Chromone linked nitrone derivative induces the expression of iNOS2 and Th1 cytokines but reduces the Th2 response in experimental visceral leishmaniasis

Leishmania LPG interacts with LRR5/LRR6 of macrophage TLR4 for parasite invasion and impairs the macrophage functions

Visceral leishmaniasis (VL) is a severe form of leishmaniasis, primarily affecting the poor in developing countries. Although several studies have highlighted the importance of toll-like receptors (TLRs) in the pathophysiology of leishmaniasis, the role of specific TLRs and their binding partners involved in Leishmania donovani uptake are still elusive. To investigate the mechanism of L. donovani entry inside the macrophages, we found that the parasite lipophosphoglycan (LPG) interacted with the macrophage TLR4, leading to parasite uptake without any significant alteration of macrophage cell viability. Increased parasite numbers within macrophages markedly inhibited lipopolysachharide-induced pro-inflammatory cytokines gene expression. Silencing of macrophage-TLR4, or inhibition of parasite-LPG, significantly stemmed parasite infection in macrophages. Interestingly, we observed a significant enhancement of macrophage migration, and generation of reactive oxygen species (ROS) in the parasite-infected TLR4-silenced macrophages, whereas parasite infection in TLR4-overexpressed macrophages exhibited a notable reduction of macrophage migration and ROS generation. Moreover, mutations in the leucine-rich repeats (LRRs), particularly LRR5 and LRR6, significantly prevented TLR4 interaction with LPG, thus inhibiting cellular parasite entry. All these results suggest that parasite LPG recognition by the LRR5 and LRR6 of macrophage-TLR4 facilitated parasite entry, and impaired macrophage functions. Therefore, targeting LRR5/LRR6 interactions with LPG could provide a novel option to prevent VL.

Evolution of chromone-like compounds as potential antileishmanial agents, through the 21st century

INTRODUCTION

Leishmaniasis is one of the most neglected diseases of modern times that mainly affects people from developing countries, with approximately 350 million people considered at risk of developing leishmaniasis. Therefore, the development of novel antileishmanial treatments is becoming the focus of numerous research groups, with the support of the World Health Organization, which hopes to eradicate this disease in the near future.

AREAS COVERED

This review focuses on the interest of chromones for the development of future treatments against leishmaniasis. In addition to plant-based chromone derivatives, structure-activity relationship studies that aim to identify the optimal structural features of the chromones' antileishmanial activity are also described and discussed.

EXPERT OPINION

The numerous examples of chromones depicted in this paper, allied with the SAR studies presented herein, suggest that the chromone scaffold is a privileged core for the design and development of novel antileishmanial agents. However, some concerns have been raised concerning the considerable variability observed in the results throughout the scientific bibliography. These inconsistencies may explain the absence of pharmacodynamic and pharmacokinetic studies as well as clinical trials.

Mutagenic and Cytotoxicity LQB 123 Profile: Safety and Tripanocidal Effect of a Phenyl-t-Butylnitrone Derivative

The therapeutic options for Chagas disease are limited and its treatment presents a number of drawbacks including toxicity, drug resistance, and insufficient effectiveness against the chronic stage of the disease. Therefore, new therapeutical options are mandatory. In the present work, we evaluated the effect of a phenyl-tert-butylnitrone (PBN) derivate, LQB 123, against Trypanosoma cruzi forms. LQB 123 presented a trypanocidal effect against bloodstream trypomastigotes (IC50 = 259.4 ± 6.1 μM) and intracellular amastigotes infecting peritoneal macrophages (IC50 = 188.2 ± 47.5 μM), with no harmful effects upon the mammalian cells (CC50 values greater than 4 mM), resulting in a high selectivity index (CC50/IC50 > 20). Additionally, metacyclic trypomastigotes submitted to LQB 123 presented an IC50 of about 191.8 ± 10.5 μM and epimastigotes forms incubated with different concentrations of LQB 123 presented an inhibition of parasite growth with an IC50 of 255.1 ± 3.6 μM. Finally, we investigated the mutagenic potential of the nitrone by the Salmonella/microsome assay and observed no induction of mutagenicity even in concentrations as high as 33000 μM. Taken together, these results present a nonmutagenic compound, with trypanocidal activity against all relevant forms of T. cruzi, offering new insights into CD treatment suggesting additional in vivo tests.

Antileishmanial ferrocenylquinoline derivatives: Synthesis and biological evaluation against Leishmania donovani

The emergence of resistance against existing antileishmanial drugs necessitates the search for new classes of antileishmanial compounds. Herein a series of structurally diverse ferrocenylquinolines have been synthesized and evaluated for in vitro antileishmanial activity against Leishmania donovani using the MTT assay. Thirteen (M2-M14) substituted ferrocenylquinoline congeners possessing triazole rings were generated by palladium mediated Suzuki-Miyaura coupling reaction of 5-iodoferrocenylquinolinetriazole and substituted arylboronic acids. All the synthesized compounds were tested for its antileishmanial activity using both promastigote and amastigote stages of L. donovani. Among them, three compounds (M4, M7 and M9) exhibited promising anti-promastigote activity, with an IC₅₀ value of 28.7 μM, 22.1 μM and 28 μM, respectively, and no cytotoxicity toward host splenocytes. These three compounds are equally effective against the intracellular amastigote stage of L. donovani showing the IC₅₀ values of 16 μM (M4), 8 μM (M7) and 16 μM (M9), respectively, with consistent nitric oxide generation as required for parasite clearance. From the battery of tests conducted in this study, it appears that these compounds induce parasite death by promoting cell cycle arrest and triggering apoptosis.

Successful Therapy of Murine Visceral Leishmaniasis with Astrakurkurone, a Triterpene Isolated from the Mushroom Astraeus hygrometricus, Involves the Induction of Protective Cell-Mediated Immunity and TLR9

In our previous report, we showed that astrakurkurone, a triterpene isolated from the Indian mushroom Astraeus hygrometricus (Pers.) Morgan, induced reactive oxygen species, leading to apoptosis in Leishmania donovani promastigotes, and also was effective in inhibiting intracellular amastigotes at the 50% inhibitory concentration of 2.5 μg/ml. The aim of the present study is to characterize the associated immunomodulatory potentials and cellular activation provided by astrakurkurone, leading to effective antileishmanial activity in vitro and in vivo Astrakurkurone-mediated antileishmanial activity was evaluated by real-time PCR and flow cytometry. The involvement of Toll-like receptor 9 (TLR9) was studied by in vitro assay in the presence of a TLR9 agonist and antagonist and by in silico modeling of a three-dimensional structure of the ectodomain of TLR9 and its interaction with astrakurkurone. Astrakurkurone caused a significant increase in TLR9 expression of L. donovani-infected macrophages along with the activation of proinflammatory responses. The involvement of TLR9 in astrakurkurone-mediated amastigote killing has been evidenced from the fact that a TLR9 agonist (CpG, ODN 1826) in combination with astrakurkurone enhanced the amastigote killing, while a TLR9 antagonist (bafilomycin A1) alone or in combination with astrakurkurone curbed the amastigote killing, which could be further justified by in silico evidence of docking between mouse TLR9 and astrakurkurone. Astrakurkurone was found to reduce the parasite burden in vivo by inducing protective cytokines, gamma interferon and interleukin 17. Moreover, astrakurkurone was nontoxic toward peripheral blood mononuclear cells of immunocompromised patients with visceral leishmaniasis. Astrakurkurone, a nontoxic antileishmanial, enhances the immune efficiency of host cells, leading to parasite clearance in vitro and in vivo.

Oxysterols: Synthesis and anti-leishmanial activities

Oxygenated sterols (2-16) were synthesized by skeletal rearrangement of steroidal allylic alcohols. All the derivatives were screened for their anti-leishmanial activities. Compounds 3, 11 and 12 showed potent activities. Compound 12 was found least toxic and induced highest nitric oxide (NO) at 48 h. Least toxicity of compound 12 on splenocytes validated its best anti-amastigote effect and induction of NO.

A novel triterpene from Astraeus hygrometricus induces reactive oxygen species leading to death in Leishmania donovani

ABSTRACT 

Aim: The effect of astrakurkurone, a novel triterpene, isolated from Indian mushroom Astraeus hygrometricus has been investigated to elucidate the mechanisms involved in selective cell death of Leishmania donovani. Materials & methods: The hypotheses were investigated using flow-cytometry, scanning electron microscopy and confocal microscopy. Results: The time dependent elevation of astrakurkurone-induced reactive oxygen species (ROS) was found intimately associated with apoptosis. The involvement of ROS in promastigote death was found confirmed as NAC and GSH could decrease the ROS level and restored the mitochondrial membrane potential (ΔΨ m). It also inhibited the intracellular amastigotes. Conclusion: We claim the present invention as substantial in depth evidences that mushroom derived active molecules can be exploited as target specific, comparatively nontoxic leads for antileishmanial therapy.

Protective effect of Croton caudatus Geisel leaf extract against experimental visceral leishmaniasis induces proinflammatory cytokines in vitro and in vivo

In the present state of overwhelming emergence of drug-unresponsive phenotypes of Leishmania donovani and persistent severe toxicity in conventional anti-leishmanial therapy, in search for novel leads, the aim of this study has been fixed to identify the active extract(s) of Croton caudatus Geisel. var. tomentosus Hook effective against the parasitic protozoans in vitro and in vivo. C. caudatus Geisel. is often used by Chakma and Hmar community, the local tribes of north-east India for medicinal and veterinary purposes. Among the five semi-purified extracts tested, C. caudatus leaves, extracted in hexane and subsequently semi-purified in a column packed with silica gel (70-130 µM; mesh size 60 A°) using ethyl acetate-hexane solvent (9:1), was found to be the most effective growth inhibitor (JDHex) against the Leishmania promastigotes and amastigotes. JDHex significantly altered the biochemical parameters (protein, lipid and carbohydrates) in promastigotes followed by the morphological changes, DNA condensation and subsequent apoptosis in L. donovani. In consequent steps, it has been also proved that JDHex reduced the replication of intracellular amastigotes with concomitant release of nitric oxide and pro-inflammatory cytokines, IL-12 and TNF-α in vitro. Significantly, the 50% inhibitory concentration of JDHex was estimated much lower against the intracellular amastigotes (2.5 µg/mL) in comparison to promastigotes (10 µg/mL). JDHex was also found efficient in reducing parasite burden in spleen and liver when treated in vivo and increased the intracellular IFN-γ and decreased the IL-10 in CD4+ T cells in splenocytes of orally treated animals. The results of this study support the importance in exploration of novel anti-leishmanial leads from C. caudatus Geisel. var. tomentosus Hook. against the L. donovani (MHOM/IN/83/AG83) infection. Partial chemical characterization of JDHex revealed the presence of terpenoids. However, the further chemical investigation of JDHex is warranted.

Synthesis and biological evaluation of ferrocenylquinoline as a potential antileishmanial agent

The emergence of resistance against antileishmanial drugs in current use necessitates the search for new classes of antileishmanial compounds. Herein we report the design, synthesis, and evaluation of a novel ferrocenylquinoline for activity against Leishmania donovani. 7-Chloro-N-[2-(1H-5-ferrocenyl-1,2,3-triazol-1-yl)ethyl]quinolin-4-amine (1) was generated by coupling an iron(II) ethynylferrocene species with 4-(2-ethylazido)amino-7-chloroquinoline using click chemistry. The synthesized compound 1 was tested for its antileishmanial activity using both promastigote and amastigote stages of L. donovani. Compound 1 showed promising anti-promastigote activity, with an IC50 value of 15.26 μM and no cytotoxicity toward host splenocytes. From the battery of tests conducted in this study, it appears that this compound induces parasite death by promoting oxidative stress and depolarizing the mitochondrial membrane potential, thereby triggering apoptosis. These results suggest that ferrocenylquinoline 1 is a suitable lead for the development of new antileishmanial drugs.

Selective inhibition of Leishmania donovani by active extracts of wild mushrooms used by the tribal population of India: An in vitro exploration for new leads against parasitic protozoans

The study was intended at evaluating the anti-proliferating effect of mushrooms used in traditional folklore of Santal tribal population in India against Leishmania donovani (MHOM/IN/83/AG83). A total of eighteen extracts, three estracts from each mushroom [(80% ethanol extracted; Fa), (water-soluble polysaccharide fraction; Fb), (polyphenolic fraction; Fc)], from six wild mushrooms were obtained. These extracts were tested against the promastigotes and amastigotes for their antileishmanial capacity. Fa fractions (250 μg/mL) of Astraeus hygrometricus and Tricholoma giganteum significantly inhibited the growth of L. donovani promastigotes and interfered in lipid biosynthesis. Moreover, both fractions induced apoptosis in promastigotes. Water soluble Fb fractions of A. hygrometricus, Russula laurocerasi, Russula albonigra, Termitomyces eurhizus, Russula delica and polyphenolic Fc fraction of R. laurocerasi were found to inhibit the replication of intracellular amastigotes in macrophages dose dependently. Significantly, 50% inhibitory concentration of the active extracts against intracellular amastigotes induced release of nitric oxide and IL-12 in murine macrophages and dendritic cells assay and also found considerably non-toxic on murine splenocytes. Results of this study can be used as a basis for further phytochemical and pharmacological investigations in the effort for search of novel anti-leishmanial leads.

Synthesis of 3-tetrazolylmethyl-4H-chromen-4-ones via Ugi-azide and biological evaluation against Entamoeba histolytica, Giardia lamblia and Trichomona vaginalis

The synthesis of novel 3-tetrazolylmethyl-4H-chromen-4-ones via an Ugi-azide multicomponent reaction and their biological evaluation against Entamoeba histolytica, Giardia lamblia and Trichomona vaginalis are described. Reported yields are moderate to good and biological results show that these compounds could be considered as candidates to anti-parasitic drugs, especially against G. lamblia.