 and 1.9 fold after 14 and 21 days post-infection, respectively. These findings implicate that CD300a is an important determinant of host phagocytic cells functions and T cells differentiation against Leishmania antigens.

The Glycosylphosphatidylinositol Anchor: A Linchpin for Cell Surface Versatility of Trypanosomatids

The use of glycosylphosphatidylinositol (GPI) to anchor proteins to the cell surface is widespread among eukaryotes. The GPI-anchor is covalently attached to the C-terminus of a protein and mediates the protein’s attachment to the outer leaflet of the lipid bilayer. GPI-anchored proteins have a wide range of functions, including acting as receptors, transporters, and adhesion molecules. In unicellular eukaryotic parasites, abundantly expressed GPI-anchored proteins are major virulence factors, which support infection and survival within distinct host environments. While, for example, the variant surface glycoprotein (VSG) is the major component of the cell surface of the bloodstream form of African trypanosomes, procyclin is the most abundant protein of the procyclic form which is found in the invertebrate host, the tsetse fly vector. Trypanosoma cruzi, on the other hand, expresses a variety of GPI-anchored molecules on their cell surface, such as mucins, that interact with their hosts. The latter is also true for Leishmania, which use GPI anchors to display, amongst others, lipophosphoglycans on their surface. Clearly, GPI-anchoring is a common feature in trypanosomatids and the fact that it has been maintained throughout eukaryote evolution indicates its adaptive value. Here, we explore and discuss GPI anchors as universal evolutionary building blocks that support the great variety of surface molecules of trypanosomatids.

Pathogenic role of mitogen activated protein kinases in protozoan parasites

Protozoan parasites with complex life cycles have high mortality rates affecting billions of human lives. Available anti-parasitic drugs are inadequate due to variable efficacy, toxicity, poor patient compliance and drug-resistance. Hence, there is an urgent need for the development of safer and better chemotherapeutics. Mitogen Activated Protein Kinases (MAPKs) have drawn much attention as potential drug targets. This review summarizes unique structural and functional features of MAP kinases and their possible role in pathogenesis of obligate intracellular protozoan parasites namely, Leishmania, Trypanosoma, Plasmodium and Toxoplasma. It also provides an overview of available knowledge concerning the target proteins of parasite MAPKs and the need to understand and unravel unknown interaction network(s) of MAPK(s).

Nitric oxide controls proliferation of Leishmania major by inhibiting the recruitment of permissive host cells

Nitric oxide (NO) is an important antimicrobial effector but also prevents unnecessary tissue damage by shutting down the recruitment of monocyte-derived phagocytes. Intracellular pathogens such as Leishmania major can hijack these cells as a niche for replication. Thus, NO might exert containment by restricting the availability of the cellular niche required for efficient pathogen proliferation. However, such indirect modes of action remain to be established. By combining mathematical modeling with intravital 2-photon biosensors of pathogen viability and proliferation, we show that low L. major proliferation results not from direct NO impact on the pathogen but from reduced availability of proliferation-permissive host cells. Although inhibiting NO production increases recruitment of these cells, and thus pathogen proliferation, blocking cell recruitment uncouples the NO effect from pathogen proliferation. Therefore, NO fulfills two distinct functions for L. major containment: permitting direct killing and restricting the supply of proliferation-permissive host cells.

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Direct killing of L. major by NO occurs only during the peak of the immune response

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Efficient L. major proliferation requires newly recruited monocyte-derived cells

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Loss of NO production increases both pathogen proliferation and monocyte recruitment

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NO dampens L. major proliferation indirectly, limiting the pathogen’s cellular niche

Identification of first-in-class plasmodium OTU inhibitors with potent anti-malarial activity

OTU proteases antagonize the cellular defense in the host cells and involve in pathogenesis. Intriguingly, P. falciparum, P. vivax, and P. yoelii have an uncharacterized and highly conserved viral OTU-like proteins. However, their structure, function or inhibitors have not been previously reported. To this end, we have performed structural modeling, small molecule screening, deconjugation assays to characterize and develop first-in-class inhibitors of P. falciparum, P. vivax, and P. yoelii OTU-like proteins. These Plasmodium OTU-like proteins have highly conserved residues in the catalytic and inhibition pockets similar to viral OTU proteins. Plasmodium OTU proteins demonstrated Ubiquitin and ISG15 deconjugation activities as evident by intracellular ubiquitinated protein content analyzed by western blot and flow cytometry. We screened a library of small molecules to determine plasmodium OTU inhibitors with potent anti-malarial activity. Enrichment and correlation studies identified structurally similar molecules. We have identified two small molecules that inhibit P. falciparum, P. vivax, and P. yoelii OTU proteins (IC50 values as low as 30 nM) with potent anti-malarial activity (IC50 of 4.1-6.5 µM). We also established enzyme kinetics, druglikeness, ADME, and QSAR model. MD simulations allowed us to resolve how inhibitors interacted with plasmodium OTU proteins. These findings suggest that targeting malarial OTU-like proteases is a plausible strategy to develop new anti-malarial therapies.

Antileishmanial and lung adenocarcinoma cell toxicity of Withania somnifera (Linn.) dunal root and fruit extracts

This study aims to evaluate the anti-Leishmania major and the lung adenocarcinoma (A549) cytotoxicity of Withania somnifera root and fruit. The total extracts were obtained by homogenisation in aqueous MeOH, and the sub-extracts [n-hexane, ethyl acetate (EtOAc), n-butanol (n-BuOH), and methanol (MeOH)] were obtained by flash chromatography. The activity evaluation showed that n-BuOH sub-extracts from root and fruit exhibited noticeable antileishmanial promastigote properties. The n-hexane and EtOAc sub-extracts from both organs, and the MeOH sub-extract from the fruit exerted mild to moderate effects on the promastigotes. In-vitro growth-inhibitory test results on axenic amastigote and cytotoxicity testing on macrophages (RAW264.7), the parasite-host at the amastigote stage, revealed that the activity was mainly concentrated in the root EtOAc and n-BuOH sub-extracts and to a lesser extent the fruit MeOH and EtOAc, and the root n-hexane sub-extracts. Only the roots' EtOAc and n-BuOH sub-extracts demonstrated low cytotoxicity on the A549 cell line.

Novel dual-fluorescent flow cytometric approach for quantification of macrophages infected with Leishmania infantum parasites

Flow cytometry analysis emerges as an alternative methodology to microscopy for determination of the Leishmania-infection rates of macrophages. Various flow cytometric approaches have been established for the quantification of Leishmania parasites within host cells, labelled either directly fluorescent dyes or indirectly with fluorescently conjugated antibodies. Although these techniques allow accurate quantification of infection, they fail at detection of non-infected macrophages specifically. This study introduces a new flow cytometric approach for the determination of infection rates of macrophages infected by Leishmania infantum parasites. Prior to infection, J774A.1 macrophages and L. infantum promastigotes were stained separately with PKH26 and PKH67 dyes, respectively. Dual staining enabled detection of each cell type, where non-infected macrophages were also recorded for the quantification. Dual-PKH staining achieved high success in selective staining of promastigotes (99.71%) and macrophages (99.57%). The percentages of parasite-infected macrophages were determined for initial 1:2.5 and 1:10 infection ratios as 15.68 and 61.70%, respectively; indicating significant increase in infection rate parallel to the initial treatment ratio. These results demonstrated that the introduced dual-fluorescence flow cytometric approach can be successfully used as an accurate and rapid quantification method for L. infantum-infected macrophages and strengthens the hypothesis that flow cytometric approaches could replace conventional microscopic methodologies.

Tissue/Biofluid Specific Molecular Cartography of Leishmania donovani Infected BALB/c Mice: Deciphering Systemic Reprogramming

Pathophysiology of visceral leishmaniasis (VL) is not fully understood and it has been widely accepted that the parasitic components and host immune response both contribute to the perpetuation of the disease. Host alterations during leishmaniasis is a feebly touched area that needs to be explored more to better understand the VL prognosis and diagnosis, which are vital to reduce mortality and post-infection sequelae. To address this, we performed untargeted metabolomics of Leishmania donovani (Ld) infected, uninfected and treated BALB/c mice’s tissues and biofluids to elucidate the host metabolome changes using gas chromatography–mass spectrometry. Univariate and multivariate data treatments provided numerous significant differential hits in several tissues like the brain, liver, spleen and bone marrow. Differential modulations were also observed in serum, urine and fecal samples of Ld-infected mice, which could be further targeted for biomarker and diagnostic validations. Several metabolic pathways were found to be upregulated/downregulated in infected (TCA, glycolysis, fatty acids, purine and pyrimidine, etcetera) and treated (arginine, fumaric acid, orotic acid, choline succinate, etcetera) samples. Results also illustrated several metabolites with different pattern of modulations in control, infected and treated samples as well as in different tissues/biofluids; for e.g. glutamic acid identified in the serum samples of infected mice. Identified metabolites include a range of amino acids, saccharides, energy-related molecules, etcetera. Furthermore, potential biomarkers have been identified in various tissues—arginine and fumaric acid in brain, choline in liver, 9-(10) EpOME in spleen and bone marrow, N-acetyl putrescine in bone marrow, etcetera. Among biofluids, glutamic acid in serum, hydrazine and deoxyribose in urine and 3-Methyl-2-oxo pentanoic acid in feces are some of the potential biomarkers identified. These metabolites could be further looked into for their role in disease complexity or as a prognostic marker. The presented profiling approach allowed us to attain a metabolic portrait of the individual tissue/biofluid modulations during VL in the host and represent a valuable system readout for further studies. Our outcomes provide an improved understanding of perturbations of the host metabolome interface during VL, including identification of many possible potential diagnostic and therapeutic targets.

Nutrient Acquisition and Attachment Strategies in Basal Lineages: A Tough Nut to Crack in the Evolutionary Puzzle of Apicomplexa

Apicomplexa are unicellular eukaryotes that parasitise a wide spectrum of invertebrates and vertebrates, including humans. In their hosts, they occupy a variety of niches, from extracellular cavities (intestine, coelom) to epicellular and intracellular locations, depending on the species and/or developmental stages. During their evolution, Apicomplexa thus developed an exceptionally wide range of unique features to reach these diversified parasitic niches and to survive there, at least long enough to ensure their own transmission or that of their progeny. This review summarises the current state of knowledge on the attachment/invasive and nutrient uptake strategies displayed by apicomplexan parasites, focusing on trophozoite stages of their so far poorly studied basal representatives, which mostly parasitise invertebrate hosts. We describe their most important morphofunctional features, and where applicable, discuss existing major similarities and/or differences in the corresponding mechanisms, incomparably better described at the molecular level in the more advanced Apicomplexa species, of medical and veterinary significance, which mainly occupy intracellular niches in vertebrate hosts.

Study the Mechanism of Antileishmanial Action of Xanthium strumarium Against Amastigotes Stages in Leishmania major: A Metabolomics Approach

Background: Leishmaniasis is among the most important neglected tropical infections, affecting millions of people worldwide. Since 1945, chemotherapy has been the primary treatment for leishmaniasis; however, lengthy and costly treatments associated with various side effects and strains resistant to the conventional therapy have dramatically reduced chemotherapy compounds’ efficacy. Objectives: The antileishmanial activity of the leaf extract of Xanthium strumarium (Asteraceae) was studied. New insights into its mechanism of action toward Leishmania major were provided through a metabolomics-based study. Methods: J774 macrophages were cultured, infected with stationary promastigotes, and treated with different leaf extract concentrations for three days. Antileishmanial activity was assayed by the MTT colorimetric method, and cell metabolites were extracted. 1HNMR spectroscopy was applied, and outliers were analyzed using multivariate statistical analysis. Results: Xanthium strumarium extract (0.15 µg/mL) showed the best activity against L. major amastigotes with the infection rate (IR) and multiplication index (MI) values of 51% and 57%, respectively. The action of X. strumarium extract on amastigotes was comparable with amphotericin B as the positive control (0.015 µg/mL). According to the obtained P-values, pentanoate and coenzyme A biosynthesis, pentose and glucuronate metabolism, valine, leucine and isoleucine biosynthesis, galactose metabolism, amino sugar and nucleotide sugar metabolism were the most important metabolic pathways affected by the plant extract in the amastigote stage of L. major. Conclusions: Our finding demonstrated that X. strumarium leaf extract could be used for discovering and producing novel leishmanicidal medicines. Moreover, the affected metabolic pathways observed in this study could be potential candidates for drug targeting against leishmaniasis.

Preliminary Characterization of Two Small Insulinase-Like Proteases in Cryptosporidium parvum

Cryptosporidium parvum is a major cause of moderate-to-severe diarrhea in humans and animals. Its compact genome contains 22 genes encoding divergent insulinase-like proteases (INS), which are poorly characterized. In this study, two small members of this family, INS-21 encoded by cgd7_2080 and INS-23 encoded by cgd5_3400, were cloned, expressed, and characterized to understand their functions. Recombinant INS-21 and INS-23 were expressed in Escherichia coli and polyclonal antibodies against these two proteins were prepared. The cgd7_2080 gene had a high transcription level during 0–2 h of in vitro C. parvum culture, while cgd5_3400 was highly transcribed at 0–6 h. INS-21 was mostly located in the apical region of sporozoites and merozoites whereas INS-23 was found as spots in sporozoites and merozoites. The immunoelectron microscopy confirmed the expression of INS-21 in the apical region of sporozoites while INS-23 appeared to be expressed in the dense granules of sporozoites. The neutralization efficiency was approximately 35%, when the cultures were treated with anti-INS23 antibodies. These results suggest that INS-21 and INS-23 are expressed in different organelles and might have different functions in the development of C. parvum.

Comparative Analysis of Virulence Mechanisms of Trypanosomatids Pathogenic to Humans

Trypanosoma brucei, Leishmania spp., and T. cruzi are flagellate protozoans of the family Trypanosomatidae and the causative agents of human African trypanosomiasis, leishmaniasis, and Chagas disease, respectively. These diseases affect humans worldwide and exert a significant impact on public health. Over the course of evolution, the parasites associated with these pathologies have developed mechanisms to circumvent the immune response system throughout the infection cycle. In cases of human infection, this function is undertaken by a group of proteins and processes that allow the parasites to propagate and survive during host invasion. In T. brucei, antigenic variation is promoted by variant surface glycoproteins and other proteins involved in evasion from the humoral immune response, which helps the parasite sustain itself in the extracellular milieu during infection. Conversely, Leishmania spp. and T. cruzi possess a more complex infection cycle, with specific intracellular stages. In addition to mechanisms for evading humoral immunity, the pathogens have also developed mechanisms for facilitating their adhesion and incorporation into host cells. In this review, the different immune evasion strategies at cellular and molecular levels developed by these human-pathogenic trypanosomatids have been discussed, with a focus on the key molecules responsible for mediating the invasion and evasion mechanisms and the effects of these molecules on virulence.

All Roads Lead to Cytosol: Trypanosoma cruzi Multi-Strategic Approach to Invasion

T. cruzi has a complex life cycle involving four developmental stages namely, epimastigotes, metacyclic trypomastigotes, amastigotes and bloodstream trypomastigotes. Although trypomastigotes are the infective forms, extracellular amastigotes have also shown the ability to invade host cells. Both stages can invade a broad spectrum of host tissues, in fact, almost any nucleated cell can be the target of infection. To add complexity, the parasite presents high genetic variability with differential characteristics such as infectivity. In this review, we address the several strategies T. cruzi has developed to subvert the host cell signaling machinery in order to gain access to the host cell cytoplasm. Special attention is made to the numerous parasite/host protein interactions and to the set of signaling cascades activated during the formation of a parasite-containing vesicle, the parasitophorous vacuole, from which the parasite escapes to the cytosol, where differentiation and replication take place.

Leishmaniasis Beyond East Africa

Climate change is having a substantial impact on our environment and ecosystems and has altered the way humans live, access, and utilize resources with increased risk of zoonotic infectious disease encounters. As global temperatures continue to increase, they impact on public health, migration, food security and land conflict, and as new environments become favorable, exposure to disease carrying vectors. Increased forests or natural habitat clearance for land repurposing, urbanization, road building, and water management are related to an increase in emerging vector borne parasitic diseases. The East African region remains one of the most impacted regions globally for leishmaniasis, a vector borne disease that impacts significantly on the health, wellbeing and livelihoods of affected communities and for which a lack of reporting and control interventions hinder progress toward elimination of this neglected tropical disease. As our world continues to transform, both politically and climatically, it is essential that measures are put in place to improve surveillance and disease management with implementation of control measures, including vector control, especially in low- and middle-income countries that are expected to be most impacted by changes in climate. Only through effective management, now, can we be sufficiently resilient to preventing the inevitable spread of vectors into suitable habitat and expansion of the geographical range of leishmaniasis. This review offers a current perspective on Leishmaniasis as an endemic disease in East Africa and examines the potential of the recent emergence of Leishmania infection in hitherto unaffected regions to become a public health concern if no disease management is achieved.

Comparative evaluation of amniotic fluid as an alternative to fetal bovine serum in the maintenance of Leishmania major and Toxoplasma gondii

This study aimed to evaluate the efficacy of amniotic fluid (AF) as an alternative to fetal bovine serum (FBS) in the maintenance of Leishmania major promastigotes and Toxoplasma gondii tachyzoites. AF was collected by an obstetrician using sterile syringes during a cesarean section. The culture medium was supplemented with 5 different concentrations of FBS or AF including 2, 5, 10, 20, and 30%. These concentrations were used to maintain both mentioned parasites. L. major was maintained at temperatures 4 and 24 °C and examined once a week for 4 weeks, while T. gondii was maintained at temperatures 4, 24, and 37 °C and examined at hours 24, 48, 72, and 96. For L. major, at both 4 and 24 °C, we observed no significant difference between FBS and AF on day 7. However, on days 14, 21, and 28, the difference between FBS and AF was significant at both temperatures. For T. gondii, no significant difference was observed between FBS and AF at hour 24 and all temperatures. However, this difference was significant at hours 48, 72, and 96 and all temperatures. According to our results, although FBS had a greater efficacy than AF in the growth of L. major and the survival of T. gondii, the number of promastigotes increased over time in AF-containing medium and the number of tachyzoites reduced slowly with a mild slop. Therefore, AF can be a potential alternative to FBS.

Blocking IL-10 signaling with soluble IL-10 receptor restores in vitro specific lymphoproliferative response in dogs with leishmaniasis caused by Leishmania infantum

rIL-10 plays a major role in restricting exaggerated inflammatory and immune responses, thus preventing tissue damage. However, the restriction of inflammatory and immune responses by IL-10 can also favor the development and/or persistence of chronic infections or neoplasms. Dogs that succumb to canine leishmaniasis (CanL) caused by L. infantum develop exhaustion of T lymphocytes and are unable to mount appropriate cellular immune responses to control the infection. These animals fail to mount specific lymphoproliferative responses and produce interferon gamma and TNF-alpha that would activate macrophages and promote destruction of intracellular parasites. Blocking IL-10 signaling may contribute to the treatment of CanL. In order to obtain a tool for this blockage, the present work endeavored to identify the canine casIL-10R1 amino acid sequence, generate a recombinant baculovirus chromosome encoding this molecule, which was expressed in insect cells and subsequently purified to obtain rcasIL-10R1. In addition, rcasIL-10R1 was able to bind to homologous IL-10 and block IL-10 signaling pathway, as well as to promote lymphoproliferation in dogs with leishmaniasis caused by L. infantum.

Redox-Responsive Nanocapsules for the Spatiotemporal Release of Miltefosine in Lysosome: Protection against Leishmania

Leishmaniasis, a vector-borne disease, is caused by intracellular parasite Leishmania donovani. Unlike most intracellular pathogens, Leishmania donovani are lodged in parasitophorous vacuoles and replicate within the phagolysosomes in macrophages. Effective vaccines against this disease are still under development, while the efficacy of the available drugs is being questioned owing to the toxicity for nonspecific distribution in human physiology and the reported drug-resistance developed by Leishmania donovani. Thus, a stimuli-responsive nanocarrier that allows specific localization and release of the drug in the lysosome has been highly sought after for addressing two crucial issues, lower drug toxicity and a higher drug efficacy. We report here a unique lysosome targeting polymeric nanocapsules, formed via inverse mini-emulsion technique, for stimuli-responsive release of the drug miltefosine in the lysosome of macrophage RAW 264.7 cell line. A benign polymeric backbone, with a disulfide bonding susceptible to an oxidative cleavage, is utilized for the organelle-specific release of miltefosine. Oxidative rupture of the disulfide bond is induced by intracellular glutathione (GSH) as an endogenous stimulus. Such a stimuli-responsive release of the drug miltefosine in the lysosome of macrophage RAW 264.7 cell line over a few hours helped in achieving an improved drug efficacy by 200 times as compared to pure miltefosine. Such a drug formulation could contribute to a new line of treatment for leishmaniasis.

Metabolomic approach of the antiprotozoal activity of medicinal Piper species used in Peruvian Amazon

ETHNOPHARMACOLOGICAL RELEVANCE

In the Peruvian Amazon as in the tropical countries of South America, the use of medicinal Piper species (cordoncillos) is common practice, particularly against symptoms of infection by protozoal parasites. However, there is few documented information about the practical aspects of their use and few scientific validation. The starting point of this work was a set of interviews of people living in six rural communities from the Peruvian Amazon (Alto Amazonas Province) about their uses of plants from Piper genus: one community of Amerindian native people (Shawi community) and five communities of mestizos. Infections caused by parasitic protozoa take a huge toll on public health in the Amazonian communities, who partly fight it using traditional remedies. Validation of these traditional practices contributes to public health care efficiency and may help to identify new antiprotozoal compounds.

AIMS OF STUDY

To record and validate the use of medicinal Piper species by rural people of Alto Amazonas Province (Peru) and annotate active compounds using a correlation study and a data mining approach.

MATERIALS AND METHODS

Rural communities were interviewed about traditional medication against parasite infections with medicinal Piper species. Ethnopharmacological surveys were undertaken in five mestizo villages, namely: Nueva Arica, Shucushuyacu, Parinari, Lagunas and Esperanza, and one Shawi community (Balsapuerto village). All communities belong to the Alto Amazonas Province (Loreto region, Peru). Seventeen Piper species were collected according to their traditional use for the treatment of parasitic diseases, 35 extracts (leaves or leaves and stems) were tested in vitro on P. falciparum (3D7 chloroquine-sensitive strain and W2 chloroquine-resistant strain), Leishmania donovani LV9 strain and Trypanosoma brucei gambiense. Assessments were performed on HUVEC cells and RAW 264.7 macrophages. The annotation of active compounds was realized by metabolomic analysis and molecular networking approach.

RESULTS

Nine extracts were active (IC₅₀ ≤ 10 μg/mL) on 3D7 P. falciparum and only one on W2 P. falciparum, six on L. donovani (axenic and intramacrophagic amastigotes) and seven on Trypanosoma brucei gambiense. Only one extract was active on all three parasites (P. lineatum). After metabolomic analyses and annotation of compounds active on Leishmania, P. strigosum and P. pseudoarboreum were considered as potential sources of leishmanicidal compounds.

CONCLUSIONS

This ethnopharmacological study and the associated in vitro bioassays corroborated the relevance of use of Piper species in the Amazonian traditional medicine, especially in Peru. A series of Piper species with few previously available phytochemical data have good antiprotozoal activity and could be a starting point for subsequent promising work. Metabolomic approach appears to be a smart, quick but still limited methodology to identify compounds with high probability of biological activity.

Drug screening using shape-based virtual screening and in vitro experimental models of cutaneous Leishmaniasis

Cutaneous leishmaniasis (CL) is one of the most disregarded tropical neglected disease with the occurrence of self-limiting ulcers and triggering mucosal damage and stigmatizing scars, leading to huge public health problems and social negative impacts. Pentavalent antimonials are the first-line drug for CL treatment for over 70 years and present several drawbacks in terms of safety and efficacy. Thus, there is an urgent need to search for non-invasive, non-toxic and potent drug candidates for CL. In this sense, we have implemented a shape-based virtual screening approach and identified a set of 32 hit compounds. In vitro phenotypic screenings were conducted using these hit compounds to check their potential leishmanicidal effect towards Leishmania amazonensis (L. amazonensis). Two (Cp1 and Cp2) out of the 32 compounds revealed promising antiparasitic activities, exhibiting considerable potency against intracellular amastigotes present in peritoneal macrophages (IC50 values of 9.35 and 7.25 μm, respectively). Also, a sterile cidality profile was reached at 20 μm after 48 h of incubation, besides a reasonable selectivity (≈8), quite similarly to pentamidine, a diamidine still in use clinically for leishmaniasis. Cp1 with an oxazolo[4,5-b]pyridine scaffold and Cp2 with benzimidazole scaffold could be developed by lead optimization studies to enhance their leishmanicidal potency.

Priming Astrocytes With HIV-Induced Reactive Oxygen Species Enhances Their Trypanosoma cruzi Infection

Introduction: Trypanosoma cruzi is an intracellular protozoa and etiological agent that causes Chagas disease. Its presence among the immunocompromised HIV-infected individuals is relevant worldwide because of its impact on the central nervous system (CNS) causing severe meningoencephalitis. The HIV infection of astrocytes – the most abundant cells in the brain, where the parasite can also be hosted – being able to modify reactive oxygen species (ROS) could influence the parasite growth. In such interaction, extracellular vesicles (EVs) shed from trypomastigotes may alter the surrounding environment including its pro-oxidant status.

Methods: We evaluated the interplay between both pathogens in human astrocytes and its consequences on the host cell pro-oxidant condition self-propitiated by the parasite – using its EVs – or by HIV infection. For this goal, we challenged cultured human primary astrocytes with both pathogens and the efficiency of infection and multiplication were measured by microscopy and flow cytometry and parasite DNA quantification. Mitochondrial and cellular ROS levels were measured by flow cytometry in the presence or not of scavengers with a concomitant evaluation of the cellular apoptosis level.

Results: We observed that increased mitochondrial and cellular ROS production boosted significantly T. cruzi infection and multiplication in astrocytes. Such oxidative condition was promoted by free trypomastigotes-derived EVs as well as by HIV infection.

Conclusions: The pathogenesis of the HIV-T. cruzi coinfection in astrocytes leads to an oxidative misbalance as a key mechanism, which exacerbates ROS generation and promotes positive feedback to parasite growth in the CNS.

Heme oxygenase-1 in protozoan infections: A tale of resistance and disease tolerance

Heme oxygenase (HO-1) mediates the enzymatic cleavage of heme, a molecule with proinflammatory and prooxidant properties. HO-1 activity deeply impacts host capacity to tolerate infection through reduction of tissue damage or affecting resistance, the ability of the host to control pathogen loads. In this Review, we will discuss the contribution of HO-1 in different and complex protozoan infections, such as malaria, leishmaniasis, Chagas disease, and toxoplasmosis. The complexity of these infections and the pleiotropic effects of HO-1 constitute an interesting area of study and an opportunity for drug development.

Toxoplasma gondii Mechanisms of Entry Into Host Cells

Toxoplasma gondii, the causative agent of toxoplasmosis, is an obligate intracellular protozoan parasite. Toxoplasma can invade and multiply inside any nucleated cell of a wide range of homeothermic hosts. The canonical process of internalization involves several steps: an initial recognition of the host cell surface and a sequential secretion of proteins from micronemes followed by rhoptries that assemble a macromolecular complex constituting a specialized and transient moving junction. The parasite is then internalized via an endocytic process with the establishment of a parasitophorous vacuole (PV), that does not fuse with lysosomes, where the parasites survive and multiply. This process of host cell invasion is usually referred to active penetration. Using different cell types and inhibitors of distinct endocytic pathways, we show that treatment of host cells with compounds that interfere with clathrin-mediated endocytosis (hypertonic sucrose medium, chlorpromazine hydrochloride, and pitstop 2 inhibited the internalization of tachyzoites). In addition, treatments that interfere with macropinocytosis, such as incubation with amiloride or IPA-3, increased parasite attachment to the host cell surface but significantly blocked parasite internalization. Immunofluorescence microscopy showed that markers of macropinocytosis, such as the Rab5 effector rabankyrin 5 and Pak1, are associated with parasite-containing cytoplasmic vacuoles. These results indicate that entrance of T. gondii into mammalian cells can take place both by the well-characterized interaction of parasite and host cell endocytic machinery and other processes, such as the clathrin-mediated endocytosis, and macropinocytosis.