Impact of sphingosine and acetylsphingosines on the aggregation and toxicity of metal-free and metal-treated amyloid-β

Zn(ii)-driven impact of monomeric transthyretin on amyloid-β amyloidogenesis

Extracellular accumulation of amyloid-β (Aβ) peptides in the brain plays a significant role in the development of Alzheimer's disease (AD). While the co-localization and interaction of proteins and metal ions with Aβ in extracellular milieu are established, their precise pathological associations remain unclear. Here we report the impact of Zn(ii) on the anti-amyloidogenic properties of monomeric transthyretin (M-TTR), which coexists spatially with Aβ and Zn(ii) in extracellular fluids. Our findings demonstrate the Zn(ii)-promoted ternary complex formation involving M-TTR, Aβ, and Zn(ii) as well as M-TTR's proteolytic activity towards Aβ. These interactions decrease the inhibitory effect of M-TTR on the primary nucleation process of Aβ as well as its ability to improve cell viability upon treatment of Aβ. This study unveils the variable activities of M-TTR towards Aβ, driven by Zn(ii), providing insights into how metal ions influence the entanglement of M-TTR in the Aβ-related pathology linked to AD.

Differential interaction modes of As(III)/As(V) with microbial cell membrane induces opposite effects on organic contaminant biodegradation in groundwater

Arsenic, a widespread toxic metalloid in groundwater, derives both from natural geological environment and industrial discharge, is extensively detected to be coexisting with organic contaminants, such as 2,4,6-trichlorophenol (TCP), a prior concerned pollutant. During biological remediation of groundwater, arsenic potentially intervenes microbial behaviors. This study found an opposite interference of arsenic in its two different valences (III and V) on the degradation of TCP by the functional bacteria, Sphingomonas fennica K101. As(III) inhibited TCP degradation in a concentration-dependent manner (from 0.1-10 mg/L), with a maximum inhibition rate of 35.5%, whereas As(V) exhibited promoting effects by 13.8% and 33.2% at 1 mg/L and 10 mg/L, respectively. Employing field emission transmission electron microscopy, quantum chemical calculations, fourier-transform ion cyclotron resonance mass spectrometry and metabolomic analysis, we unveil distinct interactions between cell membranes and arsenic in two valence states. Exposure to As(III) led to significant accumulation of As(III) in the cytoplasm, followed by interaction with intracellular ferritin (ferritin heavy chain 1), releasing iron ions and generating ROS. Subsequently, it induced ferroptosis and disrupted bacterial basal metabolism, thereby inhibiting TCP biodegradation. Oppositely, As(V) bound to a critical component sphingosine and triggered sphingosine polymerization, increasing membrane permeability, which was evidenced by measuring lactate dehydrogenase release. This process facilitated TCP transmembrane permeation by reducing membrane or extracellular secretion resistance. As(V) concurrently upregulated energy metabolism and accelerated TCP degradation. Our study elucidates the influence of prevalent arsenic on biodegradation efficacy, particularly amidst changing redox conditions associated with varying arsenic valences.

Design, synthesis, and evaluation of 2,2'-bipyridyl derivatives as bifunctional agents against Alzheimer's disease

Alzheimer's disease (AD) is a complex multifactorial neurodegenerative disease. Metal ion dyshomeostasis and Aβ aggregation have been proposed to contribute to AD progression. Metal ions can bind to Aβ and promote Aβ aggregation, and ultimately lead to neuronal death. Bifunctional (metal chelation and Aβ interaction) compounds are showing promise against AD. In this work, eleven new 3,3'-diamino-2,2'-bipyridine derivatives 4a-4k were synthesized, and evaluated as bifunctional agents for AD treatment. In vitro Aβ aggregation inhibition assay confirmed that most of the synthesized compounds exhibited significant self-induced Aβ1-42 aggregation inhibition. Among them, compound 4d displayed the best inhibitory potency of self-induced Aβ1-42 aggregation with IC50 value of 9.4 µM, and it could selectively chelate with Cu2+ and exhibited 66.2% inhibition of Cu2+-induced Aβ1-42 aggregation. Meanwhile, compound 4d showed strong neuroprotective activity against Aβ1-42 and Cu2+-treated Aβ1-42 induced cell damage. Moreover, compound 4d in high dose significantly reversed Aβ-induced memory impairment in mice.

A nanoscale polymolybdate builded by two hexavacant Keggin-type fragments via a novel {Ca6P6O38} cluster with β-sheet conformation modulation ability

A novel sandwich-type phosphomolybdate based on two hexavacant Keggin-type building block [PMo6O28]15– incorporating a novel hexagonal calcium phosphorus oxygen cluster {Ca6P6O38} was successfully synthesized. It can modulate the β-sheet-rich misfolding...

Multifunctional molecules with bipyridyl core ameliorate multifaceted amyloid toxicity

A series of 2,2’-bipyridine derivatives appended with structurally unique biomolecular auxiliaries were synthesized and investigated for their ability to ameliorate multifaceted amyloid toxicity. Our results highlight the roles of metal-chelating...

Drug repurposing: small molecules against Cu(II)-amyloid-β and free radicals

Alzheimer's disease (AD) presents a complex pathology entangling numerous pathological factors, including amyloid-β (Aβ), metal ions, and reactive oxygen species (ROS). Increasing evidence reveals pathological connections among these distinct components in AD. For instance, the association between the amyloid cascade and metal ion hypotheses has introduced a novel pathogenic target: metal-bound Aβ. Investigation of such interconnections requires substantial research and can be expedited by chemical reagents that are able to modify multiple pathogenic factors in AD. Drug repurposing is an efficient approach for rediscovering previously utilized molecules with desirable biological and pharmaceutical properties as chemical reagents. Herein, we report the evaluation of three pre-approved drug molecules, selected based on their chemical structure and properties, as chemical reagents that can be used for elucidating the complicated pathology of AD.

Cell Death via Lipid Peroxidation and Protein Aggregation Diseases

Lipid peroxidation of cellular membranes is a complicated cellular event, and it is both the cause and result of various diseases, such as ischemia-reperfusion injury, neurodegenerative diseases, and atherosclerosis. Lipid peroxidation causes non-apoptotic cell death, which is associated with cell fate determination: survival or cell death. During the radical chain reaction of lipid peroxidation, various oxidized lipid products accumulate in cells, followed by organelle dysfunction and the induction of non-apoptotic cell death. Highly reactive oxidized products from unsaturated fatty acids are detected under pathological conditions. Pathological protein aggregation is the general cause of these diseases. The cellular response to misfolded proteins is well-known as the unfolded protein response (UPR) and it is partially concomitant with the response to lipid peroxidation. Moreover, the association between protein aggregation and non-apoptotic cell death by lipid peroxidation is attracting attention. The link between lipid peroxidation and protein aggregation is a matter of concern in biomedical fields. Here, we focus on lethal protein aggregation in non-apoptotic cell death via lipid peroxidation. We reviewed the roles of protein aggregation in the initiation and execution of non-apoptotic cell death. We also considered the relationship between protein aggregation and oxidized lipid production. We provide an overview of non-apoptotic cell death with a focus on lipid peroxidation for therapeutic targeting during protein aggregation diseases.

Modification of amyloid-beta peptide aggregation via photoactivation of strained Ru(ii) polypyridyl complexes

Alzheimer's disease (AD) is a chronic neurodegenerative disorder characterized by progressive and irreversible damage to the brain. One of the hallmarks of the disease is the presence of both soluble and insoluble aggregates of the amyloid beta (Aβ) peptide in the brain, and these aggregates are considered central to disease progression. Thus, the development of small molecules capable of modulating Aβ peptide aggregation may provide critical insight into the pathophysiology of AD. In this work we investigate how photoactivation of three distorted Ru(ii) polypyridyl complexes (Ru1-3) alters the aggregation profile of the Aβ peptide. Photoactivation of Ru1-3 results in the loss of a 6,6'-dimethyl-2,2'-bipyridyl (6,6'-dmb) ligand, affording cis-exchangeable coordination sites for binding to the Aβ peptide. Both Ru1 and Ru2 contain an extended planar imidazo[4,5-f][1,10]phenanthroline ligand, as compared to a 2,2'-bipyridine ligand for Ru3, and we show that the presence of the phenanthroline ligand promotes covalent binding to Aβ peptide His residues, and in addition, leads to a pronounced effect on peptide aggregation immediately after photoactivation. Interestingly, all three complexes resulted in a similar aggregate size distribution at 24 h, forming insoluble amorphous aggregates as compared to significant fibril formation for peptide alone. Photoactivation of Ru1-3 in the presence of pre-formed Aβ1-42 fibrils results in a change to amorphous aggregate morphology, with Ru1 and Ru2 forming large amorphous aggregates immediately after activation. Our results show that photoactivation of Ru1-3 in the presence of either monomeric or fibrillar Aβ1-42 results in the formation of large amorphous aggregates as a common endpoint, with Ru complexes incorporating the extended phenanthroline ligand accelerating this process and thereby limiting the formation of oligomeric species in the initial stages of the aggregation process that are reported to show considerable toxicity.