O(2)-dependent efficacy of novel piperidine- and piperazine-based chalcones against the human parasite Giardia intestinalis

Giardia duodenalis flavohemoglobin is a target of 5-nitroheterocycle and benzimidazole compounds acting as enzymatic inhibitors or subversive substrates

Giardia duodenalis causes giardiasis in humans, companion, livestock and wild animals. Control of infection involves drugs as benzimidazoles (e.g., albendazole, ABZ) and 5-nitroheterocyclics [5-NHs: metronidazole (MTZ), furazolidone (FZD), nitazoxanide (NTZ)] as first-line agents. During infection, Giardia is exposed to immune and pro-oxidant host responses involving nitric oxide (NO). In Giardia, NO is detoxified by a flavohemoglobin (gFlHb), a heme-containing enzyme which is absent in mammals. gFlHb has NO dioxygenase and NADH oxidase activities converting NO into nitrate and producing a superoxide anion (O2•-) that causes oxidative stress and parasite death. The modulation of gFlHb activities may provide novel approaches for treatment of giardiasis. We investigated the capacity of selected benzimidazole-2-carbamates (BZCs: ABZ, oxibendazole, nocodazole), non-BZCs (thiabendazole), an ehtylphenylcarbamate (LQM-996) and 5-NHs (MTZ, NTZ, FZD and some derivatives) to bind to recombinant gFlHb at the heme group, modifying NADH consumption activity and/or inducing ROS production. Of these, BZCs and NTZ bind to heme and increased O2•- production (i.e. caused enzyme subversion), whereas MTZ binds to heme but inhibited NADH consumption. LQM-996 decreased NADH consumption and two out of four NTZ derivatives altered NADH oxidase activity. In silico docking and molecular dynamics studies suggested the interaction of distinct drug moieties in ABZ and NTZ with gFlHb sites involved in NADH and NO catalysis. These findings provide new insights on gFlHb as a novel target of BZCs, MTZ and NTZ, and provides a useful platform to assess the compounds binding capacity to gFlHb prior to experimental and clinical trials in giardiasis.

Inhibition of Giardia duodenalis by isocryptolepine -triazole adducts and derivatives

Giardia duodenalis, a widespread parasitic flagellate protozoan causing giardiasis, affects millions annually, particularly impacting children and travellers. With no effective vaccine available, treatment primarily relies on the oral administration of drugs targeting trophozoites in the small intestine. However, existing medications pose challenges due to side effects and drug resistance, necessitating the exploration of novel therapeutic options. Isocryptolepine, derived from Cryptolepis sanguinolenta, has demonstrated promising antimicrobial and anticancer properties. This study evaluated eighteen isocryptolepine-triazole adducts for their antigiardial activities and cytotoxicity, with ISO2 demonstrating potent antigiardial activity and minimal cytotoxicity on human intestinal cells. Metabolomics analysis revealed significant alterations in G. duodenalis metabolism upon ISO2 treatment, particularly affecting phospholipid metabolism. Notably, the upregulation of phytosphingosine and triglycerides, and downregulation of certain fatty acids, suggest a profound impact on membrane composition and integrity, potentially contributing to the parasite's demise. Pathway analysis highlighted glycerophospholipid metabolism, cytochrome b5 family heme/steroid binding domain, and P-type ATPase mechanisms as critical pathways affected by ISO2 treatment, underscoring its importance as a potential target for antigiardial therapy. These findings shed light on the mode of action of ISO2 against G. duodenalis and provide valuable insights for further drug development. Moreover, the study also offers a promising avenue for the exploration of isocryptolepine derivatives as novel therapeutic agents for giardiasis, addressing the urgent need for more effective and safer treatment options.

Synthesis and Pharmacological Activities of Chalcone and Its Derivatives Bearing N-Heterocyclic Scaffolds: A Review

The incorporation of heterocyclic moieties into the standard chemical structure with a biologically active scaffold has become of crucial practice for the construction of pharmacologically potent candidates in the drug arena. Currently, numerous kinds of chalcones and their derivatives have been synthesized using the incorporation of heterocyclic scaffolds, especially chalcones bearing heterocyclic moieties that display improved efficiency and potential for drug production in pharmaceutical sectors. The current Review focuses on recent advances in the synthetic approaches and pharmacological activities such as antibacterial, antifungal, antitubercular, antioxidant, antimalarial, anticancer, anti-inflammatory, antigiardial, and antifilarial activities of chalcone derivatives incorporating N-heterocyclic moieties at either the A-ring or B-ring.

Mass Spectrometry-Based Metabolomics Revealed Effects of Metronidazole on Giardia duodenalis

Giardia duodenalis is a significant protozoan that affects humans and animals. An estimated 280 million G. duodenalis diarrheal cases are recorded annually. Pharmacological therapy is crucial for controlling giardiasis. Metronidazole is the first-line therapy for treating giardiasis. Several metronidazole targets have been proposed. However, the downstream signaling pathways of these targets with respect to their antigiardial action are unclear. In addition, several giardiasis cases have demonstrated treatment failures and drug resistance. Therefore, the development of novel drugs is an urgent need. In this study, we performed a mass spectrometry-based metabolomics study to understand the systemic effects of metronidazole in G. duodenalis. A thorough analysis of metronidazole processes helps identify potential molecular pathways essential for parasite survival. The results demonstrated 350 altered metabolites after exposure to metronidazole. Squamosinin A and N-(2-hydroxyethyl)hexacosanamide were the most up-regulated and down-regulated metabolites, respectively. Proteasome and glycerophospholipid metabolisms demonstrated significant differential pathways. Comparing glycerophospholipid metabolisms of G. duodenalis and humans, the parasite glycerophosphodiester phosphodiesterase was distinct from humans. This protein is considered a potential drug target for treating giardiasis. This study improved our understanding of the effects of metronidazole and identified new potential therapeutic targets for future drug development.

Oxygen levels are key to understanding "Anaerobic" protozoan pathogens with micro-aerophilic lifestyles

Publications abound on the physiology, biochemistry and molecular biology of "anaerobic" protozoal parasites as usually grown under "anaerobic" culture conditions. The media routinely used are poised at low redox potentials using techniques that remove O₂ to "undetectable" levels in sealed containers. However there is growing understanding that these culture conditions do not faithfully resemble the O₂ environments these organisms inhabit. Here we review for protists lacking oxidative energy metabolism, the oxygen cascade from atmospheric to intracellular concentrations and relevant methods of measurements of O₂, some well-studied parasitic or symbiotic protozoan lifestyles, their homeodynamic metabolic and redox balances, organism-drug-oxygen interactions, and the present and future prospects for improved drugs and treatment regimes.

Antigiardial Activity of Acetylsalicylic Acid Is Associated with Overexpression of HSP70 and Membrane Transporters

Giardia lamblia is a flagellated protozoan responsible for giardiasis, a worldwide diarrheal disease. The adverse effects of the pharmacological treatments and the appearance of drug resistance have increased the rate of therapeutic failures. In the search for alternative therapeutics, drug repositioning has become a popular strategy. Acetylsalicylic acid (ASA) exhibits diverse biological activities through multiple mechanisms. However, the full spectrum of its activities is incompletely understood. In this study we show that ASA displayed direct antigiardial activity and affected the adhesion and growth of trophozoites in a time-dose-dependent manner. Electron microscopy images revealed remarkable morphological alterations in the membrane, ventral disk, and caudal region. Using mass spectrometry and real-time quantitative reverse transcription (qRT-PCR), we identified that ASA induced the overexpression of heat shock protein 70 (HSP70). ASA also showed a significant increase of five ATP-binding cassette (ABC) transporters (giABC, giABCP, giMDRP, giMRPL and giMDRAP1). Additionally, we found low toxicity on Caco-2 cells. Taken together, these results suggest an important role of HSPs and ABC drug transporters in contributing to stress tolerance and protecting cells from ASA-induced stress.

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.

Antigiardial activity of novel triazolyl-quinolone-based chalcone derivatives: when oxygen makes the difference

Giardiasis is a common diarrheal disease worldwide caused by the protozoan parasite Giardia intestinalis. It is urgent to develop novel drugs to treat giardiasis, due to increasing clinical resistance to the gold standard drug metronidazole (MTZ). New potential antiparasitic compounds are usually tested for their killing efficacy against G. intestinalis under anaerobic conditions, in which MTZ is maximally effective. On the other hand, though commonly regarded as an ‘anaerobic pathogen,’ G. intestinalis is exposed to relatively high O₂ levels in vivo, living attached to the mucosa of the proximal small intestine. It is thus important to test the effect of O₂ when searching for novel potential antigiardial agents, as outlined in a previous study [Bahadur et al. (2014) Antimicrob. Agents Chemother. 58, 543]. Here, 45 novel chalcone derivatives with triazolyl-quinolone scaffold were synthesized, purified, and characterized by high resolution mass spectrometry, ¹H and ¹³C nuclear magnetic resonance and infrared spectroscopy. Efficacy of the compounds against G. intestinalis trophozoites was tested under both anaerobic and microaerobic conditions, and selectivity was assessed in a counter-screen on human epithelial colorectal adenocarcinoma cells. MTZ was used as a positive control in the assays. All the tested compounds proved to be more effective against the parasite in the presence of O₂, with the exception of MTZ that was less effective. Under anaerobiosis eighteen compounds were found to be as effective as MTZ or more (up to three to fourfold); the same compounds proved to be up to >100-fold more effective than MTZ under microaerobic conditions. Four of them represent potential candidates for the design of novel antigiardial drugs, being highly selective against Giardia trophozoites. This study further underlines the importance of taking O₂ into account when testing novel potential antigiardial compounds.