Three Structural Features of Functional Food Components and Herbal Medicine with Amyloid β42 Anti-Aggregation Properties

Natural flavonoid hesperetin blocks amyloid β-protein fibrillogenesis, depolymerizes preformed fibrils and alleviates cytotoxicity caused by amyloids

The aggregation of β-amyloid (Aβ) peptides to form amyloid plaques is one of the primary hallmarks for Alzheimer's disease (AD). Dietary flavonoid supplements containing hesperetin have an ability to decline the risk of developing AD, but the molecular mechanism is still unclear. In this work, hesperetin, a flavanone abundant in citrus fruits, has been proven to prevent the formation of Aβ aggregates and depolymerized preformed fibrils in a concentration-dependent fashion. Hesperetin inhibited the conformational conversion from the natural structure to a β-sheet-rich conformation. It was found that hesperetin significantly reduced the cytotoxicity and relieved oxidative stress eventuated by Aβ aggregates in a concentration-dependent manner. Additionally, the beneficial effects of hesperetin were confirmed in Caenorhabditis elegans, including the inhibition of the formation and deposition of Aβ aggregates and extension of their lifespan. Finally, the results of molecular dynamics simulations showed that hesperetin directly interacted with an Aβ42 pentamer mainly through strong non-polar and electrostatic interactions, which destroyed the structural stability of the preformed pentamer. To summarize, hesperetin exhibits great potential as a prospective dietary supplement for preventing and improving AD.

Detection of Dietary Chalcone and Flavonoid Metabolites in Mice Using UPLC-MS/MS and Their Modulatory Effects on Amyloid β Aggregation

Amyloid β-protein (Aβ42) aggregates have been demonstrated to induce cognitive decline and neurodegeneration in Alzheimer's disease (AD). Thus, functional food ingredients that inhibit Aβ42 aggregation are valuable for AD prevention. Although several food ingredients have been studied for their anti-aggregation activity, information on their bioavailability in the brain, incorporated forms, and relevance to AD etiology is limited. Here, we first detected the sulfate- and glucuronic-acid-conjugated forms of green perilla-derived chalcone (1) and taxifolin (2), which inhibit Aβ42 aggregation, in the brain, small intestine, and plasma of mice (1 and 2 were administered orally) using ultra-performance liquid chromatography-tandem mass spectrometry. We observed that the conjugated metabolites (sulfate (4) and glucuronide (5)) of 1 prevented the fibrillization and oligomerization of Aβ42. These findings imply that the conjugated metabolites of 1 can prove beneficial for AD treatment.

Identification of Catechins' Binding Sites in Monomeric Aβ42 through Ensemble Docking and MD Simulations

The assembly of the amyloid-β peptide (Aβ) into toxic oligomers and fibrils is associated with Alzheimer's disease and dementia. Therefore, disrupting amyloid assembly by direct targeting of the Aβ monomeric form with small molecules or antibodies is a promising therapeutic strategy. However, given the dynamic nature of Aβ, standard computational tools cannot be easily applied for high-throughput structure-based virtual screening in drug discovery projects. In the current study, we propose a computational pipeline-in the framework of the ensemble docking strategy-to identify catechins' binding sites in monomeric Aβ₄₂. It is shown that both hydrophobic aromatic interactions and hydrogen bonding are crucial for the binding of catechins to Aβ₄₂. Additionally, it has been found that all the studied ligands, especially EGCG, can act as potent inhibitors against amyloid aggregation by blocking the central hydrophobic region of Aβ. Our findings are evaluated and confirmed with multi-microsecond MD simulations. Finally, it is suggested that our proposed pipeline, with low computational cost in comparison with MD simulations, is a suitable approach for the virtual screening of ligand libraries against Aβ.

Understanding the screening effect of aqueous DES on the IDPs: A molecular dynamics simulation study using amyloid β42 monomer

Deep eutectic solvents (DESs) have emerged as the promising replacement to the ionic liquids in solvent engineering for bio-compatibility. We aim to understand the effect of aqueous deep eutectic solvents on the conformation of intrinsically disordered proteins (IDPs). In this context, we have studied the effect on amyloid beta (Aβ₄₂) monomer in the hydrated DES composed of tetrabutylammonium chloride and ethylene glycol in a 3:1 ratio using all-atom molecular dynamics simulations. DES is found to effectively screen the interaction of four zones of the amyloid beta monomer with water. Water molecules and the DES constituents modulate the local protein-solvent interactions, in the solvation shell of the protein. In addition, the aqueous DES medium conserves the secondary structure of the Aβ₄₂ monomer by increasing the intramolecular hydrogen bonding and D23-K28 salt-bridge interactions when compared to the pure water medium. The current study provides insights into the impact of DES in stabilizing an IDP, at molecular level. We envisage the hindered aggregation of the amyloid beta structures in DES medium over the pure water medium due to the screening of hydrophobic intramolecular interactions.

An update on the novel and approved drugs for Alzheimer disease

Introduction

Given the severity of the condition and the increasing number of patients, developing effective therapies for Alzheimer's disease has become a significant necessity. Aggregation of Amyloid-Beta (Aβ) plaques and Tau Protein Tangles in the brain's nerve tissue are two of the most histopathological/pathophysiological symptoms. Another important element involved in the etiology of Alzheimer's disease is the reduction in acetylcholine (ACh) levels in the brain. Currently available medications for Alzheimer's disease treatment, such as cholinesterase inhibitors and an antagonist of the N-methyl-d-aspartate receptor, can temporarily reduce dementia symptoms but not stop or reverse disease development. In addition, several medicinal plants have been shown to diminish the degenerative characteristics associated with Alzheimer's disease, either in its crude form or as isolated chemicals.

Aim

This review summarises the results from previous studies that reflect an array of novel therapies underway in various phases of clinical trials. Many are discontinued due to non-adherence to the designed endpoints or the surfacing of unavoidable side effects. The present piece of article focuses on the approved drugs for the treatment of Alzheimer's disease and their related mode of action as well as the promising therapies for the treatment of the said disease. Special attention has been placed on the researched herbal drugs, with the pipeline of novel therapies underway in various phases of clinical trials.

Result

The current article includes a list of approved pharmaceuticals for treating Alzheimer's disease, prospective therapies for the illness's treatment, and a pipeline of novel therapies in various stages of clinical trials.

Conclusion

The results suggest that the drugs under clinical trials may open new pathways for the effective treatment of patients with Alzheimer's disease while improving their quality of life.

Lysine-targeting inhibition of amyloid β oligomerization by a green perilla-derived metastable chalcone in vitro and in vivo

Oligomers of amyloid β (Aβ) represent an early aggregative form that causes neurotoxicity in the pathogenesis of Alzheimer's disease (AD). Thus, preventing Aβ aggregation is important for preventing AD. Despite intensive studies on dietary compounds with anti-aggregation properties, some identified compounds are susceptible to autoxidation and/or hydration upon incubation in water, leaving unanswered issues regarding which active structures in metastable compounds are actually responsible for the inhibition of Aβ aggregation. In this study, we observed the site-specific inhibition of 42-mer Aβ (Aβ42) oligomerization by the green perilla-derived chalcone 2',3'-dihydroxy-4',6'-dimethoxychalcone (DDC), which was converted to its decomposed flavonoids (dDDC, 1-3) via nucleophilic aromatic substitution with water molecules. DDC suppressed Aβ42 fibrillization and slowed the transformation of the β-sheet structure, which is rich in Aβ42 aggregates. To validate the contribution of dDDC to the inhibitory effects of DDC on Aβ42 aggregation, we synthesized 1-3 and identified 3, a catechol-type flavonoid, as one of the active forms of DDC. ¹H-¹⁵N SOFAST-HMQC NMR revealed that 1-3 as well as DDC could interact with residues between His13 and Leu17, which were near the intermolecular β-sheet (Gln15-Ala21). The nucleation in Aβ42 aggregates involves the rate-limiting formation of low-molecular-weight oligomers. The formation of a Schiff base with dDDC at Lys16 and Lys28 in the dimer through autoxidation of dDDC was associated with the suppression of Aβ42 nucleation. Of note, in two AD mouse models using immunoaffinity purification-mass spectrometry, adduct formation between dDDC and brain Aβ was observed in a similar manner as reported in vitro. The present findings unraveled the lysine-targeting inhibitory mechanism of metastable dietary ingredients regarding Aβ oligomerization.

Protective Effects of Flavonoids against Alzheimer's Disease: Pathological Hypothesis, Potential Targets, and Structure-Activity Relationship

Alzheimer’s disease (AD) is a neurodegenerative disease with high morbidity and mortality, for which there is no available cure. Currently, it is generally believed that AD is a disease caused by multiple factors, such as amyloid-beta accumulation, tau protein hyperphosphorylation, oxidative stress, and inflammation. Multitarget prevention and treatment strategies for AD are recommended. Interestingly, naturally occurring dietary flavonoids, a class of polyphenols, have been reported to have multiple biological activities and anti-AD effects in several AD models owing to their antioxidative, anti-inflammatory, and anti-amyloidogenic properties. In this review, we summarize and discuss the existing multiple pathogenic factors of AD. Moreover, we further elaborate on the biological activities of natural flavonoids and their potential mode of action and targets in managing AD by presenting a wide range of experimental evidence. The gathered data indicate that flavonoids can be regarded as prophylactics to slow the advancement of AD or avert its onset. Different flavonoids have different activities and varying levels of activity. Further, this review summarizes the structure–activity relationship of flavonoids based on the existing literature and can provide guidance on the design and selection of flavonoids as anti-AD drugs.

Activity-differential search for amyloid-β aggregation inhibitors using LC-MS combined with principal component analysis

Aggregation of amyloid β42 (Aβ42) is one of the hallmarks of Alzheimer's disease (AD). Inhibition of Aβ42 aggregation is thus a promising approach for AD therapy. Kampo medicine has been widely used to combat dementias such as AD. Crude drug known as Shoyaku is an ingredient of Kampo that could have potential as a natural source of novel drugs. However, given that a mixture of compounds, rather than singular compounds, could contribute to the biological functions of crude drug, there are very limited studies on the structure and mechanism of each constituent in crude drug which may have anti-Aβ42 aggregation properties. Herein we provide an efficient method, using LC-MS combined with principal component analysis (PCA), to search for activity-dependent compounds that inhibit Aβ42 aggregation from 46 crude drug extracts originating from 18 plants. Only 5 extracts (Kakou, Kayou, Gusetsu, Rensu, and Renbou) from lotus demonstrated differentially inhibitory activities depending on the part of the plant from which they are derived (e.g. petiole, leaf, root node, stamen, and receptacle, respectively). To compare the anti-aggregative properties of compounds of active crude drug with those of inactive crude drug, these extracts were subjected to LC-MS measurement, followed by PCA. From 12 candidate compounds identified from the analysis, glucuronized and glucosidized quercetin, as well as 6 flavonoids (datiscetin, kaempferol, morin, robinetin, quercetin, and myricitrin), including catechol or flatness moiety suppressed Aβ42 aggregation, whereas curcumol, a sesquiterpene, did not. In conclusion, this study offers a new activity-differential methodology to identify bioactive natural products in crude drugs that inhibit Aβ42 aggregation and that could be applied to future AD therapies.

Searching for Natural Products That Delay Nucleation Phase and Promote Elongation Phase of Amyloid β42 toward Alzheimer's Disease Therapeutics

Aggregation of amyloid β42 (Aβ42) is one of the hallmarks of Alzheimer's disease (AD). The mechanism of Aβ42 aggregation mainly consists of two phases, nucleation and elongation (including plateau region as a saturation phase). During the nucleation phase, the monomer gradually forms toxic oligomers. During the elongation phase, each nucleus acts as a template and associates with monomers to initiate less toxic fibrillization. We previously proposed a method of classifying compounds into nine groups based on their ability to modulate the nucleation and/or elongation phases. An orcein derivative (O4), which is a phenoxazine dye isolated from the lichen Roccella tinctoria and containing a 2,5-cyclohexadienone moiety, was reported to convert oligomers into relatively inert fibrils, resulting in the reduction of the neurotoxicity of Aβ42. Focusing on O4 in the pursuit of anti-AD drugs, we herein screened 480 natural products including NPDepo (RIKEN) for the compounds that delayed the nucleation phase and promoted the elongation phase. The signal intensities for Aβ42 treated with each of the 15 compounds that met these criteria were lowered in dot blotting using antioligomer antibody, and the fibril formation of Aβ42 in the presence of these compounds was observed in transmission electron microscopy. Among the 15 compounds, 12 compounds (80%) reduced the toxicity of Aβ42 against mouse neuroblastoma Neuro-2a cells. Some of these anticytotoxic compounds contain 2-pyrone and 4-pyrone that interacted with Aβ42, maybe by shifting the equilibrium of Aβ from toxic oligomer into inert fibrils.

Azobioisosteres of Curcumin with Pronounced Activity against Amyloid Aggregation, Intracellular Oxidative Stress, and Neuroinflammation

Many (poly-)phenolic natural products, for example, curcumin and taxifolin, have been studied for their activity against specific hallmarks of neurodegeneration, such as amyloid-β 42 (Aβ42) aggregation and neuroinflammation. Due to their drawbacks, arising from poor pharmacokinetics, rapid metabolism, and even instability in aqueous medium, the biological activity of azobenzene compounds carrying a pharmacophoric catechol group, which have been designed as bioisoteres of curcumin has been examined. Molecular simulations reveal the ability of these compounds to form a hydrophobic cluster with Aβ42, which adopts different folds, affecting the propensity to populate fibril-like conformations. Furthermore, the curcumin bioisosteres exceeded the parent compound in activity against Aβ42 aggregation inhibition, glutamate-induced intracellular oxidative stress in HT22 cells, and neuroinflammation in microglial BV-2 cells. The most active compound prevented apoptosis of HT22 cells at a concentration of 2.5 μm (83 % cell survival), whereas curcumin only showed very low protection at 10 μm (21 % cell survival).

Natural Compounds as Inhibitors of Aβ Peptide Aggregation: Chemical Requirements and Molecular Mechanisms

Alzheimer’s disease (AD) is one of the most common neurodegenerative disorders, with no cure and preventive therapy. Misfolding and extracellular aggregation of Amyloid-β (Aβ) peptides are recognized as the main cause of AD progression, leading to the formation of toxic Aβ oligomers and to the deposition of β-amyloid plaques in the brain, representing the hallmarks of AD. Given the urgent need to provide alternative therapies, natural products serve as vital resources for novel drugs. In recent years, several natural compounds with different chemical structures, such as polyphenols, alkaloids, terpenes, flavonoids, tannins, saponins and vitamins from plants have received attention for their role against the neurodegenerative pathological processes. However, only for a small subset of them experimental evidences are provided on their mechanism of action. This review focuses on those natural compounds shown to interfere with Aβ aggregation by direct interaction with Aβ peptide and whose inhibitory mechanism has been investigated by means of biophysical and structural biology experimental approaches. In few cases, the combination of approaches offering a macroscopic characterization of the oligomers, such as TEM, AFM, fluorescence, together with high-resolution methods could shed light on the complex mechanism of inhibition. In particular, solution NMR spectroscopy, through peptide-based and ligand-based observation, was successfully employed to investigate the interactions of the natural compounds with both soluble NMR-visible (monomer and low molecular weight oligomers) and NMR-invisible (high molecular weight oligomers and protofibrils) species. The molecular determinants of the interaction of promising natural compounds are here compared to infer the chemical requirements of the inhibitors and the common mechanisms of inhibition. Most of the data converge to indicate that the Aβ regions relevant to perturb the aggregation cascade and regulate the toxicity of the stabilized oligomers, are the N-term and β1 region. The ability of the natural aggregation inhibitors to cross the brain blood barrier, together with the tactics to improve their low bioavailability are discussed. The analysis of the data ensemble can provide a rationale for the selection of natural compounds as molecular scaffolds for the design of new therapeutic strategies against the progression of early and late stages of AD.

Design, Synthesis, and Biological Activity of Conformationally Restricted Analogues of Silibinin

Silibinin (Sib), one of the main components of milk thistle extract, has attracted considerable attention because of its various biological activities, which include antioxidant activity and potential effects in diabetes and Alzheimer's disease (AD). In a previous study, we synthesized catechin analogues by constraining the geometries of (+)-catechin and (-)-epicatechin. The constrained analogues exhibited enhanced bioactivities, with the only major difference between the two being their three-dimensional structures. The constrained geometry in (+)-catechin resulted in a high degree of planarity (PCat), while (-)-epicatechin failed to maintain planarity (PEC). The three-dimensional structure of Sib may be related to its ability to inhibit aggregation of amyloid beta (Aβ). We therefore introduced PCat and PEC into Sib to demonstrate how the constrained molecular geometry and differences in three-dimensional structures may enhance such activities. Introduction of PCat into Sib (SibC) resulted in effective inhibition of Aβ aggregation, α-glucosidase activity, and cell growth, suggesting that not only reduced flexibility but also the high degree of planarity may enhance the biological activity. SibC is expected to be a promising lead compound for the treatment of several diseases.

Advances in Non-Pharmacological Interventions for Subjective Cognitive Decline: A Systematic Review and Meta-Analysis

Background: Subjective cognitive decline (SCD) is considered the earliest symptomatic manifestation of preclinical Alzheimer’s disease (AD). Currently, given the lack of effective and curable pharmacological treatments for AD, non-pharmacological interventions (NPIs) for individuals with SCD may provide a valuable opportunity for the secondary prevention of AD. Objective: This systematic review and meta-analysis, conducted in accordance with the PRISMA guidelines, aimed to investigate the benefits of current NPIs in the population with SCD. Methods: The online electronic databases, including MEDLINE, Cochrane Central Register of Controlled Trials, EMBASE, PsycInfo, and CINAHL, were searched to identify randomized controlled trials of NPIs for SCD. Intervention strategies were psychological and health-related education interventions, mind-body therapy, lifestyle modification, cognitive training, and multidomain interventions. Outcomes included subjective memory, objective memory, global cognitive function, psychological well-being, and mood. Study quality was determined using the criteria of the Cochrane collaboration’s tool. The Hedges’ g of change was analyzed. Results: Eighteen studies were included in this review and meta-analysis. Overall, psychological and health-related education interventions exhibited a medium effect on objective memory function (Hedges’ g = 0.53, p = 0.01). Cognitive training led to a small effect on objective memory, which was marginal statistically (Hedges’ g = 0.19, p = 0.05). In addition, cognitive training also significantly improved subjective memory performance (Hedges’ g = 0.49, p = 0.0003) and psychological well-being (Hedges’ g = 0.27, p = 0.03). Conclusion: Overall, the psychological intervention and cognitive training may be beneficial to cognitive function and psychological well-being. NPIs may be effectively implemented in older adults with SCD.

Polyphenols with Anti-Amyloid β Aggregation Show Potential Risk of Toxicity Via Pro-Oxidant Properties

Alzheimer's disease (AD) is the most common form of dementia among older people. Amyloid β (Aβ) aggregation has been the focus for a therapeutic target for the treatment of AD. Naturally occurring polyphenols have an inhibitory effect on Aβ aggregation and have attracted a lot of attention for the development of treatment strategies which could mitigate the symptoms of AD. However, considerable evidence has shown that the pro-oxidant mechanisms of polyphenols could have a deleterious effect. Our group has established an assay system to evaluate the pro-oxidant characteristics of chemical compounds, based on their reactivity with DNA. In this review, we have summarized the anti-Aβ aggregation and pro-oxidant properties of polyphenols. These findings could contribute to understanding the mechanism underlying the potential risk of polyphenols. We would like to emphasize the importance of assessing the pro-oxidant properties of polyphenols from a safety point of view.

Potential Therapeutic Approaches for Cerebral Amyloid Angiopathy and Alzheimer's Disease

Cerebral amyloid angiopathy (CAA) is a cerebrovascular disease directly implicated in Alzheimer’s disease (AD) pathogenesis through amyloid-β (Aβ) deposition, which may cause the development and progression of dementia. Despite extensive studies to explore drugs targeting Aβ, clinical benefits have not been reported in large clinical trials in AD patients or presymptomatic individuals at a risk for AD. However, recent studies on CAA and AD have provided novel insights regarding CAA- and AD-related pathogenesis. This work has revealed potential therapeutic targets, including Aβ drainage pathways, Aβ aggregation, oxidative stress, and neuroinflammation. The functional significance and therapeutic potential of bioactive molecules such as cilostazol and taxifolin have also become increasingly evident. Furthermore, recent epidemiological studies have demonstrated that serum levels of a soluble form of triggering receptor expressed on myeloid cells 2 (TREM2) may have clinical significance as a potential novel predictive biomarker for dementia incidence. This review summarizes recent advances in CAA and AD research with a focus on discussing future research directions regarding novel therapeutic approaches and predictive biomarkers for CAA and AD.

Molecular Insight into the Therapeutic Promise of Flavonoids against Alzheimer's Disease

Alzheimer's disease (AD) is one of the utmost chronic neurodegenerative disorders, which is characterized from a neuropathological point of view by the aggregates of amyloid beta (Aβ) peptides that are deposited as senile plaques and tau proteins which form neurofibrillary tangles (NFTs). Even though advancement has been observed in order to understand AD pathogenesis, currently available therapeutic methods can only deliver modest symptomatic relief. Interestingly, naturally occurring dietary flavonoids have gained substantial attention due to their antioxidative, anti-inflammatory, and anti-amyloidogenic properties as alternative candidates for AD therapy. Experimental proof provides support to the idea that some flavonoids might protect AD by interfering with the production and aggregation of Aβ peptides and/or decreasing the aggregation of tau. Flavonoids have the ability to promote clearance of Aβ peptides and inhibit tau phosphorylation by the mTOR/autophagy signaling pathway. Moreover, due to their cholinesterase inhibitory potential, flavonoids can represent promising symptomatic anti-Alzheimer agents. Several processes have been suggested for the aptitude of flavonoids to slow down the advancement or to avert the onset of Alzheimer's pathogenesis. To enhance cognitive performance and to prevent the onset and progress of AD, the interaction of flavonoids with various signaling pathways is proposed to exert their therapeutic potential. Therefore, this review elaborates on the probable therapeutic approaches of flavonoids aimed at averting or slowing the progression of the AD pathogenesis.

Clinical trials of new drugs for Alzheimer disease

Alzheimer disease (AD) accounts for 60-70% of dementia cases. Given the seriousness of the disease and continual increase in patient numbers, developing effective therapies to treat AD has become urgent. Presently, the drugs available for AD treatment, including cholinesterase inhibitors and an antagonist of the N-methyl-D-aspartate receptor, can only inhibit dementia symptoms for a limited period of time but cannot stop or reverse disease progression. On the basis of the amyloid hypothesis, many global drug companies have conducted many clinical trials on amyloid clearing therapy but without success. Thus, the amyloid hypothesis may not be completely feasible. The number of anti-amyloid trials decreased in 2019, which might be a turning point. An in-depth and comprehensive understanding of the contribution of amyloid beta and other factors of AD is crucial for developing novel pharmacotherapies.In ongoing clinical trials, researchers have developed and are testing several possible interventions aimed at various targets, including anti-amyloid and anti-tau interventions, neurotransmitter modification, anti-neuroinflammation and neuroprotection interventions, and cognitive enhancement, and interventions to relieve behavioral psychological symptoms. In this article, we present the current state of clinical trials for AD at clinicaltrials.gov. We reviewed the underlying mechanisms of these trials, tried to understand the reason why prior clinical trials failed, and analyzed the future trend of AD clinical trials.

New diagnostic method for Alzheimer’s disease based on the toxic conformation theory of amyloid β

Recent investigations suggest that soluble oligomeric amyloid β (Aβ) species may be involved in early onset of Alzheimer’s disease (AD). Using systematic proline replacement, solid-state NMR, and ESR, we identified a toxic turn at position 22 and 23 of Aβ42, the most potent neurotoxic Aβ species. Through radicalization, the toxic turn can induce formation of the C-terminal hydrophobic core to obtain putative Aβ42 dimers and trimers. Synthesized dimer and trimer models showed that the C-terminal hydrophobic core plays a critical role in the formation of high molecular weight oligomers with neurotoxicity. Accordingly, an anti-toxic turn antibody (24B3) that selectively recognizes a toxic dimer model of E22P-Aβ42 was developed. Sandwich enzyme-linked immunosorbent assay with 24B3 and 82E1 detected a significantly higher ratio of Aβ42 with a toxic turn to total Aβ42 in cerebrospinal fluid of AD patients compared with controls, suggesting that 24B3 could be useful for early onset of AD diagnosis.

Aggregation of biologically important peptides and proteins: inhibition or acceleration depending on protein and metal ion concentrations

The process of aggregation of proteins and peptides is dependent on the concentration of proteins, and the rate of aggregation can be altered by the presence of metal ions, but this dependence is not always a straightforward relationship. In general, aggregation does not occur under normal physiological conditions, yet it can be induced in the presence of certain metal ions. However, the extent of the influence of metal ion interactions on protein aggregation has not yet been fully comprehended. A consensus has thus been difficult to reach because the acceleration/inhibition of the aggregation of proteins in the presence of metal ions depends on several factors such as pH and the concentration of the aggregated proteins involved as well as metal concentration level of metal ions. Metal ions, like Cu2+, Zn2+, Pb2+ etc. may either accelerate or inhibit aggregation simply because the experimental conditions affect the behavior of biomolecules. It is clear that understanding the relationship between metal ion concentration and protein aggregation will prove useful for future scientific applications. This review focuses on the dependence of the aggregation of selected important biomolecules (peptides and proteins) on metal ion concentrations. We review proteins that are prone to aggregation, the result of which can cause serious neurodegenerative disorders. Furthering our understanding of the relationship between metal ion concentration and protein aggregation will prove useful for future scientific applications, such as finding therapies for neurodegenerative diseases.