Amyloid-ß oligomers in cellular models of Alzheimer's disease.

Amyloid-ß (Aß) dysmetabolism is tightly associated with pathological processes in Alzheimer's disease (AD). Currently, it is thought that, in addition to Aß fibrils that give rise to plaque formation, Aß aggregates into non-fibrillar soluble oligomers (AßOs). Soluble AßOs have been extensively studied for their synaptotoxic and neurotoxic properties. In this review, we discuss physicochemical properties of AßOs and their impact on different brain cell types in AD. Additionally, we summarize three decades of studies with AßOs, providing a compelling bulk of evidence regarding cell-specific mechanisms of toxicity. Cellular models may lead us to a deeper understanding of the detrimental effects of AßOs in neurons and glial cells, putatively shedding light on the development of innovative therapies for AD.

Semisynthesis, cytotoxicity, antimalarial evaluation and structure-activity relationship of two series of triterpene derivatives.

In this report, we describe the semisynthesis of two series of ursolic and betulinic acid derivatives through designed by modifications at the C-3 and C-28 positions and demonstrate their antimalarial activity against chloroquine-resistant P. falciparum (W2 strain). Structural modifications at C-3 were more advantageous to antimalarial activity than simultaneous modifications at C-3 and C-28 positions. The ester derivative, 3ß-butanoyl betulinic acid (7b), was the most active compound (IC50 = 3.4 µM) and it did not exhibit cytotoxicity against VERO nor HepG2 cells (CC50 > 400 µM), showing selectivity towards parasites (selectivity index > 117.47). In combination with artemisinin, compound 7b showed an additive effect (CI = 1.14). While docking analysis showed a possible interaction of 7b with the Plasmodium protease PfSUB1, with an optimum binding affinity of -7.02 kcal/mol, the rather low inhibition displayed on a Bacillus licheniformis subtilisin A protease activity assay (IC50 = 93 µM) and the observed accumulation of ring forms together with a delay of appearance of trophozoites in vitro suggests that the main target of 3ß-butanoyl betulinic acid on Plasmodium may be related to other molecules and processes pertaining to the ring stage. Therefore, compound 7b is the most promising compound for further studies on antimalarial chemotherapy. The results obtained in this study provide suitable information about scaffolds to develop novel antimalarials from natural sources.

Investigation of antimalarial activity, cytotoxicity and action mechanism of piperazine derivatives of betulinic acid.

OBJECTIVES: To semisynthesise piperazine derivatives of betulinic acid to evaluate antimalarial activity, cytotoxicity and action mechanism. METHODS: The new derivatives were evaluated against the CQ-sensitive Plasmodium falciparum 3D7 strain by flow cytometry (FC) using YOYO-1 as stain. Cytotoxicity of 4a and 4b was performed with HEK293T cells for 24 and 48 h by MTT assay. The capability of compound 4a to modulate Ca(2+) in the trophozoite stage was investigated. The trophozoites were stained with Fluo4-AM and analysed by spectrofluorimetry. Effect on mitochondrial membrane potential (ΔΨm) was tested for 4a by FC with DiOC6 (3) as stain. For ß-haematin assay, 4a was incubated for 24 h with reagents such as haemin, and the fluorescence was measured by FlexStation at an absorbance of 405 nm. RESULTS: Antimalarial activity of 4a and 4b was IC50 = 1 and 4 µm, respectively. Compound 4a displayed cytotoxicity with IC50 = 69 and 29 µm for 24 and 48 h, respectively, and 4b was not cytotoxic at the tested concentrations. Addition of 4a leads to an increase in cytosolic Ca(2+) . We have measured ΔΨm after treating parasites with the compound. Data on Figure 4a show that mitochondria were not affected. The action mechanism for 4a, inhibition of ß-haematin formation (17%), was lower than CQ treatment (83%; IC50 = 3 mm). CONCLUSION: Compound 4a showed excellent antimalarial activity, and its action mechanism is involved in Ca(2+) pathway(s).

Synthesis and biological evaluation of hydrazone derivatives as antifungal agents.

Emerging yeasts are among the most prevalent causes of systemic infections with high mortality rates and there is an urgent need to develop specific, effective and non-toxic antifungal agents to respond to this issue. In this study 35 aldehydes, hydrazones and hydrazines were obtained and their antifungal activity was evaluated against Candida species (C. parapsilosis, C. tropicalis, C. krusei, C. albicans, C. glabrata and C. lusitaneae) and Trichosporon asahii, in an in vitro screening. The minimum inhibitory concentrations (MICs) of the active compounds in the screening was determined against 10 clinical isolates of C. parapsilosis and 10 of T. asahii. The compounds 4-pyridin-2-ylbenzaldehyde] (13a) and tert-butyl-(2Z)-2-(3,4,5-trihydroxybenzylidine)hydrazine carboxylate (7b) showed the most promising MIC values in the range of 16-32 µg/mL and 8-16 µg/mL, respectively. The compounds' action on the stability of the cell membrane and cell wall was evaluated, which suggested the action of the compounds on the fungal cell membrane. Cell viability of leukocytes and an alkaline comet assay were performed to evaluate the cytotoxicity. Compound 13a was not cytotoxic at the active concentrations. These results support the discovery of promising candidates for the development of new antifungal agents.

Anti-Trichomonas vaginalis activity from triterpenoid derivatives.

Trichomonas vaginalis is a flagellated parasite that causes trichomonosis, the most common non-viral sexually transmitted disease (STD) in the world. Worryingly, trichomonosis is associated to increased transmission of HIV. Due to high frequency of the infection during pregnancy and the development of metronidazole-resistant isolates, therapeutic alternatives to 5-nitroimidazole are being searched. Triterpenes are natural products presenting several biological activities such as anti-protozoal activity. The aim of this study was to evaluate the in vitro anti-T. vaginalis activity from betulinic and ursolic acids, as well as semisynthetic derivatives obtained. Compounds obtained from betulinic acid presented better activity than those from ursolic acid. Piperazine derivatived from betulinic acid presented minimum inhibitory concentration (MIC) value of 91.2 µM, and the kinetic growth curve performed with parasites treated with this most active compound revealed complete inhibition of trophozoite proliferation at 2 h of incubation and total abolition of trophozoite growth in 24 h, revealing that the piperazine derivative is an efficient trichomonacidal molecule. The same compound promoted total erythrocyte lysis and lactate dehydrogenase (LDH) liberation of 83 and 100% (at 45.6 and 91.2 µM, respectively), indicating parasite membrane damage. The piperazine derivative demonstrated cytotoxic effect against the HMVII and HeLa cell lineages at the MIC value. This is the first report of semisynthetic triterpenoid derivatives with anti-T. vaginalis activity, revealing the high potential of these compounds as trichomonacidal agents.

Two series of new semisynthetic triterpene derivatives: differences in anti-malarial activity, cytotoxicity and mechanism of action.

BACKGROUND: The discovery and development of anti-malarial compounds of plant origin and semisynthetic derivatives thereof, such as quinine (QN) and chloroquine (CQ), has highlighted the importance of these compounds in the treatment of malaria. Ursolic acid analogues bearing an acetyl group at C-3 have demonstrated significant anti-malarial activity. With this in mind, two new series of betulinic acid (BA) and ursolic acid (UA) derivatives with ester groups at C-3 were synthesized in an attempt to improve anti-malarial activity, reduce cytotoxicity, and search for new targets. In vitro activity against CQ-sensitive Plasmodium falciparum 3D7 and an evaluation of cytotoxicity in a mammalian cell line (HEK293T) are reported. Furthermore, two possible mechanisms of action of anti-malarial compounds have been evaluated: effects on mitochondrial membrane potential (ΔΨm) and inhibition of ß-haematin formation. RESULTS: Among the 18 derivatives synthesized, those having shorter side chains were most effective against CQ-sensitive P. falciparum 3D7, and were non-cytotoxic. These derivatives were three to five times more active than BA and UA. A DiOC(6)(3) ΔΨm assay showed that mitochondria are not involved in their mechanism of action. Inhibition of ß-haematin formation by the active derivatives was weaker than with CQ. Compounds of the BA series were generally more active against P. falciparum 3D7 than those of the UA series. CONCLUSIONS: Three new anti-malarial prototypes were obtained from natural sources through an easy and relatively inexpensive synthesis. They represent an alternative for new lead compounds for anti-malarial chemotherapy.

The inhibitory effects of phenolic and terpenoid compounds from Baccharis trimera in Siha cells: differences in their activity and mechanism of action.

Baccharis trimera is used in folk medicine as a tea for digestive and liver diseases. It possesses anti-inflammatory and antioxidant properties that are related to the presence of phenolic compounds. The aim of this work was to investigate the anti-proliferative properties of phenolic (PHE) and terpenoid (SAP) compounds from B. trimera on human cervical cancer. The treatment of SiHa cells with PHE for 24 h suppressed colony formation in a dose-dependent manner, inhibited proliferation and inhibited cell motility. Although SAP inhibited the proliferation of SiHa cells in a dose-dependent manner, it increased colony formation and did not inhibit cell motility. PHE and SAP also promoted a significant increase in lactate dehydrogenase levels in the culture medium in a dose-dependent manner, indicating a loss of cell membrane integrity. Moreover, PHE promoted necrotic cell death, whereas SAP induced apoptosis. These compounds are new anticancer prototypes due their significant anticancer activity demonstrated herein.

Capsicum baccatum Red Pepper Prevents Cardiometabolic Risk in Rats Fed with an Ultra-Processed Diet.

Metabolic syndrome is a serious health condition reaching epidemic proportions worldwide and is closely linked to an increased risk of cardiovascular problems. The lack of appropriate treatment paves the way for developing new therapeutic agents as a high priority in the current research. In this study, we evaluated the protective effects of Capsicum baccatum red pepper on metabolic syndrome scenarios induced by an ultra-processed diet in rats. After four months, the ultra-processed diet increased central obesity, triglycerides, total cholesterol, LDL-cholesterol plasma levels, and impaired glucose tolerance. The oral administration of C. baccatum concomitantly with the ultra-processed diet avoided the accumulation of adipose tissue in the visceral region, reduced the total cholesterol and LDL fraction, and improved glucose homeostasis, factors commonly associated with metabolic syndrome. The data presented herein reveal an important preventive action of C. baccatum in developing metabolic disorders among animals fed a hypercaloric diet, significantly reducing their cardiometabolic risk. Allied with the absence of toxic effects after chronic use, our study suggests C. baccatum red pepper as a secure and enriched source of bioactive compounds promising to protect against pathological processes associated with metabolic syndrome.

Long-Term Oral Administration of Capsicum baccatum Extracts Does Not Alter Behavioral, Hematological, and Metabolic Parameters in CF1 Mice.

Our group showed that crude ethanol (CE) and butanol (BUT) extracts of Capsicum baccatum presented anti-inflammatory and antioxidant properties. Furthermore, the flavonoid and total phenolic contents were positively correlated with both of these properties observed for C. baccatum extracts. The present study demonstrated that 60 days of oral administration of CE and BUT (200 mg/kg) in mice did not cause significant differences in the following parameters evaluated: hematological profile, body weight and relative weight of visceral organs, systemic lipid profile, glucose homeostasis (GTT), kidney and hepatic biochemical markers, and spontaneous locomotion and anxiety-like behavior. Altogether, these results indicate for the first time that the long-term oral administration of C. baccatum extracts does not affect specific aspects of CF1 mice physiology, suggesting their safety, building up the venue to test their efficacy in animal models underlying persistent activation of oxidative and inflammatory pathways.

Bioguided Fractionation Shows Cassia alata Extract to Inhibit Staphylococcus epidermidis and Pseudomonas aeruginosa Growth and Biofilm Formation.

Plant extracts have a long history to be used in folk medicine. Cassia alata extracts are known to exert antibacterial activity but details on compounds and mechanism of action remain poorly explored. We purified and concentrated the aqueous leaf extract of C. alata by reverse phase-solid phase extraction and screened the resulting CaRP extract for antimicrobial activity. CaRP extract exhibited antimicrobial activity for Pseudomonas aeruginosa, Staphylococcus epidermidis, S. aureus, and Bacillus subtilis. CaRP also inhibited biofilm formation of S. epidermidis and P. aeruginosa. Several bacterial growth-inhibiting compounds were detected when CaRP extract was fractionated by TLC chromatography coupled to bioautography agar overlay technique. HPLC chromatography of CaRP extract yielded 20 subfractions that were tested by bioautography for antimicrobial activity against S. aureus and S. epidermidis. Five bioactive fractions were detected and chemically characterized, using high-resolution mass spectrometry (qTOF-MS/MS). Six compounds from four fractions could be characterized as kaempferol, kaempferol-O-diglucoside, kaempferol-O-glucoside, quercetin-O-glucoside, rhein, and danthron. In the Salmonella/microsome assay CaRP showed weak mutagenicity (MI < 3) only in strain TA98, pointing to a frameshift mutation activity. These results indicate that C. alata leaf extract contains a minimum of 7 compounds with antimicrobial activity and that these together or as single substance are active in preventing formation of bacterial biofilm, indicating potential for therapeutic applications.

Anti-Trichomonas vaginalis activity of saponins from Quillaja, Passiflora, and Ilex species.

Trichomonas vaginalis is a flagellated protozoan that causes trichomonosis, the most prevalent non-viral STD worldwide. The pathogen has been associated with serious health consequences including predisposition to cervical cancer and adverse pregnancy outcomes and infertility. It also acts as a co-factor in HIV transmission and acquisition. The 5-nitroimidazole drugs are used in the treatment, however, treatment noncompliance is observed, and a growing number of T. vaginalis isolates resistant to the drugs have been related. Saponins are natural products possessing many biological activities such as antiprotozoan activity. The aim of this study was to evaluate the anti-T. vaginalis activity of saponins from Quillaja, Passiflora, and Ilex species. Saponins from Passiflora alata and Quillaja saponaria presented the best anti-T. vaginalis activity (MIC = 0.025%). In addition, all samples induced erythrocyte lysis and LDH release. As far as we know, this is the first report demonstrating the potential anti-T. vaginalis activity of these saponins.

Astragalin from Cassia alata induces DNA adducts in vitro and repairable DNA damage in the yeast Saccharomyces cerevisiae.

Reverse phase-solid phase extraction from Cassia alata leaves (CaRP) was used to obtain a refined extract. Higher than wild-type sensitivity to CaRP was exhibited by 16 haploid Saccharomyces cerevisiae mutants with defects in DNA repair and membrane transport. CaRP had a strong DPPH free radical scavenging activity with an IC(50) value of 2.27 µg mL(-1) and showed no pro-oxidant activity in yeast. CaRP compounds were separated by HPLC and the three major components were shown to bind to DNA in vitro. The major HPLC peak was identified as kampferol-3-O-ß-d-glucoside (astragalin), which showed high affinity to DNA as seen by HPLC-UV measurement after using centrifugal ultrafiltration of astragalin-DNA mixtures. Astragalin-DNA interaction was further studied by spectroscopic methods and its interaction with DNA was evaluated using solid-state FTIR. These and computational (in silico) docking studies revealed that astragalin-DNA binding occurs through interaction with G-C base pairs, possibly by intercalation stabilized by H-bond formation.

Synthesis and antiplasmodial activity of betulinic acid and ursolic acid analogues.

More than 40% of the World population is at risk of contracting malaria, which affects primarily poor populations in tropical and subtropical areas. Antimalarial pharmacotherapy has utilised plant-derived products such as quinine and artemisinin as well as their derivatives. However, worldwide use of these antimalarials has caused the spread of resistant parasites, resulting in increased malaria morbidity and mortality. Considering that the literature has demonstrated the antimalarial potential of triterpenes, specially betulinic acid (1) and ursolic acid (2), this study investigated the antimalarial activity against P. falciparum chloroquine-sensitive 3D7 strain of some new derivatives of 1 and 2 with modifications at C-3 and C-28. The antiplasmodial study employed flow cytometry and spectrofluorimetric analyses using YOYO-1, dihydroethidium and Fluo4/AM for staining. Among the six analogues obtained, compounds 1c and 2c showed excellent activity (IC50 = 220 and 175 nM, respectively) while 1a and b demonstrated good activity (IC50 = 4 and 5 µM, respectively). After cytotoxicity evaluation against HEK293T cells, 1a was not toxic, while 1c and 2c showed IC50 of 4 µM and a selectivity index (SI) value of 18 and 23, respectively. Moreover, compound 2c, which presents the best antiplasmodial activity, is involved in the calcium-regulated pathway(s).

Phenolic enriched extract of Baccharis trimera presents anti-inflammatory and antioxidant activities.

Baccharis trimera is a plant popularly used as a tea and to treat gastrointestinal diseases and inflammatory processes as well. The total phenolic content was determined and the antioxidant and anti-inflammatory activities of six extracts (dichloromethane, ethyl acetate, butanol, aqueous, saponin and phenolic) from B. trimera were evaluated. Using carrageenan-induced pleurisy as a model of acute inflammation, the phenolic extract at 15 mg/kg decreased significantly the analyzed parameters when compared to the carrageenan group ( p < 0.05), thus showing potential anti-inflammatory activity. The total phenolic content and antioxidant activity were evaluated by the Folin-Ciocalteau and DPPH methods, respectively. Phenolic and ethyl acetate extracts presented higher antioxidant activity ( p < 0.05) than ascorbic acid. The phenolic extract also showed the highest antioxidant potential in relation to the other extracts, thus suggesting that the antioxidant and anti-inflammatory activities were due to the presence of phenolic compounds.

Phenolic compounds from maté (Ilex paraguariensis) inhibit adipogenesis in 3T3-L1 preadipocytes.

Leaves of Ilex paraguariensis are used to prepare a tea known as maté which is a common beverage in several South American countries. The ethanol extract was fractionated to identify the compounds responsible for the anti-adipogenic activity in 3T3-L1 cells. Extracts of both fresh and dried maté leaves were subjected to column chromatography using molecular permeation to obtain the saponin (20 % yields) and the polyphenol extracts (40 % yields) from the fresh and dried leaves. The phenolic content was determined using high-performance liquid chromatography analysis and the Folin-Ciocalteau method. Also, maté extracts (50 µg/ml to 1,000 µg/ml) did not display citotoxicity using MTT. The polyphenol extract from the dried leaves was the most effective (50 µg/ml) in the inhibition of triglyceride accumulation in 3T3-L1 adipocytes, and rutin (100 µg/ml) likely accounted for a large portion of this activity. Additionally, maté extracts had a modulatory effect on the expression of genes related to the adipogenesis as PPARγ2, leptin, TNF-α and C/EBPα.

Limonene and Perillyl Alcohol Derivatives: Synthesis and Anticancer Activity.

Limonene and perillyl alcohol are natural monoterpenes that have attracted the attention of medicinal chemists due to their promising anticancer activities. Considering this, both compounds were explored as scaffolds to obtain various derivatives with anticancer activity. In this review, the data are organized for the first time, with a focus on the synthetic methods and strategies to obtain the derivatives throughout the period from 2000 to 2020. A brief discussion regarding the structure and activity relationships of the most active derivatives, stereoisomers, and their mechanisms of action is presented. Among the active compounds, a series of limonenes with thiosemicarbazone groups and perillyl alcohol hybrids with glycosides or drugs are illustrated. Taking all of this into account, this review may help researchers develop new promising anticancer candidates based on the structures of limonene and perillyl alcohol.

Novel Antimicrobial 8-Hydroxyquinoline-Based Agents: Current Development, Structure-Activity Relationships, and Perspectives.

The search for new antimicrobials is imperative due to the emergent resistance of new microorganism strains. In this context, revisiting known classes like 8-hydroxyquinolines could be an interesting strategy to discover new agents. The 8-hydroxyquinoline derivatives nitroxoline and clioquinol are used to treat microbial infections; however, these drugs are underused, being available in few countries or limited to topical use. After years of few advances, in the last two decades, the potent activity of clioquinol and nitroxoline against several targets and the privileged structure of 8-hydroxyquinoline nucleus have prompted an increased interest in the design of novel antimicrobial, anticancer, and anti-Alzheimer agents based on this class. Herein, we discuss the current development and antimicrobial structure-activity relationships of this class in the perspective of using the 8-hydroxyquinoline nucleus for the search for novel antimicrobial agents. Furthermore, the most investigated molecular targets concerning 8-hydroxyquinoline derivatives are explored in the final section.

Rapid size-exclusion high performance liquid chromatography method for the quality control of amyloid-ß oligomers.

Amyloid-ß (Aß) dysmetabolism is thought to be the main trigger for neurodegenerative events in Alzheimer's disease (AD). In particular, soluble Aß oligomers (AßOs) are proposed as key mediators of synaptic and cognitive dysfunction in AD. Over the past few decades, AßOs prepared from synthetic Aß have been widely applied in vitro and in vivo, the so-called chemical models of AD, uncovering their multiple neurotoxic mechanisms. However, the lack of a reliable quality control (QC) for synthetic AßOs may reflect poor experimental reproducibility. In keeping with this, we optimized and validated a rapid and reproducible SECHPLC method using fluorescence detection for the QC of synthetic AßOs. Our analytical method offers an unprecedent alternative to improve the reproducibility of AD chemical models.

Inhibitory effect of ursolic acid derivatives on hydrogen peroxide- and glutathione-mediated degradation of hemin: a possible additional mechanism of action for antimalarial activity.

Compounds obtained by the condensation of ursolic acid (UA) with 1,4-bis(3-aminopropyl)piperazines have previously been shown as cytocidal to Plasmodium falciparum strains. Preliminary results indicated that the inhibition of beta-hematin formation (one of the possible mechanisms of action of antimalarial drugs) was achieved by a few of these molecules with varying efficiencies. To gain further insight in the antimalarial action of UA derivatives, we report here the results of additional pathways that may explain their in vitro cytocidal activity such as inhibition of hemin degradation by H(2)O(2) or glutathione (GSH). H(2)O(2)-mediated hemin degradation was drastically reduced by hydroxybenzyl-substituted UA derivatives while UA and intermediate compounds displayed weaker inhibitory actions. The results of GSH-mediated hemin degradation inhibition did not parallel those of H(2)O(2) degradation as hydroxybenzyl-substituted UA only proved to be a weak inhibitor. As H(2)O(2) interaction with the iron moiety of hemin is the first step towards its degradation, we assume that the interaction of our products with the ferric ion in the hemin structure is of upmost importance in inhibiting its peroxidative degradation. A two-step mechanism of action implying (1) stacking of the acetylursolic acid structure to hemin and (2) additive protection of hemin ferric iron from H(2)O(2) by hydroxyphenyl groups through steric hindrance and/or trapping of oxygen reactive species in the direct neighborhood of ferric iron can be put forward. For GSH degradation pathway, grafting of UA structure with a piperazine structure gave the best inhibition, pleading for the implication of this latter moiety in the inhibitory process.

Modeling Diet-Induced Metabolic Syndrome in Rodents.

Standardized animal models represent one of the most valuable tools available to understand the mechanism underlying the metabolic syndrome (MetS) and to seek for new therapeutic strategies. However, there is considerable variability in the studies conducted with this essential purpose. This review presents an updated discussion of the most recent studies using diverse experimental conditions to induce MetS in rodents with unbalanced diets, discusses the key findings in metabolic outcomes, and critically evaluates what we have been learned from them and how to advance in the field. The study includes scientific reports sourced from the Web of Science and PubMed databases, published between January 2013 and June 2020, which used hypercaloric diets to induce metabolic disorders, and address the impact of the diet on metabolic parameters. The collected data are used as support to discuss variables such as sex, species, and age of the animals, the most favorable type of diet, and the ideal diet length to generate metabolic changes. The experimental characteristics propose herein improve the performance of a preclinical model that resembles the human MetS and will guide researchers to investigate new therapeutic alternatives with confidence and higher translational validity.