Plant-type trehalose synthetic pathway in cryptosporidium and some other apicomplexans

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.

Dissection of Besnoitia besnoiti intermediate host life cycle stages: From morphology to gene expression

Cyst-forming Apicomplexa (CFA) of the Sarcocystidae have a ubiquitous presence as pathogens of humans and farm animals transmitted through the food chain between hosts with few notable exceptions. The defining hallmark of this family of obligate intracellular protists consists of their ability to remain for very long periods as infectious tissue cysts in chronically infected intermediate hosts. Nevertheless, each closely related species has evolved unique strategies to maintain distinct reservoirs on global scales and ensuring efficient transmission to definitive hosts as well as between intermediate hosts. Here, we present an in-depth comparative mRNA expression analysis of the tachyzoite and bradyzoite stages of Besnoitia besnoiti strain Lisbon14 isolated from an infected farm animal based on its annotated genome sequence. The B. besnoiti genome is highly syntenic with that of other CFA and also retains the capacity to encode a large majority of known and inferred factors essential for completing a sexual cycle in a yet unknown definitive host. This work introduces Besnoitia besnoiti as a new model for comparative biology of coccidian tissue cysts which can be readily obtained in high purity. This model provides a framework for addressing fundamental questions about the evolution of tissue cysts and the biology of this pharmacologically intractable infectious parasite stage.

Evolution and function of carbohydrate reserve biosynthesis in parasitic protists

Nearly all eukaryotic cells synthesize carbohydrate reserves, such as glycogen, starch, or low-molecular-weight oligosaccharides. However, a number of parasitic protists have lost this capacity while others have lost, and subsequently evolved, entirely new pathways. Recent studies suggest that retention, loss, or acquisition of these pathways in different protists is intimately linked to their lifestyle. In particular, parasites with carbohydrate reserves often establish long-lived chronic infections and/or produce environmental cysts, whereas loss of these pathways is associated with parasites that have highly proliferative and metabolically active life-cycle stages. The evolution of mannogen biosynthesis in Leishmania and related parasites indicates that these pathways have played a role in defining the host range and niches occupied by some protists.

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.

Cryopreservation of infectious Cryptosporidium parvum oocysts achieved through vitrification using high aspect ratio specimen containers

Infection with protozoa of the genus Cryptosporidium is a leading cause of child morbidity and mortality associated with diarrhea in the developing world. Research on this parasite has been impeded by many technical limitations, including the lack of cryopreservation methods. While cryopreservation of Cryptosporidium oocysts by vitrification was recently achieved, the method is restricted to small sample volumes, thereby limiting widespread implementation of this procedure. Here, a second-generation method is described for cryopreservation of C. parvum oocysts by vitrification using custom high aspect ratio specimen containers, which enable a 100-fold increase in sample volume compared to previous methods. Oocysts cryopreserved using the described protocol exhibit high viability, maintain in vitro infectivity, and are infectious to interferon-gamma (IFN-γ) knockout mice. Importantly, the course of the infection is comparable to that observed in mice infected with unfrozen oocysts. Vitrification of C. parvum oocysts in larger volumes will expedite progress of research by enabling the sharing of isolates among different laboratories and the standardization of clinical trials.

Molecular docking studies of phytochemicals against trehalose–6–phosphate phosphatases of pathogenic microbes

Background

Many of the pathogenic microbes use trehalose–6–phosphate phosphatase (TPP) enzymes for biosynthesis of sugar trehalose from trehalose–6–phosphate (T6P) in their pathway of infection and proliferation. Therefore, the present work is an approach to design new generation candidate drugs to inhibit TPP through in silico methods.

Results

Blast P and Clustal Omega phylogenetic analysis of TPP sequences were done for 12 organisms that indicate and confirm the presence of three conserved active site regions of known TPPs. Docking studies of 3D model of TPP with 17 phytochemicals revealed most of them have good binding affinity to an enzyme with rutin exhibiting highest affinity (Binding energy of − 7 kcal/mole). It has been found that during docking, phytochemical leads bind to active site region 3 of TPP sequences which coordinates Mg2+ and essential for catalysis.

Conclusions

Binding poses and distance measurement of TPP-phytochemical complexes of rutin, carpaine, stigmasterol, β-caryophyllene, and α-eudesmol reveals that the lead phytochemicals were in close proximity with most of the active site amino acids of region 3 (distance range from 1.796 to 2.747 Ao). This confirms the tight binding between enzyme and leads which may pave way for the discovery of new generation drugs against TPP producing pathogenic microbes to manage diseases.

Invertebrate Trehalose-6-Phosphate Synthase Gene: Genetic Architecture, Biochemistry, Physiological Function, and Potential Applications

The non-reducing disaccharide trehalose is widely distributed among various organisms. It plays a crucial role as an instant source of energy, being the major blood sugar in insects. In addition, it helps countering abiotic stresses. Trehalose synthesis in insects and other invertebrates is thought to occur via the trehalose-6-phosphate synthase (TPS) and trehalose-6-phosphate phosphatase (TPP) pathways. In many insects, the TPP gene has not been identified, whereas multiple TPS genes that encode proteins harboring TPS/OtsA and TPP/OtsB conserved domains have been found and cloned in the same species. The function of the TPS gene in insects and other invertebrates has not been reviewed in depth, and the available information is quite fragmented. The present review discusses the current understanding of the trehalose synthesis pathway, TPS genetic architecture, biochemistry, physiological function, and potential sensitivity to insecticides. We note the variability in the number of TPS genes in different invertebrate species, consider whether trehalose synthesis may rely only on the TPS gene, and discuss the results of in vitro TPS overexpression experiment. Tissue expression profile and developmental characteristics of the TPS gene indicate that it is important in energy production, growth and development, metamorphosis, stress recovery, chitin synthesis, insect flight, and other biological processes. We highlight the molecular and biochemical properties of insect TPS that make it a suitable target of potential pest control inhibitors. The application of trehalose synthesis inhibitors is a promising direction in insect pest control because vertebrates do not synthesize trehalose; therefore, TPS inhibitors would be relatively safe for humans and higher animals, making them ideal insecticidal agents without off-target effects.

Evolution of the Apicomplexan Sugar Transporter Gene Family Repertoire

Apicomplexan protist parasites utilize host sugars transported into the parasite by sugar transporter proteins for use as an energy source. We performed a phylum-wide phylogenetic analysis of the apicomplexan sugar transporter repertoire. Phylogenetic analyses revealed six major subfamilies of apicomplexan sugar transporters. Transporters in one subfamily have undergone expansions in Piroplasma species and Gregarina niphandrodes, while other subfamilies are highly divergent and contain genes found in only one or two species. Analyses of the divergent apicomplexan subfamilies revealed their presence in ciliates, indicating their alveolate ancestry and subsequent loss in chromerids and many apicomplexans.

A unique hexokinase in Cryptosporidium parvum, an apicomplexan pathogen lacking the Krebs cycle and oxidative phosphorylation

Cryptosporidium parvum may cause virtually untreatable infections in AIDS patients, and is recently identified as one of the top four diarrheal pathogens in children in developing countries. Cryptosporidium differs from other apicomplexans (e.g., Plasmodium and Toxoplasma) by lacking many metabolic pathways including the Krebs cycle and cytochrome-based respiratory chain, thus relying mainly on glycolysis for ATP production. Here we report the molecular and biochemical characterizations of a hexokinase in C. parvum (CpHK). Our phylogenetic reconstructions indicated that apicomplexan hexokinases including CpHK were highly divergent from those of humans and animals (i.e., at the base of the eukaryotic clade). CpHK displays unique kinetic features that differ from those in mammals and Toxoplasma gondii (TgHK) in the preference towards various hexoses and its capacity to use ATP and other NTPs. CpHK also displays substrate inhibition by ATP. Moreover, 2-deoxy-D-glucose (2DG) could not only inhibit the CpHK activity, but also the parasite growth in vitro at concentrations nontoxic to host cells (IC(50) = 0.54 mM). While the exact action of 2-deoxy-D-glucose on the parasite is subject to further verification, our data suggest that CpHK and the glycolytic pathway may be explored for developing anti-cryptosporidial therapeutics.

Characterization of biochemical properties of a selenium-independent glutathione peroxidase ofCryptosporidium parvum

Glutathione peroxidase (GPx; EC 1.11.1.9) is an important antioxidant enzyme that catalyses the reduction of organic and inorganic hydroperoxides to water in oxygen-consuming organisms, using glutathione as an electron donor. Here, we report the characterization of a GPx ofCryptosporidium parvum(CpGPx). CpGPx contained a standard UGU codon for cysteine instead of a UGA opal codon for seleno-cysteine (SeCys) at the active site, and no SeCys insertion sequence (SECIS) motif was identified within the 3′-untranslated region (UTR) of CpGPx, which suggested its selenium-independent nature.In silicoand biochemical analyses indicated that CpGPx is a cytosolic protein with a monomeric structure. Recombinant CpGPx was active over a wide pH range and was stable under physiological conditions. It showed a substrate preference against organic hydroperoxides, such as cumene hydroperoxide andt-butyl hydroperoxide, but it also showed activity against inorganic hydroperoxide, hydrogen peroxide. Recombinant CpGPx was not inhibited by potassium cyanide or by sodium azide. The enzyme effectively protected DNA and protein from oxidative damage induced by hydrogen peroxide, and was functionally expressed in various developmental stages ofC. parvum. These results collectively suggest the essential role of CpGPx for the parasite's antioxidant defence system.

Transcriptome analysis reveals unique metabolic features in the Cryptosporidium parvum Oocysts associated with environmental survival and stresses

Background

Cryptosporidium parvum is a globally distributed zoonotic parasite and an important opportunistic pathogen in immunocompromised patients. Little is known on the metabolic dynamics of the parasite, and study is hampered by the lack of molecular and genetic tools. Here we report the development of the first Agilent microarray for C. parvum (CpArray15K) that covers all predicted ORFs in the parasite genome. Global transcriptome analysis using CpArray15K coupled with real-time qRT-PCR uncovered a number of unique metabolic features in oocysts, the infectious and environmental stage of the parasite.

Results

Oocyst stage parasites were found to be highly active in protein synthesis, based on the high transcript levels of genes associated with ribosome biogenesis, transcription and translation. The proteasome and ubiquitin associated components were also highly active, implying that oocysts might employ protein degradation pathways to recycle amino acids in order to overcome the inability to synthesize amino acids de novo. Energy metabolism in oocysts was featured by the highest level of expression of lactate dehydrogenase (LDH) gene. We also studied parasite responses to UV-irradiation, and observed complex and dynamic regulations of gene expression. Notable changes included increased transcript levels of genes involved in DNA repair and intracellular trafficking. Among the stress-related genes, TCP-1 family members and some thioredoxin-associated genes appear to play more important roles in the recovery of UV-induced damages in the oocysts. Our observations also suggest that UV irradiation of oocysts results in increased activities in cytoskeletal rearrangement and intracellular membrane trafficking.

Conclusions

CpArray15K is the first microarray chip developed for C. parvum, which provides the Cryptosporidium research community a needed tool to study the parasite transcriptome and functional genomics. CpArray15K has been successfully used in profiling the gene expressions in the parasite oocysts as well as their responses to UV-irradiation. These observations shed light on how the parasite oocysts might adapt and respond to the hostile external environment and associated stress such as UV irradiation.

Foodborne cryptosporidiosis: is there really more in Nordic countries?

Most waterborne outbreaks of cryptosporidiosis are reported from the USA, and in Europe from the UK. However, since 2000 reports of foodborne cryptosporidiosis seem to be skewed towards Nordic countries, although consumers in these countries are apparently less concerned about microbiological contamination of food than consumers elsewhere. Possible reasons for this unexpected geographical distribution might include prolonged survival of oocysts in the Nordic climate, greater exposure due to elevated consumption of higher-risk products (possibly including imported foods), and better outbreak investigation and reporting. Although the risk of foodborne cryptosporidiosis is probably underestimated globally, we suggest that the next outbreak is no more likely to be in a Nordic country than anywhere else.

Trehalose-6-phosphate synthase from the cat flea Ctenocephalides felis and Drosophila melanogaster: gene identification, cloning, heterologous functional expression and identification of inhibitors by high throughput screening

Trehalose phosphate synthase (EC 2.4.1.15; TPS) is the crucial enzyme for the biosynthesis of trehalose, the main haemolymph sugar of insects, and therefore a potential insecticidal molecular target. In this study, we report the functional heterologous expression of Drosophila melanogaster TPS, the gene identification, full length cDNA cloning and functional expression of cat flea (Ctenocephalides felis) TPS, and the Michaelis-Menten constants for their specific substrates glucose-6-phosphate and uridinediphosphate-glucose. A novel high throughput screening-compatible TPS assay and its use for the identification of the first potent insect TPS inhibitors from a large synthetic compound collection (>115 000 compounds) is described. One compound class that emerged in this screening, the 4-substituted 2,6-diamino-3,5-dicyano-4H-thiopyrans, was further investigated by analysing preliminary structure-activity relationships. Here, compounds were identified that show low µM to high nM half maximal inhibitory concentrations on insect TPS and that may serve as lead compounds for the development of insecticides with a novel mode of action.