Establishment of cell cultures from hydatid cysts of Echinococcus granulosus

Establishment and application of unbiased in vitro drug screening assays for the identification of compounds against Echinococcus granulosus sensu stricto

Echinococcus multilocularis and E. granulosus s.l. are the causative agents of alveolar and cystic echinococcosis, respectively. Drug treatment options for these severe and neglected diseases are limited to benzimidazoles, which are not always efficacious, and adverse side effects are reported. Thus, novel and improved treatments are needed. In this study, the previously established platform for E. multilocularis in vitro drug assessment was adapted to E. granulosus s.s. In a first step, in vitro culture protocols for E. granulosus s.s. were established. This resulted in the generation of large amounts of E. granulosus s.s. metacestode vesicles as well as germinal layer (GL) cells. In vitro culture of these cells formed metacestode vesicles displaying structural characteristics of metacestode cysts generated in vivo. Next, drug susceptibilities of E. multilocularis and E. granulosus s.s. protoscoleces, metacestode vesicles and GL cells were comparatively assessed employing established assays including (i) metacestode vesicle damage marker release assay, (ii) metacestode vesicle viability assay, (iii) GL cell viability assay, and (iv) protoscolex motility assay. The standard drugs albendazole, buparvaquone, mefloquine, MMV665807, monepantel, niclosamide and nitazoxanide were included. MMV665807, niclosamide and nitazoxanide were active against the parasite in all four assays against both species. MMV665807 and monepantel were significantly more active against E. multilocularis metacestode vesicles, while albendazole and nitazoxanide were significantly more active against E. multilocularis GL cells. Albendazole displayed activity against E. multilocularis GL cells, but no effects were seen in albendazole-treated E. granulosus s.s. GL cells within five days. Treatment of protoscoleces with albendazole and monepantel had no impact on motility. Similar results were observed for both species with praziquantel and its enantiomers against protoscoleces. In conclusion, in vitro culture techniques and drug screening methods previously established for E. multilocularis were successfully implemented for E. granulosus s.s., allowing comparisons of drug efficacy between the two species. This study provides in vitro culture techniques for the reliable generation of E. granulosus s.s. metacestode vesicles and GL cell cultures and describes the validation of standardized in vitro drug screening methods for E. granulosus s.s.

Effects of Zataria multiflora essential oil on the germinative cells of Echinococcus granulosus

Background

Novel and more efficient compounds are urgently required for medical treatment of cystic echinococcosis (CE). Germinative cell culture of Echinococcus granulosus could be used for anti-echinococcosis agent tests and other biological studies on CE. This study was performed to establish an in vitro cell culture model for E. granulosus germinative cells and to evaluate the lethal effect of Zataria multiflora essential oil (ZMEO) on the cultured cells.

Methods

The inner surface of germinal layers of CE cysts was scraped, and the obtained materials were trypsinized to obtain a suspension of single germinative cells. Medium 199 was used as the basic culture medium and was supplemented with fetal bovine serum, 2-mercaptoethanol, l-cysteine, l-glutamine, glucose, sodium pyruvate, hydatid fluid, amphotericin B and antibiotics. The cells were cultured at a concentration of 10⁴ cells/ml of culture medium and incubated at 37 °C. The culture medium was replaced every 7 days. Chemical composition of ZMEO was identified by GC-MS analysis. ZMEO was tested at concentrations of 0.5–8 mg/ml. Viability of the cells was assessed by trypan blue exclusion assay.

Results

A significant increase in the cell number was evident at 20, 30 and 45 days after cultivation. At 45 days of cultivation, the number of cells was approximately five-fold higher than on the first day. In GC-MC analysis, carvacrol, p-cymene, g-terpinene and thymol were found to be the main compounds of ZMEO. The lethal effect of ZMEO on the germinative cells at concentrations of 6, 7 and 8 mg/ml was 100% after 60, 25 and 7 min of exposure, respectively.

Conclusions

At 45 days of cultivation, the cell concentration was suitable for the desired in vitro experiments. A high lethal effect of ZMEO on the germinative cells of E. granulosus may be considered an opportunity for the introduction of a novel, more effective and safer therapeutic agent for treatment of CE using an herbal product.

Graphic abstract

In vivo and in vitro efficacies of mebendazole, mefloquine and nitazoxanide against cyst echinococcosis

Echinococcus granulosus is a cestode parasite. The metacestode stage causes cystic echinococcosis (CE) mainly in the human liver and lung. Current chemotherapy against CE is based on mebendazole and albendazole. However, benzimidazoles result in a low cure rate or are ineffective in many patients; therefore, novel compounds for the treatment of this disease have been studied. Mefloquine was reported to be dramatically effective on cultured Echinococcus multilocularis metacestodes in vitro. And, nitazoxanide has a prominent protoscolicidal effect. However, these compounds have no impact on the growth of cysts harbored in mice. In this study, we investigated the in vitro and in vivo efficacy of mebendazole, mefloquine, and nitazoxanide against E. granulosus protoscoleces, germinal cells, and infected mice. The effect of mebendazole on protoscoleces and germinal cell was proved to be dose-dependent in vitro. And, a reduction of the cyst weight was also the found after oral application of mebendazole to infected mice. Mefloquine (5 and 10 μg/ml) caused death within 24 h of protoscoleces and germinal cells in vitro, whereas a lower concentration of 1 μg/ml was ineffective. In mice infected with E. granulosus, oral mefloquine (200 and 400 mg/kg twice weekly for 2 weeks) showed no reduction in parasite weight. Without affecting the viability of germinal cells and the growth of hydatid cysts, nitazoxanide only showed protoscolicidal effects in infected mice. In conclusion, mebendazole, mefloquine, and nitazoxanide showed various effects on E. granulosus under different conditions. These drugs could be useful to some extent in the treatment of CE.

Development of a cell line from Echinococcus granulosus germinal layer

In vitro culture of parasitic helminths provides an important tool to study cell regeneration and physiology, as well as for molecular biology and genetic engineering studies. In the present study, we established in vitro propagation of cells from Echinococcus granulosus germinal cyst layer. E. granulosus germinal cells grew beyond 100 passages and showed no signs of reduced proliferation capacity. Microscopic analysis revealed that cells grew both attached to the substrate and in suspension, forming three-dimensional structures like mammalian stem cell aggregates. Examination of the chromosome number of attached germinal cells showed a high degree of heteroploidy, suggesting the occurrence of transformation during culture. Monolayer cells survived cryopreservation and were able to proliferate after thawing. Based on the characteristics displayed by E. granulosus germinal cells, we establish a cell line from the E. granulosus germinal layer. Furthermore, we propose that this cell line could be useful for drug screening and for obtaining parasite material.

The genome of the hydatid tapeworm Echinococcus granulosus

Cystic echinococcosis (hydatid disease), caused by the tapeworm E. granulosus, is responsible for considerable human morbidity and mortality. This cosmopolitan disease is difficult to diagnose, treat and control. We present a draft genomic sequence for the worm comprising 151.6 Mb encoding 11,325 genes. Comparisons with the genome sequences from other taxa show that E. granulosus has acquired a spectrum of genes, including the EgAgB family, whose products are secreted by the parasite to interact and redirect host immune responses. We also find that genes in bile salt pathways may control the bidirectional development of E. granulosus, and sequence differences in the calcium channel subunit EgCavβ1 may be associated with praziquantel sensitivity. Our study offers insights into host interaction, nutrient acquisition, strobilization, reproduction, immune evasion and maturation in the parasite and provides a platform to facilitate the development of new, effective treatments and interventions for echinococcosis control.

Morphological and biological characterization of cell line developed from bovine Echinococcus granulosus

The taeniid tapeworm Echinococcus granulosus is the causative agent of echinococcal disease, a major zoonosis with worldwide distribution. Several efforts to establish an in vitro model of E. granulosus have been undertaken; however, many of them have been designed for Echinococcus multilocularis. In the present study, we have described and characterized a stable cell line obtained from E. granulosus bovine protoscoleces maintained 3 yr in vitro. Growth characterization, morphology by light, fluorescent and electronic microscopy, and karyotyping were carried out. Cell culture origin was confirmed by immunofluorescent detection of AgB4 antigen and by PCR for the mitochondrial cytochrome c-oxidase subunit 1 (DCO1) gene. Cells seeded in agarose biphasic culture resembled a cystic structure, similar to the one formed in secondary hosts. This cell line could be a useful tool to research equinococcal behavior, allowing additional physiological and pharmacological studies, such as the effect of growth factors, nutrients, and antiparasitic drugs on cell viability and growth and on cyst formation.

Transient transfection of Echinococcus multilocularis primary cells and complete in vitro regeneration of metacestode vesicles

A major limitation in studying molecular interactions between parasitic helminths and their hosts is the lack of suitable in vitro cultivation systems for helminth cells and larvae. Here we present a method for long-term in vitro cultivation of larval cells of the tapeworm Echinococcus multilocularis, the causative agent of alveolar echinococcosis. Primary cells isolated from cultivated metacestode vesicles in vitro showed a morphology typical of Echinococcus germinal cells, displayed an Echinococcus-specific gene expression profile and a cestode-like DNA content of approximately 300Mbp. When kept under reducing conditions in the presence of Echinococcus vesicle fluid, the primary cells could be maintained in vitro for several months and proliferated. Most interestingly, upon co-cultivation with host hepatocytes in a trans-well system, mitotically active Echinococcus cells formed cell aggregates that subsequently developed central cavities, surrounded by germinal cells. After 4 weeks, the cell aggregates gave rise to young metacestode vesicles lacking an outer laminated layer. This layer was formed after 6 weeks of cultivation indicating the complete in vitro regeneration of metacestode larvae. As an initial step toward the creation of a fully transgenic strain, we carried out transient transfection of Echinococcus primary cells using plasmids and obtained heterologous expression of a reporter gene. Furthermore, we successfully carried out targeted infection of Echinococcus cells with the facultatively intracellular bacterium Listeria monocytogenes, a DNA delivery system for genetic manipulation of mammalian cells. Taken together, the methods presented herein constitute important new tools for molecular investigations on host-parasite interactions in alveolar echinococcosis and on the roles of totipotent germinal cells in parasite regeneration and metastasis formation. Moreover, they enable the development of fully transgenic techniques in this group of helminth parasites for the first time.

Invertebrate cell culture considerations: insects, ticks, shellfish, and worms

Establishment of cell lines from insect and arachnid invertebrates has become routine, whereas other invertebrate taxa have been frustratingly unproductive of cell lines. None is available for any marine invertebrate, despite a strong and well-recognized need for cell lines from species that are important in aquaculture, from parasite vectors and intermediate hosts of parasites, from parasites themselves, from certain biomedical models, and from other species that are pests. Drawing on experiences gained attempting to establish cell lines from molluscs and trematodes and on published and ongoing research with diverse invertebrates, this chapter attempts to anticipate the problems that are likely to be encountered in such endeavors and discusses possible solutions. Criteria to be considered in the selection of basic culture media, temperature, pH, and media additives; approaches that have been developed to yield sterile primary cultures; and factors to consider in decisions about feeding schedules, retention of tissue fragments and nonadherent cells, use of heterologous feeder layers, and other variables are described. Suggestions are made concerning means to objectively score the success of tested variables and means to induce cell replication. The chapter ends with notes on conventional means to characterize cell lines and an account of contemporary efforts to immortalize cells by means of genome manipulation. Enduring success with a single molluscan cell line, transient successes with crustacean and helminth cell lines, and promising developments in transgenesis with invertebrates all lead to the hopeful conclusion that the invisible barrier to cell propagation in historically refractory species will soon be a thing of the past.

Contact-dependent disruption of the host cell membrane skeleton induced by Trichomonas vaginalis

This report presents evidence showing that the pathogenetic process of the protozoan parasite Trichomonas vaginalis involves degradation of the target cell membrane skeleton; spectrin, the most representative protein within this structure, has been identified as the main molecular target. Degradation of the target cell spectrin is accomplished only upon contact with the parasite, and immunochemical and immunofluorescence studies performed with the erythrocyte as a model demonstrate that degradation of the protein takes place before target cell lysis. A preliminary characterization of the effectors involved has led to the identification of a nonsecreted 30-kDa proteinase which is characterized by a high specificity for spectrin. This molecule is suggested as the main effector responsible for cytoskeletal disruption.

An established cell line of larval Echinococcus multilocularis

A cell line of larval Echinococcus multilocularis has been established from an echinococcal cyst excised surgically from a patient with alveolar hydatid disease. A standardized procedure established for the preparation and continuation of primary cultures was applied to isolate the E. multilocularis cells from the tissue fragments. Trypsin was used for the enzymatic release of the monodispersed cells from the tissue fragments and for dispersing monolayers. The culture medium was RPMI 1640 with 10% fetal calf serum. Cell supports were collagen-coated plastic dishes and flasks. The morphological features of the cultured cells showed spindle-like cells during the first few subcultures, and then polygonal or star-like cells. Population doubling time at passage 34 was approximately 23 h and plating efficiency at the same passage was 15%. Chromosome numbers obtained from 70 metaphase plates at passage 40 ranged between 14 and 104 and cells with 91-100 chromosomes were clearly predominant. The chromosomes could be morphologically classified into telocentric, subtelocentric, and metacentric types. Over 90% of the chromosomes were of the telocentric type. Cells collected at passage 57 were intraperitoneally inoculated into two cotton rats (Sigmodon hispidus) at a cell concentration of 10(7) and the rats were sacrificed 100 days later. It was found that the two rats had echinococcal cyst masses in the peritoneal cavity. This result indicates that our isolated cells are germinal cells with ability to differentiate into cystic structures in vivo.

Echinococcus: biology and strain variation

Biology and strain variation in the causative agent of hydatid disease is reviewed with emphasis on developmental and genetic aspects. In vitro cultivation experiments have made a significant contribution to current knowledge of the developmental plasticity of Echinococcus. However, the mechanisms which regulate and determine developmental strategies in the parasite, as well as the characteristics, source and cytodifferentiation of germinal cells, are not understood. The nature, significance and origin of strain variation in Echinococcus are examined. Before we can fully appreciate the phenotypic consequences of genetic differentiation between populations, we need to know something about the genetic and environmental components of variation in traits such as development rate, host preference, host specificity, virulence and drug resistance. There is an urgent need for research on the developmental pathways by which genetic differences within and between strains of E. granulosus are translated to phenotypic differences in these traits.

Echinococcus multilocularis: in vitro secretion of antigen by hybridomas from metacestode germinal cells and murine tumor cells

Hybrid cells were produced from Echinococcus multilocularis metacestode germinal cells and murine tumor cells. Small colonies were formed which, while ceasing to grow after a few generations, remained viable for at least 10 weeks. These hybridoma cells secrete antigen(s) reacting in indirect immunofluorescence and ELISA specifically with sera from patients suffering from an E. multilocularis infection. The antigen(s) appear suitable for the differential diagnosis of E. multilocularis and E. granulosus. Thus, hybridoma cells may produce helminth antigens.