Antileishmanial activity of standardized fractions of Stryphnodendron obovatum (Barbatimão) extract and constituent compounds

Targeting with Structural Analogs of Natural Products the Purine Salvage Pathway in Leishmania (Leishmania) infantum by Computer-Aided Drug-Design Approaches

Visceral Leishmaniasis (VL) has a high death rate, with 500,000 new cases and 50,000 deaths occurring annually. Despite the development of novel strategies and technologies, there is no adequate treatment for the disease. Therefore, the purpose of this study is to find structural analogs of natural products as potential novel drugs to treat VL. We selected structural analogs from natural products that have shown antileishmanial activities, and that may impede the purine salvage pathway using computer-aided drug-design (CADD) approaches. For these, we started with the vastly studied target in the pathway, the adenine phosphoribosyl transferase (APRT) protein, which alone is non-essential for the survival of the parasite. Keeping this in mind, we search for a substance that can bind to multiple targets throughout the pathway. Computational techniques were used to study the purine salvage pathway from Leishmania infantum, and molecular dynamic simulations were used to gather information on the interactions between ligands and proteins. Because of its low homology to human proteins and its essential role in the purine salvage pathway proteins network interaction, the findings further highlight the significance of adenylosuccinate lyase protein (ADL) as a therapeutic target. An analog of the alkaloid Skimmianine, N,N-diethyl-4-methoxy-1-benzofuran-6-carboxamide, demonstrated a good binding affinity to APRT and ADL targets, no expected toxicity, and potential for oral route administration. This study indicates that the compound may have antileishmanial activity, which was granted in vitro and in vivo experiments to settle this finding in the future.

Computer-aided drug design approaches applied to screen natural product's structural analogs targeting arginase in Leishmania spp

Introduction: Leishmaniasis is a disease with high mortality rates and approximately 1.5 million new cases each year. Despite the new approaches and advances to fight the disease, there are no effective therapies. Methods: Hence, this study aims to screen for natural products' structural analogs as new drug candidates against leishmaniasis. We applied Computer-aided drug design (CADD) approaches, such as virtual screening, molecular docking, molecular dynamics simulation, molecular mechanics-generalized Born surface area (MM-GBSA) binding free estimation, and free energy perturbation (FEP) aiming to select structural analogs from natural products that have shown anti-leishmanial and anti-arginase activities and that could bind selectively against the Leishmania arginase enzyme. Results: The compounds 2H-1-benzopyran, 3,4-dihydro-2-(2-methylphenyl)-(9CI), echioidinin, and malvidin showed good results against arginase targets from three parasite species and negative results for potential toxicities. The echioidinin and malvidin ligands generated interactions in the active center at pH 2.0 conditions by MM-GBSA and FEP methods. Conclusions: This work suggests the potential anti-leishmanial activity of the compounds and thus can be further in vitro and in vivo experimentally validated.

Human Lung Cancer (A549) Cell Line Cytotoxicity and Anti-Leishmania major Activity of Carissa macrocarpa Leaves: A Study Supported by UPLC-ESI-MS/MS Metabolites Profiling and Molecular Docking

Lung cancer and cutaneous leishmaniasis are critical diseases with a relatively higher incidence in developing countries. In this research, the activity of Carissa macrocarpa leaf hydromethanolic extract and its solvent-fractions (n-hexane, EtOAc, n-butanol, and MeOH) against the lung adenocarcinoma cell line (A549) and Leishmania major was investigated. The MeOH fraction exhibited higher cytotoxic activity (IC₅₀ 1.57 ± 0.04 μg/mL) than the standard drug, etoposide (IC₅₀ 50.8 ± 3.16 μg/mL). The anti-L. major results revealed strong growth inhibitory effects of the EtOAc fraction against L. major promastigotes (IC₅₀ 27.52 ± 0.7 μg/mL) and axenic amastigotes (29.33 ± 4.86% growth inhibition at 100 μg/mL), while the butanol fraction exerted moderate activity against promastigotes (IC₅₀ 73.17 ± 1.62), as compared with miltefosine against promastigotes (IC₅₀ 6.39 ± 0.29 μg/mL) and sodium stibogluconate against axenic amastigotes (IC₅₀ 22.45 ± 2.22 μg/mL). A total of 102 compounds were tentatively identified using UPLC-ESI-MS/MS analysis of the total extract and its fractions. The MeOH fraction was found to contain several flavonoids and flavan-3-ol derivatives with known cytotoxic properties, whereas the EtOAc fractions contained triterpene, hydroxycinnamoyl, sterol, and flavanol derivatives with known antileishmanial activity. Molecular docking of various polyphenolics of the MeOH fraction with HDAC6 and PDK3 enzymes demonstrates high binding affinity of the epicatechin 3-O-β-D-glucopyranoside and catechin-7-O-β-D-glucopyranoside toward HDAC6, and procyanidin C2, procyanidin B5 toward PDK3. These results are promising and encourage the pursuit of preclinical research using C. macrocarpa's MeOH fraction as anti-lung cancer and the EtOAc fraction as an anti-L. major drug candidates.

Silk Fibroin Hydrogels Incorporated with the Antioxidant Extract of Stryphnodendron adstringens Bark

Barbatimão (Stryphnodendron adstringens) is a Brazilian medicinal plant known for its pharmacological properties, including healing activity related to its phenolic composition, which is chiefly given by tannins. In order to preserve its stability and bioactivity, barbatimão extracts can be incorporated into (bio-)polymeric matrixes, of which silk fibroin stands out due to its versatility and tunable properties. This work aimed to obtain barbatimão bark extract rich in phenolic compounds and evaluate its incorporation in fibroin hydrogels. From the extraction process, it was observed that the PG (propylene glycol) extract presented a higher global yield (X₀) and phenolic compounds (TPC) than the ET (ethanol) extract. Furthermore, the antioxidant activity (ORAC and FRAP) was similar between both extracts. Regarding the hydrogels, morphological, chemical, thermal, and mechanical characterizations were performed to understand the influence of the barbatimão extract and the solvent on the fibroin hydrogel properties. As a result, the hydrogels containing the barbatimão PG extract (BT/PG hydrogels) showed the better physical-chemical and structural performance. Therefore, these hydrogels should be further investigated regarding their potential in medical and pharmaceutical applications, especially in wound healing.

Feature-Based Molecular Network-Guided Dereplication of Natural Bioactive Products from Leaves of Stryphnodendron pulcherrimum (Willd.) Hochr

Stryphnodendron pulcherrimum is a species known to have a high content of tannins. Accordingly, its preparations are used in southern Pará, Brazil, for their anti-inflammatory and antimicrobial activities, but so far, its chemical profile composition remains essentially unknown. We herein describe the compounds present in a hydro-acetonic extract from S. pulcherrimum leaves as revealed by dereplication via ultra-high performance liquid chromatography coupled to high-resolution mass spectrometry. The data were combined with spectral organization, spectral matching through the Global Natural Products Social platform, in silico annotation and taxonomical ponderation. Several types of phenolic compounds were identified such as gallic acids, flavan-3-ols and flavone-like compounds. From these, 5 have been recently reported by our group, whereas 44 are reported here for the first time in this tree species, and 41 (out of 49) for this genus. The results highlight the possible role of Stryphnodendron pulcherrimum as a renewable source for natural bioactive products with potential pharmaceutical applications.

Natural Products That Target the Arginase in Leishmania Parasites Hold Therapeutic Promise

Parasites of the genus Leishmania cause a variety of devastating and often fatal diseases in humans worldwide. Because a vaccine is not available and the currently small number of existing drugs are less than ideal due to lack of specificity and emerging drug resistance, the need for new therapeutic strategies is urgent. Natural products and their derivatives are being used and explored as therapeutics and interest in developing such products as antileishmanials is high. The enzyme arginase, the first enzyme of the polyamine biosynthetic pathway in Leishmania, has emerged as a potential therapeutic target. The flavonols quercetin and fisetin, green tea flavanols such as catechin (C), epicatechin (EC), epicatechin gallate (ECG), and epigallocatechin-3-gallate (EGCG), and cinnamic acid derivates such as caffeic acid inhibit the leishmanial enzyme and modulate the host’s immune response toward parasite defense while showing little toxicity to the host. Quercetin, EGCG, gallic acid, caffeic acid, and rosmarinic acid have proven to be effective against Leishmania in rodent infectivity studies. Here, we review research on these natural products with a focus on their promise for the development of treatment strategies as well as unique structural and pharmacokinetic/pharmacodynamic features of the most promising agents.

Catechins as Model Bioactive Compounds for Biomedical Applications

Research regarding polyphenols has gained prominence over the years because of their potential as pharmacological nutrients. Most polyphenols are flavanols, commonly known as catechins, which are present in high amounts in green tea. Catechins are promising candidates in the field of biomedicine. The health benefits of catechins, notably their antioxidant effects, are related to their chemical structure and the total number of hydroxyl groups. In addition, catechins possess strong activities against several pathogens, including bacteria, viruses, parasites, and fungi. One major limitation of these compounds is low bioavailability. Catechins are poorly absorbed by intestinal barriers. Some protective mechanisms may be required to maintain or even increase the stability and bioavailability of these molecules within living organisms. Moreover, novel delivery systems, such as scaffolds, fibers, sponges, and capsules, have been proposed. This review focuses on the unique structures and bioactive properties of catechins and their role in inflammatory responses as well as provides a perspective on their use in future human health applications.

Determination of chemical structure and anti-Trypanosoma cruzi activity of extracts from the roots of Lonchocarpus cultratus (Vell.) A.M.G. Azevedo & H.C. Lima

Trypanosoma cruzi is the agent of Chagas disease, an infection that affects around 8 million people worldwide. The search for new anti-T. cruzi drugs are relevant, mainly because the treatment of this disease is limited to two drugs. The objective of this study was to investigate the trypanocidal and cytotoxic activity and elucidate the chemical profile of extracts from the roots of the Lonchocarpus cultratus. Roots from L. cultratus were submitted to successive extractions with hexane, dichloromethane, and methanol, resulting in LCH, LCD, and LCM extracts, respectively. Characterization of extracts was done using 1H-RMN, 13C-RMN, CC and TLC. Treatment of T. cruzi forms (epimastigotes, trypomastigotes, and amastigotes) with crescent concentrations of LCH, LCD, and LCM was done for 72, 48, and 48 h, respectively. After this, the percentage of inhibition and IC50/LC50 were calculated. Benznidazole was used as a positive control. Murine macrophages were treated with different concentrations of both extracts for 48 h, and after, the cellular viability was determined by the MTT method and CC50 was calculated. The chalcones derricin and lonchocarpine were identified in the hexane extract, and for the first time in the genus Lonchocarpus, the presence of a dihydrolonchocarpine derivative was observed. Other chalcones such as isocordoin and erioschalcone B were detected in the dichloromethane extract. The dichloromethane extract showed higher activity against all tested forms of T. cruzi than the other two extracts, with IC50 values of 10.98, 2.42, and 0.83 µg/mL, respectively; these values are very close to those of benznidazole. Although the dichloromethane extract presented a cytotoxic effect against mammalian cells, it showed selectivity against amastigotes. The methanolic extract showed the lowest anti-T. cruzi activity but was non-toxic to peritoneal murine macrophages. Thus, the genus Lonchocarpus had demonstrated in the past action against epimastigotes forms of T. cruzi but is the first time that the activity against infective forms is showed, which leading to further studies with in vivo tests.

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

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

Leishmania infantum arginase: biochemical characterization and inhibition by naturally occurring phenolic substances

Inhibition of Leishmania arginase leads to a decrease in parasite growth and infectivity and thus represents an attractive therapeutic strategy. We evaluated the inhibitory potential of selected naturally occurring phenolic substances on Leishmania infantum arginase (ARGLi) and investigated their antileishmanial activity in vivo. ARGLi exhibited a V_max of 0.28 ± 0.016 mM/min and a K_m of 5.1 ± 1.1 mM for L-arginine. The phenylpropanoids rosmarinic acid and caffeic acid (100 µM) showed percentages of inhibition of 71.48 ± 0.85% and 56.98 ± 5.51%, respectively. Moreover, rosmarinic acid and caffeic acid displayed the greatest effects against L. infantum with IC₅₀ values of 57.3 ± 2.65 and 60.8 ± 11 μM for promastigotes, and 7.9 ± 1.7 and 21.9 ± 5.0 µM for intracellular amastigotes, respectively. Only caffeic acid significantly increased nitric oxide production by infected macrophages. Altogether, our results broaden the current spectrum of known arginase inhibitors and revealed promising drug candidates for the therapy of visceral leishmaniasis.

Stryphnodendron Species Known as "Barbatimão": A Comprehensive Report

Stryphnodendron spp., popularly known as "barbatimão", is the native Brazilian tree most often employed to treat wounds and infections. The aim of the present study was to highlight the importance of S. adstringens, as well as other Stryphnodendron species recognized as "barbatimão", to human health, depicting the relevance of ethnopharmacological knowledge to scientific evidence for uses, related chemical compounds, development of pharmaceutical formulations, and the establishment of toxicity parameters. For this purpose, the literature databases PubMed, Scielo, Lilacs, CAPES Thesis and Google Scholar were searched until 2017. It was observed that stem bark was the primary part of the plant used, mainly as a decoction, for wound healing and treatment of infectious and inflammatory disorders. Confirmed biological activities, including wound healing, anti-inflammatory, antioxidant, and antimicrobial activities, were related to the presence of compounds from tannin class, mostly proanthocyanidins. Toxicity parameters for stem bark were inconclusive, but toxicity was observed to a significant extent when seeds were ingested by cattle or other animals. Due to these important and confirmed biological activities, government policy encourages the phytotherapic use of S. adstringens, and some formulations with stem bark extracts were developed and patented. Furthermore, antiprotozoal, hypoglycemic and antiviral activities were identified as promising.

A Computational Approach Using Bioinformatics to Screening Drug Targets for Leishmania infantum Species

Background

The development of new therapeutic strategies to treat patients for leishmaniasis has become a priority. The antileishmanial activity of the strychnobiflavone flavonoid was recently demonstrated against Leishmania amazonensis and Leishmania infantum amastigotes and promastigotes. The biological effect of this molecule was identified due to its capacity to interfere in the parasite mitochondrial membrane; however, the underlying molecular mechanism remains unclear.

Methods and Results

In this study, a computational approach using bioinformatics was performed to screen biological targets of strychnobiflavone in L. infantum. Computational programs, such as the target fishing approach and molecular docking assays, were used. Results showed that the putative pathway targeted by strychnobiflavone in L. infantum is the methylglyoxal degradation superpathway, and one hydrolase-like protein was predicted to be the molecular target of this flavonoid in the parasites.

Conclusion

In this context, this study provides the basis for understanding the mechanism of action of strychnobiflavone in L. infantum and presents a strategy based on bioinformatics programs to screen targets of other molecules with biological action against distinct pathogens.

Treatment of murine visceral leishmaniasis using an 8-hydroxyquinoline-containing polymeric micelle system

New therapeutics are urgently needed to treat visceral leishmaniasis (VL). Due to the fact that drug discovery is a long and expensive process, the development of delivery systems to carry old and toxic drugs could be considered, as well as the evaluation of new molecules that have already shown to present biological activity. In this context, the present study evaluated the in vitro and in vivo antileishmanial activity of an 8-hydroxyquinoline (8-HQN)-containing polymeric micelle (8-HQN/M) system against Leishmania infantum, the main causative agent of VL in the Americas. The experimental strategy used was based on the evaluation of the parasite load by a limiting-dilution technique in the spleen, liver, bone marrow and draining lymph nodes of the infected and treated animals, as well as by a quantitative PCR (qPCR) technique to also assess the splenic parasite load. The immune response developed was evaluated by the production of IFN-γ, IL-4, IL-10, IL-12 and GM-CSF cytokines, as well as by antileishmanial nitrite dosage and antibodies production. Hepatic and renal enzymes were also investigated to verify cellular injury as a result of treatments toxicity. In the results, 8-HQN/M-treated mice, when compared to the other groups: saline, free amphotericin B (AmpB, as a drug control), 8-HQN and B-8-HQN/M (as a micelle control) showed more significant reductions in their parasite burden in all evaluated organs. These animals also showed an antileishmanial Th1 immunity, which was represented by high levels of IFN-γ, IL-12, GM-CSF and nitrite, associated with a low production of IL-4 and IL-10 and anti-Leishmania IgG1 isotype antibodies. In addition, any hepatic or renal damage was found in these treated animals. In conclusion, 8-HQN/M was effective in treating L. infantum-infected BALB/c mice, and can be considered alone, or combined with other drugs, as an alternative treatment for VL.

Antileishmanial activity and mechanism of action from a purified fraction of Zingiber officinalis Roscoe against Leishmania amazonensis

In recent years, considerable attention has been given to identify new antileishmanial products derived from medicinal plants, although, to date, no new effective compound has been recently applied to treat leishmaniasis. In the present study, the antileishmanial activity of a water extract from Zingiber officinalis Roscoe (ginger) was investigated and a purified fraction, named F10, was identified as responsible by this biological activity. The chemical characterization performed for this fraction showed that it is mainly composed by flavonoids and saponins. The water extract and the F10 fraction presented IC50 values of 125.5 and 49.8 μg/mL, respectively. Their selectivity indexes (SI) were calculated and values were seven and 40 times higher, respectively, in relation to the value found for amphotericin B, which was used as a control. Additional studies were performed to evaluate the toxicity of these compounds in human red blood cells, besides of the production of nitrite, as an indicator of nitric oxide (NO), in treated and infected macrophages. The results showed that both F10 fraction and water extract were not toxic to human cells, and they were able to stimulate the nitrite production, with values of 13.6 and 5.4 μM, respectively, suggesting that their biological activity could be due to macrophages activation via NO production. In conclusion, the present study shows that a purified fraction from ginger could be evaluated in future works as a therapeutic alternative, on its own or in association with other drugs, to treat disease caused by L. amazonensis.

Antileishmanial, antioxidant, and cytotoxic activities of Quercus infectoria Olivier extract

Currently, there is no effective vaccine available, and chemotherapy is the main approach for treatment of cutaneous leishmaniasis (CL). During recent decades, studies have demonstrated that a number of plant-derived compounds may act as new therapeutic tools against leishmaniasis. This study was evaluated the antileishmanial, antioxidant, and cytotoxic activities of Quercus infectoria Olivier (oak) extract. The total amount of phenolic and flavonoid compounds was measured in oak extract. High performance liquid chromatography (HPLC) analysis was also performed to determine the amount of quercetin and gallic acid in this plant. This extract (0-80g/mL) was evaluated in vitro against promastigote and intracellular amastigote forms of Leishmania major (MRHO/IR/75/ER) using MTT assay and in a macro-phage model, respectively. Then oak extract was tested on CL in infected male BALB/c mice with L. major in order to evaluate the antileishmanial activity topically. Moreover, cytotoxicity effects of oak in murine macrophage cells were tested by MTT assay. Antioxidative activity of oak was also determined by the 2,2-diphenyl-1,1-picrylhydrazyl (DPPH) scavenging test. The amount of phenolic and flavonoid compounds in the oak extract was 57.50 and 1.86%, respectively. The amount of quercetin and gallic acid in the oak extract was 0.0064 and 0.22%, respectively. The findings revealed that oak significantly (P<0.05) inhibited the growth rate of promastigote of (IC50 12.65μg/mL) and amastigotes (IC50 10.31μg/mL) as a dose-dependent response. In the in vivo assay, after 4 weeks of treatment, 91.6, 66.66, and 50% recovery was observed in the infected mice treated with 20, 10, and 5mg/kg of oak extract, respectively. After treatment of the infected mice with the concentration of 10 and 20mg/kg of oak, the mean diameter of lesions, parasite load and mean number of parasites was significantly (P<0.05) reduced. Selectivity index of greater than 10 for oak revealed that oak extract had no cytotoxic effects on macrophage cells. Moreover, DPPH test demonstrated that radical inhibition occurred at greater power with increasing the concentration of oak. To conclude, the present study showed potent antileishmanial and antioxidant activity of oak extract; whereas this plant had no toxic effect on mammalian cells.