Roles of Trypanothione S -Transferase and Tryparedoxin Peroxidase in Resistance to Antimonials

Abstract

The clinical value of antimonial drugs, the mainstay therapy for leishmaniasis, is now threatened by the emergence of acquired drug resistance, and a comprehensive understanding of the underlying mechanisms is required. Using the model organism Leishmania tarentolae, we have examined the role of trypanothione S-transferase (TST) in trivalent antimony [Sb(III)] resistance. TST has S-transferase activity with substrates such as chlorodinitrobenzene as well as peroxidase activity with alkyl and aryl hydroperoxides but not with hydrogen peroxide. Although S-transferase activity and TST protein levels were unchanged in Sb(III)-sensitive and -resistant lines, rates of metabolism of hydrogen peroxide, t-butyl hydroperoxide, and cumene hydroperoxide were significantly increased. Elevated peroxidase activities were shown to be both trypanothione and tryparedoxin dependent and were associated with the overexpression of classical tryparedoxin peroxidase (TryP) in the cytosol of L. tarentolae. The role of TryP in Sb(III) resistance was verified by overexpression of the recombinant Leishmania major protein in Sb(III)-sensitive promastigotes. An approximate twofold increase in the level of TryP activity in this transgenic cell line was accompanied by a significant decrease in sensitivity to Sb(III) (twofold; P < 0.001). Overexpression of an enzymatically inactive TryP failed to result in Sb(III) resistance. This indicates that TryP-dependent resistance is not due to sequestration of Sb(III) and suggests that enhanced antioxidant defenses may well be a key feature of mechanisms of clinical resistance to antimonial drugs.

Molecular characterization of cytosolic and mitochondrial tryparedoxin peroxidase in Trypanosoma cruzi populations susceptible and resistant to benznidazole

“…Lin et al (2005) also described a concomitant increase in the expression of cytosolic and mitochondrial TXNP in arsenite-resistant L. amazonensis. In addition, the largest increase in cytosolic TXNPx protein levels has been observed in L. tarentolae resistant to trivalent antimony (Wyllie et al 2008).…”

“…Similarly, in arsenate-resistant Leishmania amazonensis an increase of five-and fourfold in the transcription levels of the cTXNPx and mTXNPx genes, respectively, was also described (Lin et al 2005). L. tarentolae resistant to trivalent antimony has been reported an increase of 6.5-and 1.8-fold in cytosolic and mitochondrial TXNPx enzymes, respectively (Wyllie et al 2008). Altogether, these findings are in agreement with our results showing an increase in the mRNA level of the TXNPx enzyme in drug-resistant parasites.…”

Leishmania antimony resistance: what we know what we can learn from the field

“…Therefore, either quantification of copy number or expression of genes known to be involved in antimony susceptibility should represent good biomarkers for addressing antimony resistance (Guimond et al 2003;Ubeda et al 2008). If some of the above-mentioned mechanisms are effectively encountered in resistant lines from the field, however, then no rules could be applied Mandal et al 2010;Mukherjee et al 2007;Torres et al 2010;Maharjan et al 2008) because of the presence of additional unrelated and less specific mechanisms (Kumar et al 2009;Wyllie et al 2008;Vergnes et al 2007) or because of other yet unidentified mechanisms of resistance (Goyeneche-Patino et al 2008). Finally, a comparative proteome mapping, carried out on drug-susceptible and drug-resistant parasites, has characterized additional protein overexpressed in field antimony-resistant isolates of L. donovani; their capacity to confer antimony resistance has been investigated .…”

Whole genome sequencing of multiple Leishmania donovani clinical isolates provides insights into population structure and mechanisms of drug resistance

“…Tryparedoxin peroxidase diminishes the inhibition of thiol redox metabolism by antimonial drugs by reactive oxygen species reduction (Wyllie et al 2004(Wyllie et al , 2008König and Fairlamb 2007;Mandal et al 2007), and is overexpressed in SSG-resistant clinical L. donovani (Wyllie et al 2010). The tryparedoxin locus itself may be associated with both host immunogenicity and drug resistance in Leishmania (Stober et al 2005), and in particular, with the murine B-cell response against L. infantum (Castro et al 2004;Cabral et al 2008).…”