Activation of artemisinin and heme degradation in Leishmania tarentolae promastigotes: A possible link

Artemisinin: An Anti-Leishmania Drug that Targets the Leishmania Parasite and Activates Apoptosis of Infected Cells

Leishmaniasis is a relevant disease worldwide due to its presence in many countries and an estimated prevalence of 10 million people. The causative agent of this disease is the obligate intracellular parasite Leishmania which can infect different cell types. Part of its success depends on its ability to evade host defense mechanisms such as apoptosis. Apoptosis is a finely programmed process of cell death in which cells silently dismantle and actively participate in several processes such as immune response, differentiation, and cell growth. Leishmania has the ability to delay its initiation to persist in the cell. It has been well documented that different Leishmania species target different pathways that lead to apoptosis of cells such as macrophages, neutrophils, and dendritic cells. In many cases, the observed anti-apoptotic effect has been associated with a significant reduction in caspase-3 activity. Leishmania has also been shown to target several pathways involved in apoptosis such as MAPK, PI3K/Akt, and the antiapoptotic protein Bcl-xL. Understanding the strategies used by Leishmania to subvert the defense mechanisms of host cells, particularly apoptosis, is very relevant for the development of therapies and vaccines. In recent years, the drug artemisinin has been shown to be effective against several parasitic diseases. Its role against Leishmania may be promising. In this review, we provide important aspects of the disease, the strategies used by the parasite to suppress apoptosis, and the role of artemisinin in Leishmania infection.

Synergistic Effects of Artesunate in Combination with Amphotericin B and Miltefosine against Leishmania infantum: Potential for Dose Reduction and Enhanced Therapeutic Strategies

Leishmaniasis is a tropical infectious disease caused by Leishmania parasites. The disease can be spread by the bite of an infected sand fly. Currently, five chemotherapeutic drugs are available in leishmaniasis treatment. However, these drugs exhibit toxicity and serious adverse effects on infected individuals, necessitating alternative treatment strategies. One such strategy involves using combinations of existing antileishmanial drugs. In this study, we evaluated the interaction between artesunate (AS) and three antileishmanial drugs-amphotericin B (AmB), miltefosine (MF), and paromomycin (PM) against Leishmania infantum. This evaluation marks the first time such an assessment has been conducted. The Chou-Talalay combination index method was employed to analyze the drug interaction. The findings revealed that the interaction between AS and AmB ranged from antagonistic to synergistic, while the interaction between AS and MF showed moderate to strong synergism. In contrast, the interaction between AS and PM resulted in an antagonistic interaction, which differs from the combinations with AmB or MF. This study provides valuable insights for developing novel drug regimens for leishmaniasis treatment, emphasizing the potential of AS and its combination with existing antileishmanial drugs. Further research is necessary to optimize drug combinations and minimize adverse effects, leading to more effective therapeutic outcomes.

Natural endoperoxides as promising anti-leishmanials

BACKGROUND

The discovery of artemisinin, an endoperoxide, encouraged the scientific community to explore endoperoxides as potential anti-parasitic molecules. Although artemisinin derivatives are rapidly evolving as potent anti-malarials, their potential as anti-leishmanials is emerging gradually. The treatment of leishmaniasis, a group of neglected tropical diseases is handicapped by lack of effective vaccines, drug toxicities and drug resistance. The weak antioxidant defense mechanism of the Leishmania parasites due to lack of catalase and a selenium dependent glutathione peroxidase system makes them vulnerable to oxidative stress, and this has been successful exploited by endoperoxides.

PURPOSE

The study aimed to review the available literature on the anti-leishmanial efficacy of natural endoperoxides with a view to achieve insights into their mode of actions.

METHODS

We reviewed more around 110 research and review articles restricted to the English language, sourced from electronic bibliographic databases including PubMed, Google, Web of Science, Google scholar etc. RESULTS: Natural endoperoxides could potentially augment the anti-leishmanial drug library, with artemisinin and ascaridole emerging as potential anti-leishmanial agents. Due to higher reactivity of the cyclic peroxide moiety, and exploiting the compromised antioxidant defense of Leishmania, endoperoxides like artemisinin and ascaridole potentiate their leishmanicidal efficacy by creating a redox imbalance. Furthermore, these molecules minimally impair oxidative phosphorylation; instead inhibit glycolytic functions, culminating in depolarization of the mitochondrial membrane and depletion of ATP. Additionally, the carbon-centered free radicals generated from endoperoxides, participate in chain reactions that can generate even more reactive organic radicals that are toxic to macromolecules, including lipids, proteins and DNA, leading to cell cycle arrest and apoptosis of Leishmania parasites. However, the precise target(s) of the toxic free radicals remains open-ended.

CONCLUSION

In this overview, the spectrum of natural endoperoxide molecules as major anti-leishmanials and their mechanism of action has been delineated. In view of the substantial evidence that natural endoperoxides (e.g., artemisinin, ascaridole) exert a noxious effect on different species of Leishmania, identification and characterization of other natural endoperoxides is a promising therapeutic option worthy of further pharmacological consideration.

PLGA Nanoparticles as New Drug Delivery Systems in Leishmaniasis Chemotherapy: A Review of Current Practices

Although leishmaniasis is one of the most common parasitic diseases, its traditional treatments suffer from some serious problems. To solve such issues, we can take advantage of the effective nanoparticle-based approaches to deliver anti-leishmanial agents into leishmania-infected macrophages either using passive targeting or using macrophagerelated receptors. Despite the high potential of nanotechnology, Liposomal Amphotericin B (AmBisome®) is the only FDA-approved nanoparticle-based anti-leishmanial therapy. In an effort to find more anti-leishmanial nano-drugs, this 2011-2021 review study aimed to investigate the in-vivo and in-vitro effectiveness of poly (lactic-co-glycolic acid) nanoparticles (PLGA-NPs) in the delivery of some traditional anti-leishmanial drugs. Based on the results, PLGA-NPs could improve solubility, controlled release, trapping efficacy, bioavailability, selectivity, and mucosal penetration of the drugs, while they decreased resistance, dose/duration of administration and organotoxicity of the agents. However, none of these nano-formulations have been able to enter clinical trials so far. We summarized the data about the common problems of anti-leishmanial agents and the positive effects of various PLGA nano-formulations on reducing these drawbacks under both in-vitro and in-vivo conditions in three separate tables. Overall, this study proposes two AmB-loaded PLGA with a 99% reduction in parasite load as promising nanoparticles for further studies.

Antileishmanial Anthracene Endoperoxides: Efficacy In Vitro, Mechanisms and Structure-Activity Relationships

Leishmaniasis is a vector-borne disease caused by protozoal Leishmania parasites. Previous studies have shown that endoperoxides (EP) can selectively kill Leishmania in host cells. Therefore, we studied in this work a set of new anthracene-derived EP (AcEP) together with their non-endoperoxidic analogs in model systems of Leishmania tarentolae promastigotes (LtP) and J774 macrophages for their antileishmanial activity and selectivity. The mechanism of effective compounds was explored by studying their reaction with iron (II) in chemical systems and in Leishmania. The correlation of structural parameters with activity demonstrated that in this compound set, active compounds had a LogPOW larger than 3.5 and a polar surface area smaller than 100 Å2. The most effective compounds (IC50 in LtP < 2 µM) with the highest selectivity (SI > 30) were pyridyl-/tert-butyl-substituted AcEP. Interestingly, also their analogs demonstrated activity and selectivity. In mechanistic studies, it was shown that EP were activated by iron in chemical systems and in LtP due to their EP group. However, the molecular structure beyond the EP group significantly contributed to their differential mitochondrial inhibition in Leishmania. The identified compound pairs are a good starting point for subsequent experiments in pathogenic Leishmania in vitro and in animal models.

Ascaridole exerts the leishmanicidal activity by inhibiting parasite glycolysis

BACKGROUND

The global burden of leishmaniasis is exacerbated by the limited repertoire of drugs, resulting in an urgent need to develop new therapeutic alternatives. Endoperoxides like ascaridole have emerged as promising anti-parasitic candidates, and its effectiveness was established in an animal model of cutaneous leishmaniasis (CL). However, its impact on Leishmania donovani parasites, causative of visceral leishmaniasis (VL) remains to be established.

PURPOSE

This study aimed to delineate the underlying mechanisms contributing towards the leishmanicidal effect of ascaridole in terms of its impact on the cellular redox status and metabolic bioenergetics of L. donovani parasites.

METHODOLOGY

The anti-promastigote activity of ascaridole was established by a cell viability assay in L. donovani [MHOM/IN/1983/AG83] and anti-amastigote activity by microscopy and ddPCR (droplet digital polymerase chain reaction). The cellular redox status, mitochondrial membrane potential (MMP), annexin V positivity and cell cycle arrest was evaluated by flow cytometry, while cellular and mitochondrial bioenergetics was assessed using Agilent XFp Analyzer, and the levels of ATP was measured by chemiluminescence.

RESULTS

Ascaridole demonstrated strong anti-promastigote and anti-amastigote activities in l. donovani, IC₅₀ (half maximal Inhibitory concentration) being 2.47 ± 0.18 µM and 2.00±0.34 µM respectively, while in J774.A1 and murine peritoneal macrophages, the CC₅₀ (half maximal cytotoxic concentration) was 41.47 ± 4.89 µM and 37.58 ± 5.75 µM respectively. Ascaridole disrupted the redox homeostasis via an enhanced generation of reactive oxygen species (ROS), lipid peroxidation and concomitant depletion of thiols. However, it failed to increase the generation of mitochondrial superoxide, which minimally impacted on mitochondrial respiration and was corroborated by energy metabolism studies. Instead, ascaridole inhibited glycolysis of promastigotes, caused a loss in MMP, which translated into ATP depletion. In promastigotes, ascaridole enhanced annexin-V positivity and caused a cell cycle arrest at sub- G₀/G₁ phase.

CONCLUSION

In summary, ascaridole displays its leishmanicidal activity possibly due to its ability to auto-generate free radicals following cleavage of its endoperoxide bridge that led to disruption of the redox homeostasis, inhibition of glycolysis and culminated in an apoptotic like cell death.

1,2,4-Trioxolane and 1,2,4,5-Tetraoxane Endoperoxides against Old-World Leishmania Parasites: In Vitro Activity and Mode of Action

Leishmaniasis remains one of the ten Neglected Tropical Diseases with significant morbidity and mortality in humans. Current treatment of visceral leishmaniasis is difficult due to a lack of effective, non-toxic, and non-extensive medications. This study aimed to evaluate the selectivity of 12 synthetic endoperoxides (1,2,4-trioxolanes; 1,2,4,5-tetraoxanes) and uncover their biochemical effects on Leishmania parasites responsible for visceral leishmaniasis. The compounds were screened for in vitro activity against L. infantum and L. donovani and for cytotoxicity in two monocytic cell lines (J774A.1 and THP-1) using the methyl thiazol tetrazolium assay. Reactive oxygen species formation, apoptosis, and mitochondrial impairment were measured by flow cytometry. The compounds exhibited fair to moderate anti-proliferative activity against promastigotes of the 2 Leishmania species, with IC₅₀ values ranging from 13.0 ± 1.7 µM to 793.0 ± 37.2 µM. Tetraoxanes LC132 and LC138 demonstrated good leishmanicidal activity on L. infantum amastigotes (IC₅₀ 13.2 ± 5.2 and 23.9 ± 2.7 µM) with low cytotoxicity in mammalian cells (SIs 22.1 and 118.6), indicating selectivity towards the parasite. Furthermore, LC138 was able to induce late apoptosis and dose-dependent oxidative stress without affecting mithocondria. Compounds LC132 and LC138 can be further explored as potential antileishmanial chemotypes.

The Antagonizing Role of Heme in the Antimalarial Function of Artemisinin: Elevating Intracellular Free Heme Negatively Impacts Artemisinin Activity in Plasmodium falciparum

The rich source of heme within malarial parasites has been considered to underly the action specificity of artemisinin. We reasoned that increasing intraparasitic free heme levels might further sensitize the parasites to artemisinin. Various means, such as modulating heme synthesis, degradation, polymerization, or hemoglobin digestion, were tried to boost intracellular heme levels, and under several scenarios, free heme levels were significantly augmented. Interestingly, all results arrived at the same conclusion, i.e., elevating heme acted in a strongly negative way, impacting the antimalarial action of artemisinin, but exerted no effect on several other antimalarial drugs. Suppression of the elevated free heme level by introducing heme oxygenase expression effectively restored artemisinin potency. Consistently, zinc protoporphyrin IX/zinc mesoporphyrin, as analogues of heme, drastically increased free heme levels and, concomitantly, the EC₅₀ values of artemisinin. We were unable to effectively mitigate free heme levels, possibly due to an unknown compensating heme uptake pathway, as evidenced by our observation of efficient uptake of a fluorescent heme homologue by the parasite. Our results thus indicate the existence of an effective and mutually compensating heme homeostasis network in the parasites, including an uncharacterized heme uptake pathway, to maintain a certain level of free heme and that augmentation of the free heme level negatively impacts the antimalarial action of artemisinin. Importance: It is commonly believed that heme is critical in activating the antimalarial action of artemisinins. In this work, we show that elevating free heme levels in the malarial parasites surprisingly negatively impacts the action of artemisinin. We tried to boost free heme levels with various means, such as by modulating heme synthesis, heme polymerization, hemoglobin degradation and using heme analogues. Whenever we saw elevation of free heme levels, reduction in artemisinin potency was also observed. The homeostasis of heme appears to be complex, as there exists an unidentified heme uptake pathway in the parasites, nullifying our attempts to effectively reduce intraparasitic free heme levels. Our results thus indicate that too much heme is not good for the antimalarial action of artemisinins. This research can help us better understand the biological properties of this mysterious drug.

Anti-Leishmania activity of artesunate and combination effects with amphotericin B against Leishmania (Mundinia) martiniquensis in vitro

Leishmaniasis is an emerging disease in several countries over the world, especially in tropical regions. In Thailand, Leishmania (Mundinia) martiniquensis is the most frequent cause of visceral leishmaniasis and disseminated cutaneous leishmaniasis among HIV/AIDs patients. Amphotericin B (AmB) is the only drug currently available for the treatment of leishmaniasis in Thailand, but has some limitations like high renal toxicity and the prolonged hospitalization required for the treatment. Moreover, recurrence of the disease has been reported in several cases, indicating that new drugs or treatment strategies should be improved. In this study, Artesunate (ARS) was determined for anti-Leishmania activity against L. martiniquensis in promastigotes and amastigotes. In addition, the combination effects of ARS and AmB against intracellular amastigotes on THP-1 derived macrophages were also investigated for the first time. The result showed that L. martiniquensis was susceptible to ARS in both stages of the parasite. ARS was effective against intracellular amastigotes and safe to macrophage host cells, showing a SI value of 1,065. Furthermore, combination effects of ARS and AmB showed five synergistic combinations with a combination index (CI) value less than 1.0 (0.28-0.92) for intracellular amastigotes ranging from slight synergism to strong synergism. The strong synergistic combination had the highest dose reduction index (DRI), approximately a 9.7-fold reduction in AmB used. None of the treatments in combination had noticeable toxicity to THP-1 derived macrophages in the concentration range examined. The data provided in this study lead to further study in vivo and to develop a novel formulation of drug combinations to improve the outcome of leishmaniasis treatment.

Artemisinin DNA Base Interaction Studies in Presence of Fe(II): LC/TOF MS Separation of Reaction Products

Artemisinin (ART) is a sesquiterpene lactone and a popular malaria drug with potential anticancer properties. In this work, LC/TOF/MS, was used to investigate the reaction of ART with DNA bases. ART-deoxyadenosine and ART-deoxycytidine interactions, were studied in the presence of iron II ions. ART-deoxyadenosine and ART-deoxycytidine reaction mixtures gave chromatographic signatures that remained fairly unchanged at room temperature but grew after incubation at 37 °C. The change in temperature from room temperature to 37 °C was the main driver of adduct formation in these reactions. ART was found to react with Fe(II) ions as observed from several new chromatographic peaks. ART-deoxyadenosine as well as ART-deoxycytidine in the presence of Fe(II) ions resulted in formation of new chromatographic signatures of adducts consisting of DNA bases and ART. It was clear that addition of iron (II) to DNA base-ART mixtures gave rise to new reaction products mediated by a different reaction mechanism. Studies of ART reactions with DNA in vitro is key in elucidating elusive mechanism of this drug.

Can the iron content of culture media impact on the leishmanicidal effect of artemisinin?

Endoperoxides (EPs) like artemisinin following cleavage of their EP bridge can kill parasites via generation of carbon-centered radicals. As the presence of low molecular mass iron and/or heme is crucial, this study aimed to establish the influence of iron on the leishmanicidal action of artemisinin when present in differing amounts in culture media. In promastigotes cultured in Schneiders insect medium (SIM), that had a 8.0-fold higher amount of iron as compared to Medium 199 (M199), the impact of artemisinin on cell viability, redox status, labile iron pool (LIP), and Annexin-V positivity was evaluated. In SIM, the IC50 of artemisinin was 25.50-fold lower than M199, and in both media its cytotoxicity was decreased by the addition of hemin or following chelation of Fe2+ by Deferoxamine (DFO). In SIM vis-a-vis M199, artemisinin caused a greater redox imbalance which translated into a higher degree of externalization of phosphatidylserine and depletion of the LIP. The presence of a higher proportion of iron in SIM as compared to M199 significantly enhanced the cytotoxicity of artemisinin in Leishmania promastigotes, and was attributed to a higher degree of iron-mediated cleavage of its EP bridge that led to a higher generation of free radicals.

Dihydroartemisinin, an active metabolite of artemisinin, interferes with Leishmania braziliensis mitochondrial bioenergetics and survival

Leishmaniasis is one of the most neglected parasitic infections of the world and current therapeutic options show several limitations. In the search for more effective drugs, plant compounds represent a powerful natural source. Artemisinin is a sesquiterpene lactone extracted from Artemisia annua L. leaves, from which dihydroartemisinin (DQHS) and artesunic acid (AA)/artesunate are examples of active derivatives. These lactones have been applied successfully on malaria therapy for decades. Herein, we investigated the sensitivity of Leishmania braziliensis, one of the most prevalent Leishmania species that cause cutaneous manifestations in the New World, to artemisinin, DQHS, and AA. L. braziliensis promastigotes and the stage that is targeted for therapy, intracelular amastigotes, were more sensitive to DQHS, showing EC₅₀ of 62.3 ± 1.8 and 8.9 ± 0.9 μM, respectively. Cytotoxicity assays showed that 50% of bone marrow-derived macrophages cultures were inhibited with 292.8 ± 3.8 μM of artemisinin, 236.2 ± 4.0 μM of DQHS, and 396.8 ± 6.7 μM of AA. The control of intracellular infection may not be essentially attributed to the production of nitric oxide. However, direct effects on mitochondrial bioenergetics and H₂O₂ production appear to be associated with the leishmanicidal effect of DQHS. Our data provide support for further studies of artemisinin and derivatives repositioning for experimental leishmaniasis.

Essential Oil from Melaleuca leucadendra: Antimicrobial, Antikinetoplastid, Antiproliferative and Cytotoxic Assessment

Essential oils (EOs) are known for their use in cosmetics, food industries, and traditional medicine. This study presents the chemical composition and therapeutic properties against kinetoplastid and eukaryotic cells of the EO from Melaleucaleucadendra (L.) L. (Myrtaceae). Forty-five compounds were identified in the oil by GC-MS, containing a major component the 1,8-cineole (61%). The EO inhibits the growth of Leishmania amazonensis and Trypanosoma brucei at IC50 values <10 μg/mL. However, 1,8 cineole was not the main compound responsible for the activity. Against malignant (22Rv1, MCF-7, EFO-21, including resistant sublines MCF-7/Rap and MCF-7/4OHTAMO) and non-malignant (MCF-10A, J774A.1 and peritoneal macrophage) cells, IC50 values from 55 to 98 μg/mL and from 94 to 144 μg/mL were obtained, respectively. However, no activity was observed on Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, Pseudomonas aeruginosa, Aspergillus niger, Candida parapsilosis, Microsporum canis, or Trypanosoma cruzi. The EO was able to control the lesion size and parasite burden in the model of cutaneous leishmaniasis in BALB/c mice caused by L. amazonensis compared to untreated animals (p < 0.05) and similar with those treated with Glucantime® (p > 0.05). This work constitutes the first evidence of antiproliferative potentialities of EO from M. leucadendra growing in Cuba and could promote further preclinical investigations to confirm the medical value of this plant, in particular for leishmaniasis treatment.

Heme oxygenase-1 in protozoan infections: A tale of resistance and disease tolerance

Heme oxygenase (HO-1) mediates the enzymatic cleavage of heme, a molecule with proinflammatory and prooxidant properties. HO-1 activity deeply impacts host capacity to tolerate infection through reduction of tissue damage or affecting resistance, the ability of the host to control pathogen loads. In this Review, we will discuss the contribution of HO-1 in different and complex protozoan infections, such as malaria, leishmaniasis, Chagas disease, and toxoplasmosis. The complexity of these infections and the pleiotropic effects of HO-1 constitute an interesting area of study and an opportunity for drug development.

Iron in parasitic protists – from uptake to storage and where we can interfere

A comprehensive review of iron metabolism in parasitic protists and its potential use as a drug target.