Machine Learning-Based Virtual Screening of Antibacterial Agents against Methicillin-Susceptible and Resistant Staphylococcus aureus

The application of computer-aided drug discovery (CADD) approaches has enabled the discovery of new antimicrobial therapeutic agents in the past. The high prevalence of methicillin-resistantStaphylococcus aureus(MRSA) strains promoted this pathogen to a high-priority pathogen for drug development. In this sense, modern CADD techniques can be valuable tools for the search for new antimicrobial agents. We employed a combination of a series of machine learning (ML) techniques to select and evaluate potential compounds with antibacterial activity against methicillin-susceptible S. aureus (MSSA) and MRSA strains. In the present study, we describe the antibacterial activity of six compounds against MSSA and MRSA reference (American Type Culture Collection (ATCC)) strains as well as two clinical strains of MRSA. These compounds showed minimal inhibitory concentrations (MIC) in the range from 12.5 to 200 μM against the different bacterial strains evaluated. Our results constitute relevant proven ML-workflow models to distinctively screen for novel MRSA antibiotics.

Nematostatic activity of isoprenylated guanidine alkaloids from Pterogyne nitens and their interaction with acetylcholinesterase

Although new nematicides have appeared, the demand for new products less toxic and more efficient for the control of plant-parasitic nematodes are still high. Consequently, studies on natural secondary metabolites from plants, to develop new nematicides, have increased. In this work, nineteen extracts from eleven Brazilian plant species were screened for activity against Meloidogyne incognita. Among them, the extracts of Piterogyne nitens showed a potent nematostatic activity. The alkaloid fraction obtained from the ethanol extract of leaves of P. nitens was more active than the coming extract. Due to the promising activity from the alkaloid fraction, three isoprenylated guanidine alkaloids isolated from this fraction, galegine (1), pterogynidine (2), and pterogynine (3) were tested, showing similar activity to the alkaloid fraction, which was comparable to that of the positive control Temik at 250 μg/mL. At lower concentrations (125-50 μg/mL), compound 2 showed to be the most active one. As several nematicides act through inhibition of acetylcholinesterase (AChE), the guanidine alkaloids were also employed in two in vitro AChE assays. In both cases, compound 2 was more active than compounds 1 and 3. Its activity was considered moderated compared to the control (physostigmine). Compound 2 was selected for an in silico study with the electric eel (Electrophorus electricus) AChE, showing to bind mostly to the same site of physostigmine in the AChEs, pointing out that this could be the mechanism of action for this compound. These results suggested that the guanidine alkaloids 1,2 and 3 from P. nitens are promising for the development of new products to control M. incognita, especially guanidine 2, and encourage new investigations to confirm the mechanism of action, as well as to determine the structure-activity relationship of the guanidine alkaloids.

Identification of natural cytochalasins as leads for neglected tropical diseases drug discovery

Investigating the chemical diversity of natural products from tropical environments is an inspiring approach to developing new drug candidates for neglected tropical diseases (NTDs). In the present study, phenotypic screenings for antiprotozoal activity and a combination of computational and biological approaches enabled the identification and characterization of four cytochalasins, which are fungal metabolites from Brazilian biodiversity sources. Cytochalasins A-D exhibited IC50 values ranging from 2 to 20 μM against intracellular Trypanosoma cruzi and Leishmania infantum amastigotes, values comparable to those of the standard drugs benznidazole and miltefosine for Chagas disease and leishmaniasis, respectively. Furthermore, cytochalasins A-D reduced L. infantum infections by more than 80% in THP-1 cells, most likely due to the inhibition of phagocytosis by interactions with actin. Molecular modelling studies have provided useful insights into the mechanism of action of this class of compounds. Furthermore, cytochalasins A-D showed moderate cytotoxicity against normal cell lines (HFF-1, THP-1, and HepG2) and a good overall profile for oral bioavailability assessed in vitro. The results of this study support the use of natural products from Brazilian biodiversity sources to find potential drug candidates for two of the most important NTDs.

Cytotoxic Cyclotides from Anchietea pyrifolia, a South American Plant Species

Cyclotides are mini-proteins with potent bioactivities and outstanding potential for agricultural and pharmaceutical applications. More than 450 different plant cyclotides have been isolated from six angiosperm families. In Brazil, studies involving this class of natural products are still scarce, despite its rich floristic diversity. Herein were investigated the cyclotides from Anchietea pyrifolia roots, a South American medicinal plant from the family Violaceae. Fourteen putative cyclotides were annotated by LC-MS. Among these, three new bracelet cyclotides, anpy A-C, and the known cycloviolacins O4 (cyO4) and O17 (cyO17) were sequenced through a combination of chemical and enzymatic reactions followed by MALDI-MS/MS analysis. Their cytotoxic activity was evaluated by a cytotoxicity assay against three human cancer cell lines (colorectal carcinoma cells: HCT 116 and HCT 116 TP53^-/- and breast adenocarcinoma, MCF 7). For all assays, the IC₅₀ values of isolated compounds ranged between 0.8 and 7.3 μM. CyO17 was the most potent cyclotide for the colorectal cancer cell lines (IC₅₀, 0.8 and 1.2 μM). Furthermore, the hemolytic activity of anpy A and B, cyO4, and cyO17 was assessed, and the cycloviolacins were the least hemolytic (HD₅₀ > 156 μM). This work sheds light on the cytotoxic effects of the anpy cyclotides against cancer cells. Moreover, this study expands the number of cyclotides obtained to date from Brazilian plant biodiversity and adds one more genus containing these molecules to the list of the Violaceae family.

In vitro antiviral activity of piperidine alkaloids from Senna spectabilis flowers on Chikungunya virus infection

BACKGROUND

Chikungunya fever is an endemic disease caused by the Chikungunya virus (CHIKV). To date there is no antiviral treatment against this infection or licensed vaccine to prevent it. Our study aims to evaluate whether (-)-cassine (1) and (-)-spectaline (2), the main alkaloids of Senna spectabilis, display anti-CHIKV activity. Both compounds have been described to be biologically active against neglected tropical diseases, including malaria, leishmaniasis, and schistosomiasis, which emphasizes that these molecules could be repurposed for chikungunya fever treatment.

METHODS

The structures of the isolated compounds 1 and 2 were identified by NMR and HRESIMS analyses, and their antiviral activity against CHIKV was assessed by a dose-response assay employing BHK-21 cells and CHIKV-nanoluc, a recombinant virus carrying the nanoluciferase gene reporter.

RESULTS

Compound 1 presented CC₅₀ of 126.5 µM and EC₅₀ of 14.9 µM, while compound 2 presented CC₅₀ of 91.9 µM and EC₅₀ of 8.3 µM. The calculated selectivity index (SI) was 8.5 for 1 and 11.3 for 2.

CONCLUSION

The data presented herein show that compounds 1 and 2 have potential for being repurposed as anti-CHIKV drug. Our promising in vitro results encourage further in vitro and in vivo assays. This is the first description of the antiviral activity of compounds 1 and 2 against CHIKV infection, which can impact the development of antiviral drug candidates against chikungunya fever, which sometimes can be debilitating.

Bioprospecting as a strategy for conservation and sustainable use of the Brazilian Flora

Abstract In Brazil, research with natural products had a strong impulse when FAPESP supported the creation of the Laboratory of Chemistry of Natural Products of the Institute of Chemistry of USP (1966). In 1999, FAPESP launched the Research Program in the Characterization, Conservation, Restoration and Sustainable Use of Biodiversity (BIOTA-FAPESP), which intensified the sustainable exploitation of biodiversity, and which evolved to form the Biota Network for Bioprospection and Bioassays (BIOprospecTA), which integrates groups from all over the country, optimizing the use of the skills already installed for the bioprospecting of microorganisms, plants, invertebrates, vertebrates and marine organisms. Of the 104 projects related to plant sciences, 35 carried out bioprospection of Brazilian flora, belonging to the areas of Chemistry, Botany, Genetics, Plant Physiology, Plant Morphology, Plant (Chemo)taxonomy, Ecosystem Ecology, Plant Genetics. Physical Sciences, Forest Resources, Forestry Engineering, Agronomy, leading to thousands of publications, engagement of hundreds of students and a deeper understanding of natural products in different biological models through macromolecules analysis aided by computational and spectrometric strategies, in addition to pharmacological evaluations. The development of omics approaches led to a more comprehensive view of the chemical profile of an organism, and enabled integrated and concomitant studies of several samples, and faster annotation of known molecules, through the use of hyphenated and chemometric techniques, and molecular networking. This also helped to overcome the lack of information on the safety and efficacy of herbal preparations, in projects dealing with the standardization of herbal products, according to international standards. The BIOTA-FAPESP program has also focused on environmental aspects, in accordance with the principles of Green Chemistry and has had positive effects on international collaboration, on the number and impact of scientific publications and on partnership with companies, a crucial step to add value and expand the production chain of bioproducts. Also, the compilation, systematization and sharing of data were contemplated with the creation of the NUBBEDB database, of free access, and that integrates with international databases (ACD/labs, American Chemical Society – ACS), helping researchers and companies in the development from different areas of science, technology, strengthening the bioeconomy and subsidizing public policies.

In vitro antiglycation and antioxidant properties of Eugenia pyriformis leaves and fruits

Eight phenolic compounds were isolated from Eugenia pyriformis leaves fraction by semi-preparative HPLC and characterized by Nuclear Magnetic Resonance (NMR) and mass spectrometry (ESI-MS). Five compounds were isolated and identified for the first time in E. pyriformis species, while this is the first report of the accumulation of isoquercitrin, quercitrin, and the aglycone quercetin in its leaves. E. pyriformis leaves and fruits extracts, as well as the compounds isolated from the leaves most active fraction, were evaluated for their antiglycation and antioxidant activities. The mixture of myricetin-3-O-(2″-O-galloyl)-α-L-rhamnoside and myricetin-3-O-(4″-O-galloyl)-α-L-rhamnoside showed the highest antiglycation activity. These results suggest that this species is a promising source of bioactive compounds. Further studies to investigate the inhibition of the glycation process in vivo are necessary to evaluate its use in the treatment and/or prevention of advanced glycation end-products (AGEs)-associated diseases.

Computational Applications in Secondary Metabolite Discovery (CAiSMD): an online workshop

We report the major conclusions of the online open-access workshop "Computational Applications in Secondary Metabolite Discovery (CAiSMD)" that took place from 08 to 10 March 2021. Invited speakers from academia and industry and about 200 registered participants from five continents (Africa, Asia, Europe, South America, and North America) took part in the workshop. The workshop highlighted the potential applications of computational methodologies in the search for secondary metabolites (SMs) or natural products (NPs) as potential drugs and drug leads. During 3 days, the participants of this online workshop received an overview of modern computer-based approaches for exploring NP discovery in the "omics" age. The invited experts gave keynote lectures, trained participants in hands-on sessions, and held round table discussions. This was followed by oral presentations with much interaction between the speakers and the audience. Selected applicants (early-career scientists) were offered the opportunity to give oral presentations (15 min) and present posters in the form of flash presentations (5 min) upon submission of an abstract. The final program available on the workshop website ( https://caismd.indiayouth.info/ ) comprised of 4 keynote lectures (KLs), 12 oral presentations (OPs), 2 round table discussions (RTDs), and 5 hands-on sessions (HSs). This meeting report also references internet resources for computational biology in the area of secondary metabolites that are of use outside of the workshop areas and will constitute a long-term valuable source for the community. The workshop concluded with an online survey form to be completed by speakers and participants for the goal of improving any subsequent editions.

Chemical composition and chromatographic fingerprint of three strains of Agaricus subrufescens cultivated with handmade and commercial supplements

Exploratory factor analysis was applied to determine the chemical differences between fruitbodies of three Agaricus subrufescens mushroom strains [from Japan (JP), Brazil (ABZ), and Belgium (T2)] grown with handmade and commercial supplements. The composition of the ABZ strain cultivated with agro-industrial waste supplement presented a high nutritional composition regarding the amounts of fibre and protein, similar to mushrooms cultivated with the commercial supplement. The chromatographic fingerprints obtained for T2 and JP strains grown with commercial supplements presented similar profiles compared to those cultivated with the supplement based on peanut and the mix of supplements. The chromatographic analysis also showed that the similarities are correlated with the relative abundance of antioxidant compounds annotated by HPLC-MS, such as vanillic acid deoxyhexoside, caffeic acid hexoside, catechin hexosemalonate, digallic acid, cinnamic acid derivative, and p-coumaroylmalic acid. This study showed that handmade supplements based on agro-industrial waste could be viable alternatives for replacing high-cost supplements.

The Potential of Biologically Active Brazilian Plant Species as a Strategy to Search for Molecular Models for Mosquito Control

Natural products are a valuable source of biologically active compounds and continue to play an important role in modern drug discovery due to their great structural diversity and unique biological properties. Brazilian biodiversity is one of the most extensive in the world and could be an effective source of new chemical entities for drug discovery. Mosquitoes are vectors for the transmission of dengue, Zika, chikungunya, yellow fever, and many other diseases of public health importance. These diseases have a major impact on tropical and subtropical countries, and their incidence has increased dramatically in recent decades, reaching billions of people at risk worldwide. The prevention of these diseases is mainly through vector control, which is becoming more difficult because of the emergence of resistant mosquito populations to the chemical insecticides. Strategies to provide efficient and safe vector control are needed, and secondary metabolites from plant species from the Brazilian biodiversity, especially Cerrado, that are biologically active for mosquito control are herein highlighted. Also, this is a literature revision of targets as insights to promote advances in the task of developing active compounds for vector control. In view of the expansion and occurrence of arboviruses diseases worldwide, scientific reviews on bioactive natural products are important to provide molecular models for vector control and contribute with effective measures to reduce their incidence.

A green, simplified, and efficient experimental setup for a high-throughput screening of agri-food by-products - From polar to nonpolar metabolites in sugarcane solid residues

From an environmental perspective, searching for useful compounds in agri-food by-products by employing inefficient and polluting analytical procedures is paradoxical. This work aimed to develop a green, simplified, and highly efficient experimental setup for extracting and tentatively identifying the broadest range of metabolites in sugarcane solid by-products collected directly within the industrial mills. Nine different extraction approaches were investigated side-by-side, including three reference methods. Based on the extraction and environmental performances assessed by two complementary metrics called Analytical-Eco Scale and the Analytical Greenness Calculator, it was possible to reach two highly efficient two liquid-phase extractions while avoiding harmful solvents and traditional time, energy, and solvent consuming sample preparation steps, such as solvent evaporation, metabolite concentration, re-suspension, and derivatization. The simultaneously produced hydroethanolic and n-heptane extracts were directly analyzed by ultra-high-performance liquid chromatography and gas chromatography, both coupled to mass spectrometry, respectively, leading to the annotation of a large dynamic range of compounds from information rich spectral data. Up to 111 metabolites were identified in a single matrix, from highly polar sucrose to nonpolar wax ester C53 in a single extraction. Orientin, apigenin-6-C-glucosylrhamnoside, 1-octacosanol, octacosanal, and other bioactive compounds were identified in these abundantly available by-products, which are currently just burned to produce energy. The best two methods developed here (Two-Liquid-Phase Ultrasound-Assisted Extraction with Probe and Two-Liquid-Phase Dynamic Maceration) appeared as a green, simplified, and highly efficient procedures to qualitatively profile metabolites in complex solid matrices.

Crotalaria spectabilis as a source of pyrrolizidine alkaloids and phenolic compounds: HPLC-MS/MS dereplication and monocrotaline quantification of seed and leaf extracts

INTRODUCTION

Crotalaria spectabilis is an important species used as a pre-plant cover for soybean crops to control the proliferation of endoparasitic nematodes. Species from the Crotalaria genus are known for presenting pyrrolizidine alkaloids (PAs) in their composition, however, C. spectabilis is still considered chemically under-explored.

OBJECTIVE

The goal of this manuscript is the development and validation of a method for PAs and flavonoids identification and quantification of C. spectabilis seeds and leaves, a toxic plant used for nematode proliferation control in soil, especially in soybean crops.

MATERIALS AND METHODS

Seeds and leaves extracts were analysed by high-performance liquid chromatography coupled to tandem mass spectrometry (HPLC-MS/MS) for the identification of the compounds.

RESULTS

PAs and phenolic compounds could be identified in both samples based on the MS/MS fragmentation pattern. Molecular formulas of the annotated compounds were confirmed by ultra-high-performace liquid chromatography-quadrupole time-of-flight (UHPLC-QToF), and monocrotaline could also be confirmed by standard comparison. The quantification of monocrotaline was performed by HPLC-MS/MS, resulting in 123 times higher monocrotaline content in seeds than in the leaves, which could explain its efficiency in combating nematode proliferation in soil.

CONCLUSION

This was the first report of phenolic compounds in C. spectabilis. The current study highlights the importance of C. spectabilis for nematode control due to the presence of toxic PAs, and the employment of analytical techniques for identification and quantification of compounds present in the extracts.

Computational methods for NMR and MS for structure elucidation I: software for basic NMR

Structure elucidation is an important and sometimes time-consuming step for natural products research. This step has evolved in the past few years to a faster and more automated process due to the development of several computational programs and analytical techniques. In this paper, the topics of NMR prediction and CASE programs are addressed. Furthermore, the elucidation of natural peptides is discussed.

Improvement of bioactive metabolite production in microbial cultures-A systems approach by OSMAC and deconvolution-based 1 HNMR quantification

Traditionally, the screening of metabolites in microbial matrices is performed by monocultures. Nonetheless, the absence of biotic and abiotic interactions generally observed in nature still limit the chemical diversity and leads to "poorer" chemical profiles. Nowadays, several methods have been developed to determine the conditions under which cryptic genes are activated, in an attempt to induce these silenced biosynthetic pathways. Among those, the one strain, many compounds (OSMAC) strategy has been applied to enhance metabolic production by a systematic variation of growth parameters. The complexity of the chemical profiles from OSMAC experiments has required increasingly robust and accurate techniques. In this sense, deconvolution-based ¹ HNMR quantification have emerged as a promising methodology to decrease complexity and provide a comprehensive perspective for metabolomics studies. Our present work shows an integrated strategy for the increased production and rapid quantification of compounds from microbial sources. Specifically, an OSMAC design of experiments (DoE) was used to optimize the microbial production of bioactive fusaric acid, cytochalasin D and 3-nitropropionic acid, and Global Spectral Deconvolution (GSD)-based ¹ HNMR quantification was carried out for their measurement. The results showed that OSMAC increased the production of the metabolites by up to 33% and that GSD was able to extract accurate NMR integrals even in heavily coalescence spectral regions. Moreover, GSD-¹ HNMR quantification was reproducible for all species and exhibited validated results that were more selective and accurate than comparative methods. Overall, this strategy up-regulated important metabolites using a reduced number of experiments and provided fast analyte monitor directly in raw extracts.

Mass Spectral Similarity Networking and Gas-Phase Fragmentation Reactions in the Structural Analysis of Flavonoid Glycoconjugates

Flavonoids represent an important class of natural products with a central role in plant physiology and human health. Their accurate annotation using untargeted mass spectrometry analysis still relies on differentiating similar chemical scaffolds through spectral matching to reference library spectra. In this work, we combined molecular network analysis with rules for fragment reactions and chemotaxonomy to enhance the annotation of similar flavonoid glyconjugates. Molecular network topology progressively propagated the flavonoid chemical functionalization according to collision-induced dissociation (CID) reactions, as the following chemical attributes: aglycone nature, saccharide type and number, and presence of methoxy substituents. This structure-based distribution across the spectral networks revealed the chemical composition of flavonoids across intra- and interspecies and guided the putatively assignment of 64 isomers and isobars in the Chrysobalanaceae plant species, most of which are not accurately annotated by automated untargeted MS² matching. These proof of concept results demonstrate how molecular networking progressively grouped structurally related molecules according to their product ion scans, abundances, and ratios. The approach can be extrapolated to other classes of metabolites sharing similar structures and diagnostic fragments from tandem mass spectrometry.

Natural deep eutectic solvents and aqueous solutions as an alternative extraction media for propolis

Ethanolic extracts of propolis are consumed for their health benefits even though direct consumption of alcoholic extracts is not always ideal. Natural Deep Eutectic Solvents (NADES) can potentially extract similar compounds as alcoholic extracts while being better for direct consumption. Therefore, in this work alternative solvents for the extraction of green propolis including its biomarker artepillin C were examined. Sixteen NADES made from low toxicity chemicals, including the essential amino acid l-lysine, were explored along with twelve individual NADES components and honey, which showed similar physical-chemical properties to NADES. At 50 °C NADES made from choline chloride-propylene glycol or lactic acid proved to be equal or better than the benchmark EtOH:Water 7:3 (v/v). Alternatively, aqueous l-lysine appeared as a potential solvent for the preparation of aqueous propolis extracts. From these findings NADES, honey and aqueous l-lysine solutions all demonstrated the potential to replace ethanol or water for extracting green propolis.

A primer on natural product-based virtual screening

Databases play an important role in various computational techniques, including virtual screening (VS) and molecular modeling in general. These collections of molecules can contain a large amount of information, making them suitable for several drug discovery applications. For example, vendor, bioactivity data or target type can be found when searching a database. The introduction of these data resources and their characteristics is used for the design of an experiment. The description of the construction of a database can also be a good advisor for the creation of a new one. There are free available databases and commercial virtual libraries of molecules. Furthermore, a computational chemist can find databases for a general purpose or a specific subset such as natural products (NPs). In this chapter, NP database resources are presented, along with some guidelines when preparing an NP database for drug discovery purposes.

A brief overview on Brazilian women in chemistry

Women have achieved great advances standing up for themselves in the last 100 years. Many important women were essential for the development of science but only a few (5% from total awarded individuals) have won Nobel prizes for their work. In this brief contribution, we would like to show that gender equality is in process and highlight the gaps that still have to be addressed. We also give an overview of the Brazilian scenario on this matter. In many countries, such as Brazil, women are already half of the researchers in Chemistry, but their representation become scarcer as their career advances, in coordination and direction positions.

Using natural deep eutectic solvents for the extraction of metabolites in Byrsonima intermedia leaves

Natural deep eutectic solvents have been used as an alternative to organic solvents for the extraction of plants metabolites, allowing for the extraction of compounds of different polarities, while being inexpensive, non-toxic, and easy to prepare. This work presents the comparison of the chromatographic profiles by high-performance liquid chromatography with diode-array detection obtained from Byrsonima intermedia (Malpighiaceae) using five choline chloride-based natural deep eutectic solvents, in addition to the most used traditional extraction solvents, methanol/water 7:3 and ethanol/water 7:3 v/v. A reference extract was used to tentatively identify compounds by high-performance liquid chromatography with tandem mass spectrometry. The water content appeared to be important for the extraction efficiency and the mixture choline chloride/glycerol was shown to be the best candidate for efficiently extracting this matrix when compared with the traditional extraction media in addition to being far greener as shown by the environmental analysis tool. Seven phenolic compounds (digalloyl quinic acid, proanthocyanidin dimer, galloylproanthocyanidin dimer, quercetin-O-hexoside, galloyl quercetin hexoside, quercetin-O-pentoside, and galloyl quercetin pentoside) were tentatively identified in all extracts. Moreover, the influence of these solvents on the antioxidant activity of the extracts was studied and the results for choline chloride/glycerol extracts were very similar to that of the traditional extraction solvents.

Isolation, leishmanicidal evaluation and molecular docking simulations of piperidine alkaloids from Senna spectabilis

Leishmaniasis is one of the most important neglected tropical diseases (NTDs) that are especially common among low-income populations in developing regions of Africa, Asia, and the Americas. Many natural products, particularly alkaloids, have been reported to have inhibitory activity against arginase, the key enzyme in the pathology caused by Leishmania sp. In this way, piperidine alkaloids (-)-cassine (1), (-)-spectaline (2), (-)-3-O-acetylcassine (3), and (-)-3-O-acetylspectaline (4) were isolated from Senna spectabilis flowers. These compounds (1/2 and 3/4) initially present as homologous mixtures were separated by high performance liquid chromatography and evaluated against the promastigote phase of Leishmania amazonensis. In addition, molecular docking simulations were implemented in order to probe the binding modes of the ligands 1-4 to the amino acids in the active site of L. amazonensis arginase. Alkaloid 2 (IC₅₀ 15.81 μg mL^-1) was the most effective against L. amazonensis. Compounds 2 and 4, with larger side chain, were more effective against the parasite than compounds 1 and 3. The cell viability test on Vero cells revealed that compound 2 (CC₅₀ 66.67 μg mL^-1) was the most toxic. The acetyl group in the 3-O position of the parent structures reduced the leishmanicidal activity and the toxicity of the alkaloids. Further, molecular docking suggested that Asn143 is essential for arginase to interact with (-)-spectaline-derived compounds, which agreed with the IC₅₀ measurements. Our findings revealed that S. spectabilis is an important source of piperidine alkaloids with leishmanicidal activity. Moreover, the natural compound 3 has been isolated for the first time. Experimental investigation combined with theoretical study advances knowledge about the enzyme binding site mode of interaction and contributes to the design of new bioactive drugs against Leishmania infection.

Nitensidine B affects proteins of the glycolytic pathway and induces apoptosis in cervical carcinoma cells immortalized by HPV16

BACKGROUND

Cervical cancer, the fourth most common type of cancer among women worldwide, accounts for approximately 12% of all types of malignancies that affect women. Natural products have contributed significantly to the development of modern therapies; approximately 70% of the drugs available for chemotherapy are naturally based products.

PURPOSE

The purpose of this study was to examine the biological activities of nitensidine B (NTB), a guanidinic alkaloid isolated from the leaves of Pterogyne nitens Tul. (Fabaceae) in a cervical cancer cell line.

METHODS

In vitro experiments were performed using cervical carcinoma cells immortalized by human papillomavirus type 16 (HPV16, SiHa cells), since epidemiological and molecular studies have demonstrated robust associations between the etiologies of cervical cancer and HPV infection. Cytotoxicity as well as the effect of NTB treatment on intracellular signals of apoptosis, fragmentation of internucleosomal DNA via terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), and levels of apoptosis effectors (Caspase 3/7) were evaluated. In addition, differential proteomic analysis (iTRAQ) and protein validation using western blot were performed.

RESULTS

The cytotoxicity of NTB treatment in the SiHa cell line was concentration-dependent, with the minimum inhibitory concentration of 50% of the cells of 40.98 µM. In the TUNEL assay, SiHa cell apoptosis with 3/7 caspase activation was reported at 12 h following treatment. Differential proteomic analysis by iTRAQ demonstrated that proteins of the glycolytic pathway, aldolase A, alpha-enolase, pyruvate kinase, and glyceraldehyde 3-phosphate dehydrogenase were underexpressed.

CONCLUSION

These results indicated that NTB could play a role in decreasing glycolysis . Since tumor cells prefer the glycolytic pathway to generate energy, these findings suggest that NTB may be a reliable model for the study of human cervical cancer cell lines immortalized by HPV16, however more experiments can be performed.

NF-κB and Angiogenesis Inhibitors from the Aerial Parts of Chresta martii

The ethyl acetate extract of the aerial parts of Chresta martii showed significant in vitro NF-κB inhibition. Bioactivity-guided isolation was undertaken using HPLC microfractionation to localize the active compounds. Different zones of the HPLC chromatogram were linked to NF-κB inhibition. In parallel to this HPLC-based activity profiling, HPLC-PDA-ESI-MS and UHPLC-TOF-HRMS were used for the early identification of some of the compounds present in the extract and to get a complete phytochemical overview. The isolation of the compounds was performed by high-speed counter-current chromatography and further semipreparative HPLC. Using this approach, 14 compounds were isolated, two of them being new sesquiterpene lactones. The structures of the isolated compounds were elucidated by spectroscopic methods including UV, ECD, NMR, and HRMS. All isolated compounds were evaluated for their inhibitory activity of NF-κB and angiogenesis, and compound 2 showed promising NF-κB inhibition activity with an IC₅₀ of 0.7 μM. The isolated compounds 1, 2, 5, 7, and 8 caused a significant reduction in angiogenesis when evaluated by an original 3D in vitro angiogenesis assay.

A Cyclotide Isolated from Noisettia orchidiflora (Violaceae)

Biologically active cyclotides have been found on some flowering plants species and are involved in the role of the plant protection. As part of studies focusing on peptides from Brazilian plant species, we are reporting the detection by LC-MS of several cyclotides from leaves and stems of Noisettia orchidiflora (Violaceae). From stems it was possible to isolate and characterize a cyclotide named Nor A. Its primary structure (amino acid sequence) was established by MALDI-TOF-MS, based on the y- and b-type ion series, after reduction and alkylation reactions, as well as enzymatic digestion using the enzymes endoproteinase glutamic acid (endoGlu-C), trypsin, and chymotrypsin. Furthermore, the amino acid analysis was also described.

Piperlongumine and some of its analogs inhibit selectively the human immunoproteasome over the constitutive proteasome

The natural small molecule piperlongumine A is toxic selectively to cancer cells in vitro and in vivo. This toxicity has been correlated with cancer cell ROS, DNA damage and apoptotic cell death increases. We demonstrate here a new mechanistic property of piperlongumine: it inhibits selectively human immunoproteasome with no noticeable inhibition of human constitutive proteasome. This result suggests that immunoproteasome inhibition, a mechanism independent of ROS elevation, may also partly play a role in the anticancer effects observed with piperlongumine. Structure-activity relationships of piperlongumine analogs suggest that the lactam (piperidonic) ring of piperlongumine A may be replaced by the linear olefin -NHCO-CH2=CH2 to improve both in vitro inhibitory efficiency against immunoproteasome and cellular toxicity.

Anti-apoptotic effects of decyl gallate on the induction of apoptosis in A549 pneumocytes by Paracoccidioides brasiliensis gp43

Apoptosis is considered an escape mechanism from the host immune system for the fungus Paracoccidioides spp, and it serves as a vehicle for entry into macrophages without stimulating microbicidal activities. Recently, gp43 of P. brasiliensis was demonstrated to be involved in this process. Therefore, as a new therapeutic alternative, it is very important to study compounds that could reduce the modulation of the induction of apoptosis caused by this fungus. Decyl gallate (G14) is a known antifungal compound, and we decided to investigate its anti-apoptotic properties. Our results demonstrate that G14 was effective against apoptosis induced by gp43, as observed in epithelial cells, and led to a reduction in DNA damage, Bak down-regulation and Bcl-2 up-regulation. Together, these data show that G14 presents promising anti-apoptotic activity.

Activity of 3'-hydroxychalcone against Cryptococcus gattii and toxicity, and efficacy in alternative animal models

AIM

This work aimed to evaluate the activity of 3'-hydroxychalcone against Cryptococcus gattii in planktonic and biofilm forms and their toxicity using alternative animal models.

MATERIALS & METHODS

Minimum inhibitory concentration and minimum fungicide concentration were determined. Biofilm formation and the susceptibility tests were performed by the 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-5-[carbonyl(phenylamino)]-2H-tetrazolium hydroxide assay. Toxicity and efficacy were checked in Danio rerio and Galleria mellonella models.

RESULTS

The compound 3'-hydroxychalcone showed fungicidal activity against C. gattii in both planktonic and biofilm forms. The toxicity in zebrafish embryos revealed a low lethal concentration. In G. mellonella, the compound did not show antifungal activity and larvae toxicity.

CONCLUSION

Because of the activity of 3'-hydroxychalcone against C. gattii in vitro, molecular modifications should be made to improve efficacy and to reduce toxicity in vivo. [Formula: see text].

Hepatitis C virus in vitro replication is efficiently inhibited by acridone Fac4

Hepatitis C virus (HCV) affects about 170 million people worldwide. The current treatment has a high cost and variable response rates according to the virus genotype. Acridones, a group of compounds extracted from natural sources, showed potential antiviral actions against HCV. Thus, this study aimed to evaluate the effect of a panel of 14 synthetic acridones on the HCV life cycle. The compounds were screened using an Huh7.5 cell line stably harbouring the HCV genotype 2a subgenomic replicon SGR-Feo-JFH-1. Cells were incubated in the presence or absence of compounds for 72 h and cell viability and replication levels were assessed by MTT and luciferase assays, respectively. At a concentration of 5 µM the acridone Fac4 exhibited a >90 % inhibition of HCV replication with no effect on cell viability. The effects of Fac4 on virus replication, entry and release steps were evaluated in Huh7.5 cells infected with the JFH-1 isolate of HCV (HCVcc). Fac4 inhibited JFH-1 replication to approximately 70 %, while no effect was observed on virus entry. The antiviral activity of Fac4 was also observed on viral release, with almost 80 % of inhibition. No inhibitory effect was observed against genotype 3 replication. Fac4 was able to intercalate into dsRNA, however did not inhibit NS5B polymerase activity or translation driven by the HCV IRES. Although its mode of action is partly understood, Fac4 presents significant inhibition of HCV replication and can therefore be considered as a candidate for the development of a future anti-HCV treatment.

Synergistic effect of pedalitin and amphotericin B against Cryptococcus neoformans by in vitro and in vivo evaluation

Cryptococcosis is an opportunistic fungal infection responsible for high morbidity and mortality in immunocompromised patients. Combination of antifungal substances is a promising way to increase the percentage of successful treatment. Pedalitin (PED) is a natural substance obtained from Pterogyne nitens. The aim of this study was to verify the efficacy of PED alone and in combination with amphotericin B (AmB) in vitro and in vivo against Cryptococcus spp. In the in vitro assay, minimum inhibitory concentrations (MICs) of 0.125 mg/L for AmB and 3.9 mg/L for PED were found when the substances were tested alone, whilst in the combination treatment the active concentration of both decreased, with MICs of 0.03 mg/L for AmB and 1 mg/L for PED. In the survival assay, fungal burden study and histopathological assays it was possible to study the efficacy of the substances alone and in combination. The efficacy of combination therapy was considered better than monotherapy as evaluated in a Galleria mellonella model and a murine model. Thus, the combination of PED and AmB is an interesting alternative for anticryptococcal fungal treatment. Moreover, a correlation was observed between the invertebrate and murine models for this antifungal treatment combination.

Metabolic profile and safety of piperlongumine

Piperlongumine (PPL), a natural plant product, has been extensively studied in cancer treatment going up on clinical trials. Since the first report related to its use on cancer research (in 2011) around 80 papers have been published in less than 10 years, but a gap still remaining. There are no metabolism studies of PPL in human organism. For the lack of a better view, here, the CYP450 in vitro oxidation of PPL was described for the first time. In addition, the enzymatic kinetic data, the predicted in vivo parameters, the produced metabolites, the phenotyping study and possible piperlongumine-drug interactions in vivo is presented.

Human ABCB1 confers cells resistance to cytotoxic guanidine alkaloids from Pterogyne nitens

Multidrug resistance (MDR) caused by human ABCB1 (P-glycoprotein/MDR1) is one of the major obstacles in chemotherapy. To understand the mechanism of MDR by ABCB1 and circumvent the MDR, in the present study, we established human ABCB1-expressing cells (Flp-In-293/ABCB1 cells) and examined the cytotoxic effects of four guanidine alkaloids from Pterogyne nitens (galegine, nitensidine A, pterogynidine and pterogynine) using Flp-In-293/Mock and Flp-In-293/ABCB1 cells. The activity of ABCB1 in Flp-In-293/ABCB1 cells were confirmed by typical substrates for ABCB1 (taxol and vinblastine) in MTT assay. Flp-In-293/ABCB1 cells were also resistant to the four guanidine alkaloids as well as taxol and vinblastine compared to Flp-In-293/Mock cells although the four guanidine alkaloids exhibited cytotoxicity against the two Flp-In-293 cells. Furthermore, the four guanidine alkaloids were also found to stimulate the ATPase activity of ABCB1 in ATPase assays. These results suggest that ABCB1 can confer the resistance to the cytotoxic guanidine alkaloids by transporting them.

Alkaloids derived from flowers of Senna spectabilis, (-)-cassine and (-)-spectaline, have antiproliferative activity on HepG2 cells for inducing cell cycle arrest in G1/S transition through ERK inactivation and downregulation of cyclin D1 expression

Cancer is one of the most critical problems of public health in the world and one of the main challenges for medicine in this century. Unfortunately, most patients are diagnosed at advanced stage, when the treatment options are palliative. Consequently, the search for novel therapeutic options is imperative. In the context, the plants represent an important source for discovering of novel compounds with pharmacological potential including antineoplastic agents. Herein, we aimed to investigate in vitro antiproliferative and cytotoxic potentials of an alkaloid mixture derived from Senna spectabilis, (−)-cassine (1) and (−)-spectaline (2). These alkaloids reduced cell viability in a concentration-dependent manner of six tumor cell lines. From initial screening, HepG2 cells were selected for further investigations. We show that alkaloids 1/2 have an important antiproliferative activity on HepG2 cells due to their ability in inducing cell cycle arrest in G1/S transition. This effect was associated to ERK inactivation and down-regulation of cyclin D1 expression. In addition, we evidenced a disruption of the microfilaments and microtubules in a consequence of the treatment. Taken together, the data showed by the first time that alkaloids 1/2 strongly inhibit cell proliferation of hepatocellular carcinoma cells. Therefore, they represent promise antitumor compounds against liver cancer and should be considered for further anticancer in vivo studies.

Redox-active biflavonoids from Garcinia brasiliensis as inhibitors of neutrophil oxidative burst and human erythrocyte membrane damage

ETHNOPHARMACOLOGICAL RELEVANCE

Garcinia brasiliensis, a plant native to the Brazilian Amazon Rainforest, is used in traditional medicine to treat inflammation of the urinary tract, peptic ulcers, arthritis and other conditions.

AIM OF THE STUDY

The purposes of this study were to analyze the chemical constituents of G. brasiliensis branches and leaves and to evaluate the potential of isolated compounds to act as inhibitors of both the oxidative burst of stimulated neutrophils and oxidative damage in human erythrocyte membranes to verify the antioxidant and anti-inflammatory effects of this plant.

MATERIALS AND METHODS

Neutrophils were isolated from the blood of healthy donors by Ficoll-Paque density gradient centrifugation. Superoxide anion and total reactive oxygen species (ROS) produced by stimulated neutrophils were measured by WST-1 reduction and luminol-enhanced chemiluminescence assays, respectively. Radical-induced lipoperoxidation and hemolysis were performed using erythrocytes from the blood of healthy donors. Compounds were isolated from G. brasiliensis branches and leaves by HPLC microfractionation, and structure elucidation of the isolated compounds was performed based on NMR and HR-MS analyses.

RESULTS

The biflavonoids procyanidin, fukugetin, amentoflavone and podocarpusflavone isolated from G. brasiliensis showed potent inhibitory effects on the oxidative burst of human neutrophils, inhibiting ROS production by 50% at 1 μmol L(-1). These biflavonoids also proved to be potent inhibitors of hemolysis (with 88 ± 7% inhibition at 50 µmol L(-1) for procyanidin) and lipid peroxidation in human erythrocytes, with a malondialdehyde level (a biomarker of oxidative stress) of 8.5 ± 0.3 nmol/mg Hb at 50 µmol L(-1) for procyanidin.

CONCLUSIONS

These findings indicate that the biflavonoids extracted from G. brasiliensis branches and leaves modulate oxidative stress via inhibition of NADPH oxidase and ROS production by stimulated human neutrophils. Furthermore, the biflavonoids exhibited potent inhibition of oxidant hemolysis and lipid peroxidation induced by AAPH in human erythrocytes. Therefore, these studies suggest the use of G. brasiliensis extract as an antioxidant and anti-inflammatory agent.

Protease-inhibiting, molecular modeling and antimicrobial activities of extracts and constituents from Helichrysum foetidum and Helichrysum mechowianum (compositae)

BACKGROUND

Helichrysum species are used extensively for stress-related ailments and as dressings for wounds normally encountered in circumcision rites, bruises, cuts and sores. It has been reported that Helichysum species are used to relief abdominal pain, heart burn, cough, cold, wounds, female sterility, menstrual pain.

RESULTS

From the extracts of Helichrysum foetidum (L.) Moench, six known compounds were isolated and identified. They were 7, 4'-dihydroxy-5-methoxy-flavanone (1), 6'-methoxy-2',4, 4'-trihydroxychalcone (2), 6'-methoxy-2',4-dihydroxychalcone -4'-O-β-D-glucoside (3), apigenin (4), apigenin-7-O-β-D-glucoside (5), kaur-16-en-18-oic acid (6) while two known compounds 3,5,7-trihydroxy-8-methoxyflavone (12), 4,5-dicaffeoyl quinic acid (13) together with a mixture of phytosterol were isolated from the methanol extract of Helichrysum mechowianum Klatt. All the compounds were characterized by spectroscopic and mass spectrometric methods, and by comparison with literature data. Both extracts and all the isolates were screened for the protease inhibition, antibacterial and antifungal activities. In addition, the phytochemical profiles of both species were investigated by ESI-MS experiments.

CONCLUSIONS

These results showed that the protease inhibition assay of H. foetidum could be mainly attributed to the constituents of flavonoids glycosides (3, 5) while the compound (13) from H. mechowianum contributes to the stomach protecting effects. In addition, among the antibacterial and antifungal activities of all the isolates, compound (6) was found to possess a potent inhibitor effect against the tested microorganisms. The heterogeneity of the genus is also reflected in its phytochemical diversity. The differential bioactivities and determined constituents support the traditional use of the species. Molecular modelling was carried out by computing selected descriptors related to drug absorption, distribution, metabolism, excretion and toxicity (ADMET). Graphical abstractCompounds isolated from Helichrysum species (Compositae).

Synthesis and evaluation of novel prenylated chalcone derivatives as anti-leishmanial and anti-trypanosomal compounds

Chalcones form a class of compounds that belong to the flavonoid family and are widely distributed in plants. Their simple structure and the ease of preparation make chalcones attractive scaffolds for the synthesis of a large number of derivatives enabling the evaluation of the effects of different functional groups on biological activities. In this Letter, we report the successful synthesis of a series of novel prenylated chalcones via Claisen-Schmidt condensation and the evaluation of their effect on the viability of the Trypanosomatidae parasites Leishmania amazonensis, Leishmania infantum and Trypanosoma cruzi.

Recent advances in the use of vibrational chiroptical spectroscopic methods for stereochemical characterization of natural products

A comprehensive look into application of vibrational optical activity methods for conformational and configurational assignments in natural product molecules over the last 15 years is provided.

In Vitro Antibacterial Activity of Prenylated Guanidine Alkaloids from Pterogyne nitens and Synthetic Analogues

The present investigation deals with the antibiotic activity of eight natural guanidine alkaloids and two synthetic analogues against a variety of clinically relevant methicillin-resistant Staphylococcus aureus strains. Galegine (1) and pterogynidine (2) were the most potent compounds, with a minimum inhibitory concentration of 4 mg/L, to all tested strains. The preliminary chemical features correlating to anti-MRSA activity showed that the size of the side chain and the substitution pattern in the guanidine core played a key role in the antibacterial activity of the imino group. Guanidine alkaloids 1 and 2 are promising molecular models for further synthetic derivatives and, thus, for medicinal chemistry studies.

Chemical composition of the bark of Tetrapterys mucronata and identification of acetylcholinesterase inhibitory constituents

The secondary metabolite content of Tetrapterys mucronata, a poorly studied plant that is used occasionally in Brazil for the preparation of a psychotropic plant decoction called "Ayahuasca", was determined to establish its chemical composition and to search for acetylcholinesterase (AChE) inhibitors. The ethanolic extract of the bark of T. mucronata exhibited in vitro AChE inhibition in a TLC bioautography assay. To localize the active compounds, biological profiling for AChE inhibition was performed using at-line HPLC-microfractionation in 96-well plates and subsequent AChE inhibition bioautography. The analytical HPLC-PDA conditions were transferred geometrically to a preparative medium-pressure liquid chromatography column using chromatographic calculations for the efficient isolation of the active compounds at the milligram scale. Twenty-two compounds were isolated, of which six are new natural products. The structures of the new compounds (9, 10, 16-18, and 20) were elucidated by spectroscopic data interpretation. Compounds 1, 5, 6, 9, and 10 inhibited AChE with IC50 values below 15 μM.

Leishmanicidal activity of the crude extract, fractions and major piperidine alkaloids from the flowers of Senna spectabilis

Senna spectabilis (sin. Cassia excelsa, C. spectabilis) is an endemic tree of South America and Africa, very common in Brazil, where it is known as "canafistula-de-besouro" and "cassia-do-nordeste". In folk medicine, this plant is indicated for the treatment of constipation, insomnia, anxiety, epilepsy, malaria, dysentery and headache. Phytopharmacological studies have also confirmed anticonvulsive, sedative, anti-malarial, antimicrobial and cytotoxic properties of many parts of S. spectabilis. In this communication, we present a comparative study of the leishmanicidal activity of the crude ethanolic extract, its fractions and also the two major alkaloidal metabolites (-)-cassine/(-)-spectaline, trying to establish a relationship between the presence of piperidine alkaloidal constituents and leishmanicidal activity. The growth inhibitory effect of promastigote forms of Leishmania major was determined for the crude extract, fractions of the flowers of S. spectabilis and a mixture of (-)-cassine/(-)-spectaline in comparison to pentamidine used as standard drug. The cytotoxic effects were assessed on macrophage strain J774 by lactate dehydrogenase assay. Fractions dichloromethane (FL-DCM) and n-butanol (FL-Bu) and a mixture of (-)-cassine/(-)-spectaline (∼7:3) exhibited significant activity against the parasite Leishmania major (IC50 values of 0.6±0.1 μg/ml, 1.6±0.9 μg/ml and 24.9±1.4 μg/ml, respectively), without toxic effects on murine macrophages. Due to the promising results elicited, further studies in vivo need to be performed to confirm the therapeutic potential of Senna spectabilis.

Nitensidine A, a guanidine alkaloid from Pterogyne nitens, is a novel substrate for human ABC transporter ABCB1

The Pterogyne nitens (Fabaceae) tree, native to South America, has been found to produce guanidine alkaloids as well as bioactive flavonols such as kaempferol, quercetin, and rutin. In the present study, we examined the possibility of interaction between human ATP-binding cassette (ABC) transporter ABCB1 and four guanidine alkaloids isolated from P. nitens (i.e., galegine, nitensidine A, pterogynidine, and pterogynine) using human T cell lymphoblast-like leukemia cell line CCRF-CEM and its multi-drug resistant (MDR) counterpart CEM/ADR5000. In XTT assays, CEM/ADR5000 cells were resistant to the four guanidine alkaloids compared to CCRF-CEM cells, although the four guanidine alkaloids exhibited some level of cytotoxicity against both CCRF-CEM and CEM/ADR5000 cells. In ATPase assays, three of the four guanidine alkaloids were found to stimulate the ATPase activity of ABCB1. Notably, nitensidine A was clearly found to stimulate the ATPase activity of ABCB1 as strongly as the control drug, verapamil. Furthermore, the cytotoxic effect of nitensidine A on CEM/ADR5000 cells was synergistically enhanced by verapamil. Nitensidine A inhibited the extrusion of calcein by ABCB1. In the present study, the possibility of interaction between ABCB1 and two synthetic nitensidine A analogs (nitensidine AT and AU) were examined to gain insight into the mechanism by which nitensidine A stimulates the ATPase activity of ABCB1. The ABCB1-dependent ATPase activity stimulated by nitensidine A was greatly reduced by substituting sulfur (S) or oxygen (O) for the imino nitrogen atom (N) in nitensidine A. Molecular docking studies on human ABCB1 showed that, guanidine alkaloids from P. nitens dock to the same binding pocket as verapamil. Nitensidine A and its analogs exhibit similar binding energies to verapamil. Taken together, this research clearly indicates that nitensidine A is a novel substrate for ABCB1. The present results also suggest that the number, binding site, and polymerization degree of the isoprenyl moiety in the guanidine alkaloids and the imino nitrogen atom cooperatively contribute to their stimulation of ABCB1's ATPase activity.

Nitensidine A, a guanidine alkaloid from Pterogyne nitens, induces osteoclastic cell death

Nitensidine A is a guanidine alkaloid isolated from Pterogyne nitens, a common plant in South America. To gain insight into the biological activity of P. nitens-produced compounds, we examined herein their biological effects on osteoclasts, multinucleated giant cells that regulate bone metabolism by resorbing bone. Among four guanidine alkaloids (i.e., galegine, nitensidine A, pterogynidine, and pterogynine), nitensidine A and pterogynine exhibited anti-osteoclastic effects at 10 μM by reducing the number of osteoclasts on the culture plate whereas galegine and pterogynidine did not. The anti-osteoclastic activities of nitensidine A and pterogynine were exerted in a concentration-dependent manner, whereas nitensidine A exhibited an approximate threefold stronger effect than pterogynine (IC50 values: nitensidine A, 0.93 ± 0.024 μM; pterogynine, 2.7 ± 0.40 μM). In the present study, the anti-osteoclastic effects of two synthetic nitensidine A derivatives (nitensidine AT and AU) were also examined to gain insight into the structural features of nitensidine A that exert an anti-osteoclastic effect. The anti-osteoclastic effect of nitensidine A was greatly reduced by substituting the imino nitrogen atom in nitensidine A with sulfur or oxygen. According to the differences in chemical structures and anti-osteoclastic effects of the four guanidine alkaloids and the two synthetic nitensidine A derivatives, it is suggested that the number, binding site, and polymerization degree of isoprenyl moiety in the guanidine alkaloids and the imino nitrogen atom cooperatively contribute to their anti-osteoclastic effects.