Evaluation Of Giardia Lamblia Thioredoxin Reductase As Drug Activating Enzyme And As Drug Target
Authors: David Leitsch, Joachim Muller, Norbert Muller
Abstract:
The enzyme thioredoxin reductase (TrxR), known for its antioxidative properties, has been proposed as a potential drug target for various pathogens, including the protist parasite Giardia lamblia. It is believed that TrxR is involved in the activation of nitro drugs such as metronidazole and furazolidone, a process necessary for rendering these compounds toxic to G. lamblia and other microaerophiles/anaerobes. The objective of this study was to evaluate TrxR's potential as a drug target in G. lamblia and to find direct evidence of its role in the activation of metronidazole and other nitro drugs.
To achieve TrxR overexpression, the researchers inserted the trxR gene downstream of the arginine deiminase (ADI) promoter on a plasmid, resulting in approximately a 10-fold increase in TrxR expression in G. lamblia WB C6 cells. Additionally, a mutant TrxR with a defective disulphide reductase catalytic site was expressed strongly in another G. lamblia WB C6 cell line. The susceptibilities of both transfectant cell lines to five antigiardial drugs (metronidazole, furazolidone, nitazoxanide, albendazole, and auranofin) were compared to those of the wildtype. Furthermore, the researchers measured the impact of all five drugs on TrxR activity in vivo.
The results showed that overexpression of TrxR made G. lamblia WB C6 more susceptible to metronidazole and furazolidone but did not affect susceptibility to nitazoxanide, albendazole, and auranofin. Among the five drugs tested, only auranofin had a noticeable negative effect on TrxR activity in vivo, although the extent was smaller than expected. Overexpression of TrxR and the mutant TrxR had minimal influence on the growth of G. lamblia WB C6, despite the enzyme's significant NADPH oxidase activity, which generates oxidative stress.
These findings provide the first direct evidence supporting the notion that TrxR activates metronidazole and furazolidone. However, they raise doubts regarding TrxR's relevance as a drug target for currently used antigiardial drugs.
Keywords
Giardia lamblia; Thioredoxin reductase; Antigiardial drugs
Citation: David Leitsch, Joachim Muller, Norbert Muller Evaluation Of Giardia Lamblia Thioredoxin Reductase As Drug Activating Enzyme And As Drug Target doi:10.1016/j.ijpddr.2016.07.003
Received: 27 June 2016, Accepted: 21 July 2016, Available online: 22 July 2016
Copyright: © 2016 The Authors. Published by Elsevier Ltd on behalf of Australian Society for Parasitology. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Acknowledgements
David Leitsch was supported by grant J3492 of the Austrian Science Fund (FWF). Norbert Müller [NM] and Joachim Müller [JM] were supported by the Swiss National Science Foundation (grants SNF 31003A_138353 [NM and JM] and 31003A_163230 [NM]).
