Anti-Trypanosoma cruzi activity of costic acid isolated from Nectandra barbellata (Lauraceae) is associated with alterations in plasma membrane electric and mitochondrial membrane potentials

Antiparasitic Activity of Narciclasine and Evaluation of Its Effects on Plasma Membrane and Mitochondria of Trypanosoma cruzi

The EtOAc extract from bulbs of Hymenocallis littoralis (Amaryllidaceae) exhibited antiprotozoal activity against Trypanosoma cruzi and afforded the alkaloids narciclasine (1), 7-deoxynarciclasine (2), and narciclasine-4-O-β-D-xylopyranoside (3). In silico studies showed adequate predictions for drug-likeness for alkaloids 1 and 2, with adherence to Lipinski's rules of five and no alerts for PAINS. When tested against clinical forms of T. cruzi, alkaloid 1 displayed in vitro effectiveness with IC50 values of 17.1 μM (trypomastigotes) and 8.2 μM (amastigotes), with no mammalian cytotoxicity for NCTC cells (CC50 > 200 μM), similar to the standard drug benznidazole. Alkaloid 3 exhibited moderate activity against intracellular amastigotes (IC50 = 64.6 μM) and no activity to trypomastigotes, whereas 2 was inactive against both forms of the parasite. These results suggested that free hydroxyl groups at the C-7 and C-4 positions are involved in the potency of the alkaloids. Considering the most potent and selective compound, the lethal action of alkaloid 1 was investigated against extracellular forms (trypomastigotes). Using the fluorescent probe Sytox Green, it was observed that alkaloid 1 presented a dual effect in the plasma membrane at different concentrations from a noninterfering action (at the IC50) to a significant alteration in the membrane permeability (IC90). At all tested concentrations, alkaloid 1 induced a dose-dependent depolarization of the mitochondrial membrane potential, leading to the lethal effect on T. cruzi. These results suggest alkaloid 1 as a new hit compound, eliminating both clinical forms of the parasite and successful in silico drug-like parameters for an oral candidate for Chagas disease.

Mining of antioxidant sesquiterpene lactones from the aerial parts of Saussurea involucrata with feature-based molecular network strategy

Sesquiterpene lactones (SLs) are a class of natural products with diverse structural scaffoldings and biological activities, making them intriguing objects in the fields of pharmaceutical industry, drug development, and pharmacology. Herein, fifteen SLs, including eleven undescribed SLs compounds sauruintones A-K (1-8 and 13-15), were isolated and identified from the aerial parts of Saussurea involucrata. Their structures were characterized by using mass spectrometry, spectroscopic methods, computational calculations, and single crystal X-ray diffraction. The Feature-Based Molecular Network (FBMN) strategy was utilized for the annotation of SLs with their MS/MS fragmentation patterns. Most of the SLs exerted their protective effects against oxidative stress by enhancing the levels of antioxidant enzyme (CAT) and reducing the malondialdehyde (MDA) levels. Among them, compound 12 exhibited potent reactive oxygen species (ROS) inhibitory activities and enhanced the activities of CAT, superoxide dismutase (SOD), and glutathione peroxidase (GSH), and decreased the content of MDA at concentrations of 10-25 μM. Further RT-qPCR assays and western blot analysis revealed it reduced the level of ROS by activating the nuclear factor erythroid 2-related factor 2 (Nrf-2) signaling pathway.

Toward New Therapeutics for Visceral Leishmaniasis: Efficacy and Mechanism of Action of Amides Inspired by Gibbilimbol B

The problems with current strategies to control canine visceral Leishmaniasis (CVL), which include the euthanasia of infected animals, and also the toxicity of the drugs currently used in human treatments for CVL, add urgency to the search for new therapeutic agents. This study aimed to evaluate the activity against Leishmania (L.) infantum of 12 amides that are chemically inspired by gibbilimbol B, a bioactive natural product that was initially obtained from Piper malacophyllum. Three of these compounds-N-(2-ethylhexyl)-4-chlorobenzamide (9), N-(2-ethylhexyl)-4-nitrobenzamide (10), and N-(2-ethylhexyl)-4-(tert-butyl)benzamide (12) -demonstrated activity against the intracellular amastigotes without toxicity to mammalian host cells (CC50 > 200 μM); compounds 9, 10, and 12 resulted in EC50 values of 12.7, 12.2, and 5.1 μM, respectively. In silico drug-likeness studies predicted that these compounds would show high levels of gastrointestinal absorption, would be able to penetrate the blood-brain barrier, would show moderate solubility, and would not show unwanted molecular interactions. Due to their promising pharmacological profiles, compounds 9 and 10 were selected for mechanism of action studies (MoA). The MoA studies in L. (L.) infantum revealed that neither of the compounds affected the permeabilization of the plasma membrane. Nevertheless, compound 9 induced strong alkalinization of acidocalcisomes, which resulted in a significant and rapid increase in intracellular Ca2+ levels, thereby causing the depolarization of the mitochondrial membrane potential and a reduction in the levels of reactive oxygen species (ROS). In contrast, compound 10 induced a gradual increase in intracellular Ca2+ levels and a similarly gradual reduction in ROS levels, but it caused neither acidocalcisome alkalinization nor mitochondrial membrane potential depolarization. Finally, the MALDI-TOF/MS assessment of protein alterations in L. (L.) infantum treated separately with compounds 9 and 10 revealed changes in mass spectral profiles from both treatments. These results highlight the anti-L. (L.) infantum potential of these amides-especially for compounds 9 and 10-and they suggest that these compounds could be promising candidates for future in vivo studies in VL-models.

Gram-scale approach for β-costic acid via allylic oxidation of β-selinene

β-Costic acid is a sesquiterpene phytoalexin with acaricidal activity against Varroa destructor and antitrypanosomal activity. A concise and efficient method was developed for the synthesis of β-costic acid via the allylic oxidation of β-selinene, a component of celery seed oil.

Barbellatanic acid, a new antitrypanosomal pseudo-disesquiterpenoid isolated from Nectandra barbellata, displayed interaction with protozoan cell membrane

As part of our ongoing studies involving the discovery of new natural prototypes with antiprotozoal activity against Trypanosoma cruzi from Brazilian plant species, the chromatographic fractionation of hexane extract from leaves of Nectandra barbellata afforded one new pseudo-disesquiterpenoid, barbellatanic acid. The structure of this compound was elucidated by NMR and HR-ESIMS data analysis. Barbellatanic acid displayed a trypanocidal effect with IC50 of 13.2 μM to trypomastigotes and no toxicity against NCTC cells (CC50 > 200 μM), resulting in an SI value higher than 15.1. The investigation of the lethal mechanism of barbellatanic acid in trypomastigotes, using both fluorescence microscopy and spectrofluorimetric analysis, revealed a time-dependent permeation of the plasma membrane. Based on these results, this compound was incorporated in cellular membrane models built with lipid Langmuir monolayers. The interaction of barbellatanic acid with the models was inferred by tensiometric, rheological, spectroscopical, and morphological techniques, which showed that this compound altered the thermodynamic, viscoelastic, structural, and morphological properties of the film. Taking together, these results could be employed when this prodrug interacts with lipidic interfaces, such as protozoa membranes or liposomes for drug delivery systems.

Enyne acetogenins from Porcelia macrocarpa displayed anti-Trypanosoma cruzi activity and cause a reduction in the intracellular calcium level

Natural products are a promising source of new compounds with a wide spectrum of pharmacological properties, including antiprotozoal activities. Chagas disease, caused by the protozoan parasite Trypanosoma cruzi, is one of several neglected tropical diseases with reduced options for treatment, which presents limitations such as toxicity and ineffectiveness in the chronic stage of the disease. Aiming to investigate the Brazilian flora for the discovery of new anti-T. cruzi compounds, the MeOH extract from Porcelia macrocarpa R.E. Fries (Annonaceae) fruit peels displayed potent activity against trypomastigotes and intracellular amastigotes and was subjected to bioactivity-guided fractionation. Using different chromatographic steps, a fraction composed of a mixture of four new chemically related acetogenins was obtained. The compounds were characterized as (2S*,3R*,4R*)-3-hydroxy-4-methyl-2-(n-octadeca-13',17'-dien-11'-inil)butanolide (1), (2S*,3R*,4R*)-3-hydroxy-4-methyl-2-(n-eicosa-13',19'-dien-11'-inil)butanolide (2), (2S*,3R*,4R*)-3-hydroxy-4-methyl-2-(n-octadec-13'-en-11'-inil)butanolide (3), and (2S*,3R*,4R*)-3-hydroxy-4-methyl-2-(n-eicosa-13'-en-11'-inil)butanolide (4) by NMR analysis and UHPLC/ESI-HRMS data. The mixture of compounds 1-4, displayed an EC50 of 4.9 and 2.5 µg/mL against trypomastigote and amastigote forms of T. cruzi, respectively, similar to the standard drug benznidazole (EC50 of 4.8 and 1.4 µg/mL). Additionally, the mixture of compounds 1-4 displayed no mammalian toxicity for murine fibroblasts (CC50 > 200 µg/mL), resulting in a SI > 40.8 and > 83.3 against trypomastigotes and amastigotes, respectively. Based on these results, the mechanism of action of this bioactive fraction was investigated. After a short-time incubation with the trypomastigotes, no alterations in the cell membrane permeability were observed. However, it was verified a decrease in the intracellular calcium of the parasites, without significant pH variations of the acidocalcisomes. The intracellular damages were followed by an upregulation of the reactive oxygen species and ATP, but no depolarization effects were observed in the mitochondrial membrane potential. These data suggest that the mixture of compounds 1-4 caused an irreversible oxidative stress in the parasites, leading to death. If adequately studied, these acetogenins can open new insights for the discovery of new routes of death in T. cruzi.

In Vitro Antioxidant and Antitrypanosomal Activities of Extract and Fractions of Terminalia catappa

Chagas disease is a severe infectious and parasitic disease caused by the protozoan Trypanosoma cruzi and considered a public health problem. Chemotherapeutics are still the main means of control and treatment of the disease, however with some limitations. As an alternative treatment, plants have been pointed out due to their proven pharmacological properties. Many studies carried out with Terminalia catappa have shown several biological activities, but its effect against T. cruzi is still unknown. The objective of this work is to evaluate the therapeutic potential of extracts and fractions obtained from T. catappa on the parasite T. cruzi, in addition to analyzing its antioxidant activity. T. catappa ethyl acetate fraction were produced and submitted the chemical characterization by Liquid Chromatography Coupled to Mass Spectrometry (LC-MS). From all T. catappa extracts and fractions evaluated, the ethyl acetate and the aqueous fraction displayed the best antioxidant activity by the 2,2-diphenyl-1-picryl-hydrazyl (DPPH) radical scavenging method (IC₅₀ of 7.77 ± 1.61 and 5.26 ± 1.26 µg/mL respectively), and by ferric ion reducing (FRAP) method (687.61 ± 0.26 and 1009.32 ± 0.13 µM of Trolox equivalent/mg extract, respectively). The ethyl acetate fraction showed remarkable T. cruzi inhibitory activity with IC₅₀ of 8.86 ± 1.13, 24.91 ± 1.15 and 85.01 ± 1.21 µg/mL against epimastigotes, trypomastigotes and intracellular amastigotes, respectively, and showed no cytotoxicity for Vero cells (CC₅₀ > 1000 µg/mL). The treatment of epimastigotes with the ethyl acetate fraction led to drastic ultrastructural changes such as the loss of cytoplasm organelles, cell disorganization, nucleus damage and the loss of integrity of the parasite. This effect could be due to secondary compounds present in this extract, such as luteolin, kaempferol, quercetin, ellagic acid and derivatives. The ethyl acetate fraction obtained from T. catappa leaves can be an effective alternative in the treatment and control of Chagas disease, and material for further investigations.

Synthetic Analogues of Gibbilimbol B Induce Bioenergetic Damage and Calcium Imbalance in Trypanosoma cruzi

Chagas disease is an endemic tropical disease caused by the protozoan Trypanosoma cruzi, which affects around 7 million people worldwide, mostly in development countries. The treatment relies on only two available drugs, with severe adverse effects and a limited efficacy. Therefore, the search for new therapies is a legitimate need. Within this context, our group reported the anti-Trypanosoma cruzi activity of gibbilimbol B, a natural alkylphenol isolated from the plant Piper malacophyllum. Two synthetic derivatives, LINS03018 (1) and LINS03024 (2), demonstrated a higher antiparasitic potency and were selected for mechanism of action investigations. Our studies revealed no alterations in the plasma membrane potential, but a rapid alkalinization of the acidocalcisomes. Nevertheless, compound 1 exhibit a pronounced effect in the bioenergetics metabolism, with a mitochondrial impairment and consequent decrease in ATP and reactive oxygen species (ROS) levels. Compound 2 only depolarized the mitochondrial membrane potential, with no interferences in the respiratory chain. Additionally, no macrophages response of nitric oxide (NO) was observed in both compounds. Noteworthy, simple structure modifications in these derivatives induced significant differences in their lethal effects. Thus, this work reinforces the importance of the mechanism of action investigations at the early phases of drug discovery and support further developments of the series.

MolPredictX: Online Biological Activity Predictions by Machine Learning Models

Here we report the development of MolPredictX, an innovate and freely accessible web interface for biological activity predictions of query molecules. MolPredictX utilizes in-house QSAR models to provide 27 qualitative predictions (active or inactive), and quantitative probabilities for bioactivity against parasitic (Trypanosoma and Leishmania), viral (Dengue, Sars-CoV and Hepatitis C), pathogenic yeast (Candida albicans), bacterial (Salmonella enterica and Escherichia coli), and Alzheimer disease enzymes. In this article, we introduce the methodology and usability of this webtool, highlighting its potential role in the development of new drugs against a variety of diseases. MolPredictX is undergoing continuous development and is freely available at https://www.molpredictx.ufpb.br/.

Plant Terpenoids as Hit Compounds against Trypanosomiasis

Human African trypanosomiasis (sleeping sickness) and American trypanosomiasis (Chagas disease) are vector-borne neglected tropical diseases, caused by the protozoan parasites Trypanosoma brucei and Trypanosoma cruzi, respectively. These diseases were circumscribed to South American and African countries in the past. However, human migration, military interventions, and climate changes have had an important effect on their worldwide propagation, particularly Chagas disease. Currently, the treatment of trypanosomiasis is not ideal, becoming a challenge in poor populations with limited resources. Exploring natural products from higher plants remains a valuable approach to find new hits and enlarge the pipeline of new drugs against protozoal human infections. This review covers the recent studies (2016–2021) on plant terpenoids, and their semi-synthetic derivatives, which have shown promising in vitro and in vivo activities against Trypanosoma parasites.

Ent-kaurane diterpenes isolated from n-hexane extract of Baccharis sphenophylla by bioactivity-guided fractionation target the acidocalcisomes in Trypanosoma cruzi

BACKGROUND

In the present work the bioactivity-guided fractionation of n-hexane extract from aerial parts of Baccharis sphenophylla (Asteraceae) against trypomastigote forms of Trypanosoma cruzi was performed.

PURPOSE

To evaluate the antitrypanosomal potential of diterpenes ent‑kaurenoic (1), grandifloric (2). and 15β-tiglinoyloxy‑ent-kaurenoic (3) acids, isolated from n-hexane extract from aerial parts of B. sphenophylla, and elucidate their mechanism of action against T. cruzi. METHODS/STUDY DESIGN: n-Hexane and MeOH extracts from aerial parts of B. sphenophylla were prepared and caused, respectively, 100% and 50% of death of trypomastigote forms of T. cruzi. Based on these results, the n-hexane extract was subjected to bioactivity-guided fractionation procedures to afford three related ent‑kaurane diterpenoids (1-3). Based on spectrofluorometric assays and flow cytometry analysis, the mechanism of action of compounds 1 and 3 was investigated.

RESULTS

Compounds 1 and 3, isolated from n-hexane extract from aerial parts of B. sphenophylla, showed potent activity against parasites with EC₅₀ values of 10.6 μM (SI > 18.8) and 2.4 μM (SI = 34.8), respectively. On the other hand, compound 2 was inactive against trypomastigotes. In mechanism of action studies using the fluorescent probe SYTOX Green, the plasma membrane permeability was unaltered after treatment with compounds 1 and 3, but compound 1 induced a depolarization of the plasma membrane electric potential (ΔΨp). No substantial alterations were observed in the mitochondria after treatment with compound 3, but a transient hyperpolarization of the mitochondrial membrane potential (ΔΨm) by compound 1. Despite the increased ATP levels induced by compounds 1 and 3, no alterations of ROS and Ca²⁺ levels were registered. However, both compounds promoted a time-dependent alkalinization of the acidocalcisomes, probably contributing to an osmotic imbalance of the cell. In silico physicochemical studies of compounds 1-3 suggested that lipophilicity and molecular complexity may play an important role in the antitrypanosomal activity. Moreover, no pan-assay interference compounds (PAINS) alerts were detected for compounds 1-3.

CONCLUSION

Obtained data indicated that the isolated ent‑kaurane diterpenes from n-hexane extract from aerial parts of B. sphenophylla, especially compound 3, could be considered interesting prototypes for further modifications aiming the discovery of new hits against T. cruzi.

(-)-T-Cadinol-a Sesquiterpene Isolated From Casearia sylvestris (Salicaceae)-Displayed In Vitro Activity and Causes Hyperpolarization of the Membrane Potential of Trypanosoma cruzi

Chagas disease is caused by the protozoan parasite Trypanosoma cruzi and affects 6-8 million people worldwide, mainly from developing countries. The treatment is limited to two approved nitro-derivatives, nifurtimox and benznidazole, with several side effects and reduced efficacy. Casearia sylvestris has been used in folk medicine as an antiseptic and cicatrizing in skin diseases. In the present work, the hexane phase from the MeOH extract from the leaves of Casearia sylvestris afforded a fraction composed by the sesquiterpene T-cadinol, which was chemically characterized by NMR and HRMS. The activity of T-cadinol was evaluated against T. cruzi, and IC₅₀ values of 18 (trypomastigotes) and 15 (amastigotes) µM were established. The relation between the mammalian toxicity and the antiparasitic activity resulted in a selectivity index >12. Based on this promising activity, the mechanism of action was investigated by different approaches using fluorescent-based techniques such as plasma membrane permeability, plasma membrane electric potential, mitochondrial membrane electric potential, reactive oxygen species, and the intracellular calcium (Ca²⁺) levels. The obtained results demonstrated that T-cadinol affected neither the parasite plasma membrane nor the electric potential of the membrane. Nevertheless, this compound induced a mitochondrial impairment, resulting in a hyperpolarization of the membrane potential, with decreased levels of reactive oxygen species. No alterations in Ca²⁺ levels were observed, suggesting that T-cadinol may affect the single mitochondria of the parasite. This is the first report about the occurrence of T-cadinol in C. sylvestris, and our data suggest this sesquiterpene as an interesting hit compound for future optimizations in drug discovery studies for Chagas disease.

γ-Lactones from Persea americana and Persea fulva - in Vitro and in Silico Evaluation of Trypanosoma cruzi Activity

In the present study, five known γ-lactones (majoranolide B - 1, majorenolide - 2, majorynolide - 3, lincomolide D - 4, and isolinderanolide E - 5), as well as a new one (perseanolide - 6), were isolated from Persea fulva and P. americana. All isolated compounds exhibited potential activity against trypomastigote forms of Trypanosoma cruzi, whereas compounds 2 (EC₅₀ of 4.8 μM) and 6 (EC₅₀ of 3.6 μM) displayed superior activity than the positive control benznidazole (EC₅₀ of 16.4 μM), with selectivity index (SI) values of 17.8 and >55.6, respectively (benznidazole, SI>12.2). Molecular docking studies were performed for 1-6 against six T. cruzi molecular targets. Using this approach, we observed that, even though perseanolide (6) showed favorable docking to several studied targets, the results were especially promising for hypoxanthine phosphoribosyl transferase (PDB 1TC1). As PDB 1TC1 is associated to the transference of a monophosphorylated ribose from phosphoribosylpyrophosphate (PRPP) in the ribonucleotide synthesis pathway, this interaction may affect the survival of T. cruzi in mammalian cells. The data herein also indicate that possible intermolecular interactions between 6 and PDB 1TC1 derive from (i) hydrogen bonds in the α,β-unsaturated-γ-lactone unity and (ii) hydrophobic interactions in the long-chain alkyl group. Based on our results, perseanolide (6), reported for the first time in this work, can auspiciously contribute to future works regarding new trypanocidal agents.

Antitrypanosomal Lactones from Nectandra barbellata

Twigs of Nectandra barbellata were extracted using a solution of the ionic liquid 1-butyl-3-methylimidazolium bromide (BMImBr) in H₂O, assisted by microwave (MAE). After successive chromatographic steps, one sesquiterpene, costic acid, and three new related lactones, (R)-3(7)-Z-3-hexadec-21-enylidene-5-(hydroxymethyl)tetrahydrofuran-2-one (1), (R)-3(7)-Z-3-hexadecylidene-5-(hydroxymethyl)tetrahydrofuran-2-one (2), and (R)-3(7)-Z-3-docosylidene-5-(hydroxymethyl)tetrahydrofuran-2-one (3), were isolated. After structural elucidation using IR, UV, HRESIMS, NMR, ECD, and VCD, compounds 1-3 were tested against trypomastigote forms of Trypanosoma cruzi. The mechanism of action of bioactive isolated compounds was studied using different fluorescent-based approaches to investigate alterations of the plasma membrane, permeability/electric potential (ΔΨ_p), reactive oxygen species levels, mitochondria (electric membrane potential, ΔΨ_m/ATP levels), Ca²⁺ levels, and pH of the acidocalcisomes. In addition, in silico studies predicted no resemblance to pan assay interference compounds (PAINS).

Aporphine Alkaloids from Ocotea puberula with Anti-Trypanosoma Cruzi Potential - Activity of Dicentrine-β-N-Oxide in the Plasma Membrane Electric Potentials

One new aporphine, dicentrine-β-N-oxide (1), together with five related known alkaloids dehydrodicentrine (2), predicentrine (3), N-methyllaurotetanine (4), cassythicine (5), and dicentrine (6) were isolated from the leaves of Ocotea puberula (Lauraceae). Antiprotozoal activity of the isolated compounds was evaluated in vitro against trypomastigote forms of Trypanosoma cruzi. Among the tested compounds, alkaloid 1 exhibited higher potential with EC₅₀ value of 18.2 μM and reduced toxicity against NCTC cells (CC₅₀ >200 μM - SI>11.0), similar to positive control benznidazole (EC₅₀ of 17.7 μM and SI=10.7). Considering the promising results of dicentrine-β-N-oxide (1) against trypomastigotes, the mechanism of parasite death caused by this alkaloid was investigated. As observed, this compound reached the plasma membrane electric potential directly after 2 h of incubation and triggered mitochondrial depolarization, which probably leads to trypomastigote death. Therefore, dicentrine-β-N-oxide (1), reported for the first time in this work, can contribute to future works for the development of new trypanocidal agents.

Metabolite profile of Nectandra oppositifolia Nees & Mart. and assessment of antitrypanosomal activity of bioactive compounds through efficiency analyses

EtOH extracts from the leaves and twigs of Nectandra oppositifolia Nees & Mart. shown activity against amastigote forms of Trypanosoma cruzi. These extracts were subjected to successive liquid-liquid partitioning to afford bioactive CH2Cl2 fractions. UHPLC-TOF-HRMS/MS and molecular networking were used to obtain an overview of the phytochemical composition of these active fractions. Aiming to isolate the active compounds, both CH2Cl2 fractions were subjected to fractionation using medium pressure chromatography combined with semi-preparative HPLC-UV. Using this approach, twelve compounds (1-12) were isolated and identified by NMR and HRMS analysis. Several isolated compounds displayed activity against the amastigote forms of T. cruzi, especially ethyl protocatechuate (7) with EC50 value of 18.1 μM, similar to positive control benznidazole (18.7 μM). Considering the potential of compound 7, protocatechuic acid and its respective methyl (7a), n-propyl (7b), n-butyl (7c), n-pentyl (7d), and n-hexyl (7e) esters were tested. Regarding antitrypanosomal activity, protocatechuic acid and compound 7a were inactive, while 7b-7e exhibited EC50 values from 20.4 to 11.7 μM, without cytotoxicity to mammalian cells. These results suggest that lipophilicity and molecular complexity play an important role in the activity while efficiency analysis indicates that the natural compound 7 is a promising prototype for further modifications to obtain compounds effective against the intracellular forms of T. cruzi.