Prenylated Flavanone Isolated from Dalea Species as a Potential Multitarget-Neuroprotector in an In Vitro Alzheimer's Disease Mice Model.

Alzheimer's disease (AD) involves a neurodegenerative process that has not yet been prevented, reversed, or stopped. Continuing with the search for natural pharmacological treatments, flavonoids are a family of compounds with proven neuroprotective effects and multi-targeting behavior. The American genus Dalea L. (Fabaceae) is an important source of bioactive flavonoids. In this opportunity, we tested the neuroprotective potential of three prenylated flavanones isolated from Dalea species in a new in vitro pre-clinical AD model previously developed by us. Our approach consisted in exposing neural cells to conditioned media (3xTg-AD ACM) from neurotoxic astrocytes derived from hippocampi and cortices of old 3xTg-AD mice, mimicking a local neurodegenerative microenvironment. Flavanone 1 and 3 showed a neuroprotective effect against 3xTg-AD ACM, being 1 more active than 3. The structural requirements to afford neuroprotective activity in this model are a 5'-dimethylallyl and 4'-hydroxy at the B ring. In order to search the mechanistic performance of the most active flavanone, we focus on the flavonoid-mediated regulation of GSK-3ß-mediated tau phosphorylation previously reported. Flavanone 1 treatment decreased the rise of hyperphosphorylated tau protein neuronal levels induced after 3xTg-AD ACM exposure and inhibited the activity of GSK-3ß. Finally, direct exposure of these neurotoxic 3xTg-AD astrocytes to flavanone 1 resulted in toxicity to these cells and reduced the neurotoxicity of 3xTg-AD ACM as well. Our results allow us to present compound 1 as a natural prenylated flavanone that could be used as a precursor to development and design of future drug therapies for AD.

Molecular Imaging of Monoamine Oxidase A Expression in Highly Aggressive Prostate Cancer: Synthesis and Preclinical Evaluation of Positron Emission Tomography Tracers.

The role of monoamine oxidase A (MAO-A) in the aggressiveness of prostate cancer (PCa) has been established in recent years. The molecular imaging of MAO-A expression could offer a noninvasive tool for the visualization and quantification of highly aggressive PCa. This study reports the synthesis and preclinical evaluation of 11C- and 18F-labeled MAO-A inhibitors as positron emission tomography (PET) tracers for proof-of-concept studies in animal models of PCa. Good manufacturing practice production and quality control of these radiotracers using an automated platform was achieved. PET imaging was performed in an LNCaP tumor model with high MAO-A expression. The tumor-to-muscle (T/M) uptake ratio of [11C]harmine (4.5 ± 0.5) was significantly higher than that for 2-[18F]fluoroethyl-harmol (2.3 ± 0.7) and [11C]clorgyline (2.0 ± 0.1). A comparable ex vivo biodistribution pattern in all radiotracers was observed. Furthermore, the tumor uptake of [11C]harmine showed a dramatic reduction (T/M = 1) in a PC3 tumor model with limited MAO-A expression, and radioactivity uptake in LNCaP tumors was blocked in the presence of nonradioactive harmine. Our findings suggest that [11C]harmine may serve as an attractive PET probe for the visualization of MAO-A expression in highly aggressive PCa. These radiotracers have the potential for clinical translation and may aid in the development of personalized therapeutic strategies for PCa patients.

Transcriptomic Analyses of Neurotoxic Astrocytes Derived from Adult Triple Transgenic Alzheimer's Disease Mice.

Neurodegenerative diseases such as Alzheimer's disease have been classically studied from a purely neuronocentric point of view. More recent evidences support the notion that other cell populations are involved in disease progression. In this sense, the possible pathogenic role of glial cells like astrocytes is increasingly being recognized. Once faced with tissue damage signals and other stimuli present in disease environments, astrocytes suffer many morphological and functional changes, a process referred as reactive astrogliosis. Studies from murine models and humans suggest that these complex and heterogeneous responses could manifest as disease-specific astrocyte phenotypes. Clear understanding of disease-associated astrocytes is a necessary step to fully disclose neurodegenerative processes, aiding in the design of new therapeutic and diagnostic strategies. In this work, we present the transcriptomics characterization of neurotoxic astrocytic cultures isolated from adult symptomatic animals of the triple transgenic mouse model of Alzheimer's disease (3xTg-AD). According to the observed profile, 3xTg-AD neurotoxic astrocytes show various reactivity features including alteration of the extracellular matrix and release of pro-inflammatory and proliferative factors that could result in harmful effects to neurons. Moreover, these alterations could be a consequence of stress responses at the endoplasmic reticulum and mitochondria as well as of concomitant metabolic adaptations. Present results support the hypothesis that adaptive changes of astrocytic function induced by a stressed microenvironment could later promote harmful astrocyte phenotypes and further accelerate or induce neurodegenerative processes.

Isolation and characterization of neurotoxic astrocytes derived from adult triple transgenic Alzheimer's disease mice.

Alzheimer's disease has been considered mostly as a neuronal pathology, although increasing evidence suggests that glial cells might play a key role in the disease onset and progression. In this sense, astrocytes, with their central role in neuronal metabolism and function, are of great interest for increasing our understanding of the disease. Thus, exploring the morphological and functional changes suffered by astrocytes along the course of this disorder has great therapeutic and diagnostic potential. In this work we isolated and cultivated astrocytes from symptomatic 9-10-months-old adult 3xTg-AD mice, with the aim of characterizing their phenotype and exploring their pathogenic potential. These "old" astrocytes occurring in the 3xTg-AD mouse model of Alzheimer's Disease presented high proliferation rate and differential expression of astrocytic markers compared with controls. They were neurotoxic to primary neuronal cultures both, in neuronal-astrocyte co-cultures and when their conditioned media (ACM) was added into neuronal cultures. ACM caused neuronal GSK3ß activation, changes in cytochrome c pattern, and increased caspase 3 activity, suggesting intrinsic apoptotic pathway activation. Exposure of neurons to ACM caused different subcellular responses. ACM application to the somato-dendritic domain in compartmentalised microfluidic chambers caused degeneration both locally in soma/dendrites and distally in axons. However, exposure of axons to ACM did not affect somato-dendritic nor axonal integrity. We propose that this newly described old 3xTg-AD neurotoxic astrocytic population can contribute towards the mechanistic understanding of the disease and shed light on new therapeutical opportunities.

A new naphthalene derivative with anti-amyloidogenic activity as potential therapeutic agent for Alzheimer's disease.

The aggregation of ß-amyloid peptides is associated to neurodegeneration in Alzheimer's disease (AD) patients. Consequently, the inhibition of both oligomerization and fibrillation of ß-amyloid peptides is considered a plausible therapeutic approach for AD. Herein, the synthesis of new naphthalene derivatives and their evaluation as anti-ß-amyloidogenic agents are presented. Molecular dynamic simulations predicted the formation of thermodynamically stable complexes between the compounds, the Aß1-42 peptide and fibrils. In human microglia cells, these compounds inhibited the aggregation of Aß1-42 peptide. The lead compound 8 showed a high affinity to amyloid plaques in mice brain ex vivo assays and an adequate log Poct/PBS value. Compound 8 also improved the cognitive function and decreased hippocampal ß-amyloid burden in the brain of 3xTg-AD female mice. Altogether, our results suggest that 8 could be a novel therapeutic agent for AD.

Neuroprotective effects of prenylated flavanones isolated from Dalea species, in vitro and in silico studies.

Neurodegenerative diseases (NDs) represent a global problem on public health, with a growing incidence as human longevity increases. Currently, although there are palliative strategies available for most of these diseases, there is a lack of effective therapies for their cure. Flavonoids are extensively studied for their multi-target behavior. Among numerous biological activities, it has been reported that they act at the CNS level, presenting neuroprotective activity through different mechanisms of action. Dalea L. (Fabaceae) is an American genus, with about 172 species. Dalea elegans Gillies ex. Hook. & Arn and Dalea pazensis Rusby, both South American species, are the important source of natural compounds of the prenylated flavanones type. In the present study, five prenylated flavanones isolated from Dalea species were assayed for their neuroprotective activity in two in vitro models of neurodegeneration. Flavanones 1 and 2 exhibited neuroprotective effects against oxidative stress-induced death in both models, granular cerebellar neurons and (NGF)-differentiated PC12 cells. Structure-activity relationships were also reported. Our results indicated that an 8-prenyl group at the A-ring accompanied by an unsubstituted B-ring, or a 2',4'-dihydroxy-5'-dimethylallyl substitution, lead to the most potent flavanones. Furthermore, in silico studies were performed, and several putative targets in NDs were identified for compounds 1 and 2. Between them, the enzyme acetylcholinesterase was selected for its validation in vitro. The present in vitro and in silico results imply that prenylated flavanones 1 and 2 may be useful in the development and design of future strategies for the treatment of NDs diseases.

Purification, structural elucidation, antioxidant capacity and neuroprotective potential of the main polyphenolic compounds contained in Achyrocline satureioides (Lam) D.C. (Compositae).

Achyrocline satureioides (Lam) D.C (Compositae) is a native medicinal plant of South America traditionally utilized for its anti-inflammatory, sedative and anti-atherosclerotic properties among others. Neuroprotective effects have been reported in vivo and could be associated to its elevated content of flavonoid aglycones. In the present study we performed the isolation and structure elucidation of the major individual flavonoids of A. satureioides along with the in vitro characterization of their individual antioxidant and neuroprotective properties in order to see their putative relevance for treating neurodegeneration. Exact mass, HPLC-MS/MS and 1H NMR identified dicaffeoyl quinic acid isomers, quercetin, luteolin, isoquercitrin, and 3-O-methylquercetin as the mayor polyphenols. Flavonoids intrinsic redox properties were evaluated in the presence of the endogenous antioxidants GSH and Ascorbate. Density Functional Theory (DFT) molecular modeling and electron density studies showed a theoretical basis for their different redox properties. Finally, in vitro neuroprotective effect of each isolated flavonoid was evaluated against hydrogen peroxide-induced toxicity in a primary neuronal culture paradigm. Our results showed that quercetin was more efficacious than luteolin and isoquercitrin, while 3-O-methylquercetin was unable to afford neuroprotection significantly. This was in accordance with the susceptibility of each flavonoid to be oxidized and to react with GSH. Overall our results shed light on chemical and molecular mechanisms underlying bioactive actions of A. satureioides main flavonoids that could contribute to its neuroprotective effects and support the positive association between the consumption of A. satureioides as a natural dietary source of polyphenols, and beneficial health effect.

Structural evidence of quercetin multi-target bioactivity: A reverse virtual screening strategy.

The ubiquitous flavonoid quercetin is broadly recognized for showing diverse biological and health-promoting effects, such as anti-cancer, anti-inflammatory and cytoprotective activities. The therapeutic potential of quercetin and similar compounds for preventing such diverse oxidative stress-related pathologies has been generally attributed to their direct antioxidant properties. Nevertheless, accumulated evidence indicates that quercetin is also able to interact with multiple cellular targets influencing the activity of diverse signaling pathways. Even though there are a number of well-established protein targets such as phosphatidylinositol 3 kinase and xanthine oxidase, there remains a lack of a comprehensive knowledge of the potential mechanisms of action of quercetin and its target space. In the present work we adopted a reverse screening strategy based on ligand similarity (SHAFTS) and target structure (idTarget, LIBRA) resulting in a set of predicted protein target candidates. Furthermore, using this method we corroborated a broad array of previously experimentally tested candidates among the predicted targets, supporting the suitability of this screening approach. Notably, all of the predicted target candidates belonged to two main protein families, protein kinases and poly [ADP-ribose] polymerases. They also included key proteins involved at different points within the same signaling pathways or within interconnected signaling pathways, supporting a pleiotropic, multilevel and potentially synergistic mechanism of action of quercetin. In this context we highlight the value of quercetin's broad target profile for its therapeutic potential in diseases like inflammation, neurodegeneration and cancer.

Quercetin in brain diseases: Potential and limits.

Quercetin is a ubiquitous flavonoid present in beverages, food and plants that has been demonstrated to have a role in the prevention of neurodegenerative and cerebrovascular diseases. In neuronal culture, quercetin increases survival against oxidative insults. Antioxidation appears to be a necessary but not sufficient condition for its neuroprotective action and modulation of intracellular signaling and transcription factors, increasing the expression of antioxidant and pro survival proteins and modulating inflammation, appears as important for neuronal protection. Quercetin also regulates the activity of kinases, changing the phosphorylation state of target molecules, resulting in modulation of cellular function and gene expression. Concentrations of quercetin higher than 100 µM consistently show cytotoxic and apoptotic effects by its autoxidation and generation of toxic quinones. In vivo, results are controversial with some studies showing neuroprotection by quercetin and others not, requiring a drug delivery system or chronic treatments to show neuroprotective effects. The blood and brain bioavailability of free quercetin after ingestion is a complex and controversial process that produces final low concentrations, a fact that has led to suggestions that metabolites would be active by themselves and/or as pro-drugs that would release the active aglycone in the brain. Available studies show that in normal or low oxidative conditions, chronic treatments with quercetin contributes to re-establish the redox regulation of proteins, transcription factors and survival signaling cascades that promote survival. In the presence of highly oxidative conditions such as in an ischemic tissue, quercetin could become pro-oxidant and toxic. At present, evidence points to quercetin as a preventive molecule for neuropathology when administered in natural matrices such as vegetables and food. More research is needed to support its use as a lead compound in its free form in acute treatments, requiring new pharmaceutical formulations and/or structural changes to limit its pro-oxidant and toxic effects.

Antioxidant activity, cellular bioavailability, and iron and calcium management of neuroprotective and nonneuroprotective flavones.

Few studies have been undertaken on the relationship of the structure of flavones and neuroprotection. Previously, we described the structural determinants of the neuroprotective activity of some natural flavones in cerebellar granule neurons in culture against an oxidative insult (H2O2). In the present work, we analyzed anti-oxidant activity, cellular iron, and Ca(2+) levels and cellular bioavailability of neuroprotective and nonneuroprotective flavones in the same experimental paradigm. Oxidative cellular damage produced by H2O2 was prevented by all of the studied flavones with rather similar potency for all of them. Labile Iron Pool was neither affected by protective nor nonprotective flavones. Intracellular Ca(2+) homeostasis was not affected by protective flavones either. Nonetheless, fisetin, the nonprotective flavone, decreased Ca(2+) levels modifying Ca(2+) homeostasis. Methylation of the catechol group, although weakens anti-oxidant capacity, keeps the neuroprotective capacity with less degradation and lower toxicity, constituting promising structural alternatives as leads for the design of neuroprotective molecules.

After cellular internalization, quercetin causes Nrf2 nuclear translocation, increases glutathione levels, and prevents neuronal death against an oxidative insult.

In this work we describe the protective effects of quercetin against H(2)O(2) in 24-h-pretreated neuronal cultures. We explored quercetin availability and subcellular fate through the use of HPLC-Diode Array Detection (DAD), epifluorescence, and confocal microscopy. We focused on quercetin modulation of thiol-redox systems by evaluating changes in mitochondrial thioredoxin Trx2, the levels of total glutathione (GSH), and the expression of the gamma-glutamate-cysteine ligase catalytic subunit (GCLC), the rate-limiting enzyme of GSH synthesis, by the use of Western blot, HPLC, and real-time PCR techniques, respectively. We further explored the activation of the protective NF-E2-related factor 2 (Nrf2)-dependent signaling pathway by quercetin using immunocytochemistry techniques. Our results showed rapid quercetin internalization into neurons, reaching the nucleus after its addition to the culture. Quercetin pretreatment increased total GSH levels, but did not increase Trx2. Interestingly it caused Nrf2 nuclear translocation and significantly increased GCLC gene expression. At the moment of H(2)O(2) addition, intracellular quercetin or related metabolites were undetectable in the cultures although quercetin pretreatment prevented neuronal death from the oxidant exposure. Our findings suggest alternative mechanisms of quercetin neuroprotection beyond its long-established ROS scavenging properties, involving Nrf2-dependent modulation of the GSH redox system.

Pretreatment with natural flavones and neuronal cell survival after oxidative stress: a structure-activity relationship study.

Quercetin shows structural features that have been related to the antioxidant potency of flavonoids and also shows neuroprotection in different models of oxidative death. Because only a few studies have focused on the flavonoid structural requirements for neuroprotection, this work evaluated the protective capacity of 13 flavones structurally related to quercetin, isolated from Kenyan plants, to rescue primary cerebellar granule neurons from death induced by a treatment with 24 h of hydrogen peroxide (150 microM). Each flavone (0-100 microM) was applied 24 h prior to the oxidative insult, and neuronal viability was evaluated by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Results suggest that the o-dihydroxy substitution in the B-ring is not necessary to afford neuroprotection and could be partly responsible for neurotoxic effects. Furthermore, the hydroxy substitutions in the positions C3 (C-ring) in C5 and C7 (A-ring) would be important for neuroprotection in this model.

Cytoprotection by neutral fraction of tannat red wine against oxidative stress-induced cell death.

Some of the beneficial effects of the Mediterranean diet on human pathologies have been attributed to red wine polyphenols. It has been postulated that the antioxidant activity of the latter would be also responsible for the cytoprotective capacity of red wine that has been reported in a few papers. Nevertheless, red wine shows a complex composition, and the active fraction is not known yet. In this context, the protective capacity of total lyophilized extracts of red wine and anthocyanin, neutral, or acidic fractions, was explored in PC12 cells in culture after a hydrogen peroxide insult. Although all fractions showed high antioxidant activity, only the neutral fraction was cytoprotective. The analysis of this active fraction showed that it was rich in the aglycons quercetin and myricetin as well as the glycosides of kaempferol, isorhamnetin, epicatechin, and catechin, some of which are known to be cytoprotective. This is the first paper to reveal the active fraction of total wine responsible of its cytoprotection.

Cell culture protection and in vivo neuroprotective capacity of flavonoids.

Flavonoids are an important group of recognized antioxidants ubiquitous in fruits, vegetables and herbs. There are epidemiological evidences for the stroke-protecting capacity of flavonoids and while the neuroprotective power of complex extracts rich in flavonoids like those of Ginkgo biloba, green tea or lyophilized red wine have been demonstrated in several studies, neuroprotection by individual flavonoids has been poorly studied in vivo. The neuroprotective capacity of individual flavonoids was studied in PC12 cells in culture and in a model of permanent focal ischemia (permanent Middle Cerebral Artery Occlusion - pMCAO). In the in vivo experiments, flavonoids were administered in lecithin preparations to facilitate the crossing of the blood brain barrier. The simultaneous incubation of PC12 cells with 200 micro M hydrogen peroxide (H2O2) and different flavonoids for 30 min resulted in a conspicuous profile: quercetin, fisetin, luteolin and myricetin significantly increased cell survival while catechin, kaempherol and taxifolin did not. Quercetin was detected in brain tissue 30 min and 1 h after intraperitoneal administration. When one of the protective flavonoids (quercetin) and one of those that failed to increase PC12 cell survival (catechin) were assessed for their protective capacity in the pMCAO model, administered i.p. 30 min after vessel occlusion, quercetin significantly decreased the brain ischemic lesion while catechin did not. It is concluded that when administered in liposomal preparations, flavonoids structurally related to quercetin could become leads for the development of a new generation of molecules to be clinically effective in human brain ischemia.