The iAβ5p β-breaker peptide regulates the Aβ(25-35) interaction with lipid bilayers through a cholesterol-mediated mechanism

Alzheimer's disease is characterized by the deposition of aggregates of the β-amyloid peptide (Aβ) in the brain. A potential therapeutic strategy for Alzheimer's disease is the use of synthetic β-sheet breaker peptides, which are capable of binding Aβ but unable to become part of a β-sheet structure, thus inhibiting the peptide aggregation. Many studies suggest that membranes play a key role in the Aβ aggregation; consequently, it is strategic to investigate the interplay between β-sheet breaker peptides and Aβ in the presence of lipid bilayers. In this work, we focused on the effect of the β-sheet breaker peptide acetyl-LPFFD-amide, iAβ5p, on the interaction of the Aβ(25-35) fragment with lipid membranes, studied by Electron Spin Resonance spectroscopy, using spin-labeled membrane components (either phospholipids or cholesterol). The ESR results show that iAβ5p influences the Aβ(25-35) interaction with the bilayer through a cholesterol-mediated mechanism: iAβ5p withholds cholesterol in the inner hydrophobic core of the bilayer, making the interfacial region more fluid and capable to accommodate Aβ(25-35). As a consequence, iAβ5p prevents the Aβ(25-35) release from the lipid membrane, which is the first step of the β-amyloid aggregation process.     

Alzheimer Aβ peptide interactions with lipid membranes

Fibrillar aggregates of misfolded amyloid proteins are involved in a variety of diseases such as Alzheimer disease (AD), type 2 diabetes, Parkinson, Huntington and prion-related diseases. In the case of AD amyloid β (Aβ) peptides, the toxicity of amyloid oligomers and larger fibrillar aggregates is related to perturbing the biological function of the adjacent cellular membrane. We used atomistic molecular dynamics (MD) simulations of Aβ_9–40 fibrillar oligomers modeled as protofilament segments, including lipid bilayers and explicit water molecules, to probe the first steps in the mechanism of Aβ-membrane interactions. Our study identified the electrostatic interaction between charged peptide residues and the lipid headgroups as the principal driving force that can modulate the further penetration of the C-termini of amyloid fibrils or fibrillar oligomers into the hydrophobic region of lipid membranes. These findings advance our understanding of the detailed molecular mechanisms and the effects related to Aβ-membrane interactions, and suggest a polymorphic structural character of amyloid ion channels embedded in lipid bilayers. While inter-peptide hydrogen bonds leading to the formation of β-strands may still play a stabilizing role in amyloid channel structures, these may also present a significant helical content in peptide regions (e.g., termini) that are subject to direct interactions with lipids rather than with neighboring Aβ peptides.     

Lamellar Gel (Lβ) Phases of Ternary Lipid Composition Containing Ceramide and Cholesterol

Lipid lateral segregation into specific domains in cellular membranes is associated with cell signaling and metabolic regulation. This phenomenon partially arises as a consequence of the very distinct bilayer-associated lipid physico-chemical properties that give rise to defined phase states at a given temperature. Until now lamellar gel (L_β) phases have been described in detail in single or two-lipid systems. Using x-ray scattering, differential scanning calorimetry, confocal fluorescence microscopy, and atomic force microscopy, we have characterized phases of ternary lipid compositions in the presence of saturated phospholipids, cholesterol, and palmitoyl ceramide mixtures. These phases stabilized by direct cholesterol-ceramide interaction can exist either with palmitoyl sphingomyelin or with dipalmitoyl phosphatidylcholine and present intermediate properties between raft-associated phospholipid-cholesterol liquid-ordered and phospholipid-ceramide L_β phases. The present data provide novel, to our knowledge, evidence of a chemically defined, multicomponent lipid system that could cooperate in building heterogeneous segregated platforms in cell membranes.     

Membrane and surface interactions of Alzheimer's Aβ peptide--insights into the mechanism of cytotoxicity

Alzheimer's disease is the most common form of dementia and its pathological hallmarks include the loss of neurones through cell death, as well as the accumulation of amyloid fibres in the form of extracellular neuritic plaques. Amyloid fibrils are composed of the amyloid-β peptide (Aβ), which is known to assemble to form 'toxic' oligomers that may be central to disease pathology. Aβ is produced by cleavage from the amyloid precursor protein within the transmembrane region, and the cleaved peptide may retain some membrane affinity. It has been shown that Aβ is capable of specifically binding to phospholipid membranes with a relatively high affinity, and that modulation of the composition of the membrane can alter both membrane-amyloid interactions and toxicity. Various biomimetic membrane models have been used (e.g. lipid vesicles in solution and tethered lipid bilayers) to examine the binding and interactions between Aβ and the membrane surfaces, as well as the resulting permeation. Oligomeric Aβ has been observed to bind more avidly to membranes and cause greater permeation than fibrillar Aβ. We review some of the recent advances in studying Aβ-membrane interactions and discuss their implications with respect to understanding the causes of Alzheimer's disease.     

Preferential accumulation of Aβ(1−42) on gel phase domains of lipid bilayers: An AFM and fluorescence study

Peptide-membrane interactions have been implicated in both the toxicity and aggregation of β-amyloid (Aβ) peptides. Recent studies have provided evidence for the involvement of liquid-ordered membrane domains known as lipid rafts in the formation and aggregation of Aβ. As a model, we have examined the interaction of Aβ(1−42) with phase separated DOPC/DPPC lipid bilayers using a combination of atomic force microscopy (AFM) and total internal reflection fluorescence microscopy (TIRF). AFM images show that addition of Aβ to preformed supported bilayers leads to accumulation of small peptide aggregates exclusively on the gel phase DPPC domains. Initial aggregates are observed approximately 90 min after peptide addition and increase in diameter to 45-150 nm within 24 h. TIRF studies with a mixture of Aβ and Aβ-Fl demonstrate that accumulation of the peptide on the gel phase domains occurs as early as 15 min after Aβ addition and is maintained for over 24 h. By contrast, Aβ is randomly distributed throughout both fluid and gel phases when the peptide is reconstituted into DOPC/DPPC vesicles prior to formation of a supported bilayer. The preferential accumulation of Aβ on DPPC domains suggests that rigid domains may act as platforms to concentrate peptide and enhance its aggregation and may be relevant to the postulated involvement of lipid rafts in modulating Aβ activity in vivo.     

Effect of amyloid β-peptide on the fluidity of phosphatidylcholine membranes: Uses and limitations of diphenylhexatriene fluorescence anisotropy

There is accumulating evidence that peptide-induced perturbations in the order and dynamics of cellular membranes may play a role in the neurotoxicity of amyloid β-peptide (Aβ). Several studies have reported that Aβ decreases fluidity of membranes based on an Aβ-induced increase in the fluorescence anisotropy of diphenylhexatriene (DPH). However, the effect of Aβ on the membrane fluidity is still a subject of controversy, because other studies that employed pyrene as a fluorescent probe have shown that Aβ has the opposite effect. To reveal the reason for this discrepancy, we have examined the effect of Aβ on the fluidity of phosphatidylcholine membranes using spectroscopic methods. The fluorescence anisotropy of DPH is dramatically increased on addition of Aβ to DPH-containing phosphatidylcholine membranes. However, Aβ does not affect the Raman spectrum of the membrane, which is sensitive to the packing order of the hydrocarbon chains of lipids. We have also found that circular dichroism (CD) bands of DPH appear during incubation of DPH-containing membranes with Aβ, whereas DPH is an achiral molecule. The observed CD bands of DPH are induced by a chiral environment of Aβ but not by that of the lipids, because positive CD bands appear regardless of the d/l-chirality of phosphatidylcholine. The findings obtained from CD measurements provide evidence that DPH molecules translocate from the membrane to Aβ. The peptide-mediated extraction of DPH from the membrane may cause changes in the fluorescence anisotropy of DPH, even though Aβ does not affect the fluidity of membranes.     

Interactions between amyloid β peptide and lipid membranes

The presence of amyloid plaques in the brain is a typical characteristic of Alzheimer's disease (AD). Amyloid plaques are formed from the deposits of aggregated amyloid β peptide (Aβ). The toxicity induced by Aβ aggregates is correlated with Aβ-membrane interactions. The mutual influences between aggregation and membranes are complicated and unclear. In recent years advanced experiments and findings are emerging to give us more detailed information on Aβ-membrane interactions. In this review, we mainly focus on the Aβ-membrane interactions and membrane-induced Aβ structures. The mechanism of Aβ-membrane interactions is also summarized, which provides insights into the prevention and treatment of AD.     

The interaction of amyloid Aβ(1-40) with lipid bilayers and ganglioside as studied by P solid-state NMR

Amyloid β-peptide (Aβ) is a major component of plaques in Alzheimer's disease, and formation of senile plaques has been suggested to originate from regions of neuronal membrane rich in gangliosides. We analyzed the mode of interaction of Aβ with lipid bilayers by multinuclear NMR using ³¹P nuclei. We found that Aβ (1-40) strongly perturbed the bilayer structure of dimyristoylphosphatidylcholine (DMPC), to form a non-lamellar phase (most likely micellar). The ganglioside GM1 potentiated the effect of Aβ (1-40), as viewed from ³¹P NMR. The difference of the isotropic peak intensity between DMPC/Aβ and DMPC/GM1/Aβ suggests a specific interaction between Aβ and GM1. We show that in the DMPC/GM1/Aβ system there are three lipid phases, namely a lamellar phase, a hexagonal phase and non-oriented lipids. The latter two phases are induced by the presence of the Aβ peptide, and facilitated by GM1.     

Amyloid-β Membrane Binding and Permeabilization are Distinct Processes Influenced Separately by Membrane Charge and Fluidity

The 40 and 42 residue amyloid-β (Aβ) peptides are major components of the proteinaceous plaques prevalent in the Alzheimer's disease-afflicted brain and have been shown to have an important role in instigating neuronal degeneration. Whereas it was previously thought that Aβ becomes cytotoxic upon forming large fibrillar aggregates, recent studies suggest that soluble intermediate-sized oligomeric species cause cell death through membrane permeabilization. The present study examines the interactions between Aβ40 and lipid membranes using liposomes as a model system to determine how changes in membrane composition influence the conversion of Aβ into these toxic species. Aβ40 membrane binding was monitored using fluorescence-based assays with a tryptophan-substituted peptide (Aβ40 [Y10W]). We extend previous observations that Aβ40 interacts preferentially with negatively charged membranes, and show that binding of nonfibrillar, low molecular mass oligomers of Aβ40 to anionic, but not neutral, membranes involves insertion of the peptide into the bilayer, as well as sequential conformational changes corresponding to the degree of oligomerization induced. Significantly, while anionic membranes in the gel, liquid crystalline, and liquid ordered phases induce these conformational changes equally, membrane permeabilization is reduced dramatically as the fluidity of the membrane is decreased. These findings demonstrate that binding alone is not sufficient for membrane permeabilization, and that the latter is also highly dependent on the fluidity and phase of the membrane. We conclude that binding and pore formation are two distinct steps. The differences in Aβ behavior induced by membrane composition may have significant implications on the development and progression of AD as neuronal membrane composition is altered with age.     

Design, synthesis, and biophysical properties of a helical Abeta1-42 analog: Inhibition of fibrillogenesis and cytotoxicity

The aggregation of amyloid β-peptide (Aβ) into β-sheet-rich aggregates is a crucial step in the etiology of Alzheimer’s disease. Helical forms of Aβ have been suggested to be intermediates in the aggregation process of the peptide in aqueous phase, micelles and membranes. A stable helical Aβ analog would be useful to investigate the role of helical intermediates in fibrillization by Aβ. Here we designed a helical analog by simply cross-linking the Cys residues of A30C, G37C-Aβ1-42 with 1,6-bismaleimidohexane. The analog assumed a weak α-helical conformation in model membranes mimicking lipid raft microdomains of neuronal membranes under conditions in which the wild-type Aβ1-42 formed a β-sheet, indicating the cross-linking locally induced a helical conformation. Furthermore, addition of equimolar helical Aβ analog significantly reduced the amyloid formation and cytotoxicity by Aβ1-42. Thus, our helical Aβ1-42 is not only a model peptide to investigate the role of helical intermediates in fibrillization by Aβ, but also an inhibitor of Aβ-induced cytotoxicity.     

A comparative molecular dynamics analysis of the amyloid beta-peptide in a lipid bilayer

Because the amyloid β-peptide (Aβ) functions as approximately half of the transmembrane domain of the amyloid precursor protein and interaction of Aβ with membranes is proposed to result in neurotoxicity, the association of Aβ with membranes likely is important in the etiology of Alzheimer’s disease. Atomic details of the interaction of Aβ with membranes are not accessible with most experimental techniques, but computational methods can provide this information. Here, we present the results of ten 100-ns molecular dynamics (MD) simulations of the 40-residue amyloid β-peptide (Aβ₄₀) embedded in a dipalmitoylphosphatidylcholine (DPPC) bilayer. The present study examines the effects of insertion depth, protonation state of key residues, and ionic strength on Aβ₄₀ in a DPPC bilayer. In all cases, a portion of the peptide remained embedded in the bilayer. In the case of deeper insertion depth, Aβ₄₀ adopted a near-transmembrane orientation, drawing water molecules into the bilayer to associate with its charged amino acids. In the case of shallower insertion, the most widely-accepted construct, the peptide associated strongly with the membrane-water interface and the phosphatidylcholine headgroups of the bilayer. In most cases, significant disordering of the extracellular segment of the peptide was observed, and the brief appearance of a β-strand was noted in one case. Our results compare well with a variety of experimental and computational findings. From this study, we conclude that Aβ associated with membranes is dynamic and capable of adopting a number of conformations, each of which may have significance in understanding the progression of Alzheimer’s disease.     

Organotin compounds promote the formation of non-lamellar phases in phosphatidylethanolamine membranes.

Organotin compounds are important contaminants in the environment. They are membrane active molecules with broad biological toxicity. We have studied the interaction of tri-n-butyltin chloride and tri-n-phenyltin chloride with model membranes composed of different phosphatidylethanolamines using differential scanning calorimetry, X-ray diffraction, 31P-nuclear magnetic resonance and infrared spectroscopy. Organotin compounds laterally segregate in phosphatidylethanolamine membranes without affecting the shape and position of the lamellar gel to lamellar liquid-crystalline phase transition thermogram of the phospholipid. This is in contrast with their reported effect on phosphatidylcholine membranes [Chicano et al. (2001) Biochim. Biophys. Acta 1510, 330-341] and emphasises the importance of the nature of the lipid headgroup in determining how the behaviour of lipid molecules is affected by these toxicants. Interestingly, we have found that organotin compounds disrupt the pattern of hydrogen-bonding in the interfacial region of dielaidoylphosphatidylethanolamine membranes and have the ability to promote the formation of hexagonal H(II) structures in this system. These results open the possibility that some of the specific toxic effects of organotin compounds might be exerted through the alteration of membrane function produced by their interaction with the lipidic component of the membrane.     

The co-effect of copper and lipid vesicles on Aβ aggregation

Both metal ions and lipid membranes have a wide distribution in amyloid plaques and play significant roles in AD pathogenesis. Although influences of different metal ions or lipid vesicles on the aggregation of Aβ peptides have been extensively studied, their combined effects are less understood. In this study, we reported a unique effect of copper ion on Aβ aggregation in the presence of lipid vesicles, different from other divalent metal ions. Cu²⁺ in a super stoichiometric amount leads to the rapid formation of β-sheet rich structure, containing abundant low molecular weight (LMW) oligomers. We demonstrated that oligomerization of Aβ40 induced by Cu²⁺ binding was an essential prerequisite for the rapid conformation transition. Overall, the finding provided a new view on the complex triple system of Aβ, copper ion and lipid vesicles, which might help understanding of Aβ pathologies.     

Strength of Ca(2+) binding to retinal lipid membranes: consequences for lipid organization

There is evidence that membranes of rod outer segment (ROS) disks are a high-affinity Ca(2+) binding site. We were interested to see if the high occurrence of sixfold unsaturated docosahexaenoic acid in ROS lipids influences Ca(2+)-membrane interaction. Ca(2+) binding to polyunsaturated model membranes that mimic the lipid composition of ROS was studied by microelectrophoresis and (2)H NMR. Ca(2+) association constants of polyunsaturated membranes were found to be a factor of approximately 2 smaller than constants of monounsaturated membranes. Furthermore, strength of Ca(2+) binding to monounsaturated membranes increased with the addition of cholesterol, while binding to polyunsaturated lipids was unaffected. The data suggest that the lipid phosphate groups of phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylserine (PS) in PC/PE/PS (4:4:1, mol/mol) are primary targets for Ca(2+). Negatively charged serine in PS controls Ca (2+) binding by lowering the electric surface potential and elevating cation concentration at the membrane/water interface. The influence of hydrocarbon chain unsaturation on Ca(2+) binding is secondary compared to membrane PS content. Order parameter analysis of individual lipids in the mixture revealed that Ca(2+) ions did not trigger lateral phase separation of lipid species as long as all lipids remained liquid-crystalline. However, depending on temperature and hydrocarbon chain unsaturation, the lipid with the highest chain melting temperature converted to the gel state, as observed for the monounsaturated phosphatidylethanolamine (PE) in PC/PE/PS (4:4:1, mol/mol) at 25 degrees C.     

Interaction of a β‐sheet breaker peptide with lipid membranes

Aggregation of β‐amyloid peptides into senile plaques has been identified as one of the hallmarks of Alzheimer's disease. An attractive therapeutic strategy for Alzheimer's disease is the inhibition of the soluble β‐amyloid aggregation using synthetic β‐sheet breaker peptides that are capable of binding Aβ but are unable to become part of a β‐sheet structure. As the early stages of the Aβ aggregation process are supposed to occur close to the neuronal membrane, it is strategic to define the β‐sheet breaker peptide positioning with respect to lipid bilayers. In this work, we have focused on the interaction between the β‐sheet breaker peptide acetyl‐LPFFD‐amide, iAβ5p, and lipid membranes, studied by ESR spectroscopy, using either peptides alternatively labeled at the C‐ and at the N‐terminus or phospholipids spin‐labeled in different positions of the acyl chain. Our results show that iAβ5p interacts directly with membranes formed by the zwitterionic phospholipid dioleoyl phosphatidylcholine and this interaction is modulated by inclusion of cholesterol in the lipid bilayer formulation, in terms of both peptide partition coefficient and the solubilization site. In particular, cholesterol decreases the peptide partition coefficient between the membrane and the aqueous medium. Moreover, in the absence of cholesterol, iAβ5p is located between the outer part of the hydrophobic core and the external hydrophilic layer of the membrane, while in the presence of cholesterol it penetrates more deeply into the lipid bilayer. Copyright © 2010 European Peptide Society and John Wiley & Sons, Ltd.     

Effect of the surface charge of artificial model membranes on the aggregation of amyloid β-peptide

The neurotoxicity effect of the β-amyloid (Aβ) peptide, the primary constituent of senile plaques in Alzheimer's disease, occurs through interactions with neuronal membranes. Here, we attempt to clarify the mechanisms and consequences of the interaction of Aβ with lipid membranes. We have used liposomes as a model of biological membrane, and have devoted particular attention to the bilayer charge effect. Our results show that insertion and surface association of peptide with membrane, increased in a membrane charge-dependent manner, lead to a reduction of Aβ soluble species, lag time elongation and an increase in the inter-molecular β-sheet ratio of amyloid fibrils. In addition, our findings suggest that the fine balance between peptide insertion and surface association modulates Aβ aggregation, influencing the amyloid fibrils concentration as well as their morphology.     

The role of sulfatide lipid domains in the membrane pore-forming activity of cobra cardiotoxin

Cobra CTX A3, the major cardiotoxin (CTX) from Naja atra, is a cytotoxic, basic β-sheet polypeptide that is known to induce a transient membrane leakage of cardiomyocytes through a sulfatide-dependent CTX membrane pore formation and internalization mechanism. The molecular specificity of CTX A3-sulfatide interaction at atomic levels has also been shown by both nuclear magnetic resonance (NMR) and X-ray diffraction techniques to reveal a role of CTX-induced sulfatide conformational changes for CTX A3 binding and dimer formation. In this study, we investigate the role of sulfatide lipid domains in CTX pore formation by various biophysical methods, including fluorescence imaging and atomic force microscopy, and suggest an important role of liquid-disordered (ld) and solid-ordered (so) phase boundary in lipid domains to facilitate the process. Fluorescence spectroscopic studies on the kinetics of membrane leakage and CTX oligomerization further reveal that, although most CTXs can oligomerize on membranes, only a small fraction of CTXs oligomerizations form leakage pores. We therefore suggest that CTX binding at the boundary between the so and so/ld phase coexistence sulfatide lipid domains could form effective pores to significantly enhance the CTX-induced membrane leakage of sulfatide-containing phosphatidylcholine vesicles. The model is consistent with our earlier observations that CTX may penetrate and lyse the bilayers into small aggregates at a lipid/protein molar ratio of about 20 in the ripple P(β)' phase of phosphatidylcholine bilayers and suggest a novel mechanism for the synergistic action of cobra secretary phospholipase A2 and CTXs.     

A synthetic amino acid substitution of Tyr10 in Aβ peptide sequence yields a dominant negative variant in amyloidogenesis

Alzheimer's disease (AD) is the most common cause of dementia in elderly people, and age is the major nongenetic risk factor for sporadic AD. A hallmark of AD is the accumulation of amyloid in the brain, which is composed mainly of the amyloid beta-peptide (Aβ) in the form of oligomers and fibrils. However, how aging induces Aβ aggregation is not yet fully determined. Some residues in the Aβ sequence seem to promote Aβ-induced toxicity in association with age-dependent risk factors for AD, such as (i) increased GM1 brain membrane content, (ii) altered lipid domain in brain membrane, (iii) oxidative stress. However, the role of Aβ sequence in promoting aggregation following interaction with the plasma membrane is not yet demonstrated. As Tyr10 is implicated in the induction of oxidative stress and stabilization of Aβ aggregation, we substituted Tyr 10 with a synthetic amino acid that abolishes Aβ-induced oxidative stress and shows an accelerated interaction with GM1. This variant peptide shows impaired aggregation properties and increased affinity for GM1. It has a dominant negative effect on amyloidogenesis in vitro, in cellulo, and in isolated synaptosomes. The present study shed new light in the understanding of Aβ-membrane interactions in Aβ-induced neurotoxicity. It demonstrates the relevance of Aβ sequence in (i) Aβ-membrane interaction, underlining the role of age-dependent enhanced GM1 content in promoting Aβ aggregation, (ii) Aβ aggregation, and (iii) Aβ-induced oxidative stress. Our results open the way for the design of peptides aimed to inhibit Aβ aggregation and neurotoxicity.     

The effect of oxysterols on the interaction of Alzheimer's amyloid beta with model membranes

The interaction of amyloid beta (Aβ) peptide with cell membranes has been shown to be influenced by Aβ conformation, membrane physicochemical properties and lipid composition. However, the effect of cholesterol and its oxidized derivatives, oxysterols, on Aβ-induced neurotoxicity to membranes is not fully understood. We employed here model membranes to investigate the localization of Aβ in membranes and the peptide-induced membrane dynamics in the presence of cholesterol and 7-ketocholesterol (7keto) or 25-hydroxycholesterol (25OH). Our results have indicated that oxysterols rendered membranes more sensitive to Aβ, in contrast to role of cholesterol in inhibiting Aβ/membrane interaction. We have demonstrated that two oxysterols had different impacts owing to distinct positions of the additional oxygen group in their structures. 7keto-containing cell-sized liposomes exhibited a high propensity toward association with Aβ, while 25OH systems were more capable of morphological changes in response to the peptide. Furthermore, we have shown that 42-amino acid Aβ (Aβ-42) pre-fibril species had higher association with membranes, and caused membrane fluctuation faster than 40-residue isoform (Aβ-40). These findings suggest the enhancing effect of oxysterols on interaction of Aβ with membranes and contribute to clarify the harmful impact of cholesterol on Aβ-induced neurotoxicity by means of its oxidation.     

Inhibitors of amyloid β-protein aggregation mediated by GM1-containing raft-like membranes

The aggregation (fibril formation) of amyloid β-protein (Aβ) is considered to be a crucial step in the etiology of Alzheimer's disease (AD). The inhibition of Aβ aggregation and/or decomposition of fibrils formed in aqueous solution by small compounds have been studied extensively for the prevention and treatment of AD. However, recent studies suggest that Aβ aggregation also occurs in lipid rafts mediated by a cluster of monosialoganglioside GM1. This study examined the effects of representative compounds on Aβ aggregation and fibril destabilization in the presence of GM1-containing raft-like liposomes. Among the compounds tested, nordihydroguaiaretic acid (NDGA), rifampicin (RIF), tannic acid (TA), and quercetin (QUE) showed strong fibrillization inhibitory activity. NDGA and RIF inhibited the binding of Aβ to GM1 liposomes by competitively binding to the membranes and/or direct interaction with Aβ in solution, thus at least partly preventing fibrils from forming. Coincubation of Aβ with NDGA, RIF, and QUE in the presence of GM1 liposomes resulted in elongate particles, whereas the presence of TA yielded protofibrillar structures. TA and RIF also destabilized fibrils. The most potent NDGA prevented Aβ-induced toxicity in PC12 cells by inhibiting Aβ accumulation. Furthermore, a comparison of the inhibitory effects of various compounds between aqueous-phase and GM1-mediated aggregation of Aβ suggested that the two aggregation processes are not identical.