Chitin derivatives as novel substrates for Trypanosoma brucei brucei attachment in vitro

Polyionic Hydrogels Obtained by Complexation between Xanthan and Chitosan: Their Properties as Supports for Enzyme Immobilization

A method for the preparation of hydrogels from the complexation of chitosan and xanthan is reported. Stable hydrogels capable of retaining be tween 65 and 95% weight water were prepared. The water retention and prop erties of the hydrogels were studied as a function of the degree of acetylation of chitosan and the ratio chitosan/xanthan used in the preparation of the gel. Spectroscopic FTIR was used to confirm complexation between the amine (chi tosan) and carboxylic (xanthan) groups. Electron micrographs (SEM and TEM) show the formation of a fibrillar structure with characteristic pore sizes be tween 100 and 1000 nm and fibril diameters between 50 and 100 nm. The diffu sion coefficient of 4- O-methyl- d-glucurono-D-xylan Remazol Brilliant Blue R (RBB-xylan) in the complex chitosan-xanthan was 2.02 × 10-12 m 2s-1 at 30°C. The chitosan-xanthan complex was used to immobilize two enzymes (endo-1,4- β-xylanase and protease) either as single enzymes or as a binary system. Immo bilization varied between 85 and 98%. The immobilized xylanase activity was significantly greater with respect to the free enzyme while the binary enzyme system promoted protease activity.

Chitin is a component of the Rhodnius prolixus midgut

Chitin is an essential component of the peritrophic matrix (PM), which is a structure that lines the insect's gut and protects against mechanical damage and pathogens. Rhodnius prolixus (Hemiptera: Reduviidae) does not have a PM, but it has an analogous structure, the perimicrovillar membrane (PMM); chitin has not been described in this structure. Here, we show that chitin is present in the R. prolixus midgut using several techniques. The FTIR spectrum of the KOH-resistant putative chitin-material extracted from the midgut bolus showed peaks characteristic of the chitin molecule at 3500, 1675 and 1085 cm(1). Both the midgut bolus material and the standard chitin NMR spectra showed a peak at 1.88 ppm, which is certainly due to methyl protons in the acetamide a group. The percentages of radioactive N-acetylglucosamine (CPM) incorporated were 2 and 4% for the entire intestine and bolus, respectively. The KOH-resistant putative chitin-material was also extracted and purified from the N-acetylglucosamine radioactive bolus, and the radioactivity was estimated through liquid scintillation. The intestinal CHS cDNA translated sequence was the same as previously described for the R. prolixus cuticle and ovaries. Phenotypic alterations were observed in the midgut of females with a silenced CHS gene after a blood meal, such as retarded blood meal digestion; the presence of fresh blood that remained red nine days after the blood meal; and reduced trachea and hemozoin content compared with the control. Wheat germ agglutinin (a specific probe that detects chitin) labeling proximal to the intestine (crop and midgut) was much lower in females with a silenced CHS gene, especially in the midgut region, where almost no fluorescence signal was detected compared with the control groups. Midguts from females with a CHS gene silenced by dsRNA-CHS and control midguts pre-treated with chitinase showed that the chitin-derived fluorescence signal decreased in the region around the epithelium, the region facing the midgut and projections towards the intestinal lumen when evaluated microscopically. The relative reduction in CHS transcripts by approximately 80% using an RNAi assay supports the phenotypical alterations in the midgut observed using fluorescence microscopy assays. These data show that chitin is present in the R. prolixus midgut epithelium and in its surface projections facing the lumen. The CHS gene expression and the presence of chitin in the R. prolixus midgut may suggest a target for controlling Chagas disease vectors and addressing this public health problem.

Interaction of Leptomonas wallacei with the intestinal tract of its natural host Oncopeltus fasciatus (Hemiptera: Lygaeidae)

While investigating the distribution of Leptomonas wallacei in the intestine of the insect host Oncopeltus fasciatus, promastigotes and cyst-like forms of L. wallacei were observed only in the midgut ventricles V(3) and V(4) and the hindgut. In video-microscopy, once contact had occurred, the parasites remained attached to the midgut epithelium. Scanning electron microscopy revealed the adhesion of flagellates and cyst-like forms to the midgut wall and to the rectal pads of the hindgut. Using transmission electron microscopy, we observed that adhesion occurred mainly between the flagellum and the perimicrovillar membranes secreted by the midgut epithelium. No modifications were observed either in the parasite or in the epithelial cells. In the hindgut, adhesion to the superficial wax layer of the epithelial cells of the rectal pads was via flagellum. Host cell morphology appeared unaffected by L. wallacei.

Binding specificity of mannose-specific carbohydrate-binding protein from the cell surface of Trypanosoma cruzi

The sugar binding specificity of the recently described mannose-specific carbohydrate-binding proteins (CBP) isolated to homogeneity from both the epimastigote and trypomastigote stages of the pathogenic protozoa Trypanosoma cruzi has been studied by quantitative hapten inhibition of the biotinylated CBPs to immobilized thyroglobulin using model oligosaccharides. The results clearly show a differential specificity toward high-mannose glycans between the CBPs from the two developmental stages. Thus, the isolated CBP from epimastigotes exhibited stronger affinity for higher mannose oligomers containing the Manalpha1-2Manalpha1-6Manalpha1-6 structure. Its affinity decreased, as did the number of mannose residues on the oligomer or removal of the terminal Manalpha1-2-linked mannose. By contrast the CBP isolated from the trypomastigote stage showed about 400-fold lower avidity than the epimastigote form, and contrary to it, it was slightly more specific toward Man5GlcNAc than Man9GlcNAc. Analysis of the interaction of epimastigote-Man-CBP with its ligands by UV difference spectroscopy indicates the existence of an extended binding site in that protein with a large enthalpic contribution to the binding. The thermodynamic parameters of binding were obtained by isothermal titration calorimetry and been found that the DeltaH values to be in good agreement with the van't Hoff values. The binding reactions are mainly enthalpically driven and exhibit enthalpy-enthropy compensation. In addition, analysis of the high-mannose glycans from different parts of the digestive tract of the reduviid insect vector of T. cruzi suggest a role of the CBP in the retention of the epimastigote stage in the anterior portion of the gut.

Trypanosoma cruzi: a gene family encoding chitin-binding-like proteins is posttranscriptionally regulated during metacyclogenesis

The development of the representation of differential expression method has lead to the cloning of Trypanosoma cruzi stage-specific genes. We used this method to characterize a multicopy gene family differentially expressed during metacyclogenesis. The genomic and cDNA clones sequenced encoded three short cysteine-rich polypeptides, of two types, with predicted molecular masses of 7.1, 10.4, and 10.8 kDa. We searched GenBank for similar sequences and found that the sequences of these clones were similar to that encoding the wheat germ agglutinin protein. The region of similarity corresponds to the chitin-binding domain, with eight similarly positioned half-cysteines and conserved aromatic residues involved in chitin recognition. Multiple copies of the genes of this family are present on a high- molecular-mass chromosome. We studied the expression of genes of this family during metacyclogenesis by determining messenger RNA (mRNA) levels. The mRNAs for the members of this gene family were present in the total RNA fraction but were mobilized to the polysomal fraction of adhered (differentiating) epimastigotes during metacyclogenesis, with a peak of accumulation at 24 of differentiation. Polyclonal antisera were raised against a recombinant protein and a synthetic peptide. The specific sera obtained detected 7- and 11-kDa proteins in T. cruzi total protein extracts. The 11-kDa protein was present in similar amounts in the various cell populations, whereas the 7-kDa protein displayed differential synthesis during metacyclogenesis, with maximal levels in 24-h-adhered (differentiating) epimastigotes.

Attachment of Trypanosoma cruzi epimastigotes to hydrophobic substrates and use of this property to separate stages and promote metacyclogenesis

In vivo, epimastigotes of Trypanosoma cruzi colonize a lipidic superficial layer of the rectal cuticle of the vector Triatoma infestans. In vitro, epimastigotes of four cultured strains and one strain from reduviids use a terminal area of the flagellum to attach to a variety of artificial hydrophobic substances, such as hydrocarbons and a range of synthetic plastics. Trypomastigotes did not attach to these substrates. Hydrophilic molecules, such as neutral or negatively charged polysaccharides, did not facilitate binding. Epimastigotes and trypomastigotes were artificially bound by electrostatic forces to positively charged chitosan or DEAE-Sephacel over their entire surface. Tween 20 and lipid-binding serum albumin effectively inhibited the hydrophobic attachment. Based on this hydrophobic interaction of epimastigotes, a new chromatography technique has been devised to gently separate trypomastigotes from epimastigotes using octacosane-coated beads. Furthermore, the in vitro transformation of epimastigotes to trypomastigotes was enhanced if epimastigotes were permitted to attach to hydrophobic, wax-coated culture vessels.

The haemoculture of Trypanosoma minasense Chagas, 1908

Trypanosoma minasense was isolated for the first time in blood axenic culture from a naturally infected marmoset, Callithrix penicillata, from Brazil. The parasite grew profusely in an overlay of Roswell Park Memorial Institute medium plus 20% foetal bovine serum, on Novy, McNeal and Nicolle medium (NNN), at 27 degrees C, with a peak around 168 hr. The morphometry of cultural forms of T. minasense, estimates of cell population size and comparative growth in four different media overlays always with NNN, were studied. The infectivity of cultural forms to marmosets (C. penicillata and C. jacchus) and transformation of epimastigotes into metacyclic-like forms in axenic culture in the presence of chitin derivates (chitosan) were evaluated.

Ultrastructural aspects of Trypanosoma (Megatrypanum) freitasi in co-cultivation with mammalian cells

Cultures of Trypanosoma (Megatrypanum) freitasi with L929 mouse fibroblasts at 27.5 degrees C were examined by scanning and transmission electron microscopy in an attempt to clarify the processes of colony formation by the epimastigotes and of their attachment to substrata. It was seen that the flagellates occupy intercellular spaces and do not associate with intact fibroblasts. As the trypanosome population increases, ever larger portions of the substratum are cleared of fibroblasts and occupied by conglomerates of epimastigote colonies consisting of about a dozen organisms that attach to the substratum by their anterior extremities and form pyramidal clusters. Attachment of the epimastigotes involves the flagellar membrane, which becomes extraordinarily enlarged and assumes various aspects of broad sheets, filaments and loops over the substratum or along the flagellum, which exhibits a shortened axoneme. Desmosome or hemidesmosome plaques are present when the attachment takes place between membranes or between the membrane and the substratum.