Human serum albumin inhibits Abeta fibrillization through a "monomer-competitor" mechanism

Serum albumin-embedding copper nanoclusters inhibit Alzheimer's β-amyloid fibrillogenesis and neuroinflammation

Increasing evidence suggests that the accumulations of reactive oxygen species (ROS), β-amyloid (Aβ), and neuroinflammation are crucial pathological hallmarks for the onset of Alzheimer's disease (AD), yet there are few effective treatment strategies. Therefore, design of nanomaterials capable of simultaneously elimination of ROS and inhibition of Aβ aggregation and neuroinflammation is urgently needed for AD treatment. Herein, we designed human serum albumin (HSA)-embedded ultrasmall copper nanoclusters (CuNCs@HSA) via an HSA-mediated fabrication strategy. The as-prepared CuNCs@HSA exhibited outstanding multiple enzyme-like properties, including superoxide dismutase (>5000 U/mg), catalase, and glutathione peroxidase activities as well as hydroxyl radicals scavenging ability. Besides, CuNCs@HSA prominently inhibited Aβ fibrillization, and its inhibitory potency was 2.5-fold higher than native HSA. Moreover, CuNCs@HSA could significantly increase the viability of Aβ-treated cells from 60 % to over 96 % at 40 μg/mL and mitigate Aβ-induced oxidative stresses. The secretion of neuroinflammatory cytokines by lipopolysaccharide-induced BV-2 cells, including tumor necrosis factor-α and interleukin-6, was alleviated by CuNCs@HSA. In vivo studies manifested that CuNCs@HSA effectively suppressed the formation of plaques in transgenic C. elegans, reduced ROS levels, and extended C. elegans lifespan by 5 d. This work, using HSA as a template to mediate the fabrication of copper nanoclusters with robust ROS scavenging capability, exhibited promising potentials in inhibiting Aβ aggregation and neuroinflammation for AD treatment.

Revolutionizing Alzheimer's treatment: Harnessing human serum albumin for targeted drug delivery and therapy advancements

Alzheimer's disease (AD) is a neurodegenerative disorder initiated by amyloid-beta (Aβ) accumulation, leading to impaired cognitive function. Several delivery approaches have been improved for AD management. Among them, human serum albumin (HSA) is broadly employed for drug delivery and targeting the Aβ in AD owing to its biocompatibility, Aβ inhibitory effect, and nanoform, which showed blood-brain barrier (BBB) crossing ability via glycoprotein 60 (gp60) receptor and secreted protein acidic and rich in cysteine (SPARC) protein to transfer the drug molecules in the brain. Thus far, there is no previous review focusing on HSA and its drug delivery system in AD. Hence, the reviewed article aimed to critically compile the HSA therapeutic as well as drug delivery role in AD management. It also delivers information on how HSA-incorporated nanoparticles with surfaced embedded ligands such as TAT, GM1, and so on, not only improve BBB permeability but also increase neuron cell targetability in AD brain. Additionally, Aβ and tau pathology, including various metabolic markers likely BACE1 and BACE2, etc., are discussed. Besides, the molecular interaction of HSA with Aβ and its distinctive forms are critically reviewed that HSA can segregate Zn(II) and Cu(II) metal ions from Aβ owing to high affinity. Furthermore, the BBB drug delivery challenges in AD are addressed. Finally, the clinical formulation of HSA for the management of AD is critically discussed on how the HSA inhibits Aβ oligomer and fibril, while glycated HSA participates in amyloid plaque formation, i.e., β-structure sheet formation. This review report provides theoretical background on HSA-based AD drug delivery and makes suggestions for future prospect-related work.

In Search for Low-Molecular-Weight Ligands of Human Serum Albumin That Affect Its Affinity for Monomeric Amyloid β Peptide

An imbalance between production and excretion of amyloid β peptide (Aβ) in the brain tissues of Alzheimer's disease (AD) patients leads to Aβ accumulation and the formation of noxious Aβ oligomers/plaques. A promising approach to AD prevention is the reduction of free Aβ levels by directed enhancement of Aβ binding to its natural depot, human serum albumin (HSA). We previously demonstrated the ability of specific low-molecular-weight ligands (LMWLs) in HSA to improve its affinity for Aβ. Here we develop this approach through a bioinformatic search for the clinically approved AD-related LMWLs in HSA, followed by classification of the candidates according to the predicted location of their binding sites on the HSA surface, ranking of the candidates, and selective experimental validation of their impact on HSA affinity for Aβ. The top 100 candidate LMWLs were classified into five clusters. The specific representatives of the different clusters exhibit dramatically different behavior, with 3- to 13-fold changes in equilibrium dissociation constants for the HSA-Aβ40 interaction: prednisone favors HSA-Aβ interaction, mefenamic acid shows the opposite effect, and levothyroxine exhibits bidirectional effects. Overall, the LMWLs in HSA chosen here provide a basis for drug repurposing for AD prevention, and for the search of medications promoting AD progression.

Inhibition of toxic metal-alpha synuclein interactions by human serum albumin

Human serum albumin (HSA), the most abundant protein in plasma and cerebrospinal fluid, not only serves as a crucial carrier of various exogenous and endogenous ligands but also modulates the aggregation of amyloidogenic proteins, including alpha synuclein (αSyn), which is associated with Parkinson's disease and other α-synucleinopathies. HSA decreases αSyn toxicity through the direct binding to monomeric and oligomeric αSyn species. However, it is possible that HSA also sequesters metal ions that otherwise promote aggregation. Cu(ii) ions, for example, enhance αSyn fibrillization in vitro, while also leading to neurotoxicity by generating reactive oxygen species (ROS). However, it is currently unclear if and how HSA affects Cu(ii)-binding to αSyn. Using an integrated set of NMR experiments, we show that HSA is able to chelate Cu(ii) ions from αSyn more efficiently than standard chelators such as EDTA, revealing an unexpected cooperativity between the HSA metal-binding sites. Notably, fatty acid binding to HSA perturbs this cooperativity, thus interfering with the sequestration of Cu(ii) ions from αSyn. We also observed that glycation of HSA diminished Cu(ii)-binding affinity, while largely preserving the degree of cooperativity between the HSA metal-binding sites. Additionally, our results show that Cu(ii)-binding to HSA stabilizes the interactions of HSA with αSyn primarily at two different regions, i.e. the N-terminus, Tyr 39 and the majority of the C-terminus. Our study not only unveils the effect of fatty acid binding and age-related posttranslational modifications, such as glycation, on the neuroprotective mechanisms of HSA, but also highlights the potential of αSyn as a viable NMR-based sensor to investigate HSA-metal interactions.

Covalent immobilization of human serum albumin on cellulose acetate membrane for scavenging amyloid beta - A stepping extracorporeal strategy for ameliorating Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by interrupted neurocognitive functions and impaired mental development presumably caused by the accumulation of amyloid beta (Aβ) in the form of plaques. Targeting Aβ has been considered a promising approach for treating AD. In the current study, human serum albumin (HSA), a natural Aβ binder, is covalently immobilized onto the surface of a cellulose acetate (CA) membrane to devise an extracorporeal Aβ sequester. The immobilization of HSA at 3.06 ± 0.22 μg/mm2 of the CA membrane was found to be active functionally, as evidenced by the esterase-like activity converting p-nitrophenyl acetate into p-nitrophenol. The green fluorescent protein-Aβ (GFP-Aβ) fusion protein, recombinantly produced as a model ligand, exhibited characteristics of native Aβ. These features include the propensity to form aggregates or fibrils and an affinity for HSA with a dissociation constant (KD) of 0.91 μM. The HSA on the CA membrane showed concentration-dependent sequestration of GFP-Aβ in the 1-10-μM range. Moreover, it had a greater binding capacity than HSA immobilized on a commercial amine-binding plate. Results suggest that the covalent immobilization of HSA on the CA surface can be used as a potential platform for sequestering Aβ to alleviate AD.

Albumin-manganese dioxide nanocomposites: a potent inhibitor and ROS scavenger against Alzheimer's β-amyloid fibrillogenesis and neuroinflammation

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease pathologically caused by amyloid-β protein (Aβ) aggregation, oxidative stress, and neuroinflammation. The pathogenesis of AD is still uncertain and intricate, and helpful therapy has rarely been recorded. So, discovering amyloid modulators is deemed a promising avenue for preventing and treating AD. In this study, human serum albumin (HSA), a protein-based Aβ inhibitor, was utilized as a template to guide the synthesis of HSA-manganese dioxide nanocomposites (HMn NCs) through biomineralization. The in situ formed MnO2 in HSA endows this nano-platform with outstanding reactive oxygen species (ROS) scavenging capability, including superoxide dismutase-mimetic and catalase-mimetic activities, which could scavenge the plethora of superoxide anion radicals and hydrogen peroxide. More importantly, the HMn NCs show enhanced potency in suppressing Aβ fibrillization compared with HSA, which further alleviates Aβ-mediated SH-SY5Y neurotoxicity by scavenging excessive ROS. Moreover, it is demonstrated that HMn NCs reduce Aβ-related inflammation in BV-2 cells by lowering tumor necrosis factor-α and interleukin-6. Furthermore, transgenic C. elegans studies showed that HMn NCs could remove Aβ plaques, reduce ROS in CL2006 worms, and promote the lifespan extension of worms. Thus, HMn NCs provide a promising tactic to facilitate the application of multifunctional nanocomposites in AD treatment.

Advances in Amyloid-β Clearance in the Brain and Periphery: Implications for Neurodegenerative Diseases

This review examines the role of impaired amyloid-β clearance in the accumulation of amyloid-β in the brain and the periphery, which is closely associated with Alzheimer's disease (AD) and cerebral amyloid angiopathy (CAA). The molecular mechanism underlying amyloid-β accumulation is largely unknown, but recent evidence suggests that impaired amyloid-β clearance plays a critical role in its accumulation. The review provides an overview of recent research and proposes strategies for efficient amyloid-β clearance in both the brain and periphery. The clearance of amyloid-β can occur through enzymatic or non-enzymatic pathways in the brain, including neuronal and glial cells, blood-brain barrier, interstitial fluid bulk flow, perivascular drainage, and cerebrospinal fluid absorption-mediated pathways. In the periphery, various mechanisms, including peripheral organs, immunomodulation/immune cells, enzymes, amyloid-β-binding proteins, and amyloid-β-binding cells, are involved in amyloid-β clearance. Although recent findings have shed light on amyloid-β clearance in both regions, opportunities remain in areas where limited data is available. Therefore, future strategies that enhance amyloid-β clearance in the brain and/or periphery, either through central or peripheral clearance approaches or in combination, are highly encouraged. These strategies will provide new insight into the disease pathogenesis at the molecular level and explore new targets for inhibiting amyloid-β deposition, which is central to the pathogenesis of sporadic AD (amyloid-β in parenchyma) and CAA (amyloid-β in blood vessels).

The Major Components of Cerebrospinal Fluid Dictate the Characteristics of Inhibitors against Amyloid-Beta Aggregation

The main pathological hallmark of Alzheimer's disease (AD) is the aggregation of amyloid-β into amyloid fibrils, leading to a neurodegeneration cascade. The current medications are far from sufficient to prevent the onset of the disease, hence requiring more research to find new alternative drugs for curing AD. In vitro inhibition experiments are one of the primary tools in testing whether a molecule may be potent to impede the aggregation of amyloid-beta peptide (Aβ₄₂). However, kinetic experiments in vitro do not match the mechanism found when aggregating Aβ₄₂ in cerebrospinal fluid. The different aggregation mechanisms and the composition of the reaction mixtures may also impact the characteristics of the inhibitor molecules. For this reason, altering the reaction mixture to resemble components found in cerebrospinal fluid (CSF) is critical to partially compensate for the mismatch between the inhibition experiments in vivo and in vitro. In this study, we used an artificial cerebrospinal fluid that contained the major components found in CSF and performed Aβ₄₂ aggregation inhibition studies using oxidized epigallocatechin-3-gallate (EGCG) and fluorinated benzenesulfonamide VR16-09. This led to a discovery of a complete turnaround of their inhibitory characteristics, rendering EGCG ineffective while significantly improving the efficacy of VR16-09. HSA was the main contributor in the mixture that significantly increased the anti-amyloid characteristics of VR16-09.

Virtual Screening of Human Serum Albumin Mutants to Optimize the Search for its Forms that Increase Affinity to Amyloid-Β Peptide

A promising approach to the treatment of Alzheimer's disease (AD) is the removal of amyloid-β peptide (Aβ) from the patient's central nervous system by acting on human serum albumin (HSA). HSA carries 90% of Aβ in blood serum and 40-90% of Aβ in the cerebrospinal fluid (CNS). In this work, virtual screening of all possible mutant forms of HSA based on the data of the I-Mutant service made it possible to predict changes in HSA stability and identify the most “sensitive” regions of its polypeptide chain to substitutions. The data obtained will be used to optimize the search for HSA forms with increased affinity to Aβ, as well as to study the mechanisms underlying the modulating effects of HSA ligands on its interaction with Aβ, which can become the basis for the development of new approaches to therapy and prevention of AD.

In Vitro Interaction of a C-Terminal Fragment of TDP-43 Protein with Human Serum Albumin Modulates Its Aggregation

An increased level of naturally occurring anti-TDP-43 antibodies was observed in the serum and cerebrospinal fluid (CSF) of amyotrophic lateral sclerosis patients. Human serum albumin (HSA), the most abundant protein in blood plasma and CSF, is found to interact with pathological proteins like Aβ and α-synuclein. Therefore, we examined the effect on the in vitro aggregation of a C-terminal fragment of TDP-43 in the presence of HSA. We found that the lag phase in TDP-43^2C aggregation is abrogated in the presence of HSA, but there is an overall decreased aggregation as examined by thioflavin-T fluorescence spectroscopy and microscopy. An early onset of TDP-43^2C oligomer formation in the presence of HSA was observed using atomic force microscopy and transmission electron microscopy. Also, a known chemical inhibitor of TDP-43^2Caggregation, AIM4, abolishes the HSA-induced early formation of TDP-43^2C oligomers. Notably, the aggregates of TDP-43^2C formed in the presence of HSA are more stable against sarkosyl detergent. Using affinity copurification, we observed that HSA can bind to TDP-43^2C, and biolayer interferometry further supported their physical interaction and suggested the binding affinity to be in sub-micromolar range. Taken together, the data support that HSA can interact with TDP-43^2C in vitro and affect its aggregation.

Testing the link between isoaspartate and Alzheimer's disease etiology

Isoaspartate (isoAsp) is a damaging amino acid residue formed in proteins as a result of spontaneous deamidation. IsoAsp disrupts protein structures, making them prone to aggregation. Here we strengthened the link between isoAsp and Alzheimer's disease (AD) by novel approaches to isoAsp analysis in human serum albumin (HSA), the most abundant blood protein and a major carrier of amyloid beta (Aβ) and phosphorylated tau (p-tau) in blood. We discovered a reduced amount of anti-isoAsp antibodies (P < 0.0001), an elevated isoAsp level in HSA (P < 0.001), more HSA aggregates (P < 0.0001), and increased levels of free Aβ (P < 0.01) in AD blood compared to controls. We also found that deamidation significantly reduces HSA capacity to bind with Aβ and p-tau (P < 0.05). These suggest the presence in AD of a bottleneck in clearance of Aβ and p-tau, leading to their increased concentrations in the brain and facilitating their aggregations there.

Human serum albumin in neurodegeneration

Serum albumin (SA) exists in relatively high concentrations, in close contact with most cells. However, in the adult brain, except for cerebrospinal fluid (CSF), SA concentration is relatively low. It is mainly produced in the liver to serve as the main protein of the blood plasma. In the plasma, it functions as a carrier, chaperon, antioxidant, source of amino acids, osmoregulator, etc. As a carrier, it facilitates the stable presence and transport of the hydrophobic and hydrophilic molecules, including free fatty acids, steroid hormones, medicines, and metal ions. As a chaperon, SA binds to and protects other proteins. As an antioxidant, thanks to a free sulfhydryl group (-SH), albumin is responsible for most antioxidant properties of plasma. These functions qualify SA as a major player in, and a mirror of, overall health status, aging, and neurodegeneration. The low concentration of SA is associated with cognitive deterioration in the elderly and negative prognosis in multiple sclerosis (MS) and amyotrophic lateral sclerosis (ALS). SA has been shown to be structurally modified in neurological conditions such as Alzheimer's disease (AD). During blood-brain barrier damage albumin enters the brain tissue and could trigger epilepsy and neurodegeneration. SA is able to bind to the precursor agent of the AD, amyloid-beta (Aβ), preventing its toxic effects in the periphery, and is being tested for treating this disease. SA therapy may also be effective in brain rejuvenation. In the current review, we will bring forward the prominent properties and roles of SA in neurodegeneration.

Interactions of intrinsically disordered proteins with the unconventional chaperone human serum albumin: From mechanisms of amyloid inhibition to therapeutic opportunities

Human Serum Albumin (HSA), the most abundant protein in plasma, serves a diverse repertoire of biological functions including regulation of oncotic pressure and redox potential, transport of serum solutes, but also chaperoning of misfolded proteins. Here we review how HSA interacts with a wide spectrum of client proteins including intrinsically disordered proteins (IDPs) such as Aβ, the islet amyloid peptide (IAPP), alpha synuclein and stressed globular proteins such as insulin. The comparative analysis of the HSA chaperone - client interactions reveals that the amyloid-inhibitory function of HSA arises from at least four emerging mechanisms. Two mechanisms (the monomer stabilizer model and the monomer competitor model) involve the direct binding of HSA to either IDP monomers or oligomers, while other mechanisms (metal chelation and membrane protection) rely on the indirect modulation by HSA of other factors that drive IDP aggregation. While HSA is not the only extracellular chaperone, given its abundance, HSA is likely to account for a significant fraction of the chaperoning effects in plasma, thus opening new therapeutic opportunities in the context of the peripheral sink hypothesis.

Extracellular protein components of amyloid plaques and their roles in Alzheimer's disease pathology

Alzheimer's disease (AD) is pathologically defined by the presence of fibrillar amyloid β (Aβ) peptide in extracellular senile plaques and tau filaments in intracellular neurofibrillary tangles. Extensive research has focused on understanding the assembly mechanisms and neurotoxic effects of Aβ during the last decades but still we only have a brief understanding of the disease associated biological processes. This review highlights the many other constituents that, beside Aβ, are accumulated in the plaques, with the focus on extracellular proteins. All living organisms rely on a delicate network of protein functionality. Deposition of significant amounts of certain proteins in insoluble inclusions will unquestionably lead to disturbances in the network, which may contribute to AD and copathology. This paper provide a comprehensive overview of extracellular proteins that have been shown to interact with Aβ and a discussion of their potential roles in AD pathology. Methods that can expand the knowledge about how the proteins are incorporated in plaques are described. Top-down methods to analyze post-mortem tissue and bottom-up approaches with the potential to provide molecular insights on the organization of plaque-like particles are compared. Finally, a network analysis of Aβ-interacting partners with enriched functional and structural key words is presented.

Multipronged Regulatory Functions of Serum Albumin in Early Stages of Amyloid-β Aggregation

Human serum albumin (HSA) is a major interacting-partner of Alzheimer's amyloid-β (Aβ) peptide in the plasma and has emerged as a promising therapeutic target. HSA inhibits Aβ fibrillization, but the underlying molecular mechanism is not well elucidated. In this work, we investigated the role of HSA in the early stages of Aβ aggregation by simulating the binding process of multiple Aβ monomers and protofibrils to HSA with extensive molecular dynamics simulations. HSA could simultaneously trap multiple Aβ monomers and accommodate the formation of nonfibrillar Aβ oligomers after binding. In particular, domains I and III show stronger binding capacities and hold preferable interaction sites for oligomers. Consequently, HSA prevents the formation of fibrillar oligomers in water, thus interfering with the nucleation process. On the other aspect, when protofibrils are preformed, HSA tends to block the β-strand spanning the central hydrophobic core located at the protofibril end, preventing the addition of monomers to protofibrils. Furthermore, Aβ protofibril structures are severely disrupted both globally and locally. Thus, further growth of protofibrils to fibrils is impeded by HSA. Our results collectively indicate that HSA performs multipronged regulatory functions in the early stages of Aβ aggregation. Our work advances the understanding of the amyloid inhibition of Aβ by HSA and provides theoretical guidance for developing rational therapies of Alzheimer's disease.

Serotonin Promotes Serum Albumin Interaction with the Monomeric Amyloid β Peptide

Prevention of amyloid β peptide (Aβ) deposition via facilitation of Aβ binding to its natural depot, human serum albumin (HSA), is a promising approach to preclude Alzheimer's disease (AD) onset and progression. Previously, we demonstrated the ability of natural HSA ligands, fatty acids, to improve the affinity of this protein to monomeric Aβ by a factor of 3 (BBRC, 510(2), 248-253). Using plasmon resonance spectroscopy, we show here that another HSA ligand related to AD pathogenesis, serotonin (SRO), increases the affinity of the Aβ monomer to HSA by a factor of 7/17 for Aβ₄₀/Aβ₄₂, respectively. Meanwhile, the structurally homologous SRO precursor, tryptophan (TRP), does not affect HSA's affinity to monomeric Aβ, despite slowdown of the association and dissociation processes. Crosslinking with glutaraldehyde and dynamic light scattering experiments reveal that, compared with the TRP-induced effects, SRO binding causes more marked changes in the quaternary structure of HSA. Furthermore, molecular docking reveals distinct structural differences between SRO/TRP complexes with HSA. The disintegration of the serotonergic system during AD pathogenesis may contribute to Aβ release from HSA in the central nervous system due to impairment of the SRO-mediated Aβ trapping by HSA.

Emerging insights into the role of albumin with plasma exchange in Alzheimer's disease management

Alzheimer's disease (AD) is a neurodegenerative process that inexorably leads to progressive deterioration of cognition function and, ultimately, death. Central pathophysiologic features of AD include the accumulation of extracellular plaques comprised of amyloid-β peptide (Aβ) and the presence of intraneuronal neurofibrillary tangles. However, a large body of evidence suggests that oxidative stress and inflammation are major contributors to the pathogenesis and progression of AD. To date, available pharmacologic treatments are only symptomatic. Clinical trials focused on amyloid and non-amyloid-targeted treatments with small molecule pharmacotherapy and immunotherapies have accumulated a long list of failures. Considering that around 90 % of the circulating Aβ is bound to albumin, and that a dynamic equilibrium exists between peripheral and central Aβ, plasma exchange with albumin replacement has emerged as a new approach in a multitargeted AD therapeutic strategy (AMBAR Program). In plasma exchange, a patient's plasma is removed by plasmapheresis to eliminate toxic endogenous substances, including Aβ and functionally impaired albumin. The fluid replacement used is therapeutic albumin, which acts not only as a plasma volume expander but also has numerous pleiotropic functions (e.g., circulating Aβ- binding capacity, transporter, detoxifier, antioxidant) that are clinically relevant for the treatment of AD. Positive results from the AMBAR Program (phase 1, 2, an 2b/3 trials), i.e., slower decline or stabilization of disease symptoms in the most relevant clinical efficacy and safety endpoints, offer a glimmer of hope to both AD patients and caregivers.

Noncanonical protein kinase A activation by oligomerization of regulatory subunits as revealed by inherited Carney complex mutations

Familial mutations of the protein kinase A (PKA) R1α regulatory subunit lead to a generalized predisposition for a wide range of tumors, from pituitary adenomas to pancreatic and liver cancers, commonly referred to as Carney complex (CNC). CNC mutations are known to cause overactivation of PKA, but the molecular mechanisms underlying such kinase overactivity are not fully understood in the context of the canonical cAMP-dependent activation of PKA. Here, we show that oligomerization-induced sequestration of R1α from the catalytic subunit of PKA (C) is a viable mechanism of PKA activation that can explain the CNC phenotype. Our investigations focus on comparative analyses at the level of structure, unfolding, aggregation, and kinase inhibition profiles of wild-type (wt) PKA R1α, the A211D and G287W CNC mutants, as well as the cognate acrodysostosis type 1 (ACRDYS1) mutations A211T and G287E. The latter exhibit a phenotype opposite to CNC with suboptimal PKA activation compared with wt. Overall, our results show that CNC mutations not only perturb the classical cAMP-dependent allosteric activation pathway of PKA, but also amplify significantly more than the cognate ACRDYS1 mutations nonclassical and previously unappreciated activation pathways, such as oligomerization-induced losses of the PKA R1α inhibitory function.

Unexpected Function of a Heptapeptide-Conjugated Zwitterionic Polymer that Coassembles into β-Amyloid Fibrils and Eliminates the Amyloid Cytotoxicity

Fibrillogenesis of amyloid β-protein (Aβ) is pathologically associated with Alzheimer's disease (AD), so modulating Aβ aggregation is crucial for AD prevention and treatment. Herein, a zwitterionic polymer with short dimethyl side chains (pID) is synthesized and conjugated with a heptapeptide inhibitor (Ac-LVFFARK-NH₂, LK7) to construct zwitterionic polymer-inhibitor conjugates for enhanced inhibition of Aβ aggregation. However, it is unexpectedly found that the LK7@pID conjugates remarkably promote Aβ fibrillization to form more fibrils than the free Aβ system but effectively eliminate Aβ-induced cytotoxicity. Such an unusual behavior of the LK7@pID conjugates is unraveled by extensive mechanistic studies. First, the hydrophobic environment within the assembled micelles of LK7@pID promotes the hydrophobic interaction between Aβ molecules and LK7@pID, which triggers Aβ aggregation at the very beginning, making fibrillization occur at an earlier stage. Second, in the aggregation process, the LK7@pID micelles disassemble by the intensive interactions with Aβ, and LK7@pID participates in the fibrillization by being embedded in the Aβ fibrils, leading to the formation of hybrid and heterogeneous fibrillar aggregates with a different structure than normal Aβ fibrils. This unique Trojan horse-like feature of LK7@pID conjugates has not been observed for any other inhibitors reported previously and may shed light on the design of new modulators against β-amyloid cytotoxicity.

Albumin Alters the Conformational Ensemble of Amyloid-β by Promiscuous Interactions: Implications for Amyloid Inhibition

Human serum albumin (HSA) is a key endogenous inhibitor of amyloid-β (Αβ) aggregation. In vitro HSA inhibits Aβ fibrillization and targets multiple species along the aggregation pathway including monomers, oligomers, and protofibrils. Amyloid inhibition by HSA has both pathological implications and therapeutic potential, but the underlying molecular mechanism remains elusive. As a first step towards addressing this complex question, we studied the interactions of an Aβ42 monomer with HSA by molecular dynamics simulations. To adequately sample the conformational space, we adapted the replica exchange with solute tempering (REST2) method to selectively heat the Aβ42 peptide in the absence and presence of HSA. Aβ42 binds to multiple sites on HSA with a preference to domain III and adopts various conformations that all differ from the free state. The β-sheet abundances of H14-E22 and A30-M33 regions are significantly reduced by HSA, so are the β-sheet lengths. HSA shifts the conformational ensemble towards more disordered states and alters the β-sheet association patterns. In particular, the frequent association of Q15-V24 and N27-V36 regions into β-hairpin which is critical for aggregation is impeded. HSA primarily interacts with the latter β-region and the N-terminal charged residues. They form promiscuous interactions characterized by salt bridges at the edge of the peptide-protein interface and hydrophobic cores at the center. Consequently, intrapeptide interactions crucial for β-sheet formation are disrupted. Our work builds the bridge between the modification of Aβ conformational ensemble and amyloid inhibition by HSA. It also illustrates the potential of the REST2 method in studying interactions between intrinsically disordered peptides and globular proteins.

A biophysical toolset to probe the microscopic processes underlying protein aggregation and its inhibition by molecular chaperones

Given the breadth and depth of the scientific contributions of Sir Christopher Dobson, with over 870 publications to date, it is inconceivable to convey in a single review the impact of his work and its legacy. This review therefore primarily focuses on his contributions to the development of strategies for preventing aberrant protein misfolding. The first section of this review highlights his seminal work on the elucidation of the microscopic nucleation processes underlying protein aggregation. Next, we discuss the specific inhibition of these steps by candidate drugs and biologics, with a particular emphasis on the role of molecular chaperones. In the final section, we review how protein aggregation principles can be exploited for the rational design of novel and more potent aggregation inhibitors. These milestones serve as excellent examples of the profound impact of Dobson's seminal work on fundamental science and its translation into drug discovery.

Liver fibrosis score, physical frailty, and the risk of dementia in older adults: The Italian Longitudinal Study on Aging

INTRODUCTION

Liver fibrosis increases progressively with aging and has been associated with poorer cognitive performance in middle-aged and older adults. We investigated the relationships between a non-invasive score for advanced liver fibrosis (non-alcoholic fatty liver disease [NAFLD] fibrosis score [NFS]) and dementia risk. We also assessed physical frailty, a common geriatric condition which is associated to dementia. We tested the joint effects of physical frailty and fibrosis on dementia incidence.

METHODS

A total of 1061 older adults (65 to 84 years), from the Italian Longitudinal Study on Aging, were prospectively evaluated for the risk of dementia in a period between 1992 and 2001. Liver fibrosis was defined according to the NFS. Physical frailty was assessed according to the Fried's criteria. Cox proportional hazards models were used to estimate the short- and long-term risk of overall dementia, associated to the NFS, testing the effect modifier of physical frailty status.

RESULTS

Older adults with only high NFS (F3-F4) did not exhibit a significant increased risk of overall dementia. Over 8 years of follow-up, frail older adults with high NFS had an increased risk of overall dementia (hazard ratio [HR]: 4.23; 95% confidence interval [CI]: 1.22 to 14.70, P = .023). Finally, physically frail older adults with low albumin serum levels (albumin < 4.3 g/dL) and with advanced liver fibrosis (F3-F4 NFS) compared to those with lower liver fibrosis score (F0-F2 NFS) were more likely to have a higher risk of overall dementia in a long term-period (HR: 16.42; 95% CI: 1.44 to 187.67, P = .024).

DISCUSSION

Advanced liver fibrosis (F3-F4 NFS) could be a long-term predictor for overall dementia in people with physical frailty. These findings should encourage a typical geriatric, multidisciplinary assessment which accounts also for the possible co-presence of frail condition in older adults with chronic liver disease and liver fibrosis.

Catechins as Tools to Understand the Molecular Basis of Neurodegeneration

Protein misfolding as well as the subsequent self-association and deposition of amyloid aggregates is implicated in the progression of several neurodegenerative disorders including Alzheimer's and Parkinson's diseases. Modulators of amyloidogenic aggregation serve as essential tools to dissect the underlying molecular mechanisms and may offer insight on potential therapeutic solutions. These modulators include green tea catechins, which are potent inhibitors of amyloid aggregation. Although catechins often exhibit poor pharmacokinetic properties and bioavailability, they are still essential tools for identifying the drivers of amyloid aggregation and for developing other aggregation modulators through structural mimicry. As an illustration of such strategies, here we review how catechins have been used to map the toxic surfaces of oligomeric amyloid-like species and develop catechin-based phenolic compounds with enhanced anti-amyloid activity.

Serum albumin and beta-amyloid deposition in the human brain

Objectives

To investigate the relationships of serum albumin with in vivo Alzheimer disease (AD) pathologies, including cerebral β-amyloid (Aβ) protein deposition, neurodegeneration of AD-signature regions, and cerebral white matter hyperintensities (WMH), in the human brain.

Methods

A total of 396 older adults without dementia underwent comprehensive clinical assessments, measurement of serum albumin level, and multimodal brain imaging, including [¹¹C] Pittsburgh compound B-PET, ¹⁸F-fluorodeoxyglucose-PET, and MRI. Serum albumin was categorized as follows: <4.4 g/dL (low albumin), 4.4 to 4.5 g/dL (middle albumin), and >4.5 g/dL (high albumin; used as a reference category). Aβ positivity, AD-signature region cerebral glucose metabolism (AD-CM), AD-signature region cortical thickness (AD-CT), and WMH volume were used as outcome measures.

Results

Serum albumin level (as a continuous variable) was inversely associated with Aβ deposition and Aβ positivity. The low albumin group showed a significantly higher Aβ positivity rate compared to the high albumin group (odds ratio 3.40, 95% confidence interval 1.67–6.92, p = 0.001), while the middle albumin group showed no difference (odds ratio 1.74, 95% confidence interval 0.80–3.77, p = 0.162). Neither serum albumin level (as a continuous variable) nor albumin categories were related to AD-CM, AD-CT, or WMH volume.

Conclusions

Low serum albumin may increase the risk of AD dementia by elevating amyloid accumulation. In terms of AD prevention, more attention needs to be paid to avoid a low serum albumin level, even within the clinical normal range, by clinicians.

Albumin domain mutants with enhanced Aβ binding capacity identified by phage display analysis for application in various peripheral Aβ elimination approaches of Alzheimer's disease treatment

Deposition of amyloid protein, particularly Aβ_1-42 , is a major contributor to the onset of Alzheimer's disease (AD). However, almost no deposition of Aβ in the peripheral tissues could be found. Human serum albumin (HSA), the most abundant protein in the blood, has been reported to inhibit amyloid formation through binding Aβ, which is believed to play an important role in the peripheral clearance of Aβ. We identified the Aβ binding site on HSA and developed HSA mutants with high binding capacities for Aβ using a phage display method. HSA fragment 187-385 (Domain II) was found to exhibit the highest binding capacity for Aβ compared with the other two HSA fragments. To elucidate the sequence that forms the binding site for Aβ on Domain II, a random screening of Domain II display phage biopanning was constructed. A number of mutants with higher Aβ binding capacities than the wild type were identified. These mutants exhibited stronger scavenging abilities than the wild type, as revealed via in vitro equilibrium dialysis of Aβ experiments. These findings provide useful basic data for developing a safer alternative therapy than Aβ vaccines and for application in plasma exchange as well as extracorporeal dialysis.

Albumin Exchange in Alzheimer's Disease: Might CSF Be an Alternative Route to Plasma?

Amyloid β (Aβ) in brain parenchyma is thought to play a central role in the pathogenesis of Alzheimer's disease (AD). Aβ is transported from the brain to the plasma via complex transport mechanisms at the blood-brain barrier (BBB). About 90-95% of plasma Aβ may be bound to albumin. Replacement of serum albumin in plasma has been proposed as a promising therapy for AD. However, the efficacy of this approach may be compromised by altered BBB Aβ receptors in AD, as well as multiple pools of Aβ from other organs in exchange with plasma Aβ, competing for albumin binding sites. The flow of interstitial fluid (ISF) into cerebrospinal fluid (CSF) is another major route of Aβ clearance. Though the concentration of albumin in CSF is much lower than in plasma, the mixing of CSF with ISF is not impeded by a highly selective barrier and, hence, Aβ in the two pools is in more direct exchange. Furthermore, unlike in plasma, Aβ in CSF is not in direct exchange with multiple organ sources of Aβ. Here we consider albumin replacement in CSF as an alternative method for therapeutic brain Aβ removal and describe the possible advantages and rationale supporting this hypothesis.

Effect of Cu2+ and Zn2+ ions on human serum albumin interaction with plasma unsaturated fatty acids

Human serum albumin (HSA) serves as a depot and carrier of multiple unrelated ligands including several participants of the pathogenesis of Alzheimer's disease (AD), such as amyloid β peptide (Aβ), Zn²⁺/Cu²⁺ ions, docosahexaenoic (DHA), linoleic (LA), and oleic (OA) acids. To explore the interplay between HSA interaction with Zn²⁺/Cu²⁺ and the plasma unsaturated fatty acids (DHA, LA, OA, and arachidonic acid (ArA)), we have studied the metal dependence of the fatty acid (FA) binding capacity of HSA (n_max) and structural consequences of the HSA-FA interactions. HSA loading with Zn²⁺ decreases n_max value by 0.3-1.5, while its saturation with Cu²⁺ causes the FA-dependent n_max changes by up to 0.9. The Cu²⁺-induced decline in n_max value for DHA is due to conformational rearrangements in HSA molecule. In other cases, the changes in n_max are attributed to steric hindarance/facilitation of the HSA-FA interaction because of the protein multimerization/monomerization, as confirmed by chemical crosslinking. The surface hydrophobicity of HSA is Cu²⁺-, Zn²⁺-, and FA-dependent and decreases upon the FA binding, according to bis-ANS fluorescence data. Overall, Zn²⁺ or Cu²⁺ binding selectively affect HSA interaction with the FAs studied, in part due to changes in quaternary structure of the protein.

Modification of Serum Albumin by High Conversion of Carboxyl to Amino Groups Creates a Potent Inhibitor of Amyloid β-Protein Fibrillogenesis

Fibrillogenesis of amyloid β-protein (Aβ) has been thought to be implicated in the progression of Alzheimer's disease (AD). Therefore, development of high-efficiency inhibitors is one of the strategies for the prevention and treatment of AD. Serum albumin has been found to capture Aβ monomers through its hydrophobic groove and suppress amyloid formation, but the inhibition efficiency is limited. Inspired by the strong inhibition potency of a basic protein, human lysozyme, we have herein proposed to develop a basified serum albumin by converting carboxyl groups into amino groups with ethylenediamine conjugated on the protein surface. The idea was verified with both bovine and human serum albumins (BSA/HSA). Four basified BSA (BSA-B) preparations with amino modification degrees (MDs) from 8.0 to 41.5 were first synthesized. Extensive biophysical and biological analyses revealed that the inhibition potency significantly increased with increasing amino MD. BSA-B of the highest MD (41.5), BSA-B4, which had an isoelectric point of 9.7, presented strong inhibition on Aβ₄₂ fibrillation at a concentration as low as 0.5 μM, at which it functioned similarly with 25 μM native BSA to impede 25 μM Aβ fibrillation. Cell viability assays also confirmed that the detoxification of 5 μM BSA-B4 was superior over 25 μM native BSA by increasing cell viability from 60.6% to 96.0%. Fluorescence quenching study unveiled the decrease of the binding affinity between Aβ₄₂ and the hydrophobic pocket region of BSA-B4, while quartz crystal microbalance experiments demonstrated that the binding constant of BSA-B4 to Aβ₄₂ increased nearly 5 times. Therefore, the increase of electrostatic interactions between BSA-B4 and Aβ₄₂ was the main reason for its high potency. Hence, aminated BSA achieved a conversion of binding way to Aβ from a mainly single-site hydrophobic binding to multiregional electrostatic interactions. Similar results were obtained with basified HSA preparations on inhibiting the amyloid formation and cytotoxicity. This work has thus provided new insights into the development of more efficient protein-based inhibitors against Aβ fibrillogenesis.

Insight into the delivery channel and selectivity of multiple binding sites in bovine serum albumin towards naphthalimide-polyamine derivatives

Naphthalimide derivatives are types of small-molecule anticancer drug candidates; however, their negative factors and potential side effects make their application limited. The pharmacophores select a direct access into the tumor cells as the first choice; this can reduce the side effect of the anti-cancer drugs on the normal cells. Herein, the delivery and binding of the naphthalimide-polyamine complex assisted by the bovine serum albumin (BSA) protein have been studied by combining several molecular dynamic simulations. The plausible transportation channels and the most favorable pathways for the delivery of the naphthalimide-polyamine complex to two drug sites (DSI and DSII), their thermodynamic and dynamic properties and the mechanisms have been discussed in detail. The residues His287 and Phe394 acted as guards in the DSI and DSII, respectively, which played a gating-switch role by flipping the ring from open to close during the compound delivery. The binding mode, binding energy and substituent effects have been also identified. The two drug sites have different preferences towards the compound with the electron-withdrawing and electron-donating substituents, and their strong interactions are more sensitive to the number of the substituent groups. The naphthalimide-polyamine complexes are more likely to choose DSI, both thermodynamically and dynamically, as compared to DSII. This selective specificity of these two drug sites manipulated by the electron-withdrawing and electron-donating substituents is quite promising for the design of new naphthalimide drugs.

The binding of monomeric amyloid β peptide to serum albumin is affected by major plasma unsaturated fatty acids

Human serum albumin (HSA) serves as a natural depot of amyloid β peptide (Aβ). Improvement of Aβ binding to HSA should impede Alzheimer's disease (AD). We developed a method for quantitation of the interaction between monomeric Aβ40/42 and HSA using surface plasmon resonance spectroscopy. The dissociation constant of HSA complex with recombinant Aβ40/42 is 0.2-0.3 μM. Flemish variant of Aβ40 has 2.5-10-fold higher affinity to HSA. The parameters of the HSA-Aβ interaction are selectively sensitive to HSA binding of major plasma unsaturated fatty acids and Cu²⁺. Linoleic and arachidonic acids promote the HSA-Aβ42 interaction. The developed methodology for quantitation of HSA-Aβ interaction may serve as a tool for search of compounds favoring HSA-Aβ interaction, thereby preventing AD progression.

Basified Human Lysozyme: A Potent Inhibitor against Amyloid β-Protein Fibrillogenesis

The aggregation of amyloid β-proteins (Aβ) has been recognized as a key process in the pathogenesis of Alzheimer's disease (AD), so inhibiting Aβ aggregation is an important strategy to prevent the onset and treatment of AD. Our recent work indicated that decreasing the positive charges (or introducing negative charges) on human lysozyme (hLys) was unfavorable in keeping the inhibiting capability of hLys on Aβ aggregation. Therefore, we have herein proposed to basify hLys by conversion of the carboxyl groups into amino groups by modification with ethylene diamine. Basified hLys (Lys-B) preparations of three modification degrees (MDs), denoted as hLys-B1 (MD, 1.5), hLys-B2 (MD, 3.3), and hLys-B3 (MD, 4.4), were synthesized for modulating Aβ fibrillogenesis. The hLys-B preparations kept the stability and biocompatibility as native hLys did, whereas the inhibitory potency of hLys-B on Aβ fibrillogenesis increased with increasing MD. Cytotoxicity analysis showed that cell viability with 2.5 μM hLys-B3 increased from 62.5% (with 25 μM Aβ only) to 76.1%, similar to the case with 12.5 μM hLys (75.5%); cell viability with 6.25 μM hLys-B3 increased to 82.0%, similar to the case with 25 μM hLys (80.9%). The results indicate about four- to fivefold increase in the inhibition efficiency of hLys by the amino modification. Mechanistic analysis suggests that such a superior inhibitory capability of hLys-B was attributed to its more widely distributed positive charges, which promoted broad electrostatic interactions between Aβ and hLys-B. Thus, hLys-B suppressed the conformational transition of Aβ to β-sheet structures at low concentrations (e.g., 2.5 μM hLys-B3), leading to changes in the aggregation pathway and the formation of Aβ species with less cytotoxicity. The findings provided new insights into the development of more potent protein-based inhibitors against Aβ fibrillogenesis.

Fatty Acids Compete with Aβ in Binding to Serum Albumin by Quenching Its Conformational Flexibility

Human serum albumin (HSA) has been identified as an important regulator of amyloid-β (Aβ) fibrillization both in blood plasma and in cerebrospinal fluid. Fatty acids bind to HSA, and high serum levels of fatty acids increase the risk of Alzheimer's disease. In vitro, fatty-acid-loaded HSA (FA·HSA) loses the protective effect against Aβ fibrillization, but the mechanism underlying the interference of fatty acids on Aβ-HSA interactions has been unclear. Here, we used molecular dynamics simulations to gain atomic-level insight on the weak binding of monomeric Aβ40 and Aβ42 peptides with apo and FA·HSA. Consistent with recent NMR data, C-terminal residues of the Aβ peptides have the highest propensities for interacting with apo HSA. Interestingly, the Aβ binding residues of apo and FA·HSA exhibit distinct patterns, which qualitatively correlate with backbone flexibility. In FA·HSA, both flexibilities and Aβ binding propensities are relatively even among the three domains. In contrast, in apo HSA, domain III shows the highest flexibility and is the primary target for Aβ binding. Specifically, deformation of apo HSA creates strong binding sites within subdomain IIIb, around the interface between subdomains IIIa and IIIb, and at the cleft between domains III and I. Therefore, much like disordered proteins, HSA can take advantage of flexibility in forming promiscuous interactions with partners, until the flexibility is quenched by fatty-acid binding. Our work explains the effect of fatty acids on Aβ-HSA binding and contributes to the understanding of HSA regulation of Aβ aggregation.

A functional assay to identify amyloidogenic light chains

INTRODUCTION

Multiple myeloma (MM) and light chain monoclonal gammopathy of undetermined significance (LCMGUS) are plasma cell disorders associated with the secretion of monoclonal free light-chain (LC) proteins. Due to the high concentrations of LC in circulation, both of these populations are at risk for developing LC-associated amyloidosis (AL) - a protein misfolding disease characterized by the deposition of LC protein fibrils in organs and tissues, leading to dysfunction and significant morbidity. At present, accurate identification of subjects at risk for developing amyloidosis is not possible, but with the advent of novel, amyloid-targeted therapies, identification of pre-symptomatic individuals is of clinical import.

METHODS

To address this, a competition assay has been developed to discern LC proteins with enhanced amyloidogenic potential. Numerous factors that may influence the efficacy of the assay have been evaluated to yield optimal conditions.

RESULTS

Using a panel of nine patient-derived LC, we have demonstrated that amyloid-associated LC inhibited the recruitment of a biotinyl-λ6 variable domain by homologous amyloid-like fibrils significantly more than MM LC (p < .01).

CONCLUSION

The assay accurately discriminated AL from MM patient populations, suggesting that it may aid in the identification of patients with monoclonal gammopathies who have an increased risk of developing amyloidosis.

Aberrant Co-localization of Synaptic Proteins Promoted by Alzheimer's Disease Amyloid-β Peptides: Protective Effect of Human Serum Albumin

Amyloid-β (Aβ), Aβ₄₀, Aβ₄₂, and, recently, Aβ_25-35 have been directly implicated in the pathogenesis of Alzheimer’s disease. We have studied the effects of Aβ on neuronal death, reactive oxygen species (ROS) production, and synaptic assembling in neurons in primary culture. Aβ_25-35, Aβ₄₀, and Aβ₄₂ significantly decreased neuronal viability, although Aβ_25-35 showed a higher effect. Aβ_25-35 showed a more penetrating ability to reach mitochondria while Aβ₄₀ did not enter the neuronal cytosol and Aβ₄₂ was scarcely internalized. We did not observe a direct correlation between ROS production and cell death because both Aβ₄₀ and Aβ₄₂ decreased neuronal viability but Aβ₄₀ did not change ROS production. Rather, ROS production seems to correlate with the penetrating ability of each Aβ. No significant differences were found between Aβ₄₀ and Aβ₄₂ regarding the extent of the deleterious effects of both peptides on neuronal viability or synaptophysin expression. However, Aβ₄₀ elicited a clear delocalization of PSD-95 and synaptotagmin from prospective synapsis to the neuronal soma, suggesting the occurrence of a crucial effect of Aβ₄₀ on synaptic disassembling. The formation of Aβ₄₀- or Aβ₄₂-serum albumin complexes avoided the effects of these peptides on neuronal viability, synaptophysin expression, and PSD-95/synaptotagmin disarrangement suggesting that sequestration of Aβ by albumin prevents deleterious effects of these peptides. We can conclude that Aβ borne by albumin can be safely transported through body fluids, a fact that may be compulsory for Aβ disposal by peripheral tissues.

Serum Albumin's Protective Inhibition of Amyloid-β Fiber Formation Is Suppressed by Cholesterol, Fatty Acids and Warfarin

Central to Alzheimer's disease (AD) pathology is the assembly of monomeric amyloid-β peptide (Aβ) into oligomers and fibers. The most abundant protein in the blood plasma and cerebrospinal fluid is human serum albumin. Albumin can bind to Aβ and is capable of inhibiting the fibrillization of Aβ at physiological (μM) concentrations. The ability of albumin to bind Aβ has recently been exploited in a phase II clinical trial, which showed a reduction in cognitive decline in AD patients undergoing albumin-plasma exchange. Here we explore the equilibrium between Aβ monomer, oligomer and fiber in the presence of albumin. Using transmission electron microscopy and thioflavin-T fluorescent dye, we have shown that albumin traps Aβ as oligomers, 9 nm in diameter. We show that albumin-trapped Aβ oligomeric assemblies are not capable of forming ion channels, which suggests a mechanism by which albumin is protective in Aβ-exposed neuronal cells. In vivo albumin binds a variety of endogenous and therapeutic exogenous hydrophobic molecules, including cholesterol, fatty acids and warfarin. We show that these molecules bind to albumin and suppress its ability to inhibit Aβ fiber formation. The interplay between Aβ, albumin and endogenous hydrophobic molecules impacts Aβ assembly; thus, changes in cholesterol and fatty acid levels in vivo may impact Aβ fibrillization, by altering the capacity of albumin to bind Aβ. These observations are particularly intriguing given that high cholesterol or fatty acid diets are well-established risk factors for late-onset AD.

A solution NMR toolset to probe the molecular mechanisms of amyloid inhibitors

A chemical exchange-based solution NMR toolset to probe the molecular mechanisms of amyloid inhibitors.

Mechanisms of recognition of amyloid-β (Aβ) monomer, oligomer, and fibril by homologous antibodies

Alzheimer's disease is one of the most devastating neurodegenerative diseases without effective therapies. Immunotherapy is a promising approach, but amyloid antibody structural information is limited. Here we simulate the recognition of monomeric, oligomeric, and fibril amyloid-β (Aβ) by three homologous antibodies (solanezumab, crenezumab, and their chimera, CreneFab). Solanezumab only binds the monomer, whereas crenezumab and CreneFab can recognize different oligomerization states; however, the structural basis for this observation is not understood. We successfully identified stable complexes of crenezumab with Aβ pentamer (oligomer model) and 16-mer (fibril model). It is noteworthy that solanezumab targets Aβ residues 16-26 preferentially in the monomeric state; conversely, crenezumab consistently targets residues 13-16 in different oligomeric states. Unlike the buried monomeric peptide in solanezumab's complementarity-determining region, crenezumab binds the oligomer's lateral and edge residues. Surprisingly, crenezumab's complementarity-determining region loops can effectively bind the Aβ fibril lateral surface around the same 13-16 region. The constant domain influences antigen recognition through entropy redistribution. Different constant domain residues in solanezumab/crenezumab/chimera influence the binding of Aβ aggregates. Collectively, we provide molecular insight into the recognition mechanisms facilitating antibody design.

Functional dynamics in cyclic nucleotide signaling and amyloid inhibition

It is now established that understanding the molecular basis of biological function requires atomic resolution maps of both structure and dynamics. Here, we review several illustrative examples of functional dynamics selected from our work on cyclic nucleotide signaling and amyloid inhibition. Although fundamentally diverse, a central aspect common to both fields is that function can only be rationalized by considering dynamic equilibria between distinct states of the accessible free energy landscape. The dynamic exchange between ground and excited states of signaling proteins is essential to explain auto-inhibition and allosteric activation. The dynamic exchange between non-toxic monomeric species and toxic oligomers of amyloidogenic proteins provides a foundation to understand amyloid inhibition. NMR ideally probes both types of dynamic exchange at atomic resolution. Specifically, we will show how NMR was utilized to reveal the dynamical basis of cyclic nucleotide affinity, selectivity, agonism and antagonism in multiple eukaryotic cAMP and cGMP receptors. We will also illustrate how NMR revealed the mechanism of action of plasma proteins that act as extracellular chaperones and inhibit the self-association of the prototypical amyloidogenic Aβ peptide. The examples outlined in this review illustrate the widespread implications of functional dynamics and the power of NMR as an indispensable tool in molecular pharmacology and pathology.

Modulating protein amyloid aggregation with nanomaterials

Direct exposure or intake of nanopaticles (NPs) to the human body can invoke a series of biological responses, some of which are deleterious, and as such the role of NPs in vivo requires thorough examination. Over the past decade, it has been established that biomolecules such as proteins can bind NPs to form a 'corona', where the structures and dynamics of NP-associated proteins can assign new functionality, systemic distribution and toxicity. However, the behavior and fate of NPs in biological systems are still far from being fully understood. Growing evidence has shown that some natural or artificial NPs could either up- or down-regulate protein amyloid aggregation, which is associated with neurodegenerative diseases like Alzheimer's and Parkinson's diseases, as well as metabolic diseases such as type 2 diabetes. These effects can be either indirect (e.g., through a crowding effect) or direct, depending on the NP composition, size, shape and surface chemistry. However, efforts to design anti-amyloid NPs for biomedical applications have been largely hindered by insufficient understanding of the complex processes, even though proof-of-concept experiments have been conducted. Therefore, exploring the general mechanisms of NP-meditated protein aggregation marks an emerging field in bio-nano research and a new stage of handling nanotechnology that not only aids in elucidating the origin of nanotoxicity, but also provides a foundation for engineering de novo anti-amyloid nanomedicines. In this review, we summarize research on NP-mediated protein amyloid aggregation, with the goal of contributing to sustained nanotechnology and safe nanomedicine against amyloid diseases.

Atomic-resolution map of the interactions between an amyloid inhibitor protein and amyloid β (Aβ) peptides in the monomer and protofibril states

Self-association of amyloid β (Aβ) peptides is a hallmark of Alzheimer's disease and serves as a general prototype for amyloid formation. A key endogenous inhibitor of Aβ self-association is human serum albumin (HSA), which binds ∼90% of plasma Aβ. However, the exact molecular mechanism by which HSA binds Aβ monomers and protofibrils is not fully understood. Here, using dark-state exchange saturation transfer NMR and relaxation experiments complemented by morphological characterization, we mapped the HSA-Aβ interactions at atomic resolution by examining the effects of HSA on Aβ monomers and soluble high-molecular weight oligomeric protofibrils. We found that HSA binds both monomeric and protofibrillar Aβ, but the affinity of HSA for Aβ monomers is lower than for Aβ protofibrils (K_d values are submillimolar rather than micromolar) yet physiologically relevant because of the ∼0.6-0.7 mm plasma HSA concentration. In both Aβ protofibrils and monomers, HSA targets key Aβ self-recognition sites spanning the β strands found in cross-β protofibril structures, leading to a net switch from direct to tethered contacts between the monomeric Aβ and the protofibril surface. These HSA-Aβ interactions are isoform-specific, because the HSA affinity of Aβ monomers is lower for Aβ(1-42) than for Aβ(1-40). In addition, the HSA-induced perturbations of the monomer/protofibrils pseudo-equilibrium extend to the C-terminal residues in the Aβ(1-42) isoform but not in Aβ(1-40). These results provide an unprecedented view of how albumin interacts with Aβ and illustrate the potential of dark-state exchange saturation transfer NMR in mapping the interactions between amyloid-inhibitory proteins and amyloidogenic peptides.

Multiple functions of insulin-degrading enzyme: a metabolic crosslight?

Insulin-degrading enzyme (IDE) is a ubiquitous zinc peptidase of the inverzincin family, which has been initially discovered as the enzyme responsible for insulin catabolism; therefore, its involvement in the onset of diabetes has been largely investigated. However, further studies on IDE unraveled its ability to degrade several other polypeptides, such as β-amyloid, amylin, and glucagon, envisaging the possible implication of IDE dys-regulation in the "aggregopathies" and, in particular, in neurodegenerative diseases. Over the last decade, a novel scenario on IDE biology has emerged, pointing out a multi-functional role of this enzyme in several basic cellular processes. In particular, latest advances indicate that IDE behaves as a heat shock protein and modulates the ubiquitin-proteasome system, suggesting a major implication in proteins turnover and cell homeostasis. In addition, recent observations have highlighted that the regulation of glucose metabolism by IDE is not merely based on its largely proposed role in the degradation of insulin in vivo. There is increasing evidence that improper IDE function, regulation, or trafficking might contribute to the etiology of metabolic diseases. In addition, the enzymatic activity of IDE is affected by metals levels, thus suggesting a role also in the metal homeostasis (metallostasis), which is thought to be tightly linked to the malfunction of the "quality control" machinery of the cell. Focusing on the physiological role of IDE, we will address a comprehensive vision of the very complex scenario in which IDE takes part, outlining its crucial role in interconnecting several relevant cellular processes.

The effects of chondroitin sulfate and serum albumin on the fibrillation of human islet amyloid polypeptide at phospholipid membranes

Glycosaminoglycans and serum albumin are important cellular components that regulate the fibril formation of proteins. Whereas the effects of cellular components on the fibrillation of amyloid proteins in bulk solution are widely studied, less attention has been paid to the effects of cellular components on amyloidogenesis occurring at cellular membranes. In this study, we focus on the impacts of chondroitin sulfate A (CSA) and bovine serum albumin (BSA) on the amyloidogenic behaviors of human islet amyloid polypeptide (hIAPP) at phospholipid membranes consisting of neutral POPC and anionic POPG. Using the thioflavin T fluorescence assay, atomic force microscopy, circular dichroism and nuclear magnetic resonance measurements, we demonstrate that CSA has an intensive promotion effect on the fibrillation of hIAPP at the POPC membrane, which is larger than the total effect of CSA alone and POPC alone. The further enhanced promotion of the fibrillation of hIAPP by CSA at the neutral membrane is associated with a specific interaction of CSA with POPC. In contrast, the activity of BSA as an inhibitor of hIAPP fibrillation observed in bulk solution decreases dramatically in the presence of POPG vesicles. The dramatic loss of the inhibition efficiency of BSA arises essentially from a specific interaction with the POPG component, but not simply from suppression by an opposite effect of the anionic membrane. The findings in this study suggest that the interactions between membranes and cellular components may have a significant effect on the activity of the cellular components in regulating the fibrillation of hIAPP.

Probing conformational dynamics in biomolecules via chemical exchange saturation transfer: a primer

Although Chemical Exchange Saturation Transfer (CEST) type NMR experiments have been used to study chemical exchange processes in molecules since the early 1960s, there has been renewed interest in the past several years in using this approach to study biomolecular conformational dynamics. The methodology is particularly powerful for the study of sparsely populated, transiently formed conformers that are recalcitrant to investigation using traditional biophysical tools, and it is complementary to relaxation dispersion and magnetization transfer experiments that have traditionally been used to study chemical exchange processes. Here we discuss the concepts behind the CEST experiment, focusing on practical aspects as well, we review some of the pulse sequences that have been developed to characterize protein and RNA conformational dynamics, and we discuss a number of examples where the CEST methodology has provided important insights into the role of dynamics in biomolecular function.