Cryptosporidium Lactate Dehydrogenase Is Associated with the Parasitophorous Vacuole Membrane and Is a Potential Target for Developing Therapeutics

Calcium-dependent protein kinases 2A involved in the growth of both asexual and sexual stages of Cryptosporidium parvum

BACKGROUND

Cryptosporidium parvum is a protozoan pathogen that causes moderate to severe diarrhea in both humans and animals. Calcium-dependent protein kinases (CDPKs) are attractive drug targets against cryptosporidiosis given their critical role in the life cycle of Cryptosporidium spp. and their absence in human and animal hosts.

METHODOLOGY/PRINCIPAL FINDINGS

We used CRISPR-Cas9 technology to endogenously tag the CpCDPK2A gene in C. parvum IIdA20G1-HLJ strain with the hemagglutinin (HA) epitope and to delete the CpCDPK2A gene. An immunofluorescence assay was performed to localize the CpCDPK2A expression in the tagged strain and a luciferase assay was performed to compare growth rates of the tagged and deletion strains in vitro. Oocyst shedding, parasite load, villus length/crypt height ratio and survival of infected mice were used to evaluate the function of CpCDPK2A in vivo. The results revealed that CpCDPK2A was expressed in all the intracellular developmental stages, especially in the motile stages of sporozoites and merozoites. While CpCDPK2A is dispensable, deletion of the gene significantly reduced the growth of late asexual and sexual stages in vitro. In an interferon-γ knockout mouse model, gene deletion of CpCDPK2A reduced oocyst shedding by 25-fold and increased survival of infected mice.

CONCLUSIONS/SIGNIFICANCE

These observations suggest that CpCDPK2A may contribute to both asexual and sexual replication of C. parvum and may be a potential target to block the transmission of this important zoonotic pathogen.

Molecular insights into anti-Protozoal action of natural compounds against Cryptosporidium parvum: a molecular simulation study

The current study used the major target protein lactate dehydrogenase Cryptosporidium parvum to identify potential binders. Our approach was a comprehensive three-step screening of 2,569 natural compounds. First, we used molecular docking techniques, followed by an advanced DeepPurpose ML model for virtual screening. The final step involved meticulous re-docking and detailed interaction analysis. The known inhibitor FX11 was considered as a control that was used for comparative analysis. Our screening process led to the identification of three promising compounds: 5353794, 18475114, and 25229652. These compounds were chosen due to their exceptional ability to form hydrogen bonds and their high binding scores with the protein. Here, all three hits showed H-bonds with the functional residues (Asn122 and Thr231) of protein, while 25229652 also showed H-bond with the catalytic site residue (His177). RMSD behaviour reflected stable and consistent complex formation for all the compounds in their last 30 ns trajectories. Principal component analysis (PCA) and free energy landscape (FEL) showed a high frequency of favourable low free energy states. Using the MM/GBSA calculation, compounds 5353794 (ΔGTOTAL = -34.92 kcal/mol) and 18475114 (ΔGTOTAL = -34.66 kcal/mol) had the highest binding affinity with the protein however, 25229652 (ΔGTOTAL = -22.62 kcal/mol) had ΔGTOTAL comparable to the control FX11. These natural compounds not only show the potential for hindering C. parvum lactate dehydrogenase but also open new avenues in its drug development. Their strong binding properties and stable interactions mark them as the prime candidates for further research and experimental validation as anti-cryptosporidiosis agents.Communicated by Ramaswamy H. Sarma.

Molecular pathogenesis of Cryptosporidium and advancements in therapeutic interventions

Cryptosporidiosis, caused by a Cryptosporidium infection, is a serious gastrointestinal disease commonly leading to diarrhea in humans. This disease poses a particular threat to infants, young children, and those with weakened immune systems. The treatment of cryptosporidiosis is challenging due to the current lack of an effective treatment or vaccine. Ongoing research is focused on understanding the molecular pathogenesis of Cryptosporidium and developing pharmacological treatments. In this review, we examine the signaling pathways activated by Cryptosporidium infection within the host and their role in protecting host epithelial cells. Additionally, we also review the research progress of chemotherapeutic targets against cryptosporidia-specific enzymes and anti-Cryptosporidium drugs (including Chinese and Western medicinal drugs), aiming at the development of more effective treatments for cryptosporidiosis.

Metabolomics-driven approaches for identifying therapeutic targets in drug discovery

Identification of therapeutic targets can directly elucidate the mechanism and effect of drug therapy, which is a central step in drug development. The disconnect between protein targets and phenotypes under complex mechanisms hampers comprehensive target understanding. Metabolomics, as a systems biology tool that captures phenotypic changes induced by exogenous compounds, has emerged as a valuable approach for target identification. A comprehensive overview was provided in this review to illustrate the principles and advantages of metabolomics, delving into the application of metabolomics in target identification. This review outlines various metabolomics-based methods, such as dose-response metabolomics, stable isotope-resolved metabolomics, and multiomics, which identify key enzymes and metabolic pathways affected by exogenous substances through dose-dependent metabolite-drug interactions. Emerging techniques, including single-cell metabolomics, artificial intelligence, and mass spectrometry imaging, are also explored for their potential to enhance target discovery. The review emphasizes metabolomics' critical role in advancing our understanding of disease mechanisms and accelerating targeted drug development, while acknowledging current challenges in the field.

Malate dehydrogenase in parasitic protozoans: roles in metabolism and potential therapeutic applications

The role of malate dehydrogenase (MDH) in the metabolism of various medically significant protozoan parasites is reviewed. MDH is an NADH-dependent oxidoreductase that catalyzes interconversion between oxaloacetate and malate, provides metabolic intermediates for both catabolic and anabolic pathways, and can contribute to NAD+/NADH balance in multiple cellular compartments. MDH is present in nearly all organisms; isoforms of MDH from apicomplexans (Plasmodium falciparum, Toxoplasma gondii, Cryptosporidium spp.), trypanosomatids (Trypanosoma brucei, T. cruzi) and anaerobic protozoans (Trichomonas vaginalis, Giardia duodenalis) are presented here. Many parasitic species have complex life cycles and depend on the environment of their hosts for carbon sources and other nutrients. Metabolic plasticity is crucial to parasite transition between host environments; thus, the regulation of metabolic processes is an important area to explore for therapeutic intervention. Common themes in protozoan parasite metabolism include emphasis on glycolytic catabolism, substrate-level phosphorylation, non-traditional uses of common pathways like tricarboxylic acid cycle and adapted or reduced mitochondria-like organelles. We describe the roles of MDH isoforms in these pathways, discuss unusual structural or functional features of these isoforms relevant to activity or drug targeting, and review current studies exploring the therapeutic potential of MDH and related genes. These studies show that MDH activity has important roles in many metabolic pathways, and thus in the metabolic transitions of protozoan parasites needed for success as pathogens.

Exploring the anti-protozoal mechanisms of Syzygium aromaticum phytochemicals targeting Cryptosporidium parvum lactate dehydrogenase through molecular dynamics simulations

Cryptosporidium parvum (C. parvum), a protozoan parasite, is known to induce significant gastrointestinal disease in humans. Lactate dehydrogenase (LDH), a protein of C. parvum, has been identified as a potential therapeutic target for developing effective drugs against infection. This study utilized a computational drug discovery approach to identify potential drug molecules against the LDH protein of C. parvum. In the present investigation, we conducted a structure-based virtual screening of 55 phytochemicals from the Syzygium aromaticum (S. aromaticum). This process identified four phytochemicals, including Gallotannin 23, Eugeniin, Strictinin, and Ellagitannin, that demonstrated significant binding affinity and dynamic stability with LDH protein. Interestingly, these four compounds have been documented to possess antibacterial, antiviral, anti-inflammatory, and antioxidant properties. The docked complexes were simulated for 100 ns using Desmond to check the dynamic stability. Finally, the free binding energy was computed from the last 10ns MD trajectories. Gallotannin 23 and Ellagitannin exhibited considerable binding affinity and stability with the target protein among all four phytochemicals. These findings suggest that these predicted phytochemicals from S. aromaticum could be further explored as potential hit candidates for developing effective drugs against C. parvum infection. The in vitro and in vivo experimental validation is still required to confirm their efficacy and safety as LDH inhibitors.

A single-pass type I membrane protein, mannose-specific L-type lectin, potentially involved in the adhesion and invasion of Cryptosporidium parvum

Cryptosporidium is a globally distributed zoonotic protozoan parasite that can cause severe diarrhea in humans and animals. L-type lectins are carbohydrate-binding proteins involved in multiple pathways in animals and plants, including protein transportation, secretion, innate immunity, and the unfolded protein response signaling pathway. However, the biological function of the L-type lectins remains unknown in Cryptosporidium parvum. Here, we preliminarily characterized an L-type lectin in C. parvum (CpLTL) that contains a lectin-leg-like domain. Immunofluorescence assay confirmed that CpLTL is located on the wall of oocysts, the surface of the mid-anterior region of the sporozoite and the cytoplasm of merozoites. The involvement of CpLTL in parasite invasion is partly supported by experiments showing that an anti-CpLTL antibody could partially block the invasion of C. parvum sporozoites into host cells. Moreover, the recombinant CpLTL showed binding ability with mannose and the surface of host cells, and competitively inhibited the invasion of C. parvum. Two host cell proteins were identified by proteomics which should be prioritized for future validation of CpLTL-binding. Our data indicated that CpLTL is potentially involved in the adhesion and invasion of C. parvum.

Treating cryptosporidiosis: A review on drug discovery strategies

Despite several decades of research on therapeutics, cryptosporidiosis remains a major concern for human and animal health. Even though this field of research to assess antiparasitic drug activity is highly active and competitive, only one molecule is authorized to be used in humans. However, this molecule was not efficacious in immunocompromised people and the lack of animal therapeutics remains a cause of concern. Indeed, the therapeutic arsenal needs to be developed for both humans and animals. Our work aims to clarify research strategies that historically were diffuse and poorly directed. This paper reviews in vitro and in vivo methodologies to assess the activity of future therapeutic compounds by screening drug libraries or through drug repurposing. It focuses on High Throughput Screening methodologies (HTS) and discusses the lack of knowledge of target mechanisms. In addition, an overview of several specific metabolic pathways and enzymatic activities used as targets against Cryptosporidium is provided. These metabolic processes include glycolytic pathways, fatty acid production, kinase activities, tRNA elaboration, nucleotide synthesis, gene expression and mRNA maturation. As a conclusion, we highlight emerging future strategies for screening natural compounds and assessing drug resistance issues.

Lower micromolar activity of the antifungal imidazoles on the bacterial-type bifunctional aldehyde/alcohol dehydrogenase (AdhE) in Cryptosporidium parvum and in vitro efficacy against the zoonotic parasite

Cryptosporidium parvum is a waterborne and foodborne zoonotic protozoan parasite, a causative agent of moderate to severe diarrheal diseases in humans and animals. However, fully effective treatments are unavailable for medical and veterinary uses. There is a need to explore new drug targets for potential development of new therapeutics. Because C. parvum relies on anaerobic metabolism to produce ATP, fermentative enzymes in this parasite are attractive targets for exploration. In this study, we investigated the ethanol-fermentation in the parasite and characterized the basic biochemical features of a bacterial-type bifunctional aldehyde/alcohol dehydrogenase, namely CpAdhE. We also screened 3892 chemical entries from three libraries and identified 14 compounds showing >50% inhibition on the enzyme activity of CpAdhE. Intriguingly, antifungal imidazoles and unsaturated fatty acids are the two major chemical groups among the top hits. We further characterized the inhibitory kinetics of selected imidazoles and unsaturated fatty acids on CpAdhE. These compounds displayed lower micromolar activities on CpAdhE (i.e., IC50 values ranging from 0.88 to 11.02 μM for imidazoles and 8.93 to 35.33 μM for unsaturated fatty acids). Finally, we evaluated the in vitro anti-cryptosporidial efficacies and cytotoxicity of three imidazoles (i.e., tioconazole, miconazole and isoconazole). The three antifungal imidazoles exhibited lower micromolar efficacies against the growth of C. parvum in vitro (EC50 values ranging from 4.85 to 10.41 μM and selectivity indices ranging from 5.19 to 10.95). The results provide a proof-of-concept data to support that imidazoles are worth being further investigated for potential development of anti-cryptosporidial therapeutics.

Preparation, Characterization, and Oral Bioavailability of Solid Dispersions of Cryptosporidium parvum Alternative Oxidase Inhibitors

The phenylpyrazole derivative 5-amino-3-[1-cyano-2-(3-phenyl-1H-pyrazol-4-yl) vinyl]-1-phenyl-1H-pyrazole-4-carbonitrile (LN002), which was screened out through high-throughput molecular docking for the AOX target, exhibits promising efficacy against Cryptosporidium. However, its poor water solubility limits its oral bioavailability and therapeutic utility. In this study, solid dispersion agents were prepared by using HP-β-CD and Soluplus® and characterized through differential scanning calorimetry, Fourier transform infrared, powder X-ray diffraction, and scanning electron microscopy. Physical and chemical characterization showed that the crystal morphology of LN002 transformed into an amorphous state, thus forming a solid dispersion of LN002. The solid dispersion prepared with an LN002/HP-β-CD/Soluplus® mass ratio of 1:3:9 (w/w/w) exhibited significantly increased solubility and cumulative dissolution. Meanwhile, LN002 SDs showed good preservation stability under accelerated conditions of 25 °C and 75% relative humidity. The complexation of LN002 with HP-β-CD and Soluplus® significantly improved water solubility, pharmacological properties, absorption, and bioavailability.

Protists: Eukaryotic single-celled organisms and the functioning of their organelles

Organelles are membrane bound structures that compartmentalize biochemical and molecular functions. With improved molecular, biochemical and microscopy tools the diversity and function of protistan organelles has increased in recent years, providing a complex panoply of structure/function relationships. This is particularly noticeable with the description of hydrogenosomes, and the diverse array of structures that followed, having hybrid hydrogenosome/mitochondria attributes. These diverse organelles have lost the major, at one time, definitive components of the mitochondrion (tricarboxylic cycle enzymes and cytochromes), however they all contain the machinery for the assembly of Fe-S clusters, which is the single unifying feature they share. The plasticity of organelles, like the mitochondrion, is therefore evident from its ability to lose its identity as an aerobic energy generating powerhouse while retaining key ancestral functions common to both aerobes and anaerobes. It is interesting to note that the apicoplast, a non-photosynthetic plastid that is present in all apicomplexan protozoa, apart from Cryptosporidium and possibly the gregarines, is also the site of Fe-S cluster assembly proteins. It turns out that in Cryptosporidium proteins involved in Fe-S cluster biosynthesis are localized in the mitochondrial remnant organelle termed the mitosome. Hence, different organisms have solved the same problem of packaging a life-requiring set of reactions in different ways, using different ancestral organelles, discarding what is not needed and keeping what is essential. Don't judge an organelle by its cover, more by the things it does, and always be prepared for surprises.

Functional characterization of CpADF, an actin depolymerizing factor protein in Cryptosporidium parvum

Cryptosporidium is a highly pathogenic water and food-borne zoonotic parasitic protozoan that causes severe diarrhea in humans and animals. Apicomplexan parasites invade host cells via a unique motility process called gliding, which relies on the parasite's microfilaments. Actin depolymerizing factor (ADF) is a fibrous-actin (F-actin) and globular actin (G-actin) binding protein essential for regulating the turnover of microfilaments. However, the role of ADF in Cryptosporidium parvum (C. parvum) remains unknown. In this study, we preliminarily characterized the biological functions of ADF in C. parvum (CpADF). The CpADF was a 135-aa protein encoded by cgd5_2800 gene containing an ADF-H domain. The expression of cgd5_2800 gene peaked at 12 h post-infection, and the CpADF was located in the cytoplasm of oocysts, middle region of sporozoites, and cytoplasm of merozoites. Neutralization efficiency of anti-CpADF serum was approximately 41.30%. Actin sedimentation assay revealed that CpADF depolymerized but did not undergo cosedimentation with F-actin and its ability of F-actin depolymerization was pH independent. These results provide a basis for further investigation of the roles of CpADF in the invasion of C. parvum.

Combination of inhibitors for two glycolytic enzymes portrays high synergistic efficacy against Cryptosporidium parvum

Cryptosporidium is an intracellular protozoan parasite that causes serious enteric disease in humans and in a wide range of animals worldwide. Despite its high prevalence, no effective therapeutic drugs are available against life-threatening cryptosporidiosis in at-risk populations including malnourished children, immunocompromised patients, and neonatal calves. Thus, new efficacious drugs are urgently needed to treat all susceptible populations with cryptosporidiosis. Unlike other apicomplexans, Cryptosporidium parvum lacks the tricarboxylic acid cycle and the oxidative phosphorylation steps, making it solely dependent on glycolysis for metabolic energy production. We have previously reported that individual inhibitors of two unique glycolytic enzymes, the plant-like pyruvate kinase (CpPyK) and the bacterial-type lactate dehydrogenase (CpLDH), are effective against C. parvum, both in vitro and in vivo. Herein, we have derived combinations of CpPyK and CpLDH inhibitors with strong synergistic effects against the growth and survival of C. parvum, both in vitro and in an infection mouse model. In infected immunocompromised mice, compound combinations of NSC303244 + NSC158011 and NSC252172 + NSC158011 depicted enhanced efficacy against C. parvum reproduction and ameliorated intestinal lesions of cryptosporidiosis at doses fourfold lower than the total effective doses of individual compounds. Importantly, unlike individual compounds, NSC303244 + NSC158011 combination was effective in clearing the infection completely without relapse in immunocompromised mice. Collectively, our study has unveiled compound combinations that simultaneously block two essential catalytic steps for metabolic energy production in C. parvum to achieve improved efficacy against the parasite. These combinations are, therefore, lead compounds for the development of a new generation of efficacious anti-cryptosporidial drugs.

Lactate Dehydrogenase Inhibitors Suppress Borrelia burgdorferi Growth In Vitro

Borrelia burgdorferi, the causative agent of Lyme disease, has a highly reduced genome and relies heavily on glycolysis for carbon metabolism. As such, established inhibitors of lactate dehydrogenase (LDH) were evaluated in cultures to determine the extent of their impacts on B. burgdorferi growth. Both racemic and enantiopure (AT-101) gossypol, as well as oxamate, galloflavin, and stiripentol, caused the dose-dependent suppression of B. burgdorferi growth in vitro. Racemic gossypol and AT-101 were shown to fully inhibit spirochetal growth at concentrations of 70.5 and 187.5 μM, respectively. Differences between racemic gossypol and AT-101 efficacy may indicate that the dextrorotatory enantiomer of gossypol is a more effective inhibitor of B. burgdorferi growth than the levorotatory enantiomer. As a whole, LDH inhibition appears to be a promising mechanism for suppressing Borrelia growth, particularly with bulky LDH inhibitors like gossypol.

Cryptosporidium parvumcompetes with the intestinal epithelial cells for glucose and impairs systemic glucose supply in neonatal calves

Cryptosporidiosis is one of the main causes of diarrhea in children and young livestock. The interaction of the parasite with the intestinal host cells has not been characterized thoroughly yet but may be affected by the nutritional demand of the parasite. Hence, we aimed to investigate the impact of C. parvum infection on glucose metabolism in neonatal calves. Therefore, N = 5 neonatal calves were infected with C. parvum on the first day of life, whereas a control group was not (N = 5). The calves were monitored clinically for one week, and glucose absorption, turnover and oxidation were assessed using stable isotope labelled glucose. The transepithelial transport of glucose was measured using the Ussing chamber technique. Glucose transporters were quantified on gene and protein expression level using RT-qPCR and Western blot in the jejunum epithelium and brush border membrane preparations. Plasma glucose concentration and oral glucose absorption were decreased despite an increased electrogenic phlorizin sensitive transepithelial transport of glucose in infected calves. No difference in the gene or protein abundance of glucose transporters, but an enrichment of glucose transporter 2 in the brush border was observed in the infected calves. Furthermore, the mRNA for enzymes of the glycolysis pathway was increased indicating enhanced glucose oxidation in the infected gut. In summary, C. parvum infection modulates intestinal epithelial glucose absorption and metabolism. We assume that the metabolic competition of the parasite for glucose causes the host cells to upregulate their uptake mechanisms and metabolic machinery to compensate for the energy losses.

Cryptosporidium uses multiple distinct secretory organelles to interact with and modify its host cell

Cryptosporidium is a leading cause of diarrheal disease in children and an important contributor to early childhood mortality. The parasite invades and extensively remodels intestinal epithelial cells, building an elaborate interface structure. How this occurs at the molecular level and the contributing parasite factors are largely unknown. Here, we generated a whole-cell spatial proteome of the Cryptosporidium sporozoite and used genetic and cell biological experimentation to discover the Cryptosporidium-secreted effector proteome. These findings reveal multiple organelles, including an original secretory organelle, and generate numerous compartment markers by tagging native gene loci. We show that secreted proteins are delivered to the parasite-host interface, where they assemble into different structures including a ring that anchors the parasite into its unique epicellular niche. Cryptosporidium thus uses a complex set of secretion systems during and following invasion that act in concert to subjugate its host cell.

Apical Secretory Glycoprotein Complex Contributes to Cell Attachment and Entry by Cryptosporidium parvum

Cryptosporidium parvum is an enteric pathogen that invades epithelial cells in the intestine, where it resides at the apical surface in a unique epicellular location. Compared with those of related apicomplexan parasites, the processes of host cell attachment and invasion by C. parvum are poorly understood. The streamlined C. parvum genome contains numerous mucin-like glycoproteins, several of which have previously been shown to mediate cell attachment, although the majority are unstudied. Here, we identified the antigens recognized by monoclonal antibody (MAb) 1A5, which stains the apical end of sporozoites and mature merozoites. Immunoprecipitation with MAb 1A5 followed by mass spectrometry identified a heterodimer comprised of paralogous proteins which are related to additional orthologs in the genome of C. parvum and related species. Paralogous glycoproteins recognized by MAb 1A5 heterodimerize as a complex displayed on the parasite surface, and they also interact with lectins that suggest that they contain mucin-like, O-linked oligosaccharides. Although the gene encoding one of the paralogs was readily disrupted by CRISPR/Cas9 gene editing, its partner, which contains a mucin-like domain related to GP900, was refractory to deletion. Combined with the ability of MAb 1A5 to partially neutralize host cell attachment by sporozoites, these findings define a new family of secretory glycoproteins that participate in cell invasion by Cryptosporidium spp. IMPORTANCE Although Cryptosporidium is extremely efficient at penetrating mucus and invading epithelial cells in the intestine, the mechanism of cell attachment is poorly understood. To expand our understanding of this process, we characterized the antigens recognized by a monoclonal antibody that stains the apical end of invasive stages called sporozoites and merozoites. Our studies identify a family of glycoproteins that form heterodimers on the parasite cell surface to facilitate host cell attachment and entry. By further defining the role of mucin-like glycoproteins in host cell attachment, our studies may lead to strategies to disrupt cell adhesion and thereby decrease infection.

Late Embryogenesis Abundant Proteins Contribute to the Resistance of Toxoplasma gondii Oocysts against Environmental Stresses

Toxoplasma gondii oocysts, which are shed in large quantities in the feces from infected felines, are very stable in the environment, resistant to most inactivation procedures, and highly infectious. The oocyst wall provides an important physical barrier for sporozoites contained inside oocysts, protecting them from many chemical and physical stressors, including most inactivation procedures. Furthermore, sporozoites can withstand large temperature changes, even freeze-thawing, as well as desiccation, high salinity, and other environmental insults; however, the genetic basis for this environmental resistance is unknown. Here, we show that a cluster of four genes encoding Late Embryogenesis Abundant (LEA)-related proteins are required to provide Toxoplasma sporozoites resistance to environmental stresses. Toxoplasma LEA-like genes (TgLEAs) exhibit the characteristic features of intrinsically disordered proteins, explaining some of their properties. Our in vitro biochemical experiments using recombinant TgLEA proteins show that they have cryoprotective effects on the oocyst-resident lactate dehydrogenase enzyme and that induced expression in E. coli of two of them leads to better survival after cold stress. Oocysts from a strain in which the four LEA genes were knocked out en bloc were significantly more susceptible to high salinity, freezing, and desiccation compared to wild-type oocysts. We discuss the evolutionary acquisition of LEA-like genes in Toxoplasma and other oocyst-producing apicomplexan parasites of the Sarcocystidae family and discuss how this has likely contributed to the ability of sporozoites within oocysts to survive outside the host for extended periods. Collectively, our data provide a first molecular detailed view on a mechanism that contributes to the remarkable resilience of oocysts against environmental stresses. IMPORTANCE Toxoplasma gondii oocysts are highly infectious and may survive in the environment for years. Their resistance against disinfectants and irradiation has been attributed to the oocyst and sporocyst walls by acting as physical and permeability barriers. However, the genetic basis for their resistance against stressors like changes in temperature, salinity, or humidity, is unknown. We show that a cluster of four genes encoding Toxoplasma Late Embryogenesis Abundant (TgLEA)-related proteins are important for this resistance to environmental stresses. TgLEAs have features of intrinsically disordered proteins, explaining some of their properties. Recombinant TgLEA proteins show cryoprotective effects on the parasite's lactate dehydrogenase, an abundant enzyme in oocysts, and expression in E. coli of two TgLEAs has a beneficial effect on growth after cold stress. Moreover, oocysts from a strain lacking all four TgLEA genes were more susceptible to high salinity, freezing, and desiccation compared to wild-type oocysts, highlighting the importance of the four TgLEAs for oocyst resilience.

An update on Cryptosporidium biology and therapeutic avenues

Cryptosporidium species has been identified as an important pediatric diarrheal pathogen in resource-limited countries, particularly in very young children (0–24 months). However, the only available drug (nitazoxanide) has limited efficacy and can only be prescribed in a medical setting to children older than one year. Many drug development projects have started to investigate new therapeutic avenues. Cryptosporidium’s unique biology is challenging for the traditional drug discovery pipeline and requires novel drug screening approaches. Notably, in recent years, new methods of oocyst generation, in vitro processing, and continuous three-dimensional cultivation capacities have been developed. This has enabled more physiologically pertinent research assays for inhibitor discovery. In a short time, many great strides have been made in the development of anti-Cryptosporidium drugs. These are expected to eventually turn into clinical candidates for cryptosporidiosis treatment in the future. This review describes the latest development in Cryptosporidium biology, genomics, transcriptomics of the parasite, assay development, and new drug discovery.

The mucin-like, secretory type-I transmembrane glycoprotein GP900 in the apicomplexan Cryptosporidium parvum is cleaved in the secretory pathway and likely plays a lubrication role

BACKGROUND

Cryptosporidium parvum is a zoonotic parasite and member of the phylum Apicomplexa with unique secretory organelles, including a rhoptry, micronemes and dense granules that discharge their contents during parasite invasion. The mucin-like glycoprotein GP900 with a single transmembrane domain is an immunodominant antigen and micronemal protein. It is relocated to the surface of excysted sporozoites and shed to form trails by sporozoites exhibiting gliding motility (gliding sporozoites). However, the biological process underlying its relocation and shedding remains unclear. The primary aim of this study was to determine whether GP900 is present as a transmembrane protein anchored to the plasma membrane on the surface of sporozoites and whether it is cleaved before being shed from the sporozoites.

METHODS

Two anti-GP900 antibodies, a mouse monoclonal antibody (mAb) to the long N-terminal domain (GP900-N) and a rabbit polyclonal antibody (pAb) to the short C-terminal domain (GP900-C), were produced for the detection of intact and cleaved GP900 proteins in sporozoites and other parasite developmental stages by microscopic immunofluorescence assay and in discharged molecules by enzyme-linked immunosorbent assay.

RESULTS

Both anti-GP900 antibodies recognized the apical region of unexcysted and excysted sporozoites. However, anti-GP900-N (but not anti-GP900-C) also stained both the pellicles/surface of excysted sporozoites and the trails of gliding sporozoites. Both antibodies stained the intracellular meronts, both developing and developed, but not the macro- and microgamonts. Additionally, the epitope was recognized by anti-GP900-N (but not anti-GP900-C) and detected in the secretions of excysted sporozoites and intracellular parasites.

CONCLUSIONS

GP900 is present in sporozoites and intracellular meronts, but absent in sexual stages. It is stored in the micronemes of sporozoites, but enters the secretory pathway during excystation and invasion. The short cytoplasmic domain of GP900 is cleaved in the secretory pathway before it reaches the extracellular space. The molecular features and behavior of GP900 imply that it plays mainly a lubrication role.

Characterization of Calcium-Dependent Protein Kinase 2A, a Potential Drug Target Against Cryptosporidiosis

Calcium-dependent protein kinases (CDPKs) are important in calcium influx, triggering several biological processes in Cryptosporidium spp. As they are not present in mammals, CDPKs are considered promising drug targets. Recent studies have characterized CpCDPK1, CpCDPK3, CpCDPK4, CpCDPK5, CpCDPK6, and CpCDPK9, but the role of CpCPK2A remains unclear. In this work, we expressed recombinant CpCDPK2A encoded by the cgd2_1060 gene in Escherichia coli and characterized the biologic functions of CpCDPK2A using qRT-PCR, immunofluorescence microscopy, immuno-electron microscopy, and in vitro neutralization. The results revealed that CpCDPK2A protein was highly expressed in the apical region of sporozoites and merozoites and in macrogamonts. Monoclonal or polyclonal antibodies against CpCDPK2A failed to block the invasion of host cells. Among the 44 candidate inhibitors from molecular docking of CpCDPK2A, one inhibitor was identified as having a potential effect on both Cryptosporidium parvum growth and CpCDPK2A enzyme activities. These data suggest that CpCDPK2A may play some roles during the development of C. parvum and might be a potential drug target against cryptosporidiosis.

Cryptosporidium: Still Open Scenarios

Cryptosporidiosis is increasingly identified as a leading cause of childhood diarrhea and malnutrition in both low-income and high-income countries. The strong impact on public health in epidemic scenarios makes it increasingly essential to identify the sources of infection and understand the transmission routes in order to apply the right prevention or treatment protocols. The objective of this literature review was to present an overview of the current state of human cryptosporidiosis, reviewing risk factors, discussing advances in the drug treatment and epidemiology, and emphasizing the need to identify a government system for reporting diagnosed cases, hitherto undervalued.

Live imaging of the Cryptosporidium parvum life cycle reveals direct development of male and female gametes from type I meronts

Cryptosporidium is a leading infectious cause of diarrhea around the world associated with waterborne outbreaks, community spread, or zoonotic transmission. The parasite has significant impact on early childhood mortality, and infection is both a consequence and cause of malnutrition and stunting. There is currently no vaccine, and treatment options are very limited. Cryptosporidium is a member of the Apicomplexa, and, as typical for this, protist phylum relies on asexual and sexual reproduction. In contrast to other Apicomplexa, including the malaria parasite Plasmodium, the entire Cryptosporidium life cycle unfolds in a single host in less than 3 days. Here, we establish a model to image life cycle progression in living cells and observe, track, and compare nuclear division of asexual and sexual stage parasites. We establish the length and sequence of the cell cycles of all stages and map the developmental fate of parasites across multiple rounds of invasion and egress. We propose that the parasite executes an intrinsic program of 3 generations of asexual replication, followed by a single generation of sexual stages that is independent of environmental stimuli. We find no evidence for a morphologically distinct intermediate stage (the tetraploid type II meront) but demonstrate direct development of gametes from 8N type I meronts. The progeny of each meront is collectively committed to either asexual or sexual fate, but, importantly, meronts committed to sexual fate give rise to both males and females. We define a Cryptosporidium life cycle matching Tyzzer’s original description and inconsistent with the coccidian life cycle now shown in many textbooks.

The Structural Basis of Babesia orientalis Lactate Dehydrogenase

Glycolytic enzymes play a crucial role in the anaerobic glycolysis of apicomplexan parasites for energy generation. Consequently, they are considered as potential targets for new drug development. Previous studies revealed that lactate dehydrogenase (LDH), a glycolytic enzyme, is a potential drug target in different parasites, such as Plasmodium, Toxoplasma, Cryptosporidium, and Piroplasma. Herein, in order to investigate the structural basis of LDH in Babesia spp., we determined the crystal structure of apo Babesia orientalis (Bo) LDH at 2.67-Å resolution in the space group P1. A five-peptide insertion appears in the active pocket loop of BoLDH to create a larger catalytic pocket, like other protozoa (except for Babesia microti LDH) and unlike its mammalian counterparts, and the absence of this extra insertion inactivates BoLDH. Without ligands, the apo BoLDH takes R-state (relaxed) with the active-site loop open. This feature is obviously different from that of allosteric LDHs in T-state (tense) with the active-site loop open. Compared with allosteric LDHs, the extra salt bridges and hydrogen bonds make the subunit interfaces of BoLDH more stable, and that results in the absence of T-state. Interestingly, BoLDH differs significantly from BmLDH, as it exhibits the ability to adapt quickly to the synthetic co-factor APAD⁺. In addition, the enzymatic activity of BoLDH was inhibited non-competitively by polyphenolic gossypol with a K_i value of 4.25 μM, indicating that BoLDH is sensitive to the inhibition of gossypol and possibly to its new derivative compounds. The current work provides the structural basis of BoLDH for the first time and suggests further investigation on the LDH structure of other Babesia spp. That knowledge would indeed facilitate the screening and designing of new LDH inhibitors to control the intracellular proliferation of Babesia spp.

Discovery of New Microneme Proteins in Cryptosporidium parvum and Implication of the Roles of a Rhomboid Membrane Protein (CpROM1) in Host-Parasite Interaction

Apicomplexan parasites possess several unique secretory organelles, including rhoptries, micronemes, and dense granules, which play critical roles in the invasion of host cells. The molecular content of these organelles and their biological roles have been well-studied in Toxoplasma and Plasmodium, but are underappreciated in Cryptosporidium, which contains many parasites of medical and veterinary importance. Only four proteins have previously been identified or proposed to be located in micronemes, one of which, GP900, was confirmed using immunogold electron microscopy (IEM) to be present in the micronemes of intracellular merozoites. Here, we report on the discovery of four new microneme proteins (MICs) in the sporozoites of the zoonotic species C. parvum, identified using immunofluorescence assay (IFA). These proteins are encoded by cgd3_980, cgd1_3550, cgd1_3680, and cgd2_1590. The presence of the protein encoded by cgd3_980 in sporozoite micronemes was further confirmed using IEM. Cgd3_980 encodes one of the three C. parvum rhomboid peptidases (ROMs) and is, thus, designated CpROM1. IEM also confirmed the presence of CpROM1 in the micronemes of intracellular merozoites, parasitophorous vacuole membranes (PVM), and feeder organelles (FO). CpROM1 was enriched in the pellicles and concentrated at the host cell–parasite interface during the invasion of sporozoites and its subsequent transformation into trophozoites. CpROM1 transcript levels were also higher in oocysts and excysted sporozoites than in the intracellular parasite stages. These observations indicate that CpROM1, an intramembrane peptidase with membrane proteolytic activity, is involved in host–parasite interactions, including invasion and proteostasis of PVM and FO.

Implication of Potential Differential Roles of the Two Phosphoglucomutase Isoforms in the Protozoan Parasite Cryptosporidium parvum

Phosphoglucomutase 1 (PGM1) catalyzes the conversion between glucose-1-phosphate and glucose-6-phosphate in the glycolysis/glucogenesis pathway. PGM1s are typically cytosolic enzymes in organisms lacking chloroplasts. However, the protozoan Cryptosporidium parasites possess two tandemly duplicated PGM1 genes evolved by a gene duplication after their split from other apicomplexans. Moreover, the downstream PGM1 isoform contains an N-terminal signal peptide, predicting a non-cytosolic location. Here we expressed recombinant proteins of the two PGM1 isoforms from the zoonotic Cryptosporidium parvum, namely CpPGM1A and CpPGM1B, and confirmed their enzyme activity. Both isoforms followed Michaelis–Menten kinetics towards glucose-1-phosphate (K_m = 0.17 and 0.13 mM, V_max = 7.30 and 2.76 μmol/min/mg, respectively). CpPGM1A and CpPGM1B genes were expressed in oocysts, sporozoites and intracellular parasites at a similar pattern of expression, however CpPGM1A was expressed at much higher levels than CpPGM1B. Immunofluorescence assay showed that CpPGM1A was present in the cytosol of sporozoites, however this was enriched towards the plasma membranes in the intracellular parasites; whereas CpPGM1B was mainly present under sporozoite pellicle, although relocated to the parasitophorous vacuole membrane in the intracellular development. These observations indicated that CpPGM1A played a house-keeping function, while CpPGM1B played a different biological role that remains to be defined by future investigations.

Comparative proteomics reveals Cryptosporidium parvum manipulation of the host cell molecular expression and immune response

Cryptosporidium is a life-threating protozoan parasite belonging to the phylum Apicomplexa, which mainly causes gastroenteritis in a variety of vertebrate hosts. Currently, there is a re-emergence of Cryptosporidium infection; however, no fully effective drug or vaccine is available to treat Cryptosporidiosis. In the present study, to better understand the detailed interaction between the host and Cryptosporidium parvum, a large-scale label-free proteomics study was conducted to characterize the changes to the proteome induced by C. parvum infection. Among 4406 proteins identified, 121 proteins were identified as differentially abundant (> 1.5-fold cutoff, P < 0.05) in C. parvum infected HCT-8 cells compared with uninfected cells. Among them, 67 proteins were upregulated, and 54 proteins were downregulated at 36 h post infection. Analysis of the differentially abundant proteins revealed an interferon-centered immune response of the host cells against C. parvum infection and extensive inhibition of metabolism-related enzymes in the host cells caused by infection. Several proteins were further verified using quantitative real-time reverse transcription polymerase chain reaction and western blotting. This systematic analysis of the proteomics of C. parvum-infected HCT-8 cells identified a wide range of functional proteins that participate in host anti-parasite immunity or act as potential targets during infection, providing new insights into the molecular mechanism of C. parvum infection.

Cryptosporidium parvum is an emerging zoonotic pathogen transmitted via the fecal–oral route, and is considered a leading cause of moderate-to-severe diarrheal disease in young children in resource limited areas. After infection, C. parvum parasitizes intestinal epithelial cells and evokes an inflammatory immune response, leading to severe damage of the intestinal mucosa. The infection can be lethal to immunosuppressed individuals. However, no fully effective drug or vaccine is available for cryptosporidiosis, and the pathogenesis and immune mechanisms during C. parvum infection are obscure. Thus, an in-depth understanding of host-parasite interaction is needed. Hence, we established a C. parvum-infected HCT-8 cell model and performed comparative quantitative proteomic analyses to profile global host-parasite interactions and determine the molecular mechanisms that are activated during infection, aiming to offer new insights into the treatment of Cryptosporidium.

Unique Tubulin-Based Structures in the Zoonotic Apicomplexan Parasite Cryptosporidium parvum

Cryptosporidium parasites are known to be highly divergent from other apicomplexan species at evolutionary and biological levels. Here we provide evidence showing that the zoonotic Cryptosporidium parvum also differs from other apicomplexans, such as Toxoplasma gondii, by possessing only two tubulin-based filamentous structures, rather than an array of subpellicular microtubules. Using an affinity-purified polyclonal antibody against C. parvum β-tubulin (CpTubB), we observed a long and a short microtubule that are rigid and stable in the sporozoites and restructured during the intracellular parasite development. In asexual development (merogony), the two restructuring microtubules are present in pairs (one pair per nucleus or merozoites). In sexual developmental stages, tubulin-based structures are detectable only in microgametes, but undetectable in macrogametes. These observations indicate that C. parvum parasites use unique microtubule structures that differ from other apicomplexans as part of their cytoskeletal elements.

Cryptosporidium rhoptry effector protein ROP1 injected during invasion targets the host cytoskeletal modulator LMO7

The parasite Cryptosporidium invades and replicates in intestinal epithelial cells and is a leading cause of diarrheal disease and early childhood mortality. The molecular mechanisms that underlie infection and pathogenesis are largely unknown. Here, we delineate the events of host cell invasion and uncover a mechanism unique to Cryptosporidium. We developed a screen to identify parasite effectors, finding the injection of multiple parasite proteins into the host from the rhoptry organelle. These factors are targeted to diverse locations within the host cell and its interface with the parasite. One identified effector, rhoptry protein 1 (ROP1), accumulates in the terminal web of enterocytes through direct interaction with the host protein LIM domain only 7 (LMO7) an organizer of epithelial cell polarity and cell-cell adhesion. Genetic ablation of LMO7 or ROP1 in mice or parasites, respectively, impacts parasite burden in vivo in opposite ways. Taken together, these data provide molecular insight into how Cryptosporidium manipulates its intestinal host niche.

'de Novo' repurposing of Daflon as anti-intestinal parasitic drug in experimental giardiasis

BACKGROUND

There is a necessity to develop or discover an alternative drug to combat the drug resistance by Giardia duodenalis and minimize the multiple doses and frequency of the conventional drug administration. Progressive repositioning or 'repurposing' of drugs has become widespread due to economic circumstances and medical emergency needs. Daflon 500 mg (DFL) is a natural product used safely as a nutrient supplement and an antidiabetic drug in many European countries and the US.

OBJECTIVE

This study aimed at investigating the efficiency of DFL, in vivo, in a murine model as a safe alternative or co-drug for giardiasis.

MATERIALS AND METHODS

Swiss Albino mice (n = 32) were inoculated with 1X10⁴Giardia cysts and assigned to four groups: One group was the infected non-treated control mice and three experimental groups that were treated differently, either with Metronidazole (MTZ), DFL, or combined therapy of DFL/MTZ. Also, eight normal mice served as a control group. All mice were sacrificed 13 days post-infection for the parasitic, histopathological, and oxidative stress analysis.

RESULTS

MTZ, DFL, and the combined therapy significantly reduced the number of trophozoites and cysts compared to their counterparts of the infected mice. The histopathological analysis of the small intestines of the mice treated with the combined therapy retained typical intestinal architecture and normal levels of malondialdehyde (MDA), superoxide dismutase (SOD), and glutathione.

CONCLUSION

This study indicated promising actions of Daflon 500 as an anti-giardial drug, and the results demonstrated its potential effect in improving the intestinal epithelial tissue and disturbing the Giardia stages when it was taken collectively with Metronidazole.

The Biology of the Intestinal Intracellular Parasite Cryptosporidium

Cryptosporidium emerged as a leading global cause of severe diarrheal disease in children. The parasite occupies a unique intracellular niche at the brush border of intestinal epithelial cells, where it undergoes a complex sexual life cycle. How this life cycle unfolds and how host and parasite interact remain largely to be discovered. A series of technical advances now offer genetic and immunological tools for mechanistic investigation of the parasite. Here we introduce the pathogen and disease and highlight important questions to tackle onward. We invite scientists to consider this versatile parasite model to probe the biology and immunology of the intestine.

A Single-Pass Type I Membrane Protein from the Apicomplexan Parasite Cryptosporidium parvum with Nanomolar Binding Affinity to Host Cell Surface

Cryptosporidium parvum is a globally recognized zoonotic parasite of medical and veterinary importance. This parasite mainly infects intestinal epithelial cells and causes mild to severe watery diarrhea that could be deadly in patients with weakened or defect immunity. However, its molecular interactions with hosts and pathogenesis, an important part in adaptation of parasitic lifestyle, remain poorly understood. Here we report the identification and characterization of a C. parvum T-cell immunomodulatory protein homolog (CpTIPH). CpTIPH is a 901-aa single-pass type I membrane protein encoded by cgd5_830 gene that also contains a short Vibrio, Colwellia, Bradyrhizobium and Shewanella (VCBS) repeat and relatively long integrin alpha (ITGA) N-terminus domain. Immunofluorescence assay confirmed the location of CpTIPH on the cell surface of C. parvum sporozoites. In congruence with the presence of VCBS repeat and ITGA domain, CpTIPH displayed high, nanomolar binding affinity to host cell surface (i.e., K_d(App) at 16.2 to 44.7 nM on fixed HCT-8 and CHO-K1 cells, respectively). The involvement of CpTIPH in the parasite invasion is partly supported by experiments showing that an anti-CpTIPH antibody could partially block the invasion of C. parvum sporozoites into host cells. These observations provide a strong basis for further investigation of the roles of CpTIPH in parasite-host cell interactions.

Current status and challenges in drug discovery against the globally important zoonotic cryptosporidiosis

The zoonotic cryptosporidiosis is globally distributed, one of the major diarrheal diseases in humans and animals. Cryptosporidium oocysts are also one of the major environmental concerns, making it a pathogen that fits well into the One Health concept. Despite its importance, fully effective drugs are not yet available. Anti-cryptosporidial drug discovery has historically faced many unusual challenges attributed to unique parasite biology and technical burdens. While significant progresses have been made recently, anti-cryptosporidial drug discovery still faces a major obstacle: identification of systemic drugs that can be absorbed by patients experiencing watery diarrhea and effectively pass through electron-dense (ED) band at the parasite-host cell interface to act on the epicellular parasite. There may be a need to develop an in vitro assay to effectively screen hits/leads for their capability to cross ED band. In the meantime, non-systemic drugs with strong mucoadhesive properties for extended gastrointestinal exposure may represent another direction in developing anti-cryptosporidial therapeutics. For developing both systemic and non-systemic drugs, a non-ruminant animal model exhibiting diarrheal symptoms suitable for routine evaluation of drug absorption and anti-cryptosporidial efficacy may be very helpful.

Cryptosporidium parvum Elongation Factor 1α Participates in the Formation of Base Structure at the Infection Site During Invasion

BACKGROUND

Cryptosporidium is a genus of apicomplexan parasites, the causative agents of cryptosporidiosis in humans and/or animals. Although most apicomplexans parasitize within the host cell cytosols, Cryptosporidium resides on top of host cells, but it is embraced by a double-layer parasitophorous vacuole membrane derived from host cell. There is an electron-dense band to separate the parasite from host cell cytoplasm, making it as an intracellular but extracytoplasmic parasite. However, little is known on the molecular machinery at the host cell-parasite interface.

METHODS

Cryptosporidium parvum at various developmental stages were obtained by infecting HCT-8 cells cultured in vitro. Immunofluorescence assay was used to detect CpEF1α with a polyclonal antibody and host cell F-actin with rhodamine-phalloidin. Recombinant CpEF1α protein was used to evaluate its effect on the invasion by the parasite.

RESULTS

We discovered that a C parvum translation elongation factor 1α (CpEF1α) was discharged from the invading sporozoites into host cells, forming a crescent-shaped patch that fully resembles the electron-dense band. At the same time, host cell F-actin aggregated to form a globular-shaped plug beneath the CpEF1α patch. The CpEF1α patch remained for most of the time but became weakened and dissolved upon the completion of the invasion process. In addition, recombinant CpEF1α protein could effectively interfere the invasion of sporozoites into host cells.

CONCLUSIONS

CpEF1α plays a role in the parasite invasion by participating in the formation of electron-dense band at the base of the parasite infection site.

Metabolic Signatures of Cryptosporidium parvum-Infected HCT-8 Cells and Impact of Selected Metabolic Inhibitors on C. parvum Infection under Physioxia and Hyperoxia

Cryptosporidium parvum is an apicomplexan zoonotic parasite recognized as the second leading-cause of diarrhoea-induced mortality in children. In contrast to other apicomplexans, C. parvum has minimalistic metabolic capacities which are almost exclusively based on glycolysis. Consequently, C. parvum is highly dependent on its host cell metabolism. In vivo (within the intestine) infected epithelial host cells are typically exposed to low oxygen pressure (1-11% O₂, termed physioxia). Here, we comparatively analyzed the metabolic signatures of C. parvum-infected HCT-8 cells cultured under both, hyperoxia (21% O₂), representing the standard oxygen condition used in most experimental settings, and physioxia (5% O₂), to be closer to the in vivo situation. The most pronounced effect of C. parvum infection on host cell metabolism was, on one side, an increase in glucose and glutamine uptake, and on the other side, an increase in lactate release. When cultured in a glutamine-deficient medium, C. parvum infection led to a massive increase in glucose consumption and lactate production. Together, these results point to the important role of both glycolysis and glutaminolysis during C. parvum intracellular replication. Referring to obtained metabolic signatures, we targeted glycolysis as well as glutaminolysis in C. parvum-infected host cells by using the inhibitors lonidamine [inhibitor of hexokinase, mitochondrial carrier protein (MCP) and monocarboxylate transporters (MCT) 1, 2, 4], galloflavin (lactate dehydrogenase inhibitor), syrosingopine (MCT1- and MCT4 inhibitor) and compound 968 (glutaminase inhibitor) under hyperoxic and physioxic conditions. In line with metabolic signatures, all inhibitors significantly reduced parasite replication under both oxygen conditions, thereby proving both energy-related metabolic pathways, glycolysis and glutaminolysis, but also lactate export mechanisms via MCTs as pivotal for C. parvum under in vivo physioxic conditions of mammals.

Cryptosporidium: host and parasite transcriptome in infection

Cryptosporidium is a waterborne gastrointestinal parasite that causes outbreaks of diarrheal disease worldwide. Despite the impact of this parasite on human health there are no effective drugs or vaccines. Transcriptomic data can provide insights into host-parasite interactions that lead to identification of targets for therapeutic interventions. However, for Cryptosporidium, interpreting transcriptomes has been challenging, in part due to the presence of multiple life cycle stages, the lack of appropriate host cells and the inability to culture the parasite through its complete life cycle. The recent improvements in cell culture and the ability to tag and isolate specific life cycle stages will radically improve transcriptomic data and advance our understanding of Cryptosporidium host-parasite interactions.

FX11 limits Mycobacterium tuberculosis growth and potentiates bactericidal activity of isoniazid through host-directed activity

Lactate dehydrogenase A (LDHA) mediates interconversion of pyruvate and lactate, and increased lactate turnover is exhibited by malignant and infected immune cells. Hypoxic lung granuloma in Mycobacterium tuberculosis-infected animals present elevated levels of Ldha and lactate. Such alterations in the metabolic milieu could influence the outcome of host-M. tuberculosis interactions. Given the central role of LDHA for tumorigenicity, targeting lactate metabolism is a promising approach for cancer therapy. Here, we sought to determine the importance of LDHA for tuberculosis (TB) disease progression and its potential as a target for host-directed therapy. To this end, we orally administered FX11, a known small-molecule NADH-competitive LDHA inhibitor, to M. tuberculosis-infected C57BL/6J mice and Nos2-/- mice with hypoxic necrotizing lung TB lesions. FX11 did not inhibit M. tuberculosis growth in aerobic/hypoxic liquid culture, but modestly reduced the pulmonary bacterial burden in C57BL/6J mice. Intriguingly, FX11 administration limited M. tuberculosis replication and onset of necrotic lung lesions in Nos2-/- mice. In this model, isoniazid (INH) monotherapy has been known to exhibit biphasic killing kinetics owing to the probable selection of an INH-tolerant bacterial subpopulation. However, adjunct FX11 treatment corrected this adverse effect and resulted in sustained bactericidal activity of INH against M. tuberculosis As a limitation, LDHA inhibition as an underlying cause of FX11-mediated effect could not be established as the on-target effect of FX11 in vivo was unconfirmed. Nevertheless, this proof-of-concept study encourages further investigation on the underlying mechanisms of LDHA inhibition and its significance in TB pathogenesis.

Cryptosporidium parvum gp40/15 Is Associated with the Parasitophorous Vacuole Membrane and Is a Potential Vaccine Target

Cryptosporidium parvum is a zoonotic intracellular protozoan responsible for the diarrheal illness cryptosporidiosis in humans and animals. Although a number of zoite surface proteins are known to be expressed during, and believed to be involved in, attachment and invasion of host cells, the molecular mechanisms by which C. parvum invades the host epithelial cells are not well understood. In the present study, we investigated the gene expression patterns, protein localization in developmental stages in culture, and in vitro neutralization characteristics of Cpgp40/15 and Cpgp40. Indirect immunofluorescence assay showed that Cpgp40/15 is associated with the parasitophorous vacuole membrane (PVM) during intracellular development. Both anti-gp40/15 and anti-gp40 antibodies demonstrated the ability to neutralize C. parvum infection in vitro. Further studies are needed to fully understand the specific role and functional mechanism of Cpgp40/15 (or gp40/15 complex) in the invasion of the host or in the PVM and to determine the feasibility of gp40/15 as a vaccine candidate for cryptosporidiosis in vivo.

Identifying the Naphthalene-Based Compound 3,5-Dihydroxy 2-Napthoic Acid as a Novel Lead Compound for Designing Lactate Dehydrogenase-Specific Antibabesial Drug

Human babesiosis is caused by apicomplexan Babesia parasites, including Babesia microti, Babesia crassa, Babesia sp. MOI, Babesia divergens, Babesia duncani, and Babesia venatorum. Among them, B. microti is the most common cause of human and rodent babesiosis. Currently, no vaccine is available, and drugs for the treatment have high failure rates and side effects. Due to lack of a traditional tricarboxylic acid cycle (TCA cycle) and its dominant dependence on anaerobic metabolism to produce ATP, B. microti lactate dehydrogenase (BmLDH) was assumed to play a critical role in B. microti ATP supply. Our previous study demonstrated that BmLDH is a potential drug target and Arg99 is a crucial site. Herein, a molecular docking was performed based on the crystal structure of BmLDH from a series of gossypol derivatives or structural analogs to find the potent inhibitors interacting with the residue Arg99, and three naphthalene-based compounds 2,6-naphthalenedicarboxylic acid (NDCA), 1,6-dibromo-2-hydroxynapthalene 3-carboxylic acid (DBHCA), and 3,5-dihydroxy 2-napthoic acid (DHNA) were selected for further tests. Enzyme activity inhibitory experiments show that DBHCA and DHNA inhibit recombinant BmLDH (rBmLDH) catalysis with ~109-fold and ~5,000-fold selectivity over human LDH, respectively. Surface plasmon resonance (SPR) assays demonstrate that DHNA has a lower K _D value to BmLDH (3.766 x 10^-5 M), in contrast to a higher value for DBHCA (3.988 x 10^-8 M). A comparison of the kinetic parameters [association constant (k _a) and dissociation constant (k _d) values] reveals that DBHCA can bind the target faster than DHNA, while the complex of DHNA with the target dissociates slower than that of DBHCA. Both DBHCA and DHNA can inhibit the growth of B. microti in vitro with half-maximal inhibitory concentration (IC₅₀) values of 84.83 and 85.65 μM, respectively. Cytotoxicity tests in vitro further indicate that DBHCA and DHNA have selectivity indexes (SI) of 2.6 and 22.1 between B. microti and Vero cells, respectively. Although the two naphthalene-based compounds only display modest inhibitory activity against both rBmLDH and the growth of B. microti, the compound DHNA features high selectivity and could serve as a novel lead compound for designing LDH-specific antibabesial drug.

Crystal structures of Babesia microti lactate dehydrogenase BmLDH reveal a critical role for Arg99 in catalysis

The tick- and transfusion-transmitted human pathogen Babesia microti infects host erythrocytes to cause the pathologic symptoms associated with human babesiosis, an emerging disease with worldwide distribution and potentially fatal clinical outcome. Drugs currently recommended for the treatment of babesiosis are associated with a high failure rate and significant adverse events, highlighting the urgent need for more-effective and safer babesiosis therapies. Unlike other apicomplexan parasites, B. microti lacks a canonical lactate dehydrogenase (LDH) but instead expresses a unique enzyme, B. microti LDH (BmLDH), acquired through evolution by horizontal transfer from a mammalian host. Here, we report the crystal structures of BmLDH in apo state and ternary complex (enzyme-NADH-oxamate) solved at 2.79 and 1.89 Å. Analysis of these structures reveals that upon binding to the coenzyme and substrate, the active pocket of BmLDH undergoes a major conformational change from an opened and disordered to a closed and stabilized state. Biochemical assays using wild-type and mutant B. microti and human LDHs identified Arg99 as a critical residue for the catalytic activity of BmLDH but not its human counterpart. Interestingly, mutation of Arg99 to Ala had no impact on the overall structure and affinity of BmLDH to NADH but dramatically altered the closure of the enzyme's active pocket. Together, these structural and biochemical data highlight significant differences between B. microti and human LDH enzymes and suggest that BmLDH could be a suitable target for the development of selective antibabesial inhibitors.-Yu, L., Shen, Z., Liu, Q., Zhan, X., Luo, X., An, X., Sun, Y., Li, M., Wang, S., Nie, Z., Ao, Y., Zhao, Y., Peng, G., Ben Mamoun, C., He, L., Zhao, J. Crystal structures of Babesia microti lactate dehydrogenase BmLDH reveal a critical role for Arg99 in catalysis.

Novel lactate dehydrogenase inhibitors with in vivo efficacy against Cryptosporidium parvum

Cryptosporidium parvum is a highly prevalent zoonotic and anthroponotic protozoan parasite that causes a diarrheal syndrome in children and neonatal livestock, culminating in growth retardation and mortalities. Despite the high prevalence of C. parvum, there are no fully effective and safe drugs for treating infections, and there is no vaccine. We have previously reported that the bacterial-like C. parvum lactate dehydrogenase (CpLDH) enzyme is essential for survival, virulence and growth of C. parvum in vitro and in vivo. In the present study, we screened compound libraries and identified inhibitors against the enzymatic activity of recombinant CpLDH protein in vitro. We tested the inhibitors for anti-Cryptosporidium effect using in vitro infection assays of HCT-8 cells monolayers and identified compounds NSC158011 and NSC10447 that inhibited the proliferation of intracellular C. parvum in vitro, with IC₅₀ values of 14.88 and 72.65 μM, respectively. At doses tolerable in mice, we found that both NSC158011 and NSC10447 consistently significantly reduced the shedding of C. parvum oocysts in infected immunocompromised mice’s feces, and prevented intestinal villous atrophy as well as mucosal erosion due to C. parvum. Together, our findings have unveiled promising anti-Cryptosporidium drug candidates that can be explored further for the development of the much needed novel therapeutic agents against C. parvum infections.

Cryptosporidium parvum is a protozoan parasite that can cause a life-threatening gastrointestinal disease in children and in immunocompromised adults. The only approved drug for treatment of Cryptosporidium infections in humans is nitazoxanide, but it is not effective in immunocompromised individuals or in children with malnutrition. C. parvum possesses a unique lactate dehydrogenase (CpLDH) enzyme that it uses for generating metabolic energy (ATP) via the glycolytic pathway to fuel its growth and proliferation in the host. We have identified novel inhibitors for the enzymatic activity of CpLDH. Further, we have demonstrated that two of the CpLDH inhibitors effectively block the growth, proliferation and pathogenicity of C. parvum at tolerable doses in immunocompromised mice. Together, our findings have unveiled novel CpLDH inhibitors that can be explored for the development of efficacious therapeutic drugs against C. parvum infections.

Molecular and Biochemical Characterization of a Type II Thioesterase From the Zoonotic Protozoan Parasite Cryptosporidium parvum

Cryptosporidium parvum is a globally important zoonotic parasite capable of causing severe to deadly diarrhea in humans and animals. Its small genome (~9.1 Mb) encodes not only a highly streamlined metabolism, but also a 25-kb, 3-module fatty acid synthase (CpFAS1) and a 40-kb, 7-module polyketide synthase (CpPKS1). The two megasynthases contain a C-terminal reductase domain to release the final products with predicted chain lengths of ≥C22 for CpFAS1 or C28 to C38 for CpPKS1.The parasite genome also encodes a discrete thioesterase ortholog, suggesting its role to be an alternative tool in releasing the final products from CpFAS1 and/or CpPKS1, or as an editor to remove non-reactive residues or aberrant intermediates, or to control starter units as seen in other parasites. In this study, we have confirmed that this C. parvum thioesterase is a type II thioesterase (thus named as CpTEII). CpTEII contains motifs and a catalytic triad characteristic to the type II thioesterase family. CpTEII is expressed during the entire parasite life cycle stages with the highest levels of expression in the later developmental stages. CpTEII showed the highest hydrolytic activity toward C10:0 decanoyl-CoA, so we speculated that CpTEII may mainly act as an editor to remove non-reactive residues and/or aberrant medium acyl chain from CpFAS1 and/or CpPKS1. However, we cannot rule out the possibility that CpTEII may also participate in the release of final products from CpFAS1 because of its moderate activity on C20:0, C:22:0 and C24:0 acyl-CoA thioesters (i.e., ~20–30% activity vs. decanoyl-CoA).

Interferon-λ3 Promotes Epithelial Defense and Barrier Function Against Cryptosporidium parvum Infection

BACKGROUND & AIMS

The epithelial response is critical for intestinal defense against Cryptosporidium, but is poorly understood. To uncover the host strategy for defense against Cryptosporidium, we examined the transcriptional response of intestinal epithelial cells (IECs) to C parvum in experimentally infected piglets by microarray. Up-regulated genes were dominated by targets of interferon (IFN) and IFN-λ3 was up-regulated significantly in infected piglet mucosa. Although IFN-λ has been described as a mediator of epithelial defense against viral pathogens, there is limited knowledge of any role against nonviral pathogens. Accordingly, the aim of the study was to determine the significance of IFN-λ3 to epithelial defense and barrier function during C parvum infection.

METHODS

The significance of C parvum-induced IFN-λ3 expression was determined using an immunoneutralization approach in neonatal C57BL/6 mice. The ability of the intestinal epithelium to up-regulate IFN-λ2/3 expression in response to C parvum infection and the influence of IFN-λ2/3 on epithelial defense against C parvum invasion, intracellular development, and loss of barrier function was examined using polarized monolayers of a nontransformed porcine-derived small intestinal epithelial cell line (IPEC-J2). Specifically, changes in barrier function were quantified by measurement of transepithelial electrical resistance and transepithelial flux studies.

RESULTS

Immunoneutralization of IFN-λ2/3 in C parvum-infected neonatal mice resulted in a significantly increased parasite burden, fecal shedding, and villus blunting with crypt hyperplasia during peak infection. In vitro, C parvum was sufficient to induce autonomous IFN-λ3 and interferon-stimulated gene 15 expression by IECs. Priming of IECs with recombinant human IFN-λ3 promoted cellular defense against C parvum infection and abrogated C parvum-induced loss of barrier function by decreasing paracellular permeability to sodium.

CONCLUSIONS

These studies identify IFN-λ3 as a key epithelial defense mechanism against C parvum infection.

The Action of the Hexokinase Inhibitor 2-deoxy-d-glucose on Cryptosporidium parvum and the Discovery of Activities against the Parasite Hexokinase from Marketed Drugs

Cryptosporidium parvum is one of the major species causing mild to severe cryptosporidiosis in humans and animals. We have previously observed that 2-deoxy-d-glucose (2DG) could inhibit both the enzyme activity of C. parvum hexokinase (CpHK) and the parasite growth in vitro. However, the action and fate of 2DG in C. parvum was not fully investigated. In the present study, we showed that, although 2DG could be phosphorylated by CpHK to form 2DG-6-phosphate (2DG6P), the anti-cryptosporidial activity of 2DG was mainly attributed to the action of 2DG on CpHK, rather than the action of 2DG or 2DG6P on the downstream enzyme glucose-6-phosphate isomerase (CpGPI) nor 2DG6P on CpHK. These observations further supported the hypothesis that CpHK could serve as a drug target in the parasite. We also screened 1,200 small molecules consisting of marketed drugs against CpHK, from which four drugs were identified as CpHK inhibitors with micromolar level of anti-cryptospordial activities at concentrations nontoxic to the host cells (i.e. hexachlorphene, thimerosal, alexidine dihydrochloride, and ebselen with EC₅₀  = 0.53, 1.77, 8.1 and 165 μM, respectively). The anti-CpHK activity of the four existing drugs provided us new reagents for studying the enzyme properties of the parasite hexokinase.

In-silico screening of small molecule inhibitors against Lactate Dehydrogenase (LDH) of Cryptosporidium parvum

Cryptosporidium parvum is a protozoan parasite which causes waterborne diseases known as Cryptosporidiosis. It is an acute enteric diarrheal disease being severe in the case of immunocompromised individuals and children. C. parvum mainly depends on the glycolysis process for energy production and LDH (Lactate Dehydrogenase) is a key controller of this process. In this study from different in-silico approaches such as structure-based, ligand-based and de novo drug design; a total of 40 compounds were selected for docking studies against LDH. The study reported a compound CHEMBL1784973 from Pathogen Box as the best inhibitor in terms of docking score and pharmacophoric features. Furthermore, the binding mode of the best-reported inhibitor was validated through molecular dynamics simulation for a time interval of 70 ns in water environment. The findings resulted in the stable conformation of the inhibitor in the active site of the protein. This study will be helpful for experimental validation.

Genome-wide analysis of differentially expressed profiles of mRNAs, lncRNAs and circRNAs during Cryptosporidium baileyi infection

Background

Cryptosporidium baileyi is the most common Cryptosporidium species in birds. However, effective prevention measures and treatment for C. baileyi infection were still not available. Long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs) play important roles in regulating occurrence and progression of many diseases and are identified as effective biomarkers for diagnosis and prognosis of several diseases. In the present study, the expression profiles of host mRNAs, lncRNAs and circRNAs associated with C. baileyi infection were investigated for the first time.

Results

The tracheal tissues of experimental (C. baileyi infection) and control chickens were collected for deep RNA sequencing, and 545,479,934 clean reads were obtained. Of them, 1376 novel lncRNAs were identified, including 1161 long intergenic non-coding RNAs (lincRNAs) and 215 anti-sense lncRNAs. A total of 124 lncRNAs were found to be significantly differentially expressed between the experimental and control groups. Additionally, 14,698 mRNAs and 9085 circRNAs were identified, and significantly different expressions were observed for 1317 mRNAs and 104 circRNAs between two groups. Bioinformatic analyses of gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway for their targets and source genes suggested that these dysregulated genes may be involved in the interaction between the host and C. baileyi.

Conclusions

The present study revealed the expression profiles of mRNAs, lncRNAs and circRNAs during C. baileyi infection for the first time, and sheds lights on the roles of lncRNAs and circRNAs underlying the pathogenesis of Cryptosporidium infection.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4754-2) contains supplementary material, which is available to authorized users.

Morpholino-mediated in vivo silencing of Cryptosporidium parvum lactate dehydrogenase decreases oocyst shedding and infectivity

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An in vivo morpholino-based approach for targeted gene knockdown of genes in Cryptosporidium parvum was developed.

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Cryptosporidium parvum lactate dehydrogenase, and sporozoite 60K were knocked down sustainably in infected mice.

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Cryptosporidium parvum lactate dehydrogenase knockdown significantly decreased oocyst shedding and infectivity.

Cryptosporidium is a highly prevalent protozoan parasite that is the second leading cause of childhood morbidity and mortality due to diarrhoea in developing countries, and causes a serious diarrheal syndrome in calves, lambs and goat kids worldwide. Development of fully effective drugs against Cryptosporidium has mainly been hindered by the lack of genetic tools for functional characterization and validation of potential molecular drug targets in the parasite. Herein, we report the development of a morpholino-based in vivo approach for Cryptosporidium parvum gene knockdown to facilitate determination of the physiological roles of the parasite’s genes in a murine model. We show that, when administered intraperitoneally at non-toxic doses, morpholinos targeting C. parvum lactate dehydrogenase (CpLDH) and sporozoite 60K protein (Cp15/60) were able to specifically and sustainably down-regulate the expression of CpLDH and Cp15/60 proteins, respectively, in C. parvum-infected interferon-γ knockout mice. Over a period of 6 days of daily administration of target morpholinos, CpLDH and Cp15/60 proteins were down-regulated by 20- to 50-fold, and 10- to 20-fold, respectively. Knockdown of CpLDH resulted in approximately 80% reduction in oocyst load in the feces of mice, and approximately 70% decrease in infectivity of the sporozoites excysted from the shed oocysts. Cp15/60 knockdown did not affect oocyst shedding nor infectivity but, nevertheless, provided a proof-of-principle for the resilience of the morpholino-mediated C. parvum gene knockdown system in vivo. Together, our findings provide a genetic tool for deciphering the physiological roles of C. parvum genes in vivo, and validate CpLDH as an essential gene for the growth and viability of C. parvum in vivo.

Functional analysis of Toxoplasma lactate dehydrogenases suggests critical roles of lactate fermentation for parasite growth in vivo

Glycolysis was thought to be the major pathway of energy supply in both fast-replicating tachyzoites and slowly growing bradyzoites of Toxoplasma gondii. However, its biological significance has not been clearly verified. The genome of T. gondii encodes two lactate dehydrogenases (LDHs), which are differentially expressed in tachyzoites and bradyzoites. In this study, we knocked out the two LDH genes individually and in combination and found that neither gene was required for tachyzoite growth in vitro under standard growth conditions. However, during infection in mice, Δldh1 and Δldh1 Δldh2 mutants were unable to propagate and displayed significant virulence attenuation and cyst formation defects. LDH2 only played minor roles in these processes. To further elucidate the mechanisms underlying the critical requirement of LDH in vivo, we found that Δldh1 Δldh2 mutants replicated significantly more slowly than wild-type parasites when cultured under conditions with physiological levels of oxygen (3%). In addition, Δldh1 Δldh2 mutants were more susceptible to the oxidative phosphorylation inhibitor oligomycin A. Together these results suggest that lactate fermentation is critical for parasite growth under physiological conditions, likely because energy production from oxidative phosphorylation is insufficient when oxygen is limited and lactate fermentation becomes a key supplementation.

Targeted gene knockdown validates the essential role of lactate dehydrogenase in Cryptosporidium parvum

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Morpholino oligomers antisense approach was developed as a reverse genetic tool in Cryptosporidium parvum.

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Significant knockdown of C. parvum LDH and arginine methyltransferase was achieved using gene-target morpholinos.

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Knockdown of C. parvum LDH dramatically decreased growth of C. parvum in vitro.

Cryptosporidium parvum is a zoonotic protozoan that can cause a life-threatening gastrointestinal syndrome in children and in immunocompromised adults. Currently, the only approved drug for treatment of Cryptosporidium infections in humans is nitazoxanide, but it is not effective in immunocompromised individuals or in children with malnutrition. This is compounded by the lack of genetic methods for studying and validating potential drug targets in the parasite. Therefore, in this study, we endeavoured to adapt the use of a phosphorodiamidate morpholino oligomer (morpholino) antisense approach to develop a targeted gene knockdown assay for use in C. parvum. We show that morpholinos, at non-toxic concentrations, are rapidly internalised by both C. parvum and host cells (HCT-8), and distribute diffusely throughout the cytosol. Using morpholinos to separately target C. parvum lactate dehydrogenase and putative arginine n-methyltransferase genes, within 36 h of in vitro culture, we achieved over 10-fold down-regulation of the respective encoded proteins in C. parvum. Pursuant to this, we observed that knockdown of C. parvum lactate dehydrogenase produced a dramatic reduction in intracellular growth and development of C. parvum by 56 h of culture. On the other hand, C. parvum putative arginine n-methyltransferase knockdown did not appear to have any effect on parasite growth, but nevertheless provided the proof-of-principle that the morpholino knockdown assay in C. parvum was consistent. Together, our findings present a gene regulation approach for interrogating gene function in C. parvum in vitro, and further provide genetic evidence for the essential role of C. parvum lactate dehydrogenase in fueling the growth and development of intracellular C. parvum.

Characterization of Host Cell Mutants Significantly Resistant to Cryptosporidium parvum Infection

Cryptosporidium parvum is a parasitic protist and a causative agent of mild-to-severe diarrheal diseases in humans and animals. Despite its globally recognized importance, knowledge on the mechanism of parasite invasion and molecular interactions between host cells and the parasite is limited. Here, we report the establishment of 43 mutant cell lines derived from HCT-8 cells by UV-induced mutagenesis and the characterization of three mutants with significantly reduced susceptibility to cryptosporidial infection. Based on qRT-PCR assay performed at 18 h postinfection time, the parasite loads could be reduced by ~45%, ~35%, and ~20% in mutants A05, B08, and B12, respectively (p < 0.001 in all three mutants vs. HCT-8 cells). The mutagenesis mainly affected the attachment of parasite in A05 (i.e. ~30% reduction, p < 0.001 vs. HCT-8), and intracellular development in B08 and B12. The three cell mutants may serve as valuable reagents to further investigate the mechanism of parasite invasion and intracellular development by identifying the gene mutations associated with the parasite attachment (A05) and intracellular development (B08 and B12).