Leishmanicidal activity of an alkenylphenol from Piper malacophyllum is related to plasma membrane disruption

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.

Gas chromatographic techniques and spectroscopic approaches for a deep characterization of Piper gaudichaudianum Kunth essential oil from Brazil

Piper gaudichaudianum Kunth essential oil (EO) is a natural source of bioactive components, having multiple therapeutic applications. Its chemical composition is highly variable, and strictly depends on abiotic factors, resulting in various biological activities. The present study details the utilization of multiple gas chromatographic techniques alongside nuclear magnetic resonance (NMR) spectroscopy to characterize the essential oil of Piper gaudichaudianum Kunth from Brazil. Seventy-six components were identified using GC-MS analysis, while enantio‑selective multidimensional gas chromatography elucidated the enantiomeric distribution of eight chiral components, for the first time in the literature. Following GC-MS analysis, an unidentified component, constituting approximately 27 % of the total oil, prompted an isolation step through preparative gas chromatography. Through the combined use of nuclear magnetic resonance, GC-Fourier transform infrared spectroscopy (FTIR), and mass spectrometry (MS), the unknown molecule was structurally identified as 4-[(3E)‑dec-3-en-1-yl]phenol. Remarkably, it was identified as a known molecule, gibbilimbol B, and not previously listed in any MS database. Subsequently, the spectrum was included in a commercial library, specifically the FFNSC 4.0 MS database, for the first time.

Multitarget anti-parasitic activities of isoquinoline alkaloids isolated from Hippeastrum aulicum (Amaryllidaceae)

BACKGROUND

Chagas disease and leishmaniasis affect a significant portion of the Latin American population and still lack efficient treatments. In this context, natural products emerge as promising compounds for developing more effective therapies, aiming to mitigate side effects and drug resistance. Notably, species from the Amaryllidaceae family emerge as potential reservoirs of antiparasitic agents due to the presence of diverse biologically active alkaloids.

PURPOSE

To assess the anti-Trypanosoma cruzi and anti-Leishmania infantum activity of five isolated alkaloids from Hippeastrum aulicum Herb. (Amaryllidaceae) against different life stages of the parasites using in silico and in vitro assays. Furthermore, molecular docking was employed to evaluate the interaction of the most active alkaloids.

METHODS

Five natural isoquinoline alkaloids isolated in suitable quantities for in vitro testing underwent preliminary in silico analysis to predict their potential efficacy against Trypanosoma cruzi (amastigote and trypomastigote forms) and Leishmania infantum (amastigote and promastigote forms). The in vitro antiparasitic activity and mammalian cytotoxicity were investigated with a subsequent comparison of both analysis (in silico and in vitro) findings. Additionally, this study employed the molecular docking technique, utilizing cruzain (T. cruzi) and sterol 14α-demethylase (CYP51, L. infantum) as crucial biological targets for parasite survival, specifically focusing on compounds that exhibited promising activities against both parasites.

RESULTS

Through computational techniques, it was identified that the alkaloids haemanthamine (1) and lycorine (8) were the most active against T. cruzi (amastigote and trypomastigote) and L. infantum (amastigote and promastigote), while also revealing unprecedented activity of alkaloid 7‑methoxy-O-methyllycorenine (6). The in vitro analysis confirmed the in silico tests, in which compound 1 presented the best activities against the promastigote and amastigote forms of L. infantum with half-maximal inhibitory concentration (IC50) 0.6 µM and 1.78 µM, respectively. Compound 8 exhibited significant activity against the amastigote form of T. cruzi (IC50 7.70 µM), and compound 6 demonstrated activity against the trypomastigote forms of T. cruzi and amastigote of L. infantum, with IC50 values of 89.55 and 86.12 µM, respectively. Molecular docking analyses indicated that alkaloids 1 and 8 exhibited superior interaction energies compared to the inhibitors.

CONCLUSION

The hitherto unreported potential of compound 6 against T. cruzi trypomastigotes and L. infantum amastigotes is now brought to the forefront. Furthermore, the acquired dataset signifies that the isolated alkaloids 1 and 8 from H. aulicum might serve as prototypes for subsequent structural refinements aimed at the exploration of novel leads against both T. cruzi and L. infantum parasites.

Volatile Metabolites of Piper eriopodon (Miq.) C.DC. from Northern Region of Colombia and Assessment of In Vitro Bioactivities of the Leaf Essential Oil

Piper eriopodon is one of the Piper species found in the Sierra Nevada de Santa Marta, and the species has been reported with different compositions of their essential oils (EO). In this study, the volatile fractions/essential oil (by HS-SPME/SDE/MWHD-GC–MS/1H-NMR) of different parts from the plant were characterized, and assessments of the in vitro bio-properties of the leaf EO were conducted. The results indicated the following: (i) in the volatile fractions were β-caryophyllene (~23%)/myrcene (~20%) (inflorescences) and β-caryophyllene (~43%)/β-selinene (~20%) (leaves) using HS-SPME; myrcene (~31%)/β-pinene (~23%) (inflorescences), gibbilimbol B (~60%) (fruits) and gibbilimbol B (~46%)/β-caryophyllene (~11%) (leaves) through SDE; (ii) leaf EO contained gibbilimbol B (~72%), confirmed with 1H-NMR; (iii) the cytotoxic values (µg/mL) in erythrocytes/lymphocytes/Hep-2 were HC50: 115 ± 3 (eryth.), LC50: 71 ± 4 (lymph.) and LC50: 33 ± 2 (cell-line); (iv) the antibacterial susceptibilities (ϕ inh. zone, mm; 4–16 µg EO) were 22.5 ± 0.4–97 ± 4 (Staphylococcus aureus), 23 ± 2–77 ± 4 (Escherichia coli) and 17 ± 1–48 ± 3 (Listeria monocytogenes); (v) the TAA value was 2249 ± 130 mmol Trolox®/kg; (vi) the IC50 value was 13±1 µg/mL (AChE) with 20 ± 0–37 ± 6% repellency (2–4 h, Sitophilus zeamais). Thus, the EO of P. eriopodon leaves from northern Colombia could be a promising species for sustainable exploitation in the future due to its outstanding bioactivities.

Structure-activity relationship study of antitrypanosomal analogues of gibbilimbol B using multivariate analysis and computation-aided drug design

Gibbilimbol B and analogues were isolated from the Brazilian plant Piper malacophyllum and displayed activity against trypomastigote forms of Trypanosoma cruzi as well as reduced toxicity against NCTC cells. These results stimulated the preparation of a series of 24 chemically related analogues to study the potential of these compounds against T. cruzi trypomastigotes and explore structure-activity relationships. Initially, 12 compounds were planned, maintaining the same extension of the linear side chain of gibbilimbol B and unsaturation on the C-4 position but changing the functional groups - ester and amide - and variating the substituent at the p-position in the aromatic ring. Other 12 compounds were prepared using a branched side chain containing an ethyl group at the C-2 position. Overall, these structurally-related analogues demonstrated promising activity against trypomastigote forms (EC₅₀ < 20 μM) and no mammalian cytotoxicity to fibroblasts (CC₅₀ > 200 μM). Using multivariate statistics and machine learning analysis, aspects associated with structure/activity were related to their three-dimensional structure and, mainly, to the substituents on the aromatic ring. Obtained results suggested that the presence of t-butyl or nitro groups at p-position with appropriate side chains causes an alteration in the electron topological state, Van der Waals volumes, surface areas, and polarizabilities of tested compounds which seem to be essential for biological activity against T. cruzi parasites.

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.

Involvement of a neutrophil-mast cell axis in the effects of Piper malacophyllum (C. PESL) C. DC extract and its isolated compounds in a mouse model of dysmenorrhoea

The effects of Piper malacophyllum (C. Pesl) C. DC extracts and its isolated compounds were analysed in a mouse model of primary dysmenorrhoea (PD). Female Swiss mice (6-8 weeks old) on proestrus were intraperitoneally treated with estradiol benzoate for 3 days, to induce PD. Twenty-four hours later, animals were treated 24 h later with vehicle, plant extract, gibbilimbol B, 4,6-dimethoxy-5-E-phenylbutenolide, mixture of 4,6-dimethoxy-5-E-phenylbutenolide and 4,6-dimethoxy-5-Z-phenylbutenolide, or ibuprofen. One hour later, oxytocin was injected and the numbers of abdominal writhing were counted. Then, mice were euthanized and uteri were collected for morphometrical and histological analyses. The effects of P. malacophyllum in inflammation were investigated in mouse peritoneal neutrophils culture stimulated with LPS or fMLP (chemotaxis and mediator release). Finally, uterus contractile and relaxing responses were assessed. Similar to ibuprofen, P. malacophyllum extract and isolated compounds reduced abdominal writhing in mice with PD. Histology indicated a marked neutrophil and mast cell infiltrate in the uterus of PD animals which was attenuated by the extract. The compounds and the extract reduced neutrophil chemotaxis and inflammatory mediator release by these cells. Reduced TNF levels were also observed in uteri of PD mice treated with P. malacophyllum. The extract did not affect spontaneous uterine contractions nor those induced by carbachol or KCl. However, it caused relaxation of oxytocin-induced uterine contraction, an effect blunted by H1 receptor antagonist. Overall the results indicate that P. malacophyllum may represent interesting natural tools for reliving PD symptoms, reducing the triad of pain, inflammation and spasmodic uterus behaviour.

Optimization of physicochemical properties is a strategy to improve drug-likeness associated with activity: novel active and selective compounds against Trypanosoma cruzi

Trypanosoma cruzi is the causing agent of Chagas disease, a parasitic infection without efficient treatment for chronic patients. Despite the efforts, no new drugs have been approved for this disease in the last 60 years. Molecular modifications based on a natural product led to the development of a series of compounds (LINS03 series) with promising antitrypanosomal activity, however previous chemometric analysis revealed a significant impact of excessive lipophilicity and low aqueous solubility on potency of amine and amide derivatives. Therefore, this work reports different modifications in the core structure to achieve adequate balance of the physicochemical properties along with biological activity. A set of 34 analogues were designed considering predicted properties related to lipophilicity/hydrosolubility and synthesized to assess their activity and selective toxicity towards the parasite. Results showed that this strategy contributed to improve the drug-likeness of the series while considerable impacts on potency were observed. The rational analysis of the obtained data led to the identification of seven active piperazine amides (28-34, IC₅₀ 8.7 to 35.3 µM against intracellular amastigotes), devoid of significant cytotoxicity to mammalian cells. The addition of water-solubilizing groups and privileged substructures such as piperazines improved the physicochemical properties and overall drug-likeness of these compounds, increased potency and maintained selectivity towards the parasite. The obtained results brought important structure-activity relationship (SAR) data and new lead structures for further modifications were identified to achieve improved antitrypanosoma compounds.

Evaluation of Gibbilimbol B, Isolated from Piper malacophyllum (Piperaceae), as an Antischistosomal Agent

Infections caused by parasitic worms impose a considerable worldwide health burden. One of the most impactful is schistosomiasis, a disease caused by blood-dwelling of the genus Schistosoma that affects more than 230 million people worldwide. Since praziquantel has also been extensively used to treat schistosomiasis and other parasitic flatworm infections, there is an urgent need to identify novel anthelmintic compounds, mainly from natural sources. In this study, the hexane extract from roots of Piper malacophyllum (Piperaceae) showed to be mainly composed for gibbilimbol B by HPLC/ESI-HRMS. Based on this result, this compound was isolated by chromatographic steps and its structure was confirmed by NMR. In vitro bioassays showed that gibbilimbol B was more active than praziquantel against larval stage of S. mansoni, with effective concentrations of 50 % (EC₅₀ ) and 90 % (EC₉₀ ) values of 2.6 and 3.4 μM, respectively. Importantly, gibbilimbol B showed no cytotoxicity to mammalian cells at a concentration 190 times greater than the antiparasitic effect, giving support for the anthelmintic potential of gibbilimbol B as lead compound for novel antischistosomal agents.

Potential of Piper spp. as a source of new compounds for the leishmaniases treatment

Current treatment guidelines for leishmaniasis is based on chemotherapy with drugs that show a set of limitations such as high cost, toxicity, difficult route of administration, and lack of efficacy in endemic areas. In this context, phytopharmaceutical products and herbal medicines emerge as promising alternatives for developing new treatment against leishmaniasis. This review discusses the perspectives of leishmaniasis treatment based on natural products and phytotherapy highlighting the Piper genus, especially P. aduncun and P. mollicomum Kunth covering the period of 1998 to 2020. Leishmanicidal activity of pure compounds of Piper spp. [3-(3,4,5-trimethoxyphenyl) propanoic acid, 3-chlorosintenpyridone, 2'-hydroxy-3',4',6'-trimethoxy-chalcone, cardamonin, conocarpan, cubebin, eupomatenoid, flavokavain B, ( +)-(7R,8S)-epoxy-5,6-didehydrokavain, N-[7-(3',4'-methylenedioxypheny l-2(E),4(E)-heptadienoyl-pyrrolidine, N-[7-(3',4'-methylenedioxyphenyl)-2(Z),4(Z)-heptadienoyl-pyrrolidine, piperovatine, pellitorine, and piplartine (piperlongumine)] were proved against the promastigote and amastigote forms of parasite related with cutaneous (L. (L.) amazonensis, L. (V.) braziliensis, and L. (V.) guyanensis) and visceral (L. (L.) donovani, L. (L.) chagasi, and L. (L.) infantum). We also discussed the perspective of leishmaniasis treatment, considering the potential synergism between different promising species of Piper, presenting some interesting interaction possibilities for future studies between plants. Finally, the necessary steps for technological development of phytomedicines and herbal medicines with the desirable quality requirements for medicines are highlighted. The data presented here highlight the use of Piper spp. as source of pharmacological compounds that can lead to effective, safe, and inexpensive treatments for leishmaniasis.

The Potential of Traditional Knowledge to Develop Effective Medicines for the Treatment of Leishmaniasis

Leishmaniasis is a neglected tropical disease that affects people living in tropical and subtropical areas of the world. There are few therapeutic options for treating this infectious disease, and available drugs induce severe side effects in patients. Different communities have limited access to hospital facilities, as well as classical treatment of leishmaniasis; therefore, they use local natural products as alternative medicines to treat this infectious disease. The present work performed a bibliographic survey worldwide to record plants used by traditional communities to treat leishmaniasis, as well as the uses and peculiarities associated with each plant, which can guide future studies regarding the characterization of new drugs to treat leishmaniasis. A bibliographic survey performed in the PubMed and Scopus databases retrieved 294 articles related to traditional knowledge, medicinal plants and leishmaniasis; however, only 20 were selected based on the traditional use of plants to treat leishmaniasis. Considering such studies, 378 quotes referring to 292 plants (216 species and 76 genera) that have been used to treat leishmaniasis were recorded, which could be grouped into 89 different families. A broad discussion has been presented regarding the most frequent families, including Fabaceae (27 quotes), Araceae (23), Solanaceae and Asteraceae (22 each). Among the available data in the 378 quotes, it was observed that the parts of the plants most frequently used in local medicine were leaves (42.3% of recipes), applied topically (74.6%) and fresh poultices (17.2%). The contribution of Latin America to studies enrolling ethnopharmacological indications to treat leishmaniasis was evident. Of the 292 plants registered, 79 were tested against Leishmania sp. Future studies on leishmanicidal activity could be guided by the 292 plants presented in this study, mainly the five species Carica papaya L. (Caricaceae), Cedrela odorata L. (Meliaceae), Copaifera paupera (Herzog) Dwyer (Fabaceae), Musa × paradisiaca L. (Musaceae), and Nicotiana tabacum L. (Solanaceae), since they are the most frequently cited in articles and by traditional communities.

Synthesis and Evaluation of Novel 2,2-Dimethylthiochromanones as Anti-Leishmanial Agents

Within this work, we describe the design and synthesis of a range of novel thiochromanones based on natural products reported to possess anti-leishmanial action, and their synthetic derivatives. All compounds were elaborated via the key intermediate 2,2,6-trimethoxythiochromanone, which was modified at the benzylic position to afford various ester, amine and amide analogues, substituted by chains of varying lipophilicity. Upon testing in Leishmania, IC₅₀ values revealed the most potent compounds to be phenylalkenyl and haloalkyl amides 11a and 11e, with IC₅₀ values of 10.5 and 7.2 μM, respectively.

Secondary metabolites in a neotropical shrub: spatiotemporal allocation and role in fruit defense and dispersal

Deciphering the ecological roles of plant secondary metabolites requires integrative studies that assess both the allocation patterns of compounds and their bioactivity in ecological interactions. Secondary metabolites have been primarily studied in leaves, but many are unique to fruits and can have numerous potential roles in interactions with both mutualists (seed dispersers) and antagonists (pathogens and predators). We described 10 alkenylphenol compounds from the plant species Piper sancti-felicis (Piperaceae), quantified their patterns of intraplant allocation across tissues and fruit development, and examined their ecological role in fruit interactions. We found that unripe and ripe fruit pulp had the highest concentrations and diversity of alkenylphenols, followed by flowers; leaves and seeds had only a few compounds at detectable concentrations. We observed a nonlinear pattern of alkenylphenol allocation across fruit development, increasing as flowers developed into unripe pulp then decreasing as pulp ripened. This pattern is consistent with the hypothesis that alkenylphenols function to defend fruits from pre-dispersal antagonists and are allocated based on the contribution of the tissue to the plant's fitness, but could also be explained by non-adaptive constraints. To assess the impacts of alkenylphenols in interactions with antagonists and mutualists, we performed fungal bioassays, field observations, and vertebrate feeding experiments. In fungal bioassays, we found that alkenylphenols had a negative effect on the growth of most fungal taxa. In field observations, nocturnal dispersers (bats) removed the majority of infructescences, and diurnal dispersers (birds) removed a larger proportion of unripe infructescences. In feeding experiments, bats exhibited an aversion to alkenylphenols, but birds did not. This observed behavior in bats, combined with our results showing a decrease in alkenylphenols during ripening, suggests that alkenylphenols in fruits represent a trade-off (defending against pathogens but reducing disperser preference). These results provide insight into the ecological significance of a little studied class of secondary metabolites in seed dispersal and fruit defense. More generally, documenting intraplant spatiotemporal allocation patterns in angiosperms and examining mechanisms behind these patterns with ecological experiments is likely to further our understanding of the evolutionary ecology of plant chemical traits.

Natural Products: Key Prototypes to Drug Discovery Against Neglected Diseases Caused by Trypanosomatids

BACKGROUND

Neglected tropical diseases are a group of infections caused by microorganisms and viruses that affect mainly poor regions of the world. In addition, most available drugs are associated with long periods of treatment and high toxicity which limits the application and patient compliance. Investment in research and development is not seen as an attractive deal by the pharmaceutical industry since the final product must ideally be cheap, not returning the amount invested. Natural products have always been an important source for bioactive compounds and are advantageous over synthetic compounds when considering the unique structural variety and biological activities. On the other hand, isolation difficulties and low yields, environmental impact and high cost usually limit their application as drug per se.

OBJECTIVE

In this review, the use of natural products as prototypes for the semi-synthesis or total synthesis, as well as natural products as promising hits is covered, specifically regarding compounds with activities against trypanosomatids such as Trypanosoma spp. and Leishmania spp.

METHODS

Selected reports from literature with this approach were retrieved.

CONCLUSION

As summary, it can be concluded that natural products are an underestimated source for designing novel agents against these parasites.

Piperaceae do nordeste brasileiro II: estado de Alagoas

Resumo Este estudo traz o tratamento taxonômico das espécies de Piperaceae ocorrentes no estado de Alagoas, com o objetivo ampliar o conhecimento sobre a flora alagoana e dar continuidade aos estudos com a família no nordeste brasileiro. Foram registradas 30 espécies de Piperaceae, distribuídas nos gêneros Peperomia (9 spp.) e Piper (21 spp.), das quais oito são pela primeira vez registradas para o estado de Alagoas (3 e 5 spp., respectivamente). Apesar da maioria dos táxons ocorrerem em áreas florestais, alguns podem ser encontrados em áreas de restinga, brejo de altitude, no agreste, cerrado e na caatinga. São apresentadas chave para a identificação dos táxons ocorrentes, descrições para as espécies analisadas, além de comentários sobre distribuição geográfica, habitat, ação biológica, e ilustrações para aquelas pouco conhecidas.

β-Amino acid derivatives as mitochondrial complex III inhibitors of L. donovani: A promising chemotype targeting visceral leishmaniasis

β-amino acids and their analogues are gathering increased attention not only because of their antibacterial and antifungal activity, but also for their use in designing peptidomimetics with increased oral bioavailability and resistance to metabolic degradation. In this study, a series of α-phenyl substituted chalcones, α-phenyl, β-amino substituted dihydrochalcones and β-amino acid derivatives were synthesized and evaluated for their antileishmanial efficacy against experimental visceral leishmaniasis (VL). Among all synthesized derivatives, 10c showed promising antileishmanial efficacy against both extracellular promastigote and intracellular amastigote (IC₅₀ 8.2 μM and 20.5 μM respectively) of L. donovani with negligible cytotoxic effect towards J774 macrophages and Vero cells. 10c effectively reduced spleen and liver parasite burden (>90%) in both hamster and Balb/c model of VL without any hepatotoxicity. In vitro pharmacokinetic analysis showed that 10c was stable in gastric fluid and plasma of Balb/c mice at 10 μg/ml. Further analysis of the molecular mechanism revealed that 10c entered into the parasite by depolarizing the plasma membrane rather than forming nonspecific pores and induced molecular events like loss in mitochondrial membrane potential with a gradual decline in ATP production. This, in turn, did not induce programmed cell death of the parasite; rather 10c induced bioenergetic collapse of the parasite by decreasing ATP synthesis through specific inhibition of mitochondrial complex III activity. Altogether, our results allude to the therapeutic potential of β-amino acid derivatives as novel antileishmanials, identifying them as lead compounds for further exploration in the design of potent candidates for the treatment of visceral leishmaniasis.

XIAP as a Target of New Small Organic Natural Molecules Inducing Human Cancer Cell Death

X-linked inhibitor of apoptosis protein (XIAP) is an emerging crucial therapeutic target in cancer. We report on the discovery and characterisation of small organic molecules from Piper genus plants exhibiting XIAP antagonism, namely erioquinol, a quinol substituted in the 4-position with an alkenyl group and the alkenylphenols eriopodols A–C. Another isolated compound was originally identified as gibbilimbol B. Erioquinol was the most potent inhibitor of human cancer cell viability when compared with gibbilimbol B and eriopodol A was listed as intermediate. Gibbilimbol B and eriopodol A induced apoptosis through mitochondrial permeabilisation and caspase activation while erioquinol acted on cell fate via caspase-independent/non-apoptotic mechanisms, likely involving mitochondrial dysfunctions and aberrant generation of reactive oxygen species. In silico modelling and molecular approaches suggested that all molecules inhibit XIAP by binding to XIAP-baculoviral IAP repeat domain. This demonstrates a novel aspect of XIAP as a key determinant of tumour control, at the molecular crossroad of caspase-dependent/independent cell death pathway and indicates molecular aspects to develop tumour-effective XIAP antagonists.

Evaluation of the antitrypanosoma activity and SAR study of novel LINS03 derivatives

Chagas' disease is a parasitic infection caused by Trypanosoma cruzi that is still treated by old and toxic drugs. In the search for novel alternatives, natural sources are an important source for new drug prototypes against T. cruzi to further structural exploitation. A set of natural-based compounds (LINS03) was designed, showing promising antitrypanosoma activity and low cytotoxicity to host cells. In this paper, nine novel LINS03 derivatives were evaluated against T. cruzi trypomastigotes and amastigotes. The selectivity was assessed through cytotoxicity assays using NCTC mammalian cells and calculating the CC₅₀/IC₅₀ ratio. The results showed that compounds 2d and 4c are noteworthy, due their high activity against amastigotes (IC₅₀ 13.9 and 5.8 µM) and low cytotoxicity (CC₅₀ 107.7 µM and >200 µM, respectively). These compounds did not showed alteration on plasma membrane permeability in a Sytox green model. SAR analysis suggested an ideal balance between hydrosolubility and lipophilicity is necessary to improve the activity, and that insertion of a meta-substituent is detrimental to the activity of the amine derivatives but not to the neutral derivatives, suggesting different mechanisms of actions. The results presented herein are valuable for designing novel compounds with improved activity and selectivity to be applied in future studies.

Antiparasitic activity of new gibbilimbol analogues and SAR analysis through efficiency and statistical methods

Chagas' disease and leishmaniasis are parasitic infections enrolled among the neglected tropical diseases, which urge for new treatments. In the search for new chemical entities as prototypes, gibbilimbols A/B have shown antiparasitic activity against Trypanosoma cruzi and Leishmania infantum, and then a set of analogues (LINS03 series) of this natural product were synthesized and evaluated in vitro against the parasites. In the present paper we reported five new compounds with activity against these protozoan parasites, and quite low cytotoxicity. Moreover, the interference of plasma membrane permeability of these analogues were also evaluated. We found that [(4-methoxyphenyl)methyl]octylamine (4) was noteworthy due to its high activity against the amastigote form of both parasites (IC₅₀ 1.3-5.8 μM) and good selectivity index. In order to unveil the SAR for this chemotype, we also presented a group efficiency analysis and PCA and HCA study, which indicated that the methoxyl provides good activity with lower cytotoxicity to mammalian cells. The results from SAR analyses suggest different mechanisms of action between the neutral and basic compounds. In summary, the analogues represent important activity against these parasites and must be prototypes for further exploitation.

New alkenyl derivative from Piper malacophyllum and analogues: Antiparasitic activity against Trypanosoma cruzi and Leishmania infantum

Alkylphenols isolated from Piper malacophyllum (Piperaceae), gibbilimbols A and B, showed interesting activity against the parasites Trypanosoma cruzi and Leishmania infantum. In continuation to our previous work, a new natural product from the essential oil of the leaves of P. malacophyllum was isolated, the 5-[(3E)-oct-3-en-1-il]-1,3-benzodioxole, and also a new set of five compounds was prepared. The antiparasitic activity of the natural product was evaluated in vitro against these parasites, indicating potential against the promastigote/trypomastigote/amastigote forms (IC₅₀ 32-83 μm) of the parasites and low toxicity (CC₅₀  > 200 μm) to mammalian cells. The results obtained to the synthetic compounds indicated that the new derivatives maintained the promising antiparasitic activity, but the cytotoxicity was considerably lowered. The amine derivative LINS03011 displayed the most potent IC₅₀ values (13.3 and 16.7 μm) against amastigotes of T. cruzi and L. infantum, respectively, indicating comparable activity to the phenolic prototype LINS03003, with threefold decreased (CC₅₀ 73.5 μm) cytotoxicity, leading the selectivity index (SI) towards the parasites up to 24.5. In counterpart, LINS03011 has not shown membrane disruptor activity in SYTOX Green model. In summary, this new set showed the hydroxyl is not essential for the antiparasitic activity, and its substitution could decrease the toxicity to mammalian cells.

Treatment with synthetic lipophilic tyrosyl ester controls Leishmania major infection by reducing parasite load in BALB/c mice

Synthesized lipophilic tyrosyl ester derivatives with increasing lipophilicity were effective against Leishmania (L.) major and Leishmania infantum species in vitro. These findings prompted us to test in vivo leishmanicidal properties of these molecules and their potential effect on the modulation of immune responses. The experimental BALB/c model of cutaneous leishmaniasis was used in this study. Mice were infected with L. major parasites and treated with three in vitro active tyrosyl esters derivatives. Among these tested tyrosylcaprate (TyC) compounds, only TyC10 exhibited an in vivo anti-leishmanial activity, when injected sub-cutaneously (s.c.). TyC10 treatment of L. major-infected BALB/c mice resulted in a decrease of lesion development and parasite load. TyC10 s.c. treatment of non-infected mice induced an imbalance in interferon γ/interleukin 4 (IFN-γ/IL-4) ratio cytokines towards a Th1 response. Our results indicate that TyC10 s.c. treatment improves lesions' healing and parasite clearance and may act on the cytokine balance towards a Th1 protective response by decreasing IL-4 and increasing IFN-γ transcripts. TyC10 is worthy of further investigation to uncover its mechanism of action that could lead to consider this molecule as a potential drug candidate.

Gibbilimbol analogues as antiparasitic agents--Synthesis and biological activity against Trypanosoma cruzi and Leishmania (L.) infantum

The essential oils from leaves of Piper malacophyllum (Piperaceae) showed to be mainly composed by two alkenylphenol derivatives: gibbilimbols A and B. After isolation and structural characterization by NMR and MS data analysis, both compounds were evaluated against promastigote/amastigote forms of Leishmania (L.) infantum as well as trypomastigote/amastigote forms of Trypanosoma cruzi. The obtained results indicated that gibbilimbol B displayed potential against the tested parasites and low toxicity to mammalian cells, stimulating the preparation of several quite simple synthetic analogues in order to improve its activity and to explore the preliminary structure-activity relationships (SAR) data. Among the prepared derivatives, compound LINS03003 (n-octyl-4-hydroxybenzylamine) displayed the most potent IC50 values of 5.5 and 1.8 μM against amastigotes of T. cruzi and L. (L.) infantum, respectively, indicating higher activity than the natural prototype. In addition, this compound showed remarkable selectivity index (SI) towards the intracellular forms of Leishmania (SI=13.1) and T. cruzi (SI=4.3). Therefore, this work indicated that preparation of synthetic compounds structurally based in the bioactive natural products could be an interesting source of novel and selective compounds against these protozoan parasites.

Cinnamic acid derived compounds loaded into liposomes: antileishmanial activity, production standardisation and characterisation

Synthetic compounds derived from cinnamic acid were tested in cultures containing the promastigote form of Leishmania amazonensis and the dimethylsulphoxide solution of B2 compound (2.0 mg/mL) led to a 92% decrease of leishmania in 96 h of treatment. Then, different liposomal systems (diameters ∼200 nm) were prepared by the extrusion method in the presence and absence of compounds studied. DSC thermograms of the liposomes in the presence of these compounds caused changes in ΔH, Tm and ΔT1/2, compared to controls, indicating that there was an interaction of the compounds with the lipid bilayer. Assays with negatively charged liposomal systems containing these drugs in L. amazonensis cultures led to a 50-80% decrease in the number of leishmanias with a concentration to 100 times lower when compared to the B2 initial test. These liposomal systems are promoting more interaction and delivery of the compounds and proved to be an efficient, stable and promising system.

Antitrypanosomal Acetylene Fatty Acid Derivatives from the Seeds of Porcelia macrocarpa (Annonaceae)

Chagas’ disease is caused by a parasitic protozoan and affects the poorest population in the world, causing high mortality and morbidity. As a result of the toxicity and long duration of current treatments, the discovery of novel and more efficacious drugs is crucial. In this work, the hexane extract from seeds of Porcelia macrocarpa R.E. Fries (Annonaceae) displayed in vitro antitrypanosomal activity against trypomastigote forms of T. cruzi by the colorimetric MTT assay (IC₅₀ of 65.44 μg/mL). Using chromatographic fractionation over SiO₂, this extract afforded a fraction composed by one active compound (IC₅₀ of 10.70 µg/mL), which was chemically characterized as 12,14-octadecadiynoic acid (macrocarpic acid). Additionally, two new inactive acetylene compounds (α,α'-dimacro-carpoyl-β-oleylglycerol and α-macrocarpoyl-α'-oleylglycerol) were also isolated from the hexane extract. The complete characterization of the isolated compounds was performed by analysis of NMR and MS data as well as preparation of derivatives.

Antiparasitic activity of natural and semi-synthetic tirucallane triterpenoids from Schinus terebinthifolius (Anacardiaceae): structure/activity relationships

Leishmaniasis and Chagas are diseases caused by parasitic protozoans that affect the poorest population in the World, causing a high mortality and morbidity. As a result of highly toxic and long-term treatments, the discovery of novel, safe and more efficacious drugs is essential. In this work, the in vitro antiparasitic activity and mammalian cytotoxicity of three natural tirucallane triterpenoids, isolated from leaves of Schinus terebinthifolius (Anacardiaceae), and nine semi-synthetic derivatives were investigated against Leishmania (L.) infantum and Trypanosoma cruzi. Trypomastigotes of T. cruzi were the most susceptible parasites and seven compounds demonstrated a trypanocidal activity with IC₅₀ values in the range between 15 and 58 µg/mL. Four compounds demonstrated selectivity towards the intracellular amastigotes of Leishmania, with IC₅₀ values in the range between 28 and 97 µg/mL. The complete characterization of triterpenoids was afforded after thorough analysis of nuclear magnetic resonance (NMR) data as well as electrospray ionization mass spectrometry (ESI-MS). Additionally, structure-activity relationships were performed using Decision Trees.

Antiparasitic activity and effect of casearins isolated from Casearia sylvestris on Leishmania and Trypanosoma cruzi plasma membrane

Leishmaniasis and Chagas disease are infectious diseases caused by parasite Leishmania sp. and Trypanosoma cruzi, respectively, and are included among the most neglected diseases in several underdeveloped and developing countries, with an urgent demand for new drugs. Considering the antiparasitic potential of MeOH extract from leaves of Casearia sylvestris Sw. (Salicaceae), a bioguided fractionation was conducted and afforded four active clerodane diterpenes (casearins A, B, G, and J). The obtained results indicated a superior efficacy of tested casearins against trypomastigotes of T. cruzi, with IC50 values ranging from 0.53 to 2.77 μg/ml. Leishmania infantum promastigotes were also susceptible to casearins, with IC50 values in a range between 4.45 and 9.48 μg/ml. These substances were also evaluated for mammalian cytotoxicity against NCTC cells resulting in 50% cytotoxic concentrations (CC50) ranging from 1.46 to 13.76 μg/ml. Additionally, the action of casearins on parasite membranes was investigated using the fluorescent probe SYTOX Green. The obtained results demonstrated a strong interaction of casearins A and B to the plasma membrane of T. cruzi parasites, corroborating their higher efficacy against these parasites. In contrast, the tested casearins induced no alteration in the permeability of plasma membrane of Leishmania parasites, suggesting that biochemical differences between Leishmania and T. cruzi plasma membrane might have contributed to the target effect of casearins on trypomastigotes. Thus, considering the importance of studying novel and selective drug candidates against protozoans, casearins A, B, G, and J could be used as tools to future drug design studies.