New Tools for Cryptosporidium Lead to New Hope for Cryptosporidiosis

Research progress on phosphatidylinositol 4-kinase inhibitors

Phosphatidylinositol 4-kinases (PI4Ks) could phosphorylate phosphatidylinositol (PI) to produce phosphatidylinositol 4-phosphate (PI4P) and maintain its metabolic balance and location. PI4P, the most abundant monophosphate inositol in eukaryotic cells, is a precursor of higher phosphoinositols and an essential substrate for the PLC/PKC and PI3K/Akt signaling pathways. PI4Ks regulate vesicle transport, signal transduction, cytokinesis, and cell unity, and are involved in various physiological and pathological processes, including infection and growth of parasites such as Plasmodium and Cryptosporidium, replication and survival of RNA viruses, and the development of tumors and nervous system diseases. The development of novel drugs targeting PI4Ks and PI4P has been the focus of the research and clinical application of drugs, especially in recent years. In particular, PI4K inhibitors have made great progress in the treatment of malaria and cryptosporidiosis. We describe the biological characteristics of PI4Ks; summarize the physiological functions and effector proteins of PI4P; and analyze the structural basis of selective PI4K inhibitors for the treatment of human diseases in this review. Herein, this review mainly summarizes the developments in the structure and enzyme activity of PI4K inhibitors.

Newly fabricated zinc oxide nanoparticles loaded materials for therapeutic nano delivery in experimental cryptosporidiosis

Cryptosporidiosis is a global health problem that threatens the lives of immunocompromised patients. This study targets to fabricate and investigate the efficiency of zinc oxide nanoparticles (ZnO-NPs), nitazoxanide (NTZ)-loaded ZnO-NPs, and Allium sativum (A. sativum)-loaded ZnO-NPs in treating cryptosporidiosis. Further FTIR, SEM, XRD, and zeta analysis were used for the characterization of ZnO-NPs and loaded materials. The morphology of loaded materials for ZnO-NPs changed into wrapped layers and well-distributed homogenous particles, which had a direct effect on the oocyst wall. The charge surface of all particles had a negative sign, which indicated well distribution into the parasite matrix. For anti-cryptosporidiosis efficiency, thirty immunosuppressed Cryptosporidium parvum-infected mice, classified into six groups, were sacrificed on the 21st day after infection with an evaluation of parasitological, histopathological, and oxidative markers. It was detected that the highest reduction percent of Cryptosporidium oocyst shedding was (81.5%) in NTZ, followed by (71.1%) in A. sativum-loaded ZnO-NPs-treated groups. Also, treatment with A. sativum and NTZ-loaded ZnO-NPs revealed remarkable amelioration of the intestinal, hepatic, and pulmonary histopathological lesions. Furthermore, they significantly produced an increase in GSH values and improved the changes in NO and MDA levels. In conclusion, this study is the first to report ZnO-NPs as an effective therapy for treating cryptosporidiosis, especially when combined with other treatments that enhance their antioxidant activity. It provides an economical and environment-friendly approach to novel delivery synthesis for antiparasitic applications.

Comparative analyses of parasites with a comprehensive database of genome-scale metabolic models

Protozoan parasites cause diverse diseases with large global impacts. Research on the pathogenesis and biology of these organisms is limited by economic and experimental constraints. Accordingly, studies of one parasite are frequently extrapolated to infer knowledge about another parasite, across and within genera. Model in vitro or in vivo systems are frequently used to enhance experimental manipulability, but these systems generally use species related to, yet distinct from, the clinically relevant causal pathogen. Characterization of functional differences among parasite species is confined to post hoc or single target studies, limiting the utility of this extrapolation approach. To address this challenge and to accelerate parasitology research broadly, we present a functional comparative analysis of 192 genomes, representing every high-quality, publicly-available protozoan parasite genome including Plasmodium, Toxoplasma, Cryptosporidium, Entamoeba, Trypanosoma, Leishmania, Giardia, and other species. We generated an automated metabolic network reconstruction pipeline optimized for eukaryotic organisms. These metabolic network reconstructions serve as biochemical knowledgebases for each parasite, enabling qualitative and quantitative comparisons of metabolic behavior across parasites. We identified putative differences in gene essentiality and pathway utilization to facilitate the comparison of experimental findings and discovered that phylogeny is not the sole predictor of metabolic similarity. This knowledgebase represents the largest collection of genome-scale metabolic models for both pathogens and eukaryotes; with this resource, we can predict species-specific functions, contextualize experimental results, and optimize selection of experimental systems for fastidious species.

Cryptosporidium parvum infection induces autophagy in intestinal epithelial cells

Autophagy, a process of degradation and recycling of macromolecules and organelles to maintain cellular homeostasis, has also been shown to help eliminate invading pathogens. Conversely, various pathogens including parasites have been shown to modulate/exploit host autophagy facilitating their intracellular infectious cycle. In this regard, Cryptosporidium parvum (CP), a protozoan parasite of small intestine is emerging as a major global health challenge. However, the pathophysiology of cryptosporidiosis is mostly unknown. We have recently demonstrated CP-induced epithelial barrier disruption via decreasing the expression of specific tight junction (TJ) and adherens junction (AJ) proteins such as occludin, claudin-4 and E-cadherin. Therefore, we utilised confluent Caco-2 cell monolayers as in vitro model of intestinal epithelial cells (IECs) to investigate the potential role of autophagy in the pathophysiology of cryptosporidiosis. Autophagy was assessed by increase in the ratio of LC3II (microtubule associated protein 1 light chain 3) to LC3I protein and decrease in p62/SQSTM1 protein levels. CP treatment of Caco-2 cells for 24 hr induced autophagy with a maximum effect observed with 0.5 × 106 oocyst/well. CP decreased mTOR (mammalian target of rapamycin, a suppressor of autophagy) phosphorylation, suggesting autophagy induction via mTOR inactivation. Measurement of autophagic flux utilizing the lysosomal inhibitor chloroquine (CQ) showed more pronounced increase in LC3II level in cells co-treated with CP + CQ as compared to CP or CQ alone, suggesting that CP-induced increase in LC3II was due to enhanced autophagosome formation rather than impaired lysosomal clearance. CP infection did not alter ATG7, a key autophagy protein. However, the decrease in occludin, claudin-4 and E-cadherin by CP was partially blocked following siRNA silencing of ATG7, suggesting the role of autophagy in CP-induced decrease in these TJ/AJ proteins. Our results provide novel evidence of autophagy induction by CP in host IECs that could alter important host cell processes contributing to the pathophysiology of cryptosporidiosis.

Anti-protozoal activity of extracts from chicory (Cichorium intybus) against Cryptosporidium parvum in cell culture

Cryptosporidium spp. are responsible for severe public health problems and livestock production losses. Treatment options are limited to only one drug available for human and bovine cryptosporidiosis, respectively, and both drugs exhibit only partial efficacy. Sesquiterpene lactones (SL) are plant bioactive compounds that function as a defence mechanism against herbivores. SL have demonstrated anti-parasitic properties against a range of parasitic taxa but knowledge about their anti-Cryptosporidium efficacy is limited. The effect of SL-rich leaf and root extracts from chicory (Cichorium intybus cv. Spadona) was investigated using human colon adenocarcinoma (HCT-8) cells infected with Cryptosporidium parvum. C. parvum oocysts were inoculated onto the cell monolayer and i) incubated for 4 hours with extracts (leaf and root extracts 300, 150, 75, 37.5, 18.75 and 9.375 μg/mL) in triplicates followed by incubation in bioactive free media (sporozoite invasion assays) or ii) incubated for 4 hours in bioactive free media followed by 48-hours incubation with extracts (growth inhibition assays). Extract toxicity on HCT-8 cells was assessed via water-soluble tetrazolium (WST)-1 assay prior to quantifying parasitic growth via immunofluorescence. Both extracts demonstrated dose-dependent inhibition in the growth inhibition assays (p = < 0.0001 for both extracts) but not in the invasion assays. Anti-parasitic activity did not appear to be solely related to SL content, with the extract with lower SL content (leaf) exhibiting higher inhibition at 300 μg/ml. However, given the limited treatment options available for Cryptosporidium spp., our study encourages further investigation into the use of chicory extracts to identify novel active compound(s) inhibiting these protozoa.

Decreased SLC26A3 expression and function in intestinal epithelial cells in response to Cryptosporidium parvum infection

The protozoan parasite Cryptosporidium parvum (CP) causes cryptosporidiosis, a diarrheal disease worldwide. Infection in immunocompetent hosts typically results in acute, self-limiting, or recurrent diarrhea. However, in immunocompromised individuals infection can cause fulminant diarrhea, extraintestinal manifestations, and death. To date, the mechanisms underlying CP-induced diarrheal pathogenesis are poorly understood. Diarrheal diseases most commonly involve increased secretion and/or decreased absorption of fluid and electrolytes. We and others have previously shown impaired chloride absorption in infectious diarrhea due to dysregulation of SLC26A3 [downregulated in adenoma (DRA)], the human intestinal apical membrane Cl^-/HCO3- exchanger protein. However, there are no studies on the effects of CP infection on DRA activity. Therefore, we examined the expression and function of DRA in intestinal epithelial cells in response to CP infection in vitro and in vivo. CP infection (0.5 × 10⁶ oocysts/well in 24-well plates, 24 h) of Caco-2 cell monolayers significantly decreased Cl^-/HCO3- exchange activity (measured as DIDS-sensitive ¹²⁵I uptake) as well as DRA mRNA and protein levels. Substantial downregulation of DRA mRNA and protein was also observed following CP infection ex vivo in mouse enteroid-derived monolayers and in vivo in the ileal and jejunal mucosa of C57BL/6 mice for 24 h. However, at 48 h after infection in vivo, the effects on DRA mRNA and protein were attenuated and at 5 days after infection DRA returned to normal levels. Our results suggest that impaired chloride absorption due to downregulation of DRA could be one of the contributing factors to CP-induced acute, self-limiting diarrhea in immunocompetent hosts.

Widespread occurrence of Cryptosporidium infections in patients with HIV/AIDS: Epidemiology, clinical feature, diagnosis, and therapy

Cryptosporidium infection is a serious threat for HIV/AIDS patients, causing severe diarrhea and even death. The overall prevalence of Cryptosporidium in HIV/AIDS patients was calculated as approximately 8.69% (7,799/89,724), with higher prevalence observed in individuals with diarrhea, individuals with low CD4⁺ T-lymphocyte counts, and antiretroviral therapy-naïve individuals. Cryptosporidium infection was not significantly associated with patient age or gender, national development levels, or continent of residence. Over the period from 2007 to 2017, Cryptosporidium prevalence was 10.09% (3,282/32,517); this figure was higher than that observed in each of the previous observation periods (1985-1995 and 1996-2006), suggesting that the prevalence of cryptosporidiosis has been increasing over time in HIV/AIDS patients. Ten Cryptosporidium species and genotypes have been identified from 1,252 isolates, with C. hominis, C. parvum, and C. meleagridis accounting for 93.53% of infections. Five subtypes each of C. hominis (Ia, Ib, Id, Ie, and If), C. parvum (IIa to IIe), and C. meleagridis (IIIa to IIIe) have been described by sequence analyses of the 60-kDa glycoprotein (gp60) gene. Variation in the clinical manifestations observed in HIV/AIDS patients might be attributed to infection by different Cryptosporidium species, genotypes and subtypes, as well as different sites of infection. New molecular and immunological diagnostic techniques are in development or already commercially available. High-throughput screening methods for development of new or repurposed therapeutics as well as novel parasite genetic manipulation strategies offer hope for improving human cryptosporidiosis therapies. Painstaking efforts by researchers as well as support from governments and funding agencies will be required to make lasting achievements in this field.

Recent Breakthroughs and Ongoing Limitations in Cryptosporidium Research

The intestinal apicomplexan parasite Cryptosporidium is a major cause of diarrheal disease in humans worldwide. However, treatment options are severely limited. The search for novel interventions is imperative, yet there are several challenges to drug development, including intractability of the parasite and limited technical tools to study it. This review addresses recent, exciting breakthroughs in this field, including novel cell culture models, strategies for genetic manipulation, transcriptomics, and promising new drug candidates. These advances will stimulate the ongoing quest to understand Cryptosporidium and the pathogenesis of cryptosporidiosis and to develop new approaches to combat this disease.

Cryptosporidium parvum disrupts intestinal epithelial barrier function via altering expression of key tight junction and adherens junction proteins

Infection with the protozoan parasite Cryptosporidium parvum (CP) causes cryptosporidiosis, a widespread diarrhoeal disease. Impaired intestinal epithelial barrier function and increased permeability are most commonly associated with diarrhoeal diseases caused by enteric infections. However, studies on barrier disruption and underlying mechanisms in cryptosporidiosis are extremely limited. Epithelial tight junctions (TJs) and adherens junctions (AJs) are important in maintaining barrier integrity. Therefore, we examined the effects of CP infection on paracellular permeability and on the expression of the major TJ and AJ proteins utilising in vitro, ex vivo, and in vivo models. CP infection (0.5 × 106  oocysts/well in Transwell inserts, 24 hr) increased paracellular permeability (FITC-dextran flux) in Caco-2 cell monolayers and substantially decreased the protein levels of occludin, claudin 4, and E-cadherin. Claudin 3, zonula occludens-1 (ZO1) and α-catenin were also significantly decreased, whereas claudins 1 and 2 and β-catenin were not altered. Substantial downregulation of occludin, claudin 4, and E-cadherin was also observed in response to CP infection ex vivo in mouse enteroid-derived monolayers and in vivo in the ileal and jejunal mocosa of C57BL/6 mice. The mRNA levels of these proteins were also significantly decreased in CP-infected mouse ileum and jejunum but were unaltered in Caco-2 cells. Further, bafilomycin-A, an inhibitor of lysosomal proton pump, partially abrogated CP effects on occludin expression in Caco-2 cells, suggesting a potential role of posttranslational mechanisms, such as induction of protein degradation pathways, in mediating the effects of the parasite. Our studies suggest that disruption of barrier function via downregulation of specific key components of TJ and AJ could be a major mechanism underlying CP infection-induced diarrhoea.

The truth about in vitro culture of Cryptosporidium species

Cryptosporidium research has focused on the development of infection control, and effective therapy that has thus far been hampered by the inability to culture Cryptosporidium in vitro. Other limitations include inadequate animal models, cumbersome screening procedures for chemotherapeutic approaches and a lack of tools for genetic manipulation. These limitations can, however, be eased by the improvement and focused development of in vitro cultivation. The ability to culture relevant Cryptosporidium isolates in vitro and to propagate the life cycle stages that are responsible for causing disease in an infected host is still a critical link. This ability will facilitate other relevant approaches, e.g., the ability to knockout genes and the application of broader screening for drug discoveries and vaccine developments, in combination with new discoveries on the parasite's basic biology, genetic manipulation and new life cycle stages. Success in this effort represents an essential step towards significant progress in the control of cryptosporidiosis.