Abstract
Glucose 6-phosphate dehydrogenase (G6PDH) fulfills an essential role in cell physiology by catalyzing the production of NADPH+ and of a precursor for the de novo synthesis of ribose 5-phosphate. In trypanosomatids, G6PDH is essential for in vitro proliferation, antioxidant defense and, thereby, drug resistance mechanisms. So far, 16α-brominated epiandrosterone represents the most potent hit targeting trypanosomal G6PDH. Here, we extended the investigations on this important drug target and its inhibition by using a small subset of androstane derivatives. In Trypanosoma cruzi, immunofluorescence revealed a cytoplasmic distribution of G6PDH and the absence of signal in major organelles. Cytochemical assays confirmed parasitic G6PDH as the molecular target of epiandrosterone. Structure-activity analysis for a set of new (dehydro)epiandrosterone derivatives revealed that bromination at position 16α of the cyclopentane moiety yielded more potent T. cruzi G6PDH inhibitors than the corresponding β-substituted analogues. For the 16α brominated compounds, the inclusion of an acetoxy group at position 3 either proved detrimental or enhanced the activity of the epiandrosterone or the dehydroepiandrosterone derivatives, respectively. Most derivatives presented single digit μM EC50 against infective T. brucei and the killing mechanism involved an early thiol-redox unbalance. This data suggests that infective African trypanosomes lack efficient NADPH+-synthesizing pathways, beyond the Pentose Phosphate, to maintain thiol-redox homeostasis.
Highlights
Chagas disease, African trypanosomiasis and leishmaniasis are “neglected tropical diseases” (NTD) that affect the most vulnerable populations around tropical and subtropical regions of the world
Whereas in the model generated on the G6P-HsG6PDH complex the representative steroids partially occupied the substrate binding sites [39], our model shows that EA and its 16α-Br derivative do not interfere with substrate binding and are tightly embedded in a hydrophobic pocket formed by the apolar side chains of Pro143, Pro144, Pro172 and Tyr249, and are located near the active site (Figure 6B,D)
In agreement with digitonin fractionation studies [24], our study confirmed by immuno-and cytochemical-based techniques that Glucose 6-phosphate dehydrogenase (G6PDH) is mostly a cytosolic and low abundant protein in the non-infective form of T. cruzi
Summary
African trypanosomiasis and leishmaniasis are “neglected tropical diseases” (NTD) that affect the most vulnerable populations around tropical and subtropical regions of the world. Several enzymes may contribute to the production of NADPH in different subcellular compartments of the infective stages of trypanosomatids [10,11] They can be grouped in dehydrogenases participating in amino acid (isocitrate dehydrogenase: IDH, malate dehydrogenase: MDH, glutamate dehydrogenase: GDH) or carbohydrate metabolism (glucose 6-phosphate dehydrogenase: G6PDH and 6-phosphogluconate dehydrogenase: 6PGDH). Based on the detection limit of the antibodies (up to 10 ng TcG6PDHL), the total cell number in the analyzed lysate and the cell volume reported for T. cruzi epimastigotes (30 fL) [40], we estimated that the intracellular concentration of G6PDH in this parasite species and stage is lower than 0.7 μM.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
