Pathobiology of opisthorchiasis: an update

Apoptosis-related gene expressions in hamsters re-infected with Opisthorchis viverrini and re-treated with praziquantel

Our objective was to reveal whether host immune response in hamster opisthorchiasis post-praziquantel treatment could induce apoptotic cell death in inflammatory cells. We, therefore, investigated apoptosis-related gene expression in hamsters re-infected with Opisthorchis viverrini (OV) and re-treated with praziquantel. Hamsters were re-infected with OV metacercariae then re-treated with praziquantel. The expression of apoptosis-related genes (i.e. apoptosis gene Bcl-2 associated protein X [BAX], caspase 9, p53 and protein kinase B [PKB]) was detected by real-time reverse transcription-polymerase chain reaction. Histopathological analyses of liver tissues were performed by staining the sections with haematoxylin and eosin using light microscopy. The results show that BAX, Akt/PKB, p53 and caspase 9 expression levels were significantly increased on day 30 post-infection and at 6 h post-treatment and gradually decreased to a level near the uninfected control and at 24 h post-treatment, perhaps because of a decrease in inflammatory cells. Apoptotic cell death was observed at the nuclei of epithelial cells of the bile ducts and of T cells. Our results suggest that repeated infection with OV and re-treatment with praziquantel induces a host immune response that increases inflammatory cells, which in turn leads to increase, apoptosis-related gene expression in the short term post-treatment.

Liver fluke induces cholangiocarcinoma

The authors discuss the molecular pathogenesis of opisthorchiasis and associated cholangiocarcinogenesis, particularly nitrative and oxidative DNA damage and the clinical manifestations of cholangiocarcinoma.

Parasitic diseases of the biliary tract

OBJECTIVE

Parasites residing in the biliary tree include Clonorchis sinensis, Opisthorchis viverrini, Opisthorchis felineus, and Fasciola hepatica. They are willowy, leaf-like, flat flukes dwelling in the bile ducts and gallbladder. Human ascarides, Ascaris lumbricoides, dwelling in the small intestine, inadvertently migrate into the bile ducts and cause biliary obstruction. The purpose of this article is to illustrate typical imaging findings of liver fluke infection and biliary ascariasis.

CONCLUSION

Adult flukes of Clonorchis and Opisthorchis measure 8-15 mm and adult flukes of Fasciola measure 20-40 mm in length. The presence of flukes in the bile ducts causes dilatation of the bile ducts, varying degrees of chronic inflammation followed by adenomatous hyperplasia, and bile duct wall thickening. Imaging findings of clonorchiasis and opisthorchiasis include visualization of adult flukes in the bile ducts and gallbladder, diffuse dilatation of the peripheral small intrahepatic bile ducts with no or minimal dilatation of the large bile ducts, and thickening of the bile duct wall. In biliary fascioliasis and ascariasis, adult worms are visualized in the dilated bile ducts and gallbladder.

Parasitic infestations of the biliary tract

Parasitic infestations of the biliary tract are a common cause of biliary obstruction in tropical countries and can lead to such serious complications as cholangitis and cholangiocarcinoma. Endoscopic therapy has helped in the management of biliary complications caused by these parasites. Ascaris lumbricoides organisms, which normally reside in the jejunum, are actively motile and can invade the papilla, thus migrating into the bile duct and causing biliary obstruction. Endoscopic retrograde cholangiopancreatography is a useful diagnostic tool with potential for therapeutic management of biliary ascariasis. Infestation with Clonorchis sinensis organisms can cause such complications as intrahepatic stones, recurrent pyogenic cholangitis, cirrhosis, cholelithiasis, pancreatitis, and cholangiocarcinoma. Opisthorchis viverrini, Opisthorchis felineus, and Dicrocoelium dendriticum are closely related to C. sinensis and can also cause serious biliary complications. Fascioliasis, caused by Fasciola hepatica and F. gigantica, is a zoonotic helminthiasis that can present as acute hepatic or chronic biliary tract infection. CT, MRI, and ultrasound guidance are useful imaging tools for identifying these parasites and their complications.

A pilot screening of prevalence of atopic states and opisthorchosis and their relationship in people of Tomsk Oblast

The study was aimed to estimate the relationship between the prevalence of allergic disease and helminth invasion by the trematode Opisthorchis felineus in rural and urban populations of Tomsk Oblast (West Siberia, Russia). Two hundred and one people from Kargasok village of Tomsk Oblast and 196 from the city of Tomsk were screened for the presence of atopy and O. felineus invasion. Opisthorchosis was found in 66 participants (32.8%) from Kargasok and in 22 people (11.2%) from Tomsk. Atopic diseases were more common in the urban population than in the rural: 52.8 and 31.4%, respectively. Positive skin-prick tests were significantly higher in the urban population than in rural people: 83.2 vs 24.4%, respectively. It was found that in the city, the presence of antibodies to O. felineus negatively correlates with the atopic sensitization by skin-prick tests. However, in the village, opisthorchosis was positively associated with atopic diseases. The data obtained confirm the negative association of rural lifestyle and atopic diseases prevalence and indicate that O. felineus invasion might be a modifying factor of this relationship in Tomsk Oblast.

Opisthorchis viverrini: identification of a glycine-tyrosine rich eggshell protein and its potential as a diagnostic tool for human opisthorchiasis

A cDNA encoding a novel eggshell protein (OvESP) with high-glycine (49.2%) and -tyrosine (27.8%) content was cloned from the human liver fluke Opisthorchis viverrini. In the adult parasite, the RNA products of the OvESP gene are limited to the vitelline follicles. They have a size of 800 nucleotides and are already present in 2-week-old juveniles. Immune sera of hamsters, experimentally infected, and humans, naturally infected with O. viverrini, detect bacterially expressed recombinant OvESP (rOvESP). A rabbit anti-rOvESP antiserum only reacts with the shells of intrauterine eggs in tissue sections of the parasite. Comparison of rOvESP with the parasite's excretion/secretion products as diagnostic tools for human opisthorchiasis shows a higher sensitivity (0.82-0.48) and specificity (0.97-0.91) of the recombinant protein in the ELISA technique. But the observed weak cross-reactivity of immune sera from mice infected with Schistosoma mansoni, Schistosoma mekongi, and Fasciola gigantica in Western blots of rOvESP indicates that the diagnostic quality of this protein might be compromised if infections by other trematodes are present.

Gene expression profiling defined pathways correlated with fibroblast cell proliferation induced by Opisthorchis viverrini excretory/secretory product

AIM: To investigate the mechanism of fibroblast cell proliferation stimulated by the Opisthorchis viverrini excretory/secretory (ES) product.

METHODS: NIH-3T3, mouse fibroblast cells were treated with O. viverrini ES product by non-contact co-cultured with the adult parasites. Total RNA from NIH-3T3 treated and untreated with O. viverrini was extracted, reverse transcribed and hybridized with the mouse 15K complementary DNA (cDNA) array. The result was analyzed by ArrayVision version 5 and GeneSpring version 5 softwares. After normalization, the ratios of gene expression of parasite treated to untreated NIH-3T3 cells of 2-and more-fold upregulated was defined as the differentially expressed genes. The expression levels of the signal transduction genes were validated by semi-quantitative SYBR-based real-time RT-PCR.

RESULTS: Among a total of 15 000 genes/ESTs, 239 genes with established cell proliferation-related function were 2 fold-and more-up-regulated by O. viverrini ES product compared to those in cells without exposure to the parasitic product. These genes were classified into groups including energy and metabolism, signal transduction, protein synthesis and translation, matrix and structural protein, transcription control, cell cycle and DNA replication. Moreover, the expressions of serine-threonine kinase receptor, receptor tyrosine kinase and collagen production-related genes were up-regulated by O. viverrini ES product. The expression level of signal transduction genes; pkC, pdgfrα, jak 1, eps 8, tgfβ 1i4, strap and h ras measured by real-time RT-PCR confirmed their expression levels to those obtained from cDNA array. However, only the up-regulated expression of pkC, eps 8 and tgfβ 1i4 which are the downstream signaling molecules of either epidermal growth factor (EGF) or transforming growth factor-β (TGF-β) showed statistical significance (P < 0.05).

CONCLUSION: O. viverrini ES product stimulates the significant changes of gene expression in several functional categories and these mainly include transcripts related to cell proliferation. The TGF-β and EGF signal transduction pathways are indicated as the possible pathways of O. viverrini-driven cell proliferation.

Fish-borne parasitic zoonoses: status and issues

The fish-borne parasitic zoonoses have been limited for the most part to populations living in low- and middle-income countries, but the geographical limits and populations at risk are expanding because of growing international markets, improved transportation systems, and demographic changes such as population movements. While many in developed countries will recognize meat-borne zoonoses such as trichinellosis and cysticercosis, far fewer are acquainted with the fish-borne parasitic zoonoses which are mostly helminthic diseases caused by trematodes, cestodes and nematodes. Yet these zoonoses are responsible for large numbers of human infections around the world. The list of potential fish-borne parasitic zoonoses is quite large. However, in this review, emphasis has been placed on liver fluke diseases such as clonorchiasis, opisthorchiasis and metorchiasis, as well as on intestinal trematodiasis (the heterophyids and echinostomes), anisakiasis (due to Anisakis simplex larvae), and diphyllobothriasis. The life cycles, distributions, epidemiology, clinical aspects, and, importantly, the research needed for improved risk assessments, clinical management and prevention and control of these important parasitic diseases are reviewed.

Acute infections as a means of cancer prevention: opposing effects to chronic infections?

PURPOSE

Epidemiological studies have found an inverse association between acute infections and cancer development. In this paper, we review the evidence examining this potentially antagonistic relationship.

METHODS

In addition to a review of the historical literature, we examined the recent epidemiological evidence on the relationship between acute infections and subsequent cancer development in adult life. We also discuss the impact of chronic infections on tumor development and the influence of the immune system in this process.

RESULTS

Exposures to febrile infectious childhood diseases were associated with subsequently reduced risks for melanoma, ovary, and multiple cancers combined, significant in the latter two groups. Epidemiological studies on common acute infections in adults and subsequent cancer development found these infections to be associated with reduced risks for meningioma, glioma, melanoma and multiple cancers combined, significantly for the latter three groups. Overall, risk reduction increased with the frequency of infections, with febrile infections affording the greatest protection. In contrast to acute infections, chronic infections can be viewed as resulting from a failed immune response and an increasing number have been associated with an elevated cancer risk.

CONCLUSION

Infections may play a paradoxical role in cancer development with chronic infections often being tumorigenic and acute infections being antagonistic to cancer.

Nitrative and oxidative DNA damage in intrahepatic cholangiocarcinoma patients in relation to tumor invasion

AIM: Nitrative and oxidative DNA damage such as 8-nitroguanine and 8-oxo-7,8-dihydro-2’-deoxyguanosine (8-oxodG) formation has been implicated in initiation and/ or promotion of inflammation-mediated carcinogenesis. The aim of this study is to clarify whether these DNA lesions participate in the progression of intrahepatic cholangiocarcinoma.

METHODS: We investigated the relation of the formation of 8-nitroguanine and 8-oxodG and the expression of hypoxia-inducible factor-1α (HIF-1α) with tumor invasion in 37 patients with intra-hepatic cholangiocarcinoma.

RESULTS: Immunohistochemical analyses revealed that 8-nitroguanine and 8-oxodG formation occurred to a much greater extent in cancerous tissues than in non-cancerous tissues. HIF-1α could be detected in cancerous tissues in all patients, suggesting low oxygen tension in the tumors. HIF-1α expression was correlated with inducible nitric oxide synthase (iNOS) expression (r = 0.369 and P = 0.025) and 8-oxodG formation (r = 0.398 and P = 0.015). Double immunofluorescence study revealed that iNOS and HIF-1α co-localized in cancerous tissues. Notably, the formation of 8-oxodG was correlated significantly with lymphatic invasion (r = 0.386 and P = 0.018). Moreover, 8-nitroguanine and 8-oxodG in non-cancerous tissues were associated significantly with neural invasion (P = 0.042 and P = 0.026, respectively). These results suggest that reciprocal activation between HIF-1α and iNOS mediates persistent DNA damage, which induces tumor invasiveness via mutations, resulting in poor prognosis.

CONCLUSION: The formation of 8-nitroguanine and 8-oxodG plays an important role in multiple steps of genetic changes leading to tumor progression, including invasiveness.

Chemotherapy for major food-borne trematodes: a review

Food-borne trematode infections, caused by liver flukes (Clonorchis, Fasciola, Opisthorchis), lung flukes (Paragonimus) and intestinal flukes (Echinostoma, Fasciolopsis, heterophyids), are significant public health problems, most notably in Southeast Asia and the Western Pacific. Globally, it is estimated that > 40 million people are infected among the 750 million people who live in endemic areas. The epidemiology of food-borne trematodiasis has changed over the past few decades, and now presents a dual picture. On the one hand, increasing numbers of infections are reported from non-endemic areas, and endemic areas are expanding due to larger areas utilised for aquaculture, domestic migration, declining socioeconomic conditions, lack of improved sanitation, and increasing availability of aquatic foods through wider distribution networks often without proper food inspections. On the other hand, social and economic advances in many Asian countries, going hand-in-hand with urbanisation, use of chemical fertilisers and, above all, the administration of safe, efficacious and inexpensive drugs, have significantly reduced the prevalence of food-borne trematode infections. In this review, the taxonomy, life cycle, and geographical distribution of the major food-borne trematodes, including issues of diagnosis and clinical disease manifestations, is summarised. The discovery, chemistry, pharmacological properties, safety, therapeutic efficacy and adverse effects of the current drugs of choice, namely praziquantel and triclabendazole, is then discussed. Recent advances on other drugs and contemporary investigations on novel compounds that might become important players in chemotherapy are highlighted. Finally, the need for research and development of new trematocidal drugs that - employed in concert with health education, improved sanitation and enhanced food safety - are key factors for sustainable control of food-borne trematodiasis, is highlighted.