Forty years of helminth biochemistry

Proteomic analysis of the excretory-secretory products from Strongyloides venezuelensis infective larvae: new insights for the immunodiagnosis of human strongyloidiasis

Serodiagnosis of human strongyloidiasis is a practical alternative to parasitological methods due to its high sensitivity. However, cross-reactivity with other helminth infections limits its utility, and this problem is due to the use of homologous or heterologous somatic extracts of the parasite as an antigen source. Excretory-secretory (E/S) products from Strongyloides infective larvae can be used to improve the serodiagnosis. The combined use of western blot and proteomics became an interesting strategy to identify immunological markers for the serodiagnosis of strongyloidiasis. The present study describes the proteomic analysis of the antigenic components from E/S products of S. venezuelensis infective larvae that were recognized by IgG antibodies from patients with strongyloidiasis. Our results showed that IgG antibodies from patients with strongyloidiasis recognized between 15 and 16 antigenic bands in the E/S products from S. venezuelensis that were incubated in PBS or in RPMI culture medium, respectively. Overall, antigenic bands of low and high molecular weight were more specific than those of intermediate molecular weight, which were cross-reactive. A 36-kDa antigenic band was 93% sensitive and 100% specific (a probably arginine kinase of 37 kDa), while other antigenic bands were highly sensitive but low specific. Proteomic analysis revealed differences between the protein profiles from E/S-RPMI and E/S-PBS since only one-third of all proteins identified were common in both types of E/S products. Bioinformatic analysis showed that more than 50% of the proteins from E/S products are secreted within extracellular vesicles and only a small percentage of them are actually released by the classical secretory pathway. Several components from the E/S products were identified as plasminogen-binding proteins, probably used as an immune evasion mechanism. The data provided here provide valuable information to increase understanding of E/S products from S. venezuelensis infective larvae. This may help us to find new targets for the immunodiagnosis of human strongyloidiasis.

Function of lipid binding proteins of parasitic helminths: still a long road

Infections with parasitic helminths cause severe debilitating and sometimes lethal diseases in humans and domestic animals on a global scale. Unable to synthesize de novo their own fatty acids and sterols, helminth parasites (nematodes, trematodes, cestodes) rely on their hosts for their supply. These organisms produce and secrete a wide range of lipid binding proteins that are, in most cases, structurally different from the ones found in their hosts, placing them as possible novel therapeutic targets. In this sense, a lot of effort has been made towards the structure determination of these proteins, but their precise function is still unknown. In this review, we aim to present the current knowledge on the functions of LBPs present in parasitic helminths as well as novel members of this highly heterogeneous group of proteins.

Sterol profile of Neobenedenia melleni, a marine ectoparasite fish

Neobenedenia melleni, a marine fish ectoparasite, is responsible for considerable losses in the mariculture industry. In maintaining the parasite's homeostasis, sterols are structural and functional lipids that perform vital functions. Thus, understanding the mechanisms of biosynthesis and the uptake of sterols can reveal potential pharmacological targets. The objective of this work was thereby to characterize the N. melleni sterols. The most abundant sterol found was cholesterol in either its free (47.48 ± 15.93 %) or esterified form. However, its precursors, squalene (3.53 ± 0.92 %) and desmosterol (0.25 ± 0.03 %), were also found, suggesting the uptake of these intermediates from hosts or an unusual active pathway of sterol biosynthesis, which can be further explored as pharmacological targets.

Genus-level evolutionary relationships of FAR proteins reflect the diversity of lifestyles of free-living and parasitic nematodes

Background

Nematodes are a widespread and diverse group comprising free-living and parasitic species, some of which have major detrimental effects on crops, animals, and human health. Genomic comparisons of nematodes may help reveal the genetic bases for the evolution of parasitic lifestyles. Fatty acid and retinol-binding proteins (FARs) are thought to be unique to nematodes and play essential roles in their development, reproduction, infection, and possibly parasitism through promoting the uptake, transport, and distribution of lipid and retinol. However, the evolution of FAR family proteins across the phylum Nematoda remains elusive.

Results

We report here the evolutionary relationship of the FAR gene family across nematodes. No FAR was found in Trichocephalida species and Romanomermis culicivorax from Clade I, and FAR could be found in species from Clades III, IV, and V. FAR proteins are conserved in Clade III species and separated into three clusters. Tandem duplications and high divergence events lead to variable richness and low homology of FARs in Steinernema of Clade IVa, Strongyloides of Clade IVb, and intestinal parasitic nematodes from Clades Vc and Ve. Moreover, different richness and sequence variations of FARs in pine wood, root-knot, stem, and cyst nematodes might be determined by reproduction mode or parasitism. However, murine lungworm Angiostrongylus and bovine lungworm Dictyocaulus viviparus from Clade Vd have only 3–4 orthologs of FAR. RNA-seq data showed that far genes, especially far-1 and far-2, were highly expressed in most nematodes. Angiostrongylus cantonensis FAR-1 and FAR-3 have low sequence homology and distinct ligand-binding properties, leading to differences in the cavity volume of proteins. These data indicate that FAR proteins diverged early and experienced low selective pressure to form genus-level diversity. The far genes are present in endophyte or root-colonized bacteria of Streptomyces, Kitasatospora sp., Bacillus subtilis, and Lysobacter, suggesting that bacterial far genes might be derived from plant-parasitic nematodes by horizontal gene transfer.

Conclusions

Data from these comparative analyses have provided insights into genus-level diversity of FAR proteins in the phylum Nematoda. FAR diversification provides a glimpse into the complicated evolution history across free-living and parasitic nematodes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-021-01111-3.

Evidence of Immune Modulators in the Secretome of the Equine Tapeworm Anoplocephala perfoliata

Anoplocephala perfoliata is a neglected gastro-intestinal tapeworm, commonly infecting horses worldwide. Molecular investigation of A. perfoliata is hampered by a lack of tools to better understand the host-parasite interface. This interface is likely influenced by parasite derived immune modulators released in the secretome as free proteins or components of extracellular vesicles (EVs). Therefore, adult RNA was sequenced and de novo assembled to generate the first A. perfoliata transcriptome. In addition, excretory secretory products (ESP) from adult A. perfoliata were collected and EVs isolated using size exclusion chromatography, prior to proteomic analysis of the EVs, the EV surface and EV depleted ESP. Transcriptome analysis revealed 454 sequences homologous to known helminth immune modulators including two novel Sigma class GSTs, five α-HSP90s, and three α-enolases with isoforms of all three observed within the proteomic analysis of the secretome. Furthermore, secretome proteomics identified common helminth proteins across each sample with known EV markers, such as annexins and tetraspanins, observed in EV fractions. Importantly, 49 of the 454 putative immune modulators were identified across the secretome proteomics contained within and on the surface of EVs in addition to those identified in free ESP. This work provides the molecular tools for A. perfoliata to reveal key players in the host-parasite interaction within the horse host.

A Whole Genome Re-Sequencing Based GWA Analysis Reveals Candidate Genes Associated with Ivermectin Resistance in Haemonchus contortus

The most important and broad-spectrum drug used to control the parasitic worms to date is ivermectin (IVM). Resistance against IVM has emerged in parasites, and preserving its efficacy is now becoming a serious issue. The parasitic nematode Haemonchus contortus (Rudolphi, 1803) is economically an important parasite of small ruminants across the globe, which has a successful track record in IVM resistance. There are growing evidences regarding the multigenic nature of IVM resistance, and although some genes have been proposed as candidates of IVM resistance using lower magnification of genome, the genetic basis of IVM resistance still remains poorly resolved. Using the full magnification of genome, we herein applied a population genomics approach to characterize genome-wide signatures of selection among pooled worms from two susceptible and six ivermectin-resistant isolates of H. contortus, and revealed candidate genes under selection in relation to IVM resistance. These candidates also included a previously known IVM-resistance-associated candidate gene HCON_00148840, glc-3. Finally, an RNA-interference-based functional validation assay revealed the HCON_00143950 as IVM-tolerance-associated gene in H. contortus. The possible role of this gene in IVM resistance could be detoxification of xenobiotic in phase I of xenobiotic metabolism. The results of this study further enhance our understanding on the IVM resistance and continue to provide further evidence in favor of multigenic nature of IVM resistance.

Polycyclic aromatic hydrocarbons in the cestode Oncomegas wageneri parasite of Mexican flounder Cyclopsetta chittendeni

The concentrations of polycyclic aromatic hydrocarbon metabolites (PAHm) and their bioconcentration factors (BCF) were determined in the larval stages of the cestode Oncomegas wageneri, recovered from the intestine of the Mexican flounder Cyclopsetta chittendeni, in the southern Gulf of Mexico. The PAHm concentrations in O. wageneri were measured using fixed-wavelength fluorescence spectrometry and compared with PAHm concentrations in host bile. Oncomegas wageneri PAHm concentrations were markedly higher than those in host tissues. The highest BCF values were obtained for 1-hydroxypyrene (OHP) and benzo(a)pyrene (BaP). Using a General Linear Model, a significant negative relationship was found between O. wageneri PAHm concentrations (as response variable) and the number of O. wageneri and oil well proximity. Low BCF values and PAHm concentrations in C. chittendeni correlated positively with O. wageneri PAHm concentrations. In contrast, high BCF values for PAHm concentrations in C. chittendeni had a negative association with O. wageneri PAHm concentrations. This study provides the first evidence of the presence of PAHm in intestinal larval cestodes of marine flatfishes, demonstrating levels of PAHm that were higher than levels in their hosts.

The effect of Triaenophorus nodulosus (Cestoda: Bothriocephalidea) infection on some biochemical parameters of the liver of Perca fluviatilis

Natural infection of 2 to 6-year-old perch with the cestode parasites Triaenophorus nodulosus was shown to have minor effects on the studied components of the antioxidant defense system, nucleic acids degradation, and carbohydrate metabolism enzymes in the liver of the fish. The level of infection of 1-4 parasite larvae per fish observed in wild population of perch was shown to be moderate in terms of its effect on the health of the host fish. The activity of hepatic enzymes β-galactosidase, β-glucosidase, cathepsin D, and glutathione S-transferase showed different responses in infected males and females, which indicates different potential resistance of fish to the stress exposure between genders.

Fatty Acid and Retinol-Binding Protein: Unusual Protein Conformational and Cavity Changes Dictated by Ligand Fluctuations

Lipid-binding proteins (LBPs) are soluble proteins responsible for the uptake, transport, and storage of a large variety of hydrophobic lipophilic molecules including fatty acids, steroids, and other lipids in the cellular environment. Among the LBPs, fatty acid binding proteins (FABPs) present preferential binding affinities for long-chain fatty acids. While most of FABPs in vertebrates and invertebrates present similar β-barrel structures with ligands accommodated in their central cavity, parasitic nematode worms exhibit additional unusual α-helix rich fatty acid- and retinol-binding proteins (FAR). Herein, we report the comparison of extended molecular dynamics (MD) simulations performed on the ligand-free and palmitic acid-bond states of the Necator americanus FAR-1 (Na-FAR-1) with respect to other classical β-barrel FABPs. Principal component analysis (PCA) has been used to identify the different conformations adopted by each system during MD simulations. The α-helix fold encompasses a complex internal ligand-binding cavity with a remarkable conformational plasticity that allows reversible switching between distinct states in the holo-Na-FAR-1. The cavity can change up to one-third of its size affected by conformational changes of the protein-ligand complex. Besides, the ligand inside the cavity is not fixed but experiences large conformational changes between bent and stretched conformations. These changes in the ligand conformation follow changes in the cavity size dictated by the transient protein conformation. On the contrary, protein-ligand complex in β-barrel FABPs fluctuates around a unique conformation. The significantly more flexible holo-Na-FAR-1 ligand-cavity explains its larger ligand multiplicity respect to β-barrel FABPs.

Schistosome infection and its effect on pulmonary circulation

Schistosomiasis is the most common parasitic disease associated with pulmonary hypertension. It induces remodelling via complex inflammatory processes, which eventually produce the clinical manifestation of pulmonary hypertension. The pulmonary hypertension shows clinical signs and symptoms that are not distinguishable from other forms of pulmonary arterial hypertension.

Comparative proteomics of the larval and adult stages of the model cestode parasite Mesocestoides corti

Mesocestoides corti is a widely used model for the study of cestode biology, and its transition from the larval tetrathyridium (TT) stage to the strobilated, adult worm (ST) stage can be induced and followed in vitro. Here, a proteomic approach was used to describe and compare M. corti TT and ST protein repertories. Overall, 571 proteins were identified, 238 proteins in TT samples and 333 proteins in ST samples. Among the identified proteins, 207 proteins were shared by TTs and STs, while 157 were stage-specific, being 31 exclusive from TTs, and 126 from STs. Functional annotation revealed fundamental metabolic differences between the TT and the ST stages. TTs perform functions related mainly to basic metabolism, responsible for growth and vegetative development by asexual reproduction. STs, in contrast, perform a wider range of functions, including macromolecule biosynthetic processes, gene expression and control pathways, which may be associated to its proglottization/segmentation, sexual differentiation and more complex physiology. Furthermore, the generated results provided an extensive list of cestode proteins of interest for functional studies in M. corti. Many of these proteins are novel candidate diagnostic antigens, and/or potential targets for the development of new and more effective antihelminthic drugs.

BIOLOGICAL SIGNIFICANCE

Cestodiases are parasitic diseases with serious impact on human and animal health. Efforts to develop more effective strategies for diagnosis, treatment or control of cestodiases are impaired by the still limited knowledge on many aspects of cestode biology, including the complex developmental processes that occur in the life cycles of these parasites. Mesocestoides corti is a good experimental model to study the transition from the larval to the adult stage, called strobilation, which occur in typical cestode life-cycles. The performed proteomics approach provided large-scale identification and quantification of M. corti proteins. Many stage-specific or differentially expressed proteins were detected in the larval tetrathyridium (TT) stage and in the strobilated, adult worm (ST) stage. Functional comparative analyses of the described protein repertoires shed light on function and processes associated to specific features of both stages, such as less differentiation and asexual reproduction in TTs, and proglottization/segmentation and sexual differentiation in ST. Moreover, many of the identified stage-specific proteins are useful as cestode developmental markers, and are potential targets for development of novel diagnostic methods and therapeutic drugs for cestodiases.

A benzimidazole derivative (RCB15) in vitro induces the alternative energetic metabolism and glycolysis in Taenia crassiceps cysticerci

The emergence of resistance to albendazole has encouraged the search for effective alternatives for cysticercosis and other parasitosis treatment. RCB15 is a benzimidazole derivative that may be used against such diseases. The aim of this study was to determine the in vitro effect of RCB15 on the alternative energetic pathways of Taenia crassiceps cysticerci. The cysticerci were in vitro exposed to albendazole sulphoxide (ABZSO) or RCB15 at different concentrations during 24h. The cysticerci extract and the culture medium were analyzed through spectrophotometry and high performance liquid chromatography as to detect glucose, urea, creatinine and organic acids of the energetic metabolism. The drugs did not influence the protein catabolism. Fatty acids oxidation was enhanced through significantly higher acetate concentrations in the groups treated with RCB15 and ABZSO. Beta-hydroxybutyrate concentrations were decreased which indicates the use of fatty acids towards acetyl-CoA synthesis. There was a decrease in glucose uptake and pyruvate concentrations. The absence of lactate indicates the use of pyruvate in gluconeogenesis. Therefore it is possible to conclude that RCB15 enhanced the alternative energetic pathways of cysticerci in vitro exposed to different concentration, with emphasis on the fatty acids catabolism.

The Role of Xenobiotic-Metabolizing Enzymes in Anthelmintic Deactivation and Resistance in Helminths

Xenobiotic-metabolizing enzymes (XMEs) modulate the biological activity and behavior of many drugs, including anthelmintics. The effects of anthelmintics can often be abolished by XMEs when the drugs are metabolized to an inefficient compound. XMEs therefore play a significant role in anthelmintic efficacy. Moreover, differences in XMEs between helminths are reflected by differences in anthelmintic metabolism between target species. Taking advantage of the newly sequenced genomes of many helminth species, progress in this field has been remarkable. The present review collects up to date information regarding the most important XMEs (phase I and phase II biotransformation enzymes; efflux transporters) in helminths. The participation of these XMEs in anthelmintic metabolism and their possible roles in drug resistance are evaluated.

α-Viniferin and resveratrol induced alteration in the activities of some energy metabolism related enzymes in the cestode parasite Raillietina echinobothrida

α-Viniferin (AVF) and its monomer resveratrol (RESV) are natural phytostilbenes produced by several plants in response to injury or under the influence of pathogens such as bacteria or fungi. Our earlier studies have revealed that both the compounds exert anthelmintic activity through alterations of cestode tegument and its associated enzymes. The present study investigates the effects of these phytochemicals on some energy metabolism related enzymes in the fowl tapeworm, Raillietina echinobothrida. The phytostilbenes AVF, RESV and the reference drug praziquantel (PZQ) were tested against some selected enzymes i.e., phosphoenolpyruvate carboxykinase (PEPCK), lactate dehydrogenase (LDH) and malate dehydrogenase (MDH) of R. echinobothrida. Exposure of the tapeworm to AVF, RESV and PZQ causes reduction in activity of PEPCK to the extent of 40.57/41.96, 24.58/23.75 and 41.11/13.47%, respectively, and LDH up to 48.95/16.25, 38.31/38.42 and 45.67/41.87%, respectively, at the time of paralysis. Whereas activity of MDH decreased by 34.22/37.7, 39.1/35.24 and 28.83/19.26%, respectively. Decrease in activities of LDH and MDH was also visible through histochemical observations. The results suggest that both the phytochemicals interfere with the energy transducing pathways by inhibiting the studied energy metabolism related enzymes of the parasite.

Alternative energy production pathways in Taenia crassiceps cysticerci in vitro exposed to a benzimidazole derivative (RCB20)

Biochemical studies of benzimidazole derivatives are important to determine their mode of action and activity against parasites. The lack of antihelminthic alternatives to treat parasitic infections and albendazole resistance cases make the search for new antiparasitary drugs of utmost importance. The 6-chloro-5-(1-naphthyloxy)-2-(trifluoromethyl)-1H-benzimidazole (RCB20) is a benzimidazole derivative with promising effect. This study evaluated the effect of different concentrations of RCB20 in the alternative energetic pathway of in vitro Taenia crassiceps cysticerci. The parasites were in vitro exposed to 6·5 and 13 µm of RCB20 and albendazole sulfoxide (ABZSO). The quantification of acetate, acetoacetate, β-hydroxybutyrate, fumarate and propionate was performed by high-performance liquid chromatography. The quantification of urea, creatinine and total proteins was performed by spectrophotometry. The increase in β-hydroxybutyrate reflects the enhancement of the fatty acid oxidation in the treated groups. Volatile fatty acids secretion, acetate and propionate, was increased in the treated groups. The secretion mechanisms of the treated parasites were impaired due to organic acids increased concentrations in the cysticerci. It is possible to conclude that the metabolic effect on alternative energetic pathways is slightly increased in the parasites treated with RCB20 than the ones treated with ABZSO.

Identification of Newly Synthesized Proteins by Echinococcus granulosus Protoscoleces upon Induction of Strobilation

Background

The proteins responsible for the key molecular events leading to the structural changes between the developmental stages of Echinococcus granulosus remain unknown. In this work, azidohomoalanine (AHA)-specific labeling was used to identify proteins expressed by E. granulosus protoscoleces (PSCs) upon the induction of strobilar development.

Methodology/Principal Findings

The in vitro incorporation of AHA with different tags into newly synthesized proteins (NSPs) by PSCs was analyzed using SDS-PAGE and confocal microscopy. The LC-MS/MS analysis of AHA-labeled NSPs by PSCs undergoing strobilation allowed for the identification of 365 proteins, of which 75 were differentially expressed in comparison between the presence or absence of strobilation stimuli and 51 were expressed exclusively in either condition. These proteins were mainly involved in metabolic, regulatory and signaling processes.

Conclusions/Significance

After the controlled-labeling of proteins during the induction of strobilar development, we identified modifications in protein expression. The changes in the metabolism and the activation of control and signaling pathways may be important for the correct parasite development and be target for further studies.

In the life cycle of the parasite Echinococcus granulosus, hydatid cysts produce the pre-adult form, which has the ability to either differentiate into an adult worm (strobilation) or dedifferentiate into a secondary hydatid cyst. We used different protein tags that allowed for the visualization and purification of proteins produced specifically after the induction of strobilar development to identify proteins that might be involved in this process (temporally controlled and context-dependent). As a result, we found proteins that are involved in important processes during development, such as energy metabolism, control pathways and cellular communication. We believe that these results will be useful for the development of scientific approaches to controlling and preventing cystic hydatid disease.

The metabolic control of schistosome egg production

Schistosomiasis is a neglected tropical disease caused by infection with trematode parasites of the genus Schistosoma. Despite ongoing treatment programmes, the prevalence of schistosomiasis has failed to decline and the disease remains a cause of severe morbidity in millions of people. Understanding the biology of egg production by schistosomes is critical since eggs allow transmission of the infection, and when trapped in host tissues induce the immune responses that are responsible for the pathologic changes that underlie disease development. Unusually among trematodes, adult schistosomes exhibit sexual dimorphism and display a fascinating codependency in that the female is dependent on the male to grow and sexually mature. Thus, virgin females are developmentally stunted compared with females from mixed-sex infections and are unable to lay eggs. Moreover, fecund female schistosomes rapidly lose the ability to produce eggs when placed in tissue culture. Here we discuss the metabolic regulation of egg production in schistosomes, and in particular the critical role played by fatty acid oxidation in this process.

NHR-176 regulates cyp-35d1 to control hydroxylation-dependent metabolism of thiabendazole in Caenorhabditis elegans

Knowledge of how drugs are metabolized and excreted is an essential component of understanding their fate within and among target and non-target organisms. Thiabendazole (TBZ) was the first benzimidazole (BZ) to be commercially available and remains one of the most important anthelmintic drugs for medical and veterinary use. We have characterized how Caenorhabditis elegans metabolizes and excretes TBZ. We have shown that TBZ directly binds to the nuclear hormone receptor (NHR)-176 and that this receptor is required for the induction by TBZ of the cytochrome P450 (CYP) encoded by cyp-35d1. Further, RNAi inhibition of cyp-35d1 in animals exposed to TBZ causes a reduction in the quantity of a hydroxylated TBZ metabolite and its glucose conjugate that is detected in C. elegans tissue by HPLC. This final metabolite is unique to nematodes and we also identify two P-glycoproteins (PGPs) necessary for its excretion. Finally, we have shown that inhibiting the metabolism we describe increases the susceptibility of C. elegans to TBZ in wild-type and in resistant genetic backgrounds.

The cytochrome P450 family in the parasitic nematode Haemonchus contortus

Haemonchus contortus, a highly pathogenic and economically important parasitic nematode of sheep, is particularly adept at developing resistance to the anthelmintic drugs used in its treatment and control. The basis of anthelmintic resistance is poorly understood for many commonly used drugs with most research being focused on mechanisms involving drug targets or drug efflux. Altered or increased drug metabolism is a possible mechanism that has yet to receive much attention despite the clear role of xenobiotic metabolism in pesticide resistance in insects. The cytochrome P450s (CYPs) are a large family of drug-metabolising enzymes present in almost all living organisms, but for many years thought to be absent from parasitic nematodes. In this paper, we describe the CYP sequences encoded in the H. contortus genome and compare their expression in different parasite life-stages, sexes and tissues. We developed a novel real-time PCR approach based on partially assembled CYP sequences "tags" and confirmed findings in the subsequent draft genome with RNA-seq. Constitutive expression was highest in larval stages for the majority of CYPs, although higher expression was detected in the adult male or female for a small subset of genes. Many CYPs were expressed in the worm intestine. A number of H. contortus genes share high identity with Caenorhabditis elegans CYPs and the similarity in their expression profiles supports their classification as putative orthologues. Notably, H. contortus appears to lack the dramatic CYP subfamily expansions seen in C. elegans and other species, which are typical of CYPs with exogenous roles. However, a small group of H. contortus genes cluster with the C. elegans CYP34 and CYP35 subfamilies and may represent candidate xenobiotic metabolising genes in the parasite.

Human schistosomiasis

Human schistosomiasis--or bilharzia--is a parasitic disease caused by trematode flukes of the genus Schistosoma. By conservative estimates, at least 230 million people worldwide are infected with Schistosoma spp. Adult schistosome worms colonise human blood vessels for years, successfully evading the immune system while excreting hundreds to thousands of eggs daily, which must either leave the body in excreta or become trapped in nearby tissues. Trapped eggs induce a distinct immune-mediated granulomatous response that causes local and systemic pathological effects ranging from anaemia, growth stunting, impaired cognition, and decreased physical fitness, to organ-specific effects such as severe hepatosplenism, periportal fibrosis with portal hypertension, and urogenital inflammation and scarring. At present, preventive public health measures in endemic regions consist of treatment once every 1 or 2 years with the isoquinolinone drug, praziquantel, to suppress morbidity. In some locations, elimination of transmission is now the goal; however, more sensitive diagnostics are needed in both the field and clinics, and integrated environmental and health-care management will be needed to ensure elimination.

Ecological morphotaxometry of trematodes of garfish (Teleostomi: Belonidae) from Gangetic riverine ecosystem in India. III. Principal component analysis in the dynamics of Cephalogonimus yamunii (Upadhyay, Jaiswal, Malhotra and Malhotra, 2012)

The attributes of multivariate analyses were applied to infer peculiarity in distribution dynamics of Cephalogonimus yamunii Upadhyay et al. (J Parasit, 2012) in Xenentodon cancilla under influence of interionic interactions amongst hydrobiological factors. Non-parametric Mann-Whitney's Test χ(2) statistic was significant for the effect of Dissolved Oxygen and magnesium. The temperature optimum 23-27 °C was concluded for expression of peak prevalence and mean intensity during change in water temperature between autumn and winter periods. The dominant Ist component (PC1 (p) ) from Principal Component Analysis of monthwise response of infection data by C. yamunii in X. cancilla was further confirmed by Scree Plot of Eigenvalues and Factor Loadings Plot to identify the critical impact of hardness of water on infection prevalence and mean intensity. The findings of larger PC1 (p) positive coefficients comprehensively substantiated predominating hardness factor, under the influence of enhanced Dissolved Oxygen and optimum thermal effect. Therefore, the role of multifactorial etiology is a definite possibility.

Partial reverse of the TCA cycle is enhanced in Taenia crassiceps experimental neurocysticercosis after in vivo treatment with anthelminthic drugs

Neurocysticercosis (NCC) is the most common helminthic infection and neglected disease of the central nervous system. It is the leading cause of acquired epilepsy and seizures worldwide. Therefore, to study this important neglected disease, it is important to use experimental models. There is no report in the literature on how the parasite's metabolism reacts to antihelminthic treatment when it is still within the central nervous system of the host. Therefore, the aim of this study was to investigate the energetic metabolism of cysticerci experimentally inoculated in the encephala of BALB/c mice after treatment with low dosages (not sufficient to kill the parasite) of albendazole (ABDZ) and praziquantel (PZQ). BALB/c mice were intracranially inoculated with Taenia crassiceps cysticerci and, after 30 days, received treatment with low dosages of ABDZ and PZQ. After 24 h of treatment, the mice were euthanized, and the cysticerci were removed and analyzed through high-performance liquid chromatography (HPLC) to quantify the organic acids related to the energetic metabolism of the parasite. The partial reverse of the TCA cycle was enhanced by the ABDZ and PZQ treatments both with the higher dosage, as the organic acids of this pathway were significantly increased when compared to the control group and to the other dosages. In conclusion, it was possible to detect the increase of this pathway in the parasites that were exposed to low dosages of ABDZ and PZQ, as it is a mechanism that would amplify the energy production in a hostile environment.

Fatty acid oxidation is essential for egg production by the parasitic flatworm Schistosoma mansoni

Schistosomes, parasitic flatworms that cause the neglected tropical disease schistosomiasis, have been considered to have an entirely carbohydrate based metabolism, with glycolysis playing a dominant role in the adult parasites. However, we have discovered a close link between mitochondrial oxygen consumption by female schistosomes and their ability to produce eggs. We show that oxygen consumption rates (OCR) and egg production are significantly diminished by pharmacologic inhibition of carnitine palmitoyl transferase 1 (CPT1), which catalyzes a rate limiting step in fatty acid β-oxidation (FAO) and by genetic loss of function of acyl CoA synthetase, which complexes with CPT1 and activates long chain FA for use in FAO, and of acyl CoA dehydrogenase, which catalyzes the first step in FAO within mitochondria. Declines in OCR and egg production correlate with changes in a network of lipid droplets within cells in a specialized reproductive organ, the vitellarium. Our data point to the importance of regulated lipid stores and FAO for the compartmentalized process of egg production in schistosomes.

Schistosomes are parasitic worms that are the cause of the Neglected Tropical Disease schistosomiasis. Female schistosomes mated with males produce eggs, which either pass out of the host's body for transmission of the infection, or become trapped in host tissues, where they induce inflammation that contributes to disease symptoms. It has been assumed that egg production is a bioenergetically-demanding process fuelled by glucose metabolism. However, we have discovered that egg production is blocked by inhibition of fatty acid oxidation (FAO), the process through which FA are utilized within mitochondria to fuel the tricarboxylic acid cycle and thereby produce substrates for ATP synthesis through oxidative phosphorylation. Consistent with a role for FAO in egg production, fecund females have extensive fat stores, in the form of lipid droplets, whereas virgin adult females have little or no fat reserves. Moreover, fecund females placed into tissue culture exhaust their fat reserves and cease to be able to produce eggs. Since schistosomes cannot produce their own FA, our data point to the acquisition of FA from the host as a key process necessary for egg production. Our findings point to the importance of regulated lipid stores and FAO for egg production by schistosomes.

Characterization of hydrophobic-ligand-binding proteins of Taenia solium that are expressed specifically in the adult stage

Taenia solium, a causative agent of taeniasis and cysticercosis, has evolved a repertoire of lipid uptake mechanisms. Proteome analysis of T. solium excretory-secretory products (TsESP) identified 10 kDa proteins displaying significant sequence identity with cestode hydrophobic-ligand-binding-proteins (HLBPs). Two distinct 362- and 352-bp-long cDNAs encoding 264- and 258-bp-long open reading frames (87 and 85 amino acid polypeptides) were isolated by mining the T. solium expressed sequence tags and a cDNA library screening (TsHLBP1 and TsHLBP2; 94% sequence identity). They clustered into the same clade with those found in Moniezia expansa and Hymenolepis diminuta. Genomic structure analysis revealed that these genes might have originated from a common ancestor. Both the crude TsESP and bacterially expressed recombinant proteins exhibited binding activity toward 1-anilinonaphthalene-8-sulfonic acid (1,8-ANS), which was competitively inhibited by oleic acid. The proteins also bound to cis-parinaric acid (cPnA) and 16-(9-anthroyloxy) palmitic acid (16-AP), but showed no binding activity against 11-[(5-dimethylaminonaphthalene-1-sulfonyl) amino] undecanoic acid (DAUDA) and dansyl-DL-α-aminocaprylic acid (DACA). Unsaturated fatty acids (FAs) showed greater affinity than saturated FAs. The proteins were specifically expressed in adult worms throughout the strobila. The TsHLBPs might be involved in uptake and/or sequestration of hydrophobic molecules provided by their hosts, thus contributing to host-parasite interface interrelationships.

Modulation of phosphofructokinase (PFK) from Setaria cervi, a bovine filarial parasite, by different effectors and its interaction with some antifilarials

BACKGROUND

Phosphofructokinase (ATP: D-fructose-6-phosphate-1-phosphotransferase, EC 2.7.1.11, PFK) is of primary importance in the regulation of glycolytic flux. This enzyme has been extensively studied from mammalian sources but relatively less attention has been paid towards its characterization from filarial parasites. Furthermore, the information about the response of filarial PFK towards the anthelmintics/antifilarial compounds is lacking. In view of these facts, PFK from Setaria cervi, a bovine filarial parasite having similarity with that of human filarial worms, was isolated, purified and characterized.

RESULTS

The S. cervi PFK was cytosolic in nature. The adult parasites (both female and male) contained more enzyme activity than the microfilarial (Mf) stage of S. cervi, which exhibited only 20% of total activity. The S. cervi PFK could be modulated by different nucleotides and the response of enzyme to these nucleotides was dependent on the concentrations of substrates (F-6-P and ATP). The enzyme possessed wide specificity towards utilization of the nucleotides as phosphate group donors. S. cervi PFK showed the presence of thiol group(s) at the active site of the enzyme, which could be protected from inhibitory action of para-chloromercuribenzoate (p-CMB) up to about 76% by pretreatment with cysteine or β-ME. The sensitivity of PFK from S. cervi towards antifilarials/anthelmintics was comparatively higher than that of mammalian PFK. With suramin, the Ki value for rat liver PFK was 40 times higher than PFK from S. cervi.

CONCLUSIONS

The results indicate that the activity of filarial PFK may be modified by different effectors (such as nucleotides, thiol group reactants and anthelmintics) in filarial worms depending on the presence of varying concentrations of substrates (F-6-P and ATP) in the cellular milieu. It may possess thiol group at its active site responsible for catalysis. Relatively, 40 times higher sensitivity of filarial PFK towards suramin as compared to the analogous enzyme from the mammalian system indicates that this enzyme could be exploited as a potential chemotherapeutic target against filariasis.

Kinetic Characterisation of Phosphofructokinase Purified from Setaria cervi: A Bovine Filarial Parasite

Phosphofructokinase (PFK), a regulatory enzyme in glycolytic pathway, has been purified to electrophoretic homogeneity from adult female Setaria cervi and partially characterized. For this enzyme, the Lineweaver-Burk's double reciprocal plots of initial rates and D-fructose-6-phosphate (F-6-P) or Mg-ATP concentrations for varying values of cosubstrate concentration gave intersecting lines indicating that K_m values for F-6-P (1.05 mM) and ATP (3 μM) were independent of each other. S. cervi PFK, when assayed at inhibitory concentration of ATP (>0.1 mM), exhibited sigmoidal behavior towards binding with F-6-P with a Hill coefficient (n) value equal to 1.8 and 1.7 at 1.0 and 0.33 mM ATP, respectively. D-fructose-1,6-diphosphate (FDP) competitively inhibited the filarial enzyme: K_i and Hill coefficient values being 0.18 μM and 2.0, respectively. Phosphoenolpyruvate (PEP) also inhibited the enzyme competitively with the K_i value equal to 0.8 mM. The Hill coefficient values (>1.5) for F-6-P (at inhibitory concentration of ATP) and FDP suggested its positive cooperative kinetics towards F-6-P and FDP, showing presence of more than one binding sites for these molecules in enzyme protein and allosteric nature of the filarial enzyme. The product inhibition studies gave us the only compatible mechanism of random addition process with a probable orientation of substrates and products on the enzyme surface.

Characterization of the xenobiotic response of Caenorhabditis elegans to the anthelmintic drug albendazole and the identification of novel drug glucoside metabolites

Knowledge of how anthelmintics are metabolized and excreted in nematodes is an integral part of understanding the factors that determine their potency, spectrum of activity and for investigating mechanisms of resistance. Although there is remarkably little information on these processes in nematodes, it is often suggested that they are of minimal importance for the major anthelmintic drugs. Consequently, we have investigated how the model nematode Caenorhabditis elegans responds to and metabolizes albendazole, one of the most important anthelmintic drugs for human and animal use. Using a mutant strain lacking the β-tubulin drug target to minimize generalized stress responses, we show that the transcriptional response is dominated by genes encoding XMEs (xenobiotic-metabolizing enzymes), particularly cytochrome P450s and UGTs (UDP-glucuronosyl transferases). The most highly induced genes are predominantly expressed in the worm intestine, supporting their role in drug metabolism. HPLC-MS/MS revealed the production of two novel glucoside metabolites in C. elegans identifying a major difference in the biotransformation of this drug between nematodes and mammals. This is the first demonstration of metabolism of a therapeutic anthelmintic in C. elegans and provides a framework for its use to functionally investigate nematode anthelmintic metabolism.