Involvement of tryparedoxin peroxidase (TryP) and trypanothione reductase (TryR) in antimony unresponsive of Leishmania tropica clinical isolates of Iran

Insights into the trypanothione system in antimony-resistant and sensitive Leishmania tropica clinical isolates

Pentavalent antimonials are the mainstay treatment against different clinical forms of leishmaniasis. The emergence of resistant isolates in endemic areas has led to treatment failure. Unraveling the underlying resistance mechanism would assist in improving the treatment strategies against resistant isolates. This study aimed to investigate the RNA expression level of glutathione synthetase (GS), Spermidine synthetase (SpS), trypanothione synthetase (TryS) genes involved in trypanothione synthesis, and thiol-dependent reductase (TDR) implicated in drug reduction, in antimony-sensitive and -resistant Leishmania tropica isolates. We investigated 11 antimony-resistant and 11 antimony-sensitive L. tropica clinical isolates from ACL patients. Drug sensitivity of amastigotes was determined in mouse macrophage cell line J774A.1. The RNA expression level in the promastigote forms was analyzed by quantitative real-time PCR. The results revealed a significant increase in the average expression of GS, SpS, and TrpS genes by 2.19, 1.56, and 2.33-fold in resistant isolates compared to sensitive ones. The average expression of TDR was 1.24-fold higher in resistant isolates, which was insignificant. The highest correlation coefficient between inhibitory concentration (IC50) values and gene expression belonged to the TryS, GS, SpS, and TDR genes. Moreover, the intracellular thiol content was increased 2.17-fold in resistant isolates compared to sensitive ones and positively correlated with IC50 values. Our findings suggest that overexpression of trypanothione biosynthesis genes and increased thiol content might play a key role in the antimony resistance of L. tropica clinical isolates. In addition, the diversity of gene expression in the trypanothione system and thiol content among L. tropica clinical isolates highlighted the phenotypic heterogeneity of antimony resistance among the parasite population.

Unveiling the role of serine o-acetyltransferase in drug resistance and oxidative stress tolerance in Leishmania donovani through the regulation of thiol-based redox metabolism

Understanding the unique metabolic pathway of L. donovani is crucial for comprehending its biology under oxidative stress conditions. The de novo cysteine biosynthetic pathway of L. donovani is absent in humans and its product, cysteine regulates the downstream components of trypanothione-based thiol metabolism, important for maintaining cellular redox homeostasis. The role of serine o-acetyl transferase (SAT), the first enzyme of this pathway remains unexplored. In order to investigate the role of SAT protein, we cloned SAT gene into pXG-GFP+ vector for episomal expression of SAT in Amphotericin B sensitive L. donovani promastigotes. The SAT overexpression was confirmed by SAT enzymatic assay, GFP fluorescence, immunoblotting and PCR. Our study unveiled an upregulated expression of both LdSAT and LdCS of cysteine biosynthetic pathway and other downstream thiol pathway proteins in LdSAT-OE promastigotes. Additionally, there was an increase in enzymatic activities of LdSAT and LdCS proteins in LdSAT-OE, which was found similar to the Amp B resistant parasites, indicating a potential role of SAT protein in modulating drug resistance. We observed that the overexpression of SAT in Amp B sensitive parasites increases tolerance to drug pressure and oxidative stress via trypanothione-dependent antioxidant mechanism. Moreover, the in vitro J774A.1 macrophage infectivity assessment showed that SAT overexpression augments parasite infectivity. In LdSAT-OE promastigotes, antioxidant enzyme activities like APx and SOD were upregulated, intracellular reactive oxygen species were reduced with a corresponding increase in thiol level, emphasizing SAT's role in stress tolerance and enhanced infectivity. Additionally, the ROS mediated upregulation in the expression of LdSAT, LdCS, LdTryS and LdcTXNPx proteins reveals an essential cross talk between SAT and proteins of thiol metabolism in combating oxidative stress and maintaining redox homeostasis. Taken together, our results provide the first insight into the role of SAT protein in parasite infectivity and survival under drug pressure and oxidative stress.

Antimony resistance and gene expression in Leishmania: spotlight on molecular and proteomic aspects

Leishmaniasis is a vector-borne parasitic disease caused by Leishmania parasites with a spectrum of clinical manifestations, ranging from skin lesions to severe visceral complications. Treatment of this infection has been extremely challenging with the concurrent emergence of drug resistance. The differential gene expression and the discrepancies in protein functions contribute to the appearance of 2 distinct phenotypes: resistant and sensitive, but the current diagnostic tools fail to differentiate between them. The identification of gene expression patterns and molecular mechanisms coupled with antimony (Sb) resistance can be leveraged to prompt diagnosis and select the most effective treatment methods. The present study attempts to use comparative expression of Sb resistance-associated genes in resistant and sensitive Leishmania, to disclose their relative abundance in clinical or in vitro selected isolates to gain an understanding of the molecular mechanisms of Sb response/resistance. Data suggest that the analysis of resistance gene expression would verify the Sb resistance or susceptibility only to a certain extent; however, none of the individual expression patterns of the studied genes was diagnostic as a biomarker of Sb response of Leishmania. The findings highlighted will be useful in bridging the knowledge gap and discovering innovative diagnostic tools and novel therapeutic targets.

Assessing the effect of antimony pressure on trypanothione reductase activity in Leishmania (Viannia) braziliensis

Leishmania parasites have an oxidative and chemical defense mechanism called trypanothione system (T[SH]₂), the most abundant thiol system in trypanosomatids. This system has a central role in processing pentavalent antimony and resistance has been related to a better capacity to metabolize it through the activation of T[SH]₂ enzymatic cascade. A biochemical approach was applied to assess the effect of trivalent (Sb^III) and pentavalent antimony (Sb^V) on Trypanothione Reductase (TR) activity of two Leishmania (Viannia) braziliensis clinical isolates, which were labeled as responder (R) and non-responder (NR) after patient treatment with Glucantime®. Both isolates were characterized based on in vitro susceptibility to Sb^III and Sb^V and trypanothione reductase (TR) activity. Sb^III and Sb^V discriminated susceptibility profiles in all parasite forms, since isolate NR had significantly higher EC₅₀ values than isolate R. Differences were observed in TR activity between promastigotes, axenic amastigotes and intracellular amastigotes: R (0.439 ± 0.009, 0.103 ± 0.01 and 0.185 ± 0.01AU.min^-1.μg of protein^-1) and NR (1.083 ± 0.04, 0.914 ± 0.04 and 0.343 ± 0.04 AU. min^-1.μg of protein^-1), respectively. Incubation with Sb^III and Sb^V using each form EC₅₀ value caused a time-dependent differential effect on TR activity suggesting that oxidative defense is related to the antimony susceptibility phenotype. Data gathered here shows a biochemical approach able to discriminate two L. (V.) braziliensis clinical isolates measurements TR activity of promastigotes, axenic amastigotes and intracellular amastigotes.