Dynamics on nilpotent character varieties

Let R(N,G) be the connected component of the identity of the variety of representations of a finitely generated nilpotent group N into a connected compact Lie group G, and let X(N,G) be the corresponding moduli space. We show that there exists a natural Out(N)-invariant measure on X(N,G) and that whenever Out(N) has at least one hyperbolic element, the action of Out(N) on X(N,G) is mixing with respect to this measure.Comment: 17 pages, Version 2 has minor updates and corrections, accepted for publication in Conformal Geometry and Dynamic

In vitro effects of isoprinosine and of a dipeptide methyl ester on Echinococcus multilocularis.

International audienceA protoscoleces/vesicles in vitro maintenance test with assessment of viability by eosin exclusion was used to evaluate the quantitative and qualitative activities of isoprinosine, its active component inosine and the dipeptide methylester L-Phe-Phe-OMe on isolated protoscoleces of Echinococcus multilocularis for 24 and 48 h. Isoprinosine and inosine showed dose- and time-dependent activity, the latter displaying a more rapid effect than the former. A high activity was shown with L-Phe-Phe-OMe, when compared to praziquantel. Ultrastructural alterations were much more striking with L-Phe-Phe-OMe, with an effect similar to that of praziquantel, whereas the chemotherapeutic activity of inosine and isoprinosine appeared to be directed against a metabolic target, with a lethal effect not immediately visible at the ultrastructural level. Thus, the previously reported in vivo activities of these drugs result largely from a direct effect on the parasite

The native form of thePlasmodium falciparum Pf68 neutral proteinase is a 105,000-Da polypeptide

International audienc

Purification and Characterization of the Alkaline Phosphatase from Echinococcus granulosus Cyst Membranes

International audienceThe purification to homogeneity and the characterization of Echinococcus granulosus alkaline phosphatase (AP; EC 3.1.3.1) from hydatid cyst membranes are described. After n-butanol extraction, the parasite enzyme was sequentially purified by affinity chromatography on concanavalin A-sepharose followed by gel filtration. The purified protein (210 kDa) had a tetrameric structure composed of 4 56-kDa subunits. Its isoelectric point (4.8) and its kinetic parameters were determined (Km = 0.24 ± 0.05 mmol/L; Vm = 173 ± 21 nmol/min/mg protein for p-nitrophenylphosphate). The parasite enzyme differed from the host liver enzyme in its thermal stability, optimum reaction temperature, optimum pH, and catalytic parameters, but not in its apparent molecular weight. Furthermore, sera from patients infected with E. granulosus recognized the parasite AP on immunoblots, whereas uninfected controls were negative. These results as well as the role of this enzyme in the host-parasite relationship emphasize its potential importance as a diagnostic and prognostic antigen in the monitoring of hydatid infection

Overexpression, purification and characterization of a hexahistidine-tagged recombinant extended nucleotide-binding domain 1 (NBD1) of the Cryptosporidium parvum CpABC3 for rational drug design

International audienceIts natural resistance to antiprotozoal chemotherapy characterizes the intestinal protozoan parasite Cryptosporidium parvum and the P-glycoprotein-related multidrug resistance proteins such as CpABC3 could be involved. In order to design and study specific inhibitors of the CpABC3 nucleotide-binding domain, a hexahistidine-tagged recombinant protein encompassing the N-terminal cytosolic NBD1 domain was over-expressed in E. coli and purified. The 45 kDa H6-NBD1 displayed intrinsic fluorescent properties consistent with the presence of two Trp residues in a hydrophobic environment. The binding of ATP and the fluorescent analogue TNP-ATP produced a dose-dependent quenching as well as progesterone and the flavone quercetin. The extrinsic fluorescence of TNP-ATP was enhanced upon binding to H6-NBD1, which was only partially displaced by the natural substrate ATP. The recombinant protein hydrolyzed ATP (K m = 145.4 ± 18.2 M), but ADP (K m = 4.3 ± 0.6 mM) and AMP (K m = 5.4 ± 1.5 M) were also substrates. TNP-ATP is a competitive inhibitor of the catalytic activity (K i = 36.6 ± 4.5 M), but quercetin and progesterone were not inhibitors, evidencing different binding sites. The recombinant C. parvum H6-NBD1 should be a valuable tool for rational drug design and will allow the discrimination between specific inhibitors of the catalytic site and molecules binding to other sites

Use of Percoll for the infection of cells in vitro with Cryptosporidium parvum oocysts

International audienceA method for the infection of non-adherent THP-1 cells and adherent MDBK cells with Cryptosporidium parÕum oocysts using isotonic Percoll solutions was developed. Excystation was maximal after 2 h, but toxicity increased with the oocystrcell ratio and the incubation time. The infection rates did not increase with the oocystrcell ratio and both cell types were equally parasitized.

Cultivation of Cryptosporidium pawum in a non-adherent human monocytic cell line

International audienceCryptosporidium parvum is a coccidian parasite responsible for severe diarrhea in immunocompromised patients. At present, only therapies of limited efficacies are available and despite recent improvements, an easy to perform and reproducible in vitro model is still lacking. The present study shows that the human monocyte cell line THP-1 supports the growth of C. parvum. After inoculation with oocysts, all the asexual and sexual developmental stages were found. Immunofluorescence controls showed that few oocysts remained after infection, disappeared within the first 24 h and that sexual stages reappeared after the second day postinoculation. A continuous asexual life-cycle proceeded throughout the experiments, with at least E-day cultures. Ultrastructural studies evidenced that the parasites were usually localized at the cell surface and also in the cytoplasm, a feature found in vivo with M cells and macrophages. This culture system is easy to initiate and to maintain with adjustable parasitemias and duration which will allow time-dependent drug-testing and also facilitate the study of the biology of this parasite

Toxoplasma gondii: Identification and immune response against a group of proteins involved in cellular invasion

International audienceToxoplasma gondii is an ubiquitous intracellular parasite, causative agent of toxoplasmosis, and a worldwide zoonosis for which an effective vaccine is needed. A group of proteins secreted by tachyzoites during host-cell invasion was isolated from the interaction medium. It induced the permeability of the cells as assessed by alpha-sarcin and consequently facilitated the entry of the parasite into the cells. SDS-PAGE of the purified proteins showed a pattern of four proteins of 67, 42, 32 and 27 kDa. MRC-5 cells incubated with the total protein and the different electroeluted bands endured a high cellular death in presence of alpha-sarcin. BALb/C mice immunized with the group of proteins had a mixed Th1/Th2 response and were protected upon challenge with the parasites

Effects of purine nucleosides on the in vitro growth of Cryptosporidium parvum

International audienceThe effect of purine nucleosides on the in vitro growth of Cryptosporidium parvum was studied. Culturing the parasite in THP-1 cells for 72 h in growth medium supplemented with adenosine or inosine improved the parasite yields especially in the first 48 h. Similar results were obtained with parasites cultured in Madin^Darby bovine kidney cells and incubated for 24 h with inosine. The addition of inosine to 72-h cultures enhanced the growth of C. parvum in THP-1 cells, especially the trophic stages, whereas the analogue formycin B was toxic to the parasites and induced a marked decrease in the gamont stages. The monitoring of the added purine nucleosides by high performance liquid chromatography showed that at 37 ‡C in the presence of THP-1 cells, a rapid uptake of inosine occurred with hypoxanthine being the main purine present after 2 h in the medium

Use of a non-adherent cell culture system for testing the effect of 2',3'-dideoxyinosine against Cryptosporidium parvum

International audienceThe in vitro cultivation of Cryptosporidium parvum in the non-adherent cell line THP-1 was evaluated for its capability as a useful additional model to investigate the effect of drugs on this parasite. The purine analog antiviral 2',3'-dideoxyinosine (ddI) was evaluated and compared to the reference molecule paromomycin in sequential 24 hour experiments beginning at 24 and 72 hour post-infection. The ability of this technique to evaluate the various parasite stages showed that ddI displayed a dose-dependent efficacy especially on the trophozoite and sexual stages. Paromomycin displayed a lower efficacy than previously reported. Both drugs induced a decrease in the number of multiparasitized cells. These results indicate that the purine salvage pathway should be a key chemotherapeutic target against C. parvum