New Benzodihydrofuran Derivatives Alter the Amyloid ß Peptide Aggregation: Strategies To Develop New Anti-Alzheimer Drugs.

Alzheimer's disease is a neurodegenerative disorder that is the leading cause of dementia in elderly patients. Amyloid-ß peptide (1-42 oligomers) has been identified as a neurotoxic factor, triggering many neuropathologic events. In this study, 15 chalcones were synthesized employing the Claisen-Schmidt condensation reaction, starting from a compound derived from fomannoxine, a natural benzodihydrofuran whose neuroprotective activity has been proven and reported, and methyl aromatic ketones with diverse patterns of halogenated substitution. As a result, chalcones were obtained, with good to excellent reaction yields from 50 to 98%. Cytotoxicity of the compounds was assessed, and their cytoprotective effect against the toxicity associated with Aß was evaluated on PC-12 cells. Out of the 15 chalcones obtained, only the 4-bromo substituted was cytotoxic at most tested concentrations. Three synthesized chalcones showed a cytoprotective effect against Aß toxicity (over 37%). The 2,4,5-trifluoro substituted chalcone was the most promising series since it showed a cytoprotective impact with more than 60 ± 5% of recovery of cellular viability; however, 3-fluoro substituted compound also exhibited important values of recovery (50 ± 6%). The fluorine substitution pattern was shown to be more effective for cytoprotective activity. Specifically, substitution with fluorine in the 3,5-positions turned out to be particularly effective for cytoprotection. Furthermore, fluorinated compounds inhibited the aggregation rate of Aß, suggesting a dual effect that can be the starting point of new molecules with therapeutic potential.

Neuroprotective Properties of Eudesmin on a Cellular Model of Amyloid-ß Peptide Toxicity.

BACKGROUND: Alzheimer's disease (AD) is a neurodegenerative disorder characterized by progressive cognitive impairment and memory loss. One of the hallmarks in AD is amyloid-ß peptide (Aß) accumulation, where the soluble oligomers of Aß (AßOs) are the most toxic species, deteriorating the synaptic function, membrane integrity, and neuronal structures, which ultimately lead to apoptosis. Currently, there are no drugs to arrest AD progression, and current scientific efforts are focused on searching for novel leads to control this disease. Lignans are compounds extracted from conifers and have several medicinal properties. Eudesmin (Eu) is an extractable lignan from the wood of Araucaria araucana, a native tree from Chile. This metabolite has shown a range of biological properties, including the ability to control inflammation and antibacterial effects. OBJECTIVE: In this study, the neuroprotective abilities of Eu on synaptic failure induced by AßOs were analyzed. METHODS: Using neuronal models, PC12 cells, and in silico simulations we evaluated the neuroprotective effect of Eu (30 nM) against the toxicity induced by AßOs. RESULTS: In primary cultures from mouse hippocampus, Eu preserved the synaptic structure against AßOs toxicity, maintaining stable levels of the presynaptic protein SV2 at the same concentration. Eu also averted synapsis failure from the AßOs toxicity by sustaining the frequencies of cytosolic Ca2+ transients. Finally, we found that Eu (30 nM) interacts with the Aß aggregation process inducing a decrease in AßOs toxicity, suggesting an alternative mechanism to explain the neuroprotective activity of Eu. CONCLUSION: We believe that Eu represents a novel lead that reduces the Aß toxicity, opening new research venues for lignans as neuroprotective agents.

Microglial Activation Modulated by P2X4R in Ischemia and Repercussions in Alzheimer's Disease.

There are over 80 million people currently living who have had a stroke. The ischemic injury in the brain starts a cascade of events that lead to neuronal death, inducing neurodegeneration which could lead to Alzheimer's disease (AD). Cerebrovascular diseases have been suggested to contribute to AD neuropathological changes, including brain atrophy and accumulation of abnormal proteins such as amyloid beta (Aß). In patients older than 60 years, the incidence of dementia a year after stroke was significantly increased. Nevertheless, the molecular links between stroke and dementia are not clearly understood but could be related to neuroinflammation. Considering that activated microglia has a central role, there are brain-resident innate immune cells and are about 10-15% of glial cells in the adult brain. Their phagocytic activity is essential for synaptic homeostasis in different areas, such as the hippocampus. These cells polarize into phenotypes or subtypes: the pro-inflammatory M1 phenotype, or the immunosuppressive M2 phenotype. Phenotype M1 is induced by classical activation, where microglia secrete a high level of pro- inflammatory factors which can cause damage to the surrounding neuronal cells. Otherwise, M2 phenotype is the major effector cell with the potential to counteract pro-inflammatory reactions and promote repair genes expression. Moreover, after the classical activation, an anti-inflammatory and a repair phase are initiated to achieve tissue homeostasis. Recently it has been described the concepts of homeostatic and reactive microglia and they had been related to major AD risk, linking to a multifunctional microglial response to Aß plaques and pathophysiology markers related, such as intracellular increased calcium. The upregulation and increased activity of purinergic receptors activated by ADP/ATP, specially P2X4R, which has a high permeability to calcium and is mainly expressed in microglial cells, is observed in diseases related to neuroinflammation, such as neuropathic pain and stroke. Thus, P2X4R is associated with microglial activation. P2X4R activation drives microglia motility via the phosphatidylinositol-3-kinase (PI3K)/Akt pathway. Also, these receptors are involved in inflammatory-mediated prostaglandin E2 (PGE2) production and induce a secretion and increase the expression of BDNF and TNF-α which could be a link between pathologies related to aging and neuroinflammation.

Regulation of PPARα by APP in Alzheimer disease affects the pharmacological modulation of synaptic activity.

Among genetic susceptibility loci associated with late-onset Alzheimer disease (LOAD), genetic polymorphisms identified in genes encoding lipid carriers led to the hypothesis that a disruption of lipid metabolism could promote disease progression. We previously reported that amyloid precursor protein (APP) involved in Alzheimer disease (AD) physiopathology impairs lipid synthesis needed for cortical networks' activity and that activation of peroxisome proliferator-activated receptor α (PPARα), a metabolic regulator involved in lipid metabolism, improves synaptic plasticity in an AD mouse model. These observations led us to investigate a possible correlation between PPARα function and full-length APP expression. Here, we report that PPARα expression and activation were inversely related to APP expression both in LOAD brains and in early-onset AD cases with a duplication of the APP gene, but not in control human brains. Moreover, human APP expression decreased PPARA expression and its related target genes in transgenic mice and in cultured cortical cells, while opposite results were observed in APP-silenced cortical networks. In cultured neurons, APP-mediated decrease or increase in synaptic activity was corrected by a PPARα-specific agonist and antagonist, respectively. APP-mediated control of synaptic activity was abolished following PPARα deficiency, indicating a key function of PPARα in this process.

Alzheimer's Disease, a Lipid Story: Involvement of Peroxisome Proliferator-Activated Receptor α.

Alzheimer's disease (AD) is the leading cause of dementia in the elderly. Mutations in genes encoding proteins involved in amyloid-ß peptide (Aß) production are responsible for inherited AD cases. The amyloid cascade hypothesis was proposed to explain the pathogeny. Despite the fact that Aß is considered as the main culprit of the pathology, most clinical trials focusing on Aß failed and suggested that earlier interventions are needed to influence the course of AD. Therefore, identifying risk factors that predispose to AD is crucial. Among them, the epsilon 4 allele of the apolipoprotein E gene that encodes the major brain lipid carrier and metabolic disorders such as obesity and type 2 diabetes were identified as AD risk factors, suggesting that abnormal lipid metabolism could influence the progression of the disease. Among lipids, fatty acids (FAs) play a fundamental role in proper brain function, including memory. Peroxisome proliferator-activated receptor α (PPARα) is a master metabolic regulator that regulates the catabolism of FA. Several studies report an essential role of PPARα in neuronal function governing synaptic plasticity and cognition. In this review, we explore the implication of lipid metabolism in AD, with a special focus on PPARα and its potential role in AD therapy.

A Natural Benzofuran from the Patagonic Aleurodiscus vitellinus Fungus has Potent Neuroprotective Properties on a Cellular Model of Amyloid-ß Peptide Toxicity.

Alzheimer's disease (AD) is characterized by amyloid plaques that form due to an increase in amyloid-ß peptide (Aß) aggregation. One strategy in the search of new treatments for AD focuses on compounds that decrease Aß accumulation. Compounds containing a benzofuran ring have been described to play an important role in decreasing Aß-induced toxicity; however, only synthetic benzofurans have been tested thus far. The aim of the present study was to examine the in vitro neuroprotective properties of fomannoxin (Fx), a natural benzofuran isolated from cultures of the Andean-Patagonian fungi Aleurodiscus vitellinus, and evaluate its effect on Aß peptide. We tested the effect of Fx at a wide concentration range (10-11-10-4 M) in PC-12 cells, and found the compound did not alter cellular viability. Fx also showed a concentration-dependent effect on the Aß-induced toxicity in PC12 cells, showing viability above 100% at 10-6 M. We then measured the effect of Fx (10-7-10-5 M) on the frequency of cytosolic Ca2+ transients in rat hippocampal neurons at both acute and chronic (24 h) times. Acute incubation with Fx increased the frequency of cytosolic Ca2+ transients to values around 200%, whereas chronic incubation with Fx increased the frequency of Ca2+ transients. Finally, the Aß-induced decrease in intracellular Ca2+ transients was prevented when Fx (10-6 M) was co-incubated with Aß (5×10-6 M). The results suggest a potent neuroprotective effect of this naturally occurring benzofuran against Aß peptide toxicity that could be mediated by an interference with it binding to plasma membrane, and lead Fx as new chemical entity to develop pharmacological tools against Aß peptide neurotoxicity.

P2X receptor overexpression induced by soluble oligomers of amyloid beta peptide potentiates synaptic failure and neuronal dyshomeostasis in cellular models of Alzheimer's disease.

The most common cause of dementia is Alzheimer's disease. The etiology of the disease is unknown, although considerable evidence suggests a critical role for the soluble oligomers of amyloid beta peptide (Aß). Because Aß increases the expression of purinergic receptors (P2XRs) in vitro and in vivo, we studied the functional correlation between long-term exposure to Aß and the ability of P2XRs to modulate network synaptic tone. We used electrophysiological recordings and Ca2+ microfluorimetry to assess the effects of chronic exposure (24 h) to Aß oligomers (0.5 µM) together with known inhibitors of P2XRs, such as PPADS and apyrase on synaptic function. Changes in the expression of P2XR were quantified using RT-qPCR. We observed changes in the expression of P2X1R, P2X7R and an increase in P2X2R; and also in protein levels in PC12 cells (143%) and hippocampal neurons (120%) with Aß. In parallel, the reduction on the frequency and amplitude of mEPSCs (72% and 35%, respectively) were prevented by P2XR inhibition using a low PPADS concentration. Additionally, the current amplitude and intracellular Ca2+ signals evoked by extracellular ATP were increased (70% and 75%, respectively), suggesting an over activation of purinergic neurotransmission in cells pre-treated with Aß. Taken together, our findings suggest that Aß disrupts the main components of synaptic transmission at both pre- and post-synaptic sites, and induces changes in the expression of key P2XRs, especially P2X2R; changing the neuromodulator function of the purinergic tone that could involve the P2X2R as a key factor for cytotoxic mechanisms. These results identify novel targets for the treatment of dementia and other diseases characterized by increased purinergic transmission.

Modulation of neuronal nicotinic receptor by quinolizidine alkaloids causes neuroprotection on a cellular Alzheimer model.

Alzheimer's disease (AD) is a progressive and neurodegenerative disorder and one of the current therapies involves strengthening the cholinergic tone in central synapses. Neuroprotective properties for nicotine have been described in AD, through its actions on nicotinic receptors and the further activation of the PI3K/Akt/Bcl-2 survival pathway. We have tested a quinolizidine alkaloid extract (TM0112) obtained from Teline monspessulanna (L.) K. Koch seeds to evaluate its action on nicotinic acetylcholine receptor (nAChR) in a neuronal AD model. Our data show that PC-12 cells pretreated with amyloid-ß (Aß) peptide for 24 h in presence of TM0112 modified Aß-reduction on cellular viability (Aß = 80 ± 3%; +TM0112 = 113 ± 4%, n = 15). In addition, this effect was blocked with atropine, MLA, and α-BTX (+TM0112+atropine = 87 ± 4%; +TM0112+MLA = 86 ± 4%; +TM0112+α-BTX = 92 ± 3%). Furthermore, similar protective effects were observed in rat cortical neurons (Aß = 63 ± 6%; +TM0112 = 114 ± 8%), but not in HEK293T cells (Aß = 61.4 ± 6.1%; +TM0112 = 62.8 ± 5.2) that do not express α7 nAChR. Moreover, the frequency of synaptic activity in the neuronal network (Aß = 51.6 ± 16.9%; +TM0112 = 210.8 ± 47.9%, n > 10), as well as the intracellular Ca2+ transients were recovered by TM0112 (Aß = 61.4 ± 6.9%; +TM0112 = 112.0 ± 5.7%; n = 3) in rat hippocampal neurons. TM0112 increased P-Akt, up to 250% with respect to control, and elevated Bcl-2/Bax percentage (Aß = 61.0 ± 8.2%; +TM0112 = 105.4 ± 19.5%, n = 4), suggesting a coupling between nAChR activation and an intracellular neuroprotective pathway. Our results suggest that TM0112 could be a new potential source for anti-AD drugs.

Synaptic silencing and plasma membrane dyshomeostasis induced by amyloid-ß peptide are prevented by Aristotelia chilensis enriched extract.

Alzheimer's disease (AD) is characterized by the presence of different types of extracellular and neurotoxic aggregates of amyloid-ß (Aß). Recently, bioactive compounds extracted from natural sources showing neuroprotective properties have become of interest in brain neurodegeneration. We have purified, characterized, and evaluated the protective potential of one extract enriched in polyphenols obtained from Aristotelia chilensis (MQ), a Chilean berry fruit, in neuronal models of AD induced by soluble oligomers of Aß1-40. For example, using primary hippocampal cultures from rats (E18), we observed neuroprotection when the neurons were co-incubated with Aß (0.5 µM) plus MQ for 24 h (Aß = 23 ± 2%; Aß + MQ = 3 ± 1%; n = 3). In parallel, co-incubation of Aß with MQ recovered the frequency of Ca2+ transient oscillations when compared to neurons treated with Aß alone (Aß = 72 ± 3%; Aß + MQ = 86 ± 2%; n = 5), correlating with the changes observed in spontaneous synaptic activity. Additionally, MAP-2 immunostaining showed a preservation of the dendritic tree, suggesting that the toxic effect of Aß is prevented in the presence of MQ. A new complex mechanism is proposed by which MQ induces neuroprotective effects including antioxidant properties, modulation of cell survival pathways, and/or direct interaction with the Aß aggregates. Our results suggest that MQ induces changes in the aggregation kinetics of Aß producing variations in the nucleation phase (Aß: k1 = 2.7 ± 0.4 × 10-3 s-1 MQ: k1 = 8.3 ± 0.6 × 10-3 s-1) and altering Thioflavin T insertion in ß-sheets. In conclusion, MQ induces a potent neuroprotection by direct interaction with the Aß aggregates, generating far less toxic species and in this way protecting the neuronal network.

Synaptic failure and adenosine triphosphate imbalance induced by amyloid-ß aggregates are prevented by blueberry-enriched polyphenols extract.

The potential neuroprotective properties of fruits have been widely recognized. In this study, we evaluated the protective properties of a blueberry extract (BB-4), rich in polyphenols, in a neurodegenerative model induced by amyloid-ß peptide (Aß). Chronic treatment with Aß drastically reduced synaptic transmission and the extent of secretory vesicles, which were recovered partially with BB-4. Also, the extract recovered Ca(2+) transients in hippocampal neurons preincubated with Aß (0.5 and 5 µM) by about 25% ± 3% and 30% ± 2, respectively. In this work, we demonstrate a novel effect of the BB-4 extract on Aß-induced ATP leakage, in which this extract was able to antagonize the acute ATP leakage but not chronic ATP depletion. On the other hand, BB-4 prevented the uncoupling of mitochondrial function induced by FCCP by about 85%, but it was unable to modify the uncoupling induced by Aß. The present results strongly indicate that BB-4 plays a role in the process of Aß aggregation by reducing the toxic species (i.e., 40 kDa). These findings suggest that a blueberry extract can protect neuronal tissue from Aß toxicity mainly through its antiaggregation property, and its antioxidant properties and mitochondrial membrane potential capacities are secondary mechanisms important in chronic stages. Our work suggests that BB-4 could be an important nutritional complement to neuronal health as well as a potential nutraceutical formulation useful as a dietary supplement in the elderly.