Cryptosporidium parvum Pyruvate Kinase Inhibitors With in vivo Anti-cryptosporidial Efficacy

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.

Anti-Cryptosporidial Drug-Discovery Challenges and Existing Therapeutic Avenues: A "One-Health" Concern

Cryptosporidiosis is the leading cause of life-threatening diarrheal infection, especially in infants. Oocysts contaminate the environment, and also, being a zoonotic disease, cryptosporidiosis is a threat to One Health. Nitazoxanide is the only FDA-approved drug, effective only in immunocompetent adults, and is not safe for infants. The absence of mitochondria and apicoplast, the presence of an electron-dense band (ED band), hindrances in its genetic and phenotypic manipulations, and its unique position inside the host cell are some challenges to the anti-cryptosporidial drug-discovery process. However, many compounds, including herbal products, have shown efficacy against Cryptosporidium during in vitro and in vivo trials. Still, the "drug of choice" against this protozoan parasite, especially in immunocompromised individuals and infants, has not yet been explored. The One-Health approach addresses this issue, focusing on the intersection of animal, human, and environmental health. The objective of this review is to provide knowledge about novel anti-cryptosporidial drug targets, available treatment options with associated limitations, and possible future shifts toward natural products to treat cryptosporidiosis. The current review is organized to address the treatment and prevention of cryptosporidiosis. An anti-cryptosporidial drug that is effective in immunocompromised individuals and infants is a necessity of our time.

MiR-4521 affects the propagation of Cryptosporidium parvum in HCT-8 cells through targeting foxm1 by regulating cell apoptosis

Cryptosporidium parvum could regulate the expression of microRNAs of epithelial cells to facilitate its intracellular propagation. MiR-4521 has been reported to play an important role during the development and progression of tumors and infectious diseases by regulating cell proliferation, apoptosis, and autophagy. However, the implication of miR-4521 during C. parvum infection was still unknown. In this study, the expression of miR-4521 was found to be upregulated in HCT-8 cells infected with C. parvum from 8 h post-infection (pi) to 48 hpi, and its upregulation would be related with the TLR/NF-κB signal pathway during C. parvum infection. One potential target of miR-4521, foxm1, was down-regulated in HCT-8 cells from 24 hpi to 48 hpi, and the expression of foxm1 was negatively regulated by miR-4521. The target relationship between miR-4521 and foxm1 was further validated by using dual luciferase reporter assay. Further studies showed that miR-4521 promoted the propagation of C. parvum in HCT-8 cells through targeting foxm1 by regulating BCL2-mediating cell apoptosis. These results contribute to further understanding of the regulatory mechanisms of host miRNAs during Cryptosporidium infection.

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.

Anti-Cryptosporidium parvum activity of Artemisia judaica L. and its fractions: in vitro and in vivo assays

Background

This study investigates the toxic activity of Artemisia judaica ethanolic extract (ArEx) as well as its phenolic fraction (ArPh), and terpenoid fraction (ArT) against Cryptosporidium parvum (C. parvum) oocysts.

Methods

Over a 4 months period, estimation of the total phenolic (TPC), total flavonoids (TFC), and total terpenoids contents (TTC) in ArEx; investigation of the in vitro antioxidant activity of ArEx, ArPh, and ArT; evaluation of ArEx, ArPh, and ArT toxic activity against C. parvum oocysts using MTT assay; parasitological analysis on ArPh-treated C. parvum oocysts and comet assay were performed both in vitro and in vivo (infectivity).

Results

The ArEx TPC, TFC, and TTC was 52.6 ± 3.1 mgGAE/g, 64.5 ± 3.1 mg QE/g, and 9.5 ± 1.1 mg Linol/g, respectively. Regarding the phytochemical in vitro antioxidant activity, the ArPh exhibited the highest antioxidant activity compared to the ArEx and ArT. The ArPh showed promising free radical scavenging activity of DPPH and ABTS^•+ with IC₅₀ values of 47.27 ± 1.86 μg/mL and 66.89 ± 1.94 μg/mL, respectively. Moreover, the FRAP of ArPh was 2.97 ± 0.65 mMol Fe⁺²/g while its TAC was 46.23 ± 3.15 mg GAE/g. The ArPh demonstrated toxic activity against C. parvum oocysts with a potent IC₅₀ value of 31.6 μg/mL compared to ArT (promising) and ArEx (non-effective). ArPh parasitological analysis demonstrated MIC₉₀ at 1000 μg/ml and effective oocysts destruction on count and morphology. ArPh fragmented oocysts nuclear DNA in comet assay. Beginning at 200 μg/mL, ArPh-treated oocysts did not infect mice.

Conclusion

To combat C. parvum infection, the phenolic fraction of A. judaica L. shows promise as an adjuvant therapy or as a source of potentially useful lead structures for drug discovery.

Microbiome-Metabolomics Analysis of the Impacts of Cryptosporidium muris Infection in BALB/C Mice

Cryptosporidium is a leading cause of diarrheal disease and mortality in young children worldwide. Cryptosporidium invades small intestinal epithelial cells and forms a unique intracellular niche, a process that may alter gut microbes and their production metabolites. However, the mechanism of interactions between gut microbes, metabolites, and parasites is poorly understood. Here, we first characterized the impacts of Cryptosporidium infection on gut microbiota using a microbiome-to-metabolome association study. BALB/c mice were gavaged with Cryptosporidium muris, and fecal samples were collected at 0, 7, 14, 21, and 28 days postinfection (dpi) to observe changes in the intestinal microbes of the body during parasite infection. The infected group had a significantly increased relative abundance of bacterial taxa, such as Lachnospiraceae and Prevotella (P < 0.05), associated with the biosynthesis of short-chain fatty acids (SCFAs). Metabolites related to the metabolic pathways, steroid hormone biosynthesis, and biosynthesis of unsaturated fatty acids pathway were upregulated at 7 dpi, indicating that related metabolites in the biosynthesis of unsaturated fatty acids may be essential for C. muris reproduction in vivo. The metabolites involved in metabolic pathways, bile secretion, and primary bile acid biosynthesis were upregulated at 14 dpi, and we speculate that these metabolites may be critical to the growth and development of Cryptosporidium oocysts in the host. Correlation analysis revealed that Firmicutes bacteria are significantly associated with α-linolenic acid metabolism pathways (P< 0.05). The gut microbiota changes dynamically, and the metabolites involved in fatty acid and bile acid biosynthesis may play important roles during cryptosporidiosis. Details of the gut microbiota and the metabolome after infection with Cryptosporidium may aid in the discovery of specific diagnostic markers and help us understand the changes in parasite metabolic pathways. IMPORTANCE Cryptosporidiosis is a gastrointestinal disease in humans and animals caused by the protozoan parasite Cryptosporidium. Control and treatment of the disease is challenging due to the lack of sensitive diagnostic tools and effective chemotherapy. The dynamics of gut microbiota and metabolites during Cryptosporidium infection may be the key to finding drugs and targets for parasite infection control. Our results indicate that C. muris infection can disrupt gut microbiota and metabolites, resulting in decreased bacterial abundance at the parasitic site. Unsaturated fatty acid pathway biosynthesis-related metabolites are significantly elevated at the patent period. Interestingly, the metabolite pathway that significantly elevated during peak parasite growth was bile acid, the metabolites of which may be important for the circulation of infection of Cryptosporidium oocysts in the host. The enhancing effects of short-chain fatty acid and bile acid metabolism on the growth and development of Cryptosporidium proposed in this study may provide a theoretical basis for future research on novel drugs and vaccines against this intestinal parasite.

Past, current, and potential treatments for cryptosporidiosis in humans and farm animals: A comprehensive review

The intracellular protozoan parasite of the genus Cryptosporidium is among the leading causes of waterborne diarrheal disease outbreaks throughout the world. The parasite is transmitted by ingestion of infective oocysts that are highly stable in the environment and resistant to almost all conventional disinfection methods and water treatments. Control of the parasite infection is exceedingly difficult due to the excretion of large numbers of oocysts in the feces of infected individuals that contaminate the environment and serve as a source of infection for susceptible hosts including humans and animals. Drug development against the parasite is challenging owing to its limited genetic tractability, absence of conventional drug targets, unique intracellular location within the host, and the paucity of robust cell culture platforms for continuous parasite propagation. Despite the high prevalence of the parasite, the only US Food and Drug Administration (FDA)-approved treatment of Cryptosporidium infections is nitazoxanide, which has shown moderate efficacy in immunocompetent patients. More importantly, no effective therapeutic drugs are available for treating severe, potentially life-threatening cryptosporidiosis in immunodeficient patients, young children, and neonatal livestock. Thus, safe, inexpensive, and efficacious drugs are urgently required to reduce the ever-increasing global cryptosporidiosis burden especially in low-resource countries. Several compounds have been tested for both in vitro and in vivo efficacy against the disease. However, to date, only a few experimental compounds have been subjected to clinical trials in natural hosts, and among those none have proven efficacious. This review provides an overview of the past and present anti-Cryptosporidium pharmacotherapy in humans and agricultural animals. Herein, we also highlight the progress made in the field over the last few years and discuss the different strategies employed for discovery and development of effective prospective treatments for cryptosporidiosis.

Characterization of a novel pyruvate kinase from Trichinella spiralis and its participation in sugar metabolism, larval molting and development

Background

Pyruvate kinase widely exists in many parasites and plays an important role in the energy production for the parasites. Pyruvate kinase might be a potential drug target for killing the parasites. The aim of the present study was to evaluate the biological characteristics and roles of T. spiralis pyruvate kinase M (TsPKM) in sugar metabolism, larval molting and development of T. spiralis.

Methodology/Principal findings

TsPKM has two functional domains of pyruvate kinase and the tertiary structure of TsPKM is tetramer which has the enzyme active site constituted by 8 amino-acid residues (Arg71, Asn73, Asp110, Phe241, Lys267, Glu269, Asp293 and Thr325). Recombinant TsPKM (rTsPKM) was expressed and purified. The rTsPKM had good immunogenicity. RT-PCR and Western blot showed that TsPKM was transcribed and expressed at various developmental stages in T. spiralis lifecycle. Immunofluorescence test showed that TsPKM was principally located in the cuticle, muscle, stichosome, intestine and the intrauterine embryos of female adults. rTsPKM catalyzed the reaction of phosphoenolpyruvate (PEP) and adenosine diphosphate (ADP) to produce pyruvic acid and adenosine triphosphate (ATP). TsPKM played an important role in the metabolism and energy production of T. spiralis. After silencing of TsPKM gene by specific dsRNA-TsPKM2, protein expression and enzyme activity of TsPKM decreased by 50.91 and 26.06%, respectively. After treatment with RNAi, natural TsPKM enzyme activity, larval molting, sugar metabolism, growth and development of T. spiralis were significantly reduced.

Conclusions

TsPKM participates in the larval molting, sugar metabolism, growth and development of T. spiralis and it might be a candidate target of therapeutic drug of trichinellosis.

Pyruvate kinases belong to transferases and can transfer the high-energy phosphate bond of phosphoenolpyruvate (PEP) to adenosine diphosphate (ADP) to produce pyruvic acid and adenosine triphosphate (ATP). Pyruvate kinases play a significant biological role in the parasite survival in hosts. Our results revealed that TsPKM was expressed at various T. spiralis developmental stages, and principally located in the cuticle, stichosome, intestine and the intrauterine embryos of female adults. rTsPKM catalyzed the reaction of phosphoenolpyruvate (PEP) and adenosine diphosphate (ADP) to produce pyruvic acid and adenosine triphosphate (ATP). TsPKM played an important role in the metabolism and energy production of T. spiralis. Protein expression and enzyme activity of TsPKM were decreased by 50.91 and 26.06% respectively through silencing of TsPKM gene using specific dsRNA-TsPKM2. After treatment with RNAi and inhibitor tannin, natural TsPKM activity, larval molting, sugar metabolism, growth and development of T. spiralis were obviously inhibited. Our results showed that TsPKM participates in T. spiralis molting, sugar metabolism and development, and it might be a candidate target for anti-Trichinella drugs.