O ₂ -Dependent Efficacy of Novel Piperidine- and Piperazine-Based Chalcones against the Human Parasite Giardia intestinalis

Abstract

dGiardia intestinalis is the most frequent protozoan agent of intestinal diseases worldwide. Though commonly regarded as an anaerobic pathogen, it preferentially colonizes the fairly oxygen-rich mucosa of the proximal small intestine. Therefore, when testing new potential antigiardial drugs, O 2 should be taken into account, since it also reduces the efficacy of metronidazole, the gold standard drug against giardiasis. In this study, 46 novel chalcones were synthesized by microwave-assisted Claisen-Schmidt condensation, purified, characterized by high-resolution mass spectrometry, 1 H and 13 C nuclear magnetic resonance, and infrared spectroscopy, and tested for their toxicity against G. intestinalis under standard anaerobic conditions. As a novel approach, compounds showing antigiardial activity under anaerobiosis were also assayed under microaerobic conditions, and their selectivity against parasitic cells was assessed in a counterscreen on human epithelial colorectal adenocarcinoma cells. Among the tested compounds, three [30(a), 31(e), and 33] were more effective in the presence of O 2 than under anaerobic conditions and killed the parasite 2 to 4 times more efficiently than metronidazole under anaerobiosis. Two of them [30(a) and 31(e)] proved to be selective against parasitic cells, thus representing potential candidates for the design of novel antigiardial drugs. This study highlights the importance of testing new potential antigiardial agents not only under anaerobic conditions but also at low, more physiological O 2 concentrations.

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

“…The antigiardial activity of the novel compounds 23–67 was tested under both anaerobic and microaerobic conditions. According to ( Dunn et al, 2010 ; Bahadur et al, 2014 ), susceptibility of Giardia trophozoites to increasing concentrations of each compound was assessed based on ATP level determination by luminescence. Dose-response curves for each compound were obtained after 48 h-incubation and compared to the data collected under identical conditions with MTZ, the drug of choice for treatment of giardiasis.…”

“…When testing new potential antigiardial drugs, it is thus important to take O 2 into account also to attempt identifying antiparasitic compounds that could be fully effective under the more physiological microaerobic conditions in which MTZ efficacy is reduced due to O 2 presence. This issue has been highlighted in a recent study by our groups ( Bahadur et al, 2014 ) in which O 2 , while making MTZ expectedly less effective, was reported to enhance the efficacy of three piperidine/piperazine chalcone derivatives, pre-selected in a screen conducted under anaerobic conditions.…”

“…The assays were performed following the procedure described in Bahadur et al (2014) , using sterile 96-well white clear-bottom plates. In each well, 50 μL of Giardia trophozoites at a density of 1 × 10 5 cells/mL was added to 50 μL medium containing either the compound to be tested, serially diluted from a stock solution in dimethyl sulfoxide (DMSO), or the same amount of DMSO as a control; this yielded a final density of 5.000 cells/100 μL in each well.…”

“…Given the fairly aerobic environment inhabited by Giardia in the host, it is important to consider possible effects of O 2 , when testing novel potential antigiardial drugs. Following this rationale, we have recently carried out a study ( Bahadur et al, 2014 ) in which a set of synthetic compounds has been initially screened for its antigiardial activity under anaerobic condition, and then the compounds with the highest activity were assayed for their efficacy under microaerobic conditions too. This innovative approach allowed us to identify two chalcone derivatives that under microaerobic conditions proved to be selectively active against Giardia trophozoites and more effective than MTZ ( Bahadur et al, 2014 ).…”

“…On the other hand, though commonly regarded as an ‘anaerobic pathogen,’ G. intestinalis is exposed to relatively high O 2 levels in vivo , living attached to the mucosa of the proximal small intestine. It is thus important to test the effect of O 2 when searching for novel potential antigiardial agents, as outlined in a previous study [ Bahadur et al (2014) Antimicrob. Agents Chemother.…”