Cell death features induced in Leishmania major by 1,3,4-thiadiazole derivatives

Fasciola hepatica fatty acid binding protein (Fh12) induces apoptosis and tolerogenic properties in murine bone marrow derived dendritic cells

In a previous study we demonstrated that Fasciola hepatica fatty acid binding protein (Fh12) significantly suppress macrophage function by inhibiting IL-6, IL-1β, tumor necrosis factor (TNF)-α and IL-12 production in TLR4-stimulated murine macrophages, an effect mediated through the signaling of CD14 co-receptor without affecting the viability of these cells. Given that dendritic cells (DCs) are immune cells that play a central role in the initiation of primary immune responses and that are the only antigen-presenting cells capable of stimulating naïve T-cells, in the present study we investigated the effect of Fh12 on DCs. We found that Fh12 exerts a strong suppressive effect on activation and function of DCs. However, in contrast to the effect observed on macrophages, Fh12 induces early and late apoptosis of DCs being this phenomenon dose-dependent and CD14-coreceptor independent. At low concentration Fh12 modulates the LPS-induced DCs maturation status by suppressing the MHC-II, and co-stimulatory molecules CD40 and CD80 surface expression together with the pro-inflammatory cytokines IL-12p70 and IL-6 production whereas increase the IL-10 levels. Besides, Fh12 decreased the ability of LPS-activated DCs to induce IFN-γ production against allogeneic splenocytes, while increasing IL-4 production. We have described for the first time the ability of Fh12 to modify selectively the viability of DCs by apoptosis induction. The selective diminution in DCs survival could be a F. hepatica strategy in order to prevent a host immune response during the earliest phases of infection.

Curzerene antileishmania activity: Effects on Leishmania amazonensis and possible action mechanisms

Leishmaniasis is a set of infectious diseases with high rates of morbidity and mortality, it affects millions of people around the world. Treatment, mainly with pentavalent antimonials, presents significant toxicity and many cases of resistance. In previous works we have demonstrated the effective and selective antileishmanial activity of Eugenia uniflora L. essential oil, being constituted (47.3%) by the sesquiterpene curzerene. Considering the high rate of parasite inhibition demonstrated for E. uniflora essential oil, and the significant presence of curzerene in the oil, this study aimed to evaluate its antileishmania activity and possible mechanisms of action. Curzerene was effective in inhibiting the growth of promastigotes (IC₅₀ 3.09 ± 0.14 µM) and axenic amastigotes (EC₅₀ 2.56 ± 0.12 µM), with low cytotoxicity to RAW 264.7 macrophages (CC₅₀ 83.87 ± 4.63 µM). It was observed that curzerene has direct effects on the parasite, inducing cell death by apoptosis with secondary necrotic effects (producing pores in the plasma membrane). Curzerene proved to be even more effective against intra-macrophage amastigote forms, with an EC₅₀ of 0.46 ± 0.02 µM. The selectivity index demonstrated by curzerene on these parasite forms was 182.32, being respectively 44.15 and 8.47 times more selective than meglumine antimoniate and amphotericin B. The antiamastigote activity of curzerene was associated with immunomodulatory activity, as it increased TNF-α, IL-12, and NO levels, and lysosomal activity, and decreased IL-10 and IL-6 cytokine levels detected in macrophages infected and treated. In conclusion, our results demonstrate that curzerene is an effective and selective antileishmanial agent, a candidate for in vivo investigation in models of antileishmanial activity.

Synthesis and biological activity of novel 4-aminoquinoline/1,2,3-triazole hybrids against Leishmania amazonensis

Quinoline and 1,2,3-triazoles are well-known nitrogen-based heterocycles presenting diverse pharmacological properties, although their antileishmanial activity is still poorly exploited. As an effort to contribute with studies involving these interesting chemical groups, in the present study, a series of compounds derived from 4-aminoquinoline and 1,2,3-triazole were synthetized and biological studies using L. amazonensis species were performed. The results pointed that the derivative 4, a hybrid of 4-aminoquinoline/1,2,3-triazole exhibited the best antileishmanial action, with inhibitory concentration (IC₅₀) values of ~1 µM against intramacrophage amastigotes of L. amazonensis , and being 16-fold more active to parasites than to the host cell. The mechanism of action of derivative 4 suggest a multi-target action on Leishmania parasites, since the treatment of L. amazonensis promastigotes caused mitochondrial membrane depolarization, accumulation of ROS products, plasma membrane permeabilization, increase in neutral lipids, exposure of phosphatidylserine to the cell surface, changes in the cell cycle and DNA fragmentation. The results suggest that the antileishmanial effect of this compound is primarily altering critical biochemical processes for the correct functioning of organelles and macromolecules of parasites, with consequent cell death by processes related to apoptosis-like and necrosis. No up-regulation of reactive oxygen and nitrogen intermediates was promoted by derivative 4 on L. amazonensis -infected macrophages, suggesting a mechanism of action independent from the activation of the host cell. In conclusion, data suggest that derivative 4 presents selective antileishmanial effect, which is associated with multi-target action, and can be considered for future studies for the treatment against disease.

The ultimate fate determinants of drug induced cell-death mechanisms in Trypanosomatids

Chemotherapy constitutes a major part of modern-day therapy for infectious and chronic diseases. A drug is said to be effective if it can inhibit its target, induce stress, and thereby trigger an array of cell death pathways in the form of programmed cell death, autophagy, necrosis, etc. Chemotherapy is the only treatment choice against trypanosomatid diseases like Leishmaniasis, Chagas disease, and sleeping sickness. Anti-trypanosomatid drugs can induce various cell death phenotypes depending upon the drug dose and growth stage of the parasites. The mechanisms and pathways triggering cell death in Trypanosomatids serve to help identify potential targets for the development of effective anti-trypanosomatids. Studies show that the key proteins involved in cell death of trypanosomatids are metacaspases, Endonuclease G, Apoptosis-Inducing Factor, cysteine proteases, serine proteases, antioxidant systems, etc. Unlike higher eukaryotes, these organisms either lack the complete set of effectors involved in cell death pathways, or are yet to be deciphered. A detailed summary of the existing knowledge of different drug-induced cell death pathways would help identify the lacuna in each of these pathways and therefore open new avenues for research and thereby new therapeutic targets to explore. The cell death pathway associated complexities in metazoans are absent in trypanosomatids; hence this summary can also help understand the trigger points as well as cross-talk between these pathways. Here we provide an in-depth overview of the existing knowledge of these drug-induced trypanosomatid cell death pathways, describe their associated physiological changes, and suggest potential interconnections amongst them.

Poly(ADP-ribose) metabolism in human parasitic protozoa

Poly(ADP-ribosyl)ation reactions constitute a post-translational protein modification synthesized in higher eukaryotes by a family of poly(ADP-ribose)polymerases (PARP) and catabolized mainly by poly(ADP-ribose) glycohydrolase (PARG). The best understood role of PARP is the maintenance of genomic integrity via the promotion of DNA repair that leads to cell survival when low levels of genotoxic stress occur. The participation of PARP in unleashing cell death at higher levels of damage has also been broadly studied. The biology of poly(ADP-ribosyl)ation in protozoan parasites, however, still remains a mystery. This review will examine the presence of the key enzyme involved in ADP-ribose polymer (PAR) metabolism in protozoan parasites associated with human diseases. Theoretical and experimental data obtained up to date have revealed the presence of PAR metabolism only in the trypanosomatids Trypanosoma cruzi and T. brucei, the apicomplexan Toxoplasma gondii and Entamoeba histolytica. T. cruzi and T. brucei, as opposed to humans and other organisms, have only one PARP and one PARG with subcellular localizations that are distinct from the ones described for their mammalian counterparts. The topics discussed in this review describe the first studies on PAR metabolism in trypanosomatids, specially the role of PAR on DNA damage response, cell cycle progression and cell death after genotoxic stimuli. The results described show differences in some aspects of PAR metabolism in trypanosomatids in comparison to other eukaryotes. New questions about the function of this metabolic pathway in the parasites under study are open and we hope it encourages the research community to explore this signaling pathway as a new possible target of clinical relevance in these and other disease-causing parasites.

β-Amino acid derivatives as mitochondrial complex III inhibitors of L. donovani: A promising chemotype targeting visceral leishmaniasis

β-amino acids and their analogues are gathering increased attention not only because of their antibacterial and antifungal activity, but also for their use in designing peptidomimetics with increased oral bioavailability and resistance to metabolic degradation. In this study, a series of α-phenyl substituted chalcones, α-phenyl, β-amino substituted dihydrochalcones and β-amino acid derivatives were synthesized and evaluated for their antileishmanial efficacy against experimental visceral leishmaniasis (VL). Among all synthesized derivatives, 10c showed promising antileishmanial efficacy against both extracellular promastigote and intracellular amastigote (IC₅₀ 8.2 μM and 20.5 μM respectively) of L. donovani with negligible cytotoxic effect towards J774 macrophages and Vero cells. 10c effectively reduced spleen and liver parasite burden (>90%) in both hamster and Balb/c model of VL without any hepatotoxicity. In vitro pharmacokinetic analysis showed that 10c was stable in gastric fluid and plasma of Balb/c mice at 10 μg/ml. Further analysis of the molecular mechanism revealed that 10c entered into the parasite by depolarizing the plasma membrane rather than forming nonspecific pores and induced molecular events like loss in mitochondrial membrane potential with a gradual decline in ATP production. This, in turn, did not induce programmed cell death of the parasite; rather 10c induced bioenergetic collapse of the parasite by decreasing ATP synthesis through specific inhibition of mitochondrial complex III activity. Altogether, our results allude to the therapeutic potential of β-amino acid derivatives as novel antileishmanials, identifying them as lead compounds for further exploration in the design of potent candidates for the treatment of visceral leishmaniasis.

Isopropyl quinoxaline-7-carboxylate 1,4-di-N-oxide derivatives induce regulated necrosis-like cell death on Leishmania (Leishmania) mexicana

Leishmaniasis is a neglected tropical disease caused by the parasite of the genus Leishmania. About 13 million people are infected worldwide, and it is estimated that 350 million are at risk of infection. Clinical manifestations depend on the parasite species and factors related to the host such as the immune system, nutrition, housing, and financial resources. Available treatments have severe side effects; therefore, research currently focuses on finding more active and less toxic compounds. Quinoxalines have been described as promising alternatives. In this context, 17 isopropyl quinoxaline-7-carboxylate 1,4-di-N-oxide derivatives were evaluated as potential leishmanicidal agents. Their effect on the cell metabolism of Leishmania mexicana promastigotes and their cytotoxic effects on the J774.A1 cell line and on erythrocytes were evaluated, and their selectivity index was calculated. Compounds T-069 (IC₅₀ = 1.49 μg/mL), T-070 (IC₅₀ = 1.71 μg/mL), T-072 (IC₅₀ = 6.62 μg/mL), T-073 (IC₅₀ = 1.25 μg/mL), T-085 (IC₅₀ = 0.74 μg/mL), and T-116 (IC₅₀ = 0.88 μg/mL) were the most active against L. mexicana promastigotes and their mechanism of action was characterized by flow cytometry and microscopy. Compound T-073, the most selective quinoxaline derivative, induced cell membrane damage, phosphatidylserine exposition, reactive oxygen species production, disruption of the mitochondrion membrane potential, and DNA fragmentation, all in a dose-dependent manner, indicating the induction of regulated necrosis. Light and transmission electron microscopy showed the drastic morphological changes induced and the mitochondrion as the most sensitive organelle in response to T-073. This study describes the mechanism by which active isopropyl quinoxaline-7-carboxylate 1,4-di-N-oxide quinoxalines affect the parasite.

Mahanine exerts in vitro and in vivo antileishmanial activity by modulation of redox homeostasis

Earlier we have established a carbazole alkaloid (mahanine) isolated from an Indian edible medicinal plant as an anticancer agent with minimal effect on normal cells. Here we report for the first time that mahanine-treated drug resistant and sensitive virulent Leishmania donovani promastigotes underwent apoptosis through phosphatidylserine externalization, DNA fragmentation and cell cycle arrest. An early induction of reactive oxygen species (ROS) suggests that the mahanine-induced apoptosis was mediated by oxidative stress. Additionally, mahanine-treated Leishmania-infected macrophages exhibited anti-amastigote activity by nitric oxide (NO)/ROS generation along with suppression of uncoupling protein 2 and Th1-biased cytokines response through modulating STAT pathway. Moreover, we have demonstrated the interaction of a few antioxidant enzymes present in parasite with mahanine through molecular modeling. Reduced genetic and protein level expression of one such enzyme namely ascorbate peroxidase was also observed in mahanine-treated promastigotes. Furthermore, oral administration of mahanine in acute murine model exhibited almost complete reduction of parasite burden, upregulation of NO/iNOS/ROS/IL-12 and T cell proliferation. Taken together, we have established a new function of mahanine as a potent antileishmanial molecule, capable of inducing ROS and exploit antioxidant enzymes in parasite along with modulation of host's immune response which could be developed as an inexpensive and nontoxic therapeutics either alone or in combination.