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Background: Chagas cardiomyopathy, caused by Trypanosoma cruzi infection, continues to be a neglected illness, and has a major impact on global health. The parasite undergoes several stages of morphological and biochemical changes during its life cycle, and utilizes an elaborated antioxidant network to overcome the oxidants barrier and establish infection in vector and mammalian hosts. Trypanothione synthetase (TryS) catalyzes the biosynthesis of glutathione-spermidine adduct trypanothione (T(SH) 2 ) that is the principal intracellular thiol-redox metabolite in trypanosomatids., Methods and Results: We utilized genetic overexpression (TryS hi ) and pharmacological inhibition approaches to examine the role of TryS in T. cruzi proliferation, tolerance to oxidative stress and resistance to anti-protozoal drugs. Our data showed the expression and activity of TryS was increased in all morphological stages of TryS hi (vs. control) parasites. In comparison to controls, the TryS hi epimastigotes (insect stage) recorded shorter doubling time, and both epimastigotes and infective trypomastigotes of TryS hi exhibited 36-71% higher resistance to H 2 O 2 (50-1000 μM) and heavy metal (1-500 μM) toxicity. Treatment with TryS inhibitors (5-30 μM) abolished the proliferation and survival advantages against H 2 O 2 pressure in a dose-dependent manner in both TryS hi and control parasites. Further, epimastigote and trypomastigote forms of TryS hi (vs. control) T. cruzi tolerated higher doses of benznidazole and nifurtimox, the drugs currently administered for acute Chagas disease treatment., Conclusions: TryS is essential for proliferation and survival of T. cruzi under normal and oxidant stress conditions, and provides an advantage to the parasite to develop resistance against currently used anti-trypanosomal drugs. TryS indispensability has been chemically validated with inhibitors that may be useful for drug combination therapy against Chagas disease., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Trypanothione is a unique and essential redox metabolite of trypanosomatid parasites, the biosynthetic pathway of which is regarded as a promising target for antiparasitic drugs. Synthesis of trypanothione occurs by the consecutive conjugation of two glutathione molecules to spermidine. Both reaction steps are catalyzed by trypanothione synthetase (TRYS), a molecule known to be essential in Trypanosoma brucei. However, other trypanosomatids (including some Leishmania species and Trypanosoma cruzi) potentially express one additional enzyme, glutathionylspermidine synthetase (GSPS), capable of driving the first step of trypanothione synthesis yielding glutathionylspermidine. Because this monothiol can substitute for trypanothione in some reactions, the possibility existed that TRYS was redundant in parasites harboring GSPS. To clarify this issue, the functional relevance of both GSPS and TRYS was investigated in Leishmania infantum (Li). Employing a gene-targeting approach, we generated a gsps(-/-) knockout line, which was viable and capable of replicating in both life cycle stages of the parasite, thus demonstrating the superfluous role of LiGSPS. In contrast, elimination of both LiTRYS alleles was not possible unless parasites were previously complemented with an episomal copy of the gene. Retention of extrachromosomal LiTRYS in the trys(-/-)/+TRYS line after several passages in culture further supported the essentiality of this gene for survival of L. infantum (including its clinically relevant stage), hence ruling out the hypothesis of functional complementation by LiGSPS. Chemical targeting of LiTRYS with a drug-like compound was shown to also lead to parasite death. Overall, this study disqualifies GSPS as a target for drug development campaigns and, by genetic and chemical evidence, validates TRYS as a chemotherapeutic target in a parasite endowed with GSPS and, thus, probably along the entire trypanosomatid lineage., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Trypanosoma cruzi is the etiologic agent of Chagas' disease, an infection that affects several million people in Latin America. With no immediate prospect of a vaccine and problems associated with current chemotherapies, the development of new treatments is an urgent priority. Several aspects of the redox metabolism of this parasite differ enough from those in the mammalian host to be considered targets for drug development. Here, we review the information about a trypanosomatid-specific molecule centrally involved in redox metabolism, the dithiol trypanothione, and the main effectors of cellular antioxidant defense. We focus mainly on data from T. cruzi, making comparisons with other trypanosomatids whenever possible. In these parasites trypanothione participates in crucial thiol-disulfide exchange reactions and serves as electron donor in different metabolic pathways, from synthesis of DNA precursors to oxidant detoxification. Interestingly, the levels of several enzymes involved in trypanothione metabolism and oxidant detoxification increase during the transformation of T. cruzi to its mammalian-infective form and the overexpression of some of them has been associated with increased resistance to macrophage-dependent oxidative killing. Together, the evidence suggests a central role of the trypanothione-dependent antioxidant systems in the infection process.

In trypanosomes, the parasite-specific thiol trypanothione [T(SH)2] fulfills various functions, the best established being detoxification of H2O2 and organic hydroperoxides and ribonucleotide reduction. Recently, a trypanothione synthetase (Tb-TryS) gene from Trypanosoma brucei was isolated and the heterologously expressed Tb-TryS catalyzed the entire synthesis of T(SH)2 from glutathione (GSH) and spermidine in vitro. To confirm the in situ function of the complex Tb-TryS activities and to evaluate the importance of T(SH)2 metabolism in T. brucei, TryS suppression by double-stranded RNA interference was performed. Knockdown of TryS led to depletion of both T(SH)2 and glutathionylspermidine (Gsp) and accumulation of GSH, while concomitantly impairment of viability and arrest of proliferation were observed. TryS-downregulated cells displayed a significantly increased sensitivity to H2O2 and tert.-butyl hydroperoxide. These data verify the hypothesis that in T. brucei, a single enzyme synthesizes the spermidine-conjugated thiols (Gsp and T(SH)2) and further confirms the significance of trypanothione in the defense against oxidative stress and the maintenance of viability and proliferation in unstressed parasites.