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1.  In Vitro Metacestodicidal Activities of Genistein and Other Isoflavones against Echinococcus multilocularis and Echinococcus granulosus▿  
Antimicrobial Agents and Chemotherapy  2006;50(11):3770-3778.
Echinococcus multilocularis and Echinococcus granulosus metacestode infections in humans cause alveolar echinococcosis and cystic echinococcosis, respectively, in which metacestode development in visceral organs often results in particular organ failure. Further, cystic hydatidosis in farm animals causes severe economic losses. Although benzimidazole derivatives such as mebendazole and albendazole are being used as therapeutic agents, there is often no complete recovery after treatment. Hence, in searching for novel treatment options, we examined the in vitro efficacies of a number of isoflavones against Echinococcus metacestodes and protoscoleces. The most prominent isoflavone, genistein, exhibits significant metacestodicidal activity in vitro. However, genistein binds to the estrogen receptor and can thus induce estrogenic effects, which is a major concern during long-term chemotherapy. We have therefore investigated the activities of a number of synthetic genistein derivatives carrying a modified estrogen receptor binding site. One of these, Rm6423, induced dramatic breakdown of the structural integrity of the metacestode germinal layer of both species within 5 to 7 days of in vitro treatment. Further, examination of the culture medium revealed increased leakage of parasite proteins into the medium during treatment, but zymography demonstrated a decrease in the activity of metalloproteases. Moreover, two of the genistein derivatives, Rm6423 and Rm6426, induced considerable damage in E. granulosus protoscoleces, rendering them nonviable. These findings demonstrate that synthetic isoflavones exhibit distinct in vitro effects on Echinococcus metacestodes and protoscoleces, which could potentially be exploited further for the development of novel chemotherapeutical tools against larval-stage Echinococcus infection.
PMCID: PMC1635224  PMID: 16954323
2.  Identification and Characterization of a Neospora caninum Microneme-Associated Protein (NcMIC4) That Exhibits Unique Lactose-Binding Properties  
Infection and Immunity  2004;72(8):4791-4800.
Microneme proteins have been shown to play an important role in the early phase of host cell adhesion, by mediating the contact between the parasite and host cell surface receptors. In this study we have identified and characterized a lectin-like protein of Neospora caninum tachyzoites which was purified by α-lactose-agarose affinity chromatography. Upon separation by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, this lactose-binding protein migrated at 70 and 55 kDa under reducing and nonreducing conditions, respectively. Immunofluorescence and immunogold electron microscopy with affinity-purified antibodies showed that the protein was associated with the tachyzoite micronemes. Mass spectrometry analyses and expressed sequence tag database mining revealed that this protein is a member of the Neospora microneme protein family; the protein was named NcMIC4 (N. caninum microneme protein 4). Upon two-dimensional gel electrophoresis, NcMIC4 separated into seven distinct isoforms. Incubation of extracellular parasites at 37°C resulted in the secretion of NcMIC4 into the medium as a soluble protein, and the secreted protein exhibited a slightly reduced Mr but retained its lactose-binding properties. Immunofluorescence was used to investigate the temporal and spatial distribution of NcMIC4 in tachyzoites entering their host cells and showed that reexpression of NcMIC4 took place 30 min after entry into the host cell. Incubation of secreted fractions and purified NcMIC4 with Vero cells demonstrated binding of NcMIC4 to Vero cells as well as binding to chondroitin sulfate A glycosaminoglycans.
PMCID: PMC470650  PMID: 15271941
3.  In Vitro Induction of Neospora caninum Bradyzoites in Vero Cells Reveals Differential Antigen Expression, Localization, and Host-Cell Recognition of Tachyzoites and Bradyzoites  
Infection and Immunity  2004;72(1):576-583.
We report on an optimized method for the in vitro culture of tissue cyst-forming Neospora caninum bradyzoites in Vero cells and the separation of viable parasites from host cells. Treatment of tachyzoite-infected Vero cell cultures with 17 μM sodium nitroprusside for 8 days severely scaled down parasite proliferation, led to reduced expression of tachyzoite surface antigens, and induced the expression of the bradyzoite marker NcBAG1 and the cyst wall antigen recognized by the monoclonal antibody MAbCC2. Transmission electron microscopy demonstrated that intracellular parasites were located within parasitophorous vacuoles that were surrounded by a cyst wall-like structure, and the dense granule antigens NcGRA1, NcGRA2, and NcGRA7 were incorporated into the cyst wall. Adhesion-invasion assays employing purified tachyzoites and bradyzoites showed that tachyzoites adhered to, and invaded, Vero cells with higher efficiency than bradyzoites. However, removal of terminal sialic acid residues from either the host cell or the parasite surface increased the invasion of Vero cells by bradyzoites, but not tachyzoites.
PMCID: PMC343979  PMID: 14688139
4.  Identification of a Neospora caninum Microneme Protein (NcMIC1) Which Interacts with Sulfated Host Cell Surface Glycosaminoglycans  
Infection and Immunity  2002;70(6):3187-3198.
The invasive stages of apicomplexan parasites enter their host cells through mechanisms which are largely conserved throughout the phylum. Host cell invasion is divided into two distinct events, namely, adhesion onto the host cell surface and the actual host cell entry process. The former is mediated largely through microneme proteins which are secreted at the onset of establishing contact with the host cell surface. Many of the microneme proteins identified so far contain adhesive domains. We here present the genomic and corresponding cDNA sequences coding for a 460-amino-acid (aa) microneme protein in Neospora caninum tachyzoites which, due to its homology to MIC1 in Toxoplasma gondii (TgMIC1), was named NcMIC1. The deduced NcMIC1 polypeptide sequence contains an N-terminal signal peptide of 20 aa followed by two tandemly internal repeats of 48 and 44 aa, respectively. Integrated into each repeat is a CXXXCG sequence motif reminiscent of the thrombospondin-related family of adhesive proteins. The positioning of this motif is strictly conserved in TgMIC1 and NcMIC1. The C-terminal part, comprised of 278 aa, was expressed in Escherichia coli, and antibodies affinity purified on recombinant NcMIC1 were used to confirm the localization within the micronemes by immunofluorescence and immunogold transmission electron microscopy of tachyzoites. Immunohistochemistry of mouse brains infected with tissue cysts showed that expression of this protein is reduced in the bradyzoite stage. Upon initiation of secretion by elevating the temperature to 37°C, NcMIC1 is released into the medium supernatant. NcMIC1 binds to trypsinized, rounded Vero cells, as well as to Vero cell monolayers. Removal of glycosaminoglycans from the host cell surface and modulation of host cell surface glycosaminoglycan sulfation significantly reduces the binding of NcMIC1 to the host cell surface. Solid-phase binding assays employing defined glycosaminoglycans confirmed that NcMIC1 binds to sulfated glycosaminoglycans.
PMCID: PMC127992  PMID: 12011014
5.  Application of Real-Time Fluorescent PCR for Quantitative Assessment of Neospora caninum Infections in Organotypic Slice Cultures of Rat Central Nervous System Tissue 
Journal of Clinical Microbiology  2002;40(1):252-255.
The previously described Nc5-specific PCR test for the diagnosis of Neospora caninum infections was used to develop a quantitative PCR assay which allows the determination of infection intensities within different experimental and diagnostic sample groups. The quantitative PCR was performed by using a dual fluorescent hybridization probe system and the LightCycler Instrument for online detection of amplified DNA. This assay was successfully applied for demonstrating the parasite proliferation kinetics in organotypic slice cultures of rat brain which were infected in vitro with N. caninum tachyzoites. This PCR-based method of parasite quantitation with organotypic brain tissue samples can be regarded as a novel ex vivo approach for exploring different aspects of cerebral N. caninum infection.
PMCID: PMC120097  PMID: 11773124
6.  Neospora caninum Microneme Protein NcMIC3: Secretion, Subcellular Localization, and Functional Involvement in Host Cell Interaction 
Infection and Immunity  2001;69(10):6483-6494.
In apicomplexan parasites, host cell adhesion and subsequent invasion involve the sequential release of molecules originating from secretory organelles named micronemes, rhoptries, and dense granules. Microneme proteins have been shown to be released at the onset of the initial contact between the parasite and the host cell and thus mediate and establish the physical interaction between the parasite and the host cell surface. This interaction most likely involves adhesive domains found within the polypeptide sequences of most microneme proteins identified to date. NcMIC3 is a microneme-associated protein found in Neospora caninum tachyzoites and bradyzoites, and a large portion of this protein is comprised of a stretch of four consecutive epidermal growth factor (EGF)-like domains. We determined the subcellular localization of NcMIC3 prior to and following host cell invasion and found that NcMIC3 was secreted onto the tachyzoite surface immediately following host cell lysis in a temperature-dependent manner. Surface-exposed NcMIC3 could be detected up to 2 to 3 h following host cell invasion, and at later time points the distribution of the protein was again restricted to the micronemes. In vitro secretion assays using purified tachyzoites showed that following secretion onto the surface, NcMIC3 was largely translocated towards the posterior end of the parasite, employing a mechanism which requires a functional actin microfilament system. Following this, the protein remained bound to the parasite surface, since it could not be detected in a soluble form in respective culture supernatants. Secretion of NcMIC3 onto the surface resulted in an outward exposure of the EGF-like domains and coincided with an increased capacity of N. caninum tachyzoites to adhere to Vero cell monolayers in vitro, a capacity which could be inhibited by addition of antibodies directed against the EGF-like domains. NcMIC3 is a prominent component of Triton X-100 lysates of tachyzoites, and cosedimentation assays employing prefixed Vero cells showed that the protein binds to the Vero cell surface. In addition, the EGF-like domains, expressed as recombinant proteins in Escherichia coli, also interacted with the Vero cell surface, while binding of NcSRS2 and NcSAG1, the major immunodominant surface antigens, was not as efficient. Our data are indicative of a functional role of NcMIC3 in host cell infection.
PMCID: PMC98784  PMID: 11553593

Results 1-6 (6)