Comparison between two common methods for measuring Giardia lamblia susceptibility to antiparasitic drugs in vitro

Identification of End-Binding 1 Protein as Novel α-4 Giardin-Binding Partners in Giardia lamblia Trophozoites

BACKGROUND

Giardia lamblia (syn. G. intestinalis, G. duodenalis) is a primitive opportunistic protozoon, and one of the earliest differentiated eukaryotes. Despite its primitive nature, G. lamblia has a sophisticated cytoskeleton system, which is closely related to its proliferation and pathogenicity. Meanwhile, α giardin is a G. lamblia-specific cytoskeleton protein, which belongs to the annexin superfamily. Interestingly, G. lamblia has 21 annexin-like α giardins, i.e., more than higher eukaryotes. The functional differences among α giardin members are not fully understood.

METHODS

We took α-4 giardin, a member of α giardin family, as a research object. A morpholino-mediated knockdown experiment was performed to identify the effect of α-4 giardin on G. lamblia trophozoites biological traits. A yeast two-hybrid cDNA library of G. lamblia strain C2 trophozoites was screened for interaction partners of α-4 giardin. Co-immunoprecipitation and fluorescent colocalization confirmed the relationship between G. lamblia EB1 (gEB1) and α-4 giardin.

RESULTS

α-4 Giardin could inhibit the proliferation and adhesion of G. lamblia trophozoites. In addition, it interacted with G. lamblia EB1 (gEB1).

CONCLUSIONS

α-4 Giardin was involved in proliferation and adhesion in G. lamblia trophozoites, and EB1, a crucial roles in mitosis, was an interacting partner of α-4 giardin.

High-throughput Giardia lamblia viability assay using bioluminescent ATP content measurements

The human pathogen Giardia lamblia is an anaerobic protozoan parasite that causes giardiasis, one of the most common diarrheal diseases worldwide. Although several drugs are available for the treatment of giardiasis, drug resistance has been reported and is likely to increase, and recurrent infections are common. The search for new drugs that can overcome the drug-resistant strains of Giardia is an unmet medical need. New drug screen methods can facilitate the drug discovery process and aid with the identification of new drug targets. Using a bioluminescent ATP content assay, we have developed a phenotypic drug screen method to identify compounds that act against the actively growing trophozoite stage of the parasite. This assay is homogeneous, robust, and suitable for high-throughput screening of large compound collections. A screen of 4,096 pharmacologically active small molecules and approved drugs revealed 43 compounds with selective anti-Giardia properties, including 32 previously reported and 11 novel anti-Giardia agents. The most potent novel compound was fumagillin, which showed 50% inhibitory concentrations of 10 nM against the WB isolate and 2 nM against the GS isolate.

A colorimetric method for the evaluation of anti-giardial drugs in vitro

The aim of this study was to develop a simple and reliable method to determine the viability of Giardia intestinalis after incubation with an anti-giardial agent by using a colorimetric method. Factors that may affect the optical density value were systematically evaluated. The most suitable conditions were obtained when G. intestinalis trophozoites, 5 × 10(5)cells/ml were incubated with the anti-giardial agent for 48 h. The culture medium was removed and trophozoites were immediately fixed by immersing the whole plate in absolute methanol for 2 min. The fixed trophozoites were then stained with 0.1% w/v methylene blue for 10 min, washed once by immersing the whole plate into distilled water. The dye was released by adding 0.1M hydrochloric acid solution (300 μl) and the optical density was read at 655 nm. The 50% inhibitory concentration values (IC(50)) of metronidazole, ornidazole and furazolidone obtained from our proposed method (0.41 ± 0.06, 0.18 ± 0.01, 0.26 ± 0.13 μg/ml, respectively) were comparable to the IC(50) values obtained by the current conventional method (0.14 ± 0.05, 0.15 ± 0.04, 0.14 ± 0.02 μg/ml, respectively). This new method did provide a convenient and reliable way to screen for potential anti-giardial agents.

The effects of dihydroartemisinin on Giardia lamblia morphology and cell cycle in vitro

Several anti-Giardia drugs, such as metronidazole, tinidazole, mebendazole, albendazole and furazolidone, are usually effective but have severe side effects and potential toxicity. An urgent need exists for more effective and less toxic agents that can act against this protozoan. For this purpose, the effects of dihydroartemisinin (DHA) on Giardia lamblia were investigated in vitro. Axenically grown G. lamblia trophozoites were treated with DHA (LD(50) = 200 microg/mL) at different time intervals. The morphological and ultrastructural changes of the treated trophozoites were observed by both light and transmission electron microscopy (TEM). Changes in the cell cycle of the treated cells were observed by flow cytometry. By light microscopy, we observed that DHA-treated trophozoites were detached from the wall of the culture tube and shown bradypraxia and bubbles in the dorsal and ventral surfaces. Ultrastructural observations by TEM revealed that DHA promoted modifications of the cell shape, pronounced dorsal vesiculation, plasma membrane blebbing, disaggregation of ribosomes, depletion of cytoplasmic matrix and heavy deposition of electron-dense precipitates on the cytoplasm and nucleus. The main changes observed in the treated group included the following: (1) trophozoites were rounder in shape and the endoplasmic reticulum was dilated, (2) enlarged trophozoites contained lamella structures and deformed nuclei, (3) trophozoites displayed dissolved cytoplasm with large vacuole spaces or decreased cytoplasmic volume, (4) adhesive disc bubbles or the lamella structures of cytoplasm were clearly observed, and (5) cell division was arrested. Using microscopy and cytometry techniques, we demonstrate that changes in G. lamblia morphology and cell cycle state were induced by DHA.

N/A

N/A

Variability and variation in drug susceptibility among Giardia duodenalis isolates and clones exposed to 5-nitroimidazoles and benzimidazoles in vitro

OBJECTIVES

We analysed, in a cell-by-cell study, the in vitro susceptibility of Giardia duodenalis strains, including Mexican isolates and their clones to 5-nitroimidazoles and benzimidazoles.

METHODS

Fluorogenic dye staining (FDA-PI) and cell morphology (CM) assays, two fast and direct techniques, replaced the indirect 'gold standard' method (subculture in liquid medium) in the evaluation of 5-nitroimidazoles and benzimidazoles, respectively.

RESULTS

Under these conditions, the activity of several 5-nitroimidazole and benzimidazole derivatives was consistent with their known efficacy, but parasite stocks exhibited a greater variability in response to 5-nitroimidazoles compared with benzimidazoles. Also, consecutive progenies from single stocks maintained in continuous subculture in drug-free media displayed changes (variations) in the proportions of drug resistant (R/T) subpopulations when exposed to sublethal concentrations of 5-nitroimidazoles and benzimidazoles. These were again more variable upon exposure to 5-nitroimidazoles than to benzimidazoles. Variations were not due to drug susceptibility shifts in parent trophozoites since analysis of cytokinetic processes showed a predominant pattern of susceptible/susceptible or resistant/resistant daughters, whereas susceptible/resistant daughters were scarce.

CONCLUSIONS

Our observations support the idea that G. duodenalis cultures exhibit variations in their response to 5-nitroimidazoles and benzimidazoles as a result of a drug-independent competition between drug-susceptible and drug-resistant subpopulations when parasites are subcultured.