Opisthorchis viverrini Proteome and Host-Parasite Interactions

Identification and functional analysis of mitogenic miRNA of the carcinogenic liver fluke Opisthorchis viverrini

Opisthorchis viverrini is a pathogenic liver fluke that is known to cause cholangiocarcinoma in chronic infections. The underlying mechanism for this carcinogenesis is believed to be multifactorial, with parasite-derived excretory-secretory (ES) products potentially playing major roles. A recent study on these ES products has identified microRNAs (miRNA) that originate from O. viverrini but their influence on carcinogenesis remains understudied. Hence, we aimed to investigate the role of these miRNAs in the carcinogenesis of O. viverrini-associated cholangiocarcinoma. The mature miRNA sequences were retrieved from published data. Bioinformatics analysis was employed to identify miRNA targets and to identify potentially mitogenic miRNAs. An in vitro study was conducted to test the effects of miRNA on the bile duct epithelial cell lines. The miRNA target prediction analysis revealed that Ov_miRNA_EV_36/ovi-miR-3479a targets cancer-associated pathways. Hence, it was selected and used to assess its effect on the cell proliferation rate of H69 and MMNK-1 cholangiocyte cell lines. The results showed that Ov_miRNA_EV_36/ovi-miR-3479a induced significant cell proliferation in both cell lines when compared to negative controls. These results indicate that Ov_miRNA_EV_36/ovi-miR-3479a may play an essential role in the carcinogenesis of O. viverrini and therefore warrant further investigations.

Development of a subunit vaccine against the cholangiocarcinoma causing Opisthorchis viverrini: a computational approach

Opisthorchis viverrini is the etiological agent of the disease opisthorchiasis and related cholangiocarcinoma (CCA). It infects fish-eating mammals and more than 10 million people in Southeast Asia suffered from opisthorchiasis with a high fatality rate. The only effective drug against this parasite is Praziquantel, which has significant side effects. Due to the lack of appropriate treatment options and the high death rate, there is a dire need to develop novel therapies against this pathogen. In this study, we designed a multi-epitope chimeric vaccine design against O. viverrini by using immunoinformatics approaches. Non-allergenic and immunogenic MHC-1, MHC-2, and B cell epitopes of three candidate proteins thioredoxin peroxidase (Ov-TPx-1), cathepsin F1 (Ov-CF-1) and calreticulin (Ov-CALR) of O. viverrini, were predicted to construct a potent multiepitope vaccine. The coverage of the HLA-alleles of these selected epitopes was determined globally. Four vaccine constructs made by different adjuvants and linkers were evaluated in the context of their physicochemical properties, antigenicity, and allergenicity. Protein-protein docking and MD simulation found that vaccines 3 was more stable and had a higher binding affinity for TLR2 and TLR4 immune receptors. In-silico restriction cloning of vaccine model led to the formation of plasmid constructs for expression in a suitable host. Finally, the immune simulation showed strong immunological reactions to the engineered vaccine. These findings suggest that the final vaccine construct has the potential to be validated by in vivo and in vitro experiments to confirm its efficacy against the CCA causing O. viverrini.

Trematode Genomics and Proteomics

Trematode infections stand out as one of the frequently overlooked tropical diseases, despite their wide global prevalence and remarkable capacity to parasitize diverse host species and tissues. Furthermore, these parasites hold significant socio-economic, medical, veterinary and agricultural implications. Over the past decades, substantial strides have been taken to bridge the information gap concerning various "omic" tools, such as proteomics and genomics, in this field. In this edition of the book, we highlight recent progress in genomics and proteomics concerning trematodes with a particular focus on the advances made in the past 5 years. Additionally, we present insights into cutting-edge technologies employed in studying trematode biology and shed light on the available resources for exploring the molecular facets of this particular group of parasitic helminths.

Liver Flukes: Clonorchis and Opisthorchis

Clonorchis sinensis, Opisthorchis viverrini and O. felineus are liver flukes of human and animal pathogens occurring across much of Europe and Asia. Nevertheless, they are often underestimated compared to other, better known neglected diseases in spite of the fact that many millions of people are infected and hundreds of millions are at risk. This is possibly because of the chronic nature of the infection and disease and that it takes several decades prior to a life-threatening pathology to develop. Several studies in the past decade have provided more information on the molecular biology of the liver flukes which clearly lead to better understanding of parasite biology, systematics and population genetics. Clonorchiasis and opisthorchiasis are characterized by a chronic infection that induces hepatobiliary inflammation, especially periductal fibrosis, which can be detected by ultrasonography. These chronic inflammations eventually lead to cholangiocarcinoma (CCA), a usually fatal bile duct cancer that develops in some infected individuals. In Thailand alone, opisthorchiasis-associated CCA kills up to 20,000 people every year and is therefore of substantial public health importance. Its socioeconomic impacts on impoverished families and communities are considerable. To reduce hepatobiliary morbidity and CCA, the primary intervention measures focus on control and elimination of the liver fluke. Accurate diagnosis of liver fluke infections in both human and other mammalian, snail and fish intermediate hosts is important for achieving these goals. While the short-term goal of liver fluke control can be achieved by praziquantel chemotherapy, a comprehensive health education package targeting school children is believed to be more beneficial for a long-term goal/solution. It is recommended that transdisciplinary research or multisectoral control approach including one health and/or eco health intervention strategy should be applied to combat the liver flukes and hence contribute to reduction of CCA in endemic areas.

Opisthorchis viverrini-Current Understanding of the Neglected Hepatobiliary Parasite

Opisthorchiasis due to Opisthorchis viverrini infection continues to be a significant public healthcare concern in various subregions of Southeast Asia, particularly in Thailand, Laos, Cambodia, Myanmar, and Vietnam. The main mode of transmission is via consumption of raw or undercooked fish, which is deeply embedded in the culture and tradition of the people living near the Mekong River. After ingestion, the flukes migrate to the bile ducts, potentially causing many hepatobiliary complications, including cholangitis, cholecystitis, cholelithiasis, advanced periductal fibrosis and cholangiocarcinoma. Several mechanisms of opisthorchiasis-associated cholangiocarcinogenesis have been proposed and elucidated in the past decade, providing insight and potential drug targets to prevent the development of the sinister complication. The gold standard for diagnosing opisthorchiasis is still via stool microscopy, but the advent of novel serological, antigen, and molecular tests shows promise as more convenient, alternative diagnostic methods. The mainstay of treatment of opisthorchiasis is praziquantel, while treatment of opisthorchiasis-associated cholangiocarcinoma depends on its anatomic subtype and resectability. Thus far, the most successful fluke control programme is the Lawa model based in Thailand, which raised awareness, incorporated education, and frequent surveillance of intermediate hosts to reduce transmission of opisthorchiasis. Development of vaccines using tetraspanins shows promise and is currently ongoing.

Small extracellular vesicles but not microvesicles from Opisthorchis viverrini promote cell proliferation in human cholangiocytes

Chronic infection with O. viverrini has been linked to the development of cholangiocarcinoma (CCA), which is a major public health burden in the Lower Mekong River Basin countries, including Thailand, Lao PDR, Vietnam and Cambodia. Despite its importance, the exact mechanisms by which O. viverrini promotes CCA are largely unknown. In this study, we characterized different extracellular vesicle populations released by O. viverrini (OvEVs) using proteomic and transcriptomic analyses and investigated their potential role in host-parasite interactions. While 120k OvEVs promoted cell proliferation in H69 cells at different concentrations, 15k OvEVs did not produce any effect compared to controls. The proteomic analysis of both populations showed differences in their composition that could contribute to this differential effect. Furthermore, the miRNAs present in 120k EVs were analysed and their potential interactions with human host genes was explored by computational target prediction. Different pathways involved in inflammation, immune response and apoptosis were identified as potentially targeted by the miRNAs present in this population of EVs. This is the first study showing specific roles for different EV populations in the pathogenesis of a parasitic helminth, and more importantly, an important advance towards deciphering the mechanisms used in establishment of opisthorchiasis and liver fluke infection-associated malignancy.

A bloody interaction: plasma proteomics reveals gilthead sea bream (Sparus aurata) impairment caused by Sparicotyle chrysophrii

Background

Sparicotylosis is an enzootic parasitic disease that is well established across the Mediterranean Sea. It is caused by the polyopisthocotylean monogenean Sparicotyle chrysophrii and affects the gills of gilthead sea bream (GSB; Sparus aurata). Current disease management, mitigation and treatment strategies are limited against sparicotylosis. To successfully develop more efficient therapeutic strategies against this disease, understanding which molecular mechanisms and metabolic pathways are altered in the host is critical. This study aims to elucidate how S. chrysophrii infection modulates the plasma proteome of GSB and to identify the main altered biological processes involved.

Methods

Experimental infections were conducted in a recirculating aquaculture system (RAS) in which naïve recipient GSB ([R]; 70 g; n = 50) were exposed to effluent water from S. chrysophrii-infected GSB (98 g; n = 50). An additional tank containing unexposed naïve fish (control [C]; 70 g; n = 50) was maintained in parallel, but with the open water flow disconnected from the RAS. Haematological and infection parameters from sampled C and R fish were recorded for 10 weeks. Plasma samples from R fish were categorised into three different groups according to their infection intensity, which was based on the number of worms fish⁻¹: low (L: 1–50), medium (51–100) and high (H: > 100). Five plasma samples from each category and five C samples were selected and subjected to a SWATH-MS proteome analysis. Additional assays on haemoglobin, cholesterol and the lytic activity of the alternative complement pathway were performed to validate the proteome analysis findings.

Results

The discriminant analysis of plasma protein abundance revealed a clear separation into three groups (H, M/L and C). A pathway analysis was performed with the differentially quantified proteins, indicating that the parasitic infection mainly affected pathways related to haemostasis, the immune system and lipid metabolism and transport. Twenty-two proteins were significantly correlated with infection intensity, highlighting the importance of apolipoproteins, globins and complement component 3. Validation assays of blood and plasma (haemoglobin, cholesterol and lytic activity of alternative complement pathway) confirmed these correlations.

Conclusions

Sparicotylosis profoundly alters the haemostasis, the innate immune system and the lipid metabolism and transport in GSB. This study gives a crucial global overview of the pathogenesis of sparicotylosis and highlights new targets for further research.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05441-1.

Immunolocalization and functional analysis of Opisthorchis viverrini-M60-like-1 metallopeptidase in animal models

Host mucins have crucial physical roles in preventing the parasitic establishment and maturation, and also in expelling the invading parasites. However, some parasites utilize mucinase enzymes to facilitate the infection. Recently, we have identified a mucinase enzyme of the liver fluke Opisthorchis viverrini, Ov-M60-like-1, which exhibits metallopeptidase activity against bovine submaxillary mucin substrate. Here, we aimed to study the localization of this enzyme in O. viverrini and the bile duct of hamsters using immunohistochemistry and functional analysis by mucin digestion in hamsters and mice tissues. The results showed that Ov-M60-like-1 was detected strongly in the tegument, tegumental cells, vitelline glands and mature eggs with miracidium. Expression in the gut, ovary and testis of the parasite was moderate while parenchyma showed slight colour intensity. In addition, the mucinase was also detected in the host biliary epithelial cells and goblet cells surrounding the worm. The mucinase assay revealed that the Ov-M60-like-1 could digest neutral mucin in the parenchyma, testis and seminal receptacle, but not the mucin in the tegument, tegumental cells and vitelline glands of the worm. The enzyme can also digest mucin in the cholangiocytes and modified the mixture type in the bile duct goblet cells of the infected hamsters, a susceptible host. In contrast, the enzyme was unable to digest neutral, acid and mixture mucin in the bile duct of the mice, a non-susceptible host. These findings indicate that Ov-M60-like-1 may have functions in both housekeeping tasks and host–parasite interactions, especially in modification of host susceptibility.

Knockout of liver fluke granulin, Ov-grn-1, impedes malignant transformation during chronic infection with Opisthorchis viverrini

Infection with the food-borne liver fluke Opisthorchis viverrini is the principal risk factor for cholangiocarcinoma (CCA) in the Mekong Basin countries of Thailand, Lao PDR, Vietnam, Myanmar and Cambodia. Using a novel model of CCA, involving infection with gene-edited liver flukes in the hamster during concurrent exposure to dietary nitrosamine, we explored the role of the fluke granulin-like growth factor Ov-GRN-1 in malignancy. We derived RNA-guided gene knockout flukes (ΔOv-grn-1) using CRISPR/Cas9/gRNA materials delivered by electroporation. Genome sequencing confirmed programmed Cas9-catalyzed mutations of the targeted genes, which was accompanied by rapid depletion of transcripts and the proteins they encode. Gene-edited parasites colonized the biliary tract of hamsters and developed into adult flukes. However, less hepatobiliary tract disease manifested during chronic infection with ΔOv-grn-1 worms in comparison to hamsters infected with control gene-edited and mock-edited parasites. Specifically, immuno- and colorimetric-histochemical analysis of livers revealed markedly less periductal fibrosis surrounding the flukes and less fibrosis globally within the hepatobiliary tract during infection with ΔOv-grn-1 genotype worms, minimal biliary epithelial cell proliferation, and significantly fewer mutations of TP53 in biliary epithelial cells. Moreover, fewer hamsters developed high-grade CCA compared to controls. The clinically relevant, pathophysiological phenotype of the hepatobiliary tract confirmed a role for this secreted growth factor in malignancy and morbidity during opisthorchiasis.

Exploring the role of macrophages in determining the pathogenesis of liver fluke infection

The food-borne trematodes, Opisthorchis viverrini and Clonorchis sinensis, are classified as group 1 biological carcinogens: definitive causes of cancer. By contrast, infections with Fasciola hepatica, also a food-borne trematode of the phylum Platyhelminthes, are not carcinogenic. This review explores the premise that the differential activation of macrophages during infection with these food-borne trematodes is a major determinant of the pathological outcome of infection. Like most helminths, the latter stages of infection with all 3 flukes induce M2 macrophages, a phenotype that mediates the functional repair of tissue damaged by the feeding and migratory activities of the parasites. However, there is a critical difference in how the development of pro-inflammatory M1 macrophages is regulated during infection with these parasites. While the activation of the M1 macrophage phenotype is largely suppressed during the early stages of infection with F. hepatica, M1 macrophages predominate in the bile ducts following infection with O. viverrini and C. sinensis. The anti-microbial factors released by M1 macrophages create an environment conducive to mutagenesis, and hence the initiation of tumour formation. Subsequently, the tissue remodelling processes induced by the M2 macrophages promote the proliferation of mutated cells, and the expansion of cancerous tissue. This review will also explore the interactions between macrophages and parasite-derived signals, and their contributions to the stark differences in the innate immune responses to infection with these parasites.

Foodborne trematodes: old foes, new kids on the block and research perspectives for control and understanding host-parasite interactions

Foodborne trematodes (FBTs) have a worldwide distribution (with particular prevalence in south-east Asia) and are believed to infect almost 75 million people, with millions more living at risk of infection. Although mortality due to trematodiasis is low, these infections cause considerable morbidity and some species are associated with the development of cancer in hyperendemic regions. Despite this, FBTs are often side-lined in terms of research funding and have been dubbed neglected tropical diseases by the World Health Organisation. Thus, the aim of this special issue was to provide an update of our understanding of FBT infections, to shine a light on current work in the field and to highlight some research priorities for the future. With contributions from leading researchers, many from endemic regions, we review the major FBT species. In doing so we revisit some old foes, uncover emerging infections and discover how outbreaks are being dealt with as a result of new approaches to parasite control. We also report advances in our understanding of the interactions of FBTs with their mammalian hosts and uncover new interplay between trematodes and host microbiome components. We hope that this article collection will stimulate discussion and further research on the FBTs and help raise them from their neglected status.

Comparative proteomics of adult Paragonimus kellicotti excretion/secretion products released in vitro or present in the lung cyst nodule

Paragonimus kellicotti is a zoonotic lung fluke infection, the agent of North American paragonimiasis, and an excellent model for other Paragonimus infections. The excretory/secretory proteins (ESP) released by parasites and presented at the parasite-host interface are frequently proposed to be useful targets for drugs and/or vaccines In vitro culture conditions may alter ESP compared to those produced in vivo. In order to investigate ESPs produced in vivo we took advantage of the fact that adult P. kellicotti reproduce in the lungs of experimentally infected gerbils in tissue cysts. We performed a mass-spectrometric analysis of adult P. kellicotti soluble somatic protein (SSPs) extracts, excreted/secreted proteins (ESPs) produced by adult worms during in vitro culture, and lung cyst fluid proteins (CFPs) from experimentally infected gerbils. We identified 2,137 P. kellicotti proteins that were present in at least two of three biological replicates and supported by at least two peptides. Among those were 1,914 proteins found in SSP, 947 in ESP and 37 in CFP. In silico analysis predicted that only 141 of the total 2,137 proteins were secreted via classical or non-classical pathways. The most abundant functional categories in SSP were storage and oxidative metabolism. The most abundant categories in ESP were proteins related to metabolism and signal transduction. The 37 parasite-related proteins in CFP belonged to 11 functional categories. The largest groups were proteins with unknown function, cytoskeletal proteins and proteasome machinery. 29 of these 37 proteins were shared among all three sample types. To our knowledge, this is the first study that compares in vitro and in vivo ESP for any Paragonimus species. This study has provided new insights into ESPs of food-borne trematodes that are produced and released in vivo. Proteins released at the host-parasite interface may help the parasite evade host immunity and may represent new targets for novel treatments or diagnostic tests for paragonimiasis.

Evolutionary Adaptations of Parasitic Flatworms to Different Oxygen Tensions

During the evolution of the Earth, the increase in the atmospheric concentration of oxygen gave rise to the development of organisms with aerobic metabolism, which utilized this molecule as the ultimate electron acceptor, whereas other organisms maintained an anaerobic metabolism. Platyhelminthes exhibit both aerobic and anaerobic metabolism depending on the availability of oxygen in their environment and/or due to differential oxygen tensions during certain stages of their life cycle. As these organisms do not have a circulatory system, gas exchange occurs by the passive diffusion through their body wall. Consequently, the flatworms developed several adaptations related to the oxygen gradient that is established between the aerobic tegument and the cellular parenchyma that is mostly anaerobic. Because of the aerobic metabolism, hydrogen peroxide (H₂O₂) is produced in abundance. Catalase usually scavenges H₂O₂ in mammals; however, this enzyme is absent in parasitic platyhelminths. Thus, the architecture of the antioxidant systems is different, depending primarily on the superoxide dismutase, glutathione peroxidase, and peroxiredoxin enzymes represented mainly in the tegument. Here, we discuss the adaptations that parasitic flatworms have developed to be able to transit from the different metabolic conditions to those they are exposed to during their life cycle.

Characterization of the Estrogen Response Helps to Predict Prognosis and Identify Potential Therapeutic Targets in Cholangiocarcinoma

Cholangiocarcinoma (CCA) is an aggressive malignancy originating from the epithelium of the bile duct. The prognosis of patients is poor regardless of radical resection and chemoradiotherapy. The current classification and prognostic model of CCA are unable to satisfy the requirements for predicting the clinical outcome and exploring therapeutic targets. Estrogen signaling is involved in diverse cancer types, and it has long been established that CCA could be regulated by estrogen. In our study, estrogen response was identified to be significantly and stably correlated with poor prognosis in CCA. Employing several algorithms, CCA was classified into ES cluster A and B. ES cluster B was mainly composed of patients with fluke infection and overlapped with CCA cluster 1/2, and ES cluster A was mainly composed of patients without fluke infection and overlapped with CCA cluster 3/4. COMT and HSD17B1 were identified to be responsible for the differential estrogen response between ES clusters A and B, and the estrogen response may be correlated with the differentiation and cancer stemness of CCA at the single-cell level. Complement activation and the expression of C3 and C5, which are mainly expressed by CCA cells, were significantly downregulated in ES cluster B. An estrogen response risk score (ESRS) model was constructed to predict the prognosis of CCA, followed by a nomogram integrating ESRS and clinical features. Finally, altered pathways, applicable drugs and sensitivity to chemical drugs were analyzed specific to the estrogen response. In summary, our results provide insights into the role of the estrogen response in CCA progression as well as applicable drugs and potential therapeutic targets in estrogen metabolism, the complement system and ESRS-related pathways.

Proteomic profiling of hydatid fluid from pulmonary cystic echinococcosis

BACKGROUND

Most cystic echinococcosis cases in Southern Brazil are caused by Echinococcus granulosus and Echinococcus ortleppi. Proteomic studies of helminths have increased our knowledge about the molecular survival strategies that are used by parasites. Here, we surveyed the protein content of the hydatid fluid compartment in E. granulosus and E. ortleppi pulmonary bovine cysts to better describe and compare their molecular arsenal at the host-parasite interface.

METHODS

Hydatid fluid samples from three isolates of each species were analyzed using mass spectrometry-based proteomics (LC-MS/MS). In silico functional analyses of the identified proteins were performed to examine parasite survival strategies.

RESULTS

The identified hydatid fluid protein profiles showed a predominance of parasite proteins compared to host proteins that infiltrate the cysts. We identified 280 parasitic proteins from E. granulosus and 251 from E. ortleppi, including 52 parasitic proteins that were common to all hydatid fluid samples. The in silico functional analysis revealed important molecular functions and processes that are active in pulmonary cystic echinococcosis, such as adhesion, extracellular structures organization, development regulation, signaling transduction, and enzyme activity.

CONCLUSIONS

The protein profiles described here provide evidence of important mechanisms related to basic cellular processes and functions that act at the host-parasite interface in cystic echinococcosis. The molecular tools used by E. granulosus and E. ortleppi for survival within the host are potential targets for new therapeutic approaches to treat cystic echinococcosis and other larval cestodiases.

Silencing of Opisthorchis viverrini Tetraspanin Gene Expression Results in Reduced Secretion of Extracellular Vesicles

Inter-phylum transfer of molecular information is exquisitely exemplified in the uptake of parasite extracellular vesicles (EVs) by their target mammalian host tissues. The oriental liver fluke, Opisthorchis viverrini is the major cause of bile duct cancer in people in Southeast Asia. A major mechanism by which O. viverrini promotes cancer is through the secretion of excretory/secretory products which contain extracellular vesicles (OvEVs). OvEVs contain microRNAs that are predicted to impact various mammalian cell proliferation pathways, and are internalized by cholangiocytes that line the bile ducts. Upon uptake, OvEVs drive relentless proliferation of cholangiocytes and promote a tumorigenic environment, but the underlying mechanisms of this process are unknown. Moreover, purification and characterization methods for helminth EVs in general are ill defined. We therefore compared different purification methods for OvEVs and characterized the sub-vesicular compartment proteomes. Two CD63-like tetraspanins (Ov-TSP-2 and TSP-3) are abundant on the surface of OvEVs, and could serve as biomarkers for these parasite vesicles. Anti-TSP-2 and -TSP-3 IgG, as well as different endocytosis pathway inhibitors significantly reduced OvEV uptake and subsequent proliferation of cholangiocytes in vitro. Silencing of Ov-tsp-2 and tsp-3 gene expression in adult flukes using RNA interference resulted in substantial reductions in OvEV secretion, and those vesicles that were secreted were deficient in their respective TSP proteins. Our findings shed light on the importance of tetraspanins in fluke EV biogenesis and/or stability, and provide a conceivable mechanism for the efficacy of anti-tetraspanin subunit vaccines against a range of parasitic helminth infections.

Cholangiocarcinoma

Cholangiocarcinoma (CCA) is a highly lethal adenocarcinoma of the hepatobiliary system, which can be classified as intrahepatic, perihilar and distal. Each anatomic subtype has distinct genetic aberrations, clinical presentations and therapeutic approaches. In endemic regions, liver fluke infection is associated with CCA, owing to the oncogenic effect of the associated chronic biliary tract inflammation. In other regions, CCA can be associated with chronic biliary tract inflammation owing to choledocholithiasis, cholelithiasis, or primary sclerosing cholangitis, but most CCAs have no identifiable cause. Administration of the anthelmintic drug praziquantel decreases the risk of CCA from liver flukes, but reinfection is common and future vaccination strategies may be more effective. Some patients with CCA are eligible for potentially curative surgical options, such as resection or liver transplantation. Genetic studies have provided new insights into the pathogenesis of CCA, and two aberrations that drive the pathogenesis of non-fluke-associated intrahepatic CCA, fibroblast growth factor receptor 2 fusions and isocitrate dehydrogenase gain-of-function mutations, can be therapeutically targeted. CCA is a highly desmoplastic cancer and targeting the tumour immune microenvironment might be a promising therapeutic approach. CCA remains a highly lethal disease and further scientific and clinical insights are needed to improve patient outcomes.

In silico prediction of secretory proteins of Opisthorchis viverrini, Clonorchis sinensis and Fasciola hepatica that target the host cell nucleus

Liver flukes Fasciola hepatica, Opisthorchis viverrini and Clonorchis sinensis are causing agents of liver and hepatobiliary diseases. A remarkable difference between such worms is the fact that O. viverrini and C. sinensis are carcinogenic organisms whereas F. hepatica is not carcinogenic. The release of secretory factors by carcinogenic flukes seems to contribute to cancer development however if some of these target the host cell nuclei is unknown. We investigated the existence of O. viverrini and C. sinensis secretory proteins that target the nucleus of host cells and compared these with the corresponding proteins predicted in F. hepatica. Here we applied an algorithm composed by in silico approaches that screened and analyzed the potential genes predicted from genomes of liver flukes. We found 31 and 22 secretory proteins that target the nucleus of host cells in O. viverrini and C. sinensis, respectively, and that have no homologs in F. hepatica. These polypeptides have enriched the transcription initiation process and nucleic acid binding in O. viverrini and C. sinensis, respectively. In addition, other 11 secretory proteins of O. viverrini and C. sinensis, that target the nucleus of host cells, had F. hepatica homologs, have enriched RNA processing function. In conclusion, O. viverrini and C. sinensis have 31 and 22 genes, respectively, that may be involved in their carcinogenic action through a direct targeting on the host cell nuclei.

Trematode Proteomics: Recent Advances and Future Directions

Trematodes cause disease in millions of people worldwide, but the absence of commercial vaccines has led to an over-reliance on a handful of monotherapies to control infections. Since drug-resistant fluke populations are emerging, a deeper understanding of parasite biology and host interactions is required to identify new drug targets and immunogenic vaccine candidates. Mass spectrometry-based proteomics represents a key tool to that end. Recent studies have capitalised on the wider availability of annotated helminth genomes to achieve greater coverage of trematode proteomes and discover new aspects of the host-parasite relationship. This review focusses on these latest advances. These include how the protein components of fluke extracellular vesicles have given insight into their biogenesis and cellular interactions. In addition, how the integration of transcriptome/proteome datasets has revealed that the expression and secretion of selected families of liver fluke virulence factors and immunomodulators are regulated in accordance with parasite development and migration within the mammalian host. Furthermore, we discuss the use of immunoproteomics as a tool to identify vaccine candidates associated with protective antibody responses. Finally, we highlight how established and emerging technologies, such as laser microdissection and single-cell proteomics, could be exploited to resolve the protein profiles of discrete trematode tissues or cell types which, in combination with functional tools, could pinpoint optimal targets for fluke control.

Spirocerca lupi Proteomics and Its Role in Cancer Development: An Overview of Spirocercosis-Induced Sarcomas and Revision of Helminth-Induced Carcinomas

Spirocerca lupi is a parasitic nematode of canids that induces a myriad of clinical manifestations in its host and, in 25% of infections, leads to the formation of sarcomas. The description of the protein composition of the excretory and secretory products (Sl-ESP) of S. lupi has shed light on its possible interactions with the host environment, including migration within the host and mechanisms of immunomodulation. Despite this, the process by which S. lupi induces cancer in the dog remains poorly understood, and some hypotheses have arisen regarding these possible mechanisms. In this review, we discuss the role of specific ESP from the carcinogenic helminths Clonorchis sinensis, Opisthorchis viverrini and Schistosoma haematobium in inducing chronic inflammation and cancer in their host’s tissues. The parasitic worms Taenia solium, Echinococcus granulosus, Heterakis gallinarum, Trichuris muris and Strongyloides stercoralis, which have less-characterized mechanisms of cancer induction, are also analyzed. Based on the pathological findings in spirocercosis and the mechanisms by which other parasitic helminths induce cancer, we propose that the sustained inflammatory response in the dog´s tissues produced in response to the release of Sl-ESP homologous to those of other carcinogenic worms may lead to the malignant process in infected dogs.

Characterization and in vitro functional analysis of thioredoxin glutathione reductase from the liver fluke Opisthorchis viverrini

The carcinogenic liver fluke Opisthorchis viverrini causes several hepatobiliary diseases including a bile duct cancer-cholangiocarcinoma (CCA), which is a major public health problem in many countries in the Greater Mekong Sub-region. Praziquantel is the main drug against this parasite, however, reduced drug efficacy has been observed in some endemic areas. Therefore, alternative drugs are needed to prepare for praziquantel resistance in the future. The selenoprotein thioredoxin glutathione reductase (TGR) enzyme, which plays a crucial role in cellular redox balance of parasitic flatworms, has been shown as a potential drug target against these parasites. Hence, this study aimed to investigate the TGR of O. viverrini and assess its potential as a drug target. An open reading frame (ORF) that encodes O. viverrini TGR (Ov-TGR) was cloned from an O. viverrini cDNA library and the nucleotide were sequenced. The 1,812 nucleotides of the Ov-TGR full ORF encoded a polypeptide of 603 amino acid residues with a predicted molecular mass of 66 kDa. The putative amino acid sequence shared 55-96.8% similarities with TGRs from other helminths and mammals. Phylogenetic analysis revealed a close relationship of Ov-TGR with that of other trematodes. The ORF of Ov-TGR was inserted into pABC2 plasmid and transformed into Escherichia coli strain C321.ΔA to facilitate selenocysteine incorporation. The recombinant Ov-TGR (rOv-TGR-SEC) was expressed as a soluble protein and detected as a dimer form in the non-reducing sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Its thioredoxin reductase (TrxR) and glutathione reductase (GR) activities were detected using DTNB, Trx and GSSG substrates with the Michaelis constant (Km) of 292.6 ± 52.3 µM, 8.09 ± 1.91 µM and 13.74 ± 1.2 µM, respectively. The TGR enzyme activities were effectively inhibited by a well-known inhibitor, auranofin in a dose-dependent manner. Moreover, auranofin expressed a lethal toxic effect on both newly excysted juveniles (NEJs) and adult worms of O. viverrini in vitro. Taken together, these results indicated that Ov-TGR is crucial for O. viverrini survival and maybe a potential target for the development of novel agents against opisthorschiasis.

Recent Progress in the Development of Liver Fluke and Blood Fluke Vaccines

Liver flukes (Fasciola spp., Opisthorchis spp., Clonorchis sinensis) and blood flukes (Schistosoma spp.) are parasitic helminths causing neglected tropical diseases that result in substantial morbidity afflicting millions globally. Affecting the world’s poorest people, fasciolosis, opisthorchiasis, clonorchiasis and schistosomiasis cause severe disability; hinder growth, productivity and cognitive development; and can end in death. Children are often disproportionately affected. F. hepatica and F. gigantica are also the most important trematode flukes parasitising ruminants and cause substantial economic losses annually. Mass drug administration (MDA) programs for the control of these liver and blood fluke infections are in place in a number of countries but treatment coverage is often low, re-infection rates are high and drug compliance and effectiveness can vary. Furthermore, the spectre of drug resistance is ever-present, so MDA is not effective or sustainable long term. Vaccination would provide an invaluable tool to achieve lasting control leading to elimination. This review summarises the status currently of vaccine development, identifies some of the major scientific targets for progression and briefly discusses future innovations that may provide effective protective immunity against these helminth parasites and the diseases they cause.

Orally Administered Bacillus Spores Expressing an Extracellular Vesicle-Derived Tetraspanin Protect Hamsters Against Challenge Infection With Carcinogenic Human Liver Fluke

BACKGROUND

The human liver fluke Opisthorchis viverrini is a food-borne trematode that causes hepatobiliary disease in humans throughout Southeast Asia. People become infected by consuming raw or undercooked fish containing metacercariae. Development of a vaccine to prevent or minimize pathology would decrease the risk of severe morbidity, including the development of bile duct cancer.

METHODS

We produced an oral vaccine based on recombinant Bacillus subtilis spores expressing the large extracellular loop (LEL) of O. viverrini tetraspanin-2 (Ov-TSP-2), a protein that is abundant on the surface of O. viverrini secreted extracellular vesicles (EVs). Recombinant spores expressing Ov-TSP-2-LEL were orally administered to hamsters prior to challenge infection with O. viverrini metacercariae.

RESULTS

Vaccinated hamsters generated serum IgG as well as bile IgG and IgA responses to Ov-TSP-2-LEL, and serum IgG from vaccinated hamsters blocked the uptake of fluke EVs by a human bile duct epithelial cell line. Vaccinated hamsters had 56% reductions in both adult flukes and fecal eggs compared to the control group.

CONCLUSIONS

These findings indicate that oral vaccination of hamsters with recombinant B. subtilis spores expressing Ov-TSP-2-LEL is efficacious at reducing infection intensity and could form the basis of a vaccine for control of carcinogenic liver fluke infection in humans.

The protein and microRNA cargo of extracellular vesicles from parasitic helminths - current status and research priorities

Helminth parasites have a remarkable ability to persist within their mammalian hosts, which is largely due to their secretion of molecules with immunomodulatory properties. Although the soluble components of helminth secretions have been extensively studied, the discovery that helminths release extracellular vesicles (EVs) has added further complexity to the host-parasite interaction. Whilst several studies have begun to characterise the molecules carried by helminth EVs, work aimed at investigating their biological functions has been hindered by a lack of helminth-specific EV markers. To begin to address this, we summarised helminth EV literature to date. With a focus on the protein and microRNA (miRNA) cargo, we aimed to detect similarities and differences across those major groups of helminths for which data are available; namely nematodes, trematodes and cestodes. Pfam analysis revealed that although there is no universal EV marker for all helminth species, the EF-hand protein family was present in all EV datasets from cestodes and trematodes, and could serve as a platyhelminth EV biomarker. In contrast, M13 metallopeptidases and actin may have potential as markers for nematode EVs. As with proteins, many miRNA families appeared to be species-, stage-, or dataset-specific. Two miRNA families were common to nematode EVs (mir-10 and let-7); the miRNA cargo of EVs secreted by clade I species appeared somewhat different from species from other clades. Five miRNA families (mir-71, mir-10, mir-190, let-7 and mir-2) were shared by all trematode species examined. Our analysis has identified novel markers that may be used in studies aimed at characterising helminth EVs and interrogating their function at the host-parasite interface. In addition, we discuss the heterogeneity of methods used for helminth EV isolation and emphasise the need for a standardised approach in reporting on helminth EV data.

Plasma metabolomics of the time resolved response to Opisthorchis felineus infection in an animal model (golden hamster, Mesocricetus auratus)

Background

Opisthorchiasis is a hepatobiliary disease caused by flukes of the trematode family Opisthorchiidae. Opisthorchiasis can lead to severe hepatobiliary morbidity and is classified as a carcinogenic agent. Here we investigate the time-resolved metabolic response to Opisthorchis felineus infection in an animal model.

Methodology

Thirty golden hamsters were divided in three groups: severe infection (50 metacercariae/hamster), mild infection (15 metacercariae/hamster) and uninfected (vehicle-PBS) groups. Each group consisted of equal number of male and female animals. Plasma samples were collected one day before the infection and then every two weeks up to week 22 after infection. The samples were subjected to ¹H Nuclear Magnetic Resonance (NMR) spectroscopy and multivariate statistical modelling.

Principal findings

The time-resolved study of the metabolic response to Opisthorchis infection in plasma in the main lines agrees with our previous report on urine data. The response reaches its peak around the 4th week of infection and stabilizes after the 10th week. Yet, unlike the urinary data there is no strong effect of the gender in the data and the intensity of infection is presented in the first two principal components of the PCA model. The main trends of the metabolic response to the infection in blood plasma are the transient depletion of essential amino acids and an increase in lipoprotein and cholesterol concentrations.

Conclusions

The time resolved metabolic signature of Opisthorchis infection in the hamster’s plasma shows a coherent shift in amino acids and lipid metabolism. Our work provides insight into the metabolic basis of the host response on the helminth infection.

Opisthorchiasis is a parasitic infection caused by liver flukes of the Opisthorchiidae family. The liver fluke infection triggers development of hepatobiliary pathologies such as chronic forms of cholecystitis, cholangitis, pancreatitis, and cholelithiasis and increases the risk of intrahepatic cholangiocarcinoma. This manuscript is the second part of our outgoing project dedicated to a comprehensive description of the metabolic response to opisthorchiasis (more specifically Opisthorchis felineus) in an animal model. We show that the metabolic response in blood plasma is unfolding according to the same scenario as in urine, reaching its peak at the 4th week and stabilizing after the 10th week post-infection. Yet, unlike the response described in urine, the observed metabolic response in plasma is less gender specific. Moreover, the biochemical basis of the detected response in blood plasma is restricted to the remodeling of the lipid metabolism and the transient depletion of essential amino acids. Together with our first manuscript this report forms the first systematic description of the metabolic response on opisthorchiasis in an animal model using two easily accessible biofluids. Thus, this contribution provides novel results and fills an information gap still existing in the analytically driven characterization of the “Siberian liver fluke”, Opisthorchis felineus.

Identification and molecular characterization of exosome-like vesicles derived from the Taenia asiatica adult worm

Taenia asiatica is an important food-borne parasite that poses a threat to food-safety and animal husbandry hygine, yet little is known about its specific infection and immune escape mechanisms. Exosome-like vesicles have recently emerged as a regulator in the interactions between parasites and hosts, providing a new direction for research on infection of T. asiatica. In this experiment, exosome-like vesicles were collected from the excretory/secretory products of cultured T. asiatica and isolated by differential centrifugation. The purified vesicles, ranging from 30 to 150 nm in size, were identified as exosome-like vesicles by transmission electron microscope and Nanoparticle tracking analysis. Proteomics analysis identified 455 proteins in the exosome-like vesicles. Of these proteins, enzymes involved in metabolic processes were identified, including glyceraldehyde 3 phosphate dehydrogenase, fructose-1, 6-bisphosphate aldolase, cytosolic malate dehydrogenase, and enolase. The two most abundant proteins from proteomic analysis, 14-3-3 and enolase, were shown to be present in the exosome-like vesicles by immunogold labeling. High-throughput RNA sequencing yielded twenty known miRNAs present in exosome-like vesicle sRNA libraries. Nine of the miRNAs, including six known miRNAs (tas-miR-71, tas-miR-1, tas-miR-7, tas-miR-9, tas-miR-10, and tas-let-7) and three newly discovered miRNAs (tas-m0022-3p, tas-m0816-3p, tas-m0082-5p), were confirmed by RT-qPCR as present in T. asiatica adult worm extracts and secreted exosome-like vesicles in T. asiatica. Additionally, we demonstrated that exosome-like vesicles experimentally labeled with PKH67 were internalized by LoVo cells in vitro. These findings provide new insights into the interaction between tapeworms and hosts mediated by exosome-like vesicles.

Vaccination of hamsters with Opisthorchis viverrini extracellular vesicles and vesicle-derived recombinant tetraspanins induces antibodies that block vesicle uptake by cholangiocytes and reduce parasite burden after challenge infection

Background

The liver fluke Opisthorchis viverrini infects several million people in Southeast Asia. Adult flukes live in the bile ducts of humans, where they cause hepatobiliary pathology, including cholangiocarcinoma. Here, we investigated the potential of extracellular vesicles (EVs) secreted by the fluke and defined recombinant proteins derived from EVs to generate protective immunity in a hamster vaccination-challenge model.

Methodology/Principal findings

EVs isolated from the excretory-secretory products of O. viverrini and two recombinant EV surface proteins encoding the large extracellular loops (LEL) of Ov-TSP-2 (rOv-TSP-2) and Ov-TSP-3 (rOv-TSP-3) were adjuvanted and used to vaccinate hamsters intraperitoneally followed by challenge infection with O. viverrini metacercariae. The number of adult flukes recovered from hamsters immunized with EVs, rOv-TSP-2, rOv-TSP-3 and rOv-TSP-2+rOv-TSP-3 were significantly reduced compared to control animals vaccinated with adjuvant alone. The number of eggs per gram feces was also significantly reduced in hamsters vaccinated with rOv-TSP-2 compared to controls, but no significant differences were found in the other groups. The average length of worms recovered from hamsters vaccinated with EVs, rOv-TSP-2 and rOv-TSP-3 was significantly shorter than that of worms recovered from the control group. Anti-EV IgG levels in serum and bile were significantly higher in hamsters vaccinated with EVs compared to control hamsters both pre- and post-challenge. In addition, levels of anti-rOv-TSP antibodies in the serum and bile were significantly higher than control hamsters both pre- and post-challenge. Finally, antibodies against rOv-TSP-2 and rOv-TSP-3 blocked uptake of EVs by human primary cholangiocyte in vitro, providing a plausible mechanism by which these vaccines exert partial efficacy and reduce the intensity of O. viverrini infection.

Conclusion/Significance

Liver fluke EVs and recombinant tetraspanins derived from the EV surface when administered to hamsters induce antibody responses that block EV uptake by target bile duct cells and exert partial efficacy and against O. viverrini challenge.

Cholangiocarcinoma (CCA) is a significant public health problem in countries throughout Southeast Asia. In these areas CCA has a strong association with chronic infection with the food-borne liver fluke Opisthorchis viverrini. Current control of the infection relies on chemotherapy and health education, however these approaches are not sustainable in isolation. Hence, there is an urgent need for a vaccine against this neglected tropical disease. A vaccine against O. viverrini would confer anti-cancer protection in similar fashion to the acclaimed vaccine for human papillomavirus and cervical cancer. Toward this goal, secreted extracellular vesicles (EVs) of O. viverrini and recombinant proteins from the surface of EVs were generated and tested as vaccines in a hamster challenge model. Vaccination of hamsters with EVs and recombinant proteins induced production of antibodies in serum and bile, and those antibodies blocked uptake of EVs by primary bile duct cells in vitro. Challenge of vaccinated hamsters with infective stage flukes markedly reduced adult fluke recovery compared to the adjuvant control group. This is the first report of successful vaccination of hamsters with O. viverrini EVs and recombinant vesicle surface proteins, and provides proof-of-concept for development of subunit vaccines for this carcinogenic infection.

Trematode Genomics and Proteomics

Trematode infections are among the most neglected tropical diseases despite their worldwide distribution and extraordinary ability to parasitise many different host species and host tissues. Furthermore, these parasites are of great socioeconomic, medical, veterinary and agricultural importance. During the last 10 years, there have been increasing efforts to overcome the lack of information on different "omic" resources such as proteomics and genomics. Herein, we focus on the recent advances in genomics and proteomics from trematodes of human importance, including liver, blood, intestinal and lung flukes. We also provide information on the latest technologies applied to study the biology of trematodes as well as on the resources available for the study of the molecular aspects of this group of helminths.

Liver Flukes: Clonorchis and Opisthorchis

Clonorchis sinensis, Opisthorchis viverrini, and O. felineus are liver flukes of human and animal pathogens occurring across much of Europe and Asia. Nevertheless, they are often underestimated compared to other, better known neglected diseases in spite of the fact that many millions of people are infected and hundreds of millions are at risk. This is possibly because of the chronic nature of the infection and disease and that it takes several decades prior to a life-threatening pathology to develop. Several studies in the past decade have provided more information on the molecular biology of the liver flukes which clearly lead to better understanding of parasite biology, systematics, and population genetics. Clonorchiasis and opisthorchiasis are characterized by a chronic infection that induces hepatobiliary inflammation, especially periductal fibrosis, which can be detected by ultrasonography. These chronic inflammations eventually lead to cholangiocarcinoma (CCA), a usually fatal bile duct cancer that develops in some infected individuals. In Thailand alone, opisthorchiasis-associated CCA kills up to 20,000 people every year and is therefore of substantial public health importance. Its socioeconomic impacts on impoverished families and communities are considerable. To reduce hepatobiliary morbidity and CCA, the primary intervention measures focus on control and elimination of the liver fluke. Accurate diagnosis of liver fluke infections in both human and other mammalian, snail and fish intermediate hosts, are important for achieving these goals. While the short-term goal of liver fluke control can be achieved by praziquantel chemotherapy, a comprehensive health education package targeting school children is believed to be more beneficial for a long-term goal/solution. It is recommended that a transdisciplinary research or multisectoral control approach including one health and/or eco health intervention strategy should be applied to combat the liver flukes, and hence contribute to reduction of cholangiocarcinoma in endemic areas.