Drug resistance in leishmaniasis: Newer developments

Cell Death in Leishmania donovani promastigotes in response to Mammalian Aurora Kinase B Inhibitor- Hesperadin

Deciphering how hesperadin, a repurposed mammalian aurora kinase B inhibitor, affects the cellular pathways in Leishmania donovani might be beneficial. This investigation sought to assess the physiological effects of hesperadin on promastigotes of L. donovani, by altering the duration of treatment following exposure to hesperadin. Groups pre-treated with inhibitors such as EGTA, NAC, and z-VAD-fmk before hesperadin exposure were also included. Morphological changes by microscopy, ATP and ROS changes by luminometry; DNA degradation using agarose gel electrophoresis and metacaspase levels through RT-PCR were assessed. Flow cytometry was used to study mitochondrial depolarization using JC-1 and MitoTracker Red; mitochondrial-superoxide accumulation using MitoSOX; plasma membrane modifications using Annexin-V and propidium iodide, and lastly, caspase activation using ApoStat. Significant alterations in promastigote morphology were noted. Caspase activity and mitochondrial-superoxide rose early after exposure whereas mitochondrial membrane potential demonstrated uncharacteristic variations, with significant functional disturbances such as leakage of superoxide radicals after prolonged treatments. ATP depletion and ROS accumulation demonstrated inverse patterns, genomic DNA showed fragmentation and plasma membrane showed Annexin-V binding, soon followed by propidium iodide uptake. Multilobed macronuclei and micronuclei accumulated in hesperadin exposed cells before they disintegrated into necrotic debris. The pathologic alterations were unlike the intrinsic or extrinsic pathways of classical apoptosis and suggest a caspase-mediated cell death most akin to mitotic-catastrophe. Most likely, a G2/M transition block caused accumulation of death signals, disorganized spindles and mechanical stresses, causing changes in morphology, organellar functions and ultimately promastigote death. Thus, death was a consequence of mitotic-arrest followed by ablation of kinetoplast functions, often implicated in L. donovani killing.

Identification and Validation of Compounds Targeting Leishmania major Leucyl-Aminopeptidase M17

Leishmaniasis is a neglected tropical disease; there is currently no vaccine and treatment is reliant upon a handful of drugs suffering from multiple issues including toxicity and resistance. There is a critical need for development of new fit-for-purpose therapeutics, with reduced toxicity and targeting new mechanisms to overcome resistance. One enzyme meriting investigation as a potential drug target in Leishmania is M17 leucyl-aminopeptidase (LAP). Here, we aimed to chemically validate LAP as a drug target in L. major through identification of potent and selective inhibitors. Using RapidFire mass spectrometry, the compounds DDD00057570 and DDD00097924 were identified as selective inhibitors of recombinant Leishmania major LAP activity. Both compounds inhibited in vitro growth of L. major and L. donovani intracellular amastigotes, and overexpression of LmLAP in L. major led to reduced susceptibility to DDD00057570 and DDD00097924, suggesting that these compounds specifically target LmLAP. Thermal proteome profiling revealed that these inhibitors thermally stabilized two M17 LAPs, indicating that these compounds selectively bind to enzymes of this class. Additionally, the selectivity of the inhibitors to act on LmLAP and not against the human ortholog was demonstrated, despite the high sequence similarities LAPs of this family share. Collectively, these data confirm LmLAP as a promising therapeutic target for Leishmania spp. that can be selectively inhibited by drug-like small molecules.

A Multi-Color Immunofluorescence Assay to Distinguish Intracellular From External Leishmania Parasites

Leishmaniasis, a neglected tropical disease, is caused by the intracellular protozoan parasite Leishmania. Upon its transmission through a sandfly bite, Leishmania binds and enters host phagocytic cells, ultimately resulting in a cutaneous or visceral form of the disease. The limited therapeutics available for leishmaniasis, in combination with this parasite's techniques to evade the host immune system, call for exploring various methods to target this infection. To this end, our laboratory has been characterizing how Leishmania is internalized by phagocytic cells through the activation of multiple host cell signaling pathways. This protocol, which we use routinely for our experiments, delineates how to infect mammalian macrophages with either promastigote or amastigote forms of the Leishmania parasite. Subsequently, the number of intracellular parasites, external parasites, and macrophages can be quantified using immunofluorescence microscopy and semi-automated analysis protocols. Studying the pathways that underlie Leishmania uptake by phagocytes will not only improve our understanding of these host-pathogen interactions but may also provide a foundation for discovering additional treatments for leishmaniasis. Key features • This protocol visualizes and quantifies multiple intracellular forms of Leishmania. • It offers flexibility at various points for researchers to introduce modifications according to their study needs.

Compounds with potentialities as novel chemotherapeutic agents in leishmaniasis at preclinical level

Leishmaniasis are neglected infectious diseases caused by kinetoplastid protozoan parasites from the genus Leishmania. These sicknesses are present mainly in tropical regions and almost 1 million new cases are reported each year. The absence of vaccines, as well as the high cost, toxicity or resistance to the current drugs determines the necessity of new treatments against these pathologies. In this review, several compounds with potentialities as new antileishmanial drugs are presented. The discussion is restricted to the preclinical level and molecules are organized according to their chemical nature, source and molecular targets. In this manner, we present antimicrobial peptides, flavonoids, withanolides, 8-aminoquinolines, compounds from Leish-Box, pyrazolopyrimidines, and inhibitors of tubulin polymerization/depolymerization, topoisomerase IB, proteases, pteridine reductase, N-myristoyltransferase, as well as enzymes involved in polyamine metabolism, response against oxidative stress, signaling pathways, and sterol biosynthesis. This work is a contribution to the general knowledge of these compounds as antileishmanial agents.

Genomic Insight of Leishmania Parasite: In-Depth Review of Drug Resistance Mechanisms and Genetic Mutations

Leishmaniasis, which is caused by a parasitic protozoan of the genus Leishmania, is still a major threat to global health, impacting millions of individuals worldwide in endemic areas. Chemotherapy has been the principal method for managing leishmaniasis; nevertheless, the evolution of drug resistance offers a significant obstacle to therapeutic success. Drug-resistant behavior in these parasites is a complex phenomenon including both innate and acquired mechanisms. Resistance is frequently related to changes in drug transportation, drug target alterations, and enhanced efflux of the drug from the pathogen. This review has revealed specific genetic mutations in Leishmania parasites that are associated with resistance to commonly used antileishmanial drugs such as pentavalent antimonials, miltefosine, amphotericin B, and paromomycin, resulting in changes in gene expression along with the functioning of various proteins involved in drug uptake, metabolism, and efflux. Understanding the genetic changes linked to drug resistance in Leishmania parasites is essential for creating approaches for tackling and avoiding the spread of drug-resistant variants. Based on which specific treatments focus on mutations and pathways could potentially improve treatment efficacy and help long-term leishmaniasis control. More study is needed to uncover the complete range of genetic changes generating medication resistance and to develop new therapies based on available information.

Shifting from Ammonium to Phosphonium Salts: A Promising Strategy to Develop Next-Generation Weapons against Biofilms

Since they are difficult and sometimes impossible to treat, infections sustained by multidrug-resistant (MDR) pathogens, emerging especially in nosocomial environments, are an increasing global public health concern, translating into high mortality and healthcare costs. In addition to having acquired intrinsic abilities to resist available antibiotic treatments, MDR bacteria can transmit genetic material encoding for resistance to non-mutated bacteria, thus strongly decreasing the number of available effective antibiotics. Moreover, several pathogens develop resistance by forming biofilms (BFs), a safe and antibiotic-resistant home for microorganisms. BFs are made of well-organized bacterial communities, encased and protected in a self-produced extracellular polymeric matrix, which impedes antibiotics' ability to reach bacteria, thus causing them to lose efficacy. By adhering to living or abiotic surfaces in healthcare settings, especially in intensive care units where immunocompromised older patients with several comorbidities are hospitalized BFs cause the onset of difficult-to-eradicate infections. In this context, recent studies have demonstrated that quaternary ammonium compounds (QACs), acting as membrane disruptors and initially with a low tendency to develop resistance, have demonstrated anti-BF potentialities. However, a paucity of innovation in this space has driven the emergence of QAC resistance. More recently, quaternary phosphonium salts (QPSs), including tri-phenyl alkyl phosphonium derivatives, achievable by easy one-step reactions and well known as intermediates of the Wittig reaction, have shown promising anti-BF effects in vitro. Here, after an overview of pathogen resistance, BFs, and QACs, we have reviewed the QPSs developed and assayed to this end, so far. Finally, the synthetic strategies used to prepare QPSs have also been provided and discussed to spur the synthesis of novel compounds of this class. We think that the extension of the knowledge about these materials by this review could be a successful approach to finding effective weapons for treating chronic infections and device-associated diseases sustained by BF-producing MDR bacteria.

In vitro screening of natural product-based compounds for leishmanicidal activity

Leishmaniasis is one of the major parasitic diseases, caused by obligate intracellular protozoa Leishmania, having high mortality as well as morbidity rate. As there is no human licensed vaccine available against leishmaniasis, chemotherapy remains the major way of combating this disease. Many disadvantages are known to be associated with the current drug regime including severe side effects and toxicity, long duration and expensive treatment, and the emergence of resistance. An alternative approach is being utilized to search for active molecules using natural sources, rather than relying on synthetic drugs. Many plant-derived secondary metabolites like phenolic compounds, steroids, quinones, etc. are being extensively investigated for their anti-leishmanial potential. One such group of complex phenolic compounds are diarylheptanoids. These compounds have been shown to exhibit anti-inflammatory, anti-parasitic, anti-fungal, and other pharmacological activities. In the present study, a set of sixteen tetrahydropyran derivatives including three natural products were obtained in lyophilized form. These compounds with trans-2,6-disubstituted tetrahydropyrans, Diospongin A, Diospongin B (isolated from Dioscorea spongiosa) and Centrolobine (Centrolobium sclerophyllum) as parent compounds were synthesized by the reaction of 1-phenyl-1-triemthylsiloxyethylene with six-membered cyclic hemiacetals in the presence of iodine as a catalyst. All the sixteen synthesized tetrahydropyran derivatives were used for toxicity analysis against L. donovani promastigotes, amastigotes and THP-1-derived human macrophages. IC50 values and selectivity index were calculated for all the compounds. Out of these sixteen, five compounds showed the best effect in vitro in terms of both leishmanicidal activity and non-toxicity to human macrophages.

Immunotherapy and immunochemotherapy in combating visceral leishmaniasis

Visceral leishmaniasis (VL), a vector-borne disease, is caused by an obligate intramacrophage, kinetoplastid protozoan parasite of the genus Leishmania. Globally, VL is construed of diversity and complexity concerned with high fatality in tropics, subtropics, and Mediterranean regions with ~50,000-90,000 new cases annually. Factors such as the unavailability of licensed vaccine(s), insubstantial measures to control vectors, and unrestrained surge of drug-resistant parasites and HIV-VL co-infections lead to difficulty in VL treatment and control. Furthermore, VL treatment, which encompasses several problems including limited efficacy, emanation of drug-resistant parasites, exorbitant therapy, and exigency of hospitalization until the completion of treatment, further exacerbates disease severity. Therefore, there is an urgent need for the development of safe and efficacious therapies to control and eliminate this devastating disease. In such a scenario, biotherapy/immunotherapy against VL can become an alternative strategy with limited side effects and no or nominal chance of drug resistance. An extensive understanding of pathogenesis and immunological events that ensue during VL infection is vital for the development of immunotherapeutic strategies against VL. Immunotherapy alone or in combination with standard anti-leishmanial chemotherapeutic agents (immunochemotherapy) has shown better therapeutic outcomes in preclinical studies. This review extensively addresses VL treatment with an emphasis on immunotherapy or immunochemotherapeutic strategies to improve therapeutic outcomes as an alternative to conventional chemotherapy.

Effective immuno-therapeutic treatment of Canine Leishmaniasis

BACKGROUND

Canine Leishmaniasis (CanL) caused by the L. infantum species is one of the biggest threats to the health of the South American canine population. Chemotherapeutics currently used for the treatment of CanL fail to induce a total parasite clearance while inducing numerous side effects. As CanL is an immunomodulated disease, the use of immuno-treatments should strengthen the deficient immune response of infected dogs. In this study, we evaluated a nasally administered immunotherapy in dogs naturally infected with L. infantum (stage 2), with both visceral and cutaneous manifestations. Noteworthy, some of them were also infected by other parasites (E. canis, D. immitis, A. platys), what worsen their chance of survival.

METHODOLOGY/PRINCIPAL FINDINGS

The treatment was based on 2 intranasal (IN.) administrations of a killed L. infantum parasite loaded into maltodextrin nanoparticles, which treatment was compared with the classical oral administration of Miltefosine (2 mg/kg) for 28 days, as well as a combination of these 2 treatments. The results showed that two IN administrations significantly reduced the serology, and were at least as efficient as the chemotherapy to reduce the skin and bone marrow parasite burden, as well as clinical scores, and that unlike Miltefosine treatments, this nasally administered nanoparticle vaccine was without side effects.

CONCLUSIONS

These results confirm the feasibility of a simple therapeutic immuno-treatment against L. infantum infected dogs, which is a promising tool for future developments.

Novel Pyrido[2',1':2,3]imidazo[4,5-c]quinoline Derivative Selectively Poisons Leishmania donovani Bisubunit Topoisomerase 1 to Inhibit the Antimony-Resistant Leishmania Infection in Vivo

The unique bisubunit structure of Leishmania donovani topoisomerase 1B (LdTop1) is a potential drug target in the parasites unlike the monomeric Top1 from its human host counterpart. Here, we report the design, synthesis, and validation of a chimeric pyrido[2',1':2,3]imidazo[4,5-c]quinoline derivative (C17) as a novel antileishmanial agent that poisons topoisomerase 1-DNA covalent complexes (LdTop1cc) inside the parasites and inhibits Top1 religation activity both in the drug sensitive and antimony-resistant L. donovani clinical isolates. Importantly, the human Top1 is not sensitive to C17. Further, C17 overcomes the chemical instability of camptothecin (CPT) by generating persistent LdTop1cc-induced DNA breaks inside the parasites even after 12 h of drug removal. Intraperitoneal administration of C17 results in marked reduction of the Leishmania amastigotes from the infected spleen and liver of BALB/c mice. C17 confers a host protective immune-response up-regulating the Th1 cytokines facilitating parasite clearance which can be exploited for treating drug-resistant leishmaniasis.

Parasite Metalo-aminopeptidases as Targets in Human Infectious Diseases

BACKGROUND

Parasitic human infectious diseases are a worldwide health problem due to the increased resistance to conventional drugs. For this reason, the identification of novel molecular targets and the discovery of new chemotherapeutic agents are urgently required. Metalo- aminopeptidases are promising targets in parasitic infections. They participate in crucial processes for parasite growth and pathogenesis.

OBJECTIVE

In this review, we describe the structural, functional and kinetic properties, and inhibitors, of several parasite metalo-aminopeptidases, for their use as targets in parasitic diseases.

CONCLUSION

Plasmodium falciparum M1 and M17 aminopeptidases are essential enzymes for parasite development, and M18 aminopeptidase could be involved in hemoglobin digestion and erythrocyte invasion and egression. Trypanosoma cruzi, T. brucei and Leishmania major acidic M17 aminopeptidases can play a nutritional role. T. brucei basic M17 aminopeptidase down-regulation delays the cytokinesis. The inhibition of Leishmania basic M17 aminopeptidase could affect parasite viability. L. donovani methionyl aminopeptidase inhibition prevents apoptosis but not the parasite death. Decrease in Acanthamoeba castellanii M17 aminopeptidase activity produces cell wall structural modifications and encystation inhibition. Inhibition of Babesia bovis growth is probably related to the inhibition of the parasite M17 aminopeptidase, probably involved in host hemoglobin degradation. Schistosoma mansoni M17 aminopeptidases inhibition may affect parasite development, since they could participate in hemoglobin degradation, surface membrane remodeling and eggs hatching. Toxoplasma gondii M17 aminopeptidase inhibition could attenuate parasite virulence, since it is apparently involved in the hydrolysis of cathepsin Cs- or proteasome-produced dipeptides and/or cell attachment/invasion processes. These data are relevant to validate these enzymes as targets.

The Anti-Leishmania amazonensis and Anti-Leishmania chagasi Action of Copper(II) and Silver(I) 1,10-Phenanthroline-5,6-dione Coordination Compounds

Leishmaniasis is a neglected disease caused by protozoa belonging to the Leishmania genus. Notably, the search for new, promising and potent anti-Leishmania compounds remains a major goal due to the inefficacy of the available drugs used nowadays. In the present work, we evaluated the effects of 1,10-phenanthroline-5,6-dione (phendione) coordinated to silver(I), [Ag(phendione)₂]ClO₄ (Ag-phendione), and copper(II), [Cu(phendione)₃](ClO₄)₂·4H₂O (Cu-phendione), as potential drugs to be used in the chemotherapy against Leishmania amazonensis and Leishmania chagasi. The results showed that promastigotes treated with Ag-phendione and Cu-phendione presented a significant reduction in the proliferation rate. The IC₅₀ values calculated to Ag-phendione and Cu-phendione, respectively, were 7.8 nM and 7.5 nM for L. amazonensis and 24.5 nM and 20.0 nM for L. chagasi. Microscopical analyses revealed several relevant morphological changes in promastigotes, such as a rounding of the cell body and a shortening/loss of the single flagellum. Moreover, the treatment promoted alterations in the unique mitochondrion of these parasites, inducing significant reductions on both metabolic activity and membrane potential parameters. All these cellular perturbations induced the triggering of apoptosis-like death in these parasites, as judged by the (i) increased percentage of annexin-positive/propidium iodide negative cells, (ii) augmentation in the proportion of parasites in the sub-G₀/G₁ phase and (iii) DNA fragmentation. Finally, the test compounds showed potent effects against intracellular amastigotes; contrarily, these molecules were well tolerated by THP-1 macrophages, which resulted in excellent selective index values. Overall, the results highlight new selective and effective drugs against Leishmania species, which are important etiological agents of both cutaneous (L. amazonensis) and visceral (L. chagasi) leishmaniasis in a global perspective.

Caecal Ameboma, colorectal malignancy mimicker in young male with ANCA-associated vasculitis

Ameboma refers to the rare development of an inflammatory, ulcerated, exophytic mass in the gastrointestinal tract that can resemble carcinoma. Typically it presents as a right lower quadrant abdominal mass, Patients may also present with diarrhea or constipation and associated systemic symptoms, including weight loss and fever. In this article we present a young man with a background of ANCA associated vasculitis, who presented with fresh lower gastrointestinal bleeding during hospital admission for severe covid-19 pneumonia which turned out to be caecal aemboma. This case is highlighted for its rarity, the diagnostic challenge, and for the major role of colonoscopy as a diagnostic tool for this pathology.

One-Pot Cascade Annulation-Triggered Synthesis of N-6-Substituted Norcryptotackieine Alkaloids and Evaluation of Their Antileishmanial Activities

Norcryptotackieine or 6H-indolo[2,3-b]quinoline is an indoloquinoline class of alkaloid isolated from Cryptolepis sanguinolenta that is traditionally used for antimalarial therapy. Additional structural tuning can extend the therapeutic potency of these indoloquinolines as antileishmanial drug leads. Synthesis of N-6-functionalized norcryptotackieines suffers from the necessity of complex pre-synthesized starting materials, restricted scope of functionalization, or tedious processes. Consequently, a straightforward synthetic procedure for accessing non-natural N-6-functionalized 6H-indolo[2,3-b]quinolines with potent antileishmanial activities is highly sought-after. Herein, we report a two-step one-pot synthesis of N-6-functionalized norcryptotackieine through a Pd-catalyzed double annulation reaction of commercially available amphipathic amines, 2-iodobenzyl cyanide, and differently functionalized 2-bromobenzaldehydes. The reported procedure allows a broad flexibility of substitution at the N-6 position and access to diversified scaffolds, including two natural products norcryptotackieine and neocryptolepine. Interestingly, 6d showed potent antileishmanial activities by causing disruption in the cytoskeletal structure and apoptotic-mediated death of parasites. Together, our work manifests the shortest route to N-6-substituted norcryptotackieine-derived antileishmanial agents.

In-Vitro Leishmanicidal Activity and Molecular Docking Simulations of a Flavonoid Isolated from Pistacia integerrima Stew ex Brandis

Pistacia integerrima Stew ex Brandis is a valued medicinal plant used for curing various diseases such as diarrhea, fever, liver disorder, pain, asthma, and inflammation. The aim of this study was the isolation of bioactive leishmanicidal agents from the methanolic extract. The methanolic extract led to the isolation of flavonoids 3,5,7,4/-tetrahydroxy-flavanone (1). The extract and isolated compound 1 were tested for antileishmanial effect. The extract showed a percent effect of 63.09 with an IC50 value (49.32 µM). The isolated compound 1 was more leishmanicidal than the extract with a percent growth inhibition of 68.09. We have performed docking studies on two antileishmanial targets; homology modeled dihydrofolate reductase (DHFR) and pteridine reductase (PTR1) from Leishmania major (L. major). Interaction with important residues of the studied enzymes revealed the possible mechanism of in-vitro activity against promastigotes of L. major.

Identification and Characterization of the miRNAs and Cytokines in Response to Leishmania infantum Infection with Different Response to Treatment

PURPOSE

Due to the complexity of cytokine and microRNA function in progression and/or suppression of an infection, in this study, we examined miR-3473f, miR-2128, miR-6994-5p, miR-7093-3p, miR-5128, miR-574-5p, miR-7235, IL-2, IL-4, IL-5, IL-10 and IL-13 in patients with VL caused by Leishmania infantum in an in vivo study.

METHODS

Sampling was carried out from patient with leishmaniasis and with different responses to treatment during March 2016-January 2020. DNA was extracted and purified using QIAamp Kit. The L. infantum were cultured in DMEM medium and protein content was determined by the Micro BCA Protein Assay Kit. Cytokines were evaluated using a MILLIPLEX MAP Mouse Cytokine/Chemokine Panel I kit. The relative expression of miRNAs was measured in duplicate using automatic thermocycler ABI Prism 7500 sequence detection system (Applied Bio-systems) using the TaqMan MicroRNA Assay kit.

RESULTS

The real-time PCR assay revealed that miR-2128, miR-6994-5p, miR-7093-3p, miR-5128, miR-574-5p and miR-7235 were down-regulated and miR-3473 were up-regulated in patients with semi-resistance and resistance parasite strain (P < 0.05). In the current work, cytokine patterns in patients who were slow-to-clear or unable-to-clear L. infantum infection during drug treatment were seen to have decreased protective Th1 cytokines (IL-2, IL-12, TNF-α, and IFN-ɤ, P < 0.001) and increased Th2 cytokines (IL-5, IL-10, and IL-13, P < 0.001). No association was seen with IL-4 in patients with different treatment outcomes.

CONCLUSION

Overall, the results of a recent study have shown that cytokines and microRNAs can play a key role in response to treatment, and more comprehensive studies are needed to support this hypothesis.

In Vitro Antileishmanial and Antitrypanosomal Activities of Plicataloside Isolated from the Leaf Latex of Aloe rugosifolia Gilbert & Sebsebe (Asphodelaceae)

Trypanosomiasis and leishmaniasis are among the major neglected diseases that affect poor people, mainly in developing countries. In Ethiopia, the latex of Aloe rugosifolia Gilbert & Sebsebe is traditionally used for the treatment of protozoal diseases, among others. In this study, the in vitro antitrypanosomal activity of the leaf latex of A. rugosifolia was evaluated against Trypanosoma congolense field isolate using in vitro motility and in vivo infectivity tests. The latex was also tested against the promastigotes of Leishmania aethiopica and L. donovani clinical isolates using alamar blue assay. Preparative thin-layer chromatography of the latex afforded a naphthalene derivative identified as plicataloside (2,8-O,O-di-(β-D-glucopyranosyl)-1,2,8-trihydroxy-3-methyl-naphthalene) by means of spectroscopic techniques (HRESI-MS, ¹H, ¹³C-NMR). Results of the study demonstrated that at 4.0 mg/mL concentration plicataloside arrested mobility of trypanosomes within 30 min of incubation period. Furthermore, plicataloside completely eliminated subsequent infectivity in mice for 30 days at concentrations of 4.0 and 2.0 mg/mL. Plicataloside also displayed antileishmanial activity against the promastigotes of L. aethopica and L. donovani with IC₅₀ values 14.22 ± 0.41 µg/mL (27.66 ± 0.80 µM) and 18.86 ± 0.03 µg/mL (36.69 ± 0.06 µM), respectively. Thus, plicataloside may be used as a scaffold for the development of novel drugs effective against trypanosomiasis and leishmaniasis.

Convenient Synthesis of Alternatively Bridged Tryptophan Ketopiperazines and their Activities Against Trypanosomatid Parasites

There is an urgent need for the development of new treatments against trypanosomatid parasites; the causative agents of some of the most debilitating diseases in the developing world. This work targets an interesting 6-5-6-6 fused carboline scaffold, accessing a range of substituted derivatives through stereospecific intramolecular Pictet-Spengler condensation. Modification of the cyclisation conditions allowed retention of the carbamate protecting group and gave insight into the reaction mechanism. Compounds' bioactivities were measured against T. brucei, T. cruzi, L. majorand HeLa cells. We have identified promising pan-trypanocidal lead compounds based on the core scaffold, and highlight key SAR trends which will be useful for the future development of these compounds as potent trypanocidal agents.

Benzimidazole Derivatives as New and Selective Inhibitors of Arginase from Leishmania mexicana with Biological Activity against Promastigotes and Amastigotes

Leishmaniasis is a disease caused by parasites of the Leishmania genus that affects 98 countries worldwide, 2 million of new cases occur each year and more than 350 million people are at risk. The use of the actual treatments is limited due to toxicity concerns and the apparition of resistance strains. Therefore, there is an urgent necessity to find new drugs for the treatment of this disease. In this context, enzymes from the polyamine biosynthesis pathway, such as arginase, have been considered a good target. In the present work, a chemical library of benzimidazole derivatives was studied performing computational, enzyme kinetics, biological activity, and cytotoxic effect characterization, as well as in silico ADME-Tox predictions, to find new inhibitors for arginase from Leishmania mexicana (LmARG). The results show that the two most potent inhibitors (compounds 1 and 2) have an I₅₀ values of 52 μM and 82 μM, respectively. Moreover, assays with human arginase 1 (HsARG) show that both compounds are selective for LmARG. According to molecular dynamics simulation studies these inhibitors interact with important residues for enzyme catalysis. Biological activity assays demonstrate that both compounds have activity against promastigote and amastigote, and low cytotoxic effect in murine macrophages. Finally, in silico prediction of their ADME-Tox properties suggest that these inhibitors support the characteristics to be considered drug candidates. Altogether, the results reported in our study suggest that the benzimidazole derivatives are an excellent starting point for design new drugs against leishmanisis.

Unravelling the myth surrounding sterol biosynthesis as plausible target for drug design against leishmaniasis

The mortality rate of leishmaniasis is increasing at an alarming rate and is currently second to malaria amongst the other neglected tropical diseases. Unfortunately, many governments and key stakeholders are not investing enough in the development of new therapeutic interventions. The available treatment options targeting different pathways of the parasite have seen inefficiencies, drug resistance, and toxic side effects coupled with longer treatment durations. Numerous studies to understand the biochemistry of leishmaniasis and its pathogenesis have identified druggable targets including ornithine decarboxylase, trypanothione reductase, and pteridine reductase, which are relevant for the survival and growth of the parasites. Another plausible target is the sterol biosynthetic pathway; however, this has not been fully investigated. Sterol biosynthesis is essential for the survival of the Leishmania species because its inhibition could lead to the death of the parasites. This review seeks to evaluate how critical the enzymes involved in sterol biosynthetic pathway are to the survival of the leishmania parasite. The review also highlights both synthetic and natural product compounds with their IC50 values against selected enzymes. Finally, recent advancements in drug design strategies targeting the sterol biosynthesis pathway of Leishmania are discussed.

Role of two aminoacyl-tRNA synthetase associated proteins (Endothelial Monocyte Activating Polypeptides 1 and 2) of Leishmania donovani in chemotaxis of human monocytes

Visceral leishmaniasis is caused by the protozoan parasite Leishmania donovani. It is a fatal form of leishmaniasis prevalent in Indian subcontinent. Since there are no human licensed vaccines available for leishmaniasis, chemotherapeutic drugs remain the only means for combating parasitic infections. We have earlier identified a total of 26 amino-acyl tRNA synthetases (aaRS) along with five stand-alone editing domains and two aaRS-associated proteins in Leishmania donovani. In addition to their canonical role of tRNA aminoacylation, aaRS have been involved in novel functions by acquiring novel domains during evolution. The aaRS-associated proteins have been reported to be analogous to a human cytokine, EMAP II, as they possess a modified version of the heptapeptide motif responsible for the cytokine activity. In this manuscript, we report the characterization of two L. donovani aminoacyl-tRNA synthetase associated proteins which showed a human chemokine like activity. Both the proteins, L. donovani EMAP-1 and EMAP-2, possess a modified form of the heptapeptide motif, which is responsible for cytokine activity in human EMAP-2. LdEMAP-1 and LdEMAP-2 were cloned, expressed, and purified. Both LdEMAP-1 and LdEMAP-2 proteins in the promastigote stage were found to be localized in cytoplasm as confirmed by immunofluorescence. In case of L. donovani infected human THP-1 derived macrophages, secretion of LdEMAP-1 and LdEMAP-2 proteins in the cytosol of the macrophages was observed. The role of LdEMAP-1 and LdEMAP-2 in the aminoacylation of rLdTyrRS was also tested and LdEMAP-2 but not LdEMAP-1 increased the rate of aminoacylation of tyrosyl tRNA synthetase (rLdTyrRS). L. donovani EMAP-1 and EMAP-2 proteins managed to exhibit the capability of attracting human origin cells as determined by chemotaxis assay, and also were able to induce the secretion of cytokines from macrophages like their human counterpart (EMAP II). Our working hypothesis is that both of these proteins might be involved in helping the parasite to establish the infection within the host.

Assay development in leishmaniasis drug discovery: a comprehensive review

INTRODUCTION

Cutaneous, muco-cutaneous and visceral leishmaniasis occur due to an infection with the protozoan parasite Leishmania. The current therapeutic options are limited mainly due to extensive toxicity, emerging resistance and variation in efficacy based on species and strain of the Leishmania parasite. There exists a high unmet medical need to identify new chemical starting points for drug discovery to tackle the disease.

AREAS COVERED

The authors have highlighted the recent progress, limitations and successes achieved in assay development for leishmaniasis drug discovery.

EXPERT OPINION

It is true that sophisticated and robust phenotypic in vitro assays have been developed during the last decade, however limitations and challenges remain with respect to variation in activity reported between different research groups and success in translating in vitro outcomes in vivo. The variability is not only due to strain and species differences but also a lack of well-defined criteria and assay conditions, e.g. culture media, host cell type, assay formats, parasite form used, multiplicity of infection and incubation periods. Thus, there is an urgent need for more physiologically relevant assays that encompass multi-species phenotypic approaches to identify new chemical starting points for leishmaniasis drug discovery.

The Bioactivity of Thiazolidin-4-Ones: A Short Review of the Most Recent Studies

Thiazolidin-4-ones is an important heterocyclic ring system of a pharmacophore and a privileged scaffold in medicinal chemistry. This review is focused on the latest scientific reports regarding biological activities of thiazolidin-4-ones published in 2020 and 2021. The review covers recent information about antioxidant, anticancer, anti-inflammatory, analgesic, anticonvulsant, antidiabetic, antiparasitic, antimicrobial, antitubercular and antiviral properties of thiazolidin-4-ones. Additionally, the influence of different substituents in molecules on their biological activity was discussed in this paper. Thus, this study may help to optimize the structure of thiazolidin-4-one derivatives as more efficient drug agents. Presented information may be used as a practical hint for rational design of new small molecules with biological activity, especially among thiazolidin-4-ones.

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.

Bioprospecting marine actinomycetes for antileishmanial drugs: current perspectives and future prospects

Revived analysis interests in natural products in the hope of discovering new and novel antileishmanial drug leads have been driven partially by the increasing incidence of drug resistance. However, the search for novel chemotherapeutics to combat drug resistance had previously concentrated on the terrestrial environment. As a result, the marine environment was often overlooked. For example, actinomycetes are an immensely important group of bacteria for antibiotic production, producing two-thirds of the known antibiotics. However, these bacteria have been isolated primarily from terrestrial sources. Consequently, there have been revived efforts to discover new compounds from uncharted or uncommon environments like the marine ecosystem. Isolation, purification and structure elucidation of target compounds from complex metabolic extract are major challenges in natural products chemistry. As a result, marine-derived natural products from actinomycetes that have antileishmanial bioactivity potentials have been understudied. This review highlights metagenomic and bioassay approaches which could help streamline the drug discovery process thereby greatly reducing time and cost of dereplication to identify suitable antileishmanial drug candidates.

Influence of N-Methylation and Conformation on Almiramide Anti-Leishmanial Activity

The almiramide N-methylated lipopeptides exhibit promising activity against trypanosomatid parasites. A structure–activity relationship study has been performed to examine the influences of N-methylation and conformation on activity against various strains of leishmaniasis protozoan and on cytotoxicity. The synthesis and biological analysis of twenty-five analogs demonstrated that derivatives with a single methyl group on either the first or fifth residue amide nitrogen exhibited greater activity than the permethylated peptides and relatively high potency against resistant strains. Replacement of amino amide residues in the peptide, by turn inducing α amino γ lactam (Agl) and N-aminoimidazalone (Nai) counterparts, reduced typically anti-parasitic activity; however, peptide amides possessing Agl residues at the second residue retained significant potency in the unmethylated and permethylated series. Systematic study of the effects of methylation and turn geometry on anti-parasitic activity indicated the relevance of an extended conformer about the central residues, and conformational mobility by tertiary amide isomerization and turn geometry at the extremities of the active peptides.

Recent advancements in anti-leishmanial research: Synthetic strategies and structural activity relationships

Leishmaniasis is a parasitic neglected tropical disease caused by various species of Leishmania parasite. Despite tremendous advancements in the therapeutic sector and drug development strategies, still the existing anti-leishmanial agents are associated with some clinical issues like drug resistance, toxicity and selectivity. Therefore, several research groups are continuously working towards the development of new therapeutic candidates to overcome these issues. Many potential heterocyclic moieties have been explored for this purpose including triazoles, chalcones, chromone, thiazoles, thiosemicarbazones, indole, quinolines, etc. It is evident from the literature that the majority of anti-leishmanial agents act by interacting with key regulators including PTR-I, DHFR, LdMetAP1, MAPK, 14 α-demethylase and pteridine reductase-I, etc. Also, these tend to induce the production of ROS which causes damage to parasites. In the present compilation, authors have summarized various significant synthetic procedures for anti-leishmanial agents reported in recent years. A brief description of the pharmacological potentials of synthesized compounds along with important aspects related to structural activity relationship has been provided. Important docking outcomes highlighting the possible mode of interaction for the reported compounds have also been included. This review would be helpful to the scientific community to design newer strategies and also to develop novel therapeutic candidates against leishmaniasis.

Expression in Escherichia coli, purification and kinetic characterization of LAPLm, a Leishmania major M17-aminopeptidase

The Leishmania major leucyl-aminopeptidase (LAPLm), a member of the M17 family of proteases, is a potential drug target for treatment of leishmaniasis. To better characterize enzyme properties, recombinant LAPLm (rLAPLm) was expressed in Escherichia coli. A LAPLm gene was designed, codon-optimized for expression in E. coli, synthesized and cloned into the pET-15b vector. Production of rLAPLm in E. coli Lemo21(DE3), induced for 4 h at 37 °C with 400 μM IPTG and 250 μM l-rhamnose, yielded insoluble enzyme with a low proportion of soluble and active protein, only detected by an anti-His antibody-based western-blot. rLAPLm was purified in a single step by immobilized metal ion affinity chromatography. rLAPLm was obtained with a purity of ~10% and a volumetric yield of 2.5 mg per liter, sufficient for further characterization. The aminopeptidase exhibits optimal activity at pH 7.0 and a substrate preference for Leu-p-nitroanilide (appK_M = 30 μM, appk_cat = 14.7 s^-1). Optimal temperature is 50 °C, and the enzyme is insensitive to 4 mM Co²⁺, Mg²⁺, Ca²⁺ and Ba²⁺. However, rLAPLm was activated by Zn²⁺, Mn²⁺ and Cd²⁺ but is insensitive towards the protease inhibitors PMSF, TLCK, E-64 and pepstatin A, being inhibited by EDTA and bestatin. Bestatin is a potent, non-competitive inhibitor of the enzyme with a K_i value of 994 nM. We suggest that rLAPLm is a suitable target for inhibitor identification.

Eugenia piauhiensis Vellaff. essential oil and γ-elemene its major constituent exhibit antileishmanial activity, promoting cell membrane damage and in vitro immunomodulation

Leishmaniasis is considered as one of the most Neglected Tropical Diseases (NTDs) in the world, caused by protozoan parasites of the genus Leishmania. Treatment of leishmaniasis by chemotherapy remains a challenge because of limited efficacy, toxic side effects, and drug resistance. The search for new therapeutic agents from natural sources has been a constant for the treatment of diseases such as leishmaniasis. The objective of this study was to evaluate the biological activity of Eugenia piauhiensis Vellaff. essential oil (EpEO) and its major constituent γ-elemene on promastigote and amastigote forms of Leishmania (Leishmania) amazonensis, its cytotoxicity, and possible mechanisms of action. EpEO was more active (IC₅₀ 6.43 ± 0.18 μg/mL) against promastigotes than γ-elemene [9.82 ± 0.15 μg/mL (48.05 ± 0.73 μM)] and the reference drug miltefosine [IC₅₀ 17.25 ± 0.26 μg/mL (42.32 ± 0.64 μM)]. EpEO and γ-elemene exhibited low cytotoxicity against J774.A1 macrophages, with CC₅₀ 225.8 ± 3.57 μg/mL and 213.21 ± 3.3 μg/mL (1043 ± 16.15 μM), respectively. Additionally, EpEO and γ-elemene present direct activity against the parasite, decreasing plasma membrane integrity. EpEO and γ-elemene also proved to be even more active against intracellular amastigotes of the parasite [IC₅₀ 4.59 ± 0.07 μg/mL and 8.06 ± 0.12 μg/mL (39.44 ± 0.59 μM)], respectively), presenting indirect effects through macrophage activity modulation. Anti-amastigote activity was associated with increased TNF-α, IL-12, NO, and ROS levels. In conclusion, our results suggest EpEO and γ-elemene as promising candidates for new drug development against leishmaniasis.

Antileishmanial activity of cordiaquinone E towards Leishmania (Leishmania) amazonensis

Leishmaniasis is caused by several protozoan species of Leishmania, and being endemically present in 98 countries around the world, it is also a severe public-health problem. The available antileishmanial drugs are toxic and yet present risks of recurrent infection. Efforts to find new, effective, and safe oral agents for the treatment of leishmaniasis are continuing throughout the world. This work aimed to evaluate the antileishmania activity of cordiaquinone E (CORe), isolated from the roots of Cordia polycephala (Lam.) I. M. Johnston. Cytotoxicity, and possible mechanisms of action against promastigote and amastigote forms of Leishmania amazonensis were examined. CORe was effective in inhibiting promastigote (IC₅₀ 4.5 ± 0.3 µM) and axenic amastigote (IC₅₀ 2.89 ± 0.11 µM) growth in concentrations found non-toxic for the host cell (CC₅₀ 246.81 ± 14.5 µM). Our results revealed that CORe presents direct activity against the parasite, inducing cell death by apoptosis. CORe present greater activity against intracellular amastigotes (EC₅₀ 1.92 ± 0.2 µM), yet with much higher selectivity indexes than the reference drugs, being respectively more benign towards RAW 264.7 macrophages than meglumine antimoniate and amphotericin B, (respectively by 4.68 and 42.84 fold). The antiamastigote activity was associated with increased TNF-α, IL-12, NO, and ROS levels, as well as decreased IL-10 levels. These results encourage the progression of studies on this compound for the development of new leishmanicidal agents.

Cytokine saga in visceral leishmaniasis

In humans, infection with Leishmania manifests into a spectrum of diseases. The manifestation of the diseases depend on the resultant evasion of the parasite to immune responses namely by macrophages, which is an exclusive host of Leishmania. The B cells valiantly mount antibody responses, however, to no avail as the Leishmania parasites occupy the intracellular niches of the macrophages and subvert the immune response. Extensive studies have been documented on the role of cell-mediated immunity (CMI) in protection and counter survival strategies of the parasites leading to downregulation of CMI. The present review attempts to discuss the cytokines in progression or resolution of visceral form of leishmaniasis or kala-azar, predominantly affecting the Indian subcontinent. The components/cytokine(s) responsible for the regulation of the critical balance of T helper cells and their subsets have been discussed in the perspective. Therefore, any strategy involving the treatment of visceral leishmania (VL) needs to consider the balance and regulation of T cell function.

Biogenic nanoparticles: a comprehensive perspective in synthesis, characterization, application and its challenges

BACKGROUND

Translating the conventional scientific concepts into a new robust invention is a much needed one at a present scenario to develop some novel materials with intriguing properties. Particles in nanoscale exhibit superior activity than their bulk counterpart. This unique feature is intensively utilized in physical, chemical, and biological sectors. Each metal is holding unique optical properties that can be utilized to synthesize metallic nanoparticles. At present, versatile nanoparticles were synthesized through chemical and biological methods. Metallic nanoparticles pose numerous scientific merits and have promising industrial applications. But concerning the pros and cons of metallic nanoparticle synthesis methods, researchers elevate to drive the synthesis process of nanoparticles through the utilization of plant resources as a substitute for use of chemicals and reagents under the theme of green chemistry. These synthesized nanoparticles exhibit superior antimicrobial, anticancer, larvicidal, leishmaniasis, wound healing, antioxidant, and as a sensor. Therefore, the utilization of such conceptualized nanoparticles in treating infectious and environmental applications is a warranted one.

CONCLUSION

Green chemistry is a keen prudence method, in which bioresources is used as a template for the synthesis of nanoparticles. Therefore, in this review, we exclusively update the context of plant-based metallic nanoparticle synthesis, characterization, and applications in detailed coverage. Hopefully, our review will be modernizing the recent trends going on in metallic nanoparticles synthesis for the blooming research fraternities.

Modified solid lipid nanoparticles encapsulated with Amphotericin B and Paromomycin: an effective oral combination against experimental murine visceral leishmaniasis

The development of an effective oral therapeutics is an immediate need for the control and elimination of visceral leishmaniasis (VL). We exemplify the preparation and optimization of 2-hydroxypropyl-β-cyclodextrin (HPCD) modified solid lipid nanoparticles (SLNs) based oral combinational cargo system of Amphotericin B (AmB) and Paromomycin (PM) against murine VL. The emulsion solvent evaporation method was employed to prepare HPCD modified dual drug-loaded solid lipid nanoparticles (m-DDSLNs). The optimized formulations have a mean particle size of 141 ± 3.2 nm, a polydispersity index of 0.248 ± 0.11 and entrapment efficiency for AmB and PM was found to be 96% and 90% respectively. The morphology of m-DDSLNs was confirmed by scanning electron microscopy and transmission electron microscopy. The developed formulations revealed a sustained drug release profile upto 57% (AmB) and 21.5% (PM) within 72 h and were stable at both 4 °C and 25 °C during short term stability studies performed for 2 months. Confocal laser scanning microscopy confirmed complete cellular internalization of SLNs within 24 h of incubation. In vitro cytotoxicity study against J774A.1 macrophage cells confirmed the safety and biocompatibility of the developed formulations. Further, m-DDSLNs did not induce any hepatic/renal toxicities in Swiss albino mice. The in vitro simulated study was performed to check the stability in simulated gastric fluids and simulated intestinal fluids and the release was found almost negligible. The in vitro anti-leishmanial activity of m-DDSLNs (1 µg/ml) has shown a maximum percentage of inhibition (96.22%) on intra-cellular amastigote growth of L. donovani. m-DDSLNs (20 mg/kg × 5 days, p.o.) has significantly (P < 0.01) reduced the liver parasite burden as compared to miltefosine (3 mg/kg × 5 days, p.o.) in L. donovani-infected BALB/c mice. This work suggests that the superiority of as-prepared m-DDSLNs as a promising approach towards the oral delivery of anti-leishmanial drugs.

Formulation, characterization and in vitro anti-leishmanial evaluation of amphotericin B loaded solid lipid nanoparticles coated with vitamin B12-stearic acid conjugate

Despite the advancement of new anti-leishmanials, amphotericin B (AmB) prevails as one of the most potent agent in the treatment of visceral leishmaniasis (VL), a neglected tropical disease affecting mostly poverty ridden and underdeveloped regions of the globe. Nonetheless, many patients display intolerance to parenteral AmB, notably at higher dosages. Also, conventional AmB presents an apparently poor absorption. Therefore, to improve AmB bioavailability and overcome multiple barriers for oral delivery of AmB, we fabricated a promising vitamin B₁₂-stearic acid (VBS) conjugate coated solid lipid nanoparticles (SLNs) encapsulated with AmB (VBS-AmB-SLNs) by a combination of double emulsion solvent evaporation and thermal sensitive hydrogel techniques. VBS-AmB-SLNs showed a particle size of 306.66 ± 3.35 nm with polydispersity index of 0.335 ± 0.08 while the encapsulation efficiency and drug loading was observed to be 97.99 ± 1.6% and 38.5 ± 5.6% respectively. In vitro drug release showed a biphasic release pattern and chemical stability of AmB was ensured against simulated gastrointestinal fluids. Cellular uptake studies confirmed complete internalization of the formulation. Anti-leishmanial evaluation against intramacrophage amastigotes showed an enhanced efficacy of 94% which was significantly (P < 0.01) higher than conventional AmB without showing any toxic effects on J774A.1 cells. VBS-AmB-SLNs could serve as a potential therapeutic strategy against VL.

Gold-Silver Bimetallic Nanoparticles Reduced with Herbal Leaf Extracts Induce ROS-Mediated Death in Both Promastigote and Amastigote Stages of Leishmania donovani

Resistance to antileishmanial drugs such as sodium stibogluconate (SSG), amphotericin B (Amp-B), and miltefosine is on the rise, and alternate strategies for effective treatment have gained importance in recent years. Although nanoparticle (NP)-based composite drugs that have emerged recently have been found to be effective, the associated toxicity limits their usage. Bimetallic NPs produced through reduction with medicinal plant extracts are proposed to overcome the toxicity of the NPs. In the present study, three types of gold-silver bimetallic nanoparticles (Au-Ag BNPs) were synthesized through a single-step reduction process using fenugreek, coriander, and soybean leaf extracts. All of the three types of BNPs exhibited high antileishmanial effects against promastigotes with half-inhibitory concentration (IC50) values in the range of 0.03-0.035 μg/mL. The IC50 values of the BNPs are much lower compared to those of miltefosine (IC50 = 10 μg/mL). The synthesized BNPs induced the reactive oxygen species (ROS)-mediated apoptosis-like death in the promastigotes and could potentiate the antileishmanial activity of macrophages. The intracellular amastigotes were reduced by 31-46% in macrophages. The biogenic BNPs synthesized in this study and their potent antileishmanial activity provide further impetus to the ongoing quest for novel drugs to effectively manage leishmaniasis.

Epigenetic regulation of defense genes by histone deacetylase1 in human cell line-derived macrophages promotes intracellular survival of Leishmania donovani

Leishmania donovani, an intracellular protozoan parasite upon infection, encounters a range of antimicrobial factors within the host cells. Consequently, the parasite has evolved mechanisms to evade this hostile defense system through inhibition of macrophage activation that, in turn, enables parasite replication and survival. There is growing evidence that epigenetic down-regulation of the host genome by intracellular pathogens leads to acute infection. Epigenetic modification is mediated by chromatin remodeling, histone modifications, or DNA methylation. Histone deacetylases (HDACs) removes acetyl groups from lysine residues on histones, thereby leading to chromatin remodeling and gene silencing. Here, using L. donovani infected macrophages differentiated from THP-1 human monocytic cells, we report a link between host chromatin modifications, transcription of defense genes and intracellular infection with L. donovani. Infection with L. donovani led to the silencing of host defense gene expression. Histone deacetylase 1 (HDAC1) transcript levels, protein expression, and enzyme activity showed a significant increase upon infection. HDAC1 occupancy at the promoters of the defense genes significantly increased upon infection, which in turn resulted in decreased histone H3 acetylation in infected cells, resulting in the down-regulation of mRNA expression of host defense genes. Small molecule mediated inhibition and siRNA mediated down-regulation of HDAC1 increased the expression levels of host defense genes. Interestingly, in this study, we demonstrate that the silencing of HDAC1 by both siRNA and pharmacological inhibitors resulted in decreased intracellular parasite survival. The present data not only demonstrate that up-regulation of HDAC1 and epigenetic silencing of host cell defense genes is essential for L. donovani infection but also provides novel therapeutic strategies against leishmaniasis.

Determination of anti-leishmanial drugs efficacy against Leishmania martiniquensis using a colorimetric assay

Autochthonous leishmaniasis caused by Leishmania martiniquensis cases in Thailand have dramatically increased in the recent years. L. martiniquensis infection primarily occurs in immunocompromised patients, especially AIDS patients. In Thailand, amphotericin B is the only drug available for leishmaniasis treatment, and some patients relapse after amphotericin B therapy. Moreover, the efficacy of anti-leishmanial drugs against L. martiniquensis has not been evaluated to date. In this study, we determined the efficacy of various anti-leishmanial drugs against the promastigote and intracellular amastigote stages of L. martiniquensis using a colorimetric assay. Two strains (CU1 and CU1R1) were isolated from leishmaniasis HIV co-infected patient from Songkhla province, southern Thailand. The CU1 strain was isolated from the patient in 2011, and CU1R1 was isolated from the same patient in 2013, when he was diagnosed as relapse leishmaniasis. The third strain (LSCM1) used in this study has been isolated from immunocompetent patient from Lamphun province, northern Thailand. All strains were identified as L. martiniquensis by sequencing of ribosomal RNA ITS-1 and large subunit of RNA polymerase II gene. Bioassays have been conducted both with promastigote and intracellular amastigote stages of the parasite. All L. martiniquensis strains have been tested against amphotericin B, miltefosine and pentamidine to determine the efficacy of the drugs against the parasite by using a PrestoBlue. The efficacy of miltefosine and pentamidine exhibit no significant difference between each stage of L. martiniquensis among all strains. Surprisingly, the promastigote and intracellular amastigote of the CU1R1 isolate, which was isolated from a relapsed patient after amphotericin B treatment, exhibited a two-fold increased inhibitory concentration (IC50) against amphotericin B compared with other strains, and the difference was statistically significant (p < 0.05). Moreover, intracellular amastigotes isolated from CU1R1 exhibited slightly increased susceptibility to amphotericin B compared with the promastigote (p < 0.05). The result of this experiment is a scientific evident to support that in case of relapsed leishmaniasis caused by L. martiniquensis, increasing dosage of amphotericin B is essential. Moreover, this study also determined efficacy of other anti-leishmanial drugs for treatment the leishmaniasis in Thailand in case of these drugs are available in the country and the clinicians should have alternative drugs for treatment leishmaniasis in Thailand apart from amphotericin B.

Outwitting an Old Neglected Nemesis: A Review on Leveraging Integrated Data-Driven Approaches to Aid in Unraveling of Leishmanicides of Therapeutic Potential

The global prevalence of leishmaniasis has increased with skyrocketed mortality in the past decade. The causative agent of leishmaniasis is Leishmania species, which infects populations in almost all the continents. Prevailing treatment regimens are consistently inefficient with reported side effects, toxicity and drug resistance. This review complements existing ones by discussing the current state of treatment options, therapeutic bottlenecks including chemoresistance and toxicity, as well as drug targets. It further highlights innovative applications of nanotherapeutics-based formulations, inhibitory potential of leishmanicides, anti-microbial peptides and organometallic compounds on leishmanial species. Moreover, it provides essential insights into recent machine learning-based models that have been used to predict novel leishmanicides and also discusses other new models that could be adopted to develop fast, efficient, robust and novel algorithms to aid in unraveling the next generation of anti-leishmanial drugs. A plethora of enriched functional genomic, proteomic, structural biology, high throughput bioassay and drug-related datasets are currently warehoused in both general and leishmania-specific databases. The warehoused datasets are essential inputs for training and testing algorithms to augment the prediction of biotherapeutic entities. In addition, we demonstrate how pharmacoinformatics techniques including ligand-, structure- and pharmacophore-based virtual screening approaches have been utilized to screen ligand libraries against both modeled and experimentally solved 3D structures of essential drug targets. In the era of data-driven decision-making, we believe that highlighting intricately linked topical issues relevant to leishmanial drug discovery offers a one-stop-shop opportunity to decipher critical literature with the potential to unlock implicit breakthroughs.

Adverse reactions to meglumine antimoniate in Brazilian inpatients with visceral leishmaniases: A case series

WHAT IS KNOWN AND OBJECTIVES

Adverse drug reactions (ADR) related to the treatment of visceral leishmaniasis (VL) can cause severe clinical complications. We report a case series of ADR in hospitalized VL patients on meglumine antimoniate (MA).

CASE DESCRIPTION

Seven cases of patients taking MA had at least one objective evidence for suspected ADR, including electrocardiographic, laboratory or clinical alteration.

WHAT IS NEW AND CONCLUSION

Meglumine antimoniate is highly toxic. Adherence to treatment guidelines is important. Pharmacists working in multidisciplinary teams may contribute to early detection and management of MA therapy-related ADR.

An Overview of Drug Resistance in Protozoal Diseases

Protozoan diseases continue to be a worldwide social and economic health problem. Increased drug resistance, emerging cross resistance, and lack of new drugs with novel mechanisms of action significantly reduce the effectiveness of current antiprotozoal therapies. While drug resistance associated to anti-infective agents is a reality, society seems to remain unaware of its proportions and consequences. Parasites usually develops ingenious and innovative mechanisms to achieve drug resistance, which requires more research and investment to fight it. In this review, drug resistance developed by protozoan parasites Plasmodium, Leishmania, and Trypanosoma will be discussed.

Synthesis and characterization of quinoline-carbaldehyde derivatives as novel inhibitors for leishmanial methionine aminopeptidase 1

Methionine aminopeptidase 1 of Leishmania donovani (LdMetAP1) is a novel antileishmanial target for its role in vital N-terminal methionine processing. After LdMetAP1 expression and purification, we employed a series of biochemical assays to determine optimal conditions for catalysis, metal dependence and substrate preferences for this ubiquitous enzyme. Screening of newly synthesized quinoline-carbaldehyde derivatives in inhibition assays led to the identification of HQ14 and HQ15 as novel and specific inhibitors for LdMetAP1 which compete with substrate for binding to the catalytic active site. Both leads bind LdMetAP1 with high affinity and possess druglikeness. Biochemical studies suggested HQ14 and HQ15 to be comparatively less effective against purified HsMetAP1 and showed no or less toxicity. We further show selectivity and inhibition of lead inhibitors is sensed through a non-catalytic Thr residue unique to LdMetAP1. Finally, structural studies highlight key differences in the binding modes of HQ14 and HQ15 to LdMetAP1 and HsMetAP1 providing structural basis for differences in inhibition. The study demonstrates the feasibility of deploying small drug like molecules to selectively target the catalytic activity of LdMetAP1 which may provide an effective treatment of leishmaniasis.

Biochemical characterization and chemical validation of Leishmania MAP Kinase-3 as a potential drug target

Protozoan parasites of the Leishmania genus have evolved unique signaling pathways that can sense various environmental changes and trigger stage differentiation for survival and host infectivity. MAP kinase (MAPK) plays a critical role in various cellular activities like cell differentiation, proliferation, stress regulation, and apoptosis. The Leishmania donovani MAPK3 (LdMAPK3) is involved in the regulation of flagella length and hence plays an important role in disease transmission. Here, we reported the gene cloning, protein expression, biochemical characterizations, inhibition studies and cell proliferation assay of LdMAPK3. The recombinant purified LdMAPK3 enzyme obeys the Michaelis-Menten equation with K_m and V_max of LdMAPK3 was found to be 20.23 nM and 38.77 ± 0.71 nmoles ATP consumed/mg LdMAPK3/min respectively. The maximum kinase activity of LdMAPK3 was recorded at 35 °C and pH 7. The in-vitro inhibition studies with two natural inhibitors genistein (GEN) and chrysin (CHY) was evaluated against LdMAPK3. The K_i value for GEN and CHY were found to be 3.76 ± 0.28 µM and K_i = 8.75 ± 0.11 µM respectively. The IC₅₀ value for the compounds, GEN and CHY against L. donovani promastigotes were calculated as 9.9 µg/mL and 13 µg/mL respectively. Our study, therefore, reports LdMAPK3 as a new target for therapeutic approach against leishmaniasis.

Environmental Conditions May Shape the Patterns of Genomic Variations in Leishmania panamensis

Due to the absence of transcriptional regulation of gene expression in Leishmania parasites, it is now well accepted that several forms of genomic variations modulate the levels of critical proteins through changes in gene dosage. We previously observed many of these variations in our reference laboratory strain of L. panamensis (PSC-1 strain), including chromosomes with an increased somy and the presence of a putative linear minichromosome derived from chromosome 34. Here, we compared the previously described genomic variations with those occurring after exposure of this strain to increasing concentrations of trivalent antimony (Sb^III), as well as those present in two geographically unrelated clinical isolates of L. panamensis. We observed changes in the somy of several chromosomes, amplifications of several chromosomal regions, and copy number variations in gene arrays after exposure to Sb^III. Occurrence of amplifications potentially beneficial for the Sb-resistant phenotype appears to be associated with the loss of other forms of amplification, such as the linear minichromosome. In contrast, we found no evidence of changes in somy or amplification of relatively large chromosomal regions in the clinical isolates. In these isolates, the predominant amplifications appear to be those that generate genes arrays; however, in many cases, the amplified arrays have a notably higher number of copies than those from the untreated and Sb-treated laboratory samples.

Therapeutic Interventions for Countering Leishmaniasis and Chagas's Disease: From Traditional Sources to Nanotechnological Systems

The incidence of neglected diseases in tropical countries, such as Leishmaniasis and Chagas's disease, is attributed to a set of biological and ecological factors associated with the socioeconomic context of developing countries and with a significant burden to health care systems. Both Leishmaniasis and Chagas's disease are caused by different protozoa and develop diverse symptoms, which depend on the specific species infecting man. Currently available drugs to treat these disorders have limited therapeutic outcomes, frequently due to microorganisms' drug resistance. In recent years, significant efforts have been made towards the development of innovative drug delivery systems aiming to improve bioavailability and pharmacokinetic profiles of classical drug therapy. This paper discusses the key facts of Leishmaniasis and Chagas's disease, the currently available pharmacological therapies and the new drug delivery systems for conventional drugs.

Cytokines: Key Determinants of Resistance or Disease Progression in Visceral Leishmaniasis: Opportunities for Novel Diagnostics and Immunotherapy

Leishmaniasis is a parasitic disease of humans, highly prevalent in parts of the tropics, subtropics, and southern Europe. The disease mainly occurs in three different clinical forms namely cutaneous, mucocutaneous, and visceral leishmaniasis (VL). The VL affects several internal organs and is the deadliest form of the disease. Epidemiology and clinical manifestations of VL are variable based on the vector, parasite (e.g., species, strains, and antigen diversity), host (e.g., genetic background, nutrition, diversity in antigen presentation and immunity) and the environment (e.g., temperature, humidity, and hygiene). Chemotherapy of VL is limited to a few drugs which is expensive and associated with profound toxicity, and could become ineffective due to the parasites developing resistance. Till date, there are no licensed vaccines for humans against leishmaniasis. Recently, immunotherapy has become an attractive strategy as it is cost-effective, causes limited side-effects and do not suffer from the downside of pathogens developing resistance. Among various immunotherapeutic approaches, cytokines (produced by helper T-lymphocytes) based immunotherapy has received great attention especially for drug refractive cases of human VL. Therefore, a comprehensive knowledge on the molecular interactions of immune cells or components and on cytokines interplay in the host defense or pathogenesis is important to determine appropriate immunotherapies for leishmaniasis. Here, we summarized the current understanding of a wide-spectrum of cytokines and their interaction with immune cells that determine the clinical outcome of leishmaniasis. We have also highlighted opportunities for the development of novel diagnostics and intervention therapies for VL.