Redox control in trypanosomatids, parasitic protozoa with trypanothione-based thiol metabolism

Role of PIP39 in oxidative stress response appears conserved in kinetoplastids

Kinetoplastids, a group of flagellated protists that are often insect intestinal parasites, encounter various sources of oxidative stress. Such stressors include reactive oxygen species, both internally produced within the protist, and induced externally by host immune responses. This investigation focuses on the role of a highly conserved aspartate-based protein phosphatase, PTP-Interacting protein (PIP39) in managing oxidative stress. In addition to its well accepted role in a Trypanosoma brucei life stage transition, there is evidence of PIP39 participation in the T. brucei oxidative stress response. To examine whether this latter PIP39 role may exist more broadly, we aimed to elucidate PIP39's contribution to redox homeostasis in the monoxenous parasite Leptomonas seymouri. Utilizing CRISPR-Cas9-mediated elimination of PIP39 in conjunction with oxidative stress assays, we demonstrate that PIP39 is required for cellular tolerance to oxidative stress in L. seymouri, positing it as a putative regulatory node for adaptive stress responses. We propose that future analysis of L. seymouri PIP39 enzymatic activity, regulation, and potential localization to a specialized organelle termed a glycosome will contribute to a deeper understanding of the molecular mechanisms by which protozoan parasites adapt to oxidative environments. Our study also demonstrates success at using gene editing tools developed for Leishmania for the related L. seymouri.

A guide to genetically-encoded redox biosensors: State of the art and opportunities

Genetically-encoded redox biosensors have become invaluable tools for monitoring cellular redox processes with high spatiotemporal resolution, coupling the presence of the redox-active analyte with a change in fluorescence signal that can be easily recorded. This review summarizes the available fluorescence recording methods and presents an in-depth classification of the redox biosensors, organized by the analytes they respond to. In addition to the fluorescent protein-based architectures, this review also describes the recent advances on fluorescent, chemigenetic-based redox biosensors and other emerging chemigenetic strategies. This review examines how these biosensors are designed, the biosensors sensing mechanism, and their practical advantages and disadvantages.

Insight into the inhibitory potential of metal complexes supported by (E)-2-morpholino-N-(thiophen-2-ylmethylene)ethanamine: synthesis, structural properties, biological evaluation and docking studies

A thiophene-derived Schiff base ligand (E)-2-morpholino-N-(thiophen-2-ylmethylene)ethanamine was used for the synthesis of M(II) complexes, [TEM(M)X2] (M = Co, Cu, Zn; X = Cl; M = Cd, X = Br). Structural characterization of the synthesized complexes revealed distorted tetrahedral geometry around the M(II) center. In vitro investigation of the synthesized ligand and its M(II) complexes showed considerable anti-urease and leishmanicidal potential. The synthesized complexes also exhibited a significant inhibitory effect on urease, with IC50 values in the range of 3.50-8.05 μM. In addition, the docking results were consistent with the experimental results. A preliminary study of human colorectal cancer (HCT), hepatic cancer (HepG2), and breast cancer (MCF-7) cell lines showed marked anticancer activities of these complexes.

Targeting Trypanothione Metabolism in Trypanosomatids

Infectious diseases caused by trypanosomatids, including African trypanosomiasis (sleeping sickness), Chagas disease, and different forms of leishmaniasis, are Neglected Tropical Diseases affecting millions of people worldwide, mainly in vulnerable territories of tropical and subtropical areas. In general, current treatments against these diseases are old-fashioned, showing adverse effects and loss of efficacy due to misuse or overuse, thus leading to the emergence of resistance. For these reasons, searching for new antitrypanosomatid drugs has become an urgent necessity, and different metabolic pathways have been studied as potential drug targets against these parasites. Considering that trypanosomatids possess a unique redox pathway based on the trypanothione molecule absent in the mammalian host, the key enzymes involved in trypanothione metabolism, trypanothione reductase and trypanothione synthetase, have been studied in detail as druggable targets. In this review, we summarize some of the recent findings on the molecules inhibiting these two essential enzymes for Trypanosoma and Leishmania viability.

Experimental structure based drug design (SBDD) applications for anti-leishmanial drugs: A paradigm shift?

Leishmaniasis is a group of neglected tropical diseases caused by at least 20 species of Leishmania protozoa, which are spread by the bite of infected sandflies. There are three main forms of the disease: cutaneous leishmaniasis (CL, the most common), visceral leishmaniasis (VL, also known as kala-azar, the most serious), and mucocutaneous leishmaniasis. One billion people live in areas endemic to leishmaniasis, with an annual estimation of 30,000 new cases of VL and more than 1 million of CL. New treatments for leishmaniasis are an urgent need, as the existing ones are inefficient, toxic, and/or expensive. We have revised the experimental structure-based drug design (SBDD) efforts applied to the discovery of new drugs against leishmaniasis. We have grouped the explored targets according to the metabolic pathways they belong to, and the key achieved advances are highlighted and evaluated. In most cases, SBDD studies follow high-throughput screening campaigns and are secondary to pharmacokinetic optimization, due to the majoritarian belief that there are few validated targets for SBDD in leishmaniasis. However, some SBDD strategies have significantly contributed to new drug candidates against leishmaniasis and a bigger number holds promise for future development.

Low-molecular-weight thiol transferases in redox regulation and antioxidant defence

Low-molecular-weight (LMW) thiols are produced in all living cells in different forms and concentrations. Glutathione (GSH), coenzyme A (CoA), bacillithiol (BSH), mycothiol (MSH), ergothioneine (ET) and trypanothione T(SH)2 are the main LMW thiols in eukaryotes and prokaryotes. LMW thiols serve as electron donors for thiol-dependent enzymes in redox-mediated metabolic and signaling processes, protect cellular macromolecules from oxidative and xenobiotic stress, and participate in the reduction of oxidative modifications. The level and function of LMW thiols, their oxidized disulfides and mixed disulfide conjugates in cells and tissues is tightly controlled by dedicated oxidoreductases, such as peroxiredoxins, glutaredoxins, disulfide reductases and LMW thiol transferases. This review provides the first summary of the current knowledge of structural and functional diversity of transferases for LMW thiols, including GSH, BSH, MSH and T(SH)2. Their role in maintaining redox homeostasis in single-cell and multicellular organisms is discussed, focusing in particular on the conjugation of specific thiols to exogenous and endogenous electrophiles, or oxidized protein substrates. Advances in the development of new research tools, analytical methodologies, and genetic models for the analysis of known LMW thiol transferases will expand our knowledge and understanding of their function in cell growth and survival under oxidative stress, nutrient deprivation, and during the detoxification of xenobiotics and harmful metabolites. The antioxidant function of CoA has been recently discovered and the breakthrough in defining the identity and functional characteristics of CoA S-transferase(s) is soon expected.

Selenosugars targeting the infective stage of Trypanosoma brucei with high selectivity

Earlier evidences showed that diglycosyl diselenides are active against the infective stage of African trypanosomes (top hits IC50 0.5 and 1.5 μM) but poorly selective (selectivity index <10). Here we extended the study to 33 new seleno-glycoconjugates with the aim to improve potency and selectivity. Three selenoglycosides and three glycosyl selenenylsulfides displayed IC50 against bloodstream Trypanosoma brucei in the sub-μM range (IC50 0.35-0.77 μM) and four of them showed an improved selectivity (selectivity index >38-folds vs. murine and human macrohages). For the glycosyl selenylsulfides, the anti-trypanosomal activity was not significantly influenced by the nature of the moiety attached to the sulfur atom. Except for a quinoline-, and to a minor extent a nitro-derivative, the most selective hits induced a rapid (within 60 min) and marked perturbation of the LMWT-redox homeostasis. The formation of selenenylsulfide glycoconjugates with free thiols has been identified as a potential mechanism involved in this process.

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.

The Potential Use of Peptides in the Fight against Chagas Disease and Leishmaniasis

Chagas disease and leishmaniasis are both neglected tropical diseases that affect millions of people around the world. Leishmaniasis is currently the second most widespread vector-borne parasitic disease after malaria. The World Health Organization records approximately 0.7-1 million newly diagnosed leishmaniasis cases each year, resulting in approximately 20,000-30,000 deaths. Also, 25 million people worldwide are at risk of Chagas disease and an estimated 6 million people are infected with Trypanosoma cruzi. Pentavalent antimonials, amphotericin B, miltefosine, paromomycin, and pentamidine are currently used to treat leishmaniasis. Also, nifurtimox and benznidazole are two drugs currently used to treat Chagas disease. These drugs are associated with toxicity problems such as nephrotoxicity and cardiotoxicity, in addition to resistance problems. As a result, the discovery of novel therapeutic agents has emerged as a top priority and a promising alternative. Overall, there is a need for new and effective treatments for Chagas disease and leishmaniasis, as the current drugs have significant limitations. Peptide-based drugs are attractive due to their high selectiveness, effectiveness, low toxicity, and ease of production. This paper reviews the potential use of peptides in the treatment of Chagas disease and leishmaniasis. Several studies have demonstrated that peptides are effective against Chagas disease and leishmaniasis, suggesting their use in drug therapy for these diseases. Overall, peptides have the potential to be effective therapeutic agents against Chagas disease and leishmaniasis, but more research is needed to fully investigate their potential.

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.

Fexinidazole induced cytotoxicity is distinct from related anti-trypanosome nitroaromatic drugs

Nitroaromatic drugs are of critical importance for the treatment of trypanosome infections in Africa and the Americas. Fexinidazole recently joined benznidazole and nifurtimox in this family when it was approved as the first oral therapy against Human African trypanosomiasis (HAT). Nitroaromatic prodrugs are bioactivated by the trypanosome-specific type I nitroreductase (NTR) enzyme that renders the compounds trypanocidal. A caveat to the specificity of NTR activation is the potential for drug resistance and cross-resistance that can arise if NTR expression or functionality is altered through mutation. The outcomes of NTR bioactivation of nitroaromatic compounds is variable but can include the formation highly reactive open chain nitriles that can damage biomolecules including DNA. A proposed mechanism of action of nitroaromatic compounds is the formation of reactive oxygen species (ROS) resulting in the formation of trypanocidal levels of DNA damage. Fexinidazole made its way to clinical approval without a significant interrogation of its effects on trypanosome biology and a limited understanding of its mechanism of action. Early reports mentioned fexinidazole potentially affects DNA synthesis but without supporting data. In this study, we evaluated and compared the cytotoxic effects of nifurtimox, benznidazole, and fexinidazole on Trypanosoma brucei using in vitro analyses. Specifically, we sought to differentiate between the proposed effects of nitroaromatics on DNA damage and DNA synthesis. Toward this goal we generated a novel γH2A-based flow cytometry assay that reports DNA damage formation in conjunction with cell cycle progression. Here we report that fexinidazole's cytotoxic outcomes are distinct from the related drugs nifurtimox and benznidazole. Specifically, we show that fexinidazole treatment results in a pronounced defect in DNA synthesis that reduces the population of parasites in S phase. In contrast, treatment with nifurtimox and benznidazole appear accumulate DNA damage early in cell cycle and result in a defective G 2 population. The findings presented here bring us closer to understanding the anti-trypanosomatid mechanisms of action of nitroaromatic compounds, which will promote improved drug design and help combat potential drug resistance in the future. Our findings also highlight DNA synthesis inhibition as a powerful anti-parasitic drug target.

Biochemical characterization of GAF domain of free-R-methionine sulfoxide reductase from Trypanosoma cruzi

Trypanosoma cruzi is the causal agent of Chagas Disease and is a unicellular parasite that infects a wide variety of mammalian hosts. The parasite exhibits auxotrophy by L-Met; consequently, it must be acquired from the extracellular environment of the host, either mammalian or invertebrate. Methionine (Met) oxidation produces a racemic mixture (R and S forms) of methionine sulfoxide (MetSO). Reduction of L-MetSO (free or protein-bound) to L-Met is catalyzed by methionine sulfoxide reductases (MSRs). Bioinformatics analyses identified the coding sequence for a free-R-MSR (fRMSR) enzyme in the genome of T. cruzi Dm28c. Structurally, this enzyme is a modular protein with a putative N-terminal GAF domain linked to a C-terminal TIP41 motif. We performed detailed biochemical and kinetic characterization of the GAF domain of fRMSR in combination with mutant versions of specific cysteine residues, namely, Cys12, Cys98, Cys108, and Cys132. The isolated recombinant GAF domain and full-length fRMSR exhibited specific catalytic activity for the reduction of free L-Met(R)SO (non-protein bound), using tryparedoxins as reducing partners. We demonstrated that this process involves two Cys residues, Cys98 and Cys132. Cys132 is the essential catalytic residue on which a sulfenic acid intermediate is formed. Cys98 is the resolutive Cys, which forms a disulfide bond with Cys132 as a catalytic step. Overall, our results provide new insights into redox metabolism in T. cruzi, contributing to previous knowledge of L-Met metabolism in this parasite.

Organogold(III)-dithiocarbamate compounds and their coordination analogues as anti-tumor and anti-leishmanial metallodrugs

The limited chemical stability of gold(III)-based compounds in physiological environment has been a challenge in drug discovery, and organometallic chemistry might provide the solution to overcome this issue. In this work, four novel cationic organogold(III)-dithiocarbamate complexes of general structure [(C^N)AuIIIDTC]PF6 (C1a - C4a, DTC = dithiocarbamate, L1 - L4, C^N = 2-anilinopyridine) are presented, and compared to their coordination gold(III)-dithiocarbamate analogues [AuIIIDTCCl2] (C1b - C4b), as potential anti-cancer and anti-leishmanial drugs. Most of the complexes effectively inhibited cancer cell growth, notably C3a presented anti-proliferative effect in the nanomolar range against breast cancer (MCF-7 and MDA-MB-231 cells with moderate selectivity. Pro-apoptotic studies on treated MCF-7 cells showed a high population of cells in early apoptosis. Reactivity studies of C3a towards model thiols (N-acetyl-L-cysteine) refer to a possible mode of action involving bonding between the organogold(III)-core and the thiolate. In the scope of neglected diseases, gold complexes are emerging as promising therapeutic alternatives against leishmaniasis. In this regard, all gold(III)-dithiocarbamate complexes presented anti-leishmanial activity against at least one Leishmania species. Complexes C1a, C4a, C1b, C4b were active against all tested parasites with IC50 values varying between 0.12 and 42 μM, and, overall, organometallic compounds presented more intriguing inhibition profiles. For C4a selectivity over 500-fold for L. braziliensis; even higher than the reference anti-leishmanial drug amphotericin B. Overall, our findings revealed that the organogold(III) moiety significantly amplified the anti-cancer and anti-leishmanial effects with respect to the coordination analogues; thus, showing the great potential of organometallic chemistry in metallodrug-based chemotherapy for cancer and leishmaniasis.

Cysteine synthase: multiple structures of a key enzyme in cysteine synthesis and a potential drug target for Chagas disease and leishmaniasis

Chagas disease is a neglected tropical disease (NTD) caused by Trypanosoma cruzi, whilst leishmaniasis, which is caused by over 20 species of Leishmania, represents a group of NTDs endemic to most countries in the tropical and subtropical belt of the planet. These diseases remain a significant health problem both in endemic countries and globally. These parasites and other trypanosomatids, including T. theileri, a bovine pathogen, rely on cysteine biosynthesis for the production of trypanothione, which is essential for parasite survival in hosts. The de novo pathway of cysteine biosynthesis requires the conversion of O-acetyl-L-serine into L-cysteine, which is catalysed by cysteine synthase (CS). These enzymes present potential for drug development against T. cruzi, Leishmania spp. and T. theileri. To enable these possibilities, biochemical and crystallographic studies of CS from T. cruzi (TcCS), L. infantum (LiCS) and T. theileri (TthCS) were conducted. Crystal structures of the three enzymes were determined at resolutions of 1.80 Å for TcCS, 1.75 Å for LiCS and 2.75 Å for TthCS. These three homodimeric structures show the same overall fold and demonstrate that the active-site geometry is conserved, supporting a common reaction mechanism. Detailed structural analysis revealed reaction intermediates of the de novo pathway ranging from an apo structure of LiCS and holo structures of both TcCS and TthCS to the substrate-bound structure of TcCS. These structures will allow exploration of the active site for the design of novel inhibitors. Additionally, unexpected binding sites discovered at the dimer interface represent new potential for the development of protein-protein inhibitors.

Thiophene-Derived Schiff Base Complexes: Synthesis, Characterization, Antimicrobial Properties, and Molecular Docking

Novel thiophene-derived Schiff base ligand DE, where DE is (E)-N¹,N¹-diethyl-N²-(thiophen-2-ylmethylene)ethane-1,2-diamine, and the corresponding M(II) complexes, [M(DE)X₂] (M = Cu or Zn, X = Cl; M = Cd, X = Br), were prepared and structurally characterized. X-ray diffraction studies revealed that the geometry around the center of the M(II) complexes, [Zn(DE)Cl₂] and [Cd(DE)Br₂], could be best described as a distorted tetrahedral. In vitro antimicrobial screening of DE and its corresponding M(II) complexes, [M(DE)X₂], was performed. The complexes were more potent and showed higher activities against Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa, fungi Candida albicans, and protozoa Leishmania major compared to the ligand. Among the studied complexes, [Cd(DE)Br₂] exhibited the most promising antimicrobial activity against all the tested microbes compared to its analogs. These results were further supported by molecular docking studies. We believe that these complexes may significantly contribute to the efficient designing of metal-derived agents to treat microbial infections.

GR1 and NTRA involved in pollen tube growth in the stigma of Arabidopsis

MAIN CONCLUSION

Arabidopsis GR1 and NTRA function in pollen tube penetrating the stigma into the transmitting tract during pollination. During pollination, recognition between pollen (tube) and stigma mediates the hydration and germination of pollen, as well as the growth of the pollen tube on the stigma. Arabidopsis glutathione reductase 1 (GR1) and NADPH-dependent thioredoxin reductase A (NTRA) are involved in regulating cell redox hemostasis. Both GR1 and NTRA are expressed in pollen, but their roles in pollen germination and the growth of the pollen tube need further investigation. In this study, we performed pollination experiments and found that the Arabidopsis gr1/ + ntra/- and gr1/- ntra/ + double mutation compromised the transmission of male gametophytes. Pollen morphology and viability of the mutants did not show obvious abnormalities. Additionally, the pollen hydration and germination of the double mutants on solid pollen germination medium were comparable to those of the wild type. However, the pollen tubes with gr1 ntra double mutation were unable to penetrate the stigma and enter the transmitting tract when they grew on the surface of the stigma. Our results indicate that GR1 and NTRA play a role in regulating the interaction between the pollen tube and the stigma during pollination.

Structure of Leishmania donovani 6-Phosphogluconate Dehydrogenase and Inhibition by Phosphine Gold(I) Complexes: A Potential Approach to Leishmaniasis Treatment

As unicellular parasites are highly dependent on NADPH as a source for reducing equivalents, the main NADPH-producing enzymes glucose 6-phosphate dehydrogenase (G6PD) and 6-phosphogluconate dehydrogenase (6PGD) of the pentose phosphate pathway are considered promising antitrypanosomatid drug targets. Here we present the biochemical characterization and crystal structure of Leishmania donovani 6PGD (Ld6PGD) in complex with NADP(H). Most interestingly, a previously unknown conformation of NADPH is visible in this structure. In addition, we identified auranofin and other gold(I)-containing compounds as efficient Ld6PGD inhibitors, although it has so far been assumed that trypanothione reductase is the sole target of auranofin in Kinetoplastida. Interestingly, 6PGD from Plasmodium falciparum is also inhibited at lower micromolar concentrations, whereas human 6PGD is not. Mode-of-inhibition studies indicate that auranofin competes with 6PG for its binding site followed by a rapid irreversible inhibition. By analogy with other enzymes, this suggests that the gold moiety is responsible for the observed inhibition. Taken together, we identified gold(I)-containing compounds as an interesting class of inhibitors against 6PGDs from Leishmania and possibly from other protozoan parasites. Together with the three-dimensional crystal structure, this provides a valid basis for further drug discovery approaches.

An anti-leishmanial compound 4',7-dihydroxyflavone elicits ROS-mediated apoptosis-like death in Leishmania parasite

The treatment for leishmaniasis is currently plagued by side effects such as toxicity and the emergence of drug resistance to the available repertoire of drugs, as well as the expense of these drugs. Considering such rising concerns, we report the anti-leishmanial activity and mechanism of a flavone compound 4',7-dihydroxyflavone (TI 4). Four flavanoids were initially screened for anti-leishmanial activity and cytotoxicity. The results showed that the compound TI 4 exhibited higher activity and selectivity index at the same time as maintaining low cytotoxicity. Preliminary microscopic studies and fluorescence-activated cell sorting analysis reported that the parasite underwent apoptosis on TI 4 treatment. Further in-depth studies revealed high reactive oxygen species (ROS) production and thiol levels in the parasites, suggesting ROS-mediated apoptosis in the parasites upon TI 4 treatment. Other apoptotic indicators such as intracellular Ca²⁺ and mitochondrial membrane potential also indicated the onset of apoptosis in the treated parasites. The mRNA expression levels signified that the redox metabolism genes were upregulated by two-fold along with the apoptotic genes. In summary, the use of TI 4 on Leishmania parasites induces ROS-mediated apoptosis; therefore, the compound has immense potential to be an anti-leishmanial drug. However, in vivo studies would be required to ascertain its safety and efficacy before we can exploit the compound against the growing leishmaniasis crisis.

Crystal structure of Leishmania donovani glucose 6-phosphate dehydrogenase reveals a unique N-terminal domain

Since unicellular parasites highly depend on NADPH as a source for reducing equivalents, the pentose phosphate pathway, especially the first and rate-limiting NADPH-producing enzyme glucose 6-phosphate dehydrogenase (G6PD), is considered an excellent antitrypanosomatid drug target. Here we present the crystal structure of Leishmania donovani G6PD (LdG6PD) elucidating the unique N-terminal domain of Kinetoplastida G6PDs. Our investigations on the function of the N-domain suggest its involvement in the formation of a tetramer that is completely different from related Trypanosoma G6PDs. Structural and functional investigations further provide interesting insights into the binding mode of LdG6PD, following an ordered mechanism, which is confirmed by a G6P-induced domain shift and rotation of the helical N-domain. Taken together, these insights into LdG6PD contribute to the understanding of G6PDs' molecular mechanisms and provide an excellent basis for further drug discovery approaches.

Glyoxalase 2: Towards a Broader View of the Second Player of the Glyoxalase System

Glyoxalase 2 is a mitochondrial and cytoplasmic protein belonging to the metallo-β-lactamase family encoded by the hydroxyacylglutathione hydrolase (HAGH) gene. This enzyme is the second enzyme of the glyoxalase system that is responsible for detoxification of the α-ketothaldehyde methylglyoxal in cells. The two enzymes glyoxalase 1 (Glo1) and glyoxalase 2 (Glo2) form the complete glyoxalase pathway, which utilizes glutathione as cofactor in eukaryotic cells. The importance of Glo2 is highlighted by its ubiquitous distribution in prokaryotic and eukaryotic organisms. Its function in the system has been well defined, but in recent years, additional roles are emerging, especially those related to oxidative stress. This review focuses on Glo2 by considering its genetics, molecular and structural properties, its involvement in post-translational modifications and its interaction with specific metabolic pathways. The purpose of this review is to focus attention on an enzyme that, from the most recent studies, appears to play a role in multiple regulatory pathways that may be important in certain diseases such as cancer or oxidative stress-related diseases.

MC, Concepción JL, Cáceres AJ. Consumption of Galactose by Trypanosoma cruzi Epimastigotes Generates Resistance against Oxidative Stress

In this study, we demonstrate that Trypanosoma cruzi epimastigotes previously grown in LIT medium supplemented with 20 mM galactose and exposed to sub-lethal concentrations of hydrogen peroxide (100 μM) showed two-fold and five-fold viability when compared to epimastigotes grown in LIT medium supplemented with two different glucose concentrations (20 mM and 1.5 mM), respectively. Similar results were obtained when exposing epimastigotes from all treatments to methylene blue 30 μM. Additionally, through differential centrifugation and the selective permeabilization of cellular membranes with digitonin, we found that phosphoglucomutase activity (a key enzyme in galactose metabolism) occurs predominantly within the cytosolic compartment. Furthermore, after partially permeabilizing epimastigotes with digitonin (0.025 mg × mg-1 of protein), intact glycosomes treated with 20 mM galactose released a higher hexose phosphate concentration to the cytosol in the form of glucose-1-phosphate, when compared to intact glycosomes treated with 20 mM glucose, which predominantly released glucose-6-phosphate. These results shine a light on T. cruzi's galactose metabolism and its interplay with mechanisms that enable resistance to oxidative stress.

The ChaC family of γ-glutamyl cyclotransferases is required for Leishmania to switch to a slow growth state and for long-term survival of the parasite

The ChaC family of γ-glutamyl cyclotransferases is conserved throughout all Kingdoms and catalyzes the degradation of GSH. So far, the ChaC family proteins in trypanosomal parasites are missing in the literature. Here, we report two members of the ChaC family of γ-glutamyl cyclotransferases (LmChaC_2a and LmChaC_2b) in the unicellular pathogen Leishmania. Activity measurements suggest that these proteins catalyze degradation of GSH but no other γ-glutamyl peptides. Recombinant LmChaC_2a protein shows ∼17-fold lower catalytic efficiency (k_cat ∼ 0.9 s⁻¹) than LmChaC_2b (k_cat ∼ 15 s⁻¹), although they showed comparable K_m values (∼1.75 mM for LmChaC_2a and ∼2.0 mM for LmChaC_2b) toward GSH. qRT-PCR and Western blot analyses suggest that the LmChaC_2a protein was found to be constitutively expressed, whereas LmChaC_2b was regulated by sulfur stress. To investigate its precise physiological function in Leishmania, we generated overexpressed, knockout, and complement cell lines. Flow cytometric analyses show the presence of a higher intracellular GSH concentration and lower intracellular ROS level, indicative of a more reductive environment in null mutants. We found LmChaC2-expressing cells grow in GSH-containing sulfur-limited media, while the null mutants failed to grow, suggesting that LmChaC2 is crucial for cell growth with GSH as the only sulfur source. Null mutants, although reach the stationary phase rapidly, display impaired long-term survival, indicating that LmChaC2-mediated GSH degradation is necessary for prolonged survival. In vivo studies suggest that LmChaC2-dependent controlled GSH degradation promotes chronic infection by the parasite. Altogether, these data indicate that LmChaC2 plays an important role in GSH homeostasis in Leishmania.

Knockout of Tyrosine Aminotransferase Gene by Homologous Recombination Arrests Growth and Disrupts Redox Homeostasis in Leishmania Parasite

Tyrosine aminotransferase is a well-characterized enzyme in the Leishmania parasite, but the role of TAT in the parasite functioning remains largely unknown. In this study, we attempt to gain a better understanding of the enzyme's role in the parasite by gene knockout and overexpression of the TAT gene. The overexpression of TAT protein was well tolerated by the parasites in two independent repeats. Single knockout of TAT gene by homologous recombination, LdTAT^+/- displayed distinct retardation in the proliferation rates and entered the death phase immediately. Morphology of LdTAT^+/- parasites had important structural defects as they rounded up with elongated flagella. Gene regulation studies suggested the upregulation of key apoptotic and redox metabolism genes in LdTAT^+/-. Moreover, LdTAT^+/- cells accumulated higher ROS, thiols, intracellular Ca²⁺ concentrations, and mitochondrial membrane depolarization signifying the onset of apoptosis. Tocopherol levels were reduced by 50% in LdTAT^+/- suggesting the involvement of TAT in tocopherol biosynthesis in the parasite. Overall, our results provide the first evidence that gene knockout of TAT results in apoptosis and that TAT is required for the survival and viability of Leishmania donovani.

- Amphotericin B: A drug of choice for Visceral Leishmaniasis

Visceral leishmaniasis or Kala-azar is a vector-borne disease caused by an intracellular parasite of the genus leishmania. In India, Amphotericin B (AmB) is a first-line medication for treating leishmaniasis. After a large-scale resistance to pentavalent antimony therapy developed in Bihar state, it was rediscovered as an effective treatment for Leishmania donovani infection. AmB which binds to the ergosterol of protozoan cells causes a change in membrane integrity resulting in ions leakage, and ultimately leading to cell death. The treatment effect of liposomal AmB can be seen more quickly than deoxycholate AmB because, it has some toxic effects, but liposomal AmB is significantly less toxic. Evidence from studies suggested that ABLC (Abelcet) and ABCD (Amphotec) are as effective as L-AmB but Liposomal form (Ambisome) is a more widely accepted treatment option than conventional ones. Nevertheless, the world needs some way more efficient antileishmanial drugs that are less toxic and less expensive for people living with parasitic infections caused by Leishmania. So, academics, researchers, and sponsors need to focus on finding such drugs. This review provides a summary of the chemical, pharmacokinetic, drug-target interactions, stability, dose efficacy, and many other characteristics of the AmB and their various formulations. We have also highlighted the clinically significant aspects of PKDL and VL co-infection with HIV/TB.

Gene expression study to elucidate the anti-trypanosomal activity of quinapyramine methyl sulphate (QPS)

The kinetoplastid protozoan parasite, Trypanosoma evansi causes a fatal disease condition known as Surra in equines throughout the globe. Disease condition being acute in nature, entrust a huge economic and health impact on the equine industry. Till date, quinapyramine methyl sulphate (QPS) is the first line of treatment and a panacea for the T. evansi infection in equines. Still after the >70 years of its discovery, there is no clue about the mode of action of QPS in T. evansi. The establishment of in vitro cultivation of T. evansi in HMI-9 media has provided opportunity to study the alteration in mRNA expression of parasite on exposure to the drug. With this research gap, the present study aimed to investigate the relative mRNA expression of 13 important drug target genes to elucidate the anti-trypanosomal activity of QPS against T. evansi. The IC₅₀ of QPS against a pony isolate of T. evansi was determined as 276.4 nM(147.21 ng/ mL) in the growth inhibitory assay. The in vitro cultured T. evansi population were further exposed to IC₅₀ of QPS and their relative mRNA expression was studied at 12 h, 24 h and 48 h interval.The mRNA expression of several genes such as hexokinase, trypanothione reductase, aurora kinase, oligopeptidase B and ribonucleotide reductase II were found refractory (non-significant, p > 0.1234) to the exposure of QPS. Significant up-regulation of trans-sialidase (p < 0.0001), ESAG8 (p < 0.0021), ribonucleotide reductase I (p < 0.0001), ornithine decarboxylase (p < 0.0001), topoisomerase II (p < 0.0021) and casein kinase I (p < 0.0021) were recorded after exposure with QPS. The arginine kinase 1 and calcium ATPase I showed highly significant (p < 0.0001) down-regulation in the drug kinetics. Therefore, the arginine kinase 1 and calcium ATPase I can be explored further to elucidate the trypanocidal activity of QPS. The preliminary data generated provide the potential of arginine kinase 1 and calcium ATPase I mRNA mediated pathway of trypanocidal action of QPS. Further, transcriptomics approach is required to investigate the possible mechanism of action of drugs at molecular level against the targeted organism.

Unique thiol metabolism in trypanosomatids: Redox homeostasis and drug resistance

Trypanosomatids are mainly responsible for heterogeneous parasitic diseases: Leishmaniasis, Sleeping sickness, and Chagas disease and control of these diseases implicates serious challenges due to the emergence of drug resistance. Redox-active biomolecules are the endogenous substances in organisms, which play important role in the regulation of redox homeostasis. The redox-active substances like glutathione, trypanothione, cysteine, cysteine persulfides, etc., and other inorganic intermediates (hydrogen peroxide, nitric oxide) are very useful as defence mechanism. In the present review, the suitability of trypanothione and other essential thiol molecules of trypanosomatids as drug targets are described in Leishmania and Trypanosoma. We have explored the role of tryparedoxin, tryparedoxin peroxidase, ascorbate peroxidase, superoxide dismutase, and glutaredoxins in the anti-oxidant mechanism and drug resistance. Up-regulation of some proteins in trypanothione metabolism helps the parasites in survival against drug pressure (sodium stibogluconate, Amphotericin B, etc.) and oxidative stress. These molecules accept electrons from the reduced trypanothione and donate their electrons to other proteins, and these proteins reduce toxic molecules, neutralize reactive oxygen, or nitrogen species; and help parasites to cope with oxidative stress. Thus, a better understanding of the role of these molecules in drug resistance and redox homeostasis will help to target metabolic pathway proteins to combat Leishmaniasis and trypanosomiases.

Lasers for cutaneous lesions: An update

There are several types of medical settings which use lasers. Dermatologists use lasers as it is non-invasive with preferential cosmetic outcomes and finer wound healing. The types of lasers are relying on their wavelengths and delivery systems. Over time, by using several distinct devices and strategies, new lasers have been generated; as a consequence, they are manipulated in a wide range of dermatological settings. In this review, laser applications in various vascular, infectious, and hyperpigmented cutaneous lesions were framed. We aimed to represent the fitness of phototherapy for each condition as well as the overall challenges that face laser. In addition, low-level laser therapy, and laser resurfacing were noted as the marketable line of lasers in the current time for cosmetic purposes.

Mitochondrial Ca2+ and Reactive Oxygen Species in Trypanosomatids

Significance: Millions of people are infected with trypanosomatids and new therapeutic approaches are needed. Trypanosomatids possess one mitochondrion per cell and its study has led to discoveries of general biological interest. These mitochondria, as in their animal counterparts, generate reactive oxygen species (ROS) and have evolved enzymatic and nonenzymatic defenses against them. Mitochondrial calcium ion (Ca2+) overload leads to generation of ROS and its study could lead to relevant information on the biology of trypanosomatids and to novel drug targets. Recent Advances: Mitochondrial Ca2+ is normally involved in maintaining the bioenergetics of trypanosomes, but when Ca2+ overload occurs, it is associated with cell death. Trypanosomes lack key players in the mechanism of cell death described in mammalian cells, although mitochondrial Ca2+ overload results in collapse of their membrane potential, production of ROS, and cytochrome c release. They are also very resistant to mitochondrial permeability transition, and cell death after mitochondrial Ca2+ overload depends on generation of ROS. Critical Issues: In this review, we consider the mechanisms of mitochondrial oxidant generation and removal and the involvement of Ca2+ in trypanosome cell death. Future Directions: More studies are required to determine the reactions involved in generation of ROS by the mitochondria of trypanosomatids, their enzymatic and nonenzymatic defenses against ROS, and the occurrence and composition of a mitochondrial permeability transition pore. Antioxid. Redox Signal. 36, 969-983.

Natural compounds based chemotherapeutic against Chagas disease and leishmaniasis: mitochondrion as a strategic target

Over the past years, natural products have been explored in order to find biological active substances to treat various diseases. Regarding their potential action against parasites such as trypanosomatids, specially Trypanosoma cruzi and Leishmania spp., much advance has been achieved. Extracts and purified molecules of several species from genera Piper, Tanacetum, Porophyllum, and Copaifera have been widely investigated by our research group and exhibited interesting antitrypanosomal and antileishmanial activities. These natural compounds affected different structures in parasites, and we believe that the mitochondrion is a strategic target to induce parasite death. Considering that these trypanosomatids have a unique mitochondrion, this cellular target has been extensively studied aiming to find more selective drugs, since the current treatment of these neglected tropical diseases has some challenges such as high toxicity and prolonged treatment time. Here, we summarise some results obtained with natural products from our research group and we further highlighted some strategies that must be considered to finally develop an effective chemotherapeutic agent against these parasites.

Mitochondrial adaptations throughout the Trypanosoma brucei life cycle

The unicellular parasite Trypanosoma brucei has a digenetic life cycle that alternates between a mammalian host and an insect vector. During programmed development, this extracellular parasite encounters strikingly different environments that determine its energy metabolism. Functioning as a bioenergetic, biosynthetic, and signaling center, the single mitochondrion of T. brucei is drastically remodeled to support the dynamic cellular demands of the parasite. This manuscript will provide an up-to-date overview of how the distinct T. brucei developmental stages differ in their mitochondrial metabolic and bioenergetic pathways, with a focus on the electron transport chain, proline oxidation, TCA cycle, acetate production, and ATP generation. Although mitochondrial metabolic rewiring has always been simply viewed as a consequence of the differentiation process, the possibility that certain mitochondrial activities reinforce parasite differentiation will be explored.

Antioxidant defence system as a rational target for Chagas disease and Leishmaniasis chemotherapy

Chagas disease and leishmaniasis are neglected tropical diseases caused by the protozoan parasites Trypanosoma cruzi and Leishmania spp., respectively. They are among the most important parasitic diseases, affecting millions of people worldwide, being a considerable global challenge. However, there is no human vaccine available against T. cruzi and Leishmania infections, and their control is based mainly on chemotherapy. Treatments for Chagas disease and leishmaniasis have multiple limitations, mainly due to the high toxicity of the available drugs, long-term treatment protocols, and the occurrence of drug-resistant parasite strains. In the case of Chagas disease, there is still the problem of low cure rates in the chronic stage of the disease. Therefore, new therapeutic agents and novel targets for drug development are urgently needed. Antioxidant defence in Trypanosomatidae is a potential target for chemotherapy because the organisms present a unique mechanism for trypanothione-dependent detoxification of peroxides, which differs from that found in vertebrates. Cellular thiol redox homeostasis is maintained by the biosynthesis and reduction of trypanothione, involving different enzymes that act in concert. This study provides an overview of the antioxidant defence focusing on iron superoxide dismutase A, tryparedoxin peroxidase, and ascorbate peroxidase and how the enzymes play an important role in the defence against oxidative stress and their involvement in drug resistance mechanisms in T. cruzi and Leishmania spp.

Treatment of Cutaneous Leishmaniasis and Insights into Species-Specific Responses: A Narrative Review

Cutaneous leishmaniasis (CL) is a complex skin infection that has imposed a heavy burden on many developing countries and is caused by more than 20 Leishmania species. This disease is predominantly associated with disfiguring scars and major social stigma upon infection. The severity of the disease seemingly depends on many factors including the species of parasite, the host, region of endemicity, socio-economic status and the accessibility to health facilities. Despite myriad studies that have been performed on current and novel therapies, the treatment outcomes of CL remain contentious, possibly because of the knowledge gaps that still exist. The differential responses to the current CL therapies have become a major drawback in disease control, and the dearth of information on critical analyses of outcomes of such studies is a hindrance to the overall understanding. On the basis of currently available literature on treatment outcomes, we discuss the most effective doses, drug susceptibilities/resistance and treatment failures of the Leishmania genus for both monotherapy and combination therapy. This review focuses on the available treatment modalities for CL caused by different Leishmania species, with insights into their species-specific efficacies, which would inform the selection of appropriate drugs for the treatment and control of leishmaniasis.

Salivary and Intestinal Transcriptomes Reveal Differential Gene Expression in Starving, Fed and Trypanosoma cruzi-Infected Rhodnius neglectus

Rhodnius neglectus is a potential vector of Trypanosoma cruzi (Tc), the causative agent of Chagas disease. The salivary glands (SGs) and intestine (INT) are actively required during blood feeding. The saliva from SGs is injected into the vertebrate host, modulating immune responses and favoring feeding for INT digestion. Tc infection significantly alters the physiology of these tissues; however, studies that assess this are still scarce. This study aimed to gain a better understanding of the global transcriptional expression of genes in SGs and INT during fasting (FA), fed (FE), and fed in the presence of Tc (FE + Tc) conditions. In FA, the expression of transcripts related to homeostasis maintenance proteins during periods of stress was predominant. Therefore, the transcript levels of Tret1-like and Hsp70Ba proteins were increased. Blood appeared to be responsible for alterations found in the FE group, as most of the expressed transcripts, such as proteases and cathepsin D, were related to digestion. In FE + Tc group, there was a decreased expression of blood processing genes for insect metabolism (e.g., Antigen-5 precursor, Pr13a, and Obp), detoxification (Sult1) in INT and acid phosphatases in SG. We also found decreased transcriptional expression of lipocalins and nitrophorins in SG and two new proteins, pacifastin and diptericin, in INT. Several transcripts of unknown proteins with investigative potential were found in both tissues. Our results also show that the presence of Tc can change the expression in both tissues for a long or short period of time. While SG homeostasis seems to be re-established on day 9, changes in INT are still evident. The findings of this study may be used for future research on parasite-vector interactions and contribute to the understanding of food physiology and post-meal/infection in triatomines.

Intrinsically Disordered Region Modulates Ligand Binding in Glutaredoxin 1 from Trypanosoma Brucei

Glutaredoxins are small proteins that share a common well-conserved thioredoxin-fold and participate in a wide variety of biological processes. Among them, class II Grx are redox-inactive proteins involved in iron-sulfur (Fe-S) metabolism. In the present work, we report different structural and dynamics aspects of 1CGrx1 from the pathogenic parasite Trypanosoma brucei that differentiate it from other orthologues by the presence of a parasite-specific unstructured N-terminal extension whose role has not been fully elucidated yet. Previous nuclear magnetic resonance (NMR) studies revealed significant differences with respect to the mutant lacking the disordered tail. Herein, we have performed atomistic molecular dynamics simulations that, complementary to NMR studies, confirm the intrinsically disordered nature of the N-terminal extension. Moreover, we confirm the main role of these residues in modulating the conformational dynamics of the glutathione-binding pocket. We observe that the N-terminal extension modifies the ligand cavity stiffening it by specific interactions that ultimately modulate its intrinsic flexibility, which may modify its role in the storage and/or transfer of preformed iron-sulfur clusters. These unique structural and dynamics aspects of Trypanosoma brucei 1CGrx1 differentiate it from other orthologues and could have functional relevance. In this way, our results encourage the study of other similar protein folding families with intrinsically disordered regions whose functional roles are still unrevealed and the screening of potential 1CGrx1 inhibitors as antitrypanosomal drug candidates.

Potential molecular targets of Leishmania pathways in developing novel antileishmanials

The illness known as leishmaniasis has not become a household name like malaria, although it stands as the second-largest parasitic disease, surpassed only by malaria. As no licensed vaccine is available, treatment for leishmaniasis mostly relies on chemotherapy. Inefficiency and drug resistance are the major impediments in current therapeutics. In this scenario, identification of novel molecular drug candidates is indispensable to develop robust antileishmanials. The exploration of structure-based drugs to target enzymes/molecules of Leishmania which differ structurally/functionally from their equivalents in mammalian hosts not only helps in developing a new class of antileishmanials, but also paves the way to understand Leishmania biology. This review provides a comprehensive overview on possible drug candidates relating to various Leishmania molecular pathways.

Molecular characterization and immune protection by cystathionine β-synthase from Eimeria tenella

Eimeria tenella is an obligate intracellular apicomplexan parasite that causes avian coccidiosis and leads to severe economic losses in the global poultry industry. Cystathionine β-synthase (CBS) and cystathionine γ-lyase (CGL) act together to generate H2S in the reverse transsulfuration pathway. In this study, E. tenella Cystathionine β-synthase (EtCBS) was cloned using rapid amplification of cDNA 5'-ends (5'RACE) and characterized, and its immunoprotective effects were evaluated. The recombinant EtCBS protein (rEtCBS) was expressed and successfully recognized by anti-sporozoites (Spz) protein rabbit serum. EtCBS mRNA levels were highest in Spz by qPCR, and the protein expression levels were higher in unsporulated oocysts (UO) than in other stages by Western blot. Indirect immunofluorescence showed that EtCBS protein was found on the surface of Spz and second-generation merozoites (Mrz). The invasion inhibition assays showed that rabbit anti-rEtCBS polyclonal antibodies effectively inhibited parasite invasion host cells. Chickens immunized with rEtCBS protein showed prominently increased weight gains and decreased oocyst output compared to nonimmunized and infected control group. The results suggest that EtCBS could be a potential vaccine candidate against E. tenella.

Critical Insight into Plausible Acquired Tocopherol Pathway in Neglected Human Trypanosomatids

Despite global therapeutic advancements, tropical parasitic infections like trypanosomiasis and leishmaniasis continue to be a major health concern in developing countries. These two tropical infectious diseases lead to enormous economic loss, significant disability, and morbidity, accounting for over one million deaths per year worldwide. The causative parasites, which shuttle between an insect vector and a mammalian host, thrive either in the bloodstream or in the intramacrophage environments. Essentially, the parasites live in an environment of oxidative stress and therefore require metabolic pathways to counterbalance the host immune response and survive the adverse conditions. Apart from the trypanothione pathway elucidated in the parasites, there exists a tocopherol pathway that functions to scavenge the reactive chemical species. This pathway, unique to photosynthetic organisms, is essential for the parasite's survival, though the enzymes involved remain largely uncharacterized. Consequently, an understanding of the origin of the pathway and where and how the interconnected tocopherol pathway functions may result in the identification of promising and potential therapeutic interventions to combat these deadly diseases. Recent works underline the presence of the tocopherol pathway in trypanosomatids and hypothesize that trypanosomatids may be tocopherol prototrophs. This review focuses on the biosynthesis of tocopherols in Trypanosoma and Leishmania in light of the current evidence.

New insights into the mechanism of action of the cyclopalladated complex - CP2 in Leishmania: Calcium Dysregulation, Mitochondrial Dysfunction and Cell Death

The current treatment of leishmaniasis is based on few drugs that present several drawbacks such as high toxicity, difficult administration route, and low efficacy. These disadvantages raise the necessity to develop novel antileishmanial compounds allied to a comprehensive understanding of their mechanisms of action. Here, we elucidate the probably mechanism of action of the antileishmanial binuclear cyclopalladated complex [Pd(dmba)(μ-N₃)]₂ (CP2) in Leishmania amazonensis. CP2 causes oxidative stress in the parasite resulting in disruption of mitochondrial Ca²⁺ homeostasis, cell cycle arrest at S-phase, increasing the ROS production and overexpression of stress-related and cell detoxification proteins, collapsing the Leishmania mitochondrial membrane potential and promotes apoptotic-like features in promastigotes leading to necrosis or directs programmed cell death (PCD)-committed cells toward necrotic-like destruction. Moreover, CP2 is able to reduce the parasite load in both liver and spleen in Leishmania infantum-infected hamsters when treated for 15 days with 1.5 mg/Kg/day CP2, expanding its potential application in addition to the already known effectiveness on cutaneous leishmaniasis for the treatment of visceral leishmaniasis, showing the broad spectrum of action of this cyclopalladated complex. The data herein presented bring new insights into the CP2 molecular mechanisms of action, assisting to promote its rational modification to improve both safety and efficacy.

A "Golden Age" for the discovery of new antileishmanial agents: Current status of leishmanicidal gold complexes and prospective targets beyond the trypanothione system

Leishmaniasis is one of the most neglected diseases worldwide and is considered a serious public health issue. The current therapeutic options have several disadvantages that make the search for new therapeutics urgent. Gold compounds are emerging as promising candidates based on encouraging in vitro and limited in vivo results for several Au^I and Au^III complexes. The antiparasitic mechanisms of these molecules remain only partially understood. However, a few studies have proposed the trypanothione redox system as a target, similar to the mammalian thioredoxin system, pointed out as the main target for several gold compounds with significant antitumor activity. In this review, we present the current status of the investigation and design of gold compounds directed at treating leishmaniasis. In addition, we explore potential targets in Leishmania parasites beyond the trypanothione system, taking into account previous studies and structure modulation performed for gold-based compounds.

Eugenia uniflora and Syzygium samarangense extracts exhibit anti-trypanosomal activity: Evidence from in-silico molecular modelling, in vitro, and in vivo studies

The parasite Trypanosoma brucei is the main cause of the sleeping sickness threatening millions of populations in many African countries. The parasitic infection is currently managed by some synthetic medications, most of them suffer limited activity spectrum and/or serious adverse effects. Some studies have pointed out the promising therapeutic potential of the plant extracts rich in polyphenols to curb down parasitic infections caused by T. brucei and other trypanosomes. In this work, the main components dominating Eugenia uniflora and Syzygium samarangense plant extracts were virtually screened, through docking, as inhibitors of seven T. brucei enzymes validated as potential drug targets. The in vitro and in vivo anti-T. brucei activities of the extracts in two treatment doses were evaluated. Moreover, the extract effects on the packed cell volume level, liver, and kidney functions were assessed. Five compounds showed strong docking and minimal binding energy to five target enzymes simultaneously and three other compounds were able to bind strongly to at least four of the target enzymes. These compounds represent lead hits to develop novel trypanocidal agents of natural origin. Both extracts showed moderate in vitro anti-trypanosomal activity. Infected animal groups treated over 5 days with the studied extracts showed an appreciable in vivo anti-trypanosomal activity and ameliorated in a dose dependent manner the anaemia, liver, and kidney damages induced by the infection. In conclusion, Eugenia uniflora and Syzygium samarangense could serve as appealing sources to treat trypanosomes infections.

A computer-aided approach to identify novel Leishmania major protein disulfide isomerase inhibitors for treatment of leishmaniasis

Leishmaniasis is an infectious disease caused by parasites of the genus Leishmania and transmitted by the bite of a sand fly. To date, most available drugs for treatment are toxic and beyond the economic means of those affected by the disease. Protein disulfide isomerase (PDI) is a chaperone protein that plays a major role in the folding of newly synthesized proteins, specifically assisting in disulfide bond formation, breakage, or rearrangement in all non-native proteins. In previous work, we demonstrated that Leishmania major PDI (LmPDI) has an essential role in pathogen virulence. Furthermore, inhibition of LmPDI further blocked parasite infection in macrophages. In this study, we utilized a computer-aided approach to design a series of LmPDI inhibitors. Fragment-based virtual screening allowed for the understanding of the inhibitors' modes of action on LmPDI active sites. The generated compounds obtained after multiple rounds of virtual screening were synthesized and significantly inhibited target LmPDI reductase activity and were shown to decrease in vitro parasite growth in human monocyte-derived macrophages. This novel cheminformatics and synthetic approach led to the identification of a new series of compounds that might be optimized into novel drugs, likely more specific and less toxic for the treatment of leishmaniasis.

Resveratrol impacts in oxidative stress in liver during Trypanosoma cruzi infection

Trypanosoma cruzi is the causative agent of Chagas disease, infecting the heart, intestines and liver tissues. There is growing evidence that oxidative stress, defined as a persistent imbalance between highly oxidative compounds and antioxidant defenses, is a marker of tissue inflammation; it is related to immune responses such as damage, as well as to strand breaks in DNA contributing to disease progression. Antioxidant agents help mitigate the damage caused by inflammation, preventing or slowing damage to cells caused by free radicals. In this sense, resveratrol (RSV) is an important polyphenol that demonstrates antioxidant effects. It reverses damage caused by several infectious diseases. The aim of the present study was to determine whether treatment with RSV would prevent or minimize oxidative damage caused by T. cruzi. The animals were divided into four groups (n = 5): A) control; B) control + RSV; C) infected and D) infected + RSV. The infected groups received 1 x 10⁴ Y strain trypomastigotes via intraperitoneal injection; after confirmation of infection, the mice received RSV 100 mg/kg for seven days orally. On the 8th day post-infection, we collected liver tissue for analysis of oxidant/antioxidant status: superoxide dismutase (SOD), catalase (CAT), and glutathione s-transferase (GST) activities, as well as reactive oxygen species (ROS), non-protein thiols (NPSH), thiols, carbonyl protein, thiobarbituric acid reactive substance (TBARS), and finally, the nitrite/nitrate ratio (NOx) levels were determined. The administration of RSV did not exert direct effect on parasitemia. The infection produced high levels of TBARS, NOx, and ROS levels in liver tissue, suggesting cellular injury with production of free radicals in animals infected by T. cruzi. RSV positively modulated SOD and aumenting GST activities enzymes in infected animals. Protein thiols levels in infected animals were lower than those of control. Taken together, the data suggest T. cruzi causes hepatic oxidative stress, and RSV 100 mg/kg for seven days it's dosen't seem minimized these negative effects in the acute phase of disease.

Effects of trypanocidal drugs on DNA synthesis: new insights into melarsoprol growth inhibition

Trypanothione is the primary thiol redox carrier in Trypanosomatids whose biosynthesis and utilization pathways contain unique enzymes that include suitable drug targets against the human parasites in this family. Overexpression of the rate-limiting enzyme, γ-glutamylcysteine synthetase (GSH1), can increase the intracellular concentration of trypanothione. Melarsoprol directly inhibits trypanothione and has predicted the effects on downstream redox biology, including ROS management and dNTP synthesis that require further investigation. Thus, we hypothesized that melarsoprol treatment would inhibit DNA synthesis, which was tested using BrdU incorporation assays and cell cycle analyses. In addition, we analysed the effects of eflornithine, which interfaces with the trypanothione pathway, fexinidazole, because of the predicted effects on DNA synthesis, and pentamidine as an experimental control. We found that melarsoprol treatment resulted in a cell cycle stall and a complete inhibition of DNA synthesis within 24 h, which were alleviated by GSH1 overexpression. In contrast, the other drugs analysed had more subtle effects on DNA synthesis that were not significantly altered by GSH1 expression. Together these findings implicate DNA synthesis as a therapeutic target that warrants further investigation in the development of antitrypanosomal drugs.

Bioenergetic consequences of FoF1-ATP synthase/ATPase deficiency in two life cycle stages of Trypanosoma brucei

Mitochondrial ATP synthase is a reversible nanomotor synthesizing or hydrolyzing ATP depending on the potential across the membrane in which it is embedded. In the unicellular parasite Trypanosoma brucei, the direction of the complex depends on the life cycle stage of this digenetic parasite: in the midgut of the tsetse fly vector (procyclic form), the F_oF₁–ATP synthase generates ATP by oxidative phosphorylation, whereas in the mammalian bloodstream form, this complex hydrolyzes ATP and maintains mitochondrial membrane potential (ΔΨm). The trypanosome F_oF₁–ATP synthase contains numerous lineage-specific subunits whose roles remain unknown. Here, we seek to elucidate the function of the lineage-specific protein Tb1, the largest membrane-bound subunit. In procyclic form cells, Tb1 silencing resulted in a decrease of F_oF₁–ATP synthase monomers and dimers, rerouting of mitochondrial electron transfer to the alternative oxidase, reduced growth rate and cellular ATP levels, and elevated ΔΨm and total cellular reactive oxygen species levels. In bloodstream form parasites, RNAi silencing of Tb1 by ∼90% resulted in decreased F_oF₁–ATPase monomers and dimers, but it had no apparent effect on growth. The same findings were obtained by silencing of the oligomycin sensitivity-conferring protein, a conserved subunit in T. brucei F_oF₁–ATP synthase. However, as expected, nearly complete Tb1 or oligomycin sensitivity-conferring protein suppression was lethal because of the inability to sustain ΔΨm. The diminishment of F_oF₁–ATPase complexes was further accompanied by a decreased ADP/ATP ratio and reduced oxygen consumption via the alternative oxidase. Our data illuminate the often diametrically opposed bioenergetic consequences of F_oF₁–ATP synthase loss in insect versus mammalian forms of the parasite.

In vitro antileishmanial potentialities of essential oils from Citrus limon and Pistacia lentiscus harvested in Tunisia

Leishmaniasis is a tropical parasitic disease that affects up to 12 million people worldwide. Current chemotherapies have limitations such as toxicity, high cost, and parasite resistance. This work aims to select an essential oil (EssOil) isolated from the Tunisian flora as a new antileishmanial candidate. Two plants were chosen for their antileishmanial potential: Citrus limon (Citrus) and Pistacia lentiscus (Pistacia). Each of these plants was harvested from two different sites (area 1 and area 2). Extracted EssOils were characterized using GC-MS. Their antiparasitic activity against axenic and intracellular Leishmania major amastigotes and their cytotoxicity were assessed. Citrus EssOil from area 1 displayed an interesting activity against L. major intramacrophage amastigotes with IC₅₀ value at 4.2 ± 1.3 μg/mL. Interestingly, this activity was close to that of miltefosine. Moderate activities against intracellular amastigote were observed for Pistacia EssOil from area 1 and Citrus EssOil from area 2. However, low cytotoxicity with high selectivity index was proved only for Citrus EssOil from area 1, revealing its safety for macrophages. This study also demonstrated for the first time the antileishmanial activity of EssOil extracted from Citrus limon leaves. The EssOil interesting activity could be related to the lipophilic properties of terpenes that were shown in literature to contribute to the disruption of parasite intracellular metabolic pathways.

Trypanothione Metabolism as Drug Target for Trypanosomatids

Chagas Disease, African sleeping sickness, and leishmaniasis are neglected diseases caused by pathogenic trypanosomatid parasites, which have a considerable impact on morbidity and mortality in poor countries. The available drugs used as treatment have high toxicity, limited access, and can cause parasite drug resistance. Long-term treatments, added to their high toxicity, result in patients that give up therapy. Trypanosomatids presents a unique trypanothione based redox system, which is responsible for maintaining the redox balance. Therefore, inhibition of these essential and exclusive parasite's metabolic pathways, absent from the mammalian host, could lead to the development of more efficient and safe drugs. The system contains different redox cascades, where trypanothione and tryparedoxins play together a central role in transferring reduced power to different enzymes, such as 2-Cys peroxiredoxins, non-selenium glutathione peroxidases, ascorbate peroxidases, glutaredoxins and methionine sulfoxide reductases, through NADPH as a source of electrons. There is sufficient evidence that this complex system is essential for parasite survival and infection. In this review, we explore what is known in terms of essentiality, kinetic and structural data, and the development of inhibitors of enzymes from this trypanothione-based redox system. The recent advances and limitations in the development of lead inhibitory compounds targeting these enzymes have been discussed. The combination of molecular biology, bioinformatics, genomics, and structural biology is fundamental since the knowledge of unique features of the trypanothione-dependent system will provide tools for rational drug design in order to develop better treatments for these diseases.