Effect of Phenolic Compounds Against Aβ Aggregation and Aβ-Induced Toxicity in Transgenic C. elegans

Natural products targeting amyloid-β oligomer neurotoxicity in Alzheimer's disease

Alzheimer's disease (AD) constitutes a major global health issue, characterized by progressive neurodegeneration and cognitive impairment, for which no curative treatment is currently available. Current therapeutic approaches are focused on symptom management, highlighting the critical need for disease-modifying therapy. The hallmark pathology of AD involves the aggregation and accumulation of amyloid-β (Aβ) peptides in the brain. Consequently, drug discovery efforts in recent decades have centered on the Aβ aggregation cascade, which includes the transition of monomeric Aβ peptides into toxic oligomers and, ultimately, mature fibrils. Historically, anti-Aβ strategies focused on the clearance of amyloid fibrils using monoclonal antibodies. However, substantial evidence has highlighted the critical role of Aβ oligomers (AβOs) in AD pathogenesis. Soluble AβOs are now recognized as more toxic than fibrils, directly contributing to synaptic impairment, neuronal damage, and the onset of AD. Targeting AβOs has emerged as a promising therapeutic approach to mitigate cognitive decline in AD. Natural products (NPs) have demonstrated promise against AβO neurotoxicity through various mechanisms, including preventing AβO formation, enhancing clearance mechanisms, or converting AβOs into non-toxic species. Understanding the mechanisms by which anti-AβO NPs operate is useful for developing disease-modifying treatments for AD. In this review, we explore the role of NPs in mitigating AβO neurotoxicity for AD drug discovery, summarizing key evidence from biophysical methods, cellular assays, and animal models. By discussing how NPs modulate AβO neurotoxicity across various experimental systems, we aim to provide valuable insights into novel therapeutic strategies targeting AβOs in AD.

Ameliorative effect of Luffa cylindrica fruits on Caenorhabditis elegans and cellular models of Alzheimer's disease-related pathology via autophagy induction

BACKGROUND

Alzheimer's disease (AD) is a prevalent neurodegenerative disorder without an effective cure. Natural products, while showing promise as potential therapeutics for AD, remain underexplored.

AIMS

This study was conducted with the goal of identifying potential anti-AD candidates from natural sources using Caenorhabditis elegans (C. elegans) AD-like models and exploring their mechanisms of action.

MATERIALS & METHODS

Our laboratory's in-house herbal extract library was utilized to screen for potential anti-AD candidates using the C. elegans AD-like model CL4176. The neuroprotective effects of the candidates were evaluated in multiple C. elegans AD-like models, specifically targeting Aβ- and Tau-induced pathology. In vitro validation was conducted using PC-12 cells. To investigate the role of autophagy in mediating the anti-AD effects of the candidates, RNAi bacteria and autophagy inhibitors were employed.

RESULTS

The ethanol extract of air-dried fruits of Luffa cylindrica (LCE), a medicine-food homology species, was found to inhibit Aβ- and Tau-induced pathology (paralysis, ROS production, neurotoxicity, and Aβ and pTau deposition) in C. elegans AD-like models. LCE was non-toxic and enhanced C. elegans' health. It was shown that LCE activates autophagy and its anti-AD efficacy is weakened with the RNAi knockdown of autophagy-related genes. Additionally, LCE induced mTOR-mediated autophagy, reduced the expression of AD-associated proteins, and decreased cell death in PC-12 cells, which was reversed by autophagy inhibitors (bafilomycin A1 and 3-methyladenine).

DISCUSSION

LCE, identified from our natural product library, emerged as a valuable autophagy enhancer that effectively protects against neurodegeneration in multiple AD-like models. RNAi knockdown of autophagy-related genes and cotreatment with autophagy inhibitors weakened its anti-AD efficacy, implying a critical role of autophagy in mediating the neuroprotective effects of LCE.

CONCLUSION

Our findings highlight the potential of LCE as a functional food or drug for targeting AD pathology and promoting human health.

Holothuria scabra extracts confer neuroprotective effect in C. elegans model of Alzheimer's disease by attenuating amyloid-β aggregation and toxicity

Background and aim

Alzheimer's disease (AD) is the most common aged-related neurodegenerative disorder that is associated with the toxic amyloid-β (Aβ) aggregation in the brain. While the efficacies of available drugs against AD are still limited, natural products have been shown to possess neuroprotective potential for prevention and therapy of AD. This study aimed to investigate the neuroprotective effects of H. scabra extracts against Aβ aggregation and proteotoxicity in C. elegans model of Alzheimer's diseases.

Experimental procedure

Whole bodies (WB) and body wall (BW) of H. scabra were extracted and fractionated into ethyl acetate (WBEA, BWEA), butanol (WBBU, BWBU), and ethanol (BWET). Then C. elegans AD models were treated with these fractions and investigated for Aβ aggregation and polymerization, biochemical and behavioral changes, and level of oxidative stress, as well as lifespan extension.

Results and conclusion

C. elegans AD model treated with H. scabra extracts, especially triterpene glycoside-rich ethyl acetate and butanol fractions, exhibited significant reduction of Aβ deposition. These H. scabra extracts also attenuated the paralysis behavior and improved the neurological defects in chemotaxis caused by Aβ aggregation. Immunoblot analysis revealed decreased level of Aβ oligomeric forms and the increased level of Aβ monomers after treatments with H. scabra extracts. In addition, H. scabra extracts reduced reactive oxygen species and increased the mean lifespan of the treated AD worms. In conclusion, this study demonstrated strong evidence of anti-Alzheimer effects by H. scabra extracts, implying that these extracts can potentially be applied as natural preventive and therapeutic agents for AD.

Taxonomy classification by EVISE

Alzheimer's disease, Neurodegenerative disorder, Traditional medicine, Experimental model systems, Molecular biology.

Unveiling the Potential of Polyphenols as Anti-Amyloid Molecules in Alzheimer's Disease

Alzheimer's disease (AD) is a devastating neurodegenerative disease that mostly affects the elderly population. Mechanisms underlying AD pathogenesis are yet to be fully revealed, but there are several hypotheses regarding AD. Even though free radicals and inflammation are likely to be linked with AD pathogenesis, still amyloid-beta (Aβ) cascade is the dominant hypothesis. According to the Aβ hypothesis, a progressive buildup of extracellular and intracellular Aβ aggregates has a significant contribution to the AD-linked neurodegeneration process. Since Aβ plays an important role in the etiology of AD, therefore Aβ-linked pathways are mainly targeted in order to develop potential AD therapies. Accumulation of Aβ plaques in the brains of AD individuals is an important hallmark of AD. These plaques are mainly composed of Aβ (a peptide of 39-42 amino acids) aggregates produced via the proteolytic cleavage of the amyloid precursor protein. Numerous studies have demonstrated that various polyphenols (PPHs), including cyanidins, anthocyanins, curcumin, catechins and their gallate esters were found to markedly suppress Aβ aggregation and prevent the formation of Aβ oligomers and toxicity, which is further suggesting that these PPHs might be regarded as effective therapeutic agents for the AD treatment. This review summarizes the roles of Aβ in AD pathogenesis, the Aβ aggregation pathway, types of PPHs, and distribution of PPHs in dietary sources. Furthermore, we have predominantly focused on the potential of food-derived PPHs as putative anti-amyloid drugs.

Cryptotanshinone Alleviates Oxidative Stress and Reduces the Level of Abnormally Aggregated Protein in Caenorhabditis elegans AD Models

Alzheimer's disease (AD) is one of the leading causes of dementia. As the first common neurodegenerative disease, there are no effective drugs that can reverse the progression. The present study is to report the anti-AD effect of cryptotanshinone (CTS), a natural product isolated from Salvia castanea. It is found that it can alleviate AD-like features associated with Aβ_1-42 toxicity in muscle cells as well as neuronal cells of Caenorhabditis elegans (C. elegans). Further studies showed that CTS reduced the level of reactive oxygen species (ROS) in nematodes, up-regulated the expression of sod-3, and enhanced superoxide dismutase activity. Cryptotanshinone reduced the level of Aβ monomers and highly toxic oligomers in C. elegans while inhibiting the abnormal aggregation of polyglutamine protein. In addition, CTS upregulated the expression of hsp-16.2 and downregulated the expression of ace-2. These results suggested that CTS could alleviate oxidative stress and reduce the level of abnormally aggregated proteins and has the potential to be developed as an anti-AD drug candidate.

Forest Biomass as a Promising Source of Bioactive Essential Oil and Phenolic Compounds for Alzheimer's Disease Therapy

Alzheimer’s disease (AD) is the most common neurodegenerative disorder affecting elderly people worldwide. Currently, there are no effective treatments for AD able to prevent disease progression, highlighting the urgency of finding new therapeutic strategies to stop or delay this pathology. Several plants exhibit potential as source of safe and multi-target new therapeutic molecules for AD treatment. Meanwhile, Eucalyptus globulus extracts revealed important pharmacological activities, namely antioxidant and anti-inflammatory properties, which can contribute to the reported neuroprotective effects. This review summarizes the chemical composition of essential oil (EO) and phenolic extracts obtained from Eucalyptus globulus leaves, disclosing major compounds and their effects on AD-relevant pathological features, including deposition of amyloid-β (Aβ) in senile plaques and hyperphosphorylated tau in neurofibrillary tangles (NFTs), abnormalities in GABAergic, cholinergic and glutamatergic neurotransmission, inflammation, and oxidative stress. In general, 1,8-cineole is the major compound identified in EO, and ellagic acid, quercetin, and rutin were described as main compounds in phenolic extracts from Eucalyptus globulus leaves. EO and phenolic extracts, and especially their major compounds, were found to prevent several pathological cellular processes and to improve cognitive function in AD animal models. Therefore, Eucalyptus globulus leaves are a relevant source of biological active and safe molecules that could be used as raw material for nutraceuticals and plant-based medicinal products useful for AD prevention and treatment.

Natural Bioactive Products and Alzheimer’s Disease Pathology: Lessons from Caenorhabditis elegans Transgenic Models

Alzheimer’s disease (AD) is an age-dependent, progressive disorder affecting millions of people. Currently, the therapeutics for AD only treat the symptoms. Although they have been used to discover new products of interest for this disease, mammalian models used to investigate the molecular determinants of this disease are often prohibitively expensive, time-consuming and very complex. On the other hand, cell cultures lack the organism complexity involved in AD. Given the highly conserved neurological pathways between mammals and invertebrates, Caenorhabditis elegans has emerged as a powerful tool for the investigation of the pathophysiology of human AD. Numerous models of both Tau- and Aβ-induced toxicity, the two prime components observed to correlate with AD pathology and the ease of performing RNA interference for any gene in the C. elegans genome, allow for the identification of multiple therapeutic targets. The effects of many natural products in main AD hallmarks using these models suggest promising health-promoting effects. However, the way in which they exert such effects is not entirely clear. One of the reasons is that various possible therapeutic targets have not been evaluated in many studies. The present review aims to explore shared therapeutical targets and the potential of each of them for AD treatment or prevention.

Red-Beet Betalain Pigments Inhibit Amyloid-β Aggregation and Toxicity in Amyloid-β Expressing Caenorhabditis elegans

Betalain pigments are mainly produced by plants belonging to the order of Caryophyllales. Betalains exhibit strong antioxidant activity and responds to environmental stimuli and stress in plants. Recent reports of antioxidant, anti-inflammatory and anti-cancer properties of betalain pigments have piqued interest in understanding their biological functions. We investigated the effects of betalain pigments (betanin and isobetanin) derived from red-beet on amyloid-β (Aβ) aggregation, which causes Alzheimer's disease. Non-specific inhibition of Aβ aggregation against Aβ40 and Aβ42 by red-beet betalain pigments, in vitro was demonstrated using the thioflavin t fluorescence assay, circular dichroism spectroscopy analysis, transmission electron microscopy and nuclear magnetic resonance (NMR) analysis. Furthermore, we examined the ability of red-beet betalain pigments to interfere with Aβ toxicity by using the transgenic Caenorhabditis elegans model, which expresses the human Aβ42 protein intracellularly within the body wall muscle. It responds to Aβ-toxicity with paralysis and treatment with 50 μM red-beet betalain pigments significantly delayed the paralysis of C. elegans. These results suggest that betalain pigments reduce Aβ-induced toxicity.

Therapeutic Potential of Ferulic Acid in Alzheimer's Disease

Alzheimer's Disease (AD) is one of the most important neurodegenerative diseases and it covers 60% of whole dementia cases. AD is a constantly progressing neurodegenerative disease as a result of the production of β-amyloid (Aβ) protein and the accumulation of hyper-phosphorylated Tau protein; it causes breakages in the synaptic bonds and neuronal deaths to a large extent. Millions of people worldwide suffer from AD because there is no definitive drug for disease prevention, treatment or slowdown. Over the last decade, multiple target applications have been developed for AD treatments. These targets include Aβ accumulations, hyper-phosphorylated Tau proteins, mitochondrial dysfunction, and oxidative stress resulting in toxicity. Various natural or semisynthetic antioxidant formulations have been shown to protect brain cells from Aβ induced toxicity and provide promising potentials for AD treatment. Ferulic acid (FA), a high-capacity antioxidant molecule, is naturally synthesized from certain plants. FA has been shown to have different substantial biological properties, such as anticancer, antidiabetic, antimicrobial, anti-inflammatory, hepatoprotective, and cardioprotective actions, etc. Furthermore, FA exerted neuroprotection via preventing Aβ-fibril formation, acting as an anti-inflammatory agent, and inhibiting free radical generation and acetylcholinesterase (AChE) enzyme activity. In this review, we present key biological roles of FA and several FA derivatives in Aβ-induced neurotoxicity, protection against free radical attacks, and enzyme inhibitions and describe them as possible therapeutic agents for the treatment of AD.

Ferulic Acid in Animal Models of Alzheimer's Disease: A Systematic Review of Preclinical Studies

Alzheimer's disease (AD) is a neurodegenerative disease with a high incidence in the elderly. Many preclinical studies show that a natural product, ferulic acid (FA), displays neuroprotective effects in AD models. This review aims to systematically review and meta-analyze published pre-clinical researches about the effects, mechanism, and clinical prospects of FA in the treatment of AD. According to the pre-determined search strategy and inclusion criteria, a total of 344 animals in 12 papers were included in the meta-analysis. We used the fixed effects model to analyze data and I2 and p values to indicate heterogeneity. Results show that FA treatment can effectively improve rodents' spatial memory ability in MWM and Y maze experiments (I2 ≥ 70, p < 0.005), and reduce the deposition of Aβ in the brains of various model animals (I2 ≥ 50, p < 0.005). The potential mechanisms include anti-amyloidogenesis, anti-inflammation, anti-oxidation, mitochondrial protection, and inhibition of apoptosis. In conclusion, we systematically review and meta-analyze the literature reporting the effects of FA treatment on AD rodent models and solidify the benefits of FA in reducing Aβ deposition and improving memory in preclinical experiments. We also point out the limitations in the current research design and provide a strategy for the production research of FA in the future.

Overview of Beneficial Effects of (Poly)phenol Metabolites in the Context of Neurodegenerative Diseases on Model Organisms

The rise of neurodegenerative diseases in an aging population is an increasing problem of health, social and economic consequences. Epidemiological and intervention studies have demonstrated that diets rich in (poly)phenols can have potent health benefits on cognitive decline and neurodegenerative diseases. Meanwhile, the role of gut microbiota is ever more evident in modulating the catabolism of (poly)phenols to dozens of low molecular weight (poly)phenol metabolites that have been identified in plasma and urine. These metabolites can reach circulation in higher concentrations than parent (poly)phenols and persist for longer periods of time. However, studies addressing their potential brain effects are still lacking. In this review, we will discuss different model organisms that have been used to study how low molecular weight (poly)phenol metabolites affect neuronal related mechanisms gathering critical insight on their potential to tackle the major hallmarks of neurodegeneration.

Drug discovery: Insights from the invertebrate Caenorhabditis elegans

Therapeutic drug development is a long, expensive, and complex process that usually takes 12-15 years. In the early phases of drug discovery, in particular, there is a growing need for animal models that ensure the reduction in both cost and time. Caenorhabditis elegans has been traditionally used to address fundamental aspects of key biological processes, such as apoptosis, aging, and gene expression regulation. During the last decade, with the advent of large-scale platforms for screenings, this invertebrate has also emerged as an essential tool in the pharmaceutical research industry to identify novel drugs and drug targets. In this review, we discuss the reasons why C. elegans has been positioned as an outstanding cost-effective option for drug discovery, highlighting both the advantages and drawbacks of this model. Particular attention is paid to the suitability of this nematode in large-scale genetic and pharmacological screenings. High-throughput screenings in C. elegans have indeed contributed to the breakthrough of a wide variety of candidate compounds involved in extensive fields including neurodegeneration, pathogen infections and metabolic disorders. The versatility of this nematode, which enables its instrumentation as a model of human diseases, is another attribute also herein underscored. As illustrative examples, we discuss the utility of C. elegans models of both human neurodegenerative diseases and parasitic nematodes in the drug discovery industry. Summing up, this review aims to demonstrate the impact of C. elegans models on the drug discovery pipeline.

Potential Role of Natural Polyphenols against Protein Aggregation Toxicity: In Vitro, In Vivo, and Clinical Studies

One of the main features of neurodegenerative disorders such as Alzheimer's disease and Parkinson's disease is the amyloidogenic behavior of disease-specific proteins including amyloid β, tau, α-synuclein, and mutant Huntingtin which participate in the formation, accumulation, and deposition of toxic misfolded aggregates. Consequently, these proteins not only associated with the progress of their respective neurodegenerative pathologies but also qualify as disease-specific biomarkers. The aim of using natural polyphenols is to target amyloid-dependent proteopathies by decreasing free radical damage and inhibiting and dissolving amyloid fibrils. We explore the effectiveness of the polyphenols epigallocatechin-3-gallate, oleuropein aglycone, and quercetin on their ability to inhibit aggregation of amyloid β, tau, and α-synuclein and mitigate other pathological features for Alzheimer's disease and Parkinson's disease. The analysis was carried from in vitro and cell line studies to animal models and clinical trials. This Review describes the use of phytochemical compounds as prophylactic agents for Alzheimer's disease, Parkinson's disease, and other proteopathies.

Protective Effect and Mechanism of Fruit Extract of Aegle marmelos Against Amyloid-β Toxicity in a Transgenic Caenorhabditis elegans

Alzheimer’s disease (AD) is the most common form of dementia found in the elderly. AD is caused by the accumulation of toxic proteins including amyloid-β (Aβ). The purpose of this study was to investigate the effect of fruit extract of Aegle marmelos against Aβ toxicity in Caenorhabditis elegans. The fruit of A. marmelos has been used in a traditional Thai herb formula in fatigue patients recovering from illnesses such as fever and diarrhea. We used a transgenic C. elegans strain CL4176, which expresses the human Aβ42, to investigate the effects and the mechanisms of action of the extracts against Aβ toxicity. The extract of A. marmelos significantly delayed Aβ-induced paralysis. Aegle marmelos lost the ability to delay Aβ-induced paralysis in worms fed with daf-16 ribonucleic acid interference (RNAi) bacteria, but not in worms fed with hsf-1 and skin-1 RNAi bacteria. These results indicated that daf-16 transcription factor was required for A. marmelos-mediated delayed paralysis. Aegle marmelos enhanced the level of daf-16 gene. Taken together, these results indicated that A. marmelos reduced Aβ toxicity via the DAF-16-mediated cell signaling pathway. In addition, A. marmelos reduced toxic Aβ oligomers. Aegle marmelos also displayed antioxidative effect in in vivo as it enhanced resistance to paraquat-induced oxidative stress in wild type worms. All of the results suggested that A. marmelos can protect against Aβ-induced toxicity and can be a potential candidate for the prevention or treatment of AD.

Ilex paraguariensis extract provides increased resistance against oxidative stress and protection against Amyloid beta-induced toxicity compared to caffeine in Caenorhabditis elegans

Ilex paraguariensis is a plant from South America, used to prepare a tea-like beverage rich in caffeine and polyphenols with antioxidant proprieties. Caffeine consumption is associated with a lower risk of age-associated neuropathologies, besides several extracts that have antioxidant proprieties are known to be neuroprotective, and oxidative stress strongly correlates with Aβ-toxicity. This study aims to investigate the neuroprotective effects of the Ilex paraguariensis hydroalcoholic extract (IPHE) and to evaluate if caffeine agent present in IPHE exerts neuroprotective effects in an amyloid beta-peptide (Aβ)-induced toxicity in Caenorhabditis elegans. The wild-type and CL2006 worms were treated with IPHE (2 and 4 mg/mL) or caffeine (200 and 400 μM) since larval stage 1 (L1) until they achieved the required age for each assay. IPHE and caffeine increased the lifespan and appeared to act directly by reactive oxygen species (ROS) scavenger in both wild-type and CL2006 worms, also conferred resistance against oxidative stress in wild-type animals. Furthermore, both treatments delayed Aβ-induced paralysis and decreased AChE activity in CL2006. The protective effect of IPHE against Aβ-induced paralysis was found to be dependent on heat shock factor hsf-1 and FOXO-family transcription factor daf-16, which are respectively involved in aging-related processes and chaperone synthesis, while that of caffeine was dependent only on daf-16. Mechanistically, IPHE and caffeine decreased the levels of Aβ mRNA in the CL2006 worms; however, only IPHE induced expression of the heat shock chaperonin hsp-16.2, involved in protein homeostasis. The results were overall better when treated with IPHE than with caffeine.

α-Methyl-α-phenylsuccinimide ameliorates neurodegeneration in a C. elegans model of TDP-43 proteinopathy

The antiepileptic drug ethosuximide has recently been shown to be neuroprotective in various Caenorhabditis elegans and rodent neurodegeneration models. It is therefore a promising repurposing candidate for the treatment of multiple neurodegenerative diseases. However, high concentrations of the drug are required for its protective effects in animal models, which may impact on its translational potential and impede the identification of its molecular mechanism of action. Therefore, we set out to develop more potent neuroprotective lead compounds based on ethosuximide as a starting scaffold. Chemoinformatic approaches were used to identify compounds with structural similarity to ethosuximide and to prioritise these based on good predicated blood-brain barrier permeability and C. elegans bioaccumulation properties. Selected compounds were initially screened for anti-convulsant activity in a C. elegans pentylenetetrazol-induced seizure assay, as a rapid primary readout of bioactivity; and then assessed for neuroprotective properties in a C. elegans TDP-43 proteinopathy model based on pan-neuronal expression of human A315T mutant TDP-43. The most potent compound screened, α-methyl-α-phenylsuccinimide (MPS), ameliorated the locomotion defects and extended the shortened lifespan of TDP-43 mutant worms. MPS also directly protected against neurodegeneration by reducing the number of neuronal breaks and cell body losses in GFP-labelled GABAergic motor neurons. Importantly, optimal neuroprotection was exhibited by external application of 50 μM MPS, compared to 8 mM for ethosuximide. This greater potency of MPS was not due to bioaccumulation to higher internal levels within the worm, based on ¹H-nuclear magnetic resonance analysis. Like ethosuximide, the activity of MPS was abolished by mutation of the evolutionarily conserved FOXO transcription factor, daf-16, suggesting that both compounds act via the same neuroprotective pathway(s). In conclusion, we have revealed a novel neuroprotective activity of MPS that is >100-fold more potent than ethosuximide. This increased potency will facilitate future biochemical studies to identify the direct molecular target(s) of both compounds, as we have shown here that they share a common downstream DAF-16-dependent mechanism of action. Furthermore, MPS is the active metabolite of another approved antiepileptic drug, methsuximide. Therefore, methsuximide may have repurposing potential for treatment of TDP-43 proteinopathies and possibly other human neurodegenerative diseases.

Cinnamon, a promising prospect towards Alzheimer's disease

Over the last decades, an exponential increase of efforts concerning the treatment of Alzheimer's disease (AD) has been practiced. Phytochemicals preparations have a millenary background to combat various pathological conditions. Various cinnamon species and their biologically active ingredients have renewed the interest towards the treatment of patients with mild-to-moderate AD through the inhibition of tau protein aggregation and prevention of the formation and accumulation of amyloid-β peptides into the neurotoxic oligomeric inclusions, both of which are considered to be the AD trademarks. In this review, we presented comprehensive data on the interactions of a number of cinnamon polyphenols (PPs) with oxidative stress and pro-inflammatory signaling pathways in the brain. In addition, we discussed the potential association between AD and diabetes mellitus (DM), vis-à-vis the effluence of cinnamon PPs. Further, an upcoming prospect of AD epigenetic pathophysiological conditions and cinnamon has been sighted. Data was retrieved from the scientific databases such as PubMed database of the National Library of Medicine, Scopus and Google Scholar without any time limitation. The extract of cinnamon efficiently inhibits tau accumulations, Aβ aggregation and toxicity in vivo and in vitro models. Indeed, cinnamon possesses neuroprotective effects interfering multiple oxidative stress and pro-inflammatory pathways. Besides, cinnamon modulates endothelial functions and attenuates the vascular cell adhesion molecules. Cinnamon PPs may induce AD epigenetic modifications. Cinnamon and in particular, cinnamaldehyde seem to be effective and safe approaches for treatment and prevention of AD onset and/or progression. However, further molecular and translational research studies as well as prolonged clinical trials are required to establish the therapeutic safety and efficacy in different cinnamon spp.

Caenorhabditis elegans as a model system for target identification and drug screening against neurodegenerative diseases

Over the past decades, Caenorhabditis elegans (C. elegans) has been widely used as a model system because of its small size, transparent body, short generation time and lifespan (~3 days and 3 weeks, respectively), completely sequenced genome and tractability to genetic manipulation. Protein misfolding and aggregation are key pathological features in neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, Huntington's disease and Amyotrophic lateral sclerosis. Animal models, including C. elegans, have been extensively used to discover and validate new drugs against neurodegenerative diseases. The well-defined and genetically tractable nervous system of C. elegans offers an effective model to explore basic mechanistic pathways of neurodegenerative diseases. Recent progress in high-throughput drug screening also provides a powerful approach for identifying chemical modulators of biological processes. Here, we summarize the latest progress of using C. elegans as a model system for target identification and drug screening in neurodegenerative diseases.

The protective role of plant biophenols in mechanisms of Alzheimer's disease

Self-assembly of amyloid beta peptide (Aβ) into the neurotoxic oligomers followed by fibrillar aggregates is a defining characteristic of Alzheimer's disease (AD). Several lines of proposed hypotheses have suggested the mechanism of AD pathology, though the exact pathophysiological mechanism is not yet elucidated. The poor understanding of AD and multitude of adverse responses reported from the current synthetic drugs are the leading cause of failure in the drug development to treat or halt the progression of AD and mandate the search for safer and more efficient alternatives. A number of natural compounds have shown the ability to prevent the formation of the toxic oligomers and disrupt the aggregates, thus attracted much attention. Referable to the abundancy and multitude of pharmacological activities of the plant active constituents, biophenols that distinguish them from the other phytochemicals as a natural weapon against the neurodegenerative disorders. This review provides a critical assessment of the current literature on in vitro and in vivo mechanistic activities of biophenols associated with the prevention and treatment of AD. We have contended the need for more comprehensive approaches to evaluate the anti-AD activity of biophenols at various pathologic levels and to assess the current evidences. Consequently, we highlighted the various problems and challenges confronting the AD research, and offer recommendations for future research.

New insights into the ameliorative effects of ferulic acid in pathophysiological conditions

Ferulic acid, a natural phytochemical has gained importance as a potential therapeutic agent by virtue of its easy commercial availability, low cost and minimal side-effects. It is a derivative of curcumin and possesses the necessary pharmacokinetic properties to be retained in the general circulation for several hours. The therapeutic effects of ferulic acid are mediated through its antioxidant and anti-inflammatory properties. It exhibits different biological activities such as anti-inflammatory, anti-apoptotic, anti-carcinogenic, anti-diabetic, hepatoprotective, cardioprotective, neuroprotective actions, etc. The current review addresses its therapeutic effects under different pathophysiological conditions (eg. cancer, cardiomyopathy, skin disorders, brain disorders, viral infections, diabetes etc.).

Putative Role of Red Wine Polyphenols against Brain Pathology in Alzheimer's and Parkinson's Disease

Alzheimer's disease (AD) and Parkinson's disease (PD) are the most common age-related neurodegenerative disorders and hence pose remarkable socio-economical burdens to both families and state. Although AD and PD have different clinical and neuropathological features, they share common molecular mechanisms that appear to be triggered by multi-factorial events, such as protein aggregation, mitochondrial dysfunction, oxidative stress (OS), and neuroinflammation, ultimately leading to neuronal cell death. Currently, there are no established and validated disease-modifying strategies for either AD or PD. Among the various lifestyle factors that may prevent or slow age-related neurodegenerative diseases, epidemiological studies on moderate consumption of red wine, especially as part of a holistic Mediterranean diet, have attracted increasing interest. Red wine is particularly rich in specific polyphenolic compounds that appear to affect the biological processes of AD and PD, such as quercetin, myricetin, catechins, tannins, anthocyanidins, resveratrol, and ferulic acid. Indeed, there is now a consistent body of in vitro and in vivo data on the neuroprotective effects of red wine polyphenols (RWP) showing that they do not merely possess antioxidant properties, but may additionally act upon, in a multi-target manner, the underlying key mechanisms featuring in both AD and PD. Furthermore, it is important that bioavailability issues are addressed in order for neuroprotection to be relevant in a clinical study scenario. This review summarizes the current knowledge about the major classes of RWP and places into perspective their potential to be considered as nutraceuticals to target neuropathology in AD and PD.

Interaction of Aβ(25-35) fibrillation products with mitochondria: Effect of small-molecule natural products

The 25-35 fragment of the amyloid β (Aβ) peptide is a naturally occurring proteolytic by-product that retains the pathophysiology of its larger parent molecule, whose deposition has been shown to involve mitochondrial dysfunction. Hence, disruption of Aβ(25-35) aggregates could afford an effective remedial strategy for Alzheimer's disease (AD). In the present study, the effect of a number of selected small-molecule natural products (polyphenols: resveratrol, quercetin, biochanin A, and indoles: indole-3-acetic acid, indole-3-carbinol (I3C)) on Aβ(25-35) fibrillogenesis was explored under physiological conditions, and interaction of the resulting structures with rat brain mitochondria was investigated. Several techniques, including fluorescence, circular dichroism, and transmission electron microscopy were utilized to characterize the aggregation products, and possible mitochondrial membrane permeabilization was determined following release of marker enzymes. Results demonstrate the capacity of Aβ(25-35) fibrils to damage mitochondria and suggest how small molecules may afford protection. While I3C appeared more effective in inhibiting the fibrillation process, all natural products behaved similarly in destabilizing preformed aggregates. It is concluded that elucidation of such protection may provide important insights into the development of preventive and therapeutic agents for AD.

Using C. elegans to discover therapeutic compounds for ageing-associated neurodegenerative diseases

Age-associated neurodegenerative disorders such as Alzheimer's disease are a major public health challenge, due to the demographic increase in the proportion of older individuals in society. However, the relatively few currently approved drugs for these conditions provide only symptomatic relief. A major goal of neurodegeneration research is therefore to identify potential new therapeutic compounds that can slow or even reverse disease progression, either by impacting directly on the neurodegenerative process or by activating endogenous physiological neuroprotective mechanisms that decline with ageing. This requires model systems that can recapitulate key features of human neurodegenerative diseases that are also amenable to compound screening approaches. Mammalian models are very powerful, but are prohibitively expensive for high-throughput drug screens. Given the highly conserved neurological pathways between mammals and invertebrates, Caenorhabditis elegans has emerged as a powerful tool for neuroprotective compound screening. Here we describe how C. elegans has been used to model various human ageing-associated neurodegenerative diseases and provide an extensive list of compounds that have therapeutic activity in these worm models and so may have translational potential.

Ferulic Acid: A Hope for Alzheimer's Disease Therapy from Plants

Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by the deposition of extracellular amyloid-beta peptide (Aβ) and intracellular neurofibrillar tangles, associated with loss of neurons in the brain and consequent learning and memory deficits. Aβ is the major component of the senile plaques and is believed to play a central role in the development and progress of AD both in oligomer and fibril forms. Inhibition of the formation of Aβ fibrils as well as the destabilization of preformed Aβ in the Central Nervous System (CNS) would be an attractive therapeutic target for the treatment of AD. Moreover, a large number of studies indicate that oxidative stress and mitochondrial dysfunction may play an important role in AD and their suppression or reduction via antioxidant use could be a promising preventive or therapeutic intervention for AD patients. Many antioxidant compounds have been demonstrated to protect the brain from Aβ neurotoxicity. Ferulic acid (FA) is an antioxidant naturally present in plant cell walls with anti-inflammatory activities and it is able to act as a free radical scavenger. Here we present the role of FA as inhibitor or disaggregating agent of amyloid structures as well as its effects on biological models.

The role of dietary coconut for the prevention and treatment of Alzheimer's disease: potential mechanisms of action

Coconut, Cocos nucifera L., is a tree that is cultivated to provide a large number of products, although it is mainly grown for its nutritional and medicinal values. Coconut oil, derived from the coconut fruit, has been recognised historically as containing high levels of saturated fat; however, closer scrutiny suggests that coconut should be regarded more favourably. Unlike most other dietary fats that are high in long-chain fatty acids, coconut oil comprises medium-chain fatty acids (MCFA). MCFA are unique in that they are easily absorbed and metabolised by the liver, and can be converted to ketones. Ketone bodies are an important alternative energy source in the brain, and may be beneficial to people developing or already with memory impairment, as in Alzheimer's disease (AD). Coconut is classified as a highly nutritious 'functional food'. It is rich in dietary fibre, vitamins and minerals; however, notably, evidence is mounting to support the concept that coconut may be beneficial in the treatment of obesity, dyslipidaemia, elevated LDL, insulin resistance and hypertension - these are the risk factors for CVD and type 2 diabetes, and also for AD. In addition, phenolic compounds and hormones (cytokinins) found in coconut may assist in preventing the aggregation of amyloid-β peptide, potentially inhibiting a key step in the pathogenesis of AD. The purpose of the present review was to explore the literature related to coconut, outlining the known mechanistic physiology, and to discuss the potential role of coconut supplementation as a therapeutic option in the prevention and management of AD.

Beneficial properties of natural phenols: highlight on protection against pathological conditions associated with amyloid aggregation

Mediterranean and Asian diets are currently considered as the most healthy traditional feeding habits effective against risk of age-associated, particularly cardiovascular and neurodegenerative, diseases. A common feature of these two regimens is the abundance of foods and beverages of plant origin (green tea, extra virgin olive oil, red wine, spices, berries, and aromatic herbs) that are considered responsible for the observed beneficial effects. Epidemiological data suggest that the phenolic component remarkably enriched in these foods plays an important role in reducing the incidence of amyloid diseases, pathological conditions associated to tissue deposition of toxic protein aggregates responsible for progressive functional deterioration. Great effort is being spent to provide knowledge on the effects of several natural phenols in this context, moving from the test tube to animal models and, more slowly, to the patient's bed. An emerging feature that makes these molecules increasingly attractive for amyloid disease prevention and therapy is their wide spectrum of activity: recent pieces of evidence suggest that they can inhibit the production of amyloidogenic peptides from precursors, increase antioxidant enzyme activity, activate autophagy and reduce inflammation. Our concept should than shift from considering natural phenols simply as antioxidants or, at the best, as amyloid aggregation inhibitors, to describing them as potentially multitargeting drugs. A main concern is the low bioavailability of such compounds and efforts aimed at improving it are underway, with encapsulation strategies being the most promising ones.

Protein folding and aggregation into amyloid: the interference by natural phenolic compounds

Amyloid aggregation is a hallmark of several degenerative diseases affecting the brain or peripheral tissues, whose intermediates (oligomers, protofibrils) and final mature fibrils display different toxicity. Consequently, compounds counteracting amyloid aggregation have been investigated for their ability (i) to stabilize toxic amyloid precursors; (ii) to prevent the growth of toxic oligomers or speed that of fibrils; (iii) to inhibit fibril growth and deposition; (iv) to disassemble preformed fibrils; and (v) to favor amyloid clearance. Natural phenols, a wide panel of plant molecules, are one of the most actively investigated categories of potential amyloid inhibitors. They are considered responsible for the beneficial effects of several traditional diets being present in green tea, extra virgin olive oil, red wine, spices, berries and aromatic herbs. Accordingly, it has been proposed that some natural phenols could be exploited to prevent and to treat amyloid diseases, and recent studies have provided significant information on their ability to inhibit peptide/protein aggregation in various ways and to stimulate cell defenses, leading to identify shared or specific mechanisms. In the first part of this review, we will overview the significance and mechanisms of amyloid aggregation and aggregate toxicity; then, we will summarize the recent achievements on protection against amyloid diseases by many natural phenols.

Polyphenols: multipotent therapeutic agents in neurodegenerative diseases

Aging leads to numerous transitions in brain physiology including synaptic dysfunction and disturbances in cognition and memory. With a few clinically relevant drugs, a substantial portion of aging population at risk for age-related neurodegenerative disorders require nutritional intervention. Dietary intake of polyphenols is known to attenuate oxidative stress and reduce the risk for related neurodegenerative diseases such as Alzheimer's disease (AD), stroke, multiple sclerosis (MS), Parkinson's disease (PD), and Huntington's disease (HD). Polyphenols exhibit strong potential to address the etiology of neurological disorders as they attenuate their complex physiology by modulating several therapeutic targets at once. Firstly, we review the advances in the therapeutic role of polyphenols in cell and animal models of AD, PD, MS, and HD and activation of drug targets for controlling pathological manifestations. Secondly, we present principle pathways in which polyphenol intake translates into therapeutic outcomes. In particular, signaling pathways like PPAR, Nrf2, STAT, HIF, and MAPK along with modulation of immune response by polyphenols are discussed. Although current polyphenol researches have limited impact on clinical practice, they have strong evidence and testable hypothesis to contribute clinical advances and drug discovery towards age-related neurological disorders.

Dye-binding assays for evaluation of the effects of small molecule inhibitors on amyloid (aβ) self-assembly

Dye-binding assays, such as those utilizing Congo red and thioflavin T, are among the most widely used tools to probe the aggregation of amyloidogenic biomolecules and for the evaluation of small molecule inhibitors of amyloid aggregation and fibrillization. A number of recent reports have indicated that these dye-binding assays could be prone to false positive effects when assessing inhibitors' potential toward Aβ peptides, species involved in Alzheimer's disease. Specifically, this review focuses on the application of thioflavin T for determining the efficiency of small molecule inhibitors of Aβ aggregation and addresses potential reasons that might be associated with the false positive effects in an effort to increase reliability of dye-binding assays.

Curcumin prevents formation of polyglutamine aggregates by inhibiting Vps36, a component of the ESCRT-II complex

Small molecules with antioxidative properties have been implicated in amyloid disorders. Curcumin is the active ingredient present in turmeric and known for several biological and medicinal effects. Adequate evidence substantiates the importance of curcumin in Alzheimer's disease and recent evidence suggests its role in Prion and Parkinson's disease. However, contradictory effects have been suggested for Huntington's disease. This difference provided a compelling reason to investigate the effect of curcumin on glutamine-rich (Q-rich) and non-glutamine-rich (non Q-rich) amyloid aggregates in the well established yeast model system. Curcumin significantly inhibited the formation of htt72Q-GFP (a Q-rich) and Het-s-GFP (a non Q-rich) aggregates in yeast. We show that curcumin prevents htt72Q-GFP aggregation by down regulating Vps36, a component of the ESCRT-II (Endosomal sorting complex required for transport). Moreover, curcumin disrupted the htt72Q-GFP aggregates that were pre-formed in yeast and cured the yeast prion, [PSI(+)].

Using bacterial inclusion bodies to screen for amyloid aggregation inhibitors

Background

The amyloid-β peptide (Aβ42) is the main component of the inter-neuronal amyloid plaques characteristic of Alzheimer's disease (AD). The mechanism by which Aβ42 and other amyloid peptides assemble into insoluble neurotoxic deposits is still not completely understood and multiple factors have been reported to trigger their formation. In particular, the presence of endogenous metal ions has been linked to the pathogenesis of AD and other neurodegenerative disorders.

Results

Here we describe a rapid and high-throughput screening method to identify molecules able to modulate amyloid aggregation. The approach exploits the inclusion bodies (IBs) formed by Aβ42 when expressed in bacteria. We have shown previously that these aggregates retain amyloid structural and functional properties. In the present work, we demonstrate that their in vitro refolding is selectively sensitive to the presence of aggregation-promoting metal ions, allowing the detection of inhibitors of metal-promoted amyloid aggregation with potential therapeutic interest.

Conclusions

Because IBs can be produced at high levels and easily purified, the method overcomes one of the main limitations in screens to detect amyloid modulators: the use of expensive and usually highly insoluble synthetic peptides.