Nitroimidazole drugs vary in their mode of action in the human parasite Giardia lamblia

Abstract

Giardia lamblia (syn. duodenalis, intestinalis) is a globally occurring micro-aerophilic human parasite that causes gastrointestinal disease. Standard treatment of G. lamblia infections is based on the 5-nitroimidazole drugs metronidazole and tinidazole. In two other micro-aerophilic parasites, Entamoeba histolytica and Trichomonas vaginalis, 5-nitroimidazole drugs bind to proteins involved in the thioredoxin-mediated redox network and disrupt the redox equilibrium by inhibiting thioredoxin reductase and depleting intracellular thiol pools. The major aim of this study was to assess whether nitroimidazoles exert a similar toxic effect on G. lamblia physiology. The 5-nitroimidazoles metronidazole and tinidazole were found to bind to the same subset of proteins including thioredoxin reductase. However, in contrast to E. histolytica and T. vaginalis, none of the other proteins bound are candidates for being involved in the thioredoxin-mediated redox network. Translation elongation factor EF-1γ, an essential factor in protein synthesis, was widely degraded upon treatment with 5-nitroimidazoles. 2-Nitroimidazole (azomycin) and the 5-nitroimidazole ronidazole did not bind to any G. lamblia proteins, which is in contrast to previous findings in E. histolytica and T. vaginalis. All nitroimidazoles tested reduced intracellular thiol pools in G. lamblia, but metronidazole, also in contrast to the situation in the other two parasites, had the slightest effect. Taken together, our results suggest that nitroimidazole drugs affect G. lamblia in a fundamentally different way than E. histolytica and T. vaginalis.

Proteomic and functional analyses reveal pleiotropic action of the anti-tumoral compound NBDHEX in Giardia duodenalis

“…Nitroimidazole adducts formation has been shown to induce molecular size and isoelectric point shift of Giardia proteins (Leitsch et al., 2012). Indeed, following Giardia exposure to NBDHEX, gOCT and gTrxR shifted towards higher molecular sizes, with the latter showing a band doublet, as observed in immunoblot experiments (Fig.…”

“…Since gTrxR and gEF1Bγ have been recognized as MTZ activator and/or drug targets, respectively (Leitsch et al., 2012), their interplay with NBDHEX was further studied using bacterial expressed HIS-tagged recombinant proteins. After drug treatment of E. coli, purified HIS-gTrxR and HIS-gEF1Bγ showed fluorescence after SDS-PAGE (Fig.…”

The effect of metronidazole on the cell cycle and DNA in metronidazole-susceptible and -resistant Giardia cell lines

“…Described formation of covalent adducts between MTZ and proteins of redox system that accompanied MTZ cytotoxicity to a human parasite Trichomonas vaginalis and a fish parasite Spironucleus vortens led authors to similar assumptions, that rapid cellular response to high concentrations of nitroimidazoles cannot be conclusively explained by DNA damage response, given the necessity of MTZ intermediates to cross the nuclear membrane and the relatively slow DNA damage response [30]. The same authors introduce redox imbalance as the mode of action of MTZ for a diplomonad Spironucleus [31], however, in contrast to Trichomonas or Spironucleus, a different mode of action has been suggested in Giardia with elongation factor 1␥ as a possible MTZ target [32]. The disrupted redox balance as the overall consequence responsible for cell death upon MTZ treatment has been drown up recently [10].…”

Click Chemistry-Facilitated Structural Diversification of Nitrothiazoles, Nitrofurans, and Nitropyrroles Enhances Antimicrobial Activity against Giardia lamblia

“…However, many of the details are not known in the target parasites. It is becoming increasingly evident that more than one reductase pathway can activate nitro drugs in G. lamblia and other microbes (16,19,(34)(35)(36)(37) and that multiple adduction targets exist (38). In addition, nitazoxanide has been shown to inhibit the interactions of a cofactor with its target enzyme, pyruvate:ferredoxin-flavodoxin oxidoreductase, and thus the activity of this critical enzyme, suggesting that nitro drugs may have other mechanisms of action beyond adduction of microbial target molecules (39).…”