Adherence and multiplication of Giardia intestinalis on human enterocyte-like differentiated cells in vitro

Recent advances in functional research in Giardia intestinalis

This review considers current advances in tools to investigate the functional biology of Giardia, it's coding and non-coding genes, features and cellular and molecular biology. We consider major gaps in current knowledge of the parasite and discuss the present state-of-the-art in its in vivo and in vitro cultivation. Advances in in silico tools, including for the modelling non-coding RNAs and genomic elements, as well as detailed exploration of coding genes through inferred homology to model organisms, have provided significant, primary level insight. Improved methods to model the three-dimensional structure of proteins offer new insights into their function, and binding interactions with ligands, other proteins or precursor drugs, and offer substantial opportunities to prioritise proteins for further study and experimentation. These approaches can be supplemented by the growing and highly accessible arsenal of systems-based methods now being applied to Giardia, led by genomic, transcriptomic and proteomic methods, but rapidly incorporating advanced tools for detection of real-time transcription, evaluation of chromatin states and direct measurement of macromolecular complexes. Methods to directly interrogate and perturb gene function have made major leaps in recent years, with CRISPr-interference now available. These approaches, coupled with protein over-expression, fluorescent labelling and in vitro and in vivo imaging, are set to revolutionize the field and herald an exciting time during which the field may finally realise Giardia's long proposed potential as a model parasite and eukaryote.

In vitro and ex vivo evaluation of the anti-Giardia duodenalis activity of the supernatant of Slab51 (SivoMixx)

The effects on Giardia duodenalis of Slab51 probiotic supernatants were evaluated in vitro and ex vivo. In vitro, Slab51 (10¹ UFC) was cultured and the obtained supernatant was filtered, adjusted at pH 7, and added (100μl/ml) as such (Slab51 FS) or after heat-treatment, to G. duodenalis cultures to evaluate its effects on G. duodenalis trophozoites growth and adherence. For comparison, negative and metronidazole (20μg/ml) treated controls were used. The morphological and ultrastructural alterations of G. duodenals trophozoites following treatment with Slab51 FS supernatant were investigated by transmission electron microscopy. Ex vivo, mice duodenal portions were cultivated in standard conditions with 5x10⁵G. duodenalis trophozoites/ml, while to further five duodenal portions similarly cultured and infected, Slab51 FS 200μl was added. After 12 and 18h, samples were fixed in 10% buffered formalin and histologically processed to score Giardia infection and cell damage. Cell proliferation/apoptosis was scored by Ki67, TUNEL and Caspase–3 tests. All experiments were conducted in triplicate throughout the study. All data were statistically evaluated (P< 0.05). Results showed that Slab51 FS significantly reduced Giardia growth and adherence respect to negative controls, but its efficacy was overall lower than that of metronidazole. Moreover, the effects of Slab51 FS were significantly lowered by heat-treatment and this reduction was statistically higher at 90°C than at 56°C, indicating a heat-sensitive nature of active Slab51 FS compounds. At the ultrastructural level, Slab51 FS treated Giardia trophozoites were swelling, increased in size and showed alterations of their cellular membrane and vacuole patterns, loss of the nuclear envelope and nuclear architecture. In ex vivo trials, viable G. duodenalis trophozoites and enterocyte TUNEL+ and Caspase-3 expression were significantly reduced in intestinal sections added with Slab51 FS, while enterocyte Ki67 expression was significantly increased, confirming the anti-G. duodenalis activity of Slab51 FS observed in vitro. In conclusion, results from this study showed that the fresh culture supernatant of the commercial probiotic Slab51 has anti-G. duodenalis properties both in vitro and ex vivo in a mouse model.

Giardia duodenalis Surface Cysteine Proteases Induce Cleavage of the Intestinal Epithelial Cytoskeletal Protein Villin via Myosin Light Chain Kinase

Giardia duodenalis infections are among the most common causes of waterborne diarrhoeal disease worldwide. At the height of infection, G. duodenalis trophozoites induce multiple pathophysiological processes within intestinal epithelial cells that contribute to the development of diarrhoeal disease. To date, our understanding of pathophysiological processes in giardiasis remains incompletely understood. The present study reveals a previously unappreciated role for G. duodenalis cathepsin cysteine proteases in intestinal epithelial pathophysiological processes that occur during giardiasis. Experiments first established that Giardia trophozoites indeed produce cathepsin B and L in strain-dependent fashion. Co-incubation of G. duodenalis with human enterocytes enhanced cathepsin production by Assemblage A (NF and S2 isolates) trophozoites, but not when epithelial cells were exposed to Assemblage B (GSM isolate) trophozoites. Direct contact between G. duodenalis parasites and human intestinal epithelial monolayers resulted in the degradation and redistribution of the intestinal epithelial cytoskeletal protein villin; these effects were abolished when parasite cathepsin cysteine proteases were inhibited. Interestingly, inhibition of parasite proteases did not prevent degradation of the intestinal tight junction-associated protein zonula occludens 1 (ZO-1), suggesting that G. duodenalis induces multiple pathophysiological processes within intestinal epithelial cells. Finally, this study demonstrates that G. duodenalis-mediated disruption of villin is, at least, in part dependent on activation of myosin light chain kinase (MLCK). Taken together, this study indicates a novel role for parasite cathepsin cysteine proteases in the pathophysiology of G. duodenalis infections.

ECC-RT-PCR: a new method to determine the viability and infectivity of Giardia cysts

BACKGROUND

Giardia sp is a major cause of diarrheal illness worldwide, and millions of people are infected each year. Rapid methods to determine the infectivity and virulence of isolates are critical for the development of intervention strategies to control the transmission of Giardia sp cysts, which occurs through contaminated surfaces, food, and water. However, determining the viability, infectivity, and virulence of Giardia sp cysts using molecular methods is a technical challenge because of the lack of a cell culture model.

METHOD

This study was designed to evaluate mRNA expression in trophozoites and to assess trophozoite attachment to cell monolayer and changes in transcellular resistance as an indicator of Giardia sp viability and infectivity. Heat shock mRNA in Giardia cysts and variant-specific protein (VSP) mRNA in trophozoites were quantified by reverse transcription polymerase chain reaction (RT-PCR). C2bb (Caco-2) cells were grown on transwell chambers to study the attachment of trophozoites, changes in transcellular resistance, and expression of VSP in trophozoites.

RESULTS

The results of these molecular and cell culture studies indicate a direct linear correlation between the viability and infectivity of fresh stocks of Giardia sp cysts. The attachment of trophozoites to cell monolayer, expression of VSP, and change in the transcellular resistance was directly correlated with their infectivity in neonatal mice. PCR was successfully combined with the electrophysiological analysis of cell culture (ECC-RT-PCR) post-trophozoite attachment.

CONCLUSION

This study shows that the ECC-RT-PCR, a new integrated cell culture assay, can be used as a rapid and cost-effective tool for assessing the viability and infectivity of environmental isolates of Giardia sp cysts.

Inhibition of in vitro attachment of Giardia trophozoites by mucin

An enzyme-linked immunoabsorbent assay was developed to quantify the number of Giardia sp. trophozoites attached to a substratum. Trophozoites were allowed to attach for 5 or 10 min to untreated or modified substratum, or allowed to attach in the presence of cytoskeletal inhibitors. Microtubule inhibitors, cochicine and nocodazole, were ineffective in blocking attachment, although the actin-disrupting agent cytochalasin B produced significant inhibition of attachment. Three different mucins were associated with significant inhibition of Giardia trophozoite attachment, which was reversed by treating the mucin-coated wells with 0.1% poly-L-arginine. Examination of mucin-treated substrata by high-resolution field emission scanning electron microscopy showed the presence of thin linear fibrils, whereas treatment of mucin-coated wells with poly-L-arginine revealed similar fibrils but of thicker dimensions. These data support the concept that mucin may inhibit Giardia sp. trophozoite attachment in vitro by electrostatic repulsion and that this can be eliminated by treatment of mucin-coated surfaces with polycationic agents, such as poly-L-arginine or poly-L-lysine.

Inhibition of Giardia intestinalis by extracellular factors from Lactobacilli: an in vitro study

The aim of the present work was to evaluate the effect of spent culture supernatants of different strains of lactobacilli on giardia trophozoites. The growth of Giardia intestinalis strain WB, as well as the attachment to the human intestinal epithelial cell line Caco-2, was evaluated by using proliferation and adhesion assays with radiolabeled parasites. In addition, scanning electron microscopy and flow cytometric analysis were performed. The effect of spent culture supernatants from lactobacilli was strain dependent. Lactobacillus johnsonii La1 significantly inhibited the proliferation of G. intestinalis trophozoites. Although the effect was strongly pH dependent, it was not simply due to lactic acid. According to flow cytometric analysis, trophozoites were arrested in G(1) phase but neither significant necrosis nor apoptosis could be detected. Bacterial cells or their spent culture supernatants were unable to modify trophozoite attachment to Caco-2 cells. However, trophozoites treated with spent culture supernatants had little, if any, proliferative capacity. These results suggest that La1 produces some substance(s) able to inhibit proliferation of Giardia trophozoites. Partial characterization of the factors involved in the antigiardiasic action showed that they have a low molecular mass and are inactivated by heating. On this basis, it seems worthwhile to explore how colonization of the proximal small bowel with these lactic acid bacteria could interfere with giardiasis in vivo.

Role of surface components in the process of interaction of Giardia duodenalis with epithelial cells in vitro

Monosaccharides, lectins, periodate, trypsin and neuraminidase were used to analyse the process of adhesion of Giardia duodenalis trophozoites to IEC cells, an intestinal epithelial cell line. Addition of N-acetyl-glucosamine, N-acetyl-galactosamine, galactose and fucose to the interaction medium inhibited attachment of the parasites to the epithelial cells. Experiments in which the parasites or epithelial cells were treated before interaction showed that these monosaccharides interfered with both cell surfaces. Trypsin-sensitive, but not neuraminidase-sensitive, groups exposed on the cell surface are important for the parasite-epithelial cell association. Fluorescein isothiocyanate (FITC)- or colloidal gold-labeled lectins were used to analyse the distribution of carbohydrates on the surface of G. duodenalis and epithelial cells. It is important to stress here the presence of fucose on the parasite surface. Treatment of the cells with lectins was also used to analyse the role of carbohydrate-containing macromolecules in the parasite-cell interaction.

Activity of metronidazole, azithromycin and three benzimidazoles on Giardia lamblia growth and attachment to a human intestinal cell line

BACKGROUND

Attachment of Giardia lamblia trophozoites to enterocytes is essential for colonization of the small intestine and is considered a prerequisite for Giardia-induced enterocyte damage. Inhibition of attachment may therefore have therapeutic potential.

METHODS

Enterocyte-like differentiated Caco-2 cells were used as a biologically appropriate attachment surface to determine the effect of three benzimidazole compounds (albendazole, mebendazole and thiabendazole), azithromycin and metronidazole on Giardia attachment. The results were compared with the ability for each drug to inhibit Giardia growth, measured using [3H]-thymidine uptake.

RESULTS

The benzimidazoles inhibited Giardia attachment at much lower concentrations than did metronidazole. However, metronidazole was a much more potent inhibitor of growth than any of the benzimidazoles. Azithromycin did not significantly impair Giardia attachment or growth. The benzimidazoles decrease attachment but are less giardiacidal than metronidazole.

CONCLUSION

This model appears useful for testing potential antigiardial compounds and investigating mechanisms of drug action.

Intestinal lipid metabolism in suckling rats infected with Giardia duodenalis

We carried out a quantitative and qualitative analysis of intestinal digestion of neutral lipids in suckling rats infected with Giardia duodenalis. Total lipids were measured after extraction from the contents of the stomach, proximal and distal small bowel, caecum and colon. Amounts gradually fell from the stomach to the colon and were identical in infected animals and controls, although high values were occasionally found in the caecum of infected rats. Relative glyceride quantities were determined by means of high-performance thin-layer chromatography. Triglycerides were absent from the distal small bowel, and only free fatty acids and cholesterol were present in the caecum, reflecting normal digestion of neutral lipids in infected suckling rats. Our results suggest that G. duodenalis does not impair intestinal fat digestion in suckling rats.

Role of cytoskeleton and surface lectins in Giardia duodenalis attachment to Caco2 cells

An in vitro model of Giardia duodenalis and the Caco2 cell line enable the study of parameters that could play a part in trophozoite attachment. We explored the role of membranous lectins of G. duodenalis in attachment-inhibition studies using carbohydrates in solution. Attachment rates were reduced by 14% and 23% in the presence of 100 mmol/l mannose-6-phosphate and glucose, respectively, as compared with control values. No significant modification was observed after trophozoite trypsinization at room temperature or at 37 degrees C. The inhibitory effects of colchicine (35%) and nocodazole (70%) suggest a primordial role of the cytoskeleton; microtubules appear to be the principal effectors of trophozoite fixation. Scanning electron microscopy revealed circular imprints on the Caco2 brush border after trophozoite detachment. The mechanisms of attachment of G. duodenalis to intestinal enterocyte-like cells in culture are thus essentially of the mechanical or hydrodynamic type; surface lectins would appear to intervene in the specificity for duodenal cells.