Methylglyoxal metabolism in trypanosomes and leishmania

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.

Metabolic Shades of S-D-Lactoylglutathione

S-D-lactoylglutathione (SDL) is an intermediate of the glutathione-dependent metabolism of methylglyoxal (MGO) by glyoxalases. MGO is an electrophilic compound that is inevitably produced in conjunction with glucose breakdown and is essentially metabolized via the glyoxalase route. In the last decades, MGO metabolism and its cytotoxic effects have been under active investigation, while almost nothing is known about SDL. This article seeks to fill the gap by presenting an overview of the chemistry, biochemistry, physiological role and clinical importance of SDL. The effects of intracellular SDL are investigated in three main directions: as a substrate for post-translational protein modifications, as a reservoir for mitochondrial reduced glutathione and as an energy currency. In essence, all three approaches point to one direction, namely, a metabolism-related regulatory role, enhancing the cellular defense against insults. It is also suggested that an increased plasma concentration of SDL or its metabolites may possibly serve as marker molecules in hemolytic states, particularly when the cause of hemolysis is a disturbance of the pay-off phase of the glycolytic chain. Finally, SDL could also represent a useful marker in such metabolic disorders as diabetes mellitus or ketotic states, in which its formation is expected to be enhanced. Despite the lack of clear-cut evidence underlying the clinical and experimental findings, the investigation of SDL metabolism is a promising field of research.

In-Depth Quantitative Proteomics Characterization of In Vitro Selected Miltefosine Resistance in Leishmania infantum

Visceral leishmaniasis (VL) is a neglected disease caused by Leishmania parasites. Although significant morbidity and mortality in tropical and subtropical regions of the world are associated with VL, the low investment for developing new treatment measures is chronic. Moreover, resistance and treatment failure are increasing for the main medications, but the emergence of resistance phenotypes is poorly understood at the protein level. Here, we analyzed the development of resistance to miltefosine upon experimental selection in a L. infantum strain. Time to miltefosine resistance emergence was ~six months and label-free quantitative mass-spectrometry-based proteomics analyses revealed that this process involves a remodeling of components of the membrane and mitochondrion, with significant increase in oxidative phosphorylation complexes, particularly on complex IV and ATP synthase, accompanied by increased energy metabolism mainly dependent on β-oxidation of fatty acids. Proteins canonically involved in ROS detoxification did not contribute to the resistant process whereas sterol biosynthesis enzymes could have a role in this development. Furthermore, changes in the abundance of proteins known to be involved in miltefosine resistance such as ABC transporters and phospholipid transport ATPase were detected. Together, our data show a more complete picture of the elements that make up the miltefosine resistance phenotype in L. infantum.

Nitric Oxide Resistance in Leishmania (Viannia) braziliensis Involves Regulation of Glucose Consumption, Glutathione Metabolism and Abundance of Pentose Phosphate Pathway Enzymes

In American Tegumentary Leishmaniasis production of cytokines, reactive oxygen species and nitric oxide (NO) by host macrophages normally lead to parasite death. However, some Leishmania braziliensis strains exhibit natural NO resistance. NO-resistant strains cause more lesions and are frequently more resistant to antimonial treatment than NO-susceptible ones, suggesting that NO-resistant parasites are endowed with specific mechanisms of survival and persistence. To tests this, we analyzed the effect of pro- and antioxidant molecules on the infectivity in vitro of L. braziliensis strains exhibiting polar phenotypes of resistance or susceptibility to NO. In addition, we conducted a comprehensive quantitative mass spectrometry-based proteomics analysis of those parasites. NO-resistant parasites were more infective to peritoneal macrophages, even in the presence of high levels of reactive species. Principal component analysis of protein concentration values clearly differentiated NO-resistant from NO-susceptible parasites, suggesting that there are natural intrinsic differences at molecular level among those strains. Upon NO exposure, NO-resistant parasites rapidly modulated their proteome, increasing their total protein content and glutathione (GSH) metabolism. Furthermore, NO-resistant parasites showed increased glucose analogue uptake, and increased abundance of phosphotransferase and G6PDH after nitrosative challenge, which can contribute to NADPH pool maintenance and fuel the reducing conditions for the recovery of GSH upon NO exposure. Thus, increased glucose consumption and GSH-mediated redox capability may explain the natural resistance of L. braziliensis against NO.

Protein Lactylation Critically Regulates Energy Metabolism in the Protozoan Parasite Trypanosoma brucei

Lysine lactylation has been recognized as a novel post-translational modification occurring on histones. However, lactylation in non-histone proteins, especially in proteins of early branching organisms, is not well understood. Energy metabolism and the histone repertoire in the early diverging protozoan parasite Trypanosoma brucei, the causative agent of African trypanosomiasis, markedly diverge from those of conventional eukaryotes. Here, we present the first exhaustive proteome-wide investigation of lactylated sites in T. brucei. We identified 387 lysine-lactylated sites in 257 proteins of various cellular localizations and biological functions. Further, we revealed that glucose metabolism critically regulates protein lactylation in T. brucei although the parasite lacks lactate dehydrogenase. However, unlike mammals, increasing the glucose concentration reduced the level of lactate, and protein lactylation decreased in T. brucei via a unique lactate production pathway. In addition to providing a valuable resource, these foregoing data reveal the regulatory roles of protein lactylation of trypanosomes in energy metabolism and gene expression.

Carbohydrate metabolism in trypanosomatids: New insights revealing novel complexity, diversity and species-unique features

The human pathogenic trypanosomatid species collectively called the "TriTryp parasites" - Trypanosoma brucei, Trypanosoma cruzi and Leishmania spp. - have complex life cycles, with each of these parasitic protists residing in a different niche during their successive developmental stages where they encounter diverse nutrients. Consequently, they adapt their metabolic network accordingly. Yet, throughout the life cycles, carbohydrate metabolism - involving the glycolytic, gluconeogenic and pentose-phosphate pathways - always plays a central role in the biology of these parasites, whether the available carbon and free energy sources are saccharides, amino acids or lipids. In this paper, we provide an updated review of the carbohydrate metabolism of the TriTryps, highlighting new data about this metabolic network, the interconnection of its pathways and the compartmentalisation of its enzymes within glycosomes, cytosol and mitochondrion. Differences in the expression of the branches of the metabolic network between the successive life-cycle stages of each of these parasitic trypanosomatids are discussed, as well as differences between them. Recent structural and kinetic studies have revealed unique regulatory mechanisms for some of the network's key enzymes with important species-specific variations. Furthermore, reports of multiple post-translational modifications of trypanosomal glycolytic enzymes suggest that additional mechanisms for stage- and/or environmental cues that regulate activity are operational in the parasites. The detailed comparison of the carbohydrate metabolism of the TriTryps has thus revealed multiple differences and a greater complexity, including for the reduced metabolic network in bloodstream-form T. brucei, than previously appreciated. Although these parasites are related, share many cytological and metabolic features and are grouped within a single taxonomic family, the differences highlighted in this review reflect their separate evolutionary tracks from a common ancestor to the extant organisms. These differences are indicative of their adaptation to the different insect vectors and niches occupied in their mammalian hosts.

Integrative Computational Framework for Understanding Metabolic Modulation in Leishmania

Background: The integration of computational and mathematical approaches is used to provide a key insight into the biological systems. Through systems biology approaches we seek to find detailed and more robust information on Leishmanial metabolic network. Forman/Forman-Ricci curvature measures were applied to identify important nodes in the network(s). This was followed by flux balance analysis (FBA) to decipher important drug targets. Results: Our results revealed several key high curvature nodes (metabolites) belonging to common yet crucial metabolic networks, thus, maintaining the integrity of the network which signifies its robustness. Further analysis revealed the presence of some of these metabolites, MGO, in redox metabolism of the parasite. Being a component in the glyoxalase pathway and highly cytotoxic, we further attempted to study the outcome of the deletion of the key enzyme (GLOI) mainly involved in the neutralization of MGO by utilizing FBA. The model and the objective function kept as simple as possible demonstrated an interesting emergent behavior. The non-functional GLOI in the model contributed to "zero" flux which signifies the key role of GLOI as a rate limiting enzyme. This has led to several fold increase production of MGO, thereby, causing an increased level of MGO•- generation. Conclusions: The integrated computational approaches have deciphered GLOI as a potential target both from curvature measures as well as FBA which could further be explored for kinetic modeling by implying various redox-dependent constraints on the model. Furthermore, a constraint-based FBA on a larger model could further be explored to get broader picture to understand the exact underlying mechanisms. Designing various in vitro experimental perspectives could churn the therapeutic importance of GLOI.

Development of analytical methods GC-MS vs LC-UV for the serum monitoring of an inflammatory glycotoxin (methylglyoxal): A new biomarker of bovine hepatobiliary distomatosis

Two analytical methods; high performance liquid chromatography and gas chromatography were used to determine the content of 2-methylquinoxaline, a methylglyoxal-derived agent in sera from cattle with fascioliasis. Methylglyoxal is a highly mutagenic and cytotoxic reactive dicarbonyl compound formed by non-enzymatic fragmentation of triose phosphate GAP and DHAP during glycolysis which regularly contributes to repositioning the energetic balance between physiological and pathological situations. The aim of this study was to propose the MGO as a new biomarker in the bovine fasciolosis. Strongly infected animals showed a correlation between the relatively high levels of Fasciola hepatica anti-f2 antibody and methylglyoxal compared to unharmed animals. Also, an acute hyperglycemia was recorded and closely related to hepatic parenchyma hyperplasia, inflammation, bile ducts obstruction and scléro-fibrous foci formation.Unlike HPLC, which has shown analytical flaws and irregularities, GC-MS remains an excellent diagnostic tool for detecting and quantifying methylglyoxal in biological fluids. The developed method has been validated under FDA guidelines. A full scan-range was set from m/z 39 to 144/999 and the molecular weight of the 2-methylquinoxaline was identified according to NIST Database and ES. Methylglyoxal was the only analyte successfully quantified in a relatively short run time. It was linear over a concentration range of 0.057-5.7  μg.ml-1with mean recoveries and RSD of 118% and 3.63% respectively. The intra and inter-day assays were satisfying and not exceed 3.00%. Results reflect the degree of precision of our method and indicate that MGO was an important contributor to understand the hepatic failure independently of other serum markers.

Scaffold hybridization strategy towards potent hydroxamate-based inhibitors of Flaviviridae viruses and Trypanosoma species

Infections with Flaviviridae viruses, such as hepatitis C virus (HCV) and dengue virus (DENV) pose global health threats. Infected individuals are at risk of developing chronic liver failure or haemorrhagic fever respectively, often with a fatal outcome if left untreated. Diseases caused by tropical parasites of the Trypanosoma species, T. brucei and T. cruzi, constitute significant socioeconomic burden in sub-Saharan Africa and continental Latin America, yet drug development is under-funded. Anti-HCV chemotherapy is associated with severe side effects and high cost, while dengue has no clinically approved therapy and antiparasitic drugs are outdated and difficult to administer. Moreover, drug resistance is an emerging concern. Consequently, the need for new revolutionary chemotherapies is urgent. By utilizing a molecular framework combination approach, we combined two distinct chemical entities with proven antiviral and trypanocidal activity into a novel hybrid scaffold attached by an acetohydroxamic acid group (CH₂CONHOH), aiming at derivatives with dual activity. The novel spiro-carbocyclic substituted hydantoin analogues were rationally designed, synthesized and evaluated for their potency against three HCV genotypes (1b, 3a, 4a), DENV and two Trypanosoma species (T. brucei, T. cruzi). They exhibited significant EC₅₀ values and remarkable selectivity indices. Several modifications were undertaken to further explore the structure activity relationships (SARs) and confirm the pivotal role of the acetohydroxamic acid metal binding group.

A role for trypanosomatid aldo-keto reductases in methylglyoxal, prostaglandin and isoprostane metabolism

Trypanosomatid parasites are the infectious agents causing Chagas disease, visceral and cutaneous leishmaniasis and human African trypanosomiasis. Recent work of others has implicated an aldo-keto reductase (AKR) in the susceptibility and resistance of Trypanosoma cruzi to benznidazole, a drug used to treat Chagas disease. Here, we show that TcAKR and homologues in the related parasites Trypanosoma brucei and Leishmania donovani do not reductively activate monocyclic (benznidazole, nifurtimox and fexinidazole) or bicyclic nitro-drugs such as PA-824. Rather, these enzymes metabolise a variety of toxic ketoaldehydes, such as glyoxal and methylglyoxal, suggesting a role in cellular defence against chemical stress. UPLC-QToF/MS analysis of benznidazole bioactivation by T. cruzi cell lysates confirms previous reports identifying numerous drug metabolites, including a dihydro-dihydroxy intermediate that can dissociate to form N-benzyl-2-guanidinoacetamide and glyoxal, a toxic DNA-glycating and cross-linking agent. Thus, we propose that TcAKR contributes to benznidazole resistance by the removal of toxic glyoxal. In addition, three of the four enzymes studied here display activity as prostaglandin F_2α synthases, despite the fact that there are no credible cyclooxygenases in these parasites to account for formation of the precursor PGH₂ from arachidonic acid. Our studies suggest that arachidonic acid is first converted non-enzymatically in parasite lysates to (PGH₂-like) regioisomers by free radical-mediated peroxidation and that AKRs convert these lipid peroxides into isoprostanes, including prostaglandin F_2α and 8-iso-prostaglandin F_2α.

A Computational Approach Using Bioinformatics to Screening Drug Targets for Leishmania infantum Species

Background

The development of new therapeutic strategies to treat patients for leishmaniasis has become a priority. The antileishmanial activity of the strychnobiflavone flavonoid was recently demonstrated against Leishmania amazonensis and Leishmania infantum amastigotes and promastigotes. The biological effect of this molecule was identified due to its capacity to interfere in the parasite mitochondrial membrane; however, the underlying molecular mechanism remains unclear.

Methods and Results

In this study, a computational approach using bioinformatics was performed to screen biological targets of strychnobiflavone in L. infantum. Computational programs, such as the target fishing approach and molecular docking assays, were used. Results showed that the putative pathway targeted by strychnobiflavone in L. infantum is the methylglyoxal degradation superpathway, and one hydrolase-like protein was predicted to be the molecular target of this flavonoid in the parasites.

Conclusion

In this context, this study provides the basis for understanding the mechanism of action of strychnobiflavone in L. infantum and presents a strategy based on bioinformatics programs to screen targets of other molecules with biological action against distinct pathogens.

Metabolism of Glutathione S-Conjugates: Multiple Pathways

Many potentially toxic electrophilic xenobiotics and some endogenous compounds are detoxified by conversion to the corresponding glutathione S-conjugate, which is metabolized to the N-acetylcysteine S-conjugate (mercapturate) and excreted. Some mercapturate pathway components, however, are toxic. Bioactivation (toxification) may occur when the glutathione S-conjugate (or mercapturate) is converted to a cysteine S-conjugate that undergoes a β-lyase reaction. If the sulfhydryl-containing fragment produced in this reaction is reactive, toxicity may ensue. Some drugs and halogenated workplace/environmental contaminants are bioactivated by this mechanism. On the other hand, cysteine S-conjugate β-lyases occur in nature as a means of generating some biologically useful sulfhydryl-containing compounds.

Pi inhibits intracellular accumulation of methylglyoxal in promastigote form of L. donovani

Similar to their mammalian counterpart, protozoan parasites including Leishmania donovani detoxify methylglyoxal (MG),(1) a toxic ubiquitous product generated in glycolysis pathway. However, it differs in one or more way(s) from the humans. It is known that MG is eliminated either through glyoxalase (GLO)(2) pathway and/or excreted across the cell membrane. This toxic metabolic by-product is known to be detoxified predominantly by the GLO pathway and excretion across the cell membrane is never considered to be a significant pathway for its detoxification. We have tried to modulate these pathways under various physiological conditions to find ways that may lead to accumulation of MG in L. donovani. Besides targeting the GLO pathway, we intend to understand the mechanism of MG release across the cell membrane and possible ways to inhibit its exclusion from parasites. In our study, it was found that inorganic phosphate (Pi)(3) in the presence of glucose inhibits the production of MG as well as promotes the expulsion of MG from the cell. Moreover, the trivalent form of antimony (Sb(III)) inhibits GLO pathway and thus detoxification of MG. Inhibition of Pi transport, which is a Na(+)/H(+) dependent process, restores the Pi mediated abrogation of MG production. Thus, Sb(III) along with inhibitors of Pi transporter may be a therapeutic advancement for treatment of antimony resistant cases of human visceral leishmaniasis. However, it requires further validation using specific inhibitor(s) of Pi transporter.

Glyoxalase biochemistry

The glyoxalase enzyme system utilizes intracellular thiols such as glutathione to convert α-ketoaldehydes, such as methylglyoxal, into D-hydroxyacids. This overview discusses several main aspects of the glyoxalase system and its likely function in the cell. The control of methylglyoxal levels in the cell is an important biochemical imperative and high levels have been associated with major medical symptoms that relate to this metabolite’s capability to covalently modify proteins, lipids and nucleic acid.

An in vitro iron superoxide dismutase inhibitor decreases the parasitemia levels of Trypanosoma cruzi in BALB/c mouse model during acute phase

In order to identify new compounds to treat Chagas disease during the acute phase with higher activity and lower toxicity than the reference drug benznidazole (Bz), two hydroxyphthalazine derivative compounds were prepared and their trypanocidal effects against Trypanosoma cruzi were evaluated by light microscopy through the determination of IC₅₀ values. Cytotoxicity was determined by flow cytometry assays against Vero cells. In vivo assays were performed in BALB/c mice, in which the parasitemia levels were quantified by fresh blood examination; the assignment of a cure was determined by reactivation of blood parasitemia levels after immunosuppression. The mechanism of action was elucidated at metabolic and ultra-structural levels, by ¹H NMR and TEM studies. Finally, as these compounds are potentially capable of causing oxidative damage in the parasites, the study was completed, by assessing their activity as potential iron superoxide dismutase (Fe-SOD) inhibitors. High-selectivity indices observed in vitro were the basis of promoting one of the tested compounds to in vivo assays. The tests on the murine model for the acute phase of Chagas disease showed better parasitemia inhibition values than those found for Bz. Compound 2 induced a remarkable decrease in the reactivation of parasitemia after immunosuppression. Compound 2 turned out to be a great inhibitor of Fe-SOD. The high antiparasitic activity and low toxicity together with the modest costs for the starting materials render this compound an appropriate molecule for the development of an affordable anti-Chagas agent.

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Low toxicity alternative treatment against Trypanosoma cruzi in murine model.

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The acute and chronic phases of Chagas disease.

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In vitro evaluation against epimastigote, amastigote and trypomastigote forms.

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Compound 2 selectively inhibits the parasite Fe-SOD enzyme.

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Compound 2 should be followed-up in future clinical experiments.

Bacterial glyoxalase I enzymes: structural and biochemical investigations

A number of bacterial glyoxalase I enzymes are maximally activated by Ni2+ and Co2+ ions, but are inactive in the presence of Zn2+, yet these enzymes will also bind this metal ion. The structure-activity relationships between these two classes of glyoxalase I serve as important clues as to how the molecular structures of these proteins control metal-activation profiles.

Glyoxalase diversity in parasitic protists

Our current knowledge of the isomerase glyoxalase I and the thioesterase glyoxalase II is based on a variety of prokaryotic and eukaryotic (model) systems with an emphasis on human glyoxalases. During the last decade, important insights on glyoxalase catalysis and structure–function relationships have also been obtained from parasitic protists. These organisms, including kinetoplastid and apicomplexan parasites, are particularly interesting, both because of their relevance as pathogens and because of their phylogenetic diversity and host–parasite co-evolution which has led to specialized organellar and metabolic adaptations. Accordingly, the glyoxalase repertoire and properties vary significantly among parasitic protists of different major eukaryotic lineages (and even between closely related organisms). For example, several protists have an insular or non-canonical glyoxalase. Furthermore, the structures and the substrate specificities of glyoxalases display drastic variations. The aim of the present review is to highlight such differences as well as similarities between the glyoxalases of parasitic protists and to emphasize the power of comparative studies for gaining insights into fundamental principles and alternative glyoxalase functions.

Nickel and human health

This review focuses on the impact of nickel on human health. In particular, the dual nature of nickel as an essential as well as toxic element in nature is described, and the main forms of nickel that can come in contact with living systems from natural sources and anthropogenic activities are discussed. Concomitantly, the main routes of nickel uptake and transport in humans are covered, and the potential dangers that nickel exposure can represent for health are described. In particular, the insurgence of nickel-derived allergies, nickel-induced carcinogenesis as well as infectious diseases caused by human pathogens that rely on nickel-based enzymes to colonize the host are reviewed at different levels, from their macroscopic aspects on human health to the molecular mechanisms underlying these points. Finally, the importance of nickel as a beneficial element for human health, especially being essential for microorganisms that colonize the human guts, is examined.