Alexey V. Katokhin

Comparative histopathology of Opisthorchis felineus and Opisthorchis viverrini in a hamster model: An implication of high pathogenicity of the European liver fluke

European liver fluke (Opisthorchis felineus) and Asian liver fluke (Opisthorchis viverrini) are similar in morphology but comparative pathology of the infections has not been described. We therefore did comparative histopathology of both parasites in an experimental animal model. The study was conducted in 3 groups of 105 Syrian golden hamsters; the first and second groups fed with 50 metacercariae of O. felineus (OF) or O. viverrini (OV) and the last group was uninfected controls. Five hamsters in each group were euthanized on weeks 1, 2, 4, 8, 12 and 24 post-infection. The liver tissue was fixed and processed for routine histopathology and immunohistochemistry for proliferation markers (BrdU or PCNA). Overall, the liver histopathology of O. felineus and O. viverrini infection was generally similar. However, various histopathogical features including intense inflammation, fibrosis, biliary and goblet cell hyperplasia and dysplasia occurred earlier in the OF group. In addition, the existence of precancerous lesions such as cholangiofibrosis in a long-term infection was observed only in this group. O. felineus is larger in size than O. viverrini which, together with its excreted and secreted antigens, likely is crucial in the induction of liver fluke induced disease. The differences in nature and timing of the histopathological profile indicate that opisthorchiasis caused by the European liver fluke O. felineus is more pathogenic than its Asian relative O. viverrini.

Low genetic diversity in wide-spread Eurasian liver fluke Opisthorchis felineus suggests special demographic history of this trematode species.

Opisthorchis felineus or Siberian liver fluke is a trematode parasite (Opisthorchiidae) that infects the hepato-biliary system of humans and other mammals. Despite its public health significance, this wide-spread Eurasian species is one of the most poorly studied human liver flukes and nothing is known about its population genetic structure and demographic history. In this paper, we attempt to fill this gap for the first time and to explore the genetic diversity in O. felineus populations from Eastern Europe (Ukraine, European part of Russia), Northern Asia (Siberia) and Central Asia (Northern Kazakhstan). Analysis of marker DNA fragments from O. felineus mitochondrial cytochrome c oxidase subunit 1 and 3 (cox1, cox3) and nuclear rDNA internal transcribed spacer 1 (ITS1) sequences revealed that genetic diversity is very low across the large geographic range of this species. Microevolutionary processes in populations of trematodes may well be influenced by their peculiar biology. Nevertheless, we suggest that lack of population genetics structure observed in O. felineus can be primarily explained by the Pleistocene glacial events and subsequent sudden population growth from a very limited group of founders. Rapid range expansion of O. felineus through Asian and European territories after severe bottleneck points to a high dispersal potential of this trematode species.

Identification of the Daphnia species (Crustacea: Cladocera) in the lakes of the Ob and Yenisei River basins: morphological and molecular phylogenetic approaches

The morphological and genetic variability of Daphnia species from 16 lakes in the upper watersheds of the Ob and Yenisei Rivers were investigated. Four species, namely D. galeata Sars 1863, D. cristata Sars 1862, D. curvirostris Eylmann, 1887 and D. longispina O.F. Müller, 1776 inhabit these lakes. In addition, longispina-like individuals in Lake Borzu-Khol (the Bolshoi Yenisei River basin) were found which were, however, clearly distinguishable from the other species by morphometric and mitochondrial DNA analyses and could belong to D. umbra based on the 12S sequences.

The first comprehensive study of praziquantel effects in vivo and in vitro on European liver fluke Opisthorchis felineus (Trematoda).

The European liver fluke Opisthorchis felineus (Rivolta, 1884) is an epidemiologically important parasite infecting mammals, including humans. Opisthorchis felineus is widespread in Russia, Kazakhstan and Eastern European countries. Praziquantel (PZQ) is the drug of choice for the treatment of opisthorchiasis, but the effects of this drug on O. felineus are poorly studied. The aims of this work were (i) to perform a study of PZQ effects in vitro, (ii) to identify morphological markers of PZQ action on O. felineus, (iii) to analyse damage to the worm surface and (iv) to assess the efficacy of PZQ in vivo in a hamster model. Light microscopy, optical sectioning and fluorescence microscopy were used to study morphological changes. In vivo, PZQ at a dose of 400mg/kg reduced the rate of infection in experimental acute and chronic opisthorchiasis in hamsters by 70% and 79%, respectively. In vitro, the drug caused destruction and vacuolisation of the tegument of O. felineus, contractions of the worm musculature, paralysis, and irreversible changes in morphology (IC50=0.14μg/mL). Differences in susceptibility to the drug between adult and newly excysted metacercariae were also observed. Qualitative effects of PZQ in vivo and in vitro were similar to the drugs effects on other trematodes, including epidemiologically important liver flukes. Nevertheless, high heterogeneity of O. felineus specimens in terms of susceptibility to the drug was observed. In addition, we describe for the first time the high rate of recovery of O. felineus following the destructive action of PZQ.

Molecular genetic identification and phylogeny of Daphnia species (Crustacea, Cladocera) from water bodies of the Lake Chany basin

The data on the molecular genetic identification of Daphnia species from the water bodies of the Lake Chany basin are presented. Phylogenetic relationships between these species have been established. The fragments of the mitochondrial DNA genes were used as genetic markers. According to the data obtained, the water bodies examined were inhabited by five Daphnia species, including Daphnia (Daphnia) galeata Sars, D. (D.) longispina O. F. Müller, D. (D.) curvirostris Eylmann, D. (D.) pulex Leydig, and D. (Ctenodaphnia) magna Straus. In addition, longispina a-like individuals that form a separate phylogenetic lineage was identified.

Whole transcriptome profiling of adult and infective stages of the trematode Opisthorchis felineus

Opisthorchis felineus, the trematode belonging to the family Opisthorchiidae, is a causative agent of the infection called opisthorchiasis or liver fluke infection. Being a close relative of Opisthorchis viverrini and Clonorchis sinensis (oriental liver flukes) it is encountered in northern Eurasia, especially in Russia, Kazakhstan, Belarus, Ukraine, and Baltic countries. Whole genome data for oriental liver flukes revealed their adaptations for life in the bile duct but our knowledge of O. felineus is scarce. To address this knowledge gap and uncover evolutionary aspect of the adaptations on the transcriptomic level, we used RNA-sequencing approach to investigate two stages of the parasite residing in different hosts. Bioinformatic analysis revealed specific features affecting various biochemical pathways and gene networks. Namely, we observed the loss of genes involved in polyamine synthesis, methionine salvage and peroxisome biogenesis. Some of the gene families, like MD-2 lipid binding proteins, calmodulins and cathepsins on the contrary have expanded compared to free living eukaryotes. We identified significant differences between the stages in homeodomain-containing genes, G-protein coupled receptors, and neuroactive signaling systems. Granulin-like growth factors specific for O. felineus were also identified. In this work, we provide the first whole transcriptome investigation of this parasite. We also hope that these results will create a background for further molecular research of helminth infections and opisthorchiasis in particular.

Adult Opisthorchis felineus major protein fractions deduced from transcripts: comparison with liver flukes Opisthorchis viverrini and Clonorchis sinensis.

The epidemiologically important liver flukes Opisthorchis felineus, Opisthorchis viverrini, and Clonorchis sinensis are of interest to health professionals, epidemiologists, pharmacologists, and molecular biologists. Recently the transcriptomes of the latter two species were intensively investigated. However our knowledge on molecular biology of O. felineus is scarce. We report the first results of the O. felineus transcriptome analysis. We isolated and annotated a total of 2560 expressed sequence tag (EST) sequences from adult O. felineus (deposited within the database of expressed sequence tags (dbEST), under accession numbers GenBank: JK624271-JK626790, JK006511-JK006547, JK649790-JK649792). Clustering and analysis resulted in the detection of 267 contigs. Of the protein sequences deduced from these, 82% had homologs in the NCBI (nr) protein database and 63% contained conserved domains, allowing the functions to be interpreted using the Gene Ontology terms. Comprehensive analysis of Opisthorchiidae- and Trematoda-specific substitutions within amino acid sequences deduced for the proteins myoglobin, vitelline precursor protein, cathepsin F, and 28kDa glutathione transferase was carried out. The gene set of the 32 ribosomal proteins for the three Opisthorchiidae species with the addition of available Schistosoma and Fasciola orthologs was created and is provided in the supplementary. The orthologous gene set created was used for inferring phylogeny within the Trematoda with special attention to interrelations within the Opisthorchiidae. The phylogenetic analysis revealed a closer relationship between C. sinensis and O. viverrini and some divergence of O. felineus from either O. viverrini or C. sinensis.

Morphological, ecological and mtDNA sequence variation in coregonid fi sh from the Baunt Lake system (the Vitim River basin)

We performed morphological, ecological and genetic analyses of taxonomically complex sympatric whitefi sh forms inhabiting the Baunt Lake system in the Vitim River basin, Transbaikalia. It was shown that the whitefi sh forms in this system clearly differed based on morphological traits, growth rate and diet. The most signifi cant differences were based on the number of gill rakers, while the number of lateral line scales was similar. These whitefi sh had distinct diets, namely euryphagous and planktivorous diets. We developed a phylogeny of mtDNA haplotypes among the whitefi sh species and populations from the Baunt Lake system and the headwater regions of the Ob and Yenisei River basins. A morphologically homogeneous cisco-like whitefi sh sample revealed two distinct mitochondrial lineages. A strong genetic divergence between the fi rst mitochondrial lineage of cisco-like whitefi sh and all of the studied whitefi sh forms was revealed. We analyzed alternative hypotheses regarding the ori gin of cisco-like whitefi sh and the densely rakered whitefi sh form from the Baunt Lake system.

Hemozoin is a product of heme detoxification in the gut of the most medically important species of the family Opisthorchiidae.

Many species of trematodes such as Schistosoma spp., Fasciola hepatica and Echinostoma trivolvis are blood-feeding parasites. Nevertheless, there is no consensus on the feeding habits of the family Opisthorchiidae (Opisthorchis felineus, Opisthorchis viverrini and Clonorchis sinensis). Previously, histological studies of O. felineus and C. sinensis revealed some dark stained material in their gut lumen. In this study we conducted a comprehensive analysis of the gut contents of three members of the family Opisthorchiidae (O. felineus, O. viverrini and C. sinensis). Using transmission electron microscopy, we demonstrated for the first known time the presence of disintegrating blood cells in the gut of O. felineus as well as electron-dense crystals in the gut of O. felineus and C. sinensis. Electron energy loss spectroscopy revealed iron atoms in these crystals, and mass spectrometry of the purified pigment demonstrated the presence of heme. Fourier-transform infrared spectroscopy identified the signature peaks of the common iron-carboxylate bond characteristic in crystals isolated from O. felineus and C. sinensis. Scanning electron microscopy showed layered ovoid crystals of various sizes from 50 nm to 2 μm. Morphological, chemical and paramagnetic properties of these crystals were similar to those of hemozoin from Schistosoma mansoni. Crystal formation occurs on the surface of lipid droplets in O. felineus and C. sinensis guts. Our results suggest that the diet of O. felineus and C. sinensis includes blood. Detoxification of the free heme produced during the digestion proceeds via formation of insoluble crystals that contain iron and heme dimers, i.e. crystals of hemozoin. Furthermore, we believe that biocrystallisation of hemozoin takes place on the surface of the lipid droplets, similar to S. mansoni. Hemozoin was not detected in the closely related species O. viverrini.

The morphofunctional and biochemical characteristics of opisthorchiasis-associated cholangiocarcinoma in a Syrian hamster model

The validity of the experimental models of pathologies is one of the key challenges in translational medicine. Cholangiocarcinoma, or bile duct cancer, ranks second among oncological diseases of the liver. There is a strong association between bile duct cancer and parasitic infestation of the liver caused by trematodes in the Opisthorchiidae family. We recently demonstrated that cholangiocarcinoma can develop in Syrian hamsters (Mesocricetus auratus) infected by Opisthorchis felineus and administered with dimethylnitrosamine. However, there is still no description of how this experimental model can be used in translational research. The aim of this work was to study the morphological, functional, and biochemical characteristics during cholangiocarcinoma development in Syrian hamsters infected by O. felineus and administered with dimethylnitrosamine. The experiment lasted 30 weeks with combined administration of dimethylnitrosamine in drinking water at a dose of 12.5 ppm and a single injection of 50 metacercariae O. felineus. It was shown that the development of cholangiocarcinoma (18 weeks) increased the total number of basophils, eosinophils, and monocytes; the relative number of granulocytes, as well as the amount of total and direct bilirubin; and the cholesterol and ALT levels; however, it reduced the relative number of lymphocytes. Based on pathological, morphometric, and biochemical analyses, our model has characteristics similar to those in patients with opisthorchiasis-associated cholangiocarcinoma. Thus, this model can be used to test anticancer drugs, to study the mechanisms of cholangiocarcinogenesis, and to search for molecular markers for early diagnosis of bile duct cancer.