Apoptosis-like cell death in Leishmania donovani treated with KalsomeTM10, a new liposomal amphotericin B

Buparvaquone Induces Ultrastructural and Physiological Alterations Leading to Mitochondrial Dysfunction and Caspase-Independent Apoptotic Cell Death in Leishmania donovani

Leishmaniasis is a neglected tropical disease (endemic in 99 countries) caused by parasitic protozoa of the genus Leishmania. As treatment options are limited, there is an unmet need for new drugs. The hydroxynaphthoquinone class of compounds demonstrates broad-spectrum activity against protozoan parasites. Buparvaquone (BPQ), a member of this class, is the only drug licensed for the treatment of theileriosis. BPQ has shown promising antileishmanial activity but its mode of action is largely unknown. The aim of this study was to evaluate the ultrastructural and physiological effects of BPQ for elucidating the mechanisms underlying the in vitro antiproliferative activity in Leishmania donovani. Transmission and scanning electron microscopy analyses of BPQ-treated parasites revealed ultrastructural effects characteristic of apoptosis-like cell death, which include alterations in the nucleus, mitochondrion, kinetoplast, flagella, and the flagellar pocket. Using flow cytometry, laser scanning confocal microscopy, and fluorometry, we found that BPQ induced caspase-independent apoptosis-like cell death by losing plasma membrane phospholipid asymmetry and cell cycle arrest at sub-G0/G1 phase. Depolarization of the mitochondrial membrane leads to the generation of oxidative stress and impaired ATP synthesis followed by disruption of intracellular calcium homeostasis. Collectively, these findings provide valuable mechanistic insights and demonstrate BPQ's potential for development as an antileishmanial agent.

Pyridoxal kinase gene deletion leads to impaired growth, deranged redox metabolism and cell cycle arrest in Leishmania donovani

Pyridoxal kinase (PdxK) is a vitamin B6 salvage pathway enzyme which produces pyridoxal phosphate. We have investigated the impact of PdxK deletion in Leishmania donovani on parasite survivability, infectivity and cellular metabolism. LdPdxK mutants were generated by gene replacement strategy. All mutants showed significant reduction in growth in comparison to wild type. For PdxK mediated biochemical perturbations, only heterozygous mutants and complementation mutants were used as the growth of null mutants were compromised. Heterozygous mutant showed reduction invitro infectivity and higher cytosolic and mitochondrial ROS levels. Glutathione levels decreased significantly in heterozygous mutant indicating its involvement in cellular oxidative metabolism. Pyridoxal kinase gene deletion resulted in reduced ATP levels in parasites and arrest at G0/G1 phase of cell cycle. All these perturbations were rescued by PdxK gene complementation. This is the first report to confirm that LdPdxK plays an indispensable role in cell survival, pathogenicity, redox metabolism and cell cycle progression of L. donovani parasites. These results provide substantial evidence supporting PdxK as a therapeutic target for the development of specific antileishmanial drug candidates.

In Vitro Leishmanicidal Activity of Copaiba Oil and Kojic Acid Combination on the Protozoan Leishmania (Leishmania) amazonensis and Host Cell

(1) Background: Leishmaniasis refers to a group of anthropozoonotic diseases caused by Leishmania. The major chemotherapeutic agent used for its treatment is Glucantime®®, but the search continues for new compounds that are economically viable and act on the protozoan without causing damage to the host cell. As an alternative approach, this study used a combination of copaiba oil (CO) and kojic acid (KA) to determine their in vitro action on host cells, on the Leishmania (Leishmania) amazonensis protozoan and its interaction with macrophages. (2) Methods: In vitro culture, analysis of cytokine release and microscopy assays were performed. Statistical analysis was performed with ANOVA (GraphPad Prism). (3) Results: The combination did not induce cytotoxic effects on macrophages after treatment but promoted morphological changes in the protozoan, such as nuclear alterations (apoptotic characteristics), alterations in the cellular body and an increase in the number of electrodense structures and acidocalcisomes, observed mainly at the concentrations of CO20KA50 and CO30KA50 μg/mL. We observed reductions in the intracellular amastigote number and in the production of proinflammatory cytokines, such as IL-6 and TNF-α, after treatment with CO30KA at 50 µg/mL. (4) Conclusions: We report here, for the first time, that the combination of CO and KA may be a promising approach against Leishmania (Leishmania) amazonensis.

Prosopis juliflora (Sw.) DC.induces apoptotic-like programmed cell death in Leishmania donovani via over production of oxidative stress, mitochondrial dysfunction and ATP depletion

Background

Leishmaniasis is endemic in more than 60 countries with a large number of mortality cases. The current chemotherapy approaches employed for managing the leishmaniasis is associated with severe side effects. Therefore there is a need to develop effective, safe, and cost affordable antileishmanial drug candidates.

Purpose of the study

This study was designed to evaluate the in vitro antileishmanial activity of a Prosopis juliflora leaves extract (PJLME) towards the Leishmania donovani parasites.

Material and methods

PJLME was evaluated for its cytotoxicity against the L. donovani parasites and the mouse macrophage cells. Further, various in vitro experiments like ROS assay, mitochondrial membrane potential assay, annexin v assay, cell cycle assay, and caspase 3/7 assay were performed to understand the mechanism of cell death. Phytochemical profiling of P. juliflorawas performed by utilizing HPTLC and GC-MS analysis.

Results

PJLME demonstrated antileishmanial activity at a remarkably lower concentration of IC50 6.5 μg/mL. Of note, interestingly PJLME IC50 concentration has not demonstrated cytotoxicity against the mouse macrophage cell line. Performed experiments confirmed ROS inducing potential of PJLME which adversely affected the mitochondrial membrane potential and caused loss of mitochondrial membrane potential and thereby ATP levels. PJLME also arrested the cell cycle and induced apoptotic-like cell death in PJLME treated L. donovani promastigotes.

Conclusion

The results clearly established the significance of Prosopis juliflora as an effective and safe natural resource for managing visceral leishmaniasis. The findings can be used as a baseline reference for developing novel leads/formulations for effective management of visceral leishmaniasis.

Antileishmanial activity of 2-amino-thiophene derivative SB-200

Leishmaniasis, presenting the highest number of cases worldwide is one of the most serious Neglected Tropical Diseases (NTDs). Clinical manifestations are intrinsically related to the host's immune response making immunomodulatory substances the target of numerous studies on antileishmanial activity. The currently available drugs used for treatment present various problems including high toxicity, low efficacy, and associated drug resistance. The search for therapeutic alternatives is urgent, and in this context, thiophene derivatives appear to be a promising therapeutic alternative (many have shown promising anti-leishmanial activity). The objective of this study was to investigate the antileishmanial activity of the 2-amino-thiophenic derivative SB-200. The thiophenic derivative was effective in inhibiting the growth of Leishmania braziliensis, Leishmania major, and Leishmania infantum promastigotes, obtaining respective IC50 values of 4.25 μM, 4.65 μM, and 3.96 μM. For L. infantum, it was demonstrated that the antipromastigote effect of SB-200 is associated with cell membrane integrity losses, and with morphological changes observed during scanning and transmission electron microscopy. Cytotoxicity was performed for J774.A1 macrophages and VERO cells, to obtain a CC50 of 42.52 μM and a SI of 10.74 for macrophages and a CC50 of 39.2 μM and an SI of 9.89 for VERO cells. The anti-amastigote activity of SB-200 revealed an IC50 of 2.85 μM and an SI of 14.97 against macrophages and SI of 13.8 for VERO cells. The anti-amastigote activity of SB-200 is associated with in vitro immunomodulation. For acute toxicity, SB-200 against Zophobas morio larvae permitted 100% survival. We conclude that the 2-amino-thiophenic derivative SB-200 is a promising candidate for in vivo anti-leishmania drug tests to evaluate its activity, efficacy, and safety.

The Antileishmanial Activity of Eugenol Associated with Lipid Storage Reduction Rather Than Membrane Properties Alterations

Leishmaniasis is a neglected tropical disease that still infects thousands of people per year throughout the world. The occurrence of resistance against major treatments for this disease causes a healthcare burden in low-income countries. Eugenol is a phenylpropanoid that has shown in vitro antileishmanial activity against Leishmania mexicana mexicana (Lmm) promastigotes with an IC₅₀ of 2.72 µg/mL and a high selectivity index. Its specific mechanism of action has yet to be studied. We prepared large unilamellar vesicles (LUVs), mimicking Lmm membranes, and observed that eugenol induced an increase in membrane permeability and a decrease in membrane fluidity at concentrations much higher than IC₅₀. The effect of eugenol was similar to the current therapeutic antibiotic, amphotericin B, although the latter was effective at lower concentrations than eugenol. However, unlike amphotericin B, eugenol also affected the permeability of LUVs without sterol. Its effect on the membrane fluidity of Lmm showed that at high concentrations (≥22.5× IC₅₀), eugenol increased membrane fluidity by 20-30%, while no effect was observed at lower concentrations. Furthermore, at concentrations below 10× IC₅₀, a decrease in metabolic activity associated with the maintenance of membrane integrity revealed a leishmaniostatic effect after 24 h of incubation with Lmm promastigotes. While acidocalcisomes distribution and abundance revealed by Trypanosoma brucei vacuolar H⁺ pyrophosphatase (TbVP1) immunolabeling was not modified by eugenol, a dose-dependent decrease of lipid droplets assessed by the Nile Red assay was observed. We hereby demonstrate that the antileishmanial activity of eugenol might not directly involve plasma membrane sterols such as ergosterol, but rather target the lipid storage of Lmm.

Natural products derived steroids as potential anti-leishmanial agents; disease prevalence, underlying mechanisms and future perspectives

Leishmaniasis is a vector-borne infection caused by protozoan parasites from the genus leishmania and is among the most neglected tropical diseases. It is highly prevalent disease, affecting about 350 million population worldwide. Only limited number of anti-leishmanial agents are approved for clinical use till now and they are associated with side effects and have limited efficacy. Subsequently, natural products based discovery of more safe and effective drugs against leishmania is under scientific consideration. Various studies reported the efficacy of natural products against intracellular and extracellular forms of leishmania species. This work is aimed to evaluate current literature focused on the anti-leihmanial efficacy of steroidal moieties from natural products and their mechanism of action. Compounds including steroidal saponins, steroidal alkaloids and phytosterols were found to exhibit considerable anti-leishmanial efficacy. For instance, steroidal saponin, (25R)-spirost-5-en-3b-ol,3-O-α-rhamnopyranosyl-(1 → 4)-α-rhamnopyranosyl-(1 → 4)-[a-rhamnopyranosyl-(1 → 2)]-glucopyranoside isolated from A. paradoxum has completely eradicated Leishmania major promastigotes at 50 µg mL-1 dose. Spirostanic saponins isolated from Solanum paniculatum L. were effective against Leishmania amazonensis promastigotes. Turgidosterones isolated from Panicum turgidum exhibited high leishmanicidal potentials against Leishmania donovani promastigotes with IC50 of 4.95-8.03 µg mL-1 and even better activity against amastigotes exhibiting an IC50 of 4.50-9.29 µg mL-1. Likewise, racemoside-A from Asparagus racemosus was found effective against an antimonial sensitive (AG83) and antimonial resistant (GE1F8R) strains of the L. donovani. Moreover, steroidal alkaloids including hookerianamide-1, hookerianamide-H, hookerianamide-J, hookerianamide-K, dehydrosarsalignone, vagenine-A, sarcovagine-C, holaphylline, saracodine, holamine, 15-α hydroxyholamine, holacurtin, N-desmethyl holacurtine and elasticine has exhibited time and dose-dependent efficacy against various strains of leishmania. β-sitosterol was found active against multiple strains of leishmania. These compounds mainly exhibit their therapeutic efficacy via liberation of ROS, mitochondrial depolarization, morphological and ultra-structural changes, accumulation of lipid droplets, depletion of non-protein thiols and triggering apoptotic pathways. In conclusion, leishmaniasis is a major health problem in many countries. Plants-derived steroids moieties have reveled efficacy against leishmaniasis and is a source of lead compounds. Further detailed molecular studies are warranted for the discovery of more effective and safe anti-leishmanial drugs.

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.

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

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

Leishmanicidal Activity of Guanidine Derivatives against Leishmania infantum

Leishmaniasis is a neglected tropical infectious disease with thousands of cases annually; it is of great concern to global health, particularly the most severe form, visceral leishmaniasis. Visceral leishmaniasis treatments are minimal and have severe adverse effects. As guanidine-bearing compounds have shown antimicrobial activity, we analyzed the cytotoxic effects of several guanidine-bearing compounds on Leishmania infantum in their promastigote and amastigote forms in vitro, their cytotoxicity in human cells, and their impact on reactive nitrogen species production. LQOFG-2, LQOFG-6, and LQOFG-7 had IC50 values of 12.7, 24.4, and 23.6 µM, respectively, in promastigotes. These compounds exhibited cytotoxicity in axenic amastigotes at 26.1, 21.1, and 18.6 µM, respectively. The compounds showed no apparent cytotoxicity in cells from healthy donors. To identify mechanisms of action, we evaluated cell death processes by annexin V and propidium iodide staining and nitrite production. Guanidine-containing compounds caused a significant percentage of death by apoptosis in amastigotes. Independent of L. infantum infection, LQOFG-7 increased nitrite production in peripheral blood mononuclear cells, which suggests a potential mechanism of action for this compound. Therefore, these data suggest that guanidine derivatives are potential anti-microbial molecules, and further research is needed to fully understand their mechanism of action, especially in anti-leishmanial studies.

Mannosylated imiquimod-terbinafine co-loaded transethosomes for cutaneous leishmaniasis; assessment of its anti-leishmanial potential, in vivo safety and immune response modulation

Current treatment options for cutaneous leishmaniasis are associated with myriad limiting factors including low penetration, poor efficacy, and drug toxicities. Herein, we reported imiquimod and terbinafine co-loaded mannosylated transethosomes (IMQ-TER-MTES) with enhanced cutaneous retention, macrophage targeting, anti-leishmanial potential, and dermal immunomodulation. IMQ-TER-MTES were optimized using Design Expert® followed by their loading into chitosan gel. Moreover, the antileishmanial response against amastigotes-infected macrophages and Leishmania-infected BALB/c mice was evaluated. Finally, the safety and immunomodulation activity of IMQ-TER-MTES gel was performed using BALB/c mice. Optimized IMQ-TER-MTES showed nano-sized particles with low poly-dispersibility index (PDI) and high drug entrapment. Mannosylation has augmented macrophage targeting and the internalization capability of TES. IMQ-TER-MTES showed significantly reduced IC₅₀ value (19.56 ± 3.62 μg/ml), higher selectivity index (29.24), and synergism against Leishmania major (L. major) amastigotes. In L. major infected BALB/c mice, the cutaneous lesion healing potential of IMQ-TER-MTES was also elevated with reduced lesion size (1.52 ± 0.43 mm). Superior safety of IMQ-TER-MTES was observed in BALB/c mice along with adequate stimulation of dermal immune cells, in contrast to the ALDARA®. Moreover, incremented Nuclear factor Kappa-β (NF-κβ) and nitric oxide (NO) biosynthesis were observed with IMQ-TER-MTES.

Ecotin: A versatile protease inhibitor of bacteria and eukaryotes

Serine protease inhibitors are a large family of proteins involved in important pathways and processes, such as inflammatory responses and blood clotting. Most are characterized by a precise mode of action, thereby targeting a narrow range of protease substrates. However, the serine-protease inhibitor ecotin is able to inhibit a broad range of serine proteases that display a wide range of specificities. This specificity is driven by special structural features which allow unique flexibility upon binding to targets. Although frequently observed in many human/animal-associated bacteria, ecotin homologs may also be found in plant-associated taxa and environmental species. The purpose of this review is to provide an update on the biological importance, role in host-microbe interactions, and evolutionary relationship between ecotin orthologs isolated from Eukaryotic and Prokaryotic species across the Tree of Life.

Amphotericin B Nano-Assemblies Circumvent Intrinsic Toxicity and Ensure Superior Protection in Experimental Visceral Leishmaniasis with Feeble Toxic Manifestation

In spite of its high effectiveness in the treatment of both leishmaniasis as well as a range of fungal infections, the free form of the polyene antibiotic amphotericin B (AmB) does not entertain the status of the most preferred drug of choice in clinical settings. The high intrinsic toxicity of the principal drug could be considered the main impedance in the frequent medicinal use of this otherwise very effective antimicrobial agent. Taking into consideration this fact, the pharma industry has introduced many novel dosage forms of AmB to alleviate its toxicity issues. However, the limited production, high cost, requirement for a strict cold chain, and need for parenteral administration are some of the limitations that explicitly compel professionals to look for the development of an alternate dosage form of this important drug. Considering the fact that the nano-size dimensions of drug formulation play an important role in increasing the efficacy of the core drug, we employed a green method for the development of nano-assemblies of AmB (AmB-NA). The as-synthesized AmB-NA manifests desirable pharmacokinetics in the treated animals. The possible mechanistic insight suggested that as-synthesized AmB-NA induces necrosis-mediated cell death and severe mitochondrial dysfunction in L. donovani promastigotes by triggering depolarization of mitochondrial membrane potential. In vivo studies demonstrate a noticeable decline in parasite burden in the spleen, liver, and bone marrow of the experimental BALB/c mice host. In addition to successfully suppressing the Leishmania donovani, the as-formed AmB-NA formulation also modulates the host immune system with predominant Th1 polarization, a key immune defender that facilitates the killing of the intracellular parasite.

Asian Ancistrocladus Lianas as Creative Producers of Naphthylisoquinoline Alkaloids

This book describes a unique class of secondary metabolites, the mono- and dimeric naphthylisoquinoline alkaloids. They occur in lianas of the paleotropical Ancistrocladaceae and Dioncophyllaceae families, exclusively. Their unprecedented structures include stereogenic centers and rotationally hindered, and thus likewise stereogenic, axes. Extended recent investigations on six Ancistrocladus species from Asia, as reported in this review, shed light on their fascinating phytochemical productivity, with over 100 such intriguing natural products. This high chemodiversity arises from a likewise unique biosynthesis from acetate-malonate units, following a novel polyketidic pathway to plant-derived isoquinoline alkaloids. Some of the compounds show most promising antiparasitic activities. Likewise presented are strategies for the regio- and stereoselective total synthesis of the alkaloids, including the directed construction of the chiral axis.

Limitations of current chemotherapy and future of nanoformulation-based AmB delivery for visceral leishmaniasis-An updated review

Visceral leishmaniasis (VL) is the most lethal of all leishmaniasis diseasesand the second most common parasiticdisease after malaria and,still, categorized as a neglected tropical disease (NTD). According to the latest WHO study, >20 Leishmania species spread 0.7-1.0 million new cases of leishmaniasis each year. VL is caused by the genus, Leishmania donovani (LD), which affects between 50,000 and 90,000 people worldwide each year. Lack of new drug development, increasing drug resistance, toxicity and high cost even with the first line of treatmentof Amphotericin B (AmB), demands new formulation for treatment of VLFurther the lack of a vaccine, allowedthe researchers to develop nanofomulation-based AmB for improved delivery. The limitation of AmB is its kidney and liver toxicity which forced the development of costly liposomal AmB (AmBisome) nanoformulation. Success of AmBisome have inspired and attracted a wide range of AmB nanoformulations ranging from polymeric, solid lipid, liposomal/micellar, metallic, macrophage receptor-targetednanoparticles (NP) and even with sophisticated carbon/quantum dot-based AmBnano delivery systems. Notably, NP-based AmB delivery has shown increased efficacy due to increased uptake, on-target delivery and synergistic impact of NP and AmB. In this review, we have discussed the different forms of leishmaniasis disease and their current treatment options with limitations. The discovery, mechanism of action of AmB, clinical status of AmB and improvement with AmBisome over fungizone (AmB-deoxycholate)for VL treatment was further discussed. At last, the development of various AmB nanoformulation was discussed along with its adavantages over traditional chemotherapy-based delivery.

Mechanistic insight into the role of mevalonate kinase by a natural fatty acid-mediated killing of Leishmania donovani

We evaluated the anti-leishmanial efficacy of different saturated medium-chain fatty acids (FAs, C8–C18) where FA containing C8 chain, caprylic acid (CA), was found to be most potent against Leishmania donovani, the causative agent for visceral leishmaniasis (VL). Different analogs of CA with C8 linear chain, but not higher, along with a carboxyl/ester group showed a similar anti-leishmanial effect. Ergosterol depletion was the major cause of CA-mediated cell death. Molecular docking and molecular dynamic simulation studies indicated the enzyme mevalonate kinase (MevK) of the ergosterol biosynthesis pathway as a possible target of CA. Enzyme assays with purified recombinant MevK and CA/CA analogs confirmed the target with a competitive inhibition pattern. Using biochemical and biophysical studies; strong binding interaction between MevK and CA/CA analogs was established. Further, using parasites with overexpressed MevK and proteomics studies of CA-treated parasites the direct role of MevK as the target was validated. We established the mechanism of the antileishmanial effect of CA, a natural product, against VL where toxicity and drug resistance with current chemotherapeutics demand an alternative. This is the first report on the identification of an enzymatic target with kinetic parameters and mechanistic insights against any organism for a natural medium-chain FA.

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

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

- Amphotericin B: A drug of choice for Visceral Leishmaniasis

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

The Pathogenicity and Virulence of Leishmania - interplay of virulence factors with host defenses

Leishmaniasis is a group of disease caused by the intracellular protozoan parasite of the genus Leishmania. Infection by different species of Leishmania results in various host immune responses, which usually lead to parasite clearance and may also contribute to pathogenesis and, hence, increasing the complexity of the disease. Interestingly, the parasite tends to reside within the unfriendly environment of the macrophages and has evolved various survival strategies to evade or modulate host immune defense. This can be attributed to the array of virulence factors of the vicious parasite, which target important host functioning and machineries. This review encompasses a holistic overview of leishmanial virulence factors, their role in assisting parasite-mediated evasion of host defense weaponries, and modulating epigenetic landscapes of host immune regulatory genes. Furthermore, the review also discusses the diagnostic potential of various leishmanial virulence factors and the advent of immunomodulators as futuristic antileishmanial drug therapy.

HO-3867 Induces ROS-Dependent Stress Response and Apoptotic Cell Death in Leishmania donovani

Lack of vaccine and increasing chemotherapeutic toxicities currently necessitate the development of effective and safe drugs against various forms of leishmaniases. We characterized the cellular stress induced by a novel curcumin analogue, HO-3867, encapsulated within the phosphatidylcholine-stearylamine (PC-SA) liposome for the first time against Leishmania. The liposomal formulation of HO-3867 (i.e., PC-SA/HO-3867) initiated oxidative stress-induced apoptosis in L. donovani, revealed by altered cell morphology, phosphatidylserine externalization, mitochondrial depolarization, intracellular lipid accumulation, and cell cycle arrest in promastigotes. Liposomal HO-3867 was observed to be a strong apoptosis inducer in L. donovani and L. major in a dose-dependent manner, yet completely safe for normal murine macrophages. Moreover, PC-SA/HO-3867 treatment induced L. donovani metacaspase and PARP1 activation along with downregulation of the Sir2 gene. PC-SA/HO-3867 arrested intracellular L. donovani amastigote burden in vitro, with reactive oxygen species (ROS) and nitric oxide (NO)-mediated parasite killing. These data suggest that liposomal HO-3867 represents a highly promising and non-toxic nanoparticle-based therapeutic platform against leishmaniasis inspiring further preclinical developments.

Sesamol Induces Apoptosis-Like Cell Death in Leishmania donovani

Background

Visceral leishmaniasis (VL), caused by the protozoan parasite Leishmania donovani (L. donovani), is the most severe form of leishmaniasis. It is largely responsible for significant morbidity and mortality in tropical and subtropical countries. Currently, available therapeutics have lots of limitations including high-cost, adverse side-effects, painful route of administration, less efficacy, and resistance. Therefore, it is time to search for cheap and effective antileishmanial agents. In the present work, we evaluated the antileishmanial potential of sesamol against promastigotes as well as intracellular amastigotes. Further, we tried to work out its mechanism of antileishmanial action on parasites through different assays.

Methodology

In vitro and ex vivo antileishmanial assays were performed to evaluate the antileishmanial potential of sesamol on L. donovani. Cytotoxicity was determined by MTT assay on human THP-1-derived macrophages. Sesamol-induced morphological and ultrastructural changes were determined by electron microscopy. H₂DCFDA staining, JC-1dye staining, and MitoSOX red staining were performed for reactive oxygen assay (ROS), mitochondrial membrane potential, and mitochondrial superoxide, respectively. Annexin V/PI staining for apoptosis, TUNEL assay, and DNA laddering for studying sesamol-induced DNA fragmentation were performed.

Conclusions

Sesamol inhibited the growth and proliferation of L. donovani promastigotes in a dose-dependent manner. It also reduced the intracellular parasite load without causing significant toxicity on host-macrophages. Overall, it showed antileishmanial effects through induction of ROS, mitochondrial dysfunction, DNA fragmentation, cell cycle arrest, and apoptosis-like cell death to parasites. Our results suggested the possible use of sesamol for the treatment of leishmaniasis after further in vivo validations.

Embilica officinalis L. inhibits the growth and proliferation of Leishmania donovani through the induction of ultrastructural changes, mitochondrial dysfunction, oxidative stress and apoptosis-like cell death

Visceral leishmaniasis (VL) is caused by a protozoan parasite, Leishmania donovani (L. donovani). It affects around 1-2 million people around the world annually. There is an urgent need to investigate new medicament of it due to difficult method of drug administration, long period of treatment, high cost of the drug, adverse side-effects, low efficacy and development of parasite resistance to the available drugs. Medicinal plants have also been used for the treatment of different diseases in traditional system of medicines due to their holistic effects. The Drugs for Neglected Diseases initiative (DNDi), Geneva, Switzerland has already started the program for identification of potential medicinal plant and plant products having antileishmanial potential. Keeping all these in consideration, we planned to study the antileishmanial activity of one of the medicinal plant, Embilica officinalis L. (EO) fruit extract. EO fruit extract inhibited the growth and proliferation of promastigotes as well as intra-macrophagic amastigotes in dose-dependent manner. EO fruit extract induced morphological and ultrastructural changes in parasites as observed under Electron Microscope. It also induced the oxidative stress, mitochondrial dysfunction, DNA laddering and apotosis-like cell death in parasites. Here, we for the first time reported such a detailed mechanism of action of antileishmanial activity of EO fruit extract. Our results suggested that EO fruit extract could be used for the development of new phytomedicine against leishmaniasis.

Larval excretion/secretion of dipters of Lucilia cuprina species induces death in promastigote and amastigote forms of Leishmania amazonensis

Leishmaniasis is a neglected tropical disease that affects millions of people around the world. Larval excretion/secretion (ES) of the larvae of flies of the Calliphoridae family has microbicidal activity against Gram-positive and Gram-negative bacteria, in addition to some species of Leishmania. Our study aimed at assessing the in vitro efficacy of Lucilia cuprina larval ES against the promastigote and amastigote forms of Leishmania amazonensis, elucidating possible microbicidal mechanisms and routes of death involved. Larval ES was able to inhibit the viability of L. amazonensis at all concentrations, induce morphological and ultrastructural changes in the parasite, retraction of the cell body, roughness of the cytoplasmic membrane, leakage of intracellular content, ROS production increase, induction of membrane depolarization, and mitochondrial swelling, the formation of cytoplasmic lipid droplets and phosphatidylserine exposure, thus indicating the possibility of apoptosis-like death. To verify the efficacy of larval ES on amastigote forms, we performed a phagocytic assay, measurement of total ROS, and NO. Treatment using larval ES reduced the percentage of infection and the number of amastigotes per macrophage of lineage J774A.1 at all concentrations, increasing the production of ROS and TNF-α, thus indicating possible pro-inflammatory immunomodulation and oxidative damage. Therefore, treatment using larval ES is effective at inducing the death of promastigotes and amastigotes of L. amazonensis even at low concentrations.

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.

In Vitro, In Vivo and In Silico Effectiveness of LASSBio-1386, an N-Acyl Hydrazone Derivative Phosphodiesterase-4 Inhibitor, Against Leishmania amazonensis

Leishmaniasis are group of neglected diseases with worldwide distribution that affect about 12 million people. The current treatment is limited and may cause severe adverse effects, and thus, the search for new drugs more effective and less toxic is relevant. We have previously investigated the immunomodulatory effects of LASSBio-1386, an N-acylhydrazone derivative. Here we investigated the in vitro and in vivo activity of LASSBio-1386 against L. amazonensis. LASSBio-1386 inhibited the proliferation of promastigotes of L. amazonensis (EC₅₀ = 2.4 ± 0.48 µM), while presenting low cytotoxicity to macrophages (CC₅₀ = 74.1 ± 2.9 µM). In vitro incubation with LASSBio-1386 reduced the percentage of Leishmania-infected macrophages and the number of intracellular parasites (EC₅₀ = 9.42 ± 0.64 µM). Also, in vivo treatment of BALB/c mice infected with L. amazonensis resulted in a decrease of lesion size, parasitic load and caused histopathological alterations, when compared to vehicle-treated control. Moreover, LASSBio-1386 caused ultrastructural changes, arrested cell cycle in G0/G1 phase and did not alter the membrane mitochondrial potential of L. amazonensis. Aiming to its possible molecular interactions, we performed docking and molecular dynamics studies on Leishmania phosphodiesterase B1 (PDB code: 2R8Q) and LASSBio-1386. The computational analyses suggest that LASSBio-1386 acts against Leishmania through the modulation of leishmanial PDE activity. In conclusion, our results indicate that LASSBio-1386 is a promising candidate for the development of new leishmaniasis treatment.

Total Phenolic Fraction (TPF) from Extra Virgin Olive Oil: Induction of apoptotic-like cell death in Leishmania spp. promastigotes and in vivo potential of therapeutic immunomodulation

BACKGROUND

Leishmaniasis is a serious multifactorial parasitic disease with limited treatment options. Current chemotherapy is mainly consisted of drugs with serious drawbacks such as toxicity, variable efficacy and resistance. Alternative bioactive phytocompounds may provide a promising source for discovering new anti-leishmanial drugs. Extra Virgin Olive Oil (EVOO), a key-product in the Mediterranean diet, is rich in phenols which are associated with anti-inflammatory, anti-cancer and anti-microbial effects. In this study, we investigate the anti-leishmanial effect of Total Phenolic Fraction (TPF) derived from EVOO in both in vitro and in vivo systems by investigating the contributing mechanism of action.

METHODOLOGY/PRINCIPAL FINDINGS

We tested the ability of TPF to cause apoptotic-like programmed cell death in L. infantum and L. major exponential-phase promastigotes by evaluating several apoptotic indices, such as reduction of proliferation rate, sub-G0/G1 phase cell cycle arrest, phosphatidylserine externalization, mitochondrial transmembrane potential disruption and increased ROS production, by using flow cytometry and microscopy techniques. Moreover, we assessed the therapeutic effect of TPF in L. major-infected BALB/c mice by determining skin lesions, parasite burden in popliteal lymph nodes, Leishmania-specific antibodies and biomarkers of tissue site cellular immune response, five weeks post-treatment termination. Our results show that TPF triggers cell-cycle arrest and apoptotic-like changes in Leishmania spp. promastigotes. Moreover, TPF treatment induces significant reduction of parasite burden in draining lymph nodes together with an antibody profile indicative of the polarization of Th1/Th2 immune balance towards the protective Th1-type response, characterized by the presence of IFN-γ-producing CD4+ T-cells and increased Tbx21/GATA-3 gene expression ratio in splenocytes.

CONCLUSIONS/SIGNIFICANCE

TPF exhibits chemotherapeutic anti-leishmanial activity by inducing programmed cell death on cell-free promastigotes and immunomodulatory properties that induce in vivo T cell-mediated responses towards the protective Th1 response in experimental cutaneous leishmaniasis. These findings enable deeper understanding of TPF's dual mode of action that encourages further studies.

Bioassay-based Corchorus capsularis L. leaf-derived β-sitosterol exerts antileishmanial effects against Leishmania donovani by targeting trypanothione reductase

Leishmaniasis, a major neglected tropical disease, affects millions of individuals worldwide. Among the various clinical forms, visceral leishmaniasis (VL) is the deadliest. Current antileishmanial drugs exhibit toxicity- and resistance-related issues. Therefore, advanced chemotherapeutic alternatives are in demand, and currently, plant sources are considered preferable choices. Our previous report has shown that the chloroform extract of Corchorus capsularis L. leaves exhibits a significant effect against Leishmania donovani promastigotes. In the current study, bioassay-guided fractionation results for Corchorus capsularis L. leaf-derived β-sitosterol (β-sitosterol_CCL) were observed by spectroscopic analysis (FTIR, ¹H NMR, ¹³C NMR and GC–MS). The inhibitory efficacy of this β-sitosterol_CCL against L. donovani promastigotes was measured (IC₅₀ = 17.7 ± 0.43 µg/ml). β-Sitosterol_CCL significantly disrupts the redox balance via intracellular ROS production, which triggers various apoptotic events, such as structural alteration, increased storage of lipid bodies, mitochondrial membrane depolarization, externalization of phosphatidylserine and non-protein thiol depletion, in promastigotes. Additionally, the antileishmanial activity of β-sitosterol_CCL was validated by enzyme inhibition and an in silico study in which β-sitosterol_CCL was found to inhibit Leishmania donovani trypanothione reductase (LdTryR). Overall, β-sitosterol_CCL appears to be a novel inhibitor of LdTryR and might represent a successful approach for treatment of VL in the future.

4-nitrochalcone exerts leishmanicidal effect on L. amazonensis promastigotes and intracellular amastigotes, and the 4-nitrochalcone encapsulation in beeswax copaiba oil nanoparticles reduces macrophages cytotoxicity

The Leishmaniasis treatment currently available involves some difficulties, such as high toxicity, variable efficacy, high cost, therefore, it is crucial to search for new therapeutic alternatives. Over the past few years, research on new drugs has focused on the use of natural compounds such as chalcones and nanotechnology. In this context, this research aimed at assessing the in vitro leishmanicidal activity of free 4-nitrochalcone (4NC) on promastigotes and encapsulated 4NC on L. amazonensis-infected macrophages, as well as their action mechanisms. Free 4NC was able to reduce the viability of promastigotes, induce reactive oxygen species production, decrease mitochondrial membrane potential, increase plasma membrane permeability, and expose phosphatidylserine, in addition to altering the morphology and lowering parasite cellular volume. Treatment containing encapsulated 4NC in beeswax-copaiba oil nanoparticles (4NC-beeswax-CO Nps) did not alter the viability of macrophages. Furthermore, 4NC-beeswax-CO Nps reduced the percentage of infected macrophages and the number of amastigotes per macrophages, increasing the production of reactive oxygen species, NO, TNF-α, and IL-10. Therefore, free 4NC proved to exert anti-promastigote effect, while 4NC-beeswax-CO Nps showed a leishmanicidal effect on L. amazonensis-infected macrophages by activating the macrophage microbicidal machinery.

Preincubation with a low-dose hydrogen peroxide enhances anti-oxidative stress ability of BMSCs

Objective

To investigate the effects of low-concentration hydrogen peroxide pretreatment on the anti-oxidative stress of the bone marrow mesenchymal stem cells (BMSCs).

Methods

Rabbit BMSCs were isolated and cultured by density gradient centrifugation combined with the adherence method. Then, the third generation of well-grown BMSCs was continuously treated with 50-μM hydrogen peroxide (H₂O₂) for 8 h as the optimal pretreatment concentration and the BMSCs were continuously applied for 24 h with 500 μM H₂O₂, and the optimal damage concentration was determined as the oxidative stress cell model. The experiment was divided into three groups: control group, high-concentration H₂O₂ injury group (500 μM), and low-concentration H₂O₂ pretreatment group (50 μM + 500 μM). In each group, the DCFH-DA fluorescence probe was used to detect the reactive oxygen species (ROS). ELISA was used to detect the activity of superoxide dismutase (SOD) and catalase (CAT), and the TBA method was used to detect malondialdehyde (MDA). The mitochondrial membrane potential was detected by JC-1. The cell viability was detected by CCK-8 method, while flow cytometry and TUNEL/DAPI double staining were performed to detect cell apoptosis. Hence, the effect of H₂O₂ pretreatment on the anti-oxidative stress of BMSCs was investigated. One-way analysis of variance was performed using SPSS 19.0 statistical software, and P < 0.05 was considered statistically significant.

Results

A large number of typical BMSCs were obtained by density gradient centrifugation and adherent culture. The oxidative stress cell model was successfully established by 500-μM H₂O₂. Compared with the high-concentration H₂O₂ injury group, the low-concentration H₂O₂ pretreatment reduced the production of ROS [(62.33 ± 5.05), P < 0.05], SOD and CAT activities significantly increased (P < 0.05), and MDA levels significantly decreased (P < 0.05). The mitochondrial membrane potential fluorescence changes, the ratio of red/green fluorescence intensity of the high-concentration H₂O₂ injury group was less, and the ratio of the low-concentration H₂O₂ pretreatment group was significantly higher than that. The ratio of red/green increased by about 1.8 times (P < 0.05). The cell viability and survival rate of BMSCs were significantly increased in low-concentration H₂O₂ pretreatment group (P < 0.05), and the cell apoptosis rate was significantly decreased (P < 0.05).

Conclusion

Pretreatment with low-concentration H₂O₂ can enhance the anti-oxidative stress ability and reduce their apoptosis of BMSCs under oxidative stress.

In vivo experiments demonstrate the potent antileishmanial efficacy of repurposed suramin in visceral leishmaniasis

BACKGROUND

Treatment failure and resistance to the commonly used drugs remains a major obstacle for successful chemotherapy against visceral leishmaniasis (VL). Since the development of novel therapeutics involves exorbitant costs, the effectiveness of the currently available antitrypanosomatid drug suramin has been investigated as an antileishmanial, specifically for VL,in vitro and in animal model experiments.

METHODOLOGY/PRINCIPAL

Leishmania donovani promastigotes were treated with suramin and studies were performed to determine the extent and mode of cell mortality, cell cycle arrest and other in vitro parameters. In addition, L. donovani infected BALB/c mice were administered suramin and a host of immunological parameters determined to estimate the antileishmanial potency of the drug. Finally, isothermal titration calorimetry (ITC) and enzymatic assays were used to probe the interaction of the drug with one of its putative targets namely parasitic phosphoglycerate kinase (LmPGK).

FINDINGS

The in vitro studies revealed the potential efficacy of suramin against the Leishmania parasite. This observation was further substantiated in the in vivo murine model, which demonstrated that upon suramin administration, the Leishmania infected BALB/c mice were able to reduce the parasitic burden and also generate the host protective immunological responses. ITC and enzyme assays confirmed the binding and consequent inhibition of LmPGK due to the drug.

CONCLUSIONS/SIGNIFICANCE

All experiments affirmed the efficacy of suramin against L. donovani infection, which could possibly lead to its inclusion in the repertoire of drugs against VL.

Tolnaftate inhibits ergosterol production and impacts cell viability of Leishmania sp

Leishmaniasis is an infectious disease caused by protozoan parasites of the genus Leishmania. The treatment of all forms of leishmaniasis relies on first-line drug, pentavalent antimonial, and in cases of drug failure, the second-line drug amphotericin B has been used. Besides the high toxicity of drugs, parasites can be resistant to antimonial in some areas of the World, making it necessary to perform further studies for the characterization of new antileishmanial agents. Thus, the aim of the present work was to evaluate the leishmanicidal activity of tolnaftate, a selective reversible and non-competitive inhibitor of the fungal enzyme squalene epoxidase, which is involved in the biosynthesis of ergosterol, essential to maintain membrane physiology in fungi as well as trypanosomatids. Tolnaftate eliminated promastigote forms of L. (L.) amazonensis, L. (V.) braziliensis and L. (L.) infantum (EC₅₀ ~ 10 μg/mL and SI ~ 20 for all leishmanial species), and intracellular amastigote forms of all studied species (EC₅₀ ~ 23 μg/mL in infections caused by dermatotropic species; and 11.7 μg/mL in infection caused by viscerotropic species) with high selectivity toward parasites [SI ~ 8 in infections caused by dermatotropic species and 17.4 for viscerotropic specie]. Promastigote forms of L. (L.) amazonensis treated with the EC₅₀ of tolnaftate displayed morphological and physiological changes in the mitochondria and cell membrane. Additionally, promastigote forms treated with tolnaftate EC₅₀ reduced the level of ergosterol by 5.6 times in comparison to the control parasites. Altogether, these results suggest that tolnaftate has leishmanicidal activity towards Leishmania sp., is selective, affects the cell membrane and mitochondria of parasites and, moreover, inhibits ergosterol production in L. (L.) amazonensis.

Experimental and Theoretical Studies of Novel Azo Benzene Functionalized Conjugated Polymers: In-vitro Antileishmanial Activity and Bioimaging

To study the effect of insertion of azobenzene moiety on the spectral, morphological and fluorescence properties of conventional conducting polymers, the present work reports ultrasound-assisted polymerization of azobenzene with aniline, 1-naphthylamine, luminol and o-phenylenediamine. The chemical structure and polymerization was established via Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (1H-NMR) spectroscopy, while the electronic properties were explored via ultraviolet-visible (UV-vis) spectroscopy. Theoretical IR and UV spectra were computed using DFT/B3LYP method with 6-311G basis set while theoretical 1H-NMR spectra was obtained by gauge independent atomic orbital (GIAO) method. The theoretically computed spectra were found to be in close agreement with the experimental findings confirming the chemical as well as electronic structure of the synthesized polymers. Morphology was investigated by X-ray diffraction and transmission electron microscopy studies. Fluorescence studies revealed emission ranging between 530-570 nm. The polymers also revealed high singlet oxygen (1O2) generation characteristics. In-vitro antileishmanial efficacy as well as live cell imaging investigations reflected the potential application of these polymers in the treatment of leishmaniasis and its diagnosis.

Lipid Systems for the Delivery of Amphotericin B in Antifungal Therapy

Amphotericin B (AmB), a broad-spectrum polyene antibiotic in the clinic for more than fifty years, remains the gold standard in the treatment of life-threatening invasive fungal infections and visceral leishmaniasis. Due to its poor water solubility and membrane permeability, AmB is conventionally formulated with deoxycholate as a micellar suspension for intravenous administration, but severe infusion-related side effects and nephrotoxicity hamper its therapeutic potential. Lipid-based formulations, such as liposomal AmB, have been developed which significantly reduce the toxic side effects of the drug. However, their high cost and the need for parenteral administration limit their widespread use. Therefore, delivery systems that can retain or even enhance antimicrobial efficacy while simultaneously reducing AmB adverse events are an active area of research. Among those, lipid systems have been extensively investigated due to the high affinity of AmB for binding lipids. The development of a safe and cost-effective oral formulation able to improve drug accessibility would be a major breakthrough, and several lipid systems for the oral delivery of AmB are currently under development. This review summarizes recent advances in lipid-based systems for targeted delivery of AmB focusing on non-parenteral nanoparticulate formulations mainly investigated over the last five years and highlighting those that are currently in clinical trials.

Synthesis, characterization, and mechanistic studies of a gold nanoparticle-amphotericin B covalent conjugate with enhanced antileishmanial efficacy and reduced cytotoxicity

Background

Amphotericin B (AmB) as a liposomal formulation of AmBisome is the first line of treatment for the disease, visceral leishmaniasis, caused by the parasite Leishmania donovani. However, nephrotoxicity is very common due to poor water solubility and aggregation of AmB. This study aimed to develop a water-soluble covalent conjugate of gold nanoparticle (GNP) with AmB for improved antileishmanial efficacy and reduced cytotoxicity.

Methods

Citrate-reduced GNPs (~39 nm) were functionalized with lipoic acid (LA), and the product GNP-LA (GL ~46 nm) was covalently conjugated with AmB using carboxyl-to-amine coupling chemistry to produce GNP-LA-AmB (GL-AmB ~48 nm). The nanoparticles were characterized by dynamic light scattering, transmission electron microscopy (TEM), and spectroscopic (ultraviolet–visible and infrared) methods. Experiments on AmB uptake of macrophages, ergosterol depletion of drug-treated parasites, cytokine ELISA, fluorescence anisotropy, flow cytometry, and gene expression studies established efficacy of GL-AmB over standard AmB.

Results

Infrared spectroscopy confirmed the presence of a covalent amide bond in the conjugate. TEM images showed uniform size with smooth surfaces of GL-AmB nanoparticles. Efficiency of AmB conjugation was ~78%. Incubation in serum for 72 h showed <7% AmB release, indicating high stability of conjugate GL-AmB. GL-AmB with AmB equivalents showed ~5-fold enhanced antileishmanial activity compared with AmB against parasite-infected macrophages ex vivo. Macrophages treated with GL-AmB showed increased immunostimulatory T_h1 (IL-12 and interferon-γ) response compared with standard AmB. In parallel, AmB uptake was ~5.5 and ~3.7-fold higher for GL-AmB-treated (P<0.001) macrophages within 1 and 2 h of treatment, respectively. The ergosterol content in GL-AmB-treated parasites was ~2-fold reduced compared with AmB-treated parasites. Moreover, GL-AmB was significantly less cytotoxic and hemolytic than AmB (P<0.01).

Conclusion

GNP-based delivery of AmB can be a better, cheaper, and safer alternative than available AmB formulations.

Natural compounds from plants controlling leishmanial growth via DNA damage and inhibiting trypanothione reductase and trypanothione synthetase: an in vitro and in silico approach

In the present study, four different natural compounds including quercetin, gallic acid, rutin, and lupeol were studied for their anti-leishmanial potentials with anticipated mechanism of action through in vitro and in silico approaches. Results showed that rutin was exceedingly active (IC₅₀; 91.2 µg/ml) against the promastigote form of Leishmania tropica compared to quercetin (IC₅₀; 182.3 µg/ml), gallic acid (IC₅₀; 198.00 µg/ml) and lupeol (IC₅₀; 200.77 µg/ml). Similarly, rutin was highly active against the amastigote form as well, followed by quercetin, gallic acid and lupeol with IC₅₀ values of 101.3 µg/ml, 137.4 µg/ml, 277.2 µg/ml, and 298.9 µg/ml, respectively. These compounds were found to be nontoxic to human blood erythrocytes even at the highest concentration (1000 µg/ml) tested. Rutin and lupeol showed promising DNA degradation/fragmentation activity against the DNA of treated promastigotes which increased with the increase in concentration of the compounds. The in silico investigation revealed that these ligands have high affinity with the important catalytic residues of trypanothione reductase (Try-R) where, rutin showed the lowest docking score (i.e., - 6.191) followed by lupeol (- 5.799), gallic acid and quercetin. In case of ligands' interaction with trypanothione synthetase (Try-S), rutin again showed highest interaction with docking score of - 6.601 followed by quercetin (- 4.996), lupeol and gallic acid. The ADMET prediction of these compounds showed that all the parameters were within the acceptable range as defined for human use while molecular dynamics simulation supported the good interaction of quercetin and rutin against both enzymes. These findings suggest that the studied compounds may control leishmanial growth via DNA damage and inhibiting Try-R and Try-S, the two unique but critical enzymes for leishmania growth.

Metacaspases: Potential Drug Target Against Protozoan Parasites

Among the numerous strategies/targets for controlling infectious diseases, parasites-derived proteases receive prime attention due to their essential contribution to parasite growth and development. Parasites produce a broad array of proteases, which are required for parasite entry/invasion, modification/degradation of host proteins for their nourishment, and activation of inflammation that ensures their survival to maintain infection. Presently, extensive research is focused on unique proteases termed as "metacaspases" (MCAs) in relation to their versatile functions in plants and non-metazoans. Such unique MCAs proteases could be considered as a potential drug target against parasites due to their absence in the human host. MCAs are cysteine proteases, having Cys-His catalytic dyad present in fungi, protozoa, and plants. Studies so far indicated that MCAs are broadly associated with apoptosis-like cell death, growth, and stress regulation in different protozoa. The present review comprises the important research outcomes from our group and published literature, showing the variable properties and function of MCAs for therapeutic purpose against infectious diseases.

Activity and Cell-Death Pathway in Leishmania infantum Induced by Sugiol: Vectorization Using Yeast Cell Wall Particles Obtained From Saccharomyces cerevisiae

Visceral leishmaniasis, caused by Leishmania infantum, is a neglected tropical disease, to which efforts in the innovation of effective and affordable treatments remain limited, despite the rising incidence in several regions of the world. In this work, the antileishmanial effects of sugiol were investigated in vitro. This compound was isolated from the bark of Cupressus lusitanica and showed promising activity against L. infantum. In spite of the positive results, it is known that the compound is a poorly water-soluble diterpene molecule, which hinders further investigation, especially in preclinical animal studies. Thus, in an alternative delivery method, sugiol was entrapped in glucan-rich particles obtained from Saccharomyces cerevisiae yeast cell walls (YCWPs). To evaluate the activity of sugiol, the experiments were divided into two parts: (i) the in vitro investigation of antileishmanial activity of free sugiol against L. infantum promastigotes after 24, 48, and 72 h of treatment and (ii) the evaluation of antileishmanial activity of sugiol entrapped in glucan-rich particles against intracellular L. infantum amastigotes. Free sugiol induced the cell-death process in promastigotes, which was triggered by enhancing cytosolic calcium level and promoting the autophagy up to the first 24 h. Over time, the presence of autophagic vacuoles became rarer, especially after treatment with lower concentrations of sugiol, but other cellular events intensified, like ROS production, cell shrinkage, and phosphatidylserine exposure. Hyperpolarization of mitochondrial membrane potential was found at 72 h, induced by the mitochondria calcium uptake, causing an increase in ROS production and lipid peroxidation as a consequence. These events resulted in the cell death of promastigotes by secondary necrosis. Sugiol entrapped in glucan-rich particles was specifically recognized by dectin-1 receptor on the plasma membrane of macrophages, the main host cell of Leishmania spp. Electron micrographs revealed particles containing sugiol within the infected macrophages and these particles were active against the intracellular L. infantum amastigotes without affecting the host cell. Therefore, the YCWPs act like a Trojan horse to successfully deliver sugiol into the macrophage, presenting an interesting strategy to deliver water-insoluble drugs to parasitized cells.

Synthesis, Biological Evaluation, Structure-Activity Relationship, and Mechanism of Action Studies of Quinoline-Metronidazole Derivatives Against Experimental Visceral Leishmaniasis

In our efforts to identify novel chemical scaffolds for the development of antileishmanial agents, a series of quinoline-metronidazole hybrid compounds was synthesized and tested against the murine model of visceral leishmaniasis. Among all synthesized derivatives, 15b and 15i showed significant antileishmanial efficacy against both extracellular promastigote (IC₅₀ 9.54 and 5.42 μM, respectively) and intracellular amastigote (IC₅₀ 9.81 and 3.75 μM, respectively) forms of Leishmania donovani with negligible cytotoxicity toward the host (J774 macrophages, Vero cells). However, compound 15i effectively inhibited the parasite burden in the liver and spleen (>80%) of infected BALB/c mice. Mechanistic studies revealed that 15i triggers oxidative stress which induces bioenergetic collapse and apoptosis of the parasite by decreasing ATP production and mitochondrial membrane potential. Structure-activity analyses and pharmacokinetic studies suggest 15i as a promising antileishmanial lead and emphasize the importance of quinoline-metronidazole series as a suitable platform for the future development of antileishmanial agents.

EB1-3 Chain of IL-35 Along With TGF-β Synergistically Regulate Anti-leishmanial Immunity

Immunosuppression is a characteristic feature of chronic leishmaniasis. The dynamicity and the functional cross talks of host immune responses during Leishmania infection are still not clearly understood. Here we explored the functional aspects of accumulation of immune suppressive cellular and cytokine milieu during the progression of murine visceral leishmaniasis. In addition to IL-10 and TGF-β, investigation on the responses of different subunit chains of IL-12 family revealed a progressive elevation of EBI-3 and p35 chains of IL-35 with Leishmania donovani infection in BALB/c mice. The expansion of CD25 and FoxP3 positive T cells is associated with loss of IFN-γ and TNF-α response in advanced disease. Ex-vivo and in vivo neutralization of TGF-β and EBI-3 suggests a synergism in suppression of host anti-leishmanial immunity. The down-regulation of EBI-3 and TGF-β is crucial for re-activation of JAK-STAT pathway for induction as well as restoration of protective immunity against L. donovani infection.

Increased ROS generation causes apoptosis-like death: Mechanistic insights into the anti-Leishmania activity of a potent ruthenium(II) complex

Some metallodrugs that exhibit interesting biological activity contain transition metals such as ruthenium, and have been extensively exploited because of their antiparasitic potential. In previous study, we reported the remarkable anti-Leishmania activity of precursor cis-[Ru^IICl₂(dppm)₂], where dppm = bis(diphenylphosphino)methane, and new ruthenium(II) complexes, cis-[Ru^II(η²-O₂CC₁₀H₁₃)(dppm)₂]PF₆ (bbato), cis-[Ru^II(η²-O₂CC₇H₇S)(dppm)²]PF⁶ (mtbato) and cis-[Ru^II(η²-O₂CC₇H₇O₂)(dppm)₂]PF₆ (hmxbato) against some Leishmania species. In view of the promising activity of the hmxbato complex against Leishmania (Leishmania) amazonensis promastigotes, the present work investigated the possible parasite death mechanism involved in the action of this hmxbato and its precursor. We report, for the first time, that hmxbato and precursor promoted an increase in reactive oxygen species production, depolarization of the mitochondrial membrane, DNA fragmentation, formation of a pre-apoptotic peak, alterations in parasite morphology and formation of autophagic vacuoles. Taken together, our results suggest that these ruthenium complexes cause parasite death by apoptosis. Thus, this work provides relevant knowledge on the activity of ruthenium(II) complexes against L. (L.) amazonensis. Such information will be essential for the exploitation of these complexes as future candidates for cutaneous leishmaniasis treatment.

Evaluation of the in vitro and in vivo antileishmanial activity of a chloroquinolin derivative against Leishmania species capable of causing tegumentary and visceral leishmaniasis

The treatment against leishmaniasis presents problems, since the currently used drugs are toxic and/or have high costs. In addition, parasite resistance has increased. As a consequence, in this study, a chloroquinolin derivative, namely 7-chloro-N,N-dimethylquinolin-4-amine or GF1059, was in vitro and in vivo tested against Leishmania parasites. Experiments were performed to evaluate in vitro antileishmanial activity and cytotoxicity, as well as the treatment of infected macrophages and the inhibition of infection using pre-treated parasites. This study also investigated the GF1059 mechanism of action in L. amazonensis. Results showed that the compound was highly effective against L. infantum and L. amazonensis, presenting a selectivity index of 154.6 and 86.4, respectively, against promastigotes and of 137.6 and 74.3, respectively, against amastigotes. GF1059 was also effective in the treatment of infected macrophages and inhibited the infection of these cells when parasites were pre-incubated with it. The molecule also induced changes in the parasites' mitochondrial membrane potential and cell integrity, and caused an increase in the reactive oxygen species production in L. amazonensis. Experiments performed in BALB/c mice, which had been previously infected with L. amazonensis promastigotes, and thus treated with GF1059, showed that these animals presented significant reductions in the parasite load when the infected tissue, spleen, liver, and draining lymph node were evaluated. GF1059-treated mice presented both lower parasitism and low levels of enzymatic markers, as compared to those receiving amphotericin B, which was used as control. In conclusion, data suggested that GF1059 can be considered a possible therapeutic target to be tested against leishmaniasis.

Disassembly of dying cells in diverse organisms

Programmed cell death (PCD) is a conserved phenomenon in multicellular organisms required to maintain homeostasis. Among the regulated cell death pathways, apoptosis is a well-described form of PCD in mammalian cells. One of the characteristic features of apoptosis is the change in cellular morphology, often leading to the fragmentation of the cell into smaller membrane-bound vesicles through a process called apoptotic cell disassembly. Interestingly, some of these morphological changes and cell disassembly are also noted in cells of other organisms including plants, fungi and protists while undergoing 'apoptosis-like PCD'. This review will describe morphologic features leading to apoptotic cell disassembly, as well as its regulation and function in mammalian cells. The occurrence of cell disassembly during cell death in other organisms namely zebrafish, fly and worm, as well as in other eukaryotic cells will also be discussed.

Berberine chloride mediates its antileishmanial activity by inhibiting Leishmania mitochondria

Berberine chloride, a plant-derived isoquinoline alkaloid, has been demonstrated to have leishmanicidal activity, which is mediated by generation of a redox imbalance and depolarization of the mitochondrial membrane, resulting in a caspase-independent apoptotic-like cell death. However, its impact on mitochondrial function remains to be delineated and is the focus of this study. In UR6 promastigotes, berberine chloride demonstrated a dose-dependent increase in generation of reactive oxygen species and mitochondrial superoxide, depolarization of the mitochondrial membrane potential, a dose-dependent inhibition of mitochondrial complexes I-III and II-III, along with a substantial depletion of ATP, collectively suggesting inhibition of parasite mitochondria. Accordingly, the oxidative stress induced by berberine chloride resulting in an apoptotic-like cell death in Leishmania can be exploited as a potent chemotherapeutic strategy, mitochondria being a prime contributor.

The leishmanicidal activity of artemisinin is mediated by cleavage of the endoperoxide bridge and mitochondrial dysfunction

Endoperoxides kill malaria parasites via cleavage of their endoperoxide bridge by haem or iron, leading to generation of cytotoxic oxygen-centred radicals. In view of the Leishmania parasites having a relatively compromised anti-oxidant defense and high iron content, this study aims to establish the underlying mechanism(s) accounting for the apoptotic-like death of Leishmania promastigotes by artemisinin, an endoperoxide. The formation of reactive oxygen species was confirmed by flow cytometry and was accompanied by inhibition of mitochondrial complexes I-III and II-III. However, this did not translate into a generation of mitochondrial superoxide or decrease in oxygen consumption, indicating minimal impairment of the electron transport chain. Artemisinin caused depolarization of the mitochondrial membrane along with a substantial depletion of adenosine triphosphatase (ATP), but it was not accompanied by enhancement of ATP hydrolysis. Collectively, the endoperoxide-mediated radical formation by artemisinin in Leishmania promastigotes was the key step for triggering its antileishmanial activity, leading secondarily to mitochondrial dysfunction indicating that endoperoxides represent a promising therapeutic strategy against Leishmania worthy of pharmacological consideration.

Leishmania phosphatase PP5 is a regulator of HSP83 phosphorylation and essential for parasite pathogenicity

Leishmania parasites are responsible for important neglected diseases in humans and animals, ranging from self-healing cutaneous lesions to fatal visceral manifestations. During the infectious cycle, Leishmania differentiates from the extracellular flagellated promastigote to the intracellular pathogenic amastigote. Parasite differentiation is triggered by changes in environmental cues, mainly pH and temperature. In general, extracellular signals are translated into stage-specific gene expression by a cascade of reversible protein phosphorylation regulated by protein kinases and phosphatases. Though protein kinases have been actively studied as potential anti-parasitic drug targets, our understanding of the biology of protein phosphatases in Leishmania is poor. We have previously reported the principal analysis of a novel protein phosphatase 5 (PP5) in Leishmania species. Here, we assessed the role of PP5 in parasite pathogenicity, where we uncovered, using transgenic PP5 over-expressing and PP5 null-mutant parasites, its importance in metacyclogeneisis, maintaining HSP83 phosphorylation homeostasis and virulence. All together, our results indicate the importance of PP5 in regulating parasite stress and adaptation during differentiation, making this protein an attractive potential target for therapeutic intervention.

Tannins Enriched Fraction of Emblica officinalis Fruits Alleviates High-Salt and Cholesterol Diet-Induced Cognitive Impairment in Rats via Nrf2-ARE Pathway

Modern diets containing high quantities of salt and cholesterol have exhibited to cause a considerable effect on our health. Such diets, when consumed in the long term, have also shown to be a precursor to several disorders such as the metabolic disorder and consequently, various other diseases, including cognitive deficits. In the present study, we used a high salt and cholesterol diet (HSCD) to induce cognitive impairment in rats and also investigated the pharmacological action of tannins enriched fractions of Emblica officinalis (EOT) – a fruit that has been traditionally used for the treatment of numerous disorders for centuries. Significant alterations in MDA, GSH, TBARS, GPx, mitochondrial ATP, and mitochondrial membrane potential levels were observed in rats fed HSCD, which indicated presence of oxidative stress. Moreover, classic signs of cognitive impairment and deficits in spatial learning and memory were observed in the neurobehavioral tests. E. officinalis tannins exhibited good affinity to Nrf2 receptors in in silico studies, significantly reversed the changes in the aforementioned biomarkers of oxidative stress which were altered in the model group, as well as improved the performance of rats in Morris water maze task. Our results also reflected that EOT supplementation significantly increased the expression of Nrf2 in the CA1 region of hippocampus and cortex. Additionally, TUNEL assay indicated that EOT supplementation led to reversal of DNA fragmentation and apoptosis caused by HSCD. Immunohistochemical analysis and western blot further revealed a surge in the nuclear location of Nrf2. Through our study, we have demonstrated that cognitive impairment can be caused in rats via HSCD as a result of the oxidative stress induced by the same. Additionally, we have investigated a novel mechanism of action for EOT (which strongly suggests to be via the Nrf2–ARE pathway) and demonstrated that it has the potential to be used in the treatment of cognitive impairment.