An antioxidant response is involved in resistance of Giardia duodenalis to albendazole

Transcriptomic analysis of albendazole resistance in human diarrheal parasite Giardia duodenalis

Benzimidazole-2-carbamates (BZ, e.g., albendazole; ALB), which bind β-tubulin to disrupt microtubule polymerization, are one of two primary compound classes used to treat giardiasis. In most parasitic nematodes and fungi, BZ-resistance is caused by β-tubulin mutations and its molecular mode of action (MOA) is well studied. In contrast, in Giardia duodenalis BZ MOA or resistance is less well understood, may involve target-specific and broader impacts including cellular damage and oxidative stress, and its underlying cause is not clearly determined. Previously, we identified acquisition of a single nucleotide polymorphism, E198K, in β-tubulin in ALB-resistant (ALB-R) G. duodenalis WB-1B relative to ALB-sensitive (ALB-S) parental controls. E198K is linked to BZ-resistance in fungi and its allelic frequency correlated with the magnitude of BZ-resistance in G. duodenalis WB-1B. Here, we undertook detailed transcriptomic comparisons of these ALB-S and ALB-R G. duodenalis WB-1B cultures. The primary transcriptional changes with ALB-R in G. duodenalis WB-1B indicated increased protein degradation and turnover, and up-regulation of tubulin, and related genes, associated with the adhesive disc and basal bodies. These findings are consistent with previous observations noting focused disintegration of the disc and associated structures in Giardia duodenalis upon ALB exposure. We also saw transcriptional changes with ALB-R in G. duodenalis WB-1B consistent with prior observations of a shift from glycolysis to arginine metabolism for ATP production and possible changes to aspects of the vesicular trafficking system that require further investigation. Finally, we saw mixed transcriptional changes associated with DNA repair and oxidative stress responses in the G. duodenalis WB-1B line. These changes may be indicative of a role for H₂O₂ degradation in ALB-R, as has been observed in other G. duodenalis cell cultures. However, they were below the transcriptional fold-change threshold (log₂FC > 1) typically employed in transcriptomic analyses and appear to be contradicted in ALB-R G. duodenalis WB-1B by down-regulation of the NAD scavenging and conversion pathways required to support these stress pathways and up-regulation of many highly oxidation sensitive iron-sulphur (FeS) cluster based metabolic enzymes.

Giardia duodenalis: Flavohemoglobin is involved in drug biotransformation and resistance to albendazole

Giardia duodenalis causes giardiasis, a major diarrheal disease in humans worldwide whose treatment relies mainly on metronidazole (MTZ) and albendazole (ABZ). The emergence of ABZ resistance in this parasite has prompted studies to elucidate the molecular mechanisms underlying this phenomenon. G. duodenalis trophozoites convert ABZ into its sulfoxide (ABZSO) and sulfone (ABZSOO) forms, despite lacking canonical enzymes involved in these processes, such as cytochrome P450s (CYP450s) and flavin-containing monooxygenases (FMOs). This study aims to identify the enzyme responsible for ABZ metabolism and its role in ABZ resistance in G. duodenalis. We first determined that the iron-containing cofactor heme induces higher mRNA expression levels of flavohemoglobin (gFlHb) in Giardia trophozoites. Molecular docking analyses predict favorable interactions of gFlHb with ABZ, ABZSO and ABZSOO. Spectral analyses of recombinant gFlHb in the presence of ABZ, ABZSO and ABZSOO showed high affinities for each of these compounds with Kd values of 22.7, 19.1 and 23.8 nM respectively. ABZ and ABZSO enhanced gFlHb NADH oxidase activity (turnover number 14.5 min-1), whereas LC-MS/MS analyses of the reaction products showed that gFlHb slowly oxygenates ABZ into ABZSO at a much lower rate (turnover number 0.01 min-1). Further spectroscopic analyses showed that ABZ is indirectly oxidized to ABZSO by superoxide generated from the NADH oxidase activity of gFlHb. In a similar manner, the superoxide-generating enzyme xanthine oxidase was able to produce ABZSO in the presence of xanthine and ABZ. Interestingly, we find that gFlHb mRNA expression is lower in albendazole-resistant clones compared to those that are sensitive to this drug. Furthermore, all albendazole-resistant clones transfected to overexpress gFlHb displayed higher susceptibility to the drug than the parent clones. Collectively these findings indicate a role for gFlHb in ABZ conversion to its sulfoxide and that gFlHb down-regulation acts as a passive pharmacokinetic mechanism of resistance in this parasite.

Albendazole ameliorates inflammatory response in a rat model of acute mesenteric ischemia reperfusion injury

BACKGROUND

Acute mesenteric ischemia is known as a life threatening condition. Re-establishment of blood flow in this condition can lead to mesenteric ischemia reperfusion (MIR) injury which is accompanied by inflammatory response. Still, clear blueprint of inflammatory mechanism underlying MIR injury has not been provided. Interestingly, Albendazole has exhibited notable effects on inflammation and cytokine production. In this study, we aimed to evaluate outcomes of MIR injury following pretreatment with Albendazole with respect to assessment of mesenteric inflammation and ischemia threshold.

METHODS

Male rats were randomly divided into sham operated, vehicle treated, Albendazole 100 mg/kg and Albendazole 200 mg/kg groups. MIR injury was induced by occlusion of superior mesenteric artery for 30 min followed by 120 min of reperfusion. Samples were utilized for assessment of epithelial survival and villous height. Immunohistochemistry study revealed intestinal expression of TNF-α and HIF-1-α. Gene expression of NF-κB/TLR4/TNF-α/IL-6 was measured using RTPCR. Also protein levels of inflammatory cytokines in serum and intestine were assessed by ELISA method.

RESULTS

Histopathological study demonstrated that pretreatment with Albendazole could ameliorate decline in villous height and epithelial survival following MIR injury. Also, systemic inflammation was suppressed after administration of Albendazole. Analysis of possible participating inflammatory pathway could demonstrate that intestinal expression of NF-κB/TLR4/TNF-α/IL-6 is significantly attenuated in treated groups. Eventually, IHC study illustrated concordant decline in mesenteric expression of HIF-1-α/TNF-α.

CONCLUSION

Single dose pretreatment with Albendazole could ameliorate inflammatory response and enhance ischemia threshold following induction of MIR injury. More studies would clarify existing causality in this phenomenon.

In vitro selection of Giardia duodenalis for Albendazole resistance identifies a β-tubulin mutation at amino acid E198K

Benzimidazole-2-carbamate (BZ) compounds, including Albendazole (Alb), are one of just two drug classes approved to treat the gastrointestinal protist Giardia duodenalis. Benzimidazoles bind to the tubulin dimer interface overlapping the colchicine binding site (CBS) of β-tubulin, thereby inhibiting microtubule polymerisation and disrupting microtubule networks. These BZ compounds are widely used as anthelmintic, anti-fungal and anti-giardial drugs. However, in helminths and fungi, BZ-resistance is widespread and caused by specific point mutations primarily occurring at F167, E198 and F200 in β-tubulin isoform 1. BZ-resistance in Giardia is reported clinically and readily generated in vitro, with significant implications for Giardia control. In Giardia, BZ mode of action (MOA) and resistance mechanisms are presumed but not proven, and no mutations in β-tubulin have been reported in association with Alb resistance (AlbR). Herein, we undertook detailed in vitro drug-susceptibility screens of 13 BZ compounds and 7 Alb structural analogues in isogenic G. duodenalis isolates selected for AlbR and podophyllotoxin, another β-tubulin inhibitor, as well as explored cross-resistance to structurally unrelated, metronidazole (Mtz). AlbR lines exhibited co-resistance to many structural variants in the BZ-pharmacophore, and cross-resistance to podophyllotoxin. AlbR lines were not cross-resistant to Mtz, but MtzR lines had enhanced survival in Alb. Lastly, Alb analogues with longer thioether substituents had decreased potency against our AlbR lines. In silico modelling indicated the Alb-β-tubulin interaction in Giardia partially overlaps the CBS and corresponds to residues associated with BZ-resistance in helminths and fungi (F167, E198, F200). Sequencing of Giardia β-tubulin identified a single nucleotide polymorphism resulting in a mutation from glutamic acid to lysine at amino acid 198 (E198K). To our knowledge, this is the first β-tubulin mutation reported for protistan BZ-resistance. This study provides insight into BZ mode of action and resistance in Giardia, and presents a potential avenue for a genetic test for clinically resistance isolates.

Probiotics in the management of Giardia duodenalis: an update on potential mechanisms and outcomes

Giardia duodenalis is a common cause of infection in children and travelers. The most frequent symptom is diarrhea in these patients. G. duodenalis trophozoites use a highly specialized adhesive disc to attach the host intestinal epithelium to induce intestinal damages. Pathological features of the small intestine following giardiasis include villous atrophy; infiltration of granulocytes, lymphocytes, and plasma cells into the lamina propria; and nodular lymphoid hyperplasia. The disturbed intestinal microbiota has been observed in patients with giardiasis. Therefore, a growing body of evidence has emphasized restoring the gut microbiome by probiotics in giardiasis. This study aimed to review the literature to find the pathologic features of giardiasis and its relationship with imbalanced microbiota. Then, benefits of probiotics in giardiasis and their potential molecular mechanisms were discussed. It has been illustrated that using probiotics (e.g., Lactobacillus and Saccharomyces) can reduce the time of gastrointestinal symptoms and repair the damages, particularly in giardiasis. Probiotics' capability in restoring the composition of commensal microbiota may lead to therapeutic outcomes. According to preclinical and clinical studies, probiotics can protect against parasite-induced mucosal damages via increasing the antioxidant capacity, suppressing oxidative products, and regulating the systemic and mucosal immune responses. In addition, they can reduce the proportion of G. duodenalis load by directly targeting the parasite. They can destroy the cellular architecture of parasites and suppress the proliferation and growth of trophozoites via the production of some factors with anti-giardial features. Further researches are required to find suitable probiotics for the prevention and treatment of giardiasis.

Antimicrobial resistance of the enteric protozoon Giardia duodenalis - A narrative review

Introduction

As therapy-refractory giardiasis is an emerging health issue, this review aimed at summarizing mechanisms of reduced antimicrobial susceptibility in Giardia duodenalis and strategies to overcome this problem.

Methods

A narrative review on antimicrobial resistance in G. duodenalis was based upon a selective literature research.

Results

Failed therapeutic success has been observed for all standard therapies of giardiasis comprising nitroimidazoles like metronidazole or tinidazole as first line substances but also benznidazoles like albendazole and mebendazole, the nitrofuran furazolidone, the thiazolide nitazoxanide, and the aminoglycoside paromomycin. Multicausality of the resistance phenotypes has been described, with differentiated gene expression due to epigenetic and post-translational modifications playing a considerable bigger role than mutational base exchanges in the parasite DNA. Standardized resistance testing algorithms are not available and clinical evidence for salvage therapies is scarce in spite of research efforts targeting new giardicidal drugs.

Conclusion

In case of therapeutic failure of first line nitroimidazoles, salvage strategies including various options for combination therapy exist in spite of limited evidence and lacking routine diagnostic-compatible assays for antimicrobial susceptibility testing in G. duodenalis. Sufficiently powered clinical and diagnostic studies are needed to overcome both the lacking evidence regarding salvage therapy and the diagnostic neglect of antimicrobial resistance.

An update on cell division of Giardia duodenalis trophozoites

Giardia duodenalis is a flagellated protozoan that is responsible for many cases of diarrheal disease worldwide and is characterized by its great divergence from the model organisms commonly used in studies of basic cellular processes. The life cycle of Giardia involves an infectious cyst form and a proliferative and mobile trophozoite form. Each Giardia trophozoite has two nuclei and a complex microtubule cytoskeleton that consists of eight flagellar axonemes, basal bodies, the adhesive disc, the funis and the median body. Since the success of Giardia infecting other organisms depends on its ability to divide and proliferate efficiently, Giardia must coordinate its cell division to ensure the duplication and partitioning of both nuclei and the multiple cytoskeletal structures. The purpose of this review is to summarize current knowledge about cell division and its regulation in this protist.

Nitroreductase Activites in Giardia lamblia: ORF 17150 Encodes a Quinone Reductase with Nitroreductase Activity

The intestinal diplomonadid Giardia lamblia is a causative agent of persistent diarrhea. Current treatments are based on nitro drugs, especially metronidazole. Nitro compounds are activated by reduction, yielding toxic intermediates. The enzymatic systems responsible for this activation are not completely understood. By fractionating cell free crude extracts by size exclusion chromatography followed by mass spectrometry, enzymes with nitroreductase (NR) activities are identified. The protein encoded by ORF 17150 found in two pools with NR activities is overexpressed and characterized. In pools of fractions with main NR activities, previously-known NRs are identified, as well as a previously uncharacterized protein encoded by ORF 17150. Recombinant protein 17150 is a flavoprotein with NADPH-dependent quinone reductase and NR activities. Besides a set of previously identified NRs, we have identified a novel enzyme with NR activity.

Drug resistance in Giardia: Mechanisms and alternative treatments for Giardiasis

The use of chemotherapeutic drugs is the main resource against clinical giardiasis due to the lack of approved vaccines. Resistance of G. duodenalis to the most used drugs to treat giardiasis, metronidazole and albendazole, is a clinical issue of growing concern and yet unknown impact, respectively. In the search of new drugs, the completion of the Giardia genome project and the use of biochemical, molecular and bioinformatics tools allowed the identification of ligands/inhibitors for about one tenth of ≈150 potential drug targets in this parasite. Further, the synthesis of second generation nitroimidazoles and benzimidazoles along with high-throughput technologies have allowed not only to define overall mechanisms of resistance to metronidazole but to screen libraries of repurposed drugs and new pharmacophores, thereby increasing the known arsenal of anti-giardial compounds to some hundreds, with most demonstrating activity against metronidazole or albendazole-resistant Giardia. In particular, cysteine-modifying agents which include omeprazole, disulfiram, allicin and auranofin outstand due to their pleiotropic activity based on the extensive repertoire of thiol-containing proteins and the microaerophilic metabolism of this parasite. Other promising agents derived from higher organisms including phytochemicals, lactoferrin and propolis as well as probiotic bacteria/fungi have also demonstrated significant potential for therapeutic and prophylactic purposes in giardiasis. In this context the present chapter offers a comprehensive review of the current knowledge, including commonly prescribed drugs, causes of therapeutic failures, drug resistance mechanisms, strategies for the discovery of new agents and alternative drug therapies.

Resistance formation to nitro drugs in Giardia lamblia: No common markers identified by comparative proteomics

In order to elucidate the question whether resistance to nitro drugs in G. lamblia is due to common resistance markers, trophozoites of three resistant G. lamblia strains, namely C4, 1062ID10, and 713M3 were grown in the presence of the two nitro drugs metronidazole and nitazoxanide and compared to their corresponding wild-types WBC6, 106, and 713 by mass spectometry shotgun analysis of their proteomes. Depending on the strain and the nitro drug, more than 200 to 500 differentially expressed proteins were identified, but there were no common patterns across strains and drugs. All resistant strains underwent antigenic variation with distinct surface antigens like variant surface proteins or cysteine rich proteins depending on strain and nitro compound. A closer look on enzymes involved in nitroreduction and detoxification of nitro radicals, NO or O₂ suggested the existence of distinct strategies for each drug and each strain. Therefore, we conclude that resistance to nitro drugs in G. lamblia is not correlated with a specific pattern of differentially expressed proteins and therefore seems not to be the result of a directed process.

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Is resistance to nitro drugs in G. lamblia due to common resistance markers?

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Three resistant strains were grown in the presence of two nitro drugs separately and compared to wild-types by MS shotgun analysis.

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More than 200 to 500 differentially expressed proteins identified depending on strain and drug.

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No common patterns across strains and drugs.

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Strain specific antigenic variation and strategies linked to nitro reduction.

Metabolism of albendazole, ricobendazole and flubendazole in Haemonchus contortus adults: Sex differences, resistance-related differences and the identification of new metabolites

Haemonchus contortus (family Trichostrongylidae, Nematoda), a hematophagous gastrointestinal parasite found in small ruminants, has a great ability to develop resistance to anthelmintic drugs. We studied the biotransformation of the three benzimidazole anthelmintics: albendazole (ABZ), ricobendazole (albendazole S-oxide; RCB) and flubendazole (FLU) in females and males of H. contortus in both a susceptible ISE strain and resistant IRE strain. The ex vivo cultivation of living nematodes in culture medium with or without the anthelmintics was used. Ultrasensitive UHPLC/MS/MS analysis revealed 9, 7 and 12 metabolites of ABZ, RCB and FLU, respectively, with most of these metabolites now described in the present study for the first time in H. contortus. The structure of certain metabolites shows the presence of biotransformation reactions not previously reported in nematodes. There were significant qualitative and semi-quantitative differences in the metabolites formed by male and female worms. In most cases, females metabolized drugs more extensively than males. Adults of the IRE strain were able to form many more metabolites of all the drugs than adults of the ISE strain. Some metabolites were even found only in adults of the IRE strain. These findings suggest that increased drug metabolism may play a role in resistance to benzimidazole drugs in H. contortus.

Validation of housekeeping genes as an internal control for gene expression studies in Giardia lamblia using quantitative real-time PCR

The analysis of transcript levels of specific genes is important for understanding transcriptional regulation and for the characterization of gene function. Real-time quantitative reverse transcriptase PCR (RT-qPCR) has become a powerful tool to quantify gene expression. The objective of this study was to identify reliable housekeeping genes in Giardia lamblia. Twelve genes were selected for this purpose, and their expression was analyzed in the wild type WB strain and in two strains with resistance to nitazoxanide (NTZ) and metronidazole (MTZ), respectively. RefFinder software analysis showed that the expression of the genes is different in the three strains. The integrated data from the four analyses showed that the NADH oxidase (NADH) and aldolase (ALD) genes were the most steadily expressed genes, whereas the glyceraldehyde-3-phosphate dehydrogenase gene was the most unstable. Additionally, the relative expression of seven genes were quantified in the NTZ- and MTZ-resistant strains by RT-qPCR, using the aldolase gene as the internal control, and the results showed a consistent differential pattern of expression in both strains. The housekeeping genes found in this work will facilitate the analysis of mRNA expression levels of other genes of interest in G. lamblia.

Albendazole induces oxidative stress and DNA damage in the parasitic protozoan Giardia duodenalis

The control of Giardia duodenalis infections is carried out mainly by drugs, among these albendazole (ABZ) is commonly used. Although the cytotoxic effect of ABZ usually involves binding to β-tubulin, it has been suggested that oxidative stress may also play a role in its parasiticidal mechanism. In this work the effect of ABZ in Giardia clones that are susceptible or resistant to different concentrations (1.35, 8, and 250 μM) of this drug was analyzed. Reactive oxygen species (ROS) were induced by ABZ in susceptible clones and this was associated with a decrease in growth that was alleviated by cysteine supplementation. Remarkably, ABZ-resistant clones exhibited partial cross-resistance to H₂O_2, whereas a Giardia H₂O₂-resistant strain can grow in the presence of ABZ. Lipid oxidation and protein carbonylation in ABZ-treated parasites did not show significant differences as compared to untreated parasites; however, ABZ induced the formation of 8OHdG adducts and DNA degradation, indicating nucleic acid oxidative damage. This was supported by observations of histone H2AX phosphorylation in ABZ-susceptible trophozoites treated with 250 μM ABZ. Flow cytometry analysis showed that ABZ partially arrested cell cycle in drug-susceptible clones at G2/M phase at the expense of cells in G1 phase. Also, ABZ treatment resulted in phosphatidylserine exposure on the parasite surface, an event related to apoptosis. All together these data suggest that ROS induced by ABZ affect Giardia genetic material through oxidative stress mechanisms and subsequent induction of apoptotic-like events.