TrypanocidalActivity of Natural Sesquiterpenoids Involves Mitochondrial Dysfunction, ROS Production and Autophagic Phenotype in Trypanosomacruzi

Meroterpenoids from Gongolaria abies-marina against Kinetoplastids: In Vitro Activity and Programmed Cell Death Study

Leishmaniasis and Chagas disease affect millions of people worldwide. The available treatments against these parasitic diseases are limited and display multiple undesired effects. The brown alga belonging to the genus Gongolaria has been previously reported as a source of compounds with different biological activities. In a recent study from our group, Gongolaria abies-marine was proven to present antiamebic activity. Hence, this brown alga could be a promising source of interesting molecules for the development of new antiprotozoal drugs. In this study, four meroterpenoids were isolated and purified from a dichloromethane/ethyl acetate crude extract through a bioguided fractionation process targeting kinetoplastids. Moreover, the in vitro activity and toxicity were evaluated, and the induction of programmed cell death was checked in the most active and less toxic compounds, namely gongolarone B (2), 6Z-1'-methoxyamentadione (3) and 1'-methoxyamentadione (4). These meroterpenoids triggered mitochondrial malfunction, oxidative stress, chromatin condensation and alterations of the tubulin network. Furthermore, a transmission electron microscopy (TEM) image analysis showed that meroterpenoids (2-4) induced the formation of autophagy vacuoles and ER and Golgi complex disorganization. The obtained results demonstrated that the mechanisms of action at the cellular level of these compounds were able to induce autophagy as well as an apoptosis-like process in the treated parasites.

Chalcone Derivative Induces Flagellar Disruption and Autophagic Phenotype in Phytomonas serpens In Vitro

Phytomonas serpens is a trypanosomatid phytoparasite, found in a great variety of species, including tomato plants. It is a significant problem for agriculture, causing high economic loss. In order to reduce the vegetal infections, different strategies have been used. The biological activity of molecules obtained from natural sources has been widely investigated to treat trypanosomatids infections. Among these compounds, chalcones have been shown to have anti-parasitic and anti-inflammatory effects, being described as having a remarkable activity on trypanosomatids, especially in Leishmania species. Here, we evaluated the antiprotozoal activity of the chalcone derivative (NaF) on P. serpens promastigotes, while also assessing its mechanism of action. The results showed that treatment with the derivative NaF for 24 h promotes an important reduction in the parasite proliferation (IC50/24 h = 23.6 ± 4.6 µM). At IC50/24 h concentration, the compound induced an increase in reactive oxygen species (ROS) production and a shortening of the unique flagellum of the parasites. Electron microscopy evaluation reinforced the flagellar phenotype in treated promastigotes, and a dilated flagellar pocket was frequently observed. The treatment also promoted a prominent autophagic phenotype. An increased number of autophagosomes were detected, presenting different levels of cargo degradation, endoplasmic reticulum profiles surrounding different cellular structures, and the presence of concentric membranar structures inside the mitochondrion. Chalcone derivatives may present an opportunity to develop a treatment for the P. serpens infection, as they are easy to synthesize and are low in cost. In order to develop a new product, further studies are still necessary.

Drimane Sesquiterpene Aldehydes Control Candida Yeast Isolated from Candidemia in Chilean Patients

Drimys winteri J.R. (Winteraceae) produce drimane sesquiterpenoids with activity against Candida yeast. In this work, drimenol, polygodial (1), isotadeonal (2), and a new drimane α,β-unsaturated 1,4-dialdehyde, named winterdial (4), were purified from barks of D. winteri. The oxidation of drimenol produced the monoaldehyde drimenal (3). These four aldehyde sesquiterpenoids were evaluated against six Candida species isolated from candidemia patients in Chilean hospitals. Results showed that 1 displays fungistatic activity against all yeasts (3.75 to 15.0 µg/mL), but irritant effects on eyes and skin, whereas its non-pungent epimer 2 has fungistatic and fungicide activities at 1.9 and 15.0 µg/mL, respectively. On the other hand, compounds 3 and 4 were less active. Molecular dynamics simulations suggested that compounds 1–4 are capable of binding to the catalytic pocket of lanosterol 14-alpha demethylase with similar binding free energies, thus suggesting a potential mechanism of action through the inhibition of ergosterol synthesis. According to our findings, compound 2 appears as a valuable molecular scaffold to pursue the future development of more potent drugs against candidiasis with fewer side effects than polygodial. These outcomes are significant to broaden the alternatives to treat fungal infections with increasing prevalence worldwide using natural compounds as a primary source for active compounds.

Different Drugs, Same End: Ultrastructural Hallmarks of Autophagy in Pathogenic Protozoa

Protozoan parasites interact with a wide variety of organisms ranging from bacteria to humans, representing one of the most common causes of parasitic diseases and an important public health problem affecting hundreds of millions of people worldwide. The current treatment for these parasitic diseases remains unsatisfactory and, in some cases, very limited. Treatment limitations together with the increased resistance of the pathogens represent a challenge for the improvement of the patient’s quality of life. The continuous search for alternative preclinical drugs is mandatory, but the mechanisms of action of several of these compounds have not been described. Electron microscopy is a powerful tool for the identification of drug targets in almost all cellular models. Interestingly, ultrastructural analysis showed that several classes of antiparasitic compounds induced similar autophagic phenotypes in trypanosomatids, trichomonadids, and apicomplexan parasites as well as in Giardia intestinalis and Entamoeba spp. with the presence of an increased number of autophagosomes as well as remarkable endoplasmic reticulum profiles surrounding different organelles. Autophagy is a physiological process of eukaryotes that maintains homeostasis by the self-digestion of nonfunctional organelles and/or macromolecules, limiting redundant and damaged cellular components. Here, we focus on protozoan autophagy to subvert drug effects, discussing its importance for successful chemotherapy.

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.

Mode of action of the sesquiterpene lactones eupatoriopicrin and estafietin on Trypanosoma cruzi

BACKGROUND

The sesquiterpene lactones (STLs) eupatoriopicrin (EP) and estafietin (ES), isolated from Stevia alpina Griseb. (Asteraceae) and Stevia maimarensis (Hieron.) Cabrera (Asteraceae) respectively, have previously showed promising trypanocidal activity, both in vitro and in vivo.

PURPOSE

In this work, using biochemical studies and electron microscopy, we aimed at characterizing the mode of action of both STLs on Trypanosoma cruzi.

METHODS

The interaction of STLs with hemin was examined by measuring modifications in the Soret absorption band of hemin; the thiol groups interaction was determined spectrophotometrically through its reaction with 5,5'-dithiobis-2-nitrobenzoate; the effect on cruzipain activity was also assayed by spectrophotometry. The synthesis of sterols were qualitatively and quantitatively tested by TLC. Mitochondrial functionality was assessed by measuring mitochondrial membrane potential and the activity of NADH-cytochrome c reductase and succinate-cytochrome c reductase enzymes. The status of the antioxidant system was assessed by quantifying the level of free thiols by spectrophotometry, together with the intracellular oxidative state by flow cytometry. Ultrastructural changes were analyzed by transmission electron microscopy.

RESULTS

EP and ES were found to impair the functionality and the redox status of the parasite. ES produced a greater decrease in the activity of succinate dehydrogenase than eupatoriopicrin, affecting the functioning of the respiratory chain and the Krebs cycle. EP increased the formation of triglycerides leading to the presence of cytoplasmic lipid droplets. By electron microscopy, alterations in the kinetoplast and the appearance of large translucent vacuoles in the cytoplasm were observed for both compounds.

CONCLUSIONS

Both sesquiterpenelactones proved to act additively on T. cruzi, supporting the hypothesis that each compound would be acting on different primary targets.. The treatment combining eupatoriopicrin and estafietin could be considered a promising alternative for the treatment of Chagas' disease.

Grandiflorenic acid isolated from Sphagneticola trilobata against Trypanosoma cruzi: Toxicity, mechanisms of action and immunomodulation

Grandiflorenic acid (GFA) is one of the main kaurane diterpenes found in different parts of Sphagneticola trilobata. It has several biological activities, especially antiprotozoal action. In turn, Chagas disease is a complex systemic disease caused by the protozoan Trypanosoma cruzi, and the drugs available to treat it involve significant side effects and impose an urgent need to search for therapeutic alternatives. In this context, our goal was to determine the effect of GFA on trypomastigote and intracellular amastigote forms. Our results showed that GFA treatment led to significantly less viability of trypomastigote forms, with morphological and ultrastructural changes in the parasites treated with IC₅₀ of GFA (24.60 nM), and larger levels of reactive oxygen species (ROS), mitochondrial depolarization, lipid droplets accumulation, presence of autophagic vacuoles, phosphatidylserine exposure, and plasma membrane damage. In addition, the GFA treatment was able to reduce the percentage of infected cells and the number of amastigotes per macrophage (J774A.1) without showing cytotoxicity in mammalian cell lines (J774A.1, LLCMK₂, THP-1, AMJ2-C11), in addition to increasing TNF-α and reducing IL-6 levels in infected macrophages. In conclusion, the GFA treatment exerted influence on trypomastigote forms through an apoptosis-like mechanism and by eliminating intracellular parasites via TNF-α/ROS pathway, without generating cellular cytotoxicity.

Comparative Study of Bioactivity and Safety Evaluation of Ethanolic Extracts of Zanthoxylum schinifolium Fruit and Pericarp

The fruit and pericarp of Zanthoxylum schinifolium (ZS) have been used in traditional medicine; however, few studies have characterized ZS fruit and pericarp. Therefore, in the present study, we evaluated the safety of ZS fruit (ZSF) and pericarp (ZSP) extracts and compared their bioactivity. To evaluate the safety of ZSF and ZSP, mutagenicity, cytotoxicity, and oxidative stress assays were performed and nontoxic concentration ranges were obtained. ZSP was found to be superior to ZSF in terms of its antimutagenic, antioxidant, and anti-inflammatory activities. In the S9 mix, the mutation inhibition rate of ZSP was close to 100% at concentrations exceeding 625 µg·plate⁻¹ for both the TA98 and TA100 strains. ZSP exhibited efficient DPPH (IC₅₀ = 75.6 ± 6.1 µg·mL⁻¹) and ABTS (IC₅₀ = 57.4 ± 6 µg·mL⁻¹) scavenging activities. ZSP inhibited the release of cytokines, involved in IL-1β (IC₅₀ = 134.4 ± 7.8), IL-6 (IC₅₀ = 262.8 ± 11.2), and TNF-α (IC₅₀ = 223.8 ± 5.8). These results indicate that ZSP contains a higher amount of biochemicals than ZSF, or that ZSP contains unique biochemicals. In conclusion, for certain physiological activities, the use of ZSP alone may be more beneficial than the combined use of ZSF and ZSP.

Ethnopharmacology, Phytochemistry and Biological Activities of Native Chilean Plants

The native flora of Chile has unique characteristics due to the geographical situation of the country, with the vast desert in the North, Patagonia in the South, the Andean Mountains on the east and the Pacific Ocean on the west. This exclusivity is reflected in high concentrations of phytochemicals in the fruits and leaves of its native plants. Some examples are Aristotelia chilensis (Molina), Stuntz (maqui), Berberis microphylla G. Forst. (calafate), Peumus boldus Molina (boldo), Ribes magellanicum Poir. (Magellan currant), Ugni molinae Turcz. (murtilla), Rubus geoides Sm. (miñe miñe), Drimys winteri J.R.Forst. & G.Forst. (canelo), Luma apiculata (DC.) Burret (arrayán) distributed throughout the entire Chilean territory. Some of these Chilean plants have been used for centuries in the country's traditional medicine. The most recent studies of phytochemical characterization of parts of Chilean plants show a wide spectrum of antioxidant compounds, phenolic components, terpenoids and alkaloids, which have shown biological activity in both in vitro and in vivo studies. This manuscript covers the entire Chilean territory characterizing the phytochemical profile and reporting some of its biological properties, focusing mainly on antioxidant, anti-inflammatory, antimicrobial, chemopreventive and cytotoxic activity, and potential against diabetes, metabolic syndrome and gastrointestinal disorders.

In vitro study of the trypanocidal activity of anilinophenanthrolines against Trypanosoma cruzi

Chagas disease is present in Latin America, North America, Europe, and Asia, where between 6 and 7 million people are infected. This illness is transmitted mainly by the insect vector during blood feeding and by oral transmission. Chagas disease is treated with benznidazole and its effectiveness depends on which phase of the disease the treatment starts. Therefore, the identification of new compounds with anti-Chagas activities is important. Protozoan parasites present cysteine proteases, important for host cell infection and differentiation, which have been explored as valid targets against pathogenic parasites. In the present study, the effects of 10 new 1,10-phenanthroline derivatives were evaluated on T. cruzi. Three of them were effective against amastigotes (IC₅₀ from 0.5 to 3 μM), epimastigotes (IC₅₀ from 0.5 to at least 10 μM) and trypomastigotes (and LD₅₀ from 1 to 10 μM), and they were not toxic to mammalian cells (CC₅₀ ≥ 20 μM). These compounds also promoted the formation of autophagosomes, alter the level of heterochromatin condensation, caused the loss of kDNA topology, and the elongated cell body shape. Apart from ultrastructural alterations, an increased generation of ROS and decreased mitochondrial membrane potential were observed. Therefore, these drugs revealed potential trypanocidal effects and warrant further antiparasitic studies against Chagas disease.

Chagas Disease Chemotherapy: What Do We Know So Far?

Chagas disease is a Neglected Tropical Disease (NTD), and although endemic in Latin America, affects around 6-7 million people infected worldwide. The treatment of Chagas disease is based on benznidazole and nifurtimox, which are the only available drugs. However, they are not effective during the chronic phase and cause several side effects. Furthermore, BZ promotes cure in 80% of the patients in the acute phase, but the cure rate drops to 20% in adults in the chronic phase of the disease. In this review, we present several studies published in the last six years, which describes the antiparasitic potential of distinct drugs, from the synthesis of new compounds aiming to target the parasite, as well as the repositioning and the combination of drugs. We highlight several compounds for having shown results that are equivalent or superior to BZ, which means that they should be further studied, either in vitro or in vivo. Furthermore, we stand out the differences in the effects of BZ on the same strain of T. cruzi, which might be related to methodological differences such as parasite and cell ratios, host cell type and the time of adding the drug. In addition, we discuss the wide variety of strains and also the cell types used as a host cell, which makes it difficult to compare the trypanocidal effect of the compounds.

Novel N,N-di-alkylnaphthoimidazolium derivative of β-lapachone impaired Trypanosoma cruzi mitochondrial electron transport system

Trypanosoma cruzi is a protozoan parasite that causes Chagas disease, a neglected tropical disease that is endemic in Latin America and spreading worldwide due to globalization. The current treatments are based on benznidazole and nifurtimox; however, these drugs have important limitations and limited efficacy during the chronic phase, reinforcing the necessity of an alternative chemotherapy. For the last 30 years, our group has been evaluating the biological activity of naphthoquinones and derivatives on T. cruzi, and of the compounds tested, N1, N2 and N3 were found to be the most active in vitro. Here, we show the synthesis of a novel β-lapachone-derived naphthoimidazolium named N4 and assess its activity on T. cruzi stages and the mechanism of action. The new compound was very active on all parasite stages (IC₅₀/24 h in the range of 0.8-7.9 μM) and had a selectivity index of 5.4. Mechanistic analyses reveal that mitochondrial ROS production begins after short treatment starts and primarily affects the activity of complexes II-III. After 24 h treatment, a partial restoration of mitochondrial physiology (normal complexes II-III and IV activities and controlled H₂O₂ release) was observed; however, an extensive injury in its morphology was still detected. During treatment with N4, we also observed that trypanothione reductase activity increased in a time-dependent manner and concomitant with increased oxidative stress. Molecular docking calculations indicated the ubiquinone binding site of succinate dehydrogenase as an important interaction point with N4, as with the FMN binding site of dihydroorotate dehydrogenase. The results presented here may be a good starting point for the development of alternative treatments for Chagas disease and for understanding the mechanism of naphthoimidazoles in T. cruzi.

Antifungal Effects of Drimane Sesquiterpenoids Isolated from Drimys winteri against Gaeumannomyces graminis var. tritici

Gaeumannomyces graminis var. tritici is a soilborne pathogen that causes "take-all" disease, affecting cereal roots. In wheat, G. graminis var. tritici is the most important biotic factor, causing around 30 to 50% losses of yield. Chemical control of this fungal disease is difficult because G. graminis var. tritici is able to reside for a long time in soils. Therefore, the development of environmentally friendly biotechnological strategies to diminish the incidence of soilborne diseases is highly desirable. Natural products are a promising strategy for biocontrol of plant pathogens. A special emphasis is on medicinal plants due to their reported fungitoxic effects. Drimys winteri (canelo) is a medicinal plant that is widely used by the Mapuche ethnic group from Chile due to its anti-inflammatory activity. In addition, inhibitory effects of canelo against phytopathogenic fungi and pest insects have been reported. In this study, we isolated, purified, and identified six drimane sesquiterpenoid compounds from canelo (drimenin, drimenol, polygodial, isodrimeninol, valdiviolide, and drimendiol). Then, we evaluated their antimicrobial effects against G. graminis var. tritici. Compounds were identified by comparing Fourier-transform infrared spectroscopy (FTIR) data and the retention time in thin-layer chromatography (TLC) with those of pure standards. The putative antagonistic effects were confirmed by assessing hyphal cell wall damage using confocal microscopy and lipid peroxidation. Here, we reported the high potential of drimane sesquiterpenoids as natural antifungals against G. graminis var. tritici. Polygodial and isodrimeninol were the most effective, with 50% lethal concentrations (LC₅₀s) between 7 and 10 μg ml^-1 and higher levels of fungal lipid peroxidation seen. Accordingly, natural sesquiterpenoids purified from canelo are biologically active against G. graminis var. tritici and could be used as natural biofungicides for sustainable agriculture.IMPORTANCE More than two billion tons of pesticides are used every year worldwide. An interesting sustainable alternative to control plant pathogens is the use of natural products obtained from plants, mainly medicinal plants that offer secondary metabolites important to human/animal health. In this study, we isolated and identified six pure drimane sesquiterpenoids obtained from the bark of Drimys winteri Additionally, we evaluated their antifungal activities against Gaeumannomyces graminis (the main biotic factor affecting cereal production, especially wheat) by assessing fungal cell wall damage and lipid peroxidation. The compounds obtained showed important antifungal properties against G. graminis var. tritici, mainly isodrimenol, which was the second-most-active compound after polygodial, with an LC₅₀ against G. graminis var. tritici of around 9.5 μg ml^-1 This information could be useful for the development of new natural or hemisynthetic antifungal agents against soilborne phytopathogens that could be used in green agriculture.

Oxidation of Isodrimeninol with PCC Yields Drimane Derivatives with Activity against Candida Yeast by Inhibition of Lanosterol 14-Alpha Demethylase

Candida species cause an opportunistic yeast infection called Candidiasis, which is responsible for more than 50,000 deaths every year around the world. Effective treatments against candidiasis caused by non-albicans Candida species such as C. glabrata, C. parapsilosis, C. aureus, and C.krusei are limited due to severe resistance to conventional antifungal drugs. Natural drimane sesquiterpenoids have shown promising antifungal properties against Candida yeast and have emerged as valuable candidates for developing new candidiasis therapies. In this work, we isolated isodrimeninol (C1) from barks of Drimys winteri and used it as starting material for the hemi-synthesis of four sesquiterpenoids by oxidation with pyridinium chlorochromate (PCC). The structure of the products (C2, C3, C4, and C5) was elucidated by 1D and 2D NMR spectroscopy resulting in C4 being a novel compound. Antifungal activity assays against C. albicans, C. glabrata, and C. krusei revealed that C4 exhibited an increased activity (IC₅₀ of 75 μg/mL) compared to C1 (IC₅₀ of 125 μg/mL) in all yeast strains. The antifungal activity of C1 and C4 was rationalized in terms of their capability to inhibit lanosterol 14-alpha demethylase using molecular docking, molecular dynamics simulations, and MM/GBSA binding free energy calculations. In silico analysis revealed that C1 and C4 bind to the outermost region of the catalytic site of 14-alpha demethylase and block the entrance of lanosterol (LAN) to the catalytic pocket. Binding free energy estimates suggested that C4 forms a more stable complex with the enzyme than C1, in agreement with the experimental evidence. Based on this new approach it is possible to design new drimane-type sesquiterpenoids for the control of Candida species as inhibitors of 14-alpha demethylase.

Trypanocidal Mechanism of Action and in silico Studies of p-Coumaric Acid Derivatives

Trypanosoma species are responsible for chronic and systemic infections in millions of people around the world, compromising life quality, and family and government budgets. This group of diseases is classified as neglected and causes thousands of deaths each year. In the present study, the trypanocidal effect of a set of 12 ester derivatives of the p-coumaric acid was tested. Of the test derivatives, pentyl p-coumarate (7) (5.16 ± 1.28 μM; 61.63 ± 28.59 μM) presented the best respective trypanocidal activities against both epimastigote and trypomastigote forms. Flow cytometry analysis revealed an increase in the percentage of 7-AAD labeled cells, an increase in reactive oxygen species, and a loss of mitochondrial membrane potential; indicating cell death by necrosis. This mechanism was confirmed by scanning electron microscopy, noting the loss of cellular integrity. Molecular docking data indicated that of the chemical compounds tested, compound 7 potentially acts through two mechanisms of action, whether by links with aldo-keto reductases (AKR) or by comprising cruzain (CZ) which is one of the key Trypanosoma cruzi development enzymes. The results indicate that for both enzymes, van der Waals interactions between ligand and receptors favor binding and hydrophobic interactions with the phenolic and aliphatic parts of the ligand. The study demonstrates that p-coumarate derivatives are promising molecules for developing new prototypes with antiprotozoal activity.

Dibenzylbutane neolignans from Saururus cernuus L. (Saururaceae) displayed anti-Trypanosoma cruzi activity via alterations in the mitochondrial membrane potential

The MeOH extract from leaves of Saururus cernuus L. (Saururaceae) displayed in vitro activity against trypomastigote forms of T. cruzi (100% of parasite death at 200 μg/mL), suggesting the presence of bioactive compounds. Thus, the bioactivity-guided fractionation was carried out, leading to the isolation of three related neolignan derivatives, identified as threo-austrobailignan-5 (1), threo-austrobailignan-6 (2), and threo-dihydroguaiaretic acid (3). Anti-T. cruzi activity of compounds 1-3 was performed against cell-derived trypomastigotes and intracellular amastigotes. Additionally, the mammalian cytotoxicity was investigated using NCTC cells. Compound 2 was the most effective against extracellular trypomastigotes with IC₅₀ of 3.7 μM, while compound 3 showed activity in both clinically relevant forms of the parasite, trypomastigotes and amastigotes, with IC₅₀ values of 7.0 and 16.2 μM, respectively. However, the structurally related compound 1 was inactive. Based on these results, compounds 2 and 3 were selected to evaluate the mechanism of cellular death. Compound 2 induced alteration in the plasma membrane permeability and consequently in the ROS levels after 120 min of incubation. By using flow cytometry and fluorescence microscopy, compound 3 showed alterations in the mitochondrial membrane potential (ΔΨ_m) of trypomastigotes. Considering the promising chemical and biological properties of neolignans 2 and 3, these compounds could be used as starting points to develop new lead compounds for Chagas disease.